Heating device for glass member, heating method for glass member, and method for manufacturing base material for optical fiber using the same

Abstract

To provide an apparatus and method for heating a glass member, capable of detecting an abnormal state due to water, and a method for manufacturing an optical fiber preform using the same.SOLUTION: A dehydration sintering apparatus 100 used as an apparatus for heating a glass member includes: a furnace core tube 31 having a storage space 31S capable of storing a core porous glass body 20 used as the glass member; a furnace body 35 surrounding a part of the furnace core tube 31; a heater 37 arranged in a space 35S surrounded by the furnace core tube 31 and the furnace body 35; and a gas measurement part 48. Carbon is included in at least one of members arranged in the space 35S; and the gas measurement part 48 can measure the concentration of gas generated due to a reaction of water with carbon in the space.SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] The present invention relates to a heating device for a glass member, a method for heating a glass member, and a method for manufacturing a preform for an optical fiber using the same.

Background Art

[0002] As a method for manufacturing a preform for an optical fiber used in the manufacture of an optical fiber, a method is known in which glass fine particles are deposited using an OVD method (Outside Vapor Deposition method), a VAD method (Vapor Phase Axial Deposition method), or the like to form a porous glass body, and the porous glass body is heated and sintered.

[0003] Patent Document 1 below discloses a heating device for heating a porous glass body. This heating device includes a hearth tube having an accommodation space for accommodating the porous glass body, a heater disposed outside the hearth tube, a furnace body surrounding a part of the hearth tube and the heater, and a gas detector. This gas detector detects leakage gas that leaks from the hearth tube into the space surrounded by the hearth tube and the furnace body and is discharged from an exhaust port provided in the furnace body. Therefore, according to this heating device, it is said that damage such as cracks in the hearth tube can be detected by the gas detector.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Incidentally, the furnace body of the heating device as described above may be cooled by cooling water. If the furnace body is damaged, the cooling water may enter the space surrounded by the core tube and the furnace body. Further, an inert gas may be supplied to this space to suppress the combustion of the members arranged in this space, and water may enter this space together with the inert gas due to a defect in the gas supply device or the like. The core tube is generally made of quartz, carbon, or the like. In such an abnormal state where water enters the above space, even if the core tube is not damaged, water may penetrate from this space into the accommodation space of the core tube. When water enters the accommodation space when sintering the porous glass body by heating with a heater, the characteristics of the finally manufactured optical fiber, such as transmission loss, may deteriorate.

[0006] Therefore, an object of the present invention is to provide a heating device for a glass member capable of detecting an abnormal state caused by water, a method for heating a glass member, and a method for manufacturing a base material for an optical fiber using the same.

Means for Solving the Problems

[0007] To achieve the above object, the heating device for a glass member of the present invention includes a core tube having an accommodation space capable of accommodating at least a part of the glass member, a furnace body surrounding at least a part of the core tube, a heater arranged in a space surrounded by the core tube and the furnace body, and a gas measurement unit. At least one of the members arranged in the space contains carbon, and the gas measurement unit is capable of measuring the concentration of the gas generated due to the reaction between water and carbon in the space.

[0008] Further, to achieve the above object, the present invention provides a method for heating a glass member, which includes accommodating at least a part of the glass member in an accommodation space in a core tube at least partially surrounded by a furnace body, and heating the glass member with a heater arranged in a space surrounded by the core tube and the furnace body. At least one of the members arranged in the space contains carbon, and the concentration of the gas generated due to the reaction between water and carbon in the space is measured while heating the glass member with the heater.

[0009] When dehydrating, sintering, melting, etc. a glass member, generally, the heater is heated to 700 °C or higher. In such a high-temperature state, if water enters the above space, the water reacts with carbon contained in the member disposed in this space to generate gas. In this heating device for a glass member and the method for heating a glass member, since the concentration of the gas thus generated can be measured, an abnormal state in which water has entered the above space can be detected.

[0010] The gas may be at least one of carbon monoxide, carbon dioxide, methane, and hydrogen.

[0011] The furnace body may have a flow path through which cooling water flows.

[0012] By adopting such a configuration, damage to the furnace body due to heat can be suppressed. Further, since the gas measurement unit can measure the concentration of the gas generated in the above space due to the reaction between water and carbon, damage to the furnace body in which cooling water enters the above space can be detected.

[0013] The heating device for the glass member may further include a gas supply unit that supplies an inert gas into the space from an air supply port formed in the furnace body and communicating with the space.

[0014] By adopting such a configuration, combustion of the member disposed in the above space can be suppressed. Further, since the gas measurement unit can measure the concentration of the gas generated in the above space due to the reaction between water and carbon, malfunctions of the gas supply unit, piping, etc. in which water enters the above space together with the inert gas can be detected.

[0015] In the heating device for the glass member, the gas measurement unit may measure the concentration of the gas from the exhaust gas exhausted from an exhaust port formed in the furnace body and communicating with the space.

[0016] By adopting such a configuration, compared with the case of measuring the concentration of the gas at a certain point in the above-mentioned space, the influence of the location where the gas is generated in the space on the concentration of the gas can be suppressed. Therefore, compared with the above-mentioned case, an abnormal state in which water has entered the above-mentioned space can be accurately detected.

[0017] The heating device for the glass member further includes an abnormality determination unit that determines whether it is in an abnormal state based on the change over time of the concentration of the gas measured by the gas measurement unit. The abnormality determination unit may determine that it is in an abnormal state when the difference between the concentration of the gas measured by the gas measurement unit and the average value of the concentration of the gas measured by the gas measurement unit before the timing when the concentration of the gas is measured is equal to or greater than a predetermined value.

[0018] Even for furnace bodies with the same configuration, the concentration of the above-mentioned gas measured in the steady state tends to change according to the installation state of the furnace body. Therefore, by adopting the above-mentioned configuration, compared with the case of determining that it is in an abnormal state when the concentration of the gas is equal to or greater than a predetermined value, it is possible to appropriately determine whether it is in an abnormal state.

[0019] The heating device for the glass member further includes a fiber defect determination unit. The glass member is a porous glass body that forms part of an optical fiber. The fiber defect determination unit may determine whether the optical fiber is defective based on the change over time of the concentration of the gas measured by the gas measurement unit.

[0020] As described above, when water enters the accommodation space during sintering of the porous glass body, the characteristics of the finally manufactured optical fiber, such as transmission loss, may deteriorate, and the more water enters the accommodation space, the more likely the characteristics are to deteriorate. Such intrusion of water into the accommodation space may not affect the appearance of the transparent glass member formed by sintering the porous glass body. Therefore, it may be difficult to determine whether the characteristics of the finally manufactured optical fiber deteriorate and the optical fiber becomes defective based on the appearance of the transparent glass member. However, the greater the amount of water that enters the accommodation space, the greater the amount of gas generated due to the reaction between water and carbon, and the higher the concentration of this gas. Therefore, by adopting the above configuration, it is possible to determine whether the finally manufactured optical fiber becomes defective at the stage of manufacturing the transparent glass member, reduce the defect rate of the optical fiber, and improve the productivity of the optical fiber.

