Method for manufacturing optical fiber

Abstract

To provide a method for manufacturing an optical fiber that can suppress deterioration in a furnace core tube and disconnection of an optical fiber.SOLUTION: A method for manufacturing an optical fiber that manufactures an optical fiber using a wire-drawing furnace including a carbon furnace core tube includes a step of drawing an optical fiber while supplying a gas containing an inert gas as the principal component and having an oxygen concentration of 3 ppm or more and 20 ppm or less into the furnace core tube.SELECTED DRAWING: Figure 1

Description

[Technical field]

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

[0002] Patent Document 1 discloses a method of drawing an optical fiber by heating and elongating a glass preform in an inert gas atmosphere. Patent Document 1 also discloses a sealing mechanism that seals the gap between the upper opening of the drawing furnace and the glass preform with a sealing gas. The flow rate of the sealing gas is controlled so that the oxygen concentration is 50 ppm or less.

[0003] Patent Document 2 discloses that a glass base material is heated and drawn in a gas atmosphere in which an inert gas is mixed with oxygen gas and fluorine gas, and then drawn into an optical fiber.

[0004] Non-Patent Document 1 discloses high-purity helium gas with an oxygen concentration of 3 ppm or less. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2012-148924 A [Patent Document 2] Japanese Patent Publication No. 122743 / 1983 [Non-patent literature]

[0006] [Non-Patent Document 1] Helium (He) Industrial gas handling Iwatani Corporation Industrial gas general site, [online], [Searched on April 20, 2023], Internet https: / / industry.iwatani.co.jp / industrial-gas / lineup / 359 / Summary of the Invention [Problem to be solved by the invention]

[0007] Incidentally, carbon is mainly used as the material for the core tube of a drawing furnace. In order to prevent the oxidation of this carbon, a high-purity inert gas that does not contain oxygen is used as the gas supplied to the core tube. However, high-purity inert gas is expensive.

[0008] An object of the present disclosure is to provide a method for manufacturing an optical fiber that can suppress deterioration of a furnace tube and breakage of the optical fiber. [Means for solving the problem]

[0009] The method for producing an optical fiber according to the present disclosure includes the steps of: A method for manufacturing an optical fiber using a drawing furnace equipped with a carbon core tube, comprising the steps of: The optical fiber is drawn while supplying a gas containing an inert gas as a main component and having an oxygen concentration of 3 ppm or more and 20 ppm or less into the inside of the furnace tube. Effect of the Invention

[0010] According to the present disclosure, it is possible to provide a method for manufacturing an optical fiber that can suppress deterioration of a furnace tube and breakage of an optical fiber. [Brief description of the drawings]

[0011] [Figure 1] FIG. 1 is a diagram illustrating the configuration of an optical fiber manufacturing apparatus according to the present embodiment. [Diagram 2] FIG. 2 is a graph showing the relationship between the oxygen concentration contained in the gas supplied into the furnace tube and the breakage rate of the optical fiber. [Diagram 3] FIG. 3 is a graph showing the relationship between the oxygen concentration contained in the gas supplied into the furnace tube and the life of the furnace tube. [Figure 4] FIG. 4 is a graph showing the results of a simulation showing the relationship between the temperature inside the furnace tube and the concentration of oxygen generated from the optical fiber preform. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] [Description of the embodiments of the present disclosure] First, the contents of the embodiments of the present disclosure will be listed and described. The method for producing an optical fiber according to the present disclosure includes the steps of: (1) A method for manufacturing an optical fiber using a drawing furnace equipped with a carbon core tube, The optical fiber is drawn while supplying a gas containing an inert gas as a main component and having an oxygen concentration of 3 ppm or more and 20 ppm or less into the inside of the furnace tube. According to the above method, the oxygen concentration of the gas supplied into the furnace tube is 3 ppm or more, so that the frequency of breakage of the optical fiber is reduced. Meanwhile, the oxygen concentration of the gas supplied into the furnace tube is 20 ppm or less, so that the deterioration of the furnace tube due to oxidation can be further suppressed.

[0013] (2) In the above (1), the gas may have an oxygen concentration of 5 ppm or more. According to the above method, the frequency of breakage of the optical fiber is further reduced.

[0014] (3) In the above (1) or (2), the gas may have an oxygen concentration of 10 ppm or less. According to the above method, the frequency of breakage of the optical fiber can be further reduced, and deterioration of the furnace tube due to oxidation can be further suppressed.

