JPS6036342A - Manufacturing method of base material for optical fiber - Google Patents

Abstract

PURPOSE:To prepare easily a parent material for optical fiber having a double structure, by hydrolyzing a raw material solution to give silica gel, arranging it in a container, adding a mixed solution containing another raw material solution to give gel having a double structure, drying, heating, and calcining it. CONSTITUTION:A raw material solution required to provide the first desired refractive index consisting of a raw material solution of a silicon alkoxide, SiCl4, etc., and, if necessary, a compound of added element to change refractive index of transparent quartz glass, and a mixed solution of water and a diluent are put in a container with a given shape, closed, and allowed to stand to give gel. The gel is then arranged on a fixed position of another container, a mixed solution containing a raw material solution required to provide glass having the second desired refractive index is put in the container, the container is closed, and allowed to stand to give gel having a double structure. The gel having a double structure is dried, heated to a temperature <= the melting temperature of it, and sintered, so that a parent material for optical fiber having a double structure of different refractive index is easily prepared without going through a glass melting process.

Description

Detailed Description of the Invention [Field of Application of the Invention] The present invention relates to a method for manufacturing an optical fiber base material without going through the process of melting glass, and more specifically relates to a method for manufacturing an optical fiber base material without going through the process of melting glass. The present invention relates to a method of manufacturing a fiber base material without going through a glass melting process.

[Background of the invention]

Optical fibers are used as a medium for a variety of optical transmissions, ranging from extremely short-distance optical transmissions used in fiberscopes for helmet cameras to long-distance optical transmissions used in optical communication systems. It is made of glass (containing a dopant for adjusting the refractive index if necessary).

The manufacturing method for such optical fibers includes: ■) melting raw materials in a crucible to form fibers, ■) forming a CV on the inner wall of a quartz tube.
D method ('Chemj, cal VaporDeposj
m) Create a glass soot using the CVD method, deposit it, sinter it, and then heat it to a high temperature. Conventionally, methods such as drawing and turning into fibers are known.

However, in the case of (2), it is difficult to obtain glass with a high silica composition, and it is difficult to obtain high-purity optical fibers using these conventional techniques, as it is difficult to obtain raw material purity and contamination from the crucible cannot be avoided. It is difficult to obtain, and in the case of ■), mass production is low.

It is also difficult to obtain large base materials, and multicomponent glass (N
It is not possible to manufacture glass containing a considerable amount of a, and since it uses a thermal oxidation reaction, when P, Qe, B, etc. are used as dopant elements, the yield is low and the manufacturing equipment is expensive; ), multi-component glass cannot be manufactured, mass productivity is low, manufacturing equipment is expensive, and I), n), m)
In either case, it is not possible to create a glass body with an arbitrary shape.

Furthermore, both methods (1) and (2) produce silicon oxide through high-temperature conditions, and method (2) requires sufficient melting of glass at high temperatures, which inevitably leads to high costs.

On the other hand, a method of creating a glass state without going through a molten state is known. A representative example of this is the synthesis of multicomponent glass by Helmut Dislich (Patent Publication, Japanese Patent Publication No. 48-6604). In this case, alkali, alkaline 10 compounds and IB of the periodic table,
II'B, m, ■.

A metal compound soluble in an organic solvent of group V, Vl, ■ or ■ is combined with each other, the solvent is then evaporated in the presence of moisture, and the resulting reaction product is hot-pressed below the melting temperature. By this process, a lump of glass is obtained.

It is also known how to obtain porous glasses at moderate temperatures. In this method, silicon alkoxide or silicon alkoxide to which an alkoxide of a desired additive element is added is hydrolyzed to obtain silica gel or a high silica gel containing an added oxide.

Furthermore, it is also known to drop a mixture containing silicon alkoxide as a main component onto the surface of a suitable liquid, or to draw it out into the liquid and heat and sinter it to obtain film-like or fibrous glass products. However, the shape of the product obtained is extremely limited, and the shape is unstable and lacks uniformity, which is a serious drawback.

[Purpose of the invention]

The object of the present invention is to provide a method for easily manufacturing an optical fiber base material having sufficient characteristics for use in optical fibers, in order to overcome the drawbacks of the conventional optical fiber manufacturing methods.

