A postdetection strategy for the reduction of error floors of optical DPSK receivers impaired by laser phase noise

A postdetection strategy for the performance enhancement of optical binary differential phase shift keying (DPSK) receivers impaired by phase noise is proposed and investigated. First, the bandwidth of integrate-and-dump (I&D) filters is increased so that multiple samples per symbol duration of the received signal are obtained. Previously, a scheme, hereafter referred to as fixed-window (FW) postdetection processing, was introduced. In this approach, the samples separated in time by a symbol time at the output of I&D filters are correlated. The decision circuitry, subsequently, provides a sum of the resulting signal over a symbol time to yield a decision variable. In the proposed scheme here, hereafter referred to as symmetrical expanding window (S-EW) postdetection processing scheme, samples that are centered about the signal transition point in a two-symbol signaling interval are correlated. Numerical results indicate that the S-EW scheme achieves an error floor that is significantly smaller than that of the its FW counterpart.