KR101310783B1 - Distributed optical fiber sensor and sensing method using simultaneous sensing of brillouin gain and loss - Google Patents

Abstract

The distributed optical fiber sensor includes a test optical fiber including a first section and a second section; An optical attenuator optically connected between the first section and the second section; An optical modulator applying a first optical signal to the test optical fiber through the first section and applying a second optical signal to the test optical fiber through the second section; And a photodetector configured to detect induced Brillouin scattered light generated by the first optical signal and the second optical signal at each of the first correlation point located in the first section and the second correlation point located in the second section. It may include. Using the distributed optical fiber sensor, the measurement distance can be doubled while maintaining the spatial resolution as compared with the conventional optical fiber sensor.

Description

DISTRIBUTED OPTICAL FIBER SENSOR AND SENSING METHOD USING SIMULTANEOUS SENSING OF BRILLOUIN GAIN AND LOSS}

Embodiments are directed to a distributed optical fiber sensor and a sensing method, and more particularly, to a distributed optical fiber sensor and a sensing method in which a measurement distance is extended by simultaneously measuring Brillouin gain and loss. will be.

Generally, the optical fiber is sensitive to changes in the intrinsic characteristics of the optical fiber itself due to changes in the external environment, for example, external physical quantities such as temperature or stress, so that the optical fiber can be used as a sensor. In addition, due to the nature of the optical fiber itself, it is insensitive to external electromagnetic waves and is resistant to harmful environments such as gas and solution, and is light, flexible, and compact. Because of these advantages, the optical fiber is very suitable for the sensor because it is easy to install and easy to install on the structure.

Fiber optic sensors are optical grating sensors fabricated by changing the refractive index of cores in optical fibers, but they are relatively weaker than distributed optical fiber sensors because only the portions engraved with gratings act as sensors. Other methods include interference, wavelength, and scattering type sensors. The dual scattering type sensor can detect long distance by measuring the back scattering light inside the optical fiber according to the physical quantity acting on the optical fiber by using a light source of a continuous wave or a continuous wave.

Such scattering type sensors include Rayleigh scattering type optical fiber sensor, Raman scattering type optical fiber sensor, and Brillouin scattering type optical fiber sensor. The Rayleigh scattering type optical fiber sensor measures the scattered light generated due to the nonuniform distribution of the density of the optical fiber while the pulse light travels inside the optical fiber, and the back scattering light proportional to the intensity of the pulse light can be obtained. However, the Rayleigh scattering type optical fiber sensor is not sensitive to changes in external temperature or strain, and can be used only when special optical fiber bending occurs. The Raman scattering type optical fiber sensor and the Brillouin scattering type optical fiber sensor are both sensors using nonlinear light scattering. For example, Japanese Patent Application Laid-Open Publication No. 10-2009-0001405 discloses a distributed optical fiber sensor system for measuring Raman scattered light and Brillouin scattered light among back scattered light generated in a sensing optical fiber.

Raman scattering refers to a phenomenon in which a backscattering signal is generated by molecular vibration when light is transmitted in an optical fiber. At this time, since the vibration of the molecule changes only by thermal change, the Raman scattering type optical fiber sensor is mostly used as a temperature sensor. The Brillouin scattering optical fiber sensor changes the Brillouin frequency value inherent to the optical fiber according to an external temperature or stress. The Brillouin scattering optical fiber sensor measures a change in the Brillouin frequency and measures a change in the external physical quantity. Brillouin scattering in an optical fiber refers to a phenomenon in which light travels in an optical fiber and combines with sound waves to produce a backscattered signal. Since the backscattered signal is proportional to the environment in which the optical fiber is located, it is used to change the temperature and / or stress. Can be measured.

Examples of distributed optical fiber sensors using Brillouin scattering include Brillouin Optical Time Domain Reflectometry (BOTDR), Brillouin Optical Time Domain Analysis (BOTDA) And Brillouin Optical Correlation Domain Analysis (BOCDA). The BOTDR method and the BOTDA method are methods of observing Brillouin scattering light using a light source of a fixed form, which is easy to detect over a long distance but has a disadvantage that the resolution is limited. On the other hand, the BOCDA method generates Brillouin scattering in a space-selective manner, so that physical changes can be measured only at a specific point. Compared with the BOTDR method or the BOTDA method, long distance measurement is difficult, but resolution is improved.

