JP2000044276A - Production of optical fiber preform and apparatus for producing optical fiber preform - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a process for producing an optical fiber preform which obviates the occurrence of an adverse influence in the quality of the optical fiber preform to be produced even if deposition conditions for depositing soot on a base material are changed at the time of producing the optical fiber preform by a shaft deposition method and the apparatus therefor. SOLUTION: The change of the deposition conditions is executed in a turn back position 8 of the reciprocating motion of a burner 3 in the case the deposition conditions for depositing the soot on the base material 1 are changed in the apparatus for producing the optical fiber preform by the shaft deposition method. The apparatus for producing the optical fiber preform by the shaft deposition method has a function to execute the change of the deposition conditions in the turn back position of the reciprocating motion of a burner 3 in the case the deposition conditions for depositing the soot on the base material 1 are changed.

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, and more particularly to a method for manufacturing an optical fiber preform by a shafting method. The invention relates to a method and an apparatus by which a material can be produced.

[0002]

2. Description of the Related Art Conventionally, in an optical fiber manufacturing process,
When trying to make an ultra-fine optical fiber directly, it is difficult to control it to have an optimum refractive index distribution. For this reason, first, a large-diameter glass preform (preform) having the same refractive index is prepared. A method is employed in which a glass base material is heated and stretched to be thin and long while controlling the outer diameter to be constant, thereby producing an ultrafine optical fiber.

One of the methods for producing such an optical fiber preform is a so-called shafting method (external method). In this shafting method, a burner that sprays a soot raw material and a reactive gas is arranged on a starting base material, and while the burner is reciprocated in parallel with the base material, soot is deposited on the base material, and an optical fiber motherboard is deposited. It is a method of manufacturing materials.

In the process of depositing soot on this substrate,
There are cases where the deposition conditions for depositing soot on the substrate are changed. That is, the porous glass body (soot body) grows in the radial direction with respect to the starting base material. At this 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 maintenance of deposition efficiency and prevention of contact between the burner and the soot body. Therefore, conventionally, every time the outer diameter of the soot body grows to some extent, the burner is retracted in accordance with the increased outer diameter of the soot body. In addition, as the soot body grows and its outer diameter increases, the outer circumference and surface area of the soot body also increase.Therefore, it is also possible to adjust the amount of the soot raw material and the amount of the reaction gas emitted from the burner to increase accordingly. It was done. Further, in order to obtain an optical fiber preform having desired specifications, the deposition conditions may be changed (see Japanese Patent Application 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 distance between the burner and the base material is adjusted in accordance with the outer diameter. Of the soot material and the amount of reactive gas released from the burner (hereinafter, these may be referred to as deposition conditions), and monitoring the outer diameter of the soot body to monitor 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 reached.

However, since the shafting method is a method in which a more uniform layer is grown on a starting base material, if the deposition conditions are changed by the above-described method, the overlapping uniform layer is formed. Leads to disturbing. For this reason, efforts have been made to reduce the turbulence by reducing the monitoring of the outer diameter of the growing soot body, but due to problems with the accuracy of the burner retreat mechanism and gas flow regulator, it is not possible to reduce the diameter to a certain degree or more. . In addition, the size of the optical fiber base material has become larger in order to satisfy the recent demands for higher quality and higher accuracy of the optical fiber, and the influence of the minute disturbance cannot be ignored.

[0007] The minute turbulence appears in a subsequent vitrification process, which is a subsequent process. In the place where the deposition conditions are changed, unmelted soot and bubbles are generated in the soot body, and the optical fiber as a final product is produced. This is a major negative factor in terms of transmission characteristics and strength. For this reason, the minute disturbance causes a decrease in the yield of the optical fiber product, which is a problem.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has been described in connection with the manufacture of an optical fiber preform by a shafting method.
Provided is a method for manufacturing an optical fiber preform and an apparatus for manufacturing an optical fiber preform, which do not adversely affect the quality of an optical fiber preform to be manufactured even if the deposition conditions for accumulating soot on a substrate are changed. The main purpose is to

[0009]

Means for Solving the Problems The present invention has been made to solve the above problems, and the invention described in claim 1 of the present invention provides a burner for blowing a soot raw material and a reactive gas onto a substrate. In the method of manufacturing soot base material by depositing soot on a substrate while reciprocating in parallel with the substrate, when changing deposition conditions for depositing soot on the substrate, changing the deposition conditions Is performed at a turn-back position of the reciprocating movement of the burner.

