Exact performance evaluation of heterodyne coherent optical systems with FSK modulation

The authors report the analysis and the performance evaluation of a coherent optical receiver with binary frequency shift keying (FSK) modulation. The receiver makes use of envelope detection with two branches for the two transmitted frequencies. The analysis is performed also in the presence of a low-pass post-detection filter. The analysis accounts for the effect of phase noise, modeled as a Brownian motion, which strongly affects the system performance. The numerical evaluation is carried out by the use of Gaussian quadrature rules and is based on previous results on the moment characterization of the phase noise