JP3396430B2 - Method for manufacturing optical fiber preform and apparatus for manufacturing optical fiber preform - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for manufacturing an optical fiber preform (preform), and particularly to a high-quality optical fiber preform for manufacturing the optical fiber preform by the axial method. It relates to a method and a device by which a material can be manufactured.

[0002]

2. Description of the Related Art Conventionally, in an optical fiber manufacturing process,
If you try to make an ultra-fine optical fiber directly, it is difficult to control to have an optimum refractive index distribution. For this reason, first make a thick glass base material (preform) with the same refractive index and A method of manufacturing an ultrafine optical fiber by heating a glass preform and stretching it thin and long while controlling the outer diameter to a constant value is adopted.

One of the methods for manufacturing such an optical fiber preform is a so-called axis attachment method (external attachment method). In this axial attachment method, a soot raw material and a burner for blowing a reaction gas are arranged on a starting base material, and while the burner is reciprocatingly moved in parallel with the base material, soot is deposited on the base material and the optical fiber mother is used. It is a method of manufacturing a material.

During the process of depositing soot on this substrate,
The deposition conditions for depositing soot on the substrate may be changed. That is, the glass porous body (soot body) grows in the radial direction with respect to the starting substrate. At that time, it is necessary to adjust the distance between the base material and the burner in accordance with the growth of the soot body for reasons such as maintaining deposition efficiency and preventing contact between the burner and the soot body. Therefore, conventionally, the burner has been retracted according to the increased outer diameter of the soot body every time the outer diameter of the soot body grows to some extent. Further, as the soot body grows and the outer diameter increases, the outer circumference and surface area of the soot body also increase.Therefore, it is also possible to make adjustments such as increasing the amount of soot raw material and the amount of reaction gas released by the burner. It was done. Further, in order to obtain an optical fiber preform having a desired specification, the deposition condition may be changed (see Japanese Patent Laid-Open No. 2-204340).

[0005]

In the above conventional method, for example, when the growth of the outer diameter of the soot body of the base material to be manufactured exceeds a certain value, the burner and the base material are adjusted in accordance with the outer diameter. Of the soot material and the amount of reaction gas emitted by the burner (hereinafter these may be referred to as deposition conditions) are changed, and the outer diameter of the soot body is monitored for the next growth. When the range is reached, the deposition conditions are changed again, and this operation is repeated until the desired outer diameter is obtained.

However, since the axial method is a method in which a more uniform layer is grown and grown on the starting substrate, if the deposition conditions are changed by the method as described above, the uniform layer being stacked. Leading to upset. For this reason, efforts have been made to reduce the turbulence by making the outer diameter of the soot body that grows finer, but due to problems with the accuracy of the burner retreat mechanism and the gas flow rate regulator, it is not possible to make it smaller than a certain degree. . In addition, the size of the optical fiber base material has become large in order to meet the recent demands for high quality and high accuracy of the optical fiber, and the influence of such minute disturbances cannot be ignored.

This minute turbulence appears in the transparent vitrification step which is the subsequent step, and at the place where the deposition conditions are changed, unmelted soot and bubbles are generated, and the optical fiber as the final product is produced. It becomes a big negative factor in terms of transmission characteristics and strength. For this reason, this minute disturbance causes a deterioration in the yield of the optical fiber product, which is a problem.

The present invention has been made in view of the above problems, and in the manufacture of an optical fiber preform by an axial method,
Provided are a method for manufacturing an optical fiber preform and an apparatus for manufacturing the optical fiber preform, which does not adversely affect the quality of the manufactured optical fiber preform even if the deposition conditions for depositing soot on a substrate are changed. The main purpose is to do.

[0009]

The present invention has been made to solve the above-mentioned problems. The invention described in claim 1 of the present invention is a burner for blowing a soot raw material and a reaction gas onto a substrate. In a method of manufacturing an optical fiber preform by depositing soot on a base material while reciprocating in parallel with the base material, when the deposition condition for depositing the soot on the base material is changed, the change of the deposition condition is performed. Is carried out at the turn-back position of the reciprocating movement of the burner, which is a method for manufacturing an optical fiber preform.

As described above, in the method of manufacturing the optical fiber preform by the axial method, when the deposition conditions for depositing soot on the substrate are changed, if the deposition conditions are changed at the turn-back position of the reciprocating movement of the burner. Since the deposition conditions are changed in the parts that cannot be originally used as products, there is no slight disturbance in the quality of the product parts that had occurred in the past, and the soot body remains unmelted in the transparent vitrification process. The generation of bubbles and bubbles can be eliminated.

