Broadband polarization-insensitive metalens with excellent achromaticity and high efficiency for the entire visible spectrum

Abstract

Metasurface-based flat optics is continuously attracting interest owing to its ability for miniaturization of optical devices and systems. Over the last few years, broadband achromatic metalenses have been extensively studied for focusing and imaging in the visible band. However, it is still a substantial challenge to design an achromatic metalens that can produce high-focusing efficiency and high-consistency focal length over the entire visible spectrum. In this Letter, we propose a polarization-independent achromatic metalens operating at wavelengths from 400 to 760 nm, which comprises only a single layer of cross-shaped and square-ring silicon nitride-based nanopillars on a glass substrate in the transmission mode. Numerical results demonstrate that the achromatic metalens has an average efficiency of 75.9% and a maximum focal shift of less than 0.3λ (λ being the operating wavelength) over the entire visible band, which indicate significant improvement over the previously reported achromatic metalenses for focusing visible light in terms of focal-shift suppression and wideband operation with high efficiency. This study recommends a means to develop a high-quality achromatic metalens for the whole visible spectrum. The proposed approach is also suitable for achromatic metalens designs of other wavebands.