Spectrum-narrowing tolerant signal-processing algorithm using maximum-likelihood sequence estimation for coherent optical detection

A digital signal-processing algorithm that is robust against strong spectrum-narrowing is proposed for optical coherent optical receivers. High spectrum-narrowed tolerance is achieved by using a hybrid architecture composed of spectrum-narrowing adaptive FIR filters with concatenated maximum-likelihood sequence estimation demodulators. A numerical simulation shows that the proposed algorithm can demodulate severely spectrum-narrowed signals, even at 80% of the bandwidth of a Nyquist pulse-shaping criterion filter.