Carrier recovery and filtering in optical BPSK heterodyne systems disturbed by phase noise from external cavity semiconductor lasers

Abstract

The performance of an optical BPSK heterodyne system using external cavity semiconductor lasers and a squaring loop carrier synchroniser is theoretically analysed by means of an analytical method. The method is based on the Gram-Charlier series and includes the effect of filtering on the baseband signal disturbed by phase error due to imperfect carrier recovery and additive Gaussian noise. A detailed modelling of the phase error term is also performed, taking into account the influence of non-Lorentzian laser phase noise. Numerical results for a typical 565 Mb/s BPSK system are presented. It is found that the filter decreases the impact of laser phase noise, namely by reducing the degradation due to relaxation oscillations of the semiconductor lasers.