JP6346852B2 - Optical fiber bending shape measuring apparatus and bending shape measuring method thereof - Google Patents

Description

  The present invention relates to an optical fiber bending shape measuring apparatus and a bending shape measuring method thereof.

  As a shape sensor using an optical fiber, for example, the technique of Non-Patent Document 1 is disclosed. The technique of Non-Patent Document 1 uses a helical optical fiber sensor head (hereinafter referred to as a helical optical fiber sensor head) in which six optical fibers are bundled in a spiral shape around an optical fiber serving as an axis. .

  In Non-Patent Document 1, an FBG (Fiber Bragg Grating) is intermittently written in the longitudinal direction of a helical optical fiber sensor head, a change in reflection wavelength is read by an OFDR (Optical Frequency Domain Reflectometer), and an OFDR is measured. A method for measuring strain from changes in Rayleigh scattering waveform by measurement is disclosed, and in either method, the bending shape of the three-dimensional helical optical fiber sensor head is determined from the distribution of the cross section of the amount of strain applied to each helical optical fiber. It is possible to measure changes in the dynamic bending shape. However, since the technique disclosed in Non-Patent Document 1 uses OFDR as a strain measurement method, the length of the optical fiber sensor head depends on the coherence length of the OFDR light source, so that the sensor head length is 30 m. Stay on.

  As another optical fiber shape sensor, for example, in Non-Patent Document 2, FBG is written on each core of a multicore fiber to form a multicore optical fiber sensor head, and the bending shape of the multicore optical fiber sensor head is measured by measuring the strain of each core. Techniques for measuring are disclosed. However, since the resolution for measuring a continuous change in the bending shape depends on the longitudinal interval in which the FBG is written, this technique is not suitable for measuring a bending shape with a high resolution and a long distance. A similar technical problem exists in the method of writing FBG in the helical optical fiber sensor head of Non-Patent Document 1.

  On the other hand, when considering the introduction of a bent optical fiber sensor for maintenance of the optical fiber communication network, an optical fiber capable of bending shape sensing is built in the structure of the communication cable or installed along the optical fiber network. As a result, the laying state of the optical fiber communication network can be expressed, for example, on a three-dimensional map at any time in real time. If the optical fiber communication network can be visualized on a three-dimensional map, it is possible to create a wiring plan for additional optical fiber cables, to create a necessary man-hour plan at the maintenance site, and to link to the facility information associated with the communication network. Realization of efficient maintenance work can be expected.

  However, in order to measure the bending shape of an optical fiber communication network, it is necessary to realize a long-distance and seamless bending shape measurement that is impossible with the above-described technology disclosed heretofore.

LUNA, "Fiber Optic Shape Sensing", Current State of Technology, June 21st, 2013. D. Barrera et al., “Multipoint two-dimensional curvature optical fiber sensor,” 23rd OFS, Proc. Of SPIE 9157, 2014.

  An object of the present invention is to provide an optical fiber bending shape measuring apparatus and bending shape measuring method capable of long-distance measurement and seamless distribution measurement in a bending shape sensor technique using an optical fiber.

In order to achieve the above object, a first aspect of the present invention includes the following components. That is, the bending shape measuring apparatus is composed of an optical fiber having four cores having the same Brillouin frequency shift amount with respect to the pump light in the peripheral portion , or four wires having the same Brillouin frequency shift amount with respect to the pump light . four core Rukoto bundling single core optical fiber a bent shape measuring apparatus using an optical fiber sensor head having a peripheral portion, with respect to each core of the optical fiber sensor head, the same pump light Brillouin analyzer for entering the same probe light, provided in each core at the exit end of the optical fiber sensor head measures the longitudinal distribution of the optical fiber sensor head Brillouin frequency shift amount for each core, from the Brillouin frequency shift amount of each core at each point calculated distortion amount of the four cores at the above point From the strain amount of the four cores at the above point, a straight line connecting the cross-sectional center of the optical fiber sensor head with the center bend of the optical fiber sensor head, the optical fiber sensor with any of the centers of the four cores An angle θ formed by a straight line connecting the center of the head is analyzed, a bending radius r is analyzed from the angle θ and the strain amount of the four cores, and the curvature of the optical fiber sensor head is calculated from the distribution of the bending radius r. A receiver for obtaining a distribution and a direction of curvature at the position, and the optical fiber sensor head further includes a reference core or a single-core optical fiber provided with a reference core on a central axis thereof, The light receiver uses the absolute value of the Brillouin frequency shift amount of the reference core as a Brillouin frequency shift reference value, and the four optical fibers at the same point of the optical fiber sensor head. Calculating the difference between the Brillouin frequency shift amount A and the Brillouin frequency shift reference value, the amount of strain in which the influence of temperature change of the four cores at the above point.

