Optical fiber cable

Abstract

To provide an optical fiber cable capable of suppressing an increase in transmission loss caused by cracks arising in an outer sheath.SOLUTION: An optical fiber cable is provided, comprising a core with optical fibers, and an outer sheath having first slits formed to extend in a circumferential direction and covering the core.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 core having an optical fiber and an outer jacket covering the core. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2008-292841 A Summary of the Invention [Problem to be solved by the invention]

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

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

[0006] In order to solve the above problems, an optical fiber cable according to a first aspect of the present invention includes a core having an optical fiber, and an outer jacket having a first circumferentially extending slit formed therein and covering the core.

[0007] A second aspect of the present invention relates to the optical fiber cable of the first aspect, further comprising a first tension member disposed in the jacket, and the first slit is connected to the first tension member in a circumferential direction.

[0008] Furthermore, aspect 3 of the present invention relates to the optical fiber cable of aspect 2, wherein a second slit extending in a circumferential direction is formed in the outer sheath, and the second slit is connected to the first tensile body from the circumferentially opposite side to the first slit.

[0009] Furthermore, a fourth aspect of the present invention relates to the optical fiber cable of the second or third aspect, further comprising a second strength member arranged in the outer sheath, the first slit being located between the first strength member and the second strength member in the circumferential direction, the first slit having a base end in contact with the first strength member and a tip end located on the opposite side of the base end in the circumferential direction, and in a cross-sectional view, a straight line connecting the center of the base end and the center of the tip end passes through the second strength member.

[0010] A fifth aspect of the present invention is the optical fiber cable according to any one of the first to fourth aspects, wherein the inside of the first slit is filled with an air layer.

[0011] A sixth aspect of the present invention is the optical fiber cable according to any one of the first to fourth aspects, further comprising an inclusion disposed inside the first slit. Effect of the Invention

[0012] According to the above aspect of the present invention, an optical fiber cable can be provided that is capable of suppressing an increase in transmission loss caused by a crack occurring in the jacket. [Brief description of the drawings]

[0013] [Figure 1] 1 is a cross-sectional view showing an optical fiber cable according to a first embodiment. [Figure 2A] FIG. 13 is a diagram showing a case where lateral pressure acts on a conventional optical fiber cable. [Figure 2B] 4A to 4C are diagrams illustrating a case where lateral pressure acts on the optical fiber cable according to the first embodiment. [Diagram 3] FIG. 5 is a cross-sectional view showing an optical fiber cable according to a second embodiment. [Figure 4] 11 is an enlarged cross-sectional view showing a portion of an optical fiber cable according to a third embodiment. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] (First embodiment) An optical fiber cable according to a first embodiment of the present invention will now be described with reference to the drawings. 1, an optical fiber cable 1 according to this embodiment includes a core (cable core) 10, an outer jacket 20 that covers (contains) the core 10, a pair of ripcords 30, and a plurality of (four in the illustrated example) strength members 40. The ripcords 30 and the strength members 40 are disposed in the outer jacket 20.

[0015] (direction definition) In this embodiment, the direction along the central axis O of the core 10 is referred to as the longitudinal direction. A cross section that intersects (e.g., perpendicular to) the longitudinal direction is referred to as a transverse cross section. When viewed from the longitudinal direction, a direction that intersects the central axis O is referred to as a radial direction, and a direction that rotates around the central axis O is referred to as a circumferential direction. The circumferential direction is also a direction that intersects (e.g., perpendicular to) the radial direction when viewed from the longitudinal direction. When viewed from the transverse cross section, a direction approaching the central axis O is referred to as the radial inner side, and a direction away from the central axis O is referred to as the radial outer side.

[0016] The core 10 according to this embodiment has a plurality of optical fibers 11 and a pressure winding 12 that wraps the plurality of optical fibers 11. Although detailed illustration is omitted, each optical fiber 11 has a fiber core and a cladding that covers the fiber core. The refractive index of the cladding is lower than the refractive index of the fiber core. This allows the optical fiber 11 to confine light in the fiber core. A coating layer of, for example, resin, may be provided on the outer periphery of the cladding.

