Nanophotonics: bright future for hyperbolic chips.

Abstract

The unusual properties of hyperbolic metamaterials, such as their ability to propagate light on the nanoscale without diffraction, have been realized in two-dimensional devices, heralding improved photonic circuits. See Letter p.192 Optical effects such as negative refraction that are not found in natural materials can be realized in metamaterials, which are made of periodic structures at a sub-wavelength scale. A recent focus in this area is on the construction of two-dimensional metamaterials — or metasurfaces — likely to have much lower propagation losses than three-dimensional equivalents. Here Hongkun Park and colleagues use single-crystal silver nanostructures defined by lithographic and etching techniques to produce 'hyperbolic' metasurfaces, in which optical excitations called surface plasmon polaritons propagate at a metal–dielectric interface. By refining their fabrication techniques, the authors produce patterns of nanoscale metallic structures of sufficiently high quality to demonstrate effects such as negative refraction for visible wavelengths. The work also introduces an optical equivalent of the electronic spin-Hall effect. These findings open up new directions in optical imaging and photonic circuits.