JP3118723B2 - Method for producing porous glass preform for optical fiber - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing a porous glass preform for an optical fiber, and in particular, to feed a glass forming raw material gas into a glass synthesizing torch to synthesize glass fine particles. The present invention relates to a method for improving the yield of a raw material in a method of depositing a starting material while performing the method.

[Conventional technology]

Conventionally, in the production of a porous glass base material using a glass synthetic torch, as shown in JP-B-59-15092, JP-B-57-19059, etc., a glass raw material gas is flowed to the center of a multi-tube torch, A method is used in which a flame is formed by flowing a combustible gas and an auxiliary combustion gas so as to surround this, and the raw material gas is subjected to a flame hydrolysis reaction and an oxidation reaction to synthesize glass fine particles. At this time, hydrogen or hydrocarbon is generally used as the combustible gas, and oxygen is generally used as the auxiliary gas. In addition, a seal gas layer is provided between the combustible gas and the auxiliary gas layer of the torch in order to prevent the torch from being deformed by the combustion heat of both gases, and a conventional seal gas such as helium or argon is used. Inert gas is used. However, in these conventional methods, the raw material gas flowing in the center of the flame mixes and reacts with the flame gas flowing in the outer peripheral layer, and furthermore, it takes a long distance from the torch outlet until glass fine particles are generated. However, there is a problem that the generation efficiency of the glass fine particles is low and the deposition yield is low.

Further, as described in, for example, Japanese Utility Model Publication No. Sho 60-4979, a structure in which a torch is held in a flame portion for heating a glass particle deposition surface where a central flame portion for synthesizing glass particles is formed on the outer periphery (double flame formation) It has been proposed that a reaction torch be used to promote the reaction and the production of glass particles. However, in this torch structure, there is a problem that the torch deteriorates due to heating from the central flame held in the torch and adhesion of glass particles deviating from the central flow.

Further, JP-A-55-121922 proposes a method of forming glass fine particles by hydrolyzing a raw material for glass formation without using a flame with only steam heated at a high temperature. In the method, the temperature of water vapor needs to be several hundred degrees or more in order to form a porous glass base material, and there is a disadvantage that an apparatus for realizing this is very complicated.

[Problems to be solved by the invention]

The present invention has been made to solve the above-described problems of the prior art, and an improved method of producing glass fine particles by flame hydrolysis or oxidation reaction of a glass raw material gas using a multi-tube torch, An object of the present invention is to provide a method for producing a porous glass preform for an optical fiber with improved deposition efficiency and raw material yield.

[Means for solving the problem]

The present invention solves the above problem by sequentially moving from the center jet port of the multi-tube glass synthetic torch to the outer jet port, and mixing the raw material gas for forming glass or the raw material gas for forming glass with a flammable gas, flammable gas, And a steam gas is supplied to a gas flow adjacent to the glass forming raw material gas flow inside the auxiliary combustion gas to deposit glass particles on the starting material while synthesizing glass particles. The problem is solved by a method for producing a porous glass preform for optical fibers, which is characterized by using a glass preform.

Further, the present invention solves the above-mentioned problem by sequentially moving from the center jet port of the multi-tube glass composite torch to the outer jet port, and mixing the raw material gas for glass forming or the raw material gas for glass forming with the flammable gas, the flammable gas. , Water vapor, a combustible gas are supplied in the order described, and a method for producing a porous glass preform for an optical fiber, comprising synthesizing glass particles and depositing them on a starting material to form a porous glass preform. Is the solution.

As one specific example according to the present invention, a porous silica glass preform is subjected to a VAD (Vapour phase Axial) method using an eight-tube torch.
The case of synthesizing by a deposition method (gas phase attachment method) will be described with reference to the schematic diagram shown in FIG. Silicon tetrachloride gas as a glass source gas is supplied to the central layer 2 (first layer) of the torch 1, hydrogen gas is supplied to the second layer 3, water vapor is supplied to the third layer 4, and oxygen gas is supplied to the fourth layer 5. Then, a central flame 6 is formed. Next, an outer flame portion 11 is formed by supplying an argon gas to the fifth layer 7, a hydrogen gas to the sixth layer 8, an argon gas to the seventh layer 9, and an oxygen gas to the eighth layer 10. Glass particles synthesized by torch 1
12 is deposited on the surface of a starting material 15 rotating around its own axis in a container 14 having an exhaust system 13, and a porous glass preform 16 is formed by gradually lifting the starting material 15 upward. . As described above, in the present invention, water vapor is used between the central portion (first and second layers) in which the glass raw material gas and the flammable gas are flowing and the auxiliary combustion gas (fourth layer) flowing in the outer periphery thereof ( (3rd layer).

Incidentally, as a glass forming raw material gas in the present invention can be used SiCl _4, GeCl ₄ silane-based gas such as chlorides glass raw material gas and SiHCl _3, such as, known glass-forming raw material gas such as BBr ₃ .

Further, as the combustible gas, H ₂ , CH ₄ , C ₂ H ₆ , C ₃ H ₈ , C ₂ H ₂
And other known combustible gases. O ₂ can be cited as an example of the auxiliary gas.

[Action]

The improvement of the raw material yield according to the present invention is explained as follows. In order for the chloride glass raw material gas to become glass fine particles and efficiently deposit into a porous body, a hydrolysis reaction or an oxidation reaction must be performed before the gas is ejected from the torch and reaches the starting material or the porous body being deposited. Oxide (silicon oxide),
That is, it is necessary that the particles be glass fine particles.