In order to achieve the above object, a second aspect of the present invention includes the following components. In other words, the bending shape measuring method is composed of an optical fiber having four cores having the same Brillouin frequency shift amount with respect to the pump light at the periphery , or four wires having the same Brillouin frequency shift amount with respect to the pump light . a bent shape measuring method using an optical fiber sensor head having a periphery with four cores in Rukoto bundling single core optical fiber, with respect to each core of the optical fiber sensor head, the same pump light a first step of Ru is incident the same probe light to measure the longitudinal distribution of the optical fiber sensor head Brillouin frequency shift amount for each core, the at the above point from the Brillouin frequency shift amount of each core in each point a second step asking you to strain amount of four cores, or the strain amount of the four cores at the above point , Connecting the cross-sectional center of the optical fiber sensor head with the center bend of the optical fiber sensor heads straight line and the straight line and the angle formed connecting the center of either of the center of the four core the optical fiber sensor head θ is analyzed, the bending radius r is analyzed from the angle θ and the strain amounts of the four cores, and the curvature distribution of the optical fiber sensor head and the direction of curvature at the position are obtained from the distribution of the bending radius r. And the optical fiber sensor head further comprises a reference core or a single-core optical fiber provided with a reference core on its central axis, and in the second step, The absolute value of the Brillouin frequency shift amount is used as a Brillouin frequency shift reference value, and the Brillouin frequency shift amounts of the four cores at the same point of the optical fiber sensor head Wherein calculating the difference between the Brillouin frequency shift reference value, the amount of strain in which the influence of temperature change of the four cores at the above point.

  That is, according to the present invention, it is possible to provide an optical fiber bending shape measuring apparatus and a bending shape measuring method capable of long-distance measurement and seamless distribution measurement in a bending shape sensor technique using an optical fiber.

FIG. 1 is a diagram illustrating a configuration example of a bending shape measuring apparatus according to a first embodiment of the present invention. FIG. 2 is a diagram for explaining an example of a frequency relationship between pump light and probe light used in the bending shape measuring apparatus according to the first embodiment of the present invention. FIG. 3 is an explanatory diagram of the basic principle of bending shape measurement according to the first embodiment. FIG. 4 is a flowchart for explaining an example of the bending shape measuring method according to the first embodiment.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
In this embodiment, the bending shape of the optical fiber sensor head is measured by analyzing the longitudinal strain amount applied to each core of the optical fiber sensor head. In this embodiment, a strain distribution sensing technique using a Brillouin gain analysis method is used as a strain measurement method in order to perform a long-distance and seamless bending shape measurement. Here, the bent shape is the distribution of the curvature change of the optical fiber sensor head and the direction of each curvature due to the external force or vibration applied to the optical fiber sensor head.

  The Brillouin gain analysis method is known to change the Brillouin frequency shift amount linearly with respect to the strain variation (or temperature variation), and is used as a strain measurement technology (or temperature measurement technology). .

  Here, the strain distribution sensing technique using the Brillouin gain analysis method is, for example, BOTDR (Brillouin Optical Time Domain Reflectometer), BOTDA (Brillouin Optical Time Domain Analysis), or BOCDA (Brillouin Optical Correlation Domain Analysis). Even if any of the above measurement methods is used, it is possible to measure a long-distance bending shape of several kilometers, which has been impossible in the past.

FIG. 1 is a diagram illustrating a configuration example of a bending shape measuring apparatus according to a first embodiment of the present invention.
The bending shape measuring apparatus of this embodiment has a Brillouin analyzer 20 and a plurality of light receivers 21 to 24. In this embodiment, a multi-core optical fiber MCF having three or more cores having a common Brillouin frequency shift amount BFS with respect to pump light is used as an optical fiber sensor head.

