JPH07223834A - Method for synthesizing porous preform for optical fiber and apparatus therefor - Google Patents

Abstract

PURPOSE:To stably synthesize a porous glass preform for optical fiber with high quality. CONSTITUTION:Flame for forming core part ejected from a core burner 4 toward a soot body 2 is measured by a CCD camera 32 and pictured image data are changed to binary digit in an image treating device 30 and the position of the middle point P is obtained using a measuring window 40. An air flow rate controller 54 is operated so that this position is kept to a prescribed position to control air amount which is made to flow from the upper part of a bell jar 11 toward the flame 8. Further, an amount of air introduced from a control valve 60 into a discharge cylinder 13 is controlled so as to suppress fluctuation of the flame 8 in a specific range to control the pressure of the bell jar 11. The fluctuation of the flame 10 for forming a clad part from a clad burner 6 is suppressed similarly to position control of the flame 8 for forming the core part by controlling an amount of air which is made to flow toward flame 10 for forming clad part.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to synthesizing a porous preform for optical fibers, and more particularly to synthesizing a porous preform for optical fibers by a CVD method with a vapor phase axis (VAD method) or the like. A method and an apparatus for improving the quality of a porous glass preform.

[0002]

2. Description of the Related Art Synthesis of a porous glass base material (soot body) for an optical fiber will be described. An optical fiber composed of a core and a clad is manufactured by drawing a porous glass preform for an optical fiber. A typical method for producing such a porous preform for optical fibers is an external CVD method (OVD).
Method) and a CVD method with a vapor phase axis (VAD method) are known. In any of these manufacturing methods, in general,
Using an oxyhydrogen burner, a source gas such as SiC
The vapor of 1 ₄ and GeC1 ₄ is hydrolyzed in an oxyhydrogen flame to form glass particles of SiO ₂ and GeO ₂ , which are then sprayed onto a target that is synthesized and becomes a porous glass base material (soot body). To produce (synthesize) the porous glass preform.

The amount of the glass particles adhered to the target and the distribution of the adhered particles vary depending on the shape of the flame injected from the burner, the state of the flow of the glass particles (hereinafter referred to as shape profile), the surface temperature of the target, and the like. Change due to various factors. Especially, the fluctuation of the flame, and
The refractive index distribution of the optical fiber changes due to a subtle change in the flame position, and the quality of the manufactured porous glass preform becomes a problem.

As a method for solving such a problem,
By controlling the shape of the target and controlling the temperature distribution on the glass particle deposition surface of the target, we have been trying to stabilize the quality of the synthesized porous glass preform, but as a factor that determines these shapes and temperature distribution. Is the position of the flame under a specific flame gas condition, or its shape, and the magnitude of fluctuation.

[0005]

By the way, if only the above-mentioned control factors under specific conditions are applied to the production of the porous glass base material, it is not possible to synthesize various porous glass base materials in practice. Is insufficient. The reason is that, due to changes in various air flows during the production of the porous glass base material, the variation occurs with time even during the production of one porous glass base material. Such variations are not reproducible and irregular. Furthermore, by replacing the components of the optical fiber porous base material synthesizing device such as the burner, for example, when the burner is replaced, even if the replaced burner is accurately positioned, the quality of the manufactured porous glass base material is improved. It is often not reproducible.

That is, there is a problem that a high quality porous glass base material cannot be synthesized by the synthesis based on the control element determined under specific conditions.

That is, according to the present invention, in order to always produce a high quality porous glass preform even if the production conditions are changed, the state of a flame or the like is measured, and the obtained state measurement result is used. Even if there is a change in the manufacturing conditions, feedback control is actually performed to the synthesis control of the porous glass base material, and the high quality of the porous glass base material can be always manufactured. A method and apparatus therefor.

[0008]

The inventor of the present application has found that the profile of the shape of the flame for forming the core portion and the flame for forming the cladding portion or the central position of these flames changes with the growth of the target. It has been found that the profile or center position can be controlled by appropriately varying the amount of rectifying gas, eg air. Furthermore, the inventor of the present application has found that the fluctuation range of the central position of the flame for forming the core portion and the flame for forming the cladding portion can be controlled within a predetermined range by controlling the pressure of a container such as a bell jar. Therefore, the first basic concept of the present invention is to measure the central positions of the flame for forming the core portion and the flame for forming the cladding portion, and control the amount of the rectified gas so that the positions are maintained at predetermined positions. . The second basic concept of the present invention controls the pressure of the container so that the fluctuation range of the center position of the flame for forming the core portion and the flame for forming the cladding portion falls within a predetermined range.

Therefore, according to the present invention, in a method for synthesizing a porous glass preform for optical fiber, which is a method for synthesizing a porous glass preform for optical fiber, the porous glass preform for optical fiber is blown onto a target to produce the porous glass preform for optical fiber. An image of the flow of the flame or glass particles to be synthesized is imaged, and the signal processing of the imaged result is performed to measure the position change of the flow of the flame or glass particle, so that the measured position of the flame or glass particle becomes a predetermined position. Further, there is provided a method for synthesizing a porous preform for an optical fiber, which comprises controlling an amount of a rectifying gas for controlling a shape profile of the flame or glass particles. Thereby, the flame for forming the core portion and the flame for forming the clad portion do not depend on the growth of the target,
It is sprayed in place on the target. as a result,
A porous glass base material with stable quality can be manufactured.

Preferably, the image pickup result is further signal-processed to measure the fluctuation range of the flame or glass particles, and the pressure of the container is controlled so that the fluctuation range falls within a predetermined range.

Further, according to the present invention, there is provided a porous base material synthesizing device for optical fibers, which comprises a container for synthesizing a porous glass base material for optical fibers, and an optical fiber toward a target in the container. A core burner for blowing a flame for forming a core portion, a clad burner for blowing a flame for forming a cladding portion of an optical fiber toward a target in the container,
An exhaust stack that discharges exhaust gas in the container, at least an image capturing unit that captures an image of the shape of the core forming flame, and a flame position measuring unit that measures the center position of the core forming flame from the image capturing result of the image capturing unit. A means for providing a rectifying gas for changing the shape of the flame for forming the core portion, and a rectifying gas control means for controlling the amount of the rectifying gas to control the central position of the flame to a reference position.

Preferably, the optical fiber porous base material synthesizing apparatus further comprises a flame position fluctuation measuring means for measuring a fluctuation of a central position of the core forming flame from the image pickup result of the image pickup means, and the discharge position measuring means. It has a pressure control means for controlling the flow rate of the exhaust gas discharged from the cylinder to control the pressure of the container to maintain the position fluctuation within a predetermined range.

