JP2003176148A - Method and apparatus for manufacturing glass preform for optical fiber - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a preform of an optical fiber by which the quality of the preform of the optical fiber can drastically be improved without causing any air bubbles caused by mixing of unvitrified glass soot into the preform of the optical fiber, and troubles on the production caused by the glass soot can be prevented, and to provide an apparatus for manufacturing the optical fiber preform. <P>SOLUTION: The method of manufacturing the preform of the optical fiber comprises coaxially attaching an exhaust tube 4 to a quartz tube 1, then introducing oxygen containing reactive gas into the quartz tube 1, rotating the quartz tube 1 around its axis heating the quartz tube 1 from outside by a heat source 6 so as to react the reactive gas with oxygen to form glass soot, and depositing the glass soot to form a glass layer, and a tip part 11a of a draft tube 11 is inserted into the exhaust tube 4, and the glass soot 13 in the exhaust tube 4 is sucked by the tip part 11a and discharged to the outside. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for manufacturing an optical fiber preform, and more particularly, to a possibility that bubbles may be generated by mixing glass soot into the optical fiber preform without vitrification. The present invention relates to a manufacturing method and a manufacturing apparatus for an optical fiber preform capable of significantly improving the quality of the optical fiber preform and preventing the manufacturing trouble caused by the glass soot. Is.

[0002]

2. Description of the Related Art Conventionally, in a silica-based optical fiber, a rod-shaped base material for a silica-based optical fiber having a core and a clad is synthesized, and the base material for an optical fiber is heated in an atmosphere of about 2000 ° C. It is manufactured by drawing. One of the methods of synthesizing this optical fiber base material is the MCVD method (Modifi
ed Chemical Vapor Deposition).

FIG. 2 is a schematic block diagram showing a conventional apparatus for producing a preform for optical fibers by the MCVD method. In the figure, reference numeral 1 is a quartz tube (glass tube) to be a clad, and 2 is both ends of the quartz tube 1. A scroll chuck 3 for holding the nozzle 3 is a nozzle for supplying an oxygen gas G containing a reactive gas for producing glass soot into the quartz tube 1 from one end side thereof, and 4 is coaxial with the other end of the quartz tube 1. A cylindrical glass exhaust pipe having a diameter larger than that of the quartz tube 1, 5 is a soot box provided on the exhaust port 4a side of the exhaust tube 4, and 6 is an acid for heating the quartz tube 1 from the outside. A heating source such as a hydrogen burner or a resistance heating furnace. The heating source 6 is movable along the longitudinal direction of the quartz tube 1 and can be fixed at any position.
Further, an exhaust device (not shown) is connected to the soot box 5, and this exhaust device discharges the exhaust gas G ′ to the outside and stabilizes the gas flow in the quartz pipe 1 and the exhaust pipe 4. ing.

A method for manufacturing an optical fiber preform using this apparatus will be described. First, the scroll chuck 2,
Into the quartz tube 1 whose both ends are gripped by 2, a nozzle 3 is used to introduce SiCl ₄ , GeCl ₄ , POC from one end of the quartz tube 1.
An oxygen (O ₂ ) gas G containing a reactive gas for producing glass soot such as l ₃ , BBr ₃ and SiF ₄ is introduced. The quartz tube 1 is heated from the outside by a heating source 6 while rotating around its axis by a rotating mechanism including scroll chucks 2 and 2. By this heating, SiCl ₄ , GeCl ₄ , POCl ₃ , BBr ₃ , S introduced into the quartz tube 1
Reactive gas such as iF ₄ is oxidized and fine particles (soot)
Glass soot and adheres to the inner wall of the quartz tube 1.

The adhered glass soot is heated to about 2000 ° C. and vitrified by the heating source 6 which moves in the same direction as the flow of the oxygen gas G containing the reactive gas in the quartz tube 1. Since this heating source 6 moves from one end of the quartz tube 1 to the position where it partially reaches the exhaust tube 4 after passing through the other end, the inside of the quartz tube 1 has a higher refractive index than that of the quartz tube 1. Alternatively, a plurality of glass layers having a low refractive index are formed. In this way, the operation of moving the heating source 6 from one end of the quartz tube 1 to the position reaching the exhaust tube 4 while introducing the oxygen gas G containing the reactive gas into the quartz tube 1 is repeated 50 to 200 times. As a result, a double-walled quartz tube having a double-walled structure in which a plurality of glass layers having a higher refractive index or a lower refractive index than the quartz tube 1 are laminated inside the quartz tube 1 is manufactured. A solidified optical fiber preform can be obtained by intensely heating and contracting this quartz tube.

