JP2016038345A - Optical fiber sensor and optical fiber sensor system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical fiber sensor and an optical fiber sensor system which are capable of suitably measuring relative displacement in mutually different directions of two portions of a measurement object.SOLUTION: An optical fiber sensor includes an optical fiber 20 to which testing light is inputted, an optical fiber holding unit 30 which is fixed to one portion 11 of a measurement object 10 and holds the optical fiber 20, and a movable unit 40 which includes a stress application unit 50 fixed to the other portion 12 of the measurement object 10 and applying stress to the optical fiber 20 and is moved in accordance with relative displacement in at least two directions of one portion 11 and the other portion 12 of the measurement object 10. The stress application unit 50 is disposed on the side opposite to at least the displacement directions relative to the optical fiber 20. When one portion 11 and the other portion 12 of the measurement object 10 are relatively displaced, the stress application unit 50 is brought into contact with the optical fiber 20 to deform the optical fiber 20.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an optical fiber sensor and an optical fiber sensor system for measuring a relative displacement between two parts of a measurement object.

  In recent years, there is a growing concern about accidents caused by the collapse of aging bridges, tunnels, buildings, etc., and the development of aging infrastructure has become a major issue. As the inspection performed on the structure as described above, there are many cases in which only the current state is visually confirmed. However, as a technique for periodically monitoring the state of the structure, there is a technique using an optical fiber sensor.

  For example, as a method of measuring strain of a structure (measurement object), a method of laying an optical fiber on the structure and observing Brillouin scattered light generated in the optical fiber has been proposed. In this method, the extension of the optical fiber is measured by measuring the frequency change of the Brillouin scattered light scattered in the direction opposite to the light incident direction (backward). This frequency change is called the Brillouin shift amount, and the Brillouin shift amount changes in proportion to the strain amount of the optical fiber. Therefore, by observing the Brillouin shift amount of the Brillouin scattered light that is back-scattered and returns to the transmission side, it is possible to obtain the distortion amount at each point in the longitudinal direction of the laid optical fiber (non-patent document). Reference 1).

  As another method for measuring the strain of the structure, there is a method using a fiber Bragg grating (FBG) having a configuration in which a diffraction grating is formed in the core of an optical fiber. When the FBG is laid on a structure to be measured and the FBG is pulled according to the displacement caused by the distortion of the structure, the period of the diffraction grating of the FBG changes and the reflected wavelength changes. Therefore, the amount of displacement of the structure can be grasped by measuring the change in the wavelength of light that has a certain broadband wavelength incident on the FBG and reflected backward (see Non-Patent Document 2).

  Patent Document 1 discloses an optical fiber sensor in which an optical fiber is provided on a pressure receiving member. In the optical fiber sensor disclosed in Patent Document 1, a debris flow or the like that occurs on a natural slope where there is a possibility of collapse is used as a monitoring target, and a pressure receiving member receives the pressing force from the monitoring target, The fiber is deformed, such as bent, or broken. Here, since the optical fiber bends or breaks due to the displacement between the two pressure receiving members on which the optical fiber sensor is laid, monitoring can be performed by measuring the intensity of the propagation light at that time.

  Further, Patent Document 2 is configured such that an optical fiber is provided between two members of a measurement object, and the optical fiber is bent and deformed by a pressing piece by widening the interval between the two members. An optical fiber sensor is disclosed.

JP 2001-99686 A Japanese Patent Laid-Open No. 2001-262583

Lightwave Sensing Technology, Today and Future-Fiber Sensor Photonics for Safety and Security-, Proceedings of the 40th Lightwave Sensing Technology Study Group LST40-7 Fiber Optic Sensing-FBG Strain Sensing and Applications PLANT Engineer, Dec. 2009, pp. 66-72

  As described above, it is required to measure the displacement of the structure. However, the above technique is suitable for measuring the displacement in a certain direction. For example, the method using Brillouin scattered light or FBG is a configuration suitable for measuring the displacement in the direction in which the optical fiber extends from the initial state. In addition, the methods disclosed in Patent Documents 1 and 2 are suitable for measuring a displacement in a direction in which the distance between two members widens from the initial state. Thus, these methods are not suitable for applications that measure displacement in, for example, two directions (eg, right and left along a certain direction).

  The present invention has been made in view of the above, and an optical fiber sensor and an optical fiber sensor system capable of suitably measuring relative displacements of two parts of a measurement object in different directions. The purpose is to provide.

  In order to solve the above-described problems and achieve the object, the optical fiber sensor of the present invention is provided across one part and the other part of the measurement object, and the relative relation between the one part and the other part is provided. An optical fiber sensor for measuring a large displacement, an optical fiber to which test light is input, an optical fiber holding part that is fixed to one part of the measurement object and holds the optical fiber, and the measurement object A movable portion that is fixed to the other portion of the optical fiber, has a stress applying portion that applies stress to the optical fiber, and moves according to the relative displacement of one portion of the measurement object and the other portion. The stress applying unit is disposed at least on the side opposite to the displacement direction with respect to the optical fiber, and one part and the other part of the measurement object are relatively displaced. When Serial stress applying portion is in contact with the optical fiber, wherein the optical fiber is deformed.

  Moreover, one aspect of the optical fiber sensor of the present invention is such that the movement of the movable part is on one axis intersecting the longitudinal direction of the optical fiber held linearly by the optical fiber holding part. It is characterized by comprising a regulating part that regulates movement.

  In one aspect of the optical fiber sensor of the present invention, the movement of the movable portion is on a surface that intersects with the longitudinal direction of the optical fiber linearly held by the optical fiber holding portion. It is characterized by comprising a regulating part that regulates movement.

  Further, in one aspect of the optical fiber sensor of the present invention, the stress application unit is detachably provided on the movable unit, and an initial distance from the optical fiber can be changed. To do.

  In one aspect of the optical fiber sensor of the present invention, the optical fiber includes a sensor optical fiber portion that deforms according to relative displacement of one part and the other part of the measurement object, and the sensor light The optical characteristic of the fiber part is different from the optical characteristic of the optical fiber for test light transmission connected to the optical fiber.

  Moreover, one mode of the optical fiber sensor of the present invention is characterized in that mode field diameters of the sensor optical fiber portion and the test optical transmission optical fiber are different.

  In one aspect of the optical fiber sensor of the present invention, the sensor optical fiber portion and the test optical transmission optical fiber have different cutoff wavelengths.

  One aspect of the optical fiber sensor of the present invention is characterized in that bending loss characteristics of the sensor optical fiber portion and the test optical transmission optical fiber are different.

  Moreover, one aspect of the optical fiber sensor of the present invention is characterized in that transmission loss characteristics of the sensor optical fiber portion and the optical fiber for test light transmission are different.

  In one aspect of the optical fiber sensor of the present invention, the test light is pulsed light, and includes a storage unit that accommodates the extra length of the optical fiber, and the extra length of the optical fiber includes the pulsed light. The pulse light has a length longer than the length of propagation of the pulsed light in a time corresponding to the time width.

  One aspect of the optical fiber sensor of the present invention is characterized in that the test light has a wavelength longer than a wavelength band in which the transmission loss of the optical fiber is lowest.

  According to another aspect of the optical fiber sensor of the present invention, in the optical fiber, a fiber Bragg grating is provided in a sensor optical fiber portion that is deformed according to a relative displacement of one part and the other part of the measurement object. It is characterized by that.

  Further, an optical fiber sensor system of the present invention includes the above-described optical fiber sensor, a light source that outputs the test light, a light receiver that can receive the test light transmitted through the optical fiber of the optical fiber sensor, An optical fiber transmission line having a first optical fiber transmission line connecting the light source and the optical fiber sensor, and a second optical fiber transmission line connecting the optical fiber sensor and the light receiver. Features.

  An optical fiber sensor system of the present invention includes the above-described optical fiber sensor, an OTDR device that outputs the test light and receives backscattered light generated from the optical fiber sensor, the OTDR device, and the optical fiber. And an optical fiber transmission line connecting the sensor.

  The optical fiber sensor system of the present invention includes the above-described optical fiber sensor, a light source that outputs the test light, an optical fiber transmission line that connects the light source and the optical fiber sensor, and light of the test light. And an optical wavelength measuring device that receives the reflected light reflected by the fiber Bragg grating of the fiber sensor and measures the wavelength of the reflected light.

  According to another aspect of the optical fiber sensor system of the present invention, the optical fiber sensor system includes a plurality of the optical fiber sensors, and the optical fiber sensors are connected in series to the optical fiber transmission line. It is characterized by that.

  According to another aspect of the optical fiber sensor system of the present invention, the optical fiber sensor system includes a plurality of the optical fiber sensors, and the optical fiber transmission line includes a main optical fiber transmission line and the main optical fiber transmission line. A plurality of branched optical fiber transmission lines branched from the optical fiber, the OTDR device or the light source is connected to the main optical fiber transmission line, and the plurality of optical fiber sensors are respectively connected to the branched optical fiber transmission line. It is connected to the main optical fiber transmission line through a line.

