JP3949425B2 - Heat treatment apparatus and method for optical fiber preform - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical fiber preform heat treatment apparatus and a heat treatment method for performing a heat treatment for vitrifying an optical fiber soot preform by dehydration and sintering to form a transparent optical fiber preform.
[0002]
[Prior art]
As an optical fiber manufacturing method, for example, a soot base material for an optical fiber synthesized by a VAD (Vapour-phase Axial Deposition) method or an OVD (Outside Vapor Deposition) method is dehydrated and sintered by a vitrification apparatus to be transparent. An intermediate base material is used, and the base material is stretched by a thermal flame, a plasma flame, or an electric furnace to form a glass rod having a core or a part of a core and a clad.
Further, a soot serving as a clad is deposited on the obtained glass rod by the OVD method or the like, and dehydrated and sintered by a vitrification apparatus to obtain a preform.
An optical fiber is manufactured by a drawing process in which the obtained preform is heated and melted in a drawing furnace and drawn from the tip of the preform.
[0003]
In the above heat treatment apparatus (vitrification apparatus) for dehydrating, fluorine-doping and sintering the soot base material, further, vacuum substitution of the gas in the fluorine dope and soot base material, and the above-mentioned treatment in a vacuum or pressurized atmosphere Sometimes.
In particular, to replace the gas in the soot base material, it is effective to make the inside of the furnace core tube of the heat treatment apparatus vacuum or reduced pressure.
[0004]
FIG. 5 is a schematic configuration diagram of an example of a heat treatment apparatus used in a vitrification heat treatment step for dehydrating and sintering the soot base material.
A furnace core tube 1 having a hollow structure made of quartz glass or the like is loaded in the furnace body 2. That is, the space in the furnace body 2 is substantially separated from the inside and the outside by the furnace core tube 1. Since the heat treatment temperature is 1000 ° C. or higher, sealing cannot be performed completely, so that it cannot be separated airtight.
Here, the inside of the core tube 1 is a heat treatment chamber TR, and the space formed by the outside of the core tube 1, that is, the outer wall surface of the core tube 1 and the inner wall surface of the furnace body 2, is a heater chamber in which the heater 3 is installed. HR.
[0005]
The soot base material 14 supported by the support shaft 14a is inserted into the heat treatment chamber TR. In this state, by generating heat in the heater 3 in the heater chamber HR, the generated heat is soaked by the soaking tube 3a made of carbon provided in the gap between the heater 3 and the core tube 1, soot base material 14 The heat treatment can be performed.
By the rotation and vertical movement of the support shaft 14a, the soot base material 14 can be rotated and moved in the heat treatment chamber TR, and heat treatment can be performed so as to give a uniform thermal history to the entire soot base material 14.
The heater chamber HR is filled with a heat insulating material 4 or the like, and is cooled by a water cooling mechanism (not shown) provided in the furnace body 2 or the like. Here, the heater is generally a carbon heater. In that case, the heat insulating material is a carbon heat insulating material using carbon fiber, and the furnace core tube is made of quartz, carbon, SiC, or the like.
[0006]
In the heat treatment chamber TR, a gas supply port 6 and a gas exhaust pipe 7 are provided.
The heater chamber HR is also provided with a gas supply port 5 and a gas exhaust pipe 8.
The gas exhaust pipes (7, 8) are connected to a vacuum pump (not shown) so that the heat treatment can be performed in the heat treatment chamber TR and the heater chamber HR under reduced pressure or vacuum, and the gas supply port. It is also possible to perform a heat treatment under pressure by supplying a gas from (5, 6).
[0007]
Corrosive gas may flow in the furnace core tube 1 serving as the heat treatment chamber TR, and since the heater chamber HR is filled with a heat insulating material or the like, the corrosive gas enters the heater chamber HR. Thus, it is possible to prevent the furnace body 2 from being corroded, and to prevent dust caused by a heat insulating material or the like from entering the furnace core tube 1 from the heater chamber HR and contaminating the soot base material 14 or the like. Therefore, the gas supply port and the gas exhaust pipe are independently provided in the heat treatment chamber TR and the heater chamber HR.
[0008]
In addition, regarding the above heat treatment apparatus, JP-A-63-201625, JP-A-5-24854 and JP-A-5-163038 disclose a vacuum atmosphere in order to achieve the purpose of reducing the amount of He used. A method of vitrification is disclosed.
In addition, in JP-A-61-247633, JP-A-62-59535 and JP-B-7-106925, in order to dope fluorine at a high concentration, the gas is pressurized with a gas containing fluorine. A method of vitrification under an atmosphere is disclosed. The higher the partial pressure of the gas containing fluorine, the higher the concentration of the fluorine doped.
[0009]
[Problems to be solved by the invention]
However, in the heat treatment apparatus as shown in FIG. 5, since the core tube is a quartz glass tube, if the difference between the pressure in the core tube and the pressure in the heater chamber increases when heated by the heater, Since there is a risk of deformation, it is necessary to keep the differential pressure between the furnace core tube and the heater chamber within a certain range. When used under normal pressure, the differential pressure is kept within a certain range even if the exhaust system is controlled independently. However, it is difficult to control the differential pressure when heat treatment is performed with a slight change in pressure, and changing the pressure while keeping the differential pressure within a certain range is very slow. Can only be realized. This is not realistic because it significantly reduces productivity.
[0010]
In the heat treatment apparatus described in JP-A-5-163038 described above, the gas flow rate supplied to the inside and outside of the core tube is controlled independently, while the exhaust pipe is connected outside the furnace body and is collectively connected by a vacuum pump. Exhaust. This heat treatment apparatus has no viewpoint of controlling the differential pressure between the furnace body and the core tube, and is considered to maintain the differential pressure by evacuating the furnace body and the core tube together. Further, it is described that the differential pressure control is controlled by the supplied flow rate.
However, when returning to the atmosphere after evacuation, the volume is different between the inside and outside of the core tube, so there is a high possibility that the gas with the smaller volume will enter the larger volume. When the core tube is small, there is a problem that the processing gas in the core tube enters the furnace body. In the opposite case, there is a problem that gas containing dust in the furnace body enters the core tube and contaminates the core tube.
In this heat treatment apparatus, there is a problem that there is no mechanism for keeping the pressure difference between the inside and outside of the core tube within a certain range when the pressure is changed, but this is not disclosed in the above publication. Moreover, since it is an apparatus for vacuum, it cannot be used when processing by pressurization or normal pressure.
