Topological Dirac-vortex modes in a three-dimensional photonic topological insulator

TL;DR

This paper introduces the first experimental realization of topological Dirac-vortex modes in a three-dimensional photonic topological insulator, enabling robust light manipulation along 1D defects in 3D structures.

Contribution

It proposes and demonstrates a 3D photonic structure exhibiting Dirac-vortex modes, extending topological photonics from 2D to 3D systems.

Findings

Observation of robust Dirac-vortex modes in 3D photonic crystal

Experimental validation with microwave near-field measurements

Matching results with tight-binding and simulation models

Abstract

Recently, topological Dirac-vortex modes in Kekul\'e-distorted photonic lattices have attracted broad interest and exhibited promising applications in robust photonic devices such as topological cavities, lasers, and fibers. However, due to the vectorial nature of electromagnetic waves that results in complicated band dispersions and fails the tight-binding model predictions, it is challenging to construct three-dimensional (3D) topological photonic structures with Kekul\'e distortion and the photonic topological Dirac-vortex modes have thus far been limited to two-dimensional (2D) systems. Here, by directly mapping a 3D Kekul\'e-distorted tight-binding model in a 3D tight-binding-like photonic crystal exhibiting scalar-wave-like band structures, we theoretically propose and experimentally demonstrate topological Dirac-vortex modes in a 3D photonic topological insulator for the first time. Using microwave near-field measurements, we directly observe robust photonic topological Dirac-vortex modes bound to and propagate along a one-dimensional (1D) Dirac-vortex line defect, matching well with the tight-binding and simulation results. Our work offers an ideal platform to map tight-binding models in 3D topological photonic crystals directly and opens a new avenue for exploiting topological lattice defects to manipulate light in 3D space.