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Design and Optimization of Microstructured Optical Fiber Sensors

Jewart, Charles (2011) Design and Optimization of Microstructured Optical Fiber Sensors. Doctoral Dissertation, University of Pittsburgh.

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    Abstract

    The integration of sensor networks into large civil and mechanical structures is becoming an important engineering practice to ensure the structural health of important infrastructure and power generation facilities. The temperature, pressure, and internal stress distribution within the structures are key parameters to monitor the structural health of a system. Optical fiber sensors are one of the most common sensing elements used in the structural health monitoring due to their compact size, low cost, electrical immunity, and multiplexing ability. In this dissertation, the design and optimization of air-hole microstructured optical fibers for use as application specific sensors is presented. Air hole matrices are used to design fiber cores with a large birefringence; while air hole arrays within the fiber cladding are studied and optimized to engineer unique geometries that can give desired sensitivity and directionality of the fiber sensors. A pure silica core microstructured photonic crystal fiber was designed for hydrostatic pressure sensing. The impact of the surrounding air-holes to the propagation mode profiles and indices were studied and improved. To improve directionality and sensitivity of fiber sensors, air holes in the fiber cladding were implemented and optimized in the design of the fiber. Finite element analysis simulations were performed to elicit the correlation between air-hole configuration and the fiber sensor's performance and impact of the fiber's opto-mechanic properties. To measure pressure and stress at high temperature, an ultrafast laser was used to inscribe type II gratings in two-hole microstructured optical fibers and suspended core fibers. The fiber Bragg grating resonance wavelength shift and peak splitting were studied as a function of external pressure, bending, and lateral compression. Fiber sensors in two-hole fibers show stable and reproducible operation above 800oC. Fiber grating sensor in suspended core fibers exhibits high directionality to transverse stress, and insensitivity to bending. All experimental results are in good agreement with the simulations. This works demonstrates that ingenious design and engineering of air hole matrices in optical fiber's cladding and core can lead to multi-functional and multiplexable fiber sensors that were previously unattainable using traditional solid-core solid cladding fiber.


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    Item Type: University of Pittsburgh ETD
    ETD Committee:
    ETD Committee TypeCommittee MemberEmail
    Committee ChairChen, Kevin P.pec9@pitt.edu
    Committee MemberAvdeev, Ilyaavdeev@uwm.edu
    Committee MemberFalk, Joelfalk@engr.pitt.edu
    Committee MemberYun, Minheeyunmh@engr.pitt.edu
    Title: Design and Optimization of Microstructured Optical Fiber Sensors
    Status: Unpublished
    Abstract: The integration of sensor networks into large civil and mechanical structures is becoming an important engineering practice to ensure the structural health of important infrastructure and power generation facilities. The temperature, pressure, and internal stress distribution within the structures are key parameters to monitor the structural health of a system. Optical fiber sensors are one of the most common sensing elements used in the structural health monitoring due to their compact size, low cost, electrical immunity, and multiplexing ability. In this dissertation, the design and optimization of air-hole microstructured optical fibers for use as application specific sensors is presented. Air hole matrices are used to design fiber cores with a large birefringence; while air hole arrays within the fiber cladding are studied and optimized to engineer unique geometries that can give desired sensitivity and directionality of the fiber sensors. A pure silica core microstructured photonic crystal fiber was designed for hydrostatic pressure sensing. The impact of the surrounding air-holes to the propagation mode profiles and indices were studied and improved. To improve directionality and sensitivity of fiber sensors, air holes in the fiber cladding were implemented and optimized in the design of the fiber. Finite element analysis simulations were performed to elicit the correlation between air-hole configuration and the fiber sensor's performance and impact of the fiber's opto-mechanic properties. To measure pressure and stress at high temperature, an ultrafast laser was used to inscribe type II gratings in two-hole microstructured optical fibers and suspended core fibers. The fiber Bragg grating resonance wavelength shift and peak splitting were studied as a function of external pressure, bending, and lateral compression. Fiber sensors in two-hole fibers show stable and reproducible operation above 800oC. Fiber grating sensor in suspended core fibers exhibits high directionality to transverse stress, and insensitivity to bending. All experimental results are in good agreement with the simulations. This works demonstrates that ingenious design and engineering of air hole matrices in optical fiber's cladding and core can lead to multi-functional and multiplexable fiber sensors that were previously unattainable using traditional solid-core solid cladding fiber.
    Date: 19 September 2011
    Date Type: Completion
    Defense Date: 10 June 2010
    Approval Date: 19 September 2011
    Submission Date: 15 July 2011
    Access Restriction: No restriction; The work is available for access worldwide immediately.
    Patent pending: No
    Institution: University of Pittsburgh
    Thesis Type: Doctoral Dissertation
    Refereed: Yes
    Degree: PhD - Doctor of Philosophy
    URN: etd-07152011-115510
    Uncontrolled Keywords: microstructure optical fibers; optical fiber design; optical fiber sensor
    Schools and Programs: Swanson School of Engineering > Electrical Engineering
    Date Deposited: 10 Nov 2011 14:51
    Last Modified: 20 Jan 2012 16:16
    Other ID: http://etd.library.pitt.edu/ETD/available/etd-07152011-115510/, etd-07152011-115510

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