CN113340458A - Intelligent safety early warning system based on new generation distributed optical fiber sensing technology - Google Patents
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- G—PHYSICS
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- G01K—MEASURING TEMPERATURE; MEASURING QUANTITY OF HEAT; THERMALLY-SENSITIVE ELEMENTS NOT OTHERWISE PROVIDED FOR
- G01K11/00—Measuring temperature based upon physical or chemical changes not covered by groups G01K3/00, G01K5/00, G01K7/00 or G01K9/00
- G01K11/32—Measuring temperature based upon physical or chemical changes not covered by groups G01K3/00, G01K5/00, G01K7/00 or G01K9/00 using changes in transmittance, scattering or luminescence in optical fibres
- G01K11/322—Measuring temperature based upon physical or chemical changes not covered by groups G01K3/00, G01K5/00, G01K7/00 or G01K9/00 using changes in transmittance, scattering or luminescence in optical fibres using Brillouin scattering
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B11/00—Measuring arrangements characterised by the use of optical techniques
- G01B11/16—Measuring arrangements characterised by the use of optical techniques for measuring the deformation in a solid, e.g. optical strain gauge
- G01B11/168—Measuring arrangements characterised by the use of optical techniques for measuring the deformation in a solid, e.g. optical strain gauge by means of polarisation
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Abstract
本发明一种基于新一代分布式光纤传感技术智慧安全预警系统，包括半导体量子级联激光器，所述半导体量子级联激光器的输出端与光隔离器输入端连接；所述光隔离器输出端与１＊２的光纤耦合器输入端连接，分光比为1:1，将半导体量子级联激光器输出的光分为泵浦光和信号光两路。本发明应用了布里渊光时域分析技术的原理，当传感光纤某处温度改变或者产生应变时，对应的布里渊偏移量也发生改变，采集到此时的布里渊散射信号。如此实际可以测得传感光纤各点处的布里渊散射光的强度和频移值，再根据其与温度和应变的对应关系，即时计算出传感光纤各点的温度和应变信息。
The present invention is an intelligent security early warning system based on a new generation of distributed optical fiber sensing technology, comprising a semiconductor quantum cascade laser, the output end of the semiconductor quantum cascade laser is connected with the input end of the optical isolator; the output end of the optical isolator is connected. It is connected to the input end of the 1*2 fiber coupler, and the splitting ratio is 1:1, and the light output by the semiconductor quantum cascade laser is divided into two paths: pump light and signal light. The invention applies the principle of Brillouin optical time domain analysis technology. When the temperature of the sensing fiber changes or strain occurs, the corresponding Brillouin offset also changes, and the Brillouin scattering signal at this time is collected. . In this way, the intensity and frequency shift of the Brillouin scattered light at each point of the sensing fiber can actually be measured, and then the temperature and strain information of each point of the sensing fiber can be calculated in real time according to the corresponding relationship with the temperature and strain.
Description
Technical Field
The invention relates to the field of simultaneous monitoring of distributed optical fiber sensing temperature and strain, in particular to a BOTDA system of stimulated Brillouin scattering based on a quantum theory.
Background
Along with the obvious acceleration of the urbanization process in China, the population, functions and scale of cities are continuously enlarged, city operation systems driven by energy sources are increasingly complex, power cable underground transmission networks and underground gas heating power pipe networks are distributed in all corners of the cities, and energy supply facilities such as gas stations, gas storage stations and the like closely related to the lives of residents are surrounded by the cities layer by layer. In recent years, large-scale safety accidents frequently occur, and urban safety risks are increasing continuously.
The electronic sensor for acquiring the traditional real-time data is influenced by the terrain and the environment, is easily subjected to flooding, corrosion, insufficient endurance and strong electromagnetic interference environment, cannot be suitable for stably providing monitoring data for a long time, causes monitoring blank and even is difficult to manually patrol; the potential safety hazard is left, the effective supervision and the like cannot be realized, and a plurality of monitoring dead angles still exist in the fields within the burying range of the power cable and the underground pipe network.
