Metal slit array Fresnel lens for wavelength-scale optical coupling to nanophotonic waveguides

We propose a novel metal slit array Fresnel lens for wavelength-scale optical coupling into a nanophotonic waveguide. Using the plasmonic waveguide structure in Fresnel lens form, a much wider beam acceptance angle and wavelength-scale working distance of the lens was realized compared to a conventional dielectric Fresnel lens. By applying the plasmon waveguide dispersion relation to a phased antenna array model, we also develop and analyze design rules and parameters for the suggested metal slit Fresnel lens. Numerical assessment of the suggested structure shows excellent coupling efficiency ( up to 59%) of the 10 mu m free-space Gaussian beam to the 0.36 mu m Si waveguide within a working distance of a few mu m. (C) 2009 Optical Society of America