JP2023014654A - Optical fiber bending direction calculation system, optical fiber bending direction calculation method, optical fiber bending direction calculation device, and optical fiber bending direction calculation program - Google Patents

Abstract

To easily manufacture a long optical fiber cable and easily increase an interval between cores to improve sensitivity to strain in calculating a bending direction of an optical fiber cable.SOLUTION: The present disclosure is an optical fiber bending direction calculation system F comprising: a change amount difference calculation unit 21 that, for two or more single-mode optical fibers, calculates an amount of change in a longitudinal distribution of the Brillouin frequency shift before and after bending of an optical fiber cable C, and calculates a difference in the amount of change in the longitudinal distribution of the Brillouin frequency shift; and an optical fiber position calculation unit 22 that, on the basis of, the difference in the amount of change in the longitudinal distribution of the Brillouin frequency shift, calculates which of the outside and the inside of a bending area of the optical fiber cable C the two or more single-mode optical fibers are located.SELECTED DRAWING: Figure 1

Description

The present disclosure relates to technology for calculating the bending direction of an optical fiber cable.

Techniques for calculating the bending direction of an optical fiber cable are disclosed in Non-Patent Documents 1, 2, and the like. In Non-Patent Document 1, the curve trajectory in the three-dimensional space of the optical fiber cable can be analytically calculated based on the curvature κ and the torsion τ in the Fresnet-Serre formula. Here, the curvature κ indicates in what direction and how much the optical fiber cable is bent. The torsion τ indicates how much the initial coordinates (absolute coordinates with respect to the top and bottom of the earth) that serve as the reference for the bending direction of the optical fiber cable are rotated.

ここで、ｓは、光ファイバケーブルの曲線軌跡上の距離を示し、ｒ_０は、光ファイバケーブルの曲線軌跡上の端点を示し、Ｔ（ｓ）は、数式２で表わされる位置ベクトルである。

ここで、Ｔは、光ファイバケーブルの曲線軌跡の単位接ベクトルを示し、Ｎは、光ファイバケーブルの曲線軌跡の単位主法線ベクトルを示し、Ｂは、光ファイバケーブルの曲線軌跡の単位従法線ベクトルを示し、ｄ／ｄｓは、光ファイバケーブルの曲線軌跡の単位弧長当たりの変化量（空間分解能）を示し、κ及びτは、上述の曲率及び捩率を示す。 A curve locus vector r(s) of an optical fiber cable is expressed by Equation (1).

Here, s indicates the distance on the curved locus of the optical fiber cable, _r0 indicates the end point on the curved locus of the optical fiber cable, and T(s) is the position vector represented by Equation (2).

Here, T denotes the unit tangent vector of the curved locus of the optical fiber cable, N denotes the unit principal normal vector of the curved locus of the optical fiber cable, and B denotes the unit minor modulus of the curved locus of the optical fiber cable. Denote line vectors, d/ds denote the variation per unit arc length (spatial resolution) of the curved locus of the fiber optic cable, and κ and τ denote the curvature and torsion mentioned above.

Jason P. Moore and MatthewD. Rogge, "Shape sensing using multi-core fiber optic cable and parametric curve solution", Optics Express, Vol. 20, No. 3, pp. 2967-2973. M. J. Gander, W.; N. MacPherson, R.; McBride, J.; D. C. Jones, L.; Zhang, I. Bennion, P.; M. Blanchard, J.; G. Burnett and A.L. H. Greenaway, "Bend measurement using Bragg gratings in multicore fiber", Electronics letters, Vol. 36, No. 2, pp. 120-121.

In Non-Patent Document 2, a multi-core optical fiber provided with FBG (Fiber Bragg Grating), in which the Bragg reflection wavelength changes when the optical fiber cable is bent, is used. Then, OFDR (Optical Frequency Domain Reflectometry) is used to measure the longitudinal distribution of strain in each core. Furthermore, the curvature κ and the torsion τ at that point are calculated based on the strain distribution in the cross-sectional direction at that point obtained from the strain of each core at the same point. Then, based on Equations 1 and 2, the curve locus vector r(s) of the optical fiber cable can be calculated.

