Modeling the trajectories of oblique rays in optical fiber with stepped refractive index profile

Within the framework of the geometric optics model, an algorithm for calculating the trajectories of oblique rays (hybrid modes) in optical fiber with stepped refractive index profile was developed. The first (three-dimensional) version of the algorithm is reduced to the sequential calculation of the coordinates of the beam reflection points in vector form, the second (two-dimensional) version – to the independent calculation of the transverse coordinate of the reflection points with subsequent calculation of the longitudinal (axial) coordinate. The calculation results for the two variants of the algorithm are the same. With the use of the developed algorithm, the trajectories of oblique rays in the optical fiber with the core diameter of 400 μm were simulated under various excitation conditions. The projections of ray trajectories onto the output end of the fiber were calculated. The characteristic topological form of projections is the envelope ring, where the inner boundary defines the caustic. ''Resonant'' types of projections of ray trajectories were identified. The developed calculation algorithm was tested in the experiments on the excitation of oblique rays (λ = 532 nm) in quartz-polymer optical fiber with the core diameter of 400 and 600 μm.