Abstract

Terrestrial laser communication systems may be limited in their performance by atmospheric turbulence, which distorts the wavefront of a propagating laser beam [1]. At low turbulence levels a laser communication link is limited by atmospheric beam wander. This effect can be corrected by implementing an adaptive pointing system at the transmitter or by increasing the beam size at the receiver [2]. At higher turbulence levels the communication link is also limited by atmospheric scintillation, i.e., amplitude and phase distortions, at the receiver. These distortions induce power fading of the optical carrier detected by the receiver, resulting in an increased bit error rate (BER) of the system. The designer of a laser communication system will therefore seek to maximize the energy collected by the receiving photodetector while minimizing variations in this quantity. One approach to this problem is to implement an adaptive optic system to correct wavefront distortions and reduce power fadings. With an eye to astronomic applications, however, adaptive optics is usually designed to improve the Strehl ratio, resulting in greater image quality [3] but not necessarily in power fading improvement. Few comparisons of the Strehl ratio and collected energy (and hence BER) have been performed [4], making it difficult to assess the benefit of adaptive optics on a communication system. In this work we present the result of Monte Carlo simulations of a strongly turbulent atmosphere and compare the improvement on Strehl ratio and collected energy at the receiver of a laser communication link with and without adaptive optics.

© 1996 Optical Society of America