Design of a nested photonic crystal fiber supporting 76 + 36 OAM modes for fiber communication

This study introduces a distinctive entwined photonic crystal fiber (PCF) featuring two distinct and independent directed mode sections, collectively supporting a total of 112 orbital angular momentum (OAM) modes, comprising 76 + 36 modes. The confinement loss (CL) ranges approximately between \(2.49701\times 1{0}^{-11}\) and \(9.13425\times 1{0}^{-9} \text{dB}/\text{m},\) while highest attained OAM purity is \(99.31969\%\) and \(98.99258\%\) at \(H{E}_{2, 1}\) mode, respectively, for both inner and outer rings. All the modes demonstrate ERIDs exceeding \(1{0}^{-4}\), and minimum dispersion variation observed is \(-856 \text{ps}/\text{km}-\text{nm}\). Additionally, we achieved an outstanding isolation performance with the highest attained ISO reaching \(294 \text{dB}\) at \({\text{HE}}_{9, 1}\) mode and observed a substantial effective mode area of 9.15 μm² and 25.8μm², respectively, for inner and outer rings. This research leverages COMSOL Multiphysics' finite element method (FEM) and perfectly matched layer (PML) capabilities alongside MATLAB processing to calculate all key properties of the proposed fiber. Therefore, the suggested PCF demonstrates promising prospects for extended-range, high-capacity data transmission within optical communications and applications related to OAM sensing.