| 摘要 |
PROBLEM TO BE SOLVED: To obtain a porous glass base material for an optical fiber, having a core part and a clad part by VAD method or OVAD method and not leaving bubbles in the core part, not causing the separation of the core/clad interface, etc., on the subsequent sintering treatment, and to provide a method for stably producing the porous base material. SOLUTION: This porous glass base material for an optical fiber comprises a core part containing GeO2 as a dopant and a clad part lower in the index of refraction than that of the core part. Therein, the difference between the average bulk density of the core part and the average bulk density of the clad part is <=0.15g/cm<3> . In the method for producing the porous glass base material comprising the core part containing the GeO2 as the dopant and the clad part lower in the index of the refraction than that of the core part by VAD method or OVAD method, the improvement comprises allowing the core part and the clad part to grow, while controlling their bulk densities so that the difference between the average bulk density of the core part and the average bulk density of the clad part is <=0.15g/cm<3> . |
