Dielectric quarter-waveplate metasurfaces for longitudinally tunable manipulation of high-order Poincaré beams

The dynamic tunability of vector beams (VBs) with metasurfaces plays an important role in the discovery of exotic optical phenomena and development of classic and quantum applications. Using the tunability with longitudinal propagation distance and multifunctional capability of the quarter-waveplate (QWP) meta-atoms, dielectric metasurfaces were designed to generate high-order Poincaré (HOP) beams with tunable elliptical polarization states at arbitrary latitudes. The metasurface contained two interleaved sub-metasurfaces of QWP meta-atoms, each configured with helical, hyperbolic, and primary and secondary axicon-phase profiles to generate a vortex, beam focus, and beam deflection, respectively. Importantly, the axicons were suitably designed by combining the propagation and geometric phases to introduce differences in the z -component wavevectors, and the amplitudes of the co- and cross-polarized vortices were tuned by the longitudinal distance. The method broke through the limitation of previously generating only the linear polarization states on the equator of the HOP sphere, and it also circumvented the traditional tunability using the troublesome waveplate-polarizer combination. This study is of great significance for the miniaturization and integration of optical systems for applications such as optical communications, micromanipulation, and high-precision detection.