Properties of nonlinear noise in long, dispersion-uncompensated fiber links

TL;DR

This paper investigates the nonlinear interference noise in long fiber-optic links with high dispersion, clarifying its true statistical nature and dependence on modulation formats, which challenges previous Gaussian assumptions.

Contribution

The study identifies flaws in the Gaussian noise model and provides a more accurate characterization of NLIN, showing its dependence on transmitted data and modulation formats.

Findings

NLIN is not additive Gaussian noise.

NLIN depends strongly on the modulation format.

The true NLIN power differs from the GN model predictions.

Abstract

We study the properties of nonlinear interference noise (NLIN) in fiber-optic communications systems with large accumulated dispersion. Our focus is on settling the discrepancy between the results of the Gaussian noise (GN) model (according to which NLIN is additive Gaussian) and a recently published time-domain analysis, which attributes drastically different properties to the NLIN. Upon reviewing the two approaches we identify several unjustified assumptions that are key in the derivation of the GN model, and that are responsible for the discrepancy. We derive the true NLIN power and verify that the NLIN is not additive Gaussian, but rather it depends strongly on the data transmitted in the channel of interest. In addition we validate the time-domain model numerically and demonstrate the strong dependence of the NLIN on the interfering channels' modulation format.