| Summary: | 碩士 === 國立成功大學 === 機械工程學系 === 87 === Developing an optical fiber refractometer to measure the refractive index change in the resolution of 0.9×10-5 or higher at the frequency response from DC to 100 Hz is presented. It is known that optical fiber sensors in a phase modulation are very sensitive to the disturbance, especially in thermal drifts or vibrations. Thereby, an optical fiber sensing system for a long-term monitoring is quite difficult in a phase modulation. This stabilization proposed in this paper is done by a cancellation technique. Two-parallel Fabry-Perot cavities as sensors corresponding to two path-matching cavities as read-out systems are to form path-matching differential interferometries (PMDI). One Fabry-Perot cavity is used for a sensing head, and the other for a reference signal. To compensate the variation effects on a PZT stack driven by a function generator in a single-channel phase tracker, a cancellation technique is utilized to stable the sensing system by subtraction. As a result, the experimental data show that the stabilization in a sensing system can be kept in 1×10-4 refractive index change without any serious variations in a four-hour monitoring. Accordingly, this system can be implemented potentially in the medical detection system for a long-term monitoring.
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