CN213842395U - Dynamic and static combined measurement distributed optical fiber sensing system - Google Patents
Dynamic and static combined measurement distributed optical fiber sensing system Download PDFInfo
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- CN213842395U CN213842395U CN202022646289.8U CN202022646289U CN213842395U CN 213842395 U CN213842395 U CN 213842395U CN 202022646289 U CN202022646289 U CN 202022646289U CN 213842395 U CN213842395 U CN 213842395U
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Abstract
一种动静态联合测量分布式光纤传感系统，包括：激光器、分光器、光调制器、声光调制器、扰偏器、掺铒光纤放大器、光纤环形器、相干接收器、信号采集和处理器，其中：分光器将激光器的一路输出端；另一路作为
A distributed optical fiber sensing system for dynamic and static joint measurement, comprising: laser, optical splitter, optical modulator, acousto-optic modulator, polarizer, erbium-doped fiber amplifier, optical fiber circulator, coherent receiver, signal acquisition and processing , wherein: the optical splitter connects one output end of the laser; the other
Description
Technical Field
The utility model relates to a technique in the optic fibre field specifically is a distributed optical fiber sensing system is jointly measured to sound attitude.
Background
The distributed sensing of strain or temperature plays an important role in various fields such as energy, buildings, aerospace, security, military and the like. At present, the distributed optical fiber sensing system existing in the market can only realize the static variables, such as: deformation, a single measurement of temperature, or a dynamic variable such as: intrusion damage, a single measurement of vibration generated by the passage of a vehicle, causes an increase in the cost of the application requirements for simultaneous measurement of dynamic and static variables. With the development of optical fiber sensing technology, corresponding dynamic and static combined measurement systems are proposed in recent years, but the systems are complex, the device requirements are high, the cost is high, and the simultaneous measurement of dynamic and static variables cannot be realized.
SUMMERY OF THE UTILITY MODEL
The utility model discloses it is not enough to the above-mentioned that prior art exists, provide a dynamic and static joint measurement distributing type optical fiber sensing system, specifically be based on brillouin optical time domain analysis technique (BOTDA) and phase sensitive optical time domain reflection technique
The dynamic and static combined measurement distributed optical fiber sensing system measures static variables by using single-ended BOTDA technology
Measuring dynamic variables by techniques
The back Rayleigh scattering light of the detection pulse is used as the detection light of the single-ended BOTDA, and the static variable and the dynamic variable of the optical fiber to be detected are measured simultaneously.
The utility model discloses a realize through following technical scheme:
the utility model relates to a dynamic and static joint measurement distributed optical fiber sensing system, include: laser instrument, two beam splitters, light modulation module, two reputation modulator, the ware of disturbing partially, erbium-doped fiber amplifier, first optic fibre circulator, coherent receiver, signal acquisition processing module, wherein: the first optical splitter connects one output end of the laser with the optical fiber to be tested through the optical modulation module, the first optical fiber circulator, the first acousto-optic modulator, the polarization scrambler, the optical splitter and the erbium-doped optical fiber amplifier in sequence; the other output end is divided into two paths by a second optical splitter, and the other output end is formed by a second acousto-optic modulator
The detection pulse is connected with the optical fiber to be detected through the optical splitter and the erbium-doped optical fiber amplifier, the other path of the detection pulse is connected with the output end of the first optical fiber circulator respectively and is connected with the coherent receiver, and the coherent receiver is sequentially connected with the signal acquisition processing module.
And a second optical fiber circulator is arranged between the erbium-doped optical fiber amplifier and the optical fiber to be detected.
The light splitter is a fiber coupler, and the splitting ratio of the light splitter is 50/50.
The light modulation module comprises: a radio frequency signal generator, an optical modulator, a DFB laser, and a polarization controller, wherein: the radio frequency signal generator is connected with the optical modulator, the DFB laser is connected with the polarization controller, one end of the optical modulator is connected with the first optical splitter, and the other end of the optical modulator is connected with the polarization controller through the first optical fiber circulator.