Preferably, a first rectifying gas passage for controlling the position of the flame for forming the core portion and a second rectifying gas passage for controlling the position of the flame for forming the cladding portion are preferably provided in the container. And a second flow rate control means for controlling the flow rate of the rectifying gas flowing through the second rectifying gas flow path, and the flame position measuring means determines the core forming flame from the imaging result of the imaging means. And the central position of the clad forming flame, and the rectifying gas control means controls the first rectifying gas flow so that the result of measuring the central position of the core forming flame becomes the reference position. The amount of the rectifying gas flowing through the passage is controlled, and the second rectifying gas control means flows through the second rectifying gas flow path so that the center position measurement result of the cladding forming flame becomes the reference position. Controls the amount of rectified gas.

Specifically, the first rectifying gas passage is
The second rectifying gas channel is provided in the container and defined between an inner cylinder and an outer cylinder of the container, and the second rectifying gas flow path is defined by a gap between the inner cylinder and the target that enters the inner cylinder. It

Specifically, the flame center position measuring means detects the center position of the flame imaging result or the detected glass particle flow result using a signal processing window.

[0016]

First, the flame ejected from the burner or the glass fine particles contained in the flame is imaged at high speed as image data. The flame can be directly imaged by the imaging means, but in the case of glass particles, the glass particles are irradiated with light such as laser light and the scattered light is imaged. Using the measurement window, the imaged image data is used to measure (detect) the midpoint of the width of the light emitting portion and its fluctuation range. That is, in the present invention, the variation width of the midpoint of the width of the light emitting portion and the variation width of the width of the light emitting portion, which cannot be visually identified, are detected separately.

The amount of the rectifying gas is controlled so that the center position of the flame or the like is maintained at a constant position. Also preferably,
The pressure of the container is controlled by controlling the amount of exhaust gas so that the fluctuation range of flame and the like falls within a certain range.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The method and apparatus for synthesizing an optical fiber porous preform of the present invention is intended for synthesizing an optical fiber porous glass preform. The synthetic state in the present specification means a state of flame and a state of glass fine particles contained in the flame.

First Embodiment First, as a first embodiment of the method and apparatus for synthesizing an optical fiber porous preform, an optical fiber porous preform synthesis state measurement will be described. FIG. 1 is a configuration diagram of an optical fiber porous base material synthesizing apparatus 100 according to a first embodiment of the present invention. The optical fiber porous base material synthesizing apparatus 100 includes a soot body synthesizing apparatus 1 and a synthetic state measuring apparatus 3.

The soot body synthesizing apparatus 1 is provided with a bell jar 11 as a container, glass fine particles introduced into the bell jar and not adhered to the target (soot body) 2 and used gas to a scrubber (not shown). An exhaust stack 13 for discharging, and a core burner 4 and a clad burner 6 mounted toward the target 2 are provided on the peripheral wall of the bell jar 11. The target 2 is inserted into the bell jar 11, and is rotated in the rotation direction R and is raised as the target 2 is synthesized. In order to synthesize the target 2, the core forming flame 8 is blown from the core burner 4 toward the core forming portion at the center of the lower portion of the target 2, and the lower side surface of the target 2 located outside the core forming portion is exposed. A flame 10 for forming a clad portion is blown from the clad burner 6 toward the clad forming portion. The flame 10 for forming the clad portion is made of argon gas (Ar), Si
It is fine glass particles produced by flame hydrolysis with Cl ₄ , hydrogen gas (H ₂ ) and oxygen gas (O ₂ ). In addition to the clad flame 10, the core forming flame 8 includes a dopant such as G for increasing the refractive index of the core forming portion.
It is glass fine particles to which eO _{2 and the} like are added. Target 2
The glass particles not attached to the exhaust gas are exhausted from the exhaust tube 13 to a scrubber (not shown).

The composite state measuring device 3 comprises a CCD camera 3
2, an image processing device 30, a first monitor device 34, a second monitor device 36, a control processing computer 38, and a recording device 39. The CCD camera 32 functions as an imaging device that captures a light emitting portion of the flame 8 for forming the core portion, the flame 10 for forming the cladding portion, or either one. In the present embodiment, the case where the CCD camera 32 mainly captures the core forming flame 8 will be described below. The image processing device 30 controls the CCD camera 32 to capture an image of the flame 8 for forming the core portion, and the image capturing result is used as “raw image data” that has not been image-processed by the second monitor device 36.
On the other hand, the "image processed image data" described below is displayed on the first monitor device 34. The control processing computer 38 cooperates with the image processing device 30 to measure the combined state of the optical fiber porous preform, and records the result in the recording device 39. Further, the control processing computer 38
The synthesis of the target 2 is controlled using the measurement result of the image processing device 30. Although the processing contents of the control processing computer 38 and the image processing apparatus 30 can be arbitrarily shared, in the present embodiment, the image processing apparatus 30 is allowed to monopolize the image processing that requires high-speed calculation, and the control processing computer 38 Man-machine communication with an operator (worker), setting of processing conditions of the image processing device 30, arrangement of results processed by the image processing device 30, recording in the recording device 39, and the like are performed.

Originally, the flame 8 for forming the core portion injected from the core burner 4 is vigorous, so that the periphery of the flame 8 is irregularly disturbed. Similarly, the clad portion forming flame 10 injected from the clad burner 6 also has momentum, and the peripheral edges of the flames 8 and 10 are irregularly disordered. In addition to this turbulence, the entire core forming flame 8 and the entire clad forming flame 10 fluctuate. The cause of the fluctuation is analyzed as follows. Usually, a large amount of air or a gas equivalent thereto is introduced into the bell jar 11 in addition to the gas supplied to the core burner 4 and the clad burner 6, and the introduction of this gas causes the entire core forming flame 8 and the clad forming flame to be introduced. Fluctuation of the whole 10 occurs. Further, when the upper end of the target 2 enters the upper cylinder part of the bell jar 11 in the process in which the target 2 rises toward the upper part of the combined bell jar 11, the upper cylinder part of the bell jar 11 and the upper end of the target 2 are separated from each other. The size of the gap between them changes, and the flow of gas flowing through this gap is disturbed, and this disturbance causes fluctuations in the entire core forming flame 8 and the entire cladding forming flame 10. As described above, this fluctuation causes the combined portion of the core forming portion and the clad forming portion of the target 2 to deviate from the desired allowable range, and deteriorates the quality of the target 2. Therefore, the core forming flame 8 and the clad forming flame 1
By accurately measuring the fluctuation of 0 and reflecting the measurement result in the control so that fluctuation does not occur, the target 2
Is expected to improve the synthesis quality of. However, the flame fluctuates fairly quickly based on the above-mentioned conditions, and how to properly measure the flame becomes a problem.
Hereinafter, as a preliminary experiment, practical and effective flame measurement according to the present invention will be described.