[0021] In this case, the gas is carbon monoxide, the glass member is the porous glass body that becomes the core of the optical fiber, and the fiber defect determination unit determines that the optical fiber is defective when the difference between the concentration of the gas measured by the gas measurement unit and the concentration of the gas in the initial state before first heating the glass member after the furnace body is installed exceeds 550 ppm.

[0022] The inventor has found that when the difference between the concentration of carbon monoxide when heating the porous glass body that becomes the core and the concentration of carbon monoxide in the above initial state exceeds 550 ppm, the optical fiber manufactured from the optical fiber preform including the core glass body made of the porous glass body becomes defective. Therefore, by adopting such a configuration, it is possible to appropriately predict whether the finally manufactured optical fiber becomes defective.

[0023] The method for manufacturing an optical fiber preform of the present invention is characterized by comprising a heating step of heating the porous glass body as the glass member by the above-described heating method of the glass member.

Effects of the Invention

[0024] As described above, according to the present invention, there are provided a heating device for a glass member capable of detecting an abnormal state caused by water, a method for heating a glass member, and a method for manufacturing a base material for an optical fiber using the same.

Brief Description of the Drawings

[0025]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Embodiments for Carrying Out the Invention

[0026] Hereinafter, a heating device for a glass member, a method for heating a glass member, and a method for manufacturing a base material for an optical fiber using the same according to the present invention are illustrated together with the accompanying drawings. The embodiments illustrated below are for facilitating the understanding of the present invention and are not for limiting the interpretation of the present invention. The present invention can be changed and improved without departing from its gist. In the drawings referred to below, for the sake of easy understanding, the dimensions of each member may be shown changed.

[0027] FIG. 1 is a diagram schematically showing a state of a cross section perpendicular to the longitudinal direction of an optical fiber according to an embodiment of the present invention. As shown in FIG. 1, the optical fiber 1 of the present embodiment mainly includes a core 10, a cladding 11 surrounding the outer peripheral surface of the core 10, and a coating layer 12 covering the outer peripheral surface of the cladding 11. The outer shape of the core 10 in the cross section is circular, and the core 10 is arranged at the center of the cladding 11. Note that the outer shape of the cladding 11 in the cross section may be non-circular such as an ellipse or a polygon. In FIG. 1, an optical fiber 1 in which the outer shape of the cladding 11 is circular is shown.

[0028] The refractive index of the core 10 is made higher than that of the cladding 11. In the present embodiment, the core 10 is made of silica glass to which a dopant having a high refractive index such as germanium (Ge) is added, and the cladding 11 is made of silica glass without any additives. Note that the core 10 may be made of silica glass without any additives, and the cladding 11 may be made of silica glass to which a dopant having a low refractive index such as fluorine (F) is added. Further, the core 10 may be made of silica glass to which a dopant for increasing the refractive index is added, and the cladding 11 may be made of silica glass to which a dopant for decreasing the refractive index is added. Further, the dopant for increasing the refractive index and the dopant for decreasing the refractive index are not particularly limited.

[0029] The coating layer 12 is made of resin. Examples of the resin constituting the coating layer 12 include a thermosetting resin and an ultraviolet curable resin. The coating layer 12 may have a single-layer structure composed of one resin layer surrounding the cladding 11, or may have a multilayer structure composed of a plurality of resin layers.

[0030] Figure 2 is a diagram schematically showing a cross-section perpendicular to the longitudinal direction of a preform for an optical fiber for manufacturing the optical fiber 1 shown in Figure 1. As shown in Figure 2, the preform 1P for an optical fiber is composed of a rod-shaped core glass body 10P that becomes the core 10 and a cladding glass body 11P that surrounds the outer peripheral surface of the core glass body 10P and becomes the cladding 11. In the present embodiment, the outer shape of the cladding glass body 11P in the cross-section is circular, and the core glass body 10P is arranged at the center of the cladding glass body 11P. Further, the outer shape of the core glass body 10P in the cross-section is circular.

[0031] Next, a method for manufacturing a preform for an optical fiber according to the present embodiment will be described.

[0032] Figure 3 is a flowchart showing the steps of a method for manufacturing a preform 1P for an optical fiber according to the present embodiment. As shown in Figure 3, the method for manufacturing the preform 1P for an optical fiber of the present embodiment includes a first deposition step P1, a first heating step P2, a second deposition step P3, and a second heating step P4.

[0033] <First deposition step P1> This step is a step of depositing glass fine particles to form a porous glass body for the core that becomes the core glass body 10P shown in Figure 2. The porous glass body can be formed by a soot method such as the OVD method or the VAD method. In the present embodiment, by the VAD method, glass fine particles are deposited from one end of the prepared glass rod along the axial direction of the glass rod to form a porous glass body for the core.

[0034] <First heating step P2> This step is a step of heating the porous glass body for the core as a glass member formed by the first deposition step P1, and as shown in Figure 3, includes a first dehydration step P2a and a first sintering step P2b. First, a dehydration and sintering apparatus as a heating apparatus for the glass member used in this step will be described.

[0035] FIG. 4 is a diagram schematically showing a dehydration sintering apparatus used in the first heating step P2. As shown in FIG. 4, the dehydration sintering apparatus 100 of the present embodiment mainly includes a heating furnace 30, a lifting unit 40, a first gas supply unit 41, a second gas supply unit 42, a gas measurement unit 48, a determination unit 50, a memory 55, a notification unit 56, and a control unit 60.

[0036] The control unit 60 is composed of, for example, an integrated circuit such as a microcontroller, an IC (Integrated Circuit), an LSI (Large-scale Integrated Circuit), an ASIC (Application Specific Integrated Circuit), or an NC (Numerical Control) device. Further, when an NC device is used, the control unit 60 may or may not use a machine learning device. As will be described below, some components of the dehydration sintering apparatus 100 are controlled by the control unit 60.

[0037] In the present embodiment, the heating furnace 30 mainly includes a furnace core tube 31, a furnace body 35, a heater 37, and a heat insulating material 38.

[0038] The furnace core tube 31 of the present embodiment is a cylindrical member extending in the vertical direction, and the porous glass body 20 for the core can be accommodated in the accommodation space 31S. In the present embodiment, the openings at both ends of the furnace core tube 31 are closed, and the part closing the upper opening is detachable from other parts. A through hole for inserting a support rod 22 for suspending the porous glass body 20 for the core is formed in the part closing the upper opening of the furnace core tube 31. A connection part 23 is provided at the lower end of the support rod 22, and a glass rod 24 on which the porous glass body 20 for the core is deposited is connected to this connection part 23. An exhaust port E1 and an air supply port S1 communicating with the accommodation space 31S are formed in the furnace core tube 31. Examples of the material constituting the furnace core tube 31 include quartz and carbon.

