| dc.description.abstract | The research described in this thesis involves the design, development, and implementation of an automated positioning system for fiber-optic interferometric sensors. The Fiber-Tip Interferometer (FTI) is an essential component in the proven Thermo-Acousto-Photonic NDE technique for characterizing a wide range of engineering materials including polymers, semiconductors and composites. The need to adapt the fiber-optic interferometric system to an industrial environment and to achieve precision control for optimizing interferometric contrast motivated the development of an automated, self-aligning FTI system design. The design enables high-resolution positioning and alignment by eliminating manual subjectivity and allows significantly improved repeatability and accuracy to be attained. Opto-electronic and electromechanical devices including a GRIN lens, 2x2 fused bi-conical taper couplers, photodiodes, motor-controlled tip/tilt stages, oscilloscopes, and a PCI card, constitute a closed-loop system with a feedback controller. The system is controlled by and communicates with a computer console using LabVIEW, a graphical language developed by National Instruments. Specifically, alignment is quantified by scanning the voltage readings at various orientations of the GRIN lens. The experimental setup specific to achieving maximum interferometric contrast intensity when interrogating silicon wafers with various surface depositions is discussed. Results corresponding to the interferometric contrast data obtained at several different standoff distances (Fizeau Cavity magnitudes) demonstrate the robustness of the novel design. | en |
