CN116592986A - Optical fiber distributed acoustic wave sensing device with adjustable dynamic strain range - Google Patents
Optical fiber distributed acoustic wave sensing device with adjustable dynamic strain range Download PDFInfo
- Publication number
- CN116592986A CN116592986A CN202310635322.2A CN202310635322A CN116592986A CN 116592986 A CN116592986 A CN 116592986A CN 202310635322 A CN202310635322 A CN 202310635322A CN 116592986 A CN116592986 A CN 116592986A
- Authority
- CN
- China
- Prior art keywords
- optical fiber
- light
- sideband
- pulse
- lfm
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Pending
Links
- 239000013307 optical fiber Substances 0.000 title claims abstract description 87
- 230000003287 optical effect Effects 0.000 claims abstract description 38
- 238000005259 measurement Methods 0.000 claims abstract description 22
- 238000000034 method Methods 0.000 claims abstract description 21
- 238000012545 processing Methods 0.000 claims abstract description 18
- 230000010287 polarization Effects 0.000 claims abstract description 14
- 239000000835 fiber Substances 0.000 claims description 34
- 206010070834 Sensitisation Diseases 0.000 claims description 27
- 230000008313 sensitization Effects 0.000 claims description 27
- 230000001427 coherent effect Effects 0.000 claims description 13
- 238000001914 filtration Methods 0.000 claims description 10
- 239000004793 Polystyrene Substances 0.000 claims description 7
- 238000001208 nuclear magnetic resonance pulse sequence Methods 0.000 claims description 7
- 229920002223 polystyrene Polymers 0.000 claims description 7
- 238000004364 calculation method Methods 0.000 claims description 5
- 238000005314 correlation function Methods 0.000 claims description 5
- 230000011218 segmentation Effects 0.000 claims description 5
- 230000002269 spontaneous effect Effects 0.000 claims description 4
- 229910052691 Erbium Inorganic materials 0.000 claims description 3
- UYAHIZSMUZPPFV-UHFFFAOYSA-N erbium Chemical compound [Er] UYAHIZSMUZPPFV-UHFFFAOYSA-N 0.000 claims description 3
- 230000035945 sensitivity Effects 0.000 abstract description 4
- 238000001514 detection method Methods 0.000 description 8
- 230000008901 benefit Effects 0.000 description 7
- 230000008859 change Effects 0.000 description 7
- 230000009977 dual effect Effects 0.000 description 6
- 238000005516 engineering process Methods 0.000 description 5
- 239000000523 sample Substances 0.000 description 5
- 239000000919 ceramic Substances 0.000 description 4
- 238000010586 diagram Methods 0.000 description 4
- 238000005070 sampling Methods 0.000 description 4
- 238000012544 monitoring process Methods 0.000 description 3
- 230000008569 process Effects 0.000 description 3
- 101150097208 MZM1 gene Proteins 0.000 description 2
- 238000004458 analytical method Methods 0.000 description 2
- 238000004891 communication Methods 0.000 description 2
- 238000010219 correlation analysis Methods 0.000 description 2
- 238000002474 experimental method Methods 0.000 description 2
- 230000006870 function Effects 0.000 description 2
- 238000011084 recovery Methods 0.000 description 2
- 238000004088 simulation Methods 0.000 description 2
- 238000001228 spectrum Methods 0.000 description 2
- 238000013519 translation Methods 0.000 description 2
- 230000009471 action Effects 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 238000004422 calculation algorithm Methods 0.000 description 1
- 238000006243 chemical reaction Methods 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 230000007613 environmental effect Effects 0.000 description 1
- 238000000605 extraction Methods 0.000 description 1
- 238000009532 heart rate measurement Methods 0.000 description 1
- 238000009413 insulation Methods 0.000 description 1
- 238000011835 investigation Methods 0.000 description 1
- 239000011159 matrix material Substances 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 238000000253 optical time-domain reflectometry Methods 0.000 description 1
- 230000010363 phase shift Effects 0.000 description 1
- 230000005855 radiation Effects 0.000 description 1
- 230000004044 response Effects 0.000 description 1
- 239000004065 semiconductor Substances 0.000 description 1
- 230000003068 static effect Effects 0.000 description 1
- 238000006467 substitution reaction Methods 0.000 description 1
- 238000004804 winding Methods 0.000 description 1
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01H—MEASUREMENT OF MECHANICAL VIBRATIONS OR ULTRASONIC, SONIC OR INFRASONIC WAVES
- G01H9/00—Measuring mechanical vibrations or ultrasonic, sonic or infrasonic waves by using radiation-sensitive means, e.g. optical means
- G01H9/004—Measuring mechanical vibrations or ultrasonic, sonic or infrasonic waves by using radiation-sensitive means, e.g. optical means using fibre optic sensors
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02A—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
- Y02A90/00—Technologies having an indirect contribution to adaptation to climate change
- Y02A90/10—Information and communication technologies [ICT] supporting adaptation to climate change, e.g. for weather forecasting or climate simulation
Landscapes
- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Length Measuring Devices By Optical Means (AREA)
Abstract
The invention belongs to the technical field of optical fiber distributed sensing, and particularly relates to an optical fiber distributed acoustic wave sensing device and method with an adjustable dynamic strain range. The laser emitted by the laser in the device is divided into two beams by the beam splitter, one beam is modulated into heterogeneous multi-sideband LFM pulse light with different frequency modulation bandwidths after passing through the LFM pulse generating module, the heterogeneous multi-sideband LFM pulse light enters the sensing optical fiber through the optical circulator, backward Rayleigh scattered light is generated in the sensing optical fiber and returns to the optical circulator and then enters the light combiner, the other beam is used as reference light, enters the light combiner after passing through the polarization controller and interferes with the backward Rayleigh scattered light, the interference signal is detected by the balance detector and then is sent to the signal acquisition and processing system, and the local correlation of the time domain signal obtained by continuous measurement is calculated to obtain the local time shift and the strain along the optical fiber. The invention has simple structure, high sensitivity and easy realization.
