Abstract
A 3D finite element model constructed to predict the intensity-dependent refractive index profile induced by femtosecond laser radiation is presented. A fiber core irradiated by a pulsed laser is modeled as a cylinder subject to predefined boundary conditions using COMSOL5.2 Multiphysics commercial package. The numerically obtained refractive index change is used to numerically design and experimentally fabricate long-period fiber grating (LPFG) in pure silica core single-mode fiber employing identical laser conditions. To reduce the high computational requirements, the beam envelope method approach is utilized in the aforementioned numerical models. The number of periods, grating length, and grating period considered in this work are numerically quantified. The numerically obtained spectral growth of the modeled LPFG seems to be consistent with the transmission of the experimentally fabricated LPFG single mode fiber. The sensing capabilities of the modeled LPFG are tested by varying the refractive index of the surrounding medium. The numerically obtained spectrum corresponding to the varied refractive index shows good agreement with the experimental findings.
Highlights
Long-period fiber gratings (LPFGs) are fiber optic devices with various applications in optical communications and sensing systems [1]
Several techniques are available to produce LPFGs, such as those based on ultraviolet, CO2, and femtosecond laser radiation, with the latter being the most versatile method [1,3,4,5]
LPFGs are usually fabricated with grating periods on the order of 100 micrometers to a millimeter
Summary
Long-period fiber gratings (LPFGs) are fiber optic devices with various applications in optical communications and sensing systems [1]. FEMcompared models solely consider a cross-of the grating devices in particular characterized large sizes to the wavelength section the waveguide in themethods analysislack to avoid daunting computation requirements guided light.ofMoreover, the reported explicitthe coupling between the numerically induced [19,21,32,36,39,40,41,42]. The reported methods lack explicit model constructed in the COMSOL 5.2 Wave Optics Module is coupled with the proposed refractive coupling between the numerically induced refractive index profiles with the proposed numerical index model to fully describe the propagation of light through a long period grating single mode fiber models.
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