JP2003313043A - Method for manufacturing porous preform for optical fiber and burner device for manufacture of optical fiber porous preform - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a porous preform for an optical fiber to improve the deposition efficiency of glass soot by controlling the flow rate of gaseous starting material for glass and additive gas jetted from a jet port of a burner during depositing and by controlling the flow rate ratio of the gaseous starting material for glass to the additive gas to an optimum state, and to provide a burner device for manufacture of an optical fiber porous preform. <P>SOLUTION: The flow velocity of the gaseous mixture of the gaseous starting material for glass and the additive gas jetted from a first jet port 21 or a second jet port 22 of a burner 10 is changed once or more during depositing the glass soot. The total flow rate V1 l/min of the gaseous starting material for glass and the total flow rate V2 l/mini of the additive gas jetted from the two jet ports are controlled to satisfy the relation of 0.25≤Rb/Rf≤4.0, where Rb=V1/V2 in the initial stage of deposition of the glass soot and Rf=V1/V2 in the terminating stage of deposition of the glass soot. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical fiber porous material applied to an external attachment method in which glass raw material gas is reacted in an oxyhydrogen flame to produce glass fine particles, which are deposited on the outer peripheral portion of a starting member. The present invention relates to a method for manufacturing a base material and a burner device for manufacturing a porous base material for an optical fiber.

[0002]

2. Description of the Related Art As one of the methods for producing an optical fiber preform, a glass raw material gas is ejected from a burner together with an additive gas, a flammable gas and a combustion supporting gas, and the glass raw material gas is hydrolyzed in a flame. To generate glass fine particles (soot), and deposit the glass fine particles on the outer peripheral portion of the cylindrical starting member having the glass material serving as the core to form a porous layer composed of a plurality of layers, thereby forming a porous layer for an optical fiber. An external method (OVD method, Outside Vapor Phas) that obtains a high quality base material, dewaters it in an electric furnace, and sinters it into transparent glass to obtain an optical fiber base material.
e Deposition).

[0003]

In recent years, the demand for optical fibers has been increasing year by year with the increasing demand for high-speed communication. Therefore, it is desired to reduce the price of the optical fiber. Therefore, in order to respond to such requests,
There is a need to speed up the production of optical fibers to shorten the production time, to produce a large number of optical fibers at a time, and to reduce the production cost. In order to realize this, it is necessary to upsize the optical fiber preform used for spinning the optical fiber.

In the external attachment method, in order to shorten the manufacturing time of the porous preform for optical fibers, for example, the flow rate of the glass raw material gas used for producing glass fine particles is increased to increase the deposition rate of glass fine particles. There is a way to speed it up. However, even if the flow rate of the glass raw material gas is simply increased, it is not always possible to produce a large-sized optical fiber preform in a short time. This is because in order to produce a large-sized optical fiber preform in a short time, it is necessary to increase the flow rate of the glass raw material gas to increase the deposition rate of the glass particles and at the same time to enhance the deposition efficiency of the glass particles. is there. Here, the deposition efficiency of the glass particles is the total amount of the glass particles deposited on the surface of the starting member with respect to the total amount of the glass particles when it is assumed that all the glass raw material gases used have been changed into the glass particles by the chemical reaction. It is defined as a ratio. Further, the deposition rate is represented by the weight of the glass particles deposited on the surface of the starting member per unit time.

Generally, when the outer diameter of a starting member for depositing glass particles or a porous preform for optical fibers (hereinafter, referred to as "target member") during deposition of glass particles is small, a glass raw material gas and addition are added. Increasing the flow rate of the mixed gas of gases is effective in improving the deposition efficiency of glass particles. This is because when the outer diameter of the target member is small,
This is because the deposition efficiency is improved by increasing the inertial force of the glass particles and increasing the probability that the glass particles directly contact the target member. On the other hand, when the outer diameter of the target member is large, it is effective to improve the deposition efficiency of the glass particles by reducing the flow rate of the mixed gas of the glass raw material gas and the additive gas. This is because when the outer diameter of the target member is large, the reaction time of the glass raw material gas is lengthened and the generated glass fine particles are diffused in the flame, so that the deposition effect of the glass fine particles due to the thermophoresis effect can be expected. is there.

