Self-amplitude modulation in PSK coherent optical transmission systems

Self-amplitude modulation due to group velocity dispersion (chromatic dispersion of an optical fiber) in phase-shift keying (PSK) coherent optical transmission systems is presented. It may place a serious limitation on performance of such systems by limiting the maximum transmission distance attainable at a given bit rate. The maximum transmission distance for any prescribed degree of self-amplitude modulation is derived for PSK coherent systems. The result shows that the distance over which appreciable amplitude modulation is impressed on a phase-modulated signal is considerably less than the dispersion-limited transmission distance for intensity modulated direct detection systems.