Polymer negative curvature ring-core fiber for OAM modes guidance

In this paper, a novel, to the best of our knowledge, polymer-based negative curvature ring-core fiber (NC-RCF) is proposed and investigated. The hollow-core NC-RCF is composed of TOPAS as background material. The inner and outer negative curvature structure layers are connected to the annular area, and the orbital angular momentum (OAM) modes can propagate in the annular core. In the frequency region of 1.0-1.5 THz, the designed NC-RCF can stably transmit 82 OAM modes. Investigation results indicate that the effective refractive index differences between the corresponding HE and EH modes are above 10^-4. The confinement losses of EH or HE modes are smaller than 10^-8 d B/m, and the dispersion variations are lower than 0.31 ps/THz/cm. Effective mode areas are larger than 5.14m m ². Additionally, the highest mode purity of all vector modes is 99.78%. In addition, modal birefringence, also known as the walk-off length, has also been discussed. All these operation performances indicate that the designed NC-RCF make contributions to the optical communication systems.