Fiber optic cable

Abstract

The purpose of the present invention is to provide a fiber optic cable capable of suppressing increased transmission loss caused by cracks in the sheath.　A fiber optic cable (1) comprises: an optical fiber (10); a binding wrap (20) covering the optical fiber (10); and a sheath (30) forming a space (31) for accommodating the optical fiber (10) and the binding wrap (20). There is a gap (G) in at least a portion of the space between the inner peripheral surface (32) of the sheath (30) and the binding wrap (20), and the binding wrap (20) has a plurality of ridges (23).

Description

fiber optic cable

[0001] This application claims priority from Japanese Patent Application No. 2024-030950, filed on March 1, 2024, the contents of which are incorporated herein by reference.

[0002] Patent Document 1 discloses an optical fiber cable including a core having an optical fiber and an outer jacket covering the core.

[0003] Japanese Patent Application Publication No. 2008-292841

[0004] Optical fiber cables may be subjected to impacts or lateral pressure. When an optical fiber cable is subjected to impacts or lateral pressure, cracks may occur in the jacket extending radially outward from the core. In this case, the cracks may widen due to deformation of the jacket caused by the impact or lateral pressure, and the optical fiber may enter the crack. When the impact or lateral pressure acting on the optical fiber cable is released in this state, the cracks close and the optical fiber becomes trapped in the cracks. This may increase the transmission loss of the optical fiber cable.

[0005] The present invention has been made in consideration of the above circumstances, and has an object to provide an optical fiber cable that can suppress an increase in transmission loss caused by cracks occurring in the jacket.

[0006] In order to solve the above problem, the optical fiber cable of aspect 1 of the present invention comprises an optical fiber, a pressure wrap that covers the optical fiber, and an outer jacket that forms a space to accommodate the optical fiber and the pressure wrap, and there is at least a partial gap between the inner surface of the outer jacket and the pressure wrap, and the pressure wrap has multiple ridges.

[0007] In addition, in a second aspect of the present invention, in the optical fiber cable of the first aspect, the circumferential length of the space is shorter than the circumferential length of the pressure winding in a cross section intersecting the longitudinal direction of the space.

[0008] A third aspect of the present invention is the optical fiber cable of the first or second aspect, wherein the extending direction of the plurality of peaks is different from the extending direction of the optical fiber.

[0009] Furthermore, in a fourth aspect of the present invention, in the optical fiber cable according to any one of the first to third aspects, the holding winding has a plurality of tapes.

[0010] A fifth aspect of the present invention is the optical fiber cable according to any one of the first to fourth aspects, wherein the pressure winding further includes an inner pressure winding.

[0011] Furthermore, aspect 6 of the present invention is an optical fiber cable according to any one of aspects 1 to 5, further comprising a component provided within the outer jacket, and the ridge portion is arranged radially inward of the component.

[0012] A seventh aspect of the present invention is the optical fiber cable according to any one of the first to sixth aspects, wherein the plurality of peaks are arranged side by side in the circumferential direction.

[0013] Furthermore, in an eighth aspect of the present invention, in the optical fiber cable according to any one of the first to sixth aspects, the plurality of peaks are arranged side by side in the longitudinal direction.

[0014] A ninth aspect of the present invention is the optical fiber cable according to any one of the first to sixth aspects, wherein the plurality of peaks are arranged side by side in the circumferential and longitudinal directions.

[0015] A tenth aspect of the present invention is the optical fiber cable according to any one of the first to ninth aspects, wherein the pressure winding has an excess length in the longitudinal direction of the optical fiber cable.

[0016] In addition, in an eleventh aspect of the present invention, in the optical fiber cable of any one of aspects 1 to 10, when the circumferential length of the space within the jacket is L and the circumferential length of the pressure winding is M, 1.07L≦M is satisfied.

[0017] A twelfth aspect of the present invention is the optical fiber cable according to any one of the first to eleventh aspects, wherein the plurality of peaks are provided over the entire surface of the pressure winding.

[0018] According to the above aspect of the present invention, an optical fiber cable can be provided that can suppress an increase in transmission loss caused by cracks occurring in the jacket.

[0019] FIG. 1 is a cross-sectional view showing an optical fiber cable according to a first embodiment; FIG. 2 is a view showing a case where lateral pressure acts on a conventional optical fiber cable; FIG. 3 is a view showing a case where lateral pressure acts on the optical fiber cable according to the first embodiment; FIG. 4 is a cross-sectional view showing an optical fiber cable according to a second embodiment; FIG. 5 is a cross-sectional view showing an optical fiber cable according to a third embodiment; FIG. 6 is a cross-sectional view showing an optical fiber cable according to a fourth embodiment; FIG. 7 is a view explaining a state in which the peaks extend along the circumferential direction in the pressure winding of the optical fiber cable according to the fifth embodiment; FIG. 8 is a view explaining a state in which the peaks extend spirally in the pressure winding of the optical fiber cable according to the fifth embodiment; FIG. 9 is a cross-sectional view of an optical fiber cable according to a modified example of this embodiment; FIG. 10 is a cross-sectional view of an optical fiber cable according to another modified example of this embodiment; FIG. 11 is a cross-sectional view of an optical fiber cable according to another modified example of this embodiment.

[0020] First Embodiment An optical fiber cable according to a first embodiment of the present invention will now be described with reference to the drawings. As shown in Fig. 1, the optical fiber cable 1 according to this embodiment includes an optical fiber 10, a tension wrap 20 that wraps around the optical fiber 10, an outer jacket 30 that forms a space 31 that accommodates the optical fiber 10 and the tension wrap 20, a strength member 40, and a ripcord 50. The ripcord 50 and the strength member 40 are disposed within the outer jacket 30.