Description
Technical Field
The invention belongs to the technical field of optical fiber distributed sensing, and particularly relates to an optical fiber distributed acoustic wave sensing device with an adjustable dynamic strain range, which can realize sensing measurement of weak sound/vibration events with different dynamic ranges.
Background
Optical time domain reflectometer based on phase sensitivityThe optical fiber distributed acoustic wave sensing (DAS) system can realize quantitative waveform recovery of acoustic/vibration signals at positions along an optical fiber link, has the advantages of electromagnetic interference resistance, severe environment resistance and the like, and has remarkable advantages and application prospects in heavy infrastructures such as seismic wave monitoring, oil and gas resource exploration, railway traffic operation monitoring and the like. However, since the acoustic/vibration signal to be measured is modulated into an optical phase, the phase information demodulated by the DAS tends to be entangled in [ -pi, pi]In between, the phase unwrapping algorithm is typically only effective when the absolute value of the phase change between adjacent tracks is less than pi, and simultaneous measurements for different dynamic range events will be constrained. Furthermore, since the signal typically detected by DAS is generally relatively weak for minute dynamic strain events, further investigation is required for dynamic strain measurement of different dynamic range minute strain events in complex environments.
Linear Frequency Modulation (LFM) is a spread spectrum modulation technique that combines the advantages of continuous and pulsed waveforms, and generally analyzes rayleigh interference patterns from a time domain perspective, which can be broadly divided into three categories. The first kind is scanned by sequentiallyTo achieve a static measurement that is very sensitive to refractive index changes. For example, in 2015, L.Zhou et al have compared different laser frequenciesThe strain of the optical fiber is detected by the signal mode, and the vibration of the optical fiber is detected from the signal with any laser frequency, so that 490n epsilon and 1kHz vibration measurement [ Zhou L, et al, IEEE Photonics technologies, lett.,2015,27 (17): 1884-1887 are realized.]. The second class of systems can be simplified by using a single LFM light pulse as the probe pulse, with the shift in the rayleigh interference pattern directly reflecting the strain change characteristics. For example, J.Zhang et al use frequency modulated pulsing to achieve dynamic strain signal extraction with a peak-to-peak 130 [ mu ] [ epsilon ] by injecting LFM pulses into the fiber [ Zhang J.et al, opt. Express,2019,27 (20): 27580-27591.]. The H.D. Bhatta et al eliminates large noise spikes in the demodulation results by median filtering, and utilizes an LFM pulse detection system to achieve sinusoidal strain waveform measurement of 1190 [ mu ] epsilon peak-to-peak on the basis of step-by-step superimposed strain [ Bhatta H D, et al, J.light.technology, 2019,37 (18): 4888-4895.]. The third type is another analysis method based on LFM pulse, and the measurement of dynamic strain can be realized by performing correlation analysis along the wavelength domain by adopting a wavelength scanning method. For example, in 2018, S.Liehr et al proposed that wavelength-scanning coherent optical time domain reflectometry techniques to extract coherent Rayleigh scattered time domain signals along the laser frequency axis for correlation analysis achieved measurement of dynamic strain [ Liehr S, et al, opt.express,2018,26 (8): 10573-10588.]。
The above studies have been mainly conducted with respect to strain of a single amplitude, which is concerned only with dynamic strain resolution or only with the dynamic range of strain. However, in practical applications, the strain ranges of the optical fibers caused by acoustic/vibration events along the optical fibers may be quite different, so that in order to ensure undistorted recovery of waveforms, both high-sensitivity strain resolution and large dynamic range are required, and therefore, it is necessary to propose an optical fiber distributed acoustic wave sensing technology with an adjustable dynamic strain range to balance the requirements of the two aspects.
Disclosure of Invention
The invention overcomes the defects existing in the prior art, and provides the optical fiber distributed acoustic wave sensing device with adjustable dynamic strain range for solving the actual application requirement and the problem that the measurement of different dynamic strain events cannot be realized simultaneously in the prior art.
In order to solve the technical problems, the invention adopts the following technical scheme: the optical fiber distributed acoustic wave sensing device with the adjustable dynamic strain range comprises a laser, a beam splitter, an LFM pulse generation module, an erbium-doped optical fiber amplifier, a filter, a circulator, a sensitization structure sensing optical fiber, a polarization controller, a light combiner, a balance detector and a signal acquisition and processing system;
the laser emitted by the laser is divided into two beams by a beam splitter, one beam is modulated into heterogeneous multi-sideband LFM pulse light with different frequency modulation bandwidths after passing through an LFM pulse generating module, and the start and stop frequencies of each LFM sideband of the heterogeneous multi-sideband LFM pulse light are not overlapped; the heterogeneous multi-sideband LFM pulse light enters a sensitization structure sensing optical fiber through an optical circulator after passing through an erbium-doped optical fiber amplifier and a filter, backward Rayleigh scattered light generated in the sensitization structure sensing optical fiber returns to the optical circulator and enters a light combiner, and the other beam of the heterogeneous multi-sideband LFM pulse light is used as reference light and enters the light combiner to interfere with the backward Rayleigh scattered light after passing through a polarization controller, an interference signal is detected by a balance detector and then sent to a signal acquisition and processing system, and the signal acquisition and processing system is used for calculating the local correlation of time domain signals obtained by continuous measurement twice to obtain local time shift delta t along the optical fiber and calculating the strain according to the local time shift delta t.
The specific structure of the sensitization structure sensing optical fiber is as follows: the common single-mode fiber is wrapped by using a polystyrene film and spirally wound on the corrugated thin tube.
