Transmission resonances of two-constituent metal/dielectric gratings with subwavelength slits

One of the mechanisms responsible for the extraordinary optical transmission of metallic gratings with narrow slits is attributed to the slit waveguide mode. We show that by constructing two-constituent metal/dielectric gratings with subwavelength slits and changing the material as well as the width of the cladding layer attached to the sidewall of the slit, the transmission resonances can be significantly modified. Since the dielectric cladding layer forms an additional dielectric cavity, the waveguide mode of the dielectric cladding layer channel contributes an extra transmission resonance. Normalized magnetic field intensity distributions confirm this conclusion.