JP7558894B2 - Optical fiber preform manufacturing apparatus and method for manufacturing optical fiber preform - Google Patents

Description

The present invention relates to an optical fiber preform manufacturing apparatus and an optical fiber preform manufacturing method.

Patent Document 1 describes a dehydration and sintering device for a porous glass base material, which heats the porous glass base material in a heating furnace by supplying gas for dehydration, etc. to the porous glass base material in the heating furnace. In the device described in Patent Document 1, an exhaust path for discharging the gas in the heating furnace to the outside of the heating furnace is provided with an aperture adjustment valve and a junction where a purge gas supply path joins between the heating furnace and the aperture adjustment valve. Patent Document 1 describes that by diluting the powder-containing gas discharged from the heating furnace with purge gas while passing through the aperture adjustment valve, powder is less likely to accumulate on the aperture adjustment valve, and blockage of the exhaust path can be prevented.

JP 2017-88458 A

However, in the device described in Patent Document 1, there is still a risk of clogging of the exhaust path due to the aperture adjustment valve located downstream of the junction where the purge gas supply paths join.

In view of the above-mentioned problems, the object of the present invention is to provide an optical fiber preform manufacturing apparatus and an optical fiber preform manufacturing method that can more reliably suppress or prevent clogging of the exhaust path.

According to one aspect of the present invention, there is provided an optical fiber preform manufacturing apparatus comprising: a heating furnace in which at least a halogen gas is supplied to heat a glass preform; and an exhaust path for exhausting gas inside the heating furnace to the outside of the heating furnace, the exhaust path having a first exhaust path connected to the heating furnace and a second exhaust path connected to the first exhaust path, the second exhaust path having a branch path for drawing in outside air, and the first exhaust path having a smaller diameter than the second exhaust path.

According to another aspect of the present invention, there is provided a method for manufacturing an optical fiber preform, comprising the steps of: heating a glass preform contained in a heating furnace while supplying at least a halogen gas into the heating furnace; discharging the gas in the heating furnace into a first exhaust path connected to the heating furnace; discharging the gas discharged from the first exhaust path into a second exhaust path connected to the first exhaust path; the second exhaust path has a branch path for drawing in outside air; and the first exhaust path has a smaller diameter than the second exhaust path.

The present invention makes it possible to more reliably suppress or prevent clogging of the exhaust path.

FIG. 1 is a schematic diagram showing an apparatus for manufacturing an optical fiber preform according to an embodiment of the present invention. FIG. 2 is a flow chart showing the operation of the apparatus for manufacturing an optical fiber preform according to the embodiment of the present invention.

[One embodiment]
An apparatus for manufacturing an optical fiber preform and a method for manufacturing an optical fiber preform according to an embodiment of the present invention will be described with reference to Fig. 1 and Fig. 2. Fig. 1 is a schematic diagram showing the apparatus for manufacturing an optical fiber preform according to the present embodiment. Fig. 2 is a flow chart showing the operation of the apparatus for manufacturing an optical fiber preform according to the present embodiment.

First, the configuration of the optical fiber preform manufacturing apparatus according to this embodiment will be described with reference to FIG. 1. The optical fiber preform manufacturing apparatus 10 according to this embodiment heats the optical fiber preform 12, which is a porous glass preform, to dehydrate the optical fiber preform 12, thereby manufacturing the dehydrated optical fiber preform 12.

As shown in FIG. 1, the optical fiber preform manufacturing apparatus 10 according to this embodiment has a heating furnace 14, a heating section 16, a heat insulating section 18, a gas introduction section 20, a fixing mechanism 22, a rotation mechanism 24, and an exhaust path 26. The exhaust path 26 has a first exhaust path 28 and a second exhaust path 30. Furthermore, the optical fiber preform manufacturing apparatus 10 has a pressure measuring section 32, an intake amount adjusting section 34, an exhaust amount adjusting section 36, and a control section 38.

The heating furnace 14 is a container into which at least halogen gas is supplied and in which the optical fiber preform 12, which is a glass preform, is heated. Inside the heating furnace 14, the optical fiber preform 12 is housed with its longitudinal axis aligned vertically, as described below. In addition, in the heating furnace 14, the optical fiber preform 12 is heated in a state in which the pressure inside the heating furnace 14 is positive relative to the atmospheric pressure outside the heating furnace 14, as described below.