  ADVANTAGE OF THE INVENTION According to this invention, the optical fiber sensor and optical fiber sensor system which can measure the relative displacement to the mutually different direction of two parts of a measuring object with a sufficient precision can be provided.

FIG. 1 is a schematic explanatory diagram of an optical fiber sensor according to Embodiment 1 of the present invention. FIG. 2 is a schematic perspective view of the optical fiber sensor according to Embodiment 1 of the present invention. FIG. 3 is a schematic explanatory diagram for explaining the bearing portion shown in FIG. 1. FIG. 4 is a schematic view when the bearing portion shown in FIG. 3 is viewed from the A direction. FIG. 5 is a schematic diagram illustrating a case where the distance between one part and the other part of the measurement object is separated in the left-right direction in the optical fiber sensor according to Embodiment 1 of the present invention. FIG. 6 is a schematic diagram illustrating a case where the distance between one part and the other part of the measurement target is separated in the front-rear direction in the optical fiber sensor according to Embodiment 1 of the present invention. FIG. 7 is a schematic explanatory diagram of an optical fiber sensor system using the optical fiber sensor according to the first embodiment of the present invention. FIG. 8 shows an optical fiber sensor with respect to relative displacement between one part and the other part of a measurement object using the optical fiber sensor system including the optical fiber sensor according to the first embodiment of the present invention. It is a figure which shows a time-dependent change at the time of measuring the light intensity which permeate | transmits. FIG. 9 is a schematic explanatory diagram of an optical fiber sensor system using the optical fiber sensor according to Embodiment 1 of the present invention. FIG. 10 shows a result of measuring the backscattered light in the initial state where the optical fiber is not deformed by the stress applying unit using the optical fiber sensor system including the optical fiber sensor according to the first embodiment of the present invention. FIG. FIG. 11 is a diagram illustrating a result of measuring the backscattered light in a state where the optical fiber is deformed by the stress applying unit using the optical fiber sensor system including the optical fiber sensor according to the first embodiment of the present invention. . FIG. 12 is a schematic explanatory diagram of an optical fiber sensor according to Embodiment 2 of the present invention. FIG. 13 is a schematic diagram showing a case where the distance between one part and the other part of the measurement object is separated in the left-right direction in the optical fiber sensor according to Embodiment 2 of the present invention. FIG. 14 is a schematic explanatory diagram of an optical fiber sensor that is Modification 1 of the optical fiber sensor according to Embodiment 2 of the present invention. FIG. 15 is a schematic diagram showing a case where the distance between one part and the other part of the measurement object is separated in the left-right direction in the optical fiber sensor shown in FIG. FIG. 16 is a schematic explanatory diagram of an optical fiber sensor that is Modification Example 2 of the optical fiber sensor according to Embodiment 2 of the present invention. FIG. 17 is a schematic diagram showing a case where the distance between one part and the other part of the measurement object is separated in the left-right direction in the optical fiber sensor shown in FIG. FIG. 18 is a diagram showing a modification of the stress applying unit used in the optical fiber sensor according to Embodiment 2 of the present invention. FIG. 19 is a diagram showing a modification of the stress applying unit used in the optical fiber sensor according to Embodiment 2 of the present invention. FIG. 20 shows an optical fiber sensor according to an embodiment of the present invention, in which an optical fiber having a large bending loss is used as an optical fiber in contact with the stress application unit, and the relative position between one part and the other part of the measurement target is measured. It is a figure which shows the result of having measured the time-dependent change of the output light intensity with respect to various displacements. FIG. 21 shows a plurality of optical fiber sensors using a single mode optical fiber having a zero dispersion wavelength in a normal 1.3 μm band as an optical fiber in contact with the stress applying unit in the optical fiber sensor according to the embodiment of the present invention. It is an OTDR waveform when these are connected in series. 22 shows an optical fiber sensor according to an embodiment of the present invention, in which an ITU-T G.G. 6 is an OTDR waveform when an optical fiber specified in 657 is used. FIG. 23 shows an OTDR waveform when a fiber having an MFD different from that of the optical fiber transmission line is used as the optical fiber in contact with the stress applying unit in the optical fiber sensor according to the embodiment of the present invention. FIG. 24 shows an OTDR waveform when an optical fiber having a transmission loss larger than that of the fiber in the optical fiber transmission line is used as the optical fiber in contact with the stress applying unit in the optical fiber sensor according to the embodiment of the present invention. FIG. 25 is a schematic explanatory diagram of an optical fiber sensor provided with a surplus length storage unit. FIG. 26 is a diagram showing an OTDR waveform measured in an optical fiber sensor in a state where there is no extra length of the optical fiber. FIG. 27 shows an OTDR waveform measured in a state in which an optical fiber sensor has a 20 m optical fiber as the extra length of the optical fiber. FIG. 28 is a schematic explanatory diagram of an optical fiber sensor according to Embodiment 3 of the present invention. FIG. 29 is a schematic perspective view for explaining an optical fiber sensor according to Embodiment 3 of the present invention. FIG. 30 is a schematic explanatory diagram of an optical fiber sensor system using the optical fiber sensor according to Embodiment 3 of the present invention. FIG. 31 is a diagram illustrating a result of measuring a change in wavelength of light reflected from the fiber Bragg grating using the optical fiber sensor according to Embodiment 3 of the present invention. FIG. 32 is a diagram showing a case where the displacement between two floor boards installed on a bridge pier is measured using an optical fiber sensor. FIG. 33 is a schematic explanatory diagram of an optical fiber sensor system according to Embodiment 5 of the present invention. FIG. 34 is a schematic explanatory diagram of an optical fiber sensor system according to Embodiment 6 of the present invention. FIG. 35 is a schematic explanatory diagram of an optical fiber sensor system according to Embodiment 7 of the present invention. FIG. 36 is a diagram showing an OTDR waveform measured using the optical fiber sensor system according to Embodiment 6 of the present invention. FIG. 37 is a diagram showing an OTDR waveform measured using the optical fiber sensor system according to Embodiment 7 of the present invention.

  Hereinafter, an optical fiber sensor and an optical fiber sensor system according to embodiments of the present invention will be described with reference to the drawings. In addition, this invention is not limited by the following embodiment. In the drawings, the same or corresponding elements are denoted by the same reference numerals as appropriate, and repeated descriptions are omitted as appropriate. Furthermore, it should be noted that the drawings are schematic, and dimensional relationships between elements may differ from actual ones. Even between the drawings, there are cases in which portions having different dimensional relationships and ratios are included. Further, in this specification, the cutoff wavelength is ITU-T (International Telecommunication Union) G.I. This is the cut-off wavelength according to the 22m method defined by 650.1. For other terms not specifically defined in this specification, the ITU-T G.G. The definition and measurement method in 650.1 shall be followed as appropriate.

(Embodiment 1)
FIG. 1 is a schematic explanatory diagram of an optical fiber sensor 1 according to Embodiment 1 of the present invention. FIG. 2 is a schematic perspective view of the optical fiber sensor 1 according to Embodiment 1 of the present invention. In FIG. 1, some members are cut out for the purpose of explaining the structure, and in FIG. 2, some members are drawn with broken lines so as to be easily visible. As shown in FIGS. 1 and 2, the optical fiber sensor 1 is provided across one part 11 and the other part 12 of the measurement object 10. The optical fiber sensor 1 is for measuring the relative displacement of one part 11 and the other part 12.

  The optical fiber sensor 1 includes an optical fiber 20 to which test light is input, an optical fiber holding unit 30 that holds the optical fiber 20, and a relative displacement of one part 11 and the other part 12 of the measurement object 10. And a movable part 40 that moves in response to the movement. In addition, the arrow drawn along the optical fiber 20 in the drawing indicates the propagation direction of the test light.

In the optical fiber 20, for example, a light source that outputs test light is connected to one end of the optical fiber 20, and a light receiver is connected to the other end of the optical fiber. Further, an optical fiber transmission path for test light transmission may be provided between the light source and the optical fiber 20 and between the light receiver and the optical fiber 20.
The optical fiber holding part 30 has a U-shaped first fixing part 31 fixed to one part 11 and a holding part 32 fixed to the first fixing part 31 and holding the optical fiber 20. Yes. The holding portions 32 are arranged to face each other and hold the optical fiber 20 in a straight line shape.

The movable part 40 is fixed to the other part 12 and extends linearly toward the one part 11 side. In the present embodiment, the movable part 40 is fixed to the other part 12 via the second fixing part 41.
The movable unit 40 includes a stress applying unit 50 that applies stress to the optical fiber 20. In the present embodiment, the stress applying unit 50 is detachably provided on the distal end side of the movable unit 40. A through hole is formed in the stress application unit 50, and the optical fiber 20 is inserted through the through hole. That is, the stress applying unit 50 is disposed around the optical fiber 20.