However, since a multi-core optical fiber with FBG is used, it is difficult to fabricate a long optical fiber cable. Considering the mechanical strength and transmission characteristics of the optical fiber cable, it is difficult to increase the distance between the cores in order to improve the sensitivity to strain. Furthermore, since OFDR is used, the measurement distance is short.

Therefore, in order to solve the above problems, the present disclosure easily fabricates a long optical fiber cable when calculating the bending direction of the optical fiber cable, and at the same time, the distance between the cores to improve the sensitivity to strain. The purpose is to easily increase the

In order to solve the above problem, for two or more single-mode optical fibers, the difference in the amount of change in the longitudinal distribution of the Brillouin frequency shift before and after bending of the optical fiber cable is calculated. Then, based on this, it is calculated on which side of the bending region of the optical fiber cable the two or more single-mode optical fibers are located.

Specifically, the present disclosure provides a method for adjusting the frequency between the frequency of incident light and the frequency of reflected light for two or more single-mode optical fibers of an optical fiber cable in which a plurality of single-mode optical fibers are housed. A frequency shift measuring unit for measuring the longitudinal distribution of the Brillouin frequency shift, and calculating the amount of change in the longitudinal distribution of the Brillouin frequency shift between before and after bending of the optical fiber cable for two or more of the single-mode optical fibers. a change amount difference calculator for calculating a difference in the amount of change in the longitudinal distribution of the Brillouin frequency shift; and two or more of the single-mode optical fibers based on the difference in the amount of change in the longitudinal distribution of the Brillouin frequency shift. and an optical fiber position calculator that calculates which side of the bending region of the optical fiber cable is located, the optical fiber bending direction calculating system.

The present disclosure also provides a Brillouin frequency shift between the frequency of incident light and the frequency of reflected light for two or more single-mode optical fibers of an optical fiber cable in which a plurality of single-mode optical fibers are housed. a frequency shift measurement step of measuring a longitudinal distribution; and calculating a variation in the longitudinal distribution of the Brillouin frequency shift between before and after bending of the optical fiber cable for two or more of the single-mode optical fibers, and a change amount difference calculating step of calculating a difference in change amount of the longitudinal distribution of the frequency shift; and an optical fiber position calculation step of calculating which side of the bending region of the optical fiber cable is located, the step of calculating the position of the optical fiber.

The present disclosure also provides a Brillouin frequency shift between the frequency of incident light and the frequency of reflected light for two or more single-mode optical fibers of an optical fiber cable in which a plurality of single-mode optical fibers are housed. A frequency shift acquisition unit that acquires a measurement result of the longitudinal distribution, and for two or more of the single mode optical fibers, calculates the amount of change in the longitudinal distribution of the Brillouin frequency shift between before and after bending of the optical fiber cable. a change amount difference calculator for calculating a difference in the amount of change in the longitudinal distribution of the Brillouin frequency shift; and two or more of the single-mode optical fibers based on the difference in the amount of change in the longitudinal distribution of the Brillouin frequency shift. and an optical fiber position calculator that calculates whether the position is located outside or inside a bending region of the optical fiber cable.

Further, the present disclosure is to cause a computer to sequentially execute each processing step performed by the frequency shift acquisition unit, the change amount difference calculation unit, and the optical fiber position calculation unit included in the optical fiber bending direction calculation device described above. is an optical fiber bending direction calculation program.

According to these configurations, since a single-mode optical fiber is used, it is easy to produce a long optical fiber cable. Also, considering the mechanical strength and transmission characteristics of the optical fiber cable, it is easy to increase the distance between the cores in order to improve the sensitivity to strain. Furthermore, without converting the amount of change in Brillouin frequency shift into strain, calculating on which side the two or more single-mode optical fibers are located outside or inside the bending region of the optical fiber cable. can be done.

Further, according to the present disclosure, the optical fiber position calculation unit determines that the single-mode optical fiber having a small change width even if the amount of change in the longitudinal distribution of the Brillouin frequency shift is positive or negative is the optical fiber cable and the single-mode optical fiber with a negative change in the longitudinal distribution of the Brillouin frequency shift or a small change even if it is positive is located outside the bending region of the optical fiber cable. An optical fiber bending direction calculation system characterized by calculating that the bending direction is positioned inside the .

