CN111637846B - Multipoint parallel high-speed chaotic Brillouin dynamic strain monitoring device and method - Google Patents
Multipoint parallel high-speed chaotic Brillouin dynamic strain monitoring device and method Download PDFInfo
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- CN111637846B CN111637846B CN202010455193.5A CN202010455193A CN111637846B CN 111637846 B CN111637846 B CN 111637846B CN 202010455193 A CN202010455193 A CN 202010455193A CN 111637846 B CN111637846 B CN 111637846B
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- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B11/00—Measuring arrangements characterised by the use of optical techniques
- G01B11/16—Measuring arrangements characterised by the use of optical techniques for measuring the deformation in a solid, e.g. optical strain gauge
- G01B11/161—Measuring arrangements characterised by the use of optical techniques for measuring the deformation in a solid, e.g. optical strain gauge by interferometric means
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B11/00—Measuring arrangements characterised by the use of optical techniques
- G01B11/16—Measuring arrangements characterised by the use of optical techniques for measuring the deformation in a solid, e.g. optical strain gauge
- G01B11/18—Measuring arrangements characterised by the use of optical techniques for measuring the deformation in a solid, e.g. optical strain gauge using photoelastic elements
Abstract
The invention relates to the field of distributed optical fiber sensing, and discloses a multi-point parallel high-speed chaotic Brillouin dynamic strain monitoring device and a method, wherein the device comprises a broadband chaotic laser source, the broadband chaotic laser source is used for outputting strong-period broadband chaotic laser, the broadband chaotic laser is divided into two beams through a beam splitter, and one beam is used as detection light and is incident to one end of a sensing optical fiber after sequentially passing through a single-side-band modulator, an erbium-doped optical fiber amplifier and a programmable optical delay generator; the other beam as pumping light is incident to the other end of the sensing optical fiber after sequentially passing through the semiconductor optical amplifier and the pulse optical amplifier; the optical signal output from the other end of the sensing optical fiber is detected by the photoelectric detector after Stokes light is filtered by the tunable optical filter, and the detection signal is acquired by the data acquisition unit and then is sent to the computer for data processing. The invention can realize multi-point parallel monitoring and can realize large-range dynamic strain real-time monitoring with long distance and high resolution.
Description
Technical Field
The invention relates to the field of distributed optical fiber sensing, in particular to a multipoint parallel high-speed Brillouin chaotic dynamic strain monitoring device and method.
Background
The rapid construction of large-scale civil infrastructures such as tunnels, bridges and oil and gas pipelines and the large-scale coverage of power grids and optical networks provide favorable conditions for the construction of smart cities and simultaneously provide higher requirements for sensing monitoring technologies. Distributed optical fiber sensing has emerged from numerous sensing monitoring technologies due to its small size, light weight, high temperature and pressure resistance, electromagnetic interference resistance, and other advantages. In order to further promote the sustainable development of society, avoid huge economic loss and guarantee the life and property safety of people, the demand of distributed optical fiber sensing on the dynamic monitoring technology is increasing day by day.
Distributed optical fiber sensing technologies are mainly classified into distributed optical fiber sensing based on rayleigh scattering, distributed optical fiber sensing based on raman scattering, and distributed optical fiber sensing based on brillouin scattering, according to the type of scattering. Compared with other two technologies, the sensing system based on the Brillouin scattering can realize simultaneous monitoring of temperature and strain information along the optical fiber, and has the advantages of high measurement precision, long distance and high spatial resolution, so that the sensing system becomes a great research hotspot for realizing dynamic parameter measurement.
