Optical fiber protective tool, terminal structure of metal pipe coating optical fiber cable using the same, and connection structure of metal pipe coating 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 that protects an optical fiber inserted into a metal-tube-covered optical fiber cable at the end or connection of the metal-tube-covered optical fiber cable, as well as an end structure of a metal-tube-covered optical fiber cable using the same, and a connection structure of a metal-tube-covered optical fiber cable. [Background technology]

[0002] Metal-tube-coated optical fiber cables are known in which the optical fiber is protected by a metal tube coating. In the metal-tube-coated optical fiber cable, the optical fiber is protected by a metal with high mechanical strength, so that it is easy to reduce the diameter and weight, and the optical fiber inside the metal tube can be protected from seawater, etc. Therefore, for example, the metal-tube-coated optical fiber cable is highly useful for applications such as a composite submarine cable in which an optical fiber cable is combined with a submarine power cable, and a submarine optical cable.

[0003] When a metal-tube-covered optical fiber cable is used as an optical cable in a submarine cable or a composite submarine line, it is laid over a long distance, and therefore the metal-tube-covered optical fiber cable needs to be made longer. Therefore, in the past, a factory joint (FJ) was constructed by connecting a plurality of metal-tube-covered optical fiber cables of a given length. Even if there is a limit to the length that can be manufactured at one time, by connecting multiple cables, it is possible to manufacture a long cable that is wound on a large-diameter drum or bobbin at the time of shipment, or even an extremely long cable of tens of kilometers.

[0004] A known technique for the structure of factory connections is to fit both ends of a metal sleeve, which has an inner diameter larger than the outer diameter of the metal pipes, over the ends of the metal pipes and weld the ends of the sleeve to the ends of each metal pipe to connect the metal pipes (see, for example, Patent Documents 1 and 2).

[0005] In this factory connection, the optical fiber protrudes from the end of the metal pipe, and if the optical fiber comes into contact with the edge of the metal pipe, it may be damaged or the quality may be reduced. Therefore, in the vicinity of the end of the metal pipe, the optical fiber is inserted into a protective tube and placed between the optical fiber and the metal pipe to protect the optical fiber.

[0006] However, the dynamic behavior of submarine cables and optical cables during installation and use can cause the protective tube set in the metal tube to shift position. The end of the metal tube is generally cut in the tightening direction from the outer circumference, so if left as is, the sharp edge faces the inner circumference. Therefore, if the protective tube shifts position, for example, if the edge of the metal tube remains sharp, the optical fiber inside may be damaged, causing transmission loss and reducing the quality of the optical fiber cable as a whole. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 8-15554 [Patent Document 2] JP 2012-93527 A Summary of the Invention [Problem to be solved by the invention]

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

[0009] The optical fiber protector according to one aspect of the present invention is used at an 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 an end of the metal tube, a small diameter section having a smallest inner diameter and into which the optical fiber is inserted, a large diameter section having a largest outer diameter, and an end opening including an expanded diameter section connecting the small diameter section and the large diameter section, and a tubular section extending from the small diameter section or the large diameter section to a side opposite the expanded diameter section in the axial direction, The diameter of the enlarged diameter portion gradually increases from the small diameter portion side to the large diameter portion side, In a cross section including the axis, at least a portion of the expanded diameter portion is curved.

[0010] In an optical fiber protector according to one aspect of the present invention, the tubular portion extends continuously from the small diameter portion to the side opposite the enlarged diameter portion, and the optical fiber is inserted into the tubular portion and is also inserted into the end of the metal tube.

[0011] In the optical fiber protector according to one aspect of the present invention, the tubular portion may extend continuously from the large diameter portion to a side opposite to the expanded diameter portion, and the metal tube may be inserted therein.

[0012] In the optical fiber protector according to one aspect of the present invention, in a cross section including the axis, at least a portion near the small diameter portion and a portion near the part of the expanded portion farthest from the small diameter portion may be curved.

[0013] In the optical fiber protector according to one aspect of the present invention, an outer diameter of the large diameter portion may be larger than an inner diameter of the metal tube.

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

[0015] The optical fiber protector according to one embodiment of the present invention may be composed of two or more separate members.

[0016] The optical fiber protector according to one aspect of the present invention may be made of a resin material.

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

[0018] Furthermore, a connection structure for a metal tube-covered optical fiber cable according to one aspect of the present invention includes two metal tube-covered optical fiber cables having a metal tube and an optical fiber into which the metal tube is inserted, the optical fiber protector according to the one aspect, and a sheath tube, The two optical fiber protectors are attached to ends of the metal tubes of the separate metal tube-covered optical fiber cables, and the optical fibers are inserted into the small diameter portions; The ends of the two metal tube-covered optical fiber cables are inserted into both sides of the sheath tube, covering the ends of the metal tube and the optical fiber inserted into the small diameter portion of the optical fiber protector. Effect of the Invention

[0019] According to one aspect of the present invention, it is possible to provide an optical fiber protector that can suppress deterioration in the quality of the optical fiber cable as a whole, such as damage to the internal optical fiber due to dynamic behavior during installation and use, as well as an end structure of a metal tube-covered optical fiber cable and a connection structure of a metal tube-covered optical fiber cable using the same. [Brief description of the drawings]