  Specifically, the stress applying unit 50 has a surface through which a stress is applied to the optical fiber 20 by a cylindrical through hole whose inner diameter is reduced toward the center. When the one part 11 and the other part 12 are relatively displaced, the stress applying unit 50 comes into contact with the optical fiber 20 and deforms the optical fiber 20. The material of the stress applying unit 50 is, for example, aluminum, plastic, rubber, or the like.

  In this embodiment, the 1st fixing | fixed part 31 and the movable part 40 are connected via the bearing mechanism 60 (regulation part), as shown in FIG. The bearing mechanism 60 has a bearing portion 61 and a ball portion 62. In FIG. 2, the bearing mechanism is not shown.

  As shown in FIGS. 1, 3, and 4, the bearing portion 61 is formed with a ball receiving groove 63 that is formed along the outer periphery to receive the ball portion 62. A through hole 64 for inserting the optical fiber 20 is formed. The movable portion 40 is also formed with a ball receiving groove 42 for receiving the ball portion 62 at a predetermined position. The bearing portions 61 and 61 and the movable portion 40 are sequentially disposed inside the first fixed portion 31, and the ball portion 62 is disposed in each ball receiving groove 63, whereby the optical fiber holding portion 30 and the movable portion 40 are movable. The part 40 is connected. As a more specific connection method, for example, the first fixed portion 31 is separated into two upper and lower members in advance, and the ball portion 62 is disposed at a predetermined position between the movable portion 40 and the bearing portion 61. The first fixing portion 31 that is separated in the vertical direction so as to sandwich the bearing portion 61 can be fixed.

  The bearing mechanism 60 has a function of regulating the first fixed portion 31 and the movable portion 40 within the movable range of the ball portion 62 of the bearing mechanism 60. That is, the movement of the movable part 40 is regulated by the bearing mechanism 60. In the present embodiment, specifically, the movement of the movable portion 40 is regulated by the bearing mechanism 60 in a plane perpendicular to the longitudinal direction of the optical fiber 20 held in a straight line.

  When the optical fiber sensor 1 is disposed on the measurement object 10, it is preferable to fix the optical fiber 20 so that the optical fiber 20 coincides with the central axis of the through hole formed by the stress applying unit 50 as the initial position. . As a result, the distance between the optical fiber 20 and the stress applying unit 50 becomes equal in all directions within the regulation surface by the bearing mechanism 60. However, the arrangement method is not limited to this, and the distance (initial distance) between the optical fiber 20 and the stress applying unit 50 at the time of arrangement may be a known value, and differs depending on the direction in the regulation plane. It may be. As an arrangement method of the optical fiber 20, for example, when the movable part 40 having the optical fiber holding part 30, the bearing mechanism 60, and the stress applying part 50 is provided, the optical fiber 20 is positioned at a predetermined position of the stress applying part 50. Each member is temporarily fixed with a pin or the like (for example, the relative position between the optical fiber holding unit 30 and the stress applying unit 50 is fixed), and the pin is removed after the arrangement of each member is completed. Also good.

  Next, the operation of the optical fiber sensor 1 according to Embodiment 1 will be described. FIG. 5 is a schematic diagram illustrating a case where the distance between one part 11 and the other part 12 of the measurement target 10 is separated in the left-right direction on the paper surface in the optical fiber sensor 1 according to the first embodiment. When the one part 11 and the other part 12 of the measuring object 10 move and the distance in the left-right direction is increased, the movable unit 40 moves (displaces) to the right relative to the one part 11. At this time, the optical fiber 20 held by the optical fiber holding unit 30 is stressed rightward by a portion of the stress applying unit 50 located on the opposite side (left side) of the displacement direction with respect to the optical fiber 20. The shape is bent along the surface of the stress applying unit 50. In this state, when the test light is input to the optical fiber 20, a loss occurs in the light propagating through the optical fiber 20 due to the above-described deformation, and the light intensity of the output test light decreases. Further, backscattered light due to Rayleigh scattering generated in the optical fiber 20 by the test light is also reduced by the deformation of the optical fiber 20 described above.

FIG. 5 shows a state in which the distance between the one part 11 and the other part 12 in the left-right direction is increased. From the initial state where the optical fiber 20 is not bent, the one part 11 and the other part 12 are shown. When the distance in the left-right direction from the part 12 approaches, the movable part 40 moves to the left relative to the one part 11. The optical fiber 20 is applied with a stress leftward by a portion of the stress applying unit 50 located on the right side of the optical fiber 20 and deforms along the surface of the stress applying unit 50. As a result, loss occurs in the test light and the backscattered light propagating through the optical fiber 20.
As described above, the optical fiber sensor 1 according to Embodiment 1 can detect the displacement regardless of whether the one part 11 and the other part 12 move in the left or right direction.

  FIG. 6 is a schematic diagram illustrating a case where the distance between one part 11 and the other part 12 of the measurement object 10 is separated in the front-rear direction of the drawing in the optical fiber sensor 1 according to Embodiment 1 of the present invention. is there. In the present embodiment, the front side is referred to as the front and the back side is referred to as the rear with respect to the paper surface. In this case, the movable part 40 moves relatively to the front side with respect to the one part 11. At this time, the optical fiber 20 held by the optical fiber holding unit 30 is applied with a forward stress by a portion of the stress applying unit 50 located on the rear side with respect to the optical fiber 20, and is applied to the surface of the stress applying unit 50. It becomes the shape bent along. As a result, loss occurs in the test light and the backscattered light propagating through the optical fiber 20.

FIG. 6 shows a state in which the distance in the front-rear direction from the one part 11 and the other part 12 is increased, but from the initial state where the optical fiber 20 is not deformed, the one part 11 and the other part 12 are shown. When the distance in the front-rear direction from the part 12 approaches the movable part 40 relative to one part 11, the optical fiber 20 moves to the optical fiber 20 in the stress application part 50. On the other hand, a stress is applied toward the rear side by a position located on the front side, and the stress is deformed along the surface of the stress applying unit 50. As a result, loss occurs in the test light and the backscattered light propagating through the optical fiber 20.
As described above, the optical fiber sensor 1 according to Embodiment 1 can detect the relative displacement regardless of whether the one part 11 and the other part 12 move in the front-rear direction. Similarly, the optical fiber sensor 1 according to Embodiment 1 detects the relative displacement even when one part 11 and the other part 12 move in a direction inclined with respect to the front, rear, left, and right within the regulation plane. can do.

  In the optical fiber sensor 1 according to the present embodiment configured as described above, when the one part 11 and the other part 12 are relatively displaced in all directions within the regulation surface, the stress application that the movable part 40 has is applied. The part 50 applies stress to the optical fiber 20 held by the optical fiber holding part 30, and the optical fiber 20 is deformed. Thereby, optical loss occurs when test light (propagation light) is input to the optical fiber 20. Therefore, by observing the intensity of the light transmitted through the optical fiber sensor 1 or the backscattered light, the displacement in any direction within the regulating surface of the one part 11 and the other part 12 of the measurement object 10 is preferably measured. can do.

Further, in the first embodiment, the movement of the movable part 40 is restricted in a plane perpendicular to the optical fiber 20 held in a straight line by the bearing mechanism 60 (the restricting part). When the one portion 11 and the other portion 12 are relatively displaced, the stress can be reliably applied to the optical fiber 20 by the stress applying unit 50. In addition, since the movement of the movable portion 40 is restricted within a plane orthogonal to the longitudinal direction of the optical fiber 20, the relative displacement in the plane of the one portion 11 and the other portion 12 can be accurately measured. Is possible.
In the first embodiment, the case where the movement of the movable portion 20 is restricted in a plane orthogonal to the longitudinal direction of the optical fiber 20 held in a straight line has been described. The movement may be restricted in a plane intersecting the longitudinal direction of the held optical fiber 20.

  Moreover, in Embodiment 1, since the stress application part 50 is provided so that attachment or detachment is possible, the stress application part attached to a movable part can be selected as needed. Moreover, in order to adjust the distance between the stress applying unit 50 and the optical fiber 20, the stress applying unit can be selected. By adjusting the initial distance between the stress applying unit 50 and the optical fiber 20, it is possible to set an allowable range of relative displacement between the one part 11 and the other part 12 of the measurement object 10.

FIG. 7 is a schematic explanatory diagram of an optical fiber sensor system 2 using the optical fiber sensor 1 according to Embodiment 1 of the present invention. The optical fiber sensor system 2 connects the optical fiber sensor 1, a light source 71 that outputs test light, a light receiver 72 that receives the test light, and the light source 71, the optical fiber sensor 1, and the light receiver 72 described above. And a first optical fiber transmission line and an optical fiber transmission line 73 as a second optical fiber transmission line. The light source 71 includes, for example, a semiconductor laser element that outputs laser light as continuous light as test light. The wavelength of the test light is, for example, 1.55 μm band light. The light receiver 72 includes, for example, a photodiode.
In the optical fiber sensor system 2, the test light output from the light source 71 propagates through the optical fiber transmission path 73 and is input to the optical fiber sensor 1. The output light from the optical fiber sensor 1 is received by the light receiver 72 and the light intensity is measured.

