Performance of 4-ary ASK for optical communication systems in dispersive, nonlinear environments

Multi-level modulations schemes for optical communication systems use less bandwidth for a given data rate, and so besides having potential spectral efficiency advantages, may also provide reduced sensitivity to fiber dispersion and nonlinearities. In this paper we model the propagation of 4-level amplitude shift keying signals, and compare their performance, for both return-to-zero and non-return-to-zero formats, to on-off keying. At the cost of a back-to-back sensitivity penalty, significantly increased dispersion reach is shown, and reduced impact of nonlinearities is also demonstrated in a multi-channel environment.