Design and investigation of a terahertz hollow-core fiber with double-layer ring core for OAM mode transmission

Abstract A terahertz hollow-core fiber having a double-layer ring core is presented and investigated to support OAM mode transmission. These two annular cores will work as two separate OAM transmission spaces that are not interfered with and can support more OAM mode transmissions. A numerical model has been developed to assess the transmission performances of EH and HE modes in the 0.3∼0.4 THz frequency band. Using only a single material to design the suggested fiber, 22 (in) + 58 (out) OAM modes can be stably transmitted at 0.36 THz. Neighboring EH and HE modes in the identical OAM family can obtain effective refractive index differences of more than 10 −4 . Furthermore, the designed fiber demonstrates excellent transmission properties, with the highest mode purities in the inner and outer rings being 92.22% and 93.78%, respectively. In the inner ring the effective mode field area is between 5.37 × 10 6 and 1.79 × 10 7 μm 2 , while in the outer ring, it is between 8.95 × 10 6 and 1.58 × 10 7 μm 2 . The HE 1,1 mode has the smallest change in dispersion, with values of 2.76 and 0.87 ps THz −1 cm −1 in two high refractive index transmission ring cores, respectively. Additionally, the isolation (ISO) parameter is also analyzed. These mode characteristics indicate that the fiber structure has significant potential for applications in high-capacity terahertz communication systems.