JPH02212327A - Production of optical fiber preform - Google Patents

Abstract

PURPOSE:To efficiently obtain a porous glass preform having uniform density by using plural burners set at specified positions to eliminate the interference between plural flames, and generating fine glass particles by flame hydrolysis. CONSTITUTION:The glass material is flame-hydrolyzed by an oxyhydrogen flame burner 1 to generate fine glass particles 3. The particles 3 are deposited on the starting member 4 of a core glass rod by external deposition to obtain the porous glass preform 5. In this case, plural burners 1 are used, and arranged in parallel. When the distance between the intersections of the radius of expanse of a flame 2 on the surface of the preform 5 is specified as unit, the expanse of the flame 2 is controlled to 0.5-1.5 times the unit.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for producing an optical fiber preform base material, and in particular to a method for producing glass particles by flame hydrolysis of a glass raw material using two or more burners. The present invention relates to a method for producing a porous glass preform.

[Prior art] The VAD method and the OVD method are known as methods for producing optical fiber preform base materials, and these methods send glass raw materials such as silicon tetrachloride to an oxyhydrogen flame burner and undergo flame hydrolysis. It is made by generating glass particles and depositing them on a starting member made of core glass to create a porous glass base material, which is then dehydrated, sintered, and vitrified to form an optical fiber base material. However, in order to improve the productivity of this porous glass base material, two or two burners were installed.
A method for using more than one book has been proposed.

[Problems to be Solved] However, as mentioned above, when performing flame hydrolysis of glass raw materials using two or more burners, if the burners are placed too close together, the burner flames may Due to mutual interference, the amount of deposition decreases, and 2
Even though you send twice as much raw material using a wood burner, you only get the effect of one or 1.5 burners.

On the other hand, if the burners are spaced too far apart, the effective deposition length will be shortened in a distance-limited device, even though the deposition rate will not change at its maximum value, and the target preform length will be shortened. A problem had arisen.

[Means for Solving the Problems] The present invention relates to a method for manufacturing an optical fiber preform base material that solves the above-mentioned disadvantages, and this invention involves flame hydrolyzing a glass raw material with an oxyhydrogen flame burner to form glass fine particles. When producing an optical fiber base material by depositing it on a starting material for a core to make a porous glass base material, dehydrating it, sintering it, and vitrifying it to produce an optical fiber base material, two or more burners are used to produce a porous glass base material. The distance between the burners is set to 0.5 to 1.5 times the radius of flame spread based on the intersection of the flame spread on the surface of the porous glass base material, and the maximum distance is the final diameter of the porous glass base material. It is characterized by being based on the following ranges.

That is, the present inventors flame-hydrolyze the glass raw material using two or more oxyhydrogen flame burners, and deposit the generated glass particles on a starting member to form an optical fiber base material. As a result of various studies on ways to rationalize the manufacturing method, we decided to set the interval between multiple burners based on the intersection of the flame spread on the surface of the porous glass base material.
If the distance is 0.5 to 1.5 times that, and the maximum distance between burners is within the final diameter of the porous glass base material,
It was discovered that it was possible to shorten the unnecessary distance of burners lined up in parallel, and to maximize the production speed per limited length. According to this, the desired optical fiber could be manufactured efficiently. The present invention was completed after confirming that it is possible.

[Work] This will be explained in detail below based on the attached drawings.

FIG. 1 is a vertical cross-sectional view illustrating the positions of two burners in the method of the present invention, FIG. 2 is a graph showing the relationship between the burner spacing and the glass particle deposition rate in this method, and FIG. A vertical cross-sectional view showing the spread of flame when one burner is used, Figure 4 shows a case where the distance between two burners is too narrow, and Figure 5 shows a vertical cross-sectional view when the distance between two burners is too wide. It is something.

That is, FIG. 3 shows that a glass raw material is supplied to an oxyhydrogen flame burner 11 according to a known method, where it is flame-hydrolyzed to generate glass fine particles, which are then transferred to a starting member 12.
When the glass raw material is flame-hydrolyzed using one oxyhydrogen flame burner 11 to create the porous glass base material 13 by depositing it on the glass, the spread of the flame 14 is within the range 15 shown in FIG. 3. It is known. However, in this case, as shown in FIG.
．． When 11 are placed relatively close together, this flame 14.14
The spread of the flame is as shown in 16.17, but since the flames 14.14 interfere with each other, the deposition interferes with each other at the boundary 18, and the deposition rate of glass particles decreases. This will result in a decline. In addition, when these two burners 11.11 are used, if the two burners 11.11 are separated with a long distance between them as shown in FIG.
The flame spread of 4.14 is now shown as 19°20, so the deposition efficiency is equivalent to two burners depositing independently or at twice the rate, but As the burner distance increases, the effective distance on the target decreases.

However, when two or more burners are used according to the method of the invention, the arrangement of the two burners 1.1 is such that the flame of the burner 1.1 is The deposition yield can be maximized by depositing at or above the intersection of the 2.2 spreads.

However, if the burner spacing becomes too large, the deposit within this spacing will taper towards the ends, as shown in Figure 6, and a uniform thickness cannot be obtained;
．． It has been found that the overall synthesis rate, taking into account the burner spacing, is the highest at a rate of 0.5 to 1.5 times the flame spread radius.

In addition, the two burners 1.1 in the case of this FIG.
The interval is 1 times the spread radius of flame 2.2, but in relation to the final diameter of the porous glass base material, this interval is the same as the flame radius at the final diameter of the porous glass base material. If the spread is larger than , the disadvantage is that the effective length will be shortened, so it is necessary that this is 1.5 times or less the spread radius of the flame 2 and the maximum interval is less than or equal to the final diameter of the porous glass base material.

Furthermore, the optical fiber base material which is the object of the present invention has a porous glass base material of 1.3 (10 to 1.800)
It can be obtained by heating it to ℃ and sintering it to make it transparent vitrified, but this transparent vitrification can be done according to a known method, and according to the method of the present invention, a porous glass base material can be produced efficiently.

[Example] Next, examples using the method of the present invention will be given.

Example 1 Two concentric quadruple tube oxyhydrogen flame burners were used, and the first inner layer of each burner contained 1.124 silicon tetrachloride! 7 minutes,
Hydrogen gas 3j2/min in the second layer, argon gas 0 in the third layer
．． 617 minutes, oxygen gas was flowed into the fourth layer for 6117 minutes, and the interval between these two burners was changed to perform an external method (OVD method).
A porous glass matrix was created by depositing glass particles generated by flame hydrolysis of silicon tetrachloride on a quartz glass rod, and the deposition rate was calculated from this weight increase. Regarding the relationship with
The results shown in the figure were obtained.

In addition, the burner interval on the horizontal axis in FIG. 2 is based on the flame spread width as 1, and the deposition rate of glass particles on the vertical axis is based on the deposition rate when one burner is used. This means that if the burner spacing is less than 0.4 times the flame spread width, the deposition rate will not reach the capacity of 1.5 burners, resulting in poor efficiency. It was confirmed that approximately two tubes worth of deposition was achieved. In addition, in this experiment, it was confirmed that the effective length for making the burner interval equal to or larger than the final diameter of the porous glass base material rapidly decreased as shown in the figure.

Example 2 Using oxygen carrier gas in the center of a quartz quadruple tube burner with an outer diameter of 18 mmΦ, 5iCj! 4 was transported, and oxyhydrogen was spouted from the outer periphery to perform gas phase hydrolysis of silicon tetrachloride. On the other hand, a dummy quartz rod with the same diameter was welded to a quartz rod with an outer diameter of 18 mm and a flea of 800 smL, the core of the entire rod was taken out, and the rod was placed horizontally and rotated about its axis at 30 rpm.

One of the burner flames is caused to collide with the side surface of this quartz rod to deposit silica particles on the quartz rod, and the burner is moved parallel to the length direction of the quartz rod to form a porous silica glass soot layer by layer by external deposition method. was deposited. At the start of deposition, the gas amount is suppressed, and finally 5ICjLa31/min, 0,
2017 minutes, H235J! 7 minutes, soot outer diameter 11
Deposition was terminated when 5 amΦ was reached, and the average deposition rate at this time was 120 g/hour.

