JP5728375B2 - Manufacturing method of optical fiber preform to which dummy rod is connected, and manufacturing method of dummy rod - Google Patents

Description

 In the production of an optical fiber preform, the optical fiber preform and the dummy rod, or the ends of the dummy rods are heated and melted, and both of them are welded and connected, whereby the optical fiber preform to which the dummy rod is connected. The present invention relates to a method of manufacturing a material or a dummy bar.

 An optical fiber is manufactured by drawing an optical fiber preform. The optical fiber preform is manufactured by first producing a deposit made of silicon oxide fine particles by the VAD method, the CVD method or the like, and dehydrating and sintering the deposit to form a transparent glass. In addition, after the optical fiber preform is manufactured, a drawing process may be performed. If necessary, the optical fiber preform is cut into a plurality of parts for convenience of processing, and the cut optical fiber preform is rotated around the axis. Then, after the external step of depositing silicon oxide fine particles, dehydration and sintering may be performed to obtain a larger optical fiber preform.

 In manufacturing the optical fiber, a dummy rod is used for supporting the optical fiber preform. A dummy rod (usually a quartz glass rod) must be connected to the optical fiber preform. For example, in the external attachment step, a dummy bar is connected to both ends of the optical fiber preform, the dummy rod is held on a glass lathe by a chuck, and at least one deposition burner is rotated while the optical fiber preform is rotated. The silicon oxide fine particles are deposited while traversing (reciprocating) in the direction of the axis (arrow). The dehydration and sintering processes are also performed by connecting dummy bars to both ends of the optical fiber preform. In some cases, a dummy bar is connected to only one end of the optical fiber preform. In some cases, the dummy rod is held by a glass lathe with a chuck and the optical fiber preform is processed. Furthermore, after that, the bending of the optical fiber preform is corrected using a glass lathe, the heat drawing process to a predetermined outer diameter and length, the removal of irregularities and scratches on the surface of the optical fiber preform, impurities, etc. There are cases where processing such as flame polishing is performed. In order to connect the dummy rod and the optical fiber preform, the end portions of both are heated and melted, and then the end portions are pressed to perform fusion.

 In recent years, with an increase in the size of an optical fiber preform due to demands for increasing the efficiency of optical fiber production, the diameter of the optical fiber preform and the diameter of a dummy rod connected thereto tend to increase. As the diameter increases, the degree of heat transfer becomes uneven. Therefore, when the ends of the optical fiber preform 30 and the dummy rod 31 are heated with the heating oxyhydrogen burner 33 when both ends are heated, the center portion and the peripheral portion of the connection end face are heat sources. The degree of heat transfer from the oxyhydrogen burner 33 is different, and a situation occurs in which the peripheral portion is heated more than the central portion of the connection end face (see FIG. 3A).

 Therefore, the peripheral edge of the optical fiber preform 30 begins to soften faster than the central portion, and the peripheral portion rises in an annular shape due to surface tension, and can be dented in the central portion of the preform (see FIG. 3B). The bulge at the peripheral edge may be as high as about 1 mm with respect to the dent at the center. At the time of connection, air is trapped in the dent, and the connection between the optical fiber preform 30 and the dummy rod 31 is connected. The phenomenon of remaining as bubbles 34 occurred in (see FIG. 3C). Then, starting from the bubble 34, there is a problem that a defect such as a crack or a crack occurs in the connection portion between the optical fiber preform 30 and the dummy rod 31, and the optical fiber preform 30 may fall and be damaged. .

 In order to solve the problems caused by residual bubbles in the connection part, when welding the optical fiber preform and the dummy rod, the connection end is machine-molded into a convex shape, then heated and melted to connect the two Is disclosed (for example, see Patent Document 1).

 In addition, a method is disclosed in which the distance between the end face of the optical fiber preform and the dummy rod is controlled during heating and melting, and the peripheral portion is prevented from rising in an annular shape (for example, see Patent Document 2).

JP 2000-327358 A JP 2005-14596 A

 However, the method described in Patent Document 1 has a problem that it takes a long time to process the connection end portion into a convex shape as the optical fiber preform becomes larger.

 Further, in the method described in Patent Document 2, when the optical fiber preform is enlarged only by controlling the distance between the optical fiber preform and the end face of the dummy rod, the temperature difference between the peripheral edge portion and the central portion of the connection end face is increased. Cannot be made small, and it is difficult to prevent the formation of bubbles in the connection portion due to the annular bulge of the peripheral edge portion of the connection end surface.

 The present invention has been made in view of the above circumstances, and does not require a great deal of time to process the connecting end portion into a convex shape, and no bubbles are formed in the connecting portion. It is an object of the present invention to provide a method for manufacturing an optical fiber preform to which a dummy rod is connected and a method for manufacturing a dummy rod, in which a defect such as a crack or a crack does not occur in a connection portion.

The first aspect of the present invention is a method of manufacturing an optical fiber preform to which a dummy bar is connected,
In the step of connecting the dummy rod and the optical fiber preform coaxially by melting the opposite ends with heat,
The angle θ formed by the plane perpendicular to the central axis of either the dummy rod or the optical fiber preform and the cross-section after cutting at either end satisfies the following condition: 0 <tan θ Cutting one of the ends, and
Melting the dummy rod and the end portions of the optical fiber preform, which include the cut section, by heat; and
A process of abutting and fusing the melted dummy rod and the ends of the optical fiber preform with each other;
The manufacturing method of the optical fiber preform | base_material to which the dummy rod was connected including is provided.

