New method for strength improvement of silica optical fibers

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 optical 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, especially during handling and in-service installation. Since the mechanical strength of the fiber is controlled by its surface characteristics, we propose a new method for increasing fiber strength.The silica optical fibers used were 125 μm in diameter, with a 62.5 μm thick epoxy-acrylate coating. Fibers were rolled up around two similar cylinders. Using a screw, these cylinders moved away from one another and thus subjected the fibers to stretching. Submitted to this mechanical loading, the distended fibers were plunged into hot water at 65 or 85 °C and aged for several days. Then, the fibers were removed from the water and various weights were suspended on the fiber ends. Thus, the fibers were subjected to a tensile loading in static fatigue for several days. Just before 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.