In this case, as described in claim 2, the deposition condition changed can be the distance between the burner and the substrate. In this way, by changing the distance between the burner and the base material at the folding position, the soot deposition efficiency can be maintained, or can be changed as necessary,
Further, it is possible to easily prevent the burner from coming into contact with the soot body having a large outer diameter without adversely affecting the quality.

Further, as described in claim 3, the deposition condition to be changed may be the amount of soot raw material and / or the amount of reaction gas. In this way, if the amount of the soot raw material and the amount of the reaction gas are changed at the folding position, it is possible to increase the outer diameter and the surface area of the soot body in accordance with the growth of the outer diameter of the soot body. It is possible to stably manufacture a high quality optical fiber base material.

The invention according to claim 4 of the present invention is
A burner for spraying a soot raw material and a reaction gas is provided on a base material, and the burner is provided with a mechanism for reciprocating in parallel with the base material, and the soot is deposited on the base material while the burner reciprocates to move the optical fiber preform. In the apparatus for manufacturing the optical fiber preform, when the deposition conditions for depositing soot on the base material are changed, the deposition conditions are changed at the turn-back position of the reciprocating movement of the burner. Is a device for manufacturing.

As described above, in the apparatus for manufacturing the optical fiber preform by the axial method, when the deposition condition for depositing soot on the substrate is changed, the deposition condition is changed at the turn-back position of the reciprocating movement of the burner. If the equipment has a function, the deposition conditions will be changed in the part that cannot be originally used as a product, and an optical fiber base material that does not have a minute quality disturbance in the product part that has been conventionally generated is manufactured. Thus, it is possible to prevent the unmelted soot body and the generation of bubbles in the transparent vitrification step.

In this case, the deposition condition changed can be the distance between the burner and the substrate. As described above, if the device has the function of changing the distance between the burner and the base material at the folding position, the soot deposition efficiency can be maintained, or can be changed as necessary. It is possible to easily prevent contact with a soot body that has grown large.

Further, as described in claim 6, the deposition condition changed may be the amount of the soot raw material and / or the amount of the reaction gas. in this way,
As long as the device has the function of changing the amount of raw material for soot and the amount of reaction gas at the folding position, the desired quality can be obtained in response to the increase in the outer diameter and surface area of the soot body as the outer diameter of the soot body grows. The optical fiber base material can be stably manufactured.

The present invention will be described in more detail below, but the present invention is not limited thereto. The inventor of the present invention, when the optical fiber preform is manufactured by the axial method, does not cause the quality of the optical fiber preform to be disturbed even if the deposition conditions for depositing soot on the substrate are changed. Various studies were conducted on the manufacturing method and manufacturing equipment of the fiber base material. As a result, the inventor has conceived that the deposition condition for depositing soot on the base material is changed at the turn-back position of the reciprocating movement of the burner, and as a result of improving and examining the various conditions, it is completed.

A drawback of the conventional method is that the deposition conditions are changed during the reciprocating movement of the burner. That is,
Since the deposition conditions were changed during the reciprocating movement of the burner, the growth of the soot body was disturbed at the actual product part of the optical fiber base material to be manufactured, and the transparent glass which is the subsequent process This was a cause of unmelted soot and bubbles in the sootification process.

On the other hand, in the optical fiber preform manufactured by the axial attachment method, the portion at the turning-back position of the reciprocating movement of the burner has not been used as a product. Here, FIG. 2 is an explanatory view showing the outer shape of the soot body at the turning-back position of the reciprocating movement of the burner by the axial attachment method. As shown in FIG. 2, at the turnaround position 8 of the reciprocating movement of the burner, the soot accumulated does not grow on a certain horizontal surface with respect to the burner, so that the burner flame is disturbed and the soot body 2 has an irregular density. Have a distribution. The irregularity of the density is larger than the minute turbulence due to the change of the deposition conditions, and therefore, this site could not be used as a product. This was especially remarkable when a burner with multiple craters was used.

Therefore, in the present invention, the deposition conditions for depositing soot on the substrate are changed at the turn-back position of the reciprocating movement of the burner. In this way, the minute disturbance of the soot growth due to the change in the deposition condition remains only in the portion that could not be originally used as a product, and does not affect the portion used as a product.
Therefore, even if the deposition conditions are freely changed, the optical fiber preform having a desired quality can be manufactured without causing disorder in soot growth. The present invention has been completed as a result of improving and examining various conditions based on the above idea.

Here, in the present invention, the change of the deposition condition at the turning-back position of the reciprocating movement of the burner means, strictly speaking, in the mechanical sense, only when the turning point of the burner is changed. Rather than that, the condition is changed within the range in which the soot is irregularly formed, for example, as shown in FIG. That is, the conditions may be changed within a range that does not affect the portion of the product where the soot is uniformly deposited in parallel.

