JP2001206729A - Method for manufacturing optical fiber preform - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method capable of manufacturing an optical fiber preform having a uniform shape in a longitudinal direction and small in the fluctuation of relative refractive index difference at the time of forming a soot preform by a VAD method. SOLUTION: The position of a burner 1 for core is moved so that a distance Lx between the center point of the tip part of the burner 1 and a core soot growth point in the X axis direction and a distance Ly therebetween in the Y axis direction are always kept constant by measuring the Lx and the Ly by a 1st image sensor 6 and a 2nd image sensor 7 mounted on the horizontal plane of a core soot growth point.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing an optical fiber preform, and more particularly to a method for manufacturing an optical fiber preform having a uniform shape and a small variation in relative refractive index difference.

[0002]

2. Description of the Related Art As a method for manufacturing an optical fiber preform, V
There is a method of forming a soot preform by the AD method and sintering the soot preform to obtain an optical fiber preform. The VAD method is a method in which a starting member made of a columnar quartz glass or the like is pulled up while rotating the central axis, and porous glass fine particles (soot) are deposited on the tip of the starting member to grow vertically.

FIG. 4 is a schematic configuration diagram showing an example of a manufacturing apparatus suitably used for implementing a conventional method of manufacturing an optical fiber preform by the VAD method. As for the manufacture of the soot preform 5, a core burner 1 for forming a core soot and clad burners 4 and 4 for forming a clad soot are used. , A plurality of burners is used. And to these burners,
When a raw material gas such as SiCl ₄ as soot, a hydrogen gas as a fuel, an oxygen gas as an oxidant, etc. are simultaneously fed, the hydrogen is burned and becomes a flame, in which the raw material gas undergoes a flame hydrolysis reaction and heat. By the oxidation reaction, soot is generated and deposited on the tip of the rotating soot preform 5.

In this manufacturing method, the core burner 1
The positions of the cladding burners 4 and 4 are fixed, and the soot preform 5 is pulled upward while growing. At this time, the lifting speed of the soot preform 5 is controlled by a method using the image analysis processing device 8. Specifically, the image of the core suite captured by the image sensor 6 such as a CCD camera is
The vertical position of the core soot growth point is measured. Then, when the position of the core soot growth point is displaced above a preset position, the pulling speed of the soot preform 5 is decreased, and when displaced downward, the pulling speed is increased. The lifting speed of the soot preform 5 is controlled. For this reason, the position of the soot preform 5 in the vertical direction is always kept constant when the soot preform 5 is manufactured.

However, in such a manufacturing method,
The change in the horizontal position of the soot preform 5 is not controlled. Therefore, even if the vertical position of the soot preform 5 is kept constant, the soot preform 5 vibrates in the horizontal direction, so that the deposition position of the core soot changes greatly. Therefore, the soot preform obtained by such a manufacturing method is:
The shape is non-uniform in the longitudinal direction, the relative refractive index difference also fluctuates greatly in the longitudinal direction, and there are problems such as defective products that do not meet the product specifications.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and can form a soot preform in which the shape of the core soot is uniform in the longitudinal direction and the variation in the relative refractive index is small. It is an object to obtain a method for manufacturing an optical fiber preform.

[0007]

SUMMARY OF THE INVENTION The present invention relates to a soot preform manufactured by the VAD method, which is located on a horizontal plane of a core soot growth point and is orthogonal to a center axis of the soot preform. The problem is solved by measuring a change in the position of the core soot growth point and moving the core burner according to the change in the position.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail. FIGS. 1 to 3 are schematic structural views showing one example of a manufacturing apparatus suitably used for carrying out the method for manufacturing an optical fiber preform of the present invention. In these figures,
The same components as those in FIG. 4 are denoted by the same reference numerals. Reference numeral 1 shown in the figure denotes a core burner, which is a burner used to form a core soot. The extension of the center axis of the burner is 50 to 85 ° in the vertical plane with respect to the center axis of the soot preform 5. Burner fixing jig 2
It is fixed to.

The burner fixing jig 2 is held on a movable burner stage 3. Movable burner stage 3
Is operated by the image analysis processing device 8 via the controller 9 according to the method described below, and the core burner 1 can be moved in the horizontal direction via the burner fixing jig 2.

The interior of the core burner 1 has a multi-layer structure, and each layer includes SiCl ₄ as a soot material and G
A core soot can be formed by supplying eCl ₄ , hydrogen gas as a fuel, and oxygen gas as an oxidant, and depositing them at the tip of a rotating starting member.

