Aiming at the phenomena of abnormal response and dark signal tailing caused by crosstalk of a linear array detector, we analyze the mechanism of crosstalk generation, establish the RC model which can reproduce the crosstalk image signal waveform. On this basis, we further propose a crosstalk image restoration method. This method is based on the crosstalk RC model and the objective is to recover the normal signal response and eliminate the dark signal tailing. The optimization objective function is established. Based on the target response curves of different frequencies, the model parameters are iterated to obtain the corresponding model parameters when the comprehensive effect of restoration is optimal for each image frequency. After the parameters of the crosstalk model are obtained, the corresponding restoration function is calculated, and the image is restored by the operations in the frequency domain. The infrared images of the linear array detector scanning camera acquired in the laboratory are restored and the results show that the proposed method can effectively restore the normal response of different targets under different image frequencies, reduce the effect of tailing dark signals, and improve the image quality.

Metamaterials and metasurfaces show great potentials to adjust the amplitude, phase, wavefront and direction of electromagnetic waves in a complex and precise manner, since the shape and size of the subwavelength unit can be designed with large degree of freedom. At the same time, with the increase of the number of structural parameters involved, the structural design time increases in an exponential way. This paper proposes a method for the fast optimization of metasurface structures based on the back-propagation (BP) neural network, and a terahertz dielectric metagrating with the merits of high diffraction efficiency, wide bandwidth, and high angular dispersion is achieved. A dataset established via a limited number of rigorous coupled wave analyses is used to train the BP neural network. It can accurately predict the diffraction spectrum of the metagrating with an arbitrary geometry. Simultaneously, the metagrating with the highest diffraction efficiency and wide bandwidth is fast selected by quickly traversing all structural parameters. The designed speed is increased by 10,000 times compared with that of the traditional traversing calculation method, which proves the high efficiency and accuracy of the metasurface optimization method based on the BP neural network. The study provides a diffractive element with excellent performance for terahertz applications.

To deal with the problem of carrier phase recovery in the probabilistic shaping (PS) scenarios, this paper proposed an adaptive algorithm based on statistical analysis. First, kernel density estimation was used for parameter estimation of the PS signals, and thereby the information entropy was estimated to assist the subsequent fourth-power frequency offset estimation (FOE) algorithm based on radius orientation. Then the estimated PS parameters were adopted to carry out targeted normalization of the signals for carrier phase noise recovery based on blind phase search. Furthermore, the FOE range, signal-to-noise ratio (SNR), and laser linewidth tolerance of the algorithm were simulated and analyzed. The results show that the proposed scheme can cope with different PS intensities and achieve good carrier phase recovery in a wide SNR range. In addition, compared with the carrier phase recovery algorithm for standard signals, the proposed scheme requires a shorter sliding window and has higher estimation accuracy when achieving optimal performance.

In this paper, we proposed a new scheme of generating vector millimeter-wave signals with stable frequency and polarization multiplexing by a single optical modulator. We have experimentally demonstrated the delivery of 64 Gbit/s@28 GHz PDM-16QAM signals in the system link was with a bit error ratio smaller than 4.2×10 -2 based on a dual-polarization Mach-Zehnder modulation (DP-MZM) and polarization-division-multiplexing 16-ary quadrature amplitude modulation (PDM-16QAM). In summary, the system has a simple structure, a high spectrum efficiency, and a greatly enhanced transmission rate, which has great application value in the future communication network of radio over fiber.

