| 摘要 |
PURPOSE:To prevent preform from cooling, to suppress occurrence of structural defects of optical fiber and to contrive to reduce loss of optical fiber, by preheating an inert gas to be sent to a furnace core tube to heat and draw preform. CONSTITUTION:An inert gas in a feed pipe 32 is preheated by a preheating means 31 and made to flow in a furnace core tube 1. Preform 4 is fed from the top of the furnace core tube 1 in which the inert gas is circulated. The inert gas is heated by a heater 2 arranged at the outer peripheral part of the furnace core tube 1 and the preform 4 is drawn. |