[0017] As the optical fiber 11, an optical fiber core wire, an optical fiber bare wire, an optical fiber ribbon core wire, etc. can be used. In the illustrated example, four optical fibers 11 constitute one optical fiber ribbon core wire T. As a type of optical fiber ribbon core wire T, the multiple optical fibers 11 may constitute a so-called intermittently fixed ribbon core wire. In the intermittently fixed ribbon core wire, the multiple optical fibers 11 are arranged in an arrangement direction perpendicular to the longitudinal direction of the optical fibers 11. Each two optical fibers 11 adjacent in the arrangement direction are connected to each other by multiple connecting parts intermittently arranged in the longitudinal direction of the optical fibers 11. In addition, each two connecting parts adjacent in the arrangement direction are arranged at different positions in the longitudinal direction of the optical fibers 11. However, the form of the optical fiber 11 included in the core 10 is not limited to the optical fiber ribbon core wire T such as an intermittently fixed ribbon core wire, and can be changed as appropriate. In addition, the number of optical fibers 11 included in the core 10 can be changed as appropriate as long as it is one or more.

[0018] The pressure wrap 12 may be made of nonwoven fabric, polyester tape, or the like. Alternatively, the pressure wrap 12 may be made of a water-absorbent tape obtained by imparting water-absorbency to nonwoven fabric, polyester tape, or the like. In this case, the waterproof performance of the optical fiber cable 1 can be improved. The core 10 does not necessarily have to have the pressure wrap 12.

[0019] The outer shape of the outer jacket 20 according to this embodiment is substantially circular in cross section, except for the protrusions 22 described later. The material of the outer jacket 20 may be a polyolefin (PO) resin such as polyethylene (PE), polypropylene (PP), ethylene ethyl acrylate copolymer (EEA), ethylene vinyl acetate copolymer (EVA), ethylene propylene copolymer (EP), polyvinyl chloride (PVC), or the like. The outer jacket 20 may be formed using a mixture (alloy, mixture) of the above resins. Various additives may be added to the outer jacket 20 depending on the purpose. Examples of additives include flame retardants, colorants, deterioration inhibitors, inorganic fillers, and the like.

[0020] The ripcords 30 are members used to tear the jacket 20. In the illustrated example, each ripcord 30 is provided adjacent to the core 10. The ripcords 30 may be made of a synthetic fiber (such as polyester) thread or a cylindrical rod made of polypropylene (PP) or nylon. A pair of ripcords 30 according to this embodiment are arranged to sandwich the core 10 therebetween in the radial direction. The number of ripcords 30 may be one, or three or more. The arrangement of the ripcords 30 is not limited to the illustrated example and can be changed as appropriate. The optical fiber cable 1 does not need to have a ripcord 30.

[0021] The jacket 20 according to this embodiment is provided with a pair of protrusions 22 that protrude radially outward from the outer circumferential surface of the jacket 20. The positions of the protrusions 22 in the circumferential direction correspond to the position of the ripcord 30. The protrusions 22 serve as a mark that allows the user to easily recognize the position of the ripcord 30 from outside the optical fiber cable 1. The jacket 20 does not have to have the protrusions 22. In this case, the protrusions 22 may be replaced by linear coloring of the jacket 20. However, the jacket 20 does not have to have the protrusions 22 and the jacket 20 does not have to be colored.

[0022] The tension body 40 is a member having a higher Young's modulus in the longitudinal direction than the jacket 20. When tension is applied to the optical fiber cable 1 in the longitudinal direction, the tension body 40 has a role of receiving the tension and protecting the optical fiber 11. The tension body 40 may be made of, for example, a metal wire (steel wire, etc.), a material in which metal wires are bundled, glass fiber, or a material in which glass fibers are bundled. Alternatively, the tension body 40 may be made of fiber reinforced plastic (FRP), for example, aramid fiber reinforced plastic (A-FRP), etc.

