Fiber optic cable

Abstract

To provide an optical fiber cable that prevents a rip cord from moving toward the inside of a sheath.SOLUTION: An optical fiber cable comprises: a core including a plurality of optical fibers; a sheath that houses the core; and a rip cord at least a part of which is embedded in the sheath. The rip cord meanders in such a way that its circumferential position changes along the longitudinal direction, or meanders in such a way that its radial position changes along the longitudinal direction within a range where the rip cord does not protrude from the sheath.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to optical fiber cables. [Background technology]

[0002] Patent Document 1 discloses an optical fiber cable including a sheath, a core having an optical fiber and a pressure winding, and a rip cord for tearing the sheath. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2020-79878 A Summary of the Invention [Problem to be solved by the invention]

[0004] When a fiber optic cable is bent, a force may act on the ripcord that moves it toward the inside of the sheath. If this force causes the ripcord to move inside the sheath, it becomes more difficult for the ripcord to tear the sheath apart.

[0005] The present invention has been made in consideration of the above circumstances, and has an object to provide an optical fiber cable in which the ripcord is prevented from moving toward the inside of the sheath. [Means for solving the problem]

[0006] In order to solve the above problems, an optical fiber cable according to one embodiment of the present invention comprises a core containing a plurality of optical fibers, a sheath that houses the core, and a ripcord at least partially embedded in the sheath, wherein the ripcord meanders so that its circumferential position changes along the longitudinal direction, or meanders so that its radial position changes along the longitudinal direction without protruding outward from the sheath. Effect of the Invention

[0007] According to the above aspect of the present invention, it is possible to provide an optical fiber cable in which the ripcord is prevented from moving toward the inside of the sheath. [Brief description of the drawings]

[0008] [Figure 1] 1 is a cross-sectional view of an optical fiber cable according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a cross-sectional view taken along the line II-II in FIG. [Diagram 3] FIG. 2 is a view taken in the direction of the arrow III in FIG. [Figure 4] FIG. 3 is a diagram showing a modification of FIG. 2. [Diagram 5] FIG. 1 is a diagram showing the relationship between the bending diameter of an optical fiber cable and the elongation strain of a ripcord. [Figure 6] FIG. 13 is a diagram showing the relationship between the average value of the distance between the neutral line and the ripcord and the elongation strain. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, the optical fiber cable of the present embodiment will be described with reference to the drawings. As shown in FIG. 1, the optical fiber cable 1 includes a core 20, a sheath 2, a pair of ripcords 3, and a pair of strength members 4.

[0010] (direction definition) In this embodiment, the direction along the central axis O of the core 20 is referred to as the longitudinal direction. In a cross-sectional view perpendicular to the longitudinal direction, the direction going around the central axis O is referred to as the circumferential direction, and the direction intersecting the central axis O is referred to as the radial direction. In the cross-sectional view, a straight line connecting the centers of a pair of strength members 4 is referred to as the neutral line L. When the optical fiber cable 1 is bent in a direction perpendicular to the neutral line L (the up-down direction in FIG. 1), the expansion and contraction of the strength members 4 is smaller than when the optical fiber cable 1 is bent in other directions. Therefore, it is relatively easy to bend the optical fiber cable 1 in a direction perpendicular to the neutral line L.

[0011] The core 20 has a plurality of optical fibers 21 and a pressure winding 22 that wraps the plurality of optical fibers 21. As the optical fibers 21, an optical fiber core wire, an optical fiber bare wire, an optical fiber ribbon core wire, etc. can be used. As a type of optical fiber ribbon core wire, the plurality of optical fibers 21 may form a so-called intermittently fixed ribbon core wire. In the intermittently fixed ribbon core wire, the plurality of optical fibers 21 are bonded to each other so as to spread in a mesh-like (spider web-like) shape when pulled in a direction perpendicular to the extending direction of the optical fibers. In detail, one optical fiber 21 is bonded to the optical fibers 21 on both sides thereof at different positions in the longitudinal direction, and the adjacent optical fibers 21 are bonded to each other at a fixed interval in the longitudinal direction. The form of the optical fiber 21 included in the core 20 is not limited to an intermittently fixed ribbon, and may be changed as appropriate.

