Enhanced THz Transmission and Polarization Conversion in Double-Layer Metal Hole Arrays

The transmission and polarization change of double-layer metal hole arrays have been studied in the terahertz region using the time-domain spectroscopy. The transmission spectrum shows drastic and complicated dependence both on the spacing and lateral displacement of the two layers. The large polarization change is observed when the symmetry of the lateral configuration of the two layers is low and the spacing is less than the wavelength of the incident THz wave. These properties are attributed to the resonant excitation of the surface plasmon-polaritons (SPPs) and the coupling of the SPPs excited on the surfaces of the metal hole arrays.