[0023] The four strength members 40 according to this embodiment are arranged at intervals in the circumferential direction so as to surround the core 10 from the radial outside. Hereinafter, the four strength members 40 may be referred to as the first strength member 40A, the second strength member 40B, the third strength member 40C, and the fourth strength member 40D in the circumferential direction. In the illustrated example, each strength member 40 is located radially outward from the ripcord 30. The positions of each strength member 40 and each ripcord 30 are offset from each other in the circumferential direction. Each strength member 40 is in contact with the outer jacket 20 both radially outward and radially inward. However, the number and arrangement of the strength members 40 are not limited to the illustrated example and can be changed as appropriate. For example, the strength members 40 may be arranged in the core 10 instead of the outer jacket 20. Alternatively, the strength members 40 may be arranged in both the outer jacket 20 and the core 10. Furthermore, depending on the application of the optical fiber cable, the optical fiber cable 1 may not have the tension members 40.

[0024] A plurality of slits 21 are formed in the jacket 20. Each slit 21 extends in the circumferential direction. The slit 21 according to the present embodiment has an arc shape in cross-sectional view. The inside of each slit 21 according to the present embodiment is filled with an air layer. In other words, nothing is disposed inside each slit 21. In the present embodiment, each slit 21 is connected to one of the four strength members 40A to 40B in the circumferential direction. In other words, each slit 21 extends from one of the four strength members 40A to 40B in the circumferential direction. Note that the jacket 20 may have a slit 21 that is not connected to a strength member 40. The optical fiber cable 1 may also have a strength member 40 to which no slit 21 is connected.

[0025] In this embodiment, one slit 21 is connected to each of both sides of each of the reinforcing members 40A to 40B in the circumferential direction. As a result, eight slits 21 are formed in the sheath 20 according to this embodiment. For example, the first reinforcing member 40A is connected to the first reinforcing member 40A from the side opposite to the first slit 21A. In other words, the second slit 21B is located on the side opposite to the first slit 21A as viewed from the first reinforcing member 40A. The first slit 21A is located between the first reinforcing member 40A and the second reinforcing member 40B in the circumferential direction. The second slit 21B is located between the first reinforcing member 40A and the fourth reinforcing member 40D in the circumferential direction.

[0026] The optical fiber cable 1 having the above-mentioned slit 21 can be manufactured, for example, by the following method. However, the method for manufacturing the optical fiber cable 1 is not limited to the following method and can be changed as appropriate.

[0027] First, a portion of the optical fiber cable 1 that is radially inward from the slit 21 is manufactured. For example, extrusion molding is performed in a state in which the ripcord 30 is vertically attached to the core 10. As a result, a portion of the jacket 20 that is radially inward from the slit 21 is formed.

[0028] Next, a portion of the optical fiber cable 1 that is radially outward from the slit 21 is manufactured. For example, extrusion molding is performed again in a state in which the tensile member 40 is vertically attached to the structure formed by the above extrusion molding. This forms a portion of the jacket 20 that is radially outward from the slit 21. With the above, the manufacture of the optical fiber cable 1 is completed.

[0029] Next, the operation of the optical fiber cable 1 configured as above will be described.

[0030] Conventionally, there has been known an optical fiber cable including a core 10' having an optical fiber 11', an outer jacket 20' covering the core 10', and a tension member 40' arranged in the outer jacket 20' as shown in Fig. 2A (see, for example, Patent Document 1). The optical fiber cable 1' may be subjected to impact or lateral pressure.

[0031] Specifically, when an impact or lateral pressure acts on the optical fiber cable 1', a crack C may occur in the jacket 20' extending radially outward from the core 10'. In the optical fiber cable 1' having the strength members 40', the crack C is particularly likely to occur connecting the core 10' and the strength members 40' in the radial direction.

