JP7370890B2 - Support rod for optical fiber base material and method for manufacturing optical fiber base material - Google Patents

Description

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

In the manufacturing process of optical fibers, support rods are used to support the optical fiber preform. Patent Document 1 describes a support rod in which a through hole is formed and a pin inserted into the through hole. The pin is suspended by a chuck, and the optical fiber preform is gripped perpendicularly to the ground plane. In this state, the glass particles are deposited on the optical fiber preform while rotating around the axis.

Patent No. 5697049

If the optical fiber preform is gripped vertically, thermally induced upward currents can result in non-uniform deposition of glass particles along the longitudinal axis of the optical fiber preform. Therefore, in the step of depositing glass particles, the optical fiber preform may be held horizontally with respect to the ground plane. On the other hand, in the vitrification step after the deposition step, the optical fiber preform is generally held vertically in a heating furnace. Therefore, in each process, the optical fiber preform may be held horizontally or vertically.

In Patent Document 1, when gripping the optical fiber preform horizontally with respect to the ground surface, it is necessary to remove the pin for vertical gripping from the through hole and grip the support rod with a chuck. However, as the size of the optical fiber preform increases, the strength of the support rod near the through hole becomes insufficient, resulting in a problem that the support rod may be damaged.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a support rod for an optical fiber preform and a method for manufacturing an optical fiber preform, which can avoid damage.

According to one aspect of the present invention, there is provided an optical fiber preform support rod for supporting an optical fiber preform having a core and a cladding formed on the outer periphery of the core, the support rod being joined to one end of the optical fiber preform. An optical fiber comprising: an end portion formed with a through hole; a reinforcing pin inserted into the through hole and having a strength greater than the strength of the support rod for the optical fiber preform. A parent material support rod is provided.

According to another aspect of the present invention, the steps include: providing a through hole in the side of the support rod for an optical fiber preform; inserting a reinforcing pin into the through hole; a step of joining an end of the optical fiber preform support rod to one end of an optical core rod having a cladding; and a step of gripping the optical fiber preform support rod with the reinforcing pin inserted into the through hole. A method for manufacturing an optical fiber preform is provided.

According to the present invention, it is possible to provide a support rod for an optical fiber preform and a method for manufacturing an optical fiber preform that can avoid damage.

FIG. 3 is an external view of a core rod and a handle in an embodiment of the present invention. It is a figure for explaining the joining method of a core rod and a handle in one embodiment of the present invention. FIG. 3 is a cross-sectional view of a handle in one embodiment of the invention. FIG. 1 is a side view of a deposition apparatus used for manufacturing an optical fiber preform in an embodiment of the present invention. 1 is a cross-sectional view of a deposition apparatus used for manufacturing an optical fiber preform in an embodiment of the present invention. FIG. 1 is a cross-sectional view of a sintering apparatus used for manufacturing an optical fiber preform in an embodiment of the present invention. It is a process diagram of the manufacturing method of the optical fiber preform in one Embodiment of this invention.

Hereinafter, one embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is an external view of the core rod and handle in this embodiment. The core rod 2 is a starting material for an optical fiber base material, and is made of quartz glass or the like. The core rod 2 can be formed by heating and stretching a rod having a core and a cladding layer formed around the outer periphery of the core. The core rod 2 has a cylindrical shape having core rod ends 21 and 22 and a core rod side portion 23. In the deposition process, glass particles are deposited on the outer periphery of the core rod side portion 23 to form an optical fiber preform. In the following description, the core rod 2 and the handles 1A, 1B may be referred to as optical fiber preforms. Further, the direction in which the imaginary core rod axis 24 of the core rod 2 extends is referred to as the X direction, and the two directions orthogonal to the X direction are referred to as the Y direction and the Z direction.

The handles 1A and 1B are made of quartz or the like like the core rod 2, and are support rods for an optical fiber base material that support the two core rod ends 21 and 22 of the core rod 2, respectively. The handles 1A and 1B are used to grip the core rod 2 during the process of depositing glass particles. Further, in the vitrification process, the handle 1B is removed and the handle 1A is held vertically by the gripping section. Note that the handle 1B may remain joined to the core rod 2 during the vitrification process.

