Multifunctional all-dielectric quarter-wave plate metasurfaces for generating focused vector beams of Bell-like states.

The generation of vector beams using metasurfaces is crucial for the manipulation of light fields and has significant application potential, ranging from classical physics to quantum science. This paper introduces a novel dielectric metasurface composed of quarter-wave plate (QWP) meta-atoms, known as a QWP metasurface, designed to generate focused vector beams (VBs) of Bell-like states under right circularly polarized illumination. The propagation phase imparted on both the co- and cross-polarized components of the output field constructs hyperbolic and helical phase profiles with topological charge , whereas the Pancharatnam-Berry (PB) phase acts only on the cross-polarized component to construct another helical phase profile with topological charge . Thus, the co- and cross-polarized components form two orthogonal vector vortex (VV) modes with topological charges and + , respectively. When the parameter conditions are satisfied by matching the incident polarization chirality and topological charges and , the focused VBs of Bell-like states are generated by simultaneously manipulating the two VV modes, in contrast to existing QWP metasurfaces. The polarization states of the generated VBs are manipulated using the initial orientation angle of the meta-atom. Overall, this research provides an innovative strategy for metasurface design, enhancing the functionality of metasurface devices for a broader range of application scenarios.