[0012] Nonwoven fabric, polyester tape, or the like can be used as the pressure wrap 22. Alternatively, a water-absorbent tape obtained by imparting water-absorbency to nonwoven fabric, polyester tape, or the like may be used as the pressure wrap 22. In this case, the waterproof performance of the optical fiber cable 1 can be improved. However, the pressure wrap 22 is not essential.

[0013] The pressure winding 22 is cylindrically shaped by being closed at the closing portion 22a. A plurality of optical fibers 21 are positioned inside the cylindrical pressure winding 22. The closing portion 22a in this embodiment is a region (overlapping region) where both ends of the pressure winding 22 in the circumferential direction are overlapped. The region of the pressure winding 22 excluding the closing portion 22a is referred to as a non-overlapping region 22b. Note that, in the closing portion 22a, both ends of the pressure winding 22 may be butted against each other so as to face each other in the circumferential direction. In other words, the pressure winding 22 does not need to have an overlapping region.

[0014] The pair of ripcords 3 are embedded in the sheath 2. The ripcords 3 are used to tear the sheath 2 and expose the core 20. The ripcords 3 may be entirely embedded in the sheath 2. In this case, the ripcords 3 are less likely to fall off from the sheath 2. However, after the sheath 2 is torn using the ripcords 3, a portion of the sheath 2 located radially inward of the ripcords 3 remains. Alternatively, the ripcords 3 may be partially exposed radially inward from the sheath 2. In this case, after the sheath 2 is torn using the ripcords 3, the sheath 2 does not remain at least in the portion where the ripcords 3 were exposed radially inward. This makes it easier to expose the core 20.

[0015] The pair of ripcords 3 are arranged so as to sandwich the core 20 therebetween in the radial direction. The direction in which the ripcords 3 face each other is perpendicular to the direction in which the tension members 4 face each other. In other words, the pair of ripcords 3 are positioned on a straight line that passes through the central axis O and is perpendicular to the neutral line L.

[0016] The number of ripcords embedded in the sheath 2 may be one or three or more. A thread made of fiber (e.g., polyester fiber) may be used as the ripcord 3. Alternatively, a cylindrical rod made of polypropylene (PP) or nylon may be used as the ripcord 3.

[0017] The sheath 2 accommodates the core 20. The material of the sheath 2 may be 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). A mixture (alloy, mixture) of the above resins may also be used.

[0018] A mark for indicating the position of the ripcord 3 may be provided on the outer peripheral surface of the sheath 2. The mark may be a protrusion that protrudes radially outward from the outer peripheral surface of the sheath 2, or may be a mark made of paint. The sheath 2 need not have a mark. Even without a mark, it is possible to ascertain the position of the ripcord 3 from, for example, the directionality of bending of the optical fiber cable 1 caused by the arrangement of the tensile members 4.

[0019] The pair of strength members 4 are embedded in the sheath 2. The pair of strength members 4 are arranged so as to sandwich the core 20 therebetween in the radial direction. Each strength member 4 extends linearly along the longitudinal direction. The number of strength members 4 embedded in the sheath 2 may be one or three or more. Alternatively, the optical fiber cable 1 may not include a strength member 4. Examples of materials that can be used for the strength members 4 include metal wires (such as steel wires) and FRP. When the strength members 4 are FRP, examples of fibers that can be used for the FRP include aramid fibers, glass fibers, and the like.

[0020] When the optical fiber cable 1 is bent, a force may act on the ripcord 3 in a radially inward direction. In particular, the optical fiber cable 1 is easily bent in a direction perpendicular to the neutral line L. For this reason, when the direction in which the ripcords 3 face each other is perpendicular to the direction in which the tensile members 8 face each other as shown in FIG. 1, the ripcord 3 located on the outside of the bend is pulled in the longitudinal direction. When the elongation strain acting on the ripcord 3 exceeds the excess length of the ripcord 3, a force acts on the ripcord 3 in a radially inward direction. For this reason, the ripcord 3 may move toward the inside of the bend (i.e., toward the inside in the radial direction).