The specific formula for calculating the local time shift delta t along the optical fiber by the signal acquisition and processing system is as follows:
Δt＝max(corrcoef[E i (t-w T :t+w T ),E i+1 (t-w T :t+w T )])；
where corrcoef () represents the cross correlation function, E i (t-w T :t+w T ) And E is i+1 (t-w T :t+w T ) Representing backward coherent Rayleigh scattering time domain signals E generated by ith pulse and i+1th pulse respectively i (t) and E i+1 (t) window data obtained by point-by-point sliding window segmentation.
The formula for calculating the stress by the signal acquisition and processing system is as follows:
wherein epsilon represents the microstrain to be measured, K ε And represents the strain coefficient, mu is the frequency modulation slope of heterogeneous multi-sideband LFM pulse light, and f represents the laser frequency.
The erbium-doped fiber amplifier is used for amplifying heterogeneous multi-sideband LFM pulse light, and the optical filter is used for filtering spontaneous radiation noise of the erbium-doped fiber amplifier.
The LFM pulse generation module includes: an arbitrary waveform generator, a double parallel Mach-Zehnder modulator, a coupler, and a bias controller;
after one beam of light split by the optical splitter enters the double parallel Mach-Zehnder modulator, the light is split into two beams by the coupler, wherein one beam feeds back the intensity of output light to the double parallel Mach-Zehnder modulator by the bias controller, and the other beam outputs the intensity of output light to the erbium-doped fiber amplifier; orthogonal single-sideband digital LFM pulse sequences output by the I and Q channels of the arbitrary waveform generator are connected with two radio frequency ports of the double parallel Mach-Zehnder modulator.
The coupler is a 99:1 optical fiber coupler, and 1% output end of the coupler is connected with the bias voltage controller;
the pulse time width of the orthogonal single-sideband digital LFM pulse sequence output by the I and Q two channels of the arbitrary waveform generator is 100ns, the pulse repetition frequency is 100kHz, and the linear frequency modulation range is from 480MHz to 520MHz.
The laser is a narrow linewidth laser, the beam splitter is a 10:90 optical fiber coupler, and the beam combiner is a 50:50 optical fiber coupler.
In addition, the invention also provides a fiber distributed acoustic wave sensing method with adjustable dynamic strain range, which is realized by adopting the device and comprises the following steps:
s1, acquiring an electric signal converted by a balance detector after receiving an interference signal;
s2, separating different sideband signals by utilizing digital bandpass filtering, and then calculating correlation of time domain signals obtained by two continuous measurements by adopting a sliding window cross-correlation method to obtain local time shift delta t along the optical fiber; the calculation formula is as follows:
Δt＝max(corrcoef[E i (t-w T :t+w T ),E i+1 (t-w T :t+w T )])；
where corrcoef () represents the cross correlation function, E i (t-w T :t+w T ) And E is i+1 (t-w T :t+w T ) Representing backward coherent Rayleigh scattering time domain signals E generated by ith pulse and i+1th pulse respectively i (t) and E i+1 (t) window data obtained by point-by-point sliding window segmentation;
s3, calculating to obtain the stress, wherein the calculation formula is as follows:
wherein epsilon represents the microstrain to be measured, K ε And represents the strain coefficient, mu is the frequency modulation slope of heterogeneous multi-sideband LFM pulse light, and f represents the laser frequency.
Compared with the prior art, the invention has the following beneficial effects:
(1) The invention adopts a digital modulation method to modulate and generate heterogeneous multi-sideband LFM pulse light with different frequency modulation bandwidths in a single pulse, and the start and stop frequencies of each LFM sideband are not overlapped. According to the inverse proportion characteristic between the frequency modulation bandwidth and the envelope translation quantity of the coherent time domain signal, the simultaneous measurement of different dynamic strain range events is realized by utilizing a sliding window cross-correlation method through digital band-pass filtering, and the method has the advantage of high reliability.
(2) The invention adopts the corrugated thin tube sensitization optical fiber, can enhance the pickup capability of weak sound/vibration signals, realizes effective sensitization to common single-mode optical fibers, and has the advantage of high detection sensitivity. The problem that the traditional standard single-mode fiber for communication has limited collection capacity for weak sound/vibration signals is solved, and the detection capacity of the DAS is improved.
(3) The scheme of the multi-isomerism sideband modem with the sensitization structure sensing optical fiber combined with the LFM pulse effectively solves the problem that the high sensitivity strain resolution and the large dynamic range are difficult to balance during distributed acoustic/vibration sensing measurement, and the system device has low complexity and simple operation and is easy to realize.
Drawings
FIG. 1 is a schematic diagram of a fiber optic distributed acoustic wave sensor with an adjustable dynamic strain range according to an embodiment of the present invention;
FIG. 2 is a schematic diagram of a sensing fiber with a sensitization structure according to an embodiment of the present invention;
FIG. 3 is a schematic diagram of optical pulse modulation of a heterogeneous multi-sideband LFM sideband employed in an embodiment of the present invention;
FIG. 4 shows simulation results of light intensity spectrum widths for different modulation bandwidths according to an embodiment of the present invention, wherein (a) is 40MHz; (b) 200MHz.
In the figure: 11 is a laser, 12 is a beam splitter, 13 is an LFM pulse generation module, 131 is an arbitrary waveform generator, 132 is a double parallel Mach-Zehnder modulator, 133 is a coupler, 134 is a bias controller, 14 is an erbium-doped optical fiber amplifier, 15 is a filter, 16 is a circulator, 17 is a sensing optical fiber with a sensitization structure, 171 is a common single-mode optical fiber, 172 is a polystyrene film, 173 is a corrugated thin tube, 18 is a piezoelectric ceramic tube, 19 is an arbitrary waveform generator, 20 is a polarization controller, 21 is a light combiner, 22 is a balance detector, and 23 is a signal acquisition and processing system.
