JP2000264665A - Production of optical fiber preform - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing an optical fiber preform by which the straight optical fiber preform can stably be produced without substantial eccentricity of a core. SOLUTION: The central axis of a porous preform for an optical fiber is aligned with the rotating shaft of a rotating mechanism for rotating the porous preform for the optical fiber to thereby reduce the whirling of the porous preform for the optical fiber to a prescribed value or below in a method for producing the optical fiber preform comprising moving the porous preform for the optical fiber containing a core in the axial direction while rotating the porous preform for the optical fiber around the central axis thereof and while making an atmospheric gas flow through the interior of a heating furnace, then passing the porous preform for the optical fiber from the front end thereof through a heating zone in the heating furnace and melting and vitrifying the porous preform for the optical fiber.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for manufacturing an optical fiber preform. In particular, the present invention relates to a method for manufacturing an optical fiber preform capable of reducing the eccentricity of a core.

[0002]

2. Description of the Related Art Conventionally, in order to produce an optical fiber preform by melt-vitrifying a porous preform for an optical fiber obtained by a VAD (axial mounting) method or an OVD (external mounting) method, for example, a porous The base material is inserted into a vertical heating furnace, and while supplying an atmosphere gas such as a dehydrating gas or an inert gas into the heating furnace, the porous base material is rotated to a high temperature part (that is, a heat zone) in the furnace. This is performed by sequentially feeding at a constant speed from the front end. However, in the above-described conventional manufacturing method, an optical fiber preform having a large eccentricity of the core or a curved optical fiber preform may be manufactured. When an optical fiber is manufactured using such an optical fiber preform having a large core eccentricity, the resulting optical fiber has a large connection loss when connecting the optical fiber, and has uniform optical characteristics over a long distance. There is a problem that it cannot be maintained.

[0003]

SUMMARY OF THE INVENTION In view of the above circumstances, the present invention provides a method of manufacturing an optical fiber preform that can stably produce a straight optical fiber preform with substantially no eccentricity of the core. The purpose is to:

[0004]

The present inventors have made intensive studies to achieve the above object, and as a result, the eccentricity of the core in the optical fiber preform was increased only when the optical fiber porous material was melted and vitrified. The base material sometimes wandered, and I came to think that this was the cause.

That is, when the porous preform for an optical fiber is swirling, only one specific direction of the porous preform approaches the heat zone. Therefore, this portion is first molten and vitrified. Then, with vitrification, the density increases only in the vitrified portion. Therefore, the surrounding non-vitrified porous material is pulled and the flow of the porous material occurs. As a result, it is considered that the melt vitrification becomes non-uniform and the core eccentricity of the optical fiber preform increases.

[0006] Further, as described above, it is considered that a curved optical fiber preform is manufactured because the rate of melt vitrification in the circumferential direction of the porous preform for an optical fiber is different. From the above findings, the inventor has completed the following invention.

That is, the first aspect of the present invention provides
While flowing the atmosphere gas into the heating furnace, the porous preform for the optical fiber including the core is moved in the axial direction while rotating around the center axis thereof, and the inside of the heating furnace is moved from the front end of the porous preform for the optical fiber. In the method for manufacturing an optical fiber preform that passes through a heat zone and is melted and vitrified, the center axis of the porous preform for optical fiber and the rotation axis of a rotating mechanism that rotates the same are matched to each other. This is a method for manufacturing an optical fiber preform in which the deflection around the material is reduced to a certain value or less.

[0008] As described above, in order to suppress the whirling of the porous preform for optical fiber, the center axis of the porous preform for optical fiber and the rotation axis of the rotating mechanism for rotating the same may be matched. . Then, by suppressing the run-around of the porous preform for optical fiber, the porous preform can be uniformly heated. As a result, the tensile flow of the porous material can be suppressed, and an optical fiber preform having an extremely small core eccentricity can be manufactured.

