Nonreciprocal Surface Waves on Gyrotropic Interfaces

Abstract

In this dissertation, the properties of highly nonreciprocal (unidirectional) surface waves guided along the interface between free-space and various 2D and 3D gyrotropic continua are investigated using analytic, numerical, and experimental methods. From a classical electromagnetics perspective, nonreciprocity in the dispersion of surface wave modes supported by the interface is achieved by breaking both time-reversal and space-inversion symmetries in the collective response of the waveguide, which consists of the two interfaced materials. More recently, however, a connection to momentum space topology via the bulk-edge correspondence principle has been made for gyrotropic continua, providing additional insights into the underlying physics that governs the unique propagation characteristics of these unidirectional modes. Building on the previous work done in the areas of nonreciprocal electromagnetics and topological photonics, we (1) develop a new analytic formalism to model excitations of the surface wave modes using a near field current source, (2) investigate a nontraditional way of achieving a gyrotropic response in a 2D continuum, and (3) demonstrate experimentally, for the first time, the unidirectional nature of a recently theorized topologically protected, unidirectional surface wave mode.