[0020] [Figure 1]FIG. 4 is a longitudinal cross-sectional view showing an end structure of a metal tube-covered optical fiber cable using an optical fiber protector according to a first embodiment, which is an exemplary aspect of the present invention, and is a cross-sectional view along the CC cross section in FIGS. 2 and 3. [Diagram 2] 2 is a cross-sectional view showing an end structure of a metal tube-covered optical fiber cable using an optical fiber protector according to the first embodiment, and is a cross-sectional view taken along the line AA in FIG. [Diagram 3] 2 is a cross-sectional view showing an end structure of a metal tube-covered optical fiber cable using an optical fiber protector according to the first embodiment, and is a cross-sectional view taken along the line BB in FIG. 1. [Figure 4] 1 is a side view of only the optical fiber protector according to the first embodiment. [Diagram 5] 1 is a perspective view of only an optical fiber protector according to a first embodiment. [Figure 6] 5 is a vertical cross-sectional view of only the optical fiber protector according to the first embodiment, and is a cross-sectional view taken along line DD in FIG. 4. [Figure 7] 1 is a schematic diagram for explaining a connection structure of a metal tube-covered optical fiber cable using an optical fiber protector according to a first embodiment. FIG. [Figure 8] 1 is an enlarged vertical cross-sectional view for explaining a connection structure of a metal tube-covered optical fiber cable using an optical fiber protector according to a first embodiment. FIG. [Figure 9] FIG. 4 is a side view of the optical fiber protector according to the second embodiment. [Figure 10] FIG. 11 is a perspective view of an optical fiber protector according to a second embodiment. [Figure 11] 10 is a cross-sectional view showing an end structure of a metal tube-covered optical fiber cable using an optical fiber protector according to a second embodiment, the cross-sectional view being taken at a location similar to that of FIG. 2 in the first embodiment. [Figure 12] FIG. 11 is a side view of an optical fiber protector according to a third embodiment. [Figure 13] FIG. 11 is a perspective view of an optical fiber protector according to a third embodiment. [Figure 14] 10 is a cross-sectional view showing the terminal structure of a metal tube-covered optical fiber cable using an optical fiber protector according to a third embodiment, the cross-sectional view being taken at a section similar to that of FIG. 2 in the first embodiment. [Figure 15] FIG. 11 is a side view of an optical fiber protector according to a fourth embodiment. [Figure 16] FIG. 11 is a perspective view of an optical fiber protector according to a fourth embodiment. [Figure 17] 13 is a cross-sectional view showing an end structure of a metal tube-covered optical fiber cable using an optical fiber protector according to a fourth embodiment, the cross-sectional view being taken at a section similar to that of FIG. 2 in the first embodiment. FIG. [Figure 18] 17. FIG. 18 is a cross-sectional view showing an end structure of a metal tube-covered optical fiber cable using a modified example of an optical fiber protector according to a fourth embodiment, the cross-sectional view being taken at a location similar to that of FIG. [Figure 19] 21 is a longitudinal sectional view showing an end structure of a metal tube-covered optical fiber cable using an optical fiber protector according to a fifth embodiment, and is a sectional view taken along the line FF in FIG. 20. [Figure 20] 19. FIG. 20 is a cross-sectional view showing an end structure of a metal tube-covered optical fiber cable using an optical fiber protector according to a fifth embodiment, and is a cross-sectional view taken along the E-E cross section in FIG. [Figure 21] 19 is a longitudinal sectional view of only the optical fiber protector according to the fifth embodiment, and is a sectional view of the same cross section as FIG. 19. [Figure 22] 23. FIG. 24 is a longitudinal sectional view showing an end structure of a metal tube-covered optical fiber cable using an optical fiber protector according to a sixth embodiment, and is a sectional view taken along the HH cross section in FIG. [Diagram 23] 23 is a cross-sectional view showing an end structure of a metal tube-covered optical fiber cable using an optical fiber protector according to a sixth embodiment, and is a cross-sectional view taken along line GG in FIG. 22. [Figure 24] 23 is a longitudinal sectional view of only the optical fiber protector according to the sixth embodiment, and is a sectional view of the same cross section as FIG. 22. [Diagram 25] 13 is a longitudinal cross-sectional view showing the terminal structure of a metal tube-covered optical fiber cable using an optical fiber protector according to a seventh embodiment, the cross-sectional view being taken at a location similar to that of FIG. 1 in the first embodiment. FIG. [Figure 26] 26 is a longitudinal sectional view of only the optical fiber protector according to the seventh embodiment, and is a sectional view of the same cross section as FIG. 25. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] A "metal-tube-covered optical fiber cable" refers to a cable in which the optical fiber is protected by a metal tube covering, but in this specification, it particularly refers to a product in which the metal tube and the optical fiber are integrally formed, and a cable in which a plurality of such cables are connected to form a longer cable is referred to in this specification as a "metal-tube-covered optical fiber cable assembly." Of course, a "metal-tube-covered optical fiber cable assembly" in which a plurality of "metal-tube-covered optical fiber cables" are connected by the connection structure of the present invention is included in the scope of the present invention.

[0022] Hereinafter, an optical fiber protector according to an embodiment of the present invention, which is an exemplary aspect of the present invention, as well as an end structure of a metal tube-covered optical fiber cable using the same and a connection structure of a metal tube-covered optical fiber cable will be specifically described with reference to the drawings.

