JP2005247636A - Method of manufacturing porous preform for optical fiber and glass preform - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing a porous glass preform by which the deposition rate of a glass fine particle on a deposition surface is increased, soot suspended in a reaction vessel is reduced and the occurrence of bubbles produced in a product is prevented and the glass preform. <P>SOLUTION: In the method of manufacturing the porous glass preform by flame-hydrolyzing a glass raw material in oxyhydrogen flame and depositing the produced glass fine particle, the glass fine particle is deposited by moving a center rod upward at almost fixed speed with the deposition of the glass fine particle and jetting flame stream containing the synthesized glass fine particle toward the glass fine particle deposition surface from the diagonally downward direction to form a recessed part on the deposition bottom surface of a deposited body. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for producing a porous glass preform by depositing glass fine particles produced by flame hydrolysis of a glass raw material on a starting member, and in particular, porous glass for an optical fiber that improves the deposition efficiency of glass fine particles. The present invention relates to a base material manufacturing method and a glass base material.

Synthetic quartz glass is used in various applications such as optical fibers, mask substrates, and lenses, and the VAD method is widely adopted as a method for producing synthetic quartz glass.
In the VAD method, glass raw materials such as SiCl ₄ are flame-hydrolyzed in a burner flame, and the generated glass particles are deposited on a starting member that rises at a constant speed while rotating to make a porous glass base material. Is a method in which synthetic quartz glass is obtained by dehydration and transparent vitrification at a high temperature.

In the VAD method, in addition to a method in which a glass rod prepared in advance is used as a starting member and glass fine particles are deposited around it to synthesize the outer peripheral portion, the central portion and the outer peripheral portion corresponding to the starting member are simultaneously synthesized. You can also.
The glass particles produced by flame hydrolysis are sprayed onto the deposition surface of the starting member together with the flame flow, and adhere and accumulate, but a part (approximately 50% depending on the conditions) is not deposited, but the exhaust gas. At the same time, it is discharged outside the system.

  The porous glass preform for optical fiber synthesized by the VAD method usually has a shape as shown in FIG. 1, and the core portion (a), the first cladding portion (b), and the second portion are sequentially formed from the center. A clad part (c) is formed. In this case, the diameter of each deposited layer monotonously increases (see Patent Document 1).

As shown in FIG. 2, in the porous glass base material, first, a central rod 2 serving as a core portion is formed by a core portion deposition burner 1, and a first cladding portion is formed thereon by a first cladding portion deposition burner 3. However, the second cladding portion is further deposited thereon by the second cladding portion deposition burner 4 to form a porous glass base material.
As indicated by hatching, the glass fine particle flow 5 generated by the first cladding portion deposition burner 3 hits the central portion 2 and rises while being divided into left and right, and then leaves the surface and is finally discharged out of the system. At this time, most of the unadhered glass fine particles (soot) that have not been deposited are discharged out of the system together with the exhaust gas, but some of them adhere to and accumulate on the inner wall of the reaction vessel.

JP 2000-63141 A

Synthetic quartz glass is used in various applications, but recently, there is a strong demand for larger size for optical fibers, and the amount of unattached soot has increased accordingly, increasing raw material costs. . Furthermore, if the adhesion rate of the glass particles on the deposition surface is low, unattached soot will adhere to and deposit on the inner wall of the reaction vessel, and if this comes off and adheres to the deposition surface, it will cause bubbles in the product. , Reduce the yield.
For this reason, a method for adhering the generated glass fine particles to the deposition surface with higher efficiency is demanded.

  The present invention relates to a method for producing a porous glass base material and glass capable of increasing the adhesion rate of glass fine particles on the deposition surface, reducing soot floating in the reaction vessel, and preventing the generation of bubbles generated in the product. To provide a base material.

  As a result of intensive studies, the present inventors have solved the above problems, that is, the method for producing a porous glass base material of the present invention is produced by flame hydrolysis of a glass raw material in an oxyhydrogen flame. When producing a porous glass base material by depositing glass particles, the central rod is raised at a substantially constant rate in accordance with the deposition of the glass particles, and synthesized by a deposition burner obliquely from below toward the glass particle deposition surface. It is characterized in that a flame flow containing the glass fine particles is sprayed to form a concave portion on the bottom surface of the deposited body and deposit.

  The center rod is made of a porous glass material obtained by depositing and growing glass particles in the axial direction using a burner different from the deposition burner, or a transparent glass material, more preferably a quartz glass material. You can also. The quartz glass material may be uniform in the radial direction or may contain a dopant in part.

The shape of the recess formed on the bottom surface of the deposition is preferably adjusted by the flow rate of the glass raw material supplied to the deposition burner, but may be adjusted by the flow rate of the combustion gas or auxiliary combustion gas supplied to the deposition burner. The deposition burner is preferably installed at an angle of 30 ° to 50 ° with respect to the vertically arranged central bar.
A glass base material excellent in optical properties can be obtained by dehydrating and sintering the produced porous glass base material and then converting it into a transparent glass.

  By dehydrating the porous glass base material thus obtained and sintering and forming a transparent glass, for example, quartz glass excellent in optical properties suitable as a glass base material for optical fibers is manufactured at low cost. be able to.

  The present inventors have found that there is a method for increasing the adhesion rate of the glass fine particles in addition to the flow rate of the glass raw material, the flow rate of the burner flame, the temperature of the deposition surface, and the like, and adjust the deposition surface to a shape suitable for deposition. Thus, specifically, the problem was achieved by depositing so as to form a recess on the bottom surface of the deposit.

  As is apparent from FIGS. 1 and 2, the lower portion of the porous glass base material being deposited is mainly formed by the first cladding portion deposition burner 3. The first cladding part deposition burner plays a role of adjusting the refractive index distribution by heating the side surface of the core part in addition to the formation of the first cladding part. The adhesion rate of glass fine particles is low compared to

  The present invention is an improvement of this, and by forming a recess on the bottom surface of the deposit, the adhesion rate of the glass particles sprayed from the first cladding portion deposition burner 3 can be increased. By increasing the outer diameter of the clad portion, the adhesion rate of the second clad portion is also improved, and excess soot floating in the reaction vessel can be reduced.

This will be described in more detail with reference to FIG.
First, a center rod 2 is formed by a core portion deposition burner 1, and a first cladding portion is formed by a first cladding portion deposition burner 3 (hereinafter simply referred to as a burner 3). A recess 6 is formed on the bottom surface of the first cladding portion so as to surround the center rod 2. The shape of the recess 6 can be adjusted by the gas flow rate supplied to the burner 3. Note that the burner 3 is installed so as to have an angle of 30 degrees to 50 degrees with respect to the center bar 2. If this angle is less than 30 degrees, the adhesion rate is low, and if it exceeds 50 degrees, it is difficult to form the recess 6, which is not preferable.

  As shown by hatching, the glass fine particle flow 5 generated by the burner 3 hits the center rod 2 and is divided into left and right through the concave groove formed by the recess 6 and on the opposite side of the center rod 2. And then move away from the deposition surface. For this reason, since the glass fine particle flow 5 passes through the concave groove of the concave portion 6, the contact time with the deposition surface increases, and the adhesion rate of the glass fine particles increases.

The shape of the recess 6 depends on the thickness of the center rod 2 to which the glass fine particle flow 5 hits, the flow rate and speed of the raw material gas and combustion gas supplied to the burner 3, the diameter of the burner 3, and the like. Although the shape adjustment is not generally discussed, it is preferable to adjust the flow rate of the glass raw material gas more than usual, and is particularly effective.
In the example of FIG. 3, the first cladding portion is formed by one burner 3, but a plurality of burners 3 may be arranged. Moreover, although the center rod 2 which becomes a core part is formed simultaneously with the core deposition burner 1, a quartz glass rod prepared in advance may be used as the center rod 2.

Example 1;
The amount of gas supplied to the burner was H ₂ 13 L / min, O ₂ 14 L / min, Ar 2 L / min, and the glass raw material (SiCl ₄ ) was 0.8 L / min, which is higher than usual. The burner is placed upward at 45 ° with respect to the center rod made of transparent quartz glass with a diameter of 30 mm, and the center rod is rotated at a speed of 0.8 mm / min while rotating the center rod to deposit glass particles around the center rod, A porous glass matrix was synthesized.
During deposition, a recess (concave groove) is formed in the shape of a passage around the bottom surface of the deposit and around the central rod, and the burner flame flow flows through the concave groove, and the adhesion rate of glass particles reaches 87%, which is extremely high. did.

Comparative Example 1;
Except that the supply rate of the glass raw material (SiCl ₄ ) was changed to the usual 0.45 L / min, the deposition was performed under the same conditions as in Example 1. As a result, no recess was formed in the deposited body, and the diameter was porous glass. It increased monotonously in the longitudinal direction of the base material. The adhesion rate of the fine glass particles was 62%.

  According to the method for producing a porous glass preform of the present invention, the adhesion rate of glass fine particles can be improved, which contributes to the cost reduction of the optical fiber.

(A), (B) is a figure which shows the outline of the porous glass preform | base_material synthesize | combined by VAD method, and, as for all, each deposited layer is increasing monotonously in the radial direction. It is the schematic which shows the mode of the conventional glass particle deposition. It is the schematic which shows the mode of deposition of the glass fine particle by this invention.

Explanation of symbols

1. ...... Core burner
2. …… Center rod (core part),
3. ... Burner for depositing the first cladding
4). ... Burner for depositing second cladding part
5). ...... Glass particulate flow,
6). ... concave.

Claims (8)

When a porous glass base material is produced by flame hydrolysis of a glass raw material in an oxyhydrogen flame and depositing the generated glass fine particles, the center rod is raised at a substantially constant rate as the glass fine particles are deposited. A porous glass base material characterized in that a flame flow containing glass fine particles synthesized by a deposition burner is jetted obliquely downward toward a fine particle deposition surface to form a concave portion on the bottom surface of the deposit and deposit. Manufacturing method. 2. The method for producing a porous glass base material according to claim 1, wherein the central bar is a porous glass material obtained by depositing and growing glass particles in the axial direction using a burner different from the deposition burner. The method for producing a porous glass base material according to claim 1, wherein the center bar is a transparent glass material. The method for producing a porous glass base material according to claim 3, wherein the transparent glass material is a quartz glass material and contains a dopant uniformly or partially in a radial direction. The manufacturing method of the porous glass base material in any one of Claims 1 thru | or 4 which adjusts the shape of the recessed part formed in the said deposition lower surface with the flow volume of the glass raw material supplied to the said deposition burner. The method for producing a porous glass base material according to any one of claims 1 to 5, wherein a shape of the concave portion formed on the deposition lower surface is adjusted by a flow rate of a combustion gas or an auxiliary combustion gas supplied to the deposition burner. The method for producing a porous glass base material according to any one of claims 1 to 6, wherein the deposition burner is installed at an angle of 30 to 50 degrees with respect to a vertically disposed central bar. A glass base material obtained by dehydrating and sintering a porous glass base material manufactured using the manufacturing method according to any one of claims 1 to 7, and then forming a transparent glass.

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