Device for manufacturing porous glass preform for optical fiber and method for manufacturing porous glass preform for optical fiber

Abstract

To provide a device and a method for manufacturing a porous glass preform for an optical fiber, capable of reducing a gas use amount and shortening non-effective parts formed at both ends of a glass fine particle deposit.SOLUTION: A device for accumulating glass fine particles using multiple burners for a starting material rotating by an outside vapor phase deposition method comprises: a mass flow controller for controlling a total flow rate of gas supplied to multiple burners 5a to 5c to be a set flow rate; a gas header 8 for branching the supplied gas toward each of the multiple burners; multiple valves provided to respective gas supply paths of the multiple burners; and a control part 10 for setting a flow rate of the mass flow controller and controlling opening / closing of the valve. The control part reduces the flow rate set to the mass flow controller by a supply amount to the burner, at which gas supply is stopped, when the gas supply to the corresponding burner is stopped by closing at least one of the multiple valves.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The present invention relates to an apparatus and a method for manufacturing a porous glass preform for an optical fiber, in which glass fine particles are deposited on a starting material by an outside vapor deposition method (OVD method).

Background Art

[0002] As a method for manufacturing a porous glass preform for an optical fiber, an outside vapor deposition method (OVD method) is known in which a glass fine particle generation burner (hereinafter simply referred to as a burner) is horizontally moved relative to a starting material that rotates about a horizontal rotation axis, and a glass fine particle layer having a predetermined thickness is deposited on the circumferential surface of the starting material (see, for example, Patent Document 1).

[0003] FIG. 1 is a schematic view of an apparatus 1 for manufacturing a porous glass preform by the outside vapor deposition method. A starting material 3 is attached to a rotation mechanism 2. The burner 5 is fixed to a burner holder 4 and horizontally moves relative to the starting material 3 by a horizontal movement guide mechanism 6 while laminating a glass fine particle layer on the circumference of the starting material 3 to form a glass fine particle deposit 7.

[0004] Non-effective portions that cannot be formed into a product having a conical shape with a smaller diameter toward the end sides are formed at both ends of the glass fine particle deposit 7. From the viewpoints of manufacturing cost and the like, it is required to shorten the non-effective portions and reduce the usage amount of various gases including the source gas.

[0005] On the other hand, in a porous glass preform manufacturing apparatus, in order to ensure a required deposition rate, it is common to arrange a plurality of burners along the axial direction of the starting material instead of a single burner for deposition. Further, in order to reduce the diameter variation in the axial direction of the deposit, a manufacturing method in which all the plurality of arranged burners are moved so as to deposit over the entire effective portion is effective. However, in this manufacturing method, the non-effective portions formed at both ends become longer as the number of burners increases. However, in order to obtain a realistic glass fine particle deposition rate, it is inevitable to use a plurality of burners.

[0006] In a porous glass base material manufacturing apparatus using a plurality of burners, as an example of a method for shortening the ineffective portions formed at both ends, there is a method of stopping the gas supply to the burner on which the ineffective portion at the end of the glass particle deposit is deposited.

[0007] Figure 2 shows a state in which a burner is depositing near the boundary between the ineffective portion and the effective portion formed at the end of the deposit in a manufacturing apparatus using a plurality of burners (in this example, three burners 5a, 5b, and 5c). The three burners 5a, 5b, and 5c fixed to the burner holder 4 are traversed in the direction of the arrow to deposit glass particles. The burners 5b and 5c are depositing the effective portion that becomes the product, while the burner 5a is depositing the ineffective portion that does not ultimately become the product. By stopping the gas supply to the burner 5a in the state where the ineffective portion is being deposited, the ineffective portion can be shortened. However, if the gas supply amounts to the burners 5b and 5c that deposit the effective portion that becomes the product are varied at that time, the effective portion may become shorter. That is, in order to shorten the ineffective portion while maintaining the length of the effective portion, it is necessary to have a gas flow control function that can stop only the gas supply to a specific burner (burner 5a in the case of Figure 2) and maintain the gas supply amounts to the other burners (burners 5b and 5c in the case of Figure 2) at that time.

