Cable, sensing cable, and sensing system

Abstract

To obtain a cable, a sensing cable, and a sensing system that are further improved so that for example, a configuration that can detect a shape can be easily constructed.SOLUTION: A cable comprises for example a transmission line and a sensing cable installed separately from the transmission line. The sensing cable has: a plurality of sensing optical fibers having a core and a clad surrounding the core; and holding members for holding the plurality of sensing optical fibers in a state of being spaced apart from each other. The cable may also have a first holding member extending in a longer direction of the sensing cable as a holding member, and having a plurality of grooves each accommodating the sensing optical fiber.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a cable, a sensing cable, and a sensing system.

Background Art

[0002] Conventionally, optical fibers have been used to detect various physical quantities (see Patent Document 1).

[0003] In recent years, a technique has been developed for detecting the shape of a multi-core optical fiber in the longitudinal direction by detecting local bending in the longitudinal direction of the multi-core optical fiber (see Non-Patent Documents 1 to 3). When a cable is deformed at a certain bending radius, considering the fiber elongation and contraction at the cable center as a reference, the fiber located on the inner side of the bend shortens, and the fiber located on the outer side elongates. From the difference in the amount of fiber strain due to the difference in the position within the cross-section of the cable, it is possible to estimate in which direction and by how much the cable is deformed.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Non-Patent Documents

[0005]

Non-Patent Document 1

Non-Patent Document 2

[0006] Cables include power cables that contain power lines as transmission lines, communication cables that have communication lines such as optical fibers or metal wires as transmission lines, and composite cables that include optical fibers and power lines. There are various types of cables. In these cables, it is important to detect their shapes. For example, in a communication cable, due to the influence of the surrounding environment during or after laying, the shape of the cable may change, and this change in shape may affect the optical transmission characteristics of the internal optical fiber line. Also, a change in the shape of the cable may cause damage or breakage of the cable. With the diversification of cable types and their usage forms, the requirements for cable shape sensing are increasing.

[0007] In such cable shape sensing, for example, it would be beneficial to obtain improved cables, sensing cables, and sensing systems that can more easily construct configurations capable of detecting shapes.

Means for Solving the Problem

[0008] The cable of the present invention includes, for example, a transmission line and a sensing cable provided separately from the transmission line. The sensing cable has three or more sensing optical fibers each having a core and a cladding surrounding the core, and a holding member that holds the three or more sensing optical fibers at intervals from each other.

[0009] The cable may have, as the holding member, a first holding member that extends in the longitudinal direction of the sensing cable and is provided with a plurality of grooves for accommodating the sensing optical fibers respectively.

[0010] The cable may have, as the holding member, a plurality of second holding members provided with a plurality of holding portions for holding the sensing optical fibers respectively and spaced apart in the longitudinal direction of the sensing cable.

[0011] The cable may have, as the holding member, a third holding member that extends in the longitudinal direction of the sensing cable and fixes the plurality of second holding members.

[0012] The cable may have, as the holding member, a fourth holding member that extends in the longitudinal direction of the sensing cable in parallel with the sensing optical fiber.

[0013] The cable may have, as the fourth holding member, a fifth holding member that is displaced in the circumferential direction of the sensing optical fiber and the sensing cable.

[0014] The cable may have, as the fourth holding member, a sixth holding member that is located radially inside the sensing cable with respect to three or more sensing optical fibers.

[0015] In the cable, the sensing cable may have a joining member that joins the three or more sensing optical fibers or joins the sensing optical fiber and the holding member.

[0016] In the cable, in the sensing cable, the three or more sensing optical fibers may be arranged in a multiple spiral shape.

[0017] In the cable, the core included in at least one of the sensing optical fibers may include a fiber Bragg grating core in which the refractive index changes periodically in the longitudinal direction.

[0018] The cable may include, as the sensing cable, a first sensing cable that is arranged in a spiral shape in the cable.

[0019] The cable may include, as the sensing cable, a second sensing cable that extends along the first axis of the cable.

[0020] In the case of the cable, the first distance from the first axis of the cable to the second axis of the sensing cable and the second distance from the second axis to the third axis of the sensing optical fiber may be set such that the amount of strain of the sensing optical fiber at the allowable minimum bending radius of the cable is equal to or less than a predetermined threshold value.

[0021] In the case of the cable, the transmission line may be a power line.

[0022] In the case of the cable, the transmission line may be a communication line.

[0023] The sensing cable of the present invention has, for example, a core and a cladding surrounding the core, and includes three or more sensing optical fibers and a holding member that holds the three or more sensing optical fibers at intervals from each other.

[0024] The sensing cable of the present invention has, for example, a sensing optical fiber having a core and a cladding surrounding the core, and the sensing optical fiber has a plurality of sections that are folded back and extend in the longitudinal direction.

[0025] In the case of the sensing cable, the plurality of sections include a first section and a second section. In a cross section orthogonal to the second axis of the sensing cable, the first section is spaced apart from the second axis in a first direction intersecting the second axis, and the second section is located on the side opposite to the first section with respect to a virtual line extending in a second direction that passes through the second axis and is orthogonal to the first direction in the cross section.

[0026] In the case of the sensing cable, the plurality of sections may be arranged at positions that are substantially rotationally symmetric in a cross section orthogonal to the second axis of the sensing cable.

[0027] The cable-shaped sensing system of the present invention includes, for example, a light source unit that outputs test light input to the sensing optical fiber of the cable, a measurement unit that measures the backward scattered light generated due to each of the test lights and output from one end of each of the cores, and a calculation unit that calculates the strain of each of the cores based on the measurement results of the backward scattered light in the measurement unit and calculates the shape of the cable based on the calculated strains of each.

[0028] The cable-shaped sensing system of the present invention includes, for example, a light source unit that outputs test light input to the sensing optical fiber of the sensing cable, a measurement unit that measures the backward scattered light generated in the sensing optical fiber corresponding to the test light, and a calculation unit that divides the measurement result of the backward scattered light in the measurement unit into the measurement results of each of the intervals and calculates the shape of the sensing cable based on the measurement results of the plurality of intervals.

[0029] In the cable-shaped sensing system, each of the backward scattered lights may be Rayleigh scattered light, and the system may be configured to calculate the strain of each of the cores using the optical frequency domain reflectometry method.

[0030] In the cable-shaped sensing system, each of the backward scattered lights may be Brillouin scattered light, and the system may be configured to calculate the strain of each of the cores based on the measurement results of the Brillouin scattered light.

[0031] The cable-shaped sensing system may include an optical device that inputs test light to the sensing optical fiber and inputs the backward scattered light output from the plurality of intervals corresponding to the test light to the measurement unit.

[0032] The cable-shaped sensing system may include a test light transmission path that transmits the test light to the optical device, and a backscattered light transmission path that is provided separately from the test light transmission path and transmits the backscattered light from the optical device to the measurement unit.

[0033] The cable-shaped sensing system includes a plurality of sensing optical fibers as the sensing optical fibers, a pump light source that outputs pump light input to one end of the plurality of sensing optical fibers, and a probe light source that outputs probe light input to the other end of the plurality of sensing optical fibers. A light source unit having, a measurement unit that measures the probe light Brillouin amplified by the pump light in the plurality of sensing optical fibers, and the pump light and the probe light are respectively input to the plurality of sensing optical fibers, and the probe light from the plurality of sensing optical fibers is input to the measurement unit. An arithmetic unit that calculates the strain of each of the sensing optical fibers based on the measurement result of the probe light from the plurality of sensing optical fibers in the measurement unit, and calculates the shape of the sensing cable based on the calculated strain may be provided.

[0034] The cable-shaped sensing system includes a sensing optical fiber having at least four sections that are folded back at longitudinal ends and connected in series as the sensing optical fiber, a pump light source that outputs pump light input to one end of the sensing optical fiber, a probe light source that outputs probe light input to the other end of the sensing optical fiber, a light source unit having the same, a measuring unit that measures the probe light Brillouin amplified by the pump light in the sensing optical fiber, an optical device that inputs each of the pump light and the probe light to the sensing optical fiber and inputs the probe light from the one end of the sensing optical fiber to the measuring unit, and an arithmetic unit that divides the measurement result of the probe light from the sensing optical fiber in the measuring unit into the measurement results of each of the at least four sections, calculates the strain of each of the at least four sections, and calculates the shape of the sensing cable based on the calculated strain. It may be provided.

[0035] The cable-shaped sensing system may include a pump light transmission path that transmits the pump light to the optical device, a probe light transmission path that transmits the probe light to the optical device, and a backward propagation probe light transmission path that transmits the probe light output from the core from the optical device to the measuring unit, where the pump light transmission path and the probe light transmission path are separate.

[0036] In the cable-shaped sensing system, the temperature distribution in the longitudinal direction of the sensing cable may be obtained based on the measurement result by the measuring unit, and the calculated strain may be corrected based on the temperature distribution.

Effects of the Invention

[0037] According to the present invention, for example, a cable, a sensing cable, and a sensing system with improved performance can be obtained, such as being able to more easily construct a configuration capable of detecting the shape.

Brief Description of the Drawings

[0038]

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MODE FOR CARRYING OUT THE INVENTION

[0039] Exemplary embodiments and modifications of the present invention are disclosed below. The configurations of the embodiments and modifications shown below, as well as the operations and results (effects) brought about by the configurations, are examples. The present invention can be realized by configurations other than those disclosed in the following embodiments and modifications. Further, according to the present invention, it is possible to obtain at least one of various effects (including derivative effects) obtained by the configuration.

[0040] The embodiments and modifications shown below have the same configuration. According to the configurations of the respective embodiments and modifications, the same operations and effects based on the same configuration can be obtained. Further, in the following, the same reference numerals are given to those same configurations, and redundant explanations may be omitted.

[0041] In this specification, ordinal numbers are provided for convenience in distinguishing components, parts, etc., and do not indicate priority or order.

[0042] Also, in each of the following figures, for simplicity, the sensing cable may be shown as just a circle.

