JP3147616B2 - Distributed waveguide sensor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a distributed sensor using a waveguide such as an optical waveguide as a sensor, and more particularly, to a magnetic field applied to a waveguide based on a change in state of an electromagnetic wave propagating through the waveguide.
The present invention relates to a distributed waveguide sensor that can detect the position and type of occurrence of physical phenomena such as vibration, shock, and sound.

[0002]

2. Description of the Related Art The following various devices and methods have been proposed for detecting physical phenomena such as magnetic fields, vibrations, shocks, and sounds applied to a waveguide.

(A) A device that detects backward Raman scattered light generated in an optical fiber using the principle of an optical time domain reflectometer (OTDR) and measures the temperature distribution along the optical fiber (particularly, Kaihei 2-276932
issue).

(B) The change of the polarization plane generated in the optical fiber
Detection using OTDR method (POTDR, Polarization OTDR) (AJRogers, Polarization Optical Time Domai
n Re-flectometry, Electronics Letters 16, 13, 1980).

(C) Light of different frequencies is input to the polarization axes of two orthogonal polarization-maintaining optical fibers, and the output light is subjected to heterodyne detection to convert the polarization mode between the two polarization axes. There is a method for finding the position where the error occurs. Among them, those using backscattered light (F.Parvaneh et al, Freqency-Der
ived Distributed Optical-Fiber Sensing: A Heterodyn
ed Version and British Patent GB 2243908A) and those using forward waves (distributed optical fiber sensors using polarization-maintaining optical fibers, Tsubokawa et al., Optical Fiber Sensor Workshop of the Japan Society of Applied Physics, WOFS-4-4, 1987). There is.

(D) CW (Continuou) from one end of the optical fiber
(s Wave, continuous) Input the laser signal light, pulsed excitation light whose wavelength differs from the CW signal light by the Brillouin shift from the other end, and measure the time change of the CW light intensity at the pulse light incident end. Measurement of strain distribution along an optical fiber (Horiguchi et al., Strain distribution measurement of optical fiber by Brillouin spectroscopy, IEICE Transactions,
I, J73-BI, 2, 1990).

(E) Using an electric conductor such as an electric wire as a waveguide, and locating the occurrence position of a short circuit accident or the like occurring in the middle of the transmission line by using the arrival time difference of the electric surge measured at both ends of the transmission line. (Komaba et al., National Institute of Electrical Engineers of Japan 1992, NO.1445, including the development of a surge current receiving type fault locating device for ultra-high voltage underground transmission lines).

[0008]

However, the above-described apparatus and method have the following problems.

(A) In order to detect weak backward Raman scattered light of about 1/10 ⁸ of the incident light, it is necessary to perform averaging processing many times. Therefore, it is not possible to measure a temporally continuous physical quantity, and the physical phenomenon to be measured is limited to only the temperature.

(B) Since the backscattered light is detected by using the OTDR technique, a weak backscattered light of about 1/10 ⁵ of the incident light must be detected. For this reason, it is not possible to measure temporally continuous physical quantities as in (a). Also,
Since the change in the polarization plane is caused by various physical phenomena such as vibration, temperature, and magnetic field, it is difficult to specify the physical phenomenon only by measuring the change in the polarization plane discretely in time.

(C) A measurement system for performing heterodyne detection becomes complicated. Further, only expensive polarization-maintaining optical fibers can be used as the sensor optical fibers. Also,
In the method of detecting the forward light, it is possible in principle to detect a time change of a signal, but it is not considered to specify a physical phenomenon by waveform analysis.

(D) Since the Brillouin shift amount differs according to the magnitude of the distortion, it is necessary to repeat the measurement at the Brillouin shift wavelength of the type determined by the measurement dynamic range and the resolution, and the measurement takes time. Also,
The measurement object is limited to the strain of the optical fiber.

(E) It is effective against a large physical phenomenon in which an electric surge reaches both ends of the electric waveguide. However, this method is a method using an electric conductor functioning as a transmission line, and there is no particular effort to efficiently propagate the generated electric surge. On the other hand, the attenuation rate of the electric surge is large, and it cannot be used when the electric surge is attenuated halfway and cannot be observed at any end of the electric waveguide. In addition, since only the fault current of the transmission line is detected and cannot respond to other physical phenomena, it is sufficient to simply locate the fault occurrence position from the time difference at which the waveform change occurred. Could not identify the type of physical phenomenon.

An object of the present invention is to solve the above-mentioned problems and to detect, with a simple configuration, the type of physical phenomenon occurring in a waveguide such as an optical fiber and its occurrence position continuously in time. It is to provide a distributed waveguide sensor that can be used.

[0015]

According to the present invention, there is provided a distributed waveguide sensor for detecting a physical phenomenon acting on an arbitrary position of a waveguide. Detecting means for detecting two sets of electromagnetic waves whose states change and propagate in the waveguide as traveling waves, and analyzing the time relationship of the time change of the states of the two sets of electromagnetic waves detected by the detecting means, Signal recognition means for estimating the occurrence position of the phenomenon.

In order to achieve the above object, the present invention provides a distributed waveguide sensor for detecting a physical phenomenon acting on an arbitrary position of a waveguide.
Alternatively, the detecting means detects two sets of electromagnetic waves whose states change and propagates in the waveguide as traveling waves, and analyzes the frequency spectrum, duration and attenuation of the two sets of electromagnetic waves detected by the detecting means. Signal recognition means for estimating the type of physical phenomenon.