Detailed Description
For the purpose of making the objects, technical solutions and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below, and it is apparent that the described embodiments are some embodiments of the present invention, but not all embodiments; all other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
Example 1
As shown in fig. 1, a first embodiment of the present invention provides an optical fiber distributed acoustic wave sensing device with an adjustable dynamic strain range, which includes a laser 11, an optical splitter 12, an LFM pulse generating module 13, an erbium-doped fiber amplifier 14, a filter 15, a circulator 16, a sensing fiber 17 with a sensitization structure, a polarization controller 20, an optical combiner 21, a balance detector 22, and a signal collecting and processing system 23; the laser emitted by the laser 11 is divided into two beams by the beam splitter 12, one beam is modulated into heterogeneous multi-sideband LFM pulse light with different frequency modulation bandwidths after passing through the LFM pulse generating module 13, and the start and stop frequencies of each LFM sideband of the heterogeneous multi-sideband LFM pulse light are not overlapped; the heterogeneous multi-sideband LFM pulse light enters a sensitization structure sensing optical fiber 17 through an optical circulator 16 after passing through an erbium-doped optical fiber amplifier 14 and a filter 15, backward Rayleigh scattered light generated in the sensitization structure sensing optical fiber 17 returns to the optical circulator 16 and enters a light combiner 21, the other beam of the heterogeneous multi-sideband LFM pulse light is used as reference light and enters the light combiner 21 to interfere with the backward Rayleigh scattered light after passing through a polarization controller 20, an interference signal is detected by a balance detector 22 and then is sent to a signal acquisition and processing system 23, and the signal acquisition and processing system 23 is used for calculating the local correlation of time domain signals obtained by continuous measurement, obtaining local time shift delta t along the optical fiber and calculating the strain according to the local time shift delta t.
Specifically, as shown in fig. 1, in this embodiment, the LFM pulse generating module 13 includes: an arbitrary waveform generator 131, a double parallel Mach-Zehnder modulator 132, a coupler 133, and a bias controller 134; after one beam of light split by the splitter 12 enters the dual parallel mach-zehnder modulator 132, the beam of light is split into two beams by the coupler 133, one beam of light is fed back to the dual parallel mach-zehnder modulator 132 by the bias controller 134, and the other beam of light is output to the erbium-doped fiber amplifier 14; the quadrature single-sideband digital LFM pulse trains output by the I and Q channels of the arbitrary waveform generator 131 are connected to two radio frequency ports of the dual parallel mach-zehnder modulator 132.
Specifically, in this embodiment, the coupler 133 is a 99:1 fiber coupler, and its 1% output end is connected to the bias controller 134; the orthogonal single-sideband digital LFM pulse sequences output by the I and Q channels of the arbitrary waveform generator 131 have a pulse time width of 100ns, a pulse repetition frequency of 100kHz, and a linear frequency modulation range from 480MHz to 520MHz.
Specifically, in this embodiment, the erbium-doped fiber amplifier 14 is configured to amplify heterogeneous multi-sideband LFM pulse light, and the optical filter 15 is configured to filter out spontaneous emission noise of the erbium-doped fiber amplifier 14.
In this embodiment, the laser 11 is a narrow linewidth laser, the beam splitter 12 may be a 90:10 polarization maintaining coupler, and the beam combiner 21 is a 50:50 fiber coupler.
Specifically, in this embodiment, the specific structure of the sensing fiber 17 with a sensitization structure is: a common single mode optical fiber 171 is wrapped with a polystyrene film 172 and spirally wound on a corrugated thin tube 173 as shown in fig. 2. When a micro-strain event acts on the sensing optical fiber 17 with the sensitization structure, the sensing optical fiber 17 with the sensitization structure is forced to axially displace, so that the back Rayleigh scattered light in the optical fiber is subjected to phase modulation.
The working process of the optical fiber distributed acoustic wave sensing device with the adjustable dynamic strain range in the embodiment is as follows.
(1) The relevant light emitted by the laser 11 is split into two parts by the beam splitter 12, wherein 90% of the parts enter the LFM pulse generating module to be modulated into LFM pulses, and 10% of the parts are used as reference light. In the LEM pulse generating module 13, the dual-channel arbitrary waveform generator 131 generates a single-sideband digital LFM pulse sequence with a pulse time width of 100ns, a pulse repetition frequency of 100kHz, and a linear frequency modulation range of 480MHz to 520MHz, and the two modulated pulse sequences are loaded into the dual parallel mach-zehnder modulator 132 to be modulated to generate a heterogeneous LFM multi-band detection pulse optical signal. The intensity modulators of both the I and Q branches are biased to zero and the phase shifter is biased to the quadrature point using bias controller 134. The 1% port of coupler 133 is connected to bias controller 134 to feedback the intensity information of the output light, 99% of which is the output of the heterogeneous LFM polygonal-band light pulse. Based on the digital I/Q modulator characteristics of the broadband, a plurality of continuous sweep modulations with different slopes are generated within a single probe light pulse, a schematic diagram of which is shown in fig. 3. Referring to fig. 4, when the pulse width is 100ns and the chirp bandwidth is 40MHz and 200MHz respectively, the numerical simulation result shows that the full width at half maximum FWHM of the light intensity signal received by the coherent detection is 45.2MHz and 225.7MHz respectively, which are consistent with the theoretical analysis result.
(2) The heterogeneous LFM polygonal-band optical pulses are amplified by the erbium-doped fiber amplifier 14 and the spontaneous emission noise of the erbium-doped fiber amplifier 14 is filtered out using the optical filter 15.
