Subwavelength focusing using a hyperbolic medium with a single slit.

A hyperbolic dispersion medium with a planar surface that can be used for subwavelength focusing is proposed. By combining the hyperbolic medium in a single slit with diffraction limit width, a laser beam could be focused to a subwavelength spot in the near field. Compared to a conventional superlens, the subdiffraction focusing in this work has higher optical throughput. Using a planar hyperbolic medium, which is actually alternating silver/dielectric multilayers, we showed that the focusing resolution of the designed device is down to ~λ/5 using green light illumination (at a wavelength of 514.5 nm).