Differential absorption lidar (DIAL) is an important equipment for the detection of noxious gases. It has a high demand for the wavelength and linewidth of the laser sources. In recent years, optical parametric oscillation and amplification (OPO/OPA) technology has made breakthroughs in medium and long-wave infrared laser, showing great potential in obtaining high-quality long-wave laser. The characteristics of different nonlinear crystals are collected. The performance of long-wave laser obtained by some crystal optical parametric oscillators is generalized, including output power, pulse energy, tuning range and output linewidth. Combined with the theoretical gain linewidth calculation and recent experimental research, the main problems in realizing narrow linewidth are analyzed and summarized, furthermore, the future technical route furthermore,the development direction are prospected.

Typically, graded-index multimode fibers feature certain spatiotemporal nonlinear effects such as geometric parametric instability (GPI), which gradually expands the spectrum of transmitted laser light under certain conditions and eventually evolves into a supercontinuum. This paper introduces the concept of GPI and its physical connotations; moreover, the status of research on GPI-induced visible supercontinuum generation in graded-index multimode fibers is reviewed, and an analysis on the influence of fiber and pulse parameters on the output spectrum is presented. In addition to this, realizing an all-fiber structure and using short wavelength lasers as pump sources constitute key future research directions. Overall, the GPI-induced generation of the visible supercontinuum is expected to break through the power limitation of the supercontinuum generated by small core traditional photonic crystal fibers.

Since the in-depth research on the theory and technology of luminescent materials, luminescent materials have been widely used in white LED lighting, optical imaging, optical storage, optical communication, optical fiber laser, and other fields. In recent years, it has been found that the luminescent materials prepared by introducing phosphorus as co-doped elements show unique advantages in optical properties, which has become the key factor to solve the bottleneck of luminescent properties of many luminescent materials. In this paper, the preparation methods and optical properties of phosphosilicate luminescent glass was reviewed. Several mainstream preparation methods of luminescent materials and their phosphorus doping technology were introduced, as well as the spectral characteristics of various luminescent ions in the coordination environment of P5+, which shows the great advantages of phosphosilicate luminescent glass and optical fiber in the fields of optical communication and optical fiber laser. Finally, the application prospect of a variety of phosphorus doped active special optical fibers is prospected.

Surface enhanced Raman scattering (SERS) is a non-contact, non-destructive and high-sensitivity spectral analysis technique. SERS has the capability to detect molecular fingerprint and has been widely applied to the subjects of materials science, chemistry, physics, geology and life science. Compared with the traditional rigid substrates, the flexible SERS substrates can conduct in situ and on-site real-time detection of analytes on non-planar surface. However, there are still some challenges in designing and fabricating the flexible SERS substrates with high-sensitivity and reproducibility. Therefore, we provide an overview of the recent advances in flexible SERS substrates. We discuss the fabrications, performances, applications and future prospects of five different types of the flexible SERS substrates, and provide some guidance for the research of SERS substrates.

InGaAs single-photon detectors are extensively used in laser 3D imaging, long-distance high-speed digital communication, free-space optical communication, and quantum communication. Different packaging formats, including coaxial packaging, butterfly packaging, and pin grid array packaging, have been designed for unit, line array, and small panel array devices. The impact of the temperature on the efficacy of InGaAs single-photon devices and the methodologies for controlling component temperature are discussed. Detailed comparisons and analyses of high-precision coupling methods for optical components such as microlenses, lenses, optical fibers, etc. to the semiconductor are provided. For high-frequency signal output, the lead type, wiring method, packaging structure design, and other issues are reviewed, and the development trend of the InGaAs single-photon detectors is forecasted.

Semiconductor saturable absorption mirror (SESAM) is the most commonly-used passive mode-locking device in ultrafast laser technology. Owing to its advantages of self-starting, low insertion loss, high integration, and flexible design, SESAM has a wide range of applications and excellent commercial prospects. This study introduces the mode-locking principle and current development status of SESAM and summarizes the current epitaxial structure, growth mode, and parameter performance of SESAM. It also provides a detailed description of its latest progress in mode-locking in solid-state, semiconductor, and fiber lasers. Moreover, the performance characteristics and future-development direction of various types of mode-locked lasers are presented.

The existence of three atypical environments involving irregular particles, nonisotropic particles, and nonuniform media is quite common. However, the transmission performance and operating distance of optical signals are badly affected due to particle scattering and absorption in the three atypical environments. For instance, low-visibility environments, such as fog, haze, and clouds, can reduce the safety of aircraft, cars, and ships, making it difficult to search and navigate in turbid waters. However, using polarization characteristics to characterize the transmission process in these atypical environments can provide feasible solution for extracting high-quality light signals and increasing operational distances. In this study, we explore the polarization transmission characteristics in three situations: irregular particles, nonisotropic particles, and nonuniform media. We analyze the domestic and international development of various nonspherical particles, present relevant data from the equivalent multilayer concentric particle model, and explain the effectiveness of addressing issues such as haze-scattering characteristics. Furthermore, we conduct a classification study on nonuniform media and analyze the impact of the medium on light transmission. By summarizing the development progress and current research status regarding scattering polarization characteristics of polarized light in the three atypical environments, we aim to clarify the importance of studying polarization transmission characteristics in such settings. Finally, we look forward to the development trend of polarization transmission problems in the three atypical environments.

In the era of artificial intelligence and big data, the demand for data storage, transmission, and processing capabilities has surged. Thus, the prerequisites for data transmission, including bandwidth and communication speed, have experienced an escalation. However, owing to the influence of dielectric materials and transmission rate, the electrical interconnections in system-level packaging present strong phenomena, such as loss, reflection, delay, and crosstalk, which cannot meet the requirements of increasing bandwidth and communication speed. Consequently, advanced packaging technology and photoelectric co-packaging technology encapsulate optical modules and electrical chips within the same package, thereby reducing the interconnection length between them and parasitic effects. Furthermore, it has numerous advantages, such as wide band, anti-electromagnetic interference, low transmission loss and power consumption, and hence, it has become a research hotspot in recent years. This article discusses the basic concepts and advantages of optoelectronic co-packaging, introduces typical 2D, 2.5D, and 3D technologies and the latest developments at home and abroad, and analyzes the challenges that must be addressed as a new generation packaging technology.

Compared with traditional optical lenses, liquid lenses have the advantages of fast response, large zoom range, and high controllability, which are widely required in various fields, such as vision correction, microscopes, cellphone cameras, endoscopes, and bionic optics. This paper summarizes the technical developments in liquid lenses and briefly describes their working principle at home and abroad. Furthermore, it analyzes the related processing methods, performance indices, and application prospects of some typical liquid lenses. Finally, this work provides an outlook on the future development trend to provide useful references for further research on liquid lenses.

The research process of optical functional glass materials involves long research and development cycles and low efficiency. Greatly hindered the development of optical glass materials. The emergence of machine learning technology has greatly promoted the development of glass materials science. By learning the laws contained in the data, learning and predicting new data from the huge and complex glass data has accelerated the research and development process of optical functional glass. This paper summarizes and demonstrates several types of machine learning algorithms involved in the prediction of optical glass and briefly introduces them. On this basis, it focuses on summarizing the important applications of these theoretical algorithms in glass research, including accelerating and improving traditional glass research methods, assisting glass composition-property correlation prediction, and suggestions for optical glass formulation design. Finally, the application prospects and future development trends of machine learning in optical functional glass research are analyzed and forecasted.

Fluorescence interference is a major challenge in Raman spectroscopy, as strong fluorescence will seriously affect the detection of Raman spectroscopy signals. This paper introduces several differential Raman spectrum restoration methods (integration method, curve fitting method, deconvolution method, etc.) of shifted excitation Raman difference spectroscopy for defluorescence technology, and discusses its principle, implementation, and performance characteristics. In addition, the application of differential Raman spectroscopy in food, medicine, agriculture and other fields is analyzed in detail, which shows that shifted excitation Raman difference spectroscopy has broad application prospects.

Compared to fully commercialized nitride blue light light emitting diode (LED), the external quantum efficiency (EQE) of current Aluminum gallium nitride (AlGaN) based deep ultraviolet LED is still at a relatively low level. This review first introduces the current development status of AlGaN based deep ultraviolet LED and analyzes the reasons for low EQE. Then, the research progress in improving the EQE direction of AlGaN based deep ultraviolet LED in recent years is elaborated from three aspects: carrier injection efficiency, carrier radiation recombination efficiency, and light extraction efficiency. Finally, the current challenges and future development opportunities of AlGaN based deep ultraviolet LED were discussed.

Atomic spin squeezing uses the interaction between light and neutral atomic ensembles to reduce the uncertainty of the atomic spin component, therefore reaching a sensitivity beyond the standard quantum limit in quantum precision measurement, which is expected to play an important role in the fields of time and frequency metrology, gravity precision measurement, fundamental physics tests, gravitational wave detection and dark matter exploration. This paper introduces the concept and criteria of atomic spin squeezing, and analyzes the methods for generating spin squeezed state through atom-light interaction in neutral atomic ensembles, and reviews the recent results and achievements and the application research progress of atomic spin squeezing in quantum precision measurement.

Laser imaging radar integrates laser and radar technology, serving as an active photoelectric imaging tool. It boasts high detection accuracy, rich image information, and robust anti-interference capabilities, making it promising in scientific and commercial sectors. As its demand increases, diverse advanced laser imaging radar systems have emerged. This paper outlines the operating principle of this advanced imaging technology, classifies the radar systems, discusses key performances across different classifications globally, compares the advantages and disadvantages of various systems, and concludes with future trends in the technology. This offers insights into the evolution of advanced laser imaging radar technology.

The expansion of high-end products in the tobacco industry and the increasing demand for product quality from consumers have created significant challenges for online tobacco testing technology. In response to problems such as the difficult removal of foreign objects from tobacco production affecting cigarette taste, various complex diseases from tobacco leaves, and difficulty in identifying cigarette packaging defects, traditional manual online detection methods are inefficient and it is difficult to ensure accuracy, which cannot adapt to the high-quality development of China's tobacco industry. From the perspective of elucidating the principle of tobacco online detection based on machine vision, this study systematically elaborates on the research status and latest progress of tobacco online detection technology based on two key aspects: the visual detection principle and deep learning models. Combined with current typical applications, this study analyzes the advantages and limitations of different visual models and deep learning detection methods, and further explores the development trend and prospects of tobacco online detection technology based on machine vision.

Thyroid nodule is one of the most common clinical nodular lesions in adults, and its incidence rate is always high. Thyroid nodule can be classified into benign and malignant, and the latter is thyroid cancer, which can cause difficulties in breathing and swallowing, and even endanger the life of patients. Therefore, the identification of benign and malignant thyroid nodule is the primary problem in the diagnosis and treatment of thyroid nodule. Deep learning can automatically extract nodule features and complete the preliminary classification of benign and malignant thyroid nodule. With the continuous improvement of classification accuracy of deep learning, it has become an important means of auxiliary diagnosis of benign and malignant thyroid nodule. To better study the classification and auxiliary diagnosis of benign and malignant thyroid nodule, we introduce the commonly used indicators for the evaluation of nodule classification performance, and classify them according to the convolutional neural network, Transformer, deep neural network, generative adversarial network, transfer learning, ensemble learning, and computer-aided diagnosis system based on deep learning, and elaborate their application in the classification of benign and malignant thyroid nodule. We conduct a comprehensive comparative analysis, summarize the existing problems in the current research, and provide prospects for future research directions.

Diffuse optical imaging is widely used in biomedical research and clinics. Compared with other medical imaging methods, such as magnetic resonance imaging (MRI), X-ray computed tomography (CT), positron emission tomography (PET), and ultrasound imaging, diffuse optical imaging uses diffused light absorbed and scattered by tissues for imaging. This approach is non-invasive and label-free, has a wide field, and quantitatively measures the concentrations of various components such as oxyhemoglobin, deoxyhemoglobin, blood oxygen, water, lipids, and melanin. Furthermore, it collects and assesses tissue functional information. Diffuse optical imaging is advantageous in terms of safety, specificity, and system cost. This article introduces the basic principles of diffuse optical imaging, including the interaction between light and tissue and light propagation models, and summarizes the relevant methods and applications of diffuse optical imaging, including pulse oximetry, diffuse optical spectroscopy, diffuse optical tomography, fluorescence molecular tomography, and spatial frequency domain imaging. Moreover, the prospects for the future development of diffuse optical imaging are presented.

Usually, lasers can be used for speech signal detection in non-contact and long-distance scenarios. Consequently, the remote laser speech detection technology has broad application prospects in laser interception, multi-mode monitoring, intrusion detection, search and rescue operations, laser microphones, and other fields. In this paper, we review research advances in the remote laser speech signal detection technology from the perspectives of remote laser vibration detection systems and detected signal analysis and processing methods; moreover, we expound the future development prospects of this technology.

The safety hazard and economic losses caused by marine corrosion have posed major challenges in shipping. With the introduction of relevant laws and regulations that require the shipping industry to improve the cleaning needs of ships and monitor their corroded parts, the issues of low efficiency, low precision, varying degrees of substrate damage, chemical pollution, resource waste, and occupational hazards of traditional rust removal have become prominent. Laser derusting technology is a noncontact green derusting method with the advantages of high efficiency, low costs, and automation. This paper introduces the research status of laser rust removal techniques and describes the typical laser rust removal methods and mechanisms, the combined application of laser derusting, and other related technologies. The development prospects of laser derusting technology in shipping is presented. The findings afford a reference for the future application of laser derusting technology in ships.

The output beam of the laser resonator is Gaussian, which makes it often unable to be used directly. It is necessary to improve the uniformity through beam shaping to meet the application requirements. Starting from the characteristics of optical system, this paper summarizes three main laser beam shaping technologies, including aperture method, field mapper method, and multi-aperture beam focusing method, respectively introduces the basic principle, application range, and main realization methods of three laser beam shaping technologies, and expounds the typical application and research progress of different laser beam shaping methods. Finally, the current problems and future development of laser beam shaping technology are comprehensively discussed. This review has certain reference significance for the research of laser beam shaping technology.

In laser shock processing (LSP) technology, as the driving source and energy source of shock loads, the different selection of laser pulse parameters determines the laser absorption mechanism, energy deposition, and even the plasma explosion behavior. This plays an important role in determining the morphological characteristics of shock loads and the surface strengthening effect of materials. This paper provides a review of the mechanisms and influencing laws of various laser parameters involved in LSP technology in laser driven shock effects, as well as the current research and cognitive status in process allocation. The importance of laser time profile in plasma explosion behavior and shock loading characteristics is reviewed, as well as the current status that Gaussian-like profiles that output from Q-switched laser is commonly used in LSP. It also points out that optimizing the laser time profile can improve the conversion efficiency of laser energy to mechanical energy. And it is possible that shock load characteristics can be accurately manipulated by adjusting laser time profiles.

Laser warning technologies are important components of optoelectronic countermeasures that detect and warn regarding hazardous laser signals, effectively improving the survival capabilities of crucial platforms such as aircrafts, ships, and satellites. These technologies also hold considerable importance in related fields. Based on their detection principles, these technologies can be categorized into four types: coherent recognition, spectral recognition, grating diffraction, and imaging technologies. This study summarizes the current development status of laser warning technologies and equipment domestically and globally and includes a comparative analysis of the performance and development trends of various laser warning technologies.

Optical frequency domain reflectometer (OFDR) is a distributed optical fiber measurement technology. The scanning laser is injected into the optical fiber link, and the position and intensity of the reflection points on the optical fiber link are located by analyzing the Rayleigh backscattering scattering light in the frequency domain. Because of its high precision, high spatial resolution and other characteristics, it is widely used in aerospace, intelligent structure, material processing, optical network monitoring, biomedicine and other high precision measurement and manufacturing fields. In this paper, the basic principle of OFDR is described. The research progress of key technologies to improve OFDR performance is introduced. Finally, the application of OFDR in different fields and to the future development trend are summarized and prospected.

Because ultra-intense ultra-short laser has a large beam in space and a short pulse in time, the spatiotemporal coupling effect, for example the pulse-front distortion, frequently appears, which leads to a separation between the pulse-front and the phase-front in space-time, such as the pulse-front tilt or curvature, and is not conducive to obtaining the expected high focused intensity. However, when this pulse-front distortion (control) is applied in the X-shape optical wave-packet, a new degree of freedom is introduced for freely controlling the group-velocity and the group-acceleration of the optical wave-packet, enabling superluminal, subluminal, accelerating, decelerating, and even dynamically-controllable group velocities. By reviewing the pulse-front distortion (control)'s adverse effects in the ultra-intense ultra-short lasers and its special performances in the X-shape optical wave-packets, we try to provide some reflections on the cross-application of the same optical phenomenon in different research directions.

Wide color gamut technology is one of the hot topics in the direction of image quality enhancement, which can considerably improve the color reproduction ability of video images and improve the visual perception of the human's eyes. The method of expanding the color gamut is divided into three main directions, the transmission of "negative" color light, high-saturation three-primary colors, and multi-primary colors. First, the research significance of wide color gamut technology is briefly described, then the existing standard color gamut and normal wide color gamut standards are introduced, and the imaging and display technology of multi-primary-color wide color gamut is elaborated. Finally, the problems to be solved in this field and the future development trend are discussed.

Single-pixel imaging applies a series of spatial light modulated patterns to subsample the target scene with the assistance of a single-pixel detector, and subsequently reconstructs the object image according to the correlation between patterns and measurements. This indirect image acquisition method ensures reconstruction quality because of the reconstruction algorithm applied, and more crucially, the measurement mask construction. With the introduction of compressed sensing theory, random patterns emerged, but making the measurements blind and lacking specificity. Such patterns fail to facilitate storage and calculation, and thus significantly limit spatial pixel resolution. Recently, Hadamard basis patterns received widespread attention owing to their structured features that enable fast computation and facilitate storage and extraction. Considering this, numerous optimized ordering methods for the Hadamard basis patterns were developed, and proven to significantly reduce the sampling ratios. This study systematically reviews the design frameworks and frontier advances of these methods, and summarizes the future development trends of deterministic pattern construction. Finally, this contribution provides a beneficial reference point including guidance for subsequent research in this specific field.

Spectral imaging is a method that integrates spectral and imaging techniques to extract spatial information and spectral information of an object to form a three-dimensional hypercube. As a fast and nondestructive optical inspection method, spectral imaging can meet the requirements of forensic science for examining physical evidence. Specifically, it plays a crucial role in the appearance, identification, and classification of trace evidence. In this study, the principle and workflow of spectral imaging are introduced, followed by cutting-edge applications in forensic science, such as examinations of document, blood stain, and fingerprint. Furthermore, the dilemma and future trend of spectral imaging are analyzed to promote further technological development that can serve forensic science.

Vision-based optical 3D reconstruction method has found wide applications in situations where the detection range is limited, and non-contact methods are preferred, as they offer rich information with minimal scene intervention. This study aims to introduce various methods used for 3D reconstruction, including laser scanning, structured light, moire method, time of flight based on active vision, stereo vision, and structure from motion based on passive vision. In addition, extensive comparisons of these methods are analyzed in detail. Next, the application of optical 3D reconstruction technology in crop information perception research is summarized and discussed. Finally, the study offers future perspectives on optical 3D reconstruction.

Near infrared spectroscopy and hyperspectral imaging techniques have been widely used in agricultural and forestry products as well as food detection in recent years due to their advantages of high efficiency, nondestructive, and noncontact. These two techniques are applied to obtain spectral and imaging information of samples, and then chemometrics and machine learning modeling methods are combined to detect their quality and safety traits, adulteration issues, physical and chemical indicators, and origin traceability. Currently, they are both well recognized by people worldwide. However, the operating environment of optical instruments and the properties of the tested samples have their own limitations. The optical detection results are susceptible to various factors, which significantly affect the detection accuracy and should be eliminated or weakened. In this manuscript, the basic principles of near infrared spectroscopy and hyperspectral imaging are briefly described, and the influencing factors of these techniques at home and abroad are summarized. Considering the works of domestic and foreign researchers in related areas, the application of related correction methods regarding five aspects including temperature, illumination, moisture, curvature change and humidity is elaborated. Suggestions are finally presented for several existing problems to provide reference for researchers in this field.

Optical diffraction tomography (ODT) uses refractive index (RI) as endogenous dyes to non-invasively obtain three-dimensional (3D) structural information of biological samples, and is promising to achieve long-term dynamic observation for living samples (such as live cells, etc.), which is of great significance in the fields of biomedical and life sciences. However, ODT relies on weak scattering approximation and interferometric measurement. The former greatly limits the observation performance of this technology on thick samples such as clustered cells and tissues, and the latter significantly increases the complexity of the imaging system. To address these issues, researchers have developed a class of diffraction tomography based on the principle of non-interferometric intensity measurement. First, a basic description of non-interferometric intensity diffraction tomography (IDT) is provided, including its imaging system, imaging metrics, and reconstruction problem; Then, we introduce the research results and latest progresses of non-interferometric IDT from four technical routes: non-interferometric phase retrieval, 3D optical transfer function, multi-layer forward propagation model, and neural network, and compare the above methods; Finally, current problems and challenges as well as future research directions are discussed.

Three-dimensional (3D) inorganic micro and nanostructures play an important role in photonics, quantum information, aerospace, energy, and other fields. Inorganic microstructures prepared using traditional methods usually exhibit low resolution and uncontrollable morphology. The precise and controllable fabrication of 3D inorganic micro and nanostructures is a critical problem. Because of advantages such as 3D fabrication capability, high precision, and controllable morphology, laser fabrication can realize the preparation of 3D, high-resolution, and multiscale micro and nanostructures; furthermore, it can address the problem of accurate and controllable preparation of these 3D structures. In this study, the research progress of laser fabrication of inorganic micro and nanostructures was reviewed. First, continuous wave and ultrafast pulse laser fabrication methods were discussed, and especially, the femtosecond laser fabrication of 3D inorganic microstructures and nanostructures, including pure inorganic material systems, organic-inorganic hybrid systems, and polymer templates, were summarized. Further, the applications of 3D micro and nanostructures in optical devices, quantum chips, information storage, aerospace, and bionic structures in recent years were summarized. Finally, we highlighted the potential future development of the laser fabrication of 3D inorganic micro and nanostructures.

The restricted optical aperture and limited measurement bandwidth of microscopy impose constraints on information acquisition, particularly during the observation of dynamic processes within fine subcellular structures and ultrafast and transient biological events in vivo, and efficient three-dimensional imaging of mesoscopic ex vivo tissues within biological systems. This limitation represents a formidable hurdle in the landscape of multidisciplinary biomedical research. Traditional constraints associated with fluorescence microscopy have prompted studies on innovative principles and methodologies. By integrating artificial intelligence, efforts have been directed toward enhancing the speed and precision of fluorescence microscopy imaging, thereby augmenting information throughput. In this study, a meticulous analysis of problems posed by throughput limitations encountered in the fields of cell biology, developmental biology, and tumor medicine. Through the integration of artificial intelligence, traditional constraints associated with fluorescence microscopy throughput were surmounted. This pioneering approach paves the way for the advancement of physical optics and image processing and greatly contributes to the evolution of biomedical research. This study offers comprehensive insights into intricate phenomena within the realms of life and health, not only holding paramount importance for biomedical exploration but also unveiling promising avenues for future studies and applications.

Antichiral topological photonic states are a new type of waveguide states that are robust against backscattering and immune to defects. They propagate unidirectionally in the same direction along two parallel boundaries of topological photonic crystal and show broad application potential in topological lasers, integrated optical circuits, and quantum information. This review focuses on the research progress in antichiral topological photonic states, starting from the Dirac model and derivation of the classical Haldane model, antichiral Haldane model, and heterogeneous Haldane model, which demonstrate the transmission behavior of different types of topological photonic states. In addition, the implementation of chiral edge states, antichiral edge states, and one-way bulk states in photonic crystals is discussed. Next, the construction of topological optical devices based on antichiral topological photonic states, such as compact unidirectional waveguides, topological ring cavities, and topological beam splitter, are introduced. Finally, the critical issues and future development trends in research on antichiral topological photonic states are analyzed.

Holographic display technology, which is considered to be the most ideal three-dimensional (3D) display technology, can accurately recover 3D image containing all the information of the object and provide the user a natural and real visual experience. Accurate acquisition of 3D real-scene data is important for realizing high-quality holographic 3D display and application. This paper compares various methods of 3D scene data reconstruction, introduces the basic principles of active, passive, and deep-learning-based reconstruction methods, analyzes the characteristics, advantages, and disadvantages of various methods, summarizes the basic methods of 3D reconstruction based on deep learning, and discusses the application prospect of combining them with holographic display technology. This article provides a reference for the further research on holographic 3D displays.

Single-shot ultrafast optical imaging is a technique that can characterize transient events under universal conditions, opening the door to the study of nonrepeatable and difficult-to-reproduce ultrafast phenomena. It is an essential tool for exploring unknown fields and has great scientific and technological value. This article introduces the research progress of single-shot ultrafast optical imaging in recent years, including the principles, technical characteristics, applications, advantages, and limitations of typical representative technologies. Specifically, we summarize the active detection methods, focusing on 15 representative techniques in 5 subcategories. Then, we provide a brief explanation of the passive detection methods. Finally, we review the applicable scenes and existing problems of various single-shot ultrafast optical imaging techniques and discuss the possible development trend in the future.

Single-pixel imaging reproduces scene images by modulating the light field to measure the intensity response of the scene with a single-pixel detector. Compared with traditional imaging techniques that rely on arrays of detectors to capture image information, single-pixel imaging excels in low-cost, broad-spectrum, and application-specific scenes. This technique is a novel imaging approach that shifts from the physical to the computational domain; hence, many studies are exploring efficient computational approaches. Owing to the powerful learning capability of neural networks in the computational domain, deep learning techniques have been extensively employed in single-pixel imaging and have made remarkable progress. In this paper, deep learning single-pixel imaging is categorized into three modes: data-driven, physical-driven, and hybrid-driven modes. Within each mode, neural networks are further categorized as "image-to-image" and "measurements-to-image" imaging methods. The basic theories and typical cases of single-pixel imaging methods based on deep learning are reviewed from six perspectives, and the advantages and shortcomings of each method are discussed. Finally, single-pixel imaging methods based on deep learning are summarized and discussed, and promising applications include hyperspectral imaging, transient observation, and target detection.

Optical scattering induced by microscopic inhomogeneities in the refractive index poses a remarkable challenge to achieve optical focusing inside deep biological tissues. The wavefront shaping technique is emerging as a promising solution to this challenge because optical focusing is achieved through scattering media by compensating phase delays among different scattering paths. The effectiveness of this technique relies on the deterministic design of the scattering medium because even minor changes in scatterers can disrupt phase compensation, thereby resulting in degraded focus quality or complete loss of focus. However, practical applications often involve dynamic scattering processes. For example, physiological activities in living organisms, such as blood flow, heartbeat, and breathing, induce dynamic scattering processes. Consequently, enhancing the modulation speed of the wavefront shaping system is crucial to ensure successful operation in biomedical applications involving live tissues. To address this challenge, this review offers a comprehensive introduction to the state of high-speed wavefront shaping systems, outlines future directions for optimizing system speed, analyzes potential applications in biomedical science, and provides a prospective outlook on the future development of wavefront shaping.

Fundus imaging plays a vital role in research on the ophthalmology, diagnosis, and treatment of fundus diseases. Confocal scanning laser ophthalmoscope has superior imaging quality, wide applicability, and unique axial resolution, making it dominant in fundus imaging. We present a review of the principle and technical developments of confocal scanning laser ophthalmoscopy in ultra-wide field and high-resolution fundus imaging and analyze the challenges of confocal scanning laser ophthalmoscopy. Finally, we discuss the future development prospects based on existing challenges.

Microlens arrays, as an optical element, can realize high-quality imaging because of their high resolution and infinite depth of field. Additionally, they exhibit important applications in the fields of optical communication and optical sensing. In recent years, advancements in optoelectronics, micro and nanotechnology, smart materials, and other disciplines have spurred research on the tunability of microlens arrays, enabling microlens arrays to overcome the defects of fixed focal lengths. Furthermore, tunable microlens arrays greatly improve the flexibility of devices. This paper summarizes the recent research progress in three aspects, including shape tuning of microlenses, refractive index tuning, and superlens tuning; describes the principles and methodologies involved in tuning microlens arrays in detail; discusses the advantages and drawbacks of various tuning methods; introduces the application potential of tunable microlens arrays; and finally envisages their future development trends.

Deflecting light waves is an important capability in the manipulation of optical fields and serves as a fundamental aspect in numerous optical applications. With the vigorous development of optical technology, there is an urgent need for optical devices that balance miniaturization and beam deflection ability. Metasurfaces, which are planar devices constructed by arranging sub-wavelength nano-structures with specific order, can redirect light waves towards non-specular directions due to the ability to modulate electromagnetic waves with arbitrary customization, offering the potential to play a significant role in practical applications. In this paper, we first introduce the physical mechanisms underlying the high-efficiency anomalous deflection metasurfaces, then provide a review and discussion of the applications of anomalous deflection metasurfaces and finally summarize potential challenges, offer a glimpse into the future development of anomalous deflection metasurfaces and their applications.

Today, we celebrate the 60th anniversary of Laser & Optoelectronics Progress (LOP), the pioneering academic journal in the fields of lasers and optoelectronics. Since 1964, LOP has been promoting development of laser and optoelectronics in China by translating and publishing the high-quality papers. Throughout its 60 years, LOP has been led by some of the most prestigious figures in the field of lasers and optoelectronics. Deng Ximing, Academician of the Chinese Academy of Sciences, was the founding Editor-in-Chief (1964—1997) and lay the foundation for the journal's scholarly pursuits. Subsequently, Fan Dianyuan, Academician of the Chinese Academy of Engineering, has become the successor since 2004. LOP has undergone transformations from its original name Guangshouji Fashe Qingbao to Jiguang Qingbao,then to Guowai Jiguang,and finally its current name Laser & Optoelectronics Progress. A notable milestone of LOP, transitioning into a semi-monthly journal, occurred in 2019. In order to report the sophisticated progress, LOP started to publish the special issue of "Advanced Imaging" in 2020. An impressive submission exceeding three thousand manuscripts was achieved. The transformation trajectory of LOP is exhibited from its inaugural publication to the enterprise and cluster publishing, ultimately adapting to the dynamics of new media and network dissemination. To learn more about LOP, the publication data, database inclusion, citation indicators and the honors from LOP's rich history are explored. We will continue in our mission to stand up for research, serve the research community and communicate the results of lasers and optoelectronics.

Frequency-locking technology has greatly promoted the development of cavity ring-down spectroscopy in the field of spectral absorption. Therefore, cavity ring-down spectroscopy has gained advantages such as higher precision, better sensitivity, and increased stability. Based on the basic principles of classical cavity ring-down spectroscopy and frequency-locking technology, this paper reviews the current research status of frequency-locking technology in the field of absorption spectroscopy and its applications pertaining to atmospheric trace gases. This paper also lists several frequency-locking technologies that are widely used in the field of cavity ring-down spectroscopy. Finally, the application prospect of frequency-locking technology is determined combining the current development trend of frequency-locking technology and cavity ring-down spectroscopy technology.

Laser cladding has the advantages of compact microstructure, good bonding between coating and substrate, and small dilution rate and deformation. Co-based alloy is widely used in laser cladding because of its high hardness, good wear resistance, high temperature resistance, and corrosion resistance. In this paper, the research status of laser cladding preparation of cobalt-based alloy coatings at home and abroad is analyzed, and the influence of main process parameters such as laser power, scanning speed, and powder feeding rate on the quality and performance of coating cladding is discussed. The related researches on additives such as hard phase ceramic powder, rare earth and solid lubricant additives, and other auxiliary processes to improve the performance of Co-based alloys are summarized. Finally, the insufficiency and development trend of laser cladding cobalt-based alloys are summarized and prospected.

Q-switching is the main way for thulium-doped fiber lasers to generate nanosecond pulses. First, the application status of active Q-switching, passive Q-switching, and gain switching in thulium-doped fiber oscillators is introduced, and the advantages and disadvantages of the three technologies are compared and analyzed. Second, the typical research results and technical bottlenecks of nanosecond thulium-doped fiber amplifiers with narrow pulse width, high average power, and high pulse energy are introduced, and the optimization measures are analyzed from three aspects: thermal management, nonlinear effect suppression, and amplified spontaneous emission suppression. Finally, the technology development trend of nanosecond thulium-doped fiber oscillator and amplifier is prospected.

Perovskite solar cells have been rapidly developed in recent years. As of 2022, solar cells based on perovskites have achieved a photoconversion efficiency of 25.7%, showing great potential in the field of photovoltaic devices. Despite their high conversion efficiency, the thermal and humidity stability of perovskite solar cells are still considered major barriers to their development. Metal ion doping has proven to be one of the most effective ways to improve the optoelectrical performance and stability of perovskite solar cells. Among the ions introduced, transition metals have been favored by researchers because of their unique properties such as multivalency. In this paper, the latest advancements of doped perovskite photovoltaic devices with transition metal ions are briefly reviewed, and the methods and strategies of doping against the electron transport layer, perovskite active layer, hole transport layer, and metal electrode layer are summarized. The law and mechanism of such methods used to optimize the structure, photoelectric performance, and stability of perovskite photovoltaic devices are discussed.

As an important passive optical component, long-period fiber gratings (LPFGs) have all the advantages of optical fiber sensors, such as anti-electromagnetic interference, corrosion resistance, high sensitivity, small volume, and compatible with fiber system, which have wide applications in the field of optical fiber sensors and optical communications. The paper summarizes the principle of mode coupling, the methods of theoretical analysis, fabrication techniques, and applications of the LPFGs in the field of optical fiber sensors and optical communications. The fabrication techniques include the laser inscribing techniques (UV laser, carbon dioxide laser, and femtosecond laser writing techniques) and non-laser techniques (arc discharge, mechanical micro-bending, cladding etching, fusion tapering, ion implantation, and acoustic wave modulation techniques). For the sensing application of the LPFGs, the characteristics of gratings on the temperature, strain, bending, torsion, and surrounding refractive index have been summarized. And their applications as all fiber filter, mode convertor, polarizer, and mode coupler have also been discussed for the applications in optical communication system. The paper is written in a tutorial style. We aim to provide a general reference for students, academics who are going to join in this field.

The excellent device performance of lead-based perovskite is attributed to its remarkable optical and electronic properties. This series of solar-cell absorber materials has greatly improved the energy conversion efficiency from approximately 3.8% initially to more than 25%. Despite the rapid development of lead-based perovskites, the toxicity of lead atoms and their instability under heat, light, and humidity hinder the practical application of this type of perovskite photovoltaic technology. Therefore, it is very important to develop lead-free, non-toxic, and eco-friendly halide perovskites to replace lead-based materials in practical applications. The research on lead-free halide perovskites is one of the current study frontiers. This review summarizes the application of lead-free double perovskite Cs2AgBiBr6 in perovskite solar cells, introduces the structure and material preparation methods of Cs2AgBiBr6, discusses the device performance of perovskite solar cells, analyzes relevant strategies to improve the performance of this type of photovoltaic device, and discusses the challenges and development directions of lead-free perovskites.

