Rod insertion jig and method for manufacturing multi-core optical fiber preform

Abstract

A rod insertion jig inserts a glass rod into a hole portion of a clad precursor. The clad precursor has a first hole portion. A first glass tube is connected to a first end of the clad precursor. A second glass tube is connected to a second end of the clad precursor. A first glass rod, which is a rod-shaped member having a first direction as an axial direction, is a glass rod to be inserted into the first hole portion. The rod insertion jig includes a support portion that is in contact with an inner surface of the first glass tube, a first holding portion that is supported by the support portion inside the first glass tube, and a first moving portion that is a member for moving the first glass rod. The first holding portion has a first placement surface on which the first glass rod is placed in the first direction. The support portion supports the first holding portion in such a manner that the entirety of the first glass rod placed on the first placement surface overlaps the first hole portion as viewed in the first direction. The first moving portion moves the first glass rod placed on the first placement surface in the first direction.

Description

Technical Field

[0001] This disclosure relates to a rod insertion fixture and a method for manufacturing a multi-core optical fiber mother material. This disclosure also relates to optical fibers and methods for manufacturing optical fibers. This application claims priority to Japanese Application No. 2021-189293, filed November 22, 2021, and invokes all the contents described in that Japanese application. Background Technology

[0002] Patent Document 1 discloses a method for manufacturing a multi-core optical fiber (hereinafter referred to as MCF) mother material, including: a step of inserting multiple core materials into multiple holes provided in a cladding material; a step of inserting a rotor into a glass tube connected to both ends of the cladding material and fixing the core materials by clamping the rotor; and a step of heating the core materials and the cladding material to integrate them.

[0003] Existing technical documents

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent Application Publication No. 2011-168464 Summary of the Invention

[0006] One aspect of this disclosure relates to a rod insertion fixture for inserting a glass rod through a hole in a cladding material. The cladding material is a cylindrical member having two opposing first and second ends, and a first hole extending along the central axis from the first end to the second end at a position off-center from the central axis in a cross-section perpendicular to the central axis of the cladding material. A first glass tube is connected to the first end of the cladding material. A second glass tube is connected to the second end of the cladding material. The first glass rod, to be inserted into the first hole, is a rod-shaped member with a first axial direction. The rod insertion fixture includes: a support portion that contacts the inner surface of the first glass tube; a first holding portion supported by the support portion inside the first glass tube; and a first moving portion that serves as a component for moving the first glass rod. The first holding portion has a first mounting surface for placing the first glass rod along the first direction. The support unit supports the first holding unit in such a way that the entire first glass rod, which is placed on the first mounting surface, overlaps with the first hole when viewed from the first direction. The first moving unit moves the first glass rod, which is placed on the first mounting surface, in the first direction. Attached Figure Description

[0007] [ Figure 1 ] Figure 1 This is a cross-sectional view of the MCF base material manufactured using the rod insertion fixture of the embodiment.

[0008] [ Figure 2 ] Figure 2 This is a flowchart illustrating a method for manufacturing the MCF base material according to an embodiment.

[0009] [ Figure 3 ] Figure 3 It is a perspective view of the cladding material connected to the glass tube.

[0010] [ Figure 4 ] Figure 4 This is a cross-sectional view of the cladding substrate.

[0011] [ Figure 5 ] Figure 5 It is a cross-sectional view used to illustrate the insertion process.

[0012] [ Figure 6 ] Figure 6 This is a perspective view showing the rod insertion fixture according to the embodiment.

[0013] [ Figure 7 ] Figure 7 It is along Figure 5 A cross-sectional view of line VII-VII.

[0014] [ Figure 8 ] Figure 8 It is a cross-sectional view used to illustrate the integrated process.

[0015] [ Figure 9 ] Figure 9 This is a cross-sectional view used to illustrate the insertion process using the rod insertion fixture involved in the first variation.

[0016] [ Figure 10 ] Figure 10 This is a cross-sectional view used to illustrate the insertion process using the rod insertion fixture involved in the second variation. Detailed Implementation

[0017] [The problem this disclosure aims to solve]

[0018] Because glass tubes are connected to both ends of the cladding material, the core is typically inserted into a hole approximately 10 mm in diameter, located about 1000 mm ahead. Furthermore, since the hole is not on the central axis of the cladding material, core insertion is difficult. Even if insertion is possible, friction causes damage to the core and the inner wall of the hole when the insertion direction deviates from the hole's axis. This damage results in air bubbles in the optical fiber, potentially reducing the yield.

[0019] Cutting the glass tube during core insertion was also considered; however, due to the cutting and reconnection of the glass tube, foreign matter may get into the pores of the cladding material. Such foreign matter may have adverse effects on the optical fiber, such as reduced strength and deterioration of propagating light characteristics.

[0020] The purpose of this disclosure is to provide a rod insertion fixture capable of inserting a glass rod into a hole in a cladding base material while suppressing damage and foreign matter ingress, as well as a method for manufacturing the MCF base material.

[0021] [The Effects of This Disclosure]

[0022] According to this disclosure, a rod insertion fixture capable of inserting a glass rod into a hole in the cladding masterbatch while suppressing damage and foreign matter ingress, and a method for manufacturing the MCF masterbatch, can be provided.

