In order to meet the requirements of ultra-lightweight high precision space optical equipment, an ultra-lightweight structure design method of Φ600mm mirror assembly combined with multi-objective integrated optimization and secondary sintering process was proposed by using parameter optimization technology, finite element analysis and advanced SiC manufacturing technology. Firstly, the root mean square value (RMS) and weight of the sic mirror shape in the X and Z directions were taken as the optimization objective, and the axial thickness of the mirror and the thickness of the mirror surface were taken as the design variables, the ultra-lightweight mirror structure with a lightweight rate of 90.55% was obtained. Secondly, the mirror supporting structure is also made of SiC material, the mirror and support are directly sintered by using the secondary sintering process method to reduce the bonding assembly link, and the mirror assembly with a lightweight rate of 92% is obtained. Finally, using the finite element analysis and test of ultra-low weight the correctness and rationality of the structure design method is verified. The results show that under the comprehensive influence of gravity load, temperature load and mirror machining residual, the RMS value of mirror assembly surface error is 10.034nm, which is better than the design requirements of 12.6nm, and the dynamic stiffness is good, which meets the requirements of use.

The absolute test method of liquid surface usually uses a high-viscosity liquid plane as a reference for calibrating the flatness of optical flat, which has a long stabilization time and recovery time after disturbance. An absolute test method of dynamic liquid surface is proposed, which uses a dynamic interferometer to measure the dynamic surface shape of a low-viscosity silicone oil surface and uses its average value as a reference surface for calibrating the systematic error of the interferometer. Based on the principle of multi-dimensional modal analysis, a liquid plane fluctuation model is established and simulations are carried out using the finite element method. The simulation results show that the dynamic liquid surface fluctuates vertically based on the standard liquid surface corresponding to the radius of the earth, and the amplitude is in the form of a cosine function. The mean value of the residual error of the liquid surface flatness over the sampling time can be controlled to the order of 10-3nm. Experiments were carried out on a Φ300mm vertical dynamic Fizeau interferometer on silicone oil of 0.65Cst viscosity and 3mm liquid thickness with a sampling time of 30s.The results of the dynamic interferometric calibration of a low-viscosity silicone oil are compared with the stable absolute test results, and the surface distribution is consistent, with a deviation of λ/63 in PV and λ/400 in RMS. The simulation and experimental results demonstrate that the interferometer system error can be calibrated with low viscosity silicone oil interferometric mean results.

A high-precision alignment method of off-axis Cassegrain optical system was provided. According to the assembly difficulties of off-axis paraboloid primary mirror, the bonding form and area are determined by theoretical calculation and simulation analysis. The self-alignment detection is performed by ainterferometer and a plane mirror to complete the micro-stress of assembly of primary mirror. Combined with the structural characteristics of the system, the relationship between the primary mirror position attitude and the mechanical reference is established by measuring the optimal surface shape of the primary mirror, so that the primary mirror optical axis is consistent with the mechanical reference. By analyzing the relationship between the amount of secondary mirror misalignment and the system wavefront aberration, the system wavefront aberration correction is realized by adjusting the secondary mirror by six degrees of freedom. The surface shape change after the primary mirror is bonded and assembled is less than 5%, and the wave aberration after the system aligned is better than 0.055λ. The data meets the design index requirements.

A machining process of hollow cone prism is introduced in this paper.The first is to use optical cold working technology to process the substrate of three glasses, and carry out external rolling and coating treatment. Next, fix the three substrates using fixtures, and then apply a layer of adhesive to the bonding area. Finally, the core technical indicators of the hollow cone prism are monitored in real time by self-collimating parallel light tube, and the UV lamp is cured to control the molding. Practice has proved that the process can accurately control the dihedral angle of hollow cone prism, which is suitable for the cool processing of large-diameter hollow cones.

To study the influence of impurity size on the damage threshold of anti-reflection film, by using photolithography technology, cylindrical Al impurities with different diameters and thickness of 100nm were added between the fused quartz and the anti-reflection film. Comsol was used to understand the damage process, and the 532nm nanosecond laser was used for threshold test, then the experimental data and the sample damage morphology are analyzed, the results show that the damage thresholds of the films with impurity diameters of 50um, 100um, 200um, 300um and 400um are respectively 18.93J/cm2,18.62J/cm2,17.11J/cm2,15.28J/cm2,13.47J/cm2,which goes down nonlinearly, and the main cause of film damage is that the "impurity absorption point" absorbs laser energy to generate heat, and the axial thermal stress generated by conduction to the anti-reflection film exceeds the tensile strength of the film.

A laser cladding head for coaxial powder feeding in optical fiber is developed. In the ideal state, the focal spot of the cladding head presents a complete ring, but in the actual process, the accumulation of the processing tolerance and assembly error of the components leads to the phenomenon of dislocation of the focal spot. In order to improve the above phenomena, optical simulation was used to simulate the position and angle parameters of key optical components inside the machining head, and fine tunes the position and angle of the optical elements in the cladding head under the guidance of simulation results, without introducing new errors as much as possible. The test results show that the optimized focus spot is symmetrical in shape and evenly distributed in energy.

Prism is one of the key components in space and military white light and infrared optical systems, which can achieve higher precision imaging quality in optical systems. Therefore, the processing and detection technology of ultra high precision prism is proposed. Firstly, the tooling materials and processing methods suitable for prism processing are analyzed, and the difficulties and key points of ultra high precision prism processing are pointed out. Then, it introduces the tooling making, prism bonding, processing, detection methods of ultra high precision prism processing, as well as protective measures to prevent damage to prism tooling. Finally, the Schmitt zinc selenide prism with a total height of 35~95mm was processed, and the surface shape was detected with a Zygo interferometer, the surface shape accuracy reached RMS 0.007μm(λ＝632.8nm);The precision goniometer Prismm aster C2000 is used for angle detection, The first optical parallel difference is less than 1″; and the second optical parallel difference is 1.048″ when measured with XQ20-GI plane laser interferometer; Atomic force microscopy Surface roughness 2.9nm.

High-power ytterbium-doped fiber lasers have important application value in precision processing, national defense, scientific research and other fields, but with the increase of power, the nonlinear effects inside the fiber begins to become prominent. Here, the generation process of nonlinear effects such as stimulated Brillouin scattering (SBS), stimulated Raman scattering (SRS), nonlinear refractive index, and transverse mode instability (TMI) is analyzed in detail, and suppression methods are proposed. In addition, from the perspectives of fiber oscillator and main oscillation power amplifier, the research progress of scholars in recent years on the basis of suppressing nonlinear effects to continuously improve the output power of ytterbium fiber lasers is briefly described. At present, the output power of the ytterbium-doped oscillator with all-fiber structure reaches 8kW; The output power of the single-fiber main oscillation power amplifier laser system has exceeded 20kW.

Ultrashort fiber lasers with GHz repetition rate have already demonstrated their applications in laser communication, advanced manufacturing, astronomical and THz detection, et al, due to their advantages of large number of pulses per unit time, wide spectral coverage and narrow pulse duration. However, the main difficulty is how to yield pulses with duration less than 50fs and above 1GHz repetition rate at the same time. A 1.003GHz repetition rate Yb-doped fiber laser was built with 48.8fs pulse duration by using nonlinear polarization rotation mode locking (NPR). In our approach, WDM-Collimator was employed in order to shorten the length of the cavity. This fiber laser had the shortest output pulse duration among all reported Yb-doped fiber lasers with fundamental repetition rate above 1GHz. Finally, the laser was integrated into a prototype, which effectively reduced the manufacturing cost and improved the stability. The laser is expected to promote the industrialization and commercialization of high repetition rate fiber ultrashort pulse lasers.

Organic aerosols exhibit a fluorescence effect, generating fluorescence when excited by laser at specific wavelengths. For such fluorescent aerosol clusters, a radial boundary detection algorithm based on horizontal detection fluorescence-Mie lidar is proposed. The algorithm employs echo signals from both fluorescence and Mie dual channels to create a function that eliminates atmospheric effects. Subsequently, adopting the intercept method to detect sudden changes of characteristic signals of fluorescent aerosol clusters, their boundaries can be determined. Numerical simulations demonstrate that the algorithm offers high accuracy and stability in detecting radial boundary for both single and double fluorescent aerosol clusters, regardless of visibility and signal-to-noise ratios. By utilizing this algorithm to detect the radial boundaries of single or double fluorescence aerosol clusters with fluorescence-Mie lidar, the accuracy and stability of boundary detection are significantly improved. Additionally, the algorithm is capable of timely detection of boundaries for single fluorescent aerosol clusters.

