Enhanced optical transmission, beaming and focusing through a subwavelength slit under excitation of dielectric waveguide modes

Abstract

We explore the transmission and beaming properties of a single subwavelength slit flanked by a finite array of indentations made on a thick metallic film for both s- and p-polarizations. If a dielectric slab is placed onto the metal film, excited dielectric waveguide modes drastically change the diffraction of a plane wave. We show that if a dielectric slab is placed at the incoming face of the film, the transmission can be greatly enhanced for wavelengths which are close to the Bragg reflection condition. For the same wavelengths, the waveguide modes can be redirected into a highly collimated beam within a few degrees; however, in this case, the slab must be placed at the outgoing face of the film.