Dual-band strong extrinsic 2D chirality in a highly symmetric metal-dielectric-metal achiral metasurface

Chirality routinely occurs in 3D metamaterials (MMs) lacking mirror symmetry or quasi 2D planar MMs lacking in-plane mirror symmetry. However, realization of such asymmetric MMs in the high frequency region remains challenging since it is hard to precisely control the asymmetric geometry of the ultrasmall meta-atom. Moreover, another limiting factor of those MMs is their weak extrinsically 2D-chiral effect such as circular polarization conversion difference (CPCD). Here, we theoretically demonstrate that a highly symmetric metasurface (MS), also known as 2D planar MMs, can produce a dual-band strong extrinsic 2D chirality: CPCD in the THz region under off-normal incidence. Our MS consists of an array of circular holes penetrating through a metal/dielectric/metal (MDM) trilayer, where the holes occupy the sites of a rectangular lattice. The CPCD is due to the mutual orientation of circular holes array (CHA) and oblique incident wave. Meanwhile, we show that the CPCD in the single metal layer CHA disappears owing to the absence of magnetic dipolar moment that can significantly enhance chiral effects. The highly symmetric achiral MS with the large CPCD may be operated as flat lenses, chiral sensing and highly efficient polarization converters. (C) 2016 Optical Society of America