[0023] [Description of embodiments of this disclosure]

[0024] First, embodiments of the present disclosure are listed and described. One aspect of the present disclosure relates to a rod insertion fixture that inserts a glass rod into a hole penetrating a cladding substrate. The cladding substrate is a columnar member having a first end and a second end opposite to each other, and has a first hole that extends along the central axis from the first end to the second end at a position offset from the central axis in a cross-section perpendicular to the central axis of the cladding substrate. A first glass tube is connected to the first end of the cladding substrate. A second glass tube is connected to the second end of the cladding substrate. The first glass rod, which is inserted into the first hole, is a rod-shaped member with a first direction as its axial direction. The rod insertion fixture includes: a support portion disposed in contact with the inner surface of the first glass tube; a first holding portion supported by the support portion inside the first glass tube; and a first moving portion serving as a member for moving the first glass rod. The first holding portion has a first mounting surface for mounting the first glass rod along the first direction. The support unit supports the first holding unit in such a way that the entire first glass rod, which is placed on the first mounting surface, overlaps with the first hole when viewed from the first direction. The first moving unit moves the first glass rod, which is placed on the first mounting surface, in the first direction.

[0025] In the aforementioned rod insertion fixture, since the first glass rod is held by the first holding part and inserted into the interior of the first glass tube, the first glass rod can be transported to the vicinity of the cladding material without cutting the first glass tube. Therefore, the first glass rod can be inserted into the first hole while suppressing the introduction of foreign matter caused by cutting and reconnecting the first glass tube. The first glass rod is placed on the first mounting surface of the first holding part and guided in the first direction by the first mounting surface. Therefore, the first moving part can move the first glass rod along the first mounting surface in the first direction. According to the support part, the insertion position and insertion direction of the first glass rod relative to the first hole can be appropriately adjusted. Therefore, the first glass rod can be inserted into the first hole while suppressing damage to the inner wall of the first glass rod and the first hole.

[0026] The cladding material may also have a second hole, different from the first hole. The second glass rod, to be inserted into the second hole, may be a rod-shaped component with a second axial direction. The rod insertion fixture may also include a second holding part supported by a support part inside the first glass tube, and a second moving part for moving the second glass rod. The second holding part may have a second mounting surface on which the second glass rod is placed along the second direction. The support part may support the second holding part in such a way that the second glass rod, placed on the second mounting surface, overlaps entirely with the second hole when viewed from the second direction. The second moving part can move the second glass rod placed on the second mounting surface in the second direction. In this case, since the second glass rod is held by the second holding part and inserted into the interior of the first glass tube, the second glass rod can be positioned near the cladding material without cutting the first glass tube. Therefore, the second glass rod can be inserted into the second hole while suppressing the intrusion of foreign matter caused by cutting and reconnecting the first glass tube. The second glass rod is placed on the second mounting surface of the second holding part and guided in the second direction by the second mounting surface. Therefore, the second moving part can move the second glass rod along the second mounting surface in the second direction. According to the support part, the insertion position and insertion direction of the second glass rod relative to the second hole can be appropriately adjusted. Therefore, the second glass rod can be inserted into the second hole while suppressing damage to the inner wall of the second glass rod and the second hole. In addition, since the first glass rod and the second glass rod can be inserted simultaneously, the manufacturing time can be shortened.

[0027] The second moving part can be the same component as the first moving part. In this case, the first glass rod and the second glass rod can be moved sequentially.

[0028] The second moving part can be a different component from the first moving part. In this case, the first glass rod and the second glass rod can be moved simultaneously.

[0029] The support portion may include a first support member and a second support member that are separated from each other in the longitudinal direction of the first retaining portion. In this case, the first retaining portion can be stably supported.

[0030] Viewed from the longitudinal direction of the first holding part, the first mounting surface can be a curved surface along the outer peripheral surface of the glass rod. In this case, it is easy to guide the first glass rod in the first direction.

[0031] The longitudinal length of the first retaining part can be longer than the longitudinal length of the first glass tube. In this case, it is easy to insert the first glass rod into the first hole.

[0032] The longitudinal length of the first moving part can be longer than the longitudinal length of the first holding part. In this case, the first moving part can apply a compressive force to the first glass rod from one end of the first holding part to the other.

[0033] The first retaining part can be configured such that its front end is separated from the first end of the cladding material. In this case, damage and foreign matter ingress can be suppressed.

[0034] One aspect of this disclosure relates to a method for manufacturing an MCF (Metallic Fluorescent Cell) base material, comprising: preparing a cladding base material to which a first glass tube is connected at a first end and to which a hole is formed at a position off-center from the central axis along the direction of the central axis; preparing a glass rod; inserting the glass rod into the hole using the aforementioned rod insertion fixture; and integrating the cladding base material and the glass rod inserted into the hole.

[0035] In the above-described method for manufacturing MCF base material, since the above-described rod insertion fixture is used, the glass rod can be inserted into the hole of the cladding base material while suppressing damage and the incorporation of foreign matter.

[0036] [Details of the embodiments disclosed herein]

[0037] The following description, with reference to the accompanying drawings, illustrates specific examples of the rod insertion fixture and the method for manufacturing the MCF base material of this disclosure. It should be noted that the invention is not limited to these examples, but is defined by the claims and is intended to include all modifications of the same meaning and scope. In the description of the drawings, the same symbols are used to denote the same elements, and repeated descriptions are omitted.

