When the vortex beam passes through atmospheric turbulence, the wavefront will be distorted, and the distorted wavefront needs to be corrected. The wavefront distortion correction system of wavefrontless sensors based on the stochastic parallel gradient descent algorithm can realize the correction of wavefront distortion, but the convergence speed and stability of the algorithm are affected by the random disturbance voltage. Combined with the improved gradient descent algorithm in deep learning theory, the iteration method of the random disturbance voltage in the stochastic parallel gradient descent algorithm is adjusted in this paper, and the correction effect of the improved algorithm under different turbulence intensities is analyzed. The simulation results show that the improved algorithm based on RMSprop is preferred under weak turbulence condition. Under moderate turbulence and strong turbulence conditions, it is necessary to consider the stability of the algorithm, the value of the performance evaluation function, and the convergence speed in accordance with actual requirements, and then select the appropriate correction algorithm.

On the basis of the survey data collected over eight cruises from 2006 to 2015 in the South China Sea, the correlation features between the spectral absorption coefficient of phytoplankton and the typical pigment concentrations in the South China Sea were investigated by the derivative spectral analysis method, and partial least squares (PLS) regression models were then developed for estimating the pigment concentrations. The study results show that the derivative spectral variation of phytoplankton absorption coefficients can be used for quantitatively estimating the key pigment concentrations, and the estimation results based on the second-order derivative spectra are slightly better than those based on the fourth-order spectra. The proposed models achieve high accuracy for TChl a, PSC, Fuco, 19But, 19Hex, and Diadino, with a high linear correlation between the predicted and measured values. However, the estimation accuracy of PPC and Zea is relatively low. Compared with the empirical models based on the TChl a concentration, the PLS regression models based on derivative spectra have an equivalent effect on estimating the pigments such as PSC, Fuco, 19Hex, and Diadino, and show certain advantages for 19But, PPC, and Zea. The internal relationship between the concentration of different types of pigments and the derivative spectra of absorption coefficients may be an important factor for the difference in the estimation accuracy of different pigments. In conclusion, the method of quantitatively extracting the pigment concentration by the derivative spectra based on the phytoplankton absorption coefficients established in this paper can provide a reference for deeply investigating the hyperspectral remote sensing of phytoplankton population structures based on the ocean color satellites.

This study establishes a whole-process simulation model of a coherent wind lidar considering the transmission process of the lidar's optical detection path and atmospheric stratification theory. Using the existing system parameters, we simulate the detection process under two models: a constant wind speed model and the typical wind shear model of NASA. We also consider two systems: a high-pulse energy low-pulse repetition frequency (HPE-LPRF) system and a low-pulse energy high-pulse repetition frequency (LPE-HPRF) system. The detection performances of both systems are compared by computing the mean square error of their inversed wind speeds. The simulated signal-to-noise ratios of both systems well agree with the theoretical values. The accuracy of the measured wind speed is improved by incoherent accumulation average process. At an incoherent accumulative time of 0.1 s, the mean square error of the wind speeds detected under the constant wind speed model and NASA shear model is lower in the LPE-HPRF system (0.75 and 1.03 m/s, respectively) than in the HPE-LPRF system (0.93 and 1.25 m/s, respectively).

In this paper, the supercontinuum generation of picosecond pump pulses in the medical photonic crystal fibers with normal dispersion were simulated using the split-step Fourier method, and the influences of the center wavelength, peak power, width, and shape of the pump pulses on the supercontinuum characteristics were studied. Furthermore, the parameters of the pump pulse source were optimized for optical coherence tomography, improving the longitudinal resolution and imaging quality of the light source. The results show that for medical photonic crystal fibers with pump center wavelengths of 1.06 μm, 1.31 μm, and 1.55 μm, in the case of the same parameters, the 1.55 μm pump pulse generates a larger bandwidth, and the 1.31 μm pump pulse obtains a smaller longitudinal resolution. In addition, for the 1.55 μm fiber, when the peak power and width of a hyperbolic secant pump pulse are 20.5 W and 2 ps, respectively, the longitudinal resolution is 5.0 μm. Moreover, when the pulse width is 0.5 ps and the peak power is 18 W, the longitudinal resolution is 3.7 μm. Compared with the Gaussian, hyperbolic secant, and chirped Gaussian pump pulses, the super-Gaussian pump pulses can obtain a wide and flat supercontinuum light source.