In the method of manufacturing an optical fiber preform to which the dummy rod of the first invention is connected, in the step of cutting either one of the dummy rod or the optical fiber preform, the end of the dummy rod It is preferable that the cross section of the end portion of the optical fiber preform facing the cross section after the end portion of the dummy rod is substantially perpendicular to the central axis of the optical fiber preform.
When the end portion of the optical fiber preform is cut, cracks may occur during cutting due to the difference in residual stress between the core and the clad. In addition, the end of the dummy rod is cut so that the cross section after cutting has an angle θ with respect to a plane perpendicular to the central axis, and the end cross section of the optical fiber preform facing the dummy rod However, it is more advantageous in terms of manufacturing efficiency to be substantially perpendicular to the central axis.

In the method for manufacturing an optical fiber preform to which the dummy rod according to the first aspect of the present invention is connected, the angle θ preferably satisfies 0.017 ≦ tan θ ≦ 0.176.
When tan θ is smaller than the above range, when the optical fiber preform is connected to the dummy rod, the connection portion between the optical fiber preform and the dummy rod due to the heating of the optical fiber preform in the peripheral edge of the end portion. It is difficult to obtain an effect of preventing bubbles from remaining when the optical fiber preform and the dummy rod are connected. On the other hand, when tan θ is larger than the above range, the outer peripheral portion of the connection portion between the optical fiber preform and the dummy rod becomes a ridge after connection between the optical fiber preform and the dummy rod, which may cause a problem in appearance. Or there may be a gap in the connection.

In the manufacturing method of the optical fiber preform to which the dummy rod according to the first aspect of the present invention is connected, the diameter of the optical fiber preform and the dummy rod is preferably in the range of 35 mm to 55 mm.
If the diameter of the optical fiber preform and the dummy rod is less than 35 mm, it is not suitable for connecting a large-diameter optical fiber preform having a large diameter and the dummy rod, and the amount of optical fiber that can be spun from the optical fiber preform is small. This is disadvantageous in terms of manufacturing efficiency. On the other hand, if the diameters of the optical fiber preform and the dummy bar exceed 55 mm, they may not be compatible with existing production equipment in the drawing process after the production of the optical fiber preform to which the dummy rod is connected.

Furthermore, the second aspect of the present invention is a method for manufacturing a dummy bar,
In the process of connecting the two dummy rods coaxially by melting opposite ends with heat,
Either of the two dummy bars is set so that an angle θ formed by a plane perpendicular to the central axis of one of the two dummy bars and a cross-section after cutting at either one of the end portions satisfies 0 <tan θ. Cutting the end of
Melting the opposing ends of the two dummy bars with heat, including the cut section;
A process of abutting and fusing the ends of the melted two dummy bars together;
A method for manufacturing a dummy bar is provided.

In the method for manufacturing a dummy bar according to the second aspect of the present invention, in the step of cutting one of the two dummy bars, relative to one of the two dummy bars whose end is cut The cross section of the other end portion of the two dummy bars is preferably substantially perpendicular to the central axis.
The end of one dummy bar is cut so that the cross-section after cutting has an angle θ with respect to a plane perpendicular to the central axis, and the end of the other dummy bar facing one dummy bar It is more advantageous in terms of manufacturing efficiency that the cross section of each is substantially perpendicular to the central axis.

In the method for manufacturing a dummy bar according to the second aspect of the present invention, the angle θ preferably satisfies 0.017 ≦ tan θ ≦ 0.176.
When tan θ is smaller than the above range, the connection between the two dummy rods is connected when the two dummy rods are connected in relation to the height of the bulge generated at the peripheral edge of the one end by heating the end of one dummy rod. Bubbles tend to stay in the dent of the part, and it is difficult to obtain the effect of preventing the bubbles from remaining when two dummy rods are connected. On the other hand, when tan θ is larger than the above range, the outer peripheral portion of the connecting portion of the two dummy rods becomes a ridge after connection of the two dummy rods, which may cause a problem in appearance or may be connected. There may be a gap in the part.

In the method for manufacturing a dummy bar according to the second aspect of the present invention, it is preferable that a diameter of the dummy bar is in a range of 35 mm to 55 mm.
If the diameter of the dummy rod is less than 35 mm, it is not suitable for connecting a large-diameter optical fiber preform with a large diameter to the dummy rod, and the amount of optical fiber that can be spun from the optical fiber preform is reduced, resulting in production efficiency. It is disadvantageous. On the other hand, if the diameter of the dummy bar exceeds 55 mm, it may not be compatible with existing manufacturing equipment in the drawing process after manufacturing the optical fiber preform to which the dummy bar is connected.