In order to achieve the above object, the present invention provides a distributed waveguide sensor for detecting a physical phenomenon acting on an arbitrary position of a waveguide.
Alternatively, detection means for detecting two sets of electromagnetic waves whose state changes and propagates as a traveling wave in the waveguide, and a time relationship of a time change of the two sets of electromagnetic waves detected by the detection means, a frequency spectrum, It is provided with signal recognition means for estimating the physical phenomenon occurrence position and its type by analyzing the duration and the attenuation state.

In order to achieve the above object, the present invention relates to a distributed waveguide sensor for detecting a physical phenomenon acting on an arbitrary position of a waveguide. A polarization beam splitter having the function of a photodetector, a light source and a light receiver connected so as to be coaxial with different polarization axes of the respective polarization beam splitters, and a position at which a physical phenomenon occurs based on information detected by the light receiver. It is an estimate.

In order to achieve the above object, the present invention relates to a distributed waveguide sensor for detecting a physical phenomenon acting on an arbitrary position of a waveguide, wherein continuous light is incident on an optical fiber for the sensor. The polarization state in the optical fiber changes when it is applied to the optical fiber, and by detecting this with a light receiver, the distance and time to the position where the physical phenomenon occurs is continuously detected. is there.

[0020]

According to the above construction, two sets of electromagnetic waves generated or changed in the waveguide due to physical phenomena and propagating as a traveling wave in the waveguide are detected, and the states of the detected two sets of electromagnetic waves are detected. Analyze the time relationship such as the difference in the time change start time and the waveform, etc. to estimate the occurrence position of physical phenomena, the time relationship of the time change of the detected two sets of electromagnetic waves, the frequency spectrum of the waveform, the continuation It analyzes the time and attenuation state to estimate the type of physical phenomenon. As described above, since the state of the waveguide is continuously monitored over time,
It is possible to estimate the instantaneous physical phenomena generated in the waveguide and the positions and types of the physical phenomena that occur continuously.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below in detail with reference to the accompanying drawings.

FIG. 1 is a conceptual diagram of one embodiment of the distributed waveguide sensor of the present invention.

In FIG. 1, reference numeral 1 denotes a sensor optical fiber as a waveguide, and optical splitters 21 and 22 are provided at both ends thereof.
Are connected respectively.

A light source 31 is connected to the input end of the optical splitter 21 via the connection optical fiber 11, and a light source 32 is connected to the input end of the optical splitter 22 via the connection optical fiber 12. . The light sources 31 and 32 have, for example, a constant output (C
A laser that oscillates the laser light of W) is used.

An optical receiver 41 as a detecting means is connected to the output end of the optical branching device 21 via the connecting optical fiber 13, and the optical receiver 41 receives the laser light emitted from the light source 32. And converts it into an electric signal. The output end of the optical splitter 22 is connected to an optical receiver 42 as a detecting means via the connecting optical fiber 14, and the optical receiver 42 receives the laser beam emitted from the light source 31 and It converts to a signal. That is, laser beams traveling in opposite directions always propagate through the optical fiber for sensor 1, and the optical receiver 41 changes the amount of the laser beam traveling to the left side of the figure in the optical fiber for sensor 1. Is continuously monitored over time, and the optical receiver 4
Numeral 2 can monitor a change in the amount of laser light traveling in the sensor optical fiber 1 to the right in the figure. Both optical receivers 41 and 42 use, for example, a photodiode or an avalanche photodiode as a photoelectric conversion element, and this output stage has an electronic circuit such as a current-voltage conversion circuit and an amplification circuit. The two optical receivers 41 and 42 are connected to received signal processing units 51 and 52, respectively.

The received signal processing unit 51 obtains the change start time of the waveform of the output signal from the optical receiver 41 by using a built-in signal level comparator (not shown) or the like.
Numeral 2 determines the change start time of the waveform of the output signal from the optical receiver 42 using a built-in signal level comparator (not shown) or the like. Both reception signal processing units 51 and 52
Are connected to the signal recognition unit 53.

The signal recognizing unit 53 analyzes a time relationship such as a difference between time points at which the output signal waveforms detected by the optical receivers 41 and 42 change with time, a waveform, and the like, and estimates a physical phenomenon occurrence position. The type of the physical phenomenon is estimated by analyzing the time relationship of the change of the output signal waveform detected by the optical receivers 41 and 42, the frequency spectrum of the waveform, the duration, the attenuation state, and the like. For example, the temperature changes relatively slowly and randomly, but the lightning current generally rises several μm.
Since the fall changes into a pulse shape of several tens of μsec in seconds, detection is made based on such a difference in waveform.

Here, the distance from the optical splitter 21 to the optical splitter 22 via the sensor optical fiber 1 is L0,
The propagation speed of light in the optical fiber for sensor 1 is represented by v, the origin of the distance along the optical fiber for sensor 1 is represented by an optical splitter 21, and the lengths of the connecting optical fibers 12 and 14 are respectively represented by L1.
2, L14.

