Tunable Fabry Perot resonator is a kind of optical devices widely used optical devices in optical communication, sensing and laser fields. Its tuning methods can be mainly divided into fiber-optic F-P cavity, micro-machine F-P cavity and electro-optic F-P cavity, each of which has corresponding advantages and areas of advantage. In this paper, the development of tunable F-P cavities is reviewed including device structure and performance parameters.In the end, the performance differences and the future directions of tunable F-P cavities is are discussed.

The problem of identifying the rigid axis of resonator in HRG is discussed. In this paper, a method for identifying the rigid axis of hemispherical resonator based on amplitude frequency characteritics is proposed. Firstly, starting from the dimensional mass vibrations model of hemispherical resonator the expression of amplitude frequency respons characteritics is derived. Secondly, the response of the resonator in different excitation directions is simulated, and the feature selction method of rigid axis is determined. Thirdly, the excitation responses under defferent frequency splitting and defferent Q values are simulated, and the applicable conditions of rigid axis of hemispherical resonator identification method are proposed. Lastly, the principle and method of rigid axis identification proposed in this paper are verified by experiments. The rigid axis identification of hemispherical resonator with a frequency splitting value of 0.3 Hz、0.18 Hz、0.01 Hz is carried out. The correctness of the identification principle and method is verfied. The principle of this method is clear, the identification device is easy to realize, and the operation efficiency is high, which provides an effective way for the subsequent process of resonator quality leveling engineering.

In the field of small unmanned helicopter, strapdown inertial navigation system (SINS) of laser gyro is not only used for navigation, but also used for flight attitude control. The requirement of navigation accuracy and real-time capability of laser gyro SINS is higher. But the traditional high-order FIR low pass filter to laser gyro IMU signals has a large time delay, so that the filter is difficult to satisfy the system. In order to take care of the measurement accuracy and response time, a filter method that combined LMS adaptive notch filter and low-order FIR low pass filter is studied, and the IIR narrowband filter is introduced in order to solve the acquisition problem of the dither frequency reference signal. Theoretical analysis and test results show that the method can not only effectively eliminate the impact of the dither offset frequency signal and the outside world high frequency noise, but also can significantly reduce delay time to 2 ms. It has very high engineering practical value.

Aiming at the problem that the navigation information source fusion algorithm of the U.S. military navigation sensor system interface relies on experience in parameter setting and does not fuse the course, a navigation information source fusion algorithm based on adaptive exponential weighted moving average (EWMA) is proposed. The algorithm uses the segmented estimation error function to adaptively adjust the parameters of the NSI algorithm, thereby avoiding the impact of improper initial parameter settings on the fusion accuracy, and further improving the position fusion accuracy. In addition, the algorithm is applied to the heading to realize the heading fusion. Under the simulation test and actual data test, the method in this paper is compared with the common NSI method based on EWMA. The results show that the NSI method based on adaptive EWMA proposed in this paper has the function of adaptive parameter adjustment, avoiding the complicated parameter adjustment process, and effectively fusing the information of multiple sensors to suppress the Strapdown Inertia Navigation System (SINS) error divergence.

In this paper， a three-dimensional magneto-optical trap based on a triangular diffraction grating is used to realize the cooling and trapping of 87Rb atoms. Firstly， the triangle diffraction grating is designed and fabricated independently， which can effectively suppress the zero-order optical efficiency under the condition of ensuring the reasonable diffraction efficiency and diffraction circular deviation， and its parameters meet the optical viscose balance conditions. Then a magneto-optical trap system is built based on the grating to carry out the atom trapping experiment. Under the reasonable parameter setting， the atomic trapping is successfully realized. It is estimated that the number of trapped atoms is in the order of 106. The success of the atom cooling trapping experiment based on the triangular diffraction grating is of great significance for the low power consumption and miniaturization of the three-dimensional magneto-optical trap， and is expected to be applied to the miniaturized precision measurement system of cold atoms.

In order to decrease the volume and increase the practicality， it is an attractive scheme of realizing the Raman laser by using the modulation of an electro-optic modulator. However， this way produces additional laser lines of a Raman laser， which gives a big impact on absolute gravity measurement. In order to ensure the accuracy of measuring the absolute gravity， we have realized the optimization and evaluation of this maximum system error in this paper， combined by the theoretical model and the modulation experiments. The result has proved the evaluation method and the uncertainty of this effect is evaluated to 20 μGal.