The distributed optical fiber sensing technology is based on the fact that optical fibers in structures built in power cables and underground pipe networks serve as transmission media and sensing media, the measurement of information such as temperature and strain of the sensing optical fibers is sequentially completed by the aid of an optical transmission principle in the optical fibers, the advantages of being passive in long distance, resistant to electromagnetic interference, resistant to corrosion and capable of achieving simultaneous monitoring of temperature and strain are integrated, and the non-replaceable technical status with complete functions and strong environmental adaptability is displayed for the safety early warning industry of the current power cables and underground pipe networks in the embedding range.
Disclosure of Invention
In order to solve the problems, the invention provides an intelligent safety early warning system based on a distributed optical fiber sensing technology of a quantum theory.
The technical scheme of the invention is as follows:
the intelligent safety early warning system based on the new generation distributed optical fiber sensing technology is characterized by comprising a semiconductor quantum cascade laser (1), wherein the output end of the semiconductor quantum cascade laser (1) is connected with the input end of an optical isolator (2); the output end of the optical isolator (2) is connected with the input end of a 1 h 2 optical fiber coupler (3), the light splitting ratio is 1:1, and light output by the semiconductor quantum cascade laser (1) is divided into two paths of pump light and signal light;
the output end of one path of the pump light of the optical fiber coupler (3) is connected with the first input end of the acousto-optic modulator (4), and the first output end of the field programmable gate array FPGA (14) is connected with the second input end of the acousto-optic modulator (4) and used for synchronously controlling the modulation pulse frequency of the input pump light; the output end of the acousto-optic modulator (4) is connected with the input end of an erbium-doped fiber amplifier (5) and amplifies input pump light to a pump light power threshold required by stimulated Brillouin scattering, the output end of the erbium-doped fiber amplifier (5) is connected with the input end of a polarization scrambler (6) and outputs unpolarized pump light with equal light intensity in all directions, and the output end of the polarization scrambler (6) is connected with a first optical circulator (7) and enters the initial end of a sensing fiber (12);
the output end of one path of signal light of the optical fiber coupler (3) is connected with the input end of a three-ring polarization controller (8), the polarization direction is adjusted and controlled to be non-polarized light, the output end of the three-ring polarization controller (8) is connected with the first input end of an electro-optical intensity modulator (9), the first output end of a microwave frequency sweep device (15) is connected with the second input end of the electro-optical intensity modulator (9), the modulated signal light generates frequency shift quantity which is equal to the frequency of a microwave signal source, the output end of the electro-optical intensity modulator (9) is connected with the first input end of a second optical circulator (10), the output end of an optical fiber Bragg grating (11) is connected with the second input end of the second optical circulator (10) and used for filtering out sidebands of which the frequency is shifted upwards in the modulated light, and the modulated light of the sidebands of which the frequency is shifted downwards enters the tail end of a sensing optical fiber as detection light; the output end of the second optical circulator (10) is connected with the tail end of the sensing optical fiber (12), the first optical circulator (7) is further connected with the input end of the photoelectric detector (13) and used for converting Brillouin scattering optical signals into electric signals, the output end of the photoelectric detector (13) is connected with the first input end of the DSP data signal acquisition processor (16), the second output end of the microwave frequency sweep device (15) is connected with the input end of the field programmable gate array FPGA (14), the second output end of the field programmable gate array FPGA (14) is connected with the second input end of the DSP data acquisition processor (16), and the output end of the DSP data acquisition processor (16) is connected with an industrial computer software operation system (17).
Preferably, the isolation of the optical isolator is more than 30dB within the range of the working wavelength of 1535 nm-1565 nm.
The preferred optical isolator insertion loss is 0.42 dB.
The preferred semiconductor quantum cascade laser emits continuous light with main wavelengths of 1um, 1.5um, 2um and 4.617 um; the line width is 1 kHz-10 MHz, and the wavelength can be adjusted in a single transverse mode far field.
Preferably the coupler is a 10 dB coupler.
