| 摘要 |
PROBLEM TO BE SOLVED: To provide both a method and an apparatus for producing a porous preform, capable of producing a glass preform which prevents the occurrence of resonance to cause a strong vibration in the porous preform and minimizes the change in refractive index distribution in the longitudinal direction (axial direction). SOLUTION: In producing a porous preform by feeding a raw material gas together with a fuel gas to a burner, oxidizing the raw material gas or subjecting to a flame hydrolysis reaction, attaching and depositing the formed glass fine particle on a target member which is pulled up while being rotated, the number of vibrations a [Hz] at the tip of the porous preform and the number of revolution b [rpm] satisfy the formula a≠(n+r)×b/60 the formula a≠(1/n+r)×b/60 (n is a positive integer; r is a numerical number from -0.2 to 0.2).
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