Method and structure for securing optical fiber cables

Abstract

This invention provides a method for securing fiber optic cables that can reduce working time. [Solution] A method for fixing an optical fiber cable 2 laid in a laying pipe 1 buried underground comprises a tube insertion step of inserting a resin tube 3 from one opening 1a to the other opening 1b in the laying pipe 1 and installing the tube 3 along the optical fiber cable 2, and a fluid injection step of injecting fluid into the tube 3 to inflate the tube 3 and pressing the optical fiber cable 2 against the inner circumferential surface 1c of the laying pipe 1.

Description

[Technical Field]

[0001] The present invention relates to a method for fixing an optical fiber cable and a fixing structure for an optical fiber cable. [Background Art]

[0002] Patent Document 1 discloses a sensor device in which an optical fiber cable is installed inside a tube buried underground. [Prior Art Documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Unexamined Patent Application Publication No. 2002-048518 [Summary of the Invention] [Problem to be Solved by the Invention]

[0004] In the device disclosed in Patent Document 1, a grout agent is injected into the tube to fix the optical fiber cable installed inside the tube.

[0005] However, when injecting a grout agent in this manner, operations for producing and injecting the grout agent are required, which demands a large amount of working time.

[0006] An object of the present invention is to provide a method for fixing an optical fiber cable that can reduce working time. [Means for Solving the Problem]

[0007] The present invention is a method for fixing an optical fiber cable laid in a laying pipe buried underground, comprising: a tube inserting step of inserting a resin tube from one opening toward the other opening in the laying pipe and installing the tube along the optical fiber cable; and a fluid injecting step of injecting a fluid into the tube to inflate the tube, thereby pressing the optical fiber cable against the inner circumferential surface of the laying pipe. [Effects of the Invention]

[0008] In this invention, the optical fiber cable can be fixed simply by installing a tube along the optical fiber cable and injecting fluid into the tube. Therefore, the working time can be reduced compared to using grout. [Brief explanation of the drawing]

[0009] [Figure 1] (A) is a cross-sectional view in the axial direction of the optical fiber cable fixing structure according to an embodiment of the present invention. (B) is a cross-sectional view along the IB-IB line of (A), and is a cross-sectional view in the radial direction of the optical fiber cable fixing structure according to this embodiment. [Figure 2] This is a diagram illustrating the procedure for fixing an optical fiber cable according to an embodiment of the present invention. [Figure 3] This is a radial cross-sectional view of a fixing structure for an optical fiber cable according to a modified embodiment of the present invention. [Modes for carrying out the invention]

[0010] Embodiments of the present invention will be described below with reference to the attached drawings.

[0011] The present invention relates to a method and structure for fixing an optical fiber cable 2 laid inside a laying pipe 1 buried underground.

[0012] As shown in Figure 1, the fixing structure for the optical fiber cable 2 comprises the optical fiber cable 2 laid in a laying pipe 1 buried underground, and a resin tube 3 inserted along the upper part of the optical fiber cable 2 within the laying pipe 1.

[0013] In this embodiment, for example, the case in which an optical fiber cable 2, which has been pre-installed as a backup within a laying pipe 1 buried in a river embankment E, is fixed within the laying pipe 1 will be explained as an example.

[0014] The laying pipe 1 is installed between a pair of handholes 6 provided in the embankment E. The laying pipe 1 is embedded in the embankment E, and the openings 1a and 1b at both ends of the laying pipe 1 open into the handholes 6, respectively.

[0015] The optical fiber cable 2 is laid inside the laying conduit 1 and connected to a repeater 7 installed inside the handhole 6.

[0016] In this embodiment, the optical fiber cable 2 is used in a linear underground displacement meter capable of detecting the displacement of the embankment E. Since the underground displacement meter using an optical fiber cable has a known configuration, detailed illustrations and explanations are omitted, but for example, it is constructed by spirally winding one or more core wires in the axial direction (longitudinal direction) inside a sheath material. When multiple core wires are used, they are wound spirally with their phases alternating relative to each other.

[0017] Since the optical fiber cable 2 experiences strain in response to the deformation and loosening of the embankment E, it is possible to measure the deformation and loosening of the embankment E (underground) by measuring the strain of the optical fiber cable 2.

[0018] Specifically, the optical fiber cable 2 (core) has the property of slightly scattering incident pulsed light backward. By utilizing this property, it is possible to measure strain at multiple locations in the optical fiber cable 2. Since the frequency of the scattered light depends on the strain of the optical fiber cable 2, the strain of the optical fiber cable 2 can be measured by incidenting pulsed light into the optical fiber cable 2 and measuring the frequency of the scattered light. Furthermore, by measuring the time from when pulsed light is incident into the optical fiber cable 2 until the scattered light generated within the optical fiber cable 2 returns to the incident point, it is possible to measure the location where the scattered light was generated, i.e., the location where strain occurred in the optical fiber cable 2.

[0019] Therefore, by inserting a ground displacement meter including the optical fiber cable 2 into the laying pipe 1 in advance, the displacement of the embankment E can be grasped by measuring the strain generated in the optical fiber cable 2.

[0020] The tube 3 is formed of, for example, a polyethylene tube. The tube 3 expands when air, water, or the like is injected into the inside thereof. When the tube 3 expands, the optical fiber cable 2 is pressed against the inner peripheral surface 1c of the laying pipe 1.

[0021] Next, with reference to Fig. 2, a method for fixing the optical fiber cable 2 according to the present embodiment will be specifically described.

