Nitrogen-vacancy (NV) color center has stable fluorescence emission at room temperature, ultra-long electron spin coherence time, and excellent optical properties. In the field of quantum sensing, it has excellent performance in electromagnetic field and temperature sensing with high sensitivity. Optical fiber sensing technology has been developed rapidly in recent years with wide applications. Optical fiber system can be combined with NV color center because of its integration, high practicability, and easy operation, showing excellent optical transmission capacity and low loss. This optical fiber-based quantum sensor system can be applied to biological, material temperature, magnetic field, and other physical measurements. This review mainly introduces the working principle, methods, and applications of fiber quantum sensing technology based on NV color center system.

Fiber-optic distributed acoustic sensing (DAS) technology based on linear frequency modulation (LFM) pulses has gained popularity due to its ability to combine the advantages of both continuous and pulse waveforms in detection light. By utilizing the principle of frequency shift, additional phases can be generated to achieve phase compensation for fiber strain sensing. This technology enables quantitative waveform recovery of acoustic signals at various locations along the fiber optic link, with fast response times and high sensitivity. DAS has significant potential for applications in geophysics and linear infrastructure monitoring. In this study, we discuss the basic sensing mechanism of LFM pulse-based DAS technology, present research progress on key scientific and technical indicators such as sensing distance, spatial resolution, frequency response, and fading noise suppression, and introduce the progress of DAS in typical applications. Finally, we discuss possible future development trends.

Optical clocks have developed rapidly in the past 20 years, and their stability and systematic uncertainty are two orders of magnitude better than the current best microwave atomic clocks, and currently, there are 10 optical transitions which have been selected as the secondary representations of the definition of the second by the International Bureau of Metrology and participate in the generation of the international atomic time. This paper introduces the operational principle and evaluations of the performance of optical clocks, the latest research progress of ionic optical clocks and optical lattice clocks, elaborates the progress of the absolute frequency measurement of optical clocks, and summarizes the measurement results of the secondary representations of the definition of the second by optical frequency transitions.

The surface plasmon resonance (SPR) phenomenon has attracted considerable attention because of its sensitivity to the changes in the surface refractive index of materials. Sensors based on SPR have broad application potential in the fields of biomarker detection, food allergen screening, and environmental monitoring as they have advantages such as unmarked, high sensitivity and rapid detection. We review SPR biosensors based on three types of structures, namely prism coupling, grating coupling, and fiber coupling structures. The detection principle, typical structures and other sensing characteristics of the three structures and the advancements in their development are emphatically studied. Furthermore, the research status and technical problems related to biological functionalization in SPR biosensor technology are discussed. SPR sensors with different material surface characteristics are also discussed. The problems encountered in the practical application of SPR biosensors are analyzed, and the future research directions are presented. Finally, the prospects for the development trend of new biosensors are discussed based on the aspects of the structure and materials used.

The white light interference type Fabry-Perot sensing technology can achieve absolute measurement of gap value. Research work in the field of fiber optic Fabry-Perot sensing technology based on white light interference is reviewed, research status of fiber optic Fabry-Perot sensor and its demodulation technology under extreme environments of high temperature and high pressure are focused on. The purpose is to analyze the principle and method of physical parameter measurement based on optical fiber Fabry-Perot sensing technology under high temperature and high pressure environment, and realize the practicality and engineering of optical fiber Fabry-Perot sensing technology based on white light interference.

Battery condition monitoring is crucial for the healthy operation of batteries. With the continuous improvement of battery performance and increasingly widespread application, it is urgent to develop an economical and effective battery sensing system. Compared to traditional battery sensing technology, optical fiber sensors have unique advantages, including high sensitivity, small size, easy integration, low cost,etc. This review summarizes all kinds of fiber optic sensors that can be used for battery condition monitoring, including fiber grating sensors, fiber optic interferometer sensors, fiber optic evanescent wave sensors, fiber optic photoluminescence sensors and fiber optic scattering sensors. Finally, the challenges and prospects for future battery sensing research are proposed.

