JP2001106543A - Method for forming supporting rod for optical fiber preform and method for manufacturing and processing optical fiber preform - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form a supporting body for an optical fiber preform constituted by fusion splicing rod-like bodies of short-sized quartz glass discarded heretofore in such a manner that such supporting body may be recycled by eliminating internal strain and surface flaws. SOLUTION: The supporting body for the optical fiber preform is formed by arranging the short-sized rod-like bodies 1a and 1b of the circular shape in cross section consisting of a plurality of the quartz glass in a longitudinal direction, butting their respective end faces against each other, fusion splicing these end faces and subjecting the connected rod-like bodies to a heat treatment by successively firing the rod-like bodies in a longitudinal direction by an oxyhydrogen burner 2. The long-sized rod-like body 1 which is not connected is also subjected to the heat treatment by successively firing the same in the longitudinal direction by the oxyhydrogen burner 2, by which the internal strain and surface flaws are eliminated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a support rod for an optical fiber preform used in each production process of an optical fiber, and a method for producing and processing an optical fiber preform using the same.

[0002]

2. Description of the Related Art Optical fibers are mainly manufactured through soot, dehydration, sintering, drawing, flame polishing and wire drawing. First, in the sooting process, a raw material gas such as silicon tetrachloride and germanium tetrachloride and a fuel gas such as hydrogen and oxygen are supplied to a reaction burner arranged in the reaction furnace to generate glass fine particles by flame hydrolysis. Then, the glass fine particles are deposited on the tip of a seed rod arranged in the reaction furnace to form a glass fine particle laminate made of cylindrical porous glass.

In the next dehydration step, the glass fine particle laminate is heated in an atmosphere gas containing chlorine gas in a heating furnace to remove OH groups in the glass fine particle laminate. Thereafter, in the sintering step, the glass fine particle laminate is heated in a heating furnace to form a transparent glass body. Next, if necessary, in the stretching step, the above-mentioned transparent glass body is placed in a heating furnace and heated by a ring-shaped heater, or the above-mentioned transparent glass body is attached to a glass lathe and heated by an oxyhydrogen burner. In the meantime, the diameter is reduced by pulling in the longitudinal direction to obtain a transparent glass body having a uniform outer diameter. In some cases, the surface of the transparent glass body obtained by the sintering process is heated by an oxyhydrogen burner in a flame polishing process to remove scratches on the surface. A transparent glass body having a uniform outer diameter and having no scratches on the surface formed in this way is also called a preform.

[0004] In the drawing process, an optical fiber is obtained by heating and melting the end of the preform in a drawing furnace to draw out a glass having a small diameter. In addition, as an intermediate product in each of the above steps, there are a glass fine particle laminate made of porous glass, a transparent glass body, a preform, and the like, all of which may be called an optical fiber preform. In the present invention, unless otherwise specified,
The optical fiber preform means all the intermediate products of each of these steps.

[0005] Further, the optical fiber preform is supplied to a reaction furnace, a heating furnace,
When disposing in a furnace such as a drawing furnace or on a glass lathe, it is necessary to connect a support member to one or both ends of the optical fiber preform to support the optical fiber preform. It is referred to as an optical fiber preform support rod. The seed rod used in the soot forming step is also referred to as an optical fiber preform support rod in the present invention.

The arrangement relationship between the optical fiber preform and the support rod for the optical fiber preform will be described using an example of a sintering process. FIG. 2 is a longitudinal sectional view showing a main device in a sintering step. In FIG. 2, 7 is an optical fiber preform, 8 is a support rod for the optical fiber preform, 9 is a heating furnace, 10 is a mounting part, 11 is a lifting device, 12
Is a stand.

One end of an optical fiber preform support rod 8 is fusion-spliced to the upper end of the optical fiber preform 7, and the other end of the optical fiber preform support rod 8 is gripped by a chuck, a pin or the like of the mounting portion 10. Have been. If the mounting unit 10 is moved up and down by the elevating device 11 on the gantry 12, the optical fiber preform support rod 8 and the optical fiber preform 7 suspended by the mounting unit 10 can be moved up and down in accordance with that. The optical fiber preform 7 can be moved into and out of the heating furnace 9 from the upper opening of the furnace 9.