[0032] Here, the crack C may widen due to deformation of the jacket 20' caused by the impact or lateral pressure, and the optical fiber 11' may enter the crack C. When the impact or lateral pressure acting on the optical fiber cable 1' in this state is eliminated, the restoring force F of the jacket 20' closes the crack C, and the optical fiber 11' becomes pinched in the crack C. This may increase the transmission loss of the optical fiber cable 1'. Depending on the magnitude of the restoring force F, the optical fiber 11' may also be damaged.

[0033] To address such problems, in the optical fiber cable 1 according to this embodiment, a slit 21 extending in the circumferential direction is formed in the slit 21 (see FIG. 1). As a result, when an impact or lateral pressure acts on the optical fiber cable 1, a crack C is likely to occur that starts from the slit 21 and propagates in the circumferential direction. In other words, the slit 21 can guide the direction in which the crack C propagates in the circumferential direction. As a result, the crack C that opens in the core 10 is less likely to occur, and an increase in the transmission loss of the optical fiber cable 1 caused by the optical fiber 11 being caught in the crack C can be suppressed.

[0034] Even if a crack C extending in the radial direction occurs, an increase in the transmission loss of the optical fiber cable 1 can be suppressed by the following principle.

[0035] FIG. 2B is a diagram showing a state in which a crack C radially connecting the core 10 and the tension member 40 occurs in the optical fiber cable 1 according to the present embodiment. The circumferentially extending slit 21 is formed in the jacket 20, so that the restoring force F (see FIG. 2A) of the jacket 20 is distributed to the radially outer side (restoring force F1) and the radially inner side (restoring force F2) of the slit 21. By distributing the restoring force F in this manner, the force (i.e., restoring force F2) that tries to close the crack C is weakened compared to the case in which the restoring force F is not distributed. Therefore, the optical fiber 11 is less likely to be pinched in the crack C, and an increase in the transmission loss of the optical fiber cable 1 can be suppressed. Even if the optical fiber 11 is pinched in the crack C, the force that pinches the optical fiber 11 (i.e., restoring force F2) is smaller compared to the case in which the restoring force F is not distributed. Therefore, an increase in the transmission loss of the optical fiber cable 1 can be suppressed compared to the case in which the slit 21 of the jacket 20 is not formed.

[0036] As described above, the optical fiber cable 1 according to this embodiment includes the core 10 having the optical fiber 11, and the jacket 20 in which the first slit 21A extending in the circumferential direction is formed and which covers the core 10.

[0037] With this configuration, an increase in transmission loss in the optical fiber cable 1 can be suppressed.

[0038] The optical fiber cable 1 further includes a first tensile member 40A disposed in the jacket 20, and the first slit 21A is connected to the first tensile member 40A in the circumferential direction. In the optical fiber cable 1 having the tensile member 40, cracks C originating from the tensile member 40 are particularly likely to occur. By providing the slit 21 near the tensile member 40, which is a portion of the jacket 20 where cracks C are particularly likely to occur, an increase in transmission loss of the optical fiber cable 1 can be more reliably suppressed.

[0039] Further, the jacket 20 has a second slit 21B extending in the circumferential direction, and the second slit 21B is connected to the first strength member 40A from the side opposite to the first slit 21A. That is, the slit 21 is provided on both sides of the strength member 40 in the circumferential direction. With this configuration, the slit 21 can be provided on both sides of the strength member 40, which is a portion of the jacket 20 where cracks C are particularly likely to occur. This makes it possible to more reliably suppress an increase in transmission loss of the optical fiber cable 1.

[0040] Moreover, the inside of the first slit 21 A is filled with an air layer. In other words, nothing is disposed inside the first slit 21 A. With this configuration, the weight of the optical fiber cable 1 can be reduced.

[0041] Second embodiment Next, a second embodiment of the present invention will be described, but the basic configuration is the same as that of the first embodiment. For this reason, the same reference numerals are used for the similar configurations, and the description thereof is omitted, and only the differences are described. Note that the features of the first embodiment are also applicable to the second embodiment to the extent that they do not impair the features of the second embodiment.