[0021] Particularly in recent years, there has been a demand for optical fiber cables with more cores (increasing the number of optical fibers 21). As the distance between the central axis O and the ripcord 3 increases due to an increase in the number of optical fibers 21, the elongation strain of the ripcord 3 also increases, making the ripcord 3 more likely to move radially inward. If the ripcord 3 moves radially inward, it becomes difficult for the user to grasp the position of the ripcord 3, reducing the efficiency of the task of tearing the sheath 2. In addition, the ripcord 3 may enter the inside of the pressure winding 22 from the closing portion 22a, damaging the optical fiber 21.

[0022] Therefore, in this embodiment, the ripcord 3 meanders in the radial or circumferential direction. "Radial meandering" refers to meandering in which the radial position of the ripcord 3 changes along the longitudinal direction, as shown in FIG. 2. "Circumferential meandering" refers to meandering in which the ripcord 3's circumferential position changes along the longitudinal direction, as shown in FIG. 3. Arrow M1 in FIG. 1 diagrammatically represents the "radial meandering" of the ripcord 3. Arrow M2 in FIG. 1 diagrammatically represents the "circumferential meandering" of the ripcord 3. The ripcord 3 meandering in the radial or circumferential direction increases the excess length rate of the ripcord 3. The ripcord 3 may meander both in the radial and circumferential directions.

[0023] As an example of a method for manufacturing the optical fiber cable 1 of this embodiment, the tension applied to the ripcord 3 may be varied at a constant time interval when the sheath 2 is extruded around the core 20. The radial position of the ripcord 3 varies depending on the tension applied to the ripcord 3 during extrusion of the sheath 2. Therefore, by varying the tension applied to the ripcord 3 at a time interval, the ripcord 3 meanders in the radial direction. If the relationship between the tension and the radial position of the ripcord 3 is experimentally determined in advance, the ripcord 3 can be positioned at a desired radial position.

[0024] Also, a rocking plate having an insertion hole through which the ripcord 3 is inserted may be used during extrusion molding of the sheath 2. The circumferential position of the ripcord 3 varies by rocking the rocking plate periodically. Thus, the ripcord 3 meanders in the circumferential direction. The circumferential meandering angle θ (see FIG. 1) can be set by the rocking angle of the rocking plate. The circumferential meandering pitch Pc (see FIG. 3) can be set by the magnitude of the rocking speed of the rocking plate relative to the extrusion molding speed of the sheath 2. The circumferential meandering pitch Pc is the repetition interval in the longitudinal direction of the circumferential meandering shape.

[0025] As shown in FIG. 2, the ripcord 3 may have a plurality of curved portions 3a (first curved portions) that are convex toward the radial inside and a plurality of curved portions 3b (second curved portions) that are convex toward the radial outside. The curved portions 3a, 3b are alternately repeated in the longitudinal direction. The radial positions of the curved portions 3a, 3b vary along the longitudinal direction. The curved portion 3a may be partially exposed from the sheath 2 toward the radial inside, and the curved portion 3b may be entirely embedded in the sheath 2. Alternatively, the curved portions 3a, 3b may be entirely embedded in the sheath 2.

[0026] Alternatively, as shown in FIG. 4, the ripcord 3 may have a plurality of curved portions 3c and a plurality of straight portions 3d. The curved portions 3c and the straight portions 3d are alternately repeated in the longitudinal direction. The radial positions of the straight portions 3d are constant along the longitudinal direction. The radial positions of the curved portions 3c vary along the longitudinal direction. The curved portions 3c may be convex radially outward as shown in FIG. 4. In this case, the curved portions 3c are positioned radially outward from the straight portions 3d. Alternatively, the curved portions 3c may be convex radially inward. In this case, the curved portions 3c are positioned radially inward from the straight portions 3d. The straight portions 3d may be partially exposed radially inward from the sheath 2, and the entire curved portions 3c may be embedded in the sheath 2. Alternatively, the curved portions 3c may be partially exposed radially inward from the sheath 2, and the entire straight portions 3d may be embedded in the sheath 2. Alternatively, the curved portions 3c and the straight portions 3d may be entirely embedded in the sheath 2.

