Guided-wave resonance transmission in one-dimensional metallic gratings with surface impedances on its walls of Slits

The resonances coupling between the incident light and surface plasmons as well as guided-wave resonance were pointed out to be the two major physical processes causing the extraordinary transmission of one-dimensionally lamellar gratings with sub-wavelength slits. To pinpoint the dominant one between the two major physical processes, we consider here the scattering of TE-polarized plane wave (with its electric field along the groove direction) by a 1D grating made of perfect metal, but with surface impedance on the side walls of the sub-wavelength slits. It is shown that a frequency-selective transmission can take place even at long wavelengths, and such a phenomenon can be related to the dispersion characteristic of the slit channel with surface-impedance walls where a surface-wave mode exists without cutoff frequency. By examining the phase angle of the surface-wave mode propagating in the slit channel, the frequency-selective transmission is verified to be mainly attributed to the Fabry-Perot resonance of the surface-wave mode.