  FIG. 8 shows the light intensity transmitted through the optical fiber sensor 1 with respect to the relative displacement between the one part 11 and the other part 12 of the measurement object 10 using the optical fiber sensor system 2 shown in FIG. It is a figure which shows a time-dependent change at the time of measuring. Here, as the optical fiber 20 used in the optical fiber sensor 1, ITU-T G.I. A single mode optical fiber conforming to 652 and having a zero dispersion wavelength in a normal 1.3 μm band is used. As shown in FIG. 8, the initial state where the optical fiber 20 is not deformed is set to a state where the relative displacement between the one portion 11 and the other portion 12 is 0, and the light intensity decreases with respect to the displacement. That is confirmed. In addition, the position of the arrow shown in FIG. 8 is the time when the stress is applied by the stress applying unit 50 and the optical fiber 20 starts to be deformed.

FIG. 9 is a schematic explanatory diagram of an optical fiber sensor system 102 using the optical fiber sensor 1 according to Embodiment 1 of the present invention. The optical fiber sensor system 102 is an optical fiber sensor 1 and an optical time domain reflectometer (OTDR) device that outputs test light, which is pulsed light having a wavelength of 1.55 μm, and receives backscattered light generated from the optical fiber sensor 1. 74 and an optical fiber transmission line 73 connecting the OTDR device 74 and the optical fiber sensor 1. The side opposite to the OTDR device 74 of the optical fiber sensor 1 is connected to a terminator.
The pulsed light output from the light source incorporated in the OTDR device 74 propagates through the optical fiber transmission path 73 and is input to the optical fiber sensor 1. In the optical fiber transmission line 73 and the optical fiber sensor 1, backscattered light due to Rayleigh scattering from pulsed light is generated in the optical fiber 20 and propagates in the direction of the OTDR device 74. The OTDR device 74 is provided with a light receiving device that receives backscattered light, and measures a delay time (arrival time of the backscattered light) with respect to the output time of the pulsed light. Thereby, the relationship between the distance from the OTDR device 74 on the optical fiber constituting the optical fiber sensor 1 and the optical fiber transmission line 73 and the light intensity at the distance can be obtained. Therefore, when the optical fiber 20 is deformed and a loss occurs in the optical fiber sensor 1, the light intensity decreases at a position (distance) corresponding to the optical fiber sensor 1.

  10 and 11 show the results of measuring the backscattered light in the vicinity of the optical fiber sensor 1 using the optical fiber sensor system 1 shown in FIG. FIG. 10 is a diagram illustrating a result of measuring the backscattered light in the initial state where the optical fiber 20 is not deformed by the stress applying unit 50. FIG. 11 is a diagram illustrating a result of measuring the backscattered light in a state where the optical fiber 20 of the optical fiber sensor 1 is deformed by the stress applying unit 50. Comparing FIG. 10 with FIG. 11, it can be seen that in FIG. 11, the light intensity at the position corresponding to the optical fiber sensor 1 is reduced, and the optical fiber 20 is deformed.

(Embodiment 2)
Next, a second embodiment of the present invention will be described. In addition, about the thing of the structure similar to Embodiment 1, the same code | symbol is attached | subjected and described, and detailed description is abbreviate | omitted.
FIG. 12 is a schematic explanatory diagram of the optical fiber sensor 101 according to Embodiment 2 of the present invention. The optical fiber sensor 101 includes an optical fiber 20 to which test light is input, an optical fiber holding unit 130 that holds the optical fiber 20, and one portion 11 and the other portion 12 of the measurement target 10. And a movable part 140 that moves in accordance with the displacement.

  The optical fiber holding part 130 has a first fixing part 131 fixed to one part 11 and a holding part 132 fixed to the first fixing part 131 and holding the optical fiber 20. The holding portions 132 are arranged to face each other, and hold the optical fiber 20 in a straight line.

  The movable part 140 is fixed to the other part 12 and extends linearly toward the one part 11 side. In the present embodiment, the movable part 140 is fixed to the other part 12 via the second fixing part 41. In addition, the movable part 140 has a stress applying part 150 that applies stress to the optical fiber 20.

  In the second embodiment, the stress applying unit 150 is detachably provided on the distal end side of the movable unit 140 with a screw or the like. Two stress applying portions 150 are arranged so as to be opposed to each other with an interval therebetween, and the optical fiber 20 is inserted between the two stress applying portions 150. That is, the stress applying unit 150 is disposed in at least two directions, that is, rightward and leftward with respect to the optical fiber 20. In the present embodiment, the stress applying unit 150 is formed such that the opposing surfaces bulge outward toward the center of the surface as shown in FIG. When the one part 11 and the other part 12 are relatively displaced, the stress applying unit 150 contacts the optical fiber 20 and deforms the optical fiber 20.

  In the optical fiber sensor 101 according to the second embodiment, the movable portion 140 is disposed on the rail 133 (regulating portion) provided in the first fixed portion 131. The rail 133 has a function of regulating the first fixed portion 131 and the movable portion 140 on the rail 133. In other words, the movable portion 140 is regulated so as to move on the rail 133 by the rail 133. In the present embodiment, specifically, the movement of the movable portion 140 is regulated by the rail 133 on one axis orthogonal to the longitudinal direction of the optical fiber 20 held in a straight line.

  When the optical fiber sensor 101 is disposed on the measurement object 10, it is preferable that the optical fiber 20 is fixed at the center position between the stress applying portions 150 arranged to face each other as the initial position.

  Next, the operation of the optical fiber sensor 101 will be described. FIG. 13 is a schematic diagram illustrating a state in which the distance between the one portion 11 and the other portion 12 of the measurement target 10 is separated in the left-right direction on the paper surface in the optical fiber sensor 101 according to the second embodiment. When one part 11 and the other part 12 of the measurement object 10 move and the distance in the left-right direction is increased, the movable unit 140 moves (displaces) in the right direction relative to the one part 11. At this time, the optical fiber 20 held by the optical fiber holding unit 130 is stressed rightward by a portion of the stress applying unit 150 located on the opposite side (left side) of the displacement direction with respect to the optical fiber 20. The shape is bent along the surface of the stress applying unit 150. In this state, when test light is input to the optical fiber 20, the test light propagating through the optical fiber 20 due to the above-described deformation causes a loss, and the light intensity of the output test light decreases. Further, the backscattered light due to Rayleigh scattering generated in the optical fiber 20 by the test light also decreases the intensity of the test light due to the deformation of the optical fiber 20 described above.

FIG. 13 shows a state in which the distance between the one part 11 and the other part 12 of the measurement object 10 is left and right, but the optical fiber 20 in the optical fiber sensor 101 is not initially deformed. From this state, when the distance between the one part 11 and the other part 12 of the measurement object 10 approaches in the left-right direction, the movable part 140 moves to the left relative to the one part 11 and the light The fiber 20 is deformed by being pushed out to the side surface of the stress applying unit 150. Thereby, a loss occurs in the light propagating through the optical fiber 20.
As described above, the optical fiber sensor 101 has its relative displacement regardless of whether the one part 11 and the other part 12 of the measuring object 10 move in the left or right direction (that is, two directions) along the regulation axis. Can be detected.

In the second embodiment, the movement of the movable part 140 is restricted on one axis orthogonal to the optical fiber 20 held in a straight line by the rail 133 (the restricting part). When the part 11 and the other part 12 are relatively displaced, the stress can be reliably applied to the optical fiber 20 by the stress application unit 150. Further, since the movement of the movable portion 140 is restricted on one axis orthogonal to the longitudinal direction of the optical fiber 20, it is possible to accurately measure the relative displacement of the one portion 11 and the other portion 12. is there.
In the second embodiment, the case where the movement of the movable portion 140 is regulated on one axis orthogonal to the longitudinal direction of the optical fiber 20 held in a straight line has been described. The movement may be restricted in a direction crossing the longitudinal direction of the optical fiber 20 held by the optical fiber 20.

  The optical fiber sensor may have a tension applying mechanism that applies tension to the optical fiber 20. FIG. 14 is a schematic explanatory diagram of an optical fiber sensor 101A that is Modification 1 of the optical fiber sensor 101 according to the second embodiment. The optical fiber sensor 101A includes an optical fiber 20 to which test light is input, an optical fiber holder 130A that holds the optical fiber 20, and a relative displacement between one part 11 and the other part 12 of the measurement target 10. And a tension applying mechanism 80A for applying a predetermined tension to the optical fiber 20.

  The optical fiber holding portion 130A includes a first fixing portion 131A that is fixed to one portion 11 and a holding portion 132A that is fixed to the first fixing portion 131A and holds the optical fiber 20, and the holding portion 132A. Are arranged opposite to each other. 131 A of 1st fixing parts are the bottom part 134 arrange | positioned on one site | part 11, the side part 135 formed in this U-shape on this bottom part 134, and the rail 133 provided on the bottom part 134 (Regulatory Department). The movable part 140 is disposed on the rail 133 (regulation part) described above. Further, two fixing portions 136 for fixing the optical fiber 20 are provided on the bottom surface portion 134. A tension applying mechanism 80 </ b> A is disposed between the fixing portions 136.