Preferably, the pumping light is modulated by the acousto-optic modulator AOM to have the working wavelength of 1530nm to 1565nm, the extinction ratio is greater than 50B, the bandwidth is 200 MHz, the insertion loss is 5 dB, the frequency shift amount is shifted up at the frequency of 200 MHz, and the rise time is 10 ns.
The pump light is modulated by the acousto-optic modulator to become pulse light and enters the initial end of the sensing optical fiber, the acousto-optic modulator is an acoustic device which is composed of an acousto-optic medium and a piezoelectric transducer and is used for modulating the laser intensity, the parameters can realize that the line width of the pulse light modulated by the acousto-optic modulator is far smaller than the wavelength shift amount of Brillouin scattering and the Brillouin gain spectrum width, the design modulation extinction ratio is high, the bearing power is high, the rising time is short, and the like. The purposes of increasing the Brillouin gain and improving the resolution of the Brillouin system can be achieved.
The preferred system deflector index is: the insertion loss is lower than 0.05 dB, the working wavelength is 1500 nm-1600 nm, the polarization mode dispersion is lower than 0.01ps, the polarization loss is lower than 0.03 dB, and the output residual polarization degree is less than 2%.
The arrangement can realize equal light intensity in all directions output by the polarization scrambler and reduce signal fluctuation caused by polarization.
The preferred electro-optical intensity modulator is driven by a 10 GHz-12 GHz microwave frequency sweep device, the LiNbQ 3 based on an M-Z push-pull structure has the working wavelength of 1525 nm-1565 nm, the insertion loss of 4.5 dB-5 dB, the extinction ratio of more than 30 dbB and the half-wave voltages of RF and Bias of 3V and 5V respectively.
An electro-optical modulator (EOM) is driven by a microwave frequency sweep device to modulate continuous light to realize frequency shift down, the frequency shift value is equal to the frequency shift of the output frequency of the microwave frequency sweep device, the wavelength of pump pulse light is equal to the wavelength of a laser, and thus the frequency difference of two paths of light which are transmitted in opposite directions and meet at each position of a sensing optical fiber is equal to the output frequency of the microwave frequency sweep device. The frequency of the working microwave frequency sweep device is cyclically scanned between 10GHz and 12GHz, frequency spectrums at all time points can be obtained once scanning is performed, and the time points correspond to positions so as to obtain Brillouin frequency spectrums at the positions along the optical fiber. And then obtaining a three-dimensional graph of light intensity-frequency-position, and extracting required frequency information and intensity information from the three-dimensional graph. The action of the microwave frequency sweep voltage and the direct current bias voltage jointly determines the working point of the electro-optical modulator.
The preferred frequency up-shifted sideband is filtered out with a filter consisting of a second circulator and a fiber bragg grating with a bandwidth of 0.19 nm.
Preferably, the wavelength range of the photoelectric detector is 800nm-1700nm, the output coupling mode is direct current coupling, the 3 dB bandwidth is 25 KHz-200 MHz, the rise time is 1.5us, the gain is 14V/mW, the output impedance is 50q, the minimum noise equivalent power is 10pW/Hz 1/2, the direct current saturation optical power is 220uW @1550nm, the maximum input optical power is 10mW, and the input mode is FC/APC optical fiber coupling.
The invention has the following technical effects:
the invention applies the principle of Brillouin optical time domain analysis technology, namely two paths of light which are transmitted in opposite directions, wherein one path of light is used as pulse pumping light which is driven by a microwave frequency sweep device to modulate; and the other path of the continuous detection light is driven by the microwave frequency sweep device to modulate, the continuous detection light is respectively incident from the head end position of the sensing optical fiber and the tail end of the sensing optical fiber, when the two paths of the continuous detection light meet at a certain position of the sensing optical fiber, the frequency difference of the two paths of the light modulated by closed loop feedback at the position is just equal to the Brillouin frequency shift value corresponding to the optical fiber at the position, the two paths of the light can interact, the high-frequency light can amplify the low-frequency light, namely the Brillouin amplification effect is stimulated, and when the temperature of the certain position of the sensing optical fiber changes or generates strain, the corresponding Brillouin offset also changes, and the Brillouin scattering signal at the moment is acquired. Therefore, the intensity and the frequency shift value of the Brillouin scattering light at each point of the sensing optical fiber can be actually measured, and the temperature and the strain information of each point of the sensing optical fiber can be calculated in real time according to the corresponding relation between the intensity and the frequency shift value and the temperature and the strain.
