JPH1163939A - Displacement detecting method and device with optical fiber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a displacement detecting method and device which can simplify the structure of a sensor and its measuring system and can check various micro-displacements stably. SOLUTION: This device is provided with a gauge base 113, the first and second ferrules 111 and 112 which are fixed, separated respectively at a prescribed interval each other along the lengthwise direction of the gauge base 113, the first optical fiber 101 fixed on the first ferrule 111, and the second optical fiber 102 fixed on the second ferrule 112. The first and second optical fibers 101 and 102 are connected so that an end surface interval di of them may change with a displacement along the lengthwise direction of the gauge base 113 inside the first ferrule 111.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for detecting a displacement using an optical fiber, and more particularly to a method and an apparatus for detecting a displacement using a connection loss between optical fibers.

[0002]

2. Description of the Related Art Optical fibers have extremely low transmission loss, and are excellent in temperature fluctuation, insulation resistance and electromagnetic induction resistance, and, above all, are thin and lightweight. Therefore, optical fiber sensors for detecting displacement in aircraft and transportation equipment. It is also expected to be used as an optical interference type vibration sensor in fields such as vibration monitoring of buildings. As a sensor or a pressure (displacement) detection method using an optical fiber, a strain sensor combining an optical interferometer and an optical fiber, a pressure (displacement) detection method using a bending loss of the optical fiber, and the like have been devised.

A strain sensor that combines an optical interferometer and an optical fiber interferes with each other when two or more lights reflected at a branch or a different place interfere with each other due to a phase shift caused by an optical path difference between the lights. The displacement / strain corresponding to the magnitude of the optical path difference is detected using the characteristics appearing in the above.

On the other hand, a pressure (displacement) detection method using the bending loss of an optical fiber is, for example, a method using a bent optical fiber and detecting the pressure (displacement) from a change in the amount of transmitted light due to a change in the radius of curvature of the optical fiber. I do. That is, in the optical fiber, the loss of the amount of transmitted light varies depending on the radius of curvature. For a radius of curvature where a certain loss occurs, the loss increases as the radius of curvature decreases, and decreases as the radius of curvature increases. A strain sensor using a bent optical fiber uses this principle to change the radius of curvature by the pressure applied to the sensor and detect pressure (displacement) from a change in the amount of transmitted light.

[0005]

In the conventional sensor and pressure (displacement) detection method using the optical fiber described above,
Those that use light coherence are highly sensitive, but require precise alignment of the optical fiber, for example, and it is difficult to measure displacement corresponding to bending or torsion other than the axial direction of the fiber due to the restrictions. Met. Further, there is a problem that the system becomes complicated as a whole.

On the other hand, the above-mentioned method using the bending loss of the optical fiber changes the radius of curvature by applying a force to the bent portion of the optical fiber, and detects the pressure (displacement) applied to the bent portion from the change in the amount of transmitted light. Therefore, there is a problem that the radius of curvature of the bent portion that can be created cannot be reduced so much that only an average value in a wide area can be detected, and that it is difficult to reproduce the creation of the same bent portion. In addition, if the optical fiber is used too much, the optical fiber is damaged and accurate measurement becomes impossible.

[0007] From such a technical background, there is a demand for a displacement detection method and apparatus (sensor) using an optical fiber in which the structure of the sensor and the measurement system thereof are simple or in which a minute displacement can be stably confirmed. .

It is an object of the present invention to provide a displacement detection method and apparatus using an optical fiber which allows a simple structure of a sensor and a measurement system thereof and enables a small displacement to be stably confirmed.

[0009]

In order to achieve the above object, a method and an apparatus for detecting displacement according to the present invention provide a method for detecting a connection loss of an optical fiber (caused by a physical cause generated when a fiber is connected to another fiber). ) Is used to measure the minute displacement.

That is, according to the displacement detecting method using the optical fiber according to the first aspect, the sensing section having the first and second optical fibers connected so that the connection loss changes with the displacement of the connecting section. And a light incident part for receiving light from the non-connection end side of the first optical fiber, and a light quantity measurement part for measuring the light quantity emitted from the non-connection end side of the second optical fiber, Light is incident on the first optical fiber from the light incident part, and based on a change in connection loss caused by displacement of the connection part in the sensing part, the light quantity measurement part is configured to detect the non-connection end of the second optical fiber. A change in the amount of light emitted from the side is detected, and a displacement of the connection unit in the sensing unit is calculated using the change in the amount of light.

