Terahertz quasi-perfect vortex beams

We have successfully demonstrated the generation of terahertz (THz) quasi-perfect vortex beams (quasi-PVBs) at 0.3 THz. These THz quasi-PVBs can carry not only an individual orbital angular momentum (OAM) mode but also a multiplexed one. The 3D printed spiral axicon and multiplexed spiral axicon were used to generate THz quasiPVBs carrying individual and multiplexed OAM modes, respectively. The individual and multiplexed OAM modes are verified using a focal hyperbolic lens method and a modified coordinate transformation method, respectively. A THz quasi-PVB with the multiplexing of multiple different OAM modes holds promise for coupling to a receiver port with a fixed annular index profile, thereby increasing the number of communication channels. These works have potential applications in compact terahertz systems, such as mode division multiplexing, which further enhances the system's capacity.