JPH07126031A - Method for synthesizing porous preform for optical fiber - Google Patents

Abstract

PURPOSE:To synthesize a porous preform for optical fiber capable of synthesizing a porous glass preform having a uniform outside diameter by increasing the amount of glass fine particles sticking to an end of a target. CONSTITUTION:This method for synthesizing a porous preform for optical fiber is to control the profile of glass fine particles ejected from a burner 16 with a rectifying gas when an end of a traversing target 10 reaches the vicinity of the burner 16, narrow the sticking region of the glass fine particles at the end of the target 10 and increase the amount of the glass fine particles sticking to the end of the target 10.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for synthesizing an optical fiber porous base material used for forming an optical fiber, and more particularly to an optical fiber porous base material (soot body) such as an external CVD method. The method of synthesizing a porous base material for optical fiber, wherein the amount of synthesis (adhesion) at the end of the porous base material for optical fiber is improved.

[0002]

2. Description of the Related Art An optical fiber having a core and a clad is manufactured by drawing a porous glass preform for an optical fiber. As a typical method for producing such a porous preform for optical fibers, an external CVD method (OVD method) and a vapor axis CVD method (VAD method) are known. Also,
The VAD method is used to manufacture a part of the optical fiber core (core forming part) and a part of the clad (clad forming part) as a porous glass base material, and after vitrification, the remaining clad part is formed by an external attachment method. A method of synthesizing is also known.

In either process, in general,
Using an oxyhydrogen burner, a source gas such as SiC
1_Four, GeC1_FourOf the steam of
And SiO ₂, GeO₂To form fine glass particles. Figure
FIG. 7 illustrates a conventional method for synthesizing a porous glass preform.
Inside the chamber (not shown), the core of the optical fiber
Minute core rod (seed rod) 12 and glass particles on it
Porosity that serves as the cladding for the deposited optical fiber
Target 10 consisting of high quality glass base material (soot) 14
Is rotated in the rotation direction R orthogonal to the axial direction of the target 10.
A traverser that is rotated and matches the axial direction of the target 10.
Is reciprocated relative to the burner 16 in the feed direction T.
It is arranged so that. Spinning and traversing
For the target 10 that is
A stream 40 of fine glass particles is sprayed. This allows Sue
Glass particles are deposited on the top 14
The porous glass base material is synthesized until the diameter is reached. Ta
Amount of glass particles adhering to the target and its adhesion distribution
Is the shape of the particle flow 40 (burner flame) (professional
File) and the temperature of the surface of the optical fiber preform.
It depends on the factor.

[0004]

As described above, the OV
In the method D, a target 1 composed of a seed rod (core rod) and a porous preform for optical fiber synthesized thereon
0 is rotated about a support shaft (not shown), and the target 10 and a burner 16 for injecting glass particles are also used.
And move relative to each other. That is, the target 10 is the burner 1
It reciprocates to the left and right in the horizontal direction with respect to 6. The turning position of this reciprocating motion, that is, the end of the target 10, the right end 10R of the target and the left end 10L of the target.
In the above, since the flame (glass particles) from the burner 16 is displaced from the center, the amount of the glass particles attached to the target is reduced. As shown by the broken line in FIG. 7, the outer diameters of the porous glass base materials (the soot left end 142 and the soot right end 143) of both ends 10L and 10R of the target 10 become smaller than the outer diameter of the soot central portion 140. The outer diameter of the soot center portion 140 of the target 10 gradually decreases toward the soot left end 142 and the soot right end 143.

The soot left end 142 and the soot right end 1 in which the outer diameters of the ends 10L and 10R of these targets are reduced.
Since the outer diameter of the soot 14 is smaller than the diameter of the core rod 12 at the center of the target 10, 43 cannot be used as a product for manufacturing an optical fiber, and the soot left end 142 and the soot right end 143 are wasted. . Therefore, as illustrated in FIG.
The parts that can be effectively used as a product even if they are combined with each other are indicated by reference symbol Lc, which is the soot left end 142 and the soot right end 1
It is the part excluding 43 and. Usually, the portion Lc is about 80% of the total length L, and about 20% of both ends of Lc is wasted. There is a demand for a reduction in the manufacturing cost of optical fibers, and for that purpose, the waste described above goes against the demand for lower prices.