Optical frequency domain reflectometry (OFDR) based on Rayleigh backscattering (RBS) has drawn significant attention in the fields of aerospace, health care, and high-precision instrument testing due to its advantages of exhibiting high spatial resolution and high sensitivity. The improvements in the spatial resolution and sensing distance of OFDR is limited by the weak RBS in the fiber and nonlinear tuning of the laser source. To address these problems, two methods, namely, optical fiber post processing and data post processing are introduced, focusing on RBS enhanced fiber using ultraviolet and femtosecond lasers. Moreover, the temperature, strain, and three-dimensional shape sensing properties are realized using RBS enhanced fiber and data post processing methods.

Residual stresses are typically generated in materials and components during their manufacturing processes, thereby significantly influencing their engineering properties, particularly the fatigue life, deformation mechanism, dimensional stability, corrosion resistance, and brittle fracture. Therefore, the measurement and evaluation of residual stresses have been the focus of current manufacturing research to provide a theoretical basis for the strength analysis and deformation prediction of materials and components. With the development of new materials and their processing technologies, the requirement for residual stress measurement techniques has increased. This paper describes existing residual stress measurement techniques, emphasizing the application of fiber Bragg grating in residual stress measurements. Furthermore, the existing problems are analyzed, and the future development trend is prospected.

The quantum precision measurement method achieves higher accuracy and resolution than conventional measurement methods. Over the past few decades, there is significant progress in the field of quantum-enhanced metrology with respect to the estimation of fixed parameters. However, estimating time-varying parameters is one of the key tasks in numerous practical engineering applications, such as gravitational wave detection, navigation, and positioning. Therefore, designing an effective quantum-enhanced time-varying parameter-estimation method and perfecting the time-varying parameter-estimation theory are important research components related to quantum precision measurement. Recent studies have demonstrated that the accuracy limits of time-varying parameter estimation are closely related to the continuous nature of the signal itself. Moreover, similar to fixed signal measurements, nonclassical sources such as squeezed states can improve the accuracy of time-varying parameter estimation. This review introduces several accuracy limits related to time-varying parameter estimation and summarizes the related research progress.

The emergence of Rydberg atom technologies is driving a paradigm shift in modern sensing and measurement by exploiting quantum phenomena to realize fundamentally new detection capabilities unmatched by their classical counterparts. This article reviews the development of radio frequency of electric field measurement with Rydberg atoms, details the sensitivity of electrical field, and looks forward to the future development trend. It will help the vigorous development of the field and the promotion of engineering.

Multimode fiber (MMF) contains rich temporal and spatial information because of the mode characteristics. As a novel optical fiber imaging method, MMF imaging based on temporal-spatial information extraction has the advantages of small device size, high resolution, large information capacity, and minimal invasion and has the potential to become a new generation of high-resolution and low-invasive endoscope. This review summarizes the basic methods and related progress of MMF imaging and introduces the related work of combining machine learning with MMF imaging. In addition, for the practical application of MMF imaging, we discuss the methods and related progress of MMF imaging under dynamic perturbation and the limitation of MMF imaging performance and quality. Finally, MMF imaging is summarized and prospected.

Super-resolution fluorescence microscopy (SRFM), which can bypass the optical diffraction limit, provide an extremely important research tool for investigations of the subcellular structures and the dynamic processes of biological macromolecules. Therefore, since its invention, SRFM has been paid attention to and applied by scientists in the field of biology and medicine. Benefiting from the rapid development of life science and biotechnology in recent years, SRFM has been developed unprecedentedly. In this paper, we will mainly focus on the research progresses of four new kinds of SRFM, including minimal photon fluxes (MINFLUX), super-resolution optical fluctuation imaging (SOFI), super-resolution image based on anti-bunching effect, and deep-learning based super-resolution microscopy, respectively. We will briefly describe the recent research progresses and applications of these SRFM techniques from the basic principles, experimental implementation methods and related requirements, imaging performance, and comparison with other technologies, as well as the combination with other super-resolution techniques, to provide some references for researchers in this field.

