JPH02145450A - Production of porous optical fiber preform - Google Patents

Abstract

PURPOSE:To improve deposition ratio of glass fine particles on a porous preform for optical fiber and to improve yield of production by depositing glass fine particles on a starting material while cooling a plate comprising a material of good thermal conductivity set close to porous optical fiber preform. CONSTITUTION:A cooling plate equipped with a pipe 8 through which cooling water is passed is set at a position opposing a burner 1 while sandwiching porous optical fiber preform 6 in between the preform and the burner and part not covered with a stream 2 of glass fine particles and with a stream 3 of oxyhydrogen flame among deposited face of glass fine particles are cooled by heat transfer of radiation. Liquid N2, liquid Ar and fluorocarbon besides H2O may be used as a cooling medium and the distance between the cooling plate 9 and the deposited face of glass fine particles is any distance, provided that the cooling plate 9 is not directly brought into contact with the stream 2 of glass fine particle or the stream of oxyhydrogen flame. SiCl4 or GeCl4 is used as the raw material for preform and a hydrocarbon-based gas such as H2, O2, CO or methane is used as a combustion assisting gas.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention uses the VAD method (Vapor Phase
Axial Deposition Method)
This invention relates to an improvement in the manufacturing method of a porous optical fiber preform.

[Conventional technology]

As a method for manufacturing a porous base material of an optical fiber, for example, VA
In method D, 5iC6a is put into an oxyhydrogen flame, and fine 810. This is a method of depositing particles in the longitudinal direction of a starting material to form a porous matrix. In this case, the burner is divided into a fully multiplexed structure in which BiO2 and combustion gas are ejected and reacted, and an additive of ()ec4% is simultaneously ejected and reacted from a part of the burner to produce Ge01, etc.
10. and Gao! etc. are made to have a predetermined spatial concentration distribution in the radial direction.

Also, the external method is 810 during oxyhydrogen flame! a and GeCj4
8 produced by flame hydrolysis by supplying additives such as
10. This is a method in which the glass rod core material is moved in the axial direction of the core material while depositing fine particles such as Sin and Ge0fi on the outer periphery of the glass rod core material, which is a starting material, to grow fine particles such as Sin and Go02 in the axial direction.

Here, Ch*C is used as an additive to create a refractive index distribution.
Although 1a is mentioned, other additives with 6≦ may also be used, and a method of mixing a plurality of additives is also discussed. Furthermore, during the flame reaction,
Do you add additives and react? lJ was shown, but the pure 8
10. Another method is known in which a porous body is made and additives are injected during sintering.

[Problem to be solved by the invention]

When rapidly synthesizing a porous original fiber base material by the VAD method, it is necessary to increase the amount of raw material input per unit time, but the layering efficiency of the glass particles on the porous optical fiber base material may decrease. Therefore, a problem frequently arises in that it is not possible to increase the deposition rate on the porous original fiber base material in proportion to the amount of raw material input.

As a method to solve the above problem, conventionally, as shown in FIG.
There is a method of cooling the porous optical fiber preform 6 by attaching a pipe 8 made of a good heat conductive material to the outer wall surface of all the walls and passing a cooling liquid or gas through the pipe 8. It had been taken. The shaded area in the figure shows the surface on which glass particles are deposited by the flow 2 of glass particles and the oxyhydrogen flame flow 5, 1 is a synthesis burner, and 5 is an exhaust vent. This method utilizes the thermophoresis effect (in a flow field where the temperature gradient is reduced, fine particles receive a force toward the lower temperature) as one of the factors that contributes to the adhesion of glass fine particles to the deposition surface. , by cooling all the wall surfaces of the Matsufuru 4, radiation heat transfer 'I from the surface of the porous optical fiber base material 6 to the inner wall surface of the Matsufuru 4 being cooled.
By increasing kt, the temperature of the glass particle deposition surface is lowered, and the negative temperature gradient toward this deposition surface from the H*102 (oxyhydrogen) flame flow 3 containing the glass particles 2 is increased;
The idea was to increase the adhesion efficiency of glass particles onto a porous optical fiber base material by the thermophoresis effect (Japanese Patent Application Laid-open No. 171938/1983).

