Topological Charge Inversion of Optical Vortex with Geometric Metasurfaces

The topological charge (TC) inversion of optical vortex is demonstrated along the beam propagation direction by using plasmonic geometric metasurfaces with the initial wave fronts designed from the principle of caustic surface. The detailed TC inversion evolution process is observed together with the transmutation point where the vortex vanishes. The orbital angular momentum (OAM) mode distributions during the TC inversion process are studied to show the dynamic redistributions of OAM mode density between the central area and the surrounding area of the beam with the total OAM conserved. Furthermore, the TC inversion of self-accelerating vortex beam along the parabolic trajectory is presented. The realization of controlling TC inversion of optical vortex along arbitrary beam trajectory paves the way for many applications with more complex functionalities in optical trapping and manipulation, optical sensing, quantum information and computation, and data communication.