Angle enhanced circular dichroism in bilayer 90°-twisted metamaterial.

Intrinsic and extrinsic chiral responses have been widely investigated in metamaterials, however the relationship between them has been seldom discussed. We numerically and experimentally demonstrate angle enhanced chiral dichroism and study the separation between intrinsic and extrinsic chiral responses in metamaterial with asymmetrically split aperture dimers. The metamaterial exhibits triple-band resonant circular dichroism at normal incidence. The oblique incidence leads to giant enhancement of circular dichroism at two low-frequency resonances while yields an obvious resonance split of the circular dichroism in the vicinity of the high-frequency resonance. The whole circular dichroism response results from the balance between intrinsic and extrinsic chirality and the circular dichroism spectra at positive and negative angles of incidence exhibit an asymmetry due to the existence of intrinsic chirality. Importantly, the intrinsic chirality in the metamaterial may be individually investigated since extrinsic chiral response may be removed from the total circular dichroism by superimposing two circular dichroism spectra at positive and negative incident angles. The metamaterial will be promising to achieve enhanced chiral response and also separately utilize intrinsic and extrinsic chirality for manipulating the polarization state of light.