[0038] Figure 1 This is a cross-sectional view of the MCF base material manufactured using the rod insertion fixture of the embodiment. The view shows a cross-section perpendicular to the central axis A1 of the MCF base material 1. The MCF base material 1 has multiple cores 2 and a common cladding portion 3. In this embodiment, the number of cores 2 is two.

[0039] The core 2 extends along the central axis A1. Multiple cores 2 are located offset from the central axis A1 in cross-section, arranged in a position symmetrical to each other with respect to the central axis A1. The cross-sectional shape of the multiple cores 2 is the same as that of each other, forming a circle. A cladding portion 3 surrounds the multiple cores 2. The cross-sectional shape of the cladding portion 3 is circular.

[0040] The refractive index of core 2 is higher than that of cladding 3. Both core 2 and cladding 3 are made of silica-based glass. Core 2 and cladding 3 are primarily composed of silica glass and contain dopants for refractive index adjustment.

[0041] Figure 2 This is a flowchart illustrating a method for manufacturing the MCF base material according to an embodiment. Figure 2As shown, the manufacturing method of MCF base material 1 includes: preparation process S1, etching process S2, insertion process S3 and integration process S4.

[0042] Preparation step S1 involves preparing multiple mandrels 4 (refer to...) Figure 5 ), and a cladding material 7 to which a first glass tube 5 is connected at the first end 7a and a second glass tube 6 is connected at the second end 7b (refer to Figure 3 The preparation of the plurality of mandrels 4 can be performed at least before the insertion step S3. In this embodiment, the plurality of mandrels 4 includes a first mandrel 41 (refer to...). Figure 5 ) and the second core rod 42 (refer to) Figure 8 The first core rod 41 and the second core rod 42 are collectively referred to as core rod 4. The preparation of the cladding substrate 7, which connects the first glass tube 5 and the second glass tube 6, is carried out before the etching process S2.

[0043] Core rod 4 is used to form core 2 (see reference). Figure 1 The core rod 4 is a glass rod. Multiple core rods 4 have the same shape. The core rod 4 is cylindrical. The diameter of the core rod 4 is, for example, 9 mm or more and 15 mm or less. The longitudinal length of the core rod 4 can be 400 mm or more, 800 mm or more, or 1200 mm or more. That is, the core rod 4 can be a rod-shaped component with an axial direction. This increases the length (fiber length) of the optical fiber that can be manufactured from a single MCF mother material 1, thereby reducing the manufacturing cost per unit length of the optical fiber.

[0044] Figure 3 It is a perspective view of the cladding material connected to the glass tube. Figure 3 The cladding material 7 shown is used to form the cladding portion 3 (see reference). Figure 1 The cladding material 7 is a columnar component, for example, having a cylindrical shape. The diameter of the cladding material 7 is, for example, 40 mm to 120 mm. The longitudinal length of the cladding material 7 is equal to the longitudinal length of the core rod 4. The cladding material 7 has a first end 7a and a second end 7b in the longitudinal direction as its two ends.

[0045] Figure 4 This is a cross-sectional view of the cladding base material. The view shows a section perpendicular to the central axis A7 of the cladding base material 7. Figure 4 As shown, the cladding material 7 is perforated. In the cladding material 7, at a position offset from the central axis A7, multiple holes 8 extend from the first end 7a to the second end 7b along the central axis A7. The central axis A8 of each hole 8 (refer to...) Figure 5It is parallel to the central axis A7. In this embodiment, the plurality of holes 8 include a first hole 81 and a second hole 82. The first hole 81 and the second hole 82 are collectively referred to as holes 8. A plurality of mandrels 4 are inserted into the plurality of holes 8. The first mandrel 41 is inserted into the first hole 81. The second mandrel 42 is inserted into the second hole 82.

[0046] The arrangement of the plurality of holes 8 in the cladding material 7 is the same as the arrangement of the plurality of cores 2 in the cladding portion 3. That is, the first hole 81 and the second hole 82 are located off-center from the central axis A7 in cross-section, and are arranged in a position that is point-symmetrical to each other with respect to the central axis A7. The plurality of holes 8 have the same shape as each other. The holes 8 have a circular cross-sectional shape. In cross-section, the first hole 81 and the second hole 82 are arranged in a direction orthogonal to the central axis A7. The diameter of each hole 8 is the same as or longer than the diameter of the core rod 4, for example, 9 mm or more and 16 mm or less. Thus, after the etching process S2, the diameter of each hole 8 becomes a size sufficient for inserting the core rod 4.

