JP7205216B2 - Manufacturing method of preform for optical fiber - Google Patents

Description

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

Patent Literature 1 describes a method for manufacturing a transparent glass body in which a glass particle deposit body in which glass particles are deposited on a glass rod is heated to be made transparent. More specifically, the following are disclosed. The glass particle deposit is heated until the temperature difference between the outer surface temperature of the glass particle deposit and the boundary temperature of the glass particle deposit and the glass rod becomes 100° C. or less. After that, the heating temperature is increased by 10° C. or higher and 60° C. or lower than the above heating, and the glass particle deposit is heated.

JP 2009-7227 A

Generally, an optical fiber composed of a core and a clad is manufactured by drawing (drawing process) a glass base material for optical fiber in a drawing furnace. An optical fiber preform is manufactured by the following steps. Glass particles generated in the flame of a burner are deposited around a rod made of quartz or the like by a vapor phase synthesis method such as the VAD method (vapor deposition method) or the OVD method (external vapor deposition method). A fine particle deposit is manufactured (glass fine particle deposit manufacturing process). After that, the glass particle deposit is heated in a heating furnace to dehydrate and sinter to obtain a transparent glass (sintering step).
However, the size (diameter or length) of the optical fiber glass preform may vary depending on the production lot, and the size may not fit in the drawing furnace for the drawing process.
If the diameter of the optical fiber glass preform is too large, the glass preform is subjected to the sintering process again to soften and stretch the glass preform, and if the glass preform is too long, the end is cut off. It was necessary to perform complicated processing such as

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a method for producing an optical fiber glass preform that is less likely to cause variations in the size of the obtained optical fiber glass preform.

A method for manufacturing an optical fiber preform according to an aspect of the present invention comprises:
(1) A step of producing a glass particle deposit body in which glass particles synthesized by supplying glass raw materials to a burner flame are deposited on the outer circumference of a rotating starting rod, and the glass particle deposit body is deposited after the glass particle deposit body manufacturing process. A method for manufacturing an optical fiber glass preform comprising a sintering step of sintering,
changing the manufacturing conditions of the sintering step according to the time from the end of the glass particulate deposit manufacturing step to the start of the sintering step;
A method for manufacturing an optical fiber preform.

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

1 is a schematic diagram showing an example of an apparatus used in the manufacturing process of a glass particle deposit in the present invention; FIG. It is a schematic diagram showing an example of an apparatus used for the sintering process in the present invention.

[Description of the embodiment of the present invention]
First, the contents of the embodiments of the present invention will be described.
A method for manufacturing an optical fiber preform according to an aspect of the present invention comprises:
(1) A step of producing a glass particle deposit body in which glass particles synthesized by supplying glass raw materials to a burner flame are deposited on the outer circumference of a rotating starting rod, and the glass particle deposit body is deposited after the glass particle deposit body manufacturing process. A method for manufacturing an optical fiber preform comprising a sintering step of sintering,
changing the manufacturing conditions of the sintering step according to the time from the end of the glass particulate deposit manufacturing step to the start of the sintering step;
A method for manufacturing an optical fiber preform.
According to this configuration, even if the time from the end of the glass particulate deposited body manufacturing process to the start of the sintering process may be long or short, by changing the sintering conditions based on the time, the sintering process can be performed. It is possible to reduce variations in the degree of shrinkage in the longitudinal direction during sintering, and to reduce variations in the outer diameter of the base material after sintering.

(2) The sintering step includes a preheating step of heating the glass particulate deposit to a temperature at which the glass particulate deposit does not shrink, and the sintering step starts after the glass particulate deposit manufacturing step is completed. It is preferable to lengthen the time of the preheating step as the time until the temperature increases.
If the time from the end of the glass particulate deposit body manufacturing process to the start of the sintering process is long, the temperature inside the glass particulate deposit body will decrease. , the interior of the glass particulate deposit and the starting rod are sufficiently warmed. As a result, even if the treatment is performed for a predetermined time in the sintering process, the variation in the degree of shrinkage in the vertical direction during sintering is reduced, and the variation in the outer diameter of the base material after sintering is reduced. A base material can be obtained.