[0027] As shown in Figs. 2 and 4, in "radial meandering", the amplitude A is set within a range where the ripcord 3 does not protrude radially outward from the sheath 2. In other words, in "radial meandering", the ripcord 3 changes its radial position along the longitudinal direction within a range where it does not protrude outward from the sheath 2. The amplitude A can be set by the fluctuation width of the tension applied to the ripcord 3 when the sheath 2 is extruded. The shape of the radial meandering and the meandering pitch Pr (see Figs. 2 and 4) can be set by the magnitude of the fluctuation period of the tension applied to the ripcord 3 relative to the speed of the extrusion of the sheath 2. The radial meandering pitch Pr is the repetition interval in the longitudinal direction of the radial meandering shape. For example, in the shape of Fig. 2, the meandering pitch Pr is the sum of the lengths of one curved portion 3a and one curved portion 3b in the longitudinal direction. In the shape of Fig. 4, the meandering pitch Pr is the sum of the length Pr1 of one curved portion 3c and the length Pr2 of one straight portion 3d.

[0028] As described above, the optical fiber cable 1 of the present embodiment includes the core 20 including a plurality of optical fibers 21, the sheath 2 housing the core 20, and the ripcord 3 at least a part of which is embedded in the sheath 2. The ripcord 3 meanders so that its circumferential position changes along the longitudinal direction, or meanders so that its radial position changes along the longitudinal direction within a range in which it does not protrude outward from the sheath 2. In this way, the ripcord 3 meanders in the radial or circumferential direction, so that a sufficient slack length can be provided to the ripcord 3. Therefore, when the optical fiber cable 1 is bent, a force directed inward in the radial direction is prevented from acting on the ripcord 3, and the movement of the ripcord 3 can also be prevented. In addition, if a part of the ripcord 3 protrudes outward in the radial direction from the sheath 2, there is a possibility that water or the like will infiltrate into the inside of the sheath 2 from the protruding part. Therefore, when the ripcord 3 meanders in the radial direction, the infiltration of water or the like can be prevented by setting the range in which it does not protrude outward from the sheath 2.

[0029] Furthermore, the ripcord 3 may meander so that its circumferential position changes along the longitudinal direction, and also meander so that its radial position changes along the longitudinal direction within a range in which it does not protrude outward from the sheath 2. In this case, it is possible to provide the ripcord 3 with a larger extra length while reducing the meandering angle θ in the circumferential meandering and the amplitude A in the radial meandering. The smaller the meandering angle θ or the amplitude A, the more tearability the ripcord 3 can be secured. Furthermore, the contact area between the ripcord 3 and the sheath 2 increases, which increases the adhesive force acting between them, making the ripcord 3 less likely to fall off the sheath 2.

[0030] The above embodiment will be described below using specific examples, but the present invention is not limited to the following examples. As shown in Table 1, samples of the optical fiber cables of the comparative example, example 1, and example 2 were prepared. In all samples, the number of optical fibers 21 was 288, the number of tension members 4 was 2, and the number of ripcords 3 was 2. In all samples, the outer diameter D of the sheath 2 was 12 mm.

[0031] [Table 1]

[0032] In the comparative example, the ripcord 3 was not meandered in either the radial or circumferential direction. In Examples 1 and 2, the ripcord 3 was meandered in the circumferential direction by oscillating the above-mentioned oscillating plate when the sheath 2 was extrusion-molded, so that the meandering angle θ was 30°. In Example 1, as shown in FIG. 2, the ripcord 3 was meandered in the radial direction so that the curved portions 3a and 3b were repeated in the longitudinal direction. In Example 2, as shown in FIG. 4, the ripcord 3 was meandered in the radial direction so that the curved portion 3c and the straight portion 3d were repeated in the longitudinal direction. The meandering in the radial direction in Examples 1 and 2 was achieved by varying the tension applied to the ripcord 3 at a predetermined cycle and amplitude when the sheath 2 was extrusion-molded.

[0033] The radial meandering pitch Pr and the circumferential meandering pitch Pc of Examples 1 and 2 were both 5.0 mm. The curved portion 3a and the curved portion 3b of Example 1 had the same length in the longitudinal direction, each being 2.5 mm. The length Pr2 of the straight portion 3d in the longitudinal direction of Example 2 was twice the length Pr1 of the curved portion 3c. That is, in the longitudinal direction, the length Pr1 of the curved portion 3c of Example 2 was about 1.7 mm, and the length Pr2 of the straight portion 3d was about 3.3 mm. The amplitude A of the meandering in the radial direction was 0.55 mm in Example 1 and 0.95 mm in Example 2. The extra length ratios E of the ripcords 3 of the comparative example, Example 1, and Example 2 were 1.0%, 3.3%, and 3.1%, respectively. The values ​​of Pr, Pc, A, and θ shown in Table 1 are average values ​​when each sample was cut out to a length of 100 mm in the longitudinal direction. Additionally, the excess length ratio E in Table 1 is based on the total length of the ripcord 3 when each sample is cut to a length of 100 mm.

