CN115385565A

CN115385565A - Glass member heating device, glass member heating method, and optical fiber preform manufacturing method using same

Info

Publication number: CN115385565A
Application number: CN202210553319.1A
Authority: CN
Inventors: 高桥纯一
Original assignee: Fujikura Ltd
Current assignee: Fujikura Ltd
Priority date: 2021-05-21
Filing date: 2022-05-20
Publication date: 2022-11-25
Also published as: JP2022179164A

Abstract

The invention provides a heating device for a glass member. A dehydration sintering device (100) as a heating device for a glass component is provided with: a furnace core tube (31), a furnace body (35), a heater (37), and a gas measuring section (48). The core tube (31) has a storage space (31S), and the storage space (31S) can store a porous glass body (20) for a core, which is a glass member. The furnace body (35) surrounds a part of the core tube (31). The heater (37) is disposed in a space (35S) surrounded by the core tube (31) and the furnace body (35). At least one of the members disposed in the space (35S) contains carbon, and the gas measurement unit (48) can measure the concentration of a gas generated by the reaction between water and carbon in the space (35S).

Description

Glass member heating device, glass member heating method, and optical fiber preform manufacturing method using same

Technical Field

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

Background

As a method for manufacturing an optical fiber preform used for manufacturing an optical fiber, the following methods are known: the porous glass body is formed by depositing fine glass particles by the OVD method (outer Vapor Deposition method), the VAD method (Vapor Axial Deposition method), or the like, and is heated and sintered.

Patent document 1 below discloses a heating device for heating a porous glass body. The heating device is provided with: a core tube having a storage space for storing the porous glass body; a heater disposed outside the muffle tube; a furnace body surrounding a part of the core tube and the heater; and a gas detector. The gas detector detects a leak gas that leaks from the muffle tube into a space surrounded by the muffle tube and the furnace body and is discharged from an exhaust port provided in the furnace body. Therefore, according to this heating device, the breakage such as the breakage of the muffle tube can be detected by the gas detector.

Documents of the prior art

Patent document

Patent document 1: japanese laid-open patent publication No. 2015-48262

Disclosure of Invention

Technical problem to be solved

However, the furnace body of the heating device has the following problems: sometimes, the furnace body is cooled by cooling water, and if the furnace body is damaged, the cooling water enters a space surrounded by the core tube and the furnace body. In addition, the inert gas may be supplied to the space to suppress combustion of the components disposed in the space, and there is a possibility that the inert gas and water may enter the space together due to a failure of a gas supply device or the like. In addition to this, water may intrude into the space due to deterioration, aging, or the like of the apparatus, and there is a high possibility that water intrudes into the space. In such an abnormal state where water enters the space, the water may permeate from the space to the receiving space of the core tube even if the core tube is not damaged. If water enters the housing space when the porous glass body is heated and sintered by the heater, the characteristics of the finally produced optical fiber, i.e., transmission loss, are deteriorated.

Accordingly, an object of the present invention is to provide a heating device for a glass member, a heating method for a glass member, and a method for manufacturing an optical fiber preform using the same, which can detect an abnormal state caused by water.

(II) technical scheme

In order to achieve the above object, the present invention provides a glass member heating apparatus, comprising: a core tube having a housing space capable of housing at least a part of the glass member; a furnace body surrounding at least a part of the core tube; a heater disposed in a space surrounded by the muffle tube and the furnace body; and a gas measurement unit configured to include carbon in at least one of the members disposed in the space, the gas measurement unit being capable of measuring a concentration of a gas generated by a reaction between water and the carbon in the space.

In order to achieve the above object, the present invention provides a method of heating a glass member, the method including accommodating at least a part of the glass member in an accommodation space in a muffle tube at least a part of which is surrounded by a furnace body, and heating the glass member by a heater disposed in a space surrounded by the muffle tube and the furnace body, wherein at least one of the members disposed in the space contains carbon, the glass member is heated by the heater, and a concentration of a gas generated by a reaction between water and carbon in the space is measured.

In the case of dehydrating, sintering, melting, etc., a glass member, the heater is usually heated to 700 ℃ or higher. In such a high temperature state, if water enters the space, the water reacts with carbon contained in the member disposed in the space to generate gas. In the heating apparatus for a glass member and the heating method for a glass member, since the concentration of the gas generated in this way can be measured, an abnormal state in which water enters the space can be detected.

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

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

With such a configuration, thermal damage to the furnace body can be suppressed. Further, since the gas measuring unit can measure the concentration of the gas generated by the reaction between the water and the carbon in the space, damage to the furnace body such as the entry of the cooling water into the space can be detected.

The above-described heating device for a glass member may further include a gas supply unit configured to supply an inert gas to the space through a gas supply port formed in the furnace body and communicating with the space.

With such a configuration, combustion of the components disposed in the space can be suppressed. Further, since the gas measuring unit can measure the concentration of the gas generated by the reaction between water and carbon in the space, it is possible to detect a problem in the gas supply unit, the piping, or the like caused by the entry of water into the space together with the inert gas.

In the above glass member heating apparatus, the gas measuring unit may measure the concentration of the gas based on an exhaust gas discharged from an exhaust port formed in the furnace body and communicating with the space.

By adopting such a configuration, compared to when the concentration of the gas is measured at a certain position in the space, the influence of the position where the gas is generated in the space on the concentration of the gas can be suppressed. Therefore, compared to the above case, the abnormal state in which water enters the space can be accurately detected.

The above-described heating apparatus for a glass member may further include an abnormality determination unit configured to determine whether or not the glass member is in an abnormal state based on a change with time in the concentration of the gas measured by the gas measurement unit.

In this case, the abnormality determination unit may determine that the state is abnormal when a difference between the concentration of the gas measured by the gas measurement unit and an average value of the concentrations of the gas measured by the gas measurement unit before a time when the concentration of the gas is measured is equal to or greater than a predetermined value.

There is a tendency that: even in a furnace body having the same structure, the concentration of the gas measured in a stable state changes depending on the installation state of the furnace body. Therefore, by adopting the above configuration, it is possible to appropriately determine whether or not an abnormal state is present, compared to a case where an abnormal state is determined when the concentration of the gas is equal to or higher than a predetermined value.

The above-described heating device for a glass member may further include an optical fiber failure determination unit that determines whether or not the optical fiber is defective based on a change with time in the concentration of the gas measured by the gas measurement unit, wherein the glass member is a porous glass body that is a part of the optical fiber.