[0022]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be specifically described below, but the present invention is not limited thereto. Here, FIG. 1 is an explanatory view showing an example of an apparatus for manufacturing an optical fiber preform of the present invention. This device is a device for manufacturing an optical fiber preform by a shafting method, and includes a rotating mechanism 7
And a burner 3 for blowing a soot raw material and a reaction gas onto the base material 1 held by the base material holding tool 6, and the burner 3 includes the burner 3 as the base material 1. The burner reciprocating mechanism 5 that can reciprocate in parallel is provided, and the soot body 2 can be grown by depositing soot on the base material 1 while the burner 3 reciprocates.

Further, the burner 3 is equipped with a burner position adjuster 4 capable of adjusting the distance between the burner 3 and the base material 1, and the amount of the raw material for soot and the reaction gas discharged from the burner 3 are adjusted. A gas flow rate controller (not shown) capable of adjusting the amount is provided, and the deposition conditions for depositing soot on the base material 1 can be changed.

Here, it is a feature of the apparatus for manufacturing the optical fiber preform of the present invention that it has a function of changing the deposition conditions at the turn-back position 8 of the reciprocating movement of the burner. That is, for example, the burner reciprocating mechanism 5, the burner position adjuster 4, and the gas flow rate adjuster are interlocked with each other, and at the turn-back position 8 of the reciprocating movement of the burner 3,
The burner position adjuster 4 and the gas flow rate adjuster are adapted to change the deposition conditions, and the deposition conditions are not changed during the reciprocating movement of the burner 3.

Next, a method of manufacturing the optical fiber preform using the above apparatus will be described. First, both ends of the base material 1 are held by the base material holding tool 6. The base material 1 gripped by the base material gripping tool 6 is rotated by the rotating mechanism 7.
Then, the soot raw material and the reaction gas are sprayed onto the base material 1 from the burner 3 which reciprocates by the burner reciprocating mechanism 5. Since the base material 1 is rotating and the burner 3 reciprocates, the soot is uniformly sprayed and deposited on the base material 1 to form the soot body 2.

Then, the soot body 2 grows due to the deposition of soot, and its outer diameter increases. Here, for example, when the growth of the outer diameter exceeds a certain value, and the burner 3
When the position of is the reciprocating folding position 8, the burner position adjuster 4 and the gas flow rate adjuster change the deposition conditions. As described above, in the apparatus for manufacturing the optical fiber preform of the present invention, the deposition conditions are changed within the range of the folding position 8 of the reciprocating motion of the burner 3 which is not used as a product. As a result, the soot body growth is not disturbed in the portion actually used as the product.

The change of the deposition condition at the folding position 8 is performed by measuring the outer diameter of the soot body 2 with a diameter measuring instrument or the like and operating at the folding position 8.
The folding position 8 may be operated by determining the position with a pulse counter or the like.

Further, the change of the deposition condition is not necessarily performed only to form the uniform soot body 2, but the desired condition can be obtained by arbitrarily changing the deposition condition during the soot deposition. You can also get the optical fiber base material. For example, by changing the deposition conditions,
It is also possible to freely change the density distribution of the soot body 2 in the radial direction. Even in that case, since the deposition condition is changed at the turn-back position 8 of the reciprocating movement of the burner 3, the soot body 2 is not disturbed by the change of the deposition condition, and the optical fiber mother having a desired characteristic in the radial direction. The material can be made.

If the glass preform for optical fibers manufactured by such an apparatus is dehydrated and made into transparent vitrification in the subsequent steps, no soot residue or bubbles are generated, As a final product, it is possible to obtain a high-quality optical fiber having excellent transmission characteristics and strength.

[0030]

EXAMPLES The present invention will be described below with reference to examples and comparative examples. (Example) A substrate 1 having an outer diameter of 40 mm, which was previously manufactured by the VAD method using the optical fiber base material manufacturing apparatus shown in FIG.
On the other hand, the soot body 2 was formed by depositing soot so that the final outer diameter was 200 mm, and the optical fiber preform was manufactured. The timing of changing the deposition condition was such that the outer diameter grew by 2 mm from the time when the condition was changed last time, and the burner was reciprocated at the turn-back position 8 for control. In this case, the outer diameter was measured by installing a measuring instrument “Optical Micro” manufactured by Anritsu Corporation in the center. Regarding the amount of soot raw material and the amount of reaction gas among the deposition conditions, the soot body 2 to be deposited and grown is controlled so as to have a density distribution as shown in FIG. From burner 3 to silicon tetrachloride 30 L / min, hydrogen 100 L / mi
Adjustment was performed so that n and oxygen of 50 L / min were released.