The coherent receiver is a polarization diversity photoelectric detector.
The signal acquisition processing module comprises: a data acquisition card and a data processor which are connected with each other.
Technical effects
The utility model discloses wholly solve and can't realize the dynamic and static strain simultaneous measurement's among the current distributed optical fiber sensing problem.
Compared with the prior art, the utility model discloses the realization reduces average number of times and measures required time to dynamic strain and static strain's vibration and temperature variation, static strain simultaneous measurement.
Drawings
FIG. 1 is a schematic view of the present embodiment;
fig. 2 is a brillouin gain spectrum measured in the present example;
FIG. 3 is a phase signal of Rayleigh probe light measured at 10km of an optical fiber according to the present embodiment;
FIG. 4 is a Brillouin gain spectrum of the temperature measuring section at 27 deg.C, 41 deg.C and 46 deg.C, respectively, in the example;
FIG. 5 is a schematic diagram of the differential phase demodulated at the fiber vibration site according to the embodiment;
FIG. 6 is a frequency spectrum of a fast Fourier transform of a vibration point of an embodiment;
in the figure: the device comprises a main laser 1, a first 50/50 optical fiber coupler 2, an optical modulator 3, a radio frequency signal generator 4, a first optical fiber circulator 5, a polarization controller 6, a DFB laser 7, a first acousto-optic modulator 8, a polarization scrambler 9, a second 50/50 optical fiber coupler 10, a second acousto-optic modulator 11, a third 50/50 optical fiber coupler 12, an erbium-doped optical fiber amplifier 13, a second optical fiber circulator 14, an optical fiber to be tested 15, a polarization diversity photoelectric detector 16, a data acquisition card 17, a data processor 18 and first to third ports a-c.
Detailed Description
As shown in fig. 1, the present embodiment includes: the optical fiber laser device comprises a main laser 1, a first 50/50 optical fiber coupler 2, an optical modulator 3, a radio frequency signal generator 4, a first optical fiber circulator 5, a polarization controller 6, a DFB laser 7, a first acousto-optic modulator 8, a polarization scrambler 9, a second 50/50 optical fiber coupler 10, a second acousto-optic modulator 11, a third 50/50 optical fiber coupler 12, an erbium-doped optical fiber amplifier 13, a second optical fiber circulator 14, a polarization diversity photodetector 16, a data acquisition card 17 and a data processor 18, wherein: the main laser 1 is connected with a first 50/50 optical fiber coupler 2, an optical modulator 3, a first optical fiber circulator 5, a first acousto-optic modulator 8, a polarization scrambler 9, a third 50/50 optical fiber coupler 12, an erbium-doped optical fiber amplifier 13, a second optical fiber circulator 14 and an optical fiber 15 to be tested in sequence, a radio frequency signal generator 4 is connected with the optical modulator 3, a DFB laser 7 and a polarization controller 6 are connected in sequence and connected with a second port b of the first optical fiber circulator 5, a third port c of the first 50/50 optical fiber coupler 2 is connected with a second port b of the second 50/50 optical fiber coupler 10, a second optical modulator 11 and a second port b of the third 50/50 optical fiber coupler 12 in sequence, a polarization diversity photoelectric detector 16 is connected between a third port c of the second 50/50 optical fiber coupler 10 and a third port c of the second optical fiber circulator 14, the polarization diversity photoelectric detector 16 is connected with a data acquisition card 17 and a data processor 18 in turn.
