Optical fiber manufacturing method

Abstract

To provide a method for manufacturing an optical fiber, capable of suppressing variation in an outside diameter in the longitudinal direction of the optical fiber.SOLUTION: A method for manufacturing an optical fiber includes using an optical fiber manufacturing apparatus. The optical fiber manufacturing apparatus includes: a rod including an optical fiber preform fixed to a lower end; a shield pipe surrounding the rod; a seal part arranged to have a space with the shield pipe in the shield pipe and penetrated by the rod; a spinning furnace including a heater for heating the optical fiber preform and formed in a hollow vessel shape; and a gas introduction port provided in the spinning furnace. When heating the optical fiber preform to melt and spin the optical fiber preform, gas is introduced into the spinning furnace from the gas introduction port and at least a part of the gas is discharged from the space to the outside of the shield pipe; and a pressure loss occurring in the gas in the space is 95 Pa or more.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing an optical fiber. [Background technology]

[0002] Patent Document 1 discloses a method for manufacturing an optical fiber using an optical fiber manufacturing apparatus. The optical fiber manufacturing apparatus includes a rod (delivery rod) to which an optical fiber preform is attached, a shield pipe surrounding the rod, a seal part (sealing member) through which the rod passes, a spinning furnace (heating furnace for spinning), and a gas inlet provided in the spinning furnace. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-6960 Summary of the Invention [Problem to be solved by the invention]

[0004] When an optical fiber preform is melt-spun in a spinning furnace, an inert gas is generally introduced into the spinning furnace. In the optical fiber manufacturing method described in Patent Document 1, at least a portion of the inert gas introduced into the spinning furnace flows from the inside of the spinning furnace into the inside of the shield pipe. The inert gas is then discharged to the outside of the optical fiber manufacturing apparatus through a gap formed between the seal portion and the shield pipe.

[0005] In such an optical fiber manufacturing method, the amount of inert gas that passes through the gap formed between the seal portion and the shield pipe and is discharged to the outside of the optical fiber manufacturing apparatus can become unstable. If the amount of discharged inert gas becomes unstable, the flow of inert gas inside the spinning furnace becomes turbulent, which tends to cause the optical fiber preform to melt non-uniformly. Non-uniform melting of the optical fiber preform can cause fluctuations in the outer diameter of the optical fiber.

[0006] The present invention has been made in consideration of the above circumstances, and has as its object to provide a method for manufacturing an optical fiber that can suppress fluctuations in the outer diameter of the optical fiber. [Means for solving the problem]

[0007] In order to solve the above problem, one embodiment of the present invention provides a method for manufacturing an optical fiber using an optical fiber manufacturing apparatus, the optical fiber manufacturing apparatus comprising: a rod having an optical fiber preform fixed to its lower end; a shield pipe surrounding the rod; a sealing portion arranged within the shield pipe with a gap between it and the shield pipe and through which the rod passes; a spinning furnace formed in the shape of a hollow container and having a heater for heating the optical fiber preform; and a gas inlet provided in the spinning furnace, wherein when the optical fiber preform is heated by the heater to melt-spin the optical fiber preform, gas is introduced into the spinning furnace from the gas inlet, and at least a portion of the gas is discharged outside the shield pipe through the gap, and a pressure loss of the gas in the gap is 95 Pa or more. [Effects of the Invention]

[0008] According to the above aspect of the present invention, it is possible to provide a method for manufacturing an optical fiber that can suppress fluctuations in the outer diameter of the optical fiber. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a partial cross-sectional view showing an optical fiber manufacturing apparatus used in the optical fiber manufacturing method according to the first embodiment. [Figure 2] FIG. 10 is a partial cross-sectional view showing an optical fiber manufacturing apparatus used in the optical fiber manufacturing method according to the second embodiment. [Figure 3] FIG. 2 is a diagram showing manufacturing conditions set in the manufacturing methods of optical fibers according to the examples and comparative examples. DETAILED DESCRIPTION OF THE INVENTION

[0010] (First embodiment) An optical fiber manufacturing method and an optical fiber manufacturing apparatus according to a first embodiment will be described below with reference to the drawings. 1, the optical fiber manufacturing apparatus 1A includes a rod 10, a shield pipe 20 surrounding the rod 10, a sealing section 30 through which the rod 10 passes, and a spinning furnace 40. The rod 10 has a first end 10a and a second end 10b. An optical fiber preform M is fixed to the first end 10a of the rod 10.