[0023] <First embodiment> Fig. 1 is a longitudinal sectional view showing the end structure of a metal tube-covered optical fiber cable 4 using an optical fiber protector 1 according to the first embodiment, Fig. 2 is a transverse sectional view showing the end structure of the metal tube-covered optical fiber cable 4, and Fig. 3 is a transverse sectional view different from Fig. 2 showing the end structure of the metal tube-covered optical fiber cable 4. In detail, Fig. 1 is a sectional view taken along the CC section in Figs. 2 and 3, Fig. 2 is a sectional view taken along the AA section in Fig. 1, and Fig. 3 is a sectional view taken along the BB section in Fig. 2.

[0024] 1 to 3, the metal tube-covered optical fiber cable 4 has a metal tube 3 and an optical fiber 2 inserted into the metal tube 3 and protruding from an end 31 of the metal tube 3. In Fig. 1, the metal tube-covered optical fiber cable 4 is elongated and extends toward the arrow J side, although the left side (arrow J side) is not shown midway through the cable, and the omitted region is covered with a sheath (not shown).

[0025] The metal tube 3 is a member that is inserted around the optical fiber 2 in order to protect the optical fiber 2 from seawater. There are no particular limitations on the material of the metal tube 3, and examples thereof include stainless steel, aluminum, copper, nickel, and lead, but stainless steel is preferred from the viewpoint of water impermeability, and SUS304 is particularly preferred from the viewpoint of the balance between various performances and cost.

[0026] An optical fiber protector 1 according to a first embodiment is attached to an end of a metal tube 3 in a metal tube-covered optical fiber cable 4. Fig. 4 to Fig. 6 show an enlarged view of only the optical fiber protector 1 according to the first embodiment. In detail, Fig. 4 shows a side view of the optical fiber protector 1, Fig. 5 shows a perspective view, and Fig. 6 shows a longitudinal cross-sectional view taken along the line DD in Fig. 4.

[0027] As shown in Figs. 4 to 6, the optical fiber protector 1 according to this embodiment has an end opening 11 and an inner tubular portion (tubular portion) 12. The end opening 11 is composed of a small diameter portion 11a having a smallest inner diameter and into which the optical fiber 2 is inserted, a large diameter portion 11b having a largest outer diameter, and an expanded 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, it is sufficient that the diameter (outer diameter) of the large diameter portion 11b is 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 expanded diameter 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 of the longitudinal cross section in FIG. 6, the same applies to the following embodiment), the expanded diameter portion 11c is curved over the entire area including the vicinity of the small diameter portion 11a in the expanded diameter portion 11c and the vicinity of the large diameter portion 11b, which is the part farthest from the small diameter portion 11a. That is, in this embodiment, the terminal opening 11 has a so-called trumpet shape that opens in the direction of the arrow K as a whole.

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

[0030] The material of the optical fiber protector 1 is not particularly limited and may be any material such as metal, resin, ceramics, etc., but is preferably made of resin from the viewpoint of ease of molding. Particularly preferred resins include, but are not limited to, polyethylene, polypropylene, polyvinyl chloride, polyvinylidene chloride, polystyrene, polytetrafluoroethylene, epoxy resin, polyether ether ketone, fluororesins such as Teflon (registered trademark), etc.

[0031] Considering the welding with the sheath tube described later, it is preferable that the material is heat resistant, and considering the suitability for crimping described later, it is preferable that the material is plastically deformable. Specifically, examples of suitable materials include heat resistant resins (fluororesins, epoxy resins, etc.) and metals (stainless steel, etc.).

[0032] In the axial x direction, a protective tube 5 is attached to the optical fiber 2 over the end 31 of the metal tube 3 and its vicinity. The protective tube 5 is a member that is interposed between the optical fiber 2 and the optical fiber protector 1 and protects the optical fiber 2. In this embodiment, since the optical fiber 2 is protected from the end 31 of the metal tube 3 by the optical fiber protector 1, the protective tube 5 is not an essential component. However, the protective tube 5 can more reliably protect the optical fiber 2.

[0033] The actual installation work of the protective tube 5 and the optical fiber protector 1 is performed, for example, as follows. That is, the optical fiber protector 1 is installed with the optical fiber 2 inserted into the protective tube 5 shifted from the end of the protective tube 5 (the positional relationship between the optical fiber protector 1 and the protective tube 5 shown in FIG. 1). At this time, although not shown in the drawing, 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.

[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 a certain extent, the inner tubular portion 12 side of the optical fiber protector 1 is inserted into the metal tube 3 from the end 31 side until the end opening 11 of the optical fiber protector 1 comes into contact with the end 31 of the metal tube 3.

[0035] When the optical fiber 2, protective tube 5, and optical fiber protector 1 reach a predetermined position in the axial x direction, a crimping tool is used to crimp the outer periphery of the metal tube 3 at the marking position indicated by the arrow M in Fig. 1. This crimping process crimps the metal tube 3 and the optical fiber protector 1, and fixes their relative positional relationship in the axial x direction. This also has the effect of pressing the protective tube 5 on the inner periphery of the optical fiber protector 1 against the optical fiber 2.

[0036] According to this embodiment, even if the optical fiber 2 or the protective tube 5 is bent and pressed toward the end 31 of the metal tube 3 due to dynamic behavior during installation or use of a submarine cable or an optical cable, the optical fiber 2 or the protective tube 5 is protected because the optical fiber protector 1 is interposed between the end 31 of the metal tube 3.

[0037] Moreover, in this embodiment, since the entire area of ​​the expanded diameter portion 11c is curved in a cross section including the axis x, the area with which the optical fiber 2 covered by the protective tube 5 may come into contact has a smoothly curved shape. Therefore, even if the optical fiber 2 to the protective tube 5 are strongly pressed against the curved shape of the expanded diameter portion 11c of the optical fiber protector 1, the pressure acts in a dispersed manner, so that the load on the optical fiber 2 to the protective tube 5 is reduced and the impact is softened, thereby suppressing the effects of damage and the like.

