High-sensitivity 40-gb/s RZ-DPSK with forward error correction

A high-sensitivity 40-Gb/s differential-phase-shift-keyed (DPSK) system with coding is demonstrated with back-to-back sensitivity as good as 8.7 photons per bit at a 10/sup -9/ bit-error rate. Coding is done on the 40-Gb/s data using high-speed electrical multiplexers and demultiplexers combined with four 10-Gb/s forward error correction chips that operate with 7% overhead. The DPSK receiver uses a simple approach to DPSK balanced detection.