Rotational and vibrational Raman signals are used to obtain profiles of atmospheric temperature and humidity, and the atmospheric pressure profile can be retrieved from these. A lidar system for detecting the atmospheric pressure and a method for inverting the data are presented in this paper. The feasibility of the given method and the factors that cause the pressure inversion error are analyzed. There are three main error sources: temperature deviation, reference point pressure deviation, and atmospheric specific humidity. Atmospheric detection and pressure inversion are carried out using a Raman lidar system at Xi'an University of Technology. The retrieved atmospheric pressure profile is compared with the pressure sounding data from the same day and a better inversion result is obtained, thus demonstrating the feasibility of the proposed research method. Finally, the performance requirements for achieving highly precise measurements of atmospheric pressure using a lidar system are analyzed from the perspective of specific applications.

A linear array infrared push scan sensor has low scanning frame rate and belt noise. Therefore, a small target detection method based on Robinson-Guard filter and pixel convergence is proposed. At the first stage, some sample windows are uniformly placed on the infrared image, so that the sample windows can focus on the high-lighted region according to the brightness gradient of image. Then, the weighted superposition of the sampling window is used as the target probability map, which combines the target energy information, local contrast, target pixel convergence, and other features of the infrared image. Finally, the target is obtained by global threshold segmentation, and the detection of small infrared target is realized. Experimental results show that the method can detect the small and medium size infrared targets and is effectively resistive to the band noise caused by the detector.

In this study, two scanning methods are designed by combining photoelectric detection equipment having different apertures. Further, a capability evaluation model is established for the multi-photoelectric detection equipment. The model is simulated and analyzed from the scanning mode, arrangement mode and aperture of the telescope, and the simulation results are evaluated. The simulation results show that for the selected catalog space debris dataset, the detection results obtained via single-elevation-area scanning are better than those obtained via multi-elevation-area scanning during the simulation time period. Under the same field of view, the number of debris detected using a combination of four 28-cm-aperture telescopes increases only by 2.4% (single-elevation-area scanning) and 3.6% (multi-elevation-area scanning) when compared with those detected using a 15-cm-aperture telescope combination. The considerably cost-effective 15-cm-aperture telescope combination must be selected to maintain a catalog of the existing space debris, and the 28-cm-aperture telescope combination must be selected for detecting small-sized space debris.

The frequent failure of the optical fiber composite overhead ground wire (OPGW) can be attributed to the local stress on the optical cable. Herein, the long-distance Brillouin optical time-domain analysis (BOTDA) and Brillouin optical time-domain reflectometry (BOTDR) sensing systems were established to achieve online monitoring of the strain with respect to the OPGW optical cable. Further, strain detection and analysis were conducted in case of a 95.14-km OPGW installed for more than 15 years in the heavily iced disaster area. The measurement distance, spatial resolution, and measurement accuracy of the BOTDA sensing system are greater than those of the BOTDR sensing system based on the comparative measurement results obtained using the same optical cable. In addition, the down conductor and zero-strain reference point can be accurately identified to achieve accurate separation of temperature and strain information. When the distance between two stations exceeds the BOTDA measurement range, the whole cable can be evaluated from two ends of the fiber cable using the BOTDR sensing system. The BOTDR sensing system exhibits single-ended measurement such that this system can continue performing the line measurement after a fiber break before the break point. In this study, the advantages and disadvantages of the BOTDA and BOTDR sensing systems in OPGW optical cable monitoring are analyzed for the first time by performing a multidimensional comparison using the same OPGW optical cable. Furthermore, this study provides a reference with respect to the application of the distributed optical fiber sensing technology in power systems.

Platform jitter is an important source of bit error in an intersatellite laser communication system. In this study, we investigate the error performance of the M-ary pulse position modulation (M-ary PPM) system with a finite extinction ratio under the influence of sighting error. Further, we obtain the relation between the bit error rate of the system and the signal-to-noise ratio based on the effects of the transmitter’s extinction ratio, platform jitter, and receiver noise. The simulation results show that the bit error rate is related to the normalized standard deviation with respect to platform jitter, the number of PPM orders, and the extinction ratio of the transmitter. Furthermore, the effects of pointing error on the performance of the communication system are independent of the extinction ratio of the transmitter. The system bit error rate does not necessarily decrease with the increasing number of modulation orders based on the analysis of the total power loss of the system. 16-PPM is the optimal choice in case of a commercial transmitter with an extinction ratio of 20 dB.

