Connection structure and connection method

Abstract

To provide a connection structure and a connection method of an optical fiber sensor for suppressing an influence of distortion of an object on an optical fiber.SOLUTION: A connection part 20 is a connection structure for connecting a communication cable 11 having an optical fiber wire 27 and a covering part 25 surrounding the optical fiber wire 27 to an optical fiber sensor 1 having an outer tube 5 fixed to a structure 3 and an optical fiber wire 7 inserted into the outer tube 5 in a state of not being restrained in an axial direction. This device is provided with a protective vessel 17 for housing the fused part 31 of optical fibers 7 and 27, and a slackened part 7s where the optical fibers 7 are slackened is formed in the protective vessel 17.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a connection structure and a connection method for an optical fiber sensor. [Background technology]

[0002] Optical fiber sensors for measuring the strain and temperature of an object have been known for some time (see, for example, Patent Document 1). This type of optical fiber sensor is installed on the object, and a measuring instrument emits laser pulsed light into the optical fiber. The backscattered light observed when this pulsed light is incident is analyzed by the measuring instrument, thereby measuring the strain distribution and temperature distribution of the object over the entire length of the optical fiber sensor. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-88155 Summary of the Invention [Problem to be solved by the invention]

[0004] Among these types of optical fiber sensors, there is one that has a structure in which an outer tube that protects the optical fiber is installed in the target object, and the optical fiber is inserted into the hollow part of the outer tube without being constrained in the axial direction. This optical fiber sensor uses the above structure to suppress the effect of strain on the optical fiber in the target object, and is used, for example, when measuring only the temperature of the target object.

[0005] For example, a communication cable for communicating with a measuring instrument is connected to both ends of the optical fiber sensor, and the optical fibers of the optical fiber sensor and the communication cable are fused at the connection. Depending on the structure of the protective part that protects the fused part, the influence of strain of the object may be transmitted to the optical fiber via the protective part. In view of this problem, an object of the present invention is to provide a connection structure and connection method for an optical fiber sensor that suppresses the influence of strain of the object on the optical fiber. [Means for solving the problem]

[0006] The gist of the present invention lies in the following [1] to [5].

[0007] [1] A connection structure for connecting an optical fiber sensor having an outer tube fixed to an object to be measured and a first optical fiber inserted into the outer tube without being constrained in the axial direction to an optical fiber cable having a second optical fiber and an enclosure material surrounding the second optical fiber, the connection structure comprising a protective container fixed to the object to be measured, to which an end of the outer tube and an end of the enclosure material are fixed, and which houses a fused portion between the first optical fiber protruding from the end of the outer tube and the second optical fiber protruding from the end of the enclosure material, and a slack portion in which the first optical fiber is slackened is formed within the protective container.

[0008] [2] The connection structure according to [1], wherein the fused portion is movable within the protective container.

[0009] [3] The connection structure according to [1] or [2], wherein a fiber guide section is provided within the protective container to guide the first optical fiber in a meandering manner and to change the radius of curvature of the meandering portion of the first optical fiber, and the slack portion is formed by the meandering portion.

[0010] [4] The connection structure according to any one of [1] to [3], wherein the optical fiber sensor is a temperature sensor for measuring the temperature of the object to be measured, and the optical fiber cable is a communication cable for communication between the optical fiber sensor and a measuring instrument.

[0011] [5] A connection method for connecting an optical fiber sensor having an outer tube fixed to an object to be measured and a first optical fiber inserted into the outer tube without being axially constrained, to an optical fiber cable having a second optical fiber and an enclosure material surrounding the second optical fiber, the connection method comprising: forming a fusion portion between the first optical fiber and the second optical fiber within a protective container that protects the connection portion between the optical fiber sensor and the optical fiber cable; fixing an end of the outer tube and an end of the enclosure material to the protective container; and, with the protective container fixed to the object to be measured, moving the fusion portion within the protective container to form a slack portion in the first optical fiber. [Effects of the Invention]

