A High Numerical Aperture All-Dielectric Near-Infrared Metalens Based on Pancharatnam-Berry Phase

Currently, the research on metalenses primarily focuses on several specific wavelength bands, and there is relatively little performance research on metalenses in the near-infrared band. Moreover, the materials chosen are mostly metallic or other composite materials, which not only increase the cost but also lead to greater losses. Furthermore, most designed metalenses have a small numerical aperture, which can also affect the imaging quality and focusing performance of the metalenses. Based on this, we propose an all-dielectric metalens, consisting of two layers of SiO2 on the top and bottom, with a lossless silicon material in the middle. Performance analysis was conducted using CST Studio Suite software. The results show that a high polarization conversion rate was obtained at 1020 nm when different circularly polarized waves were incident, along with a significant cross-polarized circular transmission rate. Based on the Pancharatnam-Berry (P-B) phase principle, eight unit cells were designed to achieve a phase variation covering 2n, while the corresponding circularly polarized transmission rate remained at a high level. According to the phase gradient changes of the eight structural units under the incident Left-handed Circularly Polarized (LCP) wave and the focusing phase distribution formula, a focusing phase gradient metasurface array was obtained to be a metalens. When LCP or Right-handed Circularly Polarized (RCP) is incident, focusing and defocusing can be achieved with a large numerical aperture (NA) of 0.97, respectively.