[0011] (direction definition) Here, in this embodiment, the direction parallel to the central axis O of the rod 10 (Z direction) is referred to as the axial direction Z. The direction from the first end 10a to the second end 10b of the rod 10 along the axial direction Z (+Z direction) is referred to as the upward direction, and the direction opposite to the upward direction (-Z direction) is referred to as the downward direction. A cross section perpendicular to the axial direction Z is referred to as a transverse cross section. A direction perpendicular to the central axis O of the rod 10 is referred to as a radial direction. A direction approaching the central axis O along the radial direction is referred to as a radially inner direction, and a direction away from the central axis O is referred to as a radially outer direction. A direction going around the central axis O as viewed from the axial direction Z is referred to as a circumferential direction.

[0012] (Optical fiber manufacturing equipment) The rod 10 extends along the axial direction Z. The rod 10 according to this embodiment has a substantially circular shape in cross section. An optical fiber preform M is attached to a first end 10a of the rod 10. A second end 10b of the rod 10 is supported by a support mechanism 50 (support portion 51). Hereinafter, in this specification, the first end 10a of the rod 10 may be referred to as the lower end 10a of the rod 10, and the second end 10b of the rod 10 may be referred to as the upper end 10b of the rod 10.

[0013] The support mechanism 50 has a support part 51 that supports the rod 10, and a lifting mechanism 52 connected to the support part 51. The lifting mechanism 52 can move the rod 10 (and the seal part 30) along the axial direction Z via the support part 51. Note that the configuration of the lifting mechanism 52 may be changed as appropriate as long as the support part 51 can be moved along the axial direction Z.

[0014] The optical fiber preform M is mainly made of glass. The optical fiber F is obtained by melt-spinning the optical fiber preform M. The optical fiber preform M has a portion that will become the core and a portion that will become the cladding of the optical fiber F. The optical fiber preform M can be formed, for example, by subjecting an untreated preform (porous glass) to processes such as sintering, dehydration, and doping.

[0015] The shield pipe 20 has a cylindrical shape and extends along the axial direction Z. The shield pipe 20 is located radially outside the rod 10 and surrounds the rod 10. In this embodiment, the inner diameter of the shield pipe 20 is approximately constant along the axial direction Z.

[0016] The seal portion 30 is disposed inside the shield pipe 20. In this embodiment, the seal portion 30 is fixed to the rod 10 by a fixing mechanism (not shown). Note that the configuration of the fixing mechanism may be changed as appropriate as long as it has a structure that allows the seal portion 30 to be fixed to the rod 10.

[0017] The seal portion 30 has a seal main body 33, a first sleeve 31, and a second sleeve 32. In this embodiment, the seal main body 33 is formed in a cylindrical shape. A through hole 33a that penetrates the seal main body 33 along the axial direction Z is formed in the radial center of the seal main body 33. The rod 10 penetrates the through hole 33a of the seal main body 33.

[0018] The first sleeve 31 and the second sleeve 32 are each a cylindrical member that surrounds the rod 10 from the outside in the radial direction. The first sleeve 31 extends upward from the seal main body 33. The second sleeve 32 extends downward from the seal main body 33. In the example of FIG. 1 in particular, the outer diameter of the seal portion 30 is approximately constant along the axial direction Z.