[0021] (Direction Definition) Here, in this embodiment, the direction along the central axis O of the space 31 is referred to as the longitudinal direction. A cross section that intersects (e.g., is perpendicular to) the longitudinal direction is referred to as a transverse cross section. When viewed from the longitudinal direction, a direction that intersects with the central axis O is referred to as the radial direction, and a direction that rotates around the central axis O is referred to as the circumferential direction. The circumferential direction is also a direction that intersects (e.g., is perpendicular to) the radial direction when viewed from the longitudinal direction. When viewed from the transverse cross section, a direction approaching the central axis O is referred to as the radially inner side, and a direction away from the central axis O is referred to as the radially outer side. Note that when the space 31 is non-circular when viewed from the transverse cross section, the central axis O is located at the centroid of the space 31.

[0022] In the optical fiber cable 1 according to this embodiment, a plurality of optical fibers 10 and a pressure wrap 20 that wraps around the plurality of optical fibers 10 are arranged in a space 31 in the jacket 30 .

[0023] The optical fiber 10 may be a coated optical fiber, an optical fiber wire, an optical fiber ribbon, or the like. The optical fiber cable 1 may have one or more coated optical fiber wires, optical fiber wires, optical fiber ribbons, or the like. The optical fiber cable 1 may have only one type of optical fiber, an optical fiber wire, an optical fiber ribbon, or the like, or a combination of multiple types. In the example shown in FIG. 1 , multiple optical fiber wires are used as the optical fiber 10. The multiple optical fibers 10 may form a so-called intermittently fixed ribbon, which is a type of optical fiber ribbon. The number of intermittently fixed ribbons may be one or more. In an intermittently fixed ribbon, the multiple optical fibers 10 are arranged in an arrangement direction perpendicular to the longitudinal direction of the optical fibers 10. Every two optical fibers 10 adjacent in the arrangement direction are connected to each other by multiple connecting portions arranged intermittently in the longitudinal direction of the optical fibers 10. Furthermore, every two connecting portions adjacent in the arrangement direction are located at different positions in the longitudinal direction of the optical fibers 10. However, the form of the optical fiber 10 is not limited to an optical fiber ribbon such as an intermittently fixed ribbon, and can be changed as appropriate. A plurality of optical fibers 10 may be bundled with a bundling material (not shown) inside the pressure winding 20 to form an optical fiber unit, and a bundle of optical fibers 10 may be formed by bundling a plurality of optical fiber units.

[0024] The plurality of optical fibers 10 are twisted together around the central axis O. The twisting pattern may be spiral or SZ. The plurality of optical fibers 10 do not have to be twisted together. The number of optical fibers 10 arranged in the space 31 can be changed as appropriate as long as it is one or more.

[0025] The pressure wrap 20 is formed in a substantially cylindrical shape that wraps around the optical fiber 10. As will be described in detail later, multiple ridges 23 are formed at equal intervals in the circumferential direction. In this embodiment, the cylindrical pressure wrap 20 is formed by overlapping both widthwise ends of a tape 20a extending in the longitudinal direction. The pressure wrap 20 has a wrap portion 21 where the ends of the tape 20a overlap, and a non-wrap portion 22 that is the portion excluding the wrap portion 21. The non-wrap portion 22 is located between the first end and second end that form the wrap portion 21. Because the pressure wrap 20 has the wrap portion 21, contact between the optical fiber 10 inside the pressure wrap 20 and the jacket 30 can be prevented. However, the wrap portion 21 may also be formed by butting both ends of the tape 20a together and bonding them together. In this manner, the pressure wrap 20 is formed from the tape 20a extending in the longitudinal direction and has the wrap portion 21 where the ends of the tape 20a contact each other. In this respect, the pressure wrap 20 of this embodiment differs from, for example, a tube formed by extruding a thermoplastic resin around a plurality of optical fibers.

[0026] The tape 20a of the pressure wrap 20 can be made of nonwoven fabric, polyester tape, or the like. Alternatively, a water-absorbing tape made by imparting water-absorbing properties to nonwoven fabric, polyester tape, or the like may be used as the tape 20a. In this case, the waterproof performance of the optical fiber cable 1 can be improved. The thickness of the tape 20a is, for example, approximately 50 to 500 μm. The thickness of the tape 20a of the pressure wrap 20 is approximately uniform, and the peaks 23 of the pressure wrap 20 are provided by deforming the tape 20a.

[0027] The pressure wrap 20 is formed of a non-metallic tape 20a. That is, the pressure wrap 20 does not include a metal tape. Because the pressure wrap 20 is a non-metallic tape, the pressure wrap 20 can easily deform when lateral pressure or an impact is applied to the optical fiber cable 1. Furthermore, in consideration of the ease of deformation during tension or compression, it is preferable that the pressure wrap 20 does not include a sheet formed of fiber-reinforced plastic (FRP). In these respects, the pressure wrap 20 of this embodiment differs from, for example, a corrugated tube in which a metal sheet is wrapped around the optical fiber.

[0028] The outer shape of the jacket 30 according to this embodiment is substantially circular in cross section, excluding the protrusions 33 described below. Examples of materials that can be used for the jacket 30 include polyolefin (PO) resins such as polyethylene (PE), polypropylene (PP), ethylene-ethyl acrylate copolymer (EEA), ethylene-vinyl acetate copolymer (EVA), and ethylene-propylene copolymer (EP), as well as polyvinyl chloride (PVC). The jacket 30 may also be formed using a mixture (alloy, mixture) of the above resins. Various additives may also be added to the jacket 30 depending on the purpose. Examples of additives include flame retardants, colorants, anti-degradants, and inorganic fillers. A space 31 is formed inside the jacket 30 to accommodate the optical fiber 10 and the pressure winding 20.