At time t ₀ , a physical phenomenon (vibration, external force, temperature change, etc.) occurs at a point (hereinafter, point P) at a distance x on the sensor optical fiber 1, and an external force, for example, is instantaneously applied as a physical quantity. In this case, the transmission loss of the sensor optical fiber 1 at the point P (generated by the microbend loss) temporarily changes. As a result, the amount of laser light traveling in the sensor optical fiber 1 in the opposite direction changes, and this change propagates as it is in the sensor optical fiber 1 as a traveling wave (electromagnetic wave). It is assumed that a traveling wave propagating in the right direction in the drawing is a forward wave and a traveling wave propagating in the left direction in the drawing is a backward wave.

FIGS. 2 (a) and 2 (b) show temporal changes in the outputs of the optical receivers 41 and 42 with reference to the time t ₀ when an external force is applied.

FIGS. 2A and 2B are diagrams showing waveforms detected by the two optical receivers shown in FIG. In FIG. 7A, the vertical axis indicates the output of the optical receiver 42, and the horizontal axis indicates time. In FIG. 3B, the vertical axis indicates the output of the optical receiver 41, and the horizontal axis indicates time.

The output of the optical receiver 42 initially has a constant value y1
, But starts to fluctuate at time t ₁ . As described above, this fluctuation is caused by an external force applied to the point P of the sensor optical fiber 1 and the transmission loss at the point P changes, and indicates a forward wave. Thus the time difference t ₁₀ between the time t ₁ and time t ₀ is equal to the time which the light emitted from the light source 31 reaches the optical receiver 42 from the point P can be expressed as in equation 1.

[0033]

[Number 1] _{t 10 = t 1 -t 0 =} ((L0-x) + L14) / v Time starts varying (backward wave) of the output of the optical receiver 41 t
₂ and the time t ₀ the time difference t ₂₀ and also can be expressed as in equation 2 as well.

[0034]

T ₂₀ = t ₂ −t ₀ = (x + L13) / v Therefore, the distance x can be expressed as in the following equation (3).

[0035]

X = ((t ₂ −t ₁ ) × v + L0 + (L14−
L13)) Time t ₀ when an external force is applied to the sensor optical fiber 1.
Can also be expressed as Equation 4.

[0036]

T ₀ = t ₂ − (x + L13) / v In the signal recognition unit 53, the sensor optical fiber 1
The distance x to the point P to which the external force is applied is accurately obtained. If necessary, the signal recognizing unit 53 can also calculate the time t _{0 at} which an external force is applied to the sensor optical fiber 1 according to Equation 4. In the signal recognition unit 53,
It is determined whether or not the signals detected by the reception signal processing units 51 and 52 are due to the physical phenomenon to be detected based on the frequency spectrum distribution of the reception waveform, the decay time of the signal, and the like (ie, whether external force, vibration, temperature change, etc.). Estimating the type of physical phenomenon). If this determination can be made before obtaining the distance x and the time t ₀ , if the signals detected by the reception signal processing units 51 and 52 are not the detection targets, the position detection by the signal recognition unit 53 or the time detection Need not be performed.

Next, the operation of the embodiment will be described.

[0038] Two sets of electromagnetic waves generated by the physical phenomenon in the sensor optical fiber 1 and propagating in the sensor optical fiber 1 as a forward wave and a backward wave are detected, and the time change of the states of the detected two sets of electromagnetic waves is started. Estimate the location of physical phenomena by analyzing the time relationship such as the time difference and the waveform, etc., the time relationship of the time change of the state of two detected electromagnetic waves, the frequency spectrum of the waveform, the duration and the attenuation state Or the like to estimate the type of physical phenomenon. As described above, since the sensor optical fiber 1 is monitored continuously in time, the instantaneous physical phenomena occurring in the sensor optical fiber 1 and the occurrence positions and types of the continuous physical phenomena are estimated. be able to.

Next, another method for obtaining the point P at which the physical quantity is added to the sensor optical fiber 1 will be described below.

[0040] correlates with what the outputs of the light receiver 42 of the light receiver 41 is delayed n × δt (n = 1,2,3 ... ) for a time, the number 3 of t ₂ -t _The distance x is obtained by replacing ₁ with the time delay Δt having the highest correlation (t ₂ −
t ₁ = Δt). In this case, even if noise slightly overlaps the outputs of the optical receivers 41 and 42, the distance x can be accurately obtained without being affected by the noise. An artificial intelligence process such as a neural network may be used for the correlation process. In this case, the sensor optical fiber 1 may be either multi-mode or single-mode, but a single-mode fiber is more preferable in order to increase the distance resolution. The optical splitters 21 and 22 may have no wavelength dependency. However, when light sources having different wavelengths are used for the light sources 31 and 32, it is better to use one having a wavelength separation function in the optical splitter. Loss can be reduced.

FIG. 3 is a schematic view of another embodiment of the distributed waveguide sensor of the present invention.

The difference from the embodiment shown in FIG. 1 is that a change in the state of the polarization plane of light propagating in the optical fiber for sensor is used. Each two sets (41a, 41b and 42a, 4
2b) The two sets are connected to the outputs of the orthogonal polarization axes of the polarization beam splitters 61 and 62, respectively.

In general, the polarization plane of light propagating through a single-mode optical fiber such as a polarization-maintaining optical fiber has a magnetic field, pressure,
It changes with vibration and temperature. The present embodiment detects this change.

