Based On The Spgd Star Optical Communication Phase Correction

The laser communication system has the advantages of higher bandwidth, higher capacity, lower energy consumption, better security and small volume. Moreover, its termination is much smaller and lighter, and thus using it as a vehicle of information became one of the most competitive high-speed and secure satellite-to-ground laser communications nowadays. In satellite-to-ground laser communications, laser beam, as the information carrier, will propagates through the aerosphere of the earth. In this process, the atmospheric turbulence effects will result in phase distortion which will reduce the performance of laser communication systems, so satellite-to-ground laser communications systems need phase correction.Adaptive Optics (AO) is a new subject researching the real-time and automatic correct of light wave-front phase distortion. Optimized adaptive optics avoids a series of problems which are encountered in the traditional adaptive optics system when measuring the distorted. It simplifies the system architecture, reduces the costs and can be applied to the complicated conditions where wave-front distortions can not be measured directly. The adaptive optics based on stochastic parallel gradient descent (SPGD) algorithm is an optimized adaptive optics that has great application potential.This thesis investigates the SPGD AO technique and the feasibility of applying it to the satellite-to-ground laser communication system to improve the quality of communication. Atmospheric turbulence effect of satellite-to-ground laser communication is analyzed and the model of satellite-to-ground laser communication link is built in this thesis. This thesis describes the structure and working principle of the adaptive optics system based on SPGD algorithm. A61-unit SPGD adaptive optics numerical model is built, and the sub-modules are simulated and analyzed, and the Power-In-Bucket(PIB), which is easy to measure and directly related to communication signal to noise ratio, is chosen as the performance metric. The affect factors to the convergence limit and the convergence speed of the SPGD adaptive optics system are analyzed by theory and numerical simulation experiments in detail. The results indicated that the perturbation amplitude and the gain coefficient both had influence on the convergence limit and the convergence speed. So the perturbation amplitude and the gain coefficient should be chosen reasonably according to the requirements for the correction effect and the correction speed of practical system to improve the system’s whole performance. The influence of different wave-front phase distortion to the convergence limit and the convergence speed is simulated and analyzed. Based on the conclusion, two methods of improve the convergence speed is simulated and analyzed. Simulation results show that gain coefficient adaptive adjustment can improve the convergence speed and has no influence of the convergence limit, and controlled variables grouping also can improve the convergence speed but sacrifice the convergence limit. Two implementations of SPGD algorithm is introduced last, That is the software realization method and the hardware realization method. To sum up, SPGD adaptive optics systems can correct the phase distortion of the satellite-to-ground laser communication system so as to improve the communication quality of satellite-to-ground laser communication systems.