Temperature sensors based on D-shaped Fiber Bragg Grating coated with different thin films

We present new temperature sensing devices based on side-polished Fiber Bragg Gratings (FBGs) coated with TiO₂, Fe and Pd thin films. The temperature sensing mechanism was based on the wavelength shift of the returned Bragg signal, as measured by an optical spectrum analyzer (OSA). The Bragg grating wavelength shift of the reflected optical signal is a function of the environmental temperature, which is related to the difference in the coefficient of thermal expansion (CTE) between thin films and SMF-28 fiber. The D-shaped FBG temperature sensors are measured in the range of 27-118.5°C. The experimental results show that the temperature sensitivity of the D-shaped FBG can be improved when it is coated with a material that has a high CTE. For the proposed temperature sensors using thin films coated on the D-shaped FBG fiber, the sensitivity of 12.2 pm/^oC for the D-shaped FBG sensor with Pd coating is higher than that without coating.