Optical spectra of silica core optical fibers exposed to hydrogen.

The reaction of H sub 2 with undoped silica core fibers was evaluated by means of "in situ" spectral loss measurements. Drawing induced loss peaks at 0.63microns decreased rapidly upon exposure to hydrogen. Simultaneous loss increases at 1.39 and 1.53micron suggest that H sub 2 reacts at nonbridging oxygens and oxygen vacancies created during the drawing process, forming SiOH and SiH. The 1.53micron SiH peak slowly decayed after its initially rapid growth, indicating that SiH is not thermodynamically stable in silica. The concentration of drawing induced defects is estimated to be on the order of 100 ppb, based on the time required for H sub 2 to diffuse to the fiber core. The appearances of peaks at 1.45microns suggests that HF is formed by reaction of H sub 2 in the fluorine doped cladding of the fibers.