High temperature resistance temperature sensor based on the hydrogen loaded fiber Bragg grating

Fiber Bragg grating (FBG) temperature sensor and sensor arrays were applied widespread particularly in harsh environments. Although FBGs are often referring to permanent refractive index modulation in the fiber core, exposure to high temperature environments usually results the bleach of the refractive index modulation. The maximum temperature reported for the conventional FBG temperature sensor is around 600 degC due to its weak bonds of germanium and oxygen. In this paper we report design and development of a novel high temperature resistance FBG temperature sensor, based on the hydrogen loaded germanium doped FBG. The refractive index modulation in the FBG is induced by the molecular water. The results of our experiments have shown that the stability of the device at high temperatures is substantially increased. Due to the high bonds energy of hydroxyl and the low diffusivity of the molecular water, the thermal testing results of this temperature sensor show the thermal stability of hydrogen loaded FBG can be increased using annealing treatment; moreover, the highest erasing temperature for the device is above 1000 degC. Furthermore, the experimental results has provided a better understanding of the formation of the hydrogen loaded FBGs and the chemical transfers at elevated temperatures in the fiber core