[0015] (4) In any of the above (1) to (3), the gas supplied to the inside of the furnace tube may be recovered, and the recovered gas may be purified before being supplied to the inside of the furnace tube. According to the above method, the manufacturing cost can be further reduced by reusing the gas.

[0016] (5) In any one of the above (1) to (4), the inert gas may be helium gas. According to the above method, since helium gas is expensive, the effect of reducing the manufacturing cost is significant.

[0017] (6) In any one of the above (1) to (5), the temperature inside the furnace tube may be 2200° C. or less. According to the above method, by keeping the temperature inside the furnace tube at 2200° C. or less, the volatilization of silica glass can be further suppressed, and deterioration of the furnace tube can be suppressed.

[0018] [Details of the embodiment of the present disclosure] Specific examples of the optical fiber manufacturing method according to the embodiment of the present disclosure will be described below with reference to the drawings. Note that the present invention is not limited to these examples, but is intended to include all modifications within the meaning and scope of the claims as set forth in the claims. In addition, the scale of each drawing used in the following description has been appropriately changed so that each component can be recognized.

[0019] Fig. 1 illustrates a portion of an optical fiber manufacturing apparatus 1. The optical fiber manufacturing apparatus 1 is an apparatus for manufacturing an optical fiber G2 by heating an optical fiber preform G1 and drawing it into an optical fiber G2. As illustrated in Fig. 1, the optical fiber manufacturing apparatus 1 includes a drawing furnace 2. The drawing furnace 2 includes a furnace core tube 21, a heater 22, an extension tube 23, and a gas recovery mechanism 24.

[0020] The furnace core tube 21 is disposed in the center of the drawing furnace 2. A carbon furnace core tube is used as the furnace core tube 21. That is, the furnace core tube 21 is formed of a material mainly composed of carbon. In the furnace core tube 21, an optical fiber preform G1 formed mainly composed of, for example, silica glass (SiO2) is suspended by a preform suspension mechanism (not shown).

[0021] The furnace core tube 21 is provided with a gas supply port 211. Gas is supplied from the gas supply port 211 into the inside of the furnace core tube 21. The gas supplied to the furnace core tube 21 is a gas containing an inert gas as the main component and a predetermined concentration of oxygen. Specifically, a gas containing an inert gas as the main component and having an oxygen concentration of 3 ppm or more and 20 ppm or less, preferably 5 ppm or more and 10 ppm or less, is used. As the inert gas, for example, helium (He) gas, argon (Ar) gas, or nitrogen (N2) gas is used.

[0022] The heater 22 is disposed so as to surround the furnace core tube 21. The heater 22 is configured to heat the furnace core tube 21. When the furnace core tube 21 is heated, the optical fiber preform G1 disposed in the furnace core tube 21 is heated.

[0023] The extension tube 23 is provided below the core tube 21 so as to be continuous with the core tube 21. The optical fiber G2 drawn in the core tube 21 passes continuously through the extension tube 23. The extension tube 23 may be formed integrally with the core tube 21, or may be provided detachably with respect to the core tube 21.

[0024] The gas recovery mechanism 24 is a mechanism for recovering the gas supplied to the drawing furnace 2. The gas recovery mechanism 24 has a gas recovery chamber 241, a gas recovery port 242, and a gas suction pipe 243.

[0025] The gas recovery chamber 241 is provided in the lower part of the extension pipe 23. The gas recovery chamber 241 may be provided continuous with the extension pipe 23, or may be provided detachably with respect to the extension pipe 23.

[0026] The gas recovery port 242 is provided in the gas recovery chamber 241. In this example, a plurality of gas recovery ports 242 are provided in the bottom surface of the gas recovery chamber 241. The gas recovery port 242 may be provided in the peripheral wall of the gas recovery chamber 241.

[0027] The gas suction pipe 243 is connected to the gas recovery port 242. In this example, the gas suction pipe 243 is connected to each of the multiple gas recovery ports 242, and the gas suction pipes 243 are connected to each other by a ring-shaped suction pipe. The gas collected in the gas recovery chamber 241 is sucked from the gas recovery port 242 to the outside by the gas suction pipe 243.

[0028] The optical fiber manufacturing apparatus 1 further includes a filter 3, a gas purification device 4, a gas supplier 5, and a gas replenishing device 6. The gas sucked by the gas suction pipe 243 is supplied to the filter 3. The filter 3 removes solid matter and the like from the sucked gas.

