The terahertz (THz) vortex beam generators are designed and theoretically investigated based on single-layer ultra-thin transmission metasurfaces. Noncontinuous phase changes of metasurfaces are obtained by utilizing Pancharatnam–Berry phase elements, which possess different rotation angles and are arranged on two concentric rings centered on the origin. The circularly polarized incident THz beam could be turned into a cross-polarization transmission wave, and the orbital angular momentum (OAM) varies in value by lℏ. The l values change from 1 to 5, and the maximal cross-polarization conversion efficiency that could be achieved is 23%, which nearly reaches the theoretical limit of a single-layer structure. The frequency range of the designed vortex generator is from 1.2 THz to 1.9 THz, and the generated THz vortex beam could keep a high fidelity in the operating bandwidth. The propagation behavior of the emerged THz vortex beam is analyzed in detail. Our work offers a novel way of designing ultra-thin and single-layer vortex beam generators, which have low process complexity, high conversion efficiency and broad bandwidth.

太赫兹（THz）涡旋光束发生器是基于单层超薄透射超表面设计和理论研究的。利用 Pancharatnam-Berry 相元获得超表面的非连续相变，这些相元具有不同的旋转角度，并排列在以原点为中心的两个同心环上。圆偏振入射太赫兹光束可以变成交叉偏振传输波，轨道角动量（OAM）的值变化lℏ。升_值从 1 变化到 5，可以达到的最大交叉极化转换效率为 23%，几乎达到了单层结构的理论极限。所设计的涡流发生器的频率范围为1.2 THz至1.9 THz，所产生的太赫兹涡流光束可以在工作带宽上保持高保真度。详细分析了出现的太赫兹涡旋光束的传播行为。我们的工作提供了一种设计超薄和单层涡流束发生器的新方法，它具有低工艺复杂性、高转换效率和宽带宽。