CN115452020A - Distributed optical fiber sensing system and method for realizing simultaneous measurement of vibration and temperature - Google Patents
Distributed optical fiber sensing system and method for realizing simultaneous measurement of vibration and temperature Download PDFInfo
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- 239000013307 optical fiber Substances 0.000 title claims abstract description 49
- 238000005259 measurement Methods 0.000 title claims abstract description 20
- 238000000034 method Methods 0.000 title claims abstract description 14
- 230000003287 optical effect Effects 0.000 claims abstract description 72
- 238000001514 detection method Methods 0.000 claims abstract description 58
- 238000001228 spectrum Methods 0.000 claims abstract description 15
- 239000000835 fiber Substances 0.000 claims description 23
- 239000004065 semiconductor Substances 0.000 claims description 22
- 238000009529 body temperature measurement Methods 0.000 claims description 6
- 239000000523 sample Substances 0.000 claims description 4
- 238000005516 engineering process Methods 0.000 description 10
- 238000012544 monitoring process Methods 0.000 description 4
- 238000010586 diagram Methods 0.000 description 3
- 230000004927 fusion Effects 0.000 description 3
- 238000012545 processing Methods 0.000 description 3
- 238000001069 Raman spectroscopy Methods 0.000 description 2
- 238000011161 development Methods 0.000 description 2
- 239000003208 petroleum Substances 0.000 description 2
- 230000010287 polarization Effects 0.000 description 2
- 230000009286 beneficial effect Effects 0.000 description 1
- 238000004364 calculation method Methods 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 238000001208 nuclear magnetic resonance pulse sequence Methods 0.000 description 1
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
- G01D5/00—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable
- G01D5/26—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light
- G01D5/32—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light
- G01D5/34—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells
- G01D5/353—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre
- G01D5/35306—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre using an interferometer arrangement
- G01D5/35329—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre using an interferometer arrangement using interferometer with two arms in transmission, e.g. Mach-Zender interferometer
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- 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
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01K—MEASURING TEMPERATURE; MEASURING QUANTITY OF HEAT; THERMALLY-SENSITIVE ELEMENTS NOT OTHERWISE PROVIDED FOR
- G01K11/00—Measuring temperature based upon physical or chemical changes not covered by groups G01K3/00, G01K5/00, G01K7/00 or G01K9/00
- G01K11/32—Measuring temperature based upon physical or chemical changes not covered by groups G01K3/00, G01K5/00, G01K7/00 or G01K9/00 using changes in transmittance, scattering or luminescence in optical fibres
- G01K11/3206—Measuring temperature based upon physical or chemical changes not covered by groups G01K3/00, G01K5/00, G01K7/00 or G01K9/00 using changes in transmittance, scattering or luminescence in optical fibres at discrete locations in the fibre, e.g. using Bragg scattering
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Abstract
The invention provides a distributed optical fiber sensing system and a method for realizing simultaneous measurement of vibration and temperature, wherein the system comprises a narrow linewidth laser, a tunable laser and a grating array; laser emitted by the narrow-linewidth laser and the tunable laser passes through a laser amplifier, and then the obtained detection pulse light is transmitted to a first optical circulator; the first optical circulator is also connected with a grating array and a second optical circulator; the second optical circulator is connected to the strong reflection grating and the unbalanced Mach-Zehnder interferometer; the strong reflection grating and the unbalanced Mach-Zehnder interferometer are both connected to the photodetector. The wavelength demodulation and the phase demodulation are fused in the same system, the distributed temperature sensing is realized by demodulating the spectrum drift of the chirped grating array, the phase change of the reflected pulse interference signal of the adjacent chirped grating array is measured to realize the distributed vibration measurement, and the system can simultaneously realize the accurate measurement of the distributed temperature and vibration.
Description
Technical Field
The invention relates to the technical field of distributed optical fiber sensing, in particular to a distributed optical fiber sensing system and a distributed optical fiber sensing method for realizing simultaneous measurement of vibration and temperature parameters.