According to this configuration, two or more single-mode optical fibers are placed on either side of the bend region of the optical fiber cable, whether the optical fiber cable is twisted or untwisted. can be calculated.

In addition, the present disclosure is directed to which side of the bending region of the optical fiber cable the two or more single-mode optical fibers are positioned, out of the outer side or the inner side, and in what direction the optical fiber cable is twisted. and whether or not the optical fiber cable is twisted at a twisting period. System.

According to this configuration, even if the optical fiber cable is twisted, it is calculated whether the two or more single-mode optical fibers are positioned outside or inside the bending region of the optical fiber cable. In addition, it is possible to calculate in what direction the optical fiber cable is bent. In addition, if the optical fiber cable is not twisted, only by calculating on which side the two or more single-mode optical fibers are located on the outside or the inside of the bending region of the optical fiber cable, It is possible to calculate in what direction the optical fiber cable is bent.

Further, according to the present disclosure, in a state in which the distance resolution of the frequency shift measurement unit in the longitudinal direction of the optical fiber cable is shorter than the twist period of the optical fiber cable, the optical fiber bend calculation unit measures the optical fiber An optical fiber bending direction calculation system characterized by calculating in what direction a cable is bent.

According to this configuration, it is possible to monitor how the amount of change in the Brillouin frequency shift changes in the distance direction over the twist period of the optical fiber cable.

Thus, in calculating the bending direction of an optical fiber cable, the present disclosure can easily fabricate a long optical fiber cable and easily increase the spacing between cores to improve sensitivity to strain. can be done.

1 is a diagram showing the configuration of an optical fiber bending direction calculation system of the present disclosure; FIG. It is a figure which shows the procedure of the optical fiber bending direction calculation method of this indication. FIG. 4 is a diagram showing a specific example of calculating the bending direction of an untwisted optical fiber of the present disclosure; FIG. 4 is a diagram showing a specific example of calculating the bending direction of an untwisted optical fiber of the present disclosure; FIG. 4 is a diagram showing a specific example of calculating the bending direction of an untwisted optical fiber of the present disclosure; FIG. 4 is a diagram showing a specific example of calculating a bending direction of a twisted optical fiber of the present disclosure; FIG. 4 is a diagram showing a specific example of calculating a bending direction of a twisted optical fiber of the present disclosure; FIG. 4 is a diagram showing a specific example of calculating a bending direction of a twisted optical fiber of the present disclosure;

Embodiments of the present disclosure will be described with reference to the accompanying drawings. The embodiments described below are examples of implementing the present disclosure, and the present disclosure is not limited to the following embodiments.

(Overview of optical fiber bending direction calculation system of the present disclosure)
FIG. 1 shows the configuration of the optical fiber bending direction calculation system of the present disclosure. FIG. 2 shows the procedure of the optical fiber bending direction calculation method of the present disclosure. An optical fiber bending direction calculation system F includes a frequency shift measuring device 1 and an optical fiber bending direction calculation device 2 . The optical fiber bending direction calculation device 2 includes a change amount difference calculation unit 21, an optical fiber position calculation unit 22, and an optical fiber bending calculation unit 23, and can also be realized by a computer and the optical fiber bending direction calculation program shown in FIG. can be done. The optical fiber bending direction calculation program shown in FIG. 2 can be recorded on a recording medium or provided through a network.

The fiber optic cable C houses a plurality of single mode optical fibers. A frequency shift measurement device 1 measures the longitudinal distribution of Brillouin frequency shifts between the frequency of incident light and the frequency of reflected light for two or more single-mode optical fibers. The frequency shift measuring apparatus 1 cannot increase the measurement distance if OFDR is used, but can increase the measurement distance if OTDR (Optical Time Domain Reflectometry) is used. The optical fiber bending direction calculator 2 can calculate the bending direction of the optical fiber cable C as shown in FIGS.

