Demonstration of a Bi-Anisotropic Meta-Waveguide Quantum Hall Analog

Photonic topological insulators (PTI) are a new class of structures that can support unidirectional propagating waves at a surface or interface. Inside a bulk structure of bi-anisotropic meta-waveguide (BMW), by carefully tuning the geometrical and electromagnetic properties, we can emulate the electronic quantum spin Hall (QSH) effect using its electromagnetic analog. Further, one can break the σ_z symmetry by opening an air gap on top of the bulk region, and introduce the bi-anisotropic response of the meta-waveguide. Both experimental and simulation efforts show that waves launched with opposite circular polarization will adopt opposite propagating direction inside the interface region of two bulk regions, thus creating a reflection-less waveguide. We next construct a quantum Hall (QH) analog BMW structure that breaks time-reversal invariance. By replacing the symmetry-breaking air gap with magnetized garnet ferrite components, theoretical studies show that an interface of the QH/QSH regions will guide the wave propagating only along one direction. We also demonstrate a 4-port circulator with high transmission efficiency based on a composite quantum spin-Hall and quantum Hall BMW structure.