Optical activity in extrinsically chiral metamaterial

We demonstrate optical activity in an intrinsically non-chiral anisotropic planar metamaterial. The phenomenon is due to extrinsic chirality resulting from the mutual orientation of the metamaterial structure and the incident electromagnetic wave. The polarization effect, which has a resonant nature, features a spectral band where linear birefringence is practically absent and can be easily tuned by tilting the plane of the metamaterial relative to the incident beam.