Singularities of Radial Gradient Perfect Vortex Beams Generated by Pancharatnam-Berry Metasurfaces

Perfect vortex beams (PVBs) have recently attracted much attention because they can maintain donut-like intensity profiles with sizes that do not depend on topological charges (TCs). The superposition of them can further expand the potential applications. However, the conventional superposition method is limited to PVBs with identical donut sizes and discrete TCs, which reduces the degrees of freedom for flexible manipulation of light. A compact metasurface approach for superposed PVBs with radial gradient sequential integer TCs and numerical aperture is proposed in this paper. This method achieves radial gradient PVBs (RGPVBs) with asymmetric intensity singularity distribution, and the singularity positions can be further modulated by introducing an initial phase in the metasurface design. Additionally, an array of RGPVBs can be realized. This kind of singularity beams of RGPVBs is expected to be used in optical trapping, optical communications, and quantum information.