CN2783349Y - Optical fibre raster wavelength demodulator - Google Patents
Optical fibre raster wavelength demodulator Download PDFInfo
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- CN2783349Y CN2783349Y CN 200520041250 CN200520041250U CN2783349Y CN 2783349 Y CN2783349 Y CN 2783349Y CN 200520041250 CN200520041250 CN 200520041250 CN 200520041250 U CN200520041250 U CN 200520041250U CN 2783349 Y CN2783349 Y CN 2783349Y
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- zehnder interferometer
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- optical fiber
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Abstract
The utility model relates to an optical fiber raster wavelength demodulator, which is characterized in that the utility model comprises a Mach-Zehnder interferometer, wherein the Mach-Zehnder interferometer is composed of a second 2*2 optical fiber coupler and a 3*3 optical fiber coupler, a broadband light source is connected with a sensing optical fiber raster through a first 2*2 coupler, and the second input end of the first 2*2 and any one of the two input ports of the second 2*2 optical fiber coupler of the Mach-Zehnder interferometer are connected. The output parts of the three output ports of the Mach-Zehnder interferometer enter a photodetection circuit, and the photodetection circuit is connected with the computer through a data acquisition card. The utility model has the advantages of passivity, simple structure, high sensitivity, large dynamic range, stable and reliable operation, and optical source interruption resistance.
Description
Technical field
The utility model relates to fiber grating, particularly a kind of optical fiber raster wavelength demodulator based on 3 * 3 coupling mechanism Mach-Zehnder interferometers.Be mainly used in the technical field of Fibre Optical Sensor, optical measurement.
Background technology
Fiber grating is a kind of optical filter with narrowband reflection characteristic that is produced on the optical fiber.Because elastic deformation, the thermal expansion character of silica fibre, with and hot light, elasto-optical effect, it has the sensitivity characteristic to temperature and stress.This sensitivity characteristic is linear in certain scope, meets following relation:
Δλ
ε/λ＝ε(1+γ) (1)
Δλ
T/λ＝(α+e)ΔT (2)
In the formula: ε is the strain of optical fiber, and γ is the elasto-optical coefficient of fiber optic materials, and α is the coefficient of thermal expansion of fiber optic materials, and Δ T is a temperature variation,
Be thermo-optical coeffecient.Just need can determine the temperature and the stress of perception according to above-mentioned relation by measuring wavelength change.Utilize this characteristic fiber grating can be made into strain transducer and temperature sensor, and derive the sensor of other physical quantitys such as gaging pressure, acceleration, flow, displacement.
The major advantage that fiber grating is used for sensory field is: anti-electromagnetic interference capability is strong; Corrosion-resistant; Sensing head is not charged, is suitable for forceful electric power and anti-electric field closes; Can directly be connected with fibre system, and can be multiplexed, be convenient to constitute various forms of optical fiber sensing networks, the distributed fiber grating sensor array that especially adopts wavelength-division multiplex technique to constitute can carry out large-area multimetering; Stability and good reliability, volume is little, precision is high; Be convenient to imbed composite element and heavy construction building interior etc., states such as the integrality of structure, security, load fatigue, degree of injury are carried out continuous real-time monitoring.1 microstrain and 1 degree centigrade of ambient temperature cause the mobile 1.2pm of being respectively and the 12pm of the fiber grating centre wavelength of C-band.This is very small variable quantity.How at low cost small wavelength being moved accurately demodulation and come out, is the key technical problem of fiber-optic grating sensor.Various optic fiber grating wavelength demodulation schemes propose in succession, and the demodulation techniques of concluding fiber grating reflected light wavelength can be divided into following several types:
1, certain light signal that has that detected sensing head reflects is directly inputted in spectrometer, monochromator or the wavemeter, directly measures the wavelength location of fiber Bragg grating reflected signal.As technology [1]: Liu Zhiguo etc. formerly, the research of high-sensitivity optical fiber grating sensing characteristics tester, photon journal, 1999,28 (2): 138-141.This demodulation mode is simple, measuring accuracy is high, but these instruments are expensive and not portable.Only be suitable for the laboratory and use, inconvenience is applied in the actual sensor-based system.
2, utilize wideband light source as testing light source, utilize wave filter or tunable optic filter to make the restitution element of sensor fibre optical grating reflection light signal, come sensed light signal with light power meter.This method can be divided into reflection-type and transmission-type two classes again.The former principle is as follows: incide on the FBG of receiving end from the reflected light of sensing FBG, if consistent with the reflected light wavelength of receiving end FBG, then be reflected on the detector.Drive reception FBG by PZT and finely tune, obtain the peak wavelength of sensing FBG.The precision of this method is subjected to the restriction of light source stability and external interference, stability requirement height to end of probe FBG spectrum: technology [4]: M.A.Davis formerly, et al., Matched-filterinterrogation technique for fiber Bragg grating arrays, Electronics Letters, 1995,31 (10): 822-823 has proposed the measurement scheme of transmission-type.The difference of this scheme and reflection-type is: photodetector is not to be placed on the catoptrical position of receiving end FBG, but places the position of transmitted light, determines whether coupling by monitoring having or not of transmitted light, thereby has improved the sensitivity of spy side.This method requirement receiving end FBG and sensing FBG wavelength are approaching, and the wavelength coverage of sensing and demodulation is smaller.