[0029] The gas refiner 4 separates and refines a gas containing an inert gas as a main component and oxygen from the gas recovered from the drawing furnace 2 and filtered by the filter 3. The gas refined by the gas refiner 4 is supplied to the gas supplier 5. The gas supplied to the gas supplier 5 is supplied into the furnace core tube 21 from the gas supply port 211 of the furnace core tube 21.

[0030] A gas replenishment device 6 is connected to the gas supply device 5, and inert gas is replenished from the gas replenishment device 6 to the gas supply device 5 as necessary. For example, when the amount of gas purified by the gas purification device 4 is insufficient to the amount of gas supplied to the furnace core tube 21, an inert gas containing oxygen is replenished from the gas replenishment device 6. The gas supplied to the gas supply device 5 and replenished with the inert gas is supplied from the gas supply port 211 of the furnace core tube 21.

[0031] The optical fiber manufacturing apparatus 1 includes a control unit 7. The control unit 7 controls the operations of the heater 22, the gas supplier 5, the gas replenishment device 6, and the like. The control unit 7 is composed of a processor and a memory, and the memory stores programs and data for controlling each operation. For example, the control unit 7 controls the flow rate of gas supplied from the gas supplier 5 into the core tube 21 and the flow rate of inert gas replenished from the gas replenishment device 6 to the gas supplier 5. The control unit 7 also controls the heating temperature of the heater 22 to control the temperature inside the core tube 21. For example, the control unit 7 controls the heater 22 so that the temperature inside the core tube 21 is 2200° C. or less.

[0032] Next, a method for manufacturing an optical fiber using the optical fiber manufacturing apparatus 1 will be described. First, the optical fiber preform G1 is inserted into the core tube 21 of the drawing furnace 2, and the lower part of the optical fiber preform G1 is heated and melted by the heater 22. The melted optical fiber preform G1 becomes an optical fiber G2 having a predetermined outer diameter by the weight of the molten glass and the tensile force, and is continuously drawn.

[0033] The optical fiber G2 drawn in the furnace core tube 21 passes through the extension tube 23 and is inserted into the gas recovery mechanism 24. The optical fiber G2 immediately after being drawn in the furnace core tube 21 is in a heat-softened state, but by passing through the extension tube 23, rapid cooling is alleviated and the optical fiber G2 is cooled and hardened to a certain extent, thereby suppressing fluctuations in the outer diameter.

[0034] During drawing of the optical fiber G2, a gas containing an inert gas as a main component and oxygen at a predetermined concentration is supplied into the core tube 21 via the gas supply port 211. The gas is supplied so as to uniformly fill the space in the core tube 21 and the space in the extension tube 23. Supplying the gas into the core tube 21 suppresses fluctuations in the outer diameter of the optical fiber G2 caused by thermal fluctuations near the lower end of the optical fiber preform G1 melted into a neck-down shape.

[0035] The gas supplied into the furnace core tube 21 is collected by the gas collection mechanism 24. Specifically, the gas collected in the gas collection chamber 241 is sucked through the gas collection port 242 by the gas suction pipe 243. The gas sucked through the gas collection port 242 is passed through the filter 3 to remove solid matter such as foreign particles contained in the gas, and is sent to the gas purification device 4. In the gas purification device 4, the gas containing oxygen and mainly inert gas is separated and purified from other gases. The purified gas containing oxygen and mainly inert gas is supplied to the gas supply device 5 for reuse. Furthermore, the gas supply device 6 supplies the gas supply device 5 with inert gas or inert gas containing oxygen as needed. The gas supplied to the gas supply device 5, or the gas further supplemented with inert gas or inert gas containing oxygen, is supplied from the gas supply device 5 to the furnace core tube 21 through the gas supply port 211.

[0036] The drawn optical fiber G2 is passed through a gas recovery mechanism 24, and then undergoes a cooling process by a cooling device (not shown), a resin coating process by a coating device, and the like, and is then wound up on a drum or the like.

[0037] Here, since the temperature inside the drawing furnace 2 in which the optical fiber preform G1 is heated and melted to be drawn into the optical fiber G2 is extremely high, carbon with excellent heat resistance is used for the furnace core tube 21. This carbon is oxidized and consumed in an atmosphere containing oxygen. Therefore, in order to suppress deterioration of the carbon furnace core tube 21 due to oxidation, it is considered to use a high-purity inert gas that does not contain oxygen as the gas supplied into the furnace core tube 21. However, high-purity inert gas is expensive.

[0038] The inventors of the present application have discovered that, by setting the oxygen concentration contained in the inert gas supplied into the furnace core tube 21 made of carbon within an appropriate range, even a low-purity inert gas can be used, while suppressing deterioration of the furnace core tube 21 and further suppressing the volatilization of silica glass more than if a high-purity inert gas were supplied.

