Numerical study of microstructured fiber with concentric dual rings for supporting orbital angular momentum mode propagation

A microstructured fiber with two concentric high-refractive-index rings is proposed to support more orbital angular momentum (OAM) beam propagations and OAM-based mode-division multiplexing (MDM) for improving the channel capacity and spectral efficiency. The two ring cores can be considered as two independent OAM channels without interference for enhancing more OAM channels. A finite element method (FEM) is employed to numerically study the properties of the designed fiber. A large effective refractive index difference between the adjacent OAM modes is achieved, which indicates that the propagated OAM modes can be well separated without multiple input, multiple output in each of the two rings. The calculated results demonstrate that a total of 80 OAM modes with a mode quality above 70% is achieved without any high-order radial modes from 1.5 to 1.6 mu m, which contains 18 inner-ring OAM modes and 62 outer-ring OAM modes. Moreover, the designed fiber possesses low confinement loss (< 2.2 x 10(-7) dB m(-1)) and can be potentially utilized for high-capacity communications by OAM-based MDM.