Receiver Performance Characterization for Modulating Retro-Reflector Atmospheric Optical Links With Pulsed Lasers and Optical Pre-Amplifiers

Abstract

Receiver performance is calculated for two types of free-space atmospheric optical communications systems -a direct detection system using a p-i-n photodiode preceded by an optical amplifier, and an ideal coherent receiver operated in its shot-noise limited regime without an optical pre-amplifier. The signal format for both is amplitude shift keying (onoff modulation) with an assumed rectangular light pulse of duration T seconds. The more accurate Beckman probability density function (pdf) is used to describe the intensity fading rather than the more commonly used log-normal pdf which overestimates receiver performance. A coherent receiver using asynchronous detection is shown to outperform the direct detection system with an optical pre-amplifier gain of 30 dB by anywhere from 7 to about 10 dB depending on Rytov variance intensity fading levels. In addition, the effect of inner scale turbulence parameter, l 0 , on system bit error rate is demonstrated.