Quarter-wave plate metasurfaces for generating full elliptical polarization vector beams via linear polarization tunability

The manipulation of vector beams using metasurfaces is important for applications ranging from classical physics to quantum technologies. In this study, two supercell metasurface designs are proposed for generating multichannel focused higher-order Poincaré (HOP) beams with full elliptical polarization only under linearly polarized incidence. Each supercell contains two pairs of quarter-wave plate meta-atoms, wherein the two meta-atoms in each pair have perpendicular orientations and opposite propagation phases. In one design, the orientation angle difference Δθj between two nanopillar pairs in each supercell was fixed, while their propagation phase difference Δφr, j was used to modulate weights of the two circularly polarized vortices; in the other design, Δφr, j was fixed and Δθj was adjusted for the manipulations. Thus, the two designs generated HOP beams with polarization states evolving along a meridian and an S-shaped trajectory, respectively. Importantly, the designs circumvented the cumbersomeness of adjusting elliptically polarized incident light with the requisite waveplate-polarizer combinations in previous HOP beam generations. Moreover, we derived a complete analytical expression instead of unsolved integrals for a tightly focused light field based on the Richards-Wolf theory. This study is significant for developing devices with compactness, integration, and multifunctionality and for their applications in classical and quantum sciences.