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In this paper, we develop a novel optical fiber temperature sensor based on Fabry-Perot interferometer (FPI). The structure of the sensor includes a spliced seven-core fiber (SCF) and a piece of quartz glass capillary. During fabrication, we use the fusion splicer to move two SCFs into glass capillaries gradually. The length of the SCF is about 4 cm. In the cavity structure, the end faces of two SCFs are parallel to each other. The light transmitted in the optical fibers will be reflected twice at the two end faces. We can use the relationship between the length of the cavity and the power change of the reflected light to realize the sensing measurement of temperature parameters. We have gradually tested seven groups of reflective spectra as the temperature increases from 20°C to 50°C. The free spectral range (FSR) of the sensor has changed, also the beam propagation in the air cavity will cause loss, and the power of the reflection spectrum will change with the cavity length. The values of FSR and extinction ratio (ER) vary nonlinearly with temperature, and through data analysis, the equation describing the sensor was obtained, like the sensitivity function of FSR is y=107.7exp(-x/12.36)+5.35, the sensitivity function of ER is y=39.6exp(- x/15.75)+3.02, and the correlation coefficients of the two non-linear fitting are 0.991 and 0.998, respectively.
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