Design of a polarization insensitive achromatic metalens with a high NA and uniform focusing efficiency based on a double layer structure of silicon and germanium

Abstract

A polarization insensitive achromatic metalens (PIAML) was designed to realize a high NA of 0.5 and uniform focusing efficiency in the visible range based on a double layer structure of silicon (Si) and germanium (Ge). Due to their high refractive indices as well as the opposite characteristics of group delay in the visible wavelength, the combination of Si and Ge can contribute to the high NA and achromatic performances. In addition, an isotropic cylindrical unit cell structure was applied to confirm polarization sensitivity. From the finite difference time domain (FDTD) simulation results, it was confirmed that the designed PIAML shows good optical performance of both polarization insensitivity and achromatic performance with uniform focusing efficiency of 27% and high NA of 0.5 in the visible wavelength.