Asymmetric transmission of transverse magnetic or radially polarized THZ waves through sub-wavelength gratings

We have developed a metallic double circular grating with sub-wavelength slits which blocks radially polarized light incident from one of its sides and acts as a focusing diffractive element in the other direction. The proposed grating has been optimized for the sub-THz frequency range. Unidirectional transmission through the grating has been demonstrated experimentally at 0.1 THz. We have also developed a planar metallic double grating with sub-wavelength slits which blocks light with a transverse magnetic polarization incident from one of the grating sides and transmits radiation incident from the opposite direction into the +1 and -1 diffraction orders. These gratings which could be used as unidirectional couplers consist of optically linear materials and their operation respects the Lorentz reciprocity theorem.