Background
The optical fiber sensing technology is a sensing technology which takes optical fibers as media and light as a carrier to sense and transmit external signals. When light is transmitted in the optical fiber, various characteristics of the transmitted light are changed correspondingly due to the change of the external environment, and information of the external environment of the optical fiber can be obtained by monitoring the change of the light wave parameters, so that sensing is realized. The distributed optical fiber sensing technology in the optical fiber sensing technology can continuously and stably measure parameters along the optical fiber in a large range, and plays an irreplaceable role in the optical fiber sensing technology. At present, the distributed optical fiber sensing technology is widely applied to the fields of perimeter security, oil exploration and development, large-scale structure health monitoring and the like. The distributed optical fiber sensing technology mainly adopts scattering signals in optical fibers and an optical time domain reflection technology for sensing, wherein Raman scattering light is sensitive to temperature change and is mostly used for realizing distributed temperature measurement, brillouin scattering is sensitive to temperature and strain change and is used for realizing distributed temperature and strain sensing, and Rayleigh scattering is mostly used for carrying out distributed vibration sensing. But due to the limitation of the principle and the structure of the device, only single parameter measurement can be respectively carried out. However, in some specific applications, such as monitoring leakage of petroleum pipelines, monitoring conditions during petroleum exploration and development, etc., the measurement of a single parameter is far from satisfying the requirement, and the simultaneous measurement of multiple parameters is becoming an important issue.
At present, a team proposes a scheme for simultaneously measuring multiple parameters according to the application requirements. The M.N. Alahbabi subject group of the university of Nanamphun proposes a fusion system of a Brillouin Optical Time Domain Reflectometer (BOTDR) and a Raman Optical Time Domain Reflectometer (ROTDR), and realizes simultaneous measurement of temperature and strain; the Rao Yunjiang topic group of the university of electronic technology provides a fusion system of a phase-sensitive optical time domain reflectometer (phi-OTDR) and a Polarization Optical Time Domain Reflectometer (POTDR), so that polarization and phase information can be simultaneously obtained to measure multiple parameters; the project group Zhang Xuping of Nanjing university provides a fusion system of POTDR and BOTDR, and strain and vibration can be measured simultaneously. The methods adopt scattered light in optical fibers as sensing signals, the scattering coefficient is low, and the scattered light intensity is usually 10-6 to 10-8 orders of magnitude of the incident light intensity, so the signal-to-noise ratio of the system is low, the sensing distance and the spatial resolution are limited to a great extent, and the temperature and pressure values measured by adopting the scattered light are subjected to average calculation after area sampling, so the positioning error is large.
Therefore, how to provide an optical fiber array distributed optical fiber sensing system and method capable of simultaneously measuring vibration and temperature with high precision is a problem that needs to be solved by those skilled in the art.
Disclosure of Invention
In view of the above, the invention adopts a sensing grating array, combines wavelength demodulation and phase demodulation in the same system, realizes distributed temperature sensing by demodulating the drift of the chirped grating array spectrum, and simultaneously measures the phase change of the reflected pulse interference signal of the adjacent chirped grating array to realize distributed vibration measurement.
In order to achieve the purpose, the invention adopts the following technical scheme:
a distributed optical fiber sensing system for realizing simultaneous measurement of vibration and temperature comprises a narrow linewidth laser, a tunable laser and a grating array; laser emitted by the narrow linewidth laser and the tunable laser passes through a laser amplifier, and then the obtained detection pulse light is transmitted to a first optical circulator; the first optical circulator is further connected with the grating array and a second optical circulator; the second optical circulator is connected to the strong reflection grating and the unbalanced Mach-Zehnder interferometer; the strong reflection grating and the unbalanced Mach-Zehnder interferometer are connected to the photoelectric detector;
the first optical circulator is used for inputting detection pulse light from a first port and injecting the detection pulse light into the grating array from a second port, and the reflected light pulse of the grating array is output to a second optical circulator from a third port of the first optical circulator;
the second optical circulator is used for inputting the reflected light pulse output by the first optical circulator from the first port and outputting the reflected light pulse to the strong reflection grating (11) from the second port of the second optical circulator (10), and the reflected pulse of the strong reflection grating (11) is output to the unbalanced Mach-Zehnder interferometer (13) from the third port;
the strong reflection grating is used for reflecting the detection pulse light of the narrow-linewidth laser through the detection pulse light of the tunable laser, and the detection pulse light of the reflected narrow-linewidth laser is output to the unbalanced Mach-Zehnder interferometer through a third port of the optical circulator II;
the unbalanced Mach-Zehnder interferometer is used for generating interference on reflected pulses of adjacent gratings in the grating array and outputting the interference light to different photoelectric detectors in a phase-splitting mode.
