Arbitrary spin–orbit conversions enabled by spin-switchable SU(2) rotation using the liquid-crystal geometric phase

Spin-orbit conversion facilitated by the geometric phase provides a promising flat optics platform for the structuring of light. However, the efficient generation of arbitrary spin-orbit states through passive and non-reconfigurable geometric phase elements remains a significant challenge. In this paper, by exploiting liquid-crystal geometric phase devices, we experimentally demonstrate arbitrary spin-orbit conversions based on spin-switchable SU(2) rotations of tunable Hermite-Gauss modes. Unlike conventional geometric phase devices, which are primarily designed for direct wavefront shaping, this SU(2) approach offers the advantages of unitary conversion and modal independence and, consequently, provides a promising spin-orbit interface with reconfigurable orbital angular momentum bases and lossless conversion.