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High-resolution fiber optic temperature sensors using nonlinear spectral curve fitting technique
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View: Figures


Image of FIG. 1.
FIG. 1.

Schematic of a fiber optic temperature sensor.

Image of FIG. 2.
FIG. 2.

(a) Spectrum of the SLD at a low current (bottom) and interference fringes from the two sensors at room temperature. Spectra are shifted vertically for clarity. Insets are the corresponding interference fringes normalized by the spectrum of SLD. (b) Cavity length as a function of temperature during heating and cooling. The solid line is a polynomial fit.

Image of FIG. 3.
FIG. 3.

Nonlinear curve fitting using Eq. (1) . Data are in black and fittings are in red. (a)–(c) Fits with three different cavity lengths L. (b) gives the best fit of 161475.18 nm, (a) and (c) give shorter (160813.80 nm) and longer (162136.62 nm) L by ∼660 nm, respectively. (d) and (e) are close-up views of curves at shorter and longer wavelength sides of (a) and (c), respectively.

Image of FIG. 4.
FIG. 4.

Evolution of cavity length calculated using three different methods: (1) direct nonlinear fit using λ as a variable, (2) FFT, and (3) nonlinear fit using 1/λ as a variable. (a) Cavity lengths at room temperature calculated using methods 1 (square) and 2 (dot). Note that data for FFT and nonlinear fit were taken at different times so that their cavity lengths do not overlap. (b) Room temperature cavity lengths calculated using method 3 (triangle). The FFT result is the same as in (a), but the vertical scale is 40 times smaller. Same data for FFT and fit. (c) Evolution of cavity length during heating and cooling monitored using methods 2 and 3. (d) Close-up view of cavity length evolution near 300 min.

Image of FIG. 5.
FIG. 5.

Flow chart used to calculate the absolute cavity length using revised nonlinear curve fitting and LabVIEW internal functions.


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: High-resolution fiber optic temperature sensors using nonlinear spectral curve fitting technique