[0011] The displacement of the connecting portion may be an axis shift between the first and second optical fibers.

[0012] The displacement of the connecting portion may be an angular displacement between the first and second optical fibers.

[0013] The displacement of the connecting portion may be a change in the interval between the end faces of the first and second optical fibers.

Further, in the displacement detecting method using an optical fiber according to the present invention, a plurality of sensing units are connected in series or in parallel to measure a displacement at multiple points.

Further, in the displacement detecting apparatus using an optical fiber according to the present invention, the first member and the first member fixed to the base member at predetermined intervals along the length direction of the base member. A first optical fiber fixed to the first support, a second optical fiber fixed to the second support, and the first and second optical fibers fixed to the second support.
The optical fibers are connected inside the first or second support so that the mutual end face distance changes with displacement along the length direction of the base member.

On the other hand, in the displacement detecting device using an optical fiber according to the present invention, the first and the second fixed members are fixed at a predetermined distance from each other in one direction of the base member. A second optical fiber fixed to the second support, a first optical fiber fixed to the first support, and a second optical fiber fixed to the second support. The fibers are connected to each other at a space between the first and second supports so that an angle shift loss changes with bending of the base member.

Further, in the displacement detecting device using the optical fiber according to the present invention, the first member fixed to the base member and separated from each other by a predetermined distance along a predetermined direction of the base member. And a second support, a first optical fiber fixed to the first support, and a second optical fiber fixed to the second support, wherein the first and second optical fibers are fixed. In the optical fiber, the axial displacement loss changes as a shear strain is generated in the base member along a direction orthogonal to the predetermined direction at a space between the first and second supports. As described above.

[0018]

Embodiments of the present invention will be described below in detail with reference to the drawings.

First Embodiment: Small Displacement Due to Axis Loss First, a displacement detection method using an optical fiber according to a first embodiment of the present invention will be described. FIG. 1 shows a basic configuration of an apparatus used for the displacement detection method of the present embodiment.

The displacement detecting device used in this embodiment is shown in FIG.
As shown in FIG. 2, the first and second optical fibers 101 and 102 are connected to each other, the light source 103 to which the other end of the first optical fiber 101 is connected, and the second optical fiber 1.
02 is connected to the light source unit 103, one end is connected to the light source unit 103, and the other end is connected to the light amount measurement unit 104.
And a third optical fiber 105 for dummy connected to the third optical fiber 105. In the figure, the part in the circle indicated by 106 is the first part.
And a sensing unit configured by a connection unit of the second optical fibers 101 and 102. The third optical fiber 105 is used as reference light when the temperature of the sensor is compensated. In the present embodiment, the first optical fiber 1
The configuration is such that the mode field radii w1 and w2 of the first optical fiber 102 and the second optical fiber 102 are equal, and w1 = w2 = w.

First, the present inventor can confirm the stable loss change with reproducibility that can be used as a strain sensor for the correlation between the connection loss of a single mode optical fiber and the minute displacement of the optical fiber. An experiment was performed. The measuring device used in the experiment measures the loss of transmitted light intensity in various connection states of the optical fiber. FIG. 2 shows the configuration of the measuring device. Two optical fibers (first and second optical fibers 101) cut by a fiber cutter
And 102) are fixed and opposed to the V-groove provided in the fiber holder unit 110, and the fiber holder unit 1
A micro displacement was given with a resolution of 0.5 μm by a micrometer head attached to the micrometer. The connection loss of the optical fiber is a stabilized light source [output -3 dBm, wavelength 1.31.
μm] (light source unit 103) and an optical power meter (light amount measurement unit 104). The loss was recorded as a relative value based on the fiber position showing the lowest loss value.
In the experiment, a single mode optical fiber was used. The core radius a and the normalized frequency V of this fiber are represented by NA, NA,
If the free space wavelength is λ and the cutoff wavelength is λce, the following equations (1) and (2) are obtained.

