OPTICAL FIBER PREFORM, METHOD FOR PRODUCING THE SAME AND RARE EARTH-ADDED OPTICAL FIBER

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PROBLEM TO BE SOLVED : To provide a method for producing an optical fiber preform including a core to which an immersion additive has been uniformly added in a radial direction thereof by a combination of an MCVD method and an immersion method. SOLUTION : In the method for producing the optical fiber preform by the combination of the MCVD method and the immersion method, a heating furnace used for increasing the bulk density of a glass fine particle layer before immersion is an electric furnace or an induction heating furnace, the heating furnace is equipped with a plurality of heating means so that at least a glass fine particle-deposited part of a glass tube can be entirely heated at the same time or the heating furnace is equipped with such a sufficiently long heating means so as to entirely heat at least the glass fine particle-deposited part of the glass tube at the same time, and heat treatment with the heating furnace comprises at least first heat treatment at a temperature at which the glass fine particle layer does not shrink and second heat treatment at a temperature which is higher than the first heat treatment temperature and at which the glass fine particle layer is not vitrefied to transparent glass. COPYRIGHT : (C)2009, JPO&INPIT