[Summary of the invention]

In order to achieve the above object, the method for producing an optical fiber base material according to the present invention is as follows: Water and a diluent solution are added to one raw material liquid necessary to obtain a glass having a first predetermined refractive index selected from the group consisting of raw material liquids that produce silica gel through a decomposition reaction to form a first mixed solution. , ■
) Putting the first mixed solution into a first solution having a predetermined shape, ■) Covering the opening of the first container with a lid and leaving it sealed, and adding the first mixed solution to the first gel. ■) selected from the group consisting of a raw material solution that produces silica gel through a hydrolysis reaction, and a raw material solution that produces silica gel through a hydrolysis reaction in which a compound of an additive element that changes the refractive index of transparent quartz glass is added. Adding water and dilute solution to one raw material solution necessary to obtain a second glass with a predetermined refractive index,
forming a second mixed solution; (i) placing the first gel at a predetermined position in a second container having a predetermined shape;

Add the second mixed solution, ■) Cover the opening of the second container with a lid, seal it, and leave it to form a double-layered gel; ■
) gradually drying the double-structured gel to form a dry gel;
and (2) heating the dry gel to raise its temperature and sintering it at a temperature below the melting temperature of the dry gel.

The raw material liquid in steps I) and () has the general formula Si (OR
) Silicon alkoxide represented by 4 or 5j-C
A raw material solution containing Q4 or a compound of an additive element that changes the refractive index of transparent quartz glass is used.

In the case of a silicon alkoxide type, alcohol is used as the diluent, and in the case of a 5iCQ4 type, CCQ4 or petroleum-based benzene is used.

The amount of the compound of the above additive element to be added is such that a desired refractive index can be obtained, and the required amount of the element in 1 quartz glass is well known. As the compound of the added element, if silicon alkoxide is used in the raw material liquid, use the alkoxide of that element, and if 5iCQ4 is used in the raw material liquid, use the chloride or bromide of the element. The above additive elements include 1 such as B, P, Ge, Zr, and Ti.
, AI2 Gel before drying is pudding-like and soft, and cracks easily even with a small stress.
The gel should dry uniformly and the shrinkage of the gel should also be uniform so that no stress is applied to the drying gel. As one method for solving this problem, good results can be obtained if the container is made into a cylindrical container and the bottom portion thereof is made into a conical shape.

The gel obtained by the hydrolysis reaction in steps m) and Vl) has a large amount of water and organic matter encapsulated therein, and will be referred to as a hydrogel from now on.

Drying of the water-containing gel in step (2) is carried out until the weight reaches the initial weight.

The drying step shown in step ①) is a process in which water and organic substances (alcohol when silicon alkoxide is used as the raw material liquid) contained in a large amount inside the gel are removed very slowly from the inside of the gel. To give an example of a drying method, several to several dozen pores with a diameter of about 1 mm are made in the lid used in step (2) to serve as exhaust holes for water and organic matter to be removed from the gel. The drying rate can be controlled by the number of pores.

High silica glass can be obtained by normally sintering the dried gel at a temperature below the melting temperature, but the sintering temperature is preferably 1000°C or higher, usually 1000-1.200°C.
This is often the case.

By carrying out the steps I) to (ii) above, it is possible to obtain an optical fiber base material having a double structure and made of two-crystalline silica glass having different refractive indexes.

In this method, the method for manufacturing an optical fiber base material of the present invention includes:
A method that takes advantage of the fact that the resulting glass body has a shape that is almost similar to the container containing the mixed solution (i.e., similar to the shape of the container excluding the upper part that is not filled with the mixed solution). It is.

[Embodiments of the invention]

Below, we will first use reference examples to describe a method for producing an optical fiber preform with a single composition, that is, a preform for an optical fiber that can produce a uniform refractive index when drawn into an optical fiber. For reference, a method of manufacturing an optical fiber preform for producing an optical fiber having portions with different refractive indexes using the method of the present invention will be described in detail below using Examples.

Reference example l 1 mol of Si(OCH3)+, 4 mol of CH30H, H
Add 4 moles of 2O and mix thoroughly to make a solution with a diameter of 3.6 mm.
, a cylindrical container with a length of 250 fields is filled to about 80%.

Seal the top of the container with aluminum foil, silver foil, or other lid, and leave it for 10 minutes.
It was left in an atmosphere of ~60°C.

