JP2000095537A - Drawing device for optical fiber preform - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent external air from being entered into a furnace tube of a drawing device by which an optical fiber preform is drawn by introducing inert gas into the furnace tube. SOLUTION: The optical fiber preform 1 is disposed in a furnace core tube 21 which is heated by an electric heater 22 to draw the preform in almost vertical direction. Argon gas is made to flow through gas flowing passages 23b, 24b of upper and lower flanges 23, 24 while the flowing argon gas and external air are sucked through a gas sucking passage 24c of the lower flange part 24.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for drawing an optical fiber preform, and more particularly to an apparatus for drawing an optical fiber preform while supplying an inert gas into a furnace tube.

[0002]

2. Description of the Related Art As a conventional stretching apparatus for an optical fiber preform, there is, for example, one as disclosed in Japanese Patent Application Laid-Open No. 2-6344. As shown in FIG. 6, this drawing apparatus holds a furnace body 2 for heating an optical fiber preform 1 made of quartz glass material, and an upper end and a lower end of the optical fiber preform 1, respectively, and vertically extends the furnace. A vertical drive unit (not shown) that extends is provided as a basic configuration.

[0003] The furnace body 2 includes a cylindrical furnace tube 3 made of carbon, an electric heater 4 surrounding the furnace tube 3 concentrically, and an upper end portion and a lower end portion of the furnace tube 3. Insertion port 5 through which optical fiber preform 1 is inserted
a, 6a, and the like, and an inert gas such as argon gas flows into the upper flange 5 and the lower flange 6 toward the insertion port. Gas outlet passages 5b and 6b are provided.

In the stretching apparatus having the above structure, the take-off support rod 7 is connected to the lower end of the optical fiber preform 1, and the optical fiber preform 1 is heated by the electric heater 4 through the furnace tube 3. The vertical drive unit is appropriately driven to move the take-up support rod 7 downward, and further, the gas outflow passage 5
The drawing process of the optical fiber preform 1 was performed while flowing out argon gas and the like from b and 6b. Here, the reason why the argon gas or the like is allowed to flow into the furnace tube 3 as described above is to prevent the carbon furnace tube 3 from being consumed by oxidation.

[0005]

However, in the above-mentioned conventional stretching apparatus, an ascending air flow is generated in the furnace tube 3 due to the temperature gradient generated in the furnace tube 3.
The lower region of the furnace tube 3 becomes a negative pressure, and the air outside the furnace body 2 is sucked into the furnace tube 3 through the opening of the lower flange portion 6, thereby oxidizing and corroding the inner wall of the furnace tube 3. there were.

As a result, the consumption of the furnace tube 3 cannot be sufficiently prevented, and dust generated when the furnace tube 3 reacts with air is generated in the stretched portion of the optical fiber preform 1, It adheres to the surface of the drawn rod and contaminates the drawn rod. Then, when the contaminated stretched rod is externally provided with a cladding layer in a later step and drawn to form an optical fiber, there has been a problem that breakage occurs inside the optical fiber.

Further, when the stretching is performed by the stretching apparatus, the core tube 3 having a wall thickness of 5 mm has a problem that a hole is formed in the wall in about 6 hours or a crack is generated. The present invention has been made in view of the above-mentioned problems of the prior art, and aims at minimizing the consumption of the reactor core tube and suppressing the generation of dust to reduce contamination of the drawn rod. It is an object of the present invention to provide an optical fiber preform stretching device that can prevent the occurrence.

[0008]

Means for Solving the Problems In order to achieve the above object, the present inventors have paid attention to the point of shutting off external air sucked into the core tube along with the rising airflow in the core tube, and have the following structure. Came to an invention consisting of:

That is, the apparatus for stretching an optical fiber preform according to the present invention comprises disposing the optical fiber preform in a furnace tube arranged to be heated by a heating element and to extend in a substantially vertical direction. An optical fiber preform stretching apparatus for stretching an optical fiber preform while supplying an inert gas to the furnace core tube, wherein a cutoff means for blocking external gas from entering the furnace tube is provided. I have.

In the above basic configuration, an upper flange portion and a lower flange portion are provided at an upper end portion and a lower end portion of the core tube, respectively, to define insertion holes through which optical fibers are inserted. The flange portion is provided with a gas outflow passage that opens toward each insertion opening and allows the inert gas to flow out, and the blocking means is formed in the lower flange portion and opens to the insertion opening. A configuration that employs a gas suction passage for sucking gas can be adopted.