Autonomous navigation is a key technology for deep space exploration, and several autonomous landing missions on extraterrestrial planets have been executed by China and other nations. Autonomous visual navigation technology based on craters is a current research hotspot. Numerous planets have rich crater features, and pose estimation based on terrain features is an important technology for visual navigation. This work first briefly introduces the recent application progress of navigation technology in the field of deep space exploration and the classification of autonomous navigation methods. Visual navigation has been classified according to sensor imaging, focusing on the terrain relative navigation method based on craters. Subsequently, the advantages and difficulties of the crater-based method are summarized, definition and data types of craters are introduced, and domestic and foreign research institutions and personnel have been presented. Moreover, the navigation method based on craters is divided into three stages, crater detection, crater recognition, and pose calculation, and the research advances in crater detection methods, from supervised detection, to unsupervised detection, and finally to composite detection, are introduced thoroughly. The work introduces domestic and foreign methods of crater recognition according to the stage and the presence or absence of initial attitude information, respectively, and then introduces the pose calculation method based on image information and the method combined with dynamic models, respectively. Finally, crater-based visual navigation technology is summarized, and prospects for its development are discussed.

Spectral imaging has been widely used in food safety, medical diagnosis, environmental monitoring, camouflage identification, and military remote sensing because of its excellent multidimensional information acquisition capability. Traditional spectral imaging systems are limited by spectroscopic components, suffering from problems such as large sizes, high costs, and low integration. Novel metasurface-based spectral imaging chips can provide an effective solution for obtaining miniaturized and low-cost sensors. With the continuous increase in demand for spectral analysis, the development of metasurface spectral imaging chips has accelerated. We review the recent research progress of metasurface spectral imaging chips. On this basis, we present the latest research results of our team. Through the innovative design of the imaging spectral chip system architecture, a high energy utilization rate, spatial resolution, and spectral resolution can be achieved simultaneously, providing a solid foundation for the application of chip-level spectral imaging systems. Finally, we discuss the development trend and application prospects of spectral imaging chips, providing a reference for the miniaturization of the spectral imaging system.

As a new type of underwater acoustic sensor, fiber optic hydrophone is of great significance to China's utilization and marine strategy planning. To satisfy the ever-growing demand for low-cost, highly integrated, and high sensitive fiber optic hydrophones, there is an urgent need to advance fiber sensor technologies. A fiber Bragg grating (FBG)-based hydrophone exhibits advantages such as ease of large-scale array, cost-effectiveness, and high reliability, making it an important technical solution for the next generation of hydrophone arrays. This study comprehensively summarizes the FBG-based hydrophone based on the aspects of sensing systems, hydrophone probes, and key technologies. Additionally, signal demodulation at the dry end, which is a key technique in the development of FBG-based hydrophones, is addressed. This study has significant guiding significance for intensive research of key technologies, improvement of detection performance, and promotion of practical application of fiber grating hydrophone system.

Due to the excellent performance of two-dimensional materials compared with conventional materials in many aspects, researchers have paid extensive attention to two-dimensional materials. At present, two-dimensional materials have become a research hotspot in various fields, and are widely used in biomedicine, electronics, optoelectronics and catalysis. This paper mainly summarizes and discusses the application of two-dimensional materials in optical sensing in the biomedical field. This paper mainly discusses the generation and development of two-dimensional materials, the advantages and disadvantages of two-dimensional materials and the types, principles and manufacturing methods of optical biosensors based on two-dimensional materials, as well as some achievements of these sensors in single-cell, RNA, protein molecule highly sensitive detection technology, and combines these results to briefly analyze some advantages of experimental schemes using two-dimensional materials compared with traditional methods. Finally, the development status of two-dimensional materials is briefly summarized, and their future development is prospected.

A spatial variable resolution scanning three-dimensional (3D) imaging method is proposed to address the problems of high redundancy of point cloud and low accuracy of image reconstruction in traditional fixed-resolution scanning 3D imaging. A model of multi-echo and spatial variable resolution scanning imaging is deduced. Target information is extracted by decomposing multi-echo to achieve high resolution depth image reconstruction. The model is verified by comparative experiments. The results show that compared with the traditional fixed-resolution scanning imaging method, the sampling rate of the proposed method is only 50% under the comparable imaging quality, which effectively reduces the redundancy of the point cloud. The results can support the related application of 3D imaging.

