Direct measurement of the bit error rate improvement of a laser communication system with low-order adaptive optics

Abstract

Recent experiments performed at UNC Charlotte indicate that we can achieve a reduction in the bit-error rate (BER) for a laser communication system with the implementation of low-order (tip/tilt) adaptive optics in a free-space communication link. We previously reported indirect measurements of the BER by measuring scintillated signals with and without an adaptive optics loop operating. By assuming standard values for receiver noise, we calculated the BER that we would expect. In this paper, we report on the direct measurements of the BER that we observe with the laboratory adaptive optics laser communication system. By directly comparing both the low (“0”) bits and the high (“1”) bits of the outgoing laser modulation signal with the PIN diode-detected signal we determine the BER as a function of various propagation, receiver electronics, and adaptive optics system parameters. Scaling our visible measurements to atmospheric paths and IR wavelengths, we compare our results with vigorous theoretical calculations.