Optical cable, optical cable structure, and method for manufacturing optical cable
Patent Information
- Application Number
- JP2023564837
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Priority Date
- 2022-11-08
- Filing Date
- 2022-11-08
- Publication Date
- 2025-06-27
Abstract
Description
Optical cable, optical cable structure, and method of manufacturing optical cable
[0001] The present invention relates to an optical cable, an optical cable structure, and a method for manufacturing an optical cable. This application claims priority based on Japanese Patent Application No. 2021-195357, filed on December 1, 2021, the contents of which are incorporated herein by reference.
[0002] Patent Document 1 describes an optical cable in which a tension member is disposed at the center of the optical cable.
[0003] Japanese Patent Application Laid-Open No. 2000-98196
[0004] In a structure in which the tension members are arranged straight along the cable length, as in the optical cable described in Patent Document 1, the tension applied to the optical cable tends to concentrate on the tension members, which results in the need to arrange thick tension members, resulting in a thick optical cable.
[0005] An object of the present invention is to provide a configuration in which tension applied to an optical cable is easily distributed to members other than tension members.
[0006] The optical cable of the present invention comprises a strength member, a plurality of optical fibers arranged around the strength member, and an outer sheath that houses the strength member and the plurality of optical fibers, wherein the boundary elongation of the strength member is smaller than the boundary elongation of the optical fibers, and wherein the boundary elongation is a cable elongation that corresponds to the boundary between an initial elongation region and an elastic region, and the initial elongation region is the range of cable elongation when cable elongation occurs due to the application of tension, and initial elongation occurs in the member, which is the strength member or the optical fiber, as the member deforms to approach a straight shape along the cable longitudinal direction, and the elastic region is the range of cable elongation when further cable elongation occurs beyond the initial elongation region and elastic elongation occurs in the member according to the elastic coefficient of the member. Furthermore, an optical cable manufacturing method according to the present invention includes providing a strength member, arranging a plurality of optical fibers around the strength member, and forming an outer jacket to accommodate the strength member and the plurality of optical fibers, wherein the boundary elongation of the strength member is smaller than the boundary elongation of the optical fibers, and the boundary elongation is a cable elongation that corresponds to the boundary between an initial elongation region and an elastic region, and the initial elongation region is a range of cable elongation when cable elongation occurs due to the application of tension, and the initial elongation region is a range of cable elongation when initial elongation occurs in a member that is the strength member or the optical fiber as a result of the member deforming to approach a straight shape along the cable longitudinal direction, and the elastic region is a range of cable elongation when further cable elongation occurs beyond the initial elongation region and elastic elongation occurs in the member according to the elastic coefficient of the member.
[0007] Other features of the present invention will become apparent from the following description and drawings.
[0008] According to the present invention, the tension applied to the optical cable is easily distributed to members other than the tension members.
[0009] FIG. 1 is a cross-sectional view of an optical cable 1. FIG. 2 is a conceptual diagram showing the relationship between the elongation of the optical cable 1 (cable elongation) and the stress of the components housed in the optical cable 1. FIG. 3A is a conceptual diagram showing the relationship between the cable elongation of the optical cable 1 of this embodiment and the stress of each component. FIG. 3B is a conceptual diagram showing the relationship between the cable elongation of the optical cable 1 of a comparative example and the stress of each component. FIG. 4A is a conceptual diagram showing the relationship between the cable elongation of the optical cable 1 of this embodiment and the tension applied to the optical cable 1. FIG. 4B is a conceptual diagram showing the relationship between the cable elongation of the optical cable 1 of a comparative example and the tension applied to the optical cable 1. FIG. 5 is an explanatory diagram of a manufacturing system for the optical cable 1. FIGS. 6A to 6D are cross-sectional views of optical cables 1 of first to fourth modified examples. FIG. 7 is a cross-sectional view of an optical cable structure 1′.
[0010] At least the following points will become clear from the description and drawings to be described later.
[0011] An optical cable according to a first aspect of the present embodiment includes a strength member, a plurality of optical fibers arranged around the strength member, and a jacket that houses the strength member and the plurality of optical fibers, wherein the boundary elongation of the strength member is smaller than the boundary elongation of the optical fibers, the boundary elongation being a cable elongation corresponding to the boundary between an initial elongation region and an elastic region, the initial elongation region being a range of cable elongation when, in the case where cable elongation occurs due to the application of tension, the initial elongation region is a range of cable elongation when the member, that is, the strength member or the optical fiber, deforms to approach a straight shape along the cable longitudinal direction, resulting in initial elongation, and the elastic region is a range of cable elongation when, in the case where cable elongation occurs further beyond the initial elongation region, elastic elongation occurs in the member according to the elastic coefficient of the member. Such an optical cable makes it easier for tension applied to the optical cable to be distributed to members other than the strength members.
[0012] An optical cable of a second aspect of the present embodiment is the optical cable of the first aspect, wherein the strength members are twisted in an SZ configuration, which makes it easier for the strength members to stretch in the cable longitudinal direction when tension is applied to them, and as a result, makes it easier for the tension applied to the optical cable to be distributed to members other than the tension members.
[0013] An optical cable according to a third aspect of the present embodiment is the optical cable according to the second aspect, wherein the optical fibers are twisted in an SZ configuration, and the twisting direction of the tension members is opposite to the twisting direction of the optical fibers, thereby suppressing undulating deformation of the optical cable.
[0014] An optical cable of a fourth aspect of the present embodiment is the optical cable of any one of the first to third aspects, in which the twisted strength members are arranged in a serpentine manner, so that when tension is applied to the strength members, the strength members tend to stretch in the cable longitudinal direction, and as a result, the tension applied to the optical cable is more likely to be distributed to members other than the strength members.
[0015] An optical cable of a fifth aspect of the present embodiment is the optical cable of the fourth aspect, wherein the strength members are made of tensile strength fibers, which makes it easier to arrange the twisted strength members in a meandering manner.
[0016] An optical cable of a sixth aspect of the present embodiment is the optical cable of any of the above first to fifth aspects, in which, when the interfacial elongation of the strength member is X1_t (%), the interfacial elongation of the optical fiber is X1_f (%), and the elongation strain of the strength member when the strength member breaks is Xu_t (%), X1_f is equal to or greater than X1_t and equal to or less than X1_t + Xu_t. This makes it possible to suppress breakage of the strength member.
[0017] An optical cable of a seventh aspect of the present embodiment is the optical cable of the sixth aspect, in which, when the elongation strain at which the strength member can elastically deform is Xe_t (%), X1_f is equal to or greater than X1_t and equal to or less than X1_t + Xe_t, thereby making it possible to suppress plastic deformation of the strength member.
[0018] An optical cable according to an eighth aspect of the present embodiment is the optical cable according to any one of the first to seventh aspects, wherein the elongation strain of the optical fiber when an allowable tension is applied to the optical cable and tension is applied to the optical fiber is 60% or less of the proof level, thereby improving reliability.
