Broadband dynamic manipulation of perfect optical vortex beams with tunable topological charge via all-dielectric moiré metasurfaces

Perfect optical vortex (POV) beams, recognized for the distinct ring profile that remains independent of the topological charge, have emerged as a research focus in orbital angular momentum manipulation and offer broad applications in optical communications, particle trapping, and information encryption. While metasurfaces have revolutionized compact and efficient generation of POV beams, their current implementations face limitations in achieving dynamic reconfigurability. Here, we leverage the moiré effect to construct vertically stacked broadband all-dielectric cascaded metasurfaces operating in the visible spectrum. Utilizing pure geometric phase modulation, the metasurface layer 1 integrates the functions of a spiral phase plate, an axicon, and a Fourier lens, while the layer 2 serves as a spiral phase element. By controlling the relative rotation angle between two metasurfaces, we achieve continuous tuning of both the magnitude and sign of the topological charge carried by the POV beam. Furthermore, fractional POV beams can be generated at specific rotation angles. This work demonstrates dynamic on-demand control of POV beams through a simple mechanical tuning mechanism. The approach significantly enhances design flexibility while providing perspectives for adaptive photonic devices, facilitating the development of compact, integrated, and multifunctional nanophotonic platforms.