JP7144348B2 - Method for manufacturing optical fiber preform and method for manufacturing optical fiber - Google Patents

Description

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

As a method of manufacturing an optical fiber preform, for example, there is a perforation method (punching method). In the perforating method, a core rod is inserted into a through hole formed in a clad glass rod to obtain an optical fiber preform. An optical fiber can be manufactured by drawing while heating a cladding glass rod and a core rod, which constitute an optical fiber preform, to integrate them. The method of drawing while integrating the glass rod for clad and the core rod has high productivity because the process is simpler than the method of drawing after integrating the glass rod for clad and the core rod.

When a method of drawing while integrating the clad glass rod and the core rod is employed, the drawing is performed while vacuuming the inside of the base material in order to prevent the formation of voids in the optical fiber (for example, see Patent Document 1). reference). To evacuate the base material, the base material is evacuated through a connector attached via a dummy tube to the end opposite to the drawing end of the base material. The dummy pipe is provided to avoid burnout of the connector due to the heat of the wire drawing device by securing the distance between the base material and the connector.

For mass production of optical fibers, it is effective to lengthen the preform. However, since there is a limit to the length of the base material that can be set in the wire drawing machine, it may be difficult to secure a sufficient effective length of the base material that can be drawn by the above-described manufacturing method using the dummy tube and connector. Also, the longer the base material, the more likely it is that the shape of the base material will be misaligned. For example, in a long base material, through-holes are likely to be misaligned, which may affect the shape of the optical fiber (for example, core-to-core distance, eccentricity, etc.).

Japanese Patent No. 5176274

An object of one aspect of the present invention is to provide a method for manufacturing an optical fiber preform and a method for manufacturing an optical fiber, in which the shape accuracy of the preform is good and productivity can be improved.

One aspect of the present invention includes a preform manufacturing step of manufacturing a plurality of unit optical fiber preforms, and a preform connecting step of connecting the plurality of unit optical fiber preforms, wherein the preform manufacturing step comprises: A rod inserting step of inserting a glass rod serving as a core into a through hole passing through a clad glass body serving as a clad of an optical fiber; a first sealing step of forming a first end sealing portion that closes the opening of the through hole that opens to a portion; A second seal is formed by heating and deforming a second end, which is an end opposite to the end, to form a second end seal that closes the opening of the through hole that opens to the second end. and a connecting step, wherein the preform connecting step provides a method of manufacturing an optical fiber preform in which a connected optical fiber preform is obtained by butting and connecting the ends of the plurality of unit optical fiber preforms.

In the method for manufacturing an optical fiber preform, the first end sealing portion and the end of the dummy rod can be connected after the first sealing step and before the second sealing step.

The plurality of unit optical fiber preforms preferably have the same configuration.

In the method for manufacturing an optical fiber preform, the second end sealing portion of at least one of the unit optical fiber preforms is formed in a shape such that the protruding height increases toward the center of the unit optical fiber preform. is preferred.

In the method for manufacturing an optical fiber preform, the second end sealing portion of at least one of the unit optical fiber preforms can be formed so that at least a tip portion thereof has a curved convex shape.

In the method for manufacturing an optical fiber preform, the ends of the plurality of unit optical fiber preforms can be welded together when butting and connecting the ends of the unit optical fiber preforms.

Another aspect of the present invention provides an optical fiber manufacturing method for obtaining an optical fiber by drawing an optical fiber preform obtained by the above-described method for manufacturing an optical fiber preform.

In the method for manufacturing an optical fiber, the portion of the optical fiber derived from the joint between the unit optical fiber preforms can be cut from the portion of the optical fiber other than the portion derived from the joint.

According to one aspect of the present invention, there are provided a method for manufacturing a multi-core fiber preform and a method for manufacturing a multi-core fiber, in which the shape accuracy of the preform is good and productivity can be improved.

It is a sectional view explaining a perforation process of a manufacturing method of an embodiment. It is a sectional view explaining a rod insertion process. It is sectional drawing explaining a dummy pipe|tube connection process. It is sectional drawing explaining a 1st sealing process. It is a sectional view explaining a dummy rod connection process. It is a sectional view explaining a decompression process. It is sectional drawing explaining a 2nd sealing process. It is sectional drawing explaining a base material connection process. It is sectional drawing explaining a base material connection process. It is a sectional view explaining a dummy rod separation process. It is a sectional view explaining a dummy rod separation process. It is a sectional view showing an example of an optical fiber preform. It is a block diagram which shows an example of a wire-drawing apparatus. It is a block diagram which shows the 1st modification of a 2nd end sealing part. It is a block diagram which shows the 2nd modification of a 2nd end sealing part. 1 is a cross-sectional view of a multi-core optical fiber that is an example of an optical fiber obtained by a manufacturing method according to an embodiment; FIG. 1 is a cross-sectional view of a single-core optical fiber, which is an example of an optical fiber obtained by a manufacturing method according to an embodiment; FIG.

