Terahertz Vortex Beam Generation based on Complementary Open Rings Metamaterial

The vortex beam has attracted much attention due to its great potential applications in communication and medicine area. To compare with the regular light, the vortex beam carrying the orbital angular momentum can greatly increase information capacity in communication. In this paper, a new method is presented to generate terahertz vortex beam based on the complementary open-rings metamaterial. The structure is composed of a metasurface-dielectric-metasurface, which top and bottom layer are both complementary open rings, and the dielectric layer is polyimide. And the vortex beam generators with topological charge of 1 and 2 have been designed according to the phase principle of Pancharatnam-Berry (P-B), which based on the different orientation of open ring unit cells. The amplitude and phase of the cross -polarized transmitted beam were manipulated by rotating the orientation of the complementary open rings, while ensure the amplitude of the transmitted beam stays unchanged, and the phase of the cross-polarized transmitted beam cover the range of 1*2 pi(where 1 is the topological charge). The vortex beam characteristics has been studied when circularly polarized light incident on the measurface of vortex beam generators with the CST MICROWAVE STUDIO. The simulation results show that the transmitted beam are well meet the characteristic of vortex beam, which the transmittance of cross-polarized vortex beam is as high as 64% at 1.48 THz while the phase can cover the range of 1*2 pi. That is, the presented transmissive vortex beam generators can convert incident circularly polarized beam into a cross-polarized vortex beam carrying orbital angular momentum. The approach demonstrated in this paper which is high conversion efficiency, simple structure, quick response, and has potential applications in the field of terahertz communication.