JP3264227B2 - Manufacturing method of preform for optical fiber - Google Patents

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 preform for an optical fiber, and more particularly, to a method for producing glass fine particles by a flame hydrolysis reaction using a burner and depositing the same to deposit a porous glass matrix. The present invention relates to an improvement in a method of manufacturing a material.

[0002]

2. Description of the Related Art One of the methods for producing a preform for an optical fiber is V
The AD method (gas phase shafting method) is known. In this method, a glass raw material gas, a combustible gas such as hydrogen, and a combustible gas such as oxygen are burned into a burner for synthesizing a porous preform for an optical fiber (hereinafter, referred to as a “burner”). (Abbreviated as "burner"), and the glass material generated by flame hydrolysis of the glass material in the formed flame is deposited on the surface of the starting material while the burner and the starting material are relatively moved. As a result, a deposited body (porous body) of glass fine particles is formed. The obtained porous preform is heated and made transparent to obtain a glass preform for optical fibers.
For example, using a multi-tube burner having concentric ports as schematically shown in FIG.
1, hydrogen gas 42 and oxygen gas 44 are supplied. At this time gas
Generally, an inert gas such as Ar is provided between 42 and oxygen gas 44.
43 as a seal gas. This is because, when an oxyhydrogen flame is generated near the nozzle outlet of the burner, the nozzle is prevented from being deformed due to its high temperature and the burner component is scattered as an impurity.

If the maximum temperature of the surface temperature distribution is to be increased in order to increase the bulk density at the center of a porous body manufactured using a burner of the type shown in FIG. As a means for solving this problem, as a means for solving this problem, a central portion of the porous body finally serving as a core is provided with a plurality of oxygen supply ports inside an outer port 53 for supplying hydrogen as schematically shown in a sectional view in FIG. Small-diameter nozzles 54
A method of synthesizing using a burner in which is disposed (Literature: JP-A-62-182129) has been proposed. In FIG. 5, a glass material is supplied to a central port 51, and an inert gas such as argon is supplied to a sealing gas port 52 provided outside the central port.

Further, in order to suppress the deterioration of the burner without using a seal gas, in a burner whose schematic cross-sectional view is shown in FIG. 6, a center port 61 has a mixed gas of a glass raw material gas and oxygen, and a hydrogen supply port. Hydrogen gas is supplied to 62, oxygen gas is supplied to the outer port 63 for supplying oxygen, and oxygen gas is supplied to the small-diameter nozzle 64.Hydrogen gas and oxygen gas are supplied adjacently at an interval of 1 mm or less at the gas ejection port. A method has also been proposed in which the average flow velocity at the nozzle outlet is set to 5 m / sec or more and 10 m / sec or less (Reference: JP-A-6-24).
No. 7722).

[0005]

When oxygen and hydrogen are ejected from ports adjacent to each other in the burner for synthesizing a porous preform for an optical fiber as described above, the tip of the nozzle between them is easily heated, so As a result, the tip of the nozzle is deformed, shortening the life of the burner.If the temperature of the tip of the nozzle rises, the burner constituent material evaporates, causing impurities to be mixed into the glass base material. Lower it. On the other hand, in order to protect the tip of the nozzle, a method of providing a seal gas port around the oxygen nozzle and flowing an inert gas is also conceivable, but the burner structure becomes complicated and expensive, so the optical fiber manufacturing cost increases. There was a problem.

In order to solve such problems, the method disclosed in the literature regulates the gas flow by reducing the thickness of the nozzle, and increases the oxygen jetting speed from the nozzle to cause the combustion reaction to move away from the nozzle. However, when the flow rate decreases, such as when the burner is ignited or extinguished, the high flow rate cannot be maintained. Also, at the time of synthesizing the porous base material, increasing the flow rate of the oxygen nozzle lowers the nozzle tip temperature, but is not sufficient, and its effect is small. Further, when only the flow velocity of the oxygen nozzle is increased, there is a problem that the difference between the flow velocity of the hydrogen jet around the nozzle becomes large and the flow of gas is disturbed, so that the porous base material cannot be synthesized stably. Further, when the flow rate of hydrogen is increased in order to suppress the disturbance of the flame, the temperature of the deposition surface rises, resulting in a porous body having a large bulk density, which is not sufficiently dehydrated during dehydration sintering. In view of this situation, using a simpler burner structure, the temperature at the tip of the nozzle can be reduced, and a porous preform can be stably manufactured, thereby reducing the production cost of an optical fiber preform. It is intended to provide a manufacturing method.

