CN103954226A - Long-distance distributed type large-measuring-range rapid response optical fiber dynamic strain sensing device - Google Patents
Long-distance distributed type large-measuring-range rapid response optical fiber dynamic strain sensing device Download PDFInfo
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Abstract
The invention provides a long-distance distributed type large-measuring-range rapid response optical fiber dynamic strain sensing device. The device comprises a phase modulator, a multi-frequency signal generating module, an intensity modulator, a microwave switch, an electric pulse generating module, a microwave signal generating module and other components. The signal generating module comprising multi-frequency components is used for modulating the phase of detection continuous light, so that multi-light-frequency components are generated in the detection continuous light, and corresponding Brillouin gain spectrum amplitudes are adjusted through controlling the amplitudes of all the light-frequency components in the detection continuous light. A Brillouin gain spectrum of a needed spectrum width and a spectrum type is obtained through splicing, and the dynamic strain measuring range is greatly enlarged under the condition that the signal-to-noise ratio and the response speed of a system are not destroyed. The frequency difference between two light beams generating a Brillouin amplification effect is fixed in the middle of a beveled edge linear region of the spliced Brillouin gain spectrum, drifting of the spliced Brillouin gain spectrum is converted into power fluctuation of the detection light, and long-distance distributed type large-measuring-range high response speed quantitative measuring on optical fiber dynamic strain and optical fiber static strain is achieved.
Description
Technical field
The present invention relates to distribution type fiber-optic dynamic strain measurement technical field, be specifically related to long-distance distributed wide-measuring range and respond fast optical fiber dynamic strain sensing device.
Background technology
The equipment being caused by dynamic strain and damage of building are more and more, and especially in earthquake district occurred frequently, vibration and shock wave etc. are very serious to the destruction in dam, bridge and house etc., therefore in the urgent need to having the dynamic strain sensing network of quick response.Due to optical fiber, there is the significant advantages such as loss is little, high temperature resistant, corrosion-resistant, insulation, anti-electromagnetic interference (EMI), and less on the health status of research structure, security, stability and integrality impact, therefore optical fiber sensing technology becomes the optimal selection that builds distributed dynamic strain monitoring in essence.
At present, the research that realizes distribution type fiber-optic dynamic strain sensing technology mainly contains following a few class: the one, based on fiber grating dynamic strain sensing technology, (refer to A.Cusano, et al., Sens.Actuator A-Phys.110,276 (2004)), extraneous dynamic strain or vibration cause the dynamic deviation of fiber grating reflection wavelength, but it is very high to build technical difficulty and the cost of ultra-large fiber grating dynamic strain sensing network; The 2nd, the dynamic strain sensing technology based on fiber interference structure (refers to Tapanes Edward E., US Patent, 20030198425, (2003)), utilize interference structure to be subject to the phase-modulation of extraneous dynamic strain or vibrational perturbation to be converted into the variation of luminous power or other parameters optical fiber, but interference structure needs phase-shifter and closed-loop control system to carry out real-time stabilization best operating point, and system stability and positioning precision are poor; The 3rd, the distributed dynamic strain sensing technology based on Rayleigh scattering, wherein comparatively successfully technology is that phase-sensitive optical time domain reflectometer (Φ-OTDR) (refers to Z.Pan, et al., Proc.of SPIE8421,842129 (2012); Z.Qin, et al., Opt.Express20,20459 (2012)), by measuring Rayleigh scattering interference of light Overlay in light pulse overlay area, carry out demodulation dynamic disturbances, but this scheme is difficult to gradual disturbance perception, and cannot realizes the quantitative measurment of dynamic strain amplitude.