[0011]
Japanese Patent Laid-Open No. 63-201025 (Patent Publication No. 2559395) discloses a method for producing a high-purity transparent glass with little foaming without using He gas. In this method, a core tube is arranged in a pressure vessel, and a heating means for heating the core tube is provided. A processing gas is supplied to the core tube, and the inside of the core tube and the furnace body are exhausted by the same exhaust pipe. Therefore, the pressure difference between the furnace body and the core tube is managed to prevent the core tube from being damaged. It is described that the core tube is preferably quartz or high purity carbon.
Japanese Patent Application Laid-Open No. 5-286737 discloses a method of heating in a vacuum with a multi-heater.
All of the above methods are effective when processing under reduced pressure, but cannot be applied when processing under normal pressure or pressurized conditions. Basically, the concept of controlling the differential pressure between the furnace body and the core tube is not shown. Since the furnace body and core tube are evacuated simultaneously, the differential pressure is considered to be small.
[0012]
On the other hand, Japanese Patent Application Laid-Open No. 62-59535 discloses an apparatus characterized by maintaining a pressure difference between inside and outside of a core tube in a pressurized atmosphere. This is because, in this apparatus, a core tube made of quartz is used, so that the core tube made of quartz is deformed unless the differential pressure is controlled at a high temperature.
Although the concept of performing heat treatment under pressure is described in this publication, it is already known in the normal pressure vitrification apparatus regarding the control of the differential pressure, so how to control the differential pressure. This is a problem, and the heat treatment apparatus described in this publication is realized by supplying He at the same time as the inside and outside of the core tube and exhausting it independently.
In this case, since expensive He has to flow outside the core tube, there is a problem that the cost becomes higher than in the past. Further, since the volume is different between the inside and outside of the core tube, there is a possibility that reactive gas that should flow only inside the core tube enters the inside of the furnace tube outside the core tube. If it does so, the metal of a furnace body will corrode and a lifetime will become short.
[0013]
In addition, controlling the pressure on the supply side is not preferable in view of safety because there is a risk that a large amount of reactive gas enters the furnace body side in the case of malfunction.
Further, since the pressure is adjusted by the pressure regulator, there is a problem that a minute differential pressure cannot be controlled. The level for adjusting the differential pressure is 0.1 kgf / cm² And very high. Also, since the supply amount is controlled by pressure, He and SiF, which are normally controlled by mass flow rate, are controlled._Four It is difficult to control fine mixing ratios. Furthermore, in order to control the pressure independently on the exhaust side, when trying to make the differential pressure constant, the exhaust pressure of the furnace body and the core tube affects both the differential pressure, making control difficult.
[0014]
Japanese Patent Laid-Open No. 61-247633 discloses SiF._Four It has been shown that when the pressure is increased to 1 atm or higher, fluorine can be doped into silica soot at a high concentration, but this method is not described in detail.
[0015]
The present invention has been made in view of the above situation. Therefore, the object of the present invention is to separate the interior and exterior spaces of the reactor core tube, so that there is almost no gas flow between them, corrosion of the reactor body and the interior of the reactor core tube. It is possible to prevent contamination and to control the differential pressure between the inside and outside of the core tube with high accuracy, especially for optical fiber preforms that can be used under pressure or reduced pressure, or a combination thereof. It is to provide a heat treatment apparatus and method.
[0016]
[Means for Solving the Problems]
In order to achieve the above object, an optical fiber preform heat treatment apparatus according to the present invention is an optical fiber that performs a heat treatment for vitrifying an optical fiber soot preform by dehydration and sintering into a transparent optical fiber preform. A heat treatment apparatus for a base material, a first chamber for heat treatment inside, a second chamber provided on the outer peripheral side of the first chamber while being separated from the first chamber, and a heater installed therein, A first exhaust pipe provided connected to the first chamber; a second exhaust pipe provided connected to the second chamber; and a third where the first exhaust pipe and the second exhaust pipe merge. The first exhaust pipe is provided with first adjusting means for adjusting at least the pressure in the first chamber or the flow rate of the gas flowing through the first chamber. A second adjusting means for adjusting the pressure of the two chambers or the flow rate of the flowing gas; Serial third is provided in the exhaust pipe.
[0017]
The above-described heat treatment apparatus for an optical fiber preform of the present invention preferably includes a first detection means for detecting a differential pressure between the pressure in the first chamber and the pressure in the second chamber, and the pressure in the second chamber. It has the 2nd detection means to detect.
More preferably, the pressure in the second chamber becomes a target value or a target range according to the detection results of the first detection means and the second detection means, and the pressure in the first chamber The apparatus further includes a controller that controls the first adjusting means and the second adjusting means so that the differential pressure between the pressures in the second chamber is a predetermined value or a predetermined range.
[0018]
Preferably, the heat treatment apparatus for an optical fiber preform according to the present invention preferably controls the first chamber and the second chamber while controlling the differential pressure between the first chamber and the second chamber to be a predetermined value or a predetermined range. The second chamber is treated in a state of increased pressure to normal pressure, normal pressure to reduced pressure, or a combination thereof.
[0019]
The above-described heat treatment apparatus for an optical fiber preform of the present invention preferably includes at least gas temperature measuring means in the first exhaust pipe and the second exhaust pipe.
[0020]
In the heat treatment apparatus for an optical fiber preform according to the present invention, a plurality of heaters are preferably installed in the second chamber.
[0021]
The above-described heat treatment apparatus for an optical fiber preform of the present invention includes a first chamber that performs heat treatment inside, a second chamber that is provided on the outer peripheral side of the first chamber while being separated from the first chamber, and has a heater installed therein. A room is provided.
Here, the first exhaust pipe provided in connection with the first chamber, the second exhaust pipe provided in connection with the second chamber, and the third exhaust in which the first exhaust pipe and the second exhaust pipe merge. It is set as the structure which has a pipe | tube. In addition, first adjusting means for adjusting at least the pressure in the first chamber or the flow rate of the gas flowing in the first chamber is provided in the first exhaust pipe, and the pressure in the first chamber and the second chamber or the flow rate of the flowing gas is adjusted. The second adjusting means for adjusting is provided in the third exhaust pipe.