In quantum communication based on polarization encoding, the polarization state cannot be maintained for a long time because of the external temperature, stress, and defects in the optical fiber. This increases the bit error rate of the system. Therefore, polarization control is necessary to maintain robust operation of the communication system. Currently, decoy states are being widely used in quantum communication networks. Using decoy photons as a polarization reference, long-term and uninterrupted locking of the system polarization state can be achieved, and communication efficiency can be improved. In this study, an integrated polarization control system is built to control the polarization state preparation and single-photon transmission. The polarization state preparation unit, strong light polarization control unit, and single-photon polarization control unit are integrated into one system using a field-programmable gate array development board, which improves the integration of the system and makes system management more convenient. The experimental results show that the polarization state preparation unit can generate different polarization states as required, and the fidelity can reach 99.11%±0.44% after strong light polarization and 97.93%±0.96% after single-photon polarization control. These results demonstrate the effectiveness and stability of our proposed system.

We report a cold atom interferometer based on the lightest alkali metal 6Li and measure its recoil frequency precisely, measuring the fine-structure constant on a preliminary basis. To overcome the challenges associated with magnetic-field sensitivity caused by the half-integer spin of atoms, a magnetically insensitive Raman transition and a conjugated Ramsey-Bordé interferometer involving crossed Raman beams and coherence time >2.3 ms is realized. The error in the angles between Raman beams is eliminated using four sets of interferometers developed based on geometric relationships. The measured recoil frequency ωr is2π×73 672.789(36) Hz, and the fine-structure constant is 1/137.035976(33). These values indicate the most accurate measurements for 6Li obtained using the reported atom interferometer. The implementation of the 6Li cold atom interferometer not only enriches the elements of atom interferometers, but also has great potential in the field of precision measurement due to its high recoil frequency.

The gravity gradiometer has important application value in resource exploration, geophysical research, autonomous navigation and other fields. The gravity gradiometer based on atom interferometers is a new type of high-precision measuring instrument, and its miniaturization and practicality are the core problems to be solved in its wide application. We design and implement a compact high-precision atom gravity gradiometer capable of measuring horizontal components. The instrument adopts the technical scheme of combining all-quartz vacuum cavity and accessory frame, which reduces the volume of the sensor part to 105 L. It adopts a double-sided optical modular structure, which reduces the volume of the optical unit to 36 L. These evolutions make the instrument very easy to carry. In laboratory, the sensitivity of the instrument is measured to be 320 E/Hz, and the resolution is 3.3 E@4800 s (1 E=1×10-9 s-2).

High-precision interferometers play a critical role in the field of metrology. The uncertainty of phase estimation can be used to evaluate the precision of an interferometer. The lower the uncertainty of phase estimation, the higher the phase sensitivity. We theoretically propose a nonlinear interferometer composed of an optical parametric amplifier and a linear optical beam splitter (BS). An optical parametric amplifier based on the hot rubidium-85 atomic ensemble four-wave mixing (FWM) process is used to combine and separate the beams in the interferometer. As a feedback controller, the BS controls the proportion of the output light returning to the input light port in the FWM process by controlling the reflectivity of the device. Through theoretical calculations, it is proved that the phase sensitivity of a nonlinear interferometer based on optical parametric amplifier feedback is enhanced compared with that of traditional interferometers. Our research results are expected to have potential applications in the field of quantum metrology.

The research of the microwave electrical field measurement which is based on the Rydberg atoms is developing fast during recent years. The prerequisite for the engineering application is the minimization and integration of the microwave electrical field measurement systems. This article introduces the basic characteristics of the Rydberg atoms, the fundamental principles of the microwave electrical field measurement, and the method of determining the resonant frequency of the transition. In addition, a transportable Rydberg atomic microwave electrometry is developed by combing the 852 nm modulation transfer frequency stabilization and 509 nm electromagnetically induced transparency frequency stabilization. Based on this instrument, we demonstrate the microwave electrical field measurement which is traced back to the standard international unit systems and the detection of the weak microwave signal.

Vector light gains an increasing interest due to its exotic spatial polarization structure texture, which is governed by the intramodal phase of two orthogonal polarization components, and, in particular, has shown great potential in optical metrology. We present and demonstrate experimentally a novel laser interferometric technique fed by a vector sensing beam. The phase variation of the interferometer is first mapped into the intramodal phase of the sensing beam. Then, by in-situ characterizing the vectorial polarization state of the sensing beam via spatial Stokes tomography, a precision phase estimation approaching standard-quantum or Heisenberg (by feeding a N00N state) limit can be achieved in arbitrary phase ranges including insensitive regions.

