Single photon detection modules have important applications in many fields. However, the existing single photon detection modules rely on imported chips. In this paper, a 1550 nm single photon detection module based on domestic components is developed. The trigger signal processing circuit is improved to avoid the use of imported chips. Under the action of trigger signal, the avalanche photodiode enters Geiger mode. When the avalanche photodiode in Geiger mode receives a photon, the avalanche signal is generated. In the output signal of the avalanche photodiode, the intensity of the avalanche signal is less than that of the noise signal. After eliminating noise and amplifying the output signal of the avalanche photodiode, the avalanche signal is identified by the comparator. In order to suppress the dark current and dark count of the avalanche diode, MCU and temperature control circuits are used to ensure that avalanche photodiode works in stable low temperature environment. The experimental results show that when the detection efficiency is 12%, the dark-count and after-pulse probability are 7.7×10-6 gate-1 and 2%, respectively. The parameters all meet the expected targets. The scheme has simple structure and realizes localization.

Optical fiber based distributed acoustic sensor (DAS) is one of the most attractive and well developed fiber sensing technologies in the recent decade. It can simultaneously detect and recover the waveforms of multiple mechanical vibrations along the sensing fiber with high sampling rate, providing abundant information of the environment, which has great potential applications in perimeter fence security, oil and gas exploration, seismic waveform detection, and other fields. This paper first reviews the principles involved in DAS system, including three types of reflectometry to locate the Rayleigh backscattering (RBS) along the long distance fiber, and the two methods to recover the vibration waveform using RBS signal. Then two typical applications of DAS system are reviewed, and finally the possible research trends of DAS technology are discussed.

Fiber-optic Fabry-Perot microcavity sensors have many advantages, such as antielectromagnetic interference, resistance to harsh environments, small size, and high accuracy. The measurement of physical parameters in high-temperature environments based on fiber-optic Fabry-Perot sensing technology has attracted wide attention from researchers. Based on the principle of fiber-optic Fabry-Perot interference, the principles of Fabry-Perot multibeam interference and beam coupling model, as well as two demodulation techniques for demodulation of interference spectrum signals were presented. In addition, the use of fiber-optic Fabry-Perot sensing technology in high-temperature environments was discussed. The research progress of physical parameter measurement based on the development trend of fiber-optic Fabry-Perot sensing in high-temperature environments toward miniaturization, batch preparation, and multipurpose due to the birth of new process manufacturing technology were analyzed as well.

Fiber optic distributed vibration/acoustic sensing (DVS/DAS) technology based on the principle of phase-sensitive optical time-domain reflectometry (Φ-OTDR) plays an important role in the national infrastructure and urban safety monitoring. However, due to the influence of strong noise background, multi-source interference and unknown buried conditions in urban areas, the accuracy of DVS/DAS detection and recognition of target has become the biggest technical bottleneck restricting its scale application. Therefore, on the basis of DVS/DAS hardware technology research at the Fiber Optics Research Center of University of Electronic Science and Technology of China, this paper analyzes the difficult problems of the current optical fiber DVS/DAS signal processing, reviews the research progress and important application cases of DVS/DAS signal-to-noise separation, multi-dimensional signal detection and recognition algorithms based on machine learning models in recent years, and the development direction and trend of DVS/DAS signal processing are prospected.

Fiber-optic biosensors have the capability of detecting chemical or biological substance relying on the interaction of the evanescent wave to the surrounding, which probe the light signal change as a result of the specific binding of the biological recognition molecule and the target molecule. With the advantages such as small size and flexibility, fiber-optic sensors are promising to serve as an advanced methodology for in-situ bio/chemical detection. In particular, the microfiber interferometric biosensor with the microfiber modal interferometer as the energy converter can achieve ultra-high sensitivity for biomolecule detection even down to the level of single-molecule, through signal amplification by optimizing the optical waveguide structure and the interface. This review introduces the microfiber modal interferometer in terms of the principle, preparation, sensitivity characteristics, biosensor implementation and interface sensitivity enhancement.

With the development of optical fiber technology, optical fiber devices have more complex structure, more diverse functions, and more compact size. This poses a great challenge to the microfabrication of optical fiber devices. Femtosecond laser induced two-photon polymerization has the advantages of ultrahigh processing accuracy which breaks through the optical diffraction limit and true three-dimensional processing ability of direct writing without mask. It has unique advantages in the processing of micro/nano-structure, and provides a new idea and possibility for the integration of micro/nano-structure and optical fiber. In this paper, the latest research progress and application prospect of femtosecond laser induced two-photon polymerization for fiber integrated micro/nano-structured devices are introduced.