[0047] like Figure 3 As shown, a first glass tube 5 is joined to the first end 7a of the cladding material 7, and a second glass tube 6 is joined to the second end 7b. The first glass tube 5 and the second glass tube 6 are dummy pipes. The first glass tube 5 and the second glass tube 6 have a cylindrical shape. The outer diameter of the first glass tube 5 and the second glass tube 6 is approximately the same as or smaller than the diameter of the cladding material 7, and the inner diameter is larger than the diameter of the mandrel 4. The first glass tube 5 and the second glass tube 6 are joined coaxially with the cladding material 7. That is, the central axis of the first glass tube 5 and the second glass tube 6 coincides with the central axis A7. The lengths of the first glass tube 5 and the second glass tube 6 are, for example, equal to each other. The length of the first glass tube 5 is long enough that heat emitted from an external heat source during the etching or integration process will not affect the holding part 9 (see reference). Figure 5 The extent to which it has a significant impact. The length of the first glass tube 5 is, for example, more than 1000 mm and less than 2000 mm. Therefore, it is difficult to hold the mandrel 4 directly by hand and insert it into the hole 8.

[0048] Etching process S2 is a process of etching the inner surfaces of the multiple holes 8 of the cladding substrate 7 for cleaning purposes. In etching process S2, etching gas acting on the glass is introduced from the second glass tube 6 into the multiple holes 8 of the cladding substrate 7 and discharged from the first glass tube 5. Heating is performed by an external heat source (not shown), thereby causing an etching reaction. The external heat source can be, for example, an induction furnace, a resistance furnace, or an oxyhydrogen burner. As a result, a certain degree of the inner surface layer of the multiple holes 8 is removed, removing impurities present on the inner surface and smoothing the inner surface.

[0049] In etching process S2, toxic gases such as chlorine (Cl2) are used as etching gases in addition to sulfur hexafluoride (SF6). Therefore, etching process S2 needs to be carried out in a closed system isolated from the external environment. Etching process S2 is performed by connecting the gas inlet (not shown) to the second glass tube 6 and the gas outlet (not shown) to the first glass tube 5. One reason for not directly connecting the gas inlet and gas outlet to the cladding substrate 7 is to maintain the cleanliness of the inner surface of the cladding substrate 7. Another reason is that in etching process S2 and integration process S4, the effective part of the cladding substrate needs to be heated at high temperatures, but it is difficult to prepare gas inlet and gas outlet that can withstand such high temperatures.

[0050] Insertion step S3 involves inserting a rod into fixture 11 (see reference). Figure 5 The process of inserting multiple mandrels 4 into multiple holes 8 in the cladding substrate 7. The insertion process S3 is performed after the preparation process S1 and the etching process S2.

[0051] Figure 5 This is a cross-sectional view used to illustrate the insertion process. For example... Figure 5 As shown, the insertion process S3 is performed in a manner that aligns the central axis A7 of the cladding material 7 with the horizontal direction, while the first glass tube 5 and the second glass tube 6 are held by the holding parts 9 and 10 of the glass lathe. Specifically, the first glass tube 5 is held by the holding part 9, and the second glass tube 6 is held by the holding part 10.

[0052] The first glass tube 5 and the second glass tube 6 are held by the holding parts 9 and 10 in a manner that allows them to rotate about the central axis A7. The holding parts 9 and 10 rotate the first glass tube 5 and the second glass tube 6 such that one of the plurality of holes 8 is positioned at the lowest position in the vertical direction D2, i.e., the direction of gravity. Here, among the plurality of holes 8, the first hole 81 is positioned at the lowest position in the vertical direction D2, and the second hole 82 is positioned at the highest position in the vertical direction D2. The first hole 81 and the second hole 82 are arranged in the same direction as the vertical direction D2.

[0053] Figure 6 This is a perspective view showing the rod insertion fixture according to the embodiment. (See attached image.) Figure 5 and Figure 6 As shown, the rod insertion fixture 11 includes a holding part 12, a supporting part 14, and a moving part 15. The rod insertion fixture 11 inserts the mandrel 4 into the hole part 8, which is located off-center from the central axis A7 and has the cladding material 7 of the first glass tube 5 and the second glass tube 6 connected at both ends.

[0054] The retaining part 12 holds the mandrel 4 and inserts it into the interior of the first glass tube 5. The retaining part 12 is supported by the supporting part 14 inside the first glass tube 5. The retaining part 12 is made of a resin with heat resistance and chemical resistance, such as fluororesin. The retaining part 12 has a hollow shape. The retaining part 12 is a cylindrical tube. The retaining part 12 is formed in such a way that it can accommodate the mandrel 4 inside. The retaining part 12 has a mounting surface 13 that supports the mandrel 4 along the axial direction D1 of the mandrel 4. It can be considered that the mounting surface 13 supports the side of the mandrel 4 in the vertical direction D2.

[0055] The mounting surface 13 is configured to guide the mandrel 4 along its axial direction D1. The mounting surface 13 extends along the longitudinal direction of the holding portion 12. The mounting surface 13 is configured to guide the mandrel 4 along the extending direction of the mounting surface 13 of the holding portion 12. The mandrel 4 is mounted on the mounting surface 13 with its axial direction D1 aligned with the extending direction of the mounting surface 13. Thus, the mandrel 4 mounted on the mounting surface 13 is guided along its axial direction D1. Viewed from the longitudinal direction of the holding portion 12, the mounting surface 13 is a curved surface that bends along the outer peripheral surface of the mandrel 4.

