Specialty Optical Fibers Handbook

temperatures, with 140 atm of H

2

pressure. As is typical for carbon-coated fibers,

there is an initial ‘‘lag’’ period followed by a period where the losses increase

linearly with time. The explanation for this behavior is discussed in the following

section.

14.5.4 Diffusion of Hydrogen in Hermetic Fibers

The time and temperature dependencies for hydrogen diffusion through

carbon coatings can be accurately predicted using classic diffusion equations

once the coating properties have been determined. When a hermetic fiber is

exposed to a hydrogen-containing atmosphere, the hydrogen will initially diffuse

into the carbon and later into the silica part of ...