[0019] An optical cable of a ninth aspect of the present embodiment is the optical cable of any one of the first to eighth aspects, in which another strength member is embedded in the sheath. In this case, compared to a case in which the tension of the optical cable is borne solely by the strength member embedded in the sheath, the diameter of the strength member embedded in the sheath can be made thinner, and the diameter of the cable can be made thinner.
[0020] An optical cable structure according to a tenth aspect of the present embodiment includes a plurality of inner cables, each of which is an optical cable according to any one of the first to ninth aspects. In such an optical cable structure, tension applied to the inner cable (the optical cable) is also easily distributed to members other than the tension members.
[0021] An eleventh aspect of the present embodiment is an optical cable manufacturing method that includes providing a strength member, arranging multiple optical fibers around the strength member, and forming an outer jacket to accommodate the strength member and the multiple optical fibers, wherein the boundary elongation of the strength member is smaller than the boundary elongation of the optical fibers, the boundary elongation being a cable elongation corresponding to the boundary between an initial elongation region and an elastic region, the initial elongation region being a range of cable elongation when, in the case of cable elongation caused by application of tension, the initial elongation region is a range of cable elongation when the member, that is, the strength member or the optical fiber, deforms to approach a straight shape along the cable longitudinal direction, resulting in initial elongation, and the elastic region is a range of cable elongation when, in the case of cable elongation caused by further elongation beyond the initial elongation region, elastic elongation occurs in the member according to the elastic coefficient of the member. This manufacturing method makes it possible to manufacture an optical cable that easily distributes tension to members other than the strength members.
[0022] An optical cable manufacturing method of a twelfth aspect of the present embodiment is the optical cable manufacturing method of the eleventh aspect, in which the twisted strength members are made to meander by shrinking the jacket in the cable longitudinal direction after extrusion molding. This makes it possible to accommodate the twisted strength members in a meandering manner within the jacket so that the strength members are likely to stretch in the cable longitudinal direction when tension is applied to them.
[0023] First Embodiment <Basic Configuration of Optical Cable> FIG. 1 is a cross-sectional view showing an example of an optical cable 1. As shown in FIG.
[0024] In the following description, the longitudinal direction of the optical cable 1 will be referred to as the "cable longitudinal direction." The cross section of the optical cable 1 shown in Fig. 1 is a plane perpendicular to the cable longitudinal direction. In the cross section shown in Fig. 1, the direction around the central axis of the optical cable 1 will be referred to as the "circumferential direction," and the direction intersecting the central axis of the optical cable 1 will be referred to as the "radial direction."
[0025] The optical cable 1 is a cable containing optical fibers 5. The optical cable 1 is a center tube type optical cable with a slotless structure. The optical cable 1 includes a tension member 2, a plurality of optical fibers 5, and an outer jacket 8.
[0026] The tension member 2 is a member that reinforces the tensile strength of the optical cable 1. The tension member 2 has relatively high strength (high Young's modulus) against tension (pulling force). For example, by retaining the tension member 2 in a connector attached to the end of the optical cable 1, the tension member 2 bears the tension applied to the optical cable 1.
[0027] The tension members 2 reduce the tension applied to the optical fiber 5. By the tension members 2 reducing the tension applied to the optical fiber 5, damage to the optical fiber 5 and an increase in transmission loss can be suppressed.
[0028] The tension members 2 are made of tensile strength fibers. Examples of such fibers include aramid fibers, polyethylene fibers, and glass fibers. By using tensile strength fibers, the tension members 2 can have a high Young's modulus and flexibility (the ability to bend easily). The flexibility of the tension members 2 makes it easier for the tension members 2 to meander, as described below. Here, the tension members 2 are made of Kevlar (registered trademark), which is made of aramid fibers. However, the tension members 2 may be made of other materials, such as glass yarn, as long as they have high tensile strength and flexibility. Furthermore, the tension members 2 do not have to be made of tensile strength fibers. However, as described below, when the tension members 2 are made to meander, it is particularly effective to use tensile strength fibers.
[0029] As shown in Figure 1, the strength member 2 is disposed in the center of the optical cable 1 (inside the accommodation space of the optical cable 1). By adopting a structure in which the strength member 2 is disposed in the center of the optical cable 1, the bending directionality of the optical cable 1 can be controlled. In other words, the difference between the force required to bend the optical cable 1 in an easy-to-bend direction and the force required to bend it in a difficult-to-bend direction can be controlled, and the optical cable 1 can be bent with a substantially uniform force in any direction. Note that the strength member 2 does not have to be disposed in the center of the optical cable 1.
[0030] The strength members 2 are also twisted and arranged. Here, a plurality of strength members 2 made of strength fibers are twisted together. The strength members 2 are twisted in an SZ pattern by reversing the twisting direction. By configuring the strength members 2 from flexible materials, the SZ-twisted strength members 2 can be stably arranged. The strength members 2 may also be twisted spirally in one direction. The twisting of the strength members 2 will be described later.
[0031] The multiple optical fibers 5 are arranged on the outer periphery of the strength member 2. In other words, when the strength member 2 is arranged in the center of the optical cable 1, the optical fibers 5 are arranged radially outside the strength member 2, and the multiple optical fibers 5 are arranged so as to surround the radial outside of the strength member 2. Here, the multiple optical fibers 5 are composed of multiple (here, six) optical fiber units 4. The optical fiber unit 4 is a component in which multiple optical fibers are bundled with a string-like bundle material 6. The optical fiber unit 4 is composed of one or multiple intermittently connected optical fiber ribbons bundled with the bundle material 6. Note that the optical fiber unit 4 may also be composed of multiple single-core optical fibers 5 bundled with the bundle material 6. Furthermore, the bundle material 6 is not limited to a string-like member and may be, for example, a tubular member. Furthermore, multiple optical fibers 5 that are not bundled with the bundle material 6 may be arranged on the outer periphery of the strength member 2. By arranging the plurality of optical fibers 5 on the outer periphery of the strength member 2, the structure makes it easy to arrange the strength member 2, for example, in the center of the cable (which results in a structure that makes it easy to suppress the bending direction of the optical cable 1). In addition, by arranging the plurality of optical fibers 5 on the outer periphery of the strength member 2, it becomes easy to maintain the structural longitudinal expansion allowance (play) described later.
[0032] The multiple optical fibers 5 are twisted and arranged. By twisting the multiple optical fibers 5, it is possible to prevent a decrease in the transmission loss of a specific optical fiber 5 when the optical cable 1 is bent. The optical fibers 5 may be twisted, for example, in one direction, or may be twisted in an SZ pattern by reversing the twisting direction. When the optical fibers 5 are twisted in an SZ pattern, the optical fibers 5 are easier to remove from the optical cable 1 than when the optical fibers 5 are twisted spirally in one direction. Furthermore, because the multiple optical fibers 5 are twisted and arranged around the outer periphery of the tension member 2, it is easier to make the excess length of the optical fibers 5 longer than the excess length of the tension member 2.