Preferably, the narrow linewidth laser is used for emitting continuous high-coherence laser; the tunable laser is used for sequentially emitting continuous sweep-frequency laser with different wavelengths.
Preferably, the laser amplifier comprises a first semiconductor laser amplifier, a second semiconductor laser amplifier, a pulse signal generator and an erbium-doped fiber amplifier;
the semiconductor laser amplifier is connected with the pulse signal generator, and is used for modulating the continuous light output by the narrow linewidth laser into detection light pulses and outputting the detection light pulses to the optical fiber coupler;
the second semiconductor laser amplifier is connected with the pulse signal generator, and is used for modulating the continuous light output by the tunable laser into a detection light pulse and outputting the detection light pulse to the optical fiber coupler;
the optical fiber coupler inputs the coupled detection light pulse to an erbium-doped optical fiber amplifier.
Preferably, the grating array is a chirped fiber grating array, and adjacent gratings are arranged at a fixed interval.
Preferably, the strong reflection grating is a narrow-band grating with a center wavelength consistent with the laser wavelength emitted by the narrow-line width laser.
Preferably, one arm of the unbalanced mach-zehnder interferometer is provided with a delay fiber with the length of 2L, and L is the distance between adjacent gratings in the grating array; the pulse light reflected by adjacent chirped fiber gratings generates interference in the unbalanced Mach-Zehnder interferometer, an interference signal is divided into three signals with phase difference degrees through an x coupler, and the three signals are input to three photoelectric detectors.
The invention also provides a distributed optical fiber sensing method of the distributed optical fiber sensing system for realizing simultaneous measurement of vibration and temperature, which comprises the following steps:
the laser emitted by the narrow-linewidth laser and the tunable laser is amplified to obtain detection pulse light, and the detection pulse light is transmitted to the first optical circulator;
the first optical circulator injects the detection pulse light into the grating array, and the reflected light pulse of the grating array is output to the second optical circulator through the first optical circulator;
the second optical circulator injects the reflected light pulse output by the first optical circulator into the strong reflection grating;
the strong reflection grating obtains reflection signals of the grating array under different wavelengths through detection pulse light of the tunable laser and outputs the detection pulse light to the first photoelectric detector, intensity values of the reflection signals with different wavelengths are fitted, a reflection spectrum of the grating array is restored, and temperature change around the grating array is detected through the change of the reflection spectrum, so that distributed temperature sensing is achieved;
the strong reflection grating reflects the detection pulse light of the narrow linewidth laser, and the reflected detection pulse light of the narrow linewidth laser is output to the unbalanced Mach-Zehnder interferometer through the second optical circulator;
the unbalanced Mach-Zehnder interferometer generates interference on reflected pulses of adjacent gratings in the grating array, enables the interference light to be divided into phases and output to different photoelectric detectors, reduces vibration signals around the grating array by demodulating phase changes of interference signals, and achieves distributed vibration sensing.
Through the technical scheme, compared with the prior art, the invention has the beneficial effects that:
the wavelength demodulation and interference demodulation technologies of the grating are integrated in a system, the measurement of the outside temperature is realized by measuring the wavelength change of the grating, and meanwhile, the phase change of the reflected pulse interference signal between adjacent gratings is measured to restore the outside vibration signal.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings needed to be used in the description of the embodiments or the prior art will be briefly introduced below, it is obvious that the drawings in the following description are only embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the provided drawings without creative efforts;
fig. 1 is a schematic structural diagram of a distributed optical fiber sensing system for implementing simultaneous measurement of vibration and temperature according to an embodiment of the present invention;
FIG. 2 is a diagram illustrating a variation of a chirped grating spectrum with temperature according to an embodiment of the present invention;
FIG. 3 is a schematic diagram of an interference pulse sequence between adjacent gratings in a grating array according to an embodiment of the present invention;
FIG. 4 is a time domain plot of a 90Hz sinusoidal signal measured in accordance with an embodiment of the present invention;
FIG. 5 is a frequency domain plot of a 90Hz sinusoidal signal measured in accordance with an embodiment of the present invention.