 According to the method of manufacturing an optical fiber preform to which the dummy rod of the present invention is connected, a plane perpendicular to the central axis of either the optical fiber preform or the dummy rod and after cutting one of the end portions A step of cutting one of the end portions so that an angle θ formed with the cross section satisfies a relation of 0 <tan θ. Therefore, when the ends of the optical fiber preform and the dummy rod to be connected are heated, the peripheral portion of either end of the optical fiber preform or the dummy rod is raised in an annular shape, and the center portion is indented. However, when the optical fiber preform and the dummy rod are brought into contact with each other, the other end of the optical fiber preform or the dummy rod is gradually increased from the obliquely cut end portion of either the optical fiber preform or the dummy rod. In contact with the annular bulge at the peripheral edge of the end. Therefore, when the optical fiber preform and the dummy rod are brought into contact with each other, the air outlet that exists in the central dent-shaped portion of the annular bulge at the peripheral portion that does not contact the obliquely cut tip portion It becomes. Therefore, it is possible to escape to the outside without leaving air in the recessed portion, and there is no air bubble remaining in the connection portion between the optical fiber preform and the dummy rod, and the optical fiber preform and the dummy rod. Can be firmly connected.

Further, according to the method of manufacturing an optical fiber preform to which the dummy rod of the present invention is connected, when both the optical fiber preform or the dummy rod are cut into necessary sizes, they are usually cut along a plane perpendicular to the central axis direction. Instead of a process, a process of cutting with a cross section forming a predetermined angle from a vertical plane is performed, so that a large amount of work time is not required as in the case of convex machining, and the optical fiber preform and the dummy rod are very easily Can be firmly connected.
Furthermore, according to the method for manufacturing an optical fiber preform to which the dummy rod of the present invention is connected, there is no air bubble at the connection portion between the optical fiber preform and the dummy rod, and the connection portion becomes strong. For this reason, it is possible to perform coaxial joining without deformation and damage to external force. Therefore, even when the silicon fiber fine particles are further deposited on the optical fiber preform connected to the dummy rod and then dehydrated and sintered, the optical fiber preform before the drawing after sintering is obtained. In the material, the eccentricity of the core with respect to the cladding and the non-circular state are excellent.

 According to the method for manufacturing a dummy bar of the present invention, the angle θ formed by the plane perpendicular to the central axis of one of the two dummy bars and the cross-section after cutting one of the end parts is 0. <It has the process of cut | disconnecting any one said edge part so that tan (theta) may be satisfy | filled. Therefore, when the ends of the two dummy rods to be connected are heated, even if the peripheral edge of one end of the two dummy rods swells in an annular shape and the center becomes a dent shape, When the bars are brought into contact with each other, they gradually come into contact with the annular bulge at the peripheral edge of the other end of the two dummy bars from the obliquely cut front end of one of the two dummy bars. Therefore, when the dummy rods are brought into contact with each other, the portion of the peripheral bulge that does not come into contact with the tip portion that is cut obliquely becomes the outlet of the air present in the recessed portion at the center. Therefore, it is possible to escape to the outside without leaving air in the dent-shaped part, and there is no air bubble remaining in the connection part of the two dummy bars, and the two dummy bars are firmly connected. It becomes possible to do.

Further, according to the method for manufacturing a dummy bar of the present invention, when the dummy bars are both cut into a necessary size, the predetermined process is normally performed from the vertical surface instead of the step of cutting the vertical axis with respect to the axial direction. Since the cutting process is performed with a cross section having an angle of (2), it does not require much work time as in the case of the convex machining, and it is possible to connect the two dummy bars firmly in a very simple manner.
Furthermore, according to the method for manufacturing a dummy bar of the present invention, there is no air bubble at the connection part of the two dummy bars, and the connection part becomes strong. Therefore, it is possible to perform coaxial bonding without deformation and breakage with respect to external force. Therefore, in the case where the optical fiber preform connected to the dummy rod obtained by integrating the two dummy rods is subjected to dehydration and sintering after further depositing silicon oxide fine particles in the external process. However, in the optical fiber preform before drawing after sintering, the eccentricity of the core with respect to the clad and the non-circular state are excellent.

It is the schematic which shows the manufacturing method of the optical fiber preform | base_material to which the dummy rod of this invention was connected. ((A) and (b) are side views, and (c) to (e) are sectional views.) It is the schematic which shows the manufacturing method of an optical fiber preform. It is the schematic which shows the manufacturing method of the optical fiber preform | base_material with which the conventional dummy rod was connected. ((A) is a side view, and (b) and (c) are sectional views.)

 Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings, but the present invention is not limited thereto.

"Manufacturing method of optical fiber preform to which dummy rod is connected"
FIG. 1 is a schematic view showing a method of manufacturing an optical fiber preform to which a dummy rod of the present invention is connected, wherein (a) and (b) are side views, and (c) to (e) are sectional views. .
FIG. 1A is a side view showing a state in which the end portion of the optical fiber preform 10 and the end portion of the dummy rod 11 face each other.
An optical fiber preform | base_material refers to the quartz glass body obtained by spin-dry | dehydrating and sintering the silicon oxide deposit obtained by the flame hydrolysis reaction of a silicon tetrachloride, for example. In a broad sense, the silicon oxide deposit before dehydration and sintering may be referred to as an optical fiber preform. The optical fiber preform may be stretched after the above-described dehydration and sintering processes, or after the stretching, and after the so-called external process in which silicon oxide is further deposited, dehydration and sintering are performed. It may have passed through the process. Further, the optical fiber preform may be further subjected to a stretching and / or external attachment process.
The optical fiber preform is made into a bare optical fiber by drawing in a subsequent spinning process, and then the bare optical fiber is coated with a resin to become an optical fiber.

