Multiple One-Way Edge States From Reciprocal Continuous Media

Topological one-way edge states promise robust information transport through the notion of photonic crystals. For further applications of edge-state circuits and devices, a high gap Chern number, C-g, is required. Contrary to previous realizations using gyrotropic photonic crystals, we show how vertical bar C-g vertical bar > 1 can be obtained by gapping multiple Dirac cones, which can surprisingly occur in a reciprocal continuous medium with limited degrees of freedom. A maximum of four one-way edge states is allowed on a single interface between two reciprocal continuous media. One-way signal combiners and splitters are designed with exact control on the branching and transmission efficiencies as immediate applications. Our theoretical investigations will be useful for constructing edge-state devices with multiplexing and demultiplexing capability.