To deal with the problem of polarization demultiplexing in coherent optical communication systems for probabilistically shaped scenes, this paper proposes a polarization demultiplexing algorithm based on independent component analysis and maximum likelihood estimation. Due to the independence between the signals, the polarization demultiplexing of signals can be realized by the independent component analysis. The iterative update based on maximum likelihood estimation is used to find the best separation matrix, which is the polarization demultiplexing matrix. The performance of the algorithm under different optical signal-to-noise ratios and the tolerance of the shaping intensity are simulated and analyzed. The results show that the proposed scheme can cope with different probabilistically shaped intensities, and can achieve good polarization demultiplexing in a large optical signal-to-noise ratio range. Compared with the constant modulus algorithm for standard signals, this scheme will not be affected by the shaping intensity. As the shaping intensity increases, the performance of the system can be improved.

A precoding scheme based on single-end channel estimation is proposed to mitigate crosstalk in received signals in intensity modulation direct detection (IM-DD) mode group division multiplexing transmission system based on photonic lantern. The scheme uses a signal feedback mechanism which is made up of a circulator and a splitter. Signals in receiving ends will return to the transmitting end for single-end channel estimation and the channel transmitting matrix will be used for precoding. The experimental results show that after the precoding processing in the back-to-back and 500-m few mode fiber mode group division multiplexing transmission systems, the transmitted power of LP01--LP01 and LP11a--LP11b channel signals can be reduced about 3 dB and 1 dB respectively when the bit error ratio (BER) is at the threshold of 1.3×10 -2 forward error correction (FEC). This paper provides an effective solution to reduce signal crosstalk in point-to-multipoint IM-DD mode group multiplexing transmission.

The curved-prism-based hyperspectral imaging technology has become a research hotspot in recent years. However, the non-coaxial characteristic of two spheres in a curved prism makes the fabricating procedure of a curved prism far harder than that in a traditional coaxial optical system. Fabricating error is the key factor influencing the final imaging quality of a spectrometer. At present, the modulation transfer function (MTF) is mostly regarded as an important evaluating indicator, however it does not consider the effect of fabricating error on spectral distortions including spectral smile and keystone. In this paper, the generation mechanism of spectral smile and keystone of curved prisms is investigated with the geometric-optical method. In addition, a mathematical model is proposed for deriving the relationship between fabricating errors of curved prisms and spectral distortions including spectral smile and keystone, and the effect of fabricating error on the spectral distortions of the hyperspectral imaging spectrometer is analyzed. Moreover, through geometric ray tracing, the analysis results of fabricating errors of curved prisms are verified. The results show that there exists an obvious difference in the sensitivity of spectral smile, keystone, and MTF to fabricating error. In order to ensure that the drop limit of the system MTF induced by fabricating errors of curved prisms is smaller than 10% of the design value, the tolerance for the second allocation is conducted to obtain the final tolerance allocation result, in which the fabricating tolerance with the minimum tolerance limit value is a tilt error at X-axis. The research here provides a reference for the actual fabricate procedure.

In order to improve the light energy utilization of equipment for measuring high-temperature optical parameters of materials and obtain better irradiance on the surface of the sample to be tested, a semi-ellipsoidal reflector is applied to the equipment. First, the equipment for measuring high-temperature optical parameters of materials and the role of the semi-ellipsoidal mirror in the equipment are introduced. Then, the optical characteristics and surface shape changes of semi-ellipsoidal mirrors are analyzed by using ray tracing and finite element analysis methods, and the influence of surface shape change of the semi-ellipsoidal mirror at 30 ℃ on optical characteristics is analyzed. Finally, the shape of the inner surface of the semi-ellipsoid mirror is measured by the three-coordinate measurement instrument, and the simulation results are verified. Experimental results show that: at 30 ℃, the root mean square (RMS) of the deformation of the semi-ellipsoidal mirror after removing ellipsoid deformation is 2.15 μm, the irradiation uniformity obtained by using a Φ15 mm blackbody radiation source is 61%, the energy utilization is 7.6%, and the RMS is 5.75 μm measured by the three-coordinate measuring instrument. This study provides a new way to measure high-temperature optical parameters of materials.