This study calculates the total phase variation of a hydrophone with a changing acoustic pressure in the sound pressure field according to the phase variation formula of the optical fiber hydrophone based on the Fizeau interference. Then, the effects of the horizontal and vertical postures and the depth of hydrophone on the acoustic sensitivity of each frequency are quantitatively analyzed through simulation. Finally, we use the vibrating liquid column method to test the experimental environment of the optical fiber hydrophone. Results show that the posture and depth factors have great influences on the final measurement results. The vertical posture of hydrophones in the frequency band of 40--2000 Hz produce a sensitivity error of approximately 0.9 dB--18.2 dB, and the sensitivity error caused by depth read deviation is within 4 dB compared those of hydrophones with horizontal posture. Owing to the acoustic pressure field difference in vertical placement conditions of hydrophone, the measured results are different from the horizontal placement results. Horizontal calibration results are more accurate than vertical results in acoustic pressure field test environment, furthermore, the measurement depth is greater, and the calibration results are more stable.

Faster-than-Nyquist technology can significantly improve the transmission rate of wireless optical communication system, but the atmospheric turbulence seriously affects the performance of faster-than-Nyquist wireless optical communication (FTN-OWC) system. In this paper, the influence of light intensity fading in exponential Weibull turbulent channel on the ergodic capacity and outage capacity of the FTN-OWC system is studied in detail. Based on pulse amplitude modulation, the ergodic capacity upper bound and outage probability of the FTN-OWC system are derived, and its closed-form expression is obtained by using the generalized hypergeometric method. In addition, the impact of acceleration factor, roll-off coefficient, turbulence intensity, and receiving aperture on the ergodic capacity and outage capacity is discussed. The results show that the ergodic capacity and outage capacity are reduced when the turbulence increases, but they can be improved by increasing the receiving aperture and roll-off coefficient. In the case of weak turbulence, the ergodic capacity of the FTN-OWC system is improved by 16.43% compared to the Nyquist wireless optical communication system using the same modulation method when the receiving aperture is 25 mm, the roll-off coefficient is 0.5, the acceleration factor is 2/3, and the average signal to noise ratio is 30 dB.

In this study, an analyzer assembly suitable for developing a midwave infrared thermal imaging camera is designed to improve the speed of traditional time-sharing infrared polarization imaging. Further, the model of the mid-wave infrared thermal imaging camera is converted into a midwave infrared polarization imaging device to obtain the infrared polarization information of the target scene. This device uses a motor to ensure that the infrared polarizer can rotate at a uniform speed of 900 r/min and collects infrared intensity images in different polarization directions. A single pixel non-uniform differential image correction method is used to remove the cold reflection of infrared images, and the iterative sorting method is used to process an image with the corrected infrared intensity. In addition, based on the constructed Stokes vector model, computing the adjacent three consecutive intensity of infrared image of the infrared polarization and polarization angle, assurance and the intensity of the infrared image has the same imaging frame frequency. Experiment results show that the aforementioned device can achieve stable output of the infrared polarization degree and polarization angle with respect to the target to be measured. The frame frequency of the output infrared polarization image is 45 frame/s, which is in accordance with the real-time infrared polarization requirements for moving target detection.

The traditional azimuth transmission technology based on magneto-optical modulation requires linear propagation of a beam and has a limited application scope. To solve this problem, a non-line-of-sight azimuth transmission technology is proposed based on polarization-maintaining fiber. First, the compositions of the system are introduced and the working principle of the system is presented. Then, by analyzing the effect of birefringence effect of a polarization-maintaining fiber on the phase difference of the transmission vector, a polarization-maintaining fiber Jones matrix containing phase difference is constructed. Finally, the Jones matrix is used to transform the Maxwell columns of the light vector, the azimuth solving model is derived, and the simulation analysis is carried out. The results show that the theoretical error of misaligned azimuth can be controlled within 0.1″ when the phase difference is not equal to π/2. In contrast, when the phase difference is π/2, the azimuth is always 0, and the error increases proportionally with the azimuth. The conclusion shows that the feasibility of this technique in azimuth transmission is confirmed. The proposed method extends the azimuth transmission mode and is of great significance to both the improvement of the non-line-of-sight azimuth transmission technology based on polarization-maintaining fiber and the improvement of the measurement accuracy of the system.

