Weight 1/2 block codes for optical communications.

The possibilities of using certain constant weight block codes in optical data links and in optical ring networks are discussed. The codes that appear particularly attractive are those that have exactly as many 1's as 0's in each codeword so that there is no penalty for a.c. coupling. Codes can be simple (such as Manchester) or more complicated so as to support control channel signaling, error detection, and/or forward error correction. The encoding schemes are described and the decoding problems explored.