Published patent publication No. 10-2009-0001405

According to an aspect of the present invention, the physical deformation and temperature of the optical fiber, etc. can be measured using Brillouin Optical Correlation Domain Analysis (BOCDA), and the measurement range is increased while maintaining the spatial resolution. The distributed optical fiber sensor and the sensing method can be provided.

According to an embodiment, a distributed optical fiber sensor may include a test optical fiber including a first period and a second period; An optical attenuator optically connected between the first section and the second section; An optical modulator applying a first optical signal to the test optical fiber through the first section and applying a second optical signal to the test optical fiber through the second section; And a light detector configured to detect Brillouin scattered light generated by the first optical signal and the second optical signal at each of the first correlation point positioned in the first section and the second correlation point positioned in the second section. It may include.

In the distributed optical fiber sensor, the light detection unit uses the Brillouin scattered light to derive the induced Brillouin gain of the first optical signal at the second correlation point and the second optical signal at the first correlation point. One or more of the induced Brillouin losses can be measured.

According to one or more exemplary embodiments, a sensing method includes: applying a first optical signal to a test optical fiber including a first section and a second section through the first section; Applying a second optical signal to the test optical fiber through the second section; Attenuating light passing through the optical attenuator using an optical attenuator optically connected between the first and second sections; And detecting Brillouin scattered light generated by the first optical signal and the second optical signal at each of the first correlation point located in the first section and the second correlation point located in the second section. can do.

The sensing method may include one of an induced Brillouin gain of the first optical signal at the second correlation point and an induced Brillouin loss of the second optical signal at the first correlation point using the Brillouin scattered light. It may further comprise the step of measuring the abnormality.

According to the distributed optical fiber sensor and the sensing method according to an aspect of the present invention, physical deformation of large buildings, bridges, aircrafts, trains, etc. using Brillouin Optical Correlation Domain Analysis (BOCDA) The temperature can be measured, and there is an advantage of doubling the measurement distance by the conventional BOCDA-type optical fiber sensor without deteriorating the spatial resolution.

1 is a schematic diagram showing a measuring principle of a distributed optical fiber sensor according to an embodiment.
2 is a schematic diagram of a distributed optical fiber sensor according to an exemplary embodiment.
3A and 3B are graphs showing gains and losses of a Brillouin signal measured by a distributed optical fiber sensor according to a distance on a test optical fiber according to an embodiment.
4 is a graph showing the results shown in FIGS. 3A and 3B as a change in Brillouin frequency.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

In a distributed optical fiber sensor of a Brillouin Optical Correlation Domain Analysis (BOCDA) scheme, pump light and probe light traveling in opposite directions in an optical fiber When the frequency difference coincides with or is close to the Brillouin transition frequency inherent to the optical fiber, the induced Brillouin scattering amplification occurs over the entire optical fiber to amplify the intensity of the probe light.

At this time, by selectively modulating the optical signal so that the frequencies of the pump light and the probe light have a sinusoidal waveform, the Brillouin scattering signal can be selectively obtained only at a specific position in the optical fiber. The measurement point can be determined based on the modulation frequency of the laser light to generate the pump light and the probe light. The Brillouin gain spectrum can be measured while varying the offset frequency between the pump light and the probe light. Since the Brillouin transition frequency of the test fiber depends on physical properties such as external temperature or stress, the frequency of the Brillouin gain spectrum having the maximum value can be used to measure the change in physical properties of the test fiber.

1 is a graph illustrating a principle of a distributed optical fiber sensor according to an embodiment.

Referring to FIG. 1, the test optical fiber may include a first section and a second section that are optically connected to each other with an optical attenuator 40 therebetween. In the test optical fiber, the first optical signal 1 and the second optical signal 2 travel in opposite directions. A second optical signal 2 is a signal having a predetermined frequency (ν _0), a first optical signal (1) is the frequency (ν _0), the offset frequency from the (ν _B) as long as the transition frequency (ν ₀ -ν _B ) signal. The values of the frequency ν ₀ and the offset frequency ν _B may be appropriately determined in consideration of the purpose and application target of the optical fiber sensor, and are not limited to specific values. At certain correlation peaks (z _q , z _{q -1} , ...) in the optical fiber, the phase difference between the second optical signal 2 and the first optical signal 1 is constant over time.

