Guiding terahertz orbital angular momentum beams in multimode Kagome hollow-core fibers.

We explore terahertz (THz) orbital angular momentum (OAM) modes supported in multimode Kagome hollow-core fibers. Numerical models are adopted to characterize the effective indices and confinement losses of vector modes over 0.2-0.9 THz, where two low-loss transmission windows are observed. Linearly combining the vector modes, THz OAM states can be generated. Covering a broad bandwidth of 0.25 THz, the purity values of OAM modes are beyond 0.9. Using numerical simulations, the hollow-core THz fibers with one and two rings of Kagome structures are also comparably investigated. We reveal that the OAM purity is dependent upon the confinement performance of THz fiber.