Coating Additives for Improved Mechanical Reliability of Optical Fiber

Fused silica glass is subject to delayed failure, i.e., failure occurring after a certain time under stress conditions far below the level required to have fast, catastrophic rupture. While the behavior at high applied stress may be described, at least empirically, by the subcritical crack growth model, it is well known that fused silica shows a transition, or “knee,” to a more severe delayed failure behavior, or “enhanced fatigue,” at low applied stress and long time to failure. This makes predictions of the expected lifetime unreliable. The addition of nanosized particles of fumed silica to the polymer coating of fused silica optical fiber is shown to improve long-term mechanical properties of the fiber: it delays the onset of the fatigue transition and reduces the strength degradation due to zero stress aging. Atomic force microscopy analysis shows that the presence of the additive dramatically reduces the rate of development of surface roughness, thus indicating that the effect of the additive is to suppress surface dissolution processes. The additive has little effect on the fatigue behavior before the transition. These results indicate that dissolution is the cause of the transition but has less importance on the pre-transition region.