Optical source linewidth criteria for heterodyne communication systems with PSK modulation

The performance of an optical heterodyne communication system is analysed for the cases of phase-shift keying (PSK) with synchronous electrical demodulation and differential PSK with non-synchronous demodulation. The combined effect on the system performance from the shot noise, quantum phase noise of the optical sources and the pulse shaping are considered. From the results, criteria are given for the maximum linewidth of the transmit and local optical sources to satisfy a given degradation in the optical receiver sensitivity.