(Equation 1)

(Equation 2) Equation (3), which is a known empirical equation proposed by Marcus

(Equation 3) Is used, the mode field radius W becomes 6.55 [μ
m].

The present embodiment relates to a displacement detecting device utilizing the loss of the optical fiber's axis shift. The axis shift loss refers to the shift d of the optical fiber as shown in FIG. Is the transmission loss caused by the According to the above-mentioned Marcus, the off-axis loss L of two fibers having different mode field radii w1 and w2.
[DB] is given by the following equation (4) when the axis shift amount is d.

(Equation 4) As described above, in the present embodiment, two optical fibers (the first and second optical fibers 101 and 102) are configured such that the mode field radii are equal and w1 = w2 = w. Therefore, the above equation (4) can be rewritten as the following equation (5).

(Equation 5)

In the experiment described above, the amount of axial deviation (d shown in FIG. 3) of the optical fiber was changed from 0 μm to 10 μm, and how the connection loss changed with respect to the amount was examined. FIG. 4 shows the results. FIG. 4 also shows the theoretical value of connection loss obtained from the above equation (5). FIG. 4 shows that the connection loss monotonically increases. In FIG. 4, the reason why the measured value is slightly larger than the theoretical value is considered to be that the interval between the end faces of the fiber was not completely zero. Therefore, it is desirable to make the end face interval of the fiber as 0 as possible and to carry out the smoothing of the end face of the fiber. Variations in the individual measured values in FIG. 4 are considered to be caused by errors in optical axis alignment in the initial state. FIG. 5 shows only the measured values □ and ◇ of FIG. 4 translated in the y direction by 0.5 μm. It can be seen that the measurements agree very well. This means that if the optical axis can be accurately aligned in the initial state, the measured values can be matched very well. Therefore, if the optical axis can be accurately aligned in the initial state, sufficient reproducibility for use as a sensor is obtained.
This shows that the relationship between the connection loss and the amount of axis deviation can be obtained. From FIG. 5, it is preferable to use about 4 μm (−3 dB) as a reference when the attenuation is actually used as a strain sensor. That is, the connection loss of the transmitted light intensity increases monotonously as the amount of axis deviation of the optical fiber increases, and when the displacement is between 4 μm and 10 μm, a linear relationship can be approximated between the two. Therefore, it is possible to provide an axis shift amount of 4 μm in advance at the initial optical axis alignment stage and use it as a strain gauge.

[Second Embodiment: Small Displacement Due to Angle Displacement Loss] Next, a displacement detection method using an optical fiber according to a second embodiment of the present invention will be described. The basic configuration of the device used in the displacement detection method according to the present embodiment is substantially the same as the displacement detection device shown in FIG. 1, and a description thereof will be omitted.

In the second embodiment, of the connection loss between the first and second optical fibers 101 and 102 (see FIG. 1), a minute displacement is detected by an angle shift loss. Angle shift loss is when connecting an optical fiber.
This is a transmission loss caused by an angle shift θ of the optical fiber as shown in FIG. According to the above-described Marcus, the angle shift loss L [dB] of two fibers having different mode field radii w1 and w2 is given by the following equation (6) when the amount of angle shift is θ [rad]. Can be

(Equation 6) Also in the present embodiment, the mode field radii of the two optical fibers (the first and second optical fibers 101 and 102) are equal, and w1 = w2 = w.
Therefore, the above equation (6) can be rewritten as the following equation (7).

(Equation 7)

In the present embodiment, the angle shift amount of the optical fiber (θ shown in FIG. 6) is changed from 0 ° to 0.189 °, and how the connection loss changes with respect to it is examined. . FIG. 7 shows the result. FIG. 7 also shows the theoretical value of the connection loss obtained from the above equation (7). It can be seen from FIG. 7 that the splice loss is measured at a great distance from the theoretical value. FIG. 8 shows only the theoretical values. The difference between the experimental value and the theoretical value is that the angle adjustment axis of the fiber holder unit used this time is an inner tilt type as shown in FIG. 9, and the rotation axis is 10 mm from the end face of the fiber cutting section.
It is thought that this occurred because the displacement of the end face was enlarged as compared with the case where the fiber was displaced around the rotation axis on the fiber end face assumed by the theoretical formula, because it was present on the near side (see FIG. 9). ). That is, as a phenomenon, it is conceivable that the axial misalignment loss occurs more than the angular misalignment loss. Now, assuming that the angle shift loss is L _{ANG ′ and the} axis shift loss is L _TRAN, it is assumed that the total loss L _H is represented by a linear sum of L _ANG and L _TRAN as in the following equation (8). ,

(Equation 8) Since L _ANG << L _TRAN , it can be approximated as in the following equation (9).

(Equation 9)

In FIG. 9, if the length of the fiber protruding from the turntable 91 is 5 mm, the distance from the center of rotation to the fiber end face is 9 mm, and the displacement d in the axis shift direction of the fiber end face when the angle shift is θ. [Mm] is
It can be expressed as the following equation (10).

(Equation 10) Therefore, using the equations (10) and (5), the equation (9) can be rewritten into the following equation (11).

[Equation 11]

Here, FIG. 10 shows the result of examining how the angle shift amount of the optical fiber is changed from 0 ° to 0.189 ° and how the connection loss changes with respect to it. FIG. 10 also shows the theoretical values of the total loss obtained from the above equation (11). From FIG. 10, the connection loss was measured in good agreement with the theoretical value until the angle shift amount was around 0.06 °, and it can be seen that the axial shift loss has a large effect.
The reason why the connection loss is measured to be smaller than the theoretical value after the angle shift amount is 0.06 ° or more is considered to be because the influence of the axial shift loss decreases as the angle shift amount increases. Therefore, in this measurement, it was not possible to confirm the relationship between the splice loss change and the angle shift amount due to only the angle shift, but even if the angle shift and the axis shift were combined, the splice loss and the small displacement of the optical fiber could not be confirmed. It was confirmed that the correlation showed a reproducible linear slope that could be used as a strain sensor.

[Third Embodiment: Small Displacement Due to End-Spacing Loss] Next, a displacement detection method using an optical fiber according to a third embodiment of the present invention will be described. The basic configuration of the device used for the displacement detection method of the present embodiment is also substantially the same as that of the displacement detection device shown in FIG. 1, and a description thereof will be omitted.

In the third embodiment, of the connection loss between the first and second optical fibers 101 and 102 (see FIG. 1), a minute displacement is detected based on a loss between end faces. The end-face spacing loss is a transmission loss caused by a displacement d of the connection end faces between the optical fibers as shown in FIG. 11 when connecting the optical fibers. Ma mentioned above
According to rcus, the end face spacing loss L [dB] of two fibers having different mode field radii w1 and w2 is given by the following equation (12) when the end face spacing is d.

(Equation 12) Here, Z is a normalized end face interval given by the following equation (13).

(Equation 13) (13) In the equation, _{n 2} is the refractive index of the fiber cladding, k represents the wave number (= 2π / λ). Also in this embodiment,
The mode field radii of the two optical fibers (first and second optical fibers 101 and 102) are equal and w1 = w
It is configured so that 2 = w. Therefore, (1)
Equation (2) can be rewritten as equation (14) below.

[Equation 14]

In the present embodiment, the distance between the end faces of the optical fiber (d shown in FIG. 11) was changed from 0 mm to 5.5 mm, and how the connection loss changes with respect to the distance was examined. FIG. 12 shows the result. FIG.
The theoretical value of the connection loss obtained from the above equation (14) is also shown therein. As shown in FIG. 12, the measurement results were in good agreement with the theoretical formula, and the reproducibility of replacing the fiber itself was also confirmed. Next, set the end face interval from 0 mm to 1 m
m, and how the connection loss changes with respect to it. The result is shown in FIG. Also,
FIG. 13 also shows the theoretical value of the connection loss obtained from the above equation (14). From FIG. 13, it can be seen that the end face spacing loss is measured larger than the theoretical value. This is considered to be caused by mismatching and local deformation of the end face of the optical fiber, an error in initial optical axis alignment, and the like.