Hereinafter, a method for manufacturing an optical fiber preform and a method for manufacturing an optical fiber according to embodiments of the present invention will be described with reference to the drawings.

[Method for producing optical fiber preform]
A method for manufacturing an optical fiber preform according to an embodiment will be described with reference to FIGS. 1 to 11. FIG. Note that in the drawings used for the following description, the scale may be changed in order to make the members recognizable in size.

The manufacturing method of the embodiment has a base material preparation step and a base material connection step.
The base material preparation process includes (1) a hole opening process, (2) a cleaning process, (3) a dummy pipe connection process, (4) a rod insertion process, (5) a first sealing process, and (6) a dummy rod connection process. , (7) a decompression step, and (8) a second sealing step. The base material connection step includes (9) base material connection step and (10) dummy rod separation step.
Each step will be described below. 1 to 11 are cross-sectional views explaining each step.

(1) Drilling Step As shown in FIG. 1, the clad glass body 11 is formed in a cylindrical shape. The clad glass body 11 is, for example, an integrally molded product made of quartz glass. A plurality of through holes 12 are formed in the clad glass body 11 using a drill tool or the like. A through hole 12 is formed through the clad glass body 11 parallel to its central axis. Both ends of the through-hole 12 are opened to end faces of the clad glass body 11 in the axial direction. The through-holes 12 are formed at a plurality of locations at intervals in the axial direction so as to surround the central portion of the clad glass body 11, for example.

(2) Cleaning process Since the cutting fluid used for drilling, metal powder derived from the drill tool, and the like may remain in the through-hole 12, a cleaning fluid such as pure water, alcohol (ethanol), or alkaline solution is used. is used to clean the outer surface of the clad glass body 11 and the inner surface of the through-hole 12 .

In the cleaning step, the inner surface of the through-hole 12 can also be processed by etching. By etching, for example, foreign matter (such as the metal powder) attached to the microcracks on the inner surface of the through hole 12 can be removed. The etching may be wet etching or dry etching. In wet etching, an etchant containing hydrofluoric acid, such as BHF (buffered hydrofluoric acid), which is a mixture of hydrofluoric acid and ammonium fluoride, can be used. In dry etching, a fluorinated gas such as SF ₆ (sulfur hexafluoride) gas or C ₂ F ₆ (hexafluoride ethane) gas can be used as an etching gas. In dry etching, an etching gas is introduced into the through holes 12 while heating the clad glass body 11 to 1200° C. or higher.

(3) Rod Inserting Step As shown in FIG. 2 , glass rods 14 serving as cores (hereinafter also referred to as core glass rods) are inserted into each of the plurality of through holes 12 of the clad glass body 11 . As a result, a glass material unit U<b>1 having a configuration in which a core glass rod 14 is inserted into each of the plurality of through holes 12 of the clad glass body 11 is obtained.

It is preferable to wash the core glass rod 14 in advance using a washing liquid such as water, alcohol, or alkaline liquid. The core glass rod 14 may be etched to remove dirt from the surface.
The rod insertion step is preferably performed in a room with a high degree of cleanliness. As a result, it is possible to prevent dust, dirt, etc., from adhering to the core glass rod 14, which causes deterioration in transmission loss.

In the rod insertion step, a core identification marker glass rod (not shown) may be inserted into one or more of the plurality of through holes 12 of the clad glass body 11 instead of the core glass rod 14 . . The core identification marker glass rod is, for example, a glass rod having a different refractive index from both the clad glass body 11 and the core glass rod 14 . The insertion of the core identification marker glass rod into the through-hole 12 can be performed in the same manner as the insertion of the core glass rod 14 into the through-hole 12 . Hereinafter, the core glass rod 14 and the core identification marker glass rod may be collectively referred to as an "insertion glass rod".

For the inserted glass rod, for example, one whose outer diameter is 80 to 99% of the inner diameter of the through-hole 12 can be preferably used. In order to ensure stable core position accuracy in the optical fiber 2 obtained by drawing, the outer diameter of the inserted glass rod is more preferably 90 to 99% of the inner diameter of the through hole 12, and more preferably 95 to 99%. is more preferred.

(4) Dummy Tube Connection Step As shown in FIG. 3, dummy tubes 13 are connected to both ends of the glass material unit U1 by welding or the like. The dummy tube 13 is, for example, a cylindrical member made of quartz glass. The dummy tube 13 is connected to the clad glass body 11 so that one axial end face of the dummy tube 13 abuts against one axial end face of the clad glass body 11 . The dummy tube 13 has an inner diameter that does not close the opening of the through hole 12 when it is welded to the clad glass body 11 .