In order to overcome the issues of clock synchronization required in time division multiplexing (TDM) technology and the inflexibility of frequency division multiplexing (FDM) systems, an accurate visible light localization algorithm based on code division multiplexing is proposed. The algorithm realized symbol synchronization in asynchronous conditions and performs visible light positioning. The Simulation results show that when covering more than 80% of the area of a room, the average positioning error of the algorithm is 6.9cm, and the maximum positioning error is about 11cm, which is suitable for most indoor location-based services. In addition, the relationship between the positioning accuracy of the system and the field of view of the receiver and the height of the receiver above the ground is analyzed. It is found that in a certain range, the larger the field of view of the receiver, the poorer the positioning performance of the system; while the larger the height of the receiver above the ground, the better the positioning performance of the system.

For the high dynamic range of echo signals in some lidar systems, it can be challenging to achieve high performance acquisition of the strong and weak signals simultaneously. A hardware and software joint acquisition method is proposed, which uses a high-speed digitizer to acquire the full waveform and then deals with the algorithm software. For the software photon counting algorithm, a dynamic voltage threshold selection method is also proposed to improve the counting accuracy. The simulation model of devices in the full-link of photoelectric detection and acquisition is established to compare and verify the feasibility of the methods. Based on a set of typical parameters of preferred devices, the simulation compared the acquisition errors of the full waveform acquisition method with the existing methods, verifying the effectiveness and technical advantages of the full waveform acquisition method and the dynamic threshold selection algorithm. This research provides a novel idea for the detection of weak optical signals with high dynamic range by leveraging a synergistic combination of hardware and software techniques.

In TDLAS detection technology, the second harmonic signal carrying gas concentration information is susceptible to the amplitude and frequency of the scanning and modulation signals. Based on TDLAS, a hardware system for CO concentration detection was built and compared with the corresponding simulation model to study the influence of modulation parameters on the peak value, signal-to-noise ratio, symmetry, and peak width of the second harmonic signal. The optimal modulation parameters for the system were determined through experiments, which improved the detection accuracy without changing the hardware. Detection of CO absorption spectroscopy at 1567.7nm revealed that the measured concentration decreases with increasing temperature, with a maximum relative error exceeding 15%. To reduce the temperature effect on measurements, compensation techniques using RBF and BP neural network, PSO-BP neural network, and WOA-BP neural network algorithm was applied to the system. The results showed that the WOA-BP neural network method provided the best compensation effect, reducing the relative error of the corrected concentration to below 1%, effectively enhancing the accuracy and stability of the system in variable temperature environments. This research provides reference for setting modulation parameters and achieving precise detection, and offers valuable guidance for subsequent experiments.

A curved fiber taper temperature sensing structure is proposed based on the simple melting pull taper technology. The length of single-mode optical fiber taper is 1.5mm, and the waist diameter is 25μm. The waist diameter of the optical fiber taper coating with polydimethylsiloxane is 100μm. The experimental results presents the temperature sensitivity of the curved fiber taper is -191.41pm/℃. In addition, polydimethylsiloxane has a good hydrophobicity, the proposed sensor can effectively avoid the humidity crosstalk in temperature measurement. At the same time, the preparation process is simple, low cost, high sensitivity, so the proposed fiber sensor has important application prospects in industrial automation, aerospace, biomedicine and other fields.

The study of topological photonics is of great significance in the field of optical communication. In order to achieve topological edge states (TESs) and corner states (TCSs), a two-dimensional square photonic crystal structure was constructed based on the Su-Schrieffer-Heeger (SSH) model. The energy bands of the structure were simulated and calculated using finite element software, and the corresponding modes and topological phases were analyzed. On this basis, edge states and corner states with topological protection properties were implemented, resulting in a relatively wider bandgap with a relative bandgap width of 35%. The unidirectional transmission characteristics and anti-interference ability of topological boundary states were verified through frequency domain simulation. Topological corner states can constrain light waves at corner positions. The results show that the photonic crystal structure based on the SSH model can achieve topological edge states and corner states with good performance. The structure is simple and easily realized.

Based on the generalized Huygens Fresnel principle, the analytical expression of the cross-spectral density matrix element of the linear edge dislocation Gaussian Schell model beam in biological tissue transmission is derived, and the effects of different waist widths ω0x, off axis distances d, edge dislocation slopes p, and spatial correlation lengths σyy, σxy on the on-axis polarization degree, azimuth, and ellipticity of the beam will be compared. The results show that the larger the waist width ω0x, the larger the off-axis distance d, the smaller the edge dislocation slope p, the larger the change of P(0,0,L) and ε(0,0,L) and the smaller the extremum in the linear edge dislocation Gaussian Schell model beam. The greater the σxy, the greater the absolute values of P(0,0,L), θ(0,0,L) and ε(0,0,L). When σyy＞σxx, θ＜0 at the source, whereas σyy＜σxx corresponds to the opposite one, namely, θ＞0 at the source. The smaller the absolute value of the difference between σyy and σxx, the larger the extreme values of P(0,0,L), θ(0,0,L) and ε(0,0,L). With increasing the transmission distance, the value of P(0,0,L), θ(0,0,L) and ε(0,0,L) tends to be stable eventually, respectively.

A fast enhancement method of polarization images in foggy weather based on median filter and polarization modulation is proposed to balance between dehazing effect and real-time processing. Firstly, the median filter method is used to estimate atmospheric light. Secondly, the semi-inverse method is applied to get the atmospheric light intensity at infinity, and the restored image is obtained by using scattering model. Finally, the image is adjusted with the degree of linear polarization to promote visual effect. In comparison with other methods, the downsampling method is used in this paper to reduce the image size. Furthermore, the smaller scale of filter window is chosen to decrease the handling time significantly in the premise of maintaining accuracy of atmospheric light estimation. What’s more, Polarization modulation and histogram equalization methods are utilized to improve the contrast ratio between the target and the background, solving the problem of defogging effect and real-time algorithm better. The experiment shows that the results of this method has a great improvement in three metrics, such as entropy, gradient ratio before and after dehazing, and contrast. For image with a resolution of 1393×986, the processing time is only 16ms, which fully meets our real-time requirements.

At present, the retinal optical coherence tomography (OCT) image classification method based on convolutional neural network (CNN) has the problem of unclear identification of small-scale lesion areas, which leads to the difficulty in diagnosing the dry and wet aspects of age-related macular degeneration (AMD), and judging the activity of choroidal neovascularization (CNV), but correct judgment of lesion type is crucial for ophthalmologists to formulate treatment plans. Therefore, a CNN model MobileX-ViT based on the self-attention mechanism is proposed, which combines the traditional convolution layers and self-attention module, and simultaneously extracts the feature information of the shallow network and obtains the global information of the image to improve the performance of the model. Experiments have proved that compared with the classic CNN classification models Inception-V3, ResNet-50, VGG-16 and MobileNeXt, the classification accuracy of the proposed model is increased by 5.6%, 5.3%, 4.5% and 2.8% respectively. The effectiveness of the model is proved, and it provides a new method to solve the problem of unclear identification of small-scale lesion areas in the current classification of retinal OCT images.

Aiming at the problem of high false alarm rate of infrared small target detection of unmanned aerial vehicle remote sensing system in complex environment, a two-stage infrared small target detection model of the unmanned aerial vehicle remote sensing system is proposed with combination of convolutional neural networks. In the first phase, the Unet neural network is taken advantage to learn the deep semantic features and shallow location features of targets in the infrared image, meanwhile, the infrared week and small target signal is enhanced and the background signal is suppressed. In the second phase, Faster R-CNN is utilized to analyze the output image of the first phase, to detect the location and bounding box of infrared small target. Validation experiment is carried on the public infrared small target detection dataset of the unmanned aerial vehicle remote sensing system, the results show that the detection precision of the proposed model for infrared small target increases by 13.2、9.8 and 13 percentage points on three complex background datasets respectively, and the processed frames per second increase 11、14 and 13.