Surface plasmon polariton excitation and extraordinary optical transmission in metallic grating structures with subwavelength slits

We explore structures composed of two gratings with subwavelength slits in silver films. We study the extraordinary transmission of electromagnetic wave in these structures and the conditions at which the transmittance is equal to zero. Dependences on various geometric parameters are analyzed. We show that the zero of transmittance i.e. the suppression of the extraordinary transmission is observed at wavelength that corresponds to the excitation of surface plasmon polariton in a gap between two gratings with subwavelength slits. We also research structures composed of arrays of slits in thick films set close to continuous thin films. We reveal that an efficiency of the transmission of the slit mode of the grating into the thin film is greater than an efficiency of the transmission of plane wave into the same film. The investigations are performed through numerical simulations with the Fourier modal method.