Evaluation of filtering effects on optical BPSK systems using external cavity semiconductor lasers

The performance of an optical BPSK (binary phase shift keying) heterodyne system using external-cavity semiconductor lasers and a squaring loop carrier recovery circuit is evaluated theoretically via an analytical method. The method is based on the Gram-Charlier series and takes into account the effect of filtering on the baseband signal disturbed by non-Lorentzian phase noise from external-cavity semiconductor lasers and additive Gaussian noise. It is found that the filter decreases the impact of laser phase noise, namely by reducing the degradation due to relaxation oscillations.<>