[0008] When performing gas flow control to stop only the gas supply to a specific burner without affecting the gas supply amounts to the other burners, as the simplest method, there is a method of providing dedicated mass flow controllers (gas flow control devices) for all types of gas supplied to each burner and making the gas flow control independent.

[0009] Figure 3 shows a piping example in which dedicated mass flow controllers are provided for each burner to make the gas flow control independent. The burners used are three burners 5a, 5b, and 5c, and three series of gas supply pipes, namely, "raw material mixed gas of raw material gas 101 and carrier gas 102", "hydrogen gas 103", and "oxygen gas 104", are connected to each burner. For all four types of gas used, they are branched at the gas header 8 and dedicated mass flow controllers 9 are provided for the gas supply pipes connected to each burner.

[0010] Since the flow rate control of all types of gas supplied to each burner is independent, simply adjusting the gas flow rate with a mass flow controller can stop the gas supply to a specific burner only, without affecting the gas supply amount to other burners at all.

[0011] However, such a configuration of the gas supply piping has a problem that the number of mass flow controllers used increases depending on the number of burners used and the types of gas used, and the gas supply piping used also becomes long and complex, resulting in a high equipment cost.

[0012] FIG. 4 shows a schematic diagram of a gas supply piping in which the number of burners used and the supplied gas content are the same as those in FIG. 3, but the mass flow controller 9 is shared and the number of units used is reduced, so that the equipment cost is relatively low. Each gas is adjusted to the flow rate for three burners by the shared mass flow controller 9, then branched by the gas header 8 arranged downstream thereof, and distributively supplied to the burners 5a, 5b, and 5c. By using such a gas supply piping, the number of mass flow controllers 9 used can be reduced. The piping that shares the mass flow controller among a plurality of burners in this way is generally used as a reasonable piping design with a low equipment cost. However, in this piping design, gas flow rate control such as stopping the gas supply only to a specific burner among a plurality of burners cannot be performed.

Prior Art Documents

Patent Documents

[0013]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0014] In order to reduce only the ineffective part without reducing the effective part of the deposit, a gas flow control function is required that can stop the gas supply to a specific burner among a plurality of burners. In order to obtain the gas flow control function at a lower equipment cost, it is required of the gas flow control mechanism that the mass flow controller can stop the gas supply to a specific burner without increasing the number while sharing.

[0015] An object of the present invention is to provide a manufacturing method for reducing the amount of gas used including the source gas and shortening the ineffective parts formed at both ends of the glass fine particle deposit by temporarily stopping the gas supply to a specific burner in the production of a porous glass base material using a plurality of burners, and a relatively inexpensive flow control mechanism that does not require a mass flow controller dedicated to each burner, and can temporarily stop only the gas supply to a specific burner, for a porous glass base material manufacturing apparatus for an optical fiber.

Means for Solving the Problems

[0016] The porous glass base material manufacturing apparatus for an optical fiber of the present invention is an apparatus for manufacturing a porous glass base material by depositing glass fine particles on a starting material using a plurality of burners, wherein a valve is provided in a gas supply pipe branched by a gas header and connected to each burner, and by a combination of the opening / closing control of the valve and the flow rate adjustment of a mass flow controller that collectively adjusts the gas flow rates of a plurality of burners upstream of the gas header, various gas supplies to a specific burner can be stopped without changing the gas supply amounts to other burners.

[0017] The porous glass preform manufacturing apparatus for an optical fiber according to an embodiment of the present invention manufactures a porous glass preform for an optical fiber by depositing glass fine particles on a starting material that rotates by an external deposition method using a plurality of burners. The manufacturing apparatus includes a mass flow controller that controls the total flow rate of the gas supplied to the plurality of burners to a set flow rate, a gas header provided downstream of the mass flow controller that branches the gas supplied through the mass flow controller toward each of the plurality of burners, a plurality of valves provided in the gas supply paths from the gas header to each of the plurality of burners corresponding to each of the plurality of burners, and a control unit that controls the setting of the flow rate in the mass flow controller and the opening and closing of the valves. When the control unit closes at least one of the plurality of valves to stop the gas supply to the burner corresponding to the valve, the control unit decreases the flow rate set in the mass flow controller by the amount of the supply to at least one burner whose gas supply is stopped.