Therefore, it is an object of the present invention, in particular, to improve the synthesis at the end of a porous preform for optical fibers.

[0007]

In order to solve the above problems and achieve the above-mentioned object, the inventor of the present invention analyzed the flow of glass particles and the state of adhesion to the target.
The analysis result will be described with reference to FIGS.
As shown in FIG. 1A, a target 10 including a core rod 12 and a soot 14 is rotated in a rotation direction R in a chamber 18 to traverse a horizontal direction (reciprocating motion).
Traversed in direction T. Argon gas (Ar) and SiCl ₄ were introduced into the central portion of the triple-tube burner 16, hydrogen gas (H ₂ ) was introduced outside thereof, and oxygen gas (O ₂ ) was introduced further outside thereof to produce a flame. Hydrolysis was performed to form fine glass particles, and a stream 40 of fine glass particles was blown from the burner 16 onto the target 10. This chamber 1
Air was blown into the burner 8 toward the combined position of the burner 16 and the target 10. The glass particle flow 40 ejected from the burner 16 is blown onto the target 10 and adheres to the surface of the target 10, so that the soot 14 increases. The gas particles that have not adhered to the target 10 are exhausted together with air from a scrubber (not shown) through the exhaust port 22.
Glass particle flow 40 sprayed on target 10
Collides with the target 10 and is separated along the surface of the target 10 into a right-side glass particle flow 42 and a left-side glass particle flow 41, and is separated from the target 10.

It has been found that the position where the glass particles are separated from the target 10 changes depending on the amount and velocity (flow velocity) of air as the rectifying gas. Therefore, in FIG.
When the amount of air was changed as shown in (B), the following results were obtained. When the amount of air is large, the flow rate _FL and the right-side glass fine particle flow 42 are pushed back toward the central axis XX of the burner 16 and adhere to the target 10 like the flow 424. In this case, the adhesion area of the target 10 is narrow. On the other hand, when the amount of air is small, the flow rate F _S and the right side glass fine particle flow 42 extend toward the end along the surface of the target 10 like the flow 422.
The ratio of being pushed back toward the central axis XX of the burner 16 is small, and the adhesion area is wide.

From the above, by controlling the flow of air toward the glass particles, that is, the flow rate and the flow velocity,
It was found that the flow profile (streamline distribution) of the glass particles with respect to the target can be controlled. Rectifying gas (rectifying gas) that controls the flow profile of glass particles
Is, of course, not limited to air. In particular, the present invention has a problem of a decrease in the amount of adhered glass fine particles on the end portion of the target 10. Therefore, at the end portion of the traversing target 10, the spread of the glass fine particles is suppressed and the adhered region is narrowed. Make sure that many glass particles adhere to the edges. That is, in order to increase the adhesion amount of the glass particles on the end portion of the target, the flow profile (streamline distribution) of the glass particle on the end portion of the target is controlled to efficiently adhere the glass particles to the end portion of the target. To do so. As a result, the amount of adhered glass particles on the edge of the target increased.

Therefore, according to the present invention, the raw material gas for synthesizing the porous glass preform in the burner is hydrolyzed in the flame to form fine glass particles, and the target is reciprocating relative to the burner. In the method of synthesizing a porous preform for optical fibers by spraying the glass fine particles, the reciprocating amount and / or flow rate of the rectifying gas flowing from both ends in the axial direction of the target toward the target synthesis position. Provided is a method for synthesizing a porous preform for an optical fiber, which comprises controlling the profile of the glass fine particles by increasing or decreasing in the vicinity of the turning point of motion.

Preferably, at the turning point of the reciprocating motion,
The amount and / or flow rate of the rectifying gas flowing from the end of the target is increased.

