JPS61186236A - Production of parent material 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 relates to a method for manufacturing an optical fiber base material by a sol-gel method using ultrafine particles.

[Conventional technology]

A sol-gel method using metal alkoxide and fine powder particles as starting materials is known as one of the methods for manufacturing optical fiber preforms. (Patent Application 1983-2 A sol solution for cladding obtained by mixing a hydrolyzed solution of metal alkoxide and fine powder particles prepared by various methods is rotated in a cylindrical container to gel it to prepare a tubular Talarado gel. Next, the core sol solution that will become the core glass is injected into the hollow part created at the center of rotation of the cylindrical container, and left to stand still to gel, creating a core-clad integral gel. The body is sufficiently dried and sintered at a predetermined temperature to obtain a transparent optical fiber base material with a radial refractive index distribution.This manufacturing method, which generally uses fine powder particles,
'Compared to the VD method, the base material for optical fiber is cheaper and easier.
Moreover, it can be produced in large quantities.

Furthermore, since the starting raw material is a liquid, it is easy to increase the purity of the raw material by repeating purification. Easily homogenize raw materials. Furthermore, since it has higher raw material efficiency than the gas phase method, there is a strong possibility that it will become a new industrial method for producing large-sized optical fiber base materials at high speed in the near future.

[Problem that the invention seeks to solve]

However, the above-mentioned conventional technology has a problem in that it is difficult to obtain a high-quality core glass with a high yield, that is, a core glass that is free of impurities such as bubbles and irregularly shaped foreign objects and has high transparency. This is because the reactivity of the solution that becomes the core gel is generally high, so it may react with trace amounts of moisture in the air during the raw material preparation stage, and the resulting oxide may be mixed into the solution as an impurity, or because the solution is highly viscous, it may react with trace amounts of moisture in the air. This is because bubbles trapped in the solution and dissolved microbubbles tend to remain as they are. Various methods have been tried to solve this problem. For example, the core sol is rotated into a gel in the same manner as in the production of Talarado gel, and impurities and microbubbles mixed in are removed using the centrifugal force during rotation. (Japanese Patent Application No. 58-186493) However, in this manufacturing method, an extremely thin impurity layer may be formed between the clad gel layer and the core gel layer due to impurities mixed in the core sol.

In this case, an abnormality occurs in the refractive index distribution, which is the most important structure of the optical fiber in this region, and when it is made into an optical fiber, it not only becomes the main cause of light scattering, but also, in the worst case, the function as an optical fiber is lost. is significantly impaired. Therefore, the present invention is intended to solve these problems, and its purpose is to turn the core sol into a rotational gel using a rotational method different from that used when producing the cladding gel, thereby preventing the contamination of impurities, that is, irregularly shaped foreign objects and microbubbles. The goal is to manufacture a gel with a cladding and core that is not

[Means to solve the problem]

In order to solve the above-mentioned problems, the method of manufacturing an optical fiber preform by the sol-gel method of the present invention involves pouring a liquid raw material into holes formed in the longitudinal direction of the container, and then It is characterized by gelling while rotating around a rotation axis that forms a 90° angle with the rotational symmetry axis of the object and whose rotation center is located outside the rotating container, thereby obtaining a gel body free of lumps and air bubbles. shall be.

A gel body prepared in advance from another liquid raw material may be present in this rotating container, and in that case, a preform for an optical fiber having a multilayer structure including a normal clad core double layer structure optical fiber. can be produced. In this case, the pre-existing gel body may have a hole in the longitudinal direction of the container.The gel body may have a hole in the longitudinal direction of the container, and the cross section of the hole may be circular or elliptical. do not have.

Furthermore, the opening body does not need to extend linearly in the longitudinal direction, and may extend spirally.

In addition, if there is no gel body in the rotating container,
A core rod for an optical fiber (for example, a pure silica rod) can be produced.

Furthermore, it is possible to use only metal alkoxide as the liquid raw material, but in terms of the size of the base material that can be produced and its yield, it is better to add fine powder particles to metal alkoxide.0 [Example] Below Now, the present invention will be explained in detail by taking as an example the production of a base material for a silica-based optical fiber.