The working process of the embodiment is as follows: the main laser 1 generates laser with 1549.38nm wavelength and constant power of 22.2mw, and transmits the laser to the first 50/50 fiber coupler 2 to be divided into two paths, one path is used as the pump light of BOTDA, and the other path is used as the pump light of BOTDA
The light source of (1). The BOTDA pump light enters the optical modulator 3, the modulator works in a carrier suppression state through direct current modulation, the frequency sweep range of the modulator is 200MHz, the step length is 1MHz, the modulated light is injected and locked by the DFB laser 7 and then modulated into stable linear frequency sweep light, the working wavelength of the DFB laser is 1549.30nm, the working current is 50mA, the linear frequency sweep light enters the first acousto-optic modulator 8 to form pulse light with the pulse width of 50ns, the frequency shift of the first acousto-optic modulator 8 is 200MHz, the linear frequency sweep light enters the erbium-doped optical fiber amplifier 13 through the deflector 9 and the third 50/50 optical fiber coupler 12 for power amplification, the index of the erbium-doped optical fiber amplifier is set to be 9.8mW, the pump light enters the optical fiber 15 to be detected and the erbium-doped optical fiber amplifier 13 through the second optical fiber circulator 14 for power amplification, and the optical fiber 15 to be detected and the modulator work in a carrier suppression state
The stimulated brillouin effect occurs in the back rayleigh scattered light of the probe pulse of (1).
The light source is divided into two paths by the second 50/50 optical fiber coupler 10, and one path is formed by the second acousto-optic modulator 11
The pulse width of the detection pulse is 100ns, the frequency shift of the second acousto-optic modulator is 80MHz, the detection pulse enters an erbium-doped fiber amplifier 13 through a third 50/50 fiber coupler 12 for power amplification and enters an optical fiber 15 to be detected through a second fiber circulator 14, the length of the optical fiber 15 to be detected is 9.3km, backward Rayleigh scattering light of the optical fiber is used as detection light to generate stimulated Brillouin effect with pumping light of BOTDA, the other path of the optical fiber is used as local light, and the local light and the pumping light passing through the second fiber circulator 14 are used as local light
The backward Rayleigh scattered light of the detection pulse enters a polarization diversity photoelectric detector 16 to interfere, the detection bandwidth of the photoelectric detector is DC-400MHz, and interference signals are photoelectrically converted into current signals I (t); and finally, the data acquisition card 17 and the data processor 18 acquire the current signals and process the data. The sampling rate of the data acquisition card 17 is set to 250 MSa/s.
As shown in fig. 2, the relationship between the brillouin gain factor and the pump frequency is:
wherein: g0For a peak gain factor, which value is related to the fiber type, g for a conventional single mode fiber0＝5.0×10-11m/W；ΓBThe bandwidth of the Brillouin gain is dozens of MHz in common single-mode optical fiber; omega is the frequency difference of the pumping light and the probe light; omegaBIs the Brillouin frequency shift of the optical fiber; when Ω is ΩBThe probe light amplitude reaches a maximum value.
In the distributed optical fiber sensing, the position of the optical fiber 15 to be measured is determined by the time of the detection light reaching the polarization diversity photoelectric detector 16, and the specific relationship is as follows: l ═ c' · 2t, where: l is the position of the optical fiber 15 to be measured, c' is the speed of light in the optical fiber 15 to be measured, and t is the time for the probe light at the corresponding position in the optical fiber 15 to be measured to reach the polarization diversity photodetector 16.
From this characteristic, brillouin frequency shifts at different positions in the optical fiber 15 to be measured can be obtained. The brillouin frequency shift is in direct proportion to the strain or temperature of the optical fiber 15 to be measured. Under the constant temperature condition, when the incident light with the wavelength of 1550nm enters the common single-mode quartz optical fiber, the corresponding Brillouin frequency shift is about 1MHz when the strain changes by 20 mu epsilon. Under the condition of room temperature, the Brillouin frequency shift of the common single-mode optical fiber in a relaxed state is about 1MHz when the incident light rises by 1 ℃.