Therefore, if the chloride glass raw material gas is ejected from the torch and then mixed earlier with the water or oxygen gas required for the hydrolysis reaction or the oxidation reaction, the synthesis of the glass particles can be accelerated and the raw material yield can be increased. Can be improved.

By the way, when a multi-tube torch is used, the gas is ejected from the torch in a laminar flow state, so that mixing of the gases is difficult to progress, and the above-described problem has occurred in the prior art.

On the other hand, according to the present invention, since the steam flow is arranged in the gas flow closer to the raw material gas flow inside the oxygen gas flow, instead of the inert gas as in the related art, the glass raw material gas is earlier. By mixing with a steam flow, glass fine particles can be synthesized, and the raw material yield can be improved.

Specific conditions of the present invention are shown in the following examples, but the present invention is not limited to these examples.

〔Example〕

(Example 1) According to the configuration shown in Fig. 1, the gas shown in the following Table 1 is supplied to each layer of the octuple tube torch, and the produced glass fine particles are rotated by a silica rod (starting) around its own axis. Material), and gradually raise the silica rod to an outer diameter of 145m.
A porous silica glass base material having a length of m and a length of 600 mm was produced. The silicon tetrachloride gas and water vapor were generated using a pressurized evaporator 17 schematically shown in FIG. 2 and led to a torch.

In this embodiment, the raw material yield [(weight of Si in porous silica glass base material / weight of Si in total supplied SiCl ₄ ) × 100 (%)]
Was 86%. Further, the porous silica glass base material obtained in this example had a uniform outer diameter and was excellent.

The porous silica glass base material obtained as described above was dehydrated in a furnace at 1050 ° C. in a helium gas atmosphere containing 5% chlorine gas, and then heated at 1600 ° C. to form a transparent glass. The resulting solid glass preform was drawn and then spun into a plastic clad fiber while being coated with a silicone resin. The transmission loss of the obtained fiber was as good as 4.5 dB / km at a wavelength of 1.3 μm.

Comparative Example 1 A porous silica glass base material was produced in the same manner as in Example 1 except that the gas conditions were as shown in Table 1, and the third layer was supplied with argon gas instead of steam. In this comparative example, the raw material yield was as low as 65%. On the surface of the obtained porous preform, glass fine particles grown in a tree shape having a height of 2 to 3 mm can be seen on one side, and even after being made transparent as in Example 1, it remains as a fine surface irregularity, and fiber Did not endure. It was considered that the dendritic growth of the glass microparticles was due to the low raw material yield, and the microparticles that did not accumulate as the porous base material and floated in the container adhered and grew to the surface of the porous base material.

(Example 2) In the configuration shown in Fig. 1, the gas shown in the following Table 2 was supplied to each layer of the octuple tube torch, and the generated fine glass powder was rotated while rotating around its own axis. Deposited around the starting material reciprocating in the direction. As a starting material, a silica glass rod having an outer diameter of 15 mm and a length of 600 mm, which contains germania in the center and has a higher refractive index than the periphery by 0.3%, was used. Deposition was performed until the porous glass base material had an outer diameter of 120 mm. The raw material yield of this example was 82%.

(Comparative Example 2) A porous silica glass preform was produced in the same manner as in Example 2, except that the gas conditions were as shown in Table 2, except that the third layer was supplied with argon gas instead of steam. The raw material yield of this comparative example was 62%.

From the results of the above Examples and Comparative Examples, it is understood that the method of the present invention can dramatically improve the raw material yield and can produce a high quality porous glass base material.

In the above description and the embodiments, the eight-tube torch is taken as an example, but it goes without saying that the present invention is not limited to this.

Further, the present invention can be applied not only to the VAD method but also to any method of producing glass fine particles by using a flame hydrolysis reaction and / or an oxidation reaction of a chloride glass raw material gas to obtain a porous glass body. .

〔The invention's effect〕

As described above, according to the present invention, the synthesis of glass fine particles by a flame hydrolysis reaction or an oxidation reaction of a glass raw material gas can be advanced earlier by using a multi-tube synthesis torch, whereby the raw material yield can be improved. Can be greatly improved. Further, in the above description, the present invention has been described based on an example in which silicon tetrachloride is used as a chloride glass raw material gas, but a glass forming raw material gas such as GeCl ₄ , BBr ₃ which has a higher molecular weight and is less likely to be mixed. The present invention is very effective when the present invention is applied to a configuration in which a combustible gas is caused to flow in a layer adjacent to a raw material gas by using such a method.

[Brief description of the drawings]

FIG. 1 is a schematic explanatory view of a specific example according to the present invention using the VAD method, and FIG. 2 is a schematic explanatory view of a steam and raw material gas vapor generating apparatus in the embodiment.

Claims (2)

(57) [Claims] 1. A multi-tube glass composite torch, in order from a central jet port to an outer jet port, a raw material gas for forming a glass or a mixed gas of a raw material gas for forming a glass and a flammable gas, a flammable gas, and an auxiliary gas. Are supplied in the order described, and a steam gas is supplied to a gas flow adjacent to the glass-forming raw material gas flow inside the auxiliary combustion gas, and is deposited on the starting material while synthesizing glass fine particles to form a porous glass matrix. A method for producing a porous glass preform for an optical fiber, comprising: 2. A multi-tubular glass composite torch, in order from a central jet port to an outer jet port, to a glass forming raw material gas or a mixed gas of a glass forming raw material gas and a flammable gas, a flammable gas, water vapor, and an auxiliary fuel. A method for producing a porous glass preform for an optical fiber, characterized in that a reactive gas is supplied in the order described, and glass fine particles are synthesized and deposited on a starting material to form a porous glass preform.