JP3358436B2 - 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, an electric field, a vibration, and a magnetic field acting on the waveguide based on a change in state of an electromagnetic wave propagating through the waveguide. Locations where physical phenomena such as impact and sound occur,
The present invention relates to a distributed waveguide sensor capable of detecting a type, a size, and the like.

[0002]

2. Description of the Related Art Detection of a physical phenomenon acting on an arbitrary position on a waveguide or a plurality of predetermined specific points is performed by detecting an electromagnetic wave generated by the physical phenomenon in the waveguide or a state of the waveguide. A distributed waveguide sensor that detects an electromagnetic wave propagating as a traveling wave in a waveguide has been proposed (see JP-A-6-307896).

FIG. 10 is a diagram showing a conventional example of a distributed waveguide sensor.

In FIG. 1, reference numeral 101 denotes a first detection device;
102 is a second detection device. Both detection devices 101, 1
The optical fiber for a sensor 1 as a waveguide installed between the optical fibers 02 is connected to the optical directional couplers 21 and 22 in both the detection devices 101 and 102, respectively.

A light source 31 is connected to the input end of the optical directional coupler 21 via the connecting optical fiber 11, and a light source 32 is connected to the input end of the optical directional coupler 22 via the connecting optical fiber 12. It is connected. As the light sources 31 and 32, lasers that oscillate laser light having a constant output (CW) are used.

[0006] An output end of the optical directional coupler 21 is connected to an optical receiver 41 as detecting means via a connection optical fiber 13, and the optical receiver 41 is a laser beam emitted from a light source 32. Is received and converted into an electric signal. An output end of the optical directional coupler 22 is connected to an optical receiver 42 as a detection means via the connection optical fiber 14, and the optical receiver 42 receives the laser light emitted from the light source 31. To convert it into an electric signal.

That is, laser beams traveling in the opposite directions always propagate in the optical fiber for sensor 1, and the optical receiver 41 transmits the laser beam traveling in the optical fiber for sensor 1 to the left in the figure. The light amount change is continuously monitored, and the optical receiver 42 can continuously monitor the light amount change of the laser light traveling in the sensor optical fiber 1 to the right side in the figure. For example, a photodiode or an avalanche photodiode is used as a photoelectric conversion element in each of the optical receivers 41 and 42, and an electronic circuit such as a current-voltage conversion circuit and an amplification circuit is connected to this output stage. The two optical receivers 41 and 42 are connected to received signal processing units 51 and 52, respectively.

The received signal processing section 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. The reception signal processing unit 52 obtains 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, 5
2 is connected to the signal recognition unit 53.

The signal recognizing section 53 analyzes the time relationship such as the difference between the time change start times of the output signal waveforms detected by the optical receivers 41 and 42, the waveform, and the like, and estimates the occurrence position of the physical phenomenon. 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, although the temperature changes relatively slowly and randomly, the lightning current is generally a pulse-like change that rises in several μsec and falls in several tens of μsec. Therefore, the type of the physical phenomenon is estimated from such a difference in the waveform. It has become.

Here, the distance from the optical directional coupler 21 to the optical directional coupler 22 via the sensor optical fiber is L0, and the propagation speed of light in the sensor optical fiber 1 is v
The origin of the distance along the sensor optical fiber is defined as the optical directional coupler 21, and the lengths of the connection optical fibers 13 and 14 are defined as L13 and L14, respectively.

If, for example, an external force acts instantaneously as a physical quantity at a point x (hereinafter referred to as point P) on the optical fiber for sensor 1 at time t0, the transmission loss of the optical fiber for sensor 1 at point P is temporarily reduced. (Caused by microbend loss). 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. Here, a traveling wave propagating in the right direction in the drawing is referred to as a forward wave, and a traveling wave propagating in the left direction in the drawing is referred to as a backward wave.

FIG. 11A shows a time change of the outputs of the optical receivers 41 and 42 with reference to the time t0 when an external force is applied.
And FIG. 11B.

FIGS. 11A and 11B are diagrams showing waveforms of signals 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.
However, the fluctuation starts at time t1. As described above, this fluctuation is caused by an external force acting on the point P of the sensor optical fiber 1 to change the transmission loss at the point P, and indicates a forward wave. Therefore, the time difference t10 between the time t1 and the time t0 is equal to the time when the light emitted from the light source 31 reaches the optical receiver 42 from the point P, and the equation (1)
Can be expressed as

T10 = t1−t0 = ((L0−x) + L14) / v (1) Time t at which the output of the optical receiver 41 starts to fluctuate (reverse wave)
The time difference t20 between 2 and time t0 can be similarly expressed as in equation (2).

T20 = t2−t0 = (x + L13) / v (2) Accordingly, the distance x can be expressed as Expression (3).

X = ((t2−t1) × v + L0 + (L14−L13)) / 2 (3) Also, the time t0 when an external force acts on the sensor optical fiber 1
Can also be expressed as in equation (4).

T0 = t2- (x + L13) / v (4) The signal recognizing unit 53 accurately obtains the distance x to the point P where the external force is applied to the sensor optical fiber 1 according to the equation (3). I have. Also, if necessary, the signal recognition unit 5
In (3), the time t0 at which the external force acts on the sensor optical fiber 1 can also be obtained according to the equation (4). Signal recognition unit 5
In 3, 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 (that is, external force, vibration, or temperature). Estimate the type of physical phenomenon, such as change.) If this determination can be made before obtaining the distance x and the time t0, the reception signal processing units 51 and 52
If the signal detected in step is not a detection target, the position detection and time detection in the reception signal processing units 51 and 52 need not be performed.

As described above, since the sensor optical fiber 1 is continuously monitored over time, instantaneous physical phenomena acting on the sensor optical fiber 1 and the positions and types of the continuous physical phenomena are generated. Can be estimated.

In order to determine the point P where the physical quantity has acted on the sensor optical fiber 1, the output of the optical receiver 41 and the output of the optical receiver 42 are time-delayed to perform a correlation process, or an artificial network such as a neural network. Intelligent processing can also be used.

It is also conceivable to detect not a change in the amount of light propagating through the sensor optical fiber but a change in the polarization state of the propagating light. In this case, the configuration of the distributed waveguide sensor shown in FIG. 12 is used.