[0012]

The function of the traverse mechanism (rotation / reciprocation mechanism) determines whether the traversed target is located at the end of the burner. Therefore, when the traverse mechanism performs the reversing operation, it controls the flow of the rectifying gas described above. It suffices if the target and the burner are in a traverse state relatively. Therefore, as described above, when traversing the target, the flow of the rectified gas is controlled at the target traverse inversion timing, and conversely,
When the target is fixed and the burner is traversed, the flow of the rectified gas is controlled at the traverse reversal timing of the burner.

As a method of controlling the flow of the rectified gas, the flow rate of the rectified gas may be changed or the flow velocity of the rectified gas may be changed. Alternatively, both of them may be changed at the same time. In short, the flow of the rectifying gas is controlled so that a desired flow profile of the glass particles is obtained at the end portion of the target.

[0014]

EXAMPLE A first example of the present invention will be described. FIG. 2 (A)-
FIG. 2C is a configuration diagram of a first embodiment of an apparatus for synthesizing an optical fiber porous preform for carrying out the method for synthesizing an optical fiber porous preform of the present invention, and FIG. 2 is a configuration diagram when the burner 16 is located substantially in the center of FIG.
FIG. 2B is a configuration diagram in the case where the burner 16 is located near the target right end 10R of the target 10 and FIG. 2C is a traverse and the burner 16 is located near the target left end 10L of the target 10. It is a block diagram when it does.

The target 10 is an airtight chamber 18
It is disposed in the inner lumen 20. Within this lumen 20, the target 10 is the left chuck 24 and the right chuck 2
It is supported by the rotary shafts 28 and 30 via 6, and the rotary shafts 28 and 30 are rotated and reciprocated by an unillustrated rotation mechanism.
When the target 10 is rotated in the rotation direction R and reciprocated, the target 10 rotates in the rotation direction R in the inner cavity 20 and reciprocates in the traverse direction T. That is,
The burner 16 and the target 10 move relatively in the traverse direction T. In this example, the burner 16 is fixed,
A case where the target 10 is traversed will be described. The target 10 is composed of a core rod 12 and a soot 14 as illustrated in FIG. 7.

A burner 16 is provided on the side wall of the chamber 18, and a glass particle stream 40 is ejected from the burner 16 toward the target 10. The generation of the glass particle stream 40 by the burner 16 is the same as that described with reference to FIG. An exhaust port 22 is provided on the side facing the chamber 18, and gas particles not attached to the target 10 are exhausted from the exhaust port 22 toward a scrubber (not shown). Further, on the side wall of the end portion of the chamber 18, the left filter 32 and the right filter 3 are provided.
4 are provided, and a left hood 44 and a right hood 46 are connected to these profiles 32 and 34, respectively. A rotatable left damper 36 is provided in the left hood 44.
Similarly, a rotatable right damper 38 is provided in the right hood 46. The rotation of the left damper 36 and the right damper 38 is performed by the control device 100 that monitors the operation of the rotating / reciprocating mechanism. Since the chamber 18 is in a negative pressure state, external air is filtered by the left filter 32 and the right filter 34 into the lumen 20 through the left filter 32 and the right filter 34, and enters the lumen 20. In this example, air (atmosphere) was used as the rectifying gas for controlling the flow profile of the glass particles.

The operation in the state shown in FIG. 2A will be described.
The central portion of the target 10 faces the burner 16. In this case, the control device 100 controls the opening degrees of the left damper 36 and the right damper 38 to the same intermediate value. As a result, the flow rate F1 of air introduced (sucked) into the lumen 20 from the left filter 32 and the flow rate F2 of air introduced into the lumen 20 from the right filter 34 are equal. These air flows from the right end 10R of the target and the left end 10L of the target to the center of the target 10, and the glass fine particle flow 40 ejected from the burner 16 is controlled to a substantially left-right glass fine particle flow 41a and a right glass fine particle flow 42a. .

