CN114353685A - High-frequency dynamic strain measuring device and method based on chaotic Brillouin phase spectrum - Google Patents
High-frequency dynamic strain measuring device and method based on chaotic Brillouin phase spectrum Download PDFInfo
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Abstract
The invention relates to the field of distributed optical fiber sensing, and discloses a high-frequency dynamic strain measuring device based on a chaotic Brillouin phase spectrum, which comprises: the high-speed electro-optical modulator is used for modulating the pump light to generate the pump light with frequency movement equal to the Doppler frequency shift in magnitude and direction; the other beam as detection light sequentially passes through a single-side band modulator, a programmable optical delay line, an erbium-doped optical fiber amplifier, an adjustable band-pass filter and an RF modulator and then enters from the other end of the sensing optical fiber, and a Brillouin scattering signal generated in the sensing optical fiber is output from an optical circulator, then is detected by a photoelectric detector and is demodulated by an IQ demodulator to obtain phase shift information. The invention realizes high-frequency high-precision dynamic strain measurement on the basis of inhibiting non-local effects.
Description
Technical Field
The invention relates to the field of distributed optical fiber sensing, in particular to a high-frequency dynamic strain measuring device and method based on a chaotic Brillouin phase spectrum.
Background
In recent years, the brillouin distributed optical fiber sensing technology has been widely applied in various structural health monitoring fields due to the distributed strain and temperature measurement capability. In the current society, a smart city with an artificial intelligent monitoring network as a core is rapidly built, so that the requirement of distributed optical fiber sensing on dynamic strain measurement is more and more obvious, and various technologies are proposed in succession for improving the sensing and measuring speed of Brillouin optical fibers.
The slope auxiliary technology is concerned with due to the advantages of simple structure, strong adaptability, high speed and the like. For example: an Enhancing string dynamic range of slope-assisted BOTDA by manipulating the bright mouth gain spectrum shape (Yang G.,et al.32599, 32607, 2018) and the subject group Effect of textual time delay signature on Brillouin gain spectrum in the slope-associated textual BOCDA (Zhao L,et al., Optics Express, 28(12): 18189-18201, 2020)、Dynamic strain measurement by a single-slope-assisted chaotic Brillouin optical correlation-domain analysis(Wang Y., et aloptics Letters, 45(7): 1822-. However, the measurement accuracy depends on the stability of the probe optical power, which is easily affected by the fluctuation of the pump optical power and the loss of the optical fiber. In 2019, the ancestor et al propose a double-slope auxiliary (DSA) technology, which realizes measurement irrelevant to pump light power and insensitive to optical fiber loss, and obtains 625 Hz repetition frequency and centimeter-level spatial resolution through experiments. Urrechelqui J. et al propose a BOTDA sensing technology based on Brillouin phase shift spectrum, which effectively avoids the influence of pump light power fluctuation and optical fiber loss in the measurement process; the technology converts dynamic strain into the change of RF phase shift in real time, and has simple device and low cost. However, when the scheme is used for measuring dynamic strain, the dynamic strain is appliedThe variation introduces doppler shift (the magnitude of which depends on the frequency of the dynamic strain and the length of the fiber under strain and even exceeds the signal strength to be measured), thus destroying the distributed brillouin strain measurement and interfering with the performance of the sensor. Therefore, the scheme has certain limitation on distributed high-frequency dynamic strain measurement and is not beneficial to practical application. And the chaotic laser has the characteristics of noise-like, broadband, strong anti-interference and the like, so that the phase spectrum can be broadened, the range of a linear region is enlarged, and the measurable dynamic tensile strain is enlarged.
Therefore, a new chaotic brillouin distributed dynamic strain measurement technology needs to be invented, which can effectively inhibit the generation of doppler shift on the premise of avoiding the influence of pumping light power fluctuation, optical fiber loss and the like on the measurement precision, and realize dynamic strain measurement with both high precision and high frequency.