[0029] The tension members 40 are members having a higher Young's modulus in the longitudinal direction than the jacket 30. When tension is applied to the optical fiber cable 1 in the longitudinal direction, the tension members 40 bear the tension and protect the optical fiber 10. Examples of materials that can be used for the tension members 40 include metal wires (steel wires, etc.), a material made of bundled metal wires, glass fiber, and a material made of bundled glass fiber. Alternatively, the tension members 40 may be made of fiber-reinforced plastic (FRP), such as aramid fiber-reinforced plastic (A-FRP).

[0030] The present embodiment employs two strength members 40, which are arranged facing each other across the space 31. However, the number and arrangement of the strength members 40 are not limited to the illustrated example and can be modified as appropriate. For example, the strength members 40 may be arranged in the space 31 instead of in the jacket 30. Alternatively, the strength members 40 may be arranged in both the jacket 30 and the space 31. Furthermore, depending on the application of the optical fiber cable 1, the optical fiber cable 1 may not have the strength members 40.

[0031] The ripcords 50 are components used to tear the jacket 30. In the illustrated example, the ripcords 50 are provided near the space 31 and are located radially inward of the strength members 40. The positions of the strength members 40 and the ripcords 50 are offset from each other in the circumferential direction. The ripcords 50 may be made of, for example, synthetic fiber (polyester, etc.) thread or cylindrical rods made of polypropylene (PP) or nylon. A pair of ripcords 50 according to this embodiment are arranged radially to sandwich the space 31 therebetween. The number of ripcords 50 may be one, or three or more. The arrangement of the ripcords 50 is not limited to the illustrated example and can be modified as appropriate. The optical fiber cable 1 does not necessarily have to include a ripcord 50.

[0032] The jacket 30 according to this embodiment is provided with a pair of protrusions 33 that protrude radially outward from the outer peripheral surface of the jacket 30. The circumferential positions of the protrusions 33 correspond to the position of the ripcord 50. The protrusions 33 serve as markers that allow the user to easily recognize the position of the ripcord 50 from outside the optical fiber cable 1. The jacket 30 does not necessarily have to have the protrusions 33. In this case, the protrusions 33 may be replaced by linear coloring of the jacket 30. However, the jacket 30 does not necessarily have to have the protrusions 33 and be uncolored.

[0033] In this embodiment, the ridges 23 are formed on the pressure wrap 20 to prevent the optical fiber from being pinched in cracks that occur in the jacket 30 when lateral pressure or an impact is applied to the optical fiber cable 1. Details of the ridges 23 will be described below.

[0034] <Crest portions 23 of pressure wrap 20> The pressure wrap 20 has a plurality of crest portions 23 formed by deforming the tape 20a so that the tape 20a protrudes radially outward, and the crest portions 23 are arranged in a line at equal intervals in the circumferential direction. The plurality of crest portions 23 are provided adjacent to each other in the circumferential direction, i.e., the crest portions 23 are provided over the entire surface of the pressure wrap 20. Furthermore, the spaces between adjacent crest portions 23 in the circumferential direction form valley portions 24 that are recessed radially inward, so that the pressure wrap 20 has an uneven shape in which the plurality of crest portions 23 and the plurality of valley portions 24 are alternately provided along the circumferential direction.

[0035] At least a portion of the peaks 23 is in contact with the inner circumferential surface 32 of the jacket 30. At valleys 24 between adjacent peaks 23, the pressure winding 20 and the jacket 30 are not in contact, leaving a gap G. In this embodiment, the circumscribing circle of the pressure winding 20 is equivalent to the space 31 in the jacket 30. In a cross-sectional view, the tape 20a of the pressure winding 20 snakes along the inner circumferential surface 32 of the space 31, wrapping around the optical fiber 10. Therefore, the circumferential length M of the pressure winding 20 is greater than the circumferential length L of the space 31 in the jacket 30. The circumferential length M is the circumferential length of a closed loop formed by the pressure winding 20 curved in a concave-convex manner in a cross-sectional view. The circumferential length M is also equal to the width direction length of the tape 20a forming the pressure winding 20 minus the length of the overlapping portion of the tape 20a in the wrap portion 21.

[0036] The peaks 23 have a curved surface that is convex outward in the radial direction. The valleys 24 have a curved surface that is convex inward in the radial direction. The radius of curvature near the apex of the peaks 23 and the bottom of the valleys 24 is smaller than the radius of the jacket 30 (the radius of the optical fiber cable 1). The radial distance from the bottom of the valleys 24 to the peaks of the peaks 23 (hereinafter also referred to as the protruding height of the peaks) may be equal to or greater than the outer diameter of the optical fiber 10. For example, the protruding height of the peaks 23 may be approximately 0.5 mm. The circumferential width of one peak 23 (hereinafter also referred to as the width of the peaks) may be equal to or less than twice the outer diameter of the optical fiber 10. In this embodiment, the width of the peaks 23 is equal to the circumferential dimension between the bottoms of two adjacent valleys 24 and is also equal to one period of the irregularities including the peaks 23 and valleys 24 that are formed at equal intervals in the circumferential direction.

[0037] Furthermore, for example, in this embodiment, 12 ridges 23 are provided, but the number of ridges 23 is not limited to 12. The protruding height and width of the ridges 23 and the number of ridges 23 in one cross section may be changed appropriately depending on the number of optical fibers 10 housed inside the pressure winding 20, the rigidity of the tape 20a of the pressure winding 20, the dimensions of the ridges 23, the susceptibility of cracks to occur in the jacket 30, and the like.

