CN1204449C - Strain tuning optical fiber grating sensing demodulator - Google Patents
Strain tuning optical fiber grating sensing demodulator Download PDFInfo
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- CN1204449C CN1204449C CN 03116042 CN03116042A CN1204449C CN 1204449 C CN1204449 C CN 1204449C CN 03116042 CN03116042 CN 03116042 CN 03116042 A CN03116042 A CN 03116042A CN 1204449 C CN1204449 C CN 1204449C
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- fiber
- fiber grating
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- detuner
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Abstract
The present invention relates to a strain tuning optical fiber grating sensing demodulator. The present invention is characterized in that an optical fiber section comprises an optical fiber grating, both ends of the optical fiber section are respectively fixed on a casing by two optical fiber holders, and a vibrator which can drive the optical fiber section to do lateral vibration is also fixed on the casing. The present invention has the advantages of simple structure, stable and reliable performance and convenient use.
Description
Technical field:
The present invention relates to the detuner of fiber-optic grating sensor, and particularly a kind of strain tunable fiber grating sensing detuner is mainly used in the technical field of Fibre Optical Sensor, optical measurement, optical device wavelength tuning.
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.Measure wavelength change just need can determine perception according to above-mentioned relation temperature and stress by profit.Therefore, as sensor, measure and read the gordian technique that the Bragg wavelength becomes practical application accurately and fast with fiber grating, the Bragg wavelength readout device that matches, promptly meaning is called the Primary Component that Bragg wavelength tuning detuner becomes Application in Sensing.
Formerly in the technology, for the demodulating process of optic fiber grating wavelength coding, traditional means is to use instruments such as spectrometer, monochromator or wavemeter.In addition people have proposed the scheme of some novel wavelength information demodulation, as Mach-Zehnder interferometer method, adjustable Fabry-perot filter method, matched fiber grating wave filter method etc.Conclusion is got up, and the demodulation techniques of 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 tunable laser as testing light source, optical maser wavelength continuous sweep in certain scope of output, according to the position of light signal in the scan period, the variation of tested optical fiber optical grating reflection optical wavelength be can draw, measuring optical fiber grating and reference optical fiber grating reflection optical wavelength perhaps drawn.As technology [2] formerly: Soek Hyun Yun, et al., Interrogation for fiber grating sensor arrayswith wavelength-swept fiber laser, Optics Letters, 1998,23 (11): 843-845; Technology [3]: Guan Baiou etc. formerly, a kind of high-resolution fiber grating sensing demodulation technology, optics journal, 2000,20 (11): 1509-1513.The advantage of this method is the energy of reflection light height, and as long as general light power meter is made receiving element, signal is easy to detect, the resolution height, and multiplexed realization is simple.But the deficiency of this method be light source to design and produce difficulty big, the cost height.
3, 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, to the stability requirement height of end of probe FBG spectrum.Technology [4]: M.A.Davis formerly, et al., Matched-filter interrogation techniquefor 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 detection sensitivity.This method requirement receiving end FBG and sensing FBG wavelength are approaching, and the wavelength coverage of sensing and demodulation is smaller.
4, 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 sensor technology, Optical FiberTechnology, 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.
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:
The technical problem to be solved in the present invention is to overcome the defective of above-mentioned technology formerly, and a kind of strain tunable fiber grating sensing detuner is provided.
Ultimate principle of the present invention is to utilize the strain tuning characteristic of fiber grating, and the spectral characteristic of optical fiber grating sensing head is scanned, and realizes demodulation.
Technical solution of the present invention is as follows:
A kind of strain tunable fiber grating sensing detuner, the formation that it is characterized in that it is: the fiber segment that contains fiber grating, the two ends of this fiber segment are fixed on the casing by two fibre holders respectively, and one can drive fiber segment makes the Vib. of transverse vibration and also be fixed on this casing;
Described fiber segment is to have anaclasis deteriorated property, can be used to prepare general communication optical fiber or the high germnium doped fiber or the plastic optical fiber of grating;
Described fibre holder is screw, stage clip or pastes glue;
Described Vib. be one in certain stroke reciprocating mechanical hook-up;
Described Vib. is to be made of micro motor, eccentric wheel, elastic transmission spare and mounting bracket, elastic transmission spare is between eccentric wheel and fiber segment, and this micro motor is fixed on the support, by its driving eccentric wheel rotation, drive elastic transmission spare, make fiber segment produce vibration;
Described a plurality of fiber segment that contains the fiber grating of different peak wavelengths is installed on the different azimuth of eccentric wheel circumference or on the eccentric different axial location.
Advantage of the present invention and characteristics are:
(1) the present invention adopts the read-out device of tunable fiber grating as the sense light wavelength signals.Compare with the method that adopts spectrometer, monochromator, wavemeter, much with low cost, easy to utilize.
(2) signal demodulating equipment of the present invention 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 present invention utilizes the strain sensitive characteristic of fiber grating to scan, and can measure the fiber grating peak wavelength of strain sensing head and Temperature probe simultaneously.As long as at the spectrum non-overlapping copies of two kinds of sensor fibre gratings, and be connected in series another reference optical fiber grating, just strain and temperature can be measured respectively.
(4) demodulation method of the present invention is a kind of spectral scan method, can read the peak of fiber grating, adopts the fixed filters method to compare with the method that adopts principle of interference with some, has the big advantage of measurement range.
(5) the present invention is a kind of method that wavelength is directly measured, rather than calculates indirectly that from light intensity data are with a high credibility.
One of advantage of fiber-optic grating sensor is the distributed measurement system that can be used as, and strain and temperature information that can the remote recording multiple spot have widely and use.Fiber grating tuning detuner of the present invention is as the requisite Primary Component of sensing measurement system, and its use value is embodied fully, has good cost performance, and expection has good market outlook.
Description of drawings:
Fig. 1: strain tunable fiber grating sensing detuner of the present invention, the fiber-optic vibration frequency is near the constitutional diagram of resonance frequency.
Fig. 2: strain tunable fiber grating sensing detuner of the present invention, the fiber-optic vibration frequency is far below the constitutional diagram of resonance frequency.
Fig. 3: the compound fiber sensor demodulator top view of multiband of the present invention.
Fig. 4: the compound fiber sensor demodulator side view of multiband of the present invention.
Fig. 5: the present invention is applied to distributed fiber grating sensor-based system figure.
Fig. 6: the waveform that measures from detuner of the present invention.
Embodiment:
See also Fig. 1 and Fig. 2 earlier, as seen from the figure, strain tunable fiber grating demodulation device of the present invention also can be described as fiber grating lateral vibration tuning demodulator, and it makes the Vib. 5 of horizontal string vibration by the fiber segment 3 that contains fiber grating 1, two fibre holders 4 that are used for fixing fiber segment 3 two ends 2, drive fiber segment 3 and the casing 6 of installation, fixed fiber clamper 4 and Vib. 5 is formed.
Component optical fiber 2 among the figure is each type optical fiber that has anaclasis deteriorated property, can be used to prepare grating, comprises general communication optical fiber, and height is mixed Ge optical fiber, plastic optical fiber etc.Fiber grating 1 is to sell off the grating that method or other means write with Ultra-Violet Laser is photic.Fibre holder 4 is a kind of machanical fasteners, can adopt that screw rotation is fastening, stage clip is fastening, solidify glue etc.In some occasion that needs, also can be heatmeltable or solvent-borne type glue.Two fibre holders 4 are fixed on the casing 6, and the distance between them can meticulously be regulated, with length and the prestress that obtains required fiber segment 3.
The principle of work of strain tunable fiber grating sensing detuner of the present invention is as follows: the optical fiber of making transverse vibration is equivalent to the vibration of one section string, and when its oscillation frequency during near the resonance frequency of string, the vibrational waveform of optical fiber as shown in Figure 1.Suppose that its direction of vibration is y, amplitude is y0, and frequency is f, and fiber axis is to being z, is initial point with the mid point of fiber segment 3, and then coordinate and the function of time thereof of the displacement of each point on the y direction is on the fiber segment 3:
y(t，x)＝y
0?sin(2πft)cos(2πx/l) (3)
Through mathematical operation, the strain that can get fiber segment 3 is:
ε(t)＝δl(t)/l≈[πy
0?sin(2πft)/l]
2 (4)
L is the length of fiber segment 3 in the formula.The natural resonance frequency of optical fiber string
Wherein F is the pulling force that fiber segment is subjected to, and ρ is the density of fiber optic materials.By (4) formula as can be known, the fiber grating 1 of preparation on fiber segment will be along with this strain by periodically tuning, thereby can be used as a kind of detuner of spectrum.
When vibration frequency was very low, the shape of fiber-optic vibration as shown in Figure 2.At this moment, the strain of optical fiber is:
ε(t)＝δl(t)/l≈[y
0sin(2πft)/l]
2/2 (5)
Quantitative relationship this moment difference to some extent, but be the same as the function of spectrum demodulator.
Strain tunable fiber grating sensing detuner of the present invention is when assembly and adjustment, earlier the two ends 2 of containing the fiber segment 3 of fiber grating 1, stretching being fixed on the clamper 4; Fiber lengths l can adjust according to different designs between two fibre holders 4; And the position of fine setting clamper is so that obtain the primary stress of fiber segment 3 as requested.Fiber segment 3 makes optical fiber avoid its side to be worn and torn when doing perpendicular to optical fiber axial vibration by the moving component contact of driving member 9 with Vib. 5.During detuner work, Vibration on Start-up device 5, the deformation shown in solid line and the dotted line among fiber segment 3 generation Fig. 1 and Fig. 2; Cause that fiber grating 1 is suffered answers the masterpiece cyclical variation, thereby cause fiber grating Bragg wavelength continuous sweep in certain bandwidth range.If the transducing signal that will test from the input of the port of fiber segment 3, survey its reflected light signal, perhaps optical signal transmissive, just can write down the convolution signal of transducing signal spectrum with detuner spectrum, thereby any sensing wavelength input that is in the bandwidth range is gone out fork-like farm tool used in ancient China, realize the function of Wavelength demodulation.
Strain tunable fiber grating sensing detuner of the present invention can be combined as the compound detuner of multiband, as shown in Figure 3 and Figure 4.This moment, a plurality of fiber segments 3 that contain the fiber grating 1 of different peak wavelengths were installed on the different azimuth of eccentric wheel 8 circumference, perhaps on the different axial locations of eccentric wheel 8.When micro motor 7 rotated, the spectrum of each fiber grating will scan with same speed.Thereby can cover bigger spectral range.
The distributed stress of fiber grating that strain tunable fiber grating sensing detuner of the present invention can be applicable to or (with) temperature-sensing system, its typical light path layout is as shown in Figure 5.Wherein 19 is that peak wavelength is λ
εFiber grating, it is fixed on strain (or stress) structural member to be measured, is the sensing head of strain (or stress).The 20th, peak wavelength is λ
εFiber grating, it is fixed on the temperature object to be measured, is Temperature probe.18 is fiber couplers, and splitting ratio is 1 to 1 usually.15 is a wideband light source, and its luminescent spectrum scope is in same wave band with the fiber grating that is adopted.16 is isolators, and its effect is the influence of light wideband light source 15 that prevents to return from the sensor fibre optical grating reflection.The 21st, be λ by wavelength
εThe wavelengt demodulator of forming with n the tunable fiber grating 1 of λ n.The 22nd, photo-detector, receive from light source 15 send, through strain or (with) Temperature probe 19,20 reflections, again through the light signal of wavelengt demodulator 21 transmissions.All elements have optical fiber interface and adopt direct welding process to connect.Wherein 17 for long optical cable, so that constitute distributed sensor-based system.
The peak wavelength λ of optical fiber grating sensing head 19 and 20 reflectance spectrums
εAnd λ
TAlong with the strain of object under test and temperature and change, shown in (1) and (2).The intensity of the light signal that receives on photo-detector is the convolution of light source, sensing head and three spectral functions of spectrum demodulator, is shown below:
I＝∫f
1(λ)f
2(λ
ε)f
3(λ
n[c])dλ＝I(λ
ε-λ
n) (6)
I＝∫f
1(λ)f
2(λ
T)f
3(λ
n[c])dλ＝I(λ
T-λ
n) (7)
F in the formula
3(λ
n[c]) be the spectrum of the strain tunable fiber grating filter of detuner of the present invention, the tuning controlled variable of c representative wherein, such as voltage, electric current, the perhaps phase place of voltage, electric current.According to formula (6) and (7), from light intensity I that measures and the spectrum f that measures demarcation in advance
3(λ
n[c]) with the data that parameter c changes,, can obtain λ through computing
εAnd λ
T, realize the demodulation of fiber grating spectrum.
The scheme of detuner according to the present invention has been set up an apparatus for sensing demodulating.When micro motor rotates, can tracer signal from the photelectric receiver.The waveform of Fig. 6 for observing on the oscillograph.In the one-period of revolution, two peak values appear in secondary is inswept tested sensor fibre grating.According to the tuning characteristic of the detuner fiber grating of prior mensuration, can determine tested λ
εOr λ
TNumerical value.
Claims (6)
1, a kind of strain tunable fiber grating sensing detuner, the formation that it is characterized in that it is: the fiber segment (3) that contains fiber grating (1), the two ends of this fiber segment (3) are fixed on the casing (6) by two fibre holders (4) respectively, and the Vib. (5) that a drive fiber segment (3) is made transverse vibration also is fixed on this casing (6).
2, strain tunable fiber grating sensing detuner according to claim 1 is characterized in that described fiber segment (3) is to have anaclasis deteriorated property, can be used to prepare general communication optical fiber or the high germnium doped fiber or the plastic optical fiber of grating.
3, strain tunable fiber grating sensing detuner according to claim 1 is characterized in that described fibre holder (4) is screw, stage clip or pastes glue.
4, strain tunable fiber grating sensing detuner according to claim 1, it is characterized in that described Vib. (5) be one in certain stroke reciprocating mechanical hook-up.
5, strain tunable fiber grating sensing detuner according to claim 4, it is characterized in that described Vib. (5) is to be made of micro motor (7), eccentric wheel (8), elastic transmission spare (9) and mounting bracket (10), elastic transmission spare (9) is positioned between eccentric wheel (8) and the fiber segment (3), this micro motor (7) is fixed on the support (10), by its driving eccentric wheel (8) rotation, drive elastic transmission spare (9), make fiber segment (3) produce vibration.
6, strain tunable fiber grating sensing detuner according to claim 5 is characterized in that described a plurality of fiber segment (3) that contains the fiber grating (1) of different peak wavelengths is installed on the different azimuth of eccentric wheel (8) circumference or on the different axial locations of eccentric wheel (8).
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| CN100378479C (en) * | 2003-11-07 | 2008-04-02 | 中国科学院上海光学精密机械研究所 | Strain tuning optical fiber grating dispersion dynamic compensation, monitoring device and method thereof |
| CN100399083C (en) * | 2006-06-19 | 2008-07-02 | 中国科学院上海光学精密机械研究所 | Tunable double parallel matched optical fiber raster demodulating system |
| CN105571619B (en) * | 2015-12-17 | 2017-10-10 | 安徽中科智泰光电测控科技有限公司 | A kind of FBG sensor sensitivity improvement methods based on cantilever beam structure |
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