The opening of the gas outflow passage and the opening of the gas suction passage may be formed so as to face each other in the radial direction of the insertion opening.

Further, as the opening of the gas outflow passage and the opening of the gas suction passage, those formed so as to be arranged in the axial direction of the insertion opening can be adopted.

[0013] In the configuration in which the opening of the gas outflow passage and the opening of the gas suction passage are arranged in the axial direction of the insertion port, the opening of the gas outflow passage is further placed on the upper side.
A configuration in which the opening of the gas suction passage is arranged on the lower side can be adopted.

Further, in the above configuration, it is possible to employ a configuration in which a plurality of pairs of the opening of the gas outflow passage and the opening of the gas suction passage are provided on the wall surface of the insertion port.

[0015]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 is a schematic structural view showing a first embodiment of a drawing apparatus according to the present invention. As shown in the drawing, the drawing apparatus includes a furnace body 20 for heating an optical fiber preform 1,
The upper drive unit 30 which holds the upper end of the optical fiber preform 1 and drives it vertically, and the lower drive unit which similarly holds the lower end of the optical fiber preform 1 via the support rod 25 and drives it vertically. A side drive unit 40 and the like are provided as its basic configuration.

The furnace body 20 has a carbon furnace tube 2 formed in a cylindrical shape and arranged to extend in the vertical direction.
1, an electric heater 22 as a heating element concentrically surrounding the furnace tube 21, and an upper flange portion 23 having a large-diameter insertion opening 23 a through which the optical fiber preform 1 is inserted at the upper end of the furnace tube 21. The lower end 21b of the furnace tube 21
The optical fiber preform 1 is constituted by a stretched portion of the optical fiber preform 1, that is, a lower flange portion 24 having a small-diameter insertion port 24a through which a stretch rod is inserted. Here, stainless steel is used as the material of the upper flange portion 23 and the lower flange portion 24, but other steel, alloy, carbon, fluororesin, or the like may be used.

An inert gas such as argon gas, nitrogen gas, helium gas, etc.
A gas outflow passage 23b whose opening 23b 'is located on the inner wall surface of the insertion port 23a is formed so that the gas flows out into the inside 3a. An opening 24b 'is formed in the lower flange 24 so that an inert gas such as argon gas flows out into the insertion opening 24a as described above.
A gas outflow passage 24b is formed on the inner wall surface of the gas discharge passage 24. Further, an opening 24c is formed so as to suck the inert gas and the outside air (both are referred to herein as gas) flowing out from the gas outflow passage 24. Is formed on the inner wall surface of the insertion port 24a to form a gas suction passage 24c as blocking means.

Here, the gas outflow passage 24b and the gas suction passage 24c will be described in detail with reference to FIG.
As shown in the figure, the gas outflow passage 24b and the gas suction passage 24
c is such that the openings 24b 'are located on the upper side and the openings 24c' are located on the lower side so that the openings 24b 'and 2
4c 'are formed so as to be arranged in the direction of the axis V.

Further, two pairs of the gas outflow passage 24b and the gas suction passage 24c are provided so as to be linearly arranged in the radial direction of the insertion opening 24a. However, the present invention is not limited to this configuration, and a plurality of pairs may be provided so as to be radial.

The gas outflow passage 24b will be described in more detail. As shown in FIGS. 2 (a) and 2 (b), the opening 24b 'has a width b, d and a height m, n. For the upstream passage having a rectangular cross section, the depth dimensions c and e
The width is enlarged to a passage having a substantially rectangular cross section that is long and lateral so as to have the width dimensions a and f. Similarly, in the gas suction passage 24c, as shown in FIGS. 2 (a) and 2 (c), the opening 24c 'has a substantially rectangular cross section with width dimensions h and j and height dimensions o and p. The passages on the downstream side are enlarged so as to have depths i and k and widths g and l, and have a substantially rectangular cross section that is long and long.

With the above configuration, the inert gas flowing out of the opening 24b 'of the gas outflow passage 24b into the insertion opening 24a is prevented from flowing into the opening of the gas suction passage 24c as shown by the arrow in FIG. The air flows downward toward 24c ', and shuts off external air that is going to enter the core tube 21.

The dimensions a, b, and c shown in FIGS.
c, d, e, f, g, h, i, j, k, l, m, n,
It is preferable that the values of o and p are set in ranges that satisfy the following equations. 3mm <a, f, g, l <100mm 3mm <m, n, o, p <20mm 3mm <b, d, h, j <20mm 3mm <c, e, i, k <100mm Set within the above range Thereby, the effect of blocking the external air can be more preferably obtained.