[0012] According to the present invention, it is possible to provide a connection structure and a connection method for an optical fiber sensor that suppress the influence of strain of an object on an optical fiber. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a diagram schematically illustrating a state in which an optical fiber sensor to which the connection structure of the first embodiment is applied is installed in a structure. [Figure 2] FIG. 3 is an enlarged cross-sectional view showing the vicinity of a connection portion in the first embodiment. [Figure 3] 10A and 10B are cross-sectional views showing an example of a connection method for constructing a connection portion. [Figure 4] 10(a) and 10(b) are cross-sectional views showing modified examples of the connection portion. [Figure 5] FIG. 10 is a cross-sectional view showing a connection portion according to a second embodiment. [Figure 6]FIG. 10 is a cross-sectional view showing a connection portion according to a third embodiment. [Figure 7] FIG. 11 is a cross-sectional view showing a modified example of the connection portion of the third embodiment. [Figure 8] FIG. 10 is a diagram schematically illustrating a state in which an optical fiber sensor to which a connection structure according to a fourth embodiment is applied is installed in a structure. [Figure 9] FIG. 10 is an enlarged cross-sectional view showing the vicinity of a connection portion in a fourth embodiment. [Figure 10] 10A and 10B are cross-sectional views showing an example of a connection method for constructing a connection portion. [Figure 11] FIG. 10 is a cross-sectional view showing a modified example of the connection portion. DETAILED DESCRIPTION OF THE INVENTION

[0014] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of a connection structure and a connection method according to the present invention will be described in detail with reference to the drawings.

[0015] [First embodiment] FIG. 1 is a diagram schematically illustrating a state in which an optical fiber sensor 1 to which a connection structure and connection method according to a first embodiment is applied is installed in a structure 3, which is an object to be measured. Hereinafter, the term "axial direction" simply refers to the axial direction of the optical fiber sensor 1. The optical fiber sensor 1 is fixed to the surface of the structure 3 (e.g., a concrete structure) and is used as a temperature sensor that measures the temperature of the structure 3. For example, an optical fiber sensor (not shown) for measuring strain is installed in parallel with the optical fiber sensor 1 in addition to the optical fiber sensor 1. Then, in order to eliminate the influence of temperature on the strain measurement sensor, the optical fiber sensor 1 of this embodiment, which can measure the temperature of the structure 3, is used.

[0016] The optical fiber sensor 1 includes an outer tube 5 made of, for example, a metal, and an optical fiber 7 inserted into the hollow portion of the outer tube 5. The outer tube 5 is, for example, a stainless steel tube, and is bonded to the surface of the structure 3 over its entire length. The optical fiber 7 is inserted into the hollow portion of the outer tube 5 without being constrained in the axial direction. In other words, the optical fiber 7 is not fixed to the inner wall surface of the outer tube 5, and is able to slide in its own axial direction within the hollow portion of the outer tube 5.

[0017] A communication cable 11 for communicating with a measuring instrument 13 is connected to each end of the optical fiber sensor 1. That is, each end of the optical fiber sensor 1 is connected to the measuring instrument 13 via the communication cable 11. A predetermined connection structure is constructed at a connection portion 20 between the optical fiber sensor 1 and the communication cable 11.

[0018] The measuring instrument 13 is a strain / temperature measuring instrument such as an OTDR (Optical Time Domain Reflectometer), BOTDR (Brillouin Optical Time Domain Reflectometer), TW-COTDR (Tunable Wavelength Coherent Optical Time Domain Reflectometry), or OFDR (Optical Frequency Domain Reflectometry). When pulsed light is incident from the measuring instrument 13 onto the optical fiber line 7 of the optical fiber sensor 1 through the communication cable 11, scattered light from various locations along the length of the optical fiber line 7 returns to the measuring instrument 13. The frequency of this scattered light is analyzed by the measuring instrument 13, thereby determining the temperature of various locations along the length of the optical fiber line 7 and, ultimately, the temperature distribution of the structure 3 over the entire length of the optical fiber sensor 1.

[0019] Intrinsically, the scattered light in this type of optical fiber sensor is affected by both the strain and temperature of the object being measured. In contrast, in the optical fiber sensor 1 of this embodiment, as described above, the optical fiber 7 is not constrained within the outer tube 5, so it can be considered that the optical fiber 7 is almost unaffected by the strain of the structure 3. Therefore, it can be considered that the measurement value in this embodiment is almost free from the influence of the strain of the structure 3 and reflects only the temperature of the structure 3. However, in order to achieve such temperature measurement, it is necessary to prevent the influence of the strain of the structure 3 from being transmitted to the optical fiber 7 at the connection part 20. Therefore, the connection parts 20, 20 in this embodiment have the following connection structure.

