CN102997949B - Method used for measuring temperature and strain simultaneously and based on brillouin scattering - Google Patents
Method used for measuring temperature and strain simultaneously and based on brillouin scattering Download PDFInfo
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Abstract
A method used for measuring temperature and strain simultaneously and based on brillouin scattering adopts one measuring system. The measuring system comprises a narrow linewidth laser, a polarization-maintaining coupler, an optical coupler, an optical modulator, an optical amplifier, a circulator, a photoelectric detector and a brillouin frequency shift and strength testing unit. A first optical port of the polarization-maintaining coupler is connected with the laser. A third optical port of the polarization-maintaining coupler is connected with a first optical port of the circulator through the optical modulator and the optical amplifier sequentially. A second optical port of the circulator is connected with sensor fiber, a third optical port of the circulator is connected with a first optical port of the optical coupler, a fourth optical port of the polarization-maintaining coupler is connected with a second optical port of the optical coupler, and a third optical port of the optical coupler is connected with the brillouin frequency shift and strength testing unit through the photoelectric detector. Under the premise that system measuring precision is not reduced, resolution ratio of a measuring space is improved, simultaneously signal to noise ratio of the system can be improved, sensing distance is increased, and measuring time is reduced.
Description
Technical field
The present invention relates to a kind of method utilizing measuring tempeature and the strain simultaneously of Brillouin light Time Domain Reflectometry system, belong to field of measuring technique.
Background technology
Brillouin distributed fiber optic temperature and strain simultaneously measuring technique have and only need that one-shot measurement can obtain, accurate positioning high along the tested field distribution information of whole optical fiber, measuring accuracy, distance can reach the particular advantages such as dozens of kilometres, have a extensive future in the industry heavy construction structural health on-line monitorings such as electric power, oil, building and water conservancy and localization of fault.Brillouin light domain reflectometer (Brillouin Optical Time Domain Reflectometer, BOTDR) be a kind of distributed optical fiber sensing system based on Brillouin scattering, this system utilizes the frequency displacement of backward Brillouin scattering light in sensor fibre and the linear changing relation of intensity and temperature and strain, in conjunction with optical time domain reflection technology, measure while temperature and strain can be realized.Advantage that BOTDR relies on single-ended measurement, device is simple, practical engineering application is convenient etc., is widely used with straining in on-line monitoring and Gernral Check-up in the temperature of a lot of infrastructure engineering facility.
In BOTDR sensor-based system, the frequency displacement of spontaneous brillouin scattering signal and intensity affect by the temperature of environment residing for optical fiber and strain, in order to obtain on sensor fibre temperature everywhere and strain information, first direct impulse light must be injected sensor fibre, then in the frequency displacement of brillouin scattering signal everywhere of same one end measuring optical fiber and intensity.The Brillouin scattering one_to_one corresponding at receiving end photoelectric detector diverse location place on the scattering spectrum do not obtained in the same time and optical fiber.Because the frequency of Brillouin scattering is up to 10
14the Hz order of magnitude, detects within the scope of general adopt optical heterodyne method the frequency of Brillouin scattering spectral signal to be down to radio frequency that photoelectric detector can respond or IF-FRE.The frequency displacement of Heterodyne detect gained Brillouin signal is about 11 GHz, need convert it to comparatively low-frequency range with microwave low-converter, and is scanned whole Brillouin spectrum by the mode of scanning microwave local oscillation frequency, realizes the measurement of Brillouin shift and intensity.Regulate local frequency to change the centre frequency of difference frequency signal, obtain a series of test curve, then at frequency domain, Lorentz fit is carried out to often some test result on optical fiber, obtain the Brillouin spectrum of every bit; The frequency that Brillouin spectrum intensity maximum point is corresponding is the Brillouin shift of this scattering point, can Brillouin's intensity of this point to spectral integral.Utilize the frequency displacement of Brillouin scattering and the linear changing relation of intensity and temperature and strain, the temperature along sensor fibre any position place and strain information can be obtained.
