Patent ID: 8341979

Claim:
A method of producing an optical fiber preform by subjecting a glass preform that has a glass rod and a silica glass porous body deposited on a periphery of the glass rod and includes a valid portion used in a production of an optical fiber, and invalid portions adjacent to the valid portion to perform a heat treatment using a heater in a heating furnace to vitrify the silica glass porous body, comprising: performing a first step of heating the glass preform while moving the glass preform along its axial direction relative to the heater, thereby creating a relative movement between the glass preform and the heater; subsequent to the first step, when an invalid portion positioned at a tail end opposite to the moving direction of the glass preform reaches a vicinity of the heater, performing a second step of stopping the relative movement between the glass preform and the heater or decreasing a speed of the relative movement between the glass preform and the heater; subsequent to the second step, performing a third step of heat treatment of the invalid portion for a retention time while retaining a heating temperature to be a temperature at which the silica glass porous body can be vitrified to a transparent glass; subsequent to the third step, performing a fourth step of decreasing the heating temperature at which the heat treatment is performed to a temperature, the temperature being 200° C. higher than an annealing point of a silica glass; and subsequent to the fourth step, performing a fifth step of removing the glass preform to the outside of the heating furnace without increasing the heating temperature at which the heat treatment is performed to a temperature at which the silica glass porous body can be vitrified.