Terahertz wave polarization rotation with double layered metal grating of complimentary chiral patterns.

We propose and demonstrate polarization rotation of a terahertz (THz) electromagnetic wave by using two-dimensional gratings consisting of two displaced layers of gold film with complimentary chiral patterns with four-fold symmetry. We develop a time domain THz polarimetry method with three wire grid polarizers and distinguish optical activity from optical anisotropy. We obtain the isotropic polarization rotation of a terahertz wave free from the birefringence of the structures. Results indicate the possibility of controlling THz polarization with artificial chiral structures fabricated with thin metal films.