In BOTDR system, spontaneous brillouin scattering light signal is very faint, therefore detection difficulty is larger; In addition, due to the restriction by phonon lifetime, System spatial resolution and measuring accuracy restrict mutually, cannot improve simultaneously.According to literature survey, the people such as Yahei Koyamada proposed dipulse (Double Pulse in 2007, DP) BOTDR technology, the coherence of the backward Brillouin scattering light produced by single sound wave improves Brillouin shift measuring accuracy and System spatial resolution simultaneously, achieves spatial resolution 20 cm, measuring accuracy
1 DEG C and
the temperature of 20 μ ε or the measurement respectively of strain.Though described method overcomes the contradiction between System spatial resolution and measuring accuracy, measure while temperature and strain can not be realized, and fail effectively to improve system signal noise ratio, limit the distance sensing of whole system.
Summary of the invention
The object of the invention is to the drawback overcoming prior art, there is provided one can improve distance sensing and measuring speed simultaneously, overcome the contradiction between System spatial resolution and measuring accuracy, be applied to the temperature based on Brillouin scattering and the strain measuring method simultaneously of long distance temperature and strain sensing.
The method of the invention realizes with following technical proposals:
A kind of temperature based on Brillouin scattering and strain measuring method simultaneously, described method adopts a measuring system to carry out, and described measuring system comprises narrow linewidth laser, polarization-maintaining coupler, photo-coupler, the photomodulator driven by step pulse generator, image intensifer, two grating filters, circulator, photoelectric detector, Brillouin shift and intensity detection unit and sensor fibre; First light mouth of described polarization-maintaining coupler connects laser instrument, 3rd light mouth connects the first light mouth of circulator successively through photomodulator, image intensifer, the first grating filter, second light mouth of circulator connects sensor fibre, 3rd light mouth connects the first light mouth of photo-coupler through the second grating filter, 4th light mouth of polarization-maintaining coupler connects the second light mouth of photo-coupler, and the 3rd light mouth of photo-coupler connects Brillouin shift and intensity detection unit through photoelectric detector.
Described measuring system is measured as follows:
The continuous light that narrow linewidth laser sends is divided into two-way after polarization-maintaining coupler, and a road, as local oscillator light, enters photoelectric detector through photo-coupler; Another road is as detection light, and being step pulse optical width through light modulator modulates is
d pre , sensing impulse optical width is
dladder light pulse after, sensor fibre is injected again through image intensifer, the first grating filter and circulator, the Brillouin scattering obtained enters the second grating filter and carries out filtering, local oscillator light and filtered Brillouin scattering light signal produce Brillouin spectrum electric signal after photoelectric detector heterodyne, Brillouin shift and intensity detection unit process this signal, temperature and the strain information of arbitrary position on sensor fibre can be obtained, measure while realizing temperature and Strain Distribution.
The above-mentioned temperature based on Brillouin scattering and strain measuring method simultaneously, described Brillouin shift and intensity detection unit are by low-converter, bandpass filter, low-pass filter, two wave detectors, high-speed data acquisition card and computing machine composition, the output terminal of the input termination photoelectric detector of described low-converter, its output signal is divided into two-way, one tunnel enters the first passage of high-speed data acquisition card successively through bandpass filter and first detector, another road enters the second channel of high-speed data acquisition card successively through low-pass filter and second detector, the output terminate computer of described high-speed data acquisition card.
Described Brillouin shift and intensity detection unit are measured as follows:
The frequency of low-converter medium frequency synthesizer is regulated to change the centre frequency of difference frequency signal, the signal of Brillouin spectrum different frequency composition is made to pass through bandpass filter successively, by first detector, Brillouin spectrum is moved tremendously low frequency without distortion again, and then obtain a series of test curve, then at frequency domain, Lorentz fit is carried out to often some test result on optical fiber, obtain the Brillouin spectrum that pre-pumping pulse produces, the frequency that Brillouin spectrum intensity maximum point is corresponding is just the Brillouin shift of this scattering point, the output frequency of adjustment low-converter medium frequency synthesizer, to change the centre frequency of the difference frequency signal of local oscillator and scattered signal, Brillouin spectrum is made intactly to pass through low-pass filter, by second detector, Brillouin spectrum is moved tremendously low frequency without distortion again, the Brillouin spectrum on whole optical fiber can be obtained, the i.e. synthesis spectrum of the Brillouin spectrum of pre-pumping pulse and sensing impulse generation, thus Brillouin's intensity of each scattering point on optical fiber can be obtained, utilize the linear changing relation of Brillouin shift and intensity and temperature and strain, through system calibrating, temperature and the strain information of arbitrary position on sensor fibre can be obtained, measure while realizing temperature and Strain Distribution.
