Study Onthe Control Method Of Enhancing The Fiber Coupling Efficiencyof The Space Optical Communication

Todays, the technology of fiber communication develops fast and is widely used in the area of civil and military for its high bandwidth and low loss of signal. As the developmentof fiber communication and the rapid growth of bandwidth of fiber communication, the space optical communication(SOC) has the chance to replace the space microwave communication as the primary space communication for it has the advantages of fiber communication and microwave communication. Therefore, many developed countries had done a mountain of researches on SOC areas of satellite-to-satellite, satellite-to-ground, space-to-ground, ground-to-ground and some significant achievements had get. Since the signal in the receive end of SOC usually is weak and the fiber coupling efficiency will influence the rate of decoding directly, the fiber coupling efficiency is the primary challenge that the system of SOC faced.The factors that influence the fiber coupling efficiency are mainly atmospheric turbulence, atmospheric attenuation and the turbulence of receive end. The atmospheric attenuation absorbs and scattering some light, which can’t be compensated. In the receive end, the turbulence of atmospheric and receive end itself will cause problems of random jitter of the light spot in the CCD, the power loss of signal light and the change of initial coupling position, and the loss of this part can be compensated to develop the fiber coupling efficiency.In recent years, the stochastic parallel-gradient-descent(SPGD) algorithm is widely used in adaptive optical since the principle and implement of SPGD is simple and SPGD convergence fast. In this paper, SPGD with two dimension and faststeering-mirror(FSM) will be used to compensate the fiber coupling efficiency loss which is caused by atmospheric and random jitter of receive end considering the advantage of SPGD in solving the stochastic problem. The principle of this method is that the SPGD generates two dimensions turbulence of plus and minus to drive the FSM, and the optical power meter gets the power of plus and minus. The difference of the plus-power and minus-power will be the judgment of SPGD to generate the next turbulence. The main factors that influence the result of using SPGD develops the fiber coupling efficiency are the initial coupling position and the parameters of disturbance gain and disturbance amplitude for SPGD. The experiments show that the initial coupling position will decide whether the SPGD can develop the power of fiber, and the parameters of SPGD will influence the velocity and stabilization of convergence.In recent years, the machine vision develops fast and is widely used in image acquisition and processing, and the CCD has superiority in parameter measurement. The application of the machine vision is an important direction of improve the fiber coupling efficiency.So, in this paper, the machine vision with the CCD is used to solve problem of finding the initial coupling position difficultly when using SPGD to develop fiber coupling efficiency and then the SPGD is used to develop the fiber coupling efficiency. The correlative experiments platform will be established to instruct how to use machine vision and SPGD to develop the fiber coupling efficiency.