Enhanced diffusion of molecular hydrogen in germanosilicate fibres loaded with hydrogen at high pressures

Absorption spectra and spontaneous Raman spectra of optical fibres with a germanosilicate core loaded with molecular hydrogen at a pressure of 150—170 MPa are studied; the variation of these spectra during the outdiffusion of hydrogen from the fibres is also investigated. The purely rotational transitions of molecular hydrogen in Raman spectra of optical fibres are recorded for the first time. The changes in the spectral parameters of fibre Bragg gratings loaded with hydrogen are analysed. It is observed for the first time that under such high loading pressures, the decrease in the hydrogen concentration in the fibre core after completion of hydrogen loading occurs in two clearly manifested stages, the initial stage being characterised by a more rapid outlet of hydrogen as compared to the dynamics of hydrogen outdiffusing at pressures of 10—15 MPa. Barodiffusion of molecular hydrogen in optical fibres is considered as the main mechanism explaining this effect. An increase in the solubility of molecular hydrogen in germanosilicate fibres exposed to UV radiation is observed for the first time.