[0038] More specifically, for example, the dimensions of each part of the optical fiber cable 1 may be as follows: Diameter of the space 31 in the jacket 30: 3 mm Protruding height of the peaks 23: 0.25 mm Width of the peaks 23: 0.5 mm Number of peaks 23 in cross section: 17 Circumferential length M of the pressure wrap 20: 12.6 mm Here, in the optical fiber cable 1 having these dimensions, the circumferential length M of the pressure wrap 20 is less than twice the circumferential length L (9.4 mm) of the space 31 in the jacket 30. From the viewpoint of preventing the optical fiber 10 from being caught in a crack that occurs in the jacket 30, it is desirable to make the width of the peaks 23 smaller or to make the protruding height of the peaks 23 larger. However, in this case, the area in which the optical fiber 10 can be arranged may be narrowed. Taking these points into consideration, the inventors conducted studies and found that, in order to prevent the optical fiber 10 from being pinched while ensuring an area for arranging the optical fiber 10, it is preferable that the circumferential length M of the pressure winding 20 be equal to or less than twice the circumferential length L of the space 31 in the outer jacket 30 (i.e., M≦2L).

[0039] When the diameter of the space 31 in the outer jacket 30 is 3 mm, 2L (twice the circumferential length L of the space 31 in the outer jacket 30) can be calculated as 18.8 mm. When multiple ridges 23 with a protruding height of 0.25 mm are formed so that the circumferential length M is equal to 2L (i.e., so that M = 18.8 mm), the following results are obtained: Width of ridge 23: 0.27 mm Number of ridges 23 in cross section: 32 Therefore, when the diameter of the space 31 is 3 mm and the protruding height of the ridges 23 is 0.25 mm, it is desirable that the number of ridges 23 be in the range of 17 to 32.

[0040] In another example, the dimensions of each part of the optical fiber cable 1 may be as follows: Diameter of the space 31 in the jacket 30: 3 mm Protruding height of the peaks 23: 0.4 mm Width of the peaks 23: 0.5 mm Number of peaks 23 in cross section: 16 Circumferential length M of the pressure winding 20: 15.9 mm Even in the optical fiber cable 1 with the above dimensions, the circumferential length M of the pressure winding 20 is less than twice the circumferential length L (9.4 mm) of the space 31 in the jacket 30. Here, if multiple peaks 23 with a protruding height of 0.4 mm are formed so that the circumferential length M is equal to 2L (i.e., M = 18.8 mm), the following results: Width of the peaks 23: 0.41 mm Number of peaks 23 in cross section: 20 Therefore, it can be seen that in this case, the number of peaks 23 is preferably in the range of 16 to 20.

[0041] In this way, the protruding height of the ridges 23 may be in the range of 0.25 to 0.4 mm, and the width of the ridges 23 may be in the range of 0.27 to 0.5 mm, so as to be able to prevent the optical fiber 10 from being pinched while ensuring an arrangement area for the optical fiber 10. Furthermore, the number of the ridges 23 in the cross section may be changed as appropriate, taking into consideration the diameter of the space 31 in the jacket 30 and the dimensions of the ridges 23. For example, when the diameter of the space 31 in the jacket 30 is 3 mm, the number of the ridges 23 may be in the range of 16 to 32.

[0042] In this embodiment, ridges 23 are also formed in the wrap portion 21 where both ends of the tape 20a overlap. This allows multiple ridges 23 to be provided so that the circumferential spacing between the ridges 23 is uniform. Concave and convex portions are also formed at the end of the tape 20a of the pressure winding 20 with the same height and pitch as the concave and convex portions in the non-wrap portion 22. The wrap portion 21 is formed by overlapping both ends of the tape 20a with the same phase of the concave and convex portions. In this embodiment, the circumferential length of the wrap portion 21 is equal to one period of the concave and convex portions. In this embodiment, to prevent the optical fiber 10 from protruding from the wrap portion 21 of the pressure winding 20 when handling the optical fiber cable 1, the circumferential length of the wrap portion 21 is equal to or greater than one period of the concave and convex portions. However, the length of the wrap portion 21 is not limited to one period of the concave and convex portions or more. For example, the circumferential length of the wrap portion 21 may be less than one period of the concave and convex portions. In particular, when the wrap portion 21 is bonded with an adhesive, the circumferential length of the wrap portion 21 may be shorter.

[0043] The peaks 23 of the pressure windings 20 extend along the longitudinal direction. Here, the direction in which the peaks 23 extend over the entire longitudinal length is different from the direction in which the optical fibers 10 extend. In other words, inside the pressure windings 20, the optical fibers 10 are arranged so as to cross the peaks 23. This makes it possible to prevent a specific optical fiber 10 out of the multiple optical fibers 10 from always being positioned radially inside the peaks 23 extending in the longitudinal direction.

[0044] When manufacturing an optical fiber cable 1 having the above-described peaks 23, for example, the tape 20a that will become the tape wrap 20 is deformed to have concaves and convexes in the width direction, and the optical fiber 10 is wrapped around the peaks 23 that extend in the longitudinal direction. The ripcord 50 and the strength members 40 are attached longitudinally to the radially outer side of the tape 20a (the tape wrap 20) that has been deformed into a cylindrical shape, and the jacket 30 is then extrusion-formed. During this process, a cylindrical space 31 is formed inside the jacket 30 to prevent the resin that will become the jacket 30 from penetrating between the valleys 24. This completes the manufacturing of the optical fiber cable 1. However, the method for manufacturing the optical fiber cable 1 is not limited to the above-described method and can be modified as appropriate.

[0045] Next, the operation of the optical fiber cable 1 configured as above will be described.

[0046] 2A , an optical fiber cable is known that includes an optical fiber 10′, an outer jacket 30′ in which a space 31′ for accommodating the optical fiber 10′ is formed, and a tensile strength member 40′ disposed in the outer jacket 30′ (see, for example, Patent Document 1). The optical fiber cable 1′ may be subjected to impact or lateral pressure.

[0047] Specifically, when an impact or lateral pressure acts on the optical fiber cable 1', a crack C may occur in the jacket 30', extending radially outward from the space 31'. In the optical fiber cable 1' having the strength members 40', the crack C is particularly likely to occur, connecting the space 31' and the strength members 40' in the radial direction.