2 μm band laser has a wide range of applications, not only in the fields of lidar, laser ranging, and medical surgery, but also as a pump source for mid and long wavelength infrared lasers. Using laser diodes to directly pump thulium-doped crystals to obtain lasers in the 2 μm band is a direct and efficient technical means, which has attracted wide attention. This paper introduces the research progress of Tm∶YAG, Tm∶YAP, and Tm∶YLF pulsed lasers, and makes a summary and prospect.

Diffractive optical components were widely used in many fields such as optical sensing, optical communication, computational optics, laser beam shaping, biomedicine, and optical data storage. This paper first summarizes the development of diffractive optical elements based on scalar diffraction theory in various stages. The development of diffractive optical elements can be divided into four stages: Fresnel zone plate, hologram and kinoform, binary optical element, and diffractive optical element. The design principles, structural characteristics, processing difficulties, diffraction efficiency, and application possibilities in reality are analyzed for each stage of diffraction elements followed by an overview of diffractive optical elements based on vector diffraction theory. Finally, a summary of current applications of diffractive optical elements in conventional and new imaging and non-imaging systems is presented. The current problems in the development of diffractive optical elements are sorted out and the future development trend is predicted according to the corresponding problems, which will be a guide for the future research of diffractive optical elements.

With the development of satellite optical communication technology, networking through optical links can meet the access, transmission, and distribution needs of the explosive growth of internet services in the future. First, the satellite internet architecture based on optical communication and constellation types are introduced. Then the key technologies of the next generation of satellite optical network are analyzed, including photoelectric hybrid switching, satellite optical network wavelength routing, wavelength demand analysis, and traffic grooming technology. Finally, the technical development directions of satellite optical network are discussed.

Photonic neural networks (PNNs) are proposed to balance the demands between a substantial increase in computation ability and a decrease in computing power consumption, owing to the superiorities in terms of large bandwidth, low latency, and low power consumption in optical transmission. Hence, in recent years, PNNs have become the research hotspot both in academia and industry. By utilizing photons as the physical media, the basic computing units in artificial neural network algorithms can be built and experimentally demonstrated. In further, PNNs might be adopted as a new computing architecture with high performances and be applied to solve the practical applications. In this paper, the working principle and characteristics of the core optical devices in PNNs are described, along with the system architecture and application scenario. In addition, the present challenges and future development trends of PNNs are discussed, after reviewing the research progress of PNNs at home and aboard.

With the development of intelligent and connected vehicles, in-vehicle networks, as information sharing platforms between sensors, processors, and actuators in automobiles, are gradually moving in the direction of simplified architecture and higher bandwidth. In this paper, the bandwidth demand trend of in-vehicle network is analyzed through the introduction of the principle and bandwidth demand of several major new in-vehicle sensors on intelligent and connected vehicles. At the same time, based on the review of the network architecture and topologies of traditional in-vehicle networks, as well as the current progress of in-vehicle networks, we point out the bandwidth bottleneck faced by the in-vehicle networks under the trend of automotive intelligence, and optical fiber transmission is the development direction of future in-vehicle networks. Finally, through the analysis of the requirements of in-vehicle networks for optical fiber and the investigation of the latest research progress of plastic optical fiber transmission technology, the article shows that the in-vehicle optical fiber transmission is worthy of further research urgently.

Satellite-to-ground laser communication (SGL) can address the spectrum limitation of traditional microwave communication and satisfy the increasing communication demand of satellite ground links. The adaptive optics (AO) system is an integral part of SGL, and it can effectively suppress the impacts of atmospheric turbulence and improve link stability and reliability. This paper introduces typical optical ground-station AO systems at home and abroad and its primary parameters. Based on the research results of AO in laser communication, the development trend followed by the AO system, including its improved wavefront detection ability, enhanced correction capability, stabilized and reliable operating performance, and improved automatic operation, is summarized. This study provides a reference for AO system development in SGL to ensure better availability of SGL link.

Integrated radar-communication refers to waveform fusion based on hardware sharing to simultaneously perform radar and communication functions using one signal. Consequently, the system performance can be optimized, and the frequency-spectrum resources can be saved. In this paper, a systematic overview of the integrated radar-communication waveform is provided. Specifically, the technical connotation and development stage of the radar-communication integration are presented, the application potential of linear frequency modulation (LFM) signal in the integrated system is analyzed. And the research progresses of LFM-integrated waveform design, high-frequency broadband LFM signal, and LFM-integrated waveform optical generation and processing are summarized. Studies have shown that microwave photons play an important role in the future of integrated radar-communication systems, and radar-communication integration is a system integrating optical and electrical technologies and linking analog and digital technologies.

Majorana fermions (MF) obey non-Abelian statistics and have potential applications in topological quantum computation and quantum information processing. Several types of hybrid devices that can possibly host MFs in low-latitude condensed matter systems have been proposed in the last decade, including hybrid semiconductor nanowire/superconductor devices, iron chains on the superconducting surface, hybrid iron-based superconductor, and topological insulator/superconductor structures, with the analogous Majorana signals have been observed in the above hybrid system with different electrical means. And the proposal that there may be Majorana fermions in topological insulators has attracted much attention. Although a mass of theoretical schemes have been proposed consecutively, and similar Majorana signatures have been experimentally demonstrated, no conclusive evidence of the existence of MFs in low-latitude condensed matter systems is available and MFs-based topological quantum computing is difficult to achieve. In this review, we introduce several schemes for detecting MFs in low-latitude condensed matter systems, as well as elaborate on the different electrical means for probing MFs. Most MFs detection schemes focus on electronic transport properties recently, and in order to obtain more conclusive evidence of MFs, it is necessary to propose alternative methods for detecting MFs. Alternative setups or proposals for detecting MFs are thus required to obtain definitive signatures of MFs. We introduced an all-optical pump-probe technology accompanying hybrid micro- and nano-systems, and proposed a series of all-optical methods for detecting MFs, benefiting from recent progress in nanotechnology. Moreover, we also review the optical detection of MFs and MFs-induced coherent optical propagation. Finally, we anticipate quantum computation using MFs in solid-state quantum devices.

Optical chiral metasurfaces are 2D or quasi-2D photonic devices composed of subwavelength-scale units, which combine novel physics and cutting-edge nanofabrication development, can generate extremely strong optical chirality, and have broad application prospects, including chiral sensing, chiral particles separation, and active control. This paper introduces the fundamental mechanisms of chiral metasurfaces, summarizes domestic and foreign state-of-the-art studies from the perspectives of metallic and dielectric materials, and focuses on the circular dichroism and near-field chiral responses. This paper also addresses the application areas of chiral metasurfaces.

Currently, resources to improve the metrology and traceability of fluorescence flow cytometer are relatively limited. To study the technical development of flow cytometer based on fluorescence detection and accelerate progress toward standardization, this paper integrates domestic and foreign literatures. Furthermore, detailed information regarding types of fluorescence flow cytometers, their applications, standardization research progresses, and critical parameters including instrument resolution, scattered light and fluorescence sensitivity, fluorescence linear correlation coefficient, detection limit, accuracy, repeatability, and stability are summarized. Foreign and domestic conventional standards are available for several widely used metrology methods to evaluate fluorescence flow cytometer performance. Various research organizations and application areas have different requirements for flow cytometer performance. A complete and traceable set of metrology standards for characterizing flow cytometry, and corresponding evaluation methods enable reproducible and comparable research communications and discussions between laboratories.

Optical waves as information carriers can process two-dimensional information in parallel with high speed and have many degrees of freedom (e.g., wavelength, amplitude, phase, and polarization). Therefore, optical encryption technologies and optical cryptosystems demonstrate great potential for applications. With the rapid growth of encrypted data transmission volume, it becomes increasingly important to realize information compression while encrypting because it shortens the time required to process these data and substantially saves storage space. In this paper, we propose the concept of generalized optical image compression-encryption and categorize its compression strategies into three types, including plaintext, ciphertext, and synchronous compressions. On this basis, the specific compression methods suitable for each strategy are specified, and the research progress of optical image compression-encryption is introduced by describing the applications of these compression methods at some instances. Moreover, the potential future research directions of optical image compression-encryption are also presented.

Photoacoustic imaging technology combines the high contrast and high resolution properties of optics and the high penetration depth property of acoustics. It has developed into a distinctive and advantageous non-destructive inspection and imaging technology that uses ultrasonic signals generated by the photoacoustic effect to resolve depth information, thus locating objects in a three-dimensional space. In the field of cultural heritage conservation, materials used to make cultural artifacts have different optical absorption properties; thus, ultrasonic signals with different amplitudes and frequencies are generated and radiated outward when they are subjected to laser light excitation. The characteristics of ultrasonic signals can reveal the material type and detect surface defects; hence, photoacoustic imaging technology can be applied in cultural heritage conservation. This paper provides an overview of existing photoacoustic imaging technologies, describes their current developments and limitations for cultural heritage conservation, and summarizes the future prospects of the technology for these applications.

Minor changes to elements in organisms can have a direct impact on their metabolism and physiological processes. Rapid and accurate qualitative and quantitative analyses of these elements are critical for both metabolism detection and clinical disease diagnosis. As medical detection technology continues to develop and clinical demand continues to increase, researchers are seeking newer, faster, and more adaptable clinical analysis and diagnostic technologies. Because of its fast, real-time, and multi-element simultaneous detection capabilities, laser-induced breakdown spectroscopy (LIBS) technology has shown great promise in recent years for use in blood and pathological tissue detection and elemental distribution imaging. This paper provides a comprehensive review of the current research status and latest progress of LIBS technology in biomedical applications and evaluates the challenges and opportunities of LIBS technology in the application fields of blood detection, biological tissue analysis, and elemental imaging. The paper also provides suggestions for further promoting the application of LIBS technology in the biomedical field.

Terahertz technology is widely used in the field of nondestructive testing owing to its unique characteristics such as excellent perspective, low energy, high spectral resolution, and exceptional time resolution. The terahertz technology is particularly useful in obtaining the spectral information of precious cultural relics and can confirm the defect positions in their internal structure. These results can provide the technical support for subsequent conservation of cultural relics. This paper summarizes the domestic and international application prospects of terahertz spectroscopy and imaging technology in nondestructive and in situ testing. Terahertz technology can satisfy the requirements of national conversation, which is contributed to solve the exact problem of domestic cultural relic restoration. It has a certain promotion value and is of considerable significance for national conversation.

Night image dehazing technology has become an important research content in the field of image processing technology. It has important significance for target tracking detection, video surveillance, remote sensing and so on. Haze images at night usually have the characteristics of low contrast, uneven illumination, color offset, etc., which makes haze removal for night images face great challenges. Through summarizing the research status of night image de-fogging algorithms at home and abroad in recent years, the classical algorithms from the perspective of the physical model, non-physical model and deep learning are summarized, and the algorithm process, advantages and disadvantages are elaborated. Finally, the future research direction of the night fog removal algorithm is prospected.

Space division multiplexing (SDM) is a critical technology that can increase the capacity of existing single-mode fiber optic communication systems by tens of times. It is worth studying as an effective means to overcome the capacity bottleneck of traditional single-mode fiber optic communication systems. This overview introduces the key technologies and research progress of the multiplexer/demultiplexer, fiber amplifier, few-mode fiber, and optical transmission system integrated device in strong coupling communication systems with few-mode fibers. This overview also introduces some of the more classic or latest experiments in strong coupling communication systems with few-mode fibers, and discusses the future research directions of few-mode optical transmission system.

In order to meet the wide demands of single longitudinal mode continuous wave laser in various fields such as optical communication, optical sensing, precision measurement, quantum technology, and atomic physics etc., the stability and signal-to-noise ratio of the single longitudinal mode laser has to be improved. This paper discusses the intensity noise which plays a major role in output stability of a single longitudinal mode laser, and shows its main source and generation mechanism. On this basis, combined with comparative analysis of various methods, this paper gives the recent developments of suppression means of intensity noise. Aimed at improving output stability of single longitudinal mode fiber laser in high power laser facility, relevant study using semiconductor optical amplifier is given, which suppressed the intensity noise.

In recent years, Thulium-doped fiber laser has attracted more and more attention because of its compact structure, near diffraction limit beam quality, and high quantum efficiency. Among these laser sources, high power continuous wave (CW) thulium-doped fiber lasers have been widely used in many fields, such as medical treatment, military security, space communication, air pollution detection, material processing, and so on. In the past 20 years, high power CW thulium-doped fiber lasers have developed rapidly, and the highest output power has reached kilowatt level. In this paper, the high power CW thulium-doped fiber lasers reported in the past are reviewed from the aspects of oscillator and amplification system, and some views on the future development trend are given.

Based on earlier reports in the lithography technology field and global list of "highly-cited scientists", the research time and distribution characteristics of countries, research institutions, research funding institutions, and high-level basic research talents in the lithography technology are analyzed. Based on these two aspects, a bibliometric analysis of published works in the lithography technology field was performed to investigate the research direction, themes, and development trends in this field. The results show that the output of lithography technology papers is currently declining, and the United States has a leading edge in this research field. Research on optical lithography and masking, photoresist and electron beam lithography, extreme ultraviolet (EUV) lithography, and other technical topics is still dominated by foreign institutions. China has launched research on emerging themes, including high-numerical-aperture EUV lithography, guided self-assembly lithography, graphene-based materials, and machine learning applications. This study proposes suggestions for improving the overall layout, involved research institutions, enterprise strength, and talent mechanism of lithography technology research and development to provide a scientific basis for decision-making and research directions in related fields.

On the basis of different light guiding principles, hollow-core microstructure fibers can be divided into hollow-core photonic band gap fibers and hollow-core anti-resonant fibers. For these two types of fibers, scattering loss caused by the roughness of the inner wall of the air hole is one of the sources of loss. Scattering loss is the main source of loss in hollow-core photonic bandgap fibers. In hollow-core anti-resonant fibers, scattering loss is also one of the important reasons for loss during operation in the short-wavelength region. To reduce the scattering loss of hollow-core microstructure optical fibers, in-depth research on the roughness of the inner wall of the air hole is necessary. Therefore, in this paper, research progress on the relevant theory, measurement technologies, and suppression methods for the roughness of the inner wall of the air hole in hollow-core microstructure optical fibers are described. Further, relevant theory and experimental results are summarized, and important future research directions are suggested.

Hydrogen possesses highly reactive physical properties, which may lead to fire and explosion accidents in cases of leakage. Based on the arrangement of point-type hydrogen sensors, employing Raman-Lidar telemetry technology can enhance noncontact, remote, and large-coverage detection of hydrogen leakage, thereby facilitating the rapid development of diversified hydrogen energy utilization scenarios and ensuring the safe and efficient utilization of hydrogen energy. First, an overview of the fundamental principles of gas Raman scattering is provided. Second, the research progress in Raman-lidar telemetry technology for hydrogen leakage is examined, both domestically and internationally, from two aspects: system structure and detection effect. Finally, the prospective applications of Raman-lidar telemetry technology in hydrogen leakage monitoring and detection are studied.

Smoke screening is an effective passive interference countermeasure that is extensively used to counter various types of electro-optical reconnaissance and guided weapons. Evaluating smoke screening and its interference effects is crucial for assessing photoelectric countermeasures and tactical deployment, which constitutes the main focus of research within the context of smoke screen technology. Current evaluation methods are complex and lack a solid foundation; therefore, we proposed evaluation methods to better describe the smoke screening and interfering effects, based on a review of existing evaluation methodologies. These methods focus on the shielding performance of the smoke screening, the operational states of the interfered targets, and the changes in the image quality before and after smoke screening. Moreover, we discussed the proposed method's advantages and disadvantages, application occasions, and limitations. Finally, this paper outlines future research directions and emerging trends concerning the effects of smoke screening.

High dynamic range imaging images are images that truly represent the high dynamic range brightness of natural scenes, and can reflect more information about natural scenes. Multi-exposure fusion has become one of the important means to reconstruct high dynamic range images due to its advantages of no need to improve hardware and simple algorithm process, and has been widely used in mobile phone cameras, industrial cameras, and other fields. In this paper, the multi-exposure image fusion methods for static scenes and dynamic scenes were classified and summarized according to the fusion level and motion pixel processing methods, and the methods based on deep learning were analyzed and summarized separately. Secondly, the relevant datasets and performance evaluation indicators of multi-exposure image fusion were reviewed, and the performance evaluation indicators used in the fusion method were summarized. Finally, the issues worthy of attention in multi-exposure image fusion research were prospected, and ideas for follow-up related research were provided.

Super-resolution optical imaging technology has significant implications for biology, life science, and materials science. The mainstream technology to achieve super-resolution optical imaging relies on fluorescence imaging, but fluorescence-based super-resolution imaging cannot reveal molecular-specific information and causes cytotoxicity to living cells. In contrast, photothermal microscopy is a promising analytical technique that allows noninvasive imaging of molecular bonds. Therefore, photothermal microscopy can overcome the inherent limitations of super-resolution fluorescence imaging, making it an attractive option with excellent application prospects. This review discusses the theoretical basis of photothermal microscopy, development of the imaging technique, and the methodological developments that improve the detection limit and spatial resolution. We further provide future perspectives for promoting the development of high-sensitivity and super-resolution photothermal imaging technology.

The large amount of unstructured data generated by the Internet of Things and cloud computing has recently increased the demand for data computing power and energy efficiency. Referencing the information processing method of the biological brain with neuron and synapse as basic units, neuromorphic computing can simulate the biological nervous system from the aspects of interconnection architecture and information processing mode, and realize ultra-low power processing of real-time information, which have become the forefront of the development of computing technology in the big data era. The processing of computational data in the optical domain makes photonic neuromorphic computing research important owing to its high application potential. On the one hand, photonic neuromorphic computing can take advantage of high-speed transmission, low power consumption, and high parallelism of photons. On the other hand, it can also prevent photoelectric and electro-optic conversion, thus, reducing additional time and power consumption. In recent years, phase-change materials (PCM), as a kind of optical material with high refractive index contrast and non-volatile property, whose refractive rate can be continuously adjusted under the driving of optical, electrical, and thermal excitations, have provided a feasible solution for non-volatile photonic neuromorphic computing and have become the current research hotspot. In this paper, we first introduce the basic principle and implementation method of photonic neuromorphic computing. Subsequently, we discuss the principle of utilizing phase-change materials in photonic neuromorphic computing. According to the unique characteristics of phase-change materials selected in different implementation schemes, two kinds of phase-change materials and different applications of optical synapse devices and integrated arrays are then summarized. Finally, we prospect the development of photonic neuromorphic computing techniques based on phase-change materials.

In the field of geology, terahertz time-domain spectroscopy, with the characteristics of high signal-to-noise ratio, wide frequency bandwidth, and low incident wave photon energy as well as the advantages of simple instrument operation and fast testing speed, is used to characterize the composition, structure, and other parameters of rocks and minerals. In particular, the optical properties of rocks and minerals, water content in minerals, characterization of filler minerals, and modulation of minerals to terahertz waves are assessed. This provides a new analytical method for studying mineral formation conditions, mineralization, and mineral applications, thereby expanding the application scope of terahertz spectroscopy.

The transmission capacity of optical wireless communication systems has approached the Shannon limit, and the emergence of orbital angular momentum (OAM), as a lateral new space dimension resource, can exponentially improve the capacity and spectral efficiency of optical wireless communication networks. Adopting technologies of OAM-related can provide a potential solution for the realization of ultra-high speed and high capacity cross-scene optical communication in the future. On the basis of comparing and summarizing the relevant research results of OAM at domestic and overseas, this paper introduces the research work of OAM technology in the field of optical wireless communication in Xi'an University of Technology, which is mainly divided into the space generation, propagation characteristics, separation detection and application of OAM beams. Finally, the future development trend and prospect of OAM technology in the field of optical wireless communication are foreseen, which provides new thoughts and reference values for the subsequent researchers to explore in this field.

Metalenses are new advanced planar optical devices based on the metamaterials. They can control the amplitude, phase, and polarization of incident lights with high free degrees to satisfy application requirements. Furthermore, they can perform various functions through different structural designs, such as diffraction-limited focusing and aberration correction. In this paper, we summarize the basic principles, applications, and progress of metalenses. Based on the excitation principle, we classify metalenses into plasmonic and dielectric metalenses. Based on the function, we classify them into tunable, aberration cancellation, and broadband achromatic metalenses. We also summarize the parameter data, advantages and disadvantages, and commercialization process of relevant research. Moreover, we discuss the problems and challenges faced by metalenses and recommend future research directions. The main purpose of this paper is to clarify metalenses and provide potential inspiration for designing high-performance metalenses.

Seismic, infrasonic, and hydroacoustic monitorings are three types of remote waveform monitoring techniques stipulated in the Comprehensive Nuclear Test Ban Treaty (CTBT). Currently, the seismic, infrasonic, and hydroacoustic stations of the CTBT International Monitoring System (IMS) have traditional electrical sensing equipments. The distributed optical fiber-sensing technique is a new sensing method for determining variations in the vibration and strain at each point along the optic fiber based on the optical effect, and it has broad application prospects in the CTBT. The principle and development of the distributed fiber-sensing technique show that it can be directly applied to the detection system for obtaining vibration data during seismic, infrasonic, and hydroacoustic monitorings and applied to existing optical fiber communication facilities for obtaining supplementary information to the monitoring data. The detection system based on the distributed fiber-sensing technique exhibits distributed measurement, high sensitivity, and good stability. This study provides a new approach to improving seismic, infrasonic, hydroacoustic, and other detection equipments. However, the characteristics of the distributed optical fiber-sensing system, such as highly dense channels, high sampling rate, and a large amount of data, pose new challenges to the real-time processing of monitoring data. In addition, the impact of the distributed fiber-sensing technique on IMS monitoring capability should be further investigated.

Semiconductor lasers can be applied as ideal laser sources toward the development of laser and sensing technologies. For laser radar measurement, optical pumping, and fiber coupling, semiconductor lasers must have high power and high beam quality. The design of high-power semiconductor lasers promotes the easy production of multi-mode beams in the lateral direction, which decreases the lateral beam quality. Hence, the limitations induced by the lateral mode and the enhancement of the lateral beam quality of high-power semiconductor lasers have become important research topics. This paper focuses on three topics: the tapered laser, the method for the improvement of the lateral beam quality of a broad-area semiconductor laser, and the package structure of a semiconductor laser. Furthermore, the results and progress of domestic and international research on the control of the lateral beam quality are reviewed.

With the continuous development of medicine, optics, chemistry, communication and other fields, various micro total analysis system, lab-on-a-chip, micro electro mechanical systems and high-precision micro-nano devices began to appear and are gradually used. Most of these systems or structures are realized by preparing three-dimensional micro-nano connected structures in transparent materials by femtosecond laser. Therefore, the main technologies of femtosecond laser preparation of three-dimensional micro-nano structures are introduced, the main applications of micro-nano connectedstructures are summarized, the existing problems of current femtosecond laser preparation of three-dimensional micro-nano connected structures are put forward, and the technology is prospected.

The application range of biomedical imaging systems composed of smartphones has been continuously expanding. By designing an optical accessory adapter, the imaging function of such systems can be improved to carry out medical and clinical auxiliary diagnoses. Smartphone imaging systems have been utilized successfully in dermatology, ophthalmology, ENT, gynecology, and other fields. This study examines the present uses of smartphone-based medical device imaging systems as clinical aids for diagnosis, as well as the concepts and characteristics of the imaging technology used. Based on their application in different departments, the features of the imaging systems are analyzed and summarized as future development trend prospects. The aim of this work is to provide a reference for future research and development of smartphone-based medical imaging systems.

Non-diffracting beams have attracted attention in recent years due to their unique properties, such as diffraction-free propagation and self-repairing and self-accelerating ability, which make them promising candidates for microscopic imaging applications. Non-diffraction beams can suppress beam diffraction during propagation, thereby improving the imaging resolution. Moreover, their self-healing characteristic facilitates quick wave-front recovery after passing through a strongly scattering medium, enhancing imaging depth and signal-to-noise ratio. Their self-acceleration feature expands the detection dimension of light field information, enabling multi-dimensional reconstruction imaging. Based on the characteristics of several biological micro-imaging technologies, this paper discusses the application and research progress of non-diffracting beams, specifically Bessel and Airy beams, in high-resolution biological micro-imaging.

Correlation imaging, also known as "ghost imaging", is a new imaging method. It calculates the coincidence between a detected light signal carrying the light intensity information of an object and the measurement matrix of the reference light path; the image information of the object is obtained by using the second-order intensity correlation characteristics between the two light paths. Different from traditional optical imaging, correlation imaging has the advantages of strong anti-noise ability and various imaging methods, which can reduce the influence of scattering medium on the disturbance and attenuation of optical signals. Since the first ghost imaging experiment in 1995, it has become one of the most popular research topics in classical and quantum physics. In this article, the history of ghost imaging development, its theoretical principle, and the latest research on ghost imaging applications are presented.

Image inpainting is a hot topic in the field of computer vision. It is a process that enables filling in damaged regions with alternative contents by estimating the relevant information either from surrounding areas or external data. With the advent of big data, image inpainting methods based on deep learning have attracted significant attention in image processing because of their excellent performance. This paper presents a brief review of existing image inpainting approaches and discusses the network structure and performance of each algorithm, along with a comparison of widely used datasets. In view of the existing challenges in this field, this paper proposes potential research directions and developmental trends in image inpainting.

Computational imaging compressively encodes high-dimensional scene data into low-dimensional measurements and recovers the high-dimensional scene information using computational reconstruction techniques. In the era of big data, the increasing demands for high spatiotemporal resolution have promoted the development of large-scale reconstruction algorithms with high accuracy, low complexity, and flexibility for various imaging systems. The existing large-scale computational reconstruction methods, including alternating projection, deep image prior, and plug-and-play optimization methods, have made great progresses over the past decades. Among the abovementioned methods, the alternating projection has been utilized in gigapixel quantitative phase imaging systems. Besides, the deep image prior and plug-and-play optimization techniques combine the advantages of conventional optimization and deep learning, which hold great potential for large-scale reconstruction. This work reviews the architectures and applications of these methods and prospects for the research trends, which can provide highlights for future works of large-scale computational imaging.

Excimer laser is a kind of deep-ultraviolet laser source with high power output, which has unique applications in many aspects. However, there is still a gap between the domestic excimer laser industry and foreign countries in key technologies and high-end products, and there is a situation of stuck neck. First, this paper introduces the basic characteristics, application classification, briefly development and status of excimer laser. Second, the basic structure and some key technologies of practical devices of discharge-pumped excimer laser are introduced, including fast pulse excitation source, gas discharge cavity, optical resonator and so on. Finally, the main applications and progress of discharge-pumped excimer laser in industry, medical treatment, scientific research, and other fields are introduced, as well as some unique key technologies.

Phase-shifting interferometry is a noncontact optical measurement method with high sensitivity. This method is widely used in optical surface and deformation measurements. However, environmental vibrations can have a significant influence on the obtained measurement results, producing fringe jitter and interference pattern ambiguity. To address these issues and improve the stability of phase-shifting interferometry, the anti-vibration technique can be used. In this article, the anti-vibration technology is divided into active and passive categories. Active anti-vibration is used for vibration isolation, that is, weakening the intensity of the vibration signal transmitted to the interference system. Passive anti-vibration is used to eliminate the influence of vibration on interferometry. Several types of passive anti-vibration technologies have been developed so far. In this article, existing passive phase-shifting interference anti-vibration technologies are classified and compared with respect to the frame number and real-time performance. Furthermore, the development direction of phase-shifting interference measurement anti-vibration technology is discussed.

The random metal grid transparent conductive film is a metal grid transparent conductive film with irregular structure, which has good light transmission and electrical conductivity. Compared with the regular structure metal grid transparent conductive film, the random metal grid transparent conductive film has better optical diffraction performance under the premise of the same optoelectronic performance. In addition, the random grid transparent conductive film based on the crack template method has obvious cost-effective advantages compared with the traditional metal grid transparent conductive film, so it has attracted much attention. The performance, research status, related preparation technology, and the latest research progress of random metal grid transparent conductive films with three structures of artificial random network, bionic random network, and self-splitting random network are discussed in detail. On this basis, the related applications of random grid transparent conductive films are introduced. Finally, the future research priority and development direction of random grid transparent conductive films are prospected.

The quality of laser cladding coating is determined by various process parameters and their interactions. Shape control of cladding coating can be realized by optimizing process parameters. In this paper, from the perspective of traditional optimization methods and intelligent optimization methods, the research status of cladding coating quality optimization at home and abroad was described in detail, the advantages and disadvantages of various optimization methods were summarized and discussed, and the role of different optimization methods in improving coating performance was analyzed. Finally, the future development trend of coating quality optimization method was prospected. The purpose of this paper is to provide an optimization method for the preparation of high quality cladding coating and to provide a reference for the future research of laser cladding process optimization method.

The power improvement of semiconductor lasers is of great significance to several fields, including those of national security, laser communication, laser detection/sensing, laser lighting, medical treatment. As the semiconductor laser beam combining technology can considerably improve the output power while ensuring the beam quality, it has attracted wide attention in recent years. Spectral beam combining (SBC) and coherent beam combining (CBC) are two typical semiconductor beam combining technologies, and many institutions have made breakthroughs in relevant research. In this paper, the development of these semiconductor laser beam combining technologies is reviewed and their prospect is discussed.

The pulse duration compression via stimulated Raman scattering (SRS) has important applications in high-power short-pulse laser generation due to its characteristics of high load, high compression ratio, and phase conjugation. In this paper, the research progress of SRS pulse duration compression is analyzed and summarized from the aspects of SRS compression mechanism, gain medium, and compression structure.

Laser rock-breaking technology has great potential in oil and gas exploration, mining, and related fields. However, most studies on laser rock breaking are in the theoretical and experimental exploration stages. High-energy laser drilling and rock breaking are complex and involve optics, material science, mechanics, and other disciplines. It is necessary to examine the physical and chemical changes, rock mechanical properties, laser parameters, and other issues during the interaction between the laser and rock. Before practical applications can be achieved, many challenges must be addressed. This paper summarizes the recent research results on the interaction mechanism between lasers and rocks. In the ongoing research on the mechanism of laser rock breaking, numerical simulations and experimental research are the main approaches. This paper also reviews the application research progress in laser rock breaking and analyzes the future development trends of laser rock breaking.

The mid-infrared band has broad applications, such as fundamental science, biomedicine, environmental testing, national defense, security, communications, and entertainment. As the core component of mid-infrared technology, a high-performance mid-infrared coherent radiation source with a wide spectral range, high energy, high conversion efficiency, miniaturization, and room-temperature operation has been a research focus in scientific research and application. There are many types of mid-infrared lasers. According to different generation principles, mid-infrared lasers are mainly divided into chemical lasers, gas lasers, and lasers based on rare earth or transition metal ion doping, quantum cascade semiconductor lasers, and lasers based on nonlinear frequency conversion. This paper focuses on the characteristics and development of these lasers and discusses their research prospects.

Femtosecond laser has been an important processing technique for micro/nano structures in recent years. It can modify and ablate materials, and is capable of machining high-precision three-dimensional structures in specific areas. Femtosecond laser machining has broad application prospects in micro/nano processing. In this paper, the general interaction process between femtosecond laser and metals is described, and the methods for the preparation of micro/nano structures are introduced, such as femtosecond laser direct writing, femtosecond laser induced surface periodic structure, and femtosecond laser composite chemistry method. Then, the applications of femtosecond laser for the preparation of micro/nano structures on metal surfaces in environmental engineering, aerospace, and biomedicine are discussed. Finally, the shortcomings and future research directions of preparation of micro/nano structures by femtosecond laser are summarized and prospected.

In recent years, fluorescent optical fiber sensors fabricated using novel fluorescent materials have been used widely in the marine environment, water quality monitoring, and blood analysis owing to their advantages of intense luminescence, high sensitivity, real-time monitoring, and simple operation. This paper discusses the most recent development of fluorescent optical fiber sensors in the fields of dissolved oxygen, pH, and carbon dioxide detection, and summarizes the detection mechanism, advantages and disadvantages, and main performance parameters of different types of fluorescent materials. Finally, future development direction for fluorescent optical fiber sensors is analyzed and prospected based on the problems and challenges encountered at present.

Chalcogenide glasses have excellent mid- and far-infrared transmittance and extremely high nonlinear coefficients, and were seen as excellent candidate materials for realizing the mid-infrared supercontinuum generation. Recently, researchers at domestic and abroad have explored continuous optimization of supercontinuum output characteristics by adjusting the matrix materials, optimizing the structural parameters, and improving the pumping source. In this article, the development course of supercontinuum generation in chalcogenide fibers was reviewed. Moreover, the most recent progresses about the spectral broadening, output power, and coherence of supercontinuum generated in three kinds of chalcogenide glass fibers, including step-index, microstructure, and tapered fibers, were reviewed. Finally, the problems existing in the researches and the development trends were analyzed and prospected.

The use of few-mode optical fiber strong coupling mode division multiplexing technology is a major solution for large-capacity optical fiber communication systems, and digital signal processing can compensate for channel damage in the digital domain, providing flexibility for signal recovery and further improving transmission capacity. In this paper, the impairments which occur in the few-mode fiber system with strong mode coupling but not in single-mode fiber system are introduced. The recovery techniques for those impairments like multiple input multiple output (MIMO) equalizer, space-time coding (STC), interference cancellation, and maximum likelihood estimation as well as their principles and research results are also introduced. The shortcomings of those algorithms in terms of complexity, delay, and transmission rate are also discussed. The results show that MIMO equalization algorithm combined with STC has obvious advantages. It has important application significance in the high-capacity long-distance few-mode fiber communication system with strong mode coupling in the future.

Infrared detection systems have the characteristics of good concealment, strong anti-jamming ability, etc. and are widely applied in military and civil fields. The detection of small and weak targets is an important part of an infrared detection system and has become an attractive research area. Recently, scholars have made remarkable achievements in the research of infrared dim small target detection algorithms based on the low-rank sparse decomposition. This study focuses on the research status and development of infrared dim small target detection algorithms based on the low-rank sparse decomposition and presents a detailed review on three aspects: background component constraints, target component constraints, and joint time-domain information constraints. First, the constraints of the background component are divided into the low-rank constraint of block image, low-rank constraint of tensor, and full variation constraints. Second, the constraints of the target component are analyzed from two aspects: the sparse representation of targets and the target component weighting strategy of fusing local priors. Then, the joint time-domain information constraint is analyzed. Furthermore, the performances of a typical detection algorithm based on the low-rank sparse decomposition and a single frame detection algorithm are compared. Finally, future research direction in this field is highlighted.

