CN103940363B - High-precision optical fiber strain low-frequency sensing demodulation method based on wavelet cross-correlation technology - Google Patents

Abstract

The invention discloses a high-precision optical fiber strain low-frequency sensing demodulation method based on a wavelet cross-correlation technology. The high-precision optical fiber strain low-frequency sensing demodulation method comprises the steps data are preprocessed, wherein wavelet denoising processing is conducted on a reference fiber bragg grating reflectance spectrum and a sensing fiber bragg grating reflectance spectrum, and zero setting processing is conducted on data outside the bandwidth of the denoised reference fiber bragg grating reflectance spectrum and the bandwidth of the denoised sensing fiber bragg grating reflectance spectrum, so that the preprocessed reference fiber bragg grating reflectance spectrum and the preprocessed sensing fiber bragg grating reflectance spectrum are obtained; wavelet domain cross-correlation is conducted, wherein a wavelet domain cross-correlation value of the preprocessed reference fiber bragg grating reflectance spectrum and the preprocessed sensing fiber bragg grating reflectance spectrum is calculated; peak value detection is carried out, wherein the peak value position of the wavelet domain cross-correlation value is obtained, and the external strain value corresponding to the sensing fiber bragg grating reflectance spectrum is obtained according to the peak value position.

Description

High-precision optical fiber based on small echo cross-correlation technique strains low frequency sensing demodulation method

Technical field

The present invention relates to technical field of optical fiber sensing, more particularly, to a kind of high-precision optical fiber based on small echo cross-correlation technique Strain low frequency sensing demodulation method.

Background technology

Recent two decades come more, and along with developing rapidly of Fibre Optical Sensor and Fibre Optical Communication Technology, various types of optical fiber pass Sensor (as Michelson interference formula Fibre Optical Sensor, method Fabry-Parot interferent formula Fibre Optical Sensor, fiber-optic grating sensor etc.) is in each row Each industry all obtains a wide range of applications.Carrying out strain measurement using Fibre Optical Sensor is a kind of modal application form, wherein Fiber grating (fbg) sensor is due to having that size is little, fast response time, large-scale linear response, the advantage of easily multiplexing, one It is directly the study hotspot in this field.

At present, on market, widely used fbg strains the strain measurement precision generally 1 μ ε of (FBG) demodulator.In bridge deformation The fields such as monitoring, slope monitoring, the 1 μ ε of fbg strains the application demand that precision can meet reality.But, many fields as Deformation Observation, acoustic emission monitor(ing) etc., the strain precision of 1 μ ε can not meet requirement.Then there has been proposed much improving fbg's The method of strain measurement precision, such as adopts phase-shifted fiber grating, fiber grating Fabry Parot interferometer to substitute common fiber grating, Fiber grating certainty of measurement etc. is improved using laser frequency locking technology.But these technology, contribute to high frequency (dynamic) signal mostly Measurement, be seldom applied to the measurement of low frequency (quasistatic) signal.

The quasistatic strain measurement resolution of fbg sensor is mainly by extraneous environmental noise (as strain measurement Plant interference factor) determine, in order to realize high-resolution strain measurement, general way is not to be subject to using one in systems The reference fbg of effects of strain compensates to noises such as temperature, light-intensity variations, then we can by calculate sensing fbg and To obtain strain information with reference to fbg wavelength change difference between the two.At present, there are a lot of algorithms for detecting this two The wavelength change of fbg sensor, including centroid detection algorithm (g.meltz, et al., " formation of bragg Gratings in optical fibers by a transverse holographic method, " optics Letters, 1989), least square curve fitting algorithm (a.ezbiri et., " high resolution Instrumentation system for fibre-bragg grating aerospace sensors, " optics Communications, 1998) and cross correlation algorithm (c.huang, et al., " demodulation of fiber bragg Grating sensor using cross-correlation algorithm, " photonics technology Letters, 2007).Wherein, cross correlation algorithm can directly determine sensing fbg and with reference to the wavelength difference between fbg, tool There is good stability, and put into practice and have been proven that it can be used for the demodulation of fbg sensor.Since two thousand and ten, Japan east The qinwen liu of capital university is employed many times cross correlation algorithm to calculate the alternate position spike of the extremely narrow fiber grating reflectance spectrum of two-way, obtains Obtained good experimental result (q.liu, et al., " realization ofnano static strain sensing With fiber bragg gratings interrogated by narrow linewidth tunable lasers, " optics express, 2011).