[0038] According to this embodiment, even if the protective tube 5 becomes displaced and no longer functions as intended, which is to protect the surface of the optical fiber 2 from the edge of the cut portion of the end 31 of the metal tube 3, the optical fiber protector 1 interposed between the end 31 of the metal tube 3 and the optical fiber 2 can function in place of the protective tube 5. This eliminates the need to perform edge treatment on the end 31 of the metal tube 3 in order to avoid problems caused by displacement of the protective tube 5.

[0039] In addition, because 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 expanded diameter portion 11c of the end opening 11 of the optical fiber protector 1 gets caught 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 almost no risk 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, it is preferable to relatively fix the entire metal tube-covered optical fiber cable 4 in the vicinity of the end 31 of the metal tube 3 in the direction of the axis x by crimping from the outer periphery of the metal tube 3 at the position of the arrow M as shown in Fig. 1. The optical fiber protector 1 is fixed to the metal tube 3 by crimping from the outer periphery of the metal tube 3.

[0041] Moreover, the protective tube 5 located immediately below the optical fiber protector 1 is also fixed at the crimping position, suppressing displacement of the protective tube 5 in the axial x direction. In consideration of 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 (more specifically, the small diameter portion 11a).

[0042] A connection structure of a metal tube-covered optical fiber cable 4 using the optical fiber protector 1 according to this embodiment will be described. Fig. 7 is a schematic diagram for explaining a connection structure of a metal tube-covered optical fiber cable 4 using the optical fiber protector 1 according to this embodiment (hereinafter, may be simply referred to as "this connection structure"). As shown in Fig. 7, in this connection structure, ends of the metal tube-covered optical fiber cable 4 are connected to each other by a sheath tube (also called a sleeve) 6.

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

[0044] The sheath tube 6 is a tube made of metal such as stainless steel, and the ends of the metal-tube-covered optical fiber cable 4 are inserted into the openings at both ends to cover the end of the metal tube 3 and the optical fiber 2 inserted in the small diameter portion 11a of the optical fiber protector 1. The metal-tube-covered optical fiber cable 4 and the sheath tube 6 are covered with a sheath 7, and the connection area between the metal-tube-covered optical fiber cable 4 and the sheath tube 6, where the sheath 7 is not covered, and the vicinity thereof are protected by wrapping a vinyl chloride tape 8 around them.

[0045] Fig. 8 is an enlarged vertical cross-sectional view of the connection portion between the metal tube-covered optical fiber cable 4 and the sheath tube 6 in this connection structure. Fig. 8 shows only the connection state between the metal tube-covered optical fiber cable 4 on the left side in Fig. 7 and the sheath tube 6. As shown in Fig. 8, the metal tube-covered optical fiber cable 4 (metal tube 3) having the end structure in the state of Fig. 1 in which the optical fiber protector 1 is interposed between the optical fiber 2 covered with the protective tube 5 and the metal tube 3 is inserted into the sheath tube 6 from the end 31 side.

[0046] As shown in Fig. 8, a crimp mark (crimp mark 32) remains on the metal tube 3 at the position indicated by the arrow M in Fig. 1. The actual connection work of the metal tube-covered optical fiber cable 4 and the sheath tube 6 is performed, for example, as follows. First, as described above, the protective tube 5 and the optical fiber protector 1 are attached to bring the terminal of the metal tube-covered optical fiber cable 4 into the state shown in Fig. 1.

[0047] Then, the metal tube-covered optical fiber cable 4 to which the protective tube 5 and the optical fiber protector 1 are attached is covered with the sheath tube 6 from the end 31 side, the metal tube-covered optical fiber cable 4 is inserted as it is, and the sheath tube 6 is retracted from the end 31 to expose the optical fiber 2 protruding from the end 31. This exposed end of the optical fiber 2 and an end of the optical fiber 2 exposed from one end of another metal tube-covered optical fiber cable 4 to be connected are fusion spliced.

[0048] Next, the sheath tube 6 is moved to a position covering the exposed portion (portion not covered by the metal tube 3) of the optical fiber 2 including the fusion spliced ​​portion between the optical fibers 2, and one end of the sheath tube 6 is welded to the metal tube 3. FIG. 8 shows a weld mark 61 caused by this welding. The welding operation between the sheath tube 6 and the metal tube 3 is also performed on the other end of the sheath tube 6 to the metal tube 3 of another metal tube-covered optical fiber cable 4 to be connected, thereby completing the connection operation of the metal tube-covered optical fiber cable 4, and obtaining the connection structure of the metal tube-covered optical fiber cable 4 according to this embodiment. In this manner, a metal tube-covered optical fiber cable joint having a connection structure using the optical fiber protector 1 of this embodiment can be manufactured.

[0049] According to this embodiment, by setting the optical fiber protector 1 on the metal tube 3, the heat generated when the metal tube 3 and the sheath tube 6 are welded together is insulated not only by the heat-insulating 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 already described, the influence of the heat generated when the metal tube 3 and the sheath tube 6 are welded together can be suppressed on the optical fiber 2.