In FIG. 2, the core forming flame 8 is directly imaged by the CCD camera 32, image-processed by the image processing device 30, and the core-forming flame 8A after image processing displayed on the first monitor device 34 is displayed. FIG. In FIG. 1, the first monitor device 34 is illustrated with the core forming flame 8A and the clad forming flame 10A, but in FIG.
Only the core forming flame 8A is shown enlarged. The inventor of the present application images the core forming flame 8 with the CCD camera 32 from the outside of the bell jar 11 through an observation window (not shown) attached to the outer wall of the bell jar 11, and the core forming flame 8 It was found that the position of the flame 8 for forming the core part can be quantitatively obtained by measuring the "emission intensity distribution" of. The emission intensity distribution is an image formed on each CCD element of the CCD camera 32, and the two-dimensional coordinate position of the CCD camera 32 (that is, the first monitor device 3).
4 or the coordinates of the second monitor device 36) and intensity information are input to the image processing device 30. In this embodiment, the CCD camera 32 is obliquely installed on the outer wall of the bell jar 11, and the flame 8 for forming the core portion is formed by the CCD camera 32 through the observation window provided on the side wall of the bell jar 11.
Of the image of the core forming flame 8
When the images are displayed on the monitor device 34 and the second monitor device 36 of FIG. This display form is for convenience, and the core forming flame 8 may be oriented in any direction. What is important is how to accurately capture the core forming flame 8 with the CCD camera 32. The image processing device 30 performs the signal processing described below in synchronization with this imaging cycle.

The image pickup result of the CCD camera 32, that is, the image data of the flame 8 for forming the core portion is displayed on the second monitor device 36 as it is via the image processing device 30.
The result of image processing performed by the image processing device 30 is displayed as the core forming flame 8A as shown in FIG. The image processing in the image processing device 30 will be described below. The image processing device 30 binarizes the image data with a threshold value of a certain size in synchronization with the image pickup cycle of the CCD camera 32 in order to extract the shape of the core forming flame 8. That is, the image pickup result of the CCD camera 32 is the CCD
For each CCD making up the camera 32, for example,
Although it has 256 gradations, for example, threshold value = 1
The image data is binarized by 25, and the image data = 1 when the gradation is 125 or more, and the image data = 0 when the gradation is less than that. Therefore, the image data displayed on the first monitor device 34 is an image binarized in this way. Figure 2
As shown in FIG. 3, the image processing apparatus 30 further adds a measurement window 40 to the binarized image data.
Is applied to measure the width W of the light emitting portion of the core forming flame 8 and the midpoint P thereof. In addition to the width W of the light emitting portion and the midpoint P of the width of the light emitting portion, the image processing device 30 measures the position of the flame surface indicated by the symbol A and the spread angle θ of the flame. Furthermore, the image processing device 30 can also measure the emission intensity of flame and other various variables (parameters).

The width W of the light emitting portion of the image processing apparatus 30.
The details of the measurement of the midpoint P of the width of the light emitting portion, the measurement of the position A of the flame surface, and the measurement of the flame spread angle θ will be described. A measurement window 40 is provided at a position where flame measurement is desired. At this time, the image of the binarized flame is completely included in the measurement window 40 in the width direction of the flame. In addition, the flame height direction is one pixel, and is a one-dimensional measurement region. The number of pixels of the binarized data “1” in the measurement window 40 means the width. Using the coordinates of each pixel in the measurement window 40, the position of the midpoint is calculated and obtained. Specifically, for example, the measurement window 40 is fixed at the position shown in FIG.
The positions of the left end and the right end of the core forming flame 8 within 0 are read from the pixel numbers, and the width W of the core forming flame 8 and the midpoint P of the width of the light emitting portion are calculated from the difference between the two. The position A of the surface of the flame 8 for forming the core portion and the spread angle θ of the flame are different from those of the measurement window 40 in the window 4
It is measured using 0A and 40B. When measuring the change in the profile of the overall shape of the flame 8 for forming the core part, FIG.
As indicated by the broken line, the width W of the light emitting portion and the midpoint P of the width of the light emitting portion are measured in the same manner as above while moving the measurement window 40 from the lower side to the upper side. Thereby, the profile parameters of the shape of the core forming flame 8A after the image processing, that is, the width W of the light emitting portion, the midpoint P of the width of the light emitting portion, and the position (edge) A of the flame surface are sequentially measured. it can.

When the core forming flame 8 hits the core forming portion at the lower tip of the target 2, it diffuses. Along with the diffusion, the core forming flame 8 diffuses in the front. The image processing device 30 also measures this diffusion angle, that is, the flame spread angle θ. Of course, the image processing device 30 may continuously measure the flame spread angle θ in the same manner as the position A of the flame surface, and determine the final flame spread angle θ from the measurement result. However, in general, as described above, the measurement window 40 is fixed at a certain position,
The width W of the core forming flame 8 and the midpoint P of the width of the light emitting portion at that position are measured.

In the present embodiment, the measurement window 40 is positioned horizontally so that the core forming flame 8A is completely set at a position 15 mm from the soot body 2 and the center point P of the core forming flame 8A is set. The position is measured, and the position is output as a signal from the control processing computer 38. In FIG. 2, it is assumed that the right side is the positive position direction and the cladding burner 6 is located in this positive position direction.

FIG. 3 is a graph showing the results measured by the image processing apparatus 30 described above. The horizontal axis shows the passage of time,
The vertical axis represents the change and fluctuation (fluctuation) of the position of the midpoint P of the width of the light emitting portion of the core forming flame 8A. Variation period of the core portion forming the flame 8 is typically several H _Z ~ tens H _Z. The curve CV1 shows, as a preliminary experiment, normal pressure control, pressure =
In -3.0mmH ₂ O, it is a graph showing the results when performing the synthesis of the soot body 2. It was found that the position of the midpoint P of the width of the light emitting portion was moved to the clad flame 10 side by about 0.5 mm 10 hours after the start of synthesis.
When analyzing the cause, it is considered that the gas flow in the bell jar 11 gradually changes due to the change in the shape of the soot body 2 due to the synthesis. Further, about 5 hours after the start of synthesis, the midpoint P of the width of the light emitting portion of the flame 8A for forming the core portion greatly changes within a range of about 1 mm. Analyzing this cause, soot body 2
It is considered that when the gas enters the upper cylindrical portion of the bell jar 11, the gap between the cylindrical portion of the bell jar 11 and the tip portion of the soot body 2 narrows, the size of the gas flow path changes, and the gas flow changes greatly. To be Curve CV2
Is the position of the midpoint P of the width of the light emitting portion of the core forming flame 8A, which is controlled so as to limit the change of the midpoint P of the width of the light emitting portion based on the above-described measurement result and its analysis. It is a graph showing the result of the change, the details of which will be described later.