Conventional BOCDA type optical fiber sensor is configured such that only one of these correlation points is located in the test fiber, whereas the distributed optical fiber sensor according to an embodiment has two correlation points (z _q , z _{q -1} ) located in the test fiber. It is configured to. One correlation point z _q may be located in the first section of the test optical fiber, and another correlation point z _q-1 may be located in the second section of the test optical fiber. In this case, the optical attenuator 40 may be able to ignore the Brillouin gain or loss due to the gain of either of the two correlation points z _q and z _{q −1} being less than or equal to the Brillouin scattering threshold. The intensity of the optical signal passing through the optical attenuator 40 can be attenuated so that the size is small.

For example, a change in light intensity due to induced Brillouin scattering with the first optical signal 1 of the second optical signal 2 incident through the second section (ie, the second optical signal 2 is a probe signal) Case), at the correlation point z _q located in the first section, the first optical signal 1 incident through the first section and the second optical signal 2 'passing through the optical attenuator 40 overlap each other. do. In this case, the first optical signal 1 serves as a pump and the second optical signal 2 'serves as a probe. The probe optical signal 2 'suffers an induced Brillouin loss because the frequency is larger by ν _B than the pump optical signal 1 (ie, located in an anti-Stokes band). On the other hand, in the second section, the first optical signal 1 ', that is, the pump optical signal is weakened by the optical attenuator 40, so that the induced Brillouin loss of the probe optical signal 2 is sufficiently smaller than that of the first section. Therefore, by measuring and analyzing the loss spectrum of the second optical signal, the amount of physical change at the first interval correlation point z _q can be known.

On the contrary, when the first optical signal is a probe signal, at the correlation point z _{q -1} located in the second section, the first optical signal 1 ′ passing through the optical attenuator 40 and the right surface of the second section are formed. The second optical signal 2 incident therethrough overlaps. In this case, the second optical signal 2 serves as a pump and the first optical signal 1 'serves as a probe. The probe optical signal 1 'obtains an induced Brillouin gain because the frequency is smaller by ν _B than the pump optical signal 1 (i.e., located in the Stokes band). On the other hand, in the first section, the second optical signal 2 ', that is, the pump optical signal is weakened by the optical attenuator 40, so that the induced Brillouin gain of the probe optical signal 1 is sufficiently smaller than that of the second section and can be ignored. Therefore, by measuring and analyzing the gain spectrum of the first optical signal, the amount of physical change at the second interval correlation point z _{q -1} can be known.

That is, the correlation point which is located in the first interval (z _q) in the second stimulated Brillouin loss occurs, and the correlation point (z _{q -1)} which is located in the second section of the optical signal (2) the first optical signal Induced Brillouin gain of (1) occurs. Therefore, the loss of the second optical signal 2 occurring in the first section of the test optical fiber and the gain of the first optical signal 1 occurring in the second section of the test optical fiber are simultaneously measured to change the physical characteristics of the test optical fiber. It can be seen. As a result, there is an advantage that the measurement distance can be doubled while maintaining the spatial resolution.

2 is a schematic diagram showing an apparatus configuration of a distributed optical fiber sensor according to an embodiment.

Referring to FIG. 2, the distributed optical fiber sensor according to the exemplary embodiment may include an optical modulator 20, a test optical fiber 30, an optical attenuator 40, and a photodetector 50. In addition, the distributed optical fiber sensor may further include a light source unit 10. The test optical fiber 30 may be disposed at a position to measure the change in physical quantity using Brillouin scattering on the optical path. The optical attenuator 40 may be optically connected between the first section 310 and the second section 320 of the test optical fiber 30.

The light source unit 10 is a device for supplying light to be used in the operation of the distributed optical fiber sensor. In one embodiment, the light source unit 10 may include a distributed feed-back laser diode (DFB LD) 110 and a function generator 120. By modulating the supply current to the DFB LD 110 using the function generator 120, it is possible to obtain a light modulated in the form of a sine wave having a predetermined frequency f _m and having a modulated signal size Δf. However, this is exemplary, and in other embodiments, the light source unit 10 may be configured to include other different types of laser generating apparatuses.

