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

Abstract

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 °C. 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 °C) or ≡GeO—H and ≡Ge—H defects under 514-nm irradiation has only been observed in the F2 fibres.