Generation of scalar and vector beams with longitudinally varying polarization based on all-silicon metasurfaces

Abstract Beams with longitudinally continuously varying polarization provide a new application dimension in fields such as optical communication and optical manipulation. The small-sized and multifunctional metasurfaces have been used to generate scalar or vector beams whose polarizations vary along the propagation direction within a single polarization mode. However, dual-mode beams with longitudinally varying polarization can further increase the dimension of manipulation, but they have been rarely explored. Here, we propose a scheme based on the spatial partitioning method for designing dual-mode beams with longitudinally evolving polarization. To validate the proposed scheme, we demonstrate three dual-mode beams generated by all-silicon metasurfaces which have evolving polarization from scalar to vector, scalar vortex to vector vortex, and first-order to second-order cylindrical vector, respectively. The transverse polarization distributions of these beams depend on their longitudinal position. The different focal lengths of the orthogonal circularly polarized components and the design of long focal depth make it possible to change the polarization distribution longitudinally. The optical fields generated based on the proposed scheme are expected to be applied in depth detection and optical manipulation.