Optical fiber protector, terminal structure for metal tube-coated optical fiber cable using the same, and connection structure for metal tube-coated optical fiber cable

Abstract

To provide an optical fiber protective tool capable of preventing damage inside an optical fiber and quality deterioration as the whole optical fiber cable due to dynamic behavior during installation or use.SOLUTION: An optical fiber protective tool 1 is used at a terminal of a metal pipe coating optical fiber cable 4 having a metal pipe 3 and an optical fiber 2 inserted into the metal pipe 3 and protruding from a terminal 31 of the metal pipe 3, and has: a terminal opening part 11 composed of a small diameter part 11a which has the smallest inner diameter and into which the optical fiber 2 is inserted, a large diameter part 11b which has the largest outer diameter, and an expanded diameter part 11c which connects the small diameter part 11a and the large diameter part 11b; and a cylindrical part 12 extending from the small diameter part 11a or the large diameter part 11b to an opposite side J from an expanded diameter part side K in an axis x direction, where a diameter of the expanded diameter part 11c gradually increases from the small diameter part 11a side toward the large diameter part 11b side, and at least a part of the expanded diameter part 11c is curved in a cross section including the axis x.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an optical fiber protector for protecting an optical fiber inserted into a metal tube-coated optical fiber cable at the end or connection part of the metal tube-coated optical fiber cable, and a terminal structure of the metal tube-coated optical fiber cable and a connection structure of the metal tube-coated optical fiber cable using the same.

Background Art

[0002] A metal tube-coated optical fiber cable in which an optical fiber is protected by coating with a metal tube is known. According to the metal tube-coated optical fiber cable, since the optical fiber is protected by a metal having high mechanical strength, it is easy to reduce the diameter and weight, and the optical fiber inside the metal tube can be protected from seawater and the like. Therefore, for example, the metal tube-coated optical fiber cable is extremely useful as an application such as a composite submarine cable in which an optical fiber cable is combined with a submarine power cable or a submarine optical cable.

[0003] When the metal tube-coated optical fiber cable is used as an optical cable in a submarine cable or a composite submarine cable, since it is laid over a long distance, it is necessary to lengthen the metal tube-coated optical fiber cable. Therefore, conventionally, a plurality of metal tube-coated optical fiber cables having a predetermined length are connected to form a factory connection part (FJ) to lengthen it. Even if there is a limit to the length that can be manufactured at one time, by connecting a plurality of them, it is possible to manufacture a long cable wound around a large-diameter drum or bobbin at the time of shipment or an extremely long cable of several tens of kilometers class.

[0004] As a structure of the factory connection part, a technique is known in which both ends of a metal sleeve having an inner diameter larger than the outer diameter of these metal tubes are externally inserted so as to straddle the ends of the metal tubes, and the ends of the sleeve and the ends of the respective metal tubes are welded to connect the metal tubes to each other (see, for example, Patent Document 1 and Patent Document 2).

[0005] In this factory connection section, the optical cable protrudes from the end of the metal conduit, and if the optical fiber comes into contact with the edge of the metal conduit, it may be damaged or its quality may deteriorate. Therefore, near the end of the metal conduit, the optical fiber is protected by inserting it into a protective tube and placing it between the tube and the metal conduit.

[0006] However, the dynamic behavior during the laying and use of submarine cables and fiber optic cables can cause the protective tubes set inside the metal conduits to shift position. At the ends of the metal conduits, they are generally cut in a direction that tightens from the outer circumference, leaving sharp edges facing inward. Therefore, if the protective tubes shift position, for example, if the edges of the metal conduits remain sharp, the optical fibers inside may be damaged, resulting in transmission loss or a deterioration in the overall quality of the fiber optic cable. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 8-15554 [Patent Document 2] Japanese Patent Publication No. 2012-93527 [Overview of the project] [Problems that the invention aims to solve]

[0008] Therefore, one of the objectives of the present invention is to provide an optical fiber protector that can suppress damage to the internal optical fiber or deterioration of the overall quality of the optical fiber cable due to dynamic behavior during installation and use, as well as a terminal structure for a metal tube-coated optical fiber cable using the same, and a connection structure for a metal tube-coated optical fiber cable. [Means for solving the problem]

[0009] One aspect of the present invention is an optical fiber protector used at the end of a metal tube-covered optical fiber cable having a metal tube and an optical fiber inserted into the metal tube and protruding from the end of the metal tube. It has a terminal opening consisting of a small-diameter section with the smallest inner diameter into which the optical fiber is inserted, a large-diameter section with the largest outer diameter, and an enlarged diameter section connecting the small-diameter section and the large-diameter section, and a cylindrical section extending from the small-diameter section or the large-diameter section in the axial direction opposite to the enlarged diameter section, The diameter of the enlarged portion gradually increases as it moves from the smaller diameter portion towards the larger diameter portion. In the cross-section including the axis, at least a portion of the enlarged diameter is curved.

[0010] In one embodiment of the present invention, the cylindrical portion extends from the small-diameter portion to the side opposite to the enlarged-diameter portion, and the optical fiber may be inserted into it, as well as into the end of the metal tube.

[0011] In one embodiment of the present invention, the cylindrical portion may extend from the large-diameter portion toward the side opposite to the enlarged-diameter portion, and the metal tube may be inserted into it.

[0012] In one embodiment of the present invention, in a cross-section including the axis, at least the vicinity of the small-diameter portion and the vicinity of the portion of the enlarged diameter portion furthest from the small-diameter portion may be curved.

[0013] In one embodiment of the present invention, the outer diameter of the large-diameter portion may be larger than the inner diameter of the metal tube.

[0014] In one aspect of the present invention, the optical fiber protector may have at least one slit extending in the axial direction.

[0015] In one aspect of the present invention, the optical fiber protector may consist of two or more divided members.

[0016] In one embodiment of the present invention, the optical fiber protector may be made of a resin material.

[0017] On the other hand, one aspect of the present invention provides a terminal structure for a metal tube-coated optical fiber cable comprising a metal tube and an optical fiber into which the metal tube is inserted, and an optical fiber protector according to the above aspect, The optical fiber protector is attached to the end of the metal tube in the metal tube-coated optical fiber cable, and the optical fiber is inserted into the small-diameter portion.

