Frequency-noise cancellation in semiconductor lasers by nonlinear heterodyne detection

The bit-error-rate (BER) performance of conventional noncoherent, heterodyne frequency-shift-keyed (FSK) optical communications systems can be surpassed by the use of a differential FSK modulation format and nonlinear postdetection processing at the receiver. A BER floor exists for conventional frequency-shift keying because of the frequency noise of the transmitter and local oscillator. The use of differential frequency-shift keying with nonlinear postdetection processing suppresses this BER floor for the semiconductor laser system considered here.