If the correlation between the end face spacing and the connection loss is actually used as a strain gauge, the fiber must be fixed with high precision. Then, the end face spacing loss when the optical fiber was guided by the ferrule, which is a component of the FC connector that is frequently used for connecting the optical fiber to the measuring equipment, was also examined by experiments. The ferrule made of zirconia used in this experiment is shown in FIG. The ferrule shown in FIG. 14 has φ1 = 0.25 mm, φ2 = 2.0 mm, φ3
= 0.125 mm, φ4 = 0.126 mm, and the ferrule length FL = 10 mm. FIG. 15 shows the results of examining how the end loss of the optical fiber was changed from 0 mm to 1 mm and how the connection loss changes with respect to this.
Shown in FIG. 15 also shows the theoretical value of the connection loss obtained from the above equation (14). From FIG. 15, it can be seen that both the measurement result and the theoretical value are decreasing and show the same tendency, but the measured value is generally lower than the theoretical formula. This is presumably because the fiber has a slight inclination inside the ferrule due to a difference of 1 μm between the inner diameter of the ferrule and the cladding diameter of the fiber, and as a result, an axial deviation and an angular deviation also occur. It is understood that the measured values vary. In FIG. 15, the end face spacing is 0.8 m.
In the vicinity of m, the change in the connection loss tends to change. This is because the reflection of light inside the ferrule becomes appropriate for the inclination of the fiber near the end face spacing of 0.8 mm, and as a result, the loss is reduced, or the minute displacement due to the backlash of the adjusting screw of the fiber unit is reduced. Errors are possible. In order to compare the case where the ferrule is used and the case where the ferrule is not used, measured values in each case are shown in FIG. 16 together with theoretical values. According to FIG. 16, when the ferrule is used, the measured value is closer to the theoretical value until the end face interval is around 0.5 mm than when the ferrule is not used, but after the end face interval exceeds 0.5 mm, The measured value when the ferrule is not used is closer to the theoretical value. This is considered to be because the influence of the inclination and the like occurring inside the ferrule increases as the end face interval increases. As described above, in the present embodiment, the connection loss of the transmitted light intensity increases monotonically as the end face interval of the optical fiber increases, and the displacement is 0.4 mm when the ferrule is not used.
It was found that the linear relationship between the two could be approximated between 1 mm and 1 mm, and the linear relationship could be approximated between the two when the displacement was between 0.1 mm and 0.5 mm when a ferrule was used.

In the first to third embodiments described above, an arbitrary minute displacement is applied to the connection portion of the optical fiber in order to examine various methods for measuring the minute displacement using the connection loss of the optical fiber. The loss of transmitted light intensity was examined. As a result, if the offset in optical axis alignment can be corrected, the relationship between the small displacement of the optical fiber and the connection loss has high reproducibility, and the small displacement measurement using the connection loss of the optical fiber is used for the strain gauge. It seemed possible.

[0034]

Embodiments of the present invention will be described below in detail with reference to the drawings.

[First to Fourth Embodiments: Application to Strain Gauge]

First Example (Measurement of Longitudinal Strain) This example is a strain gauge for measuring longitudinal strain using the end face spacing loss of the optical fiber (the third embodiment). FIG. 17 shows a conceptual diagram of this strain gauge. This strain gauge includes a first ferrule 111, a second ferrule 112, a first optical fiber 101, a second optical fiber 102, and a gauge base 113. First
The first ferrule 111 and the first optical fiber 101 are bonded to each other, and the second ferrule 112 and the second optical fiber 102 are bonded to each other, and the first and second optical fibers 101 and 102 are formed inside the first ferrule 111. Is changed. The first and second ferrules 111 and 112 have a gauge length of G.S. L. It is adhered to the gauge base 113 so that Now, for example, when the elastic strain of 0.2% (ε = 0.002) is applied to G.A. L. = 15mm
Consider measuring with. Since the end face interval change amount d of the optical fiber is expressed by the following equation (15),

(Equation 15) d = 0.002 × 15 = 0.03 [mm]. FIG.
6, the measured value can be approximated to a straight line by di = 0.1 mm
From 0.5 mm, and in this range, the amount of change in transmitted light intensity corresponding to d = 0.03 mm is 0.6 dB.
This displacement can be measured sufficiently. Therefore, if the strain gauge shown in FIG. 17 is manufactured in a state where the end face interval di of the optical fiber is given from 0.1 mm to 0.5 mm in advance,
It can be used as a strain gauge.

