Terahertz Ring-Core Fiber for First-Order Radial OAM Modes Transmission Without Phase Distortion

We propose a hollow ring core fiber with multi-layer annular cladding that can stably transmit 34 orbital angular momentum (OAM) modes without the excitation of second-order radial modes and phase distortion. Our research demonstrates that the odd or even number of first layer circular tubes has different effects on the phase distortion of the OAM modes. In addition, a novel method is proposed to utilize the mode coupling effect of multi-layer annular cladding structures to suppress the excitation of second-order radial modes. The research process and parameter optimization of the proposed fiber is also fully explored. In the frequency range of 0.13 - 0.14 THz, the proposed fiber exhibits excellent performances in the effective refractive index (include difference), mode purity, confinement loss, effective mode area and waveguide dispersion aspects.