The above-mentioned temperature based on Brillouin scattering and strain measuring method simultaneously, in order to reduce the impact of Brillouin scattering polarization state change on Heterodyne detect, adds scrambler between polarization-maintaining coupler and photo-coupler.
The above-mentioned temperature based on Brillouin scattering and strain measuring method simultaneously, described step pulse generator comprises t connector, signal synthesizer and two pulse signal generators, the input end of the output termination t connector of the first pulse signal generator, first of t connector exports the input end of termination second pulse signal generator, the first input end of the output termination signal synthesizer of the second pulse signal generator, second output terminal of t connector connects the second input end of signal synthesizer through time delay device, the radio-frequency head of the output termination photomodulator of signal synthesizer.
Described step pulse generator production burst as follows: first produce by the first pulse signal generator the electric pulse that a width is less than phonon lifetime, this electric pulse is divided into two-way after t connector, wherein a road is as the trigger pip of the second pulse signal generator, when there is rising edge in this trigger pip, second pulse signal generator send a width be greater than phonon lifetime and amplitude lower than the pulse signal of sensing impulse, and this pulse signal is delivered to the first input end of signal synthesizer, the pulse signal of t connector second output terminal enters the second input end of signal synthesizer after time delay device time delay, by signal synthesizer its two input signal synthesized a stepped electrical pulse and send into the radio-frequency head of photomodulator.
The above-mentioned temperature based on Brillouin scattering and strain measuring method simultaneously, described photomodulator also can be replaced by two end to end lithium niobate light intensity modulators, first utilizes the working point (DC offset voltage) of the first lithium niobate light intensity modulator to determine the amplitude of pre-pumping pulse light; The width of sensing impulse light is decided subsequently by controlling electronic pulse width; Eventually through the width of the pulse width determination step pulse light of control second lithium niobate light intensity modulator.
The present invention adopts the modulation system of the pre-pumping of pulse, the shaping of Brillouin spectrum and the amplification of transducing signal is realized by the stimulated Brillouin scattering effect between pre-pumping pulse and sensing impulse, can under the prerequisite not reducing the measuring precision, improve measurement space resolution, also system signal noise ratio can be improved simultaneously, increase distance sensing, reduce Measuring Time.
Accompanying drawing explanation
Below in conjunction with accompanying drawing, the invention will be further described.
Fig. 1 is measuring system schematic diagram provided by the present invention;
Fig. 2 is the schematic diagram of incident ladder light pulse and BSS shaping principle;
Fig. 3 is the energy trasfer schematic diagram of sensing impulse and spontaneous brillouin scattering signal SBS effect;
Fig. 4 and Fig. 5 is respectively the principle schematic of two kinds of producing methods of ladder light pulse.
In figure, list of reference numerals used is: LD, narrow linewidth laser, C1, polarization-maintaining coupler, C2, photo-coupler, SPG, step pulse generator, EOM, photomodulator, EOM1, first lithium niobate light intensity modulator, EOM2, second lithium niobate light intensity modulator, EDFA, image intensifer, OC, circulator, GF1, first grating filter, GF2, second grating filter, PD, photoelectric detector, FUT, sensor fibre, PS, scrambler, FC, low-converter, BPF, bandpass filter, LPF, low-pass filter, D1, first detector, D2, second detector, DAQ, high-speed data acquisition card, PC, computing machine, TDU, Brillouin shift and intensity detection unit.