(3) It is preferable that the temperature of the preheating step is 1200° C. or lower.
(4) When the time from the end of the glass particle deposited body manufacturing process to the start of the sintering process is 3 hours or less, the preheating process is preferably 1 hour or less.
According to the above configurations (3) to (4), an optical fiber preform in which variation in the degree of shrinkage in the vertical direction during sintering is reduced and fluctuation in the outer diameter of the preform after sintering is reduced. It can be manufactured efficiently.

(5) The sintering step includes a temperature raising step of gradually heating the glass particle deposit to a temperature at which the glass particle deposit is turned into transparent glass. It is preferable that the longer the time until the sintering process starts, the lower the heating rate in the heating process.
According to this configuration, variations in the degree of contraction in the vertical direction during sintering are reduced, and an optical fiber preform in which the amount of variation in the outer diameter of the preform after sintering is reduced can be manufactured without damage.
(6) The rate of temperature increase is preferably 1° C./min or more and 10° C./min or less.
According to this configuration, variation in the degree of contraction in the vertical direction during sintering is reduced, and an optical fiber preform having a reduced amount of variation in the outer diameter of the preform after sintering can be more reliably manufactured without damage. can be done.

[Details of the embodiment of the present 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 accompanying drawings.

(Glass fine particle deposit manufacturing process)
FIG. 1 shows an apparatus (hereinafter also referred to as "glass particulate deposit manufacturing apparatus" or "deposit manufacturing apparatus") 1 for carrying out the glass particulate deposit manufacturing process in the method for manufacturing an optical fiber preform according to the present embodiment. 1 is a schematic diagram of FIG. The deposited body manufacturing apparatus 1 has a reaction vessel 11 . A suspension device 14 is installed above the outside of the reaction vessel 11 , and the seed rod 13 is suspended by the suspension device 14 . A starting rod 12 is attached to the lower end of the suspended seed rod 13 , and the starting rod 12 is introduced into the reaction vessel 11 .

The suspending device 14 can rotate and move the starting rod 12 attached to the seed rod 13 in the axial direction, and can change the moving speed of the starting rod 12 in the axial direction (lifting speed of the starting rod 12). can be changed.
By depositing glass particles on the outer circumference of the starting rod 12, a substantially columnar glass particle deposited body 18 having the starting rod 12 at the center can be manufactured.

Below the reaction vessel 11, a glass particle synthesizing burner 15 (hereinafter simply referred to as "burner 15") for generating glass particles is provided. A gas supply tank (not shown) capable of supplying combustion gas and frit gas is connected to the burner 15 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, hydrogen (H ₂ ) as the combustible gas, and oxygen (O ₂ ) as the combustion-supporting gas. As an example. Silicon tetrachloride (SiCl ₄ ) and siloxane are examples of the glass material gas.
The burner 15 has a multi-port (multi-tube) structure in which gas outlets have a plurality of ports. 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 can be oxidized or hydrolyzed to generate glass microparticles.

A gas flow controller 16 is installed in a gas supply path 17 connected to the burner 15 . The gas flow control device 16 can control the flow rate of each gas supplied to the burner 15 .

Further, the inner wall surface 11A of the reaction container 11 is provided with an exhaust port 114, and the exhaust port 114 is communicated with the exhaust pipe 110. As shown in FIG. Water vapor, inert gas, undeposited glass particles, etc. generated in the reaction vessel 11 are discharged from the exhaust pipe 110 through the exhaust port 114 to the exhaust gas treatment device.

A light projector 111 is provided outside the reaction vessel 11 toward the deposition surface 18A of the glass fine particle deposit 18 formed by the burner 15. are placed. With the light projector 111 and the light receiver 112, the growth rate of the point P1 on the deposition surface 18A of the glass fine particle deposition body 18 can be measured. Receiver 112 is connected to suspension device 14 via line 113 and is configured to vary the lifting speed of starting rod 12 based on position data from receiver 112 .

