JPH0967131A - Apparatus for producing porous glass body - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stabilize the characteristics in a region where deposition grows initially in a stage for producing a porous glass body by a VAD(vapor axial deposition) method. SOLUTION: While a target rod 12 is rotated by a rotary pulling up device 13, this target rod is pulled up and the glass particulates formed from burners 16, 17 are deposited at the bottom end thereof to form the porous glass body 11. The base of a chamber 14 is provided with an IR transparent observation window 15 and the heat image reflected by a mirror 22 is picked up by an IR radiation thermometer 21. The central position of the core part is determined with a computer by this image signal and a burner driving device 24 is controlled according to thereto, by which the position relation between the burner 16 for the core and the core part of the porous glass body 11 is maintained always constant.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for producing a porous glass body, which is suitable for producing a glass preform for an optical fiber, by a VAD (vapor phase axising) method utilizing a vapor phase reaction process.

[0002]

2. Description of the Related Art The VAD method is known as a method for producing a high-purity porous glass body for use as a glass preform for optical fibers. In this method, a fuel gas (hydrogen gas and oxygen gas) is sent to a burner to generate an oxyhydrogen flame, and a glass raw material gas such as silicon tetrachloride is introduced into the flame to cause a hydrolysis reaction to produce glass fine particles. (Fine particles of silicon dioxide, soot) are generated. By depositing the generated glass fine particles on the lower end of the rotating target rod, a porous glass body (glass fine particle deposit body, soot preform) is grown in a cylindrical shape.

[0003]

However, when a glass preform for an optical fiber is produced by using the above-mentioned VAD method for producing a porous glass body, a portion formed at the beginning of deposition (start of deposition) There is a problem that the characteristics are not stable from time to several hundred mm. That is, when the glass base material actually made is analyzed and evaluated by the preform analyzer, for example, as shown by the dotted line in FIG. 2, the MFD is measured at the first about 500 mm in the soot length direction.
As (mode field diameter) is greatly deviated,
The fluctuations in the characteristics such as the refractive index distribution (profile) in the first part are significantly larger than those in the other parts. This is a major cause of lowering the manufacturing yield of optical fiber products.

In view of the above, the present invention has been improved so as to stabilize the characteristics of the portion grown at the start of deposition and improve the yield of the optical fiber preform manufacturing process. An object is to provide a body manufacturing apparatus.

[0005]

In order to achieve the above object, in the apparatus for producing a porous glass body according to the present invention, a pulling means for pulling up the target rod while rotating it, and glass fine particles are generated and are used as above. Glass fine particle generating means for depositing on the lower end of the target rod, imaging means for capturing an image near the lower end of the porous glass body formed by this glass fine particle deposition, and the porous glass body from the image signal obtained thereby Is provided, and means for adjusting the positional relationship between the porous glass body and the glass fine particle generating means according to the position is obtained.

The image pickup means may be a means for picking up a thermal image seen from below near the lower end of the porous glass body.

At this time, if the image reflected by the mirror disposed below the porous glass body is input to the image pickup means, the image pickup means is separated from the high temperature porous glass body to protect it. You can

Further, the positional relationship adjusting means determines the horizontal center position of the lower end portion of the porous glass body from the input image signal, and the positional relationship between the porous glass body and the glass fine particle generating means. May be adjusted.

The large variation in the characteristics of the portion grown at the initial stage of deposition is due to the large variation of the air flow (exhaust gas) and the misalignment of the pulling device at the initial stage of deposition, which causes It is considered that the cause is that the position of the tip (core part) moves greatly. Therefore, an image near the lower end of the porous glass body is captured, and the glass particle producing means or the like is moved accordingly to adjust the positional relationship between the porous glass body and the glass particle producing means. Then, the glass fine particle generating means can be moved in accordance with the movement of the porous glass body at the initial stage of growth, so that the fluctuation of the characteristics at the initially grown portion can be suppressed.

[0010]

Next, embodiments of the present invention will be described in detail with reference to the drawings. In FIG. 1, some burners 16 and 17 that generate glass particles are arranged near the lower end of the target rod 12. Here, the burner 16 arranged at the lowermost end is a core burner for forming a core portion, and the others are clad burners 17 for forming a clad portion. An oxyhydrogen flame is generated from these burners 16 and 17, and a raw material gas of glass such as silicon tetrachloride is fed into the flame to generate glass particles by a hydrolysis reaction. The glass particles are deposited on the lower end of the target rod 12,
A cylindrical porous glass body (glass fine particle deposit body, soot preform) 11 is formed by pulling the target rod 12 while rotating it by the rotary pulling device 13 during the deposition.