With the development of the digital projection technology, the three-dimensional (3D) measurement technology based on fringe projection is being widely used in many fields. However, in most application environments, there are various periodic light sources in most application environments, which cause interference to the imaging process of grating projection. Nonlinear errors are introduced in the phase extraction process, thus affecting the accuracy of 3D reconstruction. To solve this problem, the interference factors of the ambient light source are analyzed in the time domain, and the light source model is established by collecting and analyzing the images affected by the periodic ambient light. For this reason, a high-precision phase compensation algorithm is proposed. Experiments illustrate that the proposed algorithm can effectively suppress the phase nonlinear error caused by the environmental light sources.

This study presents an online size measurement method for burning particles based on the Fraunhofer diffraction theory. According to the spectral characteristics of medicinal strip combustion flame radiation in solid propellants, a blue-violet laser with a wavelength of 450 nm is used as the light source, and a filtering detection method with a passing band of 450 nm is used to eliminate self-luminous radiation influence of solid propellant combustion. An online measurement system for measuring the particle sizes of burning particles in solid propellants is developed. For calibrating this measurement system, standard particles with size of 10。9 μm, 160 μm, and mixed standard particles are measured. The combustion experimental results show that the size of burning particles in solid propellants are approximately 10 μm and 160 μm, presenting a bimodal distribution, and the number distribution is mainly concentrated around 160 μm. As the combustion time increases, the number of particles with a size of 10 μm increases and the number of particles with a size of around 160 μm decreases. For a solid propellant with same burning rate, the higher the initial measurement height, the smaller the combustion particle size. For measurements with same initial heights, there is no considerable difference in the average particle size of burning particles at different burning rates. This study provides a reference for the investigation of the solid propellant combustion process.

The measurement of circular feature on the components is an important aspect of quality control and automation in industrial manufacturing. Aiming at the problem of weak adaptability and weak robustness of measuring spatial circular pose based on computer vision principle, a measurement method based on linear structured light sensor is studied. According to the transformation relation between the ellipse on the image and the two quadric surface equations corresponding to the spatial circle, the normal vector of the circular hole is obtained. Then the circular hole plane is constructed by combining the vector and the three-dimensional coordinate data of the two intersection points of the laser line and the circumference. Experimental verification of the measurement method shows that,when the radius of the circular hole is within the range of 2--4 mm, the average error of the normal vector is 0.3°, the average error of the radius is 0.02 mm, and the average error of the coordinates of the center of the hole is 0.02 mm under the various attitudes of the line structured light sensor and the space circle. In the comparison experiment, the maximum radius error of this method is 0.04 mm for the circular hole whose radius of 3.054 mm, and the maximum error value of the old method is 0.23 mm.It is proved that the method can achieve high precision, wide adaptability and strong robustness in various situations.

In this study, a femtosecond laser cloud and fog transmission model, which considers the nonlinear optical effect, turbulence disturbance, and particle scattering, is established based on the concept of the stratified scattering medium transmission model. Further, the influence of atmospheric disturbances, including atmospheric turbulence and particle scattering, on dynamic evolution of the femtosecond laser transmission filaments is numerically studied. The results show that atmospheric turbulence can cause the pulse shape to change in an irregular manner; in addition, atmospheric turbulence significantly affects the pulse energy flow during the self-focusing filamentation process. The attenuation of pulse energy can be attributed to particle scattering, thereby affecting the formation process of optical filaments. As the femtosecond laser travels through the cloud and fog, the length of the optical filament will decrease, the energy attenuation during the filamentation process will be accelerated, and the total deposited pulse energy will increase with the increasing particle number concentration and particle radius. The results presented here can provide some theoretical basis to evaluate the efficiency of the femtosecond laser related applications under real atmospheric conditions.

