Generating iso-propagating vortex using dielectric metasurface

The iso-propagating vortices (IPVs), as it possesses a ring radius independent of topological charges as well as propagation evolution characteristics independent of orbital angular momentum (OAM), has recently attracted great interest in optical communication, particle manipulation, and quantum information. However, its generation currently requires a series of bulky and high-cost discrete optical elements, which seriously hinders its practical application. Here, we construct the desired phase by extracting phases of every discrete optical element in the IPVs system and propose a scheme of realizing IPVs using geometric metasurface for the first time. The simulation results prove that the generated beam is indeed an IPV, whose ring radius and divergence angle are independent of OAM. Moreover, it offers an additional advantage of maintaining the perfect vortex characteristics over a longer propagation distance and with a narrower divergence angle when compared to the conventional perfect vortex beams (PVBs). This approach of implementing IPVs exhibits the characteristics of miniaturization, planarization, integration, and robustness, providing valuable perspective on generating suitable vortex beams for OAM communication and various other application scenarios.