Title page for ETD etd-05202015-113311


Type of Document Master's Thesis
Author Bonnell, Elizabeth Ann
Author's Email Address ebonnell@vt.edu
URN etd-05202015-113311
Title Temperature Dependent Behavior of Optical Loss from Hydrogen Species in Optical Fibers at High Temperature
Degree Master of Science
Department Materials Science and Engineering
Advisory Committee
Advisor Name Title
Gary Pickrell Committee Chair
Christopher Winkler Committee Member
Daniel Homa Committee Member
Keywords
  • Infrared Spectroscopy
  • Diffusion
  • Glass Structure
  • OH Species
  • Temperature Dependence
  • Fiber Optics
  • Hydrogen
Date of Defense 2015-04-07
Availability unrestricted
Abstract
This study reports on the behavior of silica based optical fibers in a hydrogen environment at high temperatures. The hydrogen response in the form of optical loss in the wavelength range of 1000-2500 nm of a germanium doped graded index 50/125 graded index fiber was examined in the temperature range of 20–800 °C. When the fiber was exposed to hydrogen at 800 °C two absorption bands appeared: ~1390 nm assigned to the first overtone of the hydroxyl stretch and ~2200 nm band with complex assignments including the combination mode of the fundamental hydroxyl stretch with SiO4 tetrahedral vibrations and the combination mode of SiOH bend and stretch. The growth rate of the 1390 nm band fits the solution to the diffusion equation in cylindrical coordinates while the 2200 nm band does not. Absorption for both bands persisted as the fiber is cooled to room temperature. Temperature dependent behavior was observed in that as temperature increases from room temperature, the absorption intensity decreases and band shifts slightly to longer wavelengths. Temperature dependence is repeatable and reversible. However, if no hydrogen is present in the environment at temperatures greater than 700 °C, the 1390 nm band will permanently decrease in intensity, while the 2200 nm band does not change. Changes in the structure of the glass appear to be causing this temperature dependent behavior. Other necessary conditions for structural changes to cause this temperature dependent behavior are examined.
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