[0020] FIG. 2 is an enlarged cross-sectional view showing the vicinity of one of the connection parts 20 (the connection part 20 on the right side shown in FIG. 1). At the connection part 20, the optical fiber sensor 1 and the communication cable 11 are connected so that they are connected in a straight line. The optical fiber line 7 of the optical fiber sensor 1 is slightly longer than the outer tube 5, and the end of the optical fiber line 7 protrudes from the end of the outer tube 5. The communication cable 11 includes an optical fiber line 27 and a covering part 25 (enveloping material) that covers the optical fiber line 27. The covering part 25 has a known structure that includes, for example, a stainless steel pipe that surrounds the optical fiber line 27, a tension member that is parallel to the stainless steel pipe, and a PE sheath that encases the stainless steel pipe and the tension member.

[0021] The connection portion 20 includes a protective container 17 for protecting the optical fiber strands 7 and 27 exposed at the connection portion 20. The optical fiber sensor 1 and the communication cable 11 are inserted into the protective container 17 so as to face each other from opposite directions, and the protective container 17 accommodates a fusion spliced ​​portion 31 between the optical fiber strand 7 (first optical fiber) and the optical fiber strand 27 (second optical fiber). The protective container 17 is a tubular member having a diameter slightly larger than that of the optical fiber sensor 1 and the communication cable 11. The protective container 17 is strong and does not easily deform, and is made of, for example, an acrylic resin. An end of the optical fiber sensor 1 is inserted into one opening of the protective container 17, and an end of the outer tube 5 is bonded and fixed to the inner wall surface of the protective container 17. Similarly, an end of the communication cable 11 is inserted into the other opening of the protective container 17, and an end of the coating 25 is bonded and fixed to the inner wall surface of the protective container 17. The protective container 17 is then bonded and fixed to the surface of the structure 3. The symbol H in the figure indicates an adhesive layer.

[0022] In the internal space 29 of the protective container 17, the optical fiber 7 of the optical fiber sensor 1 protrudes from the end opening of the outer tube 5, and the optical fiber 27 of the communication cable 11 protrudes from the end face of the coating 25. The optical fiber 7 and the optical fiber 27 are butted together in the axial direction and fused. A protective material 33 made of, for example, a heat-shrinkable tube is provided so as to be tightly wound around the fused portion 31. A gap is provided between the protective material 33 and the inner wall surface of the protective container 17, and the optical fiber 7, 27 and the protective material 33 are not constrained by the protective container 17.

[0023] As described above, one of the connection parts 20 (the connection part 20 on the right side shown in FIG. 1) has been described, but the other connection part 20 (the connection part 20 on the left side shown in FIG. 1) also has a similar configuration with a symmetrical structure to that shown in FIG. 2.

[0024] As described above, in order to prevent the influence of the distortion of the structure 3 from being transmitted to the optical fiber 7, it is sufficient to prevent tensile and compressive forces from acting on the optical fiber 7 due to the positional fluctuation of the fused portion 31 caused by the distortion of the structure 3. That is, for example, a slack portion may be formed at any position of the optical fiber 7. As an example of this configuration, in this embodiment, as shown in FIG. 2, a slack portion 7s is formed in the internal space 29 by slackening a part of the optical fiber 7. The slack portion 7s may extend into the outer tube 5.

[0025] An example of a connection method for constructing the connection portion 20 having the slack portion 7s will be described. First, the optical fiber 27 of the communication cable 11 is exposed from the coating 25, and as shown in FIG. 3 , the optical fiber 27 is fusion-spliced ​​to the optical fiber 7 of the optical fiber sensor 1. This fusion splicing process is performed using a conventional fusion splicer. A heat-shrinkable tube is placed around the fusion portion 31 and heat-treated, thereby tightly adhering the protective material 33 to the optical fiber 7 and the optical fiber 27. Then, a protective container 17 is placed around the protective material 33, and the outer tube 5 of the optical fiber sensor 1 and the coating 25 of the communication cable 11 are bonded to both ends of the protective container 17, respectively, thereby sealing the internal space 29. The protective container 17 is bonded to the surface of the structure 3. The above process is performed for each of the two connection portions 20, 20 at both ends of the optical fiber sensor 1.