<Example 1> Preparation of ultrafine silica particles: Commercially available ethyl silicate (trade name: Colcoat 28.Colcoat ni, Ni,) 4577f
, 99.5% ethyl alcohol (Kanto Kagaku, Ni,) 1
157.45', 29% ammonia water 39mQ, water 15
8.4 Mix and stir vigorously for about 2 hours. After leaving the solution in a cool place for a day and night, the concentration of amorphous silica spheres in the solution was concentrated to about 0.4 t/rnn, and a highly monodisperse ultrafine silica particle solution with an average particle size of 0.14 μm order was obtained. Synthesized.

Preparation of sol for cladding: Commercially available ethyl silicate (trade name: Colcoat 28, Colcoat ni, Ni,) 244.1
f, 99.5% ethyl alcohol (Kanto Kagaku, Ni,
) 1275? , 002 normal hydrochloric acid solution was mixed and stirred to prepare a hydrolysis solution for cladding.

Preparation of sol for core: Commercially available ethyl silicate (trade name Layer Colcoat 28, Colcoat ni, Ni,) 56.2f, 9
9.5% ethyl alcohol (Kanto Kagaku, Ni,) 19
．． Of', 02 normal hydrochloric acid solution 485f was thoroughly mixed and stirred, and tetraethoxygermanium (Trichemical Institute) 18.42 and 995% were added as a refractive index controlling material.
After gradually dropping a solution containing 12.9 r of ethyl alcohol mixed in advance, add 18 ml of 02N hydrochloric acid solution.
51 was added and sufficiently stirred to prepare a hydrolyzed solution for the core.

After adjusting the hydrogen ion concentration (hereinafter referred to as pH value) of the silica ultrafine particle solution to 4.0 using 2N hydrochloric acid solution,
Add the hydrolyzed solution for cladding to it and stir thoroughly until it becomes uniform. The pH value of the mixed solution was adjusted to 55 again using 02N ammonia solution, and the pH value of the mixed solution was adjusted to 55 using a rotating cylindrical container (
After pouring the specified amount into a tube (inner diameter: 40 words, length: 2 som, made of m-vinyl vinyl, inner surface coated with silicone), 1000 m/min.
The cylindrical container was rotated at a rotational speed as shown in FIG. 1, and a clad gel having a cylindrical shape and a hollow portion in the direction of the rotation axis was obtained in about 60 minutes. Next, the silica ultrafine particle solution whose pH value had been adjusted to 40 and the core hydrolysis solution were uniformly mixed, and the pH value was adjusted to 48 again using a 0.2N ammonia solution. , it was poured into the hollow space created at the center of rotation of the clad gel, and it was attached to a rotating device with a distance of 400 words from one end of the gel body to the center of rotation, and the gel was heated at a speed of 200 revolutions per minute (equivalent to 30 G, G = 9800 Tn).
/S2) as shown in FIG. 2, and a clad-core-integrated gel was obtained in about 50 minutes. Due to the action of centrifugal force caused by the rotation operation, lumpy foreign matter in the hydrolyzed solutions for cladding and core move outward from the rotating surface, and air bubbles move inward, so that the central part of the rotating rod is free of lumpy foreign matter and air bubbles. A homogeneous gel body will be obtained.

This clad/core integrated gel is packed in a polypropylene container (
300Mtrb x 250MX 150m1), the top lid was covered with a number of 1m diameter holes made so that the opening ratio was 0.2%, and the gel was placed in a constant temperature dryer at 55°C to obtain a dried solid gel in about 14 days. . This dried gel was heated to 900°C in an air atmosphere using a silicon carbide heating element at a heating rate of 1°C/-=.
It was heated to °C, and at that temperature, chlorine gas was flowed using helium gas as a carrier, and then oxygen gas was flowed to sufficiently remove water molecules, hydroxyl groups, organic molecules, etc. present in the dried gel body. After that, the heating rate was increased to 1℃/i again for 14 hours.
A transparent sintered body was obtained by making the gel body non-porous by heating it to 00℃.0 When the quality of the obtained transparent sintered body was examined, it was found that 1 was present.
The number of amorphous foreign objects and bubbles larger than μm is less than 1 per 010 m3, and light scattering is extremely small, so it is expected that sufficient optical properties will be obtained when used as a base material for optical fibers. Ta. Incidentally, amorphous foreign matter and air bubbles were concentrated at both ends of the transparent sintered body.

