Photonic Bandgap Fibers For Transverse Strain Sensing

bragg fiber;transverse;photonic bandgap;optical fiber;strain sensing

Van Vickle, Patrick Stephen ; Dr. Kara Peters, Committee Chair,Dr. Tasnim Hassan, Committee Member,Dr. Larry Silverberg, Committee Member,Dr. Jeffrey Eischen, Committee Member,Van Vickle, Patrick Stephen ; Dr. Kara Peters ; Committee Chair ; Dr. Tasnim Hassan ; Committee Member ; Dr. Larry Silverberg ; Committee Member ; Dr. Jeffrey Eischen ; Committee Member

University:North Carolina State University

关键词: bragg fiber;    transverse;    photonic bandgap;    optical fiber;    strain sensing;   

Others  :  https://repository.lib.ncsu.edu/bitstream/handle/1840.16/3065/etd.pdf?sequence=1&isAllowed=y

美国|英语

来源: null

【 摘 要 】

This research examines the change in bandgap characteristics of Photonic Bandgap (PBG)fibers under transverse loading for applications such as fabrication and service lifemonitoring of composite structures. Photonic Bandgap (PBG) fibers rely on Braggreflection conditions in the plane of optical fiber crosssectionand therefore offer greatpotential as transverse strain sensors which are insensitive to axial loading and temperaturevariations.A numerical study of the effect on the bandgap in PBG fibers under transverse loads is thusperformed in this dissertation. First the fundamental equations for lightwave propagation inclassical stepindexfibers, microstrucured holeyfibersand PBG fibers are reviewed. Thebehavior of each for sensing purposes is also discussed. The structural deformation andelectromagnetics modeling of a PBG fiber is then performed using the Finite ElementMethod (FEM) because this method offers the ability to examine arbitrary fiberconfigurations, specifically through deformation where the fiber is no longer circularlysymmetric.The FEM models were run for both uniaxial crush loads and uniform pressure loads for bothsilica and a doped PMMA material targeting strains up to approximately 6% at the boundaryof the fiber. The results showed that degradation of the bandgap occurs with loading and thataxis specific loading information may be obtained in fibers whose material normal and shearPockel’s constants differ by approximately 50% or more, although the exact differencerequired is not known. In the case of the PMMA uniform pressure load it was determinedthat the combination of loading and fiber characteristics may cause the bandgap to switchmodes which may interfere with actual sensor implementation and should be avoided. Thecross-sectionof the fiber studied was not rotationally symmetric which resulted in nonsymmetricoptical output from the uniform pressure case. While fibers of this constructionare likely to not be rotationally symmetric by design, the actual manufacture of the fibersresults in a cross section that more closely approximates this condition.