Aging behavior of low-strength fused silica fibers

The strength of the long lengths of fiber contained in optical cables is determined by the presence of the few large flaws that are produced infrequently by normal fiber production methods. To investigate the behavior of low strength fiber containing these critical flaws, we have produced a fiber containing many large flaws by passing an as-drawn, uncoated fiber over a wheel coated with abrasive. The effect of aging the low strength fiber at zero stress in either 85° C, deionized water or in high humidity (85° C, 94%RH) has been evaluated using dynamic fatigue in tension. After aging in either environment, the strength is found to increase and flaws are found to grow more slowly than flaws in unaged fibers. Both results show that aging actually improves the mechanical behavior of the large flaws that control the strength of fibers in cables.