Method for manufacturing an optical fiber preform

Abstract

Provided is a method for manufacturing an optical fiber preform, which makes it difficult for the central axis of a starting material to deviate from the rotation axis and which lengthens the optical fiber preform. In the method for manufacturing an optical fiber preform, a starting material held by a starting material holder is moved in a vertical direction relative to a first burner while being rotated around a rotation axis in a reaction vessel, and glass particles generated by hydrolysis of a glass raw material in a flame by the first burner are accumulated on the outer periphery of the starting material. The method for manufacturing an optical fiber preform includes: a first accumulation step of accumulating the glass particles on the outer periphery of the starting material while applying a pressing force to the lower end of the starting material by a jig freely provided in rotation on a support table mounted so as to be movable in the vertical direction while moving the starting material relative to the first burner in the vertical direction; and a second accumulation step of accumulating the glass particles on the outer periphery of the starting material after the first accumulation step while moving the starting material relative to the first burner in the vertical direction in a state in which the lower end of the starting material is separated from the jig.

Description

Technical Field

[0001] This disclosure relates to a method for manufacturing optical fiber preforms. Background Technology

[0002] Patent Document 1 discloses a method for manufacturing an optical fiber preform. In this method, glass microparticles are deposited on the outer periphery of the starting material while it is being pulled up and rotated around a rotation axis. In the manufacturing method of Patent Document 1, a freely rotating starting material support fixture is provided at the lower end of the starting material, and while applying a certain pressure to the lower end of the starting material, the starting material is pulled up in the vertical direction. This prevents the central axis of the starting material from deviating from the rotation axis while depositing the glass microparticles.

[0003] Existing technical documents

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent Application Publication No. 7-109142 Summary of the Invention

[0006] The technical problem that the invention aims to solve

[0007] Patent Document 1's starting material includes an accumulation section formed by stacking glass microparticles in a burner, and a dummy section located vertically below the accumulation section with its lower end abutting against a starting material support fixture. The starting material support fixture applies pressure to the lower end of the dummy section while being pulled vertically along with the starting material until the stack is formed by the burner. At this point, to prevent the pulled starting material support fixture from breaking due to excessive proximity to the burner, the dummy section needs to have a predetermined length in the vertical direction. Given the limited total length of the starting material in the vertical direction due to equipment constraints, a longer dummy section results in a shorter accumulation section, leaving room for improvement in the lengthening of the accumulation section that becomes the optical fiber mother material.

[0008] The purpose of this disclosure is to provide a method for manufacturing an optical fiber mother material in which the central axis of the starting material is not easily deviated from the axis of rotation and the optical fiber mother material is made into a long dimension.

[0009] Technical solutions for solving technical problems

[0010] In one aspect of the optical fiber preform manufacturing method disclosed herein, a starting material held by a starting material holding rod is rotated about a rotation axis within a reaction vessel while moving relative to a first burner in a vertical direction, and glass microparticles are deposited on the outer periphery of the starting material, the glass microparticles being generated by hydrolyzing glass raw materials in a flame via the first burner. The manufacturing method of the optical fiber preform includes: a first deposition step in which the glass microparticles are deposited on the outer periphery of the starting material, and while pressure is applied to the lower end of the starting material supported by a fixture, the starting material is moved relative to the first burner in a vertical direction, the fixture being rotatably mounted on a support platform, the support platform being mounted to be movable in the vertical direction; and a second deposition step in which, after the first deposition step, the glass microparticles are deposited on the outer periphery of the starting material, and while the lower end of the starting material is separated from the fixture, the starting material is moved relative to the first burner in a vertical direction.

[0011] Invention Effects

[0012] According to this disclosure, there is a method for manufacturing an optical fiber mother material in which the central axis of the starting material is not easily deviated from the axis of rotation, and the optical fiber mother material is made to be of long dimensions. Attached Figure Description

[0013] Figure 1 This is a structural diagram illustrating an example of the manufacturing apparatus for the optical fiber preform of this disclosure.

[0014] Figure 2 This is a diagram illustrating the first deposition process of the method for manufacturing optical fiber preform in the first embodiment.

[0015] Figure 3 This is an example from Figure 2 The diagram shows the transition from the first stacking process to the second stacking process.

[0016] Figure 4 This is a diagram illustrating the second deposition process of the method for manufacturing the optical fiber preform in the first embodiment.

