Switchable frequency terahertz vortex beam generator

Most of the reported vortex beam generators generate beams at a fixed frequency, which limits practical applications. Therefore, it is inevitable to explore generator, can actively control operating frequency. We propose switchable frequency terahertz metasurface, freely under single-frequency mode and dual-frequency by changing external temperature, phase state vanadium dioxide (VO<sub>2</sub>) also changeable. External temperature changes will cause VO<sub>2</sub> transform from insulating metallic state. Generally, conductivity increase several orders magnitude as changes. By using change property VO<sub>2</sub>, we obtain metasurface with frequencies. For room proposed behaves generator. When (left-handed circularly polarized, LCP) wave vertically incident on generates different topological charge numbers 1.1 THz, purity above 85%. The simulation results show that <i>l</i> = 1 90%, about 91.1% for 2, 85.4% 3. 68 ℃, designed becomes At this time, frequencies charges (<i>l</i> 1, 3) are 0.7 1.23 whose purities both 60%. That say, corresponding with<i> l</i> two 89.1% 71.6%, respectively. 83.2% 94.4% 62.4% 68.2% charge<i> 3, generator provides new design idea working modulation in wireless communication.