The operation in the state shown in FIG. 2B will be described.
The control device 100 detects that the operation of the rotating / reciprocating mechanism has reached the reversal position, and makes the opening degree of the right damper 38 almost fully open (about 100%) to reduce the opening degree of the left damper 36 ( 10-20%). As a result, a large amount of air is introduced into the lumen 20 from the right filter 34, and a small amount of air is introduced into the lumen 20 from the left filter 32. As illustrated in FIG. 1B, the flow rate F of the air on the right side
4 is large, the right side glass particle flow 42b near the right end 10R of the target is pushed back to the burner 16 side.
As a result, the adhesion region of the glass particles on the right end 10R of the target becomes narrower, but more glass particles adhere to the right end 10R of the target. Therefore, the thinning of the outer diameter of the target 10 at the right end 10R of the target as shown by the broken line in FIG. 7 is eliminated. That is, in FIG. 7, the glass particles adhere to the soot right end increasing portion 146 indicated by the solid line. Since many glass particles adhere to the right end 10R of the target, the amount of the glass particles exhausted from the exhaust port 22 without adhering to the target 10 decreases, and the glass particles themselves are less wasted.
On the other hand, since the flow rate F3 of the air on the left side is low, the left glass fine particle flow 41b extends to the surface of the target 10 toward the center of the target 10. Here, in FIG.
Target 10 of glass particles similar to that shown in (A)
Is adhered to.

The operation in the state shown in FIG. 2C will be described.
In the state shown in FIG. 2C, the same thing as described for the right end 10R of the target is performed at the left end 10L of the target. That is, the control device 100 detects that the operation of the rotating / reciprocating mechanism has reached the reversal position, opens the opening of the left damper 36 almost fully (about 100%), and reduces the opening of the right damper 38. (About 10 to 20%).
As a result, a large amount of air is drawn from the left filter 32 into the lumen 2
0, and less air is introduced from the right filter 34 into the lumen 20. Since the flow rate F5 of the air on the left side is large, the left glass fine particle flow 41c near the left end 10L of the target is pushed back to the burner 16 side. As a result, the adhesion region of the glass particles on the left end 10L of the target becomes narrower, but more glass particles adhere to the left end 10L of the target. Therefore, the thinning of the outer diameter of the target 10 at the left end 10L of the target as shown by the broken line in FIG. 7 is eliminated. That is, the glass particles also adhere to the soot left end increasing portion 145 shown by the solid line in FIG. 7.
Since many glass particles adhere to the left end 10L of the target, the exhaust port 22 does not adhere to the target 10 and is not adhered.
The amount of glass particles discharged from the chamber is reduced, and the glass particles themselves are less wasted. On the other hand, since the flow rate F6 of the air on the right side is small, the right glass particle flow 42c is
The surface of the target 10 extends toward the center of the target 10. Here, the same glass fine particles as shown in FIG. 2A are attached to the target 10.

Experimental Example 1 The target 10 was rotated at a rotational speed of about 300 RPM and traversed left and right at a speed of 500 mm / min. The outer diameter of the core rod 12 was 20 mm and the length was 1 m. Glass (SiO ₂ ) particles were attached to the outer periphery of the core rod 12 to an outer diameter of about 150 mm. Burner 2
Oxygen = 30 SLM, Hydrogen = 80 SLM, Argon = 20
SLM and SiC1 ₄ gas = 10 SLM were introduced. Target 10 and burner 16 are airtight chamber 1
The target 1 is installed in the chamber 18.
Outside air (air) is taken in through the filters 32 and 34 from the axial direction of 0. As shown in FIG. 2 (A), when the central portion of the target 10 is combined, a bilaterally symmetric air volume, for example, 3 m ³ / min is sucked in each of the experiments. As shown in FIG. 2B, the target 1
When 0 moves to the left end, the opening degree of the right side damper 36 of the left side filter 32 is reduced, and conversely, the right side damper 38 of the right side filter 34 is fully opened. As a result, from the right side, the fine glass particles ejected from the burner 16 were blown on the target 10 to increase the air flow rate F4 toward the synthesis position where the porous glass preform is synthesized, F4.
Due to this imbalance, the spread of the glass fine particles generated in the burner 16 to the left and right is shortened on the target right end 10R side, and as a result, the taper length of the target right end 10R is shortened. In the case of the reverse direction shown in FIG. 2 (C), the operation was completely reversed. By the above operation,
The effective portion of the porous glass preform that can be used as a product, that is, the portion L _E in FIG. 7 is improved to 95% of the whole.