Embodiment
Technical scheme of the present invention is: the light sent by narrow linewidth laser LD exports through polarization-maintaining coupler C1, and a road light is as local oscillator light, and another Lu Guangjing photomodulator (Electro-Optic Modulator, EOM) is modulated into ladder light pulse.First the pre-pumping pulse light that width is greater than phonon lifetime enter sensor fibre FUT preexciting sound wave, and produce spontaneous brillouin scattering signal, and the sensing impulse light frequency that width is less than phonon lifetime remains unchanged, sensing impulse light will by stimulated Brillouin scattering (Stimulated Brillouin Scattering, SBS) effect is amplified the spontaneous brillouin scattering that pre-pumping pulse light produces, return Brillouin spectrum (the Brillouin Scattering Spectrum of incidence end, BSS) BSS that the BSS then produced by the very wide sensing impulse of spectrum width and the very narrow pre-pumping pulse of spectrum width produce is formed by stacking, thus achieve the shaping of BSS.Local oscillator light and Brillouin scattering light signal produce Brillouin spectrum electric signal after photoelectric detector PD heterodyne, and output signal only comprises the brillouin frequency shifting signal after heterodyne, and direct current and second harmonic component are all by filtering.Because Brillouin shift is about 11 GHz, inconvenience directly carries out accurate signal transacting, therefore converts it to comparatively low-frequency range by low-converter FC, and system is measured while adopting the method for scanning microwave local oscillation frequency and electrical domain shift frequency to realize Brillouin shift and intensity.The frequency of microwave frequency synthesizer in low-converter FC is regulated to change the centre frequency of difference frequency signal, make Brillouin spectrum different frequency composition successively by bandpass filter BPF that centre frequency is fixing, by first detector D1, Brillouin spectrum is moved tremendously low frequency without distortion again, and then obtain a series of test curve, then at frequency domain, Lorentz fit is carried out to often some test result on optical fiber, obtain the BSS that the spectrum width of every bit is very narrow, the frequency that BSS intensity maximum point is corresponding is just the Brillouin shift of this scattering point.To adjust frequency the output frequency of synthesizer, to change the centre frequency of difference frequency signal, make Brillouin spectrum intactly by low-pass filter LPF, by second detector D2, Brillouin spectrum is moved tremendously low frequency without distortion again, the Brillouin spectrum on whole optical fiber can be obtained, the synthesis spectrum of the BSS that namely spectrum width is very narrow and the very wide BSS of spectrum width, thus Brillouin's intensity of each scattering point on optical fiber can be obtained.
In order to eliminate polarization decay, in local oscillator light path, adding scrambler (Polarization Scrambler, PS) upset local oscillator polarisation of light state, to reduce not mate by polarization the signal fluctuation brought.
The generation scheme of ladder light pulse in the present invention is as follows:
(1) ladder light pulse is produced by the electric pulse of synthesis two different in width, different amplitude.First pulse signal generator produces a narrow spaces, high-power electric pulse, is divided into two-way through t connector.Wherein a road is input to the second pulse signal generator as trigger pip, and when rising edge appears in trigger pip, the second pulse signal generator sends a wide pulse width, lower powered electric pulse.Another road narrow pulse signal through certain hour delay (being generally the difference of step pulse width and sensing impulse width, to ensure the stringent synchronization of pre-pumping pulse and sensing impulse) and broad pulse together input signal compositor synthesize a stepped electrical pulse.By the radio-frequency head of this stepped electrical pulse input photomodulator EOM, controlled the drift of photomodulator EOM direct current biasing working point simultaneously by bias system, ladder light pulse required in sensor-based system can be modulated.
(2) two lithium niobate light intensity modulators are utilized to produce ladder light pulse.First the working point (DC offset voltage) of the first lithium niobate light intensity modulator EOM1 is utilized to determine pre-pumping pulse light amplitude C
plevel; Width D and the amplitude A of sensing impulse light is decided subsequently by control electronic pulse width and amplitude
p; Finally by the width D of the electronic pulse width determination step pulse light of control second lithium niobate light intensity modulator EOM2
pre.In order to not make the response of the pulse width of impact position information spread, make the average power of the average power of sensing impulse light and pre-pumping pulse light for certain specific ratio.
Feature of the present invention:
(1) SBS is provided to amplify and BSS shaping
When the pulsed light with one section of pre-pumping injects sensor fibre FUT, width is greater than the pre-pumping pulse of phonon lifetime by preexciting sound wave, and produces spontaneous brillouin scattering signal, and the frequency that width is less than the sensing impulse of phonon lifetime remains unchanged.The difference on the frequency of sensing impulse and spontaneous brillouin scattering signal is Brillouin shift, now sensing impulse will amplify the spontaneous brillouin scattering signal of pre-pumping pulse generation by SBS effect, like this, the BSS that the BSS returning incidence end is then produced by the sensing impulse that spectrum width is the very wide and BSS that the very narrow pre-pumping pulse of the spectrum width after amplifying produces is formed by stacking, thus achieves the shaping of BSS.
