Broadband high-efficiency reflective metasurfaces for sub-diffraction focusing in the visible

Super-oscillation phenomenon provides an effective solution for realizing far-field non-invasive super-resolution imaging. However, most super-oscillatory lenses are challenging to balance the working bandwidth and working efficiency, which greatly limits the practical applications of super-oscillation lenses in optical systems. In this work, a broadband high-efficiency super-oscillatory metalens for sub-diffraction focusing about 0.75 times the diffraction limit based on the reflective metasurface is proposed for super-resolution imaging in the visible ranging from 400 nm to 700 nm. Moreover, another metalens with a sub-diffraction focusing spot equal to 0.6 times of the diffraction limit is also designed to prove the universal applicability of the proposed method. The proposed method provides an effective pathway for the development of microscopy, holography, and machine vision.