[0043] [First Embodiment] FIG. 1 is a cross-sectional view perpendicular to the longitudinal direction of the cable 10 of the first embodiment. The cable 10 is a composite cable with a circular cross-section, and includes a power line 1 which is a transmission line for transmitting power, an earth line 2, an optical fiber line 3 which is a communication line for transmitting optical signals, a sensing cable 4, an inner coating layer 5, a tension member 6, an outer coating layer 7, and a filling material 8. The power line 1, the earth line 2, the optical fiber line 3, the inner coating layer 5, the tension member 6, the outer coating layer 7, and the filling material 8 are structural materials that constitute the structure of the cable 10. In this embodiment, the cable 10 includes a plurality of power lines 1, one earth line 2, a plurality of optical fiber lines 3, one sensing cable 4, and a plurality of tension members 6. However, the number, thickness, configuration, and layout of the power line 1, the earth line 2, the optical fiber line 3, the sensing cable 4, and the tension member 6 are not limited to this example. The optical fiber line 3 is an example of a transmission line.

[0044] The power line 1 and the earth line 2 each have a stranded wire made of a conductor and an insulating coating made of resin or the like covering the outer periphery of the stranded wire. The three power lines 1 are twisted in a spiral shape in the longitudinal direction. Each optical fiber line 3 has a so-called glass optical fiber having a core and a cladding, and a coating made of synthetic resin or the like surrounding the periphery of the cladding. Note that each optical fiber line 3 may include a plurality of glass optical fibers.

[0045] The inner coating layer 5 is provided inside the cable 10. The inner coating layer 5 is configured to surround the power line 1, the ground line 2, the optical fiber line 3, and the sensing cable 4 with a resin or the like. The gap portion inside the inner coating layer 5 is filled with a filler 8 such as silicone.

[0046] A plurality of tension members 6 are arranged to surround the inner coating layer 5. Each tension member 6 has a steel wire, FRP, or the like, and protects the internal wire materials (mainly the power line 1 and the optical fiber line 3 which are transmission lines) from the external force applied to the cable 10. The outer coating layer 7 constitutes the outer periphery of the cable 10 and is, for example, a blade coating including a metal wire or the like.

[0047] Figure 2 is a cross-sectional view perpendicular to the longitudinal direction of the sensing cable 4. As shown in Figure 2, the sensing cable 4 has three sensing optical fibers 4a, an optical fiber 4b not used as the sensing optical fiber 4a, a tension member 4c, a coating layer 4d, and a bonding material 4f.

[0048] The sensing optical fiber 4a is a so-called glass optical fiber having a core 4a1 and a cladding 4a2. The sensing optical fiber 4a extends in the longitudinal direction of the sensing cable 4. Note that the sensing optical fiber 4a may have a coating made of, for example, a synthetic resin material and surrounding the cladding 4a2.

[0049] When cable 10 bends locally, sensing cable 4 also bends and deforms accordingly. As a result, the shape and strain distribution in the longitudinal direction of the plurality of sensing optical fibers 4a change according to the change in the shape of cable 10 in the longitudinal direction. Therefore, by detecting the strain distribution in the longitudinal direction of the plurality of sensing optical fibers 4a by the method disclosed in Non-Patent Documents 1 and 2, the shape of sensing cable 4 and thus the shape of cable 10 in the longitudinal direction can be detected. In this embodiment, sensing cable 4 is arranged at a position passing through the axis Ax1 of cable 10 and extends in the longitudinal direction of cable 10 along the axis Ax1. Axis Ax1 is an example of a first axis. Also, in this embodiment, sensing cable 4 is an example of a second sensing cable.

[0050] Optical fiber 4b is a so-called glass optical fiber having a core 4b1 and a cladding 4b2. Optical fiber 4b extends in the longitudinal direction of sensing cable 4. In this embodiment, optical fiber 4b has the same specifications as sensing optical fiber 4a, but is not limited thereto, and optical fiber 4b may have specifications different from those of sensing optical fiber 4a. Since optical fiber 4b is not used for communication or sensing, it may also be referred to as a dummy fiber. Note that optical fiber 4b may be made of, for example, a synthetic resin material and have a coating surrounding the cladding 4b2.

[0051] Tension member 4c is located at approximately the center of the cross-section of sensing cable 4 and extends in the longitudinal direction of sensing cable 4 at a position passing through the axis Ax2 along the axis Ax2 of sensing cable 4. Tension member 4c can be made of a steel wire, FRP, or the like. Note that tension member 4c may be made of, for example, a synthetic resin material and have a coating surrounding it. Axis Ax2 is an example of a second axis.

[0052] The plurality of sensing optical fibers 4a and the plurality of optical fibers 4b are arranged so as to surround the tension member 4c. In other words, the tension member 4c is arranged radially inside the sensing cable 4 with respect to the plurality of sensing optical fibers 4a and the plurality of optical fibers 4b.

[0053] Around the tension member 4c, the plurality of sensing optical fibers 4a and the plurality of optical fibers 4b are alternately arranged. That is, the optical fibers 4b are each arranged side by side with the sensing optical fibers 4a in the circumferential direction of the sensing cable 4. In other words, the optical fibers 4b are positioned offset in the circumferential direction of the sensing cable 4 with respect to the sensing optical fibers 4a. Also, the optical fibers 4b are each positioned between two sensing optical fibers 4a.

[0054] The coating layer 4d surrounds the plurality of sensing optical fibers 4a and the plurality of optical fibers 4b. The coating layer 4d can be made of, for example, a synthetic resin material.

[0055] The bonding material 4f is interposed between the sensing optical fiber 4a, the optical fiber 4b, the tension member 4c, and the coating layer 4d, and bonds the sensing optical fiber 4a, the optical fiber 4b, the tension member 4c, and the coating layer 4d. The bonding material 4f bonds the sensing optical fiber 4a and the components other than the sensing optical fiber 4a, and indirectly bonds a plurality of sensing optical fibers 4a. Further, the bonding material 4f may be provided over the entire longitudinal direction of the sensing cable 4, or may be provided partially at predetermined intervals in the longitudinal direction of the sensing cable 4. The bonding material 4f is, for example, a synthetic adhesive. Also, as the bonding material 4f, a fluororesin, a silicone resin, an ultraviolet curable resin, a polyethylene-based resin, a fluorine-based resin, a polyolefin-based resin, a polystyrene-based resin, a polypropylene-based resin, a polyurethane-based resin, a polyamide-based resin, a polyethylene terephthalate-based resin, a polyvinyl chloride-based resin, an ABS-based resin, etc. may be used. The bonding material 4f is an example of a bonding member. Note that the bonding material 4f may directly bond a plurality of sensing optical fibers 4a. Further, instead of the bonding material 4f, a filler may be filled between the sensing optical fiber 4a, the optical fiber 4b, the tension member 4c, and the coating layer 4d, or there may be no intervening member.

[0056] FIG. 3 is a schematic perspective view of a partial section of the sensing cable 4. In FIG. 3, only the shape of the sensing optical fiber 4a is shown, and illustration of components other than the sensing optical fiber 4a is omitted. As shown in FIG. 3, in the sensing cable 4, a plurality of sensing optical fibers 4a extend spirally while maintaining a predetermined interval around the axis Ax2 and the tension member 4c along the longitudinal direction of the sensing cable 4. That is, the plurality of sensing optical fibers 4a are arranged in a multi-helical shape. In the present embodiment, as an example, three sensing optical fibers 4a are arranged in a triple-helical shape. The tension member 4c extends along the axis Ax2. The optical fibers 4b extend spirally between the sensing optical fibers 4a, respectively. That is, the three optical fibers 4b are also arranged in a triple-helical (multi-helical) shape.

[0057] As is apparent from FIGS. 2 and 3, in each cross section orthogonal to the axis Ax2, the plurality of sensing optical fibers 4a have a predetermined positional relationship. In the present embodiment, they are arranged at substantially 120° intervals around the axis Ax2. In other words, they are arranged in a rotationally symmetric positional relationship at substantially equal intervals in the circumferential direction of the sensing cable 4. Further, as shown in FIG. 2, in the cross section orthogonal to the axis Ax2, the sensing optical fiber 4a-1 is positioned at a distance from the axis Ax2 in the direction Dr, and the other sensing optical fibers 4a-2 and 4a-3 are positioned on the side opposite to the sensing optical fiber 4a-1 with respect to the virtual line Lv passing through the axis Ax2 and orthogonal to the direction Dr. Even if the sensing optical fiber 4a-2 is separated from the axis Ax2 in the direction Dr, and even if the sensing optical fiber 4a-3 is separated from the axis Ax2 in the direction Dr, a similar positional relationship is established with the other two sensing optical fibers 4a. According to such an arrangement, for example, when the sensing cable 4 is bent, the difference in strain between the plurality of sensing optical fibers 4a becomes larger, so that the advantage of improved detection sensitivity can be obtained. The direction Dr is an example of the first direction.

[0058] In the sensing cable 4 configured as described above, the optical fiber 4b, the tension member 4c, and the coating layer 4d hold a plurality of sensing optical fibers 4a in a spaced-apart posture from each other. That is, the optical fiber 4b, the tension member 4c, and the coating layer 4d are an example of a holding member. The optical fiber 4b, the tension member 4c, and the coating layer 4d all extend in the longitudinal direction of the sensing cable 4 in parallel with the sensing optical fiber 4a, and are also an example of a fourth holding member. The optical fiber 4b is displaced in the circumferential direction of the sensing cable 4 from the sensing optical fiber 4a and is also an example of a fifth holding member. Further, the tension member 4c is positioned radially inside the sensing cable 4 with respect to the sensing optical fiber 4a and is also an example of a sixth holding member.

[0059] Furthermore, in the present embodiment, the outer diameters of the sensing optical fiber 4a, the optical fiber 4b, and the tension member 4c are substantially the same, and one sensing optical fiber 4a and one optical fiber 4b are alternately arranged one by one around one tension member 4c, for a total of six. Therefore, in a cross section orthogonal to the axis Ax2 at each position in the longitudinal direction, the sensing optical fiber 4a, the optical fiber 4b, and the tension member 4c are arranged in a form close to the densest packing, and further, the coating layer 4d surrounds them. Therefore, in the present embodiment, at each position in the longitudinal direction, the three sensing optical fibers 4a are arranged on the three vertices of a virtual equilateral triangle. According to such a configuration, a configuration capable of maintaining the relative positional relationship of the three sensing optical fibers 4a in the longitudinal direction of the sensing cable 4 can be realized with a relatively simple configuration. Note that the number, thickness, layout, etc. of the sensing optical fiber 4a, the optical fiber 4b, and the tension member 4c are not limited to the present embodiment and can be variously changed and implemented. For example, the number of sensing optical fibers 4a may be four or more. Also, the rigidity and strength of the sensing cable 4 can be adjusted according to the specifications of the optical fiber 4b, the tension member 4c, and the coating layer 4d.

