Optical fiber installation structure and optical fiber material

Abstract

To provide an optical fiber material that makes it possible to measure stably and with high measurement accuracy in an optical fiber sensing, and to provide a manufacturing method of the optical fiber material.SOLUTION: In an optical fiber material of the present invention, a plurality of optical fiber installation structures is provided with prescribed intervals. A part of resin coating 21 of a coated optical fiber 20 is removed, in which an optical fiber bare wire 24 is in an exposed state. The optical fiber bare wire 24 and the coated optical fiber 20 in both ends of the optical fiber bare wire are fixed by a same member (fixation unit 30). The fixation unit 30 has a structure in which a foundation flat plate 31 and a convexity flat plate 32 partially provided in an almost center part are integrated, in which the optical fiber bare wire 24 is fixed by the convexity flat plate 32 and the coated optical fiber 20 is fixed by the foundation flat plate 31. The convexity flat plate 32 does not contact with a cross section 21A of the resin coating 21 of the coated optical fiber 20. In this state, a space S around a coating removal part is filled with a filler, thereby an optical fiber installation structure is manufactured.SELECTED DRAWING: Figure 9

Description

[Technical Field]

[0001] The present invention relates to an optical fiber installation structure and a method for manufacturing the same, an optical fiber material on which a plurality of such optical fiber installation structures are installed and a method for manufacturing the same, and a method for installing such an optical fiber material. [Background technology]

[0002] There is a method (optical fiber sensing) in which optical fiber sensors are attached to structures to measure strain, deformation, etc. Various improvements have been made to optical fiber sensing from the perspective of improving measurement accuracy, etc.

[0003] In Patent Document 1, an optical fiber sensor is adhesively fixed at multiple locations spaced apart in the longitudinal direction using pieces of cloth. In Patent Document 1, the pieces of cloth are made by cutting out a portion of a nonwoven fabric, which is a material used in civil engineering structures, and the reason for this is said to be that when buried in a river bank, the fabric blends well with the sediment, and the sediment and the optical fiber are displaced together.

[0004] Patent Document 2 discloses an optical fiber grating strain sensor having a structure in which an optical fiber grating section, in which a periodic refractive index distribution structure is formed in at least one of the core or cladding, is sandwiched between a first thin plate and a second thin plate via a brazing material and fused. In the invention described in Patent Document 2, when considering any cross section of the optical fiber grating section, it always comes into contact with the thin plate at two points, which allows the sensor to be accurately positioned relative to the thin plate.

[0005] Patent Document 3 discloses a method for fixing an optical fiber cable, in which an optical fiber cable is brought into contact with or close to the surface of a structure to be attached while being subjected to a tension that generates a desired elastic elongation strain, and more than half of the outer periphery of the optical fiber cable, together with the nearby surface of the structure, is covered with a reactive-curing resin-based composition containing aggregate to form a coating layer, and then the resin-based composition is cured to fix the cable to the surface of the structure as a support surface. In the invention described in Patent Document 3, the coating layer of the resin-based composition containing aggregate maintains its adhesive strength for a long period of time and does not creep, so that the optical fiber cable can be fixed to the surface of the structure while being given a uniform elastic elongation strain for a long period of time.

[0006] Patent Document 4 discloses an optical fiber tensioning system for ground movement observation, characterized in that cables are stretched along the ground surface, supported by a group of piles arranged like stepping stones in the observation area and fixed to the ground, and optical fibers are attached and tensioned in parallel to the tension cables, which act as splint-like supports. The optical fiber tensioning system for ground movement observation described in Patent Document 4 is capable of detecting ground movement stably and with high accuracy over a long period of time.

[0007] As such, various improvements have been made to optical fiber sensing, such as the method of attaching optical fiber cables, but further improvements in measurement accuracy are required, and the development of technology that can meet these demands is desired. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Laid-Open No. 2001-249035 [Patent Document 2] Japanese Patent Application Laid-Open No. 2005-121769 [Patent Document 3] Japanese Patent Application Laid-Open No. 2002-131024 [Patent Document 4] Japanese Patent Application Laid-Open No. 2002-317451 Summary of the Invention [Problem to be solved by the invention]

[0009] The present invention has been made in consideration of the above-mentioned background art, and its object is to provide an optical fiber material and a manufacturing method thereof that enable stable, high-precision measurements in optical fiber sensing. [Means for solving the problem]

[0010] The present inventors have conducted extensive research to solve the above problems and have discovered that measurement accuracy may be reduced due to the internal structure of the optical fiber cable.

[0011] The structure of an optical fiber cable (optical fiber core 20) used for optical fiber sensing is shown in Figure 1. The optical fiber cable (optical fiber core 20) has a structure in which a bare optical fiber 24 is covered with two layers of resin coating 21 (a primary coating 22 and a secondary coating 23). The bare optical fiber 24 consists of a core and an outer cladding, with the core having a higher refractive index than the cladding. The core and cladding are made of quartz glass or plastic, which have very high light transmittance. The primary coating 22 is made of ultraviolet (UV) curable resin, and the combined portion of the bare optical fiber 24 and primary coating 22 is called an optical fiber strand. The secondary coating 23 is made of thermoplastic resin.

[0012] The inventors have estimated that because the friction between the bare optical fiber 24 and the resin coating 21 inside the optical fiber cable is small, when tension is applied to the optical fiber core 20, the bare optical fiber 24 slips inside the optical fiber cable, which significantly reduces measurement accuracy.

[0013] The inventor discovered that such slippage can be prevented by removing a portion of the optical fiber cable (optical fiber core 20) to expose the bare optical fiber 24, and then fixing the bare optical fiber 24 and the optical fiber core 20 at both ends with the same member, and thus completed the present invention.

