CN103063325B - BOTDA temperature and strain simultaneous measurement method based on LEAF optical fiber - Google Patents

Abstract

The invention discloses a BOTDA temperature and strain simultaneous measurement method based on a LEAF optical fiber, and provides simultaneous measurement of temperature and stress by utilizing the characteristic that a stimulated Brillouin gain spectrum in the LEAF optical fiber has a plurality of gain peaks, aiming at the defect that the absolute power of an optical signal cannot be accurately measured in the conventional temperature and strain simultaneous measurement method, so that the measurement precision cannot be improved. Stimulated Brillouin scattering is generated in the LEAF optical fiber by using continuous detection light and narrow-linewidth pulse pumping light, Brillouin frequency shift and linewidth of a first gain peak and a second gain peak of a Brillouin scattering signal are measured, and measured data are fitted by using a fitting algorithm, so that measurement of temperature and stress distribution along the optical fiber is completed. The invention does not need to measure the absolute power of the Brillouin scattering signal, effectively improves the dynamic performance and the spatial resolution of the BOTDA system, and has wide application prospect in a distributed optical fiber sensing system.

Description

BOTDA temperature based on LEAF optical fiber and strain be measuring method simultaneously

Technical field

The invention belongs to photoelectron technology field, relate to optical fiber sensing technology, particularly a kind of BOTDA temperature and strain measuring method simultaneously based on LEAF optical fiber.

Background technology

In distributed Brillouin sensing, there are two kinds of Brillouin light domain reflectometer BOTDR and Brillouin light time domain reflection technology BOTDA.In conventional temperature and strain sensing system, no matter be that BOTDR or BOTDA all use single-mode fiber as sensor information, and by analyzing Brillouin scattering gain spectral, i.e. the variation of the power of Brillouin's signal and Brillouin shift (centre frequency of pump light pulse and Brillouin scattering centre frequency poor) obtains the information of temperature and strain.

In distributed Brillouin sensing system, the transmission range difference of the transducing signal of diverse location in light path, signal has different losses, and this has greatly affected the measurement to brillouin scattering signal power.Light source self power is unstable in addition, and the factors such as interchannel noise have also caused very large impact to the measurement of brillouin scattering signal power.In current brillouin distributed sensor-based system, the measuring error of the overwhelming majority is to be caused by the measuring error of brillouin scattering signal power.

In order to improve the precision to brillouin scattering signal power measurement, the method for introducing reference light in measuring system is suggested.Under current technical conditions, conventionally adopt Rayleigh scattering light signal and oppositely Stokes light signal as with reference to light, thereby comparatively efficiently solve the impacts of problem on signal power such as the fixed and long Distance Transmission of flashing.But the measured value fluctuation that the factor such as noise and measuring accuracy of optical power detector self causes remains the principal element of restriction temperature and strain measurement precision and sensor-based system resolution and dynamic range.

Based on this, the present invention proposes the multimodal measuring method based on LEAF optical fiber Brillouin gain spectral with multiple gain peak.In this method, abandon the measurement to brillouin scattering signal absolute power, thereby avoided the impact of optical signal power measuring error on measurement result.

Summary of the invention

For above-mentioned prior art, the object of the present invention is to provide a kind of BOTDA temperature based on LEAF optical fiber and strain measuring method simultaneously, make temperature and the strain can be simultaneously measured, avoid the impact of optical signal power measuring error on measurement result.

In order to solve the problems of the technologies described above, the present invention adopts following technical scheme

Principle of work of the present invention is: adopt continuous probe light and burst pulse single-frequency pump light to produce stimulated Brillouin scattering in LEAF optical fiber, brillouin scattering signal and local reference optical signal are carried out after difference frequency detection, obtain Brillouin shift and the live width of first and second gain peak of LEAF stimulated Brillouin scattering in optical fiber signal, obtain temperature and the strain on this measurement space by data fitting, the change measurement moment can obtain temperature and the Strain Distribution along optical fiber.