 An optical fiber preform is composed of a portion that becomes a core where light is guided after drawing in the spinning process, and a portion that protects the core after drawing in the spinning process and becomes a clad having a refractive index slightly lower than that of the core. It may be.

 The dummy rod is a member that is used by being coaxially connected to the optical fiber preform in order to install the optical fiber preform in the apparatus by a chuck or the like. The optical fiber preform is installed in the apparatus via a chuck or the like by a dummy rod connected to one end or both ends thereof.

 Usually, the dummy bar is made of a quartz glass body. The dummy rod may be obtained, for example, by dehydrating and sintering a silicon oxide deposit obtained by a flame hydrolysis reaction of silicon tetrachloride, or may be obtained by melting natural quartz.

 The dummy bar is not usually drawn, and after the connected optical fiber preform is drawn, it is repaired and processed as necessary, and is used repeatedly. Thus, by using the optical fiber preform connected to the dummy rod, the optical fiber preform can be used for drawing without waste and a longer optical fiber can be obtained.

An angle θ formed by a plane perpendicular to the central axis of one of the optical fiber preform 10 and the dummy rod 11 and a cross-section after cutting at either end of the optical fiber preform 10 satisfies the relationship 0 <tan θ. Then, a step of cutting one of the end portions is performed.
In this embodiment, in the dummy bar 11, the dummy bar 11 is set so that the angle θ formed by the plane 11b perpendicular to the central axis 11a and the section 11c after cutting the end portion satisfies the relationship 0 <tan θ. The case where the process of cut | disconnecting the edge part of this is performed is illustrated (refer FIG.1 (b)).

 When the cross section after cutting (the cross section 11c of the dummy bar 11 in FIG. 1B) is not composed of a single plane, the plane that occupies the widest area of the cross section after cutting is cut after cutting. It is defined as a cross-section.

 In the step of cutting either one end of the optical fiber preform 10 or the dummy rod 11, the cutting method is not particularly limited. For example, a high-speed cutting machine (fine cutter) provided with a precision cutting grindstone The method of cutting with is mentioned. When using a high-speed cutting machine equipped with a precision cutting grindstone, the optical fiber preform 10 or the dummy rod 11 is inclined at a predetermined angle from the vertical direction with respect to the precision cutting grindstone, set in the cutting machine, and then cut. I do.

 Moreover, a pipe cutter can also be used in the process of cutting either one end of the optical fiber preform 10 or the dummy rod 11. When using a pipe cutter, a jig capable of fixing the base material at a predetermined angle with respect to the vertical direction is used, and after cutting a crack at a predetermined angle, cutting is performed. In the case of using a pipe cutter, there is an advantage that the cutting process can be performed more simply because it is not necessary to move the optical fiber preform 10 or the dummy rod 11 to the apparatus for cutting.

 Regarding the angle at which the end of the optical fiber preform 10 or the dummy rod 11 is cut, the angle θ formed by the cut surface of either the optical fiber preform 10 or the dummy rod 11 with respect to a plane perpendicular to the central axis thereof. May satisfy the relationship 0 <tan θ, that is, a range larger than 0 °, but preferably satisfy the relationship 0 <tan θ ≦ 1, that is, a range greater than 0 ° and 45 ° or less. It is more preferable that the relationship of 0.017 ≦ tan θ ≦ 0.176 is satisfied, that is, the range is 1 ° or more and 10 ° or less.

In the step of melting the opposite end portions of the optical fiber preform 10 and the dummy rod 11 by heat, the peripheral portion rises in an annular shape due to surface tension at the end portion of the member that is not cut obliquely, and in the center portion. You can dent. When the diameter of the optical fiber preform 10 or the dummy rod 11 is 50 mm, this rise may be as high as 1 mm. Note that the height of the rise is considered to be proportional to the size of the diameter of the optical fiber preform 10 or the dummy rod 11.
In the present embodiment, the case where the edge of the optical fiber preform 10 rises in a ring shape due to surface tension (portion indicated by reference numeral 10a) and the dent (portion indicated by reference numeral 10b) is formed in the central portion is exemplified (in the end portion of the optical fiber preform 10). (Refer FIG.1 (c)).

When the angle of the cut surface of either the optical fiber preform 10 or the dummy rod 11 is 1 ° with respect to a plane perpendicular to the central axis, tan 1 ° is about 0.017.
Here, the maximum value h of the length difference in the central axis direction of the cut surface generated by obliquely cutting the end of the dummy bar 11 is h = diameter of the dummy bar 11 × tan θ (see FIG. 1B). ). When the diameter of the dummy rod 11 is 50 mm, the maximum length h of the length difference is 50 mm × 0.017 = 0.87 mm. Therefore, if the angle of the cut surface of the dummy rod 11 with respect to the plane perpendicular to the central axis of the dummy rod 11 is 1 °, the optical fiber preform 10 and the dummy rod 11 at the subsequent stage are taken into account from the height of the above-mentioned rise. In the process of fusing the optical fiber preform 10, the air bubbles are allowed to escape from the dent 10 b at the end of the optical fiber preform 10 in the direction of the arrow, so that no bubbles are present on the joint surface between the optical fiber preform 10 and the dummy rod 11. It can be said that this is certainly possible (see FIG. 1D).

