Method for producing optical fiber and fiber drawing apparatus for optical fibers
Patent Information
- Application Number
- JP2024512748
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Filing Date
- 2024-06-21
- Publication Date
- 2024-12-17
Abstract
Description
Optical fiber manufacturing method and optical fiber drawing device
[0001] This disclosure relates to a method for manufacturing an optical fiber and an optical fiber drawing apparatus. This application claims priority to Japanese Application No. 2022-055713, filed on March 30, 2022, and incorporates by reference all of the contents of said Japanese application.
[0002] Patent Document 1 discloses an optical fiber drawing furnace having a lower extension tube below a core tube into which an optical fiber glass preform is inserted. In this drawing furnace, the lower extension tube recovers a portion of a first inert gas that is introduced into the core tube and flows into the lower extension tube. A gas screen is also provided below the lower extension tube. A second inert gas is supplied inside the gas screen to prevent air from being mixed into the lower extension tube due to the recovery of the portion of the first inert gas.
[0003] US Patent Application Publication No. 2017-101336
[0004] An optical fiber manufacturing method according to one aspect of the present disclosure is a manufacturing method of an optical fiber in which an optical fiber preform is heated and melted in a drawing furnace and drawn to form a glass fiber, wherein the drawing furnace comprises: a heating furnace for heating and melting the optical fiber preform; and a lower extension tube provided at the lower end of the heating furnace and through which the glass fiber passes, the lower extension tube comprising a fiber outlet port from which the glass fiber exits, and the drawing is performed while the fiber outlet port is covered with an atmosphere having a dew point temperature of 10°C or less.
[0005] An optical fiber drawing apparatus according to another aspect of the present disclosure is an optical fiber drawing apparatus that heats and melts an optical fiber preform and draws it to form a glass fiber, the drawing apparatus comprising: a heating furnace that heats and melts the optical fiber preform; a lower extension tube that is provided at the lower end of the heating furnace and through which the glass fiber passes and exits from a fiber outlet; a booth that surrounds the fiber outlet and has a supply port for supplying an inert gas into the booth; and an inert gas generator that generates the inert gas and supplies the generated inert gas to the supply port.
[0006] According to the configuration of the present disclosure, it is possible to prevent moisture contained in the atmosphere from adhering to the glass fiber coming out of the fiber outlet of the drawing furnace, and to prevent a decrease in the strength of the resulting optical fiber.
[0007] Fig. 1 is a schematic configuration diagram of an optical fiber manufacturing apparatus according to an embodiment of the present disclosure. Fig. 2 is a partially enlarged view showing a portion of a lower extension tube shown in Fig. 1. Fig. 3 is a partially enlarged view showing a modified example of the optical fiber manufacturing apparatus. Fig. 4 is a partially enlarged view showing another modified example of the optical fiber manufacturing apparatus. Fig. 5 is a schematic perspective view of a booth related to the modified example shown in Fig. 4.
[0008] [Problem to be Solved by the Present Disclosure] In an optical fiber drawing furnace, if moisture contained in the atmosphere adheres to a glass fiber emerging from a fiber outlet of the drawing furnace, this may result in a decrease in the strength of the resulting optical fiber.
[0009] An object of the present disclosure is to prevent moisture contained in the atmosphere from adhering to a glass fiber emerging from a fiber outlet of a drawing furnace, thereby preventing a decrease in the strength of the resulting optical fiber.
[0010] [Description of Embodiments of the Present Disclosure] First, embodiments of the present disclosure will be listed and described.
[0011] (1) An optical fiber manufacturing method according to one aspect of the present disclosure is a method of manufacturing an optical fiber by heating and melting an optical fiber preform in a drawing furnace and drawing it to form a glass fiber, the drawing furnace comprising: a heating furnace for heating and melting the optical fiber preform; and a lower extension tube provided at a lower end of the heating furnace and through which the glass fiber passes, the lower extension tube comprising a fiber outlet from which the glass fiber exits, and drawing is performed while covering the fiber outlet with an atmosphere having a dew point temperature of 10° C. or less. This method can prevent moisture contained in the atmosphere from adhering to the glass fiber exiting from the fiber outlet of the drawing furnace, thereby preventing a decrease in the strength of the resulting optical fiber.