[0039] The furnace body 35 of this embodiment is formed in a hollow box shape, and has a flow path 36 through which cooling water supplied from a cooling water supply unit (not shown) flows inside the outer wall of the furnace body 35. When the cooling water flows through the flow path 36, the furnace body 35 is cooled, and damage to the furnace body 35 due to heat is suppressed. Further, a through hole penetrating in the vertical direction is formed in the central portion of the furnace body 35, and the core tube 31 is inserted into the through hole. The upper end portion and the lower end portion of the core tube 31 each protrude from the furnace body 35, and the furnace body 35 surrounds the central portion of the core tube 31 in the vertical direction, and a space 35S surrounded by the core tube 31 and the furnace body 35 is formed. Further, an air supply port S2 and an exhaust port E2 communicating with this space 35S are formed in the furnace body 35. The air supply port S2 is located on one side in the horizontal direction with respect to the core tube 31, and the exhaust port E2 is located on the other side. Examples of the material constituting the furnace body 35 include metal.

[0040] The heater 37 is disposed in the space 35S so as to be able to heat the porous glass body 20 for the core accommodated in the accommodation space 31S of the core tube 31 by generating heat. The heater 37 of this embodiment is made of carbon and is formed in a ring shape surrounding the core tube 31. However, the heater 37 may be configured by being divided into a plurality of heating parts, and these plurality of heating parts may be discontinuously arranged so as to surround the core tube 31. The heater 37 adjusts the heat generation temperature according to a control signal from the control unit 60. In order to effectively utilize the heat generated by the heater 37, a heat insulating material 38 is disposed between the heater 37 and the furnace body 35 in the space 35S. The number of the heat insulating materials 38 is not particularly limited, and the heat insulating material 38 may be divided into a plurality of parts. The heat insulating material 38 of this embodiment is made of carbon. Therefore, in this embodiment, the heater 37 and the heat insulating material 38, which are members disposed in the space 35S, contain carbon. Note that it is sufficient that at least one of the members disposed in the space 35S contains carbon. For example, one of the heater 37 and the heat insulating material 38 may be made of, for example, silicon carbide, and the heating furnace 30 may not include the heat insulating material 38.

[0041] The elevating part 40 raises and lowers the support rod 22 to be gripped. The elevating part 40 moves the porous glass body 20 for core up and down by raising and lowering the support rod 22 according to a control signal from the control part 60. Note that the configuration of the elevating part 40 is not particularly limited.

[0042] The first gas supply part 41 supplies a first gas containing a dehydration gas into the accommodation space 31S through a pipe 43 connected to the air supply port S1 of the core tube 31. The first gas supply part 41 adjusts the supply amount of the first gas according to a control signal from the control part 60. The first gas supplied into the accommodation space 31S is exhausted from the exhaust port E1 of the core tube 31 to the exhaust pipe 44. In this embodiment, the first gas is a mixed gas of a dehydration gas and an inert gas. Examples of the dehydration gas include chlorine-based gases such as chlorine, SiCl4, thionyl chloride (SOCl2), carbon tetrachloride (CCl4), and carbon monoxide. Examples of the inert gas include He, Ar, N2, etc.

[0043] The second gas supply part 42 supplies a second gas, which is an inert gas, into the space 35S through a pipe 45 connected to the air supply port S2 of the furnace body 35. The second gas supply part 42 adjusts the supply amount of the second gas according to a control signal from the control part 60. The second gas supplied into the space 35S is exhausted from the exhaust port E2 of the furnace body 35 to the exhaust pipe 46. Examples of the second gas include He, Ar, N2, etc.

[0044] In this embodiment, the gas measurement unit 48 is attached to the exhaust pipe 46, measures the concentration of a predetermined gas in the exhaust gas exhausted from the exhaust port E2, and outputs a signal indicating the measured concentration of the predetermined gas to the determination unit 50. The gas measurement unit 48 repeats this measurement and output intermittently or continuously. The predetermined gas is a gas generated due to the reaction between water and carbon. As described above, at least one of the members disposed in the space 35S contains carbon. Therefore, when water enters the space 35S in a state where the temperature of the space 35S is such that water and carbon react, for example, at a temperature of 700 °C or higher, the water reacts with the carbon contained in the member disposed in the space 35S, and a predetermined gas may be generated. In a high-temperature state where water and carbon react, it is considered that water is decomposed into hydrogen atoms and oxygen atoms, and the hydrogen atoms and oxygen atoms react with carbon. Examples of the predetermined gas include carbon monoxide, carbon dioxide, methane, oxygen, and hydrogen, and the gas measurement unit 48 is configured to be able to measure the concentration of at least one of these. Examples of those for measuring the concentration of carbon monoxide include a constant potential electrolytic sensor, examples of those for measuring the concentration of carbon dioxide include a non-dispersive infrared sensor, examples of those for measuring the concentration of methane or hydrogen include a semiconductor laser absorption spectroscopic sensor, and examples of those for measuring the concentration of oxygen include a zirconia concentration difference cell sensor. The gas measurement unit 48 of this embodiment is configured to be able to measure the concentration of carbon monoxide. Note that the gas measurement unit 48 only needs to be able to measure the concentration of the above-described predetermined gas in the space 35S, and may be attached to the furnace body 35, for example.

[0045] The determination unit 50 of this embodiment causes the memory 55 to store the concentration of the predetermined gas measured by the gas measurement unit 48, and based on the change over time of the concentration of the predetermined gas, determines whether the dehydration sintering apparatus 100 is in an abnormal state and whether the manufactured optical fiber becomes defective. As a configuration of the determination unit 50, for example, a configuration similar to that of the control unit 60 can be mentioned.

[0046] The memory 55 is, for example, a non-transitory recording medium, and a semiconductor recording medium such as a RAM (Random Access Memory) or a ROM (Read Only Memory) is suitable, but it may include any form of recording medium such as an optical recording medium or a magnetic recording medium. In the present embodiment, programs and information for executing these determination processes are stored in the memory 55. The determination unit 50 reads programs and information from the memory 55, and in this state, includes an abnormality determination unit 51 and a fiber defect determination unit 52, and executes the above-described determination process.

[0047] The abnormality determination unit 51 determines whether the dehydration sintering apparatus 100 is in an abnormal state based on the change over time in the concentration of a predetermined gas measured by the gas measurement unit 48. As will be described later, the present inventor has found that when the difference between the concentration of the predetermined gas measured by the gas measurement unit 48 and the average value of the concentration of the predetermined gas measured by the gas measurement unit 48 before the timing at which the concentration of the gas is measured is equal to or greater than a first predetermined value, it is an abnormal state in which water has entered the space 35S. This is presumably because water enters the space 35S and a predetermined gas is generated by the reaction between the water and carbon, causing the concentration of the predetermined gas to increase. Therefore, in the abnormality determination unit 51 of the present embodiment, when the difference between the concentration of the predetermined gas measured by the gas measurement unit 48 and the average value of the concentration of the predetermined gas measured by the gas measurement unit 48 before the timing at which the concentration of the gas is measured is equal to or greater than a first predetermined value, a signal indicating an abnormal state is output to the notification unit 56 via the control unit 60. On the other hand, when the above difference is less than the first predetermined value, the abnormality determination unit 51 does not output a signal to the control unit 60, but may output a signal indicating that it is not in an abnormal state to the notification unit 56 via the control unit 60. Therefore, the determination by the abnormality determination unit 51 is to change the output signal in response to the signal from the gas measurement unit 48. Note that the above first predetermined value can be set in advance by experiments or the like. For example, when the predetermined gas is carbon monoxide, the first predetermined value is 500 ppm, and when the predetermined gas is carbon dioxide, the first predetermined value is 450 ppm. Further, the abnormality determination unit 51 may output a signal directly to the notification unit 56.

