Strain detection optical fiber cable and its manufacturing method

Abstract

To provide an optical fiber cable for strain detection constituted in such a manner that the primary coated optical fiber of the optical fiber cable is hardly damaged when the optical fiber cable is installed in a measurement target and the end portion of the primary coated optical fiber can be easily exposed, and a method for manufacturing the optical fiber cable for strain detection.SOLUTION: An optical fiber cable 10 installed in a measurement target and used for detection of the strain thereof is configured to comprise: one or two or more coated optical fiber 1; a reinforcing layer 2 which is provided around the coated optical fiber 1 and in which a plurality of fiber-reinforced resin layers 2a, 2b formed of a long fiber bundle impregnated with thermoset resin are laminated in such a manner that the fiber-reinforced resin layers 2a, 2b are peelable from each other; and a coating layer 3 which is formed of the thermoset resin and coats the reinforcing layer 2.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an optical fiber cable that is installed on an object to be measured and used to detect strain thereon, and a method for manufacturing the same. [Background technology]

[0002] In the fields of civil engineering and construction, one method for detecting strain occurring in structures, the ground, etc. is an optical fiber sensing system, in which an optical fiber cable is installed in the object to be measured and the modulation of light propagating through the optical fiber is confirmed. Generally, optical fiber cables used for this purpose are strengthened by covering the optical fiber strands with a fiber-reinforced resin or the like to prevent breakage during installation and ensure ease of handling (see, for example, Patent Document 1). Also proposed is an optical fiber cable for strain detection that forms recesses on the surface of the covering layer to improve adhesion to the object to be measured (see, for example, Patent Document 2).

[0003] On the other hand, in order to prevent a decrease in measurement accuracy due to the influence of environmental humidity, an optical fiber cable has also been proposed that does not have a reinforcing coating layer made of fiber-reinforced resin or the like, and that the tensile modulus of the coating that protects the optical fiber is smaller than the tensile modulus of the optical fiber (see Patent Document 3). Furthermore, the present inventors have proposed an optical fiber cable for strain detection that reduces transmission loss and makes the optical fiber less likely to break or disconnect during handling or installation work by providing a protective buffer layer in addition to a reinforcing layer and a fixing layer around the optical fiber strand (see Patent Document 4). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 11-60286 [Patent Document 2] Japanese Patent Application Laid-Open No. 2002-23030 [Patent Document 3] Japanese Patent Application Laid-Open No. 2012-229992 [Patent Document 4] Japanese Patent Application Publication No. 2019-184596 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the above-mentioned conventional optical fiber cables for strain detection have the following problems: When burying an optical fiber cable for strain detection in an object to be measured, concrete is poured, and then vibrations are applied using a vibrator or the like to fill and densify the concrete, but the optical fiber cables described in Patent Documents 1 to 3 have the problem that the optical fiber strands are prone to bending or breaking during installation.

[0006] On the other hand, the optical fiber cable described in Patent Document 4 has a high protective effect for the optical fiber strands and can prevent bending or breakage during handling or installation, but recently, there has been a demand for optical fiber cables with larger diameters to reliably prevent damage due to strong vibrations during concrete pouring. Normally, when connecting an optical fiber cable for strain detection to equipment, the end of the optical fiber strand needs to be exposed, but if the optical fiber cable described in Patent Document 4 is made larger in diameter by thickening the resin coating layer that covers the optical fiber strands, it becomes difficult to strip off the layers that make up the resin coating layer to expose the optical fiber strands.

[0007] Therefore, the present invention aims to provide an optical fiber cable for strain detection that is less likely to damage the optical fiber wire when installed on an object to be measured and that allows the end of the optical fiber wire to be easily exposed, and a method for manufacturing the same. [Means for solving the problem]

[0008] The strain detection optical fiber cable of the present invention is an optical fiber cable that is installed in an object to be measured and used to detect strain in the object to be measured, and includes one or more optical fiber strands, a reinforcing layer that is provided around the optical fiber strands and is made up of a plurality of fiber-reinforced resin layers formed from long fiber bundles impregnated with a thermosetting resin and that are peelably stacked together, and a coating layer that is made of a thermoplastic resin and that covers the reinforcing layer. The reinforcing layer may be composed of, for example, a first fiber-reinforced resin layer provided around the optical fiber and a second fiber-reinforced resin layer removably provided on the first fiber-reinforced resin layer, and the thickness of the first fiber-reinforced resin layer may be equal to or less than the thickness of the second fiber-reinforced resin layer. In the strain detecting optical fiber cable of the present invention, the outermost layer may be provided with a fixing layer made of a thermoplastic resin and having a plurality of recesses and / or protrusions formed on the surface. Furthermore, the strain detecting optical fiber cable of the present invention can have an outer diameter of 0.9 mm or more.

[0009] The manufacturing method of the strain detection optical fiber cable of the present invention includes the steps of forming a reinforced layer by peeling off multiple fiber-reinforced resin layers made of long fiber bundles impregnated with thermosetting resin around one or more optical fiber strands, and extruding a thermoplastic resin around the reinforced layer to form a coating layer that covers the reinforced layer. The process of forming the reinforced layer includes, for example, a process of placing a long fiber bundle impregnated with uncured thermosetting resin around the optical fiber strand, and then heating the bundle to harden the thermosetting resin, thereby forming a first fiber-reinforced resin layer around the optical fiber strand, and a process of placing a long fiber bundle impregnated with uncured thermosetting resin around the first fiber-reinforced resin layer, and then heating the bundle to harden the thermosetting resin, thereby forming a second fiber-reinforced resin layer on the first fiber-reinforced resin layer. In this case, in the step of forming the reinforced layer, the periphery of the long fiber bundles impregnated with the uncured thermosetting resin may be covered with a fluororesin, and after the thermosetting resin is cured, the fluororesin may be peeled off, and further long fiber bundles impregnated with the uncured thermosetting resin may be arranged around the formed fiber reinforced resin layer. Furthermore, in the manufacturing method of the detection optical fiber cable of the present invention, a step may be carried out in which a thermoplastic resin is extruded around the coating layer, and then the surface is processed to form a fixing layer having a plurality of recesses and / or protrusions. [Effects of the Invention]

[0010] According to the present invention, a reinforcing layer is provided around the optical fiber strand, making it less likely for the optical fiber strand to be damaged when installed on the object to be measured.Furthermore, since the reinforcing layer is composed of multiple layers that are peelably stacked, the end of the optical fiber strand can be easily exposed. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a cross-sectional view showing the structure of an optical fiber cable according to a first embodiment of the present invention. [Figure 2] 2 is a flowchart showing the manufacturing process of the optical fiber cable 10 shown in FIG. [Figure 3] FIG. 3 is a cross-sectional view showing the structure of an optical fiber cable according to a second embodiment of the present invention. [Figure 4] 4 is a flowchart showing the manufacturing process of the optical fiber cable 20 shown in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0012] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to the accompanying drawings. However, the present invention is not limited to the following embodiments.

[0013] (First embodiment) First, an optical fiber cable according to a first embodiment of the present invention will be described. Fig. 1 is a cross-sectional view showing the structure of the optical fiber cable of this embodiment. As shown in Fig. 1, the optical fiber cable 10 of this embodiment has an optical fiber strand 1 around which a reinforcing layer 2 and a coating layer 3 are provided in this order. This optical fiber cable 10 is used to detect strain in a measurement object, and is a large-diameter optical fiber cable for detection, with an outer diameter of 0.9 mm or more.

[0014] [Optical fiber 1] The optical fiber 1 is an optical fiber made of a material with high light transmittance, such as quartz glass, with one or two resin protective layers formed around it. A UV-curable resin, such as UV-curable urethane acrylate, is generally used as the resin for forming the protective layer. The diameter of the optical fiber 1 is not particularly limited and can be selected appropriately depending on the object to be measured and the required detection accuracy, but an outer diameter of 0.25 mm is generally used.

[0015] [Reinforcement layer 2] The reinforcing layer 2 is provided to ensure the strength of the optical fiber 1 and is disposed around the optical fiber 1. The reinforcing layer 2 of the optical fiber cable 10 of this embodiment is configured such that a plurality of fiber-reinforced resin layers 2a, 2b formed from long fiber bundles impregnated with a thermosetting resin are releasably stacked together. Here, "releasably stacked" means that the plurality of fiber-reinforced resin layers 2a, 2b are individually cured and are not chemically or physically bonded, and are normally in close contact with each other but can be easily separated by applying force.