When the optical fiber base material produced in this manner was dehydrated and made into a transparent vitreous material, no unmelted residue or bubbles due to minute quality disturbance, which was seen in the conventional production apparatus, was not seen.

(Comparative Example) The optical fiber preform was manufactured by performing the deposition in the same manner as in the example except for the apparatus and other conditions other than the condition regarding the changing position of the deposition condition. The change of the deposition condition is not limited to the turn-back position 8 of the reciprocating movement of the burner 3, and the control is performed so that the change is made when the condition has grown by 2 mm from the previous condition change. The amount of raw material for soot and the amount of reaction gas were the same as in the example.

When the optical fiber base material thus produced was dehydrated and made into a transparent vitrified material, unmelted spots and large bubbles were formed at points with a thickness of 5 to 70% of the layer deposited by the shafting method. . These are consistent with where the deposition conditions were changed, and are believed to be caused by the changes in the deposition conditions.

The present invention is not limited to the above embodiment. The above-described embodiment is an exemplification, has substantially the same configuration as the technical idea described in the scope of the claims of the present invention, and has any similar effect to the present invention. It is included in the technical scope of the invention.

For example, in the above-described embodiment, the case where the base material is held horizontally and the burner for blowing the soot raw material and the reaction gas is arranged substantially vertically to the base material has been mainly described, but the scope of the present invention is not limited to this. It is not limited to. For example,
The soot body may be grown by gripping the base material vertically, and even in the burner, the raw material is not limited to being sprayed vertically to the base material, and the raw material is sprayed from any angle, Also in the case of growing the soot body, it is included in the scope of the present invention as long as the deposition conditions are changed within the range of the folding position.

[0036]

As described above, according to the present invention, the deposition conditions are changed at the turning-back position of the reciprocating movement of the burner. Therefore, in the production of the optical fiber preform, the deposition conditions for depositing soot are required. Even if it is changed accordingly, a good optical fiber preform can be obtained without affecting the product part of the optical fiber preform by the influence of the disturbance of the quality of the soot body caused by the change of the deposition conditions.

[Brief description of drawings]

FIG. 1 is an explanatory view showing an example of an optical fiber preform manufacturing apparatus of the present invention.

FIG. 2 is an explanatory diagram showing an outer shape of a soot body at a turning-back position of reciprocating movement of a burner by a shafting method.

FIG. 3 shows a density distribution of a soot body in an example.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Base material, 2 ... Soot body, 3 ... Burner, 4 ... Burner position adjusting machine, 5 ... Burner reciprocating mechanism, 6 ... Base material gripping tool, 7 ... Rotation mechanism, 8 ... Reciprocating folding position.

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Hiroyuki Koide, Hiroyuki Koide 2-13-1, Isobe, Annaka City, Gunma Prefecture Shin-Etsu Chemical Co., Ltd., Institute for Precision Materials (72) Inventor, Tadakatsu Shimada Annaka City, Gunma Prefecture 2-13-1, Isobe Shin-Etsu Chemical Co., Ltd., Precision Materials Research Laboratory (72) Inventor Hideo Hirasawa 2-13-1, Isobe, Annaka-shi, Gunma Shin-Etsu Chemical Industry Co., Ltd. (56) ) Reference JP-A-7-215727 (JP, A) JP-A-6-87624 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) C03B 37/00-37/16 C03B 8/04 C03B 20/00

Claims (6)

(57) [Claims] 1. A method for producing an optical fiber preform by depositing soot on a base material while reciprocally moving a burner for blowing a soot raw material and a reaction gas on the base material in parallel with the base material, A method for manufacturing an optical fiber preform, wherein, when the deposition conditions for depositing soot are changed, the deposition conditions are changed at a turn-back position of the reciprocating movement of the burner. 2. The method of manufacturing an optical fiber preform according to claim 1, wherein the deposition condition changed is a distance between the burner and the base material. 3. The method for producing an optical fiber preform according to claim 1, wherein the deposition condition changed is the amount of soot raw material and / or the amount of reaction gas. 4. A soot raw material is provided on a base material, and a burner for blowing a reaction gas is provided on the base material. The burner has a mechanism for reciprocating in parallel with the base material, and the soot is deposited on the base material while the burner reciprocates. In the apparatus for manufacturing the optical fiber preform according to the above, when changing the deposition condition for depositing soot on the base material, the device has a function of changing the deposition condition at the turn-back position of the reciprocating movement of the burner. Equipment for manufacturing optical fiber preforms. 5. The apparatus for manufacturing an optical fiber preform according to claim 4, wherein the modified deposition condition is a distance between a burner and a substrate. 6. The apparatus for producing an optical fiber preform according to claim 4 or 5, wherein the changed deposition condition is an amount of soot raw material and / or an amount of reaction gas. .