JPH111338A - Production of optical fiber base material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an optical fiber base material in good workability and in a good yield by uniformly controlling the temperature of a reaction oven main body, accumulating a clad portion on a starting core base material in the reaction oven and subsequently converting the obtained soot into sintered glass. SOLUTION: This method for producing an optical fiber base material comprises setting a core base material 3 welded to a dummy portion 11 in a reaction over main body 10, rotating the set core main material 3 with a rotation motor 7, charging oxygen gas, hydrogen gas and SiCl4 gas as a raw material into plural large oxyhydrogen flame burners 8 having large diameters, respectively, traversing the burners 8 in the longitudinal direction of the core base material 3 and simultaneously accumulating soot generated by the flame hydrolysis of the raw material gas. A jacket 1 for circulating a cooling medium is attached to the periphery of the reaction oven main body 10, and the cooling medium is circulated in the jacket. Thus, the temperature of a combustion gas is controlled at 50-120 deg.C to prevent the local thermal distortion of the reaction oven main body 10. The oxygen gas, hydrogen gas and the raw material gas can thereby be charged in large amounts, respectively, and the soot base material 4 can be accumulated at a high accumulation rate. The soot base material 4 is charged in a sintering oven and subsequently subjected to a dehydrative sintering glass- forming reaction to give an ingot in which foreign matters, bubbles, etc. are not recognized.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing an optical fiber preform having good workability and yield.

[0002]

2. Description of the Related Art When an optical fiber preform ingot is manufactured on the surface of a starting core preform by, for example, an OVD method (external attachment method), the preform becomes a preform ingot through processes such as dehydration and sintering. As a general method for improving the production rate in the step of depositing soot (porous glass base material) on the surface of the starting core base material by the OVD method, a glass raw material gas is supplied, and the raw material gas is hydrolyzed in an oxyhydrogen flame to produce SiO 2. There are methods of depositing the glass fine particles of No. ₂ , increasing the diameter of the burner, increasing the number of the burners, and increasing the supply amount of the raw material gas. In the method of increasing the supply amount by increasing the diameter of the burner for supplying the raw material gas, the adhesion of the glass particles is extremely poor at the initial stage of depositing soot on the surface of the starting core base material. Further, when a plurality of burners are used, there is interference of a flame, and the deposition efficiency is not improved as expected. In the method of increasing the number of burners, when the burners are moved in parallel and left and right with respect to the generally known starting core base material, defective parts are formed on the left and right ends of the deposited soot, which is a disadvantage of this method. Would. When high-speed deposition is performed by increasing the amount of source gas in order to improve productivity, the amount of heat generated as a result thereof causes a metal strain phenomenon as a heat load on the reaction furnace, and concavities and convexities on the inner surface of the reaction furnace are remarkably exhibited. When this unevenness increases over time,
Vibration occurs when the combustion gas expands due to heat generation. This vibration causes foreign matter and soot (silica powder) adhering to the inner surface of the reactor to be scattered and attached to the soot surface during deposition. When this soot is sintered and vitrified, bubbles are generated from foreign matter and soot as starting points. When this ingot is used as an optical fiber preform, the bubbles may affect the workability and yield in the processing step. Therefore, a reactor for depositing a clad portion by the OVD method has a great limitation on a material, a structure, a combustion gas amount, and the like, so that a deposition rate is limited, which hinders an increase in speed. Therefore, in order to dramatically increase the soot deposition rate in a method of manufacturing a glass preform for an optical fiber using the OVD method, it is necessary to solve these problems.

[0003]

The object of the present invention is to provide an OVD
In the method of manufacturing a glass preform for optical fiber using the method, when using a plurality of burners for depositing fine glass particles and increasing the amount of raw material gas to perform high-speed deposition, the surface of the soot is subjected to thermal distortion of the reactor. An object of the present invention is to produce a glass base material which prevents foreign substances and bubbles caused by vibrations caused by the above, and provides good workability and yield when processing the obtained ingot into an optical fiber preform.

[0004]

Means for Solving the Problems Conventionally, the OVD method of depositing glass fine particles on the surface of a starting core base material controls the amount of oxyhydrogen gas and the amount of raw material gas in the initial stage of deposition to reduce the flame, Fine soot has been obtained by making the fine particles easily adhere to the surface of the core base material, increasing the gas amount as the soot diameter increases, and increasing the deposition rate.
Therefore, as a result of examining a method of obtaining a glass base material that can be deposited at a higher speed and has good workability and yield when forming a preform for an optical fiber, the deformation due to the distortion due to the increase in the heat load due to the increase of the raw material gas is also considered. A method for synthesizing using a reaction furnace which does not cause quenching has been found. That is, the present invention provides a method of manufacturing an optical fiber preform by depositing a clad portion on a starting core preform in a reaction furnace by an external method and sintering the obtained soot to produce an optical fiber preform. It is characterized by controlling the temperature. Hereinafter, details of the present invention will be described.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION When synthesizing soot by the OVD method,
A source gas is supplied and deposited in an oxygen / hydrogen flame on the outer periphery of the starting core base material in the reactor. At that time, in order to synthesize a large soot at a higher speed, it is necessary to supply a large amount of oxygen and hydrogen, and this combustion heat greatly affects the reaction furnace. When silicon tetrachloride is used as a source gas, hydrochloric acid is generated as a reaction by-product. This combustion gas is discharged out of the system, but the remaining hydrochloric acid causes a problem that the reactor is corroded. Therefore, in general, the reactor is made of corrosion-resistant SUS material, etc., but if the thermal load increases with the high-speed synthesis, the reactor history will be distorted due to the heat history due to the heat cycle, and in the case of SUS material, Has a small thermal conductivity, so that phenomenon is remarkable. Therefore, the present invention can prevent the deformation and the like of the reactor by controlling the temperature of the reactor main body to a uniform temperature in order to reduce the thermal load of the reactor and to make the temperature distribution on the inner surface of the reactor uniform. . With these methods, it has become possible to synthesize an optical fiber preform soot free of foreign matter and bubbles at a high speed.

The present invention will be described below with reference to the drawings.
FIGS. 1A and 1B show an example of an optical fiber preform manufacturing apparatus used in the present invention. FIG. 1A is a side view, and FIG. 1B is a sectional view of FIG. . In the figure, 1 is a jacket for refrigerant circulation, 2 is a tapered portion of soot, 3 is a core base material, 4 is a soot base material, 5 is an oxyhydrogen flame burner, 6 is an exhaust hood, 7 is a rotation motor, and 8 is oxyhydrogen. A traverse (reciprocating motion) motor for the flame burner, 9 is a burner guide mechanism, 10 is a reactor main body, and 11 is a dummy part.

[0007] By providing the jacket 1 in the reactor 10 and circulating the refrigerant to uniformly cool the reactor body below the temperature of the combustion gas, local thermal distortion can be prevented. A conventionally known refrigerant may be used.

When the temperature of the reactor main body exceeds 120 ° C., its effect is diminished, and when it is lower than 50 ° C., hydrochloric acid as a reaction by-product condenses on the inner surface of the reactor at the initial stage of soot deposition, causing corrosion. It is preferable to control the temperature within a range of 50 ° C. or more and 120 ° C. or less.

A manufacturing apparatus having a jacket 1 for circulating a refrigerant around a reaction furnace 10 for performing a synthesis reaction by depositing glass fine particles on the surface of the starting core base material 3 is conventionally used. A plurality of burners 5 larger in diameter and larger than the burner are attached, and glass particles are deposited while traversing in the longitudinal direction of the core base material. In the present invention, a large amount of oxygen gas / hydrogen gas / source gas is supplied while the deposition proceeds, which could not be performed because the surface of the reactor was distorted (irregular) due to the heat generated by the combustion gas. The production of the soot 4 can be performed under the conditions.

[0010] The soot on which the target amount has been deposited is placed in a sintering furnace, and dehydrated and sintered to form an ingot. When this ingot was confirmed, no foreign matter or bubbles were found in the vitrified part, and it was no inferior to the ingot produced by the conventional manufacturing method, and the time required to synthesize an ingot of the same size was It can be reduced to about 1/2 of the law. When this ingot was processed into a preform for optical fiber of the desired diameter, no foreign matter or bubbles were observed, and the occurrence of defective parts in the conventionally attempted high-speed synthesis method was greatly improved. The property and yield can be obtained.

The above is a method in which the reactor is provided with a jacket and the coolant is circulated to uniformly cool the reactor main body. However, the present invention is not particularly limited to this method.
Any method can be used as long as the temperature of the reactor main body can be controlled to a uniform temperature.

[0012]

Next, examples of the present invention will be described. (Example) An apparatus for manufacturing an optical fiber preform shown in FIGS. 1A and 1B was prepared. The closed reactor body 10 has heat resistance
This is an optical fiber soot manufacturing apparatus made of austenitic stainless steel in consideration of corrosion resistance. Refrigerant adjusted to 50 ° C. was circulated through the jacket 1 from equipment (not shown) having a mechanism for controlling the temperature of the refrigerant. The starting core preform 3 is a quartz glass rod for the core whose refractive index has been adjusted for a single mode optical fiber having an outer diameter of 25 mm and a length of 1200 mm, which is welded to the quartz rod 11 for the dummy, and which is welded in the sealed reactor 10. It was attached to the rotation motor 7. The rotation motor 7 is rotated at 40 rpm while the refrigerant is circulated, and two oxyhydrogen flame burners 5 are supplied from a raw material supply device (not shown) as oxygen forming gas at 75 liter / min. The glass raw material gas, SiCl _4, 38 g / min was introduced along with 9 liter / min of oxygen gas as a carrier gas at a rate of 1 liter / min. The two burners are reciprocated in the longitudinal direction of the base material by the motor 8 at a speed of 150 mm / min within a range of 1600 mm, and the SiO ₂ glass fine particles generated by the flame hydrolysis of SiCl ₄ are deposited on the quartz glass 3 for the core. I let it. As the deposition proceeds, the raw material gas, oxygen gas,
After increasing the amount of hydrogen gas, a soot having an outer diameter of 230 mm was obtained 24 hours later. Immediately before the end of the deposition, 150 liters of oxygen gas as a flame forming gas was supplied from the raw material supply device to the burner 5.
300 l / min of hydrogen gas and 15 l / min of oxygen gas as a carrier gas
Supply SiCl ₄ to the burner at 80 g / min, average deposition rate 28 g
/ Min high-speed synthesis. The soot on which the target diameter of 230 mm was deposited was placed in a sintering furnace, and dehydrated and sintered into glass under ordinary post-process conditions to produce a transparent optical fiber preform ingot. Table 1 shows the result of visually confirming foreign matter and bubbles of the ingot. No foreign matter or bubbles were observed in the vitrified portion, which was inferior to the ingot obtained by the conventional deposition method. When this ingot was processed into a preform for an optical fiber having a desired diameter, no foreign matter or bubbles were observed. After the completion of the reaction, the inner surface of the reaction furnace was checked. As a result, the shape was unchanged from that before the reaction, and no irregularities were observed.

Further, the reaction was repeated under the above conditions, and the inner surface of the reactor was confirmed in the course of reaching 25 times, but no change in the shape was confirmed. Table 1 also shows the results of visually confirming foreign matter and bubbles of the ingots manufactured at the 10th and 25th times.
The bubbles in Table 1 had a diameter of 0.5 mm or more, and the foreign substances were other than bubbles.

[0014]

[Table 1]

Comparative Example A soot was synthesized using the same production apparatus and production gas conditions as in Example 1 except that the reactor did not have a jacket for cooling medium circulation. This soot was dehydrated and sintered into a glass in a sintering furnace in the same manner as in the example to produce a transparent optical fiber base material ingot. Table 1 also shows the results of visually confirming foreign matter, bubbles, and the like of the ingot. When this ingot was processed to a desired diameter and foreign matters and bubbles were confirmed, the presence thereof was clearly recognized, and much time was required for removing the portion, and the yield was reduced. After completion of the reaction, the inner surface of the reaction furnace was checked. As a result, the shape was slightly changed from that before the reaction, and slight irregularities were confirmed.

When the reaction is repeated under the above-mentioned conditions, this tendency becomes more conspicuous, and the foreign matter of the finished ingot is
Bubbles etc. increased. The reaction was repeated, and the results of visually confirming foreign substances and bubbles of the ingot produced at the tenth time are also shown in Table 1. At the tenth time, the reactor was significantly deteriorated, and the operation was abandoned. When the cause was investigated in the course of repeating the reaction, it was confirmed that once the reaction was completed, the inner surface shape of the reactor changed, and in particular, the position of the irregularities was shifted. Since the foreign matter and bubbles of the base material ingot correspond to the position of the portion having large irregularities, when the inner surface of the reaction furnace is deformed due to thermal strain, vibration occurs, and glass fine particles and foreign matter attached to the surface fall, It is presumed that it adheres to the soot surface during deposition. In order to suppress the deterioration of the reactor during the repetition of the reaction, no method was found other than reducing the supply amount of the raw material gas. From Table 1, it can be seen that the occurrence of defective portions and the like in the high-speed synthesis method according to the conventional method has been greatly improved in the example.

[0017]

According to the present invention, even when a large thermal load is generated in the reactor due to the high-speed synthesis of the optical fiber preform, deformation of the inner surface of the reactor due to thermal strain is prevented and foreign substances are prevented from being mixed. Thus, an optical fiber preform with reduced foreign matter and bubbles can be obtained. Thereby, when processing the optical fiber preform into a preform of a predetermined diameter, good workability and
Yield is obtained.

[Brief description of the drawings]

FIG. 1 is a schematic view of an apparatus for manufacturing an optical fiber preform used in the present invention, (a) is a side view thereof, and (b) is (a).
FIG.

[Explanation of symbols]

1 ‥‥‥ Refrigerant jacket 2 ‥‥‥ Soot taper 3 ‥‥‥ Core base material 4 ‥‥‥ Soot base material 5 ‥‥‥ Burner 6 ‥‥‥ Exhaust hood 7 ‥‥‥ Rotary motor 8 ‥モ ー タ Motor for burner traverse 9 ‥‥‥ Burner guide mechanism 10 ‥‥ Reactor body 11 ‥‥ Dummy part

Claims (3)

[Claims] 1. A method of manufacturing an optical fiber preform by depositing a clad portion on a starting core preform in a reactor by an external method and sintering the obtained soot to produce an optical fiber preform. A method for producing an optical fiber preform, comprising controlling the temperature. 2. The optical fiber mother according to claim 1, wherein a jacket is provided in the reactor to circulate a refrigerant, and the reactor body is uniformly cooled to a temperature equal to or lower than the temperature of the combustion gas to prevent local thermal distortion. The method of manufacturing the material. 3. The method for producing an optical fiber preform according to claim 1, wherein the temperature of the reactor main body is controlled within a range from 50 ° C. to 120 ° C.