Currently, researchers have realized distributed brillouin dynamic strain measurement by demodulating brillouin gain spectrum through fast scanning probe optical frequency. For example: a sweep-free brillouin optical time domain analysis technique (a. voskoboiik,et al.opt. Express2011, 19(26): B842-B847), and fast frequency agile Brillouin optical time domain analysis (Y. Peled,et al.opt. Express2012, 20(8): 8584-. However, the technology uses a high-performance arbitrary waveform generator to realize the rapid switching of the optical wave frequency, the cost is high, the practical application is not facilitated, the brillouin optical time domain system utilizes an optical pulse signal to excite an optical wave field to realize the positioning and extraction of the optical fiber along line strain, the optical fiber is limited by the service life (10 ns) of an acoustic phonon of the optical fiber, and the spatial resolution is difficult to break through 1 m. In contrast, the Brillouin Optical Correlation Domain Analysis (BOCDA) technology utilizes continuous light to measure strain, and the spatial resolution can reach centimeter magnitude. For example: chaotic laser based single slope assisted BOCDA technology (y.h. Wang,et alopt-lett.2020, 45(7): 1822-1825) and dual slope assisted BOCDA technology (b-Wang,et al.j. Lightwave Technol. 2019, 37(18): 4573-4583'). The dynamic strain is converted into the change of the detection optical power in real time, the device is simple, the cost is low, the adaptability is strong, however, the system realizes the positioning of the strain information along the optical fiber by controlling a single related peak, so that only one point on the optical fiber can be measured at each time, and the requirement of long-distance high-speed dynamic strain measurement is difficult to meet. In the prior art, in the BOCDA technology based on sinusoidal modulation combined with time domain data processing, the position of a correlation peak is controlled by a sinusoidal modulation frequency to realize random access of a sensing position. By varying the modulation frequency, scanning the position of each correlation peak, for the whole transmissionThe fiber-sensing (FUT) performs distributed measurements. Since the variation of the modulation frequency causes the variation of the pitch of each correlation peak, the shift amount of the position of the correlation peak is not constant, and increases as the order of the correlation peak increases. This characteristic introduces position scanning errors, poor system positioning accuracy, and poor spatial resolution.
The traditional sensing technology based on chaotic light, such as a chaotic Brillouin optical time domain/coherent domain fusion analysis device and method (Chinese invention patent ZL 201710848003.4) and a distributed optical fiber dynamic strain sensing device and method (Chinese invention patent ZL 201810408414.6) based on broadband chaotic laser, adopts the traditional chaotic laser (with weak period and weak delay characteristic signal) as a light source, only has a unique related peak in a sensing optical fiber, can only realize single-point positioning and measurement in the optical fiber, and if distributed measurement is realized, a single related peak needs to scan the whole optical fiber, so that the process is time-consuming and difficult to realize high-speed distributed dynamic strain measurement. In addition, a time delay side lobe peak is introduced near a central correlation peak in a weak period of a time sequence signal, so that a periodic intrinsic Brillouin gain (non-peak amplification) is generated by excitation at a position corresponding to delay time in an optical fiber, the gain and the gain at the position of the central correlation peak jointly act on a Brillouin gain spectrum, a double peak is generated in the finally measured Brillouin gain spectrum under the condition of large strain, a linear region of the gain spectrum is destroyed, and the dynamic strain range is greatly limited.
Therefore, a new brillouin distributed dynamic strain measurement technology needs to be invented to realize high-speed dynamic strain measurement with high spatial resolution, long distance and multipoint parallel monitoring.
Disclosure of Invention
The invention provides a multipoint parallel high-speed chaotic Brillouin dynamic strain monitoring device and method, aims to solve the problems of slow scanning and long time consumption caused by the fact that only a single point can be measured in a Brillouin optical coherence domain analysis system, and meets the current application requirements of distributed sensing on high resolution, long distance, large dynamic range, real time and high speed, and solves the problem that the existing dynamic strain measurement technology cannot realize both multipoint real-time monitoring and high spatial resolution.
In order to solve the technical problems, the invention adopts the technical scheme that: a multipoint parallel high-speed Brillouin chaotic dynamic strain monitoring device comprises a broadband chaotic laser source, wherein the broadband chaotic laser source is used for outputting strong-period broadband chaotic laser, the broadband chaotic laser is divided into two beams through a beam splitter, and one beam is used as detection light and enters one end of a sensing optical fiber after sequentially passing through a single-side-band modulator, an erbium-doped optical fiber amplifier and a programmable optical delay generator; the other beam as pumping light is incident to the other end of the sensing optical fiber after sequentially passing through the semiconductor optical amplifier and the pulse optical amplifier; the optical signal output from the other end of the sensing optical fiber is detected by the photoelectric detector after Stokes light is filtered by the tunable optical filter, and the detected signal is acquired by the data acquisition unit and then is sent to the computer for data processing;
the single-sideband modulator is used for performing single-sideband modulation on the detection light to enable the frequency difference between the detection light and the pump light to be locked at the rising edge or the falling edge of the Brillouin gain spectral region, and the programmable optical delay generator is used for adjusting the optical path of the detection light; the semiconductor optical amplifier is used for modulating the pumping light into pulse light with the pulse width smaller than the feedback delay time tau.
The multipoint parallel high-speed Brillouin chaotic dynamic strain monitoring device further comprises a broadband microwave signal source and a pulse signal generator, wherein the pulse signal generator is used for driving the semiconductor optical amplifier, and the broadband microwave signal source is used for driving the single-side-band modulator.
The multipoint parallel high-speed Brillouin chaotic dynamic strain monitoring device further comprises an optical scrambler, an optical isolator and an optical circulator, wherein the optical scrambler and the optical isolator are arranged between the erbium-doped optical fiber amplifier and one end of the sensing optical fiber; the first port of the optical circulator is connected with the output end of the pulse optical amplifier, the second port of the optical circulator is connected with the other end of the sensing optical fiber, and the output signal of the third port is transmitted to the photoelectric detector through the tunable optical filter.
The beam splitter is a 1 × 2 optical fiber coupler, and the output end of the broadband chaotic laser source 1) is connected with the input end of the 1 × 2 optical fiber coupler through a single-mode optical fiber jumper; the first output end of the 1 multiplied by 2 optical fiber coupler is connected with the input end of the single-side band modulator through a single-mode optical fiber jumper; the output end of the single-side band modulator is connected with the input end of the erbium-doped fiber amplifier through a single-mode fiber jumper; the output end of the erbium-doped fiber amplifier is connected with the input end of the optical polarization scrambler through a single-mode fiber jumper; the output end of the optical polarization scrambler is connected with the input end of the optical isolator through a single-mode optical fiber jumper; the output end of the optical isolator is connected with one end of the sensing optical fiber;
the second output end of the 1 multiplied by 2 optical fiber coupler is connected with the input end of the semiconductor optical amplifier through a single mode optical fiber jumper; the output end of the semiconductor optical amplifier is connected with the input end of the pulse optical amplifier through a single-mode optical fiber jumper: the output end of the pulse light amplifier is connected with the first port end of the optical circulator through a single-mode optical fiber jumper; the second port of the optical circulator is connected with the other end of the sensing optical fiber, and the third port is connected with the input end of the tunable optical filter through a single-mode optical fiber jumper; the output end of the tunable optical filter is connected with the input end of the photoelectric detector through a single-mode optical fiber jumper.
The broadband chaotic laser source is used for outputting strong-period broadband chaotic laser with-3 dB spectral line width larger than 5GHz and-3 dB power spectral bandwidth larger than 10GHz, the type of the pulse signal generator is Agilent-81150A, the semiconductor optical amplifier is an OAM-SOA-PL type semiconductor optical amplifier with high extinction ratio, and the sensing optical fiber adopts G652 single-mode optical fiber or G655 single-mode optical fiber.
6. A multipoint parallel high-speed Brillouin chaotic dynamic strain monitoring method is characterized by comprising the following steps:
s1, dividing the strong periodic broadband chaotic laser output by the same laser into two beams which are respectively used as detection light and pump light;
s2, frequency shifting the detection light by the detection light through a single-side band modulator, locking the frequency difference between the detection light and the pumping light at the rising edge or the falling edge of the Brillouin gain spectral region, and simultaneously driving a semiconductor optical amplifier through a pulse signal generator to modulate the pumping light into chaotic pumping pulse light with the pulse width smaller than the feedback delay time tau; then pumping pulse light and the probe light after frequency shift are respectively input into sensing optical fibers from two ends of the sensing light;
s3, collecting the chaos Stokes light signal output from the sensing optical fiber; by calculating the pulse flight time and demodulating the chaotic Stokes optical signal output from the sensing optical fiber, the multi-point dynamic strain information in the optical fiber is obtained;
s4, the optical path of the probe light is adjusted through the programmable optical delay generator, stimulated Brillouin amplification is carried out on the chaotic probe light and the pump light at different positions of the sensing optical fiber, the step S3 is repeated, scanning of multiple related peaks along the optical fiber to be detected is achieved, and dynamic strain information along the whole sensing optical fiber is obtained.
Compared with the prior art, the invention has the following beneficial effects:
1. the invention uses strong periodic chaotic laser as a light source, an autocorrelation curve of a time sequence signal of the light source shows strong periodicity (the autocorrelation coefficient is more than 0.8), the light source has strong correlation, a plurality of correlation peaks can be excited in an optical fiber, separation of a plurality of correlation peak times can be realized by utilizing sequential interaction of pulse pumping light and detection light in different correlation peaks, a sensing position is determined by pulse flight time, multi-point parallel monitoring is finally realized, high-speed distributed measurement can be realized by adjusting a programmable optical delay line to enable the correlation peaks to sweep the interval of adjacent correlation peaks, and the sampling rate of the system is greatly improved. In addition, the stimulated Brillouin scattering is excited by using the pulse signal with the pulse duration time less than the feedback delay time, so that the deterioration of a non-zero noise substrate along the optical fiber to the signal-to-noise ratio of a system can be effectively inhibited, and long-distance sensing is realized; meanwhile, the influence of non-peak amplification on a Brillouin gain spectral region is avoided by the application of multiple correlation peaks, so that an intrinsically broadened perfect Lorentz linear chaotic Brillouin gain spectrum can be obtained, a linear region at a slope can be fully utilized, and the large-range dynamic strain measurement is realized.
