Evolution of strength silica optical fibers under various moisture conditions

The reliability and the expected lifetime of optical links are closely related to the chemical action of the water molecules on silica network. However, polymeric coating also contributes largely to the mechanical properties of the fiber. Dynamic fatigue measurements were performed on silica optical fibers, either bare or coated, using two-point bending bench. Water concentration in test atmosphere was 50% relative humidity or very dry atmosphere. When water content is a few ppm, the dynamic fatigue curve, which expresses the breaking strength as a function of stress rate deviates from linearity at high stress rate. The same behaviour is observed in ambient atmosphere for very high testing speeds. The comparison between bare and coated fibers shows that the fatigue behaviour at high stressing rate is influenced by the polymer coating.