[0048] Here, the crack C may widen due to deformation of the jacket 30' caused by the impact or lateral pressure, and the optical fiber 10' may enter the crack C. When the impact or lateral pressure acting on the optical fiber cable 1' is released in this state, the restoring force of the jacket 30' closes the crack C, and the optical fiber 10' becomes pinched in the crack C. This may increase the transmission loss of the optical fiber cable 1'. Depending on the magnitude of the restoring force, the optical fiber 10' may also be damaged. Furthermore, in conventional optical fiber cables 1', a pressure wrap having a shape that conforms to the shape of the inner circumferential surface of the jacket 30' may be provided. However, because the jacket 30', the pressure wrap, and the optical fiber 10' are adjacent in the radial direction, the optical fiber 10' may become pinched in the crack C together with the pressure wrap.

[0049] To address this problem, in the optical fiber cable 1 according to this embodiment, a ridge portion 23 is formed on the pressure winding 20 .

[0050] 2B is a diagram showing a state in which a crack C has occurred in the optical fiber cable 1 according to this embodiment, extending from the space 31 toward the strength member 40. For example, if a crack C in the jacket 30 occurs near the peaks 23 of the pressure wrap 20, the peaks 23 will penetrate into the crack C. When the impact or lateral pressure acting on the optical fiber cable 1 in this state is eliminated, the restoring force of the jacket 30 may close the crack C, and the peaks 23 may become trapped in the crack C. In this embodiment, the peaks 23 create a gap G at least partially between the inner circumferential surface 32 of the jacket 30 and the pressure wrap 20, making it difficult for the optical fiber 10 to be placed near the jacket 30. Therefore, the distance from the inner circumferential surface of the jacket 30 to the optical fiber 10 is greater than when the optical fiber 10 is wrapped by a pressure wrap that does not have the peaks 23 formed therein.

[0051] Furthermore, a specific optical fiber 10 among the multiple optical fibers 10 is not always disposed radially inside the peaks 23 extending in the longitudinal direction, and the optical fibers 10 are arranged so as to straddle the peaks 23, so that even if the peaks 23 are caught in a crack, for example, the optical fiber 10 can easily move from inside the peaks 23 compressed in the circumferential direction by the jacket 30. Therefore, even if the peaks 23 of the pressure winding 20 are caught in the crack C, it is possible to prevent the optical fiber 10 from being caught in the crack C.

[0052] Although not shown, even if a crack C occurs radially outside the valley portion 24, the jacket 30 and the pressure wrap 20 are not in contact at the valley portion 24, and the distance from the inner peripheral surface of the jacket 30 to the optical fiber 10 can be secured, preventing the optical fiber 10 from being pinched by the jacket 30. As a result, compared to a case in which the peak portion 23 is not formed in the pressure wrap 20, an increase in transmission loss of the optical fiber cable 1 caused by the optical fiber 10 being pinched in the crack C can be suppressed.

[0053] As described above, the optical fiber cable 1 of this embodiment comprises an optical fiber 10, a pressure wrap 20 that covers the optical fiber 10, and an outer jacket 30 that forms a space 31 to accommodate the optical fiber 10 and the pressure wrap 20, and there is a gap G at least in part between the inner surface 32 of the outer jacket 30 and the pressure wrap 20, and the pressure wrap 20 has multiple ridges 23.

[0054] With this configuration, even if an impact or lateral pressure acts on the optical fiber cable 1 and a crack C occurs in the outer sheath 30, the provision of the ridge portion 23 prevents the optical fiber 10 from being pinched in the crack C, making it possible to suppress an increase in transmission loss caused by the crack C.

[0055] Furthermore, in a cross section intersecting the longitudinal direction of the space 31, the circumferential length L of the space 31 is shorter than the circumferential length M of the pressure winding 20. This makes it possible to provide an appropriate distance between the optical fiber 10 and the jacket 30, thereby preventing the optical fiber 10 from being caught in the crack C.

[0056] Furthermore, the direction in which the peaks 23 extend is different from the direction in which the optical fiber 10 extends. That is, inside the pressure winding 20, the optical fiber 10 is provided so as to straddle the peaks 23, making it difficult for the optical fiber 10 to be provided radially inside the apex of the peaks 23. Therefore, the distance from the inner peripheral surface of the jacket 30 to the optical fiber 10 can be appropriately set.

[0057] Furthermore, the plurality of ridges 23 are arranged side by side in the circumferential direction, which makes it possible to prevent the optical fiber 10 from being caught in the crack C even when a lateral pressure or an impact is applied from any direction.

[0058] Furthermore, the ridges 23 are provided on the entire surface of the pressure winding 20. This makes it possible to more reliably prevent the optical fiber 10 from being caught in the crack C over the entire circumference of the optical fiber 10.

[0059] Second Embodiment Next, a second embodiment of the present invention will be described. The basic configuration is the same as that of the first embodiment. Therefore, the same components are denoted by the same reference numerals, and their description will be omitted. Only the differences will be described. Note that the features of the first embodiment can also be applied to the second embodiment to the extent that they do not impair the features of the second embodiment.

[0060] The optical fiber cable 1 according to the second embodiment (see FIG. 3) and the optical fiber cable 1 according to the first embodiment (see FIG. 1) differ in the number of tapes in the pressure wrap 20 that form the ring with the projections and recesses. As shown in FIG. 3, the pressure wrap 20 is formed of a plurality of tapes, and in this embodiment, it is formed of three tapes 20a to 20c.

[0061] The tape wrap 20 includes a first tape 20a, a second tape 20b, and a third tape 20c, which are arranged clockwise in this order. In this embodiment, the first to third tapes 20a to 20c are made of the same material and have the same width. The material and width of each tape may be changed as needed.