[0034] A bending test was performed on each sample in accordance with IEC60794-1-21: "Repeated Bending". Specifically, a cylindrical mandrel with a diameter of 240 mm was prepared, and each sample was wound around this mandrel. The outer diameter D of the sheath 2 of each sample was 12 mm. Therefore, when each sample was wound around the mandrel, it was possible to bend each sample with a bending diameter 20 times the outer diameter D. Each sample was wound around the mandrel so that the two ripcords 3 were aligned in the radial direction of the mandrel. This applied an elongation strain to the ripcord 3 located on the outside of the bend. The theoretical elongation strain of the ripcord 3 located on the outside of the bend was 2.8% in the comparative example and 2.9% in Examples 1 and 2.

[0035] The reason why the elongation strain in Examples 1 and 2 is larger than that in the Comparative Example is that the ripcords 3 in Examples 1 and 2 meander in the radial direction. That is, the ripcords 3 in Examples 1 and 2 are partially located radially outward of the ripcord 3 in the Comparative Example. In this respect, the circumferential meandering has the advantage, compared to the radial meandering, of being able to increase the excess length ratio without increasing the elongation strain of the ripcord 3.

[0036] After the bending test, it was confirmed whether the ripcord 3 had fallen off from the sheath 2 in the radial direction. As a result, the ripcord 3 had fallen off in the comparative example, and the ripcord 3 had not fallen off in the examples 1 and 2. This result can be explained by the relationship between the elongation strain and the excess length ratio. That is, in the comparative example, the elongation strain (2.8%) was greater than the excess length ratio E (1.0%), so a force was applied to the ripcord 3 in the radial direction inward, causing the ripcord 3 to fall off. On the other hand, in the examples 1 and 2, the elongation strain (2.9%) was smaller than the excess length ratio E (3.3% and 3.1%, respectively), so it was possible to prevent the force applied to the ripcord 3 in the radial direction inward. As a result, it was possible to prevent the ripcord 3 from falling off in the examples 1 and 2.

[0037] As described above, by snaking the ripcord 3 in both the radial and circumferential directions, the slack ratio E of the ripcord 3 is increased, and it is possible to prevent the ripcord 3 from falling off when the optical fiber cable 1 is bent. In Examples 1 and 2, the ripcord 3 is snaking in both the radial and circumferential directions. However, if the ripcord 3 is snaking in either the radial or circumferential direction, it is believed that the slack ratio E of the ripcord 3 can be increased more than before and the above-mentioned effect can be obtained.

[0038] Next, a preferable range of the excess length ratio E will be described. As shown in Table 2, a number of Samples 1 to 10 were created with different excess length ratios E under the same conditions as in Example 2. Samples 1 to 10 have different excess length ratios E due to different amplitudes A. As with Table 1, the excess length ratios E in Table 2 are based on the total length of the ripcord 3 when each sample was cut out to a length of 100 mm.

[0039] [Table 2]

[0040] Samples 1 to 10 were subjected to the same bending test as in Table 1. Thereafter, it was confirmed whether the ripcord 3 had fallen off from the sheath 2 and how easy it was to use the ripcord 3 to tear the sheath 2 and expose the core 20. For samples 1 to 3 with an excess length ratio E of 2.5% or less, the ripcord 3 fell off from the sheath 2 during the bending test. This made it difficult to tear the sheath 2 using the ripcord 3. As mentioned above, this result occurred because the excess length ratio E was smaller than the elongation strain (2.9%).

[0041] For sample 10, in which the excess length rate E was 6.0%, the ripcord 3 did not fall off from the sheath 2. However, because the amount of meandering was too large, it was not easy to tear the sheath 2 with the ripcord 3. From the above results, it is preferable that the excess length ratio E is 6.0% or less.

