JPS63123828A - Production of porous preform for optical fiber - Google Patents

Abstract

PURPOSE:To obtain the titled preform of having a large bulk density and a desired shape in high and stable yield of synthesis while preventing dropping and cracking, by using a multiple-pipe burner having a nozzle with an outer diameter of a specific ratio to that of a porous preform to be prepared. CONSTITUTION:A concentric multiple-pipe burner 2 is constructed in such a way that, for example, raw material SiCl4 is fed to a central boat 1 at about 1l/min flow rate, H2 to a boat 2 at about 10l/min flow rate, Ar to a boat 3 at about 3l/min flow rate and O2 is fed to a boat 4 at about 20l/min flow rate and the outer diameter of the concentric multiple-pipe burner is 0.2-0.5 times as large as the outer diameter of a porous preform to be prepared. The burner 2 is set in the reactor 1 of a reaction apparatus for the vapor-phase axial deposition method of a porous preform for optical fiber; for example at the flow rates above-mentioned, each raw material gas and carrier gas are fed to the reactor; the raw material gases are hydrolyzed in an oxyhydrogen flame 3 to synthesize glass fine particles, which are deposited at the axial end part of a starting material at a revolving shaft 4, and the deposited material is grown in the revolving- and axial directions to give the aimed preform 5.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to the so-called soot method in which a porous base material for optical fibers is manufactured by synthesizing fine glass particles through a hydrolysis reaction in a flame and depositing the same. It is something.

Conventional methods for producing optical fibers include two methods: producing a porous preform for optical fiber with a desired composition, making the porous preform for optical fiber transparent and drawing it, and producing glass with the desired composition. The main method is to manufacture a rod, cover the glass rod with a glass jacket, integrate it, and then draw it.

The above-mentioned porous preform for optical fibers is produced by generating glass particles from frit gas using a flame hydrolysis reaction and depositing them on a starting material.

Briefly, as shown in FIG.
The combustion gas and the glass raw material are ejected from the combustion gas, and the glass raw material is subjected to a hydrolysis reaction in the oxyhydrogen flame 3 generated by the combustion of the combustion gas, and the glass fine particles generated as a result are deposited on the rotating starting material to form a porous matrix. A method of growing material 5 is used. FIG. 1 shows the so-called axial method, in which glass particles are deposited on the axial end of a rotating starting material, and the deposit grows in the rotational direction of the starting material as well as in the axial direction.

The burner 2 is generally a concentric multi-tube burner as shown in FIG. 2, and the diameter of each port of this burner is one of the important parameters.

In the production of such porous preforms for optical fibers, the synthesis speed of porous preforms has recently been increased to improve productivity. Although it is necessary to increase the gas flow rate for this high-speed synthesis, a method of increasing the gas flow rate cannot be adopted. This is because the glass particle production reaction that occurs within the flame requires sufficient reaction time, so it is necessary to slow down the flame flow rate. Therefore, it is necessary to increase the outer diameter of the burner for high-speed synthesis of porous preforms for optical fibers. As a result, as the synthesis rate of the porous base material increases, the outer diameter of the porous base material generally tends to increase.

Problems to be Solved by the Invention As described above, as the synthesis speed of the porous base material increases, the outer diameter of the porous base material increases. Defects such as falling or cracks on the surface are becoming more likely to occur.

These problems, such as falling of the porous base material and cracks on the surface, depend on the hardness of the porous base material being synthesized. is likely to occur.

Therefore, it is possible to increase the flow rate of combustion gas fed into the burner to raise the synthesis temperature, but as the flow rate of gas increases, the flow velocity increases and the reaction time in the flame becomes insufficient. arise.

Further, the size of the flame is limited by simply increasing the amount of combustion gas, and it is difficult to sufficiently heat a large porous base material.

Furthermore, if the size of the flame is too large, the glass particles will become large and the outer diameter of the porous base material will become too large, which will reduce the synthesis yield (porous base material and raw materials) of the porous base material in the desired form. (ratio)) is difficult to form well.

Therefore, an object of the present invention is to solve these problems and provide a method for synthesizing a stable porous preform for optical fibers with good yield.

