JP2014201475A - Manufacturing method and manufacturing apparatus for optical fiber preform - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method and a manufacturing apparatus for optical fiber preform that can suppress a cracking defect due to soot.SOLUTION: There is provided a manufacturing method for an optical fiber preform in which the optical fiber preform is manufactured by depositing soot 14 on an extension 11a of the center axis of a target 11 and a periphery of the target 11 from a tip 11t of the target 11, the manufacturing method using a core burner 12 for forming a part 14a as a core of the optical fiber preform and a clad burner 13 for forming a part 14b as a clad around an outer periphery of the part as the core. During the deposition of the part 14b as the clad, the clad burner 13 is so moved that the distance from the tip 13t of the clad burner 13 to the center axis of the target 11 or its extension 11a gradually increases.

Description

  The present invention relates to an optical fiber preform manufacturing method and manufacturing apparatus.

  In general, in the production of optical fibers, a quartz glass base material used for an optical fiber base material or the like is obtained by depositing soot (glass fine particles) by a VAD (Vapor phase axial deposition) method or an OVD (Outside vapor deposition) method. This is produced by forming a transparent glass by sintering. The optical fiber is manufactured by drawing the optical fiber preform manufactured in this way.

Conventionally, in the case of the VAD method, a core burner for synthesizing a soot as a core of an optical fiber preform and a cladding burner for synthesizing a soot as a clad of an optical fiber preform are fixedly disposed on the target. Soot is deposited and grown to synthesize an optical fiber preform.
Further, as in Patent Documents 1 to 3, the core burner may be moved.

Japanese Patent No. 3401382 JP-A-5-105469 JP-A 61-146726

  The clad burner is fixed in position so that thick soot can be produced stably in a steady state. Therefore, when starting production, soot is deposited on the surface of the target and the distance to the target is large. . For this reason, the oxyhydrogen flame becomes unstable on the surface of the target, and the surface temperature of the target and the deposition of soot become unstable, which is one of the causes of soot crack failure.

  This invention is made | formed in view of the said situation, and makes it a subject to provide the manufacturing method and manufacturing apparatus of an optical fiber preform which can suppress the crack defect of soot.

In order to solve the above-mentioned problems, the present invention provides an optical fiber preform that deposits soot on an extension line of a central axis of the target from the tip of the target and around the target to produce an optical fiber preform. A method comprising: a core burner that forms a core portion of the optical fiber preform; and a clad burner that forms a cladding portion on an outer periphery of the core portion. Manufacturing the optical fiber preform, wherein the cladding burner is moved so that the distance from the tip of the cladding burner to the central axis of the target or an extension thereof gradually increases during the deposition of Provide a method.
The clad burner is preferably moved so that the distance from the tip of the clad burner to the surface of the outermost layer of the soot being deposited on the target is constant.
It is preferable to use a uniaxial stage that moves the cladding burner so that the distance from the tip of the cladding burner to the central axis of the target or an extension line thereof can be increased or decreased.

Further, the present invention is an optical fiber preform manufacturing apparatus for manufacturing an optical fiber preform by depositing soot on the extension line of the center axis of the target from the tip of the target and around the target, A core burner that forms a core portion of the optical fiber preform, and a cladding burner that forms a cladding portion on the outer periphery of the core portion, during the deposition of the cladding portion, Manufacturing of an optical fiber preform characterized in that the cladding burner can be moved so that the distance from the tip of the cladding burner to the central axis of the target or its extension gradually increases. Providing equipment.
The cladding burner is preferably movable so that the distance from the tip of the cladding burner to the surface of the outermost layer of the soot being deposited on the target is constant.
It is preferable to provide a uniaxial stage for moving the cladding burner so that the distance from the tip of the cladding burner to the central axis of the target or its extension can be increased or decreased.

  According to the present invention, since the change in the distance from the tip of the cladding burner to the soot being deposited can be reduced during the deposition of the portion to be the cladding, it is possible to suppress soot cracking failure.

It is one Embodiment of this invention, Comprising: (a) is a front view which shows the initial stage of deposition, (b) is a front view which shows the state which deposition advanced. It is arrangement | positioning of the several burner for clads, Comprising: (a) is a front view which shows arrangement | positioning which made the distance to a target constant, (b) It is a front view which shows arrangement | positioning which increased / decreased the distance to a target in order. . It is an example of an optical fiber preform | base_material, Comprising: (a) is sectional drawing of the vertical direction, (b) is sectional drawing of a horizontal direction. It is explanatory drawing of a uniaxial stage.