Thereby, the space inside the furnace core tube (first chamber) and the outside (second chamber) are separated, and the first exhaust pipe and the second exhaust pipe are joined by the third exhaust pipe. Since the differential pressure between the exhaust pipe and the second exhaust pipe is almost zero and there is a gas flow toward the third exhaust pipe, there is no gas flow back and forth to prevent corrosion of the furnace body and contamination in the core tube, Since the first exhaust pipe and the second exhaust pipe are joined by the third exhaust pipe, the pressures in the first chamber (furnace core tube) and the second chamber (furnace body) can be made substantially equal. In addition, the differential pressure between the inside and outside of the core tube can be controlled with high accuracy by the first detector and the first adjusting means, and the furnace is not only in the normal pressure state but also in the pressurized or depressurized state. The body pressure control and the pressure control of the furnace body and core tube can be performed with high accuracy.
It should be noted that the above-mentioned separation means that the pressure difference within a predetermined range (0.01 kgf / cm) is not completely airtight.² , About 1 kPa) or less, preferably 30 to 100 Pa, indicating that substantially airtightness is maintained.
[0022]
In order to achieve the above object, the optical fiber preform heat treatment method of the present invention performs a heat treatment for vitrifying the optical fiber soot preform by dehydration and sintering to form a transparent optical fiber preform. A heat treatment method for an optical fiber preform, wherein a first chamber that performs heat treatment therein and a second chamber that is provided on an outer peripheral side of the first chamber while being separated from the first chamber and in which a heater is installed A first exhaust pipe provided connected to the first chamber, a second exhaust pipe provided connected to the second chamber, and the first exhaust pipe and the second exhaust pipe join together. The first exhaust pipe has a third exhaust pipe, and at least a first adjusting means for adjusting the pressure in the first chamber or the flow rate of the gas flowing through the first chamber is provided in the first exhaust pipe. Second adjustment for adjusting the pressure in the second chamber or the flow rate of the flowing gas A heat treatment device having a stage provided in the third exhaust pipe so that the pressure in the second chamber becomes a target value or a target range, and a difference between the pressure in the first chamber and the pressure in the second chamber. The first adjusting means and the second adjusting means are controlled so that the pressure becomes a predetermined value or a predetermined range, and the soot base material for optical fiber is subjected to heat treatment.
[0023]
The above-described heat treatment method for an optical fiber preform according to the present invention preferably includes a step of treating the first chamber and the second chamber under pressure or reduced pressure.
[0024]
In the heat treatment method for an optical fiber preform according to the present invention, preferably, at least the gas temperatures in the first exhaust pipe and the second exhaust pipe are measured by temperature measuring means, and the temperature is within a predetermined temperature range. For example, a gas supply condition that falls within a predetermined range (40 to 200 ° C.) is selected in advance, or a range in which the first and second exhaust pipes are water-cooled is selected in advance, and the above processing is performed.
[0025]
In the above-described heat treatment method for an optical fiber preform according to the present invention, the heat treatment is preferably performed by heating with a plurality of heaters installed in the second chamber.
[0026]
The above-described heat treatment method for an optical fiber preform according to the present invention includes a first chamber in which heat treatment is performed inside, and an outer peripheral side of the first chamber that is substantially separated from the first chamber. A second chamber installed; a first exhaust pipe provided connected to the first chamber; a second exhaust pipe provided connected to the second chamber; the first exhaust pipe; A heat treatment device having a third exhaust pipe joined by two exhaust pipes, adjusting at least the pressure in the first chamber or the flow rate of the gas flowing in the first chamber by adjusting means provided in the first exhaust pipe; and The soot base material for optical fiber is subjected to heat treatment while adjusting the pressure in the first chamber and the second chamber or the flow rate of the flowing gas by adjusting means provided in the third exhaust pipe.
The space between the interior (first chamber) and the exterior (second chamber) of the core tube is substantially separated, and the first exhaust pipe and the second exhaust pipe are joined by the third exhaust pipe. The first adjusting means provided in the exhaust pipe controls the differential pressure between the first chamber and the second chamber to a predetermined value or range, and the gas flows in the first and second exhaust pipes Therefore, there is no gas flow between the first chamber and the second chamber to prevent corrosion of the furnace body and contamination in the core tube, and the first exhaust pipe and the second exhaust pipe are connected by the third exhaust pipe. Due to the merged configuration, the pressure in the core tube and the furnace body can be controlled almost simultaneously and substantially at the same pressure. Therefore, it can be used not only under normal pressure but also under pressure or reduced pressure.
[0027]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0028]
First embodiment
An optical fiber preform heat treatment apparatus according to the present embodiment is a heat treatment apparatus used in a vitrification heat treatment process for dehydrating, fluorine-doping and sintering a soot preform in an optical fiber manufacturing process, and FIG. It is a block diagram.
A furnace core tube 1 having a hollow structure made of quartz glass or the like is loaded in the furnace body 2. That is, the space in the furnace body 2 is substantially separated from the inside and the outside by the furnace core tube 1. As the inner and outer seals of the core tube 1, sealing is performed using an elastic material such as carbon felt. At this time, a structure that takes thermal expansion into consideration is preferable.
Here, the inside of the core tube 1 is a heat treatment chamber TR, and the space formed by the outside of the core tube 1, that is, the outer wall surface of the core tube 1 and the inner wall surface of the furnace body 2, is a heater chamber in which the heater 3 is installed. HR.
[0029]
The soot base material 14 supported by the support shaft 14a is inserted into the heat treatment chamber TR. In this state, by generating heat in the heater 3 in the heater chamber HR, the generated heat is soaked by a soaking tube 3a made of high-purity carbon or SiC provided in the gap between the heater 3 and the core tube 1. The soot base material 14 is radiated and heat treatment can be performed.
By the rotation and vertical movement of the support shaft 14a, the soot base material 14 can be rotated and moved in the heat treatment chamber TR, and heat treatment can be performed so as to give a uniform thermal history to the entire soot base material 14.
The heater chamber HR is filled with a heat insulating material 4 formed of carbon fiber and is cooled by a water cooling mechanism (not shown) provided in the furnace body 2 or the like.
[0030]
In the heat treatment chamber TR, a gas supply port 6 and a gas exhaust pipe 7 are provided.
The heater chamber HR is also provided with a gas supply port 5 and a gas exhaust pipe 8.
The gas exhaust pipe 7 provided in the heat treatment chamber TR and the gas exhaust pipe 8 provided in the heater chamber HR are joined by a merged exhaust pipe 9a and then exhausted outside the system such as a gas processing apparatus.
[0031]
Here, a needle type motor valve MV17 is provided in the gas exhaust pipe 7 provided in the heat treatment chamber TR.
