3 Gbit/s optically preamplified direct detection DPSK receiver with 116 photon/bit sensitivity

For the first time experimental bit error rate curves are presented for an optically preamplified direct detection differential phase and shift keying (DPSK) communication link. DPSK offers approximately 6 dB peak power sensitivity improvement over more traditionally optically preamplified on/off keying (OOK). Using an erbium doped fibre preamplifier, a fibre Fabry-Perot filter, an optical DPSK demodulator consisting of a fibre-optic Mach-Zehnder interferometer with a 1 bit differential delay, and a balanced receiver, a sensitivity of 116 photon/bit was obtained. To the authors´ knowledge these results represent the first demonstration of optically preamplified DPSK with better sensitivity than previously reported multigigabit per second heterodyne DPSK and approximately 3 dB more sensitivity on a peak power basis than previously reported preamplified OOK systems.