For continuous distribution formula sensing, stress deformation and temperature that Brillouin's type Distributed Optical Fiber Sensing Techniques can be gone up any position along the line to optical fiber are carried out continuous coverage, through the development of twenties years, the Distributed Optical Fiber Sensing Techniques advantage based on Brillouin's nonlinear effect obtained abundant displaying and has got being widely applied.But the scheme that this routine distributes based on reconstruct brillouin gain spectrum also cannot meet the active demand of dynamic strain sensing in essence aspect response speed.Some research groups, in conventional brillouin distributed optical fiber sensing technical foundation, explore targetedly correlation technique and realize distributed dynamic strain sensing in the world.Relevant exploration mainly concentrates on following two aspects:
To improve response speed on the one hand.2009, the scheme that the people such as A.Minardo have proposed a kind of frequency difference hypotenuse biasing detection (refers to R.Bernini, et al., Opt.Lett.34,2613 (2009)), realization is converted into the fluctuation of detection of optical power by the drift of brillouin gain spectrum, thereby greatly improves system response time to 98Hz, but be less than ± 350 μ ε (deformation range ± 0.035%) of the scope of this scheme dynamic strain measurement.2011, the people such as A.Voskoboinik propose a kind of scheme without frequency sweep reconstruct brillouin gain spectrum and (refer to A.Voskoboinik, et al., US Patent, US20130025374A1, (2013)), realize without scanning and can cover sensing frequency spectrum, therefore response speed also can reach tens Hz magnitudes, but also can only reach ± 900 μ ε of this scheme technical scheme dynamic strain measurement scope.2012, the people such as A.Loayssa propose a kind of distributed dynamic strain measurement scheme based on Brillouin's phase shift analysis type and (refer to J.Urricelqui, et al., Opt.Express20,26942 (2012)), by demodulation strain, cause the phase place of brillouin gain to change to realize dynamic strain sensing, also only reach ± 1280 μ ε of strain sensing scope in this scheme.Although these technical schemes have effectively improved system, the response speed of dynamic strain is arrived to 100Hz left and right, be less than ± 1000 μ ε of strain sensing scope, cannot meet practical application to the demand of wide-measuring range (more than ± 4000 μ ε).
Research on the other hand concentrates on and expands dynamic strain measurement scope.2011, on aforesaid frequency difference hypotenuse biasing detecting strategy basis, the people such as Q.Cui adopt the pulsed light of 6.5ns pulsewidth as pumping pulse, make brillouin gain spectrum spectrum width broadening to 160MHz, thereby realize strain measurement scope is expanded to ± 1600 μ ε and (refer to Q.Cui, et al., IEEE Photon.Technol.Lett.23,1887 (2011)), but this technical scheme has been sacrificed system response time and Signal-to-Noise.2012, the people such as Y.Peled adopt AWG (Arbitrary Waveform Generator) to drive the scheme of electrooptic modulator, the distribution that realizes high-speed reconstruction brillouin gain spectrum (refers to Y.Peled, et al., Opt.Express20,8584 (2012)), but signal needs the Brillouin shift information of extraction strain-dependent consuming time while processing, therefore the response speed of this scheme sacrificial system when obtaining larger strain sensing scope, is unfavorable for the high speed demodulation of dynamic strain.Although these technical schemes effectively measurement range of extended dynamic strain arrive ± 2000 μ ε left and right, but sacrificed sensor-based system signal to noise ratio (S/N ratio), make response speed can only reach 10Hz left and right, cannot meet practical application to the demand of high response speed (100Hz).
Above-mentioned all distribution type fiber-optic dynamic strain measurement technical schemes, comprise grating type optical fiber, interference structure type and Rayleigh scattering type, all because have be difficult to build large-scale sensing network, working state of system is unstable or be difficult to the shortcomings such as quantitative measurment, and cannot meet the demand of practical application.And in the most potential dynamic strain sensing scheme based on brillouin effect, do not invent a kind of technology that can simultaneously take into account wide-measuring range and high response speed yet.
Summary of the invention
The shortcoming and defect existing in order to overcome current technology, make full use of the technical advantage that the length based on brillouin effect is measured apart from continuous distribution formula, further solve again the dynamic strain sensing that realizes wide-measuring range and high response speed, the invention provides long-distance distributed wide-measuring range and respond fast optical fiber dynamic strain sensing device, concrete technical scheme is as follows.
