Reflection-Free One-Way Edge Modes in a Gyromagnetic Photonic Crystal

TL;DR

This paper demonstrates the existence of reflection-free one-way edge modes in gyromagnetic photonic crystals without Dirac points, showing their robustness and potential for practical microwave applications.

Contribution

It generalizes the conditions for one-way edge modes in gyromagnetic photonic crystals, removing the need for Dirac points and providing numerical evidence of their robustness.

Findings

Edge modes exist in non-Dirac gyromagnetic photonic crystals with non-zero Chern numbers.

Numerical simulations show 100% transmission across defects in a one-way waveguide.

Edge modes occupy a 10% band gap in realistic material parameters.

Abstract

We point out that electromagnetic one-way edge modes analogous to quantum Hall edge states, originally predicted by Raghu and Haldane in 2D gyroelectric photonic crystals possessing Dirac point-derived bandgaps, can appear in more general settings. In particular, we show that the TM modes in a gyromagnetic photonic crystal can be formally mapped to electronic wavefunctions in a periodic electromagnetic field, so that the only requirement for the existence of one-way edge modes is that the Chern number for all bands below a gap is non-zero. In a square-lattice gyromagnetic Yttrium-Iron-Garnet photonic crystal operating at microwave frequencies, which lacks Dirac points, time-reversal breaking is strong enough that the effect should be easily observable. For realistic material parameters, the edge modes occupy a 10% band gap. Numerical simulations of a one-way waveguide incorporating this crystal show 100% transmission across strong defects, such as perfect conductors several lattice constants wide, larger than the width of the waveguide.