JP7406767B2 - Fiber optic cable sensing system, fiber optic cable sensing method, and fiber optic cable - Google Patents

Description

The present disclosure relates to an optical fiber cable sensing system, an optical fiber cable sensing method, and the optical fiber cable that estimate the position of a laid optical fiber cable.

A laid optical fiber cable can be expressed as a curved locus in three-dimensional space. The locus of a curve in three-dimensional space can be analyzed by obtaining the curvature κ and torsion τ and using the Frenet-Séret formula. Here, the curvature κ is a value expressing how much and in which direction the curve is curved. The torsion coefficient τ is a value that expresses how much the object rotates with respect to the initial coordinates (absolute coordinates based on the earth's top and bottom) that serve as a reference for the bending direction. In addition, "absolute coordinates" are, for example, coordinates where a plane parallel to an arbitrary tangential surface when the earth is a sphere is expressed by the orthogonal x and z axes, and a perpendicular to the xz plane is expressed by the y axis. be.

By substituting the curvature κ and torsion τ obtained at an arbitrary position of the curve into the Frenet-Celet formula, the position vector T(s) at an arbitrary position can be obtained, and by integrating the position vector T(s), the curve The trajectory vector r(s) of can be obtained.

FIG. 1 is an image explaining a method for estimating the position of an optical fiber cable. As shown in FIG. 1, if the "rotation Ω due to twisting" and the "direction vector r due to bending" are known, the position of the optical fiber cable can be estimated. Here, "rotation Ω due to twisting" means rotation by Ω about the z-axis (direction of the central axis of the optical fiber cable) with respect to the initial position _r0 . "Direction vector r due to bending" is the trajectory vector r(s). Moreover, r _j (j is an integer of 0 or more) in FIG. 1 means a position in the longitudinal direction of the optical fiber cable, and L _j means a section of the optical fiber cable. The x'-axis and y'-axis are reference axes of the optical fiber cable, and are rotated by Ω with respect to the absolute coordinate x-axis and y-axis.

When analyzing a curve trajectory in this way, there is a known method of calculating the curvature κ and torsion τ using a multi-core optical fiber provided with FBG (Fiber Bragg Grating) (for example, Non-Patent Documents 1 and 2). ). Since the wavelength of reflected light changes due to fiber bending due to FBG (Bragg wavelength shifts), the strain distribution in the longitudinal direction of each core is measured using OFDR (Optical Frequency Domain Reflectometry). Then, the curvature κ and torsion rate τ are calculated based on the strain distribution in the cross-sectional direction obtained from the strain of each core at the same point.

“Shape sensing using multi-core fiber optical cable and parametric curve solution”, Optics Express, Vol. 20, No. 3, pp. 2967-2973 “Bend measurement using Bragg gratings in multicore fiber”, Electronics letters, vol. 36, no. 2, pp. 120-121

The conventional method of using a multi-core optical fiber provided with FBG as a sensor medium has the following problems.
First, a multi-core optical fiber provided with an FBG has a special structure that makes it difficult to make it long and has a large optical loss, making it difficult to analyze long-distance curved trajectories using conventional methods.
Furthermore, in order to improve the sensitivity to distortion, it is necessary to increase the core pitch of a multi-core optical fiber provided with an FBG, but it is difficult to increase the core pitch from the viewpoint of ensuring mechanical strength and transmission characteristics. At present, the core pitch is limited to several tens of μm. In other words, it is difficult to improve measurement accuracy with conventional methods.
Furthermore, OFDR, which is a measurement means, has a short measurement distance (several tens of meters to hundreds of meters), making it difficult to measure long distances.

On the other hand, the installed optical fiber cable is not a multi-core optical fiber, but a general-purpose single mode optical fiber. For this reason, there is also the problem that it is difficult to perform curve locus analysis using a multi-core optical fiber as described above.

Therefore, in order to solve the above problems, the present invention provides an optical fiber cable sensing system, an optical fiber cable sensing method, and an optical fiber cable sensing method that can perform curve trajectory analysis on an optical fiber cable configured with a general-purpose single mode optical fiber. and its optical fiber cable.

In order to achieve the above object, the optical fiber cable sensing system according to the present invention limits the twisting pitch range of the optical fiber cable that is the sensing cable.

