JPH06117883A - Optical fiber type physical quantity measuring system - Google Patents

Abstract

PURPOSE:To perform highly accurate measurement at a low cost by correcting time series pulses for measurement based on the loss characteristic of an optical fiber for reference and back scattered light distribution of Rayleigh scattered light. CONSTITUTION:While the optical pulse of an optical pulse generator 5 is made incident to an optical fiber 34 through a demultiplexer 9 and optical switch 15, part of the pulse is branched to another optical fiber 36. A photoreceptor 40 detects the optical information received through the fiber 36 and switch 15 as time series pulse signals for measurement based on the delay time corresponding to the positions of the branching devices 18 and 4a-4d. In addition, the back scattered light component in the scattered light generated in the fiber 34 returns to the demultiplexer 8 and the photodetector 40 outputs the component to a signal processor 42 as Rayleigh scattered light signals, time series pulse signals for measurement, etc. The processor 42 corrects the time series pulses by using the loss distance characteristic of the fiber 34 found from the Rayleigh scattered light distribution and a reference level passing through an optical fiber 22 for reference. In addition, the processor 42 uses the attenuation factor along the fiber 34 found from the Rayleigh scattering light distribution and for the correction of the time series pulses.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical fiber type physical quantity measuring system, and more particularly to a transmission type time division multiplex type optical fiber type physical quantity measuring system.

[0002]

2. Description of the Related Art Conventionally, as an optical fiber type multipoint measuring system for detecting physical quantities such as temperature, humidity and liquid leakage, an OTDR (Optical Time Domain Reflectometr) shown in FIG.
A method using y) and a transparent time division multiplexing method as shown in FIG. 7 have been devised. In the method using the OTDR of FIG. 6, an optical physical quantity sensor 3 whose optical loss changes due to a physical quantity change is connected in series in the middle of one optical fiber 2 and
The backscattered light distribution is detected by the DR device 1. Then, the change in the light loss of each sensor unit is obtained from this scattered light distribution, and a predetermined physical quantity such as the temperature distribution is measured based on the light loss.

On the other hand, in the transmission type time division system of FIG. 7, the optical branching device 4 is provided at each corresponding position of the two optical fibers 2a and 2b.
And the optical physical quantity sensor 3 is connected between these branching devices 4. One end of the optical fiber 2a is connected to the optical pulse generator 5 of the measuring device 8, and one end of the optical fiber 2b is connected to the light receiver 6. The optical pulse incident on the optical fiber 2a from the optical pulse generator 5 is branched by the optical branching device 4, and returns to the light receiver 6 via each sensor 3 and the optical fiber 2b.
The light receiver 6 detects a light reception pulse at each delay time corresponding to the position of each physical quantity sensor 3. After that, the signal processing device 7 corrects the optical loss in the reciprocating optical fibers 2a and 2b or the branching device 4 to obtain a sensor pulse signal 11 as shown in FIG. 8 as a measurement time series pulse train.
Then, the sensor output (physical quantity) is obtained based on such a time series pulse train for measurement. In addition,
In the figure, reference numeral 12 indicates background noise.

[0004]

However, the conventional optical fiber type distributed physical quantity measuring system as described above has the following various problems.

In the system using the OTDR device 1 shown in FIG. 6, the signal is attenuated when the loss of the physical quantity sensor 3 in the vicinity of the OTDR device 1 is increased, whereby information from a distant sensor (rear sensor) is obtained. Sometimes I couldn't.

On the other hand, the transmission type time division system shown in FIG. 7 does not have the problem of the OTDR system, but when the output fluctuation of the optical pulse generator 5 or the light receiving sensitivity of the light receiving unit 6 fluctuates, the light receiving pulse is generated. The signal level also changed, and it was difficult to accurately grasp the detection signal from the optical physical quantity sensor 3. Therefore, it is conceivable to add a stabilizing mechanism to the optical pulse generator 5 and the light receiver 6, but there is a problem that the device is large and economically disadvantageous. Also, the optical fiber 2
When microbending loss such as bending occurs in a and 2b, there is a problem that the level of the received light pulse signal changes and accurate measurement cannot be performed.

Furthermore, according to the conventional method, when measuring a plurality of types of physical quantities, it is necessary to construct a plurality of systems for each measured physical quantity, and due to an increase in the number of optical fiber cores and the number of devices, the overall system is extremely difficult. It becomes big and expensive.

[0008]

SUMMARY OF THE INVENTION It is, therefore, a first object of the present invention to provide an optical fiber type physical quantity measuring system capable of performing highly accurate measurement at low cost. A second object of the present invention is to provide a low cost and compact optical fiber type physical quantity measuring system capable of collectively measuring a plurality of physical quantities.

[0009]

According to the present invention, in order to achieve the above-mentioned first object, a sensor is connected between a first optical fiber and a second optical fiber, and the light is emitted from an optical pulse generator. The optical pulse is transmitted through the paths of the first optical fiber, the sensor, and the second optical fiber, and this is detected as a time-series pulse for measurement, and based on the intensity change of the optical pulse in the sensor, a predetermined physical quantity in the sensor unit is detected. In the optical fiber type physical quantity measuring system for measuring the above, a reference optical fiber connected between the first optical fiber and the second optical fiber, and a first and a second optical fiber so as not to be affected by the change of the physical quantity in the sensor. A demultiplexer that detects at least Rayleigh scattered light among the backscattered light generated in the second optical fiber, the intensity of the light pulse that has passed through the reference optical fiber, and the Rayleigh scattered light distribution are detected. It includes a detecting means and a signal processing unit for correcting the time series pulse for measurement based on the output data of the detection means.

Further, in order to achieve the second object, the demultiplexer is configured to detect Raman scattered light generated in the first and second optical fibers in addition to the Rayleigh scattered light, and the signal processing is performed. The first part and the second part based on the distribution of Raman scattered light.
The temperature distribution along the optical fiber is measured.

[0011]

As described above, in the optical fiber type physical quantity measuring system according to the present invention, the reference optical fiber is directly connected between the first optical fiber and the second optical fiber. The optical fiber is not affected by the change in the physical quantity in the sensor, and changes in the output of the optical pulse generator and the sensitivity of the light receiver appear as optical loss as they are. Therefore,
By correcting the measurement time-series pulse based on the optical loss in the reference optical fiber, it is possible to surely remove the error due to the fluctuation of the output of the optical pulse generator and the sensitivity of the light receiver. Furthermore, the demultiplexer determines the attenuation rate (optical loss ratio) along the first and second optical fibers from the Rayleigh scattered light generated in the first and second optical fibers, and based on this, the measurement time Since the series pulse is corrected, the microbending loss due to the bending of the optical fiber can be reliably removed.

Furthermore, the demultiplexer detects Raman scattered light generated in the first and second optical fibers in addition to the Rayleigh scattered light, and the signal processing unit detects the first and the first Raman scattered light based on the distribution of the Raman scattered light. Since the temperature distribution along the two optical fibers is measured, at least three types of physical quantities can be measured by one system. That is, a predetermined physical quantity in the sensor unit can be measured as usual, and the light loss distribution along the first and second optical fibers can be detected by detecting Rayleigh scattered light, and the first and second light can be detected by detecting Raman scattered light. Each temperature distribution along the fiber can be measured.

[0013]

An embodiment of the present invention will now be described in detail with reference to the accompanying drawings. FIG. 1 shows the configuration of an optical fiber type multipoint physical quantity measuring system according to an embodiment. This optical fiber type multipoint physical quantity measuring system is provided with a sensor unit 30 for obtaining optical data necessary for detecting a physical quantity.
And a measuring unit 32 that measures a predetermined physical quantity from the output data of the sensor unit 30.

The sensor unit 30 is provided with two optical fibers (first optical fiber 34 and second optical fiber 36) arranged in parallel to the longitudinal direction and a predetermined interval in the middle of both fibers 34, 36. Optical splitters 4a-4d, 16a-16d,
18, 20 and the optical splitters 4a-16a, 4b-opposing each other
16b, 4c-16c, and 4d-16d, and optical physical quantity sensors 3a to 3d respectively connected. An optical physical quantity sensor is not connected between the branchers 18 and 20, and both branchers 18 and 20 are connected to the reference optical fiber 2
Connected by two.

The measuring unit 32 selectively guides the optical pulse generator 5 and the pulsed light emitted from the optical pulse generator 5 to either one of the first and second optical fibers 34 and 36 (first Optical switch 15 for switching between the mode and the second mode
And a demultiplexer 9 for guiding (demultiplexing) the backscattered light from the optical fiber 34 while guiding the optical pulse emitted from the optical pulse generator 5 to the sensor unit 30 side, and the demultiplexer 9 or the optical switch. The light receiver 40 receives the light pulse returned from the sensor unit 30 via 15, and the signal processing device 42 that measures a predetermined physical quantity based on the output signal of the light receiver 40.

Next, the operation of the embodiment configured as described above will be described. First, the optical switch 15 is set to the first mode (the incident light is guided to the first optical fiber 34).
Then, the optical pulse emitted from the optical pulse generator 5 is
The light enters the first optical fiber 34 selected by the optical switch 15 via the optical demultiplexer 9 and propagates in the longitudinal direction of the optical fiber 34. Then, part of the incident light pulse is output from the branching device 1.
It is branched at 8, 4a to 4d and branched toward the second optical fiber 36.

The optical information received by the photodetector 6 via the second optical fiber 36 and the optical switch 15 is converted into an electric signal, and then the delay time corresponding to the position of the optical branching device 18, 4a-4d. Is detected as a measurement time-series pulse signal. In addition, the backscattered light component of the scattered light generated in the first optical fiber 34 returns to the demultiplexer 9 via the optical switch 15 and is demultiplexed into the Rayleigh scattered light signal and the Raman scattered light signal. The light receiver 40 converts the electric signal.
In this way, the light receiver 40 detects three types of optical information: the Rayleigh scattered light signal, the Raman scattered light signal, and the measurement time-series pulse signal. Then, each of these signals is sent to the signal processing device 42.

FIG. 2 shows the time series pulse waveform for measurement detected as described above. Each optical pulse signal level is sufficiently higher than the level of the background noise 12, and the sensor section pulse signals 11a to 11d are detected in order from the reference level 10 transmitted through the reference optical fiber 22.

FIG. 3 shows a distribution waveform of Rayleigh scattered light. The position of each of the sensors 3a to 3d is evaluated from the reflection peak 14 at the branching device 18. On the other hand, when the optical loss of the first optical fiber 34 is detected (calculated) from the gradient of the scattered light distribution waveform and the loss changes due to local bending or the like in the middle of the optical fiber 34, it changes as shown by 13 in FIG. It is detected as a bending point. In this case, between 11b and 11c in FIG.
That is, it is found that the loss change (bending) of the optical fiber 34 occurs between the branchers 4b and 4c.

In the signal processing device 42, the first optical fiber 34 is calculated from the Rayleigh scattered light distribution (FIG. 3) obtained as described above.
The loss distance characteristic of the reference optical fiber 2
2 is used to correct the measurement time series pulse (FIG. 2), and each of the sensors 3a to 3 is corrected.
The relative intensity at d (FIG. 4) is determined. As described above, in the present embodiment, the measurement time series pulse transmitted through the sensors 3a to 3d is corrected based on the intensity distribution of the light pulse transmitted through the reference optical fiber 22, and thus the optical pulse generator 5 is used. The error due to the change in the output and the sensitivity of the light receiver 40 is eliminated. In addition, since the attenuation rate (optical loss ratio) along the optical fiber 34 is obtained from the Rayleigh scattered light distribution generated in the optical fiber 34, and the time series pulse for measurement is corrected based on this, the optical fiber 34 It is possible to eliminate the micro-bending loss due to the bending of the. Then, a predetermined physical quantity of each of the sensors 3a to 3d is calculated based on the relative intensity (FIG. 4). On the other hand, the temperature distribution (FIG. 5) along the first optical fiber 34 is obtained from the signal intensity ratio of the Stokes light and the anti-Stokes light, which are the two components of the Raman scattered light.