[0039] Specifically, in the method for manufacturing an optical fiber according to this embodiment, a gas containing an inert gas as a main component and having an oxygen concentration of 3 ppm or more is supplied to the furnace tube 21. This makes it possible to suppress volatilization of silica glass from the optical fiber preform G1 and the optical fiber G2. As a result, the frequency of breakage of the drawn optical fiber G2 is reduced. Furthermore, when the oxygen concentration contained in the gas is 5 ppm or more, the frequency of breakage of the optical fiber G2 is further reduced.

[0040] On the other hand, when the oxygen concentration contained in the gas supplied to the core tube 21 exceeds 20 ppm, deterioration due to oxidation of the core tube 21 is accelerated. Therefore, according to the optical fiber manufacturing method of this embodiment, a gas containing an inert gas as a main component and having an oxygen concentration of 20 ppm or less is supplied to the core tube 21. This makes it possible to suppress deterioration due to oxidation of the core tube 21. Furthermore, when the oxygen concentration contained in the gas is 10 ppm or less, the frequency of breakage of the optical fiber G2 is further reduced and deterioration due to oxidation of the core tube 21 can be further suppressed.

[0041] In addition, since a gas containing oxygen is used as the gas supplied into the furnace core tube 21, the manufacturing costs can be reduced compared to the case where a high-purity inert gas is used. In particular, since high-purity helium gas is expensive, the manufacturing cost reduction effect is increased when a gas containing helium gas as a main component is used.

[0042] Furthermore, in this embodiment, the gas supplied to the inside of the furnace core tube 21 is recovered by the gas recovery mechanism 24 and reused, so that the manufacturing costs can be further reduced.

[0043] In addition, in this embodiment, the temperature inside the core tube 21 of the drawing furnace 2 is controlled to be 2200° C. or less, which further suppresses the volatilization of silica glass from the optical fiber preform G1. Specifically, the higher the temperature inside the core tube 21 of the drawing furnace 2, the more oxygen is generated from the optical fiber preform G1. Therefore, by setting the temperature inside the core tube 21 to be 2200° C. or less, the generation of oxygen from the optical fiber preform G1 can be suppressed, and deterioration of the core tube 21 can be suppressed.

[0044] [Example] The present disclosure will be described in more detail below by showing examples according to the present disclosure. Note that the present disclosure is not limited to the following examples.

[0045] When optical fiber G2 was manufactured using the optical fiber manufacturing apparatus 1, the oxygen concentration contained in the gas supplied into the furnace tube 21 was measured, and the relationship between the breakage rate of the optical fiber G2 and the lifespan of the furnace tube 21 was obtained. As the gas supplied into the furnace tube 21, helium gas was used as an inert gas, and a gas containing the helium gas as a main component and containing an oxygen concentration of 1 ppm to 25 ppm was used.

[0046] Fig. 2 shows the relationship between the oxygen concentration [ppm] contained in the gas supplied into the core tube 21 and the breakage rate [items / Mm] of the optical fiber G2. Fig. 3 shows the relationship between the oxygen concentration [ppm] contained in the gas supplied into the core tube 21 and the lifespan of the core tube 21. The lifespan is defined as the time until the weight loss of the core tube 21 reaches a predetermined amount due to use, and the lifespan of the core tube 21 when gas with an oxygen concentration of 1 ppm or less is supplied is defined as 1. Table 1 shows the relationship between the oxygen concentration contained in the gas supplied into the core tube 21, the breakage rate of the optical fiber G2, and the lifespan of the core tube 21 based on the results of Figs. 2 and 3.

[0047] [Table 1]

[0048] As shown in Figure 2 and Table 1, the higher the oxygen concentration, the lower the break rate of the optical fiber, up to an oxygen concentration of 10 ppm. Between 15 ppm and 25 ppm, the break rate of the optical fiber increases with the oxygen concentration, but is lower than the break rate when the oxygen concentration is 1 ppm or less. In addition, between 3 ppm and 20 ppm, the break rate of the optical fiber is less than 0.1.

[0049] As shown in FIG. 3 and Table 1, the life of the furnace core tube 21 remains almost unchanged up to an oxygen concentration of 20 ppm, but decreases significantly at an oxygen concentration of 25 ppm.