The present invention will be described below based on preferred embodiments with reference to the drawings.
In FIG. 1, (a) shows the initial stage of deposition and (b) shows a state in which deposition has progressed in one embodiment of the present invention.
The schematic configuration of the manufacturing apparatus 10 shown in FIG. 1 includes a target 11 on which soot 14 is deposited, a plurality of burners 12 and 13 that generate the soot 14, and a chamber 15. The chamber 15 includes a storage unit 15a that stores the target 11, and an exhaust unit 15b that exhausts exhaust gas from the inside of the storage unit 15a. The drawing shown in FIG. 1 is a simplified schematic diagram, and various other accessories can be provided.

  The target 11 is also called a starting member, a support rod (rod) or the like, but is generally a columnar rod, and is formed of a heat resistant material such as quartz glass. An optical fiber preform is formed by depositing soot 14 on the surface of the target 11 and further growing the soot 14. In the case of the VAD method, not only the soot 14 is deposited around the target 11, but also the soot 14 is grown from the tip 11 t of the target 11 to the extension line 11 a of the center axis of the target 11. An optical fiber preform made of soot 14 can be obtained. As shown in FIG. 1B, the soot 14 has a portion (core portion) 14a that becomes a core of the optical fiber preform, and a portion (cladding portion) 14b that becomes a clad on the outer periphery of the core portion 14a. The core portion 14a grows mainly from the tip 11t of the target 11 so as to extend in the longitudinal direction of the target 11, and the clad portion 14b grows mainly around the core portion 14a so as to increase the outer diameter.

  The core burner 12 forming the core portion 14a emits a flame 12f containing soot toward the tip of the core portion 14a of the soot 14 extending from the tip 11t of the target 11 rotating around the axis. The tip 12t of the core burner 12 generally faces obliquely upward. Although it is necessary to correct the positional relationship between the target 11 and the core burner 12 in accordance with the growth of the core portion 14a of the soot 14, for example, the target 11 may be gradually raised upward.

  The clad burner 13 forming the clad portion 14b emits a flame 13f containing soot toward the periphery of the target 11 rotating around the axis and the core portion 14a of the soot 14 extending from the tip 11t of the target 11. . Although the tip 13t of the cladding burner 13 can be directed obliquely, in the case of FIG. 1, it is perpendicular to the longitudinal direction of the target 11. The positional relationship between the target 11 and the cladding burner 13 is corrected in accordance with the growth of the cladding portion 14b of the soot 14.

The core burner 12 and the cladding burner 13 include oxygen gas (support gas) for generating an oxyhydrogen flame, hydrogen gas (fuel gas), and silicon such as silicon tetrachloride (SiCl ₄ ) as a soot raw material. A compound gas (raw material gas) containing (Si) is supplied. The types, ratios, and the like of the auxiliary combustion gas, the fuel gas, and the raw material gas can be appropriately changed according to the target glass composition, manufacturing method, and the like. In order to obtain the refractive index difference between the core and the clad, for example, when germanium (Ge) is added to the core or fluorine (F) is added to the clad, Ge such as germanium tetrachloride (GeCl ₄ ) is contained. And a compound gas containing F such as carbon tetrafluoride (CF ₄ ), silicon tetrafluoride (SiF ₄ ), sulfur hexafluoride (SF ₆ ), and the like are added. It is also possible to change the glass composition in the radial direction of the fiber preform by changing the concentration of the source gas stepwise or continuously. Additives added to quartz glass are not limited to Ge and F, and other various elements such as phosphorus (P), boron (B), aluminum (Al), chlorine (Cl), and the like. .
In addition, an inert gas such as nitrogen (N ₂ ), argon (Ar), helium (He), neon (Ne), carbon dioxide (CO ₂ ) or the like is added to the source gas or the like for the purpose of adjusting the gas concentration. You can also. In order to stabilize the shape of the flame, an inert gas flow can be formed around the source gas.

In the aspect in which the conventional cladding burner is not moved, when soot is deposited on the surface of the target, since the distance from the tip of the burner to the target is large, the surface temperature of the target and the soot deposition become unstable. The suit may break.
In the present invention, during the deposition of the clad portion 14b, the clad burner so that the distance D (see FIG. 4) from the tip 13t of the clad burner 13 to the central axis of the target 11 or its extension line 11a gradually increases. 13 is moved. Thereby, as shown in FIG. 1A, the distance D is appropriately set from the initial stage of depositing the clad portion 14b. That is, in the initial stage, the distance D is shorter than the conventional distance. Then, at the time of seeding, the distance from the tip 13t of the cladding burner 13 to the surface of the target 11 is appropriately set (the radius of the target 11 is known), the surface temperature of the target 11 and the deposition of the soot 14 become stable, and the target 11 Soot can be reliably adhered to the surface of the material in a good state, and soot cracking can be suppressed.
Even in the process of increasing the thickness of the clad portion 14 b of the soot 14, the cladding burner 13 that forms the outermost layer of the soot 14 being deposited on the target 11 is moved from the tip 13 t of the cladding burner 13 to the soot 14. The distance d to the outermost surface 14c is preferably moved so as to be substantially constant. Thereby, the deposition state of the new soot on the surface 14c of the outermost layer of the soot 14 becomes stable, and the soot can be reliably deposited on the surface of the soot 14 in a good state.