[0012] (2) In the above (1), the heating furnace may include a gas inlet port for introducing a gas containing helium gas into the heating furnace, and the lower extension tube may include a gas suction port for sucking in the gas containing helium gas from inside the heating furnace and discharging it to the outside of the lower extension tube. The gas containing helium gas discharged from the gas suction port may be recycled and reused during drawing. When helium gas is sucked from the lower extension tube, the amount of helium gas flowing out of the fiber outlet along with the glass fiber decreases, and the glass fiber exiting the fiber outlet becomes more likely to be exposed to the atmosphere. According to the above method, the fiber outlet is covered with an atmosphere having a dew point temperature of 10°C or less, thereby preventing moisture from adhering to the glass fiber in the atmosphere. Therefore, it is possible to prevent a decrease in the strength of the optical fiber while allowing the expensive helium gas to be reused.
[0013] (3) In the above (1) or (2), the temperature of the glass fiber exiting the fiber outlet may be 1300°C or higher and 1700°C or lower. The higher the temperature of the glass fiber exiting the fiber outlet of the lower extension tube, the more the reaction between moisture in the atmosphere and the surface of the glass fiber is accelerated, making the surface of the glass fiber more susceptible to damage. According to the above method, even when the glass fiber is exiting the fiber outlet at a high temperature of 1300°C or higher, the fiber outlet is covered with an atmosphere having a dew point of 10°C or lower, thereby preventing moisture in the atmosphere from adhering to the glass fiber. This prevents a decrease in the strength of the optical fiber. Furthermore, by setting the glass fiber exit temperature to 1300°C or higher, it is possible to prevent the glass fiber from being rapidly cooled before exiting the fiber outlet of the lower extension tube, resulting in fluctuations in its outer diameter. On the other hand, by setting the glass fiber exit temperature to 1700°C or lower, it is possible to prevent defects on the surface of the glass fiber due to collision with dust in the atmosphere. As a result, it is possible to further prevent a decrease in the strength of the optical fiber.
[0014] (4) In any of the above (1) to (3), an inert gas may be supplied around the fiber outlet. This method allows the fiber outlet of the lower extension tube to be efficiently covered with an atmosphere having a dew point temperature of 10°C or less. Furthermore, by using an inert gas, it is possible to prevent air from entering the lower extension tube. As a result, it is possible to further prevent a decrease in the strength of the optical fiber.
[0015] (5) In any of the above (1) to (4), an inert gas may be supplied into the booth surrounding the fiber outlet. This method allows the fiber outlet of the lower extension pipe to be more effectively covered with an atmosphere having a dew point temperature of 10°C or less.
[0016] (6) In the above (5), the booth may have a first side surface and a second side surface opposite to the first side surface, and the inert gas may be supplied from the first side surface and discharged from the second side surface. According to this method, a flow of the inert gas is formed in the booth. Therefore, dust and gases such as dicyan ejected in the drawing furnace are less likely to remain.
[0017] (7) An optical fiber drawing apparatus according to an aspect of the present disclosure is an optical fiber drawing apparatus that heats and melts an optical fiber preform and draws it to form a glass fiber, the drawing apparatus comprising: a heating furnace that heats and melts the optical fiber preform; a lower extension tube that is provided at a lower end of the heating furnace and through which the glass fiber passes and exits from a fiber outlet; a booth that surrounds the fiber outlet and has a supply port for supplying an inert gas therein; and an inert gas generator that generates the inert gas and supplies the generated inert gas to the supply port. The drawing apparatus of the present disclosure generates the inert gas from the inert gas generator and supplies the inert gas into the booth from the supply port, thereby preventing moisture contained in the atmosphere from adhering to the glass fiber exiting from the fiber outlet and preventing a decrease in the strength of the resulting optical fiber.
[0018] (8) In the above (7), a plate may be provided between the supply port and a position inside the booth through which the glass fiber passes. With this configuration, the inert gas does not directly hit the glass fiber, thereby suppressing vibration of the glass fiber.
