Abstract
This work reports a novel method to create a 3D map of the refractive index of different graded-index polymer optical fibers (GI-POF), measuring the Raman spectra at different points of their transverse sections. Raman fingerprints provide accurate molecular information of the sample with high spatial resolution. The refractive index of GI-POFs is modified by adding a dopant in the preform; therefore, by recording the intensities of the Raman peaks related to the dopant material, a 3D map of the refractive index is rendered. In order to demonstrate the usefulness of the method, three different GI-POFs were characterized and the obtained results were compared with the information provided by the manufacturers. The results show accurate 3D maps of the refractive index taken in the actual GI-POF end faces, showing different imperfections that manufacturers do not take into account, such as the slight deviations of the azimuthal symmetry. The simplicity and the feasibility of the technique mean this method has high potential for fiber characterization purposes.
Highlights
In the last few decades, there have been continual advances in the performance of polymer optical fibers (POFs)
We present a novel method to characterize the refractive-index distribution directly from graded-index polymer optical fibers (GI-POF) based on Raman spectroscopy
The first analyzed GI-POF was manufactured by FiberFinn
Summary
In the last few decades, there have been continual advances in the performance of polymer optical fibers (POFs). The disadvantages of destructive methods are obvious, while non-destructive methods (such as light focusing method, optical interference method, or methods based on the measurements of the bending of transverse rays) usually require the construction of highly accurate set-ups and the geometry of the samples must be perfectly circular or elliptical [16] Raman spectroscopy is a spectroscopic technique used to obtain information from molecular vibrations, in which the measured spectra provide an insight into both intramolecular information and intermolecular interactions, playing an important role in the elucidation of molecular structures [17,18] In recent years, this spectroscopy technique has been widely used for different purposes [19,20,21], including for polymer characterization in POFs [22,23,24,25,26].
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