Next, a method for manufacturing the glass particle deposit 18 using this deposit manufacturing apparatus 1 will be described. First, the starting rod 12 is attached to the tip of the seed rod 13 , and the seed rod 13 is hung from the hanging device 14 . Then, the suspending device 14 is operated to lower the starting rod 12 so that the distance between the starting point of the deposition of glass particles on the starting rod 12 and the blowout port of the burner 15 becomes a desired distance.
Meanwhile, the supply of combustion gas (O ₂ and H ₂ ) and frit gas (SiCl ₄ or siloxane) to burner 15 is started. If necessary, a gas supply tank is added to supply inert gases such as nitrogen, argon, and helium, and raw material gases for refractive index control such as germanium tetrachloride (GeCl ₄ ) and POCl ₃ to the burner 15 . good too.

The starting rod 12 is rotated about its axis, and an oxyhydrogen flame is emitted from the burner 15 toward the starting rod 12 . In this oxyhydrogen flame, glass microparticles are produced by an oxidation reaction or a hydrolysis reaction of the glass raw material gas. The starting rod 12 is pulled up at a predetermined speed while the generated glass particles are adhered to the outer periphery of the starting rod 12 to gradually form and grow the glass particle deposit 18 .

When growing the glass particle deposit 18, the light projector 111 and the light receiver 112 always detect the point P1 on the deposition surface 18A of the glass particle deposit 18, and based on the position information of this point P1, the suspension is performed. A device 14 controls the lifting speed of the starting rod 12 .

In controlling the flow rate of the combustion gas or frit gas, the flow rate of any one of hydrogen gas, oxygen gas, and frit gas may be controlled. Therefore, it is preferable to control the flow rate of the hydrogen gas.
Furthermore, the flow rates of a plurality of gases (two or three selected from hydrogen gas, oxygen gas and frit gas) may be controlled simultaneously.

It should be noted that, in the method of manufacturing an optical fiber preform according to the present embodiment, the glass fine particle deposition body manufacturing process is not limited to the above-described embodiment, and appropriate modifications, improvements, and the like are possible. For example, although one burner 15 is used in the above-described embodiment, the number of burners is not limited to one, and the present invention can be applied even when a plurality of burners are used.

In the above embodiment, the production of the glass particle deposit by the VAD method has been described. While attaching the fine glass particles to the outer circumference of the starting rod 12, the glass particle deposit 18 is gradually grown in the radial direction.

(Sintering process)
FIG. 2 is an outline of an apparatus (hereinafter also referred to as a "sintering apparatus" or a "sintering furnace") 2 for carrying out the step of sintering the glass fine particle deposit in the method of manufacturing an optical fiber preform according to the present embodiment. It is a diagram.
The sintering furnace 2 shown in FIG. 2 is for manufacturing an optical fiber preform 28 by sintering and transparentizing the glass particle deposit 18 put therein. The sintering furnace 2 includes a furnace core tube 21 , a heater 22 and a heat shield 23 inside a vacuum vessel 24 .

The sintering furnace 2 further includes an exhaust pipe 25 , a vacuum pump 26 , a gas introduction pipe 27 and a pressure control valve 29 . The vacuum pump 26 is connected to the vacuum container 24 via an exhaust pipe 25 and evacuates the inside of the vacuum container 24 . The gas introduction pipe 27 is connected to the furnace core tube 21 and introduces an inert gas or the like into the furnace core tube 21 from a gas supply source (not shown). A pressure regulating valve 29 is provided in the middle of the exhaust pipe 25 and regulates the pressure inside the vacuum vessel 24 .

Next, a method of sintering the glass particle deposited body 18 using this sintering furnace 2 to produce an optical fiber preform will be described.
In the sintering step in the method of manufacturing an optical fiber preform according to the present embodiment, an optical fiber preform 28 is manufactured by sintering the glass particle deposit 18 in the sintering furnace 2 shown in FIG. is. The glass particle deposited body 18 is obtained by depositing glass particles on a starting rod made of quartz glass or the like by the OVD method, the VAD method, or the like. Then, the glass particle deposited body 18 is placed inside the furnace core tube 21, the gas in the furnace is He, for example, and the heater 22 heats it under this atmosphere to manufacture the optical fiber preform 28. As shown in FIG. Note that the furnace gas may be changed during production, such as by adding fluorine (F).

