Design of 3bit encoded THz ultra-widebandvortex beam generator based on metasurface

With the rapid development of high-speed THz communications, there has been a growing interest in exploring the potential of the orbital angular momentum (OAM) of electromagnetic waves. In this study, we propose a cross-polarized reflective broadband metasurface operating in the THz band to harness the benefits of OAM in the optical field. We quantitatively analyze the reflection amplitude and phase characteristics of the metasurface elements, which supports the design of a reflective broadband element surface array with an ordered arrangement of 3-bit elements. By combining the 3-bit metasurface elements in an array, linearly polarized waves can effectively be converted into vortex beams in the operating frequency range of 0.6THz-1.3THz. The simulation results demonstrate that the designed metasurface element structure can achieve not only efficient cross-polarization reflection amplitude but also effective phase control by adjusting the size parameters. Our proposed metasurface is able to convert linearly polarized waves into vortex beams with an efficiency exceeding 85% and can achieve high-purity OAM beam acquisition. Furthermore, the metasurface structure is simple to implement and can be easily integrated with photoelectric circuits, making it ideal for use in ultrahigh-speed THz communications.