(Specific example of calculating bending direction of untwisted optical fiber of the present disclosure)
A specific example of calculating the bending direction of an untwisted optical fiber according to the present disclosure is shown in FIGS. 3 to 5. FIG. In FIG. 3, the optical fiber cable C is bundled with eight optical fiber slots S in which four tape optical fibers are laminated in five layers, and is not twisted.

The change amount difference calculator 21 acquires the measurement result of the longitudinal distribution of the Brillouin frequency shift between the frequency of the incident light and the frequency of the reflected light for two or more single-mode optical fibers (step S1). In FIG. 3, the change amount difference calculator 21 calculates the outer optical fiber FO of the outermost layer tape optical fiber and the inner optical fiber FI of the innermost layer tape optical fiber in the same optical fiber slot S, Measurements of the longitudinal distribution of the Brillouin frequency shift are obtained. Here, the change amount difference calculator 21 may acquire the measurement result of the longitudinal distribution of the Brillouin frequency shift for any two or more single-mode optical fibers of the optical fiber cable C. FIG. However, any two or more single-mode optical fibers should desirably have the same transmission characteristic specifications, manufacturing conditions, and the like.

The change amount difference calculator 21 calculates the Brillouin frequency shift between before and after bending of the optical fiber cable C for two or more single-mode optical fibers (the outer optical fiber FO and the inner optical fiber FI in FIGS. 3 to 5). The amount of change in the distribution in the longitudinal direction is calculated, and the difference in the amount of change in the distribution in the longitudinal direction of the Brillouin frequency shift is calculated (step S2).

The upper part of FIG. 4 shows the state before the optical fiber cable C is bent. At _a distance z1 on the locus of the fiber optic cable C, the outer optical fiber FO/inner optical fiber FI is at the higher/lower x-coordinate position of the outer absolute coordinate of the fiber optic cable C. FIG. At the distance z2 on the trajectory of the optical fiber cable _C , the outer optical fiber FO/inner optical fiber FI is also located at the larger/smaller x-coordinate position of the outer absolute coordinate of the optical fiber cable C. FIG.

The upper part of FIG. 5 also shows the state before the optical fiber cable C is bent. At distances z ₁ to z ₂ on the trajectory of the optical fiber cable C, the Brillouin frequency shifts in the outer optical fiber FO/inner optical fiber FI are almost constant and almost the same.

The lower part of FIG. 4 shows the state after the optical fiber cable C is bent. The optical fiber cable C is bent in the positive direction of the x-coordinate of the external absolute coordinates of the optical fiber cable C as it moves from the distance z1 to the distance z2 _on the locus of the optical fiber cable C. _FIG . At _a distance z1 on the locus of the fiber optic cable C, the outer optical fiber FO/inner optical fiber FI is at the higher/lower x-coordinate position of the outer absolute coordinate of the fiber optic cable C. FIG. At the distance z2 on the trajectory of the optical fiber cable _C , the outer optical fiber FO/inner optical fiber FI is also located at the larger/smaller x-coordinate position of the outer absolute coordinate of the optical fiber cable C. FIG.

The lower part of FIG. 5 also shows the state after the optical fiber cable C is bent. At distances z ₁ to z ₂ on the trajectory of fiber optic cable C, the outer optical fiber FO lies inside the bending region of the fiber optic cable C, and the Brillouin frequency shift at the outer optical fiber FO changes in the negative direction. However, the width of change is small, the inner optical fiber FI is located outside the bending region of the optical fiber cable C, and the Brillouin frequency shift in the inner optical fiber FI changes in the positive direction.

The optical fiber position calculator 22 calculates two or more single-mode optical fibers (outer optical fiber FO and inner optical fiber FI ) is located outside or inside the bending region of the optical fiber cable C (step S3).

Specifically, the optical fiber position calculation unit 22 uses a single-mode optical fiber (in FIGS. 4 and 5, distance Calculate that the inner optical fiber FI) is located outside the bend region of the optical fiber cable C in z ₁ to z ₂ . On the other hand, the optical fiber position calculation unit 22 determines whether the variation in the longitudinal distribution of the Brillouin frequency shift is negative or even if the variation is positive, the single-mode optical fiber (in FIGS. 4 and 5, distance z ₁ to z ₂ , the outer optical fiber FO) is calculated to lie inside the bending region of the optical fiber cable C.

