An optical fiber having a core comprising silica and greater than 1.5 wt % chlorine and less than 0.5 wt % F, said core having a refractive index .sub.1MAX, and an inner cladding region having refractive index .sub.2MIN surrounding the core, where .sub.1MAX>.sub.2MIN.

The present invention relates to a method for manufacturing a preform of silica for optical fiber production, as well as to a method for the production of optical fibers comprising a step of drawing the optical fiber from such a preform of silica, the method comprising a step of vaporization of a siloxane feedstock added with a compound having the following formula (I): wherein R, R and R, equal or different each other, are an alkyl group having from 1 to 5 carbon atoms, and A is a saturated or unsaturated chain of atoms selected from the group consisting of carbon atom, nitrogen atom, and oxygen atom, said chain A forming with the nitrogen atom linked thereto a saturated, unsaturated or aromatic heterocyclic moiety.

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A manufacturing method of a porous glass preform for optical fiber by depositing glass microparticles on a starting member, including supplying a vaporizer with organic silicon compound raw material in a liquid state and a carrier gas; in the vaporizer, mixing and vaporizing the organic silicon compound raw material in a liquid state and the carrier gas to convert the organic silicon compound raw material and the carrier gas into a raw material mixed gas; supplying a burner with the raw material mixed gas and a combustible gas, combusting the raw material mixed gas and the combustible gas in the burner, and ejecting SiO.sub.2 microparticles generated by the combustion from the burner; and depositing the SiO.sub.2 microparticles ejected from the burner on the starting member by repeatedly moving the vaporizer and the burner together, in a synchronized manner, parallel to the starting member in a longitudinal direction thereof.

An optical fiber having a core comprising silica and greater than 1.5 wt % chlorine and less than 0.5 wt % F, said core having a refractive index .sub.1MAX, and a inner cladding region having refractive index .sub.2MIN surrounding the core, where .sub.1MAX>.sub.2MIN.

A method for manufacturing a porous glass fine particle body including: forming a deposit layer of glass fine particles, generated from raw material gas including a silicon-containing organic compound, on a rotary starting member; supplying the raw material gas to a burner; switching the raw material gas to purge gas; supplying the purge gas to the burner at a first flow rate when the raw material gas is discharged from inside the burner; and switching the first flow rate to a second flow rate smaller than the first flow rate.

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.

In a method of manufacturing porous glass base for optical fiber, a liquid organic siloxane raw material stored in a raw material tank of internal pressure P1 is controlled by a mass flow controller at a predetermined flow rate and pumped through pipe of internal pressure P2 to a vaporizer, the liquid raw material is vaporized in the vaporizer and supplied as a gas raw material to a burner, and the silica fine particles formed by burning the gas raw material in the burner are deposited to form a porous glass base material, where P1?P2 is satisfied.

A method for manufacturing a glass preform includes transporting a liquid-form raw material compound including an organic silicon compound by pressurizing the raw material compound using a pressurization gas, deaerating a dissolved gas from the pressurized raw material compound, controlling a flow rate of the deaerated raw material compound using a mass flow controller, gasifying the raw material compound transported through the mass flow controller, and combusting the gasified raw material compound using a burner to generate SiO.sub.2.

A method for manufacturing a glass ingot includes preparing a supply system including a gasifier that gasifies a raw material compound and a burner that combusts the gasified raw material compound; adding an oxygen-containing gas to the raw material compound at a plurality of addition places including an upstream addition place located in the gasifier or on an upstream side of the gasifier and a downstream addition place located on a downstream side of the gasifier in which locations of the raw material compound in a flow direction are different in the supply system so as to form a raw material mixture; and adding the oxygen-containing gas at the upstream addition place so that a concentration of oxygen or a concentration of the raw material compound in the raw material mixture is not in a combustible range of the raw material mixture.

A manufacturing method of a porous glass base material for optical fiber includes: controlling a flow rate of a raw material liquid of an organic siloxane by a liquid mass flow controller; introducing raw material liquid to a raw material liquid nozzle of a vaporizer by a raw material liquid pipe; ejecting raw material liquid into the vaporizer; mixing raw material liquid and carrier gas to vaporize raw material liquid to form mixed gas; supplying mixed gas to a burner; combusting mixed gas together with a combustible gas and a combustion supporting gas in the burner to produce SiO.sub.2 particles; depositing SiO.sub.2 particles on a starting core base material to form the porous glass base material; and closing an open/close valve on a flow path of the raw material liquid pipe to stop supply of raw material liquid, while continuing to supply carrier gas, combustible gas, and combustion supporting gas.