(3) The shaped and amplified heterogeneous LFM polygonal band light pulse enters a sensing optical fiber 17 of the sensitization structure through a light circulator 16, and then back Rayleigh scattered light is generated. The sensing optical fiber 17 is formed by wrapping a common single-mode optical fiber 171 with a polystyrene film 172 and spirally winding the film on a corrugated thin tube 173; as shown in fig. 2, when the sensing optical fiber 17 of the sensitization structure is under the action of sound wave, the polystyrene film 172 and the corrugated thin tube 173 can enlarge the sound field receiving surface, so as to drive the micro deformation of the short optical fiber. In the experiment, the sensitization structure sensing optical fiber 17 is placed in a self-made sound insulation box, the influence of environmental noise can be avoided, the piezoelectric ceramic tube 18 is driven by the signal generator 19, the acoustic vibration signal can be simulated, and the acoustic wave sensing is realized through the device. In a specific measurement, the entire sensing fiber 17 of the sensitization structure is disposed at the measured position.
(4) The back rayleigh scattered light and the reference light are injected into the combiner 21 and interfere, and the polarization controller 20 in the reference light path is used to adjust the polarization states of the two light paths so as to match each other. The interference light signal is detected by the balanced detector 22 and sent to the signal acquisition and processing system 23, the bandwidth of the balanced detector 22 ranges from 30kHz to 1.6GHz, the signal acquisition and processing system 23 further processes the acquired signal with a sampling rate set to 5GSa/s per channel.
Specifically, compared with a direct detection method relying on interference between scattered light and a scattering body, in this embodiment, a heterodyne interference demodulation structure is formed by the polarization controller 20 and the light combiner 21, the reference light and the backward rayleigh scattered light are coherently enhanced in signal intensity, and the balanced detector 22 is used for detecting the optical signal, so as to eliminate common mode noise in the detected optical signal. The internal circuit structure of the balance detector 22 includes two rf monitoring outputs that can independently monitor each photodetector in the experiment. The detector structure has the advantages that common mode noise or common mode imbalance can be eliminated, so that the detector is suitable for detecting micro signals, and the dynamic range requirement of an analog-to-digital conversion device can be reduced.
Specifically, in this embodiment, the input ends of the laser 11 and the optical splitter 12 are connected through a single-mode fiber jumper, 90% output ends of the optical splitter 12 are respectively connected with input ends of the couplers 133 of the double parallel mach-zehnder modulators 132 and 99:1 in sequence through single-mode fiber jumpers, and 1% output ends of the couplers 133 are connected with input ends of the bias controller 134 through single-mode fiber jumpers. The input end of the bias controller 134 is connected with the dual-parallel Mach-Zehnder modulator 132 through a radio frequency connection line to provide feedback, and the I path and the Q path of the arbitrary waveform generator 131 are respectively connected with the dual-parallel Mach-Zehnder modulator 132 through the radio frequency connection line. The 99:1 coupler 133 has 99% output end connected with the erbium doped fiber amplifier 14, the filter 15 and the input end 1 of the optical circulator 16 in sequence through a single mode fiber jumper, and the output end 2 of the optical circulator 16 is connected with the sensing fiber 17 of the sensitization structure. The piezoelectric ceramic tube 18 is wound by the tail end sensitization structure sensing optical fiber 17 and is connected with the signal generator 19 through a radio frequency connecting wire. The 10% output end of the beam splitter 12 is connected with the input end of the polarization controller 20 through a single-mode fiber jumper, and the two input ends of the beam combiner 21 are respectively connected with the 3 port of the output end of the optical circulator 16 and the output end of the polarization controller 20 through a single-mode fiber jumper. The output end of the light combiner 21 is connected with the balance detector 22, and the balance detector 22 is sequentially connected with the signal acquisition and processing system 23 through a radio frequency connecting wire and is communicated with the RS232 connecting wire.
In this embodiment, a semiconductor laser with a wavelength of 1559.72nm and a linewidth of 3kHz with high stability is used as the external cavity laser source of the LFM pulse generating module for the laser 11. The LFM pulse generating module 13 further uses an input-output modulator for communication, namely a double parallel mach-zehnder modulator 132,also known as an I/Q modulator, may be used to generate the carrier suppressed LFM pulsed optical signal. The dual parallel mach-zehnder modulator 132 internally contains three mach-zehnder structures, wherein two sub-modulators MZM1 and MZM2 are nested on two arms of MZM3, the performance of these sub-modulators MZM1 and MZM2 are identical and the structure is symmetrical, and each sub-modulator has an independent radio frequency signal input terminal. In addition, the three modulators all have DC bias voltage input ports, can control respective working points and introduce corresponding phase shifts delta phi 1 、Δφ 2 And delta phi 3 。
The optical fiber distributed acoustic wave sensing principle with adjustable dynamic strain range according to the embodiment of the invention is described below.
The embodiments of the present invention use piezo-ceramic tubes 18 to simulate vibrations generated in a real environment, and use dual parallel mach-zehnder modulators 132 to generate heterogeneous LFM multi-band optical pulses with high side-mode rejection ratios. The chirp frequency is from f for the duration T of each pulse s Increase to f e In-phase signal V I (t) and quadrature-phase signal V Q (t) are all linearly modulated radio frequency signals, which can be written as:
v in D For modulating the amplitude of the voltage signal by the double parallel mach-zehnder modulator 132, μ= (f) e -f s ) T is the frequency modulation slope of the LFM pulse and rect (. Let the continuous light frequency emitted by the laser 11 with narrow linewidth be f 0 The heterogeneous LFM polygonal band light pulse outputs a light field E out Can be written as:
in E 0 For amplitude at the input of modulator 132, V π The voltage required to change the output optical power from minimum to maximum. When V is D And V π Satisfy V D /V π <<At pi, the above formula can be linearized to:
at the sampling time t, the heterogeneous LFM multi-band light pulse injected into the optical fiber is scattered by a large number of scattering points to generate back Rayleigh scattered light. Since the pulse has a certain width, the back rayleigh scattering light field returned to the receiving end is the mutual superposition of the back rayleigh scattering light generated by the scattering points covered by the half pulse space length. Dividing the pulse space of the whole LFM pulse light corresponding to the optical fiber position into a series of discrete scattering units with equal length according to a one-dimensional impulse response model by a single frequency component, and marking as [ z ] 1 ,z 2 ,...z n ]The light frequency of the corresponding discrete scattering element is denoted as f 1 ,f 2 ,...f n ]. Let the elapsed time tau i The light field expression of the back Rayleigh scattered light returned to the receiving end is as follows:
wherein ρ is i The scattering coefficient corresponding to the i-th discrete scattering element is represented, and α represents the attenuation coefficient of the optical fiber. Time delay τ from initial position to ith scattering element i And the corresponding distance satisfies z i ＝cτ i And/2 n, c represents the speed of light in vacuum.