(2) without single-ended SBS
Threshold property is one of key property of stimulated Brillouin scattering, and and if only if after incident optical power exceedes certain excitation threshold, and single-ended SBS just can occur.In order to improve the signal to noise ratio (S/N ratio) of BOTDR system, wish to obtain incident optical power high as far as possible, but, inject and exceed the increase that the more energy of threshold value can not bring transducing signal energy, a large amount of loss when light can be made on the contrary to transmit in sensor fibre FUT, and coherent noise in system and polarization noise strengthen, signal oscillating is obvious, and the quality of Received signal strength reduces.Choose reasonably pre-pumping pulse and sensing impulse width and amplitude in the present invention, make incident optical power be less than the stimulated Brillouin scattering threshold value of sensor fibre FUT, do not produce single-ended SBS, therefore, the coherent noise in system and polarization noise little.
(3) pumping depletion effect is reduced
When sensor fibre FUT is injected in ladder light pulse, pre-pumping pulse by preexciting sound wave, and produces frequency and is
with
stokes (Stokes) light and anti-Stokes (anti-Stokes) light, and the frequency of sensing impulse
remain unchanged.In the SBS mechanism of anti-Stokes light and sensing impulse, energy is transferred to sensing impulse by anti-Stokes light, and in the SBS mechanism of Stokes light and sensing impulse, energy is transferred to Stokes light by sensing impulse, and in whole mechanism, the energy reduction of sensing impulse is very little.In long-distance optical fiber sensing, the energy of sensing impulse light mainly reduces because of fibre loss, reduces pumping depletion effect.
(4) the SBS effect of light leak generation is little
In system, the extinction ratio of EOM is limited, the ground unrest of system is increased, and comprises the continuous light of leakage in modulated pulse light.Due to the participation of light leak, in BOTDR system, also can there is the SBS effect between spontaneous brillouin scattering that light leak and sensing impulse produce.The selected sufficiently high photomodulator EOM of extinction ratio in the present invention, imitates the impact of answering system with the SBS reducing system background noise and light leak generation.
(5) impact of non-local effect is little
Non-local effect causes due to the energy conversion accumulation of pump light and detection light, reduces pump light and can effectively reduce non-local effect with the interaction length of detection light, make Brillouin spectrum that serious distortion not occur.There is SBS effect in the spontaneous brillouin scattering signal that in the present invention, pre-pumping pulse produces and sensing impulse, only carry temperature in the corresponding length of fibre of pre-pumping pulse and strain information through the Brillouin scattering of SBS effect, the impact of non-local effect on system performance is little.
(6) advantage of the pre-pumping of existing pulse, has again the advantage of spontaneous brillouin scattering
The use of pre-pumping pulse, System spatial resolution is determined primarily of the sensing impulse width of narrower in width, the BSS that frequency measurement accuracy produces primarily of the pre-pumping pulse that spectrum width is very narrow determines, the contradiction between spatial resolution and frequency measurement accuracy can be solved, make the two be improved simultaneously; The existence of SBS amplification in system, makes faint spontaneous brillouin scattering signal be amplified, can improve system signal noise ratio, increases distance sensing, reduces Measuring Time.Suitably choose width and the amplitude of pre-pumping pulse and sensing impulse, SBS effect is therebetween controlled in reasonable level, the linear changing relation of Brillouin's intensity and temperature and strain can be kept, measure while being conducive to high-precision temperature and strain.
