Exciting Reflectionless Unidirectional Edge Modes in a Reciprocal Photonic Topological Insulator Medium

TL;DR

This paper introduces a rotating magnetic dipole antenna that efficiently excites unidirectional, reflectionless topological edge modes in a reciprocal photonic topological insulator medium, with tunable amplitude ratios demonstrated experimentally.

Contribution

It presents a novel antenna design capable of exciting and tuning topologically protected edge modes in a reciprocal medium, expanding control over photonic topological insulator systems.

Findings

Successfully excites unidirectional edge modes in experiments

Achieves high directivity and tunability of edge mode excitation

Matches experimental results with simulations

Abstract

Photonic topological insulators are an interesting class of materials whose photonic band structure can have a bandgap in the bulk while supporting topologically protected unidirectional edge modes. Recent studies [1-6] on bianisotropic metamaterials that emulate the electronic quantum spin Hall effect using its electromagnetic analog are examples of such systems with relatively simple and elegant design. In this paper, we present a rotating magnetic dipole antenna, composed of two perpendicularly oriented coils, that can efficiently excite the unidirectional topologically protected surface waves in the bianisotropic metawaveguide (BMW) structure recently realized by Ma, et al. [1], despite the fact that the BMW medium does not break time-reversal invariance. In addition to achieving high directivity, the antenna can be tuned continuously to excite reflectionless edge modes to the two opposite directions with various amplitude ratios. We demonstrate its performance through experiment and compare to simulation results.