Observation of surface flaws in fused silica optical fibers

Surface flaws existing in optical fibers are directly observed using an optical microscope and SEM. Among scattering centers observed by launching a He-Ne laser beam into a fiber, those still remaining after careful cleaning of the fiber surface are found to be most probably the flaws. Several cracks and voidlike defects observed by SEM correspond to the scattering centers. Tensile tests have been accomplished for fiber specimens containing the centers. It is found that fractures occur just at the centers in high probability and that fracture strength for the specimens is one-third to two-thirds of the strength for a specimen without an observable scattering center.