The light sources 31 and 32 have a linearly polarized light output, and the sensor optical fiber 1 is a single mode optical fiber. Among them, it is preferable to use an optical fiber having good polarization preserving characteristics.

Outputs of the optical receivers 41a and 41b are connected to a reception signal processing unit 51, and outputs of the optical receivers 42a and 42b are connected to a reception signal processing unit 52. Outputs of the reception signal processing units 51 and 52 are connected to a signal recognition unit 53. Time t ₀ to the optical receiver 41a when the physical quantity is applied instantaneously to the point P of the optical fiber for the sensor 1, 41
b, 42a and 42b are output waveforms shown in FIGS.
(D).

FIGS. 4A to 4D are diagrams showing the relationship between the output of the optical receiver shown in FIG. 3 and time.

6A to 6D, the vertical axis represents the output of the optical receiver, and the horizontal axis represents time.

The optical receiver 41a and the optical receiver 41b have outputs of polarization axes orthogonal to each other, and are output from time t ₀ to time t
Both up ₁ is substantially constant value has changed from the time t _1. The waveforms of these changing parts are different,
The change start time is the same. This means that the optical receiver 42
The same applies to the outputs a and b. Therefore, the time t ₁ is obtained from the average value of one or both of the output of the optical receiver 41a and the output of the optical receiver 41b, and one or both of the output of the optical receiver 42a and the output of the optical receiver 42b are obtained. The time t ₂ is obtained from the average value of the above, and the point P where the physical quantity is added to the sensor optical fiber 1 is obtained from Equations 3 and 4.
, And the time t ₀ can be estimated.

Further, the output of the light sources 31 and 32 fluctuates and the optical receivers 41a and 41a are caused by factors other than the phenomenon to be detected.
It is also conceivable that the outputs of b, 42a and 42b fluctuate. In such a case, the optical receivers 41a, 41b, 4
By using the outputs of 2a and 42b, for example, by using Equation 5 or Equation 6 and normalizing them by the sum of squares of the reception results of orthogonal polarizations, it is possible to avoid the influence of output fluctuation.

[0050]

## EQU5 ## Sij '= Sij / (√ (Sia ² + Si)
b ² )); i = 1, 2; j = a, b

[0051]

Sj '= Sij / (Sia ² + Sib ² );
i = 1, 2; j = a, b Next, a description will be given of a case where a physical phenomenon continuously occurring at an arbitrary point such as a leak sound of a gas pipe is detected.

Even a physical phenomenon that occurs continuously rarely continues in a completely constant state, and it is generally considered that the state always fluctuates. In such a case, FIG.
The waveform observed at both ends of the optical fiber for the sensor shown in as shown in FIG. 5, a waveform at a certain time t _10, it is almost the same shape when combining the waveform at a certain time t _20. Therefore, at times t ₁₀ and t ₂₀ at which the same shape is obtained.
Are obtained from the time lag at which the correlation calculation result of the two waveforms becomes maximum, and these times t ₁₀ and t ₂₀ are respectively calculated at the time t
By substituting ₁ and t ₂ , the occurrence position of a physical phenomenon that continuously occurs at an arbitrary point can be estimated.

FIG. 5 is an explanatory diagram for explaining waveform processing when applied to the distributed waveguide sensor shown in FIG. 1 for continuous physical phenomena.

Next, a case where physical phenomena occur simultaneously at two different points will be described.

FIGS. 6A and 6B are explanatory diagrams for explaining the waveform processing of the distributed waveguide sensor shown in FIG. 1 when a physical phenomenon occurs simultaneously at two different points. . 6A and 6B, the horizontal axis represents time, and the vertical axis represents the output of the optical receiver.

The waveforms at both ends of the sensor optical fiber 1 are as follows:
Since the order of receiving the physical phenomena at the two points is different, the waveforms do not have the same shape, and the waveform change start times t ₁₁ and t ₂₁ due to the physical phenomena generated at the point x ₁ (not shown) on the optical fiber. And point x ₂ on optical fiber (not shown)
Change start time t ₁₂ , t due to the physical phenomenon generated in
₂₂ are shown in FIGS. 6A and 6B, respectively.

Therefore, the correlation is obtained while shifting the time relationship between the two waveforms, and the time t is calculated from the time lag at which the correlation result becomes maximum.
_11, t _12, may be determined to t _21, t _22.

FIG. 7 is a schematic view of another embodiment of the distributed waveguide sensor of the present invention.

In the above-described embodiment, the method of performing measurement at both ends of one optical fiber for a sensor has been described. However, two optical fibers which are provided side by side and connected to each other at one end are used as optical fibers for a sensor. You can also.

In the figure, a light source 30 for generating continuous light is connected to one end (left side in the figure) of the sensor optical fiber 1a, and the other end of the sensor optical fiber 1a is provided alongside the sensor optical fiber 1a. At the same time, a sensor optical fiber 1b to which one end is connected is connected. The other end of the optical fiber for sensor 1b is connected via the polarizing beam splitter 60 in the direction in which the polarization outputs are orthogonal to each other.
b. Outputs of the light receivers 40a and 40b are connected to a reception signal processing unit 51. Received signal processing unit 5
The output of 1 is connected to the signal recognition unit 53.

When a magnetic field having a pulse width of about 1 μsec is applied to a point P at a distance x, two pulse waveforms are observed from the outputs of the photodetectors 40a and 40b as shown in FIGS. 8 (a) and 8 (b). You.