Optical coherence tomography (OCT) is a new imaging technique widely used in ophthalmic disease diagnosis and other measurement and detection fields. A swept source OCT (SS-OCT), as a main technical path of OCT, has become the research focus in the field of OCT in recent years because of its advantages of fast imaging speed, deep depth, and high resolution. Because the performance of SS-OCT is mainly determined by the performance of the frequency swept laser, the research and development of the frequency swept laser are very important. This paper mainly summarizes the research progress of frequency swept laser. From the aspects of technical means, design ideas, performance indicators, etc., the research progress of frequency swept laser and the research status of the frontier in the field are introduced and summarized in detail.

The development of silicon-based optoelectronics technology can integrate discrete active and passive components in the transmitting module and receiving module of the LiDAR system on the chip, making the LiDAR smaller in size, more stable and lower in cost, and accelerating the application of LiDAR in autonomous driving and other fields. In this paper, the basic concept and principle of LiDAR is first analyzed. Then, according to the different scanning modes, the LiDAR on silicon substrate is divided into four categories: array flash, optical phased array, lens-assisted beam steering, and slow light grating. The technical characteristics and recent progress of these four categories are described respectively. Finally, the development trend of LiDAR on silicon substrate is summarized and prospected.

Camera calibration is essential in photogrammetry and computer vision. Herein, the application and classification of camera calibration are first introduced. Subsequently, the theoretical basis of calibration is summarized, including spatial coordinate system transformation, geometric imaging model, internal and external parameter calculation methods, and camera calibration methods described based on classical and intelligent aspects. Conventional calibration methods include reference object-based, active vision, and self-calibration methods. Then, a comprehensive analysis of their advantages and disadvantages is provided. Meanwhile, in intelligent calibration, error backpropagation, multilayer perceptrons, and convolution neural networks are involved. The typical indexes used to evaluate camera calibration methods are summarized. Finally, a summary is provided, and the development direction of camera calibration technology is discussed, which can provide a reference for researchers investigating camera calibration.

Dye-sensitized solar cells (DSSC) are one of the ways to effectively utilize solar energy because of their characteristics of simple preparation process and low cost. The composition, structure and working principle of dye-sensitized solar cells are briefly introduced. The TiO2 photoanode material, as an important part of dye-sensitized solar cells, is introduced in detail. The current research results of TiO2 electrode are summarized, and the influence of TiO2 photoanode material modification on DSSC performance is analyzed. At the same time, the future development direction of TiO2 photoanode is prospected.

Laser lithotripsy is one of the many fields in which laser has been used since its inception. The thulium-doped lithotripsy fiber laser has evolved in recent years and has gradually been proven to achieve faster lithotripsy rates with powdered lithotripsy, generate less lithotripsy counter-thrust, allow higher liquid irrigation rates, and other surgical advantages, while the whole system supports water-free operation, high electro-optical efficiency operation, efficient all-fiber coupling, and substantial volume reduction. Therefore the thulium-doped lithotripsy fiber laser has attracted increasing interest. In this paper, some important research progresses of thulium-doped fiber lasers are summarized in detail from three aspects: continuous-wave, quasi-continuous-wave, and nanosecond short-pulsed thulium-doped fiber lasers, and the applications in the field of lithotripsy are introduced. We present the advantages and principles of thulium-doped fiber laser for lithotripsy and look forward to the directions and challenges for future research.

Inverted perovskite solar cells (PSCs) have been attracted more and more attention thanks to its simple architecture, negligible hysteresis, and low manufacturing cost. Electron transport layer is an important component of perovskite solar cells, which is facilitate with electrons transfer and blocks holes. The modification of electron transport layer can effectively improve the roughness for surface, energy level, and electron mobility, so as to improve the photoelectric conversion efficiency. In this paper, the influence of ETL on the performance of inverted perovskite solar cells is reviewed from the selection of electron transport layer materials, interface modification and doping of electron transport layer and the modification, and the commercialization of inverted perovskite solar cells in the future is prospected.

Quantum precision measurements are crucial for basic research and original innovations. As a vital research topic, the interaction between a laser and thermal-alkali atomic ensemble is significant for the frontier investigations of physics and technical applications, being one of the frontiers of scientific research. Notably, studies and applications based on laser-atom interactions have facilitated breakthroughs in the principles and technologies for ultrahigh precision and miniaturization of an array of precision measurement sensors represented by spin exchange relaxation-free (SERF) atomic magnetometers, coherent population trapping (CPT) atomic clocks, and SERF atomic spin gyroscopes. This review analyzes the achievements and progress in the magnetic field, time, and inertial measurements in recent ten years, and these are summarized from the perspective of the principle and application of the interaction between a laser and thermal-alkali atomic ensemble. Furthermore, prospects for the future development of devices based on the interaction between a laser and thermal-alkali atomic ensemble are discussed.

Lead selenide colloidal quantum dots (PbSe QDs) have huge application prospects in room temperature infrared optoelectronic devices due to their excellent properties such as enhanced multiple exciton generation, large exciton Bohr radius, wide range of the tunable wavelength, and high photoluminescence quantum yield. However, the problems of poor photoluminescence stability and low efficiency of PbSe QDs synthesized via the solution method further limit their development owing to the oxidation of quantum dot surfaces and poor carrier transport performance. Therefore, a systematic discussion of the effects of the surface modification engineering of PbSe QDs on its mobility, trap states, energy level shift, photoluminescence efficiency, and stability modification is presented in this paper. Additionally, a summary of the application of surface modification engineering in PbSe QDs solar cells, light-emitting diodes, and photodetectors is provided. Finally, the problems existing in the practical application of optoelectronic devices and future research directions are outlined.

As a core component of the acquisition tracking and pointing (ATP) system, the fast steering mirror (FSM) is widely used in satellite laser communication, laser weapons, adaptive optics imaging, high-precision laser aiming, and other applications because of its fast response, high accuracy, and high resolution. This paper presents the working principles of the FSM and ATP system. Various FSM devices of global research institutions are reviewed based on several parameters, such as driving mode, FSM figure, working bandwidth, range of scan angle, control precision, volume, weight, power consumption, and applications in satellite laser communication. Three main classes of FSMs [the voice coil motor, piezoelectric ceramics, and micro-electro-mechanical system (MEMS)] are elaborated. The operating mode and performance difference of FSMs with different driving structures are described, and the critical parameters for applying FSM in the ATP system are analyzed. The key technologies of FSM in laser communication are prospected. It is concluded that high precision, digitalization, and miniaturization are the future trends of FSM.

With the rising and research deepening of new technologies such as laser radar, gravitational wave detection, and optical atomic clock, The breadth and depth of applications covered by optical precision measurement are expanding, the stability of the traditional free operation of the laser is difficult to meet the application requirements, ultra-narrow linewidth, low noise, and long-term stability of light source has become the urgent goal in this field. Fiber laser has the characteristics of compact structure, easy integration, and narrow limit line width. Through noise suppression and frequency stabilization technology, fiber laser can output ultra-high stability and ultra-narrow linewidth laser. In recent years, ultra-narrow line width fiber laser has gradually become a hot research direction. In this paper, starting from the theory of noise of fiber laser, the noise source, classification, and testing method of fiber laser are introduced, based on the theory of noise, the principle of different intensity and frequency noise suppression technology, development course, and the current progress of fiber laser are summarized, respectively, and the development tendency of narrow linewidth fiber laser is discussed.

High-power narrow-linewidth continuous-wave fiber lasers have a wide range of application values in scientific research, industrial processing, and military defense. On the premise of ensuring the output quality, continuously improving the output power is one of the key goals of high-power lasers. This research focuses on the suppression of the stimulated Brillouin scattering effect, which is one of the key factors restricting the laser power improvement. Various methods of nonlinear effect suppression and the corresponding performances are introduced, especially the spectral broadening method. In addition, the current problems and the development prospects of this technology are analyzed.

Non-line-of-sight imaging can reconstruct images of scenes outside the line-of-sight. Different from traditional imaging, it imports the indirect signal returned from the hidden scene into the reconstruction algorithm to realize the reconstruction of the target scene, which is important in the fields of national defense, biomedicine, automatic driving, aerospace, and post-disaster search and rescue. This paper summarizes the research progresses of non-line-of-sight imaging technology, and introduces three non-line-of-sight imaging modes, including non-line-of-sight imaging based on time-of-flight, and non-line-of-sight imaging based on coherent information (including speckle pattern and spatial coherence methods), and non-line-of-sight imaging based on intensity information. Focusing on the characteristics and limitations of hardware parameters, reconstruction algorithms, reconstruction time, and image resolution of coherent information and intensity information imaging modes, the development trend of non-line-of-sight imaging is analyzed and discussed.

The traditional optical inspection of physical evidence has some drawbacks, including difficulties in obtaining sample spatial structure, poor pertinence, and cumbersome operation process. Optical coherence tomography (OCT) has the benefits of being in situ, noninvasive, high resolution, high speed, and low cost, which has potential uses in the field of forensic research. Through literature analysis, this study introduces the imaging principle of OCT. This study analyzes the viability of using OCT in the field of material evidence identification to apply this technology in many forensic science research directions, such as fingerprint inspection, forensic science, document inspection, and biological evidence inspection. The research and development ideas, methods, and application prospects of OCT in the field of forensic science have been examined.

Based on the principle of chromatic aberration confocal microscopy, the chromatic confocal microscopy (CCM) technology utilizes different focal positions of different wavelengths to achieve effective depth measurement; moreover, CCM employs a confocal setting to filter out defocused and stray light to improve the signal-to-noise ratio. This paper first introduces the basic principles of CCM and different scanning schemes, then reviews the development of CCM, and expounds the research progress of CCM at home and abroad. Considering the key issues such as optical design, signal generation model, spectral data processing, and crosstalk reduction, this paper summarizes relevant research schemes. CCM technology has several advantages such as nondestructive testing, high resolution, high signal-to-noise ratio, and effective tomography. Thus, it can be broadly utilized in various fields, including the biomedical, industrial testing, and other fields.

Fundus disease is a major cause of blindness. Early detection and timely treatment of fundus diseases can be achieved using optical coherence tomography (OCT), which is an effective approach for preventing blindness. Computer-aided diagnostic techniques are gaining attention as they relieve the pressure on physicians to read films. However, researchers studying computer-aided technology cannot access fundus OCT data owing to privacy concerns. To address this issue, in this study, we searched and combed eight free publicly available fundus OCT databases, interpreted the OCT image features of typical fundus diseases, screened 64 papers based on these computer-assisted algorithm data, and categorized the contributions of these studies. To facilitate the clinical application of computer-aided technology in the early diagnosis of fundus diseases, future efforts can be made in three aspects: improving the stability, repeatability, and generalization of high-precision classification for fundus OCT images; improving the segmentation ability for fundus OCT images; and improving the interpretability of computer-aided algorithms.

Microspheres can modulate the light field and focus the incident beam into an extremely narrow area on the back of the microsphere, so that the incident beam's full width at half maxima is smaller than the optical diffraction limit, and the focused intensity is considerably higher than the incident one. In addition, the microspheres have high numerical aperture characteristics, which can improve the collection efficiency of detection signals. Based on these benefits, microspheres offer a novel concept and method for realizing optical super-resolution imaging and fluorescence enhancement. Super-resolution imaging and fluorescence enhancement technologies based on optical microspheres are simpler, more direct, and easier to implement than traditional technologies. Their imaging and enhancement effects are comparable to those of traditional technologies. They have significant research value and application prospects in biological imaging and medical detection. Although the studies on microsphere-modulated light field to achieve fluorescence enhancement has made significant progress in recent years, review papers focusing on this topic are still limited. A systematic summary of microsphere-enhanced fluorescence and microsphere-modulated light field is critical for future studies and developments in this field. First, microsphere-based optical super-resolution imaging, including bright field super-resolution imaging and fluorescence super resolution imaging, is introduced. Subsequently, the microspheres-based fluorescence enhancement research is described, including phenomenon research, mechanism exploration, and discussion of influencing factors. Finally, the progress and applications of microsphere-based super-resolution imaging and fluorescence enhancement are summarized, and the future development challenges and trends in this field are discussed and prospected.

Ultra-high-speed laser cladding is an emerging surface coating technology. Through the optimal coupling of powder and laser, the cladding efficiency can be substantially enhanced, surface quality can be made better than that of traditional laser cladding coating, and damage to the substrate can be minimized. The principle and technical benefits of ultra-high-speed laser cladding are introduced in this study. The influence of laser power, scanning rate, powder feeding speed, and overlap rate on the cladding layer formation is summarized by comparing with the characteristics of traditional laser cladding technology. In addition, investigation status of the major properties of ultra-high-speed laser cladding coating, such as hardness, wear resistance, and corrosion resistance, is introduced in detail, and the industrial application status of ultra-high-speed laser cladding technology at home and abroad is listed. Finally, based on the current investigation progress, it is pointed out that there is a gap in the study on the interface bonding state of the ultra-high-speed laser cladding coating and the mechanics of the coating component, and prospects for the development of this technology are presented. It is predicted to offer theoretical support for the extensive application of ultra-high-speed laser cladding technology.

Distributed feedback fiber laser hydrophones are small in size, high in sensitivity, easy to be reused into arrays and recycled, which has become an important technical path in the field of fiber optic hydrophones. In this paper, the probe package structures and application of distributed feedback fiber laser hydrophones are reviewed. According to the characteristics of package structures, three main package structures and their array applications are introduced, which are bending beam type, side compression type and axial tension or compression type. By analyzing the research indexes of main research institutions at home and abroad, the advantages and disadvantages of different package structures of distributed feedback fiber laser hydrophones are compared, and the future development of distributed feedback fiber laser hydrophones array is prospected.

The integration of communication and sensing (ICAS) in optical networks is an effective design based on optical cable resources, and is in line with the development trend of communication system resource integration. The use of this integrated system will not only facilitate the intelligent operation and maintenance of optical networks and improve network quality, but will also expedite intensive acquisition of sensor data and innovation of new applications, effectively revitalizing the optical fiber assets of operators. In this paper, the key technologies of optical-network ICAS system are described. Sensing technologies based on the principles of Rayleigh, Raman, and Brillouin scattering are compared and analyzed. Combined with relevant research, several potential application scenarios of optical-network ICAS technology are discussed, thus providing ideas for the popularization and application of this technology.

Reflectance transformation imaging is a type of digital image acquisition technology, which has the characteristics of interactive arbitrary light distribution, multimode image reconstruction, and subtle three-dimensional feature presentation. This study mainly introduces the basic principle and development of the reflectance transformation imaging technology, analyzes its application in the cultural heritage and forensic science field, and presents the potential application of this technology in the forensic science field.

In recent years, there has been an increase in the number of people diagnosed with thyroid cancer. Thyroid cancer mortality can be considerably reduced by early detection of thyroid nodules. Ultrasound is usually the first choice for thyroid imaging. This paper systematically summarizes the thyroid nodule diagnosis algorithm of convolutional neural network (CNN) for ultrasonic images based on the relevant literature published at home and abroad in recent years. The main content includes the application of CNN in the three aspects of thyroid nodule region extraction, benign and malignant classification, and calcification recognition. To provide a clearer reference to researchers, the basic design idea, network architecture form, related improvement purpose, and method of each algorithm are described. Finally, the algorithms for thyroid nodule diagnosis based on CNN are summarized and analyzed, and future research hotspots and related challenges are discussed.

Optogenetics uses optical technologies to control brain neural activity, providing important techniques and developing contemporary neuroscience. Because the noninvasive penetration depth of light is restricted in biological tissue, traditional optogenetics implants an invasive optical fiber, resulting in the inability to guarantee the spatial precision of light stimulation. Recently, with the advancement of optical technology, precision optogenetics has gradually emerged. Precision optogenetics primarily uses a deep-penetration optical system with a high spatiotemporal resolution, single-cell precision neuromodulation capabilities, and real-time detection capabilities for subcellular precision neuronal cluster activity. In this study, we analyzed and discussed the technical principles, optical path construction, and system optimization of precision optogenetics. Finally, we look forward to the future developments and applications of precision optogenetics by discussing the technical limitations and possible solutions.

The performance of indirect X-ray detector (IXD) has been improved with the gradual improvement of imaging requirements in medical diagnosis, industrial non-destructive testing, safety monitoring, and scientific research, which promotes the further development of low radiation dose, high resolution, and fast real-time X-ray imaging detection technology. As the core devices of IXD, scintillation screen and image sensor have developed rapidly with the progress of scintillator materials, semiconductor manufacturing process, and integrated circuit technology. In order to realize the effective transmission of image between scintillation screen and image sensor, three coupling modes are usually adopted: fiber coupling, optical lens coupling, and direct coupling. This paper mainly introduces the research progress of scintillation screen and image sensor, as well as the structure and characteristics of the three coupling modes, and prospects the future development trend of IXD.

At present, most of the wireless solutions applied in various medical scenarios are based on the conventional radio frequency technology paradigm, which have to face several potential risks, such as electromagnetic interference and medical data leakage. On the other hand, wireless optical technology has many inherent advantages, such as abundant spectrum resources, high security, anti-electromagnetic interference, and no spectrum regulation. Therefore, for sufficiently illustrating the potentialities of this technology, the academia and industry are actively incorporating various wireless optical schemes into electromagnetic sensitive medical scenarios from multiple dimensions. In order to clearly present the state of art of the wireless optical application in medical scenarios, this paper sorted out the medical wireless optical active links, the passive links, the relay links, and the relevant experimental prototypes. In addition, the main technical challenges and potential solutions for the further development of healthcare wireless optical technology are presented.

The propagation of intense femtosecond laser pulses in atmospheric air can lead to a channel with high laser intensity, high plasma density, and capability for remote generation and control, namely filament. When the filaments interact with the materials, high laser intensity can excite the materials and induce the finger-print fluorescence of the materials. Supercontinuum can also be generated during filamentation which can cover the entire atmospheric optical transmission windows. The supercontinuum provides an idea source for sensing multiple atmospheric components through differential optical absorption spectroscopy. Intense femtosecond laser filamentation provides a new approach for atmospheric sensing of multiple phases and multiple components. In this paper, we focus on the new atmospheric sensing techniques based on intense femtosecond lasers, namely, remote femtosecond laser filament induced breakdown spectroscopy and filament induced supercontinuum Lidar. The working principles, the methods for spectral measurement and analysis as well as the recent research progress are briefly reviewed. Finally, the scientific and technique problems and future development of intense femtosecond laser remote atmospheric sensing are discussed.

Currently, microscopic imaging methods based on fluorescent labeling are the mainstream approaches in biomedical research. However, fluorescent labeling faces bottlenecks, such as photobleaching, photo quenching, specific labeling difficulty, and fluorescence disturbance. Therefore, the development of label-free microscopic imaging techniques has attracted numerous attentions. In this review, four label-free optical microscopy techniques are described: coherent Raman scattering imaging, photothermal imaging, surface plasmon resonance imaging, and interference scattering imaging. The basic principles of these techniques are illustrated, and their applications in biomedical fields, including morphology of biomolecules, viruses, and cells, as well as biodynamics, are described. Finally, the performance of the four imaging techniques is compared, and the advantages, limitations, and application prospects are summarized.

Optical fiber has the advantages of low loss, high stability, and strong anti-interference ability, which plays an outstanding role in the construction of long-distance, high-precision, and highly reliable time-frequency transmission system. This paper combs the implementation scheme and related research results of the long-distance optical fiber time-frequency transmission system, and analyzes the influence of bidirectional delay asymmetry and various noises on the transmission accuracy, stability, and transmission distance. In addition, this paper puts forward the next development research suggestion for the fusion of optical fiber time-frequency transmission network and existing optical fiber communication network.

Photonic crystal lasers can further reduce the optical mode volume and the lasing threshold using the band gap effect and localized effect, which can meet the needs of device miniaturization and optoelectronic integration. Photonic crystal lasers have broad application prospects in light-emitting diodes, sensors and other aspects, so they have attracted much attention. The lasing threshold is defined as the minimum energy density of lasing oscillation and is an important index for the integrated application of laser devices. Perovskite material has the characteristics of high optical gain, which makes it an ideal gain material for realizing low threshold laser. When combined with photonic crystal laser, low threshold or no threshold pumping lasing can be realized. Based on the resonator and gain medium, the two factors (gain and loss), which are the two main factors affecting the threshold of the laser, are briefly described in terms of the resonant cavity and the gain medium, and some methods to reduce the threshold is proposed. Then, photonic crystal lasers are classified according to the dimension and structure of photonic crystals. In addition, the research progress of low threshold of perovskite photonic crystal lasers is reviewed. Finally, the development prospect of perovskite photonic crystal lasers is prospected, in order to achieve low threshold or even zero threshold, high power, high quality lasing output, and promote the integration and multi-field application of semiconductor lasers

The magnetic properties and fluidity of a magnetic fluid have great potential applications in the field of temperature and magnetic field sensing. The combination of a magnetic fluid and an optical fiber sensing structure can modulate the light wave according to the changes in external temperature and magnetic field and obtain the sensing variation of temperature and magnetic field by demodulating the parameters of the characteristic spectra. This review summarizes the research progress of temperature and magnetic field sensors based on magnetic fluids according to different combinations of magnetic fluids and sensing structures. Furthermore, it introduces the temperature and magnetic field sensors based on mode interference, evanescent wave, fiber grating, fiber ring mirror, photonic crystal fiber, surface plasma, and Fabry-Perot interference. This review analyzes the sensing principle and sensitivity of each sensing structure and presents the future development trend. The temperature and magnetic field sensor with special fiber filled by magnetic fluid is shown to have a high sensitivity, a stable structure, and a strong anti-interference ability.

The coating layer of traditional silica optical fiber is generally polymer, which is prone to thermal aging at high temperatures. This characteristic is the main reason why optical fiber is difficult to be applied in a high temperature environment. Metal materials have better high temperature resistance than polymer, which can effectively protect the surface of the optical fiber from water vapor. It is a hot research topic of high temperature optical fiber coating materials. This paper analyzes and compares five main optical fiber surface metallization coating methods (vacuum evaporation, sputtering, electroplating, electroless plating, and freezing method). The results show that electroless plating is the main method for metallization of optical fiber devices due to its economical and environmentally friendly features. Melt coating technology is the mainstream choice of metal-chemical industry production.

Aiming at the transceiver technology in wireless optical communication, this paper combs the relevant research progress from two aspects of free space optical communication and underwater optical communication, summarizes the development trend of wireless optical communication transceiver technology from communication bands, modulation modes, and photodetectors according to different scenarios, analyzes the application prospect of single photon detection in wireless optical communication. Then we report our team's results of applying superconducting series nanowire single-photon detectors to space optical communication, which is expected to provide reference and ideas for related research.

With the development of optical microscopy, people have been able to observe the microcosm on sub-micron scale, which has played a key role in deciphering the code of life activities. Among them, coherent Raman scattering (CRS) microscopy provides imaging contrast based on molecular specific vibration and enhances the spontaneous Raman scattering signal by several orders through a nonlinear optical process, improving the imaging rate and detection sensitivity. According to different nonlinear optical processes, coherent Raman scattering can be divided into coherent anti-Stokes Raman scattering (CARS) and stimulated Raman scattering (SRS). Compared with CARS, SRS has the advantages of no non-resonant background interference, quantitative analysis, etc. This article will introduce the basic principles of coherent Raman scattering, and focus on the development and application of stimulated Raman scattering.

To improve fiber optic communication capacity, multicore fiber, a space division multiplexing implementation option, has attracted increasing research interest. At the same time, various new active and passive optical devices based on multicore fibers are emerging. Multicore fiber grating, which can combine the unique advantages of multicore fiber and fiber grating, offers a wide range of possibilities for the design and application of new all-fiber devices in various fields, such as fiber optic communication, fiber optic sensing, and fiber lasers. In this paper, multi-core optical fiber inscription is classified as selective inscription and full-core inscription. Various multi-core fiber grating inscription schemes based on different light sources and different inscription methods are introduced. The technical characteristics of the different schemes are analysed relative to different application scenarios.

Laser micro-nano connection connection technology is the basis for mass production of micro-nano structures and electronic components, and is a key technology in the field of micro-nano manufacturing. Based on a brief introduction to the application requirements and main technical methods of micro-nano connection technology, this paper focuses on the analysis and discussion of the micro-nano-scale laser connection technology. Firstly, the dimension range of laser connection technology is introduced, and then three typical laser micro-nano connection technologies are selected according to the different process characteristics, namely laser micro welding technology, micro-nano-scale laser soldering technology and laser soldering bumping technology, the research on the processing principles and characteristics, process parameters and application status of the three technology are reviewed, respectively. Through the summary of the research and application status of laser micro-nano connection technology, this paper discusses the important role of laser micro-nano connection technology in the field of aerospace, microelectronic packaging, medical device,etc., and summarizes the development direction and future research work of laser micro-nano connection technology.

The self-assembly template method is a low-cost method suitable for making large-area nanostructures. Compared with the polystyrene microsphere template, the through-hole anodized aluminum oxide (AAO) template has the advantages of adjustable parameters, good insulation and stability, and is widely used in the preparation of many large-area patterned nanostructures which can be used to improve the performances of optoelectronic devices. In this paper, the preparation methods of AAO template are introduced firstly. Then the methods of preparing patterned nanostructures such as nanoparticles, nanowires/rods, nanotubes by AAO template are summarized. Next, the applications of the patterned nanostructures in optoelectronic devices such as solar cells, photodetectors and light-emitting diodes are introduced. Finally, the full text is summarized and the development of through-hole AAO template assisted patterning nanostructures are prospected.

In the field of holographic three-dimensional (3D) display, the development of fast algorithms with which to generate computed holograms is an important research task, as the generation of computed holograms is currently time-consuming. The wavefront recording plane (WRP) technique is an effective method to accelerate the generation of holograms based on point clouds. This study analyzes the latest progress in the development and application of the WRP technique for computed holograms. We first introduce the principles of the WRP technique, before going on to analyze the latest research methods for wavefront recording in detail. We summarize and analyze the ways in which these techniques are used to accelerate the generation of the computed hologram and to improve the quality of 3D image reconstruction, and we also review special applications such as surface holographic imaging. We analyze the current utility of the various WRP methods for increasing the speed of computation, improving the quality of image reconstruction, reducing the size of the look-up table in computer memory, increasing the field-of-view angle, and removing aliasing noise. The role of the WRP technique in the creation of real-time, dynamic, high-quality, and large-view holographic 3D displays is also analyzed. Finally, the advantages and disadvantages of various methods are analyzed, and future directions for the development of the WRP technique are proposed.

Terahertz (THz) radiation is an electromagnetic radiation with a frequency that lies between the microwave and infrared regions of a spectrum. It has various unique properties, including transmission, transience, broadband, coherence, and low energy and can reveal the weak interactions between molecules. The THz application became possible due to the development of THz sources and detectors. Accordingly, with the development of machine learning, THz applications are being expanded to test many commonly used nonpolar dielectric materials and mixtures with a similar fingerprint. In this work, we introduce the theory of the optical system and the analytical method of a spectrum. We discuss the advanced applications of the THz technology in agriculture, including agricultural bio-molecular material detection, crop physiology inspection, soil detection, pesticide and antibiotic residue detection, and agricultural product and seed quality detection. In summary, we outlook the prospect of the development of terahertz time domain spectroscopy to promote its application in agriculture.

Electromagnetic waves have linear momentum, orbital angular momentum, and spin angular momentum. The orbital angular momentum carried via vortex beams has considerable application potential in contemporary optical technology and has important application value in the fields of classical communication, quantum communication, optical manipulation, and rotation detection. Recently, domestic and foreign researchers proposed various techniques for detecting beam orbital angular momentum, including diffraction grating, interferometry, Doppler analysis, and metasurface methods. Compared with other methods, the metasurface method has the advantages of high efficiency and strong light manipulation. This paper primarily introduces several methods for measuring beam orbital angular momentum using metasurfaces, as well as their research progress and development status.

With the rapid development of mobile communication and multimedia services, the bandwidth demand for the next generation access network demonstrates an explosive growth trend. The passive optical network (PON) is a key technology of optical access that provides huge bandwidth resources and long-distance links, but its flexibility is severely limited by optical fiber laying. However, the radio over fiber (RoF) technology can combine wireless access and optical fiber communication to benefit from low loss and high bandwidth, and thus, promote the integration and development of the two. Therefore, making full use of the huge bandwidth provided by optical fiber and the flexible access of wireless communication, the integration of RoF technology and PON can better generate, process, and transmit wired signals and microwave signals to meet people's needs for multi-services. This paper reviews the subsystems and key technologies of converged RoF-PON in recent years. The photon generation technology of microwave signal, RoF system, and next generation-PON (NG-PON2) are also summarized. Furthermore, the paper emphasizes the converged schemes of RoF technology and wavelength division multiplexing-PON (WDM-PON), time/wavelength division multiplexing-PON (TWDM-PON), and orthogonal frequency division-PON (OFDM-PON). The proposed four-channel RoF-WDM-PON and RoF-TWDM-PON system transmission capacity after 20 km of optical fiber transmission is 10 Gbit/s, with a bit error rate of 10-9. The RoF-WDM-OFDM-PON can realize a downstream system capacity of 50 Gbit/s, 50 km of optical fiber transmission, and passive optical network unit (ONU). Finally, the feasibility, advantages, and disadvantages of these systems are compared and analyzed in terms of transmission distance and bit error rate. In a nutshell, the converged RoF-PON system based on microwave photonics can not only reduce the system cost and provide high bandwidth and multi-services but also effectively improve the capacity and link quality of future access networks.

The phase-sensitive optical time domain reflectometer (φ-OTDR) is characterized by distributed sensing, fast response, simple structure, long detection distance, and anti-electromagnetic interference. However, due to the use of a light source with a long coherence length, the backward Rayleigh scattering of the pulsed light interferes inside the optical pulse, thereby affecting the φ-OTDR by factors, such as coherent fading, polarization fading, and common mode noise, which sharply reduce the signal-to-noise ratio. Therefore, this article discusses the working principle of φ-OTDR, summarizes and analyzes recent methods for reducing various types of noise in φ-OTDR system, and proposes future development directions for noise reduction in φ-OTDR systems.

Laser direct deposition technology can be used for producing large metal parts due to its unlimited capacity for manufacturing size and high material freedom. However, conventional laser direct deposition technology makes it challenging to consider both printing efficiency and printing quality, thereby restricting the popularization and application of this technology. Therefore, high-speed laser direct deposition technology has gained research popularity. In this paper, the effects of scanning speed and laser power on the process characteristics of Inconel 718 laser direct deposition are discussed, and the changes in surface morphology, microstructure characteristics, internal defects, and mechanical properties of conventional and high-speed laser direct deposition are analyzed. Finally, the challenges of applying high-speed laser direct deposition technology in three-dimensional additive manufacturing are discussed, which offers guidance for the development of high-speed laser direct deposition technology in the future.

Speckle blood perfusion imaging is a medical imaging technique that monitors blood perfusion information based on the scattering characteristics of red blood cells to the laser. Its benefits over traditional blood perfusion monitoring technologies include real-time imaging, high resolution, cheap cost, and the absence of contrast chemicals, particularly in surface blood flow monitoring. This review focuses on the basic principle of speckle blood perfusion imaging, technical advancements, and its application in monitoring fundus blood flow, cerebral blood flow, body surface microcirculation, and tumor blood perfusion, as well as its new application in monitoring angiogenesis of chicken embryo tumors.

Intravascular optical coherence tomography (IVOCT) is a minimally invasive imaging model that currently has the highest resolution. It is capable of providing information of the vascular lumen morphology and near-microscopic structures of the vessel wall. For each pullback of the target vessel, hundreds or thousands of B-scan images are obtained in routine clinical applications. Manual image analysis is time-consuming and laborious, and the findings depend on the operators' professional ability in some sense. Recently, as deep learning technology has continuously made significant breakthroughs in the medical imaging field, it has also been used in the computer-aided automated analysis of IVOCT images. This study outlines the applications of deep learning in IVOCT, primarily involving image segmentation, tissue characterization, plaque classification, and object detection. The benefits and limitations of the existing approaches are discussed, and the future possible development is described.

The ptychographic iterative engine (PIE), a recently developed lens-less imaging technique, provides a reliable access and solution to the phase problem. It has superior convergence speed and accuracy compared with conventional coherent diffraction imaging technologies. PIE is used extensively in various imaging and measurement fields owing to its unlimited field-of-view, high resolution, and high robustness to noise. In this review, we discuss the background and principle of PIE and summarize the major technological advances. The primary milestones of PIE in X-ray, electron, and visible light over the past decade are also discussed. Furthermore, we also elaborate on the latest PIE-based techniques and potential future developments and challenges.

Photon detection technology plays an important role in high-energy physics, astrophysics, medical imaging and other disciplines. Especially in radiation detection applications, it has been the ultimate goal of photodetector development in recent decades to achieve high-level sensitive detection of single photons. Silicon photomultiplier (SiPM) technology is an unprecedented attempt in the field of ideal solid-state photon detectors. With its excellent performance (high gain, low bias voltage, fast time response, magnetic field insensitivity, etc.), SiPM technology is attracting more and more researchers' attention. Focusing on the structure principle of SiPM, this paper reviews, classifies and summarizes the research progress of SiPM in the aspects of structure, performance and application in recent years.

One of the most important components of an infrared optical system is the infrared optical element. Owing to its wide transmission band, good achromatic and athermalization performance, and abundant raw materials, chalcogenide glass is an excellent infrared optical material. It has broad application prospects in the infrared field. However, when compared to other infrared optical materials, chalcogenide glass has a high thermal expansion coefficient and a low softening point temperature, making surface coating and film deposition difficult. In this paper, the surface processing and coating methods of the waiting-to-be coated chalcogenide glass surface are introduced, and the methods and research progress of depositing anti-reflection and protective coating on the surface of chalcogenide glass elements are reviewed. In addition, the current situation and existing problems of the surface processing and coating of the waiting-to-be coated chalcogenide glass surface, as well as the development trend of its optical surface preparation and cohesion are summarized.

The mid-infrared 2 μm band solid-state laser has a wide range of applications in the fields of industry, military, medical, and scientific research. Single-doped holmium solid-state laser is an important method to produce 2 μm lasers. 2 μm lasers can also provide an effective pump source for mid-infrared optical parametric oscillator. This paper introduces the advantages of single-doped holmium solid-state laser, and summarizes the research progress of single-doped holmium solid-state lasers based on various substrates in the past decades. Finally, the future development prospect of single-doped holmium solid-state lasers is prospected.

