Broadband sub-diffraction focusing of oblique radially polarized wave by a high-numerical-aperture metalens

Lenses with sub-diffraction focusing are extensively used in advanced optical imaging and microscope. Due to the longitudinal electric component, the radially polarized beam could offer sub-diffraction focusing by high-numerical-aperture (NA) lenses. However, slightly oblique incidence light could pose serious off-axis aberrations for high-NA metalens. Here, we demonstrate that a high NA (0.97) metalens design approach can simultaneously provide sub-diffraction focusing for oblique incidence and broadband operation. Simulation results demonstrate that the metalens with an aperture stop, R (stop), of 7 & mu;m have the operating angle range of [-15 & DEG;, +15 & DEG;] for sub-wavelength focusing. For the case of R (stop) = 9 & mu;m, sub-diffraction focusing is realized in the oblique angle range at & PLUSMN;6 & DEG;. Significantly, the metalens is able to realize a sub-diffraction focusing over the wavelength range 600-750 nm. These types of metalens have the important advantages of sub-diffraction focusing and broadband operation. They are also ultra-thin and easy to integrate, allowing such metalens could be used in miniaturized and integrated optical systems.