[0007]

Means for Solving the Problems As means for solving the above problems, the present invention provides (1) glass produced by introducing a glass raw material into an oxyhydrogen flame formed by hydrogen gas and oxygen gas ejected from a burner. In a method of forming a glass base material by depositing fine particles on a starting material, a mixed gas obtained by adding an inert gas or a nitrogen gas to the hydrogen gas and an oxygen gas are supplied from ports adjacent to each other on the burner. A method of manufacturing a glass preform for an optical fiber, characterized in that (2) using a burner having a structure in which a plurality of small-diameter nozzles are arranged in a port as the burner, and ejecting oxygen gas from the small-diameter nozzle Wherein a mixed gas of hydrogen gas and an inert gas or a nitrogen gas is jetted from a port in which the small-diameter nozzle is disposed. (3) A burner consisting of concentric multi-tubes is used as the burner, and a mixed gas obtained by adding inert gas or nitrogen gas to hydrogen gas is spouted from a port adjacent to a port spouting oxygen gas. The method for producing a glass preform for an optical fiber according to the above (1), and (4) a mixed gas obtained by adding an inert gas or a nitrogen gas to a hydrogen gas, wherein an inert gas or a nitrogen gas with respect to a hydrogen gas flow rate Gas flow rate ratio is 0.1 ~
1.0. The method for producing a preform for an optical fiber according to any one of (1) to (3) above, wherein

[0008]

DETAILED DESCRIPTION OF THE INVENTION In view of the above problems, the present inventors have proposed a method for lowering the temperature at the nozzle tip while forming a stable flame, by adding argon, hydrogen gas ejected from a port adjacent to an oxygen nozzle to the nozzle. A method of mixing and supplying an inert gas such as helium or a nitrogen gas has been devised. In the following description, the inert gas and the nitrogen gas are collectively referred to as “inert gas”. FIG. 1 is a schematic cross-sectional view for explaining one embodiment of the present invention. A glass material gas and a hydrogen gas are provided at a center port 1, a hydrogen gas is provided at a second port 2, and a third port is provided.
3 is inert gas, 4th port 4a is a mixed gas of hydrogen gas and inert gas, 4th port 4a is a small diameter nozzle 4b
, Oxygen gas to the fifth port 5, and oxygen gas to the sixth port 6.

When supplied in this manner, the hydrogen gas is diluted with the inert gas, so that an oxyhydrogen flame is formed at a portion distant from the nozzle tip. As a result, the temperature at the nozzle tip decreases, and the nozzle tip decreases. The deterioration of the part is suppressed, and the life of the burner can be prolonged. By mixing the inert gas with the hydrogen gas, the temperature at the nozzle tip can be sufficiently reduced even when the flow rate of the oxygen nozzle is low,
Even when the burner is ignited or extinguished, the effect of preventing deterioration of the nozzle tip can be expected. Further, according to the present invention, the temperature at the nozzle tip can be reduced as compared with a burner in which the flow velocity of the oxygen nozzle is simply increased, and thus the effect of extending the life of the burner is great. In addition, the present invention can be applied to a burner in which hydrogen gas and oxygen gas are adjacent to each other at an interval of 1 mm or more at a gas ejection port, so that the present invention can be applied to a burner structure different from the burner shown in the literature.

In the present invention, the effect of lowering the temperature of the burner tip is greater as the proportion of the inert gas mixed with the hydrogen gas is higher, but if the flow rate of the inert gas is excessively increased, the growth rate of the porous base material is increased. Is undesirably reduced. According to the experiments of the present inventors, as shown in the graph of FIG.
A range of 1.0 has been found to be desirable. In FIG. 2, the horizontal axis represents the flow rate of argon gas / the flow rate of hydrogen (ratio), and the vertical axis represents the average temperature (° C.) at the tip of the oxygen nozzle.

In the present invention, the tendency that the temperature at the nozzle tip decreases as the flow velocity of the oxygen nozzle increases is not changed. Therefore, also in the present invention, increasing the flow velocity of the oxygen nozzle is more effective in suppressing deterioration of the nozzle tip. That is, as described above, in the conventional method, when the flow rate of the oxygen nozzle is increased as compared with the flow rate of the adjacent hydrogen gas port, the gas flow becomes unstable, and the porous base material cannot be stably synthesized. there were. Also, if the flow rate of hydrogen gas is increased to stabilize the gas flow,
There is also a problem that the temperature of the deposition surface increases, the bulk density of the porous base material increases, and sufficient dehydration cannot be performed in the dehydration and sintering step. According to the present invention, since the hydrogen gas mixed with the inert gas is ejected from the hydrogen port, even if the gas flow is stabilized by increasing the flow rate of the hydrogen port in response to the increase in the oxygen flow rate, the temperature of the deposition surface can be increased. Never rise. Therefore, the bulk density of the porous preform can be set in a suitable range, and a high-quality optical fiber preform can be manufactured.

