Abstract

The lifetime of an optical fiber becomes longer with metal coating on it thereby avoiding moisture penetration. Aluminum has been used as one of the coating metais.¹ However, it has not been easy to coat aluminum onto fibers without causing a large microbending loss. We used pure indium as the coating metal. The strength of the fiber was high, and the microbending loss was fairly small. Normally the softer the coating material, the smaller the microbending toss. In this respect indium is suitable because the Brinell hardness of indium is only 0.9, which is much smaller than the 14 of aluminum. Furthermore, the melting point of indium is very low (156.4°C), and indium adheres well to glass surfaces. However, the coated indium is too thin and too soft to protect the fiber from mechanical attack. Therefore, silicone resin was coated over the indium, with structure and dimension shown in Fig. 1(a). The structure of the indium-coated fiber is similar to the normal one we are using at present except for the thin indium; Fig. 1(b) is the structure and dimension of the normal fiber.

© 1981 Optical Society of America