[0014] That is, the present invention provides an optical fiber installation structure for installing an optical fiber in a structure that is a target for measurement by an optical fiber sensor, comprising: the optical fiber installation structure has a coating removal portion where a resin coating of the optical fiber core wire is removed to expose a bare optical fiber, the bare optical fiber in the coating removal portion and the two coated optical fiber cores in the coating remaining portions at both ends of the coating removal portion from which the resin coating has not been removed are fixed by fixing units, The fixing unit has a structure in which a base plate and a convex plate partially provided in the approximate center of the base plate are integrated together, the bare optical fiber in the coating-removed portion is fixed by the convex plate; the optical fiber cores in the coating remaining portions at both ends of the coating removal portion are fixed by the surface of the base plate that has the convex plate, the convex plate is not in contact with the cross section of the resin coating of the optical fiber core; The space around the coating removal portion is filled with a filler. The present invention provides an optical fiber installation structure characterized by the above features.

[0015] The present invention also provides an optical fiber material comprising a core optical fiber and a plurality of the optical fiber installation structures described above installed on the core optical fiber.

[0016] The present invention also provides a method for manufacturing an optical fiber installation structure for installing an optical fiber in a structure that is a target for measurement by an optical fiber sensor, the method comprising: (1) a step of removing a resin coating from an optical fiber core to form a coating-removed portion where a bare optical fiber is exposed between two remaining coating portions where the resin coating has not been removed; (2) A step of adhering a convex plate of a fixing unit having an integrated structure of a base plate and a convex plate partially provided in the approximately central portion of the base plate to the bare optical fiber in the coating removal portion without contacting the cross section of the resin coating of the optical fiber core wire in the coating remaining portions at both ends of the coating removal portion; (3) a step of adhering the base plate of the fixing unit to the optical fiber in the remaining coating portion at both ends of the coating removal portion on the surface having the convex plate; and (4) A step of filling the space around the coating removal portion with a filler. The present invention provides a method for manufacturing an optical fiber installation structure, which comprises:

[0017] The present invention also provides a method for manufacturing an optical fiber material, characterized in that the method for manufacturing the optical fiber installation structure is used to manufacture an optical fiber material in which a plurality of the optical fiber installation structures are installed on an optical fiber core.

[0018] The present invention also provides a structural member comprising the above-mentioned optical fiber material.

[0019] The present invention also provides an optical fiber installation method, characterized in that a structure to be measured by an optical fiber sensor is fabricated using a structural member.

[0020] The present invention also provides a method for installing an optical fiber, which comprises installing the optical fiber material in a structure that is to be measured by an optical fiber sensor.

[0021] The present invention also provides a structure comprising the above-mentioned optical fiber material. [Effects of the Invention]

[0022] In the present invention, the bare optical fiber 24 and the optical fiber cores 20 at both ends are fixed with the same member (fixing unit 30), so when tension is applied to the optical fiber core 20, the bare optical fiber 24 is less likely to slip inside the optical fiber cable, and problems such as reduced measurement accuracy due to friction inside the cable are less likely to occur.

[0023] In the present invention, a portion of the resin coating 21 of the optical fiber core 20 is removed and the bare optical fiber 24 is fixed with the fixing unit 30, so that deformation of the structure is easily transmitted to the bare optical fiber 24, which makes it easier to improve measurement accuracy.

[0024] In the present invention, the bare optical fiber 24 and the coated optical fibers 20 at both ends thereof are fixed on the plane of a fixing unit 30, and the fixing unit 30 is then fixed on the structure to be measured. Therefore, compared to a method in which the coated optical fiber 20 is placed in a metal tube and fixed on the structure, the contact area between the structure and the fixing unit 30 can be increased, improving the stability of the bare optical fiber 24 (measuring element). In particular, when the structure is a soft material such as a geogrid, these advantages of the present invention are easily exhibited. [Brief explanation of the drawings]

[0025] [Figure 1] 1A and 1B are diagrams illustrating the structure of an optical fiber cable. [Figure 2] 1 is a schematic diagram of an optical fiber material of the present invention. [Figure 3] FIG. 1 is a diagram showing a state in which a coating-removed portion 10 is formed between two coating-remaining portions 11 in step (1). [Figure 4] 1A and 1B are diagrams illustrating a method for forming the coating removal portion 10 by joining the tips 24A of the bare optical fibers 24 together in step (1). (a) State before removing the resin coating 21, (b) State after removing the resin coating 21, and (c) State after joining the tips 24A of the bare optical fibers 24 together. [Figure 5] 1A and 1B are diagrams illustrating an example of a fixing unit 30. (a) Plan view, (b) Front view, and (c) Right side view. [Figure 6] 1A and 1B are diagrams illustrating an example of a fixing unit 30. (a) Plan view, (b) Front view, and (c) Right side view. [Figure 7] 10 is a diagram showing a state in which the fixing unit 30 is positioned near the bare optical fiber 24 in the coating removal section 10 in step (2). FIG. [Figure 8] 10 is a diagram showing a state in which two fixing units 30 are positioned near the bare optical fiber 24 in the coating removal section 10 in step (2). FIG. [Figure 9] FIG. 10 is a diagram showing an example of the "space S around the coating removal portion 10" to be filled with a filler 40 in step (4). [Figure 10] FIG. 10 is a diagram showing an example of the optical fiber installation structure 1 after the step (4) is completed. [Figure 11] 1A and 1B are diagrams showing a method for joining optical fiber materials 2 together to produce a long optical fiber material 2. FIG. [Figure 12] FIG. 2 is a diagram showing a state in which the optical fiber material 2 of the present invention is placed on a geogrid G. DETAILED DESCRIPTION OF THE INVENTION

[0026] The present invention will be described below, but the present invention is not limited to the following embodiments and can be practiced with any modifications.