Distributed optical fiber acoustic sensing (DAS) technology provides unique advantages such as dynamic online monitoring, long-haul dense measurement, convenient installation, and maintenance-free operation. Hence, it has attracted extensive research attention in various fields, including perimeter security, structural health monitoring, transportation, oil and gas exploration, and submarine acoustics. Combined with standard communication optical cables or dedicated optical cables, DAS can conveniently form large-scale detection arrays, meet the requirements of seismic wave monitoring for geophysics and natural disaster detection, and achieve applicability in diverse fields. This paper is focused on the emerging seismic wave monitoring application of DAS. In particular, the basic sensing principles, technology development, and application progress of DAS-based seismic wave monitoring are discussed. In addition, the key technical problems and future development trends of DAS for seismic wave detection are analyzed.

The continuous grating array sensing technology has the characteristics of large capacity, long distance, high density, and so on, if compared with the traditional distributed optical fiber sensing technology. This article reviews the on-line fabrication technology, demodulation methods and typical applications of continuous grating arrays at home and abroad. The development trend of the continuous grating array sensing technology is also outlined.

The phase-sensitive optical time domain reflectometry (Φ-OTDR) utilizes distributed Rayleigh scattering sensing to achieve sensing, and it has the advantages of high sensitivity and fast response speed to environmental disturbances. It has become one of the most important branches in the field of distributed optical fiber sensing. However, the high-coherence lightwave of Φ-OTDR will inevitably induce interference fading during the scattering process, and the corresponding positions will become blind zones for the sensing system. Fading phenomenon has been a research focus in this field for many years. In this paper, we first briefly describe the generation mechanism and mathematical characteristics of interference fading. Then, typical sensing mechanisms of Φ-OTDR are systematically introduced, as well as the influence of interference fading on the sensing signal demodulation. In addition, the research progress of anti-interference fading technologies is comprehensively reviewed. Finally, the future developments of Φ-OTDR are discussed.

Fiber optic hydrophone (FOH) is a new type of underwater acoustic sensor, which can be used in both military and civilian fields such as underwater target detection, oil and natural gas prospecting, and earthquake inspection. With the increase of ocean ambient noise and the development of noise suppression techniques for the underwater targets, people's demand for high-performance FOH is becoming more and more urgent. Therefore, this article introduces FOH technology from three aspects, including main development trends, key technologies and new-type FOH. In detail, large-scale FOH array, very low frequency detection, deep-sea and long-haul transmission, towed linear array, narrow-linewidth laser, signal processing, fiber optic vector hydrophone and distributed FOH are introduced. This research has certain guiding significance for the theoretical research and practical application of FOH system.

Distributed Brillouin fiber sensors can measure the temperature and strain information along optical fibers over distances of hundreds of kilometers. They are used to monitor major national projects such as bridges, tunnels, power lines, and oil and gas pipelines. The main method of Brillouin sensing is to measure the Brillouin frequency shift, which is linearly related to the temperature and strain of an optical fiber. The Brillouin frequency shift is usually obtained by measuring the Brillouin spectrum of the optical fiber. The spectral line of Brillouin spectrum theoretically satisfies a Lorentz line shape, and the frequency corresponding to its peak is Brillouin frequency shift. To reduce the influence of sampling accuracy and noise, the most common method used to extract the Brillouin frequency shift from the Brillouin spectrum is Lorentz curve fitting. However, curve fitting is sensitive to initial values and the fitting error significantly increases when the signal-to-noise ratio is low. In addition, the processing time of curve fitting is too long, which reduces the response speed of the system. To improve the accuracy and speed of Brillouin frequency shift extraction, machine learning has recently been applied in this field, which has provided better results than traditional curve-fitting algorithms. This article mainly presents the achievements of machine learning in Brillouin frequency shift extraction in recent years, including singular value decomposition, support vector machines, and artificial neural network technology.

Distributed optical fiber sensing technology has been widely applied in the areas of infrastructure health monitoring, national defense security and etc. Long-reach high-spatial-resolution chaotic Brillouin optical correlation-domain analysis (chaotic BOCDA) technology has extensive development and application prospects. Chaotic laser of noise-like, wide-band radio frequency spectrum and broadband optical spectrum is served as signal source in chaotic BOCDA. Therefore, the sensing distance is extended by its δ-like function, the spatial resolution is improved by its auto-correlation property, and the intrinsically broadened Brillouin gain spectrum is obtained by its Gaussian optical spectrum. Based on these characteristics, this review article provides an overview of our recent progresses in chaotic BOCDA system with 10.2 km-long sensing distance, 3.5 mm-high spatial resolution and 1200 με-large dynamic range. Moreover, the relative merits and avenues for future research and development of chaotic BOCDA technology are also discussed and prospected.

