In order to study the influence of the solar radiation diffuse distribution on the measurement of sunshine duration, based on atmospheric radiation transmission theory, the Sigmoid function models of diffuse fraction, clearness index, and atmospheric optical quality are established by Taylor series expansion. Using the training dataset of radiation data with different time scales, the mathematical model of the diffuse fraction varying with the clearness index and the atmospheric optical mass is obtained by nonlinear fitting, and the one-dimensional model S0 and the two-dimensional model S1 are given. Based on the solar radiation data from different observation sites, the diffuse fraction is calculated by the Sigmoid model. The correlation coefficient between the measured and calculated values, mean deviation, root mean square error, and t-statistic are analyzed. The results show that the correlation coefficient between the diffuse fraction calculated with the Sigmoid model and the measured value is above 0.8, the average deviation is within ±0.2, the root mean square error is within 0.25, and the minimum t-statistic is as low as 0.0172. This study provides a new thought for the construction of the solar radiation diffuse distribution model, and the next step should introduce more extensive radiation data to study the applicability of the model across regions.

Based on the three-dimensional (3D) split-ring resonator (SRR) array and microfluidic channel, a high-sensitivity refractive index sensor based on a metamaterial (MM) absorber is realized in the terahertz (THz) band. The 3D SRR array is completely immersed in the microfluidic channel. The liquid-phase analyte in the microfluidic channel serves as the intermediate layer of the MM absorber while serving as the analyte to be measured. When the height of the microfluidic channel is fixed at 33.1 μm and the refractive index of the liquid-phase analyte injected into the microfluidic channel changes from 1.0 to 1.8, the THz MM absorber can be used as a refractive index sensor, and the refractive index frequency sensitivity reaches 379 GHz/RIU. Simulation results show that the resonant electromagnetic (EM) field of the THz MM absorber sensor is extended to 3D space, and is greatly concentrated and enhanced in the microfluidic channel, thereby realizing the spatial overlap of the resonant EM field and the analyte to be measured. The interaction between the resonant EM field and the measured analyte is enhanced, and thus the high-sensitivity sensing of liquid analytes is achieved. The influences of the height of the microfluidic channel and the thickness of the top-layer covering dielectric on the refractive index sensitivity of the MM absorber sensor are also studied based on CST Microwave Studio simulation software. In short, the THz MM absorber sensor based on the 3D SRR array and microfluidic channel has a higher quality factor and refractive index frequency sensitivity, and has potential applications in label-free fast biomedical sensing.

Excessive solar UV radiation can cause erythema on human skin and even skin cancers in severe cases. In this paper, we study the solar erythemal UV radiation and UV spectra in the Mount Everest region (Tingri), Lhasa, and Nyingchi of Tibet by using a NILU-UV irradiance meter and a RAMSES-ACC-UV spectrometer during the period from January 2014 to December 2018. In addition, we observe the characteristics of solar UV spectra in Lhasa at local noon near the vernal equinox and autumnal equinox and at the winter solstice and summer solstice. We figure out that almost all the solar UV radiation with wavelength less than 300 nm is absorbed by the atmosphere and can not reach the surface of Tibet. Based on the analysis of solar erythemal UV radiation doses on clear days measured in Tibet, we find that only UVB causes the human skin erythema. Moreover, the field observation data show that the dose rate of solar erythemal UV radiation on clear days in Tibet changes in a typical parabola shape with the time of the day. Moreover, the average occurrence time of the maximum dose rate is about 10 min around the local noon as the solar altitude angle increases. In theory, the solar erythemal UV radiation intensity on clear days rises day by day from the winter solstice and reaches the highest value at or near the summer solstice in Tibet. However, in fact, the peak intensity on clear days during the observation period generally appears at the end of March due to few clear days in the summer of Tibet. The research results disclose that the maximum dose rates of solar erythemal UV radiation on clear days in the Mount Everest region (Tingri), Lhasa, and Nyingchi during the observation period from the winter solstice to the summer solstice are 113.40--343.10 mW·m -2, 85.26--344.2 mW·m -2, and 62.78--197.10 mW·m -2, respectively, in contrast, the total maximum daily doses reach 7181.00 J·m -2, 7623.00 J·m -2, and 3994.00 J·m -2, respectively. These indicate that skin erythema is easily induced in Lhasa and the Mount Everest region (Tingri).