Further, a shutter having a hole through which only the optical fiber preform support rod 8 penetrates is provided at the upper opening of the heating furnace 9, and is closed after the optical fiber preform 7 enters. The optical fiber preform 7 is heated in an atmosphere of an inert gas or the like in a heating furnace 9, and the optical fiber preform 7 made of a laminated glass particle is turned into a transparent glass by heating, and the optical fiber preform made of a transparent glass body is heated. Processed into wood. In addition,
FIG. 2 shows an example of the sintering process. However, in other processes, the optical fiber preform is supported by being fused and spliced to one or both ends of the optical fiber preform. The members are arranged such that the longitudinal direction of the members is vertical or horizontal.

Further, the optical fiber preform placed in the heating furnace in each of the above-described steps or on a glass lathe or the like is heated to a temperature of several hundred degrees to several hundred degrees. At this time, the support rod for the optical fiber preform is heated to a temperature of several hundred degrees to several hundreds degrees by heating the preform of the optical fiber.Therefore, the support rod for the optical fiber preform is a rod-shaped body having a heat-resistant circular cross section such as quartz glass. Be composed. In addition, optical fiber preforms have recently been increasing in size,
Since a large one weighs 30 kg, a support rod for an optical fiber preform needs to have a diameter of about 50 mm.

The size of the support rod for the optical fiber preform varies depending on the size of the optical fiber preform and the type of processing step, but is usually about 15 mm to 50 mm in diameter and 200 mm in length.
A rod having a circular cross section of about 1 mm to 1400 mm is required. Accordingly, a quartz glass rod having a circular section with a length of 1200 mm to 1500 mm, which is longer than the required length according to their diameter, is prepared, and cut in accordance with the required length in each processing step. I'm using

The support rod for the optical fiber preform is not disposable each time the optical fiber preform is processed. Instead, the connecting portion between the support rod for the optical fiber preform and the optical fiber preform and the support for the optical fiber preform are used. Cut off the parts that caused deformation of the support rod,
The remaining portion of the support rod for the optical fiber preform is reused. However, since connection and disconnection of the optical fiber preform support rod and the optical fiber preform are repeated, the length of the optical fiber preform support rod becomes shorter each time. Further, the support rod for the optical fiber preform shorter than the required minimum length cannot be used and is discarded.

[0012]

When the surface of a support rod for an optical fiber preform has minute scratches, stress is concentrated and the damage is likely to start from the scratches. , May be damaged when subjected to stress.
Also, when strain remains inside the support rod for the optical fiber preform, there is a danger of breakage even with a slight external force, since the glass structure is constantly stressed at the location where the strain is concentrated, unlike other locations. is there. Further, when the support rod for the optical fiber preform is damaged, the optical fiber preform falls along with the damage, so that not only the optical fiber preform is damaged but also there is a problem in personal safety. Therefore, when the optical fiber preform support is transported, stored, or attached to the optical fiber preform, extreme care must be taken not to cause damage.

Further, since a glass rod made of quartz glass is expensive, it is necessary to study the reuse of a short rod which is shorter than the required minimum length as a support rod for an optical fiber preform and which is now discarded. Have been. Therefore, a plurality of short rods were fusion-spliced in the longitudinal direction to make them long, and the rods were experimentally used as support rods for optical fiber preforms. However, the support rod for the optical fiber preform was damaged during the processing step, and the processing could not be continued. In addition, an inspection of the broken portion of the support rod for the optical fiber preform revealed that a strain was generated in the vicinity of the fusion splicing portion and the portion was broken therefrom.

The present invention has been made through the process of studying the above-mentioned prior art, and a method of forming a support rod for an optical fiber preform that can be used with security and a method of manufacturing an optical fiber preform using the same. A processing method is provided.

[0015]

According to the present invention, there is provided an optical fiber preform support rod comprising a rod-shaped body made of quartz glass having a circular cross section, which is sequentially heated in a longitudinal direction with an oxyhydrogen burner to perform a heat treatment. It is a support rod for the base material. This heat treatment eliminates surface damage of the rod-shaped body and also eliminates internal distortion, so that the rod-shaped body can be safely used as a support rod for an optical fiber preform.

Further, when the rod is burned with an oxyhydrogen burner, glass rods serving as grippers are fusion-bonded to both ends of the rod, and the rods including the grips are successively longitudinally moved with an oxyhydrogen burner. By roasting and then cutting and removing the gripping body, almost the entire length of the rod-shaped body can be used as a support rod for an optical fiber preform.