When the dummy tube 13 is welded to the glass material unit U1, the clad glass body 11 and the core glass rod 14 may be integrated at the heating point. During welding, it is preferable to adjust the heating range so that the integrated portion of the clad glass body 11 and the core glass rod 14 is as long as possible. As a result, cracks are less likely to occur in the preform (optical fiber preform 1A shown in FIG. 8) in the preform connecting step, which will be described later.

In this embodiment, the dummy pipes 13 are connected to both ends of the glass material unit U1, but the dummy pipes may be connected to one end of the glass material unit and the dummy rods may be connected to the other end. In that case, in the second sealing step, the inside of the through-hole of the glass material unit can be depressurized through, for example, a dummy tube.

(5) First sealing step As shown in FIG. 4, one end of the glass material unit U1 (hereinafter referred to as the first end; the right end in FIG. 4) is connected to a flame 16 (eg, an oxyhydrogen flame). ) or the like to reduce the diameter and close all the openings of the through-holes 12 (that is, to airtightly seal). As a result, the dummy tube 13 on the first end side of the glass material unit U1 is separated from the glass material unit U1 by fusing. Note that the means for heating the glass material unit U1 is not limited to the flame 16, and an electric furnace or the like may be used.

A first end portion of the glass unit U<b>1 with the opening of the through hole 12 hermetically sealed is referred to as a first end sealing portion 17 . The first end sealing portion 17 is solidified by heating the first end of the clad glass body 11 together with the first end of the core glass rod 14 to reduce the diameter. The first end sealing portion 17 is formed, for example, in a tapered shape (for example, conical shape).

When the core identification marker glass rod is inserted into one or more of the through-holes 12 of the clad glass body 11, the first end sealing portion 17 seals the first end of the clad glass body 11 with the core glass. Together with the first end portion of the rod 14 and the first end portion of the glass rod for the core identification marker, the diameter is reduced by heating to form a solid configuration.
In the first sealing step, the glass material unit U1 is held at a predetermined position by gripping the dummy tube 13 with the chuck 20 .

(6) Dummy Rod Connecting Step As shown in FIG. 5, the end of the dummy rod 15 is welded and integrated with the first end sealing portion 17 of the glass material unit U1. The dummy rod 15 is made of quartz glass, for example. The dummy rod 15 has a solid structure and is formed in a cylindrical shape. The dummy rod 15 closes (that is, airtightly seals) the opening of the through hole 12 at the first end of the clad glass body 11 . The dummy rod 15 is abutted against the end face of the first end of the glass material unit U1, aligned coaxially with the glass material unit U1, and welded and integrated. The dummy rod 15 has an outer diameter that can close all the openings of the through holes 12 when welded to the glass material unit U1.

In the second sealing step, which will be described later, the glass material unit U1 can be held by gripping the dummy rod 15 with the chuck 20 . Therefore, damage to the glass material unit U1 can be suppressed. Moreover, since the dummy rod 15 can ensure a long distance between the chuck 20 and the heating portion, it is possible to prevent the chuck 20 from burning.
Note that the dummy rod 15 may not be used. In that case, the chuck 20 grips the glass material unit U1 in the second sealing step, which will be described later.

(7) Depressurization step As shown in FIG. 6, a vacuum pump 22 is connected to the open end of the dummy tube 13 on the side opposite to the clad glass body 11 via a connector 21, and the vacuum pump 22 depressurizes the inside of the through hole 12. is decompressed (evacuated). In the decompression step, the inside of all the through holes 12 of the clad glass body 11 is evacuated via the inner space of the dummy tube 13 .

At this time, the glass material unit U1 may be heated to a temperature at which the clad glass body 11 and the core glass rod 14 are not integrated. As a result, the gas inside the through-hole 12 expands, so that the degree of vacuum inside the through-hole 12 can be increased when the temperature of the glass material unit U1 drops. Therefore, it is possible to suppress the generation of voids (bubbles) in the optical fiber 2 (see FIG. 13).

In the depressurizing step, after decompressing the inside of the through-hole 12 , helium gas may be introduced into the through-hole 12 and then the interior of the through-hole 12 may be decompressed. Even if the helium gas remains in the through-hole 12, it can easily escape from the clad glass body 11. Therefore, this method makes it difficult for voids (bubbles) to occur in the optical fiber 2 (see FIG. 13).
Although the connector 21 is attached to the dummy tube 13 in this embodiment, the connector may be attached directly to the glass material unit. In this case, the inside of the through hole can be decompressed (evacuated) without passing through the dummy pipe.

(8) Second sealing step As shown in FIG. 7, the end opposite to the first end of the glass material unit U1 (hereinafter referred to as the second end; the left end in FIG. 7) is exposed to the flame. 16 or the like is used to heat and reduce the diameter to close all the openings of the through-holes 12 (that is, to hermetically seal them). The second end portion of the glass unit U<b>1 with the opening of the through hole 12 hermetically sealed is also called a second end sealing portion 19 . The second end of the clad glass body 11 and the second end of the core glass rod 14 are heat-reduced in a portion including the tip of the second end sealing portion 19 to be solidified. The second end of the glass material unit U1 is sealed while the inside of the through hole 12 is under negative pressure (negative pressure relative to the atmospheric pressure). The second end sealing portion 19 is formed, for example, in a tapered shape (for example, conical shape).