[0033] The twisting direction of the strength members 2 may be opposite to that of the optical fibers 5. For example, in the cross-sectional view of Figure 1, if the strength members 2 are twisted clockwise toward the front of the page, the optical fibers 5 may be twisted counterclockwise toward the front of the page. In this way, by twisting the strength members 2 and the optical fibers 5 in opposite directions, undulating deformation of the optical cable 1 can be suppressed.
[0034] The jacket 8 is a member that houses the strength members 2 and the plurality of optical fibers 5. The jacket 8 has a hollow cross section (here, the cross section is cylindrical), and has an internal storage space. Here, the outer shape of the jacket 8 is approximately circular, but the outer shape of the jacket 8 is not limited to a circular shape and may be other shapes such as rectangular or elliptical. The jacket 8 is made of a resin such as a polyolefin (PO) resin, such as polyethylene (PE), polypropylene (PP), ethylene-ethyl acrylate copolymer (EEA), ethylene-vinyl acetate copolymer (EVA), or ethylene-propylene copolymer (EP), or polyvinyl chloride (PVC). As described below, the jacket 8 is molded by extrusion molding of a molten resin.
[0035] In the optical cable 1 shown in FIG. 1 , a core composed of a tensile strength member 2 and a plurality of optical fibers 5 is housed inside a jacket 8 and is wrapped with a pressure winding tape 7. By wrapping the optical fibers 5 with the pressure winding tape 7 in this manner, it is possible to prevent the optical fibers 5 from being buried in the jacket 8 when the jacket 8 is molded with molten resin. However, the pressure winding tape 7 does not have to be disposed inside the jacket 8. The optical cable 1 may also include other components. For example, the optical cable 1 may include a tear cord (not shown in FIG. 1 ) for tearing the jacket 8, an inclusion (not shown in FIG. 1 ) that fills the space inside the optical cable 1, or the like.
[0036] <Initial Elongation Region, Elastic Region, and Boundary Elongation> Fig. 2 is a conceptual diagram showing the relationship between the elongation of the optical cable 1 (cable elongation) and the stress of the members (e.g., the tensile strength member 2 and the optical fiber 5) housed in the optical cable 1. In the following description, the elongation of the optical cable 1 in the cable longitudinal direction due to the application of tension, or the amount of elongation, may be referred to as "cable elongation." The horizontal axis of the graph indicates cable elongation (unit: %), which indicates the ratio of the elongated length of the optical cable 1 to the original length of the optical cable 1 (the length before tension is applied) (in other words, the elongation strain of the optical cable 1 is shown as cable elongation). The vertical axis of the graph indicates the tensile stress (unit: N / mm ２ ) is shown.
[0037] When components (e.g., the strength members 2 and the optical fibers 5) are housed in the optical cable 1 in a twisted state, the components deform to approach a straight shape along the cable longitudinal direction when tension is applied to the optical cable 1, causing cable elongation. For example, when the components are twisted in an SZ configuration, the components deform to approach a straight shape along the cable longitudinal direction as the twist of the components unwinds. Even when the components are twisted in a spiral configuration in one direction, the components deform to approach a straight shape along the cable longitudinal direction as the twisted components tighten. This elongation of the components along the cable longitudinal direction due to deformation to approach a straight shape along the cable longitudinal direction is sometimes referred to as "initial elongation." Furthermore, as shown in FIG. 2 , the range of cable elongation of the optical cable 1 when the components (e.g., the strength members 2 and the optical fibers 5) undergo initial elongation is sometimes referred to as the "initial elongation region."
[0038] When further cable elongation occurs beyond the initial elongation region, the components (e.g., the strength members 2 and the optical fiber 5) undergo elastic deformation, causing the components to deform so as to elongate in the cable longitudinal direction. When further cable elongation occurs beyond the initial elongation region, the elastic deformation of the components (e.g., the strength members 2 and the optical fiber 5) in the cable longitudinal direction according to the elastic modulus of the components is sometimes referred to as "elastic elongation." Furthermore, when further cable elongation occurs beyond the initial elongation region, the range of cable elongation of the optical cable 1 when the components (e.g., the strength members 2 and the optical fiber 5) undergo elastic elongation according to the elastic modulus of the components is sometimes referred to as the "elastic region." The slope of the graph in the elastic region corresponds to the elastic modulus of the components.
[0039] In the following description, the cable elongation of the optical cable 1 corresponding to the boundary between the initial elongation region and the elastic region may be referred to as "boundary elongation." Figure 2 shows that the boundary elongation is X1 (%). Therefore, the initial elongation region is the range of cable elongation of the optical cable 1 from 0 to X1 (%). Furthermore, the elastic region is the range of cable elongation of the optical cable 1 equal to or greater than X1 (%).
[0040] The "initial elongation" of a certain component corresponds to the structural elongation (play) of the component in the longitudinal direction. When a certain component is twisted in an SZ configuration, the initial elongation of the component (the structural elongation of the component in the longitudinal direction) corresponds to the excess length ratio X (unit: %) of the component. In other words, when a certain component is twisted in an SZ configuration, the boundary elongation X1 (unit: %) of the component corresponds to the excess length ratio X (unit: %) of the component. Here, "excess length" refers to the difference between the length of the component housed in the optical cable 1 (the longitudinal dimension of the component) and the length of the optical cable 1 (the longitudinal dimension of the optical cable 1) (or, "excess length" refers to the component housed in the optical cable 1 being longer than the length of the optical cable 1). Furthermore, "excess length ratio" refers to the ratio of the excess length of the component to the length of the optical cable 1. For example, if the length of a component (such as a tension member 2 or an optical fiber 5) extracted from an optical cable 1 cut to a predetermined length L0 (unit: mm) is L1 (unit: mm), the excess length of the component is L1-L0, and the excess length ratio X (unit: %) is X = 100 × (L1-L0) / L0. When a component is spirally twisted in one direction, the initial elongation of the component (the component's structural longitudinal elongation) corresponds to the elongation allowance when the loosely twisted component is tightened and elongated in the longitudinal direction. Therefore, when a component is spirally twisted in one direction, the elongation X1 at the component's boundary is shorter than the excess length ratio X of the component. It is possible to provide structural longitudinal elongation (play) to a component even if it is not twisted. For example, when a component is arranged in a serpentine pattern, structural longitudinal elongation (play) can be provided to the component even if it is not twisted.
[0041] Here, the elastic region is defined as a cable elongation range of X1 to X1+Xe, where Xe corresponds to the elongation (here, tensile strain) of a member (e.g., the strength member 2 or the optical fiber 5) that is capable of elastic deformation. Note that when the cable elongation is X1 (%), the elongation of the member (e.g., the strength member 2 or the optical fiber 5) is 0 (%), and the member will elastically deform when the elongation (here, tensile strain) of the member is in the range of 0 to Xe (%).
[0042] If the cable elongates further from the elastic region, the member (e.g., the strength member 2) will undergo plastic deformation and then break. Figure 2 shows that the cable elongation at which the member breaks is X1 + Xu (%). Xu corresponds to the elongation (here, the elongation strain) of the member at which the member breaks.