2. According to the invention, multiple correlation peaks are excited by adopting strong periodic chaotic light, and the interval of the correlation peaks can be controlled by adjusting the cavity length of the chaotic laser, namely the feedback delay time; for distributed measurement along the optical fiber, the scanning times of the related peaks are determined by the intervals of the related peaks, but not the length of the optical fiber, and the scanning times cannot be increased due to the increase of the length of the sensing optical fiber, so that the invention can realize long-distance high-speed dynamic strain real-time monitoring.
3. Compared with the BOCDA technology based on sinusoidal modulation combined with time domain data processing, the multipoint parallel high-speed chaotic Brillouin dynamic strain monitoring device and method provided by the invention have the advantages that the interval of each correlation peak and the spatial resolution of the system are respectively determined by the feedback cavity length of chaotic laser and the light source line width, the optical path difference between probe light and pump light is changed by using the programmable optical delay line so as to realize the movement of the position of the correlation peak, and the cavity length and the line width of the light source cannot be changed. Therefore, the offset of the position of the related peak is always constant in the distributed measurement process, the system has no position scanning error, and the accurate positioning of multiple sensing points can be realized.
4. Compared with Brillouin optical time domain sensing technology, the strain positioning is carried out by using pulsed light, the spatial resolution is difficult to break through 1 meter due to the influence of the phonon service life, the system gain spectrum line width is about 30 MHz, and the dynamic strain range measured by using a slope auxiliary method is limited. To obtain a wider brillouin gain spectrum requires multi-frequency modulation of the probe light, which greatly increases the complexity and cost of the system, for example: based on a multi-slope auxiliary large dynamic range Brillouin rapid measurement system (Chinese invention patent, application number: 201910006107. X), the invention uses a broadband chaotic laser with-3 dB spectral line width larger than 5GHz and-3 dB power spectral bandwidth larger than 10GHz as a light source, and has the following advantages: (1) the stimulated Brillouin scattering is limited in an extremely narrow correlation peak, and the spatial resolution of the system is determined by the full width at half maximum of the correlation peak and can reach millimeter magnitude. (2) The wide-band chaotic laser contains rich frequency components, so that the Brillouin gain spectrum is intrinsically broadened, a wide linear region range can be obtained without a complex modulation means, the system is simple in structure and low in cost, and real-time measurement of high-spatial resolution, large range and high-frequency dynamic strain can be realized.
Drawings
Fig. 1 is a schematic structural diagram of a multipoint parallel high-speed chaotic brillouin dynamic strain monitoring device according to an embodiment of the present invention;
in the figure: the optical fiber chaotic laser system comprises a 1-broadband chaotic laser source, a 2-beam splitter, a 3-single side band modulator, a 4-broadband microwave signal source, a 5-erbium-doped optical fiber amplifier, a 6-programmable optical delay generator, a 7-optical scrambler, an 8-optical isolator, a 9-semiconductor optical amplifier, a 10-pulse signal generator, an 11-pulse optical amplifier, a 12-optical circulator, a 13-sensing optical fiber, a 14-tunable optical filter, a 15-photoelectric detector, a 16-oscilloscope and a 17-computer.
Fig. 2 shows a schematic diagram of multiple correlation peaks excited in a sensing fiber.
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 multipoint parallel high-speed brillouin chaotic dynamic strain monitoring device, which includes a broadband chaotic laser source 1, where the broadband chaotic laser source 1 is configured to output a strong periodic broadband chaotic laser, the broadband chaotic laser is divided into two beams by a beam splitter 2, and one beam is used as a detection light and enters one end of a sensing optical fiber 13 after sequentially passing through a single-sideband modulator 3, an erbium-doped fiber amplifier 5, and a programmable optical delay generator 6; the other beam as pumping light is incident to the other end of the sensing optical fiber 13 after sequentially passing through the semiconductor optical amplifier 9 and the pulse optical amplifier 11; the optical signal output from the other end of the sensing optical fiber 13 is detected by the photoelectric detector 15 after stokes light is filtered by the tunable optical filter 14, and the detection signal is collected by the data collection unit 16 and then sent to the computer 17 for data processing; the single-sideband modulator 3 is used for performing single-sideband modulation on the detection light to enable the frequency difference between the detection light and the pump light to be locked at the rising edge or the falling edge of the Brillouin gain spectral region, and the programmable optical delay generator 6 is used for adjusting the optical path of the detection light; the semiconductor optical amplifier 9 is configured to modulate the pump light into pulsed light with a pulse width smaller than the feedback delay time τ.
Further, as shown in fig. 1, the multipoint parallel high-speed brillouin chaotic dynamic strain monitoring device provided in this embodiment further includes a broadband microwave signal source 4 and a pulse signal generator 10, where the pulse signal generator 10 is configured to drive the semiconductor optical amplifier 9, and the broadband microwave signal source 4 is configured to drive the single-sideband modulator 3.
Further, as shown in fig. 1, the multipoint parallel high-speed brillouin chaotic dynamic strain monitoring device provided in this embodiment further includes an optical scrambler 7, an optical isolator 8 and an optical circulator 12, where the optical scrambler 7 and the optical isolator 8 are disposed between the erbium-doped fiber amplifier 5 and one end of the sensing fiber 13; a first port of the optical circulator 12 is connected to an output end of the pulsed optical amplifier 11, a second port is connected to the other end of the sensing optical fiber 13, and a third port output signal is incident to the photodetector 15 through the tunable optical filter 14.
Further, as shown in fig. 1, the beam splitter 2 is a 1 × 2 fiber coupler, and an output end of the broadband chaotic laser source 1 is connected to an input end of the 1 × 2 fiber coupler through a single-mode fiber jumper; the first output end of the 1 multiplied by 2 optical fiber coupler is connected with the input end of the single-side band modulator 3 through a single-mode optical fiber jumper; the output end of the single-side band modulator 3 is connected with the input end of the erbium-doped fiber amplifier 5 through a single-mode fiber jumper; the output end of the erbium-doped fiber amplifier 5 is connected with the input end of the optical polarization scrambler 7 through a single-mode fiber jumper; the output end of the optical polarization scrambler 7 is connected with the input end of the optical isolator 8 through a single-mode optical fiber jumper; the output end of the optical isolator 8 is connected with one end of a sensing optical fiber 13; the second output end of the 1 × 2 optical fiber coupler is connected with the input end of the semiconductor optical amplifier 9 through a single-mode optical fiber jumper; the output end of the semiconductor optical amplifier 9 is connected with the input end of the pulse optical amplifier 11 through a single-mode optical fiber jumper: the output end of the pulsed light amplifier 11 is connected with the first port end of the optical circulator 12 through a single-mode optical fiber jumper; a second port of the optical circulator 12 is connected with the other end of the sensing optical fiber 13, and a third port is connected with the input end of the tunable optical filter 14 through a single-mode optical fiber jumper; the output end of the tunable optical filter 14 is connected to the input end of the photodetector 15 through a single-mode optical fiber jumper.
Further, in this embodiment, the broadband chaotic laser source 1 is configured to output strong periodic broadband chaotic laser light with-3 dB spectral line width greater than 5GHz and-3 dB power spectral bandwidth greater than 10GHz, the type of the pulse signal generator 10 is Agilent-81150a, the semiconductor optical amplifier 9 is an OAM-SOA-PL type semiconductor optical amplifier with a high extinction ratio, and the sensing fiber 13 is a G652 single-mode fiber or a G655 single-mode fiber. In addition, in this embodiment, the strong periodic broadband chaotic laser means that a time sequence signal of the chaotic laser has a strong time delay characteristic, the size of the time delay characteristic does not change significantly with the increase of the delay time, and an autocorrelation curve shows strong periodicity, that is, an autocorrelation coefficient is greater than 0.8. The time sequence signal of the chaotic laser shows random oscillation but has certain periodicity, and the periodicity is represented by the size of a correlation peak on an autocorrelation curve of the time sequence signal, namely the strength of time delay characteristics. In the embodiment, the broadband chaotic laser source 1 is obtained by feeding back the output light of the broadband laser to the broadband laser, the feedback light intensity and the polarization state of the broadband chaotic laser source are properly adjusted, the autocorrelation coefficient of the chaotic laser can be changed to be more than 0.8, namely the broadband chaotic laser with strong time delay characteristic can be generated, and the cycle of the chaotic laser output by the chaotic laser source is equal to the external cavity time delay, namely the feedback delay time.
The working principle of this embodiment is as follows.
1. The output center wavelength of the broadband chaotic laser source 1 is 1550nm, the time sequence signal has strong time delay characteristic, and the center frequency isν 0 The-3 dB spectral line width is larger than 5GHz, and the-3 dB power spectral bandwidth is larger than 10 GHz. The light output by the light source is composed of 10: 90 1X 2 optical fiber coupler is divided into two paths, one path is used as detection light (90%)And the other path is used as pump light (10%).