In order to further improve the classification accuracy of hyperspectral images, a classification method based on local Gaussian mixture feature extraction (LGMFEC) is proposed. The LGMFEC method first constructs a local neighborhood set for each sample based on the spatial structure of the hyperspectral image, and then extracts Gaussian mixture features from the local neighborhood set to fully characterize the spatial-spectral information and the related change information between them, and finally the local Gaussian mixture features are integrated into a support vector machine (SVM) classifier containing a Riemann kernel function to complete the classification task. The experimental results of three sets of general hyperspectral datasets show that the classification performance of the LGMFEC method is better than several advanced classification methods to a large extent, especially when there are fewer training samples.

A catheter based fiber polarization-sensitive optical coherence tomography (PS-OCT) system has significant advantages in quantitative analysis of cardiovascular plaques. A dual polarization state catheter based PS-OCT system is established based on polarization maintaining fibers (PMFs) with imaging depth multiplexing. Due to the strong birefringence dispersion of PMFs, it is difficult to use a set of dispersion coefficients to realize the dual-input-state dispersion compensation. In order to solve this problem, this paper proposes a dual-state numerical dispersion compensation method for the catheter based PS-OCT system. This method can adjust dispersion coefficients of different input polarization states to compensate for the difference in dispersion of different input polarization states caused by the birefringence dispersion of the polarization maintaining fiber. Experimental results show that the proposed method can effectively solve the problems such as pulse broadening, image blurring, and poor polarization contrast caused by material dispersion and birefringence dispersion, which ensures high-quality phase retardation imaging of biological samples in the catheter based PS-OCT.

Large-size, high-density workpieces used in industrial computed tomography (CT) scanning can cause problems such as incomplete projection data and terrible artifacts in reconstructed images owing to a lack of penetration and limited scanning angles. To address such limitations, this study uses a CAD model of the workpieces as prior knowledge and realizes superior reconstruction of the limited CT angle occurring in these types of objects. The layered position corresponding to the CAD model is calculated by the tomography workpiece position of the CT scan, and the pixel section of the model is obtained. Then, an attenuation coefficient image is obtained and generated according to the X-ray energy of the CT system and material of each part of the model that is registered into a zero gray image to obtain a prior image. Finally, the simultaneous algebraic reconstruction technique+total variation minimization+prior image (SART+TVM+PRIOR) algorithm is used to iterate the scanned projection data to obtain the reconstructed image. The experimental results of the simulation and actual workpiece scanning indicate that the quality of reconstructed image with the prior image is significantly improved over that without the prior image. This improvement is reflected mainly by a substantial reduction in artifacts in the clearer edge structure.

Computed tomography (CT) has been widely applied in medical diagnosis, industrial testing, and other fields. Recently, parallel translational computed tomography (PTCT) was proposed, in which the source and the detector were translated in parallel and opposite directions for data collection, featuring a simple structure, flexible applications, and low costs. In this paper, derivation-Hilbert transform-backprojection for PTCT (PTCT-DHB) based on Radon inverse transform was proposed for image reconstruction. Compared with the conventional algorithm of filtered backprojection for PTCT (PTCT-FBP), the proposed algorithm decomposed a ramp filter into two steps: derivation and Hilbert transform, which improved the noise resistance. Furthermore, a PTCT experimental system was established, and numerical simulations and practical experiments were performed. The results show that in comparison with the PTCT-FBP algorithm, the root mean squared error value of the images reconstructed by the PTCT-DHB algorithm is reduced by 0.0108, the peak signal-to-noise ratio value is increased by 4.437, and the structural similarity value is increased by 0.0041. The PTCT-DHB algorithm can effectively suppress high-frequency noise and quickly reconstruct high-quality CT images.

