Abstract
In the last years, mid-infrared radiation emitted by CO2 lasers has become increasing popular as a tool in the development of long-period fiber gratings. However, although the development and characterization of the resulting sensing devices have progressed quickly, further research is still necessary to consolidate functional models, especially regarding the interaction between laser radiation and the fiber's material. In this paper, a 3D finite element model is presented to simulate the interaction between laser radiation and an optical fiber and to determine the resulting refractive index change. Dependence with temperature of the main parameters of the optical fiber materials (with special focus on the absorption of incident laser radiation) is considered, as well as convection and radiation losses. Thermal and residual stress analyses are made for a standard single mode fiber, and experimental results are presented.
Highlights
Long-period fiber grating, or LPFG, play an important role in the development of fiber-based sensors in several areas of engineering
In order to introduce some of the complexity of stress-related issues regarding the processing of the optical fibers, the residual axial elastic stresses were implemented considering Equations (9) and (10) and the total resulting stress was obtained adding the thermally-induced residual stresses obtained with the program
The latter was obtained using the refractive index changes obtained by the finite element method (FEM) model and using a simulation tool developed by Baptista [34] based on the three layer model developed by Erdogran [35,36]
Summary
Long-period fiber grating, or LPFG, play an important role in the development of fiber-based sensors in several areas of engineering. Based on several experimental analysis, most of the existing work has considered that the main mechanism responsible for inducing a refractive-index change is the relaxation of internal stresses by the exposure to the laser radiation [16,17,18,19,20,21]. Taking this in consideration, several analytical models were developed, based mainly on solutions of the general heat conduction equation [22,23]. Multiphysics program, is described, considering temperature dependence of the main parameters, in particular the absorption of laser radiation by the fiber’s material
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