[0043] In the following description, when the member is a tension member 2, the values corresponding to X1, Xe, and Xu in Fig. 2 may be indicated as X1_t, Xe_t, and Xu_t. When the member is an optical fiber 5, the values corresponding to X1, Xe, and Xu in Fig. 2 may be indicated as X1_f, Xe_f, and Xu_f. (When the member is a tension member 2, the subscript "t" is added, and when the member is an optical fiber 5, the subscript "f" is added.)
[0044] <Regarding twisting of tension members> Fig. 3A is a conceptual diagram showing the relationship between cable elongation and stress of each member of the optical cable 1 of this embodiment. Fig. 3B is a conceptual diagram showing the relationship between cable elongation and stress of each member of the optical cable 1 of a comparative example. The horizontal axis of the graph represents the cable elongation of the optical cable 1 (unit: %; elongation strain). The vertical axis of the graph represents the tensile stress (unit: N / mm ２ ) are shown. The thick lines in the figure represent the graph for the reinforcing member 2. The thin lines in the figure represent the graph for the optical fiber 5. FIG. 4A is a conceptual diagram showing the relationship between the cable elongation of the optical cable 1 of this embodiment and the tension applied to the optical cable 1. FIG. 4B is a conceptual diagram showing the relationship between the cable elongation of the optical cable 1 of a comparative example and the tension applied to the optical cable 1. The horizontal axis of the graph represents the cable elongation of the optical cable 1 (unit: %). The vertical axis of the graph represents the tension applied to the optical cable 1 (unit: N). The tension Ta in the graph represents the allowable tension of the optical cable 1.
[0045] The tension applied to the optical cable 1 is borne not only by the tension members 2 and the optical fibers 5 but also by other components such as the jacket 8. However, for the sake of simplicity, the tension applied to the optical cable 1 will be assumed to be borne by the tension members 2 and the optical fibers 5, and the tension borne by the jacket 8 will not be considered. Note that the tension members 2 and the optical fibers 5 have a larger product (E x S) of their Young's modulus of elasticity E and their cross-sectional area S than other components such as the jacket 8, and therefore it is possible to approximate the tension applied to the optical cable 1 as being borne by the tension members 2 and the optical fibers 5. In particular, when the optical cable 1 is an ultra-high-core cable having several thousand optical fibers 5, it is possible to approximate the tension applied to the optical cable 1 as being borne by the tension members 2 and the optical fibers 5. For example, the Young's modulus of elasticity of the tension members 2 is approximately 42.1 GPa, the Young's modulus of elasticity of the optical fibers 5 is approximately 72.0 GPa, and the Young's modulus of elasticity of the jacket 8 is approximately 0.98 GPa. In addition, for example, when the optical cable 1 shown in FIG. 1 is an ultra-multi-core cable having 1,728 optical fibers 5, the cross-sectional area of the tension members 2 (the total cross-sectional area of the plurality of tension members 2) is about 0.4 mm ２ The total cross-sectional area of the optical fiber 5 is approximately 21.2 mm ２ The cross-sectional area of the outer jacket 8 is about 49.5 mm ２ Therefore, the values of the product of the Young's modulus E and the cross-sectional area S of the strength members 2, the optical fiber 5, and the jacket 8 are approximately 16.8 kN, approximately 1526 kN, and approximately 53.9 kN, respectively. Note that in this embodiment, the strength members 2 are arranged in an SZ twisted state, whereas in the comparative example, the strength members 2 are arranged straight along the cable longitudinal direction.
[0046] - Case where there is no structural longitudinal elongation (play) (Comparative Example) In the comparative example, the strength members 2 are arranged straight along the cable longitudinal direction, so there is no initial elongation region in the strength members 2 of the comparative example. Therefore, as shown in FIG. 3B , once cable elongation begins to occur in the optical cable 1 due to the application of tension to the optical cable 1, tension is applied to the strength members 2 (the strength members 2 bear the tension), causing the strength members 2 to elongate and deform. Here, the strength members 2 elastically deform when the cable elongation (unit: %; elongation strain) of the optical cable 1 (or the strength members 2) is in the range of 0 to Xe_t (elastic region of the strength members 2). Note that if the cable elongation of the optical cable 1 (or the strength members 2) exceeds Xe_t, the strength members 2 undergo plastic deformation and then break. Here, the elongation strain of the tension member 2 when the tension member 2 breaks (breaking point) is defined as Xu_t (unit: %).
[0047] Because the optical fibers 5 are twisted in an SZ pattern, when tension is applied to the optical cable 1 and cable elongation begins to occur in the optical cable 1, the twisting of the optical fibers 5 simply returns, and almost no tension is applied to the optical fibers 5 (at this stage, almost no elongation strain occurs in the optical fibers 5). For this reason, as shown in Fig. 3B , when the cable elongation (unit: %) of the optical cable 1 is in the range of 0 to X1_f (initial elongation region of the optical fibers 5), almost no tension is applied to the optical fibers 5.
[0048] 3B , in the case of the optical cable 1 of the comparative example, there is a large difference between the cable elongation (almost 0%) of the optical cable 1 when tension begins to be applied to the strength member 2 and the cable elongation (X1_f) of the optical cable 1 when tension begins to be applied to the optical cable 1. For this reason, in the case of the optical cable 1 of the comparative example, when tension within the range of the allowable tension Ta shown in FIG. 4B is applied to the optical cable 1, the tension of the optical cable 1 cannot be distributed to the optical fibers 5, and the tension of the optical cable 1 is mainly borne by the strength member 2. For this reason, in the case of the comparative example, in order to be able to withstand tension within the range of the allowable tension Ta within the elastic range of the strength member 2 (or to be able to withstand tension within the range of the allowable tension Ta without breaking), a thick strength member 2 is required, and as a result, the optical cable 1 becomes thicker.
[0049] When there is no structural longitudinal elongation (play) in the tension members 2, twisting the tension members 2 in an SZ pattern provides the tension members 2 with structural longitudinal elongation. When tension is applied to the optical cable 1, the tension members 2 simply untwist, and almost no tension is applied to the tension members 2 (at this stage, almost no elongation strain occurs in the tension members 2). Therefore, as shown in FIG. 3A , when the cable elongation of the optical cable 1 is in the range of 0 to X1_t (the initial elongation region of the tension members 2), almost no tension is applied to the tension members 2. As the tension members 2 untwist, the tension members 2 approach a straight shape along the cable longitudinal direction. When the cable elongation (unit: %) of the optical cable 1 reaches the boundary elongation X1_t of the tension members 2, the untwisting of the tension members 2 ends, and the tension members 2 become almost straight within the optical cable 1. When further cable elongation occurs in the optical cable 1 after the cable elongation of the optical cable 1 reaches the boundary elongation X1_t of the strength members 2 (a state in which the untwisting of the strength members 2 has finished; a state in which the strength members 2 are straightened), tension is applied to the strength members 2 from that stage (the strength members 2 bear the tension), causing the strength members 2 to elongate and deform. Here, the strength members 2 elastically deform when the cable elongation of the optical cable 1 ranges from X1_t to X1_t + Xe_t (the elastic region of the strength members 2). Note that when the cable elongation of the optical cable 1 exceeds X1_t + Xe_t, the strength members 2 undergo plastic deformation. Furthermore, when the cable elongation of the optical cable 1 exceeds X1_t + Xu_t, the strength members 2 will break.
