JP2991397B2 - Method for manufacturing optical fiber preform and apparatus for manufacturing optical fiber preform - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an optical fiber preform in which fine glass particles are produced by a flame hydrolysis reaction and deposited on a starting material to obtain a porous glass body. The present invention relates to a method for manufacturing an optical fiber preform and an apparatus for manufacturing an optical fiber preform, which can prevent the residual microbubbles and obtain a high-quality optical fiber preform.

[0002]

2. Description of the Related Art Generally, in an optical fiber, light propagates through the core while undergoing total reflection at the interface between the core and the clad of the optical fiber. In such an optical fiber, it is ideal that the intensity of the incident light is emitted without attenuation, but the light is transmitted for various reasons while propagating through the core of the optical fiber. Causes loss. The degree to which the light intensity becomes weaker while propagating through the optical fiber is the transmission loss of the optical fiber.

Conventionally, such an optical fiber preform is manufactured by an optical fiber preform manufacturing apparatus based on a hybrid method as shown in FIG. In the figure, 1 is a reaction chamber, 2 is a torch, 3 is an enclosing tube, 4 and 5 are end burners, 6 is a flame containing fine glass particles, 7 is a glass seed rod, 8 is a soot, and 9 is an exhaust duct. That is, a torch 2 disposed below the reaction chamber 1 is provided with Si as a glass raw material.
Cl ₄ and GeCl ₄ as a dope raw material are supplied, and a flame 6 containing fine glass particles is injected from the torch 2 toward a glass seed rod 7 as a target thereabove through the surrounding tube 3, and the fine glass particles are discharged. The core soot 8 is attached and deposited on the tip of the glass seed rod 7 to form a porous optical fiber preform. The surrounding tube 3 is for preventing the flame 6 containing fine glass particles radiated from the torch 2 from fluctuating due to airflow. The core soot 8 rotates on the torch 2 and the flame 6 containing glass fine particles blown out of the torch 2 as shown by an arrow D in FIG.
Reciprocating as shown in FIG. 4 and glass particles adhere and grow into clad soot. The density of this clad soot is
The optimum value is 0.24 to 0.30 g / cm ³ , and below this value, there is a possibility that air bubbles remain after vitrification.

When the soot 8 is deposited on the glass seed rod 7 by spraying the flame 6 containing glass fine particles from the torch 2, the flame 6 containing glass fine particles sprayed from the torch 2 is used.
As shown in FIG. 7, glass fine particles are diffused in the longitudinal direction of the soot on the surface of the core soot 8 as shown in FIG. For this reason,
On the surface of the core soot 8, a low-density soot layer (0.2 g
/ Cm ³ or less). Therefore, in a conventional optical fiber preform manufacturing apparatus, as shown in FIG. 6, end burners 4, 5 are provided at a predetermined distance from the torch 2 at a position in the longitudinal direction of the soot with the torch 2 therebetween. Such glass particles are prevented from diffusing in the longitudinal direction of the soot. That is, the oxyhydrogen flames 41 and 51 are radiated from the end burners 4 and 5 toward the surface of the core soot 8, and are shown in FIG. 8 by the oxyhydrogen flames 41 and 51 radiated from the end burners 4 and 5. As described above, the glass fine particles are prevented from diffusing in the longitudinal direction so as to float on the surface of the core soot 8. Thus, the end burners 4 and 5 prevent the glass fine particles from diffusing in the longitudinal direction to some extent, and increase the density of the low-density soot layer by heating. Corrosive gas and residual soot generated when the soot 8 is deposited on the tip of the glass seed rod 7 by the flame 6 containing glass fine particles injected from the torch 2 is exhausted from the exhaust duct 9 as shown by an arrow F in the drawing. Sent to an exhaust gas treatment device that has not been treated.

Another conventional example is disclosed in Japanese Patent Application Laid-Open No. 63-7 / 1988.
JP-A-63-79055,
It uses a protective tube with a double tube structure and is configured to be extendable and contractible. The protective tube having the double tube structure is for focusing glass fine particles.

[0006]

By the way, the deposition efficiency ρ, which is the efficiency with which glass fine particles adhere and deposit on the soot 8, is as follows: ρ = kΔT, where ρ: deposition efficiency k: proportional constant ΔT: fine particles and soot deposition It has the relationship of temperature difference with the surface. That is, the efficiency of deposition of the glass particles on the soot surface depends on the thermophoresis force proportional to the temperature difference between the particles and the deposition surface.