In the figure, 1 is a narrow linewidth laser, 2 is a tunable laser, 3 is a semiconductor laser amplifier I, 4 is a semiconductor laser amplifier II, 5 is a pulse signal generator, 6 is an optical fiber coupler, 7 is an erbium-doped optical fiber amplifier, 8 is an optical circulator I, 9 is a grating array, 10 is an optical circulator II, 11 is a strong reflection grating, 12 is a photoelectric detector I, 13 is an unbalanced Mach Zehnder interferometer, 14 is a photoelectric detector II, 15 is a photoelectric detector III, 16 is a photoelectric detector IV, and 17 is a data acquisition card.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the 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.
The first aspect of the present embodiment discloses a distributed optical fiber sensing system for simultaneously measuring vibration and temperature, which includes a narrow linewidth laser 1, a tunable laser 2, and a grating array 9; laser emitted by the narrow linewidth laser 1 and the tunable laser 2 passes through a laser amplifier, and then the obtained detection pulse light is transmitted to an optical circulator I8; the first optical circulator 8 is also connected with a grating array 9 and a second optical circulator 10; the second optical circulator 10 is connected to the strong reflection grating 11 and the unbalanced Mach-Zehnder interferometer 13; the strong reflection grating 11 and the unbalanced Mach-Zehnder interferometer 13 are connected to the photoelectric detector;
the first optical circulator 8 is used for inputting detection pulse light from a first port and injecting the detection pulse light into the grating array 9 from a second port, and the reflected light pulse of the grating array 9 is output to a second optical circulator 10 from a third port of the first optical circulator 8;
the second optical circulator 10 is used for inputting the reflected light pulse output by the first optical circulator 8 from the first port and outputting the reflected light pulse to the strong reflection grating 11 from the second port of the second optical circulator 10, and the reflected pulse of the strong reflection grating 11 is output to the unbalanced Mach-Zehnder interferometer 13 from the third port of the second optical circulator 10;
the strong reflection grating 11 is used for reflecting the detection pulse light of the narrow linewidth laser 1 through the detection pulse light of the tunable laser 2, and the reflected detection pulse light of the narrow linewidth laser 1 is output to the unbalanced Mach-Zehnder interferometer 13 through a third port of the optical circulator II 10;
and the unbalanced Mach-Zehnder interferometer 13 is used for generating interference of reflected pulses of adjacent gratings in the grating array 9 and outputting the phase of the interference light to different photodetectors in a phase mode, as shown in figure 1.
In one embodiment: the narrow linewidth laser 1 is used for generating continuous high-coherence laser to a semiconductor laser amplifier I3;
the tunable laser 2 is used for sequentially emitting continuous frequency sweeping laser with different wavelengths to the second semiconductor laser amplifier 4.
In one embodiment, the laser amplifier includes a first semiconductor laser amplifier 3, a second semiconductor laser amplifier 4, a pulse signal generator 5, and an erbium-doped fiber amplifier 7. The semiconductor laser amplifier I1 and the semiconductor laser amplifier II 4 are used for modulating continuous light into detection light pulses and outputting the detection light pulses to the erbium-doped fiber amplifier 7.
In the embodiment, the first semiconductor laser amplifier 3 is connected with the pulse signal generator 5, and is used for modulating continuous light output by the narrow linewidth laser 1 into detection light pulses and outputting the detection light pulses to the optical fiber coupler 6; the second semiconductor laser amplifier 4 is connected with the pulse signal generator 5 and used for modulating the continuous light output by the tunable laser 2 into detection light pulses and outputting the detection light pulses to the optical fiber coupler 6; the fiber coupler 6 inputs the coupled probe light pulse to the erbium-doped fiber amplifier 7.
