Topological Chiral Edge States in Deep‐Subwavelength Valley Photonic Metamaterials

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, topological CESs are proposed and experimentally demonstrated 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, the bulk bandgap, the edge dispersions, and the robust edge transport passing through sharp corners, which are hallmark signatures of the CESs, are observed. This work paves a way to explore novel topological edge states in valley photonics and sheds light on robust and miniaturized photonic devices.