JPH0873235A - Method for positioning burner of apparatus for producing optical fiber preform - Google Patents

Abstract

PURPOSE: To provide a method for positioning a burner of an apparatus for forming optical fiber preforms capable of setting the posture and position of the multitube burner with good accuracy. CONSTITUTION: This apparatus produces the porous optical fiber preform by depositing glass particulates on an object by using the multitube burner 1 which has a structure in which light passes through in the central tube of the multitube structure and synthesizes the glass particulates in the flame at a front end. The multitube burner 1 is so positioned that the main light 20a emitted outside from the front end through the center of the multitube burner 1 respectively pass reference points 40, 41 in plural directions formed by the intersected points of plural auxiliary light rays 32, 34, 36, 38 and that the front end of the multitube burner 1 is aligned to the position reference consisting of the auxiliary light 38 for positioning the front end of the burner.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention uses a multi-tube burner to deposit fine glass particles synthesized in a flame at the tip of the burner on an object to manufacture a porous optical fiber base material. The present invention relates to a burner positioning method in an apparatus.

[0002]

2. Description of the Related Art An optical fiber preform is first manufactured by the VAD method. In the VAD method, a seed rod is attached to the lower end of a rotating shaft that is vertically supported and rotates downward, and glass fine particles such as SiO ₂ and GeO ₂ synthesized in the flame of a multi-tube burner for cores are obliquely downward from the seed rod. From above to the lower end of the seed rod to grow the porous optical fiber preform while pulling up the rotating shaft. The porous optical fiber preform thus obtained is dehydrated and sintered to form a transparent core optical fiber preform. Next, while rotating this transparent optical fiber base material for cores around its axis, glass particles made of pure SiO ₂ synthesized in the flame of the multi-tube burner for cladding were deposited on the outer periphery thereof. , Likewise dehydrated, sintered and transparent core,
An optical fiber preform composed of a clad is obtained.

In the VAD method, it is important that the refractive index distribution in the manufactured optical fiber preform is always stable.

The shape of the refractive index distribution in the optical fiber preform is
In particular, the posture of the multi-tube burner, specifically, the axial direction of the multi-tube burner, and the tip position of the multi-tube burner greatly change.

However, since the posture of the multi-tube burner could not be accurately determined in the past, the refractive index distribution of the finished product was measured, and the posture of the multi-tube burner was adjusted based on the result. Therefore, there was a problem that it was very laborious.

In the OVD method, the deposition efficiency is highest when the burner axis and the base material axis are exactly orthogonal to each other in the same plane.

However, it is very difficult to optimally adjust the posture of the multi-tube burner for cladding in this way.

The adjustment of the posture of the burner must be performed especially immediately after installing the burner or replacing the burner.

The reason is as follows.

(A) The posture of the burner was roughly determined from the position of the burner holder, but since it is necessary to sandwich a cushion material between the burner holder and the burner (otherwise, the glass is The burner made of the product will crack.), But there was a problem with the mechanical accuracy.

(B) When the posture of the burner is to be determined more finely, it was obtained from the image observed from outside the lens of the window of the reaction container. However, since the image through the lens has distortion, it is still sufficient. Accuracy was not obtained.

Conventionally, as a method for measuring the attitude of the burner, a method as disclosed in Japanese Patent Laid-Open No. 55-116637 has been proposed. In this method, a laser light source is attached to the rear part of the multi-tube burner via a burner moving table, and the laser light from this laser light source is passed through the center tube of the multi-tube burner and focused on the surface of the optical fiber preform. The position measuring device measures the position where the laser beam is focused on the surface of the optical fiber preform.

[0013]

However, such a burner posture measuring method has the following problems.

(A) Since the blowing direction of the burner and the emitting direction of the laser light do not actually coincide with each other, it is necessary to set the conditions of the burner after replacement of the burner.

(B) Only the position where the laser light is focused on the surface of the optical fiber preform is detected. However, in reality, the surface shape of the optical fiber preform changes due to the fluctuation of the flame. The point moves and I cannot measure it well.

(C) Actually, it is the angle between the preform axis and the burner axis that largely affects the refractive index distribution of the optical fiber preform, but it was not possible to measure that angle.

An object of the present invention is to provide a burner positioning method in an optical fiber preform manufacturing apparatus which can easily position the main light penetrating from the rear part of the multi-tube burner into the central tube and going out from the tip. To provide.