As described above, if water enters the housing space when the porous glass body is sintered, the characteristics of the finally manufactured optical fiber, i.e., transmission loss and the like, are deteriorated, and the more the amount of water entering the housing space, the more the characteristics are deteriorated. Such water intrusion into the housing space may not affect the appearance of the transparent glass member formed by sintering the porous glass body. There are therefore cases where: it is difficult to determine whether the characteristics of the finally manufactured optical fiber are deteriorated and the optical fiber is defective from the appearance of the transparent glass member. However, as the amount of water entering the housing space increases, the amount of gas generated by the reaction between water and carbon increases, and the concentration of the gas increases. Therefore, by adopting the above-described configuration, it is possible to determine whether or not the optical fiber finally manufactured is defective at the stage of manufacturing the transparent glass member, and it is possible to reduce the defective rate of the optical fiber and improve the productivity of the optical fiber.

In this case, the gas may be carbon monoxide, the glass member may be a porous glass body which becomes a core of the optical fiber, and the optical fiber defect determining unit may determine that the optical fiber is defective when a difference between the concentration of the gas measured by the gas measuring unit and the concentration of the gas in an initial state from installation of the furnace body to the first heating of the glass member exceeds 550ppm.

The inventor finds that: when the difference between the carbon monoxide concentration at the time of heating the porous glass body to be a core and the carbon monoxide concentration in the initial state exceeds 550ppm, an optical fiber manufactured using an optical fiber preform including a core glass body made of the porous glass body is defective. Therefore, by adopting such a configuration, it is possible to appropriately predict whether or not the finally manufactured optical fiber is defective.

The present invention provides a method for manufacturing an optical fiber preform, comprising a heating step of heating a porous glass body as the glass member by the above-described method for heating a glass member.

(III) advantageous effects

As described above, according to the present invention, there are provided a heating device for a glass member, a heating method for a glass member, and a method for manufacturing an optical fiber preform using the same, which can detect an abnormal state caused by water.

Drawings

Fig. 1 is a diagram schematically showing a cross section perpendicular to a longitudinal direction of an optical fiber according to an embodiment of the present invention.

Fig. 2 is a schematic view of a cross section perpendicular to the longitudinal direction of the optical fiber preform for manufacturing the optical fiber shown in fig. 1.

Fig. 3 is a flowchart showing steps of a method for manufacturing an optical fiber preform and a method for manufacturing an optical fiber according to an embodiment of the present invention.

Fig. 4 is a schematic view of a dehydration sintering apparatus used in the first heating step.

Fig. 5 is a graph showing the relationship between each core glass rod in the experimental example, the concentrations of carbon monoxide and carbon dioxide measured at the time of sintering, and the transmission loss of the manufactured optical fiber.

Detailed Description

The heating apparatus for a glass member, the heating method for a glass member, and the method for manufacturing an optical fiber preform using the same according to the present invention will be described below with reference to the accompanying drawings. The following illustrative embodiments are provided to facilitate understanding of the present invention and are not to be construed as limiting the present invention. The present invention can be modified and improved without departing from the scope of the present invention. In addition, in some cases, the dimensions of the respective members are changed for easy understanding in the drawings to be referred to below.

Fig. 1 is a diagram schematically showing a cross section perpendicular to a 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 includes, as main components: a core 10, a cladding 11 surrounding the outer peripheral surface of the core 10, and a cladding 12 covering the outer peripheral surface of the cladding 11. The outer shape of the core 10 on the cross section is circular, and the core 10 is disposed at the center of the cladding 11. The outer shape of the clad layer 11 on the cross section may be a non-circular shape such as an ellipse or a polygon. In fig. 1, an optical fiber 1 in which the outer shape of a cladding 11 is circular is shown.

The refractive index of the core 10 is higher than that of the cladding 11. In the present embodiment, the core 10 is made of silica glass to which a dopant for increasing the refractive index such as germanium (Ge) is added, and the cladding 11 is made of silica glass without any additive. The core 10 may be made of silica glass without any additive, and the cladding 11 may be made of silica glass to which a dopant for lowering the 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. In addition, the dopant for increasing the refractive index and the dopant for decreasing the refractive index are not particularly limited.

The coating layer 12 is made of resin. Examples of the resin constituting the coating layer 12 include thermosetting resins and ultraviolet-curable resins. The clad layer 12 may have a single-layer structure including one resin layer surrounding the clad layer 11, or may have a multilayer structure including a plurality of resin layers.

Fig. 2 is a schematic diagram showing a cross section perpendicular to the longitudinal direction of an optical fiber preform used for manufacturing the optical fiber 1 shown in fig. 1. As shown in fig. 2, the optical fiber preform 1P includes a rod-shaped core glass 10P serving as the core 10, and a clad glass 11P surrounding the outer peripheral surface of the core glass 10P and serving as the clad 11. In the present embodiment, the outer shape of the clad glass body 11P on the cross section is circular, and the core glass body 10P is disposed at the center of the clad glass body 11P. The outer shape of the core glass body 10P on the cross section is circular.

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

Fig. 3 is a flowchart showing the steps of the method for producing the optical fiber preform 1P according to the present embodiment. As shown in fig. 3, the method for manufacturing the optical fiber preform 1P according to 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.

(first Stacking Process P1)

This step is a step of depositing glass microparticles to form a core porous glass body 10P shown in fig. 2, i.e., a core porous glass body. The porous glass body can be formed by a powder method such as OVD method or VAD method. In the present embodiment, glass microparticles are deposited from one end of a prepared glass rod in the axial direction of the glass rod by the VAD method to form a porous glass body for a core.

(first heating Process P2)

This step is a step of heating the porous glass body for a core, which is the glass member formed in the first deposition step P1, and includes, as shown in fig. 3: a first dehydration step P2a and a first sintering step P2b. First, a dehydration sintering apparatus as a heating apparatus for a glass member used in this step will be described.

Fig. 4 is a schematic view of the dehydration sintering apparatus used in the first heating step P2. As shown in fig. 4, the dehydration sintering apparatus 100 of the present embodiment includes, as main components: the heating furnace 30, the elevating unit 40, the first gas supply unit 41, the second gas supply unit 42, the gas measurement unit 48, the determination unit 50, the memory 55, the notification unit 56, and the control unit 60.

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 (digital Control) device. When the NC apparatus is used, the control unit 60 may or may not use a machine learning device. As described below, some configurations of the dehydration/sintering apparatus 100 are controlled by the control unit 60.

In the present embodiment, the heating furnace 30 includes, as main components: a furnace core pipe 31, a furnace body 35, a heater 37 and a heat insulating material 38.

The core tube 31 of the present embodiment is a cylindrical member extending in the vertical direction, and can house the porous core glass body 20 in the housing space 31S. In the present embodiment, the openings at both ends of the muffle tube 31 are closed, and the portion closing the upper opening can be removed from other portions. A through hole is formed in a portion closing the upper opening of the muffle tube 31, and the support rod 22 for suspending the core porous glass body 20 is inserted into the through hole. A connecting portion 23 is provided at the lower end of the support rod 22, and a glass rod 24 on which the core porous glass body 20 is deposited is connected to the connecting portion 23. The muffle tube 31 is provided with an exhaust port E1 and an air supply port S1 which communicate with the storage space 31S. Examples of the material constituting the muffle tube 31 include quartz and carbon.

