3D Dielectric Chiral Metamaterials Achieving Nondispersive Near‐Zero Ellipticity

Abstract Chiral metamaterials based on mirror‐symmetry broken resonators are engineered to achieve a strong interaction with circularly polarized (CP) waves. However, in contrast to the widely‐observed enhanced circular dichroism (CD), moderate/narrow‐band optical activity (OA) responses are usually seen in chiral metadevices. Here, by engineering the chirality parameter that determines the effective refractive indices associated with the two CP eigenstates, a three‐dimensional (3D) metamaterial consisting of 3D‐printed ceramic meta‐atoms exhibiting broadband strong OA with nondispersive near‐zero ellipticity in the millimeter‐wave regime is demonstrated. With four‐fold rotational symmetry ( C 4 ), the 3D dielectric metamaterial shows near‐identical co‐polarized transmission magnitude but distinct phase retardations under left‐handed circularly polarized (LCP) and right‐handed circularly polarized (RCP) illumination over a broad frequency range. Field analysis indicates that the observed OA behavior originates from the handedness‐dependent light‐matter interaction between the chiral meta‐atoms and CP waves. Furthermore, large transmission CD and CP polarization conversion are observed in a metamaterial with C 2 ‐symmetry, demonstrating the proposed systems’ versatility in CP wave control. As revealed by the present study, coherently exploring the complex parametric space offered by 3D meta‐atoms based on state‐of‐the‐art 3D fabrication techniques can become a promising paradigm for engineering metamaterials with sophisticated functionalities.