Depending on the temperature, the gel will be created in about 4 to 100 hours. The relationship between gelation rate and temperature is shown in Figure 1. Figure 1 shows the relationship between gelation rate (gelation time (hours)) φ number (h'')), temperature (°C), and reciprocal of temperature T (k'). Since the gel has a large amount of water and alcohol encapsulated inside it, water and alcohol are then removed very slowly from within the gel. This can be done by making several dozen pinholes of about 1 mm in diameter.The gel gradually shrinks due to dehydration and dealcoholization, but when the gel volume becomes 1/8th of the initial volume and the weight becomes 115% of the initial value, The alcohol and water are removed. This is called a dry gel. The size of the gel was approximately 1.8 volumes in diameter and 100 strokes in length. The dried gel was taken out of the container and heated in an electric furnace. A pure silica glass rod with a diameter of about 1.5 nwn and a length of about 80 nwn was created by slowly raising the temperature to 1050°C and maintaining it at that temperature for 2 to 48 hours. It is almost similar to the container described above (similar to the shape of the container excluding the upper part that is not filled with the mixed solution),
In addition, a glass body was obtained that had a shape similar to the shape when the mixed solution was gelled.

The properties of the obtained silica glass, such as density, refractive index, hardness, and thermal expansion, are 1.46 compared to commercially available tp1 fused silica glass.]
, 780kg/nun2.5.5 X 10-7”C:
Therefore, it could be fully used as an optical fiber rod.

Reference Example 2 10% of PO(CzHs○)3 was added to the raw materials with the molar ratio of Reference Example 1.
A gel was prepared by adding mol%, and a glass rod was prepared using the same process as described above. As a result, S i O
A S j O2-P206 glass rod having a higher refractive index than that of the S.sub.2 glass was created. In this case, the yield of P is about 75
%Met.

Reference example 3 Ge(○C2, T(s)4) was added to the same raw material as in reference example 1.
By adding 10 mol% of and following the same process,
It was possible to create a glass rod of SiO2-GeO2.

The above examples are just a few of the glasses we have created, but we also have glasses containing dopants such as B, AQ, Ti, and Zr.
○It can be easily prepared by mixing it with CH3)4. In this case as well, the yield of Ge was about 75%.

Reference Example 4 When creating a long glass rod for use in optical fibers, etc., it is possible to put the raw material into a corresponding long container, gel it, and gradually dry it to create a gel rod before sintering. Conceivable. However, since the hydrogel immediately after hydrolysis contains water and alcohol, it is pudding-like and easily cracks even under small stress. Therefore, it is necessary to use a method that uniformly dries the hydrogel, uniformly shrinks the gel due to dehydration and dealcoholization, and prevents stress imbalance.

In this reference example, in order to dry the hydrogel evenly,
A part of the container was devised as follows.

As shown in FIG. 2, the lower part of the cylindrical container 1 in which the solution is to be gelled is formed into a conical shape, and the solution is put therein to be gelled.

3 is a lid with pores. Using such a container,
Even if the water-containing gel 2 begins to shrink in the longitudinal and radial directions due to dehydration and dealcoholization as shown in the figure, the gel always remains concentric with the container, maintains a cylindrical shape, and dries uniformly. . Conditions other than the container were the same as in Reference Example 1.

Reference Example 5 Dry gel contains 10-20 wt% H20 and 4-5
wt % of undecomposed metal alkoxide organic groups are left behind. In vitrification, these H20 and organic groups must be removed by an appropriate treatment method.

Removal of these H2O and organic groups is generally possible by heating. The results of thermal analysis shown in FIG. 4 show the temperature at which H20 removal and organophilic groups occur by heating the dry gel obtained by hydrolyzing Si(○CH3)+. In FIG. 4, 21 shows a curve of weight change, and 22 shows a curve of differential weight change. This curve is data obtained at a heating rate of 10° C./min in air.

As shown in Figure 4, deH20 is carried out at temperatures ranging from room temperature to 200°C.
In a temperature range of
It can be seen that this occurs in the range from °C to 600 °C.

On the other hand, gel sintering starts at around 400°C, especially at 50°C.
This is noticeable at temperatures above 0°C.

