Reliable sensing and monitoring systems based on optical fibers operating at high temperatures and in harsh environments are of high demand. One of the limitations of such systems is the devitrification of the fused silica based core and cladding glass at elevated temperatures. Crystallites can nucleate on the surface of the cladding and grow into the core. The formation of these crystalline flaws in the optical fiber causes stress concentration and extrinsic optical scattering and in addition leads to decreased mechanical properties and reduced optical stability. Commercial optical fibers of different compositions and core-cladding design were characterized in this study with respect to crystallization rate under various conditions. The optical stability was monitored with an optical spectrum analyzer. The crystallites were characterized with SEM and optical microscopy. The activation energies of crystallization for High OH and Low OH multimode fibers were estimated by measuring the crystal growth rate at different temperatures. The residual stress resulting from the formation of the crystals, which can lead to decreased mechanical performance of the fibers, was characterized with polarized light optical microscopy. The influence of water vapor in the atmosphere on the crystallization rate was determined. The features induced in the attenuation spectra were consistent with hydroxyl (OH) absorption peak. Spectral features such as thermal emission and hydroxyl absorption bands are discussed.
The results obtained in this study can be used for selecting optical fibers for high temperature applications. / Master of Science / Reliable sensing and monitoring systems based on glass optical fibers operating at high temperatures and in harsh environments are in high demand. One of the limitations of such systems is the tendency of glass material to crystallize at elevated temperatures.
Crystallites can nucleate on the surface of the fiber and grow inwards, impairing the optical and mechanical properties of the optical fiber. The formation of these crystalline flaws in the optical fiber can decrease the mechanical strength by causing stress concentrations and leading to formation of cracks, and reduce optical stability by causing light to scatter from the crystals. Commercial optical fibers of different compositions and geometry were characterized in this study with respect to crystal growth rate under various conditions, such as different temperatures (400-1350 °C), and different atmospheres (laboratory air and water vapor). The effect of crystals was demonstrated with respect to optical and mechanical performance.
The results obtained in this study can be used for selecting optical fibers for high temperature applications.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/83487 |
| Date | 07 June 2018 |
| Creators | Yakusheva, Anastasia A. |
| Contributors | Materials Science and Engineering, Pickrell, Gary R., Wang, Anbo, Homa, Daniel S. |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Detected Language | English |
| Type | Thesis |
| Format | ETD, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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