title: Achromatic Metalens over 60 nm Bandwidth in the Visible and Metalens with Reverse Chromatic Dispersion.
abstract: In this Letter, we experimentally report an achromatic metalens (AML) operating over a continuous bandwidth in the visible. This is accomplished via dispersion engineering of dielectric phase shifters: titanium dioxide nanopillars tiled on a dielectric spacer layer above a metallic mirror. The AML works in reflection mode with a focal length independent of wavelength from λ = 490 to 550 nm. We also design a metalens with reverse chromatic dispersion, where the focal length increases as the wavelength increases, contrary to conventional diffractive lenses. The ability to engineer the chromatic dispersion of metalenses at will enables a wide variety of applications that were not previously possible. In particular, for the AML design, we envision applications such as imaging under LED illumination, fluorescence, and photoluminescence spectroscopy.
authors.forename: M
authors.identifier: 0000-0002-0293-9113
authors.initials: M
authors.lastname: Khorasaninejad
authors.forename: Z
authors.initials: Z
authors.lastname: Shi
authors.forename: A Y
authors.initials: AY
authors.lastname: Zhu
authors.forename: W T
authors.initials: WT
authors.lastname: Chen
authors.affiliation: University of Waterloo , Waterloo, Ontario N2L 3G1, Canada.
authors.forename: V
authors.initials: V
authors.lastname: Sanjeev
authors.forename: A
authors.initials: A
authors.lastname: Zaidi
authors.forename: F
authors.initials: F
authors.lastname: Capasso
keywords: Metasurface; achromatic metalens; dispersion engineering; titanium dioxide; visible spectrum