[0016] The fibers constituting the long fiber bundle can be synthetic fibers (organic fibers) made of polyolefin, polyester, etc., or inorganic fibers such as carbon fiber, glass fiber, and metal fiber, but inorganic fibers are preferred in terms of strength, elastic modulus, etc., from the viewpoint of protecting the optical fiber 1. In particular, when the optical fiber is made of glass, it is preferable to use carbon fiber or glass fiber for the long fiber bundle. This improves the ability to conform to the optical fiber 1, making it possible to prevent breakage when bent. Furthermore, using a large number of fine yarns in the long fiber bundle makes it more susceptible to cracking, so it is preferable to use fibers with a count of 60 tex or more.

[0017] On the other hand, the thermosetting resin may be any resin that cures when heated, such as an unsaturated polyester resin, a vinyl ester resin, an unsaturated alkyd resin, or an epoxy resin. In view of the hardness after curing and the thermal stability of the shape after shaping, the thermosetting resin preferably contains a crosslinkable substance, and more preferably contains at least one of an unsaturated polyester resin, an unsaturated alkyd resin, or an epoxy acrylate, a crosslinkable substance such as a crosslinkable monomer, and a polymerization initiator such as a diacyl peroxide.

[0018] The fiber-reinforced resin layers 2a, 2b constituting the reinforced layer 2 may be formed from the same type of thermosetting resin or different types of thermosetting resin, but since different shrinkage rates of the layers may cause peeling at unintended times, it is preferable to form the fiber-reinforced resin layers 2a, 2b using the same type of fiber and the same type of thermosetting resin.

[0019] Although there are no particular limitations on the thickness of the fiber reinforced resin layers 2a and 2b that make up the reinforcing layer 2, it is preferable that the thickness of the first fiber reinforced resin layer 2a provided around the optical fiber 1 be equal to or less than the thickness of the second fiber reinforced resin layer 2b provided on the first fiber reinforced resin layer 2a. This makes it possible to achieve both improved strength and ease of removal of the optical fiber 1.

[0020] Specifically, the thickness of the first fiber-reinforced resin layer 2a is preferably 0.1 to 0.5 mm, and more preferably 0.3 to 0.4 mm, from the viewpoint of facilitating the extraction of the optical fiber 1 and arranging the optical fiber 1 at the center of the optical fiber cable 10. On the other hand, the second fiber-reinforced resin layer 2b is preferably thicker from the viewpoint of improving strength, but is preferably thinner from the viewpoints of accurate detection of strain, facilitating the extraction of the optical fiber 1, weight during operation, and winding diameter during handling, and the thickness is preferably 0.3 to 1.5 mm, and more preferably 0.5 to 1.0 mm.

[0021] Furthermore, from the viewpoint of ease of peeling, the outer diameter ratio of the first fiber reinforced resin layer 2a to the second fiber reinforced resin layer 2b is preferably in the range of outer diameter D1 of the first fiber reinforced resin layer 2a:outer diameter D2 of the second fiber reinforced resin layer 2b = 1:1.5 to 1:5, and more preferably in the range of 1:2 to 1:3.

[0022] [Coating layer 3] The coating layer 3 may be formed of a flexible thermoplastic resin, and the type of resin is not particularly limited, but a polyolefin resin, for example, can be used. The resin forming the thermoplastic resin layer 3 may also be one that is endowed with properties such as weather resistance, chemical resistance, and flame retardancy. The thickness of the coating layer 3 is not particularly limited, but is preferably 0.05 to 1.50 mm from the viewpoints of sensitivity transmission to the optical fiber 1, protection, and ease of stripping.

[0023] [Manufacturing method] Next, a method for manufacturing the optical fiber cable 10 of this embodiment will be described. Fig. 2 is a flowchart showing the manufacturing steps for the optical fiber cable 10 of this embodiment. As shown in Fig. 2, when manufacturing the optical fiber cable 10 of this embodiment, first, a long fiber bundle impregnated with uncured thermosetting resin is arranged around the optical fiber 1, and then heated to cure the thermosetting resin, thereby forming a first fiber-reinforced resin layer 2a around the optical fiber 1 (step S1). Specifically, the long fiber bundle impregnated with thermosetting resin is arranged around the optical fiber 1, or the optical fiber 1 is arranged at the center of the long fiber bundle impregnated with thermosetting resin, and the bundle is passed through a constriction nozzle or the like to form it into a predetermined diameter and remove excess thermosetting resin, and then heated to cure the thermosetting resin.

[0024] In this case, it is preferable to coat the periphery of the long fiber bundle impregnated with the uncured thermosetting resin with a fluororesin, and peel off the fluororesin coating after the thermosetting resin is cured. In this way, the fluororesin serves as a mold, and deformation of the long fiber bundle due to heating when curing the thermosetting resin can be prevented. In other words, the thermosetting resin can be cured without deforming the long fiber bundle.

[0025] Furthermore, this fluorine-based resin coating can be easily peeled off without damaging the long fiber bundle, and the first fiber-reinforced resin layer 2a has a very smooth surface and maintains its shape after the coating is peeled off. If the surface of the first fiber-reinforced resin layer 2a is smooth and free of irregularities, it will adhere to the second fiber-reinforced resin layer 2b formed on top of it, but will not physically bond to it. That is, the first fiber-reinforced resin layer 2a and the second fiber-reinforced resin layer 2b are releasably stacked. As a result, when the second fiber-reinforced resin layer 2b is peeled off to remove the optical fiber 1, the first fiber-reinforced resin layer 2a remains, and the optical fiber 1 is covered only by the thin first fiber-reinforced resin layer 2a, making it easy to expose the optical fiber 1.

[0026] Next, a long fiber bundle impregnated with an uncured thermosetting resin is arranged around the first fiber reinforced resin layer 2a, and then heated to cure the thermosetting resin, thereby forming a second fiber reinforced resin layer 2b on the first fiber reinforced resin layer 2a (step S2). Specifically, the long fiber bundle impregnated with the thermosetting resin is arranged around the optical fiber 1 on which the first fiber reinforced resin layer 2a has been formed in step S1, or the optical fiber 1 on which the first fiber reinforced resin layer 2a has been formed is arranged at the center of the long fiber bundle impregnated with the thermosetting resin, and then it is shaped to a predetermined diameter by passing it through a constriction nozzle or the like, and excess thermosetting resin is removed, and then it is heated to cure the thermosetting resin.

[0027] As a result, a reinforcing layer 2 is formed around the optical fiber 1, in which a first fiber-reinforced resin layer 2a and a second fiber-reinforced resin layer 2b are releasably laminated. If the reinforcing layer 2 is configured to have three or more fiber-reinforced resin layers laminated together, step S2 described above can be repeated multiple times. When three or more fiber-reinforced resin layers are formed, it is desirable to coat the periphery of a long fiber bundle impregnated with an uncured thermosetting resin with a fluororesin when forming the lower fiber-reinforced resin layer, and then peel off the fluororesin coating after curing the thermosetting resin, so that the upper fiber-reinforced resin layer is releasably laminated. However, if the reinforcing layer 2 has three or more fiber-reinforced resin layers, the number of heating cycles increases, which is expected to increase damage to the optical fiber 1, and there is also a risk of misalignment between the fiber-reinforced resin layers, reducing the sensitivity of the sensor. Therefore, it is preferable that the reinforcing layer 2 has two fiber-reinforced resin layers.

[0028] Furthermore, it is preferable to prevent the inclusion of air bubbles when the long fiber bundle is impregnated with the uncured thermosetting resin in steps S1 and S2. If air bubbles exist in the fiber reinforced resin layers 2a and 2b and there are areas where the thermosetting resin is not sufficiently impregnated, defects such as breakage may occur when the manufactured optical fiber cable 10 is subjected to bending stress.

[0029] Subsequently, a thermoplastic resin is extruded around the reinforcing layer 2 and immediately water-cooled to form the coating layer 3 (step S3). As a result, the reinforcing layer 2 is coated with the coating layer 3, and an optical fiber cable 10 having a predetermined outer diameter is obtained.

[0030] As described above in detail, the optical fiber cable of this embodiment has a small-diameter fiber-reinforced resin layer formed around the optical fiber, and then a further fiber-reinforced resin layer is laminated to increase the diameter, so that the optical fiber can be positioned at the center even if the outer diameter of the optical fiber cable is 0.9 mm or more. By forming the reinforcing layer in multiple steps in this way, the amount of heat applied to the optical fiber can be reduced compared to forming a large-diameter (thick) reinforcing layer all at once, and damage to the optical fiber during the manufacturing process can be reduced.