[0018] Furthermore, a connection structure for a metal tube-coated optical fiber cable according to one aspect of the present invention comprises a metal tube and two metal tube-coated optical fiber cables having optical fibers into which the metal tubes are inserted, an optical fiber protector according to the above aspect, and a sheath tube. Each of the two optical fiber protectors is attached to the end of the metal tube in a separate metal tube-coated optical fiber cable, and the optical fiber is inserted into the small diameter portion. The aforementioned sheath tube has the ends of the two metal tube-covered optical fiber cables inserted into its respective sides, and covers the ends of the metal tube and the optical fiber inserted through the small diameter portion of the optical fiber protector. [Effects of the Invention]

[0019] According to one aspect of the present invention, it is possible to provide an optical fiber protector that can suppress the deterioration of the overall quality of an optical fiber cable, such as damage to the internal optical fiber due to dynamic behavior during installation or use, as well as a terminal structure for a metal tube-coated optical fiber cable using the same, and a connection structure for a metal tube-coated optical fiber cable. [Brief explanation of the drawing]

[0020] [Figure 1]A longitudinal sectional view showing the end structure of a metal tube-coated optical fiber cable using an optical fiber protector according to a first exemplary embodiment of the present invention, which is a sectional view taken along the C-C section in FIGS. 2 and 3. [Figure 2] A cross-sectional view showing the end structure of a metal tube-coated optical fiber cable using an optical fiber protector according to a first exemplary embodiment, which is a sectional view taken along the A-A section in FIG. 1. [Figure 3] A cross-sectional view showing the end structure of a metal tube-coated optical fiber cable using an optical fiber protector according to a first exemplary embodiment, which is a sectional view taken along the B-B section in FIG. 1. [Figure 4] A side view showing only the optical fiber protector according to a first exemplary embodiment. [Figure 5] A perspective view showing only the optical fiber protector according to a first exemplary embodiment. [Figure 6] A longitudinal sectional view showing only the optical fiber protector according to a first exemplary embodiment, which is a sectional view taken along the D-D section in FIG. 4. [Figure 7] A schematic diagram for explaining the connection structure of a metal tube-coated optical fiber cable using an optical fiber protector according to a first exemplary embodiment. [Figure 8] An enlarged longitudinal sectional view for explaining the connection structure of a metal tube-coated optical fiber cable using an optical fiber protector according to a first exemplary embodiment. [Figure 9] A side view of an optical fiber protector according to a second exemplary embodiment. [Figure 10] A perspective view of an optical fiber protector according to a second exemplary embodiment. [Figure 11] A cross-sectional view showing the end structure of a metal tube-coated optical fiber cable using an optical fiber protector according to a second exemplary embodiment, which is a sectional view of the same location as in FIG. 2 in the first exemplary embodiment. [Figure 12] A side view of an optical fiber protector according to a third exemplary embodiment. [Figure 13] A perspective view of an optical fiber protector according to a third exemplary embodiment. [Figure 14] This is a cross-sectional view showing the end structure of a metal tube-coated optical fiber cable using an optical fiber protector according to the third embodiment, and is a cross-sectional view of the same location as in Figure 2 of the first embodiment. [Figure 15] This is a side view of an optical fiber protector according to the fourth embodiment. [Figure 16] This is a perspective view of an optical fiber protector according to the fourth embodiment. [Figure 17] This is a cross-sectional view showing the end structure of a metal tube-coated optical fiber cable using an optical fiber protector according to the fourth embodiment, and is a cross-sectional view of the same location as in Figure 2 of the first embodiment. [Figure 18] This is a cross-sectional view showing the end structure of a metal tube-coated optical fiber cable using a modified example of the optical fiber protector according to the fourth embodiment, and is a cross-sectional view of the same location as in Figure 17. [Figure 19] This is a longitudinal cross-sectional view showing the terminal structure of a metal tube-coated optical fiber cable using an optical fiber protector according to the fifth embodiment, and is a cross-sectional view of the FF cross section in Figure 20. [Figure 20] This is a cross-sectional view showing the terminal structure of a metal tube-coated optical fiber cable using an optical fiber protector according to the fifth embodiment, and is a cross-sectional view of the EE section in Figure 19. [Figure 21] This is a vertical cross-sectional view showing only the optical fiber protector according to the fifth embodiment, and it is a cross-sectional view covering the same cross-section as Figure 19. [Figure 22] This is a longitudinal cross-sectional view showing the terminal structure of a metal tube-coated optical fiber cable using an optical fiber protector according to the sixth embodiment, and is a cross-sectional view of the HH section in Figure 23. [Figure 23] This is a cross-sectional view showing the terminal structure of a metal tube-coated optical fiber cable using an optical fiber protector according to the sixth embodiment, and is a cross-sectional view of the GG section in Figure 22. [Figure 24] This is a vertical cross-sectional view showing only the optical fiber protector according to the sixth embodiment, and it is a cross-sectional view covering the same cross-section as Figure 22. [Figure 25] This is a longitudinal cross-sectional view showing the terminal structure of a metal tube-coated optical fiber cable using an optical fiber protector according to the seventh embodiment, and is a cross-sectional view of the same location as in Figure 1 in the first embodiment. [Figure 26] This is a vertical cross-sectional view showing only the optical fiber protector according to the seventh embodiment, and it is a cross-sectional view covering the same cross-section as Figure 25. [Modes for carrying out the invention]

[0021] The term "metal tube-coated optical fiber cable" refers to a cable in which an optical fiber is protected by a metal tube coating. In this specification, however, it specifically refers to a cable in which the metal tube and optical fiber are integrally molded, and a cable made by connecting multiple such cables to create a longer cable is referred to as a "metal tube-coated optical fiber cable assembly" in this specification. Of course, a "metal tube-coated optical fiber cable assembly" in which multiple "metal tube-coated optical fiber cables" are connected by the connection structure of the present invention is included within the scope of the present invention.

[0022] Hereinafter, an optical fiber protector according to an exemplary embodiment of the present invention, as well as a terminal structure for a metal tube-coated optical fiber cable using the same, and a connection structure for a metal tube-coated optical fiber cable will be described in detail with reference to the drawings.

[0023] <First Embodiment> Figure 1 is a longitudinal cross-sectional view showing the end structure of a metal tube-coated optical fiber cable 4 using the optical fiber protector 1 according to the first embodiment, Figure 2 is a transverse cross-sectional view showing the end structure of the metal tube-coated optical fiber cable 4, and Figure 3 is a transverse cross-sectional view different from Figure 2 showing the end structure of the metal tube-coated optical fiber cable 4. Specifically, Figure 1 is a cross-sectional view relating to the CC section in Figures 2 and 3, Figure 2 is a cross-sectional view relating to the AA section in Figure 1, and Figure 3 is a cross-sectional view relating to the BB section in Figure 2.

[0024] As shown in Figures 1 to 3, the metal tube-coated optical fiber cable 4 comprises a metal tube 3 and an optical fiber 2 inserted into the metal tube 3 and protruding from the end 31 of the metal tube 3. In Figure 1, the metal tube-coated optical fiber cable 4 is a long length extending in the direction of arrow J, although the illustration is omitted from the middle on the left side (arrow J side). The area omitted from the illustration is covered with a sheath not shown.