In fact, the wavelength location calculating two-way fiber grating reflectance spectrum is poor, it is substantially to look for two-way fiber grating to reflect The time delay of spectrum.Current various delay time estimation methods, major part is improved on the basis of generalized correlation for time delay estimation, such as certainly Adapt to time delay is estimated, generalized phase time delay is estimated, lms time delay is estimated etc..These methods can directly be used for reference for fiber grating High precision low frequency demodulation.But it is stable that these algorithms require signal, and require signal and noise be separate, Known signal and the priori of noise, which has limited the demodulation accuracy of the method.

Wavelet analysises are a kind of powerfuls processing non-stationary signal, and achieve a lot of successes in time delay is estimated Application, wavelet field cross-correlation calculation wavelength difference is incorporated into the demodulation of high-precision fiber strain sensing low frequency by first here , it is expected to solve the deficiency of traditional calculating Fibre Optical Sensor reflectance spectrum wavelength difference algorithm, improve the measurement essence of whole system Degree.At present, have not yet seen the wavelet field cross-correlation that wavelet transformation is used for calculating two-way Fibre Optical Sensor reflectance spectrum and realize height The report of precision strain demodulation.

Content of the invention

(1) technical problem to be solved

In view of this, the main object of the present invention is to provide a kind of high-precision optical fiber strain sensing low frequency demodulating algorithm, adopts With wavelet transformation technique, calculate the cross-correlation of two-way Fibre Optical Sensor reflectance spectrum in wavelet field, should to improve optical fiber measurement low frequency Become demodulation accuracy, and emphasis solve tradition based on the Fibre Optical Sensor demodulating algorithm of cross-correlation cannot be used for high accuracy demodulate non-flat Steady fiber grating sensing signal, require the priori of known fiber optic transducing signal and noise, require Fibre Optical Sensor signal and make an uproar The problems such as sound is independent mutually.

(2) technical scheme

The invention provides a kind of high-precision optical fiber strain low frequency sensing demodulation method based on small echo cross-correlation technique, its It is characterised by, comprising:

Data prediction step, for carrying out small echo fall to reference optical fiber optical grating reflection spectrum and sensor fibre optical grating reflection spectrum Make an uproar process, and the reference optical fiber optical grating reflection spectrum after noise reduction and the data beyond sensor fibre optical grating reflection bands of a spectrum width are put Zero process, obtains pretreated reference optical fiber optical grating reflection spectrum and sensor fibre optical grating reflection spectrum；

Wavelet field cross-correlation step, for calculating pretreated described reference optical fiber optical grating reflection spectrum and sensor fibre light The wavelet field cross correlation value of grid reflectance spectrum；

Peak detection step, for asking for the peak of described wavelet field cross correlation value, and according to described peak Obtain described sensor fibre optical grating reflection spectrum corresponding external world strain value.

(3) beneficial effect

From technique scheme as can be seen that the method have the advantages that

1st, a kind of high-precision optical fiber strain low frequency sensing and demodulating algorithm that the present invention provides, can effectively improve wavelength solution Adjust precision, better than traditional cross correlation algorithm.

2nd, a kind of high-precision optical fiber strain low frequency sensing and demodulating algorithm that the present invention provides, calculates two-way optical fiber in wavelet field The cross-correlation of sensor, can eliminate reference optical fiber sensor and the nonstationary noise of sensor fibre sensor.

3rd, a kind of high-precision optical fiber strain low frequency sensing and demodulating algorithm that the present invention provides, calculates two-way optical fiber in wavelet field The cross-correlation of sensor, does not require the priori of known fiber optic transducing signal and noise, does not require Fibre Optical Sensor signal and makes an uproar Sound is independent mutually.

Brief description

The flow chart of the high-precision optical fiber strain sensing low frequency demodulation method that Fig. 1 provides for the present invention；

The reflectance spectrum measured drawing of the two-way fiber grating that Fig. 2 provides for the present invention；

The Wavelength demodulation result figure based on traditional cross correlation algorithm that Fig. 3 (a) provides for the present invention；

The Wavelength demodulation result based on high-precision optical fiber strain sensing low frequency demodulating algorithm that Fig. 3 (b) provides for the present invention Figure；

Specific embodiment

For making the object, technical solutions and advantages of the present invention become more apparent, below in conjunction with specific embodiment, and reference Accompanying drawing, the present invention is described in further detail.