A conventional optical fiber preform manufacturing apparatus uses end burners 4 and 5 to prevent glass particles from diffusing in the longitudinal direction by oxyhydrogen flames of the end burners 4 and 5 and deposit the glass particles. By heating the surface, the density of the low-density soot layer is increased, and the formation of a low-density cladding layer is suppressed. For this reason, in the conventional optical fiber preform manufacturing apparatus, the soot deposition surface is heated by the oxyhydrogen flame of the end burners 4 and 5, and the temperature difference between the soot deposition surface and the fine particles is reduced. There is a problem that the effect of the foresis force is small. For this reason, the deposition rate of the clad soot is as low as 1.0 g / min, and it takes a long time to deposit the required amount of clad soot.
about 2.2 kg in iCl ₄ ), combustion gas CH ₄ ,
O ₂ consumes about 900 sccm and 2300 sccm, respectively, and has a problem that the production cost increases.

It is an object of the present invention to increase the deposition rate by the thermophoresis effect, and to uniformly increase the density to 0.1.
Without depositing the clad soot at 24 to 0.30 g / cm ³ to form a low-density soot portion in the clad soot, eliminating microbubble residue after vitrification and greatly reducing production cost It is to obtain a high-quality optical fiber preform.

[0009]

In order to achieve the above object, a method of manufacturing an optical fiber preform according to the present invention is directed to a method of manufacturing a method for manufacturing a glass preform, which comprises irradiating a flame containing glass fine particles from a torch and producing glass fine particles produced by flame hydrolysis. In the method of manufacturing an optical fiber preform to obtain a porous preform for optical fiber, injecting a cooling inert gas around the glass particle-containing flame radiated from the torch simultaneously with the glass particle-containing flame radiation, The glass fine particles are prevented from diffusing in the longitudinal direction of the glass seed rod, and the soot deposition surface is not heated so that the temperature difference between the soot deposition surface and the fine particles is kept large.

[0010] To achieve the above object, an apparatus for manufacturing an optical fiber preform according to the present invention comprises a torch disposed below a reaction chamber and radiating a flame containing glass particles to deposit soot on a glass seed rod. An optical fiber preform manufacturing apparatus comprising an exhaust duct provided above the soot deposition point in the upper part of the reaction chamber and connected to an exhaust gas processing chamber, wherein an inner pipe and an outer pipe are provided on the torch; A hollow path is formed by forming a double pipe structure, sealing both ends of the inner pipe and the outer pipe, and providing a blowout port in the radial direction of the glass particle-containing flame, and passing the inert gas cooling medium from the outer pipe side face. Provide an surrounding pipe connected to an introduction pipe to be supplied into the hollow passage, supply an inert gas cooling medium from the introduction pipe at the time of radiating the flame containing glass fine particles, and radiate from the torch by spraying from the outlet through the hollow passage. Glass granules It is obtained so as to deposit soot on a glass seed rod to form a coolant layer around the containing flame.

The outlet for injecting the cooling medium to be supplied to the surrounding tube is provided at the radiation-side end of the flame containing fine glass particles at the radiation side which intersects the longitudinal direction of the glass seed rod and is located immediately below the soot deposition position. Openings are provided at at least two places at the ends so as to intersect the soot longitudinal direction.

Further, the cooling medium introduced into the hollow passage of the surrounding tube is an inert gas such as N ₂ , Ar, He, etc., and the inert gas is cooled by cooling the periphery of the introducing tube with liquefied N ₂ or the like. Cooling.

[0013]

A method of manufacturing an optical fiber preform for obtaining a porous preform for an optical fiber by radiating a flame containing glass fine particles from a torch and depositing glass fine particles generated by flame hydrolysis on a glass seed rod to radiate from the torch. A cooling inert gas is sprayed around the flame containing the glass particles to be sprayed simultaneously with the emission of the flame containing the glass particles to prevent the glass particles from diffusing in the longitudinal direction of the glass seed rod and to prevent the soot deposition surface from being heated. Since the temperature difference between the deposition surface and the fine particles is kept large, the deposition rate is increased by the thermophoresis effect, and the density is uniformly increased from 0.24 to
Without depositing the cladding soot at 0.30 g / cm ³ to form a low density soot portion in the cladding soot,
After the vitrification, the residual fine bubbles can be eliminated.