 In consideration of variations in the manufacturing process, in order to make it easier for air bubbles to escape in the process of fusing the optical fiber preform 10 and the dummy rod 11, the angle between the cut surfaces of the optical fiber preform 10 and the dummy rod 11 is set. The angle is more preferably 3 ° with respect to a plane perpendicular to the central axis, and further preferably 5 °.

On the other hand, when the angle of the cut surface of either the optical fiber preform 10 or the dummy rod 11 is 10 ° with respect to a plane perpendicular to the central axis, tan 10 ° is about 0.176.
Here, when the diameter of the dummy bar 11 is 50 mm, the maximum value h of the length difference in the central axis direction of the cut surface generated by obliquely cutting the end of the dummy bar 11 is 50 mm × 0.176. = 8.82 mm. In the step of fusing the dummy rod 11 and the optical fiber preform 10 in the subsequent stage, as the melted ends of the optical fiber preform 10 and the dummy rod 11 are brought into contact with each other, the tip of the cut surface of the dummy rod 11 melted by heat The gap formed in the joined portion due to the maximum value h of the difference in length in the central axis direction of the cut surface due to the surface tension (the portion corresponding to the upper right half toward the joined portion in FIG. 1D) ). Therefore, when the angle of the cut surface of the dummy bar 11 with respect to the surface perpendicular to the central axis direction of the dummy bar 11 is 10 °, it is caused by the maximum difference h in the length of the cut surface in the central axis direction. Thus, the gap generated in the bonded portion disappears with the fusion, and no gap is formed on the bonding surface, and there is no bubble, and a high-strength connection is possible.

 However, when the angle of the cut surface of either the optical fiber preform 10 or the dummy rod 11 exceeds 10 ° with respect to a plane perpendicular to the central axis, the sharp tip of the cut surface is outside the outer peripheral portion. By protruding, the outer peripheral portion of the connection portion between the optical fiber preform 10 and the dummy rod 11 may be in the shape of a knob. Further, in FIG. 1 (d), the bonding is caused by the maximum value h of the difference in length in the central axis direction of the cut surface corresponding to the upper right half of the connection portion between the optical fiber preform 10 and the dummy rod 11. Since the gap generated in the portion is difficult to disappear, the strength of the connection portion may be weakened.

The diameters of the optical fiber preform 10 and the dummy rod 11 are preferably in the range of 35 mm or more and 55 mm or less.
If the diameter of the optical fiber preform 10 and the dummy rod 11 is less than 35 mm, the amount of optical fiber strands that can be spun from the optical fiber preform 10 is reduced, which is disadvantageous in terms of manufacturing efficiency. On the other hand, if the diameters of the optical fiber preform 10 and the dummy rod 11 exceed 55 mm, the drawing process after the fabrication of the optical fiber preform 10 to which the dummy rod 11 is connected may not be suitable for existing production equipment. is there. The diameters of the optical fiber preform 10 and the dummy rod 11 may be in the range of 25 mm to 75 mm.

In the step of fusing the opposite ends of the optical fiber preform 10 and the dummy rod 11 including the cut cross-section, the optical fiber preform 10 and the dummy rod 11 are held by a rotating device (not shown). The end surfaces of the optical fiber preform 10 and / or the dummy rod 11 are heated by the oxyhydrogen flame from the oxyhydrogen burner 13 while rotating them around the central axis. The oxyhydrogen burner 13 may traverse (reciprocate) the vicinity of the heated portion of the optical fiber preform 10 and / or the dummy rod 11 as necessary.
In this way, the ends of the optical fiber preform 10 and the dummy rod 11 are melted and softened. In addition, the temperature of the flame by the oxyhydrogen burner 13 is preferably 2,000 to 3,000 ° C., and the surface temperature of the optical fiber preform 10 and the dummy rod 11 heated by the flame is about 1,500 to 2, About 000 ° C. is preferable.
In the above-described heating power, it takes approximately 3 to 10 minutes to melt the ends of the optical fiber preform 10 and the dummy rod 11.

Next, in the process of fusing the optical fiber preform 10 and the dummy rod 11, as shown in FIG. 1 (d), they are pressed by abutting the melted ends.
It should be noted that the direction when pressing the optical fiber preform 10 and the dummy rod 11 is made so that the optical fiber preform 10 and the dummy rod 11 are coaxial. When either one end of the optical fiber preform 10 or the dummy rod 11 is heated, the end portion of the optical fiber preform 10 and the dummy rod 11 are pressed even if the end bulges in an annular shape and can be dented in the center. In this case, since the melted ends are brought into contact with each other, the air remaining in the dent shape escapes in the direction of the arrow in FIG. In addition, connection work can be performed. Moreover, it is preferable to perform the speed | rate of butting in the range of 5 cm-600 cm per minute, for example.
Note that the step of fusing the optical fiber preform 10 and the dummy rod 11 may be performed while performing the fusing step as long as the end portion thereof is sufficiently melted for fusing.

