Laser noise impact in the design of an heterodyne optical PSK receiver

Abstract

An evaluation of the performance of a coherent optical receiver for binary PSK (phase-shift keying) is carried out. Both AM and FM noise due to transmitter and local oscillator semiconductor lasers have been taken into account. The nonlinear dependence between the phase noise variance and the laser linewidth is considered. A heterodyne receiver is studied in terms of its output SNR (signal-to-noise ratio), taking into account AM noise and both thermal and shot noises. The required SNR to achieve a BER (bit error rate) of 10-9 is studied, considering the FM noise in both semiconductor lasers. The importance of taking into account the effects of AM and FM noise in the investigation of the receiver sensitivity in a binary PSK coherent optical system is demonstrated. An accurate evaluation of the penalty in the sensitivity due to the laser quantum noise is obtained. It is shown that the AM noise due to the laser working as local oscillator degrades the expected SNR