Multi-core fiber with the unique advantages in space division multiplexing has attracted more attention in many fields. As a new technology of optical fiber sensing, multicore fiber shape sensing technology can be used to detect the three-dimensional shape and the position without other visual aids. Meanwhile, this technology shows the characteristics of compact structure and easy integration without electromagnetic interference, which can be applied in aerospace, industrial machinery and building structure monitoring, interventional therapy tracking and other fields. This article reviewed the latest progress of multicore fiber shape sensing in recent years, and the key technique of shape sensing technology, are covered in detail. Finally, challenges and future perspectives of multi-core fiber shape sensing in practical applications are discussed.

The excessively tilted fiber grating (Ex-TFG) is a novel fiber grating device with unique structure, which has the characteristics of orthogonal polarization coupling, high refractive index sensitivity, low temperature sensitivity and vector sensing response. Recent years, benefitting from the fact that Ex-TFG is sensitive to the surrounding environment refractive index, Ex-TFG has been widely investigated and applied in the field of biochemical sensing. Meanwhile, the non-circular symmetric evanescent field distribution of Ex-TFG provides the possibility for vector sensing applications. Based on the theoretical and experimental research, the basic theory and research progress of sensing characteristics of Ex-TFG are exhibited in detail in terms of basic coupled-mode theory of gratings and properties of transmitted cladding modes.

Fiber optic sensors are expected to become an auxiliary measurement method in the field of ocean observation due to their small size, easy networking, and intrinsic resistance to electromagnetic interference. Recently, the research of optical fiber sensing technology in the field of physical ocean observation has received broad attention from scientific researchers. According to the different classifications of measurement objects and principles, this article focuses on the seawater temperature, salinity, and pressure sensors based on fiber grating, the seawater salinity sensor based on multi-core fiber, and the interferometer based on Michelson and Mach-Zehnder. Seawater salinity and pressure sensors based on Fabry-Perot cavity, new optical fiber ocean temperature and salt depth sensor based on resonance and coupling technology, and fiber optic turbulence sensor based on two principles of heat and turbulent energy dissipation. This article analyzes the measurement methods and experimental results of various sensors and highlights the technical advantages and disadvantages. Finally, the development of optical fiber sensors in the field of physical ocean observation has prospects.

Microfiber is a kind of novel fiber with diameter in the micrometer level, which aroused people's widespread attention in recent years. In this paper, first, sensing principle, guiding properties, and the calculation method of propagation constant of the microfiber are introduced, and the general expression used for estimating the sensitivity of interferometric microfiber sensor is summarized. Then, the common preparation methods of microfiber and typical interferometric microfiber sensors used in temperature, salinity and pressure sensing are introduced, such as microfiber ring resonator, microfiber directional coupler and microfiber coaxial Mach-Zehnder interferometer (MZI). Secondly, it focuses on the packaging method, environmental adaptability and response time of the microfiber coaxial MZI. Finally, the existing problems and the trend of future development of these sensors is summarized and prospected.

The working conditions of coal mines in our country are complex, and there are potential safety hazards such as gas explosion, fire, equipment failure, and subsequent safety hazards. Optical fiber/laser sensors, with their features of passive, intrinsically safe characteristics, high precision, low drift and other performance, have incomparable advantages in the field of coal mine safety that traditional electronic sensors cannot match. This paper introduces the research progress and application of the laser methane sensors, carbon monoxide sensors, optical fiber Bragg grating wind speed sensor, and fiber distributed temperature sensor in the construction of intelligent mines, for coal mine gas monitoring, intelligent fire provention, safety monitoring, and early warning.

Fiber optical laser interferometry is the main technical scheme for dynamic signal demodulation of external Fabry-Perot interferometer (EFPI) sensors. It has the advantages of high measurement sensitivity, wide dynamic range, and wide measurement frequency range. Based on the measuring principle of an extrinsic Fabry-Perot interferometric sensor, this article presents the demodulation principles, advantages, and disadvantages of presently used phase recovering technologies,and focuses on several new passive demodulation technologies proposed by the author's research group, it mainly solves the problems of existing demodulators which can only measure the sensor with a single cavity length, direct current component removal, and signal demodulation when cavity length changes or even unknown.

