Generation of OAM Beams With Constant Beam Radius

The utilisation of orbital angular momentum (OAM) in next-generation wireless communication has become a research focus in recent years. The extremely high spectral efficiency of OAM is crucial for meeting future wireless communication demands. However, OAM-based wireless communication faces a significant challenge known as the hollow divergence effect, which reduces received power and signal integrity. This letter proposes a method to focus the OAM beam using the transmitting array to eliminate the divergence. Our proposed method generates an approximate ideal OAM (A-OAM) beam within a specific tolerance range around the receiver. Compared to traditional diverging OAM (D-OAM), the A-OAM beam does not diverge within its tolerance range. Specifically, we first propose the focusing method and system model for A-OAM by investigating its propagation characteristics. Then, we evaluate the focusing method through simulations ranging from 6 to 14 metres. The results are consistent with our theoretical expectations. A-OAM enables the simultaneous reception of multiple OAM modes over long distances, significantly enhancing the robustness of OAM-based wireless communication.