In the above conventional method, the temperature of the inner wall surface of Matsuful is lowered to cool the deposition surface through the flame flow, and in this case, the temperature of the glass particle deposition surface is the amount of heat transferred from the oxyhydrogen flame flow containing glass particles to the deposition surface side. From the amount of heat transferred from the deposition surface to the inner wall surface of Matsufuru, it is determined as shown in the following equation 0). That is, αa('I'r-T8)=α(Tf'-To')
+ (Ts' - TM'), °, α5 (Tf - Ts
)=α(Tf'-TM')...+
1) Here, Tf* TBe TM in equation (1) is the temperature of the oxyhydrogen flame flow containing glass particles, the temperature of the glass particle deposition surface, and the temperature of the inner wall surface of the pine tree, respectively.

Further, α8 is the heat transfer coefficient between the flame flow and the deposition surface, and σ is the Stefan-Holtzmann foot number.

In the conventional method, all the wall surfaces of the matsufuru were cooled in order to increase the temperature difference Tf-'rB between the flame flow and the surface on which the glass particles were deposited. As a result, since the deposit @i is cooled through the flame flow, the flame flow temperature Tf also decreases, and (1)
The temperature difference T between the flame flow and the glass particle deposition surface in Eq.
It was not possible to increase f-'I', and therefore it was not possible to significantly improve the adhesion efficiency of glass fine particles.

The present invention was made to solve the problem of the Zhao point in the prior art, and is a novel optical fiber that can improve the adhesion rate of glass particles on the porous optical fiber base material and improve the manufacturing yield. The purpose of this invention is to provide a method for manufacturing base materials for use in industrial applications.

[Means to solve the problem]

The present invention was achieved as a result of efforts by the Ministry of the Invention and others to develop a means for effectively cooling the surface of the glass particle pile 4x with less influence on the flame flow temperature.

That is, the present invention provides a method for producing a porous actual fiber preform by depositing glass particles produced on the surface of a starting material by supplying a glass raw material and combustion gas to a burner and causing a flame hydrolysis reaction. , a plate made of a good heat conductive material is installed near the porous original fiber base material at a position facing the burner across the porous original fiber base material, and while cooling the plate, The present invention relates to a method for producing a porous optical fiber preform, which comprises depositing glass particles on the starting material.

FIG. 1 is a schematic diagram showing an embodiment of a method for producing a porous 5iL original fiber preform according to the present invention and an apparatus used therefor. In FIG. 1, a cooling plate 9 disposed inside a pipe 8t through which cooling water flows is installed at a position facing the burner 1 with the porous optical fiber base material 6 removed, and the cooling plate 9 is placed in a position facing the burner 1 with the porous optical fiber base material 6 removed. Of these, the portions that are not covered by the glass particle flow 2 and the oxyhydrogen flame flow 3 are cooled by radiant heat transfer. In addition to H and O, the cooling water can also be liquid NII e liquid Ar,
A refrigerant such as liquid He or chlorofluorocarbon can be used. The size of the cooling plate 9 is approximately %n~2D based on the outer diameter of the porous optical fiber preform 6, and the height is approximately D~2D. Furthermore, the distance between the cooling plate 9 and the glass particle deposition surface is such that the cooling plate 9 is directly connected to the flow 2 of the glass particles.
It suffices to take care that it does not come into contact with the oxyhydrogen flame flow 5. Furthermore, the constituent material of the cooling plate 9 is not limited to metals (for example, iron, stainless steel, nickel, aluminum, etc., or alloys thereof), but may also be glass (quartz, Pyrex, etc.) or ceramic materials. Further, even if the above-mentioned metal is combined with a glass material or a ceramic material, no problem will arise.