In this study, we used a single optical modulator to generate multiple path wireless and wired signals. We successfully transmitted two channels of 5 Gbaud quadrature phase-shift keying (QPSK) wireless signal and one channel of 5 Gb/s binary amplitude on-off keying (OOK) baseband signal over 80-km single-mode fiber (SMF). By employing dual-polarization Mach-Zehnder modulator, power divider, optical filter, and other devices, we realized the dual services of multi-channel wireless and wireline signals with high-frequency efficiency and simple structure. This method reduces the influence of signal interference and optical fiber dispersion effect, avoids the limitation of transmission distance, and improves the reliability of the system. The experimental results show that the power penalty of 5 Gb/s OOK baseband wireline signal after 80-km SMF transmission is only 1 dB, and the power penalty of 15 GHz and 30 GHz signals carrying 5 Gbaud QPSK after 80-km SMF transmission are 2 dB and 4 dB, respectively.

Dielectric metallic hollow waveguides have attracted wide attention as flexible gas absorption cells for spectroscopic gas sensing. Advantages of the hollow waveguide include low loss, stable coupling with the optical transmission system, strong anti-interference ability, and a small sample volume. A spectroscopic gas sensing system was established using the Fourier infrared spectrometer (FTIR) and the flexible waveguide absorption cell. Durability characteristics of the waveguides were studied experimentally for various waveguides in alkaline gas, acidic gas, and volatile organic solvents. Loss properties of the hollow waveguide were measured before and after the corrosive treatment. Damage was evaluated and the degradation mechanism was discussed. The applicable sensing bands and corrosive environments of various commonly used waveguides were summarized systematically. Helpful choices are provided in the design and production for engineering application of the waveguide as the absorption cell.

To handle the problems of illumination change, mutual occlusion of objects, and complicated semantic categories in indoor scenes, a color-depth (RGB-D) image semantic segmentation method based on the dual-stream weighted Gabor convolutional network fusion is proposed in this work. In order to obtain direction and scale invariant features, a weighted Gabor direction filter is designed to construct a deep convolution network (DCN) to extract feature information that is adaptive to direction and scale changes. In order to build a lightweight feature extraction network, a wide residual weighted Gabor convolutional network module is used to extract color and depth dual-stream image features, and a pyramid pooling module is used to fuse the extracted depth features to enrich the image context information. The proposed semantic segmentation method is tested on NYUDv2 dataset, and different comparison methods are set up. The results show that the proposed method is reasonable and effective, and the segmentation effect is competitive.

This study proposes a multi-pose face recognition method with a two-cycle generative adversarial network to address low face recognition accuracy of non-frontal poses. The network consists of two aspects: face frontalization and face rotation. The face frontalization aspect converts profile faces to frontal faces and implements many-to-one pose category mapping. The face rotation aspect converts frontal faces to profile faces with specified poses, extracts the identity features of the frontal faces, and implements one-to-many pose category mapping. To further improve the face recognition of profile poses, two cyclic paths are used to combine the face frontalization and face rotation processes. One path is used for the cyclic conversion of profile faces to frontal faces and then to profile faces, and the other path is used for the cyclic conversion of frontal faces to profile faces and then to frontal faces. To reduce the difficulty in the training process and speed up the convergence of the network, the training process will be performed in two different stages: partial and complete training. Experiment results on Multi-PIE and CFP show that this method can effectively improve the recognition accuracy of profile poses.