[0019] 1, the first sleeve 31 and the second sleeve 32 are formed separately from the seal main body 33. The material of the first sleeve 31 and the second sleeve 32 may be, for example, carbon. Alternatively, the first sleeve 31 and the second sleeve 32 and the seal main body 33 may be formed integrally.

[0020] A gap G1 is provided between the seal portion 30 and the shield pipe 20 in the radial direction. In this embodiment, the size of the gap G1 is approximately constant throughout the seal portion 30 in the axial direction Z. The size of the gap G1 is also approximately constant in the circumferential direction. However, the sizes of the gap G1 in the axial direction Z and the circumferential direction do not have to be approximately constant.

[0021] The seal portion 30 serves to adjust the flow rate of gas discharged upward from the shield pipe 20. Due to the presence of a gap G1 between the seal portion 30 and the shield pipe 20, some of the gas leaks upward from the seal portion 30 through the gap G1.

[0022] The spinning furnace 40 is connected to the lower end of the shield pipe 20. The spinning furnace 40 is formed in the shape of a hollow cylindrical container. In this embodiment, a portion of the space S2 surrounded by the shield pipe 20, which is located below the seal unit 30, communicates with the space S4 inside the spinning furnace 40. Note that the space S2 and the space S4 do not have to communicate with each other. For example, a second seal unit may be provided at the upper end of the spinning furnace 40, and the space S2 and the space S4 may be separated by the second seal unit. The second seal unit may be provided at the lower end of the shield pipe 20.

[0023] The spinning furnace 40 has a heater 41 that heats the optical fiber preform M. The optical fiber preform M is heated by the heater 41 and melt-spun downward. In this embodiment, the heater 41 has a cylindrical shape and is arranged to surround the space S4 in the spinning furnace 40 in the circumferential direction. The heater 41 may be, for example, an electric heater. Although only one heater 41 is provided in this embodiment, multiple heaters 41 may be provided. In this case, the multiple heaters 41 may surround the space S4 in the circumferential direction. Furthermore, the multiple heaters 41 may be arranged side by side in the axial direction Z.

[0024] The spinning furnace 40 is provided with gas inlets 42 for introducing an inert gas (such as argon) into the space S4 within the spinning furnace 40. In the example of Fig. 1, two gas inlets 42 are provided. The number of gas inlets 42 can be changed as appropriate, and the number of gas inlets 42 is not limited as long as it is one or more.

[0025] The spinning furnace 40 is provided with a drawing port 43 for drawing out the melt-spun optical fiber preform M (optical fiber F). In this embodiment, the drawing port 43 is formed on the bottom surface of the spinning furnace 40.

[0026] In addition to the above-described configuration, the optical fiber manufacturing apparatus 1A according to this embodiment may also include an outer diameter measuring unit, a cooling unit, a coating unit, a hardening unit, a take-up unit, a winding unit, and the like, which are not shown. The position measuring unit measures the outer diameter of the optical fiber F. The cooling unit cools the optical fiber F. The coating unit forms a coating layer on the outer periphery of the optical fiber F by applying (coating) a coating material to the optical fiber F. If the coating material applied to the optical fiber F is an ultraviolet-curable resin, the hardening unit hardens the coating layer by irradiating the resin with ultraviolet light. The take-up unit takes up the optical fiber F and directs it toward the winding unit. The winding unit winds the optical fiber around a drum. It should be noted that known configurations can be adopted for the outer diameter measuring unit, cooling unit, coating unit, hardening unit, and take-up unit described above.

[0027] In this specification, for example, "substantially circular" includes cases where the shape can be considered circular if manufacturing errors are removed. Similarly, "substantially identical" includes cases where the shape can be considered identical if manufacturing errors are removed.

[0028] (Optical fiber manufacturing method) Next, an example of a method for manufacturing an optical fiber according to this embodiment will be described. In the method for manufacturing an optical fiber according to this embodiment, the optical fiber F is manufactured using the optical fiber manufacturing apparatus 1A configured as described above.