Another object of the present invention is to provide a burner positioning method in an optical fiber preform manufacturing apparatus capable of accurately setting the posture and position of a multi-tube burner.

[0019]

SUMMARY OF THE INVENTION The present invention uses a multi-tube burner which has a multi-tube structure in which light penetrates through a central tube and which synthesizes glass particles in a flame at the tip. The object of the present invention is to improve a burner positioning method in an optical fiber preform manufacturing apparatus that manufactures a porous optical fiber preform by depositing the above on an object.

One of the methods for positioning the burner in the optical fiber preform manufacturing apparatus according to the present invention is that the multi-tube burner is arranged at the rear portion of the multi-tube burner and passes through the center of the multi-tube burner to the tip of the multi-tube burner. Positioning of the main light emitted from the outside in the emission direction of the main light is performed with reference to the outermost tube of the multi-tube burner.

In another method of positioning the burner in the optical fiber preform manufacturing apparatus according to the present invention, the main light passing through the center of the multi-tube burner and exiting from the tip of the multi-tube burner is a plurality of main lights. Pass through a plurality of directional reference points formed by the intersections of the auxiliary light or the auxiliary filaments, and the tip of the multi-tube burner should match the position reference consisting of the auxiliary light for the burner tip positioning or the auxiliary filaments. The multi-tube burner is positioned.

Yet another method of positioning the burner in the optical fiber preform manufacturing apparatus according to the present invention is that the multi-tube burner is arranged at the rear of the multi-tube burner and passes through the center of the multi-tube burner. Positioning for aligning the optical axis of the main light in the light source of the main light emitted from the tip of the burner with the axis of the multi-tube burner is performed with reference to the outermost tube of the multi-tube burner. Main light emitted from the tip of the multi-tube burner through the center of the burner passes through a plurality of auxiliary lights or a plurality of direction reference points formed by the intersections of the auxiliary filaments, and the main light of the multi-tube burner. The multi-tube burner is positioned such that the tip of the multi-tube burner coincides with the position reference of the auxiliary light for locating the burner tip or the auxiliary filament.

[0023]

In this way, the positioning of the main light in the emitting direction of the main light source, which is arranged at the rear portion of the multi-tube burner and passes through the center of the multi-tube burner and goes out from the tip of the multi-tube burner, is performed. When the outermost tube of the multi-tube burner is used as a reference, the optical axis of the main light can be easily and accurately aligned with the axis of the multi-tube burner.

When the multi-tube burner is positioned by using the direction reference and the position reference, the multi-tube burner is positioned in the axial direction and the position of the tip. Therefore, the posture and position of the multi-tube burner can be set accurately.

Further, the main light source is positioned in the emission direction of the main light with reference to the outermost tube of the multi-tube burner, and then the multi-tube burner is positioned using the direction reference and the position reference. Then, the direction of the multi-tube burner in the axial direction and the position of the tip of the multi-tube burner are positioned more accurately, and the posture and position of the multi-tube burner can be set with higher accuracy.

[0026]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First, an example of a method for positioning a multi-tube burner for a core in an optical fiber preform manufacturing apparatus in the core forming process by the VAD method will be described with reference to FIGS.

FIG. 1 shows an embodiment of a multi-tube burner 1 for a core used in this embodiment. The multi-tube burner 1 includes a second tube, a second tube, and a fourth tube on the outer circumference of a first tube 2 as a central tube.
The tubes 3 to 5 are arranged concentrically, and the
The fourth passages 2a to 5a are formed concentrically. In the present embodiment, these first to fourth pipes 2 to 5 are 50 from each tip.
The mm length portion is reduced diameter portions 2b to 5b reduced in diameter. The first to third pipes 2 to 4 are configured so that their lengths are sequentially shortened, so that the positions of the base end sides of these first to third pipes 2 to 4 are displaced in the longitudinal direction. Are arranged as shown in FIG. These first to third tubes 2 to
Collar-shaped partition bodies 2c to 4c are provided at each base end of 4, and these partition bodies 2c to 4c are hermetically connected to the inner circumference of the fourth pipe 5, whereby the passages 2a to 5a are mutually connected. The space is divided. Behind the partition body 2c of the first pipe 2, partition bodies 6 and 7 for partitioning the interior of the fourth pipe 5 at intervals in the longitudinal direction are provided, and the purge gas chamber 8 is provided between the partition bodies 6 and 7. Are formed. A light passage hole 9 is provided at the center of the partition body 6. A lens 10 is fitted in the center of the partition body 7.