Further, the present invention is not limited to a burner having a structure in which a plurality of small-diameter oxygen nozzles are provided in a hydrogen port. That is, in the conventional concentric multi-tube burner, between the oxygen port and the hydrogen port,
A seal gas port is provided to protect the burner, but by mixing hydrogen and inert gas into the hydrogen port and ejecting it, it is possible to prevent deterioration of the burner tip even without a seal gas port Becomes That is, although three ports of the oxygen gas port-the seal gas port-the hydrogen gas port are used, only the oxygen gas port-the (hydrogen gas + the seal gas) port is sufficient. Therefore,
The burner structure is simple and inexpensive, and the effect of reducing the cost of the optical fiber can be expected.

[0013]

Examples of the present invention will be described below. [Example 1] A glass core burner (hereinafter abbreviated as "core burner") and a clad synthesizing burner (hereinafter abbreviated as "clad burner") are arranged, and oxygen gas and hydrogen are supplied to each burner. A gas is supplied to form a flame, and the core burner is supplied with silicon tetrachloride and germanium tetrachloride as glass raw materials, and the clad burner is supplied with only silicon tetrachloride as a glass raw material. By depositing in the axial direction, a porous preform for an optical fiber was synthesized. At that time, a burner having a cross-sectional shape as shown in FIG. 1 was used as the structure of the core burner, and a mixed gas of hydrogen and argon (flow ratio: 1: 0.6) was blown out from the fourth port 4a. Oxygen gas was ejected from a plurality of small-diameter nozzles 4b. The center port 1 is a mixed gas of silicon tetrachloride, germanium tetrachloride and hydrogen gas, the second port 2 is a hydrogen gas, the third port 3 and the fifth port 5 are an argon gas, and the sixth port is a sixth port. 6 was supplied with oxygen gas. The flow rate of each port is as follows: center port 1 has 0.2 l / min of silicon tetrachloride and 0.04 g of germanium tetrachloride.
2 liters / minute and hydrogen gas at 0.3 liters / minute, second port 2 with hydrogen gas at 1.5 liters / minute, third port 3 with argon gas at 1.5 liters / minute, fourth port In 4a, hydrogen gas 3 liter / min and argon gas 1.
A mixed gas of 8 liter / min is supplied to the small-diameter nozzle 4b in the fourth port at 6 liter / min of oxygen gas, a fifth port 5 of 2 liter / min of argon gas, and a sixth port 6 of oxygen gas 10 liter / min. Liters / minute were fed. When the porous base material was synthesized in this way, when the tip of the nozzle was visually observed, no phenomenon of redness due to heating was observed, and the average of the tip of the oxygen gas nozzle was measured with a non-contact radiation thermometer. When the temperature was measured, it was 500 ° C.

[Embodiment 2] The average temperature at the tip of the oxygen nozzle was measured by a radiation thermometer while changing the flow ratio of argon gas to hydrogen gas in the same configuration as in Embodiment 1. As a result, as shown in FIG. 2, as the flow rate ratio increases, the average temperature at the nozzle tip decreases, and in the range where the flow rate ratio is less than 0.1, a portion heated red at the nozzle tip is seen. Was. Therefore, it was found that a flow rate ratio of 0.1 or more was necessary to suppress the deformation and evaporation of the burner. On the other hand, when the flow rate ratio exceeded 1.0, the growth rate of the porous base material was reduced, and thus it was found that the flow rate ratio between the argon gas and the hydrogen gas was preferably in the range of 0.1 to 1.0.

[Embodiment 3] The core burner of Embodiment 1 is shown in FIG.
And a mixed gas of silicon tetrachloride, germanium tetrachloride and hydrogen gas in the central port 1, a hydrogen gas in the second port 2, an argon gas in the third port 3, Oxygen gas was supplied to the fourth port 4, a mixed gas of argon gas and hydrogen gas was supplied to the fifth port 5, and oxygen gas was supplied to the sixth port 6, respectively, to synthesize a porous glass body. At that time, the argon gas at the fifth port 5 was supplied at a flow rate 0.7 times that of the hydrogen gas. The specific flow rate of each port is
0.2 liter / min of silicon tetrachloride, 0.01 liter / min of germanium tetrachloride and hydrogen gas 0.
2 liters / min mixed gas, 1.5 liters / minute of hydrogen gas at the second port 2, 1 liter / minute of argon gas at the third port, 5 liters / minute of oxygen gas at the fourth port 4, hydrogen at the fifth port 2. 5 liters / min gas and argon gas
A mixed gas of 5 liter / min and an oxygen gas of 8 liter / min were supplied to the sixth port 6, respectively. When the tip of the burner was observed in the same manner as in Example 1, it was not observed that the burner became red when heated.