[0029] First, an optical fiber preform M is fixed to the lower end of a rod 10. For example, the rod 10 may be used as a starting member, and glass particles may be deposited directly around the rod 10. Alternatively, an optical fiber preform M separate from the rod 10 may be prepared, and the optical fiber preform M may be attached to the rod 10. Next, the rod 10 (optical fiber preform M) is inserted into the spinning furnace 40 from above by the lifting mechanism 52.

[0030] Next, the optical fiber preform M is melt-spun in the spinning furnace 40. At this time, the optical fiber preform M can be moved along the axial direction Z by the lifting mechanism 52. This makes it possible to adjust the relative distance between the heater 41 and the optical fiber preform M, and to adjust the amount of heat applied to the optical fiber preform M. By melt-spinning the optical fiber preform M, an optical fiber F is obtained.

[0031] When melt-spinning the optical fiber preform M, an inert gas is introduced into the space S4 in the spinning furnace 40 through the gas inlet 42. The inert gas is continuously introduced. This makes it possible to suppress deterioration of the spinning furnace 40, to suppress the intrusion of impurities into the spinning furnace 40, and to maintain the flow of gas in the spinning furnace 40.

[0032] The inert gas supplied to space S4 is discharged to the outside of the optical fiber manufacturing apparatus 1A through either the first path or the second path described below. The first path is a path in which the gas flows upward from space S4 to reach space S2, and is then discharged to the outside through gap G1 formed between seal portion 30 and shield pipe 20. On the other hand, the second path is a path in which the gas flows downward from space S4, passes through outlet 43, and is discharged to the outside. Note that the amount of gas leaking from the sliding surface between through hole 33a of seal main body 33 and rod 10 is negligibly small compared to the amount of gas discharged through the two paths described above.

[0033] Incidentally, if the amount of gas discharged to the outside of the optical fiber manufacturing apparatus 1A becomes unstable, the gas flow becomes turbulent in the space S4 within the spinning furnace 40. If the gas flow becomes turbulent in the space S4, the optical fiber preform M is likely to melt non-uniformly. Such non-uniform melting of the optical fiber preform M can cause fluctuations in the outer diameter of the optical fiber F. As a result of extensive research, the inventors of the present application have found that instability in the amount of gas discharged to the outside, particularly via the first path (gap G1), is likely to cause fluctuations in the outer diameter of the optical fiber F.

[0034] Therefore, in the optical fiber manufacturing method according to this embodiment, when the optical fiber preform M is melt-spun, the pressure loss generated in the gas in the gap G1 is set to 95 Pa or more. By increasing the pressure loss generated in the gas by the gap G1 to a certain extent in this way, the amount of gas discharged to the outside through the gap G1 is reduced, and the change over time in the amount of gas discharged to the outside through the gap G1 is suppressed. Therefore, turbulence in the gas flow in the space S4 is suppressed, and fluctuations in the outer diameter of the optical fiber F are suppressed.

[0035] It is advisable to consider the inner diameter of the shield pipe 20, the outer diameter of the seal main body 33, the dimensions of the seal portion 30 in the axial direction Z, and the like so that the pressure loss of the gas occurring in the gap G1 is 95 Pa or more. Similarly, the flow rate of the inert gas introduced from the gas inlet 42 may be adjusted. Alternatively, the flow rate of the inert gas introduced from the gas inlet 42 may be controlled based on the actual measured value of the pressure loss in the gap G1. In this case, a pressure measuring device (such as a pressure sensor) (not shown) may be provided in the gap G1 or near the gap G1.

[0036] Here, because the first sleeve 31 extends upward from the seal main body 33, the flow of gas being discharged upward from the gap G1 can be regulated. In other words, the formation of turbulent gas flow in the portion of the space S2 located above the seal portion 30 can be suppressed. Similarly, because the second sleeve 32 extends downward from the seal main body 33, the flow of gas flowing into the gap G1 can be regulated. In other words, the formation of turbulent gas flow in the portion of the space S2 located below the seal portion 30 can be suppressed. This makes the amount of gas passing through the gap G1 more stable, and makes it possible to further suppress fluctuations in the outer diameter of the optical fiber F.