The furnace body 35 of the present embodiment is formed in a hollow box shape, and a flow path 36 through which cooling water supplied from a cooling water supply unit, not shown, flows is provided in an outer wall of the furnace body 35. The furnace body 35 is cooled by flowing cooling water through the flow path 36, and damage to the furnace body 35 due to heat is suppressed. A through hole penetrating in the vertical direction is formed in the center of the furnace body 35, and the muffle tube 31 is inserted into the through hole. The upper end and the lower end of the core tube 31 protrude from the furnace body 35, respectively, and the furnace body 35 surrounds the center 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. The furnace body 35 is provided with an air supply port S2 and an exhaust port E2 communicating with the space 35S. The air supply port S2 is located on one side in the horizontal direction with respect to the muffle tube 31, and the exhaust port E2 is located on the other side. Examples of the material constituting the furnace body 35 include metals.

The heater 37 is disposed in the space 35S and can heat the porous core glass body 20 stored in the storage space 31S of the core tube 31 by heat generation. The heater 37 of the present embodiment is made of carbon and formed in a ring shape surrounding the muffle tube 31, but the heater 37 may be divided into a plurality of heating portions, and the plurality of heating portions may be discontinuously disposed so as to surround the muffle tube 31. The heater 37 adjusts the heat generation temperature in accordance with a control signal from the control unit 60. In order to effectively use 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 material 38 is not particularly limited, and the heat insulating material 38 may be divided into a plurality of pieces. The heat insulating material 38 of the present embodiment is made of carbon. Therefore, in the present embodiment, the heater 37 and the heat insulating material 38, which are members disposed in the space 35S, contain carbon. The member disposed in the space 35S may contain at least one carbon, and 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.

The elevating unit 40 elevates the gripped support rod 22. The lifting unit 40 moves the support rod 22 up and down in accordance with a control signal from the control unit 60, thereby moving the porous core glass body 20 attached to the support rod 22 up and down. The structure of the elevating unit 40 is not particularly limited.

The first gas supply unit 41 supplies a first gas containing a dehydration gas to the housing space 31S through a pipe 43, and the pipe 43 is connected to the gas supply port S1 of the muffle tube 31. The first gas supply unit 41 adjusts the supply amount of the first gas in accordance with a control signal from the control unit 60. The first gas supplied to the housing space 31S is discharged from the exhaust port E1 of the muffle tube 31 to the discharge tube 44. In the present embodiment, the first gas is a mixed gas of a dehydration gas and an inert gas, and examples of the dehydration gas include chlorine gas and SiCl ₄ Thionyl chloride (SOCl) ₂ ) Carbon tetrachloride (CCl) ₄ ) Chlorine-containing gas, and carbon monoxide, and examples of the inert gas include He, ar and N ₂ And the like.

The second gas supply unit 42 supplies the second gas, which is an inert gas, to the space 35S through the pipe 45, and the pipe 45 is connected to the gas supply port S2 of the furnace body 35. The second gas supply unit 42 adjusts the supply amount of the second gas in accordance with a control signal from the control unit 60. The second gas supplied to the space 35S is discharged from the exhaust port E2 of the furnace body 35 to the discharge pipe 46. Examples of the second gas include He, ar, and N ₂ And the like.

In the present embodiment, the gas measuring unit 48 is attached to the discharge pipe 46, measures the concentration of a predetermined gas in the exhaust gas discharged from the exhaust port E2, and outputs a signal indicating the measured concentration of the predetermined gas to the determination unit 50. The gas measuring section 48 repeats the measurement and output intermittently or continuously. The predetermined gas is a gas generated by a reaction between water and carbon. As described above, at least one of the components disposed in the space 35S contains carbon. Therefore, if water enters the space 35S in a state where the temperature of the space 35S is, for example, 700 ℃. In addition, it is considered that water is decomposed into hydrogen atoms and oxygen atoms in a high temperature state in which water reacts with carbon, 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 gases. Examples of the device for measuring the concentration of carbon monoxide include a constant-potential electrolytic sensor, examples of the device for measuring the concentration of carbon dioxide include a non-dispersive infrared sensor, examples of the device for measuring the concentration of methane or hydrogen include a semiconductor laser absorption spectroscopic sensor, and examples of the device for measuring the concentration of oxygen include a zirconia concentration cell sensor. The gas measuring unit 48 of the present embodiment is configured to be able to measure the concentration of carbon monoxide. The gas measuring unit 48 may be attached to the furnace body 35, for example, as long as it can measure the concentration of the predetermined gas in the space 35S.

The determination unit 50 of the present embodiment stores the concentration of the predetermined gas measured by the gas measurement unit 48 in the memory 55, and determines whether or not the dehydration/sintering apparatus 100 is in an abnormal state and whether or not the manufactured optical fiber is defective based on the change with time of the concentration of the predetermined gas. The determination unit 50 may be configured in the same manner as the control unit 60, for example.

The Memory 55 is, for example, a non-transitory (non-transitory) storage medium, and is preferably a semiconductor storage medium such as a RAM (Random Access Memory) or a ROM (Read Only Memory), but may include any type of storage medium such as an optical storage medium or a magnetic storage medium. In the present embodiment, a program and information for executing these determination processes are stored in the memory 55. The determination unit 50 reads out the program and information from the memory 55, and in this state, includes the abnormality determination unit 51 and the optical fiber failure determination unit 52, and executes the above-described determination processing.

The abnormality determination unit 51 determines whether or not the dehydration sintering apparatus 100 is in an abnormal state based on the change with time in the concentration of the predetermined gas measured by the gas measurement unit 48. As described later, the present inventors found that: if the difference between the concentration of the predetermined gas measured by the gas measurement unit 48 and the average value of the concentrations of the predetermined gases measured by the gas measurement unit 48 before the time when the concentration of the gas is measured is equal to or greater than the first predetermined value, the water intrusion space 35S is in an abnormal state. This is because the water enters the space 35S, and a predetermined gas is generated by the reaction between the water and the carbon, and the concentration of the predetermined gas increases. Therefore, when the difference between the concentration of the predetermined gas measured by the gas measurement unit 48 and the average value of the concentrations of the predetermined gases measured by the gas measurement unit 48 before the time when the concentration of the gas is measured is equal to or greater than the first predetermined value, the abnormality determination unit 51 of the present embodiment outputs a signal indicating an abnormal state to the notification unit 56 via the control unit 60. On the other hand, when the difference is smaller 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 the state is not abnormal to the notification unit 56 via the control unit 60. Therefore, the judgment by the abnormality judgment unit 51 is: the output signal is changed according to the signal from the gas measuring unit 48. The first predetermined value can be set in advance by an experiment or the like, and for example, the first predetermined value when the predetermined gas is carbon monoxide is set to 500ppm, and the first predetermined value when the predetermined gas is carbon dioxide is set to 450ppm. The abnormality determination unit 51 may output a signal directly to the notification unit 56.