According to a second aspect of the present invention, there is provided the optical fiber preform wherein at least one of the front end, the center, and the rear end of the porous preform for the optical fiber has a run-out around 3 mm or less. It is a method of manufacturing a material.

In general, the whirling of the porous preform for an optical fiber, particularly its front end, tends to increase, and it is important to suppress the whirling. Also, it is necessary to suppress the whirling of the porous base material in the middle and second half of the melt vitrification. Therefore, it is necessary to suppress the whirling of the central portion and the rear end portion of the porous base material. Therefore, reducing the deflection around at least one of the front end, the center, and the rear end of the porous preform to 3 mm or less is necessary for manufacturing an optical fiber preform having a very small core eccentricity. Is particularly preferred.

Further, the invention according to claim 3 is the method for producing an optical fiber preform in which the deflection around the entire area of the porous preform for optical fibers is 1.5 mm or less. As described above, not only the front end portion, the center portion, and the rear end portion of the porous preform for optical fiber, but also the deflection around the entire area of the porous preform for optical fiber is further reduced to 1.5 mm or less. Thus, an ideal optical fiber preform having a very small core eccentricity can be manufactured.

[0012]

Embodiments of the present invention will be described below with reference to the drawings, but the present invention is not limited thereto. In the method for producing an optical fiber preform of the present invention, the porous preform for optical fiber is melted and vitrified by using a heating furnace. As the heating furnace, for example, a vertical heating furnace shown in FIG. 1 can be mentioned. The orientation of the heating furnace is not particularly limited, and may be, for example, a horizontal heating furnace.

In the manufacturing method of the present invention, heating and melting are performed while flowing an atmospheric gas into the heating furnace. Examples of the atmosphere gas include a gas for dehydrating the porous base material (specifically, a halogen gas such as a chlorine gas), an inert gas (specifically, helium or the like), and a mixed gas thereof. In order to flow the atmospheric gas into the heating furnace, for example, a gas inlet 10 is provided at a lower portion of the furnace tube 1 of the heating furnace, gas is introduced from here, and the gas is discharged from an exhaust port 11 at an upper portion of the furnace tube 1. Performed by The flow rate of the gas is, for example, 0.
5 to 1.5 L / min and the inert gas is 5 to 15 L / min.

In the manufacturing method of the present invention, the porous preform for an optical fiber including a core is melted and vitrified in the above-mentioned heating furnace. The porous preform for an optical fiber can be manufactured by, for example, the OVD method. That is, the porous base material can be manufactured by depositing glass fine particles on the outer peripheral portion of the rotating core. Examples of the core include a quartz rod. The glass fine particles are generated by supplying a raw material gas such as silicon tetrachloride gas and a fuel gas such as a hydrogen-oxygen mixed gas to the same burner, and hydrolyzing the raw material gas in an oxyhydrogen flame. And, by repeatedly reciprocating the burner over the entire length of the core, the generated glass particles are deposited on the outer periphery of the core,
Obtain a porous matrix.

The manufacturing method of the present invention is intended to suppress the whirling of the porous preform for an optical fiber during melt vitrification, thereby producing an optical fiber preform having a small core eccentricity. It is. Therefore, it is necessary to use a porous base material which is not curved and has a small core eccentricity as the first step.

In the manufacturing method of the present invention, the porous preform for an optical fiber is moved in the axial direction while being rotated around its central axis, and is melted and vitrified. At this time, it is a feature of the present invention that the deflection around the porous base material is set to a certain value or less. For this purpose, when rotating the porous preform for optical fiber, it is necessary to match the center axis 2 of the porous preform with the rotation axis 4 of a rotation mechanism (for example, a rotation motor) 3 for rotating the same. is there.