[0027] The present invention relates to an optical fiber installation structure 1 for installing an optical fiber in a structure that is the target of measurement by an optical fiber sensor, and an optical fiber material 2 characterized in that multiple optical fiber installation structures 1 are installed on an optical fiber core 20.

[0028] 2 shows a schematic diagram of an optical fiber material 2 of the present invention (light source and light receiving element are omitted). The optical fiber material 2 of the present invention is a component in which a plurality of optical fiber installation structures 1 are provided at predetermined intervals on an optical fiber cable (optical fiber core 20). By installing the optical fiber material 2 of the present invention in a structure to be measured, the structure can be used for optical fiber sensing.

[0029] [Optical fiber installation structure and manufacturing method thereof] The optical fiber installation structure 1 of the present invention will be described below together with an example of a manufacturing method thereof. The example of the manufacturing method of the optical fiber installation structure 1 of the present invention includes the following steps (1) to (4).

[0030] <Process (1)> In step (1), the resin coating 21 of the optical fiber core 20 is removed to form a coating-removed portion 10 where a bare optical fiber 24 is exposed between two remaining coating portions 11 where the resin coating 21 has not been removed (FIG. 3). The resin coating 21 consists of two layers, a primary coating 22 and a secondary coating 23, and the coating-removed portion 10 is formed by removing both layers.

[0031] There are no particular limitations on the method for forming the coating removal portion 10, i.e., the method for removing the resin coating 21, and examples include a method using a jacket stripper, a method of cutting off the resin coating with a knife, and a method of burning and removing the resin coating.

[0032] The length of the coating removal portion 10 is preferably 10 mm or more, more preferably 15 mm or more, and particularly preferably 20 mm or more, and is preferably 40 mm or less, more preferably 35 mm or less, and particularly preferably 30 mm or less. If the length of the coating removal portion 10 is within the above range, the optical fiber installation structure 1 can be easily manufactured in terms of dimensions.

[0033] Step (1) can be performed by removing the resin coatings 21 from the tip portions 20A of the two coated optical fibers 20 and joining the tips 24A of the exposed bare optical fibers 24 together (FIG. 4). That is, in this case, two optical fiber cores 20 are prepared (FIG. 4(a)), and the resin coating 21 is removed from the tip portion 20A of each optical fiber core 20 (FIG. 4(b)). Next, the tips 24A of the bare optical fibers 24 are joined together to form a joint 24B (FIG. 4(c)).

[0034] In this way, the step (1) can be carried out using a jacket stripper, thereby improving the work efficiency. The "two coated optical fibers 20" can be obtained by cutting one coated optical fiber 20, for example.

[0035] Examples of joining include fusion, mechanical splicing, etc. Examples of fusion include plasma fusion, etc.

[0036] Although there is no particular limitation on the position of the joint 24B, it is desirable that the joint 24B be located near the midpoint of the coating removal section 10. That is, when removing the resin coating 21 from the tip end portions 20A of the two optical fiber cores 20, it is desirable to remove approximately the same length.

[0037] Step (1) can also be performed by cutting off the resin coating with a knife, etc. In this case, the joint portion 24B of the bare optical fiber 24 does not exist.

[0038] <Process (2)> In step (2), the convex plate 32 of the fixing unit 30, which has an integrated structure of a base plate 31 and a convex plate 32 partially provided in approximately the center of the base plate 31, is adhered to the bare optical fiber 24 of the coating removal section 10 without coming into contact with the cross section 21A of the resin coating 21 of the optical fiber core 20 in the remaining coating section 11 at both ends of the coating removal section 10.

[0039] The fixing unit 30 is a member for fixing the exposed bare optical fiber 24 and the optical fiber cores 20 at both ends thereof. The fixing unit 30 has a structure in which two flat plates (a base flat plate 31 and a convex flat plate 32) are integrated together. An example of the shape of the fixing unit 30 is shown in FIGS.

[0040] In the fixed unit 30, the convex plate 32 is partially provided in the approximate center of the base plate 31. The area of ​​the convex plate 32 is smaller than the area of ​​the base plate 31.

[0041] In step (2), the convex plate 32 of the fixing unit 30 is positioned near the bare optical fiber 24 in the coating removal section 10, and the end of the base plate 31 (the part where the convex plate 32 is not provided) is positioned near the resin coating 21 of the optical fiber core 20 in the coating remaining section 11 at both ends of the coating removal section 10 (Figure 7).

[0042] At this time, the convex plate 32 is prevented from coming into contact with the cross section 21A of the resin coating 21 of the optical fiber 20 in the remaining coating portion 11 at both ends of the coating removal portion 10. If the convex plate 32 were to come into contact with the cross section 21A, the bare optical fiber 24 may break around the contact point between the convex plate 32 and the cross section 21A.

[0043] Next, the convex plate 32 and the bare optical fiber 24 are bonded together at the approximate contact portion C between the convex plate 32 and the bare optical fiber 24 , thereby fixing the bare optical fiber 24 onto the convex plate 32 .

[0044] There are no particular limitations on the materials of the base plate 31 and the convex plate 32 that make up the fixed unit 30, and specific examples include metals such as iron, copper, stainless steel, titanium, and alloys thereof; resins such as polystyrene, polyester, polyethylene, polypropylene, polyamide, FRP; and the like.