[0042] The optical fiber cable 2 according to the second embodiment (see FIG. 3) is different from the optical fiber cable 1 according to the first embodiment (see FIG. 1) in the number and arrangement of the slits 21. As shown in FIG. 3, two slits 21 are formed in the jacket 20 according to the present embodiment.

[0043] One slit 21 extends in the circumferential direction so as to connect the first tensile body 40A and the fourth tensile body 40D. The other slit 21 extends in the circumferential direction so as to connect the second tensile body 40B and the third tensile body 40C. No slit 21 is arranged between the third tensile body 40C and the fourth tensile body 40D in the circumferential direction. No slit 21 is arranged between the first tensile body 40A and the second tensile body 40B in the circumferential direction. In this way, the slit 21 may be connected to only one side in the circumferential direction in each tensile body 40.

[0044] Moreover, each slit 21 is disposed at a position overlapping with the ripcord 30 in the radial direction. The portion of the sheath 20 where the ripcord 30 is disposed has a smaller thickness (diameter) than the other portions of the sheath 20, or the sheath 20 has a recessed shape. Therefore, the portion of the sheath 20 where the ripcord 30 is disposed is more likely to develop a crack C than the other portions of the sheath 20. By disposing the slit 21 at a position overlapping with the ripcord 30 in the radial direction, the slit 21 is disposed in the portion of the sheath 20 where the crack C is likely to develop, and an increase in the transmission loss of the optical fiber cable 2 can be more reliably suppressed. More specifically, by disposing the slit 21 at a position overlapping with the ripcord 30 in the radial direction, an impact applied to the portion of the sheath 20 where the ripcord 30 is disposed is buffered by the slit 21 and dispersed in the circumferential direction by the slit 21. As a result, the crack C extending radially from the ripcord 30 is less likely to develop, and an increase in the transmission loss of the optical fiber cable 2 can be more reliably suppressed.

[0045] Third embodiment Next, a third embodiment of the present invention will be described, which has the same basic configuration as the first embodiment. For this reason, the same reference numerals are used for the same configurations, and the description thereof is omitted, and only the differences are described. Note that the features of the first and second embodiments are also applicable to the third embodiment to the extent that they do not impair the features of the third embodiment.

[0046] The optical fiber cable 3 according to the third embodiment (see FIG. 4) and the optical fiber cable 1 according to the first embodiment (see FIG. 1) have different shapes of the slits 21. As shown in FIG. 4, the slits 21 according to this embodiment have a notch shape extending from the strength members 40. In this embodiment, one slit 21 is connected to each strength member 40. As a result, the strength members 40 and the slits 21 are arranged alternately in the circumferential direction. Also, compared to the optical fiber cable 1 according to the first embodiment, the number of strength members 40 is greater (detailed illustration is omitted), and the distance between the strength members 40 in the circumferential direction is smaller.

[0047] Specifically, the slit 21 according to this embodiment has a triangular shape in cross section with a radial dimension decreasing from the base end 21a to the tip end 21b. The base end 21a is an end of the slit 21 that contacts the tensile member 40 (first tensile member 40A) in the circumferential direction. The tip end 21b is an end of the slit 21 that is located on the opposite side to the base end 21a in the circumferential direction.

[0048] In this embodiment, the center line L of the slit 21 connected to a certain tensile member 40 passes through a tensile member 40 adjacent to the tensile member 40 in the cross-sectional view. For example, the center line L of the first slit 21A connected to the first tensile member 40A passes through the second tensile member 40B adjacent to the first tensile member 40A. In other words, the center line L of the first slit 21A does not intersect with either of the two line segments L1 and L2 circumscribing both of the two tensile members 40A and 40B. The center line L of the slit 21 is defined as a straight line connecting the center P1 of the base end portion 21a and the center P2 of the tip end portion 21b in the cross-sectional view.