The optical fiber preform 12 is a porous glass preform consisting of a soot deposit deposited by, for example, the VAD (Vapor phase Axial Deposition) method or the OVD (Outside Vapor Deposition) method. The optical fiber preform 12 obtained by the VAD method is formed by depositing soot, which is glass particles, on one end of a rod-shaped starting material in the axial direction. The optical fiber preform 12 obtained by the OVD method is formed by depositing soot on the outer periphery of a rod-shaped starting material.

The heating section 16 is installed around the side of the heating furnace 14. The heating section 16 is a heater that heats the heating furnace 14 and heats the optical fiber preform 12 contained inside the heating furnace 14. The insulating section 18 is installed around the side of the heating section 16 so as to cover the heating section 16. The insulating section 18 is an insulating material that suppresses or prevents the radiation of heat from the heating section 16 to the outside of the heating furnace 14, thereby allowing the heating section 16 to effectively heat the optical fiber preform 12.

The gas introduction unit 20 is connected to the bottom or lower end side of the heating furnace 14 so that the processing gas can be introduced into the heating furnace 14 from the lower part of the heating furnace 14, i.e., the bottom or lower end side of the heating furnace 14. The gas introduction unit 20 introduces the processing gas into the heating furnace 14 when the optical fiber preform 12 is heated. The processing gas contains a dehydration gas, which is a gas for dehydrating the optical fiber preform 12. The dehydration gas is, for example, a halogen gas such as chlorine gas. The processing gas may also contain a refractive index adjustment gas for adjusting the refractive index of the optical fiber preform. The refractive index adjustment gas is, for example, fluorine gas. In addition to these, the processing gas may contain an inert gas such as argon gas.

The fixing mechanism 22 is installed inside the heating furnace 14. Inside the heating furnace 14, the fixing mechanism 22 holds the upper end of the optical fiber preform 12 and fixes the optical fiber preform 12 in a suspended state so that the longitudinal direction of the optical fiber preform 12 is aligned vertically. For example, the fixing mechanism 22 can fix one end of the starting material on which the soot deposit of the optical fiber preform 12 is deposited, and fix the optical fiber preform 12 in a suspended state.

The rotation mechanism 24 is rotatably connected to the fixing mechanism 22 that fixes the optical fiber preform 12 and is installed at the top of the heating furnace 14. The rotation mechanism 24 rotates the fixing mechanism 22 so that the optical fiber preform 12 rotates around the central axis along the longitudinal direction of the optical fiber preform 12 fixed by the fixing mechanism 22 as the rotation axis.

The exhaust path 26 is a path for exhausting exhaust gas, which is gas discharged from inside the heating furnace 14, to the outside of the heating furnace 14. The exhaust path 26 has a first exhaust path 28 on the upstream side connected to the heating furnace 14, and a second exhaust path 30 on the downstream side connected to the first exhaust path 28.

The first exhaust path 28 and the second exhaust path 30 have different diameters. That is, the diameter of the first exhaust path 28 is smaller than the diameter of the second exhaust path 30. The ratio of the diameter of the first exhaust path 28 to the diameter of the second exhaust path 30 is preferably 0.2 to 0.5 from the viewpoint of suppressing or preventing clogging of the exhaust path 26, as described below.

The upstream end of the first exhaust path 28 is connected to the upper part of the heating furnace 14, i.e., the part above the center in the vertical direction of the heating furnace 14. The first exhaust path 28 and the second exhaust path 30 are connected to each other by inserting the downstream end of the first exhaust path 28 into the upstream end of the main path 30a (described later) of the second exhaust path 30 through the wall of the upstream end of the main path 30a. Therefore, the downstream end of the first exhaust path 28 is located inside the second exhaust path 30.

The first exhaust path 28 can be configured with an exhaust pipe. Specifically, the first exhaust path 28 can be configured with a bright annealing tube with an inner diameter of, for example, about 10 mm. By using such a bright annealing tube, clogging due to corrosion of the first exhaust path 28 can be suppressed or prevented. Note that the first exhaust path 28 is not provided with a flow rate adjustment unit such as a valve for adjusting the flow rate of the exhaust gas.

The second exhaust path 30 has a main path 30a and a branch path 30b branching off from the main path 30a. The second exhaust path 30, including the main path 30a and the branch path 30b, can be made of an exhaust pipe. Specifically, the temperature of the exhaust gas flowing through the second exhaust path 30 is reduced by introducing outside air from the branch path 30b, which will be described later, so the second exhaust path 30 can be made of, for example, an inexpensive hard polyvinyl chloride pipe. In addition, the second exhaust path 30 can be made of, for example, a Teflon (registered trademark) lined pipe to suppress or prevent the accumulation of deposits due to dust and the like on the inner surface.