For this reason, since the temperature range in which organophilic groups occur and the temperature at the beginning of sintering C8 overlap, some of the closed pores of the gel are changed into closed pores by sintering, creating a state in which the organic groups are confined inside. If the temperature continues to rise and sintering and vitrification is performed, the organic groups left behind in the closed pores will decompose and gas will be generated, causing the gel to rupture or the resulting glass to be colored due to the organic matter. .

This reference example was made to prevent such a phenomenon from occurring, and is a method in which 03 (ozone) is used instead of the usual 02 to oxidize residual organic groups, especially for non-melting glass. It is effective when used to process gels created.

It is well known that 03 has stronger oxidizing power than 02. In this reference example, in order to avoid the overlap of the organophilic groups in the gel and the sintering temperature range in a normal O2 atmosphere, we focused on the strong oxidizing power of O3 and used it effectively. By this method, we created a silica-based glass that was free from impurities such as carbon and prevented the overlap of Gaussian temperatures.

As a result of using 03, the initiation temperature of the reaction of the organophilic group was reduced to 20
It is now possible to shift the temperature to around 0℃, so that the processing temperature for removing H2O and residual organic matter from the gel does not overlap with the sintering temperature, and the gel is heat-treated smoothly and homogeneously, free from the effects of organic impurities. No clear glass was obtained.

In addition to the methods described in the reference examples above, there are also methods for synthesizing glass by hydrolyzing hydrolyzable glass raw materials in a liquid phase.

5jCQ4 is a liquid at room temperature and is known to be hydrolyzed in the liquid phase when mixed with water. However, 5iCIII4 decomposes into two phases with water and reacts vigorously at the interface to generate hydrogen chloride. Therefore, the reaction cannot be uniformly carried out.

The present inventors have discovered that 5iCf14 does not react with 5iCf14 and
A substance that has a complete solution with CQ4 was used as a dilute solution, and the reaction with water was gradually carried out. As a result, the entire reactant reacts uniformly and becomes a gel-like substance. Furthermore, the shape of the gel-like substance can be made into any shape depending on the shape of the reaction vessel. After drying and heat-treating the gel-like substance to remove the components of the dilute solution, the gel-like substance is heated at 800°C while maintaining its shape.
Sintering and vitrification can be carried out preferably at a temperature of 1000° C. or higher.

In addition to carbon tetrachloride CCα4, n -C
A variety of materials can be used, including petroleum-based benzenes such as 3814.

For optical fibers, GeC124 is used for refractive index control.

Known dopant raw materials such as POCf13 and BBr3 can also be used at the same time.

Reference example 6 Approximately 5 cc in 50 cc of hexane (n-C++HX4)
A uniformly diluted 5jCf14 was prepared by adding 5jC(14) to the diluted 5jCf14.Next, about 5cc of pure water was added to the diluted 5iCQ4 and left to stand.At first, the water phase and The phase of 5iCQ4 had been separated into two layers, but as the reaction progressed, it became uniform and a gel-like substance was obtained.Next, a part of this gel substance was taken and gradually heated from room temperature in an electric furnace. Heat and dry at 1000°C for about a week.
The temperature was raised to 100% and vitrified. As a result, a transparent glass body was obtained.

Example Similar to Reference Example 2, Si(OCH3)4 and PO(○C
A mixed solution of 2H5)3 was simultaneously hydrolyzed to prepare a sol solution. This is placed in a cylindrical container with a conical bottom and allowed to gel. This gel was a hydrogel containing a large amount of water and alcohol, and then gradually began to shrink due to dehydration and dealcoholization.

When the gel begins to shrink and separate from the container, the hydrogel is placed in a similar container 13 having a larger diameter than the hydrogel 11 as shown in FIG. For example, a sol solution containing only 5j(OCH3)4 or 5j(OCH3)4-PO(C2H50)3, which contains less P alkoxide than a hydrous gel.

5j (QC) + 3 ) 4-B (QC2H5) 3 or other hydrolyzed sol solution J2 is poured in, sealed, and gelated concentrically using the hydrogel as a core to create a hydrogel with a double structure. did.

Next, this gel was gradually dried to form a dry gel that contained less water and alcohol and would not cause cracks even when taken indoors. By treating this in an electric furnace at a temperature of 1000° C. to 1200° C., it was converted into a transparent glass-like preform, and this preform was drawn into an optical fiber.