In this manufacturing process, part of the glass soot generated in the quartz tube 1 rides on the flow of oxygen gas containing the reactive gas and reaches the exhaust pipe 4 without adhering to the quartz tube 1. In order to deposit in the exhaust pipe 4, the exhaust pipe 4 is clogged by the deposited glass soot, and the quartz pipe 1
There is a risk of problems such as bursting. Therefore,
The soot removing method of scraping out the glass soot accumulated in the exhaust pipe 4 using a scraping rod and storing it in the soot box 5 is regularly adopted.

[0007]

By the way, it is difficult to completely remove the glass soot accumulated in the exhaust pipe 4 by the above-mentioned conventional soot removing method, and a part of the glass soot remains in the exhaust pipe 4. Therefore, there is a problem that the remaining glass soot may enter the inside of the quartz tube 1 and bubbles may be generated inside the solidified optical fiber preform due to the glass soot. there were. This bubble becomes a defective portion when the optical fiber preform is heated and drawn to spin the optical fiber later, which causes a reduction in manufacturing yield.

Further, since this glass soot easily deposits near the connecting portion between the quartz tube 1 and the exhaust pipe 4, the glass soot deposited near this connecting portion is melted by the heating source 6 and then solidified, As a result of repeating the phenomenon that glass soot is further deposited on the solidified glass soot, the exhaust pipe 4 may be clogged and the quartz pipe 1 may burst. The solidified portion of the glass soot must be discarded, which is one of the reasons for increasing the manufacturing cost.

The present invention has been made in order to solve the above-mentioned problems, and there is no possibility that bubbles or the like will be generated by mixing the glass soot into the optical fiber preform in a state where the glass soot is not vitrified. An object of the present invention is to provide a manufacturing method and a manufacturing apparatus of an optical fiber preform that can significantly improve the quality of the preform and prevent manufacturing troubles and the like due to glass soot. .

[0010]

In order to solve the above problems, the present invention employs the following method and apparatus for manufacturing a preform for optical fibers. That is, in the method for producing a base material for an optical fiber according to claim 1 of the present invention, an exhaust pipe is coaxially attached to a glass tube, and oxygen gas containing a reactive gas for producing glass soot is introduced into the glass tube. By rotating the glass tube around the axis and heating it from the outside, the reactive gas and the oxygen gas are reacted to generate glass soot, and the glass soot is deposited in the glass tube. In the method for manufacturing a glass fiber preform, a method is characterized in that one end of a suction pipe is inserted into the exhaust pipe, and the glass soot in the exhaust pipe is sucked and discharged outward by the suction pipe. .

In this method of manufacturing a preform for an optical fiber, one end of a suction pipe is inserted into the exhaust pipe, and the glass soot in the exhaust pipe is sucked by the suction pipe to be discharged to the outside. The glass soot flowing from the inside into the exhaust pipe is quickly sucked at one end of the suction pipe without being solidified in the exhaust pipe, and is discharged to the outside. As a result, glass soot is less likely to be deposited in the exhaust pipe, and there is no possibility that bubbles or the like will be generated by mixing the glass soot into the optical fiber preform in a state where the glass soot is not vitrified. As a result, the quality of the optical fiber preform is significantly improved. In addition, the exhaust pipe is less likely to be clogged, and there is no risk of problems such as rupture of the glass pipe attached to the exhaust pipe, and it is possible to prevent manufacturing troubles and the like due to the glass soot. .

According to a second aspect of the present invention, there is provided an optical fiber preform manufacturing method according to the first aspect, wherein the suction pipe is moved along a longitudinal direction of the exhaust pipe. The glass soot in the exhaust pipe is sucked and discharged to the outside. In this method of manufacturing a base material for an optical fiber, the suction pipe is moved along the longitudinal direction of the exhaust pipe, and the glass soot in the exhaust pipe is sucked and discharged outward to flow into the exhaust pipe. The glass soot is sucked and discharged over the entire length of the exhaust pipe, and it is difficult for the glass soot to be deposited over the entire length of the exhaust pipe.

