Emerging advanced metasurfaces: Alternatives to conventional bulk optical devices

Optical metasurfaces are ultra-thin planar optical components that are composed of arrays of subwavelength nanostructures modulating the amplitude, phase, and polarization of incident light. Metasurfaces can overcome the limitations of conventional optical components for use in diffractive devices and produce structural color and enable high-resolution imaging. Replacement of traditional bulk components with metasurfaces could reduce the size and weight of optical systems while improving them. Metasurfaces have already been integrated with functional devices such as image sensors, cameras, and microscopes. Here we review applications of optical metasurfaces as color filters, metalenses, beam generators or splitters, and meta-holograms. We briefly outline the designs and fundamentals of the metasurfaces. Finally, we identify potential practical applications of each metasurface, and the challenges that must be overcome to realize them commercially.