As described above, in the method of manufacturing the optical fiber preform by the shafting method, when the deposition conditions for depositing soot on the substrate are changed, the deposition conditions should be changed at the turn-back position of the reciprocation of the burner. The deposition conditions will be changed in parts that cannot be used as a product originally, and there will be no minute disturbance of quality in the product part, which occurred in the past. And generation of bubbles and the like can be eliminated.

In this case, the deposition condition to be changed can be a distance between the burner and the base material. In this way, if the distance between the burner and the base material is changed at the turnback 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 conditions to be changed can be the amount of the soot raw material and / or the amount of the reaction gas. As described above, if the amount of the soot raw material and the amount of the reaction gas are changed at the turnback position, the desired outer diameter and surface area of the soot body can be increased in accordance with the growth of the outer diameter of the soot body. An optical fiber preform of high quality can be stably manufactured.

[0013] The invention described in claim 4 of the present invention provides:
An optical fiber preform is provided by providing a burner for spraying a soot raw material and a reaction gas onto the base material, the burner having a mechanism for reciprocating in parallel with the base material, and depositing soot on the base material while the burner reciprocates. An optical fiber preform having a function of, when changing deposition conditions for depositing soot on the substrate, changing the deposition conditions at a turn-back position of the reciprocating movement of the burner. This is an apparatus for manufacturing.

As described above, in the apparatus for manufacturing the optical fiber preform by the shafting method, when the deposition conditions for depositing the soot on the substrate are changed, the deposition conditions are changed at the turn-back position of the reciprocation of the burner. If the device has a function, the deposition conditions will be changed in a part that cannot be used as a product originally, and an optical fiber preform without minute disturbance of quality in the product part which has occurred conventionally will be manufactured. This makes it possible to prevent the soot body from being left undissolved or generating bubbles in the transparent vitrification step.

In this case, it is possible that the deposition condition to be changed is a distance between the burner and the base material. As described above, if the apparatus has a function of changing the distance between the burner and the base material at the turnback position, the soot deposition efficiency can be maintained or can be changed as necessary. Can be easily prevented from coming into contact with the soot body that has grown greatly.

Further, as described in claim 6, the deposition conditions to be changed can be the amount of the soot raw material and / or the amount of the reaction gas. in this way,
If the device has a function to change the amount of the raw material for soot and the amount of the reaction gas at the turnback position, the desired quality can be achieved in accordance with the increase in the outer diameter and surface area of the soot body due to the growth of the outer diameter of the soot body. Can be stably manufactured.

Hereinafter, the present invention will be described in more detail, but the present invention is not limited thereto. The inventor of the present invention has proposed a method of manufacturing an optical fiber preform by a shafting method, in which the quality of the optical fiber preform is not disturbed even if the deposition conditions for depositing soot on the substrate are changed. Various investigations were conducted on the manufacturing method and manufacturing apparatus of the fiber base material. As a result, the inventor has conceived of changing the deposition conditions for depositing soot on the base material at the turn-back position of the reciprocating movement of the burner, and has completed and improved the various conditions as a result.

A disadvantage of the conventional method is that the deposition conditions are changed during the reciprocation 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 in the actual product of the optical fiber base material to be manufactured, and the subsequent process, transparent glass In the forming process, unmelted soot and bubbles were generated.

On the other hand, in the conventional optical fiber preform manufactured by the shafting method, a portion which is a turning position of the reciprocating movement of the burner has not been used as a product. Here, FIG. 2 is an explanatory diagram showing the outer shape of the soot body at the turnback position of the reciprocating movement of the burner by the shafting method. As shown in FIG. 2, at the turning position 8 of the reciprocation of the burner, the soot to be deposited does not grow on a constant 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. This irregularity of the density is larger than the minute disturbance due to the change of the deposition conditions, and therefore, this portion cannot be used as a product. This was particularly noticeable when using a burner with multiple craters.

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, a minute disturbance in soot growth due to a change in the deposition conditions remains in a portion that could not be used as a product originally, and does not affect a portion used as a product.
Therefore, even if the deposition conditions are freely changed, an optical fiber preform of desired quality can be manufactured without disturbing the soot growth. The present invention has been completed as a result of improving and examining various conditions from the above idea.

Here, the term "change of the deposition conditions at the turn-back position of the reciprocating movement of the burner" in the present invention means, in a strictly mechanical sense, only a case where the change is made at the end point at which the burner turns. However, as shown in FIG. 2, for example, it indicates that the condition is changed within a range where the soot is irregularly formed. That is, the conditions may be changed within a range that does not affect the part where the soot is deposited in parallel and uniformly as a product.

[0022]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be specifically described below, but the present invention is not limited to these embodiments. Here, FIG. 1 is an explanatory view showing an example of an optical fiber preform manufacturing apparatus of the present invention. This apparatus is an apparatus for manufacturing an optical fiber preform by a shafting method.
And a burner 3 for spraying a soot material and a reactive gas onto the base material 1 held by the base material holding tool 6, and the burner 3 is formed by combining the burner 3 with the base material 1. A burner reciprocating mechanism 5 that can reciprocate in parallel is provided, and the soot body 2 can be grown by depositing soot on the substrate 1 while the burner 3 reciprocates.

The burner 3 is provided with a burner position adjuster 4 capable of adjusting the distance between the burner 3 and the base material 1. A gas flow controller (not shown) capable of adjusting the amount is provided, and the deposition conditions for depositing soot on the substrate 1 can be changed.

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

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

The soot body 2 grows due to the soot deposition, 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 is the turning position 8 of the reciprocating movement, the burner position adjuster 4 and the gas flow adjuster change the deposition conditions. As described above, in the apparatus for manufacturing an optical fiber preform according to the present invention, since the deposition conditions are changed within the range of the reversing position 8 of the reciprocating motion of the burner 3 which is not used as a product, the optical fiber preform is changed. The soot body growth is not disturbed in a part actually used as a product.

It should be noted that the change of the deposition conditions at the turning position 8 is performed, for example, by measuring the outer diameter of the soot body 2 with a diameter measuring device or the like, and operating at the turning position 8.
The return position 8 may be operated by judging the position with a pulse counter or the like.

The change of the deposition conditions is not necessarily performed only to form the soot body 2 having a constant uniformity. The desired conditions can be changed by arbitrarily changing the deposition conditions during the deposition of the soot. Can be obtained. 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 such a case, the change of the deposition conditions is performed at the turnback position 8 of the reciprocating movement of the burner 3, so that the change of the deposition conditions does not cause the soot body 2 to be disturbed and the optical fiber mother having desired characteristics in the radial direction. Materials can be made.

Then, if the glass preform for optical fiber manufactured by such an apparatus is subjected to dehydration and vitrification in a subsequent step, the soot body will not be left unmelted or bubbles will not be generated. As a final product, a high-quality optical fiber having excellent transmission characteristics and strength can be obtained.

[0030]

The present invention will be described below with reference to examples and comparative examples. (Embodiment) A substrate 1 having an outer diameter of 40 mm, which was prepared in advance by the VAD method using the optical fiber preform manufacturing apparatus shown in FIG.
On the other hand, soot was deposited so as to have a final outer diameter of 200 mm to form a soot body 2, and an optical fiber preform was manufactured. The timing for changing the deposition conditions was such that the outer diameter grew by 2 mm from the time when the previous condition was changed, and control was performed at the turnback position 8 of the reciprocation of the burner. The measurement of the outer diameter in this case was performed by installing a “light micro” measuring instrument manufactured by Anritsu Corporation at the center. Further, among the deposition conditions, the amount of the soot raw material and the amount of the reaction gas are controlled so that the soot body 2 to be deposited and grown has a density distribution as shown in FIG. Burner 3 to silicon tetrachloride 30 L / min, hydrogen 100 L / mi
Adjustment was performed so that n and 50 L / min of oxygen were released.