FIGS. 8A and 8B are explanatory diagrams of waveforms detected by the distributed waveguide sensor shown in FIG. In the figure, the horizontal axis represents time, and the vertical axis represents the output of the light receiver.

The relationship between the time difference δt ₁₂ between these two pulses and the distance x is expressed by equation (7).

[0064]

X = L ₀ −L ₁ where L1 = (δt ₁₂ × v) / 2 The position (distance) of the magnetic field applied to the sensor optical fibers 1a and 1b can be obtained from the expression (7). For processing such as waveform processing, the same method as in the above-described embodiment can be applied. This distributed waveguide sensor can detect physical phenomena occurring within a relatively short period of time, and can easily install a detection unit including the light source 30 and the light receivers 40a and 40b in one place. It is. The light source 30
And the light receivers 40a and 40b may be a single set, so that the size of the detection unit can be reduced.

Next, a case where a plurality of sensor optical fibers having different coupling lengths are used as the waveguide will be described.

The ease of change of the polarization state of the polarization-maintaining optical fiber is determined by its coupling length. Therefore, once the coupling length is determined, the detectable sensitivity and dynamic range are determined. Therefore, by using a plurality of polarization-maintaining optical fibers with different coupling lengths in parallel, high sensitivity,
In addition, detection in a wide dynamic range becomes possible.

Next, a multi-point distributed waveguide sensor will be described.

A plurality of insensitive waveguides are connected in series so as not to cause a change in the state of the propagation wave to be detected in response to a physical phenomenon, and a state change of the propagating wave in response to the physical phenomenon is provided between these insensitive waveguides. By inserting a sensor part such as a waveguide or a dedicated sensor that causes the above, a multi-point distributed waveguide sensor can be configured. For example, when detecting vibration, use a polarization-maintaining optical fiber whose coupling length is short and the polarization state does not easily change with vibration as the insensitive waveguide, and the coupling length is long and the sensor has a long coupling length against vibration. It is conceivable to use a polarization-maintaining single-mode fiber or a polarization-maintaining single-mode fiber in which the polarization state easily changes. In the case of the multipoint type, since the correlation process only needs to be performed with a time lag corresponding to the position of the sensor unit, the detection unit can be simplified.

FIG. 9 is a schematic view of another embodiment of the distributed waveguide sensor of the present invention.

The difference from the embodiment shown in FIG. 1 is that an electric conductor is used for the waveguide.

In this case, if a coaxial cable that can reduce transmission loss is used, a high-performance distributed waveguide sensor can be constructed.

In FIG. 9, the sensor coaxial cable 19
The DC power supply 33 and the receiver 43 are connected to one end (the left side in the figure) of the device via the branching device 29 and the connecting coaxial cable 19a. A receiver 44 is connected to the other end (right side in the figure) of the sensor coaxial cable 19. Outputs of the receivers 43 and 44 are connected to reception signal processing units 51 and 52, respectively, as in the above-described embodiment. Outputs of both reception signal processing units 51 and 52 are connected to a signal recognition unit 53.

When an external force is momentarily applied to the point P of the sensor coaxial cable 19, the impedance of the sensor coaxial cable 19 at that position changes and a pulse wave is generated. The generated pulse wave (traveling wave) starts propagating from point P toward both ends of the sensor coaxial cable 19. These two pulse waves (forward wave and backward wave) are received by the receivers 43 and 44 at both ends of the coaxial cable 19 for the sensor, and the processing described in the previous embodiments is performed. The point P (distance x) to which the external force is applied can be obtained.

As described above, the distributed waveguide sensor according to the present embodiment detects two sets of electromagnetic waves which are generated in the waveguide due to a physical phenomenon or whose state changes and propagate as a traveling wave in the waveguide. Analyze the time relationship, waveform, etc., such as the difference between the two sets of electromagnetic wave state time change start times, to estimate the location of occurrence of a physical phenomenon, or detect the time change of the detected two sets of electromagnetic wave states. Since the type of physical phenomenon is estimated by analyzing the relationship, the frequency spectrum of the waveform, the duration, the attenuation state, etc., the type and location of the physical phenomenon that has occurred in a waveguide such as an optical fiber with a simple configuration. Can be continuously detected in time.

FIG. 10 is a schematic view of another embodiment of the distributed waveguide sensor of the present invention.

The difference from the embodiment shown in FIG. 1 is that one polarizing beam splitter has the functions of one optical splitter and two polarizers. The same members as those of the distributed waveguide sensor shown in FIG. 1 are denoted by the same reference numerals.

In FIG. 10, polarization beam splitters 70 and 71 are used in place of the optical splitter. These polarization beam splitters 70 and 71 have an x-axis polarization output section for outputting polarization in the x-axis direction. , A y-axis polarization output unit that outputs polarizations in the y-axis direction, and a dual-axis output unit that outputs polarizations in both the x and y axes. The sensor optical fiber 1 is connected to the biaxial output units of the polarization beam splitters 70 and 71. The x-axis output of the polarizing beam splitter 70 is the connection optical fiber 1
1 is connected to the light source 31, and the x-axis output of the polarizing beam splitter 71 is connected to the light source 3 via the connection optical fiber 12.
2 are connected. The y-axis output of the polarization beam splitter 70 is connected to the optical receiver 41 via the connection optical fiber 13, and the y-axis output of the polarization beam splitter 71 is connected to the optical receiver 42 via the connection optical fiber 14. I have. Both optical receivers 41 and 42 include reception signal processing units 51 and 52
, And both received signal processing units 51 and 52 are connected to a signal recognition unit 53.

