CN103063325A - BOTDA temperature and strain simultaneous measurement method based on LEAF optical fiber - Google Patents
BOTDA temperature and strain simultaneous measurement method based on LEAF optical fiber Download PDFInfo
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Abstract
The invention discloses a BOTDA temperature and strain simultaneous measurement method based on a LEAF optical fiber, and provides simultaneous measurement of temperature and stress by utilizing the characteristic that a stimulated Brillouin gain spectrum in the LEAF optical fiber has a plurality of gain peaks, aiming at the defect that the absolute power of an optical signal cannot be accurately measured in the conventional temperature and strain simultaneous measurement method, so that the measurement precision cannot be improved. Stimulated Brillouin scattering is generated in the LEAF optical fiber by using continuous detection light and narrow-linewidth pulse pumping light, Brillouin frequency shift and linewidth of a first gain peak and a second gain peak of a Brillouin scattering signal are measured, and measured data are fitted by using a fitting algorithm, so that measurement of temperature and stress distribution along the optical fiber is completed. The invention does not need to measure the absolute power of the Brillouin scattering signal, effectively improves the dynamic performance and the spatial resolution of the BOTDA system, and has wide application prospect in a distributed optical fiber sensing system.
Description
Technical field
The invention belongs to the photoelectron technology field, relate to optical fiber sensing technology, particularly a kind of BOTDA temperature and strain while measuring method based on LEAF optical fiber.
Background technology
In distributed Brillouin sensing, two kinds of Brillouin light domain reflectometer BOTDR and Brillouin light time domain reflection technology BOTDA are arranged.In the temperature and strain sensing system of routine, no matter be that BOTDR or BOTDA all use single-mode fiber as sensor information, and by analyzing the Brillouin scattering gain spectral, i.e. the variation of the power of Brillouin's signal and Brillouin shift (centre frequency of pump light pulse and Brillouin scattering centre frequency poor) obtains the information of temperature and strain.
In distributed Brillouin sensing system, the transmission range of the transducing signal of diverse location in light path is different, and signal has different losses, and this has greatly affected the measurement to brillouin scattering signal power.Light source self power is unstable in addition, and the factors such as interchannel noise have also caused very large impact to the measurement of brillouin scattering signal power.In the present brillouin distributed sensor-based system, the measuring error of the overwhelming majority is that the measuring error by brillouin scattering signal power causes.
In order to improve the precision to the brillouin scattering signal power measurement, the method for introducing reference light in measuring system is suggested.Under the present technical conditions, usually adopt the Rayleigh scattering light signal and oppositely the Stokes light signal as reference light, thereby comparatively efficiently solve the problem such as the fixed and long Distance Transmission of flashing to the impact of signal power.But the measured value fluctuation that the factors such as the noise of optical power detector self and measuring accuracy cause remains the principal element of restriction temperature and strain measurement precision and sensor-based system resolution and dynamic range.
Based on this, the present invention proposes the multimodal measuring method that has a plurality of gain peak based on LEAF optical fiber Brillouin gain spectral.In this method, abandoned the measurement to the brillouin scattering signal absolute power, thereby avoided the impact of optical signal power measuring error on measurement result.
Summary of the invention
For above-mentioned prior art, the object of the present invention is to provide simultaneously measuring method of a kind of BOTDA temperature based on LEAF optical fiber and strain, make temperature and the strain can be simultaneously measured, avoided the impact of optical signal power measuring error on measurement result.
In order to solve the problems of the technologies described above, the present invention adopts following technical scheme
Principle of work of the present invention is: adopt continuous probe light and burst pulse single-frequency pump light to produce stimulated Brillouin scattering in LEAF optical fiber, brillouin scattering signal and local reference optical signal are carried out after difference frequency detects, obtain Brillouin shift and the live width of first and second gain peak of LEAF stimulated Brillouin scattering in optical fiber signal, obtain temperature and strain on this measurement space by data fitting, change and measure temperature and the Strain Distribution that constantly then can obtain along optical fiber.