The porous glass body 11 and the target rod 12 are arranged in a chamber 14, and the deposition process of the glass particles is performed in the chamber 14. An observation window 15 is provided on the bottom surface of the chamber in which the core portion is formed. The observation window 15 is made of calcium fluoride or the like having a good infrared transmitting property. A mirror 22 is arranged below the chamber 14. The mirror 22 is formed by depositing gold on a silicon substrate to suppress the loss of infrared light due to reflection.

The infrared radiation thermometer 21 is arranged so that the light guided downward through the observation window 15 is reflected by the mirror 22 and enters the infrared radiation thermometer 21. The infrared radiation thermometer 21 obtains a two-dimensional temperature distribution image (thermal image) and outputs the image signal. In this way, a thermal image of the tip (lower end) of the core portion deposited by the core burner 16 viewed from below is captured by the infrared radiation thermometer 21 via the observation window 15 and the mirror 22. Since the infrared radiation thermometer 21 is configured to capture the reflection image, the infrared radiation thermometer 21 can be placed at a place distant from the chamber 14, and the infrared radiation thermometer 21 susceptible to heat can be protected.

The signal of the thermal image picked up by the infrared radiation thermometer 21 is sent to the computer 23 and subjected to image processing to obtain the center position of the core portion. For example, the outer circumference of the core portion viewed from below is approximated, and the center position of the core portion viewed from below in the horizontal plane is calculated from the approximate data.

The burner 16 for the core is held by a burner driving device 24. By the burner driving device 24, the position of the burner 16 in the biaxial direction (x direction, y direction) in the horizontal plane, the position in the height direction (h direction), the angle θ with respect to the horizontal plane, and the advancing / retreating direction in this angle θ direction. The position (z direction) can be adjusted arbitrarily. In addition, the burner driving device 24 is arranged so that the absolute positions (x, y,
A position detector such as a potentiometer for determining z, h, θ) is provided, and those position signals of the actual burner 16 are sent to the computer 23.

Therefore, the computer 23 can grasp the relative relationship between the central position of the core portion in the horizontal plane and the actual position of the burner 16, and the relationship is always constant (or appropriate). A burner position control signal to the burner drive 24. Therefore, the core burner 16 and the core portion of the porous glass body 11 are always kept in a fixed positional relationship or in an optimal positional relationship, and as a result, the characteristics of the portion grown in the initial stage of deposition are unstable. Can be suppressed, and the characteristics can be stabilized even in that part.

That is, when the MFD of the porous glass body 11 thus produced was examined in the lengthwise direction, the result as shown by the solid line in FIG. 2 was obtained. The horizontal axis of the figure is the length L from the position where the porous glass body 11 grew first.
(Mm) 50 grown early in deposition
Even in the portion up to 0 mm, the MFD is within ± 5.0% of the center value. On the other hand, in the conventional case, as shown by the dotted line as described above, in the range of about 500 mm from the beginning, the MFD
Is greatly deviated.

Next, the reason why such a good result can be obtained according to the present invention will be described. First, since the position of the core burner 16 is fixed in the prior art, the burner driving device 24 does not move the position of the burner 16 in each direction as described above, but fixes the burner 16 at a fixed position to perform the deposition. View. At this time, when the growth rate of the porous glass body 11 is measured for each growth position L (mm), several hundred mm (4 in the figure) from the start of deposition as shown in FIG.
The growth rate is not stable until around (00 mm) and is lower than the growth rate thereafter.

Further, when the temperature distribution of the core portion was measured by the thermal image captured by the infrared radiation thermometer 21, the peak temperature of the core portion was as low as around 400 mm as shown in FIG. 4 and was not stable. Further, when the position in the horizontal plane (xy plane) of the portion having the peak temperature of the core portion was obtained from this thermal image, what was at the lower right at L = 50 mm as shown in FIG. = 300 mm, it has moved largely to the upper left. In this way, the peak temperature position moves to around L = 300 mm.

At the same time, several hundred mm from the start of deposition
To some extent, when the state of the core portion was monitored with a visible image by a TV camera (not shown) prepared separately, it was found that the core portion itself was moving. This can also be seen from the fact that the contour of the thermal image is moving. Examining the relationship between the center position of the core portion (the position indicating the peak temperature) obtained from the thermal image and the center position of the core portion obtained from the visible image, as shown in FIG. Therefore, it turns out that it is good to see that the two agree.