[0056] The longitudinal length of the holding part 12 is longer than the length of the first glass tube 5. The longitudinal length of the holding part 12 can be 800 mm or more, 1200 mm or more, or 1600 mm or more. By extending the length of the first glass tube 5, the heating part 18 (see reference) can be extended. Figure 8 The length between the holding part 9 and the gripping part 9. This allows for the suppression of thermal effects on the gripping part 9. Therefore, it increases heating capacity, shortens processing time, and increases output.

[0057] The support portion 14 is disposed in contact with the inner surface of the first glass tube 5 and supports the retaining portion 12 in the vertical direction D2. The support portion 14 may also be fixed to the retaining portion 12. The support portion 14 includes a first support member 141 and a second support member 142 disposed separately from each other in the longitudinal direction of the retaining portion 12. The first support member 141 and the second support member 142 are plate-shaped members with a predetermined thickness, on which the retaining portion 12 is disposed. The first support member 141 and the second support member 142 are, for example, made of a heat-resistant resin such as fluororesin. The first support member 141 and the second support member 142 have, for example, the same shape.

[0058] The moving part 15 moves the mandrel 4 by applying an axial compressive force D1 to the end face of the mandrel 4 held by the holding part 12. The moving part 15 is, for example, a rod-shaped component with a circular cross-section. The moving part 15 is made of, for example, a heat-resistant resin such as fluoropolymer. The longitudinal length of the moving part 15 is longer than the longitudinal length of the holding part 12. As a result, the moving part 15 can apply compressive force to the mandrel 4 from one end of the holding part 12 to the other end.

[0059] Figure 7It is along Figure 5 A cross-sectional view of line VII-VII. (See attached image.) Figure 5 and Figure 7 As shown, in the insertion process S3, firstly, in the rod insertion fixture 11, the holding part 12 holding the mandrel 4 is arranged together with the support part 14 in the internal space SP1 of the first glass tube 5. Thus, the mandrel 4 is positioned in the internal space SP1. The front end of the holding part 12 is separated from the first end 7a in a manner that is opposite to but does not contact the first end 7a of the cladding material 7.

[0060] The support portion 14 is arranged to contact the inner surface of the first glass tube 5. The support portion 14 is arranged such that its thickness direction is aligned with the vertical direction D2. The support portion 14 is configured to allow adjustment of the insertion position and insertion direction of the mandrel 4 relative to the hole portion 8. The support portion 14 supports the retaining portion 12 such that the axial direction D1 of the mandrel 4 is parallel to the central axis A7, and the entire mandrel 4, placed on the mounting surface 13, overlaps with the hole portion 8 when viewed along the central axis A7.

[0061] The height of the mandrel 4 is set, for example, based on the thickness of the support portion 14. The thickness T of the support portion 14 is selected as follows: when the width of the support portion 14 is set to W, the inner radius of the first glass tube 5 is set to R, the distance from the inner surface of the first glass tube 5 to the center of the hole 8 is set to H, and the distance from the bottom surface of the holding portion 12 to the center of the mandrel 4 is set to C, T = H - {R - (R 2 -{W / 2} 2 ) 1 / 2 +C}. Where the width W is defined as... Figure 7 The minimum width of the cross-section, in the horizontal direction perpendicular to the vertical direction D2, includes all the inner contact points of the support portion 14 and the inner surface of the first glass tube 5. As a result, the mandrel 4 (here, the first mandrel 41) held by the holding portion 12 and disposed on the upper part of the support portion 14 is substantially coaxial with the hole 8 (here, the first hole 81) disposed at the lowest position in the vertical direction D2 among the plurality of holes 8. When the support portion 14 is disposed in the inner space SP1 of the first glass tube 5, it is fixed to the holding portion 12 in such a way that the longitudinal direction of the holding portion 12 is parallel to the central axis A7. Thus, the axial direction D1 of the mandrel 4 is parallel to the central axis A7.

[0062] On the other hand, an abutment portion 16 is disposed in the internal space SP2 of the second glass tube 6, where the front end of the mandrel 4 abuts. The abutment portion 16 is disposed separately from the second end 7b of the cladding material 7 in a manner that is opposite to but does not contact the second end 7b. The abutment portion 16 is made of glass, for example. The abutment portion 16 functions as a stopper that restricts the movement of the mandrel 4 along the axial direction D1. A vent hole of a size that prevents the mandrel 4 from passing through is provided in the abutment portion 16.

[0063] Next, the moving part 15 applies an axial force D1 to the mandrel 4 held by the holding part 12. The mandrel 4 is guided axially D1 along the mounting surface 13 of the holding part 12. The mandrel 4 moves axially D1 until it abuts against the abutting part 16 and is pressed into the hole 8. Thus, the mandrel 4 is inserted into the hole 8.

[0064] Next, after removing the rod insertion fixture 11 to the outside of the first glass tube 5, the first glass tube 5 and the second glass tube 6 are rotated 180 degrees using the holding parts 9 and 10. This positions the other hole 8 (here, the second hole 82) among the plurality of holes 8 where the core rod 4 is not inserted at the lowest position in the vertical direction D2. Then, similarly to the insertion of the first core rod 41, the second core rod 42 is inserted into the second hole 82 using the rod insertion fixture 11. In this embodiment, the number of holes 8 is 2, but in cases of 3 or more, the same method applies: each core rod 4 is inserted into a hole 8 using the rod insertion fixture 11. After all the core rods 4 to be inserted are inserted, the abutment part 17 is inserted into the first glass tube 5 in a manner that abuts against the inserted core rod 4. The abutment part 17 prevents the core rod 4 from shifting into the interior of the first glass tube 5.