However, when the outer diameter of the target member is small, if the flow rate of the mixed gas of the glass raw material gas and the additive gas is increased in order to increase the flow velocity of the glass raw material gas,
The ratio of the added gas in this mixed gas becomes large. Under such a situation, the amount of glass particles not deposited on the target member increases, resulting in an increase in manufacturing cost. On the other hand, when the outer diameter of the target member is large, in order to reduce the flow rate of the glass raw material gas, the flow rate of the mixed gas of the glass raw material gas and the added gas is reduced, and the ratio of the added gas in this mixed gas becomes small. I will end up. Under such circumstances, the amount of glass particles produced is reduced, the time required to deposit the glass particles becomes longer, and as a result, the manufacturing cost increases.

In the production of a porous preform for optical fibers,
When the mixed gas of the glass raw material gas and the additive gas is ejected from the same ejection port, the flow rate of the additive gas is determined in order to optimize the flow velocity of this mixed gas. The ratio of is also determined accordingly. However, in consideration of the reaction acceleration of the glass raw material gas, the surface temperature of the glass particles during deposition, the size of the bulk density, etc., by adjusting the flow rate of the added gas,
It is not always possible to set the flow rate of the glass raw material gas to the optimum amount. Therefore, such a method may not be able to improve the deposition efficiency of the glass particles.

For example, using a burner as shown in FIG. 11, the glass raw material gas and the additive gas are supplied from the first ejection port 1, the inert gas is supplied from the second ejection port 2, and the flammability is supplied from the third ejection port 3. Gas, fourth outlet 4 and fifth outlet 5,
In the method for producing a porous base material for an optical fiber, in which a combustion-supporting gas is ejected from 5, to produce a porous base material for an optical fiber, when the outer diameter of the target member is small, the first ejection port The flow rate of the additional gas ejected from No. 1 increases, and the amount of the additional gas that does not contribute to the reaction of producing glass particles increases.
On the other hand, when the outer diameter of the target member becomes large, the flow rate of the additive gas ejected from the first ejection port 1 decreases,
There is a problem that the glass material gas does not sufficiently react.

By the way, a method for producing a porous preform for optical fibers in which a mixed gas of a glass raw material gas and an additive gas is jetted from a plurality of jet outlets is described in, for example, Japanese Patent Laid-Open No. 10-
It is disclosed in Japanese Patent No. 101343. Further, a method for producing a porous preform for optical fibers in which an additive gas is ejected from an ejection port adjacent to an ejection port from which a glass material gas is ejected is disclosed in Japanese Patent Application Laid-Open No. 10-167748. However, these methods for producing a porous preform for optical fibers merely exemplify the relationship between the type of gas ejected from each ejection port and the flow rate, and as the outer diameter of the target member increases. There is no description about a method of changing the flow rate of the gas or a method of keeping the flow rate ratio of the glass raw material gas and the additive gas substantially constant.

The present invention has been made in view of the above circumstances, and controls the flow rates of the glass raw material gas and the additive gas ejected from the jet port of the burner during the deposition of the glass fine particles so that the flow rates of the glass raw material gas and the additive gas are controlled. An object of the present invention is to provide a method for producing a porous base material for an optical fiber and a burner device for producing a porous base material for an optical fiber, in which the ratio is optimized and the deposition efficiency of glass particles is improved.

[0011]

