Coding of optical on-off-keying signals impaired by phase noise

The benefits of coding an optical communications system that employs binary on-off-keying heterodyne detection are shown. The system is impaired by laser phase noise as well as by additive white Gaussian noise (AWGN). A receiver structure especially designed to mitigate the effects of phase noise in the presence of AWGN is assumed. This special receiver structure requires a wider band front-end IF filter than would be required for a phase-noise-free signal. Results computed for several different coding schemes indicate that the benefits of coding are large and the costs are small. For a linewidth-to-bit-rate ratio of 0.64, a half-rate binary code that can correct three bit errors provides a 50% reduction in the required IF filter bandwidth (and therefore the required IF) and about 5 dB of reduction in required laser power. The benefits of coding are greatest under high-βT conditions, corresponding to low bit rates, where coders and decoders are most practical to implement. The results obtained suggest the possibility that forward error correction could be used to improve the channel packing efficiency of FDMA (frequency division multiple access) networks