COATING ADDITIVES FOR IMPROVED MECHANICAL RELIABILITY OF OPTICAL-FIBER

Fused silica glass is subject to delayed failure, i.e., failure occurr ing after a certain time under stress conditions far below the level r equired to have fast, catastrophic rupture. While the behavior at high applied stress may be described, at least empirically, by the subcrit ical crack growth model, it is well known that fused silica shows a tr ansition, or ''knee,'' to a more severe delayed failure behavior, or ' 'enhanced fatigue,'' at low applied stress and long time to failure. T his makes predictions of the expected lifetime unreliable. The additio n of nanosized particles of fumed silica to the polymer coating of fus ed silica optical fiber is shown to improve long-term mechanical prope rties of the fiber: it delays the onset of the fatigue transition and reduces the strength degradation due to zero stress aging. Atomic forc e microscopy analysis shows that the presence of the additive dramatic ally reduces the rate of development of surface roughness, thus indica ting that the effect of the additive is to suppress surface dissolutio n processes. The additive has little effect on the fatigue behavior be fore the transition. These results indicate that dissolution is the ca use of the transition but has less importance on the pre-transition re gion.