Method for manufacturing optical fiber

Abstract

A method for manufacturing an optical fiber, in which an optical fiber glass preform is inserted into a drawing furnace filled with a gas containing argon, helium, or nitrogen and heated and melted in the drawing furnace and then an optical fiber is drawn, comprises: a gas supply step for supplying gas, with a gas supply part, into the drawing furnace; a pressure measurement step for measuring a gauge pressure in the drawing furnace, with a measurement part connected to the drawing furnace; a gas discharge step for discharging the gas in the drawing furnace to the outside of the drawing furnace; and an adjustment step for adjusting the gauge pressure by setting a control target value of the gauge pressure to a value smaller than a first target value which is the average value of gauge pressures.

Description

Optical fiber manufacturing method

[0001] This disclosure relates to a method for manufacturing optical fibers. This application claims priority under Japanese application No. 2025-007814, filed on 20 January 2025, and incorporates all the provisions contained herein.

[0002] For example, in a method for manufacturing optical fibers, a glass matrix for optical fibers is inserted into a drawing furnace filled with a gas containing argon, helium, or nitrogen, and the optical fiber is drawn by heating and melting it in the drawing furnace (see, for example, Patent Document 1). In this optical fiber manufacturing method, a gas supply unit sends a certain amount of gas into the drawing furnace so that the pressure inside the drawing furnace is higher than a preset target pressure.

[0003] Japanese Patent Publication No. 2015-839

[0004] The present disclosure is a method for manufacturing an optical fiber, comprising inserting a glass matrix for optical fibers into a drawing furnace filled with a gas containing argon, helium, or nitrogen, and heating and melting it in the drawing furnace to draw an optical fiber, the method comprising: a gas supply step of supplying the gas into the drawing furnace using a gas supply unit; a pressure measurement step of measuring the gauge pressure in the drawing furnace using a measuring unit connected to the drawing furnace; a gas discharge step of discharging the gas from the drawing furnace to the outside of the drawing furnace; and an adjustment step of adjusting the gauge pressure by setting a control target value for the gauge pressure to be smaller than a first target value which is the average value of the gauge pressure.

[0005] Figure 1 is a cross-sectional view showing a drawing furnace applied to the optical fiber manufacturing method according to the embodiment. Figure 2 is a block diagram showing the hardware configuration of the optical fiber manufacturing apparatus. Figure 3 is a process diagram showing the procedure of the optical fiber manufacturing method according to the embodiment. Figure 4 is a graph showing the fluctuation of gauge pressure when an optical fiber is manufactured using the optical fiber manufacturing method according to the embodiment.

[0006] In conventional optical fiber manufacturing methods, there is a need to minimize variations in glass diameter.

[0007] This disclosure aims to provide a method for manufacturing optical fibers that can reduce variations in glass diameter.

[0008] According to this disclosure, variations in glass diameter can be reduced in a method for manufacturing optical fibers.

[0009] First, the embodiments of this disclosure will be listed and described.

[0010] [1] A method for manufacturing an optical fiber according to one aspect of the present disclosure is a method for manufacturing an optical fiber comprising inserting a glass matrix for optical fibers into a drawing furnace filled with a gas containing argon, helium, or nitrogen, and heating and melting it in the drawing furnace to draw an optical fiber, the method comprising: a gas supply step of supplying the gas into the drawing furnace by a gas supply unit; a pressure measurement step of measuring the gauge pressure in the drawing furnace by a measuring unit connected to the drawing furnace; a gas discharge step of discharging the gas from the drawing furnace to the outside of the drawing furnace; and an adjustment step of adjusting the gauge pressure by setting a control target value for the gauge pressure to be smaller than a first target value which is the average value of the gauge pressure.

[0011] In the optical fiber manufacturing method of this embodiment, fluctuations in gauge pressure can be reduced by making the control target value of the gauge pressure smaller than the first target value, which is the average value of the gauge pressure. This reduces fluctuations in the gas flow in the drawing furnace and reduces fluctuations in the glass diameter.