The clad burners 4, 4 are burners used for forming a clad soot, and are installed above the core burner 1. The insides of the clad burners 4 and 4 also have a multiplex structure, and SiCl ₄ as a soot material, hydrogen gas as a fuel, and oxygen gas as an oxidant are supplied to each layer, and these are deposited on the core soot. Thereby, a clad soot can be formed.

The first image sensor 6 and the second image sensor 7 are on a horizontal plane of the core soot growth point, and the extension lines of the respective central axes are mutually orthogonal at the central axis of the soot preform 5. It is fixed to. The first image sensor 6 and the second image sensor 7 are both for imaging the core suite growth point from the horizontal direction,
A CCD camera or the like is used and connected to the image analysis processing device 8.

In the image analysis processor 8, the position of the core soot growth point in the vertical direction is measured from the image of the core soot growth point transferred from the first image sensor 6 and the second image sensor 7. Has become. Then, a controller (not shown) is connected to the image analysis processing device 8, and the pull-up speed of the soot preform 5 is controlled in accordance with the measured vertical position change of the core soot growth point. The vertical distance Lz between the center point of the leading end of the core burner 1 and the core soot growth point is controlled to be constant. Lz above
Is appropriately set depending on the soot diameter to be manufactured.
About 25 mm.

The image analysis processor 8 also measures the position of the core soot growth point in the horizontal direction. Specifically, the position of the core soot growth point in the X-axis direction shown in FIG. 2 is measured from the image transferred by the first image sensor 6, and the Y-axis is calculated from the image transferred by the second image sensor 7. The position of the core soot growth point in the direction is measured. A controller 9 connected to the movable burner stage 3 is connected to the image analysis processing device 8, and the position of the core burner 1 is controlled according to a change in the horizontal position of the core soot growth point. It has become so. And FIG.
The distance Lx in the X-axis direction and the distance Ly in the Y-axis direction between the center point of the tip of the core burner 1 and the core soot growth point shown in FIG. The above Lx and Ly are appropriately set depending on the soot diameter to be manufactured, but Lx is about 30 to 50 mm,
Ly is set to about 1 to 10 mm.

Next, a method of manufacturing an optical fiber preform using the above-described apparatus will be described. In order to manufacture the soot preform 5 using the core burner 1 and the clad burners 4, 4, a raw material gas is supplied to each burner, and the core soot is deposited on the tip of the rotating starting member, and the core soot is deposited thereon. Then, a soot preform 5 is formed by depositing a clad soot. Then, core soot and clad soot are continuously deposited on the soot preform 5 to be pulled up, and the soot preform 5 is grown.

At the time of manufacturing the soot preform 5,
The image analysis processing device 8 measures the position of the core soot growth point in the vertical direction, and controls the pulling speed of the soot preform 5. As a specific control method, the image analysis processing device 8 uses the image of the core suite growth point transferred by the first image sensor 6 and the second image sensor 7 to
The vertical position of the core soot growth point is measured, and when the core soot growth point is displaced to a position where Lz shown in FIG. 3 is larger than a set value, the pull-up speed of the soot preform 5 is reduced, and When the core soot growth point is displaced to a position where Lz becomes smaller than the set value, a method of controlling the pulling speed of the soot preform 5 via a controller (not shown) so as to increase the pulling speed. Can be The lifting speed of the soot preform 5 controlled by such a method is 80 to 1
It is about 20 mm / hr.

The image analysis processing device 8 also measures the horizontal position of the core soot growth point, and determines the position of the core soot growth point so that the swing width of the core soot growth point is within 2% of the core soot diameter D. The position of the core burner 1 is controlled according to the change. Here, the fluctuation width is the distance at which the core soot growth point has changed. If this exceeds 2% of the core soot diameter D, the fluctuation of the core soot deposition position cannot be ignored, so that the shape of the core soot cannot be ignored. It becomes non-uniform in the longitudinal direction, and an optical fiber preform having a stable relative refractive index difference cannot be obtained.

As a method of controlling the position of the core burner 1 by the image analysis processing device 8, the following method can be mentioned. From the video transferred by the first image sensor 6, the image analysis processing device 8 measures the position of the core suite growth point in the X-axis direction. Then, Lx shown in FIG.
However, when the core soot growth point is displaced to a position smaller than the set value, the core burner 1 is moved away from the central axis of the soot preform 5 in the X-axis direction, and Lx
When the core burner 1 is displaced to a position where it becomes larger than the set value, the core burner 1
The image analysis processing device 8 moves the core burner 1 connected to the movable burner stage 3 via the controller 9 so as to approach the axial direction so that Lx shown in FIG. 2 is always constant. I do. The image analysis processing device 8 also moves the position of the core burner 1 according to a similar method for the position of the core soot growth point in the Y-axis direction, and controls the Ly shown in FIG. 2 to be always constant.