A second embodiment of the present invention will be described. Figure 3 (A)
~ (C) is a second of the apparatus for synthesizing the porous preform for optical fiber for carrying out the method for synthesizing the porous preform for optical fiber of the present invention.
FIG. 3A is a configuration diagram of the embodiment, and FIG. 3A is a configuration diagram when the burner 16 is located substantially in the center of the target 10.
FIG. 3B is a configuration diagram when the burner 16 is located near the target right end 10R of the target 10, and FIG. 3C is a case where the burner 16 is located near the target left end 10L of the target 10 in FIG. It is a block diagram of. In the third embodiment, the lumen 2 of the chamber 18 is used.
2 (A) to control the amount of air introduced into 0.
The left side damper 36 and the right side damper 38 illustrated in FIG.
Instead of this, an example in which a left blower 50 and a right blower 52 are provided is shown. The rotational speeds of the left blower 50 and the right blower 52 are controlled by the control device 100, respectively.

The operation in the state shown in FIG. 3A will be described.
The central portion of the target 10 faces the burner 16. In this case, the control device 100 makes the left blower 50 and the right blower 52 have the same rotation speed, that is, the maximum rotation speed of about 5 times.
Set to 0%. As a result, the flow rate F1 of air introduced (sucked) into the lumen 20 from the left filter 32 and the flow rate F2 of air introduced into the lumen 20 from the right filter 34 are equal. These air flows from the right end 10R of the target and the left end 10L of the target to the center of the target 10, and the glass fine particle flow 40 ejected from the burner 16 is controlled to a substantially left-right glass fine particle flow 41a and a right glass fine particle flow 42a. .

The operation in the state shown in FIG. 3B will be described.
The control device 100 detects that the operation of the rotation / reciprocating mechanism has reached the reversal position, sets the rotation speed of the right blower 52 to almost 100%, and lowers the rotation speed of the left blower 50 (10 to 20). %degree). As a result, a large amount of air is introduced into the lumen 20 from the right filter 34, and a small amount of air is introduced into the lumen 20 from the left filter 32. Since the flow rate F4 of the air on the right side is large, the target right end 10R
The right-hand side glass particle flow 42b in the vicinity of is pushed back to the burner 16 side. As a result, the adhesion region of the glass particles on the right end 10R of the target becomes narrower, but more glass particles adhere to the right end 10R of the target. Therefore, as shown by the broken line in FIG.
The outer diameter of the target 10 in R disappears, and the glass particles adhere to the soot right end increasing portion 146 indicated by the solid line. Since many glass particles adhere to the right end 10R of the target, the amount of the glass particles exhausted from the exhaust port 22 without being adhered to the target 10 is reduced, and the waste of the glass particles themselves is reduced. On the other hand, since the flow rate F3 of the air on the left side is low, the left glass fine particle flow 41b extends to the surface of the target 10 toward the center of the target 10. Here, the same glass fine particles as shown in FIG. 2A are attached to the target 10.

The operation in the state shown in FIG. 3C will be described.
The control device 100 detects that the operation of the rotation / reciprocating mechanism has reached the reversal position, sets the rotation speed of the left blower 50 to almost 100%, and lowers the rotation speed of the right blower 52 (10 to 20%). degree). This allows the left filter 3
More air is introduced into the lumen 20 from 2 and less air is introduced into the lumen 20 from the right filter 34. Since the flow rate F5 of the air on the left side is large, the left glass fine particle flow 41c near the left end 10L of the target is pushed back to the burner 16 side. As a result, the adhesion region of the glass particles on the left end 10L of the target becomes narrower, but more glass particles adhere to the left end 10L of the target. Therefore, as shown by the broken line in FIG.
The outer diameter of the target 10 in FIG. Since many glass particles adhere to the left end 10L of the target, the amount of glass particles exhausted from the exhaust port 22 without adhering to the target 10 decreases, and the glass particles themselves are less wasted. On the other hand, the flow rate F of the air on the right side
Since there are few 6, the right side glass particle flow 42c extends to the surface of the target 10 toward the center of the target 10. Here, the same glass fine particles as shown in FIG. 2A are attached to the target 10. Also in this second embodiment, the glass particles are attached to the right end 10R of the target and the left end 10L of the target in the same manner as in the first embodiment.