Next, two identical burners were lined up and the burner spacing at which double the deposition rate could be obtained with the same gas conditions was investigated, and the results were as shown in Table 1. From this result, when two burners are used, the amount of deposition increases as the distance between the burners increases, but it becomes saturated at the Bancho spread radius (8◆r2) or more, and the amount is almost doubled.

On the other hand, when the length is limited to 80011111, the distance of the steady deposition zone decreases as the burner interval increases, and the unsteady (cone part whose shape changes) increases with twice the burner interval as one unit ( (See Figure 7), in order to arrange two or more burners, the relationship L/(2nr) ≧ 5 is established between the burner pressure M (2nr) and the soot deposition distance (L), and if it is 5 or less, one It is clear that the production speed may be lower than that of the conventional burner, so the raw materials, time, and labor costs will be more than twice as high. therefore,
The distance between the burners that can increase the production rate even if the deposition efficiency is reduced, and the maximum distance between the burners where it is meaningless to separate them any further are preferably 0.5 < nr < 1.5, and a deposition ratio of 11L/distance between the burners. M(2
It was found that nr) must be 5 (see Figure 8).

[Effects of the Invention] The present invention involves depositing silica particles obtained by flame hydrolyzing a glass raw material in an oxyhydrogen flame on a starting member to produce a porous glass base material using two or more particles. According to this method, a plurality of burners are used, and the interval between the plurality of burners is set to be larger than one times the spread radius of the burner flame, based on the intersection of the spread radius of the burner flame. Since there is no mutual interference of flames, there is an advantage that a porous glass base material having a uniform bulk density can be efficiently obtained.

[Brief explanation of the drawing]

FIG. 1 is a vertical cross-sectional view showing the positions of two burners in the method of the present invention, FIG. 2 is a graph showing the relationship between the burner spacing and the deposition rate of glass particles in this method, and FIG. Figure 4 is a vertical cross-sectional view showing the spread of flame when one burner is used according to the conventional method, Figure 4 is a vertical cross-sectional view of a case where the distance between two burners is too narrow, and Figures 5 and 7 are vertical cross-sectional views of cases where the distance between the burners is too wide. The top view and Figure 's6 show a vertical cross-sectional view when one burner is moved from side to side, and Figure 8 shows the relationship between burner spacing and product production speed when two burners are used. This shows a relationship graph. 1.1! ...Oxyhydrogen flame burner 2.14--Flame, 3...Glass particles, 4.
12...Starting member, 5.13...Porous glass base material, 15, ia, tfu, 19.20...Flame spreading part, IB, 21 River boundary part, Figure 3, 4th circle 2nd day 5th day 0.5 1.0 □ Burner inner corner Applicant name (206) Shin-Etsu Chemical Co., Ltd. 4. Agent starting point May 30, 1999 6. “Detailed description of the invention column” in the power of attorney subject to amendment and specification 7. Contents of amendment Amend the power of attorney as shown in the attached document. Procedural amendment 2, name of the invention, method for manufacturing optical fiber preform base material 3, name of person making the amendment related to the case (20 4, agent

Claims (1)

[Claims] 1. Glass particles are generated by flame hydrolyzing the glass raw material with an oxyhydrogen flame burner, and these are deposited on the starting material of the core glass rod by an external method to create a porous glass base material. In a method for producing an optical fiber preform base material which is dehydrated, sintered and vitrified, two or more burners are arranged in parallel, and the flame spreads on the surface of the porous glass base material being deposited. A method for manufacturing an optical fiber preform base material, characterized in that the distance to the intersection point where the radii intersect is 1, and the flame is installed in a range where the spread of the flame is 0.5 times to 1.5 times the distance. 2. The method for manufacturing an optical fiber preform base material according to claim 1, characterized in that the porous glass member is created at burner intervals based on the final soot diameter. 3. The method for manufacturing an optical fiber preform preform according to claim 1, wherein the moving distance is at least five times the burner interval.