As shown in FIG. 14, the tension applying mechanism 80 </ b> A includes a spring portion 81, a pulley portion 82, and a rail portion 83.
One end of the spring portion 81 is connected to the side surface portion 135 of the first fixed portion 131, and the other end of the spring portion 81 is connected to the pulley portion 82. The pulley portion 82 is disposed on the rail portion 83 so as to be movable back and forth, and the optical fiber 20 is applied to the pulley portion 83. The rail portion 83 is disposed on the bottom surface portion 134 and extends in one direction (left and right direction in FIG. 14).

In the optical fiber sensor 101A configured as described above, in the initial state, the optical fiber 20 is fixed by the fixing unit 136 and maintained in a state in which tension is applied by the tension applying mechanism 80A. The optical fiber 20 disposed around the stress applying unit 150 is linear.
FIG. 15 is a schematic diagram showing a state in which the distance between the one part 11 and the other part 12 of the measurement object 10 is separated in the left-right direction on the paper surface in the optical fiber sensor 101A. When one part 11 and the other part 12 of the measurement object 10 move and the distance in the left-right direction is increased, the movable unit 140 moves (displaces) in the right direction relative to the one part 11. In this example, the movable part 140 is relatively larger and relatively moved to the right than in the case of the optical fiber sensor 101 described above. When the optical fiber 20 is applied with stress by the stress applying unit 150, the pulley unit 82 advances and retreats on the rail unit 83 according to the stress. At this time, since the pulley portion 82 is connected to the spring portion 81, a tension within a predetermined range is applied to the optical fiber 20 by the biasing force of the spring portion 82. Thus, even if the movable part 140 moves relatively large and the optical fiber is relatively deformed by the stress applying part 150, the tension applied to the optical fiber 20 by the tension applying mechanism 80A is within a predetermined range, The optical fiber 20 can be deformed without applying excessive tension to the optical fiber 20.

  FIG. 16 is a schematic explanatory diagram of an optical fiber sensor 101B that is a second modification of the optical fiber sensor 101 according to the second embodiment. The optical fiber sensor 101B includes an optical fiber 20 to which test light is input, an optical fiber holding unit 130B that holds the optical fiber 20, and a relative displacement of one part 11 and the other part 12 of the measurement object 10. And a tension applying mechanism 80B that applies a predetermined tension to the optical fiber 20.

  The optical fiber holding portion 130B includes a first fixing portion 131B fixed to one portion 11 and a holding portion 132B that is fixed to the first fixing portion 131B and holds the optical fiber 20. Two holding parts 132 </ b> B are arranged and hold the optical fiber 20. In the optical fiber sensor 101B, the optical fiber 20 extending from one optical fiber holding portion 130B is bent through a support point 137 provided on the bottom surface portion 134 and extends to the other optical fiber holding portion 130B. ing. The first fixing portion 131B includes a bottom surface portion 134 disposed on one part 11, a side surface portion 135 formed in a U-shape on the bottom surface portion 134, and a rail 133 provided on the bottom surface portion 134. (Regulatory Department). The movable part 140 is disposed on the rail 133 (regulation part) described above. Further, three fixing portions 136 for fixing the optical fiber 20 are provided on the bottom surface portion 134.

As shown in FIG. 16, the tension applying mechanism 80 </ b> B includes a winding unit 84 (reel unit) that applies a predetermined tension to the optical fiber 20 and winds the optical fiber 20 around the accommodation unit.
The winding portion 84 is disposed on the bottom surface portion 134 of the first fixing portion 131B. The winding portion 84 changes its winding diameter when the optical fiber 20 is wound. The winding portion 84 is, for example, a spiral spring (spring spring).

In the optical fiber sensor 101B configured as described above, in the initial state, the optical fiber is maintained in a state where the optical fiber is fixed by the fixing unit 136 and tension is applied by the tension applying mechanism 80B. The optical fiber 20 disposed around the stress application unit 150 is linear.
FIG. 17 is a schematic view showing a state in which the distance between the one part 11 and the other part 12 of the measurement object 10 is separated in the left-right direction on the paper surface in the optical fiber sensor 101. When one part 11 and the other part 12 of the measurement object 10 move and the distance in the left-right direction is increased, the movable unit 140 moves (displaces) in the right direction relative to the one part 11. When a stress is applied to the optical fiber 20 by the stress applying unit 150, the spiral spring contracts according to the stress, thereby maintaining the tension applied to the optical fiber 20 within a predetermined range. Thus, even if the movable part 140 moves and the optical fiber 20 is deformed relatively greatly by the stress applying part 150, the tension applied to the optical fiber 20 is within a predetermined range, and excessive tension is applied to the optical fiber 20. The optical fiber 20 can be deformed without being added.
Note that the optical fiber sensor 1 described in the first embodiment may be configured to include the above-described tension applying mechanism.

  In addition, the stress application part 150 which the optical fiber 20 contacts can be made into various shapes. For example, when the stress applying part of the optical fiber sensor 101 is a stress applying part 151 having an arcuate cross section with an arbitrary curvature radius as shown in FIG. 18, bending loss corresponding to the curvature radius is generated. It becomes possible to make it.

  Further, the stress applying part of the optical fiber sensor 101 may be a triangular stress applying part 152 having an acute angle part as shown in FIG. In this case, when the one portion 11 and the other portion 12 are relatively displaced and the optical fiber 20 comes into contact with the stress applying unit 152, the optical fiber 20 is strongly bent by the triangular convex portion, and thus the loss of light intensity. The amount can be increased. Furthermore, the optical fiber 20 can be disconnected according to the relative displacement of the one part 11 and the other part 12. Limiting the relative displacement of the one part 11 and the other part 12 by matching the relative displacement of the one part 11 and the other part 12 with a predetermined limit displacement when the disconnection occurs. It is also possible to use an optical fiber sensor that warns the user. Moreover, it is good also considering the blade part which has a blade which cut | disconnects the optical fiber 20 when the optical fiber 20 contacts as a stress application part.

Further, as the optical fiber 20 used in the optical fiber sensors 1 and 101, optical fibers having various characteristics can be used.
In order to measure the relative displacement of the one part 11 and the other part 12 of the measurement object 10, when detecting a loss change due to the deformation of the optical fiber in the optical fiber sensor, it is more effective against the deformation of the optical fiber. An optical fiber whose loss changes sensitively is easier to detect the change. FIG. 20 shows an optical fiber having a bending loss larger than that of the optical fiber in the optical fiber transmission line between the optical fiber sensor 1 and the light source (for example, used in the optical fiber transmission line). When the optical fiber is an optical fiber defined by ITU-T G.652, an optical fiber having a bending loss characteristic of 30 mm at a wavelength of 1550 nm and a maximum loss of more than 0.1 dB at 100 turns) 6 is a diagram showing a result of measuring a change with time of output light intensity of the optical fiber sensor with respect to relative displacement of one part 11 and the other part 12 of the measurement object 10. It can be seen that the amount of loss is large and the displacement of the object to be measured can be measured with higher sensitivity than when a single mode optical fiber having a zero dispersion wavelength in a normal 1.3 μm band is used (see FIG. 8).

  For the purpose of detecting breakage of the optical fiber 20 in the optical fiber sensors 1 and 101, it is effective to use an optical fiber with a small bending loss. The reason will be described below. First, when an optical fiber having a small bending loss is used, when the optical fiber 20 is deformed by being in contact with the stress applying unit 50, the generation of loss is small. As an example of an optical fiber with little bending loss, ITU-T G.G. The optical fiber prescribed | regulated to 657 is mentioned.

  Here, an optical fiber sensor system in which a plurality of optical fiber sensors are connected in series is configured, and a warning is detected when the displacement of one part 11 and the other part 12 of the measurement object 10 reaches a certain limit point. In order to achieve this, it is desirable that the loss due to the deformation of the optical fiber in the process in which the displacement of the one part 11 and the other part 12 reaches the limit point is small. The reason is that when a plurality of optical fiber sensors are connected in series and the loss of test light occurs due to the deformation of the optical fiber in the optical fiber sensor provided at a certain location, the light source is more than the optical fiber sensor. This is because the intensity of the test light reaching the optical fiber sensor at a remote position is lowered by the loss, and it is difficult for the optical fiber sensor at a position remote from the light source to detect a change in intensity.

  FIG. 21 shows an OTDR waveform when a plurality of optical fiber sensors 1 using a single mode optical fiber having a zero dispersion wavelength in the normal 1.3 μm band as the optical fiber 20 are connected in series. Here, the optical fiber sensor 1 is disposed at a distance of 1700 m, 3000 m, and 4000 m. Here, since a loss is generated in each optical fiber sensor 1 at a distance of 1700 m and 3000 m, the light intensity is greatly reduced. For this reason, the light intensity reaching the optical fiber sensor 1 at the far end disposed at a distance of 4000 m becomes weak and the loss change in the optical fiber sensor cannot be observed with high sensitivity, and reaches a certain critical displacement. Even if a rupture occurs, it is difficult to detect a loss change caused by the break.