The optical fiber defect determining unit 52 determines whether or not an optical fiber manufactured from an optical fiber preform including a member made of a porous glass body is defective, based on a change with time in the concentration of a predetermined gas measured by the gas measuring unit 48 when the porous glass body serving as a part of the optical fiber is heated. As described later, the present inventors found that: if the difference between the concentration of the predetermined gas when the porous glass body is heated and the concentration of the predetermined gas in the initial state exceeds a second predetermined value, it is considered that an optical fiber manufactured from an optical fiber preform including a glass member made of the porous glass body is defective. If the amount of water entering the space 35S is large, the amount of water that permeates the muffle tube 31 and enters the housing space 31S is also large, which deteriorates the characteristics of the manufactured optical fiber, for example, transmission loss. It is also understood that if the difference exceeds the second predetermined value, the characteristics normally required for an optical fiber for long-distance transmission cannot be satisfied. The initial state is a state before the porous core glass body 20 is heated for the first time from the installation of the furnace body 35. The second predetermined value can be set in advance by an experiment or the like, and is 550ppm, for example, when the predetermined gas is carbon monoxide and the porous glass body is the porous glass body 20 for the core 10 of the optical fiber 1. When the difference between the carbon monoxide concentration and the carbon monoxide concentration in the initial state exceeds 550ppm, the optical fiber failure determination unit 52 of the present embodiment outputs a signal indicating a failure of the optical fiber 1 to the control unit 60. On the other hand, when the difference is less than 550ppm, the optical fiber failure determination unit 52 may not output a signal to the control unit 60, but may output a signal indicating that the optical fiber 1 has no failure to the control unit 60. Therefore, the judgment by the optical fiber failure judging section 52 is: the output signal is changed according to the signal from the gas measuring unit 48. The optical fiber failure determination unit 52 may output a signal directly to the notification unit 56.

The notification unit 56 of the present embodiment performs notification based on the signal from the abnormality determination unit 51 and the signal from the optical fiber failure determination unit 52. The notification unit 56 may be configured to include at least one of a display and a speaker, for example.

Next, the first dehydration step P2a and the first sintering step P2b in the first heating step P2 will be described.

(first dehydration step P2 a)

This step is a step of heating the porous core glass body 20 using the dehydration sintering apparatus 100 to dehydrate the porous core glass body 20. In this step, first, as shown in fig. 4, the porous glass core body 20 suspended from the support rod 22 is stored in the storage space 31S of the muffle tube 31. The first gas supply unit 41 supplies the first gas to the storage space 31S in accordance with a control signal from the control unit 60, fills the storage space 31S with the first gas, and discharges the gas in the storage space 31S from the discharge pipe 44. The second gas supply unit 42 supplies the second gas to the space 35S in accordance with a control signal from the control unit 60, fills the space 35S with the second gas, and discharges the gas in the space 35S from the discharge pipe 46. Therefore, combustion of the heater 37, the heat insulating material 38, and the like in the space 35S can be suppressed.

In the state where the gas is supplied by the first gas supply unit 41 and the second gas supply unit 42, the heater 37 generates heat in accordance with a control signal from the control unit 60. In a state where the heater 37 generates heat, the elevating unit 40 moves the porous core glass body 20 at a predetermined speed in accordance with a control signal from the control unit 60 so that the entire porous core glass body 20 traverses the heater 37. Therefore, the core porous glass body 20 is heated by the heater 37 at a predetermined temperature. By this heating, the OH groups and the attached moisture of the porous glass body for core 20 are removed by the dehydration gas contained in the first gas. The heating temperature may be lower than the sintering temperature of the porous glass core body 20 and may be a temperature at which moisture can be removed from the porous glass core body 20, and is preferably 1100 ℃ to 1400 ℃. The heating temperature of 1100 ℃ or higher promotes diffusion of the gas into the porous core glass body 20, and the heating temperature of 1400 ℃ or lower sufficiently suppresses softening of the porous core glass body 20.

When the porous core glass body 20 is heated by the heater 37 in this manner, the gas measurement unit 48 measures the concentration of carbon monoxide at predetermined time intervals, for example, at intervals of 1 minute, and outputs a signal indicating the measured concentration of carbon monoxide to the determination unit 50. That is, in this step, the porous core glass body 20 is heated by the heater 37, and the concentration of carbon monoxide is measured by the gas measuring unit 48, thereby heating the porous core glass body 20.

When the difference between the concentration of carbon monoxide, which is a predetermined gas, measured by the gas measurement unit 48 and the average value of the concentrations of carbon monoxide measured by the gas measurement unit 48 before the time when 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 notifies the abnormality determination unit 51 of the abnormal state based on the signal from the abnormality determination unit 51. Therefore, the operator can recognize the abnormal state based on the notification by the notification unit 56. When the difference between the carbon monoxide concentration measured by the gas measuring unit 48 and the carbon monoxide concentration measured by the gas measuring unit 48 in advance in the initial state described above exceeds 550ppm, the optical fiber failure determining unit 52 outputs a signal indicating an optical fiber failure to the control unit 60, and the notification unit 56 notifies the optical fiber failure determining unit 52 of the signal. Therefore, the operator can determine a defect in the manufactured optical fiber based on the notification from the notification unit 56.

(first sintering Process P2 b)

This step is a step of heating the porous core glass body 20 by the dehydration sintering apparatus 100 used in the first dehydration step P2a after the first dehydration step P2a to sinter the porous core glass body 20. Similarly to the first dehydration step P2a, the first gas supply unit 41 supplies the first gas to the housing space 31S, and the second gas supply unit 42 supplies the second gas to the space 35S. In the state where the gas is supplied in this way from the first gas supply unit 41 and the second gas supply unit 42, the heater 37 generates heat. In a state where the heater 37 generates heat, the elevating unit 40 moves the porous core glass body 20 at a predetermined speed so that the entire porous core glass body 20 passes across the heater 37. Therefore, the porous glass body for core 20 is heated by the heater 37 at a predetermined temperature, and the porous glass body for core 20 is sintered by the heating. The heating temperature may be a temperature at which the porous glass body for core 20 is sintered to be vitrified in a transparent state, and is preferably 1300 ℃ or higher and 1650 ℃ or lower, for example.

