Optical fiber cable and method of installing same

Abstract

An optical fiber cable (1) is provided with: an optical fiber unit (10) that includes at least one optical fiber (11); and a deployment unit (20) that is formed in a tubular shape for accommodating the optical fiber unit (10) inside, is peelably adhered to the optical fiber unit (10), and is stretchable in the radial direction and the circumferential direction.

Description

Optical fiber cable and method of laying the same

[0001] The present disclosure relates to an optical fiber cable and a method of laying the same.

[0002] It is known that optical fibers are optimal for long-distance, large-capacity communication due to their low transmission loss. An optical fiber cable including such optical fibers is laid outdoors in infrastructure facilities such as underground conduits. When laying an optical fiber cable in a conduit, an end portion or an intermediate portion of the optical fiber cable is pulled within the conduit (see Patent Document 1).

[0003] Japanese Patent Application Laid-Open No. 57-192903

[0004] In order to suppress connection loss in a transmission path, it is desirable to lay an optical fiber cable as long as possible. On the other hand, from the viewpoint of ensuring reliability, the maximum allowable tension is specified for optical fiber cables. When an optical fiber cable is pulled for laying, frictional force applied to the cable accumulates in accordance with the laying distance. If the laying distance is excessively long, the tension on the leading end side of the optical fiber cable in the pulling direction exceeds the maximum allowable tension. That is, the increase in tension caused by frictional force is one of the factors that limit the extension of the laying distance of an optical fiber cable.

[0005] An object of the present disclosure is to provide an optical fiber cable capable of suppressing frictional force generated during laying and a method of laying the same.

[0006] An optical fiber cable according to an aspect of the present disclosure includes: an optical fiber unit including at least one optical fiber; and an advancing portion that extends along the extending direction of the optical fiber unit, is formed in a tubular shape that accommodates the optical fiber unit inside, and has elasticity that allows the inner surface of the advancing portion to be turned radially outward. The inner surface of the advancing portion is releasably in close contact with the optical fiber unit.

[0007] A method according to one aspect of the present disclosure is a method for laying an optical fiber cable comprising an optical fiber unit including at least one optical fiber, and an extension portion that extends along the extension direction of the optical fiber unit and is formed in a tubular shape to house the optical fiber unit on the inside, and is peelably attached to the optical fiber unit, wherein a fluid is pumped from the outside of the conduit towards the inside of the conduit so as to press the peeled extension portion, while the opening of the extension portion, which has been peeled from the optical fiber unit, is in close contact with the inner surface of the conduit over its entire circumferential area.

[0008] According to this disclosure, it is possible to provide an optical fiber cable and a method for laying the same that can suppress the frictional force generated during installation.

[0009] Figure 1 is a side view of an optical fiber cable according to one embodiment of the present disclosure. Figure 2 is a cross-sectional view of an example of an optical fiber cable viewed from the axial direction. Figure 3A is a diagram showing the initial state in which the optical fiber cable is fixed to a conduit. Figure 3B is a cross-sectional view taken along line A-A in Figure 3A. Figure 4A is a diagram illustrating one step in the method of laying an optical fiber cable according to the embodiment. Figure 4B is a diagram illustrating one step in the method of laying an optical fiber cable according to the embodiment. Figure 4C is a diagram illustrating one step in the method of laying an optical fiber cable according to the embodiment. Figure 5 is a cross-sectional view of an optical fiber cable according to a first modified example of the embodiment, viewed from the radial direction. Figure 6 is a cross-sectional view of an optical fiber cable according to a second modified example of the embodiment, viewed from the radial direction.

[0010] Several embodiments of this disclosure will be described below. First, an optical fiber cable 1 according to an embodiment will be described. In each figure, common parts are denoted by the same reference numerals, and redundant explanations will be omitted. Also, for the sake of convenience of explanation, the axial direction, circumferential direction, and radial direction will be defined. The axial direction is the direction of extension of the central axis Z, and is the direction of extension of the optical fiber cable 1 and the conduit 30. The circumferential direction and radial direction are defined with respect to the central axis Z.