In measuring the horizontal position of the core soot growth point, first and second laser displacement meters may be used instead of the first and second image sensors 6 and 7. Good. Here, a laser displacement meter is a method of irradiating a core soot growth point with laser light,
Measure the distance between the core soot growth point and the laser displacement meter,
A device that reads the position of the core soot growth point.
And about 1st and 2nd laser displacement meter,
Similarly to the case where the first image sensor 6 and the second image sensor 7 are used, the extension lines of the respective central axes on the horizontal plane of the core soot growth point are mutually reciprocated at the central axis of the soot preform 5. Fix so as to be orthogonal.

In the case where the first and second laser displacement meters are used, instead of the image analysis processing device 8, a computer is connected, and the arithmetic device is connected to the core according to the same method as the image analysis processing device 8. By moving the burner 1, it is possible to control so that Lx and Ly shown in FIG. 2 are always constant, as in the case where the first and second image sensors 6 and 7 are used.

The soot preform 5 thus obtained is subjected to dewatering and sintering steps by a conventional method to become an optical fiber preform. In such a method of manufacturing an optical fiber preform, Lx, Ly, Lz shown in FIGS.
Can always be controlled to be a constant value, so that the swing width of the core soot growth point can be controlled by 2 times the core soot diameter D.
% Can be kept. As a result, the core soot deposition position is stabilized, and the core soot growth rate is also stabilized, so that the fluctuation of the pull-up speed of the soot preform 5 can be reduced, and the shape in the longitudinal direction is uniform. An optical fiber preform having a small change in the refractive index difference can be obtained.

[0022]

The present invention will be described below more specifically with reference to examples. These examples show one embodiment of the present invention, and do not limit the present invention, and can be arbitrarily changed within the scope of the present invention. (Example) A soot preform 5 was manufactured using the manufacturing apparatus shown in FIGS. 1 to 3, and was sintered and made transparent to obtain an optical fiber preform. As the above manufacturing conditions, first, an extension of the central axis of the core burner 1 is positioned within a vertical plane with respect to the central axis of the soot preform 5.
The core burner 1 inclined at an angle of ゜ was fixed to a burner fixing jig 2, which was fixed to a movable burner stage 3. It is movable so that the vertical distance Lz between the center point of the tip of the core burner 1 and the core soot growth point is 17 mm, the distance Lx in the X axis direction is 38 mm, and the distance Ly in the Y axis direction is 4 mm. Type burner stage 3
, A core burner 1 connected via a burner fixing jig 2 was arranged. Then, the clad burners 4 and 4 were fixed above the core burner 1.

The core burner 1 contains 0.1% SiCl ₄ .
Core soot was deposited at the tip of the rotating soot preform 5 by supplying 36 l / min, GeCl ₄ at 0.02 l / min, hydrogen gas at 5.0 l / min, and oxygen gas at 13.0 l / min. The cladding burners 4 and 4 were each supplied with 1.5 l / min of SiCl ₄ and 15 l / min of hydrogen gas.
Min, oxygen gas at 13.5 l / min, SiCl ₄ at 2.0 l / min, hydrogen gas at 24 l / min, oxygen gas at 16 l / min.
At a rate of 1 / min, the cladding soot was deposited on the core soot of the rotating soot preform 5.

(Comparative Example) Using the manufacturing apparatus shown in FIG.
A soot preform 5 was manufactured, sintered, and made transparent to obtain an optical fiber preform. As the above manufacturing conditions, first, the center point of the tip of the core burner 1 is defined as
66 in the vertical plane with respect to the central axis of the soot preform 5
゜ Incline, the vertical distance Lz between the core burner 1 and the core soot growth point is 17 mm, and the distance Lx in the X axis direction is 38.
mm and the distance Ly in the Y-axis direction was fixed at a position of 4 mm.
The clad burners 4 and 4 were fixed above the core burner 1.

The core burner 1 contains 0.1% SiCl ₄ .
Core soot was deposited at the tip of the rotating soot preform 5 by supplying 36 l / min, GeCl ₄ at 0.02 l / min, hydrogen gas at 5.0 l / min, and oxygen gas at 13.0 l / min. The cladding burners 4 and 4 were each supplied with 1.5 l / min of SiCl ₄ and 15 l / min of hydrogen gas.
Min, oxygen gas at 13.5 l / min, SiCl ₄ at 2.0 l / min, hydrogen gas at 24 l / min, oxygen gas at 16 l / min.
At a rate of 1 / min, the cladding soot was deposited on the core soot of the rotating soot preform 5.