Active optics is a key technology in the field of modern large reflective optical telescopes, which can effectively reduce the aberration and improve the imaging quality. The calibration algorithm depends heavily on the response matrix and physical parameters of the system. Due to the randomness and nonlinearity of the errors of the actual telescope system, the accurate response matrix and physical parameter model are often difficult to obtain, which leads to the unsatisfactory correction accuracy or the need for multiple corrections. To solve these problems, this paper proposes a deep learning calibration algorithm (DLCM) which does not depend on response matrix and physical parameter model. With the powerful prediction and self-learning ability of the deep neural network, this algorithm establishes the dynamic model network, strategy network, and decision-making unit needed by the correction algorithm. The control system can learn and optimize automatically by combining the corresponding equipment, so as to complete the mirror calibration work. Finally, using ANSYS finite element simulation to verify the DLCM algorithm, the results show that the proposed control algorithm can quickly and accurately complete the calibration work, and the calibration speed and accuracy are better than the traditional calibration algorithm.

The existing coaxial focusing techniques such as critical angle method, Foucault knife-edge test, pinhole method, and astigmatism method are susceptible to the intensity fluctuation and have a high requirement for the system alignment. Therefore, we proposed a novel coaxial focusing method based on differential modulation evaluation. In this technique, the imaging space was first coded by a physical grating. After that, the modulation distribution of the coded image after the substrate height modulation was calculated by the Fourier transform algorithm. Furthermore, the accurate measurement of the substrate height can be realized through combining the modulation with a differential detection system. The theoretical and experimental results demonstrate that the focusing accuracy is better than 10 nm after an objective lens with a numerical aperture of 0.9 and a magnification of 100 is applied. In conclusion, the proposed method does not need any complex optical component and features a simple structure and high testing accuracy, thus providing a novel high-precision coaxial focusing approach for emerging lithography techniques.

Diffraction gratings are widely used in the soft X-ray and vacuum ultraviolet grating monochromators of the synchrotron radiation source, and thus the deviation of the groove density of the gratings directly affects the performance of the monochromators. In order to detect the deviation of the groove density, we built a long trace profiler (LTP) system in the pre-research process of Hefei Advanced Light Source (HALS). First, an autocollimator was used to calibrate the detection accuracy of the LTP system within 26 μrad. Then, the LTP was applied to detect the groove density uniformity of the self-developed 760 line/mm and 2400 line/mm uniform-line-spacing diffraction gratings adopted in the pre-research of HALS. Furthermore, an interferometer was employed to detect the zeroth and first-order diffraction wavefronts of the 760 line/mm grating. Finally, the above detection results were compared with the LTP-based measurement results. The results show that the root mean square error of the system calibration is 30 nrad, and the height profile curves at the same position are in good agreement in terms of LTP detection and interferometer measurement. This indicates that the LTP system can detect the groove density of diffraction gratings with high precision, providing a platform for detecting the deviation of the groove density of synchrotron radiation gratings.

The peak power of ultra-short picosecond pulses is high, and the realization of the large energy output is difficult. The single pulse is divided into multiple adjacent pulses, which can increase the total energy of the pulse envelope and increase the laser output power. A single-channel mode-locked picosecond seed laser output with an optical-to-optical conversion efficiency of 39.3% is designed and obtained, and a method of dividing a single pulse into multiple pulses is proposed. By using Bragg volume grating (VBG) pulse broadening, multiple pulse generation, regeneration amplification, traveling wave amplification, and frequency conversion, a laser output at 532 nm with four pulses, 1 ns pulse spacing, 10 W output power, 10 mJ pulse envelope energy, 100 ps pulse width of the single pulse, 1.67 beam quality, and 1 kHz repetition frequency is obtained. Through the thermal lens effect pumped by the laser module, the laser output emission angle can be adjusted continuously and accurately by adjusting the pump current, and the minimum divergence angle is 0.2 mrad. The designed method is applied to the space laser ranging station of Shanghai Observatory to carry out the ranging of multiple space debris, and the ranging accuracy is 16.44 cm. The results show that multiple pulses can increase the total laser output energy and laser output power, which provides an effective technical way to improve the ability of space debris laser ranging detection.