A kind of BOTDA temperature and strain while measuring method based on LEAF optical fiber may further comprise the steps:
1. wavelength continuous light source signal obtains suitable signal intensity by optical attenuator, as surveying light signal;
2. the narrow linewidth light signal is divided into first via light signal and the second road light signal by coupling mechanism;
3. first via light signal adopts the electric light intensity modulated to modulate by behind the Polarization Controller, rationally arrange obtain after the modulation parameter frequency shifts be approximately equal to Brillouin shift on the pump light pulse that moves and move down;
4. the signal that moves on the optical filter selecting frequency is as the pumping pulse signal, and makes the pumping pulse signal by polarization scrambler, can reduce like this polarization mismatch between pump light signals and the detection light signal;
5. will survey light signal and pump light signals and be injected into the LEAF optical fiber from two ends, produce stimulated Brillouin scattering;
6. the second road light signal carries out heterodyne reception with the stimulated Brillouin scattering signal and obtains heterodyne signal as local reference light, thereby obtains the frequency spectrum of brillouin frequency shifting signal; By heterodyne signal and obtain in the LEAF optical fiber first and Brillouin shift and the live width of second gain peak, Brillouin shift and the live width of first and second gain peak are carried out data fitting, thereby obtain temperature and strain on this locus;
7. change Measuring Time and obtain temperature and Strain Distribution along optical fiber.
Compared with prior art, the invention has the beneficial effects as follows:
Improved the BOTDA system and measured simultaneously dynamic range and the resolution of temperature and strain, effectively overcome the restriction of measuring light power error to measurement result, in distributed fiber-optic sensor, had broad application prospects.
Description of drawings
Fig. 1 is continuous probe optical spectrum of the present invention;
Fig. 2 is that the present invention surveys optical spectrum, pump light frequency spectrum and brillouin gain spectrum;
Fig. 3 is the frequency spectrum after the present invention surveys light and pump light interaction;
Fig. 4 is the frequency spectrum after the heterodyne of the present invention;
Fig. 5 is structural representation of the present invention;
Reference numeral is: 1 is that wavelength continuous light source, 2 is that optical attenuator, 3 is that LEAF optical fiber, 4 is that optical circulator, 5 is that polarization scrambling instrument, 6 is that electric light intensity modulator, 7 is that Polarization Controller, 8 is that narrow linewidth light source, 9 is that coupling mechanism, 10 is that photodetector, 11 is electric frequency spectrograph.
Embodiment
The invention will be further described below in conjunction with the drawings and the specific embodiments.
A kind of BOTDA temperature and strain while measuring method based on LEAF optical fiber, may further comprise the steps: 1. wavelength continuous light source signal obtains suitable signal intensity by optical attenuator, as surveying light signal; 2. the narrow linewidth light signal is divided into first via light signal and the second road light signal by coupling mechanism; 3. first via light signal adopts the electric light intensity modulated to modulate by behind the Polarization Controller, rationally arrange obtain after the modulation parameter frequency shifts be approximately equal to Brillouin shift on the pump light pulse that moves and move down; 4. the signal that moves on the optical filter selecting frequency is as the pumping pulse signal, and makes the pumping pulse signal by polarization scrambler, can reduce like this polarization mismatch between pump light signals and the detection light signal; 5. will survey light signal and pump light signals and be injected into the LEAF optical fiber from two ends, produce stimulated Brillouin scattering; 6. the second road light signal carries out heterodyne reception with the stimulated Brillouin scattering signal and obtains heterodyne signal as local reference light, thereby obtains the frequency spectrum of brillouin frequency shifting signal; By heterodyne signal and obtain in the LEAF optical fiber first and Brillouin shift and the live width of second gain peak, Brillouin shift and the live width of first and second gain peak are carried out data fitting, thereby obtain temperature and strain on this locus; 7. change Measuring Time and obtain temperature and Strain Distribution along optical fiber.
Embodiment
Wavelength coverage be the wavelength continuous light source of 400nm-2400nm through obtaining the suitable detection light of intensity behind the optical attenuator 2, its frequency spectrum and remembers that its centre frequency is as shown in Figure 1
Frequency is the narrow linewidth light source about 1MHz, is divided into two by 1:2 coupling mechanism 10.First via light signal is modulated by Polarization Controller 8 rear employing electric light intensity modulators 7, parameters so that modulator 7 output frequencies be
, pulsewidth is the pulsed light of 10ns, wherein
Be Brillouin shift.After adopting the filtering of optical filter pulse signals, only output frequency is
Pulse.Pulse signal enters polarization scrambling instrument 6 afterwards, so that the polarization state of pulse signal obtains continuous change, thereby avoids the polarization mismatch of pumping pulse light signal and continuous probe light signal.Pulsed optical signals enters in the LEAF optical fiber 3 through behind the optical circulator 4, pumping pulse light and continuous probe light will interact and produce stimulated Brillouin scattering in LEAF optical fiber 3, survey optical spectrum, pump light frequency spectrum and stimulated Brillouin scattering gain spectral as shown in Figure 2, the frequency spectrum of the stimulated Brillouin scattering that detection light and pump light interaction produce as shown in Figure 3.The stimulated Brillouin scattering signal carries out heterodyne reception through the second road signal in circulator 4 and the coupling mechanism 10 in photodetector 11 afterwards, and the heterodyne signal frequency spectrum that obtains after the heterodyne as shown in Figure 4.Can be obtained Brillouin shift and the live width of LEAF stimulated Brillouin scattering in optical fiber signal first and second gain peak by heterodyne signal shown in Figure 4, thereby can obtain temperature and strain on this locus, change and measure temperature and the Strain Distribution that constantly can obtain along optical fiber, need to prove that the live width at excited Brillouin spectrum gain peak in this example of the present invention refers to the full width at half maximum FWHM of peak value.