[0050] <Second embodiment> Fig. 9 is a side view of the optical fiber protector 101 according to the second embodiment, and Fig. 10 is a perspective view of the optical fiber protector 101. Fig. 11 is a cross-sectional view showing an end structure of a metal tube-covered optical fiber cable 104 using the optical fiber protector 101 according to the second embodiment, and is a cross-sectional view of a section similar to that of Fig. 2 in the first embodiment.

[0051] The vertical 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 almost the same as that of the first embodiment shown in FIG. 1, and therefore will not be described.

[0052] 9 to 11, each member having the same configuration as the optical fiber protector 1 according to the first embodiment and the terminal structure of the metal tube-coated optical fiber cable 4 using the same is given a reference numeral in the hundreds with the last two digits being the same as those of the member in the first embodiment, and the description of the similar configuration of each member will be omitted. The following description will focus on the differences from the first embodiment.

[0053] 9 to 11, the optical fiber protector 101 according to this embodiment has one slit 113 extending in the axial x direction. The slit 113 reaches both ends of the optical fiber protector 101 in the axial x direction.

[0054] In this embodiment, the inner tubular portion (tubular portion) 112 does not form a complete tube because the circumferential portion of the slit 113 is missing. However, in this specification, if a part in the circumferential direction is missing, but the missing part is repaired to form a tube, it is considered to be included in the concept of "tube". The same applies to the case where there are two or more missing parts (e.g., the third embodiment described later) (the above also applies to the outer tubular 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 the optical fiber 102 from the side of the optical fiber protector 101.

[0056] The width of the slit 113 is set to a size that allows the optical fiber 102 to 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 while widening the slit 113. In this embodiment, the work of inserting the optical fiber 102 into the optical fiber protector 101 is easier than when the optical fiber 102 is inserted from the end opening on the opposite side to the end opening 111 of the optical fiber protector 101.

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

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

[0059] <Third embodiment> Fig. 12 is a side view of the optical fiber protector 201 according to the third embodiment, and Fig. 13 is a perspective view of the optical fiber protector 201. Fig. 14 is a cross-sectional view showing an end structure of a metal tube-covered optical fiber cable 204 using the optical fiber protector 201 according to the third embodiment, and is a cross-sectional view of a section similar to that of Fig. 2 in the first embodiment.

[0060] The vertical cross section of the end structure of the metal tube covered optical fiber cable 204 using the optical fiber protector 201 according to the third embodiment is almost the same as that of the first embodiment shown in FIG. 1, and therefore will not be described.

[0061] 12 to 14, each member having the same configuration as the optical fiber protector 1 according to the first embodiment and the terminal structure of the metal tube-coated optical fiber cable 4 using the same is given a reference numeral in the two hundredths having the same last two digits as each member in the first embodiment, and the description of the similar configuration of each member is omitted. The following description will focus on the differences from the first embodiment.

[0062] 12 to 14, the optical fiber protector 201 according to this embodiment has two slits 214 extending in the axial x direction. The slits 214 extend from the end of the optical fiber protector 101 on the side of the arrow J in the axial x direction and terminate halfway, not reaching both ends in the axial x direction. The slits 214 are provided in a pair (two in total), one on the left and one on the right, when viewed from either side in the axial x direction (either the left or right in FIG. 12; also visible in the cross-sectional view of FIG. 14).

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

[0064] The optical fiber protector 201 of this embodiment, like the optical fiber protector 1 of the first embodiment, can be applied to the end structure of a metal tube-covered optical fiber cable 204 and the connection structure of a metal tube-covered optical fiber cable 204, and similar actions and effects can be expected. In this embodiment, the number of slits 214 is two, but this is not limited thereto, and the number may be one or three or more.

[0065] <Fourth embodiment> Fig. 15 is a side view of an optical fiber protector 301 according to the fourth embodiment, and Fig. 16 is a perspective view of the optical fiber protector 301. Fig. 17 is a cross-sectional view showing an end structure of a metal tube-covered optical fiber cable 304 using the optical fiber protector 301 according to the fourth embodiment, and is a cross-sectional view of a section similar to that of Fig. 2 in the first embodiment.

[0066] The vertical 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 almost the same as that of the first embodiment shown in FIG. 1, and therefore will not be described.

[0067] 15 to 17, each member having the same configuration as the optical fiber protector 1 according to the first embodiment and the terminal structure of the metal tube-coated optical fiber cable 4 using the same is given a reference numeral in the three hundred range with the same last two digits as the corresponding member in the first embodiment, and the description of the similar configuration of each member will be omitted. The following description will focus on the differences from the first embodiment.

[0068] 15 to 17, the optical fiber protector 301 according to this embodiment is composed of two members 301x and 301y that are divided along a plane including the axis x (a plane in the depth direction including the axis x in the drawing of FIG. 15). 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 tubular piece 312x, 312y, respectively, and the two members 301x, 301y are integrated together so that the end opening piece 311x and the end opening piece 311y form one end opening 311, and the inner tubular piece 312x and the inner tubular piece 312y form one end opening 311.

[0070] As described above, since the optical fiber protector 301 is divided into two components 301x, 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 the optical fiber 302 between the two components 301x, 301y.

[0071] Assuming that the two members 301x, 301y are not separate, the optical fiber 302 is inserted by inserting it into the end opening 311 of the optical fiber protector 301. In this embodiment, in which the optical fiber 302 is separated into two members 301x, 301y, the task of setting (inserting) the optical fiber 302 into the optical fiber protector 301 is easier than in the case where the optical fiber 302 is inserted by inserting it into the end opening 311 of the optical fiber protector 301.