Similarly to the first dehydration step P2a, the gas measurement unit 48 measures the concentration of carbon monoxide at intervals of, for example, 1 minute, and outputs a signal indicating the measured concentration of carbon monoxide to the determination unit 50. Therefore, in this step, as in the first dehydration step P2a, the porous glass core body 20 is heated by the heating method in which the heater 37 heats the porous glass core body 20 and the concentration of carbon monoxide is measured by the gas measurement unit 48. In the same manner as the first dehydration step P2a, the notification unit 56 notifies the abnormality determination unit 51 and the optical fiber failure determination unit 52 of the abnormality. In this step, the porous core glass body 20 is vitrified into a transparent state to form a core glass rod as 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.

(second deposition step P3)

This step is a step of depositing glass microparticles on the outer surface of the core glass rod formed in the first sintering step P2b to form a cladding porous glass body 11P shown in fig. 2, i.e., a cladding porous glass body. In the present embodiment, the porous glass body for cladding is formed by depositing glass fine particles on the outer peripheral surface of the core glass rod by the OVD method, but the method for forming the porous glass body for cladding is not particularly limited.

(second heating Process P4)

This step is a step of heating the porous glass body for cladding formed in the second deposition step P3, and includes, as shown in fig. 3: a second dehydration step P4a and a second sintering step P4b. In the present embodiment, these steps are performed by using another dehydration sintering apparatus 100 having the same configuration as the dehydration sintering apparatus 100 used in the first heating step P2, but the dehydration sintering apparatus 100 used in the first heating step P2 may be used.

(second dehydration step P4 a)

This step is a step of heating the porous glass body for cladding by the dehydration sintering apparatus 100 to dehydrate the porous glass body for cladding. The main differences between this step and the first dehydration step P2a are: the core glass rod formed with the cladding porous glass body is housed in the housing space 31S of the core tube 31. Therefore, the present step, in which the porous glass body for cladding is heated by the heater 37 to dehydrate the porous glass body for cladding and the concentration of carbon monoxide is measured by the gas measuring unit 48, will not be described in detail. In this step, the optical fiber failure determination unit 52 does not determine whether or not the optical fiber is defective, and the notification unit 56 notifies the optical fiber failure determination unit based on a signal from the abnormality determination unit 51.

(second sintering step P4 b)

This step is a step of heating the porous glass body for cladding by 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 cladding. The main differences between this step and the first dehydration step P2a are: a core glass rod formed with a porous glass body for cladding dehydrated in the second dehydration step P4a is stored in the storage space 31S of the core pipe 31. Therefore, the present step, in which the porous glass body for cladding is heated by the heater 37 to sinter the porous glass body for cladding and the concentration of carbon monoxide is measured by the gas measuring unit 48, will not be described in detail. In this step, the optical fiber failure determination unit 52 does not determine whether the optical fiber is defective, and the notification unit 56 notifies the optical fiber failure determination unit based on a signal from the abnormality determination unit 51.

In this step, the core glass rod is substantially unchanged, and becomes a core glass body 10P shown in fig. 2. The porous glass body for cladding is vitrified to be a clad glass body 11P. Thus, the optical fiber preform 1P shown in FIG. 2 was obtained.

The optical fiber preform 1P thus obtained is heated and drawn in a spinning furnace, so that the core glass body 10P becomes the core 10 and the cladding glass body 11P becomes the cladding 11, thereby obtaining a bare optical fiber composed of the core 10 and the cladding 11. The bare optical fiber is coated with a resin serving as the coating layer 12 to form the coating layer 12, thereby obtaining the optical fiber 1 shown in fig. 1.

As described above, the dehydration sintering apparatus 100 as the heating apparatus for a glass member of the present embodiment includes: a furnace core tube 31, a furnace body 35, a heater 37, and a gas measuring part 48. The muffle tube 31 has a housing space 31S, and the housing space 31S can house the entire porous glass core body 20 as a glass member. The furnace body 35 surrounds at least a part of the muffle tube 31, and the heater 37 is disposed in a space 35S surrounded by the muffle tube 31 and the furnace body 35. At least one of the members disposed in the space 35S contains carbon. The gas measuring unit 48 can measure the concentration of a predetermined gas generated by the reaction between water and carbon in the space 35S.

In the method for heating the core porous glass body 20 and the cladding porous glass body as glass members according to the present embodiment, these glass members are heated by the heater 37 disposed in the space 35S surrounded by the core tube 31 and the furnace body 35. At least one of the members disposed in the space 35S contains carbon. These glass members are heated by the heater 37, and the concentration of a predetermined gas generated by the reaction between water and carbon in the space 35S is measured.

In the case of dehydrating, sintering, melting, etc. a glass member, the heater is usually heated to 700 ℃ or higher. In such a high temperature state, if water enters the space 35S surrounded by the muffle tube 31 and the furnace body 35, the water reacts with carbon contained in the members disposed in the space to generate gas. In the dehydration sintering apparatus 100 and the method of heating a glass member according to the present embodiment, since the concentration of the gas generated in this manner can be measured, an abnormal state in which water enters the space 35S can be detected.

In addition, in the dehydration sintering apparatus 100 and the method of heating a glass member according to the present embodiment, since the furnace body 35 has the flow path 36 through which cooling water flows, damage to the furnace body 35 due to heat can be suppressed. Further, since the gas measuring unit 48 can measure the concentration of the gas generated by the reaction of the water and the carbon in the space 35S, damage to the furnace body 35 such as the cooling water entering the space 35S can be detected.

The dehydration sintering apparatus 100 of the present embodiment further includes a second gas supply unit 42, and the second gas supply unit 42 supplies an inert gas to the space 35S from a gas supply port S2 formed in the furnace body 35 and communicating with the space 35S. Therefore, the burning of the heater 37, the heat insulating material 38, and the like, which are members disposed in the space 35S, can be suppressed. Further, since the gas measuring unit 48 can measure the concentration of the gas generated by the reaction between water and carbon in the space 35S, it is possible to detect a problem with the second gas supply unit 42, the pipe 45 connected to the second gas supply unit 42, and the like, which is caused when water enters the space 35S together with the inert gas.

In the dehydration sintering apparatus 100 and the method of heating a glass member according to the present embodiment, the concentration of a predetermined gas is measured from an exhaust gas discharged from an exhaust port E2 formed in the furnace body 35 and communicating with the space 35S. Therefore, compared to when the concentration of the predetermined gas is measured at a certain position in the space 35S, the influence of the position where the predetermined gas is generated in the space 35S on the concentration of the predetermined gas can be suppressed. Therefore, compared to the above case, the abnormal state of the water entry space 35S can be accurately detected.

The dehydration sintering apparatus 100 according to the present embodiment further includes an abnormality determination unit 51, and the abnormality determination unit 51 determines whether or not the state is abnormal based on the change with time in the concentration of the predetermined gas measured by the gas measurement unit 48. The abnormality determination unit 51 determines that the state is abnormal when the difference between the concentration of the predetermined gas measured by the gas measurement unit 48 and the average value of the concentrations of the predetermined gases measured by the gas measurement unit 48 before the time when the concentration of the predetermined gas is measured is equal to or greater than a first predetermined value. There is a tendency that: even in the furnace body 35 having the same configuration, the concentration of the predetermined gas measured in a steady state changes depending on the installation state of the furnace body 35. Therefore, by adopting the above configuration, it is possible to appropriately determine whether or not an abnormal state is present, compared to a case where an abnormal state is determined when the concentration of the gas is equal to or higher than a predetermined value.

The dehydration sintering apparatus 100 of the present embodiment further includes an optical fiber failure determination unit 52, and heats the porous glass body for core 20, which is a porous glass body that is a part of the optical fiber 1. The optical fiber defect determining unit 52 determines whether or not the optical fiber 1 is defective based on the change with time in the concentration of the predetermined gas measured by the gas measuring unit 48 when the porous glass core body 20 is heated.

When water enters the housing space 31S during the sintering of the porous core glass body 20, the characteristics of the finally produced optical fiber 1, i.e., transmission loss and the like, are deteriorated, and the more the amount of water entering the housing space 31S, the worse the characteristics tend to be. Such water intrusion into the housing space 31S may not affect the appearance of the transparent glass member formed by sintering the porous core glass body 20. There are therefore cases where: it is difficult to determine whether or not the characteristics of the finally manufactured optical fiber 1 are deteriorated and the optical fiber 1 is defective, based on the appearance of the transparent glass member. However, as the amount of water entering the housing space 31S increases, the amount of gas generated by the reaction between water and carbon increases, and the concentration of the gas increases. Therefore, by adopting the above configuration, it is possible to determine whether or not the optical fiber 1 finally manufactured is defective at the stage of manufacturing the transparent glass member, and it is possible to reduce the defective rate of the optical fiber 1 and improve the productivity of the optical fiber 1.

In the present embodiment, the predetermined gas is carbon monoxide, and when the difference between the carbon monoxide concentration measured by the gas measuring unit 48 and the carbon monoxide concentration in the initial state exceeds 550ppm when the porous core glass body 20 serving as the core 10 of the optical fiber 1 is heated, the optical fiber defect determining unit 52 determines that the optical fiber 1 is defective. As described above, the present inventors found that: if the difference exceeds 550ppm, the optical fiber 1 manufactured from the optical fiber preform 1P including the core glass body 10P made of the core porous glass body 20 is defective. Therefore, by adopting such a configuration, it is possible to appropriately determine whether or not the finally manufactured optical fiber 1 is defective.

The present invention has been described above by taking the above embodiments as examples, but the present invention is not limited thereto.

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

In the above-described embodiment, the abnormality determination unit 51 has been described by taking as an example the case where the abnormality determination unit 51 determines that the state is abnormal when the difference between the concentration of the predetermined gas measured by the gas measurement unit 48 and the average value of the concentrations of the predetermined gases measured by the gas measurement unit 48 before the time of measuring the concentration of the predetermined gas is equal to or greater than the first predetermined value. However, the abnormality determination unit 51 may be any unit that determines whether or not an abnormal state is present based on the change with time in the concentration of the predetermined gas measured by the gas measurement unit 48. For example, the abnormality determination unit 51 may output a signal indicating that the state is abnormal when the concentration of the predetermined gas is equal to or higher than a predetermined threshold value. For example, the predetermined threshold value is 700ppm when the predetermined gas is carbon monoxide, and 800ppm when the predetermined gas is carbon dioxide. However, in order to appropriately determine whether or not the abnormal state is present, it is preferable that the abnormality determination unit 51 determine whether or not the abnormal state is present as in the present embodiment. The abnormality determination unit 51 may determine that the state is abnormal based on a difference between the concentration of the predetermined gas and a central value of the concentration of the predetermined gas before the time of measuring the concentration of the predetermined gas, a difference between the concentration of the predetermined gas and a value obtained by subtracting a standard deviation from an average value of the concentrations of the predetermined gas before the time of measuring the concentration of the predetermined gas, a difference between the concentration of the predetermined gas and a minimum value of the concentration of the predetermined gas before the time of measuring the concentration of the predetermined gas, and the like. In this case, when the difference is equal to or greater than a predetermined value set for each difference based on an experiment or the like, the abnormality determination unit 51 determines that the state is abnormal. The abnormality determination unit 51 may determine that the predetermined gas is in an abnormal state when the concentration of the predetermined gas continuously increases by a value equal to or more than a predetermined amount for a predetermined period. The state in which the optical fiber 1 is defective is an abnormal state. Therefore, for example, the abnormality determination unit 51 may determine that the glass member is in the abnormal state when the difference between the carbon monoxide concentration measured by the gas measurement unit 48 during heating of the glass member and the carbon monoxide concentration in the initial state exceeds 550ppm, as in the optical fiber failure determination unit 52 of the above-described embodiment.

In the above embodiment, the optical fiber failure determination unit 52 has been described as an example in which the optical fiber failure determination unit 52 determines that the optical fiber 1 is defective when the difference between the carbon monoxide concentration measured by the gas measurement unit 48 when the porous glass body for core 20 is heated and the carbon monoxide concentration in the initial state exceeds 400 ppm. However, the optical fiber failure determination unit 52 may be any unit that determines whether or not the state is abnormal based on the change with time in the concentration of the predetermined gas measured by the gas measurement unit 48. For example, the optical fiber failure determination unit 52 may output a signal indicating a failure of the optical fiber 1 when the concentration of the predetermined gas is equal to or higher than a predetermined threshold value. For example, the predetermined threshold value is 700ppm when the predetermined gas is carbon monoxide, and 800ppm when the predetermined gas is carbon dioxide. In the above embodiment, the optical fiber defect determining unit 52 determines whether or not the optical fiber 1 is defective based on the temporal change in the concentration of the predetermined gas measured in the first heating step P2. Here, if water enters the housing space 31S when the porous glass body for cladding which becomes the cladding 11 of the optical fiber 1 is sintered, the transmission loss, which is the characteristic of the finally manufactured optical fiber 1, is deteriorated, and there is a tendency that the transmission loss is deteriorated as the amount of water entering the housing space 31S is larger. Therefore, the optical fiber defect determining unit 52 may determine whether or not the optical fiber 1 is defective based on the change with time of the concentration of the predetermined gas measured in the second heating step P4. In this case, a threshold value or the like for determining the concentration of the predetermined gas whether the optical fiber 1 is defective is set based on an experimental value or the like.

In the above embodiment, the furnace body 35 surrounding a part of the muffle tube 31 is described as an example. However, the furnace body 35 may surround at least a part of the muffle tube 31, and may surround the entire muffle tube 31, for example.