[0018] In the present invention, the gas supplied to the plurality of burners preferably includes a raw material mixed gas in which oxygen as a carrier gas is mixed with a raw material gas such as silicon tetrachloride or octamethylcyclotetrasiloxane (OMCTS), a combustible gas such as hydrogen, and an oxygen-containing combustion-supporting gas. The mass flow controller is preferably provided for each of the raw material gas, oxygen as a carrier gas, hydrogen as a combustible gas, and oxygen as a combustion-supporting gas. Then, the raw material gas and the carrier gas are preferably mixed upstream of the gas header to form a raw material mixed gas and supplied to a common gas header.

[0019] In the present invention, the gas header and the valves are preferably provided for at least one of the raw material mixed gas, the combustible gas, and the combustion-supporting gas. The gas header and the valves may be provided for each of the raw material mixed gas, the combustible gas, and the combustion-supporting gas.

[0020] In the present invention, a purge gas pipe for supplying purge gas is connected via a valve downstream of a valve provided in a raw material mixed gas pipe, which is a gas supply path for supplying a raw material mixed gas to a burner. The control unit may control to close the valve provided in the raw material mixed gas pipe to stop the supply of the raw material mixed gas to the burner, and at the same time open the valve provided in the purge gas pipe to supply the purge gas to the burner instead of the raw material mixed gas.

[0021] In the present invention, it is preferable that a plurality of burners are movable relative to a starting material along the axial direction of the starting material, and it is preferable that the stop section of the gas supply and the type of gas to be stopped from being supplied within the moving section of the plurality of burners can be freely set for each burner. At that time, in the moving section of the plurality of burners, for at least one burner located in at least a part of the section for depositing the ineffective part of the porous glass base material for optical fiber, it is particularly preferable to stop the supply of at least the raw material mixed gas by closing the corresponding valve.

[0022] In the present invention, the valve is preferably an air-operated valve or a proportional control valve.

[0023] The method for manufacturing a porous glass base material for optical fiber according to an embodiment of the present invention is realized by using any of the above manufacturing apparatuses. In this manufacturing method, while moving a plurality of burners relative to a starting material along the axial direction of the starting material, glass fine particles are deposited. In the moving section of the plurality of burners, for at least one burner located in at least a part of the section for depositing the ineffective part of the porous glass base material for optical fiber, the supply of gas is stopped by closing the corresponding valve, and the flow rate set in the mass flow controller is decreased by the amount of supply to at least one burner whose gas supply is stopped, so as to control that the gas supply amount to the burner whose gas supply is not stopped does not change.

Advantages of the Invention

[0024] According to the present invention, in the production of a porous glass base material using a plurality of burners, by stopping only the gas supply to at least a part of the burner that deposits the ineffective part, only the ineffective part can be shortened while maintaining the length of the effective part, and the usage amount of various gases including the raw material gas can be reduced.

[0025] Also, according to the present invention, by combining flow rate control and valve control by a shared mass flow controller, a flow rate control function capable of temporarily stopping only the gas supply to a specific burner can be obtained at a relatively low equipment cost.

Brief Description of the Drawings

[0026]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Embodiments for Carrying Out the Invention

[0027] Hereinafter, the porous glass base material manufacturing apparatus 1 and the porous glass base material manufacturing method of the present invention will be described with reference to the drawings, but various changes and modifications can be made without departing from the basic concept of the present invention.

[0028] The porous glass base material manufacturing apparatus 1 according to the present invention generally has the same configuration as the external attachment method porous glass base material manufacturing apparatus described with reference to FIG. 1, but is characterized in the configuration of the gas supply pipe and the control of the gas supply. In the porous glass base material manufacturing apparatus 1, the starting material 3 is attached to the rotating mechanism 2. The burner 5 is fixed to the burner holder 4 and moves horizontally with respect to the starting material 3 by the horizontal movement guide mechanism 6 while laminating a glass fine particle layer on the circumference of the starting material 3 to form a glass fine particle deposit 7. Non-effective portions that cannot be formed into a product having a conical shape with a smaller diameter toward the end side are formed at both ends of the glass fine particle deposit 7.

