Nature Commun. 3, 870 (2012)

Credit: © 2012 NPG

Optical metamaterials are artificially engineered structures that can be used to realize optical properties not normally found in nature, and are usually made from an array of complex-shaped metal–dielectric nanostructures. Three-dimensional metamaterial geometries, which can provide additional functionalities such as broadband chirality for manipulating the circular polarization of light, become increasingly difficult to fabricate at smaller dimensions. Y. Zhao and co-workers from the University of Texas at Austin in the USA have now shown that such three-dimensional effects can be achieved by tailoring the relative orientation of each layer within a stacked lattice. Their approach involves using conventional lithographic techniques to produce an array of stacked planar metasurfaces whose constituent layers differ by a predetermined twist in the lattice orientation. The resulting planarized, broadband bianisotropic metamaterial acts as an ultrathin, broadband circular polarizer that can be directly integrated into a nanophotonic system. The approach may help to realize a wide variety of novel metamaterial devices for controlling optical behaviour, such as modal propagation and spatial dispersion.