The optical fiber bending calculator 23 determines whether two or more single-mode optical fibers (the outer optical fiber FO and the inner optical fiber FI in FIGS. 3 to 5) and that the fiber optic cable C is untwisted (in FIGS. 4 and 5, at distances z ₁ to z ₂ ). It is calculated whether it is bent in the bending direction (step S4).

Specifically, the optical fiber bend calculator 23 obtains information on the outside and inside of the outer optical fiber FO and the inner optical fiber FI shown in FIG. 4 and information on the twist of the optical fiber cable C shown in FIG. After that, it is calculated that the optical fiber cable C is bent in the positive direction of the _{x -} coordinate of the external absolute coordinates as it moves from the distance z1 to the distance z2.

(Specific example of calculating bending direction of twisted optical fiber of the present disclosure)
A specific example of calculating the bending direction of a twisted optical fiber according to the present disclosure is shown in FIGS. 6 to 8. FIG. In FIG. 6, the optical fiber cable C is formed by bundling 8 optical fiber slots S in which 4 tape optical fibers are laminated in 5 layers and then twisting.

The change amount difference calculator 21 acquires the measurement result of the longitudinal distribution of the Brillouin frequency shift between the frequency of the incident light and the frequency of the reflected light for two or more single-mode optical fibers (step S1). In FIG. 6, the change amount difference calculator 21 calculates the outer optical fiber FO of the outermost layer tape optical fiber and the inner optical fiber FI of the innermost layer tape optical fiber in the same optical fiber slot S, Measurements of the longitudinal distribution of the Brillouin frequency shift are obtained. Here, the change amount difference calculator 21 may acquire the measurement result of the longitudinal distribution of the Brillouin frequency shift for any two or more single-mode optical fibers of the optical fiber cable C. FIG. However, any two or more single-mode optical fibers should desirably have the same transmission characteristic specifications, manufacturing conditions, and the like.

The variation difference calculator 21 calculates the Brillouin frequency shift between before and after bending of the optical fiber cable C for two or more single-mode optical fibers (the outer optical fiber FO and the inner optical fiber FI in FIGS. 6 to 8). The amount of change in the distribution in the longitudinal direction is calculated, and the difference in the amount of change in the distribution in the longitudinal direction of the Brillouin frequency shift is calculated (step S2).

The upper part of FIG. 7 shows the state before the optical fiber cable C is bent. At _a distance z1 on the locus of the fiber optic cable C, the outer optical fiber FO/inner optical fiber FI is at the higher/lower x-coordinate position of the outer absolute coordinate of the fiber optic cable C. FIG. At a distance z2 on the locus of the optical fiber cable _C , the outer optical fiber FO/inner optical fiber FI is at the lower/larger x-coordinate position of the outer absolute coordinate of the optical fiber cable C. FIG.

The upper part of FIG. 8 also shows the state before the optical fiber cable C is bent. At distances z ₁ to z ₂ on the trajectory of the optical fiber cable C, the Brillouin frequency shifts in the outer optical fiber FO/inner optical fiber FI are almost constant and almost the same.

The lower part of FIG. 7 shows the state after the optical fiber cable C is bent. The optical fiber cable C is bent in the positive direction of the x-coordinate of the external absolute coordinates of the optical fiber cable C as it moves from the distance z1 to the distance z2 _on the locus of the optical fiber cable C. _FIG . At _a distance z1 on the locus of the fiber optic cable C, the outer optical fiber FO/inner optical fiber FI is at the higher/lower x-coordinate position of the outer absolute coordinate of the fiber optic cable C. FIG. At a distance z2 on the locus of the optical fiber cable _C , the outer optical fiber FO/inner optical fiber FI is at the lower/larger x-coordinate position of the outer absolute coordinate of the optical fiber cable C. FIG.

The lower part of FIG. 8 also shows the state after the optical fiber cable C is bent. Near the distance z ₁ on the trajectory of the optical fiber cable C, the outer optical fiber FO is located inside the bending region of the optical fiber cable C, and the Brillouin frequency shift at the outer optical fiber FO changes in the negative direction. The width of the change is small, the inner optical fiber FI is located outside the bending region of the optical fiber cable C, and the Brillouin frequency shift in the inner optical fiber FI changes in the positive direction.