The handle 1A has a substantially cylindrical shape and includes handle end portions 11A, 12A and a handle side portion 13A. The handle end 11A is joined to the core rod end 21, and the handle shaft 14A, which is the central axis of the handle 1A, is located approximately on the same straight line as the core rod shaft 24. A circular through hole 15 is formed in the handle side portion 13A at a position near the handle end portion 12A. The through hole 15 is formed in a direction (Y direction) perpendicular to the handle shaft 14A, and intersects with the handle shaft 14A inside the handle 1A. As will be described later, when the core rod 2 is held vertically, a quartz pin is inserted into the through hole 15. The diameter of the through hole 15 can be appropriately determined so as to ensure sufficient strength of the quartz pin and not to significantly impair the strength of the handle 1A. That is, by increasing the diameter of the through hole 15, the strength of the pin inserted into the through hole 15 can be increased. On the other hand, if the diameter of the through hole 15 is too large, the strength of the handle 1A in the vicinity of the through hole 15 may decrease. For this reason, it is preferable that the diameter of the through hole 15 is determined in consideration of the trade-off between the respective strengths of the pin and the handle 1A.

The handle 1B is formed in the same manner as the handle 1A except that no through hole is formed. That is, the handle 1B includes handle ends 11B, 12B and a handle side part 13B, and the handle end 11B is joined to the core rod end 22. The handle shaft 14B, which is the central axis of the handle 1B, is located approximately on the same straight line as the core rod shaft 24 and the handle shaft 14A.

FIG. 2 is a diagram for explaining the method of joining the core rod and handle in this embodiment. In FIG. 2(A), a handle 1A made of quartz is prepared, and a through hole 15 is formed in the handle side 13A. In FIG. 2(B), the handle end 11A is joined to the core rod end 21 so that the handle shaft 14A and the core rod shaft 24 are aligned. The handle end 11A and the core rod end 21 may be welded together using, for example, a burner or an electric furnace. In FIG. 2C, a handle 1B made of quartz is prepared, and the handle end 11B is joined to the core rod end 22 so that the handle shaft 14B and the core rod shaft 24 are aligned.

In FIG. 2(D), a reinforcing pin 41 is inserted into the through hole 15 as a reinforcing material. Here, it is desirable that the strength of the reinforcing pin 41 is greater than the strength of the handle 1A. The material of the reinforcing pin 41 is, for example, ceramics or the like, and specifically may be Si ₃ N ₄ . Further, in order to prevent damage caused by a difference in the coefficient of thermal expansion of the reinforcing pin 41 or the handle 1A, it is desirable that the coefficient of thermal expansion of the reinforcing pin 41 and the coefficient of thermal expansion of the handle 1A have values that are close to each other. Note that the material of the reinforcing pin 41 is not necessarily limited to ceramics or the like. Even if the strength of the reinforcing pin 41 is equal to or smaller than the strength of the handle 1A, the material of the reinforcing pin 41 does not matter as long as it can reinforce the strength of the handle 1A. For example, the reinforcing pin 41 may be made of quartz, which is the same material as the handle 1A.

FIG. 3 is a sectional view of the handle in this embodiment, and is a sectional view taken along line III-III' in FIG. 2. 3(A) is a cross-sectional view of the handle 1A in which the reinforcing pin 41 is not inserted into the through-hole 15, and FIG. 3(B) is a cross-sectional view of the handle 1A in which the reinforcing pin 41 is inserted into the through-hole 15. .

The through hole 15 extends in a direction perpendicular to the handle shaft 14A. By forming the through hole 15 in the handle 1A, the strength of the handle 1A near the through hole 15 may be reduced. In this embodiment, by inserting the reinforcing pin 41 into the through hole 15, it is possible to prevent the strength of the handle 1A from decreasing.

