Ultra-Wideband High-Purity OAM Generator Using Polarization Conversion Metasurface

Orbital angular momentum (OAM) has garnered significant attention due to its advantages in channel capacity. In this letter, a polarization conversion metasurface (PCM) that utilizes orthogonal gratings combined with a split ring to achieve asymmetric transmission is proposed. The PCM unit cells can achieve polarization conversion over broadband and exhibit highly linear phase response characteristics. The transmissive OAM generator is designed based on the PCM unit cells, which can effectively approximate the actual phase distribution to the ideal distribution at different frequency points by utilizing highly linear phase responses. Both the simulation and measurement results confirm the successful and effective generation of +1 OAM beam. The OAM generator demonstrates its exceptional ultra-wideband characteristics, achieving gain variations within a 3-dB range from 24.8 GHz to 44.5 GHz (57%) and maintaining a 1-dB bandwidth across 28 GHz to 42 GHz (40%). This makes it the most extensive bandwidth OAM generator available today. The purity of the generated OAM beam exceeds 0.9 in simulation and 0.83 in measurement, making it the widest bandwidth OAM generator with high purity.