Performance analysis of coherent optical phase-diversity receivers with DPSK modulation

The transmission performance of two phase-diversity receiver structures using a six-port fiber coupler is investigated for coherent optical communication systems with differential phase-shift-keying (DPSK) modulation. A general method for evaluating the error probability of phase-diversity DPSK receivers using delay-and-multiply demonstrators is derived. The method is used to show that, in the shot-noise limited case, the performance of the phase-diversity DPSK receivers is close to that achievable with a heterodyne receiver, provided the frequency offset between lasers is less that about 1% of the bit rate. The allowable total laser linewidth is in the range of 0.3-0.4% of the bit rate.>