PURPOSE: To stably deposit soot at a high rate without causing peeling in the interface by heating the contact area of the deposition surface of the soot and a glass core body with an auxiliary burner in VAD method.
CONSTITUTION: The optical fiber preform is produced by spraying soot around a glass core body which is moved in the vertical direction while rotated. This soot is produced by the reaction of gaseous glass source material injected from a burner 11 into a flame. In the process, the lowermost part 14 of the deposited body 15 is independently heated by a small-size auxiliary burner 17. This flame is controlled to avoid interference with the flame 12 of burner 11. If the flame 18 is too large, interference with the flame 12 affects deposition of soot. Moreover, the burner 11 is adjusted to satisfy the relation of angles θm-60°<θs<θm+20°, wherein θm and θs are angles of the burner 11 and the burner 17, respectively, to the axis of the glass core body 16. The flow rate of hydrogen in the burner 17 is specified to 5-20% of the flow rate of the burner 11.
DANZUKA TOSHIO
ISHIKAWA SHINJI
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