A third embodiment of the present invention will be described. In the third embodiment, instead of controlling the amount of air in the first and second embodiments to control the flow profile of glass fine particles, the flow velocity of air is controlled to change the profile of glass fine particles. . 4A to 4C are configuration diagrams of a third embodiment of the apparatus for synthesizing an optical fiber porous preform for carrying out the method for synthesizing an optical fiber porous preform of the present invention, and FIG. (A) is a burner 1 in the approximate center of the target 10.
6 is a configuration diagram when the burner 16 is located, FIG. 4B is a configuration diagram when the burner 16 is located near the target right end 10R of the target 10, and FIG. 4C is a traversed target of the target 10. It is a block diagram when the burner 16 is located near the left end 10L.

In the third embodiment, in order to change the flow velocity of air at the target right end 10R and the target left end 10L, the left throttle mechanism 54 and the right throttle mechanism 56, the front views of which are shown in FIG. Was provided in the vicinity of the burner 16. The left hood 44 and the right hood 46 are provided with a left blower 50 and a right blower 52, but in the third embodiment, the rotational speeds of the left blower 50 and the right blower 52 are not controlled, and the left blower 5 is not controlled.
The rotation speeds of 0 and the right blower 52 are constant. In FIG. 5, the left diaphragm mechanism 54 is provided with an openable / closable diaphragm 542 housed in an annular support frame 540, and the controller 100 controls the diaphragm of the openable / closable diaphragm 542. As a result, even if the amount of air introduced from the left filter 32 into the lumen 20 and the amount of air introduced from the right filter 34 into the lumen 20 is constant, the air introduced into the lumen 20 is left in the left throttle mechanism 54 and the right throttle. When passing through the mechanism 56 toward the burner 16 side, the flow velocity thereof changes. Changes in the flow velocity also change the flow profile of the glass particles.

The operation in the state shown in FIG. 4A will be described.
The central portion of the target 10 faces the burner 16. In this case, the control device 100 controls the diaphragms of the left diaphragm mechanism 54 and the right diaphragm mechanism 56 as shown in FIG.
The opening d _m is set to, for example, 50%. As a result, the filter is introduced (sucked) from the left filter 32 into the lumen 20, passes through the left diaphragm mechanism 54, that is, the center of the target 10, that is,
The flow velocity F11 of air toward the burner 16 is equal to the flow velocity F12 of air introduced from the right filter 34 into the lumen 20 and passing through the right throttle mechanism 56 toward the burner 16. Air having these flow velocities flows from the right end 10R of the target and the left end 10L of the target to the center of the target 10, and the glass fine particle flow 40 ejected from the burner 16 is divided into a left-right glass fine particle flow 41a and a right-side glass fine particle flow 42a which are substantially symmetrical. Control.

The operation in the state shown in FIG. 4B will be described.
Controller 100 detects that the operation of the rotating-reciprocating mechanism reaches the inverted position, as shown in FIG. 6 (A), a small opening d _n the aperture of the right diaphragm mechanism 56, for example, 10 6 to 20%, and as shown in FIG. 6B, the left diaphragm mechanism 54 is throttled to a large opening d _n , for example, 80 to 90%. This opening is target 1
It is also a value at which 0 does not collide with the diaphragm of the left diaphragm mechanism 54. Thereby, the target right end 10 of the target 10
The gap between R and the throttle of the right throttle mechanism 56 becomes narrower, and the flow velocity F14 of air from the right throttle mechanism 56 toward the target right end 10R becomes higher. On the other hand, the gap between the left throttle mechanism 54 and the target 10 becomes large, and the flow velocity F13 of the air passing through this gap becomes lower than the flow velocity F14. as a result,
Since the air flow velocity F14 on the right side is high, the target right end 1
The right side glass particle flow 42b near 0R is the burner 16
The glass fine particles are pushed back to the side and the adhesion region of the glass particles on the right end 10R of the target becomes narrower, but more glass particles adhere to the right end 10R of the target. Therefore, the thinning of the outer diameter of the target 10 at the right end 10R of the target as shown by the broken line in FIG. 7 disappears, and the adhesion of glass fine particles at the soot right end increasing portion 146 is seen. Since many glass particles adhere to the right end 10R of the target, the amount of the glass particles exhausted from the exhaust port 22 without being adhered to the target 10 is reduced, and the waste of the glass particles themselves is reduced. On the other hand, since the flow velocity F13 of the left air is low, the left glass particle flow 41b
Is the target 10 toward the center of the target 10.
Extends long on the surface of. Here, the same glass fine particles as shown in FIG. 2A are attached to the target 10.