Aiming at the problems of low target detection accuracy for small-sized drones and the deep network has a large number of parameters and a high memory footprint, a drone detection method based on improved YOLOv5 was proposed. Firstly, the number of YOLOv5 multi-scale prediction layers was adjusted, and the redundant network layers was cut, which effectively reduced the amount of network parameters, and improved the speed of drone detection. Secondly, multiple parallel atrous convolutions with different sampling rates were introduced into the feature extraction stage to enhance the ability of multi-scale detail feature extraction of small targets. Finally, the attention mechanism was introduced into the multi-scale feature fusion stage to enhance the feature expression ability of small targets by Fusion of shallow features and deep features were channel-weighted. The experimental results illustrate that the improved YOLOv5 model achieves 99.02% mAP on the self-made data set, and has better detection effect for small-sized drone targets. Compared with the network before the improvement, the detection speed is increased by 10.3% and the memory cost is saved by 65%, and the requirements of computing capabilities and storage capabilities for devices are reduced, and which is more conducive to practical applications and engineering deployment of drone detection systems.

With the high-technique developing quickly, the traditional multi-target tracking algorithm is facing new challenges and requirements in the application of infrared warning equipment. In recent years, the approaches to MTT based on random finite set (RFS) have been achieved substantial results.This paper discusses MTT problem of sector scanning infrared warning equipment image based on multiple model label multi-Bernoulli support vector machine(MM-LMB-SVM). Firstly, the problems existing in the application of traditional algorithms to sector scanning infrared warning equipment are discussed. The advantages of MM-LMB-SVM filtering algorithm are proposed. At the same time, the problems faced by the application of MM-LMB-SVM filtering to sector scanning infrared warning equipment are analyzed and the solution are provided. The simulation results shows that under the typical complex background, the track anti-jamming success rate of weak and small targets is improved by more than 20%, and the tracking success rate of weak and small targets with only 50% detection rate is improved by more than 45%. It significantly improves the weak and small multi-target tracking ability.

In this paper, an interference phenomenon and its elimination method in Fourier infrared imaging spectral data are analyzed and studied. In Fourier infrared imaging spectrometer, in some cases, a sharp convex interference peak appears in the spectral data. The peak position of this kind of interference peak is not fixed, and the amplitude will change greatly. The phenomenon from infrared detector, atmospheric absorption characteristics, target radiation characteristics, system noise and so on are analyzed. The reason for this phenomenon is the gray fluctuation of infrared detector. In view of the formation mechanism of the interference, the noise fitting method is proposed to eliminate the interference. The experimental results show that the proposed method can effectively eliminate the interference peak in Fourier infrared imaging spectrometer, and improve the detection effect and anti-interference ability of Fourier infrared imaging spectrometer.

Lithium niobate thin film has become the preferred optical material in the field of tunable Fabry-Perot filter, electro-optic modulator and other devices towards integration and miniaturization because of its excellent optical properties and the advantages of easy integration with compact optical waveguides and other devices. However, due to the size difference between optical waveguide and optical fiber, there is a serious mode field mismatch, which leads to a large insertion loss when the optical fiber is coupled with optical waveguide. In this paper, as an ultra-high numerical aperture (UHNA) fiber is directly coupled with ridge waveguide, optical properties such as light field mode distribution, coupling efficiency and loss are analyzed by simulation. The results show that as the etching depth and width are 300 nm and 0.8 μm, respectively, the coupling efficiency between the LiNbO3 ridge waveguide and the single-mode fiber (UHNA7) can reach 33.8% and the coupling loss is 4.71 dB. The simulation also compares that when the upper cladding material is replaced with silicon dioxide and silicon nitride materials, the coupling efficiency value of the ridge waveguide and single-mode fiber is significantly increased to 63.4% and the coupling loss is reduced to 1.98 dB.

After the laser welding of the receptacle and the sleeve, the coupling efficiency will fall obviously. In order to study this problem, based on finite element thermal theory and structural coupling theory, laser welding model was developed and the post-weld shift was calculated. According to the experiment, compared to the devices without compensation, the coupling efficiency has increased 50% after the compensation of the PWS. This result has a certain guiding significance for the packaging development and production of high-speed optical devices, especially multi-channel integrated optical devices.

Constant phase front with random fluctuation caused by turbulence will make wavefront angle of arrival change continuous in atmosphere channel. New plane and spherical waves angle of arrival models under non-Kolmogorov turbulence in slant atmosphere turbulent channel are investigated, which featured the small rise at high wave numbers near 1/l0. Turbulence inner and outer scales has different effects on the angle of arrival in different slant link: the downlink angle of arrival fluctuation is smaller than the uplink, the angle of arrival fluctuation increases with the increase of the inner and outer scales, and it is significantly reduced with the increase of the diameter of the receiver aperture. The result will provide reference for related applications such as satellite laser communication.