[0062] The first end of the second tape 20b is disposed radially inward of the first end of the first tape 20a, forming the first lap portion 21a. The first end of the third tape 20c is disposed radially inward of the second end of the second tape 20b, forming the second lap portion 21b. The second end of the first tape 20a is disposed radially inward of the second end of the third tape 20c, forming the third lap portion 21c. The first to third lap portions 21a to 21c have the same circumferential length. In this manner, the pressure wrap 20 forms a ring that encases the optical fiber 10 by using multiple tapes (the first tape 20a, the second tape 20b, and the third tape 20c) and providing lap portions 21a to 21c with their respective ends connected. Note that the two tapes do not necessarily overlap each other in the lap portion. For example, the ends of two of the tapes 20a, 20b, and 20c may be butted together and bonded together. The annular shape of the pressure winding 20 having projections and recesses is the same as that of the first embodiment, and therefore a detailed description thereof will be omitted.

[0063] As described above, in the optical fiber cable 1 according to this embodiment, the pressure wrap 20 includes a plurality of tapes 20 a, 20 b, and 20 c. This allows the tape ridges 23 to be provided in the pressure wrap 20, while still allowing the optical fibers 10 in the optical fiber cable 1 to be arranged within the pressure wrap 20 even when the number of optical fibers 10 is increased.

[0064] (Third Embodiment) Next, a third embodiment of the present invention will be described. The basic configuration is the same as that of the first embodiment. Therefore, the same components are denoted by the same reference numerals, and their description will be omitted. Only the differences will be described. Note that the features of the first and second embodiments can also be applied to the third embodiment to the extent that they do not impair the features of the third embodiment.

[0065] The optical fiber cable 1 according to the third embodiment (see FIG. 4) differs from the optical fiber cable 1 according to the first embodiment (see FIG. 1) in that an inner pressure wrap 20i is provided, that is, the pressure wrap is formed in multiple layers in the radial direction.

[0066] The inner pressure wrap 20i is formed in a cylindrical shape using a tape having a width shorter than that of the pressure wrap 20 so as to wrap around the optical fiber 10. The inner pressure wrap 20i does not have a ridge portion. The optical fiber 10 is wrapped in the inner pressure wrap 20i, and no optical fiber is disposed between the pressure wrap 20 and the inner pressure wrap 20i.

[0067] The inner pressure wrap 20i has a wrap portion 21i and a non-wrap portion 22i. The wrap portion 21i of the inner pressure wrap 20i is preferably positioned at a different circumferential position from the wrap portion 21 of the pressure wrap 20. In this embodiment, the wrap portion 21i of the inner pressure wrap 20i is disposed opposite the wrap portion 21 of the pressure wrap 20 across the central axis O. For example, even if the optical fiber 10 protrudes from the wrap portion 21i of the inner pressure wrap 20i, the wrap portion 21 of the pressure wrap 20 is positioned away from the central axis O, thereby preventing the optical fiber 10 from further protruding from the wrap portion 21 toward the jacket 30. This more reliably prevents the optical fiber 10 from being caught in the crack C in the jacket 30. The inner pressure wrap 20i may be a tape made of the same material as the pressure wrap 20, or a tape made of a different material. For example, one of the inner pressure wrap 20i and the pressure wrap 20 may be formed of water-absorbent tape, and the other may be formed of PET tape. In this case, the optical fiber cable 1 can be provided with both the waterproofing provided by the water-absorbent tape and the protection of the optical fiber 10 provided by the PET tape. Note that the inner pressure wrap 20i may have a ridge. In this case, the ridges 23 of the pressure wrap 20 and the ridges of the inner pressure wrap 20i may be positioned differently in the circumferential direction. This increases the distance from the inner circumferential surface 32 of the jacket 30 to the optical fiber 10, thereby further preventing the optical fiber 10 from being trapped in the crack C.

[0068] As described above, in the optical fiber cable 1 according to this embodiment, the pressure wrap 20 further includes the inner pressure wrap 20i, which more reliably prevents the optical fiber 10 from being caught in the crack C in the jacket 30.

[0069] (Fourth Embodiment) Next, a fourth embodiment of the present invention will be described. The basic configuration is the same as that of the first embodiment. Therefore, the same components are denoted by the same reference numerals, and their description will be omitted. Only the differences will be described. Note that the features of the first to third embodiments can also be applied to the fourth embodiment to the extent that they do not impair the features of the fourth embodiment.

[0070] The optical fiber cable 1 according to the fourth embodiment (see FIG. 5) differs from the optical fiber cable 1 according to the first embodiment (see FIG. 1) in that the number of peaks 23 of the pressure winding 20 is reduced.

[0071] In this embodiment, the number of peaks 23 in the pressure wrap 20 is four. The positions of the peaks 23 correspond to the positions of the ripcord 50 and the tensile strength members 40; that is, the peaks 23 are provided radially inward of the component E other than the material of the outer jacket 30 that is provided inside the outer jacket 30.

[0072] Each valley portion 24 has two connecting portions 24a and a bottom surface 24b. The connecting portions 24a are connected to the radially inner ends of the circumferentially adjacent peak portions 23. The bottom surface 24b is located between the two connecting portions 24a. As shown in FIG. 5 , the connecting portions 24a are formed as a curved surface that convexly extends radially inward. The bottom surface 24b is a curved surface centered on the central axis O, and in a cross-sectional view, is an arc shape centered on the central axis O. However, the shape of the bottom surface 24b is not limited to a curved surface centered on the central axis O. For example, the bottom surface 24b may be a shape that linearly connects the two connecting portions 24a. In this embodiment, the width of the peak portion 23 is the circumferential dimension between the two connecting portions 24a that sandwich one peak portion 23. The wrap portion 21 of the pressure winding 20 is provided on the bottom surface 24b of the valley portion 24. Therefore, in this embodiment, the wrap portion 21 does not have a concave or convex shape, and the wrap portion 21 has an arc shape with the central axis O as the center.

