Figure 1.

Comparison between a traditional grating, a broadband metasurface and a color-selective metasurface. (a) For a traditional grating, light is diffracted at various orders, as given by the grating equation. (b) In the diffraction diagram, integer multiples of the momentum Δk are added to the incoming light, regardless of its frequency. (c) Phase map along the interface for diffraction orders of –1, 0, and 1. (d) A broadband metasurface induces anomalous reflections over a large spectral range; (e) its diffraction diagram consists of a single channel. (f) Phase map induced by a gradient antenna array with an orientation axis that is independent of frequency. (g–i) A metasurface that selectively induces a gradient phase at a certain wavelength; as shown by h, its diffraction diagram and (i) its phase map, only light with the wavelength indicated by green dots accrues a growing phase along the interface.