[0026] Then, in each of the two connection portions 20, 20, the protective material 33 is slid within the internal space 29 in a direction toward the outer tube 5 (in the direction of arrow A in the figure). As a result, as shown in FIG. 2, the fused portion 31 is pushed toward the optical fiber 7, and a slack portion 7s is formed in the optical fiber 7 (slack portion forming process). Note that at this time, the optical fiber 27 may be pulled and pulled out of the coating portion 25, or distortion may occur in the optical fiber 27, but this does not affect the temperature measurement results using the optical fiber 7. The protective material 33 slid as described above is not fixed to the protective container 17 and is able to slide axially within the internal space 29. This completes the connection portion 20. In the completed connection portion 20, the slack portion 7s of the optical fiber 7 exists within the internal space 29, and the protective material 33 is able to slide axially within the internal space 29 of the protective container 17.

[0027] In the above-described connection method, as shown in FIG. 4( a), a magnet 32 ​​may be fixed to the protective material 33 as a mechanism for sliding the protective material 33 within the sealed protective container 17. In this case, the protective material 33 of the protective container 17 can be moved using another magnet from outside the protective container 17. A member made of a magnetic material may be used instead of the magnet 32. A sliding mechanism may also be provided to allow the protective material 33 to smoothly slide along the inner wall surface of the protective container 17. For example, as shown in FIG. 4( b), a sliding member 34 that slides on the inner wall surface of the protective container 17 may be attached to the protective material 33. A rail or the like that guides the sliding member 34 in the axial direction may also be provided on the inner wall surface of the protective container 17. Such a sliding mechanism remains in place even after the connection portion 20 is completed, facilitating the sliding of the protective material 33 within the internal space 29. The protective container 17 may also have a split structure. In this case, the protective container 17 may be temporarily opened to directly move the protective material 33 during the loosened portion forming process.

[0028] The effects of the splice 20 and splice method described above will be explained. When strain occurs in the structure 3, the position of the splice 20 relative to the optical fiber lines 7 fluctuates, which may result in a change in the positional relationship between the optical fiber lines 7 and the fused part 31. In this case, according to the connection structure of the splice 20, the displacement of the fused part 31 is absorbed by the slack part 7s of the optical fiber lines 7, and the tensile and compressive forces acting on the optical fiber lines 7 are suppressed. Furthermore, the fused part 31 (protective material 33) is free to displace in the axial direction within the protective container 17, which also suppresses the tensile and compressive forces acting on the optical fiber lines 7.

[0029] Furthermore, distortion of the structure 3 may cause the relative positions of the two spliced ​​portions 20, 20 (FIG. 1) to fluctuate, which may result in a change in the relative positions of both ends (two fused portions 31, 31) of the optical fiber line 7. Even in this case, the change in the relative positions of the two fused portions 31, 31 is absorbed by the slack portion 7s of the optical fiber line 7 and also by the fused portion 31 (protective material 33) being freely displaceable in the axial direction within the protective container 17. Therefore, the tensile and compressive forces acting on the optical fiber line 7 are suppressed.

[0030] As described above, the above-described connection part 20 and connection method suppress the influence of the distortion of the structure 3 transmitted to the optical fiber strand 7. Therefore, in measuring the temperature of the structure 3 using the measuring instrument 13 (FIG. 1), the influence of the distortion of the structure 3 is suppressed, and the temperature of the structure 3 can be measured accurately.

[0031] Second Embodiment Next, the connection structure of a connection part 40 according to a second embodiment will be described with reference to Fig. 5. In this embodiment, a connection part 40 described below is used instead of the connection part 20 shown in Fig. 1. Below, differences from the first embodiment will be mainly described, and identical or equivalent components will be denoted by the same reference numerals in the drawings, and redundant description will be omitted.

