Single- and multi-peak solitons in two-component models of metamaterials and photonic crystals

TL;DR

This paper investigates complex single- and multi-peak solitons in coupled nonlinear Schrödinger equations modeling metamaterials and photonic crystals, revealing broad bistability, stability, and methods to manage GVM and loss effects.

Contribution

It introduces a novel coupled NLS model with unequal GVD coefficients leading to complex soliton shapes and bistability, extending understanding beyond previous equal-GVD studies.

Findings

Families of complex-shaped solitons with tails and double peaks identified.

Bistability regions for single- and double-peak solitons demonstrated.

Stability of solitons confirmed across entire existence regions.

Abstract

We report results of the study of solitons in a system of two nonlinear-Schrodinger (NLS) equations coupled by the XPM interaction, which models the co-propagation of two waves in metamaterials(MMs). The same model applies to photonic crystals (PCs), as well as to ordinary optical fibers, close to the zero-dispersion point. A peculiarity of the system is a small positive or negative value of the relative group-velocity dispersion (GVD) coefficient in one equation, assuming that the dispersion is anomalous in the other. In contrast to earlier studied systems of nonlinearly coupled NLS equations with equal GVD coefficients, which generate only simple single-peak solitons, the present model gives rise to families of solitons with complex shapes, which feature extended oscillatory tails and/or a double-peak structure at the center. Regions of existence are identified for single- and double-peak bimodal solitons, demonstrating a broad bistability in the system. Behind the existence border, they degenerate into single-component solutions. Direct simulations demonstrate stability of the solitons in the entire existence regions. Effects of the group-velocity mismatch (GVM) and optical loss are considered too. It is demonstrated that the solitons can be stabilized against the GVM by means of the respective "management" scheme. Under the action of the loss, complex shapes of the solitons degenerate into simple ones, but periodic compensation of the loss supports the complexity.