Specialty Optical Fibers Handbook

24.4 COATINGS

24.4.1 General Comments and Polymer Coatings

Very early in the development of the light-guide technology, it was clear that

the pristine surface of the as-drawn fibers would have to be protected from

mechanical damage by applying a thin polymer coating to isolate the fiber

surface from any hard sharp particles in the environment. As their development

progressed, dual coatings were developed; the inner compliant coating reduced

the microbending losses, while the harder more abrasion resistant outer second-

ary coating made the assembly more robust. Contrary to much early literature,

polymer coatings were found to be quite permeable to water [53]. It was found

that penetration through typical coatings, which are approximately 60 mm thick ...