[0012] [2] In [1], the measuring unit is connected to the upper chamber or lower chamber of the drawing furnace, and the first target value is greater than 0 Pa and less than or equal to 100 Pa. In the optical fiber manufacturing method of this embodiment, the gauge pressure inside the drawing furnace can be controlled to an appropriate value by measuring the gauge pressure in the upper chamber or lower chamber of the drawing furnace. Furthermore, by setting the control target value to a value greater than 0 Pa and less than or equal to 100 Pa, fluctuations in gauge pressure can be kept to a minimum.

[0013] [3] In [1], the measuring unit is connected to a position within a range of 10% of the total length of the lower chamber, from a first position above the outlet shutter of the lower chamber. In the optical fiber manufacturing method of this embodiment, by measuring the gauge pressure at a position close to the outlet shutter of the lower chamber of the drawing furnace, the gauge pressure at a position close to the outlet shutter can be controlled to an appropriate value. In this case, the pressure can be appropriately controlled with positive pressure so that outside air does not flow into the furnace through the outlet.

[0014] [4] In [3], the first target value may be greater than 0 Pa and 14 Pa or less. In this case, the gauge pressure at a position close to the outlet shutter can be appropriately maintained, and the inflow of air into the furnace can be prevented.

[0015] [5] In any of [1] to [4], the adjustment step may include a step of reducing the supply flow rate of the gas supplied into the wire drawing furnace. In this case, by reducing the supply flow rate of the gas, the gauge pressure can be made smaller than the first target value, which is the average value of the gauge pressure, and fluctuations in the gauge pressure can be reduced. By reducing the absolute flow rate of the gas, the amount of heat transferred from the neck down, which is the molten part of the glass base material, to the gas can be reduced, and thus fluctuations in the glass diameter can be reduced.

[0016] [6] In any of [1] to [5], the adjustment step may include a step of adjusting the discharge flow rate of the gas discharged from the drawing furnace. In this case, by adjusting the gas discharge flow rate, the gauge pressure can be made smaller than the first target value, which is the average value of the gauge pressure, and fluctuations in the overall furnace pressure can be reduced. As a result, in the optical fiber manufacturing method of this embodiment, fluctuations in the glass diameter can be reduced.

[0017] [7] In any of [1] to [6], the control target value may be a value less than or equal to the average value of the gauge pressure minus 3σ. In this case, the variation in glass diameter can be further reduced.

[0018] [8] Any of [1] to [7] includes a linear velocity measurement step for measuring the linear velocity of the optical fiber drawn from the drawing furnace, and the adjustment step may include a step of adjusting the supply flow rate of the gas supplied into the drawing furnace according to the linear velocity of the optical fiber. In this case, fluctuations in the gas inside the drawing furnace can be reduced by adjusting the supply flow rate of the gas considering the linear velocity of the optical fiber inside the drawing furnace.

[0019] [Details of Embodiments of the Disclosure] Embodiments of the Disclosure will be described in detail below, but the Disclosure is not limited thereto. In this Specification and the drawings, components having substantially the same functional configuration are denoted by the same reference numerals to avoid redundant descriptions.

[0020] Figure 1 is a cross-sectional view showing a drawing furnace 20 applied to a method for manufacturing an optical fiber 10 according to an embodiment. The drawing furnace 20 shown in Figure 1 is a resistance furnace that heats a furnace tube 22 with a heater 24. The drawing furnace 20 is not limited to a resistance furnace; it may also be an induction furnace that applies a high-frequency voltage to a coil to inductively heat the furnace tube, or any other type.

[0021] [Drawing Furnace 20] The optical fiber manufacturing apparatus 100 includes a drawing furnace 20. The inside of the drawing furnace 20 is filled with a gas containing, for example, argon, helium, or nitrogen. The drawing furnace 20 heats and melts the glass preform 11 for optical fibers to draw the optical fibers 10. Note that "glass preform for optical fibers" may be written as "glass preform". The drawing furnace 20 includes an upper chamber 21, a furnace core tube 22, and a lower chamber 23. The upper chamber 21, the furnace core tube 22, and the lower chamber 23 are arranged and connected in this order from top to bottom. The upper chamber 21, the furnace core tube 22, and the lower chamber 23 are, for example, cylindrical in shape and are in communication with each other.