[0025] The metal tube 3 is a component that is fitted over the optical fiber 2 to protect the internal optical fiber 2 from seawater. There are no particular restrictions on the material of the metal tube 3, and examples include stainless steel, aluminum, copper, nickel, and lead. However, from the viewpoint of watertightness, stainless steel is preferred, and SUS304 is particularly preferred in terms of the balance between various performance and cost.

[0026] An optical fiber protector 1 according to the first embodiment is attached to the end of the metal tube 3 in the metal tube-coated optical fiber cable 4. Figures 4 to 6 show only the optical fiber protector 1 according to the first embodiment in enlarged view. Specifically, Figure 4 shows a side view of the optical fiber protector 1, Figure 5 shows a perspective view, and Figure 6 is a longitudinal cross-sectional view, showing the DD cross-section in Figure 4.

[0027] As shown in Figures 4 to 6, the optical fiber protector 1 according to this embodiment has an end opening 11 and an inner cylindrical portion (cylindrical portion) 12. The end opening 11 consists of a small-diameter portion 11a, which has the smallest inner diameter and into which the optical fiber 2 is inserted, a large-diameter portion 11b, which has the largest outer diameter, and an enlarged-diameter portion 11c connecting the small-diameter portion 11a and the large-diameter portion 11b. In this embodiment, the diameter (outer diameter) of the large-diameter portion 11b is larger than the outer diameter of the metal tube 3. However, the diameter (outer diameter) of the large-diameter portion 11b only needs to be larger than the inner diameter of the metal tube 3. On the other hand, the diameter (outer diameter) of the small-diameter portion 11a is smaller than the inner diameter of the metal tube 3.

[0028] The diameter of the enlarged portion 11c gradually increases from the small diameter portion 11a side to the large diameter portion 11b side. In this embodiment, in a cross-section including the axis x (corresponding to the cross-section in the vertical cross-sectional view of Figure 6; the same applies hereafter in this embodiment), the entire area of ​​the enlarged portion 11c, including the vicinity of the small diameter portion 11a and the vicinity of the large diameter portion 11b, which is the part furthest from the small diameter portion 11a, is curved. That is, in this embodiment, the end opening 11 has a so-called trumpet shape that opens in the direction of arrow K as a whole.

[0029] On the other hand, the inner cylindrical portion 12 extends from the small diameter portion 11a in the axial x direction, opposite to the enlarged diameter portion 11c side (arrow K side) (arrow J side). The optical fiber 2 is inserted into the inside of this inner cylindrical portion 12, and it is also inserted into the end 31 of the metal tube 3, so that the outer circumference of the inner cylindrical portion 12 faces the inner circumference of the metal tube 3.

[0030] There are no particular restrictions on the material of the optical fiber protector 1; it may be made of any material such as metal, resin, or ceramic, but it is preferably made of resin due to its ease of molding. Particularly preferred resins include, but are not limited to, polyethylene, polypropylene, polyvinyl chloride, polyvinylidene chloride, polystyrene, polytetrafluoroethylene, epoxy resin, polyetheretherketone, and fluororesins such as Teflon (registered trademark).

[0031] Considering the welding to the conduit described later, it is preferable that the material has heat resistance, and considering its suitability for crimping described later, it is preferable that the material is plastically deformable. Specifically, heat-resistant resins (fluororesin, epoxy resin, etc.) and metals (stainless steel, etc.) can be cited as examples of suitable materials.

[0032] In the x-axis direction, a protective tube 5 is attached to the optical fiber 2 at and near the end 31 of the metal tube 3. The protective tube 5 is interposed between the optical fiber 2 and the optical fiber protector 1 and is a component for protecting the optical fiber 2. In this embodiment, the optical fiber 2 is protected from the end 31 of the metal tube 3 by the optical fiber protector 1, so the protective tube 5 is not an essential component, but the protective tube 5 can protect the optical fiber 2 more reliably.

[0033] The actual installation of the protective tube 5 and the optical fiber protector 1 is carried out as follows, for example. That is, the optical fiber protector 1 is installed offset from the end of the protective tube 5 (as shown in Figure 1 for the positional relationship between the optical fiber protector 1 and the protective tube 5) relative to the optical fiber 2 inserted into the protective tube 5. At this time, a predetermined clearance is maintained between the optical fiber 2 and the protective tube 5, and between the protective tube 5 and the optical fiber protector 1, although this is not shown in the drawing.

[0034] Then, with the protective tube 5 inserted into the optical fiber protector 1 and the optical fiber 2 further inserted into the protective tube 5 and positioned to some extent, the inner cylindrical portion 12 side of the optical fiber protector 1 is inserted into the metal tube 3 from the end 31 side, and inserted until the end opening 11 of the optical fiber protector 1 contacts the end 31 of the metal tube 3.

[0035] Once the optical fiber 2, protective tube 5, and optical fiber protector 1 reach their predetermined positions in the x-axis direction, a crimping tool is used to crimp the outer circumference of the metal tube 3 at the marked position indicated by arrow M in Figure 1. This crimping process crimps the metal tube 3 and the optical fiber protector 1 together, fixing their relative positions in the x-axis direction. It is also expected to have the effect of pressing the protective tube 5 on the inner circumference of the optical fiber protector 1 against the optical fiber 2.

[0036] According to this embodiment, even if the optical fibers 2 to the protective tube 5 are bent and pressed toward the end 31 of the metal pipe 3 due to the dynamic behavior during the laying or use of submarine cables or optical cables, the optical fiber protector 1 is interposed between them and the end 31 of the metal pipe 3, thus protecting the optical fibers 2 to the protective tube 5.

[0037] Furthermore, in this embodiment, since the entire area of ​​the enlarged diameter portion 11c is curved in the cross-section including the axis x, the area in which the optical fiber 2 covered by the protective tube 5 can come into contact has a smooth curved shape. Therefore, even if the optical fiber 2 to the protective tube 5 is strongly pressed against the curved shape of the enlarged diameter portion 11c of the optical fiber protector 1, the pressure is distributed and acts in a manner that reduces the load on the optical fiber 2 to the protective tube 5, softens the impact, and suppresses damage and other effects.

[0038] According to this embodiment, even if the protective tube 5 becomes misaligned and ceases to function, the optical fiber protector 1 interposed between the end 31 of the metal tube 3 and the optical fiber 2 can take over the protective tube 5's original purpose of protecting the surface of the optical fiber 2 from the cut edge of the end 31 of the metal tube 3. Therefore, the effort required to process the edge of the end 31 of the metal tube 3 to avoid problems caused by misalignment of the protective tube 5 is eliminated.