Specifically, the optical fiber cable sensing system according to the present invention includes:
An optical fiber cable that stores M single-mode optical fibers (M is an integer of 3 or more), and the single-mode optical fibers have a twist pitch of A;
Among the single mode optical fibers, a test light is incident on any N single mode optical fibers (N is an integer less than M), and a longitudinal distribution of physical quantities representing bending is determined for each of the N single mode optical fibers. a measuring device to measure the
Equipped with
A>Δz
It is characterized by satisfying the following.

Further, the optical fiber cable sensing method according to the present invention includes:
Storing M (M is an integer of 3 or more) single mode optical fibers in an optical fiber cable with a twist pitch A;
Injecting a test light into arbitrary N single mode optical fibers (N is an integer less than M) among the single mode optical fibers, and determining the length of a physical quantity representing bending for each of the N single mode optical fibers. measuring the directional distribution with a measuring device;
It is characterized by
However, A>Δz (Δz is the distance resolution of the measuring device).

Furthermore, the optical fiber cable according to the present invention stores M single-mode optical fibers (M is an integer of 3 or more), and the twist pitch A of the single-mode optical fibers is A>Δz.
It is characterized by satisfying the following.
However, Δz is a physical quantity representing the bending of each of the N single-mode optical fibers when test light is incident on any N single-mode optical fibers (N is an integer less than M) among the single-mode optical fibers. is the distance resolution of the measuring instrument that measures the longitudinal distribution of

By setting the twist pitch A of the optical fiber cable within the above range, it is possible to measure the twist pitch and small strain of single mode optical fiber over a long distance even using a measuring instrument with low distance resolution (long measurement interval). can. Therefore, the present invention provides an optical fiber cable sensing system, an optical fiber cable sensing method, and the optical fiber cable capable of performing curve trajectory analysis on an optical fiber cable made of a general-purpose single mode optical fiber. be able to.

The optical fiber cable sensing system according to the present invention is characterized in that the distance resolution Δz of the measuring device is approximately equal to the twist pitch A. It is possible to measure a physical quantity ε that exceeds the measurement limit Δε of the measuring instrument.

The measuring device of the optical fiber cable sensing system according to the present invention is characterized in that the measuring device measures an amount of distortion, bending loss, or polarization variation as the physical quantity.
For example, if OFDR is used as a measuring device, the amount of distortion can be measured. Bending loss can be measured using a 1μ-OTDR, which performs highly sensitive measurements by using light in the 1μm wavelength band, which is a two-mode region, and observing scattered light in higher-order modes. Polarization fluctuations can be measured using a P-OTDR that measures each polarization state as a measuring device.

Note that the above inventions can be combined as much as possible.

The present invention provides an optical fiber cable sensing system, an optical fiber cable sensing method, and the optical fiber cable capable of performing curve trajectory analysis on an optical fiber cable made of a general-purpose single mode optical fiber. can.

This is an image explaining a method for estimating the position of an optical fiber cable. FIG. 1 is a diagram illustrating an optical fiber cable sensing system according to the present invention. FIG. 2 is a diagram showing one of the single mode optical fibers included in the optical fiber cable being measured using the optical fiber cable sensing system according to the present invention. FIG. 3 is a diagram illustrating the position of a single mode optical fiber within an optical fiber cable cross section measured by the optical fiber cable sensing system according to the present invention. 1 is an example of a cable cross-sectional strain distribution calculated by the optical fiber cable sensing system according to the present invention. It is a figure explaining the definition of a "bending axis." FIG. 3 is a diagram illustrating calculations performed by the optical fiber cable sensing system according to the present invention. 1 is a flowchart illustrating an optical fiber cable sensing method according to the present invention. FIG. 1 is a diagram illustrating an optical fiber cable sensing system according to the present invention. FIG. 1 is a diagram illustrating an optical fiber cable according to the present invention. 1 is a flowchart illustrating an optical fiber cable sensing method according to the present invention.

Embodiments of the invention will be described with reference to the accompanying drawings. The embodiments described below are examples of the present invention, and the present invention is not limited to the following embodiments. Note that components with the same reference numerals in this specification and the drawings indicate the same components.

(Embodiment 1)
The optical fiber cable sensing system of the present invention is characterized by the longitudinal distribution of strain (which may also be bending loss or polarization variation) measured for each single-mode optical fiber stored in an optical fiber cable to be measured with a limited twist pitch. A means for inputting data and data indicating the position on the cable cross section of each optical fiber to be measured, and the distortion (bending loss or polarization fluctuation may be also acceptable) of each optical fiber at the same point and the cable cross section of the optical fiber concerned. means for calculating the curvature vector κ of the optical fiber cable to be measured at the point based on the above position using equation 1, and the torsion factor τ of the optical fiber cable to be measured at the point from the calculated curvature vector κ. and means for calculating using Equation 2.

FIG. 2 is a diagram illustrating the optical fiber cable sensing system 301 of this embodiment. Moreover, FIG. 3 is a diagram in which one of the single mode optical fibers included in the optical fiber cable 20 is measured using the optical fiber cable sensing device 10. The optical fiber cable 20 is of a tape slot type, and five sets of four-core optical fiber ribbons 23 are inserted into the grooves 22 of the slots 21. The optical fiber ribbon 23 has four single mode optical fibers 24 arranged in parallel. In this embodiment, the tape slot type optical fiber cable 20 will be described, but the optical fiber cable that can be measured by the optical fiber cable sensing device 10 is not limited to the tape slot type.
Note that the single mode optical fiber means an optical fiber in which light propagates in a single mode at the wavelength of the test light.

The optical fiber cable sensing device 10 includes:
Inject the test light into any N single mode optical fibers 24 (N is an integer less than M) among the M single mode optical fibers 24 (M is an integer of 3 or more) stored in the optical fiber cable 20. and a measuring device 11 that measures the longitudinal distribution of physical quantities representing bending for each of the N single mode optical fibers 24;
At an arbitrary point in the longitudinal direction of the optical fiber cable 20, the curvature κ at the arbitrary point of the optical fiber cable 20 can be calculated by formula 1 from the respective positions of the N single mode optical fibers 24 in the cross section of the optical fiber cable 20 and the physical quantity. an arithmetic unit 12 that calculates the torsion coefficient τ at the arbitrary point of the optical fiber cable 20 using equation 2;
Equipped with.
In the example of FIG. 3, M=160.
Further, Equation 1 and Equation 2 will be described later.

The fiber optic cable sensing device 10 does not have to measure all single mode optical fibers 24. FIG. 4 is a diagram illustrating the position of the single mode optical fiber 24 measured by the optical fiber cable sensing device 10. The optical fiber cable sensing device 10 measures the four single-mode optical fibers 24 at the outermost circumference and the four single-mode optical fibers 24 at the innermost circumference for each groove 22. That is, in the example of FIG. 4, N=64. Note that the x-axis and y-axis shown in FIGS. 4 and 5 are shown assuming that the central axis of the optical fiber cable 20 is x=0 and y=0.

The measuring device 11 is characterized in that it measures the amount of distortion, bending loss, or polarization fluctuation as the physical quantity. In the following description, a case will be explained in which the amount of strain is measured as the physical quantity, but the curvature κ and torsion τ can be similarly calculated even when other physical quantities are measured. The measuring device 11 measures the amount of strain at position z for each single mode optical fiber 24 in the optical fiber cable 20 by measuring the strain distribution in the longitudinal direction. Examples of such means include OFDR and B-OFDR (OFDR that measures strain distribution by observing Brillouin scattered light). Note that if B-OTDR (OTDR that measures strain distribution by observing Brillouin scattered light) is used as the means, long-distance measurement becomes possible compared to the above-mentioned OFDR.

The computing unit 12 maps the strain amount of each single mode optical fiber 24 at an arbitrary position z of the optical fiber cable 20 on three-dimensional spatial coordinates (the center position of the cable corresponds to coordinate 0), and calculates the cable cross-sectional strain distribution. do. FIG. 5 is an example of cable cross-sectional strain distribution. In the example of FIG. 5, it can be seen that the single mode optical fiber 24 in the first quadrant is contracted and the single mode optical fiber 24 in the third quadrant is extended. From this, it is predicted that the optical fiber cable 20 is bent toward the positive side of the x-axis and the positive side of the y-axis at an arbitrary position z.