2. The single sideband modulator 3 modulates the probe light signal (90%) to generate probe light with a frequency down shifted byν 0 -ν B Whereinν B The Brillouin frequency shift is about 11GHz for a common single-mode fiber. The single-sideband modulator 3 is driven by a broadband microwave signal source 4, and the signal source can output sinusoidal signals with the frequency range of 9 kHz-13 GHz and the amplitude range of-20 dBm-19 dBm. The modulated optical signal is amplified using an erbium doped fiber amplifier 5 to compensate for the optical power loss due to the modulation. The amplified optical signal is incident into an ODG-101 type high-precision long-distance programmable optical delay generator 6, and then is incident into a sensing optical fiber 13 through an optical scrambler 7 and an optical isolator 8, wherein the sensing optical fiber 13 adopts a G652 single-mode optical fiber or a G655 single-mode optical fiber.
3. The pulse signal generator 10 of Agilent-81150A type drives the OAM-SOA-PL type semiconductor optical amplifier 9 with high extinction ratio to perform pulse modulation on the pump optical signal (10%). The purpose of modulation is to modulate continuous laser into pulse laser, so that time separation of multiple correlation peaks is realized, and multipoint rapid positioning and real-time monitoring of strain information are guaranteed. Meanwhile, the pulse width is smaller than the feedback delay time tau, so that the crosstalk of information between adjacent correlation peaks is avoided, non-peak amplification outside the central correlation peak and noise accumulation along the optical fiber can be effectively prevented, and the sensing distance of the system is increased. The modulated pump light is amplified to an appropriate level by the pulsed light amplifier 11 to excite the stimulated brillouin scattering effect. Then, the light is incident into the sensing fiber 13 through the optical circulator 12, meets the probe light in the sensing fiber 13, and generates stimulated brillouin scattering. The stimulated Brillouin scattering at different relevant peak positions can be excited by the pulse light passing through the different relevant peak positions, and the stimulated Brillouin scattering information of the different relevant peak positions corresponding to different times is calculated according to the pulse flight time, so that the time separation of multiple relevant peaks can be realized. However, in order to avoid crosstalk of information at different correlation peak positions, the action length of the pulsed light must be smaller than the distance between adjacent correlation peaks, i.e. the pulse width is smaller than the feedback delay time τ.
4. Chaotic probe light and pump light transmitted in opposite directions meet at a certain position in the sensing optical fiber, and multiple correlation peaks can be excited in the optical fiber by using the strong periodicity of the chaotic signal, as shown in fig. 2, the interval between adjacent correlation peaks isΔLThe full width at half maximum of the correlation peak isΔl c . Wherein adjacent correlation peaks are spacedΔLCan be represented by formula (1):
whereinτThe feedback delay time of the chaotic light depends on the cavity length of the chaotic laser;cis the propagation speed of light in a vacuum,nis the refractive index of a common single mode optical fiber. The expression (1) shows that the correlation peak interval can be controlled by adjusting the cavity length of the chaotic laser, namely the feedback delay time.
The stimulated Brillouin amplification effect is limited in each independent relevant peak, stimulated Brillouin scattering only exists at the position where the pulse light and the relevant peak exist simultaneously, and the pulse light can stimulate the stimulated Brillouin scattering at different relevant peak positions along with the change of time, so that the stimulated Brillouin scattering at each relevant peak can be performed in sequence through the pulse pumping light, and the stimulated Brillouin scattering information at different positions can be obtained according to the pulse flight time of the pulse signal returned to the signal receiving end, so that the independent parallel monitoring of the multi-point strain information can be realized. For distributed measurements along the fiber, the number of correlation peak scans is N, which can be expressed by equation (2):
whereinΔl c The invention adopts the broadband light source to ensure that the related peak is very narrow, so the narrow related peak can ensure that the spatial resolution of the system can reach centimeter or even millimeter level, and the measurement is improvedAnd (4) precision. In addition, as can be seen from equation (2), in the present invention, the number of scans of the correlation peak is determined by the interval of the correlation peak, not the length of the optical fiber, and the number of scans is not increased due to the increase of the length of the sensing optical fiber, so that the system can realize high-speed dynamic strain real-time monitoring over a long distance.
