Demodulation and Detection Schemes for a Memoryless Optical WDM Channel

TL;DR

The paper addresses demodulation and detection for a memoryless optical WDM channel with Kerr nonlinearity modeled via SPM and XPM, where MFS is suboptimal. It analyzes six receivers built from three demodulators (MFS, SS, MxM) and three detectors (MD, MAP, TS), deriving high-power SER asymptotics or bounds and validating with Monte Carlo simulations. It shows that MFS-based receivers cannot achieve zero SER while the optimal SS-MAP can, and proposes low-complexity near-optimal solutions using MxM with MD or TS that achieve arbitrarily low SER. It additionally evaluates performance under single-span fiber-optical conditions using split-step simulations, highlighting practical relevance for nonlinear compensation strategies.

Abstract

It is well known that matched filtering and sampling (MFS) demodulation together with minimum Euclidean distance (MD) detection constitute the optimal receiver for the additive white Gaussian noise channel. However, for a general nonlinear transmission medium, MFS does not provide sufficient statistics, and therefore is suboptimal. Nonetheless, this receiver is widely used in optical systems, where the Kerr nonlinearity is the dominant impairment at high powers. In this paper, we consider a suite of receivers for a two-user channel subject to a type of nonlinear interference that occurs in wavelength-division-multiplexed channels. The asymptotes of the symbol error rate (SER) of the considered receivers at high powers are derived or bounded analytically. Moreover, Monte-Carlo simulations are conducted to evaluate the SER for all the receivers. Our results show that receivers that are based on MFS cannot achieve arbitrary low SERs, whereas the SER goes to zero as the power grows for the optimal receiver. Furthermore, we devise a heuristic demodulator, which together with the MD detector yields a receiver that is simpler than the optimal one and can achieve arbitrary low SERs. The SER performance of the proposed receivers is also evaluated for some single-span fiber-optical channels via split-step Fourier simulations.