Optically implemented DPSK and CPFSK systems: effect of post-detection filtering

Results for the sensitivity of preamplifier differential phase-shift keying (DPSK) and continuous phase-shift keying (CPFSK) systems with electronic post-detection filtering are presented based on a rigorous model which is outlined. It takes into account amplifier and laser phase noise. The best sensitivities for a 10/sup -9/ error probability are 20 (DPSK) and 36 (CPFSK) received photons. It is found that the CPFSK system can tolerate significant phase noise by increasing the modulation index and the bandpass filter bandwidth. A linewidth of 5 times the bit-rate causes 4.3 dB penalty using polarization control and for a modulation index of 51. DPSK systems cannot tolerate linewidths larger than about 1% of the bit-rate.<>