Nippon Telegraph and Telephone Public Corporation

Shoichi Suto

Masao Kawachi

Takao Edahiro

Satoru Tomaru

Motohiro Nakahara

Fumiaki Hanawa

Nobuo Inagaki

Hiroyuki Suda

Manufacturing method of doped silica glass suitable for optical fiber wherein quartz powder or SiO.sub.2 glass fine particles are exposed to a gas for producing the doped silica glass containing SiCl.sub.4, a gaseous additive and water vapor (H.sub.2 O) to add the dopant to the glass body, and then the resulting glass body is fused at a high temperature, thereby producing a transparent doped silica glass in which the production of the glass particles, the addition of the dopant, and the vitrification of the glass body are carried out by separate steps under respective suitable conditions. The manufacturing speed is remarkably increased because of the separate steps. The content of the dopant is not limited, but can be adjusted with any desired amount by changing the reaction time of dissolution. Dopant components like PbO.sub.2, SnO.sub.2, ZnO which were typically not added to the glass body can now be added thereto. Also, a method of manufacturing an optical fiber preform is disclosed wherein the doped silica glass is deposited and fused on a starting material which is inclined by an angle within a range of 5.degree.-90.degree. with respect to a blow-off direction of the flow of the doped silica glass to form a transparent doped silica glass body having a uniform outer diameter and a uniform boundary surface at a high synthesizing speed. This latter method aids mass production of optical fibers at low cost.

Fabrication methods of doped silica glass and optical fiber preform by

A core torch for fabricating a single-mode optical fiber preform wherein fine glass particles are produced eccentrically with respect to the center area of a flame stream, the core torch being so arranged as to blow the flame stream at an angle inclined to a seed rod. The porous glass body forming the core is grown on one end of the rod and in the direction of the axis of the rod. A cladding layer is formed on the periphery of the porous glass core body by at least one torch for forming the cladding. The obtained porous glass body is heated and vitrified into a transparent glass body, which is sealed in a silica tube for jacketting to form a single-mode optical fiber preform. At least one exhaust port is disposed within a distance of 1 mm to 50 mm from the periphery of the porous glass body and in the vicinity of the growing surface of the glass body to exhaust residual glass fine particles and undesired gases. A porous glass body having a diameter of 20 mm or less is easily formed. Single-mode optical fiber having a cladding-to-core-diameter ratio of 3 or more is fabricated by the VAD method. Accordingly, a long-length and low-loss single-mode optical fiber is mass-produced.

Core torch for fabricating single-mode optical fiber preforms

A method of fabricating an optical fiber preform wherein a synthesizing torch is inclined between 10.degree. and 60.degree. with respect to the rotation axis of a seed rod. Moving the rod while rotating it, a glass raw material gas and a flame forming gas are blown out individually from the torch to synthesize glass particles which are deposited onto one end of the rod, so that a cylindrical porous preform is grown in the direction of the rotation axis of the rod. Then the porous preform is heated at a high temperature to vitrify the porous preform into a transparent optical fiber preform. At least one exhaust port is disposed at a distance of 1 mm to 50 mm from the periphery of the porous preform and in the vicinity of the growing surface of the porous preform. In fabricating the porous preform the outer diameter fluctuations are small, and the preform is formed stably without formation of cracking on the periphery of the preform.

Method of fabricating multi-mode optical fiber preforms

A method of fabricating a single-mode optical fiber preform wherein a core torch produces fine glass particles eccentrically with respect to the center area of a flame stream, the core torch being so arranged as to blow the flame stream at an angle inclined to a seed rod. The porous glass body forming the core is grown on one end of the rod and in the direction of the axis of the rod. A cladding layer is formed on the periphery of the porous glass core body by at least one torch for forming the cladding. The obtained porous glass body is heated and vitrified into a transparent glass body, which is sealed in a silica tube for jacketting to form a single-mode optical fiber preform. At least one exhaust port is disposed within a distance of 1 mm to 50 mm from the periphery of the porous glass body and in the vicinity of the growing surface of the glass body to exhaust residual glass fine particles and undesired gases. A porous glass body having a diameter of 20 mm or less is easily formed. Single-mode optical fiber having a cladding-to-core-diameter ratio of 3 or more is fabricated by the VAD method. Accordingly, a long-length and low-loss single-mode optical fiber is mass-produced.

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Mito, Japan

Shoichi Suto