<Comparative Example 1> A silica ultrafine particle solution, a cladding hydrolysis solution, and a core hydrolysis solution having the same composition as in Example 1 were prepared, and a cladding gel was produced by rotational gelation in the same manner as in Example 1. Next, after pouring the core hydrolysis solution into the hollow part along the rotational axis direction of the clad gel, the core hydrolysis solution is allowed to stand still without rotational gelation, and the core hydrolysis solution is gelled.
A core-integrated gel was prepared. Subsequent drying and sintering were performed under exactly the same conditions as in Example 1 to obtain a transparent sintered body.

When the quality of the obtained transparent sintered body was examined, it was found that 1
The number of amorphous foreign matter of μm or larger and bubbles was less than 7 and 11 per Q and j cm3, respectively, and the quality was clearly lower than that of the transparent sintered body obtained in Example 1. This was thought to be due to the high viscosity of the core hydrolysis solution, which caused the gelation to occur in a dispersed state of the lumpy foreign matter and microbubbles mixed in the solution.

<Example 2> Silica ultrafine particle solution: Commercially available silica ultrafine particle (trade name;
Aerosil 0x5X (Japan Aerosil Co., Ltd.) 3002 was dissolved in water 6007, thoroughly stirred, and then irradiated with ultrasonic waves for about 2 hours to prepare a solution in which ultrafine silica particles were uniformly dispersed. Thereafter, by performing centrifugation under a centrifugal force of 500 G, lumpy foreign matter mixed in the solution was removed, and the monodispersity of the ultrafine silica particles was improved.

Preparation of sol for cladding: Commercially available ethyl silicate (trade name: Colcoat 28, Colcoat) K, Ni,) 576.
5t, 99.5% ethyl alcohol (to Kanto Kagaku, to
) 202.91i', 002 normal hydrochloric acid solution 199,
A hydrolyzed solution for cladding was prepared by mixing and stirring 2 f.

Preparation of sol for core: Commercially available ethyl silicate (trade name;
colcoat 28, colcoat ni, ni,) 134.1S
', 99.5% ethyl alcohol (Mto Kagaku x, x,)
45.2? , 0.02N hydrochloric acid solution 11.6
After mixing f and stirring for about 30 minutes, add tetraethoxygermanium (Trichemical Institute) 11.67 and 9 in advance.
A germanium solution prepared by mixing 95% ethyl alcohol 647 was gradually added dropwise, and the mixture was further stirred for 15 minutes. Thereafter, 54.8 Y of 002N hydrochloric acid solution was added and stirred for 15 minutes to prepare a hydrolyzed solution for the core.

Mix and stir the silica ultrafine particle solution 6101 and the hydrolyzed solution for cladding 9787 (~02 when it becomes sufficiently homogeneous.
The pH value was adjusted to 54 using regular aqueous ammonia.

When a predetermined amount of this solution was poured into a cylindrical container similar to that used in Example 1 and rotated under the same conditions, a clad gel that was cylindrical and had a hollow part in the direction of the rotation axis was obtained in about 55 minutes. Ta.

Next, the core hydrolysis solution 2441 and the silica ultrafine particle solution 1532 were mixed and stirred, and when they became sufficiently homogeneous, the pH value was adjusted to 475 using 02N aqueous ammonia.

This solution was poured into the hollow space created during the preparation of the clad gel and rotated under the same conditions as in Example 1 to obtain a clad/core integral gel in about 27 minutes. Dry, about 1
A dry gel was obtained in 8 days. This dried gel was heated to 85°C in an electric furnace with a silicon carbide heating element at a heating rate of 1°C/i in an atmospheric atmosphere.
Water molecules, hydroxyl groups, organic molecules, etc. present in the dried gel were sufficiently removed by heating to 0° C. and flowing chlorine gas using helium gas as a carrier and then oxygen gas at that temperature. After that, the heating rate was increased to 1℃/i again to 13℃.
The gel body was made non-porous by heating to 50°C, and a transparent sintered body was obtained.