Furthermore, a plurality of rod-shaped rods each having a circular cross section made of quartz glass are arranged in the longitudinal direction, their ends are butt-butted and fusion-bonded, and the connected rod-shaped rods are lengthened with an oxyhydrogen burner. If a long rod is made by performing heat treatment by sequentially baking in the direction, a short rod that has been conventionally discarded without being used can be regenerated as a support rod for an optical fiber preform without discarding. .

Further, the support rod for the optical fiber preform prepared as described above is fusion-bonded to one or both ends of the optical fiber preform to form a support member, or as a seed rod in a soot attaching step. If used, the optical fiber preform can be safely manufactured without being damaged during use.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a view for explaining an embodiment of a method for producing a support rod for an optical fiber preform according to the present invention. FIG. 1 (A) shows two rod-like members connected. 1 (B) is a side view showing a rod-like body connected according to FIG. 1 (A) being burned with an oxyhydrogen burner, and FIG. 1 (C) is a rod-like body without connection. It is a side view which shows the place where is burned with the oxyhydrogen burner. In FIG. 1, 1, 1a and 1b are rods, 2 is an oxyhydrogen burner, 3 is a joint surface, 4 is a strain, 5 is a surface flaw, and 6a and 6b are chucks.

When connecting rods having a circular cross section made of quartz glass and shortened by use as a support rod for an optical fiber preform, first, as shown in FIG. Is gripped by the chucks 6a and 6b, and is rotated around an axis while the rod-shaped body 1a is held.
And 1b are pressed against each other with their end faces facing each other.
Then, it is heated by the flame of the oxyhydrogen burner 2 along the end face. Then, the quartz glass in the vicinity of the end face is melted and joined to each other, and integrated by a surface tension as a long rod having a circular cross section.

At this time, since the vicinity of the bonding surface 3 is heated, and the portion farther from the bonding surface 3 is not heated, distortion 4 is generated inside the glass at the boundary of the heating as shown in FIG. 1B. is there. Whether or not distortion has occurred is determined by the rod-shaped body 1
It can be easily understood by observing a or 1b from the side through a polarizing plate.

Next, as shown in FIG. 1B, while the rods 1a and 1b connected by the rotation of the chucks 6a and 6b are rotated around the central axis, the acid is applied from one end to the other end. While moving the hydrogen burner in one direction at a constant speed, the connected rods 1a and 1b are sequentially burned with an oxyhydrogen burner. The flow rate of the gas supplied to the oxyhydrogen burner and the moving speed of the oxyhydrogen burner are set to such an extent that the rod is not deformed and is sufficiently heated.

For example, rods 1a, 1b having a diameter of 36 mm
In the case of, the hydrogen gas is supplied to the oxyhydrogen burner 2 from 190 SLM to 2
50 SLM, oxygen gas is supplied at 50 SLM to 150 SLM and burned, and the oxyhydrogen burner is moved at a constant speed of 40 mm / min to 95 mm / min in one direction in the longitudinal direction of the rod to sequentially roast the rods 1a and 1b. In this case, a necessary and sufficient heat treatment can be performed. Note that “SLM” is a gas flow rate unit, and indicates a flow rate (liter unit) per minute of a gas in a standard state (0 ° C., 1 atm).

Through such a heating process, even if a portion where distortion occurs inside the glass of the rod-shaped body after the connection and before the heating is recognized, the distortion of the inside of the glass due to the heating is reduced. The glass composition is homogenized and distortion is eliminated.

Actually, two or three short rods made of quartz glass having a diameter of 36 mm were fusion-spliced in the longitudinal direction, and 50 long rods having a length of 500 mm to 1400 mm were prepared. Then, the long rod was heat-treated under the following conditions. Hydrogen gas 200 SLM for oxyhydrogen burner
Was burned by supplying 110 SLM of oxygen gas, the oxyhydrogen burner was moved in the longitudinal direction at a speed of 80 mm / min, and the long rods were sequentially burned in the longitudinal direction to perform heat treatment.

