A super-oscillatory step-zoom metalens for visible light.

In recent years, the super-oscillation method based on the fine interference of optical fields has been successfully applied to sub-diffraction focusing and super-resolution imaging. However, most previously reported works only describe static super-oscillatory lenses. Super-oscillatory lenses using phase-change materials still have issues regarding dynamic tunability and inflexibility. Therefore, it is vital to develop a flexible and tunable modulation approach for super-oscillatory lenses. In this paper, we propose a super-oscillatory step-zoom lens based on the geometric phase principle, which can switch between two focal lengths within a certain field of view. The designed device consists of nanopillars with high efficiency of up to 80%, and the super-resolution focusing with 0.84 times of diffraction limit is verified by the full-wave simulation. The proposed method bears the potential to become a useful tool for label-free super-resolution microscopic imaging and optical precision machining.