Coupled Topological Surface Modes in Gyrotropic Structures: Green's Function Analysis

TL;DR

This paper analyzes topological surface modes in gyrotropic structures using Green's function, revealing how mode conversion occurs independently of geometry when interfaces merge, highlighting unique nonreciprocal wave phenomena.

Contribution

It provides an exact Green's function analysis of topological surface modes in gyrotropic media and explores mode transformation when interfaces are merged, a novel insight in topological photonics.

Findings

Mode conversion is independent of transition geometry.

Merged interfaces support modified topological modes.

Exact Green's function approach reveals mode behavior.

Abstract

At a transition in a wave-guiding structure, part of the incident energy is transmitted and part of the energy is reflected. When the waveguide has non-trivial topological properties, however, the transition may occur with no backscattering, and with unusual modal coupling/transformations. Within this context, we discuss the response of a nonreciprocal topological structure composed of two nearby interfaces between oppositely-biased gyrotropic media and an isotropic medium, which support unidirectional surface modes (topological modes). We provide an exact Green's function analysis of this structure, and we discuss how the topological surface modes are modified when the two interfaces are brought closer and eventually merged. We show that the resulting mode conversion is independent of the transition geometry.