Here, the definition of "bending axis" is shown in FIG. The "bending axis" is a "neutral axis", which is a straight line Ax that passes perpendicularly through the center Ce of a circle having a radius of curvature R at the point of contact of a tangent line tangent to the central axis of the optical fiber cable 20 at an arbitrary position z. It is a straight line Nx that is parallel and passes through the center O of the optical fiber cable 20 at an arbitrary position z.

ただし、
ｉ：シングルモード光ファイバの番号
ε_ｉ：シングルモード光ファイバのうちｉ番目のシングルモード光ファイバの任意地点ｚにおける物理量
ｒ_ｉ：断面におけるｉ番目のシングルモード光ファイバと前記曲げ軸との距離
θ_ｉ：断面におけるｉ番目のシングルモード光ファイバのｘ軸に対する角度オフセット
ａｎｇｌｅ（ｖ）：ベクトルｖのｘ軸に対する角度
θ：任意位置ｚにおける曲率κのベクトルのｘ軸に対する傾き
θ’（ｓ）：前記θの、光ファイバケーブルの中心弧長ｓに関する微分
である。 The computing unit 12 extracts the strain amount for each position of the single mode optical fiber from the cable cross-sectional strain distribution in FIG. 5, calculates the curvature κ using Equation 1 as shown in FIG. Calculate the rate τ.

however,
i: Number of single-mode optical fiber ε _i : Physical quantity at arbitrary point z of the i-th single-mode optical fiber among the single-mode optical fibers r _i : Distance θ between the i-th single-mode optical fiber and the bending axis in the cross section _i : Angle offset with respect to the x-axis of the i-th single mode optical fiber in the cross section angle (v): Angle θ of the vector v with respect to the x-axis: Inclination of the vector of curvature κ with respect to the x-axis at an arbitrary position z θ'(s): This is the differential of θ with respect to the central arc length s of the optical fiber cable.

数１のΣの中の式は、各シングルモード光ファイバの歪を「ケーブル中心からの方向θを持ち、歪の大きさεを持つ歪ベクトル」として考え、その歪ベクトルの各成分を曲げ軸Ｎｘからの距離ｒで規格化したもの、といえる。なお、光ファイバケーブル断面中心Ｏ（ｒ＝０）では歪がなく、軸Ａｘ側で縮む歪が発生し、軸Ａｘの反対側で伸びる歪が発生する。 The amount of strain ε _i can be expressed as ε _i =r _i /R using the radius of curvature R at an arbitrary position and the distance r _i from the center of the cross section of the optical fiber cable to the single mode optical fiber. Here, since the bending radius R of the optical fiber cable 20 is 1/κ and the strain difference Δε is proportional to (distance difference)/R, ε _i ∝κr _i holds true if the bending axis is used as a reference.

The equation in Σ of Equation 1 considers the strain in each single-mode optical fiber as a "strain vector with direction θ from the cable center and strain magnitude ε", and each component of the strain vector is defined as the bending axis. It can be said that it is normalized by the distance r from Nx. Note that there is no strain at the optical fiber cable cross-sectional center O (r=0), a shrinking strain occurs on the axis Ax side, and an elongating strain occurs on the opposite side of the axis Ax.

ただし、
Ｔ（ｓ）：位置ベクトル
ｒ_０：初期位置
ｅ_１：単位接ベクトル
ｅ_２：単位主法線ベクトル
ｅ_３：単位従法線ベクトル
ｄ／ｄｓ：単位弧長当たりの変化量
である。 The calculator 12 calculates the central axis trajectory r(s) of the optical fiber cable 20 by substituting the curvature κ and the torsion rate τ into Equation 3 (Frenet-Celet formula), thereby determining the length of the installed optical fiber. The location of the cable can be estimated.

however,
T(s): Position vector r ₀ : Initial position e ₁ : Unit tangent vector e ₂ : Unit principal normal vector e ₃ : Unit binormal vector d/ds: Amount of change per unit arc length.

The computing unit 12 takes at least two of the amount of distortion, bending loss, and polarization fluctuation as the physical quantities, and calculates a value obtained by statistically processing the curvature κ calculated for each physical quantity, and a value obtained by statistically processing the curvature κ calculated for each physical quantity, and the torsion factor τ calculated for each physical quantity. The values obtained by statistically processing the above are respectively set as the new curvature κ and the new torsion τ. Here, statistical processing means averaging the values measured by each measurement technique or taking the median value. The accuracy of bend estimation can be improved by using various measurement techniques.
The calculator 12 causes the measuring device 11 to measure not only the amount of distortion of the single mode optical fiber 24 but also the bending loss and polarization fluctuation, and substitutes these physical quantities into Equations 1 and 2 to obtain the curvature κ and torsion τ. can be calculated. By averaging or taking the median value of the curvature κ and torsion rate τ calculated from a plurality of physical quantities in this way, more accurate curvature κ and torsion rate τ can be obtained.

FIG. 8 is a flowchart illustrating an optical fiber cable sensing method performed by the optical fiber cable sensing device 10. The optical fiber cable sensing method is
Inject the test light into any N single mode optical fibers 24 (N is an integer less than M) among the M single mode optical fibers 24 (M is an integer of 3 or more) stored in the optical fiber cable 20. to do (step S01),
Measuring the longitudinal distribution of physical quantities representing bending for each of the N single mode optical fibers 24 (step S02); and From each position of the single mode optical fiber 24 and the physical quantity, the curvature κ at the arbitrary point of the optical fiber cable 20 is calculated by equation 1, and the torsion coefficient τ at the arbitrary point of the optical fiber cable 20 is calculated by equation 2. That (step S03),
I do.

The arithmetic unit 12 can also be realized by a computer and a program, and the program can be recorded on a recording medium or provided through a network.

(Embodiment 2)
FIG. 9 is a diagram illustrating an example of the optical fiber cable sensing system 301 of this embodiment. The optical fiber cable sensing system 301 includes the optical fiber cable sensing device 10 and the optical fiber cable 20 described above. The optical fiber cable 20 is buried under a road 51 in a city area 50. One of the single mode optical fibers 24 is branched from the optical fiber cable 20 and is led into the home of a user who has signed an optical communication contract. Alternatively, it may be brought into the user's home via an optical splitter connected to the single mode optical fiber 24.

The optical fiber cable sensing system 301 is a system for estimating the position of the communication optical fiber cable 20 buried underground in this way from the communication company's office building 15 side. Such a communication optical fiber cable 20 uses a general-purpose single-mode optical fiber instead of a multi-core optical fiber, and the conventional 3D sensing technology using multi-core optical fibers cannot be applied as is. Furthermore, the optical fiber cable 20 is often buried over a long distance, and it is required to be able to measure the position of the optical fiber cable 20 over its entire length.
In order to grasp the position of the optical fiber cable 20, it is necessary to detect the bending that occurs in the optical fiber cable 20 for each facility such as a manhole (detect the strain that occurs in the optical fiber due to the bending). However, the optical fibers of the optical fiber cable 20 are usually twisted, and distortion due to this twisting also occurs in the optical fibers. Therefore, there has been a problem that distortion caused by this twisting becomes noise in bending detection.

Therefore, in the optical fiber cable sensing system 301, the optical fiber cable 20 has a structure as shown in FIG.
That is, the optical fiber cable 20 stores M single mode optical fibers 24 (M is an integer of 3 or more), and the twist pitch A of the single mode optical fibers 24 is A>Δz.
It is characterized by satisfying the following.
However, Δz is calculated by inputting test light into arbitrary N (N is an integer less than M) single-mode optical fibers 24 among the single-mode optical fibers 24, and bending each of the N single-mode optical fibers. This is the distance resolution of the measuring instrument 11 that measures the longitudinal distribution of the physical quantity represented.
The twist pitch is the distance (m) that the single mode optical fiber 24 makes one turn around the slot 21 along the groove 22 of the slot 21. For example, A is 10 m.