From the supply passage 11 to the first passage 2a, Si
A glass material gas such as Cl ₄ or GeCl ₄ is supplied, a combustion gas such as H ₂ is supplied from the supply passage 12 to the second passage 3a, and a seal such as Ar is supplied from the supply passage 13 to the third passage 4a. Gas is supplied, and auxiliary combustion gas such as O ₂ is supplied from the supply passage 14 to the fourth passage 5a. A purge gas such as Ar is supplied to the purge gas chamber 8 from a supply passage 15. The presence of the purge gas in the purge gas chamber 8 prevents the optical system described later from coming into contact with the glass raw material gas.

At the base end of the fourth tube 5, a light source holder 16
Are attached via a focus adjustment ring 17. The base end of the focus adjustment ring 17 is rotatably supported on the outer periphery of the light source holder 16, and the front end of the focus adjustment ring 17 is screwed to the base end of the fourth tube 5 by a screw coupling portion 18.

The light source holder 16 is fitted with a laser 20 as a light source in a hole 19 on the base end side of its axis, and the laser 20 is adjusted by an adjusting screw 21 screwed into the light source holder 16.
Is positioned, and adjustment is made so that the main light 20a made of the laser light emitted from the laser 20 goes out through the center of the first tube 2 which is the central tube. A lens 16a for narrowing down the main light 20a is provided at the tip of the light source holder 16.

By the way, in the VAD method, the multi-tube burner 1 for such a core is in the same plane with respect to the axial center of the optical fiber preform and has a specific angle (for example, 20 degrees to 30 degrees).
It is necessary to meet each other.

In setting the multi-tube burner 1 for the core in the reaction vessel of the optical fiber preform manufacturing apparatus as described above, first, referring to FIGS. 2A and 2B, the center of the multi-tube burner 1 for the core is set. The operation of aligning the axis with the optical axis of the laser 20 will be described.

As described above, the multi-tube burner 1 for the core, which supports the laser 20 for emitting the main light 20a of the laser light at the rear portion, is placed horizontally on the V block 22 in the multi-tube burner. The main light 20a passing through 1 is applied to the screen 23. In this state, V block 2
The position of the laser 20 is adjusted by the adjusting screw 21 so that the position of the point on the screen 23 where the main light 20a strikes does not move even if the multi-tube burner 1 is rotated around its axis on the screen 2.

Next, the core multi-tube burner 1 in which the attitude of the laser 20 is adjusted as described above is used to produce a porous core optical fiber preform 25 in the reaction vessel 24 as shown in FIG. An operation for setting the posture and position of the multi-tube burner 1 with accuracy by setting the fiber preform manufacturing apparatus will be described.

In this optical fiber preform manufacturing apparatus,
A main shaft 27 is rotatably and vertically movable inserted from the upper part into the center of an opening 26 in the upper part of the reaction container 24, and a seed rod 29 is supported by a chuck 28 at the lower end thereof.
The above-described multi-tube burner 1 for a core is inserted obliquely upward in the lower portion of the peripheral wall of the reaction vessel 24, and is formed at the lower end of the seed rod 29 or the optical fiber preform 25 formed by being deposited on the lower end of the seed rod 29. It is designed to be directed toward the bottom of. The multi-tube burner 1 is supported by a burner holder 30.
An exhaust port 31 is provided in another portion of the peripheral wall of the reaction container 24.

In the reaction container 24, a positioning light source 33 which emits auxiliary light 32 consisting of horizontally oriented sheet light showing the height at which the central axis of the multi-tube burner 1 intersects with the central axis of the optical fiber preform 25, is multiplexed. A positioning light source 35 that emits auxiliary light 34 composed of horizontally oriented sheet light indicating the height of the tip of the tube burner 1 is provided supported by the reaction container 24. The sheet light can be formed by passing the light beam through, for example, a semi-cylindrical cylindrical lens.