BOTDA temperature based on LEAF optical fiber and strain be a measuring method simultaneously, comprises the following steps:

1. wavelength continuous light source signal obtains suitable signal intensity by optical attenuator, as surveying light signal;

2. narrow linewidth light signal is divided into first via light signal and the second road light signal by coupling mechanism;

3. first via light signal, by after Polarization Controller, adopts electric light intensity modulated to modulate, rationally arrange obtain after modulation parameter frequency shifts be approximately equal to Brillouin shift on the pump light pulse that moves and move down;

4. the signal moving on optical filter selecting frequency is as pump light signals, and makes pump light signals pass through polarization scrambler, can reduce like this pump light signals and survey the polarization mismatch between light signal;

5. detection light signal and pump light signals are injected into LEAF optical fiber from two ends, produce stimulated Brillouin scattering;

6. the second road light signal, as local reference light, carries out heterodyne reception with stimulated Brillouin scattering signal and obtains heterodyne signal, thereby obtains the frequency spectrum of brillouin frequency shifting signal; By heterodyne signal and obtain in LEAF optical fiber first and Brillouin shift and the live width of second gain peak, Brillouin shift and the live width of first and second gain peak are carried out to data fitting, thereby obtain temperature and strain on this locus;

7. change Measuring Time and obtain temperature and the Strain Distribution along optical fiber.

Compared with prior art, the invention has the beneficial effects as follows:

Improve BOTDA system and measured dynamic range and the resolution of temperature and strain simultaneously, effectively overcome the restriction of measuring light power error to measurement result, in distributed fiber-optic sensor, had broad application prospects.

Brief description of the drawings

Fig. 1 is continuous probe optical spectrum of the present invention.

Fig. 2 is that the present invention surveys optical spectrum, pump light frequency spectrum and brillouin gain spectrum.

Fig. 3 is that the present invention surveys the frequency spectrum after light and pump light interaction.

Fig. 4 is the frequency spectrum after heterodyne of the present invention.

Fig. 5 is structural representation of the present invention.

Reference numeral is: 1 is that wavelength continuous light source, 2 is that optical attenuator, 3 is that LEAF optical fiber, 4 is that optical circulator, 5 is that polarization scrambling instrument, 6 is that electric light intensity modulator, 7 is that Polarization Controller, 8 is that narrow linewidth light source, 9 is that coupling mechanism, 10 is that photodetector, 11 is electric frequency spectrograph.

Embodiment

Below in conjunction with the drawings and the specific embodiments, the invention will be further described.

BOTDA temperature based on LEAF optical fiber and strain be a measuring method simultaneously, comprises the following steps: 1. wavelength continuous light source signal obtains suitable signal intensity by optical attenuator, as surveying light signal; 2. narrow linewidth light signal is divided into first via light signal and the second road light signal by coupling mechanism; 3. first via light signal, by after Polarization Controller, adopts electric light intensity modulated to modulate, rationally arrange obtain after modulation parameter frequency shifts be approximately equal to Brillouin shift on the pump light pulse that moves and move down; 4. the signal moving on optical filter selecting frequency is as pump light signals, and makes pump light signals pass through polarization scrambler, can reduce like this pump light signals and survey the polarization mismatch between light signal; 5. detection light signal and pump light signals are injected into LEAF optical fiber from two ends, produce stimulated Brillouin scattering; 6. the second road light signal, as local reference light, carries out heterodyne reception with stimulated Brillouin scattering signal and obtains heterodyne signal, thereby obtains the frequency spectrum of brillouin frequency shifting signal; By heterodyne signal and obtain in LEAF optical fiber first and Brillouin shift and the live width of second gain peak, Brillouin shift and the live width of first and second gain peak are carried out to data fitting, thereby obtain temperature and strain on this locus; 7. change Measuring Time and obtain temperature and the Strain Distribution along optical fiber.