In such a configuration, since the polarizing beam splitters 70 and 71 have the function of one optical splitter and two polarizers, conventionally, one optical splitter and two polarizers are combined. Although two sets are required, only two (two sets) polarizing beam splitters are required. As a result, the number of parts can be reduced, and the adjustment of the optical axis is simplified.

Further, the polarization maintaining optical fiber 1a is used as the optical fiber for the sensor, and the polarization beam splitters 70 and 71 are arranged at both ends of the polarization maintaining optical fiber 1a along the x-axis.
May be connected so that the y-axis at both ends of the polarization-maintaining single-mode fiber 1a coincides with the y-axis of the polarization beam splitters 70 and 71. In this case, as shown in FIG. 11, the x-axis is connected to the x-axis of the polarization beam splitters 70 and 71 at both ends of the polarization-maintaining optical fiber 1a, and the y-axis is connected to the polarization beam splitter at both ends of the polarization-maintaining optical fiber 1a. 70 and 71 are connected so as to coincide with the y-axis.
FIG. 11 is a diagram showing a connection part of the optical fiber for a sensor shown in FIG. 10 to a polarization beam splitter.

With such a connection, when there is no disturbance, the light emitted from the light source 31 is
Light propagating in the x-axis direction in a and entering the polarization beam splitter 71 enters the optical receiver 42 with maximum efficiency. Conversely, light emitted from the light source 32 propagates in the polarization-maintaining optical fiber 1a in the y-axis direction and
The light input to 0 enters the optical receiver 41 with the maximum efficiency.

When an external force is applied to the polarization-maintaining optical fiber 1a used as the sensor optical fiber, distortion occurs in the polarization-maintaining optical fiber 1a, and the distortion shifts the polarization axes in the x-axis direction and the y-axis direction. Therefore, the outputs of the optical receivers 41 and 42 change in a decreasing direction.

If the polarization axis is insufficiently adjusted or not adjusted in such a distributed waveguide sensor, the output of the optical receivers 41 and 42 when there is no disturbance is not always the maximum value. Therefore, the output waveform of the optical receiver 41 and the output waveform of the optical receiver 42 may be different. In this case, an error may occur when a position where an external force is applied is obtained by correlation processing of both waveforms. In the worst case, the output of the optical receiver 41 (42) may become zero when no external force is applied,
In this case, it may be difficult to check whether the sensor system is functioning properly. Therefore, the adjustment of the polarization axis is indispensable. However, in the distributed waveguide sensor of this embodiment, adjustment is easy because the number of adjustment positions of the polarization axis is smaller than that in the related art.

As described above, in this embodiment, the number of parts is small, so that the number of steps for adjusting the polarization axis is reduced, and the adjustment is easy. Therefore, sufficient adjustment can be performed, and the cost can be reduced. Further, by using a polarization-maintaining optical fiber as the optical fiber for the sensor and optimizing and connecting the direction of the polarization axis, it is possible to improve the positioning accuracy and the reliability of the sensor system.

FIG. 12 is a partial schematic view of another embodiment of the distributed waveguide sensor of the present invention.

The difference from the embodiment shown in FIG. 1 is that the sound pressure or the like generated by a physical phenomenon is regarded as a change in the polarization state of the continuous light incident on the optical fiber, so that the longitudinal direction of the optical fiber is changed. This is a point in which physical quantities along the distance are measured continuously in terms of distance and time. The same members as those of the distributed waveguide sensor shown in FIG. 1 are denoted by the same reference numerals.

In FIG. 12, optical splitters 80 and 81 are connected to both ends of the sensor optical fiber 1, respectively. The light splitter 80 is connected to a polarizer 83 via a connection optical fiber 82, and the light source 31 is connected to the polarizer 83 via a connection optical fiber 84. Further, a polarizer 86 is connected to the optical splitter 80 via a connection optical fiber 85, and the optical receiver 41 is connected to the polarizer 86 via a connection optical fiber 87.

The light splitter 81 is connected to a polarizer 89 via a connection optical fiber 88, and the light source 32 is connected to the polarizer 89 via a connection optical fiber 90. Further, a polarizer 92 is connected to the optical branching device 81 via a connection optical fiber 91, and the connection optical fiber 9 is connected to the polarizer 92.
3, an optical receiver 42 is connected.

As the light sources 31 and 32, for example, CW oscillation lasers are used as in the embodiment shown in FIG.

The light emitted from the light source 31 and converted into linearly polarized light through the polarizer 83 enters the optical fiber for sensor 1 and propagates in the optical fiber for sensor 1 from left to right in FIG. The signal is photoelectrically converted by the receiver 42 and sent to an analyzer not shown.

At this time, suppose that a sound pressure generated due to a certain physical phenomenon, for example, a ground fault of a cable is applied to the point a of the optical fiber for sensor 1, and the time at this time is set to t = 0.

