A soot glass deposit body is manufactured by placing a starting rod and a burner 22 for producing glass particulates in a reaction container, introducing a source material gas to the burner 22 through a supplying pipe 26, producing glass particulates by a pyrolytic oxidation reaction of the source material gas in a flame formed by the burner 22, and depositing the produced glass particulates on the starting rod. At the time, the source material gas to be supplied to the burner 22 is a siloxane, the burner 22 is heated so that temperature of the burner 22 falls within the range of from 30 C. to +30 C. relative to the boiling point of the siloxane, and also temperature of the supplying pipe is controlled within the range of from the boiling point of the siloxane to the boiling point plus 30 C.

A method of manufacturing multi-mode optical fiber is disclosed. The method of manufacturing includes: a step of forming a first glass base material while controlling a supply rate of an additive for adjusting a refractive index to achieve a desired refractive index distribution; a step of drawing the first glass base material; a step of measuring a residual stress distribution in a radial direction of the multi-mode optical fiber after being drawn; a step of readjusting the supply rate of the additive in accordance with deviation of a refractive index, acquired from the residual stress distribution measured, from the desired refractive index distribution; a step of forming a second glass base material while supplying the additive at the supply rate after being readjusted; and a step of drawing the second glass base material.

Described is a process for the production of synthetic fused silica in which the deposition surface is located for a period of at least 50% of the build-up time of the soot body at a burner distance in which the horizontally integrated luminous intensity of the flame of the burner used in the targetless state is still at least of the maximum horizontally integrated luminous intensity of the flame.

The present invention intends to suppress variation in characteristics in the longitudinal direction of the optical fiber preform. The method of manufacturing method of manufacturing an optical fiber preform including forming a core by blowing a first raw material gas from a core burner to a starting base material, and forming a first clad by blowing a second raw material gas from a clad burner to the core, after forming the first clad, forming a second clad by blowing a third raw material gas from the clad burner to an end portion of the core, forming a core rod by heating the first clad and the second clad, and forming a third clad on an outer periphery of the core rod.

A method of manufacturing synthetic quartz glass through an outside vapor deposition (OVD) process with improved deposition efficiency. When a hollow cylindrical synthetic quartz glass product is manufactured through an OVD method or the like, it is environmentally friendly in view of using a smaller amount of chlorine and is economical in view of requiring no separate treatment equipment, as compared to a conventional technique using silicon chloride (SiCl.sub.4). Also, the method, in which octamethylcyclotetrasiloxane is supplied to a deposition burner while being sprayed in the form of a droplet along with a high-pressure carrier gas and vaporized by the deposition burner, can effectively address the high-temperature heating and slow decomposition involved when octamethylcyclotetrasiloxane ([(CH.sub.3).sub.2SiO].sub.4) is used as a source for depositing silicon dioxide particles.

Provided is a production method for a porous glass preform which forms the porous glass preform by depositing glass fine particles, which are generated by burner flame from a burner, on a tip of a starting material rotating about a vertical axis, and lifting the starting material, the production method including: imaging, with one or more cameras, a deposition surface of the glass fine particles in the starting material and the burner flame, and acquiring image data obtained by projecting an image of the deposition surface and an image of the burner flame on a same coordinate plane; and performing image processing on the image data to calculate a feature quantity of a spatial relationship between the deposition surface and the burner flame.