As a preliminary experiment, the curve CV3 in FIG. 4 shows the relationship between the length (horizontal axis) of the soot body 2 synthesized under the conditions of the curve CV1 shown in FIG. 3 and the relative refractive index difference Δ (vertical axis). It is a graph which shows. It was found that the relative refractive index difference Δ increases as the positional variation of the midpoint P of the width of the light emitting portion of the core forming flame 8A increases. It was also found that the relative refractive index difference Δ decreases as the position of the midpoint P of the width of the light emitting portion moves away. In addition, from the synthesis of soot body 2 shown in FIG.
The relative refractive index difference Δ also temporarily increases due to the change in the midpoint P of the width of the light emitting portion before and after the passage of time. Curve C
V4 is a graph showing the result of the relative refractive index difference Δ, which is controlled so as to limit the change of the midpoint P of the width of the light emitting portion based on the above-mentioned measurement result and its analysis. Will be described later.

Of course, depending on the shape of the bell jar 11, the installation positions of the core burner 4 and the clad burner 6, and the like, the moving direction of the flame 8 for forming the core portion and the accompanying change in the relative refractive index difference Δ are the same as those described above. However, it is clear from the results of the above preliminary experiments that the conventional method has a problem in the quality of the synthesized soot body 2 and thus in the quality of the finally manufactured optical fiber. It is shown that.

What should be noted in the above measurement is the cloudiness of the observation window attached to the bell jar 11. CCD
The camera 32 images the core forming flame 8 through the observation window. In this example, the observation window was purged to suppress fogging. As a result, it wasn't affected by cloudiness. Regarding the binarization of the image data described above, it is also possible to provide a reference light source in the bell jar 11 and measure the intensity change thereof to change the binarization threshold value. By changing the threshold value in this way, it is possible to perform binarization with higher accuracy without the influence of noise.

In the above example, the CCD camera 32 is provided on the extension line of the core burner 4 and the clad burner 6 to measure the flame around the flame 8 for forming the core portion. The core forming flame 8 may be individually imaged from the orthogonal position, and the core forming flame 8 may be measured in the same manner as described above. Furthermore, two CCD cameras 32 are provided, the core part forming flame 8 and the clad part forming flame 10 are individually imaged, and the core part forming flame 8 and the clad part forming flame 10 are described above. Similarly to the above, the flames for the core forming flame 8 and the clad forming flame 10 can be measured in the same manner as above.

Second Example Hereinafter, in order to improve the results of the above-mentioned preliminary experiment, the shape of the flame was measured, and the measured shape of the flame was controlled to
The method and apparatus for synthesizing the porous preform for optical fibers of the present invention, which controls the synthesis state of the soot body 2, will be described. FIG. 5 is a configuration diagram of an optical fiber porous base material synthesizing apparatus 100A as an embodiment of the present invention. The optical fiber porous base material synthesizing apparatus 100A is a soot body synthesizing apparatus 1A.
And a combined state measurement / control device 3A.

The soot body synthesizing apparatus 1A is similar to the soot body synthesizing apparatus 1 illustrated in FIG. 1, except that the soot body synthesizing apparatus 1A illustrated in FIG. An air introducing portion 70 for introducing the air into the bell jar 11 is provided. Further, in the soot body synthesizing apparatus 1A, a bellows 72 is provided around a shaft 16 that axially supports the soot body 2 in order to enclose air introduced into the bell jar 11, and a shaft is provided at the head of the bellows 72. A magnetic seal portion 74 is provided so as to surround 16. Other parts of the soot body synthesizing apparatus 1A, the bell jar 11, the core burner 4, the clad burner 6, the exhaust pipe 13, and the like are almost the same as the corresponding portions of the soot body synthesizing apparatus 1 illustrated in FIG.

The composite state measuring / controlling device 3A includes a CCD camera 32, as in the composite state measuring device 3 illustrated in FIG.
An image processing device equivalent to the first monitor device 34, the second monitor device 36 (not shown), the control processing computer 38 (not shown), the recording device 39 (not shown), and the image processing device 30. It has 30A. Image processing device 30
The processing of A is the same as the processing of the shape of the flame for forming the core portion 8 and the midpoint P of the width of the light emitting portion described as the processing of the image processing apparatus 30, but will be described later. Perform processing to Combined state measurement / control device 3A
Further has a flame position controller 50, a fluctuation (fluctuation) controller 52, an air flow controller 54, an air pressure controller 56, a pressure sensor 58, and a control valve 60. Air flow controller 54
The air for controlling the position and shape profile of the core forming flame 8 through the air introduction portion 70 to the bell jar 1.
As the rectifying gas that is poured into the inside of the No. 1 but controls the position and shape profile of the flame 8 for forming the core portion, an inert gas such as argon gas or other gas can be used in addition to air. In this embodiment, a case where air (atmosphere) is used as the rectifying gas will be described.

In this embodiment, the movement of the flame 8 for forming the core portion with the passage of time illustrated as the curve CV1 in FIG. 3 is improved, and thus the change in the relative refractive index difference Δ illustrated as the curve CV3 in FIG. 4 is improved. In order to improve the above, a preliminary experiment was performed in the above-mentioned configuration.

The control operation amount in this embodiment is (1) the air volume of air (atmosphere) introduced into the bell jar 11 from the air introduction part 70 above the bell jar 11 via the air flow controller 54, and (2) It is the pressure inside the bell jar 11.
The air volume control is performed by controlling the amount of air introduced from the air flow rate controller 54 to the bell jar 11 via the air introduction unit 70. Therefore, the air flow controller 5
4 introduces air according to the air volume control command S50 from the position controller 50 into the bell jar 11. Air flow controller 54
Is composed of, for example, a combination of a hot-wire type flow sensor and a control valve for controlling air. Position controller 5
In order to define the control command S50 of 0, the position signal S30A of the midpoint P of the width of the light emitting portion of the core forming flame 8A measured by the image processing device 30A is determined by the method described above in the first embodiment. 50 is applied. To control the pressure in the bell jar 11, the pressure sensor 58 measures the pressure of the exhaust pipe 13, and the opening of the control valve 60 is controlled via the air pressure controller 56 so that the pressure becomes a predetermined value. The amount of air flowing into the exhaust pipe 13 via the control valve 60 is changed, the amount of exhaust gas discharged from the exhaust pipe 13 is controlled, and the pressure in the bell jar 11 is controlled. The pressure control command S52 is set to the air pressure controller 56 from the fluctuation controller 52. In order to define the control command S52, the fluctuation of the position of the midpoint P of the width of the light emitting portion of the core forming flame 8 is output from the image processing device 30A to the fluctuation controller 52 as a position fluctuation signal S30B.