In the second sealing step, it is preferable to form the second end sealing portion 19 in a state in which the pressure inside the through hole 12 is reduced by about 100 kPa from the atmospheric pressure. The internal pressure of the through-hole 12 after forming the second end sealing portion 19 is preferably 1 kPa or less.
In addition, in the second sealing step, it is sufficient that the inside of the through-hole 12 is maintained in a decompressed state. In the second sealing step, the vacuum pump 22 may be operated following the decompression step to continue decompressing the inside of the through hole 12, or the vacuum pump 22 may be stopped.

An optical fiber preform 1A (unit optical fiber preform) is obtained by the second sealing step. The optical fiber preform 1A includes a glass material unit U1 and dummy rods 15 connected to the glass material unit U1. An inner hole 18 is formed inside the clad glass body 11 of the optical fiber preform 1A. The inner hole 18 is a hole formed by sealing the first end side of the through hole 12 with the first end sealing portion 17 and sealing the second end side with the dummy rod 15 . The internal pressure of the inner hole 18 is equivalent to the pressure of the through hole 12 before the second end seal 19 is formed.

FIG. 12 is a cross-sectional view showing an example of the optical fiber preform 1A. The optical fiber preform 1A shown in FIG. 12 has four inner holes 18, and these inner holes 18 are arranged around the central axis of the clad glass body 11 at equal intervals.

As shown in FIG. 7, in the second sealing step, the second end sealing portion 19 is formed in a state where the inside of the through hole 12 is reduced in pressure by about 100 kPa from the atmospheric pressure, and the inner hole 18 with an internal pressure of 1 kPa or less is secured. is not limited to
The internal pressure of the inner hole 18 may be set so as to maintain a negative pressure from the start to the end of the wire drawing process, and may be, for example, more than 1 kPa to 20 kPa.
However, when the degree of vacuum of the inner hole 18 formed in the second sealing step is low (for example, the inner pressure of the inner hole 18 is more than 1 kPa to 20 kPa), the inner pressure of the inner hole 18 is 1 kPa or less. It becomes susceptible to the temperature of the glass body 11 . Therefore, the vacuum pressure applied to the through hole 12 by the vacuum pump 22 reduces the volume of the inner hole 18 as the drawing process progresses, and also reduces the temperature of the constituent members (cladding glass body 11, etc.) of the coupling optical fiber preform 1B. Considering fluctuations in the internal pressure of the inner hole 18 due to the change, it is preferable to set the inside of the inner hole 18 so that the state of negative pressure can be stably maintained during the wire drawing process.

In the second sealing step, for example, the inner hole 18 having an inner pressure of 20 kPa or less can be formed, and the inner pressure of the inner hole 18 can be reduced to a negative pressure in the wire drawing step. If the internal pressure of the inner hole 18 of the coupling optical fiber preform 1B before the start of drawing is 20 kPa or less, a sufficient length of optical fiber can be drawn while maintaining the negative pressure of the inner hole 18 in the drawing process. It is possible. The internal pressure of the inner hole 18 is, for example, 20 kPa or less, but may be 10 kPa or less, or 1 kPa or less.

An optical fiber preform 1A (see FIG. 7) is further produced according to the hole-opening step to the second sealing step shown in FIGS. Thereby, two or more optical fiber preforms 1A are obtained (see FIG. 8).

(9) Preform Connecting Step As shown in FIG. 8, the second end sealing portions 19, 19 of the two optical fiber preforms 1A, 1A face each other.
Next, as shown in FIG. 9, the second end sealing portions 19, 19 of both the optical fiber preforms 1A, 1A are heated using a flame 16 or the like to weld them together. As a result, the two optical fiber preforms 1A, 1A are butt-connected at the connecting portion 23. As shown in FIG.
By connecting the second end sealing portions 19, 19 by welding, the two optical fiber preforms 1A, 1A can be connected without any intervening material. Therefore, in the drawing process to be described later, the optical fiber preforms 1A, 1A in the portion including the connecting portion 23 can be drawn smoothly.

The connection portion 23 may have a larger diameter or a smaller diameter than the optical fiber preform 1A, but it is desirable that the difference in outer diameter between the connection portion 23 and the optical fiber preform 1A is small. If this difference in outer diameter is small, fluctuations in the outer diameter of the optical fiber 2 can be reduced in the drawing process, which will be described later.

(10) Dummy Rod Separating Step Next, as shown in FIGS. or the like. The fused first end is airtightly sealed by closing all the openings of the through holes 12 . A first end portion where the opening of the through hole 12 is closed is called a front end sealing portion 24 .
In this way, an optical fiber preform (multi-core fiber preform, hereinafter referred to as a concatenated optical fiber preform 1B) in which a plurality of glass material units U1 are connected is obtained.

