Whatever the type of fiber, singlemode or multimode, graded index or step index, it will have to operate in a given environment.
Consequently fiber coating will have to be carefully selected because it will dramatically influence the performances and life time in some environments.
Note that it is necessary to make a distinction between the coating, either primary or secondary, which is applied during the drawing process and any other protective structures such as tubes or cables which are generally designed and manufactured under the cable maker responsibility.
Commonly used materials are accrylate, ETFE, and time to time Nylon.
• Accrylate is the most common coating of singlemode and graded index fibers
• ETFE is currently used to protect silica /silica fibers. It is soft and easy to strip but it's temperature range is -65°C to +125°C.
Two versions of special harsh environments coating are proposed:
• Polyimide coating for high temperature resistant fibers
• Carbon + Polyimide for hermeticity against hydrogen penetration and aging. (Hermetic Fibers)