Long-distance distributed wide-measuring range responds optical fiber dynamic strain sensing device fast, and it comprises: narrow linewidth laser, fiber coupler, intensity modulator, lock-in amplifier, microwave switch, electric pulse generation module, microwave signal generation module, the first optical fiber circulator, fiber grating, the second optical fiber circulator, phase-modulator, multifrequency signal generation module, sensor fibre, photodetector, signal high-speed parallel processing unit; The tail optical fiber output of narrow linewidth laser is connected with the input port of fiber coupler, realization is divided into two-way by laser, wherein a road is connected with the input port of intensity modulator through the first output port of fiber coupler, the DC voltage offset port of intensity modulator is connected with lock-in amplifier, realize stable control of automatic feedback of best operating point, the rf inputs mouth of intensity modulator is connected with the output terminal of microwave switch, the input end of microwave switch is connected with microwave signal generation module, and the input end of microwave switch is connected with electric pulse generation module; The High Extinction Ratio broadband shift frequency pumping pulse light that intensity modulator modulation obtains is exported by the output port of intensity modulator, and be connected to the input port of the first optical fiber circulator, the first optical fiber circulator also has a port to be connected with the fiber grating of realizing filtering, the output port of the first optical fiber circulator is connected with the input port of the second optical fiber circulator, realizes pumping pulse light is injected in sensor fibre; Another Lu Jingqi second output port of fiber coupler light splitting is connected with the input port of phase-modulator, the rf inputs mouth of phase-modulator is connected with multifrequency signal generation module, and the output port output packet of phase-modulator contains the detection continuous light of multi-frequency composition and is injected in sensor fibre; Surveying continuous light is connected with the another port of the second optical fiber circulator after transmission in sensor fibre in opposite directions with pumping pulse light, the output port of the second optical fiber circulator connects the input port of photodetector, the output port of photodetector is connected with signal high-speed parallel processing unit, realizes the demodulation of transducing signal.It can realize distribution type fiber-optic dynamic strain sensor monitoring, more than its sensing scope can reach 10km, and spatial resolution 1～10m, can reach ± 5000 μ ε of dynamic strain measurement scope, more than dynamic strain response speed can reach 100Hz.
Above-mentioned long-distance distributed wide-measuring range responds in optical fiber dynamic strain sensing device fast, by phase-modulator and multifrequency signal generation module construction, go out a kind of optical texture of brillouin gain splicing spectrum, the multifrequency signal generation module that use comprises multi-frequency composition acts on phase-modulator, realize modulation and survey the phase place of continuous light, make to survey and in continuous light, produce many optical frequencies composition, the amplitude of surveying each optical frequency of continuous light by control regulates each self-corresponding brillouin gain spectral amplitude, splice the brillouin gain spectrum of required spectrum width and spectral pattern, the in the situation that of lossless system signal to noise ratio (S/N ratio) and response speed, realize very big extended dynamic strain measurement scope.
Above-mentioned long-distance distributed wide-measuring range responds in optical fiber dynamic strain sensing device fast, utilize intensity modulator, lock-in amplifier, microwave switch, electric pulse generation module, microwave signal generation module, the first optical fiber circulator, fiber grating and the second optical fiber circulator build the optical texture that pumping pulse light produces, obtain High Extinction Ratio microwave shift frequency pumping pulse light, and then the frequency difference that produces Brillouin amplification effect two-beam is fixed in the middle of the brillouin gain splicing spectrum hypotenuse range of linearity, the drift of the brillouin gain splicing spectrum that strain is caused is converted into the fluctuation of detection of optical power, can realize distributed dynamic, the quantitative measurment of static strain.
Further preferred, the live width of described narrow linewidth laser is less than 1MHz, is operated in 1550nm wave band, more than output power need reach 20mW.
Further preferred, described fiber grating is Prague short period fiber grating, and its reflection kernel wavelength selects customization under the microwave broadband shift frequency of pump light pulse in frequency band range; By temperature or strain, be applied on fiber grating, carry out the tuning of reflection kernel wavelength.
Further preferred, described fiber grating herein fiber grating also can be substituted by narrow band filter.
Further preferred, described photodetector responsive bandwidth is higher than 100MHz.
Further preferred, described signal high-speed parallel processing unit sampling rate is more than 100MS/s.
Described narrow linewidth laser, requires live width to be less than 1MHz.
Further preferred, described fiber coupler, is 1 * 2 three port general single mode fiber coupling mechanism, is operated in 1550nm wave band.
Further preferred, described intensity modulator, is electric light intensity modulator, is operated in 1550nm wave band, requires modulation band-width to be greater than 11GHz.Described lock-in amplifier, is the bias voltage feedback control unit of electrooptic modulator, feedback response speed kHz magnitude.Described microwave switch, controls the opening and closing of microwave signal channels, and response speed is less than 1ns, reach-45dB of isolation.Described microwave signal generation module, frequency range 10～13GHz.Described electric pulse generation module, pulsewidth 10ns magnitude, repetition frequency 10kHz magnitude.
