CN102052930A - Fiber grating distributed strain sensor and strain monitoring method thereof - Google Patents

Fiber grating distributed strain sensor and strain monitoring method thereof Download PDF

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CN102052930A
CN102052930A CN2010105596287A CN201010559628A CN102052930A CN 102052930 A CN102052930 A CN 102052930A CN 2010105596287 A CN2010105596287 A CN 2010105596287A CN 201010559628 A CN201010559628 A CN 201010559628A CN 102052930 A CN102052930 A CN 102052930A
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optical fiber
fiber grating
fiber
wavelength
port
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CN2010105596287A
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CN102052930B (en
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甘久林
郝蕴琦
叶青
潘政清
蔡海文
瞿荣辉
方祖捷
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中国科学院上海光学精密机械研究所
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Abstract

The invention relates to a fiber grating distributed strain sensor and a strain monitoring method thereof, which are characterized in that an erbium-doped fiber amplifier is added into an optical fiber fading cavity to form an active fading cavity, and an optical pulse fading sequence is obtained, so the positioning accuracy of submillimeter-magnitude spatial length measurement can be realized; and a wavelength of a tunable laser is in one-to-one correspondence with positioning data of fiber grating bragg reflection space by taking a linear chirped fiber grating or a uniform fiber grating as a sensing device, and the corresponding local strain capacity is demodulated by positioning the variable quantity of a local bragg reflection wavelength to realize distributed strain sensing. In the fiber grating distributed strain sensor, the spatial resolution ratio is improved to a submillimeter magnitude by a direct time domain measurement method, and the fiber grating distributed strain sensor has a compact structure and simple algorithm, can perform on-line monitor in real time and can be used for networking, so that the fiber grating distributed strain sensor has the large application space in the field of optical fiber sensing.

Description

Fiber grating distributed strain sensor and strain monitoring method thereof
Technical field
The present invention relates to optical fibre distribution type sensor, particularly a kind of fiber grating distributed strain sensor and strain monitoring method thereof that declines and swing the chamber technology based on optical fiber.
Background technology
Fibre Optical Sensor is owing to have that anti-electromagnetic interference capability is strong, highly sensitive, electrical insulating property is good, safe and reliable, corrosion-resistant, can constitute plurality of advantages such as optical fiber sensor network, thereby in each fields such as industry, agricultural, biologic medical, national defence broad prospect of application arranged all.
Fibre optic strain sensor has several like this technical schemes at present haply, comprise Fiber Bragg Grating FBG (FiberBragg Grating, FBG), long-period gratings (Long Period Grating, LPG), Mach-Zehnder interferometer (Mach-Zehnder Interferometer, MZ-I), optical fiber Sagnac ring etc.Strain transducer based on fiber grating has highly sensitive characteristics, and networking forms distributed sensing system easily.Distributed sensing network based on fiber grating wavelength-division multiplex technique, space division multiplexing technology and time-division multiplex technology has obtained developing widely and using at present, but in these fiber grating distributed strain sensing networks, all FBG all are equivalent to independently sensing point, and sensing result is the resultant effect in the scope of whole grid region.Therefore, this distributed sensing system is called quasi-distributed.Optical fiber distributed type strain transducer based on Brillouin scattering has the long advantage of distance sensing, and distance sensing can reach 80km, and the strain precision can reach 20 μ ε, spatial resolution can reach several meters magnitudes, and can measure Temperature Distribution simultaneously, and this kind distributed strain sensor is at large scale structure such as pipeline, off-shore oil rig, oil well, dam, dykes and dams, bridge, buildings, tunnel, fields such as cable have obtained using widely.But the spatial resolution of above several optical fiber distributed type strain transducers that are most widely used is all limited, brillouin distributed sensor spatial resolution is several meters magnitudes, the spatial resolution of FBG sensor is several centimetres of magnitudes, all be not suitable for the occasion of high spatial resolution, as the tomography monitoring of the Crack Monitoring of buildings and location, organic synthesis material and local train sudden change etc.
Optical fiber distributed type strain sensing field at high spatial resolution, utilize FBG as sensing element, design of Optical System and demodulation scheme by the advanced person, obtain the distribution of FBG grid region scope internal strain, thereby in research before, FBG develops into distributed sensor as just point sensor, has promoted the performance of FBG strain transducer greatly.This research thinking and potential widespread use have attracted a lot of researchists' interest and attention, and in order to be implemented in a distributed strain sensing on the FBG, people have proposed and developed some technical schemes.Formerly associated fiber grating distributed strain sensing technology has [Mark Volanthen, Harald Geiger, and John P.Dakin, " Distributed Grating Sensors Using Low-Coherence Reflectometry; " J.LightwaveTechnol.15,2076 (1997) .], this technology is utilized the Michelson interferometer structure of low-coherence light source, FBG is fixed on arm of interferometer, the length of an other arm changes or mobile end reflector by stretching, by the technology of this low coherence interference, interference spectrum is carried out modeling analysis, obtain the spatial discrimination effect of 300 μ m.Because based on interference technique, the system stability of this scheme is very poor, and adopt the mode or the mobile mirror of stretching optical fiber to position, therefore there is mechanical mobile device in the structure, increased the instability of system, also limit simultaneously the scope that distributed sensing is measured greatly, be difficult to realize networking.
