Planar focusing elements using spatially varying near-resonant aperture arrays

Resonances in subwavelength apertures are accompanied by wavelength-dependent phase shifts in the transmitted fields offering a potential for manipulation of wavefields. Here, we present Finite Element Method simulations and experiments investigating light passing through arrays of nanometric spatially varying near-resonant slits perforated in a silver film. We demonstrate that a one-dimensional focusing element can be obtained by tailoring the phase across the device through varying slit sizes around the resonant dimensions for a particular design wavelength.