| 摘要 |
PURPOSE:To produce the title preform for fluoride optical fiber for a low-loss optical transmission line by successively injecting the melt of fluoride clad glass and the melt of core glass into a bottomed cylindrical casting mold, and opening the bottom of the casting mold before solidification. CONSTITUTION:The melt 4 of the clad fluoride glass obtained by adding NH4 F4.HF to a mixture of fluorides such as ZrF4, BaF2, GdF3, and AlF3, and heating and melting the mixture is charged into a bottomed cylindrical casting mold A made of brass and plated with gold. The melt 5 of the core fluoride glass obtained by adding NH4F.HF to a mixture of fluorides such as ZrF4, BaF3, AlF3, and PbF3, and heating and melting the mixture is then charged. The bottom lid is opened before the materials are solidified, and the melt in the central part of the casting mold is discharged. A double-structure preform 6, wherein a core glass layer is formed on the inner surface of a clad glass tube, is formed in the casting mold, the preform is cooled to room temp. in an inert gas atmosphere having <=0<= dew point, then the upper and lower openings are closed with a resin, and a preform for fluorine optical fiber having extremely low transmission loss is produced. |