Second Embodiment (Measurement of Shear Strain) This embodiment is a strain gauge for measuring a shear strain using the end face spacing loss of an optical fiber (the third embodiment). FIG. 18 shows a conceptual diagram of this strain gauge. FIG.
As shown in FIG. 8, in order to measure shear strain, a strain gauge (see FIG. 17) used for measuring longitudinal strain was used.
Put the book in parallel. L. May be made equal to each other and adhered to the surface of the object to be measured. As shown in FIG. 18, the parallel interval between the two gauges is t, and the displacement of the end face interval is d1 and d, respectively.
Assuming that 2, the shear strain γ is given by the following equation (16).

(Equation 16) Now, for example, a shear strain of 0.5% (γ = 0.005)
To G. L. = 15 mm and t = 10 mm. The difference d1-d2 between the end face spacing displacements of the optical fiber is (1
From equation (6), d1−d2 = γt = 0.005 × 10 = 0.
05 [mm]. Therefore, d1 and d2 are set to 0.0
If it can be measured in the order of 1 mm, it is possible to sufficiently measure the shear strain. From FIG. 16, the measured value can be approximated to a straight line from di = 0.1 mm to 0.5 mm.
Variation of the transmitted light intensities corresponding to ₁ of 0.10mm to 0.15mm is sufficient measurable 1.0dB next. Therefore, the end face distance di of the optical fiber is set to 0.1 m in advance.
If the strain gauge shown in FIG. 18 is manufactured in a state where 0.5 mm is given from m, it is possible to measure the shear strain.

Third Embodiment (Measurement of Bending Moment) In this embodiment, a strain gauge capable of measuring a bending moment applied to a beam or a flat plate by using the angle shift loss of the optical fiber (the second embodiment). It is. FIG. 19 shows a conceptual diagram of this strain gauge. Now, any two points P.D. on the center axis of the bend as shown in FIG. Assuming that the angles formed by the tangent line at Q with the positive direction of the X-axis of the rectangular coordinate system are θ _P and θ _Q , the central angle dθ that gives the arc PQ is dθ = θ _P + θ.
_The radius of curvature that gives the arc PQ is ρ, P
Assuming that the distance between Q is ds, the following equation (17) is established.

[Equation 17] Further, between the curvature ρ and the bending moment M, assuming a longitudinal elastic modulus E of the beam and a second moment of area I, the following (1)
8) There is a relation of the expression.

(Equation 18) From the equations (17) and (18), the bending moment M is obtained by the following equation (19).

[Equation 19] Therefore, the angle shift amount θ _p can be calculated from the angle shift loss of the optical fiber.
By measuring + θ _Q (= dθ), the moment M can be obtained from the equation (19).

Fourth Embodiment (Measurement of Torsional Moment) In this embodiment, a strain gauge capable of measuring a torsional moment applied to an axis is manufactured by using the loss of axial deviation of an optical fiber (the first embodiment). did. FIG. 21 shows a conceptual diagram of this strain gauge. Now, on an axis as shown in FIG. 22 where the radius is r and the axis length is L, the helical strain γ with the torsion angle φ is expressed by the following equation (20).

(Equation 20) Here, the torsion angle θ per unit length is expressed by the following equation (21) using the equation (20).

(Equation 21) The shear stress τ on the shaft surface is determined by the following equation (22), where G is the transverse elastic modulus and Ip is the second moment of area pole with respect to the shaft center.

(Equation 22) Then, the torsional moment T is obtained by the following equation (23).

(Equation 23) Therefore, rdφ is determined by measuring the amount of axis deviation from the axis deviation loss of the optical fiber, and (20), (21), (2)
From Equations 2) and (23), any of γ, θ, τ, and T can be measured.

Fifth Embodiment: Multipoint Measurement (Line Sensor)
Application to Multiplicity] By connecting a plurality of displacement detectors using the connection loss of the optical fiber described above in series or in parallel, multipoint measurement of displacement can be performed.