Basic structure and the principle of traditional Brillouin optical time domain analysis instrument (BOTDA) are: the laser instrument in sensor fibre two ends injects sensor fibre in opposite directions by pumping pulse light and detection continuous light respectively, when pumping pulse light and the optical frequency of surveying continuous light poor in optical fiber regional area brillouin gain spectral limit time, in this region, will produce the non-linear enlarge-effect of excited Brillouin, between pumping pulse light and detection continuous light, there is energy and shift (for loss-type BOTDA, energy is transferred to pulsed light from continuous light).According to pumping pulse light, be injected into the transmission time Δ t in optical fiber, can locate particular location (L=c * Δ t/n that Brillouin's nonlinear effect occurs, wherein c is light velocity of propagation in a vacuum, and n is optical fibre refractivity), realize accordingly the positioning analysis of sensing.Continuous light frequency is carried out to hair-breadth tuning within the specific limits, detect the detection continuous light luminous power transmitting from the optical fiber other end simultaneously, just can determine that on each segment region of optical fiber, energy shifts corresponding difference on the frequency while reaching maximum, owing to there is linear relationship in the Brillouin shift in optical fiber and temperature, strain, shown in following formula, according to brillouin gain spectrum, can obtain temperature, the strain information of each localized positions, and then realize the distributed measurement of temperature and strain:
ν
B＝C
εΔε+C
TΔT+ν
BO
Wherein, ν
bfor the Brillouin shift amount of optical fiber in strain, thermal perturbation situation, ν
bOfor the initial Brillouin shift amount in undisturbed situation, C
εfor strain affects the linear coefficient of Brillouin shift, Δ ε is strain applied amount, C
tfor temperature affects the linear coefficient of Brillouin shift, Δ T is temperature applied amount.
This traditional BOTDA scheme is by laser instrument tuning, to scan reconstruct to obtain optical fiber brillouin gain spectrum along the line ν
bdistribution, and then realize the distributed measurement of temperature and strain, general required frequency tuning sweep limit is about 200MHz, tuning precision is about 1MHz, to the tuning performance of laser instrument, require very high, when processing, the restriction of Stimulated Light device tuned speed and signal need to do repeatedly cumulative mean to improve signal to noise ratio (S/N ratio), realizing once long-distance distributed global solution mediation measures, generally at least need the time of a few minutes even longer, and this metering system cannot meet the rapid response to customer's need of 100Hz magnitude dynamic strain completely in speed.
v
B(t)＝C
εA
εcosft+v
BO
A wherein
εfor the amplitude of dynamic strain, the frequency that f is dynamic strain, as above, shown in formula, this dynamic restructuring brillouin gain is composed v
b(t) scheme distributing, is difficult to realize the measurement of dynamic strain in essence.Therefore described in background technology above, there is researchist to propose the scheme that a kind of frequency difference hypotenuse biasing is surveyed, in the middle of the hypotenuse range of linearity, brillouin gain spectrum left side when the frequency difference of the two-beam relatively transmitting is fixed on to undisturbed, if optical fiber part has the disturbance of temperature or strain to cause the drift of brillouin gain spectrum, this scheme just can realize fluctuation (P (the t)=B that the drift of brillouin gain spectrum is converted into detection of optical power
εcosft, the luminous power fluctuation that wherein P (t) causes for dynamic strain, B
εfor strain causes the linear coefficient of luminous power fluctuation), thus reconstruct brillouin gain spectrum v can be avoided
b(t), greatly improve system response time, make more than long-distance distributed dynamic strain response speed can reach 100Hz magnitude.But consider brillouin gain spectrum spectrum width limited (～35MHz), be less than ± 350 μ ε (deformation range ± 0.035%) of the scope of this scheme dynamic strain measurement, this measurement range is too little and cannot meet most Practical Project demands.Also have other some schemes, sacrifice to a certain extent response speed, expand the scope of dynamic strain measurement, but temporarily also do not have a kind of technology can take into account high response speed and wide-measuring range simultaneously.
In the present invention, long-distance distributed optical fiber dynamic strain sensing technology scheme based on brillouin gain splicing spectrum, utilization comprises multifrequency signal generation module and modulates the phase place of surveying continuous light, make to survey and in continuous light, produce many optical frequencies composition, the amplitude of surveying each optical frequency of continuous light by control regulates each self-corresponding brillouin gain spectral amplitude, splice the brillouin gain spectrum of required spectrum width and spectral pattern, the in the situation that of lossless system signal to noise ratio (S/N ratio) and response speed, realize very big extended dynamic strain measurement scope; The frequency difference that produces Brillouin amplification effect two-beam is fixed in the middle of the brillouin gain splicing spectrum hypotenuse range of linearity, the drift of brillouin gain splicing spectrum is converted into the fluctuation of detection of optical power, can realizes the quantitative measurment of distributed dynamic, static strain simultaneously.
