Hermetically Coated Optical Fibers: Hydrogen Permeation and Fatigue Properties.

Hydrogen permeation rates have been measured for fibers coated with a CVD applied amorphous carbon hermetic barrier. The H sub 2 permeation was characterized by measuring optical loss increases at elevated temperatures at both high and low hydrogen pressures. Very low predicted values for the rates of hydrogen permeation over a wide range of operating temperatures were found, with an experimentally determined activation energy of 23.7 kcal/mole. In-situ measurements of loss increases upon exposure to hydrogen have shown the existence of a lag time where no hydrogen reaches the core of the fiber.