The paper considers a quasi – periodic microheterogeneity structure formed under the effect of optical fiber melting, which can be used as a sensitive element for an optical sensor based on a Fabry – Perot interferometer or an optical radiation scatterer with improved flexibility and strength parameters. Mathematical modeling of the process of transmission and reflection of radiation on the microcavities of the intrafiber structure will make it possible to predict the characteristics of the developed sensors. The simulation was carried out in the COMSOL Multyphysics simulation package. A section of a single – mode SMF-28e fiber with microinhomogeneities located in the core, the dimensions of which were measured in the course of an empirical study, is considered. To solve the problem, a system of equations was compiled that describes the propagation of a plane electromagnetic wave in matter. The results obtained showed that the calculated reflection spectrum qualitatively coincides with the measured value, but does not describe it with high accuracy. This may be due to the fact that the model does not take into account intermode interference in the fiber, and does not have an introduced melt zone around microcavities, since such a melt zone has a complex refractive index distribution and composition

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This work focuses on the methods of creating in-fiber devices, such as sensors, filters, and scatterers, using the fiber fuse effect. The effect allows for the creation of structures in a fiber core. However, it is necessary to know exactly how this process works, when the plasma spark occurs, what size it reaches, and how it depends on external parameters such as power and wavelength of radiation. Thus, this present study aims to create the possibility of predicting the consequences of optical breakdown. This paper describes a mathematical model of the optical breakdown initiation in a fiber core based on the thermal conductivity equation. The breakdown generates a plasma spark, which subsequently moves along the fiber. The problem is solved in the axisymmetric formulation. The computational domain consists of four elements with different thermophysical properties at the boundaries of which conjugation conditions are fulfilled. The term describing the heat source in the model is determined by the wavelength of radiation and the refractive indices of the core and the shell and also includes the radiation absorption on the released electrons during the thermal ionization of the quartz glass. The temperature field distributions in the optical fiber are obtained. Based on the calculations, it is possible to estimate the occurrence times of various phase states inside the fiber, in particular, the plasma spark occurrence time.