[0011] Figure 1 is a side view of the optical fiber cable 1. Figure 2 is a cross-sectional view of the optical fiber cable 1. As shown in Figure 1, the optical fiber cable 1 comprises an optical fiber unit 10 and an extension portion 20. The optical fiber unit 10 extends in the Z direction with respect to its central axis Z. The extension portion 20 also extends in the Z direction with respect to its central axis. The extension portion 20 is located radially outside the optical fiber unit 10 and covers the optical fiber unit 10 from the radial outside.

[0012] As shown in Figure 2, the optical fiber unit 10 includes at least one optical fiber 11. The optical fiber 11 is an optical fiber with a well-known configuration. The operating mode (propagation mode), number of cores, and core structure of the optical fiber can also be arbitrarily set. If the optical fiber unit 10 includes multiple optical fibers 11, the multiple optical fibers 11 may be bundled together by a strip-shaped or thread-shaped linear member (not shown). The linear member is formed, for example, from a synthetic resin film or fiber.

[0013] The optical fiber unit 10 may include an outer sheath 12. The outer sheath 12 is a tubular member extending in the Z direction and protects the optical fiber 11 from the radially outer side. The outer sheath 12 is formed of, for example, a well-known synthetic resin. The tubular outer sheath 12 has an inner circumferential surface 12a facing radially inward and an outer circumferential surface 12b facing radially outward. The outer sheath 12 may be composed of a single layer or a multilayer structure. As described later, the inner surface (back surface) 20a of the extension portion 20 adheres peelably to the outer circumferential surface 12b.

[0014] The extension portion 20 is a tubular member that is concentric with the optical fiber unit 10 and extends in the Z direction. The extension portion 20 is located radially outside the optical fiber unit 10 and covers the outer circumference of the optical fiber unit 10. In other words, the extension portion 20 houses the optical fiber unit 10 radially inside it. Furthermore, the extension portion 20 is configured to be reversible. That is, the extension portion 20 has the flexibility (flexibility, stretchability) and thickness to be reversible.

[0015] The extension portion 20 is peelably attached to the outer circumferential surface 10b of the optical fiber unit 10. For example, the inner surface 20a of the extension portion 20 is peelably attached to the outer circumferential surface 12b of the outer sheath 12. The extension portion 20 may be peelably attached to the outer circumferential surface 12b of the outer sheath 12 by utilizing the thermal shrinkage that occurs during its formation. Alternatively, the extension portion 20 may be peelably attached by interposing an adhesive (not shown) between the inner surface 20a of the extension portion 20 and the outer circumferential surface 12b of the outer sheath 12. Specifically, for example, the inner surface 20a of the extension portion 20 itself may have a surface formed of an adhesive material, or an adhesive (not shown) may be applied to the inner surface 20a. In this case, the detached extension portion 20 (i.e., the second portion 24b described later) can be attached to the inner circumferential surface of the conduit 30 in the state shown in Figures 4B and 4C.

[0016] As described later, when laying the optical fiber cable 1 inside the conduit 30, the end (open end) 21 of the extension portion 20 is separated from the optical fiber unit 10 and stretched in the radial and circumferential directions. Then, the end 21 (or a portion of the end 21) adheres tightly to the inner circumferential surface 30a of the conduit 30 over its entire circumferential area.

[0017] Because such a process is necessary, the extension portion 20 has elasticity in at least the radial and circumferential directions. For example, the extension portion 20 is formed of an elastic material such as an elastomer. That is, the extension portion 20 has elasticity obtained from its material.

[0018] The expandability of the extension portion 20 may be obtained by its shape (structure). That is, the extension portion 20 may be folded so as to have multiple expandable folds in the axial, radial, and circumferential directions (see Figure 5). However, in both of the above examples, the permeability of the extension portion 20 to the fluid 50 (see Figures 3A and 3B) is zero or extremely low. This prevents the fluid 50 (see Figures 3A and 3B) from passing excessively through the extension portion 20 during pumping.

[0019] Next, a method for laying the optical fiber cable 1 according to this embodiment will be described. Figure 3A shows the initial state in which the optical fiber cable 1 is fixed to the conduit 30. Figure 3B is a cross-sectional view taken along line A-A in Figure 3A. Figures 4A to 4C illustrate each step in the method for laying the optical fiber cable 1 according to this embodiment.

