Active and Tuneable Metallic Nanoslit Lenses

In diffractive optics, typical feature sizes are on the order of the wavelength—around 1 μm for visible and near-infrared light. Although nanometer-scale features do not diffract optical waves, nanosized structures could enable us to design novel diffractive optical devices. Plasmonics and metamaterials are the two ways to couple light into nanoscale. This chapter talks about planar plasmonic diffractive focusing devices that consist of arrays of nanoslits milled in gold films. It gives a brief overview on the experimental characterization and full-wave numerical simulations of light propagation in the fabricated prototypes. Next, it shows that the focusing properties of nanoslit lenses can be externally tuned by filling the slits with index-changing materials such as a liquid crystal (LC) material. The chapter also discusses hyperbolic metamaterials (HMMs)-assisted nanoslit devices for subwavelength focusing. A case study on active HMM dispersions is discussed.