Specifically, in order to make the center axis 2 of the porous preform coincide with the rotation axis 4 of the rotating mechanism, the porous preform is first rotated and its whirling is measured by an appropriate measuring means, for example, a measure or the like. Measure in advance. Then, according to the degree of the run-out, fine adjustment of the connection portion between the porous base material and the rotary chuck 5, the installation position of the bearing 6, and the like eliminate the run-out.

Here, even if the center axis of the porous preform coincides with the rotation axis of the rotating mechanism, the center axis of the porous preform coincides with the center axis of the furnace tube 1 or the heater 7. Otherwise, the porous preform is not uniformly melted. Therefore, these axes also need to be accurately matched in advance.

The operation of matching the center axis of the porous preform with the rotation axis of the rotating mechanism may be performed at least at one or more of the front end, the center, and the rear end of the porous preform for optical fibers, particularly, It is preferable to perform the operation so that the swing circumference at two or more locations is 3 mm or less. In this case, the front end portion of the porous base material tends to have a large run-around. Therefore, the run-out around the front end tends to cause eccentricity of the core, and it is preferable to suppress the run-out around the front end to 3 mm or less. In addition, if there is a swing around the rear end of the porous base material, a large swing around the front end may be reflected, so that the swing around the rear end of the porous base material is also suppressed to 3 mm or less. Is preferred. Therefore, it is particularly preferable that both the deflection around the front end and the rear end of the porous preform for an optical fiber be 3 mm or less.

The whirling of the porous base material is preferably as small as possible and as small as possible.
Accordingly, it is desirable that the deflection around the porous base material is 1.5 mm or less over the entire area of the porous base material, not only at the front end, the center, and the rear end. In this way, it is possible to obtain an extremely high quality glass preform without eccentricity over the entire length of the porous preform.

As described above, the porous preform is rotated while moving around the porous preform for the optical fiber, and is moved in the direction of the central axis. The moving speed is, for example, 1 to
5 mm / min. The porous base material can be moved, for example, by moving the rotating mechanism 3 up and down by the elevating mechanism 14 as described later. The rotation speed of the porous preform for an optical fiber around the central axis is, for example, 1 to 100 rpm.

Then, the porous base material is moved from the front end to the heat zone in the heating furnace by the movement of the porous base material, and is sequentially vitrified in the order of the front end, the center, and the rear end. In this case, the heat zone is heated by the heater 7.
Melt vitrification is performed, for example, by increasing the heater temperature to 1500 ° C. or higher. At this time, if the melt vitrification is performed in a dehydrating gas atmosphere such as chlorine gas, the porous base material can be dehydrated at the same time.

As described above, in the method of manufacturing an optical fiber preform according to the present invention, the center axis of the porous preform for optical fiber and the rotation axis of the rotating mechanism are made to coincide with each other, and Is reduced, so that only one specific direction of the porous base material does not approach the heat zone. Therefore, a part does not melt vitrify first, so that the flow of the porous material does not occur. As a result, the melt vitrification becomes uniform, so that the core of the optical fiber preform is not eccentric. Further, since the rate of melt vitrification in the circumferential direction of the porous preform is the same, a curved optical fiber preform is not produced. As described above, according to the optical fiber preform manufacturing method of the present invention, a straight optical fiber preform having substantially no eccentricity of the core can be manufactured.

In order to manufacture an optical fiber from the optical fiber preform manufactured in the present invention, an ordinary method may be used. For example, the optical fiber preform obtained as described above is subjected to 2100 in an electric furnace or the like. It may be carried out by heating and melting at a temperature of not less than ° C., stretching to a desired diameter and spinning. By using an optical fiber preform having an extremely small core eccentricity, an optical fiber having uniform optical characteristics over an extremely long distance can be stably manufactured.

[0025]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. Example 1 An optical fiber preform was manufactured using the vertical heating furnace shown in FIG. That is, as shown in FIG. 1, the porous preform 8 for an optical fiber was attached to a rotary chuck 5 at the tip of a rotary shaft 4 as a ceramic seed rod. Then, the rotation motor 3 as a rotation mechanism was rotated at 20 rpm. At that time, the whirling of the front end a of the porous base material 8 was measured by a measure. Next, the connection position between the rotary chuck 5 and the core 9 was finely adjusted so that the whirling of the front end a measured in this manner was 3 mm.