Compared with prior art, the features and advantages of the invention are:
(1) compare as the optical fiber dynamic strain sensing network of grating type optical fiber, interference structure type and Rayleigh scattering type with traditional scheme, the present invention is based on excited Brillouin nonlinear effect, do not exist be difficult to build large-scale sensing network, working state of system is unstable or be difficult to the shortcomings such as quantitative measurment, can effectively realize the quantitative real-time online of long-distance distributed optical fiber strain and measure at a high speed.
(2) compare with current existing Brillouin's type optical fiber dynamic strain sensing technology, for the shortcoming that in current brillouin distributed dynamic strain sensing technology, measurement range and response speed cannot be taken into account mutually, the present invention adopts the technology of brillouin gain splicing spectrum, take to utilize multiple brillouin gain splicing spectrum to realize the Research Thinking of wide-measuring range and high response speed simultaneously, can effectively realize that dynamic strain measurement scope is expanded to ± more than 5000 μ ε, simultaneity factor response speed can guarantee to reach the highest level of similar technology completely.
(3) based on this technology, can effectively realize distribution type fiber-optic dynamic strain sensor monitoring, more than its sensing scope can reach 10km, spatial resolution 1～10m, can reach ± 5000 μ ε of dynamic strain measurement scope, more than dynamic strain response speed can reach 100Hz.
Accompanying drawing explanation
Fig. 1 is pumping pulse light of the present invention and the schematic diagram of surveying the Frequency Design of continuous light.
Fig. 2 is the principle schematic of optical fiber Brillouin gain splicing spectrum of the present invention.
Fig. 3 is the long-distance distributed wide-measuring range high response speed optical fiber dynamic strain sensing device structural drawing based on brillouin gain splicing spectrum of the present invention.
Embodiment
Below in conjunction with embodiment and accompanying drawing, enforcement of the present invention is described further, but enforcement of the present invention and protection are not limited to this.
The structural design that long-distance distributed wide-measuring range responds optical fiber dynamic strain sensing device fast as shown in Figure 3, the tail optical fiber output of narrow linewidth laser 1 is connected with the input port 2-1 of fiber coupler 2, seed laser is divided into two-way, wherein a road is connected through the output port 2-2 of fiber coupler 2 and the input port 3-1 of intensity modulator 3, the DC voltage offset port 3-2 of intensity modulator 3 is connected with lock-in amplifier 4, realizes stable control of automatic feedback of intensity modulator 3 best operating points; The rf inputs mouth 3-3 of intensity modulator 3 is connected with the output port 5-3 of microwave switch 5, and the input end 5-1 of microwave switch 5 is connected with microwave signal generation module 7, and the input end 5-2 of microwave switch 5 is connected with electric pulse generation module 6.The High Extinction Ratio broadband shift frequency pumping pulse light obtaining through intensity modulator 3 modulation is exported and is connected to the input port 8-1 of the first optical fiber circulator 8 by output port 3-4, the port 8-2 of the first optical fiber circulator 8 is connected with the fiber grating 9 of realizing filter action, the output port 8-3 of the first optical fiber circulator 8 is connected with the input port 10-1 of the second optical fiber circulator 10, realizes pumping pulse light is injected in sensor fibre 13.Another Lu Jingqi output port 2-3 of fiber coupler 2 light splitting is connected with the input port 11-1 of phase-modulator 11, the rf inputs mouth 11-2 of phase-modulator 11 is connected with multifrequency signal generation module 12, and the detection continuous light that comprises multi-frequency composition is injected in sensor fibre 13 through the output port 11-3 of phase-modulator 11.Survey the transmission in opposite directions in sensor fibre 13 of continuous light and pumping pulse light, survey continuous light transmission is connected with the port one 0-2 of the second optical fiber circulator 10 after sensor fibre 13, and by the output port 10-3 of the second optical fiber circulator 10, be connected to the input port 14-1 of high-speed photodetector 14, the output port 14-2 of high-speed photodetector 14 is connected with signal high-speed parallel processing unit 15, realizes the demodulation of transducing signal.