The downstream end of the first exhaust path 28, which penetrates the wall at the upstream end of the trunk path 30a as described above, is inserted inside the upstream end of the trunk path 30a. The downstream end of the first exhaust path 28 inside the second exhaust path 30 is located downstream of the position where the branch path 30b branches off from the trunk path 30a. By positioning the downstream end of the first exhaust path 28 in this manner, the flow direction of the exhaust gas discharged from the downstream end of the first exhaust path 28 to the trunk path 30a can be aligned to the same direction as the flow direction of the outside air flowing through the trunk path 30a. This reduces or prevents turbulence that occurs in the flow of the exhaust gas discharged from the downstream end of the first exhaust path 28, thereby achieving smooth exhaust of the exhaust gas.

The downstream end of the first exhaust path 28 does not necessarily have to be inserted inside the upstream end of the main path 30a. The downstream end of the first exhaust path 28 and the upstream end of the main path 30a may be connected.

It is preferable that the first exhaust path 28 and the trunk path 30a are installed so as to be parallel to each other in the same direction. For example, it is preferable that the trunk path 30a is also installed so as to be parallel to the horizontal direction with respect to the first exhaust path 28 installed so as to be parallel to the heating furnace 14. By installing the first exhaust path 28 and the trunk path 30a so as to be parallel to each other in the same direction in this way, it is possible to suppress or prevent the stagnation of exhaust gas and suppress or prevent clogging of the first exhaust path 28 and the second exhaust path 30. Note that the first exhaust path 28 and the trunk path 30a may be installed so as to be parallel to each other in the same direction other than the horizontal direction. Furthermore, from the viewpoint of suppressing or preventing the stagnation of exhaust gas, it is preferable that the central axes of the longitudinal directions of the first exhaust path 28 and the trunk path 30a installed so as to be parallel to each other in the same direction coincide with each other.

The branch path 30b branches off from a predetermined position at the upstream end of the main path 30a. The branch path 30b is a path for drawing in outside air. That is, the branch path 30b is a path for introducing outside air into the second exhaust path 30 from the tip opposite to the base end branched from the main path 30a. Outside air is drawn in from the tip of the branch path 30b and introduced into the second exhaust path 30. For example, the branch path 30b is installed so that the tip faces upward along the vertical direction with respect to the main path 30a installed along the horizontal direction. Note that FIG. 1 shows a case where one branch path 30b branches off from the main path 30a, but multiple branch paths 30b may branch off from the main path 30a. The exhaust gas introduced into the main path 30a from the first exhaust path 28 is diluted by the outside air drawn in from the branch path 30b, so that condensation of the exhaust gas in the main path 30a can be suppressed or reduced.

The pressure measuring unit 32 is a pressure gauge installed to measure the pressure inside the first exhaust path 28. The pressure measuring unit 32 is preferably installed to measure the internal pressure on the side of the second exhaust path 30 of the first exhaust path 28, particularly the internal pressure at or near the connection part of the first exhaust path 28 with the second exhaust path 30. By measuring such pressure, it is possible to more reliably determine whether the pressure inside the first exhaust path 28 is positive pressure or not. The connection part of the first exhaust path 28 with the second exhaust path 30 is the part where the first exhaust path 28 is connected to the second exhaust path 30 through it. The pressure measuring unit 32 is connected to the control unit 38 so as to be able to communicate with the control unit 38. The pressure measuring unit 32 outputs an output signal indicating the value of the measured pressure to the control unit 38.

The intake amount adjustment unit 34 is an opening/closing valve installed at the tip of the branch path 30b in the second exhaust path 30, which is the intake port for outside air, and is an adjustment unit that can adjust the intake amount of outside air by adjusting the opening degree. The opening/closing valve that constitutes the intake amount adjustment unit 34 is, for example, an electric valve whose opening degree can be controlled. This opening/closing valve only allows outside air to pass through, but does not allow corrosive gases to pass through, so an inexpensive ball valve, butterfly valve, etc. can be used. The intake amount adjustment unit 34 is controllably connected to the control unit 38. The intake amount adjustment unit 34 adjusts the intake amount of outside air that is sucked in from the tip of the branch path 30b according to the control by the control unit 38.