[0039] Furthermore, since the outer diameter of the large-diameter portion 11b of the end opening 11 of the optical fiber protector 1 is larger than the inner diameter of the metal tube 3, the enlarged-diameter portion 11c of the end opening 11 of the optical fiber protector 1 catches on the end 31 of the metal tube 3, preventing the optical fiber protector 1 from being pulled into the metal tube 3. Therefore, according to this embodiment, there is virtually no concern that the edge of the end 31 of the metal tube 3 will come into contact with the optical fiber 2 or the protective tube 5.

[0040] In this embodiment, as shown in Figure 1, it is preferable to crimp the entire metal tube-covered optical fiber cable 4 near the end 31 of the metal tube 3 from the outer circumference at the position indicated by arrow M, thereby relatively fixing it in the x-axis direction. By crimping from the outer circumference of the metal tube 3, the optical fiber protector 1 is fixed to the metal tube 3.

[0041] Furthermore, the protective tube 5 located directly beneath the optical fiber protector 1 is also fixed at the crimped position, suppressing displacement of the protective tube 5 in the axial x direction. Considering this effect, it is preferable that the protective tube 5 has an outer diameter close to the inner diameter of the optical fiber protector 1 (specifically, the small diameter portion 11a).

[0042] This section describes the connection structure of a metal tube-coated optical fiber cable 4 using the optical fiber protector 1 according to this embodiment. Figure 7 is a schematic diagram illustrating the connection structure of a metal tube-coated optical fiber cable 4 using the optical fiber protector 1 according to this embodiment (hereinafter sometimes simply referred to as "this connection structure"). As shown in Figure 7, in this connection structure, the ends of the metal tube-coated optical fiber cables 4 are connected by a sheath tube (also called a sleeve) 6.

[0043] This connection structure comprises two metal tube-coated optical fiber cables 4, two optical fiber protectors 1, and a sheath tube 6. The two optical fiber protectors 1 are each attached to the ends of the metal tubes 3 of separate metal tube-coated optical fiber cables 4, and the optical fibers 2 are inserted into the small-diameter portions 11a.

[0044] The sheath tube 6 is a metal tube, such as stainless steel, into which the ends of the metal tube-coated optical fiber cable 4 are inserted, covering the ends of the metal tube 3 and the optical fiber 2 inserted through the small-diameter portion 11a of the optical fiber protector 1. The metal tube-coated optical fiber cable 4 and the sheath tube 6 are covered with a sheath 7, and the connection area between the metal tube-coated optical fiber cable 4 and the sheath tube 6, and its vicinity, which are not covered with the sheath 7, are protected by wrapping them with polyvinyl chloride tape 8.

[0045] Figure 8 is an enlarged longitudinal cross-sectional view of the connection between the metal tube-coated optical fiber cable 4 and the sheath tube 6 in this connection structure. In Figure 8, only the connection state between the metal tube-coated optical fiber cable 4 and the sheath tube 6 on the left side of Figure 7 is shown. As shown in Figure 8, the metal tube-coated optical fiber cable 4 (or rather, the metal tube 3) in the terminal structure of Figure 1, in which an optical fiber protector 1 is interposed between the optical fiber 2 covered with a protective tube 5 and the metal tube 3, is inserted into the sheath tube 6 from the terminal side 31.

[0046] As shown in Figure 8, the metal tube 3 has crimping marks (crimping marks 32) at the position indicated by arrow M in Figure 1. The actual connection work of the metal tube-covered optical fiber cable 4 and the sheath tube 6 is performed as follows, for example. First, as described above, the metal tube-covered optical fiber cable 4 is brought to the end state shown in Figure 1 by attaching the protective tube 5 and the optical fiber protector 1.

[0047] Then, the protective tube 5 and optical fiber protector 1 are attached to the metal tube-coated optical fiber cable 4, and the sheath tube 6 is placed over it from the end 31 side. The metal tube-coated optical fiber cable 4 is then inserted, and the sheath tube 6 is moved out from the end 31, exposing the optical fiber 2 protruding from the end 31. The end of this exposed optical fiber 2 is fusion spliced ​​with the end of the optical fiber 2 exposed from one end of another metal tube-coated optical fiber cable 4 to be connected.

[0048] Next, the sheath tube 6 is moved to a position that covers the exposed portion of the optical fiber 2 (the portion not covered by the metal tube 3), including the fusion splice joint between the optical fibers 2, and one end of the sheath tube 6 is welded to the metal tube 3. Figure 8 shows the weld marks 61 resulting from this welding. By performing this welding operation between the sheath tube 6 and the metal tube 3 on the other end of the sheath tube 6 and the metal tube 3 of the other metal tube-covered optical fiber cable 4 to be connected, the connection work of the metal tube-covered optical fiber cable 4 is completed, and the connection structure of the metal tube-covered optical fiber cable 4 according to this embodiment is obtained. In this way, a metal tube-covered optical fiber cable connection body using the connection structure with the optical fiber protector 1 of this embodiment can be manufactured.

[0049] According to this embodiment, since the optical fiber protector 1 is set on the metal tube 3, the heat generated when welding the metal tube 3 and the sheath tube 6 is not only shielded by the heat shielding effect of the protective tube 5, but also by the optical fiber protector 1 and the protective tube 5, making it difficult for the heat to be transmitted to the optical fiber 2. Therefore, by using the optical fiber protector 1 according to this embodiment, in addition to the effects described above, it is possible to suppress the effect on the optical fiber 2 caused by the heat generated during welding the metal tube 3 and the sheath tube 6.

[0050] <Second Embodiment> Figure 9 is a side view of the optical fiber protector 101 according to the second embodiment, and Figure 10 is a perspective view of the optical fiber protector 101. Figure 11 is a cross-sectional view showing the end structure of a metal tube-coated optical fiber cable 104 using the optical fiber protector 101 according to the second embodiment, and is a cross-sectional view of the same location as in Figure 2 of the first embodiment.

[0051] Furthermore, the longitudinal cross-section of the end structure of the metal tube-covered optical fiber cable 104 using the optical fiber protector 101 according to the second embodiment is substantially the same as that shown in Figure 1 of the first embodiment, and therefore its description is omitted.

[0052] In Figures 9 to 11, each component with a configuration similar to that of the optical fiber protector 1 and the end structure of the metal tube-covered optical fiber cable 4 using the first embodiment is assigned a code in the hundreds range with the same last two digits as the components in the first embodiment, and the explanation of the similar configurations of each component is omitted. The following explanation will focus on the differences from the first embodiment.

