Observation of edge solitons in topological trimer arrays

TL;DR

This paper experimentally demonstrates the formation of topological edge solitons in nonlinear trimer waveguide arrays, revealing how topological phases influence soliton behavior and coexistence in different topological gaps.

Contribution

First experimental observation of topological edge solitons in nonlinear systems with multiple topological gaps, showing phase-dependent soliton formation and coexistence.

Findings

Edge solitons occur above a power threshold in non-topological regimes.

In topological regimes, edge solitons bifurcate from linear states.

Multiple topological gaps host different types of edge solitons.

Abstract

We report the experimental observation of nonlinear light localization and edge soliton formation at the edges of fs-laser written trimer waveguide arrays, where transition from non-topological to topological phases is controlled by the spacing between neighboring trimers. We found that, in the former regime, edge solitons occur only above a considerable power threshold, whereas in the latter one they bifurcate from linear states. Edge solitons are observed in a broad power range where their propagation constant falls into one of the topological gaps of the system, while partial delocalization is observed when considerable nonlinearity drives the propagation constant into an allowed band, causing coupling with bulk modes. Our results provide direct experimental evidence of the coexistence and selective excitation in the same or in different topological gaps of two types of topological edge solitons with different internal structures, which can rarely be observed even in nontopological systems. This also constitutes the first experimental evidence of formation of topological solitons in a nonlinear system with more than one topological gap.