Further, the gas exhaust pipe 8 provided in the heater chamber HR is also provided with a needle type motor valve MV18. However, the motor valve MV18 may be omitted in some cases.
The gas exhaust pipe 8 is provided with a pressure gauge 20 and can measure the pressure in the heater chamber HR.
Further, a differential pressure gauge 30 is provided between the gas exhaust pipe 7 and the gas exhaust pipe 8, and a pressure difference between the heat treatment chamber TR and the heater chamber HR can be measured.
[0032]
A combined exhaust pipe 9a where the gas exhaust pipe 7 and the gas exhaust pipe 8 merge is connected to an exhaust pipe 9b connected to an external device (not shown) such as a gas processing device via a needle type motor valve MV19 and an air valve 13, and a normal one. Are connected to the air valve 15 and the exhaust pipe 9c connected to the vacuum pump 16 and the like. A filter, a mechanical booster pump, a rotary pump, or a dry pump is preferably used for the exhaust pipe connected to the vacuum pump, and a pressure sensor and a vacuum gauge for opening and closing these pumps and the accompanying valves are provided. Although it is normal, it is omitted in FIG.
[0033]
In the above configuration, the heat treatment can be performed with the vacuum pump 16 in the heat treatment chamber TR and the heater chamber HR under reduced pressure or vacuum.
Further, it is possible to perform heat treatment under pressure by supplying gas independently from the gas supply ports (5, 6) to the furnace body and the core tube.
As the gas supplied in the case of pressurization, for example, an inert gas such as nitrogen gas, He, or Ar, or in the case of doping with fluorine when vitrifying by heat treatment, for example, SiF_Four , Si₂ F₆ , Si_Three F₈ Or CF_Four , C₂ F₆ , C_Three F₈ A pressurized atmosphere can also be formed with a gas containing fluorine. Depending on the processing content, Cl₂ Or oxygen may be used. As described above, even if halogen gas or oxygen is flowed into the furnace core tube, the differential pressure is kept very small, so that the gas does not enter the furnace body from the seal portion and does not flow backward from the exhaust pipe.
[0034]
In the optical fiber preform heat treatment apparatus of the present embodiment, when the air valve 15 is closed, the differential pressure between the heat treatment chamber TR and the heater chamber HR is measured by the differential pressure gauge 30, and according to the measurement result, for example, not shown. And the motor valve MV17 and / or the motor valve MV18 can be used to control the differential pressure gauge 30 to have a predetermined value or range.
At this time, since the gas exhaust pipe 7 on the heat treatment chamber side and the gas exhaust pipe 8 on the heater chamber side merge on the downstream side of the motor valve MV17 and the motor valve MV18, the inside of the heat treatment chamber TR is more negative than the heater chamber HR. It is possible to perform stable control of a minute differential pressure of 0 to 1000 Pa without any pressure. Preferably it is 30-100 Pa.
[0035]
In addition, when the air valve 15 is closed, the present heat treatment apparatus can pressurize the furnace body and the core tube integrally by changing the opening of the motor valve MV19 according to the value of the pressure gauge 20. ing. That is, the pressure of the furnace body and the core tube can be made substantially the same at the same time by the motor valve MV19 (second adjusting means).
The inside of the heat treatment chamber TR and the heater are controlled by the motor valve MV19 provided in the exhaust pipe 9b connected to the merged exhaust pipe 9a where the gas exhaust pipe 7 on the heat treatment chamber side and the gas exhaust pipe 8 on the heater chamber side merge. Since the inside of the chamber HR can be pressurized at the same time, there is a great advantage that the minute pressure difference between the heat treatment chamber TR and the heater chamber HR can be kept stable. This differential pressure can be adjusted by the motor valve MV17 (first adjusting means), and the differential pressure ΔP = core pressure (Ps) −furnace body pressure (Pf) = 0 to 1000 Pa, preferably 30 to 100 Pa. Control to be
As a result, it is possible to heat-treat the optical fiber soot base material in a pressurized atmosphere without damaging even if quartz is used for the reactor core tube 1. For example, a gas containing fluorine has a concentration of 100% and a flow rate. It is possible to dope fluorine at a high concentration by heating to 1200 ° C. while flowing into the heat treatment chamber with 2 SLM, with the pressure in the heater chamber being 90 kPa and the pressure in the heat treatment chamber being 40 Pa higher than the pressure in the heater chamber. At this time, the differential pressure fluctuation width between the heat treatment chamber and the heater chamber can be suppressed to about 30 Pa. Of course, the conditions are not limited to the above-described conditions. If an inert gas such as He and a gas containing fluorine are combined and flowed for 1 SLM or more, the pressure in the heat treatment chamber and the heat treatment chamber and heater It is possible to heat-treat the fiber soot base material while controlling the differential pressure with the chamber to an arbitrary value.
[0036]
Further, when the motor valve MV19 is closed, or the air valve 13 provided downstream of the motor valve MV19 or the valve provided upstream is closed, the air valve 15 is opened to simultaneously depressurize the heat treatment chamber TR and the heater chamber HR. It is possible.
At this time, similarly to the case of normal pressure or pressurization, since the gas exhaust pipe 7 on the heat treatment chamber side and the gas exhaust pipe 8 on the heater chamber side merge, the pressure is reduced while keeping a minute differential pressure stable. It becomes possible to perform heat treatment such as dehydration, sintering and annealing in a reduced pressure atmosphere using a quartz furnace tube.
For example, in a state where heat treatment is performed at 1200 ° C., the pressure difference between the heat treatment chamber and the heater chamber can be maintained at about 40 Pa even if the pressure is reduced to 4 kPa.
[0037]
According to the heat treatment apparatus for an optical fiber preform of the present embodiment, the first exhaust pipe provided connected to the first chamber (heat treatment chamber) and the first exhaust pipe provided connected to the second chamber (heater chamber). And a first adjusting means for adjusting at least the pressure in the first chamber or the flow rate of the gas flowing in the first chamber, the second exhaust pipe, and the third exhaust pipe joining the first exhaust pipe and the second exhaust pipe. The second exhaust pipe is provided in the first exhaust pipe, and second adjusting means for adjusting the pressure in the first chamber and the second chamber or the flow rate of the flowing gas is provided in the third exhaust pipe.
