Weakly nonlinear topological gap solitons in Su-Schrieffer-Heeger photonic lattices

TL;DR

This paper investigates how nonlinearity affects topologically protected interface modes in SSH photonic lattices, revealing the formation of stable, weakly nonlinear topological gap solitons through theoretical and experimental methods.

Contribution

It introduces the concept of weakly nonlinear topological gap solitons in SSH lattices and demonstrates their stability and properties both theoretically and experimentally.

Findings

Linear topological modes become stable gap solitons under nonlinearity

Solitons are weakly nonlinear with low amplitude and power

High-power beams tend to delocalize or form non-topological solitons

Abstract

We study both theoretically and experimentally the effect of nonlinearity on topologically protected linear interface modes in a photonic Su-Schrieffer-Heeger (SSH) lattice. It is shown that under either focusing or defocusing nonlinearity, this linear topological mode of the SSH lattice turns into a family of topological gap solitons. These solitons are stable. However, they exhibit only a low amplitude and power and are thus weakly nonlinear, even when the bandgap of the SSH lattice is wide. As a consequence, if the initial beam has modest or high power, it will either delocalize, or evolve into a soliton not belonging to the family of topological gap solitons. These theoretical predictions are observed in our experiments with optically induced SSH-type photorefractive lattices.