Herein, we propose a scheme for developing a large-momentum-transfer atom interferometer based on the top-hat composite light pulse technique. Additionally, we analyze the contrast and phase noise using a theoretical model of the sensitivity function of the proposed atom interferometer. A top-hat composite light pulse is used to simulate calculations based on the atom interferometer. We confirm that compared with a Gaussian beam, a top-hat composite light pulse can improve the consistency of atom cloud transitions and increase the contrast of atom interference fringes. By designing symmetrical and reversed composite pulse sequences, the phase noise and vibration noise in the time interval and free evolution process of multipulse action can be suppressed. The numerical simulation results show that the sensitivity of the proposed atom interferometer using a top-hat composite light pulse increases by one order of magnitude compared with that using a Gaussian beam. Moreover, the proposed atom interferometer achieves satisfactory suppression of external technical noise.

In this paper, a tapered optical fiber sensor based on chelating agent functionalization is presented for the quantitative detection of low concentration heavy metal Pb2+. The sensor is made of single mode and four core fiber, and the middle four core fiber is tapered to a diameter of 15 microns. On this basis, ethylenediamine tetraacetic acid was used as a metal chelating agent to coat on the surface of a tapered four-core optical fiber sensor, so as to achieve high sensitivity detection of lead ions Pb2+. Experimental results show that the detection limit of Pb2+ is 1 ng/mL. In addition, the sensor has the advantages of good stability, simple preparation process and fast response speed.

With the aim of achieving the simultaneous monitoring of changes in seawater temperature and salinity, we propose a surface plasmon resonance (SPR) sensor based on photonic crystal fibers (PCFs). The sensor probe is realized by fusing a segment of PCF between two segments of multimode fiber and plating a gold film on the surface of the PCF to stimulate the SPR phenomenon. This scheme combines the fiber optic SPR sensing probe with the temperature-sensitive material polydimethylsiloxane to form a dual SPR effect, achieving the simultaneous detection of the temperature and salinity of seawater. The experimental results show that the maximum temperature sensitivity of the sensor is－2.021 nm/℃, and the maximum salinity sensitivity is 0.418 nm/‰. This sensor has a small volume, simple production, and excellent performance. It is suitable for multi-parameter and distributed measurements of seawater and has good application prospects in liquid substance measurement.

Raman random fiber laser combined with passive sensing units can realize quasi-distributed sensing over ultra-long distances. However, limited by the spectrum detection speed, this sensing scheme is usually only applicable to static sensing fields. To address this issue, a novel Raman random fiber laser long-distance dynamic sensing system is proposed by integrating Raman random fiber laser with beat frequency interrogation. Firstly, the suitability of rapid spectral measurement for long-distance dynamic sensing is demonstrated based on the time-dependent spectrum-balanced model. Then, in the proof-of-concept experiment, the spectrum of Raman random fiber laser can be measured rapidly by processing the temporal signals of the local oscillator light and the random fiber laser after beating, breaking through the limitation of the round-trip time of the light on the sensing bandwidth. Meanwhile, the center wavelength of the spectrum is calibrated by using a denoising convolutional neural network, which significantly improves the signal quality of disturbance signal detection and achieves accurate measurement of disturbance information with different frequencies and waveforms. This research provides new insights for further expanding the application fields of Raman random fiber laser.

In this paper, the polarized luminescence of single hexagonal NaYF4∶Sm3+ and monoclinic BiPO4∶Sm3+ microcrystals are measured by using high-precision single-particle polarization-resolved spectroscopy. Experimental results are analyzed by applying Poincare? sphere and polarization fitting methods, which show that the emissions from Sm3+ ions in hexagonal and monoclinic microcrystals are partially polarized. However, the linear polarization angles of emissions from hexagonal microcrystals are completely parallel and perpendicular to the crystalline c-axis, whereas the angles of monoclinic microcrystals are not. From the perspectives of point group theory and macroscopic crystal symmetry, the orthogonally linear polarization angles of hexagonal microcrystals are due to the rotational symmetry of optical transition dipoles around the c-axis. However, the transition dipoles in the monoclinic phase do not allow rotational symmetry, resulting in the random linear polarization angles of the emissions. This finding will facilitate the achievement of rare-earth-ion-doped single micro/nanocrystals with desirable polarization properties originating from their crystal structure design.