Means for Solving the Problems The above-mentioned problems are solved by introducing a glass raw material gas and an additive gas to be added thereto into a burner equipped with a plurality of nozzles arranged with the same central axis. A method for producing a porous preform for optical fiber, in which glass microparticles are produced by performing a flame hydrolysis reaction in an oxyhydrogen flame, and the glass microparticles are deposited on the outer peripheral portion of the starting member to obtain a porous preform for optical fiber. In the ejection port formed by the nozzle, the gas ejected from two adjacent ejection ports is a mixed gas of the glass raw material gas and the additive gas having the same composition, or two adjacent ejection ports The gas ejected from one is a mixed gas of the glass raw material gas and the additive gas, the gas ejected from the other is the additive gas, during the deposition of the glass fine particles, As the outer diameter of the starting member changes, the flow velocity of the mixed gas of the glass raw material gas and the additive gas ejected from at least one of the ejection ports is changed one or more times, and the admixture from the two adjacent ejection ports is changed. The total flow rate of the glass raw material gas ejected is V1 liter / min, the total flow rate of the additive gas ejected from the two adjacent ejection ports is V2 liter / min, and V1 / in the initial stage of the deposition of the glass particles. If V2 is Rb and V1 / V2 at the end stage of the deposition of the glass particles is Rf,
This can be solved by a method of manufacturing a porous preform for optical fibers in which the relationship between Rb and Rf is 0.25 ≦ Rb / Rf ≦ 4.0. Here, the initial stage of depositing glass fine particles means a time when glass fine particles are deposited by about 5 to 15% of the total deposition amount from the start of the production of the porous preform for optical fibers.
The final stage means that the glass particles are 85 to 95% of the total deposition amount.
It shows the time when it has been accumulated. In the method for producing a porous base material for an optical fiber, it is preferable that the additive gas is oxygen or hydrogen. The problem is a burner device for producing a porous preform for an optical fiber, which has a burner, a gas supply source, and a gas control unit, and the burner has a plurality of nozzles arranged with the same central axis. A plurality of nozzles are formed by the plurality of nozzles, and the two adjacent nozzles of the plurality of nozzles are both nozzles of the mixed gas of the glass raw material gas and the additive gas, or one of them is A mixed gas of a glass raw material gas and an additive gas is ejected, and the other is an ejected gas of the additive gas. The gas control unit sets the total flow rate of the glass raw material gas ejected from the two adjacent ejection ports to V1 liter / min, and the total amount of the additive gas ejected from the two adjacent ejection ports. Flow rate To 2 liters / min, V1 in the initial stage of the deposition of glass particles
/ V2 is Rb and V1 / V2 is Rf at the final stage of the deposition of glass particles, the relationship between Rb and Rf is 0.25 ≦ Rb / Rf ≦ 4.0. It can be solved by a burner device for manufacturing a porous base material.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention is described in detail below.
The burner device for producing a porous preform for an optical fiber of the present invention,
From a burner that produces fine glass particles, a gas supply source that supplies glass raw material gas, a combustible gas, a combustion-supporting gas, and an inert gas to this burner, and a gas control unit that controls the flow rate or flow velocity of these gases. Is roughly configured

FIG. 1 is a schematic diagram showing an example of a burner provided in the burner apparatus for producing a porous preform for optical fibers of the present invention. A first nozzle 11 is provided at the center of the end surface of the burner 10, and a second nozzle 12 having the same central axis as the first nozzle 11 is provided around the first nozzle 11. Further, a third nozzle 13 having the same central axis as that of the first nozzle 11 is provided around the second nozzle 12, and hereinafter, similarly to the fourth nozzle.
The nozzle 14 and the fifth nozzle 15 are provided. Further, between the third nozzle 13 and the fourth nozzle 14, a plurality of sixth nozzles 16, 16 having the same inner diameter and outer diameter are provided on the concentric circle of the first nozzle 11. There is.

Further, the first nozzle 11 is connected to the first ejection port 2
1, the portion between the first nozzle 11 and the second nozzle 12 forms the second jet port 22, and the portion between the second nozzle 12 and the third nozzle 13 forms the third jet port. 23,
The portion between the third nozzle 13 and the fourth nozzle 14 is the fourth
Of the fourth nozzle 14 and the fifth nozzle 15 form a fifth jet port 25, and the sixth nozzles 16, 16, ... , ...

The burner 10 has a cylindrical shape with an outer diameter of about 40 to 60 mm and is generally made of quartz glass. The inner diameter of the first nozzle 11 is about 2.5 to 6 mm, the inner diameter of the second nozzle 12 is about 4 to 10 mm,
The nozzle 13 has an inner diameter of about 6 to 15 mm, the third nozzle 13 has an inner diameter of about 6 to 15 mm, the fourth nozzle 14 has an inner diameter of about 25 to 45 mm, and the fifth nozzle 15 has an inner diameter of about 3 to 15.
About 5 to 55 mm, the inner diameter of the sixth nozzle 16 is 1 to 2 m
It is about m. The distance from the center of the first nozzle 11 to the center of the sixth nozzle 16 is 10 to 30 m.
It is about m. By setting the inner diameter of each nozzle constituting the burner 10 within the above range, a method for producing a porous preform for an optical fiber described later becomes possible.

