High-NA broadband achromatic metalens in the visible range

We designed a high-NA (High numerical aperture) broadband achromatic metalens consisting of elliptical TiO ₂ -based integrated-resonant unit-cells. The phase profile for the designed metalens is constituted by incorporating the geometric phase with the transmission phase, where the geometric phase contributes to the basic phase profile of the metalens and the transmission phase is used to compensate phase profile at different incident wavelengths. With the method of finite element simulation, the results demonstrate that the metalens has an average focusing efficiency of 36.4% in the visible range from 530 nm to 850 nm. Compared with chromatic metalens, the axial chromatic aberration of achromatic metalens is reduced by 2.66 times. Furthermore, the designed metalens has a high-NA of 0.564. This work can be potentially applied in various fields, such as optical communications, microscopy imaging, and optical instruments.