CN111377605B - Method for manufacturing base material for optical fiber - Google Patents

Abstract

[Problem] An object of the present invention is to provide a method for producing a glass preform for an optical fiber in which there is no variation in the size of the obtained glass preform for an optical fiber. [Solution] A method of manufacturing a base material (28) for an optical fiber, comprising: glass particles synthesized by supplying glass raw materials to the flame of a burner (15) and depositing them on the outer periphery of a rotating initial rod (12). A fine particle deposit body (18) manufacturing process, and a sintering process of sintering the glass fine particle deposit body (18) after the glass fine particle deposit body (18) manufacturing process, wherein the manufacturing process of the glass fine particle deposit body (18) ends Then, the manufacturing conditions of the sintering process are changed corresponding to the time between the start of the sintering process and the sintering process.

Description

Manufacturing method of base material for optical fiber

technical field

The present invention relates to a method for manufacturing a base material for an optical fiber.

Background technique

Patent Document 1 describes a method for producing a transparent glass body in which glass particles are deposited on a glass rod to form a glass particle deposit and heated to make it transparent. In more detail, the following are disclosed. The glass particle deposit is heated until a temperature difference between an outer surface temperature of the glass particle deposit and a boundary portion temperature between the glass rods of the glass particle deposit becomes 100° C. or less. Then, the glass fine particle deposition body is heated under the condition that the heating temperature of the heating is 10° C. or more and 60° C. or less.

prior art literature

patent documents

Patent Document 1: Japanese Unexamined Patent Publication No. 2009-7227

Contents of the invention

[Problem to be solved by the invention]

Generally, an optical fiber composed of a core and a cladding is manufactured by drawing a glass base material for an optical fiber in a drawing furnace (drawing process). The optical fiber base material is produced in the following steps. Glass particle deposition is produced by depositing glass particles generated in the flame of a burner around a rod made of quartz or the like by vapor phase synthesis methods such as VAD (Vapor Axial Deposition) or OVD (Outside Vapor Deposition) body (glass particle deposition body manufacturing process). Then, the glass fine particle deposit is heated in a heating furnace to dehydrate and sinter to make it transparent and vitrified (sintering process).

However, the base material for an optical fiber may vary in size (diameter or length) depending on the production lot, and may be of a size that cannot be accommodated in the drawing furnace used in the above-mentioned drawing step.

When the diameter of the glass base material for optical fiber is too large, it is necessary to re-sinter the glass base material to soften the glass base material and then stretch it. When the glass base material is too long, it is necessary to cut off the end and other complicated processing. .

Therefore, an object of the present invention is to provide a method for producing a glass preform for an optical fiber in which variations in the dimensions of the obtained glass preform for an optical fiber are less likely to occur.

[means to solve the problem]

A method of manufacturing a preform for an optical fiber according to an aspect of the present invention is as follows:

(1) A method for manufacturing a base material for an optical fiber, comprising:

A process of depositing glass particles synthesized by supplying glass raw material to a burner flame on the outer periphery of a rotating initial rod, and a process of sintering the glass particle deposit after the glass particle production process sintering process,

Here, the production conditions of the sintering process are changed corresponding to the time from the completion of the glass fine particle deposit production process to the start of the sintering process.

[Effect of the invention]

As described above, it is possible to make it difficult to cause variations in the size of the obtained glass preform for an optical fiber.

Description of drawings

[ Fig. 1 ] is a schematic view showing an example of an apparatus used in the manufacturing process of the glass fine particle deposit of the present invention.

[ Fig. 2 ] is a schematic view showing an example of an apparatus used in the sintering step of the present invention.

[explanation of the symbol]

1 Sediment manufacturing device

11 reaction vessel

11A inner wall

12 starter sticks

13 seed sticks

13 Suspension

15 burners

16 Gas flow control device

17 Gas supply path

18 Glass particle deposits

18A deposition surface

110 exhaust pipe

111 light projector

112 Receiver

113 line

114 Exhaust port

115 laser

2 sintering furnace

21 furnace core tube

22 heater

23 heat shield

24 vacuum container

25 Piping for exhaust

26 vacuum pump

27 Gas inlet pipe

28 Base material for optical fiber

29 Pressure adjustment valve

Detailed ways

[Description of Embodiments of the Present Invention]

First, the contents of the embodiments of the present invention will be described.

