Reliability of optical fibers exposed to hydrogen: prediction of long-term loss increases

Abstract

Hydrogen-induced loss increases are known to occur in optical fibers, due both to the presence of molecular H₂ and to the reaction of hydrogen with defects in the fibers. To predict the long-term loss increases expected for fibers under normal conditions, it is necessary to rely on accelerated aging experiments in which fiber loss increases are measured at high temperatures and high P_H₂'S. For the predictions to be reliable, the dependences must be characterized on temperature, P_H₂, and time for each of the hydrogen-induced loss mechanisms. In some cases, simplifying assumptions can be made in arriving at conservative lifetime predictions. Hermetic coatings can be used as one means of minimizing the amount of hydrogen seen by a fiber. The performance of a hermetic coating can often be evaluated by using accelerated experiments performed at high P_H₂'s and moderate temperatures. The presence of reactive gettering sites can have a significant effect on the loss increases measured in high-temperature experiments with hermetic fibers. Experimental resuIts are presented for hermetic and nonhermetic fibers as examples of how long-term predictions can be made.