JPH01201040A - Production of matrix for optical fiber - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] [Industrial application field] The present invention uses a multi-tube burner to perform the VAD method (vapor phase axial method).
In a method of manufacturing a porous base material for a fiber by producing granular glass (soot) such as OVPO method (external vapor phase oxidation method), j#! of granular glass is used. The present invention relates to a manufacturing method that can improve product efficiency.

[Conventional technology]

In the soot generation method, glass raw materials are fed into the flame of a combustion burner and subjected to flame hydrolysis or oxidation reaction to synthesize granular glass, which is deposited around a rotating starting material or mandrel. A porous glass preform is manufactured by this process.

As a combustion burner at this time, a burner having a concentric one-tube structure and having a plurality of ejection ports for glass raw material and flame formation for combustion gas, auxiliary gas, and inert gas is usually used.

This kind of combustion burner has a concentric multiple structure with a set of frit ports and a flame forming port on the outside of the inner flame forming nozzle, and a concentric multiple structure with a set of frit ports on the outside of the inner flame forming nozzle. an outer flame-forming nozzle comprising ports for use and/or flame-forming, the outer flame-forming nozzle being elevated relative to the inner flame-forming nozzle by a distance sufficient to complete synthesis of the granular glass; A burner with steps has been proposed (Japanese Utility Model Publication No. 60-4979). With such a double structure, synthesis of granular glass and temperature control of the deposition surface can be performed separately.

Furthermore, in Japanese Patent Publication No. 62-50418, as shown in Fig. 4, a double structure multi-tube burner (double flame burner) is used.
The inner flame forming nozzle 41 is replaced by the outer flame forming nozzle 42.
A burner has been proposed in which the step L' between the tips of both nozzles can be adjusted.This burner can increase the diameter of the granular glass by increasing the burner flame length. , it is stated that by doubling the flame in the radial direction, the amount of granular glass deposited can be increased, and high-speed synthesis of the porous base material for the original fiber can be realized.

[Problem to be solved by the invention]

In the synthesis of porous base materials for original fibers, one important issue is how to efficiently deposit granular glass synthesized by a burner on the base material. The percentage of granular glass that adheres to the base material is called the yield. If the yield is low, not only will it not be possible to increase the synthesis rate of the porous base material, but also the inside of the reaction vessel for synthesizing the base material for the original fiber (called Matsufuru) will be contaminated with granular glass that did not adhere to the base material. Floating soot) causes various alignments as described below.

■ If floating soot adheres to the deposition surface, it will turn the porous base material into transparent glass and then create bubbles within the glass, making it impossible to obtain a high-quality base material.

■ If soot adheres to the inner wall of the manifold L,'% = 11 = If it adheres to the niter window, etc., it will be impossible to monitor the manufacturing status and it will not be possible to stably form the surface of the base material.

Regarding alignment when the raw material flow rate is increased to improve the synthesis rate, it is described in Japanese Patent Publication No. 62-50418, but the growth (particle size) of the granular glass is insufficient. This can be considered as one factor. Therefore, in the conventional burner shown in FIG. 4, the present inventors attempted to deposit the layer by roughly lengthening the step L' between the inner layer 41 and the outer layer 42 in order to increase the grain size, but L' was too long. On the contrary, it has been found that the yield deteriorates and that the granular glass adheres to the tip of the inner wall 43, which is the boundary between the inner and outer layers. FIG. 5 shows the change in yield when the step L' (m) is changed. In addition, even if the length L' was short, the particle size could be increased by increasing the distance between the burner and the base material for the original fiber and increasing the flame length, so we carried out production by separating the burner from the base material, but the yield was It remained unchanged. It was also found that even when the flame was removed, the particle size only grew to about 0.3 μm and did not grow any further.

The present invention has been made in view of the current situation, and it is an object of the present invention to provide a method that can completely improve the deposition efficiency of granular glass and synthesize a base material for an original fiber using such a dual flame forming burner. The purpose is to

[Means to solve the problem]

As a result of a detailed study of the relationship between the frit flow rate and the dual flame formation type burner structure, the present inventors determined that the relationship between the frit flow rate and the burner step L1 raw material ejection port size satisfies a certain relational expression. It was discovered that the above object could be achieved by making the following selections, and the present invention was achieved.

That is, the present invention provides a method for producing a porous preform for optical fiber by supplying a gaseous glass raw material into the flame of a multi-tube burner and subjecting it to flame hydrolysis, thereby laminating granular glass 1 * synthesized. The multi-tube burner includes an inner flame forming part in which multiple ejection ports for flame formation are provided on the outer periphery of a central port for ejecting raw material, and multiple ejection ports for flame formation arranged on the outer periphery of the flame forming part. Using a double large flame forming type burner having an outer flame forming part consisting of,
and the step 'k L (III) between the tips of the inner flame forming part and the outer flame forming part, and the inner diameter of the raw material ejection port 4 (
fi), frit flow IIQ (cc/m1n)
The present invention relates to a method for developing a base material for optical fiber, characterized in that granular glass is deposited while satisfying the relationship of 0.4Q≦LX (12≦0.6Q).