It is desirable that the two optical fiber preforms 1A, 1A to be connected have the same configuration. The configuration here is represented by numerical values such as the outer diameter of the clad glass body 11, the porosity of the inner holes 18, the number of the inner holes 18, the arrangement of the inner holes 18, the distance between the inner holes 18, and the like. Among them, the outer diameter of the clad glass body 11 and the porosity of the inner hole 18 are particularly important because they greatly affect the outer diameter of the optical fiber 2 . If the difference between the numerical values of the two optical fiber preforms 1A, 1A is within ±10% of one numerical value, the two numerical values may be regarded as the same.

If the two optical fiber preforms 1A, 1A to be connected have the same configuration, in the drawing process, the optical fiber 2 obtained from one optical fiber preform 1A and the light obtained from the other optical fiber preform 1A It is easy to make the outer diameter of the fiber 2 the same. Therefore, adjustment of the diameter of the optical fiber 2 is facilitated.

In the manufacturing method of the present embodiment, the connected optical fiber preform 1B is produced by connecting two glass material units U1. may be any number of

[Method for manufacturing optical fiber]
The drawing process of the optical fiber manufacturing method according to the embodiment will be described with reference to FIG.
FIG. 13 is a configuration diagram showing a drawing device 50 for manufacturing an optical fiber 2 (multi-core fiber) by drawing from a connecting optical fiber preform 1B.
As shown in FIG. 13, the wire drawing device 50 includes a preform elevating device 51 that suspends the coupling optical fiber preform 1B, and a lower end portion (tip end) of the coupling optical fiber preform 1B that is suspended by the preform elevating device 51. part) and a ring-shaped heating furnace 52 for heating. The base material lifting device 51 has a lifting frame 51a and a lifting device body 51b for lifting and lowering the lifting frame 51a. The lifting frame 51a is arranged above the heating furnace 52 and is lifted and lowered by a lifting device main body 51b.

The connecting optical fiber preform 1B is suspended from the lifting frame 51a by attaching the protruding end of the dummy rod 15 to the lifting frame 51a so that the tip sealing portion 24 becomes the lower end. The front end sealing portion 24 at the lower end of the coupling optical fiber preform 1B suspended from the lifting frame 51a is inserted into the inner through hole 52a (preform insertion hole) of the ring-shaped heating furnace 52. As shown in FIG.

The optical fiber 2 is drawn downward from the lower end of the connecting optical fiber preform 1B while the lower end of the connecting optical fiber preform 1B is heated by the heating furnace 52 to keep the glass viscosity lowered (softened). The drawing of the optical fiber 2 from the lower end of the connecting optical fiber preform 1B is continued while the connecting optical fiber preform 1B is fed into the heating furnace 52 (specifically, its inner through-hole 52a) by lowering the elevating frame 51a.

The lower end of the connecting optical fiber preform 1B is heated to a temperature (heating temperature for drawing) at which the glass viscosity is reduced (softened) to a level at which the optical fiber 2 can be drawn, whereby the viscosity of the glass decreases and the connecting optical fiber preform is softened. Shrinkage of the glass material forming the material 1B occurs, and the clad glass body 11 having a reduced diameter is integrated with the core glass rod 14 .
When there is a core identification marker glass rod inserted into the through-hole 12, the clad glass body 11 is not only the core glass rod 14 but also the core identification marker at the lower end of the heated coupling optical fiber preform 1B. It is also integrated with the glass rod.

The integration of the clad glass body 11 with the inserted glass rod progresses as the connecting optical fiber preform 1B is fed into the heating furnace 52 by lowering the elevating frame 51a. That is, the drawing of the optical fiber 2 from the coupling optical fiber preform 1B is performed while the clad glass body 11 is integrated with the inserted glass rod as the coupling optical fiber preform 1B is fed into the heating furnace 52. .

The inserted glass rod and the clad glass body 11 heated to the drawing heating temperature are softened and the surface tension is lowered as compared with the normal temperature. The clad glass body 11 that has been heated to the heating temperature during wire drawing becomes susceptible to the internal pressure of the inner hole 18 .
When the lower end of the coupling optical fiber preform 1B is heated to the heating temperature for drawing, the clad glass body 11 is affected not only by its own contraction but also by the internal pressure (negative pressure) of the inner hole 18, and the through hole 12 is deformed. An overall diameter reduction with diameter reduction is produced and integrated into the inserted glass rod. Therefore, in the step (drawing step) of drawing the optical fiber 2 from the lower end (tip) of the coupling optical fiber preform 1B, the clad glass body 11 and the inserted glass rod are integrally formed by the inner hole 18 having a negative internal pressure. efficient conversion.