By combining accompanying drawing, highly preferred embodiment of the present invention is described in detail, the advantage of other aspects of the present invention It will be readily understood it is and clear.

The high-precision optical fiber based on small echo cross-correlation technique that the present invention provides strains the basic of low frequency sensing demodulation method Principle is as follows:

The reflectance spectrum of hypothesis reference and sensor fibre sensor () respectively x (t), y (t) taking fiber grating as a example, two Data in the 3db bandwidth of reflectance spectrum is s (t), and other parts are z (t), and the time delay of two-way reflectance spectrum is taken as t₀, then x (t), y T the expression formula of () is as follows:

X (t)=s (t)+z (t)

(1)

Y (t)=s (t-t₀)+z (t) cries

Thus it is possible to obtain x (t), the wavelet transformation of y (t), as follows:

$\begin{array}{c}{w}_{\mathrm{\φ},x}(a,b)={\&integral;}_{-\∞}^{+\∞}x\left(t\right){\mathrm{\φ}}^{*}\left(\frac{t-b}{a}\right)\mathrm{dt}={\&integral;}_{-\∞}^{+\∞}[s\left(t\right)+z\left(t\right)]{\mathrm{\φ}}^{*}\left(\frac{t-b}{a}\right)\mathrm{dt}=w_{\mathrm{\φ},s}(a,b)+w_{\mathrm{\φ},z}(a,b)\\ w_{\mathrm{\φ},y}(a,b)={\&integral;}_{-\∞}^{+\∞}x\left(t\right){\mathrm{\φ}}^{*}\left(\frac{t-b}{a}\right)\mathrm{dt}={\&integral;}_{-\∞}^{+\∞}[s(t-t_0)+z\left(t\right)]{\mathrm{\φ}}^{*}\left(\frac{t-b}{a}\right)\mathrm{dt}=w_{\mathrm{\φ},s}(a,b-t_0)+w_{\mathrm{\φ},z}(a,b)\end{array}---\left(2\right)$

Wherein, w_{φ, x}For wavelet transformation, φ^*For morther wavelet, a is scale factor, and b is the time-shifting factor.

In wavelet field, cross-correlation calculation is carried out to x (t), y (t), obtain the wavelet field cross-correlation function of x (t) and y (t)

$\begin{array}{c}{c}_{y,x}^f\left(\mathrm{\τ}\right)={\&integral;}_a{\&integral;}_b{w}_{\mathrm{\φ},y}(a,b)w_{\mathrm{\φ},x}(a,b-\mathrm{\τ})\mathrm{dadb}\\ ={\&integral;}_a{\&integral;}_b[w_{\mathrm{\φ},s}(a,b-t_0)+w_{\mathrm{\φ},z}(a,b)][w_{\mathrm{\φ},s}(a,b-\mathrm{\τ})+w_{\mathrm{\φ},z}(a,b)]\mathrm{dadb}\\ =w_{\mathrm{ss}}(\mathrm{\τ}-t_0)+w_{\mathrm{zs}}\left(\mathrm{\τ}\right)\end{array}---\left(3\right)$

Wherein, w_ss(τ-t₀) it is the auto-correlation function in wavelet field for the s (t), w_zs(τ) be s (t) and z (t) is mutual in wavelet field Correlation function, w_ss(τ-t₀) compare w_zs(τ) big very big, and it is equal to t in time delay τ₀When obtain maximum.Therefore, calculate x (t) and y T the peak of the wavelet field cross-correlation of () is it is only necessary to calculate w_ss(τ-t₀) peak, and w_zs(τ) to final small echo The peak of cross-correlation does not affect, and therefore can eliminate the impact of noise z (t) all systems here.Spy according to cross-correlation Point, it is known that w_ss(τ-t₀) obtain corresponding τ during maximum (equal to t₀) it is the wavelength difference of two-way reflectance spectrum (for base In tunable laser demodulating system, time delay τ and wavelength difference have linear relationship), therefore pass through to find x (t) and y (t) little The peak of the cross correlation value of wave zone realizes Wavelength demodulation, that is, pass through to find the time delay τ corresponding to peak of formula (3) Conversion obtains the wavelength difference of two-way reflectance spectrum.Meanwhile, from formula (3) as can be seen that for wavelet field cross-correlation, only working as optical fiber When sensory reflex spectrum is overlapped over time and frequency with noise signal simultaneously, just can produce impact to demodulation result.But In fact, noise and useful reflection spectrum signal are different, therefore pass through wavelet field cross-correlation calculation, there is noise suppression simultaneously The effect of system, is beneficial to improve Wavelength demodulation precision.

