Refraction and Coupling of Topological Edge State Based on Silicon Valley Photonic Crystals

Abstract

Topological edge states in valley photonic crystals (VPCs) have gained significant attention due to their capabilities for sharp-turn transmission, defect immunity, and robust photon transport on chips. However, research on the refraction within the VPC domain in photonic integrated chips is still lacking, impeding various applications of VPCs. In this work, the refraction mechanisms of topological edge modes at different external coupling boundaries are investigated, and demonstrate topological interconnections and switches on a chip. The reflection of topological modes refracted into slab waveguides is compared through zigzag, armchair, and vertical zigzag terminations. The vertical zigzag termination demonstrates high external coupling efficiency with a constant refraction angle at different wavelengths. Based on these findings, a compact and low-loss waveguide crossing for configurable topological interconnections. To demonstrate practical applications a compact 2 × 2 topological switch is presented that utilizes the proposed crossing and a topological Mach-Zehnder interferometer (MZI) structure is proposed. This work explores the refraction mechanisms of topological edge modes at different external coupling boundaries, expanding the potential applications of topological edge states in integrated photonic circuits, optical communications, and quantum information processing.