[0065] The integration process S4 is a process in which the cladding base material 7 and the multiple mandrels 4 inserted into the multiple holes 8 of the cladding base material 7 are heated and melted together to form an integrated structure. The integration process S4 is performed after the insertion process S3.

[0066] Figure 8 This is a cross-sectional view used to illustrate the integrated process. For example... Figure 8 As shown, in the integration process S4, the cladding base material 7 and the mandrel 4 are heated by the heating unit 18. The heating unit 18 is arranged, for example, to surround the cladding base material 7 in the circumferential direction. The integration process S4 is performed, for example, while the cladding base material 7 is rotated by the holding parts 9 and 10. As a result, the cladding base material 7 and the mandrel 4 can be heated uniformly.

[0067] In the integrated process S4, the movement of the mandrel 4 along the central axis A7 is restricted by the abutment portions 16 and 17. As described above, the abutment portion 16 is disposed in the internal space SP2. The abutment portion 17 is disposed in the internal space SP1. The abutment portion 17 is disposed separately from the first end 7a of the cladding material 7 in a manner that is opposite to but does not contact the first end 7a. The abutment portions 16 and 17 are disposed such that they clamp the cladding material 7 in the direction (horizontal direction) along the central axis A7.

[0068] The integration process S4 is performed while the pressure within the multiple orifices 8 is reduced via pressure regulating units 19 and 20. Pressure regulating unit 19 is connected to the first glass tube 5. Pressure regulating unit 20 is connected to the second glass tube 6. As a result, the orifices 8 shrink, and the cladding material 7 and the core rod 4 become integrated. The heating unit 18 moves along the central axis A7 while integrating the cladding material 7 and the core rod 4 along their entire length. As a result, the MCF cladding material 1 is produced.

[0069] As explained above, in the rod insertion fixture 11, the mandrel 4 is held by the holding part 12 and inserted into the interior of the first glass tube 5, thus allowing the mandrel 4 to be transported to the vicinity of the cladding material 7 without cutting the first glass tube 5. Therefore, the mandrel 4 can be inserted into the hole 8 while suppressing the introduction of foreign matter caused by cutting and reconnecting the first glass tube 5. The mandrel 4 is placed on the mounting surface 13 of the holding part 12 and guided axially D1 through the mounting surface 13. Therefore, the moving part 15 allows the mandrel 4 to move axially D1 along the mounting surface 13. According to the support part 14, the insertion position and direction of the mandrel 4 relative to the hole 8 can be appropriately adjusted. Therefore, the mandrel 4 can be inserted into the hole 8 while suppressing damage to the inner wall of the mandrel 4 and the hole 8.

[0070] In the manufacturing method of MCF base material 1 according to this embodiment, since the rod insertion jig 11 is used, the mandrel 4 can be inserted into the hole 8 while suppressing damage and the mixing of foreign matter.

[0071] The support portion 14 includes a first support member 141 and a second support member 142 that are separated from each other in the longitudinal direction of the retaining portion 12. Therefore, the retaining portion 12 can be stably supported.

[0072] Viewed from the longitudinal direction of the holding part 12, the mounting surface 13 is a curved surface that bends along the outer peripheral surface of the mandrel 4. Therefore, the mandrel 4 is mounted on the mounting surface 13 in such a way that the axial direction D1 is aligned with the extending direction of the mounting surface 13. Therefore, the mandrel 4 can be easily guided along the axial direction D1.

[0073] Figure 9 This is a cross-sectional view used to illustrate the insertion process using the rod insertion fixture involved in the first variation. For example... Figure 9 As shown, the rod insertion fixture 11A involved in the first modification is similar in shape to the rod insertion fixture 11 (see reference 11) in terms of the shape of the holding part 12. Figure 7 The retaining part 12 of the rod insertion fixture 11A is not a round tube, but a U-shaped groove member with an open upper section. In this modified example, the retaining part 12 is composed of a half-tube that divides the round tube in half.

[0074] In the rod insertion fixture 11A, the retaining part 12 also holds the mandrel 4 and inserts it into the first glass tube 5. Furthermore, the retaining part 12 has a mounting surface 13 for placing the mandrel 4, which guides the mandrel 4 in the axial direction D1. Therefore, by using the rod insertion fixture 11A, the mandrel 4 can be inserted into the hole 8 while suppressing damage and the intrusion of foreign matter. The weight of the retaining part 12 can be reduced by using the rod insertion fixture 11A. Therefore, the operability of the rod insertion fixture 11A is improved, and the insertion of the mandrel 4 into the hole 8 becomes easier.

[0075] In the rod insertion fixture 11A, the retaining portion 12 has a shape in which the upper part is open throughout the entire longitudinal direction, but it can also have a shape in which the upper part is open only in a portion of the longitudinal direction. In this case, the weight of the retaining portion 12 can be reduced compared to a retaining portion 12 that is a circular tube throughout the longitudinal direction. Therefore, the insertion of the mandrel 4 into the hole portion 8 becomes easier.

