STRUCTURAL STRENGTH OF OPTICAL SILICA FIBERS: THE EFFECT OF COATING AND MEDIUM

摘要

Structural strength of optical silica fibers has been studied by the method of three-point bending at the variation of types of coating, following aging and removal of coating. The assumption has been made that the influence of these factors on the strength dispersion is mainly controlled by interaction of water molecules with glass surface enhanced by structural stresses existing in real glass structure due to its inhomogeneity. It has been shown that the strength of fibers alter removal of coating depends on the conditions of testing. The strength decreases and its dispersion increases when bare fibers are tested in air. The strength can be partly or completely restored after repeated application of coating or upon testing bare fibers in waterless liquid (nonane). In our opinion, the degree of strength restoration depends on the value of structural stresses associated with microinhomogeneity of glass structure and the distribution of hydroxil groups on glass surface which are active centers of adsorption. The strength of fibers doped with the titania restores completely after repeated application of coating, i.e. in this case we have more favourable structure than in silica fibers.