[0050] From the above results, it was found that by using a gas containing helium gas as the main component and an oxygen concentration of 3 ppm or more and 20 ppm or less as the gas supplied to the furnace core tube 21, the frequency of breakage of the optical fiber G2 was reduced, and the effect on the life of the furnace core tube 21 was almost the same as when the oxygen concentration was 1 ppm or less. It was also found that by using a gas containing helium gas as the main component and an oxygen concentration of 5 ppm or more, the frequency of breakage of the optical fiber G2 was further reduced. It was also found that by using a gas containing helium gas as the main component and an oxygen concentration of 10 ppm or less, the frequency of breakage of the optical fiber was low, and the life of the furnace core tube 21 was the same as when the oxygen concentration was 1 ppm or less.

[0051] In the above results, helium gas is used as the inert gas, but similar results can be obtained when an inert gas other than helium (for example, argon gas or nitrogen gas) is used. This is because, even when an inert gas other than helium is used, it is considered that, by setting the oxygen concentration contained in the inert gas within an appropriate range, it is possible to suppress the deterioration of the furnace core tube 21 while suppressing the volatilization of silica glass from the optical fiber preform G1 and the optical fiber G2, similarly to the case where helium gas is used as the inert gas.

[0052] Next, a simulation was performed on the relationship between the temperature in the furnace core tube 21 and the oxygen concentration generated from the optical fiber preform G1 in the furnace core tube 21 when the optical fiber G2 was manufactured using the optical fiber manufacturing apparatus 1. The simulation results are shown in Fig. 4. Note that this simulation was performed by performing chemical equilibrium calculations using general-purpose thermodynamic analysis software.

[0053] As shown in Fig. 4, the oxygen concentration generated from the optical fiber preform G1 increases exponentially when the temperature inside the furnace core tube 21 reaches around 2000°C. When the temperature inside the furnace core tube 21 is below 2200°C, the oxygen concentration generated from the optical fiber preform G1 is below 1500 ppm. By keeping the temperature inside the furnace core tube 21 below 2200°C, the concentration of oxygen generated by the volatilization of silica glass can be suppressed, and the life of the furnace core tube 21 can be further extended. Note that the oxygen concentration in Fig. 4 indicates the total concentration of O, O2, and O3.

[0054] Although the present invention has been described in detail and with reference to specific embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the present invention. Furthermore, the number, position, shape, etc. of the components described above are not limited to the above embodiments, and can be changed to the number, position, shape, etc. that are suitable for implementing the present invention.

[0055] In the above embodiment, in the manufacturing process of the optical fiber, the breakage of the optical fiber G2 and the deterioration of the furnace tube 21 are suppressed by setting the oxygen concentration within an appropriate range. However, the present disclosure can also be applied to a manufacturing process of an optical fiber preform using, for example, a sintering furnace having a quartz furnace tube. That is, by setting the oxygen concentration contained in an inert gas such as helium supplied into the quartz furnace tube within an appropriate range, it is possible to suppress the volatilization of silica glass from the optical fiber preform and the furnace tube. This makes it possible to suppress the deterioration of the quartz furnace tube and to suppress the deposition of the volatilized silica glass at the exhaust port downstream of the furnace tube. [Explanation of symbols]

[0056] 1: Optical fiber manufacturing equipment 2: Wire drawing furnace 21: Furnace tube 211: Gas supply port 22: Heater 23: Extension tube 24: Gas recovery mechanism 241: Gas recovery room 242: Gas recovery port 243: Gas suction tube 3: Filter 4: Gas purification equipment 5: Gas supply 6: Gas supply device 7: Control unit G1: Optical fiber base material G2: Optical fiber

Claims

1. A method for manufacturing an optical fiber using a drawing furnace equipped with a carbon core tube, comprising the steps of: The method for manufacturing an optical fiber comprises drawing the optical fiber while supplying a gas containing an inert gas as a main component and having an oxygen concentration of 3 ppm or more and 20 ppm or less into the inside of the furnace tube.

2. 2. The method for producing an optical fiber according to claim 1, wherein the gas has an oxygen concentration of 5 ppm or more.

3. 3. The method for producing an optical fiber according to claim 1, wherein the gas has an oxygen concentration of 10 ppm or less.

4. 2. The method for producing an optical fiber according to claim 1, further comprising recovering the gas supplied to the inside of the furnace tube, purifying the gas, and supplying the purified gas to the inside of the furnace tube.

5. 5. The method for producing an optical fiber according to claim 1, wherein the inert gas is helium gas.

6. 5. The method for producing an optical fiber according to claim 1, wherein the temperature inside the furnace tube is 2200° C. or less.

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