In the above-described embodiment, the axis of the gas outflow passage 24b and the axis of the gas suction passage 24c are formed in the same plane, but are twisted in the range of 0 to 180 degrees. They may be formed so as to have a relationship.

Further, the widths of the opening of the gas outflow passage 24b and the opening of the gas suction passage 24c are not limited to a, f, g, and l, but as shown in FIG. , 24e, and this annular passage 24d,
A plurality of openings 24d 'and 24e' opening from 24e to the entire inner wall surface of the insertion port 24a may be formed. In this way, a flow is generated in which the inert gas flows downward from the entire inner wall surface of the insertion port 24a and flows downward, so that the effect of blocking external air can be further enhanced.

In the above stretching apparatus, in addition to the above-described structure, the upper drive motor 31 for moving the upper drive unit 30 up and down along the elevating rail 30a, and the lower drive unit 40 for up and down movement along the elevating rail 40a. Lower drive motor 4
1. Outer diameter measuring device 50 for measuring the drawn outer diameter of optical fiber preform 1, outer diameter setting device 5 for setting a target value of drawn outer diameter
1. Measurement value measured by the outer diameter measuring device 50 and outer diameter setting device 5
1 and sends a speed command signal to the upper and lower drive motors 31 and 41 based on the difference (deviation), and sends the speed of the upper drive unit 30 and the lower drive unit 40. Proportional integral derivative control of pick-up speed (PID control)
And a mass flow controller 63 from an inert gas supply source (not shown).
a, a valve for adjusting a flow rate when an inert gas such as an argon gas is supplied into the gas outflow passages 23b, 24b through the a, 63b, a suction pump 61, a suction pump 61 connected to the gas suction passage 24c. And a flow meter 62 for measuring the flow rate of the gas to be sucked. Here, the adjustment of the valve 60 may be performed manually, or
A function of transmitting a control signal to the flow meter 62 is provided,
The valve 60 may be provided with a function of receiving the control signal and automatically controlling the opening and closing of the valve 60 itself, and a control signal may be transmitted from the flow meter 62 to the valve 60 to perform the control automatically.

Next, a procedure for performing a stretching process using the above stretching apparatus will be described. First, the upper end of the optical fiber preform 1 is attached to the upper drive unit 30, and the optical fiber preform 1 is inserted into the furnace tube 21 so as to be heated by the electric heater 22 in the lower region. Subsequently, the take-off support rod 25 made of a columnar quartz glass is attached to the lower drive unit 40, and the lower drive unit 40 is moved upward,
The optical fiber preform 1 heated in an atmosphere of 1700 ° C. to 2000 ° C. is connected to the lower end of the optical fiber preform 1 by abutting the upper end of the support rod 25 for welding and welding.

Thereafter, the lower drive unit 40 is moved downward at a predetermined take-up speed to pull the lower end region of the optical fiber preform 1, and further, the upper drive unit 30 is moved in accordance with the drawing speed at this time. Is stretched so that the stretched portion (stretched rod) has a predetermined outer diameter while lowering at a predetermined feed speed.

In the stretching step, the outer diameter (stretched outer diameter) of the stretched portion is always or optionally measured by an outer diameter measuring device 50, and the measured value is compared with a target value set in the outer diameter setting device 51. Is calculated, and the difference (deviation) is calculated. The calculated result is fed back, and the controller 53 controls the take-up speed of the lower drive unit 40 so that the target drawing outer diameter is obtained. The feed speed of the upper drive unit 30 at this time is constant.

In the above-mentioned stretching step, gas outflow passages 23b, 24 provided in the upper flange portion 23 and the lower flange portion 24 are supplied from an inert gas supply source (not shown).
b, an inert gas is supplied here, and an argon gas is supplied to flow out into the respective insertion ports 23a and 24a, and the suction pump 61 is driven to drive the lower flange 2
Argon gas and the outside air which flow out are suctioned from the gas suction passage 24c provided in 4.

At this time, the flow rate of the supplied argon gas is controlled in the range of 0 to 100 liter / min, and the flow rate of the sucked gas is adjustable in the range of 0 to 100 liter / min. Is controlled by

Based on the procedure described above, the outer diameter should be 50 to
The 200 mm optical fiber preform 1 was stretched so as to obtain a stretched rod having a stretched outer diameter of 10 to 150 mm. As a result, the surface of the drawn rod after drawing can be kept clean without being contaminated.
The life of No. 1 could be increased to 150 hours or more.