Fiber optic distributed acoustic sensing (DAS) based on phase sensitive time domain reflectometry can realize large-scale distributed acoustic detection, which has attracted the research attention in many application fields in recent years, such as oil and gas exploration, geological imaging, pipeline safety and perimeter security. In this paper, the sensing principle of fiber optic DAS is discussed, and the fading mechanism and performance bottleneck of single mode fiber DAS are analyzed. To solve these problems, the acoustic sensing mechanisms and performances of various scattering enhanced fibers are introduced. Furthermore, the recent technologies and applications of the microstructured scattering enhanced optical fiber-based DAS system are briefly reviewed, and the possible development directions of DAS technology in the future is prospected.

Recently, with the developments of deep learning technology, deep neural networks have been widely applied in the field of medical image segmentation. Due to its good segmentation performance, U-Net has gradually become a research focus in the field of image segmentation. First, the improved works of U-Net are summarized from two perspectives: structural and non-structural improvements. Then, four medical images of retinal vessels, pulmonary nodules, liver and liver tumors, and brain tumors are used as examples to demonstrate the characteristics and segmentation difficulties of various images and to summarize the application of U-Net and its improved networks in relevant images. Finally, the problems encountered in the improvement of U-Net are discussed, and future developments are forecasted.

The wavefront modulation system, which swiftly and flexibly performed the wavefront measuring and shaping in a coherent time, is vital in biomedical and optical communications. This high-speed wavefront modulation system, in particular, sets the basis for the effective application of coherent beams in the rapidly-changing scattering media, and digital micromirror devices combined with computed holography are an efficient method for the implementation of this technology. In this study, first, the importance, research advancement, and the application of high-speed wavefront modulation at coherent optical areas were introduced; thereafter, various binary computed holographic methods used in the current wavefront modulation technique were reviewed. The principles and the features of the holographic methods were specifically discussed, existing challenges in the holographic algorithm were summarized, and the trend of the binary computed holography was forecasted.

Ultrasonic imaging detection (UID) technology has the advantages of intuitive test results, and is one of the main development directions in the field of nondestructive testing in the future. Compared to traditional ultrasonic testing methods, laser ultrasonic detection has gained popularity due to its non-contact characteristics. The time reversal imaging method has a potential application in locating and detecting targets in inhomogeneous media due to its ability of acoustic beam self-focusing in time and space domains. This study primarily reviews the time reversal method and other conventional ultrasonic imaging methods. The results of different imaging algorithms used in the data post-processing are compared and analyzed. Moreover, the professional simulation softwares available for use in the ultrasonic imaging field are briefly summarized. Starting from laser ultrasound and compared to conventional ultrasound, the general situation of the modern ultrasonic testing technology and the advanced industrial ultrasonic imaging testing instruments and equipment at home and abroad are discussed. Further, the future imaging testing technology is briefly analyzed.

Synthetic holographic stereogram technology is a research hotspot in the field of three-dimensional display, which is widely used in military, economics, and other industries. Based on the development of synthetic holographic stereogram technology at home and abroad, we summarizes the basic writing methods, image quality improvement methods, and performance improvement methods. We introduce the development process and research status of basic writing methods, summarize their implementation methods, and evaluate the comprehensive performance of several main methods at this stage. Focusing on the imaging quality and comprehensive performance of synthetic holographic stereogram technology, we summarize the recent progress in improving synthetic holographic stereogram technology. Finally, the conclusion and prospect are given.

Ghost imaging and single-pixel imaging originate from different physical concepts. They have been closely integrated and developed together due to many similarities they share in the system schemes and image reconstruction algorithms. As typical computational imaging technologies, these two imaging schemes have received extensive attention in the fields of optics, imaging, and information acquisition. Different from traditional area array imaging, ghost imaging and single-pixel imaging obtain images by using the reconstruction algorithms, which is one important feature of computational imaging. In this paper, the history of ghost imaging and single-pixel imaging is briefly reviewed with a focus on typical image reconstruction algorithms. The principles of ghost imaging and single-pixel imaging using light field second-order correlation, sampling theory, compressed sensing, and machine learning are explained. Their application potential and prospects are discussed.

Femtosecond laser-assisted chemical etching technology has unique advantages in high quality, high depth to diameter ratio and high controllability of microporous processing, which provides a new way and method for the preparation of microporous. It has great application potential in micro total analysis system, three-dimensional optical flow control system in optical fiber and resonator manufacturing. In this paper, the research progress of femtosecond laser-assisted chemical etching for transparent media materials in recent years is reviewed, including the effect of femtosecond laser-modified zone on etching rate, the effect of strong acid and strong alkali chemical solution on etching effect, the optimization of chemical etching process, and the application of femtosecond laser-assisted chemical etching. The challenges faced by femtosecond laser-assisted chemical etching of microchannels, structure processing mechanism, and technology are summarized, and the research focus in the future is prospected.

Starting from the superhydrophobic theory, the importance of material surface roughness and solid-liquid contact area for the preparation of superhydrophobic surface based on three typical basic wettability models is revealed in this paper. On this basis, the advantages and disadvantages of direct laser writing (DLW), direct laser interference patterning (DLIP) and laser induced periodic surface structure (LIPSS) methods are reviewed. Among them, high-energy-density laser pulses are used to ablate the surface of materials in DLW method and it can construct any three-dimensional structure on the surface of various materials because of its high degree of freedom, but its surface processing accuracy is poor, and it is difficult to build multi-level structure. DLIP method removes the surface material selectively with the interference patterns formed by multiple coherent lasers such that a finer periodic, three-dimensional, and micro-nano hierarchical structures can be directly defined on substrates. LIPSS method can obtain a large number of ripple structures with spatial period of hundreds of nanometers on the surface of materials, but the corresponding processing time will be longer. Finally, different fabrication methods of superhydrophobic surface are summarized from the aspects of preparation parameters, surface structures and morphologies, and hydrophobic properties. In addition, the research status and development direction of these methods are analyzed and discussed.

In recent years, with the rapid development of modern industry, the non-contact measurement technology has attracted more and more attention. As an interferometric measurement technique, the laser Doppler vibration measurement can be applied to application scenarios where it is difficult to obtain vibration measurements through accelerometers or other surface contact sensors. Since the birth of the laser Doppler vibrometer (LDV) in 1983, it has gradually become the most widely used non-contact vibration measuring equipment in various fields due to its advantages of high precision, high efficiency, and portability. Based on the analysis of the basic principles of LDV, this paper discusses the applications of LDV in agriculture, life medicine, aerospace, and construction engineering in recent years.

Laser absorption spectroscopy (LAS) technology is widely used in gas flow detection due to its advantages of high sensitivity, high precision, and non-contact measurement. In the application scenarios of combustion diagnosis, leakage detection, and localization, the demand for spatial distribution measurement has been presented. Laser absorption tomography (LAT) and laser absorption imaging (LAI) based on LAS technology can not only realize the two-/three-dimensional (2D/3D) imaging of flow field but also have good adaptability to the complex environment in practical engineering with high time resolution, which will still be the focus of research in related fields in the future. Here, the basic principles of LAS technology and the LAT and LAI methods were discussed. Moreover, the research and application states of the LAT and LAI methods at home and abroad in the past decade were mainly introduced, including linear and nonlinear measurements of LAT and 2D/3D imaging of LAI. Finally, the perspectives and trends of LAS-based 2D/3D imaging technology were reviewed.

With the in-depth promotion of various complex key projects in China, engineering safety has attracted more and more attention. However, deformation monitoring of rock and soil mass is one of the essential means to ensure engineering safety. Compared with traditional rock and soil deformation monitoring technologies such as electromagnetic method, acoustic emission, theodolite, level gauge, displacement gauge, and strain gauge, distributed fiber optic sensing technology has the advantages of real-time, high precision, full distribution, long-distance, and anti-interference. It has become the focus of the research and application field of rock and soil deformation monitoring. This paper summarizes the application status of fiber optic sensing technology in rock and soil deformation monitoring, the principles and application scenes of several typical distributed fiber optic sensing technologies are introduced, the critical problems of fiber optic sensing technology in rock and soil deformation monitoring are discussed, and the application achievements and challenges of fiber optic sensing technology in slope, water conservancy, tunnel, pipeline, railway, land subsidence, and collapse monitoring are analyzed. Finally, the problems and solutions of fiber optic sensing technology in rock and soil deformation monitoring have been prospected.

Silicon-based photonic integration technology has made breakthroughs in several fields, but the silicon germanium material system is currently the only material that can realize all silicon-based integrated active devices and is compatible with complementary metal oxide semiconductor processes. Ge/SiGe multiple quantum wells as silicon-based optical modulators can realize short-distance optical interconnections on silicon chips, and Ge/SiGe multiple quantum well modulators based on the quantum-confined Stark effect have the advantages of low power consumption, low bias voltage, and high speed. This paper summarizes the research status and progress of Ge/SiGe-based multiple quantum well modulators. The extinction ratio, optical loss, bias voltage, electric field, modulation bandwidth, dark current, and other performance parameters of Ge/SiGe multiple quantum well modulators are discussed and compared. The development direction and challenges of Ge/SiGe multiple quantum well modulators in integrated photonics are evaluated.

Disease diagnosis technology based on human breath analysis, which belongs to the scope of non-destructive medical diagnosis research, is an important development direction of medical diagnosis in the future and will play an important role in non-destructive medical disease diagnosis in the future. Especially in the context of the current rampant new crown epidemic, the demand for non-invasive, real-time, and highly accurate disease diagnosis technology is more urgent. Based on the basic principles and technical characteristics of cavity-enhanced absorption spectroscopy, this paper outlines the history and current situation of the development of cavity-enhanced human breath diagnosis technology at home and abroad, and analyzes the future development direction of cavity-enhanced human breath diagnosis technology on the basis of summarizing the characteristics of human breath diagnosis, which can provide reference for the development and application of the subsequent technology.

The fiber lasers operating at 1.7 μm band have important applications in many fields, such as biological imaging, gas detection, material processing, and generation of mid-infrared laser. Thus, it has received extensive attention in recent years. In this paper, the progress of 1.7 μm fiber laser is reviewed in detail, and the characteristics of different technical schemes are discussed comprehensively, including fiber gas Raman lasers based on hollow-core fibers. Combined with application requirements, the development trend of fiber lasers in the 1.7 μm band is briefly prospected.

In recent years, bacterial infectious diseases have been occurring, and the frequent use of antibiotics has led to a significant increase in the number of drug-resistant bacteria, and the phenomenon of drug resistance is becoming more and more serious. There is an urgent need for an efficient and accurate detection technology to make a judgment on the pathogenic bacteria. Different species of bacteria have different molecular compositions and structures. Surface-enhanced Raman spectroscopy (SERS) is used to distinguish and reflect the cellular state mainly due to its ability to reflect the unique spectral fingerprint of bacteria. The detection of pathogenic bacteria by SERS is influenced by several factors, and this paper introduces three aspects of SERS detection of pathogenic bacteria and provides a brief review. Firstly, the design of substrates is summarized in terms of different structures and sizes of SERS substrates for pathogenic bacteria. Secondly, the co-culture, in situ reduction and electrostatic binding of pathogenic bacteria for non-labeling detection and labeling detection including external and internal labeling methods for SERS detection of pathogenic bacteria are reviewed. Finally, the identification of pathogenic bacteria is combined with the traditional multivariate statistical analysis method of Raman spectroscopy of pathogenic bacteria and advanced machine learning algorithms, and the application of SERS in pathogenic bacteria detection is summarized and prospected.

In double-helix point spread function (DH-PSF) engineering, the PSF of the conventional imaging system is transformed into DH-PSF using a regulation of pupil surface wavefront phase of imaging system to realize large-depth, high-precision nanoscale three-dimensional (3D) imaging. The DH-PSF is widely applied in life-science and material-science research, industrial detection, and other fields. In this study, the basic principle of the DH-PSF and the design and application methods of the DH phase mask are described in detail. Based on these, the applications of the DH-PSF to depth estimation, nanoscale 3D single-particle tracking, super-resolution fluorescence microscopy, and laser scanning fluorescence microscopy are introduced. The advantages of the DH-PSF technology in these application examples are emphasized, providing a useful reference for research in related fields. Finally, the prospects of the development direction of the DH-PSF technology and its application are discussed.

All-fiber optic current sensor is applied for micro-current detection, which can expand the application of optical fiber sensing technology in weak magnetic field detection. On the basis of analyzing the basic principle and main optical path structure of the all-fiber microcurrent sensor, the latest research results of the all-fiber microcurrent sensor are reviewed from three aspects: increasing the number of optical circuit cycles, improving the performance of the sensing fiber, and reducing the system noise. And the future development trend of all-fiber microcurrent sensor is prospected.

The design of new material structure is an effective way to improve the performance of the infrared detector. Antimony-based type-II superlattice InAs/InAsSb, as infrared photosensitive material, has stable structure, low dark current, high temperature operating characteristics and superior photoelectric conversion efficiency, which is the ideal material for developing infrared detectors at high temperature. This paper reviews the research progress of antimony-based type-II super-lattices InAs/InAsSb, introduces the performance of two kinds of infrared detectors applied in typical unipolar barrier structures, and prospects the development of antimony-based type-II superlattice InAs/InAsSb.

Lasers as a form of specialized radiation appeared in the 20th century. Laser technology is still evolving after more than 60 years of development. It has achieved positive outcomes in various fields, including cultural relic protection, and has various uses. This study analyzed the application of laser cleaning technology, three-dimensional laser scanning technology, laser Raman analysis technology, laser denudation technology, laser welding technology, and other progress in cultural relic protection research. The application characteristics of these laser technologies were examined, and the future direction of laser technology in cultural relic protection was provided to establish a new standard for laser technology and cultural relic protection-related research.

Opioids are among the most abused drugs globally, and their adverse effects on human health and social security cannot be disregarded. Effective drug detection technology is important in drug control and drug crime prevention. As a new molecular spectroscopic analysis technology, surface-enhanced Raman spectroscopy (SERS) is expected to become an effective method for detecting trace drugs owing to its advantages of accurate identification, high sensitivity, simple operation, and fast analysis. This study gives an overview of the recent developments in the detection of opioids (morphine, heroin, and codeine) using SERS. In addition, this study proposes the future directions of SERS technology in the application of drug detection for the relevant research and case handling.

It is crucial to characterize optical properties of nanomaterials for application and development of nanotechnology. Specifically, instead of averaging the observation across a large number of particles, measuring the spectra of a single nanoparticle has recently gained considerable attention, which can accurately and quantitatively analyze itself and its surrounding environment. Among various near-field and far-field approaches, the spatial modulation spectroscopy (SMS) technique can be employed to determine the extinction cross-section spectra using a high signal-to-noise ratio. In this paper, we introduce the modulation scheme, approach development, applications, and the latest research progress of SMS technique, and discuss its prospect for the future application.

Terahertz time-domain spectroscopy utilizes the absorption of a substance in a specific frequency range to acquire optical parameters such as refractive index, absorption coefficient, and the reflection coefficient of a substance. It has made significant contributions in the fields of food, drugs, and environment recently due to its benefits such as fingerprint, low energy, strong penetration, and coherence. This study focuses on the current research status of terahertz time‐domain spectroscopy in food, drugs, and environment based on an introduction to the principle of terahertz time-domain spectroscopy and method of acquiring optical parameters. Furthermore, for the future application of terahertz time‐domain spectroscopy in the fields of food, drugs, and environment, we summarize and assess its limits in practical work and its development possibilities.

Three-dimensional (3D) stereoscopic display is a promising direction of display technology development, and color asymmetry of left and right eye views is a common phenomenon in stereoscopic 3D displays, which can cause visual discomfort. Under the 3D display, the study of binocular fusion of asymmetric colors is an extension and supplement of traditional color vision research, which has a certain scientific significance to understanding the process and mechanism of visual information processing in the human visual system as well as has application value to solve the problem of visual discomfort in existing stereoscopic display technology. In this study, the relevant literature on binocular color fusion was sorted, and the research status of binocular color fusion was summarized from three aspects: binocular color fusion, the interaction between color and stereo fusions, and the influence of binocular color fusion on the visual comfort of 3D displays. We highlight that the interaction mechanism of binocular color fusion and stereo fusion is still uncleart, and the research results stay on the phenomenon description, lacking quantitative experimental data to establish a color fusion model. We infer that binocular color asymmetry affects the visual comfort of 3D displays. In addition, 3D display-based image enhancement may become a research hotspot in the future.

The global 5G communication network subscriber base has surpassed 400 million as of May 2021, thanks to the commercial deployment of 5G communication technologies around the world. Research on the next-generation wireless communication technologies has been conducted to address the demand for ultrahigh data rates and ultralow latency for future applications. The large number of absolute bandwidth resources in the terahertz band is the most significant advantage of the terahertz communication, making it suitable for various applications. Herein, the relevant research in the field of terahertz communication is described. First, we introduce the plan and vision of 6G communication network, as well as the current status of the terahertz communication technology on a domestic and worldwide scale. Second, the key terahertz communication technology and potential application scenarios are discussed. Finally, we present a summary of the current research results and an outlook on future research directions to provide new ideas for moving into the “terahertz era.”

From a global perspective, fossil energy remains the main source of energy supply. For fossil energy development, the petroleum industry has high requirements regarding the detection and monitoring of various gases, which are important for environmental protection and safe production. Tunable diode laser absorption spectroscopy (TDLAS) is a type of trace gas detection technology with advantages of high sensitivity, good selectivity, fast response, and availability for multispecies and multiparameter measurements. It can be widely used for detecting gas volume fraction in the petroleum industry site and monitoring the leakage of hazardous gas. This paper presents, classifies, and summarizes the principle and various detection methods of TDLAS. Furthermore, the application of TDLAS for on-site gas detection in the petroleum industry is reviewed, including detection for flammable and explosive gases (methane, ethane, propane, butane, acetylene, and ethylene), toxic gases (hydrogen sulfide and carbon monoxide), and other gases (oxygen and water). The current applications of the TDLAS standoff detection technology are summarized and future development areas of the TDLAS technology in the petroleum industry are outlined.

The fiber Bragg grating sensor reflects the change of the physical quantity measured by the change of the center wavelength, so it is of great significance to improve the demodulation accuracy of the wavelength of the fiber Bragg grating. Most of the traditional demodulation algorithms cannot accurately demodulate overlapping spectra and distorted spectra because of poor anti-noise performance and limited demodulation accuracy, which limits the development of demodulation systems. The high-precision demodulation algorithm can realize accurate demodulation of sensor networks by solving the problems such as poor anti-noise performance and low peak-finding accuracy. The article introduces the sensing principle of fiber grating, explains the main types and production method on fiber grating, and summarizes the high-precision wavelength demodulation algorithms of fiber Bragg grating in recent years. The principle, advantages, and disadvantages of each demodulation algorithm are explained which is divided into two types: single-peak peak-finding algorithm and multi-peak peak-finding algorithm. And the article briefly analyzes and prospects the future of high-precision demodulation algorithms of fiber Bragg grating.

Minimally invasive medical treatment has significant advantages compared with general medical treatment. Particularly, minimally invasive surgery can reduce intraoperative blood loss and trauma, improve postoperative recovery, reduce patient pain and doctor fatigue, etc. In recent years, robot-assisted medical system suitable for minimally invasive medical treatment has become one of the hot topics in the world. In addition to easy integration, optical fiber Bragg grating sensor is immunity to electric-magnetic interference, wavelength encoded nature, good linearity, etc. Compared to those traditional electrical sensors, such as piezoresistive sensor, capacitive sensor, and piezoelectric sensor, FBG presents more potentials in the field of minimally invasive medical intelligent robot. In this work, we review the applications of fiber Bragg grating sensor in minimally invasive medical treatment at length and discuss the exiting problems and perspectives.

Laser polishing technology has the advantages of non-contact processing, no mechanical stress, high polishing accuracy, etc. It is especially suitable for surface processing of brittle and hard materials. This article describes the characteristics and mechanism of laser polishing process, introduces the influence of various parameters in laser polishing process on processing quality, and reviews the research results and current status of laser polishing technology for hard and brittle materials in various countries. The difference and characteristics of laser hot polishing and laser cold polishing, as well as the polishing principle and research progress are emphatically introduced.

Laser additive manufacturing is widely used in the manufacturing and repairing of petrochemical, aerospace, and marine equipment. However, the residual stress caused by the rapid heating and cooling in the preparation of alloy materials via laser additive manufacturing likely poses a major risk of stress corrosion cracking of the material in harsh environments. This study first reviews the mechanism of residual stress in alloy materials produced via laser additive manufacturing. Second, the main measurement and elimination methods of residual stress in materials are summarized. In addition, the test methods and the mechanism of stress corrosion cracking in alloy materials caused by laser additive manufacturing are summarized. Finally, based on the research status of residual stress and stress corrosion cracking of alloy materials in laser additive manufacturing, the key problems that need to be solved in this field and future development trends are summarized.

Terahertz (THz) technology is gaining lots of attention for its unique applications in nondestructive testing, communications, spectral analysis and sensing. However, the traditional THz waveplate has a large size and high loss. As a two-dimensional planar material composed of artificially designed subwavelength periodic meta-atoms, the metasurface can flexibly adjust the amplitude, phase and polarization of electromagnetic waves within the subwavelength thickness, providing a platform for the design of ultra-compact and high-performance THz waveplate. In this paper, the THz polarization waveplate based on natural materials, dielectric gratings and metasurface are reviewed respectively. In particular, the THz polarization waveplate based on metasurface is mainly focused, including different resonant structures, switchable and continuously tuned, etc. Finally, the development of these terahertz polarization waveplate is summarized.

Laser point cloud data has the characteristics of high measurement accuracy, fast processing efficiency, strong three-dimensional (3D) vision, and wide application fields. It will be one of the core data sets of the new generation national global topographic database. The rapid advancement of spaceborne laser earth observation technology allows the collection of global 3D point cloud data, as well as a quick and efficient technical method for constructing a high-precision 3D digital geospatial information framework. Herein, we first examined the current state and the issues of global high-precision 3D mapping. Further, the rapid construction setup of 3D digital earth spatial information framework based on global laser point cloud was proposed, mainly including the technical processes of spaceborne photon laser point cloud data detection, processing, and application. Finally, the characteristics and benefits of the rapid construction of 3D digital earth framework, based on point cloud, as well as the main problem and future development directions that must be addressed were discussed.

Label-free optical imaging technology can perform long-term, noninvasive, high-resolution imaging on living cells owing to its noninvasive characteristics. This technology has promising applications in biomedical research and clinical diagnosis. Label-free imaging technologies can be categorized into specific imaging and nonspecific imaging. In this paper, we review the commonly used label-free imaging. Herein, the imaging principles, advantages and disadvantages, as well as the recent progresses of unmarked imaging are introduced in detail. Furthermore, the future development of the label-free imaging technology is prospected.

Maskless lithography has a wide range of applications in microstructure fabrication due to its advantages of no physical mask, low cost and suitability for mass production. Maskless digital lithography based on digital micromirror device (DMD) has the advantages of high resolution, good flexibility and high processing accuracy, which has become a research hotspot in the field of lithography in recent years. This paper reviews the research progress of DMD digital lithography, including DMD-based scanning lithography, stepping lithography and gray-scale lithography, and introduces the applications of the method in integrated circuit, micro-optics, three-dimensional printing and other fields, the paper also summarizes the current problems of DMD lithography and its future development trend.

Parallel micro/nano lithography is essential for rapidly fabricating microstructures. This review briefly introduces the principle and advantages of parallel micro/nano lithography and then analyzes and discusses spatial light modulator (SLM)-based parallel micro/nano lithography. In terms of modulation to incident light, the principle and progress of SLM-based parallel micro/nano lithography (which is divided into two types, i.e., multifocus parallel lithography and projection parallel lithography) are reviewed. This review summarizes the current situation, existing problems, and future prospects of these two types of SLM-based parallel micro/nano lithography.

The test quality of optical force accelerometer is isolated from the external environment, and the optical detection accuracy is excellent. It can detect ultrasensitive acceleration and is widely used in different navigation systems, ultraprecision microgravity detection, entertainment, and other fields. The optical accelerometer system comprises four modules: a loading module, an optical trapping module, a displacement detection module, and a cooling feedback module. From a practical standpoint, the existing technical methods of each module are combed and summarized in this research. The optical accelerometer will be developed in the future for simplifying and compacting each module, and its acceleration detection accuracy and reliability will be continuously improved during this process.

Phase sensitive optical time-domain reflectometer (Φ-OTDR) transmits light pulses into the sensing optical fiber, and uses the method of analyzing the back Rayleigh scattered light or forward scattered light of the sensing fiber to identify and analyze intrusion disturbance events. Compared with other distributed optical fiber sensing technology, Φ-OTDR can perform long-distance distributed multi-point measurement with high accuracy and reliability. The study of Φ-OTDR has important application value. In this paper, the basic principle, structure, system performance, signal demodulation, and application of Φ-OTDR are introduced, and the extension Φ-OTDR technology is prospected.

Electromagnetic metamaterial perfect absorbers have unique subwavelength structures, which can generate effective electromagnetic resonance with the incident electromagnetic wave, and achieve nearly 100% perfect absorption over a specific frequency range. Electromagnetic metamaterial perfect absorbers, especially the terahertz band perfect absorbers, have been widely concerned by researchers at home and abroad, and have made some progress. In this paper, the research progress of the terahertz band-based electromagnetic metamaterial perfect absorber is reviewed, the basic structural characteristics, performance, and theoretical model of the metamaterial absorber are described, and the future development trend and application prospect of them are briefly discussed.

Infrared spectroscopy detection provides a reliable and stable method of analysis. Micro electro mechanical system (MEMS) Fabry-Perot (F-P) tunable filters are the core components of instruments, such as infrared spectrometers, mobile phone camera modules, portable high spectral imagers, and remote sensing devices. Traditional infrared analysis systems and spectrometers are bulky, power-consuming, and expensive. Due to their large size and power consumption, they are not suitable for miniaturized devices. Compared with traditional types of filters, MEMS F-P tunable filters have the advantages of small size, high resolution, easy integration, and low power consumption. This article summarizes the progress made in the research on MEMS F-P tunable filters in China and other countries in recent years and discusses their wavelength tuning range, spectral resolution and aperture size, and the complexity and cost of manufacturing. Finally, the future development trends and application prospects of MEMS F-P filters are prospected, and these provide a reference for future research on MEMS F-P tunable filters.

As one optimization technique for modulation format, constellation shaping technique greatly improves the flexibility, nonlinear compensation and error performance of traditional coding modulation scheme. It can achieve high spectral efficiency and signal transmission close to Shannon’s limit without increasing the transmission power and complexity of the system, which has been widely used in many fields. The research status and the latest advances in the fields of constellation shaping technology schemes are introduced, especially the type, method, architecture and other aspects. The basic principle, performance comparison and related applications of probabilistic shaping with arithmetic coding are mainly discussed and the current problems and future trends of probabilistic shaping techniques are summarized.

The 1 μm band ultrafast laser has a wide application prospect in material surface modification and material micromachining. Laser oscillation and amplification technology can enhance the mode selection ability of resonator, and laser gain and compensation device can increase the peak power of laser, and further reduce the pulse width of output laser. This paper mainly summarizes the latest research progress of ultrafast laser oscillator (pure passive mode-locking, soliton clamping, and Kerr lens mode locking) and ultrafast laser amplifier (chirp pulse amplification, pulse shaping, and nonlinear compression technique) of the 1 μm band period, and 1 μm ultrafast laser control devices and systems (laser gain medium, dispersion control device, high order transverse mode generation, and ultrafast laser intelligent control). Finally, the development prospect and trend of 1 μm band period ultrafast laser are prospected.

The direct-detection optical fiber communication system has become the main solution for the future short-reach optical transmission links due to its simple structure and low cost. The field-signal recovery (FSR) technique is a critical technique to improve the capacity of the direct-detection system. This paper introduces a system structure, working principle and main research progress of Stokes vector receiver, carrier-assisted differential detection receiver and Kramers-Kronig (KK) receiver in direct detection optical fiber communication systems. The advantages and disadvantages of three commonly used FSR techniques are compared. The results show that compared with the other two techniques, and the KK receiver technology has obvious advantages. Finally, the important position of KK receiver in the future direct-detection optical fiber communication systems is clarified. Meanwhile, the key technical challenges faced by KK receiver are analyzed and the solutions for reference are given ultimately.

In 1981, Professor Caves first proposed the concept of "squeezed state" and indicated that the sensitivity of laser interference gravitational wave detection can be improved using the squeezed states of a light field. For the past forty years, the squeezed states of light have been successfully used in quantum precision measurements such as gravitational wave detection, displacement measurement, and phase measurement that beat the standard quantum limit. Two-mode squeezed and multi-party entangled states prepared based on single-mode squeezed states also play an important role in quantum information processing, such as quantum computation and quantum communication. This review briefly introduces the basic concepts, preparation, and detection methods of the squeezed states of light and their application progress in quantum precision measurement, quantum communication, and quantum computing.

Vegetables are one of the most essential foods in human's daily diet. They not only provide various vitamins required by the human body but also supplement nutrients, such as dietary fiber. Detecting vegetable traits is critical during the growth and development precesses. Hyperspectral imaging technology is a new type of non-destructive testing technology that combines traditional spectroscopy with machine vision technology. It can not only obtain image dimension information but also delve deeper into the spectral dimension information within vegetables and investigate the changes of vegetable traits at the same time, based on the image dimension level and spectral dimension level of vegetable images. This article reviewed the research results of hyperspectral imaging on the non-destructive detection of vegetable traits from three aspects: the internal quality detection of vegetables, nutrient element monitoring, and disease diagnosis. The future development direction is proposed combined with the existing problems.

Imaging ellipsometry is a measurement technology developed using traditional ellipsometry combined with imaging technology to adapt to the small and precise trends of various devices and materials. With the rapid development of nanotechnology, the technology has shown a trend of rapid developments and a wide range of applications in many fields, such as materials science, biology, and semiconductor. In this paper, we introduce the principle, advantages, and disadvantages of this technology. Furthermore, we comb the development history and describe the application progresses of this technology in material science and biomedicine, while discussing developing trends of this technology. This study hopes to serve as a review article on ellipsometric imaging technology and help promote the development of the technology and its application in more fields.

Continuous variable squeezed light plays an important role in quantum information processing, and the most effective generation tool known is the optical parametric oscillator. At present, most research focus on the fundamental mode, however, the intensity and phase distribution of higher-order mode are more complicated. In addition, based on the characteristics of different order modes and their orthogonal characteristics, high-order mode squeezed light brings more choices and applications for quantum communication and quantum precision measurement. This review introduces the experimental research progress of the continuous variable higher-order mode squeezed light based on the optical parametric oscillator, and expounds two common methods for generating high-order mode squeezed light field, including operation in high-order mode OPO and fundamental mode squeezed light combined mode shaping device.

Thulium-doped lasers are an ideal choice for biological tissue ablation and lithotripsy applications due to the advantage of efficient absorption by water molecules. They have great application prospects in the field of biomedicine. This paper briefly describes the principle of thulium-doped lasers and biological action, introduces the latest research results for thulium-doped lasers at home and abroad and their application in tissue ablation and lithotripsy surgery, and summarizes different laser parameters, including working mode and power. The effects of the irradiation time, spot area, and pulse frequency, among others, on tissue ablation and lithotripsy surgery reveal that the thulium-doped fiber lasers are an important development direction for medical lasers in the future. In addition, suggestions are made for the development of domestic thulium-doped lasers in the biomedical field.

Using the photomultiplication (PM) effect to enhance the external quantum efficiency of the device is a significant way to realize high-sensitivity organic photodetectors. This review introduces the research progress of PM-type organic photodetectors in recent years based on charge accumulation-type PM. The strategies for achieving PM and the corresponding PM mechanisms are clarified in detail from the perspective of the methods of implementing charge accumulation. Furthermore, the future research of the PM-type organic photodetectors is prospected.

In recent years, vortex beams have been widely used in optical communication, optical manipulation, imaging, sensing quantum information, and other fields owing to their unique phase structure and the characteristic of carrying orbital angular momentum (OAM). However, these applications must rely on the generation of high-quality vortex beams so that the optical microcavity occupies a very important position in the modern optoelectronic device manufacturing because of its compact structure, high quality factor, small element size, and other advantages. The developed new integrated optical device can emit high-quality vortex beam. The principle, research progress, design schemes, and experimental generation of optical microcavities to generate OAM beams are discussed in this paper. Simultaneously, the performance of existing OAM lasers is analyzed. Finally, the challenges faced by the applications of integrated optical devices and the directions for further improvement are considered.

In recent years, topological photonic crystals have attracted growing interest for their unique propagation characteristics. With the development of theoretical models in topological photonics, numerous novel applications have emerged. Topological edge states formed by topological photonic crystals can realize optical enhancement and unidirectional transmission in optoelectronic devices. Such optoelectronic devices can have distinct characteristics such as immunity to local defects and high transmission efficiency, offering enormous potential benefits to chip development, biosensor, military communication, and other applications. This study summarizes and analyzes a range of optical devices based on theoretical models of edge states formed by topological photonics in different dimensions: topological lasers, optical waveguides, unidirectional conduction devices, and optical modulators. The presented examples demonstrate the huge potential of topological photonic crystals in structural design and material selection. Finally, the current research progress of topological photonic crystals is clarified and the defects and optimization direction of topological photonic devices in the design process are evaluated and prospected.

Nanomaterials are emerging materials developed at the end of the 20th century that have attracted wide attention owing to their excellent and unique properties. Moreover, nanomaterial preparation is a key field in nanotechnology. In this paper, two important methods to prepare nanomaterials using pulsed laser ablation(pulsed laser deposition and pulsed laser liquid-phase ablation) are introduced, including their principles, characteristics, applications, and research progress at home and abroad. Finally, the challenges and development trends of pulsed laser deposition and pulsed laser liquid-phase ablation in terms of the preparation process and properties of nanomaterials are discussed.

Landslides occur frequently in China, often causing serious property losses and casualties. Therefore, scientific and effective landslide monitoring is of great significance for disaster prevention and mitigation. In recent decades, with the continuous development of monitoring technology, the level of landslide monitoring has been observably developed and improved in recent decades. It has gradually transferred from the past low-precision, point-type and manual monitoring to high-precision, distributed, and automated monitoring, which strongly supports the ability of governments at all levels from the national to the local level to cope with landslide disasters. In this paper, the current landslide monitoring methods and techniques are summarized and evaluated from four aspects: space (space satellite remote sensing), air (low altitude unmanned aerial vehicle remote sensing), ground (surface), and interior (inside the landslide body). The application method and effect of distributed optical fiber sensing technology in landslide monitoring are described, emphatically. The results show that the multi-source and multi-field monitoring inside the landslide body can obtain the multi-field information of the landslide, and the correlation model of the multi-field information can be established through further analysis, which can provide reliable data support for the evaluation and management of the landslide stability and has good research potential and application prospect. Finally, a new thinking of accurate and reliable monitoring, prediction and early warning of landslide deformation is proposed in this paper.