4. The XTM-50 broadband wavelength-adjustable filter 14 is adopted to filter the detection light, the required Stokes light is filtered out, the filtered light signal is converted into an electric signal by a photoelectric detector 15, and the electric signal is input into an oscilloscope 16 through a high-frequency coaxial cable for real-time signal power acquisition. The data acquisition unit 16 acquires the signal power after stimulated brillouin amplification, in which the frequency difference between the probe light and the pump light is fixed at the midpoint of the rising edge or the falling edge of the brillouin gain spectral region by the broadband microwave source 4. The change of signal power in the linear region of the brillouin gain spectrum and the brillouin frequency shift amount are in a linear relation, the brillouin frequency shift amount and the strain are also in a linear relation, and the computer 17 analyzes the acquired data to obtain dynamic strain information.
5. The optical path difference of the pump light and the detection light is adjusted by adopting a high-precision long-distance programmable optical delay generator 6 on a pump detection path, so that the generated multiple correlation peaks scan in the range of a sensing optical fiberΔL/Δl c And then, the rapid detection and the accurate positioning along the sensing optical fiber can be realized. In addition, the system spatial resolution is determined byΔl c The broadband characteristic of the chaotic laser guarantees the millimeter-magnitude ultrahigh spatial resolution, the application of multiple related peaks and the time gating effect of the pump light can effectively inhibit the noise along the optical fiber, so that the chaotic Brillouin gain spectrum without secondary peaks and with a wide linear region range is obtained, the sensing distance is increased finally, the dynamic strain range of the slope auxiliary technology is expanded greatly, and the large-range dynamic strain rapid real-time monitoring with long distance and high resolution is realized.
Further, the embodiment of the invention also provides a multipoint parallel high-speed brillouin chaotic dynamic strain monitoring method, which comprises the following steps:
s1, dividing the strong periodic broadband chaotic laser output by the same laser into two beams which are respectively used as detection light and pump light;
s2, frequency shifting the detection light by the detection light through a single-side band modulator, locking the frequency difference between the detection light and the pumping light at the rising edge or the falling edge of the Brillouin gain spectral region, and simultaneously driving a semiconductor optical amplifier through a pulse signal generator to modulate the pumping light into chaotic pumping pulse light with the pulse width smaller than the feedback delay time tau; then pumping pulse light and the probe light after frequency shift are respectively input into sensing optical fibers from two ends of the sensing light;
s3, collecting the chaos Stokes light signal output from the sensing optical fiber; by calculating the pulse flight time and demodulating the chaotic Stokes optical signal output from the sensing optical fiber, the multi-point dynamic strain information in the optical fiber is obtained;
s4, the optical path of the probe light is adjusted through the programmable optical delay generator 6, the chaotic probe light and the pump light are subjected to stimulated Brillouin amplification at different positions of the sensing optical fiber, the step S3 is repeated, the scanning of multiple related peaks along the optical fiber to be detected is realized, and the dynamic strain information along the whole sensing optical fiber is obtained.
The invention uses strong periodic broadband chaotic laser to excite multiple narrow-band related peaks, uses pulsed light with the pulse duration less than the feedback delay time to sequentially extract the intensity information of each related peak, and demodulates a corresponding dynamic strain value according to the relationship between the intensity information and strain in a linear region range. The multiple narrow-band correlation peaks can realize multi-point parallel monitoring, greatly reduce the scanning times of the correlation peaks, improve the speed of distributed measurement, have high system signal-to-noise ratio, and can realize large-range dynamic strain real-time monitoring with long distance and high resolution.
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 (6)
1. The multipoint parallel high-speed Brillouin chaotic dynamic strain monitoring device is characterized by comprising a broadband chaotic laser source (1), wherein the broadband chaotic laser source (1) is used for outputting strong periodic broadband chaotic laser with an autocorrelation coefficient larger than 0.8, the broadband chaotic laser is divided into two beams through a beam splitter (2), and one beam is used as detection light and enters one end of a sensing optical fiber (13) after sequentially passing through a single-sideband modulator (3), an erbium-doped optical fiber amplifier (5) and a programmable optical delay generator (6); the other beam as pumping light is incident to the other end of the sensing optical fiber (13) after sequentially passing through a semiconductor optical amplifier (9) and a pulse optical amplifier (11); an optical signal output from the other end of the sensing optical fiber (13) is detected by a photoelectric detector (15) after Stokes light is filtered by a tunable optical filter (14), and the detected signal is acquired by a data acquisition unit (16) and then sent to a computer (17) for data processing;
the single-sideband modulator (3) is used for performing single-sideband modulation on the detection light to enable the frequency difference between the detection light and the pump light to be locked at the rising edge or the falling edge of the Brillouin gain spectral region, and the programmable optical delay generator (6) is used for adjusting the optical path of the detection light; the semiconductor optical amplifier (9) is used for modulating the pump light into pulse light with the pulse width smaller than the feedback delay time tau.