[0053] As shown in Figures 9 to 11, the optical fiber protector 101 according to this embodiment has a single slit 113 extending in the x-axis direction. The slit 113 reaches both ends of the optical fiber protector 101 in the x-axis direction.

[0054] In this embodiment, the inner cylindrical portion (tube portion) 112 does not form a complete cylindrical shape because the slit 113 portion in the circumferential direction is missing. However, even if a part in the circumferential direction is missing in this way, if the missing portion can be filled in to form a cylindrical shape, it will be included in the concept of "tube" in this specification. The same applies when there are two or more missing portions (e.g., the third embodiment described later) (the above also applies to the outer cylindrical portion described later).

[0055] According to the optical fiber protector 101 of this embodiment, by having a slit 113, the optical fiber 102 (hereinafter simply referred to as "optical fiber 102") covered with a protective tube 105 can be inserted into the optical fiber protector 101 by fitting it in from the side of the optical fiber protector 101.

[0056] The width of the slit 113 is such that the optical fiber 102 can pass through from the side and be fitted into the optical fiber protector 101. Therefore, even if the diameter of the optical fiber 102 is slightly larger than the slit 113, the optical fiber 102 can be fitted in by widening the slit 113. Compared to inserting the optical fiber 102 from the end opening on the opposite side of the end opening 111 of the optical fiber protector 101, the insertion of the optical fiber 102 into the optical fiber protector 101 is easier in this embodiment.

[0057] Furthermore, even if the difference between the inner diameter of the metal tube 103 and the outer diameter of the inner cylindrical portion 112 is small, or if the inner diameter of the metal tube 103 is larger, narrowing the slit 113 reduces the outer diameter of the inner cylindrical portion 112, making it easier to insert the optical fiber protector 101 into the metal tube 103 from the end 131.

[0058] The optical fiber protector 101 according to this embodiment can be applied to the end structure and connection structure of the metal tube-coated optical fiber cable 104, similar to the optical fiber protector 1 according to the first embodiment, and similar functions and effects can be expected.

[0059] <Third Embodiment> Figure 12 is a side view of the optical fiber protector 201 according to the third embodiment, and Figure 13 is a perspective view of the optical fiber protector 201. Figure 14 is a cross-sectional view showing the end structure of a metal tube-coated optical fiber cable 204 using the optical fiber protector 201 according to the third embodiment, and is a cross-sectional view of the same location as in Figure 2 of the first embodiment.

[0060] Furthermore, the longitudinal cross-section of the end structure of the metal tube-coated optical fiber cable 204 using the optical fiber protector 201 according to the third embodiment is substantially the same as that shown in Figure 1 of the first embodiment, and therefore its description is omitted.

[0061] In Figures 12 to 14, each component with a configuration similar to that of the optical fiber protector 1 and the end structure of the metal tube-covered optical fiber cable 4 using the first embodiment is assigned a code in the 200s range with the same last two digits as the components in the first embodiment, and the explanation of the similar configurations of each component is omitted. The following explanation will focus on the differences from the first embodiment.

[0062] As shown in Figures 12 to 14, the optical fiber protector 201 according to this embodiment has two slits 214 extending in the x-axis direction. The slits 214 extend from the end of the optical fiber protector 101 on the side of arrow J in the x-axis direction and end midway, not reaching either end in the x-axis direction. There are two pairs of these slits 214, one on the left and one on the right when viewed from either side in the x-axis direction (either left or right in Figure 12; this can also be confirmed in the cross-sectional view of Figure 14).

[0063] According to the optical fiber protector 201 of this embodiment, having a slit 214 makes it easy to insert the optical fiber protector 201 into the metal tube 203 from the end 231 by narrowing the slit 214 and reducing the outer diameter of the inner cylinder portion 212, even when the difference between the inner diameter of the metal tube 203 and the outer diameter of the inner cylinder portion 12 is small, or when the inner diameter of the metal tube 203 is larger.

[0064] The optical fiber protector 201 according to this embodiment can be applied to the end structure and connection structure of the metal tube-coated optical fiber cable 204, similar to the optical fiber protector 1 according to the first embodiment, and similar functions and effects can be expected. In this embodiment, the number of slits 214 was two, but this is not limited to two; there may be one, three or more, or any other number.

[0065] <Fourth Embodiment> Figure 15 is a side view of the optical fiber protector 301 according to the fourth embodiment, and Figure 16 is a perspective view of the optical fiber protector 301. Figure 17 is a cross-sectional view showing the end structure of a metal tube-coated optical fiber cable 304 using the optical fiber protector 301 according to the fourth embodiment, and is a cross-sectional view of the same location as in Figure 2 of the first embodiment.

[0066] Furthermore, the longitudinal cross-section of the end structure of the metal tube-covered optical fiber cable 304 using the optical fiber protector 301 according to the fourth embodiment is substantially the same as that shown in Figure 1 of the first embodiment, and therefore its description is omitted.

[0067] In Figures 15 to 17, each component with a configuration similar to that of the optical fiber protector 1 and the end structure of the metal tube-covered optical fiber cable 4 using the first embodiment is assigned a reference number in the 300s with the same last two digits as the components in the first embodiment, and the explanation of the similar configurations of each component is omitted. The following explanation will focus on the differences from the first embodiment.

[0068] As shown in Figures 15 to 17, the optical fiber protector 301 according to this embodiment consists of two members 301x and 301y, which are divided using a plane containing axis x as a dividing plane (in the drawing of Figure 15, the plane in the depth direction containing axis x). The two members 301x and 301y are combined to form one optical fiber protector 301.

[0069] Each member 301x, 301y has an end opening piece 311x, 311y and an inner cylindrical piece 312x, 312y. The two members 301x, 301y are integrated to form one end opening 311 with the end opening piece 311x and the end opening piece 311y, and one end opening 311 with the inner cylindrical piece 312x and the inner cylindrical piece 312y.

[0070] Because the optical fiber protector 301 is divided into two components 301x and 301y, the optical fiber 302 (hereinafter simply referred to as "optical fiber 302") covered with the protective tube 305 can be inserted into the optical fiber protector 301 by sandwiching it between the two components 301x and 301y.

[0071] In this embodiment, where the optical fiber 302 is separated into two components 301x and 301y, the process of setting (inserting) the optical fiber 302 into the optical fiber protector 301 is easier compared to the case where the optical fiber 302 is inserted by inserting it through the end opening 311 of the optical fiber protector 301, assuming that the two components 301x and 301y are not separated.

