Specialty Optical Fibers Handbook

aging experiments or under aggressive use conditions. Whether a carbon-coated

fiber is suitable for use in a hydrogen environment depends on the tolerable loss

changes, the operating temperature, the concentration of hydrogen around the

fiber, and the material properties of both the fiber and the carbon coating.

Determining whether a coating is adequately hermetic requires a quantitative

analysis. No carbon fiber coating made to date has been shown to be perfectly

hermetic. Increases in ambient hydrogen levels, pressure, temperature, and fiber

length all lead to increased demands on the fiber coating. Similarly, if the fiber’s

core glass material is highly reactive with hydrogen (e.g., some erbium-doped

fibers and Ge-P co-doped multimode fibers),