[0060] Note that the sensing optical fiber 4a and the optical fiber 4b in the above embodiment may be single-mode optical fibers compliant with G.652, G.653, G.654, G.655, G.656, and G.657 defined by the International Telecommunication Union.

[0061] As described above, in this embodiment, the sensing cable 4 includes a plurality of sensing optical fibers 4a each having a core 4a1 and a cladding 4a2 surrounding the core 4a1, and an optical fiber 4b, a tension member 4c, and a coating layer 4d as holding members that hold the plurality of sensing optical fibers 4a at intervals from each other.

[0062] With such a configuration, the plurality of sensing optical fibers 4a can be maintained in a state where they are separated from each other and positioned at predetermined relative positions over the longitudinal direction of the sensing cable 4. Therefore, based on the strain distribution in the longitudinal direction of the plurality of sensing optical fibers 4a, the bending state of the sensing cable 4 and thus the cable 10 can be detected with higher accuracy. Further, since the sensing cable 4 has a plurality of sensing optical fibers 4a each as an optical fiber and can be realized with a relatively simple configuration, the labor and cost of manufacturing can be further reduced compared to a sensing cable having a special structure. Also, since the plurality of sensing optical fibers 4a are unitized as the sensing cable 4, the labor and cost of manufacturing can be further reduced compared to the case where a plurality of sensing optical fibers 4a are separately incorporated into the cable 10. Note that the sensing cable 4 has three sensing optical fibers 4a, but is not limited thereto and may have three or more sensing optical fibers 4a.

[0063] Also, in this embodiment, the sensing cable 4 has an optical fiber 4b, a tension member 4c, and a coating layer 4d as a fourth holding member that extends in the longitudinal direction of the sensing cable 4 in parallel with the sensing optical fiber 4a.

[0064] Also, in the present embodiment, the sensing cable 4 has an optical fiber 4b as a fifth holding member that is displaced in the circumferential direction of the sensing optical fiber 4a and the sensing cable 4.

[0065] Also, in the present embodiment, the sensing cable 4 has a tension member 4c as a sixth holding member that is positioned radially inward of the sensing cable 4 with respect to the plurality of sensing optical fibers 4a.

[0066] Also, in the present embodiment, the sensing cable 4 has a bonding material 4f as a bonding member that bonds the plurality of sensing optical fibers 4a or bonds the sensing optical fiber 4a and the holding member.

[0067] According to such a configuration, for example, the intervals and relative positional relationships of the plurality of sensing optical fibers 4a can be maintained by a relatively simple configuration over the longitudinal direction of the sensing cable 4.

[0068] Also, in the present embodiment, in the sensing cable 4, the plurality of sensing optical fibers 4a are arranged in a multi-helical shape.

[0069] According to such a configuration, for example, when the sensing cable 4 is twisted about the axis Ax2 as the central axis, the direction of the twist can be calculated. When the sensing optical fiber 4a is helical, if the direction of the generated twist is the same as the direction in which the sensing optical fiber 4a is helically wound, the strain generated in the sensing optical fiber 4a is in the increasing direction. On the other hand, if the direction of the generated twist is opposite to the direction in which the sensing optical fiber 4a is helically wound, the strain generated in the sensing optical fiber 4a is in the direction of relaxing the helical state, so the amount of strain is reduced. Therefore, it is possible to determine in which direction the twist occurred based on the increase or decrease in the amount of strain. Note that when the sensing optical fiber 4a is not helical but in a straight state, the direction of the twist cannot be determined.

[0070] In addition, in the present embodiment, the core 4a1 included in at least one sensing optical fiber 4a may include a fiber Bragg grating core in which the refractive index periodically changes in the longitudinal direction. The refractive index of the fiber Bragg grating core periodically changes in the longitudinal direction. In the case where the core 4a1 is at least partially the sensing optical fiber 4a having a fiber Bragg grating core, light of a specific wavelength can be efficiently returned backward. As a result, the intensity of the backward scattered light in the core 4a1 can be increased, so that the detection sensitivity of the strain distribution of the sensing optical fiber 4a and thus the bending state of the sensing cable 4 and the cable 10 can be improved (see Non-Patent Document 3).

[0071] Also, in the present embodiment, the sensing cable 4 extends along the axis Ax1 of the cable 10.

[0072] According to such a configuration, for example, the bending state of the axis Ax1 of the cable 10 can be detected with higher accuracy.

[0073] [First Modified Example] FIG. 4 is a cross-sectional view perpendicular to the longitudinal direction of the cable 10A of the first modified example, which is a modified example of the first embodiment. As shown in FIG. 4, the cable 10A of this modified example has the same configuration as the cable 10 of the first embodiment, except that the position of the sensing cable 4 is different from that of the first embodiment. The sensing cable 4 is located away from the axis Ax1 and between the power line 1, the ground line 2, and the inner coating layer 5. Further, the sensing cable 4 extends spirally along the longitudinal direction around the axis Ax1. Note that the sensing cable 4 may be located between the power line 1 and the optical fiber line 3 or between the ground line 2 and the optical fiber line 3. In this modified example, the sensing cable 4 is an example of the first sensing cable.

[0074] According to this modification example, for example, in the cable 10A, the space between the power line 1, the ground line 2, and the optical fiber line 3 can be more effectively utilized as the space for laying the sensing cable 4.

[0075] [Second Embodiment] FIG. 5 is a cross-sectional view perpendicular to the longitudinal direction of the cable 10B of the second embodiment. As shown in FIG. 5, the cable 10B includes a plurality of optical fiber ribbon core wires 3B which are transmission lines for transmitting optical signals, a sensing cable 4, a tension member 6B, outer covering layers 7Ba and 7Bb, and a slot member 9B. The slot member 9B extends in the longitudinal direction of the cable 10B.

[0076] The slot member 9B is provided with a plurality of grooves 9a provided at equal intervals in the circumferential direction on its outer periphery. Each of the grooves 9a extends in an S-twist (left twist), a Z-twist (right twist), or an SZ-twist in which the twisting direction is reversed at regular intervals in the longitudinal direction around the axis Ax1. That is, multiple twists are provided in the plurality of grooves 9a. The slot member 9B can be made of, for example, a synthetic resin material.

[0077] The sensing cable 4 is accommodated in one of the plurality of grooves 9a of the slot member 9. In the other grooves 9a, a plurality of optical fiber ribbon core wires 3B laminated in the radial direction are accommodated. The optical fiber ribbon core wire 3B has a coated optical fiber element wire arranged in parallel and a coating that collectively covers the parallel optical fiber element wires. Note that the optical fiber ribbon core wire 3B and the sensing cable 4 may be accommodated in the same groove 9a.

[0078] Also, a through hole extending in the longitudinal direction is provided at a position close to the cross-sectional center of the slot member 9B, and the tension member 6B is inserted into the through hole. The tension member 6B extends in the longitudinal direction at a position overlapping the axis Ax1.

[0079] The outer covering layer 7Ba is formed, for example, by winding a non-woven fabric tape around the outer periphery of the slot material 9, and is also called a press winding. Further, the outer covering layer 7Bb constituting the outermost periphery of the cable 10B can be made of a synthetic resin material.

[0080] According to the present embodiment, the sensing cable 4 can be accommodated in the groove 9a provided in the slot material 9. Therefore, for example, in the manufacturing process of the cable 10B, the effect that the sensing cable 4 can be more easily incorporated into the cable 10B, and the effect that the sensing cable 4 is likely to be arranged at a desired position and posture within the cable 10B can be obtained.

[0081] [Third Embodiment] FIG. 6 is a cross-sectional view perpendicular to the longitudinal direction of the sensing cable 4C of the third embodiment. As shown in FIG. 6, the sensing cable 4C has a slot material 4e extending in the longitudinal direction of the sensing cable 4. The slot material 4e is provided with a plurality of grooves 4e1 opened radially outward of the sensing cable 4C on its outer periphery. The plurality of grooves 4e1 are provided at predetermined intervals in the circumferential direction. In the present embodiment, as an example, three grooves are provided at equal intervals, that is, at 120° intervals, in the circumferential direction of the sensing cable 4. Further, the grooves 4e1 each extend spirally around the axis Ax2. That is, the plurality of grooves 4e1 are provided in a multi-helical shape. The slot material 4e can be made of, for example, a synthetic resin material. In the present embodiment, the groove 4e1 can also be referred to as a slot.

[0082] The plurality of sensing optical fibers 4a are each accommodated in the groove 4e1 of the slot material 4e. As described above, the plurality of grooves 4e1 are provided in a multi-helical shape. Therefore, the plurality of sensing optical fibers 4a are arranged in a multi-helical shape. The slot material 4e is an example of a holding member that holds the sensing optical fiber 4a, and is also an example of a first holding member. Further, the slot material 4e extends in the longitudinal direction of the sensing cable 4 in parallel with the sensing optical fiber 4a, and is also an example of a fourth holding member.

[0083] Also, a through hole extending in the longitudinal direction is provided at a position near the center of the cross section of the slot member 4e, and a tension member 4c is inserted into the through hole. The tension member 4c extends in the longitudinal direction at a position overlapping the axis Ax2.

[0084] According to the present embodiment, the sensing optical fiber 4a can be accommodated in the groove 4e1 provided in the slot member 4e. Therefore, for example, in the manufacturing process of the sensing cable 4C, the effect that the sensing optical fiber 4a can be more easily incorporated into the sensing cable 4C, and the effect that the sensing optical fiber 4a is likely to be arranged at the intended position and posture in the sensing cable 4C can be obtained.

[0085] In FIG. 6, if the sensing optical fiber 4a is fixed in the groove 4e1 provided in the slot member 4e, the tension member 4c is not necessarily required.