After that, the optical switch 15 is switched to the second mode (the incident light is guided to the second optical fiber 36), the optical pulse emitted from the optical pulse generator 5 is guided to the second optical fiber 36, and the first As in the case of the optical fiber 34, Rayleigh scattered light and Raman scattered light generated in the optical fiber 36 are detected. Then, the signal processing device 42 obtains the loss distance characteristic and the temperature distribution of the second optical fiber 36 from the above backscattered light.

[0022]

As described above, the optical fiber type physical quantity measuring system according to the present invention is based on the loss characteristic of the reference optical fiber and the backscattered light distribution due to Rayleigh scattered light, and is used for measurement through the sensor. Since the series pulse is corrected, there is an effect that highly accurate measurement can be performed. That is, by correcting the measurement time-series pulse based on the optical loss in the reference optical fiber, it is possible to remove the error due to the fluctuation of the output of the optical pulse generator and the sensitivity of the light receiver. Further, since the attenuation rate (optical loss ratio) along the first and second optical fibers is obtained from the Rayleigh scattered light distribution and the measurement time series pulse is corrected based on this,
Microbending loss due to bending of the optical fiber can be eliminated.

Further, in the demultiplexer, Raman scattered light generated in the optical fiber is detected in addition to the Rayleigh scattered light, and the signal processor measures the temperature distribution along the optical fiber based on the distribution of the Raman scattered light. Multiple (at least 3
There is an effect that the physical quantity of (type) can be measured.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of an optical fiber type multipoint physical quantity measuring system according to an embodiment of the present invention.

FIG. 2 is a graph for explaining the operation of the embodiment.

FIG. 3 is a graph for explaining the operation of the embodiment.

FIG. 4 is a graph for explaining the operation of the embodiment.

FIG. 5 is a graph for explaining the operation of the embodiment.

FIG. 6 is a block diagram showing a configuration of a conventional optical fiber type multipoint physical quantity measuring system.

FIG. 7 is a block diagram showing a configuration of a conventional optical fiber type multipoint physical quantity measuring system.

FIG. 8 is a graph for explaining the operation of the conventional technique.

[Explanation of symbols]

 3a-3d Physical quantity sensor 4a-4d, 16a-16d, 18, 20 Brancher 5 Optical pulse generator 9 Demultiplexer 15 Optical switch 22 Reference optical fiber 30 Sensor part 32 Measuring part 34 1st optical fiber 36 2nd light Fiber 40 Light receiver 42 Signal processing device

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Keiichi Hashiba 5-1-1 Hidaka-cho, Hitachi-shi, Ibaraki Hitachi Cable Co., Ltd. Hidaka factory

Claims (3)

[Claims] 1. A first optical fiber and a second optical fiber arranged in parallel, a sensor connected between these two optical fibers, and a predetermined optical pulse to the first optical fiber. And an optical pulse generator for supplying the optical pulse generator for detecting the optical pulse transmitted through the paths of the first optical fiber, the sensor, and the second optical fiber as a measurement time series pulse, and measuring the time series. In an optical fiber type physical quantity measuring system for measuring a predetermined physical quantity in the sensor unit based on a pulse, in the first optical fiber and the second optical fiber, the physical quantity of the first optical fiber and the second optical fiber are prevented from being affected by the change of the physical quantity in the sensor. A reference optical fiber connected between the first and second optical fibers,
Of the backscattered light generated in the optical fiber of the demultiplexer that detects at least Rayleigh scattered light, the intensity of the optical pulse that has passed through the reference optical fiber, the detection means for detecting the Rayleigh scattered light distribution, An optical fiber type physical quantity measuring system, comprising: a signal processing unit that corrects the measuring time series pulse based on output data of the detecting means. 2. The demultiplexer is configured to detect Raman scattered light generated in the first and second optical fibers in addition to the Rayleigh scattered light, and the signal processing unit is the Raman scattered light. The optical fiber type physical quantity measuring system according to claim 1, wherein the temperature distribution along the first and second optical fibers is measured based on the distribution of light. 3. The optical fiber type physical quantity measuring system further includes an optical switch for selectively guiding the optical pulse emitted from the optical pulse generator to the first optical fiber and the second optical fiber. The optical fiber type physical quantity measuring system according to claim 1 or 2, characterized in that it is provided.