Further, in the reaction container 24, a positioning light source 37 which emits auxiliary light 36 consisting of a beam of light showing the axis of the optical fiber preform 25 is held by the chuck 28 before holding the seed rod 29. It is provided. Further, the reaction container 24
Is provided with a positioning light source 39 that emits auxiliary light 38 for positioning the burner tip, which is a beam of light, from directly below to above the position where the tip of the multi-tube burner 1 should be located.

First, the main light 20a and the auxiliary light 3
2, 34, 36, 38 will be used to describe the work of setting the posture of the multi-tube burner 1 for the core.

In this optical fiber preform manufacturing apparatus,
A direction reference point 40 formed by the intersection of the auxiliary light 32 made of the sheet light and an auxiliary light 36 made of the beam light, and a direction reference point 41 made of the intersection of the auxiliary light 34 made of the sheet light and the auxiliary light 38 made of the beam light. And the attitude of the multi-tube burner 1 is adjusted so that the main light 20a passes through (and the direction of the multi-tube burner 1 is determined). Further, the tip of the multi-tube burner 1 is aligned with the position reference formed by the auxiliary light 38 for positioning the burner tip (this determines the distance between the tip of the multi-tube burner 1 and the center of the lower surface of the optical fiber preform 25). The tip of the multi-tube burner 1 is positioned. In this case, the distance between the direction reference point 40 and the direction reference point 41 is set to the optimum distance between the center of the lower surface of the optical fiber preform 25 and the tip of the multi-tube burner 1. The interval between the auxiliary light 36 and the auxiliary light 38 is set in advance so that such a condition is satisfied.

In this way, the posture and position of the core multi-tube burner 1 can be set with high accuracy.

The position of the light can be confirmed by, for example, using a piece of paper 50 of a business card size as shown in FIG. 9, and moving the piece of paper 50 near the intersection of light by hand and moving it. You can know the position of the intersection.

When the optical fiber preform 25 was manufactured using the multi-tube burner 1 for the core thus set, as shown in FIG. 6, immediately after the multi-tube burner 1 was replaced, The optical fiber preform 25 having a stable refractive index distribution could be manufactured. That is, when the optical fiber preform 25 is manufactured using the multi-tube burner 1 positioned by the conventional method, the refractive index distribution defect rate immediately after the multi-tube burner replacement is 72.
%, However, when the optical fiber preform 25 was manufactured using the multi-tube burner 1 positioned by the method of the present invention, the refractive index distribution defect rate immediately after the multi-tube burner exchange was 5%.

Next, the clad multi-tube burner 1 in which the attitude of the laser 20 is adjusted as described above, is provided in the reaction vessel 24 as shown in FIG. ) Is set in an optical fiber preform manufacturing apparatus for manufacturing the above (1) to accurately set the posture and position of the multi-tube burner 1.

In this optical fiber preform manufacturing apparatus,
The multi-tube burner 1 for clad is arranged horizontally at substantially the center of the reaction vessel 24 in the vertical direction.

The reaction container 24 is provided with a positioning light source 43 which emits auxiliary light 42 consisting of horizontally oriented sheet light indicating the height of the multi-tube burner 1. Also, the reaction container 2
In FIG. 4, a positioning light source 37 that emits auxiliary light 36 composed of a light beam indicating the axis of the optical fiber preform 25 is provided as a seed rod 29.
Is held by the chuck 28 before gripping. Further, the reaction container 24 is provided with a positioning light source 45 which emits auxiliary light 44 for positioning the burner tip, which is a beam of light, from directly below to above the position where the tip of the multi-tube burner 1 should be located. Here, the optical fiber preform 25
It is preferable to attach the positioning light source 37 that emits the auxiliary light 36 including the beam light indicating the axis of the above to the chuck 28 at the lower end of the main shaft 27 because the center can be performed while rotating the main shaft 27.

Next, the main light 20a and the auxiliary light 3
The operation of setting the posture of the multi-tube burner 1 for cladding will be described with reference to Nos. 6, 42 and 44.

