High-Performance Transmissive Broadband Vortex Beam Generator Based on Pancharatnam-Berry Metasurface

Vortex beam generators, particularly those operating in transmission mode, are extremely important in modern communication systems because they are believed to be an effective way to extend the capacity of a communication channel. However, current approaches have suffered from complex configurations, fixed operation modes, and low efficiency, particularly in a transmissive case. In this study, we propose a new strategy for improving the transmissive amplitude and bandwidth of metasurfaces by optimizing microstructures with a non-uniform thickness based on the transfer matrix method (TMM). As a result, our designed meta-atom can achieve a high transmission of greater than 0.9 within a wide frequency interval of 12.6-16.2 GHz. As a proof of concept, we designed a vortex beam generator with topological charge l = 1 using the designed meta-atom. We conducted near- and far-field experiments to characterize its performance, indicating that our meta-device can realize a pure vortex beam with an efficiency of higher than 82.1% at a central frequency of 15 GHz. Our findings will lay a theoretical foundation for studies on metasurfaces with a non-uniform thickness and provide a way to design high-performance meta-devices with broad bandwidths.