JPH0442820A - Production of quartz-based preform - Google Patents

Abstract

PURPOSE:To obtain a quartz-based preform enhanced in yield of an article with good quality by reacting a dope raw material gas for increasing refraction index with water content or oxygen contained in a porous preform to hydrolyze or oxidize the raw material gas. CONSTITUTION:In a furnace core tube 12 of electric furnace 11, reaction of GeCl4 with H2O and O2 is carried out to produce GeO2 and the GeO2 is diffused into a porous preform 15. Then the porous preform 15 is raised to an initial position of the furnace core tube 12 and GeCl4 remaining in the furnace core tube 12 is excluded out of the furnace core tube 12. Then the inside of furnace core tube 12 of the electric furnace 11 is heated to temperature (e.g. 1350 deg.C) for changing to transparent glass by a heater 13 and then He and O2 are fed from a gas feed system 14 into the furnace core tube 12. Further, the porous preform 15 in the furnace core tube 12 is moved downward while rotating the preform 15 and changed to transparent glass successively from the lower end.

Description

DETAILED DESCRIPTION OF THE INVENTION r Industrial Application Field 1 The present invention relates to a method for producing a quartz base material containing a dopant for increasing the refractive index.

rConventional technologyj As is well known, the mainstream of optical fibers for communications, image fibers, light guides, etc. are quartz-based fibers that have a core with a high refractive index and a cladding with a low refractive index. .

Usually, the quartz-based base material of these optical fibers is manufactured by a process of generating fine glass particles and depositing them in a predetermined shape, and a process of dehydrating and converting the deposit of glass fine particles into transparent vitrification.

By the way, in the manufacturing method of the quartz-based base material mainly based on the VAD method, glass fine particles with a high refractive index generated by a flame hydrolysis reaction of a glass raw material (gas phase) and a dope raw material (gas phase) are deposited and grown in the axial direction. to make porous glass for the core,
At the same time, glass microparticles with a low refractive index produced in the same manner as above were deposited on the outer periphery of the porous glass for the core to create a porous glass for the cladding. These porous glasses are dehydrated and made into transparent glass in a high-temperature heated atmosphere containing gas.

r Problems to be Solved by the Invention j Among the above-mentioned quartz-based base materials, those for image fibers are of the step index (Sl) type with a large numerical aperture (NA) from the viewpoint of light receiving efficiency.

In this case, the glass for the core preferably has a clear SI type refractive index distribution as shown in FIG. 2(A), and it is not good to have a refractive index distribution as shown in FIG. 2(B).

That is, a large number of quartz base materials are gathered together and heated and stretched.
Next, a large number of preform rods obtained in this way are assembled and heated and stretched again, and these operations are repeated to produce an image fiber with a pixel count of 2,000 to 10,000 or more. If the refractive index of the barrel quartz base material has a distribution as shown in Figure 2 (A), then as shown in Figure 3 (A),
Although the effective core diameter of each pixel does not become small and sufficient image resolution can be secured, if a quartz base material with a refractive index distribution as shown in Fig. 2 (B) is used, the effective core diameter as shown in Fig. 3 ( As shown in B), the effective core diameter of each pixel becomes as small as 70 holes at a length of 20 m, and the image resolution decreases.

In order to deal with this, for example, if the glass for the cladding is made thinner with a quartz-based base material and an image fiber is manufactured using such a base material, the transmitted light leaks from the pixel core to the cladding, which is called crosstalk. increases, and the contrast of the transmitted image decreases.

When considering a method for manufacturing a quartz-based base material from such a viewpoint, the conventional technology that uses an oxyhydrogen flame burner as a means for producing glass particles has the following technical problems.

One of them is that the dopant in the oxyhydrogen flame has a concentration distribution, which makes it difficult to form a complete SI type refractive index distribution [Fig. It will be August. Therefore, an image fiber with high image resolution cannot be obtained.

The other one, regarding oxyhydrogen flame burners, is the location of the burner;
Depending on the flow rate ratio of fuel gas (H2) and auxiliary combustion gas (02),
The moldability, refractive index profile, etc. of the porous base material are greatly affected, resulting in a decrease in productivity. #: The moldability of the porous base material is difficult to adjust because it depends on the bulk density.

Another problem is that when the dopant concentration (for increasing the refractive index) of the core glass is increased in order to achieve a high NA, the softening point
Since the physical properties of the porous base material, such as the coefficient of linear expansion, change, the formability of the porous base material becomes worse and the base material is more likely to crack. Therefore, the yield in obtaining a good quality porous base material decreases.

In view of these technical issues, the present invention seeks to provide a method for manufacturing a quartz-based base material that satisfies appropriate refractive index distribution, high NA, high productivity, etc., and can increase the yield of non-defective products. It is something.