[0031] Furthermore, in the optical fiber cable of this embodiment, the fiber-reinforced resin layers that make up the reinforcing layer are not bonded together and are peelable, so they can be easily peeled off to expose the optical fiber. As a result, the optical fiber cable of this embodiment is less likely to be damaged when installed in an object to be measured, and the end of the optical fiber can be easily exposed.

[0032] (Second embodiment) Next, an optical fiber cable according to a second embodiment of the present invention will be described. Fig. 3 is a cross-sectional view showing the structure of the optical fiber cable of this embodiment. In Fig. 3, the same components as those of the optical fiber cable 10 of the first embodiment shown in Fig. 1 are denoted by the same reference numerals, and detailed description thereof will be omitted. As shown in Fig. 3, the optical fiber cable 20 of this embodiment is similar to the optical fiber cable 10 of the first embodiment described above, except that a fixing layer 4 is provided around the coating layer 3.

[0033] [Fixing layer 4] The fixing layer 4 is provided as the outermost layer and is intended to ensure adhesion between the optical fiber cable and concrete, soil, etc. after it is buried in a measurement target such as a structure or the ground, and has a plurality of recesses 4a and / or protrusions formed therein. Note that, although Fig. 3 shows an example in which recesses 4a are formed at predetermined intervals in the fixing layer 4, the present invention is not limited to this, and the fixing layer 4 may be provided with protrusions or may have an uneven shape. Furthermore, the recesses and protrusions may be formed either regularly or irregularly (randomly).

[0034] The provision of the fixing layer 4 prevents the optical fiber cable from falling off from the concrete, soil, etc., and also allows the optical fiber cable to more easily follow the strain and stress applied to the object to be measured after being buried, thereby achieving good detection performance. The type of resin that forms the fixing layer 4 is not particularly limited, and for example, a polyolefin resin such as polyethylene can be used. However, from the viewpoint of improving adhesion to the coating layer 3, it is preferable to use a resin that is the same type as the coating layer 3 but has a higher hardness than the coating layer 3.

[0035] [Manufacturing method] Next, a method for manufacturing the optical fiber cable 20 of this embodiment will be described. Fig. 4 is a flowchart showing the manufacturing steps for the optical fiber cable 20 of this embodiment. As shown in Fig. 4, when manufacturing the optical fiber cable 20 of this embodiment, after the above-mentioned steps S1 to S3 are performed, a thermoplastic resin is extruded around the coating layer 3, and immediately after that, a process is performed to impart irregularities to the surface, and the thermoplastic resin is cooled and solidified (step S4). As a result, a fixing layer 4 having a plurality of recesses 4a and / or protrusions provided on the surface is formed around the coating layer 3, i.e., on the outermost layer of the optical fiber cable 20.

[0036] If each fiber-reinforced resin layer constituting the reinforcing layer is in an uncured state when the fixing layer is formed, the reinforcing layer may be damaged when the fixing layer is formed. Furthermore, when providing the fixing layer with irregularities, if the solidified resin is melted and processed, the optical fiber strand and the reinforcing layer may be damaged. On the other hand, in the optical fiber cable of this embodiment, each fiber-reinforced resin layer constituting the reinforcing layer is completely cured when the fixing layer is formed, and the irregularities are formed on the surface before the thermoplastic resin is cooled and solidified. Therefore, a fixing layer having multiple recesses 4a and / or protrusions on the surface can be formed without damaging the optical fiber strand and the reinforcing layer.

[0037] The configuration and effects of this embodiment other than those described above are the same as those of the first embodiment. [Example]

[0038] The effects of the present invention will be specifically described below using examples. In this example, an optical fiber cable 20 having the configuration shown in FIG. 3 was fabricated using the process shown in FIG. 4. Specifically, three 280 tex glass fibers were impregnated with a non-styrene thermosetting resin while being drawn, and then passed through a 0.9 mm diameter constriction nozzle. An optical fiber 1 with a blue protective layer and an outer diameter of 0.25 mm was placed at the center. The fiber was then passed through a T-die of an extruder and coated with FEP resin to reduce the outer diameter to 0.9 mm. After immediate water cooling, the thermosetting resin was cured in a curing tank to form a first fiber-reinforced resin layer 2a, and the FEP resin was then peeled off. The outer diameter at this point, i.e., when the first fiber-reinforced resin layer 2a was formed, was 0.9 mm.