[0086] [Second Modification Example] FIG. 7 is a cross-sectional view perpendicular to the longitudinal direction of the sensing cable 4D of the second modification example, which is a modification of the third embodiment. As shown in FIG. 7, in this modification example, a through hole extending in the longitudinal direction of the sensing cable 4D is provided at a position near the center of the cross section of the tension member 4c, and the sensing optical fiber 4a is inserted into the through hole. The sensing optical fiber 4a extends in the longitudinal direction at a position overlapping the axis Ax2. According to this modification example, more sensing optical fibers 4a can be provided in the sensing cable 4D.

[0087] Further, as is apparent from FIG. 7, the four sensing optical fibers 4a are arranged at rotationally symmetric positions in a cross section orthogonal to the axis Ax2. Also, as shown in FIG. 7, in a cross section orthogonal to the axis Ax2, the sensing optical fiber 4a-1 is positioned at a distance from the axis Ax2 in the direction Dr, and the other sensing optical fibers 4a-2 and 4a-3 are positioned on the side opposite to the sensing optical fiber 4a-1 with respect to the virtual line Lv passing through the axis Ax2 and orthogonal to the direction Dr. In addition, even when the sensing optical fiber 4a-2 is separated from the axis Ax2 in the direction Dr, and when the sensing optical fiber 4a-3 is separated from the axis Ax2 in the direction Dr, a similar positional relationship is established with the other two sensing optical fibers 4a. According to such an arrangement, for example, when the sensing cable 4D is bent, the difference in strain becomes larger among the plurality of sensing optical fibers 4a, and thus the advantage of further improving the detection sensitivity is obtained.

[0088] [Third Modified Example] FIG. 8 is a cross-sectional view perpendicular to the longitudinal direction of the sensing cable 4E of the third modified example, which is a modified example of the first embodiment. As shown in FIG. 8, in this modified example, instead of the tension member 4c of the first embodiment, an optical fiber 4b that is not used for communication or sensing is arranged. The optical fiber 4b arranged along the axis Ax2 can also be referred to as a dummy fiber. In this modified example, the optical fiber 4b arranged along the axis Ax2 is an example of the sixth holding member.

[0089] [Fourth Modified Example] FIG. 9 is a cross-sectional view perpendicular to the longitudinal direction of the sensing cable 4F of the fourth modification, which is a modification of the third embodiment, and FIG. 10 is a side view of a partial section of the sensing cable 4F. As shown in FIGS. 9 and 10, in this modification, the sensing cable 4F has a plurality of slot members 4e. Each slot member 4e has a relatively thin plate-like shape in the longitudinal direction of the sensing cable 4F. Also, the plurality of slot members 4e are spaced apart at a predetermined interval, for example, at equal intervals, in the longitudinal direction. The slot member 4e can be made of, for example, a synthetic resin material. Note that the slot member 4e shown in FIG. 9 is the slot member 4e located on the leftmost side in FIG. 10.

[0090] Also in this modification, a plurality of grooves 4e1 that are open radially outward of the sensing cable 4F are provided on the outer periphery of the slot member 4e. The plurality of grooves 4e1 are provided at equal intervals, that is, at 120° intervals, in the circumferential direction of the sensing cable 4F and extend in the longitudinal direction of the sensing cable 4F. Note that in this modification, the groove 4e1 can also be referred to as a notch.

[0091] Also in this modification, a through-hole extending in the longitudinal direction is provided at a position close to the center of the cross-section of the slot member 4e, and a tension member 4c is inserted into the through-hole. The tension member 4c extends in the longitudinal direction at a position overlapping the axis Ax2. Also, the tension member 4c can be made of a steel wire, FRP, or the like.

[0092] The plurality of slot members 4e are all fixed to the tension member 4c in the same posture. Therefore, in each slot member 4e, the plurality of grooves 4e1 (4e1-1, 4e1-2, 4e1-3) are also arranged in the same posture with respect to the tension member 4c.

[0093] As shown in Fig. 9, the sensing optical fibers 4a are respectively accommodated in the grooves 4e1. As shown in Fig. 10, a plurality of sensing optical fibers 4a, in this modified example, three sensing optical fibers 4a (4a-1, 4a-2, 4a-3), are respectively accommodated in the grooves 4e1 of the plurality of slot members 4e so as to extend spirally around the axis Ax2. Specifically, the sensing optical fiber 4a-1 is accommodated in the groove 4e1-1 in the leftmost slot member 4e in Fig. 10, in the groove 4e1-2 in the slot member 4e located in the middle in the left-right direction in Fig. 10, and in the groove 4e1-3 in the rightmost slot member 4e in Fig. 10. The sensing optical fiber 4a-2 is accommodated in the groove 4e1-2 in the leftmost slot member 4e in Fig. 10, in the groove 4e1-3 in the slot member 4e located in the middle in the left-right direction in Fig. 10, and in the groove 4e1-1 in the rightmost slot member 4e in Fig. 10. Also, the sensing optical fiber 4a-3 is accommodated in the groove 4e1-3 in the leftmost slot member 4e in Fig. 10, in the groove 4e1-1 in the slot member 4e located in the middle in the left-right direction in Fig. 10, and in the groove 4e1-2 in the rightmost slot member 4e in Fig. 10. Thereby, the three sensing optical fibers 4a (4a-1, 4a-2, 4a-3) can respectively extend spirally around the axis Ax2 and the tension member 4c so as to be twisted in the counterclockwise direction in the view of Fig. 9. Thus, even in a configuration having a tension member 4c extending in the longitudinal direction of the sensing cable 4E, a plurality of slot members 4e fixed to the tension member 4c at a predetermined interval in the longitudinal direction, and a plurality of grooves 4e1 provided in each slot member 4e and the sensing optical fibers 4a being respectively accommodated in the grooves 4e1, like the sensing cable 4E of this modified example, the plurality of sensing optical fibers 4a can be arranged in a multi-helical shape around the axis Ax2 along the longitudinal direction of the sensing cable 4E. The slot member 4e is an example of a second holding member, and the tension member 4c is an example of a third holding member. Also, the groove 4e1 is an example of a holding portion.

[0094] As described above, in this modification example, the sensing cable 4E has a slot member 4e as a plurality of second holding members provided at intervals in the longitudinal direction of the sensing cable 4E, with grooves 4e1 as a plurality of holding portions each holding a sensing optical fiber 4a provided therein.

[0095] According to such a configuration, for example, the slot member 4e can be made shorter, and the amount of the material constituting the slot member 4e can be further reduced.

[0096] Also, in this modification example, the sensing cable 4E has a tension member 4c as a third holding member that extends in the longitudinal direction of the sensing cable 4E and fixes a plurality of slot members 4e.

[0097] According to such a configuration, for example, the mutual displacement such as the twist of the plurality of slot members 4e can be suppressed by the tension member 4c, and the sensing optical fiber 4a can be held more stably by the plurality of slot members 4e. Note that the sensing cable 4E may have a coating layer (not shown) that is the outermost layer of the sensing cable 4E as the third holding member instead of the tension member 4c, or may have other members extending in the longitudinal direction. Also, the sensing cable 4E may have a joining member that directly joins a plurality of sensing optical fibers 4a or indirectly joins them via other members such as the tension member 4c or the coating layer, or may have an intervening member interposed between the plurality of sensing optical fibers 4a. The joining member may be, for example, a synthetic adhesive, and the intervening member may be, for example, a filling member such as silicone.

[0098] [Fourth Embodiment] FIG. 11 is a cross-sectional view in a plane perpendicular to the longitudinal direction of the cable 10G including the sensing cable 4G of the fourth embodiment. FIG. 11 shows a state in which the cable 10G is bent at a bending radius R. The bending radius R is the distance between the bending center C0 and the axis Ax1 of the cable 10G.

[0099] Here, let the distance between the axis Ax1 of the 10G cable 10 and the axis Ax2 of the 4G sensing cable be D1, the distance between the axis Ax2 and the axis Ax3 of the sensing optical fiber 4a be D2, the length of one period of the twist in the longitudinal direction of the 4G sensing cable within the cable 10 be H (hereinafter referred to as the first twist pitch), and the length of one period of the twist in the longitudinal direction of the sensing optical fiber 4a be h (hereinafter referred to as the second twist pitch). Then, when the 10G cable 10 is bent with a bending radius R, the strain amount ε generated in the sensing optical fiber 4a is represented by the following formula (1).

Equation

[0100] FIG. 12 shows, as an example, the value of the strain amount ε in the longitudinal direction of the sensing optical fiber 4a when R = 500 [mm], D1 = 6 [mm], D2 = 1.35 [mm], H = 900 [mm], and h = 50 [mm]. The horizontal axis is the longitudinal distance from the reference point of the sensing optical fiber 4a. The strain amount ε indicates the change amount with respect to the length of the sensing optical fiber 4a when there is no strain, and when ε = 1, it indicates a state where no strain is applied.

[0101] In the measurement of the strain distribution for calculating the shape of the 10G cable 10, the larger the strain amount ε generated in the sensing optical fiber 4a is, the smaller the relative measurement error ratio becomes, and the measurement accuracy is improved. However, if the sensing optical fiber 4a is tested at a proof level: x [%] (x: elongation rate) during manufacturing (see Non-Patent Document 4), when the strain amount ε applied to the sensing optical fiber 4a due to the bending deformation of the cable 10 becomes equal to or greater than the proof level: x [%], the reliability of the sensing optical fiber 4a significantly decreases. The proof level is an example of a predetermined threshold value.

[0102] That is, in order to improve the accuracy of the shape calculation of the 10G cable, it is desirable that the amount of strain ε generated in the sensing optical fiber 4a is large. However, there is an upper limit to the amount of strain ε that can ensure reliability without breaking the sensing optical fiber 4a. As described above, since the amount of strain ε increases as the distances D1 and D2 increase, the distances D1 and D2 may be set within a range where the amount of strain ε is equal to or less than the upper limit value at the allowable minimum bending radius of the cable 10. Note that the predetermined threshold value may be the same as the proof level or may be set lower than the proof level.

[0103] FIG. 13 shows, in the example of FIG. 12, the change in the maximum tensile strain amount εmax generated in the sensing optical fiber 4a when the bending radius R, the distance D2, the first twist pitch H, and the second twist pitch h are unchanged and the distance D1 is changed. In other words, it shows the change in the maximum tensile strain amount εmax generated in the sensing optical fiber 4a when only the position of the sensing cable 4G within the 10G cable is changed in the example of FIG. 12.