The above-mentioned air flow rate control and bell jar 11
In order to avoid mutual interference that may occur when the pressure control in the inside is performed at the same time, the control cycles of the air flow rate control and the pressure control are made different. First, as illustrated as a curve CV5 in FIG. 6, the pressure inside the bell jar 11 is set to −3.
The curve CV in the state of being kept constant at 0 mmH ₂ O
As illustrated in FIG. 6, the amount of air introduced into the bell jar 11 via the air flow rate controller 54 and the air introduction part 70 is from 500 l (liter) / min (min) to 700.
The behavior of the core forming flame 8 was measured in the image processing apparatus 30 </ b> A by increasing it to 1 (liter) / min.
As a result, as illustrated in FIG. 7, the variation width of the position of the midpoint P of the width of the light emitting portion was 0.35 mm, and although the variation width was not significantly changed, It was confirmed that the position of the middle point P of the width of the light emitting portion of the flame 8 is on the lower side, that is, the flame 8 moves from the cladding burner 6 side to the core burner 4 side by an average value of about 0.8 mm.

Next, as illustrated in FIG. 6, with the amount of air maintained at 700 l (liter) / min, the opening of the control valve 60 is adjusted so that the pressure inside the bell jar 11 becomes -4. It was changed to 0 mmH ₂ O. as a result,
As shown in FIG. 7, although the average value of the positions of the midpoints P of the widths of the light emitting portions of the core forming flame 8 does not change, the fluctuation range may increase from 0.35 mm to about 1.0 mm. understood.

The conclusion from the above preliminary experiments is that
(1) When the valve opening in the air flow controller 54 is adjusted to increase the amount of air introduced into the bell jar 11 via the air introduction part 70, the width of the light emitting part of the flame 8 for forming the core part is increased. When the position of the point P moves downward and (2) the valve opening of the control valve 60 is adjusted to reduce the pressure in the bell jar 11,
That is, the variation of the position of the midpoint P of the width of the light emitting portion of the flame 8 for forming the core portion increases. Also, from these facts,
(A) When the amount of air introduced from the air introduction part 70 to the bell jar 11 is changed, the position of the midpoint P of the width of the light emitting part of the core forming flame 8 can be controlled, and (b) the pressure of the bell jar 11 is changed. By doing so, it can be seen that the magnitude (width) of the variation of the position of the midpoint P of the width of the light emitting portion can be controlled.

Using the optical fiber porous base material synthesizing apparatus 100A illustrated in FIG. 5, the air amount control and the pressure control of the bell jar 11 were performed based on the above-mentioned preliminary experiment.
If the air amount control operation and the pressure control operation are performed at the same time, the position change and fluctuation (fluctuation) of the core forming flame 8 may change at the same time, and the control may become unstable.
In this embodiment, the air amount control and the pressure control are not applied at the same time in order to simplify the control operation. Of course, it is also possible to control the air amount control and the pressure control at the same time by forming a control system considering mutual interference. Like the image processing device 30, the image processing device 30A measures the midpoint P of the width of the light emitting portion of the flame 8 for forming the core portion, and further applies the position signal S30A to the position controller 50. The position signal S30A is the average value of the position of the midpoint P of the width of the light emitting portion for one minute. In addition, the image processing device 3
Position fluctuation signal S3 applied to fluctuation controller 52 from 0A
For 0B, the standard deviation of the position variation of the midpoint P of the width of the light emitting portion was used. When the position controller 50 receives the position signal S30A from the image processing device 30A, the position controller 50 performs a comparison calculation with a set value,
The result is used as the air volume control command S50 and the air flow rate controller 5
Output to 4. For example, the air flow rate controller 54, which is configured by combining a hot wire type flow sensor and a control valve for controlling air, has a deviation between the reading of the hot wire type flow sensor and the set value designated by the air volume control command S50. The opening of the control valve is controlled so that Air flow controller 54
As the control algorithm of, for example, the well-known PID (proportional, integral, derivative) control, P control, or PI control can be applied. The fluctuation controller 52 receives the position fluctuation signal S30B from the image processing device 30A.
Is input, the result is compared with the set value, and the result is output to the air pressure controller 56 as a pressure control command S52.
The air pressure controller 56 calculates the deviation between the set value of the pressure control command S52 from the fluctuation controller 52 and the reading of the pressure sensor 58, and adjusts the valve opening degree of the control valve 60 so that this deviation becomes zero. Control. The control algorithm of the air pressure controller 56 is also the normal PID control, P control, or P control.
I control or the like can be applied.

Curve CV2 of FIG. 3 and curve C of FIG.
V4 indicates the result obtained by the above control operation. As is clear from the curve CV2 shown in FIG. 3, the position of the midpoint P of the width of the light emitting portion of the flame 8 for forming the core portion was substantially constant over time. As is clear from the curve CV4 shown in FIG. 4, the relative refractive index difference Δ is less dependent on the longitudinal direction of the soot body 2. That is, a uniform relative refractive index difference Δ was obtained in the longitudinal direction of the soot body 2. Therefore, when an optical fiber is synthesized using the soot body 2 synthesized in this way, an optical fiber having a uniform relative refractive index difference Δ can be manufactured.

Third Embodiment Another embodiment of the method for synthesizing the porous preform for optical fibers and the apparatus therefor according to the present invention will be described. In the above-described embodiment, the core burner 4 is used.
The flame 8 for forming a core portion from No. 1 was measured, and the amount of air introduced into the bell jar 11 and the pressure of the bell jar 11 were controlled with reference to the position and variation of the midpoint P of the width of the light emitting portion. However, in the present embodiment, the flame 10 for forming the clad portion from the clad burner 6 is further performed.
FIG. 8 shows a porous base material synthesizing apparatus 10 for optical fibers according to this embodiment.
The structure of 0B is shown. Optical fiber porous base material synthesizer 1
00B includes a soot body synthesis device 1B and a synthesis state measurement / control device 3B.

