Extrinsically 2D-Chiral Metamirror in Near-Infrared Region

Many previously observed strong chiroptical effects are limited to chiral metamaterials with complex three-dimensional building blocks. Recently, chiral metamirrors consisting of planar elements are proposed to selectively reflect one particular circularly polarized light (CPL) while absorbing the other, with the reflected one either preserving or altering its spin state. However, they are limited by complicated subwavelength chiral profiles of their unit cells, which are challenging to fabricate in the visible-near-infrared (NIR) region. We present an extrinsically chiral metamirror that reflects one CPL preserving its handedness while strongly absorbing the other, reaching a circular conversion dichroism (CCD) in reflectance as large as 0.43 in the NIR region. Our polarization-conserving mirror possesses an Au pillar array and a continuous Al film separated by a SiO2 dielectric layer, where the Au pillars are periodically arranged by a rectangular lattice. The rather simple geometry of mirror significantly simplifies its fabrication in the high frequency region. The pronounced CCD originates from a chiral triad of the achiral resonator array and light's propagation direction. Such a chiral mirror provides an efficient methodology toward handedness-selective modulation of the CPL and finds applications in planar photonic devices such as molecular spectroscopy, quantum information, and polarimetric imaging.