Hydrogen-loaded fiber Bragg grating for high-temperature sensor applications

Abstract

Bragg gratings have widespread applications in the rapidly growing field of optical sensors. Although fiber Bragg gratings are often referring to permanent refractive index structures, exposure in increased temperature usually results the decay of the refractive index modulation. Basically, the stability of the grating competence at high temperature is an important criterion for high temperature sensor applications. This report is a part on going research to develop high temperature optical sensors. We report our design and analyze of a hydrogen loaded fiber Bragg grating temperature sensor range from room temperature to around 1000°C. A basic setup has been built in our lab to examine the performance of the point temperature sensor based on the hydrogen loaded fiber Bragg grating. Until now, a grating has been shown to stabilize at temperatures in excess of 700°C and to survive at temperatures in excess of 930°C. The tested operation gratings around 700°C retain up to 80% reflectivity after one and a half hours. The thermal treatment of the tested hydrogen loaded fiber Bragg gratings is demonstrated capable to enhance effectively the grating's thermal stability. Our experimental results provide a better understanding of thermal response to the hydrogen loaded fiber Bragg gratings and their decay behavior at elevated temperatures.