CN111377605A - Method for manufacturing optical fiber preform - Google Patents

Abstract

[ problem ] to provide a method for producing an optical fiber glass base material, wherein the size of the obtained optical fiber glass base material is not deviated. [ solution ] A method for manufacturing an optical fiber preform (28), comprising: the method comprises a glass particle deposition body (18) manufacturing step of depositing glass particles synthesized by supplying glass raw materials into a flame of a burner (15) on the outer periphery of a rotating starting rod (12), and a sintering step of sintering the glass particle deposition body (18) after the glass particle deposition body (18) manufacturing step, wherein the manufacturing conditions of the sintering step are changed according to the time from the end of the glass particle deposition body (18) manufacturing step to the start of the sintering step.

Description

Manufacturing method of base material for optical fiber

technical field

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

Background technique

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

prior art literature

Patent Literature

Patent Document 1: Japanese Patent Laid-Open No. 2009-7227

SUMMARY OF THE INVENTION

[The problem to be solved by the invention]

Generally, an optical fiber composed of a core and a cladding is produced 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 a vapor phase synthesis method such as VAD (Vapor Axial Deposition) or OVD (Outer Vapor Deposition) body (glass particle deposition body manufacturing process). Then, the glass fine particle deposited body is heated in a heating furnace to dehydrate and sinter to make it transparent and vitrified (sintering step).

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

When the diameter of the glass base material for optical fiber is too large, the glass base material needs to be re-sintered to soften the glass base material and then stretched, and when the glass base material is too long, some complicated treatments such as cutting the ends are required. .

Then, the objective of this invention is to provide the manufacturing method of the glass preform for optical fibers which makes it difficult to generate|occur|produce the dimension of the glass preform for optical fibers obtained.

[Means to solve the problem]

According to one aspect of the present invention, a method for producing an optical fiber base material includes:

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

A process for producing a glass fine particle deposit body in which glass fine particles synthesized by supplying glass raw materials to a burner flame are deposited on the outer periphery of a rotating initial rod, and a process for sintering the glass fine particle deposit body after the glass fine particle deposit body producing step sintering process,

However, the manufacturing conditions of the sintering step were changed in accordance with the time period after the end of the manufacturing step of the glass fine particle deposit until the start of the sintering step.

[Effect of invention]

As described above, variation in the dimensions of the obtained glass base material for optical fibers can be made less likely to occur.

Description of drawings

1 is a schematic diagram showing an example of an apparatus used in the production process of the glass fine particle deposit of the present invention.

2 is a schematic diagram showing an example of an apparatus used in the sintering step of the present invention.

[Explanation of symbols]

1 Deposition body manufacturing apparatus

11 Reaction Vessel

11A inner wall

12 initial sticks

13 Seed Rod

13 Suspension

15 burners

16 Gas flow control device

17 Gas supply path

18 Glass particle deposits

18A deposition surface

110 Exhaust pipe

111 Emitter

112 Receiver

113 lines

114 Exhaust port

115 Laser

2 Sintering furnace

21 Furnace tube

22 heater

23 Heat shield

24 Vacuum container

25 Exhaust piping

26 Vacuum pump

27 Gas inlet pipe

28 Optical fiber base material

29 Pressure regulating valve

Detailed ways

[Description of Embodiments of the Present Invention]

First, the content of the embodiment of the present invention will be described.

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

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

A process for producing a glass fine particle deposit body in which glass fine particles synthesized by supplying glass raw materials to a burner flame are deposited on the outer periphery of a rotating initial rod, and a process for sintering the glass fine particle deposit body after the glass fine particle deposit body producing step sintering process,

However, the manufacturing conditions of the sintering step were changed in accordance with the time period after the end of the manufacturing step of the glass fine particle deposit until the start of the sintering step.