The integration of the clad glass body 11 and the insertion glass rod is achieved by the fact that the space between the inner surface of the inner hole 18 of the clad glass body 11 and the insertion glass rod is crushed as the coupling optical fiber preform 1B is fed into the heating furnace 52. proceed while This reduces the volume of the inner bore 18 .

The optical fiber 2 drawn from the connection portion 23 of the coupling optical fiber preform 1B may not have a stable shape compared to the optical fiber 2 obtained from other portions of the coupling optical fiber preform 1B. In this case, after manufacturing the optical fiber 2 , the above problem can be solved by cutting the portion of the optical fiber 2 derived from the connection portion 23 from the portion of the optical fiber 2 other than the portion derived from the connection portion 23 .

The optical fiber 2 may be drawn until it reaches the end of the connecting optical fiber preform 1B on the side of the dummy rod 15 (one end; hereinafter also referred to as the base end), or the base end may be used for drawing. May be stopped before being used. If the base end of the coupling optical fiber preform 1B is deformed due to welding with the dummy rod 15, the effect of the deformation can be avoided by stopping the drawing of the optical fiber 2 before reaching the base end.

The internal pressure of the inner hole 18 of the connecting optical fiber preform 1B before the start of the drawing is ensured to be a negative pressure when the drawing of the optical fiber 2 is completed. As a result, the internal pressure of the inner hole 18 of the connecting optical fiber preform 1B can be maintained at a negative pressure from the start of drawing of the optical fiber 2 to the completion thereof. In the second sealing step in manufacturing the connecting optical fiber preform 1B, the through hole 12 of the clad glass body 11 is evacuated by a vacuum pump so that a negative pressure is ensured in the inner hole 18 when the drawing of the optical fiber 2 is completed. while forming the inner hole 18 .
The internal pressure of the inner hole 18 of the coupling optical fiber preform 1B before the start of drawing may be determined to be a negative pressure immediately before the completion of the drawing of the optical fiber 2. FIG.

[Effects of the method for manufacturing an optical fiber preform and the method for manufacturing an optical fiber according to the embodiment]
According to the manufacturing method of the present embodiment, a connected optical fiber preform in which a plurality of glass material units U1 are connected through a preform connecting step (see FIGS. 8 and 9) and a dummy rod separating step (see FIGS. 10 and 11). Material 1B is obtained. Since the connecting optical fiber preform 1B includes a plurality of glass material units U1, a long effective length of the preform that can be drawn in the drawing process can be ensured. Therefore, productivity of the optical fiber 2 can be improved.
On the other hand, when a plurality of glass material units are individually drawn, for each glass material unit, the diameter of the optical fiber should be adjusted at the start of drawing, and the base material left undrawn to stabilize the optical fiber diameter. As required, the total effective length of the glazing unit is reduced.

According to the manufacturing method of the present embodiment, since the internal pressure of the inner hole 18 of the coupling optical fiber preform 1B becomes a negative pressure, the space between the inner surface of the inner hole 18 and the insertion glass rod disappears in the drawing process. An optical fiber 2 in which voids (bubbles) are suppressed is obtained. Therefore, there is no need for a vacuum pump for evacuating the inner hole 18 in the wire drawing process. Since a connector for connecting a vacuum pump to the coupling optical fiber base material 1B is not required, it is not necessary to secure a distance between the base material and the connector, and a long effective length of the base material that can be drawn can be secured. Therefore, productivity of the optical fiber 2 can be improved.

According to the manufacturing method of the present embodiment, wire drawing can be performed while integrating the clad glass body 11 and the inserted glass rod. Since there is no need to completely integrate the clad glass body 11 and the inserted glass rod prior to the wire drawing process, the number of processes can be reduced. Therefore, the manufacturing method of this embodiment is excellent in terms of productivity of the optical fiber 2 and ease of manufacture.

The glass material unit U1, which is a component of the connecting optical fiber preform 1B, is shorter than a non-connecting optical fiber preform (for example, an optical fiber preform integrally formed over the entire length). Since the glass material unit U1 is short, the shape (for example, the formation position of the through hole, etc.) is less likely to change in the length direction. Therefore, the glass material unit U1 has high shape accuracy (for example, the accuracy of the formation position of the through holes, the distance between the cores, etc.) in the main portions other than the sealing portion, the connection portion, and the like. Therefore, the connected optical fiber preform 1B, in which a plurality of glass material units U1 are connected, is superior in shape accuracy in the main part to non-connected optical fiber preforms.