In one embodiment, the grating array 9 is a chirped fiber grating array, with adjacent gratings arranged at a fixed pitch.
In one embodiment, the erbium-doped fiber amplifier 7 is used for amplifying the power of the probe pulse light and outputting the probe pulse light to the first port of the circulator;
in one embodiment, one arm of the unbalanced mach-zehnder interferometer 13 is provided with a delay fiber having a length of 2L, L being the spacing between adjacent gratings in the grating array; the pulse light reflected by the adjacent chirped fiber gratings generates interference in the unbalanced Mach-Zehnder interferometer 13, an interference signal is divided into three signals with the phase difference of 120 degrees through a 3 multiplied by 3 coupler, and the three signals are respectively output to a second photoelectric detector 14, a third photoelectric detector 15 and a fourth photoelectric detector 16;
in one embodiment, photo detectors one 12, two 14, three 15 and four 16 are used to convert the optical signals into electrical signals and upload them to the data acquisition card.
In one embodiment, the data acquisition card 17 is configured to receive the electrical signal of the reflected pulse of the tunable laser reflected by the grating array and the electrical signal of the grating array interference light, and perform subsequent data processing.
The second aspect of the present embodiment further discloses a distributed optical fiber sensing method for a distributed optical fiber sensing system based on the first aspect, wherein the distributed optical fiber sensing method includes the following steps:
the laser emitted by the narrow linewidth laser 1 and the tunable laser 2 is amplified to obtain detection pulse light, and the detection pulse light is transmitted to an optical circulator I8;
the first optical circulator 8 injects detection pulse light into the grating array 9, and reflected light pulses of the grating array 9 are output to the second optical circulator 10 through the first optical circulator 8;
the second optical circulator 10 injects the reflected light pulse output by the first optical circulator 8 into the grating array, and the reflected light of the grating array 9 is output to the strong reflection grating 11 through the second optical circulator 10;
the strong reflection grating 11 obtains reflection signals of the grating array 9 under different wavelengths through detection pulse light of the tunable laser 2 and outputs the detection pulse light to the first photoelectric detector 12, intensity values of the reflection signals with different wavelengths are fitted, reflection spectrums of the grating array 9 are reduced, temperature change around the grating array 9 is detected through change of the reflection spectrums, and distributed temperature sensing is achieved;
the strong reflection grating 11 reflects the detection pulse light of the narrow linewidth laser 1, and the reflected detection pulse light of the narrow linewidth laser 1 is output to the unbalanced Mach-Zehnder interferometer 13 through the second optical circulator 10;
the unbalanced mach-zehnder interferometer 13 interferes the reflected pulses of the adjacent gratings in the grating array 9, divides the phases of the interference light into different photodetectors, and demodulates the phase change of the interference signal to restore the vibration signal around the grating array 9, thereby realizing distributed vibration sensing.
It should be understood that the functions implemented by the above distributed optical fiber sensing method for implementing simultaneous measurement of vibration and temperature correspond to one of the distributed optical fiber sensing systems for implementing simultaneous measurement of vibration and temperature provided in the above embodiments, and a more detailed processing flow is implemented for the system.
The method comprises the following specific steps:
the narrow linewidth laser 1 emits continuous high-coherence light with the wavelength of 1550.1nm and the output power of 10mW, and the continuous light reaches the semiconductor laser amplifier I3. The tunable laser 2 sequentially emits continuous light with different wavelengths to the semiconductor laser amplifier II 4, the wavelength scanning range is 1551-1555nm, and the wavelength scanning step is 10pm. The pulse signal generator 5 drives the first semiconductor laser amplifier 3 and the second semiconductor laser amplifier 4 to adjust the continuous light into a detection light pulse with the pulse width of 30ns and the repetition frequency of 10kHz, the detection light pulse is output to the erbium-doped fiber amplifier 7, the detection light pulse enters the chirped fiber grating array 9 through the first optical circulator 8 after being amplified, and the distance between adjacent gratings is 5m. Each grating can reflect a part of pulse light, the reflected light reaches a narrow-band grating with the central wavelength of 1550.1nm after passing through a second optical circulator 10, the 3dB bandwidth of the grating is 0.1nm, the reflectivity exceeds 99%, the light of a narrow-line-width light source is reflected, the light with the rest wavelengths penetrates through a strong reflection grating 11, is received by a first photoelectric detector 12 and is converted into an electric signal, the electric signal is uploaded to a data acquisition card 17, then the reflection signals of the grating array under different wavelengths are obtained, the intensity of the signals reflected by the chirped gratings with different wavelengths is different, the reflection spectrum of the chirped grating can be restored by fitting the intensity values, the change of the ambient temperature of the grating can be detected through the change of the reflection spectrum, and distributed temperature sensing is realized.