The reinforcing pin 41 has a cylindrical shape and has pin end portions 411, 412 and a pin side portion 413. It is desirable that the length of the reinforcing pin 41 does not exceed the length of the through hole 15, and it is more desirable that the length of the reinforcing pin 41 be approximately equal to the length of the through hole 15 so that the handle 1A can be sufficiently reinforced. If the length of the reinforcing pin 41 exceeds the length of the through hole 15, the pin ends 411, 412 will protrude from the through hole 15. The protruding pin ends 411 and 412 may be pressed against a gripping portion (chuck) described later, and the reinforcing pin 41 may be damaged. For this reason, it is preferable that the corners of the pin ends 411 and 412 be polished so that the pin ends 411 and 412 do not protrude from the through hole 15. Further, the pin ends 411, 412 may be curved so that the pin ends 411, 412 and the handle side portion 13A form a continuous surface.

The diameter of the reinforcing pin 41 is preferably equal to or smaller than the diameter of the through hole 15 so that the reinforcing pin 41 can be inserted into the through hole 15. Furthermore, it is preferable that no large gap be formed between the pin side portion 413 and the inner wall 153 of the through hole 15. If the gap between the reinforcing pin 41 and the through hole 15 is too large, the reinforcing pin 41 cannot sufficiently reinforce the handle 1A. On the other hand, if the gap between the reinforcing pin 41 and the through hole 15 is too small, the handle 1A may be damaged due to thermal expansion of the reinforcing pin 41. Therefore, it is preferable that an appropriate gap be formed between the pin side portion 413 and the inner wall 153.

FIG. 4 is a side view of the deposition apparatus used for manufacturing the optical fiber preform in this embodiment. FIG. 5 is a sectional view of the deposition apparatus used for manufacturing the optical fiber preform in this embodiment, and is a sectional view of the deposition apparatus taken along the line VV' in FIG. 4. The deposition device 5 is a device that deposits glass particles forming a cladding on the core rod 2 to form an optical fiber preform 3. As a method for depositing glass particles, for example, a VAD (Vapor Phase Axial Deposition) method, an OVD (Outside Vapor Deposition) method, etc. can be used. The VAD method is a method in which the core rod 2 is held vertically and glass particles are deposited vertically from the lower end of the core rod 2 toward the upper end. The OVD method is a method in which the core rod 2 is held horizontally and glass particles are deposited horizontally on the side portion 23 of the core rod. The deposition apparatus 5 in this embodiment is capable of depositing glass fine particles by the OVD method.

The deposition device 5 includes a base 51, support parts 52A and 52B, a grip part 53, a stress applying part 54, and a burner 59. The base 51 is a member that serves as the base of the deposition apparatus 5, and has a substantially rectangular parallelepiped shape. The base 51 is installed horizontally to the ground surface. The base 51 includes a rail extending in the longitudinal direction of the base 51, and the support portion 52A or 52B and the burner 59 are movable along the rail. In plan view, the longitudinal direction of the base 51 is the X direction, and the lateral direction of the base 51 is the Y direction. Further, the vertical direction of the base 51 is defined as the Z direction.

The support parts 52A and 52B are columnar and are provided on the upper part of the base 51 while facing each other. That is, the support part 52A is provided at the end 511 of the base 51, and the support part 52B is provided at the end 512 of the base 51. At least one of the supports 52A and 52B is movable on a rail laid on the base 51. Further, the support parts 52A and 52B are equipped with a rotary motor, a transmission, etc. that rotate the core rod 2.

The grip portion 53 and the stress applying portion 54 constitute a chuck, and are provided on the support portions 52A and 52B, respectively. The grip portion 53 is made of, for example, a metal such as SUS or a heat-resistant fluororesin, and includes a plurality of claws 531 that can be moved close to each other or separated from each other. The claws 531 are made of metal such as SUS, and a gripping hole 532 is formed in the center of the plurality of claws 531 so that the handle side parts 13A and 13B can be gripped. The stress applying part 54 is provided around the grip part 53 and can apply stress to the grip part 53. When the gripping portion 53 receives stress from the stress applying portion 54, the plurality of claws 531 move closer to each other, and the diameter of the gripping hole 542 decreases. As a result, the handle side portions 13A and 13B inserted into the grip hole 542 are gripped by the grip portion 53. Since the length of the reinforcing pin 41 does not exceed the length of the through hole 15, the end of the reinforcing pin 41 is not pressed against the grip part 53, and damage to the reinforcing pin 41 can be prevented.

