JP2002122413A - Optical fiber strain measuring system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical fiber strain measuring system capable of executing multipoint strain measurement utilizing backward scattered light of optical fibers accurately in a short measuring time. SOLUTION: A basic optical fiber 8 and branched optical fibers 8a are laid in a comb tooth shape, and light including plural wavelengths is sent from a light source 2 of a strain measuring device 1 to the basic optical fiber 8, and light is passed through spectroscopes 9, to send mono-wavelength light having different wavelengths to each branched optical fiber 8a. Then, backward scattered light returned from each branched optical fiber is measured, and strain values of the branched optical fibers 8a are determined, and simultaneously the wavelength of light received by a wavelength scanner 4 is classified, to thereby specify a strain generation point.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical fiber strain measuring system for measuring the strain of an optical fiber provided at a monitoring point to monitor the behavior of a bank and a landslide on a slope.

[0002]

2. Description of the Related Art An optical fiber utilizing the characteristic that the frequency shift of the Brillouin scattered light in the backscattered light returning from each part of the optical fiber when the light is sent into the optical fiber is proportional to the distortion of the optical fiber. Techniques for measuring the distortion of a sphere are generally known. An optical fiber strain measurement system that uses this strain measurement technology to monitor the behavior of embankments and landslides on road slopes does not require a power source or signal transmission device at the site (monitoring point), and additionally requires one optical fiber. Since it has the advantage of being able to measure a distance of about 20 km with fiber, it has been used for monitoring places where remote monitoring was considered difficult.

FIG. 2 shows a conventional example of a practically used optical fiber strain measurement system for condition monitoring. In this system, one optical fiber 16 is laid in a zigzag manner on, for example, a slope (slope) of a dike, and the optical fiber 1 is laid.
Each of the folded portions 6 is wound around and fixed to the fiber fixture 17, and a portion including the fixed portion to function as a sensor is embedded in the bank body. Then, the optical fiber 16 drawn into the monitoring center or the relay station is connected to a strain measuring instrument 11 having a single wavelength light source 12, a light receiving section 13 for backscattered light, and a signal processing section 14, and this measuring instrument 11 uses the optical fiber. The distortion amount of each part 16 is measured, and the measurement result is taken into the monitoring processing device 15 to monitor the behavior (state change) of the embankment.

When the embankment body is displaced, collapsed, or the like, the optical fiber in that portion is stretched or the optical fiber to which an appropriate prestress has been applied contracts, so that the measured strain value changes. The change in the strain is constantly monitored to check the amount of change in the strain and the change point (specifying the strain change point is determined from the measurement time of the Brillouin scattered light), and an alarm is issued when an abnormality occurs.

According to this system, precursory phenomena such as a levee can be detected, and damage can be prevented from occurring due to early repair.

[0006]

In the conventional optical fiber strain measuring system shown in FIG. 2, the time required for one measurement is 5-1.
Monitoring is coarse, as long as about 0 minutes.

Further, since the optical fibers are arranged in a zigzag manner, if the monitoring area is widened, one system cannot cope with the situation, and a plurality of expensive strain measuring instruments are required.

[0008] Further, as the measurement distance increases, the accuracy of strain measurement and the accuracy of specifying the location of the strain decrease.

[0009] Among the optical fiber sensors proposed in Japanese Patent Application Laid-Open No. 6-241929, there is included an optical fiber sensor having an optical fiber laying configuration similar to that of the present invention. Measures the amount of change in the optical path length of the optical fiber due to disturbances such as temperature and pressure, and obtains the amount of distortion and the like from the amount of change, so that the system is more complicated than that of the present invention.

An object of the present invention is to eliminate the disadvantages and disadvantages described herein.

[0011]

In order to solve the above-mentioned problems, the present invention provides a strain measuring system for determining the strain of an optical fiber from the backscattered light of the optical fiber.
Provided is an optical fiber strain measurement system in which optical fibers to be measured are arranged in a comb shape, and the strain value of each optical fiber is measured using light having different wavelengths.

Also, a strain measuring device having a light source for light projection and a means for distinguishing a wavelength of light to be received, a main optical fiber connected to the measuring device, and a comb-shaped branch from the main optical fiber for monitoring. A plurality of branch optical fibers provided at a point, and a spectroscope provided at a branch portion of each branch optical fiber, light including a plurality of wavelengths is sent from a strain measuring device to a main optical fiber, and the wavelength-multiplexed light is transmitted. A single wavelength light having a different wavelength is sent to each branch optical fiber after being split by the spectroscope, and the backscattered light from each branch optical fiber is distinguished by the wavelength distinguishing means of the strain measuring device, and each branch optical fiber is separated. Provided is an optical fiber strain measurement system for obtaining strain from backscattered light.

[0013]

In the system according to the present invention, since backscattered light having different wavelengths returns from each branch optical fiber, a branch optical fiber having a strain change can be specified by the difference in wavelength.

Further, since the wavelength multiplexed light is measured through a main optical fiber, the measurement is the same as that of the conventional system of FIG. 2 in which serial measurement is performed using a single optical fiber using light of a single wavelength. Measurement time at distance is reduced.

Further, since the measurement is performed using light having different wavelengths for each of the branch optical fibers, it is possible to prevent a decrease in strain measurement accuracy and a specific resolution of a position, thereby preventing the system from becoming complicated. .

In addition, by improving the resolution, it is possible to extend the measurement distance in one system. In addition, it is not necessary to lay the optical fibers in a zigzag, and the monitoring area can be extended as compared with the system of FIG. 2 even when using optical fibers of the same length.

[0017]

FIG. 1 shows an embodiment of an optical fiber strain measuring system according to the present invention. In this system, a branch optical fiber 8a functioning as a sensor is buried, for example, on a slope of an embankment, and is used for monitoring the behavior of an embankment.

FIG. 1 shows a distortion measuring device 1 having a light source 2, a half mirror 3, a wavelength scanner 4, a light receiving section 5, and a signal processing section 6, a monitoring and processing device 7, a basic optical fiber 8, and a basic optical fiber 8a. A branch optical fiber branched from the middle of the fiber, 9 is a spectroscope provided at a branch portion of each branch optical fiber, 1
Numeral 0 is a fiber fixture for retaining each of the branch optical fibers.

As shown in FIG. 1, a plurality of branch optical fibers 8a are laid in a comb shape at a monitoring point via a spectroscope 9. The spectroscope 9 uses, for example, a photocoupler and causes each of the spectroscopes to separate light having a different wavelength.

The fixing of each branch optical fiber 8a by the fiber fixing device 10 is performed by using a roller as the fiber fixing device 10 and winding the branch optical fiber 8a around the roller. Of course, the present invention is not limited to this method, as long as the branch optical fiber can be stably fixed without damaging it.

One end of the main optical fiber 8 is connected to the strain measuring instrument 1. The light source 2 in the strain measuring instrument 1 preferably generates light of a plurality of wavelengths. Incandescent light bulbs and the like generate light having a wide wavelength range, and such light can be used as a light source. When the incandescent light bulb or the like is used as a light source, it is preferable to send the light collected by the condenser lens to the main optical fiber 8.

The light source 2 may be a light emitting diode or the like.
In this case, a light emitting diode having a wide emission wavelength range is preferable, but even a single-wavelength light emitting diode is used by combining several light emitting diodes having different emission wavelengths, combining light from each light emitting diode through a coupler or the like, and combining the light into a basic optical fiber. When sent, the measurement system of the present invention is established.

The wavelength scanner 4 is connected to each of the branch optical fibers 8a.
The wavelength of the backscattered light from With this, it is possible to specify at which position the received backscattered light is returned from the branch optical fiber.

