A method of producing soot, including: combusting a first fuel stream and a first oxidizer at a burner face; combusting a second fuel stream and a second oxidizer at the burner face, wherein the second fuel stream and the second oxidizer are premixed in advance of the burner face and a second equivalence ratio of the second fuel stream and the second oxidizer is less than about 1; and combusting a silicon-containing fuel into a plurality of soot particles, wherein the second fuel stream and the second oxidizer are combusted between the first fuel stream and the silicon-containing fuel. Applying this method of producing soot to deposit a preform suitable for the manufacture of optical fibers.

A method is provided for producing a glass fine particle deposit by a VAD method using a core deposition burner and a cladding deposition burner disposed adjacent to the core 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 the inner side. The method includes 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.

A method of forming an optical fiber preform includes the steps: igniting a burner having a fume tube assembly to produce a first spray size of silicon dioxide particles; depositing the silicon dioxide particles on a core cane to produce a soot blank; and adjusting an effective diameter of an aperture of the fume tube assembly to produce a second spray size of the silicon dioxide particles. The second spray size is larger than the first spray size.

In the method for manufacturing a glass-fine-particle-deposited body according to the present invention, at least a part of a gas supplying pipe 25 from a temperature controlled booth 24 to a burner 18 for cladding is temperature-controlled so that the temperature at the burner side becomes high and temperature gradient becomes 5 C./m or more. The temperature control is performed so that the temperature gradient becomes preferably 15 C./m or more, more preferably 25 C./m or more. Specifically, the part is controlled to the predetermined temperature gradient by winding a tape heater 26 that is a heating element on the outer circumference of the gas supplying pipe 25 from the temperature controlled booth 24 to the burner 18 for cladding and temperature-controlling the tape heater 26.

In the method for manufacturing a glass-fine-particle-deposited body according to the present invention, at least a part of a gas supplying pipe 25 from a temperature controlled booth 24 to a burner 18 for cladding is temperature-controlled so that the temperature at the burner side becomes high and temperature gradient becomes 5 C./m or more. The temperature control is performed so that the temperature gradient becomes preferably 15 C./m or more, more preferably 25 C./m or more. Specifically, the part is controlled to the predetermined temperature gradient by winding a tape heater 26 that is a heating element on the outer circumference of the gas supplying pipe 25 from the temperature controlled booth 24 to the burner 18 for cladding and temperature-controlling the tape heater 26.