The burner 59 is an oxyhydrogen burner that sprays glass particles onto the core rod 2, and is installed on a rail provided below the core rod of the base 51. The burner 59 can blow glass particles onto the core rod 2 rotating around the core rod shaft 24 while moving on the rail. The burner 59 may include a nozzle for supplying combustible gas, a nozzle for supplying combustion auxiliary gas, a nozzle for supplying glass raw material, and the like. For example, the combustible gas may be hydrogen or the like, and the combustible gas may be oxygen or the like. Further, the glass raw material may be, for example, SiCl ₄ or the like. The burner 59 injects glass raw material into a flame and generates glass particles through a flame hydrolysis reaction. The position of the nozzle of the burner 59 in the vertical direction of the core rod axis 24 can be adjusted depending on the thickness of the glass particles deposited on the core rod side part 23. In this way, porous glass particles are deposited on the outer periphery of the core rod 2 to form the optical fiber preform 3.

As the weight of the optical fiber preform 3 increases due to the accumulation of glass particles, the stress in the handles 1A and 1B increases. Since the reinforcing pin 41 is inserted into the through hole 15 of the handle side portion 13A, the strength in the vicinity of the through hole 15 of the handle side portion 13A can be increased. Therefore, it is possible to avoid breaking the handle 1A.

FIG. 6 is a cross-sectional view of a sintering apparatus used for manufacturing the optical fiber preform in this embodiment. The sintering device 7 is a device for sintering the optical fiber preform 3. The sintering device 7 includes a furnace core tube 71, an intake hole 72, an exhaust hole 73, a heater 74, an upper lid 75, a grip portion 76, and a shaft 77.

The furnace core tube 71 is a cylindrical reaction vessel capable of storing the optical fiber preform 3, and may be made of transparent quartz glass or the like. The intake hole 72 is provided at the bottom 711 of the furnace core tube 71, and introduces dehydration gas, inert gas, etc. into the furnace core tube 71. For example, the dehydration gas can be chlorine, thionyl chloride, etc., and the inert gas can be argon, helium, etc. The exhaust hole 73 is provided above the side portion 712 of the reactor core tube 71, and exhausts dehydrated gas, inert gas, etc. filled in the reactor core tube 71 as necessary. The heater 74 is provided around the furnace core tube 71 and heats the optical fiber preform 3. The upper lid 75 is provided on the upper part of the furnace core tube 71, and can seal the upper part of the furnace core tube 71 after the optical fiber preform 3 is stored in the furnace core tube 71. Further, the upper lid 75 is formed with an opening 751 into which the handle 1A can be inserted.

The grip part 76 is provided on the upper part of the upper lid 75 and may be made of quartz or the like, but may also be made of metal such as titanium or nickel. Further, the grip portion 76 may be provided at the lower part of the upper lid 75. The grip portion 76 has a U-shaped cross section, and a through hole 762 is formed in a side portion 761 of the grip portion 76 . A pin 42 for vertical gripping is inserted into the through hole 762, and the handle 1A is vertically suspended by the gripping portion 76. The pin 42 has a substantially cylindrical shape, is longer than the through hole 15, and has a full length sufficient to pass through the two through holes 762 of the grip portion 76. Since the pin 42 is exposed to an atmosphere such as chlorine, it is preferably made of quartz or the like.

The shaft 77 is provided at the upper part 763 of the gripping part 76 and is configured to be rotatable by a drive mechanism (not shown). As the shaft 77 rotates, the optical fiber preform 3 is heated by the heater 74 while rotating inside the furnace tube 71 . As a result, the porous glass of the optical fiber preform 3 is sintered and vitrified.

FIG. 7 is a process diagram of a method for manufacturing a glass base material in this embodiment. First, a through hole 15 is formed in the handle 1A using a router or the like (step S101). Next, the handles 1A, 1B are melt-bonded to the core rod 2 using an oxyhydrogen burner or the like so that the handle shafts 14A, 14B and the core rod shaft 24 are aligned (step S102). A reinforcing pin 41 made of ceramic or the like is inserted into the through hole 15 (step S103).