[0104] As an example, when the sensing cable 4G has a sensing optical fiber 4a tested at a proof level of 1%, the length of the distance D1 at which a strain of 1% equivalent to the proof level is applied to the sensing optical fiber 4a is D1 = 3.705 [mm] (upper limit value). Further, as another example, when the sensing cable 4G has a sensing optical fiber 4a tested at a proof level of 2%, the length of the distance D1 at which a strain of 2% equivalent to the proof level is applied to the sensing optical fiber 4a is D1 = 8.7818 [mm] (upper limit value). In order to ensure the reliability of the sensing optical fiber 4a, it is necessary to arrange the sensing cable 4G at a position where the distance D1 does not exceed the upper limit value within the 10G cable.

[0105] Further, FIG. 14 shows, as an example, the values of the strain ε in the longitudinal direction of the sensing optical fiber 4a when R = 500 [mm], D1 = 0 [mm], D2 = 1.35 [mm], H = 900 [mm], and h = 50 [mm]. The horizontal axis is the longitudinal distance from the reference point of the sensing optical fiber 4a. In the case of the cable 10 of the first embodiment, the sensing cable 4 is located at the center of the cross-section of the cable 10, and the distance D1 is 0. That is, FIG. 14 shows the case of the first embodiment.

[0106] FIG. 15 shows, in the example of FIG. 14, the change in the maximum tensile strain εmax generated in the sensing optical fiber 4a when the bending radius R, the distance D1, the first twist pitch H, and the second twist pitch h are kept unchanged and the distance D2 is changed, in other words, when only the position of the sensing optical fiber 4a in the sensing cable 4G in the example of FIG. 14 is changed.

[0107] As an example, when the sensing cable 4G has a sensing optical fiber 4a tested at a proof level of 1 [%], the length of the distance D1 at which a strain equivalent to the proof level: 1 [%] is applied to the sensing optical fiber 4a is D2 = 5.0 [mm] (upper limit value). Also, as another example, when the sensing cable 4G has a sensing optical fiber 4a tested at a proof level of 2 [%], the length of the distance D2 at which a strain equivalent to the proof level: 2 [%] is applied to the sensing optical fiber 4a is D2 = 10.0 [mm] (upper limit value). In order to ensure the reliability of the sensing optical fiber 4a, it is necessary to arrange the sensing optical fiber 4a at a position where the distance D2 does not exceed the upper limit value within the sensing cable 4G.

[0108] [Fifth Embodiment] FIG. 16 is a configuration diagram of the sensing system 100A according to the fifth embodiment. The sensing system 100A of the present embodiment is for detecting the shape of the sensing cable 4 having three sensing optical fibers 4a (or the cable 10 having the sensing cable 4) as in the first embodiment or the like, or the sensing cable 4D having four sensing optical fibers 4a (or the cable 10 having the sensing cable 4D) as in the second modification. The sensing system 100A includes a light source unit 110A, an optical device 120A, a measurement unit 130A, and a calculation unit 140A. The sensing system 100A can apply optical frequency domain reflectometry (hereinafter referred to as OFDR). Here, the configuration of OFDR is described in, for example, Non-Patent Document 5. The light source unit 110A inputs the test light L1 whose wavelength (frequency) is swept at a predetermined period into the test light transmission path 152A in the extension cable 150A. Further, the light source unit 110A inputs the reference light L2 into the measurement unit 130A.

[0109] The extension cable 150A has a backscattered light transmission path 151A and a test light transmission path 152A separate from this. The test light transmission path 152A transmits the test light L1 output from the light source unit 110A to the optical device 120A.

[0110] The optical device 120A has an optical circulator 121A. The optical circulator 121A inputs the test light L1 into the sensing optical fiber 4a (core 4a1) of the sensing cable 4. The test light L1 from the optical circulator 121A is input to one end of the sensing optical fiber 4a-1. The test light L1 input to the sensing optical fiber 4a-1 is input to the other end of another sensing optical fiber 4a-2 at the terminal connection part 180. The test light L1 input to the sensing optical fiber 4a-2 is input to another sensing optical fiber 4a-3 at one end of the sensing cable 4. The test light L1 input to the sensing optical fiber 4a-3 passes through the sensing optical fiber 4a-3 and reaches the other end of the sensing optical fiber 4a-3. That is, in the present embodiment, a plurality of sensing optical fibers 4a are connected in series, and the sensing optical fibers 4a connected in series and integrated have a plurality of sections folded at the longitudinal ends. The three sensing optical fibers 4a-1 to 4a-3 in this case are an example of the plurality of sections.

[0111] Also, when the sensing cable 4D has four sensing optical fibers 4a, the test light L1 that has reached the other end of the sensing optical fiber 4a-3 is input to the other end of another sensing optical fiber 4a-4. The test light L1 input to the sensing optical fiber 4a-4 passes through the sensing optical fiber 4a-4 and reaches one end of the sensing optical fiber 4a-4. The four sensing optical fibers 4a-1 to 4a-3 in this case are an example of the plurality of sections.

[0112] In the sensing optical fibers 4a-1 to 4a-4, due to the test light L1, Rayleigh scattered light is generated in the longitudinal direction, transmitted as backscattered light in the direction opposite to the test light L1, and output from the end of the sensing optical fiber 4a-1 where the test light L1 is input. The optical circulator 121A inputs the output backscattered light L3 into the backscattered light transmission path 151A of the extension cable 150A. The backscattered light L3 output to the backscattered light transmission path 151A is measured by the measurement unit 130A.

[0113] In the measurement unit 130A, the input reference light L2 and the backscattered light L3 are made to interfere with each other and converted into an electrical signal. The calculation unit 140A can obtain information on the strain distribution in the longitudinal direction of the sensing optical fiber 4a by analyzing this electrical signal. Details of the data processing are described in Non-Patent Document 5.

[0114] Based on the measurement results for each backscattered light, the calculation unit 140A calculates the strain of each of the plurality of sensing optical fibers 4a-1 to 4a-4, and calculates the shape of the sensing cables 4 and 4D (cable 10) based on the calculated strains. Specifically, the calculation unit 140A calculates the strain distribution based on the data signal including information on the strain distribution in the longitudinal direction of the sensing optical fiber 4a obtained by performing a Fourier transform on the waveform data of the interference signal, and further calculates the shape of the sensing cables 4 and 4D (cable 10) based on the calculated strain distribution. This method is a known calculation method that applies the Frenet-Serret equations in the longitudinal direction of the optical fiber (Non-Patent Documents 1 and 2).

[0115] In the present embodiment, the sensing system 100 is configured to be able to use the principle of OFDR. OFDR can achieve a high spatial resolution ranging from several millimeters to several micrometers, and by introducing it into the sensing system of the present invention, more precise measurement results can be obtained in the longitudinal direction of the optical fiber.

[0116] However, the measurement principle used in the sensing system of the present invention is not limited to OFDR. For example, the Brillouin scattered light can be measured as the backward scattered light from the sensing optical fiber 4a, and the sensing system may be configured both software - wise and hardware - wise so that the respective strains of the sensing optical fiber 4a can be calculated based on the measurement results regarding the respective Brillouin scattered lights. In this case, the sensing system is configured to be able to use the principles of Brillouin optical time domain reflectometry (hereinafter referred to as BOTDR) and Brillouin optical correlation domain reflectometry (hereinafter referred to as BOCDR). BOTDR is described in Non - Patent Document 6, and BOCDR is described in Non - Patent Document 7, respectively.

[0117] When using BOTDR, the light source unit 110A inputs the pulsed test light L1 into the test light transmission path 152A in the extension cable 150A. Also, the light source unit 110A inputs the reference light L2, which is continuous light, into the measurement unit 130A.

[0118] When using BOCDR, the light source unit 110A inputs the test light L1 whose frequency is sinusoidally modulated into the test light transmission path 152A in the extension cable 150A. Also, the light source unit 110A inputs the reference light L2 into the measurement unit 130A.

[0119] When using BOTDR or BOCDR, different from the case of the above - mentioned OFDR, the Brillouin backward scattered light generated longitudinally due to the test light L1 is observed from the sensing optical fibers 4a - 1 to 4a - 4.

[0120] Also, when using BOTDR or BOCDR, the measurement unit 130A removes the Rayleigh scattered light, extracts only the Brillouin Stokes light, then multiplexes it with the reference light L2, and converts it into an electrical signal. The measurement unit 130A detects only the frequency components of the Brillouin scattered light.

[0121] Based on the measurement results regarding the respective backward scattered lights, the calculation unit 140A calculates the strain of each of the plurality of sensing optical fibers 4a-1 to 4a-4, and calculates the shape of the sensing cables 4 and 4D (cable 10) based on the calculated strains. Specifically, the calculation unit 140A obtains the amount of frequency change from the frequency components of the Brillouin scattered light, calculates the strain distribution in the longitudinal direction of the sensing optical fiber 4a from that value, and further calculates the shape of the sensing cables 4 and 4D (cable 10) based on the calculated strain distribution.

[0122] A sensing system that measures Brillouin scattering has the advantage of having a long measurable distance. Therefore, these sensing systems can be appropriately selected according to the total length of the sensing cables 4 and 4D (cable 10) and the total length of the sensing optical fibers 4a mounted on the sensing cables 4 and 4D (cable 10).

[0123] As described above, the sensing system 100A of the present embodiment can detect the shape of the sensing cables 4 and 4D (cable 10).

[0124] [Sixth Embodiment] FIG. 17 is a configuration diagram of the sensing system 100B according to the sixth embodiment. The sensing system 100B of this embodiment is for detecting the shape of a sensing cable 4D having four sensing optical fibers 4a as in the second modification example, or a cable 10 having the sensing cable 4D. The sensing system 100B includes an optical device 120B, an arithmetic unit 140B, a light source unit 110B, a measurement unit 130B, and an extension cable 150B. The sensing system 100B is configured both software-wise and hardware-wise so that the principle of Brillouin optical correlation domain analysis (hereinafter referred to as BOTDA) or Brillouin optical time domain analysis (hereinafter referred to as BOCDA) can be used. BOTDA is described in Non-Patent Document 8, and BOCDA is described in Non-Patent Document 9, respectively.