[0029] FIG. 5 shows an example of the gas supply pipe in the porous glass base material manufacturing apparatus 1 according to the present invention. The gas supply pipe shown in this example can temporarily stop the gas supply to a specific burner. In this example, three burners 5a, 5b, and 5c are used for depositing glass fine particles, and three series of gases, namely, the "raw material mixed gas of the raw material gas 101 and the carrier gas 102", the "hydrogen gas 103" as the combustible gas, and the "oxygen gas 104" as the combustion-supporting gas, are supplied to each burner.

[0030] A purge gas pipe for supplying a purge gas 105 is connected to the raw material mixed gas pipe, which is a gas supply path for supplying the raw material mixed gas to the burner, downstream of the valve. When the supply of the raw material mixed gas is stopped, the purge gas 105 is supplied to the raw material mixed gas pipe. The purge gas 105 uses an inert gas such as nitrogen and is preheated to a temperature at which the raw material gas 101 such as silicon tetrachloride or OMCTS is not liquefied when supplied to the raw material mixed gas pipe.

[0031] The mass flow controllers 9a to 9e control the flow rate of each gas. Instead of individually adjusting the gas flow rate supplied to each burner, the mass flow controllers 9a to 9e collectively adjust the gas amounts for a plurality (three in this example) of burners, and after adjusting the flow rate, the gas is branched at the gas header 8 and supplied to each burner. That is, the mass flow controllers 9a to 9e control the total flow rate of the gas supplied to the plurality of burners to the set flow rate. The mass flow controller is provided for each of the raw material gas 101, the carrier gas 102, the hydrogen gas 103 as the combustible gas, and the oxygen gas 104 as the combustion-supporting gas. The raw material gas 101 and the carrier gas 102 are mixed upstream of the gas header 8 after passing through the mass flow controller to form a raw material mixed gas and supplied to the common gas header 8.

[0032] The gas header 8 is provided downstream of the mass flow controllers 9a to 9e and branches the gas supplied through the mass flow controllers 9a to 9e toward each of the plurality of burners. Valves 11a to 11c, 12a to 12c, 13a to 13c, and 14a to 14c controlled by the control unit 10 to start / stop the gas supply are provided in the gas pipes branched at each gas header 8 and connected to each burner. The control unit 10 controls the setting of the flow rate in the mass flow controller and the opening and closing of the valves. By combining the opening and closing control of these valves and the gas flow rate control by the mass flow controller, the control unit 10 can temporarily stop the gas supply to a specific burner without affecting the gas supply to other burners. Specifically, when the control unit 10 closes at least one of the plurality of valves to stop the gas supply to the burner corresponding to the valve, the control unit 10 decreases the flow rate set in the mass flow controller by the supply amount to at least one burner whose gas supply is stopped. In addition, when the control unit 10 closes the valve provided in the raw material mixed gas pipe to stop the supply of the raw material mixed gas to the burner and at the same time opens the valve provided in the purge gas pipe to supply the purge gas to the burner instead of the raw material mixed gas.

[0033] Each burner (5a to 5c) is fixed to the burner holder 4 and is movable relative to the starting material along the axial direction of the starting material. In the porous glass base material manufacturing apparatus 1, the gas supply stop section within the movement section of the burner and the type of gas to be stopped from being supplied can be freely set for each burner. At that time, as will be described later, for at least one burner located in at least a part of the section for depositing the ineffective part of the porous glass base material for optical fiber within the movement section of the burner, it is advisable to stop the supply of at least the raw material mixed gas by closing the corresponding valve.

[0034] Air-operated valves are preferably used for the valves 11a to 11c, 12a to 12c, 13a to 13c, and 14a to 14c attached to the pipes branched from the gas header 8 and connected to each burner. When stopping and restarting the gas supply to a specific burner, if the valve operation of the air-operated valve is too rapid and the variation in the gas supply amount to the burner where deposition to the effective part is continuing becomes a problem, it is advisable to use a proportional control valve capable of controlling the valve opening and closing speed and adjust the valve opening and closing speed and the gas flow rate change speed by the mass flow controller. In this way, the variation in the gas supply amount to the burner where the effective part is being deposited can be suppressed within an allowable range.