[0050] The graph of the optical fiber 5 shown in FIG. 3A is similar to the graph of the optical fiber 5 of the comparative example shown in FIG. 3B. Because the optical fiber 5 is twisted in an SZ configuration, when cable elongation begins to occur in the optical cable 1, the optical fiber 5 simply untwists, and almost no tension is applied to the optical fiber 5 (at this stage, almost no elongation strain occurs in the optical fiber 5). For this reason, as shown in FIG. 3A , when the cable elongation of the optical cable 1 is in the range of 0 to X1_f (the initial elongation region of the optical fiber 5), almost no tension is applied to the optical fiber 5. As the optical fiber 5 untwists, the optical fiber 5 approaches a straight shape along the cable longitudinal direction. Here, when the cable elongation of the optical cable 1 reaches the boundary elongation X1_f of the optical fiber 5, the untwisting of the optical fiber 5 ends, and the optical fiber 5 becomes almost straight within the optical cable 1. The cable elongation X1_f of the optical cable 1 when the untwisting of the optical fiber 5 is completed (the boundary elongation of the optical fiber 5) is greater than the cable elongation X1_t of the optical cable 1 when the untwisting of the strength members 2 is completed (the boundary elongation of the strength members 2) (X1_f>X1_t). If further cable elongation occurs in the optical cable 1 after the cable elongation of the optical fiber 1 reaches the boundary elongation X1_f of the optical fiber 5 (the state where the untwisting of the optical fiber 5 is completed; the state where the optical fiber 5 is straightened), tension is applied to the optical fiber 5 from that stage (the optical fiber 5 bears the tension), and the optical fiber 5 is elongated and deformed. If the cable elongation of the optical cable 1 becomes even greater, the optical fiber 5 will break.
[0051] As shown in Figure 3A, when the strength members 2 are twisted, there is a small difference between the cable elongation X1_t of the optical cable 1 when tension begins to be applied to the strength members 2 (interfacial elongation of the strength members 2; equivalent to the excess length ratio of the strength members 2) and the cable elongation X1_f of the optical cable 1 when tension begins to be applied to the optical cable 1 (interfacial elongation of the optical fibers 5; equivalent to the excess length ratio of the optical fibers 5). Therefore, when the strength members 2 are twisted, when tension within the range of the allowable tension Ta shown in Figure 4A is applied to the optical cable 1, the structure makes it easy to distribute the tension of the optical cable 1 to the optical fibers 5. Here, when tension Tf shown in Figure 4A is applied to the optical cable 1, the cable elongation of the optical cable 1 reaches X1_f (see Figure 3A). Therefore, when tension in the range of Tf or more and Ta or less is applied to the optical cable 1, the tension is distributed to the strength members 2 and the optical fibers 5. Since the tension equivalent to the allowable tension Ta can be distributed and borne by the tension member 2 and the optical fiber 5, the diameter of the tension member 2 can be made thinner than in the comparative example, and the diameter of the optical cable 1 can be made thinner.
[0052] In the above description, the tension is distributed to the optical fibers 5. However, the tension may be distributed to components other than the optical fibers 5. For example, the tension applied to the optical cable 1 may be distributed to components other than the strength members 2, such as the bundle material 6, the jacket 8, a tear cord (not shown in FIG. 1 ), or an inclusion (not shown in FIG. 1 ). By twisting the strength members 2, a structure is achieved that makes it easier to distribute the tension applied to the optical cable 1 to these components as well. However, because the optical fibers 5 made of glass have a high modulus of longitudinal elasticity, distributing the tension to the optical fibers 5 is effective. In particular, when the optical cable 1 has a large number of optical fibers 5 (for example, when the optical cable 1 is an ultra-high-core cable having several thousand optical fibers 5), a large tension can be applied to the entire optical fibers 5, and therefore distributing the tension to the optical fibers 5 is particularly effective.
[0053] As described above, the optical cable 1 of this embodiment includes the strength members 2, the plurality of optical fibers 5, and the jacket 8. The strength members 2 are twisted and housed in the jacket 8 so that the interfacial elongation X1_t of the strength members 2 is smaller than the interfacial elongation X1_f of the optical fibers 5 (X1_t<X1_f). By adopting such a configuration, the tension applied to the optical cable 1 is easily distributed to members other than the strength members 2. This also allows the diameter of the strength members 2 to be reduced, thereby enabling the diameter of the optical cable 1 to be reduced.
[0054] In the above description, the strength members 2 are twisted in an SZ shape, but the strength members 2 may also be twisted helically in one direction. Even when the strength members 2 are twisted helically in one direction, when tension is applied to the strength members 2, the twisted strength members tighten and stretch in the cable longitudinal direction, making it easier to distribute the tension applied to the optical cable 1 to members other than the strength members 2. However, when the strength members 2 are twisted in an SZ shape, the strength members 2 straighten out as they untwist, resulting in a structure in which the strength members 2 are more likely to stretch in the cable longitudinal direction than when the strength members 2 are twisted helically in one direction. That is, when the tension members 2 are twisted in an SZ shape, the boundary elongation X1_t of the tension members 2 becomes larger than when the tension members 2 are twisted spirally in one direction, and therefore the tension applied to the optical cable 1 is more likely to be distributed to members other than the tension members 2. For this reason, it is desirable that the tension members 2 are twisted in an SZ shape.
[0055] As shown in FIG. 3A , it is desirable that the strength members 2 do not break when the cable elongation of the optical fiber 5 is the boundary elongation X1_f of the optical fiber 5. To achieve this configuration, if the boundary elongation of the strength members 2 is X1_t (unit: %), the boundary elongation of the optical fiber is X1_f (unit: %), and the tensile strain (unit: %) of the strength members 2 when the strength members 2 break is Xu_t, then, as shown in FIG. 3A , X1_f is desirably greater than or equal to X1_t and less than or equal to X1_t + Xu_t (X1_t≦X1_f≦X1_t+Xu_t). In other words, it is desirably the tensile strain Xu_t (unit: %) when the strength members 2 break is greater than the difference between X1_f and X1_t (Xu_t>X1_f−X1_t). An optical cable 1 containing the strength members 2 and the optical fiber 5 that satisfy these conditions can suppress breakage of the strength members 2. In addition, when the members are twisted in an SZ shape, the boundary elongation X1 (unit: %) of the members corresponds to the excess length ratio X (unit: %) of the members, and therefore it is desirable that the elongation strain Xu_t (unit: %) when the reinforcing member 2 breaks be greater than the difference between the excess length ratio X1_f (unit: %) of the optical fiber 5 and the excess length ratio X1_t (unit: %) of the reinforcing member 2.