The elongated rod after the heat treatment was observed through a polarizing plate, but no distortion was found inside the glass. Therefore, these long rods are used as a support for the optical fiber preform in the stretching step, and one at each end of the optical fiber preform made of a transparent glass body prepared for performing the stretching step. Splicing was performed and stretching was performed. A total of 25 optical fiber preforms were stretched, but there was no breakage of the optical fiber preform support rod in the middle, and the stretching operation could be performed safely.

Further, the following strength test was carried out to examine how much the strength of the rod was improved by the heat treatment. FIG. 3 is a perspective view for explaining a strength test of a rod-shaped body, where reference numeral 13 denotes a connected long rod-shaped body, 13a, 13
b is a short rod, 14 is a joint surface, 15a and 15b are holding members, and 16 is a steel ball. The end faces of the short rods 13a and 13b each having a diameter of 36 mm were butted and welded to each other to form a long rod 13, and a comparison was made between those subjected to heat treatment and those not subjected to heat treatment. The conditions of the heat treatment were the same as those in the above-mentioned 50 experiments.

In the strength test, the holding members 15a and 15a
The interval L of 5b was set to 200 mm, and the long rod 13 was horizontally held by the holding members 15a and 15b with the joint surface 14 at the center. Then, a steel ball having a weight of 108 g was dropped from the portion having a height H above the joint surface 14 toward the joint surface 14, and the height H at which the long rod 13 was broken was examined. As a result, the heat-treated product had a height H at the time of destruction of 700 mm.
However, those without heat treatment had a height H at the time of breakage of 500 mm, and those with heat treatment were confirmed to have improved strength. When the connection was just made, an internal strain was observed in the vicinity of the bonding surface 14 when observed with a polarizing plate, but no internal distortion was found after the heat treatment.

Further, instead of connecting the short rods to form a long one, a long rod stored as originally prepared may be used depending on the storage state and the heat history. The surface may be scratched or the inside may be distorted. The presence or absence of distortion can be confirmed by checking the internal distortion through a polarizing plate, but the surface flaw may not be found visually. Therefore, even in the case of a long rod-shaped body having no connection, the rod-shaped body 1 is sequentially moved in the longitudinal direction by the oxyhydrogen burner 2 as shown in FIG. It is desirable to perform a heat treatment by roasting. Thereby, even if there is a surface flaw 5 or internal strain 4 of the rod-shaped body 1, the surface flaw 5 and the strain 4 are removed by the heat treatment, so that the rod 1 can be used as a support rod for the optical fiber preform with ease. Can be used.

In the heat treatment of the rod, the ends of the rod are usually held by chucks 6a and 6a as shown in FIG.
Hold with b. For this reason, uniform heat treatment cannot be performed in the vicinity of both ends of the rod-shaped body, and it is necessary to cut and remove the vicinity of both ends, resulting in loss. Therefore, a glass rod serving as a holding body is fusion-spliced to both ends of the rod to be subjected to the heat treatment, heat treatment is performed including the holding body, and then the holding bodies on both sides are cut and removed. Since it is possible to carry out a uniform heat treatment for almost the entire length, it is possible to reduce a portion to be cut and discarded, and it is economical.

When the rod is sequentially roasted in the longitudinal direction with an oxyhydrogen burner, the rod is usually roasted while moving the oxyhydrogen burner in one direction at a constant speed, but the position of the oxyhydrogen burner is fixed. Alternatively, the bar may be moved. Further, the same rod-shaped body can be subjected to the heat treatment a plurality of times.

In attaching the optical fiber preform support made of a rod-shaped body to the optical fiber preform, the two end faces of the two are butted and fused. At this time, the vicinity of the fusion spliced portion of the support for the optical fiber preform is heated and undergoes a heat history, but the optical fiber preform contains a dopant and the like, and the heating temperature at that time depends on the support for the optical fiber preform. Since it is not higher than the case where the rod-shaped bodies are connected to each other, this heat history does not cause distortion such as damage to the inside of the support for the optical fiber preform.

[0033]

The support rod for an optical fiber preform according to the present invention is obtained by heat-treating the rod-shaped body by sequentially burning it in the longitudinal direction with an oxyhydrogen burner. Distortion is eliminated, and it can be used as a support rod for an optical fiber preform with ease. In addition, a plurality of short rods are arranged in the longitudinal direction, their ends are butt-butted and fusion-bonded, and the connected rods are sequentially heated in the longitudinal direction with an oxyhydrogen burner to perform a heat treatment. If a long rod is used, the short rod that has been conventionally discarded without being used can be regenerated as an optical fiber preform support rod without being discarded.