This will be explained in more detail. In addition, "cable scale" described in the following explanation is the range (length) of distortion that occurs due to bending and twisting applied to each facility (manhole, etc.) when optical fiber cable for communication is installed outdoors. Yes, the value is about several meters. This "cable scale" strain occurs in installed optical fiber cables at intervals between facilities.
Let L (m) be the length of the strain range applied to the single mode optical fiber 24 on the cable scale of which we want to know the bending radius, twist, etc. of the optical fiber cable 20. The strain Ε _i of the single mode optical fiber 24 is determined by the physical quantity ε _i that can be measured by the measuring device 11 as ε _i ∝Ε _i × (the smaller of L or Δz)
It can be expressed as The unit of the physical quantity ε _i is dimensionless (amount of change/length before change).
For this reason, for example, even if the strain _Ei is large, if the range L where the strain occurs is smaller than the distance resolution Δz, it may be smaller than the measurable physical quantity limit value Δε determined by the measuring instrument 11 and cannot be measured. In other words, the limit amount of strain ΔE that can be measured by the optical fiber cable sensing system 301 is determined by the strained length L, the measurement resolution Δz, and the measurement performance Δε.

Here, it is assumed that a weak strain of _Ei is applied to the single mode optical fiber 20 in a relatively large range of R due to bending of the optical fiber cable 20. In this case, the measured physical quantity ε _i is, as described above,
ε _i =E _i × (smaller of R and Δz)
becomes. Normally, the measuring instrument 11 can observe bending at multiple points, so R>Δz,
ε _i =E _i Δz
It is.

At this time, even if the bending strain E _i is small, the physical quantity ε _i can be made larger than the physical quantity limit value Δε by increasing the distance resolution Δz of the measuring instrument 11 to a larger value close to R (lengthening the measurement interval). , and the fiber optic cable sensing system 301 can measure _Ei .

In this way, the optical fiber cable sensing system 301 can obtain the following effects by increasing the twist pitch A of the optical fiber cable 20.
(1) Even if the measuring device 11 with low distance resolution (measurement interval is coarse) is used, the twist pitch can be measured, and the twist pitch can be identified from the result. In other words, the strain Ε _i due to twisting is small, but by increasing the pitch A (for example, making the pitch A longer than the pitch of commercially available optical fiber cables), the physical quantity ε _i can be made larger than the physical quantity limit value Δε. (It is possible to determine that the strain is caused by twisting.)
(2) If the strain is in the range L, which is smaller than the twist pitch A and corresponds to a larger cable scale, even smaller strain can be measured by making the distance resolution Δz as coarse as possible. In other words, since the measuring instrument 11 measures the physical quantity ε _i as the product of the strain E _i and the distance resolution Δz, by bringing Δz closer to the pitch A, the physical quantity ε _i is made larger than the physical quantity limit value Δε, which makes measurement difficult. Even small distortions can be detected.
For example, the twist pitch A is preferably set as follows.
The twist pitch A is set to be longer than the length of bending or twisting imparted to the optical fiber cable during installation. In other words, by setting the twist pitch A to a value larger than the bend radius of the bend you want to know (bending that occurs for each piece of equipment), the optical fiber sensing device 10 can create a gentle curve with a bend radius larger than the twist pitch A. It will no longer be detected, and only bends that occur in the equipment can be detected. Specifically, it is preferable that the twist pitch A≧10 m. If the twist pitch A is set to 10 m, a gentle curve with a bending radius as large as 10 m can be made undetectable.

Therefore, the optical fiber cable sensing system 301 is characterized in that the cable structure of the optical fiber cable 20 can be designed to implement measurements that match the cable scale. In other words, by increasing the twist pitch A to such an extent that the optical fiber cable sensing device 10 cannot detect the strain caused by the twisting of the optical fiber cable 20, it is possible to detect only the bending that occurs in the optical fiber cable 20 for each facility. It is characterized by what it did.

FIG. 11 is a diagram illustrating a cable sensing method performed by the optical fiber cable sensing system 301. The cable sensing method is
M pieces (M is an integer of 3 or more) of single-mode optical fibers 24 are stored in the optical fiber cable 20 at a twist pitch A (however, A>Δz), and connected to the measuring device 11 of the optical fiber cable sensing device 10. (Step S00),
Injecting test light into arbitrary N single mode optical fibers (N is an integer less than M) among the single mode optical fibers 24 (step S01), and bending each of the N single mode optical fibers. Measuring the longitudinal distribution of the physical quantity represented by the measuring device 11 (step S02);
I do.

First, the twist pitch A of the optical fiber cable is determined based on the desired cable scale, the distance resolution Δz of the measuring device 11, and the measurement resolution Δε. Then, the optical fiber cable 20 with the twist pitch A is connected to the measuring device 11 (step S00).

