Simulation of laser-excited optical pulse propagation over graded-index multimode optical fiber with distorted asymmetrical structure

This work presents simulation results of laser-excited optical pulse propagation over piecewise regular fiber optic link with multimode optical fiber (MMF). Here really fabricated MMF of ISO/TIA OM2 Cat. was considered. According to end-face photo image and data of refractive index measurement reports, it has asymmetrical non-circular cross-section and asymmetrical highly-distorted graded-index refractive index profile with great dip in the core center. Here, we utilized earlier on proposed method for detailed reconstruction of researched optical fiber 3D-structure by limited data from the reports of refractive index profile measurement (produced by commercially available lab kits of optical fiber analyzers) over conditional transversal cross-sections “X” and “Y” to prepare input data. Mode analysis and computation of dispersion parameters were performed by earlier on extended developed modified Gaussian approximation (EMGA) and by rigorous finite element method (FEM by commercially available software COMSOL Multiphysics® 6.1). Profile distortions were taken into account in all cases, while following three samples were researched: distorted symmetrical MMF by EMGA, distorted symmetrical MMF by FEM and distorted asymmetrical MMF by FEM. Some differences were noticed in the results obtained for the symmetrical and asymmetrical structures. By using calculated mode dispersion parameters (mode delay and chromatic dispersion parameter) and recently developed model of piecewise regular fiber optic link, operating in a few-mode regime, we computed envelopes of laser-excited Gaussian optical pulse with initial duration 40 ps at the receiving end of 500 m fiber-optic link with described above MMF under operating wavelength λ=1310 nm. Overlapped computed pulse responses demonstrated strong influence of MMF asymmetry on nature and degree of laser-excited optical pulse distortions during its propagation over large-core MMF. This confirms the necessity of taking into account real-structure details of fabricated optical fibers during simulations of high bit rate fiber optic links with MMFs for short-range optical networks.