Silicon-nitride based microcavities are widely used integrated optical devices that are not only capable of outputting optical frequency combs for precision ranging and optical clocks but also serve as efficient on-chip quantum light sources. The stability of optical frequency combs in microcavities is a major condition for the practical application of these devices. In this study, the evolution and thermal self-stability of optical combs in silicon nitride microcavities are theoretically and experimentally investigated. Based on the nonlinear process and thermal dynamics of microcavities, the comb evolution and thermal self-stability of an optical comb in a microcavity under different powers and detuned continuous optical pumping are analyzed. Results show that the output of the “Turing Ring” state can be adjusted by precisely controlling the pump power and by detuning. Moreover, the effects of noise can be compensated by resonance drift caused by power and wavelength disturbance to achieve stable operation. This study provides a critical foundation for experiments based on microcavity quantum sources.

The respiratory measurement and classification system based on fiber Bragg grating is studied in this paper. In order to facilitate the needs of intelligent wear, the bare fiber grating was encapsulated with polydimethylsiloxane (PDMS), and the respiratory monitoring system was built to measure the respiratory signal. Four kinds of respiratory signals including breath-holding, cough, normal breathing and post-exercise breathing were collected. Based on wavelet decomposition and reconstruction, the collected respiratory signals were preprocessed and the frequency, amplitude factor, waveform factor and energy of the respiratory signals were extracted as characteristics to distinguish respiratory types. A respiration classification model based on support vector machine (SVM) was constructed, and the model parameters of SVM were optimized by particle swarm optimization. Finally, the classification accuracy was achieved at 97.1875%. The system is characterized by low cost, compact structure and simple design, which can enrich the digital diagnosis and treatment technology.

In this study, a miniaturized light source with an intensity-difference squeezed state is fabricated. The light source uses a dispersion-shifted fiber as the nonlinear medium, and its pulse pump light repetition frequency is approximately 50 MHz. The light source has a stable structure and small size. The intensity difference compression characteristics of the light source in a wide range of frequencies are measured and analyzed using a broadband wide difference detector. The results show that the intensity difference noise measured at a frequency less than 65 MHz at room temperature is lower than the shot noise limit; furthermore, the intensity difference compression at 20 MHz is about 3.8 dB. This study lays a foundation for the measurement of the intensity difference squeeze in time domain.

In this study, a high-temperature sensing array based on a femtosecond fiber grating was designed to address the temperature measurement needs of high-power spallation targets. The temperature range and mechanical strength of the sensor were enhanced using a femtosecond laser-engraved fiber grating and a tubular encapsulation method. The annealing process, i.e., annealing steps, annealing time, and annealing temperature, was investigated and optimized. Additionally, multiple annealing (800 ℃, 20 h) was conducted to improve the stability of the fiber Bragg grating. An accurate fitting function of temperature-wavelength was obtained through its calibration test. The sensor has an accuracy of ±0.2 ℃ in the temperature range of 100-500 ℃, with good repeatability. Moreover, on-site testing results indicate that the proposed sensor can achieve precise temperature testing of high-power spallation targets.

This study investigates a roof separation sensor based on fiber Bragg grating. Simple structure, easy installation, and low cost are the advantages of this fiber optic sensor. This sensor does not exhibit charged characteristics, and it is suitable for coal mine applications. The sensor consists of mechanical structures and shifts the displacement of a wire rope through the rotation of multiple mechanical structures. Thus, it is convenient to use the wire rope to connect to the roof separation and vary the range and sensitivity. The sensor has three fiber gratings, which not only satisfies the requirements for monitoring multiple points but also provides a method for eliminating the temperature effects. The experimental results verify the reliable linearity of the sensor at multiple temperatures, and the accuracy can reach ±2 mm with a range of up to 300 mm.