This paper reviews and summarizes various methods for linewidth measurement, introduces their development process, principles, and the required experimental equipment. According to the difference in principle, the methods for linewidth measurement are divided into two categories based on signal power spectra or phase noises. The limiting factors of linewidth measurement accuracy for these methods are analyzed and the precautions for the operation of these methods are summarized. In addition, the advantages and disadvantages of these methods as well as the corresponding detection ranges are comprehensively listed. According to the performance parameters and experimental conditions for different lasers, suitable linewidth detection methods are recommended. Finally, as for their practical applications, the methods for linewidth measurement of narrow-linewidth tunable lasers (widely used for coherent communications) are analyzed and discussed in detail.

Spectral combining technologies of fiber laser can overcome the limitation of the output power limit of a single-fiber laser, which is an effective technical means to obtain laser output with high power and perfect beam quality. The basic combining principles and research progress of the four spectral combining technologies are introduced. The structure, limiting factors, and characteristics of various synthetic components are analyzed separately. The key technologies of spectral combining based on dichromatic mirrors and their domestic and foreign research progress are introduced. The development prospects of spectral combining technologies are introduced.

Laser power meter is widely used in measuring the power of continuous laser and average power of pulsed laser. Fast and accurate measurement of laser power is of great significance in scientific research and industrial development. In this paper, the working principle of various laser power meters is introduced systematically. The advantages and disadvantages of various measurement methods, and the wavelength, measurement range and uncertainty of power measurement, are analyzed. The laser power measurement method based on photodynamics and its development potential are discussed. Furthermore, the future development and application of laser power measurement are prospected.

The research background, design scheme, and structure characteristics of a convex grating imaging spectrometer based on a concentric structure are introduced. Five main configuration types of concentric imaging spectrometers with a convex grating at home and abroad are reviewed, including Offner type, off-plane type, catadioptric type, +1st order diffraction type, and freeform surface type. The advantages and disadvantages of these five configuration types are summarized. It has important guiding significance for the research and development of a new generation of light and small imaging spectrometers with high imaging quality, high resolution, high diffraction efficiency, large relative aperture, long slit, and wide wavelength range.

A dynamic metasurface is a metasurface in which adjustable elements are integrated into static metaatoms and whose functions are controlled by different external excitation methods. Various adjustable devices have been realized based on dynamic metasurfaces, including frequency conversion filters or absorbers, zoom lenses, dynamic beam controllers, dynamic holographic elements, etc. In this review, first, the modulation method of dynamic metasurfaces is summarized systematically, and then the related research work is reviewed. Dynamic metasurfaces can be divided into two categories: one is a uniformly regulated dynamic metasurface that controls all metaatoms uniformly, and is used to achieve dynamic conversion of spectrum, polarization, and wavefront; the other is a dynamically reconfigurable/programmable metasurface with individually controlled metaatoms, and is used to realize flexible control of the wavefront. Dynamic devices with flexible and controllable functions are the main direction of future research on metasurfaces. The existing dynamic devices are summarized, and the development direction and challenges of dynamic metasurfaces are further discussed and prospected.

Persistent luminescence nanoparticles (PLNPs) can realize nondestructive imaging, detection, diagnosis and treatment without background interference due to their unique and outstanding luminescence phenomena. In addition, the emission wavelength of PLNPs is determined by their luminescence center. Thus, Cr 3+-doped PLNPs (Cr-PLNPs) have attracted much attention in the biomedical field due to their near-infrared (NIR) light emission, good tissue penetrability, and ultra-strong persistent luminescence (PL) excited by NIR light. In this paper, we discussed the application of Cr-PLNPs to biological detection, imaging, and therapy, analyzed their problems, and pointed out their future research directions.

Through the early screening of diseases, the development of targeted treatment programs of precision medicine has been essential to medical development. Medical imaging detection is an important foundation for precision medicine. There is no obvious characterization in the early stage of the disease, thus, the conventional detection method has certain limitations, but the body will show abnormal temperature distribution, and infrared thermography can detect the change of temperature sensitively. So, its application in early disease detection has attracted significant attention. In this study, the advantages and disadvantages of X-ray examination, ultrasound, magnetic resonance imaging, and other medical imaging detection methods, especially the mechanism of infrared thermography applied to disease detection, are introduced. Then, it systematically expounds on the domestic and foreign current situation of infrared thermography and advanced image recognition technology in early disease detection and recognition. It analyzes the advantages and disadvantages of infrared thermography in early disease detection, with the advantages of lossless, fast, and high accuracy and disadvantages such as the need for a large amount of data and poor performance of image processing algorithm. It suggested that the combination of infrared thermography and deep learning will be the main research direction in the future.

In recent years, the demand for three-dimensional (3D) information of the objective world and scene has increased sharply and drives the rapid development of 3D measurement techniques based on structured light illumination. The 3D imaging technique based on fringe projection and phase-shift fringe analysis has high accuracy and robustness, standing out among many techniques, and is widely used in industrial inspection, digitalization of antique, biomedicine detection, and so on. In the application scenarios with timeliness requirements such as human-computer interaction, virtual reality, online detection, and remote surgery, realizing real-time 3D measurement is of great significance and obvious value. In this paper, the basic theory of 3D imaging technique based on phase-shift fringe analysis was introduced. Several optimization directions for real-time 3D imaging were discussed, and different methods in various optimization directions were reviewed. Finally, the challenges and potential research directions of real-time 3D imaging technique based on phase-shift fringe analysis were summarized.

Vertical cavity surface emitting laser (VCSEL) as an ideal laser light source has a broad development prospect. In the application fields of optical fiber communication, optical interconnection, and laser printing, VCSEL is required to work in a single fundamental mode. Due to the structural characteristics of VCSEL, it is easy to shoot multiple horizontal modes, so the limitation of the lateral mode of VCSEL has become a research hotspot. In this paper, the research reports of VCSEL transverse mode control method are reviewed, and the research progress of photonic crystal, surface relief, anti-waveguide, extended resonator, and high contrast grating structure is classified and analyzed.

Laser-induced surface periodic structure (LIPSS) is a universal characteristic of solid materials. The LIPSS on the material surface can change the properties of the material. Many special functions can be achieved using these characteristics. This study summarizes recent representative studies on LIPSS. First, the surface energy distribution and material flow under the action of laser are used as the starting point to theoretically explain the formation principle of LIPSS. Then, the research work on the formation of LIPSS on the surface of thin films and etched materials and the influence of laser parameters on LIPSS are described. Finally, applications of LIPSS in modern industry, such as special crystal preparation, superhydrophilic/hydrophobic materials, and medical materials, are introduced. This study sorts out and summarizes the recent study on LIPSS-related fields from the above three aspects and looks forward to the future development of LIPSS-related technologies.

Laser cladding, an advanced surface modification technique, is widely applied to aerospace, petrochemical, and other fields. Herein, the research progress with respect to cracks in laser cladding coating is reviewed. Furthermore, the classification, formation mechanism, and detection methods of cracks are described. In terms of the optimization of process parameters, cladding design, powder composition, and process methods, the countermeasures to prevent and control cracks are summarized; some suggestions to solve the problem of cladding cracks and future research directions and ideas are suggested.

The photonic integrated circuit (PIC) has led to the development of miniaturized optical devices that can achieve very complex functions on a single chip. Many integrated optical devices, such as beam splitters, resonators, lasers, amplifiers, filters, and modulators, have achieved monolithic integration or hybrid integration. Countries have invested a lot in designing and manufacturing complex PICs research work. The optical gyroscope manufactured by integrated optical technology can effectively reduce the weight and size of the gyroscope, reduce the cost and power consumption, and increase the reliability of the system. The performance index is also gradually improved, and it has good development potential. This article introduces the research status of integrated optical gyroscopes at home and abroad, and briefly analyzes the current research characteristics of improving the performance of integrated optical gyroscopes by using different material platforms and new resonant structure designs.

Brillouin dynamic grating (BDG) based on stimulated Brillouin scattering effect has been extensively investigated globally. Compared with fiber Bragg grating (FBG), BDG has many advantages, such as fast reconstruction, read-write separation, and parameter control. It has been realized in polarization-maintaining, single-mode, low-mode, and photonic crystal fibers. Simultaneously, different types of BDG research, such as chirped BDG, phase-shifted BDG, chaotic BDG, and random BDG, are constantly emerging. This paper briefly introduces the generation principle of BDG and gives a detailed overview of different BDG fibers, different types of BDG, and BDG application in distributed fiber sensing and all-optical signal processing. Finally, the development trend of BDG is summarized and prospected.

The power of diode-pumped alkali laser (DPAL) with high power has reached 10 kW and shows great potential because of its high optical-optical conversion efficiency, light weight, small size and so on. Alkali vapor lasers are under extensive investigation and development during the past decade because of their potential for scaling to high power and maintaining good beam quality. First, the basic principles and research development of DPAL are introduced. Then, a historical review of the alkali laser research and development, and the most important achievements and future perspectives in this field, are presented. Besides, the obstacles in research are analyzed. The solutions are summarized and their deficiencies are presented. Finally, the future development of alkali vapor laser is discussed.

Improving the performance of the photoelectric-detectors, as a kind of the important optoelectronic devices, is a key research topic. In recent years, using nanostructure has resolved the bottleneck in the development of traditional infrared photoelectric-detectors. Metal nanoparticle, patterned-graphene with nanostructure, and resonators have been extensively used to stimulate the surface plasmon, promoting the interaction between light and matter to obtain a relatively high-performance photodetector. Herein, graphene photodetectors based on surface plasmons are mainly introduced, which have been developed from the aspects of patterned-graphene nanostructure, metal nanoparticle, quantum dots, and periodic nanostructure.

In recent years, as a novel strategy based on the excitation mechanism of photon-matter interaction, laser-controlled optimization of noble metal nanocomposite configuration can not only effectively construct multifunctional nanomaterials with clean surface, but also obtain metastable phase composite configuration which is difficult to achieve by conventional synthesis methods. Therefore, it has significant advantages in many frontier applications. In a simple liquid phase environment, this strategy mainly generates high-temperature and high-pressure metal plasma by focusing a high-power pulsed laser beam to ablate target materials, and then instantaneously cools and nucleates under the thermodynamic non-equilibrium state, thereby constructing various unique nanostructures. In addition, making full use of the high photon energy of the short wavelength laser beam, this strategy can also excite the substrate material to produce hot electrons, which can be used as a unique reducing agent to realize the reduction of metal ions in the surrounding solution, and finally grows multi-morphology metal nanostructures on the precursor. By adjusting the laser liquid phase irradiation parameters, the surface atom microscopic morphology of the optimized noble metal nanocomposite configuration can be effectively adjusted to make it have excellent light excitation performance, and then it is widely used in surface enhanced Raman scattering, photocatalysis, near infrared strong absorption, and other application areas. In this paper, the controllable synthesis mechanism of the laser-induced liquid-phase strategy is summarized based on laser-induced optimization of metal matrix nanocomposites, and the potential applications and future development trend of laser-controlled optimization of noble metal composite configurations are prospected.

Bloodstain is a biological examination material with high occurrence rate in the scene of violent cases. Inspection and identification work can provide a lot of information for the rapid detection of these cases. Hyperspectral imaging technology can be used for nondestructive and rapid imaging of bloodstains in crime scenes. Compared with the chemical reagent method and traditional spectral analysis method for bloodstain detection, the characteristic of image-spectrum merging is a significant advantage of hyperspectral imaging technology. Based on the brief analysis of the characteristics of hyperspectral imaging, data expression, and data processing methods, this paper introduces the applications of hyperspectral imaging technology in the fields such as national defense, ecology, and food. This paper focuses on the application status of hyperspectral imaging technology as a technical means of bloodstain detection in potential bloodstain appearance, bloodstain component analysis, bloodstain classification and identification, and bloodstain age prediction. The paper summarizes the challenges encountered in the application process and the later key research directions and development prospects.

The traditional microscope usually needs to change the magnification of the system by changing the magnification of objective lens, which is same as that of the eyepiece, and the magnification is not continuous. Applying the continuous zoom optical system design to the microscopic imaging system can realize the continuous change of imaging magnification. Continuous zoom optical systems and their zoom principles are summarized in this review. Various types of continuous zoom microscopes are discussed. The future development of continuous zoom microscopes are also discussed and prospected.

The detection of video abnormal behavior is paramount to ensure public safety. In this paper, the abnormal behavior detection algorithm based on deep learning is classified and summarized. First, the overall process of abnormal behavior detection is presented. Then, based on the neural network training method, the development and application of deep learning in the field of abnormal behavior detection are discussed from three aspects: supervised learning, weakly supervised learning, and unsupervised learning, and the advantages and disadvantages of different training methods are analyzed. Finally, commonly used datasets and performance evaluation criteria are presented, the performance of the different algorithms is analyzed, and future directions are discussed.

The basis of various laser-biological tissue interaction studies such as photothermal, actinic, and photomechanical effect studies is the accurate description of the light distribution in biological tissues under laser irradiation, and the effective methods to accurately describe the light distribution are various mathematical models and simulation methods. Therefore, the paper systematically summarizes the main theories, research models, and quantitative analysis methods that describe the light distribution in the biotissue at home and abroad. At the same time, the horizontal comparison and analysis of the application scope, advantages, and limitations of each method model is carried out. We longitudinally review the theoretical basis of most simulations and experiments, and focus on summarizing the latest theoretical breakthroughs and solutions of practical problems proposed by domestic and foreign scholars, so as to facilitate readers to track the frontier quickly and comprehensively. Finally, we point out some deficiencies in the current research in this field and make a certain prospect for the future development direction.

The positioning accuracy of star points is essential in astronomical navigation, which affects the accuracy of astronomical navigation. The traditional method for improving the resolution of a star map based on linear interpolation directly uses the linear relationship to calculate the gray value of insertion, however it ignores the own change characteristics of original functions. In view of the imaging characteristics of star points, a method of star location is proposed based on improved linear interpolation. First, we establish the imaging model of star points, deduce the one-dimensional model, and obtain the concave convex boundary point by calculating the second-order derivative. Then we give the method for calculating the weighting factor of improved linear interpolation, and finally the location of star points is realized. The simulation results show that, compared with the traditional method, the proposed method has an average deviation error reduced by 15.4%, and it can effectively extract the center of star points.

Due to the absorption of water body and strong scattering of suspended particles, there is a serious “curtain effect” in underwater optical imaging, which causes the details of the target in the scene to be submerged in the background scattered light, and the image contrast is greatly reduced. Due to the uniqueness and difference of target information and background information, the underwater polarization imaging technology developed from the polarization characteristics of light field can effectively suppress the scattering light of underwater background. The polarization differences between the target information light and the background scattered light are used to separate them effectively and realize the clear imaging. At present, underwater polarization imaging technology is developing rapidly, which has been widely used in many fields and new research results. This paper systematically introduces the basic principle, implementation algorithm, and imaging effect of underwater polarization imaging technology, and analyzes and prospects the future development of underwater polarization imaging technology according to the advantages and disadvantages of existing technologies.

As an important laser application in industrial production， laser material removal has many advantages， such as no contact， high efficiency， and high processing accuracy. Herein， two aspects of the single-laser-beam removal material and laser hybrid reduction technology were elaborated. Further， four laser processing technologies of laser drilling， laser cutting， laser ablation， and laser lithography were introduced， and these technologies were compared with other processing technologies. The laser composite technology supplemented by the laser removal of materials and multiple energy fields is also introduced. Aiming at the problem of difficulty in efficiently processing grooves using single-laser-beam removal material technology， an electromagnetic-field-assisted laser groove processing method was introduced.

Atmospheric pressure and large volume non-equilibrium plasma technology has played a good role in promoting the development of combustion and laser fields. This article focuses on solving the problem of discharge instability at atmospheric pressure， and introduces the structural characteristics and design of array needle cathode discharge， capillary dielectric barrier discharge， plasma cathode discharge， micro hollow cathode discharge， and micro hollow cathode glow discharge generator. The advantages and disadvantages of different discharge devices has been analyzed， and the challenges facing the improvement of the characteristics of atmospheric pressure and large volume non-equilibrium plasmas in practical applications has been summarized in the article.

An ultra-dense wavelength division multiplexing passive optical network can substantially increase the number of users and transmission capacity because it exhibits a channel spacing of only a few GHz， power budget of up to tens of dB， and other superior performance characteristics. Herein， the recent progress on the ultra-dense wavelength division multiplexing passive optical networks at home and abroad was comprehensively reviewed based on several key research directions， such as the improved spectral efficiency， simplified coherent receivers， photonic integrated device application， and optimized digital signal processing. Moreover， possible research directions and development trends were discussed.

As a significant micro-optical element， microlens arrays are widely used in optical communication， optical signal processing， wavefront sensing， optical field regulation， data storage， medical diagnosis， and other fields owing to their good imaging performance and miniaturization and lightening advantages. Femtosecond laser processing technology exhibits high controllability， good flexibility， no masking requirement， and high processing accuracy， and it has recently become an important processing method for microlens arrays. Herein， the research progress of femtosecond laser processing methods for microlens arrays， including two-photon polymerization and chemical-etching-assisted ablation， were summarized. Additionally， the application of microlens arrays was introduced， and the problems and development trends pertaining to the femtosecond laser processing method for microlens arrays were analyzed.

Fast development of photonic integration has promoted researches on grating couplers. Asymmetrical gratings can realize high-efficiency coupling because they break the symmetrical coupling conditions. Slanted gratings， blazed gratings， binary blazed gratings， and others have obtained important development， especially their structural design， manufacturing methods， and test methods have obtained improvement. The working principles and main features for various gratings as couplers between optical fibers and waveguides are introduced. The main types and the main problems and solution methods faced by each type of gratings are systematically analyzed， and some remarkable research results are enumerated. The aim is to help researchers know about the research status and potential development directions， and thus provide some reference for the future related researches.

Free space laser communication technology has been a research hotspot in the field of satecom and payload technology for a long time， with characteristics such as large band width and high speed. High earth orbit relay satellites are the backbone nodes of data transmission between satellites. With the maturity of laser communication technology， laser communication link has become a reliable technical means for data transmission of high earth orbit relay satellites at home and abroad. This paper introduces the latest development trends of high earth orbit satellite laser relay links at home and abroad and its future development plans， which provides a reference for the construction of space laser information networks in China.

In recent years, synthetic aperture radar imaging technology (SAR) has played an important role in the real-time monitoring and control of the ocean due to its all-time and all-weather target sensing capabilities. In particular, the detection of ship targets in high-resolution SAR images has become current one of the research hotspots. First, the process of ship target detection based on deep learning in SAR images is analyzed, and the key steps such as the construction of sample training datasets are summarized, the extraction of target features and the design of target frame selection. Then, the influence of each part of the detection process on the detection accuracy and speed of the ship target in the SAR image is compared and analyzed. Finally, according to the current research status, the problems of deep learning algorithms in the application of ship detection are deeply analyzed, and the further research direction of ship target detection based on deep learning in SAR images is discussed.

The hyperspectral image contains rich spectral and spatial features, which are essential for the classification of surface materials. However, the spatial resolution of hyperspectral images is relatively low, resulting in a large number of mixed pixels in the image, which severely restricts the accuracy of substance classification. Affected by factors such as observation noise, target area size, and endmember variability, hyperspectral image classification still faces many challenges. With the continuous progress of artificial intelligence and information processing technology, hyperspectral image classification has become a hot issue in the field of remote sensing. First, the literature on hyperspectral image classification based on feature fusion is systematically reviewed, and several classification strategies are analyzed and compared. Then, the development status of hyperspectral image classification and the corresponding problems are introduced. Finally, some suggestions can improve the classification performance are proposed, which provide guidance and assistance for the technical research of the subject.

The smoke detection technology plays an important role in preventing early fire spread. An accurate and fast smoke detection algorithm has very important practical application value. In recent years, with the rapid development of machine vision and image processing technology, smoke detection algorithms for video-oriented images have attracted extensive attention due to their non-contact and strong robustness. The smoke detection algorithm based on video images can effectively overcome the deficiency of traditional smoke detectors working close to fire sources. However, the smoke detection algorithm based on video images still faces great challenges due to the complexity of scenes and the uncertainty of environmental factors. First, the basic process of the smoke detection technology is briefly introduced, including pretreatment, feature extraction, and classification recognition. Second, the preprocessing method based on color and motion segmentation is introduced, and the visual characteristics and movement characteristics of smoke are further analyzed and the related smoke extraction algorithms are introduced. Third, some of the current commonly used smoke detection classifiers and the deep learning network models are discussed and summarized. Finally, the deficiencies of the smoke detection algorithm are mainly introduced and the future of the smoke detection algorithm is prospected.

At present, the commonly used auto focusing methods for digital microscopes are divided into active auto focusing and passive auto focusing. Active auto focusing relies on a specific sensor or a distance measuring device, which automatically emits light and receives reflected light to determine the distance from the object to the focusing device and achieve focusing. Passive auto focusing can determine the focus direction and focus position by analyzing the image information of each position, therefore realizing focusing. Passive auto focusing is the most commonly used auto focusing method for digital microscopes due to its low structure requirements and low cost. This paper mainly introduces the auto focusing algorithm for digital microscopes, briefly describes the principle and development direction of active and passive auto focusing methods, focuses on the depth from focus method of passive auto focusing methods, and analyzes two key technologies of the depth from focus method, that is, the sharpness evaluation function and its focus search algorithm.

Multispectral imaging (MSI) combines spectroscopy and imaging technology and can acquire the spectral feature and spatial information of the detected target simultaneously. Due to the non-invasive imaging manner, this technology has many important applications in the biomedical field. The basic principle and technical development of MSI are introduced, and its applications are briefly reviewed from three aspects: pathological research, surgical guidance, and biological recognition.

Segmented telescopes are among the expected future directions of large-diameter telescopes owing to the low difficulty of their processing technology， convenient carrying， and low manufacturing cost. The active support technology provides an important guarantee for the confocal and cophase adjustment of segmented telescopes. This study briefly summarizes the main technologies of the active support system for the main mirror of a segmented telescope and then summarizes and analyzes specific application examples. Finally， it provides design suggestions for the main mirror support system of a segmented telescope. It will provide a valuable reference for the future development of the segmented telescope support technology.

Fiber evanescent wave sensor （FEWS） exhibits the advantages of a simple design， high sensitivity， and easy combination with other sensing technologies and is widely used in the field of biological and chemical sensing. Herein， we first describe the definition of FEWS and two types of common fibers and then summarize the optimization methods and principles of FEWS. Second， we review the research advancements of silica and chalcogenide fibers in the fields of gas， liquid， and biological sensing. Finally， the future development trends are prospected.

In order to further quantitatively analyze the physical dose of laser to biological tissue， and to provide theoretical basis for related research in medical， military， and many other fields， it is necessary to accurately measure the optical characteristic parameters of biological tissue. This paper systematically summarizes the mainstream techniques and methods for measuring the optical parameters of biological tissues at home and abroad， summarizes the applicable scope of each method and compares the advantages and disadvantages of related methods horizontally and vertically. It reviews the theoretical basis of most simulations and experiments， and also summarizes the latest research results and applications in this field， which is convenient for readers to track the frontier quickly and accurately. Finally， it summarizes some major problems currently facing in this field research and makes a certain prospect for the future development direction.

High power ultra-short lasers have a wide range of applications in fields such as high-field physics， precise processing， and national defense. The output power of ultra-short fiber lasers has been improved significantly with the development of diode pump sources and fiber manufacturing process. Besides， the high power ultra-short fiber laser and its amplification and compression technologies have attracted more and more interest in recent years due to the advantages of fibers including good heat dissipation， high environment stability， good beam quality， and so on. This paper focuses on the advanced research of high power ultra-short fiber lasers and its amplification and compression technology. Several new methods， such as Mamyshev mode-locking，“9-type cavity” mode-locking， and spatiotemporal mode-locking， for producing high power and high energy ultra-short fiber lasers are reviewed. The recent progress of coherent combination and non-linear compression technology to produce high power ultra-short pulse in fibers is introduced.

As all countries pay more and more attention to marine security and territorial issues， underwater laser communication plays a more and more important role. The realization of high-speed transmission and confidentiality of information in a complex marine environment is an urgent subject for underwater laser communication. This paper sorts out the development history of underwater laser communication systems at home and abroad， summarizes their technical advantages， gives their communications principles， analyzes the key technologies influencing the system''s performance. Finally， the future underwater laser communication systems will not only possess high communication rate， low bit-error rate， long transmission distance， large capacity， low power consumption， and small size， but also develop from point-to-point communication to network-type communication.

High-order harmonics generated by the interaction between intense femtosecond laser and matter have the characteristics of high single photon energy， ultrashort pulse duration， and excellent spatiotemporal coherence. It can be used as the tabletop ultrafast vacuum ultraviolet laser source and soft X-ray laser source in laboratory. At the same time， high-order harmonics are used to generate attosecond pulses. The generation of these advanced laser sources has greatly enriched the research tools of material science. In this review article， we introduce the principle， optimization， and application of high-order harmonics of gases and solids.

Researchers can now identify dynamic activities in living cells at the nanoscale with remarkable temporal and spatial resolution because of the advancement in fluorescent super-resolution imaging. Traditional super-resolution microscopy requires high-power lasers or numerous raw images to rebuild a single super-resolution image, limiting its applications in live cell dynamic imaging. In many ways, deep learning-driven super-resolution imaging approaches break the bottleneck of existing super-resolution imaging technology. In this review, we explain the theory of optical super-resolution imaging systems and discuss their limitations. Furthermore, we outline the most recent advances and applications of deep learning in the field of super-resolution imaging, as well as address challenging difficulties and future possibilities.

The traditional fluorescence microscopy imaging technique takes fluorescence intensity as imaging contrast, which plays an important role in obtaining the position and concentration information of biomolecules and provides an imaging tool for biomedical research at the molecular level. As another important characteristic of fluorescence, polarization can provide the orientation and structural information of biomolecules in another dimension and has been widely used in the fluorescence polarization microscopy imaging technique. In addition, fluorescence polarization modulation can also be used to obtain the position and orientation information of biomolecules at the super-resolution scale by enhancing the sparsity of fluorescence images and thus enhancing the image contrast. In this paper, as for the different fluorescence polarization modulation imaging techniques based on fluorescence polarization characteristics, their developments in the molecular orientation structure imaging, super-resolution microscopy imaging and the combination of the two aspects are summarized from the physical bases, technical principles, basic implementation devices, and biological applications. Moreover, the future of these techniques is prospected.

The research progress of human pose estimation method based on deep learning is comprehensively summarized. On the basis of comparison and analysis of various single-person pose estimation methods, a variety of multi-person pose estimation algorithms are summarized from the top-down and bottom-up approaches. In the top-down approach, the solutions to local area overlap, articulation point confusion, and difficulty in detecting the articulation point of atypical parts of human body are mainly introduced. In the bottom-up approach, the contribution of clustering method to articulation point detection is emphasized. Representative methods to achieve excellent performance on current public datasets are compared and analyzed. The review enables researchers to understand and familiarize themselves with the existing research results in this field, expand research ideas and methods, and look forward to the possible research directions in the future.

Biological evidence is individual-specific, easily ignored by criminals, stably attached to the crime scene, and difficult to destroy completely. It has a high investigative value. Based on the photoacoustic effect, the photoacoustic spectroscopy realize detection using the mechanism by which the sample absorbs light energy, converts it into heat energy, and generates a sound signal. The photoacoustic spectroscopy provides a sensitive and nondestructive effective method for the research of biological materials, and it has become an essential analysis tool in the field of forensic science. Based on a brief introduction to the photoacoustic effect and the principle of photoacoustic signal generation, this article focuses on the research status of photoacoustic spectroscopy in the identification and analysis of gas, liquid, and biological tissue materials that can be used as forensic biological evidence. The application limitations and development prospects of the technology are summarized and prospected.

Brain tumor image segmentation based on convolutional neural network has become a research hotspot in the field of image processing in recent years. Based on this situation, the significance and research status of brain tumor image segmentation, and the specific advantages of applying convolutional neural network to brain tumor image segmentation are described. Then, the research progress of two-dimensional convolutional neural network, three-dimensional convolutional neural network and the classical improved model of convolutional neural network applied to brain tumor image segmentation is reviewed in detail, and the segmentation results of training in the dataset of multi-mode brain tumor segmentation challenge are summarized. Finally, the future development of convolutional neural networks in magnetic resonance imaging segmentation of brain tumors is discussed.

Nowadays, cardiovascular diseases have become the No. 1 killer of human health. Developing high-resolution intracavitary imaging technology is conducive to the accurate diagnosis and treatment of cardiovascular diseases. Optical coherence tomography (OCT) has the advantages of non-contact, non-invasive, high-resolution, and fast imaging capabilities, which plays a crucial role in the guidance for the treatments of cardiovascular diseases. In this work, we first described the situation of increasing cases of percutaneous coronary intervention (PCI) in China in recent years, and then the development and application of OCT, endoscopic OCT, and cardiovascular OCT were introduced. We gave a detailed review of the progress of the cardiovascular OCT in academic research and commercial translation. The importance of cardiovascular OCT in clinical diagnosis of coronary plaques and the guidance of stents and prognosis were illustrated. In the end, this article provided the prospect outlook of cardiovascular OCT in future development, and the important research and application values of cardiovascular OCT were summarized.

Camera calibration is the basis for imaging and computer vision as well as the premise for sensing and vision detection. The camera presents the three-dimensional feature points of space objects in a two-dimensional form on the imaging plane. Each parameter of the camera is determined by the three-dimensional feature points in space and the corresponding two-dimensional image points. This process is called camera calibration, including the calibrations of the internal parameters and the position and pose of the camera in the three-dimensional spatial coordinate system. Based on a brief introduction of the working principle of the area-array camera, this paper summarizes the area-array camera calibration model, calibration methods, rapid calibration methods for large field-of-view cameras, and discusses the latest camera application fields and calibration technologies. Finally, the future research direction of camera calibration is prospected.

Laser technology is extensively utilized in the field of medicine. Not only does it have different indications in vascular diseases but also its distinctive physical properties and precise biological tissue interaction effect has encouraged considerable research. This article reviews the applications of laser technology in endovascular imaging and therapy in recent years, summarizes its history and research status, and discusses its likelihood for development in the future.

In recent years, pulsed laser time-of-flight ranging (TOFR) has become a research hotspot topic in the field of laser ranging, which has been widely used in industrial precision measurement, robot autonomous motion, unmanned aerial vehicle control, and other fields. Due to the influences of background noise, electrical environment of measurement circuits, and rise time of echo pulses, the pulsed laser TOFR usually has certain errors, which causes the problem of distance measurement accuracy degradation. This paper firstly introduces the basic principle of pulsed laser TOFR technology, analyzes the formation causes of time-of-flight measurement errors in the pulsed laser TOFR process, and classifies the errors. Further, the various error compensation methods for time-of-flight measurement errors and the latest research results are sorted out, and finally, the current challenges of pulsed laser TOFR error compensation are summarized.

Recently, the spectroscopy technology has advanced extremely rapidly. It can utilize the characteristics of light absorption, reflection, and transmission of materials to perform the qualitative and quantitative analysis of materials. It is a fast, nondestructive detection technology widely used in the testing of agricultural products. Walnut is an important agricultural product with rich nutritional value and long cultivation history in my country. Many scholars have conducted long-term and in-depth research on walnut. This review summarizes the research progress on hyperspectral and infrared spectroscopy with respect to walnut detection from four aspects: variety identification, growth monitoring, quality identification, and sorting and processing. Furthermore, this review compares and analyzes the advantages and disadvantages of various spectral detection technologies and proposes existing problems in walnut correlation detection. The development prospect of walnut nondestructive testing is prospected.

As an important traditional Chinese medicines (TCMs) for promoting qi, activating blood, and relieving pain, Curcuma has attracted wide attention in recent years. In order to identify and control the quality of four origins of Curcuma, the terahertz time-domain spectroscopy combined with chemometric method (support vector machine method and principal component analysis method) was used to classify and identify the four origins of Curcuma. In this study, three models of slope loss multi-class support vector machine methods (Ramp Loss K-SVC method), random forest (RF), and extreme learning machine algorithm (ELM) were constructed to distinguish Curcuma with four different origins. It was developed the Ramp Loss K-SVC method and optimized the model parameters that the identification rate of the four types of Curcuma were increased to 93%. This paper provides a new identification technique for the identification of four easily confused origins.

Super-resolution microscopy techniques are versatile and powerful tools for visualizing organelle structures, interactions, and protein functions in biomedical research, and its resolution ability to break the optical diffraction limit provides new analytical frameworks for cell biology on the nanoscale, which is indispensable to life science related fields. However, due to the effect of the diffraction limit, the axial resolution of a super-resolution microscope is more arduous to improve than the lateral resolution, which hinders the realization of sub-hundred-nanometer resolution three-dimensional imaging of cellular structures. Therefore, based on the two main techniques, stimulated emission depletion microscopy and single-molecule localization microscopy, the present paper introduces the principles and characteristics of a variety of existing three-dimensional imaging techniques, and finally discusses the future of that. Finally, we briefly discuss the research trend of the two techniques in the three-dimensional imaging area.

Star sensor is an important device of satellite attitude control. The star simulator is used as a ground performance test and precision calibration equipment of the star sensor, of which accuracy plays an important role in the precision of attitude control. The composition and working principle of the star simulator are briefly described in this paper. In the last 20 years, the selection of light source for the representative star simulator with adjustable colour temperature has been emphatically described. LED, tungsten bromide lamp, xenon lamp and supercontinuum laser are the most common light sources. The development trend of colour temperature tunable star simulator light source is provided through a comparative analysis of these light source simulation schemes.

The spectral imaging system on chip has many advantages, such as compact structure, light weight and portability. It can be flexibly mounted on unmanned aerial vehicle and cubic star platform, showing broad application prospects. This paper reviews the research progress and applications of spectral imaging system on chip in recent years, also summarizes the spectrum achieving principle and integration mode of chip-scale spectral imaging system. In addition, some key applications of spectral imaging system on chip in biomedical, environmental monitoring, military equipment, intelligent consumer electronics and other fields are shown in the paper. This paper reveals that the on-chip spectral imaging system is currently facing challenges and development direction in the future.

Recently, the rapid advancements in tissue optical clearing technology have brought new opportunities for modern orthopedic optical imaging research. Tissue optical clearing technology primarily reduces tissue light scattering and light absorption through various physical and chemical methods, allowing light energy to better spread in the tissue in order to increase the depth and contrast of optical imaging. Deeper and higher resolution bone tissue images and 3D spatial microstructure information can be obtained when combined with various fluorescence-labeling strategies, presenting a novel perspective and method for a breakthrough in the molecular imaging study of bone tissue with high scattering and bone disease. In this study, we will discuss the principle and mechanism of tissue optical clearing technology, focusing on the current state, most recent methods, and the mechanism of bone tissue clearing imaging, and prospect the possibility of using this technique in the molecular imaging of bone.

