JP2000119034A - Production of quartz glass preform for optical fiber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a large-sized quartz glass preform for an optical fiber free from any bubbles on a welded surface suitable for mass production and lower cost. SOLUTION: This method uses a quartz glass tube for a preform prepared by mechanically grinding the inner and outer peripheral surfaces of a high-purity quartz glass ingot with diamond abrasive grains and mechanically polishing the inner peripheral surface with cerium oxide abrasive grains in the method for producing the quartz glass preform for an optical fiber comprising inserting a core glass rod for the preform for the optical fiber into a quartz glass tube for the preform for the optical fiber, heating, welding and integrating both.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a quartz glass preform for an optical fiber, and more particularly, to a method for producing a quartz glass tube having a high surface accuracy using a quartz glass tube for a preform, which is welded to a core glass rod for a preform. The present invention relates to a method for producing a quartz glass preform for an optical fiber having no bubbles.

[0002]

2. Description of the Related Art In recent years, as optical fibers have been used in large quantities, mass production and cost reduction have been eagerly desired. For mass production and cost reduction, it is the easiest method to prepare a large optical fiber preform and draw it. However, the shafting method (V
In the AD method) or the external method (OVD method), both the core and the clad are made by the VAD method or the OVD method.
Attempts to further increase the size have the disadvantage that the productivity of the optical fiber preform may be reduced. Also,
When the base material is formed into a large porous body (a soot body on which silica glass fine particles are deposited, hereinafter referred to as a "porous soot body") itself before being made into a transparent glass, cracks occur, There is a problem that productivity may be significantly reduced due to troubles such as dropping of the porous soot body. As a method for manufacturing an optical fiber that solves this problem, a clad portion occupying 80% or more of the cross-sectional area is formed by a method capable of reducing cost and high performance, and a core glass rod formed by a VAD method or an OVD method. JP-A-7-10
9141 and the like.

[0003]

However, in the manufacturing method described in the above publication, the inner peripheral surface of the quartz glass tube is formed by mechanical grinding and polishing, while the outer peripheral surface is mechanically ground. From the point where the processing state of the outer peripheral surface is rough, irregularities and cracks are generated, coolant and grinding powder at the time of grinding enter there, and the foreign matter is sufficiently removed even by washing with hydrofluoric acid after processing. It cannot be removed, bubbles are generated when welding and integrating with the core glass rod,
There are drawbacks such as that the connection of the optical fiber after drawing is hindered due to the remaining bubbles and the like. Although a strong etching process may be considered to completely remove the irregularities and cracks, the etching process selectively etches the dents and scratches of the quartz glass tube, which further roughens the inner and outer surfaces of the quartz glass tube. It did not eliminate the shortcomings. However, the method of manufacturing an optical fiber described in JP-A-7-109141 is easy to increase the size of the optical fiber preform, and is a manufacturing method suitable for mass production and cost reduction. The present inventors have conducted intensive studies to improve the manufacturing method and found that the inner and outer peripheral surfaces of the quartz glass ingot were accurately ground with diamond abrasive grains, and then the inner peripheral surface was polished with cerium oxide abrasive grains. Finding that the above disadvantage can be solved by increasing the accuracy,
The present invention has been completed. That is,

An object of the present invention is to provide a method of manufacturing a quartz glass preform for an optical fiber in which no bubbles are present at a welding interface between a quartz glass tube for an optical fiber preform and a core glass rod.

Another object of the present invention is to provide a method for producing a large-sized quartz glass preform for an optical fiber suitable for mass production and cost reduction.

[0006]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention relates to a quartz for optical fiber in which a core glass rod for an optical fiber preform is inserted into a quartz glass tube for an optical fiber preform, which is heated and welded and integrated. In the method of manufacturing a glass base material, the quartz glass tube for the base material is subjected to mechanical grinding of the inner and outer peripheral surfaces of a high-purity quartz glass ingot with diamond abrasive grains, and then the inner peripheral surface is mechanically polished with cerium oxide abrasive grains. The present invention relates to a method for producing a quartz glass preform for an optical fiber, which is a processed quartz glass tube.

