Fiber Bragg grating regeneration at 450°C for improved high temperature sensing.

Type-I fiber Bragg gratings photo-inscribed in hydrogen-loaded B/Ge co-doped silica single-mode optical fibers have been regenerated efficiently at 450°C, which is the lowest temperature reported so far. The mechanical strength of the annealed fiber is preserved while ensuring temperature sensing of the regenerated gratings up to 900°C. Unlike low temperature cycles (≤600°C), an annealing process at higher temperatures revealed faster regeneration for strong gratings. Changes in grating strength were also measured before the regeneration cycle. These behaviors suggest the contribution of different mechanisms to the regeneration process with different relative dynamics.