KR20090092686A - Burner for deposition of optical fiber preform - Google Patents

Abstract

A burner for depositing optical fiber preforms is provided to secure high deposition efficiency in a whole deposition process even when a large material is produced. A burner for depositing optical fiber preforms has a port for jetting a combustible gas with a plurality of small caliber supporting gas jetting ports. The burner having a concentric multi pipe structure is located further than a glass source gas jetting port(6). Optical fiber preforms are manufactured by hydrolyzing the glass source gas to generate glass particles using the burner and depositing the generated glass particles on a starting member. If the focal distance of the small caliber supporting gas jetting ports is L1 and the distance from the end of the small caliber supporting gas jetting ports to a glass particle deposited surface(7) is L2, L1 is greater than L2 at early deposition stage and L1 becomes smaller than L2 during deposition.

Description

BURNER FOR DEPOSITION OF OPTICAL FIBER PREFORM}

This invention relates to the manufacturing method of the base material for optical fibers which hydrolyzes a glass raw material gas in a flame, produces | generates glass fine particles, and deposits this on a rotating starting member.

Conventionally, various methods are proposed in order to manufacture the base material for optical fibers. Among such methods, the glass fine particles generated in the burner flame on the rotating starting member are attached and deposited by relative reciprocating movement of the burner or starting member to synthesize a porous base material, which is dehydrated and sintered in an electric furnace. The adhesion method (OVD method) is widely used because a relatively arbitrary refractive index distribution can be obtained and a large diameter base material for optical fibers can be mass produced.

1 shows an example of an apparatus for producing a base material for optical fibers. In Fig. 1, the starting member for depositing glass fine particles (soot) is obtained by welding a dummy rod 2 to both ends of a core rod 1 and not shown. The rotation is freely supported by the ingot chuck mechanism 4 in the axial rotation by the base material supporting member. The raw material for optical fibers, for example, steam and combustion gas (hydrogen gas and oxygen gas), such as SiCl ₄ , is blown toward the starting member from the freely moving burner 3 disposed toward the starting member, and the water in the oxyhydrogen flame By depositing the soot produced by decomposition on the starting member, a porous base material for the optical fiber is formed. Also, reference numeral 5 denotes an exhaust hood.

The burner 3 is freely supported in the longitudinal direction by a burner guide mechanism (not shown), injects a flame toward the starting member while rotating the starting member in an axial rotation, and supplies the raw material gas in the flame. A porous base material is manufactured by depositing glass fine particles produced by hydrolysis. Next, by passing through a heater portion of the heating furnace, dehydration and vitrification become an optical fiber base material.

Conventionally, concentric multi-tube burners have been used to synthesize glass fine particles and deposit soot on the starting member, but the burner of such a structure is not sufficiently mixed with the glass raw material gas, the combustible gas, and the flammable gas. The production of particulates was not enough. As a result, the yield did not increase and high speed synthesis was difficult.

In order to solve this problem, patent document 1 arrange | positions a small diameter flammable gas ejection port (henceforth a small diameter ejection port) in a flammable gas ejection port so that a center source gas ejection port may be enclosed. One multi-nozzle type burner has been proposed.

Further, in Patent Document 2, as a method of preventing disturbance of source gas flows, when the focal length of the small-diameter injection port is L ₁ , and the distance from the tip of the small-diameter injection port to the deposition surface of the base material is L ₂ , L _1. It is proposed to make the ratio larger than L ₂ . Conversely, Patent Document 3 says that the deposition efficiency can be improved by making L ₁ smaller than L ₂ and increasing the gas mixing efficiency.

However, in the OVD method of depositing and depositing glass fine particles generated in a burner flame on a rotating starting member by reciprocating the burner or the starting member, as the deposition proceeds, the weight increases and the diameter of the deposit becomes large. As the deposition progresses, the amount of gas is usually increased and the density of the deposited body is adjusted. For example, deposition starts from 50 mmφ of the starting member and continues until it reaches 300 mmφ.

In the initial stage of deposition, since the deposition area is small, the amount of gas is reduced and it is performed at a small gas flux. Therefore, the flow of glass fine particles is easily disturbed by the gas ejected from the small-diameter jet port, and when it is disturbed, the deposition efficiency is lowered. In the second half of the deposition, the diameter of the deposition body increases and the deposition area is large, so that the amount of gas is increased and a large gas flux is performed. As a result, the disturbance of the glass fine particles caused by the gas ejected from the small-diameter jet port becomes small, but there is a problem that the gas mixing rate is lowered and the deposition efficiency does not increase because the gas linear velocity is large.

Patent Document 1: Japanese Patent No. 1773359

Patent Document 2: Japanese Patent No. 3543537

Patent Document 3: Japanese Patent Application Laid-Open No. 2003-226544

The present invention solves the above-mentioned problems, and the method for efficiently producing and depositing glass fine particles, especially for synthesizing a large base material, for the optical fiber that provides stable and high deposition efficiency from the start of deposition to the end of deposition. It aims at providing the manufacturing method of a base material.

The manufacturing method of the base material for optical fibers of this invention has a concentric multi-pipe structure, and arrange | positions one row or multiple rows concentrically with respect to the said glass raw material gas blowing port outside the center glass raw material gas blowing port, Using a burner having a combustible gas ejection port containing a plurality of small-diameter combustible gases having ejection ports arranged in the same row having the same focal length, the glass fine particles generated by hydrolyzing the glass raw material gas in the flame are started. On the basis of the deposition on the member to produce the base material for the optical fiber, the focal lengths of the plurality of small-diameter flammable gas injection ports are set to L ₁ , and from the tip of the small-diameter flammable gas injection port to the glass fine particle deposition surface. when the distance to the L _2, initially deposited so that the L ₁ <L ₂ in the middle, is deposited by L _1> L _2, the particular largely going to the L ₂ Gong. Further, as the deposition amount increases and the outer diameter of the base material increases, the burner can be removed from the deposition surface, and the distance L ₂ can be increased to set L ₁ <L ₂ .

According to the present invention, the deposition can be continued in a stable state from the start of deposition to the end of the deposition, a sudden change in density does not occur, and a high deposition efficiency is obtained.

BRIEF DESCRIPTION OF THE DRAWINGS It is a schematic diagram which shows the manufacturing apparatus of the porous glass base material by an external adhesion method (OVD method).

FIG. 2 is a schematic diagram showing a burner tip for synthesizing glass particles having a small diameter ejection port. FIG.

3 is a diagram illustrating a relationship between the focal length L ₁ and the distance L ₂ from the burner tip to the deposition surface.

4 is a diagram showing a relationship between deposition weight and deposition rate.

<Code description>

1 core

2 dummy rod

3 burner

4 ingot chuck mechanism

5 exhaust hood

6 small diameter jet port

7 sedimentary surface

As a result of diligent research to achieve the above-mentioned problems, it is desirable to appropriately set the relationship between the focal length of the small-diameter jet port and the distance from the tip of the jet port to the deposition surface of the glass fine particles in the initial deposition stage and the late deposition stage, respectively. It was found out that it was important and the present invention was reached.

That is, as shown in FIG. 3, the focal length at which the gas flows from the plurality of small-diameter jet ports arranged concentrically is formed as L ₁ , and the distance from the tip of the jet port to the glass fine particle deposition surface is L _2. In the initial stage of deposition where the flow of the glass fine particles tends to be disturbed by the flammable gas ejected from the jet port, L ₁ &gt; L ₂ , so that the flow of the central glass fine particles is not disturbed. Can be promoted to increase the deposition efficiency.

In addition, in the present invention, the latter half of the deposition refers to a point after the point where the diameter of the deposited body grows to approximately three times the diameter of the starting member.

Conversely, in the second half of the deposition in which the gas amount increases and the flow velocity of the gas flow is large, it is difficult to be influenced by the flammable gas streams ejected from the small-diameter jet port, and the glass fine particles are difficult to be disturbed. Since the gas mixing rate is deteriorating, by setting L ₁ <L ₂ , the flammable gas from the small-diameter jet port concentrates at the focal position and collides with the raw material flame before colliding with the deposit, thereby combustible gas and the flammable gas, In addition, the mixing and reaction of the glass fine particles can be actively promoted, and the deposition efficiency can be increased.

Since the adjustment of the focal length L ₁ of the small-diameter injection port is difficult during deposition, the adjustment of the relationship between L ₁ and L ₂ can be performed by adjusting the distance L ₂ from the burner tip to the deposition surface. Specifically, the burner is removed from the deposition surface smoothly from the initial deposition stage to the second deposition stage, and L ₂ is increased to make L ₁ <L ₂ , without causing a sudden density change of the deposition base material. The deposition can continue in a stable state.

EMBODIMENT OF THE INVENTION Hereinafter, although embodiment and a comparative example are given and described in detail about embodiment of this invention, this invention is not limited to these.

<Example>

Example 1

On the starting member which welded the dummy rod of outer diameter 50mm to the both ends of the core rod of outer diameter 50mm and length 2000mm by the external attachment method using the apparatus as shown in FIG. Using the burner which has a concentric pentagonal structure as shown to it, glass microparticles | fine-particles were deposited and the base material for optical fibers was manufactured.

The used burners are arranged in a row concentrically with respect to the second pipe which ejects a seal gas to the outer side of the glass raw material gas blowing port of a 1st tube, and the glass raw material gas blowing port centered on the outer side, A third pipe (combustible gas ejection port) containing eight small-diameter ejection ports having a focal length L ₁ = 150 mm for ejecting the combustible gas, and ejecting the combustible gas, a fourth pipe for ejecting the seal gas, the combustible gas Consists of a fifth pipe to eject the.

In addition, the first pipe of the burner was supplied with 10 L / min of SiCl ₄ and 20 L / min of flammable gas O ₂ as the glass raw material gas, ₄ L / min of the seal gas N ₂ was supplied to the second pipe, and the combustible gas was supplied to the third pipe. 170 L / min of H ₂ , 5 L / min of sealing gas N ₂ to the fourth pipe, 40 L / min of flammable gas O ₂ to the fifth pipe, and the main pipe of the small-diameter injection port contained in the third pipe (主管) there was 100kg depositing the glass particles on a 16L / min feed, and the starting member the O ₂ as a supporting gases. The kind and supply amount of the gas supplied to each pipe of the burner were shown in Table 1 together with Comparative Examples 1 and 2.

The deposition is started by setting the focal lengths of the plurality of small-diameter jet ports to L ₁ = 150 mm and the distance to the deposition surface L ₂ = 125 mm, and the burner is adjusted in accordance with the growth of the deposit, and the diameter of the deposit is equal to the diameter of the starting member. is almost three times as L ₁ = L ₂ is the time to 150mmφ, such that L ₂ = 175mm is deposited at the end, were put slowly removed from the deposition surface.

The deposition results are shown in Table 2 together with the results of Comparative Examples 1 and 2, and the average deposition rate for every 5 kg is shown in FIG. It is recognized from FIG. 4 that the deposition rate of the example is superior to Comparative Examples 1 and 2 described later during deposition.

Comparative Example 1

100 kg of glass fine particles were deposited on the starting member in the same manner as in Example 1 except that the focal length L ₁ = 150 mm of the small-diameter jet port was maintained while the distance L ₂ = 125 mm to the deposition surface was deposited. 4, the deposition speed was almost the same as that of the embodiment in the initial stage of deposition, but was inferior to the embodiment in the latter stage of deposition.

Comparative Example 2

100 kg of glass fine particles were deposited on the starting member in the same manner as in Example 1 except that the focal length L ₁ = 150 mm of the small-diameter jet port was maintained while the distance L ₂ = 175 mm to the deposition surface was deposited.

Although it was inferior to an Example at the beginning of deposition from FIG. 4, the deposition rate of the latter half of deposition was about the same as an Example.

Industrial availability

According to this invention, the deposition efficiency of glass microparticles | fine-particles improves and it contributes greatly to the productivity improvement of a porous glass base material.

Claims (2)

It has a concentric multi-pipe structure, one row or plural rows are arranged concentrically with respect to the glass raw material gas blowing port outside the center glass raw material gas blowing port, and the blowing ports arranged in the same row have the same focal length, By using a burner having a flammable gas ejection port containing a plurality of small-diameter flammable gases, glass fine particles generated by hydrolyzing the glass raw material gas in a flame are deposited on the starting member to produce a base material for the optical fiber, When the focal lengths of the plurality of small-diameter flammable gas blowing ports are set to L ₁ , and the distance from the tip of the small-diameter flammable gas blowing port to the glass fine particle deposition surface is set to L ₂ , at the initial stage of deposition, L ₁ > to L _2, and L ₁ is deposited during the method for fabricating a preform for optical fibers, it characterized in that the thin greatly, so that the L ₂ <L _2. The method of claim 1, The deposition method increases, and as the outer diameter of the base material increases, the burner is removed from the deposition surface, and the distance L ₂ is increased so that L ₁ <L ₂ .