[0045] Furthermore, the base plate 31 and the convex plate 32 may be made of the same or different materials. If they are made of the same material, the base plate 31 and the convex plate 32 may be molded integrally to produce the fixing unit 30, or the base plate 31 and the convex plate 32 may be molded separately and then joined together. When the base plate 31 and the convex plate 32 are made of different materials, or when they are made of the same material but molded separately, examples of methods for joining the base plate 31 and the convex plate 32 include adhesive bonding, fusion bonding, screw fastening, etc. In the case of adhesion, it is preferable to use an epoxy resin adhesive.

[0046] When the optical fiber installation structure 1 is completed and the optical fiber material 2 having a plurality of optical fiber installation structures 1 is to be installed in the soil or in a tunnel, or in a structure near a coast where there is a lot of airborne salt, the base plate 31 is required to have strength and weather resistance. For this reason, stainless steel, titanium, titanium alloy, and FRP are preferred among the above materials for the base plate 31.

[0047] In step (2), the convex plate 32 and the bare optical fiber 24 may be bonded using an adhesive, but the convex plate 32 may also be formed from a material that is soluble in a solvent and then dissolved, allowing the bond to be achieved without using an adhesive.

[0048] If no adhesive is used in step (2) (if the convex plate 32 is bonded by dissolving it in a solvent), a solvent capable of dissolving the convex plate 32 is supplied to the approximate contact point C between the convex plate 32 and the bare optical fiber 24 while the convex plate 32 and the bare optical fiber 24 are in approximate contact with each other. As a result, the convex plate 32 in the vicinity of the contact portion C is dissolved, and the solvent is evaporated, thereby bonding the convex plate 32 and the bare optical fiber 24 together.

[0049] By adhering the convex plate 32 by dissolving it in a solvent, not only is it not necessary to prepare a separate adhesive, but even if there is a dimensional error in the thickness of the convex plate 32, the bare optical fiber 24 can be easily and stably fixed onto the convex plate 32 without distortion or bending.

[0050] From this point of view, it is desirable that the material of the convex plate 32 is a material that can be dissolved in a solvent, and among the above-mentioned materials, polystyrene is specifically preferred.

[0051] The solvent for dissolving the convex flat plate 32 is preferably one that easily dissolves and volatilizes the convex flat plate 32. Examples of such a solvent include tetrahydrofuran (THF) and toluene. These solvents may be used alone or in combination of two or more.

[0052] The area of ​​the base plate 31 is 650 mm 2 It is preferable that it is 715 mm or more. 2 More preferably, it is 780 mm or more. 2 It is particularly preferable that the length is 975 mm or more. 2 Preferably, it is less than 910 mm 2 It is more preferable that it is less than 845 mm 2 It is particularly preferred that:

[0053] The thickness of the base plate 31 is preferably 1.0 mm or more, more preferably 1.5 mm or more, and particularly preferably 2.0 mm or more, and is preferably 4.0 mm or less, more preferably 3.5 mm or less, and particularly preferably 3.0 mm or less. When the thickness of the base plate 31 is within the above range, strength, durability, and cost can be both achieved.

[0054] The area of ​​the convex plate 32 is 72 mm 2 It is preferable that it is 78 mm or more. 2 More preferably, it is 84 mm or more. 2 It is particularly preferable that the thickness is 120 mm or more. 2 Preferably, it is less than 114 mm 2 It is more preferable that it is 108 mm or less. 2 It is particularly preferred that:

[0055] The thickness of the convex plate 32 is necessarily determined to be approximately equal to L [mm] expressed by the following formula.

[0056] L = (outer diameter of the optical fiber core 20 - outer diameter of the optical fiber bare wire 24) / 2

[0057] When the convex plate 32 and the bare optical fiber 24 are bonded together by dissolving the convex plate 32 in a solvent, it is preferable that the thickness of the convex plate 32 be the same as or slightly larger than L. If the thickness of the convex plate 32 is slightly greater than L, it is preferably (L + 0.05) mm or more, more preferably (L + 0.10) mm or more, and particularly preferably (L + 0.15) mm or more. It is also preferably (L + 0.30) mm or less, more preferably (L + 0.25) mm or less, and particularly preferably (L + 0.20) mm or less. When the thickness of the convex plate 32 is slightly larger than L, the difference between the thickness of the convex plate 32 and L roughly corresponds to the thickness of the adhesive layer between the optical fiber core 20 of the remaining coating portion 11 and the base plate 31, which is formed in step (3) described below.

[0058] When a separate adhesive is used to bond the convex plate 32 and the bare optical fiber 24, it is desirable that the thickness of the convex plate 32 be approximately the same as L. Specifically, the thickness of the convex plate 32 is preferably (L - 0.09) mm or more, more preferably (L - 0.06) mm or more, and particularly preferably (L - 0.03) mm or more. Also, it is preferably (L + 0.15) mm or less, more preferably (L + 0.10) mm or less, and particularly preferably (L + 0.05) mm or less.

[0059] There are no particular limitations on the shapes of the base plate 31 and the convex plate 32, and examples include rectangular, square, oval, etc., but rectangular is the most suitable shape in terms of ease of manufacture, ease of installation, etc. Note that when we say "rectangle," it also includes "approximately rectangular" shapes such as rectangular shapes with chamfered corners. When the base plate 31 and the convex plate 32 are rectangular, it is desirable that the direction of the coated optical fiber 20 and the bare optical fiber 24 (the direction of the arrow in FIGS. 5 and 6) be the long side. In the following, the preferred ranges of the shapes of the base plate 31 and the convex plate 32 in such a case will be described.

