Spin-to-orbital angular momentum conversion in symmetric dielectric nanorings

Recently, tremendous remarkable studies on spin-orbit interactions (SOIs) have attracted interest of scientists across the world in various fields. Among contemporary technologies of probing SOI, photonic metasurfaces have become a prevalent tool to guide and steer wavefront of light at the subwavelength scale. Nevertheless, the discretized nanoantennas of metasurfaces have been plagued for the shortcoming of bandwidth. In contrast to the discretized strategy, symmetric nanorings possessing a continuous phase gradient are exploited in this work. Benefiting from lossless dielectric material and nondispersive characteristic of the Pancharatnam-Berry phase principle, the designer nanorings are viable to realize high efficient spin-to-vortex conversion over a wide spectrum. The nanorings also accomplish a high purity of orbit angular momentum mode, which is of vital importance in many applications. Our findings would be beneficial to delve spin-controllable nanodevices and hold promise for applications of atomic manipulation and optical tweezers.