[0042] The lower limit of the excess length ratio E should not be specified from the results in Table 2, since it is determined by the elongation strain acting on the ripcord 3. The elongation strain acting on the ripcord 3 is determined by the average distance from the neutral line L to the ripcord 3 (hereinafter referred to as distance R). Therefore, the relationship between distance R and excess length ratio E was examined.

[0043] As shown in Figure 5, the relationship between bending diameter and elongation strain of the ripcord 3 was investigated for multiple optical fiber cables with different numbers of cores (number of optical fibers 21). The horizontal axis of Figure 5 is bending diameter, shown as a multiple of the diameter D of each optical fiber cable. For example, data for "20D" indicates that each optical fiber cable was bent at a bending diameter 20 times the diameter D of the optical fiber cable.

[0044] Fig. 6 shows the relationship between the distance R [mm] and the elongation strain [%] of the ripcord 3 when the bending diameter is 20D. The plots in Fig. 6 correspond to the data of 144 fibers, 288 fibers, 432 fibers, 864 fibers, 1728 fibers, 3456 fibers, and 6912 fibers shown in Fig. 5. Here, for any optical fiber cable, if a plot in which the slack ratio E of the ripcord 3 is the vertical axis value (y) and the distance R is the horizontal axis value (x) is located above the line y = 0.0007x + 0.00246 in Fig. 6, it means that the slack ratio E of the ripcord 3 of that optical fiber cable is greater than the elongation strain. In other words, it is preferable that the slack ratio E and the distance R satisfy the following relational expression (1). E≧(0.0007×R+0.0246)×100 …(1)

[0045] Furthermore, as described above, the excess length ratio E is preferably 6.0% or less. Therefore, it is preferable that the excess length ratio E [%] satisfies the following formula (2). (0.0007×R+0.0246)×100≦E≦6.0 …(2) By satisfying formula (2), the excess length ratio E of the ripcord 3 can be made greater than the elongation strain caused by bending, thereby preventing the ripcord 3 from falling off, while making it easier to tear the sheath 2 with the ripcord 3.

[0046] Furthermore, if the amplitude A when the ripcord 3 meanders in the radial direction is too large, a large proportion of the sheath 2 remains connected without being torn apart after it is torn apart by the ripcord 3, making it difficult to expose the core 20. According to the inventors' investigations, when the amplitude A is greater than 1.0 mm, it becomes difficult to expose the core 20. Therefore, it is preferable that the amplitude A is 1.0 mm or less.

[0047] Furthermore, if the radial meandering pitch Pr or the circumferential meandering pitch Pc is too large relative to the bending diameter of the optical fiber cable, the meandering shape of the ripcord 3 will not be substantially included in the bent portion of the optical fiber cable. Therefore, it is preferable that the meandering pitch Pr or the meandering pitch Pc is 15 mm or less.

[0048] 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.

[0049] For example, in the above embodiment, both of the two ripcords 3 are meandering. However, it is possible to obtain an effect if at least one of the ripcords 3 is meandering. For example, when the direction in which the optical fiber cable 1 is bent is specified, the ripcord 3 located on the outside of the bend may be meandering, and the ripcord 3 located on the inside of the bend may not be meandering.

[0050] In addition, within the scope of the spirit of the present invention, 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. [Explanation of symbols]

[0051] 1... Optical fiber cable 2... Sheath 3... Ripcord 20... Core 21... Optical fiber

Claims

1. a core including a plurality of optical fibers; a sheath that houses the core; Two ripcords at least partially embedded in the sheath; A pair of tension members, The two ripcords are arranged to sandwich the core therebetween and meander so that their circumferential positions change along the longitudinal direction, For each of the two ripcords, when the excess length ratio of the ripcord is E [%] and the average distance between the ripcord and a neutral line passing through the center of the pair of tension members in a cross-sectional view is R [mm], (0.0007×R+0.0246)×100≦E≦6.0 A fiber optic cable that satisfies the above requirements.

2. 2. The optical fiber cable according to claim 1, wherein the meandering pitch of the two ripcords in the circumferential direction is 15 mm or less.

3. 3. The optical fiber cable according to claim 1, wherein the two ripcords meander so that their circumferential positions change along the longitudinal direction, and also meander so that their radial positions change along the longitudinal direction without protruding outward from the sheath.

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