[0032] In the splice 40 of this embodiment, a fiber guide 41 for forming a slack portion 7s is provided in the internal space 29 of the protective container 17. The fiber guide 41 has a plurality of protrusions 43 extending from the inner wall surface of the protective container 17 in a direction perpendicular to the axial direction. The optical fiber line 7 extends in a meandering manner, alternately bypassing the plurality of protrusions 43, and this meandering portion forms the slack portion 7s. The optical fiber line 7 in the slack portion 7s meanders along a path that leaves a gap between the optical fiber line 7 in the slack portion 7s and the outer peripheral surfaces of the protrusions 43. Because there is a gap between the optical fiber line 7 in the slack portion 7s and the outer peripheral surfaces of the protrusions 43, when tension or compression in the axial direction acts on the optical fiber line 7, the radius of curvature of the slack portion 7s (meandering portion) changes, and the tension or compression is absorbed. As described above, the fiber guide section 41 guides the optical fiber strand 7 in a meandering manner within the protective container 17, making the radius of curvature of the meandering portion variable, and the slack portion 7s of the optical fiber strand 7 is formed by the meandering portion.

[0033] The connection structure of the connection part 40 as described above also provides the same effects as the connection part 20 of the first embodiment. That is, when the positional relationship between the optical fiber line 7 and the fused part 31 changes due to distortion of the structure 3, the displacement of the fused part 31 is absorbed by the change in the curvature of the meandering of the slack part 7s. Also, when the positional relationship between both ends (two fused parts 31, 31) of the optical fiber line 7 changes due to distortion of the structure 3, this change is absorbed by the change in the curvature of the meandering of the slack part 7s. Therefore, tensile and compressive forces acting on the optical fiber line 7 are suppressed, that is, the influence of distortion of the structure 3 transmitted to the optical fiber line 7 is suppressed. Note that, as illustrated in FIG. 5 , a fiber guide part 41 may also be provided on the optical fiber line 27 side, and a slack part 27s in which the optical fiber line 27 is slackened may be formed.

[0034] Third Embodiment Next, the connection structure of a connection unit 60 according to a third embodiment will be described with reference to Fig. 6. Fig. 6 is a cross-sectional view of the connection unit 60 as seen from a direction perpendicular to the surface of the structure 3 on which the optical fiber sensor 1 is installed. In this embodiment, the connection unit 60 described below is used instead of the connection unit 20 shown in Fig. 1. Below, differences from the first and second embodiments will be mainly described, and identical or equivalent components will be denoted by the same reference numerals in the drawings, and redundant description will be omitted.

[0035] In the connection portion 60 of this embodiment, the optical fiber sensor 1 and the communication cable 11 are inserted parallel to each other in the same direction into a protective container 67. The protective container 67 is strong and does not easily deform, and is made of, for example, an acrylic resin. The protective container 67 has two parallel insertion openings 63, 63 adjacent to each other. The end of the optical fiber sensor 1 is inserted into one of the insertion openings 63, and the end of the outer tube 5 is adhered and fixed to the inner wall surface of the protective container 67. The end of the communication cable 11 is inserted into the other insertion opening 63, and the end of the coating 25 is adhered and fixed to the inner wall surface of the protective container 67. The protective container 67 is adhered and fixed to the surface of the structure 3.

[0036] In the internal space 69 of the protective container 67, the optical fiber line 7 and the optical fiber line 27 are bent and fused so that their end faces face each other. A protective material 33 is installed at this fused portion 31. The optical fiber lines 7, 27 and the protective material 33 are not constrained by the protective container 17. A slack portion 7s, in which part of the optical fiber line 7 is slackened, is formed in the internal space 29.

[0037] An example of a connection method for constructing such a connection portion 60 will be described. The optical fiber wires 7 and 27 are fused together, and a protective material 33 is provided around the fused portion 31. A protective container 67 is then placed over the protective material 33, and the outer tube 5 of the optical fiber sensor 1 and the sheath 25 of the communication cable 11 are adhered to the insertion openings 63, 63, respectively, thereby sealing the internal space 69. The protective container 67 is adhered to the surface of the structure 3. The above process is performed for each of the two connection portions 60, 60 at both ends of the optical fiber sensor 1.