FIG. 23 shows a sensing device in a series connection, in which a band-pass filter (BPF),
High-pass filter (HPF), low-pass filter (LP
F) is an optical coupler C, which is a combination as shown in the figure, wherein L indicates a connection loss portion of the optical fiber. In the sensing device of the present embodiment, λ1 <λ2, and the light having a wavelength between λ1 and λ2 is
Light having a wavelength shorter than λ1 is applied to the PF, and wavelength λ is applied to the LPF.
Those that let light longer than 2 pass were chosen. Now, when light having a wavelength λ is input from a in the figure, if λ1 <λ <λ2, the light proceeds as a → b → d → h in the figure, and the displacement amount at L can be detected as a connection loss. . Otherwise, λ <λ
If 1, the light travels a → c → e → g → h and λ> λ2
In this case, the light travels in the order of a → c → f → g → h, so that the influence of L does not appear.

In such a sensing device,
The characteristic of each filter is defined as (wavelength that can pass through BPF1) <(wavelength that can pass through BPF2) <
(Wavelength that can pass through BPF3), and connecting them in series to form a line sensor is shown in FIG.
It is. Light having a wavelength that can pass through the BPF1 emitted from the light source travels in the order of BPF1, HPF2, and HPF3, and is detected by the optical power detection unit. Similarly, light having a wavelength that can pass through the BPF 2 travels in the order of LPF 1 → BPF 2 → HPF 3,
3 can pass through LPF1 → LPF2 → BP
Proceeding to F3, it is detected by the optical power detection unit. Thus, by changing the wavelength of the light to be measured, the connection losses L1 to L3 at each sensing device can be measured independently.

On the other hand, as shown in FIG. 25, it is also possible to perform multipoint measurement by connecting a BPF in series with a displacement detection portion L and selecting a transmission wavelength of each BPF separately. In this case, the light emitted from the light source is changed from BPF1 to BPF4 according to the wavelength.
Pass through only one of them, and is detected by the optical power detector. Therefore, by changing the measurement wavelength, the connection losses L1 to L4 can be measured independently.

As described above, according to the present embodiment, a plurality of displacement detectors using the connection loss of the optical fiber are connected to the BPF,
HPF. By combining the LPF and the optical coupler C and connecting them in series or in parallel, a line sensor capable of measuring displacement at multiple points can be configured.

[0045]

As is apparent from the above description,
According to the present invention, the minute displacement is measured using the connection loss of the optical fiber, so the structure of the sensor and its measurement system are simple and the displacement detecting method can stably confirm various minute displacements. And an apparatus can be provided.

As described above, various small displacements can be stably confirmed using an optical fiber having characteristics such as non-induction, explosion proof and corrosion resistance, while having a simple structure. , Long-term online measurement, strain measurement in linear motor cars, transmission lines, generators, etc.
A displacement detection method and apparatus suitable for use in a measurement under a strong electromagnetic field noise environment, a measurement under a lightning strike environment, and the like are obtained, and their industrial value is great.

[Brief description of the drawings]

FIG. 1 is a diagram showing a basic configuration of a displacement detection method and device according to an embodiment of the present invention.

FIG. 2 is a diagram for explaining a configuration of a measuring apparatus used in an experiment on a correlation between a connection loss of an optical fiber and a minute displacement.

FIG. 3 is a diagram for explaining axis shift loss of an optical fiber.

FIG. 4 is a diagram illustrating a relationship between an axial deviation amount of an optical fiber and a connection loss.

FIG. 5 is a diagram after correcting data indicating a relationship between an axial deviation amount and a connection loss of the optical fiber of FIG. 4;

FIG. 6 is a diagram for explaining an angle shift loss of an optical fiber.

FIG. 7 is a diagram illustrating a relationship between an angle shift amount of an optical fiber and a connection loss.

8 is a diagram showing only theoretical values of the relationship between the angle shift amount and the connection loss of the optical fiber of FIG. 7;

FIG. 9 is a diagram illustrating a configuration of a fiber holder unit according to a second embodiment of the present invention.

FIG. 10 is a diagram illustrating a relationship between an angle shift amount of an optical fiber and a connection loss in the configuration of the fiber holder unit illustrated in FIG. 9;

FIG. 11 is a diagram for explaining an end face spacing loss of an optical fiber.

FIG. 12 shows an end face interval of an optical fiber (0 mm to 5.5 m).
It is a figure which shows the relationship between m) and connection loss.