Means for solving the problem, namely, according to the present invention, glass fine particles produced by reacting glass raw materials supplied from a multi-tube burner in a flame produced by a multi-tube burner are rotated as a starting material. In the method of manufacturing a porous glass preform by depositing the material on the substrate and growing the deposited body in the rotational direction, the diameter of the outlet of the multi-tube burner is set to 0.2 of the outer diameter of the porous preform.
-0.5 times.

Effect As mentioned above, as the synthesis speed of the porous base material increases, the outer diameter of the porous base material increases, making it easier for defects such as dropping of the porous base material and cracks on the surface to occur. Become. Therefore, when we compared the porous base material that had fallen and the porous base material that had stably maintained its shape, we found that their bulk densities were different. That is, the fallen porous base material has a low bulk density and therefore cannot maintain its shape.

Therefore, it can be said that the greater the bulk density, the greater the adhesive force between particles. It was also found that the bulk density of the porous base material is affected by heating with an oxyhydrogen flame, and that the bulk density becomes higher when the heating effect is increased.

Therefore, it is preferable to use a sufficiently large flame to stably produce a large porous base material. In the case of a multi-tube burner, the flame size is determined by the burner's outer diameter because the feed gas is ejected from a central port while the combustion gas is ejected from surrounding outer ports. As a result of various studies, it has been found that it is possible to produce a porous base material that is sufficiently stable, that is, has a high bulk density, by using a burner that has an outermost diameter that is 0.2 times or more the outer diameter of the porous base material. I found out.

On the other hand, if the size of the burner is increased, a large porous base material can be stably manufactured, but as the size of the burner is increased, the outer diameter of the porous base material also tends to increase. this is,
As mentioned above, since the raw material is fed into the center of the concentric multi-tube burner, a particle flow is formed at the center of the flame, but as the flame becomes larger, the particles diffuse to the outside of the flame. This is because the cross-sectional area of the particle flow becomes larger.

There are various restrictions on the outer diameter of the porous preform depending on the manufacturing process of the optical fiber, and it is necessary to fit it into a desired shape. Therefore, it was found that when the outer diameter of the porous base material to be synthesized was reduced by using a large burner and changing the flow rate, angle, etc., a phenomenon appeared in which the synthesis yield decreased. . It has been found that this becomes noticeable when a burner having an outermost diameter that is 0.5 times or more the outer diameter of the porous base material is used.

From the above, in order to stably produce a large porous base material by high-speed synthesis, it is necessary to have an outer diameter of 0.
It is sufficient to use a burner with an outer diameter of 2 to 0.5 times, and conversely, if there are restrictions on the burner, it is preferable to manufacture a porous base material with an outer diameter of 2 to 5 times the outer diameter of the burner.

Here, the "burner outer diameter" refers to the outermost diameter of a combustion gas ejection port ejected to form an oxyhydrogen flame. Therefore, the outer diameter of the windshield attached to the tip of the burner to regulate the flow is not included in the "burner outer diameter." In addition, when nonflammable gas is flowed around the burner, that is, around the outermost combustion gas, in order to adjust the flow inside the reaction vessel, the outside diameter of the nozzle for this nonflammable gas is the "burner outside diameter". is not included.

Thus, by making the diameter of the outlet of the combustion burner at least 0.2 times the outer diameter of the porous base material, the heating effect can be increased with a sufficiently large flame, and the bulk density can be reduced without falling or cracking on the surface. It is possible to obtain a stable porous base material with a large value, and by reducing the amount by 0.5 times or less, a porous base material can be obtained with a sufficient synthesis yield.

EXAMPLES Hereinafter, the present invention will be described in detail with reference to the accompanying drawings. However, the invention is in no way limited to the embodiments described and illustrated below.

Example 1 A conventionally used porous preform for optical fiber shown in FIG. 1 was manufactured using a method manufacturing apparatus under the following conditions. In this example, a concentric quadruple tube burner as shown in FIG. 2 was used. At this time, the center 1
The raw material 3iC1a is supplied to the boat at a flow rate of If/min, H2 is supplied at a flow rate of 101/min to 2 ports surrounding the central 1 port, ^r is supplied at a flow rate of 3β/min to 3 ports surrounding the 2 ports, 0□ was supplied to the four boats surrounding the two ports at a flow rate of 201/min. 2g when using a burner with an outer diameter of 20mm
A porous base material with a diameter of 80 mm could be synthesized at a deposition rate of /min.