[0020] In this installation method, the optical fiber cable 1 is laid in a conduit 30. The conduit 30 is a tubular member that extends in the axial direction. The inner diameter of the conduit 30 is larger than the outer diameter of the optical fiber cable 1 before the extension portion 20 is unfolded. The material of the conduit 30 is arbitrary and can be, for example, metal (alloy) or resin. The conduit 30 may also have through holes (not shown) formed on its side. The conduit 30 may be installed horizontally or vertically. The conduit 30 may also be inclined with respect to these directions. Furthermore, the conduit 30 may extend in a straight line or curved.

[0021] As shown in Figure 3A, the optical fiber cable 1 is drawn out from the drum 40 on which the optical fiber cable 1 is wound. The optical fiber cable 1 is then attached to the inner circumferential surface 30a of the conduit 30 via the extension portion 20.

[0022] Specifically, the end portion 21 of the extension portion 20 is detached from the optical fiber unit 10. Next, the detached end portion 21 is folded back in the opposite direction to the insertion direction of the optical fiber cable 1 and made to adhere tightly to the inner surface 30a of the conduit 30 over its entire circumference (see Figure 3B). That is, the end portion 21 is fixed to the inner surface 30a so that the fluid 50 (see Figure 4A), which will be described later, does not leak into the internal space at the back of the conduit 30. The portion of the extension portion 20 that has been detached from the optical fiber unit 10 constitutes the sealing portion 22. In the state shown in Figure 3A, the opening of the conduit 30 is sealed by the sealing portion 22.

[0023] When attaching the end portion 21 of the extension portion 20 to the inner circumferential surface 30a of the conduit 30, the extension portion 20 may be inverted (or folded over) so that the inner surface 20a of the extension portion 20 faces radially outward, as shown in Figure 3A. In this case, the inner surface 20a of the extension portion 20 comes into contact with the inner circumferential surface 30a of the conduit 30. For the sake of explanation, the portion of the sealing portion 22 that extends from the optical fiber unit 10 to the inner circumferential surface 30a of the conduit 30 (i.e., the folded portion) will be referred to as the folded portion 22a.

[0024] The end portion 21 of the extension portion 20 is fixed to the inner circumferential surface 30a of the conduit 30 using a fixing member 35. This constitutes the sealing portion 22 described above. The fixing member 35 is, for example, an adhesive. Alternatively, the fixing member 35 may be a metallic or resin ring capable of pressing the extension portion 20 toward the inner circumferential surface 30a of the conduit 30.

[0025] Next, as shown in Figure 4A, with the end portion 21 of the extension portion 20 in close contact with the inner circumferential surface 30a of the conduit 30, fluid 50 is pumped from the outside of the conduit 30 toward the inside of the conduit 30. As a result, the folded portion 22a of the sealing portion 22 is pressed toward the inside of the conduit 30 and moves toward the inside of the conduit 30. At this time, the extension portion 20 that has detached from the optical fiber unit 10 moves radially outward while reversing at the folded portion 22a, and approaches the inner circumferential surface 30a of the conduit 30. In this way, the detachment of the extension portion 20 from the optical fiber unit 10 progresses.

[0026] As shown in Figure 4B, as the peeling of the extension portion 20 progresses, the optical fiber unit 10 is dragged into the conduit 30 and protrudes from the extension portion 20. Then, as shown in Figure 4C, when the folded portion 22a reaches a predetermined position in the conduit 30 (for example, the opposite end of the conduit 30), the pumping of the fluid 50 is stopped. As a result, the optical fiber cable 1 is laid in the desired range within the conduit 30.

[0027] As the extension section 20 unfolds, the optical fiber unit 10, which is in close contact with the extension section 20, moves through the conduit 30. The extension section 20 basically only contacts the inner circumferential surface 30a of the conduit 30 and does not slide on the inner circumferential surface 30a. As a result, no resistance due to dynamic friction is generated. Furthermore, the force required for the advancement of the optical fiber unit 10 is obtained from the total length of the portion in which the optical fiber unit 10 and the extension section 20 are in close contact. Therefore, the tension applied to the optical fiber 11 remains constant regardless of the laying distance. In other words, the frictional force between the optical fiber cable 1 and the conduit 30 is suppressed, and the laying distance of the optical fiber cable 1 within the maximum allowable tension range can be increased.