Further, the gas supply source is a glass raw material gas,
It is composed of a gas cylinder (not shown) filled with oxygen, hydrogen, an inert gas, etc., and is connected to the rear end of the burner 10 via a gas supply pipe (not shown). And
The gas control unit is composed of an electromagnetic valve, a flow rate control device, and the like, and is provided in the middle of the above-mentioned gas supply line, and the flow rate control device controls the flow rate or flow velocity of the gas.

The method for producing the porous preform for optical fibers of the present invention will be described below. In the method for producing a porous glass preform of the present invention, first, on the outer peripheral portion of the starting member that rotates around its axis, for example, from the first ejection port 21 of the burner 10, glass raw material gas SiCl ₄ , GeCl _4, etc. , And oxygen gas or hydrogen gas as an additive gas are supplied, oxygen gas as a combustion-supporting gas is supplied from the second ejection port 22, and argon gas as an inert gas is supplied from the third ejection port 23. Hydrogen gas, which is a combustible gas, is supplied from the fourth ejection port 24, oxygen gas, which is a combustion-supporting gas, is supplied from the fifth ejection port 25 and the sixth ejection port 26, and the oxyhydrogen flame of the burner 10 is supplied. Glass particles are synthesized by a hydrolysis reaction in the glass particles, and the glass particles are deposited on the outer peripheral portion of the starting member to obtain a porous preform for optical fibers.

In the method for producing a porous base material for an optical fiber according to the present invention, the first ejection port 21 and the second ejection port 2 are provided.
The gas supplied from 2 is a mixed gas of a glass raw material gas and an additive gas having the same composition, or one of the gases supplied from the first ejection port 21 or the second ejection port 22 is glass. A mixed gas of a source gas and an additive gas is used, and the other is used as an additive gas. Then, during the deposition of the glass particles, the first ejection port 21 or the second ejection port 22 is changed according to the change of the outer diameter of the porous preform for optical fiber, which increases with the passage of the deposition time of the glass particles. Among them, the flow rate of the mixed gas of the glass raw material gas and the additive gas ejected from at least one ejection port is changed once or more so that the glass fine particles are accelerated in the initial stage and delayed in the final stage. Further, the flow rate of the glass material gas ejected from the first ejection port 21 is set to V1 liter / min, and the total flow rate of the oxygen gas of the additive gas ejected from the first ejection port 21 and the second ejection port 22 is V2 liters / minute, these ratios V1 / V2 are Rb at the initial stage of glass particulate deposition and Rf at the final stage of glass particulate deposition, the relationship between Rb and Rf is 0.25 ≦ Rb / Rf ≤4.0
And A more preferable relationship between Rb and Rf is 0.5 ≦ Rb
/Rf≦2.0, more preferably 0.8 ≦ Rb
/Rf≦1.2.

As described above, in the method for producing a porous base material for an optical fiber of the present invention, the glass raw material gas and the additive gas ejected from at least one of the two adjoining jet ports of the burner are added. The flow rate of the mixed gas of gases is set to be high in the initial stage of glass particulate deposition and slow in the final stage, and the ratio of Rb and Rf is not significantly changed in the initial stage and the final stage of glass particulate deposition. By doing so, oxygen gas with sufficient excess and deficiency in the reaction is always
It comes to exist around the glass raw material gas. That is,
The flow rate ratio between the glass raw material gas and the oxygen gas is always in an optimum state according to the change in the outer diameter of the porous preform for optical fibers during the deposition of glass particles. Therefore, the glass raw material gas reacts sufficiently, and the deposition efficiency of the glass particles is improved.

The same applies when the additive gas is changed from oxygen gas to hydrogen gas. In this case, the preferred R
The values of b and Rf inevitably differ from those in the case where the additive gas is oxygen gas, but it is completely desirable that the ratio of Rb and Rf is not significantly changed at the initial stage and the final stage of the deposition of the glass particles. It is the same.

