Topological states in arrays of optical waveguides engineered via mode interference

TL;DR

This paper proposes a novel method to engineer topological states in photonic systems by tuning individual waveguide parameters to induce mode degeneracy, bypassing complex lattice designs, and demonstrates topological edge modes in a nanophotonic array.

Contribution

It introduces a new approach to create topological photonic states through mode interference without complex lattice geometries, generalizing the SSH model.

Findings

Supports topological edge modes in a nanophotonic waveguide array

Achieves mode degeneracy through parameter tuning of individual waveguides

Provides a flexible method for designing topological photonic structures

Abstract

Photonic structures with topologically nontrivial bands are usually designed by arranging simple meta-atoms, ideally, single-mode ones, in a carefully designed photonic lattice with symmetry that guarantees the emergence of topological states. Here we investigate an alternative option that does not require complex lattice geometry but instead relies on the tuning of the parameters of the individual meta-atoms to achieve the degeneracy of the modes with different symmetry. As an illustrative example, we consider a one-dimensional array of equidistant identical periodic nanophotonic waveguides supporting degenerate modes with strongly asymmetric near field profiles giving rise to the coupling modulation. Exploiting this feature, we demonstrate that the proposed system supports topological edge modes and can be viewed as a generalization of the paradigmatic Su-Schrieffer-Heeger model, reducing to it for the suitable parameter choice. Our results thus provide an avenue to engineer topological states via mode interference which further expands the plethora of topological structures available in photonics being especially promising for nonlinear topological systems.