Research On Pre-compensation Of Beam Phase Distortions Of Ground-to-satellite Uplink Laser Communication

Satellite laser communication technology has many unique superiorities,such as high data transmission rate,good confidentiality,strong anti-interference ability,small size of terminal equipment,light mass,etc.Therefore,it has been paid great attention internationally and has become a key research direction of many space powers.During the laser communication between the satellite and the ground,laser beam,as the information carrier,will propagate through the atmosphere of the earth's surface.In this process,the refractive index fluctuation caused by the atmospheric turbulence will destroy the coherence of the optical field and make the distortion of the beam wavefront phase,resulting in a series of optical effects,such as intensity fluctuation,arrival angle fluctuation,beam wander,etc.For various effects caused by atmospheric turbulence,there have been many kinds of suppression techniques,especially the compensation technique for satellite-to-ground laser downlink,which has been relatively mature.Compared with the downlink,atmospheric turbulence has a more serious effect on the uplink laser beam.But there are few reports on the compensation technology for this kind of situation.In this paper,the theory and simulation of the pre-compensation method for the beam phase distortion of ground-to-satellite uplink laser communication system are studied,and the system performance in pre-compensation is analyzed.The specific research contents are as follows:Aiming at the influence of atmospheric turbulence on laser propagation between satellite and ground,the method of pre-compensation using Zernike polynomials is studied.The principle of phase pre-compensation is analyzed and the function relation between the number of compensation terms and the wavefront error is given.This paper also studies the influence of point-ahead-angle on the effect of pre-compensation.The relation of wavefront error with point-ahead-angle and the number of compensation is found,and the feasibility of the phase pre-compensation method in the case of pointahead-angle is been evaluated.The influence of atmospheric turbulence on laser propagation is simulated by using the phase screen generated by numerical simulation,and the phase distortion improvement of ground-to-satellite uplink laser beam under the pre-compensation is simulated.The far-field beam intensity distribution and beam wander of the uplink beam after pre-compensated by different terms are obtained in the case of whether thereis a point-ahead-angle or not.The influence of pre-compensation item number and point-ahead-angle on the result of compensation is analyzed and the effect of beam scatter angle on the ground-to-satellite uplink with point-ahead-angle is studiedThis paper studies the bit error rate of ground-to-satellite uplink laser communication system under the condition of pre-compensation,analyzes the improvement of the bit error rate caused by pre-compensation.The influence of the point-ahead-angle and beam scatter angle on the bit error rate of ground-to-satellite uplink laser communication system is studies,and optimizes the propagation parameters under the condition of the optimal pre-compensation terms.The research work in this paper will provide some reference for the design of ground-to-satellite uplink laser communication system.