Low-loss polymer porous ring core fiber for transmitting terahertz vortex beams

What believe to be a novel polymer porous ring-core fiber (PRCF) is proposed for terahertz (THz) vortex beams guidance, featuring a central hollow region, a porous ring-core, and a cladding composed of pomelo-type air-hole array. Notably, we introduce circular air holes into the ring core to reduce the transmission loss of THz vortex fiber for what we believe to be the first time. The results demonstrate that the total transmission loss of the PRCF decreases by 2.9146 ∼ 18.2480% compared with the THz vortex fiber without air holes within the ring core in the 0.5 ∼1.5 THz range. Moreover, the proposed PRCF exhibits the lowest total transmission loss among the reported vortex fibers operating in the same frequency band (0.6 ∼ 1.25 THz). In addition, the relationship between structure parameters of air holes in the ring-core and the transmission characteristics of THz vortex beams is studied to optimize the number of orbital angular momentum (OAM) modes and the operation bandwidth while maintaining low transmission loss. The simulation results show that the proposed PRCF can support 40 modes (36 THz OAM modes) with large mode effective refractive index separation (> 3.9101 × 10^-3) in the range of 0.5 ∼ 1.5 THz, while maintaining a single-mode condition radially. Furthermore, it exhibits good mode quality (MQ > 77.82%) and flat dispersion of 0.1781 ± 0.27 ps/THz/cm within the whole operation range. Hence, our study provides a promising solution for reducing the transmission loss of THz vortex fiber, which is expected to realize low-loss and wide-bandwidth guidance of THz vortex beams, offering great potential in short-distance, high-capacity data transmission links for next-generation THz communications.