Waveguide Channel Splitting Induced by Artificial Gauge Fields

Abstract

Initially considered not to interact with photons, a sort of neutral particle, gauge fields have been created artificially in engineered structures to control light, enabling fascinating phenomena such as topologically robust propagation, waveguiding, and negative refraction. Here we theoretically propose and experimentally demonstrate a mechanism to use uniform curl-free artificial gauge fields to split two counterpropagating transmission channels of a waveguide. By assigning oppositely oriented artificial gauge fields to a waveguide, two initially overlapped counterpropagating transmission channels can be separated spatially, resembling a photonic highway that was previously achieved in the form of chiral edge states in photonic Chern insulators. Interestingly, these two channels are naturally separated and do not need a cladding or wave-forbidden layer in between to avoid crosstalk, another unusual property enabled by gauge fields. This mechanism has been demonstrated experimentally in bilayer moiré metagratings with the synthetic gauge fields being continuously tuned. Our work provides an alternative mechanism to design photonic highways without requiring complicated band structure engineering and large-area bulks to separate two channels, which are favorable for future ultracompact and high-density photonic integrated circuits.