A torch disposed at a lower portion in the reaction chamber to emit soot on the glass seed rod by irradiating a flame containing fine glass particles, and a torch provided at an upper portion of the reaction chamber above the soot deposition point and connected to an exhaust gas treatment chamber; A hollow path is formed on the torch of an optical fiber preform manufacturing apparatus having an exhaust duct with an inner pipe and an outer pipe by forming a hollow pipe, and both ends of the inner pipe and the outer pipe are sealed. Also provided is an outlet in the emission direction of the glass-particle-containing flame, and an surrounding pipe connected to an introduction pipe for supplying an inert gas cooling medium into the hollow passage from the outer pipe side surface. A cooling medium layer is formed around a flame containing glass fine particles radiating from a torch by supplying an inert gas cooling medium, spraying from an outlet through a hollow passage, and depositing soot on a glass seed rod. Because sir Increase the deposition rate by iontophoresis effect, uniformly depositing a cladding soot density 0.24~0.30g / cm ³ and not to form a low density soot portion in the cladding soot, microbubbles after the transparent vitrification It is possible to obtain a high-quality optical fiber preform by suppressing the residue and greatly reducing the production cost.

An outlet for injecting the cooling medium to be supplied to the surrounding tube is provided at the radiation end of the flame containing glass fine particles at the radiation end which intersects the longitudinal direction of the glass seed rod and is located immediately below the soot deposition position. Since the openings are provided at least at two locations so as to intersect the longitudinal direction of the soot, the thermophoresis effect can be efficiently increased and the deposition rate can be increased.

The cooling medium introduced into the hollow passage of the surrounding tube includes:
Since an inert gas such as N ₂ , Ar, He or the like is used and the periphery of the introduction pipe is cooled to cool the inert gas,
The deposition rate can be increased by effectively increasing the thermophoresis effect.

[0017]

Embodiments of the present invention will be described below. 1 to 5 show one embodiment of a method for manufacturing an optical fiber preform and an apparatus for manufacturing an optical fiber preform according to the present invention.

In the figure, the members denoted by the same reference numerals as those shown in FIG. 6 are the same as the members shown in FIG. 6, and the description thereof will be omitted. This embodiment differs from the conventional example shown in FIG. 6 in that the end burners 4 and 5 are removed, and a surrounding tube having a different configuration from the conventional example is provided on the torch 2. That is, in FIG. 1, 1 is a reaction chamber, 2 is a torch, 6 is a flame containing fine glass particles, 7 is a glass seed rod, 8
Is a soot and 9 is an exhaust duct. Reference numeral 10 denotes an enclosing tube provided on the torch 2. The surrounding tube 10 may be fixed on the torch 2 or may be provided slightly away from the torch 2 as shown in FIG. The surrounding tube 10 has a configuration as shown in FIG. The surrounding tube 10 is constituted by a quartz glass tube having a double tube structure of an inner tube 11 and an outer tube 12. Reference numeral 13 denotes an upper lid for sealing a space formed by a double pipe of the inner pipe 11 and the outer pipe 12 provided at a predetermined interval at an upper end. The hollow path 2 is formed by the space formed by the double pipe of the inner pipe 11 and the outer pipe 12.
0 is configured. The inner pipe 11 and the outer pipe 12
The side on which the upper lid 13 is attached is the radiation direction of the flame containing glass fine particles.

14 and 15 are outlets, 16 is a taxiway, 17
Is a lower lid, and 18 is an introduction tube. The taxiway 16 includes the inner pipe 11
And guides the glass particle-containing flame 6 radiated from the torch 2 in a predetermined direction (upward in FIG. 1) to prevent the glass particle-containing flame 6 from fluctuating due to airflow. .

The lower lid 17 seals the space of the double pipe of the inner pipe 11 and the outer pipe 12 provided at a predetermined space at the lower end. In addition, the introduction pipe 18 is the outer pipe 1
2 (specifically, soldering, welding, or the like), which is in communication with the hollow passage 20 and is for introducing an inert gas cooling medium into the hollow passage 20. Therefore, the hollow path 20 is formed by the lower lid 17 and the upper lid 13.
Has a configuration in which an inert gas cooling medium introduced from the introduction pipe 18 is filled along the outer wall of the inner pipe 11 and the inert gas 30 and 40 cooled from the outlets 14 and 15 are injected. I have. Inert gas cooling medium introduced from the inlet pipe 18, N _2, Ar, an inert gas such as He, surrounding inlet tube 18 is not shown liquefied N ₂
And so on. Therefore, introduction pipe 1
The inert gas introduced from 8 is cooled by cooling around the introduction pipe 18.

