Research On Stray Light Problems Of Optical Transceivers For LEO Intersatellite Laser Communication

Space laser communication has the advantages of wide communication frequency band,high-speed data transmission,good cost performance,easy deployment and communication security,the overall system is small,light weight,low power consumption in many fields have the demand and application.At present,the communication mode of laser communication terminal is more the use of transceiver integrated duplex communication,using the same optical antenna,the same signal transceiver channel to receive and transmit signals.However,in the process of signal transmission and reception,the optical devices in the whole optical system,such as optical elements,produce backscattered stray light into the signal receiving detector,resulting in the reduction of signal-to-noise ratio or directly drown the effective signal.The communication quality of laser communication terminal is seriously affected.Therefore,good isolation between signal transmission and reception is the key to establish duplex bidirectional laser communication.In this paper,the transmission theory of stray light in laser communication system is analyzed firstly,and then the influence of space background stray light on laser communication system is analyzed.Then,through the structure of the laser communication terminal and the design of the optical system on the suppression of stray light is studied,the isolation simulation model is established,and the factors affecting the isolation effect of the communication terminal are analyzed.The main factors are the surface roughness of the optical element and the surface cleanliness of the optical element.Finally,Matlab mathematical model and Trace Pro simulation model are used to analyze and verify the design of transceiver isolation degree of each optical element.The results have a significant effect on the improvement of the internal transceiver isolation degree of laser communication system.The specific content of this paper is as follows:(1)The optical antenna,communication transceiver branch optical path and infrared detection branch of laser communication system are designed by using Zemax software according to the optical design index,and the image quality evaluation of optical design is completed.(2)According to the design and calculation formula of the light shield,a cylindrical light shielding system with increasing position of the light shield ring is designed.Simulate and analyze the ability of the light shield to suppress stray light,mainly analyzing the impact of solar stray light at different incident angles on laser communication terminals and the impact of earth surface stray light at different satellite orbital heights on laser communication terminals.(3)Derive the formula for signal transmission and reception isolation based on Jones matrix,and use Matlab software to calculate the isolation degree.Calculate the end machine isolation degree for different surface roughness and cleanliness.Then,a simulation model was established based on the optical structure,and the ABg model and Harvey Shack model parameters were derived.The stray light analysis software Trace Pro was used to further analyze the isolation simulation analysis of the overall structure of the end machine.Based on the comparison of simulation results between two models,a method is provided to improve the isolation effect of laser communication systems in transmitting and receiving signals.(4)According to the results of simulation analysis,the surface roughness of the half wave plate,the quarter wave plate and the optical antenna telescopic element has an influence on the isolation effect.The greater the roughness,the smaller the isolation effect.At the same time,with the increase of the contamination level of each lens,the isolation degree of laser communication terminal will gradually decrease.Finally,model simulation is carried out to optimize the parameters of communication terminal components,and an optimization scheme is proposed.The surface roughness of lens of each component is set to0.5nm,the contamination level is lower than CL=300,and the internal isolation degree of laser communication terminal can reach 78.35 d B.This optimization scheme has guiding significance for the design of remote transceiver laser communication system with higher isolation requirements.