Research On The Method For Optimizing Optical Isolation Of Laser Communication System

Space laser communication has become a key technology to increase the communication rate in the field of satellite space communication because of its wide frequency band,high speed,strong confidentiality,strong anti-electromagnetic interference capability,small size and low power consumption.The space laser communication optical system is an important component for realizing long-distance and high-speed transmission of spatial light.It is a weak light detection system,which emits strong light energy and receives weak light energy during communication,so the high transmitting-receiving isolation must be guaranteed in its optical system.In this paper,the following research is carried out on the optical isolation optimization method for space laser communication system.Firstly,the object of this paper is established as the space laser communication optical system using Cassegrain optical antenna through analysis.The requirements of various requirements of space laser communication optical system are calculated and established.Based on the bidirectional scattering distribution function,the surface scattering theory,which is an important theoretical basis of the isolation problem,is studied.The factors affecting the isolation degree of optical system are analyzed.Second,in order to improve the isolation of the optical antenna,a method for optimizing the backscatter in the surface of eyepiece is proposed and implemented based on establishing the surface scattering model.A method for measuring the backscattering contribution in the eyepiece's surface is proposed based on the surface scattering model and an evaluation model is established based on the method.The backscattering evaluation model is calculated and the custom operand is established by using the ZEMAX macro instruction.Based on the design and isolation simulation for the initial system of optical antenna,the backscatter in eyepiece's surface of the initial system is optimized using the established operands.The isolation after optimization is improved 1.178 dB compared with the initial system.Thirdly,a method is proposed and realized for improving the isolation of the optical antenna by shaping the transmitting beam into a ring beam.According to the transmitting efficiency and isolation of the optical antenna,the parameters of the ring transmitting beam are calculated and established,and the scheme shaping the transmitted beam into a ring beam by using the diffractive optical device is established.The design method of each subsystem in the ring shaping scheme is studied and designing each subsystem.The isolation and transmitting efficiency of optical antenna is raised to 48.01 dB and 92.34% by using the designed transmitting subsystem through the simulation analysis,which is 7.61 dB and 10.92% higher than before.The design of the experiment by using the spatial light modulator is used to verify the correctness of the design of the diffraction shaping device.The experimental results show that the designed diffraction shaping device basically realizes the circular shaping of the transmitting beam.Fourthly,the isolation optimization method based on spectroscopic adjustment is studied.A device is designed for accurately measuring the incident angle while measuring the optical efficiency and the splitting power of the spectroscope based on designing the spectroscopic optical path.The experiment analyzed the method of improving the isolation degree by fine tuning when using the measured spectroscope,and improved the isolation degree 0.79 dB of the system by precisely fine tuning the installation Angle of the spectroscope under the premise of ensuring the efficiency of the system.The design of the tracking subsystem and the communication receiving subsystem was completed,and the overall combination of the various subsystems in space laser communication optical system was completed.