[0073] In the present embodiment, one ridge portion 23 is provided for one component E, but multiple ridge portions 23 may be provided on the radially inner side of one component E. In this case, the total width of the multiple adjacent ridge portions 23 provided on the radially inner side of one component E may be equal to or greater than the circumferential width of one component E. For example, multiple ridge portions 23 having a width narrower than the circumferential width of the component E may be arranged consecutively in the circumferential direction. This more reliably prevents the optical fiber 10 from being pinched by the crack C in the jacket 30, regardless of where the crack C occurs on the radially inner side of the component E.

[0074] Although the ridges 23 are provided in accordance with the positions of the two strength members 40 and the two ripcords 50, the present invention is not limited to this example, and the ridges 23 may be provided near locations where cracks C are likely to occur. For example, the ridges 23 may be provided only on the radially inner side of the tensile members 40, where cracks C are more likely to occur, and no ridges 23 may be provided on the radially inner side of the ripcords 50.

[0075] As described above, in the optical fiber cable 1 according to this embodiment, the ridges 23 are arranged radially inward of the component E provided within the jacket 30. For example, since cracks C in the jacket 30 often occur from the component E toward the inner circumferential surface 32 of the jacket 30, it is possible to more reliably prevent the optical fiber 10 from being pinched in the cracks C in the jacket 30.

[0076] Fifth Embodiment Next, a fifth embodiment of the present invention will be described. The basic configuration is the same as that of the first embodiment. Therefore, the same components are denoted by the same reference numerals, and their description will be omitted. Only the differences will be described. Note that the features of the first to fourth embodiments can also be applied to the fifth embodiment to the extent that they do not impair the features of the fifth embodiment.

[0077] The optical fiber cable 1 according to the fifth embodiment and the optical fiber cable 1 according to the first embodiment differ in the extending direction of the peaks 23 of the pressure windings 20 .

[0078] As shown in Fig. 6A , in this embodiment, the peaks 23 of the pressure wrap 20 extend in the circumferential direction, and multiple peaks 23 are arranged side by side in the longitudinal direction. This allows for a greater difference between the extending direction of the peaks 23 and the extending direction of the optical fiber 10. In the optical fiber cable 1 including the pressure wrap 20 shown in Fig. 6A , in a cross section including the apex of the peaks 23, the circumferential length L of the space 31 is equal to the circumferential length M of the pressure wrap 20, and in other cross sections, the circumferential length L of the space 31 may be longer than the circumferential length M of the pressure wrap 20. This allows for an appropriate distance between the optical fiber 10 and the jacket 30, thereby preventing the optical fiber 10 from being pinched in the crack C.

[0079] 6B , the peaks 23 of the pressure winding 20 may extend helically, and multiple peaks 23 may be arranged side by side in the circumferential and longitudinal directions. When the optical fiber 10 is twisted helically in the clockwise direction, the peaks 23 are preferably formed helically in the counterclockwise direction. When both the optical fiber 10 and the peaks 23 are helically twisted in the same direction, it is preferable that the period at which the optical fiber 10 is twisted helically differs from the period at which the peaks 23 are formed helically. This allows the inclination of the helically twisted optical fiber 10 on the outer periphery of the optical fiber bundle relative to the longitudinal direction to differ from the inclination of the peaks 23.

[0080] When the optical fibers 10 are twisted in an SZ configuration, the helical pitch of the ridges 23 and the SZ twisting pitch and twist angle of the optical fibers 10 may be adjusted so that the inclination of the optical fibers 10 twisted in an SZ configuration on the outer periphery of the optical fiber bundle relative to the longitudinal direction does not coincide with the inclination of the ridges 23 over a portion of the longitudinal direction. This makes it possible to make the inclination of the optical fibers 10 twisted in an SZ configuration on the outer periphery of the optical fiber bundle relative to the longitudinal direction different from the inclination of the ridges 23 over the entire length. In this way, by making the extending direction of the ridges 23 different from the extending direction of the optical fibers 10, it is possible to prevent the optical fibers 10 from being caught in the crack C even if a crack C occurs in the jacket 30.

[0081] As shown in Figures 6A and 6B, by forming the peaks 23 extending in a direction intersecting or perpendicular to the longitudinal direction, the pressure wrap 20 can be made to have an excess length relative to the longitudinal length of the optical fiber cable 1. That is, in a longitudinal cross-sectional view of the optical fiber cable 1 including the central axis O, the longitudinal length of the space 31 is shorter than the meandering length of the pressure wrap 20, including the longitudinal irregularities. Since the longitudinal length of the pressure wrap 20 can be made longer than the longitudinal length of the optical fiber cable 1, for example, the optical fiber cable 1 can be made easier to bend. Note that methods other than adjusting the extending direction of the peaks 23 may also be used to make the pressure wrap 20 have an excess length relative to the longitudinal length of the optical fiber cable 1. For example, the excess length may be provided by providing the ribbon 20a within the optical fiber cable 1 so that it is compressed to some extent in the longitudinal direction.

[0082] Next, specific examples of the optical fiber cable 1 of this embodiment will be described. Note that the present invention is not limited to the following examples.

[0083] In this example, optical fiber cables were manufactured in which the circumferential length M of the pressure wrap 20 was varied relative to the circumferential length L of the space 31 in the jacket 30 in the optical fiber cable 1 shown in Figure 1, and impact tests and lateral pressure tests were performed on each cable to confirm whether or not the optical fiber 10 was pinched in the crack C in the jacket 30. Table 1 summarizes the circumferential length M of the pressure wrap 20 relative to the circumferential length L of the space 31 in the jacket 30, and whether or not the optical fiber 10 was pinched. In Table 1, a rating of "x" indicates a case in which the optical fiber 10 was pinched, a rating of "△" indicates a case in which the optical fiber 10 was pinched, although the frequency was lower than that of the rating of "x", and a rating of "o" indicates a case in which the optical fiber 10 was not pinched.

