Attenuation/time relation for OH formation in optical fibres exposed to H2

The increase in attenuation due to POH and GeOH formation, when fibres are exposed to hydrogen, has been found to follow a log (time) relation. Results are given for fibres with different phosphorus content. A possible explanation for the log t behaviour is discussed and, using the relationship, a prediction of long-term attenuation rise is made. The rise thus predicted is very small for current low-phosphorus fibres.