[0035] In the piping example shown in FIG. 5, in the normal deposition state where the raw material mixed gas is supplied to all three burners and all three burners generate and deposit glass fine particles, all the valves 11a to 11c, 12a to 12c, and 13a to 13c provided in the pipes branched from the gas header 8 are opened. Also, all the valves 14a to 14c for supplying the purge gas 105 to the raw material mixed gas pipe are closed and the supply of the purge gas 105 is stopped. The mass flow controllers 9a to 9d have adjusted the flow rate of each gas to the supply amount for three burners.

[0036] Next, the control when shifting from the state where deposition is occurring with all three burners to a state where the supply of the raw material mixed gas to burner 5a is stopped and the supply amounts of the raw material mixed gas to burners 5b and 5c are maintained will be described. When valve 11a is closed, the supply of the raw material mixed gas to burner 5a stops, but at the same time, the supply flow rates of the raw material mixed gas to burners 5b and 5c increase. To avoid this increase in the gas flow rate to burners 5b and 5c, the control unit 10 controls mass flow controllers 9a and 9b to reduce the flow rates of the raw material gas 101 and the carrier gas 102 to 2 / 3 (the gas flow rate for two burners out of three burners) simultaneously when closing valve 11a. By this combination of valve control and mass flow controller control, it becomes possible to stop the supply of the raw material mixed gas to burner 5a and maintain the supply amounts of the raw material mixed gas to burners 5b and 5c. That is, in the method for manufacturing a porous glass base material for an optical fiber, within the moving section of the burner, for at least one burner located in at least a part of the section for depositing the ineffective portion of the porous glass base material for an optical fiber, the supply of the gas is stopped by closing the corresponding valve, and the flow rate set in the mass flow controller is decreased by the amount of the supply to the at least one burner where the gas supply is stopped, so as to control such that the supply amount of the gas to the burners where the gas supply is not stopped does not change.

[0037] Also, when the supply of the raw material gas 101 such as silicon tetrachloride is stopped and the raw material gas is left to stagnate in the pipe, there are concerns about problems such as local liquefaction. Therefore, when stopping the raw material mixed gas supplied to burner 5a, valve 14a is opened simultaneously to supply a purge gas 105 such as nitrogen to the raw material mixed gas pipe to avoid problems.

[0038] Next, the control when restarting the gas supply from the state where only the supply of the raw material mixed gas to the burner 5a is stopped will be described. Open the valve 11a to restart the supply of the raw material gas 101 and the carrier gas 102, and at the same time, increase the gas flow rate, which was reduced to two burners by the mass flow controllers 9a and 9b, to three burners. Also, at the same time, close the valve 14a to stop the supply of the purge gas 105 to the raw material mixed gas pipe. By the above control, the supply of the raw material mixed gas to the temporarily stopped burner 5a is restarted, and the deposition state returns to that of the three burners including the burners 5b and 5c.

[0039] In the piping example of FIG. 5, the stop of the supply of the hydrogen gas 103 and the oxygen gas 104 to the specific burner can be realized by a combination of the control of the valve provided in the pipe branched from the gas header and connected to each burner, similar to the stop of the raw material mixed gas, and the control of the mass flow controller that collectively adjusts the gas amount supplied to a plurality of burners upstream of the gas header. For example, when stopping the supply of the oxygen gas 104 to the burner 5a, close the valve 13a, and at the same time, reduce the flow rate of the oxygen gas 104 by the mass flow controller 9d to 2 / 3 (the gas flow rate from three burners to two burners). As a result, only the supply of the oxygen gas 104 to the burner 5a is stopped, and the supply amount of the oxygen gas 104 to the burners 5b and 5c does not change.

[0040] When restarting the gas supply from the state where only the supply of the oxygen gas 104 to the burner 5a is stopped, open the closed valve 13a to restart the supply of the oxygen gas 104 to the burner 5a, and at the same time, increase the flow rate of the oxygen gas 104, which was reduced to two burners by the mass flow controller 9d, to three burners. As a result, the supply of the oxygen gas 104 to the stopped burner 5a is restarted without changing the oxygen gas 104 to the burners 5b and 5c.

[0041] The control of stopping and restarting the hydrogen gas 103 to a specific burner is also possible with the same control as the oxygen gas 104.

[0042] In an apparatus for manufacturing a glass microparticle deposit using three burners, a setting example of a gas supply stop section for each burner is shown to shorten ineffective portions formed at both ends of the deposit.