The movement amount of the clad burner 13 can be realized by observing the deposition amount of the soot 14 in advance and an appropriate movement amount according to the deposition amount of the soot by a program or the like. It is also possible to control the amount of movement of the cladding burner 13 by observing the current amount of deposited soot 14 with a sensor or the like and predicting the amount of deposited soot thereafter.
When creating the program, different programs may be prepared for different conditions depending on the dimensions (length, outer diameter, etc.) of the soot base material and the deposition conditions. Also, when some conditions are different but other conditions are common, it is possible to input different conditions as variable parameters (variables) so that an appropriate amount of movement can be calculated even under new conditions. it can.

In the program, a change pattern of the moving amount of the cladding burner 13 is prepared. The change pattern of the moving amount of the cladding burner 13 can be expressed as a function of the position of the cladding burner 13 with respect to the time from the start of manufacture. It can also be expressed as a function of the moving speed of the cladding burner 13 with respect to the time from the start of manufacture.
The function for describing the change pattern is not limited to a continuous function such as a linear function or a quadratic function, but is a discontinuous function such as a step function that associates a specific time range (section) with a specific value (position or velocity). It may be a function. The position of the cladding burner 13 can be represented by, for example, the distance (D in FIG. 4) from the tip 13t of the cladding burner 13 to the central axis of the target 11 or its extension line 11a.

FIG. 2 shows an example of a manufacturing apparatus in which a plurality of clad burners 13 a, 13 b, and 13 c are arranged along the longitudinal direction of the target 11. Here, an example using three clad burners is shown, but the number is not particularly limited to three, and may be two or less, or four or more.
In the case of Fig.2 (a), the aspect which aligned the position of each burner 13a, 13b, 13c for each cladding up and down is shown. In the case of FIG. 2B, the clad burners 13 a, 13 b, and 13 c are separated from the target 11 as the target 11 is moved upward.

Each of the cladding burners 13a, 13b, 13c may be used simultaneously or sequentially. If there is a cladding burner that is not used at the same time, only the cladding burner that is being used for soot deposition may be moved appropriately in accordance with the soot deposition amount. The cladding burner that is not used for soot deposition may not be moved, and may be moved regardless of the amount of soot deposition.
Also, depending on the length and outer diameter of the soot base material to be manufactured, if the length or outer diameter is small, use a smaller number of cladding burners, and if the length or outer diameter is large, It is also possible to properly use a large number of clad burners.
In the case of FIG. 2B, the innermost layer of the clad part is formed by the clad burner 13a having a small distance (D in FIG. 4) to the central axis of the target 11 or its extension line 11a, and the distance D is medium. An embodiment is also possible in which the cladding burner 13b forms an intermediate layer of the cladding part, and the cladding burner 13c having a large distance D forms the outermost layer of the cladding part.

  FIG. 3 shows an example of the obtained optical fiber preform 20. As shown in FIG. 3A, a core portion 21 is formed at the center of the optical fiber preform 20 and extends in the longitudinal direction of the target 11. A clad portion 22 is formed around the core portion 21. The core portion 21 is a portion that finally becomes the core of the optical fiber, and the cladding portion 22 is a portion that becomes the cladding of the optical fiber. The diameter of the core portion 21 may be the same as or coincide with the diameter of the target 11 or may be different.

  In general, a material having a higher refractive index than that of the cladding portion 22 is used for the core portion 21. The clad portion 22 may be made of a uniform material as a whole, and using a plurality of materials having different refractive indexes, a plurality of layers 22a, 22b, and 22c are distributed concentrically as shown in FIG. May have. The composition of the soot can be changed stepwise, or it can have a continuously inclined change or a quadratic function change. In any case, in the clad part 22, the inside close to the core part 21 is formed first, and soot is deposited from the outside so that the outer diameter gradually increases.

