Photonic metasurfaces consisting of sub-wavelength nanostructures can introduce an effective refractive index and dispersion dictated mainly by the geometrical parameters and arrangement of the nanostructures, rather than their material composition. Recent advances in nanofabrication has led to high quality optical metasurfaces which perform at a level comparable to their state-of-the-art refractive counterparts. These nanostructures have a uniform height profile resulting in essentially a flat surface topology and can be patterned by a single step of lithography. This is promising for mass-production by semiconductor foundries in the near future.
Below are videos for introduction to metasurface technology.