Doublet Metalens for Polarization Conversion as Well as Focusing

The metalens created in accordance with the Pancharatnan-Berry (PB) phase principle are always addressed with circularly polarised (CP) incidence, resulting in a limitation in efficiency and optical path miniaturisation. This article proposes a cascaded two-layer structure for linear-to-circular polarization conversion and PB phase focusing. The structure consists of arrays on the upper and lower sides of the substrate, with periodic Au-elliptical-cylindrical (AEC) array arranged below the substrate to convert incident linearly polarised (LP) light into CP light, acting as a Quarter-wave plate (QWP); the TiO2 array with different rotation angles are arranged on top of the substrate using the PB phase, so that the converted CP light will converge at one point. Comparing this design to a metalens with the same numerical aperture (NA) but without polarization conversion for CP light incidence effectively verifies the polarization conversion and focusing function of this integrated doublet metasurface. In addition to metalens focusing, this design concept is applicable to optical communication, sensing, storage, and other optically integrated devices.