When sound pressure is applied to the sensor optical fiber 1,
The polarization state of the light propagating in the sensor optical fiber 1 changes. Then, the intensity of the light incident on the optical receivers 41 and 42 (the received light intensity I) is changed by the action of the polarizers 86 and 92 that select the light having the specific polarization axis. Further, due to the difference in the optical fiber length from the point a to the optical receivers 41 and 42, a time difference occurs until the two optical receivers 41 and 42 show a change in intensity as shown in FIG. FIG. 13 is a principle diagram for explaining position determination of the distributed waveguide sensor shown in FIG. In the figure, the horizontal axis indicates the time axis, and the vertical axis indicates the received light intensity.

Here, the length X (hereinafter referred to as fiber length) of the sensor optical fiber 1 is known, and the optical receiver 41,
The time difference of the waveform of the intensity change of the received light intensity I shown at 42 becomes known as the measurement result.

Assuming that the fiber lengths from point a to the optical receivers 41 and 42 are x ₁ and x ₂ , respectively, the delay of the received light signal at the optical receiver 42 is x ₂ / c, and the delay of the received light signal at the optical receiver 41 is x ₂ / c. The delay is x ₁ / c.

In the above, the fiber length X and the optical receiver 4
Regarding the time difference T between the signal waveforms at 1, 42,
Equation 9 holds.

[0095]

X = x ₁ + x ₂

[0096]

T = (x ₁ −x ₂ ) / c where c represents the speed of light in the optical fiber.

From equations 8 and 9, equations 10 and 11 are obtained.
The position of the point is determined.

[0098]

X ₁ = (X + cT) / 2

[0099]

X ₂ = (X−cT) / 2 In order to determine the coincidence of the signal waveforms in both optical receivers 41 and 42 (to obtain T), for example, the two optical receivers 41 and 42
What is necessary is just to take the correlation by the time delay of the output of 42, or use artificial intelligence processing, such as a neural network.

In this manner, sensing can be performed temporally continuously as described below. By laying the sensor optical fiber on the surface of the underground power cable or in the tunnel, the power cable can be monitored continuously in time. For example, a small ground fault in the power cable generates a sound wave of about 10 KHz to 100 KHz, which can be detected.

Further, by laying an optical fiber for a sensor in a building or a plant and constructing a system, it is also possible to apply the system as a security system.

In this embodiment, a laser is used as the light source. However, the present invention is not limited to this, and another type of light source such as a light emitting diode may be used. In the present embodiment, continuous light is used as light emitted from the light source. However, the present invention is not limited to this. Modulation may be performed at a constant period. In this case, a detection circuit that detects only that period is used. Are provided downstream of the optical receiver, respectively, so that the S / N ratio of detection can be improved.

[0103]

In summary, according to the present invention, the following excellent effects are exhibited.

(1) It is possible to detect ruptures, leaks, traumas, and the like of oil pipelines, gas pipes, water pipes, and the like.

(2) It is possible to detect a collapse of a railroad or a road, a landslide, or a train position.

(3) Accident detection of underground power cables, communication cables, etc. can be performed.

(4) It is possible to detect an accident of an overhead transmission line or galloping.

(5) Opening and closing of doors, windows, manhole covers and the like can be detected.

(6) An intruder can be monitored by laying a sensor optical fiber on the floor or the like.

(7) When a general distributed waveguide sensor is used, the positional relationship between the object to be measured and the sensor waveguide can be detected by, for example, hitting the sensor waveguide.

(8) Deterioration diagnosis of a structure can be performed by combining with a vibration source.

(9) It is possible to detect the position of a phenomenon in which fluorescent light is generated by disturbance in the sensor optical fiber.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram of one embodiment of a distributed waveguide sensor of the present invention.

FIG. 2 is a diagram showing waveforms detected by both optical receivers shown in FIG.

FIG. 3 is a schematic view of another embodiment of the distributed waveguide sensor of the present invention.

FIG. 4 is a diagram showing a relationship between output of the optical receiver shown in FIG. 3 and time.

FIG. 5 is an explanatory diagram for explaining waveform processing when applied to the distributed waveguide sensor shown in FIG. 1 for continuous physical phenomena.

6 is an explanatory diagram for explaining waveform processing of the distributed waveguide sensor shown in FIG. 1 when physical phenomena occur simultaneously at two different points.

FIG. 7 is a schematic view of another embodiment of the distributed waveguide sensor of the present invention.

8 is an explanatory diagram of a waveform detected by the distributed waveguide sensor shown in FIG.

FIG. 9 is a schematic view of another embodiment of the distributed waveguide sensor of the present invention.

FIG. 10 is a schematic view of another embodiment of the distributed waveguide sensor of the present invention.

11 is a diagram showing a connection portion of the optical fiber for a sensor shown in FIG. 10 to a polarization beam splitter.

FIG. 12 is a partial schematic view of another embodiment of the distributed waveguide sensor of the present invention.

