# Modulation instability, rogue waves and spectral analysis for the sixth-order nonlinear Schrodinger equation

## TL;DR

This paper investigates modulation instability, rogue waves, and spectral properties of the sixth-order nonlinear Schrödinger equation, revealing how higher-order dispersion influences stability and wave structures, and constructing explicit rogue wave solutions.

## Contribution

It introduces higher-order rational solutions for the sixth-order nonlinear Schrödinger equation using Darboux transformation, and analyzes the spectral transition between rogue waves and solitons.

## Key findings

- Higher-order dispersion affects modulation stability regimes.
- Explicit Nth-order rogue wave solutions are derived.
- Spectral analysis shows transition between rogue waves and W-shaped solitons.

## Abstract

Modulation instability, rogue wave and spectral analysis are investigated for the nonlinear Schrodinger equation with the higher-order terms. The modulation instability distribution characteristics from the sixth-order to the eighth-order nonlinear Schrodinger equations are studied. Higher-order dispersion terms are closely related to the distribution of modulation stability regime, and n-order dispersion term corresponds to $n-2$ modulation stability curves in the modulation instability band. Based on the generalized Darboux transformation method, the higher-order rational solutions are constructed. Then the compact algebraic expression of the Nth-order rogue wave is given. Dynamic phenomena of first- to third-order rogue waves are illustrated, which exhibit meaningful structures. Two arbitrary parameters play important roles in the rogue wave solution. One can control deflection of crest of rogue wave and its width, while the other can cause the change of width and amplitude of rogue wave. When it comes to the third-order rogue wave, three typical nonlinear wave constructions, namely fundamental, circular and triangular are displayed and discussed. Through the spectral analysis on first-order rogue wave, when these parameters satisfy certain conditions, it occurs a transition between W-shaped soliton and rogue wave.