This paper proposes a de-hazing and enhancement method for underwater and low-light images to effectively enhance the images. Multi-scale Retinex color recovery (MSRCR) and guided filtering methods are used for de-hazing; super-resolution convolutional neural network (SRCNN) and non-subsampled contour transform (NSCT) technology are combined to enhance the image. Experimental results show that compared with similar existing image processing methods, this method can effectively improve the image exposure, and at the same time, it can sufficiently preserve and enhance the color saturation and edge texture details of images. It uses a unified method to achieve the enhancement of underwater and low-light images, and the results are more efficient, which has a good visual effect.

A multi-angle polarization imager (MAPI) can obtain multi-spectral and multi-angle polarization information, which is used to retrieve the microphysical properties of aerosols and clouds. Polarization high-precision detection requires accurate polarization calibration. Since MAPI is without an on-orbit calibrator, we use natural scenes as the sources of polarization calibration. A full-field on-orbit polarization calibration model is established, and the polarization characteristics of water clouds are analyzed. Water cloud pixels with a scattering angle of 100°are selected as unpolarized calibration sources. The relative transmittance of the polarizer-filter combination, the polarization degree of the optical lens, and the low frequency relative transmittance required by the polarization response matrix are solved, and finally the polarization response matrix of the full image is calculated. The average value of relative transmittance of the polarizer-filter combination for three years is analyzed and verified by laboratory calibration results. The relative error is 0.71%. The least squares method is used to fit the variations of the polarization degree of the optical lens and the low frequency relative transmittance with the angle of view. The laboratory polarization calibration results are used to verify that the relative error of the central field of view is 1.22%. The uncertainty of the algorithm is analyzed. The synthetic uncertainty of the central field of view and the marginal field of view is 1.27% and 2.19%, respectively, which meet the design specifications. The calibration method can be used as a reference for the on-orbit calibration of wide-field polarized imaging devices, and provides quality assurance for aerosol inversion.

The traditional method is to establish a mapping calculation from the light field to the display surface to generate elemental images, but there will be a lot of redundancy. To solve this problem, an iterative algorithm along a mapped light path is proposed so that a single shot from an elemental image display surface to a reconstructed light field can be established. Each pixel in an elemental image only corresponds to a unique light-field pixel, which can improve the pixel matching accuracy and eliminate a depth void at a step. The core of the proposed algorithm is based on each point on a display surface of an elemental image as the starting point, passing through the optical center of a lens as a ray through an iterative search to find the intersection of the ray and light field surface closest to an observer. Such an intersection is used as the matching point of the elemental image. The time complexity of the proposed algorithm is mainly controlled by the sum of pixels of an elemental image array. Calculation and generation rates of elemental images using the proposed algorithm are usually more than eight times those of the existing algorithm. An advantage of the proposed algorithm is that the total number of pixels in the image is directly proportional to the speed of the algorithm. The experimental results verify the correctness of the theoretical statements emphasized in this study.

A precise tilt platform driven by piezoelectric ceramics and the control method for tilt angle are designed to achieve high precision tilt control. The control system is mainly composed of a main controller, a displacement detection module, a digital-to-analog conversion module, and a high-voltage driving module, which can realize fast and precise tilt control. The method combining the ball lens and the position sensitive sensor is used to measure and control the tilt angle of the precise tilt control platform. Experimental results show that the control precision of the platform is better than 0.5 μrad, and the structure is simple and easy to install. It is especially suitable for engineering application environments that have the requirements of precise tilt control and low cost.

Long-distance and high-precision range and attitude measurements are key technologies in fields such as aerospace remote sensing, target recognition, and navigation control. Here, we theoretically and experimentally study the second-order correlations of the thermal light field for deep Fresnel-zone ranging, and we achieve a precision of 0.5 mm. In addition, we demonstrate with a proof-of-principle simulation experiment that this ranging method can be utilized to measure the target attitude. This method, which can achieve high-precision range measurements over long distances, can be used as a supplement to traditional laser-ranging technology. This method can employ natural light sources such as stars light to measure distance and attitude, and has less demand for energy and other resources. It can provide a new solution for satellite positioning and other space ranging needs.