[0017] Figure 5 This is a diagram illustrating the middle of the first stacking process in the second embodiment. Detailed Implementation

[0018] (A description of one method of this disclosure)

[0019] First, we will describe the implementation aspects of this disclosure.

[0020] (1) In the method for manufacturing optical fiber preform according to one aspect of this disclosure, a starting material held by a starting material holding rod is rotated about a rotation axis in a reaction vessel while moving relative to a first burner in a vertical direction, and glass microparticles are deposited on the outer periphery of the starting material, the glass microparticles being generated by hydrolyzing glass raw materials in a flame through the first burner. The method for manufacturing optical fiber preform includes: a first depositing step in which the glass microparticles are deposited on the outer periphery of the starting material, and while the lower end of the starting material is supported by a fixture and pressure is applied to the lower end of the starting material, the starting material is moved relative to the first burner in the vertical direction, the fixture being rotatably disposed on a support table, the support table being mounted to be movable in the vertical direction; and a second depositing step in which, after the first depositing step, the glass microparticles are deposited on the outer periphery of the starting material, and while the lower end of the starting material is separated from the fixture, the starting material is moved relative to the first burner in the vertical direction.

[0021] According to this disclosure, since the lower end of the starting material is supported by a fixture and pressure is applied to the lower end of the starting material during the first stacking process, the central axis of the starting material is less likely to deviate from the axis of rotation. Furthermore, according to this disclosure, after the first stacking process, in other words, after the glass particles have been stacked on the outer periphery of the starting material through the first stacking process and the weight of the glass particle stack has become relatively large, the second stacking process is performed. Since the weight of the starting material is relatively large, the central axis of the starting material is less likely to deviate from the axis of rotation even when the lower end of the starting material is far away from the fixture. Thus, since the second stacking process is performed after the first stacking process with the lower end of the starting material far away from the fixture, fixture breakage due to excessive proximity to the first burner can be prevented, and glass particles can be stacked near the lower end of the starting material, making it easier to achieve long-length optical fiber preforms.

[0022] (2) Alternatively, the manufacturing method described in (1) may further include a flame milling process in at least a portion of the first stacking process, in which the outer surface of the starting material is vaporized by a second burner located in the vertical direction below the first burner, and the flame milling process is ended when switching from the first stacking process to the second stacking process.

[0023] If the starting material softens due to heating by the second burner, the deviation between the rotation axis and the central axis of the starting material tends to increase. According to this disclosure, since the flame milling process ends when switching from the first stacking process to the second stacking process, the deviation between the rotation axis and the central axis of the starting material is smaller. Furthermore, glass particles can be deposited near the lower end of the starting material without damaging the fixture due to the second burner, enabling the optical fiber preform to be dimensionally extended.

[0024] (3) Alternatively, the manufacturing method of (1) above may further include a flame milling process in at least a part of the first stacking process, in which the outer peripheral surface of the starting material is vaporized by a second burner located in the vertical direction below the first burner, and the flame milling process is ended by extinguishing the second burner in the first stacking process.

[0025] According to this disclosure, the flame milling process is completed in the first stacking process. Since the lower end of the starting material is also supported by the fixture after the second burner is extinguished, the central axis of the starting material is less likely to deviate from the axis of rotation.

[0026] (Details of one method disclosed herein)

[0027] Referring to the accompanying drawings, a specific example of a method for manufacturing an optical fiber preform according to one aspect of this disclosure will be described.

[0028] It should be noted that this disclosure is not limited to these examples, but is illustrated by the claims and is intended to include all changes within the meaning and scope of the claims.

[0029] (Fiber optic preform manufacturing apparatus)

[0030] Figure 1 This is a structural diagram illustrating an example of the optical fiber preform manufacturing apparatus 1 of this disclosure. The manufacturing apparatus 1 is configured to form a glass particle accumulation by depositing glass particles on the outer periphery of a starting material. In the following embodiments, the VAD (Vapor phase Axial Deposition) method will be used as an example of the optical fiber preform manufacturing method, but it is not limited to the VAD method. This embodiment can also be applied to methods that, similar to the VAD method, utilize flame pyrolysis to deposit glass particles from glass raw materials, such as the OVD (Outside Vapor phase Deposition) method.