As shown in Figure 1, narrow linewidth laser LD sends frequency and is
continuous light, be divided into two-way through polarization-maintaining coupler C1, wherein a road is as local oscillator light, injects photoelectric detector PD through polarization-maintaining coupler C1, photo-coupler C2; Another road, as detection light, is first modulated into ladder light pulse through photomodulator EOM, then injects sensor fibre FUT through image intensifer EDFA, the first grating filter GF1 and circulator OC.Width is greater than the pre-pumping pulse light of phonon lifetime by preexciting sound wave, and produce spontaneous brillouin scattering signal, and the frequency that width is less than the sensing impulse light of phonon lifetime remains unchanged, sensing impulse light amplifies by SBS effect the spontaneous brillouin scattering signal that pre-pumping pulse light produces.Modulation signal spectrum width
time very narrow, Brillouin scattering spectrum is primarily of optical fiber spontaneous Brillouin spectrum width
determine, be about tens of megahertz;
much larger than
time, primarily of
determine; The two quite time, can be by
estimate, wherein the frequency at scattering spectra peak value place is
,
for Brillouin shift.The Brillouin scattering back-propagating successively at optical fiber diverse location place, injects photoelectric detector PD through circulator OC, the second grating filter GF2 and photo-coupler C2, the anti-Stokes light in the second grating filter GF2 filtering Brillouin scattering.In photoelectric detector PD, frequency is
local oscillator light and centre frequency be
brillouin scattering optical heterodyne, through opto-electronic conversion, produce centre frequency be
brillouin spectrum electric signal.The electric signal exported only comprises the brillouin frequency shifting signal after heterodyne, and direct current and second harmonic component are all by filtering.But the Brillouin shift signal frequency obtained like this is about 11 GHz, directly cannot carry out accurate signal transacting, need to adopt low-converter FC signal frequency to be moved in lower frequency band, then carry out signal transacting.Adopt in system and Brillouin's frequency spectrum to be scanned and the mode of electrical domain shift frequency realizes the detection of brillouin scattering signal.The frequency of low-converter FC medium frequency synthesizer is regulated to change the centre frequency of difference frequency signal, make the signal of Brillouin spectrum different frequency composition successively by bandpass filter BPF, by first detector D1, Brillouin spectrum is moved tremendously low frequency without distortion again, and then obtain a series of test curve, then at frequency domain, Lorentz fit is carried out to often some test result on optical fiber, obtain the BSS that the very narrow pre-pumping pulse of spectrum width produces, the frequency that Brillouin spectrum intensity maximum point is corresponding is just the Brillouin shift of this scattering point.The frequency of adjustment low-converter FC medium frequency synthesizer changes the centre frequency of Brillouin spectrum electric signal, make Brillouin spectrum intactly by low-pass filter LPF, by second detector D2, Brillouin spectrum is moved tremendously low frequency without distortion again, the Brillouin spectrum on whole optical fiber can be obtained, the synthesis spectrum of the BSS that namely spectrum width is very narrow and the BSS that the very wide sensing impulse of spectrum width produces, thus Brillouin's intensity of each scattering point on optical fiber can be obtained.
In Fig. 1, narrow linewidth laser LD employing wavelength is the distributed feedback type semiconductor laser of 1550.12 nm, and the splitting ratio of polarization-maintaining coupler C1 is 90:10, the light that narrow linewidth laser LD sends is divided into detection light and local oscillator light.In detection light path, photomodulator EOM is the lithium niobate light intensity modulator of one 10 Gb/s, the burst pulse that the broad pulse that pulsewidth is 30 ns by step pulse generator, amplitude is 0.5 V and pulsewidth are 3 ns, amplitude is 4.5 V sends into photomodulator EOM after signal synthesizer synthesis, and continuous light is modulated into the ladder light pulse that pre-pumping pulse width is 30 ns, narrow pulse width is 3 ns by photomodulator EOM.Amplifying device in image intensifer EDFA is Erbium-Doped Fiber Amplifier, in order to the spontaneous heating radiated noise that filtering Erbium-Doped Fiber Amplifier is brought, is provided with the first grating filter GF1 in detection light path.Ladder light pulse after amplification injects sensor fibre FUT through circulator OC, and its backward Brillouin scattering light produced carries out heterodyne with local oscillator light after the second grating filter GF2 filtering anti-Stokes light on photoelectric detector PD, produces centre frequency and is