In this optical fiber preform manufacturing apparatus,
A direction reference point 40 formed by an intersection of the auxiliary light 42 made of sheet light and the auxiliary light 36 made of beam light, and a direction reference point 41 made of an intersection of the auxiliary light 42 made of sheet light and the auxiliary light 44 made of beam light. And the attitude of the multi-tube burner 1 is adjusted so that the main light 20a passes through (and the direction of the multi-tube burner 1 is determined). Further, the tip of the multi-tube burner 1 is aligned with the position reference of the auxiliary light 44 for positioning the burner tip (this determines the distance between the tip of the multi-tube burner 1 and the axis of the optical fiber preform). The tip of the multi-tube burner 1 is positioned. In this case, the direction reference point 4
The distance between 0 and the direction reference point 41 is set to the optimum distance between the axial center of the optical fiber preform 25 and the tip of the multi-tube burner 1. The interval between the auxiliary light 36 and the auxiliary light 44 is set in advance so that such a condition is satisfied.

In this way, the posture and position of the cladding multi-tube burner 1 can be set with high accuracy.

When the optical fiber preform was manufactured using the multi-tube burner 1 for clad thus set, as shown in FIG. 7, the core was immediately after the multi-tube burner 1 was replaced. It was possible to manufacture an optical fiber preform with a stable / cladding ratio. That is, when the optical fiber preform was manufactured using the multi-tube burner 1 positioned by the conventional method, the defective ratio of core / cladding ratio immediately after the multi-tube burner replacement was 63%. When the optical fiber preform 25 was manufactured using the positioned multi-tube burner 1, the defective ratio of core / cladding ratio immediately after the multi-tube burner exchange was 7%.

Next, the multi-tube burner 1 in the optical fiber preform manufacturing apparatus by the OVD method, in which the starting preform is placed horizontally and rotated around its axis, and the optical fiber preform for cladding is synthesized on its outer periphery, is used. An example of the positioning method will be described with reference to FIG.

Both ends of the starting base material 46 are supported by the main shaft 27 via chucks 28. The starting base material 46 is disposed in the middle of the starting base material 46 in a direction orthogonal to the axis of the starting base material 46.

In this case, the attitude and position of the multi-tube burner 1 can be set with high accuracy by the same method as in the case of FIG.

When the optical fiber preform 47 for cladding was manufactured using the multi-tube burner 1 set in this way, as shown in FIG. 8, deposition immediately after the multi-tube burner 1 was replaced. I was able to stabilize the speed. That is,
When the optical fiber preform was manufactured using the multi-tube burner 1 positioned by the conventional method, the deposition rate failure rate immediately after the multi-tube burner replacement was 51%, but the multi-tube positioned by the method of the present invention was When the cladding optical fiber preform 47 was manufactured using the burner 1, the deposition rate defect rate immediately after the replacement of the multi-tube burner was 4%.

The light used in the present invention is preferably laser light, but other light may be used if an appropriate optical system is used.

Regarding the laser 20, it is also possible to place the laser 20 in another place as shown in FIG. 5 and introduce it into the light source holder 16 by the optical fiber 48.

In order to identify each light, it is convenient to use lasers having different wavelengths or use blinking light.

In the above example, the direction reference and the position reference are all formed by light, but a thin linear member such as a thread or a piano wire may be used instead of light.

Some of the inventions described above will be summarized and described as follows.

(1) Using a multi-tube burner for the core, which has a multi-tube structure in which light penetrates through the central tube and synthesizes glass particles in a flame at the tip, the glass particles are removed by the VAD method. In a method of positioning a burner in an optical fiber preform manufacturing apparatus for manufacturing a porous optical fiber preform for a core by depositing on a target object, in a method of passing through the center of the multi-tube burner to outside from the tip of the multi-tube burner. The main light emitted is from auxiliary light composed of horizontally oriented sheet light indicating the height at which the central axis of the multi-tube burner intersects with the central axis of the optical fiber preform and beam light indicating the axial center of the optical fiber preform. Direction reference point consisting of the intersection of the auxiliary light and the auxiliary light consisting of horizontal sheet light showing the height of the tip of the multi-tube burner and the vertical direction of the position where the tip of the multi-tube burner should be. Each of the multi-tube burners has a tip that matches a position reference formed by the burner tip positioning auxiliary light, which passes through a direction reference point formed by an intersection with the burner tip positioning auxiliary light formed by the directed beam light. A method for positioning a burner in an optical fiber preform manufacturing apparatus, characterized in that the multi-tube burner is positioned as described above.