Subsequently, the core rod 2 is installed in the deposition device 5 (step S104). The handles 1A and 1B are each gripped by a gripper 53 of the deposition device 5. Here, although the reinforcing pin 41 is inserted into the through hole 15, the length of the reinforcing pin 41 does not exceed the length of the through hole 15. Therefore, the end portion of the reinforcing pin 41 is not pressed against the grip portion 53, and damage to the reinforcing pin 41 can be prevented.

The deposition device 5 causes the burner 59 to deposit the glass particles 35 on the core rod side portion 23 while rotating the core rod 2 (step S105). Depending on the amount of glass fine particles 35 deposited on the core rod 2, the load applied to the handles 1A, 1B may increase. Since the reinforcing pin 41 is inserted into the handle 1A, it is possible to reinforce the strength near the through hole 15 of the handle 1A and prevent damage to the handle 1A.

When the glass particles are sufficiently deposited on the core rod 2, the handles 1A and 1B are removed from the grip portion 53. Further, the joint portion between the handle 1B and the core rod 2 is melted by a burner or an electric furnace, and the handle 1B is separated from the core rod 2 (step S107).

Subsequently, in the handle 1A, the reinforcing pin 41 and the vertical gripping pin 42 are replaced (step S108). That is, the reinforcing pin 41 is taken out from the through hole 15 of the handle 1A, and the pin 42 made of quartz is inserted into the through hole 15. The pin 42 is gripped by the gripper 76 of the sintering device 7, and the optical fiber preform 3 is vertically installed inside the furnace tube 71 (step S109).

The sintering device 7 heats the optical fiber preform 3 and performs sintering (step S110). The sintering device 7 introduces chlorine or the like into the interior 713 through the intake hole 72 . The optical fiber preform 3 is heated by the heater 74 while rotating within the furnace tube 71 . This removes impurities and the like contained in the optical fiber preform. Subsequently, the sintering device 7 discharges chlorine (Cl ₂ ) from the exhaust hole 73 and introduces helium (He) as an atmospheric gas into the interior 713 from the intake hole 72 . The optical fiber preform 3 is heated to a predetermined temperature by the heater 74 while rotating within the furnace tube 71 . The predetermined temperature may be, for example, 1500 degrees Celsius. When the sintering of the optical fiber preform 3 is completed, helium is discharged from the exhaust hole 73, and the transparent vitrified optical fiber preform 3 is taken out from the furnace tube 71. In a later step, the transparent vitrified optical fiber preform 3 is heated and drawn to form an optical fiber.

As described above, according to this embodiment, when gripping an optical fiber base material horizontally, the strength of the handle is increased by inserting a reinforcing pin with a strength greater than that of the handle into the through hole. , it becomes possible to avoid damage to the handle. On the other hand, when gripping the optical fiber preform vertically, it is possible to insert a quartz pin into the through hole and grip the pin.

Note that it may be possible to avoid damage to the handle by using the first to third methods described below without using the reinforcing pin. However, when the first to third methods are used, problems other than handle breakage may occur.

A first method is to increase the strength of the handle by increasing its diameter. Further, as a second method, by increasing the overall length of the handle and having the grip portion grip a portion where the through hole is not provided, damage in the vicinity of the through hole can be avoided. However, increasing the diameter and overall length of the handle increases the cost of manufacturing the handle. According to this embodiment, it is possible to avoid damage to the handle without increasing the manufacturing cost of the handle. As a third method, it is also possible to avoid damage to the handle by reducing the diameter of the through hole. However, if the diameter of the through hole is reduced, the diameter of the pin for vertical gripping is also reduced, making the pin more susceptible to deformation and breakage. According to this embodiment, the strength of the handle can be increased by the reinforcing pin without reducing the diameter of the through hole, so deformation and breakage of the pin for vertical gripping can be avoided. That is, in this embodiment, it is possible to avoid damage to the handle without creating new problems.