In the present embodiment, the Brillouin shift by LEAF stimulated Brillouin scattering in optical fiber signal first and second gain peak and live width obtain the process that temperature on this locus and strain need a demarcation.Temperature and strain on stimulated Brillouin scattering spectrum and the locus, LAEF optical fiber place have following relation:
In the formula
Be respectively strain, temperature, Brillouin shift, live width;
,
,
,
,
,
,
,
Be corresponding constant coefficient, wherein 1,2 represent respectively stimulated Brillouin scattering and compose first and second gain peak.Changing the temperature at place, a certain locus and strain takes multiple measurements the LEAF of this place, space and can obtain the corresponding sensing variable space:
The dependent variable space:
Then can get:
Can be in the hope of the constant coefficient matrix by data fitting:
Then for the spectrum of the stimulated Brillouin scattering in arbitrary LEAF optical fiber, bring formula (1) with its first into Brillouin shift and the live width of second gain peak, adopt optimization algorithm to ask optimum solution can obtain temperature and the strain of this locus.
Claims (2)
1. BOTDA temperature and strain while measuring method based on a LEAF optical fiber is characterized in that, may further comprise the steps:
1. wavelength continuous light source signal obtains suitable signal intensity by optical attenuator, as surveying light signal;
2. the narrow linewidth light signal is divided into first via light signal and the second road light signal by coupling mechanism;
3. first via light signal adopts the electric light intensity modulated to modulate by behind the Polarization Controller, rationally arrange obtain after the modulation parameter frequency shifts be approximately equal to Brillouin shift on the pump light pulse that moves and move down;
4. the signal that moves on the optical filter selecting frequency is as the pumping pulse signal, and makes the pumping pulse signal by polarization scrambler, can reduce like this polarization mismatch between pump light signals and the detection light signal;
5. will survey light signal and pump light signals and be injected into the LEAF optical fiber from two ends, produce stimulated Brillouin scattering;
6. the second road light signal carries out heterodyne reception with the stimulated Brillouin scattering signal and obtains heterodyne signal as local reference light, thereby obtains the frequency spectrum of brillouin frequency shifting signal; By heterodyne signal and obtain in the LEAF optical fiber first and Brillouin shift and the live width of second gain peak, Brillouin shift and the live width of first and second gain peak are carried out data fitting, thereby obtain temperature and strain on this locus;
7. change Measuring Time and obtain temperature and Strain Distribution along optical fiber.
2. BOTDA temperature and strain while measuring method based on LEAF optical fiber according to claim 1 is characterized in that, temperature and strain on described stimulated Brillouin scattering spectrum and the locus, LAEF optical fiber place have following relation:
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CN103954226A (en) * | 2014-04-03 | 2014-07-30 | 华南理工大学 | Long-distance distributed type large-measuring-range rapid response optical fiber dynamic strain sensing device |
CN104568019A (en) * | 2015-02-06 | 2015-04-29 | 华北电力大学(保定) | Multimode fiber-based method and multimode fiber-based system for simultaneously measuring temperature and strain |
CN105784190A (en) * | 2014-12-23 | 2016-07-20 | 北京邮电大学 | Stimulated Brillouin effect-based differential temperature sensor |
CN109632134A (en) * | 2019-01-07 | 2019-04-16 | 东莞理工学院 | A kind of Brillouin optical time domain analysis temperature, strain decoupling method and system |
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CN111121873A (en) * | 2019-12-30 | 2020-05-08 | 武汉奥旭正源电力科技有限公司 | Distributed optical fiber sensing device |
CN112050747A (en) * | 2020-09-30 | 2020-12-08 | 中电科仪器仪表有限公司 | Brillouin strength and frequency shift strain temperature coefficient automatic test system and method |
CN113375837A (en) * | 2021-06-11 | 2021-09-10 | 中电科思仪科技股份有限公司 | Method and device for automatically measuring temperature coefficient of optical quantum BOTDR optical fiber |
CN114812855A (en) * | 2022-03-16 | 2022-07-29 | 上海波汇科技有限公司 | Brillouin optical time domain scattering system based on optical flight time and self-calibration method |
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