Optimum APD Gain Evaluation of FSO System for Inter-building Laser Communication Application

Abstract

This paper evaluates the optimum gain performance of avalanche photodetector (APD) for various modulation techniques under dense fog condition of visibility within 50 m in Indian subcontinent. The comparative BER performance study has been outlined for the above conditions and weak atmospheric turbulence (Log-normal). Joint effects of shot, thermal, and background noise together with pointing error are taken into consideration for evaluation of error performance. In particular, it is observed that the performance of free-space optical (FSO) system at optimum APD gain is exceptionally well and good up to standard limit. Furthermore, the capacity evaluation in fog conditions is outlined for On-Off keying (OOK), binary phase-shift keying (BPSK), differential phase-shift keying (DPSK), and binary pulse position modulation (BPPM). From the diversity of performance study, this article finally suggests the suitable modulation technique for dense fog conditions and proposes the optimum gain of APD.