By optimizing the doping distribution of the waveguide structure and the P-cladding layer, the overlap between the optical field and the P-cladding layer doped area is reduced, thereby reducing the internal optical loss of the semiconductor laser. At the same time, the use of wide band gap GaAsP as the barrier layer reduces the carrier leakage in the active region and achieves an internal optical loss of 0.259 cm -1. The prepared single emitter device with a wavelength of 975 nm, a stripe width of 100 μm and a cavity length of 4 mm has a continuous-wave output optical power of 21 W at room temperature. When the output power is 20 W, the power conversion efficiency is still greater than 50%.

The method to increase the core diameter of a crystal waveguide laser with high beam quality is theoretically investigated and experimentally verified. Through the simulation calculation of the relative gain of each guiding mode and considering the mode competition, the fundamental mode cut-off thickness of the core layer can reach 360 μm, twice of that by the traditional calculation method, when 1.0% Yb∶YAG is used as the core material and 0.5% Er∶YAG is used as the inner cladding material. A crystal waveguide with a core size of 400 μm×320 μm×77 mm is fabricated by diffusion bonding, and a waveguide laser is constructed. The maximum output power of this waveguide laser is 31 W, the conversion efficiency from light to light is 55.3%, and the near-diffraction-limited laser output with beam quality of 1.2×1.05 is obtained. The experimental results show that it is reliable to calculate the core diameter of the fundamental mode of a crystal waveguide by mode competition.

With the widespread use of unmanned aerial vehicle (UAV) technology in military, civilian, and other fields, the demand for high-precision, low-power intelligent UAV tracking systems is also increasing. Aiming at the problems of scale variation, out-of-view, and occlusion in UAV tracking tasks, a real-time tracking algorithm for UAV based on light-weight Siamese network was proposed. Firstly, the lightweight convolutional neural network MobileNetV2, which is easy to be deployed in embedded devices, is selected as the feature extraction backbone network. Secondly, the channel spatial coordination attention module is designed to enhance the adaptive and discriminative ability of the model. Thirdly, the region proposal network is equipped, and the foreground background classification and boundary box regression response map are obtained through correlation. Finally, the weighted fusion multilayer response map is calculated and proposal region screening strategy is adjusted to obtain more accurate tracking results. Simulation experimental results on the UAV tracking dataset show that the tracking accuracy is improved by 3.5% compared to the current mainstream algorithm SiamRPN, and the algorithm can better cope with complex and changeable scenes. Meanwhile, on the NIVIDA RTX 2060 GPU, the tracking speed achieves 60 frame/s.

Aiming at the fact that the pose parameter measurement of moving targets in a large field of view is susceptible to factors such as model cumulative error, imaging distortion and insufficient feature information, a new vision measurement method is proposed. First, an efficient multi-source feature data fusion model is established, and it suitable for the visual measurement process, which can solve the problem of single feature point. Then, a bidirectional closed measurement mode based on feature point cloud information is build, which changes the one-way transfer process from image data to spatial feature information in the traditional method, and returns the confirmed spatial data as control information to the measurement process, which can effectively avoid the larger the measurement space, the larger the cumulative error of the measurement model. Finally, the experimental results show that the proposed method achieves a target attitude measurement accuracy better than ±1.5° in a large field of view space of 10 m×8 m×3 m, and the position accuracy is better than 2 mm. The obtained measurement results verify that the target pose parameters obtained by the bidirectional closed cloud control measurement mode have high accuracy and strong stability, and can meet the actual engineering application requirements.

We fabricate a micro-rod cavity with an ultrahigh Q-factor on a fused silica rod via CO2 laser, and investigate the effects of micro-rod curvature, coupling position, and radius of tapered fiber at coupling position on number of excited modes, Q-factor and coupling efficiency. Through optimizing the parameters in the fabrication and coupling process and exciting a few modes with ultrahigh quality factors, one can avoid mode crossing, thus generate a soliton frequency comb with a smooth envelope at different wavelengths.