The light modulator 20 receives the modulated light from the light source unit 10, and generates first and second optical signals from both ends of the test optical fiber 30. In one embodiment, the light modulator 20 may include an optical splitter 210, a first optical modulator 230, a second optical modulator 240, and a single sideband modulator 220. The light splitter 210 may receive the modulated light from the light source unit 10 and split the received light into a plurality of output light. For example, the light splitter 210 may branch the light applied from the light source unit 10 into the first output light for generating the first optical signal and the second output light for generating the second optical signal. In one embodiment, the optical splitter 210 may be a 50:50 optical splitter, but is not limited thereto.

The first optical modulator 230 may be optically connected between the optical splitter 210 and the single sideband modulator 220. The first optical modulator 230 may chop the first output light received from the optical splitter 210 using the first modulated signal received from the signal generator 235. Signal generator 235 may provide a modulation signal having a first frequency (f 1, _l) to the first optical modulator 230. The first modulated signal may be a square wave signal, but is not limited thereto. In addition, the first optical modulator 230 may be an electro-optic modulator, but is not limited thereto.

The short sideband modulator 220 may be optically connected between the first optical modulator 230 and one end of the test optical fiber 30. The first output light chopped at the first frequency by the first optical modulator 230 may be input to the single sideband modulator 220. The short sideband modulator 220 may generate a first optical signal including a sideband signal using the first output light. The single sideband modulator 220 may receive a modulated signal having a predetermined frequency ν _B from the signal generator 225. For example, the single sideband modulator 220 receives the first output light having the frequency ν ₀ , and then shifts the frequency ν ₀ -ν by the offset frequency ν _B received from the signal generator 225. A first optical signal including the sideband signal of _B ) may be generated.

The second optical modulator 240 may be optically connected between the optical splitter 210 and the other end of the test optical fiber 30. The second optical modulator 240 may generate a second optical signal by chopping the second output light received from the optical splitter 210. The second optical modulator 240 may perform the chopping of the second output light by using the second chopping signal received from the signal generator 245. The signal generator 245 may provide the second optical modulator 240 with the chopping signal having the second frequency f ₁ . The second frequency f _l 2 may be a frequency different from the first frequency f _l 1 for the chopping of the first output light. The second chopping signal may be a square wave signal, but is not limited thereto. In addition, the second optical modulator 240 may be an electro-optic modulator, but is not limited thereto.

The light modulator 20 may include a delayed optical fiber 270 optically connected to the test optical fiber 30. The delayed optical fiber 270 is an auxiliary optical fiber for making it possible to measure the physical change of the test optical fiber 30. The delayed optical fiber 270 is a first section 310 of the test optical fiber 30 by appropriately adjusting the length of the delayed optical fiber 270. ) And at least one Brillouin gain peak may be positioned in each of the second and second sections 320. In addition, the delay optical fiber 270 is optically connected to the test optical fiber 30 through the optical circulator 62, and since the first optical signal is branched by the optical circulator 62 and is not input to the delay optical fiber 270, Only Brillouin scattered light may be generated in the test optical fiber 30. In one embodiment, the delayed optical fiber 270 may be made of the same material as the test fiber 30.

The light modulator 20 may include one or more optical amplifiers 250 and 260. The optical modulator 20 may include a first optical amplifier 250 for amplifying the first optical signal. For example, the first optical amplifier 250 may be optically connected between the single sideband modulator 20 and one end of the test optical fiber 30. In addition, the optical modulator 20 may include a second optical amplifier 260 for amplifying the second optical signal. For example, the second optical amplifier 260 may be optically coupled between the delayed optical fiber 270 and the other end of the test optical fiber 30. In an embodiment, the first and second optical amplifiers 250 and 260 may be Erbium-Doped Fiber Amplifiers (EDFAs), but are not limited thereto.

The light modulator 20 may include one or more polarization controllers (not shown) and / or one or more polarization switches (not shown). Since the induced Brillouin scattering amplification occurs when the polarization of the probe optical signal and the pump optical signal coincide, the polarization of the first optical signal and the second optical signal may be equally adjusted using one or more polarization controllers. Furthermore, polarization of the first optical signal or the second optical signal may be alternately rotated once by 0 degrees and once by 90 degrees using the polarization switch. Although the induced Brillouin scattering amplification occurs when the polarization of the first optical signal and the second optical signal coincide, the polarization of the first optical signal and / or the second optical signal may change with time and space. Therefore, the polarization problem can be solved by performing the measurement while changing the polarization of the first optical signal or the second optical signal using the polarization switch and using the average value of the measured values. The above-described polarization angles of 0 degrees and 90 degrees are merely exemplary, and may periodically change the polarization of the first optical signal or the second optical signal to another different angle.

