Regeneration experiments with fibre Bragg gratings in hydrogen out-diffused fibres

Abstract

The regeneration of fibre Bragg gratings (FBG) is supposed to be seeded by the relief of the in-frozen core cladding stress of the fibre. Earlier results lead to the assumption that the diffusion process of small atoms or molecules through the glass matrix is sufficient to seed regeneration of an FBG. To prove this theory, a regeneration experiment was performed with hydrogen loaded, pristine and out-diffused SMF28 fibers, respectively. For the FBG in an out-diffused fibre, the fibre was stored at room temperature after hydrogen loading to get rid of the total amount of hydrogen before FBG inscription. The FBG inscription experiments confirmed that the diffusion of hydrogen changes the fibre intrinsic stresses. From all three kinds of SMF28 fibers, one FBG was annealed with a stepwise temperature profile for regeneration. Only the FBG in hydrogen loaded fibre regenerated, what implies that the formation of hydroxyl groups is necessary for the regeneration process. The reduction of the in-frozen stress due to the hydrogen diffusion, in contrast, was not sufficient to seed regeneration.