Graphene-integrated silicon metasurface for dynamically tunable chirality and enhanced sensing enabled by high-Q quasi-bound states in the continuum

Abstract Bound states in the continuum (BICs) supported by high-Q metasurfaces offer extreme optical field localization, leading to dramatically enhanced light-matter interactions. These features present broad prospects for applications in lasing, sensing, communications, and nonlinear optics. Here, we report a planar chiral silicon metasurface designed to support such confined states. By breaking in-plane and illumination symmetries, the structure achieves near-ideal circular dichroism (CD) in both configurations, along with an ultrahigh quality factor of up to 10 5 under broken inplane symmetry. Moreover, by integrating with single-layer graphene, the proposed metasurface configuration can provide a promising route toward functional tunability. Through Fermi level modulation, our design enables dynamic and reversible tuning of CD across a wide range from 0.91 to 0.01. It also delivers outstanding sensing performance, with a sensitivity of 125 nm/RIU and a figure of merit (FOM) of 1.56 × 10 4 RIU⁻¹, surpassing existing chiral sensors. These capabilities highlight the potential of our platform for real-world optical sensing and provide a versatile foundation for exploring enhanced light-matter interactions.