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 …

… Abstract: We demonstrate an achromatic metalens with a constant focal length over 60
nm bandwidth (λ= 490 nm to 550 nm). We also design metalenses with reverse chromatic
dispersion, opposite of a Fresnel lens. … Here, we present reflective achromatic
metalenses (AML) over a 60 nm bandwidth in the visible (λ=490nm-550 nm) with a
numerical aperture NA=0.2. This is accomplished by dispersion engineering of the AML’s
phase shifter. To demonstrate the versatility of our approach, we also design a …