From these facts, it is considered that the peak temperature of the core portion fluctuates as shown in FIG. 4 because the position of the core portion itself moves especially in the initial stage of deposition, and the core portion is displaced from the flame of the burner 16. . The reason why the position of the core part fluctuates is not clear, but until the porous glass body 11 grows to a certain degree, the fluctuation of the air flow such as exhaust gas is large, and the rotation center position of the rotary pulling device 13 is displaced. It seems that the fact that you are there is an influence.

Conventionally, the core burner 16 can only be moved manually, and its position is adjusted and fixed in accordance with the steady growth after the porous glass body 11 has grown to a certain extent. There is. Therefore, since the lower end portion of the porous glass body 11 cannot cope with the above movement, the lower end portion deviates from the flame of the burner 16, and the peak temperature decreases or the growth rate decreases, resulting in a steady state. It seems that the characteristics were not stable in the part that had grown before the transition to growth.

According to the present invention, the thermal image of the core portion is picked up as described above, the movement of the core portion is detected, and the position of the core burner 16 is moved so as to follow the movement. MFD even at the beginning of deposition
It is possible to produce the porous glass body 11 having stable characteristics such as and other refractive index distributions.

Although the infrared radiation thermometer 21 is used to capture the thermal image of the core in the above description, another imaging device can be used as long as it can capture the image of the heat ray in the infrared region. Can also be used. Further, as shown in FIG. 6, since it is considered that the center of the thermal image and the center of the visible image have a good correspondence, the infrared radiation thermometer 2 is not always necessary.
It is not necessary to use the thermal image pickup device such as No. 1 and a normal visible image TV camera can also be used. However, since an infrared radiation thermometer (thermal image pickup device) is often used for monitoring the temperature of the core, it is advantageous in that it can be used also for position control of the burner 16 for core.

Further, here, a thermal image of the core portion viewed from below is taken to determine the position of the core portion in the horizontal plane. However, a thermal image of the core portion viewed from the side direction is provided in a separately installed red image. Take an image with an outside radiation thermometer (not shown), find the position seen from the side of the core part (position within the vertical plane), and in this direction,
You may make it adjust the positional relationship of the core part and the burner 16 for cores. Further, such control of the burner position is not limited to the core burner 16 and may be performed for other cladding burners 17 and the like.

[0025]

As described above, according to the porous glass body manufacturing apparatus of the present invention, an image of the vicinity of the growth point (lower end) of the porous glass body is picked up, its position is captured, and Since the relative positional relationship between the glass fine particle generating means and the porous glass body is controlled according to the position, the position of the glass fine particle generating means can be moved following the movement of the porous glass body at the initial stage of growth. Can be
It is possible to manufacture a porous glass body having stable characteristics from the initial growth stage. Therefore, M is included over the entire length of the porous glass body, including the region grown at the initial stage of deposition.
The characteristics such as FD and profile can be made very stable. Since the initial growth region, which has been poor in the past, can be used as a good product, the porous glass body can be manufactured more efficiently.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention.

FIG. 2 is a graph showing MFD characteristics in the length direction of a porous glass body.

FIG. 3 is a graph showing a conventional growth rate of a porous glass body in the length direction.

FIG. 4 is a graph showing a core peak temperature in the length direction of a conventional porous glass body.

FIG. 5 is a diagram showing positions of peak temperatures of a porous glass body.

FIG. 6 is a graph showing the relationship between the center of a thermal image and the center of a visible image.

[Explanation of symbols]

11 Porous Glass Body (Soot Preform) 12 Target Rod 13 Rotation Lifting Device 14 Chamber 15 Observation Window 16 Burner for Core 17 Burner for Clad 21 Infrared Radiation Thermometer 22 Mirror 23 Computer 24 Burner Driving Device

Claims (3)

[Claims] 1. A pulling means for pulling up a target rod while rotating it, a glass fine particle producing means for producing glass fine particles and depositing the glass fine particles on the lower end of the target rod, and a porous glass body formed by the glass fine particle deposition. And an image pickup means for picking up an image in the vicinity of the lower end of the porous glass body, and the positional relationship between the porous glass body and the glass fine particle generation means according to the position of the porous glass body obtained from the image signal obtained thereby. A device for manufacturing a porous glass body, comprising: 2. The apparatus for manufacturing a porous glass body according to claim 1, wherein the imaging means captures a thermal image of the porous glass body near a lower end thereof as seen from below. 3. The positional relationship adjusting means obtains the horizontal center position of the lower end portion of the porous glass body from the input image signal, and the positional relationship between the porous glass body and the glass fine particle generating means. The apparatus for producing a porous glass body according to claim 1 or 2, characterized in that: