Frederic Lesage - Maison de la Modélisation, de la Simulation, et des Interactions (MSI), Université Côte d'Azur - Keywords: Electrical optical experimental study, Thermal gradients, Temperature gradient Sensors

Frederic Lesage - Maison de la Modélisation, de la Simulation, et des Interactions (MSI), Université Côte d'Azur - Keywords: Electrical optical experimental study, Thermal gradients, Temperature gradient Sensors

Contribution title: Measurement of temperature and thermal gradients using fiber optic Long Period Gratings (LPG)

We report on the use of fiber optic UV-written long period gratings (LPG) to measure thermal gradients attached along a thermally conductive material. Temperature changes along an LPG lead to changes in the LPG spectral response. While it is well known the uniform temperature leads to pure wavelength shifts of the LPG minimum, we have observed changes in the depth of the LPG minimum Im in the case of thermal gradients dT/dx. The used LPG of length L = 5 cm exhibited a sensitivity of d lc/dT=0.1286 nm/K for the center wavelength shift of the mean temperature Tm = (T1+T2)/2 over 35K. For a temperature difference of DT= T2-T1 = 40 K over a grating length L = Dx = 5 cm the gradient of dT/dx » 0.8 K/cm leads the rate of the depth change of the LPG at a rate of dIm/dT = 0.0295 dB/K. Center wavelength lc of the LPG can be measured with an accuracy of 0.05 nm which translates into a mean temperature accuracy measurement of 0.4 K. As losses and minimum power level measurements can be performed an accuracy of 0.01 dB, the temperature gradient with a minimum temperature difference of d(DT) » 0.34 K can be detected.

Thus LPG-based fiber optic sensors for the simultaneous measurement of temperature gradient dT/dx and mean temperature Tm can be developed by tracking the changes of the shifts of the spectral minimum dIm and the center wavelength d lc.