Based on principles above, Fig. 1 gives the stream of the high-precision optical fiber strain sensing low frequency demodulation method of present invention offer The reflectance spectrum measured drawing of the two-way fiber grating that Cheng Tu, Fig. 2 provide for the present invention, Fig. 3 a are provided by the present invention based on tradition The Wavelength demodulation result figure of cross correlation algorithm, Fig. 3 b are provided by the present invention based on the demodulation of high-precision optical fiber strain sensing low frequency The Wavelength demodulation result figure of algorithm.

As shown in figure 1, this high-precision optical fiber strain sensing low frequency demodulation method includes:

Data prediction step 1, is carried out for reference optical fiber optical grating reflection is composed with r1 and sensor fibre optical grating reflection spectrum r2 Wavelet de-noising processes fiber grating reflectance spectrum d1, the d2 after obtaining noise reduction, eliminates in reflectance spectrum by factors such as light intensity, external environments The various noises causing；And (this bandwidth can be straight by reflectance spectrum r1, r2 to fiber grating reflectance spectrum d1, d2 bandwidth after noise reduction Connect and find out, determine) beyond data carry out zero setting process, reduce the impact to certainty of measurement for the otiose data, obtain pre- place Fiber grating reflectance spectrum z1, z2 after reason；Finally export pretreated result z1, z2；

Wavelet field cross-correlation step 2, for calculating two-way fiber grating reflectance spectrum z1, z2 after data prediction Wavelet field cross-correlation, the compensation of go forward side by side trip temperature and noise, obtain wavelet field cross correlation results w；And to wavelet field cross-correlation Result w carries out gaussian curve approximation and obtains result g, to improve the certainty of measurement of peak.Here with wavelet field cross-correlation The ultimate principle realizing the wavelength difference detection of two-way fiber grating is as follows: carries out wavelet field to two-way fiber grating reflectance spectrum mutual Guan Hou, obtains wavelet field cross correlation results w, (each sampling of position corresponding to the peak value of wavelet field cross correlation results w in time domain The data point certain wavelength value of correspondence) be exactly two-way fiber grating reflectance spectrum wavelength difference, and to wavelet field cross correlation results w Carry out Gauss curve fitting and obtain result g, main purpose is the peak detection precision for improving next peak detection.

Peak detection step 3, mutual for the wavelet field after Gauss curve fitting is asked for according to result g after Gauss curve fitting The peak s (i.e. the value of the abscissa corresponding to peak value, i.e. time delay τ) closing.Because the wavelet field after Gauss curve fitting is mutual Peak s in time domain for related result g, is equal to two fiber gratings (sensor fibre grating and reference optical fiber grating) Central wavelength difference, therefore we can be derived by sensor fibre grating with respect to reference optical fiber grating according to peak s Wavelength variable quantity/strain variation amount (i.e., it is possible to obtaining the extraneous strain value that sensor fibre grating is subject to).This be due to and in Heart wavelength variable quantity and suffered strain value are one-to-one relations, and reference optical fiber grating is not strained, sensor fibre grating Strained, so the centre wavelength that the centre wavelength of sensor fibre grating deducts reference optical fiber grating is exactly sensor fibre grating The wavelength variable quantity leading in response to change.

Wherein, reference optical fiber optical grating reflection spectrum r1 and sensor fibre optical grating reflection spectrum r2, is to be swashed by narrow line width regulatable Light device scans reference optical fiber grating sensor and sensor fibre grating sensor and obtains, described reference optical fiber grating sensor Not strained by the external world is affected, and described sensor fibre grating sensor is used for receiving described extraneous strain；Due to sensor fibre light Grid and reference optical fiber grating, all have two orthogonal polarization states, and we can eliminate each optical fiber light by Polarization Controller The impact of the one of polarization state in grid.Here tunable laser is required to have narrow live width and larger tunable model Enclose；In order to improve strain measurement precision, fiber grating should also have narrower bandwidth.