A method of manufacturing an optical fiber base material according to an aspect of the present invention is as follows:

(1) A method for manufacturing a base material for an optical fiber, comprising:

A process of depositing glass particles synthesized by supplying glass raw material to a burner flame on the outer periphery of a rotating initial rod, and a process of sintering the glass particle deposit after the glass particle production process sintering process,

Here, the production conditions of the sintering process are changed corresponding to the time from the completion of the glass fine particle deposit production process to the start of the sintering process.

According to this configuration, even if the time between the end of the glass particle deposit manufacturing process and the start of the sintering process varies, the sintering conditions can be changed based on this time, thereby reducing the degree of shrinkage in the longitudinal direction during sintering. Deviation, and can reduce the variation of the outer diameter of the base material after sintering.

(2) The sintering step includes a preheating step of heating the glass particle deposit at a temperature at which the glass particle deposit does not shrink, and after the glass particle deposit manufacturing step is completed until the sintering step The longer the time between the start times, the longer the time of the preheating step is preferably.

If the time between the end of the glass particle deposit manufacturing process and the start of the sintering process is long, the temperature inside the glass particle deposit body will decrease, so the longer the time, the longer the preheating process time, So that the interior of the glass particle deposit and the initial rod are sufficiently heated. Thereby, even if the treatment is performed for a predetermined time in the sintering step, it is possible to obtain a preform for an optical fiber in which variation in shrinkage in the longitudinal direction during sintering is reduced and variation in the outer diameter of the preform after sintering is reduced.

(3) The temperature in the preheating step is preferably 1200° C. or lower.

(4) When the time from the end of the glass fine particle deposit manufacturing step to the start of the sintering step is 3 hours or less, the preheating step is preferably 1 hour or less.

According to the configurations (3) to (4), it is possible to efficiently manufacture a preform for an optical fiber in which variation in shrinkage in the longitudinal direction during sintering is reduced and variation in the outer diameter of the preform after sintering is reduced.

(5) The sintering step includes a step of gradually raising the temperature of the glass particle deposit to a temperature at which the glass particle deposit becomes transparent and vitrified, and after the completion of the glass particle deposit manufacturing step The longer the time until the start of the sintering step is, the slower the temperature increase rate in the temperature increase step is preferably.

With this configuration, it is possible to manufacture a base material for an optical fiber with reduced variations in the degree of shrinkage in the longitudinal direction during sintering and a reduced variation in the outer diameter of the base material after sintering without damage.

(6) The temperature increase rate is preferably not less than 1° C./min and not more than 10° C./min.

According to this configuration, it is possible to more reliably manufacture a base material for an optical fiber with less variation in shrinkage in the longitudinal direction during sintering and less variation in the outer diameter of the base material after sintering without damage.

[Details of Embodiments of the Invention]

Hereinafter, an example of a method for manufacturing an optical fiber preform according to an embodiment of the present invention will be described with reference to the drawings.

(Glass particle deposit manufacturing process)

1 is a schematic diagram of an apparatus (hereinafter also referred to as "glass particle deposit manufacturing apparatus" or "deposit manufacturing apparatus") 1 for performing a glass particle deposit manufacturing step in the method for manufacturing an optical fiber base material according to this embodiment. The deposit production device 1 has a reaction vessel 11 . A suspension device 14 is provided above the outer side of the reaction vessel 11 , and the seed rod 13 is suspended by the suspension device 14 . An initial rod 12 is installed at the lower end of the hanging seed rod 13 , and the initial rod 12 is inserted into the inside of the reaction vessel 11 .

The suspension device 14 can rotate the initial rod 12 installed on the seed crystal rod 13 on the shaft, and can move in the axial direction, and can change the axial moving speed of the initial rod 12 (the ascent speed of the initial rod 12 ) in addition.

If the glass particles are deposited on the outer periphery of the initial rod 12, an approximately cylindrical glass particle deposition body 18 having the initial rod 12 at the center can be manufactured.

Below the reaction vessel 11, a burner 15 for synthesizing glass fine particles (hereinafter simply referred to as "burner 15") for generating glass fine particles is provided. The burner 15 is connected to a gas supply tank (not shown) capable of supplying combustion gas and glass raw material gas through a gas supply path 17 . Here, the combustion gas supplied to the burner 15 is mainly composed of a combustible gas and a combustible gas, and the combustible gas includes hydrogen (H ₂ ), and the combustible gas includes oxygen (O ₂ ). Examples of the glass raw material gas include silicon tetrachloride (SiCl ₄ ) and siloxane.

