TRELLIS-CODED POLARIZATION SHIFT KEYING MODULATION FOR DIGITAL OPTICAL COMMUNICATIONS

The application of the well-known technique of Trellis Coded Modulatio n to coherent optical communications using Polarization Shift Keying ( POLSK) is described and analyzed. The resulting receiver is formed by a front-end which performs the heterodyne detection and the Stokes par ameter extraction; cascaded with an electronic Viterbi processor opera ting the maximum likelihood estimate of the transmitted sequence. Resu lts in terms of the error event probability using optimum as well as a simpler suboptimum branch metric show power gains on the order of 3-4 dB, at the expense of a reasonable increase in complexity, only conce rning the processing in the electronic domain. These coding gains are not lost even in the presence of high levels of phase noise, to which POLSK in general is highly insensitive.