| 摘要 |
PURPOSE:To improve mechanical strength and weather resistance strength of an optical fiber consisting of fluoride glass by forming a high oxygen concentration layer having higher oxygen concentration than the interior on the surface. CONSTITUTION:This optical fiber is prepared, e.g. by a rotational casting method. As shown in the Figure (a), a clad melt to which oxygen is added is cast from a crucible 1 into an ingot mold 2. The ingot mold 2 is rotated and the melt is solidified in the inner circumferential face of the mold 2 by the centrifugation to afford a high-oxygen concentration layer having 1000-20000ppm oxygen concentration and 20mum thickness from the surface. Then, as shown in the Figure (b), another clad melt to which oxygen is not added is cast from the crucible 1 into the ingot mold 2 in which a clad layer containing oxygen is formed and the ingot mold 2 is rotated and the clad melt to which oxygen is not added is solidified on the inner layer. Then, as shown in the Figure (c), a core melt is cast from the crucible 1 into the ingot mold 2 in which the clad layer containing oxygen and the clad layer containing no oxygen are formed and solidified to provide a preform 3. |