The outlets 14 and 15 are for injecting the inert gas cooling medium introduced from the introduction pipe 18 and supplied into the hollow passage 20 in the same direction as the emission direction of the flame 6 containing glass fine particles. . And these outlets 14, 15
Is an upper lid 1 which is a radiation-side end of the flame 6 containing glass fine particles.
At 3, at least two opposing positions intersecting the longitudinal direction of the glass seed rod and located immediately below the soot deposition position,
The opening is provided so as to intersect the soot longitudinal direction. Here, the formation positions of the outlets 14 and 15 are provided on the upper lid 13 of the surrounding tube 10 so as to oppose each other in the longitudinal direction of the soot. At other positions, the flow of glass particles on the soot deposition surface is disturbed. That's why. Therefore, the inert gas cooling medium is introduced from the inlet pipe 18, passes through the hollow passage 20, and flows from the outlets 14 and 15 in the longitudinal direction of the surrounding pipe 10 (FIG. 3).
(Upward direction).

Next, the operation of this embodiment will be described.
The flame 6 containing fine glass particles blown out from the torch 2 is blown to the soot 8 through the guide path 16 of the surrounding tube 10. This inert gas is cooled such as N ₂ blown from the air outlet 14, 15 of the envelope tube 10 at the same time 30, 40
Is sprayed near the left and right sides of the soot 8 deposition surface. Then, the flame 6 containing glass fine particles which is about to flow to the left and right in the longitudinal direction of the soot 8 is cooled by the inert gas 30,
40 pushes it back to the soot 8 deposition surface. By this action, the soot is deposited on the soot 8 only near the deposition surface where the flame is blown, so that the low-density clad soot does not occur unlike the conventional case.

Also, cooled inert gas 30 or 40 such as N ₂ blown out from the outlets 14 and 15 of the surrounding tube 10.
When is sprayed on the soot 8 deposition surface, the flame 6 containing glass fine particles cools the left and right deposition surfaces of the soot 8 on which the soot is deposited, so that the effect of thermophoresis increases and the deposition rate can be increased. .

Here, the inert gas 30, 40 such as N ₂ is
If the part guided to the surrounding tube 10 is cooled by liquefied N ₂ or the like, the effect is more exhibited. Further, the flow rate of the cooling inert gas is suitably about 40 SLPM in total, and if it is more than this, the flame from the torch 2 will be disturbed, so that it is not suitable.

[0025]

According to the present invention, a cooling inert gas is sprayed around a flame containing glass fine particles radiated from a torch simultaneously with the emission of the flame containing glass fine particles, whereby the glass fine particles are diffused in the longitudinal direction of the glass seed rod. Therefore, the soot-deposited surface is not heated so that the temperature difference between the soot-deposited surface and the fine particles is kept large, and the clad soot is uniformly distributed in the clad soot at a density of 0.24 to 0.30 g / cm ^3. Is deposited, no low-density soot portion is formed, no microbubbles remain after vitrification, and a high-quality optical fiber preform can be obtained.

Further, according to the present invention, a hollow passage is formed on the torch by forming a double tube structure of an inner tube and an outer tube, both ends of the inner tube and the outer tube are sealed, and glass particles are contained. An enclosure is provided which has a blow-out port in the direction of emission of the flame, and is connected to an introduction pipe for supplying an inert gas cooling medium into the hollow passage from the side of the outer pipe. Because a gas cooling medium is supplied, a cooling medium layer is formed around a flame containing glass fine particles radiated from a torch and injected from an outlet through the hollow path, soot is deposited on a glass seed rod. The temperature difference between the soot deposition surface and the fine particles is kept large by preventing the soot deposition surface from being heated, and 0.24 to 0.30 g is contained in the clad soot.
The clad soot is uniformly deposited at a density of / cm ³ , without forming a low-density soot portion, leaving no microbubbles after vitrification, and a high-quality optical fiber preform can be obtained.

