Demonstration of focal length tuning by rotational varifocal moiré metalens in an ir-A wavelength

Abstract: This paper reports an experimental demonstration of moir\'e metalens which shows wide focal length tunability from negative to positive by mutual angle rotation at the wavelength of 900 nm. The moir\'e metalens was developed using high index contrast transmitarray meta-atoms made of amorphous silicon octagonal pillars, which is designed to have polarization insensitivity and full 2$\pi$ phase coverage. The fabricated moir\'e metalens showed focal length tunability at the ranges between $\pm$1.73 -- $\pm$5 mm, which corresponds to the optical power ranges between $\pm$578 -- $\pm$200 m$^{-1}$ at the mutual rotation between $\pm$90 degrees.