The exhaust amount adjustment unit 36 is an opening/closing valve installed in the main path 30a of the second exhaust path 30, and is an adjustment unit that can adjust the amount of exhaust of outside air by adjusting its opening. The exhaust amount adjustment unit 36 is installed in the main path 30a at a position downstream of the downstream end of the first exhaust path 28 inserted inside the main path 30a. The exhaust amount adjustment unit 36 adjusts the amount of exhaust from the downstream end of the main path 30a. The exhaust amount adjustment unit 36 may also be controllably connected to the control unit 38. In this case, the exhaust amount adjustment unit 36 adjusts the amount of exhaust from the downstream end of the main path 30a according to the control by the control unit 38. Note that the exhaust amount adjustment unit 36 does not necessarily have to be provided, and can be provided as appropriate depending on whether or not adjustment of the exhaust amount is required.

An exhaust gas treatment device 40 is connected to the downstream end of the main path 30a of the second exhaust path 30. The exhaust gas treatment device 40 performs a predetermined process on the exhaust gas, such as removing harmful gases, and is, for example, a scrubber. The exhaust gas treatment device 40 can suck in the exhaust gas exhausted from the downstream end of the main path 30a and remove harmful gases from the exhaust gas. The exhaust gas treatment device 40 discharges the exhaust gas from which harmful gases have been removed into the atmosphere.

The control unit 38 is a control device that manages and controls each part of the manufacturing apparatus 10 while the optical fiber preform 12 is being dehydrated. The control unit 38 may be composed of a single control device, or may be composed of multiple control devices installed for each control target.

Specifically, the control unit 38 can control the gas introduction unit 20 to control the flow rate of the processing gas introduced into the heating furnace 14, the timing of introducing the processing gas, etc. The control unit 38 can also control the heating unit 16 to control the temperature, time, etc. for heating the optical fiber preform 12. The control unit 38 can also control the rotation mechanism 24 to control the rotation speed of the fixing mechanism 22 that fixes the optical fiber preform 12.

The control unit 38 can also control the amount of outside air drawn in from the branch path 30b by controlling the suction amount adjustment unit 34 based on the pressure measured by the pressure measurement unit 32. That is, the control unit 38 can control the amount of outside air drawn in from the tip of the branch path 30b by controlling the suction amount adjustment unit 34 based on the output signal indicating the pressure value inside the first exhaust path 28 received from the pressure measurement unit 32.

In this way, the manufacturing apparatus 10 according to this embodiment is configured to perform a dehydration process on the optical fiber preform 12.

Next, the method for manufacturing an optical fiber preform using the manufacturing apparatus 10 according to this embodiment will be further explained with reference to FIG. 2.

As shown in FIG. 2, the manufacturing apparatus 10 starts the dehydration process of the optical fiber preform 12 fixed by the fixing mechanism 22 (step S102). When starting the dehydration process of the optical fiber preform 12, the exhaust amount adjustment unit 36 adjusts the exhaust gas to be exhausted from the downstream end of the trunk path 30a of the second exhaust path 30 at a predetermined exhaust amount. The control unit 38 also controls the gas introduction unit 20 to start introducing the processing gas into the heating furnace 14 by the gas introduction unit 20. The control unit 38 also controls the heating unit 16 to start heating the optical fiber preform 12 by the heating unit 16. The control unit 38 also controls the rotation mechanism 24 to start rotating the fixing mechanism 22 and the optical fiber preform 12 fixed thereto by the rotation mechanism 24. In this way, the dehydration process of the optical fiber preform 12 by heating is started inside the heating furnace 14. In the dehydration process, the optical fiber preform 12 accommodated inside the heating furnace 14 is heated while supplying a processing gas containing at least halogen gas into the heating furnace 14.

When the dehydration process of the optical fiber preform 12 is started as described above, dust is generated inside the heating furnace 14 due to a reaction between the halogen gas in the processing gas and the optical fiber preform 12. During the dehydration process, the pressure inside the heating furnace 14 is kept positive relative to the outside air outside the heating furnace 14. Exhaust gas containing dust is discharged from the inside of the heating furnace 14, where the pressure is kept positive, into the first exhaust path 28.

