Research On The Influence Of Active Stray Light On The Performance Of Laser Communiciation System

Laser communication system is a system that uses laser as an information transmission carrier to perform high-speed communication in free space.The environment where the laser communication system terminal is located generally has a large amount of external stray light,among which the active stray light has the greatest influence on the laser communication system.At present,most researches on stray light in laser communication systems are focused on natural stray light and lack of research on active stray light.In this thesis,the influence of active stray light on the optical system performance,tracking performance and communication performance of the laser communication is studied in theory and simulation,and the ground simulation experiments are carried out.The active stray light characteristics of laser communication system are analyzed.A Cassegrain optical antenna model for laser communication was established and simulated.The propagation characteristics of the small-angle active stray light inside the Cassegrain antenna are studied,and the main mirror baffle is optimized to reduce the active stray light.The active stray light intensity of the optimized structure has been reduced by 61.6% compared with the general structure.This dissertation analyzes the error of tracking angle deviation laser communication system caused by active stray light theoretically and simulates the influence of the incident angle and intensity of active stray light on the rough tracking and fine tracking of laser communication system;Then,this thesis studies the Optimum light spot detection algorithm under different interference conditions.The results show that the error of tracking angle deviation decreases with the increase of the incidence angle of the active stray light,and increases with th e increase of the interference intensity.The error of tracking angle deviation of the fine tracking measurement decreases with the increase of the incidence angle of the active stray light,and increases with the increase of the interference intensity and the "field of view" of the “window”.When the interference intensity is less than 60 d B,the square centroid algorithm is more accurate,and when the interference intensity is greater than 60 d B,the centroid algorithm is more accurate.This dissertation studies the theory and Simulation of channel matrix、error rate and channel capacity of laser communication system,in which beacon light or signal light is interfered by active stray light.The results show that when the beacon light is disturbed,the bit error rate increases with the increase of the standa rd deviation of the tracking angle deviation.In the case of satisfying the use requirement of the bit error rate,reducing the decision threshold can improve the system anti-jamming capability.When the signal light is interfered,the bit error rate and channel capacity are affected by the mean and standard deviation of the active stray light intensity.To keep the bit error rate below the minimum tolerance of 10-6,the best decision can be made by the simulation to ensure that the bit error rate meets the requirements.The threshold value range is 0.38-0.59.According to the decision threshold and active stray light intensity,adjusting the signal strength can improve the channel capacity of the interfered laser communication system.This dissertation sets up an active stray light ground simulation experiment system for laser communication terminals.Experiments were carried out to investigate the effect of active stray light on the laser communication optical system and its tracking performance.The results showed that the small-angle active stray light can pass through the Cassegrain antenna.The error of tracking angle deviation with the angle and intensity of the active stray light is basically the same as that of the simulation.