Raman spectroscopic study of Bragg gratings regeneration

Fibre Bragg grating regeneration involves, at its simplest, the annealing and resurrection of a seed FBG through thermal annealing. Micro-Raman spectroscopy provides evidence that inscribing the seed structure has changed the thermal history of the glass so that whilst the annealing is identical in all areas, the local glass relaxation is different in the UV irradiated regions. Notably, there is a significant decrease of the D1 and D2 defects bands within the core and the inner cladding of regenerated FBG revealing the complex nature of this two- or three materials system.