The system of the present invention differs from the conventional system of FIG. 2 in that the single-wavelength light source 12 included in the distortion measuring device 11 of FIG. 2 is replaced by the light source 2 capable of transmitting light of a plurality of wavelengths in the present invention. And a newly added wavelength scanner 4 for discriminating the wavelength of the light to be received. The other main components remain unchanged. The monitoring processor 7 that determines a change in the state of the embankment from the measured strain value of the optical fiber is the same as the monitoring processor 15 in FIG.

The light including a plurality of wavelengths (λ1, λ2, λ3,...) Sent from the light source 2 to the main optical fiber 8 passes through the spectroscope 9 provided at the branch portion of the branch optical fiber 8a. It flows to the other end of the fiber 8. At that time, for example, the first spectroscope 9 counting from the left side of FIG.
Is extracted and the first branch optical fiber 8a is extracted.
Then, the light having the wavelength of λ2 is taken out by the second spectroscope and sent to the second branch optical fiber. Thereafter, similarly, the light having the wavelength of λ3 and thereafter is also sequentially spectrally processed. Single-wavelength light having different wavelengths is sent to the branch optical fiber 8a.

On the other hand, the Brillouin scattered light returning from each branch optical fiber 8a is collected by the strain measuring device 1,
The wavelength is distinguished by the wavelength scanner 4, the amount of frequency shift of the Brillouin scattered light for each wavelength is measured, the amount of distortion for each wavelength is calculated from the amount of shift, and output to the monitoring processing device 8.

Since it is determined in advance which wavelength of light is to be transmitted to which position of the branch optical fiber, the wavelength is used to specify the position of the measured strain value of the branch optical fiber, and
It is possible to know at which position in the monitoring area the abnormality has occurred.

[0028]

As described above, according to the measuring system of the present invention, the distortion value of the optical fiber arranged in a comb-teeth shape is
Since measurement is performed using light with different wavelengths for each optical fiber,
The measurement time can be shortened, the measurement accuracy can be improved, and the resolution at which the distortion occurs can be improved without increasing the complexity of the system. In addition, the measurement distance of one system can be made longer than before, and the monitoring area of one system can be expanded, so that fine monitoring and multipoint monitoring with higher reliability can be performed.

[Brief description of the drawings]

FIG. 1 is a diagram showing an embodiment of an optical fiber strain measurement system of the present invention.

FIG. 2 is a diagram showing an example of a conventional optical fiber strain measurement system.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Strain measuring device 2 Light source 3 Half mirror 4 Wavelength scanner 5 Light receiving part 6 Signal processing part 7 Monitoring processing device 8 Main optical fiber 8a Branch optical fiber 9 Spectroscope 10 Fiber fixture

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2F065 AA65 CC00 CC40 FF00 GG02 GG07 GG23 GG24 LL00 LL02 LL04 LL67 PP00 2F073 AA21 AB02 AB06 BB06 BC04 CC01 FH01 GG01

Claims (2)

[Claims] In a strain measuring system for determining the strain of an optical fiber from the backscattered light of the optical fiber, the optical fibers to be measured are arranged in a comb-like shape, and the strain value of each optical fiber is measured by a light having a different wavelength. An optical fiber strain measurement system characterized in that measurement is performed by using an optical fiber. 2. A strain measuring device comprising a light source for light emission and a means for distinguishing a wavelength of light to be received, a main optical fiber connected to the measuring device, and a comb-shaped branch from the basic optical fiber for monitoring. A plurality of branch optical fibers provided at a point, and a spectroscope provided at a branch portion of each branch optical fiber, light including a plurality of wavelengths is sent from a strain measuring device to a main optical fiber, and the wavelength-multiplexed light is transmitted. A single wavelength light having a different wavelength is sent to each branch optical fiber after being split by the spectroscope, and the backscattered light from each branch optical fiber is distinguished by the wavelength distinguishing means of the strain measuring device, and each branch optical fiber is separated. An optical fiber strain measurement system that calculates strain from backscattered light.