According to this configuration, even if the time from the end of the glass fine particle deposit production process to the start of the sintering process is long or short, the sintering conditions can be changed based on the time, and the degree of shrinkage in the longitudinal direction during sintering can be reduced. It is possible to reduce the variation in the outer diameter of the base metal after sintering.

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

When the time from the end of the glass particle deposit body manufacturing process to the start of the sintering process is long, the temperature inside the glass particle deposit body decreases, so the longer the time is, the longer the preheating process time is. so that the inside 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 base material for optical fibers in which variation in the degree of shrinkage in the longitudinal direction during sintering is reduced and variation in the outer diameter of the base material after sintering is reduced.

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

(4) When the time between the completion of the glass fine particle deposit production process and the start of the sintering process is 3 hours or less, the preheating process is preferably 1 hour or less.

According to the configurations (3) to (4), the optical fiber base material can be efficiently produced with reduced variation in the degree of shrinkage in the longitudinal direction during sintering and reduced variation in the outer diameter of the base material after sintering.

(5) The sintering step includes a temperature raising step of gradually heating the glass fine particle deposit to a temperature at which the glass fine particle deposit is transparently vitrified, and after the glass fine particle deposit manufacturing step is completed The longer the time until the start of the sintering step, the more preferably the temperature increasing rate of the temperature increasing step is decreased.

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

(6) The temperature increase rate is preferably 1°C/min or more and 10°C/min or less.

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

[Details of Embodiments of the Present Invention]

Hereinafter, an example of a method for producing an optical fiber preform according to an embodiment of the present invention will be described based on the drawings.

(Manufacturing process of glass fine particle deposit)

1 is a schematic diagram of an apparatus (hereinafter also referred to as "glass fine particle deposit manufacturing apparatus" or "deposited body manufacturing apparatus") 1 for carrying out a glass fine particle deposit manufacturing process in the method for manufacturing an optical fiber base material of the present embodiment. The deposited body manufacturing apparatus 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 . A preliminary rod 12 is attached to the lower end of the suspended seed rod 13 , and the preliminary rod 12 is inserted into the interior of the reaction vessel 11 .

The suspension device 14 can rotate the initial rod 12 mounted on the seed rod 13 on the axis, and can move it in the axial direction, and can also change the moving speed of the initial rod 12 in the axial direction (the rising speed of the initial rod 12 ).

By depositing glass fine particles on the outer periphery of the initial rod 12, a substantially cylindrical glass fine particle deposited body 18 having the initial rod 12 in the center can be produced.

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 via a gas supply path 17 . Here, the combustion gas supplied to the burner 15 is mainly composed of a combustible gas and a combustion-supporting gas, among which, hydrogen (H ₂ ) is used as the combustible gas, and oxygen (O ₂ ) is used as the combustion-supporting gas. As a glass raw material gas, silicon tetrachloride (SiCl ₄ ) or siloxane can be mentioned as an example.

The burner 15 has a multi-port (multi-pipe) structure in which the gas outlet has a plurality of ports. The burner 15 blows 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 undergoes an oxidation reaction or a hydrolysis reaction to generate glass fine particles.

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

In addition, an exhaust port 114 is provided on the inner wall surface 11A of the reaction container 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 vessel 11 are discharged from the exhaust pipe 110 to the exhaust gas treatment device through the exhaust port 114 .

On the outside of the reaction vessel 11, a light projector 111 is provided facing the deposition surface 18A of the glass fine particle deposit body 18 formed by the burner 15, and the light receiver 112 is arranged at a position capable of receiving the laser light 115 emitted from the light 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 the line 113 and to vary the ascending 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 deposited body 18 using the deposited body manufacturing apparatus 1 will be described. First, the initial rod 12 is installed on the lower end of the seed rod 13 , and the seed rod 13 is suspended 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 starting point of the glass particle deposition of the initial rod 12 and the air outlet of the burner 15 becomes a desired distance.

On the other hand, the 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 gas such as nitrogen, argon, and helium, or raw material gas for refractive index control such as germanium tetrachloride (GeCl ₄ ) and POCl ₃ to the burner 15 .