[0048] When the fiber defect determination unit 52 heats the porous glass body that is part of the optical fiber, based on the change over time of the concentration of a predetermined gas measured by the gas measurement unit 48, it determines whether the optical fiber manufactured from the optical fiber preform including the member made of the porous glass body is defective. As will be described later, the inventor has found that when the difference between the concentration of the predetermined gas when heating the porous glass body and the concentration of the predetermined gas in the initial state exceeds a second predetermined value, the optical fiber manufactured from the optical fiber preform including the glass member made of the porous glass body becomes defective. When the amount of water entering the space 35S increases, the amount of water penetrating the furnace core tube 31 and entering the accommodation space 31S also increases, and the characteristics of the manufactured optical fiber, for example, the transmission loss deteriorates. And it has been found that when the above difference exceeds the second predetermined value, the characteristics generally required for an optical fiber for long-distance transmission cannot be satisfied. The above initial state is the state before first heating the core porous glass body 20 after the furnace body 35 is installed. Also, the above second predetermined value can be set in advance by experiments or the like. For example, when the predetermined gas is carbon monoxide and the porous glass body is the core porous glass body 20 that becomes the core 10 of the optical fiber 1, it is 550 ppm. The fiber defect determination unit 52 of the present embodiment outputs a signal indicating that the optical fiber 1 is defective to the control unit 60 when the difference between the concentration of carbon monoxide and the concentration of carbon monoxide in the initial state exceeds 550 ppm. On the other hand, when this difference is less than 550 ppm, the fiber defect determination unit 52 does not output a signal to the control unit 60, but may output a signal indicating that the optical fiber 1 is not defective to the control unit 60. Therefore, the determination by the fiber defect determination unit 52 is to change the output signal according to the signal from the gas measurement unit 48. Also, the fiber defect determination unit 52 may directly output the signal to the notification unit 56.

[0049] The notification unit 56 of the present embodiment makes a notification based on the signal from the abnormality determination unit 51 and the signal from the fiber defect determination unit 52. Examples of the notification unit 56 include a configuration having at least one of a display and a speaker.

[0050] Next, the first dehydration step P2a and the first sintering step P2b of the first heating step P2 will be described.

[0051] <First dehydration step P2a> This step is a step of heating the porous glass body 20 for the core using the dehydration sintering apparatus 100 to dehydrate the porous glass body 20 for the core. In this step, first, as shown in FIG. 4, the porous glass body 20 for the core suspended from the support rod 22 is accommodated in the accommodation space 31S of the furnace core tube 31. The first gas supply unit 41 supplies the first gas to the accommodation space 31S according to a control signal from the control unit 60, fills the accommodation space 31S with the first gas, and exhausts the gas in the accommodation space 31S from the exhaust pipe 44. Further, the second gas supply unit 42 supplies the second gas to the space 35S according to a control signal from the control unit 60, fills the space 35S with the second gas, and exhausts the gas in the space 35S from the exhaust pipe 46. Therefore, combustion of the heater 37, the heat insulating material 38, etc. in the space 35S can be suppressed.

[0052] The heater 37 generates heat according to a control signal from the control unit 60 while the first gas supply unit 41 and the second gas supply unit 42 are supplying gas in this way. In a state where the heater 37 is generating heat, the lifting unit 40 moves the porous glass body 20 for the core at a predetermined speed so that the entire porous glass body 20 for the core crosses the heater 37 according to a control signal from the control unit 60. Therefore, the porous glass body 20 for the core is heated to a predetermined temperature by the heater 37. By this heating, the OH groups and the attached moisture of the porous glass body 20 for the core are removed by the dehydration gas contained in the first gas. The heating temperature may be a temperature lower than the sintering temperature of the porous glass body 20 for the core and at which moisture can be removed from the porous glass body 20 for the core. For example, it is preferably 1100 °C or higher and 1400 °C or lower. When the heating temperature is 1100 °C or higher, the diffusion of gas into the porous glass body 20 for the core is promoted, and when the heating temperature is 1400 °C or lower, softening of the porous glass body 20 for the core can be sufficiently suppressed.

[0053] When the porous glass body 20 for the core is heated by the heater 37 in this way, the gas measurement unit 48 measures the concentration of carbon monoxide at predetermined time intervals, for example, at one-minute intervals, and outputs a signal indicating the measured concentration of carbon monoxide to the determination unit 50. That is, in this step, while the porous glass body 20 for the core is heated by the heater 37, the gas measurement unit 48 measures the concentration of carbon monoxide, and the porous glass body 20 for the core is heated by such a heating method.

[0054] When the difference between the concentration of carbon monoxide as a predetermined gas measured by the gas measurement unit 48 and the average value of the concentration of carbon monoxide measured by the gas measurement unit 48 before the timing at which the concentration of carbon monoxide is measured is equal to or greater than a first predetermined value, the abnormality determination unit 51 outputs a signal indicating an abnormal state to the notification unit 56, and the notification unit 56 makes a notification based on the signal from the abnormality determination unit 51. Therefore, the operator can recognize the abnormal state by the notification of the notification unit 56. Further, when the difference between the concentration of carbon monoxide measured by the gas measurement unit 48 and the concentration of carbon monoxide previously measured by the gas measurement unit 48 in the above initial state exceeds 550 ppm, the optical fiber defect determination unit 52 outputs a signal indicating that the optical fiber is defective to the control unit 60, and the notification unit 56 makes a notification based on the signal from the optical fiber defect determination unit 52. Therefore, the operator can determine that the optical fiber produced is defective by the notification of the notification unit 56.

[0055] <First sintering step P2b> This process is a step of heating the porous glass body 20 for the core using the dehydration sintering apparatus 100 used in the first dehydration step P2a after the first dehydration step P2a, and sintering the porous glass body 20 for the core. Similar to the first dehydration step P2a, the first gas supply unit 41 supplies the first gas to the accommodation space 31S, and the second gas supply unit 42 supplies the second gas to the space 35S. Further, the heater 37 generates heat in a state where the first gas supply unit 41 and the second gas supply unit 42 are supplying gas in this way. Also, in a state where the heater 37 is generating heat, the elevating unit 40 moves the porous glass body 20 for the core at a predetermined speed so that the entire porous glass body 20 for the core crosses the heater 37. For this reason, the porous glass body 20 for the core is heated to a predetermined temperature by the heater 37, and the porous glass body 20 for the core is sintered by this heating. Note that the heating temperature may be a temperature at which the porous glass body 20 for the core is sintered and vitrified into transparent glass, and for example, it is preferably 1300 °C or higher and 1650 °C or lower.