Thereby, the space inside the furnace core tube (first chamber) and the outside (second chamber) are separated, and the first exhaust pipe and the second exhaust pipe are joined by the third exhaust pipe. The first adjustment means is provided in the exhaust pipe, the differential pressure is set higher in the core tube, and there is a flow in both pipes. Contamination in the furnace core tube can be prevented, and the first chamber (heat treatment chamber) and the second chamber (with the first exhaust pipe and the second exhaust pipe joined by the third exhaust pipe and the first adjusting means ( The differential pressure with respect to the heater chamber) can be controlled with high accuracy, and can be used not only under normal pressure but also under pressure or reduced pressure.
[0038]
In the heat treatment apparatus for an optical fiber preform and the heat treatment method using the same according to the present embodiment, the differential pressure between the heat treatment chamber and the heater chamber is measured, and the heat treatment chamber side exhaust pipe and the heater chamber side exhaust pipe are further measured. Since a motor valve is installed and these exhaust pipes are merged downstream, the motor valve is controlled according to the measured differential pressure results even if the amount of gas supplied to the core tube and furnace body is reduced. By doing so, the differential pressure between the heat treatment chamber interior and the heater chamber interior can be stably controlled at a minute level. Moreover, even if there is a pressure fluctuation or a differential pressure fluctuation, it is possible to prevent backflow to the core tube and the furnace body.
[0039]
Furthermore, since the heat treatment chamber side exhaust pipe and the heater chamber side exhaust pipe are merged, the heat treatment chamber inner portion does not have a negative pressure compared to the heater chamber inner portion. It is possible to prevent breakage and extend the life. Even when other than a quartz core tube is used, the inside and outside of the core tube cannot be completely sealed (because the core tube is connected), and if the differential pressure can be reduced, the gas in the core tube will not leak into the heater chamber, Cl₂ And SiF_Four , CF_Four The corrosion of the heater chamber (furnace body) due to such decomposition materials can be almost eliminated, and the life can be extended.
[0040]
In addition, by installing a pressure gauge or differential pressure gauge in the heat treatment chamber or the heater chamber or both, measuring the pressure, and controlling the motor valve installed after joining the heat treatment chamber side exhaust pipe and the heater chamber side exhaust pipe, Even if the inside of the heat treatment chamber and the heater chamber are pressurized simultaneously, the differential pressure between the heat treatment chamber and the heater chamber can be stably controlled at a minute level as described above, and the inside of the heat treatment chamber becomes negative pressure. Therefore, quartz can be used for the heat treatment chamber.
Similarly, the above-mentioned effect can be obtained even if the vacuum pump is installed and decompressed after the heat treatment chamber side exhaust pipe and the heater chamber side exhaust pipe are joined.
[0041]
Example 1
Using the apparatus according to this embodiment, an optical fiber preform was created under the following conditions.
(1) Dehydration process
Temperature: 1100 ° C., gas flowing into heat treatment chamber and flow rate: He / Cl₂ = 10 / 0.1 SLM, pressure: normal pressure, differential pressure between heat treatment chamber and heater chamber: 50 Pa, soot base material lowering speed: 300 mm / hour
(2) Sintering process:
Temperature: 1450 ° C., gas flowing into heat treatment chamber and flow rate: He = 10 SLM, pressure: normal pressure, differential pressure between heat treatment chamber and heater chamber: 50 Pa, soot base material lowering speed: 250 mm / hour
By each of the above steps, the fluctuation range of the differential pressure was about 30 Pa, and an optical fiber preform without bubbles and bright spots could be created.
[0042]
An optical fiber preform was prepared under the following conditions.
(1) Pressure reduction process
Temperature: 1000 ° C., gas flowing into the heat treatment chamber: none, pressure: 4 kPa, differential pressure between the heat treatment chamber and the heater chamber: 30 Pa
(2) Dehydration process
Temperature: 1100 ° C., gas flowing into heat treatment chamber and flow rate: He / Cl₂ / O₂ = 10 / 0.1 / 1 SLM, pressure: normal pressure, differential pressure between heat treatment chamber and heater chamber: 50 Pa, soot base material pulling speed: 250 mm / hour
(3) Sintering process:
Temperature: 1400 ° C., gas flowing into heat treatment chamber and flow rate: gas containing fluorine = 2SLM, pressure: 0.15 MPa, differential pressure between heat treatment chamber and heater chamber: 30 Pa, soot base material lowering speed: 200 mm / hour
By each of the above steps, an optical fiber preform having a relative refractive index difference of −0.8% could be created.
At this time, no bubbles or bright spots were generated. As a result, high-concentration fluorine doping was achieved without contamination by dust in the heater chamber. The differential pressure fluctuation was about 30 Pa, and the pressure in the heat treatment chamber did not become lower than the pressure in the heater chamber. Therefore, no deformation occurred even when a quartz core tube was used.
[0043]
Second embodiment
An optical fiber preform heat treatment apparatus according to the present embodiment is a heat treatment apparatus used in a vitrification heat treatment process for dehydrating and sintering a soot preform in an optical fiber manufacturing process, and FIG. 2 is a schematic configuration diagram thereof. is there.
Although the configuration is substantially the same as that of the optical fiber preform heat treatment apparatus of the first embodiment, a gas supply port 24a is provided in the gas exhaust pipe 7 on the heat treatment chamber side, and nitrogen is supplied via the air valve 21a and the mass flow controller MFC22a. An inert gas supply source GS23 such as gas, helium gas or argon gas is connected, and further, a gas supply port 24b is provided in the gas exhaust pipe 8 on the heater chamber side, and the gas is supplied via the air valve 21b and the mass flow controller MFC22b. A difference is that a supply source GS23 is connected and gas can be supplied to the gas exhaust pipes 7 and 8.
[0044]
In the optical fiber preform heat treatment apparatus of the present embodiment, when the air valve 15 is closed, the differential pressure between the heat treatment chamber TR and the heater chamber HR is measured by the differential pressure gauge 30, and according to the measurement result, for example, not shown. And the motor valve MV17 and / or the motor valve MV18 can be used to adjust the value of the differential pressure gauge 30 to a predetermined value.
Further, in this heat treatment apparatus, an inert gas such as nitrogen gas, helium gas or argon gas is supplied from the gas supply ports 24a and 24b while controlling the flow rate, so that the inside of the heat treatment chamber TR and the heater chamber HR. The differential pressure can be adjusted. This can be used in combination with the motor valve MV17 and the motor valve MV18.
