| 摘要 |
PURPOSE:To obtain a completely round optical fiber by making uniformly a temperature distribution in the radius direction in a muffle furnace, and heating an optical fiber preform from the circumference. CONSTITUTION:The central part 12 of a muffle tube 10 is made thick, the upper and lower parts of the muffle furnace are made thicker than the central part. The length of the thick central part is somewhat longer than that of an electric heater 1 and is just equal to a distance between an upper and a lower heat insulating materials 6. Consequently, reduction in temperature occurs in the vicinity of a flange part of the heater connected to a pair of electrodes 2 by influence of heat dissipation resulting from cooling the electrodes with water to cause nonuniformity of temperature distribution in the radius direction in the muffle tube 10. However, since the muffle tube 10 is made thick, heat is smoothly transferred to uniform the temperature distribution in the radius direction in the muffle tube 10. |