Disclosure of Invention
The invention provides a high-frequency dynamic strain measuring device based on a chaotic Brillouin phase spectrum, which aims to solve the problem that the conventional dynamic strain measurement cannot realize measurement with both high frequency and high precision.
In order to solve the technical problems, the invention adopts the technical scheme that: a high-frequency dynamic strain measuring device based on a chaotic Brillouin phase spectrum comprises: the high-speed electro-optical modulator is used for modulating the pump light, generating the pump light with frequency movement which is equal to the Doppler frequency shift in magnitude and in the moving direction, and further generating phase movement which is equal to the non-local phase shift in magnitude and in opposite direction;
the other beam as detection light sequentially passes through a single-side band modulator, a programmable optical delay line, an erbium-doped optical fiber amplifier, an adjustable band-pass filter and an RF modulator and then enters from the other end of the sensing optical fiber, and the single-side band modulator is used for modulating the detection light to enable the detection light to generate frequency shift down; the RF modulator is used for modulating the probe light after the frequency is shifted down, so that the probe light generates two sideband frequencies comprising an original carrier frequency and having a phase difference of 180 degrees; the stimulated Brillouin scattering is generated under the action of the probe light subjected to frequency shift down and phase modulation in the sensing optical fiber and the pump light, and a generated Brillouin scattering signal is output from the optical circulator and then detected by the photoelectric detector;
and the signal detected by the photoelectric detector is demodulated by the IQ demodulator to obtain phase shift information.
The high-frequency dynamic strain measuring device based on the chaotic Brillouin phase spectrum further comprises an arbitrary waveform generator, wherein the output end of the arbitrary waveform generator is connected with the RF modulator and the IQ demodulator and used for driving the RF modulator to modulate pump light, and the IQ demodulator is used for demodulating a detection signal of the photoelectric detector according to a synchronous signal output by the arbitrary waveform generator.
The-3 dB spectral line width of the broadband chaotic laser output by the broadband chaotic laser source is greater than 5GHz, and the-3 dB power spectral bandwidth is greater than 10 GHz.
The beam splitter is a 90:10 1 × 2 fiber coupler, wherein 90% is used as probe light and 10% is used as pump light.
The high-frequency dynamic strain measuring device based on the chaotic Brillouin phase spectrum further comprises an adjustable microwave signal source, wherein the adjustable microwave signal source is used for driving the high-speed electro-optical modulator by the output sinusoidal signal.
The high-frequency dynamic strain measuring device based on the chaotic Brillouin phase spectrum further comprises a first polarization controller and a second polarization controller, wherein the first polarization controller is arranged between the beam splitter and the high-speed electro-optical modulator, and the second polarization controller is arranged between the beam splitter and the single-side band modulator.
The high-frequency dynamic strain measuring device based on the chaotic Brillouin phase spectrum further comprises a real-time digital oscilloscope which is used for acquiring phase shift information obtained by demodulation of an IQ demodulator.
In addition, the invention also provides a high-frequency dynamic strain measurement method based on the chaotic Brillouin phase spectrum, and the modulation frequency of the high-speed electro-optical modulator is adjusted by adopting the high-frequency dynamic strain measurement device based on the chaotic Brillouin phase spectrum in comparison with the Brillouin gain spectrum and the Brillouin absorption spectrum in the non-strain state, so that the central peak positions of the Brillouin gain spectrum and the Brillouin absorption spectrum are kept unchanged.
Compared with the prior art, the invention has the following beneficial effects:
1. the invention provides the probe light with the frequency movement opposite to the Doppler frequency shift by changing the frequency of the pump light, so that the invention generates the phase movement opposite to the non-local phase shift, and can eliminate the influence of the Doppler frequency shift on the system by superposition. And obtaining the one-to-one correspondence between the phase angle and the Brillouin frequency shift through later-stage algorithm operation, so as to demodulate the strain to be measured on the basis of inhibiting the non-local effect and realize high-frequency high-precision dynamic strain measurement.