[0045]
At this time, since the gas exhaust pipe 7 on the heat treatment chamber side and the gas exhaust pipe 8 on the heater chamber side merge after the motor valve MV17 and the motor valve MV18, measurement is performed with a pressure gauge 20 provided in the gas exhaust pipe 8. The pressure of the pressure gauge 20 can be set to a desired value by using a motor valve MV19 by a control unit (not shown) so that the pressures in the heat treatment chamber TR and the heater chamber HR can be adjusted to be approximately equal. The gas inside the heat treatment chamber TR enters the heater chamber HR by guiding the gas to a gas processing device (not shown) connected to the outlet of the exhaust pipe 9b while maintaining a minute differential pressure during It is possible to prevent.
[0046]
With the above structure, as in the first embodiment, in the heat treatment under a pressurized atmosphere or a reduced pressure atmosphere, the pressure difference between the heat treatment chamber TR and the heater chamber HR is controlled to control the inside of the heat treatment chamber TR. It is possible to prevent gas from entering the heater chamber HR.
[0047]
In the heat treatment apparatus for an optical fiber preform and the heat treatment method using the same according to the present embodiment, the differential pressure between the heat treatment chamber (core tube) and the heater chamber (furnace body) is measured, and the heat treatment chamber side exhaust pipe is further measured. And a heater valve on the heater chamber side exhaust pipe, these exhaust pipes are merged on the downstream side, and the pressure of the two chambers is adjusted by the motor valve provided after the merge, By controlling each motor valve by the pressure, the pressure difference between the heat treatment chamber and the heater chamber can be stably controlled at a minute level of 0 to 1000 Pa simultaneously with the pressures of both chambers.
[0048]
In addition, even if an inert gas such as nitrogen gas, helium gas or argon gas is flowed from the gas supply port provided between the heat treatment chamber and the motor valve, the differential pressure between the heat treatment chamber and the heater chamber can be stabilized at a minute level. Can be controlled. Of course, a combination of these is also possible.
At this time, the heat treatment chamber side exhaust pipe and the heater chamber side exhaust pipe are merged on the downstream side of the motor valve, and the motor valve MV19 is provided there to adjust the pressure of both chambers at the same time. Regardless of the state, a flow toward the motor valve MV19 can be made in both pipes, and the gas in the heat treatment chamber can be prevented from entering the heater chamber. In addition, the differential pressure can be controlled with a large motor valve for a small flow rate, and the opening adjustment range of the motor valve in a pressurized or decompressed atmosphere can be made relatively small. It is stable. Moreover, it is possible to control a relatively wide range of pressure with a single motor valve. For this reason, the reproducibility of the process is improved, and the probability of breakage of the quartz heat treatment chamber can be significantly reduced. There is also an advantage that the amount of gas supplied to the core tube can be further reduced. In addition, since large-sized pipes and motor valves can be used, the structure is strong against pipe clogging with dust.
[0049]
Third embodiment
The heat treatment apparatus for an optical fiber preform according to the present embodiment is a heat treatment apparatus used in a vitrification heat treatment process for dehydrating and sintering a soot preform in an optical fiber manufacturing process, and FIG. 3 is a schematic configuration diagram thereof. is there.
The exhaust pipe connected to the gas exhaust pipe 7 on the heat treatment chamber side, the gas exhaust pipe 8 on the heater chamber side, and the merged exhaust pipe 9a has substantially the same configuration as the heat treatment apparatus for the optical fiber preform of the first embodiment. The difference is that 9b is provided with thermocouple openings (25a, 25b, 25c, 25d, 25e) for temperature measurement.
The present embodiment also provides a heat treatment method and apparatus for an optical fiber preform in which exhaust gas is prevented from condensing in the pipe or in which dew countermeasures are taken.
[0050]
In the present embodiment, the thermocouple opening (25a, 25b, as temperature measuring means) is connected to the gas exhaust pipe 7 on the heat treatment chamber side, the gas exhaust pipe 8 on the heater chamber side, and the exhaust pipe 9b connected to the combined exhaust pipe 9a. 25c, 25d, 25e) are provided (five on the drawing).
By installing a thermocouple in this opening, the temperature of the gas in each pipe can be measured directly.
At this time, it is desirable that the surface of the thermocouple to be installed has a corrosion-resistant coating such as a fluororesin. Of course, the gas exhaust pipes 7 and 8, the combined exhaust pipe 9a, the exhaust pipe 9b, and the like are also coated with corrosion resistance.
[0051]
According to the result of measuring the temperature at each part of the exhaust pipe as described above, for example, the temperature of the exhaust gas at the time of passing through the motor valve MV17, the motor valve MV18, and the motor valve MV19 becomes about 60 to 180 ° C. It is preferable to adjust the temperature. The temperature is adjusted by supplying a gas as in the second embodiment or by using a part of the gas exhaust pipe 7 on the heat treatment chamber side and the gas exhaust pipe 8 on the heater chamber side as water-cooled exhaust pipes (7a, 8a). It can also be realized by adjusting the length of.
[0052]
Since the temperature in the vicinity of the outlets of the heat treatment chamber TR and the heater chamber HR is high, the water-cooled exhaust pipe (7a, 8a) equipped with a cooling mechanism such as cooling water is first cooled to enter a predetermined temperature range. From here, it is possible to adjust the exhaust gas temperature by covering the pipe with a heat insulating material.
Further, when the temperature does not decrease even if the pipe is not covered with the heat insulating material, there is no need for the heat insulating material, and conversely, when the temperature is decreased only with the heat insulating material, it can be adjusted by winding a heater.
For example, the cooling length is determined according to the temperature measured by the thermocouple. Therefore, a configuration in which the cooling water flow path is divided into a plurality of parts in advance, and the cooling water can be flowed by selecting a necessary length is preferable.
If the temperature of the exhaust gas can be adjusted as in this embodiment, it is possible to prevent the gas from condensing in the piping, and it is possible to prevent clogging of the piping and the motor valve.
[0053]
In the optical fiber preform heat treatment apparatus and the heat treatment method using the same according to the present embodiment, the exhaust pipe is provided with a plurality of thermocouple openings as temperature measuring means, and a thermocouple is provided in the openings. By installing, it is possible to directly measure the temperature of the gas in the pipe. A plurality of flow paths for flowing cooling water are provided outside the exhaust pipe in the length direction of the pipe, and the cooling water can be flowed by selecting the exhaust gas temperature within a predetermined range. The exhaust pipe ahead is covered with a heat insulating material, or the temperature of the exhaust gas is adjusted by means such as winding a heater.
Thus, by adjusting the temperature of the exhaust gas, it is possible to prevent the gas from condensing in the piping, and it is possible to prevent clogging of the piping and the motor valve.