[0056] The gas measurement unit 48 measures the concentration of carbon monoxide, for example, at one-minute intervals, similar to the first dehydration step P2a, and outputs a signal indicating the measured concentration of carbon monoxide to the determination unit 50. For this reason, in this process, similar to the first dehydration step P2a, while heating the porous glass body 20 for the core by the heater 37, the gas measurement unit 48 measures the concentration of carbon monoxide, and the porous glass body 20 for the core is heated by such a heating method. Then, similar to the first dehydration step P2a, the notification unit 56 makes a notification based on signals from the abnormality determination unit 51 and the fiber defect determination unit 52. By this process, the porous glass body 20 for the core is vitrified into transparent glass, becoming a core glass rod that is the core glass body 10P shown in FIG. 2, and the core glass rod is obtained from the glass rod 24 by cutting or the like.

[0057] <Second Deposition Step P3> This step is to deposit glass fine particles on the outer surface of the core glass rod formed in the first sintering step P2b to form a porous glass body for the cladding, which becomes the cladding glass body 11P shown in FIG. 2. In this embodiment, the glass fine particles are deposited on the outer peripheral surface of the core glass rod by the OVD method to form the porous glass body for the cladding. However, the method for forming the porous glass body for the cladding is not particularly limited.

[0058] <Second heating step P4> This step is to heat the porous glass body for the cladding formed in the second deposition step P3, and as shown in FIG. 3, it includes a second dehydration step P4a and a second sintering step P4b. In this embodiment, these steps are performed using another dehydration and sintering apparatus 100 having the same configuration as the dehydration and sintering apparatus 100 used in the first heating step P2. However, the dehydration and sintering apparatus 100 used in the first heating step P2 may also be used.

[0059] <Second dehydration step P4a> This step is to heat the porous glass body for the cladding using the dehydration and sintering apparatus 100 to dehydrate the porous glass body for the cladding. This step is mainly different from the first dehydration step P2a in that the core glass rod on which the porous glass body for the cladding is formed is accommodated in the accommodation space 31S of the furnace core tube 31. Therefore, although a detailed description of this step is omitted, in this step, the porous glass body for the cladding is heated by the heater 37 to dehydrate the porous glass body for the cladding, and the concentration of carbon monoxide is measured by the gas measurement unit 48. Note that in this step, the fiber defect determination unit 52 does not determine whether the optical fiber is defective, and the notification unit 56 makes a notification based on a signal from the abnormality determination unit 51.

[0060] <Second sintering step P4b> This process is a step of heating the porous glass body for the cladding using the dehydration sintering apparatus 100 used in the second dehydration step P4a after the second dehydration step P4a to sinter the porous glass body for the cladding. This process is mainly different from the first dehydration step P2a in that the core glass rod on which the porous glass body for the cladding dehydrated by the second dehydration step P4a is formed is accommodated in the accommodation space 31S of the furnace core tube 31. For this reason, although a detailed description of this process is omitted, in this process, while heating the porous glass body for the cladding with the heater 37 to sinter the porous glass body for the cladding, the concentration of carbon monoxide is measured by the gas measurement unit 48. Note that in this process, the fiber defect determination unit 52 does not determine whether the optical fiber is defective, and the notification unit 56 makes a notification based on the signal from the abnormality determination unit 51.

[0061] In this process, the core glass rod hardly changes and becomes the core glass body 10P shown in FIG. 2. Further, the porous glass body for the cladding is vitrified into a transparent glass to become the cladding glass body 11P. Thus, the base material 1P for the optical fiber shown in FIG. 2 is obtained.

[0062] By heating and drawing the base material 1P for the optical fiber thus obtained with a spinning furnace, the core glass body 10P becomes the core 10, the cladding glass body 11P becomes the cladding 11, and an optical fiber bare wire composed of the core 10 and the cladding 11 is obtained. Then, by coating this optical fiber bare wire with a resin that becomes the coating layer 12, the coating layer 12 is formed, and the optical fiber 1 shown in FIG. 1 is manufactured.

[0063] As described above, the dehydration sintering apparatus 100 as a heating device for the glass member of the present embodiment includes a furnace core tube 31, a furnace body 35, a heater 37, and a gas measurement unit 48. The furnace core tube 31 has an accommodation space 31S capable of accommodating the entire porous glass body 20 for the core as the glass member. The furnace body 35 surrounds at least a part of the furnace core tube 31, and the heater 37 is disposed in a space 35S surrounded by the furnace core tube 31 and the furnace body 35. At least one of the members disposed in this space 35S contains carbon. The gas measurement unit 48 can measure the concentration of a predetermined gas generated due to the reaction between water and carbon in the space 35S.

[0064] Further, in the heating method for the porous glass body for the core 20 and the porous glass body for the clad as the glass members of the present embodiment, these glass members are heated by the heater 37 disposed in the space 35S surrounded by the furnace core tube 31 and the furnace body 35. At least one of the members disposed in this space 35S contains carbon. Then, while heating these glass members by the heater 37, the concentration of a predetermined gas generated due to the reaction between water and carbon in the space 35S is measured.

[0065] When dehydrating, sintering, melting, etc. the glass member, generally, the heater is heated to 700 °C or higher. In such a high-temperature state, if water enters the space 35S surrounded by the furnace core tube 31 and the furnace body 35, the water reacts with the carbon contained in the member disposed in this space, generating gas. In the dehydration sintering apparatus 100 and the heating method for the glass member of the present embodiment, since the concentration of the gas generated in this way can be measured, an abnormal state in which water enters the space 35S can be detected.

[0066] Further, in the dehydration sintering apparatus 100 and the heating method for the glass member of the present embodiment, since the furnace body 35 has a flow path 36 through which cooling water flows, damage to the furnace body 35 due to heat can be suppressed. Also, since the gas measurement unit 48 can measure the concentration of the gas generated due to the reaction between water and carbon in the space 35S, damage to the furnace body 35 in which the cooling water enters the space 35S can be detected.

[0067] Further, the dehydration sintering apparatus 100 of the present embodiment further includes a second gas supply unit 42 that supplies an inert gas into the space 35S from a gas supply port S2 formed in the furnace body 35 and communicating with the space 35S. Therefore, combustion of members such as the heater 37 and the heat insulating material 38 disposed in the space 35S can be suppressed. Further, since the gas measurement unit 48 can measure the concentration of the gas generated due to the reaction between water and carbon in the space 35S, it is possible to detect a defect in the second gas supply unit 42 or the pipe 45 connected to the second gas supply unit 42, etc., such that water enters the space 35S together with the inert gas.

[0068] Further, in the dehydration sintering apparatus 100 and the method for heating a glass member of the present embodiment, the concentration of a predetermined gas is measured from the exhaust gas exhausted from the exhaust port E2 formed in the furnace body 35 and communicating with the space 35S. Therefore, compared with the case of measuring the concentration of the predetermined gas at a certain point in the space 35S, the influence on the concentration of the predetermined gas due to the location where the predetermined gas is generated in the space 35S can be suppressed. Therefore, compared with the above case, an abnormal state in which water enters the space 35S can be accurately detected.