[0072] The two components 301x and 301y may or may not be fixed. If the two components 301x and 301y are to be fixed, it is preferable to fix them after the optical fiber 302 has been set (inserted). Methods of fixing include, but are not limited to, methods such as bonding with adhesive, providing a locking structure on both beforehand, or using fasteners such as screws.

[0073] Even if the two members 301x and 301y are not fixed together, it is preferable to take measures to stabilize the shape of the optical fiber protector 301, such as providing a fitting structure between them in advance.

[0074] In this embodiment, two members 301x and 301y have circumferentially opposing surfaces that come into contact to form one optical fiber protector 301, but there may be areas that overlap radially at each end in the circumferential direction. Figure 18 shows the end structure of a metal tube-coated optical fiber cable using an optical fiber protector according to a modified example whose structure differs from that of this embodiment. Figure 18 is a cross-sectional view showing the end structure of a metal tube-coated optical fiber cable using a modified example of the optical fiber protector according to the fourth embodiment, and is a cross-sectional view of the same location as in Figure 17. However, Figure 18 is shown in a larger size than Figure 17.

[0075] As shown in Figure 18, the optical fiber protector 301' according to this modified example consists of two divided members 301x' and 301y', similar to the optical fiber protector 301 according to the fourth embodiment. The two members 301x' and 301y' combine to form one optical fiber protector 301'.

[0076] Each member 301x', 301y' has inner circumferential protrusions 316x', 316y' and outer circumferential protrusions 317x', 317y' at its respective circumferential ends. At each circumferential end of member 301x', 301y', the inner circumferential protrusions 316x', 316y' and the outer circumferential protrusions 317x', 317y' overlap radially to form a single optical fiber protector 301'.

[0077] By appropriately adjusting the overlapping length in the region where the inner circumferential protrusions 316x', 316y' and the outer circumferential protrusions 317x', 317y' overlap, the size of the inner and outer diameters of the optical fiber protector 301' can be appropriately controlled. Therefore, the optical fiber protector 301' according to this modified example can accommodate optical fibers 302 and metal tubes 303 of different thicknesses. The thickness of the inner circumferential protrusions 316x', 316y' and the outer circumferential protrusions 317x', 317y' can be made thinner (preferably half) than other parts (non-overlapping regions) of the member 301x', 301y', thereby stabilizing the shape of the optical fiber protector 301'.

[0078] In this modified example, we have given an example where the two members 301x' and 301y' have the same shape, both having an inner circumferential protrusion and an outer circumferential protrusion. However, it is also acceptable for one member to have only an inner circumferential protrusion and the other member to have only an outer circumferential protrusion, resulting in different shapes. In this case, on both sides in the circumferential direction, regions are formed where the inner circumferential protrusion of one member fits into and overlaps with the outer circumferential protrusion of the other member, thus constituting a single optical fiber protector.

[0079] The optical fiber protector 301 according to this embodiment and the modified optical fiber protector 301' can be applied to the end structure and connection structure of the metal tube-coated optical fiber cable 304, similar to the optical fiber protector 1 according to the first embodiment, and similar functions and effects can be expected.

[0080] <Fifth Embodiment> Figure 19 is a longitudinal cross-sectional view showing the end structure of a metal tube-coated optical fiber cable 404 using the optical fiber protector 401 according to the fifth embodiment, and Figure 20 is a transverse cross-sectional view showing the end structure of the metal tube-coated optical fiber cable 404. More specifically, Figure 19 is a cross-sectional view relating to the FF cross-section in Figure 20, and Figure 20 is a cross-sectional view relating to the EE cross-section in Figure 19. Furthermore, Figure 21 is a longitudinal cross-sectional view showing only the optical fiber protector 401 according to the fifth embodiment, and is a cross-sectional view relating to the same cross-section as Figure 19.

[0081] In Figures 19 to 21, each component with a configuration similar to that of the optical fiber protector 1 and the end structure of the metal tube-covered optical fiber cable 4 using the first embodiment is assigned a reference number in the 400s with the same last two digits as the components in the first embodiment, and the explanation of the similar configurations of each component is omitted. The following explanation will focus on the differences from the first embodiment.

[0082] In this embodiment, the shape of the terminal opening 411 differs from that of the first embodiment. Specifically, the terminal opening 11 in the optical fiber protector 1 according to the first embodiment has a trumpet shape, in a cross-section including the axis x, which expands in diameter in a curved manner from the small diameter portion 11a to the large diameter portion 11b, progressing toward the arrow K in the direction of the axis x.

[0083] In contrast, the terminal opening 411 in this embodiment has a shape that expands in a curved manner while returning to the arrow J side in the axis x direction in a cross section including the axis x (corresponding to the cross section in the vertical cross section of Figure 21; the same applies hereinafter in this embodiment), extending further from the portion corresponding to the large diameter portion 11b (the portion indicated by reference numeral 411d in Figure 21; such a portion will be referred to as the "protruding end") (see Figures 19 and 21). Hereinafter, this extension in one direction (in the direction of arrow K in this embodiment) followed by a return in the opposite direction (similarly in the direction of arrow J) will be referred to as a "return," and the shape including this return will be referred to as a "shape with a return."

[0084] In this embodiment, the small-diameter portion 411a is in the same position as in the first embodiment, but the large-diameter portion 411b is in a different position from the protruding end portion 411d, which corresponds to the large-diameter portion 11b in the first embodiment. In this embodiment as well, in the cross-section including the axis x, the enlarged-diameter portion 411c is curved over the entire area including the vicinity of the small-diameter portion 411a in the enlarged-diameter portion 411c and the vicinity of the protruding end portion 411d, which is the part furthest from the small-diameter portion 411a.

[0085] The optical fiber protector 401 according to this embodiment has a shape in which the end opening 311 has a barb, making it easier to achieve strength as a standalone optical fiber protector 401. In addition, because the end opening 411 has a shape in which a barb is present, the end 431 of the metal tube 403 is more likely to catch on it, further enhancing the effect of preventing the optical fiber protector 401 from being pulled into the metal tube 403.

[0086] The optical fiber protector 401 according to this embodiment can be applied to the end structure and connection structure of the metal tube-coated optical fiber cable 404, similar to the optical fiber protector 1 according to the first embodiment, and similar functions and effects can be expected.

[0087] <Sixth Embodiment> Figure 22 is a longitudinal cross-sectional view showing the end structure of a metal tube-coated optical fiber cable 504 using the optical fiber protector 501 according to the sixth embodiment, and Figure 23 is a transverse cross-sectional view showing the end structure of the metal tube-coated optical fiber cable 504. More specifically, Figure 22 is a cross-sectional view corresponding to the HH section in Figure 23, and Figure 23 is a cross-sectional view corresponding to the GG section in Figure 22. Furthermore, Figure 24 is a longitudinal cross-sectional view showing only the optical fiber protector 501 according to the sixth embodiment, and is a cross-sectional view corresponding to the same section as Figure 22.