Further, when the rod is roasted with an oxyhydrogen burner, glass rods to be gripped are fusion-bonded to both ends of the rod, and the rod including the grip is sequentially roasted in a longitudinal direction with an oxyhydrogen burner. If the gripping body is cut and removed thereafter, almost the entire length of the rod-shaped body can be used as a support rod for an optical fiber preform, which is economical.

[Brief description of the drawings]

1A and 1B are diagrams illustrating an embodiment of a method for producing a support rod for an optical fiber preform according to the present invention, wherein FIG. 1A is a side view illustrating a state where two rods are connected, (B)
FIG. 2 is a side view showing a rod-like body connected according to FIG. 1 (A) being roasted with an oxyhydrogen burner, and FIG. 1 (C) is a side view showing a rod-like body without connection being roasted with an oxyhydrogen burner.

FIG. 2 is a longitudinal sectional view showing a main device in a sintering step.

FIG. 3 is a perspective view illustrating a strength test of a rod.

[Explanation of symbols]

 1, 1a, 1b: rod-shaped body 2: oxyhydrogen burner 3: joint surface 4: strain 5: surface scratch 6a, 6b: chuck 7: optical fiber preform 8: support rod for optical fiber preform 9: heating furnace 10: Mounting part 11: lifting device 12: gantry 13: long rod 13a, 13b: short rod 14: joining surface 15a, 15b: holding member 16: steel ball

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Hidenori Hirata 1 Tayacho, Sakae-ku, Yokohama-shi, Kanagawa Prefecture Sumitomo Electric Industries, Ltd. Yokohama Works (72) Inventor Kazumasa Saito 1-Tagamachi, Sakae-ku, Yokohama-shi, Kanagawa Prefecture Sumitomo Inside Electric Machinery Yokohama Works (72) Inventor Tetsu Kanazawa 1st place, Tayacho, Sakae-ku, Yokohama-shi, Kanagawa Prefecture Sumitomo Electric Industries Ltd. Inside Yokohama Works (72) Tadahiko Endo 1st place, Tayacho, Sakae-ku, Yokohama-shi, Kanagawa Prefecture Sumitomo (72) Inventor Yuji Kakeda 1-chome, Taya-machi, Sakae-ku, Yokohama-shi, Kanagawa Prefecture F-term (reference) in Yokohama Works, Sumitomo Electric Industries, Ltd. 4G015 BA02 BA05 4G021 BA00

Claims (5)

[Claims] 1. A method for producing a support rod for an optical fiber preform, wherein a rod-shaped body made of quartz glass having a circular cross section is heat-treated by sequentially burning in a longitudinal direction with an oxyhydrogen burner. 2. A glass rod serving as a holding body is fusion-spliced to both ends of a rod-shaped body made of quartz glass having a circular cross section, and the rod-shaped body including the holding body is sequentially roasted in a longitudinal direction with an oxyhydrogen burner. A method for producing a support rod for an optical fiber preform, which comprises performing a heat treatment, and thereafter cutting and removing the gripping body portion. 3. A rod-shaped body made of a plurality of quartz glass and having a circular cross section is arranged in the longitudinal direction, the end faces thereof are butted and fusion-bonded, and the connected rod-like body is longitudinally moved by an oxyhydrogen burner. A method for producing a support rod for an optical fiber preform, characterized in that a heat treatment is performed by sequentially baking. 4. An optical fiber preform comprising a support rod for an optical fiber preform made of quartz glass which has been subjected to heat treatment by burning with an oxyhydrogen burner to one or both ends of the optical fiber preform. An optical fiber preform processing method, wherein the optical fiber preform is processed while the preform is supported by the optical fiber preform support rod. 5. A support rod for an optical fiber preform made of quartz glass which has been subjected to heat treatment by burning with an oxyhydrogen burner is disposed in a reaction furnace, and a raw material gas and a raw material gas are supplied to the reaction burner disposed in the reaction furnace. The glass fine particles are deposited on the tip of the support rod for the optical fiber preform while supplying the combustion gas to generate the glass fine particles by flame hydrolysis, thereby producing an optical fiber preform composed of a glass fine particle deposit. A method for producing an optical fiber preform, comprising: