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 l_p, whereas the Pancharatnam–Berry (PB) phase acts only on the cross-polarized component to construct another helical phase profile with topological charge l_g. Thus, the co- and cross-polarized components form two orthogonal vector vortex (VV) modes with topological charges l_p and l_p + l_g, respectively. When the parameter conditions are satisfied by matching the incident polarization chirality σ and topological charges l_p and l_g, 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 θ₀ 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.