[0019] (9) In the above (7) or (8), a door may be provided on the front of the booth, which makes it easy for an operator to perform the initial work of drawing a glass fiber from an optical fiber preform (so-called seed removal work).
[0020] [Effects of the Present Disclosure] According to the configuration of the present disclosure, it is possible to prevent moisture contained in the atmosphere from adhering to the glass fiber coming out of the fiber outlet of the drawing furnace, and to prevent a decrease in the strength of the obtained optical fiber.
[0021] [Details of the Embodiments of the Present Disclosure] Examples of embodiments of an optical fiber manufacturing apparatus and manufacturing method according to the present disclosure will be described below with reference to the drawings. In the following description, the same or equivalent elements will be given the same reference numerals or names even in different drawings, and duplicate explanations will be omitted as appropriate. Furthermore, the dimensions of each component shown in each drawing are for convenience of explanation and may differ from the actual dimensions of each component.
[0022] (Optical fiber manufacturing apparatus) Fig. 1 is a schematic diagram of an optical fiber manufacturing apparatus 1 according to an embodiment of the present disclosure. The manufacturing apparatus 1 includes a drawing furnace 100. The drawing furnace 100 is an apparatus that heats and melts an optical fiber preform 2 and draws it to form a glass fiber 3. Although not shown, the manufacturing apparatus 1 may further include a cooling device that cools the glass fiber 3, an application device that applies a coating resin to the outer periphery of the glass fiber 3, a winding device that winds up the glass fiber 3 coated with the coating resin, and the like. The drawing furnace 100 is an example of an optical fiber drawing apparatus.
[0023] The drawing furnace 100 includes a heating furnace 10 and a lower extension tube 20. The heating furnace 10 heats and melts the optical fiber preform 2. The heating furnace 10 includes a housing 11, a furnace core tube 12, and a heater 13. The housing 11 is configured to surround the furnace core tube 12 and the heater 13. The heater 13 is arranged to surround the furnace core tube 12. A heat insulating material (not shown) is arranged between the heater 13 and the housing 11. The optical fiber preform 2 is suspended within the furnace core tube 12 by a preform suspension mechanism (not shown). The suspended optical fiber preform 2 has its lower portion melted by heat from the heater 13, and is drawn so as to continuously obtain glass fibers 3 having a predetermined outer diameter.
[0024] The furnace core tube 12 has a gas inlet 16. One end of a gas pipe 14 is connected to the gas inlet 16. The other end of the gas pipe 14 is connected to an inert gas supplier 15 that supplies an inert gas such as argon gas, helium gas, or nitrogen gas. The inert gas supplied from the inert gas supplier 15 passes through the gas pipe 14 and is supplied into the furnace core tube 12 from the gas inlet 16. The inert gas supplied into the furnace core tube 12 flows into the lower extension tube 20.
[0025] The lower extension tube 20 is provided at the lower end of the heating furnace 10. The lower extension tube 20 is provided so that its inlet is connected to the outlet of the muffle tube 12. The lower extension tube 20 is preferably provided, for example, below the heating furnace 10 so as to be in close contact with the heating furnace 10. The lower extension tube 20 may be formed integrally with the heating furnace 10, or may be provided detachably with respect to the heating furnace 10. A fiber outlet 21 is formed at the lower end of the lower extension tube 20. The glass fiber 3 drawn in the muffle tube 12 passes continuously through the lower extension tube 20 and exits from the fiber outlet 21. By providing the lower extension tube 20, rapid cooling of the heated and softened glass fiber 3 can be suppressed, while still allowing it to be cooled and hardened to a certain extent, thereby suppressing fluctuations in the outer diameter of the glass fiber 3.
