US Patent 10408416 Achromatic metalens and metalens with reverse chromatic dispersion

An optical device includes a substrate, a reflective layer disposed over the substrate, and a metalens disposed over the reflective layer. The metalens includes a plurality of nanopillars, the plurality of nanopillars together specifying a phase profile such that the metalens has a focal length that is substantially constant over a wavelength range of an incident light of about 490 nm to about 550 nm.