Because the system adopts a coherent detection structure, the backward Rayleigh scattered light of each discrete scattering unit interferes with the local reference light, and the alternating current component and the phase difference phi output by the detector 22 are balanced i The method comprises the following steps of:
wherein A is LO Indicating the amplitude of the reference light,the common phase, which represents the current position of the probe pulse, is a constant for a particular position.
According to the document [ Koyamada Y, et al journal of Lightwave Technology,2009,27 (9): 1142-1146 ], the relation between the disturbance-induced laser frequency (wavelength) offset Δf and the microstrain ε to be measured is:
wherein K is ε Approximately-0.78 denotes the strain coefficient, and f denotes the laser frequency. From equation (10), the offset Δf of the laser frequency (wavelength) caused by the disturbance can be compensated by the horizontal shift time Δt of the coherent rayleigh scattering time domain signal, and the ratio of Δf and Δt is the frequency modulation slope μ of the LFM pulse. Thus, the relationship between the microstrain ε to be measured and the local time shift Δt is as follows:
the above is based on LFM pulseMeasurement principle of the sensor. If a dynamic strain is applied to a certain position z of the optical fiber to cause a change in the optical path difference, the local time domain signal E (t) at that position will be horizontally shifted, and the corresponding shift change Δf can be used to compensate for the change in the optical path difference. By calculating the local correlation of the time domain signals obtained by two consecutive measurements, it is possible to determine the optical fiber along which two different time domain signals are alongA change in the local time shift Δt. The expansion of the dynamic strain measurement range can be realized by separating the signals of a plurality of sweep bandwidths contained in a single detection light pulse through digital band-pass filtering.
The time shift deltat in the invention is usually estimated by using a sliding window cross-correlation method on subsequences of two adjacent frames of coherent time domain signals, and the value of deltat can be obtained by recording the track of the correlation peak. The specific operation process is as follows:
(1) Recording backward coherent Rayleigh scattering time domain signal E of pulse successively injected into optical fiber i (t) and E i+1 (t), wherein i represents the i-th pulse excited backward rayleigh scattering signal;
(2) Pair E i (t) and E i+1 (t) obtaining window data E after performing point-by-point sliding window segmentation respectively i (t-w T :t+w T ) And E is i+1 (t-w T :t+w T ). Wherein, the value range of t is { w } T ,N/f osc -w T N represents the number of sampling points contained in one pulse period, f osc Represents the sampling rate, w, of the oscilloscope T Representing and pulse time width, t-w T :t+w T Representing traversals from t-w T To t+w T Is a single-phase signal. Through the above operation, for E i (t) and E i+1 (t) after the above operations are performed, (N-2 w) is obtained respectively T ×f osc ) Window data;
(3) Pair E i (t) and E i+1 (N-2 w of (t) T ×f osc ) Performing cross-correlation operation on the window data to obtain a cross-correlation coefficient matrix, and recording a time delay amount corresponding to the maximum cross-correlation coefficient, wherein the time delay amount is the local time shift delta t of two different time domain signals along the optical fiber, and the expression can be written as follows:
Δt＝max(corrcoef[E i (t-w T :t+w T ),E i+1 (t-w T :t+w T )]) (13)
where corrcoef () represents a cross correlation function for calculating the correlation between two variables, and returning its correlation coefficient and index of the subscript, max () represents a maximum function for finding the two variables with the greatest correlation and returning their index to obtain Δt corresponding to the index.
(4) Substituting the value of Deltat into the formula (11) to obtain the micro-strain epsilon to be detected.
In a word, the invention separates different sideband signals through digital band-pass filtering and adopts a sliding window cross-correlation method to invert the micro-strain size, and the dynamic range expansion can be realized by fully utilizing the sensitivity difference of different sidebands.
Example two
The second embodiment of the invention provides an optical fiber distributed acoustic wave sensing method with an adjustable dynamic strain range, which is realized by adopting the device in the first embodiment, and comprises the following steps:
s1, opening a device, and generating heterogeneous multi-sideband LFM pulse optical signals through an LFM pulse generation module;
s2, acquiring an electric signal converted by the balance detector after receiving the interference signal;
s3, separating different sideband signals by utilizing digital bandpass filtering, and then calculating correlation of time domain signals obtained by two continuous measurements by adopting a sliding window cross-correlation method to obtain local time shift delta t along the optical fiber; the calculation formula is the above formula (13).
And S4, calculating the strain through the formula (12).
Specifically, in the step S1, the heterogeneous LFM multi-band probe pulse optical signal generates a plurality of continuous sweep frequency modulations with different slopes in a single probe optical pulse, and the modulation parameters include a modulation function, a modulation depth, and the like to realize a high carrier rejection ratio. The intensity modulators of the I and Q branches of the digital I/Q modulator are biased to zero, the phase shifter is biased to the quadrature point, and the state of the phase shifter is based on the state of the output light, and a bias voltage is fed back to the digital I/Q modulator by a bias controller to keep the light output state stable.