[0060] The length of the long side of the convex flat plate 32 is necessarily set to a value shorter than the length of the coating removal portion 10. The value obtained by subtracting the length of the long side of the convex flat plate 32 from the length of the coating removal portion 10 is preferably 8 mm or more, more preferably 9 mm or more, and particularly preferably 10 mm or more. Also, it is preferably 15 mm or less, more preferably 14 mm or less, and particularly preferably 13 mm or less.

[0061] When installing the fixing unit 30 and adhering the convex plate 32 to the bare optical fiber 24, it is desirable to position the convex plate 32 near the center of the coating removal portion 10, as shown in Figures 5 and 6.

[0062] In this case, the distance between the cross section 21A of the resin coating 21 of the optical fiber core 20 and the convex flat plate 32 is half the above-mentioned "value obtained by subtracting the length of the long side of the convex flat plate 32 from the length of the coating removal portion 10." That is, the distance between the cross section 21A of the resin coating 21 of the optical fiber 20 and the convex flat plate 32 is preferably 1.0 mm or more, more preferably 2.0 mm or more, and particularly preferably 3.0 mm or more. Also, it is preferably 6.0 mm or less, more preferably 5.0 mm or less, and particularly preferably 4.0 mm or less. When the distance between the cross section 21A of the resin coating 21 of the optical fiber core 20 and the convex flat plate 32 is within the above range, the bare optical fiber 24 can be prevented from breaking around the contact point between the convex flat plate 32 and the cross section 21A.

[0063] The length of the long side of the base plate 31 is necessarily determined to be longer than the length of the coating removal portion 10. The value obtained by subtracting the length of the coating removal portion 10 from the length of the long side of the base plate 31 is preferably 30 mm or more, more preferably 35 mm or more, and particularly preferably 40 mm or more. Also, it is preferably 60 mm or less, more preferably 55 mm or less, and particularly preferably 50 mm or less.

[0064] By determining the relationship between the lengths of the long sides of the base plate 31 and the convex plate 32 and the length of the coating removal section 10, and by determining the installation position of the convex plate 32 as described above, the bare optical fiber 24 can be stably fixed on the convex plate 32, which tends to improve measurement accuracy.

[0065] The length of the short side of the base plate 31 is preferably 8 mm or more, more preferably 9 mm or more, and particularly preferably 10 mm or more, and is preferably 22 mm or less, more preferably 21 mm or less, and particularly preferably 20 mm or less.

[0066] The length of the short side of the convex plate 32 may be the same as the length of the short side of the base plate 31 (FIG. 6), or may be different (FIG. 5). The length of the short side of the convex plate 32 is preferably 5 mm or more, more preferably 6 mm or more, and particularly preferably 7 mm or more, and is preferably 10 mm or less, more preferably 9 mm or less, and particularly preferably 8 mm or less.

[0067] In step (2), when bonding the convex flat plate 32 and the bare optical fiber 24, it is desirable to bond them while applying tension to both ends of the coated optical fiber 20 so that the bare optical fiber 24 does not bend. The tension at this time is preferably 0.3 N or more, more preferably 0.4 N or more, and particularly preferably 0.5 N or more. Also, it is preferably 0.8 N or less, more preferably 0.7 N or less, and particularly preferably 0.6 N or less.

[0068] In the present invention, step (2) may be performed twice on one coating removal section 10. In this way, one coating removal section 10 is sandwiched between two fixing units 30 (FIG. 8).

[0069] By sandwiching one coating removal portion 10 between two fixing units 30, the stability of the optical fiber installation structure 1 is improved.

[0070] <Process (3)> In step (3), the base plate 31 of the fixing unit 30 is adhered to the optical fiber core wire 20 in the remaining coating portion 11 at both ends of the coating removal portion 10 on the side having the convex plate 32, thereby fixing the optical fiber core wire 20 to the base plate 31. As shown in Figures 7 and 8, the base plate 31 is larger than the convex plate 32, and the peripheral portion of the base plate 31 is in approximate contact with the optical fiber core 20, so that in step (3), the base plate 31 and the optical fiber core 20 are bonded together.

[0071] After the installation of the optical fiber material 2 is completed, the base plate 31 is exposed to the air or water, and therefore the base plate 31 is required to be made of a material that is not dissolved in water or organic solvents.

[0072] For this reason, a known adhesive is appropriately used for bonding in step (3), such as an epoxy resin adhesive. The known adhesives may be used alone or in combination of two or more.

[0073] The thickness of the adhesive layer formed in step (3) is preferably 1.0 mm or more, more preferably 1.5 mm or more, and particularly preferably 2.0 mm or more, and is preferably 4.0 mm or less, more preferably 3.5 mm or less, and particularly preferably 3.0 mm or less. When the thickness of the adhesive layer is within the above range, the optical fiber 20 can be stably fixed to the fixing unit 30, and the measurement accuracy is stable. In addition, the cost can be reduced.

[0074] <Process (4)> In step (4), the space S around the coating removal portion 10 is filled with the filler 40.

[0075] The "space S around the coating removal portion 10" refers to at least the space around the bare optical fiber 24. By filling the space around the bare optical fiber 24 with the filler material 40, the bare optical fiber 24 is stabilized, and measurement accuracy is improved.

[0076] Furthermore, ignoring factors other than the raw material cost of the filler 40, the range of the "space S around the coating removal portion 10," i.e., the space filled with the filler 40, may be large; for example, the range shown in Figure 9 can be the "space S around the coating removal portion 10."

[0077] As the filler 40, known adhesives, wax materials, etc. can be used. As the adhesive, the same adhesives as those exemplified in the above step (3) can be used.