[0054]
Fourth embodiment
The heat treatment apparatus for an optical fiber preform according to the present embodiment is a heat treatment apparatus used in a vitrification heat treatment process for dehydrating and sintering a soot preform in an optical fiber manufacturing process, and FIG. 4 is a schematic configuration diagram thereof. is there.
The configuration is substantially the same as the heat treatment apparatus for the optical fiber preform of the first embodiment, but a plurality of heaters are arranged in the heater chamber HR on the outer peripheral surface of the core tube 1 serving as the heat treatment chamber TR. It has been different. A soaking tube 3 a made of carbon or SiC is provided in the gap between each heater 3 and the core tube 1.
In addition, the gas exhaust pipe 7 on the heat treatment chamber side and part of the gas exhaust pipe 8 on the heater chamber side are water-cooled exhaust pipes (7a, 8a) equipped with a cooling mechanism such as cooling water, and the exhaust gas temperature can be adjusted. It has become.
According to the optical fiber preform heat treatment apparatus of this embodiment, uniform heat treatment can be performed in a wide range, and it is possible to give a uniform thermal history to the entire surface without moving the soot preform up and down. Become.
For example, the temperature in the heat treatment chamber can be made uniform in a length of 80% or more from the upper end of the uppermost heater to the lower end of the lowermost heater, and the difference can be suppressed to within ± 5 ° C at 1600 ° C or less. is there. It is also possible to create a maximum temperature point at an arbitrary location inside the heat treatment chamber and move it. Therefore, the same heat treatment can be performed without raising and lowering the support shaft. The maximum temperature at this time can be set to an arbitrary temperature of 1600 ° C. or lower.
Therefore, heat treatment for a large soot base material is facilitated. Also, when the pressure and vacuum are applied, the shaft seal is only rotated, so that it becomes relatively easy.
In the present embodiment, the heat treatment apparatus according to the optical fiber preform and the heat treatment method using the same can achieve the same effects as those of the first embodiment.
[0055]
For example, even if the temperature inside the heat treatment chamber is kept uniform at 1100 ° C., a gas containing chlorine or fluorine and an inert gas such as He are allowed to flow into the heat treatment chamber, and the pressure inside the heat treatment chamber is reduced to 4 kPa. Since the differential pressure with respect to the chamber can be maintained at about 40 Pa, the entire length of the optical fiber preform can be efficiently and simultaneously dehydrated without damaging the core tube made of quartz glass or the like.
Further, here, the gas in the heat treatment chamber is a gas containing fluorine, and it is possible to simultaneously dope fluorine into the entire length of the optical fiber by pressurization. It is also possible to dope fluorine by supplying a fluorine-containing gas during sintering.
[0056]
(Example 2)
Using the apparatus according to this embodiment, an optical fiber preform was created under the following conditions.
(1) Dehydration process
Maximum temperature point: 1100 ° C., gas flowing into heat treatment chamber and flow rate: He / Cl₂ = 10 / 0.1 SLM, pressure: normal pressure, differential pressure between heat treatment chamber and heater chamber: 40 Pa, maximum temperature point moving speed: 250 mm / hour
(2) Sintering process:
Maximum temperature point: 1450 ° C., gas and flow rate to heat treatment chamber: He = 2SLM, pressure: normal pressure, differential pressure between heat treatment chamber and heater chamber: 40 Pa, maximum temperature point moving speed: 250 mm / hour
By each of the above steps, the fluctuation range of the differential pressure was about 30 Pa, and an optical fiber preform without bubbles and bright spots could be created.
[0057]
An optical fiber preform was prepared under the following conditions.
(1) Pressure reduction process
Temperature: 1000 ° C. soaking (temperature difference ± 3 ° C.), gas flowing into heat treatment chamber: none, pressure: 4 kPa, differential pressure between heat treatment chamber and heater chamber: 0 to 100 Pa
(2) Atmospheric pressure return process
Temperature: 1000 ° C. soaking (temperature difference ± 3 ° C.), gas flowing into the heater chamber: argon gas, gas flowing into the heat treatment chamber: helium gas, pressure difference between the heat treatment chamber and the heater chamber: 0 to 100 Pa
(3) Dehydration process
Temperature: 1000 ° C. soaking (temperature difference ± 3 ° C.), gas flowing in heat treatment chamber and flow rate: He / Cl₂ / O₂ = 10 / 0.3 / 1 SLM, pressure: normal pressure, differential pressure between heat treatment chamber and heater chamber: 40 Pa
(4) Sintering process:
Temperature: 1300 ° C. soaking (temperature difference ± 3 ° C.), gas flowing into the heat treatment chamber and flow rate: fluorine-containing gas = 2 SLM, pressure: 0.2 MPa, pressure difference between the heat treatment chamber and the heater chamber: 30 Pa
Through each of the above steps, an optical fiber preform having a relative refractive index difference of −0.9% was produced.
At this time, no bubbles or bright spots were generated. As a result, high-concentration fluorine doping was achieved without contamination by dust in the heater chamber. The differential pressure fluctuation was about 30 Pa, and the pressure in the heat treatment chamber did not become lower than the pressure in the heater chamber. Therefore, no deformation occurred even when a quartz core tube was used.
[0058]
An optical fiber preform was prepared under the following conditions.
(1) Dehydration process
Temperature: 1000 ° C. soaking (temperature difference ± 3 ° C.), gas flowing in heat treatment chamber and flow rate: He / Cl₂ / O₂ = 10 / 0.3 / 1 SLM, pressure: normal pressure, differential pressure between heat treatment chamber and heater chamber: 40 Pa
(2) Fluorine doping process
Temperature: 1230 ° C. soaking (temperature difference ± 3 ° C.), gas flowing into the heat treatment chamber and flow rate: fluorine-containing gas = 1 SLM, pressure: 0.15 MPa, pressure difference between the heat treatment chamber and the heater chamber: 30 Pa
(3) Sintering process:
Maximum temperature point: 1300 ° C., gas and flow rate to heat treatment chamber: He = 2SLM, pressure: normal pressure, differential pressure between heat treatment chamber and heater chamber: 50 Pa, maximum temperature point moving speed: 200 mm / hour
Through each of the above steps, an optical fiber preform having a relative refractive index difference of −0.85% could be created.