  The number of light receivers 21 to 24 is the same as the number of cores of the multi-core optical fiber MCF to be measured. In the example shown in FIG. 2, the multi-core optical fiber MCF to be measured has 4 cores, so the bending shape measuring device has four light receivers 21 to 24.

  The Brillouin analyzer 20 outputs pump light having a single frequency and branches into a plurality through the branching device A2, and outputs a single frequency probe light and branches into a plurality through the branching device A1. The probe light and the same pump light are incident on the cores C1 to C4 of the multicore optical fiber MCF.

  The light receivers 21 to 24 are provided for each of the cores C1 to C4 at the far end (outgoing end) of the multicore optical fiber MCF. The light receivers 21 to 24 receive light emitted from the cores C1 to C4 of the multicore optical fiber MCF and pump light. The light receivers 21 to 24 observe the probe light that has obtained the Brillouin gain, and analyze the Brillouin frequency shift. The light receivers 21 to 24 obtain the strain distribution in the longitudinal direction of each core by Brillouin analysis, and analyze the bending shape from the strain amount of each of the cores C1 to C4 by the bending shape analysis means described later. The analysis results of the light receivers 21 to 24 may be output to the outside by wired or wireless communication means.

  In the optical receivers 21 to 24, for example, the change in the strain amount at each position of each core of the optical fiber sensor head including the Brillouin frequency shift amounts BFS1 to BFS4 is not strained (the state in which no bending is applied). The Brillouin gain spectrum profile is acquired in advance, and the change in the Brillouin frequency shift amount is analyzed from the change in the absolute amount of the Brillouin gain amount when the bending is applied.

FIG. 2 is a diagram illustrating an example of a relationship between frequencies of pump light and probe light used in the bending shape measuring apparatus according to the first embodiment.
In the present embodiment, the same pump light and the same probe light are incident on each of the cores C1 to C4 of the multicore optical fiber MCF. As shown in FIG. 2, the frequency of the probe light is a frequency that matches the Brillouin frequency shift (BFS) that is the median value of the Brillouin gain spectrum (BGS) induced by the pump light. In the present embodiment, the Brillouin gain analysis of each of the cores C1 to C4 can be performed by making the above-described pump light and probe light common to all the cores C1 to C4 of the multicore optical fiber MCF.

FIG. 3 is an explanatory diagram of the basic principle of bending shape measurement according to the first embodiment.
The method described below is referred to as bending shape analyzing means in the present application. As a principle of measuring the bending shape of a multi-core optical fiber, for example, the method disclosed in Non-Patent Document 2 can be used.

  The bending shape is assumed to be bent on an arc having a bending center C and a bending radius r. At this time, the bending shape in the 4-core multi-core optical fiber MCF is such that the distance between each of the cores C1 to C4 and the optical fiber central axis is d, the center of bending C, and the amount of strain measured at each of the cores C1 to C4. Let ε1 to ε4 be an angle θ formed by a straight line connecting the center of bending and the center of the multicore optical fiber MCF and a straight line connecting the center of the core C1 and the center of the multicore optical fiber MCF.

と表せる。

It can be expressed.

  By measuring the strain amounts ε1 to ε4 applied to each of the cores C1 to C4 by applying or changing the bending shape, the bending radius of the bending applying portion can be obtained. By measuring the bending radius in a distributed manner, the curvature of the multi-core optical fiber MCF can be obtained, and the bending shape can be measured.

  However, it should be noted that according to the above means, the direction of the bending shape cannot be accurately measured from a remote location unless the multi-core optical fiber MCF is twisted or the amount of twist is not known.

FIG. 4 is a flowchart for explaining an example of the bending shape measuring method according to the first embodiment.
In the present embodiment, a multi-core optical fiber (or bundle optical fiber) having three or more cores having the same Brillouin frequency shift amount with respect to pump light is used as an optical fiber sensor head. Here, the multi-core optical fiber MCF including the cores C1 to C4 having the same Brillouin frequency shift amount is used as the optical fiber sensor head (step A1).

  The Brillouin analyzer 20 causes the same pump light and the same probe light to enter the cores C1 to C4 of the optical fiber sensor head (step A2).

  Next, the light receivers 21 to 24 measure the longitudinal distribution of the Brillouin frequency shift amount of each of the cores C1 to C4 in the optical fiber sensor head, and determine the Brillouin frequency shift amount of each of the cores C1 to C4 at each point at the corresponding point. The amount of strain of each core is obtained (Step A3).

