Possible model for the degradation due to hydrogen of multimode fibre

Reaction kinetics is applied to the case of hydrogen reacting with defect centres in an optical fibre. The equations are extended to the case of a general distribution of activation energies and to a time varying hydrogen concentration. Experimental results on loss increase at two difference hydrogen pressures are consistent with the reaction being first order with respect to hydrogen concentration. A new method of forecasting long-term degradation is derived from the kinetics equation. Experimental results from a test at 50¿¿C are reported, which enable forecasts to be extended to temperatures different from the laboratory ambient. Some recovery in the `permanent¿¿ loss increase has been measured and the impact of this reverse reaction is discussed.