2. The invention uses the center frequency v0The wide-band chaotic laser with the-3 dB spectral line width larger than 5GHz and the-3 dB power spectral bandwidth larger than 10GHz can widen the Brillouin gain spectrum, and the corresponding gain spectral line width can be increased. From equation (5), it can be seen that the phase angle decreases with the increase of the line width of the gain spectrum, i.e. the speed of change of the phase angle with the brillouin frequency shift becomes slower. Therefore, the broadband chaotic laser can broaden the Brillouin phase spectrum, expand the linear range for slope assistance and further expand the measurable dynamic strain range.
3. In the traditional Brillouin dynamic strain measurement device and method based on double slope assistance, a new parameter R can be obtained by comparing Brillouin gains obtained when the frequency difference of pumping light and detection light is set at the rising edge and the falling edge of a Brillouin gain spectrumBTo achieve its immunity to pump light power fluctuations and fiber loss, a low pass filter is typically used at the output port to eliminate high frequency noise. In this case, when the repetition frequency is too high, the measured brillouin signal will be distorted due to the limited output bandwidth. In experiments, to achieve higher repetition rates, lock-in amplifiers with higher input and output bandwidths were employed. However, for high speed measurements, the signal-to-noise ratio and the sum of the signal-to-noise ratio are increased since the receiver module will detect more high frequency noiseThe measurement accuracy is degraded. The high-frequency high-precision dynamic strain measurement device and method based on the chaotic Brillouin phase spectrum improve the signal-to-noise ratio by increasing the carrier power, and further improve the measurement precision.
Drawings
Fig. 1 is a schematic structural diagram of a high-frequency dynamic strain measurement device based on a chaotic brillouin phase spectrum according to an embodiment of the present invention;
FIG. 2 is a schematic diagram of the principle of suppressing non-local effects in an embodiment of the present invention;
the optical fiber laser device comprises a 1-broadband chaotic laser source, a 2-beam splitter, a 3-first polarization controller, a 4-high-speed electro-optical modulator, a 5-adjustable microwave signal source, a 6-high-power erbium-doped optical fiber amplifier, a 7-optical circulator, an 8-photoelectric detector, a 9-sensing optical fiber, a 10-IQ demodulator, an 11-real-time digital oscilloscope, a 12-second polarization controller, a 13-single-sideband modulator, a 14-microwave signal source, a 15-programmable optical delay line, a 16-erbium-doped optical fiber amplifier, a 17-adjustable band-pass filter, an 18-RF modulator, a 19-arbitrary waveform generator and a 20-optical isolator.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below, and it is obvious that the described embodiments are some embodiments of the present invention, but not all embodiments; all other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
As shown in fig. 1, an embodiment of the present invention provides a high-frequency dynamic strain measurement apparatus based on a chaotic brillouin phase spectrum, including: the optical fiber sensor comprises a broadband chaotic laser source 1, wherein a light beam emitted by the broadband chaotic laser source 1 is divided into two beams after passing through a beam splitter 2, one beam is used as pump light and enters a sensing optical fiber 9 after passing through a high-speed electro-optical modulator 4, an erbium-doped optical fiber amplifier 6 and an optical circulator 7, the high-speed electro-optical modulator 4 is used for modulating the pump light to generate the pump light with the frequency movement which is equal to the Doppler frequency shift and the same movement direction, and further generate the phase movement which is equal to the non-local phase shift and opposite to the non-local phase shift; the other beam as detection light sequentially passes through a single-side band modulator 13, a programmable optical delay line 15, an erbium-doped fiber amplifier 16, an adjustable band-pass filter 17 and an RF modulator 18 and then enters from the other end of the sensing fiber 9, and the single-side band modulator 13 is used for modulating the detection light to enable the detection light to generate frequency shift down; the RF modulator 18 is configured to modulate the frequency-shifted probe light to generate two sideband frequencies including the original carrier frequency and having a phase difference of 180 °; the detection light with the frequency shifted downwards and the phase modulated in the sensing optical fiber 9 and the pumping light act to generate stimulated Brillouin scattering, and a generated Brillouin scattering signal is output from the optical circulator 7 and then is detected by the photoelectric detector 8; the signal detected by the photodetector 8 is demodulated by the IQ demodulator 10 to obtain the phase shift information.