Aiming at the problem of how to obtain the relative position and posture of non-cooperative targets in space at close range for on-orbit service mission, a trinocular stereo vision measurement method is proposed. First, three large-field visible light cameras arranged in equilateral triangles are used to acquire images. Then, the proposed method is used to match the feature points. Second, the RANSAC method is used to calculate the pose parameters of the measured target in the world coordinate system. Finally, the static motion, position movement and attitude rotation of the non-cooperative satellite model are tested. Experimental results show that the relative position accuracy is better than 2.2 mm in the static state, and the relative angle measurement accuracy is better than 0.3°; when the model position moves, the absolute position accuracy is better than 3 mm; when the model posture rotates, the relative position accuracy is better than 5.6 mm, the relative angle measurement accuracy is better than 1.7°, indicating that the proposed method can improve the shortcomings of binocular stereo vision technology, such as measurement blind spots, mismatched feature points location and limited measurement field of view.

At present, most thermal infrared (TIR) tracking methods are based on correlation filters or RGB trackers for feature extraction. However, both of them are only suitable for RGB object tracking but not sensitive to the TIR object features, thus failing to be applied to the TIR object tracking. To this end, a TIR object tracker based on the global-aware siamese neural network was proposed in this paper. First, the features from the last three layers of the siamese neural network were fused to obtain new features. Second, the spatial-aware module composed of the spatial transformer network and channel attention was added to get the global effective information. Simultaneously, the self-attention mechanism was introduced to make the algorithm more focus on extracting the discriminant information of the objects. At last, the final response map was acquired by response fusion of the results. The experimental results on the TIR pedestrian tracking benchmark (PTB-TIR) show that the proposed algorithm can adapt to a variety of TIR environments while maintaining a high tracking speed (20.2 frame/s), achieving effective and stable real-time tracking of TIR objects.

Chlorophyll fluorescence kinetics is closely related to the algae photosynthesis and is a natural tool to detect viable algae cells. Compared with the common method of combining fluorescein staining in ballast water with the microscopic examination of viable algae cells number, chlorophyll fluorescence kinetics has the characteristics of rapid measurement, high sensitivity, and no need for pretreatment. However, there are a large number of dead algae cells and colored dissolved organic matter (CDOM) in marine ballast water, and the fluorescence background is complex. Therefore, obtaining the photosynthetic fluorescence parameters that are not affected by the fluorescence background and can accurately characterize the viable algae cells number is the key to directly measuring the viable algae cells number in ballast water through chlorophyll fluorescence kinetics. In this paper, with the dead cells and CDOM solution simulating the complex fluorescence background of ballast water and the 3-(3c,4-(dichlorophenyl)-1,1-dimethylurea (DCMU) stress condition simulating the practical application, the relationship of various photosynthetic fluorescence parameters such as Fm, F0, [RCII], and Fv with the viable algae cells number was investigated at different fluorescence backgrounds. The results show that Fm, F0, and [RCII] are all affected by the dead cells number and the CDOM concentration to varying degrees, and only Fv is not affected by the fluorescence background, with a relative standard deviation being less than 5%. In an experiment of diluting the solution of viable algae cells with different diluents, Fv and the viable cells number have a good linear correlation, with the correlation coefficient R2 above 0.98. Under the stress of DCMU, only Fv displays an excellent positive correlation with the viable algae cells number, and the correlation coefficient is 0.986. These results demonstrate that Fv is not disturbed by the fluorescence background and is the best photosynthetic fluorescence parameter to characterize the number of viable algae cells in ballast water.

Optical second-harmonic generation technology is an important tool for studying the polarization characteristics and symmetry of materials. Second-harmonic generation test is carried out on BaTiO3 film samples grown on SrTiO3 substrates by using the built-up microscopic second-harmonic generation light path. The results show that BaTiO3 film has double rotational symmetry in the in-plane direction. The second-harmonic signal of the sample was measured in four polarization modes. The results show that with the change of the incident power of the fundamental frequency light, the second-harmonic intensity pattern also changed. When the incident light power is 7.5--7.7 mW, the signal changes suddenly; when the incident light power is greater than 7.5 mW, the main peak of the second-harmonic pattern of the horizontally polarized outgoing light pattern is weakened, and the secondary peak is strengthened.