The operation in the state shown in FIG. 4C will be described.
In this case, the operation reverse to that described with reference to FIG. As a result, as shown in FIG.
The adhered amount of the glass particles on the target 10 at the left end 10L of the target increases. Also in the third example, the glass particles were adhered to the right end 10R of the target and the left end 10L of the target, similar to the first and second examples.

A fourth embodiment of the present invention will be described. The outer diameter of the target 10 increases as the porous glass base material grows. The gap between the left diaphragm mechanism 54 and the right diaphragm mechanism 56 and the target 10 shown in FIG. 4A and the gap between the left diaphragm mechanism 54 and the target 10 shown in FIG. It changes depending on the stage. In order to keep the gap between the left-hand throttle mechanism 54 and the target 10 or the right-hand throttle mechanism 56 and the target 10 constant so as to keep the flow profile of the glass particles constant, the controller 100 monitors the diameter of the target 10. Then, in relation to the diameter of the target 10 at that time, the diaphragms of the left diaphragm mechanism 54 and the right diaphragm mechanism 56 are controlled so that the gap between the left diaphragm mechanism 54 or the right diaphragm mechanism 56 and the target 10 becomes constant. Is desirable. Therefore, in the present embodiment, the diameter of the target 10 is measured using a laser diameter measuring device or the like, and based on the measurement result, the control device 100 executes the above-mentioned aperture opening control of the target. The left diaphragm mechanism 54 and the right diaphragm mechanism 56 are controlled so that the gap between 10 and the diaphragm becomes constant. As a result, the glass particles could be attached to the target 10 in a higher degree.

A fifth embodiment of the present invention will be described. This embodiment is an improvement of the third and fourth embodiments. In the third embodiment and the fourth embodiment, only the flow velocity of the air introduced into the lumen 20 is changed in a state where the rotation speeds of the left blower 50 and the right blower 52 which are controlled in the second embodiment are fixed. Let In the fifth embodiment, in addition to the operations of the third and fourth embodiments, as described in the second embodiment, the rotation speeds of the left blower 50 and the right blower 52 are simultaneously changed via the control device 100. Control. Thereby, the flow rate and the flow velocity of the air introduced into the target 10, the target right end 10R, and the target left end 10L via the lumen 20 can be controlled at the same time, and more preferable glass fine particle profile control becomes possible. Can be increased.

In carrying out the present invention, the above-described embodiments and numerical values are not limited, and various modifications can be made. For example, as a fifth embodiment, the left blower 5
Although the control of the rotational speeds of 0 and the right blower 52 has been described, as in the first embodiment, the left blower 50 and the right blower 5 are
Instead of 2, the left damper 36 and the right damper 38 may be used to control the flow rate of air.

In the above embodiment, the case where air (outside air) is used as the rectifying gas to be introduced into the inner cavity 20 has been described, but not limited to air, flammable gas such as H ₂ and methane gas is used. You can also In particular, when a combustible gas is used as the rectifying gas, there is an advantage that the temperature of the surface of the target 10 becomes high and the density of the porous glass base material is improved. In particular, it is preferable to increase the density of the porous glass base material at the end portion in order to improve the quality of the porous glass base material.

