Spin–Orbit Interaction Enabled Nonlinear Metasurface Holography

Nonlinear optical metasurfaces have emerged as a powerful platform for efficient and multi-dimensional manipulation of harmonic waves, offering distinct advantages such as high-integration capability and phase-matching-free operation. Spin and orbital angular momentum (SAM and OAM) provide rich degrees of freedom for advanced light field control. While SAM- and OAM-multiplexing metasurface holograms have been realized in the linear optical regime, their performance is hindered by a low signal-to-noise ratio stemming from residual light mode conversion. Nonlinear OAM holography has recently been demonstrated; however, its practicality remains limited by reliance on bulky nonlinear optical crystals that exhibit only intrinsic spin-orbit interaction (SOI). Here, we introduce nonlinear SOI holography via second harmonic generation on optical metasurfaces composed of gold plasmonic meta-atoms. By controlling the local rotational symmetry and topological charges, these metasurface holograms can fully harness optical SOI through both intrinsic and extrinsic angular momentum mode conversions. Information hidden in second harmonic holographic images can only be reconstructed from the spin-orbit tomography of the fundamental waves, ensuring high-security nonlinear optical encryption. The proposed approach offers promising applications in optical communications, optical information processing, high-dimensional optical storage, and so on.