Metasurfaces of quarter-wave-plate (QWP) meta-atoms exhibit high flexibility and versatility in light-field manipulations; however, using them to generate multi-channel focused vector beams is challenging. This study proposes dielectric metasurfaces comprising two interleaving sets of QWP meta-atoms. Their parameters are adjusted based on the pre-set orders of the target vector beams to manipulate higher-order Poincaré beams and vortex superpositions in multiple channels. The metasurface phase profiles include hyperbolic, vortex, and gradient phases for focusing wavefronts, generating circularly polarized vortices, and deflecting vortices into two cross-polarization and one co-polarization channel. Four metasurface samples were designed to generate different order higher-order Poincaré beams in different channels, demonstrating the feasibility of QWP meta-atoms metasurface for manipulation of complicated vector light fields. Theoretical analysis, simulations, and experiments all demonstrate the feasibility of the proposed metasurfaces. Thus, this study is significant for compact, integrated, and multifunctional nanophotonic platforms with applications in high-capacity communication, image processing, quantum entanglement, and quantum communication.

Metasurfaces of quarter-wave plate (QWP) meta-atoms have exhibited high flexibility and versatile functionalities in the manipulation of light fields. However, the generation of multi-channel vortex beams with the QWP meta-atom metasurfaces presents a significant challenge. In this study, we propose dielectric metasurfaces composed of QWP meta-atoms to manipulate multi-channel vortex beams. QWP meta-atoms, systematically arranged in concentric circular rings, are designed to introduce the modulations via the propagation phase and geometric phase, leading to the generation of co- and cross-polarized vortex beams in distinct channels. Theoretical investigations and simulations are employed to analyze the modulation process, confirming the capability of QWP meta-atom metasurfaces for generating the multi-channel vortex beams. This study presents prospective advancements for the compact, integrated, and multifunctional nanophotonic platforms, which have potential applications in classical physics and quantum domains.

Vector beams (VBs) and their superposition have found important applications in versatile fields such as optical communications, super-resolution microscopy and quantum information, and metasurfaces have enabled the miniaturization and integration of the optical systems manipulating the vector beams, providing potential applications to subwavelength regimes. In this work, we propose a metasurface to realize the superposition of profile-tunable tightly focused VBs, with the novel structured light fields generated. The metasurface is composed of two sets of orthogonal-nanoslit pairs arranged on the inner and outer rings. By realizing the chiral conversion of circularly polarized light with the slit-pairs which act as half-wave plates, and by creating helical phase profiles of optical vortices with the geometrical phase of rotational nano-slit pairs, two focused Bessel VBs are formed. By finely varying the diameters of two sets of rings, the doughnuts of the two Bessel VBs of different orders are tuned to be of the same size, and the superposition of the two VBs is realized. The theoretical analyses of the superimposed fields were presented, the FDTD simulations were performed to optimize the designed metasurfaces, and the experimental measurements were carried out to validate feasibility of the metasurface. The novel and interesting characteristics of the superposed fields different from those of the conventional VBs were demonstrated. This work will be of significance for classical and quantum applications of VBs in various fields.