1 Means for Solving the Problem J In order to achieve the intended purpose, the method for producing a quartz-based base material according to the present invention includes, for example, Ge(lla, TiCl4).
In a heated atmosphere below the transparent vitrification temperature containing a dope material gas for increasing the refractive index such as AICb and an inert gas, the above-mentioned refractive index increasing material is added to an undehydrated porous base material consisting only of Si02. It is characterized by diffusing the dope raw material gas for use in the porous base material, and reacting the dope raw material gas with moisture and/or oxygen contained in the porous base material to cause hydrolysis or oxidation.

Effect 1 In the method of the present invention, a non-dehydrated porous matrix made of Si02 is used.

As is obvious, this porous base material is made of SiO7 alone, contains moisture and oxygen, has a large surface area, and has hygroscopic properties.

This SiO2 porous base material does not require any adjustment of the refractive index profile when producing it, so it is easy to mold, and the physical properties (softening point, coefficient of linear expansion) of the porous base material do not change. Therefore, there is no risk of base material cracking, and productivity is extremely high.

In the case of the method of the present invention, the transparent vitrification temperature (500 to 800
0°C) in a heated atmosphere, the undehydrated SiO2
Treat porous matrix.

That is, in the above-mentioned atmosphere at low temperature, undehydrated S
i02 A dope raw material gas for increasing the refractive index is diffused into the porous base material, and the dope raw material gas is reacted with moisture, oxygen, etc. contained in the porous base material to be hydrolyzed or oxidized.

In this case, any dopant may be used as long as it increases the refractive index, and examples thereof include Ge, AI, and D1.

As the inert gas, well-known Ar, He, N2, etc. are arbitrarily employed.

As an example, Ge
Cl4 and Ar is used as the carrier gas. When the SiO2 porous base material contains a sufficient amount of N20.02, the following (1
) reaction occurs, and GeO2 is formed in the SiO2 porous matrix.
is generated・GeCl4+H20(0)−+GeO2+HC1+(C
12)""(1) At this time, GeO2 is generated by the reaction of the following equation (2) in a reducing or inert gas atmosphere.

2Ge02 → 2GeO+0"" (2) This GeO has a high vapor pressure and evaporates in a high temperature range such as the transparent vitrification temperature, so it is difficult to dope into the SiO2 porous base material. At low temperatures, GeO hardly evaporates.

Therefore, in the case of the method of the present invention, GeO2 can be sufficiently doped into the SiO2 porous matrix.

Thus, a SiO2 porous matrix doped with GeO2,
That is, the SiO2-Ge02-based porous base material has a transparent vitrification temperature (1150 to 1
GeO2 is made into transparent glass in a heated atmosphere (350° C.), but GeO2 remains stable in this oxidizing atmosphere without volatilizing.

Therefore, the porous base material during transparent vitrification is Si
O2 fine particles are melted while taking in GeO2 to form SiO
2 It becomes a GeO2-based glass and forms a network of predetermined molecules.

``Example'' FIG. 1 shows an electric furnace used to carry out the method of the present invention.

In FIG. 1, an electric furnace 11 includes a core tube 12 made of quartz and a ring-shaped heater 13 provided around the outer circumference of the core tube 12.
A gas supply system 14 is connected to the lower part of the reactor core tube 12.

In FIG. 1, the porous base material 15 is made only of SiO2 (pure silica), and is produced by known or well-known means.

As an example, the porous base material 15 is manufactured by the VAD method, and on the other side, the porous base material 15 is manufactured by the patent application No.
It is manufactured by the slurry casting method of No. 21111153 (Japanese Unexamined Patent Publication No. 64-56331).

Hereinafter, a specific example of the method of the present invention using the electric furnace 11 shown in FIG. 1 will be described in detail.

[Specific Example 1] As the Si02 porous base material 15, one having an outer diameter of 70 mraφ and manufactured by a VAD method (frit gas: 5iGla, carrier gas: Ar) was used.

In the case of the electric furnace 11, the center of the furnace tube 12 is connected to the heater 1.
3, the temperature is below the transparent vitrification temperature (e.g. 800°C)
The porous base material 15 is set in the upper part of the furnace core tube 12 (below 100° C.).

After completing the preparation in this way, GeCl4 bubbled with Ar is supplied to the gas supply system 14 at a supply rate of 2 m/layer.
The porous base material 15 inside the furnace core tube 12 is rotated and lowered at a speed of 150 mm/win.

In the furnace core tube 12 of the electric furnace 11, a reaction according to the above equation (1) occurs to generate GeO2, and this GeO2 diffuses into the SiO2 porous base material 15.

Thereafter, the porous base material 15 is raised to the initial position within the furnace tube 12, and A
r, an inert gas such as N2 is supplied to the reactor core tube 12.
GeC1a remaining inside the reactor core tube 12 is removed to the outside.

