Information Transmission using the Nonlinear Fourier Transform, Part III: Spectrum Modulation

TL;DR

This paper introduces a nonlinear frequency-division multiplexing scheme that leverages the integrability of the nonlinear Schrödinger equation to improve fiber-optic communication by mitigating nonlinear distortions and inter-channel interference.

Contribution

It presents a novel NFDM method that directly modulates the nonlinear Fourier spectrum, effectively handling nonlinearity and reducing cross-talk in fiber-optic channels.

Findings

NFDM can cope with increasing signal power and transmission distance.

The method reduces deterministic cross-talk compared to traditional linear approaches.

Simple spectral efficiency examples demonstrate potential improvements.

Abstract

Motivated by the looming "capacity crunch" in fiber-optic networks, information transmission over such systems is revisited. Among numerous distortions, inter-channel interference in multiuser wavelength-division multiplexing (WDM) is identified as the seemingly intractable factor limiting the achievable rate at high launch power. However, this distortion and similar ones arising from nonlinearity are primarily due to the use of methods suited for linear systems, namely WDM and linear pulse-train transmission, for the nonlinear optical channel. Exploiting the integrability of the nonlinear Schr\"odinger (NLS) equation, a nonlinear frequency-division multiplexing (NFDM) scheme is presented, which directly modulates non-interacting signal degrees-of-freedom under NLS propagation. The main distinction between this and previous methods is that NFDM is able to cope with the nonlinearity, and thus, as the the signal power or transmission distance is increased, the new method does not suffer from the deterministic cross-talk between signal components which has degraded the performance of previous approaches. In this paper, emphasis is placed on modulation of the discrete component of the nonlinear Fourier transform of the signal and some simple examples of achievable spectral efficiencies are provided.