Effects of Hydrogen Scavenging Cable Gel on the Strength and Attenuation of Optical Fibers

Optical fibers are widely used in gel-filled and Fiber-In-Metal Tube (FIMT) cables. Cable gels are believed to protect optical fibers from interactions with moisture and oxygen, while their hydrogen scavenging components reduce the hydrogen ingression in the fiber. However, if used at elevated temperatures, the gel environment may lead to the fiber coating swelling, partial dissolution, and other types of degradation. Furthermore, at high temperatures cable gels may themselves become sources of hydrogen generation. For studying potential favorable and adverse effects of cable gels, a series of optical fibers was aged in a hydrogen scavenging gel (HSG) at a pressure of 500 psi and temperatures of 50 – 300 °C. The fibers under investigation used various coatings, including dual and single acrylate, silicone/acrylate, carbon/acrylate, silsesquioxane-type hybrid, polyimide, carbon/polyimide, acrylate/PFA and polyimide/PFA. Residual coating diameter and mechanical strength of the fibers were used as an indicator of the gel influence. Effects of HSG on hydrogen ingression were evaluated from the attenuation spectra of the immersed fibers. In separate experiments, the cable gel and the fiber coatings were investigated as potential sources of hydrogen.