[0026] The lower extension tube 20 has a gas suction port 22. The gas suction port 22 is provided to suck in a mixed gas containing an inert gas supplied into the furnace core tube 12 and flowing into the lower extension tube 20 and other gases containing impurities generated during the drawing process, and discharge the mixed gas to the outside of the lower extension tube 20. In the example of FIG. 1 , two gas suction ports 22 are provided. One end of a gas pipe 23 a is connected to one gas suction port 22. One end of a gas pipe 23 b is connected to the other gas suction port 22. Although part of the gas pipe 23 b is not shown, a gas regeneration device 24 is connected to the other ends of the gas pipes 23 a and 23 b. The gas regeneration device 24 separates and purifies an inert gas (e.g., helium gas) from the mixed gas sucked through the gas suction port 22, thereby regenerating the inert gas into a reusable state. The gas regeneration device 24 and the inert gas supplier 15 may be connected by a pipe 25 so that the inert gas regenerated by the gas regeneration device 24 is supplied to the inert gas supplier 15 .
[0027] 1, the lower extension tube 20 includes a shutter mechanism 26. As illustrated in FIG. 2, the shutter mechanism 26 includes an upper shutter 261 and a lower shutter 262. A gas recovery space 263 is formed between the upper shutter 261 and the lower shutter 262. The mixed gas G1 that has passed through the passage hole 261a of the upper shutter 261 and recovered in the gas recovery space 263 is sucked from the gas recovery space 263 to the outside by the gas suction port 22 formed in the bottom surface of the lower shutter 262.
[0028] The fiber outlet 21 formed in the center of the bottom surface of the lower shutter 262 is covered with an atmosphere having a dew point temperature of 10° C. or less. For example, as shown in FIG. 2 , a gas G2 whose dew point temperature is controlled to 10° C. or less is supplied around the fiber outlet 21.
[0029] (Method for Manufacturing Optical Fiber) Next, as a method for manufacturing an optical fiber according to this embodiment, a method for manufacturing an optical fiber using the manufacturing apparatus 1 shown in FIG. 1 will be described.
[0030] The method for manufacturing an optical fiber according to this embodiment includes a first step of heating and melting an optical fiber preform 2 in a heating furnace 10, a second step of passing the glass fiber 3 exiting the heating furnace 10 through a lower extension tube 20, and a third step of exiting the glass fiber 3 from a fiber outlet 21 covered with an atmosphere having a dew point temperature of 10°C or less.
[0031] In the first step, an optical fiber preform 2 is suspended in a furnace tube 12, and a heater 13 heats and melts the lower portion of the optical fiber preform 2. The molten optical fiber preform 2 is continuously drawn into a glass fiber 3 having a predetermined outer diameter by the weight of the molten glass and the tensile force. Also, in the first step, an inert gas is introduced into the furnace tube 12 from a gas inlet 16. The inert gas may be any of those mentioned above. The following describes the case where helium gas is used as the inert gas.
[0032] In the furnace core tube 12, for example, silica particles formed from silica components volatilized from the optical fiber preform 2, carbon particles peeled off from carbon parts used in the heating furnace 10, and the like are constantly generated. These impurities are carried to the lower extension tube 20 by the drag flow of the inert gas.
[0033] In the second step, the glass fiber 3 emerging from the heating furnace 10 (furnace core tube 12) passes through the lower extension tube 20. By passing through the lower extension tube 20, rapid cooling of the glass fiber 3 is alleviated and the glass fiber 3 is cooled and hardened to a certain extent, thereby suppressing fluctuations in its outer diameter. Also, in the second step, a mixed gas G1 containing helium gas in the lower extension tube 20 and other gases containing impurities and the like generated in the first and second steps is sucked in through the gas suction port 22. The sucked mixed gas is separated and purified by the gas regeneration device 24 to be regenerated as reusable helium gas.
[0034] In the third step, the glass fiber 3 that has passed through the lower extension tube 20 is output from the fiber outlet 21 that is covered with an atmosphere having a dew-point temperature of 10° C. or less. For example, the fiber outlet 21 is covered with an atmosphere having a dew-point temperature of 10° C. or less by supplying a gas G2 that is controlled to have a dew-point temperature of 10° C. or less around the fiber outlet 21. The glass fiber 3 that has been output from the fiber outlet 21 passes through an atmosphere having a dew-point temperature of 10° C. or less.
[0035] Incidentally, moisture contained in the atmosphere may adhere to the glass fiber 3 exiting from the fiber outlet 21 of the lower extension tube 20, thereby reducing the strength of the glass fiber 3. In particular, when the dew point temperature in the area where the optical fiber manufacturing apparatus is installed is high, a large amount of moisture may adhere to the glass fiber 3, increasing the frequency of breakage of the obtained optical fiber.