Formerly the distributed strain sensing technology also has [H.Murayama, H.Igawa, K.Kageyama, K.Ohta, I.Ohsawa, K.Uzawa, M Kanai, T.Kasai, and I.Yamaguchi, " Distributed StrainMeasurement with High Spatial Resolution Using Fiber Bragg Gratings and OpticalFrequency Domain Reflectometry, " 18 ThIntern.Conf.Opt.Fiber Sensors, ThE40 (2006) .], utilize the Michelson interferometer structure of scanning light source in this piece paper, FBG is fixed on arm of interferometer, an other arm is also fixing, by the wavelength of tuning source, interference spectrum is carried out modeling analysis, realize the distributed sensing of the high spatial resolution under the reflection configuration of optical frequency territory.A last technology is compared, and the structure of this technical scheme is more compact, do not have any mechanical mobile device, so antijamming capability is stronger.But owing to still be based on interference structure, so system stability is very poor, and being limited in scope of distributed measurement, be difficult to realize networking.
Formerly the distributed strain sensing technology also has [Kazuo Hotate and Koji Kajiwara, " Proposal andexperimental verification of Bragg wavelength distribution measurement within along-length FBG by synthesis of optical coherence function ", Opt.Express 16,7881 (2008)], utilize the local reflex spectrum in synthetic (synthesis of optical coherence function) the commercial measurement FBG grid region of optical coherence function in this piece paper, obtain the local reflex Wavelength distribution in FBG grid region, realize distributed sensing.This system architecture complexity, and need complicated demodulating algorithm, be difficult to realize networking.
Summary of the invention
In order to overcome the shortcoming of above-mentioned technology formerly, better meet fiber grating distributed strain sensing applications demand, propose a kind of fiber grating distributed strain sensor and strain monitoring method thereof that declines and swing the chamber technology based on optical fiber, realize the strain sensing monitoring of submillimeter magnitude high spatial resolution location; The network-building method of fiber grating distributed strain sensor and the prioritization scheme of group network system are proposed; To realize distributed strain sensor monitoring in a big way.
Technical solution of the present invention is as follows:
A kind of fiber grating distributed strain sensor that declines and swing the chamber based on optical fiber, its characteristics are to comprise:
Light source module, this light source module is made up of tunable laser, acousto-optic modulator and radio-frequency modulator, the input end of the described acousto-optic modulator of output termination of described tunable laser, the modulated terminal of the described acousto-optic modulator of output termination of described radio-frequency modulator;
More than one optical fiber declines and swings the chamber, described optical fiber declines and swings the chamber and be made up of fiber optic loop and optical fiber grating sensing unit, described fiber optic loop comprises fiber coupler, Erbium-Doped Fiber Amplifier (EDFA) and the optical fiber circulator that is connected by optical fiber at least, the 4th port of described fiber coupler connects into ring with first port of described Erbium-Doped Fiber Amplifier (EDFA) and optical fiber circulator, the 3rd port of optical fiber circulator and second port of fiber coupler successively by optical fiber, and second port of described optical fiber circulator connects an end of described optical fiber grating sensing unit;
Web member links to each other the output terminal of described acousto-optic modulator and first port of described fiber coupler;
The 3rd port of described fiber coupler connects the input end of photodetector, the output terminal of this photodetector links to each other with signal Processing and display system through high-speed data acquisition card, and the synchronous triggering port of described high-speed data acquisition card links to each other with second output port of described radio-frequency modulator.
Described web member is an optical fiber, or the 1xn photoswitch of end input multiterminal output.
Described optical fiber grating sensing unit is for being distributed with a fiber grating or being distributed with the cascade fiber grating sequence that a plurality of fiber gratings constitute on an optical fiber, wherein r is the positive integer more than 2, in same cascade fiber grating sequence, all fiber gratings select for use linear chirp optical fiber grating (being designated hereinafter simply as LCFBG) or uniform fiber grating (being designated hereinafter simply as FBG) as senser element, the fiber grating of choosing different reflection wavelengths successively with proper spacing in the tuning range of described tunable laser is as the networking sensing element, and the reflectance spectrum of all fiber gratings is not overlapping.
Fiber grating distributed strain sensor has declining more than 2 and swings the chamber, each second port that swings the optical fiber circulator in the ring that declines respectively connects a cascade fiber grating sequence, the output terminal of the acousto-optic modulator of described light source module) web member by the 1xn photoswitch links to each other respectively with first port of a plurality of fiber couplers of swinging ring of declining.
Inserted second optical fiber circulator between the 3rd port of the optical fiber circulator in described fiber optic loop and second port of fiber coupler, second port of this second optical fiber circulator connects the filtering fiber grating, this filtering fiber grating is fixed on the tuning or thermal tuning device of stress, this filtering fiber grating is connected with described tunable laser by automatic synchronous triggering device, be consistent with the wavelength of maintenance light source output and the foveal reflex wavelength of filtering fiber grating, with the spontaneous emission noise filtering of described Erbium-Doped Fiber Amplifier (EDFA).
