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ALT'23 The 30th International Conference on Advanced Laser Technologies
LD-P-2
Simulation of oblique ray trajectories in an optical fiber with a step-index profile
A.A. Makovetskii, S.M. Popov, D.V. Ryakhovskii, A.A. Zamyatin
Kotelnikov Institute ofRadioengineering and Electronics (Fryazino Branch), Russian Academy of Sciences, Vvedensky
Sq. 1, 141190 Fryazino, Moscow region, Russia
maz226@ms.ire. rssi.ru
Within the framework of the geometric optics model, an algorithm for calculating the trajectories of oblique rays (hybrid modes) [1-3] in an optical fiber with a stepped refractive index profile has been developed. The first (three-dimensional) version of the algorithm is reduced to the sequential calculation of the coordinates of the ray reflection points in vector form. The second (two-dimensional) version of the algorithm is reduced to an independent calculation of the transverse coordinates of the reflection points, followed by the calculation of the longitudinal (axial) coordinates. The calculation results for the two variants of the algorithm are the same. Using the developed algorithm, the trajectories of oblique rays in an optical fiber with a core diameter of 400 ^m were simulated under various excitation conditions. The projections of the ray trajectories onto the output end of the fiber are calculated. A characteristic topological form of projections is an envelope ring, the inner boundary of which determines the caustic. "Resonant" types of projections of ray trajectories are revealed. An experimental verification of the developed calculation algorithm was carried out in experiments on the excitation of oblique rays (X = 532 nm) in silica-polymer optical fibers with a core diameter of 400 and 600 ^m.
Figure 1. and experiment (left) and Simulation (right) of distribution of intensity.
Figure 1 shows photographs of the radiation intensity distributions of the hybrid modes obtained under some conditions of input of radiation, as well as their calculated analog (projections of trajectories). It can be seen that the experimentally recorded intensity distributions and their calculated analogues are topologically similar to each other.
Note that in works on the excitation of multimode OFs, close in subject matter to this work, the analysis of the features of the caustics of oblique rays was not carried out.
The work was carried out within the framework of the state task of the Kotelnikov IRE RAS.
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