The test optical fiber 30 may include a first section 310 and a second section 320. The first section 310 and the second section 320 may be optically connected to each other. In addition, the optical attenuator 40 may be optically connected between the first section 310 and the second section 320 of the test optical fiber 30. The first optical signal generated by the optical modulator 20 may be incident to the test optical fiber 30 through the first optical cycle 61 through the first optical cycle 61. Meanwhile, the second optical signal generated by the optical modulator 20 may be incident on the test optical fiber 30 through the second optical cycle 62 through the second period 320. The second optical signal and the first optical signal propagate in opposite directions in the test optical fiber 30.

In one embodiment, as the test optical fiber 30, an optical fiber having a length of about 200 m was added to the first and second sections 310 and 320. In addition, the optical attenuator 40 between the first section 310 and the second section 320 is configured to attenuate the intensity of the optical signal passing therethrough by about 10 dB. However, this is merely an example, and the length of the optical fiber, the intensity of the optical signal, and the like may be appropriately determined according to the purpose and object of use of the distributed optical fiber sensor.

As described above with reference to FIG. 1, the phase difference between the first optical signal and the second optical signal propagated in opposite directions in the test optical fiber 30 has a constant value at a specific correlation point in the test optical fiber 30. . The correlation point includes one or more correlation points located in the first section 310 and one or more other correlation points located in the second section 320. At this time, as the intensity of the optical signal is attenuated using the optical attenuator 40, the induced Brillouin loss of the second optical signal is generated at the correlation point of the first section 310 and the correlation point of the second section 320. Induced Brillouin gain of the first optical signal may be generated.

The photodetector 50 is a device for detecting the Brillouin scattered light generated in the test optical fiber 30. The photodetector 50 includes one or more phase lock amplifiers for simultaneously measuring a component corresponding to induced Brillouin loss of the second optical signal and a component corresponding to induced Brillouin gain of the first optical signal in the Brillouin scattered light. in amplifiers 531 and 532. In addition, the photodetector 50 may further include one or more attenuators 511 and 512 and one or more photo diodes (PDs) 521 and 522 for adjusting and converting a signal.

While the first optical signal incident on the test optical fiber 30 through the first optical circulator 61 passes through the test optical fiber 30, an induced Brillouin gain is generated in the first optical signal in the second section 320. . Brillouin scattered light corresponding to the induced Brillouin gain of the first optical signal may be branched from the second optical circulator 62 to be incident to the first attenuator 511. The first attenuator 511 attenuates the incident Brillouin scattered light and enters the first photodiode 521, and the first photodiode 521 may convert the incident optical signal into an electrical signal.

On the other hand, while the second optical signal incident on the test optical fiber 30 through the second optical circulator 62 passes through the test optical fiber 30, induced Brillouin loss is induced in the second optical signal in the first section 310. Occurs. Brillouin scattered light corresponding to induced Brillouin loss of the second optical signal may be branched from the first optical circulator 61 to be incident on the second attenuator 512. The first attenuator 512 attenuates the incident Brillouin scattered light and enters the first photodiode 522. The first photodiode 521 may convert the incident optical signal into an electrical signal.

The first and second phase lock amplifiers 531 and 532 are parts for measuring components corresponding to the gain of the first optical signal and the loss of the second optical signal, respectively, in the Brillouin scattered light. The first and second phase lock amplifiers 531 and 532 may extract only a component having a desired frequency from the received signal by comparing the received signal with a predetermined reference signal. The first and second phase lock amplifiers 531 and 532 may receive a reference signal through the RF signal splitter 530, respectively. For example, the first and second phase lock amplifiers 531 and 532 may include the first and second phase lock amplifiers 531 and 532 as an AC signal channel, a mixer, and a DC amplifier. amplifier, a low-pass filter, and the like, but is not limited thereto.