The difference from the distributed waveguide sensor shown in FIG. 10 is that two sets of optical receivers (41x, 41y and 42x, 42y) are used at both ends of the optical fiber 1 for the sensor. Each set is a polarizing beam splitter 6
This is a point connected to outputs of two orthogonal polarization axes of x-polarized light and y-polarized light which are divided by 1, 62.

In general, the polarization state of light propagating through an optical fiber changes depending on the magnetic field, electric field, pressure, vibration, temperature, and the like. By detecting the change, it is possible to estimate the position or time at which the magnetic field, electric field, pressure, vibration, temperature, or the like applied to the sensor optical fiber 1 is applied.

The configuration and operation for detecting the polarization fluctuation are as follows. The light sources 31 and 32 have a linearly polarized light output. The outputs of the optical receivers 41x and 41y are connected to the received signal processing unit 51, and the optical receivers 42x and 41y
The output of 2y is connected to the reception signal processing unit 52. Outputs of the reception signal processing units 51 and 52 are connected to a signal recognition unit 53. Each optical receiver 41 when a physical phenomenon instantaneously acts on the point P of the sensor optical fiber 1 at time t0
The output waveforms of x, 41y, 42x, and 42y are shown in FIG.
FIG. 13 (d).

FIGS. 13A to 13D are diagrams showing the relationship between the output of the optical receiver shown in FIG. 12 and time. 13A to 13D, the vertical axis represents the output of the optical receiver, and the horizontal axis represents time.

The optical receiver 42x and the optical receiver 42y have outputs of polarization axes orthogonal to each other, and are output from time t0 to time t.
Both values are substantially constant up to 1 and change from time t1. The waveforms of these changing parts are different,
The change start time is the same. This means that the optical receiver 41
The same applies to the outputs of x and 41y. Therefore, the time t1 is obtained from the average value or difference value of one or both of the output S42x (t) of the optical receiver 42x and the output S42y (t) of the optical receiver 42y, and the output S4 of the optical receiver 41x is obtained.
The time t2 is obtained from the average value or the difference value of one or both of 1x (t) and the output S41y (t) of the optical receiver 41y, and the physical phenomena is obtained from the equations (3) and (4). Can be estimated to the distance P to the point P that has acted on. Due to factors other than the physical phenomenon to be detected due to fluctuations in the outputs of the light sources 31 and 32, the optical receivers 41x and
It is also conceivable that the outputs of 1y, 42x and 42y fluctuate. In such a case, the optical receivers 41x, 41y, 4y
The outputs of 2x and 42y are calculated using, for example, Equation (5) or Equation (6), and the square of the sum of squares of the reception results of orthogonal polarizations, respectively.
By converting and using values such as roots (S41 (t), S42 (t)), it is possible to avoid the influence of output fluctuation.

In order to measure the polarization fluctuation more accurately,
In addition to the reception results of orthogonal x and y polarizations, １ ／ of the light source wavelength
In some cases, a time change received by shifting the phase of the electromagnetic wave only is added.

S41 (t) = √ (S41x ² (t) + S41y ² (t)) (5) S42 (t) = √ (S42x ² (t) + S42y ² (t)) (6) With such a configuration, the position and time at which the physical phenomenon acting on the sensor optical fiber can be obtained,
In the above configuration, there is a problem that detection devices are required at both ends of the sensor optical fiber, and time adjustment and data transmission / reception between these detection devices are required. As a method for avoiding such a problem, a configuration such as a distributed waveguide type sensor shown in FIG. 14 has been studied.

The distributed waveguide sensor shown in FIG. 14 uses two juxtaposed optical fibers 1a and 1b, which are connected to each other at the far end, with the detecting device connected to the detecting device 103 as a sensor optical fiber. Used. A light source 3 for generating continuous light is provided at the near end (left side in the figure) of the sensor optical fiber 1a.
0 is connected, and optical receivers 40x and 40y are connected to the near end (left side in the figure) of the sensor optical fiber 1b via the polarization beam splitter 60 in the directions in which the polarization outputs are orthogonal to each other. Outputs of the optical receivers 40x and 40y are connected to a reception signal processing unit 51. The output of the reception signal processing unit 51 is connected to the signal recognition unit 53.

The optical receiver 40 when a magnetic field having a pulse width of about 1 μsec acts on a point P at a distance x from the detection device 103
As for the outputs of x and 40y, two pulse waveforms are observed as shown in FIGS. 15 (a) and 15 (b).

FIGS. 15 (a) and 15 (b) correspond to FIG.
FIG. 4 is an explanatory diagram of a waveform detected by the distributed waveguide sensor shown in FIG. 15A and 15B, the vertical axis indicates the output of the optical receiver, and the horizontal axis indicates time. The relationship between the time difference δt12 between these two pulses and the distance x is expressed by equation (7).

X = L0−L1 (7) where L1 = (δt12 × v) / 2.

The position (distance) of the magnetic field acting on the sensor optical fibers 1a and 1b can be obtained from the equation (7). In this distributed waveguide sensor, the light source 30 and the optical receivers 40a and 40b may be a single set, so that the size of the detection device can be reduced.

[0034]

However, the above-mentioned prior art has the following problems.

In this configuration, the detection devices are not required at both ends of the sensor optical fiber, and the time alignment and data transmission / reception between the detection devices at both ends have been solved. However, the following problems remain.

When the duration of the physical phenomenon is long or the waveform of the electromagnetic wave changed by the physical phenomenon is complicated, as shown in FIG.
16 (b) and the waveform diagram 16 (a) of the electromagnetic wave propagating in the return path are superimposed (FIG. 16 (c)), and the accuracy of the waveform change start time t2 due to the physical phenomenon acting on the outward path is reduced. In some cases, it is impossible to detect the location, type, size, and the like of the physical phenomenon. FIG. 16 is a diagram for explaining the operation of the conventional example shown in FIG. 14, in which the horizontal axis represents time and the vertical axis represents intensity.

Therefore, an object of the present invention is to solve the above-mentioned problems, and to provide the position, type, and the like of occurrence of a physical phenomenon even when the duration of the physical phenomenon is long or the waveform of an electromagnetic wave changed by the physical phenomenon is complicated. An object of the present invention is to provide a distributed waveguide sensor capable of detecting a size or the like.

