Method for producing porous glass deposit for optical fiber

A method for producing a glass fine particle deposit by a VAD method using a core deposition burner and a cladding deposition burner,

• the cladding deposition burner including five cylindrical tubes having different outer diameters and concentrically superimposed on one another and a group of small-diameter nozzles arranged in a ring shape in a third region from an inner side, the method comprising:
• flowing, in the cladding deposition burner, a glass raw material gas and a combustion supporting gas in a first region from the inner side, air in a second region from the inner side, a combustible gas in the third region from the inner side, a combustion supporting gas in the group of small-diameter nozzles, an inert gas in a fourth region from the inner side, and a combustion supporting gas in a fifth region from the inner side, respectively,
• wherein, in the flowing, a ratio obtained by dividing a linear velocity of the combustion supporting gas flowing in the group of small-diameter nozzles by a linear velocity of the combustible gas flowing in the third region is from 2.2 to 4.3, and the cladding deposition burner deposits a cladding portion on a core portion deposited by the core deposition burner while heating the core portion.