Thereafter, He gas and chlorine-based gas are supplied at a gas introduction port 10 at a flow rate of 8 L / min and 0.8 L / min, respectively.
The gas was introduced into the furnace tube 1 and exhausted from the exhaust port 11. Then, the inside of the furnace tube 1 is set to a dehydrating atmosphere, and the heater 7 is set to 1550.
The temperature was raised to ° C.

Next, while rotating the porous base material 8 at 20 rpm by the rotating motor 3, the rotating motor 3 is lowered by the elevating mechanism 14 at a speed of 2.1 mm / min along the direction of the rotating shaft, and The base material 8 was lowered in the axial direction while rotating. The vertical movement of the rotary motor 3 is achieved by biting the end of a support rod 12 that supports the rotary motor 3 with a screw rod 13 and rotating the screw rod 13 about its axis by a lifting mechanism 14. Can be moved up and down along the screw rod 13.

The porous preform 8 for an optical fiber was lowered as described above, and passed through the heat zone heated by the heater 7 from the front end a of the porous preform 8. And sequentially,
The front end a, the center b, and the rear end c of the porous preform were melted and vitrified to produce an optical fiber preform. The eccentricity of the core with respect to the optical fiber preform in the center axis direction of the obtained optical fiber preform was examined by examining the distribution of the refractive index adjusting dopant. The eccentricity was 0.1% or less.

(Examples 2 and 3) The whirling of the front end portion a of the porous preform 8 for an optical fiber was 2 mm and 1 mm, respectively.
The optical fiber preforms of Examples 2 and 3 were manufactured in the same manner as in Example 1 except that the connection position between the rotary chuck 5 and the core 9 was finely adjusted so that The eccentricity of the refractive index adjusting dopant with respect to the optical fiber preform in the central axis direction of each of the obtained optical fiber preforms was 0.1% or less.

(Examples 4 to 6) Fine adjustment of the connection position between the rotary chuck 5 and the core 9 so that the whirling of the central part b of the porous preform 8 for optical fiber is 3 mm, 2 mm and 1 mm, respectively. Except that, the optical fiber preforms of Examples 4 to 6 were manufactured in the same manner as Example 1. The eccentricity of the refractive index adjusting dopant with respect to the optical fiber preform in the center axis direction of each of the obtained optical fiber preforms is 0.1%.
It was below.

(Examples 7 to 9) The connection position between the rotary chuck 5 and the core 9 is finely adjusted so that the whirling of the rear end portion c of the porous preform 8 for optical fiber is 3 mm, 2 mm and 1 mm, respectively. Except for the adjustment, the optical fiber preforms of Examples 7 to 9 were manufactured in the same manner as in Example 1. The eccentricity of the refractive index adjusting dopant with respect to the optical fiber preform in the center axis direction of each of the obtained optical fiber preforms is 0.1%.
It was below.

(Comparative Examples 1 to 3) The connection position between the rotary chuck 5 and the core 9 is finely adjusted so that the whirling of the front end portion a of the optical fiber porous preform 8 becomes 5 mm, 7 mm, and 10 mm, respectively. Except that, the optical fiber preforms of Comparative Examples 1 to 3 were manufactured in the same manner as in Example 1. The eccentricity of the refractive index adjusting dopant with respect to the optical fiber preform in the central axis direction of each obtained optical fiber preform was 0.8
% Or more.

(Comparative Examples 4 to 6) The connection positions of the rotary chuck 5 and the core 9 were finely adjusted so that the whirling of the central portion b of the porous preform 8 for an optical fiber was 5 mm, 7 mm, and 10 mm, respectively. Except for the adjustment, the optical fiber preforms of Comparative Examples 4 to 6 were manufactured in the same manner as in Example 1. The eccentricity of the refractive index adjusting dopant with respect to the optical fiber preform in the central axis direction of each of the obtained optical fiber preforms was 0.8% or more.