Below again the realization of each device blocks is described as follows:
Narrow linewidth laser 1 is the seed light source of the distributed wide-measuring range high response speed optical fiber dynamic strain sensor-based system based on brillouin gain splicing spectrum.Because single-mode fiber brillouin gain spectrum spectrum width is 35MHz left and right, therefore need the live width of pumping seed light source narrower.The light source adopting in the present invention is 1550nm wave band narrow-line width single frequency optical fiber laser, its live width is 2kHz, laser power can reach 100mW above (REFERENCE TO RELATED people has authorized patent of invention 200810220661.X, 201110280866.9,201110241520.8); Also can adopt the commercial narrow linewidth laser of other types, but require live width to be less than 1MHz.
Fiber coupler 2, general single mode fiber 1550nm wave band, 1 * 2 three port, luminous power when splitting ratio need to be implemented according to reality is set.
Intensity modulator 3 is to realize the modulation device that obtains High Extinction Ratio, broadband shift frequency pumping pulse light in device, is operated in 1550nm wave band, can adopt 20GHz bandwidth lithium niobate electric light intensity modulator.
Lock-in amplifier 4, is the bias voltage feedback control unit of electrooptic modulator, makes it operate at best operating point place, can adopt the lock-in amplifier of commercial kHz magnitude response speed.
Microwave switch 5 is for controlling the opening and closing of microwave signal channels in device, requires response speed to be less than 1ns, isolation reaches-more than 45dB, can select to meet the commercial microwave switch of parameter request.
Electric pulse generation module 6, it in device, is the electric pulse for generation of high-contrast, narrow pulsewidth, trigger the opening and closing of controlling microwave switch, require the electric pulse pulsewidth producing to reach 10ns magnitude, pulse repetition rate 10kHz magnitude, can select to meet the commercial pulse signal generator of parameter request.
Microwave signal generation module 7, in device, for generation of microwave signal, export and be applied in electric light intensity modulator, make modulated laser frequency obtain broadband shift frequency, because single-mode fiber Brillouin shift is about 11GHz, therefore the commercial microwave signal generator that microwave signal generation module can proportion scope 10～13GHz, its microwave output power need to drive and match with used intensity modulator.
The first fiber optical circulator 8 and the second fiber optical circulator 10, are all three fiber port circulators, and one-way conduction also can adopt the way of incoming fiber optic coupling mechanism and isolator, plays the effect of fiber optical circulator.
Fiber grating 9, Prague short period fiber grating, its reflection kernel wavelength selects customization under the microwave broadband shift frequency of pump light pulse in frequency band range; Can be applied on fiber grating by temperature or strain in addition, carry out the tuning of reflection kernel wavelength in certain limit.Fiber grating also can be substituted by narrow band filter herein.
Phase-modulator 11 is to realize the modulation device that obtains the detection continuous light that comprises multi-frequency composition in device, is operated in 1550nm wave band, can adopt 2.5GHz bandwidth lithium niobate electro-optic phase modulator.
Multifrequency signal generation module 12, in device, be for generation of the sinusoidal wave electric signal of the high frequency modulated that comprises multi-frequency composition, its working frequency range is at 750～1250MHz, the quantity that interval between multi-frequency composition is about 1MHz and multi-frequency composition can reach more than 500, this signal generating module is applied in electro-optic phase modulator, make to obtain multi-frequency composition after modulated laser frequency shift frequency, can select to meet the commercialization programming function signal generator of parameter request.
Sensor fibre 13, it is the basic sensing unit of whole distribution type fiber-optic dynamic strain sensor-based system, extraneous dynamic strain is applied on sensor fibre, affects the brillouin gain spectrum of this section of optical fiber, by obtaining relevant strain and positional information in terminal demodulation.In this system, can adopt the communication unit mode fiber of commercial G652 model as sensor fibre.
Photodetector 14, is converted to electric signal by light signal, can select responsive bandwidth higher than the high-speed photodetector of 100MHz.
Signal high-speed parallel processing unit 15, acquisition of information and the processing section of whole distribution type fiber-optic dynamic strain sensor-based system, comprise that signals collecting, data transmission, data high-speed are processed and sensing result shows and preserve a plurality of parts, wherein, in order to obtain high time resolution, need to adopt high-speed data acquisition card, more than sampling rate need reach 100MS/s, data processing can take high-speed parallel to process framework, realizes real-Time Signal Transfer and processing.