With the wide applications of three-dimensional (3D) meshes in digital entertainment, television animation, virtual reality, and other fields, there are more and more processing techniques for 3D meshes, including compression, simplification, watermarking, and denoising. These processing techniques will inevitably lead to various distortions in 3D meshes. Therefore, how to preferably evaluate the visual quality of 3D meshes becomes an urgent problem to be solved at present. This paper reviews the objective quality assessment methods for 3D meshes developed during the past 20 years. First, some technical indexes for 3D mesh quality assessment and several public databases are introduced. Second, the quality assessment methods for existing typical three-dimensional meshes are classified, and their respective characteristics are introduced. Then, the typical algorithms introduced in the commonly used databases are tested and compared. Finally, the objective quality assessment methods of 3D meshes are summarized and prospected.

Flammable liquids are widely used in food, chemical industry, energy, and other fields, and have created great economic value. However, these liquids are flammable and explosive and sometimes generate toxic vapor, and thus their nondestructive detection is of great importance for promoting industrial production and guaranteeing personal and property safety. Spectroscopic methodologies have the advantages of fast response, online and nondestructive detection, no need of sample pretreatment, and high precision, playing an important role in the detection of flammable liquids. In this paper, we expounded the technical principles of the spectroscopic methodologies for flammable liquids and highlighted the development history and application status of five typical spectroscopic methodologies for flammable liquids, including near-infrared spectrometry, Raman spectrometry, ultraviolet-visible spectrophotometry, fluorescence spectrometry, and terahertz time-domain spectroscopy. Furthermore, we discussed the future potential applications of these spectroscopic methodologies in combination with their advantages and disadvantages.

When a coherent beam propagates through a strong scattering medium, a speckle pattern of the output field can be formed due to random scattering. As a consequence, it is impossible to directly acquire the original information of the input beam from the output scattering field. However, in the random scattering process, the output speckle pattern still contains the original information of the incident beam. The acquirement of the original information based on speckle patterns for the reconstruction of an object has become a hot research topic. As for this problem, the techniques including speckle correlation, transmission matrix, wavefront control as well as time reversal and phase conjugation have been proposed. The scattering imaging technique based on correlation holographic theory is mainly introduced, in which its principle, history and recent new progress are included. In addition, its future development is prospected.

Owing to their unique optical and electronic properties, two-dimensional (2D) materials have demonstrated broad promising applications in optoelectronic devices. Molybdenum disulfide (MoS2), a representative 2D material, has shown remarkable advantages in the field of photodetection because of its atomic-level interfaces and thickness-dependent tunable band structure. However, after many years of extensive studies, MoS2 devices have reached a bottleneck in terms of performance. To further improve the performance of MoS2 devices, various methods, such as band engineering, ferroelectric polarization, and plasmon resonance, have been investigated. However, a thorough review of such studies has not been conducted. In this paper, we briefly summarize the latest theoretical and practical research into MoS2 photodetectors. The principles, structure design, preparation, and optoelectronic characteristics of the new MoS2 photodetectors based on the three aforementioned methods were reviewed. This comprehensive review can broaden the existing understanding of MoS2 devices and provide important guidelines for future applications.

At present, the rapid development of micro-machining and finishing technology has put forward higher requirements for miniaturization processing technology: the processing scale needs to be improved to the micron or even nanometer scale, and three-dimensional micro-machining can be achieved inside the material. Femtosecond laser can break through the limit of diffraction limit and machining limit, and is the hot spot of advanced manufacturing technology. In this paper, the development and mechanism of femtosecond laser machining are reviewed, and the mechanism of laser machining is described from the Coulomb explosion model, microexplosion model, color center model and two-photon ionization model. For femtosecond laser ultrafast action process, simulation is the main means to analyze the machining mechanism and study the laser and material action process. The characteristics and application range of the two-temperature model, molecular dynamics model and composite model used in femtosecond laser simulation are analyzed in order to provide a basis for the theoretical research of femtosecond laser machining. Finally, the existing problems of femtosecond laser machining technology are pointed out, and the development of this technology is prospected.

As semiconductor lasers have excellent characteristics including wide output wavelength range, simple structure, and easy to be integrated, they are widely used in medical, sensing, optical communications, military, and aerospace fields. With the increase of application requirements and output optical power, the reliability of lasers suffers from severe challenges. This paper reviews the failure mechanism of semiconductor lasers and analyzes the five effective failure detection and analysis methods of photoluminescence technology, electroluminescence technology, cathodoluminescence technology, infrared thermal imaging, and emission microscope. Furthermore, this paper summarizes and suggests the improvement measurements of the failure induced by the active area, cavity surface, welding, and operating environment. These will provide effective suggestions for the research and production of semiconductor lasers.

With the unique advantages of high processing accuracy, high efficiency, no pollution, and wide range of application materials, laser processing has become the first choice for micro-hole fabrication, especially in the processing of high-quality micro-holes. The advantages and research significance of laser processing micro-holes are introduced. The quality characteristics of laser processing micro-holes (such as depth-diameter ratio, taper, roundness, and recast layer) are summarized. The current research status of micro-hole quality of laser processing is reviewed and discussed. The impact of drilling methods, laser process parameters (such as pulse width, wavelength, and repetition frequency), and processing environment (such as vacuum, gas, and liquid) on the quality of laser processing micro-holes and the reasons for the impact are discussed. The development direction of laser processing of micro-holes and the focus of future research are summarized.

Cavity ring-down absorption spectroscopy is a direct absorption spectroscopy detection technology with high sensitivity, strong selectivity, and fast response speed. This technology has the smallest noise absorption coefficient of 10-12 cm-1·Hz-1/2 due to continuous improvement and expansion of excitation light source, cavity structure, and modulation method etc. The working principle, technical characteristics, and typical applications of cavity ring-down absorption spectroscopy detection equipment are summarized in this study, and the effects of the excitation light source, cavity structure, and modulation methods on cavity ring-down spectroscopy detection technology are analyzed. Finally, the technology's application prospect is prospected by merging the typical applications of cavity ring-down absorption spectroscopy in different fields.

The GH3536 alloy is an important structural material for the high-temperature components of aeroengines owing to its excellent high-temperature oxidation and corrosion resistances and good performance during cold and hot forming and welding. The traditional manufacturing method of GH3536 high-temperature components has the disadvantages of long production cycle, complicated procedures, and low yield. Therefore, its production applications are limited. This study provides a comprehensive introduction to the research progress of the laser powder bed fusion of the GH3536 alloy and clarifies its structure and strengthening mechanism. Meanwhile, relevant research results were systematically investigated, conventional methods were compared, and the preparation of GH3536 alloy by laser powder bed technology is comprehensively discussed from the aspects of technical principle, microstructure, and mechanical properties. Furthermore, the composite technology of additive and traditional manufacturing is investigated. Finally, the future application and development trends of the GH3536 alloy prepared by laser powder bed technology are discussed.

Liquid crystal optical phased array has been widely investigated by researchers because of its small size, simple structure, easy integration, low power consumption, and ability to automatically acquire, point, and track, meeting the requirements of future space communication and military development. This study introduces the research progress of the precise deflection of liquid crystal optical phased array beams worldwide based on the performance indicator perspective and summarizes the methods for improving performance. Furthermore, it introduces the research progress of liquid crystal optical phased array in multiple access communication and high-power laser phased-system. Finally, this study can provide a reference for the future development of liquid crystal optical phased array.

Microchannel plate (MCP) photon detectors with picosecond timing properties are expected to transform future particle physics experiments. Herein, the development and commercialization process of large-area flat-panel MCP photon detectors were briefly reviewed, the basic design elements of MCP photon detectors were summarized, and the factors influencing time resolution characteristics were analyzed. Moreover, the existing physical limitations and technical bottlenecks related to the development and commercialization of large-area flat-panel MCP photon detectors are summarized.

A weak-reflection fiber Bragg grating (WFBG) array has been widely concerned due to its characteristics such as single fiber tensile strength and large-scale multiplexing in recent years. These characteristics make it have potential application value in large-scale structural health monitoring and very-low-frequency (VLF) underwater acoustic signal detection. In this paper, the fabrication, demodulation and application progress of WFBG arrays are systematically reviewed. In the fabrication of WFBG arrays, the grating device is mainly with the drawing-tower Talbot and phase mask technology. In the selection of optical fibers, there are ultraviolet transparent coated fibers, cerium doped fibers, and so on. In the term of signal demodulation, it can be roughly divided into four demodulation technologies: time domain wavelength, frequency domain, microwave photons and matched interference. In the term of application, WFBG arrays can be used as a laser device or as a sensor for monitoring.

Owing to the existence of gain saturation and depletion, the temporal pulse shape experiences large deformations in the master oscillator power amplifier systems, resulting in large, deviation from that of the seed laser and thus an uncontrollable output shape. In order to obtain specific temporal shape in the output laser pulses, researchers have proposed the temporal pulse shaping technology in the master oscillator power amplifiers. Both the theoretical and the experimental studies are introduced to achieve proper temporal shaping in this paper. It is also pointed out that the pulse shaping can be useful in getting flexible, accurate, and extensive control over temporal features of laser pulses.

Burst-mode lasers have wide applications in nonplanar laser-induced fluorescence diagnosis, laser fine processing, and laser remote sensing detection. Based on the different key technical schemes, the research progresses of burst-mode lasers based on pulse-slicer method and pump pulse Q-switched method are summarized respectively, analyzing their technical characteristics in detail, and the development tendency of burst-mode lasers is prospected.

Improving the photoelectric conversion efficiency has been the main research direction in the development of solar cells. It is an effective technology and method to improve the efficiency of silicon film solar cells by using plasmon resonance effect. The enhanced scattering mechanism of plasmon generated by incident light at the metal/semiconductor interface increases light absorption for the active layer, thereby improving the energy conversion efficiency of solar cells. We introduce the working mechanism and basic parameters of solar cells; then, detail the research progress in improving efficiency of silicon thin-film solar cells based on metal nanoparticles and compound nanomaterials, plasmon, surface passivation, grating, and trapping structures. After comparing the effects and cost factors of different metal nanoparticles [i.e., gold (Au), silver (Ag), and aluminum (Al)] on the efficiency of the solar cell of monocrystalline silicon solar cells, the feasibility and application significance of using Al nanoparticles to enhance the performance of such solar cells are affirmed.

Great progress has been made in the generation of ultrashort laser pulses in the mid-infrared (MIR) band of femtosecond laser by intra-pulse difference frequency technology, and it has been widely used in physics, chemistry, biomedicine, and other scientific areas. Firstly, the development and research background of MIR laser are introduced. Then the basic principle of intra-pulse difference frequency generation (DFG) of femtosecond laser is introduced. The progress on MIR pulse generation by intra-pulse DFG with different driving sources, such as Ti:sapphire laser, femtosecond laser at 1 μm waveband, femtosecond laser at 2 μm waveband, and fiber laser, is reviewed and compared. Finally, the future developments of the MIR femtosecond laser generated by intra-pulse DFG are prospected.

Minute amounts of noncotton fiber impurities that mix with cotton fiber during cotton picking, drying, transportation, and processing are known as cotton foreign fibers. Foreign fibers reduce the cotton grade and affect the quality of cotton processing, causing problems such as stains and uneven dyeing of textile fabrics, leading to quality decline of the final product. Therefore, detecting foreign fiber in cotton is essential. In this paper, we analyze the harm due to foreign fiber in cotton and problems associated with its detection and summarize the foreign fiber-related detection equipment. Simultaneously, a summary of the recent studies and progress in foreign fiber-detection technologies and methods with regard to image segmentation, feature selection, and image classification, and prospects for future research directions is discussed in this paper.

The brain-computer interface (BCI) technology enables direct interaction between the human brain and computers or other external devices by analyzing and decoding neural activity. It can be used as a means of information exchange or the restoration of motor functions and has been applied in communications, intelligent robot control, biomedicine, and neurorehabilitation, etc. Functional near-infrared spectroscopy (fNIRS), an optical imaging technique that can be used to detect changes in hemoglobin concentration within the cerebral cortex, has been employed recently in the development of noninvasive BCI. The development history, composition principles, key technologies, future development trends, limitations, and problems of fNIRS-BCI are reviewed systematically and in detail. Particularly, the feature-classification algorithm was analyzed comprehensively, and the result was compared with statistical data from its predecessors to summarize several valuable conclusions and opinions. This review is designed to provide a comprehensive and specific understanding of fNIRS-BCI and references and guidance.

Lung cancer is the malignant tumor with the highest mortality rate in the world. Its early diagnosis can remarkably improve the survival rate of lung cancer patients. Deep learning can extract the hidden layer features of medical images and can complete the classification and segmentation of medical images. The application of deep learning methods for the early diagnosis of lung nodules has become a key point of research. This article introduces several databases commonly used in the field of lung nodule diagnosis and combines the relevant literature recently published at home and abroad to classify the latest research progress and summarize and analyze the application of deep learning frameworks for lung nodule image segmentation and classification. The basic ideas of various algorithms, network architecture forms, representative improvement schemes, and a summary of advantages and disadvantages are presented. Finally, some problems encountered while using deep learning for the diagnosis of pulmonary nodules, conclusions, and the development prospects are discussed. This study is expected to provide a reference for future research applications and accelerate the maturity of research and clinical applications in the concerned field.

Factors such as low spatial resolution and material heterogeneity result in the issue of mixed pixels in images, which makes pixel-level data processing and applications unable to meet the practical requirements. Spectral unmixing extracts information of endmembers and abundances at the sub-pixel level and offers technical support for fine quantitative analysis of data in real applications. This paper introduces research advances of spectral unmixing theories, methods, and applications in recent years. Technical research results include linear and nonlinear mixture models, and methods under the principle frameworks of geometry, regularized optimization, and statistical machine learning. Moreover, improvements provided by spectral unmixing for other techniques such as classification, and theoretical and practical values of spectral unmixing in handling problems from remote sensing to indoor applications such as medical science are analyzed. Finally, drawbacks in spectral unmixing technical and application researches and the necessity of their synergistic development are summarized.

As an important three-dimensional (3D) data type, point cloud has been widely used in many applications with the development of 3D acquisition technology. Owing to its high efficiency in processing large-scale data sets and the autonomy of extracting features, deep learning has become the leading method for investigating the latest studies in a point cloud classification. This paper introduces the current research status of the point cloud classification methods. Furthermore, some main and latest methods of point cloud classification based on deep learning are analyzed and classified according to the data processing method. Additionally, this paper summarizes the key ideas, advantages, and disadvantages of each type of method and discusses the realization process of some representative and innovative algorithms in detail. Finally, the challenges and future research directions of the point cloud classification are outlined.

The development of precision manufacturing has put forward a higher requirement for the 3D topographical measurement of complex microstructures. It is a little difficult for the existing non-contract measurement method to measure a slope surface with a big gradient although it has a high vertical solution. In recent years, the focus variation measurement method based on ultrashort depth-of-field imaging performs well in the measurement of tilted surface and can be used to truly realize the 3D surface measurement of a microscopic complex structure. Firstly, the principle of microscopic 3D measurement based on focus variation is summarized. Then, the latest theoretical and technological research progress on this method is addressed. Finally, the challenge and future development trend of microscopic 3D measurement based on focus variation are discussed and prospected.

The explosive development of deep learning technology has led another wave of machine learning in recent years. Deep neural network, with the ability to recognize and extract abstract features, fit nonlinear relationships, against interference factors and generalization, is widely used in autopilot, target recognition, machine translation, speech recognition and other fields. The convolutional neural networks (CNN) are popular in optical information processing. In this paper, we introduce the basic concepts and structural components of CNN in detail, and review the applications in digital holography, fringe patterns analysis, phase unwrapping, ghost imaging, Fourier ptychographic microscopy, super-resolution microscopy, scattering medium imaging, optical tomography imaging, etc. We summarize the typical applications and existing shortages of CNN in optical information processing, and finally prospect the future development of convolutional neural networks.

Clinical detection of soft tissue biomechanics is of great significance for the early diagnosis, progress tracking and treatment evaluation of certain diseases. Optical coherence elastography (OCE) has been developed to visualize and quantify tissue biomechanics based on optical coherence tomography (OCT), in which to observe the static or dynamic mechanical responses of soft tissue organs under load excitation to quantify and reconstruct their biomechanical properties and thus to obtain the pathological information of diseased parts. Due to its advantages of non-invasive 3D imaging mode, real-time imaging treatment performance and high resolution, the OCE technique has the unique advantage and development potential in the clinical biomechanical measurement of soft tissue organs such as eyes. From the aspects of the static/dynamic excitation methods of OCE, the speckle tracking technology and phase sensitive detection technology of OCT, and the analytical and finite element analysis methods for biomechanical property quantification, we introduce the theory and method of OCE, review the development history of OCE, introduce and summarize in detail its newest achievements, and prospect its development trend.

As a fundamental technique, object counting has broad applications, such as crowd counting, cell counting, and vehicle counting. With the information explosion in the internet era, video data has been growing exponentially. How to obtain the number of objects efficiently and accurately is one of the problems that most users care about. By virtue of the great development of computer vision, the counting methods are gradually turned from the traditional machine learning based methods to deep learning based methods, and the accuracy has been improved substantially. First, this paper introduces the background and applications of object counting. Then according to the model task classification, three counting model frameworks are summarized and the computer vision based counting methods in the recent 10 years are introduced from different aspects. Some public datasets in the fields of crowd counting, cell counting, and vehicle counting are introduced and the performance of various models is compared horizontally. Finally, the challenges to be solved and the prospects for future research are summarized.

Large field of view, high resolution, and phase imaging are long-term goals pursued in the field of optical microscopy. Nevertheless, it is difficult to balance these performances in the conventional optical microscopic framework, which largely limits the application scope of conventional optical microscopy. Conventional microscopic imaging methods improve the imaging space-bandwidth product (SBP) or phase-imaging capability at the expense of a significant increase in the system construction cost or decrease in other imaging performances. Fourier ptychographic microscopy (FPM), as a representative computational microscopy imaging technology framework, can achieve large SBP and quantitative phase imaging simultaneously, without requiring precision mechanical scanning devices and interferometric systems. FPM has been widely studied and used in the fields of digital microscopy and life sciences; it has high research value and application prospects. In this article, the related research progress of FPM from the aspects of basic physical model, phase-recovery algorithm, and system-construction method is reviewed. In addition, the theory and application development direction of FPM are analyzed and discussed.

Image semantic segmentation is an important research field of computer vision and also one of the key technologies for scene understanding. In the field of unmanned driving, high-quality semantic segmentation of road scenes provides a guarantee for the safe driving of autonomous vehicles. First, this paper starts with the definition of semantic segmentation of road scenes and discusses the current challenges in this field. Second, this paper divides the semantic segmentation technology into a traditional segmentation technology, a traditional segmentation technology combined with deep learning and a segmentation technology based on deep learning, focuses on the semantic segmentation technology based on deep learning, and elaborates it according to three different network training methods of strong supervision, weak supervision and unsupervison. Then, the datasets and performance evaluation indicators related to the semantic segmentation of road scenes are summarized and compared, and the segmentation results using the common image semantic segmentation methods are analyzed. Finally, the challenges faced by the road scene semantic segmentation technologies and the future development direction are prospected.

Super-resolution microscopy invented at the beginning of the 21 st century has rapidly become a indispensable method in life science research owing to their nanoscale spatial resolution, low damage of sample preparation, and so on. Among a variety of super-resolution imaging techniques, single-molecule localization super-resolution microscopy (SMLM) with straightforward principle and outstanding spatial resolution gains more and more attention from researchers, thereby continuously making significant progress on the techniques and applications. Firstly, this paper reviewed the principle of SMLM and discussed some technical problems including the optical path building, the image reconstruction, and the drift correction. Two types of representative SMLMs were indroduced and discussed. Then, diversified multi-color SMLMs were introduced and their advantages and disadvantages were analyzed. The improvement of imaging parameters including the lateral/axial spatial resolution, imaging field, and imaging depth of SMLM was subsequently discussed. The research progress of correlated imaging of the SMLM combined with deep learning and SMLM combined with the electron microscope was further introduced. Moreover, the extraction and analysis methods of SMLM data were discussed. Finally, some important applications of SMLM in cell biology were listed and the development prospects of SMLM were discussed. We hope the present review could be a useful reference for the SMLM users and provides novel insights for them, thus promoting the in-depth applications of SMLM in life science research.

Connecting rod cracking processing is a key technology for connecting rod processing, which contains many advantages, such as fewer processing procedures, which can minimize equipment investment; the material loss is low, which can achieve the effect of energy saving and material saving; and the products have higher quality and improve the carrying capacity of connecting rods. Its core technologies include three types, the first is connecting rod cracking groove processing, the second is the directional splitting connecting rod, and the last is fixed torque assembly bolts. The main processing method of connecting rod cracking groove processing is laser processing. This article mainly introduces the principle and characteristics of laser processing connecting rod cracking tank and the development status, and characteristics and prospects of laser processing connecting rod cracking tank equipment at home and abroad. The characteristics of laser processing connecting rod cracking tank are mainly high precision and high efficiency. At present, domestic and foreign laser processing connecting rod cracking tank equipment is developing in the direction of improving processing efficiency and reducing costs.

Laser-induced liquid micro-jet technology is a medical method that uses lasers to induce cavitation bubbles used to generate micro-jets, so as to cut target tissues in a narrow chamber. It has advantages of low thermal damage, high precision, minimal invasiveness, and a high degree of choice for elastic tissues such as membranes and blood vessels. The mechanism of laser-induced micro-jet generation and the structure of a typical micro-jet system are introduced. Its application and research progress in medical field are reviewed. The key issues that restrict the clinical application of laser-induced micro-jet technology are summarized, and its application potential in medical application is prospected.

Due to the periodic nonlinear error, the measurement accuracy of heterodyne laser interferometer is difficult to improve. In this regard, this paper first analyzes the sources of nonlinear errors in heterodyne laser interferometers, including frequency aliasing, polarization aliasing, and ghost ghosting. Second, it discusses nonlinear error compensation and suppression techniques, including interference signal processing, traditional structure improvement, space separation of polarized light, and phase modulation dual-homodyne interference, and then introduces the measurement technology of nonlinear error, including interference signal processing measurement, dual-phase differential detection, and Fabry-Perot interferometer detection. Finally, it summarizes and prospects the compensation, suppression, and measurement technology of nonlinear error, which provides reference for research in related fields.

Convex grating is the core of Offner structure imaging spectrometers. To improve the imaging quality of a spectrometer and realize remote sensing detection, it is key to use convex grating with high diffraction efficiency and high resolution. The diffraction efficiency of convex gratings is analysed by strictly coupled wave theory. In this study, we present the research status of convex grating and discuss the main methods for designing and manufacturing convex blazed grating, including electron beam direct writing, X-ray lithography, mechanical etching, and holographic ion beam etching. Owing to the advantages of holographic ion beam etching, such as low cost, controllable groove type, and ghost-free, we introduce in detail the fabrication of convex grating via holographic ion beam etching and present related studies. Based on the investigation and analysis, we aim to optimize and improve the uniformity of the light intensity distribution of holographic exposure, the adjustable rotation axis of swing-etching device, and the process parameters of ion beam etching to produce a practical convex-blazed grating.

Perovskite light-emitting diodes show great potential in the fields such as display, lighting, and imaging because of their high efficiency, high color purity, low fabrication cost, and widely tunable light emission spectra. Starting from the basic structure and working mechanism of perovskite light-emitting diodes, this review focuses on the main technical means to improve the fluorescence quantum yield, light extraction efficiency, carrier injection efficiency, and reliability of perovskite light-emitting diode devices. The development process of the key parameter improvement method for the blue, green, red, and near-infrared perovskite light-emitting diodes is systematically explained, and the latest research progress of lead-free perovskite light-emitting diodes is briefly introduced. The technology development trend of light-emitting diodes is discussed, and the methods and ideas to further improve the performance and reliability of perovskite light-emitting diodes are prospected.

Laser additive manufacturing （LAM） involves a complex heat-processed process, and the produced multilayer parts also have complex microstructure characteristics. The microstructure characteristics of the parts determine their mechanical properties, thus the optimization of microstructure characteristics is the key to further realize the precise control of the mechanical properties. This article reviews the microstructure characteristics of the LAM multilayer parts and summarizes the factors influencing the evolution of the microstructure characteristics, which provides a reference for the optimization of the microstructure characteristics of the LAM multilayer parts.

Frequency-swept fiber lasers have extremely important application values in the fields of fiber sensing, biomedical, and spectroscopy. The parameters such as the center wavelength, sweep speed, sweep range, and output power of the frequency-swept fiber laser determine the performance of the fiber sensing system and the biological imaging system. Therefore, it is of great significance to study the frequency-swept fiber laser and its various performance parameters. The frequency-swept fiber lasers currently studied can be divided into two major categories, one is based on dispersion-modulated frequency-swept fiber lasers, and the other one is based on optical filters. This article mainly introduces the research progress of the frequency-swept fiber laser based on the optical filter and the research results on various performance parameters. At the same time, it points out its existing problems and prospects the development of frequency-swept fiber lasers.

Terahertz time-domain spectroscopy （THz-TDS）, as an emerging detection technology developed rapidly in recent years, has been widely used in the agriculture, chemical industry, pharmacy, and other detection fields due to its powerful perspectivity, high security, and efficient spectral resolution. In this paper, we introduced the recent research status of terahertz spectroscopy in the detection of inferior agricultural products, the detection of pesticide residues, the detection of banned additives, the identification of genetically modified crops, and the detection of moisture content in agricultural products. Furthermore, we summarized the main technical problems of terahertz spectroscopy in the detection of agricultural products and forecasted the development prospects of this technology. As science and technology develop forwards, terahertz spectroscopy will have more bright application prospects in the future.

Pulsed laser deposition has broad applications in scientific research and industry as a simple, versatile, and efficient film growth technology. The requirements for film quality are becoming more and more stringent in many high-tech applications. Reducing or eliminating the particulates inside and on the surface of a film has become an urgent problem. This paper introduces the source of particulates in pulsed laser deposition and discusses the advantages and disadvantages associated with various particulate control techniques. Finally, the trend of particulate control based on pulsed laser deposition is discussed.

In recent years, porous graphene nanomaterials have attracted significant attention owing to their unique physical and chemical properties as well as their numerous potential applications in the fields of biology, materials, energy, and information technology. However, the synthesis of porous graphene usually requires high-temperature treatment or multistep chemical synthesis methods, making the process complicated. It is also challenging to form a patterned structure. In 2014, American researchers proposed laser-induced graphene （LIG） technology to achieve low-cost patterned porous graphene structures. LIG technology is a method that prepares three-dimensional porous graphene material by direct laser writing on a carbon precursor material using a laser in an ordinary atmospheric environment. This technology combines the preparation and patterning progress of three-dimensional graphene. It does not require traditional wet chemical steps, thus reducing the cost of production. Since its advent, LIG has stimulated researcher’s interest. Researchers have explored the LIG formation mechanism and its applications in various fields, such as energy, sensing, and environment. This study summarizes LIG’s various synthesis schemes, including controlling the LIG product quality, surface properties, electrical conductivity, and methods for converting different carbon precursors to LIG. Based on the characteristics of LIG, the application of LIG in supercapacitors, sensors, self-cleaning filters, triboelectric nanogenerators, and terahertz modulation devices has been investigated in recent years. Finally, this study prospects the development of LIG-based absorbing materials and metasurfaces.

A light detection and ranging （LiDAR） system can actively emit laser light to capture the distance, direction, speed, and contour of an intrusion target with high accuracy and high resolution, and thus it is widely used in the urban security, industrial fields, etc. This paper briefly introduces the mainstream manufacturers of security LiDAR at home and abroad as well as the technical indicators of their products. The principle, characteristics and current status of security LiDAR under different technological regimes are mainly discussed in terms of LiDAR ranging schemes, scanning methods and light source selection, combined with different security applications. The application trend and development future of security LiDAR are summarized and prospected in the end. Security LiDAR will develop toward low-cost, high-performance, serialization, miniaturization, solidification, chip, and multi-source integration.

Compared with single vortex beam, vortex beam array has multiple phase singularities, which can not only increase information transmission capacity, but also increase the number of particles captured and observed. At present, there are various methods for generating vortex beam array in the field of optics, such as interferometry, Talbot effect method, optical wedge diffraction method, mode conversion method, Dammann vortex grating method, computational holography method, spatial light modulation method, and metamaterial pattern method. In this paper, the theoretical model, experimental principle, experimental results, and research status of these methods are introduced in detail, and their application prospects are presented.

Due to the wide spectral bandwidth of ultra-short and ultra-intense laser facility, the use of traditional spatial filter lens groups to expand the beam will cause the accumulation of chromatic aberrations of the device, which will seriously affect the quality of the terminal focal spot. In this paper, the main technology and research progress of eliminating chromatic aberration in ultra-short and ultra-intense laser facilities are reviewed, and both the advantages and disadvantages of several main schemes are compared and summarized. On this basis, a scheme for dynamic and accurate compensation of the chromatic aberration of the facility is proposed, which has been verified and used in actual engineering. This paper also analyses and prospects the development direction of chromatic aberration compensation.

Hyperspectral imaging method can obtain two-dimensional images and spectral information of in vivo tissues, which has the advantages of high spatial and spectral resolution, large imaging range, non-invasive nature, and fast speed, providing abundant information for in vivo tissue diagnosis. In recent years, researchers have made great progress in imaging methods, instruments, and applications. In this study, the main advances of hyperspectral imaging methods and applications are reviewed, and the spectral imaging methods, system composition, and characteristics are discussed. This study introduces the research progress in in vivo tissue imaging methods and application in terms of spectral reconstruction, tissue optical parameter measurement, and image processing based on deep learning. Simultaneously, the application progress of hyperspectral imaging in clinical medicine, such as skin trauma and healing process detection, diagnosis of diabetic foot and retinal diseases, intraoperative detection, and microcirculation function evaluation, is also summarized.

Lensless digital holographic imaging could support high resolution, large field of view and three-dimensional (3D) imaging, but improving the resolution and quality of the reconstruction is still challenging. In this review paper, the compressive holographic models based on diffraction propagation method are introduced. Compressive sensing are developed based on total variation regularization and two-step iterative shrinkage/thresholding algorithm. The physical mechanism of removing two-order noise and twin image is discussed. A filter layer is designed to improve the signal to noise ratio of 3D reconstruction. A block-wise algorithm based on effective anti-aliasing region is proposed, which can improve computational efficiency of compressive holography. A single-shot compressive holographic model based on two-angle illumination beam is proposed. It effectively improves the axial resolution of 3D imaging. High-resolution 3D reconstruction of multilayer masks and particle flow field are demonstrated by using this algorithm.

Content-based medical image retrieval method is a research hotspot in the field of computer vision in recent years, and has been widely used in the research of computer-aided diagnosis. This paper summarizes the research progress and significance of content-based medical image retrieval methods, introduces the current mainstream medical image retrieval algorithms and their advantages and disadvantages, and aims to guide researchers to quickly understand the research content in this field. The research of medical image retrieval is mainly divided into two parts: feature extraction and similarity measurement. This paper introduces the feature extraction method of medical images starting with the extraction of traditional features and the feature extraction based on deep learning emerging in recent years. The similarity measure part enumerates the Mahalanobis distance metric, vocabulary tree, and hash algorithm. Finally, the related feedback technology in the field of medical image retrieval and the commonly used image retrieval system are summarized. The possible research directions and related difficulties in medical image retrieval are discussed.

We summarize key technologies of underwater target exploration in more details, including underwater image preprocessing, target detection and recognition, and target tracking algorithms. First, underwater image preprocessing algorithms are divided into image enhancement and restoration by judging whether they need to build a model, and then we discuss the basic ideas and characteristics of enhancement and restoration. Besides, the principles and methods of target detection and recognition, and target tracking for underwater optical images are reviewed across the board. After summarizing and analyzing the research results of the above processes, we untangle the core issues to be addressed and related difficulties existing in key technologies of underwater target exploration, and discuss the solutions and further development directions as well.

Correlated imaging has attracted noteworthy attention due to the advantages in non-local property, strong anti-interference capability, etc. And it has wide applications in three-dimensional imaging, remote sensing, biomedical technique, and national defense and military. In this paper, according to different stages of development,we introduce the development history and applications of the entangled two-photon correlated imaging, (pseudo) thermooptical correlated imaging, and computational correlated imaging, especially focusing on the improvement arising from the ICCD camera. Also, we briefly discuss the physical nature of the thermooptical correlated imaging. Finally, we give a pithy view of the practical applications.

Vortex beams carry orbital angular momentum (OAM), and have wide application prospects in optical manipulation, optical communication, and quantum optics. To produce ultrashort vortex pulses, we combine vortex beams with the time domain control technique. The method is very important in physical experiments performed under extreme strong field conditions and the researches about ultrafast nonlinear spectroscopy and precision laser material processing. In this paper, the research progress on ultrashort vortex pulse generation methods at home and abroad in recent years is summarized. The main methods for generating ultrashort vortex pulses are reviewed, and the advantages and disadvantages of each method are compared and analyzed.

As an important branch in the field of distributed optical fiber sensing, optical frequency domain reflectometer (OFDR)has the advantages of high sensitivity and high spatial resolution, and is the research hotspot in the field of distributed optical fiber sensing in recent years. The principle and key technologies of OFDR are introduced and the recent progress of optical frequency domain reflectometer is systematically reviewed from two aspects of high spatial performance and remote frequency domain reflectometer. Then, the latest applications of OFDR in different fields are analyzed and the characteristics of different OFDRs are summarized.

2 μm single-frequency pulse laser is the key light source of lidar for the detection of the atmospheric wind field and CO2 concentration. In the paper, the research progress of the continuous-wave 2 μm single-frequency laser, pulsed high-repetition-frequency laser and pulsed low-repetition-frequency laser are summarized respectively, according to different application requirements. Their technical characteristics are analyzed as well. The development tendency of the pulsed single-frequency 2 μm all-solid-state laser is prospected.

As a new green and efficient paint stripping technology, laser paint stripping has broad application prospects in the field of manufacturing and maintenance, and is gradually replacing the traditional methods to become the most advanced approach. We introduce the principle of laser paint stripping technology, review the research progress based on different lasers at home and abroad, and look forward the development prospect of laser paint removal technology.

Time-frequency synchronization technology based on optical fiber transmission has advantages of high accuracy, high stability and low loss. In recent years, optical fiber time-frequency synchronization technology developed rapidly, with the emergence of new methods, new technologies and new applications, and it has strong military application needs and civil promotion prospects too. It is extremely necessary to review its development status and objectively examine its future development trend. On the basis of defining the principle and technical characteristics of optical fiber time-frequency synchronization technology, the current status of optical fiber time synchronization, frequency synchronization and networked synchronization technologies are introduced, the key points in the construction of ground-based time-frequency network are proposed. The problem of restricting the practicality of optical fiber time-frequency synchronization technology is analyzed. It is considered that ultra-long-distance and high precision transmission on commercial networks is the difficulty of restricting optical fiber time-frequency synchronization technology and the key problem to be solved in the future research.