Further, in order to grasp the state of the air flow in the furnace core tube 21 and the area of the insertion port 24a in the stretching step, a visible laser beam is provided by using a visualization device having a window through which the inside of the furnace body 20 can be observed. It was irradiated and observed. At this time, in order to facilitate observation, a silica powder was supplied as a tracer together with argon gas, and observation was performed. As a result, as shown in FIG. 1, in the region of the lower flange portion 24,
The argon gas flowing out of the gas outlet passage 24b into the insertion opening 24a flows downward and flows into the gas inlet passage 24c.
It was confirmed that external air below the lower flange portion 24 was also drawn into the gas suction passage 24c. That is, it was confirmed that outside air was blocked from entering the furnace tube 21.

On the other hand, inside the core tube 21, a part of the argon gas flowing out from the gas outflow passage 24 b of the lower flange portion 24 and the gas outflow passage 2 of the upper flange portion 23 are formed.
3b and a part of the argon gas flowing out is introduced,
In a space surrounded by the outer peripheral surface of the optical fiber preform 1 and the inner wall surface of the furnace tube 21, convection of argon gas occurs due to a temperature gradient as shown in FIG. Covering over a wide area was confirmed.

In the above-described stretching apparatus, the optical fiber preform 1 is held and fixed by using a three-jaw chuck, but other collet chucks or the like may be used. Also,
Although the optical fiber preform 1 is stretched without being rotated, the stretching may be performed while rotating. Further, in the above-described stretching device, the gas outflow passage 24b is provided on the upper side in the vertical direction and the gas suction passage 24c is provided on the lower side in the vertical direction in the lower flange portion 24. On the side, the gas suction passage 24
Even if the configuration is such that c is provided on the upper side in the vertical direction, this configuration is adopted as long as the argon gas and the external air flowing out from the gas outflow passage are sucked into the gas suction passage and the external air blocking function is obtained. be able to.

FIGS. 4 and 5 are schematic structural views showing a second embodiment of the stretching apparatus according to the present invention. This stretching apparatus differs from the stretching apparatus according to the first embodiment only in the configuration of the lower flange portion, and other configurations similar to those in the first embodiment are similar to the first embodiment in FIG. The same reference numerals as in the first embodiment denote the same parts, and a description thereof will be omitted.

The lower flange portion 70 in this stretching device
As shown in FIGS. 5A and 5B, the insertion port 70a
A gas outflow passage 70b and a gas suction passage 70c are formed so as to be arranged in a straight line in the radial direction, and each of the openings 70b 'and 70c' is formed with an insertion port 70a.
Are arranged to face each other.

Further, as shown in FIG. 5B, the pair of the gas outflow passage 70b and the gas suction passage 70c has a central angle θ (intersection angle) of 90 degrees in the circumferential direction, ie,
Two pairs are provided so as to be orthogonal. The central angle (crossing angle) in this case may be in the range of 0 degree <θ <180 degrees, but the most preferable convection is obtained when θ = 90 degrees. The relationship between the pair of the gas outflow passage 70b and the gas suction passage 70c is not limited to one pair and two pairs. For example, three pairs may be provided with the central angle θ being 60 degrees, and more pairs may be provided. May be provided. As shown in FIG. 5C, the gas outflow passage 70b and the gas suction passage 70b
It is more desirable that c and c are alternately arranged in the circumferential direction.
The adjustment of the valve 60 for adjusting the flow rate when the inert gas is supplied to the gas outflow passage 70b formed in the lower flange portion 70 can be performed manually as in the first embodiment. Alternatively, the flowmeter 62 may be provided with a function of transmitting a control signal, and the valve 60 may be provided with a function of receiving the control signal and automatically opening and closing the valve 60 itself. A signal may be transmitted to perform the operation automatically.

Further, the widths r and s in the region of the opening 70b 'of the gas outflow passage 70b and the widths t and u in the region of the opening 70c' of the gas suction passage 70c.
When the argon gas flowing out of each gas outflow passage 70b is sucked into each gas suction passage 70c, the space surrounded by the outer peripheral surface of the extension rod and the inner wall surface of the insertion port 70a is bisected in a plane. It is preferable to select the flow so that the flow is interrupted.