According to the manufacturing method of the present embodiment, since the connecting optical fiber preform 1B is used, compared with the case where a plurality of short optical fiber preforms are independently drawn, the step of adjusting the diameter of the optical fiber at the start of drawing is reduced. can be reduced in number. For example, when two optical fiber preforms are drawn by one drawing apparatus, part of the preform is consumed to adjust the diameter of the optical fiber at the start of drawing of the first preform, and Part of the preform is also consumed to adjust the diameter of the optical fiber when starting to draw the material. The optical fiber generated in the process of adjusting the diameter of the optical fiber is discarded.
On the other hand, according to the manufacturing method of the present embodiment, the connecting optical fiber preform 1B having a structure in which two glass material units U1 are connected can be used, so that the drawing process can be performed continuously. Therefore, the diameter of the optical fiber needs to be adjusted only once at the beginning. Therefore, the manufacturing method of the present embodiment can reduce the amount of discarded optical fibers 2 compared to the case where a plurality of short optical fiber preforms are drawn independently, so that a long effective length of the preform that can be drawn can be ensured. Therefore, productivity of the optical fiber 2 can be improved.

As shown in FIG. 8, the end portion of the second end sealing portion 19 of the optical fiber preform 1A to be butt-connected in the preform connecting step tapers toward the distal end side, that is, a tapered shape ( For example, it has a conical shape). The second end sealing portion 19 has a shape in which the protruding height increases toward the center of the optical fiber preform 1A. Therefore, when the second end sealing portions 19 are welded together in the base material connecting step, the central portions of the second end sealing portions 19 first come into contact with each other, and the contact range gradually expands outward. To go. Therefore, even if there is gas between the second end seals 19, this gas is pushed outward and removed. Therefore, compared with the case where the second end sealing portion is flat, a gap is less likely to occur at the connection portion between the two optical fiber preforms 1A that are butt-connected.

In this embodiment, both of the second end sealing portions 19 of the two optical fiber preforms 1A have the shape shown in FIG. If at least one of the two second end sealing portions has the shape shown in FIG. 8, the above-mentioned effect (a gap is unlikely to occur in the connecting portion) can be obtained.
Incidentally, the number of connections of the optical fiber preform is not limited to two, and may be any number of three or more. When the number of connections of the optical fiber preforms is 3 or more, at least one optical fiber preform has not only the second end sealing portion but also the first end sealing portion connected to the sealing portion of the other optical fiber preforms. Butt connected. A seal having the shape shown in FIG. 8 can also be applied to the first end seal.

FIG. 14 is a configuration diagram showing a second end sealing portion 29 which is a first modification of the second end sealing portion 19 of the optical fiber preform 1A. The second end sealing portion 29 is formed at the second end of the glass material unit U1 of the optical fiber preform 21A. The entire surface of the second end sealing portion 29 is formed in a curved convex shape (for example, hemispherical shape). The second end sealing portion 29 is formed to protrude in the distal direction.

Since the second end sealing portion 29 has a curved convex shape, the tip portion of the second end sealing portion of the mating optical fiber preform (hereinafter referred to as the mating second end sealing portion) in the preform connecting step Even if the position of is shifted from the center, it is easy to secure contact with the tip. Therefore, in the base material connecting step, the tip portion of the second end sealing portion 29 comes into contact with the tip portion of the mating second end sealing portion, and the contact range gradually expands outward. Therefore, even if there is gas between the second end sealing portion 29 and the mating second end sealing portion, the gas is pushed outward and removed. Therefore, voids are less likely to occur in the connecting portion.

Two optical fiber preforms to be butt-connected have at least one sealing portion (first end sealing portion or second end sealing portion) having a curved convex second end sealing portion 29 shown in FIG. If the shape is similar to , the above-mentioned effect (difficult to generate voids in the connecting portion) can be obtained.

FIG. 15 is a configuration diagram showing a second end sealing portion 39 that is a second modification of the second end sealing portion 19. As shown in FIG. The second end seal 39 has a base 39a and a tip 39b. The base portion 39a is formed in a truncated cone shape whose diameter is reduced in the distal direction. The tip portion 39b is formed so as to be smoothly connected to the base portion 39a. The tip portion 39b is formed in a curved convex shape (for example, a spherical shape). The second end sealing portion 39 is formed to protrude in the distal direction.

Since the tip portion 39b of the second end sealing portion 39 has a curved convex shape, even if the tip portion of the mating second end sealing portion is displaced from the center in the step of connecting the base materials, easy to ensure contact. Therefore, voids are less likely to occur in the connecting portion.

At least one sealing portion (first end sealing portion or second end sealing portion) of the two optical fiber preforms to be butt-connected has the same shape as the second end sealing portion 39 shown in FIG. If so, the above-described effect (difficulty in forming voids in the connecting portion) can be obtained.

Although the present invention has been described above based on the best mode, the present invention is not limited to the above-described best mode, and various modifications are possible without departing from the gist of the present invention. In the manufacturing method of the above embodiment, the inner hole pressure is reduced using a pump, but the inner hole pressure can also be reduced without using the pump. For example, in order to manufacture a multi-core fiber preform having decompressed inner holes, the depressurizing step is omitted, and the inner holes are removed as the optical fiber preform heated in the second sealing step cools after the completion of sealing. The internal pressure may be lowered.
The order of steps is not limited to the order of steps in the embodiment described above. For example, the rod insertion step may be performed before completing the second sealing step. Specifically, the rod insertion step may be performed after the dummy pipe connection step and before the first sealing step. The rod insertion step may be after the first sealing step and before the second sealing step.

