Evaluation of optimal bandwidth in optical FSK system influenced by laser phase noise

In this paper, an optical frequency shift keying (FSK) system with TFS (two-filter structure), also known as dual-filter FSK, is observed in the presence of laser phase noise. Sensitivity of the receiver is shown as a function of intermediate frequency (IF) bandwidth and a bandwidth of the low-pass postdetection filter. It is shown that there is an optimal pair of bandwidths which minimizes required sensitivity; a few figures for different amounts of phase noise are given. The results in this paper are based on truncated Taylor expansion method and a method based on complex analysis is used to evaluate the integrals involved.