The burner 15 is a multi-port (multi-pipe) structure with multiple ports at the gas outlet. The burner 15 blows out the combustion gas and the glass raw material gas from each port, and in the flame generated by the combustion gas, the glass raw material is oxidized or hydrolyzed to generate glass fine particles.

A gas flow control device 16 is provided in a gas supply path 17 connected to the burner 15 . The flow rate of each gas supplied to the burner 15 can be controlled by this gas flow rate control device 16 .

In addition, an exhaust port 114 is provided on the inner wall surface 11A of the reaction vessel 11 , and the exhaust port 114 communicates with the exhaust pipe 110 . Water vapor, inert gas, undeposited glass particles, and the like generated in the reaction container 11 are discharged from the exhaust pipe 110 to the exhaust gas treatment device through the exhaust port 114 .

Outside reaction vessel 11 , projector 111 is provided facing deposition surface 18A of glass particle deposition body 18 formed by burner 15 , and photoreceiver 112 is arranged at a position capable of receiving laser light 115 emitted from projector 111 . The growth rate of the point P1 on the deposition surface 18A of the glass fine particle deposition body 18 can be measured by the light projector 111 and the light receiver 112 . The light receiver 112 is configured to be connected to the suspension device 14 via a line 113 , and varies the rising speed of the initial rod 12 based on the position data from the light receiver 112 .

Next, a method of manufacturing the glass fine particle deposit 18 using the deposit manufacturing apparatus 1 will be described. First, install the initial rod 12 at the lower end of the seed rod 13, and hang the seed rod 13 on the suspension device 14. Then, the suspension device 14 is activated, and the initial rod 12 is lowered so that the distance between the glass particle deposition start point of the initial rod 12 and the air outlet of the burner 15 becomes a desired distance.

On the other hand, supply of combustion gas (O ₂ and H ₂ ) and glass raw material gas (SiCl ₄ or siloxane) to the burner 15 is started. If necessary, a gas supply tank may be added to supply inert gases such as nitrogen, argon, and helium, or source gases for controlling refractive index such as germanium tetrachloride (GeCl ₄ ) and POCl ₃ , to the burner 15 .

The primary rod 12 is rotated axially, and an oxyhydrogen flame is emitted from the burner 15 toward the primary rod 12 . In this oxyhydrogen flame, glass fine particles are produced by an oxidation reaction or a hydrolysis reaction of the glass raw material gas. The generated glass particles are attached to the outer periphery of the initial rod 12, while the initial rod 12 is raised at a predetermined speed, and the glass particle deposit 18 is gradually formed and grown.

In the process of growing the glass particle deposit body 18, the point P1 on the deposition surface 18A of the glass particle deposit body 18 is detected at any time by the light projector 111 and the light receiver 112, and based on the position information of the point P1, the The ascent speed of the initial rod 12 is controlled.

When controlling the flow rate of the combustion gas or the gas for glass raw material, the gas flow rate of any one of hydrogen, oxygen, and glass raw material gas can be controlled, but among them, it is easy to adjust the flame of the burner 15. In consideration of temperature, it is preferable to control the flow rate of hydrogen.

Further, the flow rates of a plurality of gases (two or three types selected from hydrogen, oxygen, and glass raw material gases) may be simultaneously controlled.

In addition, in the manufacturing method of the base material for optical fibers of this embodiment, the manufacturing process of a glass fine particle deposition body is not limited to the above-mentioned embodiment, A suitable deformation|transformation, modification, etc. are possible. For example, in the above-mentioned embodiment, an example of using one burner 15 was shown, but the number of burners is not limited to one, and the case of using a plurality of burners can also be applied to the present invention.

In the above embodiment, the manufacture of the glass particle deposit body by the VAD method has been described, but in the case of the manufacture of the glass particle deposit body by the OVD method, the initial rod 12 is opposed to the burner 15. While moving back and forth, the generated glass particles are attached to the outer periphery of the initial rod 12, and at the same time, the glass particle deposit 18 is gradually grown in the diameter direction.

(Sintering process)

2 is a schematic diagram of an apparatus (hereinafter also referred to as "sintering apparatus" or "sintering furnace") 2 for performing a sintering step of a glass fine particle deposit in the method for manufacturing an optical fiber base material according to this embodiment.

The sintering furnace 2 shown in FIG. 2 is used to sinter and make the glass fine particle deposition body 18 placed therein so as to make it transparent, and to manufacture a base material 28 for an optical fiber. The sintering furnace 2 includes a core tube 21 , a heater 22 , and a heat shield 23 in a vacuum vessel 24 .