Ultrasonic waves can penetrate into opaque media, such as metals and ceramic, which has become an important testing tool for ultrasonic safety monitoring. Compared with traditional piezoelectric-based ultrasonic sensors, optical fiber ultrasonic sensors exhibit strong anti-interference, strong multiplexing, high sensitivity, and broadband frequency response, which has applications in structural nondestructive detection and electric power system. Aiming at the characteristics and detection methods of acoustic emission signals in safety monitoring, we mainly review optical fiber ultrasonic sensing technologies and applications in ultrasonic safety monitoring. Furthermore, the sensing mechanisms, detection methods, and existing issues are analyzed. The next step will focus on the discussion of the future research direction and potential applications.

In response to the practical measurement requirements of marine hydrological environmental parameters, this article focuses on the sensing mechanism, research progress, performance indicators, and existing technical bottlenecks of various types of fiber optic ocean conductivity-temperature-depth (CTD) sensors, and also briefly introduces the research progress and engineering application of marine environmental parameter sensor arrays. Judging by the research progress at home and abroad, the fiber Bragg grating CTD sensor has strong stability and environmental adaptability. First, it has initially satisfied the demand of marine environmental engineering monitoring and has had important application value in the research of marine environmental parameter sensing arrays; while fiber-optic surface plasmon resonance (SPR) based CTD and tapered fiber-based CTD have high sensitivity so they have good potential for application in multi-parameter integrated monitoring of the marine environment. Finally, based on the brief description of the development needs of a new generation of marine monitoring networks represented by the “Marine Internet of Things”,it proposed the developing trend and technical requirements of all-optical sensors for marine environmental parameters, which will provide scholars engaged in related research with reference materials and ideas.

In recent years, polymer optical fibers have received increasing attention in the fields of sensing and communication because of their small size, light weight, softness, low cost, and excellent characteristics such as biocompatibility compared with silica optical fibers. We analyze various materials for polymer fibers, including polymethyl methacrylate (PMMA), ring olefin copolymer, ring olefin polymer, and polycarbonate; different grating fabrication techniques, including those using lasers with different wavelengths (e.g., 248, 266, and 325 nm); and different engraving techniques, including phase mask, femtosecond laser direct writing, and femtosecond laser two-photon polymerization. In addition, we review the research progress in polymer optical fiber grating in the fields of sensing and communication in recent years and summarize the major developments.

Distributed optical fiber sensing based on Brillouin optical time-domain analysis (BOTDA) allows the simultaneous measurement of parameters such as temperature and strain. In addition, it provides an ultralong sensing distance, high spatial resolution, and high precision, and is widely used in structural health monitoring in areas such as infrastructure and aerospace engineering. However, the BOTDA sensing system exhibits cross-sensitivity between temperature and strain, hindering the discrimination of the influencing factors during measurement and severely restricting the sensing and monitoring capabilities. To address these problems, this article introduces, analyzes, and compares seven methods based on reference fiber, grating assistance, multiparameter assistance, special fiber, dual-wavelength sensing, Raman/Rayleigh scattering assistance, and neural networks to provide a reference for research and application of cross-sensitivity in optical fiber sensing.

Brillouin optical time domain analysis (BOTDA) has shown its unique advantages in distributed optical fiber sensing systems and has received widespread attention. The rapid and accurate extraction of temperature distribution information in BOTDA sensing system is extremely desirable. With the rapid development of machine learning, it shows great potential in temperature extraction of BOTDA sensing system. First, the principle of BOTDA sensing system is introduced. Then, some machine learning algorithms are illustrated and their applications and advantages for temperature extraction of BOTDA sensing system are analyzed. Finally, outlook for future research is given.

Aiming at the problem that the decoding algorithm of encoding target is complicated and the decoding accuracy is easily affected by the shooting angle in the field of photogrammetry, a encoding target and its decoding method based on the principle of projective invariance are designed. The template of the coded target includes a reference circle and several coded circles, 4 coded circles and reference circles are selected from the template to form the target, and the coding function is realized by selecting different coded circle combinations. In the decoding process, the geometric position and area relationship between the reference circle and the code circle are used to realize the rapid and automatic positioning of the reference circle and the code circle. By calculating the projective invariant of the intersection ratio of the center of five circles in the target, the fast automatic decoding of the target is realized. The experimental results show that the decoding accuracy of the designed target is higher than that of the traditional coding target when the shooting angle is large, because the projective invariant is used as the encoding information, and the decoding accuracy of the designed target can reach 100% when the shooting angle is 60°.