 At the same time, as described above, as the molten fiber ends of the optical fiber preform 10 and the dummy rod 11 are brought into contact with each other, the tip portion of the cut surface of the dummy rod 11 that is melted by heat is caused by the surface tension. It penetrates into a gap (a portion corresponding to the upper right half toward the joined portion in FIG. 1D) due to the maximum value h of the difference in length in the central axis direction, and the gap is formed on the joined surface. Connection without any connection becomes possible.

 In this manner, the optical fiber preform 10 to which the dummy rod 11 is connected is obtained without enclosing bubbles that cause cracks or the like in the connection portion between the optical fiber preform 10 and the dummy rod 11 (see FIG. 1 (e)).

Thereafter, an external process is performed on the optical fiber preform 10 to which the dummy rod 11 is connected.
Specifically, in the external attaching process, for example, as shown in FIG. 2, dummy rods 11 are connected to both ends of the optical fiber preform 10, and the dummy rods 11 are held on a glass lathe by a chuck 12, While rotating the fiber preform 10 and at least one deposition burner 23 is traversed (reciprocated) in the direction of the central axis (arrow) of the optical fiber preform 10, it is oxidized on the outer periphery of the optical fiber preform 10. This is done by depositing silicon.

The dehydration and sintering processes are also performed with the dummy rods 11 connected to both ends of the optical fiber preform 10, but the dummy rods 11 may be connected to only one end of the optical fiber preform 10.
In some cases, the dummy rod 11 is held on a glass lathe by a chuck and the optical fiber preform 10 is processed.
Further, after that, the bending of the optical fiber preform 10 is corrected using a glass lathe, the heat stretching process to a predetermined outer diameter or length, the surface irregularities, scratches, impurities, etc. of the optical fiber preform 10 are removed. In some cases, a process such as a flame polishing process is performed.

"Dummy rod manufacturing method"
The manufacturing method of the dummy rod of the present invention is performed in the same manner as the manufacturing method of the optical fiber preform to which the above-described dummy rod of the present invention is connected. That is, in the method for manufacturing a dummy bar according to the present invention, two dummy bars are connected in the same manner as the method for manufacturing an optical fiber preform to which the dummy bar according to the present invention is connected.

 EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention further more concretely, this invention is not limited to a following example.

"Example 1"
By the method shown in FIG. 1, an optical fiber preform 10 having a diameter of 50 mm and a dummy rod 11 having a diameter of 50 mm were connected to produce an optical fiber preform 10 to which the dummy rod 11 was connected.
As the optical fiber base material 10 and the dummy rod 11, those whose cross-sections at the opposite end portions were planes perpendicular to the central axis were prepared (see FIG. 1 (a)).
In the dummy rod 11, the angle θ formed by the cross-section of the end portion of the dummy rod 11 facing the end portion of the optical fiber preform 10 and the plane perpendicular to the central axis of the dummy rod 11 is 1 °, that is, tan θ = 0. The end portion of the dummy bar 11 was cut with a high-speed cutting machine equipped with a precision cutting grindstone so that 017 was obtained (see FIG. 1B).

Thereafter, while rotating the optical fiber preform 10 and the dummy rod 11 about the central axis thereof, the opposite ends of the optical fiber preform 10 and the dummy rod 11 are connected to each other with an oxyhydrogen burner 13 having a hydrogen amount of 300 L / min. For 6 minutes and melted sufficiently (see FIG. 1C).
Thereafter, the optical fiber preform 10 and the dummy rod 11 are brought into contact with each other at opposite ends, and are fused and connected to each other at a speed of 10 cm per minute, and the optical fiber preform having the dummy rod 11 connected to one end thereof. A material 10 was produced (see FIGS. 1D and 1E).

Similarly, the connection processing of the optical fiber preform 10 and the dummy rod 11 was repeated 10 times, and 10 optical fiber preforms 10 to which the dummy rod 11 was connected as shown in FIG.
There were no bubbles in the connection portion of the optical fiber preform 10 to which all the dummy rods 11 were connected. Even if there is a possibility that bubbles exist on the joint surface, it is considered that the bubbles escaped from the cut portion in the direction of the arrow shown in FIG. It is done.

 Here, both ends of the optical fiber preform 10 to which the dummy rod 11 is connected are gripped by a lathe chuck, and tension is applied to the optical fiber preform 10 with a load of 100 kg. No cracks or cracks occurred in the connection part of the fiber preform 10.

Further, an optical fiber preform in which a dummy rod 11 having a diameter of 50 mm is connected to the other end of the optical fiber preform 10 and the dummy rods 11 are connected to both ends by the same method as the above connection processing. 10 was produced.
By holding the dummy rod 11 connected to both ends of the optical fiber preform 10 with a chuck and performing an external process on the optical fiber preform 10, silicon oxide is deposited on the outer periphery of the optical fiber preform 10. (See FIG. 2).
Thereafter, the optical fiber preform 10 on which silicon oxide was deposited was dehydrated and sintered to obtain a vitrified optical fiber preform.

The non-circularity and the amount of eccentricity were measured for all of the vitrified optical fiber preforms (10).
[Non-yen rate]
Based on the following definition formula, the non-circularity of the optical fiber preform was measured with an outer diameter measuring instrument.
(Maximum value of outer diameter a of optical fiber preform−minimum value of outer diameter a of optical fiber preform) / (average value of outer diameter a of optical fiber preform) × 100 (%)
[Eccentricity]
Using a preform analyzer, the amount of eccentricity of the optical fiber preform was measured as follows.
The maximum value of the difference in thickness (bc) between the clads on both sides of the core was determined on one diameter of the optical fiber preform.

