CN101852626A - Narrow-band distributed feedback laser wavelength scanning fiber bragg grating sensing device - Google Patents
Narrow-band distributed feedback laser wavelength scanning fiber bragg grating sensing device Download PDFInfo
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Abstract
The invention discloses a narrow-band distributed feedback laser wavelength scanning fiber bragg grating sensing device, which senses and detects external physical quantities in the following way that: the device comprises a current-driven distributed feedback laser controlled by a temperature control circuit; light emitted from the laser enters a sensing fiber bragg grating through an optical isolation unit; the light passing through the fiber bragg grating enters an opto-electric receiving unit and then enters a control analysis unit in a form of electrical signal; the output wavelength of the distributed feedback laser can be regulated by changing a control temperature; and a grating reflection centre wavelength and a corresponding external physical quantity are reckoned according to an extremum output by the opto-electric receiving unit when the output wavelength of the laser is matched with the fiber bragg grating reflection centre wavelength by temperature scanning. Compared with a conventional structure where sensing is realized by performing wavelength demodulation at the output end of the fiber bragg grating with a broadband light source, the narrow-band distributed feedback laser wavelength scanning fiber bragg grating sensing device has the characteristics of great production cost reduction, and miniature and low-cost engineering.
Description
Technical field
The present invention relates to utilize fiber grating to realize temperature or pressure sensing technology at sensory field of optic fibre.
Background technology
Fiber grating (or claiming Fiber Bragg Grating, Fiber Bragg Grating-FBG) is a big focus of present sensory field of optic fibre research and application.Compare with conventional sensing technology, Fibre Optical Sensor have anti-electromagnetic interference (EMI) and atomic radiation, in light weight, volume is little, the performance of insulation, numerous excellences such as high temperature resistant, corrosion-resistant, more and more is subjected to the favor of special occasions or severe environment applications.Fiber-optic grating sensor has been widely used in civil engineering work (bridge, mine, tunnel, dam and buildings etc.), Aero-Space, ocean, medical science, electric power, field of petrochemical industry, and correlation technique is more and more ripe.
Fig. 1 has represented the ultimate principle of fiber-optic grating sensor.The Bragg fiber grating is meant and utilizes the single mode germnium doped fiber (sandwich layer refractive index own is n
1, cladding index is n
2) (Fig. 1 a) to become the brand-new optical-fiber type Bragg grating that gate technique forms through UV-irradiation.Fiber core refractive index (the sensitometric refraction rate is n) behind the one-tenth grid presents periodic distribution (cycle is Λ), therefore, the basic optical characteristic of this grating is exactly to be the narrowband optical filtering at center with the resonant wavelength, that is to say, generally most of wavelength can pass through (λ 2..... λ n), and the wavelength X 1 that satisfies specified conditions is then with reflected back.Bragg grating reflection spectrum is mainly by its bandwidth and peak reflectivity decision, and these parameters are grating length, index modulation coefficient and the isoparametric function of Bragg wavelength.Utilize this principle, when we adopt wideband light source to be input in the fiber grating (Fig. 1 b),, will occur a low ebb in its transmitted spectrum, and emission spectrum will be to be the narrow-band peak at center with resonant wavelength λ 1 because resonant wavelength λ 1 will be reflected.When the extraneous parameter that is closely related when fiber grating changes (as temperature variation, pressure etc.), its resonant wavelength will drift about, and for example become λ 2 from λ 1, and the peak value of reflectance spectrum (or transmission valley) will directly reflect the variation of these extraneous parameters like this.Therefore, just can realize sensor monitoring by the drift value of measuring center wavelength to correlation parameter.Fig. 2 has represented a kind of typical fiber bragg grating sensing device, adopt wideband light source to be input in the sensor fibre, sensor fibre has comprised a series of fiber gratings (FBG) probe, the drift situation of each grating centre wavelength can realize monitoring by spectrometer or so-called (FBG) demodulator, so just can finish distributed multiple spot (temperature or pressure) monitoring.
