Photonic Bandgap Fibers For Transverse Strain Sensing
No Thumbnail Available
Files
Date
2009-02-22
Authors
Journal Title
Series/Report No.
Journal ISSN
Volume Title
Publisher
Abstract
This research examines the change in bandgap characteristics of Photonic Bandgap (PBG)
fibers under transverse loading for applications such as fabrication and service life
monitoring of composite structures. Photonic Bandgap (PBG) fibers rely on Bragg
reflection conditions in the plane of optical fiber crosssection
and therefore offer great
potential as transverse strain sensors which are insensitive to axial loading and temperature
variations.
A numerical study of the effect on the bandgap in PBG fibers under transverse loads is thus
performed in this dissertation. First the fundamental equations for lightwave propagation in
classical stepindex
fibers, microstrucured holeyfibers
and PBG fibers are reviewed. The
behavior of each for sensing purposes is also discussed. The structural deformation and
electromagnetics modeling of a PBG fiber is then performed using the Finite Element
Method (FEM) because this method offers the ability to examine arbitrary fiber
configurations, specifically through deformation where the fiber is no longer circularly
symmetric.
The FEM models were run for both uniaxial crush loads and uniform pressure loads for both
silica and a doped PMMA material targeting strains up to approximately 6% at the boundary
of the fiber. The results showed that degradation of the bandgap occurs with loading and that
axis specific loading information may be obtained in fibers whose material normal and shear
Pockel’s constants differ by approximately 50% or more, although the exact difference
required is not known. In the case of the PMMA uniform pressure load it was determined
that the combination of loading and fiber characteristics may cause the bandgap to switch
modes which may interfere with actual sensor implementation and should be avoided. The
cross-section
of the fiber studied was not rotationally symmetric which resulted in nonsymmetric
optical output from the uniform pressure case. While fibers of this construction
are likely to not be rotationally symmetric by design, the actual manufacture of the fibers
results in a cross section that more closely approximates this condition.
Description
Keywords
bragg fiber, transverse, photonic bandgap, optical fiber, strain sensing
Citation
Degree
PhD
Discipline
Mechanical Engineering