Numerical Study of Photonic Crystal Fiber Supporting 180 Orbital Angular Momentum Modes With High Mode Quality and Flat Dispersion

We propose a photonic crystal fiber with a high refractive index ring, which supports up to 180 orbital angular momentum (OAM) modes without any high order radial modes from 1.5 um to 1.7 um. The finite element method is employed to numerically study the properties of the designed fiber. Further research shows that the refractive index differences of all the eigenmodes are above 2 ×10
^{- 3}
, which indicates that the corresponding eigenmodes can be well-separated and ensures the stable transmission of OAM modes. In addition, it is quite interesting that the high order radial modes are significantly suppressed via increasing the radius of the cladding in the design, while most of the OAM modes are without phase distortion, which is beneficial for the (de)multiplexing of the OAM modes. Particularly, the mode quality of all the eigenmodes is higher than 94.9% and the chromatic dispersion is flat with minimum value of the dispersion variation is 0.36 ps/(km·nm). Moreover, the designed fiber possesses various advantages such as low nonlinear coefficient (<; 0.7 /W/km) and confinement loss (on the order between 10
^-12
and 10
^{- 7}
dB/m). The proposed fiber has shown great potential for high capacity OAM mode division multiplexing communications.