[0038] Thereafter, in each of the two connection portions 60, 60, the protective material 33 is slid within the internal space 69 toward the optical fiber 7 in the axial direction of the optical fiber 7 (in the direction of arrow A3 in the figure). As a result, the fused portion 31 is pushed and moved toward the optical fiber 7, and a slack portion 7s is generated in the optical fiber 7 (slack portion forming process). The protective material 33 slid as described above is no longer fixed to the protective container 67 and is movable within the internal space 69. This completes the connection portion 60. In the completed connection portion 60, the slack portion 7s of the optical fiber 7 exists within the internal space 69, and the protective material 33 is movable within the internal space 69 of the protective container 67. This connection portion 60 also provides the same effects as the connection portion 20 of the first embodiment.

[0039] Furthermore, even in this structure in which the optical fiber sensor 1 and the communication cable 11 are inserted parallel to each other from the same direction into the protective container 67, a fiber guide 41 for forming a slack portion 7s in the optical fiber 7 may be installed in the internal space 69 of the protective container 67, as shown in Fig. 7. The structure of the fiber guide 41 is similar to that of the connection part 40 of the second embodiment. Furthermore, a fiber guide 41 may also be provided on the optical fiber line 27 side, and a slack portion 27s may be formed by slackening the optical fiber line 27. With such a connection structure, the same effects as those of the connection part 40 of the second embodiment can be obtained.

[0040] [Fourth embodiment] Next, the connection structure of a connection section 80 according to a fourth embodiment will be described with reference to Fig. 8 and Fig. 9. Fig. 8 is a diagram schematically showing a state in which an optical fiber sensor 1 to which the connection structure and connection method of this embodiment is applied is installed in a structure 3. Fig. 9 is a cross-sectional view of the connection section 80 as seen from a direction perpendicular to the surface of the structure 3 on which the optical fiber sensor 1 is installed. Below, differences from the first to third embodiments will be mainly described, and identical or equivalent components will be denoted by the same reference numerals in the drawings, and redundant description will be omitted.

[0041] As shown in FIG. 8 , in this embodiment, optical fiber sensors 1 and 1B are installed parallel to and close to each other on a structure 3. Optical fiber sensor 1B has the same configuration as optical fiber sensor 1 and includes an outer tube 5B (enclosure material) and an optical fiber wire 7B (second optical fiber). The right ends of optical fiber sensors 1 and 1B are connected to each other, and a communication cable 11 for connecting to a measuring instrument 13 is connected to each left end of each of optical fiber sensors 1 and 1B. With this wiring, the two optical fiber sensors 1 and 1B are connected in series so as to travel back and forth through the structure 3, and each independently measures the temperature of the structure 3. The left ends of optical fiber sensors 1 and 1B and the communication cable 11 are connected by the aforementioned connection part 20 ( FIG. 2 ). A connection part 80 connecting the right ends of optical fiber sensors 1 and 1B has the following connection structure.

[0042] 9, the connection part 80 has a structure in which the communication cable 11 of the connection part 60 (FIG. 6) in the third embodiment is replaced with an optical fiber sensor 1B. The optical fiber wire 7 (first optical fiber) of the optical fiber sensor 1 has a slack portion 7s formed in the internal space 69 by slackening a portion of the optical fiber wire 7. Similarly, the optical fiber wire 7B (second optical fiber) of the optical fiber sensor 1B has a slack portion 7Bs formed in the internal space 69 by slackening a portion of the optical fiber wire 7B.

[0043] An example of a connection method for constructing such a connection portion 80 will be described below. As shown in Fig. 10, the optical fiber wires 7 and 7B are fused together, and a protective material 33 is provided around the fused portion 31. Thereafter, a protective container 67 is placed over the protective material 33, and the outer tube 5 of the optical fiber sensor 1 and the outer tube 5B of the optical fiber sensor 1B are adhered to the insertion openings 63, 63, respectively, thereby sealing the internal space 69. The protective container 67 is adhered to the surface of the structure 3.

[0044] Thereafter, the protective material 33 is slid within the internal space 69 in the axial direction of the optical fiber sensors 1, 1B (in the direction of arrow A4 in the figure) toward the outer tubes 5, 5B. As a result, as shown in FIG. 9 , the fused portion 31 is pushed and moved toward the outer tubes 5, 5B, causing a slack portion 7s in the optical fiber 7 and a slack portion 7Bs in the optical fiber 7B (slack portion forming process). The protective material 33 slid as described above is no longer fixed to the protective container 67 and is movable within the internal space 69. This completes the connection 80. In the completed connection 80, the slack portion 7s of the optical fiber 7 and the slack portion 7Bs of the optical fiber 7B exist within the internal space 69, and the protective material 33 is movable within the internal space 69 of the protective container 67.