The additive gas added to the glass raw material gas is preferably either oxygen gas or hydrogen gas, as described above, from the viewpoint that it contributes to the reaction for producing glass particles. Further, the structure of the burner provided in the burner device for producing the optical fiber porous preform is as shown in FIG.
Whether a structure having a double nozzle or a structure having a double nozzle provided with the same central axis at the center as shown in FIG. 11 is satisfied as long as the above conditions are satisfied,
Either may be used.

Specific examples will be shown below with reference to FIGS. 1 and 11 to clarify the effects of the present invention. In the examples shown below, the burner structure, the gas flow rate,
The size of the starting member is not limited to that shown here. Further, the present invention is not limited to this embodiment.

Example 1 Diameter 30 mm, Length 1100
A cylindrical mm-shaped starting member is rotated about its axis 30 times per minute, and a plurality of burners whose burner end faces have a schematic shape as shown in FIG. 1 are used to make this burner parallel to the longitudinal direction of the starting member. While reciprocating, SiO is formed on the outer periphery of the starting member.
₂ Glass particles were deposited. Hydrogen gas was used as an additive gas of the glass raw material gas, and the glass raw material gas was supplied only to the first ejection port 21. The gas supplied to the burner was changed as shown in Table 1 and FIG. 2 according to the change in the outer diameter of the porous preform for optical fibers during the deposition of glass particles.

[0024]

[Table 1]

(Embodiment 2) The schematic shape of the burner end face is shown in FIG.
SiO ₂ glass fine particles were deposited on the outer peripheral portion of the starting member in the same manner as in Example 1 except that the burner as shown in 1 was used and oxygen gas was used as the additive gas of the glass raw material gas. The gas supplied to the burner was changed as shown in Table 2 and FIG. 3 according to the change in the outer diameter of the porous preform for optical fibers during the deposition of glass particles.

[0026]

[Table 2]

(Embodiment 3) The schematic shape of the burner end face is shown in FIG.
A starting member was used in the same manner as in Example 1 except that the burner as shown in FIG. 1 was used, hydrogen gas was used as an additive gas of the glass raw material gas, and the glass raw material gas was supplied only to the first ejection port 1. SiO ₂ glass fine particles were deposited on the outer peripheral portion of the.
The gas supplied to the burner was changed according to the change in the outer diameter of the porous preform for optical fibers during the deposition of glass particles in Table 3 and FIG.
It changed like.

[0028]

[Table 3]

(Embodiment 4) The schematic shape of the burner end face is shown in FIG.
The SiO ₂ glass fine particles were deposited on the outer peripheral portion of the starting member in the same manner as in Example 1 except that the glass raw material gas was supplied only to the second ejection port 22 using the burner as shown in FIG. The gas supplied to the burner was changed as shown in Table 4 and FIG. 5 according to the change in the outer diameter of the porous preform for optical fibers during the deposition of glass particles.

[0030]

[Table 4]

(Embodiment 5) The schematic shape of the end surface of the burner is shown in FIG.
The burner as shown in Fig. 2 is used, oxygen gas is used as an additive gas of the glass raw material gas, and the first ejection port 21 and the second ejection port 21
SiO ₂ glass fine particles were deposited on the outer peripheral portion of the starting member in the same manner as in Example 1 except that the glass raw material gas was supplied to the ejection port 22 of the above. The gas supplied to the burner was changed as shown in Table 5 and FIG. 6 according to the change in the outer diameter of the porous preform for optical fibers during the deposition of glass particles.

[0032]

[Table 5]

(Comparative Example 1) The schematic shape of the burner end face is shown in FIG.
SiO ₂ glass fine particles were deposited on the outer peripheral portion of the starting member in the same manner as in Example 1 except that the burner as shown in 1 was used and oxygen gas was used as the additive gas of the glass raw material gas. The gas supplied to the burner was changed as shown in Table 6 and FIG. 7 according to the change in the outer diameter of the porous preform for optical fibers during the deposition of glass particles.