The spatial positioning is realized by the principle of Optical Time Domain Reflection (OTDR), wherein the pump light is incident from the initial end of the sensing fiber, the backward brillouin scattering generated at the Z point at any position of the sensing fiber returns in the opposite direction to the incident light, the scattered light is received from the pulse incidence for a time f, the transmission distance of the pulse light is 2Z, and the following relations exist: (Z = ct/2n), and the relationship between the scattering signal and the position where the scattering occurs can be determined.
The intelligent safety early warning system for simultaneously monitoring the temperature and the strain in the embedding range of the power cable and the underground pipe network is based on the fact that the built-in or extended optical fiber with the length of tens of kilometers transmits and senses the temperature and the strain information of thousands of points at the same time, and is a safety early warning technology which integrates the advantages of distribution, long distance, electromagnetic interference resistance, corrosion resistance and capability of simultaneously monitoring the temperature and the strain. Meanwhile, the method is also suitable for the fields of building industry, rail transit, electric power systems, hydraulic engineering, petroleum industry, geological detection, aerospace industry and the like.
Drawings
FIG. 1 is a schematic diagram of the system of the present invention.
The reference numbers in the figure are as follows:
the system comprises a semiconductor quantum cascade laser 1, a semiconductor quantum cascade laser 2, an optical isolator 3, a coupler 4, an acousto-optic modulator 5, an erbium-doped optical fiber amplifier 6, a polarization scrambler 7, an optical circulator 8, a three-ring polarization controller 9, an electro-optic intensity modulator 10, a second circulator 11, an optical fiber Bragg grating 12, a sensing optical fiber 13, a photoelectric detector 14, a field programmable gate array FPGA (field programmable gate array) device 15, a microwave frequency scanner 16, a DSP (digital signal processor) data signal acquisition processor 17 and an industrial computer software operation system.
Detailed Description
For a better understanding of the present invention, reference is made to the following detailed description of the invention in conjunction with the accompanying drawings.
As shown in fig. 1, in this embodiment, a high-energy single-frequency low-noise narrow-linewidth semiconductor quantum cascade laser emits 1 continuous light with main wavelengths of 1um, 1.5um, and 2 um; 4.617 um; the line width is 1 kHz-10 MHz, the wavelength can be adjusted in a single transverse mode far field, the output end of the semiconductor quantum cascade laser 1 is connected with the input end of the optical isolator 2, the isolation degree is larger than 30dB within the range of 1535 nm-1565 nm of the working wavelength through the optical isolator 2, and the insertion loss is 0.42 dB. The output end of the optical isolator 2 is connected with the input end of the optical fiber coupler 3 of 10 dB 1 multiplied by 2, the light splitting ratio is 1:1, and the optical fiber coupler is used for splitting the light output by the semiconductor quantum cascade laser 1 into two paths of pump light and signal light.