Specifically, the high-frequency dynamic strain measurement device based on the chaotic brillouin phase spectrum further includes an arbitrary waveform generator 19, an output end of the arbitrary waveform generator 19 is connected to the RF modulator 18 and the IQ demodulator 10, and is configured to drive the RF modulator 18 to modulate the pump light, and the IQ demodulator 10 is configured to demodulate the detection signal of the photodetector according to the synchronization signal output by the arbitrary waveform generator 19. Further, an optical isolator 20 is included, and the probe light passes through the optical isolator 20 and then enters the sensing fiber 9 after being modulated by the RF modulator 18, so as to isolate the influence caused by stray light.
Specifically, in this embodiment, the-3 dB spectral line width of the broadband chaotic laser output by the broadband chaotic laser source 1 is greater than 5GHz, and the-3 dB power spectral bandwidth is greater than 10 GHz.
Specifically, in this embodiment, the beam splitter 2 is a 90:10 1 × 2 fiber coupler, in which 90% is used as probe light and 10% is used as pump light.
Further, the high-frequency dynamic strain measurement device based on the chaotic brillouin phase spectrum of the embodiment further includes an adjustable microwave signal source 5, and the adjustable microwave signal source 5 is used for driving the high-speed electro-optical modulator 4 by the output sinusoidal signal. Furthermore, a microwave signal source 13 for driving the single sideband modulator 13 is included.
Further, the high-frequency dynamic strain measurement device based on the chaotic brillouin phase spectrum of the embodiment further includes a first polarization controller 3 and a second polarization controller 12, the first polarization controller 3 is disposed between the beam splitter 2 and the high-speed electro-optical modulator 4, and the second polarization controller 12 is disposed between the beam splitter 2 and the single-sideband modulator 13.
Further, the high-precision dynamic strain measurement device based on the chaotic brillouin phase spectrum of the embodiment further includes a real-time digital oscilloscope 11, which is used for acquiring phase shift information demodulated by the IQ demodulator.
Further, in this embodiment, the output end of the broadband chaotic laser source 1 is connected to the input end of the beam splitter 2; the first output end of the beam splitter 2 is connected with the input end of the polarization controller 3; the output end of the polarization controller 3 is connected with the optical fiber input end of the high-speed electro-optical modulator 4; the radio frequency output end of the adjustable microwave signal source 5 is connected with the radio frequency input end of the high-speed electro-optical modulator 4 through a high-frequency coaxial cable; the optical fiber output end of the high-speed electro-optical modulator 4 is connected with the input end of the high-power erbium-doped optical fiber amplifier 6 through a single-mode optical fiber jumper; the output end of the high-power erbium-doped fiber amplifier 6 is connected with the input end of an optical circulator 7 through a single-mode fiber jumper, the output end of the optical circulator 7 is connected with the input end of a photoelectric detector 8 through the single-mode fiber jumper, the output end of the photoelectric detector 8 is connected with the signal input end of an IQ demodulator 10 through a high-frequency coaxial cable, the radio-frequency output end 1 of an arbitrary waveform generator 19 is connected with the radio-frequency input end of the IQ demodulator 10 through the high-frequency coaxial cable, and the signal output end of the IQ demodulator 10 is connected with the input end of a real-time digital oscilloscope 11 through the high-frequency coaxial cable. The second output end of the beam splitter 2 is connected with the input end of a second polarization controller 12, the output end of the second polarization controller 12 is connected with the optical fiber input end of a single-side band modulator 13, the radio frequency output end of a microwave signal source 14 is connected with the radio frequency input end of the single-side band modulator 13 through a high-frequency coaxial cable, the signal output end of the single-side band modulator 13 is connected with the input end of a