[0088] In Figures 22 to 24, each component with a configuration similar to that of the optical fiber protector 1 and the end structure of the metal tube-covered optical fiber cable 4 using the first embodiment is assigned a reference number in the 500s with the same last two digits as the components in the first embodiment, and the explanation of the similar configurations of each component is omitted. The following explanation will focus on the differences from the first embodiment.

[0089] As shown in Figures 22 to 24, the optical fiber protector 501 according to this embodiment has a terminal opening 511 and an outer cylindrical portion (cylindrical portion) 512. The terminal opening 511 consists of a small-diameter portion 511a, which has the smallest inner diameter and into which the optical fiber 502 is inserted, a large-diameter portion 511b, which has the largest outer diameter, and an enlarged-diameter portion 511c connecting the small-diameter portion 511a and the large-diameter portion 511b. The diameter (outer diameter) of the large-diameter portion 511b is larger than the outer diameter of the metal tube 503. On the other hand, the diameter (outer diameter) of the small-diameter portion 511a is smaller than the inner diameter of the metal tube 503.

[0090] The diameter of the enlarged portion 511c gradually increases from the small diameter portion 511a side to the large diameter portion 511b side. In this embodiment, in a cross-section including the axis x (corresponding to the cross-section in the longitudinal cross-sectional view of Figure 22; the same applies hereafter in this embodiment), the enlarged portion 511c is curved over its entire length, including the vicinity of the small diameter portion 511a and the vicinity of the tip end 511d, which is the part furthest from the small diameter portion 511a. That is, in this embodiment, the end opening 511 has a shape with a return, similar to the fifth embodiment (however, in this embodiment, the return is formed from the tip end 511d toward the small diameter portion 511a).

[0091] The optical fiber protector 501 according to this embodiment has a shape in which the end opening 511 has a barb, making it easier to achieve strength as a standalone optical fiber protector 501. In addition, because the end opening 511 has a shape in which a barb is present, the end 531 of the metal tube 503 is more likely to catch on it, further enhancing the effect of preventing the optical fiber protector 501 from falling off the metal tube 503.

[0092] On the other hand, the outer cylindrical portion 513 extends from the large-diameter portion 511b in the axial x direction, opposite to the enlarged-diameter portion 511c side (arrow K side) (arrow J side). The metal pipe 503 is inserted into this outer cylindrical portion 513 from its end 531, so that the inner circumference of the outer cylindrical portion 513 faces the outer circumference of the metal pipe 503.

[0093] In this embodiment, since the entire area of ​​the enlarged diameter portion 511c is curved in the cross-section including the axis x, the area that the optical fiber 502 covered by the protective tube 505 can come into contact with (the small diameter portion 511a and the area near the small diameter portion 511a in the enlarged diameter portion 511c) has a smooth curved shape. Therefore, even if the optical fiber 502 to the protective tube 505 is strongly pressed against the curved shape of the enlarged diameter portion 511c of the optical fiber protector 501, the pressure is distributed and acts in a manner that reduces the load on the optical fiber 502 to the protective tube 505, softens the impact, and suppresses the effects of damage, etc.

[0094] In this embodiment, unlike the first embodiment, the cylindrical portion of the optical fiber protector 501 is not inside the metal tube 503, but only has an outer cylindrical portion 513. Therefore, the end opening 511 has a shape that protrudes inward from the outer cylindrical portion 513. However, in this embodiment, since the enlarged diameter portion 511c connecting the small diameter portion 511a and the large diameter portion 511b of the end opening 51 is curved, even if the optical fiber 502 to the protective tube 505 is strongly pressed near the end opening 511, the load on the optical fiber 502 to the protective tube 505 is reduced, the impact is softened, and the effects such as damage can be suppressed.

[0095] To fully utilize the effect of the curved shape near the small-diameter portion 511a and to cover the end 531 of the metal tube with the end opening 511, it is desirable that the inner lip of the end opening 511 be somewhat large. Regarding the degree of the inner lip of the end opening 511, it is preferable that, in a plane including the axis x direction, the tangent on the inner circumference side of the small-diameter portion 511a is parallel to the axis x, or that the end of the small-diameter portion 511a faces outward, as this enhances the protection effect of the optical fiber.

[0096] The optical fiber protector 501 according to this embodiment can be applied to the end structure and connection structure of the metal tube-coated optical fiber cable 504, similar to the optical fiber protector 501 according to the first embodiment, and similar functions and effects can be expected.

[0097] In this embodiment, the crimping process from the outer circumference of the metal tube 3, as described in the first embodiment, can also be performed at the marking position indicated by arrow M. However, in this embodiment, the positional relationship between the metal tube 503 and the optical fiber protector 501 is reversed radially, so in this embodiment, the crimping process is performed from the outer circumference of the outer cylindrical portion 513 of the optical fiber protector 501. Since the action and effect brought about by the crimping are the same as in the first embodiment, only the positional relationship between the metal tube 503 and the outer cylindrical portion 513 is reversed, a detailed explanation is omitted.

[0098] <Seventh Embodiment> Figure 25 is a longitudinal cross-sectional view showing the end structure of a metal tube-coated optical fiber cable 604 using the optical fiber protector 601 according to the seventh embodiment, and is a cross-sectional view of the same location as in Figure 1 of the first embodiment. Figure 26 is a longitudinal cross-sectional view showing only the optical fiber protector 601 according to the seventh embodiment, and is a cross-sectional view of the same location as in Figure 25.

[0099] In Figures 25 and 26, each component with a configuration similar to that of the optical fiber protector 1 and the end structure of the metal tube-covered optical fiber cable 4 using the first embodiment is assigned a reference numeral in the 600s range with the same last two digits as the components in the first embodiment, and the explanation of the similar configurations of each component is omitted. The following explanation will focus on the differences from the first embodiment.

[0100] In this embodiment, the shape of the optical fiber protector 601 differs from that of the fifth embodiment. Specifically, in the seventh embodiment, the optical fiber protector 601 has a winding end portion 615 that extends from the large-diameter portion 611b of the end opening 611. In a cross-section including axis x (corresponding to the cross-section in the vertical cross-sectional view of Figure 26; the same applies hereafter in this embodiment), the winding end portion 615 is curved with approximately the same curvature as the enlarged-diameter portion 611c of the end opening 611, extends toward the inner cylindrical portion (cylindrical portion) 612, and the edge is where it begins to move toward the arrow K side.

