Spin-orbital interaction characterizes the momentum coupling between polarization and spatial behaviors of electromagnetic waves. The corresponding transition phenomena have been recently manifested by geometric phase metasurfaces, which provide compact and intuitive platforms to replace traditional optical waveplate cascading systems. Nevertheless, metasurfaces based on geometric phase can only impose two opposite modes of orbital angular momentum (OAM) in conjugate spin channels. Although cross-talks among adjacent channels can be exhaustedly minimized, the purity and efficiency of spin-orbital transitions would still be impacted by the coexisting conjugate coupling. Here, we exploit a metasurface with non-orthogonal eigen formalism to achieve the channel-locked spin-orbital transitions, where the output spin state can be constantly fixed while at the same time imposed with versatile modes of OAM with high purity and efficiency. Besides, the robustness of the channel-locked spin-orbital transition is also demonstrated under full polarization illuminations. Such results provide a scheme for full-Stokes beam generation and high-performance meta-polarizer design, which shows the potential of reconfigurable polarization control in wireless communication systems.
Yuan et al. (2025) studied this question.