Temperature dependence of type I-IA dual-fibre Bragg gratings

Fibre Bragg gratings (FBGs) of a new IA type have been reported to show thermal behaviour that is different from that of conventional type I gratings. Given a sufficiently large temperature coefficient difference between the two grating types, a dual-grating sensor formed by both types of gratings could allow simultaneous temperature and strain measurement. Such dual-grating sensors were prepared for the 830 nm wavelength region and tested at temperatures of up to 300°C. As far as the variation of the different temperature coefficients is concerned, the temperature coefficient of type IA FBGs and the temperature coefficient of type I FBGs have been found to converge as the temperature increases. The difference in temperature coefficients drops to 1% after annealing at 300°C.