Optical power splitter (OPS) is one of the basic components in photonic integrated circuits and it is widely used in many fields. The OPS with tunable power splitting ratio (PSR) can enhance the flexibility of photonic integrated circuits and simplify the photonic integrated circuit system. We propose an integrated chip scheme Si-based OPS with large tunable range of PSR. The scheme combines Si-based devices such as a symmetric 2×2 multimode interferometer, a waveguide grating, and a slot structure. By varying the wavelength of the input signal and adjusting the voltages applied at both ends of the thermo-optic micro modulator, the wide range adjustable PSR is realized. Experimental results show that the two OPS structure can obtain PSR changes 0.51--36.91 and 0.88--230.46 respectively within the wavelength range of 6.72 nm and 5.56 nm, respectively, and PSR changes of 8.58--29.75 and 5.01--425.43 in the temperature changes by 50 ℃. The OPS has the advantages of small size, light weight, and high flexibility, which can be widely used in optical switch, channel division, power distribution and other communication and signal processing fields.

For a pulse laser detection system, the existing peak extraction methods can only detect the unsaturated waveform in the linear region but cannot detect the saturated waveform in the nonlinear region. The methods based on pulse duration analysis can detect the saturated waveform within a certain range but have complicated models and difficult fitting, resulting in the limited detection range of the system. In view of the detection difficulty of the laser positioning system in the nonlinear region, we established an energy response model based on the back propagation neural network algorithm in this paper, which can be used to detect the waveforms in both the linear and nonlinear regions. Finally, the inversion fitting effect of the proposed model on the waveform in the nonlinear region was experimentally verified. The experimental results show that the incident light intensity could be obtained by inversion fitting based on the proposed method and its maximum relative error with the actual light intensity was only 3.79%. Besides, the detection range was expanded to 10.25 times that of the peak extraction methods, and the proposed model was simple and had a small error. In conclusion, the model proposed in this paper can be used to detect the pulse laser in the nonlinear region and applied to improve the dynamic range and detection ability of the pulse laser detection and positioning system based on the four-quadrant detectors.

In order to measure the graininess of metallic paints, a measuring device and evaluation method were developed, the evaluation model of metallic paint graininess effect applied to the measuring device was established. According to different color distributions and particle sizes, 56 metallic paints were selected to construct the sample database. The particle parameters of samples were collected by BYKMac, and visual experiments were performed to verify the accuracy of BYKMac data. The measuring device was designed to obtain sample image information, the existing texture evaluation methods were used to process the image information and the data is compared with the visual experiment data. At the same time, an evaluation method suitable for the device was designed to get the graininess value of the samples. The correlation coefficients between the measurement results and the visual values and BYKMac values were 0.8770 and 0.9329, respectively. Experimental results show that the measuring device and evaluation method can effectively measure and obtain the graininess of metallic paints that meet the perception of human eyes.

Angel lobster-eye X-ray micro-pore optics (MPO) device, as a novel X-ray focusing device, has unique 4π stereoangle focusing ability and the optimal ratio of effective area to weight, thus being one of the most promising X-ray optical imaging systems. According to the structure characteristics of a lobster eye, a lobster eye optical device was successfully fabricated based on the fabrication technique of micro-channel plate square hole array in this paper. Then, the spherical surface accuracy and focusing characteristics of the device were tested by a Zygo interferometer, a fringe reflection profiler, and X-ray beam equipment. The test results show that the fabricated MPO device has a root-mean-square spherical surface accuracy of 0.72 μm, a peak-to-valley value of 2.27 μm, and a radius of curvature of about 752.3 mm. In addition, at a voltage of 2 kV and a current of 50 μA, the diameters of the full width at half maximum of the focal spots on the horizontal and vertical axes are approximately 0.39 mm and 0.42 mm, and the corresponding angular resolution is 3.65 arcmin and 3.93 arcmin, respectively.