Dual temperature and strain sensor using a combined fiber Bragg grating and fluorescence intensity ratio technique in Er3+-doped fiber

Abstract

A prototype dual temperature–strain point sensor has been demonstrated by combining a short length of erbium-doped fiber in close proximity to a fiber Bragg grating. By measurement of the green fluorescence intensity ratio in erbium $({\mathrm{Er}}^{\text{3+}})$ and the Bragg wavelength shift of a fiber Bragg grating the temperature and strain are deduced. Calibrations reveal that the sensitivity of the fluorescence intensity ratio in ${\mathrm{Er}}^{\text{3+}}$ -doped fiber to strain is near zero. Three alternative analysis methods were used; the conventional matrix method, and two variations of a technique that provides a better fit to the fluorescence intensity ratio temperature data using a quadratic. The quadratic methods considered two cases of the strain dependence of the fluorescence intensity ratio, namely, zero and linear. The matrix method showed standard deviations of 2.2 °C and 20.6 με, while the quadratic fit with a linear strain dependence yielded 1.0 °C and 22.9 με over temperature and strain ranges of 18–150 °C and 350–2534 με, respectively.