 In any of the optical fiber preforms, the non-circularity was within 0.5%, and the amount of eccentricity was within 1 mm. This is because the joining portion of the optical fiber preform and the dummy rod is sufficiently strong that there is no deformation or breakage due to stress in the external attachment process, and the optical fiber preform to which the dummy rod of the present invention is connected. The optical fiber preform manufactured by this manufacturing method shows that the problem of decentration and non-circular deterioration does not occur at all in the external attachment process.

"Example 2"
The angle θ formed by the section of the dummy rod 11 that is opposite to the end of the optical fiber preform 10 and the plane perpendicular to the central axis of the dummy rod 11 is 7 °, that is, tan θ = 0. 123, an optical fiber mother having a dummy rod 11 connected to one end thereof in the same manner as in Example 1 except that the end portion of the dummy rod 11 was cut by a high-speed cutter equipped with a precision cutting grindstone. Material 10 was produced.

Similarly, the connection processing of the optical fiber preform 10 and the dummy rod 11 was repeated 10 times, and 10 optical fiber preforms 10 to which the dummy rod 11 was connected as shown in FIG.
There were no bubbles in the connection portion of the optical fiber preform 10 to which all the dummy rods 11 were connected. Even if there is a possibility that bubbles exist on the joint surface, it is considered that the bubbles escaped from the cut portion in the direction of the arrow shown in FIG. It is done.

 Here, both ends of the optical fiber preform 10 to which the dummy rod 11 is connected are gripped by a lathe chuck, and tension is applied to the optical fiber preform 10 with a load of 100 kg. No cracks or cracks occurred in the connection part of the fiber preform 10.

Further, an optical fiber preform in which a dummy rod 11 having a diameter of 50 mm is connected to the other end of the optical fiber preform 10 and the dummy rods 11 are connected to both ends by the same method as the above connection processing. 10 was produced.
By holding the dummy rod 11 connected to both ends of the optical fiber preform 10 with a chuck and performing an external process on the optical fiber preform 10, silicon oxide is deposited on the outer periphery of the optical fiber preform 10. (See FIG. 2).
Thereafter, the optical fiber preform 10 on which silicon oxide was deposited was dehydrated and sintered to obtain a vitrified optical fiber preform.

 The non-circularity and the amount of eccentricity were measured in the same manner as in Example 1 for all (10) vitrified optical fiber preforms.

 In any of the optical fiber preforms, the non-circularity was within 0.5%, and the amount of eccentricity was within 1 mm. This is because the joining portion of the optical fiber preform and the dummy rod is sufficiently strong that there is no deformation or breakage due to stress in the external attachment process, and the optical fiber preform to which the dummy rod of the present invention is connected. The optical fiber preform manufactured by this manufacturing method shows that the problem of decentration and non-circular deterioration does not occur at all in the external attachment process.

"Example 3"
An angle θ formed by a cross-section of the dummy rod 11 that is opposite to the end of the optical fiber preform 10 and a plane perpendicular to the central axis of the dummy rod 11 is 10 °, that is, tan θ = 0. In the same manner as in Example 1 except that the end portion of the dummy bar 11 was cut by a high-speed cutting machine equipped with a precision cutting grindstone so as to be 176, the optical fiber mother having the dummy rod 11 connected to one end portion Material 10 was produced.

Similarly, the connection processing of the optical fiber preform 10 and the dummy rod 11 was repeated 10 times, and 10 optical fiber preforms 10 to which the dummy rod 11 was connected as shown in FIG.
There were no bubbles in the connection portion of the optical fiber preform 10 to which all the dummy rods 11 were connected. Even if there is a possibility that bubbles exist on the joint surface, it is considered that the bubbles escaped from the cut portion in the direction of the arrow shown in FIG. It is done.

 Here, both ends of the optical fiber preform 10 to which the dummy rod 11 is connected are gripped by a lathe chuck, and tension is applied to the optical fiber preform 10 with a load of 100 kg. No cracks or cracks occurred in the connection part of the fiber preform 10.

Further, an optical fiber preform in which a dummy rod 11 having a diameter of 50 mm is connected to the other end of the optical fiber preform 10 and the dummy rods 11 are connected to both ends by the same method as the above connection processing. 10 was produced.
By holding the dummy rod 11 connected to both ends of the optical fiber preform 10 with a chuck and performing an external process on the optical fiber preform 10, silicon oxide is deposited on the outer periphery of the optical fiber preform 10. (See FIG. 2).
Thereafter, the optical fiber preform 10 on which silicon oxide was deposited was dehydrated and sintered to obtain a vitrified optical fiber preform.

 The non-circularity and the amount of eccentricity were measured in the same manner as in Example 1 for all (10) vitrified optical fiber preforms.

 In any of the optical fiber preforms, the non-circularity was within 0.5%, and the amount of eccentricity was within 1 mm. This is because the joining portion of the optical fiber preform and the dummy rod is sufficiently strong that there is no deformation or breakage due to stress in the external attachment process, and the optical fiber preform to which the dummy rod of the present invention is connected. The optical fiber preform manufactured by this manufacturing method shows that the problem of decentration and non-circular deterioration does not occur at all in the external attachment process.

