Abstract

The mechanical properties of coatings for silica lightguide fibers useful at elevated temperatures has been recently reviewed.¹ Of the metal coatings, which must be used above ~350°C, only aluminum has been studied to any extent.^2,3 It has been shown, however, that substantial strength degradation occurs in aluminum-coated fibers at temperatures greater than 400°C as a result of the SiO₂ + Al reaction.^2,3 Wysocki et al.⁴ suggested that this reaction might be avoided by the use of multiple metal coatings. The primary coating would be a metal that is substantially inert with respect to silica, and the other desired physical or chemical properties would be provided by the secondary coating. Although no detailed description of such a dual-metal-coated fiber is available, we recently described a somewhat similar carbon + metal (Al) dual hermetic coating (DHC).⁵ It was supposed that the primary carbon coating would reduce the SiO₂ + Al reaction and that the aluminum secondary coating would reduce the C + O₂ reaction. The high-temperature stability of these fibers is, therefore, the subject of the present study.

© 1993 Optical Society of America