At this time, no bubbles or bright spots were generated. As a result, high-concentration fluorine doping was achieved without contamination by dust in the heater chamber. The differential pressure fluctuation was about 30 Pa, and the pressure in the heat treatment chamber did not become lower than the pressure in the heater chamber. Therefore, no deformation occurred even when a quartz core tube was used.
[0059]
The present invention is not limited to the above embodiment.
For example, means other than the motor valve can be used as the pressure adjusting means.
The gas exhaust pipe provided in the heat treatment chamber (first chamber) and the heater chamber (second chamber) may have openings for various purposes in addition to the gas supply port and the thermocouple opening. Good.
Gases supplied to the heat treatment chamber (first chamber) include He, Ar, N₂ In addition to inert gases such as fluorine and gases containing fluorine, active gases such as chlorine and oxygen can also be employed.
In addition, various modifications can be made without departing from the scope of the present invention.
[0060]
【The invention's effect】
According to the heat treatment apparatus for an optical fiber preform and the heat treatment method using the same according to the present invention, the space inside the core tube (first chamber) and the outside (second chamber) are substantially separated from each other. The exhaust pipe and the second exhaust pipe are joined by the third exhaust pipe, but since the first exhaust pipe is provided with the first adjusting means, there is no gas flow between the exhaust pipe and the furnace core. Contamination is prevented, and the differential pressure between the inside and outside of the core tube is controlled with high accuracy by the fact that the first exhaust pipe and the second exhaust pipe are joined by the third exhaust pipe and the first adjusting means. In particular, it can be used under pressure or reduced pressure.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of a heat treatment apparatus for an optical fiber preform according to a first embodiment.
FIG. 2 is a schematic configuration diagram of a heat treatment apparatus for an optical fiber preform according to a second embodiment.
FIG. 3 is a schematic configuration diagram of a heat treatment apparatus for an optical fiber preform according to a third embodiment.
FIG. 4 is a schematic configuration diagram of a heat treatment apparatus for an optical fiber preform according to a fourth embodiment.
FIG. 5 is a schematic configuration diagram of an example of a heat treatment apparatus for an optical fiber preform according to a conventional example.
[Explanation of symbols]
1 ... Core tube
2 ... Furnace
3 ... Heater
3a ... Soaking tube
4… Insulation
5, 6 ... Gas supply port
7, 8 ... Gas exhaust pipe
7a, 8a ... Water-cooled exhaust pipe
9a ... Junction exhaust pipe
9b, 9c ... exhaust pipe
13 ... Air valve
14 ... Soot base material
14a ... support shaft
15 ... Air valve
16 ... Vacuum pump
17, 18, 19 ... motor valve
20 ... Pressure gauge
21a, 21b ... Air valve
22a, 22b ... Mass flow controller
23 ... Gas supply source
24a, 24b ... Gas supply ports
25a, 25b, 25c, 25d, 25e ... Thermocouple openings
30 ... Differential pressure gauge
TR ... Heat treatment room
HR ... Heater room

Claims (10)

An optical fiber preform heat treatment apparatus that performs heat treatment for vitrifying a soot preform for an optical fiber to form a transparent optical fiber preform by dehydration and sintering,
A first chamber for heat treatment inside;
A second chamber provided on the outer peripheral side of the first chamber while being separated from the first chamber, the heater being installed therein;
A first exhaust pipe provided connected to the first chamber;
A second exhaust pipe provided connected to the second chamber;
A third exhaust pipe where the first exhaust pipe and the second exhaust pipe merge;
First adjusting means for adjusting at least the pressure in the first chamber or the flow rate of the gas flowing in the first chamber is provided in the first exhaust pipe,
An optical fiber preform heat treatment apparatus in which second adjusting means for adjusting the pressure in the first chamber and the second chamber or the flow rate of flowing gas is provided in the third exhaust pipe. 2. The optical fiber preform according to claim 1, further comprising: first detection means for detecting a differential pressure between the pressure in the first chamber and the pressure in the second chamber; and second detection means for detecting the pressure in the second chamber. Heat treatment equipment. According to the detection results of the first detection means and the second detection means, the pressure in the second chamber becomes a target value or a target range, and the pressure in the first chamber and the pressure in the second chamber The heat treatment apparatus for an optical fiber preform according to claim 2, further comprising a control unit that controls the first adjusting means and the second adjusting means so that the differential pressure of becomes a predetermined value or a predetermined range. The processing is performed with the first chamber and the second chamber under pressure or reduced pressure while controlling the differential pressure between the first chamber and the second chamber to be a predetermined value or a predetermined range. 4. The heat treatment apparatus for an optical fiber preform according to any one of 3 above. The heat processing apparatus for an optical fiber preform according to any one of claims 1 to 4, wherein an inner gas temperature measuring means is provided at least in the first exhaust pipe and the second exhaust pipe. The optical fiber preform heat treatment apparatus according to claim 1, wherein a plurality of heaters are installed in the second chamber. A method for heat-treating an optical fiber preform, wherein the soot preform for optical fiber is vitrified by dehydration and sintering to form a transparent optical fiber preform,
A first chamber for heat treatment inside, a second chamber provided on the outer peripheral side of the first chamber while being separated from the first chamber, and provided in connection with the first chamber provided with a heater therein A first exhaust pipe, a second exhaust pipe connected to the second chamber, a third exhaust pipe where the first exhaust pipe and the second exhaust pipe join, and at least the above-mentioned First adjusting means for adjusting the pressure in the first chamber or the flow rate of the gas flowing in the first chamber is provided in the first exhaust pipe, and the pressure in the first chamber and the second chamber or the flow rate of the flowing gas. By a heat treatment device provided with second adjusting means for adjusting the third exhaust pipe in the third exhaust pipe,
The first chamber is set so that the pressure in the second chamber becomes a target value or a target range, and the pressure difference between the pressure in the first chamber and the pressure in the second chamber is a predetermined value or a predetermined range. A heat treatment method for an optical fiber preform, wherein the adjustment means and the second adjustment means are controlled to heat-treat the optical fiber soot preform. The method for heat-treating an optical fiber preform according to claim 7, further comprising a step of processing the first chamber and the second chamber under pressure or under reduced pressure. Measuring the gas temperature in at least the first exhaust pipe and the second exhaust pipe with a temperature measuring means;
The method for heat-treating an optical fiber preform according to claim 7 or 8, wherein the treatment is performed under conditions that are within a predetermined temperature range. The heat treatment method for an optical fiber preform according to any one of claims 7 to 9, wherein the heat treatment is performed by a plurality of heaters installed in the second chamber.

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