Example 4
Using dummy bars instead of the optical fiber preform, the same connection processing as in Example 2 was performed, and the dummy bars were connected to produce a dummy bar to which two dummy bars were connected.

Similarly, the connecting process of two dummy bars was repeated 10 times to produce ten dummy bars to which two dummy bars were connected.
There were no bubbles at the connection of all the dummy bars.

 Here, both ends of the dummy bar were gripped by a lathe chuck, and tension was applied to the dummy bar with a load of 100 kg, but no cracks or cracks occurred in the connection part of the dummy bar.

"Comparative Example 1"
The optical fiber preform 30 to which the dummy rod 31 was connected was manufactured by connecting the optical fiber preform 30 having a diameter of 50 mm and the dummy rod 31 having a diameter of 50 mm by the method shown in FIG.
As the optical fiber preform 30 and the dummy rod 31, those in which the cross-sections of the opposite end portions are planes perpendicular to the central axis were prepared.

Thereafter, as in the first to fourth embodiments, the optical fiber preform 30 and the dummy rod 31 are rotated around the central axis line without cutting the end portion of the dummy rod 31, and the optical fiber preform 30 is rotated. The opposing ends of the dummy rod 31 were heated for 6 minutes with an oxyhydrogen burner 33 with a hydrogen amount of 300 L / min to be sufficiently melted. At this time, in the end surfaces of the optical fiber preform 30 and the dummy rod 31, the peripheral edge was raised in a ring shape (see FIG. 3B).
Thereafter, the opposite ends of the optical fiber preform 30 and the dummy rod 31 are brought into contact with each other and fusion-bonded while being abutted against each other, so that an optical fiber preform 30 having the dummy rod 31 connected to one end is fabricated (see FIG. 3 (c)).

Similarly, the connecting process of the optical fiber preform 30 and the dummy rod 31 was repeated 10 times, and 10 optical fiber preforms 30 to which the dummy rod 31 was connected were produced.
Bubbles were present in the connection portion of the optical fiber preform 30 to which all the dummy bars 31 were connected.
Further, both ends of the optical fiber preform 30 to which the dummy rod 31 is connected are gripped by a lathe chuck, and tension is applied to the optical fiber preform 30 with a load of 100 kg. Cracks and cracks occurred in the connection part of the base material 30.

10, 30 Optical fiber preform 11, 31 Dummy rod 12 Chuck 13, 33 Oxyhydrogen burner 23 Deposition burner

Claims (8)

A method of manufacturing an optical fiber preform to which a dummy rod is connected,
In the step of connecting the dummy rod and the optical fiber preform coaxially by melting the opposite ends with heat,
The angle θ formed by the plane perpendicular to the central axis of either the dummy rod or the optical fiber preform and the cross-section after cutting at either end satisfies the following condition: 0 <tan θ Cutting one of the ends, and
Melting the dummy rod and the end portions of the optical fiber preform, which include the cut section, by heat; and
A process of abutting and fusing the melted dummy rod and the ends of the optical fiber preform with each other;
The manufacturing method of the optical fiber preform | base_material with which the dummy rod was connected characterized by the above-mentioned.   In the step of cutting one end of either the dummy rod or the optical fiber preform, the end of the dummy rod is cut, and the cross section of the optical fiber preform after the end of the dummy rod is cut. 2. The method of manufacturing an optical fiber preform to which a dummy rod is connected according to claim 1, wherein the cross-sections of the opposite ends are substantially perpendicular to the central axis of the optical fiber preform.   3. The method of manufacturing an optical fiber preform to which a dummy rod is connected according to claim 1, wherein the angle θ satisfies 0.017 ≦ tan θ ≦ 0.176.   The diameter of the said optical fiber preform and the said dummy rod exists in the range of 35 mm or more and 55 mm or less, The manufacture of the optical fiber preform to which the dummy rod of any one of Claims 1-3 was connected Method. A method of manufacturing a dummy rod for connecting to an optical fiber preform ,
In the process of connecting the two dummy rods coaxially by melting opposite ends with heat,
Either of the two dummy bars is set so that an angle θ formed by a plane perpendicular to the central axis of one of the two dummy bars and a cross-section after cutting at either one of the end portions satisfies 0 <tan θ. Cutting the end of
Melting the opposing ends of the two dummy bars with heat, including the cut section;
A process of abutting and fusing the ends of the melted two dummy bars together;
A method of manufacturing a dummy bar for connection to an optical fiber preform characterized by comprising: In the step of cutting either one of the two dummy bars, the other end of the two dummy bars is opposed to one of the two dummy bars to be cut. 6. The method for manufacturing a dummy rod for connecting to an optical fiber preform according to claim 5, wherein the cross section is substantially perpendicular to the central axis. The method of manufacturing a dummy rod for connecting to an optical fiber preform according to claim 5 or 6, wherein the angle θ satisfies 0.017 ≦ tan θ ≦ 0.176. The method for manufacturing a dummy rod for connecting to an optical fiber preform according to any one of claims 5 to 7, wherein a diameter of the dummy rod is in a range of 35 mm to 55 mm.

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