The exhaust gas discharged into the first exhaust path 28 flows from upstream to downstream through the first exhaust path 28, and is then discharged and introduced into the main path 30a of the second exhaust path 30. The exhaust gas introduced into the main path 30a flows from upstream to downstream through the main path 30a while being diluted by outside air drawn in from the branch path 30b, and is then discharged into the exhaust gas treatment device 40. The exhaust gas treatment device 40 performs a predetermined treatment on the exhaust gas discharged from the main path 30a, such as removing harmful gases, and then discharges the exhaust gas into the atmosphere. In this way, the exhaust gas discharged from the heating furnace 14 is discharged into the atmosphere through the exhaust path 26, which includes the first exhaust path 28 and the second exhaust path 30.

In this embodiment, the diameter of the first exhaust path 28 is smaller than the diameter of the second exhaust path 30. By including the first exhaust path 28, which has a small diameter and a relatively large pressure loss, in the exhaust path 26, the pressure inside the heating furnace 14 can be kept positive and backflow of exhaust gas from the second exhaust path 30 to the first exhaust path 28 can be prevented.

In addition, in this embodiment, in the second exhaust path 30, the exhaust gas is diluted by the outside air drawn in from the branch path 30b. As a result, the flow rate of the exhaust gas flowing through the first exhaust path 28 and the second exhaust path 30 increases, making it possible to make the first exhaust path 28 and the second exhaust path 30 less likely to become clogged.

Furthermore, in this embodiment, in the exhaust path 26, no valves for adjusting the flow rate, which can cause clogging, are installed in either the first exhaust path 28 or the main path 30a of the second exhaust path 30 through which the exhaust gas flows. Therefore, clogging of the first exhaust path 28 and the second exhaust path 30 can be suppressed or prevented.

The pressure measuring unit 32 measures the pressure inside the first exhaust path 28 during the dehydration process of the optical fiber preform 12 (step S104). The pressure measuring unit 32 transmits an output signal indicating the measured pressure value to the control unit 38.

Based on the output signal transmitted from the pressure measuring unit 32, the control unit 38 determines whether the pressure value inside the first exhaust path 28 is a predetermined value (step S106). For example, the control unit 38 can determine whether the pressure value inside the first exhaust path 28 is 100 Pa. At a high pressure exceeding 100 Pa, the heating furnace 14 may be damaged during heating, so it is preferable to control the pressure inside the first exhaust path 28 to about 100 Pa. Note that instead of determining whether the pressure value inside the first exhaust path 28 is a predetermined target value, the control unit 38 can also determine whether the pressure value inside the first exhaust path 28 is within a predetermined target value range.

When the control unit 38 determines that the pressure value inside the first exhaust path 28 is not the predetermined target value (step S106, NO), it controls the suction amount adjustment unit 34 to adjust the amount of outside air sucked in from the tip of the branch path 30b by the suction amount adjustment unit 34 (step S108). The control unit 38 adjusts the amount of outside air sucked in by the suction amount adjustment unit 34 so that the pressure value inside the first exhaust path 28 becomes the predetermined target value. By controlling the pressure inside the first exhaust path 28, the control unit 38 can also control the pressure inside the heating furnace 14, which is correlated with the pressure inside the first exhaust path 28.

The greater the amount of outside air that is sucked in, the more diluted the exhaust gas flowing through the main path 30a of the second exhaust path 30 becomes, and the faster the flow rate of the exhaust gas becomes. As a result, the pressure inside the first exhaust path 28 connected to the main path 30a decreases. Therefore, when the value of the pressure inside the first exhaust path 28 is smaller than a predetermined target value, the control unit 38 adjusts the amount of outside air sucked in by the suction amount adjustment unit 34 so that the amount of outside air sucked in becomes larger. On the other hand, when the value of the pressure inside the first exhaust path 28 is larger than the predetermined target value, the control unit 38 adjusts the amount of outside air sucked in by the suction amount adjustment unit 34 so that the amount of outside air sucked in becomes smaller.

In this embodiment, no valve for adjusting pressure is installed in the first exhaust path 28, and the pressure is adjusted by adjusting the amount of outside air taken in by the intake amount adjuster 34 installed at the tip of the branch path 30b, which is the outside air intake port. In this way, because no valve that could cause clogging is installed in the first exhaust path 28, clogging of the exhaust path 26 can be suppressed or prevented.

On the other hand, when the control unit 38 determines that the pressure value inside the first exhaust path 28 is the predetermined target value (step S106, YES), it determines whether or not to terminate the dehydration process of the optical fiber preform 12 (step S110). For example, the control unit 38 can determine whether or not to terminate the dehydration process based on the result of detecting the weight change of the optical fiber preform 12, the elapsed time from the start of the dehydration process, etc.

