MLSE-based receivers on DWDM lightwave systems

In dense wavelength division multiplexed (DWDM) links, the need for greater available bandwidth results in smaller channel separation and larger channel count. This increases the importance of nonlinear coupling effects such as four wave mixing (FWM) and cross-phase modulation (CPM). These impairments, together with chromatic dispersion (CD), polarization mode dispersion (PMD), and amplified spontaneous emission (ASE) noise limit the maximum reach of the optical links. Maximum likelihood sequence estimation (MLSE) receivers can incorporate detailed knowledge of the statistical properties of noise and crosstalk into the decision process, therefore improving performance in the presence of these impairments. These receivers have been previously proposed in [(W. Sauer-Greff et al., 2003), (H.F. Haunstein et al., 2001)] to combat CD and PMD in IM/DD optical channels. In this paper we propose to extend the use of MLSE to DWDM links to combat the combined effect of nonlinear crosstalk, dispersion and noise. We derive a new analytical expression for the statistics of the received signal in the presence of FWM which is necessary to implement the MLSE receiver. As a second important contribution of this paper, we present a theoretical performance analysis of MLSE in DWDM optical channels. Computer simulations show excellent agreement between the prediction of the theory and simulation results