programmable optical delay line 15 through a single-mode optical fiber jumper wire, the output end of the programmable optical delay line 15 is connected with the input end of an erbium-doped optical fiber amplifier 16 through a single-mode optical fiber jumper wire, the output end of the erbium-doped optical fiber amplifier 16 is connected with the input end of an adjustable band-pass filter 17 through a single-mode optical fiber jumper wire, the output end of the adjustable band-pass filter 17 is connected with the signal input end of an RF phase modulator 18 through a single-mode optical fiber jumper wire, the radio frequency output end 2 of an arbitrary waveform generator 19 is connected with the radio frequency input end of the RF phase modulator 18 through a high-frequency coaxial cable, the signal output end of the RF phase modulator 18 is connected with the input end of the optical isolator 20 through a single-mode optical fiber jumper, the output end of the optical isolator 20 is connected with one end of the sensing optical fiber 9 through a single-mode optical fiber jumper, and the other end of the sensing optical fiber 9 is connected with the reflection end of the optical circulator 7.
The working principle of the invention is as follows.
The single-sideband modulator 13 modulates the probe light (90%) modulated by the second polarization controller 12 to generate probe light with a frequency v shifted downward0-νBWherein v isBIs the frequency shift amount, which is equal to the Brillouin frequency shift amount (the Brillouin frequency shift value of the common single mode fiber is about 11 GHz). The single sideband modulator 13 is driven by an adjustable microwave signal source 14, which outputs sinusoidal signals with a frequency range of 9kHz to 13 kHz and an amplitude range of-20 dBm to 19 dBm. The single-sideband modulated probe light is incident into an ODG-101 type long-distance high-precision programmable optical delay line 15, and the programmable optical delay line 15 is used for controlling the position of a correlation peak. The probe light passing through the delay line is incident to the erbium-doped fiber amplifier 16 to compensate the optical power loss caused by single-side band modulation. The amplified probe light is incident on a tunable bandpass filter 17 to filter the upper sideband generated by the intensity modulation. And then to an RF modulator 18, the RF modulator 18 being driven by an arbitrary waveform generator 19 of the Agilent-81150a type, the phase-modulated probe light containing three frequency components (the original carrier frequency and the sideband frequencies with a phase difference of 180 °), only probe light of one sideband frequency being strongly interactive with pump light due to the modulated probe light frequency. The phase-modulated probe light is incident into the sensing fiber 9 through the optical isolator 20, and here, the sensing fiber 9 adopts a G655 single-mode fiber.
The pump light is incident to the high-speed electro-optical modulator 4 through the polarization controller 3, wherein the high-speed electro-optical modulator 4 is modulated by a sinusoidal signal output by the first adjustable microwave signal source 5, and the purpose of the modulation is to generate the pump light with the same frequency movement as the Doppler frequency shift and the same moving direction, and further generate the phase movement with the same magnitude and the opposite direction as the non-local phase shift. The modulated chaotic pump light is amplified to an appropriate level by the high power erbium-doped fiber amplifier 6 to excite the stimulated brillouin scattering effect. Then, the light enters the sensing fiber 9 through the optical circulator 7, meets the probe light in the sensing fiber 9, and generates stimulated brillouin scattering.
The detection light and the pumping light which are transmitted in opposite directions meet at a certain position in the sensing optical fiber 9, the Brillouin gain measurement of each point of the sensing optical fiber can be realized by changing the length of the programmable optical delay line, the Brillouin gain information output by the circulator is converted into the intensity of an electric signal by the photoelectric detector and then demodulated by the IQ demodulator to obtain phase shift information, and the phase shift information is acquired on the real-time digital oscilloscope.