[0031] like Figure 1As shown, the optical fiber preform manufacturing apparatus 1 of this embodiment includes a reaction vessel 2, a rotary chuck 3, a holding rod 4, an exhaust pipe 6, a first burner 7, and a second burner 8. The holding rod 4, held by the rotary chuck 3, is suspended from above inside the reaction vessel 2, and the upper part of the starting material 5 is held at the lower part of the holding rod 4. By rotating the chuck 3, the holding rod 4 rotates about the rotation axis A1 in the direction indicated by arrow B while moving in the vertical direction indicated by arrow C, thereby causing the starting material 5 to move while rotating. Furthermore, a glass particle accumulation body M is formed by depositing glass particles on the outer periphery of the starting material 5. An exhaust pipe 6 is installed on the side wall of the reaction vessel 2. The holding rod 4 is an example of a starting material holding rod.

[0032] A first burner 7 and a second burner 8 are provided at the lower part of the reaction vessel 2. The front ends of the first burner 7 and the second burner 8 are configured to expose into the interior of the reaction vessel 2 and face at least a portion of the outer periphery of the starting material 5.

[0033] The first burner 7 is configured to hydrolyze the glass raw material in a flame to generate glass microparticles, and then spray the generated glass microparticles toward the starting material 5. By causing the sprayed glass microparticles to accumulate on the outer periphery of the starting material 5, a glass microparticle accumulation body M is formed.

[0034] The second burner 8 is located further below the first burner 7. The second burner 8 burns by causing the supplied oxygen and hydrogen to undergo an oxidation reaction, thereby ejecting a hydrogen-oxygen flame from the front end of the second burner 8. The second burner 8 is configured to vaporize the surface of the starting material 5 by ejecting the hydrogen-oxygen flame, remove impurities adhering to the surface, and grind the surface.

[0035] The optical fiber preform manufacturing apparatus 1 of this embodiment also includes a cleanroom 10. Clean air is supplied to the cleanroom 10 from the supply pipe 11 to prevent foreign matter in the air from adhering to the surface of the starting material 5. The upper part of the cleanroom 10 is connected to the lower part of the reaction vessel 2 via a gas purification fixture 12. The gas purification fixture 12 is configured to isolate the atmosphere in the atmosphere from the atmosphere inside the reaction vessel 2, preventing external air from flowing into the reaction vessel 2. Inert gases such as nitrogen, which prevent corrosive gases from flowing out of the reaction vessel 2, can also flow into the gas purification fixture 12.

[0036] The clean booth 10 is equipped with a jig 13, a support platform 14, a guide 15, a counterweight 16, a pulley 17, and a cable 18.

[0037] The jig 13 is rotatably mounted on the support platform 14. The jig 13 is configured to support the lower end of the starting material 5. The support platform 14 is mounted on the guide portion 15 extending in the vertical direction so as to be movable in the vertical direction. Furthermore, the support platform 14 is connected to the counterweight 16 via a cable 18 suspended on a plurality of pulleys 17. Due to the weight of the counterweight 16, the support platform 14 connected to the counterweight 16 via the cable 18 is pulled upward. For this purpose, the jig 13 mounted on the support platform 14 applies pressure to the lower end of the starting material 5 in the upward direction while supporting the lower end of the starting material 5.

[0038] By rotating the chuck 3, the holding rod 4, the starting material 5, and the fixture 13 supporting the lower end of the starting material 5 are rotated together around the rotation axis A1 in the direction indicated by arrow B, causing the glass microparticles generated by the first burner 7 to accumulate on the outer periphery of the starting material 5. By pulling the rotating chuck 3 upward in coordination with the growth of the glass microparticle accumulation M, the starting material 5 moves upward relative to the first burner 7. As the starting material 5 moves, the fixture 13 also moves upward vertically while applying pressure to the lower end of the starting material 5, forming the glass microparticle accumulation M on the outer periphery of the starting material 5. The glass microparticle accumulation M is then made transparent through dehydration and sintering processes in subsequent steps to form the optical fiber mother material. The upward movement relative to the first burner 7 is an example of movement relative to the first burner.

[0039] (First Implementation)

[0040] Next, refer to Figures 2 to 4 The manufacturing method of the optical fiber preform in the manufacturing apparatus 1 using optical fiber preform will be described in detail. For the sake of brevity, Figures 2 to 4 The main examples are the starting material 5, the first burner 7, the second burner 8, and the fixture 13, while other structures are omitted.

[0041] The method for manufacturing optical fiber preform in this embodiment includes a first deposition process, a flame grinding process, and a second deposition process.