[0125] When using BOTDA, the light source unit 110B outputs a pump light having a pulse shape and a probe light that is a continuous light.

[0126] When using BOCDA, the light source unit 110B outputs a pump light having a pulse shape and a probe light whose frequency is modulated. The probe light is modulated by a sine wave having a frequency corresponding to the Brillouin frequency shift amount (Stokes shift amount) of the sensing optical fiber 4a that is the measurement target.

[0127] The extension cable 150B has backscattered light transmission paths 151B and 152B, and test light transmission paths 153B and 154B that are separate from these. The test light transmission path 153B transmits the probe light output from the light source unit 110B to the optical device 120B. The test light transmission path 154B transmits the pump pulse light output from the light source unit 110B to the optical device 120B.

[0128] The optical device 120B includes 1×2 couplers 121B and 122B, optical isolators 123B and 124B, and optical circulators 125B and 126B. One port side of the 1×2 coupler 121B is connected to the test optical transmission path 153B, and the two port sides are respectively connected to the input ports of the optical isolators 123B and 124B. One port side of the 1×2 coupler 122B is connected to the test optical transmission path 154B, and the two port sides are respectively connected to the input ports on the two port sides of the optical circulators 125B and 126B. The other sides of the two port sides of the optical circulators 125B and 126B are respectively connected to the backscattered light transmission paths 151B and 152B. The output ports of the optical isolators 123B and 124B are connected to different sensing optical fibers 4a. The one port sides of the optical circulators 125B and 126B are connected to different sensing optical fibers 4a.

[0129] The 1×2 coupler 121B splits the probe light input from the test optical transmission path 153B into two branches and inputs the branched probe light into the optical isolators 123B and 124B respectively. The optical isolators 123B and 124B respectively input the input probe light into the sensing optical fibers 4a-1 and 4a-2 (core 4a1). The 1×2 coupler 122B splits the pump pulse light input from the test optical transmission path 154B into two branches and inputs the branched probe light into the optical circulators 125B and 126B respectively. The optical circulators 125B and 126B respectively input the input pump pulse light into the sensing optical fibers 4a-3 and 4a-4 (core 4a1).

[0130] The sensing optical fibers 4a-1 and 4a-4 are connected at the terminal connection part 180 on the side opposite to the side to which the optical isolator 123B and the optical circulator 125B are connected. Also, the sensing optical fibers 4a-2 and 4a-3 are connected at the terminal connection part 180 on the side opposite to the side to which the optical isolator 124B and the optical circulator 126B are connected. That is, the sensing cable 4 includes a sensing optical fiber 4a in which the sensing optical fibers 4a-1 and 4a-4 are connected in series and integrated, and a sensing optical fiber 4a in which the sensing optical fibers 4a-2 and 4a-3 are connected in series and integrated.

[0131] The sensing optical fibers 4a-1 and 4a-4 and the sensing optical fibers 4a-2 and 4a-3 each transmit the pump pulse light from one end to the other end, and transmit the probe light in the direction opposite to the pump pulse light, from the other end to one end. During transmission, due to the pump pulse light, Brillouin scattered light is generated along the longitudinal direction of each of the sensing optical fibers 4a, the probe light is Brillouin amplified and transmitted in the direction opposite to the pump pulse light, and is input to the optical circulators 125B and 126B to which the pump pulse light is input. The optical circulators 125B and 126B respectively input the probe light Lb1 that has passed through the sensing optical fibers 4a-1 and 4a-4 and has been Brillouin amplified, and the probe light Lb2 that has passed through the sensing optical fibers 4a-2 and 4a-3 and has been Brillouin amplified, into the backscattered light transmission paths 151B and 152B. The backscattered light transmission path 151B transmits the Brillouin amplified probe light Lb1 and inputs it to the measurement unit 130Ba. Also, the backscattered light transmission path 152B transmits the Brillouin amplified probe light Lb2 and inputs it to the measurement unit 130Bb.

[0132] When using BOTDA, the measurement units 130Ba and 130Bb each receive the light output from the backscattered light transmission paths 151B and 152B, convert it into a current signal, and input it to the calculation unit 140B.

[0133] On the other hand, when using BOCDR, the measuring units 130Ba and 130Bb receive the light output from the backscattered light transmission paths 151B and 152B, respectively, convert it into a current signal, and further input a lock-in detected signal synchronized with the modulation of the probe light to the arithmetic unit 140B.

[0134] The arithmetic unit 140B obtains the amount of frequency change from the frequency components of the Brillouin scattered light, calculates the strain distribution in the longitudinal direction of the sensing optical fiber 4a from that value, and further calculates the shape of the sensing cable 4D (cable 10) based on the calculated strain distribution. This method is a known calculation method that applies the Frenet-Serret equations in the longitudinal direction of the optical fiber (Non-Patent Documents 1 and 2).

[0135] As described above, the sensing system 100B of the present embodiment can detect the shape of the sensing cable 4D (cable 10).

[0136] [Seventh Embodiment] FIG. 18 is a configuration diagram of the sensing system 100C of the seventh embodiment. The sensing system 100C of the present embodiment is for detecting the shape of the sensing cable 4D having four sensing optical fibers 4a as in the second embodiment, or the cable 10 having the sensing cable 4D. The sensing system 100C includes a light source unit 110C, an extension cable 150C, an optical device 120C, a measuring unit 130C, and an arithmetic unit 140C. The sensing system 100C is configured both software-wise and hardware-wise so as to be able to use the principles of BOTDA or BOCDA, similar to the sensing system 100B of the sixth embodiment.

[0137] When using BOTDA and when using BOCDR, the light source unit 110C has the same configuration as the sensing system 100B of the sixth embodiment and operates in the same manner, so the description is omitted.

[0138] The extension cable 150C has a backscattered light transmission path 151C, and separate test light transmission paths 152C and 153C. The test light transmission path 152C transmits the probe light output from the light source unit 110C to the optical device. The test light transmission path 153C transmits the pump light output from the light source unit 110C to the optical device.

[0139] The extension cable 150C inputs the pump light and the probe light to the optical device 120C. The optical device 120C has an optical isolator 121C and an optical circulator 122C. The optical isolator 121C inputs the probe light to the sensing optical fiber 4a-1. The optical circulator 122C inputs the pump light to a sensing optical fiber 4a-4 different from the sensing optical fiber 4a-1.

[0140] The probe light from the optical isolator 121C reaches the optical circulator 122C via the sensing optical fibers 4a-1, 4a-2, 4a-3, 4a-4 in this order and is blocked.

[0141] On the other hand, the pump light from the optical circulator 122C reaches the optical isolator 121C via the sensing optical fibers 4a-4, 4a-3, 4a-2, 4a-1 in this order and is blocked.

[0142] The optical circulator 122C inputs the Brillouin-amplified probe light to the backscattered light transmission path 151C in the extension cable 150C. The backscattered light transmission path 151C inputs the Brillouin-amplified probe light to the measurement unit 130C.

[0143] In each case of using BOTDA and using BOCDR, the measurement unit 130C has the same configuration as the sensing system 100B of the sixth embodiment and operates in the same manner. That is, the measurement unit 130C measures the Brillouin-amplified probe light input from one end of each of the plurality of sensing optical fibers 4a-1 to 4a-4, and outputs an electrical signal to the arithmetic unit 140C.

[0144] In the calculation unit 140C, the strain distribution state in the longitudinal direction of these fibers can be continuously calculated from the detected digital data. Then, it is divided into data of the strain distribution state of each of the sensing optical fibers 4a-1 to 4a-4, and the shape of the sensing cable 4D (cable 10) is calculated based on each strain. This method is a known calculation method that applies the Frenet-Serret equations in the longitudinal direction of the optical fiber (Non-Patent Documents 1 and 2).

[0145] As described above, the sensing system 100C of the present embodiment can detect the shape of the sensing cable 4D (cable 10).

[0146] Also, as another embodiment, in the configurations of the sensing systems 100A to 100C of the fifth to seventh embodiments, the extension cables 150A to 150C are deleted, and the test light L1 from the light source units 110A to 110C is input to the optical devices 120A to 120C without passing through the extension cables 150A to 150C, and the backward scattered light L3a, L3b, L3c, L3d from each of the sensing optical fibers 4a is input to the measurement units 130A to 130C.

[0147] [Eighth Embodiment] The sensing systems 100 and 100A as described in the above fifth to seventh embodiments can be applied to various systems. Hereinafter, embodiments of a system including the sensing system 100 (or 100A to 100C) will be described.

[0148] FIG. 19 is a configuration diagram of a system 1000 according to the seventh embodiment including the sensing system 100. This system 1000 includes cables 10A and 10 and the sensing system 100. The system 1000 includes an ocean exploration ship 1001 floating on the sea S, a launcher 1002 which is an unmanned exploration machine, and a vehicle 1003 which is a slave unit, and is configured as a subsea exploration system for exploring the seabed. The system 1000 may also be referred to as a sensing system.

[0149] The sensing system 100 is mounted on the ocean exploration ship 1001. The cable 10A is connected to the sensing system 100. The cable 10A, also called the primary cable, has the same cross-sectional structure as the cable 10, and its length is relatively long, for example, 10 km.

[0150] The launcher 1002 is connected to the ocean exploration ship 1001 via the cable 10A. The launcher 1002 is equipped with various exploration devices and has a mechanism for accommodating, guiding, and recovering the vehicle 1003.

[0151] The cable 10 is connected to the cable 10A via the launcher 1002. The cable 10, also called the secondary cable, has a relatively short length, for example, 200 m.

[0152] The vehicle 1003 is connected to the launcher 1002 by the cable 10. The vehicle 1003 departs from the launcher 1002 and moves near the seabed. The vehicle 1003 is equipped with various exploration devices. The vehicle 1003 is located on the tip side opposite to the end where the test light is input from the sensing system 100 in the cables 10A and 10.

[0153] The cables 10A and 10 are composite cables having functions of supplying power from the ocean exploration ship 1001 to the launcher 1002 and the vehicle 1003 and performing communication.

[0154] As described in the fifth embodiment, the sensing system 100 can detect the shapes of the cables 10A and 10.

[0155] In the sea, cables 10A and 10 are moving due to tidal currents, but their behavior is often unclear. In some cases, the strain of cables 10A and 10 may concentrate at specific locations, or a part of the twist of cables 10A and 10 may be transmitted to the cable tip, resulting in kinks, which may cause damage. Therefore, as the structural design of cables 10A and 10, a design considering torque balance is carried out. However, it is difficult to surely avoid factors leading to the breakage of cables 10A and 10, such as the above-mentioned local strain and kink generation, or damage caused by contact with rocks protruding from the seabed at positions close to the seabed surface.

[0156] On the other hand, in this system 1000, since the sensing system 100 can detect the shapes of cables 10A and 10, it is possible to identify the locations where local strain and kinks occur without retrieving cables 10A and 10 from the sea. As a result, it is possible to predict to some extent the damage and breakage of cables 10A and 10. In addition, thereby, more efficient cable inspections can be performed, and data for elucidating the mechanisms of strain and kink generation can be collected.

[0157] Moreover, the arithmetic unit 140 of the sensing system 100 may calculate the three-dimensional relative position of the vehicle 1003, which is the measurement object, with respect to the ocean exploration ship 1001 based on the shapes of cable 10A and cable 10. Thereby, the system 1000 can detect the three-dimensional relative position of the vehicle 1003. Note that the ocean exploration ship 1001 is equipped with a GPS device, and the GPS device can obtain information on the absolute position (latitude and longitude) of the ocean exploration ship 1001 on the earth. In this case, the arithmetic unit 140 can take in the position information of the ocean exploration ship 1001 from the GPS device and detect the three-dimensional absolute position of the vehicle 1003 in the sea based on the position information and the shape information of cable 10A and cable 10.

[0158] [Embodiment 9] FIG. 20 is a configuration diagram of a system 1000A according to a ninth embodiment including a sensing system 100B. This system 1000A includes a cable 10 and a sensing system 100B. The system 1000A may also be referred to as a sensing system. The sensing system 100B includes an optical device 120A, an arithmetic unit 140, a light source / measurement unit 160, and a primary cable 170B. Since the optical device 120A, the arithmetic unit 140, and the light source / measurement unit 160 have the same configuration as the corresponding elements in the sensing system 100A shown in FIG. 17, the description thereof is omitted. Note that the arithmetic unit 140 and the light source / measurement unit 160 are mounted on the ocean exploration ship 1001. The optical device 120A is mounted on the launcher 1002.

[0159] The configuration of the primary cable 170B is obtained by deleting the sensing optical fiber 4a (sensing cable 4) from the configuration of the cable 10 and adding four backscattered light transmission paths similar to the extension cable 150B shown in FIG. 17 and a test light transmission path separate from these. The length of the primary cable 170B is relatively long, for example, 10 km.

[0160] The primary cable 170B is a composite cable and is used for power supply and communication between the ocean exploration ship 1001, the launcher 1002, and the vehicle 1003, similar to the cable 10. Also, the primary cable 170B has a function of transmitting the test light L1 to the optical device 120A through the test light transmission path, similar to the extension cable 150B. Further, the primary cable 170B has a function of transmitting each of the backscattered lights L3a, L3b, L3c, and L3d from the sensing optical fiber 4a of the cable 10 to the light source / measurement unit 160 through each of the four backscattered light transmission paths.

[0161] In this system 1000A, the sensing system 100B can detect the shape of the cable 10 connected to the end of a cable several kilometers long or more from the light source / measurement unit 160 via the primary cable 170B. In particular, it can preferably detect the shape of the cable 10 located on the tip side of the primary cable 170B, close to the seabed, where kinks and the like are likely to occur.

[0162] Also, based on the shape of the cable 10, the arithmetic unit 140 of the sensing system 100B may calculate the approximate three-dimensional relative position of the vehicle 1003, which is the object to be measured, with respect to the ocean exploration ship 1001. Thereby, the system 1000 can detect the approximate three-dimensional relative position of the vehicle 1003. Note that the arithmetic unit 140 can take in the position information of the ocean exploration ship 1001 from the GPS device and detect the approximate three-dimensional absolute position of the vehicle 1003 in the sea based on the position information and the shape information of the cable 10A and the cable 10.

[0163] [Tenth Embodiment] FIG. 21 is a configuration diagram of a system 1000B according to the tenth embodiment including the sensing system 100. In this system 1000B, the sensing system 100 for detecting the shape of the cable 10 is mounted on the launcher 1002. The ocean exploration ship 1001 and the launcher 1002 are connected by a primary cable 1004, which is a composite cable used for power supply and communication. The system 1000B may also be referred to as a sensing system.

[0164] In this system 1000B, it is possible to preferably detect the shape of the cable 10 located on the tip side of the primary cable 1004, close to the seabed, where kinks and the like are likely to occur.

[0165] Note that since the launcher 1002 can reach the deep sea corresponding to the cable length of the primary cable 1004, a high water pressure is applied. Therefore, the sensing system 100 mounted on the launcher 1002 needs to have a waterproof structure, such as installing the whole inside a waterproof container.

[0166] [11th Embodiment] FIG. 22 is a configuration diagram of a system 1000C according to the 11th embodiment including a sensing system 100. This system 1000C includes cables 10A and 10, a sensing system 100, and a sonar device 1005 which is a distance measuring device. That is, the system 1000C has a configuration in which the sonar device 1005 is added to the configuration of the system 1000 shown in FIG. 18. The system 1000C may also be referred to as a sensing system.

[0167] The sonar device 1005 is mounted on the vehicle 1003. The sonar device 1005 transmits a sound wave signal SS toward a predetermined location of the seabed SF and receives the sound wave signal reflected at the predetermined location. Thereby, the sonar device 1005 measures the distance to the predetermined location of the seabed SF.

[0168] As described above, in the system 1000, the three-dimensional absolute position of the vehicle 1003 in the sea can be detected. Further, in the system 1000C, the calculation unit 140 can calculate the three-dimensional absolute position of a predetermined location of the seabed SF using the information on the three-dimensional absolute position of the vehicle 1003 and the information on the distance to the predetermined location of the seabed SF measured by the sonar device 1005. Then, by the sonar device 1005 measuring the distance to the seabed SF at various locations, the calculation unit 140 can calculate the three-dimensional coordinates of the seabed SF. As a result, the system 1000C can detect the three-dimensional coordinates and shape of the seabed SF. In this case, the seabed SF corresponds to the measurement object located on the tip side of the cable 10.

[0169] In the above-described 8th to 11th embodiments, the measurement objects for detecting the position or shape are the vehicle 1003 and the seabed SF, but the measurement objects for detecting the position or shape are not limited thereto. For example, the sensing system of the present invention is also applicable to applications for detecting the position of an inspection robot that enters a building and inspects the inside of the building and the shape of the inside of the building.

[0170] [Embodiment 12] FIG. 23 is a configuration diagram of a system 2000 according to Embodiment 12 including a sensing system 100. This system 2000 includes a cable 10 and a sensing system 100. The system 2000 may also be referred to as a sensing system. The cable 10 is laid along a track 2001 such as a railway which is an object to be measured. The cable 10 is in contact with the track 2001 and is fixed continuously or intermittently in the longitudinal direction.

[0171] When the shape of the track 2001 is deformed such as expansion, contraction, or bending, the shape of the cable 10 changes accordingly. The sensing system 100 can sense the deformation of the track 2001 by detecting the shape deformation of the cable 10. Thereby, in the system 2000, it is possible to monitor the occurrence of a shape abnormality in the track 2001.

[0172] Note that the object to be measured is not limited to a track and may be a structure such as a bridge. Also, a sensing system may be configured using a sensing system 100A instead of the sensing system 100. When the sensing system 100A is used, the cable 10 of the sensing system 100A can be laid on the object to be measured, and the arithmetic unit 140 and the light source / measurement unit 160 can be installed at a location remote from the object to be measured by the extension cable 150A. Thereby, for example, the shape of a building or the like existing in a mountainous area where it is difficult to install the arithmetic unit 140 and the light source / measurement unit 160 or where it is difficult for a measurer to reach can be sensed by the cable 10, and the occurrence of a shape abnormality can be monitored.

[0173] Also, the cable 10 of the systems according to the above-described Embodiments 5 to 12 can be replaced with the cables 10A, 10B, 10G of other embodiments and modification examples and cables similar thereto, and the sensing cable 4 included in the cable 10 can be replaced with the sensing cables 4C to 4F of other embodiments and modification examples and sensing cables similar thereto. Also, the number of the sensing optical fibers 4a is not limited to 4.

[0174] Also, generally, an optical fiber expands and contracts due to temperature changes. Therefore, when measuring the strain distribution of the sensing optical fiber 4a, if the temperature of the sensing optical fiber 4a changes, it will affect the strain measurement. Therefore, in the arithmetic units of the sensing systems 100, 100A to 100C, based on the measurement results of the backscattered light from at least one of the sensing optical fibers 4a, the temperature distribution in the longitudinal direction of the cable for detecting the shape is obtained, and the respective strains of the plurality of calculated sensing optical fibers 4a are corrected based on the temperature distribution. It is preferable to do so. Such measurement of the temperature distribution in the longitudinal direction of the sensing optical fiber 4a can use the R-OTDR (Raman OTDR) method using the change in Raman scattering in the sensing optical fiber 4a, the BOTDR method using the frequency change of Brillouin scattering, the BOTDA method, the BOCDA method, and the BOCDR method. Therefore, it is preferable that the sensing systems 100, 100A, 100B and the systems 1000, 1000A to 1000C, 2000 equipped with these are configured both software-wise and hardware-wise so as to measure the temperature distribution using these methods and correct the strain based on this. Note that the sensing optical fiber 4a used for measuring the temperature distribution may be located at any position within the sensing cable 4.

[0175] As described above, the embodiments and modified examples of the present invention have been illustrated, but the above embodiments and modified examples are merely examples and are not intended to limit the scope of the invention. The above embodiments and modified examples can be implemented in various other forms, and various omissions, replacements, combinations, and changes can be made without departing from the gist of the invention. Also, each configuration, shape, etc. of the specifications (structure, type, direction, model, size, length, width, thickness, height, number, arrangement, position, material, etc.) can be appropriately changed and implemented.

Explanation of Reference Numerals

[0176] 1…Power line (transmission line) 2…Ground line 3…Optical fiber line (transmission line, communication line) 3B... Optical fiber ribbon core wire 4... Sensing cable (first sensing cable, second sensing cable) 4C~4G... Sensing cable 4a, 4a-1, 4a-2, 4a-3, 4a-4... Sensing optical fiber 4a1... Core 4a2... Cladding 4b... Optical fiber (holding member, fourth holding member, fifth holding member, sixth holding member) 4b1... Core 4b2... Cladding 4c... Tension member (holding member, third holding member, fourth holding member, sixth holding member) 4d... Coating layer (holding member, third holding member, fourth holding member) 4e... Slot material (holding member, first holding member, second holding member, fourth holding member) 4e1, 4e1-1, 4e1-2, 4e1-3... Groove (holding part) 4f... Bonding material (bonding member) 5... Inner coating layer 6, 6B... Tension member 7, 7Ba, 7Bb... Outer coating layer 8... Filling material 9, 9B... Slot material 9a... Groove 10, 10A, 10B, 10G... Cable 100, 100A, 100B, 100C... Sensing system 110A, 110B, 110C... Light source unit 120A, 120B, 120C... Optical device 121A, 125B, 126B, 122C... Optical circulator 123B, 124B, 121C... Optical isolator 121B, 122B... 1×2 coupler 130A, 130B, 130Ba, 130Bb, 130C... Measuring part 140, 140A, 140B, 140C... Arithmetic unit 150A, 150B, 150C... Extension cable 151A, 151B, 152B, 151C... Backscattered light transmission path 152A, 153B, 154B, 152C, 153C… Test optical transmission path 160… Light source / measurement unit 170B, 1004… Primary cable 180… End connection part 1000, 1000A~1000C, 2000… System (sensing system) 1001… Ocean exploration ship 1002… Launcher 1003… Vehicle 1005… Sonar device 2001… Line Ax1… Axis (first axis) Ax2… Axis (second axis) Ax3… Axis (third axis) C0… Center D1… Distance (first distance) D2… Distance (second distance) Dr… Direction (first direction) H… First twist pitch h… Second twist pitch L1… Test light L2… Reference light L3, L3a, L3b, L3c, L3d… Backscattered light Lb1, Lb2… Probe light Lv… Virtual line S… Sea SF… Seabed SS… Sound wave signal R… Bending radius

Claims

1. A cable comprising a transmission line and a sensing cable provided separately from the transmission line, wherein the sensing cable has three or more sensing optical fibers each having a core and a clad surrounding the core, and a holding member that holds the three or more sensing optical fibers at intervals from each other, and a first distance from a first axis of the cable to a second axis of the sensing cable and a second distance from the second axis to a third axis of the sensing optical fiber are set such that a strain amount ε represented by the following formula (1) of the sensing optical fiber at the allowable minimum bending radius of the cable is equal to or less than a proof level tested during manufacture of the sensing optical fiber. Here, R: bending radius, D1: first distance, D2: second distance, h: length of one period of twist in the longitudinal direction of the sensing optical fiber, H: length of one period of twist in the longitudinal direction of the cable 【Number 1】 The cable is set as such.

2. The cable according to claim 1, further comprising a first holding member provided with a plurality of grooves extending in the longitudinal direction of the sensing cable and each accommodating the sensing optical fiber as the holding member.

3. The cable according to claim 1 or 2, further comprising a plurality of second holding members provided with a plurality of holding portions each holding the sensing optical fiber and spaced apart in the longitudinal direction of the sensing cable as the holding member.

4. The cable according to claim 3, further comprising a third holding member extending in the longitudinal direction of the sensing cable and fixing the plurality of second holding members as the holding member.

5. The cable according to any one of claims 1 to 4, further comprising a fourth holding member extending in the longitudinal direction of the sensing cable in parallel with the sensing optical fiber as the holding member.

6. The cable according to claim 5, further comprising a fifth holding member offset in the circumferential direction of the sensing optical fiber and the sensing cable as the fourth holding member.

7. The cable according to claim 5 or 6, further comprising a sixth holding member positioned radially inside the sensing cable with respect to three or more sensing optical fibers as the fourth holding member.

8. ​ The sensing cable has a joining member that joins the three or more sensing optical fibers or joins the sensing optical fiber and the holding member, and is the cable according to any one of claims 1 to 7.

9. In the sensing cable, the three or more sensing optical fibers are arranged in a multi-helical shape, and it is the cable according to any one of claims 1 to 8.

10. The core included in at least one of the sensing optical fibers includes a fiber Bragg grating core in which the refractive index periodically changes in the longitudinal direction, and it is the cable according to any one of claims 1 to 9.

11. As the sensing cable, the cable according to any one of claims 1 to 10, comprising a first sensing cable arranged in a spiral shape in the cable.

12. As the sensing cable, the cable according to any one of claims 1 to 11, comprising a second sensing cable along the first axis of the cable.

13. The transmission line is a power line, and it is the cable according to any one of claims 1 to 12.

14. The transmission line is a communication line, and it is the cable according to any one of claims 1 to 13.

15. A transmission line, A sensing cable provided separately from the transmission line, A cable comprising: The sensing cable, A sensing optical fiber having a core and a cladding surrounding the core, respectively, A holding member for holding the sensing optical fiber, Having, The sensing optical fiber is folded back two or more times in its longitudinal direction and has three or more plural sections passing through a predetermined range in the longitudinal direction of the sensing cable, The holding member holds the plurality of sections in a state of being spaced apart from each other in the circumferential direction of the second axis of the sensing cable within the predetermined range, The first distance from the first axis to the second axis of the cable and the second distance from the second axis to the third axis of the section are the following formula (1) of the sensing optical fiber at the allowable minimum bending radius of the cable 【Number 1】 Here, R: bending radius, D1: first distance, D2: second distance, h: length of one period of the twist in the longitudinal direction of the sensing optical fiber, H: length of one period of the twist in the longitudinal direction of the cable A cable configured such that the strain amount ε shown by [reference numeral] is equal to or less than the proof level tested during the manufacture of the sensing optical fiber.

16. The plurality of sections include a first section and a second section, The first section is positioned at a distance in a first direction intersecting the second axis with respect to the second axis in a cross section orthogonal to the second axis, The second section is positioned on the opposite side of the first section with respect to a virtual line passing through the second axis and extending in a second direction orthogonal to the second axis and the first direction in the cross section. The cable according to claim 15.

17. The plurality of sections are arranged at positions that are substantially rotationally symmetric in a cross section orthogonal to the second axis. The cable according to claim 15 or 16.

18. The sensing cable included in the cable according to any one of claims 1 to 17.

19. A light source unit that outputs test light to be input to the sensing optical fiber of the cable according to any one of claims 1 to 14, A measurement unit that measures the backward scattered light output corresponding to the test light from the sensing optical fiber, An arithmetic unit that calculates the shape of the cable based on the measurement results of the backward scattered light of each of the sensing optical fibers in the measurement unit. A cable shape sensing system comprising:

20. A light source unit that outputs test light to be input to the sensing optical fiber of the cable according to any one of claims 15 to 17, A measurement unit that measures the backward scattered light generated in the sensing optical fiber corresponding to the test light, An arithmetic unit that divides the measurement result of the backward scattered light in the measurement unit into the measurement results of each of the sections and calculates the shape of the sensing cable based on the measurement results of the plurality of sections. A cable shape sensing system comprising:

21. Each of the backward scattered lights is Rayleigh scattered light, The cable shape sensing system according to claim 19 or 20, configured to be able to calculate the strain of each of the cores using the optical frequency domain reflectometry method.

22. Each of the backward scattered lights is Brillouin scattered light, The cable shape sensing system according to claim 19 or 20, configured to be able to calculate the strain of each of the cores based on the measurement results regarding the Brillouin scattered light.

23. A cable-shaped sensing system according to claim 20, comprising an optical device that inputs test light into the sensing optical fiber and inputs the backward scattered light output from the plurality of sections corresponding to the test light into the measuring unit.

24. A test light transmission path that transmits the test light to the optical device, A backward scattered light transmission path that is provided separately from the test light transmission path and transmits the backward scattered light from the optical device to the measuring unit, A cable-shaped sensing system according to claim 23, comprising:

25. Comprising a plurality of sensing optical fibers as the sensing optical fiber, A light source unit having a pump light source that outputs pump light input to one end of the plurality of sensing optical fibers and a probe light source that outputs probe light input to the other end of the plurality of sensing optical fibers, A measuring unit that measures the probe light amplified by Brillouin by the pump light in the plurality of sensing optical fibers, An optical device that inputs each of the pump light and the probe light into the plurality of sensing optical fibers and inputs the probe light from the plurality of sensing optical fibers into the measuring unit, An arithmetic unit that calculates the strain of each of the sensing optical fibers based on the measurement results of the probe light from the plurality of sensing optical fibers in the measuring unit and calculates the shape of the sensing cable based on the calculated strain, A cable-shaped sensing system according to claim 20, comprising:

26. Comprising a sensing optical fiber having at least four sections that are folded back at the longitudinal ends and connected in series, A light source unit having a pump light source that outputs pump light input to one end of the sensing optical fiber and a probe light source that outputs probe light input to the other end of the sensing optical fiber, A measuring unit that measures the probe light amplified by Brillouin by the pump light in the sensing optical fiber, An optical device that inputs each of the pump light and the probe light into the sensing optical fiber and inputs the probe light from the one end of the sensing optical fiber into the measuring unit, An arithmetic unit that divides the measurement result of the probe light from the sensing optical fiber in the measurement unit into the measurement results of each of the at least four sections, calculates the strain of each of the at least four sections, and calculates the shape of the sensing cable based on the calculated strain; The cable shape sensing system according to claim 20, comprising the above.

27. A pump light transmission path that transmits the pump light to the optical device; A probe light transmission path that transmits the probe light to the optical device; The pump light transmission path and the probe light transmission path are separate, and a backward propagation probe light transmission path that transmits the probe light output from the core from the optical device to the measurement unit; The cable shape sensing system according to claim 25 or 26, comprising the above.

28. The cable shape sensing system according to any one of claims 19 to 27, wherein a temperature distribution in the longitudinal direction of the sensing cable is obtained based on the measurement result by the measurement unit, and the calculated strain is corrected based on the temperature distribution.

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