  FIG. 22 shows ITU-T GG. 6 shows an OTDR waveform when a plurality of optical fiber sensors 1 using an optical fiber with a small bending loss defined in 657 as an optical fiber 20 are connected in series. Also here, the optical fiber sensor 1 is disposed at a distance of 1700 m, 3000 m, and 4000 m. In each of the optical fiber sensors 1 arranged at a distance of 1700 m and 3000 m, the same deformation as that in the case of using the above-described normal single mode optical fiber occurs in the optical fiber 20, but almost no loss occurs. Not. Therefore, the test light propagates at the far-end optical fiber sensor 1 with the light intensity necessary for the measurement, and a significant loss change can be detected when breakage occurs. Note that ITU-T G.I. When the optical fiber specified in 657 is used, loss may not occur until just before the break, which is preferable.

  Further, when measuring the loss change of the optical fiber in the optical fiber sensor by the OTDR apparatus, it is important to specify the position of the optical fiber in the optical fiber sensor on the OTDR waveform. Therefore, as the optical fiber 20 used in the optical fiber sensor, an optical fiber having optical characteristics different from those of the optical fiber transmission line connecting the light source to the optical fiber sensor and between the optical fiber sensors is used. Thus, the position of the optical fiber sensor on the OTDR waveform can be easily specified.

FIG. 23 is a diagram showing an OTDR waveform when an optical fiber having a mode field diameter (MFD) different from that of the optical fiber of the optical fiber transmission line is used as the optical fiber 20 in the optical fiber sensor 1. Here, the optical fiber of the optical fiber transmission line is a single mode optical fiber having a zero dispersion wavelength in a normal 1.3 μm band, and the MFD is about 10 μm at a wavelength of 1550 nm. The MFD of the optical fiber used in the optical fiber sensor is 4 μm. When the OTDR waveform is observed in a configuration in which optical fibers having different MFDs are connected as described above, a step in intensity is observed at the connection portion.
In general, an optical fiber having a larger MFD has a smaller backscattering coefficient, which is a ratio of the generation of backscattered light, and if a fiber having a small MFD is incident on a large fiber, the loss at the connection portion is large. On the contrary, when the MFD is incident on the small optical fiber from the large optical fiber, the light intensity increases as if amplified at the connecting portion. By connecting optical fibers having different MFDs as described above, the connection point can be more clearly confirmed on the OTDR waveform, and the optical fiber sensor in the optical fiber sensor system can be easily identified.

Further, the use of optical fibers having different transmission losses also makes it easy to specify the position of the optical fiber sensor in the optical fiber sensor system.
FIG. 24 is a diagram showing an OTDR waveform when a fiber having a transmission loss larger than that of the optical fiber in the optical fiber transmission line is used as the optical fiber 20 in the optical fiber sensor 1. Here, the optical fiber of the optical fiber transmission line is a single mode optical fiber having a zero dispersion wavelength in a normal 1.3 μm band, and the transmission loss is about 0.2 dB / km. Further, the transmission loss of the optical fiber 20 (corresponding to a position of distance 1695 m to 1700 m) used in the optical fiber sensor 1 is about 2.0 dB / km, and on the OTDR waveform, the difference in the gradient of the light intensity change with respect to the distance. It becomes easy to specify the position of the optical fiber sensor.

  Moreover, you may use the optical fiber from which a bending loss and a cutoff wavelength differ. In this case, for example, an optical fiber having a bending loss larger than that of the fiber of the optical fiber transmission line is used as the optical fiber in the optical fiber sensor. It is possible to suppress the attenuation of the test light due to bending that occurs during laying or the like. Note that bending loss can be varied by using optical fibers having different cutoff wavelengths. For example, there is (MFD / λc) as a parameter for determining the bending loss of an optical fiber at a certain wavelength. Here, MFD is the mode field diameter of the optical fiber at that wavelength, and λc is the cutoff frequency. The smaller the (MFD / λc), the smaller the bending loss.

  As described above, when the optical fiber 20 used for the optical sensor fiber is an optical fiber having different optical characteristics, the relative position of the one part 11 and the other part 12 of the measurement object 10 in the optical fiber 20 is relatively small. If the sensor optical fiber portion is a portion that deforms in response to a general displacement, the optical properties of the sensor optical fiber portion are the optical properties of the optical fiber transmission path 73 (optical fiber for test light transmission) connected to the optical fiber 20. And may be different.

  In addition, the optical fiber sensor may include a storage unit that stores the extra length of the optical fiber. The pulsed light is transmitted at a time corresponding to the time width (pulse width) of the pulsed light as the test light between the input connection part to the optical fiber transmission path for propagating light from the light source and the optical fiber in contact with the stress applying part. An optical fiber having a distance longer than the propagating length can be provided.

  In FIG. 25, an optical fiber sensor 201 in which an accommodating portion 85 that accommodates the extra length of the optical fiber 20 is provided between the first fixing portion 31 and the stress applying portion 50, and the optical fiber 20 is accommodated in the accommodating portion 85. Indicates.

  Two optical fiber sensors 201 are connected in series, and the backscattered light in the vicinity of the optical fiber sensor is measured by the OTDR device in a state where the optical fiber 20 is deformed by the stress applying unit 50 in the two optical fiber sensors 201. Are shown in FIGS. In the OTDR device, the distance corresponding to the pulse width (the distance that the pulsed light travels through the optical fiber during the time corresponding to the pulse width) is used as a guide for the distance resolution (minimum distance that can be identified in the distance direction) on the waveform. Yes. The relationship between the pulse width Δt and the distance resolution Δz in the OTDR apparatus is generally expressed by Δz = Δt × c / n (c: speed of light, n: effective refractive index of optical fiber). Therefore, the optical fiber 20 having a length equal to or longer than the distance corresponding to the pulse width of the pulsed light output from the OTDR apparatus is disposed between the stress applying unit 50 and the first fixing unit 31, so that The position of the optical fiber sensor can be easily identified.

  FIG. 26 shows an OTDR waveform in a state where the optical fiber sensor does not have an extra optical fiber length between the first fixing portion 31 and the stress applying portion 50, and FIG. 27 shows the optical fiber sensor 201 in the first fixing state. It is an OTDR waveform measured with the 20 m optical fiber 20 as an extra length between the portion 31 and the stress applying portion 50. The time width of the optical pulse when measuring the OTDR waveform is 50 ns, which corresponds to 5 m as the distance resolution. When comparing FIG. 26 and FIG. 27, it is difficult to discriminate the position of the loss change in the two optical fiber sensors in FIG. 26, whereas in FIG. 27, it occurs in each of the two optical fiber sensors. The loss occurrence position can be clearly identified.

(Embodiment 3)
Next, an optical fiber sensor according to Embodiment 3 of the present invention will be described. FIG. 28 is a schematic explanatory diagram of an optical fiber sensor 301 according to Embodiment 3 of the present invention. In addition, about the thing of the structure similar to the above-mentioned embodiment, the same code | symbol is attached | subjected and described, and detailed description is abbreviate | omitted. The optical fiber sensor 301 includes an optical fiber 20 to which test light is input, an optical fiber holding unit 30 that holds the optical fiber 20, and one part 11 and the other part 12 of the measurement target 10. And a movable part 40 that moves in accordance with the displacement.
The optical fiber holding part 30 has a U-shaped first fixing part 31 fixed to one part 11 and a holding part 31 fixed to the first fixing part 31 and holding an optical fiber. . The holding portions 32 are arranged to face each other and hold the optical fiber 20 in a straight line.

  The movable part 40 is fixed to the other part 12 and extends linearly toward the one part 11 side. The movable part 40 is fixed to the other part 12 via the second fixing part 41. The movable part 40 has a stress applying part 50 that applies stress to the optical fiber 20.

  The optical fiber 20 includes a fiber Bragg grating (FBG) 90 in a portion (sensor optical fiber portion) that is deformed by the stress applying unit 50. In the present embodiment, the first fixed portion 31 and the movable portion 40 are connected via the bearing mechanism 60.

  Next, the operation of the optical fiber sensor 301 according to Embodiment 3 will be described. FIG. 29 is a schematic diagram illustrating a case where the distance between the one portion 11 and the other portion 12 of the measurement target 10 is separated in the left-right direction on the paper surface in the optical fiber sensor 301. When one part 11 and the other part 12 of the measurement object 10 move and the distance in the left-right direction increases, the movable part 40 moves to the right relative to the one part 11. At this time, the optical fiber 20 held by the optical fiber holding unit 30 is applied with stress in the right direction by the stress applying unit 50 and is bent along the surface of the stress applying unit 50. At this time, tension is applied to the fiber Bragg grating 90 included in the optical fiber 20. The fiber Bragg grating 90 has a lattice structure in which the refractive index of the core in the optical fiber is periodically changed, and has a characteristic of reflecting light having a specific wavelength corresponding to the period. When the fiber Bragg grating 90 is tensioned by the deformation of the optical fiber and the periodic grating interval is changed, the wavelength of the reflected light also changes. For this reason, the amount of distortion of the optical fiber 20 can be obtained by observing the amount of change in the wavelength of the light reflected backward. This amount of distortion corresponds to the relative displacement of one part 11 and the other part 12 of the measurement object 10.