[0037] Furthermore, the gas that flows out upward from the gap G1 is cooled by the atmosphere. Therefore, once the gas flows out, it descends as it is cooled, and there is a possibility that it may accumulate in a portion of the space S2 that is located above the seal portion 30. In contrast, in the optical fiber manufacturing apparatus 1A according to this embodiment, the first sleeve 31 extends upward from the seal main body 33, so that the cooled gas is more likely to accumulate in the region where the inner circumferential surface of the first sleeve 31 and the rod 10 face each other. This prevents the accumulated gas from flowing back from the gap G1. Therefore, fluctuations in the outer diameter of the optical fiber F can be more reliably suppressed.

[0038] The optical fiber F obtained by melt-spinning the optical fiber preform M is drawn out of the spinning furnace 40 through the drawing outlet 43. Thereafter, the optical fiber F may be subjected to outer diameter measurement, cooling, coating, hardening, drawing, etc.

[0039] As described above, the optical fiber manufacturing method according to this embodiment is a method for manufacturing an optical fiber F using an optical fiber manufacturing apparatus 1A, and the optical fiber manufacturing apparatus 1A includes a rod 10 having an optical fiber preform M fixed to a lower end 10a thereof, a shield pipe 20 surrounding the rod 10, a sealing portion 30 arranged within the shield pipe 20 with a gap G1 between the rod 10 and the shield pipe 20 and through which the rod 10 passes, a spinning furnace 40 formed in the shape of a hollow container and having a heater 41 for heating the optical fiber preform M, and a gas inlet 42 provided in the spinning furnace 40, and when the optical fiber preform M is heated by the heater 41 to melt-spin the optical fiber preform M, gas is introduced into the spinning furnace 40 from the gas inlet 42 and at least a part of the gas is discharged to the outside of the shield pipe 20 through the gap G1, and the pressure loss of the gas in the gap G1 is 95 Pa or more.

[0040] In this way, by increasing the pressure loss of the gas in the gap G1 to a certain extent, the flow rate of the gas that passes through the gap G1 and is discharged to the outside is reduced. Furthermore, a small gas flow rate can also reduce the change in the flow rate over time. Therefore, turbulence of the gas flow in the space S4 is suppressed, and fluctuations in the outer diameter of the optical fiber F are suppressed.

[0041] The seal portion 30 also has a seal body 33 through which the rod 10 passes, and a first sleeve 31 extending upward from the seal body 33. This configuration can prevent the inert gas being discharged from the gap G1 from forming a turbulent flow. It can also prevent the inert gas from flowing back from the gap G1. This further reduces fluctuations in the outer diameter of the optical fiber F.

[0042] The seal portion 30 also has a seal body 33 through which the rod 10 passes, and a second sleeve 32 extending downward from the seal body 33. This configuration can prevent the inert gas flowing into the gap G1 from forming a turbulent flow. Therefore, fluctuations in the outer diameter of the optical fiber F are further suppressed.

[0043] Furthermore, the portion of the space S2 surrounded by the shield pipe 20 that is located below the sealing unit 30 communicates with the space S4 inside the spinning furnace 40. With this configuration, the structure of the optical fiber manufacturing apparatus 1A can be simplified compared to, for example, a case where the second sealing unit is provided at the upper end of the spinning furnace 40.

[0044] (Second embodiment) Next, a second embodiment will be described, but the basic configuration is similar to that of the first embodiment. Therefore, the same components are given the same reference numerals, and the description thereof will be omitted, and only the differences will be described. In the optical fiber manufacturing apparatus 1B shown in FIG. 2, the support mechanism 50 has an alignment mechanism 53. The seal portion 30 is fixed to the rod 10 by a fixing mechanism (not shown). A gap G1 is provided between the seal portion 30 and the shield pipe 20, as in the first embodiment. A gap G2 is formed in the radial direction between the rod 10 and the seal portion 30 (seal main body portion 33). The seal portion 30 is provided with an auxiliary seal portion 60.