[0042] Figure 2 This is a diagram illustrating the first deposition process of the optical fiber preform manufacturing method in the first embodiment. (See diagram for example.) Figure 2As shown, the first stacking process is carried out under the condition that glass microparticles are stacked on the outer periphery of the starting material 5 by ignition of the first burner 7, and the lower end of the starting material 5 is supported by the jig 13 and pressure is applied to the lower end of the starting material 5 by the jig 13. In the first stacking process, under the condition that the lower end of the starting material 5 is supported by the jig 13 and pressure is applied to the lower end of the starting material 5 by the jig 13, the chuck 3 is pulled upward in the vertical direction, so that the starting material 5 moves upward in the vertical direction relative to the first burner 7.

[0043] The flame milling process is performed in at least a portion of the first stacking process. In the flame milling process, the outer peripheral surface of the starting material 5 is vaporized by ignition of the second burner 8. For this purpose, impurities adhering to the surface of the starting material 5 are removed, and the outer peripheral surface of the starting material 5 is milled.

[0044] The flame milling process begins with the ignition of the second burner 8 and ends with the extinguishing of the second burner 8. The flame milling process can begin just before the first stacking process begins, or it can begin midway through the first stacking process.

[0045] Figure 3 This is an example from Figure 2 The diagram shows the transition from the first stacking process to the second stacking process. (See diagram below.) Figure 3 As shown, in this embodiment, when switching from the first stacking process to the second stacking process, the second burner 8 is extinguished to end the flame grinding process.

[0046] Figure 4 This diagram illustrates the second deposition process of the optical fiber preform manufacturing method in the first embodiment. The second deposition process is performed after the first deposition process. The second deposition process is performed while glass microparticles are deposited on the outer periphery of the starting material 5 by the continuous operation of the first burner 7 from the first deposition process, and the lower end of the starting material 5 is separated from the fixture 13. In the second deposition process, with the lower end of the starting material 5 separated from the fixture 13, the rotating chuck 3 is pulled upward in the vertical direction, causing the starting material 5 to move upward in the vertical direction relative to the first burner 7.

[0047] After the glass microparticle stack M formed in the first and second stacking processes is subjected to dehydration and sintering treatments to achieve transparency, it forms the optical fiber mother material.

[0048] As explained above, according to this embodiment, the lower end of the starting material 5 is supported by the fixture 13, and pressure is applied to the lower end of the starting material 5 to perform the first stacking process. Therefore, the central axis A5 of the starting material 5 is less likely to deviate from the rotation axis A1 of the manufacturing apparatus 1.

[0049] Furthermore, according to this embodiment, the second stacking process is performed after the first stacking process. In other words, the second stacking process is performed after the glass microparticles have been stacked on the outer periphery of the starting material 5 through the first stacking process, resulting in a relatively large weight of the glass microparticle stack M. Because the weight of the glass microparticle stack M is relatively large, the central axis A5 of the starting material 5 is less likely to deviate from the rotation axis A1 of the manufacturing apparatus 1, even when the lower end of the starting material 5 is far away from the fixture 13. Thus, since the second stacking process is performed after the first stacking process with the lower end of the starting material 5 far away from the fixture 13, damage to the fixture 13 due to excessive proximity to the first burner 7 can be prevented.

[0050] Furthermore, the starting material 5 includes an accumulation portion formed by depositing glass microparticles into a glass microparticle pile M by the first burner 7, and a dummy portion located vertically below the accumulation portion and whose lower end abuts against the fixture 13. Assuming that, unlike this embodiment, only the first accumulation process is performed without a second accumulation process, the process is carried out with the lower end of the dummy portion of the starting material 5 supported by the fixture 13 until the glass microparticle pile M is formed by the first burner 7. In this case, to prevent the fixture 13, which is being pulled upwards, from getting too close to the flame of the first burner 7 and breaking, the dummy portion needs to have a predetermined length in the vertical direction. The longer the dummy portion, the greater the distance between the flame of the first burner 7 and the fixture 13 can be increased, making it easier to prevent the fixture 13 from breaking. However, given the limitation on the total length of the starting material 5 in the vertical direction due to equipment constraints in the manufacturing apparatus 1, if the dummy portion is long, the glass microparticle pile M will correspondingly become shorter, making it difficult to achieve the desired length of the glass microparticle pile M that becomes the optical fiber preform.