FIG. 30 is a schematic explanatory diagram of an optical fiber sensor system 202 using the optical fiber sensor 301 according to the third embodiment. The optical fiber sensor system 202 according to the third embodiment includes an optical fiber sensor 301, a light source 71 that outputs test light, an optical fiber transmission path 73 that connects the light source 71 and the optical fiber sensor 301, a light source 71, and light. The optical circulator 76 provided in the optical fiber transmission path 73 between the fiber sensors 301, and the optical wavelength measuring device 75 which measures the wavelength of the light branched from the optical circulator 76 are provided.
In the optical fiber sensor system 202, the light source 71 outputs light including at least a specific wavelength component reflected by the fiber Bragg grating 90 as test light. When the test light is input, the fiber Bragg grating 90 in the optical fiber sensor 301 reflects light having a specific wavelength component included in the test light. Then, the reflected light from the fiber Bragg grating 90 is output from the optical fiber transmission path 73 via the circulator 76, received by the optical wavelength measuring device 75, and the wavelength is measured. In general, a wavelength meter or an optical spectrum analyzer is used as the optical wavelength measuring device 75.

  FIG. 31 shows a fiber Bragg grating 90 in the optical fiber sensor 301 with respect to the relative displacement of one part 11 and the other part 12 of the measurement object 10 using the optical fiber sensor system 202 according to the third embodiment. It is a figure which shows the result of having measured the change of the wavelength of the light reflected from. Here, as the light source 71, an LED light source that outputs light having a wavelength of 1.55 μm and a relatively wide spectrum is used. Moreover, when measuring, the initial state in which the optical fiber 20 is not deformed is set to a state in which the relative displacement of the one part 11 and the other part 12 of the measurement object 10 is zero. As shown in FIG. 31, it is confirmed that the wavelength of the reflected light is shifted with respect to the relative displacement of one part 11 and the other part 12.

(Embodiment 4)
Next, a fourth embodiment of the present invention will be described.
Specific examples of use of the above-described optical fiber sensor and optical fiber sensor system include, for example, strain detection for a bridge. For example, as shown in FIG. 32, it can be used as an optical fiber sensor 1 and an optical fiber sensor system 2 that measure relative displacements of a first floor board 16 and a second floor board 17 installed on a pier 15. . The upper diagram in FIG. 32 shows a state before the first floor plate 16 and the second floor plate 17 are relatively displaced, and the lower diagram in FIG. 32 shows the relative relationship between the first floor plate 16 and the second floor plate 17. It shows the state after being displaced.

(Embodiment 5)
Next, an optical fiber sensor system according to Embodiment 5 will be described. FIG. 33 is a schematic explanatory diagram of an optical fiber sensor system 302 according to Embodiment 5 of the present invention. The optical fiber sensor system 302 includes a light source 71 that outputs test light, a light receiver 72 that receives a plurality of test lights, a plurality of optical fiber sensors 1, and an optical fiber transmission path 73 that connects them. Yes. The plurality of optical fiber sensors 1 are connected in series to the optical fiber transmission path 73. Each optical fiber sensor 1 is attached to each measurement object 10 such as a bridge. Note that an optical branching device 78 for branching the test light into N branches (N is an integer of 2 or more) is connected to the output side of the light source 71. In FIG. 33, a plurality of optical fiber sensors 1 of one system connected to the optical splitter 78 and the optical fiber transmission path 73 connecting them are shown. -1) A plurality of optical fiber sensors 1 (not shown) of the system and an optical fiber transmission path 73 connecting them are connected, and a light receiver 72 shown in the figure is connected to each system.
In the optical fiber sensor system 302, the light output from the light source 71 propagates through the optical fiber transmission path 73 of each system, passes through the plurality of optical fiber sensors 1 of each system, and the light intensity is observed by the light receiver 72. The When some displacement occurs in the measurement object 10 of each system, a change appears in the light intensity detected by the light receiver 72 of each system. By observing the change, the displacement generated in the measurement object 10 of each system can be detected.

(Embodiment 6)
Next, an optical fiber sensor system according to Embodiment 6 will be described. FIG. 34 is a schematic explanatory diagram of an optical fiber sensor system 402 according to Embodiment 6 of the present invention. An optical fiber sensor system 402 according to Embodiment 6 includes a plurality of optical fiber sensors 1, an OTDR device 74 that outputs test light and receives backscattered light generated from the optical fiber sensor 1, an OTDR device 74, and a plurality of optical fiber sensor systems 402 And an optical fiber transmission line 73 for connecting the optical fiber sensor 1. The plurality of optical fiber sensors 1 are connected in series to the optical fiber transmission line 73, and each optical fiber sensor 1 is attached to each measurement object 10. Note that an optical branching device 78 that branches the test light into N branches (N is an integer of 2 or more) is connected to the output side of the OTDR device 74. In FIG. 34, a plurality of optical fiber sensors 1 of one system connected to the optical branching device and the optical fiber transmission path 73 connecting them are shown. ) A plurality of optical fiber sensors 1 (not shown) of the system and an optical fiber transmission line 73 connecting them are connected.

  In the optical fiber sensor system 402, the pulsed light output from the OTDR device 74 propagates through the optical fiber transmission path 73 of each system, passes through the plurality of optical fiber sensors 1 of each system, and reaches the end. Backscattered light due to Rayleigh scattering from the optical fiber transmission path 73 from the OTDR device 74 to the terminal and the optical fiber sensor 1 disposed between them travels to the OTDR device 74 side. The OTDR device 74 receives the return light, and calculates the change in the light intensity of each system with respect to the distance from the difference in delay time. Thereby, by observing the change of the light intensity at the position of each optical fiber sensor 1, it is possible to simultaneously observe the displacement generated in the measurement object 10 of each system.

(Embodiment 7)
Next, an optical fiber sensor system according to Embodiment 7 will be described. FIG. 35 is a diagram showing an optical fiber sensor system 502 according to Embodiment 7 of the present invention. The optical fiber sensor system 502 includes a plurality of optical fiber sensors 1, an OTDR device 74 that outputs test light and receives backscattered light generated from the optical fiber sensor 1, an OTDR device 74, and the plurality of optical fiber sensors 1. And an optical fiber transmission line 73 to be connected. The optical fiber transmission line 73 has a main optical fiber transmission line 73a connected to the OTDR device 74 via the optical branching device 78, and a plurality of branched optical fiber transmission lines 73b branched from the main optical fiber transmission line 73a. The branched optical fiber transmission line 73 b is branched from the main optical fiber transmission line 73 a through the optical branching unit 77. Each optical fiber sensor 1 is connected to the main optical fiber transmission line 73a via the branched optical fiber transmission line 73b and attached to each measurement object 10. Note that an optical branching device 78 that branches the test light into N branches (N is an integer of 2 or more) is connected to the output side of the OTDR device 74. In FIG. 35, a plurality of optical fiber sensors 1 connected to the optical branching device and the optical fiber transmission path 73 connecting them are illustrated. ) A plurality of optical fiber sensors 1 (not shown) of the system and an optical fiber transmission line 73 connecting them are connected.

  In the optical fiber sensor system 502 configured as described above, the pulsed light output from the OTDR device 74 propagates through the main optical fiber transmission path 73a of each system, is divided by the optical branching device 77, and is branched. The light enters the optical fiber sensors 1 of each system through the fiber transmission path 73b. At this time, nothing is connected to the output side of each optical fiber sensor 1 and it is terminated. Backscattered light from each optical fiber sensor 1 returns to the OTDR device 74 through the branch optical fiber transmission path 73b, the optical branching device 77, and the main optical fiber transmission path 73a. The OTDR device 74 receives the return light and calculates the change in the light intensity of each system with respect to the distance from the difference in delay time. In this case, in the observed OTDR waveform, the light scattered back from the optical branching device 77 to the end of the optical fiber sensor 1 is the OTDR device 74 in the main optical fiber transmission line 73 a connecting the optical branching devices 77. Is observed as the intensity combined with the backscattered light from the portion equal to the distance from the OTDR device 74 between the optical branching device 77 and the end of the optical fiber sensor 1.