[0028] Furthermore, while the fluid 50 is being pumped, the optical fiber unit 10 may be pulled from the downstream side in the direction of pumping the fluid 50. Pulling the optical fiber unit 10 assists in the movement of the optical fiber unit 10 due to the pumping of the fluid 50. This makes it possible to reduce the pressure applied to the fluid 50 during pumping. In addition, the thickness of the extension portion 20 can be reduced, making the optical fiber cable 1 lighter. Also, since the movement of the optical fiber unit 10 can be promoted, the adhesion strength between the optical fiber unit 10 and the extension portion 20 can be reduced.

[0029] Figure 4C shows the optical fiber cable laying structure according to this embodiment. As shown in Figure 4C, the extension portion 20 can be classified into a first portion 24a and a second portion 24b by inversion. That is, the first portion 24a is the portion of the extension portion 20 that is in close contact with the optical fiber unit 10. On the other hand, the second portion 24b is the portion of the extension portion 20 that is folded back from the first portion 24a and inverted, and is located radially outside the first portion 24a. The optical fiber unit 10 is then pulled out (exposed) to the outside of the optical fiber cable 1 from the position where the extension portion 20 is folded back from the first portion 24a to the second portion 24b (i.e., the folded portion 22a). After the pumping of the fluid 50 is completed, the fluid 50 may be discharged from the conduit 30 or may remain inside the conduit 30.

[0030] When the conduit 30 is arranged horizontally, the portion of the optical fiber cable 1 where the optical fiber unit 10 and the extension portion 20 (first portion) are in close contact with each other may sag due to gravity and come into contact with the extension portion 20 (second portion) below it. To avoid this contact, the extension portion 20 may have bending rigidity that makes it difficult for the aforementioned sagging to occur.

[0031] Furthermore, a low-friction member (not shown) made of a material such as fluororesin may be interposed between the first portion 24a and the second portion 24b in the radial direction. This low-friction member is, for example, a tubular member surrounding the outer circumference of the first portion 24a, and reduces friction between the first portion 24a and the second portion 24b. The low-friction member may be inserted between the first portion 24a and the second portion 24b after the fluid has been pumped, or it may be provided in advance on the outer circumference of the extension portion 20 and folded back together with the extension portion 20 when the fluid 50 is pumped.

[0032] The fluid 50 may be a liquid or a gas. If the fluid 50 is a liquid, the liquid may have a specific gravity similar to (for example, identical to) that of the composite of the extension portion 20 and the optical fiber unit 10. This reduces the opportunities for the first portion 24a and the second portion 24b to come into contact with each other due to gravity, and also reduces the frictional force when they do come into contact, thereby suppressing an increase in stress generated in the optical fiber cable 1.

[0033] If the fluid 50 is a liquid, it may have lubricating properties. For example, the fluid 50 may be a lubricating oil such as silicone oil. By using a lubricating liquid for the fluid 50, the frictional force when the first part 24a and the second part 24b come into contact can be reduced.

[0034] Figure 5 is a cross-sectional view of the optical fiber cable 1 according to the first modified example of this embodiment. The extension portion 20 may be configured such that its length after unfolding along the axial direction is longer than its length before unfolding. That is, as described above, the extension portion 20 may be folded so as to have a plurality of unfoldable folds in the axial, radial, and circumferential directions, respectively. For example, as shown in Figure 5, the extension portion 20 may have a bellows structure that extends along the extension direction of the optical fiber unit 10 while meandering in the radial direction.

[0035] In the first modified example, the inner surface 20a of the extension portion 20 is radially meandering and adheres to the optical fiber unit 10 in a peelable manner at the position closest to the optical fiber unit 10. In this case, the extension portion 20 may also be formed of an expandable material.

[0036] As shown in Figure 4C, when the optical fiber cable 1 is laid in the conduit 30, the extension portion 20 travels back and forth along the conduit 30. Therefore, the distance traveled by the extension portion 20 per unit length along the axial direction is shorter than the distance traveled by the optical fiber unit 10 along the same direction. Consequently, as the optical fiber cable 1 advances, the protruding length of the optical fiber unit 10 from the folded portion 22a increases.

[0037] Therefore, the extension portion 20 according to the first modified example is configured such that its length after unfolding along the axial direction is longer than that before unfolding, by employing a bellows structure or the like. As a result, the length of the extension portion 20 detached from the optical fiber unit 10 increases. Therefore, the difference in length between the detached extension portion 20 and the optical fiber unit 10 protruding from the folded portion 22a can be reduced. In other words, the increase in the protruding length of the optical fiber unit 10 relative to the unfolding of the extension portion 20 can be suppressed, and the utilization rate of the optical fiber cable 1 can be improved.

[0038] Figure 6 is a cross-sectional view of an optical fiber cable 1 according to a second modification of this embodiment. The outer circumferential surface 10b of the optical fiber unit 10 according to the second modification includes a plurality of protrusions 13. For example, if the optical fiber unit 10 includes an outer sheath 12, the plurality of protrusions 13 are formed on the outer circumferential surface 12b of the outer sheath. The plurality of protrusions 13 are provided at intervals along the extending direction of the optical fiber unit 10 and project radially outward (i.e., toward the extension portion 20). Each protrusion 13 may be formed as an annular shape extending in the circumferential direction, or it may be scattered at intervals in the circumferential direction. Each protrusion 13 may be formed with an adhesive that adheres peelably to the extension portion 20. Alternatively, if the optical fiber unit 10 includes an outer sheath 13, each protrusion 13 may be formed integrally with the outer sheath 13 using the same material as the outer sheath 13.

[0039] The multiple protrusions 13 improve the adhesion strength between the optical fiber unit 10 and the extension portion 20. Therefore, when laying the optical fiber cable 1 in the conduit 30, it is possible to suppress the occurrence of slippage of the extension portion 20 relative to the optical fiber unit 10. In other words, it is possible to suppress the reduction in the extension length of the optical fiber unit 10 caused by slippage between the two.

[0040] Furthermore, the inner surface 20a of the extension portion 20 according to the second modification may include a plurality of recesses 23 that can engage with each of the protrusions 13. In this case, the plurality of recesses 23 are provided on the inner surface 20a at the same intervals as the plurality of protrusions 13. Also, each recess 23 has a cross-sectional shape complementary to the protrusions 13. When the extension portion 20 unfolds, the protrusions 13 engage with the recesses 23, which further suppresses the occurrence of slippage of the extension portion 20 relative to the optical fiber unit 10. Therefore, the reduction in the extension length of the optical fiber unit 10 described above can be further suppressed.

[0041] This disclosure is not limited to the embodiments described above, but includes all modifications within the meaning and scope of the claims as indicated by the claims.

[0042] 1 Optical fiber cable 10 Optical fiber unit 11 Optical fiber 12 Outer sheath 13 Protrusion 20 Extension portion 22 Sealing portion 22a Folded portion 23 Recess 24a First portion 24b Second portion 30 Conduit 50 Fluid

Claims

1. An optical fiber cable comprising: an optical fiber unit containing at least one optical fiber; and an extension portion formed in a tubular shape that houses the optical fiber unit inside, is peelably attached to the optical fiber unit, and is expandable in the radial and circumferential directions.

2. The optical fiber cable according to claim 1, wherein the extension portion has a bellows structure that extends along the extension direction of the optical fiber unit while meandering in the radial direction.

3. The optical fiber cable according to claim 1 or 2, wherein the outer surface of the optical fiber unit is provided at intervals along the extending direction of the optical fiber unit and includes protrusions projecting radially outward.

4. A method for laying an optical fiber cable comprising an optical fiber unit containing at least one optical fiber, and an extension portion formed in a tubular shape that houses the optical fiber unit and is peelably attached to the optical fiber unit, wherein a fluid is pumped from outside the conduit towards the inside of the conduit so as to press the peeled extension portion against the inner surface of the conduit over its entire circumferential area.

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