[0045] Such a connecting part 80 also provides the same effects as the connecting part 20 of the first embodiment. In this case, the influence of strain of the structure 3 transmitted to the optical fiber lines 7, 7B of both the two optical fiber sensors 1, 1B is suppressed.

[0046] 7, a fiber guide 41 for forming a slack portion 7s in the optical fiber 7 may be installed in the internal space 69 of the protective container 67. The structure of the fiber guide 41 is similar to that of the connection part 40 of the second embodiment. Also, a fiber guide 41 may be provided on the optical fiber 7B side, and a slack portion 7Bs may be formed by slackening the optical fiber 7B. With such a connection structure, the same effects as those of the connection part 40 of the second embodiment can be obtained.

[0047] The present invention can be implemented in various forms, including the above-described embodiment, with various modifications and improvements based on the knowledge of those skilled in the art. It is also possible to configure modified examples by utilizing the technical matters described in the above-described embodiment. The configurations of the respective embodiments may be used in appropriate combination.

[0048] In the first embodiment, the optical fiber sensor 1 is installed on the surface of the structure 3. However, as shown in FIG. 11 , a connection portion 20 with a similar connection structure can be constructed even when the optical fiber sensor 1 is embedded inside the structure 3. In this case, the protective container 17 is also embedded and fixed inside the structure 3. In each embodiment, a plurality of optical fiber wires may be wired inside the protective container 17, 67, and the above-described slack portion may be formed in each optical fiber wire. In each embodiment, the optical fiber sensor 1 is connected to the communication cable 11 or the optical fiber sensor 1B, but the connection structure of the present invention can also be applied to connection structures in which various other optical fiber cables are connected. [Explanation of symbols]

[0049] 1...optical fiber sensor, 3...structure (object to be measured), 5...outer tube, 7...optical fiber wire (first optical fiber), 11...communication cable (optical fiber cable), 20, 40, 60, 80...connection part, 27...optical fiber wire (second optical fiber), 25...coating part (enclosure material), 17, 67...protective container, 31...fusion part, 7s...slack part, 41...fiber guide part, 1B...optical fiber sensor (optical fiber cable), 5B...outer tube (enclosure material), 7B...optical fiber wire (second optical fiber).

Claims

1. A connection structure for connecting an optical fiber sensor having an outer tube fixed to an object to be measured and a first optical fiber inserted into the outer tube without being constrained in the axial direction to an optical fiber cable having a second optical fiber and an enclosure material surrounding the second optical fiber, a protective container that is fixed to the measurement object, that fixes an end of the outer tube and an end of the envelope material, and that houses a fused portion between the first optical fiber protruding from the end of the outer tube and the second optical fiber protruding from the end of the envelope material; A connection structure in which a slack portion where the first optical fiber is slackened is formed inside the protective container.

2. The connection structure according to claim 1 , wherein the fusion portion is movable within the protective container.

3. a fiber guide section is provided in the protective container to guide the first optical fiber in a meandering manner and to vary the radius of curvature of the meandering portion of the first optical fiber; The connection structure according to claim 1 , wherein the slack portion is formed by the meandering portion.

4. the optical fiber sensor is a temperature sensor for measuring the temperature of the measurement object, 2. The connection structure according to claim 1, wherein the optical fiber cable is a communication cable for communication between the optical fiber sensor and a measuring instrument.

5. A connection method for connecting an optical fiber sensor having an outer tube fixed to a measurement object and a first optical fiber inserted into the outer tube without being constrained in an axial direction to an optical fiber cable having a second optical fiber and an enclosure material surrounding the second optical fiber, the method comprising: a fusion portion between the first optical fiber and the second optical fiber is formed within a protective container that protects the connection between the optical fiber sensor and the optical fiber cable, an end of the outer tube and an end of the surrounding material are fixed to the protective container, and in a state where the protective container is fixed to the object to be measured, the fusion portion is moved within the protective container to form a slack portion in the first optical fiber.

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