We have performed finite-difference time-domain (FDTD) analysis of optical transmission through a nanoslit surrounded by a finite array of gratings formed on a silver film, embedded in a high index dielectric medium. The investigation result shows that the transmission of the structure is strongly influenced by thickness of the dielectric film. In addition, we investigate the directional properties of radiated beam from the structure. It is demonstrated and explained that the directionality can be improved by tapering height of the grating elements on the exiting plane. We propose that the structure could be used as a plasmonic antenna for axial injection of light from single mode fiber to photonic crystal waveguide.
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