In this study, an all-fiber polarization-dependent device based on a 45° radiated tilted fiber grating (RTFG) is reported. Owing to its unique polarization-dependent mode coupling characteristics, this device can be used as an ideal all-fiber polarizer, polarization-dependent coupler, and all-fiber diffraction device. Based on the volume current method, the polarization coupling theory for tilted fiber gratings is established. The polarization radiation coupling, diffraction splitting, and polarization characteristics of the 45° RTFG are systematically analyzed theoretically and experimentally. Simulation and experimental results show that the transmission and radiation of the 45° RTFG exhibit good polarization function. The 45° RTFG with a length of 24 mm shows a polarization extinction ratio (PER) of 22 dB at a wavelength of 1550 nm, and the 3-dB bandwidth is more than 300 nm. Moreover, the grating with different PER can be prepared by changing the grating length. The radiation mode distribution of the 45° RTFG is measured, which indicates a quasi-Gaussian profile and exponential reduction along the azimuthal and axial directions, respectively. The spatial diffraction angular dispersion is approximately 0.054 (°)/nm, which is consistent with the simulation result. The 45° RTFG has potential application prospects.

In order to further improve the overall performance of the coupling cone structure optical fiber ultrasonic sensor and make it better serve the optical fiber ultrasonic nondestructive testing, the influence of the material parameters of the coupling cone on the response sensitivity of the sensor is simulated and analyzed by using the finite element analysis method in this paper. Based on this, 4 kinds of cone materials with excellent ultrasonic energy accumulation effect are selected and the best response cone angle is calculated to match with them. 4 optical fiber ultrasonic sensors based on 74° aluminum cone, 30° plexiglass cone, 130° polystyrene cone, and 126° natural rubber cone are optimized and designed. Experimental results show that these 4 sensors can effectively detect ultrasonic signals with a frequency of 1 MHz, and compared with the existing sensors, have a greater improvement in response sensitivity, which can effectively improve the sensor's sensing performance. Moreover, the structures are smaller and lighter, which can be used in more extensive occasions.

According to the time-domain perturbation wave equation, we derived the mode-coupled equation with the refractive index perturbation in the few-mode fibers. Then, the equation was used to analyze the mode coupling characteristics and their influence on the mode extinction ratio of signals in the case of few-mode fiber connection. Taking a two-mode fiber as an example, we investigated the relationship between the maximum mode coupling efficiency and the connection loss coefficient of perturbative/non-perturbative fibers. It is found that the maximum mode coupling efficiency is about 4 times the connection loss coefficient when the inter-mode coupling is very small. Furthermore, we put forward a formula of mode extinction ratio in the presence of refractive index perturbation in few-mode fibers. The calculation results show that the mode extinction ratio of the signals can be higher than 20 dB when the ratio of the effective phase mismatch factor to the mode coupling coefficient is greater than 10 or the product of mode coupling coefficient and length is less than 0.2.

In this work, we simulate a fiber mode-division multiplexing (MDM) transmission system with mode-dependent loss (MDL), and simultaneously explore the impact of MDL and burst perturbation on system performance. The impact of MDL on a 4×4 MDM transmission system is analyzed with fast perturbation of different intensities applied. Adaptive algorithms containing least mean square (LMS) and recursive least square (RLS) routines are used for fast channel compensation. The performance of these channel-compensation algorithms is calculated using mean square error (MSE). Simulation results show that MDL degrades system performance. Both LMS and RLS algorithms can compensate for the effects of dynamic perturbation on the system; however, MDL causes system performance to change greatly after compensation, i.e., the variance of MSE varies greatly.

According to the tensor based polarization light holography theory, we find that the faithful reconstruction of the polarization state of the signal light can be realized as long as the polarization directions of the read reference light and the reconstructed light are not orthogonal to each other, when the linearly polarized light with polarization direction in the incident plane is taken as the recording reference light and the interference angle at the recording stage is 90°. Besides, the intensity of the reconstructed light is affected by the polarization state of the read reference light. Furthermore, the faithful reconstruction of signal light under more relaxed conditions is verified by the theoretical and experimental results. This conclusion is helpful to extend our cognition of polarization holography, and based on this, we can design and fabricate polarization devices to change the propagation direction of the incident light.