[0034]

[Table 6]

(Comparative Example 2) A schematic shape of the end surface of the burner is shown in FIG.
1 was used in the same manner as in Example 1 except that the burner as shown in FIG. 1 was used, oxygen gas was used as the additive gas of the glass raw material gas, and the glass raw material gas was supplied only to the first ejection port 1. SiO ₂ glass fine particles were deposited on the outer peripheral portion of the.
The gas supplied to the burner was changed according to the change in the outer diameter of the porous preform for optical fibers during the deposition of glass particles in Table 7 and FIG.
It changed like.

[0036]

[Table 7]

(Comparative Example 3) The schematic shape of the burner end face is shown in FIG.
In the same manner as in Example 1 except that a burner as shown in 1) was used and oxygen gas was used as an additive gas of the glass raw material gas,
SiO ₂ glass particles were deposited on the outer peripheral portion of the starting member. The gas supplied to the burner was changed as shown in Table 8 and FIG. 9 according to the change in the outer diameter of the porous preform for optical fibers during the deposition of glass particles.

[0038]

[Table 8]

FIG. 10 shows the relationship between the outer diameter of the porous preform for optical fibers during the deposition of glass particles and the deposition efficiency of glass particles in Examples 1 to 5 and Comparative Examples 1 to 3. From the result of FIG. 10, the first jet port 11 or the second jet port 12, or the first jet port 1 or the second jet port 2
The flow rate of the mixed gas of the glass raw material gas and the additive gas ejected from at least one of the ejection ports is set to be high at the initial stage of the deposition of glass fine particles and slow at the end stage thereof, and at the initial stage of the deposition of glass fine particles. It was confirmed that the deposition efficiency of the glass particles can be improved if the ratio of Rb and Rf is not changed significantly in the stage and the termination stage.

[0040]

As described above, according to the method for producing a porous base material for an optical fiber of the present invention, the glass raw material ejected from at least one of the two adjacent ejection ports of the burner. The flow rate of the mixed gas of the gas and the additive gas is set to be high in the initial stage of the glass particulate deposition and slow in the final stage, and the total flow rate of the glass raw material gas in the initial stage and the final stage of the glass particulate deposition. Since the ratio with the total flow rate of the additive gas is not significantly changed, an oxygen gas with no excess or deficiency in the reaction is always present around the glass raw material gas, and the flow rate ratio between the glass raw material gas and the oxygen gas is It is always in an optimum state according to the change in the outer diameter of the porous preform for optical fibers during the deposition of glass particles.
Therefore, the glass raw material gas reacts sufficiently, and the deposition efficiency of the glass particles is improved. Further, according to the burner device for producing a porous base material for an optical fiber of the present invention, the flow rate ratio between the glass raw material gas and the oxygen gas is changed according to the change in the outer diameter of the porous base material for an optical fiber during the deposition of glass particles. Since the optimum state can always be achieved, the glass raw material gas reacts sufficiently and the deposition efficiency of the glass particles can be improved.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing an example of a burner included in a burner device for producing a porous preform for optical fibers according to the present invention.

FIG. 2 is a graph showing the relationship between the outer diameter of the porous preform for optical fibers during deposition of glass particles and the ratio of the total flow rate V1 of glass raw material gas to the total flow rate V2 of additive gas in Example 1. .

FIG. 3 is a graph showing the relationship between the outer diameter of the porous preform for optical fibers during deposition of glass particles and the ratio of the total flow rate V1 of glass raw material gas to the total flow rate V2 of additive gas in Example 2. .

FIG. 4 is a graph showing the relationship between the outer diameter of the porous preform for optical fibers during deposition of glass particles and the ratio of the total flow rate V1 of glass raw material gas to the total flow rate V2 of additive gas in Example 3. .

FIG. 5 is a graph showing the relationship between the outer diameter of the porous preform for optical fibers during glass particulate deposition and the ratio of the total flow rate V1 of glass raw material gas to the total flow rate V2 of additive gas in Example 4. .

FIG. 6 is a graph showing the relationship between the outer diameter of the porous preform for optical fibers during glass particulate deposition and the ratio of the total flow rate V1 of glass raw material gas to the total flow rate V2 of additive gas in Example 5. .

