JP2003020243A - Method for manufacturing ingot of optical fiber preform - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing an ingot of an optical fiber preform so that a clad layer can be fast deposited without requiring a large- scale facility for treating waste gas, that the ingot of the optical fiber preform obtained by vitrifying the clad layer does not contain foreign matter or bubbles and that, when the ingot is stretched into a preform, a glass preform for an optical fiber having excellent optical characteristics can be obtained with a high yield. SOLUTION: In the method for manufacturing the ingot of the optical fiber preform by the outside vapor-phase deposition method by depositing glass fine particles on a start core preform 1 to form a clad layer and sintering and vitrifying the obtained soot deposit 9, silica powder is dispersed in a solvent and sprayed. Immediately after the silica powder deposits on the surface of the start core preform 1, heat energy necessary to volatilize the solvent is supplied.

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 an optical fiber base material ingot (hereinafter simply referred to as a base material ingot) capable of depositing a clad layer on a starting core base material at high speed and having good optical characteristics. Regarding

[0002]

2. Description of the Related Art A base material ingot is manufactured by, for example, the OVD method.
By the (external method), glass fine particles are formed on the peripheral surface of the starting core base material
After (silica powder) is deposited to form a clad layer, it is made into vitrified through processes such as dehydration and sintering. In the step of depositing silica powder on the surface of the starting core base material by the OVD method, a generally known method is to supply a raw material gas and hydrolyze it in an oxyhydrogen flame to deposit the generated silica powder. Is the way.

In recent years, there has been a demand for a larger glass base material for optical fibers. However, in order to synthesize a large soot deposit (porous glass base material) at higher speed,
It is necessary to supply a large amount of oxygen and hydrogen, and this heat of combustion has a great adverse effect on the reactor. Further, when SiCl ₄ is used as the raw material gas, HCl gas is produced as a reaction by-product, and the exhaust gas contains a large amount of HCl gas.
This exhaust gas is discharged to the outside of the reaction system, but the remaining HCl
Corrodes the reactor.

In particular, for exhaust gas treatment, since the combustion exhaust gas is a high temperature and is an acidic gas containing silica powder not deposited on the clad layer, a large-scale facility for removing silica powder and HCl was required. Further, since HCl having a dew point or lower corrodes most metal materials, improving durability of exhaust gas treatment equipment has been a serious problem. Therefore, in order to manufacture a large glass base material for an optical fiber by using the OVD method, it is necessary to improve productivity as well as durability of equipment, which solves the above problems. Had to do.

From the viewpoint of the chemical reaction theory of silicon, when considering a reactor using SiCl ₄ as a raw material, control of the purity of the raw material is an important issue. For example, cost-effective Si
(CH ₃₎ Cl ₃ or Si (CH _{3) 2} Cl _2, in addition to corresponding to the hazardous materials fourth class, since reaction rate is slow compared with SiCl _4, the reaction distance from the burner to the starting core preform However, the physical properties of the deposited clad layer are significantly different from each other. Therefore, the reactor / exhaust gas treatment facility for depositing the cladding layer by the external method is greatly restricted by the material, structure, amount of gas to be burned, and the like. Therefore, there is a limit to the deposition rate and the like, which hinders high-speed deposition and cost reduction.

[0006]

Therefore, an object of the present invention is to provide a base material ingot which does not require a large-scale exhaust gas treatment facility and can deposit a clad layer at a high speed and which is obtained by vitrifying the clad layer. It is to provide a method for producing a base material ingot, which is free from foreign matter, bubbles, etc., and when it is drawn into a preform to obtain a glass base material for an optical fiber having excellent optical characteristics with a high yield. .

[0007]

The method for manufacturing a base material ingot according to the present invention is to deposit glass fine particles on a starting core base material by an external attachment method to form a clad layer, and sinter the obtained soot deposit body. Then, in the method of producing a base material ingot by transparent vitrification, silica powder is dispersed and sprayed in a solvent, immediately after the silica powder is attached to the surface of the starting core base material,
It is characterized by supplying the thermal energy necessary for the solvent to volatilize.

The above silica powder is composed of SiCl ₄ , Si (CH ₃ )
It is preferable to use a silane compound synthesized by flame hydrolysis reaction such as Cl ₃ and Si (CH ₃ ) ₂ Cl ₂ . When the silica powder is dispersed and sprayed in a solvent, it is preferable to supply the silica powder and the thermal energy by different supply means, and the solvent in which the silica powder is dispersed is preferably water. Also, the oxyhydrogen flame is good as the thermal energy to be supplied, and the amount of hydrogen of the thermal energy source supplied to volatilize the solvent is
It is preferably 1 mol or more with respect to 100 parts by weight of the solvent. The base material ingot of the present invention is manufactured using the above manufacturing method.

[0009]

DETAILED DESCRIPTION OF THE INVENTION As a result of diligent study of the above problems, the present inventor has found a method for producing a base material ingot by spraying and depositing silica powder dispersed in a solvent on the surface of a starting core base material. I paid attention. However, it was found that the solvent remained in the deposited clad layer, and when it was attempted to be removed after completion of the deposition, a new problem of cracking occurred. In order to solve this, it was found that it is necessary to volatilize the sprayed silica powder so that it does not contain a solvent immediately after it is attached to the surface of the starting core base material, and the present invention has been accomplished.

In the present invention, in order to deposit the glass fine particles on the surface of the starting core base material, silica powder is dispersed in a solvent and sprayed under pressure with compressed air using a spray nozzle used for coating or the like. Immediately after the sprayed silica powder adheres to the surface of the starting core base material, the deposition container (reaction container) is preheated in order to prevent the solvent from being contained. It is recommended that the solvent be easily volatilized in the exhaust gas. In addition, the solvent in which the silica powder is dispersed may be heated to a temperature near its boiling point so that the solvent is easily vaporized after spraying. As the solvent, water is preferable, and other nonflammable solvents can be used.

However, as the deposition progresses,
Water, which is the solvent, is less likely to volatilize, and a soot deposit that has been deposited in a target amount may crack during storage, which may cause a defect. In order to prevent the occurrence of cracks, the heat energy necessary for the solvent water to evaporate, that is, the heat energy equivalent to the latent heat of vaporization of the spray amount is supplied,
Volatilize so that water does not remain in the soot deposit. This heat energy is good for an oxyhydrogen flame, and the amount of hydrogen supplied is preferably 1 mol or more per 100 parts by weight of the solvent.
If the amount of hydrogen is less than 1 mol, the heat energy will be insufficient and the water cannot be sufficiently volatilized.

[0012] The soot deposit body, which has been deposited with the target amount as described above, is placed in a sintering furnace, dehydrated and sintered, and made into transparent vitrified material, and the obtained base material ingot is inspected.
No foreign matter or bubbles were found in the vitrified part, which was comparable in quality to that obtained by the conventional manufacturing method.
Whereas the conventional method contains a large amount of HCl gas in the exhaust gas, the manufacturing method of the present invention does not contain HCl gas at all in the exhaust gas. Further, when the ingot is processed to have a desired diameter, foreign matters and bubbles are not seen, the complicated exhaust gas treatment step conventionally required is eliminated, and the trouble occurrence of the equipment is significantly improved.

Further, according to the manufacturing method of the present invention, the silica powder is Si synthesized by reacting metallic silicon with MeCl.
Crude silanes such as (CH ₃ ) Cl ₃ and Si (CH ₃ ) ₂ Cl ₂ can be rapidly synthesized by a hydrolysis reaction with an oxyhydrogen flame without purification using a dedicated silica synthesis facility. According to this method, the generated silica can be collected almost completely. Further, since the generated HCl gas has a high concentration, it can be efficiently collected and reused, so that silica powder can be synthesized in a closed system and a manufacturing system having a small influence on the environment can be constructed.

The silica powder thus synthesized is dispersed in a solvent and sprayed to deposit the silica powder on the surface of the starting core base material to form a clad layer. At this time, cracks caused by the solvent remaining in the soot are improved by adding thermal energy in an amount equivalent to the latent heat of vaporization of the solvent, and high-speed synthesis of the soot deposit is possible. A base material ingot that does not contain foreign matter or bubbles can be obtained.

[0015]

[Example] (Preparation of raw material solution) SiC as a starting material
Using a crudely purified silane mixture consisting of 1, ₄ , Si (CH ₃ ) Cl ₃ , Si (CH ₃ ) ₂ Cl _2, etc., using a dedicated burner for producing silica powder, hydrolysis in an oxyhydrogen flame was performed. By the decomposition reaction,
A silica powder having a bulk density of 0.098 was synthesized. This silica powder synthesizing method can produce silica powder at a rate of several tens to several hundreds of times compared with the amount synthesized by the conventional method for producing a porous glass preform by an external method. Further, since the exhaust gas is the minimum necessary amount, the generated HCl gas can also be efficiently recovered, and the exhaust gas treatment facility can be handled on an extremely efficient scale. Next, 80 parts by weight of the silica powder was uniformly dispersed in 100 parts by weight of pure water to prepare a raw material solution.

(Embodiment 1) FIG. 1 is an example of a closed type manufacturing apparatus for a porous glass base material (soot deposit) used in this embodiment, and FIG. 2 is a manufacturing apparatus shown in FIG. It is a schematic side view of. First, outer diameter 25mmφ, length 1200m
A quartz glass starting core base material 1 whose refractive index is adjusted for a single mode optical fiber of m is welded with a quartz glass dummy rod 2, and this is placed in a heating medium circulating jacket 3. Attached to the rotating mechanism 4 of the core base material 1, 40
Rotated at rpm. In addition, in the jacket 3, a heat medium whose temperature was adjusted to 140 ° C. by a heat medium supply device having a temperature control mechanism, for example, air was circulated.

Next, two spray nozzles set at 180 mm intervals so that they can freely reciprocate along the guide mechanism 5.
(Made by Fuyo Seiki, Lumina spray gun PR-30-1.0) 6
In addition, from the raw material supply device (not shown), the previously prepared raw material solution was supplied at 120 g / min while maintaining the temperature at 95 ° C.
It was atomized with 5 Mpa N ₂ gas. At the same time, the heating burner 7 that operates in synchronization with the spray nozzle 6 is supplied with H ₂ 27 L / min and O ₂ 1.
5 L / min was supplied and the soot deposition surface was heated by this oxyhydrogen flame to volatilize water as a solvent.

The spray nozzle 6 rotates the traverse motor 8 at a speed of 200 mm / min to reciprocate along a guide mechanism 5 in a range of 1600 mm, so that silica powder is deposited on the peripheral surface of the rotating starting core base material 1. Deposited. In order to discharge the silica powder that did not adhere to the starting core base material 1 or the soot deposit 9 out of the system, air adjusted to 140 ° C. by the air heater 11 equipped with a temperature control mechanism was supplied into the jacket 3. .

As the deposition progresses, the amount of water in the soot deposit is approximately calculated from the diameter and weight of the soot deposit while controlling the temperature and amount of air to be supplied by the computer while further increasing the amount of the raw material solution. Then, after 28 hours, a soot deposit having an outer diameter of 220 mmφ was obtained. Immediately before the completion of the deposition, a raw material supply device supplied a raw material solution at a rate of 150 g / min to perform high-speed deposition at an average deposition rate of 26 g / min. During this time,
H ₂ 34 L / min and O ₂ 19 L / min were supplied to the heating burner, the soot deposition surface was heated by the generated oxyhydrogen flame, and deposition was performed while volatilizing the solvent. It should be noted that it is effective that the amount of oxygen / hydrogen supplied is such that a calorific value approximately equal to the latent heat of vaporization of pure water as a solvent is generated.

The soot deposit obtained by depositing the target amount is 48
No change was observed on the surface even after standing for hr, and when the base material ingot was placed in a sintering furnace and dehydrated / sintered to form a transparent vitrified base material, no foreign matter or bubbles were found in the vitrified part. The quality was not inferior to that obtained by the conventional manufacturing method. In addition, important problems such as acidic exhaust gas treatment and corrosion of equipment have been greatly improved.

(Comparative Example 1) FIG. 3 is a schematic front view of a closed type manufacturing apparatus for a porous glass base material (soot deposit) used in this comparative example. First, outer diameter 25mmφ, length 1200
A dummy rod 22 made of quartz glass is welded to a starting core base material 21 made of quartz glass whose refractive index is adjusted for a mm single mode optical fiber, and this is used as a heating medium circulating jacket 23.
It was attached to the rotating mechanism 24 of the starting core base material 21 installed in the above and was rotated at 40 rpm. The jacket 23
There is a heating medium supply device with a temperature control mechanism
The heating medium whose temperature was adjusted to 0 ° C. was circulated.

Next, two spray nozzles (made by Fuyo Seiki, Lumina Spray Gun PR-30-1.0) set at 180 mm intervals so that they can freely reciprocate along the guide mechanism 25.
6. While keeping the raw material solution prepared above at 95 ° C,
It was supplied at a rate of 0 g / min and sprayed with 0.35 Mpa of N ₂ gas.

The spray nozzle 26 is connected to the traverse motor 2
8 was rotated at a speed of 200 mm / min to reciprocate in a range of 1600 mm along the guide mechanism 25, and silica powder was deposited from the spray nozzle 26 on the peripheral surface of the rotating starting core base material 21. In order to discharge the silica powder that did not adhere to the starting core base material 21 or the soot deposit 29 to the outside of the system, air adjusted to 140 ° C. was supplied into the jacket 23 by an air heater equipped with a temperature control mechanism.

As the deposition progressed, the amount of the raw material solution was further increased, and after 28 hours, a soot deposit having an outer diameter of 220 mmφ was obtained. Immediately before the end of deposition, 15
A raw material solution of 0 g / min was supplied, and high-speed deposition was performed at an average deposition rate of 26 g / min.

Dehydrate the soot deposit obtained by depositing the target amount
It was found that when the sintered and transparent vitrified base material ingot was stored for the next step, a defect that cracks were formed on the surface of the soot deposit body. It was also found that this tendency became more prominent as the finished outer diameter of the soot stack increased (see Table 1). Table 1 shows the defect occurrence states of the soot deposits obtained in Examples 1 and Comparative Example 1 and the measurement results of the optical characteristics of the base material ingots that were dehydrated and sintered to be vitrified.

[0026]

[Table 1]

As can be seen from Table 1, even if the base material ingot of Example 1 has a large outer diameter, cracks do not occur during storage as in Comparative Example 1 and the optical characteristics are comparable. It was In Table 1, the foreign matter in the appearance column is the number of things other than bubbles, and the number of bubbles is 0.5 mmφ or more. The crack generation status column shows changes over time, and the optical property column measures optical properties of an optical fiber obtained by drawing a base material ingot. In addition, in Example 1, the average value of 10 base material ingots was compared with Comparative Example 1
Indicates the average value of 10 base material ingots excluding cracked products.

[0028]

According to the present invention, the silica powder can be deposited at a high speed by spraying the solution in which the silica powder is dispersed in the solvent on the peripheral surface of the starting core base material, and at the same time, the silica powder is supplied. By supplying the thermal energy corresponding to the latent heat of vaporization of the solvent, the soot deposit can be prevented from cracking during the deposition process, and the soot deposit does not crack during storage after the target amount is deposited. The base material ingot, which is obtained by sintering this into a transparent glass, has a quality comparable to that of a product manufactured by a conventional method, has few foreign matters and bubbles, and has excellent optical characteristics. Further, since the manufacturing facility does not need to flame-hydrolyze the raw material gas such as SiCl ₄ , it is not necessary to consider heat resistance, acid resistance, etc., and in addition, a complicated gas control system as in the past is not required. . Furthermore, exhaust gas treatment that affects the environment can be sufficiently achieved with a small-scale device. As described above, according to the present invention, a large-sized base material ingot can be manufactured at high speed and in an environment-friendly manner.

[Brief description of drawings]

FIG. 1 is a schematic front view of a porous glass base material (soot deposit body) manufacturing apparatus used in Example 1.

FIG. 2 is a schematic side view of the manufacturing apparatus shown in FIG.

FIG. 3 is a schematic front view of a porous glass base material (soot deposit body) manufacturing apparatus used in Comparative Example 1.

[Explanation of symbols]

1,21. Starting core matrix, 2,22. Dummy stick, 3,23. Jacket for circulating heat medium, 4, 24. Rotation mechanism, 5,25. Guide mechanism, 6,26. Spray nozzle, 7. Heating burner, 8, 28. Motor for traverse, 9, 29. Soot deposit, 10, 30. Exhaust hood, 11, 31. Air heater.

Claims (7)

[Claims] 1. A method for producing an optical fiber preform ingot by depositing glass fine particles on a starting core preform by an external attachment method to form a clad layer, and sintering the obtained soot deposit to form transparent vitrification. , An optical fiber preform, characterized in that silica powder is dispersed in a solvent and sprayed, and immediately after the silica powder adheres to the surface of the starting core preform, the thermal energy necessary for the solvent to volatilize is supplied. Ingot manufacturing method. 2. Silica powder is SiCl_Four, Si (CH₃) Cl
₃And Si (CH₃)₂Cl ₂Silane compounds such as
The optical fiber according to claim 1, which is synthesized by a desolvation reaction.
Manufacturing method of base metal ingot. 3. The method for producing an optical fiber preform ingot according to claim 1, wherein when the silica powder is dispersed in a solvent and sprayed, the silica powder and the thermal energy are supplied by different supply means. 4. The method for producing an optical fiber preform ingot according to claim 1, wherein the solvent in which the silica powder is dispersed is water. 5. The method for producing an optical fiber preform ingot according to claim 1, wherein the thermal energy supplied is an oxyhydrogen flame. 6. The optical fiber preform ingot according to claim 1, wherein the amount of hydrogen of the thermal energy source supplied for volatilizing the solvent is 1 mol or more per 100 parts by weight of the solvent. Production method. 7. An optical fiber preform ingot manufactured by using the manufacturing method according to any one of claims 1 to 6.