| Summary: | 碩士 === 國立高雄師範大學 === 物理學系 === 92 === Because of their simple structure, high sensitivity, fast response and large detection dynamic range, fiber Bragg gratings have been broadly applied in structural and undersea vibration detection. The working principle is that the vibration of the sensor causes strain, which then results in the changes of the index of refraction and propagation distance, in the embedded fiber Bragg grating. Utilization of interference configuration with proper demodulation technique can detect the variation of phase and frequency. This work utilized Mach-Zehnder interferometer configuration and combined two such interferometers to form a dual interferometer vibration sensing system. We used PZT to simulate the vibrating environment and applied phase generated carrier (PGC) method to demodulate the signal. It is shown that this system based on the dual Mach-Zehnder interferometer configuration can effectively detect the vibration frequency with error less than 0.1％. Besides, there is an 11.9 dB increase in the S/N ratio of the system at 170 Hz, when compared with the single Mach-Zehnder configuration, and the dynamic range of detection in this system can be as high as 67 dB.
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