Influence of blanket postexposure on the thermal stability of the spectralcharacteristics of gratings written in a telecommunication fiber using light at 193 nm

Bragg gratings have been written in a nonhydrogenated Coming's SMF28 teleco mmunication fiber using ultraviolet (UV) pulses at a high power density fro m an ArF laser. Some of these gratings were uniformly exposed with light at 193 nm, The isothermal accelerated aging method was used to characterize t he thermal decays of both pristine and postexposed grating spectral charact eristics. UV postprocessing led to an increase in the stability of the Brag g grating reflectivity meanwhile the shifts in the Bragg wavelengths of the postexposed gratings proved to be higher than those of untreated gratings. It is shown that the isothermal decays of the refractive index modulation cannot be used to predict the annealing induced irreversible shifts in the Bragg wavelengths. Our observations are discussed within the frame of the c urrent theoretical descriptions of the links that may exist between the wri ting and the thermal stability of Bragg gratings.