In the above embodiment, the dehydration sintering apparatus 100 including the second gas supply unit 42 is described as an example. However, the dehydration sintering apparatus 100 may not include the second gas supply unit 42, and may include, for example, a discharge unit that discharges the air in the space 35S from the discharge pipe 46 to make the space 35S in a vacuum state, instead of the second gas supply unit 42. By thus making the space 35S in a vacuum state, burning of the heater 37, the heat insulator 38, and the like in the space 35S can be suppressed. In the above embodiment, the furnace body 35 having a cooling function by cooling water is described as an example, but the method for cooling the furnace body 35 is not particularly limited. If the furnace body 35 has sufficient heat resistance, the furnace body 35 may not have a cooling function. In the above embodiment, the concentration of the predetermined gas is measured with respect to the space 35S of the furnace body 35, but the present invention is not limited thereto.

In the above embodiment, the first stacking step P1 of forming the porous core glass body 20 as the core glass body 10P is explained as an example. However, the porous glass body formed in the first deposition step P1 is not particularly limited, and may be, for example, a porous glass body that forms a part of the core glass body 10P and the cladding 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 in the first sintering step P2b to form a porous glass body as another part of the clad glass body 11P.

In the above embodiment, the method of manufacturing the optical fiber preform 1P including the first stacking step P1, the first heating step P2, the second stacking step P3, and the second heating step P4 is described as an example. However, the method for producing the optical fiber preform 1P may include a heating step of heating the porous glass body as the glass member by the above-described method for heating the glass member. For example, the method of manufacturing the optical fiber preform 1P may not include the first stacking step P1 and the first heating step P2. In this case, for example, in the second deposition step P3, a core glass rod is first prepared by procurement or the like, and glass microparticles are deposited on the outer peripheral surface of the core glass rod to form a porous glass body for cladding.

In the above embodiment, the first sintering step P2b and the second sintering step P4b were described as an example in which the first gas was set as a mixed gas of a dehydration gas and an inert gas, and the porous glass body was heated in a state where the first gas was supplied from the first gas supply portion 41 to the housing space 31S in the first sintering step P2b and the second sintering step P4b. 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 housing space 31S. In this case, for example, the first gas supply unit 41 may be configured to be able to change the first gas to be supplied between a gas containing a dehydration gas and an inert gas and only the inert gas. The control unit 60 controls the first gas supply unit 41 so as to switch the first gas supplied from the first gas supply unit 41 according to the process.

In the above embodiment, the core porous glass body 20 is heated by the same dehydration sintering apparatus 100 in the first dehydration step P2a and the first sintering step P2b, and the cladding porous glass body is heated by the same dehydration sintering apparatus 100 in the second dehydration step P4a and the second sintering step P4b. However, for example, the porous glass body may be heated by different dehydration sintering apparatuses 100 in the respective steps. The method for producing the optical fiber preform 1P may further include an elongation step of elongating a glass body obtained by sintering the porous glass body for core 20 in the first heating step P2 to obtain a core glass rod. The core tube 31 may have a housing space 31S for housing at least a part of the glass member, and may have openings at both ends of the core tube 31. For example, the device for elongating the glass body, the spinning furnace for heating the optical fiber preform 1P, and the tip end processing furnace are also included in the heating device for the glass member of the present invention.

The present invention will be described in more detail below with reference to examples, but the present invention is not limited thereto.

The first stacking process P1 and the first heating process P2 shown in fig. 3 were repeated 32 times by the dehydration sintering apparatus 100 shown in fig. 4, and 32 core glass rods were produced. In the dehydration sintering apparatus 100, the heater 37 is not heated until the first core glass rod is produced after the furnace body 35 is installed. The concentrations of carbon monoxide and carbon dioxide in the space 35S in the initial state from the installation of the furnace body 35 to the first heating step P2 for producing the first core glass rod were measured by the gas measuring unit 48. The carbon monoxide concentration in the initial state was 150ppm and the carbon dioxide concentration was 260ppm. In the first heating step P2 in the production of each core glass rod, the concentrations of carbon monoxide and carbon dioxide in the space 35S were measured by the gas measuring unit 48. Fig. 5 shows the measurement results. Fig. 5 also shows a transmission loss which will be described later.

Further, the second deposition step P3 and the second heating step P4 shown in fig. 3 are performed by another dehydration sintering apparatus 100, and an optical fiber preform 1P similar to the optical fiber preform 1P shown in fig. 2 is produced from these core glass rods. In the second heating step P4 in the production of each optical fiber preform 1P, the concentrations of carbon monoxide and carbon dioxide in the space 35S are measured by the gas measuring unit 48. The carbon monoxide concentration is 150ppm to 250ppm, and the carbon dioxide concentration is 250ppm to 400 ppm. After the optical fiber preform 1P is manufactured, the space 35S is checked, and as a result, water does not enter the space 35S.

Further, the produced 32 optical fiber preforms 1P were heated and drawn in a spinning furnace, and optical fibers 1 similar to the optical fiber 1 shown in fig. 1 were produced from the respective optical fiber preforms 1P. The diameter of the core 10 and the diameter of the cladding 11 in each optical fiber 1 are approximately 10 μm and 125 μm, respectively. Further, the transmission loss of light having a wavelength of 1383nm was measured for each Optical fiber 1 by using an OTDR (Optical Time Domain Reflectometer). The measurement results are shown in fig. 5 as described above. The one-dot chain line shown in FIG. 5 indicates 0.31dB/km, which is a value of transmission loss generally required for an optical fiber for long-distance transmission.

As shown in FIG. 5, the transmission loss of the optical fiber 1 manufactured by using the 1 st to 27 th core glass rods was approximately 0.28dB/km, and the transmission loss of the optical fiber 1 manufactured by using the 28 th core glass rod was 0.309dB/km. The optical fiber 1 manufactured by the core glass rod of the 29 th and later had a transmission loss exceeding 0.31dB/km, and the transmission loss tended to increase as the number of the optical fibers increased from the 29 th and later. In addition, the carbon monoxide concentration in the 1 st to 28 th core glass rods was the 28 th and the carbon monoxide concentration in the 28 th rod was 397ppm. In addition, the maximum carbon dioxide concentration in the 1 st to 28 th core glass rods was 28 th, and the carbon dioxide concentration in the 28 th was 448ppm. The carbon monoxide concentration of the 29 th group was 703ppm, the carbon dioxide concentration of the 29 th group was 813ppm, and the concentrations of carbon monoxide and carbon dioxide of the 29 th and subsequent groups increased as the number of the groups increased. It is therefore assumed that: when the 28 th root is produced, water starts to intrude into the space 35S, and as the number of roots increases from the 28 th root to the later root, the amount of water intruded into the space 35S increases. As described above, the carbon monoxide concentration in the initial state was 150ppm, and the carbon dioxide concentration was 260ppm. Therefore, it is found that when the difference between the carbon monoxide concentration at the time of heating the core porous glass body 20 as a glass member and the carbon monoxide concentration in the initial state from the installation furnace body 35 to the time before the first heating of the core porous glass body 20 exceeds 550ppm, the optical fiber 1 is defective. It is also found that when the difference between the carbon dioxide concentration at the time of heating the porous core glass body 20 and the carbon dioxide concentration in the initial state exceeds 550ppm, the optical fiber 1 is defective. It is also found that when the carbon monoxide concentration is 700ppm or more and the carbon dioxide concentration is 800ppm or more, the optical fiber 1 is defective. In addition, if water reacts with carbon, methane, oxygen, and hydrogen are produced along with carbon monoxide and carbon dioxide. The amounts of methane, oxygen, and hydrogen produced tend to be stoichiometrically proportional to the amounts of carbon monoxide and carbon dioxide produced. Therefore, reference values for determining whether the optical fiber 1 is defective or not can be set for the respective concentrations of methane, oxygen, and hydrogen based on experimental values or the like.