[0049] By arranging the slit 21 so that the center line L passes through the adjacent tensile member 40, the crack C easily progresses from the slit 21 to the adjacent tensile member 40. For example, the crack C generated in the first slit 21A of the first tensile member 40A easily progresses to the second tensile member 40B. This makes it difficult for the crack C to reach the core 10, and it is possible to suppress an increase in the transmission loss of the optical fiber cable 3 caused by the optical fiber 11 being pinched in the crack C.

[0050] 4, the slits 21 are formed only on one side in the circumferential direction of each of the strength members 40, but the slits 21 may be formed on both sides in the circumferential direction of the strength members 40. In this case, the center lines L of the slits 21 formed on both sides may pass through the adjacent strength members 40.

[0051] As described above, the optical fiber cable 3 according to the present embodiment further includes the second tension member 40B disposed in the jacket 20, the first slit 21A is located between the first tension member 40A and the second tension member 40B in the circumferential direction, the first slit 21A has a base end 21a in contact with the first tension member 40A and a tip end 21b located on the opposite side of the base end 21a in the circumferential direction, and in the cross-sectional view, a straight line connecting the center P1 of the base end 21a and the center P2 of the tip end 21b (center line L of the first slit 21A) passes through the second tension member 40B. This configuration can suppress an increase in transmission loss of the optical fiber cable 3 caused by the optical fiber 11 being pinched in the crack C.

[0052] 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.

[0053] For example, an inclusion may be disposed inside the slit 21 (for example, the first slit 21A). An example of the inclusion is a waterproof material. By disposing an inclusion inside the slit 21, it is possible to impart a function corresponding to the type of inclusion to the optical fiber cables 1 to 3. In addition, the jacket 20 may be formed with both slits 21 with an inclusion disposed therein and slits 21 with nothing disposed therein (i.e., filled with an air layer). A different inclusion may be disposed in each slit 21.

[0054] Furthermore, a self-supporting wire for supporting the optical fiber cable 1 may be provided on the outside of the optical fiber cable 1 (sheath 20).

[0055] Furthermore, the configuration of the core 10 is not limited to the example of the embodiment, and can be changed as appropriate. For example, a plurality of optical fibers 11 may be bundled together to form an optical fiber unit, and the core 10 may be formed by bundling the plurality of optical fiber units. Examples of optical fiber cables other than those of the embodiment include loose tube cables and slotted cables. In an optical fiber cable that is a loose tube cable, a bundle of tubes in which the optical fibers 11 are housed corresponds to the core 10. In an optical fiber cable that is a slotted cable, the entire spacer provided with the slots in which the optical fibers 11 are housed corresponds to the core 10. In other words, the entire set of optical fibers 11 housed in the optical fiber cable can be regarded as the core 10.

[0056] 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]

[0057] 1, 2, 3... Optical fiber cable 10... Core 11... Optical fiber 20... Sheath 21A... First slit 21B... Second slit 21a... Base end portion 21b... Tip portion 40A... First tension member 40B... Second tension member L... Center line (straight line)

Claims

1. a core having an optical fiber; A first slit extending in a circumferential direction is formed, and an outer cover covering the core is provided. Fiber optic cable.

2. A first tension member is disposed in the outer cover, The first slit is connected to the first tension member in a circumferential direction.

2. The optical fiber cable according to claim 1.

3. A second slit is formed in the outer cover and extends in a circumferential direction. The second slit is connected to the first tensile member from a side opposite to the first slit in the circumferential direction.

3. The optical fiber cable according to claim 2.

4. Further comprising a second tension member disposed in the outer cover, the first slit is located between the first tension member and the second tension member in the circumferential direction, the first slit has a base end portion in contact with the first tension member and a tip end portion located on the opposite side to the base end portion in the circumferential direction, In a cross-sectional view, a straight line connecting the center of the base end portion and the center of the tip end portion passes through the second tensile member.

4. The optical fiber cable according to claim 2 or 3.

5. The inside of the first slit is filled with an air layer.

4. The optical fiber cable according to claim 1 .

6. An inclusion is disposed inside the first slit.

4. The optical fiber cable according to claim 1 .

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