First, the glass particle deposit 18 is supported inside the sintering furnace 2 so that its central axis is oriented vertically (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. As a result, moisture (H ₂ O) accumulated in the gaps between the glass particles of the glass particle deposit body 18, chlorine-based gases, oxygen, nitrogen, air, and other gases can be removed. If the dehydration time is short, dehydration may be insufficient.

Next, the temperature of the heater 22 is raised to the contraction temperature of the glass particles (1400° C. or higher) and held for a predetermined time. As a result, the entire glass fine particle deposit 18 is shrunk to obtain a transparent optical fiber preform 28 .

As described above, the glass particle deposit body 18 obtained by the glass particle deposit body manufacturing process is heated in the sintering furnace 2 in the sintering process to dehydrate and sinter, thereby manufacturing the transparent optical fiber preform 28. be.

However, the size (diameter or length) of the optical fiber preform may differ depending on the production lot, and the size may not fit in the drawing furnace for the subsequent drawing process.
One of the reasons for the difference in size is presumed to be that the time from the end of the glass particulate deposit manufacturing process to the sintering process (hereinafter also simply referred to as "waiting time") varies depending on the manufacturing lot. rice field.
For example, when the standby time is long and short, the temperature of the glass particle deposit body is relatively low when the standby time is long, and the temperature is relatively high when the standby time is short.
When one with a long waiting time and one with a short waiting time are sintered under the same conditions, the one with a longer waiting time has a larger outer diameter of the optical fiber preform after sintering than the one with a shorter waiting time. tend to be smaller and longer. If the waiting time is long, the temperature of the glass fine particle deposit is relatively low, so even if the heater 22 heats the body, the temperature of the central portion is less likely to increase, and the starting rod 12 is less likely to soften. Therefore, it is thought that the vertical contraction of the starting rod 12 is suppressed, resulting in a small outer diameter and a long length.

In contrast, in the method of manufacturing an optical fiber preform according to the present embodiment, the manufacturing conditions of the sintering step are changed according to the length of the waiting time.
A specific method for changing the manufacturing conditions of the sintering step according to the length of the waiting time is not particularly limited, but the following two examples of embodiments can be given as preferable examples.

As a first mode example, the sintering step includes a preheating step of heating the glass particle deposit to a temperature at which the glass particle deposit does not shrink, and the longer the standby time, the longer the time of the preheating step. It is to be.
By adopting this mode, it is possible to reduce variations in the degree of shrinkage in the longitudinal direction during sintering, and to reduce variations in the outer diameter of the base material after sintering.
In this case, the temperature of the preheating step is not particularly limited as long as it is a temperature at which the glass particle deposit does not shrink, but it is preferably 1200° C. or less, more preferably 1100° C. or less, and still more preferably 1000° C. ℃ or less. A lower temperature in the preheating step is preferable because the preheating time can be shortened. However, if the temperature is too low and the waiting time is short, the temperature becomes lower than the temperature of the glass fine particle deposit, and the variation in the degree of shrinkage in the vertical direction during sintering cannot be reduced. It becomes impossible to reduce the fluctuation amount of the outer diameter of the material. Therefore, the temperature of the preheating step is preferably 700° C. or higher.
Although the waiting time is not particularly limited, it is preferable that the waiting time is as short as possible in that the energy cost for heating required for the preheating step can be suppressed.
Further, when the standby time is 3 hours or less, the preheating step is preferably 1 hour or less.
According to the preferred conditions described above, it is possible to efficiently manufacture an optical fiber preform in which variations in the degree of shrinkage in the longitudinal direction during sintering are reduced and the variation in the outer diameter of the preform after sintering is reduced. can.

