| 摘要 |
PURPOSE:To form thin glass film part to an elliptical shape by reducing the pressure in a quartz glass tube during heating and welding at the time of forming a preform rod by heating and welding a circular quartz glass tube formed with the different thin glass films on the inside wall. CONSTITUTION:The quartz glass tube 1 is prepd. If the diameter of this tube is large and the thickness is small, the prescribed shape is hardly obtainable in a later pressure reduction stage and, therefore, a diametral reduction stage is included at need and the tube 1 having 5 to 50mm outside diameter and 0.3 to 5mm thickness is preferable. The thin glass films 2, 3 to form the intermediate layer and central layer of an optical fiber are formed on the inside wall of the tube 1 by a chemical deposition method. Both ends of the tube 1 are mounted to a glass lathe and while the tube 1 is rotated, the pipe ends are heated by a burner 4 and are thereby crushed. A discharge tank 5 is provided in the other aperture of the tube and while a control valve 7 is controlled, the pressure in the tube is reduced from a discharge pipe 6 to maintain the specified pressure. A burner 4 is gradually moved in this state to obtain the solid preform rod. The rod is melted by by burner 4 and is drawn from one side. The optical fiber having the elliptical shape in a part of the inside layer is thus obtd. |