Existing plant light source systems do not provide a sufficiently high-quality lighting environment for optimal plant growth, the theory of spatial illumination uniformity is proposed. The plant light source system with multiple light source modules is adopted to achieve high spatial illumination uniformity and color-mixed uniformity in the plant growth space. The multi-light source module is composed of inverted light source, straight down light source and central light source in the growth space. The experimental process is simplified according to the Taguchi theory and the key factors are optimized in conjunction with an analysis of varianceto find the optimal plant light source system. The shape and spacing of LED beads are further optimized to obtain a three-dimensional plant light source system with the illumination uniformity of horizontal and vertical planes of 91.35% and 89.71%, and color-mixed uniformity of 87.67% and 88.54%, respectively. Plant growth is simulated and tested in kind, the experimental results show that the three-dimensional plant light source system can provide high-quality lighting effects for the entire plant growth space.

This study proposes a design method combining variable density topology optimization and multi-objective integration optimization with minimum size constraints for the overall design of multispectral cameras, adhering to the design concept of integration, miniaturization, and ultra-lightweight. This approach is used for spatial separation, and the optimized design of an axis microcrystalline mirror and a back support structure (heat dissipation mandrel, flexible joint, and backplate). The mirror has an aperture of 218 mm×166 mm, mass of 0.917 kg, and weight reduction rate of 71.3%. In addition, the processed and assembled reflector components are subjected to engineering environmental tests and surface interference detection. Test results show that the root mean square value of the mirror surface before and after the environmental test is greater than 1/50λ, detection wavelength λ=632.8 nm, and fundamental frequency is 397.8 Hz, meeting the design requirements of an optical system and optical satellite platform. Load requirements validate the feasibility and accuracy of the proposed method.

Owing to the large errors in the calculation of glint gain in the existing glint recovery algorithms for remote sensing images, the need for near-infrared band information assistance, and the insufficient utilization of remote sensing image information, a glint-detection algorithm based on the water index and chromaticity-separation method and a glint image based on discrete cosine transform are proposed herein. For the proposed recovery algorithm, first, the chromaticity-separation method is used to extract the highlighted areas of the image that are suspected of glint. Then, the scattered points and isolated areas are removed by combining the water index with an area threshold and morphological filtering so as to achieve precise positioning and extraction of the glint area. Then, an optimization function is constructed based on the fidelity and local smoothness of the image, and the discrete cosine transform is used to iteratively solve the pixels inside the glint region of the remote sensing image. Finally, the restored image is obtained. Furthermore, the field flight experiments are conducted. Experimental results show that the proposed algorithm can accurately extract and restore the image water glint area, and the effect of the restored image in terms of texture and spectral characteristics is improved.

To achieve efficient aggregation of gold nanoparticles, obtain high-sensitive surface-enhanced Raman scattering (SERS) substrates, and study the photothermal effect of laser on the gold nanoparticles, a set of optical manipulations combined with a micro Raman spectroscopy system was developed, which has the combined functions of micro imaging, SERS detection, and optical manipulation. The influence of the photothermal effect on the gold nanoparticles in a solution and the SERS signal enhancement effect of pyrene were studied. Theoretically, the electric field enhancement effects of aggregated and single gold nanoparticles are calculated using the finite difference time domain (FDTD) method. The results show that the gold nanoparticles in the solution formed aggregates on the surface of the quartz substrate due to the thermophoretic force and convection, and their aggregation speed was affected by the temperature of the environment. The intensity of the SERS signal of the analyte pyrene increased with an increase in the aggregation time, and its stable SERS signal intensity was 15 times stronger than that of the gold colloid solution. FDTD simulation shows that gold nanoparticle aggregates would yield a higher SERS enhancement factor than single gold nanoparticle, the enhancement factor of the aggregates was 1.30×10 7. This study employed the photothermal effect to achieve optical manipulation of gold nanoparticles (large-scale and high-efficiency capture of gold nanoparticles). This method can significantly improve the SERS effect of gold nanoparticles and has potential in detection and analysis in fields such as chemistry and biology.