According to a third aspect of the present invention, there is provided an apparatus for manufacturing an optical fiber preform, which comprises a rotating mechanism for rotating the glass tube around its axis, and an exhaust pipe coaxially attached to the glass tube.
An optical fiber preform manufacturing apparatus including a heating source that heats the glass tube from the outside, including a suction tube that is inserted into the exhaust tube to suck the glass soot in the exhaust tube and discharge the glass soot to the outside. It is characterized by

This optical fiber preform manufacturing apparatus is provided with a suction pipe which is inserted into the exhaust pipe to suck the glass soot in the exhaust pipe and discharge the glass soot to the outside. The glass soot flowing into the exhaust pipe from the glass pipe is quickly sucked and discharged to the outside without solidifying in the exhaust pipe, and the glass soot in the exhaust pipe is effectively removed. As a result, there is no risk that the glass soot will be mixed with the optical fiber preform in a state where the glass soot is not vitrified and bubbles will be generated, and the optical fiber preform with improved quality can be stably manufactured. Further, since the exhaust pipe is less likely to be clogged, manufacturing troubles and the like due to the glass soot are prevented, and the number of reuses of the exhaust pipe is increased. This significantly reduces the manufacturing cost of the optical fiber preform.

An optical fiber preform producing apparatus according to a fourth aspect is the optical fiber preform producing apparatus according to the third aspect, wherein an end surface of one end of the suction pipe is inclined with respect to an axis thereof. It is characterized by being a slanted surface. In this optical fiber preform manufacturing apparatus, the end surface of the one end of the suction tube is an inclined surface that is inclined with respect to the axis thereof, so that clogging of the glass soot at this one end is prevented. Further, even if the glass soot deposited in the exhaust pipe adheres, the quality of the optical fiber preform is further improved by scraping it off and quickly removing it.

An optical fiber preform manufacturing apparatus according to claim 5 is the optical fiber preform manufacturing apparatus according to claim 3 or 4, wherein the outer circumference of the suction pipe is the outer circumference of the exhaust pipe. The length is 20 to 50%.

According to a sixth aspect of the present invention, there is provided an apparatus for producing an optical fiber preform according to the third or fourth or fifth aspect, wherein the suction pipe is a quartz glass tube. Characterize.

An optical fiber preform manufacturing apparatus according to claim 7 is the optical fiber preform manufacturing apparatus according to any one of claims 3 to 6, wherein the suction pipe is movable in a longitudinal direction thereof. In addition, it is characterized in that a movable holding mechanism for holding it at an arbitrary position in a fixable manner is provided. In this optical fiber preform manufacturing apparatus, by providing the moving holding mechanism that holds the suction pipe so that it can move in the longitudinal direction and can be fixed at any position, the glass soot flowing into the exhaust pipe is sucked into the suction pipe. It is possible to prevent the suction pipe from being clogged in a concentrated manner to cause clogging of the suction pipe, thereby improving the productivity of the optical fiber preform. Further, the movement and holding of the suction pipe become smoother and more reliable, and the workability is improved.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of a method and an apparatus for manufacturing an optical fiber preform according to the present invention will be described with reference to the drawings. It should be noted that the present embodiment is specifically described for better understanding of the gist of the invention, and does not limit the present invention unless otherwise specified.

FIG. 1 is a sectional view showing an essential part of an optical fiber preform manufacturing apparatus according to an embodiment of the present invention, and the same components as those in FIG. 2 are designated by the same reference numerals. In the figure, reference numeral 11 is a suction pipe, and 12 is a traverse device (movement holding mechanism) which holds the suction pipe 11 and is movable in the longitudinal direction thereof and can be fixed at an arbitrary position.

The suction pipe 11 is composed of a long quartz glass tube containing quartz as a main component, and its tip portion (one end portion).
11 a is inserted into the exhaust pipe 4 from the exhaust port 4 a side, and has a function of sucking the glass soot 13 accumulated in the exhaust pipe 4 and discharging it to the outside. The end surface of the tip portion 11a of the suction pipe 11 is cut obliquely to prevent the glass soot 13 from clogging, and the cut end is an inclined surface 14 inclined with respect to the axis. This tip 11a is
When the fixed glass soot is hit by the rotation around the axis of the exhaust pipe 4 by being inserted in the vicinity of the inner wall of the exhaust pipe 4 or while being in contact with the inner wall, it is scraped off and sucked out. It can be quickly discharged to the outside of the exhaust pipe 4.

The outer peripheral length of the suction pipe 11 is equal to that of the exhaust pipe 4.
20 to 50%, preferably 30 to 40% of the outer circumference of
Is set to be The suction pipe 11 is the exhaust pipe 4
It is effective to operate after the glass soot 13 is deposited to some extent inside. Considering this point, the deposition amount of the glass soot 13 deposited in the exhaust pipe 4 is preferably about 30 to 40% of the outer diameter of the exhaust pipe 4. If the outer diameter of the suction pipe 11 is too small, the glass soot 1
3 becomes easily clogged, and when the outer diameter is too large, turbulent flow occurs at the one end 11a of the suction pipe 11, which adversely affects the deposition of the glass soot in the glass pipe 1 and, in some cases, the exhaust pipe 4 The glass soot 13 that has flowed in and accumulated may be returned to the inside of the glass tube 1 again. Therefore, the suction pipe 1
The outer peripheral length of 1 was limited as described above.

The traverse device 12 is provided with a gripping mechanism 22 such as a chuck provided on the upper surface of the device main body 21 for holding the other end 11b of the suction pipe 11, and a drive of an air cylinder or the like (not shown) for driving the gripping mechanism 22. It is equipped with a mechanism and a control unit, and is movable forward and backward with respect to the quartz pipe 1 and the exhaust pipe 4 by the above-mentioned drive mechanism so that the suction pipe 11 can be moved in the longitudinal direction and fixed at any position. And it can be fixed at any position between them.

In the traverse device 12, the tip end portion 11a of the suction pipe 11 can be taken in and out of the exhaust pipe 4 by advancing and retracting with respect to the exhaust pipe 4. This is because when the tip portion 11a of the suction pipe 11 is fixed at a predetermined position in the exhaust pipe 4, the glass soot 13 flowing into the exhaust pipe 4 concentrates toward the tip portion 11a of the suction pipe 11. This is to prevent the suction pipe 11 from flowing in and being clogged.

Next, a method of manufacturing an optical fiber preform using this manufacturing apparatus will be described. While rotating the quartz tube 1 around the axis, inside the quartz tube 1, from one end thereof, SiCl ₄ , GeCl ₄ , POCl ₃ , BBr ₃ , SiF ₄
Oxygen (O ₂ ) gas containing a reactive gas for producing glass soot is introduced, and the quartz tube 1 is heated from the outside by the heating source 6. Since the heating source 6 is initially arranged near one end of the quartz tube 1, that is, at a position farthest from the exhaust tube 4, the suction tube 11 is arranged outside the exhaust tube 4 without being inserted therein. Has been done. After that, this heating source 6
Is gradually moved from one end of the quartz tube 1 toward the other end thereof, that is, toward the exhaust pipe 4.

Thereafter, when the heating source 6 moves to the vicinity of the boundary between the quartz tube 1 and the exhaust tube 4, the traverse device 12
Is driven to advance the tip portion 11a of the suction pipe 11 toward the exhaust pipe 4, and the tip portion 11a of the suction pipe 11 is inserted into the exhaust pipe 4. The tip portion 11a of the suction pipe 11
Moves gradually in the axial direction along the lower inner wall surface of the rotating exhaust pipe 4, so that the glass soot 13 deposited in the exhaust pipe 4 is sucked by the suction pipe 11, It does not remain inside.

When the heating source 6 and the suction tube 11 are further moved so that the heating source 6 and the tip portion 11a of the suction tube 11 overlap with each other, they are moved in opposite directions to each other, and the heating source 6 is moved to the quartz tube 1. The suction pipe 11 is arranged at a predetermined position outside the exhaust pipe 4 near the one end. In this way, each time the heating source 6 is reciprocated about 5 to 10 times along the quartz tube 1 as described above while introducing the oxygen gas G containing the reactive gas into the quartz tube 1, An operation of moving the tip 11a into and out of the exhaust pipe 4 is performed.

As described above, a plurality of glass layers having a refractive index higher than that of the quartz tube 1 are laminated inside the quartz tube 1 to have a thickness of 2
It is possible to manufacture a quartz tube having a double structure. Then, the quartz tube having the double structure is strongly heated and shrunk to obtain a solid optical fiber preform.