[0045] The aligning mechanism 53 can move the rod 10 in a direction (radial direction) perpendicular to the axial direction Z via the support part 51. More specifically, the aligning mechanism 53 can move the rod 10 in a direction perpendicular to the axial direction Z within the range of the gap G2.

[0046] The auxiliary seal portion 60 surrounds the rod 10 from the radial outside. The auxiliary seal portion 60 is configured so as not to move away from the seal portion 30 in the axial direction Z. On the other hand, the auxiliary seal portion 60 is configured so as to be movable relative to the seal portion 30 in a direction perpendicular to the axial direction Z (radial direction). Therefore, when the rod 10 moves in a direction perpendicular to the axial direction Z, the auxiliary seal portion 60 moves relative to the rod 10 and the seal portion 30.

[0047] In this embodiment, the auxiliary seal part 60 has a guide part 61 and a sliding part 62. The guide part 61 extends upward from the sliding part 62. The auxiliary seal part 60 does not necessarily have to have the guide part 61. The inner circumferential surface of the guide part 61 and the inner circumferential surface of the sliding part 62 each abut against the rod 10. When the rod 10 moves along the axial direction Z, the rod 10 slides against the inner circumferential surface of the guide part 61 and the inner circumferential surface of the sliding part 62. The amount of gas leaking from the sliding surface between the rod 10 and the sliding part 62 and the sliding surface between the rod 10 and the guide part 61 is negligibly small compared to the amount of gas discharged through the gap G1.

[0048] The upper surface of the sliding portion 62 abuts against the lower surface of the seal body 33. When the rod 10 moves in a direction perpendicular to the axial direction Z, the upper surface of the sliding portion 62 slides against the lower surface of the seal body 33. Note that the amount of gas leaking from the sliding surface between the sliding portion 62 and the seal body 33 is negligibly small compared to the amount of gas discharged through the gap G1.

[0049] By using the optical fiber manufacturing apparatus 1B configured as described above, when melt-spinning the optical fiber preform M, the position of the optical fiber preform M can be adjusted by moving the rod 10 in a direction perpendicular to the axial direction Z. Adjusting the position of the rod 10 in this manner can suppress bending of the optical fiber F and eccentricity of the core. Furthermore, a position measuring device (position sensor, etc.) that measures the position of the optical fiber F may be provided near the drawing outlet 43, and the position of the rod 10 may be adjusted based on the measurement value of the position of the optical fiber F obtained by the position measuring device. In this case, bending of the optical fiber F and eccentricity of the core can be suppressed more reliably. In this embodiment, the rod 10 is fixed to the seal portion 30, but the rod 10 and the seal portion 30 do not necessarily have to be fixed to each other. For example, the rod 10 and the seal portion 30 may be relatively movable in the axial direction Z, and may be relatively movable in the radial direction within the range of the gap G2. [Example]

[0050] The above embodiment will be described below using specific examples, but the present invention is not limited to the following examples.

[0051] A total of 16 optical fibers F according to Comparative Examples 1 and 2 and Examples 1 to 14 were manufactured using optical fiber manufacturing methods with different manufacturing conditions. The manufacturing conditions included the dimension (length) of gap G1 in the axial direction Z, the cross-sectional area of ​​gap G1, and the pressure loss of the inert gas in gap G1. FIG. 3 is a diagram showing the manufacturing conditions for the Examples and Comparative Examples. Note that, when changing the length of gap G1, the lengths of the seal main body 33 and second sleeve 32 were fixed, and the length of the first sleeve 31 was changed.