In the present invention, using the method for Threshold Denoising, two-way fiber grating reflectance spectrum r1, r2 are carried out at noise reduction Reason, eliminates the various stationary noises being caused in reflectance spectrum and nonstationary noise by factors such as light intensity, external environments；After noise reduction Data beyond fiber grating reflectance spectrum d1, d2 bandwidth carries out zero setting process, reduces beyond fiber grating reflectance spectrum d1, d2 bandwidth The impact to certainty of measurement for the otiose data.

In the present invention, calculate two-way fiber grating reflectance spectrum z1, z2 after data prediction using wavelet transformation Wavelet field cross-correlation, for calculating the reflection peak wavelength difference of two-way fiber grating reflectance spectrum z1, z2, go forward side by side trip temperature and noise Compensation；Because wavelet transformation has time frequency analysis ability, try to achieve the mutual of two-way fiber grating reflectance spectrum z1, z2 in wavelet field The cross-correlation calculation of the reflectance spectrum with nonstationary noise while pass, can be applied to.Compared with traditional cross-correlation calculation, Small echo cross-correlation calculation has higher wavelength difference computational accuracy, and interference, noise signal have higher flexibility to external world.? Afterwards, result w of wavelet field cross-correlation is carried out with Gauss curve fitting, improves the certainty of measurement of peak, eventually through Gauss curve fitting The peak of result g afterwards obtains the wavelength difference of two-way fiber grating reflection peak.

In the present invention, described fiber grating reflectance spectrum r1, r2, can pass through fibre grating method amber formula interferometer, phase shift Fiber grating obtains, and can also be obtained by other interference type optical fiber sensors；This two fiber grating reflectance spectrums, a conduct Reference, a conduct sensing, and their corresponding Fibre Optical Sensors have identical technical specification (as reflectance, bandwidth, freedom Spectrum length, temperature-sensitivity coefficient etc.).

In the present invention, when obtaining two-way fiber grating reflectance spectrum r1, r2 using fibre grating method amber formula interferometer, can The wavelength scanning range of tuned laser should be more than fibre grating method amber formula interferometer a free spectral limit, so in order to Improve the dynamic range of final demodulating algorithm, can be by judging the wavelength difference saltus step of two-way fiber grating reflectance spectrum r1, r2 The size of value should be changed direction to realize that sensor fibre grating is subject to, with the dynamic model of strain measurement expanding whole system algorithm Enclose.

In the present invention, corresponding two fiber gratings of described fiber grating reflectance spectrum r1, r2 are it should be in temperature phase In the less environment to constant, noise, in such as cavern, in rustless steel seal pipe, to ensure the correctness of demodulation result.

Refer to Fig. 1, the operation principle that this high-precision optical fiber strains low frequency sensing and demodulating algorithm is: first passes through narrow linewidth Tunable laser scans two-way fiber grating, and eliminates one of each fiber grating polarization state by Polarization Controller Impact, obtains two-way fiber grating reflectance spectrum r1, r2, and then two-way fiber grating reflectance spectrum passes through Threshold Denoising respectively Process, eliminate the various noises being caused by factors such as light intensity, external environments in reflectance spectrum；Again by the bandwidth of the reflectance spectrum after noise reduction Outer data zero setting, to reduce the impact to certainty of measurement for the otiose data；Then pass through wavelet transformation, calculate two-way through number The wavelet field cross-correlation of fiber grating reflectance spectrum r1, r2 after Data preprocess, to obtain the position of two-way fiber grating reflection peak Difference, the compensation of go forward side by side trip temperature and noise；Again to wavelet field cross correlation results Gauss curve fitting, to improve the measurement essence of peak Degree；Finally, ask for the peak of wavelet field cross-correlation Gauss curve fitting, and the relation according to optic fiber grating wavelength and strain, push away Lead the extraneous strain value obtaining that sensor fibre grating receives；Here, wavelet transformation is the powerful processing non-stationary signal, this The high-precision optical fiber strain sensing low frequency demodulating algorithm that invention provides, calculates the cross-correlation of two-way fiber grating in wavelet field, can To eliminate the nonstationary noise of reference optical fiber grating and sensor fibre grating；Meanwhile, the light based on cross-correlation for the tradition can be solved Fine grating demodulation algorithm cannot be used for high accuracy and demodulates non-stationary fiber grating sensing signal, requires known fiber optic grating sensing to believe Number and noise priori, the problems such as require fiber grating sensing signal and noise independent mutually.

Refer to Fig. 2, in order to more clearly explain the operation principle of high-precision optical fiber strain low frequency sensing and demodulating algorithm, this Invention provide one group of reflectance spectrum measured drawing (above for the reflectance spectrum of reference optical fiber grating, be below sensor fibre grating Reflectance spectrum), demodulating algorithm is to calculate two-way fiber grating reflectance spectrum in real time every one piece of data (differences of two reflection peaks) Wavelet field cross-correlation, and then judge the alternate position spike of two-way fiber grating reflection peak, realize sensing and demodulating.

Refer to Fig. 3 (a), 3 (b), in order to verify high-precision optical fiber strain sensing low frequency demodulating algorithm, the present invention further To traditional cross correlation algorithm and high-precision optical fiber strain low frequency sensing and demodulating algorithm carried out measurement of comparison experiment it can be seen that The demodulation accuracy that high-precision optical fiber strains low frequency sensing and demodulating algorithm is better than the demodulation accuracy of traditional cross correlation algorithm (1 μ ε is about Cause the wavelength change of 1.2pm).

Particular embodiments described above, has carried out detailed further to the purpose of the present invention, technical scheme and beneficial effect Describing in detail bright it should be understood that the foregoing is only the specific embodiment of the present invention, being not limited to the present invention, all Within the spirit and principles in the present invention, any modification, equivalent substitution and improvement done etc., should be included in the protection of the present invention Within the scope of.

Claims (10)

1. a kind of high-precision optical fiber strain low frequency sensing demodulation method based on small echo cross-correlation technique is it is characterised in that include:

Data prediction step, for carrying out at wavelet de-noising to reference optical fiber optical grating reflection spectrum and sensor fibre optical grating reflection spectrum Reason, and the reference optical fiber optical grating reflection spectrum after noise reduction and the data beyond sensor fibre optical grating reflection bands of a spectrum width are carried out at zero setting Reason, obtains pretreated reference optical fiber optical grating reflection spectrum and sensor fibre optical grating reflection spectrum；

Wavelet field cross-correlation step, anti-for calculating pretreated described reference optical fiber optical grating reflection spectrum and sensor fibre grating Penetrate the wavelet field cross correlation value of spectrum；

Peak detection step, for asking for the peak of described wavelet field cross correlation value, and obtains according to described peak Described sensor fibre optical grating reflection spectrum corresponding external world strain value.

2. high-precision optical fiber according to claim 1 strain low frequency sensing demodulation method is it is characterised in that in described data Include before pre-treatment step:

Reference optical fiber grating sensor is scanned by narrow line width regulatable laser and the acquisition of sensor fibre grating sensor is described Reference optical fiber optical grating reflection spectrum and sensor fibre optical grating reflection spectrum.

3. high-precision optical fiber according to claim 1 strain low frequency sensing demodulation method is it is characterised in that described reference light Fiber grating sensor is not strained by the external world to be affected, and described sensor fibre grating sensor is used for receiving described extraneous strain.

4. high-precision optical fiber strain low frequency sensing demodulation method according to claim 2 is it is characterised in that scanning obtains institute After stating reference optical fiber optical grating reflection spectrum and sensor fibre optical grating reflection spectrum, eliminate one of polarization state using Polarization Controller Impact.

5. high-precision optical fiber according to claim 1 strain low frequency sensing demodulation method is it is characterised in that described wavelet field Cross-correlation step, specifically includes:

Calculate pretreated described reference optical fiber optical grating reflection spectrum using wavelet transformation little with what sensor fibre optical grating reflection was composed Wave zone cross correlation value；

Trip temperature and noise compensation are entered to described wavelet field cross correlation value；

Gauss curve fitting is carried out to the wavelet field cross correlation value after compensating.

6. high-precision optical fiber strain low frequency sensing demodulation method according to claim 5 is it is characterised in that described peak value is visited Survey step and peak is obtained according to the wavelet field cross correlation value after described Gauss curve fitting, the corresponding delay value of described peak It is the wavelength difference of described reference optical fiber optical grating reflection spectrum and sensor fibre optical grating reflection spectrum, described wavelength difference represents extraneous strain Value.

7. high-precision optical fiber according to claim 1 strain low frequency sensing demodulation method is it is characterised in that described reference light Fine optical grating reflection spectrum and sensor fibre optical grating reflection spectrum pass through tunable laser scanning fiber bragg grating Fa Poshi interferometer or phase Shifting fiber grating obtains, and the fibre grating method amber formula interferometer being adopted or phase-shifted fiber grating have identical technology and refer to Mark.

8. high-precision optical fiber strain low frequency sensing demodulation method according to claim 7 uses optical fiber it is characterised in that working as Raster method amber formula interferometer obtains reference optical fiber optical grating reflection spectrum and sensor fibre optical grating reflection time spectrum described in two-way fiber grating, The wavelength scanning range of tunable laser is more than a free spectral limit of fibre grating method amber formula interferometer.

9. the high-precision optical fiber strain low frequency sensing demodulation method according to claim 7 or 8 is it is characterised in that will be described Fibre grating method amber formula interferometer or phase-shifted fiber grating be placed in temperature relative constancy, in the less environment of noise, and it is entered Row scanning.

10. the high-precision optical fiber strain low frequency sensing demodulation method according to claim 7 or 8 is it is characterised in that described ginseng Examine fiber grating reflectance spectrum and the wavelet field cross correlation value of sensor fibre optical grating reflection spectrum be calculated as below:

X (t)=s (t)+z (t)

Y (t)=s (t-t₀)+z(t)

$w_{\mathrm{\φ},x}(a,b)={\&integral;}_{-\mathrm{\∞}}^{+\mathrm{\∞}}x\left(t\right){\mathrm{\φ}}^{*}\left(\frac{t-b}{a}\right)dt={\&integral;}_{-\mathrm{\∞}}^{+\mathrm{\∞}}\[s\left(t\right)+z\left(t\right)\]{\mathrm{\φ}}^{*}\left(\frac{t-b}{a}\right)dt=w_{\mathrm{\φ},s}(a,b)+w_{\mathrm{\φ},z}(a,b)$

$w_{\mathrm{\φ},y}(a,b)={\&integral;}_{-\mathrm{\∞}}^{+\mathrm{\∞}}x\left(t\right){\mathrm{\φ}}^{*}\left(\frac{t-b}{a}\right)dt={\&integral;}_{-\mathrm{\∞}}^{+\mathrm{\∞}}\[s(t-t_0)+z\left(t\right)\]{\mathrm{\φ}}^{*}\left(\frac{t-b}{a}\right)dt=w_{\mathrm{\φ},s}(a,b-t_0)+w_{\mathrm{\φ},z}(a,b)$

$\begin{array}{c}{c}_{y,x}^f\left(\mathrm{\τ}\right)={\&integral;}_a{\&integral;}_b{w}_{\mathrm{\φ},y}(a,b)w_{\mathrm{\φ},x}(a,b-\mathrm{\τ})dadb\\ ={\&integral;}_a{\&integral;}_b\[w_{\mathrm{\φ},s}(a,b-t_0)+w_{\mathrm{\φ},z}(a,b)\]\[w_{\mathrm{\φ},s}(a,b-\mathrm{\τ})+w_{\mathrm{\φ},z}(a,b)\]dadb\\ =w_{ss}(\mathrm{\τ}-t_0)+w_{zs}\left(\mathrm{\τ}\right)\end{array}$

Wherein, x (t), y (t) are respectively described reference optical fiber optical grating reflection spectrum and sensor fibre optical grating reflection spectrum, and s (t) is described The reference optical fiber optical grating reflection spectrum and sensor fibre optical grating reflection spectrum data in 3db bandwidth, z (t) is the data of other parts； t₀Time delay for described reference optical fiber optical grating reflection spectrum and sensor fibre optical grating reflection spectrum；Small echo for x (t) and y (t) Domain cross-correlation function, w_{φ, x}、w_{φ, y}、w_{φ, z}、w_{φ, s}It is respectively the wavelet transformation of x (t), y (t), z (t) and s (t), φ^*Little for mother Ripple, a is scale factor, and b is the time-shifting factor；w_ss(τ-t₀) it is the auto-correlation function in wavelet field for the s (t), w_zs(τ) it is s (t) With z (t) wavelet field cross-correlation function.