High speed image detector appliance in free space optical communication

Application of very fast image detectors to the fine tracking system of free space optical (FSO) communication has been demonstrated in several projects. In the near surface of the earth, the influence of the atmosphere on the optical communication system must be considered. The optical communication system must be designed to be able to suppress the influence of atmospheric turbulence. We have used the high speed CMOS image sensor for the fine tracking system of 15 Km free space optical communication demonstration. In this paper we present the atmospheric influence on the fine tracking detector, and find out the tracking algorithm for the fine tracking detector to detect the center of the received spot. We have four parts: first, briefly discuss the advantage of using image detector; second, review the theory used to the atmospheric turbulence model, and analyze its influence on the fine tracking system; third describe a new centroid algorithm for the image detector; last, we give the result of using this algorithm in the experiment.