Abstracts Category : Other

Post-exposed fiber Bragg gratings

by Gary A Miller

This thesis explains the development andcharacterization of a novel technique to fabricate weak fiber Bragggratings for highly specific multi-element sensor arrays. Thismethod. termed the "rescan technique." involves re-exposing a localregion of a grating to fringeless ultraviolet light to "trim"unwanted portions of the reflection spectrum. The spectral effectsthat result from a rescan can only be adequately described byinventing the concept of a three-dimensional index growth surface.where induced index is a function of both the writing intensity andthe exposure time. Using this information. it is possible 10predict the spectral response of a rescanned grating using anumerical model. For our model. we have modified thepiecewise-uniform approach to include coefficients within thecoupled-mode formulism that imitate the same scattering propertiesas the actual grating. By taking high accuracy measurements of therefractive index change in germanosilicate fiber. we have createdthe necessary 3D map of photoinduced index to accurately modelgratings and their post-exposure spectra. We will also demonstratethat optical fiber exhibits what we call "exposure history"; thefinal index change in a region depends on the previous exposuresconditions.