  Subsequently, the optical receivers 21 to 24 use the above-described mathematical formulas to calculate a straight line connecting the bending center C and the cross-sectional center of the optical fiber sensor head from the strain amount of each of the cores C1 to C4 at a certain position, and an optical fiber. The angle θ formed by the straight line connecting the center of the arbitrary core of the sensor head (or the center of the arbitrary core of the bundle optical fiber) and the center of the cross section of the optical fiber sensor head is analyzed, and the angle θ and the strain amount of each of the cores C1 to C4 The bending radius r is analyzed, and the curvature distribution of the optical fiber sensor head and the direction of curvature at each position are obtained from the distribution of the bending radius r (step A4).

Hereinafter, a method for further improving the measurement accuracy of the bending shape by the Brillouin gain analysis method will be described.
In the Brillouin gain analysis method, since the Brillouin frequency shift amount generally changes due to strain and temperature change applied to the optical fiber sensor head, in the present embodiment, compensating for the influence of the temperature distribution is important in high-precision measurement of the curvature distribution. It is essential.

  First, a reference core (reference core) is arranged at the center of the cross section of the multi-core optical fiber MCF. When bending is applied to the multi-core optical fiber MCF, even if the strain measurement is performed by the Brillouin gain analysis method on the reference core arranged at the center of the cross-section of the multi-core optical fiber MCF, the effects of the compression and expansion strain are the same. Since it cancels out in the core, a change in the Brillouin frequency shift amount due to distortion is not detected.

  That is, a reference core is arranged in the center of the cross-section of the multicore optical fiber MCF, the absolute value of the Brillouin frequency shift amount of the reference core is used as the Brillouin frequency shift reference value, and the Brillouin frequency shift amount of the other core at the same point and the Brillouin frequency shift reference By measuring the difference from the value, it becomes possible to perform the strain measurement that completely eliminates the influence of the temperature change in the longitudinal direction of the optical fiber sensor head.

  In other words, the light receivers 21 to 24 use the Brillouin frequency shift amount of the reference core as the reference Brillouin frequency shift amount, analyze the temperature distribution from the distribution of the reference Brillouin frequency shift amount, and perform the Brillouin of the cores C1 to C4 of the optical fiber sensor head. By calculating the difference between the frequency shift amount and the reference Brillouin frequency shift amount of the reference core and setting it as the strain amount at that point, strain measurement that completely eliminates the effects of temperature changes in the longitudinal direction of the multi-core optical fiber MCF is possible. Become.

  According to this embodiment, the strain distribution in the longitudinal direction of the optical fiber is measured using Brillouin gain analysis, and the bending shape of the optical fiber can be measured seamlessly over a long distance, for example, the wiring state of the optical fiber communication network Can be measured remotely, which can contribute to the creation of a three-dimensional optical cable map for improving the efficiency of operation and management of the optical fiber communication network.

  By installing an optical fiber capable of bending shape sensing in the center of the structure inside the communication cable, or by constructing it along the optical fiber network, the installation status of the optical fiber communication network can be displayed on the 3D map in real time at any time. If the optical fiber communication network can be visualized on a three-dimensional map, it will be possible to express the optical fiber cable wiring plan to be additionally laid, drafting the necessary man-hour plan at the maintenance site, communication network Efficient maintenance work can be realized by linking with facility information attached to the.

  In this embodiment, a multi-core optical fiber MCF (Multi-core fiber) is used as an optical fiber sensor head, and the bending shape of the multi-core optical fiber MCF is measured. However, the optical fiber sensor head is not limited to the multi-core optical fiber MCF. Alternatively, a bundle optical fiber in which a plurality of single-core optical fibers are bundled may be used. Here, when the optical fiber sensor head is not a multi-core optical fiber MCF, if a single-core optical fiber for reference is built in the center (axis) of the optical fiber sensor head, high-accuracy measurement that compensates for the influence of the above temperature distribution Is possible.

  In the present embodiment, a 4-core multi-core optical fiber MCF has been described as an example. However, if the number of cores is 3 or more, the bending shape of the optical fiber sensor head can be measured three-dimensionally, and the number of cores (or bundled) can be measured. By increasing the number of single-core optical fibers) and measuring the surface distribution of the strain of the optical fiber cross section at each position over the longitudinal direction, more accurate bending shape measurement can be performed.

