Gap solitons in grating superstructures

TL;DR

This paper investigates gap solitons in periodically modulated Bragg gratings, revealing that chirp modulation stabilizes new soliton families and their bound states, with implications for soliton control.

Contribution

It introduces a novel periodic chirp modulation in Bragg gratings that stabilizes new families of gap solitons and their bound states, expanding understanding of soliton dynamics.

Findings

Chirp modulation stabilizes gap solitons in certain bandgaps.

Reflectivity modulation destabilizes solitons.

Stable 4-peak bound states are formed by pairs of fundamental solitons.

Abstract

We report results of the investigation of gap solitons (GSs) in the generic model of a periodically modulated Bragg grating (BG), which includes periodic modulation of the BG chirp or local refractive index, and periodic variation of the local reflectivity. We demonstrate that, while the previously studied reflectivity modulation strongly destabilizes all solitons, the periodic chirp modulation, which is a novel feature, stabilizes a new family of double-peak fundamental BGs in the side bandgap at negative frequencies (gap No. -1), and keeps solitons stable in the central bandgap (No. 0). The two soliton families demonstrate bistability, coexisting at equal values of energy. In addition, stable 4-peak bound states are formed by pairs of fundamental GSs in bandgap -1. Self-trapping and mobility of the solitons are studied too.