In view of the poor image stabilization of the EO platform based on the moving vehicle, an effective method is proposed, reducing gyro sampling frequency and system control cycle, adding a current loop in the driving circuit, and adding an expanded state observer to observe and compensate the disturbance in the control loop. The effectiveness of the method is verified from swing table test and actual moving vehicle test. Under the three axes swing condition at 3 °、 2s, the dual axis stabilization of the EO platform is better than 0.15 mil (1σ). Under the condition of earth rock pavement and at the vehicle speed of 15~30 km/h, the dual axis stabilization of EO platform is better than 0.2 mil (1σ). Based on the traditional PID algorithm, this method is simple and effective, it can achieve obvious improved stability only by little optimization. This method is also applied on the shipborne and airborne EO platforms.

The airborne electro-optical platform system is usually used to identify the sensitive or fixed target, which can provide laser irradiation designation for semi-active laser guided weapon. In order to evaluate the irradiation accuracy of the laser designator that integrated with electro-optical platform system, theoretical analysis and numerical simulation are performed for the irradiation accuracy, which is changed with atmospheric turbulence intensity and laser propagation distance, and the field tests about irradiation error is carried out that caused by parallelism of optical axis based on actual equipments, the irradiation errors measured in the three tests are about 0.352 5 mrad、0.521 9 mrad and 0.511 3 mrad, respectively. The results show that the designation error would be increased as designation range and atmospheric turbulence intensity increase, and the designation error induced by parallelism of optical axis is about milliradian magnitude, which effectiveness is much larger than the atmospheric turbulence.

Synthetic aperture imaging system is the trend of the next generation optical telescope. The imaging quality of the system can be guaranteed only when the piston errors between sub apertures are corrected within a certain range. A precise common phase piston error correction method based on Q-Learning with a correction range of ±λ/2 is proposed. The image clarity of the synthetic aperture imaging system is taken as the reward function, and the optical path compensation control action of the sub aperture is combined with the state to improve the decision-making ability of the agent in continuous learning, so as to generate the optimal control strategy, and quickly correct the piston. Through the simulation environment, the established agent model can obtain the state-value table in Q-learning in the environment with piston error, and can obtain the fast correction path sequence from the initial state to the best imaging performance through the q-table. At the same time, it is not limited by the target scene, which verifies the effectiveness and reliability of this method.

The detection and recognition accuracy of deep learning algorithm based on convolutional neural network is greater than the traditional pattern recognition algorithm, but the convolution and nonlinear activation function of neural network takes a lot of computing power to do it efficiently, this makes it hard for a lot of deep learning algorithm model in power limit embedded platform for deployment. In this paper, the target detection algorithm YOLO-V3 is taken as an example, and the corresponding FPGA implementation method is designed for different layers of the network, and the parallel operation element based on tiles is designed especially for the convolution layer. Finally, a target detection hardware accelerator is realized in FPGA. The accelerator can make full use of the hardware computing resources of FPGA, and its overall average performance is 192.229 GOP/s. Through experimental comparison, it is proved that this paper can provide a solution of high energy efficiency and high recognition accuracy for embedded infrared target recognition system.

Space optical remote sensors are developing in the direction of higher resolution and detection function density. High-resolution, light and small cameras with both visible and infrared detection functions have gradually become a research hotpot. As the main vibration source, the micro-vibration of the refrigerator is one of the key factors affecting the imaging quality of the optical remote sensor. In order to quantitatively evaluate the micro vibration characteristics of infrared refrigerator and its influence on imaging performance, and solve the disturbance of micro vibration to high-resolution imaging system, the micro vibration generation mechanism of pulse tube stirling refrigerator is analyzed, and the micro vibration performance is tested and analyzed under different power and service conditions by fixed support dynamometer. Based on the micro-vibration test of the refrigerator, the micro vibration suppression strategy of micro vibration transmission path in the application link is proposed. The finite element simulation analysis of the whole machine shows that the influence of micro vibration on the imaging system is reduced to 0.02%, which proves its effectiveness.

Terahertz antenna is the key component of terahertz detector. The terahertz antenna can assist detectors to detect terahertz signal more efficiently. In this paper, the point effect of fractal butterfly antenna is deeply studied and a fractal butterfly antenna which can work in frequency band of 0.1~2 THz is designed. The proposed fractal butterfly antenna resonates at 0.6 THz frequency, and the minimum return loss can reach -15.89 dB and the maximum gain can reach 6.87 dB. The fractal butterfly antenna was optimized to generate a highly enhanced local field at the point of antenna. This highly concentrated energy coupling effect can effectively improve the performance of the terahertz detector.

Infrared search and tracking system has the advantages of high angular resolution, good concealment, strong detection ability and strong anti-electromagnetic interference ability. It has been widely used in the field of ship early warning and detection. In this paper, the working principle, classification and development status of ship infrared search and tracking system are introduced in detail. Finally, the development trend of ship infrared search and tracking system is summarized.