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

During the process of growing the glass particle deposit body 18, the light projector 111 and the light receiver 112 detect the point P1 on the deposition surface 18A of the glass particle deposit body 18 at any time, and based on the position information of the point P1, the suspension device 14 The ascending speed of the initial rod 12 is controlled.

When controlling the flow rate of the combustion gas or the glass raw material gas, the gas flow rate of any one of hydrogen, oxygen, and glass raw material gas can be controlled. However, 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 gas.

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

In addition, in the manufacturing method of the preform for optical fibers of the present embodiment, the glass particle deposit body manufacturing process is not limited to the above-described embodiment, and appropriate deformation, modification, etc. can be carried out. For example, in the above-mentioned embodiment, the example in which one burner 15 is used is shown, but the number of burners is not limited to one, and the present invention may be applied to the case of using a plurality of burners.

In the above embodiment, the production of the glass fine particle deposit by the VAD method has been described, but in the case of producing the glass fine particle deposit by the OVD method, the initial rod 12 is made to face the burner 15 . The glass particle deposit 18 is gradually grown in the diameter direction while moving back and forth to make the generated glass particles adhere to the outer periphery of the initial rod 12 .

(Sintering process)

2 is a schematic diagram of an apparatus (hereinafter also referred to as a “sintering apparatus” or a “sintering furnace”) 2 for carrying out a sintering step of a glass fine particle deposit in the method for producing an optical fiber base material of the present embodiment.

The sintering furnace 2 shown in FIG. 2 is for sintering the glass fine particle deposited body 18 placed therein to make it transparent, thereby producing a base material 28 for an optical fiber. The sintering furnace 2 includes a furnace core tube 21 , a heater 22 , and a heat shield 23 in a vacuum container 24 .

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

Next, a method of sintering the glass fine particle deposited body 18 using the sintering furnace 2 to manufacture a preform for an optical fiber will be described.

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

First, the glass fine particle deposited body 18 is supported inside the sintering furnace 2 so that the central axis thereof faces the vertical 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. Thereby, 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. Thereby, the entirety of the glass fine particle deposited body 18 is shrunk to obtain a transparent optical fiber preform 28 .

As described above, in the sintering step, the glass fine particle deposit 18 obtained in the glass fine particle deposit manufacturing step is heated, dehydrated and sintered in the sintering furnace 2 to produce a transparent optical fiber base material 28 .

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

As one of the main reasons for the difference in size, it is presumed that the time from the completion of the manufacturing process of the glass fine particle deposited body to the sintering process (hereinafter simply referred to as "standby time") varies depending on the manufacturing lot. different.

For example, comparing the case where the standby 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 the temperature becomes relatively high when it is short.

When both the long-waiting-time and short-waiting-time glass fine-particle deposited bodies are sintered under the same conditions, the glass fine-particle depositing body with a long waiting time is sintered after sintering compared with the glass fine-particle depositing body having a short waiting time. The optical fiber base material tends to be smaller in outer diameter and longer in length. Since the temperature of the glass fine particle deposit is relatively low due to the long standby time, even if the heater 22 is used for heating, the temperature of the central portion is not easily increased, and the initial rod 12 is not easily softened. Therefore, it is considered that the 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 manufacturing method of the optical fiber base material of this embodiment, the manufacturing conditions of the said sintering process are changed according to the length of the said waiting time.

Although it does not specifically limit as a specific method of changing the manufacturing conditions of the said sintering process according to the length of the said waiting time, the following two form examples can be mentioned as a preferable example.

As an example of the first aspect, the sintering step includes a preheating step of heating the glass fine particle deposit at a temperature at which the glass fine particle deposit does not shrink, and the longer the waiting time is, the longer the Time for preheating process.

By adopting this method, variation in the degree of shrinkage in the longitudinal direction during sintering can be reduced, and the amount of fluctuation in the outer diameter of the base metal after sintering can be reduced.