brillouin spectrum electric signal.Frequency because of brillouin frequency shifting signal is about 11 GHz, directly cannot carry out accurate signal transacting, low-converter FC need be adopted signal frequency to be moved in lower frequency band, adopt the method for scanning microwave local oscillation and electrical domain shift frequency to realize the measurement of Brillouin spectrum.Wherein, the output frequency of frequency synthesizer be 10.5 GHz ~ 11.5 GHz, scanning stepping be 2 MHz (programming Control); The centre frequency of bandpass filter BPF is 500 MHz, bandwidth is 2 MHz; The bandwidth of low-pass filter LPF is 1 GHz; The sample frequency of high-speed data acquisition card DAQ is 4 GHz.The frequency of low-converter FC medium frequency synthesizer is regulated to change the centre frequency of difference frequency signal, make the signal of Brillouin spectrum different frequency composition successively by bandpass filter BPF, by first detector D1, Brillouin spectrum is moved tremendously low frequency without distortion again, and then obtain a series of test curve, then at frequency domain, Lorentz fit is carried out to often some test result on optical fiber, obtain the BSS that spectrum width is very narrow, the frequency that Brillouin spectrum intensity maximum point is corresponding is just the Brillouin shift of this scattering point.The output frequency of adjustment low-converter FC medium frequency synthesizer, make Brillouin spectrum intactly by low-pass filter LPF, by second detector D2, Brillouin spectrum is moved tremendously low frequency without distortion again, the Brillouin spectrum on whole optical fiber can be obtained, the synthesis spectrum of the BSS that namely spectrum width is very narrow and the very wide BSS of spectrum width, thus Brillouin's intensity of each scattering point on optical fiber can be obtained.Utilize the linear changing relation of Brillouin shift and intensity and temperature and strain, obtain the temperature on whole sensor fibre FUT and strain information, measure while realizing temperature and Strain Distribution.
The computings such as the linear superposition carried out time-domain signal in the present invention is average, Lorentz fit complete in a computer.In addition in order to reduce the impact of Brillouin scattering polarization state change on Heterodyne detect, in the present invention, in local oscillator light path, add scrambler PS.
In above-described embodiment, SBS effect comprises the SBS effect between anti-Stokes light and sensing impulse light and the SBS effect between sensing impulse light and Stokes light, and the SBS mechanism between above-mentioned NM anti-Stokes light and sensing impulse light is similar to the SBS mechanism between sensing impulse light and Stokes light.
Claims (4)
1. the temperature based on Brillouin scattering and strain measuring method simultaneously, it is characterized in that, described method adopts a measuring system to carry out, and described measuring system comprises narrow linewidth laser (LD), polarization-maintaining coupler (C1), photo-coupler (C2), the photomodulator (EOM) driven by step pulse generator (SPG), image intensifer (EDFA), two grating filters, circulator (OC), photoelectric detector (PD), Brillouin shift and intensity detection unit (TDU) and sensor fibre (FUT), first light mouth of described polarization-maintaining coupler (C1) connects laser instrument (LD), 3rd light mouth is successively through photomodulator (EOM), image intensifer (EDFA), first grating filter (GF1) connects the first light mouth of circulator (OC), second light mouth of circulator (OC) connects sensor fibre (FUT), 3rd light mouth connects the first light mouth of photo-coupler (C2) through the second grating filter (GF2), 4th light mouth of polarization-maintaining coupler (C1) connects the second light mouth of photo-coupler (C2), 3rd light mouth of photo-coupler (C2) connects Brillouin shift and intensity detection unit (TDU) through photoelectric detector (PD),
Described measuring system is measured as follows:
The continuous light that narrow linewidth laser (LD) sends is divided into two-way after polarization-maintaining coupler (C1), and a road, as local oscillator light, enters photoelectric detector (PD) through photo-coupler (C2), another road is as detection light, and being modulated to step pulse optical width through photomodulator (EOM) is
d pre , sensing impulse optical width is
dladder light pulse after, again through image intensifer (EDFA), first grating filter (GF1) and circulator (OC) inject sensor fibre (FUT), the Brillouin scattering obtained enters the second grating filter (GF2) and carries out filtering, local oscillator light and filtered Brillouin scattering light signal produce Brillouin spectrum electric signal after photoelectric detector (PD) heterodyne, Brillouin shift and intensity detection unit (TDU) process this signal, temperature and the strain information of the upper arbitrary position of sensor fibre (FUT) can be obtained, measure while realizing temperature and Strain Distribution,