The first and second phase lock amplifiers 531 and 532 may measure the Brillouin scattered light using a reference signal having a third frequency, wherein the third frequency is a first frequency for chopping the first optical signal. It may be equal to the difference (f _l 1-f _l 2) of the second frequency (f _l 2) for the chopping of the f _l 1) and the second optical signal. The first and second phase lock amplifiers 531 and 532 may measure components corresponding to a gain of the second optical signal and a loss of the first optical signal among the received signals by using the reference signal.

라 하고 프로브 광신호를

라 할 경우, 브릴루앙 산란광은 다음 수학식 1과 같이 나타내어질 수 있다.For example, in Brillouin scattering, pump light signals

And the probe optical signal

In this case, the Brillouin scattered light may be represented by Equation 1 below.

In Equation 1, BS denotes Brillouin scattered light, I ₁ and I ₂ are constants representing the maximum magnitude of the pump optical signal and the probe optical signal, respectively, and g _B is the Brillouin gain coefficient. Further, ω ₁ and ω ₂ represent the chopping frequencies of the pump optical signal and the probe optical signal, respectively.

In the Brillouin scattered light of Equation 1, the cosω ₁ t term in parentheses includes the reflected signal components of the amplified probe optical signal and the pump optical signal. In addition, the cosω ₂ t term includes the amplified probe optical signal and the original probe optical signal. Meanwhile, the 1 / 2cos (ω ₁ -ω ₂ ) t term includes only the amplified probe optical signal when g _B is greater than zero. In addition, when g _B is less than 0, only the pump optical signal absorbed through 1 / 2cos (ω ₁ -ω ₂ ) t term can be detected. Therefore, when the frequency difference between the pump optical signal and the probe optical signal is used as the reference signal of the phase lock amplifier, only the pure gain of the probe optical signal can be measured.

By using the reference signal as described above, the first phase lock amplifier 531 receives the photoelectrically converted signal from the first photodiode 521 and receives an amplified signal corresponding to the induced Brillouin gain from the received signal. You can print In addition, the second phase lock amplifier 532 may receive a photoelectrically converted signal from the second photodiode 522 and output an absorption signal corresponding to induced Brillouin loss from the received signal.

The light detector 50 may include a multi-channel data acquisition (DAQ) 540 and a personal computer (PC) 550. The DAQ 540 and the PC 550 receive the amplified signal output from the first phase lock amplifier 531 and the absorption signal output from the second phase lock amplifier 512, and receive the received signals from the Brillouin gain spectrum. By converting the shape, the physical change of the test optical fiber 30 can be measured. However, the configuration of the photodetector 50 described above is merely exemplary, and in other embodiments, signal processing and analysis may be performed using other different one or more data processing means.

By using the distributed optical fiber sensor configured as described above, the measurement distance by the conventional BOCDA type optical fiber sensor can be doubled without degrading the spatial resolution. For example, the inventors modulated the supply current of the DFB laser at a frequency f _m of about 99 kHz to about 1 MHz, wherein the magnitude of the modulation frequency Δf was set to about 6.85 GHz by adjusting the magnitude of the modulation current. In the conventional BOCDA-type optical fiber sensor, the spatial resolution using the modulated light is about 15 cm and the measurement range is about 100 m. Can extend up to 200m.

3A and 3B are three-dimensional graphs illustrating gains of a Brillouin signal measured by a distributed optical fiber sensor according to distances on a test optical fiber. The gain of the Brillouin signal was measured over distance, with stresses corresponding to strains of about 4.4 m, about 2 m, and about 2 mε, respectively, in a test fiber of about 200 m length, about 70 m, about 130 m and about 170 m, respectively. Stress was applied in the section of about 50 cm at each location. 3A shows the gain of the Brillouin signal in the first section of the test fiber, and FIG. 3B shows the gain of the Brillouin signal in the second section of the test fiber.

4 is a graph showing the results shown in FIGS. 3A and 3B as a change in Brillouin frequency. It can be seen that the frequency change due to stress at about 70 m is about 220 MHz, and the frequency change due to stress at about 130 m and about 170 m is about 100 MHz. In addition, while maintaining the spatial resolution it can be confirmed that the measurement range is doubled conventionally, it is possible to measure the two points at the same time without affecting each other.