  In short, the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. Further, various inventions can be formed by appropriately combining a plurality of constituent elements disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, you may combine suitably the component covering different embodiment.

  20 ... Brillouin analyzer, 21-24 ... Light receiver, A1, A2 ... Optical demultiplexer, BFS1-BFS4 ... Brillouin frequency shift amount, C1-C4 ... Core, MCF ... Multi-core optical fiber

Claims (4)

An optical fiber having four cores in the peripheral portion having the same Brillouin frequency shift amount with respect to the pump light, or Rukoto bundling single core optical fiber four having the same Brillouin frequency shift amount with respect to the pump light And a bending shape measuring apparatus using an optical fiber sensor head having four cores in the periphery ,
A Brillouin analyzer that makes the same pump light and the same probe light incident on each core of the optical fiber sensor head;
Provided in each core at the exit end of the optical fiber sensor head measures the longitudinal distribution of the optical fiber sensor head Brillouin frequency shift amount for each core, the point from the Brillouin frequency shift amount of each core in each point A strain amount of the four cores at the point, and from the strain amount of the four cores at the point, a straight line connecting the bending center of the optical fiber sensor head and the cross-sectional center of the optical fiber sensor head ; An angle θ formed by a straight line connecting any one of the cores and the center of the optical fiber sensor head is analyzed, a bending radius r is analyzed from the angle θ and the strain amount of the four cores, and the bending radius is analyzed. a light receiver for obtaining a curvature distribution of the optical fiber sensor head and a direction of curvature at the position from the distribution of r;
Equipped with a,
The optical fiber sensor head further comprises a reference core on the central axis, or a single-core optical fiber provided with a reference core,
The optical receiver uses the absolute value of the Brillouin frequency shift amount of the reference core as a Brillouin frequency shift reference value, and the Brillouin frequency shift amount of the four cores and the Brillouin frequency shift reference value at the same point of the optical fiber sensor head, A bending shape measuring apparatus characterized in that the difference is calculated to obtain a strain amount excluding the influence of temperature change of the four cores at the point .   The Brillouin optical time domain reflectometer (BOTDR), BOTDA (Brillouin Optical Time Domain Analysis), or BOCDA (Brillouin Optical Correlation Domain Analysis) is adopted as the Brillouin gain analysis method. Bending shape measuring device. An optical fiber having four cores in the peripheral portion having the same Brillouin frequency shift amount with respect to the pump light, or Rukoto bundling single core optical fiber four having the same Brillouin frequency shift amount with respect to the pump light And a bending shape measuring method using an optical fiber sensor head having four cores at the periphery ,
For each core of the optical fiber sensor head, a first step of Ru is incident the same pump light and the same probe light,
A second step of measuring the longitudinal distribution, Ru determine the strain amount of the four cores at the above point from the Brillouin frequency shift amount of each core in each point in the optical fiber sensor head of the Brillouin frequency shift amount for each core,
From the strain amount of the four cores at the point, a straight line connecting the center of bending of the optical fiber sensor head and the cross-sectional center of the optical fiber sensor head, the center of any of the four cores, and the optical fiber sensor An angle θ formed by a straight line connecting the center of the head is analyzed, a bending radius r is analyzed from the angle θ and the strain amount of the four cores, and the curvature of the optical fiber sensor head is calculated from the distribution of the bending radius r. A third step for determining a distribution and a direction of curvature at the position;
Have
The optical fiber sensor head further comprises a reference core on the central axis, or a single-core optical fiber provided with a reference core,
In the second step, the absolute value of the Brillouin frequency shift amount of the reference core is set as a Brillouin frequency shift reference value, and the Brillouin frequency shift amounts of the four cores and the Brillouin frequency shift reference value at the same point of the optical fiber sensor head. The bending shape measuring method , wherein the difference is calculated as a strain amount excluding the influence of temperature change of the four cores at the point . As Brillouin gain analysis method, BOTDR (Brillouin Optical Time Domain Reflectometer ), BOTDA (Brillouin Optical Time Domain Analysis), and, BOCDA according to claim 3, characterized in that employing either (Brillouin Optical Correlation Domain Analysis) Bending shape measurement method.

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