PURPOSE: At the start of clear glass formation, the starting material is changed from in pulled-up state to in pulled-down state to keep the growing surface of the porous parental material at a constant position to avoid axis deviation.
CONSTITUTION: After the porous parental material 3 is made to grow up to the top of the heater 7, as it is pulled up, the pulling-up is stopped to heat the parental material 3 by the heater 7 to effect rapid shrinkage so that a part of the parental material 3 remains between the starting material 5 and the shrinking part and the rotation center of the clear glass part of the parental material 3 is allowed to coincide with the rotation center of the growing surface of the material 3. Then, the starting material is kept in pulling-down state, a part of the parental material 3 remaining at the top end of the starting material 5 is made completely clear to cause shrinkage only on the boundary surface between the optical fiber material 4 and the parental material 3, then the starting material is shifted to in the pulling-down state. Thus, the growing surface of the porous parental material is kept constant whereby optical fiber with little fluctuation is obtained without deterioration in band characteristics.
SUDOU SHIYOUICHI
NAKAHARA MOTOHIRO