The manufacturing method of the embodiment may be applied to the stack-and-draw method. A manufacturing method to which the stack-and-draw method is applied has a base material preparation process and a base material connection process.
In the base material preparation step, one or more core covering rods are inserted into the through-holes of the glass tube (cladding glass body) (rod insertion step). A core-coated rod is a rod in which a core glass rod is coated with a clad glass layer. One or more glass rods are inserted into the gap between the glass tube and the core covering rod. Next, the first end portion of the glass tube is heated and deformed to form a first end sealing portion that closes the opening of the through hole (first sealing step). Next, while the pressure inside the through-hole is maintained, the second end of the glass tube is heated and deformed to form a second end sealing portion that closes the opening of the through-hole (second sealing). process). Thereby, a unit optical fiber preform is obtained. A plurality of unit optical fiber preforms are produced.
In the preform connecting step, end portions of a plurality of unit optical fiber preforms are butt-connected to obtain a connected optical fiber preform.

The connection form of the optical fiber preform includes (i) connection between the first end seals, (ii) connection between the first end seals and the second end seals, and (iii) second end seals. There is a connection between the seals.

In the production method of the embodiment, the multi-core fiber preform is produced, but the optical fiber preform produced by the production method of the embodiment is not limited to the multi-core fiber preform, and may be a single-core optical fiber preform. . When producing a single-core optical fiber preform, in the rod insertion step, a clad glass body having one through hole is used, and one glass rod is inserted into the through hole.

FIG. 16 is a cross-sectional view of a multi-core optical fiber 2A, which is an example of the optical fiber 2 obtained by the manufacturing method of the embodiment. The optical fiber 2A has a plurality of cores 31 and a clad 32 provided on the outer periphery thereof.
FIG. 17 is a cross-sectional view of a single-core optical fiber 2B, which is another example of the optical fiber 2 obtained by the manufacturing method of the embodiment. The optical fiber 2B has one core 33 and a clad 34 provided on its outer circumference.

1A... Optical fiber preform (unit optical fiber preform) 1B... Connection optical fiber preform (multi-core fiber preform) 2... Optical fiber (multi-core fiber) 11... Clad glass body 12... Through hole 13... Dummy tube 14 Glass rod (core glass rod) 15 Dummy rod 16 Flame 17 First end sealing portion 18 Inner hole 19 Second end sealing portion 22 Vacuum pump , 23... Connecting part, 24... Tip sealing part, 50... Wire drawing device.

Claims (8)

a preform manufacturing step of manufacturing a plurality of unit optical fiber preforms; and a preform connecting step of connecting the plurality of unit optical fiber preforms,
The base material preparation step includes:
a rod inserting step of inserting a glass rod serving as a core into a through hole penetrating a clad glass body serving as a clad of an optical fiber;
a first sealing step of heating and deforming the first end of the clad glass body to form a first end sealing portion that closes the opening of the through hole that opens to the first end;
While the pressure inside the through hole is maintained, the second end of the clad glass body, which is the end opposite to the first end, is heated and deformed to form the second end. a second sealing step of forming a second end sealing portion that closes the opening of the open through hole,
In the optical fiber preform manufacturing method, the preform connecting step obtains a connected optical fiber preform by butting and connecting the ends of the plurality of unit optical fiber preforms. 2. The method of manufacturing an optical fiber preform according to claim 1, wherein said first end sealing portion and an end portion of a dummy rod are connected after said first sealing step and before said second sealing step. 3. The method of manufacturing an optical fiber preform according to claim 1, wherein said plurality of unit optical fiber preforms have the same configuration. 4. Any one of claims 1 to 3, wherein said second end sealing portion of at least one of said unit optical fiber preforms is formed in such a shape that the height of the projection increases toward the center of said unit optical fiber preform. 2. A method for manufacturing an optical fiber preform according to item 1. 5. The optical fiber according to any one of claims 1 to 4, wherein the second end sealing portion of at least one of the unit optical fiber preforms is formed so that at least a tip portion thereof has a curved convex shape. A manufacturing method of the base material. 6. The method for manufacturing an optical fiber preform according to claim 1, wherein the end portions are welded together when the end portions of the plurality of unit optical fiber preforms are butt-connected. An optical fiber manufacturing method, wherein an optical fiber is obtained by drawing an optical fiber preform obtained by the optical fiber preform manufacturing method according to any one of claims 1 to 6. 8. The method of manufacturing an optical fiber according to claim 7, wherein the portion of the optical fiber derived from the connecting portion between the unit optical fiber preforms is cut from the portion of the optical fiber other than the portion derived from the connecting portion.

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