[0022] First, the tube 3 is inserted from one opening 1a toward the other opening 1b in the laying pipe 1. Specifically, a pilot wire 5 is inserted through one opening 1a of the laying pipe 1 and pulled out from the other opening 1b (see Fig. 2(A)). Next, the tube 3 is connected to an end portion of the pilot wire 5, and the tube 3 is inserted into the laying pipe 1 by pulling the pilot wire 5 (see Fig. 2(B)). This step corresponds to the "tube inserting step" in the claims.

[0023] Next, a fluid is injected into the tube 3 to inflate the tube 3. When air (compressed air) is used as the fluid, air is injected using an air compressor or the like until the entire tube 3 comes into contact with the inner peripheral surface 1c of the laying pipe 1, thereby inflating the tube 3. As a result, the optical fiber cable 2 is pressed against the inner peripheral surface 1c of the laying pipe 1 by the tube 3, whereby the optical fiber cable 2 is fixed inside the laying pipe 1.

[0024] Furthermore, when using a liquid such as water as the fluid, a predetermined amount of water is injected into the tube 3 using a pump or the like to inflate the tube 3. When water is injected, the weight of the water supplied into the tube 3 can press the optical fiber cable 2 against the inner surface 1c of the laying pipe 1. Therefore, it is not necessary to inject water until the entire tube 3 is in contact with the inner surface 1c of the laying pipe 1. Note that this step of injecting fluid into the tube 3 corresponds to the "fluid injection step" in the claims.

[0025] Thus, according to the fixing method of this embodiment, the optical fiber cable 2 can be easily fixed inside the laying pipe 1 simply by injecting fluid into the tube 3 and inflating the tube 3.

[0026] Furthermore, when inserting the tube 3 into the laying pipe 1, a sheet member 4 may be inserted between the optical fiber cable 2 and the tube 3 (see Figure 3). By providing a sheet member 4 between the optical fiber cable 2 and the tube 3 in this way, the frictional resistance between the optical fiber cable 2 and the tube 3 can be reduced when inserting the tube 3 into the laying pipe 1. For this reason, the sheet member 4 may be made of a nonwoven fabric made of a resin with a low coefficient of friction, such as nylon or polyacetal.

[0027] When inserting the sheet member 4 into the laying pipe 1, it is preferable to insert it together with the tube 3, but it is also possible to first insert the sheet member 4 into the laying pipe 1 and then insert the tube 3.

[0028] In the above embodiment, the example described was one in which the optical fiber cable 2 is already laid in the laying pipe 1. However, the method is not limited to this, and can also be applied when laying a new optical fiber cable 2 in the laying pipe 1, or when laying both the laying pipe 1 and the optical fiber cable 2 for the first time. When laying a new laying pipe 1, the laying pipe 1 can be laid in a hole or trench excavated in the embankment E, and then the optical fiber cable 2 and tube 3 can be inserted. The process of laying the optical fiber cable 2 when laying a new optical fiber cable 2 in the laying pipe 1 corresponds to the "optical fiber cable laying process" in the claims.

[0029] Furthermore, although the above embodiment was described using the example of the laying pipe 1 being laid on the embankment E, the laying location of the laying pipe 1 can be any location, such as a road or tunnel.

[0030] Furthermore, although the above embodiment described an example in which a tube 3 is connected to the end of a pilot wire 5 and the tube 3 is inserted into the laying pipe 1, the method of inserting the tube 3 is not limited to this. For example, a self-propelled robot may be used to insert the tube 3 into the laying pipe 1.

[0031] In the above embodiments, air and water were used as examples of fluids, but the invention is not limited to these. For example, a fluid that is less affected by temperature, specifically antifreeze, may also be used.

[0032] The method and structure for fixing the optical fiber cable 2 as described above will produce the following effects.

[0033] In this embodiment of the method for fixing the optical fiber cable 2, the optical fiber cable 2 can be fixed simply by installing the tube 3 along the optical fiber cable 2 and injecting fluid into the tube 3. Therefore, compared to, for example, the method of fixing the optical fiber cable 2 by injecting grout into the laying pipe 1, the work of manufacturing and injecting grout is not required, thus reducing working time.

[0034] Furthermore, using air or water as the fluid injected into tube 3 reduces costs compared to injecting grout or other materials. In addition, if air or water leaks out of tube 3, it prevents adverse environmental impacts. Moreover, if water is used as the fluid, even if some leaks out of tube 3, the weight of the water remaining inside tube 3 will keep the optical fiber cable 2 fixed in place.

[0035] Although embodiments of the present invention have been described above, these embodiments only represent a part of the application examples of the present invention, and are not intended to limit the technical scope of the present invention to the specific configurations of the above embodiments. [Explanation of Symbols]

[0036] 1... Laying pipe 2. Fiber optic cable 3... Tube 4. Sheet material E... Embankment

Claims

1. A method for securing optical fiber cables laid in a laying conduit buried underground, A tube insertion step involves inserting a resin tube from one opening in the laying pipe towards the other opening, and installing the tube along the optical fiber cable. A method for fixing an optical fiber cable, comprising a fluid injection step of injecting a fluid into the tube to inflate the tube, thereby pressing the optical fiber cable against the inner surface of the laying pipe.

2. A method for fixing an optical fiber cable according to claim 1, A method for fixing an optical fiber cable, wherein in the tube insertion step, a sheet member provided between the optical fiber cable and the tube is inserted together with the tube.

3. A method for fixing an optical fiber cable according to claim 1, A method for fixing an optical fiber cable, further comprising an optical fiber cable laying step of laying the optical fiber cable inside the laying conduit before the tube insertion step.

4. Optical fiber cables laid in conduits buried underground, The aforementioned laying pipe includes a resin tube inserted along the upper part of the optical fiber cable, A fixing structure for an optical fiber cable, wherein a fluid is injected into the tube to press the optical fiber cable against the inner surface of the laying pipe.

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