Next, after heating the inside of the furnace core tube 12 of the electric furnace 11 to a transparent vitrification temperature (e.g. 1350° C.) using the heater 13, 0.2 sentences/win is supplied into the furnace core tube 12 from the gas supply system 14.
of He and 02 of 1 sentence/set n, and while rotating the porous base material 15 in the furnace tube 12, the heating rate was 250 mm/w.
The porous base material 15 is lowered again at a speed of 1.5 in to transparently vitrify the porous base material 15 sequentially from its lower end.

The thus obtained transparent glass base material has 5iO2 fine particles of G
It is a 5iO2-Ge02 system that is melted while incorporating eO2.

The outer diameter of this transparent glass base material was 30 mmφ, and no bubbles, cracks, etc. were observed therein.

After the outer diameter of the transparent glass base material was reduced to 18 mφ by heating and stretching means, a cladding glass having an outer diameter of 27 lφ was formed on the outer periphery of the base material by a known or well-known OVD method. , used as a base material for image fiber.

In this case, the cladding glass contains fluorine (F) and boron (
It is made of doped quartz containing B).

When the refractive index distribution of the core glass (germanium-doped quartz) of the image fiber base material was measured, it exhibited a clear SI type as shown in FIG. 2(A).
The relative refractive index with respect to quartz was 2z.

This is because the relative refractive index of the cladding glass made of fluorine- and boron-doped quartz is 1% relative to quartz, so the relative refractive index difference between the core glass and the cladding glass is 3z.

When an image fiber having a pixel count of 10,000 was produced using the above-mentioned image fiber base material by known or well-known means, an image fiber having a refractive index distribution as shown in FIG. 3(A) was obtained.

This image fiber had an effective core diameter of 1002 for each pixel over a length of 20 m or more, and a clear image was obtained without crosstalk.

[Specific Example 2] As SiO2 porous base material 15, Japanese Patent Application No. 82-2119
53 (Japanese Unexamined Patent Publication No. 84-58331) manufactured by the slurry casting method was used.

The slurry casting method at this time was carried out as follows according to the above-mentioned known technique.

First, SiO2 powder was pre-sintered at 800℃ for 1 hour, and this was crushed to make the particle size distribution uniform. Next, 400g of SiO2 powder with uniform particle size was mixed with BOO+IfL.
A dispersion of Si02 powder is prepared by adding pure water of
The dispersion was poured into a mold having a diameter of 300 mm and slurry casting.

If you wait for time to pass in this state, most of the water in the dispersion liquid will be dehydrated by the water-absorbing mold. The porous base material is placed in a dryer maintained at 80° C. and dried until the moisture content becomes 10 to 20%.

The following steps are carried out in accordance with Example 1: doping a porous base material with a dopant for increasing the refractive index, making the porous base material transparent, vitrifying the porous base material, heating and stretching the transparent glass base material, and producing an image fiber base material (transparent glass base material). (formation of cladding glass on the outer periphery of the material),
The image fiber is manufactured by carrying out each of these steps such as manufacturing the image fiber. In this specific example 2, when doping the porous base material 15 with the dopant for increasing the refractive index, the core maintained at 600°C TlC1 in tube 12
a to diffuse TiO2 into the porous base material 15.

Other technical matters in Example 2 are substantially the same as in Example 1.

In the image fiber base material in Example 2, the refractive index distribution of the core glass exhibits a clear SI type as shown in FIG. 2 (A), and the number of pixels produced using this image fiber base material: 10,000. The image fiber of Figure 3 (A)
Since the image fiber had a refractive index distribution as follows, the image fiber had a good effective core diameter of 10 oz for each pixel over a length of 20 m or more, had no crosstalk, and had a clear image.

“Effect of the Invention 1 As explained above, the method of the present invention diffuses a dope material gas for increasing the refractive index into an undehydrated Si02 porous base material in a predetermined atmosphere maintained at a predetermined temperature. let me,
Since the dope raw material gas is reacted with moisture, oxygen, etc. contained in the porous base material to be hydrolyzed or oxidized, the manufacturing conditions for the porous base material are eased, and the production conditions for the porous base material are eased. in the doping of the well-defined SI type, high N
High-concentration doping for achieving A conversion can be performed appropriately and efficiently, and furthermore, the dopant does not volatilize when the base material is made into transparent glass.

Therefore, when using the method of the present invention, it is possible to increase the number of non-defective products of the quartz-based base material, and it is also possible to reduce the cost of the quartz-based base material.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram schematically showing an embodiment of the method of the present invention, and FIG.
Figures (A) and (B) are the refractive index distribution diagrams of the quartz base material in Figure 3 (
A) and (B) are refractive index distribution diagrams of the image fiber. 11... Electric furnace 12... Furnace tube 13... Heater 14... Gas supply system 15... Porous base material

Claims (1)

[Claims] SiO_
Diffusion of the dope raw material gas for increasing the refractive index into an undehydrated porous base material consisting of only 2, and causing the dope raw material gas to react with moisture and/or oxygen contained in the porous base material. A method for producing a quartz-based base material, which comprises hydrolyzing or oxidizing the quartz base material.