The result after the beat frequency of the local light and the detection light is as follows: p ^ ELEP| a (z) | sin (Δ ω t + φ (z)), where: eLAmplitude of local light, EPTo detect the amplitude of the light, Δ ω represents the frequency difference between the detected light and the local light, and φ (z) represents the phase of the detected light assuming that the initial phase of the local light is zero. Amplitude and phase information is extracted from the beat frequency signal by using a Hilbert transform algorithm, and two orthogonal components are as follows: i ═<Pcos(Δωt)>∝ELEP| a (z) | sin Φ (z) and Q ═ Q<Psin(Δωt)>∝ELEP| a (z) | cos φ (z); the amplitude and phase information of the probe light are:
and phi (z) ═ arctan (I/Q); the phase shift of the probe light caused by the strain of the optical fiber 15 to be measured is:
wherein: n is the refractive index of the optical fiber 15 to be measured, ε is the strain of the optical fiber 15 to be measured, p12And p11And v is the elastic-optical coefficient, v is the Young modulus constant, and L is the length of the strain section of the optical fiber 15 to be measured.
Since the phase shift and the strain are in a linear relationship, the phase of the detection light in space and time can be differentiated to obtain the dynamic strain information of the optical fiber 15 to be measured.
In the embodiment, a pulse pair is input in each distributed measurement period, the length of the measurement period should be greater than or equal to the time that light travels back and forth over the whole sensing fiber, where the length of the sensing fiber is 9.3km, and the sensing period is set to 100 μ s. Pulse pair composed of
The detection pulse 1 and the pump pumping of the BOTDA are more accurately formed, the detection pulse 1 is more accurately input into the sensing optical fiber before the pumping, the pulse width of the detection pulse 1 is 100ns in the embodiment, the pulse width of the pumping is more accurately 50ns, and the interval between the two pulses is 100 ns. The rayleigh scattered light generated by the probe pulse 1 is more accurately brillouin amplified by the immediately following pump, and the gain thereof is determined by the difference between the two frequencies and the brillouin frequency shift of the optical fiber. Rayleigh scattered light generated by the probe pulse 1 is received coherently, the center frequency of the coherently received signal in the embodiment is 80MHz, the received signal is filtered before data processing, and the bandwidth of a filter is 70MHz-90 MHz. And then extracting the intensity and phase of the signal through Hilbert transform, normalizing the intensity of each point on the optical fiber and averaging for 260 times to obtain the gain change of the signal gain of each point on the optical fiber along with the change of the frequency of the pump light, and performing Lorentz fitting on a gain spectrum to more accurately extract the Brillouin frequency shift. The phase is differentiated temporally and spatially by a spatial difference distance of 10m, i.e. the temporal difference is the subtraction of the phase of the signal obtained for each sensing period from the first. Finally, the vibration information can be demodulated.
Based on the above arrangement, in the present embodiment, a test experiment is performed on a 9260m long optical fiber to be tested, the front 9175m of the optical fiber to be tested is placed at room temperature without additional strain, then 5m is wound on the piezoelectric ceramic, the piezoelectric ceramic is used for applying vibration to the optical fiber wound thereon, and the last 80m optical fiber is placed in a constant temperature water bath kettle which can change the temperature of the optical fiber placed therein. An electric signal is applied to the piezoelectric ceramic to generate 3000 Hz sinusoidal vibration, and the temperature of the water bath is set to be 27.2 ℃, 41.2 ℃ and 47.7 ℃. These 3 different cases were measured separately.
The experimental results are as follows: for the temperature measurement results shown in fig. 2 to 4, a vibration point of 5m and a temperature change section of 100m are simultaneously arranged at the front and back of the tail end of the optical fiber, for static measurement, as shown in fig. 2, the system can realize a spatial resolution of 5m and a measurement distance of 9.3Km, fig. 3 shows the brillouin gain spectrum of the last 500m of the sensing optical fiber, the temperature of the temperature change section is set to 41 ℃, the rest of the optical fibers are placed at room temperature of 27 ℃, and fig. 4 shows the brillouin gain spectrum of the temperature measurement section at temperatures of 27 ℃, 41 ℃ and 46 ℃ respectively. For static variables, the measurement precision is 20 microstrain/1 ℃, and the measurement range is 4 millistrain/200 ℃; the measured temperature coefficient is 1.0843 MHz/DEG C, which accords with the actual situation. The measurement accuracy is 1.0122MHz, and the measurement accuracy of the traditional BOTDA system is about 1MHz, and it can be seen that the measurement result of the subsystem of the static measurement of the system has no index deterioration compared with the traditional system for measuring the static variable alone.