[0078] When the filler 40 is an adhesive, steps (3) and (4) may be carried out simultaneously, which is preferable in terms of work efficiency.

[0079] When step (2) is performed twice on one coating removal section 10, step (2) may be performed twice in succession, followed by steps (3) and (4), or step (2) may be performed once, followed by steps (3) and (4), followed by step (2) a second time, and finally steps (3) and (4). From the viewpoint of work efficiency, it is desirable to carry out step (2) twice in succession, and then carry out steps (3) and (4).

[0080] FIG. 10 shows an example of the optical fiber installation structure 1 after the step (4) is completed (when two fixing units 30 are used and the space S around the coating removal portion 10 is made wider). The bare optical fiber 24 is fixed to the fixing unit 30 and is surrounded by a filler 40, making it stable.

[0081] [Optical fiber material and its manufacturing method] The optical fiber material 2 of the present invention is an optical fiber core 20 provided with a plurality of the optical fiber installation structures 1 (FIG. 2).

[0082] The optical fiber installation structure 1 provided on the optical fiber material 2 can be manufactured by carrying out the above-mentioned steps (step (1) to step (4)).

[0083] When manufacturing the optical fiber material 2, the optical fiber installation structure 1 may be provided by performing each of the above-mentioned steps at each installation location of the optical fiber installation structure 1, or each step may be performed collectively at multiple installation locations.

[0084] As described above, when performing step (1), the resin coating 21 is removed from the tip portions 20A of the two optical fiber cores 20, and the tips 24A of the exposed bare optical fibers 24 are joined together to form the coating-removed portion 10. When performed in this manner, the optical fiber installation structure 1 joins the optical fiber materials 2 that have already been installed, and the optical fiber installation structure 1 is provided at the joint, thereby making it possible to produce a long optical fiber material 2 (FIG. 11).

[0085] The installation interval of the optical fiber installation structures 1 in the optical fiber material 2 (the distance between the optical fiber installation structures 1 and the adjacent optical fiber installation structures 1) may be equal to or greater than the length of the long side of the base plate 31, and is preferably as short as possible in order to integrate the optical fiber material 2 with the structure. A specific example is 10 cm or more and 500 cm or less.

[0086] [Optical fiber installation method] The fabricated optical fiber material 2 is installed in a structure, whereby the structure can be used for optical fiber sensing.

[0087] When installing the optical fiber material 2 in a structure, the optical fiber material 2 is first installed in a structural component, which is a component of the structure, and the structure can be fabricated using such a structural component (a structural component having an optical fiber material). It is also possible to fabricate a structure using structural members on which the optical fiber material 2 is not installed, and then install the optical fiber material 2 in the structure.

[0088] That is, the present invention relates to a structural component characterized by including the above-mentioned optical fiber material, and an optical fiber installation method characterized by using the structural component to fabricate a structure that is the target of measurement by an optical fiber sensor. The present invention also relates to a method for installing an optical fiber, which comprises installing the optical fiber material in a structure that is the target of measurement by an optical fiber sensor. Furthermore, the present invention relates to a structure comprising the above-mentioned optical fiber material.

[0089] In the present invention, there are no particular restrictions on the structure to be measured by the optical fiber sensor, but if the structural components that make up the structure are made of a soft material, the advantage of the present invention, that the bare optical fiber 24 (measuring element) is firmly and stably fixed, can be easily utilized, and the structure is suitable as a target for installing the optical fiber material 2 of the present invention. Here, a structural member made of a soft material is, for example, a structural member having a modulus of longitudinal elasticity of 1 GPa to 10 GPa at room temperature. Specific examples of the material for such a structural member include composites of resin fibers such as polyester fibers and aramid fibers with other resin materials.

[0090] Examples of structures in the present invention include earth structures such as embankments, etc. Examples of structural members (members used to fabricate structures) in the present invention include structural members and civil engineering and construction materials such as geogrids.

[0091] Geogrid G ​​is a mesh-like civil engineering and construction material made of synthetic resins and other materials that has tensile resistance, and is primarily used to reinforce slopes and road embankments. The geogrid G ​​often satisfies the range of the longitudinal elastic modulus described above, and is therefore suitable as an installation target for the optical fiber material 2 of the present invention.

[0092] As shown in Figure 12, when installing the optical fiber material 2 on a geogrid G, the side of the base plate 31 of the fixing unit 30 of the optical fiber installation structure 1 on which the convex plate 32 does not exist is fixed to the geogrid G ​​by gluing or the like. It is desirable to install the optical fiber installation structure 1 (the point where it is fixed by adhesive or the like) on the intersection of the lattice of the geogrid G. By installing the optical fiber installation structure 1 using the intersection of the lattice of the geogrid G ​​as a guide, construction efficiency during installation can be improved.

[0093] When the optical fiber material 2 is installed on the geogrid G, fixing points 3 to which the optical fiber core 20 is fixed by adhesive or the like may be provided in addition to (the base plate 31 of) the optical fiber installation structure 1. It is desirable that such fixing points 3 are also provided on the intersections of the lattice of the geogrid G. By providing the fixing points 3 using the intersections of the lattice of the geogrid G ​​as a guide, construction efficiency during installation can be improved.

[0094] The geogrid G ​​is made of polyethylene or the like, which generally does not have good adhesive properties. When fixing the optical fiber material 2 onto the geogrid G ​​by adhesion, it is necessary to select an adhesive that exhibits good adhesive properties to polyethylene or the like. Specific examples of such adhesives include styrene-butadiene rubber adhesives and modified silicone adhesives. These adhesives may be used alone or in combination of two or more.

