Hydrogen-induced O–H peak growth in Ge-doped optical fibers: Verification of empirical and theoretical models

Migration of hydrogen in optical fibers and its chemical reactions with the glass fiber core create added optical loss, that may deteriorate the light transmission through the fiber. Although this subject has been extensively studied and a few theoretical and empirical models linking the attenuation to hydrogen pressure, temperature and time were proposed, none of the models was verified in a broad range of experimental conditions. In this work we investigate a single mode germanium doped fiber that was exposed to 25–––100 psi H₂ pressures at temperatures in the range 150 – 250 °C and the exposure times up to 28 days. Different aging protocols were applied to the fiber, and the focus was given to O–H peak development. An empirical approach and a theoretical model, that assumes Gaussian distribution of the activation energies were applied to fit the experimental results. From the theoretical model, it was found that the concentration of precursor available for reaction with hydrogen is orders of magnitude higher than that of non-bridging oxygen hole centers, and that at the applied temperatures the reacted sites belong to the lower-energy wing of the Gaussian distribution. It was also found that parameters of the theoretical model cannot be accurately determined via fitting even a large array of experimental data. In contrast, parameters of the empirical model are easily obtainable from the experiment which makes this approach more practical in hydrogen-related lifetime predictions.