Insert an optical fiber FP wave filter between the 3rd port of the optical fiber circulator in described fiber optic loop and second port of fiber coupler, this optical fiber FP wave filter is connected with described tunable laser by automatic synchronous triggering device, be consistent with the wavelength of maintenance light source output and the central homology wavelength of this optical fiber FP wave filter, with the spontaneous emission noise filtering of described Erbium-Doped Fiber Amplifier (EDFA).
Utilize above-mentioned fiber grating distributed strain sensor to carry out the method for distributed strain monitoring, its characteristics are that this method comprises the following steps:
1. the laser output wavelength of tuning tunable laser is λ 0The continuous laser of narrow linewidth, this wavelength X 0Foveal reflex consistent wavelength with described optical fiber grating sensing unit;
2. the continuous light that described acousto-optic modulator injects tunable laser is modulated to the pulsed light sequence;
3. regulate described gain of EDFA, the pulse number that swings the pulsed light sequence that declines that described photodetector is detected surpasses 100;
4. pass through the external trigger function of radio-frequency modulator, described acousto-optic modulator of synchronous triggering and high-speed data acquisition card, make pulsed light of described acousto-optic modulator output inject described declining when swinging ring, the high-speed data acquisition card synchronous acquisition declines and swings pulse train, gather many group pulses sequence and do average acquisition average pulse sequence, with noise reduction process;
5. obtain the time to peak of pulse train, take out the time of (m+1) individual pulse and the 1st pulse, subtract each other again, obtain declining and swing recurrence interval T divided by m;
6. calculate the long L in chamber decline and swing the chamber by formula L=c/nT, wherein c is the light velocity, and n is the refractive index of optical fiber, the long L in this chamber by described optical fiber grating sensing unit with incident wavelength λ 0The position D of reflection spot one to one 0Determine;
7. the output light wavelength λ of tuning described tunable laser 1, λ 2..., λ i..., λ q, repeat above-mentioned the respectively 1. to the 6. step, obtain the position D of each wavelength reflection in the optical fiber grating sensing unit bandwidth range successively 1, D 2..., D i..., D q, the relation calibration λ between completing place-reflection wavelength i(D i), be called the calibration data, be written as more general form λ (z);
8. the optical fiber grating sensing unit is fixed on sensitive zones, is used for strain sensing monitoring, repeat above-mentioned the 1. to the 6. step, obtain sensitive zones position-reflection wavelength relation sensing data λ ' (z);
9. described sensing data and described calibration data are compared, obtain the wavelength variable quantity Δ λ (z) of the sensitive zones at place, described optical fiber grating sensing unit,
λ’(z)-λ(z)=Δλ(z)
In the formula: z is the position coordinates along the measurement point of the sensitive zones at place, described optical fiber grating sensing unit, utilize following formula to calculate the dependent variable ε (z) of all sensitive zones, realize that the distributed strain in the scope of grid region, optical fiber grating sensing unit is measured: ε (z)=Δ λ (z)/(0.78 * λ (z)).
Compare with traditional fiber Bragg grating strain sensor, characteristics of the present invention and advantage are:
(1) the present invention is based on the fiber grating distributed strain sensor that optical fiber declines and swings the chamber technology, decline to swing in the chamber at optical fiber and add Erbium-Doped Fiber Amplifier (EDFA) and form active declining and swing the chamber, most losses in the compensated cavity, make pulse decay very slowly in the chamber declining to swing, obtaining light pulse declines and swings sequence, utilization declines and swings the method that the mistiming is averaged between (n+1) individual pulse in the pulse train and the 1st pulse and obtain average pulse at interval, can significantly improve declines swings the measuring accuracy of recurrence interval, thereby the chamber of swinging the chamber of being declined accurately is long, be the precision of the position coordinates that swings wave reflection point of declining of the sensitive zones at place, described optical fiber grating sensing unit, realize the space length measurement and positioning precision of submillimeter magnitude.Use linear chirp optical fiber grating (LCFBG) or uniform fiber grating (FBG) as senser element, the wavelength of tunable laser and the space orientation data of acquisition are mapped one by one, can obtain the information of local bragg reflection wavelength, variable quantity according to local bragg reflection wavelength, can demodulate corresponding local train amount, thereby realize the distributed strain sensing.Can be in the scope of the grid region of a fiber grating, realize distributed measurement, overcome the defective of traditional use fiber grating as point sensor, can be applied in much needs the sensing of high-space resolution occasion, as the fine cracks monitoring of buildings and the tomography monitoring of organic composite material etc.
(2) the present invention utilizes optical fiber to decline to swing the technology in chamber, realizes submillimeter magnitude high spatial resolution location, and then utilizes LCFBG or FBG as sensing element, realizes the distributed strain sensing.The method that the present invention adopts direct time-domain to measure, principle is simple, need not complicated transfer algorithm, and system's employing all optical fibre structure, compares the method at the interference spectrum of preceding technology, and structure is highly stable.
(3) the present invention is based on to decline and swing the distributed sensing of chamber technology, cascade fiber grating carries out networking very easily, each root fiber grating all can be realized distributed sensing in the scope of the grid region of grating, expanded the practicality of system greatly, has reduced the cost of whole system.