[0056] Furthermore, as shown in FIG. 3A , it is desirable that the strength members 2 are elastically deformed when the cable elongation of the optical cable 1 is the boundary elongation X1_f of the optical fiber 5. This prevents the strength members 2 from undergoing plastic deformation. To achieve this configuration, it is desirable that the cable elongation corresponding to the boundary elongation X1_f of the optical fiber 5 be within the elastic region of the strength members 2. In other words, when the elastic region of the strength members 2 is equal to or greater than X1_t and equal to or less than X1_t + Xe_t, it is desirable that X1_f be equal to or greater than X1_t and equal to or less than X1_t + Xe_t (X1_t≦X1_f≦X1_t+Xe_t). In other words, it is desirable that the elongation strain Xe_t (unit: %) at which the strength members 2 can elastically deform is greater than the difference between X1_f and X1_t (Xe_t>X1_f−X1_t). An optical cable 1 containing the strength members 2 and the optical fibers 5 that satisfy these conditions prevents the strength members 2 from undergoing plastic deformation. In addition, when the members are twisted in an SZ shape, the boundary elongation X1 (unit: %) of the members corresponds to the excess length ratio X (unit: %) of the members, and therefore, it is desirable that the elongation strain Xe_t (unit: %) at which the reinforcing member 2 can elastically deform is greater than the difference between the excess length ratio X1_f (unit: %) of the optical fiber 5 and the excess length ratio X1_t (unit: %) of the reinforcing member 2.
[0057] Incidentally, when the strength members 2 are disposed in the center of the optical cable 1 and the multiple optical fibers 5 are twisted around the strength members 2 as shown in FIG. 1 , the difference between X1_t and X1_f is likely to increase (as a result, the strength members 2 may undergo plastic deformation or break when the cable elongation of the optical cable 1 reaches X1_f). Therefore, in such a case, it is effective to arrange the twisted strength members 2 in a more serpentine manner. Furthermore, by arranging the twisted strength members 2 in a serpentine manner, the difference between X1_t and X1_f is likely to decrease (as a result, the tension of the optical cable is likely to be distributed to members other than the strength members 2, and plastic deformation of the strength members 2 is likely to be suppressed). Therefore, when the strength members 2 are disposed in the center of the optical cable 1 and the multiple optical fibers 5 are twisted around the strength members 2 as shown in FIG. 1 , it is effective to arrange the twisted strength members 2 in a serpentine manner.
[0058] It is desirable that the elongation strain of the optical fiber 5 when an allowable tension Ta is applied to the optical cable 1 and tension is applied to the optical fiber 5 be 60% or less of the proof level (screening level during a proof test) in accordance with, for example, ICEA-S-87-640. For example, when an optical fiber with a proof level of 1.5% is used, the elongation strain of the optical fiber 5 when an allowable tension Ta is applied to the optical cable 1 is desirably 0.9% or less, and may be 0.3% or less if greater reliability is desired.
[0059] <Method of Manufacturing Optical Cable> Fig. 5 is an explanatory diagram of a system for manufacturing the optical cable 1. The manufacturing system includes a first supply unit 11, a first batten 12, a second supply unit 21, a second batten 22, an extrusion molding unit 31, a cooling unit 32, a take-up unit 33, and a drum 34.
[0060] The first supply section 11 is a supply source that supplies the strength members 2. Each of the plurality of first supply sections 11 supplies the strength members 2 to the first battens 12.
[0061] The first batten 12 is a plate-shaped member for twisting the strength members 2. The first batten 12 has a plurality of insertion holes. The insertion holes are through-holes that pass through the first batten 12 and are holes for inserting the strength members 2. The strength members 2 are supplied from the first supply unit 11 toward each insertion hole of the first batten 12. The first batten 12 swings around a central rotation axis with the strength members 2 inserted into the insertion holes. As the first batten 12 swings, the plurality of strength members 2 are twisted together in an SZ configuration. The strength members 2 twisted in an SZ configuration are supplied to the second batten 22.
[0062] The second supply unit 21 is a supply source that supplies the optical fiber 5. Here, the second supply unit 21 is configured as a drum around which the optical fiber unit 4 is wound. Note that, instead of supplying the optical fiber unit 4 (a member in which a plurality of optical fibers 5 are bundled with a bundling material 6), the second supply unit 21 may supply a plurality of optical fibers 5 (for example, an intermittently connected optical fiber tape) that are not bundled with a bundling material 6. Furthermore, instead of a drum, the second supply unit 21 may be configured as a manufacturing device for the optical fiber unit 4 (or optical fiber tape). Each of the plurality of second supply units 21 supplies the optical fiber 5 (here, the optical fiber unit 4) to the second batten 22.
[0063] The second batten 22 is a plate-shaped member for twisting the optical fibers 5. The second batten 22 has a first insertion hole and a plurality of second insertion holes. The first insertion hole and the second insertion hole are through holes that penetrate the second batten 22. The first insertion hole is provided in the center of the second batten 22 and is a hole for inserting the strength members 2. The strength members 2 in a twisted state are supplied from the first batten 22 toward the first insertion hole. The second insertion hole is a hole for inserting the optical fibers 5, and the plurality of second insertion holes are arranged to surround the first insertion hole. The optical fibers 5 (here, optical fiber units 4) are supplied from the second supply unit 21 toward each of the second insertion holes.
[0064] The second batten 22 swings around a central rotation axis while inserting the twisted strength members 2 into the first insertion holes and the optical fibers 5 (here, optical fiber units 4) into the second insertion holes. The swinging of the second batten 22 causes the optical fibers 5 to be twisted in an SZ pattern around the outer periphery of the strength members 2. The reversal timing of the swinging of the second batten 22 may be synchronized with the reversal timing of the swinging of the first batten 12 so that the twisting direction of the optical fibers 5 is opposite to the twisting direction of the strength members 2. The strength members 2 in an SZ twisted state and the optical fibers 5 in an SZ twisted state outside the strength members 2 are supplied to the extrusion molding section 31.
[0065] As shown in Figure 5, the second batten 22 is disposed downstream of the first batten 12 in the supply direction. However, the position of the second batten 22 in the supply direction may be the same as that of the first batten 12. In this case, the first batten 12 is disposed inside the first insertion hole of the second batten 22, and the first batten 12 and the second batten 22 are swung independently. In this case, to make the twist direction of the optical fibers 5 opposite to that of the tension members 2, the first batten 12 and the second batten 22 may be swung synchronously so that the second batten 22 rotates in the opposite direction to that of the first batten 12. If the first batten 12 and the second batten 22 are disposed at the same position in the supply direction, the first batten 12 and the second batten 22 may be swung synchronously by disposing a power transmission mechanism between the first batten 12 and the second batten 22.
