Special issue paper. Low-loss light-focusing fibres manufactured by a continuous process

A light-focusing fibre guide named Selfoc was developed in 1968 by the joint research work of the Nippon Sheet Glass Co. Ltd. and the Nippon Electric Co. Ltd. During the past seven years of research work, the losses of Selfoc fibres have been reduced to 6 dB/km at a wavelength of 830nm. The optimum glass composition for low-loss Selfoc fibres and the purification methods of raw materials for them have been extensively studied. To prepare low-loss glasses, two different types of furnaces were constructed. The fibre-fabrication technique has been improved from a preform method employing an ion-exchange treatment in a molten:salt bath, to a continuous method using a fast ion exchange in a double crucible. A parabolic distribution of the refractive index is obtained by selecting the optimum operation parameters of fibre drawing. In this paper, the manufacturing process and the low-loss broad-band transmission characteristics of the recent Selfoc fibres are described.