With respect to the obtained optical fiber preform, the relative refractive index difference in the longitudinal direction, the core soot diameter, the core soot growth rate, and the fluctuation width of the core soot in the X-axis direction were measured based on the following methods. Regarding the relative refractive index difference,
The measurement was performed by a laser-type preform analyzer, and the change in the relative refractive index difference based on the average value of the refractive index is shown in FIG. The core soot diameter was measured by a laser type outer diameter measuring instrument, and the variation of the core soot diameter based on the average core soot diameter is shown in FIG. Regarding the core soot growth rate, the growth rate is a value obtained by dividing the length from the tip of the starting member to the tip of the core soot deposited by the time required to reach the length,
FIG. 7 shows the fluctuation of the growth rate based on the target pulling rate.
It was shown to. Regarding the swing width in the X-axis direction, the difference between the actually measured Lx value and a preset Lx value is defined as the swing width in the X-axis direction, and the fluctuation in the longitudinal direction is shown in FIG.

From the graph of FIG. 5, it can be seen that the optical fiber preform obtained in the example of the present invention has a small variation in the relative refractive index difference. In contrast, the optical fiber preforms obtained in the comparative examples show that the relative refractive index difference shows a large variation in the longitudinal direction. From the graph of FIG. 6, it can be seen that the optical fiber preform obtained in the example has a small variation in core soot diameter. On the other hand, the optical fiber preform obtained in the comparative example shows that the core soot diameter shows a large variation in the longitudinal direction. From the graph of FIG. 7, it can be seen that the growth rate of the core soot is stable in the example, whereas the growth rate is not stable and greatly fluctuates in the comparative example. From the graph of FIG. 8, it can be seen that in the example, the swing width in the X-axis direction is small, whereas in the comparative example, the swing width in the X-axis direction is large and fluctuates in the longitudinal direction. .

[0028]

As described above, in the method of manufacturing an optical fiber preform according to the present invention, the positional relationship between the center point of the tip of the core burner 1 and the core soot growth point is determined only in the vertical direction. In addition, since the control can be performed so as to be constant also in the horizontal direction, the swing width of the core soot growth point can be kept within 2% of the core soot diameter. As a result, the core soot deposition position is stabilized, and the core soot growth rate is also stable.Thus, during soot preform formation, fluctuations in the pulling rate can be reduced, and the longitudinal shape can be uniform. In addition, it is possible to manufacture an optical fiber preform having a small variation in the relative refractive index difference.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing an example of an apparatus used in a manufacturing method of the present invention.

FIG. 2 shows a core burner 1 viewed from above in FIG.
FIG. 2 is a schematic configuration diagram illustrating a positional relationship between a first image sensor 6 and a second image sensor 7.

FIG. 3 is an enlarged schematic diagram showing a positional relationship between a core burner 1 and a core soot growth point viewed from the Y-axis direction in FIG. 1, and is a schematic configuration diagram showing Lx and Lz.

FIG. 4 is a schematic configuration diagram showing an example of an apparatus used in a conventional manufacturing method.

FIG. 5 is a graph showing a change in a relative refractive index difference in a longitudinal direction of an optical fiber preform in an example and a comparative example.

FIG. 6 is a graph showing a variation of a core soot diameter in a longitudinal direction of an optical fiber preform in an example and a comparative example.

FIG. 7 is a graph showing a change in a growth rate during production of a soot preform in Examples and Comparative Examples.

FIG. 8 is a graph showing the fluctuation in the longitudinal direction of the swing width in the X-axis direction in Examples and Comparative Examples.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Core burner, 2 ... Burner fixing jig, 3 ... Movable burner stage, 4 ... Clad burner, 5 ... Soot preform, 6 ... First image sensor, 7 ... Second image sensor, 8 ... Image analysis processing device, 9 Controller

 ────────────────────────────────────────────────── ─── Continuing from the front page (72) Inventor Koichi Harada 1440, Musaki, Sakura City, Chiba Prefecture Fujikura Co., Ltd. Sakura Plant F-term (reference) 4G021 EA01 EB14 EB26

Claims (1)

[Claims] 1. The method according to claim 1, further comprising:
In a method for manufacturing an optical fiber preform in which a core soot is deposited by a core burner and a clad soot is further deposited by a clad burner to form a soot preform, the core soot is on a horizontal plane at a growth point of the core soot, and the central axis of the soot preform. A method for measuring a position change of a core soot growth point from two directions perpendicular to each other, and moving a core burner according to the position change.