Unphysical metastability of the fundamental Raman soliton in the reduced nonlinear Schroedinger equation

TL;DR

This paper reveals that the fundamental Raman soliton in the reduced NLSE model is metastable and unphysical, as it eventually collapses due to an instability not present in the full model, impacting accurate optical fiber simulations.

Contribution

It demonstrates the unphysical metastability of the Raman soliton in the reduced NLSE and highlights the importance of using the full convolution model for accurate results.

Findings

Raman soliton in reduced NLSE is metastable and collapses after hundreds of dispersion lengths.

The instability is absent in the full convolution model of the Raman effect.

Noise eigenfunction analysis confirms the numerical simulation results.

Abstract

We demonstrate theoretically and numerically that the fundamental Raman soliton of the widely used nonlinear Schroedinger equation (NLSE) with a linear approximation of the Raman gain ({\em reduced} NLSE) is metastable. It can propagate for hundreds of dispersion lengths along the optical fibre before eventually disappearing due to a peculiar instability, leading to a collapse. The noise eigenfunction analysis agrees well with the results obtained via direct pulse propagation simulations. This instability is not present when modelling the Raman effect via a full convolution, and thus the reduced NLSE often leads to unphysical results, and should be avoided.