[0072] The two members 301x, 301y may or may not be fixed to each other. When fixing the two members 301x, 301y, it is preferable to fix them after setting (inserting) the optical fiber 302. When fixing them, the fixing method may include, but is not limited to, a method of bonding them with an adhesive, a method of providing a locking structure in advance on both members, a method of using a fixing tool such as a screw, and the like.

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

[0074] In this embodiment, the circumferentially opposing surfaces of the two members 301x and 301y come into contact with each other to form one optical fiber protector 301, but there may be a radially overlapping area at each circumferential end. Fig. 18 shows an end structure of a metal tube-covered optical fiber cable using an optical fiber protector according to a modified example having a structure different from that of this embodiment. Fig. 18 is a cross-sectional view showing an end structure of a metal tube-covered optical fiber cable using a modified example of the optical fiber protector according to the fourth embodiment, and is a cross-sectional view of a section similar to that of Fig. 17. However, Fig. 18 is enlarged in size compared to Fig. 17.

[0075] 18, an optical fiber protector 301' according to this modification is composed of two separate members 301x' and 301y', similar to the optical fiber protector 301 according to the fourth embodiment. The two members 301x' and 301y' are combined to form one optical fiber protector 301'.

[0076] The members 301x', 301y' are provided with inner peripheral protrusions 316x', 316y' and outer peripheral protrusions 317x', 317y' at their respective circumferential ends. The inner peripheral protrusions 316x', 316y' and the outer peripheral protrusions 317x', 317y' at their respective circumferential ends overlap in the radial direction to form one optical fiber protector 301'.

[0077] By appropriately adjusting the overlapping length in the overlapping region of the inner peripheral protrusions 316x', 316y' and the outer peripheral protrusions 317x', 317y', 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. By making the thicknesses of the inner peripheral protrusions 316x', 316y' and the outer peripheral protrusions 317x', 317y' thinner (preferably half) than other portions (non-overlapping regions) of the members 301x', 301y', the shape of the optical fiber protector 301' can be stabilized.

[0078] In this modification, an example is given in which the two members 301x', 301y' have the same shape and include an inner circumferential protrusion and an outer circumferential protrusion, but they may have different shapes, with one member only including an inner circumferential protrusion and the other member only including an outer circumferential protrusion. In this case, an overlapping region is formed on both sides in the circumferential direction, where the inner circumferential protrusion of one member fits into the outer circumferential protrusion of the other member, forming one optical fiber protector.

[0079] The optical fiber protector 301 of this embodiment and the optical fiber protector 301' of the modified example can be applied to the terminal structure of a metal tube-covered optical fiber cable 304 and the connection structure of a metal tube-covered optical fiber cable 304, similar to the optical fiber protector 1 of the first embodiment, and similar actions and effects can be expected.

[0080] <Fifth embodiment> Fig. 19 is a longitudinal sectional view showing the end structure of a metal tube-covered optical fiber cable 404 using an optical fiber protector 401 according to the fifth embodiment, and Fig. 20 is a transverse sectional view showing the end structure of the metal tube-covered optical fiber cable 404. In particular, Fig. 19 is a sectional view taken along the FF section in Fig. 20, and Fig. 20 is a sectional view taken along the EE section in Fig. 19. Fig. 21 is a longitudinal sectional view of only the optical fiber protector 401 according to the fifth embodiment, and is a sectional view taken along the same section as Fig. 19.

[0081] 19 to 21, each member having the same configuration as the optical fiber protector 1 according to the first embodiment and the terminal structure of the metal tube-coated optical fiber cable 4 using the same is given a reference numeral in the four hundred range with the same last two digits as the corresponding member in the first embodiment, and the description of the similar configuration of each member will be omitted. The following description will focus on the differences from the first embodiment.

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

[0083] In contrast, in the terminal opening 411 of this embodiment, in a cross section including axis x (corresponding to the cross section of the longitudinal cross section in FIG. 21; the same applies hereinafter in this embodiment), it has a shape that proceeds further from a portion corresponding to large diameter portion 11b (the portion shown by reference symbol 411d in FIG. 21; hereinafter such a portion will be referred to as the "tip") and curves and expands in diameter while returning to the side of arrow J in the direction of axis x (see FIGS. 19 and 21). Hereinafter, this progression in one direction (in this embodiment, the direction of arrow K) and then returning in the opposite direction (similarly, the direction of arrow J) will be referred to as a "turn," and a shape including such a turn will be referred to as a "shape having a turn."

[0084] In this embodiment, the small diameter portion 411a is located in the same position as in the first embodiment, but the large diameter portion 411b is located in a different position from the tip 411d that corresponds to the large diameter portion 11b in the first embodiment. In this embodiment, in a cross section including the axis x, the entire area of ​​the enlarged diameter portion 411c is curved, including the vicinity of the small diameter portion 411a in the enlarged diameter portion 411c and the vicinity of the tip 411d that is the part farthest from the small diameter portion 411a.

[0085] In the optical fiber protector 401 according to this embodiment, the end opening 311 has a barbed shape, so that the optical fiber protector 401 alone can easily achieve strength. In addition, since the end opening 411 has a barbed shape, the end 431 of the metal tube 403 can be easily caught therein, so that the effect of preventing the optical fiber protector 401 from being pulled into the inside of the metal tube 403 is further improved.

[0086] The optical fiber protector 401 of this embodiment, like the optical fiber protector 1 of the first embodiment, can be applied to the terminal structure of a metal tube-covered optical fiber cable 404 and the connection structure of a metal tube-covered optical fiber cable 404, and similar actions and effects can be expected.