Congruent lithium niobate (CLN) is the most commonly used terahertz parametric gain crystal. The terahertz-wave parametric source based on the CLN crystal has the advantages of high terahertz-wave output energy and continuous tunability, but its tuning range is relatively narrow, generally during 0.6-3 THz, which limits its practical applications. Therefore, an injection pulse-seeded terahertz-wave parametric generator based on 5% mol MgO∶CLN crystal is proposed. The terahertz-wave frequency tuning range is 1-4 THz, and the maximum output energy is 1.02 μJ at 2.0 THz. The 3 dB bandwidth of the output terahertz wave is 1.94 THz, accounting for 64.67% of the tuning range. The terahertz radiation source has the characteristics of broadband and flat gain, and has higher value in practical applications.

The structure of Cassegrain optical system severely limits its field of view (FOV). Generally, additional optical elements are needed to expand the FOV, but this approach leads to a complicated structure and does not facilitate a miniaturized and lightweight optical system. In this paper, a new method to expand the FOV of Cassegrain system using computational imaging was proposed. First, the structural parameters of the system were optimized to control the aberrations; then, a point spread function model was established; finally, a deconvolution algorithm was used to process the image. Eventually, the FOV of the Cassegrain system could be expanded using the structure that only comprised primary and secondary mirrors. A simulation experiment was conducted wherein a Cassegrain system with an F of 5.5 and 470-mm focal length was developed. The experimental result shows that in the FOV of 1.5°, the off-axis FOV modulation transfer function of the processed image is approximately improved by 0.2 at 20 lp/mm. Moreover, the quality of the image is significantly improved.

The focusing and leveling sensor is one of the key subsystems in lithography system. It is used to measure the height map of silicon wafers before exposure. The projection optics is the most important module of the focusing and leveling sensor, its' imaging quality directly affect the measurement accuracy of the sensor. According to the measurement principle of the sensor and aberration theory, the influence of magnification, distortion, tele-centricity, and resolution on the measurement accuracy of focusing and leveling sensor is analyzed. A reflective optical design is chosen for the projection optics, which has characteristics of simple structure, no chromatic, and small distortion. After the optimization and tolerance analysis by using Zemax software, the working wavelength of designed system is 600-1000 nm, root-mean-square radius of the diffuse spot is less than 0.189 μm within a field of view of 3 mm×26 mm, its magnification is 1.000, maximum distortion is 0.0008%, modulation transfer function is 0.74@33 lp/mm, and tele-centricity is 0.04 mrad. The results show that the reflective optical design for lithographic focusing and leveling sensor is engineering feasible with the current opto-mechanical manufacturing and assembling capability.

A multilayer rectangular absorber with wide band and high absorption rate is designed based on multilayer waveguide structure and hybrid coupling theory. The absorber unit is composed of a rectangular slot antenna and a multi-layer metal-dielectric-metal rectangular structure. We use finite-difference time-domain method to analyze the absorption characteristics of the multilayer rectangular absorber under the conditions of wide band, different polarization states and large angle oblique incidence. Numerical results reveal that the absorption band of the absorber is 400--1400 nm, and its average absorption rate can reach 95%, showing a certain polarization insensitivity, and it can still maintain an average absorbance of 93% at 60° oblique incidence. By monitoring the electromagnetic field distribution at the resonance frequency point, we find that the high-absorption characteristics of the absorber in a broadband which is mainly caused by Fabry-Perot resonance, slow-wave effects, local surface plasmon resonance, and the hybrid coupling among them. The proposed metamaterial absorber is expected to play a role in invisible devices, solar cells and other fields owing to its wide bandwidth, high absorption, insensitivity to polarization and oblique incidence angle.

