Photoinduced and thermal reactions involving hydrogen in high-germania-core optical fibres

We report a Raman scattering study of photoinduced and thermal reactions between H2 and germanosilicate optical fibres with 22 mol % and 97 mol % GeO2 in the core (F1 and F2, respectively) after H2 loading at 150 MPa (1500 atm). The mechanisms of photoreactions are investigated in a wide range of incident laser wavelengths (244, 333, 354, 361 and 514 nm). Thermal reactions are studied at 500 0C. The results indicate that the main mechanism behind the formation of hydrogen-containing defects with Raman bands at 700, 750, 2190, 3600 and 3680 cm-1 involves ≡Ge-O-Ge≡ or ≡Ge-O-Si≡ bond breaking and formation of hydride and hydroxyl species: =GeH2 (700, 750 cm-1), ≡Ge-H (2190 cm-1), ≡GeO-H (3600 cm-1) and ≡SiO-H (3680 cm-1). The key features of the reactions in the F1 and F2 fibres are analysed. In particular, photoinduced reactions give ≡Si-OH groups only in the F1 fibres, whereas the formation of germanium nanoclusters at a relatively low temperature (∼500 0C) or ≡GeO-H and ≡Ge-H defects under 514-nm irradiation has only been observed in the F2 fibres. (optical fibres)