Performance of DPSK and CPFSK systems with significant post-detection filtering

A rigorous model for preamplifier implemented DPSK and CPFSK systems with delay-detection and postdetection filtering is presented. The system performance is impaired by amplifier spontaneous emission noise as well as laser phase noise. A best sensitivity for the system is 20 (DPSK) and 36 (CPFSK) received signal photons for a 10/sup -9/ bit error probability. It is found that, using the CPFSK system, significant amounts of phase noise can be tolerated provided that sufficient bandpass bandwidth is allocated and a large modulation index value is used. A linewidth as large as five times the bit rate causes only a 4.2-dB penalty for a receiver employing polarization control and a 5.3-dB penalty for a polarization diversity receiver.>