High‐Q and Strong Chiroptical Responses in Planar Metasurfaces Empowered by Mie Surface Lattice Resonances

Abstract Planar chiral metasurfaces have emerged as a versatile platform for manipulating chiral light‐matter interactions in diverse applications. However, it remains challenging to achieve high quality factors together with strong chirality. Here, chiral all‐dielectric metasurfaces with a high Q factor of 1220 and relatively large planar chirality of circular dichroism −0.37 under normal incidence, or with a high Q factor of 872 and large extrinsic 3D chirality of circular dichroism 0.7, based on Mie surface lattice resonances (SLRs) are proposed and experimentally demonstrated. Both SLR‐induced planar chirality under normal incidence and SLR‐assisted extrinsic 3D chirality under oblique incidence are achieved by perturbing the square lattice and by slightly tilting the incidence angle, respectively. It shows that the high‐Q and strong chirality arises from the different excitation efficiencies of Mie SLRs under the incidences of left‐ and right‐handed circularly polarized light. With these findings, this study provides a new direction for realizing high‐performance chiral metasurfaces and holds great promise for chiral nanophotonic applications in biochemical sensing, emission or lasing, and nonlinear optics.