[0101] Because the end portion 714 extends further from the small-diameter portion 611a of the terminal opening 611, the optical fiber protector 601 can be made stronger as a standalone unit. In addition, because the area that can come into contact with the inner surface of the metal tube 603 (large-diameter portion 611b and its vicinity) has a smooth curved shape, the load on the metal tube 603 can be reduced.

[0102] The optical fiber protector 601 according to this embodiment can be applied to the end structure and connection structure of the metal tube-coated optical fiber cable 604, similar to the optical fiber protector 601 according to the first embodiment, and similar functions and effects can be expected.

[0103] The embodiments described above are merely examples of typical forms of the present invention, and the present invention is not limited to these embodiments. That is, those skilled in the art can implement the present invention in various ways without departing from the core principles, in accordance with prior art knowledge. As long as such modifications still incorporate the configuration of the optical fiber protector of the present invention, the terminal structure of a metal tube-coated optical fiber cable using the same, and the connection structure of a metal tube-coated optical fiber cable, they are of course included within the scope of the present invention.

[0104] For example, in the embodiments described above, all examples are given in which the curve extends over the entire area of ​​the enlarged diameter portion of the terminal opening in a cross-section including the axis, but the present invention is not limited to this. In a cross-section including the axis, for example, even if a region of linear expansion is included in a part of the enlarged diameter portion, it is acceptable as long as at least a part of the enlarged diameter portion is curved. However, in a cross-section including the axis, it is preferable that at least the vicinity of the part of the enlarged diameter portion furthest from the small diameter portion (the end of the terminal opening) is curved to cover the end of the metal tube, because, for example, if the optical fiber comes into contact with the vicinity of the end of the metal tube and a bending load is applied, the optical fiber is less likely to be damaged.

[0105] Furthermore, while the fourth embodiment provides an example of an optical fiber protector divided into two members using a plane containing the axis as the dividing plane, the present invention is not limited to this, and may consist of three or more members. Also, the dividing plane does not have to include the axis. In this specification, "dividing plane" refers to the dividing plane between adjacent divided members.

[0106] Furthermore, the configuration in which the optical fiber protector is divided into multiple components is not limited to the shape of the optical fiber protector 401 exemplified in the fourth embodiment, but can be applied to any shape. Therefore, for example, even if the optical fiber protector 501, 601 in the fifth or sixth embodiment is divided into multiple components, it can still be configured. Also, for example, even if the optical fiber protector 201, 301 in the second or third embodiment is divided into multiple components, it can still be configured, although the significance of the slits 113, 214 is reduced.

[0107] While the above embodiments primarily describe the connection structure between metal-tube-coated optical fiber cables in a metal-tube-coated optical fiber cable assembly, it is also possible to apply the "end structure for metal-tube-coated optical fiber cables" of the present invention to the ends of metal-tube-coated optical fiber cable assemblies or to the ends of metal-tube-coated optical fiber cables used without being connected. [Explanation of symbols]

[0108] 1,101,201,301,301′,401,501,601 Fiber optic protective devices, 2,102,202,302,402,502,602 optical fibers, 3,103,203,303,403,503,603 Metal pipe, 4,104,204,304,404,504,604 Metal-coated optical fiber cables, 5,105,205,305,405,505,605 protective tubes, 11,111,211,311,311′,411,511,611 End openings, 11a,111a,211a,311a,411a,511a,611a Small diameter part, 11b, 111b, 211b, 311b, 411b, 511b, 611b Large diameter section, 11c,111c,211c,311c,411c,511c,611c Expanded diameter part, 12,112,212,312,312′,412,612 Inner cylinder part (cylindrical part), 513 Outer cylinder part (cylindrical part), 31 Terminal, 32 crimping marks, 113,214 slits, 301x, 301y, 301x′, 301y′ members, 311x,311y end opening piece, 312x,312y inner cylinder piece, 316x′,316y′ Inner peripheral side protrusion, 317x′,317y′ Outer protrusion, 411d, 511d, 611d Protruding ends, 513 Outer cylinder part (cylindrical part), 615 Wrapped end

Claims

1. An optical fiber protector used at the end of a metal tube-covered optical fiber cable, comprising a metal tube and an optical fiber inserted into the metal tube and protruding from the end of the metal tube, wherein the metal tube and the optical fiber protector are configured such that one is inserted from the end of the other. The device has a terminal opening comprising a small-diameter section with a minimum inner diameter into which the optical fiber is inserted, a large-diameter section with a maximum outer diameter, and an enlarged diameter section connecting the small-diameter section and the large-diameter section, and a cylindrical section extending from the small-diameter section or the large-diameter section in the axial direction opposite to the direction from the small-diameter section to the enlarged diameter section, which is inserted into the end of the metal tube when it is connected from the small-diameter section, and into which the metal tube is inserted when it is connected from the large-diameter section. The diameter of the enlarged portion gradually increases as it moves from the smaller diameter portion towards the larger diameter portion. An optical fiber protector in which, in a cross-section including the axis, at least a portion of the enlarged diameter portion is curved.

2. The optical fiber protector according to claim 1, wherein the end opening is insertable until it contacts the end of the metal tube.

3. The optical fiber protector according to claim 1 or 2, wherein in a cross-section including the axis, at least the vicinity of the small-diameter portion and the vicinity of the portion of the enlarged diameter portion furthest from the small-diameter portion are curved.

4. The optical fiber protector according to claim 1 or 2, wherein the outer diameter of the large-diameter portion is larger than the inner diameter of the metal tube.

5. The optical fiber protector according to claim 1 or 2, having at least one slit extending in the axial direction.

6. An optical fiber protector according to claim 1 or 2, comprising two or more divided members.

7. An optical fiber protector according to claim 1 or 2, made of a resin material.

8. A metal tube-coated optical fiber cable having a metal tube and an optical fiber into which the metal tube is inserted, and an optical fiber protector according to claim 1 or 2, A terminal structure for a metal tube-coated optical fiber cable, wherein the optical fiber protector is attached to the end of the metal tube in the metal tube-coated optical fiber cable, and the optical fiber is inserted into the small-diameter portion.

9. The present invention comprises two metal tube-coated optical fiber cables having a metal tube and an optical fiber into which the metal tube is inserted, two optical fiber protectors according to claim 1 or 2, and a sheath tube, Each of the two optical fiber protectors is attached to the end of the metal tube in a separate metal tube-coated optical fiber cable, and the optical fiber is inserted into the small diameter portion. A connection structure for metal-tube-coated optical fiber cables, wherein the ends of the two metal-tube-coated optical fiber cables are inserted into each of the two metal-tube-coated optical fiber cables on either side thereof, and the ends of the metal tube and the optical fibers inserted through the small-diameter portion of the optical fiber protector are covered.

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