[0038]

In order to achieve the above object, the present invention provides a method for detecting an electromagnetic wave which is connected as at least one electromagnetic wave source and propagates as a traveling wave in a waveguide having a forward path and a return path. , in the distribution type waveguide sensor for detecting the state change generated on the waveguide by the physical phenomena, at least one return path, the return on electromagnetic waves Den <br/> transportable, can be distinguished from the electromagnetic wave propagating in the forward path Other electromagnetic waves are included, and the above-mentioned outgoing and returning routes are common
To detect time change S1 (t) of electromagnetic wave propagating
Step and time change S2 (t) of electromagnetic wave propagating only in the return path
From the time change S1 (t).
By subtracting the change S2 (t),
Change Sa (t) generated in the electromagnetic wave propagating in the outward path
And propagate the return path by a physical phenomenon acting on the waveguide.
Time change Sb (t) generated in the electromagnetic wave is equal to S2 (t).
It is characterized by the fact that it is determined to be good.

[0039]

In the present invention, in addition to the above configuration, two waveguides are laid in parallel with each other, and one of them is used as an outward path and the other is used as a return path, and these waveguides are used. It is preferable that the optical waveguide is optically connected at a far end, an electromagnetic wave source is connected to at least a near end of the outward waveguide, and a time change detecting unit of the electromagnetic wave is connected to a near end of the return waveguide. .

In the present invention, in addition to the above configuration, three waveguides are laid in parallel, one of which is used as the outward path and the other two are used as the return path, and the outward waveguide is used. One of the return waveguides is optically connected at the far end, an electromagnetic wave source is connected to at least the near end of the outward waveguide, and the electromagnetic wave time is connected to the near end of the two return waveguides. Preferably, a change detection means is connected.

In the present invention, in addition to the above configuration, it is preferable that the outward waveguide and the return waveguide optically connected at the far end are the same.

In the present invention, in addition to the above configuration, it is preferable to use an optical fiber as the waveguide.

In addition to the above configuration, the present invention has an electromagnetic wave source that generates an electromagnetic wave that can be distinguished from the electromagnetic wave generated by the electromagnetic wave source at the near end at the far end of at least one return waveguide. Is preferred.

In addition to the above configuration, the present invention preferably has a function of converting a part of the characteristics of the electromagnetic wave reaching the far end of at least one return waveguide.

According to the present invention, in addition to the above configuration, an electromagnetic wave that can be distinguished from an electromagnetic wave propagating in the outward path propagates to at least one return path due to a difference in the frequency of the electromagnetic wave, the intensity modulation method of the electromagnetic wave, the polarization state modulation method of the electromagnetic wave, and the like. It is preferable to do so.

In the present invention, in addition to the above configuration, it is preferable to provide a reference signal application section in the return waveguide.

In addition to the above configuration, in the present invention, it is preferable to provide a polarization state modulator at one or both of the output section of the electromagnetic wave source and the input section of the electromagnetic wave receiver.

According to the above configuration, the time change S1 (t) of the electromagnetic wave propagating in the forward path and the return path and the time change S2 (t) of the electromagnetic wave propagating only in the return path can be detected separately. , A time change Sb (t) generated in an electromagnetic wave propagating in the return path due to a physical phenomenon acting on the waveguide
Is equal to the time change S2 (t) of the electromagnetic wave propagating only in the return path. Further, the time change Sa (t) generated in the electromagnetic wave propagating on the outward path due to the physical phenomenon acting on the waveguide is represented by S
It can be obtained by subtracting S2 (t) from 1 (t).

[0050]

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

FIG. 1 is a block diagram showing an embodiment of the distributed waveguide sensor according to the present invention. This embodiment uses the optical fiber as a waveguide and detects the change in the state of polarization of the propagation light of the optical fiber, which changes due to the physical phenomenon acting on the optical fiber, so that the effect of the physical phenomenon acting on the optical fiber can be obtained. The purpose is to obtain the position and the operation time. Further, even when the detection device is installed on only one side, the waveform affected by the physical phenomenon when the electromagnetic wave propagates on the outward path and the waveform affected by the physical phenomenon when the electromagnetic wave propagates on the return path. Is superimposed on the electromagnetic wave, the position and time of application of the physical phenomenon can be detected.

The difference from the conventional example shown in FIG. 14 is that the portion where the optical fibers 1a and 1b laid in parallel are connected at the far end has a wavelength λ2 different from the wavelength λ1 of the light source 30 in the detector 150. The point where the optical multiplexer 71 to which the light source 31 is connected is inserted, and the optical demultiplexer 70 that demultiplexes the light propagating through the optical fiber 1b and returning to the inside of the detection device into the light of the wavelengths λ1 and λ2. Through the light measuring system 221 and the wavelength λ2
This is a point that the light is guided to the light measurement system 222, converted into an electric signal, subjected to post-processing, and the processing results of these two measurement systems are sent to the waveform separation unit 80.

Next, the operation of this embodiment will be described.

Light having a high degree of polarization such as linearly polarized light, elliptically polarized light, or circularly polarized light is always output from the light source 30 having the wavelength λ1. (Right side), the light passes through the optical multiplexer 71, and returns to the detection device 150 through the optical fiber 1b.

On the other hand, light with a high degree of polarization, such as linearly polarized light, elliptically polarized light, or circularly polarized light, is always output from the light source 31 of wavelength λ2 installed at the far end. The light enters the optical fiber 1b via the optical fiber 1b and reaches the detection device 150. Of the light that reaches the detection device 150 through the optical fiber 1b, the light of the wavelength λ1 emitted from the light source 30 is guided to the measurement system 221 via the optical demultiplexer 70.

On the other hand, the detection device 1 passes through the optical fiber 1b.
Of the light that has reached 50, the light of wavelength λ2 emitted from light source 31 is guided to measurement system 222 via optical demultiplexer 70. The light guided to the measurement system 221 is divided into x-polarized light and y-polarized light whose polarization axes are orthogonal by the polarization beam splitter 261, and converted into electric signals by the optical receivers 241 x and 241 y, respectively. Waveform S1x (t)
And the received waveform S1y (t) are input to the received signal processing unit 251.

