Thermal decay of laser induced refractive index changes in SMF-28 and Bi-doped silicate laser fibres

Optical fibre components that are based on laser induced refractive index changes may show changes in their performance during their lifetime, since the underlying physical processes responsible for the refractive index change are more or less stable over time. The stability of refractive index changes depends on the optical fibre and the irradiation conditions. We show that it is possible to denote fibre or material parameters responsible for the refractive index stability using high and low power UV laser irradiation, accelerated annealing tests, and a decomposition of the characteristic annealing function (master curve) into individual activation energy spectra (AES). The SMF-28 fibre exhibits four different AES, indicating different underlying physical mechanisms. Their contribution to the annealing depends on the laser intensity. The bismuth doped fibres exhibit 3 different AES. Their contribution to the total characteristic function depends also on laser intensity and in addition to active dopant concentration. Comparing GeO ₂ -SiO ₂ fibre with Bi-Al ₂ O ₃ -SiO ₂ fibres, activation energy spectra are attributed to glass species or dopants.