Pulse light of the narrow-linewidth laser 1 is reflected by the strong reflection grating 11 and enters an unbalanced Mach-Zehnder interferometer 13 (MZI) through the second optical circulator 10 to be divided into two beams of pulse light, wherein one arm of the unbalanced Mach-Zehnder interferometer 13 is provided with a section of delay optical fiber, and certain time delay exists when the two beams of pulse light are transmitted along the two arms. When the length of the delay fiber of one arm of the unbalanced mach-zehnder interferometer 13 is 2L, pulses reflected by adjacent chirped fiber gratings meet at the other end of the unbalanced mach-zehnder interferometer 13, thereby generating interference. The interference signal is divided into three paths by a 3 x 3 coupler, the phase difference is 120 degrees, the optical signals output by the three paths are converted into electric signals by three photoelectric detectors and are uploaded to a data acquisition card 17 for data processing, and the phase change of the interference signal is demodulated by a 3 x 3 coupler demodulation algorithm, so that the external vibration signal is restored.
Fig. 2 is a reflection spectrum of a grating measured after a certain grating in the grating array is heated in a high-temperature furnace, the spectrum of the grating drifts with the increase of temperature, the drift amount of the spectrum and the change of the temperature have a good linear relationship, and the change of the external temperature can be measured by measuring the drift amount of the grating spectrum. Fig. 3 shows interference signals of a certain section of grating array collected by the system, and reflected pulses between adjacent gratings all form stable interference signals, and vibration signals can be restored by detecting the phase change of the interference signals. Fig. 4 is a time domain and frequency domain map of the measured 90Hz sinusoidal signal, which shows that the vibration signal is well restored.
The distributed optical fiber sensing system and the method for realizing simultaneous measurement of vibration and temperature provided by the invention are described in detail above, and specific examples are applied in the description to explain the principle and the implementation mode of the invention, and the description of the above embodiments is only used for helping to understand the method and the core idea of the invention; meanwhile, for a person skilled in the art, according to the idea of the present invention, there may be variations in the specific embodiments and the application scope, and in summary, the content of the present specification should not be construed as a limitation to the present invention.
The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.
Claims (7)
1. A distributed optical fiber sensing system for realizing simultaneous measurement of vibration and temperature is characterized by comprising a narrow linewidth laser (1), a tunable laser (2) and a grating array (9); lasers emitted by the narrow-linewidth laser (1) and the tunable laser (2) pass through a laser amplifier, and then the obtained detection pulse light is transmitted to a first optical circulator (8); the first optical circulator (8) is also connected with the grating array (9) and a second optical circulator (10); the second optical circulator (10) is connected to the strong reflection grating (11) and the unbalanced Mach-Zehnder interferometer (13); the strong reflection grating (11) and the unbalanced Mach-Zehnder interferometer (13) are connected to the photoelectric detector;
the first optical circulator (8) is used for inputting the detection pulse light from the first port and injecting the detection pulse light into the grating array (9) from the second port, and the reflected light pulse of the grating array (9) is output to the second optical circulator (10) from the third port of the first optical circulator (8);
the second optical circulator (10) is used for inputting the reflected light pulse output by the first optical circulator (8) from the first port and outputting the reflected light pulse to the strong reflection grating (11) from the second port of the second optical circulator (10), and the reflected pulse of the strong reflection grating (11) is output to the unbalanced Mach-Zehnder interferometer (13) from the third port;
the strong reflection grating (11) is used for reflecting the detection pulse light of the narrow linewidth laser (1) through the detection pulse light of the tunable laser (2), and the reflected detection pulse light of the narrow linewidth laser (1) is output to the unbalanced Mach-Zehnder interferometer (13) through the third port of the second optical circulator (10);
and the unbalanced Mach-Zehnder interferometer (13) is used for generating interference on the reflected pulses of the adjacent gratings in the grating array (9) and outputting the interference light to different photoelectric detectors in a phase-splitting mode.