In the optical fiber cable sensing system 301, as described in the first embodiment, the measuring device 11 detects one of the M single mode optical fibers 24 (M is an integer of 3 or more) stored in the optical fiber cable 20. , test light is incident on arbitrary N single mode optical fibers 24 (N is an integer less than M) (step S01), and the longitudinal distribution of physical quantities representing bending is measured for each N single mode optical fibers 24. (Step S02). As described in the first embodiment, the arithmetic unit 12 calculates the respective positions of the N single mode optical fibers 24 in the cross section of the optical fiber cable 20 and the physical quantity at an arbitrary point in the longitudinal direction of the optical fiber cable 20. From this, the curvature κ at the arbitrary point of the optical fiber cable 20 is calculated using equation 1, and the torsion ratio τ at the arbitrary point of the optical fiber cable 20 is calculated using equation 2 (step S03).

Further, the calculator 12 calculates the center trajectory r(s) using Equation 3, and analyzes the trajectory of the optical fiber cable 20.

(Other embodiments)
Note that the present invention is not limited to the above-described embodiments, and can be implemented with various modifications without departing from the gist of the present invention. In short, the present invention is not limited to the higher-level embodiment as it is, but can be embodied by modifying the constituent elements within the scope of the gist at the implementation stage.

Moreover, various inventions can be formed by appropriately combining the plurality of components disclosed in the above embodiments. For example, some components may be deleted from all the components shown in the embodiments. Furthermore, components from different embodiments may be combined as appropriate.

The optical fiber cable sensing device 10 can also be realized by a computer and a program, and the program can be recorded on a recording medium or provided through a network.

10: Optical fiber cable sensing device 11: Measuring device 12: Computing unit 20: Optical fiber cable 21: Slot 22: Groove 23: Optical fiber tape core 24: Single mode optical fiber 50: City area 51: Road 301: Optical fiber cable sensing system

Claims (4)

An optical fiber cable that stores M single-mode optical fibers (M is an integer of 3 or more), and the single-mode optical fibers have a twist pitch of A;
The test light is connected to one end side of the single mode optical fiber, and the test light is incident on the one end of any N single mode optical fibers (N is an integer less than M) among the single mode optical fibers, and the test light is connected to one end of the single mode optical fiber. a measuring device that measures the longitudinal distribution of physical quantities representing bending for each of the N single-mode optical fibers from scattered light returning to the one end of the single-mode optical fibers;
Equipped with
The twist pitch A is
A>Δz
An optical fiber cable sensing system that satisfies the following and is longer than the length of bending and twisting applied when the optical fiber cable is laid .
However, Δz is the distance resolution of the measuring device. The optical fiber cable sensing system according to claim 1, wherein the measuring device measures an amount of distortion, bending loss, or polarization variation as the physical quantity. Connect M single mode optical fibers (M is an integer of 3 or more) to the optical fiber cable with A>Δz
and storage at a twist pitch A that satisfies the above and is longer than the length of bending and twisting applied when laying the optical fiber cable ,
connecting a measuring device to one end side of the single mode optical fiber;
Injecting test light from the measuring device into the one end of any N (N is an integer less than M) single mode optical fibers among the single mode optical fibers, and the N single mode optical fibers. measuring with the measuring device a longitudinal distribution of physical quantities representing bending for each of the N single mode optical fibers from scattered light returning to the one end of the optical fiber;
An optical fiber cable sensing method characterized by:
However , Δz is the distance resolution of the measuring instrument. An optical fiber cable storing M (M is an integer of 3 or more) single mode optical fibers, wherein the twist pitch A of the single mode optical fibers is A>Δz.
1. An optical fiber cable that satisfies the above requirements and is longer than the length of bending and twisting applied during installation of the optical fiber cable.
However, Δz is connected to one end side of the single mode optical fiber, and the test light is input to the one end of any N single mode optical fibers (N is an integer less than M) among the single mode optical fibers. is the distance resolution of a measuring instrument that measures the longitudinal distribution of physical quantities representing bending for each of the N single-mode optical fibers from the scattered light returning to the one end of the N single-mode optical fibers.

Images