Furthermore, the sintering furnace 2 is further equipped with the piping 25 for exhaust, the vacuum pump 26, the gas introduction pipe 27, and the pressure adjustment valve 29. The vacuum pump 26 is connected to the vacuum container 24 through the exhaust pipe 25 to exhaust the inside of the vacuum container 24 . The gas introduction pipe 27 is connected to the core tube 21 to introduce an inert gas or the like into the core tube 21 from a gas supply source (not shown). A pressure regulating valve 29 is provided in the middle of the exhaust piping 25 to regulate the internal pressure of the vacuum vessel 24 .

Next, a method for manufacturing an optical fiber base material by sintering the glass fine particle deposit 18 using the sintering furnace 2 will be described.

In the sintering step in the method for manufacturing an optical fiber base material according to this embodiment, the glass fine particle deposit 18 is sintered using the sintering furnace 2 shown in FIG. 2 to manufacture an optical fiber base material 28 . The glass particle deposition body 18 used is obtained by depositing glass particles on an initial rod of quartz glass or the like by an OVD method, a VAD method, or the like. Then, the glass particle deposit 18 is inserted into the furnace core tube 21, and the gas in the furnace is He, for example, and heated by the heater 22 in this atmosphere to manufacture the optical fiber preform 28 . In addition, you may add fluorine (F) etc. during manufacture, and may change the gas in a furnace midway.

First, the glass fine particle deposition body 18 is supported inside the sintering furnace 2 so that the center axis thereof faces the up-down direction (see FIG. 2 ). In this state, the inside of the sintering furnace 2 is evacuated, and the temperature of the heater 22 is raised to the dehydration temperature to perform dehydration. Accordingly, moisture (H ₂ O), chlorine-based gas, or gases such as oxygen, nitrogen, and air accumulated in the gaps between the glass fine particles of the glass fine particle deposit 18 can be removed. A short dehydration time may result in insufficient dehydration.

Next, the temperature of the heater 22 is raised to the shrinkage temperature of the glass fine particles (1400° C. or higher), and maintained for a predetermined time. In this way, the whole of the glass particle deposit 18 is shrunk to obtain a transparent optical fiber preform 28 .

As described above, in the sintering process, the glass particle deposit 18 obtained in the glass particle deposit manufacturing process is heated, dehydrated and sintered in the sintering furnace 2 to manufacture a transparent optical fiber preform 28 .

However, the base material for an optical fiber may vary in size (diameter or length) depending on the production lot, and may be of a size that cannot be accommodated in a drawing furnace used in a subsequent drawing process.

As one of the main reasons for the size difference, it is presumed that the time between the end of the glass particle deposit manufacturing process and the sintering process (hereinafter simply referred to as "standby time") varies depending on the production lot. different.

For example, comparing the case where the waiting time is long and the case where it is short, the temperature of the glass fine particle deposit becomes relatively low when it is long, and becomes relatively high when it is short.

When both the glass particle deposits with long standby time and short standby time are sintered under the same conditions, compared with the glass particle deposits with short standby time, the glass particle deposits with long standby time after sintering The optical fiber base material tends to have a smaller outer diameter and a longer length. The reason why the waiting time is long is that the temperature of the glass particle deposit is relatively low, so even if the heater 22 is used for heating, the temperature of the central portion is difficult to increase, and the initial rod 12 is difficult to soften. Therefore, it is considered that shrinkage in the longitudinal direction of the initial rod 12 is suppressed, so that the outer diameter becomes smaller and the length becomes longer.

On the other hand, in the method for manufacturing an optical fiber base material according to the present embodiment, the manufacturing conditions in the sintering step are changed according to the length of the waiting time.

A specific method of changing the manufacturing conditions of the sintering step according to the length of the waiting time is not particularly limited, but the following two embodiments can be given as preferable examples.

As a first example, the sintering step includes a preheating step of heating the glass particle deposit at a temperature at which the glass particle deposit does not shrink, and the longer the waiting time, the longer the The time of the preheating process.

By adopting this aspect, it is possible to reduce variation in the degree of shrinkage in the longitudinal direction during sintering, and reduce variation in the outer diameter of the base material after sintering.

In this case, the temperature in the preheating step is not particularly limited as long as it is a temperature at which the glass fine particle deposit does not shrink, but it is preferably 1200°C or lower, more preferably 1100°C or lower, even more preferably below 1000°C. If the temperature of the said preheating process is low, since the preheating time can be shortened, it is preferable. However, if the temperature is too low and the standby time is short, the temperature of the glass particle deposition body becomes lower than that of the glass particle deposit, so that the variation in the degree of shrinkage in the longitudinal direction during sintering cannot be reduced, and the degree of sintering cannot be reduced. The amount of change in the outer diameter of the base metal. Therefore, the temperature in the preheating step is preferably 700° C. or higher.