The light guided to the measurement system 222 is converted by the polarization beam splitter 262 into x whose polarization axes are orthogonal to each other.
The optical receiver 242x,
242y is converted into an electric signal, and each received waveform S
2x (t) and the received waveform S2y (t) are input to the received signal processing unit 252. Both reception signal processing units 251 and 252
Then, for example, in the same manner as Expressions (5) and (6), a waveform S1 (t) such as the square root of the sum of squares of the reception results of orthogonal polarizations.
And a waveform S2 (t). Waveform S1 (t) indicates that light of wavelength λ1 emitted from light source 30 is
b, and the signal received via waveform S2 (t)
Means that the light of wavelength λ2 emitted from the light source 31 is
b is the signal received via b.

That is, the waveform of the waveform S1 (t) is a polarization fluctuation waveform caused by a physical phenomenon acting on the optical fiber 1a and the optical fiber 1b, and the waveform of the waveform S2 (t) is
It is a waveform of a polarization fluctuation caused by a physical phenomenon acting only on the optical fiber 1b. Therefore, by subtracting the waveform S2 (t) from the waveform S1 (t) while adjusting the time axis as shown in Expression (8), a polarization fluctuation waveform Sa (t) due to a physical phenomenon acting on the optical fiber 1a is obtained. be able to. Polarization fluctuation waveform S due to physical phenomenon acting on optical fiber 1b
b (t) is the same as waveform S2 (t) as shown in equation (9).

Sa (t) = S1 (t) −S2 (t) (8) Sb (t) = S2 (t) (9) The bias due to the physical phenomenon acting on the optical fiber 1a by such signal processing. Wave fluctuation waveform Sa (t) and optical fiber 1
The process of obtaining the polarization fluctuation waveform Sb (t) acting on b is performed by the waveform separation unit 80. By using the waveform Sa (t) and the waveform Sb (t) separated by the waveform separation unit 80, the signal recognition unit 53 uses the optical fibers 1a and 1b in the same manner as in the conventional example (see FIG. 10). The operation position and the operation time of the physical phenomenon that has acted on can be obtained.

The time change shown in FIG. 2A is shown at a point Lx from the detectors of the optical fibers 1a and 1b laid in parallel (the length of the optical fiber in the detector is short and will be ignored here). A specific example of waveform processing when a physical phenomenon such as a magnetic field shown in FIG. 2 (a) to 2 (d) are diagrams for explaining the operation of the embodiment shown in FIG. 1, and the horizontal axis shows a time axis with time t0 as the origin. The vertical axis in FIGS. 2B to 2D indicates the received signal strength.

The light of wavelength λ2 emitted from the light source 31 is
At time t0 during propagation through the optical fiber 1b, the above-described physical phenomenon is affected at the point Lx. Thereafter, the light having the wavelength λ2 propagates a distance Lx to the detection device, and then the time change of two orthogonal polarization components is converted into an electric signal by the measurement system 222, and is expressed by the formulas (5) and (6). FIG. 2
The waveform shown in (c) is obtained. Detector 1 from Lx point
With a delay of time t10 (= t1−t0) during which light propagates to 50, a waveform having the same shape as the waveform of the signal shown in FIG. t1 } is represented by Expression (10), where v is the speed of light in the optical fiber.

T10 = t1-t0 = Lx / v (10) On the other hand, the light of wavelength λ1 emitted from the light source 30 is affected by a physical phenomenon at time t0 at the point Lx while propagating through the optical fiber 1a and the optical fiber 1b. The light affected by the physical phenomenon while propagating through the optical fiber 1b is thereafter transmitted to the detection device 15
However, the light propagates the distance Lx until the light reaches 0, but the propagation light affected by the physical phenomenon while propagating through the optical fiber 1a is affected by the physical phenomenon while propagating in the far end direction.
Propagating a distance of (2 × (L0−Lx) + Lx) before reaching 0, receiving the action of a physical phenomenon, and then detecting
T20 (= t2) represented by the equation (11) until the value reaches 0.
−t0).

As described above, the optical fiber 1a and the optical fiber 1
Since the time from when the light propagating through b to the physical phenomenon is applied to when the light reaches the detection device 150 is different, these change waveforms arrive at the detection device 150 in a superimposed manner. Accordingly, a waveform obtained by converting the light of two orthogonal polarization components into an electric signal in the measurement system 222 and performing signal processing in the same manner as in Equations (5) and (6) is obtained as shown in FIG. Two waveforms having the same shape as in FIG. 2A are synthesized with a time lag. It can be seen that the waveform changes with a delay of time t10 during which light propagates from the point Lx to the detection device 150. From FIG. 2B, the start time t2 of the waveform change received by the light propagating through the optical fiber 1a cannot be read.

However, from the waveform of FIG.
2d can be easily obtained from the waveform of FIG.

T20 = t2−t0 = (2 × (L0−Lx) + Lx) / v = (2 × L0−Lx) / v (11) When t1 and t2 are obtained in this manner, the equation (10) is obtained. The position Lx at which the physical quantity has acted on the optical fiber and the time t using the equations (12) and (13) obtained from
0 can be obtained.

Lx = L0− (v × (t2−t1) / 2) (12) t0 = t1−Lx / v (13) In the present embodiment, the optical fiber propagating light reaching the detection device 150 In order to analyze the polarization state, orthogonal x, y
Although the reception result of the polarization was used, as can be seen in the polarization state analysis method used in the conventional distributed waveguide sensor, in order to more accurately measure the polarization fluctuation, orthogonal x, y In addition to the reception result of the polarized wave, a time change received by shifting the phase of the electromagnetic wave by １ ／ of the wavelength of the light source may be additionally used. This is the same in other embodiments using the polarization state change described below.

In this embodiment, an optical fiber is used for the waveguide, and a difference in the wavelength of light is used to distinguish between an electromagnetic wave propagating on the outward path and an electromagnetic wave propagating only on the return path.
If this is considered as a general electromagnetic wave, the difference in the frequency of the electromagnetic wave will be used.

(Other Embodiments) If the amount of light emitted from the light source of wavelength λ1 and returning to the detection device is different from the amount of light emitted from the light source of wavelength λ2 and reaching the detection device, the light is calculated by using equation (8). An error occurs when obtaining the waveform Sa (t) of the physical quantity acting on the fiber 1a. In order to reduce this error, a configuration as shown in FIG. 3 may be used.