The soot body synthesizing apparatus 1B is similar to the soot body synthesizing apparatus 1A illustrated in FIG.
In addition to 0, a second air introducing portion 76 is provided, and an inner cylinder 82 is provided in the soot body synthesizing apparatus 1A. Inner cylinder 82
The inner diameter of is designed to be larger than the outer diameter of the soot body 2. The air introduced from the air flow rate controller 54 and the air introduction unit 70 flows downward between the outer cylinder 80 and the inner cylinder 82 of the bell jar 11 as a first air flow F1, and the second air flow rate controller 64. And the air introduced from the second air introduction part 76 flows in the inner cylinder 82, and flows downward in the gap between the inner cylinder 82 and the soot body 2 as the second air flow F2.

The combined state measuring / controlling device 3B comprises a CCD camera 32, a first monitor device 34, and a second monitor device 3.
6 (not shown), a control processing computer 38 (not shown), a recording device 39 (not shown), and an image processing device 30B. The image processing device 30B is similar to the image processing device 30A described above, but as described below,
The processing content is different from that of the image processing apparatus 30A. CCD
The camera 32 images the core forming flame 8 and the clad forming flame 10 at the same time, and the results are signal-processed by the image processing device 30B and displayed on the first monitor device 34. The measurement of the midpoint position of the width of the light emitting portion of the clad flame for forming part 10A and the variation thereof performed in the image processing apparatus 30B using the window 40B is performed using the measurement window 40 described with reference to FIG. This is the same as the position measurement of the middle point P of the width of the light emitting portion of the core forming flame 8A and the variation measurement thereof. Combined state measurement / control device 3
B further has a position controller 50, a fluctuation controller 52, an air flow controller 54, an air pressure controller 56, a pressure sensor 58, and a control valve 60 similar to those illustrated in FIG. Further, the combined state measurement / control device 3B has a second position setter 62 and a second air flow controller 64.

Also in this example, a preliminary experiment was conducted as illustrated in FIG. In this experiment, the pressure control of the bell jar 11 using the fluctuation controller 52 and the air pressure controller 56 was kept constant. That is, it is assumed that the fluctuation range of the position of the flame 8 for forming the core portion is maintained constant.
In FIG. 9, a curve CV8 shows a change in the flow rate of the second air flow F2 flowing between the inner cylinder 82 and the soot body 2, and a curve CV9 runs between the outer cylinder 80 and the inner cylinder 82 of the bell jar 11. The change in the flow rate of the first air flow F1 is shown. The horizontal axis indicates the passage of time. FIG. 10 is a graph showing a change in the position of the midpoint of the widths of the light emitting portions of the core forming flame 8 and the clad forming flame 10 due to the change in the air amount shown in FIG. A curve CV10 shows the position change of the flame 8 for forming the core portion, and a curve CV11 shows the flame 10 for forming the cladding portion.
Shows the position change of. The horizontal axis indicates the passage of time. Analyzing the graphs of FIGS. 9 and 10, when the amount of the first air flow F1 is changed, the position of the flame 8 for forming the core portion is largely changed, and when the amount of the second air flow F2 is changed, the clad is changed. It was found that the position of the flame 10 for forming a part greatly changed. The second air flow F2 is close to the cladding flame 10 and directly affects the position of the cladding forming flame 10. When the amount of the second air flow F2 is increased, the clad forming flame 10 moves to the core forming flame 8 side,
When the amount of the second air flow F2 is reduced, the cladding forming flame 10 separates from the core forming flame 8. Further, the first air flow F1 passes by the side of the second air flow F2, and further hits the bottom of the bell jar 11 to affect the inverted core forming flame 8. Therefore, increasing the first air flow F1 to 0.2 m ³ / min to 0.7 m ³ / min, rather midpoint P position of the width of the light emitting portion of the core portion forming the flame 8, the cladding portion forming flame 10 Move to the side. Of course, the above experimental results show that the bell jar 1
1, the outer diameter of the outer cylinder 80, the outer diameter of the inner cylinder 82, and the amounts of the first air flow F1 and the second air flow F2. It is understood that the positions of the core forming flame 8 and the clad forming flame 10 can be controlled by changing the amount of the flow F2.

Based on the results of the preliminary experiments described above, the position signal S30A at the midpoint of the width of the light emitting portion of the core forming flame 8 from the image processing apparatus 30B is applied to the position controller 50, and the air flow rate is increased. The first air flow F1 via the controller 54
At the same time, the position signal S30C of the midpoint of the width of the light emitting portion of the clad flame 10 is applied to the position setter 62 from the image processing device 30B and the second air flow rate controller 64 is used to control the position signal S30C. The air flow F2 was controlled. Also in this case, the pressure control of the bell jar 11 was kept constant. The result is shown in FIG. The horizontal axis indicates the passage of time, and the vertical axis indicates the positions of the core forming flame 8 and the clad forming flame 10. A curve CV12 shows a temporal change in the position of the core forming flame 8 when no control is performed, and a curve CV13 shows a temporal change in the position of the cladding forming flame 10 when no control is performed. On the other hand, the curve CV14 shows the change with time of the position of the core forming flame 8 when the control based on the present embodiment is performed, and the curve CV15 shows the clad when the control based on the present embodiment is performed. The time-dependent change of the position of the flame 10 for forming a part is shown. When the control is not performed, the cladding forming flame 10 moves upward by about 0.8 mm, and the core forming flame 8 moves by about 0.5 mm. As is clear from the curves CV14 and CV15, the first air flow F1 and the second air flow F2 of the present embodiment.
It is understood that when the control is performed, the core forming flame 8 and the clad forming flame 10 are maintained at substantially constant positions without depending on the passage of time. The change is about 0.1 mm.

In this embodiment, the pressure control is kept constant under appropriate conditions. As illustrated in FIGS. 6 and 7,
Since the pressure control mainly influences the fluctuation range (fluctuation) of the flame, the pressure control may be performed so that the fluctuation of the core forming flame 8 and the clad forming flame 10 becomes small.

The above-described examples and experimental results are merely examples, and the above numerical values and the like will not change if conditions such as the shape of the bell jar 11, the mounting position of the core burner 4 and the mounting position of the clad burner 6 change. Of course. Therefore, the above-mentioned numerical values need to be set according to the conditions of the bell jar 11 and the like. However, it is clear from the present invention that the position of the core forming flame 8 from the core burner 4 can be controlled by introducing air into the bell jar 11. In addition, bell jar 11
It is clear that the fluctuation range of the core forming flame 8 can be controlled by controlling the pressure of. These principles are similarly applied to the flame 10 for forming the cladding portion from the cladding burner 6.

