Topologically Protected Refraction of Robust Kink Mode from Photonic Crystal into Free Space

Abstract

Similar to those electronic topological insulators that are based on the quantum valley Hall effect, valley photonic topological insulators (PTIs) guide unidirectional electromagnetic modes. A recent research studies how that unidirectional mode couples into the free space, aiming to incorporate this PTI into integrated photonic structures. Here we focus on light-refraction from a two-dimensional valley PTI into the free space. We understand this PTI as a waveguide, model its refraction as the radiation of an array of dipoles, and demonstrate several ways to engineer its dispersion relation. We also confirm the nontrivial topology of this PTI by unveiling its non-zero Berry curvature at the valley. This study may benefit future research on photonic topological behaviors and realizing novel photonic phenomenon.