For fiber bragg grating sensing device, most crucial technology is the Wavelength demodulation technology at present, has also occupied the exhausted big component of whole installation cost simultaneously, and therefore, studying cheaply, demodulation techniques have extremely important actual application value.Existing several practicability demodulation techniques comprise: (1) spectrometer or wavemeter method--spectrometer resolution height, but extremely expensive; Wavemeter is simple relatively, but dynamic range is generally very limited; (2) wave filter method-as adopting boundary filter method (S.M.Melle, K.Liu, R.M.Measures, " A passive wavelength demodulation system for guided-wave Bragg grating sensor; " IEEEPhotonics Technology Letters, vol.4, no.5,516-518,1992; M.A.Davis, A.D.Kersey, " All-fibre Bragg Grating strain-sensor demodulation technique using a wavelength division coupler; " Electronics Lettes, vol.30, no.1,75-77,1994), Fabry-Perot tunable optic filter method (A.D.Kersey, T.A.Berkoff, W.W.Morey, " Multiplexed fiber Bragg grating strain-sensor system with a fiber Fabry-Perot wavelength filter, " Optics Letters, vol.18, no.16,1370-1372,1993), tunable fiber grating filter method (G.P.Brady, S.Hope, A.B.L.Riberio, " Demultiplexing of fiber Bragg grating temperature and strain sensors, " Optics Communications, vol.111,51-54,1994; M.A.Davis, A.D.Kersey, " Matched-filter interrogation technique for fibre Bragg grating arrays; " Electronics Letters, vol.31, no.10,822-823,1995), acousto-optic tunable filter method (M.G.Xu, H.Geiger, J.L.Archambault, et al, " Novel inteerogating system for fiber Bragg gating sensors using an acousto-optic tunable filter, " Electronics Letters, vol.29,1510-1511,1993), semiconductor filter method (T.Coroy, R.M.Measures, " Active wavelength demodulation of a Bragg grating fibre optic strain sensor using a quantum well electroabsorption filtering detector; " Electronics Letters, vol.32, no.19,1811-1812,1996) etc.; Wherein adopt the commercial at present popularization of FP wave filter method, but cost still higher (own 3-4 ten thousand of FP wave filter, equipment set reaches tens0000 or higher); (3) interferometric method: utilize interferometer that the drift value of wavelength is changed into phase changing capacity and measure (K.P.Koo, A.D.Kersy, " Bragg grating based laser sensor system with interferometric interrogation and wavelength division multiplexing; " Journal of Lightwave Technology, vol.13, no.7,1243-1249,1995; R.Ashoori, Y.M.Gebremichael, S.Xiao, et al, " Time domain multiplexing for Bragg grating strain measurement sensor network, " Proc.of SPIE, vol.3746,308-311,1998; D.Zhao, X.Shu, L.Y.Zhang, " Fiber Bragg grating sensor interrogation using chirped fiber grating based Sagnac loop, " IEEE Sensors Journal, vol.3, no.6,734-738,2003), but because the complicacy of structure and reliability are relatively more difficult in actual applications; (4) Wavelength tunable light source method: adopt piezoelectric ceramics (PZT) modulation DBR laser instrument (G.A.Ball, W.W.Morey, P.K.Cheo, " Fiber laser source/analyzer for Bragg grating sensor array interrogation; " Journal of Lightwave Technology, vol.12, no.4,700-703,1994), locked mode modulation method (A.D.Kersey, W.W.Morey, " Multiplexed Bragg grating fibre-laser strain-sensor system with mode-locked interrogation, " Electronics Letters, vol.29, no.1,112-114,1993), circular cavity optic fibre laser method (S.H.Yun, D.J.Richardson, B.Y.Kim, " Interrogation of fiber grating sensor arrays with a wavelength swept fiber laser, " Optics Letters, vol.23, no.11,843-845,1998) or the like.
From generally, practical is exactly wave filter method and spectrographic method etc., but cost is all very high.Therefore, purpose of the present invention just is based on the product of existing marketization, finds the approach that significantly reduces the optical fiber grating sensing equipment cost, and has comparatively ripe application prospect.
Summary of the invention
In view of shortcomings such as the expensive cost of prior art and labyrinths, the objective of the invention is to design a kind of low cost and practical fiber bragg grating sensing device.The objective of the invention is to realize by following means:
Narrow-band distributed feedback laser wavelength scanning fiber bragg grating sensing device adopts following working method to carry out the sensor measuring of external physical amount: to include the distributed feedback laser by the current drives of temperature-control circuit control in the device; The light of described laser instrument emission enters the sensor fibre grating through optical isolator element, and the light that fiber grating sees through enters the control analysis unit in the electric signal mode after entering the photoelectricity receiving element; The distributed feedback laser output wavelength can be adjusted by changing the control temperature; Extreme value according to laser output wavelength photoelectricity receiving element output when temperature scanning and fiber grating reflection kernel are Wavelength matched is extrapolated optical grating reflection centre wavelength and corresponding external physical quantity.
Light source of the present invention adopts distributed feedback laser (Distributed Feedback Laser, Distributed Feedback Laser), this laser instrument is carried out temperature control, can change its output wavelength, and the change of optical fiber grating sensing wavelength is carried out matching detection by adjusting wavelength with laser instrument, make that the drift of grating centre wavelength is corresponding with the Laser Drive temperature, realize temperature or pressure sensing.
Description of drawings is as follows:
Fig. 1 is the principle schematic of fiber bragg grating sensing device.
Fig. 2 is the optical fiber grating sensing equipment exemplary device synoptic diagram of existing marketization.
Fig. 3 the present invention adopts optical circulator and analysis emission or transmission spectrum to implement the structural representation of single optical fiber grating sensing.
Fig. 4 the present invention adopts optoisolator and analyzes the structural representation that transmitted spectrum is implemented single optical fiber grating sensing.
Fig. 5 is invention test philosophy figure.
Fig. 6 invents the structural representation of implementing cascaded fiber grating measuring temperature or stress gradient distribution.
Fig. 7 the present invention further combines the synoptic diagram that practicability is used with radio communication or optical fiber communication.
Fig. 8 is monitoring means is realized the distributing optical fiber sensing network along optical fiber link a synoptic diagram based on the present invention.
Fig. 9 typical case of the present invention uses the frozen soils temperature monitoring and uses synoptic diagram.
Figure 10 typical case of the present invention uses the railway bed settlement monitoring and uses synoptic diagram.
Embodiment
The invention will be further described below in conjunction with accompanying drawing.
Fig. 3 is an exemplary device figure of the invention process, and distributed feed-back (DFB) laser instrument 101 provides current emission laser by driving circuit 102, carries out temperature control simultaneously, and Current Temperatures information and adjustment mode are by control and processing unit 107 storages and control.The live width of general Distributed Feedback Laser can be thought narrow-band light source at several million to tens megahertzes in conventional Application in Sensing.By adjusting the output wavelength that temperature can change Distributed Feedback Laser, most of laser instrument can be adjusted the wavelength (for example the Distributed Feedback Laser that we adopted wavelength in adjusting 30 ℃ of scopes can change about 6nm) of several nanometers in the temperature range of tens degree.The laser of output enters sensor fibre grating 104 through optical circulator 103, and the light of reflected back is realized opto-electronic conversion through circulator by receiving element 105 again.Signal after the conversion combines temperature control information by control with processing unit 107 again and analyzes.On the other hand, also can deliver to 107 then and carry out Treatment Analysis by carrying out Photoelectric Detection by receiving element 106 at grating 104 transmission ends.
In the application of adopting transmission spectrum to analyze, as shown in Figure 4, distributed feed-back (DFB) laser instrument 201 provides current emission laser by driving circuit 202, carries out temperature control simultaneously, and Current Temperatures information and adjustment mode are by control and processing unit 206 storages and control.Laser instrument output enters sensing grating 204 through optoisolator 203, and its transmission spectrum is detected and sent into 206 and carry out analyzing and processing by photoelectricity receiving element 205 then.
The principle of sensing assays as shown in Figure 5, when arrowband DFB light source carries out wavelength X by adjusting temperature
LDIn scanning time, is (Fig. 5 a), when its wavelength and grating reflection central wavelength lambda
FBGWhen overlapping (coupling), the peak value (105 detected peak values in the corresponding diagram 3, Fig. 5 b figure below) of reflected optical power will appear; And bring in from transmission, under most of situation of DFB light source scanning, laser can transmission be crossed grating, and corresponding detected luminous power (106 among Fig. 3) is a higher value always, works as λ
LDWith λ
FBGUnder the situation of coupling, light intensity will mostly be returned (general fiber grating exists certain transmission and reflectivity) by optical grating reflection, and a low valley (the last figure of Fig. 5 b) will appear in detected luminous power.Therefore, two kinds of different detection methods can obtain corresponding fiber grating centre wavelength.In the middle of cardiac wave is long when drifting about owing to temperature or pressure influence, by can find at a certain temperature the coupling between two wavelength equally to the scanning of Distributed Feedback Laser temperature.And be (to obtain by the demarcation between actuation temperature and the output wavelength) as can be known to laser output wavelength that should temperature value, so drift value that can be easy to calculate grating wavelength, thus converse the temperature or the pressure parameter of monitoring.
Further, we can be with the series connection of several fiber gratings, as shown in Figure 6, formant 30X substantially with Fig. 3 in 104 corresponding (X=1,2 ... .), just changing single the grating 104 among Fig. 3 into a series of gratings 304 (comprises 304
1, 304
2... 304
N), if be made into the centre wavelength initial value of these gratings identical, we can be by being placed on these gratings a sensing environment (for example monitoring the thermograde of frozen soil layer or the stress gradient of dam) that needs distributed measurement, by scanning the sequence luminous power peak value that Distributed Feedback Laser obtains, we can analyze the wavelength and the corresponding parameter sensing of this point of each power peak correspondence, thereby further converse corresponding temperature or stress gradient.If reflection peak has only a value or closes on very much, just mean that also the distribution of temperature or stress is more even.Certainly the centre wavelength initial value of these gratings also can be different, but must be through strict calibration, so as in data analysis the difference of these initial values of deduction.
In experiment, what we adopted is the CQF series Distributed Feedback Laser that JDSU company produces, designed corresponding current drives and temperature-control circuit, temperature control circuit can return the currency of being controlled, can be more than the wavelength shift 5-6nm with laser instrument by the temperature adjustment.The about 0.1nm of the bandwidth of fiber grating 3dB, its reflection wavelength can drift about under different temperatures, and we measure 80 ℃ from 0 ℃, and its wave length shift can arrive 1.1nm (promptly～0.014nm/ ℃), in the range of adjustment of Distributed Feedback Laser output wavelength.By temperature scanning, when laser wavelength and fiber grating centre wavelength coupling, output power reaches peak value by very little value, and we can estimate the temperature value of present fiber grating correspondence, and present estimation precision mainly is subjected to the restriction of grating sensitivity.What we adopted is that common fiber grating adds the heat conduction processing, if and adopt other sensitive handle (as washing layer), the susceptibility of its temperature can reach more than 0.2nm/ ℃, will improve measuring accuracy of the present invention, but this is not an innovative point covering scope of the present invention.
Consider practical application, we have designed three kinds of different application examples.Fig. 7 has represented that single temperature or the measured parameter of pressure fiber bragg grating sensing device can transmit by two kinds of approach: a kind of is that the electrical signal conversion that will analyze is that light signal transmits through optical fiber telecommunications system; Second kind is through wireless transmitting unit monitoring information to be sent to wireless communication system.And if a plurality of like this monitoring means are scattered in a network, by radio communication the information unified Analysis of each unit is handled, so just constituted wireless optical fiber grating sensing monitor network.And if many fiber gratings are distributed along optical fiber link, carry out gated sweep and analysis by the transmitting terminal unification, whole like this optical fiber link and optical fiber grating sensing node have just constituted optical fiber sensing network as shown in Figure 8.
Compare with the technology on the market, structure of the present invention is very simple, and cost estimate only has about 1/10th of present technology. More worth pointing out and since the present invention institute based on monotechnics all be very ripe (such as Distributed Feedback Laser, fiber grating, high speed optoelectronic detection etc.), whole invention practical application and popularization do not have problems. The present invention can carry out multi-form temperature and pressure (stress) sensing in principle, and for the great demand of industrial sectors of national economy, we underline typical case of the present invention and use:
(1) tundra monitoring temperature: required mainly for western Development of High Speed Railway, around the track of tundra, must monitor the frozen soil state, and the present invention can realize single-point frozen soils temperature monitoring, vertical thermograde monitoring and frozen soils temperature network monitor along the line etc. (Fig. 9) after buried.
(2) Temperature of Power Cables or pressure monitor: power cable is because its load difference causes the temperature inequality, and sensor device of the present invention can be installed in the monitoring that key point (such as high voltage substation) realizes different cable temperatures and loading condition; Simultaneously, consider that the solidifying weather cable of snow bears that bending can appear in freezing pressure or the situation such as fracture, the pressure distribution situation that the present invention also can monitoring cable realizes prevention. Fiber grating in the sensor of the present invention is contained in the aerial cable line, and laser instrument and processing unit and fiber grating are discrete, realize sensing and monitoring.
(3) stress of critical infrastructures (such as dam, bridge, tunnel, petrochemical pipe etc.) monitoring: stress distribution is extremely important for these critical infrastructures, the monitoring of partial points stress and multiple spot stress situation can be realized by the present invention, and its stress overall distribution situation can be further analyzed.
(4) railway bed settlement monitoring:, analyze the sedimentation situation of roadbed according to the STRESS VARIATION situation by grating being embedded in the subgrade settlement monitoring pipe.This also is one of crucial difficult point of present Development of High Speed Railway (Figure 10).
Claims (8)
1. narrow-band distributed feedback laser wavelength scanning fiber bragg grating sensing device adopts following working method to carry out the sensor measuring of external physical amount: to include the distributed feedback laser by the current drives of temperature-control circuit control in the device; The light of described laser instrument emission enters the sensor fibre grating through optical isolator element, and the light that fiber grating sees through enters the control analysis unit in the electric signal mode after entering the photoelectricity receiving element; The distributed feedback laser output wavelength can be adjusted by changing the control temperature; Extreme value according to laser output wavelength photoelectricity receiving element output when temperature scanning and fiber grating reflection kernel are Wavelength matched is extrapolated optical grating reflection centre wavelength and corresponding external physical quantity.
2. the narrow-band distributed feedback laser wavelength scanning fiber bragg grating sensing device according to claim 1, it is characterized in that, the light of laser instrument emission enters the sensor fibre grating through optical isolator element, and the light of fiber grating reflected back enters the photoelectricity receiving element through optical isolator element again.
3. the narrow-band distributed feedback laser wavelength scanning fiber bragg grating sensing device according to claim 1 is characterized in that, described optical isolator element can be optoisolator or optical circulator.
4. the narrow-band distributed feedback laser wavelength scanning fiber bragg grating sensing device according to claim 1 is characterized in that, described sensor fibre grating can be the fiber grating of independent or a plurality of cascades.
5. the narrow-band distributed feedback laser wavelength scanning fiber bragg grating sensing device according to claim 4 is characterized in that, described a plurality of cascade fiber grating centre wavelengths can be identical or different.
6. the narrow-band distributed feedback laser wavelength scanning fiber bragg grating sensing device according to claim 1 is characterized in that, can monitor the distribution situation of a plurality of points by the relation of measuring a plurality of cascaded fiber grating centre wavelength drifts.
7. the narrow-band distributed feedback laser wavelength scanning fiber bragg grating sensing device according to claim 1 is characterized in that described external physical quantity comprises temperature, thermograde, pressure or stress gradient at least.
8. the application of the described narrow-band distributed feedback laser wavelength scanning fiber bragg grating sensing device of claim 1 to 7 is characterized in that, can be applicable to following at least a purposes: 1) the tomography temperature and the gradient of monitoring tundra; 2) temperature of monitoring power cable or pressure distribution; 3) stress distribution of monitoring critical infrastructures; 4) situation of monitoring railway bed sedimentation.
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