[Example]
The reinforcing pin 41 described above was inserted into the through hole 15 of the handle 1A, and the handle 1A was examined for damage. The length of the core rod 2 used in the example was 4000 mm, and the diameter was 50 mm. The handles 1A and 1B made of quartz had a length of 500 mm and a diameter of 70 mm. A through hole 15 with a diameter of 25 mm was formed in the handle 1A, and a reinforcing pin 41 made of Si ₃ N ₄ was inserted into the through hole 15 . The length of the reinforcing pin 41 was 70 mm, and the diameter was 24.9 mm. In the deposition device 5, glass fine particles were deposited on the core rod 2 using SiCl ₄ as a combustible gas and a combustion assisting gas to form an optical fiber preform 3. Although the weight of the optical fiber preform 3 was 220 kg, no damage to the handle 1A was observed.

Subsequently, the handle 1B in which the through-hole 15 was not formed was separated from the optical fiber base material 3 using flame or the like, and the pin 42 made of quartz was inserted into the through-hole 15. Note that the handle 1B does not necessarily have to be separated from the optical fiber preform 3. The pin 42 was held by the sintering device 7, and the optical fiber preform 3 was heated to 1500 degrees Celsius in the furnace tube 71. The transparent vitrified optical fiber preform 3 could be formed without deforming or breaking the pin 42.

[Comparative example]
On the other hand, as a comparative example, the reinforcing pin 41 was not inserted into the through hole 15, and glass fine particles were deposited on the core rod 2 using the deposition device 5. The core rod 2, handles 1A, 1B, and through hole 15 were formed in the same manner as in the above embodiment. In the deposition device 5, when the glass particles were deposited on the core rod 2 and the weight of the optical fiber preform 3 exceeded 220 kg, the vicinity of the through hole 15 of the handle 1A was damaged in the grip portion 53. Therefore, it has been confirmed that when the reinforcing pin 41 is not inserted into the through hole 15, the strength of the handle 1A in the vicinity of the through hole 15 becomes insufficient.

[Modified example]
The present invention is not limited to the above-described embodiments and examples, but can be applied in various modifications. For example, it is desirable that the reinforcing pin 41 has greater strength than the handle. Further, the material of the reinforcing pin 41 is not limited to ceramics as long as it has a coefficient of thermal expansion close to that of the handle. Further, the through hole 15 may be formed in both the handles 1A and 1B.

1A, 1B Handle 2 Core rod 3 Optical fiber base material 5 Deposition device 7 Sintering device 15 Through hole 41 Reinforcement pin 42 Pin 53 Stress applying part 54 Gripping part 71 Furnace tube 76 Gripping part

Claims (8)

An optical fiber preform support rod that supports an optical fiber preform having a core and a cladding formed on the outer periphery of the core,
an end portion joined to one end of the optical fiber preform;
a side portion with a through hole formed;
a reinforcing pin inserted into the through hole;
Equipped with
A support rod for an optical fiber base material , wherein the length of the reinforcing pin does not exceed the length of the through hole . The support rod for an optical fiber preform according to claim 1, wherein the end of the reinforcing pin and the side portion of the support rod for an optical fiber preform form a continuous surface. The support rod for the optical fiber base material is made of quartz,
The support rod for an optical fiber base material according to claim 1 or 2, wherein the reinforcing pin is made of ceramics. The support rod for an optical fiber preform according to claim 3 , wherein _the reinforcing pin is made of _Si3N4 . The through hole has a circular shape,
The support rod for an optical fiber preform according to any one of claims 1 to 4 , wherein the reinforcing pin has a substantially cylindrical shape. providing a through hole in the side of the support rod for the optical fiber base material;
inserting a reinforcing pin into the through hole;
joining an end of the optical fiber preform support rod to one end of a core rod having a core and a cladding formed on the outer periphery of the core;
gripping the optical fiber preform support rod in which the reinforcing pin is inserted into the through hole ,
A method for manufacturing an optical fiber preform, characterized in that the length of the reinforcing pin does not exceed the length of the through hole . The support rod for the optical fiber base material is made of quartz,
7. The method of manufacturing an optical fiber preform according to claim 6 , wherein the reinforcing pin is made of ceramic. 8. The method of manufacturing an optical fiber preform according to claim 6, wherein the _reinforcing pin is made of _Si3N4 .

Images