FIG. 13 is a principle diagram of position locating of the distributed waveguide sensor shown in FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Waveguide (optical fiber for sensors) 41, 42 Optical receiver (detection means) 53 Signal recognition part (signal recognition means)

Continuation of the front page (72) Inventor Shigehiro Endo 5-1-1, Hidaka-cho, Hitachi City, Ibaraki Pref. Opto-System Laboratory, Hitachi Cable Ltd. (56) References JP-A-1-142717 (JP, A JP-A-2-98646 (JP, A) JP-A-61-170604 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01D 21/00 G01B 11/16 G01R 27 / 06 G01R 31/08

Claims (16)

(57) [Claims] In a distributed waveguide sensor for detecting a physical phenomenon acting on an arbitrary position of a waveguide, the waveguide is generated by a physical phenomenon or its state changes and propagates in the waveguide as a traveling wave. Detecting means for detecting two sets of electromagnetic waves, and signal recognizing means for estimating a position where a physical phenomenon occurs by analyzing a time relationship of a time change of states of the two sets of electromagnetic waves detected by the detecting means; A distributed waveguide sensor characterized by the following. 2. In a distributed waveguide sensor for detecting a physical phenomenon acting on an arbitrary position of a waveguide, the waveguide is generated as a result of a physical phenomenon or changes its state and propagates as a traveling wave in the waveguide. Detecting means for detecting two sets of electromagnetic waves, and signal recognizing means for analyzing the frequency spectrum, duration and attenuation state of the two sets of electromagnetic waves detected by the detecting means to estimate the type of physical phenomenon; A distributed waveguide sensor, characterized in that: 3. In a distributed waveguide sensor for detecting a physical phenomenon acting on an arbitrary position of a waveguide, the waveguide is generated by a physical phenomenon or changes its state and propagates in the waveguide as a traveling wave. Detecting means for detecting two sets of electromagnetic waves, and analyzing the time relationship, frequency spectrum, duration, and attenuation state of the two sets of electromagnetic waves detected by the detecting means with respect to time, and the location of occurrence of a physical phenomenon and its A distributed waveguide sensor, comprising: signal recognition means for estimating a type. 4. A method of detecting physical phenomena by analyzing a time change of two sets of electromagnetic waves generated or generated by a physical phenomenon in one waveguide or changing its state and propagating in both directions. The distributed waveguide sensor according to any one of claims 1 to 3, wherein: 5. A light source is connected to the other end of one of two waveguides that are provided side by side and connected to each other at one end,
Detecting means connected to the other end of the other waveguide for detecting two sets of electromagnetic waves which are generated in the two waveguides by a physical phenomenon or whose states change and propagate as traveling waves in each of the waveguides; 4. The distribution-type waveguide according to claim 1, wherein a physical phenomenon is detected by analyzing a time change of a state of the two sets of electromagnetic waves detected by the detection unit. Wave path sensor. 6. A physical quantity that causes a change in the state of the electromagnetic wave based on a time difference when the waveforms of the electromagnetic waves coincide with each other is obtained by shifting the correlation of the time-changed waveforms of the two sets of electromagnetic waves. The distributed waveguide sensor according to any one of claims 1 to 5, wherein the position added to (1) is estimated. 7. An electromagnetic wave propagating in both directions along the axis of the waveguide is received by different receivers at both ends of the waveguide. The distributed waveguide sensor according to any one of the above items. 8. The distributed waveguide sensor according to claim 1, further comprising an electromagnetic wave source at an end of the waveguide opposite to a receiver. 9. The signal recognizing means has a time delay function and a function of correlating time-varying waveforms of two sets of electromagnetic wave states, and an electromagnetic wave generated by a physical phenomenon acting on a plurality of points on the waveguide. 9. The method according to claim 1, wherein when processing is performed, the physical phenomena at a plurality of points are detected by using a delay time corresponding to each point in the time delay / correlation processing. Distributed waveguide sensor. 10. An optical fiber is used as the waveguide, and the time change of the state of light propagating in both directions along the axis of the optical fiber is measured based on these two sets of measurement results. The distributed waveguide sensor according to any one of claims 1 to 9, wherein a physical phenomenon that causes a change in a light amount or a polarization state is detected. 11. The distributed waveguide sensor according to claim 10, wherein said optical fiber is a single mode optical fiber or a polarization maintaining optical fiber. 12. The distributed waveguide sensor according to claim 10, wherein said optical fiber is a bundle of a plurality of polarization-maintaining optical fibers having different coupling lengths. 13. A coaxial cable for a sensor is used for the waveguide.
As a traveling wave along the axis of the sensor coaxial cable.
Claims: Detecting two sets of propagating electromagnetic waves
A distributed waveguide according to any one of claims 1 to 4.
Sensor. 14. A physical phenomenon acting on an arbitrary position of a waveguide.
In a distributed waveguide sensor that detects
It is connected to both ends of the fiber, and functions as an optical splitter and polarizer.
Polarization beam splitters and their respective polarization beams
Connected to be coaxial with the different polarization axes of the splitter
Light source and a light receiver, and information detected by the light receiver is provided.
Estimating the occurrence position of the physical phenomenon.
Distributed waveguide sensor. 15. A polarization preserving optical fiber for the sensor.
Using the existing optical fiber, the opposite ends of the sensor optical fiber
Two sets of light sources, each having a different polarization-maintaining optical fiber.
Connected to the input / output part of the polarization beam splitter
15. The distributed waveguide sensor according to claim 14, wherein
Sa. 16. A physical phenomenon acting on an arbitrary position of a waveguide.
In a distributed waveguide sensor that detects
Continuous light is incident on the fiber, and the physical phenomenon
Changes in the polarization state in the optical fiber
By detecting this with a light receiver,
Continuous distance and time to the location where the physical phenomenon occurred
A distributed waveguide sensor characterized by sensing
Sa.