2. The multipoint parallel high-speed Brillouin chaotic dynamic strain monitoring device according to claim 1, further comprising a broadband microwave signal source (4) and a pulse signal generator (10), wherein the pulse signal generator (10) is used for driving the semiconductor optical amplifier (9), and the broadband microwave signal source (4) is used for driving the single-sideband modulator (3).
3. The multipoint parallel high-speed Brillouin chaotic dynamic strain monitoring device according to claim 2, further comprising an optical scrambler (7), an optical isolator (8) and an optical circulator (12), wherein the optical scrambler (7) and the optical isolator (8) are arranged between the erbium-doped fiber amplifier (5) and one end of the sensing fiber (13); the first port of the optical circulator (12) is connected with the output end of the pulse optical amplifier (11), the second port is connected with the other end of the sensing optical fiber (13), and the output signal of the third port is transmitted to the photoelectric detector (15) through the tunable optical filter (14).
4. The multipoint parallel high-speed Brillouin chaotic dynamic strain monitoring device according to claim 3, wherein the beam splitter (2) is a 1 x 2 fiber coupler, and the output end of the broadband chaotic laser source (1) is connected with the input end of the 1 x 2 fiber coupler through a single-mode fiber jumper; the first output end of the 1 multiplied by 2 optical fiber coupler is connected with the input end of the single-side band modulator (3) through a single-mode optical fiber jumper; the output end of the single-side band modulator (3) is connected with the input end of the erbium-doped fiber amplifier (5) through a single-mode fiber jumper; the output end of the erbium-doped fiber amplifier (5) is connected with the input end of the optical polarization scrambler (7) through a single-mode fiber jumper; the output end of the optical polarization scrambler (7) is connected with the input end of the optical isolator (8) through a single-mode optical fiber jumper; the output end of the optical isolator (8) is connected with one end of the sensing optical fiber (13);
the second output end of the 1 multiplied by 2 optical fiber coupler is connected with the input end of the semiconductor optical amplifier (9) through a single-mode optical fiber jumper; the output end of the semiconductor optical amplifier (9) is connected with the input end of the pulse optical amplifier (11) through a single-mode optical fiber jumper: the output end of the pulse light amplifier (11) is connected with the first port end of the optical circulator (12) through a single-mode optical fiber jumper; a second port of the optical circulator (12) is connected with the other end of the sensing optical fiber (13), and a third port is connected with the input end of the tunable optical filter (14) through a single-mode optical fiber jumper; the output end of the tunable optical filter (14) is connected with the input end of the photoelectric detector (15) through a single-mode optical fiber jumper.
5. The multipoint parallel high-speed Brillouin chaotic dynamic strain monitoring device according to claim 4, wherein the broadband chaotic laser source (1) is used for outputting strong periodic broadband chaotic laser with-3 dB spectral line width larger than 5GHz and-3 dB power spectral bandwidth larger than 10GHz, the pulse signal generator (10) is Agilent-81150A, the semiconductor optical amplifier (9) is an OAM-SOA-PL type semiconductor optical amplifier with high extinction ratio, and the sensing optical fiber (13) adopts G652 single-mode fiber or G655 single-mode fiber.
6. A multipoint parallel high-speed Brillouin chaotic dynamic strain monitoring method is characterized by comprising the following steps:
s1, dividing the strong periodic broadband chaotic laser with the autocorrelation coefficient larger than 0.8 output by the same laser into two beams which are respectively used as detection light and pumping light;
s2, frequency shifting the detection light through the single side band modulator (3), enabling the frequency difference between the detection light and the pumping light to be locked at the rising edge or the falling edge of the Brillouin gain spectral region, and meanwhile, driving the semiconductor optical amplifier through the pulse signal generator to modulate the pumping light into pumping pulse light with the pulse width smaller than the feedback delay time tau; then pumping pulse light and the probe light after frequency shift are respectively input into the sensing optical fibers from two ends of the sensing optical fibers;
s3, collecting the chaos Stokes light signal output from the sensing optical fiber; by calculating the pulse flight time and demodulating the chaos stokes optical signal output by the sensing optical fiber, the multi-point dynamic strain information in the sensing optical fiber is obtained;
s4, the optical path of the probe light is adjusted through the programmable optical delay generator (6), so that the probe light and the pump pulse light generate stimulated Brillouin amplification at different positions of the sensing optical fiber, the step S3 is repeated, the scanning of multiple related peaks along the optical fiber to be detected is realized, and the dynamic strain information along the whole sensing optical fiber is obtained.
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