Nonimaging metaoptics

So far, metalenses have only been studied in imaging optics, where a point from the object space is mapped to a corresponding point in the image space. Here we explore metalenses and metamirrors for dealing with the optimal transfer of light energy. Owing to its compactness and high design flexibility, metasurface-based flat optics may open new opportunities in the nonimaging field, which deals with light concentration and illumination. The building blocks of metalenses are subwavelength-spaced scatterers. By suitably adjusting their shape, size, position, and orientation, one can control the light spatial distribution, as is desired in nonimaging problems. In this Letter, we introduce nonimaging metaoptics, review its basics, and briefly explore three cases: the compound-metasurface concentrator [analogous to the compound parabolic concentrator (CPC)], the total internal reflection (TIR) metalens (analogous to the TIR lens), and a simple condensing metalens.