To study the effects of process parameters on the microstructure and mechanical properties of AlSi10Mg samples during selective laser melting (SLM), different laser powers are adopted to form AlSi10Mg samples. Scanning electron microscopy, X-ray diffraction, tensile testing, nano-indentation testing were used to characterize the melting tracks, forming defects, phase composition, microstructure, mechanical properties, and fracture morphologies of AlSi10Mg samples. Results show that the relative density reaches a maximum value of 99.3% at 350 W, as well as the minimum void defects, the optimum overlap of melting tracks, and the finest gains in the fine grained region. The above sample obtained at 350 W has best mechanical properties, namely, the micro-hardness is 2.338 GPa, the tensile strength is 371.9 MPa and the elongation is 12.67%.

Aluminum alloy liquid cold plates are important parts of heat dissipation for the electronic equipments used in aerospace and national defense industries. Usually they have complex outlines and microchannels; thus, they are suitable to be fabricated via selective laser melting (SLM) additive manufacturing technology. To elevate the build rate of the SLM-processed liquid cold plates, a high-power (1 kW) SLM apparatus was used to process AlSi10Mg alloy in this study, and the densification behavior, microstructure, mechanical properties, and minimum hole diameter of the SLM-processed samples were investigated. Results show that the relative density of the high-power SLM-processed samples first increase with the increase in laser volume energy density, and then remain unchanged at high laser volume energy densities. To obtain a high relative density of more than 99.5%, the laser volume energy density should be set in the range of 47.6‒200 J/mm3 during the high-power SLM process. The microstructure of the as-fabricated sample comprises α-Al cellular dendritic matrix possessing a 〈100〉 texture along the building direction and reticular eutectic Si. Owing to the comprehensive effects of grain boundary, solid solution, and second phase strengthening, the tensile strength, yield strength, and elongation of the high-power SLM-processed samples were (433±10) MPa, (267±8) MPa, and (5.5±0.5)%, respectively, which were higher than the corresponding values of the die casting AlSi10Mg. When the 1 kW high-power laser was used in the SLM process of AlSi10Mg, the minimum horizontal and vertical hole diameters that could be fabricated were 0.6 mm and 0.4 mm, respectively, which could satisfy almost all design and forming requirements for a liquid cold plate. Based on the above technology, local simulation parts of an aluminum alloy liquid cold plate were successfully fabricated using high-power SLM, and the build rate was up to 75.6 cm3/h.

In this work, a tunable single-frequency fiber laser with asymmetric compound ring cavity is designed. Fiber ring resonator, fiber optic tunable filter, and fiber ring filter are respectively embedded into the main fiber ring cavity. An efficient and stable tunable single-frequency fiber laser from 1020 nm to 1090 nm is achieved based on the principle of the vernier effect. A 980 nm semiconductor laser is used as the pump source, when the pump power is 200 mW, the output linewidth of the single-frequency laser measured by the delayed self-heterodyne method is 3.325 kHz, and the optical signal-to-noise ratio is greater than 50 dB, with 5 min as the interval, the measured output laser wavelength stability is 0.02 nm within 40 min.

In the beam transmission system, there are usually wide-band disturbances with energy inversely proportional to the frequency caused by the transmission medium and narrow-band disturbances at a specific frequency caused by platform vibration, which causes the beam to jitter or drift and lead to the decrease of the spot energy. In order to solve the beam jitter caused by large amplitude, high frequency narrow-band disturbance and wide-band disturbance in the beam transmission system, this paper designs a beam jitter control method based on a hybrid adaptive filter with high-speed tilting mirror resonance compensation. The method adopts the control structure of the least mean square (LMS) adaptive filter and the classic proportional integral controller working in parallel. The LMS adaptive filter is used to suppress high frequency and large narrow-band disturbances, and the proportional integral controller is used to suppress the wide-band disturbance, so as to realize the simultaneous suppression of the large amplitude, high frequency narrow-band disturbance and wide-band disturbance. Experimental results show that the system structure and control method proposed in this paper can effectively suppress the beam jitter in the beam transmission system.

To realize the dynamic adjustable function of the broadband absorber, this paper proposes and designs a symmetrical absorber structure composed of a square top layer with embedded cross, a SiO2 dielectric layer, and a VO2 bottom layer. In the range from 2 THz to 4 THz, the absorption efficiency of the device can be adjusted from less than 10% to more than 90% by adjusting the conductivity of the bottom layer of VO2, and its switching modulation depth is greater than 65%. In a wide frequency range, the device can be dynamically switched between the reflector and perfect absorber modes. The simulation results show that the absorber has wide-angle and polarization-insensitive characteristics, and the incident angle range of electromagnetic waves to the absorber can reach 75°. Based on the above advantages, the absorber has great potential in terahertz device applications such as smart attenuators, reflectors, and spatial modulators.