Circular dichroism in planar achiral metamaterial

We investigate the polarization properties of a two-dimensional array of metallic elliptical nanoholes in the visible wavelength region. The calculated spectra reveal that such a nonchiral structure exhibits a circular dichroism. The proposed structure is a 2D anisotropic system that possesses two principle polarization directions, which gives rise to different polarization modes along long and short diameters of an elliptical nanohole. When the nonchiral elliptical hole forms a chiral arrangement with the off-normal incident wave vector, the two different polarization modes introduce a net polar vector that forms a chiral triad. Therefore, circular dichroism can be observed in a nonchiral elliptical nanohole array.