Switchable perfect optical vortex beam generator with high efficiency based on geometric phase

Vortex beams carrying orbital angular momentum have attracted increasing attention due to the helical wavefront, extensive high-dimensional state space, and cross-disciplinary applicability in fields such as high-capacity optical communication, optical manipulation, and super-resolution optical imaging. However, the intensity profile of vortex beams exhibits a topological charge-dependent annular structure, which imposes fundamental constraints on wavefront modulation flexibility, particularly in multi-mode coupling systems. In this study, we report a switchable perfect vortex beam (PVB) generator with high efficiency in the visible by combining spatially patterned photoalignment of nematic liquid crystal (LC) with multiplexed geometric phase profiles. Comprehensive simulations and experimental characterization demonstrate that the LC geometric-phase-based PVB generator produces high-quality vortex beams with spatially invariant intensity profiles across topological charges ranging from l = - 8 to + 8 and with an average conversion efficiency up to 86%. Moreover, we reveal that the PVB generator is switchable between left- and right-handed circularly polarized beams. This study demonstrates the feasibility of generating high-quality PVB through highly integrated flat LC photonic device, and may find applications in OAM multiplexing in quantum communication networks and ultrahigh-capacity photonic interconnects.