Applications of trellis coding to coherent optical communications employing polarisation shift keying modulation

The application of the concept of trellis coded modulation to coherent optical communications using polarisation shift keying modulation is described and analysed. It leads to a receiver formed by a front end which performs the heterodyne detection and the Stokes parameters extraction cascaded with an electronic Viterbi processor operating the maximum likelihood estimate of the transmitted sequence. Results in terms of error event probability obtained analytically and confirmed by simulation show power gains of the order of 3-4 dB without sacrificing bandwidth.