One path of pump light output end of the optical fiber coupler 3 is connected with a first input end of the acousto-optic modulator 4 (AOM), a first output end of the field programmable gate array FPGA 14 is connected with a second input end of the acousto-optic modulator 4 to synchronously control the frequency of input pump light modulation pulse, one path of pump light is modulated by the acousto-optic modulator 4 (AOM), the working wavelength is 1530 nm-1565 nm, the extinction ratio is more than 50B, the bandwidth is 200 MHz, the insertion loss is 5 dB, the frequency shift amount is up shift of the frequency of 200 MHz, the rise time is 10ns, and the pump light is synchronously controlled with the field programmable gate array FPGA 14 to be pumped with the frequency modulated by the microwave signal source. The output end of the acousto-optic modulator 4 is connected with the input end of an erbium-doped fiber amplifier 5 (EDFA), pumping pulse light is excited by pumping energy through the EDFA, population inversion distribution occurs, and a stimulated radiation effect is generated, so that incident light is amplified in power, the modulated pumping pulse light reaches a threshold value of stimulated Brillouin scattering, and the pumping light power threshold value required by the stimulated Brillouin scattering for amplifying the input pumping light is completed. The output end of the erbium-doped fiber amplifier 5 is connected with the input end of the polarization scrambler 6, and is used for outputting unpolarized pump light with equal light intensity in each direction, the Brillouin gain is closely related to the polarization state of the pump pulse light and the signal light, if the polarization directions of the two beams of light are consistent, the gain is the largest, and the polarization directions are orthogonal and the smallest, so that if the polarization is not processed, signal fluctuation can be caused, and the stability of the Brillouin system is influenced. Thus, a polarization scrambler 6 is connected to the pump light path. The polarization scrambler 6 is a device that changes the polarization state of the light wave by using a high-speed polarization scrambling technology and reduces the polarization degree to 0, so that the light wave passing through the polarization scrambler becomes unpolarized light, namely, the light intensity in each direction is equal, and the signal fluctuation caused by polarization is reduced. System scrambler 6 index: the insertion loss is lower than 0.05 dB, the working wavelength is 1500 nm-1600 nm, the polarization mode dispersion is lower than 0.01ps, the polarization loss is lower than 0.03 dB, and the output residual polarization degree is lower than 2%. The output end of the polarization scrambler 6 is connected with the end (i) of the first optical circulator 7 and enters the initial end of the sensing optical fiber 12.
The other signal light output end of the optical fiber coupler 3 is connected with the input end of the three-ring polarization controller 8, the three-ring polarization controller 8 is used for adjusting and controlling signal light to be unpolarized light, the first output end of the microwave frequency sweep device 15 is connected with the second input end of the electro-optical intensity modulator 9 (EOM), the electro-optical intensity modulator 9 (EOM) is driven by the microwave frequency sweep device 15 with 10 GHz-12 GHz and is used for generating frequency shift quantity with the size equal to the frequency of a microwave signal source through continuous light of the electro-optical intensity modulator 9 (EOM), the EOM of LiNbQ 3 based on an M-Z push-pull structure utilizes the Pockel effect of an electro-optical crystal, the working wavelength is 1525 nm-1565 nm, the insertion loss is 4.5 dB-5 dB, the extinction ratio is larger than 30 dbB, and the half-wave voltages of RF and Bias are respectively 3V and 5V.
The modulated light passing through the electro-optical intensity modulator 9 will generate two sidebands, wherein the sidebands (upper sidebands) with upward frequency are filtered by a filter composed of a second circulator 10 and a fiber bragg grating 11 (FBG) with a bandwidth of 0.19nm, so that the modulated light of the sidebands (lower sidebands) with downward frequency enters the photodetector 13 as probe light through the end of the sensing fiber 12. The output end of the second optical circulator 10 is connected with the tail end of the sensing optical fiber 12, the initial end of the sensing optical fiber 12 is connected with the 7 end of the first optical circulator, the 7 end of the first optical circulator is connected with the input end of the photoelectric detector 13, the weak Brillouin scattering optical signals are converted into electric signals, the PIN photodiode is configured as an optical radiation detector, the quantum efficiency is high, the response time is short, and noise sources such as dark current and surface leakage current can cause small additional noise, so that the technical indexes are as follows: the wavelength range is 800nm-1700nm, the output coupling mode direct current coupling is realized, the 3 dB bandwidth is 25 KHz-200 MHz, the rise time is 1.5us, the gain is 14V/mW, the output impedance is 50q, the minimum noise equivalent power is 10pW/Hz 1/2, the direct current saturated optical power is 220uW @1550nm, the maximum input optical power is 10mW, and the input mode FC/APC optical fiber coupling is realized.