Near the distance z2 _on the trajectory of the optical fiber cable C, the outer optical fiber FO is located outside the bending region of the optical fiber cable C, the Brillouin frequency shift at the outer optical fiber FO changes in the positive direction, The inner optical fiber FI is located inside the bending region of the optical fiber cable C, and the Brillouin frequency shift in the inner optical fiber FI changes in the negative direction, but the change width is small. Between the distances z ₁ and z ₂ on the trajectory of the optical fiber cable C, the states near the distances z ₁ and z ₂ on the trajectory of the optical fiber cable C are switched.

The optical fiber position calculator 22 calculates two or more single-mode optical fibers (outer optical fiber FO and inner optical fiber FI ) is located outside or inside the bending region of the optical fiber cable C (step S3).

Specifically, the optical fiber position calculation unit 22 uses a single-mode optical fiber (in FIGS. 7 and 8, distance It is calculated that the inner optical fiber FI in the vicinity of _z1 and the outer optical fiber FO in the vicinity of z2 _are located outside the bending region of the optical fiber cable C. On the other hand, the optical fiber position calculator 22 determines whether the change in the longitudinal distribution of the Brillouin frequency shift is negative or even if positive, the single-mode optical fiber with a small change width (in FIGS. 7 and 8, distance z It is calculated that the outer optical fiber FO is positioned inside the bending region of the optical fiber cable _C in the vicinity of ₁ and the inner optical fiber FI in the vicinity of distance z2.

The optical fiber bending calculator 23 determines whether two or more single-mode optical fibers (the outer optical fiber FO and the inner optical fiber FI in FIGS. 6 to 8) In what direction the optical fiber cable C is bent is determined based on which side of the optical fiber cable C is located and in what twist direction and twist cycle the optical fiber cable C is twisted. Calculate (step S4).

Specifically, the optical fiber bend calculator 23 obtains information on the outside and inside of the outer optical fiber FO and the inner optical fiber FI shown in FIG. 7 and information on the twist of the optical fiber cable C shown in FIG. After that, it is calculated that the optical fiber cable C is bent in the positive direction of the _{x -} coordinate of the external absolute coordinates as it moves from the distance z1 to the distance z2.

Here, when the distance resolution of the frequency shift measuring device 1 in the longitudinal direction of the optical fiber cable C is shorter than the twist period of the optical fiber cable C, the optical fiber bending calculator 23 It is desirable to calculate whether it is bent in such a bending direction. Then, it is possible to monitor how the amount of change in the Brillouin frequency shift changes in the distance direction over the twist period of the optical fiber cable C. FIG.

(Effect of optical fiber bending direction calculation system of the present disclosure)
As described above, since a single-mode optical fiber is used, it is easy to fabricate a long optical fiber cable C. FIG. Also, considering the mechanical strength and transmission characteristics of the optical fiber cable C, it is easy to increase the distance between the cores in order to improve the sensitivity to strain. Furthermore, without converting the amount of change in the Brillouin frequency shift into strain, it is calculated which side of the bending region of the optical fiber cable C the two or more single-mode optical fibers are positioned outside or inside. be able to.

Also, even if the optical fiber cable C is twisted, it is only necessary to calculate on which side of the bending region of the optical fiber cable C two or more single-mode optical fibers are located. Instead, it is possible to calculate in what direction the optical fiber cable C is bent. In addition, if the optical fiber cable C is not twisted, it is only calculated which side of the bending region of the optical fiber cable C the two or more single mode optical fibers are located on the outside or inside. , it is possible to calculate in what direction the optical fiber cable C is bent.

The optical fiber bending direction calculation system, the optical fiber bending direction calculation method, the optical fiber bending direction calculation device, and the optical fiber bending direction calculation program of the present disclosure are applicable not only to optical fiber cables used in optical fiber communication and distributed in urban areas, Bend directions can also be calculated for fiber optic cables used in structural strain sensors and installed in structures.

