Proposal for superfocusing at visible wavelengths using radiationless interference of a plasmonic array.

Radiationless electromagnetic interference has been proposed to focus light below the diffraction limit. This has been demonstrated for microwave wavelengths; however, those approaches cannot be extended directly to visible wavelengths due to the material response and limitations from nanofabrication. In this Letter, a different approach is proposed to enable subdiffraction-limit focusing in the visible. The approach is based on the highest-order mode of a metal-dielectric waveguide array. Comprehensive simulations of focusing are provided for two different extreme examples: a structure that gives a 0.21 wavelength focus spot at a relatively large distance of 0.5 wavelength, and a sharp 0.057 wavelength focus spot at distance of 0.1 wavelength. The proposed nanostructures are comparable to those found in recent experiments.