Reconfigurable BIC‐Based Intrinsic Chiral All‐Dielectric Terahertz Metasurfaces

Abstract Chiral metasurfaces with high‐quality factors can significantly enhance light‐matter interactions, making them highly valuable in biomolecular detection, optical sensing, and related applications. However, most experimentally demonstrated chiral devices rely on extrinsic chirality induced by oblique incidence or fabrication techniques involving slanted etching, which limits their practical applicability. Furthermore, the operation modes and functionalities of these devices are typically fixed after fabrication, restricting their adaptability. Here, a reconfigurable intrinsic chiral metasurface consisting of bi‐layer photonic crystal slabs are experimentally demonstrated. The bi‐layer architecture introduces strong interlayer coupling effects, enabling the realization of a nearly unity circular dichroism (CD) value under normal incidence in the terahertz regime by leveraging tunable topological polarization singularities. Our approach allows tunable and independent manipulation of CD in multiple operation modes, significantly enhancing the flexibility of chiral devices. This work paves the way for advanced polarization and phase manipulation, with promising applications in chiral lasers, chiral filters, and beyond.