[0022] The upper chamber 21, the core tube 22, and the lower chamber 23 have a predetermined heat resistance and may be made of metal or carbon, for example.

[0023] The upper end of the upper chamber 21 is sealed by a lid 27. The lid 27 has an upper opening 27a into which the glass base material 11 is inserted. The glass base material 11 is inserted into the upper chamber 21 through the upper opening 27a. The glass base material 11 is positioned from inside the upper chamber 21 into the core tube 22.

[0024] A heater 24 is positioned outside the reactor core tube 22. The heater 24 is positioned circumferentially around the reactor core tube 22, surrounding it. Insulation material is placed around the heater 24. The heater 24 heats and melts the glass base material 11 inside the reactor core tube 22. The melted and reduced-diameter optical fiber 10 hangs down from inside the reactor core tube 22 into the lower chamber 23.

[0025] An exit shutter 28 is provided at the lower end of the lower chamber 23. The exit shutter 28 has a lower end opening 28a through which the optical fiber 10 is led out. The optical fiber 10 inside the lower chamber 23 passes through the lower end opening 28a and is led out to the outside of the lower chamber 23.

[0026] The optical fiber 10, which is led out from the lower chamber 23, is wound onto a drum, for example. The optical fiber manufacturing apparatus 100 is equipped with a moving mechanism for moving the optical fiber 10.

[0027] [Gas Supply Unit 30] The optical fiber manufacturing apparatus 100 has a gas supply unit 30 that supplies inert gas into the drawing furnace 20. The gas supply unit 30 may include a gas supply pipe L30 that supplies inert gas into the drawing furnace 20. The inert gas may be, for example, a mixture of argon gas and helium gas. The inert gas flows through the gas supply pipe L30 and is supplied into the drawing furnace 20. The gas supply pipe L30 may also supply the inert gas inside the upper chamber 21. The inert gas inside the upper chamber 21 can flow into the furnace core tube 22. The inert gas that has flowed into the furnace core tube 22 is discharged to the outside of the drawing furnace 20 through the gap at the upper end opening 27a or the gap at the lower end opening 28a.

[0028] The gas supply unit 30 is equipped with an MFC (mass flow controller) 31 that controls the amount of inert gas supplied. The MFC 31 is connected to the gas supply piping L30 and controls the amount of inert gas supplied. By supplying a fixed amount of inert gas into the reactor core tube 22, oxidation and deterioration can be prevented inside the reactor core tube 22 and around the heater 24.

[0029] [Gas discharge section 40] The optical fiber manufacturing apparatus 100 has a gas discharge section 40 that discharges the gas inside the drawing furnace 20 to the outside of the drawing furnace 20. In the gas discharge section 40, the gas discharge pipe L40 that discharges the gas inside the drawing furnace 20 to the outside of the drawing furnace 20 may be connected to, for example, the upper chamber 21. The gas discharge pipe L40 may be connected to the upper end of the upper chamber 21.

[0030] A control valve 41 is provided in the gas discharge piping L40. The control valve 41 is electrically connected to the controller 200. The control valve 41 is driven according to command signals from the controller 200.

[0031] [Pressure Sensor 221] The optical fiber manufacturing apparatus 100 is equipped with a pressure sensor 221 that detects the absolute value (gauge pressure) of the pressure inside the drawing furnace 20. The gauge pressure may be, for example, the absolute value of the pressure inside the lower chamber 23 at the lower end of the lower chamber 23, or it may be the absolute value of the pressure inside the upper chamber 21.

