Experimental verification of substrate-induced bianisotropy in optical metamaterials

This paper reports on substrate-induced bianisotropy in an impedance-matched near-zero-index metallodielectric fishnet nanostructure with vertical sidewalls and a supporting substrate. The effect of bianisotropy on the metamaterial optical properties is confirmed through spectral holography measurements and full-wave electromagnetic simulations, showing asymmetric reflection coefficients from opposite sides of the structure at normal incidence. The non-zero magnetoelectric coupling parameter causes a 0.03 μm shift in the near-infrared zero-index band centered at 1.5 μm and a 38% reduction in transmitted power. The substrate-induced bianisotropy is due to the excitation of an anti-symmetric plasmonic resonance mode identified by comparing simulations of the current distributions on free-standing and substrate-mounted fishnet structures. This experimental demonstration of substrate-induced bianisotropy verifies the previously proposed theory and provides valuable guidance for future plasmonic and metamaterial nanostructures that include substrates.