| 摘要 |
PROBLEM TO BE SOLVED: To provide a porous glass material produced by VAD process, having high quality and stabilized outer diameter and specific refractive index difference in longitudinal direction and suitable as an optical fiber preform. SOLUTION: Glass soot formed by burners 21, 22, 23 is deposited on the lower end of a rotating target rod 12 and the rod 12 is pulled up according to the deposition to form a deposition 11 of glass soot having a columnar form. In the above process, the lower end position of the glass soot deposition 11 is detected with a position detector 31 and the rotating and lifting apparatus 13 is controlled by a computer 32 according to the detected result to vary the lifting speed so as to keep the lower end position at a definite level. The flow rate of hydrogen gas supplied to the burner 21 is controlled by a flow rate controlling apparatus 33 according to the lifting speed. |