In the stretching apparatus having the above configuration, the optical fiber preform 1 can be stretched in the same procedure as in the first embodiment. The optical fiber preform 1 having an outer diameter of 50 to 200 mm was stretched using the stretching apparatus having the above-described configuration so that a stretch rod having an outer diameter of 10 to 150 mm was obtained. As a result, the stretch rod surface after the stretching process could be kept clean without being contaminated, and the life of the furnace tube 21 could be made 150 hours or more.

Further, in order to grasp the state of the air flow in the furnace tube 21 and in the area of the insertion port 70a in the stretching step, the visible laser light is applied by using a visualization device having a window through which the inside of the furnace body 20 can be observed. It was irradiated and observed. At this time, in order to facilitate observation, a silica powder was supplied as a tracer together with argon gas, and observation was performed. As a result, as shown in FIGS. 4 and 5, in the region of the lower flange portion 70, the respective gas outflow passages 70b are
The argon gas flowing out into a is sucked into the gas suction passages 70c adjacent to each other in the horizontal plane.
It was confirmed that the external air below the lower flange portion 70 was also sucked into the gas suction passage 70c. That is, it was confirmed that outside air was blocked from entering the furnace tube 21.

On the other hand, inside the furnace tube 21, part of the argon gas flowing out from the gas outflow passage 70 b of the lower flange 70 and the gas outflow passage 2 of the upper flange 23 are formed.
3b and a part of the argon gas flowing out is introduced,
In a space surrounded by the outer peripheral surface of the optical fiber preform 1 and the inner wall surface of the furnace tube 21, convection of argon gas occurs due to a temperature gradient as shown in FIG. Covering over a wide area was confirmed.

In the stretching apparatus of this embodiment, the optical fiber preform 1 is gripped and fixed by using a three-jaw chuck as in the first embodiment, but may be formed by using a collet chuck or the like. good. Although the optical fiber preform 1 is stretched without being rotated, the optical fiber preform 1 may be stretched while being rotated.

In the stretching apparatuses according to the first and second embodiments described above, the inert gas is allowed to flow into the core tube 21 from both upper and lower directions of the upper flange portion 23 and the lower flange portions 24 and 70. In the outside air (gas)
Gas suction passages 24c, 70 as blocking means for blocking the air.
However, the present invention is not limited to this. For example, as shown in Japanese Patent Application No. 2-6344, a structure is provided in which an inert gas flows out from a substantially central portion in the vertical direction of a reactor core tube. The blocking means according to the present invention can also be employed in the stretching apparatus.

That is, by providing a lower flange portion provided with a gas suction passage in the lower end region of the furnace tube, argon gas flowing vertically downward from a substantially central portion of the furnace tube is sucked and its velocity energy is reduced. Can be increased to antagonize external air rising into the furnace tube, and the rising external air can also be sucked into the gas suction passage.

[0046]

According to the apparatus for stretching an optical fiber preform according to the present invention described above, a shut-off means for shutting off the intrusion of an external gas, particularly air, is provided in the furnace tube. With the resulting ascending airflow, external air that is about to enter the furnace tube can be blocked, for example, in the lower end region of the furnace tube.

Thus, a favorable convection of the inert gas is obtained in the furnace tube, the inner wall of the furnace tube is covered with the inert gas, the oxidation of the furnace tube is suppressed, and the consumption of the furnace tube is reduced. Life can be extended. Further, since oxidation corrosion of the furnace tube is suppressed, generation of dust can be reduced, and contamination of the surface of the drawn rod that has been drawn can be prevented.

Further, according to the optical fiber preform stretching apparatus of the present invention, gas outflow passages through which inert gas flows out are provided at the upper and lower flanges provided at the upper end and the lower end of the furnace tube. At the same time, since the lower flange portion is provided with a gas suction passage as a shut-off means, by making a slight change from the conventional configuration, external air that is going to enter the core tube can be moved to the lower end region of the core tube. Can be shut off. Thereby, it is possible to achieve the above-described external air blocking function while achieving simplification of the structure.

By forming the opening of the gas outflow passage and the opening of the gas suction passage so as to face each other in the radial direction of the insertion port, it is possible to efficiently prevent external air from entering the furnace tube. Can be shut off.

Further, by forming the opening of the gas outflow passage and the opening of the gas suction passage so as to be arranged in the axial direction of the insertion port, external air can enter the furnace tube as described above. Can be efficiently blocked.

