Design, Analysis and Experiment on High-Performance Orbital Angular Momentum Beam Based on 1-Bit Programmable Metasurface

In this study, a high-performance orbital angular momentum (OAM) beam is designed, analyzed and experimented using a 1-bit programmable metasurface. OAM as a novel technology is investigated systematically in this paper. Moreover, this study is motivated by the application requirements of real-time controllable communication. The proposed programmable metasurface comprises 1-bit phase modulation units with only two phase states, which is evolved from an electromagnetic surface composed of 360° continuous phase units based on the principle of 1-bit phase quantization. First, the necessity and feasibility of developing the OAM beam based on 1-bit programmable metasurface are studied. Then, qualitative analysis of OAM beams is conducted on different OAM modes and phase modulation elements. Next, the quantitative indexes of OAM beams such as the peak gain in far-field, the divergence angle of main lobe, and circumferential symmetry in azimuth planes are systematically analyzed through a survey of key factors. It is noteworthy that this analysis provides a powerful research basis to achieve an excellent OAM beam with the adjustable function. Thereafter, an active reflective programmable metasurface with $48\times48$ elements is fabricated to verify the feasibility of developing an OAM beam using a 1-bit element. The experimental and simulation results are in good agreement. Furthermore, a high gain OAM beam with a narrow divergence angle is realized by using the large-scale 1-bit programmable metasurface. Notably, a high-gain beam and an OAM beam can be both generated and can converted into each other, which lays the foundation to achieve the OAM beam with the function of real time dynamic control in future.