[0032] The pressure sensor 221 is connected to the wire drawing furnace 20 through a connecting pipe L221. The connecting pipe L221 may be connected to the upper chamber 21, or it may be connected to the lower end of the lower chamber 23. The connecting pipe L221 may be connected in the longitudinal direction of the lower chamber 23, just above the outlet shutter 28. The connecting pipe L221 may be connected within the range of the lower chamber 23 from a first position PP1 to a second position PP2. The first position PP1 is, for example, the lower end of the lower chamber 23, just above the outlet shutter 28. The second position PP2 is above the first position PP1, for example, by a length L12 of 10% of the total length L11 of the lower chamber 23 (the distance between the first position PP1 and the third position PP3).

[0033] [Controller 200] Next, the controller 200 of the optical fiber manufacturing apparatus 100 will be described with reference to Figure 2. Figure 2 is a block diagram showing the hardware configuration of the optical fiber manufacturing apparatus 100 according to the embodiment. As shown in Figure 2, the controller 200 is electrically connected to the pressure sensor 221, the flow sensor 231, the linear velocity sensor 241, the MFC 31, and the control valve 41.

[0034] The controller 200 may include a control circuit 210. The control circuit 210 comprises a CPU (Center Processing Unit) 211 and a memory unit 212. The CPU 211 is responsible for the overall control of the optical fiber manufacturing apparatus 100.

[0035] The memory unit 212 includes a ROM (Read Only Memory) 213 and a RAM (Random Access Memory) 214. The ROM 213 stores various programs for the CPU 211 to execute control processing, as well as various data necessary for the operation of the optical fiber manufacturing apparatus 100. The RAM 214 temporarily stores data acquired from the pressure sensor 221. The controller 200 can perform various calculations.

[0036] [Method for manufacturing optical fiber] FIG. 3 is a process diagram showing the procedure of the method for manufacturing the optical fiber 10 according to the embodiment. In the method for manufacturing the optical fiber 10, the glass preform 11 is lowered into the core tube 22 from above the wire drawing furnace 20 while heating and melting its tip, and the tip of the glass preform 11 is thinned and drawn from below the wire drawing furnace 20 to manufacture the optical fiber 10. The method for manufacturing the optical fiber 10 includes a gas supply step (step S11), a pressure measurement step (step S12), a gas discharge step (step S13), an adjustment step (step S14), and a wire drawing step (step S15).

[0037] [Gas supply step] In the gas supply step (step S11), a gas is supplied into the wire drawing furnace 20 by the gas supply unit 30. In the gas supply step, a gas containing argon, helium, or nitrogen is supplied into the wire drawing furnace 20. The gas flows through the gas supply pipe L30, and the flow rate of the gas is controlled by the MFC 31. The gas supplied into the wire drawing furnace 20 flows into the core tube 22.

[0038] [Pressure measurement step] In the pressure measurement step (step S12), the gauge pressure, which is the absolute value of the pressure in the wire drawing furnace 20, is measured by the pressure sensor 221 connected to a region near the outlet of the lower chamber 23 of the wire drawing furnace 20. Data regarding the gauge pressure measured by the pressure sensor 221 is input to the controller 200.

[0039] The pressure sensor 221 for detecting the furnace internal pressure in the pressure measurement step may be connected to the upper chamber 21. Also, the pressure sensor 221 may be connected to the lower chamber 23, and may be connected to a position within a range of a length L12 of 10% of the total length L11 of the lower chamber 23 from the first position PP1 above the outlet shutter 28 of the lower chamber 23. The first position PP1 may be the position of the lower end of the lower chamber 23. The total length L11 of the lower chamber 23 is the length from the first position PP1 at the lower end of the lower chamber 23 to the position (third position) PP3 at the upper end.

[0040] [Gas Discharge Process] In the gas discharge process (step S13), the gas discharge unit 40 discharges the gas in the wire drawing furnace 20 to the outside of the wire drawing furnace 20. The gas in the wire drawing furnace 20 flows through the gas discharge pipe L40 and is discharged to the outside of the wire drawing furnace 20. The controller 200 can control the control valve 41 to control the flow rate of the gas flowing through the gas discharge pipe L40.

