Optical fiber producing method and apparatus and optical fiber

An optical fiber producing method, using an apparatus comprising a susceptor into which an optical fiber preform is inserted and a heater disposed outside the susceptor to heat the susceptor from the outside, for producing an optical fiber by drawing a glass fiber while the optical fiber preform is heated and melted and by drawing out the fiber through the outlet at the lower section of the susceptor to the outside,

• wherein a gas containing 50% or more of argon or nitrogen is used as a gas to be supplied into the susceptor, and a protective pipe with a length of Da (mm) is provided under the susceptor, the protective pipe having a heat insulating region enclosed with a heat insulator with a length of Db (mm) at the upper section thereof and a non-heat insulating region not enclosed with any heat insulators at the lower section thereof, and
• wherein, when the drawing velocity of the glass fiber is V (m/min), the lengths of Da and Db are set to satisfy “V/Da≦1.2 and V/Db≦2.3” so that the temperature of the glass fiber at the outlet of the protective pipe becomes 1700° C. or less and so that the outer diameter of the glass fiber at the outlet of the protective pipe is within a range of the target outer diameter of the glass fiber+6 μm or less.