When the quality of the obtained transparent sintered body was examined, it was found that 1
The number of irregularly shaped foreign particles and bubbles larger than μm was 2 and 1 or less per cm3, respectively.Same as Example 1, there were very few irregularly shaped foreign particles and bubbles, and the sintered body was of extremely high quality. As can be seen from the above Examples and Comparative Examples, rotational gelation of the hydrolysis solution for the core is particularly effective for removing air bubbles.

<Comparative Example 2> As in Example 2, an experiment was conducted using commercially available silica ultrafine particles as a starting material, a silica ultrafine particle solution of exactly the same composition and volume, a hydrolyzed solution for the cladding, and a hydrolyzed solution for the core. I did it. The difference from Example 2 is that, as in the case of Example 1 and Comparative Ratio 1, the core hydrolyzed solution was not gelated by rotation, but gelled while standing, and the cladding and core integrated gel was formed. It is in the point where I got it.

Furthermore, all conditions for subsequent drying, sintering, etc. were the same as in Example 2. When the quality of the transparent sintered body obtained under such conditions was examined, the number of amorphous foreign particles and bubbles of 1 μm or more present was 7 and 16 per cm3, respectively, which was the same as in Example 2. The quality was clearly lower than that of the obtained transparent sintered body.

<Example 6> A silica ultrafine particle solution, a cladding hydrolyzed solution, and a core hydrolyzed solution having the same composition as in Example 1 were prepared, and a cladding gel was produced in the same manner as in Example 1, followed by a core gel. - Obtained gel. However, the rotation speed during rotational gelation of the hydrolyzed solution for the core should be set at 60 revolutions per minute (2, 6
(equivalent to G). The obtained integral gel was dried and sintered in the same manner as in Example 1 to obtain a transparent sintered body. When examining the quality of the obtained transparent sintered body, it was found that there were 6 irregularly shaped foreign particles and bubbles of 1 μm or more in size and 6 bubbles per 31 cm3.
There were no more than 2 pieces. Compared to the case of Example 1, irregularly shaped foreign matter,
Although the number of bubbles was somewhat large, this is thought to be due to the difference in rotational speed.

However, when compared with Comparative Example 1, it can be said that the effect of rotational gelation of the core is remarkable.

<Example 4> As in Example 6, only the rotation speed during core rotation gelation was changed to 1000 revolutions per minute (equivalent to 730 G) to examine the difference in quality.

The quality of the obtained transparent sintered body was examined under the same conditions as in Example 1 for drying, sintering, etc., and the number of amorphous foreign matter of 1 μm or more and bubbles was Q and i cry3, respectively. It was of high quality with less than 1 piece, and the effect of core rotation gelation was remarkable as in Example 1. Example 5 As in Example 3, only the rotation speed during core rotation gelation was The difference in quality was examined by changing the speed to 2200 revolutions per minute (equivalent to 3500 G). When an attempt was made to perform rotational gelation at this rotational speed, the centrifugal force generated by the rotation was too large, causing cracks in the existing cylindrical gel body, making it impossible to obtain a clad-core integrated gel.

<Example 6> In order to produce a core rod material for an optical fiber (pure silica rod), a silica ultrafine particle solution with the same composition as in Example 1,
A hydrolysis solution for cladding was prepared. After adjusting the pH value of the silica ultrafine particle solution to 4.6 using 2N hydrochloric acid solution, thoroughly mix and stir with the hydrolysis solution for cladding, and adjust the pH value to 56 again using 02N ammonia solution. did.

A predetermined amount of the solution was poured into a cylindrical container similar to that in Example 1, and the solution was attached to the rotating device shown in Fig. 2, and gelatinized while rotating at a rotational speed of 200 revolutions per minute to obtain a core rod gel in about 56 minutes. Ta. The conditions for subsequent drying, sintering, etc. were all the same as in Example 1.

When the quality of the obtained transparent sintered body was investigated, there was 1
The number of amorphous foreign matter of μm or larger and the number of bubbles was 1 or less per 01 Cm3, and the quality was such that almost no light scattering was observed. Therefore, it can be said that this optical fiber core rod is fully suitable for practical use.