Here, 30 optical fiber preforms (hereinafter referred to as examples) produced based on the method for producing an optical fiber preform of the present embodiment and light produced by the conventional production method. Fiber base material (hereinafter referred to as conventional example)
When compared with 30 pipes, in all of the 30 pipes in the example, no trouble such as bursting of the quartz pipe occurred during production, but in the conventional example, 2 of 30 pipes burst the quartz pipe. Was occurring.

Further, for each of the embodiment and the conventional example,
When the number of bubbles per volume of the optical fiber preform was counted using an optical microscope or the like, in the example, the number of bubbles per volume of the optical fiber preform was 0.8 / 1000 cm.
^{While the} number was extremely small as ³ , it was 4.2 pieces / 1000 cm ³ in the conventional example, which was more than 5 times that of the example.

Further, regarding each of the embodiment and the conventional example,
When the number of recycles of the exhaust pipe 4 was examined, the number of recycles of the exhaust pipe 4 was 5 or more on average in the example, whereas the number of recycles was 3 on average in the conventional example. In the above embodiment, the exhaust pipe 4
It was confirmed that it was excellent in terms of recycling.

As described above, according to the manufacturing method of the optical fiber preform of this embodiment, the quartz tube 1 to the exhaust tube 4 are used.
The glass soot 13 flowing into the inside is the tip portion 1 of the suction pipe 11.
Since it is quickly sucked from 1a and discharged to the outside, it is possible to prevent problems such as the glass soot 13 being mixed in the optical fiber preform and causing bubbles and the like, and to improve the quality of the optical fiber preform. It can be greatly improved. Further, since the exhaust pipe 4 is less likely to be clogged, there is no risk of problems such as bursting of the quartz pipe 1 connected to the exhaust pipe 4, and prevention of manufacturing troubles and the like due to the glass soot 13. You can

Further, according to the optical fiber preform manufacturing apparatus of this embodiment, the glass soot deposited in the exhaust pipe 4 by inserting the tip portion 11a into the exhaust pipe 4 from the exhaust port 4a side thereof. Since the suction pipe 11 for sucking 13 and discharging it to the outside is provided, the glass soot 13 flowing into the exhaust pipe 4 can be quickly discharged to the outside, and as a result, for the optical fiber with extremely few bubbles and the like. The base material can be easily manufactured. Further, since the exhaust pipe 4 is less likely to be clogged, it is possible to prevent manufacturing troubles and the like due to the glass soot 13, the number of reuses of the exhaust pipe 4 is increased, and the manufacturing cost of the optical fiber preform is increased. Can be significantly reduced.

Further, since the tip end portion 11a of the suction pipe 11 is obliquely cut and the cut end is the inclined surface 14, the clogging of the glass soot 13 at the tip end portion 11a can be prevented. Further, even if the glass soot 13 deposited in the exhaust pipe 4 adheres, it is scraped off,
Since it can be removed promptly, the glass soot 13
Is no longer mixed in the optical fiber preform, and the quality of the optical fiber preform can be further improved.

Further, the traverse device 12 which can move the suction pipe 11 in its longitudinal direction and fix it at an arbitrary position.
Since the glass soot 13 is provided, it is possible to prevent the suction pipe 11 from being clogged. Further, the suction pipe 11 can be moved and held more smoothly and more reliably, and the workability can be improved.

Although one embodiment of the manufacturing method and the manufacturing apparatus for the optical fiber preform of the present invention has been described above with reference to the drawings, the specific configuration is not limited to the above embodiment, and the present invention is not limited thereto. Design changes can be made without departing from the scope of the invention. For example, in the present embodiment, the suction pipe 11 is composed of a long quartz glass tube containing quartz as a main component, but the material forming the suction pipe 11 is a material that can withstand the temperature during use. There is no limitation to quartz glass as long as it is available. Also, the traverse device 12
In the above example, the gripping mechanism 22 for holding the suction pipe 11 is provided, but any structure for holding and fixing the suction pipe 11 may be used, and a fastener other than the chuck may be used.