The standby time is not particularly limited, but it is preferable to keep the standby time as short as possible in order to suppress the energy cost of heating required in the preheating step.

Moreover, when the said standby time is 3 hours or less, it is preferable that the said preheating process is 1 hour or less.

According to the above preferable conditions, it is possible to efficiently manufacture a base material for an optical fiber in which the variation in shrinkage degree in the longitudinal direction during sintering is reduced, and the variation in the outer diameter of the base material after sintering is reduced.

As a second example, the sintering step includes a heating step of gradually raising the temperature of the glass particle deposit to a temperature at which the glass particle deposit undergoes transparent vitrification, and the longer the waiting time, the The temperature increase rate in the temperature increase step is reduced more.

By employing this method, it is possible to manufacture a preform for an optical fiber in which variation in shrinkage degree in the longitudinal direction during sintering is reduced and variation in the outer diameter of the preform after sintering is reduced without damage.

In the case of rapid heating of the low-temperature glass particle deposition body that has been left for a long time, a high-temperature portion and a low-temperature portion are partially generated in one deposition body, and cracks may sometimes be generated under the influence of the deposition body.

The temperature increase rate is set according to various conditions of the production method, and is not particularly limited, but specifically, it is preferably 1° C./minute or more and 10° C./minute or less.

According to the above preferable conditions, it is possible to more reliably manufacture a base material for an optical fiber with less variation in shrinkage in the longitudinal direction during sintering and less variation in the outer diameter of the base material after sintering without damage.

In the preform for an optical fiber obtained by the method of the present embodiment, even if there is a difference in the above-mentioned standby time, it is difficult to cause dimensional variation depending on the production lot. Therefore, even in the subsequent drawing process for producing an optical fiber from this optical fiber base material, the size can be accommodated in the drawing furnace, so it is not necessary to re-sinter the optical fiber base material, or cut off the end, etc. Complicated processing.

In addition, according to the present embodiment, shortening the waiting time can shorten the preheating time, and thus the time required for the sintering process can be shortened, thereby improving productivity.

The optical fiber base material obtained by the method of this embodiment can be used in a known or well-known drawing process to produce an optical fiber.

Claims (6)

1. A method for manufacturing a base material for an optical fiber, comprising: A glass particle deposit manufacturing process of depositing glass particles synthesized by supplying glass raw materials to a burner flame on the outer periphery of a rotating initial rod, and sintering the glass particle deposit body after the glass particle deposit manufacturing process the sintering process, Wherein, the production conditions of the sintering process are changed corresponding to the time between the completion of the glass particle deposit production process and the start of the sintering process, The sintering step includes a preheating step of heating the glass particle deposit at a temperature at which the glass particle deposit does not shrink, The time for the preheating step is extended as the time between the end of the glass particle deposit manufacturing step and the start of the sintering step is longer. 2. The method for producing a base material for an optical fiber according to claim 1, wherein the temperature in the preheating step is 1200° C. or lower. 3. The method for manufacturing an optical fiber preform according to claim 2, wherein the temperature in the preheating step is 700° C. or higher. 4. The method for manufacturing an optical fiber base material according to any one of claims 1 to 3, wherein the time between the end of the manufacturing process of the glass particle deposit and the start of the sintering process is When it is less than 3 hours, the preheating step is less than 1 hour. 5. A method for manufacturing a base material for an optical fiber, comprising: A glass particle deposit manufacturing process of depositing glass particles synthesized by supplying glass raw materials to a burner flame on the outer periphery of a rotating initial rod, and sintering the glass particle deposit body after the glass particle deposit manufacturing process the sintering process, Wherein, the production conditions of the sintering process are changed corresponding to the time between the completion of the glass particle deposit production process and the start of the sintering process, Wherein the sintering step includes a heating step of gradually raising the temperature of the glass particle deposition body to a temperature at which the glass particle deposition body undergoes transparent vitrification, The longer the time between the end of the glass particle deposit manufacturing process and the start of the sintering process, the slower the temperature increase rate in the temperature increase process. 6 . The method for manufacturing a base material for an optical fiber according to claim 5 , wherein the temperature increase rate is not less than 1° C./min and not more than 10° C./min.

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