[0036] Table 1 shows the relationship between the dew point temperature in the area where the optical fiber manufacturing apparatus is installed and the frequency of fiber breakage. Using the same apparatus as optical fiber manufacturing apparatus 1, but without controlling the dew point temperature at the fiber outlet 21, facilities A to E were prepared in which the outlet temperature of the glass fiber 3 and the recovery of helium gas were varied, and the frequency of fiber breakage in the optical fiber was evaluated when the dew point temperature in the area was changed. The frequency of fiber breakage indicates the number of breakages that occurred per 1,000 km of optical fiber when a screening test was conducted in a process after fiber drawing.
[0037]
[0038] As shown in Table 1, it was found that when the dew point temperature of the area was low, the frequency of fiber breakage was stable in all of the equipment A to E. On the other hand, when the dew point temperature of the area was high, it was found that the frequency of fiber breakage increased in the equipment (equipment C, D) with a high outlet temperature of the glass fiber 3. Furthermore, when the outlet temperature of the glass fiber 3 was the same (equipment D, E), it was found that the increase in the frequency of fiber breakage when the dew point temperature was high was reduced when helium gas was not recovered (equipment E).
[0039] As described above, according to the optical fiber manufacturing method of the present disclosure, drawing is performed while the fiber outlet 21 of the lower extension tube 20 is covered with an atmosphere having a dew point temperature of 10° C. or less. This makes it possible to prevent moisture in the atmosphere from adhering to the glass fiber 3 exiting from the fiber outlet 21 of the lower extension tube 20, regardless of the dew point temperature of the area where the optical fiber manufacturing apparatus 1 is installed or the exit temperature of the glass fiber. As a result, the surface of the glass fiber 3 is less likely to be scratched, and a decrease in the strength of the obtained optical fiber can be suppressed.
[0040] Furthermore, when the helium gas introduced into the heating furnace 10 is recovered and reused, the frequency of fiber breakage increases compared to when the helium gas is not recovered, as shown in Table 1. This is thought to be because the amount of helium gas flowing out of the fiber outlet 21 decreases, making the glass fiber 3 more susceptible to exposure to the atmosphere. However, as described above, the fiber outlet 21 is covered with an atmosphere having a dew point temperature of 10°C or less, which prevents moisture from the atmosphere from adhering to the glass fiber 3. Therefore, it is possible to prevent a decrease in the strength of the optical fiber while allowing the expensive helium gas to be reused.
[0041] The temperature of the glass fiber 3 exiting from the fiber outlet 21 is preferably 1300° C. or higher. The temperature of the glass fiber 3 exiting from the fiber outlet 21 is preferably 1700° C. or lower. The temperature of the glass fiber 3 exiting from the fiber outlet 21 can be controlled, for example, by changing the length of the lower extension tube 20 or by changing the temperature or flow rate of the helium gas.
[0042] As the outlet temperature of the glass fiber 3 increases, the reaction between moisture in the atmosphere and the surface of the glass fiber is promoted, resulting in an increased frequency of breakage, as shown in Table 1. However, even when the glass fiber 3 is taken out of the fiber outlet 21 at a high temperature of 1300°C or higher, the fiber outlet 21 is covered with an atmosphere with a dew-point temperature of 10°C or lower, which prevents moisture from adhering to the glass fiber 3. Furthermore, by setting the outlet temperature of the glass fiber 3 to 1300°C or higher, it is possible to prevent the glass fiber 3 from being rapidly cooled before it is taken out of the fiber outlet 21 of the lower extension tube 20, thereby preventing fluctuations in its outer diameter. On the other hand, by setting the outlet temperature of the glass fiber 3 to 1700°C or lower, it is possible to prevent defects on the surface of the glass fiber due to collision with dust in the atmosphere.