[0087] Sixth embodiment Fig. 22 is a longitudinal sectional view showing the end structure of a metal tube-covered optical fiber cable 504 using an optical fiber protector 501 according to the sixth embodiment, and Fig. 23 is a transverse sectional view showing the end structure of the metal tube-covered optical fiber cable 504. In particular, Fig. 22 is a sectional view taken along the HH section in Fig. 23, and Fig. 23 is a sectional view taken along the GG section in Fig. 22. Fig. 24 is a longitudinal sectional view of only the optical fiber protector 501 according to the sixth embodiment, and is a sectional view taken along the same section as Fig. 22.

[0088] 22 to 24, each member having the same configuration as the optical fiber protector 1 according to the first embodiment and the terminal structure of the metal tube-coated optical fiber cable 4 using the same is given a reference numeral in the 500s with the same last two digits as the corresponding member in the first embodiment, and a description of the similar configuration of each member will be omitted. The following description will focus on the differences from the first embodiment.

[0089] 22 to 24, the optical fiber protector 501 according to this embodiment has an end opening 511 and an outer tubular portion (tubular portion) 512. The end opening 511 is composed of a small diameter portion 511a having a smallest inner diameter and into which the optical fiber 502 is inserted, a large diameter portion 511b having a largest outer diameter, and an expanded 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 expanded diameter 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 of the longitudinal cross section in FIG. 22, the same applies to the following embodiment), the expanded diameter portion 511c is curved over the entire area including the vicinity of the small diameter portion 511a in the expanded diameter portion 511c and the vicinity of the tip portion 511d, which is the part farthest from the small diameter portion 511a. That is, in this embodiment, the terminal opening 511 has a shape with a barb, similar to the fifth embodiment (however, in this embodiment, the barb is formed from the tip portion 511d toward the small diameter portion 511a).

[0091] In the optical fiber protector 501 according to this embodiment, the end opening 511 has a barbed shape, so that the optical fiber protector 501 alone can easily achieve strength. In addition, since the end opening 511 has a barbed shape, the end 531 of the metal tube 503 can be easily caught therein, so that the optical fiber protector 501 is more effectively prevented from falling off the metal tube 503.

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

[0093] In this embodiment, since the entire area of ​​the expanded diameter portion 511c is curved in a cross section including the axis x, the area (the small diameter portion 511a and the area of ​​the expanded diameter portion 511c near the small diameter portion 511a) with which the optical fiber 502 covered by the protective tube 505 may come into contact is smoothly curved. Therefore, even if the optical fiber 502 to the protective tube 505 are strongly pressed against the curved shape of the expanded diameter portion 511c of the optical fiber protector 501, the pressure acts in a dispersed manner, so that the load on the optical fiber 502 to the protective tube 505 is reduced and the impact is softened, thereby suppressing the effects of damage and the like.

[0094] In this embodiment, unlike the first embodiment, the tubular portion of the optical fiber protector 501 is not inside the metal tube 503, but only has an outer tubular portion 513 on the outside. Therefore, the terminal opening 511 has a shape that protrudes from the outer tubular portion 513 to the inner periphery side. However, in this embodiment, since the expanded diameter portion 511c that connects the small diameter portion 511a and the large diameter portion 511b in the terminal opening 51 is curved, even if the optical fiber 502 to the protective tube 505 are strongly pressed against the vicinity of the terminal opening 511, the load on the optical fiber 502 to the protective tube 505 is reduced and the impact is softened, and the influence of damage and the like can be suppressed.

[0095] To fully utilize the effect of the curved shape in the vicinity of small diameter portion 511a and to cover end 531 of the metal tube with end opening 511, it is desirable that the inward return at end opening 511 is relatively large. As for the degree of inward return at end opening 511, it is preferable that, in a plane including the direction of axis x, the tangent on the inner circumference side of small diameter portion 511a is parallel to axis x or the end of small diameter portion 511a faces the outer circumference side, since this enhances the protection effect of the optical fiber.

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

[0097] Note that the crimping process from the outer periphery of the metal tube 3 described in the first embodiment may also be performed in this embodiment at the marking position indicated by the arrow M. However, in this embodiment, the positional relationship between the metal tube 503 and the optical fiber protector 501 in the radial direction is reversed, so in this embodiment, the crimping process is performed from the outer periphery of the outer tubular portion 513 of the optical fiber protector 501. Since the action and effect brought about by the crimping are the same as those in the first embodiment, except that the positional relationship between the metal tube 503 and the outer tubular portion 513 is reversed, a detailed description will be omitted.

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

[0099] 25 and 26, each member having the same configuration as the optical fiber protector 1 according to the first embodiment and the terminal structure of the metal tube-coated optical fiber cable 4 using the same is given a reference number in the six hundredths with the same last two digits as the corresponding member in the first embodiment, and the description of the similar configuration of each member will be omitted. The following description will focus on the differences from the first embodiment.

[0100] In this embodiment, the shape of the optical fiber protector 601 is different from that of the fifth embodiment. That is, in the optical fiber protector 601 according to the seventh embodiment, a rolled end 615 extends from the large diameter portion 611b of the terminal opening 611. In a cross section including the axis x (corresponding to the cross section of the longitudinal cross section in FIG. 26; the same applies to the following embodiments), the rolled end 615 is curved with substantially the same curvature as the enlarged diameter portion 611c of the terminal opening 611, extends toward the inner cylindrical portion (cylindrical portion) 612, and further begins to move toward the arrow K side, forming an edge.