[0041] [Adjustment Process] In the adjustment process (step S14), as shown in FIG. 4, the control target value of the gauge pressure is set to be smaller than the first target value which is the average value of the gauge pressure, and the gauge pressure is adjusted. The variation of the glass diameter can be made smaller as the absolute value of the gauge pressure is smaller. In the adjustment process, the flow rate of the gas supplied into the wire drawing furnace 20 may be controlled, or the flow rate of the gas discharged from the wire drawing furnace 20 may be controlled. In the adjustment process, the control target value of the gauge pressure is set to be smaller than the first target value, and the gauge pressure is adjusted so as to be smaller than the first target value. By executing the adjustment process, the gauge pressure can be made smaller than the first target value.

[0042] In the adjustment process, for example, by controlling the supply flow rate of the gas supplied into the wire drawing furnace 20 by the MFC 31, the control target value of the gauge pressure is set to be smaller than the first target value, and the absolute value of the gauge pressure and the variation of the gauge pressure are adjusted to be smaller. In the adjustment process, by reducing the supply flow rate of the gas supplied into the wire drawing furnace 20, the control target value of the gauge pressure is set to be smaller than the first target value, and the variation of the gauge pressure may be adjusted to be smaller.

[0043] In the adjustment process, for example, by controlling the flow rate of the gas flowing through the gas discharge pipe L40 by the control valve 41, the control target value of the gauge pressure is set to be smaller than the first target value, and the absolute value of the gauge pressure and the variation of the gauge pressure are adjusted to be smaller. In the adjustment process, by adjusting the discharge flow rate of the gas discharged from the wire drawing furnace 20, the control target value of the gauge pressure is set to be smaller than the first target value, and the variation of the gauge pressure may be adjusted to be smaller.

[0044] In the adjustment process, the MFC 31 may control the supply flow rate of gas supplied to the wire drawing furnace 20, and the control valve 41 may control the discharge flow rate of gas discharged from the wire drawing furnace 20.

[0045] [First Target Value] The gauge pressure, which is the first target value, may be greater than 0 Pa and less than or equal to 100 Pa. Alternatively, the gauge pressure, which is the first target value, may be less than or equal to 50 Pa, or less than or equal to 14 Pa. Note that the first target value is the average value of the gauge pressure to be controlled. In conventional control, for example, the control target value is set as the first target value, and the control is performed so that the gauge pressure falls within the range of the average value of the gauge pressure ± 3σ.

[0046] In this embodiment, the control target value may be a value less than or equal to the average value of the gauge pressure minus 3σ. Figure 4 shows the "first target value," "control target value," "gauge pressure before control," and "gauge pressure after control." In Figure 4, the horizontal axis shows the passage of time, and the vertical axis shows the gauge pressure. In Figure 4, the first target value is shown by a dashed line, the gauge pressure before control is shown by a dashed line, the gauge pressure after control is shown by a solid line, the control target value is shown by a dashed line, and "-3σ" is shown by a dotted line. The control target value is the average value of the gauge pressure after control.

[0047] [Furnace pressure] The furnace pressure Δ(l, V), which is the pressure inside the drawing furnace 20, can be expressed using the following equation (1).

[0048]

[0049] In equation (1), "(ρ Ａｉｒ -ρ)gl depends on the gas density inside the drawing furnace 20. Ａｉｒ ρ is the density of air. ρ is the density of the gas inside the furnace. ρ is the density of air at 25°C. Ａｉｒ This is 1.293 kg / m³ ３ The density of helium at 25°C is ρ. Ｈｅ This is 0.179 kg / m ３ The value is "l", which is the height from the top of the lower end opening 28a to the connection position of the communication pipe L221 at the bottom of the lower chamber 23.

[0050] In equation (1), "ΔP ｏｕｔ"(V)" is the outlet pressure loss of the drawing furnace 20. The outlet pressure loss of the drawing furnace 20 depends on the outlet shape of the drawing furnace 20 and the gas flow rate (≈ flow velocity). The outlet shape of the drawing furnace 20 may be the shape of the lower end opening 28a of the outlet shutter 28. The gas flow rate here is the flow rate of the gas discharged from the lower end opening 28a.