When the optical fiber base material thus manufactured was dehydrated and transparently vitrified, no unmelted residue or bubbles due to minute disturbance in quality, which were observed in the conventional manufacturing apparatus, were observed.

(Comparative Example) The deposition was performed in the same manner as in the example except for the apparatus and other conditions other than the condition relating to the change position of the deposition condition, and the optical fiber preform was manufactured. The change of the deposition condition was not limited to the reversing position 8 of the reciprocating movement of the burner 3, but was controlled so as to be performed when the growth was 2 mm from the previous condition change. The amounts of the soot raw material and the reaction gas were the same as in the example.

When the optical fiber base material thus manufactured was dehydrated and transparently vitrified, unmelted residue and large bubbles were generated at a position of 5 to 70% of the thickness of the layer deposited by the shafting method. . These coincide with the change in the deposition conditions, and are considered to have occurred due to the change in the deposition conditions.

The present invention is not limited to the above embodiment. The above embodiment is an exemplification, and has substantially the same configuration as the technical idea described in the scope of the claims of 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 gripped horizontally and the burner for spraying the soot raw material and the reactive gas is arranged substantially vertically on the base material has been described, but the scope of the present invention is not limited to this. However, the present invention is not limited to this. For example,
The soot body may be grown by vertically gripping the base material, or even in a burner, the material is not limited to spraying the raw material and the like vertically to the base material, and the raw material and the like are sprayed from any angle, In the case of growing a soot body, any method that changes the deposition conditions within the range of the turning position is included in the scope of the present invention.

[0036]

As described above, according to the present invention, the deposition conditions are changed at the turn-back position of the reciprocating movement of the burner. Therefore, in the production of the optical fiber preform, the deposition conditions for soot deposition are required. Even if it is changed accordingly, it is possible to obtain a good optical fiber preform without affecting the product portion of the optical fiber preform due to disturbances such as the quality of the soot body caused by changing the deposition conditions.

[Brief description of the 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 view showing an outer shape of a soot body at a turning position of a 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 ... Substrate, 2 ... Soot body, 3 ... Burner, 4 ... Burner position adjuster, 5 ... Burner reciprocating movement mechanism, 6 ... Substrate gripper, 7 ... Rotation mechanism, 8 ... Reversing position of reciprocating movement.

Continued on the front page (72) Inventor Tadakatsu Shimada 2-3-1-1, Isobe, Annaka-shi, Gunma Shin-Etsu Kagaku Kogyo Co., Ltd. Precision Functional Materials Laboratory (72) Inventor Hideo Hirasawa 2--13 Isobe, Annaka-shi, Gunma No. 1 Shin-Etsu Kagaku Kogyo Co., Ltd. Precision Functional Materials Laboratory F-term (reference) 4G021 EA03 EB14 EB26

Claims (6)

[Claims] 1. A method for producing an optical fiber preform by depositing soot on a substrate while reciprocating a burner for spraying a soot raw material and a reaction gas onto the substrate in parallel with the substrate. Wherein the deposition conditions for depositing soot are changed at the turn-back position of the reciprocating movement of the burner. 2. The method for manufacturing an optical fiber preform according to claim 1, wherein the changed deposition condition is a distance between a burner and a substrate. 3. The method of manufacturing an optical fiber preform according to claim 1, wherein the changed deposition condition is an amount of a soot raw material and / or an amount of a reaction gas. 4. A burner for spraying a soot material and a reaction gas onto a base material, the burner having a mechanism for reciprocating in parallel with the base material, wherein the burner deposits soot on the base material while reciprocating. An apparatus for manufacturing an optical fiber preform according to the present invention, characterized in that when changing deposition conditions for depositing soot on the base material, a function is provided for changing the deposition conditions at a turn-back position of the reciprocating movement of the burner. For manufacturing optical fiber preforms. 5. The apparatus for manufacturing an optical fiber preform according to claim 4, wherein the changed deposition condition is a distance between a burner and a substrate. 6. The apparatus for manufacturing an optical fiber preform according to claim 4, wherein the deposition condition to be changed is an amount of a soot raw material and / or an amount of a reaction gas. .