(Comparative Examples 7 to 9) The connection position between the rotary chuck 5 and the core 9 was finely adjusted so that the whirling of the rear end c of the porous preform 8 for an optical fiber was 5 mm, 7 mm, and 10 mm, respectively. Except for the adjustment, the optical fiber preforms of Comparative Examples 7 to 9 were manufactured in the same manner as in Example 1. The eccentricity of the refractive index adjusting dopant with respect to the optical fiber preform in the central axis direction of each obtained optical fiber preform was 0.8
% Or more.

Each part of the porous preform for optical fibers a to
FIG. 2 shows a partial result of the correlation between the magnitude of the deflection around c and the eccentricity of the optical fiber preform. As is apparent from FIG. 2, any part a of the porous preform for optical fiber
It can be seen that the eccentricity of the optical fiber preform suddenly decreases when the runout becomes 3 mm or less in the cases of -c. In particular,
When the deflection around the porous base material is set to 1.5 mm or less,
The core eccentricity of the optical fiber preform can be substantially eliminated.

Although the present invention has been described based on the above embodiment, 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.

[0037]

According to the method for manufacturing an optical fiber preform of the present invention, the deflection around the porous preform for an optical fiber during melt vitrification can be made extremely small. As a result, an optical fiber preform having a very small eccentricity of the core and having no curvature can be manufactured. Therefore, by using such an optical fiber preform, it is possible to stably produce an optical fiber having uniform optical characteristics over an extremely long distance.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view of a vertical heating furnace for melt-vitrifying a porous preform for optical fibers.

FIG. 2 is a front end portion a of a porous preform for an optical fiber;
The size around the run-out at the center b or the rear end c;
The relationship with the eccentricity of the optical fiber preform is shown.

[Explanation of symbols]

1. core tube, 2. central axis of porous preform for optical fiber,
3 ... rotating mechanism, 4 ... rotating shaft, 5 ... rotating chuck,
6 bearing, 7 heater, 8 porous preform for optical fiber, 9 core, 10 gas inlet, 11 exhaust port,
12: support rod, 13: screw rod, 14: elevating mechanism,
a: front end of the porous preform for optical fiber, b: central part of the porous preform for optical fiber, c: rear end of the porous preform for optical fiber.

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Tadakatsu Shimada 2-3-1-1, Isobe, Annaka-shi, Gunma Shin-Etsu Chemical Industry Co., Ltd. Precision Functional Materials Laboratory (72) Inventor Hideo Hirasawa Isobe, Annaka-shi, Gunma 2-13-1 Shin-Etsu Kagaku Kogyo Co., Ltd. Precision Functional Materials Laboratory F-term (reference) 4G021 CA12

Claims (3)

[Claims] 1. A front end portion of a porous preform for an optical fiber, wherein a porous preform for an optical fiber including a core is moved in an axial direction while rotating around a central axis thereof while flowing an atmospheric gas into a heating furnace. In a method of manufacturing an optical fiber preform that passes through a heat zone in a heating furnace and melts and vitrifies, the optical axis is adjusted by aligning the center axis of a porous preform for an optical fiber with the rotation axis of a rotation mechanism that rotates the same. A method for producing an optical fiber preform, wherein the deflection around a fiber porous preform is set to a predetermined value or less. 2. A front end of the porous preform for an optical fiber,
2. The method of manufacturing an optical fiber preform according to claim 1, wherein a run-out around at least one of a central portion and a rear end portion is 3 mm or less. 3. The method of manufacturing an optical fiber preform according to claim 1, wherein the swing circumference is set to 1.5 mm or less over the entire area of the porous preform for optical fiber.