2. The distributed fiber optic sensing system for enabling simultaneous vibration and temperature measurement according to claim 1, wherein the narrow linewidth laser (1) is configured to emit continuous high coherence laser light; the tunable laser (2) is used for sequentially emitting continuous sweep-frequency laser with different wavelengths.
3. The distributed optical fiber sensing system for achieving simultaneous vibration and temperature measurement according to claim 1, wherein the laser amplifier comprises a first semiconductor laser amplifier (3), a second semiconductor laser amplifier (4), a pulse signal generator (5) and an erbium-doped fiber amplifier (7);
the semiconductor laser amplifier I (3) is connected with the pulse signal generator (5) and is used for modulating continuous light output by the narrow linewidth laser (1) into detection light pulses and outputting the detection light pulses to the optical fiber coupler (6);
the second semiconductor laser amplifier (4) is connected with the pulse signal generator (5) and is used for modulating the continuous light output by the tunable laser (2) into a detection light pulse and outputting the detection light pulse to the optical fiber coupler (6);
the optical fiber coupler (6) inputs the coupled detection light pulse to an erbium-doped optical fiber amplifier (7).
4. The distributed fiber optic sensing system for achieving simultaneous vibration and temperature measurement according to claim 1, wherein the grating array (9) is a chirped fiber grating array, with adjacent gratings arranged at a fixed pitch.
5. The distributed fiber optic sensing system for achieving simultaneous vibration and temperature measurement according to claim 1, wherein the strong reflection grating (11) is a narrow-band grating having a center wavelength coincident with a lasing wavelength of the narrow-linewidth laser (1).
6. The distributed optical fiber sensing system for realizing simultaneous measurement of vibration and temperature according to claim 1, wherein one arm of the unbalanced mach-zehnder interferometer (13) is provided with a delay fiber with a length of 2L, L being the spacing between adjacent gratings in the grating array; the pulse light reflected by the adjacent chirped fiber grating generates interference in the unbalanced Mach-Zehnder interferometer (13), an interference signal is divided into three signals with phase difference of 120 degrees through a 3 multiplied by 3 coupler, and the three signals are input to three photoelectric detectors.
7. A distributed optical fiber sensing method of a distributed optical fiber sensing system for achieving simultaneous vibration and temperature measurement according to any one of claims 1-6, comprising the steps of:
the laser emitted by the narrow linewidth laser (1) and the tunable laser (2) is amplified to obtain detection pulse light, and the detection pulse light is transmitted to a first optical circulator (8);
the first optical circulator (8) injects the probe pulse light into the grating array (9), and the reflected light pulse of the grating array (9) is output to the second optical circulator (10) through the first optical circulator (8);
the second optical circulator (10) injects the reflected light pulse output by the first optical circulator (8) into a strong reflection grating (11);
the strong reflection grating (11) obtains reflection signals of the grating array (9) under different wavelengths through detection pulse light of the tunable laser (2) and outputs the detection pulse light to the photoelectric detector I (12), fitting intensity values of the reflection signals with different wavelengths, reducing reflection spectrums of the grating array (9), and detecting temperature change around the grating array (9) through change of the reflection spectrums to realize distributed temperature sensing;
the strong reflection grating (11) reflects the detection pulse light of the narrow linewidth laser (1), and the reflected detection pulse light of the narrow linewidth laser (1) is output to the unbalanced Mach-Zehnder interferometer (13) through the second optical circulator (10);
the unbalanced Mach-Zehnder interferometer (13) generates interference on reflected pulses of adjacent gratings in the grating array (9), enables the interference light to be divided into phases and output to different photoelectric detectors, reduces vibration signals around the grating array (9) by demodulating phase changes of interference signals, and achieves distributed vibration sensing.
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