FIG. 13: End face spacing of optical fiber (0 mm to 1 mm)
FIG. 4 is a diagram showing a relationship between the connection loss and the connection loss.

FIG. 14 is a diagram showing a configuration of a ferrule according to the embodiment of the present invention.

FIG. 15 is a diagram showing a relationship between an end face interval (0 mm to 1 mm) of an optical fiber and a connection loss when a ferrule is used.

FIG. 16 is a diagram for comparing a relationship between an end face interval (0 mm to 1 mm) of an optical fiber and a connection loss when a ferrule is used and when a ferrule is not used.

FIG. 17 is a conceptual diagram of a strain gauge according to the first embodiment of the present invention.

FIG. 18 is a conceptual diagram of a strain gauge according to a second embodiment of the present invention.

FIG. 19 is a conceptual diagram of a strain gauge according to a third embodiment of the present invention.

FIG. 20 is a diagram showing a schematic configuration of a bending beam receiving a bending moment.

FIG. 21 is a conceptual diagram of a strain gauge according to a fourth embodiment of the present invention.

FIG. 22 is a diagram showing a schematic configuration of a shaft receiving a torsional moment.

FIG. 23 is a diagram illustrating a configuration of a sensing device of a line sensor according to a fifth embodiment of the present invention.

FIG. 24 is a diagram showing a multipoint measuring method by series connection in the fifth embodiment of the present invention.

FIG. 25 is a diagram illustrating a multipoint measuring method by parallel connection in the fifth embodiment of the present invention.

[Explanation of symbols]

 Reference Signs List 101 first optical fiber 102 second optical fiber 103 light source unit 104 light quantity measuring unit 106 sensing unit 111 first ferrule 112 second ferrule 113 gauge base

Claims (8)

[Claims] 1. A sensing unit having first and second optical fibers connected so that a connection loss changes according to displacement of a connecting unit, and light is incident from a non-connection end side of the first optical fiber. A light incident portion, and a light amount measuring portion for measuring a light amount emitted from the non-connection end side of the second optical fiber, light is incident on the first optical fiber from the light incident portion, Based on a change in connection loss due to displacement of the connection unit in the sensing unit, the light amount measurement unit detects a change in the light amount emitted from the non-connection end side of the second optical fiber, and detects the change in the light amount. A displacement detection method using an optical fiber, wherein the displacement of the connection part in the sensing part is calculated using the optical fiber. 2. The displacement detecting method according to claim 1, wherein the displacement of the connecting portion is an axis shift between the first and second optical fibers. The displacement detection method used. 3. The displacement detecting method according to claim 1, wherein the displacement of the connecting portion is an angular displacement between the first and second optical fibers. The displacement detection method used. 4. The method according to claim 1, wherein the displacement of the connecting portion is a change in a distance between end faces of the first and second optical fibers. A displacement detection method using a fiber. 5. A displacement detection method using an optical fiber according to claim 1, wherein a plurality of said sensing units are connected in series or in parallel to perform multipoint measurement of displacement. Displacement detection method using. 6. A base member, first and second supports fixed to each other at a predetermined distance from each other along a length direction of the base member, and fixed to the first support. A first optical fiber, and a second optical fiber fixed to the second support, wherein the first and second optical fibers are provided inside the first or second support. 3. The displacement detecting device using an optical fiber according to claim 1, wherein the end members are connected to each other such that a distance between the end surfaces thereof changes in accordance with a displacement along a length direction of the base member. 7. A base member, first and second supports respectively fixed at a predetermined distance from each other along one direction of the base member, and fixed to the first support. A first optical fiber, and a second optical fiber fixed to the second support, wherein the first and second optical fibers are disposed between the first and second supports. A displacement detecting device using an optical fiber, wherein the separated portions are connected to each other such that an angle shift loss changes with bending of the base member. 8. A base member, first and second supports fixed to each other at a predetermined distance from each other along a predetermined direction of the base member, and fixed to the first support. A first optical fiber, and a second optical fiber fixed to the second support, wherein the first and second optical fibers are located between the first and the second support. In the separated portion, an optical fiber characterized by being connected to each other such that the off-axis loss changes as shear strain occurs in the base member along a direction orthogonal to the predetermined direction. The displacement detector used.