Transformation optics based on metasurfaces

The development of transformation optics and metamaterials provides a new paradigm for efficiently controlling electromagnetic waves. It is well known that the metamaterial is a novel artificial material with periodic structure, and the unit geometric size and distance between the units are much smaller than the working wavelength. Therefore, for an electromagnetic wave, a macroscopic system comprising these sub-wavelength units can be regarded as a novelty artificial material with a different permittivity, permeability and refractive index compared to the original material. Furthermore, these electromagnetic parameters of the artificial material can be freely manipulated by modifying their unit structure, especially for a material that does not exist in nature. Among these materials, negative refractive index materials have been widely reported. For a negative refractive index material, when light is incident on its interface, the incident and refracted light are distributed on the same side of the surface normal, rather than on both sides as typical materials do. However, the field of transformation optics proposes the concept that the propagation of an electromagnetic wave in curved spacetime is identical in inhomogeneous and anisotropic optical mediums.