In addition, the difference between the carbon monoxide concentration and the average value of the carbon monoxide concentrations measured before the time of measuring the carbon monoxide is 500ppm or less in the 1 st to 28 th roots. In addition, the difference was 506ppm for the 29 th root. Therefore, it is understood that if the difference is 500ppm or more, the dehydration sintering apparatus 100 is in an abnormal state. In addition, the difference between the carbon dioxide concentration and the average value of the carbon dioxide concentrations measured before the time of measuring the carbon dioxide was 550ppm or less for the 1 st to 28 th roots. In addition, the difference was 553ppm for the 29 th root. Therefore, it is understood that when the difference is 550ppm or more, the dehydration sintering apparatus 100 is in an abnormal state. It is also understood that when the carbon monoxide concentration is 700ppm or more and the carbon dioxide concentration is 800ppm or more, the dehydration sintering apparatus 100 is in an abnormal state. Further, since the amounts of methane, oxygen, and hydrogen generated tend to be proportional to the amounts of carbon monoxide and carbon dioxide generated as described above, reference values for determining whether or not the dehydration-sintering apparatus 100 is in an abnormal state can be set based on experimental values or the like for the concentrations of methane, oxygen, and hydrogen, respectively.

As described above, it is possible to provide a heating device for a glass member, a heating method for a glass member, and a manufacturing method for an optical fiber preform using the same, which can detect an abnormal state caused by water, and can be applied to the fields of optical fiber communication and the like.

Claims

1. A glass member heating device is characterized by comprising:

a core tube having a housing space capable of housing at least a part of the glass member;

a furnace body surrounding at least a part of the core tube;

a heater disposed in a space surrounded by the muffle tube and the furnace body; and

a gas measuring part for measuring the gas flow rate of the gas,

at least one of the components disposed in the space contains carbon,

the gas measuring unit is capable of measuring a concentration of a gas generated by a reaction between water and carbon in the space.

2. The glass member heating apparatus according to claim 1,

the gas is at least one of carbon monoxide, carbon dioxide, methane, and hydrogen.

3. The heating device for glass member according to claim 1 or 2,

the furnace body has a flow path through which cooling water flows.

4. The heating device for glass member as set forth in any one of claims 1 to 3,

the furnace further includes a gas supply unit for supplying an inert gas to the space through a gas supply port formed in the furnace body and communicating with the space.

5. The heating device for glass member as set forth in any one of claims 1 to 4,

the gas measuring portion measures a concentration of the gas based on an exhaust gas discharged from an exhaust port formed in the furnace body and communicating with the space.

6. The heating device for glass member as set forth in any one of claims 1 to 5,

the gas measurement device further includes an abnormality determination unit that determines whether or not the gas measurement device is in an abnormal state based on a change with time in the concentration of the gas measured by the gas measurement unit.

7. The heating device for glass member according to claim 6,

the abnormality determination unit determines that the state is abnormal when a difference between the concentration of the gas measured by the gas measurement unit and an average value of the concentrations of the gas measured by the gas measurement unit before a time when the concentration of the gas is measured is equal to or greater than a predetermined value.

8. The heating device for glass member according to any one of claims 1 to 7,

further comprises an optical fiber defect judging section for judging whether the optical fiber is defective,

the glass member is a porous glass body that becomes part of an optical fiber,

the optical fiber failure determination unit determines whether or not the optical fiber is defective based on a change with time of the concentration of the gas measured by the gas measurement unit.

9. The heating device for glass member according to claim 8,

the gas is carbon monoxide and the gas is,

the glass member is a porous glass body which becomes a core of the optical fiber,

the optical fiber defect determination unit determines that the optical fiber is defective when a difference between the concentration of the gas measured by the gas measurement unit and the concentration of the gas in an initial state before the glass member is heated for the first time after the furnace body is installed exceeds 550ppm.

10. A method of heating a glass member, wherein at least a part of the glass member is accommodated in an accommodation space in a core tube at least a part of which is surrounded by a furnace body, and the glass member is heated by a heater disposed in a space surrounded by the core tube and the furnace body,

at least one of the components arranged in said space contains carbon,

the glass member is heated by the heater, and the concentration of a gas generated by the reaction of water and carbon in the space is measured.

11. The method of heating a glass member according to claim 10, wherein the gas is at least one of carbon monoxide, carbon dioxide, methane, and hydrogen.

12. The method of heating a glass member according to claim 10 or 11,

the furnace body has a flow path through which cooling water flows.

13. The method for heating a glass member according to any one of claims 10 to 12,

when the glass member is heated, an inert gas is supplied to the space from a gas supply port formed in the furnace body and communicating with the space.

14. The method for heating a glass member according to any one of claims 10 to 13,

the concentration of the gas is measured from the exhaust gas discharged from an exhaust port formed in the furnace body and communicating with the space.

15. The method for heating a glass member according to any one of claims 10 to 14,

determining whether the gas is in an abnormal state based on the measured change with time of the concentration of the gas.

16. The method for heating a glass member according to claim 15,

and determining that the gas is in an abnormal state when a difference between the measured concentration of the gas and an average value of the concentrations of the gas measured before a time point at which the concentration of the gas is measured is a predetermined value or more.

17. A method for manufacturing a base material for an optical fiber,

the method for manufacturing a glass member according to any one of claims 10 to 16, wherein the method for manufacturing a glass member is characterized by comprising a heating step of heating a porous glass body that is a part of an optical fiber and is the glass member.

18. The method for manufacturing an optical fiber preform according to claim 17,

and determining whether or not the optical fiber is defective based on a change with time of the concentration of the gas measured in the heating step.

19. The method for manufacturing an optical fiber preform according to claim 18,

the gas is a gas of carbon monoxide in which,

the porous glass body is a porous glass body which becomes a core of the optical fiber,

and determining that the optical fiber is defective when a difference between the concentration of the gas measured in the heating step and the concentration of the gas in an initial state before the porous glass body is heated for the first time since the furnace body is installed exceeds 550ppm.