[0084]

[0085] As shown in Table 1, when the circumferential lengths L and M are equal, it is difficult to ensure a sufficient distance between the crack and the optical fiber, resulting in the optical fiber being pinched, when the circumferential length M is 1.03 and 1.05 times the circumferential length L. In contrast, when the circumferential length M is 1.07 times or more the circumferential length L, the peaks can prevent the optical fiber from being pinched in the crack. Note that if the circumferential length M is excessively greater than the circumferential length L, the peaks 23 may narrow the arrangement area for the optical fiber 10, so it is preferable to set M≦2L.

[0086] The technical scope of the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the present invention.

[0087] For example, in the above embodiment, an example has been described in which the circumscribing circle of the pressure wrap 20 is equivalent to the space 31 of the outer jacket 30, but the vicinity of the apex of the ridge portion 23 may intrude into the outer jacket 30. In this case, the above-mentioned circumferential length L may be the circumferential length of a ring when the inner circumferential surface 32 of the outer jacket 30 describes a closed ring along a curve having projections and recesses in a cross-sectional view.

[0088] Although the example in which the ridges 23 are provided at equal intervals in the circumferential or longitudinal direction has been described, the intervals at which the ridges 23 are provided are not limited to being equal. For example, as described in the fifth embodiment, the distance between the ridges 23 may be changed as appropriate in accordance with the arrangement of the component E. Furthermore, the protruding heights and widths of the multiple ridges 23 may not be the same, and ridges 23 of different sizes may be included.

[0089] Furthermore, the peaks 23 are not limited to having a shape that forms a curved surface that is convex outward in the radial direction, and the apex of the peaks 23 may form an inner circumferential angle that contacts the inner circumferential surface 32 of the jacket 30. Furthermore, the unevenness of the peaks 23 and the valleys 24 is not limited to being formed by a curved surface, and the unevenness may be formed in a zigzag pattern. In this case, for example, the tape 20a that will become the pressure wrap 20 may be folded alternately in a mountain fold and a valley fold to form a plurality of zigzag folds, and then the optical fiber 10 may be wrapped. Furthermore, the unevenness may be formed by embossing the tape 20a that will become the pressure wrap 20. The tape 20a may be wrapped around the outer periphery of the optical fiber 10 so that the longitudinal direction of the tape 20a extends spirally around the central axis O.

[0090] Furthermore, the number of strength members 40 included in the optical fiber cable 1 is not limited to two. For example, as shown in Fig. 7A, the number of strength members 40 may be four, and a pair of strength member groups 40A, each including two strength members 40, may be arranged to sandwich the space 31. Furthermore, as shown in Fig. 7B, three or more (six in the illustrated example) strength members 40 may be arranged at intervals in the circumferential direction so as to surround the space 31 from the radial outside.

[0091] Furthermore, the outer shape of the optical fiber cable 1 and the shape of the space 31 in cross section are not limited to a circle. For example, as shown in Fig. 7C , the outer shape of the optical fiber cable 1 and the shape of the space 31 in cross section may be rectangular. Note that the jacket 30 may be provided with a pair of separators S that sandwich the pressure wrap 20 in the vertical direction, for example. In this case, the ridges 23 come into contact with the separators S and the jacket 30.

[0092] Furthermore, a self-supporting wire for supporting the optical fiber cable 1 may be provided on the outside of the optical fiber cable 1 (outer jacket 30).

[0093] In addition, it is possible to replace the components in the above-described embodiments with well-known components as appropriate, and the above-described embodiments and variations may be combined as appropriate, without departing from the spirit of the present invention.

[0094] REFERENCE SIGNS LIST 1... Optical fiber cable 10... Optical fiber 20... Pressure wrap 20a, 20b, 20c... Tape 20i... Inner pressure wrap 23... Mountain portion 30... Outer jacket 31... Space 32... Inner peripheral surface E... Constituent member G... Gap L... Perimeter of space M... Perimeter of pressure wrap

Claims

1. An optical fiber cable comprising: an optical fiber; a pressure winding covering the optical fiber; and an outer jacket forming a space to accommodate the optical fiber and the pressure winding, wherein there is at least a partial gap between the inner surface of the jacket and the pressure winding, and the pressure winding has a plurality of ridges.

2. The optical fiber cable according to claim 1, wherein in a cross section intersecting the longitudinal direction of said space, the perimeter of said space is shorter than the perimeter of said pressure winding.

3. An optical fiber cable according to claim 1 or 2, wherein the direction in which the plurality of peaks extend is different from the direction in which the optical fiber extends.

4. The optical fiber cable according to any one of claims 1 to 3, wherein the tension winding comprises a plurality of tapes.

5. An optical fiber cable according to any one of claims 1 to 4, wherein the pressure winding further comprises an inner pressure winding.

6. An optical fiber cable according to any one of claims 1 to 5, further comprising a component provided within the jacket, wherein the ridge portion is disposed radially inward of the component.

7. An optical fiber cable according to any one of claims 1 to 6, wherein the plurality of peaks are arranged side by side in the circumferential direction.

8. An optical fiber cable according to any one of claims 1 to 6, wherein the plurality of peaks are arranged side by side in the longitudinal direction.

9. An optical fiber cable according to any one of claims 1 to 6, wherein the plurality of peaks are arranged side by side in the circumferential direction and the longitudinal direction.

10. An optical fiber cable according to any one of claims 1 to 9, wherein the pressure winding has an excess length in the longitudinal direction of the optical fiber cable.

11. An optical fiber cable according to any one of claims 1 to 10, wherein, where L is the circumferential length of the space within the jacket and M is the circumferential length of the pressure winding, 1.07L≦M is satisfied.

12. An optical fiber cable according to any one of claims 1 to 11, wherein the plurality of peaks are provided over the entire surface of the pressure winding.

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