[0101] The rolled end 714 extends from the small diameter portion 611a of the terminal opening 611 into a rolled shape, which makes it easier to obtain strength as a single optical fiber protector 601. In addition, the area that may come into contact with the inner surface of the metal tube 603 (the large diameter portion 611b and its vicinity) has a smoothly curved shape, which reduces the load on the metal tube 603.

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

[0103] The above-described embodiments merely show examples of typical forms of the present invention, and the present invention is not limited to these embodiments. In other words, a person skilled in the art can implement the present invention by making various modifications in accordance with conventionally known knowledge without departing from the gist of the present invention. As long as the optical fiber protector of the present invention, the terminal structure of a metal-tube-covered optical fiber cable using the same, and the connection structure of a metal-tube-covered optical fiber cable are still included in the scope of the present invention even after such modifications.

[0104] For example, in all of the above embodiments, examples are given in which the entire expanded diameter portion of the terminal opening is curved in a cross section including the axis, but the present invention is not limited to this. For example, even if a part of the expanded diameter portion includes a linearly expanding region in a cross section including the axis, it does not matter as long as at least a part of the expanded diameter portion is curved. However, it is preferable that at least the vicinity of the part of the expanded diameter portion farthest from the small diameter portion (the end of the terminal opening) in the cross section including the axis is curved to cover the end of the metal tube, because this makes it difficult for the optical fiber to be damaged even if the optical fiber comes into contact with the vicinity of the end of the metal tube and is subjected to a bending load.

[0105] In the fourth embodiment, an example of an optical fiber protector divided into two members with a dividing surface including the axis is given, but the present invention is not limited to this, and an optical fiber protector made of three or more members may be used. Also, the dividing surface does not have to include the axis. In this specification, the "dividing surface" refers to the dividing surface between adjacent divided members.

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

[0107] In the above embodiment, the explanation has been centered on the connection structure between metal-tube-covered optical fiber cables in a metal-tube-covered optical fiber cable assembly, but it is of course also possible to apply the "terminal structure of a metal-tube-covered optical fiber cable" of the present invention to the terminal of a metal-tube-covered optical fiber cable assembly or to the terminal of a metal-tube-covered optical fiber cable that is used without being connected. [Explanation of symbols]

[0108] 1,101,201,301,301',401,501,601 Optical fiber protection equipment, 2,102,202,302,402,502,602 Optical fiber, 3,103,203,303,403,503,603 Metal pipe, 4,104,204,304,404,504,604 Metallic tube covered optical fiber cable, 5,105,205,305,405,505,605 Protective tube, 11,111,211,311,311',411,511,611 terminal opening, 11a,111a,211a,311a,411a,511a,611a Small diameter part, 11b, 111b, 211b, 311b, 411b, 511b, 611b Large diameter part, 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 Crimp 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 tip, 513 Outer cylinder part (cylindrical part), 615 Roll-up end

Claims

1. The present invention is 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, a small diameter section having a smallest inner diameter and into which the optical fiber is inserted, a large diameter section having a largest outer diameter, and an end opening including an expanded diameter section connecting the small diameter section and the large diameter section, and a tubular section extending from the small diameter section or the large diameter section to a side opposite the expanded diameter section in the axial direction, The diameter of the enlarged diameter portion gradually increases from the small diameter portion side to the large diameter portion side, An optical fiber protector, wherein at least a portion of the expanded portion is curved in a cross section including the axis.

2. 2. The optical fiber protector according to claim 1, wherein the tubular portion extends continuously from the small diameter portion to a side opposite to the enlarged diameter portion, and the optical fiber is inserted into the tubular portion and is inserted into an end of the metal tube.

3. The optical fiber protector according to claim 1 , wherein the tubular portion extends continuously from the large diameter portion to a side opposite to the expanded diameter portion, and the metal tube is inserted into the tubular portion.

4. The optical fiber protector according to any one of claims 1 to 3, wherein in a cross section including the axis, at least a portion near the small diameter portion and a portion near the part of the expanded portion farthest from the small diameter portion are curved.

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

6. The optical fiber protector according to any one of claims 1 to 3, having at least one slit extending in the axial direction.

7. The optical fiber protector according to any one of claims 1 to 3, which is composed of two or more divided members.

8. The optical fiber protector according to any one of claims 1 to 3, which is made of a resin material.

9. A metal-tube-covered optical fiber cable having a metal tube and an optical fiber into which the metal tube is inserted, and the optical fiber protector according to any one of claims 1 to 3, An end structure of a metal-tube-covered optical fiber cable, wherein the optical fiber protector is attached to an end of the metal tube in the metal-tube-covered optical fiber cable, and the optical fiber is inserted into the small diameter portion.

10. A metal-tube-covered optical fiber cable including two metal-tube-covered optical fiber cables each having a metal tube and an optical fiber into which the metal tube is inserted, two optical fiber protectors according to any one of claims 1 to 3, and a sheath tube, The two optical fiber protectors are attached to ends of the metal tubes of the separate metal tube-covered optical fiber cables, and the optical fibers are inserted into the small diameter portions; A connection structure for a metal tube-covered optical fiber cable, in which the ends of the two metal tube-covered optical fiber cables are inserted into both sides of the sheath tube, covering the ends of the metal tubes and the optical fiber inserted into the small diameter portion of the optical fiber protector.

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