Design of Au-LiNbO ₃ hybrid metasurfaces for the simultaneous generation of linear and nonlinear perfect vortex beams

A perfect vortex beam (PVB) is a unique type of vortex beam that carries orbital angular momentum (OAM) while maintaining a constant radius independent of its topological charge. Compared with conventional vortex beams, PVBs exhibit a more stable intensity distribution, leading to improved performance in particle manipulation and optical fiber communication. Extending PVBs from linear to nonlinear regime offers an additional frequency-domain control dimension, thereby increasing their information capacity. However, compact and efficient approaches for generating nonlinear PVBs (NPVBs) are still in high demand. Here, we numerically design an Au-LiNbO ₃ hybrid metasurface based on nonlinear geometric phase engineering, and show that the designed metasurface can simultaneously generate a fundamental-frequency PVB and a second-harmonic NPVB. The generated NPVB retains the constant beam radius characteristic of PVB, while exhibiting a 1.5-fold increase in topological charge compared with its linear counterpart. This compact nonlinear metasurface platform enables the simultaneous generation of PVBs at dual-frequency, offering what we believe to be new opportunities for multi-dimensional OAM encoding, particle manipulation, and on-chip nonlinear photonic systems.