Hereinafter, the method of the present invention will be explained with reference to the drawings.
The reason for this is a schematic explanatory diagram of a specific example of a double flame forming burner used in the method of the present invention, in which 1 to 8 are ejection ports, and in this example, from center port 1 to fourth port 4 are on the inside. It is a flame forming part, and the center port 1 is for raw material gas, and the 2nd port is for raw material gas.
Port 2 is for combustion gas, third port 3 is for auxiliary gas, and fourth port 4 is for inert gas. Also, the 5th to 8th
The ports are the outer flame forming part, and the fifth port 5 is for inert gas, the sixth port 6 is for combustion gas, the seventh port 7 is for inert gas, and the eighth port 8 is for combustion gas. 9 is the inner wall. When the inner diameter of the central port 1 for frit gas is (1 (, ur), and the step difference between the tip of the inner flame forming part and the tip of the outer flame forming part is L (tm), in the present invention, the flow rate Q of the frit gas is (CC/m1n), the deposition is performed so as to satisfy the following relationship: 0.4Q≦L×d2≦0.69. Note that FIG. 1 is just an example, and The number of ejection ports is not limited to this.

[Effect]

The present inventors have conducted a detailed study on the mechanism by which granular glass generated in the flame of a combustion burner is deposited on the original fiber base material. As a result, as shown in FIG. rlft, MjA15, and while flowing over the surface of the base material 10, due to diffusion or thermophoresis effect (a dust phenomenon in which fine particles receive force and move from a high temperature area to a low temperature area), the base metal 10 In other words, in order for the granular glass 11 to be deposited on the base material 10, it is necessary for the particles to flow near the center of the flame 12.

Based on this knowledge, using the burner shown in Figure 1, the yield was examined by changing the parameters of L (dragon) + d (mi' +) while keeping the flow rate of the glass raw material constant at Q = 5500 cc/min. As a result, the results shown in the graph of FIG. 3 were obtained. t, x a2/Q represents the time for the raw material gas to pass through the burner, and is 0.2 to 0.5 in time.
This corresponds to about sec. From Figure 3, 0.4≦L(12
It can be seen that when /Q≦0.6, a high yield of around 70% can be obtained. If L is too short, the glass particles will diffuse to the outside after leaving the outer flame forming part, reducing the deposition efficiency. If L is too long, the glass particles will mix in the inner flame forming part. Fine particles tend to adhere to the inner wall 9, and the PL and di-deposition effects deteriorate due to diffusion.

The above explanation has been made using a double flame forming type burner made of concentric multi-tubes, but even if the multi-tube burner has a cross section other than circular, it can be used as a circle with a cross-sectional area S of 4=Z]-. Regarding the assumed radius d, 0.4≦L(12/
If the deposition is performed to satisfy the relationship Q≦0.6,
Similar effects can be expected.

〔Example〕

Example 1 Using the concentric 8-tube double flame forming burner shown in FIG. 1, granular glass was synthesized and deposited according to the present invention to produce a porous base material gold for an original fiber. The conditions are as follows.

Burner parameters: L=80i+m, d=61rm
Inner flame forming layer (center port 1 to 4th port) Nigaras raw material is flowed only to center port 1. 310/45.51/
mln, H12, g/mln, 0225A/
m1n, Ar 5 J3/mxn0 outer flame forming layer (5th to 8th ports): A to the 5th and 7th ports
Flow the r gas. Ar 8 A/m1n.

H40A/mxn, 022613/m1n0 At this time, t, xa,'q-soxs6÷5500=0.5
It was 2. The deposition rate of the porous actual glass base material synthesized above was 10.61/@1n, and the yield was good at about 72%.

Comparative Example 1 In Example 11C, only L was changed to 120 dragons, and a porous glass base material was assembled under the same conditions as above. At this time LX
(1/Q = 0.78, which was outside the scope of the present invention. As a result, the deposition rate was as low as 71/1 ain, and the yield was ~48
I only have x. In addition, soot accumulates on the burner inner wall 9,
It stuck. By comparing the deposition rate and yield of Example 1 and Comparative Example 1, the effects of the present invention can be clearly understood.

〔Effect of the invention〕

As explained above, the method of the present invention has a glass raw material flow rate,
By adjusting the step size of the double flame forming burner O and the inner diameter of the raw material ejection port to synthesize and deposit granular glass, the base material for the original fiber can be produced at an improved deposition rate and at a high yield. be able to. Therefore, the present invention can be widely used in a method of manufacturing a base material for an original fiber by so-called sooting, thereby improving productivity and contributing to cost reduction.

[Brief explanation of the drawing]

FIG. 1 is a schematic sectional view showing a gas ejection part of a specific example of a double flame forming burner for granular glass synthesis used in the present invention;
FIG. 2 is a schematic diagram explaining how granular glass flows in a flame, and FIG. 3 is a diagram showing the relationship between L X +1 / Q (horizontal axis) and yield (%, vertical axis) in the present invention. Figure 4 is a schematic illustration of the gas ejection part of the burner used in the conventional method, and Figure 5 shows the synthesis and deposition of granular glass by the conventional method using the burner in Figure 4. , horizontal axis) is a graph showing changes in yield (X, vertical axis).

Claims (1)

[Claims] (1) In a method for producing a porous preform for optical fiber by depositing granular glass synthesized by supplying a gaseous glass raw material into the flame of a multi-tube burner and subjecting it to flame hydrolysis, the multi-tube burner , an inner flame forming part including multiple ejection ports for flame formation provided on the outer periphery of a central port for ejecting raw material, and an outer flame forming part consisting of multiple ejection ports for flame formation arranged on the outer periphery of the flame forming part. A double flame forming burner is used, and the difference in level between the tips of the inner flame forming part and the outer flame forming part is L(m).
m), the inner diameter of the raw material ejection port d (mm), and the glass raw material flow rate Q (cc/min), 0.4Q≦L×d^
A method for manufacturing an optical fiber preform, characterized in that granular glass is deposited while satisfying the relationship 2≦0.6Q.