Further, regarding the relationship between the opening of the gas outflow passage and the opening of the gas suction passage, in the axial direction of the insertion port, the opening of the gas outflow passage is located on the upper side, and the opening of the gas suction passage is located on the lower side. , It is possible to more efficiently block external air from entering the furnace tube.

In the above optical fiber drawing apparatus, the lower flange portion is provided with a plurality of pairs including the opening of the gas outflow passage and the opening of the gas suction passage. And the outer peripheral surface of the extension rod can more reliably form a shut-off flow due to the inert gas, thereby making it possible to more efficiently shut off the intrusion of external air into the core tube in the entire region. it can.

[Brief description of the drawings]

FIG. 1 is a first view of an optical fiber preform stretching apparatus according to the present invention.
It is a schematic structure figure showing an embodiment.

FIGS. 2A and 2B show a lower flange portion of the optical fiber preform stretching device shown in FIG. 1, in which FIG. 2A is a longitudinal sectional view and FIG. 2B is an AA portion in FIG. Cross-sectional view at
(C) is a cross-sectional view taken along the line BB in (a).

FIG. 3 is a view showing another embodiment of the lower flange portion of the optical fiber preform stretching device shown in FIG. 1;
(A) is a longitudinal sectional view thereof, (b) is a transverse sectional view taken along a line CC in (a), and (c) is a transverse sectional view taken along a line DD in (a).

FIG. 4 is a second view of the optical fiber preform stretching apparatus according to the present invention.
It is a schematic structure figure showing an embodiment.

5A and 5B show a lower flange portion of the optical fiber preform stretching device shown in FIG. 4, wherein FIG. 5A is a longitudinal sectional view thereof, and FIGS. It is a cross-sectional view in the EE part.

FIG. 6 is a schematic configuration diagram showing a conventional optical fiber preform stretching apparatus.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Optical fiber preform 20 Furnace body 21 Furnace tube 22 Electric heater 23 Upper flange portion 23a Insertion port 23b Gas outflow passage 23b 'Opening 24 Lower flange portion 24a Insertion opening 24b Gas outflow passage 24b' Opening 24c Gas suction passage (Blocking means) 24c 'opening 24d annular passage 24d' opening 24e annular passage 24e 'opening 25 take-up support rod 30 upper driving unit 31 upper driving motor 40 lower driving unit 41 lower driving motor 50 outer diameter measuring instrument 51 Outer diameter setting device 53 Controller 60 Valve 61 Suction pump 62 Flow meter 63a Mass flow controller 63b Mass flow controller 70 Lower flange portion 70a Insertion port 70b Gas outflow passage 70b 'Opening 70c Gas suction passage 70c' Opening

Continued on the front page (72) Inventor Yukio Kamura 2-6-1 Marunouchi, Chiyoda-ku, Tokyo Furukawa Electric Co., Ltd. F-term (reference) 4G021 BA00

Claims (6)

[Claims] 1. An optical fiber preform is arranged in a furnace tube which is heated by a heating element and is arranged to extend in a substantially vertical direction, and the optical fiber preform is stretched while supplying an inert gas into the furnace tube. An apparatus for stretching an optical fiber preform, comprising: a blocking means for blocking entry of external gas into the furnace tube. 2. An upper end portion and a lower end portion of the core tube have an upper flange portion and a lower flange portion respectively defining an insertion port through which an optical fiber preform is inserted, and the upper flange portion and the lower flange portion. Has a gas outflow passage that opens toward each insertion opening and allows an inert gas to flow out, and the blocking means is formed in the lower flange portion and opens into the insertion opening to suck gas. 2. The optical fiber preform stretching apparatus according to claim 1, wherein the apparatus comprises a gas suction passage. 3. An opening of the gas outflow passage and an opening of the gas suction passage are formed so as to face each other in a radial direction of the insertion opening.
An apparatus for stretching an optical fiber preform according to the above. 4. The light according to claim 2, wherein the opening of the gas outflow passage and the opening of the gas suction passage are formed so as to be arranged in the axial direction of the insertion opening. Fiber preform drawing equipment. 5. The optical fiber according to claim 4, wherein, in the axial direction of the insertion port, the opening of the gas outflow passage is arranged on the upper side, and the opening of the gas suction passage is arranged on the lower side. Base material stretching device. 6. The optical fiber mother according to claim 3, wherein a plurality of pairs comprising an opening of the gas outflow passage and an opening of the gas suction passage are provided. Equipment for stretching materials.