2005-2006 Colloquium Series

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NAU Physical Sciences (Bldg 19, Rm 321), Monday, December 5, 2005, 4:00 PM
(Refreshments at 3:45pm)

Fabrication and Characterization of Specialized Fiber Bragg Grating Sensors

Gary Miller
Naval Research Laboratory
NAU Physics & Astronomy Alumnus

Abstract

Following a brief overview of fiber optics and fiber optic sensors, this presentation will explain the development and characterization of a novel technique to fabricate weak fiber Bragg gratings for highly specific multi-element sensor arrays. This method, termed the rescan technique, involves re-exposing a local region of a fiber grating to fringeless ultraviolet light to trim unwanted portions of the reflection spectrum. The spectral effects that result from a rescan can only be adequately described by inventing the concept of a three-dimensional index growth surface, where induced index is a function of both the writing intensity and the exposure time. Using this information, it is possible to predict the spectral response of a rescanned grating using a numerical model. For our model, we have modified coefficients within the coupled-mode formulism that imitate the same scattering properties as the actual grating. By taking high accuracy measurements of the refractive index change in germanosilicate fiber, we have created the necessary 3D map of photoinduced index to accurately model gratings and their post-exposure spectra. We will also demonstrate that optical fiber exhibits what we call exposure history; the final index change in a region depends on the previous exposures conditions.

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Local Host: Dave Cornelison, (928) 523-7641.