The electro-optical modulator 9 driven by the microwave frequency sweep device 15 modulates the continuous light to realize the frequency shift of the signal light, the generated frequency shift value is equal to the frequency shift of the output frequency of the microwave frequency sweep device 15, the wavelength of the pump pulse light is equal to the wavelength of the laser, and thus, the frequency difference of two paths of light which are transmitted in opposite directions and meet at each position of the sensing optical fiber is equal to the output frequency of the microwave frequency sweep device. In order to acquire the magnitude of stimulated Brillouin gain under different frequency differences and obtain a frequency shift value corresponding to a gain peak value, the frequency of the microwave frequency sweep device 15 is circularly scanned between 10GHz and 12GHz, each time of scanning, a frequency spectrum on each time point can be obtained, the time points correspond to positions to obtain Brillouin frequency spectrums at positions along an optical fiber, a three-dimensional graph of light intensity, frequency and position is further obtained, and required frequency information and intensity information can be extracted from the three-dimensional graph.
The output end of the photoelectric detector 13 is connected with a first input end of the DSP data acquisition processor 16, a second output end of the microwave frequency sweep device 15 is connected with an input end of the field programmable gate array FPGA 14, a second output end of the field programmable gate array FPGA 14 is connected with a second input end of the DSP data acquisition processor 16, and the output end of the DSP data acquisition processor 16 is connected with an industrial computer software operation system 17. The DSP data signal acquisition and processing 16 is a very critical part in the whole system construction, and compared to other scattering type distributed optical fiber sensing systems, the brillouin system has multiple frequencies, multiple positions, complex signals, and many devices, so that the noise sources are many, such as light source noise, ASE noise, noise of scattered light caused by uneven transmission medium, random noise brought by the amplification circuit of the photodetector, and the like.
For data acquisition, an FPGA (field programmable gate array) is used, the main body part of the FPGA is composed of a plurality of groups of programmable logic modules, and the logic modules are connected into a required DSP (digital signal processor) data signal acquisition and processing digital system through programming.
The microwave frequency sweep device 15 outputs a negative pulse synchronization signal to an external trigger signal input end of the FPGA from an output end at the beginning of each frequency sweep, the duration between the time when the next synchronization signal negative pulse is sent is 3000000 us, the arrival of each negative pulse means that the frequency of the microwave frequency sweep device 15 is converted once, the conversion step of each time is 1 MHz, the microwave source is set to be 10500-10900 MHz at the moment, and the frequency of the microwave source is circularly scanned between 10500 MHz and 10900 MHz.
After receiving the trigger signal, the FPGA sequentially generates microwave signals of 400 frequencies within 3000000 us, the period of each frequency is 7500us, the pulse width is 30ns square wave signals, two groups of square wave signals are respectively provided for the drive source input end of the acousto-optic modulator 4 and the synchronous signal end of the DSP data acquisition processor 16 from the first output end (r) and the second output end (r) by the FPGA, the DSP data acquisition processor 16 can sequentially acquire signals of 75 times under each frequency, and if the accumulation number of times of the DSP data acquisition processor 16 is set to 75, the signals under each frequency can be cyclically acquired to obtain a brillouin gain spectrum required by on-site monitoring. The data collected in each period under each fixed frequency shows the change of the signal intensity with the position under the frequency, the signal intensity under each frequency collected at the same time point of each period, namely the same position of the optical fiber, and the frequency corresponding to the maximum intensity point is calculated through software, so that the Brillouin frequency shift value corresponding to the point information is obtained. Therefore, the intensity and the frequency shift value of the Brillouin scattering light at each point of the sensing optical fiber can be actually measured, and the temperature and the strain information of each point of the sensing optical fiber can be calculated in real time according to the corresponding relation between the intensity and the frequency shift value and the temperature and the strain, and are displayed on a computer monitoring interface.
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Application publication date: 20210903 |