  However, the intensity fluctuation of the backscattered light in the main optical fiber transmission line 73a overlapped with the portion of the optical fiber sensor 1 over the distance from the OTDR device 74 is the light due to the displacement of the measurement object 10 in the optical fiber sensor 1. Since the fluctuation is smaller than the fluctuation in intensity, if the fluctuation in intensity at the position of the optical fiber sensor 1 occurs even on the OTDR waveform shown as the combined intensity, it is clear that the displacement of the measuring object 10 is a factor. Be identifiable. Further, in the optical fiber sensor system 502, compared with the optical fiber sensor system 402, the light intensity incident on each optical fiber sensor 1 is constant, and the influence of the light intensity fluctuation generated in each optical fiber sensor 1 is affected. I do not receive it. Therefore, on the OTDR waveform, the intensity on the optical fiber transmission path 73 propagating between the optical fiber sensors 1 is substantially constant with respect to the distance according to the transmission loss, and the intensity fluctuation at the position of each optical fiber sensor 1 Reflects only the intensity fluctuation in the optical fiber sensor 1 itself, that is, the displacement of the measurement object 10.

  36 and 37 show examples of OTDR waveforms observed in the optical fiber sensor system 402 and the optical fiber sensor system 502. FIG. 36 shows the measurement results using the optical fiber sensor system 402, and FIG. 37 shows the measurement results using the optical fiber sensor system 502. As shown in FIG. 36, in the optical fiber sensor system 402, when a loss occurs in a certain optical fiber sensor 1, the light intensity decreases and propagates on the test light output side of the optical fiber sensor 1. As a result, the intensity of the test light reaching the optical fiber sensor 1 far from the OTDR device 74 and the intensity of backscattered light returning from the optical fiber sensor 1 are reduced. Furthermore, if a loss is generated in the plurality of optical fiber sensors 1, the loss is accumulated to cause a decrease in the intensity of the test light and the backscattered light. In FIG. 36, a region surrounded by a broken line indicates light loss in the optical fiber sensor 1.

On the other hand, as shown in FIG. 37, in the optical fiber sensor system 502, even if a loss occurs in a certain optical fiber sensor 1, the test light that reaches the optical fiber sensor 1 that is further away from the test light Since the light is not transmitted through the fiber sensor 1 but is propagated through the main optical fiber transmission line 73a, the test light and the backscattered light as shown in FIG. It will be.
When the fiber is cut by contact with the stress application unit 50 of the optical fiber 20 in the optical fiber sensor 1, the rear side of the optical fiber sensor 1 in which the optical fiber 20 is cut in the configuration of the optical fiber sensor system 402. However, in the case of the optical fiber sensor system 502, only the light intensity from the optical fiber sensor 1 in which the optical fiber 20 is cut is lowered, and the optical fiber sensor 1 behind the optical fiber sensor 1 Has no effect.

  In the above embodiment, the wavelength of the test light is in the 1.55 μm band. The reason is that the 1.55 μm band is the wavelength band with the lowest transmission loss of a single mode optical fiber having a zero dispersion wavelength in the normal 1.3 μm band. However, the wavelength of the test light is not limited to this. For example, the wavelength of the test light may be longer than the 1.55 μm band, such as the 1.6 μm band. In this case, since the bending loss of the optical fiber becomes larger than that in the case where the wavelength of the test light is in the 1.55 μm band, it is possible to perform measurement with higher sensitivity.

  Further, the present invention is not limited by the above embodiment. What was comprised combining each component mentioned above suitably is also contained in this invention. Further effects and modifications can be easily derived by those skilled in the art. Therefore, the broader aspect of the present invention is not limited to the above-described embodiment, and various modifications can be made.

1, 101, 101A, 101B, 201, 301 Optical fiber sensor 2, 102, 202, 302, 402 Optical fiber sensor system 10 Measurement object 11 One part 12 Other part 15 Bridge pier 16 First floor board 17 Second Floor plate 20 Optical fibers 30, 130, 130A, 130B Optical fiber holding portions 31, 131, 131A, 131B First fixing portions 32, 132, 132A, 132B Holding portions 40, 140 Movable portion 41 Second fixing portion 42 Ball receiving groove 50 , 150, 151, 152 Stress application unit 60 Bearing mechanism (regulation unit)
61 Bearing portion 62 Ball portion 63 Ball receiving groove 64 Through hole 71 Light source 72 Light receiver 73 Optical fiber transmission path 73a Main optical fiber transmission path 73b Branch optical fiber transmission path 74 OTDR device 75 Optical wavelength measuring device 76 Circulators 77, 78 Optical branching 80A, 80B Tension applying mechanism 81 Spring portion 82 Pulley portion 83 Rail portion 84 Winding portion (reel portion)
85 Extra length storage part 90 Fiber Bragg grating 133 Rail (regulation part)
134 Bottom part 135 Side part 136 Fixing part 137 Support point

Claims (17)

An optical fiber sensor that is provided across one part and the other part of the measurement object and measures the relative displacement of the one part and the other part,
An optical fiber to which test light is input;
An optical fiber holding unit fixed to one part of the measurement object and holding the optical fiber;
It is fixed to the other part of the measurement object, has a stress applying part for applying stress to the optical fiber, and corresponds to the relative displacement of one part and the other part of the measurement object Moving parts that move and
The stress applying unit is disposed at least on the side opposite to the direction of displacement with respect to the optical fiber,
An optical fiber sensor, wherein when one part and the other part of the measurement object are relatively displaced, the stress applying unit contacts the optical fiber, and the optical fiber is deformed.   It is provided with a restricting part that restricts the movement of the movable part so that the movement of the movable part is on one axis intersecting with the longitudinal direction of the optical fiber held linearly by the optical fiber holding part. The optical fiber sensor according to claim 1.   It is provided with a restricting part that restricts the movement of the movable part so that the movement of the movable part is on a plane that intersects the longitudinal direction of the optical fiber that is linearly held by the optical fiber holding part. The optical fiber sensor according to claim 1.   The said stress application part is provided in the said movable part so that attachment or detachment is possible, and can change the initial distance with the said optical fiber, It is any one of Claim 1 to 3 characterized by the above-mentioned. Fiber optic sensor.   The optical fiber includes a sensor optical fiber part that deforms according to relative displacement of one part and the other part of the measurement object, and the optical characteristics of the sensor optical fiber part are connected to the optical fiber. 5. The optical fiber sensor according to claim 1, wherein the optical fiber sensor is different from the optical characteristic of the optical fiber for test light transmission.   The optical fiber sensor according to claim 5, wherein mode field diameters of the sensor optical fiber portion and the test optical transmission optical fiber are different.   The optical fiber sensor according to claim 5 or 6, wherein the sensor optical fiber portion and the test optical transmission optical fiber have different cutoff wavelengths.   8. The optical fiber sensor according to claim 5, wherein bending loss characteristics of the sensor optical fiber portion and the test optical transmission optical fiber are different. 9.   The optical fiber sensor according to any one of claims 5 to 8, wherein transmission loss characteristics of the sensor optical fiber portion and the optical fiber for test light transmission are different. The test light is pulsed light,
A storage unit for storing the extra length of the optical fiber,
The extra length of the optical fiber has a length equal to or longer than a length of propagation of the pulsed light in a time corresponding to a time width of the pulsed light. The optical fiber sensor described.   The optical fiber sensor according to any one of claims 1 to 10, wherein the test light has a wavelength longer than a wavelength band in which the transmission loss of the optical fiber is lowest.   12. The optical fiber includes a fiber Bragg grating in a sensor optical fiber portion that is deformed in accordance with relative displacement of one part and the other part of the measurement object. An optical fiber sensor according to claim 1. An optical fiber sensor according to any one of claims 1 to 11,
A light source that outputs the test light;
A light receiver capable of receiving the test light transmitted through the optical fiber of the optical fiber sensor;
An optical fiber transmission line having a first optical fiber transmission line connecting the light source and the optical fiber sensor; and a second optical fiber transmission line connecting the optical fiber sensor and the light receiver;
An optical fiber sensor system comprising: An optical fiber sensor according to any one of claims 1 to 11,
An OTDR device that outputs the test light and receives backscattered light generated from the optical fiber sensor;
An optical fiber transmission line connecting the OTDR device and the optical fiber sensor;
An optical fiber sensor system comprising: An optical fiber sensor according to claim 12,
A light source that outputs the test light;
An optical fiber transmission line connecting the light source and the optical fiber sensor;
An optical wavelength measuring device that receives the reflected light reflected by the fiber Bragg grating of the optical fiber sensor from the test light, and measures the wavelength of the reflected light;
An optical fiber sensor system comprising: The optical fiber sensor system according to any one of claims 13 to 15, comprising a plurality of the optical fiber sensors,
The optical fiber sensor system, wherein the plurality of optical fiber sensors are connected in series to the optical fiber transmission line. The optical fiber sensor system according to claim 14 or 15,
A plurality of the optical fiber sensors,
The optical fiber transmission line has a main optical fiber transmission line and a plurality of branched optical fiber transmission lines branched from the main optical fiber transmission line,
The OTDR device or the light source is connected to the main optical fiber transmission line,
Each of the plurality of optical fiber sensors is connected to the main optical fiber transmission line via the branch optical fiber transmission line.

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