[0043] The burner holder 4 with three burners 5a, 5b, and 5c attached traverses the section from E1 to E2 repeatedly (horizontal movement of the burner and the burner holder with respect to the starting material), and glass microparticles are laminated.

[0044] The traversing section for each burner is "between a and d" for burner 5a, "between b and e" for burner 5b, and "between c and f" for burner 5c. The section "between c and d" where all burners traverse is the deposition section of the effective portion where the amount of glass microparticle deposition is uniform in the traversing direction and becomes a product. The traversing sections "between a and c" and "between d and f" at both ends thereof are deposition sections of ineffective portions where the amount of glass microparticle deposition changes in the traversing direction and does not become a product.

[0045] The deposition sections of the ineffective portions in each burner are "between a and c" for burner 5a, "between b and c" and "between d and e" for burner 5b, and "between d and f" for burner 5c. By stopping the gas supply to the burner in at least a part of these deposition sections of the ineffective portions and interrupting the deposition of glass microparticles, the ineffective portions formed at both ends of the glass microparticle deposit can be shortened while maintaining the length of the effective portion, and the gas usage can also be reduced.

[0046] Example 1 shows the case where the gas supply to burner 5a and burner 5c is temporarily stopped. In this example, the gas supply stop section for burner 5a is set as "between a and g", which is the deposition section of the ineffective portion, and the gas supply stop section for burner 5c is similarly set as "between h and f". By setting such gas supply stop sections at both ends of the traversing section, the ineffective portions formed at both ends of the traversing section become shorter compared to the case where no gas supply stop section is set.

[0047] On the other hand, since the gas supply is not stopped in the deposition section (between c and d) of the effective portion, the length of the effective portion is maintained.

[0048] In Example 2, control for stopping the gas supply to burner 5b is added to Example 1. In this example, the gas supply is stopped during the deposition intervals of the ineffective portions in burner 5b, namely, between "b" and "g" and between "h" and "e". Since the amount of gas supply stopped in the ineffective portion increases compared to Example 1, the ineffective portion becomes shorter than in Example 1, and the gas consumption can also be reduced.

[0049] It is assumed that the stop interval of the gas supply within the traversing interval of the burner can be arbitrarily set for each burner, and the type of gas for which the supply is stopped can also be arbitrarily selected.

[0050] The stop pattern of the gas supply to the specific burner shown in Examples 1 and 2 can be realized by using the piping shown in Fig. 5. However, the piping shown in Fig. 5 is designed to be able to stop the supply of all types of gas supplied in all burners used. By simplifying the piping by limiting the number of burners for which the gas supply is stopped and the type of gas for which the supply is stopped, the equipment cost can be suppressed. That is, the gas header and valves only need to be provided for at least one of the raw material mixed gas, combustible gas, and combustion-supporting gas.

[0051] Fig. 7 shows an example of a simplified piping diagram by limiting the number of burners for which the above gas supply is stopped and the type of gas. The number of burners used for deposition and the type of gas supplied to the burners are the same as in Fig. 5. With the piping in Fig. 5, it is possible to stop the gas supply for all three burners, but in the example of Fig. 7, the burners for which the gas supply can be stopped are limited to two, namely 5a and 5c. Also, the types of gas for which the supply can be stopped are all three series of gas in the piping of Fig. 5, but in the example of Fig. 7, the gases for which the supply can be stopped are limited to two series, namely "the raw material mixed gas of raw material gas 101 and carrier gas 102" and "oxygen gas 104", and the supply stop to the specific burner of "hydrogen gas 103" cannot be achieved.

[0052] In the configuration shown in FIG. 7, by limiting the functions related to the stop of gas supply to the minimum necessary, the piping can be made simpler, so a manufacturing apparatus having a gas flow control mechanism for stopping the gas supply to a specific burner can be obtained at a lower cost.