Described narrow linewidth laser 1 becomes two-way by coupling mechanism 2 light splitting, wherein a road is modulated into High Extinction Ratio, broadband shift frequency pumping pulse light through intensity modulator 3, it retains shift frequency optical frequency composition by fiber grating 9 filtering, through circulator 10, enters into sensor fibre 13; Another road enters phase-modulator 11 as surveying continuous light, use multi-frequency composition composite signal generation module 12 to drive phase-modulator 11, detection continuous light is modulated into and comprises many shift frequencies optical frequency composition, utilizes many brillouin gains spectrums splicing corresponding to many optical frequencies in its downshift frequency band to cut out wider more linear brillouin gain spectrum.The difference on the frequency of pumping pulse light and detection continuous light is fixed in the middle of the brillouin gain splicing spectrum left side line style spectrum hypotenuse of sensor fibre 13, when sensor fibre 13 parts are subject to dynamic strain disturbance, also can there is dynamic deviation in the local brillouin gain splicing of optical fiber spectrum, use the fluctuation of high-speed photodetector 14 detection of optical power can demodulate dynamic strain, without reconstruct optical fiber brillouin gain spectrum along the line, utilize signal high-speed parallel processing unit 15 to realize the demodulation of the distributed dynamic strain signal of wide-measuring range high response speed.
In scheme, building initial brillouin gain splicing spectrum is the key that realizes the optical fiber dynamic strain sensing of long-distance distributed wide-measuring range high response speed.Its ultimate principle is as follows: be first the pumping pulse light based on Brillouin's nonlinear effect and the design of surveying continuous light frequency, select the frequency matching method of Brillouin's loss-type, also survey continuous light frequency in anti-Stokes frequency, as shown in Figure 1, pumping pulse light frequency is v
p-, use multi-frequency compound signal generator to drive electro-optic phase modulator, the quantity (～500) of working frequency range (750～1250MHz), the interval (～1MHz) between multi-frequency composition and the multi-frequency composition of design multi-frequency compound signal generator, makes to be modulated in a few rank optical frequency and the good spectral range in Brillouin's nonlinear interaction of pumping pulse light positive in the detection continuous light downshift frequency band that comprises many shift frequencies optical frequency composition; Meanwhile, the amplitude of every fundamental frequency signal that multi-frequency compound signal generator produces is controlled, and to realize, to survey the amplitude of the every single order optical frequency of light adjustable.The downshift frequency band of this part controlled multifrequency phase modulation reasonable in design is the key that builds optical fiber Brillouin gain splicing spectrum.
Next is the design of optical fiber Brillouin gain splicing spectrum, as shown in Figure 2, survey the equal corresponding brillouin gain spectrum of every single order optical frequency in continuous light, many optical frequencies frequency interval (～1MHz) is consistent with each self-corresponding multiple Brillouin's frequency spectrum centre frequency interval, the amplitude of brillouin gain spectrum is determined by the Nonlinear Coupling of surveying continuous light and pumping pulse light, the fixing amplitude of pumping pulsed light, the amplitude of surveying each optical frequency of continuous light by control regulates each self-corresponding brillouin gain spectral amplitude, many brillouin gains corresponding to many optical frequencies are composed non-completely overlapping on frequency domain, effectively suppress the weak coupling action effect between many brillouin gain spectrums, the amplitude of brillouin gain spectrum that can realize every single order is controlled, centre frequency and the amplitude of each rank brillouin gain spectrum of appropriate design, on frequency domain, can realize the brillouin gain spectrum of splicing various spectrum widths and spectral pattern, comprise the required linear sideband on a large scale of dynamic strain sensing as shown in Figure 2.
Claims (8)
1. long-distance distributed wide-measuring range responds optical fiber dynamic strain sensing device fast, it is characterized in that comprising: narrow linewidth laser (1), fiber coupler (2), intensity modulator (3), lock-in amplifier (4), microwave switch (5), electric pulse generation module (6), microwave signal generation module (7), the first optical fiber circulator (8), fiber grating (9), the second optical fiber circulator (10), phase-modulator (11), multifrequency signal generation module (12), sensor fibre (13), photodetector (14), signal high-speed parallel processing unit (15), the tail optical fiber output of narrow linewidth laser (1) is connected with the input port (2-1) of fiber coupler 2, realization is divided into two-way by laser, wherein a road is connected through first output port (2-2) of fiber coupler and the input port (3-1) of intensity modulator, the DC voltage offset port (3-2) of intensity modulator is connected with lock-in amplifier (4), realize stable control of automatic feedback of best operating point, the rf inputs mouth (3-3) of intensity modulator is connected with the output terminal (5-3) of microwave switch, the input end of microwave switch (5-1) is connected with microwave signal generation module (7), the input end of microwave switch (5-2) is connected with electric pulse generation module (6), the High Extinction Ratio broadband shift frequency pumping pulse light that intensity modulator 3 modulation obtain is by output port (3-4) output of intensity modulator, and be connected to the input port (8-1) of the first optical fiber circulator, the first optical fiber circulator (8) also has a port (8-2) to be connected with the fiber grating (9) of realizing filtering, the output port of the first optical fiber circulator (8-3) is connected with the input port (10-1) of the second optical fiber circulator, realizes pumping pulse light is injected in sensor fibre (13), another Lu Jingqi second output port (2-3) of fiber coupler (2) light splitting is connected with the input port (11-1) of phase-modulator, the rf inputs mouth (11-2) of phase-modulator is connected with multifrequency signal generation module (12), and the output port of phase-modulator (11-3) output packet contains the detection continuous light of multi-frequency composition and is injected in sensor fibre (13), surveying continuous light is connected with the another port (10-2) of the second optical fiber circulator after transmission in sensor fibre (13) in opposite directions with pumping pulse light, the output port of the second optical fiber circulator (10-3) connects the input port (14-1) of photodetector, the output port of photodetector (14-2) is connected with signal high-speed parallel processing unit (15), realizes the demodulation of transducing signal.
2. long-distance distributed wide-measuring range responds optical fiber dynamic strain sensing device fast as claimed in claim 1, it is characterized in that constructing by phase-modulator (11) and multifrequency signal generation module (12) a kind of optical texture of brillouin gain splicing spectrum, the multifrequency signal generation module (12) that use comprises multi-frequency composition acts on phase-modulator (11), realize modulation and survey the phase place of continuous light, make to survey and in continuous light, produce many optical frequencies composition, the amplitude of surveying each optical frequency of continuous light by control regulates each self-corresponding brillouin gain spectral amplitude, splice the brillouin gain spectrum of required spectrum width and spectral pattern.
3. long-distance distributed wide-measuring range responds optical fiber dynamic strain sensing device fast as claimed in claim 1, it is characterized in that utilizing intensity modulator (3), lock-in amplifier (4), microwave switch (5), electric pulse generation module (6), microwave signal generation module (7), the first optical fiber circulator (8), fiber grating (9) and the second optical fiber circulator (10) build the optical texture that pumping pulse light produces, obtain High Extinction Ratio microwave shift frequency pumping pulse light, and then the frequency difference that produces Brillouin amplification effect two-beam is fixed in the middle of the brillouin gain splicing spectrum hypotenuse range of linearity, the drift of the brillouin gain splicing spectrum that strain is caused is converted into the fluctuation of detection of optical power, realize distributed dynamic, the quantitative measurment of static strain.
4. long-distance distributed wide-measuring range responds optical fiber dynamic strain sensing device fast as claimed in claim 1, it is characterized in that the live width of described narrow linewidth laser (1) is less than 1MHz.
5. long-distance distributed wide-measuring range responds optical fiber dynamic strain sensing device fast as claimed in claim 1, it is characterized in that described fiber grating (9) is Prague short period fiber grating, its reflection kernel wavelength selects customization under the microwave broadband shift frequency of pump light pulse in frequency band range; By temperature or strain, be applied on fiber grating, carry out the tuning of reflection kernel wavelength.
6. long-distance distributed wide-measuring range responds optical fiber dynamic strain sensing device fast as claimed in claim 1, it is characterized in that described fiber grating (9) herein fiber grating also can be substituted by narrow band filter.
7. long-distance distributed wide-measuring range responds optical fiber dynamic strain sensing device fast as claimed in claim 1, it is characterized in that described photodetector (14) responsive bandwidth is higher than 100MHz.
8. long-distance distributed wide-measuring range responds optical fiber dynamic strain sensing device fast as claimed in claim 1, it is characterized in that described signal high-speed parallel processing unit (15) sampling rate is more than 100MS/s.
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