[0095] When the optical fiber material 2 is fixed on the geogrid G ​​by adhesive or the like, it is desirable to fix the optical fiber material 2 in a state where it is strained. The strain applied to the optical fiber material 2 is preferably 500 με or more, more preferably 1000 με or more, and particularly preferably 2000 με or more, and is preferably 5000 με or less, more preferably 4000 με or less, and particularly preferably 3000 με or less. When the strain applied to the optical fiber material 2 is within the above range, the bare optical fiber 24 is stably fixed, and measurement accuracy is likely to improve.

[0096] According to the present invention, the optical fiber material 2 installed on a structure such as a geogrid is used for optical fiber sensing.

[0097] There are no particular limitations on the measurement method used when performing optical fiber sensing using the optical fiber installed according to the present invention, and examples include FBG (Fiber Bragg Grating), BOTDA (Brillouin Optical Time Domain Analysis), BOTDR (Brillouin Optical Time Domain Reflectometry), BOCDA (Brillouin Optical Correlation Domain Analysis), and BOCDR (Brillouin Optical Correlation Domain Reflectometry).

[0098] The optical fiber installed according to the present invention is particularly suitable for optical fiber sensing using a BOTDR, because the optical fiber installation structure 1 allows the optical fiber core 20 to be intermittently and stably fixed, thereby improving both the installation efficiency and measurement accuracy of the optical fiber sensor. [Example]

[0099] The present invention will be explained in more detail below by way of examples, but the present invention is not limited to these examples as long as it does not depart from the gist of the invention.

[0100] Example 1 An optical fiber material 2 having a plurality of optical fiber installation structures 1 was fabricated and installed on a geogrid G ​​as follows.

[0101] <1> The resin coating 21 at the tip end 20A of each of the pair of coated optical fibers 20 was removed by about 10 mm using a jacket stripper, to expose the bare optical fiber 24.

[0102] <2> the above <1> The tips 24A of the pair of coated optical fibers 20, from which the bare optical fibers 24 were exposed, were butted together and fusion-spliced.

[0103] <3> A polystyrene plate (long side 12 mm, short side 6 mm, thickness 0.3 mm) was glued to the center of a SUS304 plate (long side 50 mm, short side 8 mm, thickness 1 mm) with epoxy resin to create a composite plate (fixing unit 30).

[0104] <4> the above <2> The joint 24B produced by fusion bonding is <3> The polystyrene plate was positioned at the center of the polystyrene plate (convex plate 32) of the composite plate (fixing unit 30) fabricated in step 1, and tetrahydrofuran was supplied to the contact area between the polystyrene plate and the bare optical fiber 24 to dissolve the polystyrene plate, thereby bonding the bare optical fiber 24 to the polystyrene plate. At this time, the optical fiber 20 was bonded with tension applied to both ends so that the bare optical fiber 24 would not bend.

[0105] <5> The entire optical fiber core 20 and bare optical fiber 24 on the SUS304 plate were adhered (resin impregnated) with epoxy resin, thereby adhering and fixing the optical fiber core 20 to the SUS304 plate (base plate 31) and filling the space S around the coating removal portion 10.

[0106] <6> the above <3> Using the composite plate prepared in the same manner as above, <4> ~ <5> By carrying out the same operation as above, an optical fiber installation structure 1 in which one coating removal portion 10 was sandwiched between two fixing units 30 was produced.

[0107] <7> the above <1> ~ <6> The resin coating 21 on the tip 20A of one of the pair of optical fiber cores 20 used to fabricate the optical fiber installation structure 1 in step 2 was removed by about 10 mm using a jacket stripper to expose the bare optical fiber 24. Similarly, the resin coating 21 on the tip 20A of a separately prepared optical fiber core 20 was also removed by about 10 mm to expose the bare optical fiber 24. Next, the tips 24A of the optical fiber cores 20 were butted together and fusion spliced.

[0108] <8> the above <7> The joint 24B produced in the above <3> Tetrahydrofuran was supplied to the contact area between the polystyrene plate and the bare optical fiber 24 so that the polystyrene plate was positioned at the center of the polystyrene plate of the composite plate fabricated in the same manner as in 1., and the polystyrene plate was dissolved, thereby bonding the bare optical fiber 24 to the polystyrene plate. At this time, the optical fiber 20 was bonded with tension applied to both ends so that the bare optical fiber 24 would not bend.

[0109] <9> The entire optical fiber core 20 and bare optical fiber 24 on the SUS304 plate were adhered (resin impregnated) with epoxy resin, thereby adhering and fixing the optical fiber core 20 to the SUS304 plate (base plate 31) and filling the space S around the coating removal portion 10.

[0110] <10> the above <3> Using the composite plate prepared in the same manner as above, <4> ~ <5> By carrying out the same operation as above, a second optical fiber installation structure 1 was fabricated.

[0111] <11> the above <7> ~ <10> By carrying out the same operation as above, a third optical fiber installation structure 1 was fabricated. In the optical fiber material 2 having three optical fiber installation structures 1, the installation intervals of the optical fiber installation structures 1 were about 100 cm.

[0112] <12> The optical fiber material 2 was temporarily fixed to the geogrid G ​​with tape or the like, and the leftmost of the three optical fiber installation structures 1 was fixed to the geogrid G ​​with a styrene butadiene rubber adhesive.

[0113] <13> the above <12> After the adhesive that had adhered and fixed the optical fiber installation structure 1 had dried, a strain of 2000 με was applied to the optical fiber material 2 using a tension jig, and the remaining optical fiber installation structure 1 was fixed to the geogrid G ​​with a styrene-butadiene rubber-based adhesive.

