Analysis and design of subwavelength focusing by cylindrical lenses

We present the design and analysis of subwavelength lenses based on air cylindrical waveguides surrounded by metal for the focusing of light in very small areas. The lenses are composed by several concentrically disposed air-metal waveguides with different widths in order to control the phase shifting necessary to focus the light. The lenses we designed to operate at visible frequencies then, the propagation mechanism of light along the air-metal waveguides is obtained by the surface plasmon polaritons (SPPs). The structures have been analyzed by an efficient finite element formulation in cylindrical coordinates with perfectly matched layer (PMLs).