Further, according to the present invention, the outlet for injecting the cooling medium to be supplied to the surrounding pipe is provided at the radiation-side end of the flame containing fine glass particles, intersecting the longitudinal direction of the glass seed rod and directly below the soot deposition position. Are provided so as to intersect with the longitudinal direction of the soot at least at two positions on the radiation side end located at the position, so that the thermophoresis effect can be efficiently increased and the deposition rate can be increased.

Still further, according to the present invention, an inert gas such as N ₂ , Ar, or He is used as a cooling medium to be introduced into the hollow passage of the surrounding pipe, and the inert gas is cooled by cooling the periphery of the introducing pipe. Since the gas is cooled, the deposition rate can be increased by effectively increasing the thermophoresis effect.

[Brief description of the drawings]

FIG. 1 is a schematic view showing an embodiment of an optical fiber preform manufacturing method and an optical fiber preform manufacturing apparatus according to the present invention.

FIG. 2 is a plan view of the surrounding tube shown in FIG. 1;

FIG. 3 is a partial sectional front view shown in FIG. 1;

FIG. 4 is a bottom view of the surrounding tube shown in FIG. 1;

FIG. 5 is an enlarged view showing an operation state of the torch and the surrounding tube shown in FIG. 1;

FIG. 6 is a schematic view showing a conventional optical fiber preform manufacturing apparatus.

FIG. 7 is a view showing a flow of a flame containing glass particles radiated from the torch shown in FIG. 6 on a soot deposition surface.

FIG. 8 is a view showing a flow of a flame containing glass fine particles on a soot deposition surface when an end burner is provided adjacent to the torch shown in FIG. 6;

[Explanation of symbols]

1 ………………………………………………………………………………………………………………………………………………… Torch 6 ……………………………………………………………………………………………………………………………………………………………… ……… Glass seed stick 8 …………………………………………………………………………………………………………………………………… ……… Surrounding tube 11 …………………………………………… Inner tube 12 ……………………………………………… ……… Outer tube 13 ……………………………………………………………………………………………………………………………………………………………………………………… …… Outlet 16 …………………………… Taxiway 17 ………………………………………………………………… …… lower lid 8 ……………………………… Introduction pipe 20 ………………………………… Hollow road 30, 40 …………………………………… Inert gas

Claims (4)

(57) [Claims] 1. A method for manufacturing an optical fiber preform for obtaining a porous preform for an optical fiber, wherein a flame containing glass fine particles is emitted from a torch and glass fine particles generated by flame hydrolysis are deposited on a glass seed rod. Injecting a cooling inert gas around the flame containing the glass particles emitted from the furnace simultaneously with the emission of the flame containing the glass particles to prevent the glass particles from diffusing in the longitudinal direction of the glass seed rod and prevent the soot deposition surface from being heated. A method for producing an optical fiber preform, wherein the temperature difference between the soot deposition surface and the fine particles is kept large. 2. A torch disposed at a lower portion of the reaction chamber to emit soot on a glass seed rod by irradiating a flame containing glass fine particles, and a torch provided at an upper portion of the reaction chamber above the soot deposition point to an exhaust gas treatment chamber. In an optical fiber preform manufacturing apparatus including an exhaust duct to be connected, a hollow path is formed on the torch by forming a double pipe structure of an inner pipe and an outer pipe,
An enclosure which seals both end portions of the inner tube and the outer tube, has a blow-out port in a radial direction of the flame containing glass fine particles, and connects an introduction tube for supplying an inert gas cooling medium into the hollow passage from the side surface of the outer tube. A tube is provided, and when the flame containing glass particles is radiated, an inert gas cooling medium is supplied from the introduction tube, and a cooling medium layer is provided around the glass particle-containing flame radiated from the torch by being injected from the outlet through the hollow passage. An apparatus for manufacturing an optical fiber preform, wherein the soot is formed and deposited on a glass seed rod. 3. An outlet for injecting a cooling medium to be supplied to the surrounding tube, at a radiation-side end of the flame containing glass fine particles, on a radiation side intersecting the longitudinal direction of the glass seed rod and located immediately below the soot deposition position. An opening is provided at at least two places of the end so as to intersect the longitudinal direction of the soot.
An apparatus for manufacturing an optical fiber preform as described in the above. 4. A cooling medium to be introduced into the hollow passage of the surrounding pipe is an inert gas such as N ₂ , Ar, He, etc., which is cooled by cooling the periphery of the introducing pipe with liquefied N ₂ or the like. 4. The apparatus for manufacturing an optical fiber preform according to claim 2, wherein: