Nonlinear generation of orbital angular momentum in metasurfaces

Structured light, denoting optical fields with non-trivial phase and/or polarization textures, plays an ever-increasing role in physical and life sciences. One of the most emblematic classes of structured light is formed by optical vortices, that is beams with helical wavefronts and a topological charge that quantifies the number and winding direction around a singularity. This phase texture is associated with an orbital angular momentum (OAM), which offers useful degrees of freedom for metrology, telecoms, and quantum optics. Metasurfaces have recently proven successful in creating OAM, especially in the linear regime. In the nonlinear domain, of importance for future classical and quantum information, to date OAM has mostly been created in qualitative ways. Here, we underscore the potential of nonlinear dielectric metasurfaces for versatile structured-light generation, with a focus on the generation of second harmonic vortices with high OAM order and purity, via meta-holograms fabricated in a III-V semiconductor monolithic platform.