As described above, in the manufacturing method of the present invention, the inner and outer peripheral surfaces of a high-purity quartz glass ingot are made of diamond abrasive grains having a high grinding speed, a small roughness of the ground surface, and little deterioration of the grinding wheel. It is essential to mechanically grind and then mechanically polish the inner peripheral surface with cerium oxide abrasive grains to increase the surface accuracy. The surface accuracy is such that the maximum roughness Rmax of the inner peripheral surface of the quartz glass tube is 1 μm or less, and the center line average roughness R
a is 0.1 μm or less, and the maximum roughness Rmax of the outer peripheral surface is 10
μm or less, and the center line average roughness Ra is 1 μm or less. If the maximum roughness and the center line average roughness of the peripheral surface exceed the above ranges, bubbles may be generated at the welding interface of the optical fiber base material, which is not preferable. In the mechanical grinding process using the diamond abrasive grains, it is preferable to use diamond abrasive grains having different grain sizes, first rough-cut with diamond grain of coarse grain size, and then finish-grind with diamond abrasive grain of fine grain size. Although fine cracks are generated on the inner and outer peripheral surfaces of the quartz glass tube by the grinding with the diamond abrasive grains, the cracks on the outer peripheral surface are smoothed by heating and melting during welding and integration with the core glass rod. On the other hand, since the inner peripheral surface has a relatively low heating temperature, fine cracks are not sufficiently melted and remain as they are, so that polishing with cerium oxide abrasive grains is required.
More preferably, after the polishing, the quartz glass tube is heated and melted, and the inner and outer peripheral surfaces of the quartz glass tube are mirror-finished to have a maximum roughness Rmax of 0.5 μm or less and a center line average roughness Ra of 0.1 μm or less. For the heating and melting, melting by a flame such as oxyhydrogen or propane, external heating and melting by an electric furnace or the like can be used. By using the quartz glass tube mirror-finished by heating and melting as a tube for cladding (or for over cladding) the core glass rod, good light free of bubbles at the welding interface with the core glass rod for the base material can be obtained. In the case where a quartz glass preform for fiber can be manufactured, and one or a plurality of other quartz glass tubes are further fused and integrated after welding and integrating the quartz glass tube for the preform and the core glass rod for the preform. Similarly, a good quartz glass preform for an optical fiber can be manufactured.

In the quartz glass ingot, silica fine particles formed by flame hydrolysis of a siloxane compound such as silicon tetrachloride or an organic silicon compound in an oxyhydrogen flame are deposited.
Melt vitrification after dehydration treatment, or a method in which quartz produced naturally is crushed and purified by chemical treatment to produce quartz powder by the Bernoulli method using an oxyhydrogen flame, etc. A long ingot is good. By using this large and long ingot, mass production of optical fibers and cost reduction can be suitably performed.

On the other hand, as a core glass rod for an optical fiber, there is a quartz glass rod which is a light transmitting portion and has an optical cladding portion formed around the quartz glass rod. That is, in the present invention, the “core glass rod” is a general term for the core rod and the clad core rod. Core rod without cladding
It can be formed by a known VAD method, OVD method, or the like. As means for producing a core rod with a clad, a method of jacketing a quartz glass tube on the core rod, or forming a clad portion around the core rod by an OVD method, or the like. Method.

In the production of a quartz glass preform for an optical fiber using the core glass rod for an optical fiber preform and the quartz glass tube for an optical fiber preform, the core glass rod for the preform is made of quartz glass for the preform. Carefully insert into the tube so that it does not come into contact with the inner peripheral surface of the tube, fix the core glass rod for the base material and the center of each circle of the quartz glass tube for the base material and fix them, and preferably connect both ends to the dummy quartz material Above, bend by connection processing while rotating the whole, to correct the twist, inserted from above the vertical electric furnace from the lower end, temperature 1900
It is preferable to perform welding and integration by sequentially heating at 2800 ° C. in a belt shape. The above-mentioned sequential heating in a strip shape is what is called a zone melt, and refers to heating in which a heating area gradually moves.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, embodiments of the present invention will be described, but the present invention is not limited thereto.