That is, the reference signal applying unit 77 is provided on the optical fiber 1b in the detecting device 151, and the reference signal applying unit 77
Apply a physical quantity such as a magnetic field or an electric field to the optical fiber 1b with
The sensitivity correction coefficient α of the waveform S1 (t) corresponding to the wavelength λ1 and the sensitivity correction coefficient α of the waveform S2 (t) corresponding to the wavelength λ2 is obtained from the ratio of the signal change amount appearing in the waveform S1 (t) and the waveform S2 (t). The waveform Sa (t) based on the physical quantity acting on the optical fiber 1a may be obtained according to the equation (15). FIG. 3 is a block diagram showing another embodiment of the distributed waveguide sensor of the present invention.

The sensitivity correction coefficient α may be a function of the signal strength.
It is sufficient to use a signal whose signal strength changes as the reference signal applied in step 7 and obtain and use the sensitivity correction coefficient α for the signal strength.

Α = S1 (tr) / S2 (tr) (14) where tr is the time when the reference signal is applied.

Sa (t) = S1 (t) −α × S2 (t) (15) The application timing of the reference signal for obtaining the sensitivity correction coefficient α may be determined in advance. If the sensitivity correction coefficient α at that time is obtained immediately after the physical phenomenon is detected and the sensitivity correction coefficient α at that time is obtained, the error due to the aging can be reduced.

These sensitivity correction methods can be similarly applied to still another embodiment described below.

In the optical fibers 1a and 1b from the detection device 151 to the action position of the physical phenomenon to be detected, detection is effected by a change other than a change in polarization state due to a physical quantity to be detected (for example, a change in temperature). It is conceivable that the conversion efficiency to the polarization state when the target physical phenomenon acts changes.

As a countermeasure in this case, as shown in the detection device 152 in FIG. 4, the output light of the light source 30 is input to the optical fiber for sensor 1a or the output light of the light source 31 is input to the optical multiplexer / demultiplexer 71. Before the light is incident, the polarization state modulator 33 and the polarization state modulator 33a that modulate the polarization state (deflection angle and phase) at the frequency f1 may be passed. FIG. 4 is a block diagram showing another embodiment of the distributed waveguide sensor of the present invention.

As the polarization state modulator 33, an element in which a magnetic field is applied to a Faraday element or an element in which an electric field is applied to a Pockels element is used. It can be performed. At this time, the polarization state modulation frequency f1 is set to f1> fsh with respect to the frequency range fsl to fsh of the signal to be detected, and for example, when the signal is received, the frequency range is (f1 + fsl) to (f1 + fs).
By passing through the band-pass filter of h), it is possible to detect a change in time of the physical quantity acting on the sensor optical fibers 1a and 1b in real time.

That is, the optical receivers 241x, 241y,
The output signals of 242x and 242y may be input to the reception signal processing units 251 and 252, for example, after passing through band-pass filters 271x, 271y, 272x and 272y in the frequency range (f1 + fsl) to (f1 + fsh).

In this way, the conversion efficiency to the polarization state change when the physical phenomenon to be detected acts on the electromagnetic wave in the optical fibers 1a and 1b due to the polarization fluctuation other than the detection target such as a temperature change. However, the polarization state of the optical fiber propagating light reaching the action position of the physical phenomenon is always modulated at the frequency f1, so that signal conversion in a state of high conversion efficiency is performed in synchronization with the frequency f1. Will be For this reason, the sensor optical fibers 1a and 1b are not affected by a change in the conversion efficiency.
The change over time of the physical quantity acting on the object can be detected in real time.

Further, in the optical fibers 1a and 1b from the position where the state of polarization has been changed by the action of the physical phenomenon to be detected to the detection device 151, the state of polarization due to temperature change other than the physical phenomenon to be detected and the like. , It is conceivable that the detection sensitivity of the polarization state change in the measurement systems 221 and 222 changes.

As a countermeasure in this case, as shown in the detection device 152 of FIG. 4, the polarization state (deflection angle and phase) of the propagation light from the optical fiber 1b is provided before the polarization beam splitters 261 and 262 in the detection device 152. ) May be passed through the polarization state modulator 34 that modulates the frequency at the frequency f2.

As the polarization state modulator 34, one that applies a magnetic field to the Faraday element or one that applies an electric field to the Pockels element is used. It can be performed. At this time, the polarization state modulation frequency f2 is set to f2> fsh with respect to the frequency range fsl to fsh of the signal to be detected. For example, when the signal is received, the frequency range is (f2 + fsl) to (f2 + f).
By passing through the band pass filter of sh), the time change of the physical quantity acting on the sensor optical fibers 1a and 1b can be detected in real time.

That is, the optical receivers 241x, 241y,
242x and 242y are output, for example, in the frequency range (f
2 + fsl) to (f2 + fsh) bandpass filters 271x, 271y, 272x, and 272y, and then input to the reception signal processing units 251 and 252.

In this manner, the optical fibers 1a, 1b
Even when the detection sensitivity of the polarization state change when the physical phenomenon of the detection object acts due to the polarization fluctuation due to the temperature change or the like other than the detection object in the optical fiber propagation light of the optical fiber propagating light reaching the measurement systems 221 and 222, The polarization state is always the frequency f2
, The signal conversion in a state of good detection sensitivity is performed in synchronization with the frequency f2, and the time change of the physical quantity acting on the sensor optical fibers 1a and 1b without receiving the fluctuation of the detection sensitivity is detected in real time. Can be detected.

When both the polarization state modulation of the frequency f1 on the light source output side and the polarization state modulation of the frequency f2 on the optical receiver side are performed, the band-pass filters 271x, 271
y, 272x, 272y, for example, the frequency range (f1 + f2 + fsl) to (f1 + f2 + fs)
h).

The optical fiber propagating light returned to the detector for the purpose of suppressing a change in detection sensitivity due to a change in the polarization state is passed through a polarization state modulator, and the modulation effect of the polarization state modulator is sufficient and When the influence of the wave fluctuation can be almost completely eliminated, the measurement systems 221 and 222 can be simplified. That is, a simple polarizer is used instead of the polarization beam splitters 261 and 262 in FIG.
The optical receiver 241y, the bandpass filter 271y, the received signal processing unit 251, the optical receiver 242y, the bandpass filter 272y, and the received signal processing unit 252 can be omitted.