In order to study the radiation damage mode and characterization of the camera system with CMOS active pixel sensor as the photosensitive element, this paper uses the method of on-line radiation experiment, combined with the radiation interference noise suppression algorithm, to study the change of color video image information with the total radiation dose, and discusses the radiation life of the hardware under the irradiation of different total radiation doses and the effect of γ-ray radiation on the digital image information. Results show that the mode of γ-ray radiation damage of the camera is mainly reflected in the light transmittance decrease caused by the radiation damage of the lens, the dark current increase, distortion and damage of the sensor, and the instantaneous damage of the main board. The total radiation dose effect of the sensor mainly results in the increase of background noise, and most of the noise signals are concentrated in the dark part of frames. The increment of the average pixel value in the gray stripe of the image caused by the dark current is far less than the decrease of the average pixel value caused by the lens radiation damage. The exposure compensation function of the camera will carry out global compensation processing after detecting the decrease of video image brightness, which increases the pixel values of all pixels. The relationship between the video image information and total ionizing dose can be used as a method to calibrate the failure probability of the CMOS active pixel sensor camera, which can improve the reliability of the application for this kind of video monitoring system in the radiation environment.

Polarization control can effectively recover the polarization state shifted from the polarization phase drift during the fiber transmission, which is a key technology in quantum communication, optical fiber sensing, and coherent optical communication. In this paper, we propose a polarization control algorithm based on adaptive moment estimation (Adam) and establish a polarization control system model. Based on this model, the Adam polarization control algorithm is simulated and compared with classical stochastic gradient descent (SGD) algorithm, at the same time, the influences of control precision and noise amplitude on polarization control effect are analyzed. Simulation results show that the global optimal polarization state can be rapidly obtained by employing the proposed method. When the attenuation rate is 0.03, the noise amplitude is 0.003, and the number of polarization iterations is 53, the control precision is up to 10 -4. Compared with the SGD algorithm, the average iterative steps are reduced by 23% and the maximum control accuracy can be improved by 1--2 orders of magnitude. The feasibility of Adam algorithm is verified by field programmable gate array. The proposed algorithm can quickly and stably compensate the polarization change in the channel, and the polarization control time can be effectively shortened by optimizing the value of attenuation rate.

In response to the needs of micro-displays for red LEDs with high external quantum efficiency, low operating current, and stable spectral wavelength,a Micro-RCLED that combines resonant cavity light-emitting diodes with AlAs lateral oxidation technology is realized. The device changes the spatial distribution of the spontaneous radiation field in the active region by a resonant cavity to concentrate more light within the light extraction angle to improve the light extraction efficiency, meanwhile, the resonant cavity is also beneficial to deminish the shift of the optical spectrum. The lateral current confinement to the AlAs oxide aperture can not only decreasing the Shockley-Read-Hall non-radiative recombination due to the sidewalls defects, but also reducing the leakage current so to improve the radiative recombination efficiency. In addition, the diameter of the light exit aperture of the P electrode is larger than that of the AlAs oxidation aperture, so that the absorption of the outgoing light by the P electrode can be effectively avoided. The 655 nm Micro-RCLED with 3 units parallel connected is fabricated, in which each unit has an exit aperture of 17 μm diameter. Fitting result of IdV/dI-I shows a reasonable 120 Ω series resistance. The output optical power of the device at 1 mA is 0.21 mW, the external quantum efficiency is greater than 10%, and a single unit can be lighted up at an injection current lower than 1 μA. In addition, when the working current density changes by 12.5 times, the peak wavelength only increases by 1.5 nm, and the full width at half maximum of the spectrum increases just 0.33 nm.

This paper proposes a method combining external modulation technology and master-slave injection-locking technology to obtain a broadband linear-chirped laser source, and the laser source is used to realize a frequency modulated continuous wave light detection and ranging (LIDAR) system for simultaneous distance and speed measurement. The master-slave injection-locking system includes a narrow line-width fiber laser as the master laser and a distributed feed-back (DFB) semiconductor laser as the slave laser, and their wavelengths are both about 1550 nm. A triangular linear-chirped microwave signal with a frequency range of 8--14 GHz is used to modulate the output from the master laser, and then the modulated laser is injected into the DFB semiconductor laser to obtain a broadband linear-chirped laser with a 6 GHz bandwidth and a side-mode suppression ratio over 20 dB. We build a frequency modulated continuous wave LIDAR based on the laser source. Using this system, we perform the distance measurement of static objects and the instantaneous measurement of distance and speed of a moving object. The distance and speed of a moving object are obtained by different formulas and verified with each other. The distance and speed resolutions are 2.5 cm and 7.8 mm/s, respectively.