In the present invention, the maximum roughness Rmax and the center line average roughness Ra are defined by Japanese Industrial Standard (JIS) B0.
According to the definition of No. 601, the measuring method is 1 with a contact type simple roughness meter (Surfcom 300B, manufactured by Tokyo Seimitsu Co., Ltd.).
Measured at every 0 mm length, the maximum roughness Rmax at that time
And the method of obtaining the center line average roughness Ra.

[0013]

Example 1 Using OVD, silicon tetrachloride was vaporized, flame-hydrolyzed in an oxyhydrogen flame, and silica glass particles were deposited around a rotating substrate to produce a large porous soot body. . The porous soot body is placed in an electric furnace, and a mixture of He and Cl2 is used in consideration of conditions such as the refractive index of the core glass rod.
Dehydration by heating at 00 ° C., followed by 1600 in a He atmosphere
Transparent vitrification was performed at ℃ to produce a cylindrical quartz glass ingot. Both ends of this cylindrical quartz glass ingot are cut, and the outer diameter is ground to a predetermined size with # 100 diamond abrasive grains, and then ground with # 300 diamond abrasive grains. Then, the center of the outer diameter is determined, and the center of the outer diameter is determined, and ground to near a predetermined size with a # 150 diamond abrasive of a core drilling device, and then with # 1000 and # 3000 cerium oxide abrasives. Polished. The obtained quartz glass tube was etched with hydrofluoric acid, washed with pure water, and dried to prepare a highly accurate quartz glass tube. When the dimensions of the quartz glass tube were measured with a laser outer diameter measuring machine and a wall thickness measuring machine, the length was 3500 mm and the outer diameter was 20 mm.
0 mm and the inner diameter was 40 mm. Further, regarding the surface roughness of the inner and outer peripheral surfaces, the maximum roughness Rmax of the inner peripheral surface is 0.7
μm, the center line average roughness Ra was 0.06 μm, the maximum outer surface roughness Rmax was 5.5 μm, and the center line average roughness Ra was 0.5 μm.

On the other hand, a core rod with a clad was prepared by the VAD method, and heated and stretched by a precision automatic stretching machine with outer diameter control so that the outer diameter was adjusted to 39 mm with respect to the inner diameter of the quartz glass tube. Carefully insert this core glass rod into the quartz glass tube so as not to contact the inner surface of the tube,
The core rod for the base material and the quartz glass tube for the base material are fixed at the center of each circle, and both ends are connected to the dummy quartz material.
After inserting the lower end from above the electric furnace at 2000 ° C and welding the lower end, the inside of the quartz glass tube is depressurized with a vacuum pump and sequentially heated to form a strip to be welded and integrated to produce a quartz glass preform for optical fibers. did. 1000 mm of the obtained base material
Each was cut, and one of the cut pieces was exposed to white light from the end in a dark room. As a result, the number of bubbles whose minimum unit visually permissible was about 0.1 mm or more per 1000 mm was 9 pieces. The outer diameter was measured at intervals of 50 mm with a laser outer diameter measuring instrument, and the dimensional error was ± 0.2 m.
m or less. Further, when the quartz glass base material for optical fiber was measured with a preform analyzer, no deviation of the center of the circle was observed.

Example 2 Using a VAD method, silicon tetrachloride was vaporized, flame-hydrolyzed in an oxyhydrogen flame, and silica glass particles were deposited on a rotating quartz glass rod to produce a large porous soot body. This porous soot body is placed in an electric furnace, and a mixed gas of He and Cl2 is used in consideration of conditions such as the refractive index of the core glass rod.
Heat dehydration at 100 ° C., and subsequently 160
It was made transparent at 0 ° C. to produce a cylindrical quartz glass ingot. After cutting both ends of this cylindrical quartz glass ingot, the outer diameter of the ingot is cut to near a predetermined size with a # 100 diamond abrasive grain of a cylindrical grinding device, and then ground with a # 300 diamond abrasive grain. The center of the outer diameter is determined, the core is drilled in accordance with the center of the outer diameter with a core drilling machine, and # 1000 and # 3000 cerium oxide abrasive grains are used with a precision honing machine. Polished. The polished quartz glass tube is heated at 2000 ° C. while flowing an inert gas into an electric furnace, and the surface is melt-mirrorized. Then, etching with hydrofluoric acid, washing with pure water, and drying are performed to achieve high precision. Was prepared. When the dimensions of this quartz glass tube were measured with a laser outer diameter measuring device and a wall thickness measuring device, the length was 1000 mm, the outer diameter was 60 mm, and the inner diameter was 20 mm. Further, when the surface roughness of the inner and outer peripheral surfaces was examined, the maximum roughness Rmax of the inner peripheral surface was 0.2 μm, and the center line average roughness Ra was
Is 0.03 μm, and the maximum roughness Rmax of the outer peripheral surface is 0.3 μm.
m, and the center line average roughness Ra was 0.05 μm.