[0076] Figure 10 This is a cross-sectional view used to illustrate the insertion process using the rod insertion fixture involved in the second variation. Figure 10 The second modified example shown involves a rod insertion fixture 11B that includes multiple holding portions 12 and multiple moving portions 15 (see reference). Figure 5 This aspect relates to the rod insertion fixture 11 (see reference). Figure 7 The multiple retaining portions 12 include a first retaining portion 121 for retaining the first core rod 41 and a second retaining portion 122 for retaining the second core rod 42. The first retaining portion 121 and the second retaining portion 122 have the same configuration as the retaining portion 12 of the rod insertion fixture 11.

[0077] The first holding portion 121 houses the first core rod 41 and has a first mounting surface 131 that axially guides the first core rod 41. The second holding portion 122 houses the second core rod 42 and has a second mounting surface 132 that axially guides the second core rod 42. The first mounting surface 131 and the second mounting surface 132 have the same configuration as the mounting surface 13 of the rod insertion fixture 11.

[0078] The plurality of moving parts 15 include a first moving part and a second moving part. The first moving part and the second moving part have the same configuration as the moving part 15 of the rod insertion fixture 11. The first moving part applies a force to the first core rod 41 held in the first holding part 121, thereby moving the first core rod 41. The second moving part applies a force to the second core rod 42 held in the second holding part 122, thereby moving the second core rod 42. The second moving part is a component different from the first moving part.

[0079] The support portion 14 is disposed in contact with the inner surface of the first glass tube 5, supporting the first holding portion 121 and the second holding portion 122. The first holding portion 121 and the second holding portion 122 are arranged parallel to each other in the longitudinal direction and are supported by the support portion 14. The axial direction of the first core rod 41 held in the first holding portion 121 is parallel to the axial direction of the second core rod 42 held in the second holding portion 122.

[0080] In the manufacturing method of the MCF base material 1 according to the second modification, in the insertion process S3, the holding parts 9 and 10 are arranged in a horizontal direction instead of the vertical direction D2, so that the first glass tube 5 and the second glass tube 6 are rotated. The support part 14 supports the first holding part 121 with the axis of the first core rod 41 parallel to the central axis A7, and the entire first core rod 41 overlaps with the first hole 81 when viewed along the central axis A7. In addition, the support part 14 supports the second holding part 122 with the axis of the second core rod 42 parallel to the central axis A7, and the entire second core rod 42 overlaps with the second hole 82 when viewed along the central axis A7. According to the rod insertion fixture 11B, the insertion of the first core rod 41 into the first hole 81 and the insertion of the second core rod 42 into the second hole 82 can be performed simultaneously, thus shortening the manufacturing time.

[0081] The implementation methods have been described above, but this disclosure is not necessarily limited to the above-described implementation methods and variations, and various changes can be made without departing from its spirit.

[0082] For example, rod insertion fixtures 11, 11A, and 11B can also be used for inserting glass rods other than the core rod 4. Examples of glass rods other than the core rod 4 include glass rods that serve as low-refractive-index sections or core position markers.

[0083] In the rod insertion fixture 11B, the number of moving parts 15 can also be one. That is, the second moving part is the same component as the first moving part. In this case, the first core rod 41 and the second core rod 42 can be moved sequentially by one moving part 15.

[0084] In the insertion process S3, the central axis A7 of the cladding material 7 is not necessarily aligned with the horizontal direction. The support part 14 supports the holding part 12 in such a way that the axial direction D1 of the mandrel 4 is parallel to the central axis A7. Therefore, when the central axis A7 is tilted significantly relative to the horizontal direction, the mandrel 4 may slip off the mounting surface 13 due to gravity. However, if it is within the range where it does not slip, the central axis A7 may also be tilted relative to the horizontal direction.

[0085] Viewed from the longitudinal direction of the holding part 12, the mounting surface 13 may also have a V-shaped shape. In this case, the mandrel 4 is also mounted on the mounting surface 13 in such a way that the axial direction D1 is aligned with the extending direction of the mounting surface 13. Therefore, the mandrel 4 can be guided axially D1 through the mounting surface 13.

[0086] The above-described embodiments and variations can also be appropriately combined.

[0087] As can be seen from the above description of the embodiments and variations, this specification includes disclosures of the following methods.

[0088] (Postscript 1)

[0089] A rod insertion fixture includes a cladding material having a first glass tube connected to a first end and a second glass tube connected to a second end (different from the first end) in which a glass rod is inserted through a hole parallel to the central axis of the cladding material in a cross-section perpendicular to the central axis of the cladding material, offset from the central axis. The rod insertion fixture comprises:

[0090] A first holding part is inserted into the interior of the first glass tube, holding the first glass rod with the first direction as the axis.

[0091] A support portion that is disposed in contact with the inner surface of the first glass tube and supports the first holding portion; and

[0092] A first moving part applies a force in the first direction to the first glass rod held by the first holding part, thereby moving the first glass rod.

[0093] The first holding portion has a first mounting surface that holds the first glass rod and extends along the first direction.

[0094] The support portion supports the first holding portion in a manner that is parallel to the central axis in the first direction, and in a manner that, when viewed from the direction along the central axis, the entire first glass rod overlaps with the first hole portion, which is the hole portion.