This is because, when there is no influence of the polarization fluctuation, the signal output from the optical receiver 241x and the band-pass filter 271x is the same as the signal output from the optical receiver 241y and the band-pass filter 271y. The waveform S1 (t) can be obtained by only one of them. Similarly, the signal output from the optical receiver 242x and the band-pass filter 272x and the optical receiver 242y and the band-pass filter 272y
The signal output from S2 becomes the same, and S2
This is because (t) can be obtained.

The method for stabilizing these detection characteristics can be applied to other embodiments using the change in the polarization state described below.

In the embodiments described above, the two waveguides, the outward and return paths, are laid in parallel.
As shown in FIG. 5, the same waveguide may be used for the outward and return waveguides. FIG. 5 is a block diagram showing another embodiment of the distributed waveguide sensor of the present invention.

In this case, for example, the optical circulator 73 and the optical circulator 73 are provided at both ends of the waveguide portion commonly used for the forward path and the return path.
74 can be used. Light emitted from the light source 30 enters the optical fiber 1 via the optical circulator 74, and is guided to the optical multiplexer 71 via the optical circulator 73 at the far end. The output of the optical multiplexer 71 enters the optical fiber 1 via the optical circulator 73, and is output from the optical multiplexer 70 via the optical circulator 74 in the detection device 100.
It is led to.

With such a configuration, components for selecting or branching the optical path, such as the optical circulator 74, are required. However, only one waveguide is required, Is advantageous in that the forward path and the return path are constituted by separate waveguides. This means
The same applies to still other embodiments described below.

In the embodiments described above, the state changes due to the physical phenomenon acting on the waveguide, and the electromagnetic wave propagating as a traveling wave in the waveguide is detected. Although a change in wave state is used, the present invention can be applied to a case where a change in the intensity of an electromagnetic wave generated in an electromagnetic wave propagating through a waveguide due to a physical phenomenon is used, as in the conventional example. This is the same for the other embodiments described below.

In the embodiments described above, the difference in the frequency (wavelength of light) of the electromagnetic wave is used to distinguish between the electromagnetic wave propagating on the outward path and the electromagnetic wave propagating only on the return path. As described above, it is also possible to distinguish between an electromagnetic wave propagating on the outward path and an electromagnetic wave propagating only on the return path by using a difference in the intensity modulation method of the electromagnetic wave.

FIG. 6 is a block diagram showing another embodiment of the distributed waveguide sensor of the present invention.

FIG. 14 shows an example of a configuration of a method using a difference in the intensity modulation method of the electromagnetic wave in order to distinguish between an electromagnetic wave propagating on the outward path and an electromagnetic wave propagating only on the return path. The difference from the embodiment shown in FIG. 1 is that the light source 30 in the detecting device 154 is controlled by a signal from the intensity modulation signal generator 38 (for example, a constant frequency f3 (no modulation, ie, f3 = 0). )), And modulates the light source 31 at the far end (the wavelength may be the same as that of the light source 30) by the intensity modulation signal generator 39.
Is modulated by a signal (for example, constant frequency f4) from the optical fiber 1a, and the light propagated from the optical fiber 1a at the far end and the light from the light source 31 are connected to the optical fiber 1b via the optical directional coupler 75. And the optical receivers 241x and 24 in the detection device 100
Band pass filter 2 having center frequency f3 on the output side of 1y
The point is that bandpass filters 271xb and 272yb of 71xa and 271ya and a center frequency f4 are connected.

The light of the intensity modulation frequency f3 propagates to the optical fiber 1a in the forward path section, and the light of the intensity modulation frequency f3 and light of f4 propagate to the optical fiber 1b in the return path section. After being converted into electric signals by the optical receivers 241x and 241y, the band-pass filters 271xa and 271y of the center frequency f3.
When the signal passed through a is input to the reception signal processing unit 251, the reception signal processing unit 251 has a time change in which the time change of the forward propagation light and the time change of the return propagation light are superimposed. , Orthogonal x and y polarized signals are input.

Therefore, the waveform S1 (t) of the electromagnetic wave propagating in the forward path and the return path in common is obtained from the reception signal processing section 251.

After being converted into electric signals by the optical receivers 241x and 241y, the bandpass filter 27 having the center frequency f4 is used.
The signals passed through 1xb and 271yb are received by the reception signal processor 25.
2, the received signal processing unit 252 provides orthogonal x and y corresponding to only the time change of the propagation light on the return path.
A polarization reception signal is input. Therefore, a time change S2 (t) of the electromagnetic wave propagating only in the return path is obtained from the reception signal processing unit 252.

The subsequent processing in the waveform separating section 80 and the signal recognizing section 53 is the same as in the above-described embodiment.

In the embodiments described above, in order to distinguish between an electromagnetic wave propagating on the outward path and an electromagnetic wave propagating only on the return path, differences in the frequency (wavelength of light) of the electromagnetic wave and the intensity modulation method of the electromagnetic wave are used. However, as described below, it is also possible to distinguish between an electromagnetic wave propagating on the outward path and an electromagnetic wave propagating only on the return path using the difference in the polarization state of the electromagnetic waves.

FIG. 7 is a block diagram showing another embodiment of the distributed waveguide sensor of the present invention.

The distributed waveguide sensor shown in the same figure performs a different modulation method on the polarization state of an electromagnetic wave in order to distinguish between an electromagnetic wave propagating on the outward path and an electromagnetic wave propagating only on the return path. The difference from the embodiment shown in FIG. 1 is that a polarization state modulator 33 is inserted into the output of the light source 30 as shown in a detection device 155, and for example, a constant frequency f5 (no modulation, that is, f5 = 0 Modulation of the polarization state (deflection angle and phase) in the light source 32 (the wavelength is
0 may be the same as the output).
To modulate the polarization state (deflection angle or phase) at, for example, a constant frequency f6. At the far end, the propagation light from the optical fiber 1a and the light from the light source 31 are transmitted through the optical directional coupler 75. And the detection device 155
The band-pass filters 271xa and 271ya having the center frequency f5 and the band-pass filters 271xb and 271 having the center frequency f6 are provided on the output side of the optical receivers 241x and 241y.
1yb.