The control unit 38 also determines whether or not to terminate the dehydration process of the optical fiber preform 12 after adjusting the suction amount in step S108 (step S110).

When the control unit 38 determines to continue the dehydration process of the optical fiber preform 12 (step S110, NO), the control unit 38 proceeds to step S104 and executes the processes from step S104 onward. In this way, the control unit 38 continues the dehydration process of the optical fiber preform 12 while adjusting the amount of outside air sucked in from the branch path 30b.

On the other hand, when the control unit 38 determines that the dehydration process of the optical fiber preform 12 is to be terminated (step S110, YES), it stops the operation of each part of the manufacturing apparatus 10 and terminates the dehydration process of the optical fiber preform 12. In this way, the optical fiber preform 12 that has been dehydrated by the dehydration process is manufactured.

In this way, according to this embodiment, clogging of the exhaust path 26 including the first exhaust path 28 and the second exhaust path 30 can be more reliably suppressed or prevented. Since clogging of the exhaust path 26 can be more reliably suppressed or prevented, according to this embodiment, the pressure inside the heating furnace 14 can be controlled with higher precision. Therefore, according to this embodiment, a dehydrated optical fiber preform 12 can be manufactured with high quality.

[Modified embodiment]
The present invention is not limited to the above-described embodiment, and various modifications are possible.

For example, in the above embodiment, the dehydration process of the optical fiber preform 12 is performed in the heating furnace 14, but the present invention is not limited to this. The heating furnace 14 can also be configured to perform a sintering process to convert the optical fiber preform 12 into transparent glass following the dehydration process.

In addition, in the above embodiment, a case where one exhaust path 26 is connected to the heating furnace 14 has been described as an example, but this is not limited to this. Multiple exhaust paths may be connected to the heating furnace 14. In this case, all or part of the multiple exhaust paths may be configured in the same manner as the exhaust path 26.

10... Optical fiber preform manufacturing apparatus 12... Optical fiber preform 14... Heating furnace 16... Heating section 18... Insulation section 20... Gas introduction section 22... Fixing mechanism 24... Rotation mechanism 26... Exhaust path 28... First exhaust path 30... Second exhaust path 30a... Main path 30b... Branch path 32... Pressure measurement section 34... Intake amount adjustment section 36... Exhaust amount adjustment section 38... Control section 40... Exhaust gas treatment device

Claims (8)

a heating furnace in which at least a halogen gas is supplied and in which the glass base material is heated;
an exhaust path for exhausting the gas inside the heating furnace to the outside of the heating furnace;
the exhaust path includes a first exhaust path connected to the heating furnace and a second exhaust path connected to the first exhaust path,
the second exhaust path has a branch path for drawing in outside air,
The apparatus for manufacturing an optical fiber preform, wherein the first exhaust path has a smaller diameter than the second exhaust path. A measurement unit that measures a pressure in the first exhaust path;
an adjustment unit that adjusts the amount of the outside air taken in through the branch path;
2. The optical fiber preform manufacturing apparatus according to claim 1, further comprising: a control unit that controls the adjustment unit based on the pressure measured by the measurement unit to control the amount of the outside air that is sucked in. 3. The optical fiber preform manufacturing apparatus according to claim 1, wherein the first exhaust path is configured so that a pressure in the first exhaust path is a positive pressure relative to a pressure outside the heating furnace. The optical fiber preform manufacturing apparatus according to any one of claims 1 to 3, characterized in that no valve is installed in the first exhaust path. 5. The apparatus for manufacturing an optical fiber preform according to claim 1, wherein a downstream end of the first exhaust path is located downstream of the branch path inside the second exhaust path. the second exhaust path has a trunk path to which the first exhaust path is connected,
the first exhaust path is connected to the main path,
6. The apparatus for manufacturing an optical fiber preform according to claim 1, wherein the first exhaust path and the trunk path are arranged along the same direction. Heating the glass base material accommodated in the heating furnace while supplying at least a halogen gas into the heating furnace;
Discharging the gas inside the heating furnace to a first exhaust path connected to the heating furnace;
The gas discharged from the first exhaust path is discharged to a second exhaust path connected to the first exhaust path;
the second exhaust path has a branch path for drawing in outside air,
The method for manufacturing an optical fiber preform, wherein the first exhaust path has a smaller diameter than the second exhaust path. measuring a pressure in the first exhaust path;
8. The method for manufacturing an optical fiber preform according to claim 7, further comprising controlling an amount of the outside air to be sucked in based on the measured pressure.

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