Forward error correction (FEC) techniques in long-haul optical transmission systems

The use of FEC provides significant coding gain, which has been used to demonstrate error-free transmission (1) under severely errored operating conditions, (2) with high spectral efficiency, (3) over distances exceeding 10,000 km, and (4) at high bit rates. Recent experiments using FEC have demonstrated aggregate transmission capacity approaching 2 Tb/s. Most importantly, FEC-coded transmission can tolerate a lower optical SNR on the line, which in turn reduces impairments induced by nonlinearity, with the net effect being an increase in the Q/sup 2/-factor when signal power is reduced. There is presently significant activity directed towards developing more powerful codes as well as more efficient decoding algorithms.