As a second embodiment, the sintering step includes a temperature raising step of gradually heating the glass particle deposit to a temperature at which the glass particle deposit is turned into transparent vitrification. It is to reduce the temperature increase rate in the temperature increase step.
By adopting this mode, variation in the degree of contraction in the vertical direction during sintering is reduced, and an optical fiber preform with reduced variation in the outer diameter of the preform after sintering can be manufactured without damage. .
If the waiting time is long and the glass fine particle deposit body having a low temperature is rapidly heated, a high temperature part and a low temperature part are partially generated in one deposit body, and cracks may occur due to the influence thereof.
The rate of temperature increase is set according to various conditions of the manufacturing method and is not particularly limited, but specifically, it is preferably 1° C./min or more and 10° C./min or less.
According to the above preferable conditions, variation in the degree of shrinkage in the vertical direction during sintering is reduced, and an optical fiber preform with reduced variation in the outer diameter of the preform after sintering is more reliably manufactured without damage. can do.

The optical fiber preforms obtained by the method of the present embodiment are less likely to vary in size depending on the manufacturing lot, even if the waiting time is different. Therefore, even in the subsequent drawing process for manufacturing an optical fiber from the optical fiber preform, the size is such that it can be accommodated in the drawing furnace, and the optical fiber preform can be subjected to the sintering process again, or the end portion can be removed. There is no need to perform complicated processing such as cutting the
Moreover, according to this embodiment, the preheating time can be shortened by shortening the standby time, so that the time required for the sintering process can be shortened, and the productivity can be improved.
The optical fiber preform obtained by the method of the present embodiment is subjected to a known drawing process to produce an optical fiber.

Reference Signs List 1 deposition body manufacturing device 11 reaction vessel 11A inner wall surface 12 starting rod 13 seed rod 14 suspension device 15 burner 16 gas flow control device 17 gas supply path 18 glass fine particle deposition body 18A deposition surface 110 exhaust pipe 111 light projector 112 light receiver 113 line 114 exhaust port 115 laser light 2 sintering furnace 21 furnace core tube 22 heater 23 heat shield 24 vacuum vessel 25 exhaust pipe 26 vacuum pump 27 gas introduction pipe 28 optical fiber base material 29 pressure control valve

Claims (5)

A step of producing a glass particle deposit body in which glass particles synthesized by supplying raw materials for glass to a burner flame are deposited on the outer circumference of a rotating starting rod; and after the step of producing a glass particle deposit body, the glass particle deposit body is sintered. A method for manufacturing an optical fiber preform comprising a sintering step,
The manufacturing conditions of the sintering step are changed so that the longer the time from the end of the glass particulate deposit manufacturing step to the start of the sintering step, the more likely the temperature of the central portion of the glass particulate deposit to rise. ,
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,
A method of manufacturing an optical fiber preform, wherein the longer the time from the end of the glass fine particle deposit manufacturing step to the start of the sintering step, the longer the time of the preheating step. 2. The method of manufacturing an optical fiber preform according to claim 1 , wherein the temperature of said preheating step is 1200[deg.] C. or less. 3. The light according to claim 1 or 2 , wherein the preheating step is set to 1 hour or less when the time from the end of the glass particle deposit manufacturing step to the start of the sintering step is 3 hours or less. A method for manufacturing a fiber preform. A step of producing a glass particle deposit body in which glass particles synthesized by supplying raw materials for glass to a burner flame are deposited on the outer circumference of a rotating starting rod; and after the step of producing a glass particle deposit body, the glass particle deposit body is sintered. A method for manufacturing an optical fiber preform comprising a sintering step,
The manufacturing conditions of the sintering step are changed so that the longer the time from the end of the glass particulate deposit manufacturing step to the start of the sintering step, the more likely the temperature of the central portion of the glass particulate deposit to rise. ,
The sintering step includes a temperature raising step of gradually heating the glass particle deposit to a temperature at which the glass particle deposit becomes transparent and vitrified,
A method of manufacturing an optical fiber preform, wherein the longer the time from the end of the glass fine particle deposition body manufacturing step to the start of the sintering step, the smaller the rate of temperature increase in the temperature increasing step. 5. The method for manufacturing an optical fiber preform according to claim 4 , wherein the temperature increase rate is 1[deg.] C./min or more and 10[deg.] C./min or less.

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