[0069] Further, the dehydration sintering apparatus 100 of the present embodiment further includes an abnormality determination unit 51 that determines whether or not it is an abnormal state based on the change over time of the concentration of a predetermined gas measured by the gas measurement unit 48. The abnormality determination unit 51 determines that it is an abnormal state when the difference between the concentration of the predetermined gas measured by the gas measurement unit 48 and the average value of the concentration of the predetermined gas measured by the gas measurement unit 48 before the timing when the concentration of the predetermined gas is measured is equal to or greater than a first predetermined value. Even for the furnace body 35 having the same configuration, the concentration of the predetermined gas measured in the steady state tends to change according to the installation state of the furnace body 35. Therefore, by adopting the above configuration, it is possible to appropriately determine whether or not it is an abnormal state as compared with the case of determining that it is an abnormal state when the concentration of the gas becomes equal to or greater than a predetermined value.

[0070] The dehydration sintering apparatus 100 of the present embodiment further includes a fiber defect determination unit 52, and heats a porous glass body 20 for the core, which is a part of the optical fiber 1. Based on the change over time in the concentration of a predetermined gas measured by the gas measurement unit 48 when heating the porous glass body 20 for the core, the fiber defect determination unit 52 determines whether or not the optical fiber 1 is defective.

[0071] When water enters the accommodation space 31S during sintering of the porous glass body 20 for the core, the transmission loss and other characteristics of the finally manufactured optical fiber 1 may deteriorate. The greater the amount of water entering the accommodation space 31S, the more the characteristics tend to deteriorate. Such intrusion of water into the accommodation space 31S may not affect the appearance of the transparent glass member formed by sintering the porous glass body 20 for the core. For this reason, it may be difficult to determine whether or not the characteristics of the finally manufactured optical fiber 1 deteriorate and the optical fiber 1 becomes defective based on the appearance of the transparent glass member. However, the greater the amount of water entering the accommodation space 31S, the greater the amount of gas generated due to the reaction between water and carbon, and the higher the concentration of the gas. Therefore, with the above configuration, it is possible to determine whether or not the finally manufactured optical fiber 1 is defective at the stage of manufacturing the transparent glass member, reduce the defect rate of the optical fiber 1, and improve the productivity of the optical fiber 1.

[0072] In the present embodiment, the predetermined gas is carbon monoxide, and when the difference between the concentration of carbon monoxide measured by the gas measurement unit 48 when heating the porous glass body 20 for the core, which becomes the core 10 of the optical fiber 1, and the concentration of carbon monoxide in the initial state exceeds 550 ppm, the fiber defect determination unit 52 determines that the optical fiber 1 is defective. As described above, the present inventor has found that when this difference exceeds 550 ppm, the optical fiber 1 manufactured from the optical fiber base material 1P including the core glass body 10P composed of the porous glass body 20 for the core becomes defective. Therefore, with such a configuration, it is possible to appropriately determine whether or not the finally manufactured optical fiber 1 is defective.

[0073] As described above, the present invention has been described by taking the above embodiments as examples. However, the present invention is not limited to these.

[0074] For example, in the above embodiment, the dehydration sintering apparatus 100 including the abnormality determination unit 51 and the fiber defect determination unit 52 has been described as an example. However, the dehydration sintering apparatus 100 may not include at least one of the abnormality determination unit 51 and the fiber defect determination unit 52. In this case, for example, an operator may determine whether it is in an abnormal state or whether the optical fiber 1 is defective based on the change over time of the concentration of the predetermined gas measured by the gas measurement unit 48.

[0075] In the above-described embodiment, the abnormal determination unit 51 that determines an abnormal state when the difference between the concentration of a predetermined gas measured by the gas measurement unit 48 and the average value of the concentration of the predetermined gas measured by the gas measurement unit 48 before the timing at which the concentration of the predetermined gas is measured is equal to or greater than a first predetermined value was described as an example. However, the abnormal determination unit 51 may determine whether or not it is an abnormal state based on the change over time of the concentration of the predetermined gas measured by the gas measurement unit 48. For example, the abnormal determination unit 51 may output a signal indicating an abnormal state when the concentration of the predetermined gas becomes equal to or greater than a predetermined threshold value. This predetermined threshold value is, for example, 700 ppm when the predetermined gas is carbon monoxide, and 800 ppm when the predetermined gas is carbon dioxide. However, from the viewpoint of appropriately determining whether or not it is an abnormal state, it is preferable that the abnormal determination unit 51 determines whether or not it is an abnormal state as in this embodiment. Further, the abnormal determination unit 51 may be based on the difference between the concentration of the predetermined gas and the median value of the concentration of the predetermined gas before the timing at which the concentration of the predetermined gas is measured, the difference between the concentration of the predetermined gas and the value obtained by subtracting the standard deviation from the average value of the concentration of the predetermined gas before the timing at which the concentration of the predetermined gas is measured, the difference between the concentration of the predetermined gas and the minimum value of the concentration of the predetermined gas before the timing at which the concentration of the predetermined gas is measured, etc. determine that it is an abnormal state. In this case, the abnormal determination unit 51 determines that it is an abnormal state when these differences are equal to or greater than a predetermined value, and this predetermined value is set based on experiments or the like for each difference. Further, a state in which the optical fiber 1 is defective is an abnormal state. Therefore, the abnormal determination unit 51, for example, similar to the fiber defect determination unit 52 of the above-described embodiment, when the difference between the concentration of carbon monoxide measured by the gas measurement unit 48 when heating the glass member and the concentration of carbon monoxide in the initial state exceeds 550 ppm, may determine that it is an abnormal state.

[0076] In the above embodiment, taking the fiber defect determination unit 52 as an example, when the difference between the concentration of carbon monoxide measured by the gas measurement unit 48 when heating the porous glass body 20 for the core and the concentration of carbon monoxide in the initial state exceeds 400 ppm, it is determined that the optical fiber 1 is defective. However, the fiber defect determination unit 52 may determine whether it is in an abnormal state based on the change over time in the concentration of a predetermined gas measured by the gas measurement unit 48. For example, when the concentration of the predetermined gas becomes equal to or higher than a predetermined threshold value, the fiber defect determination unit 52 may output a signal indicating that the optical fiber 1 is defective. This predetermined threshold value is, for example, 700 ppm when the predetermined gas is carbon monoxide, and 800 ppm when the predetermined gas is carbon dioxide. Further, in the above embodiment, the fiber defect determination unit 52 determines whether the optical fiber 1 is defective based on the change over time in the concentration of the predetermined gas measured in the first heating step P2. Here, when water enters the accommodation space 31S when sintering the porous glass body for the cladding that becomes the cladding 11 of the optical fiber 1, the transmission loss, which is a characteristic of the finally manufactured optical fiber 1, may deteriorate, and the greater the amount of water that enters the accommodation space 31S, the more likely the transmission loss is to deteriorate. Therefore, the fiber defect determination unit 52 may determine whether the optical fiber 1 is defective based on the change over time in the concentration of the predetermined gas measured in the second heating step P4. In this case, based on experimental values and the like, a threshold value of the concentration of the predetermined gas for determining whether the optical fiber 1 is defective is set.

[0077] In the above embodiment, the furnace body 35 surrounding a part of the core tube 31 was described as an example. However, the furnace body 35 only needs to surround at least a part of the core tube 31, and may surround the entire core tube 31, for example.