Fourth Embodiment Further, in the above-described embodiments, one CCD camera 32 is used to form the core forming flame 8 and the clad forming flame 1.
Although the case of simultaneously imaging 0 is illustrated, two CCD cameras may be used to respectively image the core forming flame 8 and the clad forming flame 10. The image processing method for the image pickup results of these CCD cameras in the image processing devices 30, 30A, and 30B is the same as that described above.

Fifth Embodiment Another embodiment of the method for measuring the state of a flame according to the present invention will be described. The fifth example shows an example of measuring the emission intensity distribution. FIG. 12A shows the configuration of the measuring device 9 for carrying out the fifth embodiment. In the fifth embodiment, the CCD camera 32 in the first embodiment is not used, but the optical processing device 9 including the condenser lens 92, the screen 94, the linear image sensor 96, and the sensor control device 98 is used. Images of the core forming flame 8 and the clad forming flame 10 are projected on the screen 94 by using the condenser lens 92, and the linear image sensor 96 is arranged so as to face the screen 94 on the side opposite to the condenser lens 92. Is provided. A plan view of the linear image sensor 96 is shown in FIG. The linear image sensor 96 is a measuring device that measures the linear intensity distribution of light. FIG. 12C shows a linear image sensor 96.
It is a figure which shows the image of the flame 8 for core part formation and the flame 10 for clad part formation which were projected on FIG. The sensor controller 98 processes the image data obtained by the linear image sensor 96.

FIG. 13 is an enlarged view of FIG. 12C and a diagram showing the flame measuring process. A first measurement window 62 and a second measurement window 64 are pasted at predetermined positions on the screen 94.
2 and 64 are used to measure the portions of the core forming flame 8 and the clad forming flame 10 where the emission intensity is high. Preferably, an appropriate threshold value is provided and the surfaces of the core forming flame 8 and the clad forming flame 10 are measured with good contrast. Unlike the first to fourth embodiments, the fifth embodiment does not require high-speed calculation for a wide range of image data, so that it is possible to perform high-speed measurement as compared with the above-described embodiments. Become. Further, there is an advantage that arbitrary points on the visual field can be measured without reducing the processing speed. That is, in the above-described first to fourth embodiments, C
Imaging cycle of the CD camera 32 and the image processing devices 30 and 3
The signal processing cycle in 0A and 30B is limited to some extent, but in the present embodiment, there is no such limitation, so that the flame can be measured at a higher speed. After the flame is thus measured, the control is performed as described in the second to third examples.

Sixth Embodiment In the sixth embodiment, as illustrated in FIG. 14, not only the core-forming flame 8 and the clad-forming flame 10 self-luminece but also the core-forming flame 8 and the clad-forming flame. An example of irradiating the forming flame 10 with laser light and measuring the distribution of the scattered light will be described. That is, the sixth embodiment relates to a method of measuring the profile of the shape of glass particles in a flame. Along with the fluctuation of the flame, the glass particles generated in the flame also play an important role in the synthesis of the porous glass base material. From this viewpoint, the sixth embodiment measures the profile of the shape of the glass particles. FIG. 14 shows the configuration of the measuring device 7 for carrying out the sixth embodiment. This measuring device 7
Has a laser light source 170, a shutter 172, a cylindrical lens 174, a bandpass filter 175, a CCD camera 176, and an image processing device 178. As a specific example, an argon ion laser with a wavelength of 524 nm and an output of 3 W was used as the laser light source 170. Shutter 17
Reference numeral 2 denotes a cylindrical lens 17 for introducing the laser light from the laser light source 170 when measuring the profile of the shape of the glass particles.
Pass to 4. The cylindrical lens 174 diffuses the argon ion laser beam L0 emitted from the argon ion laser 170 into a sheet-shaped light L1 in accordance with the spread of the core forming flame 8 and irradiates the core forming flame 8 with the light.

The sheet-shaped diffused light L1 applied to the core forming flame 8 is scattered when the glass particles 8B are present in the core forming flame 8 and is transmitted when the glass particles 8B are not present. To do. The CCD camera 1 similar to the CCD camera 32 uses the scattered light L2 scattered by the glass particles.
The image is taken at 76. In order to remove the natural light of the flame 8 for forming the core portion, a bandpass filter 175 that allows only light having a wavelength of 514 nm, which is the wavelength of scattered light, to pass through is provided in front of the CCD camera 176. Therefore, CCD
Only the scattered light from the glass particles 8B is incident on the camera 176. The image data captured by the CCD camera 176 is used as the image processing device 30, 30 in the above-described embodiment.
Similar to the flame measurement by A and 30B, the image processing apparatus 1
When the signal processing is performed at 78, the profile of the shape of the glass particles can be measured similarly to the measurement of the flame. As a result, the position change of the glass particles, that is, the width WG of the glass particles and its fluctuation width WGσ, the midpoint PG of the glass particles and its fluctuation width PGσ, the edge position AG of the glass particles, and the flame spread angle Gθ. Etc. could be quantified. The synthesis is performed by returning the profile of the shape of the glass fine particles to the control of the synthesis of the porous glass base material to perform the synthesis.
This is similar to the third embodiment.

In the above embodiments, the case where air (atmosphere) is used as the rectifying gas for the core forming flame 8 or the clad forming flame 10 has been described, but the rectifying gas is not limited to air. You may use inert gas, such as argon gas.

[0056]

According to the present invention, the position of the flame that synthesizes the porous glass preform for optical fibers can be accurately controlled. Further, according to the present invention, the fluctuation of the flame can be controlled within a predetermined range. As a result, the quality of the porous glass base material synthesized according to the present invention is stable.

[Brief description of drawings]

1 is a first embodiment of a method for synthesizing a porous base material for an optical fiber according to the present invention, an apparatus for synthesizing a porous base material for an optical fiber and a method for synthesizing a porous base material for an optical fiber; It is a block diagram of the porous base material synthetic | combination state measuring device for optical fibers.

2 is a graph showing a flame for forming a core portion displayed on the first monitor device shown in FIG. 1 by image-processing the result of imaging the core flame with the CCD camera shown in FIG. .

FIG. 3 is a graph showing the position variation of the midpoint P of the width of the light emitting portion of the flame for forming the core portion with respect to the passage of time measured by the image processing apparatus shown in FIG.

FIG. 4 is a graph showing the relationship between the length of the optical fiber preform and the relative refractive index difference measured by the image processing apparatus shown in FIG.

FIG. 5 is a first configuration diagram of an optical fiber porous base material synthesizing apparatus for performing the optical fiber porous base material synthesizing method of the present invention.