[0051] "ΔP ｓｅａｌ " in Equation (1) is the airtight leakage pressure drop. The airtight leakage pressure drop is the pressure drop that depends on the seal structure such as the upper end opening 27a of the drawing furnace 20.

[0052] "ΔP ｖａｌｖｅ " in Equation (1) is the exhaust control pressure drop. In the optical fiber manufacturing apparatus 100, in order to adjust the furnace internal pressure of the drawing furnace 20, for example, the gas discharge amount is controlled by the control valve 41. The exhaust control pressure drop is the pressure drop in the control of the gas discharge amount. When the gas discharge amount is not controlled by the control valve 41 or the like, ΔP ｖａｌｖｅ is zero.

[0053] In the method for manufacturing the optical fiber 10, the gauge pressure can be reduced by reducing the outlet pressure loss "ΔP ｏｕｔ (V)" of the drawing furnace 20. In the method for manufacturing the optical fiber 10, the gas flow rate in the furnace may be reduced. The gas flow rate in the furnace preferably satisfies the following formula (2) from the viewpoint of discharging dust from the furnace. The gas flow rate in the furnace is defined by the square of the inner diameter ID22 of the core tube 22.

[0054]

[0055] In formula (2), it is preferable that "a = 0.0008" and "b = 9".

[0056] Further, in the method for manufacturing the optical fiber 10, the outlet pressure loss "ΔP ｏｕｔ (V)" of the drawing furnace 20 can be reduced by increasing the outlet diameter. The outlet diameter may be, for example, the inner diameter ID28a of the lower end opening 28a. The outlet diameter may be, for example, 5 mm or more, 10 mm or more, or 20 mm or more.

[0057] Furthermore, in the manufacturing method of the optical fiber 10, by shortening the outlet length, the outlet pressure loss "ΔP" of the drawing furnace 20 is reduced. ｏｕｔ The (V) can be reduced. The outlet length may be, for example, the opening length L28 of the outlet shutter 28. The opening length L28 is the length along the longitudinal direction of the wire drawing furnace 20. The outlet length may be, for example, 100 mm or less, 30 mm or less, 10 mm or less, or 5 mm or less.

[0058] Furthermore, the method for manufacturing the optical fiber 10 may include a linear velocity measurement step for measuring the linear velocity of the optical fiber 10 drawn from the drawing furnace 20. The adjustment step (step S14) may include a step of adjusting the supply flow rate of the gas supplied into the drawing furnace 20 according to the linear velocity of the optical fiber 10. The controller 200 can control the supply flow rate of the gas according to the linear velocity of the optical fiber 10. When the linear velocity is high, the controller 200 may increase the supply flow rate of the gas compared to when the linear velocity is low.

[0059] Furthermore, the adjustment step (step S14) may include a step of adjusting the discharge flow rate of the gas discharged from the drawing furnace 20 according to the linear velocity of the optical fiber 10. The controller 200 can control the gas discharge flow rate according to the linear velocity of the optical fiber 10. When the supply flow rate is constant and the linear velocity is high, the controller 200 may perform control to reduce the gas discharge flow rate compared to when the linear velocity is low.

[0060] [Effects of the Method for Manufacturing Optical Fibers According to the Embodiment] The method for manufacturing optical fibers 10 according to this embodiment is a method for manufacturing optical fibers 10 in which a glass base material 11 for optical fibers is inserted into a drawing furnace 20 filled with a gas containing argon, helium, or nitrogen, and the optical fiber 10 is drawn by heating and melting it in the drawing furnace 20. The method for manufacturing optical fibers 10 includes a gas supply step of supplying gas into the drawing furnace 20 by a gas supply unit 30, a pressure measurement step of measuring the gauge pressure in the drawing furnace 20 by a pressure sensor (measuring unit) 221 connected to the drawing furnace 20, a gas discharge step of discharging the gas in the drawing furnace 20 to the outside of the drawing furnace 20, and an adjustment step of setting a control target value for the gauge pressure to be smaller than a first target value which is the average value of the gauge pressure, and adjusting the gauge pressure so that fluctuations become smaller. The pressure sensor 221 is connected to a position within a range of a length L12 which is 10% of the total length L11 of the lower chamber 23, from a first position above the outlet shutter 28 of the lower chamber 23. The pressure sensor may also be connected to the upper chamber 21.