[0078] In addition, in the above-described embodiment, the dehydration sintering apparatus 100 including the second gas supply unit 42 has been described as an example. However, the dehydration sintering apparatus 100 may not include the second gas supply unit 42. For example, instead of the second gas supply unit 42, an exhaust unit that exhausts the air in the space 35S from the exhaust pipe 46 to make the space 35S in a vacuum state may be provided. By making the space 35S in a vacuum state in this way, combustion of the heater 37, the heat insulating material 38, etc. in the space 35S can be suppressed.

[0079] In addition, in the above-described embodiment, the first deposition step P1 of forming the porous glass body 20 for the core that becomes the core glass body 10P has been described as an example. However, the porous glass body formed in the first deposition step P1 is not particularly limited. For example, it may be a porous glass body that becomes a part of the core glass body 10P and the clad glass body 11P. In this case, in the second deposition step P3, glass fine particles are deposited on the outer surface of the glass rod formed by the first sintering step P2b to form a porous glass body that becomes the other part of the clad glass body 11P.

[0080] In addition, in the above-described embodiment, the manufacturing method of the preform 1P for an optical fiber including the first deposition step P1, the first heating step P2, the second deposition step P3, and the second heating step P4 has been described as an example. However, the manufacturing method of the preform 1P for an optical fiber only needs to include a heating step of heating the porous glass body as a glass member by the above-described heating method of the glass member. For example, the manufacturing method of the preform 1P for an optical fiber may not include the first deposition step P1 and the first heating step P2. In this case, for example, in the second deposition step P3, first, a core glass rod is prepared by purchase or the like, and glass fine particles are deposited on the outer peripheral surface of the core glass rod to form a porous glass body for the clad.

[0081] Further, in the above-described embodiment, the first gas is a mixed gas of a dehydration gas and an inert gas, and the first sintering step P2b and the second sintering step P4b of heating the porous glass body while the first gas is supplied from the first gas supply unit 41 to the accommodation space 31S have been described as examples. However, in the first sintering step P2b and the second sintering step P4b, the porous glass body may be heated in a state where only the inert gas is supplied to the accommodation space 31S. In this case, for example, the configuration of the first gas supply unit 41 can be made a configuration that can be changed between a gas containing a dehydration gas and an inert gas and only an inert gas as the first gas to be supplied. Then, the control unit 60 controls the first gas supply unit 41 so that the first gas supplied from the first gas supply unit 41 is switched according to the process.

[0082] Further, in the above-described embodiment, in the first dehydration step P2a and the first sintering step P2b, the core porous glass body 20 was heated by the same dehydration sintering apparatus 100, and in the second dehydration step P4a and the second sintering step P4b, the clad porous glass body was heated by the same dehydration sintering apparatus 100. However, for example, in each step, the porous glass body may be heated by different dehydration sintering apparatuses 100. Further, the method for manufacturing the optical fiber preform 1P may further include a stretching step of stretching the glass body obtained by sintering the core porous glass body 20 in the first heating step P2 to obtain a core glass rod. The core tube 31 only needs to have an accommodation space 31S for accommodating at least a part of the glass member, and openings may be formed at both ends of the core tube 31. For example, the above-described apparatus for stretching the glass body, the spinning furnace for heating the optical fiber preform 1P, and the tip processing furnace are also included in the glass member heating apparatus of the present invention.

[0083] Hereinafter, the present invention will be described in more detail with reference to experimental examples, but the present invention is not limited thereto.

[0084] Using the dehydration sintering apparatus 100 shown in FIG. 4, 32 core glass rods were manufactured by repeating the first deposition step P1 and the first heating step P2 shown in FIG. 3 thirty-two times. In this dehydration sintering apparatus 100, the heater 37 was not heated from when the furnace body 35 was installed until the first core glass rod was manufactured. Also, the concentrations of carbon monoxide and carbon dioxide in the respective spaces 35S in the initial state before the first heating step P2 for manufacturing the first core glass rod after the furnace body 35 was installed were measured by the gas measurement unit 48. The concentration of carbon monoxide in the initial state was 150 ppm, and the concentration of carbon dioxide was 260 ppm. Also, during the first heating step P2 when each core glass rod was manufactured, the concentrations of carbon monoxide and carbon dioxide in the respective spaces 35S were measured by the gas measurement unit 48. The measurement results are shown in FIG. 5. Note that FIG. 5 also shows the transmission loss described later.

[0085] Also, using another dehydration sintering apparatus 100, by performing the second deposition step P3 and the second heating step P4 shown in FIG. 3, a preform 1P for an optical fiber similar to the preform 1P for an optical fiber shown in FIG. 2 was manufactured from each of these core glass rods. During the second heating step P4 when each preform 1P for an optical fiber was manufactured, the concentrations of carbon monoxide and carbon dioxide in the respective spaces 35S were measured by the gas measurement unit 48. The concentration of carbon monoxide was 150 ppm or more and 250 ppm or less, and the concentration of carbon dioxide was 250 ppm or more and 400 ppm or less. Also, when the space 35S was checked after the manufacture of the preform 1P for an optical fiber, there was no intrusion of water into the space 35S.

[0086] Further, each of the 32 produced preforms 1P for optical fibers was heated and drawn by a spinning furnace to produce an optical fiber 1 similar to the optical fiber 1 shown in FIG. 1 from each preform 1P for optical fibers. The diameter of the core 10 in each optical fiber 1 was approximately 10 μm, and the diameter of the cladding 11 was approximately 125 μm. Also, for each optical fiber 1, the transmission loss at a wavelength of 1383 nm was measured using an OTDR (Optical Time Domain Reflectometer). The measurement results are shown in FIG. 5 as described above. Note that in FIG. 5, a dashed-dotted line indicating 0.31 dB / km, which is a value of transmission loss generally required for an optical fiber for long-distance transmission, is described.

[0087] As shown in Fig. 5, the transmission loss of the optical fiber 1 manufactured from the 1st to the 27th core glass rods was approximately 0.28 dB / km, and the transmission loss of the optical fiber 1 manufactured from the 28th core glass rod was 0.309 dB / km. The transmission loss of the optical fiber 1 manufactured from the 29th and subsequent core glass rods exceeded 0.31 dB / km, and from the 29th onwards, the transmission loss tended to increase as the number of rods increased. Also, the concentration of carbon monoxide was maximum at the 28th when manufacturing the 1st to 28th core glass rods, and the concentration of carbon monoxide at the 28th was 397 ppm. Among the 1st to 28th core glass rods, the concentration of carbon dioxide was maximum at the 28th, and the concentration of carbon dioxide at the 28th was 448 ppm. The concentration of carbon monoxide at the 29th was 703 ppm, the concentration of carbon dioxide at the 29th was 813 ppm, and the concentrations of carbon monoxide and carbon dioxide from the 29th onwards increased as the number increased. For this reason, it is considered that water began to infiltrate into the space 35S when manufacturing the 28th, and from the 28th onwards, the amount of water infiltrating into the space 35S increased as the number increased. Also, as described above, the concentration of carbon monoxide in the initial state was 150 ppm, and the concentration of carbon dioxide was 260 ppm. For this reason, it was found that when the difference between the concentration of carbon monoxide when heating the porous glass body 20 for the core as a glass member and the concentration of carbon monoxide in the initial state before first heating the porous glass body 20 for the core after the furnace body 35 was installed exceeded 550 ppm, the optical fiber 1 became defective. It was also found that when the difference between the concentration of carbon dioxide when heating the porous glass body 20 for the core and the concentration of carbon dioxide in this initial state exceeded 550 ppm, the optical fiber 1 became defective. Also, it was found that when the concentration of carbon monoxide became 700 ppm or more and when the concentration of carbon dioxide became 800 ppm or more, the optical fiber 1 became defective. Note that when water and carbon react, methane, oxygen, and hydrogen are also generated together with carbon monoxide and carbon dioxide. The generation amounts of methane, oxygen, and hydrogen tend to be stoichiometrically proportional to the generation amounts of carbon monoxide and carbon dioxide.Therefore, based on experimental values and the like, reference values for determining whether or not the optical fiber 1 is defective can also be set for the respective concentrations of methane, oxygen, and hydrogen.