In the third embodiment, hydrogen was supplied to the second port and argon was supplied to the third port. However, a mixed gas of hydrogen gas and argon gas was supplied to the second port using a five-tube burner. It is similarly effective to flow oxygen gas to the third port, mixed gas of hydrogen gas and argon gas to the fourth port, and oxygen gas to the fifth port.

According to the experiment on the burner life of the present inventors, when the present invention and the conventional method are compared with respect to the deformation and the evaporation rate of the burner tip, the mixing ratio of argon and hydrogen (flow rate ratio) and the conventional method are compared. FIG. 7 shows the burner consumption speed ratio in the case of the present invention where the consumption speed in the case is 1.0.
The result shown in the graph of FIG. FIG. 7 clearly shows that the addition of the inert gas (argon) to the hydrogen gas in accordance with the present invention significantly reduces the evaporation speed of the burner tip and significantly increases the life.
The present invention is a burner having a large number of small-diameter nozzles described in the examples, in addition to the concentric multi-tube burner, a double flame burner,
It is very effective when applied to triple flame burners and the like.

[0018]

As described above, according to the present invention, a burner having a simpler structure than the conventional one can reduce the temperature at the nozzle tip and extend the life of the burner. Can be synthesized within a suitable range, so that the quality of the optical fiber preform can be improved and the production cost can be reduced.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view for explaining a method of the present invention.

FIG. 2 is a graph showing a relationship between a flow ratio of an inert gas and a hydrogen gas and an average temperature at the tip of an oxygen nozzle.

FIG. 3 is a cross-sectional view illustrating a structure of a multi-tube burner used in an embodiment of the present invention.

FIG. 4 is a schematic sectional view for explaining an example of a conventional method.

FIG. 5 is a schematic sectional view for explaining another example of the conventional method.

FIG. 6 is a schematic sectional view for explaining another example of the conventional method.

FIG. 7 is a graph showing a relationship between a flow rate ratio of both gases and a burner consumption rate ratio (conventional method is set to 1.0) when argon gas and hydrogen gas are mixed and flowed according to the present invention.

[Explanation of symbols]

1 center port, 2 second port, 3
3rd port, 4 and 4a 4th port, 4b small diameter port, 5 5th port, 6 6th port.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-59-232935 (JP, A) JP-A-2-1644734 (JP, A) JP-A 9-175827 (JP, A) 89224 (JP, A) JP-A-9-175826 (JP, A) JP-A-7-300334 (JP, A) JP-A 9-188522 (JP, A) JP-A-63-115041 (JP, U) JP-B-57-19059 (JP, B2) (58) Field surveyed (Int. Cl. ⁷ , DB name) C03B 37/018 C03B 8/04

Claims (4)

(57) [Claims] 1. A method of forming a glass base material by introducing a glass raw material into an oxyhydrogen flame formed by a hydrogen gas and an oxygen gas ejected from a burner and depositing generated glass fine particles on a starting material. A method for producing a glass preform for an optical fiber, characterized in that a mixed gas obtained by adding an inert gas or a nitrogen gas to a hydrogen gas and an oxygen gas are supplied from adjacent ports of the burner, respectively. 2. A burner having a structure in which a plurality of small-diameter nozzles are arranged in a port as the burner, wherein oxygen gas is ejected from the small-diameter nozzle, and hydrogen gas is ejected from a port in which the small-diameter nozzle is arranged. 2. The method for producing a preform for an optical fiber according to claim 1, wherein a mixed gas of nitrogen and an inert gas or a nitrogen gas is ejected. 3. A mixed gas obtained by adding an inert gas or a nitrogen gas to a hydrogen gas from a port adjacent to a port from which an oxygen gas is jetted, wherein a burner comprising a concentric multi-tube is used as the burner. The method for producing a glass preform for an optical fiber according to claim 1, wherein: 4. In a mixed gas obtained by adding an inert gas or a nitrogen gas to a hydrogen gas, the ratio of the flow rate of the inert gas or the nitrogen gas to the flow rate of the hydrogen gas is 0.1 to 1.0.
The method for producing a preform for an optical fiber according to any one of claims 1 to 3, wherein