Spatially dispersive dichroism in bianisotropic metamirrors

Dichroism refers to the differential absorption of a material for different polarized waves and has important applications in polarimetry and optical wavefront manipulation. The coexistence of strong linear and circular dichroism at thin optical interfaces is usually challenging due to the weak chiral anisotropy in natural materials. Here, we investigate the spatially dispersive dichroism of bianisotropic metamirror, in which giant linear and circular dichroism can be achieved simultaneously. By covering the metallic mirror with an array of bianisotropic resonators, specific linearly and circularly polarized waves can be largely absorbed under normal and oblique incidences, respectively. This intriguing phenomenon is attributed to the anisotropic magneto-electric coupling, that is, the handedness and the strength of the equivalent transverse electric surface current are determined by the angle of incidence. Furthermore, dual-band and hybrid-chirality metamirrors for asymmetric spin reflection have been realized by adjusting the geometries and arrangement of the bianisotropic resonators. The overall thickness of the bianisotropic metamirror is only 1/50 of the wavelength and thus highly suitable for on-chip integration. Our findings may provide an alternative approach towards multifunctional optical mirrors, signal detectors, chiral imaging devices, and molecular analyzers.