3, edge filter method, adopt promptly that a kind of to have live width bigger, transmitance is the wave filter of linear change, with the reflecting light appearance convolution of sensing FBG, the signal that obtains is proportional with the position of FBG peak wavelength, thereby can know the FBG wavelength location by inference from signal magnitude, and as technology [5]: A.D.Kersey formerly, A review of recent developments in fiber optic sensortechnology, Optical Fiber Technology, 1996,2,291-317.This method requires the demodulator filter good linearity, requires each component parameter stability of system.Therefore service condition is relatively harsher.
4, adopt the Mach-Zehnder interferometer of forming by two 2 * 2 fiber couplers and piezoelectric ceramics that the light that wideband light source sends is carried out phase modulation (PM), again to the sensing grating that reflects with carry out the signal comparison process with reference to the flashlight of grating and obtain demodulation value.As technology [6]: A.D.Kersey formerly, Fiber-optic Bragg grating strain senseor with drift-compensatedhigh resolution interferometric wavelength-shift detection, OPTICS LETTERS, 1993,72-74.This scheme need add active device, the signal Processing complexity, and cost is too high.
Because the defective that said method exists, the demodulation techniques in the fiber grating sensing system become one of major obstacle that this sensing technology applies.
Summary of the invention
In order to overcome the shortcoming of above-mentioned prior art, the utility model provides a kind of optical fiber raster wavelength demodulator, and that the utility model should have is simple in structure, highly sensitive, dynamic range is big, working stability is reliable and the advantage of the interference of anti-light source fluctuation.
Principle of the present utility model is to adopt the non-equilibrium Mach-Zehnder interferometer of 2 * 2 fiber couplers and one 3 * 3 fiber coupler composition that sensor fibre grating reflection wavelength is carried out demodulation.
The technical scheme of the utility model patent is as follows:
A kind of optical fiber raster wavelength demodulator, it is characterized in that comprising a Mach-Zehnder interferometer, this Mach-Zehnder interferometer is made up of with one 3 * 3 fiber couplers the 22 * 2 fiber coupler: two output terminals of the 22 * 2 fiber coupler link to each other with any two input ends of described 3 * 3 fiber couplers and constitute two arms of Mach-Zehnder interferometer, three output terminals of this 3 * 3 fiber coupler are three output ports of Mach-Zehnder interferometer, one wideband light source links to each other with a sensor fibre grating by the one 2 * 2 coupling mechanism, arbitrary port links to each other in two input ports of second input end of the one 2 * 2 coupling mechanism and the 22 * 2 fiber coupler of described Mach-Zehnder interferometer, the output of three output ports of this Mach-Zehnder interferometer enters the photodetection circuit, and this photodetection circuit links to each other with computing machine through data collecting card.
The arm length difference of two arms of described Mach-Zehnder interferometer is between 1mm-5mm.
The coupling ratio of described the one 2 * 2 fiber coupler and the 22 * 2 fiber coupler is 1: 1.The coupling ratio of described 3 * 3 fiber couplers is 1: 1: 1.
Described computing machine recovers actual sensor fibre grating centre wavelength amount of movement by trigonometric function formula and phase place Descrambling Algorithms.
Advantage of the present utility model and characteristics are as follows:
1, the utility model adopts based on the Mach-Zehnder interferometer of 3 * 3 fiber couplers read-out device as the sense light wavelength signals.With adopting spectrometer, monochromator, wavemeter and traditional method to compare, much with low cost, easy to utilize based on 2 * 2 fiber couplers.
2, signal demodulating equipment of the present utility model all adopts optical fiber and fiber optic element device, is a kind of system of full optical fiber.Between each device and the element, can all use the optical fiber splicer welding, constitute an integral body.Therefore, use reliable and stablely, realize instrumentation easily.
3, the utility model has adopted passive device (optical fiber mach Zehnder interferometer) to make the core devices of demodulation scheme, makes demodulating process not be subject to the interference of external electromagnetic environment;
4, the utility model measurement range is big.In data handling procedure, adopt the phase place Descrambling Algorithms, make under the data acquisition situation of high frequency, measurement range can break through the restriction of the 2 π phase places that conventional interference instrument scheme is difficult to go beyond, and measurement range can reach the stress limit that fiber grating can bear, approximately ± and 1500 microstrains;
5, the utility model is simple in structure, and volume is little, uses reliable and stablely, has good cost performance.
Description of drawings
Fig. 1 is a structured flowchart of the present utility model;
Fig. 2 is a Mach-Zehnder interferometer structural representation of the present utility model;
Among the figure: 1-wideband light source, 2-the one 2 * 2 fiber coupler, 3-sensor fibre grating, 4-Mach-Zehnder interferometer, 4-1,4-2-be the input port of the 22 * 2 fiber coupler, 4-3-the 22 * 2 fiber coupler, 4-4,4-5-be the output port of the 22 * 2 fiber coupler, 4-6,4-7-be two arms of interferometer, 4-8-be 3 * 3 fiber couplers, 4-9,4-10,4-11 are the output port of 3 * 3 fiber couplers, 5-photodetection circuit, 6-computing machine.
Embodiment
See also Fig. 1 and Fig. 2 earlier, as seen from the figure, the utility model optical fiber raster wavelength demodulator, comprise a Mach-Zehnder interferometer 4, this Mach-Zehnder interferometer 4 is made up of the 22 * 2 fiber coupler 4-3 and one 3 * 3 fiber coupler 4-8: two output terminal 4-4 of the 22 * 2 fiber coupler, 4-5 links to each other with any two input ends of described 3 * 3 fiber coupler 4-8 and constitutes two arm 4-6 of Mach-Zehnder interferometer, 4-7, three output terminals of this 3 * 3 fiber coupler are three output port 4-9 of Mach-Zehnder interferometer, 4-10,4-11, one wideband light source 1 links to each other with a sensor fibre grating 3 by the one 2 * 2 coupling mechanism 2, two input port 4-1 of second input end of the one 2 * 2 fiber coupler 2 and the 22 * 2 fiber coupler 4-3 of described Mach-Zehnder interferometer 4, arbitrary port links to each other among the 4-2, the output of three output ports of this Mach-Zehnder interferometer 4 enters photodetection circuit 5, and this photodetection circuit 5 links to each other with computing machine 6 through data collecting card.The arm length difference of two arms of described Mach-Zehnder interferometer 4 is between 1mm-5mm.All can make sensitivity descend less than 1mm or greater than 5mm.
The coupling ratio of described the one 2 * 2 fiber coupler 2 and the 22 * 2 fiber coupler 4-3 is 1: 1.The coupling ratio of described 3 * 3 fiber couplers is 1: 1: 1.
During wideband light source 1 irradiation, then the output port of interferometer use the spectrometer spectra re-recorded, obtain arm length difference Δ d and modulation period ξ.
Wideband light source 1 is by the one 2 * 2 fiber coupler 2 irradiation sensor fibre gratings 3, the centre wavelength of sensor fibre grating 3 reflected backs is that the flashlight of λ enters Mach-Zehnder interferometer 4 through the one 2 * 2 coupling mechanism 2 again, and 4 pairs of signal light intensities of this Mach-Zehnder interferometer are modulated.The light distribution of 3 output ports of modulation back Mach-Zehnder interferometer 4 can be expressed as
I
nz＝A
n+B
ncos(Δφ+2π(n-1)/3) n＝1，2，3. (3)
I
nBe the light intensity value of interferometer output port, A
nAnd B
nBe the systematic parameter of interferometer output port, Δ φ is the phase place of flashlight, can further be expressed as
Δφ＝φ
2-φ
1＝2π·Δd/λ (4)
The fluctuating of the intensity of light source can cause A
nAnd B
nVariation, but therefore this fluctuating is in proportion for three ports, can define three normalized parameter α that do not change with the intensity of light source
1=1, α
2=A
2/ A
1=B
2/ B
1And α
3=A
3/ A
1=B
3/ B
1, derive (5) formula by (3) formula again, formula (5) has been made normalized to the signal of each port, and advantage is to avoid the interference that light source fluctuation brings.Photodetection circuit 5 is converted into the electric signal amplification and input computing machine 6 after data collecting card carries out data acquisition with light signal.Computing machine 6 calculates data the variation of phase place with formula (5).Adopt following phase place Descrambling Algorithms to be used for when surpassing 2 π phase places, recovering total phase changing capacity of reality simultaneously to be used for the measurement range of expansion project.
When carrying out data processing, computing machine adopts a cover phase-unwrapping algorithm to solve the ambiguity problem of φ (t): establish total phase changing capacity φ
Sum(t), fixed phase variable quantity φ
REF, single Phase Processing amount φ ' (t) and state variable tag.During deal with data, if | tan φ (t) |＜1, (φ (t)＜π/4), then get φ ' (t)=arctan (tan φ (t)); Otherwise get φ ' (t)=-arctan (1/tan φ (t)).If simultaneously | tan φ (t) |＜1, it is 0 that state variable tag is made as; Otherwise be 1.φ
REFAdd during each calculating or deduct pi/2, determine jointly that by three factors of the state variable of positive and negative, previous state of previous state value (Pre-value) (Pre-value ' s tag) and current state (Current-value ' s tag) relation therebetween can be provided by table 1.Each sampling is calculated the total phase change value that finally obtains and is expressed as: φ
Sum(t)=φ
REF+ φ ' (t).This process lasts till always and stops till the data acquisition.Solve φ
Sum(t) after, according to φ
Sum(t) relative variation Δ φ
Sum(t) and ξ modulation period of interferometer just can obtain corresponding FBG centre wavelength relative changing value Δ λ=Δ φ
Sum(t) ξ.
The utility model shows to have advantage simple in structure, that working stability is reliable, easy to use based on the Mach-Zehnder interferometer of 3 * 3 fiber couplers through on probation.
Table 1 φ
REFValue
| Previous state symbol Pre-value | Previous state variable Pre-value ' s tag | Current state variable Current-value ' s tag | φREF |
| ＜0 | 0 | 1 | -π/2 |
| ＞0 | 0 | 1 | +π/2 |
| ＜0 | 1 | 0 | -π/2 |
| ＞0 | 1 | 0 | +π/2 |
Claims (4)
1, a kind of optical fiber raster wavelength demodulator, it is characterized in that comprising a Mach-Zehnder interferometer (4), this Mach-Zehnder interferometer (4) is made up of the 22 * 2 fiber coupler (4-3) and one 3 * 3 fiber couplers (4-8): two output terminals (4-4 of the 22 * 2 fiber coupler, 4-5) link to each other with any two input ends of described 3 * 3 fiber couplers (4-8) and constitute two arm (4-6 of Mach-Zehnder interferometer, 4-7), three output terminals of this 3 * 3 fiber coupler are three output port (4-9 of Mach-Zehnder interferometer, 4-10,4-11), one wideband light source (1) links to each other with a sensor fibre grating (3) by the one 2 * 2 coupling mechanism (2), two input ports (4-1 of the 22 * 2 fiber coupler (4-3) of second input end of the one 2 * 2 coupling mechanism (2) and described Mach-Zehnder interferometer (4), arbitrary port links to each other 4-2), the output of three output ports of this Mach-Zehnder interferometer (4) enters photodetection circuit (5), and this photodetection circuit (5) links to each other with computing machine (6) through data collecting card.
2, optical fiber raster wavelength demodulator according to claim 1, the arm length difference of two arms (4-6,4-7) that it is characterized in that described Mach-Zehnder interferometer (4) is between 1mm-5mm.
3, optical fiber raster wavelength demodulator according to claim 1 is characterized in that the coupling ratio of described the one 2 * 2 fiber coupler (2) and the 22 * 2 fiber coupler (2) is 1: 1.
4, optical fiber raster wavelength demodulator according to claim 1, the coupling ratio that it is characterized in that described 3 * 3 fiber couplers is 1: 1: 1.
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| CN 200520041250 CN2783349Y (en) | 2005-04-29 | 2005-04-29 | Optical fibre raster wavelength demodulator |
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Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN106500822A (en) * | 2016-11-28 | 2017-03-15 | 华北电力大学 | Based on the transformer core system of condition monitoring that M Z interferometers are demodulated |
| CN106646097A (en) * | 2016-11-28 | 2017-05-10 | 华北电力大学 | Transformer winding deformation on-line monitoring system by employing fiber grating strain sensors |
| CN109959403A (en) * | 2019-03-29 | 2019-07-02 | 武汉理工大学 | A kind of many reference amounts large capacity sensor-based system |
-
2005
- 2005-04-29 CN CN 200520041250 patent/CN2783349Y/en not_active Expired - Fee Related
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN106500822A (en) * | 2016-11-28 | 2017-03-15 | 华北电力大学 | Based on the transformer core system of condition monitoring that M Z interferometers are demodulated |
| CN106646097A (en) * | 2016-11-28 | 2017-05-10 | 华北电力大学 | Transformer winding deformation on-line monitoring system by employing fiber grating strain sensors |
| CN106646097B (en) * | 2016-11-28 | 2019-07-02 | 华北电力大学 | Using the deformation of transformer winding on-line monitoring system of fiber Bragg grating strain sensor |
| CN109959403A (en) * | 2019-03-29 | 2019-07-02 | 武汉理工大学 | A kind of many reference amounts large capacity sensor-based system |
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|---|---|---|---|
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| GR01 | Patent grant | ||
| C17 | Cessation of patent right | ||
| CF01 | Termination of patent right due to non-payment of annual fee |
Granted publication date: 20060524 |