In summary, the invention discloses an optical fiber distributed acoustic wave sensing device and method with an adjustable dynamic strain range. According to the invention, a Linear Frequency Modulation (LFM) technology is introduced into a DAS system, and the distributed sensing measurement with adjustable dynamic strain range is realized by combining sensing optical fibers of a sensitization structure with heterogeneous multi-sideband modems of LFM pulses according to the problem that tiny strain events of different dynamic ranges are difficult to sense and measure simultaneously. Specifically, a corrugated thin tube and a polystyrene film sensitized single mode fiber are used as a sensitization structure sensing optical fiber sensor to enhance the pickup effect of weak signals. A dynamic range adjustable demodulator based on LFM pulse is built, flexible heterogeneous polygonal band modulated LFM pulse light is generated by digital modulation, and multi-modulation side bands with different frequency modulation bandwidths are generated in a single pulse to sense according to the inverse proportion characteristic of frequency modulation bandwidth and coherent time domain signal envelope translation. And separating different sideband signals by using digital bandpass filtering and inverting the micro-strain value along the optical fiber by adopting a sliding window cross-correlation method.
Finally, it should be noted that: the above embodiments are only for illustrating the technical solution of the present invention, and not for limiting the same; although the invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical scheme described in the foregoing embodiments can be modified or some or all of the technical features thereof can be replaced by equivalents; such modifications and substitutions do not depart from the spirit of the invention.
Claims (9)
1. The optical fiber distributed acoustic wave sensing device with the adjustable dynamic strain range is characterized by comprising a laser (11), a beam splitter (12), an LFM pulse generation module (13), an erbium-doped optical fiber amplifier (14), a filter (15), a circulator (16), a sensitization structure sensing optical fiber (17), a polarization controller (20), a beam combiner (21), a balance detector (22) and a signal acquisition and processing system (23);
the laser emitted by the laser (11) is divided into two beams by a beam splitter (12), one beam is modulated into heterogeneous multi-sideband LFM pulse light with different frequency modulation bandwidths by an LFM pulse generating module (13), and the start and stop frequencies of each LFM sideband of the heterogeneous multi-sideband LFM pulse light are not overlapped; the heterogeneous multi-sideband LFM pulse light enters a sensitization structure sensing optical fiber (17) through an optical circulator (16) after passing through an erbium-doped optical fiber amplifier (14) and a filter (15), backward Rayleigh scattered light generated in the sensitization structure sensing optical fiber (17) returns to the optical circulator (16) and then enters a light combiner (21), the other beam of the heterogeneous multi-sideband LFM pulse light is used as reference light and enters the light combiner (21) to interfere with the backward Rayleigh scattered light after passing through a polarization controller (20), an interference signal is detected by a balance detector (22) and then is sent to a signal acquisition and processing system (23), and the signal acquisition and processing system (23) is used for calculating local correlation of time domain signals obtained by continuous measurement twice to obtain local time shift delta t along the optical fiber and calculating the strain according to the local time shift delta t.
2. The optical fiber distributed acoustic wave sensing device with adjustable dynamic strain range according to claim 1, wherein the specific structure of the sensitization structure sensing optical fiber (17) is as follows: a polystyrene film (172) is used to wrap a common single-mode fiber (171) and is spirally wound on a corrugated thin tube (173).
3. The optical fiber distributed acoustic wave sensing device with adjustable dynamic strain range according to claim 1, wherein the specific formula of calculating the local time shift Δt along the optical fiber by the signal acquisition and processing system (23) is:
Δt＝max(corrcoef[E i (t-w T :t+w T ),E i+1 (t-w T :t+w T )])；
where corrcoef () represents the cross correlation function, E i (t-w T :t+w T ) And E is i+1 (t-w T :t+w T ) Representing backward coherent Rayleigh scattering time domain signals E generated by ith pulse and i+1th pulse respectively i (t) and E i+1 (t) window data obtained by point-by-point sliding window segmentation.
4. The optical fiber distributed acoustic wave sensing device with adjustable dynamic strain range according to claim 1, wherein the formula for calculating the stress by the signal acquisition and processing system (23) is:
wherein epsilon represents the microstrain to be measured, K ε And represents the strain coefficient, mu is the frequency modulation slope of heterogeneous multi-sideband LFM pulse light, and f represents the laser frequency.
5. A dynamic strain range adjustable optical fiber distributed acoustic wave sensing device according to claim 1, characterized in that the erbium doped fiber amplifier (15) is used for amplifying heterogeneous multi-sideband LFM pulse light, and the optical filter (15) is used for filtering out spontaneous emission noise of the erbium doped fiber amplifier (14).
6. A dynamic strain range adjustable fiber optic distributed acoustic wave sensing device according to claim 1, wherein the LFM pulse generating module (13) comprises: an arbitrary waveform generator (131), a double parallel Mach-Zehnder modulator (132), a coupler (133), a bias controller (134);
after one beam of light split by the optical splitter (12) enters the double parallel Mach-Zehnder modulator (132), the light is split into two beams by the coupler (133), one beam feeds back the intensity of output light to the double parallel Mach-Zehnder modulator (132) by the bias controller (134), and the other beam outputs to the erbium-doped fiber amplifier (14); orthogonal single-sideband digital LFM pulse sequences output by the I and Q channels of the arbitrary waveform generator (131) are connected with two radio frequency ports of the double parallel Mach-Zehnder modulator (132).
7. The optical fiber distributed acoustic wave sensing device with adjustable dynamic strain range according to claim 6, wherein the coupler (133) is a 99:1 optical fiber coupler, and 1% output end of the coupler is connected with the bias controller (134);
the orthogonal single-sideband digital LFM pulse sequences output by the I and Q channels of the arbitrary waveform generator (131) have a pulse time width of 100ns, a pulse repetition frequency of 100kHz and a linear frequency modulation range from 480MHz to 520MHz.
8. The optical fiber distributed acoustic wave sensing device with the adjustable dynamic strain range according to claim 1, wherein the laser (11) is a narrow linewidth laser, the optical splitter (12) is a 10:90 optical fiber coupler, and the optical combiner (21) is a 50:50 optical fiber coupler.
