Aging and strength improvement of silica optical fibers

Abstract

The reliability and the expected lifetime of optical fibers used in telecommunication technologies are closely related to the chemical environment action on the silica network. To ensure the long-term mechanical strength of the optical fibers, a polymer coating was applied onto the fiber surface during fiber fabrication. This external coating is vital to ensure a long fiber lifetime. Its protective action includes several functions, such as to protect glass fiber from any external damage, to limit chemical attack, in particular that of water, and finally to ensure fatigue protection and bending insensitivity. Since the mechanical strength of the fiber is controlled by its surface characteristics, we propose a new method for increasing fiber strength. Submitted to a mechanical stretching, fibers were plunged into hot water and aged for several days. Then, the fibers were removed from the water and various weights were suspended on the fiber ends. Just before the fiber rupture, the fibers were unloaded and subjected to dynamic tensile tests at different velocities. Result analysis proved that the aging in hot water increased the fiber strength. The Weibull's diagram study shows a bimodal dispersion of defects on the fiber surface and the important role of polymer coating.