Enhanced Optical Activity with Zero Circular Dichroism in a Dielectric Chiral Metasurface

Abstract Enhanced chiral optical responses of metamaterials have widespread applications in chiral biosensor and polarization optics. Metamaterials with intrinsic chirality are commonly composed of complicated 3D structures, which leads to significant fabrication challenges. Recent works involving planar chiral metasurfaces have demonstrated chiral optical response by symmetry breaking, but the intrinsic optical chirality at normal incidence is usually weak. Here, a dielectric chiral metasurface is designed and fabricated, and its strong intrinsic optical chirality in visible spectrum is experimentally demonstrated. Particularly, giant optical activity with zero circular dichroism can be obtained, implying that linear polarization of the incident light passing through the metasurface can be rotated. A phenomenological model is proposed to explain the chiral optical response of the metasurface based on the superposition of two chiral optical resonances in opposite handedness. The multipole decomposition of the electric fields corroborates how the high‐order multipoles are related to the chiral optical response. These results enable the development of flat compact devices to manipulate the polarization of light flexibly.