Explanation of Signs

[0053] 1 Porous glass base material manufacturing apparatus 2 Rotation mechanism 3 Starting material 4 Burner holder 5, 5a - 5c Burners 6 Horizontal movement guide mechanism 7 Glass particle deposit 8 Gas header 9, 9a - 9e Mass flow controllers 10 Control unit 11a - 11c Valves (for raw material mixed gas) 12a - 12c Valves (for carrier gas) 13a - 13c Valves (for hydrogen gas) 14a - 14c Valves (for oxygen gas) 101 Raw material gas 102 Carrier gas 103 Hydrogen gas 104 Oxygen gas 105 Purge gas

Claims

1. A porous glass preform manufacturing apparatus for an optical fiber, which manufactures a porous glass preform for an optical fiber by depositing glass fine particles on a starting material that rotates by an external attachment method using a plurality of burners, a mass flow controller that controls the total flow rate of the gas supplied to the plurality of burners to a set flow rate, a gas header provided downstream of the mass flow controller and branching the gas supplied through the mass flow controller toward each of the plurality of burners, a plurality of valves provided in the gas supply paths from the gas header to each of the plurality of burners, corresponding to each of the plurality of burners, and a control unit that sets the flow rate in the mass flow controller and controls the opening and closing of the valves, The control unit reduces the flow rate set in the mass flow controller by the amount of the supply to at least one burner to which the gas supply is stopped when closing at least one of the plurality of valves to stop the gas supply to the burner corresponding to the valve. A porous glass preform manufacturing apparatus for an optical fiber, characterized by this.

2. The gas supplied to the plurality of burners includes a raw material mixed gas in which oxygen as a carrier gas is mixed with a raw material gas that is silicon tetrachloride or octamethylcyclotetrasiloxane (OMCTS), a combustible gas that is hydrogen, and an oxygen gas that is an oxygen gas for combustion support. The mass flow controller is provided for each of the raw material gas, oxygen as the carrier gas, hydrogen as the combustible gas, and oxygen as the oxygen gas for combustion support. The raw material gas and the carrier gas are mixed upstream of the gas header to become the raw material mixed gas and supplied to the common gas header. The porous glass preform manufacturing apparatus for an optical fiber according to claim 1, characterized by this.

3. The gas header and the valve are provided for at least one of the raw material mixed gas, the combustible gas, and the combustion-supporting gas, and the porous glass base material manufacturing apparatus for an optical fiber according to claim 2 is characterized in that.

4. The gas header and the valve are provided for each of the raw material mixed gas, the combustible gas, and the combustion-supporting gas, and the porous glass base material manufacturing apparatus for an optical fiber according to claim 3 is characterized in that.

5. Downstream of the valve provided in the raw material mixed gas pipe, which is a gas supply path for supplying the raw material mixed gas to the burner, a purge gas pipe for supplying a purge gas is connected via the valve, The control unit closes the valve provided in the raw material mixed gas pipe to stop the supply of the raw material mixed gas to the burner, and at the same time opens the valve provided in the purge gas pipe to supply the purge gas to the burner instead of the raw material mixed gas, and the porous glass base material manufacturing apparatus for an optical fiber according to claim 3 or 4 is characterized in that it controls.

6. The plurality of burners are movable relative to the starting material along the axial direction of the starting material, The porous glass base material manufacturing apparatus for an optical fiber according to claim 1, wherein the stop section of the gas supply and the type of gas to be stopped from being supplied within the moving section of the plurality of burners can be freely set for each burner.

7. In the moving section of the plurality of burners, for at least one burner located in at least a part of the section for depositing the ineffective part of the porous glass base material for an optical fiber, the supply of at least the raw material mixed gas is stopped by closing the corresponding valve, and the porous glass base material manufacturing apparatus for an optical fiber according to claim 6 is characterized in that.

8. The valve is an air-operated valve or a proportional control valve, and the porous glass base material manufacturing apparatus for an optical fiber according to claim 1 is characterized in that.

9. A method for manufacturing a porous glass preform for an optical fiber using the manufacturing apparatus according to claim 1, while depositing glass fine particles while relatively moving the plurality of burners along the axial direction of the starting material with respect to the starting material, for at least one burner located in at least a part of a section for depositing an ineffective part of the porous glass preform for an optical fiber within the moving section of the plurality of burners, by closing the corresponding valve, the gas supply is stopped, and the flow rate set in the mass flow controller is decreased by the amount of supply to the at least one burner where the gas supply is stopped, so as to control the gas supply amount to the burners where the gas supply is not stopped not to change. A method for manufacturing a porous glass preform for an optical fiber, characterized in that.

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