[0061] According to this method for manufacturing optical fibers 10, by making the control target value of the gauge pressure smaller than the first target value, which is the average value of the gauge pressure, fluctuations in the gauge pressure can be reduced. This reduces fluctuations in the gas flow inside the drawing furnace and reduces fluctuations in the glass diameter.

[0062] Although embodiments have been described in detail above, this disclosure is not limited to any particular embodiment, and various modifications and changes are possible within the scope of the claims.

[0063] 100 Optical fiber manufacturing apparatus 10 Optical fiber 11 Glass base material (glass base material for optical fiber) 20 Wire drawing furnace 21 Upper chamber 22 Furnace tube 23 Lower chamber 24 Heater 25 Insulation material 27 Cover 27a Upper end opening 28 Outlet shutter 28a Lower end opening 30 Gas supply unit 31 MFC 40 Gas discharge unit 41 Control valve 200 Controller 210 Control circuit 211 CPU 212 Memory unit 213 ROM 214 RAM 221 Pressure sensor 231 Flow sensor 241 Linear velocity sensor L30 Gas supply piping L40 Gas discharge piping L221 Connecting pipe PP1 First position PP2 Second position PP3 Upper end position (Third position) L11 Total length L12 Length L28 Opening length ID22 Inner diameter of core tube 22 ID28a Inner diameter of lower end opening 28a

Claims

1. A method for manufacturing optical fibers, comprising inserting a glass matrix for optical fibers into a drawing furnace filled with a gas containing argon, helium, or nitrogen, and heating and melting it in the drawing furnace to draw an optical fiber, the method comprising: a gas supply step of supplying the gas into the drawing furnace by a gas supply unit; a pressure measurement step of measuring the gauge pressure in the drawing furnace by a measuring unit connected to the drawing furnace; a gas discharge step of discharging the gas from the drawing furnace to the outside of the drawing furnace; and an adjustment step of adjusting the gauge pressure by setting a control target value for the gauge pressure to be smaller than a first target value which is the average value of the gauge pressure.

2. The method for manufacturing an optical fiber according to claim 1, wherein the measuring unit is connected to the upper or lower chamber of the drawing furnace, and the first target value is greater than 0 Pa and less than or equal to 100 Pa.

3. The method for manufacturing an optical fiber according to claim 1, wherein the measuring unit is connected to a position within a range of 10% of the total length of the lower chamber, from a first position above the exit shutter of the lower chamber of the drawing furnace.

4. The method for manufacturing an optical fiber according to claim 3, wherein the first target value is greater than 0 Pa and less than or equal to 14 Pa.

5. The method for manufacturing an optical fiber according to any one of claims 1 to 4, wherein the adjustment step includes a step of reducing the supply flow rate of the gas supplied into the drawing furnace.

6. The method for manufacturing an optical fiber according to any one of claims 1 to 5, wherein the adjustment step includes a step of adjusting the discharge flow rate of the gas discharged from the drawing furnace.

7. The method for manufacturing an optical fiber according to any one of claims 1 to 6, wherein the control target value is a value less than or equal to the average value of the gauge pressure minus 3σ.

8. A method for manufacturing an optical fiber according to any one of claims 1 to 7, comprising a linear velocity measurement step for measuring the linear velocity of the optical fiber drawn out from the drawing furnace, wherein the adjustment step includes a step of adjusting the supply flow rate of the gas supplied into the drawing furnace according to the linear velocity of the optical fiber.

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