(4) all devices of the present invention's employing all are normal component, can programme and realize automatic triggering collection and data processing, and the realization real-time online is measured automatically, realizes the distributed measurement of dynamic strain.
Description of drawings
Fig. 1 is a fiber grating distributed strain sensor construction synoptic diagram of the present invention;
Fig. 2 is based on declining of the present invention's realization and swings chamber multipulse sequence experimental result picture;
Fig. 3 utilizes optical fiber to decline to swing the chamber technology to carry out high-space resolution Positioning Principle figure among the present invention;
Fig. 4 is based on wavelength-division multiplex networking operational version;
Fig. 5 is based on wavelength-division multiplex and adds multiplexing networking operational version of time-division;
Fig. 6 is one of performance optimization scheme of group network system structure;
Fig. 7 be the group network system structure the performance optimization scheme two.
Embodiment
The invention will be further described below in conjunction with embodiment and accompanying drawing, but should not limit protection scope of the present invention with this.
See also Fig. 1 earlier, Fig. 1 the present invention is based on the fiber grating distributed strain sensor construction synoptic diagram that optical fiber declines and swings the chamber, also is the structural representation of the embodiment of the invention 1, as seen from the figure, the present invention is based on the fiber grating distributed strain sensor that optical fiber declines and swings the chamber, comprising:
Light source module 1, this light source module 1 is made up of tunable laser 11, acousto-optic modulator 12 and radio-frequency modulator 13, the input end 1201 of the described acousto-optic modulator 12 of output termination of described tunable laser 11, the modulated terminal 1202 of the described acousto-optic modulator 12 of output termination of described radio-frequency modulator 13;
More than one optical fiber declines and swings the chamber, each optical fiber declines and swings the chamber and be made up of fiber optic loop 3 and optical fiber grating sensing unit 4, described fiber optic loop 3 comprises the fiber coupler 31 that is connected by optical fiber at least, Erbium-Doped Fiber Amplifier (EDFA) 32 and optical fiber circulator 33 constitute, the 4th port 3104 of described fiber coupler 31 by optical fiber successively with first port 3301 of described Erbium-Doped Fiber Amplifier (EDFA) 32 and optical fiber circulator 33, the 3rd port 3303 of optical fiber circulator 33 and second port 3102 of fiber coupler 31 connect into ring, and second port 3302 of described optical fiber circulator 33 connects an end of described optical fiber grating sensing unit 4;
Web member 2 links to each other the output terminal 1203 of described acousto-optic modulator 12 and first port 3101 of described fiber coupler 31;
The 3rd port 3103 of described fiber coupler 31 connects the input end of photodetector 5, the output terminal of this photodetector 5 links to each other with signal Processing and display system 7 through high-speed data acquisition card 6, and the synchronous triggering port 602 of described high-speed data acquisition card 6 links to each other with second output port 1302 of described radio-frequency modulator 13.
Being described as follows of each device blocks in the embodiments of the invention:
Tunable laser 11, be based on the fiber grating distributed strain sensing system optical signal transmitting source that optical fiber declines and swings the chamber technology, need to adopt tunable laser, the light source that adopts in the example of the present invention is that a model of Photonetics company is the semiconductor extenal cavity tunable laser device of TUNICS-Plus, tuning range is 1510nm~1590nm, laser linewidth also can adopt the tunable laser of other types less than 1pm.
Acousto-optic modulator 12, be to be used for the continuous output optical modulation of tunable laser is become the pulsed light sequence, the acousto-optic modulator that adopts in the example of the present invention is that a model of AA company is the modulator of MT160-IIR10-FIO, also can be with the acousto-optic modulator or the electrooptic modulator of other models.
Radio-frequency modulator 13 is to be used for applying rf modulated signal on acousto-optic modulator drives, and can use signal generator instrument or signal generating circuit.
Fiber coupler 31 is that general single mode fiber constitutes, the 1550nm wave band, and port 2 * 2, splitting ratio are 50: 50.
EDFA 32, adopt commercial photoelectricity one EDFA module or the EDFA that oneself builds all can.
Fiber optical circulator 33 is one three fiber port circulators, also can adopt the way of incoming fiber optic coupling mechanism and isolator, plays the scheme that is equal to the fiber optical circulator effect.
Optical fiber grating sensing unit 4 is sensing units of system, can adopt LCFBG or FBG.
Photodetector 5, it is the high speed detector that light signal is converted to electric signal, the photodetector that adopts in the example of the present invention is that a model of Newport company is the detector of 1617-AC-FC, the bandwidth of this detector is 800MHz, can realize the high-speed optical pulse acquisition of signal, also can use the high-speed photodetector of other models.
Data collecting card 6 mainly is to carry out the data-triggered collection.In order to obtain high time resolution, need to adopt high-speed data acquisition card.The data collecting card that adopts among the present invention is that a model of Gage company is the digitizer of CS82G, and sampling rate is 2GS/s.Also can adopt the PCI-5152 digitizer of NI company or the high-speed collection card of other companies.
Signal Processing and display system 7 mainly are that the data that data capture card 6 collects are handled in real time and shown.The system handles software of writing in the example of the present invention is based on data collecting card and LabVIEW programmes, also can be based on other platform such as the realization of programming of Matlab or C language.
Ultimate principle of the present invention is as follows:
A branch of pulsed light is injected into to decline and swings in the chamber, and a part of light is exported by coupling mechanism, and another part light continues to swing circle transmission in the chamber declining, and the pulsed light peak power satisfies attenuation law in the chamber:
dI dt = - IAc nL
Wherein, I is a pulsed light peak power in the chamber that changes of t in time, and A is loss, and c is the light velocity, and n is a refractive index, and L is that optical fiber declines that to swing the chamber, chamber long.
So decay index of coincidence rule of pulse power Loss A=α L+ δ-G wherein, α is the loss factor of optical fiber, and the 1550nm single-mode fiber is about 0.2dB/km, and δ is the loss that junction loss, device loss and the FBG transmission in the chamber introduced, and G is that the optical loss that image intensifer is introduced in the chamber in compensates.
Definition τ 0For the light pulse power attenuation is the required time of 1/e of initial incident power, be called the ring-down time constant:
τ 0=nL/c(αL+δ-G)
Extract ring-down time constant τ by impulse chamber ring-down spectroscopy (being designated hereinafter simply as CRDS) 0Come the inverting cavity loss.Obviously, cavity loss is big more, and pulse power decline ground is fast more, ring-down time constant τ 0More little.Because what CRDS directly measured is power attenuation speed, and power attenuation speed and light source power are irrelevant, so this technology can be eliminated the influence of light source power fluctuation automatically, simultaneously because time measurement at present can reach very high precision, so the resolution of this method is very high.The problem of CRDS is to have only very little a part of luminous power can pass resonator cavity, for having relatively high expectations of photodetection.The speed ratio of power attenuation is very fast among the CRDS simultaneously, has relatively high expectations for the temporal resolution of surveying, and has increased the cost of system.
In the present invention, adopt active declining to swing the chamber, promptly swing in the chamber loss that inserts in the EDFA compensated cavity declining, making light pulse to decline in the chamber swings many times, as it is shown in Figure 2 to test the result, and can obtain declines swings pulse train, and the rate of decay of pulse is very slow, a light pulse enters into to decline swings the chamber, can obtain up to a hundred even hundreds of declines and to swing pulse.If the time of pulse circle transmission one circle in the chamber, promptly decline and swing the period T of pulse, obtain in the pulse train time to peak of the 1st pulse and (m+1) individual pulse, ask the averaging time at adjacent pulse interval again, thereby can obtain declining more accurately swings recurrence interval T, also promptly corresponding decline more accurately that to swing the chamber, chamber long, therefore can realize the length measurement of high-precision chamber with the method.Use this principle to carry out high spatial resolution distributed strain sensing, LCFBG is as sensing element, and the characteristics of LCFBG device are: axial along the grid region, different wavelength is in different position reflections.The schematic diagram that utilization LCFBG carries out the high spatial resolution strain sensing is as shown in Figure 3: suppose that on LCFBG A, B all are in the grid region at 2, apart from being spaced apart 2cm.The reflection wavelength that A, B are 2 is respectively λ AAnd λ BImport λ respectively AAnd λ BThe pulsewidth 25ns light pulse of wavelength is swung in the chamber to declining, and wavelength is λ AAnd λ BLight be respectively T (A) and T (B) in the recurrence interval of declining that swinging declines in the chamber and swing to swing the chamber, chamber long because 2 correspondences of A and B different declining, so λ AAnd λ BDecline and swing recurrence interval difference and be Δ T=T (A)-T (B)=0.2ns, and present surveying instrument is difficult to realize the time resolution effect of 0.2ns, supposes that the time measurement inaccuracy is 0.5ns, then can't distinguish the A and B 2 points in grid region according to pulse interval; Suppose λ AAnd λ BLight pulse under the wavelength is declining that swinging declines in the chamber and is swinging the p circle, and the accumulated time effect makes and is spaced apart Δ T=p * 0.2ns, and the time measurement uncertainty still is 0.5ns, if p>25, then Δ T>5ns so can well orient λ from time domain AAnd λ BRelative position, choose p>100, can realize the high spatial resolution of submillimeter magnitude.
According to principle of the present invention, utilize to the present invention is based on optical fiber and decline that to carry out the basic procedure of distributed strain sensing as follows for the fiber grating distributed strain sensor that swings the chamber:
1. tunable laser 11, and tuning to go out wavelength be λ 0The continuous laser of narrow linewidth, this wavelength X 0Foveal reflex consistent wavelength with described optical fiber grating sensing unit sensing unit 4;
2. acousto-optic modulator 12, and the continuous light that tunable laser 11 is injected is modulated to the pulsed light sequence;
3. regulate the gain of EDFA 32, the pulse number that swings pulse train light that declines that described photodetector 5 is detected surpasses 100;
4. utilize the external trigger function of radio-frequency modulator 13, described acousto-optic modulator 12 of synchronous triggering and high-speed data acquisition card 6, make pulsed light of described acousto-optic modulator 12 outputs inject described declining when swinging ring, high-speed data acquisition card 6 synchronous triggering collections decline and swing pulse train, gather many group pulses sequence and do average acquisition average pulse sequence, with noise reduction process;
5. obtain the time to peak of pulse train, take out the time of (m+1) individual pulse and the 1st pulse, subtract each other again, obtain declining and swing recurrence interval T divided by m;
6. calculate the long L in chamber decline and swing the chamber by formula L=c/nT, wherein c is the light velocity, and n is the refractive index of optical fiber, the long L in this chamber by described optical fiber grating sensing unit 4 with incident wavelength λ 0The position D of relevant corresponding reflection spot 0Determine;
The output light wavelength λ of 7. tuning described tunable laser 11 1, λ 2..., λ i..., λ q, repeat above-mentioned the respectively 1. to the 6. step, obtain the position D of each wavelength reflection in optical fiber grating sensing unit 4 bandwidth ranges successively 1, D 2..., D i..., D q, the relation calibration λ between completing place-reflection wavelength i(D i), be called the calibration data, be written as more general form λ (z);
8. optical fiber grating sensing unit 4 is fixed on sensitive zones, is used for strain sensing monitoring, repeat above-mentioned the 1. to the 6. step, obtain sensitive zones position-reflection wavelength relation sensing data λ ' (z);
9. described sensing data and described calibration data are compared, obtain the wavelength variable quantity Δ λ (z) of the sensitive zones at 4 places, described optical fiber grating sensing unit,
λ’(z)-λ(z)=Δλ(z)
In the formula: z is the position coordinates along the measurement point of the sensitive zones at 4 places, described optical fiber grating sensing unit, utilize following formula to calculate the dependent variable ε (z) of all sensitive zones, realize that the distributed strain in the optical fiber grating sensing unit 4 grid region scopes is measured: ε (z)=Δ λ (z)/(0.78 * λ (z)).The source of this formula sees also document [Philippe Giaccari, Gabriel R Dunkel, Laurent Humbert, John Botsis, Hans GLimberger and Ren ' e P Salath ' e, " On a direct determination of non-uniform internalstrain fields using fibre Bragg gratings ", Smart Mater.Struct.14 (2005) 127-136]
Obtain the dependent variable of all positions, thereby realize the distributed strain measurement in the optical fiber grating sensing unit 4 grid region scopes.
The utilization technical solution of the present invention can realize the distributed strain sensing in the grid region scope of fiber grating, makes in other researchists' before research, uses fiber grating to be further enhanced and to expand as just the application function of point sensor.Simultaneously, technical solution of the present invention possesses the function of fiber grating networking sensing.
Embodiment 2, and based on the group network system scheme of wavelength-division multiplex as shown in Figure 4: wherein 1 is light source module, adopt as in Fig. 1 structure employed tunable laser 11 connect acousto-optic modulators 12 and radio-frequency modulator 13 formations, output optical pulse sequence.2 is the light web member.3 is the fiber optic loop in Fig. 1 structure.411,412,413,414 ... 41r swings the cascade fiber grating sequence in the chamber for declining by circulator 33 accesses, 411 access waies are consistent with the optical fiber grating sensing unit 4 in Fig. 1 structure, other fiber grating successively the cascade welding after 411 fiber gratings.By this structure, can realize the interior distributed strain sensing of grid region scope of a plurality of fiber gratings, distributed strain demodulation method and the flow process in the above-mentioned experimental principle in each root fiber grating grid region are just the same, thereby realize networking, significantly reduce the cost of sensor.In this structure, 2 that should be noted that are:
One, the fiber grating of all cascades can be selected LCFBG or FBG for use, but the reflectance spectrum of all fiber gratings can not be overlapping, can choose the fiber grating of different reflection wavelengths successively as the networking sensing element with suitable interval in the tuning range of tunable laser 11;
Two, the reflectivity of all fiber gratings unanimity of should trying one's best so just need not to remove to regulate the gain compensation of EDFA in the chamber separately for each unit, root optical fiber grating sensing unit, thereby makes measuring speed fast, realizes automatic real-time measurement.In the use of reality, the fiber grating of all cascades all can be made as the fiber grating of reflectivity>99%, and this point is easy in the process of making realize.
Embodiment 3, add time-multiplexed group network system scheme as shown in Figure 5 based on wavelength-division multiplex: wherein 1 is light source module, the same with employed light source in Fig. 4 structure.31,32 ..., 3j is fiber optic loop as being constituted in Fig. 1 structure.411,412 ... 41r; 421,422 ... 42r; 4j1,4j2 ..., 4jr is respectively incoming fiber optic ring 31,32 ... cascade fiber grating sequence set among the 3j, the building mode of each cascade fiber grating sequence are all the same with building mode in Fig. 4 WDM structure.Each fiber optic loop and corresponding cascade fiber grating sequence constitute one and measure passage, 2 open the light for s road light, the light way of opening the light can reach 16 the tunnel even 32 the tunnel, utilize light to open the light, each passage of gating, need to measure the Strain Distribution of which cascade fiber grating sequence, just corresponding passage is connected.In like manner, in this structure, the problem of the required attention of the cascade fiber grating sequence construct of each passage rule is the same with the group network system scheme of wavelength-division multiplex shown in Figure 4, but the fiber grating spectrum between the different passage can be overlapping.By this scheme networking, can more increase the access quantity of fiber grating, make sensing scope further expand, the cost of sensor further reduces.
Because in the networking, need use a plurality of optical fiber grating sensings unit, and in each passage, the reflectance spectrum of all optical fiber grating sensing unit can not be overlapping, and therefore, the superimposed light spectral width of all sensing units just increases along with the increase of sensing unit quantity, the EDFA noise that swings in the chamber that declines also increases thereupon, when optical noise in the chamber increased, the quality of the light pulse of circulating propagation just descended in the chamber in, just was difficult to a lot of high-quality chamber of acquisition number and declined and swing pulse train.Therefore, in group network system, clunk management is a problem must considering.
Embodiment 4, Fig. 6 is one of performance optimization scheme of group network system structure, on the basis of distributed sensing basic structure Fig. 1 and networking structure Fig. 4, add a kind of filtering and noise reduction functional module, the access scheme of filtering and noise reduction functional module that mainly draws, other parts of not drawing are consistent with aforementioned schemes.Insert a filtering fiber grating 8 declining to swing in the chamber by the second optics circulator 34.Swing transmission direction in the chamber, chamber along light pulse declining, this second optics circulator 34 is connected on after first optical fiber circulator 33.Filtering fiber grating 8 is fixed on the tuning or thermal tuning device of stress, and be connected with tunable laser 11 by automatic synchronous triggering device 9, keep the wavelength of light source output and the foveal reflex wavelength of filtering fiber grating 8 to be consistent, with the filtering of EDFA spontaneous emission noise.By this clunk management scheme, can be so that in the group network system, it is best that the distributed sensing effect of each root sensing unit FBG all reaches.
Embodiment 5, Fig. 7 be the group network system structure the performance optimization scheme two, on the basis of distributed sensing basic structure Fig. 1 and networking structure Fig. 4, added another kind of filtering and noise reduction functional module, the access scheme of filtering and noise reduction functional module that mainly draws, other parts of not drawing are consistent with aforementioned schemes.Insert an optical fiber FP wave filter 10 declining to swing in the chamber, can adopt the optical fiber FP wave filter of low-light company.Along the transmission direction of light pulse in the chamber, this optical fiber FP filter module 10 is connected on after first optical fiber circulator 33.This optical fiber FP wave filter 10 is connected with tunable laser 11 by automatic synchronous triggering device 9, keeps the wavelength of light source output and the central homology wavelength of optical fiber FP wave filter 10 to be consistent, with the filtering of EDFA spontaneous emission noise.By this clunk management scheme, can be so that in the group network system, it is best that the distributed sensing effect of each root sensing unit FBG all reaches.
The method that the present invention has adopted direct time-domain to measure is brought up to the submillimeter magnitude with spatial resolution, and compact conformation, and algorithm is simple, but real time on-line monitoring, but therefore the networking use will have very big application space in sensory field of optic fibre.

Claims (7)

1. fiber grating distributed strain sensor is characterized in that comprising:
Light source module (1), this light source module (1) is made up of tunable laser (11), acousto-optic modulator (12) and radio-frequency modulator (13), the input end (1201) of the described acousto-optic modulator of output termination (12) of described tunable laser (11), (1301 connect the modulated terminal (1202) of described acousto-optic modulator (12) to the output terminal of described radio-frequency modulator (13);
More than one optical fiber declines and swings the chamber, described optical fiber declines and swings the chamber and be made up of fiber optic loop (3) and optical fiber grating sensing unit (4), described fiber optic loop (3) comprises the fiber coupler (31) that is connected by optical fiber at least, Erbium-Doped Fiber Amplifier (EDFA) (32) and optical fiber circulator (33), the 4th port (3104) of described fiber coupler (31) by optical fiber successively with first port (3301) of described Erbium-Doped Fiber Amplifier (EDFA) (32) and optical fiber circulator (33), the 3rd port (3303) of optical fiber circulator (33) and second port (3102) of fiber coupler (31) connect into ring, and second port (3302) of described optical fiber circulator (33) connects an end of described optical fiber grating sensing unit (4);
Web member (2) links to each other the output terminal (1203) of described acousto-optic modulator (12) and first port (3101) of described fiber coupler (31);
The 3rd port (3103) of described fiber coupler (31) connects the input end of photodetector (5), the output terminal of this photodetector (5) links to each other with signal Processing and display system (7) through high-speed data acquisition card (6), and the synchronous triggering port (602) of described high-speed data acquisition card (6) links to each other with second output port (1302) of described radio-frequency modulator (13).
2. fiber grating distributed strain sensor according to claim 1 is characterized in that described web member (2) is an optical fiber, or the 1xn photoswitch of end input multiterminal output.
3. fiber grating distributed strain sensor according to claim 1, it is characterized in that described optical fiber grating sensing unit (4) is for to be distributed with a fiber grating or to be distributed with a plurality of fiber gratings (411 on an optical fiber, 412,413,41r) the cascade fiber grating sequence of Gou Chenging, wherein r is the positive integer more than 2, in same cascade fiber grating sequence, all fiber gratings are selected LCFBG or FBG for use, the fiber grating of choosing different reflection wavelengths successively with proper spacing in the tuning range of described tunable laser (11) is as the networking sensing element, and the reflectance spectrum of all fiber gratings is not overlapping.
4. fiber grating distributed strain sensor according to claim 2, it is characterized in that having a plurality of declining and swing the chamber, each second port (3302) of swinging the optical fiber circulator (33) in the ring (3j) of declining respectively connect a cascade fiber grating sequence (4j1,4j2 ..., 4jr), wherein j is the positive integer more than 2, and the web member (2) of the output terminal (123) of the acousto-optic modulator (12) of described light source module (1) by a 1xn photoswitch links to each other respectively with first port (3101) of a plurality of fiber couplers (31) of swinging ring (3j) of declining.
5. according to claim 1 or 2 or 3 or 4 each described fiber grating distributed strain sensors, it is characterized in that having inserted second optical fiber circulator (34) between second port (3102) of the 3rd port (3303) of the optical fiber circulator (33) in described fiber optic loop (3) and fiber coupler (31), second port of this second optical fiber circulator (34) connects filtering fiber grating (8), this filtering fiber grating (8) is fixed on the tuning or thermal tuning device of stress, this filtering fiber grating (8) is connected with described tunable laser (11) by automatic synchronous triggering device (9), be consistent with the wavelength of maintenance light source output and the foveal reflex wavelength of filtering fiber grating (8), with the spontaneous emission noise filtering of described Erbium-Doped Fiber Amplifier (EDFA) (32).
6. according to claim 1 or 2 or 3 or 4 each described fiber grating distributed strain sensors, it is characterized in that inserting an optical fiber FP wave filter (10) between second port (3102) of the 3rd port (3303) of the optical fiber circulator (33) in described fiber optic loop (3) and fiber coupler (31), this optical fiber FP wave filter (10) is connected with described tunable laser (11) by automatic synchronous triggering device (9), be consistent with the wavelength of maintenance light source output and the central homology wavelength of this optical fiber FP wave filter (10), with the spontaneous emission noise filtering of described Erbium-Doped Fiber Amplifier (EDFA) (32).
7. utilize the described fiber grating distributed strain of claim 1 sensor to carry out the method for distributed strain monitoring, it is characterized in that this method comprises the following steps:
The laser output wavelength of 1. tuning tunable laser (11) is λ 0The continuous laser of narrow linewidth, this wavelength X 0Foveal reflex consistent wavelength with described optical fiber grating sensing unit (4);
2. the continuous light that described acousto-optic modulator (12) injects tunable laser (11) is modulated to the pulsed light sequence;
3. regulate the gain of described Erbium-Doped Fiber Amplifier (EDFA) (32), the pulse number that swings the pulsed light sequence that declines that described photodetector (5) is detected surpasses 100;
4. pass through the external trigger function of radio-frequency modulator (13), described acousto-optic modulator of synchronous triggering (12) and high-speed data acquisition card (6), make pulsed light of described acousto-optic modulator (12) output inject described declining when swinging ring, high-speed data acquisition card 6 synchronous acquisition decline and swing pulse train, gather many group pulses sequence and do average acquisition average pulse sequence, with noise reduction process;
5. obtain the time to peak of pulse train, take out the time of (m+1) individual pulse and the 1st pulse, subtract each other again, obtain declining and swing recurrence interval T divided by m;
6. calculate the long L in chamber decline and swing the chamber by formula L=c/nT, wherein c is the light velocity, and n is the refractive index of optical fiber, the long L in this chamber by described optical fiber grating sensing unit (4) with incident wavelength λ 0The position D of relevant corresponding reflection spot 0Determine;
The output light wavelength λ of 7. tuning described tunable laser (11) 1, λ 2..., λ i..., λ q, repeat above-mentioned the respectively 1. to the 6. step, obtain the position D of each wavelength reflection in optical fiber grating sensing unit (4) bandwidth range successively 1, D 2..., D i..., D q, the relation calibration λ between completing place-reflection wavelength i(D i), be called the calibration data, be written as more general form λ (z);
8. optical fiber grating sensing unit (4) are fixed on sensitive zones, are used for strain sensing monitoring, repeat above-mentioned the 1. to the 6. step, obtain sensitive zones position-reflection wavelength relation sensing data λ ' (z);
9. described sensing data and described calibration data are compared, obtain the wavelength variable quantity Δ λ (z) of the sensitive zones at place, described optical fiber grating sensing unit (4),
λ’(z)-λ(z)=Δλ(z)
In the formula: z is the position coordinates along the measurement point of the sensitive zones at place, described optical fiber grating sensing unit (4), utilize following formula to calculate the dependent variable ε (z) of all sensitive zones, realize that the distributed strain in the scope of grid region, optical fiber grating sensing unit (4) is measured: ε (z)=Δ λ (z)/(0.78 * λ (z)).
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