An improved optical heterodyne DPSK receiver to combat laser phase noise

Presents a method to improve the performance of a standard delay-and-multiply type optical heterodyne binary-DPSK receiver. This is achieved by using separate “weighting” bandpass filters to shape the phase noise corrupted direct and delayed signals before combining and decoding as for the standard receiver. The optimization of a filter parameter allows this “weighted” receiver to exhibit a lower phase noise sensitivity than the standard receiver. The most significant achievement of the weighted receiver is the ability to tradeoff excess signal power to obtain low bit error rates when large amounts of phase noise are present