In this case, the temperature of 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 is preferably 1200°C or lower, more preferably 1100°C or lower, and even more below 1000°C. When the temperature of the preheating step is low, the preheating time can be shortened, which is preferable. However, when the temperature is too low and the standby time is short, the temperature becomes lower than the temperature of the glass fine particle deposit, so that the variation in the degree of shrinkage in the longitudinal direction during sintering cannot be reduced, and the sintering cannot be reduced. The amount of change in the outer diameter of the base metal after that. Therefore, the temperature of the preheating step is preferably 700°C or higher.

Although the standby time is not particularly limited, it is preferable that the standby time is as short as possible because the energy cost of the heating required in the preheating process can be suppressed.

In addition, when the standby time is 3 hours or less, the preheating step is preferably 1 hour or less.

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

As a second aspect, the sintering step includes a heating step of gradually heating the glass fine particle deposit to a temperature at which the glass fine particle deposit is transparently vitrified, and the longer the waiting time is, the more The temperature increase rate of the temperature increase process is made smaller.

By adopting this method, it is possible to manufacture a base material for optical fibers in which the variation in the degree of shrinkage in the longitudinal direction during sintering is reduced and the variation in the outer diameter of the base material after sintering is reduced without damage.

In the case of rapidly heating the glass fine particle deposit body with a long waiting time and a low temperature, a high temperature part and a low temperature part are partially generated in one deposit body, and cracks may occur under the influence of these.

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

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

In the optical fiber base material obtained by the method of the present embodiment, even if the waiting time varies, it is difficult for the size to vary depending on the production lot. Therefore, even in the subsequent drawing process for producing the optical fiber from the optical fiber base material, the size can be accommodated in the drawing furnace, so that it is not necessary to re-sinter the optical fiber base material, or to cut the ends. complicated processing.

In addition, according to the present embodiment, if the standby time is shortened, the preheating time can be shortened, so that the time required for the sintering process can be shortened, and the productivity can be improved.

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

Claims (7)

1. A method for manufacturing a base material for an optical fiber, comprising: A glass fine particle deposit body manufacturing process of depositing glass fine particles synthesized by supplying glass raw material to a burner flame on the outer periphery of a rotating initial rod, and sintering the glass fine particle deposit body after the glass fine particle deposit body manufacturing process sintering process, However, the manufacturing conditions of the sintering step were changed in accordance with the time period after the end of the manufacturing step of the glass fine particle deposit until the start of the sintering step. 2 . The method for producing an optical fiber base material according to claim 1 , wherein the sintering step includes a preheating step of heating the glass fine particle deposit at a temperature at which the glass fine particle deposit does not shrink, 3 . The longer the time from the end of the glass fine particle deposit body manufacturing process to the start of the sintering process, the longer the time of the preheating process. 3 . The method for producing an optical fiber base material according to claim 2 , wherein the temperature of the preheating step is 1200° C. or lower. 4 . 4 . The method for producing an optical fiber base material according to claim 3 , wherein the temperature of the preheating step is 700° C. or higher. 5 . 5. The method for producing an optical fiber base material according to any one of claims 2 to 4, wherein the time from the end of the production step of the glass fine particle deposit body to the start of the sintering step is When it is 3 hours or less, the preheating step is 1 hour or less. 6 . The method for producing an optical fiber base material according to claim 1 , wherein the sintering step includes a step of gradually increasing the temperature of the glass fine particle deposit and heating the glass fine particle deposit to a temperature at which the glass fine particle deposit is transparent and vitrified. 7 . heating process, The temperature increase rate of the temperature increase process is decreased as the time from the completion of the glass fine particle deposit body manufacturing process to the start of the sintering process becomes longer. 7 . The method for producing an optical fiber base material according to claim 6 , wherein the temperature increase rate is 1° C./min or more and 10° C./min or less. 8 .

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