The dynamic strain applied to the sensing fiber causes a brillouin frequency shift change, which is actually represented by a frequency shift generated by the gain probe light and the loss probe light, respectively, that is, a frequency shift amount Δ generated by the gain probe light and the loss probe light by the dynamic strainf DS,probe,GAnd Δf DS,probe,AComprises the following steps:
Δf DS,probe,G=+Δf L； （1）
Δf DS,probe,A=+Δf L； （2）
as shown in FIG. 2 (a), the brillouin phase of the corresponding gain detection light and loss detection light shifts by φDS,probe,GΔ φDS,probe,AComprises the following steps:
∆φDS,probe,G=-∆φL； （3）
∆φDS,probe,A=-∆φL； （4）
wherein is Δ #LIndicating the magnitude of the phase shift of the gain probe light/loss probe light due to the dynamic strain.
In addition, during measurement, a doppler shift is introduced by the dynamic strain, as shown in fig. 2 (b), which is expressed in the present invention that the gain probe light and the loss probe light respectively generate frequency shifts, that is, the frequency shifts generated by the gain probe light and the loss probe light due to the doppler shift are respectively:
Δf D,probe,G=-Δf NL； （5）
Δf D,probe,A=+Δf NL； （6）
wherein, Deltaf NLIndicating the magnitude of the frequency shift of the gain probe light/loss probe light caused by the doppler shift.
The frequency shift is directly related to the dynamic strain frequency, the Brillouin phase is shifted due to the accumulation of Doppler shift, and the corresponding Brillouin phase shifts of the gain detection light and the loss detection light are equal to phi in contrast to the Brillouin gain and the absorption spectrumD,probe,G ∆φD,probe,ARespectively as follows:
∆φD,probe,G=+∆φNL； （7）
∆φD,probe,A=-∆φNL； （8）
wherein is Δ #NLIndicating the magnitude of brillouin phase shift of the gain probe light/loss probe light due to doppler shift.
Thus, the presence of doppler shift causes dynamic strain measurements to have certain limitations. The invention detects both brillouin gain and absorption spectra. As shown in fig. 2 (c), by changing the frequency of the pump light, the center frequencies of the brillouin gain and the absorption spectrum are shifted by Δ, respectivelyf NLEquivalent to a shift of the frequencies of the gain detection light and the loss detection light in opposite directions by Δf NLRespectively occur in corresponding Brillouin phases [. DELTA. ]NLΔ +NLAnd (4) moving. The three Brillouin frequency shifts and the phase shifts are superposed by changing the frequency of the pump light to offset the Brillouin phase shift generated by the pump light and the non-local phase shift originally caused by Doppler frequency shift, so that new frequency shift and phase shift parameters are defined:
Δf G=Δf D,probe,G+Δf DS,probe,G+Δf P,probe,G；（9）
Δf A=Δf D,probe,A+Δf DS,probe,A+Δf P,probe,A；（10）
∆φG=∆φD,probe,G+∆φDS,probe,G+∆φP,probe,G；（11）
∆φA=∆φD,probe,A+∆φDS,probe,A+∆φP,probe,A；（12）
in the formula,. DELTA.f P,probe,GAnd Δf P,probe,ARespectively representing the frequency shift of the gain detection light and the loss detection light due to the change of the frequency of the pump light; Δ φP,probe,GΔ φP,probe,ARespectively, represent the gain probe light and the loss probe light phase shifts generated by varying the frequency of the pump light. As can be seen from the formula: the frequency of the pump light is modulated by modulating an adjustable microwave signal source applied to the high-speed electro-optical modulator, so that:
Δf P,probe,G=+Δf NL；（13）
Δf P,probe,A=-Δf NL；（14）
∆φP,probe,G=+∆φNL；（15）
∆φP,probe,A=-∆φNL；（16）
the influence caused by Doppler frequency shift can be avoided; therefore, the invention can measure the parameter Δ #GOr Δ #AThe influence of non-local effect caused by Doppler frequency shift is avoided, and finally, large-range dynamic strain measurement with high precision and high frequency is realized.
