Circular photonic crystal fiber supporting orbital angular momentum modes transmission

A new type of circular photonic crystal fiber supporting orbital angular momentum was proposed. The designed circular photonic crystal fiber is composed of well-ordered rectangular air hole rings in the cladding, a large air-core in the center and the annular high-index region for orbital angular momentum modes transmission. Utilizing the COMSOL Multiphysics software based on the finite element method, propagation properties of orbital angular momentum modes in fibers were discussed in detail. The results show that the designed circular photonic crystal fiber realizes effective segregation and stable transmission of 50 orbital angular momentum modes over the bandwidth from 1.2 m to 2.0 m. Large effective index differences(10-4) guarantee the stable transmission of every mode, confinement losses are lower than 10-9 dBm-1, and nonlinear coefficients are as low as 0.833 km-1W-1. The proposed rectangular holes circular photonic crystal fiber applied in mode-division multiplexing fiber communication systems might greatly improve channel capacity and spectral efficiency.