[0052] The inventors measured the outer diameter variation (the difference between the maximum and minimum outer diameters of the optical fibers F) for each of the 16 optical fibers F. Furthermore, for the outer diameter variation of each optical fiber F, a measured value of 0.5 μm or less was judged to be "good," and a measured value of more than 0.5 μm was judged to be "poor." Table 1 summarizes the above judgment results.

[0053] [Table 1]

[0054] As shown in Table 1, in Examples 1 to 14, in which the pressure loss generated in the inert gas in the gap G1 is 95 Pa or more, the outer diameter fluctuation judgment result is "good" regardless of the length of the first sleeve 31 and the cross-sectional area of ​​the gap G1. On the other hand, in Comparative Examples 1 and 2, in which the pressure loss generated in the inert gas in the gap G1 is less than 95 Pa, the outer diameter fluctuation judgment result is "poor" regardless of the length of the first sleeve 31 and the cross-sectional area of ​​the gap G1. In this way, by setting the pressure loss generated in the inert gas in the gap G1 to 95 Pa or more, it is possible to suppress outer diameter fluctuation of the optical fiber F.

[0055] The technical scope of the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the present invention.

[0056] For example, the shapes of the rod 10, the shield pipe 20, the seal portion 30, and the spinning furnace 40 do not have to be circular in cross section. For example, each of the above shapes may be elliptical or polygonal in cross section. Furthermore, the seal portion 30 does not necessarily have to include the first sleeve 31 and the second sleeve 32 .

[0057] In addition, it is possible to replace the components in the above-described embodiments with well-known components as appropriate, and the above-described embodiments and variations may be combined as appropriate, without departing from the spirit of the present invention. [Explanation of symbols]

[0058] 1A, 1B... Optical fiber manufacturing apparatus 10... Rod 20... Shield pipe 30... Seal portion 31... First sleeve 32... Second sleeve 33... Seal main body 40... Spinning furnace 41... Heater 42... Gas inlet G1... Gap

Claims

1. A method for manufacturing an optical fiber using an optical fiber manufacturing apparatus, The optical fiber manufacturing apparatus includes: a rod to which an optical fiber preform is fixed at the lower end; a shield pipe surrounding the rod; a seal portion that is disposed within the shield pipe with a gap between it and the shield pipe, and through which the rod passes; a spinning furnace having a heater for heating the optical fiber preform and formed in a hollow vessel shape; a gas inlet provided in the spinning furnace; When the optical fiber preform is heated by the heater to melt-spin the optical fiber preform, a gas is introduced into the spinning furnace from the gas inlet, and at least a part of the gas is discharged to the outside of the shield pipe through the gap; A method for manufacturing an optical fiber, wherein a pressure loss occurring in the gas in the gap is 95 Pa or more.

2. 2. The method for manufacturing an optical fiber according to claim 1, wherein the seal portion has a seal body portion through which the rod passes, and a first sleeve extending upward from the seal body portion.

3. 3. The method for manufacturing an optical fiber according to claim 1, wherein the seal portion comprises a seal body portion through which the rod passes, and a second sleeve extending downward from the seal body portion.

4. 4. The method for manufacturing an optical fiber according to claim 1, wherein the position of the optical fiber preform is adjusted by moving the rod in a direction perpendicular to an axial direction of the rod when melt-spinning the optical fiber preform.

5. The method for producing an optical fiber according to claim 1 , wherein a portion of the space surrounded by the shield pipe that is located below the seal portion communicates with a space within the spinning furnace.

6. The seal portion has a seal body portion through which the rod passes, 6. The method for manufacturing an optical fiber according to claim 1, wherein an inner diameter of the shield pipe, an outer diameter of the seal body, and an axial dimension of the seal portion are set so that the pressure loss is 95 Pa or more.

7. A method for manufacturing an optical fiber described in any one of claims 1 to 6, wherein the flow rate of the inert gas introduced from the gas inlet is adjusted so that the pressure loss is 95 Pa or more.

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