 Although the present invention described above has been described with reference to the embodiments illustrated in the drawings, this is merely exemplary, and it will be understood by those skilled in the art that various modifications and variations may be made therefrom. However, such modifications should be considered to be within the technical protection scope of the present invention. Therefore, the true technical protection scope of the present invention will be defined by the technical spirit of the appended claims.

Claims (14)

A test optical fiber including a first section and a second section;
An optical attenuator optically connected between the first section and the second section;
An optical modulator applying a first optical signal to the test optical fiber through the first section and applying a second optical signal to the test optical fiber through the second section; And
And a photodetector configured to detect Brillouin scattered light generated by the first optical signal and the second optical signal at each of the first correlation point located in the first section and the second correlation point located in the second section. But
The optical attenuator attenuates the magnitudes of the first optical signal and the second optical signal passing through the optical attenuator,
At the first correlation point, induced Brillouin loss of the second optical signal is generated by the first optical signal and the second optical signal whose magnitude is attenuated.
The distributed optical fiber sensor of claim 2, wherein the induced Brillouin gain of the first optical signal is generated by the second optical signal and the first optical signal whose magnitude is attenuated.
The method of claim 1,
The photodetector may be one of an induced Brillouin gain of the first optical signal at the second correlation point and an induced Brillouin loss of the second optical signal at the first correlation point using the Brillouin scattered light. Distribution type optical fiber sensor characterized by measuring the abnormality.
The method of claim 1,
The first optical signal is a signal chopped at a first frequency, and the second optical signal is a signal chopped at a second frequency different from the first frequency.
The method of claim 3, wherein
Wherein the optical modulator comprises:
A first optical modulator for chopping light output from a light source at the first frequency;
A single sideband modulator for generating a first optical signal by generating a sideband signal on the light chopped at the first frequency; And
And a second optical modulator for chopping the light output from the light source at the second frequency to generate the second optical signal.
5. The method of claim 4,
The photodetector may include a phase locking amplifier configured to detect a Brillouin scattering signal corresponding to each of the first and second optical signals among the Brillouin scattered light using a reference signal having a third frequency. Distributed optical fiber sensor.
6. The method of claim 5,
And said third frequency corresponds to a difference between the first frequency and the second frequency.
6. The method of claim 5,
The phase lock amplifier,
A first phase lock amplifier optically coupled to the second section to receive Brillouin scattered light corresponding to the gain of the first optical signal; And
And a second phase lock amplifier optically coupled to the first section to receive Brillouin scattered light corresponding to the loss of the second optical signal.
Applying a first optical signal to the test optical fiber including a first section and a second section through the first section;
Applying a second optical signal to the test optical fiber through the second section;
Attenuating light passing through the optical attenuator using an optical attenuator optically connected between the first and second sections; And
Detecting the Brillouin scattered light generated by the first optical signal and the second optical signal at each of the first correlation point located in the first section and the second correlation point located in the second section; ,
At the first correlation point, induced Brillouin loss of the second optical signal is generated by the first optical signal and the second optical signal whose magnitude is attenuated.
The second correlation point is a sensing method characterized in that the induced Brillouin gain of the first optical signal is generated by the second optical signal and the first optical signal whose magnitude is attenuated.
The method of claim 8,
Measuring at least one of the induced Brillouin gain of the first optical signal at the second correlation point and the induced Brillouin loss of the second optical signal at the first correlation point using the Brillouin scattered light Sensing method further comprises.
The method of claim 8,
And the first optical signal is a signal chopped at a first frequency, and the second optical signal is a signal chopped at a second frequency different from the first frequency.
The method of claim 10,
The step of applying the first optical signal,
Chopping the light output from the light source at the first frequency; And
Generating the first optical signal by generating a sideband signal on the light chopped at the first frequency.
12. The method of claim 11,
The applying of the second optical signal may include generating the second optical signal by chopping the light output from the light source at the second frequency.
13. The method of claim 12,
The detecting of the Brillouin scattered light may include detecting an induced Brillouin gain of the first optical signal and an induced Brillouin loss of the second optical signal among the Brillouin scattered light using a reference signal having a third frequency. Sensing method comprising a.
The method of claim 13,
And wherein the third frequency corresponds to a difference between the first frequency and the second frequency.

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