20 photon/bit 565 Mbit/s PSK homodyne receiver using synchronisation bits

The method for and results of a sensitivity measurement of a PSK homodyne receiver are presented. This receiver achieves phase locking of the local oscillator by means of synchronisation bits. The departure from an ideal receiver at the shot noise limit is 3.5 dB. For BER=10^-9 only 20 photon/bit are required. This may be the highest sensitivity obtained to date with any optical communication system.