[0043] In this example, gas G2, whose dew point temperature is controlled to be 10° C. or less, is supplied to the periphery of the fiber outlet 21. This allows the fiber outlet 21 to be efficiently covered with an atmosphere having a dew point temperature of 10° C. or less. Examples of gas G2 include inert gases such as argon gas and nitrogen gas. When an inert gas is used, it is possible to prevent air from entering the lower extension tube 20.
[0044] As a configuration for supplying gas G2 to the periphery of the fiber outlet port 21, for example, as shown in Fig. 3, the optical fiber manufacturing apparatus 1 may include a gas purge pipe 30. The gas purge pipe 30 is provided at the lower end of the lower extension pipe 20. The gas purge pipe 30 is provided so as to connect the outlet of the lower extension pipe 20 and the inlet of the gas purge pipe 30, and is preferably provided, for example, so as to be in close contact with the lower extension pipe 20. The gas purge pipe 30 may be formed integrally with the lower extension pipe 20, or may be provided detachably with respect to the lower extension pipe 20. The glass fiber 3 exiting from the fiber outlet port 21 of the lower extension pipe 20 passes continuously through the gas purge pipe 30.
[0045] The gas purge pipe 30 has a gas inlet 31. The gas inlet 31 is provided to supply the gas G2 into the gas purge pipe 30. In the example of FIG. 3 , two gas inlets 31 are provided. A first end of a gas pipe 32a is connected to one of the gas inlets 31. A first end of a gas pipe 32b is connected to the other gas inlet 31. Although a portion of the gas pipe 32b is not shown, a gas supplier 33 is connected to second ends of the gas pipes 32a and 32b. The gas G2 supplied from the gas supplier 33 passes through the gas pipes 32a and 32b and is supplied from the gas inlet 31 into the gas purge pipe 30. The gas G2 supplied into the gas purge pipe 30 is supplied to the periphery of the glass fiber 3 passing through the gas purge pipe 30.
[0046] In the example shown in FIG. 3 , the gas purge pipe 30 includes an outer wall 34 and an inner wall 35. The inner wall 35 is provided inside the outer wall 34. The outer wall 34 and the inner wall 35 form a double-pipe structure. Specifically, the outer wall 34 and the inner wall 35 each form a pipe extending along the traveling direction of the glass fiber 3. A cavity is formed between the outer wall 34 and the inner wall 35. The inner wall 35 is shorter than the outer wall 34. The gas inlet 31 is provided in the outer wall 34 above the lower end of the inner wall 35. With this configuration, the inner wall 35 prevents the gas G2 introduced from the gas inlet 31 from directly hitting the glass fiber 3. That is, the gas G2 introduced into the gas purge pipe 30 collides with the inner wall 35 and is diffused inside the gas purge pipe 30.
[0047] The gas G2 may be supplied to the periphery of the fiber outlet port 21 using a configuration other than the gas purge tube 30. As another configuration for supplying the gas G2 to the periphery of the fiber outlet port 21, for example, as shown in FIG. 4 , the optical fiber manufacturing apparatus 1 may include a booth 40. The booth 40 is provided at the lower end of the lower extension tube 20. The booth 40 is provided so that the outlet of the lower extension tube 20 and the inlet of the booth 40 are connected, and is preferably provided, for example, so as to be in close contact below the lower extension tube 20. The booth 40 may be formed integrally with the lower extension tube 20, or may be provided detachably with respect to the lower extension tube 20. In the example of FIG. 4 , the inlet of the booth 40 is wider than the outlet of the lower extension tube 20, and the booth 40 is provided so as to surround the fiber outlet port 21 of the lower extension tube 20. The glass fiber 3 output from the fiber outlet port 21 of the lower extension tube 20 passes continuously through the interior of the booth 40.
[0048] In the example of FIG. 4 , the booth 40 has a rectangular parallelepiped shape extending in the traveling direction of the glass fiber 3. The booth 40 has a first side surface 41 and a second side surface 42. The second side surface 42 is a surface opposite to the first side surface 41. The glass fiber 3 passes between the first side surface 41 and the second side surface 42. A supply port 43 is provided in the first side surface 41. A discharge port 44 is provided in the second side surface 42. The discharge port 44 may be, for example, a slit whose opening size can be changed. The gas G2 is supplied from the supply port 43 and discharged from the discharge port 44. In other words, the supply port 43 is provided to supply the gas G2 into the booth 40, and the discharge port 44 is provided to discharge the gas G2 from the booth 40. In this way, the gas G2 is supplied from the supply port 43 to the discharge port 44, passing around the glass fiber 3 and blowing through.
[0049] 4 , a first end of a supply pipe 43 a is connected to the supply port 43. A gas generator 45 is connected to a second end of the supply pipe 43 a. A first end of an exhaust pipe 44 a is connected to the exhaust port 44. A second end of the exhaust pipe 44 a is connected to the outside of the drawing furnace 100 (not shown).
[0050] The gas generator 45 is configured to generate gas G2 and supply the generated gas G2 to the supply port 43. In this example, the gas G2 may also be an inert gas that is controlled so that the dew-point temperature around the fiber outlet 21 is 10°C or lower. The gas G2 may also be dry air that is controlled so that the dew-point temperature around the fiber outlet 21 is 10°C or lower. The dry air is air in which water vapor in the air has been adsorbed by a desiccant, thereby reducing the water vapor content. The desiccant includes at least one of zeolite, silica gel, and a refrigerated desiccant.
[0051] The gas G2 generated in the gas generator 45 passes through a supply pipe 43a and is supplied into the booth 40 from a supply port 43 on the first side surface 41. The gas G2 supplied into the booth 40 is supplied to the periphery of the glass fiber 3 passing through the booth 40. The gas G2 supplied into the booth 40 is further discharged from an exhaust port 44 on the second side surface 42 through an exhaust pipe 44a to the outside of the drawing furnace 100. The gas generator 45 is an example of an inert gas generator.
[0052] In this way, gas G2 is supplied into the booth 40 covering the fiber outlet 21. This makes it possible to more effectively cover the fiber outlet 21 of the lower extension tube 20 with an atmosphere having a dew point temperature of 10° C. or less. Furthermore, since gas G2 is supplied from the supply port 43 and discharged from the discharge port 44, a flow of gas G2 is formed in the booth 40 so as to pass around the glass fiber 3. Therefore, gases such as dust and dicyan ejected from the drawing furnace 100 are less likely to remain.
[0053] In the example of FIG. 4 , the booth 40 further includes a plate 46 between the supply port 43 and a position inside the booth 40 through which the glass fiber 3 passes. Specifically, the plate 46 extends between the supply port 43 and the glass fiber 3 along the traveling direction of the glass fiber 3. The plate 46 may be supported directly or indirectly on the first side surface 41, or may be supported directly or indirectly on the upper surface of the booth 40. A cavity is formed between the supply port 43 and the plate 46. The length of the plate 46 in the traveling direction of the glass fiber 3 is longer than the opening length of the supply port 43 in the traveling direction of the glass fiber 3. Furthermore, the supply port 43 is provided on the first side surface 41 above the lower end of the plate 46. With this configuration, the plate 46 prevents the gas G2 supplied from the supply port 43 from directly hitting the glass fiber 3. That is, the gas G2 supplied into the booth 40 hits the plate 46 and is diffused inside the booth 40. Therefore, vibration of the glass fiber 3 can be suppressed.
[0054] Furthermore, the booth 40 may be provided with an opening / closing door 48 on a front surface 47 that is different from the first side surface 41 and the second side surface 42. Fig. 5 is a schematic perspective view of the booth 40. As shown in Fig. 5, the opening / closing door 48 is provided on the front surface 47 of the booth 40. With this configuration, an operator can open the opening / closing door 48 to check the inside of the booth 40, which makes it easier to perform the initial work of drawing a glass fiber from an optical fiber preform (so-called seed removal work).
[0055] Although the present disclosure 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 disclosure. 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 disclosure. Furthermore, the elements included in each of the above-described examples can be combined with each other.
[0056] The lower extension tube 20 may be configured without including the shutter mechanism 26 .
[0057] The gas purge pipe 30 has a double pipe structure, but is not limited to this structure.
[0058] The gas G2 may be supplied to the periphery of the fiber outlet port 21 using a configuration other than the gas purge pipe 30 and the booth 40 .
[0059] The methods shown here are a method of supplying gas G2 around the fiber outlet 21 and a method of providing a booth 40. However, other methods may be used to cover the fiber outlet 21 with an atmosphere having a dew point temperature of 10° C. or less. For example, the air conditioning in the room in which the optical fiber manufacturing apparatus 1 is installed may be controlled so that the dew point temperature throughout the room is 10° C. or less.
[0060] The optical fiber manufacturing apparatus 1 may include, in addition to the drawing furnace 100, a cooling device, a coating device, and a winding device (none of which are shown), an annealing furnace between the drawing furnace 100 and the cooling device, which slowly lowers the temperature of the glass fiber 3 drawn from the drawing furnace 100. An inert gas or dry air may be supplied to the inside of the annealing furnace. The booth 40 may be provided between the drawing furnace 100 and the annealing furnace, or between the annealing furnace and the cooling device.
[0061] 1: Optical fiber manufacturing apparatus 2: Optical fiber preform 3: Glass fiber 10: Heating furnace 11: Housing 12: Furnace tube 13: Heater 14: Gas pipe 15: Inert gas supplier 16: Gas inlet 20: Lower extension tube 21: Fiber outlet 22: Gas suction port 23a, 23b: Gas pipe 24: Gas regeneration device 25: Pipe 26: Shutter mechanism 261: Upper shutter 261a: Passage hole 262: Lower shutter 263: Gas recovery space 30: Gas purge pipe 31: Gas inlet 32a, 32b: Gas pipe 33: Gas supplier 34: Outer wall 35: Inner wall 40: Booth 41: First side surface 42: Second side surface 43: Supply port 43a: Supply pipe 44: Discharge port 44a: Discharge pipe 45: Gas generator 46: Plate 47: Front 48: Openable door 100: Drawing furnace G1: Mixed gas G2: Gas
Claims
1. A method for manufacturing an optical fiber, comprising the steps of: heating and melting an optical fiber preform in a drawing furnace and drawing the preform to form a glass fiber, The wire drawing furnace is a heating furnace for heating and melting the optical fiber preform; a lower extension tube provided at a lower end of the heating furnace and through which the glass fiber passes; the lower extension tube has a fiber outlet from which the glass fiber is led out, The fiber is drawn while covering the fiber outlet with an atmosphere having a dew point of 10° C. or less. A method for manufacturing optical fiber.
2. the heating furnace includes a gas inlet for introducing a gas containing helium gas into the heating furnace; the lower extension tube has a gas suction port for suctioning gas including helium gas therein and discharging it to the outside of the lower extension tube, A wire is drawn while regenerating and reusing the gas including the helium gas discharged from the gas suction port. The method for producing the optical fiber according to claim 1 .
3. 2. The method for producing an optical fiber according to claim 1, wherein the temperature of the glass fiber exiting from the fiber outlet is 1300° C. or higher and 1700° C. or lower.
4. The method for producing an optical fiber according to claim 1 , further comprising the step of supplying an inert gas to a periphery of said fiber outlet.
5. The method for producing an optical fiber according to claim 1 , further comprising the step of supplying an inert gas into a booth surrounding the fiber outlet port.
6. The booth has a first side and a second side opposite the first side, The method for producing an optical fiber according to claim 5 , wherein the inert gas is supplied from the first side and exhausted from the second side.
7. An optical fiber drawing apparatus for forming a glass fiber by heating and melting an optical fiber preform and drawing the preform, the optical fiber drawing apparatus comprising: a heating furnace for heating and melting the optical fiber preform; a lower extension tube provided at a lower end of the heating furnace through which the glass fiber passes and through which the glass fiber exits from a fiber outlet; a booth surrounding the fiber outlet and having a supply port for supplying an inert gas therein; an inert gas generator that generates the inert gas and supplies the generated inert gas to the supply port.
8. 8. The optical fiber drawing apparatus of claim 7, further comprising a plate disposed between said feed opening and a location in said interior of said booth through which said glass fiber passes.
9. 9. The optical fiber drawing apparatus according to claim 7, wherein an opening and closing door is provided on a front surface of the booth.