In addition, the existing distributed optical fiber dynamic strain measurement systems are all based on slope-assisted chaotic brillouin dynamic strain detection, such as: a slope-assisted Brillouin optical fiber sensing vibration measurement device and a measurement method (Chinese invention patent, CN 201810789456.9) capable of fixing a frequency shift structure, a high-precision dynamic strain monitoring device and method (CN 202010132428.7) based on non-delay chaotic laser and a multipoint parallel high-speed chaotic Brillouin dynamic strain monitoring device and method (CN 202010455193.5) which are provided by the subject group are used for carrying out dynamic strain real-time measurement by utilizing the one-to-one correspondence relationship between the Brillouin gain size and the strain in a linear region of a Brillouin gain spectrum rising edge or falling edge, so that a time-consuming frequency sweeping process is avoided, but the measurement result is easily influenced by the power fluctuation of pumping light and the loss of optical fibers. The invention relates to a high-frequency high-precision dynamic strain measuring device and method based on a chaotic Brillouin phase spectrum, which injects detection light after phase modulation and pump light in reverse propagation into two ends of an optical fiber to be measured respectively, and generates stimulated Brillouin interaction at a certain position of the optical fiber to be measured, wherein a light field at a specific position z in the optical fiber is as follows:
wherein E is0And ESBRespectively the amplitude of the carrier optical field and the first sideband of the phase modulated probe wave,υ 0is the frequency of the carrier light and,f RFindicating the frequency of the phase modulator (high-speed electro-optical modulator 5), i.e. the modulation frequency, HSBSIs the complex brillouin gain spectrum at position z and can be expressed as:
wherein G isSBSAnd phiSBSRespectively representing the brillouin gain and the brillouin phase shift, and obtaining the RF amplitude and phase shift information by detecting and demodulating in the electrical domain, if the phase angle of the radio frequency signal is defined as:
wherein, gBIs the peak gain, Δ νBIs the line width of the brillouin line,
is the difference between the interaction frequency and the brillouin center frequency,υ Pis the frequency of the pump light and,υ B(z) is the Brillouin frequency shift at position z, E0Representing the light field amplitude of the carrier wave, ESBRepresenting the first sideband of the phase modulated probe wave.
From vector analysis of the RF signal, θRFThe strain demodulation method is quantitative, is irrelevant to the pump light power and the optical fiber loss, has a one-to-one correspondence relationship with the Brillouin frequency shift, and can demodulate the strain through the correspondence relationship between the Brillouin frequency shift and the strain. Therefore, the invention can effectively avoid the influence of the power fluctuation of the pump light and the loss of the optical fiber.
In the invention, dynamic strain applied on a sensing optical fiber forms Doppler shift in an optical fiber to be measured (the Doppler shift is changed along with the frequency of the dynamic strain), certain non-local phase shift is introduced into the Doppler shift generated in a system, and a measurement error caused by the non-local phase shift is increased along with the increase of the dynamic strain frequency. And obtaining the one-to-one correspondence between the phase angle and the Brillouin frequency shift through later-stage algorithm operation, so as to demodulate the strain to be measured on the basis of inhibiting the non-local effect and realize high-frequency high-precision dynamic strain measurement.
Finally, it should be noted that: the above embodiments are only used to illustrate the technical solution of the present invention, and not to limit the same; while the invention has been described in detail and with reference to the foregoing embodiments, it will be understood by those skilled in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some or all of the technical features may be equivalently replaced; and the modifications or the substitutions do not make the essence of the corresponding technical solutions depart from the scope of the technical solutions of the embodiments of the present invention.