9. An optical fiber distributed acoustic wave sensing method with adjustable dynamic strain range, which is characterized by being realized by adopting the device as claimed in claim 1, comprising the following steps:
s1, acquiring an electric signal converted by a balance detector after receiving an interference signal;
s2, separating different sideband signals by utilizing digital bandpass filtering, and then calculating correlation of time domain signals obtained by two continuous measurements by adopting a sliding window cross-correlation method to obtain local time shift delta t along the optical fiber; the calculation formula is as follows:
Δt＝max(corrcoef[E i (t-w T :t+w T ),E i+1 (t-w T :t+w T )])；
where corrcoef () represents the cross correlation function, E i (t-w T :t+w T ) And E is i+1 (t-w T :t+w T ) Representing backward coherent Rayleigh scattering time domain signals E generated by ith pulse and i+1th pulse respectively i (t) and E i+1 (t) window data obtained by point-by-point sliding window segmentation;
s3, calculating to obtain the stress, wherein the calculation formula is as follows:
wherein epsilon represents the microstrain to be measured, K ε And represents the strain coefficient, mu is the frequency modulation slope of heterogeneous multi-sideband LFM pulse light, and f represents the laser frequency.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202310635322.2A CN116592986A (en) | 2023-05-31 | 2023-05-31 | Optical fiber distributed acoustic wave sensing device with adjustable dynamic strain range |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202310635322.2A CN116592986A (en) | 2023-05-31 | 2023-05-31 | Optical fiber distributed acoustic wave sensing device with adjustable dynamic strain range |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CN116592986A true CN116592986A (en) | 2023-08-15 |
Family
ID=87606112
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CN202310635322.2A Pending CN116592986A (en) | 2023-05-31 | 2023-05-31 | Optical fiber distributed acoustic wave sensing device with adjustable dynamic strain range |
Country Status (1)
| Country | Link |
|---|---|
| CN (1) | CN116592986A (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN116907627A (en) * | 2023-09-13 | 2023-10-20 | 之江实验室 | Optical path difference auxiliary-based large dynamic range distributed phase sensing method and device |
| CN117030000A (en) * | 2023-10-10 | 2023-11-10 | 之江实验室 | Distributed acoustic wave sensing polarization control system and polarization fading inhibition method |
-
2023
- 2023-05-31 CN CN202310635322.2A patent/CN116592986A/en active Pending
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN116907627A (en) * | 2023-09-13 | 2023-10-20 | 之江实验室 | Optical path difference auxiliary-based large dynamic range distributed phase sensing method and device |
| CN116907627B (en) * | 2023-09-13 | 2023-12-19 | 之江实验室 | Optical path difference auxiliary-based large dynamic range distributed phase sensing method and device |
| CN117030000A (en) * | 2023-10-10 | 2023-11-10 | 之江实验室 | Distributed acoustic wave sensing polarization control system and polarization fading inhibition method |
| CN117030000B (en) * | 2023-10-10 | 2024-01-12 | 之江实验室 | Distributed acoustic wave sensing polarization control system and polarization fading inhibition method |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| JP6698164B2 (en) | Optical frequency domain reflection method and system based on frequency synthesis | |
| RU2566606C1 (en) | Distributed fibre-optic sound wave detector | |
| CN116592986A (en) | Optical fiber distributed acoustic wave sensing device with adjustable dynamic strain range | |
| JP2019525181A (en) | Distributed optical fiber sensing system and vibration detection positioning method thereof | |
| CN108507662B (en) | Optical fiber distributed sensing method and device based on multi-wavelength double-optical pulse | |
| AU2020102296A4 (en) | A distributed optical fiber sensing system based on heterodyne detection technology | |
| CN105067103A (en) | Vibration detection device and method based on optical frequency domain reflectometer | |
| CN111157101A (en) | Weak grating array distributed vibration sensing system and method | |
| CN112697181B (en) | Phase-sensitive optical time domain reflection device and method based on frequency modulation | |
| Yan et al. | Forward transmission based ultra-long distributed vibration sensing with wide frequency response | |
| CN107907151A (en) | Phi OTDR and sensing method based on optical frequency modulation and direct detection | |
| CN108303626B (en) | Partial discharge ultrasonic measurement system and method based on distributed optical fiber sensing array | |
| CN113176075B (en) | Coherent and polarization fading suppression method for synchronous monitoring of loss and vibration | |
| CN113432701B (en) | Distributed optical fiber sensing method and device based on double pulses and sideband modulation | |
| CN106768277A (en) | A kind of distributed optical fiber vibration sensing device based on coherent phase detection | |
| CN109186739B (en) | Distributed optical fiber sensing device with multi-spatial resolution performance and method | |
| CN112697257A (en) | Non-fading multi-wavelength distributed acoustic wave sensing system and differential rotation vector superposition method | |
| CN113835002A (en) | Distributed detection method and detection system for partial discharge of power cable | |
| Yu et al. | Distributed optical fiber vibration sensing using phase-generated carrier demodulation algorithm | |
| Zhong et al. | Performance enhancement of phase-demodulation ϕ-OTDR using improved two-path DCM algorithm | |
| CN111912516A (en) | Phase-synchronized optical fiber distributed vibration measurement device, driver and method | |
| KR101889351B1 (en) | Spatially-selective brillouin distributed optical fiber sensor with increased effective sensing points and sensing method using brillouin scattering | |
| Xiao et al. | Frequency response enhancement of Φ-OTDR using interval-sweeping pulse equivalent sampling based on compressed sensing | |
| CN116907627B (en) | Optical path difference auxiliary-based large dynamic range distributed phase sensing method and device | |
| Xiong et al. | High performance CP-ΦOTDR utilizing the negative band |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PB01 | Publication | ||
| PB01 | Publication | ||
| SE01 | Entry into force of request for substantive examination | ||
| SE01 | Entry into force of request for substantive examination |