| 摘要 |
PURPOSE:To obtain the titled long preform having low scattering, OH content and loss, by casting a core and a clad glass melts melted in a crucible of double structure having heating members arranged on the periphery, and discharging the melts into a mold. CONSTITUTION:Core and clad fluoride glass raw materials are charged into a core glass melting part 2 and a clad glass melting part 3 surrounding the part 2 of a double crucible 4 placed on a crucible table 1, and a lid 5 is placed thereon. The crucible 4 is then contained in a quartz vessel 9 and closed. Ar gas is then introduced from the upper inlet, and the crucible 4 is heated with a heater 10 to melt the glass raw materials in the melting parts 2 and 3. A plug 8 for controlling the discharge of the melts is moved downward to open nozzles 6 and 7 for discharging the core and clad at the bottom of the crucible 4. These melts are cast into a hollow cylindrical mold 11, integrated with a ring 12 and the bottom ring 13, and dividable into three parts in the longitudinal direction, and cooled with a surrounding heater 14 for heating the mold 11 at about 260 deg.C and solidified. The rings 7 and 8 are then removed to take out the aimed preform. |