[0037]

As described above, according to the manufacturing method of the optical fiber preform of the present invention, one end of the suction pipe is inserted into the exhaust pipe, and the glass soot in the exhaust pipe is sucked by the suction pipe. However, since the glass soot is less likely to accumulate in the exhaust pipe, it is possible to prevent the glass soot from mixing into the optical fiber preform and causing bubbles, etc. The quality of can be greatly improved. Further, since the exhaust pipe is less likely to be clogged, it is possible to prevent problems such as the glass pipe attached to the exhaust pipe from bursting, thus effectively preventing manufacturing troubles and the like due to the glass soot. can do.

According to the optical fiber preform manufacturing apparatus of the present invention, since the suction pipe is inserted into the exhaust pipe to suck the glass soot in the exhaust pipe and discharge the glass soot to the outside, the inside of the exhaust pipe is cut from the glass pipe. The glass soot flowing into the exhaust pipe can be promptly discharged to the outside without being solidified in the exhaust pipe and removed. Therefore, there is no generation of bubbles or the like due to the glass soot, and it is possible to easily manufacture the optical fiber preform with improved quality. Further, since the exhaust pipe is less likely to be clogged, it is possible to prevent manufacturing troubles and the like due to the glass soot, and the number of times the exhaust pipe is reused is increased, thereby reducing the manufacturing cost of the optical fiber preform. It can be significantly reduced.

Further, since the end face of the one end of the suction pipe is an inclined face inclined with respect to the axis thereof, clogging of the glass soot can be prevented. Further, even if the glass soot deposited in the exhaust pipe is fixed, it can be quickly removed, and the quality of the optical fiber preform can be further improved.

Further, since the moving and holding mechanism for holding the suction pipe so as to be movable in the longitudinal direction thereof and fixable at an arbitrary position is provided, it is possible to prevent the suction pipe from being clogged with the glass soot. The productivity of the base material can be improved. Further, since the suction pipe can be moved and held more smoothly and more reliably, the workability can be improved and the manufacturing cost can be further reduced.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a main part of an apparatus for manufacturing an optical fiber preform according to an embodiment of the present invention.

FIG. 2 is a schematic configuration diagram showing a conventional manufacturing apparatus for optical fiber preforms.

[Explanation of symbols]

1 ... Quartz tube (glass tube), 2 ... Scroll chuck, 3
... Nozzle, 4 ... Exhaust pipe, 4a ... Exhaust port, 5 ... Soot box, 6 ... Heating source, 11 ... Exhaust pipe, 11a ... Tip part (one end part), 11b ... Other end part, 12 ... Traverse device (moving and holding) Mechanism), 13 ... glass soot, 14 ... inclined surface, 21
... device body, 22 ... gripping mechanism.

Claims (7)

[Claims] 1. An exhaust pipe is coaxially attached to a glass pipe,
An oxygen gas containing a reactive gas for producing glass soot is introduced into the glass tube, and the glass tube is rotated around the axis and heated from the outside to react the reactive gas with the oxygen gas. By producing a glass soot, by depositing the glass soot in the glass tube to form a glass layer in the optical fiber preform manufacturing method, one end of a suction tube is inserted into the exhaust tube, and the suction tube is used. A method of manufacturing a preform for an optical fiber, which comprises sucking the glass soot in the exhaust pipe and discharging the glass soot to the outside. 2. The optical fiber according to claim 1, wherein the soot tube is moved along the longitudinal direction of the exhaust tube while the glass soot in the exhaust tube is sucked and discharged outward. Base material manufacturing method. 3. An optical fiber comprising a rotating mechanism for rotating a glass tube around its axis, an exhaust pipe coaxially attached to the glass tube, and a heating source for heating the glass tube from the outside. An apparatus for producing a preform for an optical fiber, which is provided with a suction pipe which is inserted into the exhaust pipe to suck the glass soot in the exhaust pipe and discharge the glass soot to the outside. 4. The apparatus for manufacturing an optical fiber preform according to claim 3, wherein an end surface of the one end of the suction tube is an inclined surface inclined with respect to the axis thereof. 5. The apparatus for manufacturing an optical fiber preform according to claim 3, wherein the outer peripheral length of the suction pipe is 20 to 50% of the outer peripheral length of the exhaust pipe. . 6. The apparatus for manufacturing an optical fiber preform according to claim 3, wherein the suction tube is made of a silica glass tube. 7. The optical fiber according to claim 3, further comprising a moving holding mechanism that holds the suction pipe so as to be movable in the longitudinal direction and fixed in an arbitrary position. Base material manufacturing equipment.