FIG. 7 is a graph showing the relationship between the outer diameter of the porous preform for optical fibers during the deposition of glass particles and the ratio of the total flow rate V1 of glass source gas to the total flow rate V2 of additive gas in Comparative Example 1. .

8 is a graph showing the relationship between the outer diameter of the porous preform for optical fibers during the deposition of glass particles and the ratio of the total flow rate V1 of glass raw material gas to the total flow rate V2 of additive gas in Comparative Example 2. FIG. .

9 is a graph showing the relationship between the outer diameter of the porous preform for optical fibers during the deposition of glass particles and the ratio of the total flow rate V1 of glass raw material gas to the total flow rate V2 of additive gas in Comparative Example 3. FIG. .

FIG. 10 is a graph showing the relationship between the outer diameter of the porous preform for optical fibers during glass particle deposition and the glass particle deposition efficiency in Examples 1 to 5 and Comparative Examples 1 to 3.

FIG. 11 is a schematic configuration diagram showing an example of a burner used for manufacturing a porous preform for optical fibers.

[Explanation of symbols]

10 ... Burner, 11 ... 1st nozzle, 12 ... 2nd nozzle, 13 ... 3rd nozzle, 14 ... 4th nozzle,
15 ... Fifth nozzle, 16 ... Sixth nozzle, 21 ...
1st jet outlet, 22 ... 2nd jet outlet, 23 ... 3rd jet outlet, 24 ... 4th jet outlet, 25 ... 5th jet outlet, 2
6 ... 6th spout

Claims (3)

[Claims] 1. A glass raw material gas and an additive gas to be added to the glass raw material gas are introduced into a burner having a plurality of nozzles arranged with the same central axis, and the glass raw material gas is flame-hydrogenated in an oxyhydrogen flame. In the method for producing a porous preform for an optical fiber, in which a glass microparticle is generated by a decomposition reaction, and the glass fine particle is deposited on an outer peripheral portion of a starting member to obtain a porous preform for an optical fiber, which is formed by the plurality of nozzles. At the spout that is
The gas ejected from two adjacent ejection ports is a mixed gas of the glass raw material gas and the additive gas having the same composition, or the gas ejected from one of the two adjacent ejection ports is the glass raw material gas. A mixed gas of the additive gas and a gas ejected from the other gas as the additive gas, and ejected from at least one of the ejection ports along with a change in the outer diameter of the starting member during the deposition of the glass particles. The flow rate of the mixed gas of the glass raw material gas and the additive gas is changed once or more, and the total flow rate of the glass raw material gas ejected from the two adjacent ejection ports is V1 liter / min. The total flow rate of the additive gas ejected from the two ejection ports is V2 liter / min, V1 / V2 in the initial stage of the deposition of the glass fine particles is Rb, and the glass is When the V1 / V2 in the final stage of the deposition of the particles and Rf, Rb and Rf
To satisfy 0.25 ≦ Rb / Rf ≦ 4.0. 2. The method for producing a porous base material for an optical fiber according to claim 1, wherein the additive gas is oxygen gas or hydrogen gas. 3. A burner apparatus for producing a porous preform for optical fibers, which has a burner, a gas supply source, and a gas control unit, wherein the burner comprises a plurality of nozzles arranged with the same central axis. A plurality of nozzles are formed by the plurality of nozzles, and two adjacent nozzles of the plurality of nozzles are both nozzles of a mixed gas of a glass raw material gas and an additive gas, or Is a jet of mixed gas of glass raw material gas and additive gas, the other is a jet of additive gas, the gas supply source, the glass raw material gas, flammable gas, flammable gas and an inert gas to the burner. The gas control unit sets the total flow rate of the glass raw material gas ejected from the two adjacent ejection ports to V1 liter / min, and controls the addition gas ejected from the two adjacent ejection ports. Total flow rate Is V2 liters / minute, V1 / V2 in the initial stage of deposition of glass particles is Rb, and V1 / V2 in the final stage of deposition of glass particles is Rf, the relationship between Rb and Rf is 0.25 ≦ Rb / Rf ≦ 4.0
A burner device for producing a porous preform for an optical fiber, which is characterized by performing the following control.