[0066] The extrusion molding unit 31 is a device that forms the jacket 8. The extrusion molding unit 31 is supplied with the twisted strength members 2 and a plurality of twisted optical fibers 5 (optical fiber units 4) that are arranged around the strength members 2. The extrusion molding unit 31 is also supplied with other components, such as a pressure winding tape 7 (not shown in FIG. 5; see FIG. 1). The strength members 2 and the optical fibers 5 that pass through the extrusion molding unit 31 are each pre-applied with a predetermined tension. In the extrusion molding unit 31, the pressure winding tape 7 is wound around the outer peripheries of the plurality of optical fibers 5, and a resin that will become the jacket 8 is extruded, thereby producing the optical cable 1 shown in FIG. 1.
[0067] The cooling unit 32 is a device that cools the optical cable 1. The cooling unit 32 is arranged downstream in the supply direction of the extrusion molding unit 31, and cools the optical cable 1 molded by the extrusion molding unit 31. In addition, the take-up unit 33 is arranged downstream in the supply direction of the cooling unit 32.
[0068] The take-up unit 33 is a device that takes up the cooled optical cable 1. The optical cable 1 taken up by the take-up unit 33 is wound onto a drum 34. A predetermined tension is applied to the tension members 2 and the optical fiber 5 on the upstream side of the take-up unit 33 in the supply direction. On the other hand, the tension applied to the tension members 2 and the optical fiber 5 on the downstream side of the take-up unit 33 in the supply direction is released.
[0069] When the tension applied to the strength members 2 and the optical fiber 5 is released downstream in the supply direction of the take-up unit 33 and the jacket 8 is cooled and shrinks in the cable longitudinal direction, the strength members 2 and the optical fiber 5 are housed in the jacket 8 with a predetermined excess length. In other words, a predetermined tension (a tension that takes into account the amount of shrinkage of the jacket 8 after cooling) is applied to the strength members 2 and the optical fiber 5 so that the strength members 2 and the optical fiber 5 are housed in the jacket 8 with a predetermined excess length. This allows the twisted strength members 2 to be housed in the jacket 8 so that the interfacial elongation X1_t of the strength members 2 is smaller than the interfacial elongation X1_f of the optical fiber 5 (X1_t<X1_f). The twisted strength members 2 may be meandered by utilizing the fact that the jacket 8 shrinks in the cable longitudinal direction after being extruded.
[0070] The drum 34 is a member for winding the optical cable 1. Since the optical fibers 5 are twisted in an SZ shape, even when the optical cable 1 is wound around the drum 34, it is possible to prevent a reduction in the transmission loss of a specific optical fiber 5.
[0071] 6A to 6D are cross-sectional views of optical cables 1 according to first to fourth modified examples. In Fig. 6A to 6D, the same reference numerals are used to designate the same components as those already described, and the description of these components may be omitted.
[0072] 6A to 6D , similar to the optical cable 1 shown in Fig. 1 , the optical cable 1 includes a strength member 2, a plurality of optical fibers 5, and an outer jacket 8. Furthermore, in each of the optical cables 1 shown in Fig. 6A to 6D , the strength members 2 are twisted and housed in the outer jacket 8 so that the interfacial elongation X1_t of the strength members 2 is smaller than the interfacial elongation X1_f of the optical fibers 5 (X1_t<X1_f). Therefore, in each of the optical cables 1 of the first to fourth variations, the tension applied to the optical cable 1 is easily distributed to members other than the strength members 2, allowing the optical cable 1 to have a smaller diameter.
[0073] 6A to 6C further include another strength member 3A embedded in the jacket 8. In the first to third modifications, the strength members 2 and the optical fibers 5 in the center of the optical cable 1 can bear the tension, so the diameter of the strength members 3A embedded in the jacket 8 can be made smaller than when the tension of the optical cable 1 is borne solely by the strength members 3A embedded in the jacket 8. Therefore, in the first to third modifications, the diameter of the optical cable 1 can be made smaller.
[0074] When the cable elongation when the strength member 3A embedded in the jacket 8 breaks is designated as Xu_t', it is desirable that the boundary elongation X1_t of the strength member 2 (the strength member housed in the jacket 8; the central strength member) and the boundary elongation X1_f of the optical fiber 5 are both smaller than the cable elongation Xu_t' when the strength member 3A breaks (X1_t<Xu_t', X1_f<Xu_t'). This allows the strength member 2 and the optical fiber 5 at the center of the optical cable 1 to bear the tension before the strength member 3A breaks (before the cable elongation occurs to the extent that the strength member 3A breaks). Therefore, it is possible to make the diameter of the strength member 3A embedded in the jacket 8 thinner than when the tension of the optical cable 1 is borne solely by the strength member 3A embedded in the jacket 8.
[0075] As in the first modified example shown in Fig. 6A , a pair of strength members 3A may be arranged to sandwich the housing space for the jacket 8. When the pair of strength members 3A are arranged in this manner, the optical cable 1 becomes easier to bend in a bending direction with the line connecting the centers of the pair of strength members 3A as the neutral plane, but becomes more difficult to bend in a direction perpendicular to this plane. This results in a bending directionality of the optical cable 1 compared to the optical cable 1 shown in Fig. 1 . However, as already explained, in the first modified example shown in Fig. 6A , the diameter of the strength members 3A embedded in the jacket 8 can be made thinner, so that even when a pair of strength members 3A is arranged as shown in Fig. 6A , the bending directionality of the optical cable 1 can be weakened.
[0076] In a second modified example shown in Fig. 6B, multiple strength members 3A are embedded in the jacket 8 while being evenly spaced in the circumferential direction. By arranging multiple strength members 3A evenly in the circumferential direction in this manner, the bending directionality of the optical cable 1 can be suppressed more effectively than in the first modified example shown in Fig. 6A. In a third modified example shown in Fig. 6C, two strength members 3A are grouped into one set, and multiple sets of strength members 3A are embedded in the jacket 8 while being evenly spaced in the circumferential direction. By arranging multiple sets of strength members 3A evenly in the circumferential direction in this manner, the bending directionality of the optical cable 1 can also be suppressed more effectively than in the first modified example shown in Fig. 6A.
[0077] The optical cable 1 of a fourth modified example shown in FIG. 6D further includes another strength member 3B arranged along the inner wall surface of the jacket 8. Here, the strength member 3B is arranged between the jacket 8 and the pressure winding tape 7. However, the strength member 3B may also be arranged between the pressure winding tape and the optical fiber unit 4. In the fourth modified example, similar to the optical cable 1 shown in FIG. 1, the strength member 2 and the optical fiber 5 in the center of the optical cable 1 can bear tension, so that the strength member 3B can be made thinner (more compact). Therefore, the diameter of the optical cable 1 can be made thinner in the fourth modified example as well.