On the other hand, a core rod with a clad was manufactured by the VAD method, and the core rod was heated and stretched by a precision automatic stretching machine with outer diameter control so that the outer diameter was adjusted to 19 mm with respect to the inner diameter of the quartz glass tube. Carefully insert this core glass rod into the quartz glass tube so as not to contact the inner surface of the tube,
Fix the core rod and the quartz glass tube so that the centers of the circles are aligned and connect both ends to the dummy quartz material.
After inserting from above the electric furnace at 000 ° C. and welding the lower end, the inside of the quartz glass tube was depressurized by a vacuum pump and sequentially heated in a belt shape to be welded and integrated to produce a quartz glass preform for optical fiber. The obtained base material is cut every 1000 mm,
When white light was applied from one end in a dark room to one of them, the number of bubbles having a minimum unit visually observable of about 0.1 mm or more per 1000 mm was four. Also,
When the outer diameter was measured at intervals of 50 mm with a laser outer diameter measuring instrument, the dimensional error was ± 0.2 mm or less. Further, when the quartz glass base material for optical fiber was measured with a preform analyzer, no deviation of the center of the circle was observed.

[0017]

According to the manufacturing method of the present invention, by using a quartz glass tube for an optical fiber preform having a high surface accuracy, a good optical fiber having no bubbles at the welding interface with the core glass rod for the optical fiber preform can be obtained. Quartz glass base material can be manufactured. In particular, a large and long quartz glass preform for an optical fiber can be manufactured at low cost, and a high-quality optical fiber can be manufactured with high productivity by drawing it.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Masanori Suzuki 88 Kawakubo, Kanaya, Tamura-cho, Koriyama-shi, Fukushima Prefecture Inside the Koriyama Plant, Shin-Etsu Quartz Co., Ltd. Shin-Etsu Quartz Co., Ltd. Koriyama Factory F-term (reference) 4G021 BA03

Claims (4)

[Claims] 1. A method for manufacturing a quartz glass preform for an optical fiber, comprising inserting a core glass rod for an optical fiber preform into a quartz glass tube for an optical fiber preform, heating and fusing and integrating the core glass rod. The glass tube is a quartz glass tube obtained by mechanically grinding the inner and outer peripheral surfaces of a high-purity quartz glass ingot with diamond abrasive grains and then mechanically polishing the inner peripheral surface with cerium oxide abrasive grains. A method for producing a quartz glass preform for a fiber. 2. The quartz glass tube for an optical fiber preform has a maximum inner surface roughness Rmax of 1 μm or less, a center line average roughness Ra of 0.1 μm or less, and a maximum outer surface roughness Rmax of 10 μm.
2. The method of claim 1, wherein the center line average roughness Ra is 1 μm or less. 3. A method for producing a quartz glass preform for an optical fiber, wherein the inner and outer peripheral surfaces of the quartz glass tube according to claim 1 are further melted by heating and mirror-finished. 4. The quartz glass tube for an optical fiber preform has a maximum roughness Rmax of 0.5 μm or less on the inner and outer peripheral surfaces, a center line average roughness Ra of 0.05 mm or less on the inner peripheral surface, and a center line of the outer peripheral surface. The method for producing a quartz glass preform for an optical fiber according to claim 3, wherein the average roughness Ra is 0.1 µm or less.