Described Brillouin shift and intensity detection unit (TDU) are by low-converter (FC), bandpass filter (BPF), low-pass filter (LPF), two wave detectors, high-speed data acquisition card (DAQ) and computing machine (PC) composition, the output terminal of the input termination photoelectric detector (PD) of described low-converter (FC), its output signal is divided into two-way, one tunnel enters the first passage of high-speed data acquisition card (DAQ) successively through bandpass filter (BPF) and first detector (D1), another road enters the second channel of high-speed data acquisition card (DAQ) successively through low-pass filter (LPF) and second detector (D2), the output terminate computer (PC) of described high-speed data acquisition card (DAQ),
Described Brillouin shift and intensity detection unit (TDU) are measured as follows:
The frequency of low-converter (FC) medium frequency synthesizer is regulated to change the centre frequency of difference frequency signal, make the signal of Brillouin spectrum different frequency composition successively by bandpass filter (BPF), by first detector (D1), Brillouin spectrum is moved tremendously low frequency without distortion again, and then obtain a series of test curve, then at frequency domain, Lorentz fit is carried out to often some test result on optical fiber, obtain the Brillouin spectrum that pre-pumping pulse produces, the frequency that Brillouin spectrum intensity maximum point is corresponding is just the Brillouin shift of this scattering point, the output frequency of adjustment low-converter (FC) medium frequency synthesizer, to change the centre frequency of the difference frequency signal of local oscillator and scattered signal, make Brillouin spectrum intactly by low-pass filter (LPF), by second detector (D2), Brillouin spectrum is moved tremendously low frequency without distortion again, the Brillouin spectrum on whole optical fiber can be obtained, the i.e. synthesis spectrum of the Brillouin spectrum of pre-pumping pulse and sensing impulse generation, thus Brillouin's intensity of each scattering point on optical fiber can be obtained, utilize the linear changing relation of Brillouin shift and intensity and temperature and strain, through system calibrating, temperature and the strain information of the upper arbitrary position of sensor fibre (FUT) can be obtained, measure while realizing temperature and Strain Distribution.
2. a kind of temperature based on Brillouin scattering according to claim 1 and strain measuring method simultaneously, it is characterized in that, in order to reduce the impact of Brillouin scattering polarization state change on Heterodyne detect, between polarization-maintaining coupler (C1) and photo-coupler (C2), add scrambler (PS).
3. a kind of temperature based on Brillouin scattering according to claim 2 and strain measuring method simultaneously, it is characterized in that, described step pulse generator (SPG) comprises t connector, signal synthesizer and the first pulse signal generator and the second pulse signal generator; The input end of the output termination t connector of the first pulse signal generator, first of t connector exports the input end of termination second pulse signal generator, the first input end of the output termination signal synthesizer of secondary signal generator, second output terminal of t connector connects the second input end of signal synthesizer through time delay device, the radio-frequency head of the output termination photomodulator (EOM) of signal synthesizer;
Described step pulse generator (SPG) production burst as follows: first produce by the first pulse signal generator the electric pulse that a width is less than phonon lifetime, this electric pulse is divided into two-way after t connector, wherein a road is as the trigger pip of the second pulse signal generator, when there is rising edge in this trigger pip, second pulse signal generator send a width be greater than phonon lifetime and amplitude lower than the pulse signal of sensing impulse, and this pulse signal is delivered to the first input end of signal synthesizer, the pulse signal of the second output terminal of t connector enters the second input end of signal synthesizer after time delay device time delay, by signal synthesizer its two input signal synthesized a stepped electrical pulse and send into the radio-frequency head of photomodulator (EOM).
4. a kind of temperature based on Brillouin scattering according to claim 3 and strain measuring method simultaneously, it is characterized in that, described photomodulator (EOM) is replaced by two end to end lithium niobate light intensity modulators, first utilizes the working point of the first lithium niobate light intensity modulator (EOM1) to determine the amplitude of pre-pumping pulse light; The width of sensing impulse light is decided subsequently by controlling electronic pulse width; Eventually through the width of the pulse width determination step pulse light of control second lithium niobate light intensity modulator (EOM2).
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