The conditions for the gelling step, drying step, and sintering step were the same as in Reference Example 1. In this way, an optical fiber having a structure consisting of a core portion with a high refractive index and a cladding portion with a low refractive index was obtained.

The example given here uses 5j(OCH3)a as the main raw material, but it is obvious that the same thing can be done with other silicon alkoxides represented by the general formula 5i(OR)4 (R: alkyl group). It is.

Furthermore, it goes without saying that concentric gels and gels on the outside thereof can be created not only by the above-mentioned examples, but also by combining liquids having different refractive indexes in the sol state.

In the example shown in Fig. 3, the container 13 containing the sol solution in advance is
It will be obvious that the hydrogel 11 may also be placed inside.

〔Effect of the invention〕

The method for manufacturing an optical fiber base material according to the present invention described above generally has the following advantages.

■) The process is simple and the equipment is simple, so the process is easy to control, has good reproducibility, and the cost of the equipment is low. ■) Excellent mass production, producing large quantities of homogeneous products in the same batch. can be obtained.

■) Since a glass block of any shape can be obtained according to the shape of the container containing the mixed solution, glass products other than optical fiber base materials can also be manufactured.■) The process up to the manufacture of dry gel is performed at or near room temperature. Therefore, it is possible to manufacture B203-3i○2 glass, etc., which was difficult to produce by conventional melting methods, and the structure of new acid materials can be expected. There is little loss and the yield of these elements is high at over 70% (for example, about 30-50% in conventional MCVD methods), so there is good correspondence between the raw material composition and the manufactured glass composition, and the additive (1) The processing temperature in the process up to dry gel production is low, so there is less contamination by impurities. (2) Because the raw material is liquid, distillation 11) Double-structured products made of glasses with different refractive indexes can be easily produced.

[Brief explanation of drawings]

Figure 1 is a graph showing the relationship between gelation rate and temperature, Figure 2 is a graph showing the relationship between gelation rate and temperature.
The figure is a schematic sectional view showing the drying state of gel in a reference example of the present invention, and FIG. A schematic cross-sectional view showing the process, and FIG. 4 is a graph showing the results of thermal analysis of the dried gel. 1... Container for gelling the solution, 2... Hydrogel during drying, 3... Lid, 11... Hydrogel, 1
2... Hydrolyzed sol liquid, 13... Container, 21...
...Curve of weight change, 22...Curve of differential heat change. Figure 2 Kuzu 3 Figures 1 and 4 Figure 0 Button θ lθθθ Continued from page 1 0 Inventor Makoto Sato Kokubunji City Meo Research Institute - ○ Inventor Toshio Katsuyama Kokubunji City 1 Central Research Institute Do @ Inventor Riki Omura Kokubunji City Meo Research Institute: Koigakubo 1-28, Hitachi, Ltd.] Koigakubo 1-28, Hitachi, Ltd.

Claims (1)

[Claims] 1. (1) Consists of a raw material solution that produces silica gel through a hydrolysis reaction, and a raw material solution that produces silica gel through a hydrolysis reaction to which a compound of an additive element that changes the refractive index of transparent quartz glass is added. Adding water and a dilute solution to one raw material solution necessary to obtain a first glass having a predetermined refractive index selected from the group to form a first mixed solution; Put the first mixed solution in a container, (1) Cover the opening of the first container with a lid, seal it, and leave it.
The mixed solution of is made into the J gel, ■) A raw material solution that produces silica gel through a hydrolysis reaction, and a raw material that produces silica gel through a hydrolysis reaction with the addition of an additive element compound that changes the refractive index of transparent quartz glass. (2) Adding water and a diluted liquid to one raw material liquid necessary to obtain a glass having a second predetermined refractive index selected from the group consisting of liquids to form a second mixed solution; The gel is placed at a predetermined position in a second container having a predetermined shape, and the second mixed solution is placed therein. Vl) Covering the opening of the second container with a lid and leaving it sealed to form a double-structured gel, ■) Gradually drying the double-structured gel to form a dry gel, and ■) 1. A method for producing an optical fiber base material, comprising the steps of heating a dry gel to raise the temperature and sintering the dry gel at a temperature below the melting temperature of the dry gel.