An optical fiber preform (soot preform) made of soot becomes a transparent and solid glass body by sintering. Further, the tip portion of the optical fiber preform 20 and the root portion including the target 11 at the center are removed, and an optical fiber preform (transparent glass preform) having a substantially uniform cross-sectional structure in the longitudinal direction is obtained. In addition, soot can be further deposited and sintered on the outer surface of the obtained transparent glass base material to increase the outer diameter of the clad portion. The optical fiber preform (transparent glass preform) can be used for manufacturing an optical fiber by a known drawing process.
The optical fiber to be manufactured is not particularly limited. For example, a single mode optical fiber, a multimode optical fiber, a dispersion shifted optical fiber, a dispersion compensating optical fiber, a cutoff shift optical fiber, a non-zero dispersion shifted optical fiber, and the like. An optical fiber is mentioned.

FIG. 4 shows a schematic configuration of a uniaxial stage 16 that moves the cladding burner 13 as a configuration in which the distance D from the tip 13t of the cladding burner 13 to the central axis of the target 11 or its extension line 11a can be increased or decreased.
The distance D from the tip 13t of the cladding burner 13 to the central axis of the target 11 or its extension line 11a is preferably as constant as possible during the deposition of the cladding portion 14b, and is within a predetermined allowable range in which soot can be deposited stably. It is desirable to fit in.

As mentioned above, although this invention has been demonstrated based on suitable embodiment, this invention is not limited to the above-mentioned example, Various modifications are possible in the range which does not deviate from the summary of this invention.
The cladding burner is not limited to being moved perpendicularly to the longitudinal direction of the target, but can also be moved obliquely relative to the longitudinal direction of the target. In this case, since the displacement is parallel to the longitudinal direction of the target, it is preferable to appropriately adjust the relationship with the target pulling speed.

The moving direction of the cladding burner may be parallel or non-parallel to the longitudinal direction of the cladding burner (the direction of the central axis from which the flame is ejected).
When there are multiple clad burners, only one of the clad burners may be moved, or two or more clad burners may be moved, or all the clad burners may be moved. Good. When there is a proper use of a clad burner for forming the innermost layer of the clad part or a clad burner for forming the outermost layer, the clad burner for forming the innermost layer of the clad part may be moved in particular. The clad burner to be formed may be moved in particular.

  The present invention can be used for manufacturing optical fiber preforms and optical fibers. Furthermore, the present invention is not limited to optical fiber preforms and optical fibers, and can also be applied to the production of glass preforms by the same soot deposition method. Examples of such a glass base material include optical glass, a glass rod, and a glass tube. The glass base material can be used for manufacturing various members and parts by further processing such as stretching, polishing, drilling, and cutting.

DESCRIPTION OF SYMBOLS 10 ... Optical fiber preform manufacturing apparatus, 11 ... Target, 12 ... Core burner, 13, 13a, 13b, 13c ... Clad burner, 14 ... Soot, 14a ... Core part (core part), 14b ... Cladding Parts (parts to be clad), 15 ... chamber, 16 ... uniaxial stage, 20 ... optical fiber preform, 21 ... core part, 22 ... clad part.

Claims (6)

An optical fiber preform manufacturing method for manufacturing an optical fiber preform by depositing soot on an extension line of a central axis of the target from the tip of the target and around the target,
A core burner that forms a core of the optical fiber preform;
Using a clad burner that forms a clad part on the outer periphery of the core part,
The light for moving the clad burner so that the distance from the tip of the clad burner to the central axis of the target or its extension line gradually increases during the deposition of the clad portion. Manufacturing method of fiber preform.   2. The optical fiber according to claim 1, wherein the cladding burner is moved so that a distance from a front end of the cladding burner to a surface of an outermost layer of soot being deposited on the target is constant. A manufacturing method of a base material.   The uniaxial stage that moves the cladding burner so that the distance from the tip of the cladding burner to the central axis of the target or an extension line thereof can be increased or decreased is used. Manufacturing method of optical fiber preform. An optical fiber preform manufacturing apparatus for manufacturing an optical fiber preform by depositing soot on the extension line of the center axis of the target from the tip of the target and around the target,
A core burner that forms a core of the optical fiber preform;
A clad burner that forms a clad portion on the outer periphery of the core portion;
It is possible to move the cladding burner so that the distance from the tip of the cladding burner to the central axis of the target or an extension line thereof gradually increases during the deposition of the portion to be the cladding. An optical fiber preform manufacturing apparatus.   5. The clad burner can be moved so that the distance from the tip of the clad burner to the surface of the outermost layer of the soot being deposited on the target is constant. An optical fiber preform manufacturing apparatus as described in 1.   The uniaxial stage for moving the cladding burner so that the distance from the tip of the cladding burner to the central axis of the target or an extension line thereof can be increased or decreased. Optical fiber preform manufacturing equipment.

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