[0114] <14> Furthermore, the optical fiber cores 20 between the optical fiber installation structures 1 were fixed at several points of the lattice of the geogrid G ​​with a styrene-butadiene rubber adhesive. [Industrial Applicability]

[0115] The optical fiber installation structure 1 and its manufacturing method of the present invention are widely used for optical fiber sensing of structures, particularly those including structural components made of soft materials such as geogrids, because the bare optical fiber 24 is less likely to slip inside the optical fiber cable and therefore is less likely to suffer from problems of reduced measurement accuracy due to friction inside the cable. [Explanation of symbols]

[0116] 1 Optical fiber installation structure 2. Optical fiber material 3 Fixing points 10. Coating removal section 11 Remaining coating 20 Optical fiber core 20A optical fiber core tip 21 Resin coating 21A Resin coated cross section 22 Resin coating (primary coating) 23 Resin coating (secondary coating) 24 Bare optical fiber 24A bare optical fiber tip 24B bare optical fiber joint 30 Fixed Unit 31 Foundation plate 32 Convex flat plate 40 Filler C: Approximate contact point between the convex plate and bare optical fiber G Geogrid S Space around the removed coating

Claims

1. An optical fiber installation structure for optical fiber sensing, comprising: the optical fiber installation structure has a coating removal portion where a resin coating of the optical fiber core wire is removed to expose a bare optical fiber, the bare optical fiber in the coating removal portion and the two coated optical fiber cores in the coating remaining portions at both ends of the coating removal portion from which the resin coating has not been removed are fixed by fixing units, The fixing unit has a structure in which a base plate and a convex plate partially provided in the approximate center of the base plate are integrated together, the bare optical fiber in the coating-removed portion is fixed by the convex plate; the optical fiber cores in the coating remaining portions at both ends of the coating removal portion are fixed by the surface of the base plate that has the convex plate, the convex plate is not in contact with the cross section of the resin coating of the optical fiber core; a space around the coating removal portion is filled with a filler; There is no joint in the bare optical fiber in the coating removed portion. An optical fiber installation structure characterized by:

2. 2. The optical fiber installation structure according to claim 1, wherein one coating removal portion is sandwiched between two fixing units.

3. 3. An optical fiber material comprising a plurality of optical fiber installation structures according to claim 1 or 2 installed on an optical fiber core.

4. A method for manufacturing an optical fiber installation structure for optical fiber sensing, comprising: (1) A step of removing a resin coating from an optical fiber core, thereby forming a coating-removed portion between two remaining coating portions from which the resin coating has not been removed, where the bare optical fiber is exposed and no splice is present in the bare optical fiber; (2) A step of adhering a fixing unit having a structure in which a base plate and a convex plate partially provided in the approximately central portion of the base plate are integrated together to the bare optical fiber in the coating removal portion without contacting the cross section of the resin coating of the optical fiber core wire in the coating remaining portions at both ends of the coating removal portion; (3) a step of adhering the base plate of the fixing unit to the optical fiber in the remaining coating portion at both ends of the coating removal portion on the surface having the convex plate; and (4) A step of filling the space around the coating removal portion with a filler.

1. A method for manufacturing an optical fiber installation structure, comprising:

5. A method for manufacturing an optical fiber installation structure for optical fiber sensing, comprising: (1) a step of removing a resin coating from an optical fiber core to form a coating-removed portion where a bare optical fiber is exposed between two coating-remaining portions where the resin coating has not been removed; (2) A step of adhering a fixing unit having a structure in which a base plate and a convex plate partially provided in the approximately central portion of the base plate are integrated together to the bare optical fiber in the coating removal portion without contacting the cross section of the resin coating of the optical fiber core wire in the coating remaining portions at both ends of the coating removal portion; (3) a step of adhering the base plate of the fixing unit to the optical fiber in the remaining coating portion at both ends of the coating removal portion on the surface having the convex plate; and (4) A step of filling the space around the coating removal portion with a filler. A method for manufacturing an optical fiber installation structure, comprising: A method for manufacturing an optical fiber installation structure, characterized in that step (1) is carried out by cutting one optical fiber core to obtain two optical fiber cores, removing the resin coating from the tip ends of the two optical fiber cores, and joining the tips of the exposed bare optical fibers.

6. A method for manufacturing an optical fiber installation structure as described in claim 4 or claim 5, wherein step (2) is performed twice on one coating removal section, so that one coating removal section is sandwiched between two fixing units.

7. 7. A method for manufacturing an optical fiber installation structure according to claim 4, wherein step (2) is carried out by supplying a solvent capable of dissolving the convex plate to the approximate contact point between the convex plate and the bare optical fiber in the coating-removed portion while the convex plate and the bare optical fiber are in approximate contact with each other.

8. A method for manufacturing an optical fiber material, characterized in that an optical fiber material is manufactured using the method for manufacturing an optical fiber installation structure described in any one of claims 4 to 7, in which a plurality of the optical fiber installation structures are installed on an optical fiber core.

9. A structural member comprising the optical fiber material according to claim 3.

10. A method for installing an optical fiber, comprising the steps of: preparing a structure to be an object of optical fiber sensing, the structure having the structural member according to claim 9.

11. 4. A method for installing an optical fiber, comprising installing the optical fiber material according to claim 3 in a structure that is the target of optical fiber sensing.

12. 12. The optical fiber installation method according to claim 10, wherein the structure includes a structural member having a modulus of longitudinal elasticity at room temperature of 1 GPa or more and 10 GPa or less.

13. A structure comprising the optical fiber material according to claim 3.

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