Aiming at the integrated interferometer components with glued grating, this paper proposes a system-level flat-field correction method based on high frequency heterodyne interference modulation data formed by flat-field correction filter. A calculation method for the frequency range of heterodyne interference required for the flat-field correction (i.e., the spectrum range of flat-field correction filter) is given based on the principle of interference modulation of spatial heterodyne spectroscopy. The main technical specifications of the flat-field correction filter are determined by theoretical and numerical analyses, and are subsequently verified by experiments. The experimental results show that the average signal-to-noise ratio of the recovery spectrum is increased by 115.7%, and the suppression of fixed frequency noise and high-frequency spectrum distortion are particularly notable.

As a new common material fabrication technique, Ge/Si heterogeneous wafer bonding exhibits enormous potentials in the fabrication of high-quality Si-based Ge films. It is also regarded as an alternative solution for the fabrication of high-performance Ge/Si photoelectric devices. However, there easily exists a nanometer GeO2 oxide layer at the Ge/Si bonded interface fabricated by the direct bonding or plasma bonding method. This leads to the formation of an interface state at the Ge/GeO2 and GeO2/Si semiconductor-insulator contact layer, which in turn affects the performance of the device. A low-temperature Ge/Si bonded interface is constructed based on the three carrier transport equations, the non-local tunneling model, and the semi-classical quantum solution. The effect of the interface state density (ISD) on the carrier electrical transport, light absorption, recombination, and high-frequency response is studied. The results show that with the increase of ISD, the dark current of the Ge/Si heterojunction increases. At the same time, the carrier capture effect becomes more obvious, leading to the decrease in the total current and the spectral response. In addition, the increase of ISD leads to the worsening frequency response and the decrease in the electric field within the Ge layer. Moreover, the ISD must be smaller than 1×10 12 cm -2 to obtain a high-performance Ge/Si bonded heterojunction. These results may give a theoretical guidance for the fabrication of high-quality Si-based Ge films and high-performance Ge/Si photoelectric devices.

Full composition range AlGaN refers to AlGaN with an Al composition of 0-1. In this paper, the composition is introduced into the complex refractive index of AlGaN, and a complex refractive index formula for full composition AlGaN is established in the spectral range of 200-800 nm. The optical parameters of sapphire are obtained by ellipsometry and verified by the transmission spectrum. The complex refractive index formula and the multilayer optical film filter model are used to study the transmission spectra of the multilayer AlGaN samples on sapphire substrates. The effect of each film on the transmission spectra of samples and the possible shift of an actual structure caused by the process are analyzed, and a fast analysis method is thus proposed for the transmission spectra of multilayer films.

The influences of the analyzed crystal bandwidth and the angular divergence of focused beams were eliminated by the high-index lattice plane diffraction, and a method for energy bandwidth measurement of focused beams was proposed. In addition, a DuMond diagram was used to analyze the measurement process of energy bandwidth, and a detection system was built on the hard X-ray spectroscopy beamline at the Shanghai Synchrotron Radiation Facility. Furthermore, the different high-index lattice planes of crystals were employed for the energy bandwidth measurement of focused beams under the same energy and diffraction angle. Besides, in the context of 10 keV beam energy, the change of energy bandwidth during the bending process of the collimating mirror was measured by Si(555) and the optimal energy bandwidth measured in the non-dispersive configuration of Si(555) was 1.50 eV, with a difference of less than 10% from the calculated value (1.40 eV) by the Shadow tracker. The results demonstrate that the high-index lattice plane diffraction of crystals can be used for the high-precision energy bandwidth measurement of synchrotron radiation focused beams.