Further, although FIG. 1 shows a cooling plate with cooling pipes disposed inside thereof, a cooling jacket may be used in which the cooling plate has a jacket structure and is provided with an inlet and an outlet for a cooling medium.

In the method for manufacturing the porous optical fiber preform, 8iC4, GeC4, and POC4 are used as raw materials, and hydrocarbon gas such as Hla 02+ COe methane is used as the combustion gas or combustion-supporting gas. Furthermore, the number of burners may be singular or plural.

[For production]

As described above, the cooling plate is installed at a position facing the burner across the porous optical fiber preform, and when manufacturing the porous optical fiber preform, the glass particles are This method, which selectively cools the uncovered part of the fine particles and oxyhydrogen flame stream by radiant heat transfer, lowers the temperature of the glass particle deposition surface without lowering the temperature of the oxyhydrogen flame stream containing glass particles, and lowers the temperature of both. You can make a big difference,
It is possible to promote thermophoresis of the generated glass particles and increase the adhesion efficiency to the porous optical fiber base material.

〔Example〕

Next, the effect of real division of the present invention will be explained using a specific example.

EXAMPLES AND COMPARATIVE EXAMPLES A porous 7-IPA base material manufacturing apparatus having the configuration shown in FIG. 1 was used, and the glass fine particle synthesis burner was a quadruple tube with an outer diameter of 20 cm. Glass raw materials, combustible gases, and combustible gases are 5
iC4α58t/min.

Gect4 α05t/min, He toz/min, H
l 6.01.7 minutes.

Argon was flown for 5 minutes at a flow rate of 0.112 t/min. The cooling water was adjusted so that the temperature of the surface of the cooling plate and the inner wall of Matsufuru was 20°C.

Under the above conditions, cooling is performed using the method according to the present invention (Example), cooling is performed using the conventional method shown in FIG. 2 (Comparative Example 1), and no cooling is performed at all (Comparative Example 2). )
About creating porous optical fiber preforms. The adhesion efficiency of glass particles onto the porous optical fiber base material was 65% without any cooling, 66-1 for the conventional method and 78% for the method of the present invention, clearly superior to the conventional method. An improvement in adhesion efficiency was observed.

In addition, the selective cooling of the glass particle deposition surface in the above example (that is, cooling only the deposition surface without lowering the temperature of the oxyhydrogen flame stream containing glass particles) is a separate form from Matsufuru. However, the Matsuful itself may have a similar cooling mechanism.

〔Effect of the invention〕

As described above, when manufacturing a porous original fiber preform by installing a cooling plate at a position facing the burner across the porous original fiber preform, glass fine particles, oxyhydrogen, etc. The method of the present invention, which selectively cools the uncovered portion of the flame stream by radiant heat transfer, lowers the temperature of the glass particle deposition surface without lowering the temperature of the oxyhydrogen flame stream containing glass particles, and reduces the temperature difference between the two. can be made larger, promoting thermophoresis of the generated glass particles and increasing the adhesion efficiency to the porous optical fiber base material.

[Brief explanation of the drawing]

FIG. 1 is an rMr side view showing an embodiment of the present invention, and FIG. 2 is a # side view of a conventional method. In the figure, 1 is a burner, 2 is a flow of glass particles, 3 is an oxyhydrogen flame flow, 4 is a matzuru, 5 is an exhaust/θ, 6 is a porous optical fiber base material, 7 is a starting material, 8 is a pipe, and 9 is cooling board,
The shaded area shows the glass particle deposit 1IY covered by the glass particle flow 2 and the oxyhydrogen flame flow 5.

Claims (1)

[Claims] A method for producing a porous optical fiber preform by depositing glass fine particles produced by a flame hydrolysis reaction on the surface of a starting material by supplying frit and combustion gas to a burner, A plate made of a good heat conductive material is installed close to the porous optical fiber base material at a position facing the burner across the porous optical fiber base material, and while cooling the plate, the A method for producing a porous optical fiber preform, which comprises depositing glass particles on a starting material.