This study reports a method for the calibration of onboard polarization based on sun glint. First, a rough-surface ocean model was used to analyze the polarization radiation characteristics of the sun glint from the ocean. For radiation transmitted through the atmosphere, the 6SV radiation transmission model was used to calculate the polarization characteristics at the top of the atmosphere (TOA). Further, to correct the effects of aerosols, a correction formula for TOA polarization was proposed; the t test was used to verify the significance of the new quadratic term of the correction formula. Finally, the correction coefficient lookup table for solar zenith angles was established to calculate the simulated degree of polarization. Using polarization data obtained from the radiance observed by POLDER 3, the relative error was verified to be less than 2%. Compared with the degree of polarization observed by the multi-angle polarization imager (MAPI), the polarization calibration accuracy was approximately 2%, which meets the requirements of the instrument polarization precision. The uncertainty showed that the synthetic uncertainty of polarization obtained using this method was 1.43%.

In this study, a multilayer perception convolutional neural network (MPCNet) was proposed for the pixel-level classification of multispectral remote sensing images, which combines the spectral information and spatial structure features of pixels. The performance of a land-cover-classification algorithm was tested based on the Jilin-1 spectral satellite (Jilin-1GP) images in the Nashik research area, India. To ensure high reliability of the experiment, the Landsat8, Sentinel-2A, and HJ-1A images were used within the same time interval for synchronized classification to perform qualitative and quantitative evaluations. Moreover, three current popular algorithms, namely, support vector machine(SVM), LightGBM, and shallow convolutional neural network(CNN), were selected to compare the algorithm performance. The experimental results indicate that the overall classification accuracy on the Jilin-1GP images can reach 94.0%-95.8%, and the Kappa coefficient can reach 0.932-0.948. The overall classification accuracy of the MPCNet increase by 3.7 percentage compared with that of the shallow CNN, which exhibits high accuracy.

In this study, a cluster-cluster aggregation (CCA) model was used to form 4-sphere and 16-sphere aerosol aggregate models for different numbers of soot aerosol particles. By combining the hygroscopic nature of individual aerosol particles and the fractal theory of aerosol aggregates, a model for aerosol aggregates covering a water layer was generated. The scattering characteristics of soot in the coating layer were simulated and analyzed using the discrete dipole approximation (DDA). Simulation results show that an increase in relative humidity has the greatest influence on the extinction, scattering, and absorption of aerosol aggregates with a rotation radius ≤40 nm. Furthermore, the influence of aerosol aggregates and relative humidity on the UV pulse response and path loss was analyzed using a single-scattering pulse response model. The simulation results show that the effects of aerosol aggregates and relative humidity on UV communication are concentrated on monomer particles with smaller radii (r0≤40 nm). When the radius of the monomer particles is fixed, if the number of particles forming a cluster or the relative humidity of the aerosol aggregates increases, the pulse response is larger, the path loss is smaller, and the signal at the UV receiver is better.

In this study, the equivalent film theory is used to develop a polarization- and phase-modulated mirror with target wavelengths of 780, 810, and 850 nm and an incidence angle of 45°. Apart from achieving polarization and phase modulation, the obtained mirror can ensure the high reflectivity of the thin films. A metallic material (Ag) and two dielectric thin film materials (such as Ta2O5 and SiO2) are selected as the film materials to obtain high reflectance over a wide waveband. The mirror film system is fabricated on an optical glass substrate (JGS-1) using the electron beam evaporation, thermal evaporation, and quartz crystal oscillation monitoring technologies. The measured spectra of the mirror film system denote that the average reflectance is greater than 95% in the wavelength range of 500--1600 nm and the extinction ratios at the target wavelengths exceed 3000∶1, 5000∶1, and 7000∶1. Thus, the proposed mirror satisfies the reliability requirement associated with space-to-ground quantum communication.