F: Optical fiber bending direction calculation system C: Optical fiber cable S: Optical fiber slot FO: Outer optical fiber FI: Inner optical fiber 1: Frequency shift measurement device 2: Optical fiber bending direction calculation device 21: Variation difference calculation unit 22 : Optical fiber position calculator 23: Optical fiber bend calculator

Claims (7)

Measuring the longitudinal distribution of Brillouin frequency shift between the frequency of incident light and the frequency of reflected light for two or more single-mode optical fibers of an optical fiber cable in which a plurality of single-mode optical fibers are housed a frequency shift measuring unit for
For the two or more single-mode optical fibers, calculating the amount of change in the longitudinal distribution of the Brillouin frequency shift between before and after bending of the optical fiber cable, and calculating the difference in the amount of change in the longitudinal distribution of the Brillouin frequency shift. a variation difference calculation unit for
Based on the difference in the amount of change in the longitudinal distribution of the Brillouin frequency shift, it is determined whether the two or more single-mode optical fibers are positioned outside or inside the bending region of the optical fiber cable. an optical fiber position calculator that calculates
An optical fiber bending direction calculation system comprising: The optical fiber position calculation unit determines whether the single-mode optical fiber having a positive change in the Brillouin frequency shift distribution in the longitudinal direction or a small change width even if the change is negative is outside the bending region of the optical fiber cable. It is calculated that the single-mode optical fiber in which the amount of change in the longitudinal distribution of the Brillouin frequency shift is negative or has a small change width even if it is positive is located inside the bending region of the optical fiber cable. The optical fiber bending direction calculation system according to claim 1, characterized in that: The two or more single-mode optical fibers are positioned outside or inside the bending region of the optical fiber cable, and in what twist direction and twist period the optical fiber cable is twisted. The optical fiber according to claim 1 or 2, further comprising an optical fiber bending calculator that calculates in what direction the optical fiber cable is bent based on whether the optical fiber cable is bent. Bending direction calculation system. In a state where the distance resolution of the frequency shift measurement unit in the longitudinal direction of the optical fiber cable is shorter than the twist period of the optical fiber cable, the optical fiber bend calculation unit determines how the optical fiber cable bends. 4. The optical fiber bending direction calculation system according to claim 3, wherein the bending direction is calculated. Measuring the longitudinal distribution of Brillouin frequency shift between the frequency of incident light and the frequency of reflected light for two or more single-mode optical fibers of an optical fiber cable in which a plurality of single-mode optical fibers are housed a frequency shift measurement step for
For the two or more single-mode optical fibers, calculating the amount of change in the longitudinal distribution of the Brillouin frequency shift between before and after bending of the optical fiber cable, and calculating the difference in the amount of change in the longitudinal distribution of the Brillouin frequency shift. a change amount difference calculation step for
Based on the difference in the amount of change in the longitudinal distribution of the Brillouin frequency shift, it is determined whether the two or more single-mode optical fibers are positioned outside or inside the bending region of the optical fiber cable. an optical fiber position calculation step to be calculated;
An optical fiber bending direction calculation method, comprising: Measurement of longitudinal distribution of Brillouin frequency shift between frequency of incident light and frequency of reflected light for two or more single-mode optical fibers of an optical fiber cable in which a plurality of single-mode optical fibers are housed a frequency shift acquisition unit that acquires a result;
For the two or more single-mode optical fibers, calculating the amount of change in the longitudinal distribution of the Brillouin frequency shift between before and after bending of the optical fiber cable, and calculating the difference in the amount of change in the longitudinal distribution of the Brillouin frequency shift. a variation difference calculation unit for
Based on the difference in the amount of change in the longitudinal distribution of the Brillouin frequency shift, it is determined whether the two or more single-mode optical fibers are positioned outside or inside the bending region of the optical fiber cable. an optical fiber position calculator that calculates
An optical fiber bending direction calculation device comprising: Optical fiber bending for causing a computer to sequentially execute each processing step performed by the frequency shift acquisition unit, the change amount difference calculation unit, and the optical fiber position calculation unit provided in the optical fiber bending direction calculation device according to claim 6 Orientation calculator.

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