Achieving high numerical aperture near-infrared imaging based on an ultrathin cylinder dielectric metalens.

An artificial subwavelength dielectric metalens (ML), the realization of being ultrathin and light-weight, provides a potential candidate with replacing a traditional bulky curved lens with a high image quality. A ML with 1.5 mm in diameter having numerical aperture (NA) $\sim{0.60}$∼0.60 at the near-infrared wavelength of $\lambda = 0.94 \,\,{\unicode{x00B5}{\rm m}}$λ=0.94µm was designed by the finite-difference time-domain (FDTD) method with speeding up optimization of the MLs' scheme by the deep neural network (DNN) model. Additionally, an ultrathin high NA ML was achieved by cost effective semiconductor manufacturing technology. The fabricated ML can focus an incident light down to a spot as small as $ \sim{5.2}\,\,{\rm \unicode{x00B5}{\rm m}} $∼5.2µm with high optical efficiency of $\sim{88.4}\% $∼88.4% (focusing efficiency achieved, 23.7%). We also provided an efficient MLs' semiconductor manufacturing technology for the development of an optical device in near-infrared image technology.