As can be seen from the above Examples and Comparative Examples, this method for obtaining an integrated cladding and core gel by rotationally gelling a hydrolyzed solution for the core is effective against irregularly shaped foreign matter and air bubbles that may be mixed in with any starting material. It was confirmed that it is sufficiently effective in removing. This effect utilizes the centrifugal force generated during rotation, so a certain amount of centrifugal force is required to achieve a sufficient removal effect, but on the other hand, an unnecessarily large centrifugal force is added. However, Examples 1 and 3.4 of the present invention may cause damage to the Talarado gel.
As shown in , it has been confirmed that the effect of removing foreign objects and air bubbles is remarkable in a fairly wide range of centrifugal force.

In the embodiments of the present invention, the manufacturing of cylindrical core glass has been explained as an example, but the shape of the glass to be manufactured does not necessarily have to be cylindrical, and may have an elliptical cross section or a spiral shape in the longitudinal direction of the base material. It may be a shape. Since it is very difficult to manufacture an optical fiber preform having such a shaped core glass by other methods such as OVD, the method of the present invention can be said to be an extremely effective method for producing the preform.

In addition, it is possible to manufacture optical fiber base material using only a hydrolyzed solution of metal alkoxide without using fine powder particles as a liquid raw material, but it is difficult to manufacture the base material for optical fibers in terms of the size of the obtained base material and its yield. It is clear that the present method using fine powder particles is superior.

〔Effect of the invention〕

As explained above, in the production of a transparent sintered body that is a precursor of a preform for an optical fiber, a tubular clad gel is produced by rotational gelation, and then a rotation method different from that used for producing the clad gel is used. The hydrolyzed solution for the core is rotated and gelled around the rotation axis that forms a 90° angle with the rotation axis during the production of Talarado gel, and the center of rotation is located outside the gel body to produce a clad/core integrated gel. This is what I am trying to do.

This production method is extremely effective in removing lump-like amorphous foreign matter and air bubbles mixed in raw materials. A very simple modification of slightly changing the rotation method during gelation is extremely effective in removing foreign matter and air bubbles, so if this method is used, it is possible to create optical fibers of higher quality than before without the gelling process. It is expected that the base material for use will be easily obtained.

Since the quality of the obtained transparent sintered body is extremely excellent, the present invention is applicable not only to the production of optical fiber base materials, but also to the production of other optical glasses, glasses for electronic materials, etc. It is. It can be said that 0 is an extremely effective manufacturing method for manufacturing multilayer glass with different refractive index distributions.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the concept of a conventional rotary gelling device, in which a rotation axis exists in a direction parallel to the longitudinal direction of the gel body. Fig. 2 is a diagram showing the concept of the rotary gelling apparatus according to the present invention, which forms an angle of 90° with the rotation axis during the production of Talarad gel, and whose rotation center is located outside the gel body. It is a characteristic. Fig. 1 1...Rotation center line 2...Bearing 3...Rotating cylindrical container 4...Holder for fixing the container 5... Rotating motor 6...Support stand Fig. 21...Rotating stand 2...Rotating cylindrical container 3...Holder for fixing the container 4... ... Rotation center line 5 ... Rotation shaft 6 ... Bearing 7 ... Rotation motor 8 ... Support stand or more

Claims (4)

[Claims] (1) After pouring the first liquid raw material into the hole formed in the longitudinal direction of the container, the rotation center of the rotating container forms an angle of 90° with the geometric rotational symmetry axis along the longitudinal direction of the container. 1. A method for producing an optical fiber preform by a sol-gel method, the method comprising gelling the preform while rotating it around a rotation axis located outside the sol-gel method. (2) In claim 1, the rotating container is characterized in that the inner surface of the rotating container has a cylindrical inner surface and is formed of a gel made from the second liquid raw material. A method for manufacturing an optical fiber preform according to claim 1. (3) The method for manufacturing an optical fiber preform according to claim 1, wherein the first liquid raw material is prepared from a metal alkoxide and fine powder particles. (4) The method for manufacturing an optical fiber preform according to claim 2, wherein the first and second liquid raw materials are prepared from metal alkoxide and fine powder particles.