[0078] Unlike the central strength members 2, the strength members 3B of the fourth modification are arranged vertically (straightly along the cable longitudinal direction). If the strength members 3B were twisted spirally in one direction, tension applied to the strength members 3B would cause the strength members 3B to displace inward, potentially compressing the optical fiber 5. For this reason, it is desirable that the strength members 3B of the fourth modification are not twisted. In contrast, the strength members 3A of the first to third modifications are embedded in the jacket 8, making them less likely to displace inward even when tension is applied to them. For this reason, the strength members 3A of the first to third modifications may be embedded in the jacket 8 in a twisted state. For example, the strength members 3A of the first to third modified examples may be embedded in the outer sheath 8 in a state where they are spirally twisted in one direction, or they may be embedded in the outer sheath 8 in a state where they are twisted in an SZ shape by reversing the twisting direction. Furthermore, the strength members 3A of the first to third modified examples may be embedded in the outer sheath 8 in a state where they are arranged straight along the cable longitudinal direction.
[0079] Second Embodiment Fig. 7 is a cross-sectional view of an optical cable structure 1'. The optical cable structure 1' has a plurality of inner cables and an outer jacket 9 that houses the plurality of inner cables.
[0080] The inner cable has the same configuration as the optical cable 1 shown in Fig. 1 and includes a strength member 2, a plurality of optical fibers 5, and an outer jacket 8. The inner cable may have a configuration different from that of the optical cable 1 shown in Fig. 1 as long as the strength members 2 in the central portion are twisted, and may be, for example, the optical cable 1 of the modified examples shown in Figs. 6A to 6D. As with the optical cable 1 shown in Fig. 1, the inner cable can be tensile with the strength members 2 and optical fibers 5 in the central portion, allowing the strength members 2 to be made thinner, thereby enabling the inner cable to have a smaller diameter. Therefore, by employing the optical cable 1 shown in Fig. 1 as the inner cable, the diameter of the optical cable structure 1' can be made thinner.
[0081] 7 , the bending directionality of the internal cable is restricted, which facilitates the routing of the internal cable and facilitates mid-span branching work for extracting the internal cable from the optical cable structure 1 ′. Furthermore, since the bending directionality of the internal cable is restricted, it is also possible to accommodate multiple internal cables in a twisted state in the outer jacket 9.
[0082] ===Other Embodiments=== The above-described embodiments are intended to facilitate understanding of the present invention and are not intended to limit the present invention. The present invention may be modified or improved without departing from the spirit thereof, and the present invention naturally includes equivalents. Furthermore, the above-described embodiments may be combined as appropriate. For example, the optical cable may be provided with other components, such as a pressure winding tape, a tear cord, or a protective layer, as appropriate. Furthermore, the cross-sectional shape of the optical cable is not limited to a circle, and may be other shapes, such as a rectangle or an ellipse. Furthermore, the features of each embodiment may be combined with other embodiments.
[0083] REFERENCE SIGNS LIST 1 Optical cable, 1' Optical cable structure, 2 Tensile strength member, 3A, 3B Another tensile strength member, 4 Optical fiber unit, 5 Optical fiber, 6 Bundle material, 7 Pressure winding tape, 8 Jacket, 9 Outer jacket, 10 Manufacturing system, 11 First supply section, 12 First batten, 21 Second supply section, 22 Second batten, 31 Extrusion molding section, 32 Cooling section, 33 Take-up section, 34 Drum
Claims
1. A tensile strength body, A plurality of optical fibers arranged on the outer periphery of the tensile strength body, A jacket that houses the tensile strength body and the plurality of optical fibers And is provided with, The boundary elongation of the tensile strength body is smaller than the boundary elongation of the optical fiber, Here, The boundary elongation is the cable elongation corresponding to the boundary between the initial elongation region and the elastic region, In the case where cable elongation occurs when tension is applied in the initial elongation region, the initial elongation occurs in a member that is the tensile strength body or the optical fiber by deforming so as to approach a straight shape along the cable longitudinal direction. It is the range of the cable elongation at this time, The elastic region is the range of the cable elongation when elastic elongation corresponding to the elastic modulus of the member occurs in the member when further cable elongation occurs from the initial elongation region. An optical cable characterized by the above.
2. The optical cable according to claim 1, The plurality of optical fibers are characterized in that they are composed of a plurality of units.
3. The optical cable according to claim 2, The plurality of units are characterized in that they are bundled with a bundling material.
4. The optical cable according to claim 3, The bundling material is characterized in that it is tubular.
5. The optical cable according to claim 2, The plurality of units are twisted in one direction or in an SZ shape, The twisting direction of the tensile strength body is characterized in that it is opposite to the twisting direction of the optical fiber.
6. The optical cable according to claim 1, The tensile strength body is characterized in that it is twisted in one direction or in an SZ shape.
7. The optical cable according to claim 6, The optical fiber is twisted in an SZ shape, The twisting direction of the tensile strength body is characterized in that it is opposite to the twisting direction of the optical fiber.
8. The optical cable according to any one of claims 1 to 7, The twisted tensile strength body is characterized in that it is arranged in a meandering manner.
9. The optical cable according to claim 8, The tensile strength body is characterized in that it is composed of tensile strength fibers.
10. The optical cable according to any one of claims 1 to 7, Let the boundary elongation of the tensile strength body be X1_t (%), Let the boundary elongation of the optical fiber be X1_f (%), When the elongation strain of the tensile member when the tensile member breaks is Xu_t (%), An optical cable, wherein X1_f is not less than X1_t and not more than X1_t + Xu_t. **Claim 11**: The optical cable according to claim 10, When the elongation strain at which the tensile member can be elastically deformed is Xe_t (%), An optical cable, wherein X1_f is not less than X1_t and not more than X1_t + Xe_t. **Claim 12** An optical cable according to any one of claims 1 to 7, wherein the elongation strain of the optical fiber when an allowable tension is applied to the optical cable and the optical fiber is tensioned is 60% or less of the proof level. **Claim 13**: The optical cable according to any one of claims 1 to 7, characterized in that another tensile member is embedded in the outer sheath. **Claim 14**: An optical cable structure characterized by including a plurality of the optical cables according to any one of claims 1 to 7 as internal cables. **Claim 15** Supplying a tensile member, Arranging a plurality of optical fibers on the outer periphery of the tensile member, and Forming an outer sheath so as to accommodate the tensile member and the plurality of optical fibers, performing, where, the boundary elongation of the tensile member is smaller than the boundary elongation of the optical fiber, the boundary elongation is the cable elongation corresponding to the boundary between the initial elongation region and the elastic region, the initial elongation region is the range of the cable elongation when, in the case where cable elongation occurs due to the application of tension, a member that is the tensile member or the optical fiber is deformed so as to approach a straight shape along the cable longitudinal direction, and an initial elongation occurs in the member, the elastic region is the range of the cable elongation when, in the case where further cable elongation occurs from the initial elongation region, an elastic elongation corresponding to the elastic coefficient of the member occurs in the member, characterized by an optical cable manufacturing method. **Claim 16**: The optical cable manufacturing method according to claim 15, characterized by meandering the twisted tensile member by contraction in the cable longitudinal direction after the outer sheath is extrusion molded.