Miniature Fiber-Optic Farby-Perot Interferometer: Fabrication, Data Processing and Temperature Sensing Application
Su, Zhihua 1983-
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Temperature sensors are extremely important in academic research and industrial application. Among various temperature sensors, optical sensors are attractive due to many advantages. This dissertation focuses on the development of a robust optical temperature sensor with promising performance and a large measurement range. Accuracy is the top concern for sensor applications. Previous study on FPI sensors shows noticeable hysteresis on temperature measurement. It can be attributed to ceramic glue in our experiment. An additional annealing is proposed for the sensor fabrication process, which can greatly reduce the hysteresis. The sensor performance before and after optimization is presented while significant improvement on hysteresis is obtained. A generic novel data processing method is developed to accurately calculate the absolute optical path difference (OPD) of the FPI sensor cavity from broadband fringes. The method combines Fast Fourier Transformation (FFT) with non-linear curve fitting of the entire spectrum. The new method successfully resolves the ambiguous problem for the direct fitting method and can provide higher resolution compared to the FFT method. Simulation on visibility shows that to achieve high visibility, careful control of the effective reflection coefficient is important. Fabry-Perot cavities with different effective reflection coefficient are synthesized, while the relationship between spectrum visibility and cavity length is plotted and compared with simulation results. A similar trend of visibility is observed, which indicates that visibility is related to the effective reflection coefficient and can be controlled by the fabrication process. Extraction of additional phase is a challenge in this area, especially when cavity length is relatively small. In this dissertation a new method, which is based on the difference of cavity length obtained from FFT method and curve fitting method, is proposed. In principle it can provide additional phase information even when the cavity length is small.