FIG. 6 is a graph showing the relationship between pressure and air volume measured by the optical fiber porous preform synthesis state measuring apparatus shown in FIG. 1.

FIG. 7 is a graph showing the change in the position of the midpoint of the width of the light emitting portion of the flame for forming the core and its fluctuation measured by the porous base material composite state measuring apparatus for optical fiber shown in FIG. is there.

FIG. 8 is a second configuration diagram of an optical fiber porous base material synthesizing apparatus for performing the optical fiber porous base material synthesizing method of the present invention.

FIG. 9 is a graph showing the results obtained in the optical fiber porous base material synthesizing apparatus of the embodiment of the present invention,
It is a graph which shows the change of an air volume.

FIG. 10 is a graph showing the results obtained in the optical fiber porous base material synthesizing apparatus of the embodiment of the present invention, and is a graph showing the flame position.

FIG. 11 is a graph showing the results obtained in the optical fiber porous base material synthesizing apparatus of the example of the present invention, and is a graph showing the change in air volume over time.

FIG. 12 (A) is a diagram showing a configuration of a measuring device for carrying out a method for measuring a composite state of a porous preform for an optical fiber, as a fifth embodiment of the method for measuring a state of a flame or the like of the present invention. 12 (B) is a plan view of the linear image sensor shown in FIG. 12 (A), and FIG. 12 (C) is a diagram showing an image of a flame projected on the linear image sensor.

FIG. 13 is an enlarged view of the figure shown in FIG. 12C and a diagram showing a flame measurement process.

FIG. 14 is a diagram showing a configuration of a measuring apparatus for carrying out a method for measuring a composite state of a porous base material for an optical fiber as a sixth embodiment of the method for measuring a state of a flame or the like of the present invention.

[Explanation of symbols]

1. ・ Soot body synthesizer 11 ・ Bellger 13 ・ ・ Exhaust stack 2 ・ ・ Target (soot body) 2A ・ ・ Silicon wafer 3 ・ ・ Synthesis state measuring device 30 ・ ・ Image processing device 32 ・ ・ CCD camera 34 ・ ・First monitor device 36. Second monitor device 38. Control processing computer 39. Recording device 40. Measurement window 4. Core burner 8. Flame for core formation 8A .. Core after image processing Forming flame 8B ・ Glass fine particles 6 ・ Clad burner 10 ・ ・ Clad part forming flame 3A, 3B ・ ・ Synthesis state measurement / control device 50 ・ ・ Position controller 52 ・ ・ Variation controller 54 ・ ・ Air flow rate control 56 ・ ・ Air pressure controller 58 ・ ・ Pressure sensor 60 ・ ・ Control valve 62 ・ ・ Position setter 64 ・ ・ Second air flow controller 70 ・ ・ Air inlet 72 ・ ・74 ・ ・ Magnetic seal part 76 ・ ・ Second air introduction part 80 ・ ・ Outer cylinder 82 ・ ・ Inner cylinder 100, 100A, 100B ・ ・ Optical fiber porous base material synthesis device 9 ・ ・ Optical processing device 92..Condensing lens 94..screen 96..linear image sensor 98..sensor control device 60..measuring device 62..first linear sensor 64..second linear sensor 7..measuring device 170 .. Laser source 172 Shutter 174 Cylindrical lens 175 Optical bandpass filter 176 CCD camera 178 Image processor 116 Exhaust pipe F1 First air flow F2 Second Air flow

Claims (7)

[Claims] 1. A method for synthesizing an optical fiber porous glass preform or an optical fiber porous waveguide preform for synthesizing an optical waveguide, which comprises a flame sprayed on a target to synthesize the optical fiber porous glass preform or An image of the flow of the glass particles is imaged, signal processing of the imaging result is performed to measure the positional change of the flow of the flame or the glass particles, and the position of the flame or the glass particles measured is adjusted to a predetermined position. A method for synthesizing a porous preform for an optical fiber, which comprises controlling an amount of a rectifying gas for controlling a shape of a flame or glass particles. 2. The signal processing of the image pickup result is performed to measure the fluctuation range of the flame or glass particles, and the pressure around the target is controlled so that the measured fluctuation range falls within a predetermined range. Item 2. The synthetic method according to Item 1. 3. A container for synthesizing a porous glass preform for an optical fiber, a core burner for blowing a flame for forming a core portion of the optical fiber toward a target in the container, and an optical fiber for the target in the container. A clad burner that blows a flame for forming a clad portion, an exhaust tube that discharges exhaust gas in the container, an image capturing unit that captures at least the shape of the flame for forming the core portion, and Flame position measuring means for measuring the center position of the flame, means for providing a rectifying gas that changes the shape of the flame for forming the core part, controlling the amount of the rectifying gas to set the center position of the measured flame to a predetermined position. A porous base material synthesizing device for an optical fiber having a rectifying gas control means for controlling. 4. A flame position variation measuring means for measuring a variation of a central position of the flame for forming the core portion from an image pickup result of the image pickup means, a pressure of the container by controlling a flow rate of exhaust gas discharged from the exhaust stack. 4. The porous fiber preform synthesizing apparatus for an optical fiber according to claim 3, further comprising a pressure control unit for controlling the measured position variation within a predetermined range. 5. A first rectifying gas passage for controlling a position of the core forming flame and a second rectifying gas passage for controlling a position of the cladding forming flame in the container. And a second flow rate control means for controlling the flow rate of the rectifying gas flowing through the second rectifying gas flow path, wherein the flame position measuring means determines the center of the core forming flame from the imaging result of the imaging means. The position and the central position of the clad part forming flame are measured, and the rectifying gas control means sets the first rectifying gas flow path so that the central position measurement result of the core part forming flame becomes a predetermined position. The amount of the rectifying gas flowing is controlled, and the second rectifying gas control unit causes the rectifying gas flowing through the second rectifying gas flow path so that the center position measurement result of the flame for forming the cladding portion is at a predetermined position. 5. The method according to claim 3, wherein the amount of Optical fiber preform synthesizing device. 6. The first rectifying gas flow passage is provided in the container and is defined between an inner cylinder and an outer cylinder of the container, and the second rectifying gas flow passage is the inner cylinder. The porous base material synthesizing apparatus for an optical fiber according to claim 5, which is defined by a gap between the target and the target that enters the inner cylinder. 7. The flame position measuring means sets the flame image pickup result or the detected glass particle flow result,
7. The optical fiber porous base material synthesizing apparatus according to claim 6, wherein the center position of the optical fiber is detected using a signal processing window.