Broadband Dielectric Metalens for Polarization Manipulating and Superoscillation Focusing of Visible Light

Superoscillatory optical devices have been widely investigated in the past several years. Due to their unique focusing properties, the ones that focus cylindrically polarized waves are attractive for such applications as super-resolution imaging and particle manipulation. However, the superoscillatory lenses reported for the focusing of cylindrically polarized light suffer from difficulties related to precise coaxial alignment, which might lead to the substantial distortions of the superoscillatory features. Moreover, conventional polarization converters only have a narrow bandwidth of several tens of nanometers in the visible spectrum, which limits the broadband focusing of cylindrically polarized waves. In this work, an amorphous silicon dielectric meta-atom is proposed with the integrated functions of independent polarization conversion and binary phase modulation in the visible spectrum range. Based on the proposed meta-atom, a superoscillatory dielectric metalens with a high numerical aperture (NA) of 0.93 is proposed and optimized for the broadband generating and superoscillation focusing of azimuthally polarized lights. The linearly polarized wave was first converted into azimuthally polarized ones, and then focused into a superoscillation hollow spot of azimuthal polarization (AP). The experimental results demonstrate the formation of hollow spots with inner sizes of 0.355 lambda-0.490 lambda in the wavelength range of 518.1-683.5 nm. This simple approach paves an alternative pathway of generating vector waves with superoscillation features for super-resolution applications.