The measurement results of the vibration are shown in fig. 5 and 6. Fig. 5 shows that the vibration of the vibration point is a sinusoidal vibration of 3 khz for the differential phase at the vibration point, which well restores the sinusoidal shape of the vibration, and fig. 6 shows the frequency spectrum of the fast fourier transform of the vibration point, which well restores the information of 3 khz. For dynamic measurement, the embodiment can realize the index with the spatial resolution of 10m and the measurement bandwidth of 5 kilohertz. It can be seen that the vibration frequency information of 3000 hz is also well extracted, and the signal-to-noise ratio is 22.1dB compared to the noise floor. The effect of a traditional independent system for measuring vibration independently is achieved.
To sum up, the utility model discloses utilize the rayleigh scattered light of previous pulse to conduct simultaneously
The detection light of the BOTDA and the detection light of the BOTDA are used, so that the static and dynamic variables can be measured simultaneously, and the system is simple. The average number of times of measurement of static variables can be reduced to one tenth or even higher than the BOTDR scheme. Meaning a significant reduction in measurement time. The measurement index is compared with BOTDA alone and BOTDA alone under the condition that the sensing distance is 9260m
The system is not significantly degraded compared to the prior art.
The foregoing embodiments may be modified in various ways by those skilled in the art without departing from the spirit and scope of the present invention, which is not limited by the above embodiments but is to be accorded the full scope defined by the appended claims, and all such modifications and variations are within the scope of the invention.
Claims (5)
1. A dynamic and static combined measurement distributed optical fiber sensing system is characterized by comprising: laser instrument, three beam splitter, light modulation module, two acousto-optic modulators, the ware of disturbing partially, erbium-doped fiber amplifier, first optic fibre circulator, coherent receiver, signal acquisition processing module, wherein: the first optical splitter connects one output end of the laser with the optical fiber to be tested through the optical modulation module, the first optical fiber circulator, the first acousto-optic modulator, the polarization scrambler, the third optical splitter and the erbium-doped optical fiber amplifier in sequence; the other output end is divided into two paths by a second optical splitter, and the other output end is formed by a second acousto-optic modulator
The detection pulse is connected with the optical fiber to be detected through a third optical splitter and an erbium-doped optical fiber amplifier, the other path of the detection pulse is connected with the output end of the second optical fiber circulator and a coherent receiver respectively, and the coherent receiver is connected with a signal acquisition processing module;
and the second optical fiber circulator is arranged between the erbium-doped optical fiber amplifier and the optical fiber to be detected.
2. The system according to claim 1, wherein the optical splitter is a fiber coupler with a splitting ratio of 50/50.
3. The system according to claim 1, wherein the optical modulation module comprises: a radio frequency signal generator, an optical modulator, a DFB laser, and a polarization controller, wherein: the radio frequency signal generator is connected with the optical modulator, the DFB laser is connected with the polarization controller, one end of the optical modulator is connected with the first optical splitter, and the other end of the optical modulator is connected with the polarization controller through the first optical fiber circulator.
4. The system according to claim 1, wherein the coherent receiver is a polarization diversity photodetector.
5. The dynamic and static combined measurement distributed optical fiber sensing system according to claim 1, wherein the signal acquisition and processing module comprises: a data acquisition card and a data processor which are connected with each other.
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| CN112284511B (en) * | 2020-11-16 | 2024-08-13 | 上海交通大学 | Distributed fiber optic sensing system for dynamic and static combined measurement |
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