Broadband Achromatic Metalenses With High Focusing Efficiency Based on Inverse Design

In this letter, we propose a broadband achromatic metalens that exhibits high focusing efficiency within the wavelength range of 1270–2070 nm and is insensitive to polarization. Within the operating wavelength range, the metalens displays a focal length shift of only $\pm 0.5~\mu \text{m}$ and exhibits excellent achromatic properties. The average focusing efficiency of the metalens is 56%, with a maximum focusing efficiency of 70.7%. Compare with no metalens, the metalens can enhance the transmissivity of incident light by approximately 10%. And the average full width at half maximum (FWHM) of this structure is $0.5526~\mu \text{m}$ . In the design process, we propose a new algorithm. The concept behind this method has significant implications for other inverse design algorithms.