Beam focusing by an anisotropic metal-dielectric multilayer structure

We demonstrate subwavelength beam focusing by a slab of anisotropic material. The proposed device consists of a slab of anisotropic material on top of which a Chromium layer with a small slit is used as the mask. By carefully designing the thickness of the anisotropic layer, we can selectively modify the phase of different wave components exiting the output surface, so that a subwavelength-sized light spot can be generated as results of near-field constructive interference. Our study showed that a light spot with FWHM of 0.36λ can be generated at optical frequencies.