Three-dimensional topological valley photonics

TL;DR

This paper introduces a theoretical and experimental framework for three-dimensional topological valley photonics, enabling advanced control of electromagnetic waves in 3D structures with potential applications in waveguiding and imaging.

Contribution

It develops the first 3D topological valley photonics system with a complete bandgap and vectorial valley physics, expanding beyond 2D limitations.

Findings

Established 3D valley systems with triple pairs of valleys and valley Chern vectors.

Demonstrated vectorial bulk valley vortices and chiral valley surface states.

Showed potential for 3D waveguiding, directional radiation, and imaging applications.

Abstract

Topological valley photonics, which exploits valley degree of freedom to manipulate electromagnetic waves, offers a practical and effective pathway for various classical and quantum photonic applications across the entire spectrum. Current valley photonics, however, has been limited to two dimensions, which typically suffer from out-of-plane losses and can only manipulate the flow of light in planar geometries. Here, we have theoretically and experimentally developed a framework of three-dimensional (3D) topological valley photonics with a complete photonic bandgap and vectorial valley contrasting physics. Unlike the two-dimensional counterparts with a pair of valleys characterized by scalar valley Chern numbers, the 3D valley systems exhibit triple pairs of valleys characterized by valley Chern vectors, enabling the creation of vectorial bulk valley vortices and canalized chiral valley surface states. Notably, the valley Chern vectors and the circulating propagation direction of the valley surface states are intrinsically governed by the right-hand-thumb rule. Our findings reveal the vectorial nature of the 3D valley states and highlight their potential applications in 3D waveguiding, directional radiation, and imaging.