| 摘要 |
PURPOSE:To produce a base material for optical fibers having an amount of fluorine to be added varying in the radial direction, by heating a soot base material consisting essentially of quartz in a high-temperature furnace with a spatially uneven concentration distribution of a fluorine-containing compound gas, and transparentizing and vitrifying the base material. CONSTITUTION:An apparatus for heatig a soot base material 9 rising while rotating with a ring heater 5 provided on the outside of a furnace core tube 6, and transparentizing and vitrifying the base material 9 to a part 12 during the passage through a high-temperature part (A-A'). In the apparatus, an inner cylinder 11, having a height reaching almost the high temperature part (A-A'), and coaxial with the furnace core tube 6 is provided in the furnace core tube 6 to give a double structure. A fluorine-containing compound gas, e.g. C2F6, is introduced from a gas inlet 7 into the above-mentioned furnace core tube 6, and an inert gas, e.g. He, is introduced from a gas inlet 10 into the inner cylinder 11. Thus, both gases are diffused and mixed near the high-temperature part (A-A') to change the concentration of the fluorine-containing compound gas continuously in the radial direction, and therefore the distribution of fluorine concentration in the radial direction of the transparentized and vitrified base material for optical fibers is continuously changed. |
