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Optical fiber sensors for ultrasonic detection have become a subject of much research in recent years. In this thesis an optical fiber ultrasonic sensor based on a π-phase-shifted fiber Bragg grating (πFBG) is experimentally investigated. Several methods of fabricating πFBGs are investigated for use in this work. The parameters used to characterize the fabricated sensors are discussed. An experimental demodulation setup is developed based on a laser-intensity demodulation scheme. The directivity of a πFBG sensor is experimentally determined to greatly depend upon the impinging angle of the ultrasonic wave. The sensitivity of a πFBG sensor to ultrasonic waves generated by a piezoelectric transducer at various frequencies is experimentally investigated. The response of a πFBG sensor to an ultrasonic acoustic emission simulated by a pencil lead break event is investigated. The noise sources of the system are theoretically analyzed. The parameters of the system affecting the signal-to-noise ratio are theoretically determined.
Advisor: Ming Han