Laser metal additive manufacturing, which is referred to a near-net-shaping process, builds metal parts by rapid melting, solidification and layer-wise cladding. The large temperature gradient in laser additive manufacturing process causes the thermal stress, thermal deformation, metallurgical defects and microstructure degradation of the part; therefore, the detection, analysis and control of the temperature fields are always the key problems of metal additive manufacturing. The review is presented of detection, analysis and control technologies of the temperature fields in additive manufacturing at home and abroad, including the finite element simulation, the in-process detection based on the infrared camera and pyrometer, the closed-loop control and the substrate preheating control. The advantages and disadvantages of the present techniques of detection, analysis and control of the temperature fields are compared, and the future trend is analyzed.

Coaxial powder feeding nozzle, as one of key components in laser metal additive manufacturing system equipment, directly affects the forming accuracy and performance of parts. Because of its importance, a variety of new powder delivery nozzles have been developed by scholars at home and abroad. In this paper, the research on coaxial powder feeding nozzles is briefly summarized from two different powder feeding methods of "powder feeding by light outside" and "powder feeding by light inside", whether the laser beam and powder beam can vary focal length or not is analyzed, the characteristics of coaxial powder feeding nozzles are pointed out, and the development of the coaxial powder feeding nozzles in the future is provided.

Distributed optical fiber acoustic sensing (DAS) technology based on coherent Rayleigh scattering can obtain the vibration and sound field information along the optical fiber in real time. Recently, DAS has received extensive attention from scholars in many fields, due to its unique advantages such as large sensing range and high time-and-space resolution. In this paper, the fundamental sensing mechanism of DAS is introduced. The research progress on key scientific and technological issues, such as coherent fading suppression, response bandwidth enhancement, and spatial resolution optimization, is briefly reviewed. The application progress of DAS in perimeter security, rail transportation, and other fields is also described. Finally, the potential future research directions are discussed and speculated.

Diffuse optical tomography (DOT) is a low-cost, non-radiative damage, deep detection in vivo optical functional imaging technology that uses near-infrared light to detect biological tissue optical structures. Due to the strong scattering, low absorption characteristics, and high spatial resolution of the biological tissue itself, the inverse problem of DOT reconstruction has serious ill-conditioned characteristics. The traditional inverse problem solution is mainly based on the algebraic iterative reconstruction method. With the development of artificial intelligence and the arrival of the era of big data, deep learning research has set off to reach another new climax. The inverse problem-solving method based on a deep learning network model is gradually used in the DOT reconstruction process. On the basis of combing the traditional DOT reconstruction algorithm, this manuscript focuses on the research progress of the latest deep learning for DOT reconstruction and provides reference for relevant research teams in this field.

Over the recent years, the popularity of depth sensors and three-dimensional(3D) scanners has enabled the rapid development of 3D point clouds. As a key step in understanding and analyzing three-dimensional scenes, semantic segmentation of point clouds has received extensive research attention. Point cloud semantic segmentation based on deep learning has become a current research hotspot owing to the excellent high-level semantic understanding ability of deep learning. This paper briefly discusses the concept of semantic segmentation, followed by the advantages and challenges of point cloud semantic segmentation. Then, the point cloud segmentation algorithms and common datasets are introduced in detail. This paper also summarizes the deep learning methods based on point ordering, feature fusion, and graph convolutional neural network in the field of point cloud semantic segmentation. Finally, it analyzes the quantitative results of proposed methods and forecasts the development trend of point cloud semantic segmentation technology in the future.

The three-dimensional (3D) imaging techniques of robotic vision in the field of intelligent manufacturing robot vision perception are reviewed. The characteristics and limitation in practical applications of some typical robot vision imaging methods are systematically summarized. The content involves time-of-flight imaging, point and line scanning imaging, chromatic confocal imaging, structured light projection imaging, deflectometric imaging, monocular and multi-view stereo imaging, and light field imaging. The tree map of various robotic vision imaging methods are drawn. The best 3D imaging methods of eye-in-hand robotic system are discussed.

Laser rock drilling technology is a new drilling technology that utilizes the advantages of high-energy laser to achieve high-efficiency and controllable destruction of complex lithologic rock formations. It exhibits great development potential in oil and gas exploitation and mining excavation. However, current research on laser rock drilling technology is based on indoor experiments and theoretical explorations; therefore, many challenges are to be overcome prior to its industrial application. This paper focus on the objects involved in the interaction between laser and rock, and the results on the influencing factors of rock removal by laser are summarized. Furthermore, the influence mechanism of laser parameters, rock properties, laser transfer medium, and the working environment are analyzed. Moreover, certain suggestions aiming at solving the existing problems and indicating future research directions in laser rock drilling technology research are presented. Numerous studies show that numerous different kinds of factors have different mechanisms for rock removal by laser. The quantification of the multi-factor influencing mechanism of rock removal by laser, the screening of the key influencing factors, and the coordination of the multi-factor interaction constitute the important subjects of the laser rock drilling technology applications.

Surface-enhanced Raman scattering (SERS) is a highly efficient molecular spectroscopy technique widely used to detect trace species in studies in many fields such as chemistry, life sciences, and pharmaceutical analysis. However, the non-uniformity of “hot spots,” instability of chemical effects, and uncertainty of the number of molecules increase the volatility of Raman signals, which presents difficulty in their use for quantitative analysis. This paper introduces the principle of an internal standard method, improvement of substrate performance, and the modes for adding three internal standards, including external addition mode, core-internal standard-shell modes, and self-calibrating substrate mode, from the following four aspects: “hot spot” effect, chemical effect, molecular adsorption, and internal standard addition mode.

Flexible photonic devices, which are bendable, foldable, and even stretchable, are not limited to the rigid physical state constraints of traditional optoelectronic devices and thus unique tunable optoelectronic properties could be achieved, which greatly expands the development and practical implementation of traditional optoelectronic devices. Combining with new functional optical materials, novel device integration technologies, and the advantages of photonic devices over electronic devices in material sensing specificity, channel capacity, and resistance to electromagnetic interference, flexible photonic devices show great research and application value in emerging and interdisciplinary fields such as wearable sensing, high-speed optical interconnect, light field manipulation, and optogenetic applications in biology. However, challenges including the fabrication difficulties, mechanical flexibility limitation, and the degree of integration exist in current flexible photonic technologies. This paper briefly reviews the recent progress on flexible photonic materials and devices to address those challenges. And further development and application demonstration for the flexible photonics has also been summarized and discussed.

Optical super-resolution microscopy, enabling to break the diffraction limit, provides a powerful observation means for research on ultra-fine structures and physiological processes. It has an important impact on studying the functions of cells and the pathogenesis of diseases, which is of great biomedical significance. As a branch of super-resolution imaging methods, single molecule localization microscopy has great scientific research value. We first introduce the research background and significance of single molecule localization microscopy. Then we describe the development process of this technology in detail. In addition, the basic principles of the existing mainstream technologies are elaborated and their corresponding advantages and disadvantages are also analyzed. Finally, we prospect the applications of the single molecule localization technology.

Optical microscopy performs an increasingly important role in clinical diagnosis and basic scientific research. With the development of novel fluorescence probes, light controllers, and detectors, super-resolution optical microscopy breaks through the diffraction limit and provides new tools for modern biomedical research. Among these techniques, structured illumination microscope (SIM) achieves super-resolution by using spatially coded structured illumination which down modulates spatial frequencies beyond the cutoff into the pass band of the microscope. SIM shows lower photo bleaching and phototoxicity, higher imaging speed, and no special requirements for fluorescent probes, which has significant advantages in application to live-cell biomedical research. In this paper, the important principles and technological progress during the development of SIM are firstly reviewed. Then we focus on the key experimental techniques and difficulties in hardware design and image reconstruction of SIM. Finally, the several applications in biological imaging are listed. It is expected that this review can provide guidance for designing and using SIM.

In this paper, laser-induced breakdown spectroscopy (LIBS) is summarized from two aspects. The first is the advantages of LIBS qualitative analysis method in element rapid monitoring and drawing the relative content distribution diagram of elements based on high spatial resolution ability of LIBS to comprehensively observe the distribution of elements in different parts of plant organs. The second is the progress and existing problems of LIBS in quantitative analysis of nutrient elements and heavy metals in soil and plants. The sensitivity of this technology to the determination of metal elements is better than that of nonmetallic elements. For the determination of nonmetallic elements, inert gases are need to eliminate atmospheric effects; for the determination of metal elements, the effects of self-absorption of metal elements can be solved by uncalibrated LIBS and optical thin LIBS.

The micro-ring resonator is an important device for the integration of silicon photonic chips. Based on the principle of micro-ring resonators, the paper mainly describes the research significance and development process of high-quality factor micro-ring resonators in the mid-infrared field, and analyzes the advantages and disadvantages of micro-ring resonators in different material systems in terms of technology and practical applications; then, we introduce the theoretical research of the cascaded micro-ring resonator based on the Vernier effect in the field of sensing and filtering in the mid-infrared region; the generation principle and development history of the mid-infrared Kerr optical frequency comb are reviewed, and we theoretically prove the germanium strip waveguide micro-ring can realize a wide-spectrum optical frequency comb with a bandwidth close to an octave at a pump power as low as 80 mW. Finally, we summarize the research progress and prospect the future applications.

In this paper, recent research progress of optical wireless communications in unmanned aerial vehicles (UAVs) was reviewed. By means of wireless optical technology, technical challenges and key enabling technologies were also surveyed for implementing robust and wideband communication links between UAV and satellite, UAV and UAV, and UAV and terrestrial terminals. The mechanisms and schemes of modeling, parameter optimization, and experimental testing under different UAV optical wireless link configurations were described in detail. Additionally, the key development trends of high-speed and high-reliability UAV-based wireless optical communication technology in modular implementation, high altitude platforms applications, and others were discussed.

As one of the basic characteristics of magnetic materials, magnetic field has attracted people's attention, and has been widely used in military, medicine, industry, and other field. The basic principles, development process, and application prospects of the high sensitivity micro-optical-atomic magnetometer are sorted out. First, the working mechanism and system composition of the miniature optical-atomic magnetometer are described. Second, the development processes of key technologies such as atomic gas cell fabrication and optimization methods, atomic gas cell heating methods, and magnetic field signal detection methods are discussed. Finally, the latest research progress of the magnetometer is reviewed, and the application prospects of the miniature optical-atomic magnetometer are prospected.

During the development of Ti∶sapphire laser crystals, the research of defects always plays a pivotal role in their performances. In recent years, some new optical phenomena have been observed in highly Ti-doped sapphire crystals, which indicates that the change in the internal defect structure may induce some influences on laser performances. This article introduces the research progress of defects in Ti∶sapphire laser crystals and also makes a brief discussion.

With the continuous improvement of the convenience of image acquisition and transmission and the rapid popularization of image editing tools, a malicious users can easily shoot, spread, edit and modify digital images to achieve the purpose of malicious behavior or crime. It becomes the key evidence for investigation and collection of evidence and judicial proceedings. The illumination response inconsistency (PRNU) causes by the defects of the image sensor manufacturing process and the unevenness of the silicon wafer is unique and stable for each camera, so it can be used as an effective device fingerprint for image source forensics. First, a comprehensive review of digital image forensics technologies including device fingerprint technology is conducted, and the main application scenarios of device fingerprints are introduced. Then, the basic technical principles of device fingerprint extraction in images is introduced, and the development of device fingerprint extraction technology is summarized. Finally, the problems to be solved and the technology development trend of the device fingerprint extraction technology are discussed.

In the big data era, we have witnessed the explosive growth of deep learning based image and video compression technologies. Such end-to-end learning-based compression frameworks have demonstrated promising efficiency for compact representation of original image data, and attracted a vast attention from both academia and industry. A systematic review of transformation, quantization, entropy coding, and loss function used in end-to-end learning-based image compression framework is introduced in this work. The research progress and key technologies are briefly introduced, as well as the comparative studies of coding performance for existing methods with leading efficiency.

Tumors are a major disease that seriously threaten the life and health of Chinese residents. Existing tumor diagnosis methods heavily rely on the subjective experience of doctors and include many issues, such as prolonged diagnosis, severe trauma, and high misdiagnosis rate. Therefore, it is crucial to develop a tumor diagnosis technology with intelligent properties to improve the level of diagnosing tumors in China. Raman spectroscopy is a label-free optical technique used for diagnosing benign and malignant tumors, classifying tumor subtypes, pathological diagnosis of biopsy, and in situ near-real-time imaging. Moreover, Raman spectroscopy combined with artificial intelligence has led to an intelligent diagnostic method. In this paper, the research progress of Raman spectroscopy for diagnosing various tumor types over the past three years was reviewed. Furthermore, three main aspects of the conventional Raman spectrum, Raman imaging, and probe diagnoses combined with the spectrum were introduced, and the prospect of Raman spectroscopy in the diagnosis of tumors in the future was discussed.

As a red emitting material, GaN∶Eu 3+ is very promising to be applied in GaN-based monolithic integrated full-color display devices. The current research focus is how to further control and optimize the luminescence characteristics of GaN∶Eu 3+ materials, and promote them to the practical stage. In this paper, the research progresses of optimizationing luminescence performance of GaN∶Eu 3+ materials from growth control, Mg 2+, Zn 2+, and Si 4+ co-doping control, and other rare earth element co-doping control, etc., are reviewed, the application potential of these methods is compared, the future work focus of GaN∶Eu 3+ materials is pointed out, and the trend of future development is prospected.

With the further integration of various emerging information technologies and power grids, various wireless optical technology schemes relying on and serving smart power have been put forward and formed a preliminary scale. In this work, the main classification and frontier development of the smart power wireless optical technology are described from the aspects of the channel characteristics and transmission schemes of the fusion of power line communication and visible light communication, hybrid radio frequency power visible light communication, power wireless optical indoor positioning and relay, high voltage line wireless light monitoring, and so on. Then, combined with a number of prototype experiments, this paper introduces the levels of main technical indicators of various smart power wireless optical technologies in terms of the transmission rate, coverage, positioning accuracy, energy consumption, and so on. Finally, the major challenges and potential solutions of the smart power wireless optical technology are provided.

Brillouin optical time domain reflection (BOTDR) technique is a kind of simultaneous sensing technology for temperature and strain that has numerous applications and huge potentials. Compared with other sensing technologies, BOTDR has the following advantages: high accuracy, convenient layout, large dynamic range, and long measurement distance. This study introduces the principle of BOTDR and illustrates its main performance indexes. Additionally, new developments and key advances in BOTDR sensing for decades are reviewed, including improvement of spatial resolution, expansion of measurement distance, improvement of measurement accuracy, reduction of measurement time, as well as the solution of temperature and strain cross-sensitivity. Moreover, the examples of BOTDR application are introduced from the structural health monitoring of infrastructure and the pre-warning of geological disaster, and their characteristics are discussed. A typical BOTDR is advanced, and the developing trend in future will be characterized by the improvement of software, field-engineering application, and combination of multiple platforms.

Although polycrystalline materials sintered from nonlinear crystal grains are macroscopically isotropic, the random distribution of grain orientation makes it possible that coherent enhancement of nonlinear polarization occurs when laser interacts with them. Meanwhile, the statistical average value of nonlinear conversion efficiency is proportional to the interaction length. Thus it is called random quasi-phase matching (RQPM). RQPM in polycrystalline materials has a distinct advantage in bandwidth over birefringence phase matching (BPM) and quasi-phase matching (QPM), thus polycrystalline materials are of great significance in frequency conversion for broadband femtosecond lasers. Recently, difference frequency generation (DFG), second harmonic generation (SHG), efficient optical parametric oscillation (OPO), and so on, have been realized based on RQPM in polycrystalline materials, which offers a new low-cost option for supercontinuum and broadband optical frequency combs. This paper summarizes the history and status of the technology and theories of RQPM, discusses the latest achievements on ultra-broadband frequency conversion, introduces the processing and modelling methods of polycrystalline materials, and gives an outlook on the development of RQPM. It is expected that this review can give references to domestic researchers in the fields of ultrafast lasers, nonlinear frequency conversion, etc.

The quantitative phase microscopy is sensitive to environmental disturbance. It has been a hot topic that how to get rid of the influence of environmental disturbance on quantitative phase imaging. This review focuses on the common-path digital holography microscopy (DHM) and single beam quantitative phase microscopy. The former mainly includes Fizeau interference microscopy, Mirau interference microscopy, off-axis and coaxial point diffraction interference microscopy, DHM of double spherical illumination, and spatially-multiplexed DHM. The latter mainly includes coaxial digital holography, and quantitative phase-contrast microscopy based on parallel light illumination, ultra-oblique illumination, and multi-point off-axis illumination. We hope that this review will provide useful reference for the construction of high stability and practical quantitative phase microscopic devices.

Computational imaging technology (CIT) refers to a novel imaging method that is different from the “what you see is what you get” information acquisition and processing methods of traditional optical imaging. With the development of new optoelectronic devices and the improvement of hardware computing capabilities, it has shown a booming trend in the field of optoelectronic imaging. By using CIT to obtain and calculate the information of light field, the information utilization and interpretation capability can be superior to traditional imaging, which can realize the requirements of “higher (resolution), farther (detection range), and larger (optical field of view)” of photoelectric imaging. We start from the description of information acquisition and loss process of the imaging chain, and further analyze the acquisition and interpretation of multi-physical information of light field through several typical computational imaging methods, such as scattering imaging, polarization imaging, and bionic imaging, and the principles of them are discussed in detail. According to the trend of imaging technology, we put forward prospectively the design idea of computational optical system based super large-aperture telescopes. Since CIT has significant advantages in improving imaging resolution, increasing detection distance, expanding imaging field of view, and reducing the size and power consumption of optical systems, it is expected to realize the imaging through the fog with longer distance and through biological tissues at a larger depth.

The imaging spectroscopy technology can obtain the spatial and spectral information of the observed object, and effectively distinguish the material composition of the object surface. It is widely used in the military and civilian fields. In recent years, the imaging spectroscopy devices based on filter arrays have received extensive attention due to their compact structure, fast imaging speed, and large coverage band. As a core component to determine the spectral performance of such devices, the filter array is a research hotspot. In this paper, by summarizing the main progress of spectral filter arrays, the advantages and disadvantages of different spectral filter arrays and their application range are analyzed, and the development trend of spectral filter arrays is prospected.

A spaceborne Doppler wind lidar is an efficient active detection device that can be used to obtain the global three-dimensional atmospheric wind field in global scale. It is able to make up for the weakness of passive sensing of meteorological satellites. The review for its requirements and progress indicates important scientific significance. First, this study describes the urgent needs for three-dimensional wind fields in various fields such as accuracy improvement of weather forecast, numerical weather forecast model assimilation, and global climate change research. Then, it reviews the development history of spaceborne wind lidar based on three schemes of coherent detection, direct detection and hybrid detection, and summarizes the challenges of the present spaceborne wind lidar. After that, according to the research progress of Chinese Doppler wind lidar, this paper summarizes the current seven key and unsolved technologies of Chinese spaceborne wind lidar. Finally, it is suggested that the spaceborne hybrid wind lidar with the advantages of both coherent detection and direct detection can well reduce the research and fabrication cost and significantly enhance the detection accuracy of atmospheric vertical wind profiles, and the spaceborne hybrid wind lidar will be the future trend in the field of spaceborne wind lidar.

Photodynamic therapy based on Cherenkov radiation is a new type of photodynamic therapy without external light excitation. Cherenkov radiation produced by radionuclides can activate photosensitizers nearby to produce reactive oxygen, so as to damage target cells and tissues. It overcomes many limitations of the traditional photodynamic therapy, such as limited tissue penetration and dependence on external light. It is a promising new field and provides a novel direction for tumor treatment. The weak Cherenkov radiation, the attenuation of Cherenkov radiation by tissues, the lack of corresponding photosensitizers, and the poor tumor targeting are the key factors limiting the further clinical applications of Cherenkov radiation. How to enhance the efficacy of photodynamic therapy based on Cherenkov radiation is the future research focus. Increasing the intensity of Cerenkov radiation and combining with nanotechnology to modify the surface of photosensitizers can improve the therapeutic effect. Meanwhile, the mechanism of photodynamic therapy is still controversial and further studies are needed. The research progress of photodynamic therapy based on Cherenkov radiation for tumors is reviewed.

One-dimensional (1D) well-ordered nanostructures of functional oxides open new avenues of applications in wide-range of fields, such as nano-laser, flat panel display, magnetic memory, nano-transistors due to their unique chemical and physical properties. Precise synthesis and assembly of well-ordered 1D oxide nanostructures is therefore essential to the development of next generation nanodevices. Pulsed laser deposition (PLD) is one of the most important methods for producing well-ordered 1D oxide nanostructures. Here we briefly introduce the fundamentals and characteristics of PLD techniques, discuss in detail on the routes and mechanism of preparing 1D well-ordered oxide nanostructures by PLD, and review current research process centering on several typical oxide nanostructures fabricated by PLD. At the end of this review, we briefly point out the existing problems in preparing well-ordered 1D nanostructures by PLD and prospect the application of ultrafast laser in this technology.

Optical coherence tomography angiography (OCTA) is a new noninvasive imaging method, which does not require dye injection and can thus be repeatedly used. It can present the fundus vascular network system including capillaries with high resolution and sensitivity. Its axial resolution up to micron level enables us to locate the primary location of lesions in the retina and choroid. OCTA can provide the same or even better vascular observation effect as the current gold standards. Therefore it has been developed rapidly, and its commercial products and applications in clinical practice have appeared. In order to help the relevant personnel quickly understand this technology, this paper introduces its principle and methods, applications in ophthalmology, current situations of products and clinical applications, existing shortcomings and prospects.

The resolution of conventional optical microscopes is limited to about half of the wavelength of illumination light due to the optical diffraction limit, which severely limits the observation of finer structures in biological and material research fields. As the most typical and earliest point scanning microscopy, the confocal microscopy has become the most widely used optical microscopy with good optical slicing ability and high signal-to-noise ratio. However, due to the limited cut-off frequency of the confocal microscopy, the improvement of resolution is also limited. Frequency shifting technique aims to move the higher frequency information to the observable frequency range, so as to improve the resolution of point scanning microscopy. In this review, the basic principle, advantages, and disadvantages of point scanning frequency shifting super-resolution imaging technology are introduced in detail, and its prospect is also given.

Curing cancer has been one of the greatest conundrums in the modern medical field. Because of side-effects associated with radiotherapy and chemotherapy, photothermal therapy ( PTT) utilizing photothermal therapeutic agents (PTA)—accumulate in tumor tissues by intravenous injection—to further generate sufficient heat under near-infrared (NIR) light irradiation for solid tumor ablation has attracted extensive attention of researchers. The method allows the local treatment process to be performed in a non-invasive direct and accurate manner due to the easy focusing and tunable properties of the incident light. In this review, we first summarize the major advances in PTA based on photothermal conversion nanomaterials in the study of ablation of solid tumors in recent years. Second, we summarize the different strategies to improve therapeutic efficacy. Finally, the limitations and challenges in the clinical application of photothermal tumor therapy based on photothermal conversion nanomaterials are discussed.

With the development of high precision optical clock and its various applications, higher and higher precision is needed for time-frequency transmission technology. Time-frequency transmission technology based on optical fiber has been relatively mature, while the time-frequency transmission technology based on free-space laser can be applied to the fields of inconvenient laying of optical fiber, fast maneuvering, and time-frequency transmission between the satellite and the Earth and between satellites. This paper introduces the research status of near-earth space and time-frequency transmission between the satellite and the Earth, and the development trend is also prospected. In the future, free-space laser time-frequency transmission will develop towards higher transmission accuracy, time-frequency transmission, ranging, communication integration, and time-frequency space networking.

The main task of person re-identification is to use computer vision to match and retrieve specific person across view fields. Compared with the traditional algorithm, deep learning is a more appropriate representative method for the discrimination between persons using data-driven extraction features. This study summarized the background and research history, main challenges, main methods, datasets, and evaluation index of person re-identification. The algorithms of person re-identification were mainly analyzed based on three aspects: feature expression, local features, and generative adversarial networks. The accuracy of 9 common datasets, 3 evaluation criteria, and 14 typical methods of person re-identification on the Market1501 dataset was listed. Finally, the prospects for the future research direction of person re-identification were established.

The sea-sky line is an important feature of sea and air background images, and its detection plays an important role in the division of sky and sea areas and target detection. However, sea clutter, clouds, strong reflection, and dynamic weather conditions in the complex sea and air background environment make it difficult to detect the sea-sky line. This paper aims to address the environmental adaptability problem of sea-sky line detection in a complex background. Three aspects were analyzed in detail: the characteristics of the original image obtained by the visual sensor and those of the sea-sky line in the image; interference factors and their suppression methods; existing methods of generating the sea-sky line. Furthermore, their advantages, disadvantages, and applicable scenarios were elaborated through comparative experiments, and the proposed morphological methods were experimentally compared. Finally, the future challenges and research directions of sea-sky line detection were discussed.

Ptychographic iterative and Fourier ptychographic imaging techniques can enhance field of view (FOV) and resolution. The parameter-changed computational imaging technique based on multi-disntance/ multi-height axial scanning and thin cylinder rotation can be used with phase retrieval algorithms to reconstruct the complex-valued fields of objects with high resolution. These imaging techniques possess prominent advantages for enlarging FOV and resolution. We review the recent research progress of the parameter-changed optical coherent diffraction imaging systems in the field of computational imaging. As a kind of indirect imaging tools, the multi-parameter imaging technique combines diffraction imaging with algorithms, which can be used to realize the accurate multi-dimensional characterization of a complex-valued light field.

The research progress on graphene/graphene oxide (GO) based fiber sensors is briefly reviewed. Detection object, sensing mechanism, structural design, and sensitivity of various graphene/GO based fiber sensors are discussed. The graphene-based micro/nano fiber sensors, graphene-based photonic crystal fiber sensors, graphene-based fiber grating sensors, and GO based fiber sensors are briefly reviewed. The preparation process of graphene/GO-fiber composite waveguide is briefly described. The existing problems of graphene/GO based fiber sensors are summarized.

Photodynamic therapy (PDT) is a minimally invasive therapeutic modality that can selectively treat malignant and benign diseases by using a combination of photosensitizers, light, and oxygen molecules. The light source is one of the three key elements of PDT, and its emission wavelength, irradiation method, and dose directly determine the efficiency of PDT. According to the required performances of light sources for clinical treatment, the technical advantages of light-emitting diode (LED) as light source in PDT applications are discussed. The LED array light source, and the development of wearable and implantable novel PDT light sources based on the organic LED, quantum dot LED, and wireless powered LED are introduced in depth. The application status of LED in isolated cells, live animals, and clinical PDT is summarized comprehensively. The development of LEDs with tunable emission wavelengths and the real-time adjustment of the illumination area and dose are the future development trends of intelligent and personalized PDT light sources.

Nano-computed tomography (nano-CT) is of great significance for the development of science and technology and the progress of production technology, especially in frontier researches of biomedicine and new material properties. The principle and classification of nano-CT imaging, as well as the implementation, advantages, and disadvantages of the nano-CT system, are reviewed. As for the specified technology detail, the principles, properties, manufacturing bottleneck, and application status of optical components in nano-CT are described. On this basis, the existing problems in nano-CT imaging system and its applications are proposed, and the future development of nano-CT imaging is summarized.

In recent years, terahertz spectroscopy has shown great potential in the fields of safety inspection, biomedicine, food detection, and resource detection. Among them, the detection of pesticide residues in agricultural products is one of the current research hotspots. This paper systematically expounds the latest research progress of terahertz spectroscopy in the field of pesticide detection, and combs the terahertz spectroscopy experimental instrument and theoretical calculation method. From the identification of pesticides, the establishment of pesticide fingerprint database, the quantitative and qualitative analysis of pesticides and the theoretical calculation of pesticides, this paper summarizes the research results obtained by scholars at home and abroad in recent years, and analyzes the existing problems and future research directions, which also provides prospects for the application of terahertz spectroscopy in the field of pesticide detection.

The distributed optical fiber vibration sensing system is a sensing system that uses optical fibers as sensing sensitive components and signal transmission media to obtain strain information. It has the characteristics of long sensing distance, real-time measurement, reversible vibration signal, and strong environmental adaptability. Distributed optical fiber vibration sensing systems based on phase-sensitive optical time domain reflectometry have been a hot spot in recent years. This paper mainly introduces the research progress of distributed optical fiber vibration sensing system based on phase sensitive optical time domain reflectometer from different detection structures and demodulation methods, and concludes the advantages and disadvantages of these methods and structures. This is of great significance for selecting the appropriate detection system in practical applications.

Time synchronization technology based on optical fiber transmission has the advantages of high precision, high stability, and low loss. It has become the main method for high-precision time synchronization, with robust application requirements and development prospects. Bidirectional comparison technology is a widely used optical fiber time synchronization method, and relevant institutions (locally and internationally) continue to propose new methods, technologies, and applications in this field. Furthermore, by combining the research history and progress of optical fiber bidirectional alignment technologies, this paper introduces the basic principles and technical characteristics of four mainstream bidirectional comparison schemes. The uncertainties and sources of errors of the synchronization system and their impact on time synchronization results are analyzed. Accordingly, this study provides a reference to further improve the accuracy of optical fiber time synchronization and establish a high-precision, safe, and stable ground-based timing system.

Photoacoustic conversion refers to the process of using photoacoustic effect to produce sound. High frequency and wide band ultrasonic signals can be generated by stimulating photoacoustic materials with pulsed light. Metal nanostructures generate localized surface plasmon resonance and therefore have high optical absorption and controllability, so that they can be used as important photoacoustic conversion materials and can be applied to biomedical imaging and other fields. In this paper, the mechanisms and principles of the photoacoustic conversion are firstly introduced. Then the research and application progresses of photoacoustic conversion of metal nanostructures such as gold nanorods, gold nanodisks, and gold nanoarrays are summarized. Finally, the possible future development directions of metal photoacoustic nanomaterials are prospected.

As one of the important tasks in machine vision, object detection is a technology branch with important research value in artificial intelligence systems. The three mainstream object detection models of convolutional neural network framework, anchor-based model, and anchor-free model are analyzed. First, the network structure and the advantages and disadvantages of the mainstream convolutional neural network framework, and the related improvement methods are reviewed. Second, the anchor-based model is deeply analyzed from one-stage and two-stage branches, and the research progresses of different object detection methods are summarized. The anchor-free model is analyzed from three parts: early exploration, key points, and intensive prediction. Finally, the future development trend of the field is considered and prospected.

As a new imaging technology, photoacoustic tomography (PAT) has attracted more and more attention in biomedical imaging due to its unique multi-scale imaging abilities of label-free, high resolution and high contrast, and has been rapidly transformed into clinical trials. Benefitting from the rapid development of ultrasonic detection technology and laser technology, the PAT system has gradually achieved real-time, large field of view, high resolution and high penetration depth of tissue structure and functional imaging. In this paper, we mainly summarize the advances of the circular array PAT system in biomedical imaging and the problems it faces in preclinical and clinical practices.

Image saliency is the most important information source to realize visual information perception. The detection of image saliency information has always been a hot topic in computer vision research. With the great improvement of data acquisition capability, the demand of three-dimensional or stereoscopic vision is becoming more and more urgent. The effective extraction of deep sensitive information is an important element that affects the current stereoscopic vision experience. Therefore, it has been paid attention by many researchers and obtained some research achievements. In this paper, through extensive research on the relevant detection templates and technologies of image saliency detection and depth sensitive information extraction research, the current status of depth sensitive information extraction research is classified and summarized, and several typical depth sensitive information extraction algorithms are analyzed through comparative experiments. Finally, the problems and development trends of depth-sensitive information extraction techniques are discussed.

Precise object detection and recognition plays an important role in information-based warfare. Due to panoramic vision sensors’ large field of view (LFOV), they are gradually applied to security and military areas. In this paper, first, the difficulties and challenges in the development of object detection and recognition in LFOV are presented from three aspects: camera imaging model, image imaging quality, and asymmetry of object. Then, based on whether the distortion correction preprocessing is carried out or not, the object detection and recognition algorithms in LFOV are classified into two categories: distortion correction based algorithms and original LFOV image based algorithms. These two kinds of algorithms are comprehensively combed and summarized. Finally, the paper analyzes the unity and difference of various algorithms for object detection and recognition in LFOV and discusses their future development trend.

Fluorescence microscope has always been the main method in biomedical researches due to its advantages such as less damage to samples, specific labeling, and being suitable for in vivo imaging. However, the defects of optical system itself, the optical inhomogeneity of biological samples, and the change in the refractive index at the interface between the sample and the microscope's immersion medium have caused aberrations and reduced the imaging contrast and imaging resolution. Adaptive optics (AO) technology uses active optical components such as deformable mirrors and spatial light modulators to correct distorted wavefronts (aberrations), eliminate dynamic wavefront errors, and restore diffraction-limited performance. In recent years, many researchers have combined AO system with fluorescence microscope to correct the aberration caused by sample inhomogeneity and improve the imaging quality. In this paper, the basic principle of the AO technology is introduced, the applications of AO technology in fluorescence microscopic imaging in recent years are reviewed, and its future development trend is prospected.

Holding advantages including high accuracy, non-contact measurement, and full-filed measurement, single-wavelength digital holographic systems are generally used for the measurement of micro-scale objects with continuous morphology. Developed from dual-wavelength interferometry techniques, multi-wavelength digital holographic systems can measure objects with complex shapes and larger scales, which extends the application range of digital holographic metrology. In recent years, there are two main research topics in multi-wavelength digital holography area. First, many types of measurement methods and/or optical setup according to realistic requirements are proposed; in addition, enhancement are achieved in image processing techniques such as noise reduction algorithm, numerical reconstruction and phase aberration compensation to improve the computational efficiency and result accuracy.

With the development of biomedical research, more advanced and comprehensive optical microscopy are required to enhance the imaging performances such as the spatial resolution, the imaging speed, the multi-dimensional information, the imaging quality, etc. Light-sheet fluorescence microscopy (LSFM), illuminating the specimen with a thin light sheet from the side and obtaining the optical sectioned image orthogonally, provides an ideal tool for long-term observation of live biological specimens due to its unique features of fast volumetric imaging speed and low photobleaching and phototoxicity to samples. In this paper, we first give an introduction to the principle and properties of LSFM. Then we address the key issues existing in LSFM and the solutions based on new principles, ideas and techniques. Some applications of LSFM in cell biology, developmental biology and neurosciences are exampled, and the development trends and prospect of LSFM are discussed. The purpose of the paper is to help researchers systematically understand the principle, the state-of-the-art techniques, and the potential applications of LSFM, and provide some references for research in this field.