It suffices that the target 10 and the burner 16 reciprocate relative to each other, and the target 10 may be fixed and the burner 16 may be traversed, contrary to the above-described embodiment.

[0035]

As described above, according to the present invention, by controlling the profile of the glass fine particles at the end portion of the target by using the rectifying gas, the amount of the glass fine particles attached at the end portion of the target can be adjusted to the center of the target. It is possible to increase the effective use portion of the manufactured porous glass preform by increasing the number of parts that can be used. As a result, the cost of the porous glass preform can be substantially reduced, and the manufacturing cost of the optical fiber can be reduced. Further, according to the present invention, waste of the glass particles exhausted at the end of the target is eliminated. Moreover, less processing of the evacuated glass particles in the scrubber is required. These also contribute to the reduction of the manufacturing cost of the optical fiber as a whole.

[Brief description of drawings]

1A and 1B are views for explaining the principle of a method for synthesizing an optical fiber porous preform according to the present invention, in which FIG. 1A is a cross-sectional view and FIG. 1B is glass fine particles that are changed by suctioned air in FIG. 1A. It is a figure which shows the flow of.

FIG. 2 is a configuration diagram of a first embodiment of an apparatus for synthesizing an optical fiber porous preform for carrying out a method for synthesizing an optical fiber porous preform of the present invention, in which (A) is a burner at the center of the target. It is a figure which shows the state when it is located in a position, (B)
FIG. 6 is a diagram showing a state when the right end of the target is located at the burner position, and (C) is a diagram showing a state when the left end of the target is located at the burner position.

FIG. 3 is a configuration diagram of a second embodiment of an apparatus for synthesizing a porous base material for an optical fiber for carrying out the method for synthesizing a porous base material for an optical fiber of the present invention, in which FIG. It is a figure which shows the state when it is located in a position, (B)
FIG. 6 is a diagram showing a state when the right end of the target is located at the burner position, and (C) is a diagram showing a state when the left end of the target is located at the burner position.

FIG. 4 is a configuration diagram of a third embodiment of an apparatus for synthesizing a porous base material for an optical fiber for carrying out a method for synthesizing a porous base material for an optical fiber of the present invention, in which FIG. It is a figure which shows the state when it is located in a position, (B)
FIG. 6 is a diagram showing a state when the right end of the target is located at the burner position, and (C) is a diagram showing a state when the left end of the target is located at the burner position.

5 is a front view of an air flow rate adjusting mechanism used in the synthesizer of the optical fiber porous preform shown in FIG. 4. FIG.

6A and 6B are diagrams showing a throttled state in FIG. 4B of the air volume adjusting mechanism shown in FIG. 5, FIG. 6A is a diagram showing a throttled state of a second air volume adjusting mechanism, and FIG. It is a figure which shows the diaphragm state of a 1st air volume adjustment mechanism.

FIG. 7 is a diagram showing the principle of synthesizing a porous glass preform and illustrating the conventional problems and the results of the present invention.

[Explanation of symbols]

 10 ... Target 12 ... Core rod 14 ... Soot 16 ... Burner 18 ... Chamber 20 ... Lumen 22 ... Exhaust port 32, 34 ... Filter 36, 38 ... Damper 40 ... Glass particulate flow 44 46 .. Hood 50, 52 .. Blower 54, 56 .. Left side throttle mechanism 100 .. Control device

Claims (2)

[Claims] 1. A raw material gas for synthesizing a porous glass base material in a burner is hydrolyzed in a flame to form glass fine particles, and the glass fine particles are sprayed onto a target that reciprocates relative to the burner. In the method for synthesizing an optical fiber porous preform, the amount and / or the flow velocity of the rectifying gas flowing from both ends in the axial direction of the target toward the synthesis position of the target, near the turning point of the reciprocating motion. A method for synthesizing a porous preform for an optical fiber, characterized in that the profile of the glass fine particles is controlled by increasing or decreasing. 2. The porous mother fiber for optical fiber according to claim 1, wherein an amount and / or a flow velocity of the rectifying gas flowing from the end portion of the target is increased at the turning point of the reciprocating motion. Method of synthesizing wood.