The present work systematically discusses the planar-feature-based registration method of high-precision fusion of terrestrial LiDAR point clouds, wherein unit quaternion is used as the description operator of spatial rotation transformation. The 4-tuple representation method of planar features in three-dimensional (3D) space is given first. Then, the planar feature-based spatial similarity transformation model is constructed on the basis of ensuring the uniqueness of those planar features' mathematical expressions. Using the parameter equivalent of each conjugate planar features after registration as the constraint condition, the objective function of the 3D spatial similarity transformation is constructed according to the least square criterion, and the iterative solution of the registration parameters is analyzed according to the extremum of the function. Finally, the correctness and effectiveness of the algorithm are verified by two sets of LiDAR point cloud data. Results show that in solving the spatial similarity transformation parameters, the 4-tuple expression method of planar features is used in judging the consistency of the same-name features after registration through the condition constraints of the parameter equivalent. Simultaneously, the two constraints of normal consistency and distance zero between the same-name plane features are considered. Introducing quaternion makes the expressions of the spatial similarity transformation model more concise, and there are fewer additional constraints in during registration. In the experimental scheme, given any initial value of an unknown parameter, the proposed algorithm can run and get correct results.

Digital micro-mirror devices (DMDs) as spatial light modulators, have the advantages of high modulation speed and accuracy and can perform amplitude or phase modulation for illumination light, which are widely used in phase imaging systems. In this paper, a DMD is used for the random coding modulation of illumination light amplitude. We simulate the influences of the smallest modulation unit and switch ratio on phase imaging when random coding patterns are loaded on the DMD. Then we use a difference mapping iterative algorithm for light field reconstruction. Furthermore, it is experimentally verified that based on the parameters obtained via numerical simulation, we can retrieve amplitude and phase with a higher iteration speed and a fewer measurement times. In addition, for an object with the field of view of 4.3 mm×4.3 mm, the reconstruction resolution reaches 6.9 μm.

Aiming at the problems that the measurement range of a monocular light pen three-dimensional measurement system is small and this system can not realize the full space measurement, a full space light pen monocular vision measurement method based on precision rotary platform is proposed. First, the camera is fixed on the precision rotary platform, and the calibration plate is photographed at different angles to obtain the position of the camera optical center in the calibration plate coordinate system under different angles. Second, through the plane fitting of principal component analysis (PCA), the plane where the camera optical center is located and the rotation axis direction vector of the camera rotation motion are obtained, and the position of the camera rotation axis is obtained by using the spatial least square circle fitting. Third, with the help of the precision rotary platform reading and Rodriguez formula, the rotation angle of the turntable is transformed into the rotation matrix and translation vector of the camera. Finally, the measurement data of the camera at different positions after rotating a certain angle are converted to the same rotary platform coordinate system by using the calculated transformation matrix to realize the full space measurement. Experimental results show that in the measuring system using the same light pen, the measurement method in this paper can almost achieve the same precision as that of the traditional monocular vision light pen measurement system, achieve 360° full space measurement, and greatly expand the scope of applications of the monocular light pen.

The problem of phase unwrapping is widespread in fringe projection profilometry. In this paper, a phase-shift coding unwrapping method is proposed. This method uses the multi-step phase-shift method to solve a phase and embeds the code of the mark fringe series into the phase-shift amount in an additional coded image. When decoding, one can solve the coded phase-shift amount at the point and thus obtain the absolute phase by analyzing the light intensity information sequence of different phase shifts at each pixel point. This method requires only a few images and can unwrap point by point. It is suitable for the shape measurement of a discontinuous object but it is easily affected by the noise of the projector and the camera. By adding the complementary coded fringe images, we propose an improved phase-shift coding unwrapping method, which can not only be used for the shape measurement of discontinuous objects but also significantly enhance the noise robustness. The simulation analysis and experiment confirm the effectiveness of the proposed phase-shift coding unwrapping method.

Reconstruction of two-dimensional temperature and CO2 concentration fields based on the tunable diode laser absorption spectroscopy (TDLAS) and traditional reconstruction algorithm requires multiple line-of-sight measurements in both axial and radial directions for axisymmetric flames. The experimental system is usually complicated, and the reconstruction efficiency is relatively low. Herein, a machine-learning-based reconstruction model is developed and used to simultaneously retrieve the two-dimensional temperature and CO2 concentration fields from 4.2-μm mid-infrared TDLAS laser absorption measurements for axisymmetric laminar diffusion flames. Compared with the traditional inversion reconstruction method, the machine-learning-based inversion model only needs to scan the central axis of the flame to simultaneously and efficiently reconstruct the two-dimensional temperature and CO2 concentration field of an axisymmetric laminar diffusion flame, and the model requires less experimental measurements only in the axial direction, which considerably simplifies the measurement system and improves the reconstruction performance.

The extent of road slippery is an important indicator of road traffic safety. The road surface meteorological sensing technologies can accurately detect the conditions of water accumulation and ice formation on the road, and thus can quantitatively analyze the slippery parameters such as critical hydroplaning velocity and road adhesion coefficient. Using these technologies, we can effectively prevent traffic accidents by adjusting vehicle speed or even closing roads in real time. The non-contact road surface meteorological sensing method is currently a hot research topic because of its high accuracy, no damage to roadbeds and flexible installation. However, its key technology is still monopolized abroad and the equipment is very expensive. Based on the characteristics of infrared reflection spectra of stagnant water and ice on road surfaces, we use the reflected laser intensities at 1310 nm and 1550 nm to study a set of mathematical models and detection methods for detecting water film thickness and distinguishing water/ice state. Based on it, a road surface meteorological sensing system is established and the optical structure of this system is optimized by optical simulation. The experimental results show that the detection distance of the system reaches 3-5 m and the measurement error of water film thickness is less than 0.1 mm in the range of 9 mm. The system can accurately distinguish the meteorological states of drying, water accumulation and ice formation on road surfaces, which has good practical value.

Concave grating imaging spectrometers operating at conventional Rowland circle mounting have excellent on-axis imaging performances. However, such spectrometers have been found to possess poor off-axis imaging performances as a result of the existence of large off-axis grating aberrations, which are not suitable for spatial and spectral imaging under a large off-axis field of view (FOV) and a broad band. Based on the aberration correction theory of toroidal varied line-space gratings operating at non-Rowland circle mounting, we designed a solar extreme ultraviolet (EUV) normal-incidence imaging spectrometer with a large off-axis FOV and a broad band. Specifically, this instrument can provide excellent imaging with high spatial and spectral resolutions for EUV spectroscopic observations of the solar corona and transition region. Besides, the instrument has only two reflective surfaces with periodic SiC/Al multilayer coating, which minimizes the loss of photon flux in the EUV band and improves the transmission efficiency of the instrument greatly. Finally, this unprecedented spectrometer, with an aperture of 100 mm and the operating bands of 40-47 nm, 53-60 nm, and 66-73 nm, achieves a spatial resolution and a spectral resolution better than 0.55″ and 30×10 -4 nm respectively, providing ultrahigh resolution imaging over the off-axis FOV of 18' along the slit.

Aiming at the real-time request of the infrared detection system for target detection, we propose a method for fast detection of infrared targets based on key points. Taking the target center as the key point of target detection, we first design a lightweight feature extraction network. Then, we design a corresponding feature fusion network using the spatial and semantic information of features at different levels combined with the characteristics of small infrared targets. Finally, the prediction of target category, location and size is realized. The model is comparatively tested on the self-built aerial infrared target dataset. Compared with the classic detection models such as YOLOv3, the detection speed is greatly improved and the detection accuracy is only slightly reduced. Compared with the same type of fast detection model, Tiny-YOLOv3, the detection accuracy increases by 8.9% and the detection speed running on the central processing unit (CPU)increases by 13.9 ms/frame under the condition that the model size is compressed to 23.39% of Tiny-YOLOv3's size. The detection performance is significantly improved and the effectiveness of the method is confirmed.

In this paper, we used femtosecond laser with a wavelength of 1040 nm, a pulse duration of 388 fs, and repetition frequency of 100 kHz to etch microgrooves with a large depth-to-width ratio on the surface of quartz glass. Firstly, the laser-induced damage threshold of quart glass was experimentally determined to be 10.61 J/cm 2 by virtue of the area calculation method. Secondly, the effects of laser single-pulse energy, scanning speed, and scanning times on the etching depth and width of the microgrooves were investigated with a single-line etching method. Finally, applying spiral etching with assistance of a laser scanning galvanometer, we found that the depth-to-width ratio of the microgrooves could be increased significantly. Experimental results indicate that the laser single-pulse energy plays an important role on the depth-to-width ratio of the microgrooves. Besides, with a laser single-pulse energy of 110 μJ, a scanning speed of 100 mm/s, and a scanning times of 30, we obtain the high-quality microgrooves with a width of 50 μm and a depth-to-width ratio of 5.4 on the surface of quartz glass.

Therefore, this paper proposed a mixed genetic algorithm and simulated annealing (GASA) algorithm for polarization control. Based on a genetic algorithm (GA), this algorithm introduced the selection mechanism of simulated annealing (SA), and introduces the Monte Carlo idea into GA, which made the algorithm have more powerful search ability. By establishing a mathematical model for the active polarization control system of fiber laser based on the GASA algorithm, we obtained the simulation images of the GASA algorithm under different parameter combinations and analyzed the convergence effect. The simulation results show that when the polarization extinction ratio of output laser is selected as the fitness function, the population number is 90, the mutation probability is 0.7, the crossover probability is 0.001, and the temperature drop ratio is 0.99, the system can achieve the optimal control effect. By comparing the simulation images of GASA algorithm and stochastic parallel gradient descent algorithm, we can see that the GASA algorithm has better ability of global search and jumping out of local optimal values, and can be used in the active polarization control system of fiber laser.

Galvanometer scanning systems are widely used in various fields such as laser rapid prototyping, laser precision marking, and laser scanning measurement for their high speed and precision. However, system measurement errors are induced because of the introduction of a galvanometer system. In view of this, firstly, a linear laser one-dimensional galvanometer scanning system is built and calibrated by the double-checkerboard calibration method. Then, the error model of the system is established and the measurement error in the scanning process is theoretically analyzed. Finally, a compensation method based on the table look-up method is proposed for the galvanometer rotation error. The experimental results show that when the measuring working distance is about 250 mm, after the error compensation, the square root error of center distance decreases from 0.733 mm to 0.061 mm and the standard deviation from 0.200 mm to 0.060 mm. It follows that this method can significantly improve the measurement accuracy and robustness of the system.

To address the tracking stability degradation caused by target scale variation, deformation, illumination variation, and background clutter in complex scenes, a target tracking algorithm based on adaptive multilayer convolutional feature decision fusion is proposed. Initially, multilayer convolutional features are extracted from a target candidate region using the VGG-Net-19 convolutional neural network. Then, under a correlation filter model framework, the extracted convolutional features are employed to construct several weak trackers. Decision weights are adjusted adaptively based on the fluctuation of the decision losses of these weak trackers, and the target position is estimated based on the multilayer convolutional features. Next, according to a scale correlation filter model, multiple scale image patches are sampled at the target center position. Taking advantage of the prior distribution of scale variation between adjacent frames, its scale is predicted. Fifty-one video sequences with multiple challenging attributes are selected to evaluate the tracking performance of the proposed algorithm. The experimental results demonstrate that the proposed algorithm has higher tracking accuracy and success rate compared with state-of-the-art target tracking algorithms. The proposed algorithm adapts well to target scale variation. In addition, it improves the target tracking robustness under target deformation, illumination variation, and background clutter conditions.

According to the characteristics of the multi-size structure and the impedance matching theory, a perfect ultra-broadband absorber with a rectangular laminated structure is designed. The absorber is composed of two layers of metal-semiconductor films-semiconductors of different sizes, which can excite multiple resonance modes and achieve perfect absorption of ultra-broadband. The finite difference time domain method is used to study and analyze the absorption spectrum and electromagnetic field energy distribution of the absorber, as well as the influence of polarization angle and incident angle on absorption performance. Numerical results show that the average absorptivity of the absorber is higher than 97% in the range of visible light to middle infrared, and it is independent of arbitrary polarization. When the incidence angle is 60°, the average absorption rate is still higher than 90%. The wide band perfect absorption is achieved by the joint action of gap-surface plasmon polaritons, propagation surface plasmon polaritons and Fabry-Perot resonance.

The neuromorphic photonic information processing technology is inspired by the high-speed and low power-consumption information processing mechanism in brain. Compared with the traditional photonic information processing technologies, it not only promotes greatly the processing speed and energy efficiency, but also possesses important applications in detection and perception. This paper proposes a neuromorphic photonic information processing scheme based on the distributed feedback(DFB) laser, which is used for high-speed motion direction selection and recognition. The influence of bias current on the DFB laser pulse response duration is analyzed. The dependence of high-speed motion direction recognition on the DFB laser pulse duration is confirmed and the module for high-speed motion direction selection based on DFB laser is constructed. The experimental test of this module is conducted. On the premise of correct recognition, the effects of link weighting parameters and current bias on the applicable speed range are analyzed. The results show that the proposed module can realize the effective recognition in one-dimensional direction within the Mach-level speed range.

The in-flight calibration of large-field atmosphere sensors without the onboard calibration system using broad sea-non equipped sites (SNES) is a recommended method. Herein, based on the working principle of the Directional Polarimetric Camera (DPC) and the characteristics of its level-1 data products and the reflection base method, the simulation of sea surface bidirectional reflectance distribution function (BRDF) transfer to the top of the atmosphere is processed to determine the appropriate threshold angle to reduce nonatmospheric molecular scattering interference. At the same time, the statistical analysis of the calibration sites’ environmental parameters is analyzed to solve the data selection and incorrect budget problems. Finally, the accurate evaluation of the in-flight calibration coefficient changes of DPC at visible bands is achieved. The final calibration error of the absolute radiation calibration coefficient is between 1.24% and 4.76% subsequent to considering the calibration source and instrument laboratory calibration error synthesis.

A mid-infrared methane and carbon dioxide dual-gas sensor system is developed herein to realize the integrated measurement of methane and carbon dioxide. A dual LED-PD(light-emitting diode-photodiode) optical-measurement structure with two narrow-band mid-infrared light-emitting diodes as the light source for methane and carbon dioxide measurements and two photodiodes as the detector sensing elements are designed. Furthermore, the selection of spectral lines and optical devices, pulse current modulation of double LED light source, and the temperature compensation algorithm are studied. The optical measurement structure is designed based on the infrared absorption spectrum characteristics of methane and carbon dioxide gas, and the pulse current modulation timing algorithm of double light sources is completed by using the high-speed response characteristics of LED devices, that is, the current is driven by narrow pulse mode. Based on the analysis of temperature experiment, the temperature influence factors are obtained through the data preprocessing of median normalization, and then the temperature compensation algorithm is obtained by linear fitting. Experimental results indicate that the average power consumption of the sensor system is as low as 38.3 mW; the minimum measurement error of methane is 0.06% (volume fraction), and the minimum measurement error of carbon dioxide is 0.05% (volume fraction). The system can satisfy the requirements of low power consumption and stable and reliable real-time measurement of methane and carbon dioxide concentrations in coal mine.