[0051] However, according to this embodiment, since the second deposition process is performed after the first deposition process with the lower end of the starting material 5 far from the fixture 13, it is possible to deposit glass particles near the lower end of the starting material 5 while preventing damage to the fixture 13. Because the dummy portion used to separate the distance between the first burner 7 and the fixture 13 can be shortened or eliminated, it is easier to increase the length of the glass particle deposit M, and consequently, it is easier to increase the length of the optical fiber preform. It has been confirmed that the manufacturing method of this embodiment can shorten the dummy portion, allowing the length of the glass particle deposit M to be 100 mm or more.

[0052] Furthermore, if the starting material softens due to heating by the second burner 8, the deviation between the rotation axis A1 and the central axis A5 of the starting material 5 can easily become large. According to this embodiment, the flame milling process ends when switching from the first stacking process to the second stacking process. Therefore, the deviation between the rotation axis A1 and the central axis A5 is smaller. Furthermore, glass particles can be deposited near the lower end of the starting material 5 without damaging the fixture 13 due to the second burner 8, enabling the optical fiber preform to be dimensionally extended.

[0053] (Second Implementation)

[0054] In the first embodiment, the flame milling process ends when switching from the first stacking process to the second stacking process, by extinguishing the second burner 8. However, the end of the flame milling process is not limited to this timing.

[0055] Figure 5 This is a diagram illustrating the intermediate stage of the first stacking process in the second embodiment. Figure 5 In the structure shown, for and Figure 3 Structures with the same designation are labeled with the same reference numerals, and their descriptions are omitted. For example... Figure 5 As shown, in this embodiment, the flame grinding process ends by extinguishing the second burner 8 midway through the first stacking process.

[0056] According to this embodiment, regarding the flame grinding process, the second burner 8 is extinguished midway through the first stacking process. Therefore, even after the second burner 8 is extinguished, the lower end of the starting material 5 is supported by the fixture 13. Consequently, the central axis A5 is less likely to deviate from the rotation axis A1.

[0057] Explanation of reference numerals in the attached figures

[0058] 1 Manufacturing apparatus

[0059] 2. Reaction Vessel

[0060] 3. Rotary chuck

[0061] 4. Holding the stick

[0062] 5. Starting materials

[0063] 6. Exhaust pipe

[0064] 7 First Burner

[0065] 8 Second burner

[0066] 10 Cleanrooms

[0067] 11 Supply Management

[0068] 12 Gas purification fixtures

[0069] 13 fixtures

[0070] 14 Support platform

[0071] 15. Guiding Department

[0072] 16 counterweights

[0073] 17. Pulleys

[0074] 18 cables

[0075] A1 Rotation axis

[0076] A5 central axis.

Claims

1. A method for manufacturing an optical fiber preform, wherein a starting material held by a starting material holding rod is rotated about a rotation axis within a reaction vessel while moving relative to a first burner in a vertical direction, and glass microparticles are deposited on the outer periphery of the starting material, the glass microparticles being generated by hydrolyzing glass raw materials in a flame using the first burner. The method for manufacturing the optical fiber mother material includes: In the first deposition process, the glass microparticles are deposited on the outer periphery of the starting material, and pressure is applied to the lower end of the starting material while the lower end of the starting material is supported by a fixture, while the starting material is moved relative to the first burner in the vertical direction. The fixture is rotatably mounted on a support platform, which is installed to be movable in the vertical direction. as well as In the second stacking process, after the first stacking process, the glass microparticles are stacked on the outer periphery of the starting material, and the starting material is moved relative to the first burner in the vertical direction while the lower end of the starting material is separated from the fixture.

2. The method for manufacturing optical fiber mother material according to claim 1, wherein, The method for manufacturing the optical fiber preform further includes a flame milling step in at least a portion of the first stacking step, wherein the outer peripheral surface of the starting material is vaporized by a second burner located further below the first burner in the vertical direction. When switching from the first stacking process to the second stacking process, the second burner is extinguished to end the flame grinding process.

3. The method for manufacturing optical fiber mother material according to claim 1, wherein, The method for manufacturing the optical fiber preform further includes a flame milling step in at least a portion of the first stacking step, wherein the outer peripheral surface of the starting material is vaporized by a second burner located further below the first burner in the vertical direction. The flame grinding process ends when the second burner is extinguished during the first stacking process.

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