(2) Using a multi-tube burner for cladding, which has a multi-tube structure in which light penetrates through the central tube and synthesizes glass particles in a flame at the tip, VA
A method of positioning a burner in an optical fiber preform manufacturing apparatus for manufacturing the porous optical fiber preform for cladding by depositing the glass fine particles on an object by the D method,
Main light emitted from the tip of the multi-tube burner through the center of the multi-tube burner is auxiliary light composed of horizontally oriented sheet light indicating the height of the multi-tube burner and the axis of the optical fiber preform. A direction reference point consisting of an intersection with an auxiliary light consisting of a beam of light, an auxiliary light consisting of a horizontally oriented sheet light indicating the height of the multi-tube burner, and the vertical direction of the position where the tip of the multi-tube burner should be. Through a direction reference point consisting of an intersection with a burner tip positioning auxiliary light consisting of a beam of light emitted toward the light source, and the tip of the multi-tube burner coincides with a position reference consisting of the burner tip positioning auxiliary light. The burner positioning method in the optical fiber preform manufacturing apparatus is characterized in that the multi-tube burner is positioned as described above.

(3) A multi-tube burner having a multi-tube structure in which light penetrates through the central tube and a multi-tube burner for clad which synthesizes glass particles in a flame at the tip is used for OV.
A method of positioning a burner in an optical fiber preform manufacturing apparatus for manufacturing a porous optical fiber preform for cladding by depositing the glass fine particles on an object by the D method,
Main light emitted from the tip of the multi-tube burner through the center of the multi-tube burner is auxiliary light composed of horizontally oriented sheet light indicating the height of the multi-tube burner and the axis of the optical fiber preform. A direction reference point consisting of an intersection with an auxiliary light consisting of a beam of light, an auxiliary light consisting of a horizontally oriented sheet light indicating the height of the multi-tube burner, and the vertical direction of the position where the tip of the multi-tube burner should be. Through a direction reference point consisting of an intersection with a burner tip positioning auxiliary light consisting of a beam of light emitted toward the light source, and the tip of the multi-tube burner coincides with a position reference consisting of the burner tip positioning auxiliary light. The burner positioning method in the optical fiber preform manufacturing apparatus is characterized in that the multi-tube burner is positioned as described above.

[0062]

As described above, according to the burner positioning method in the optical fiber preform manufacturing apparatus of the present invention, the following excellent effects can be achieved.

In the present invention, the positioning of the main light in the emitting direction of the main light is arranged at the rear of the multi-tube burner, passes through the center of the multi-tube burner and goes out from the tip of the multi-tube burner. Is performed with reference to the outermost tube of the multi-tube burner, the optical axis of the main light can be easily and accurately aligned with the axis of the multi-tube burner.

Further, in the present invention, since the multi-tube burner is positioned by using the direction reference and the position reference, the multi-tube burner is positioned in the axial direction and the tip position. Therefore, the posture and position of the multi-tube burner can be set accurately.

Further, in the present invention, the main light source is positioned in the emission direction of the main light with reference to the outermost tube of the multi-tube burner, and then multiplexed using the direction reference and the position reference. Since the tube burner is positioned, the multiple tube burner can be positioned more accurately in the axial direction and the position of the tip, and the posture and position of the multiple tube burner can be more accurately determined. Can be set.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view showing an example of a multi-tube burner used in a burner positioning method in an optical fiber preform manufacturing apparatus according to the present invention.

2A is a side view of the multi-tube burner showing a method of aligning the optical axis of main light with the axis of the multi-tube burner shown in FIG. 1, and FIG. 2B is a XX line of FIG. FIG.

FIG. 3 is an explanatory diagram showing an example of a method of positioning a multi-tube burner for a core in an optical fiber preform manufacturing apparatus in the core forming process by the VAD method.

FIG. 4 is an explanatory diagram showing an example of a method of positioning a multi-tube burner for a clad in an optical fiber preform manufacturing apparatus in the clad formation process by the VAD method.

FIG. 5 is an explanatory diagram showing an example of a method of positioning a multi-tube burner for a clad in an optical fiber preform manufacturing apparatus in a clad forming process by the OVD method.

FIG. 6 is a view immediately after the burner exchange between the optical fiber preform formed by using the multi-tube burner positioned by the method shown in FIG. 3 and the optical fiber preform formed by using the multi-tube burner positioned by the conventional method. It is a comparison diagram of the refractive index distribution defective rate.