[0088] Also, from the 1st to the 28th, the difference between the concentration of carbon monoxide and the average value of the concentration of carbon monoxide measured before the timing at which the carbon monoxide is measured was 500 ppm or less. Also, for the 29th, the difference was 506 ppm. For this reason, it was found that the dehydration sintering apparatus 100 is in an abnormal state when the difference is 500 or more. Also, from the 1st to the 28th, the difference between the concentration of carbon dioxide and the average value of the concentration of carbon dioxide measured before the timing at which the carbon dioxide is measured was 550 ppm or less. Also, for the 29th, the difference was 553 ppm. For this reason, it was found that the dehydration sintering apparatus 100 is in an abnormal state when the difference is 550 or more. Also, it was found that the dehydration sintering apparatus 100 is in an abnormal state when the concentration of carbon monoxide is 700 ppm or more and when the concentration of carbon dioxide is 800 ppm or more. Note that as described above, since the generation amounts of methane, oxygen, and hydrogen tend to be proportional to the generation amounts of carbon monoxide and carbon dioxide, reference values for determining whether or not the dehydration sintering apparatus 100 is in an abnormal state can also be set for the respective concentrations of methane, oxygen, and hydrogen based on experimental values and the like.

Industrial Applicability

[0089] As described above, there are provided a heating device for a glass member capable of detecting an abnormal state caused by water, a method for heating a glass member, and a method for manufacturing a base material for an optical fiber using the same, and it is expected to be used in fields such as optical fiber communication.

Explanation of Reference Numerals

[0090] 1 ··· Optical fiber 1P ··· Base material for optical fiber 20 ··· Porous glass body for core (porous glass body) 31 ··· Furnace core tube 31S ··· Accommodation space 35···Furnace body 35S···Space 36···Flow path 37···Heater 41···First gas supply unit 42···Second gas supply unit 48···Gas measurement unit 51···Abnormality determination unit 52···Optical fiber defect determination unit 60···Control unit 100···Dehydration sintering device (heating device) S1, S2···Air inlet E1, E2···Exhaust port P1···First deposition process P2···First heating process P3···Second deposition process P4···Second heating process

Claims

1. A core tube having an accommodation space capable of accommodating at least a part of a glass member, A furnace body surrounding at least a part of the core tube, A heater disposed in a space surrounded by the core tube and the furnace body, A gas measurement unit, Comprising: At least one of the members disposed in the space contains carbon, The gas measurement unit is capable of measuring the concentration of a gas generated due to the reaction between water and carbon in the space, The furnace body has a flow path located inside the outer wall of the furnace body through which cooling water flows A heating device for a glass member, characterized in that.

2. A core tube having an accommodation space capable of accommodating at least a part of a glass member, A furnace body surrounding at least a part of the core tube, A heater disposed in a space surrounded by the core tube and the furnace body, A gas measurement unit, Comprising: At least one of the members disposed in the space contains carbon, The gas measurement unit is capable of measuring the concentration of a gas generated due to the reaction between water and carbon in the space, Further comprising an abnormality determination unit that determines whether it is an abnormal state based on the change over time of the concentration of the gas measured by the gas measurement unit, The abnormality determination unit determines that it is an abnormal state when the difference between the concentration of the gas measured by the gas measurement unit and the average value of the concentration of the gas measured by the gas measurement unit before the timing when the concentration of the gas is measured is equal to or greater than a predetermined value A heating device for a glass member, characterized in that.

3. The furnace body has a flow path through which cooling water flows The heating device for a glass member according to claim 2, characterized in that.

4. Further comprising an abnormality determination unit that determines whether it is an abnormal state based on the change over time of the concentration of the gas measured by the gas measurement unit, The abnormality determination unit determines that it is an abnormal state when the difference between the concentration of the gas measured by the gas measurement unit and the average value of the concentration of the gas measured by the gas measurement unit before the timing when the concentration of the gas is measured is equal to or greater than a predetermined value The heating device for a glass member according to claim 1, characterized in that.

5. The gas is at least one of carbon monoxide, carbon dioxide, methane, and hydrogen The heating device for a glass member according to any one of claims 1 to 4, characterized in that.

6. Further comprising a gas supply unit that supplies an inert gas to the space from an air supply port formed in the furnace body and communicating with the space The heating device for a glass member according to any one of claims 1 to 5, characterized in that...

7. The gas measurement unit measures the concentration of the gas from the exhaust gas exhausted from the exhaust port formed in the furnace body and communicating with the space. The heating device for a glass member according to any one of claims 1 to 6, characterized in that...

8. Further comprising a fiber defect determination unit, The glass member is a porous glass body that forms part of an optical fiber, The fiber defect determination unit determines whether the optical fiber is defective based on the change over time of the concentration of the gas measured by the gas measurement unit. The heating device for a glass member according to any one of claims 1 to 7, characterized in that...

9. The gas is carbon monoxide, The glass member is a porous glass body that forms the core of the optical fiber, The fiber defect determination unit determines that the optical fiber is defective when the difference between the concentration of the gas measured by the gas measurement unit and the concentration of the gas in the initial state before the glass member is first heated after the furnace body is installed exceeds 550 ppm. The heating device for a glass member according to claim 8, characterized in that...

10. A hearth tube having an accommodation space capable of accommodating at least a part of the glass member, A furnace body surrounding at least a part of the hearth tube, A heater disposed in the space surrounded by the hearth tube and the furnace body, A gas measurement unit, A fiber defect determination unit are provided, At least one of the members disposed in the space contains carbon, The gas measurement unit can measure the concentration of the gas generated due to the reaction between water and carbon in the space, The glass member is a porous glass body that forms the core of the optical fiber, The gas is carbon monoxide, The fiber defect determination unit determines that the optical fiber is defective when the difference between the concentration of the gas measured by the gas measurement unit and the concentration of the gas in the initial state before the glass member is first heated after the furnace body is installed exceeds 550 ppm. The heating device for a glass member, characterized in that...

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