Fig. 3.

(a) The wrapped and discretized (12 equally spaced levels) phase profile cross section ($0<x<100\mu \mathrm{m}$) of the metalens designed in Fig. 2(a). (b) Nanopost phase and transmission response calculated by RCWA, with cSi nanoposts on $460\text{-}\mu \mathrm{m}$-thick ${\mathrm{Al}}_2{\mathrm{O}}_3$ substrate at a wavelength of 1310 nm. The height of the nanoposts are $h=1000\mathrm{nm}$ and the periodicity of the nanopost array is $p=600\mathrm{nm}$. (c) SEM images of the fabricated metalens from the top. (d) SEM image at the oblique angle of 40 deg.