[0039] Next, 14 glass fibers of 280 tex were pulled and impregnated with thermosetting resin, and passed through a constriction nozzle with a diameter of 2.0 mm, with the optical fiber 1 provided with the first fiber-reinforced resin layer 2a placed at the center. In this state, the fiber was passed through a T-die of an extruder and coated with polyethylene resin so that the outer diameter became 3.0 mm. After immediate water cooling, the thermosetting resin was cured in a curing tank to form the second fiber-reinforced resin layer 2b and the coating layer 3 made of polyethylene resin.

[0040] Subsequently, the optical fiber wire provided with the reinforcing layer 2 and the coating layer 3 was passed through a T-die of an extruder to coat the coating layer 3 with polyethylene resin, and immediately thereafter, the surface was roughened with a gear to form a fixing layer 4, and then the cable was taken up. This resulted in an optical fiber cable 20 with a fixing layer and an outer diameter of 3.7 mm.

[0041] When the cross section of the optical fiber cable 20 manufactured by the above-mentioned method was observed under a microscope, it was found that the optical fiber 1 was located approximately in the center. Furthermore, when 100 mm of the coating at the end of the optical fiber cable 20 was stripped off with a razor, and the inner second fiber reinforced resin layer 2b was further split vertically several times, the first fiber reinforced resin layer 2a remained. When this first fiber reinforced resin layer 2a was carefully split, the optical fiber 1 located in the center could be easily exposed. [Explanation of symbols]

[0042] 1. Optical fiber strand 2 reinforcement layer 2a, 2b Fiber reinforced resin layer 3 Covering layer 4 Fixing layer 4a Recess 10, 20 fiber optic cable

Claims

1. An optical fiber cable that is installed on a measurement object and used to detect strain on the measurement object, one or more optical fiber strands; a reinforcing layer provided around the optical fiber core, the reinforcing layer being formed by laminating a plurality of fiber-reinforced resin layers formed of long fiber bundles impregnated with a thermosetting resin in a manner that allows the layers to be peeled from each other; a coating layer formed from a thermoplastic resin and coating the reinforcing layer; A strain sensing optical fiber cable having a

2. 2. The optical fiber cable for strain detection according to claim 1, wherein the reinforcing layer is composed of a first fiber-reinforced resin layer provided around the optical fiber strand and a second fiber-reinforced resin layer provided releasably on the first fiber-reinforced resin layer.

3. 3. The strain-sensing optical fiber cable according to claim 2, wherein the thickness of the first fiber-reinforced resin layer is equal to or less than the thickness of the second fiber-reinforced resin layer.

4. The strain detection optical fiber cable according to any one of claims 1 to 3, wherein the outermost layer is provided with a fixing layer made of a thermoplastic resin and having a plurality of recesses and / or protrusions formed on its surface.

5. The strain detecting optical fiber cable according to any one of claims 1 to 4, wherein the outer diameter is 0.9 mm or more.

6. a step of forming a reinforced layer by laminating a plurality of fiber-reinforced resin layers, each of which is made of a long fiber bundle impregnated with a thermosetting resin, around one or more optical fiber strands in a peelable manner; a step of extruding a thermoplastic resin around the reinforcing layer to form a coating layer that covers the reinforcing layer; A method for manufacturing a strain detection optical fiber cable having the above structure.

7. The step of forming the reinforcing layer includes: a step of disposing a long fiber bundle impregnated with an uncured thermosetting resin around the optical fiber core, and then heating the bundle to cure the thermosetting resin, thereby forming a first fiber-reinforced resin layer around the optical fiber core; a step of arranging a long fiber bundle impregnated with an uncured thermosetting resin around the first fiber reinforced resin layer, and then heating the bundle to cure the thermosetting resin, thereby forming a second fiber reinforced resin on the first fiber reinforced resin layer; 7. The method for manufacturing a strain detecting optical fiber cable according to claim 6, further comprising:

8. 8. The method for manufacturing a strain detecting optical fiber cable according to claim 7, wherein in the step of forming the reinforced layer, the periphery of the long fiber bundle impregnated with uncured thermosetting resin is covered with a fluororesin, the thermosetting resin is cured, and then the fluororesin is peeled off, and a long fiber bundle further impregnated with uncured thermosetting resin is placed around the formed fiber reinforced resin layer.

9. 9. The method for manufacturing a strain detection optical fiber cable according to claim 6, further comprising the steps of extruding a thermoplastic resin around the coating layer, and then processing the surface to form a fixing layer having a plurality of recesses and / or protrusions.

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