Claims (8)
1. A high-frequency dynamic strain measuring device based on a chaotic Brillouin phase spectrum is characterized by comprising: the optical fiber laser comprises a broadband chaotic laser source (1), wherein a light beam emitted by the broadband chaotic laser source (1) is divided into two beams after passing through a beam splitter (2), one beam as a pumping light is incident to a sensing optical fiber (9) after passing through a high-speed electro-optical modulator (4), an erbium-doped optical fiber amplifier (6) and an optical circulator (7), and the high-speed electro-optical modulator (4) is used for modulating the pumping light to generate the pumping light with frequency movement equal to Doppler frequency shift and in the same moving direction, and further generate phase movement equal to non-local phase shift and in the opposite direction;
the other beam as detection light enters from the other end of the sensing optical fiber (9) after sequentially passing through a single-side band modulator (13), a programmable optical delay line (15), an erbium-doped optical fiber amplifier (16), an adjustable band-pass filter (17) and an RF modulator (18), and the single-side band modulator (13) is used for modulating the detection light to enable the detection light to generate frequency shift down; the RF modulator (18) is used for modulating the probe light after frequency down shift to generate two sideband frequencies including an original carrier frequency and having a phase difference of 180 degrees; the frequency is shifted downwards in the sensing optical fiber (9), the detection light after phase modulation and the pumping light act to generate stimulated Brillouin scattering, and the generated Brillouin scattering signal is output from the optical circulator (7) and then is detected by the photoelectric detector (8);
the signal detected by the photoelectric detector (8) is demodulated by the IQ demodulator (10) to obtain phase shift information.
2. The high-frequency dynamic strain measurement device based on the chaotic brillouin phase spectrum is characterized by further comprising an arbitrary waveform generator (19), wherein an output end of the arbitrary waveform generator (19) is connected with the RF modulator (18) and the IQ demodulator (10) for driving the RF modulator (18) to modulate the pump light, and the IQ demodulator (10) is used for demodulating the detection signal of the photodetector according to the synchronous signal output by the arbitrary waveform generator (19).
3. The high-frequency dynamic strain measurement device based on the chaotic Brillouin phase spectrum according to claim 1, wherein-3 dB spectral line width and-3 dB power spectral bandwidth of the broadband chaotic laser output by the broadband chaotic laser source (1) are greater than 5GHz and greater than 10GHz respectively.
4. The high-frequency dynamic strain measurement device based on the chaotic brillouin phase spectrum according to claim 1, wherein the beam splitter (2) is a 90:10 1 x 2 fiber coupler, wherein 90% is used as probe light and 10% is used as pump light.
5. The high-frequency dynamic strain measurement device based on the chaotic Brillouin phase spectrum is characterized by further comprising an adjustable microwave signal source (5), wherein the adjustable microwave signal source (5) is used for outputting a sinusoidal signal to drive the high-speed electro-optical modulator (4).
6. The high-frequency dynamic strain measurement device based on the chaotic Brillouin phase spectrum is characterized by further comprising a first polarization controller (3) and a second polarization controller (12), wherein the first polarization controller (3) is arranged between the beam splitter (2) and the high-speed electro-optical modulator (4), and the second polarization controller (12) is arranged between the beam splitter (2) and the single-sideband modulator (13).
7. The high-frequency dynamic strain measurement device based on the chaotic brillouin phase spectrum according to claim 1, further comprising a real-time digital oscilloscope (11) for acquiring phase shift information demodulated by the IQ demodulator.
8. A high-frequency dynamic strain measurement method based on a chaotic Brillouin phase spectrum, which adopts the high-frequency dynamic strain measurement device based on the chaotic Brillouin phase spectrum according to claim 1, is characterized in that the modulation frequency of the high-speed electro-optical modulator (4) is adjusted by comparing a Brillouin gain spectrum and a Brillouin absorption spectrum in the absence of strain, so that the central peak positions of the Brillouin gain spectrum and the Brillouin absorption spectrum are kept unchanged.
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