That is, in this case, the burner outer diameter was 0.25 times the outer diameter of the porous base material. The defect rate [ratio of defective products (porous base material with falling or surface cracks) to the manufactured porous base material] was 0.2.

Furthermore, under the same conditions as in Example 1, a porous base material of 80 mmφ was synthesized using a burner with an outer diameter of 25 Ωm. The defect rate in this case was 0.05.

Comparative Example 1 A porous base material having the same shape as in Example 1 and having an outer diameter of 3Q mmφ was manufactured using burners with an outer diameter of 15 mmφ and an IQ+r+mφ, respectively.

At this time, the flow rate of gas sent to the burner was the same as in the first embodiment. As a result of this experiment, the defective rates of burners with outer diameters of 15 mmφ and 10 mmφ were 0.7 and 0.0, respectively.
It was 8. With such a result, stable production of a porous base material cannot be expected.

In addition to the results of Example 1 and Comparative Example 1, the results of manufacturing porous base materials using burners with other outer diameters show that when the outer diameter of the porous base material is 80 φ, The relationship between the outer diameter and the defective rate was as shown in FIG.

Example 2 Using a quadruple pipe type burner with an outer diameter of 40 mm as shown in Fig. 2, 1 port raw material 5iC1,3R/min, 2 ports H215j! / minute, 3 points Ar5j! / minute, 4 po)
When supplied at a rate of 0225β/min, the deposition rate was 4g.
A porous base material with an outer diameter of 120 mmφ could be produced at a rate of 120 mmφ.

At this time, the same gas waterfall pot was flowed through the same burner, and the outer diameter of the porous base material was adjusted in various ways by changing the angle of the burner relative to the porous base material. As a result, the deposition rate changed as shown in Figure 4. did.

As can be seen from FIG. 4, when synthesizing a porous preform for an optical fiber having a diameter less than twice the outer diameter of the burner of 40 mm, that is, less than 80 mm, the productivity is extremely poor.

In the above embodiments, the present invention is applied to the manufacture of porous preforms for optical fibers using the so-called shaft-mounting method, but the so-called externally-attached porous preforms can also be manufactured using the method. Therefore, the present invention is equally applicable.

As described in detail, the present invention uses a burner having an outer diameter 0.2 to 0.5 times the outer diameter of the porous base material so that the porous base material falls. It becomes possible to produce a porous base material in a desired shape with a high bulk density without any problems, and with a high synthesis yield, which is effective in improving productivity.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram showing a typical example of a method-based manufacturing apparatus for shafting a porous base material. 2 is an end view and a longitudinal sectional view schematically showing a concentric multi-tube burner used in the porous preform manufacturing apparatus shown in FIG. 1. FIG. FIG. 3 is a graph showing the defect rate due to falling and surface cracks when porous base materials with an outer diameter of 80 mmφ were manufactured with different burner outer diameters. FIG. 4 is a graph showing the change in deposition rate depending on the outer diameter of the porous base material produced when the porous base material was produced using a burner having an outer diameter of 40 mmφ. (Main reference numbers) 1. Reaction vessel, 2. Burner, 3. Oxyhydrogen flame, 4. Rotating shaft, 5. Porous base material

Claims (2)

[Claims] (1) By depositing glass particles produced by reacting the glass raw materials supplied from the multi-tube burner in the flame created by the multi-tube burner on a rotating starting material and growing the deposit in the direction of rotation. A method for producing a porous glass preform, wherein the diameter of the outlet of the multi-tube burner is within a range of 0.2 to 0.5 times the outer diameter of the porous preform. Method for manufacturing porous base material for use. (2) The porous glass base material is attached to a shaft by depositing the glass particles on the shaft end of the rotating starting material and growing the deposited body in the rotational direction of the starting material as well as in the axial direction of the starting material. Claim No. 1 (1) characterized in that it is manufactured by
) A method for producing a porous preform for optical fibers as described in item 2.