Abstract

The strength and reliability of fibers in harsh environments depend for the most part on the nature of the protective coating and on its application technology. The coating should protect the silica glass surface from moisture and external influences and, in many cases, do it at high temperatures. Recent improvements of the freezing method have made it possible to fabricate fibers with In, Sn, Pb, Zn, and Al coatings, which have an ultrahigh strength and an acceptable level of excess losses.¹ The low melting temperatures of In, Sn, and Pb strongly limit the areas of application of fibers coated with these materials. The melting point of A1 is 660°C, but at temperatures higher than 400°C the strength significantly decreases with time because of the chemical reaction of Al with silica glass. Although there are soldering methods for all the metals used, these methods are often very peculiar and are much more complicated than those used for Cu wires.

© 1993 Optical Society of America