The light of the polarization state modulation frequency f5 propagates through the optical fiber 1a in the forward path, and the optical fiber 1b in the backward path.
, The light of the polarization state modulation frequency f5 and the light of f6 propagate. Therefore, if the signals that have been converted into electric signals by the optical receivers 241x and 241y and then passed through the band-pass filter having the center frequency f5 are input to the reception signal processing unit 251, the reception signal processing unit 251 will transmit the forward propagation light. And the orthogonal x and y polarized light reception signals corresponding to the time change superimposed on the time change of the return light and the time change of the propagation light on the return path are input. Therefore, the waveform S1 (t) of the electromagnetic wave propagating in the forward path and the return path in common is obtained from the reception signal processing unit 251.

If the optical receivers 241x and 241y convert the signals into electric signals and then input the signals passed through the band-pass filter of the center frequency f6 to the reception signal processing unit 252, the reception signal processing unit 252 transmits the signals on the return path. A received signal of orthogonally polarized light corresponding to only the time change of light is input. Therefore, a time change S2 (t) of the electromagnetic wave propagating only in the return path is obtained from the reception signal processing unit 252.

The subsequent processing in the waveform separating section 80 and the signal recognizing section 53 is the same as in the above-described embodiment.

This embodiment is similar to the embodiment shown in FIG. 4 in which the polarization state of the output light of the light source is modulated in order to stabilize the detection performance. The difference from the embodiment shown in FIG. 4 is that the polarization modulation frequency at the output section of the light source on the end side is different. However, in the present embodiment, similarly to the embodiment shown in FIG. 4, the polarization state is modulated on the light source side, other than the detection target from the light source to the position where the physical phenomenon to be detected acts on the sensor optical fiber. It is the same in that it has the effect of suppressing the change in conversion efficiency due to the polarization fluctuation of
This embodiment is more advantageous in that it is not necessary to specify the wavelengths of the near-end light source and the far-end light source. Also in this embodiment, by inserting a polarization state modulator in front of the deflection beam splitter 261 on the receiving side, the optical fiber 1 from the position where the physical phenomenon to be detected acts to the detection device can be obtained.
It is clear that the effect of suppressing a change in detection sensitivity due to polarization fluctuations other than the physical phenomenon to be detected in a and 1b can be provided.

FIG. 8 is a part of a block diagram showing another embodiment of the distributed waveguide sensor of the present invention.

This is an application of a method of distinguishing between an electromagnetic wave propagating on the outward path and an electromagnetic wave propagating only on the return path using the difference in the polarization state of the electromagnetic waves. The difference from the previous embodiment is that the light propagating on the return path is subjected to polarization state modulation using a part of the light propagating on the outward path.

A light splitting directional coupler 76 is connected to the far end of the optical fiber 1a, and the light to be directly incident on the return optical fiber 1b via another light directional coupler 75 and the depolarizer 35. , The light to be incident on the optical fiber 1b via the optical directional coupler 75 via the polarizer 36 and the polarization state modulator 37. By passing through a depolarizer 35 such as a quartz depolarizer or a Corne pseudo depolarizer, the light is converted into light with a low degree of polarization, and the polarization state modulator 37 outputs the polarization modulator 33 at the output of the light source 30. (For example, modulation at a constant frequency f6) and a different polarization method (eg, modulation at a constant frequency f6).
Modulation. The other points are the same as those of the embodiment in which the electromagnetic wave propagating on the outward path and the electromagnetic wave propagating only on the return path at the polarization state modulation frequency described above are distinguished.

In the embodiments described so far, the method for transmitting the electromagnetic wave propagating in the outward path is applied to the waveguide for the return path. However, the waveguide for the return path is no longer provided as described below. A configuration may be provided in which the electromagnetic wave propagating in the outward path does not propagate in at least one return waveguide.

FIG. 9 is a block diagram showing another embodiment of the distributed waveguide sensor of the present invention.

As shown in the drawing, three waveguides 1a, 1
b and 1c are laid in parallel, and one of them is used for the forward path, and the other two are used for the return path.
a is optically connected to the backward waveguide 1b at the far end, and the other backward waveguide 1c is not optically connected to the forward waveguide 1a. The difference from the embodiment shown in FIG. 1 is that the outgoing optical fiber 1a is directly connected to the return optical fiber 1b at the far end without passing through an optical multiplexer.
Is connected directly to the polarizing beam splitter 261 on the detector side, and the optical fiber 1c is added and the light source 3
1 is connected and connected to the polarizing beam splitter 262 at the near end.

The wavelength of the light source 30 and the wavelength of the light source 31 may be the same, and the intensity modulation state and the polarization modulation state of the light incident on the optical fiber 1a and the light incident on the optical fiber 1c are the same. Is also good.

In the configuration shown in FIG. 11, the signal waveform S1 (t) emitted from the light source 30 and propagated on the forward and return paths and the signal waveform S2 (t) propagated only on the return path are the same as those of the embodiment shown in FIG. Similarly, the received signal processing unit 251,
252 can be obtained. Subsequent processes in the waveform separating unit 80 and the signal recognizing unit 53 are the same as those in the embodiment shown in FIG.

(How to use, application system, etc.) OPGW
As a method for locating the lightning strike of an overhead transmission line having
A method has been proposed that utilizes the rotation of the polarization plane of the light propagated through the GW built-in optical fiber. However, when the present invention is applied to this application, the lightning current waveform is complicated, and it is difficult to perform the orientation using the conventional method. It will also be possible to locate lightning strikes.

In this case, since the frequency band of the signal to be detected is from DC to several tens of kHz, the output of the light source and the polarization state modulation frequency before receiving the light are set to, for example, f1 = f2 = 10 kHz.
By setting the pass frequency to 0 kHz and the pass frequency of the band-pass filter at the subsequent stage of the optical receiver to 200 kHz to 300 kHz, it is possible to perform signal detection in which a change in detection characteristics due to a polarization change due to an influence of a temperature change or the like is suppressed.

When the position or time at which a sound wave or vibration is applied to an optical fiber is determined, the duration of the sound wave or vibration is longer than the propagation time of the light propagated through the optical fiber. Although it was not possible to separate the change in the propagating light that occurred on the outward path and the return path, by applying the present invention to this application, the change in the propagating light that occurred on the outward path and the return path was separated, and the sound waves and vibrations were converted into optical fibers. It is possible to determine the position and the time applied to.

