Topological chiral edge states in deep-subwavelength valley photonic metamaterials

TL;DR

This paper demonstrates experimentally the existence of topological chiral edge states in valley photonic metamaterials at deep-subwavelength scales, enabling highly confined, robust, and miniaturized photonic devices.

Contribution

It introduces and experimentally verifies a new class of topological chiral edge states at external boundaries in valley photonic metamaterials, tunable via on-site edge potentials.

Findings

Observation of bulk bandgap and edge dispersions

Robust edge transport through sharp corners

CESs operate at deep-subwavelength scales

Abstract

Topological valley photonics has emerged as a new frontier in photonics with many promising applications. Previous valley boundary transport relies on kink states at internal boundaries between two topologically distinct domains. However, recent studies have revealed a novel class of topological chiral edge states (CESs) at external boundaries of valley materials, which have remained elusive in photonics. Here, we propose and experimentally demonstrate the topological CESs in valley photonic metamaterials (VPMMs) by accurately tuning on-site edge potentials. Moreover, the VPMMs work at deep-subwavelength scales. Thus, the supported CESs are highly confined and self-guiding without relying on a cladding layer to prevent leakage radiation. Via direct near-field measurements, we observe the bulk bandgap, the edge dispersions, and the robust edge transport passing through sharp corners, which are hallmarks of the CESs. Our work paves a way to explore novel topological edge states in valley photonics and sheds light on robust and miniaturized photonic devices.