Recent progress in forward error correction and its interplay with transmission impairments

Recent progress in forward error correction (FEC) for optical communications is reviewed. The various types of FEC are classified as belonging to one of three generations. A third-generation FEC, based on a block turbo code, has been fully integrated in very large scale integration, and thanks to the use of 3-bit soft decision, a net coding gain of 10.1 dB was demonstrated experimentally. That has brought a number of positive impacts to existing systems. The Shannon limit is discussed for hard and soft decision decoding. The interplay between FEC and error bursts is discussed. Fast polarization scrambling with FEC has been effective in mitigating polarization mode dispersion (PMD). The error count function has proved useful for the adaptive equalization of both chromatic dispersion and PMD.