Virtual reality (VR) and its derivatives, namely augmented reality (AR) and mixed reality (MR), can overlap the three-dimensional virtual scene with the real world and can significantly improve the intuition, accuracy, and real-time nature of the user's sensory world. The popularization and application of this technology is expected to revolutionize the medical field. Herein, the concept of VR/AR/MR is analyzed and its development process is briefly described. The applications of VR and AR in the medical field are elaborated, and the advantages of solutions based on MR are analyzed based on HoloLens. Finally, the deficiencies of VR/AR/MR applications in the medical field are summarized, and the future development trend is prospected.

Ultra-fast laser heating technology has been gradually applied in many fields, and the thermal conduction mechanism has received significant attention. The traditional Fourier heat-transfer law is insufficient for correctly describing the thermal conduction mechanism in the ultra-fast process. Therefore, based on the results of the previous researches on heat-transfer theory of ultra-fast laser heating technology, this paper summarizes an overview of the heat transfer of ultra-fast laser heating technology. Simultaneously, applications of the lattice Boltzmann, Monte Carlo, and molecular dynamics methods in ultra-fast laser heating heat-transfer theory research, which have attracted considerable attention in recent years, are briefly introduced. Finally, future prospects for heat transfer theory in ultra-fast laser heating technology are examined in this paper.

Ultra-short and ultra-high-energy pulsed laser is a powerful tool for investigating the interaction between laser and matter, and they have thereby been extensively investigated. A chirped-pulse amplification (CPA) system is the critical component for generating ultra-short and ultra-high-energy laser pulses. A pulse-compression grating (PCG) is an essential part of CPA, and it plays an important role in CPA performance. Metal/multilayer-dielectric gratings (MMDGs) have attracted considerable attention owing to their characteristics of high diffraction efficiency, broad bandwidth, and high laser-induced-damage threshold. To improve the understanding of metal/multilayer-dielectric pulse compression grating, we provide a comprehensive review of the status, design principles, and manufacturing processes of MMDGs. Finally, we discuss the prospects for future developments of MMDGs.

Fluorescence spectroscopy is an important testing method. Recently, the optical-fiber-probe-based fluorescence testing technology has become a popular research topic. This technology exhibits the advantages of high efficiency, micro, real-time, in-situ, small size, and easy integration. This review briefly describes the principle of fluorescence analysis, the spatial conduction theory of laser emission and fluorescence collection using optical-fiber probes, the typical structure and preparation of the optical-fiber fluorescent probes, and the status of research in the fields of biology, environment, and food safety. Finally, this review looks forward to the development trend of optical-fiber fluorescent probes.

Chronic liver injury induces liver fibrosis that must be diagnosed and treated within an appropriate timeframe. Otherwise, it can easily evolve into liver cirrhosis, or other more severe liver diseases. In recent years, fluorescence imaging and spectral analysis techniques have greatly promoted the detection and research of liver fibrosis diseases because they offer rapid, simple, and non-instrusive detection, and thus have great potential. This review highlights the latest achievements of fluorescence imaging and spectral analysis techniques in the investigation of tissue, cell, and molecular mechanisms of liver fibrosis. The research difficulties and potential application prospects of the technique regarding liver fibrosis are also discussed.

With the development of wireless communication, visible light communication (VLC) has become very promising technology owing to its many advantages. However, the nonlinear effect of VLC introduces many challenges for signal processing and deteriorates system performance. As machine learning has many advantages and significant potential for solving nonlinearity issues, the VLC that utilizes machine learning algorithms is bound to have tremendous research value. Existing research shows that traditional machine learning algorithms, such as K-means, DBSCAN, and support vector machine, perform well in pre-equalization, post-equalization, anti-system jitter, and phase correction. A deep neural network can further improve the performance of the VLC system because of its strong nonlinear fitting ability. In this article, we analyze the aforementioned methods and introduce their application to the signal processing in VLC. We hope this paper provides a reference for solving the nonlinearity problems related to machine learning in VLC.

The latest research results and applications of superpixel algorithms and evaluation indexes are summarized. Many superpixel methods are compared by using the evaluation indexes such as boundary recall, under-segmentation error rate, and compactness. The corresponding advantages and limitations are also analyzed. The experimental results show that the current superpixel methods are greatly superior to the previous methods in terms of accuracy and efficiency, and the applications of superpixel algorithms are growing constantly. However, it remains difficult to satisfy the requirements of the superpixel performances in some special applications. Therefore, it is necessary to develop the new methods that are more robust and have better adaptability.

In this paper, we discuss the optical properties of all-dielectric nanoparticles in detail, introduce the preparation methods of all-dielectric nanoparticles, and analyze the advantages and disadvantages of various preparation methods. Further, we review the applications of all-dielectric nanoparticles in the fields such as high-index nanometer resonators, nano-antennas, metamaterials and metasurfaces, and nonlinear nanophotonics. Finally, the research focus and development direction of all-dielectric nanoparticles are proposed.

Biospeckle is an optical non-destructive testing technology that uses laser refraction and reflection inside the object to reflect its internal information. Biospeckle imaging equipment and image processing algorithms are constantly improved, and the application fields are gradually expanding. Due to the existence of interference factors, the precision of modelling is still the focus of researchers at present. The speckle image processing algorithm is reviewed in detail, and the application of biospeckle technology in fruit quality detection is investigated. The main imaging equipments are summarized and suggestions for improvement are proposed to provide inspiration for future research.

The formation mechanism of a femtosecond-laser plasma channel is mainly discussed. The research progress on electromagnetic wave transmission in a femtosecond-laser plasma channel is reviewed. The plasma channels are classified into three types: single-channel transmission line, double-channel transmission line, and cylindrical hollow waveguide. Finally, the development trend of electromagnetic energy transmission via femtosecond laser plasma channels is prospected.

Taking different requirements for image motion detection as orientation, the development of image motion detection methods is traced, and the whole detection process of image motion is clarified as three stages: image motion calculation based on engineering parameters, image motion estimation based on joint optical correlators, and image motion detection based on remote sensing images. For each stage, the existing solved problems and the remaining technical bottlenecks are analyzed objectively. In combination with the development trend of space cameras, three pivotal scientific problems that need to be solved in the existing image motion detection methods are deeply analyzed. This study provides a possible research thought for wide-band image motion detection.

The basic principle of recording and reconstructing for the coded aperture correlation holography is clarified, and the existing systems and methods for recording the coded aperture correlation holography are introduced. The imaging resolution and reconstruction quality are mainly analyzed. The existing problems and the research directions for this technology are also discussed. Coded aperture correlation holography has been demonstrated its potential applications in the fields of dynamic three-dimensional imaging, multi-spectral imaging, adaptive optics, biomedicine, and military.

The interactive holographic display technology, due to its unique true three-dimensional (3D) display ability, can bring users a natural and real human-computer interactive mode. As an important part of the interactive holographic display system, the gesture recognition module has an important impact on the success, nature and comfort of the interaction process. There are mainly three gesture recognition ways in the interactive holographic display system, recognition based on wearable devices, recognition based on visual inspection, and 3D touch detection based on holographic 3D display. The research progress of the interactive holographic display system is firstly reviewed, then the development, merits and faults of these three interactive modes are discussed, and the current problems and development prospects of the interactive holographic display system are finally analyzed. This study can provid a reference for the further research on the interactive holographic display.

Photonic crystal is a kind of artificial structure crystal formed by a plurality of dielectric materials with different dielectric constants arranged in a certain spatial period, whose photonic band gap has high reflectivity to electromagnetic waves. The photonic crystals can alter the radiation characteristics of targets. The study of infrared stealth materials based on photonic crystals is one of the research hot spots of the current infrared stealth technologies. The structures and characteristics of photonic crystals are introduced in detail and the current application status of photonic crystals in infrared stealth is systematically reviewed. The outlook for the study of novel infrared photonic crystal materials is also discussed in order to provide some solutions for the needs of wide-band stealth, multi-band compatibility, and band gap adjustment of photonic crystal infrared stealth materials.

The basic principle of the photoelectric mixing technology is elaborated. The research progress of the photoelectric mixing technology is traced and summarized from two ways of the independent photoelectric devices and the combined photoelectric devices. Inspired by the microwave photon frequency conversion technology, a photoelectric mixing method is proposed based on the bulk electro-optic modulator. This method uses the electro-optic modulator to demodulate the frequency mixing on the optical field and uses the high-resolution and low-cost image sensors at the back end, which breaks through the limitation of the array size on the image resolution and achieves the advantages of high energy efficiency and high signal-to-noise ratio.

The infrared dim small target detection technology has become a research focus in the infrared field at home and abroad. The characteristics of infrared dim small targets are introduced. The principles, main steps and features of the existing infrared algorithms for the dim small target detection in single-frame images are reviewed from three aspects of filtering based on spatial domain and transform domain, human visual systems, and image data structures. The development trend of infrared dim small target detection technologies is analyzed.

The investigation of various soliton dynamics in a mode-locked fiber laser is briefly summarized, especially the recent progress of soliton transient dynamics in an ultrafast laser based on the dispersive Fourier transformation (DFT) technique is introduced. In addition, the multi-scale detection of ultrafast phenomena simultaneously using a time lens and the DFT technique is also briefly discussed, which helps to completely understand the physical nature of optical solitons. The development of real-time diagnostic methods can greatly inspire researchers to explore the soliton dynamics, and thus further promote the investigation of soliton dynamic characteristics as well as the development of ultrafast laser technologies.

Label-free microscopic imaging technology includes the optical coherence tomography, photoacoustic imaging, nonlinear imaging, and microsphere lens imaging technology. The commonly used label-free imaging techniques are introduced, and the traditional and advanced imaging principles are summarized. The advantages and disadvantages of such various of label-free imaging technologies and the latest research progress are introduced in detail, including the applications of such imaging technology in various fields. Finally, the future development of multi-modal imaging technology based on unmarked microscopy technology is prospected.

The D-type photonic crystal fiber (PCF) refractive index sensors, the multi-core porous PCF surface plasmon resonance (SPR) refractive index sensors with a large dynamic refractive index measurement range, and the dual-channel SPR-PCF refractive index sensors are introduced. Their advantages are summarized and their inherent limitations are analyzed. The SPR-PCF sensors are expected to make breakthroughs in the technical fields such as biomedical testing, food safety testing, mine exploration testing, and environmental chemical testing.

The technical characteristics and development history of magnetic-optical-electric hybrid storageis are reviewed, and its key technologies and research status are summarized, including storage system structure, some key technologies of software and hardware, as well as related standard formulation and patent applications. And the development trends of hybrid storage technology are described. The future for the development of magnetic-optical-electric hybrid storage is prospected. This review will help researchers to understand magnetic-optical-electric hybrid storage more systematically, clearly and accurately, and contribute to the development of big data storage in the future.

The crystal structure and optoelectrical properties of two-dimensional layered perovskite materials are introduced. The latest applications of two-dimensional layered perovskite materials in the fields of solar cells, light-emitting diodes and photodetectors are summarized. The main problems and future development prospects of these materials are given, aiming to guide the design and fabrication of high performance two-dimensional layered perovskite optoelectronic devices.

Photoacoustic imaging technique overcomes the strong scattering effects of light when transmitting in organisms by detecting the ultrasonic signals based on the photoacoustic effect, which avoids the limitations of low depth of traditional optical imaging and low contrast of acoustic imaging. This technique has potential applications in early cancer diagnosis and it can possibly become an effective method for tumor diagnosis, locating, staging and treating. The principle of photoacoustic imaging and the research status of its clinical applications in early cancer diagnosis and treatment at home and abroad are mainly described. The potential application of photoacoustic imaging technique in biological medicine is prospected, and its future development trend and limitations are also analyzed.

The process of petroleum extraction is often accompanied by the production of corrosive gases, metal particles and minerals, resulting in the serious corrosion and wear of petroleum machinery and equipment. Laser surface treatment technology can improve the material properties, such as wear resistance, corrosion resistance and fatigue resistance of parts and workpieces. The applications of laser surface treatment technologies in the petroleum machinery are summarized. The laser quenching, laser cladding and laser alloying are introduced in detail. The other laser surface treatment technologies and their applications are also summarized. The application status and exiting problems of laser surface treatment technologies in the petroleum machinery are analyzed and their development prospects are also put forward.

The important role and major achievements of a wireless laser and radio frequency (RF) complementary communication system are introduced, and the superiority and importance of the wireless laser and RF complementary communication technologies are explained. And the basic working principle of the wireless laser and RF complementary communication system is expounded, and the feasibility of the wireless laser and RF complementary communication system is illustrated. Combining with the latest research results of the complementary communication systems in foreign countries in recent years, the key problems encountered are mainly analyzed. The challenges faced by the complementary communication systems at present are presented. The key technologies to solve these challenges are put forward. The application prospect and development trend of the complementary communication are pointed out.

Compared with traditional Fabry-Perot (F-P) cavity semiconductor lasers, the edge-emitting semiconductor lasers with distributed Bragg reflector (DBR) gratings exhibit excellent characteristics in terms of narrow linewidth and stable output wavelength. They have huge application requirements in the fields of laser communication, optical interconnection and nonlinear frequency conversion. The DBR semiconductor laser can achieve laser narrow linewidth, dual wavelength output and wavelength tunability by properly designing the DBR grating and device structure. The DBR tapered semiconductor laser can simultaneously combine high power, narrow linewidth and high beam quality owing to the built-in DBR grating structure. In this paper, the structural design, fabrication process and performance advantages of these types of lasers are discussed, and the present situation of research and development at home and abroad are summarized. Based on this, the research work and development trend of DBR semiconductor lasers are further discussed and prospected.

As the transmission capacity and distance increase, Kerr nonlinearity becomes more and more obvious, which is currently becoming a major factor limiting the fiber transmission performances. The basic principles of some techniques for fiber Kerr nonlinearity compensation in fiber communications are introduced in detail, such as the digital backward propagation algorithm and the perturbation-based nonlinear compensation method. The development status of these technologies is reviewed. The advantages and disadvantages of each algorithm are also presented. Furthermore, the trend and potential applications of these technologies are prospected.

Currently, the external quantum efficiency (EQE) for deep ultraviolet light-emitting diodes (DUV LEDs) with emission wavelengths shorter than 360 nm is generally lower than 10%. On one hand, the transverse-magnetic (TM) polarized light dominates the light emission from the AlN-rich AlGaN based quantum wells, which strongly reduces the light-extraction efficiency (LEE) for DUV LEDs. On the other hand, limited by the current hetero-epitaxial growth technologies for AlGaN materials, the crystal quality for DUV LEDs is still poor, which increases the non-radiative recombination rate in the active region, thereby causing the reduction of the internal quantum efficiency (IQE) for DUV LEDs. Besides, the carrier injection efficiency, especially the hole injection efficiency, also strongly influences the IQE for DUV LEDs. Thus, the researchers have made extensive efforts to increase the hole injection efficiency and thus improve the EQE for DUV LEDs. The recently proposed approaches for the improvement of the hole injection efficiency for DUV LEDs are reviewed and discussed. Moreover, the underlying physical mechanisms are disclosed in the in-depth level. These are important for the improvement of the device performances for DUV LEDs.

The research progress and development status of spectral beam combining (SBC) using high-power fiber lasers is reviewed briefly, and a detailed introduction to the external factors that affect the beam quality is made. The influences of components in the SBC system and the linewidth broadening of the sub-light source array are mainly considered in the evaluation of beam quality. The summary of the existing theories and experimental results as well as the groundbreaking works for improving the beam quality of SBC in Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, is helpful to optimize the design of the built-in parameters of SBC and thus the further development of high-brightness SBC techniques is promoted.

The recent research achievements on high-power semiconductor lasers in various countries of the world are reviewed. The research progress is mainly introduced in terms of output power, brightness, electro-optical conversion efficiency, beam quality, lifetime, and reliability of GaAs-based near-infrared high-power semiconductor lasers. Combined with the current market analysis, the application prospect of these semiconductor lasers is elaborated. The development trend of high-power semiconductor lasers in the future is forecasted.

Scene understanding is an important research content in information science. Compared with the two-dimensional (2D) data, the three-dimensional (3D) data has many advantages. At present, there are many ways to acquire the point clouds, and meanwhile the point clouds with different acquisition methods have different characteristics. In addition, there lacks a complete and systematic research review on the key techniques for 3D scenes understanding. Thus, the different methods for point cloud acquisition are summarized, and the different point cloud data and related databases are compared and analyzed as well. Based on the current research progress of 3D scene understanding, the techniques for point cloud filtering, feature extraction, point cloud segmentation, and point cloud semantic segmentation in 3D scene understanding are compared and summarized. By the summary of the domestic and foreign literatures published in recent years, the problems occurred in the key technologies for 3D scene understanding are condensed, and the development trend of the 3D scene understanding problems is prospected. The 3D scene understanding based on point clouds is widely used in many fields due to its richness of data. However, as for the scene understanding effect of 3D point clouds, especially the scene understanding of laser point clouds with color information, there are still many contents needed to be investigated in depth.

The research progress on photodynamic therapy (PDT) in the treatment of gastrointestinal diseases is reviewed, including the related in vitro, in vivo studies and clinical practices. The therapeutic effects and application prospects of PDT for different types of gastrointestinal diseases are explored in order to provide the necessary technical supports for the more applications of PDT in the clinical treatments of gastrointestinal diseases.

Chalcogenide glasses (ChGs) have a very wide range of infrared transmittance, extremely high linear and nonlinear refractive index. In this article, research progress on ChG photonic devices based on stimulated Brillouin scattering is reviewed, as well as applications of ChG fibers and waveguides in Brillouin fibers lasers, slow light generation, and microwave photonic filters. Moreover, current problems are summarized, and their potential developments are discussed.

The discovery of multi-principal high-entropy alloys breaks the shackles of complex intermetallic compounds produced by the traditional multi-component alloys. Based on its unique high-entropy effect, a simple phase structure that exhibits excellent comprehensive performance can be generated. The high-entropy alloys exhibit many unique properties, including mechanical properties, high-temperature properties, and corrosion resistance. This study introduces the composition control of high-entropy alloys. Further, the research status of high-entropy alloy coatings, which are prepared using the laser cladding technology, with high hardness, thermal stability, high-temperature oxidation resistance, corrosion resistance, and wear resistance is reviewed. The development foreground of the laser cladding high-entropy alloy coatings is prospected.

Ultra-resolution optical microscopy, which breaks through the diffraction limit, is typically used to observe structural characteristics and interactions of subcells. This method has great significance for the study of genomes and tackling major diseases. This paper begins by introducing the working principles of four typical super-resolution microscopic imaging techniques. Subsequently, research progress in the areas of multi-color fluorescence imaging and three-dimensional imaging is emphasized. Finally, recent applications of super-resolution optical imaging for cell activity observation, bacterial cell research, and cytoskeleton observation are reviewed both domestically and abroad. The main factors reportedly affecting the imaging quality are poor light stability of the fluorescent protein, low light activation rate, and weak fluorescence intensity. Solution of the above problems will lead to the widespread use of super-resolution optical imaging for the three-dimensional imaging of thick samples, multi-color fluorescence imaging, and fast imaging of living cells, ultimately furthering the development of life science and materials science.

The application of holographic technology has enabled three-dimensional (3D) displays to develop rapidly, providing users an unparalleled visual experience. The calculation and generation processes of holographic images and video generate a considerable amount of data, causing great difficulties for transmission and storage. To meet the high-definition and real-time requirements of 3D displays, the compression of holographic data is critical. Since holographic images have distinct characteristics than ordinary images, it is difficult to achieve optimal results using existing compression techniques. This study introduces the main technical challenges of holographic compression and summarizes the commonly used metrics for holographic data compression. The cutting-edge technologies proposed by national research groups related to holographic-image-coding-quantization processing, transform-coefficient simplification, optimization of the international standard hologram format, and development of a new standard framework are discussed in detail, and their respective advantages and disadvantages are detailed. Finally, a future direction for research on holographic-compression technology is proposed.

The design of novel light beams and investigation of their propagation properties are important topics in optics, particularly for beams that are nondiffracting, self-accelerating, or self-repairing. The evolution of these beams in either free-space or a waveguide and their applications have attracted a significant amount of research. Although wave optics has been developed as a rigorous and self-consistent framework, it does not offer intuitive processes for solving optical wave propagation. However, geometrical optics, also known as ray optics, can provide an intuitive and understandable method for analyzing light beam propagation and constructing targeted beam shapes in addition to designing optical systems. With the development of modern geometrical optics, rays have extended their physical meaning and are widely used to characterize optical wave propagation. Furthermore, ray characterization can explain nondiffracting, self-accelerating, and self-repairing properties. In this work, beginning with the fundamental theory of geometrical optics, we review the development, applications, and recent advances of significance of ray in modern ray optics. Meanwhile, some typical beams, such as fundamental-mode Gaussian, non-diffraction, and Airy beams, as well as beams with spiral wavefronts and structured Gaussian beams, have been characterized and designed using rays. Lastly, some challenging problems and future research directions of geometrical optics are discussed.

The focusing methods of solar concentrators are mainly classified into three categories. This study introduces the structural designs and operating principles of various solar concentrators, analyses their focusing performance, and summaries the latest research status at home and abroad. First, we consider a refractive concentrator, which involves the usage of Fresnel lens with varying shapes as the main optical element and exhibits a high design freedom, but the lens is sensitive to the spectrum and easy to produce dispersion. Second, we consider a reflective concentrator, which exhibits a simple structure, has natural advantages with respect to the solar spectrum, and covers a larger area, but its concentration ratio is generally low and its concentration efficiency is related to the refractive index of the coating on the reflector and other factors. Finally, we consider a hybrid concentrator, which can be obtained by combining concentrators under different operating principles to achieve maximum utilization of the solar energy and generate a uniform spot at the exit. With respect to the hybrid concentrator, the planar concentrator has attracted increasing attention because of its dynamic concentration ratio and high concentration efficiency; however, the manufacturing and coupling errors associated with the planar concentrator still need to be considered. Regardless, the solar concentrator is one of the key components of a concentrating photovoltaic system, and its research demonstrates considerable futuristic applications. From the development perspective, the optical concentrator designs exhibit considerable potentials because of their high efficiency, uniformity with respect to the focusing spot on the receiving surface, and advanced compact system structure. With the continuous development of the processing technology, the concentrator will become increasingly efficient and lightweight, thereby reducing its cost.

Colloidal crystals are materials that exhibit an ordered structure formed by dispersed micron or submicron colloidal particles. The self-assembly technology is a commonly used method to manufacture colloidal crystals. The basic concepts of colloidal crystals and the related self-assembly processes are outlined in this review. Furthermore, the applications of self-assembled colloidal crystals in case of micro-nano optics are presented in detail. Subsequently, other applications of self-assembled colloidal crystals, such as color printing, holograms, anti-reflective coatings, and optical devices, are presented and the roles of colloidal crystals in those applications are summarized. The unique periodic structure of colloidal crystals ensures its broad application prospects. Therefore, improving the quality of colloidal crystals using various self-assembly techniques is of considerable importance.

A single photon avalanche photodiode detector (SPAD) has many advantages such as large avalanche gain, fast response, high detection efficiency, and easy integration. SPAD array devices can be used for low-light three-dimensional imaging; these devices have important applications in fields such as biochemistry, quantum communication, and lidar. Therefore, it is significant to study the detection technology of SPAD and its array. In this paper, we review and present the working principle and array structure performance of a near-infrared InGaAs/InP SPAD unit. We analyze the major influencing factors such as the dark counting rate, detection efficiency, and after pulses; moreover, we investigate the main direction for device optimization. Further, the main technical schemes of the SPAD array devices used in recent years have been summarized. We provide the sources of crosstalk and methods for eliminating crosstalk. In addition, we compare the technologies used and the results of relevant research institutions.

Coherent wind lidar uses the heterodyne detection method to amplify the backscatter signal by the local oscillation laser. Because the signal-to-noise ratio can reach the theoretical quantum limit, the lidar has high spatial and temporal resolution and high precision. Coherent wind lidar is widely used to measure wind shear, atmospheric turbulence, aircraft wake, gustiness, and gravity waves. Researchers in China and other countries are presently studying on coherent wind lidar. This study introduces the history of coherent wind lidar, describes the theory using different wavelengths, and briefly summarizes the development trends in this field.

Magnesium alloys are the lightest structural material; thus, their demand in the automotive, aerospace, electronics, and medical fields has increased remarkably. The development of laser additive manufacturing technique allows for the production of high-performance magnesium alloy parts with complex structures. In this paper, we review the local and international manufacturing of magnesium alloys via laser additive manufacturing. The effects of laser process parameters and powder material on surface morphology, spheroidization, defect, porosity, loss of alloying elements, microstructure characteristics, mechanical properties, and numerical modeling are introduced. The limitations and gaps in the researches on magnesium alloys are summarized herein. In addition, an overview of future research prospects and the applications of magnesium alloys are discussed.

Space division multiplexing (SDM),high order modulation, digital coherent detection,and digital signal process have become the necessary technologies for realizing a optical fiber transmission system with ultra-large capacity, ultra-high rate, and ultra-long distance. SDM technology has become the key part to realize Pbit/s transmission, and has become a research hotspot in resent years. A multicore fiber amplifier with SDM is analyzed systematically. In this paper, the research progress of multicore amplifiers, including multicore erbium-doped fiber amplifiers, multicore few-mode erbium-doped fiber amplifiers, multicore erbium-ytterbium co-doped fiber amplifiers, multicore Raman amplifiers, multicore remote pump amplifier,and hybrid multicore amplifiers, are reviewed. Finally, the future of multicore amplifier technologies is prospected.

Green lasers having a compact structure, high efficiency, and stable performance are widely used in optical storage, laser printing, stage performance, medical treatment, and underwater communication, particularly in laser displays. All-solid-state lasers based on frequency doubling technology are currently the most effective means of generating green lasers because of the lack of efficient semiconductor lasers having the corresponding output spectrum. With the developed technology of a periodically poled crystal, green lasers based on quasi-phase-matched intracavity frequency doubling in PPMgLN have been rapidly developed in recent years. Hence, this study reviews the multiple structures, performance advantages, and development status of green lasers based on PPMgLN.

Compared with the conventional laser processing, femtosecond laser processing exhibits a smaller melting zone and a negligible heat-affected zone. In addition, the shock waves and cracks caused by femtosecond laser processing are almost invisible under normal conditions. Therefore, the usage of femtosecond laser has already been extensively adopted in precision manufacturing, organism processing, special material processing, and other fields and exhibits promising prospects for future development. Herein, the processing of ultrahard material using the femtosecond laser technology is reviewed with respect to its mechanisms, methods, and applications at home and aboard in recent years. Machining and processing methods for ultrahard material tools are also introduced and evaluated using the recently developed femtosecond laser techniques. Finally, the potential problems and future prospects associated with the femtosecond laser technology applications in ultrahard material machining are discussed.

The development of semiconductor lithography technology requires light sources with short wavelengths. Excimer laser-based lithography light sources (i.e., KrF-248 nm and ArF-193 nm) are gradually replacing the previously used light sources based on a Hg lamp, which are the commonly used light sources in current semiconductor lithography technology. The optical components that are currently employed in lithographic light sources primarily use calcium fluoride (CaF2) materials, which have excellent transmission characteristics in the deep ultraviolet region. In this study, the damage characteristics of the laser-material interaction in the development of the light source are analyzed. The development of the research on ultraviolet resistance of CaF2 materials is comprehensively analyzed by investigating the physicochemical properties of CaF2 materials, characteristics of laser radiation, and damage mechanism of the laser-material interaction. The laser damage characteristics of CaF2 materials for different applications are compared. The approaches and methods to improve the damage thresholds of optical components are summarized.

Obtaining depth estimation of a scene from a two-dimensional image is a classic computer vision problem that plays an important role in three-dimensional reconstruction and scene perception. Monocular image depth estimation based on deep learning has been developing rapidly in recent years with new methods being proposed rapidly. This study discusses the application history and research progress in deep learning-based monocular depth estimation and analyzes several representative deep learning algorithms and network architectures in detail for both supervised and unsupervised learning. Finally, the research progress and trend of the deep learning in the monocular depth estimation field are summarized. Existing problems and future research priorities are discussed as well.

Terahertz (THz) waves have great application potential because of their unique atmosphere sensitivity features and spatial transmission properties. This study summarizes the research achievements of major research institutions at home and abroad in THz space exploration. Further, we describe the parameters, working environment, and detection results of large ground-, aircraft-, and space-based THz space exploration platforms and compare the experimental results of these platforms. In addition, the features of THz remote sensing equipment are also analyzed. Finally, we present the application prospect and future development trends of THz space exploration. The THz space exploration technique can obtain unique information that cannot be acquired using optical methods or microwave technology, which makes it a prospective research area in the future. The development of THz space exploration technology will lay an important foundation for high-resolution space remote sensing.

Doppler wind lidar can ensure non-contact measurement of the atmospheric wind field based on optical Doppler effect. Doppler wind lidar is scalable with high resolution in time and space and exhibits large coverage and wide detection range. Further, it is suitable for mobile, foundation, vehicle, shipboard, airborne, and spaceborne platforms and is extensively used in flight safety, wind power generation, weather forecasting, scientific research, military defense, and so on. Herein, the main systems, technologies, latest developments, and applications of Doppler wind lidar at home and abroad are introduced and analyzed. Further, two techniques for direct and coherent detection are compared and summarized based on our analysis. In addition, the development trends, research hotspots, and application development of Doppler wind lidar are briefly summarized.

Semantic segmentation, which classifies all pixels in an image and divides the image into several regions with specific semantic categories, is a key technology in the field of computer vision. In recent years, convolutional neural networks (CNNs) have been making breakthroughs and have demonstrated great potential in using deep learning to perform semantic segmentation. Herein, beginning with the definition of semantic segmentation, existing challenges in the field of semantic segmentation are discussed. Based on CNN principles, several datasets used for semantic segmentation algorithm evaluation are compared in detail, and recent deep learning methods based on decoders, information fusion, and recurrent neural networks in semantic segmentation are summarized. Finally, future development trends (e.g. enriching database scenes, improving real-time performance of algorithms, and researching the semantic segmentation) of three-dimensional point cloud data in semantic segmentation are summarized.

Holographic stereogram technology is a three-dimensional display technology that can be used with the naked eye. Several holographic stereogram products have been successfully commercialized and have realized amazing visual experiences. However, in practical applications, several problems remain, such as an inadequate field of view (FOV) in the reconstructed image applications, excessive number of sampled images required to print a high-quality holographic stereogram, and lack of simulation results used for comparison with experimental results. In recent years, several research groups have conducted in-depth research on these issues. This study introduces the two most widely used holographic stereogram techniques, and then summarizes recent progresses in enlarging the FOV of a holographic stereogram, reducing the number of required samples,and numerical reconstruction of holographic stereograms.

Black phosphorus is a new type of two-dimensional semiconductor material that has attracted extensive attention because of its tunable direct band gap and high carrier mobility. Compared with bulk black phosphorus, low-dimensional black phosphorus has a greater potential application value because of its structural and performance advantages. In recent years, many research groups have successfully prepared low-dimensional black phosphorus with different morphologies and applied them to the active layer, electron transport layer, and hole transport layer of solar cells, such that the conversion efficiency is improved to different degrees. This study introduces a preparation method of low-dimensional black phosphorus, focuses on its research progress in the field of solar cells, puts forward the problems that must be solved, and forecasts the future development trend of low-dimensional black phosphorus.

Laser beams with evenly distributed or specifically modulated intensity profiles are required in many practical applications, thereby necessitating theoretical and experimental studies in laser beam shaping techniques. A variety of laser beam shaping methods, wherein the beam integration plays an important role as a result of its simple principle and wide applicability, have been proposed thus far. Therefore, it has great value in engineering. This study introduces the usage of optical components, such as prisms, mirrors, and micro-lens arrays, in beam integration systems. In this paper, the typical optical paths and recent progress are presented along with a discussion of the characteristics of these shaping methods.

The environmental perception of unmanned vehicles is a vital technology for automatic driving. The usage of three-dimensional (3D) LiDAR for obstacle detection becomes a popular research topic. In this paper, we first introduce the classification of obstacle detection methods for an unmanned vehicle according to different sensors. The basic principle of obstacle detection based on 3D LiDAR is then introduced in detail along with an analysis of the traditional method of obstacle detection using 3D LiDAR. Deep learning is an important method for two-dimensional object detection and classification. We analyze the characteristics of the 3D LiDAR point clouds and the challenges of deep learning for point clouds. Finally, we analyze the research status and development trend of deep learning in the point cloud obstacle detection application and introduce relevant datasets in the field of automatic driving, such as KITTI and ApolloScape.

Light-emitting diodes (LEDs) are incoherent light sources with limited bandwidths, and the discovery of biological effects of LED light sources promotes its application in biomedicine. Based on the phenomenon that tissue penetration depths of lights with different wavelengths are different, this work introduces the target tissue specificity and biological effects of LED light sources at each band. This article also reviews the current application of these LED light sources in a clinical setting for the treatment of dominant diseases. Finally, the application of LED light sources in the biomedical field is prospected herein to help guide their clinical application together with instrument research and development.

When compared with the traditional edge-emitting semiconductor lasers, the vertical-cavity surface-emitting lasers (VCSELs) offer several advantageous properties, including a narrow line width, superior beam quality, high reliability, and low manufacturing cost. Recently, with an increase in the output power and power conversion efficiency of the 808 nm VCSEL arrays, they have become an attractive alternative for the pumping sources of solid-state lasers. In this study, we introduce the performance advantages, applications, and status of the VCSELs. As for the VCSEL-array-pumped solid-state lasers, the research progress is reviewed, and the development prospect as well as their technical shortcomings are discussed.

Graphene is an excellent base material for a nanoelectromechanical system (NEMS) because of its extraordinary characteristics, including a large specific surface area, high Young's modulus, enormous stiffness, and low density. The graphene NEMS mainly studies the electromechanical properties of graphene films. Its resonant frequency has a very sensitive response to mass, force, and heat, which has a great application prospect in the sensing field. Meanwhile, the optical fiber sensor has been widely studied and applied, whose combination with graphene can possess a greater advantage. In this paper, the working principle, preparation process, sensing application of the graphene NEMS as well as the fiber-based graphene NEMS sensors are reviewed and prospected.

In recent years, Raman spectroscopy is being used more frequently in biomedical analyses, especially for in-situ nondestructive detection of target samples or tissues. Raman probe, as the essential detection component in Raman spectroscopy, is also being developed for better diversity and functionality. Since Raman signal is extremely weak and noise interference is common, the new design and production of Raman probe are also extremely critical. This review provides an in-depth introduction to the existing general design and construction of Raman probe for biomedical applications, including the selection of fiber and filter/membranes, the design of probe tip, and the optimization of probe backend. Subsequently, the expansion and application of the Raman probe technology in the biomedical field are reviewed. The probes based on a combination of Raman and other spectra or imaging modes bring new vitality and prospects for broad applications in the biomedical and clinical detection of target samples or tissues.