Suppression of fluctuation on the angle of arrival for freespace optical communication

In order to increase the coupling efficiency and suppress the random angular jitter induced by atmosphere turbulent, the fine tracking system with fast steering mirror （FSM） is demonstrated. The field experiment results of free-space optical communication link across 16 km show that when there is no tracking, the range of the x-axis coordinates＇ fluctuation achieves 46 pixels, corresponding to the incident angle of 73.6 μrad, and its mean square deviation is 6.5 pixels, corre- sponding to the incident angle of 10.4/.trad. When there is tracking, the range of fiuctuation is suppressed to 10 pixels and 16 ktrad, and the mean square deviation reduces to 1.5 pixels and 2.6 brad for the spot＇s centroid and the incident angle, respectively. Significantly, the coupling efficiency increases by 6 times, and the fluctuation of received light power decreases obviously.