Photonic crystal fiber supporting 394 orbital angular momentum modes with flat dispersion, low nonlinear coefficient, and high mode quality

A photonic crystal fiber (PCF) with an SSK2 dense crown glass ring is designed and analyzed. After optimization of the radius of the central air hole and thickness of the annular region, 394 orbital angular momentum (OAM) modes in the range of 1.48 to 1.62 μm can be transmitted stably. The effective refractive index, effective index difference, dispersion, effective mode area, nonlinear coefficient, numerical aperture (NA), mode quality, and confinement loss are analyzed numerically by the finite element method. The results show that the effective index difference of all the OAM modes is greater than 1 × 10^-4 and they can propagate stably in the PCF. Besides, the fiber shows flat dispersion with a minimum variation of 8.55 ps/(km•nm), very small nonlinear coefficient of less than 0.232 W^-1•km^-1, as well as high mode quality bigger than 94.57%. This high-performance PCF has immense application potential in optical fiber communication.