Molding light propagation with phase discontinuities

The shaping of the wavefront of light with optical components such as lenses and prisms, as well as diffractive elements, such as gratings and holograms, relies on gradual phase changes accumulated along the optical path. This approach is generalized in transformation optics [1, 2], which uses metamaterials to bend light in unusual ways, achieving such phenomena as negative refraction, subwavelength-focusing, and cloaking [3, 4].