FIG. 7 is a view immediately after the burner exchange between the optical fiber preform formed by using the multi-tube burner positioned by the method shown in FIG. 4 and the optical fiber preform formed by using the multi-tube burner positioned by the conventional method. It is a comparison diagram of the core / clad ratio defective rate.

FIG. 8 is a view immediately after the burner exchange between the optical fiber preform formed by using the multi-tube burner positioned by the method shown in FIG. 5 and the optical fiber preform formed by using the multi-tube burner positioned by the conventional method. It is a comparison figure of a deposition rate defect rate.

FIG. 9 is an explanatory diagram showing an example of a method of finding the position of a light intersection in the present invention.

[Explanation of symbols]

 1 Multi-tube burner 2 1st tube 3 2nd tube 4 3rd tube 5 4th tube 2a-5a 1st-4th passages 2b-5b Reduced diameter part 2c-4c Partition body 6,7 Partition body 8 Purge Gas Chamber 9 Light Passing Hole 10 Lens 11-15 Supply Passage 16 Light Source Holder 17 Focus Adjusting Ring 18 Screw Joint 19 Hole 20 Laser 20a Main Light 21 Adjusting Screw 22 V Block 23 Screen 24 Reaction Container 25 Optical Fiber Preform for Core 26 Aperture 27 Spindle 28 Chuck 29 Type Rod 30 Burner Holder 31 Exhaust Port 32,34,36 Auxiliary Light 33,35,37 Positioning Light Source 38 Burner Tip Positioning Auxiliary Light 39 Positioning Light Source 40,41 Directional Reference Point 42 Auxiliary Light 43 Positioning Light Source 44 Burner Tip Positioning Auxiliary Light 45 Positioning Light Source 46 Starting Base Material 7 clad optical fiber preform 48 optical fiber 50 paper

Claims (3)

[Claims] 1. A multi-tube structure having a multi-tube structure in which light penetrates through a central tube and a multi-tube burner for synthesizing glass particles in a flame at the tip is used to deposit the glass particles on an object to be porous. A method of positioning a burner in an optical fiber preform manufacturing apparatus for producing a high-quality optical fiber preform, wherein the multi-tube burner is disposed at a rear portion of the multi-tube burner and passes through a center of the multi-tube burner from a tip of the multi-tube burner. A burner positioning method in an optical fiber preform manufacturing apparatus, characterized in that the light source of the main light emitted to the outside is positioned in the emitting direction of the main light with reference to the outermost tube of the multi-tube burner. 2. Using a multi-tube burner having a multi-tube structure in which light penetrates through a central tube and synthesizing glass particles in a flame at the tip, the glass particles are deposited on an object to be porous. In the method of positioning a burner in an optical fiber base material manufacturing apparatus for manufacturing a high-quality optical fiber base material, main light exiting from the tip of the multi-tube burner through the center of the multi-tube burner is a plurality of auxiliary lights or The multiple tubes pass through a plurality of directional reference points formed by the intersections of the auxiliary filaments, and the tip of the multi-tube burner coincides with the position reference consisting of auxiliary light for positioning the burner tip or auxiliary filaments. A method for positioning a burner in an optical fiber preform manufacturing apparatus, characterized by positioning the burner. 3. A multi-tube structure, in which light penetrates through a central tube, and a multi-tube burner for synthesizing glass particles in a flame at the tip is used to deposit the glass particles on an object and to make them porous. A method of positioning a burner in an optical fiber preform manufacturing apparatus for producing a high-quality optical fiber preform, wherein the multi-tube burner is disposed at a rear portion of the multi-tube burner and passes through a center of the multi-tube burner from a tip of the multi-tube burner. Positioning is performed so that the optical axis of the main light in the light source of the main light emitted to the outside coincides with the axis of the multi-tube burner, with reference to the outermost tube of the multi-tube burner, and then the center of the multi-tube burner is set. The main light passing through the tip of the multi-tube burner passes through a plurality of directional reference points formed by intersections of a plurality of auxiliary lights or auxiliary filaments, and the tip of the multi-tube burner is Burner positioning method in an optical fiber preform manufacturing apparatus characterized by the positioning of the multi-tube burner to match the burner tip positioning auxiliary light or position reference consisting auxiliary striatum.