Embodiment

Wavelength coverage is that the wavelength continuous light source of 400nm-2400nm obtains the detection light that intensity is suitable after optical attenuator 2, and its frequency spectrum as shown in Figure 1, and remembers that its centre frequency is v ₀.Frequency is the narrow linewidth light source of 1MHz left and right, is divided into two by 1:2 coupling mechanism 10.First via light signal is modulated by the rear employing electric light of Polarization Controller 8 intensity modulator 7, and it is v that parameters makes modulator 7 output frequencies ₀± v _b, the pulsed light that pulsewidth is 10ns, wherein v _bfor Brillouin shift.Adopt after the filtering of optical filter pulse signals, only output frequency is v ₀+ v _bpulse.Pulse signal enters polarization scrambling instrument 6 afterwards, makes the polarization state of pulse signal obtain continuous change, thereby avoids the polarization mismatch of pumping pulse light signal and continuous probe light signal.Pulsed optical signals enters in LEAF optical fiber 3 after optical circulator 4, in LEAF optical fiber 3, pumping pulse light and continuous probe light will interact and produce stimulated Brillouin scattering, survey optical spectrum, pump light frequency spectrum and stimulated Brillouin scattering gain spectral as shown in Figure 2, the frequency spectrum of the stimulated Brillouin scattering that detection light and pump light interaction produce as shown in Figure 3.Stimulated Brillouin scattering signal carries out heterodyne reception through circulator 4 and the second road signal in coupling mechanism 10 in photodetector 11 afterwards, and the heterodyne signal frequency spectrum obtaining after heterodyne as shown in Figure 4.Heterodyne signal can obtain Brillouin shift and the live width of LEAF stimulated Brillouin scattering in optical fiber signal first and second gain peak as shown in Figure 4, thereby can obtain temperature and strain on this locus, the change measurement moment can obtain temperature and the Strain Distribution along optical fiber, it should be noted that the live width at excited Brillouin spectrum gain peak in this example of the present invention refers to the full width at half maximum FWHM of peak value.

In the present embodiment, the Brillouin shift by LEAF stimulated Brillouin scattering in optical fiber signal first and second gain peak and live width obtain the process that temperature on this locus and strain need a demarcation.Stimulated Brillouin scattering spectrum has following relation with temperature and strain on locus, LAEF optical fiber place:

$\left\{\begin{array}{c}{C}_{\mathrm{\ϵv}}^1\mathrm{\δ\ϵ}+C_{\mathrm{Tv}}^1\mathrm{\δT}={\mathrm{\δV}}_B^1\\ C_{\mathrm{\ϵl}}^1\mathrm{\δ\ϵ}+C_{\mathrm{Tl}}^1\mathrm{\δT}={\mathrm{\δl}}^1\\ C_{\mathrm{\ϵv}}^2\mathrm{\δ\ϵ}+C_{\mathrm{Tv}}^2\mathrm{\δT}={\mathrm{\δV}}_B^2\\ C_{\mathrm{\ϵl}}^2\mathrm{\δ\ϵ}+C_{\mathrm{Tl}}^2\mathrm{\δT}={\mathrm{\δl}}^2\end{array}\right.---\left(1\right)$

ε in formula, T, V _b, l is respectively strain, temperature, Brillouin shift, live width; for corresponding constant coefficient, wherein 1,2 represent that respectively stimulated Brillouin scattering composes first and second gain peak.The temperature and the strain that change a certain locus place take multiple measurements and can obtain the corresponding sensing variable space the LEAF of this space place:

(δε，δT)＝[(δε ₁,δT ₁),(δε ₂,δT ₂),……,(δε _n,δT _n)]

Dependent variable space:

$({\mathrm{\δV}}_B^1,{\mathrm{\δl}}^1,{\mathrm{\δV}}_B^2,{\mathrm{\δl}}^2)=[({\mathrm{\δV}}_{B1}^1,{\mathrm{\δl}}_1^1,{\mathrm{\δV}}_{B1}^2,{\mathrm{\δl}}_1^2),({\mathrm{\δV}}_{B2}^1,{\mathrm{\δl}}_2^1,{\mathrm{\δV}}_{B2}^2,{\mathrm{\δl}}_2^2),......,({\mathrm{\δV}}_{\mathrm{Bn}}^1,$ $\mathrm{\δ}{l}_n^1,{\mathrm{\δV}}_{\mathrm{Bn}}^2,{\mathrm{\δl}}_n^2\left)\right]$

Can obtain:

$\left[\begin{array}{cc}{C}_{\mathrm{\ϵv}}^1& C_{\mathrm{Tv}}^1\\ C_{\mathrm{\ϵl}}^2& C_{\mathrm{Tl}}^1\\ C_{\mathrm{\ϵv}}^2& C_{\mathrm{Tv}}^2\\ C_{\mathrm{\ϵl}}^2& C_{\mathrm{Tl}}^2\end{array}\right]\·(\mathrm{\δ\ϵ},\mathrm{\δT})=({\mathrm{\δV}}_B^1,{\mathrm{\δl}}^1,{\mathrm{\δV}}_B^2,{\mathrm{\δl}}^2)$

Can be in the hope of constant coefficient matrix by data fitting:

$\left[\begin{array}{cc}{C}_{\mathrm{\ϵv}}^1& C_{\mathrm{Tv}}^1\\ C_{\mathrm{\ϵl}}^1& C_{\mathrm{Tl}}^1\\ C_{\mathrm{\ϵv}}^2& C_{\mathrm{Tv}}^2\\ C_{\mathrm{\ϵl}}^2& C_{\mathrm{Tl}}^2\end{array}\right]$

, for the stimulated Brillouin scattering spectrum in arbitrary LEAF optical fiber, bring formula (1) by its first into Brillouin shift and the live width of second gain peak, adopt optimization algorithm to ask optimum solution can obtain temperature and the strain of this locus.

Claims (2)

1. the BOTDA temperature based on a LEAF optical fiber and strain measuring method simultaneously, is characterized in that, comprises the following steps:

1. wavelength continuous light source signal obtains suitable signal intensity by optical attenuator, as surveying light signal;

2. narrow linewidth light signal is divided into first via light signal and the second road light signal by coupling mechanism;

3. first via light signal, by after Polarization Controller, adopts electric light intensity modulator to modulate, rationally arrange obtain after modulation parameter frequency shifts be approximately equal to Brillouin shift on the pump light pulse that moves and move down;

4. the pump light pulse moving on optical filter selecting frequency is as pump light signals, and makes pump light signals pass through polarization scrambler, can reduce like this pump light signals and survey the polarization mismatch between light signal;

5. pump light signals is injected in LEAF optical fiber after optical circulator, makes to survey light signal and pump light signals and is injected into LEAF optical fiber from two ends, produces stimulated Brillouin scattering;

6. the second road light signal is as local reference light, and stimulated Brillouin scattering signal process ring of light device and the second road light signal carry out heterodyne reception and obtain heterodyne signal in photodetector, thereby obtain the frequency spectrum of brillouin frequency shifting signal; Obtained in LEAF optical fiber Brillouin shift and the live width of first and second gain peak by heterodyne signal, Brillouin shift and the live width of first and second gain peak are carried out to data fitting, thereby obtain temperature and strain on locus;

7. change Measuring Time and obtain temperature and the Strain Distribution along optical fiber.

2. BOTDA temperature and the strain measuring method simultaneously based on LEAF optical fiber according to claim 1, is characterized in that, described stimulated Brillouin scattering spectrum has following relation with temperature and strain on locus, LAEF optical fiber place:

$\left\{\begin{array}{c}{C}_{\mathrm{\ϵv}}^1\mathrm{\δ\ϵ}+C_{\mathrm{Tv}}^1\mathrm{\δT}={\mathrm{\δV}}_B^1\\ C_{\mathrm{\ϵl}}^1\mathrm{\δ\ϵ}+C_{\mathrm{Tl}}^1\mathrm{\δT}={\mathrm{\δl}}^1\\ C_{\mathrm{\ϵv}}^2\mathrm{\δ\ϵ}+C_{\mathrm{Tv}}^2\mathrm{\δT}={\mathrm{\δV}}_B^2\\ C_{\mathrm{\ϵl}}^2\mathrm{\δ\ϵ}+C_{\mathrm{Tl}}^2\mathrm{\δT}={\mathrm{\δl}}^2\end{array}\right.,$ ε in formula, T, V _b, l is respectively strain, temperature, Brillouin shift, live width; for corresponding constant coefficient, wherein 1,2 represent that respectively stimulated Brillouin scattering composes first and second gain peak.