Detection of a physical phenomenon acting on an arbitrary position of the waveguide or a plurality of predetermined specific points is performed by:
In a distributed waveguide sensor that changes its state due to a physical phenomenon acting on the waveguide and detects an electromagnetic wave propagating as a traveling wave in the waveguide, a plurality of spot type (eg, current) sensors are connected in series. Although it has been conventionally proposed to use such a method, it is possible to cope with a time change of a complicated physical phenomenon which cannot be conventionally handled by applying the present invention.

In short, according to the present invention, it is not necessary to provide detection devices at both ends of the sensor optical fiber. There is no need for time adjustment or data transmission / reception between the detectors at both ends. The duration of the physical phenomenon acting on the waveguide is long, or the state change waveform of the electromagnetic wave propagating through the waveguide caused by the action of the physical phenomenon has a complex shape. Even if the waveform affected by the phenomenon and the waveform affected by the physical phenomenon when propagating in the return path overlap in time, it is possible to detect the location, type, size, etc. of the physical phenomenon based on the detection signal. A possible distributed waveguide sensor can be realized.

[0119]

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

[0120] By having at least one return path, the electromagnetic wave propagating on the return path includes another electromagnetic wave that can be distinguished from the electromagnetic wave propagating on the outward path, so that the physical phenomenon has a long duration or Even if the waveform of the electromagnetic wave changed by the physical phenomenon is complicated, it is possible to provide a distributed waveguide sensor that can detect the position, type, size, and the like of the physical phenomenon.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of a distributed waveguide sensor according to the present invention.

FIG. 2 is a diagram for explaining the operation of the embodiment shown in FIG. 1;

FIG. 3 is a block diagram showing another embodiment of the distributed waveguide sensor of the present invention.

FIG. 4 is a block diagram showing another embodiment of the distributed waveguide sensor of the present invention.

FIG. 5 is a block diagram showing another embodiment of the distributed waveguide sensor of the present invention.

FIG. 6 is a block diagram showing another embodiment of the distributed waveguide sensor of the present invention.

FIG. 7 is a block diagram showing another embodiment of the distributed waveguide sensor of the present invention.

FIG. 8 is a part of a block diagram showing another embodiment of the distributed waveguide sensor of the present invention.

FIG. 9 is a block diagram showing another embodiment of the distributed waveguide sensor of the present invention.

FIG. 10 is a diagram showing a conventional example of a distributed waveguide sensor.

FIG. 11 is a diagram showing waveforms of signals detected by both optical receivers shown in FIG.

FIG. 12 is a diagram showing a conventional example of a distributed waveguide sensor.

FIG. 13 is a diagram showing a relationship between output of the optical receiver shown in FIG. 12 and time.

FIG. 14 is a diagram showing a conventional example of a distributed waveguide sensor.

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

16 is a diagram for explaining the operation of the conventional example shown in FIG.

[Explanation of symbols]

 1a, 1b Optical fiber 30, 31 Light source 53 Signal recognition unit 70, 71 Optical multiplexer / demultiplexer 80 Waveform separation unit 150 Detection device 221, 222 Measurement system 251, 252 Received signal processing unit 261, 262 Polarized beam splitter

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) G01D 21/00 G01R 15/24 G01R 29/12 G01R 31/08 G01R 33/032

Claims (10)

(57) [Claims] 1. A distribution for detecting a state change occurring on a waveguide due to a physical phenomenon by detecting an electromagnetic wave which is connected to at least one electromagnetic wave source and propagates as a traveling wave in a waveguide having a forward path and a return path. in type waveguide sensor has at least one return path, the return on electromagnetic waves Den <br/> transportable, and moistened with other electromagnetic waves can be distinguished from the electromagnetic wave propagating in the forward path, a backward said forward and said Common
To detect time change S1 (t) of electromagnetic wave propagating
Step and time change S2 (t) of electromagnetic wave propagating only in the return path
From the time change S1 (t).
By subtracting the change S2 (t),
Change Sa (t) generated in the electromagnetic wave propagating in the outward path
And propagate the return path by a physical phenomenon acting on the waveguide.
Time change Sb (t) generated in the electromagnetic wave is equal to S2 (t).
A distributed waveguide sensor characterized in that it is determined to be suitable . 2. The two waveguides are laid in parallel with each other.
One of which is used as the outbound route and the other one
Are used as return paths, and these waveguides are optically connected at the far end.
At least near the end of the outgoing waveguide.
The wave source is connected, and the electromagnetic wave time is
The distributed waveguide sensor according to claim 1, wherein a change detecting means is connected . 3. The three waveguides are laid in parallel,
One of these is used as the forward path and the other two are used as the return path, and the forward path waveguide is optically connected to one of the return path waveguides at the far end. electromagnetic wave source is connected to the near end of the outgoing waveguide, the two distribution type waveguide sensor according to claim 1 Symbol placement electromagnetic wave time change detector means at the proximal end side is connected on the return path for the waveguide. 4. A forward waveguide optically connected at a far end.
And the return waveguide is the same.
A distributed waveguide sensor according to any one of the claims. 5. The distributed waveguide sensor according to claim 1, wherein an optical fiber is used as said waveguide. 6. The far end side of at least one return waveguide.
To be distinguished from electromagnetic waves generated by the near-end electromagnetic wave source
The distributed waveguide sensor according to any one of claims 1 to 5, further comprising an electromagnetic wave source that generates an electromagnetic wave . 7. A method according to claim 7, wherein at least one return waveguide is provided at a far end side.
The distributed waveguide sensor according to any one of claims 1 to 5 , wherein the distributed waveguide sensor has a function of converting a part of characteristics of the arrived electromagnetic wave . 8. A method for modulating the frequency of an electromagnetic wave or the intensity of an electromagnetic wave,
Propagation on the outward path due to differences in the method of modulating the polarization state of electromagnetic waves
At least one return path that can be distinguished from the incoming electromagnetic wave
The distributed waveguide sensor according to any one of claims 1 to 7 , wherein the distributed waveguide sensor is adapted to propagate through the waveguide. 9. A reference signal applying unit is provided in the return waveguide.
Distribution type waveguide sensor according to any one of claims 1 to 8. 10. An output part of said electromagnetic wave source and an electromagnetic wave receiver.
Polarization state modulator at one or both of the inputs
Distribution type waveguide sensor according to any digit of claims 1 to 9.