[0095] (Postscript 2)

[0096] The rod insertion fixture described in Appendix 1 further comprises:

[0097] A second retaining part, which holds the first glass rod axially in the second direction and is inserted into the interior of the first glass tube; and

[0098] A second moving part applies a force to the second glass rod held by the second holding part to move the second glass rod.

[0099] The second holding portion has a second mounting surface that holds the second glass rod and extends along the second direction.

[0100] The support portion is parallel to the central axis in the second direction, and the second retaining portion is supported by the second glass rod as a whole, which overlaps with the second hole portion, which is different from the first hole portion, when viewed from the direction along the central axis.

[0101] Explanation of symbols

[0102] 1… Multi-core optical fiber

[0103] 2…core

[0104] 3…cladding section

[0105] 4… mandrel

[0106] 5…First glass tube

[0107] 6…Second glass tube

[0108] 7…cladding base material

[0109] 7a…First End

[0110] 7b…Second end

[0111] 8…hole

[0112] 9…Control Department

[0113] 10…Control Department

[0114] 11… Rod insertion fixture

[0115] 11A… Rod insertion fixture

[0116] 11B… Rod insertion fixture

[0117] 12…Maintenance Department

[0118] 13… Placement Surface

[0119] 14… Support Department

[0120] 15…Moving sections (First moving section, Second moving section)

[0121] 16…butt part

[0122] 17…butt part

[0123] 18… Heating section

[0124] 19…Pressure Regulation Section

[0125] 20…Pressure Regulation Section

[0126] 41…First core rod (first glass rod)

[0127] 42…Second core rod (Second glass rod)

[0128] 81…First Hole

[0129] 82…Second Hole

[0130] 121…First Maintenance Section

[0131] 122…Second Maintenance Section

[0132] 131…First mounting surface

[0133] 132…Second mounting surface

[0134] 141…First Support Component

[0135] 142…Second Support Component

[0136] A1…Central Axis

[0137] A7…Central Axis

[0138] D1…Axial direction

[0139] D2…Vertical direction

[0140] SP1…Internal Space

[0141] SP2…Internal Space

Claims

1. A rod insertion fixture, which is a fixture for inserting a glass rod through a hole in the cladding material. The cladding parent material It is a columnar component with a first end and a second end that are opposite each other. It has a first hole, which is a hole extending along the central axis from the first end to the second end at a position offset from the central axis in a cross-section perpendicular to the central axis of the cladding base material. A first glass tube is connected to the first end of the cladding material. A second glass tube is connected to the second end of the cladding material. The first glass rod, which is to be inserted into the first hole, is a rod-shaped component with the first direction as its axial direction. The rod insertion fixture includes: The support portion is provided in contact with the inner surface of the first glass tube. The first retaining part supported by the support part inside the first glass tube, and The first moving part is a component used to move the first glass rod. The first holding part has a first mounting surface for mounting the first glass rod along the first direction. The support portion supports the first retaining portion in such a manner that, viewed from the first direction, the entire first glass rod placed on the first mounting surface overlaps with the first hole portion. The first moving part causes the first glass rod, which is placed on the first mounting surface, to move in the first direction.

2. The rod insertion fixture according to claim 1, wherein, The cladding material also has a second hole, which is different from the first hole. The second glass rod, which is to be inserted into the second hole, is a rod-shaped component with the second direction as its axial direction. The rod insertion fixture also includes: The second retaining part, which is supported by the support part inside the first glass tube, and The second moving part is a component used to move the second glass rod. The second holding part has a second mounting surface for mounting the second glass rod along the second direction. The support portion supports the second holding portion in such a manner that, viewed from the second direction, the entire second glass rod placed on the second mounting surface overlaps with the second hole portion. The second moving part causes the second glass rod, which is placed on the second mounting surface, to move in the second direction.

3. The rod insertion fixture according to claim 2, wherein, The second moving part is the same component as the first moving part.

4. The rod insertion fixture according to claim 2, wherein, The second moving part is a component different from the first moving part.

5. The rod insertion fixture according to any one of claims 1 to 4, wherein, The support portion includes a first support component and a second support component that are separated from each other in the longitudinal direction of the first retaining portion.

6. The rod insertion fixture according to any one of claims 1 to 4, wherein, Viewed from the longitudinal direction of the first holding part, the first mounting surface is a curved surface along the outer peripheral surface of the first glass rod.

7. The rod insertion fixture according to any one of claims 1 to 4, wherein, The longitudinal length of the first holding part is longer than the longitudinal length of the first glass tube.

8. The rod insertion fixture according to any one of claims 1 to 4, wherein, The length of the first moving part in the longitudinal direction is longer than the length of the first holding part in the longitudinal direction.

9. The rod insertion fixture according to any one of claims 1 to 4, wherein, The first retaining part is configured such that its front end is separated from the first end of the cladding material.

10. A method for manufacturing a multi-core optical fiber mother material, comprising: A cladding material is prepared with a first glass tube connected to the first end and a hole penetrating along the direction of the central axis at a position off-center from the central axis. Prepare a glass rod; The glass rod is inserted into the hole using the rod insertion fixture according to any one of claims 1 to 9; and The cladding material and the glass rod inserted into the hole are integrated.

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