CN109282839B - Distributed optical fiber sensing system and method based on multi-pulse and multi-wavelength - Google Patents
Distributed optical fiber sensing system and method based on multi-pulse and multi-wavelength Download PDFInfo
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- CN109282839B CN109282839B CN201811405196.7A CN201811405196A CN109282839B CN 109282839 B CN109282839 B CN 109282839B CN 201811405196 A CN201811405196 A CN 201811405196A CN 109282839 B CN109282839 B CN 109282839B
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- 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
- G01D5/35325—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 reflection, e.g. Mickelson interferometer
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- 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
- G01D5/344—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 using polarisation
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- 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
- G01D5/35338—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 other arrangements than interferometer arrangements
- G01D5/35354—Sensor working in reflection
- G01D5/35358—Sensor working in reflection using backscattering to detect the measured quantity
- G01D5/35361—Sensor working in reflection using backscattering to detect the measured quantity using elastic backscattering to detect the measured quantity, e.g. using Rayleigh backscattering
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- 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
- G01D5/3537—Optical fibre sensor using a particular arrangement of the optical fibre itself
- G01D5/35374—Particular layout of the fiber
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Abstract
The invention discloses a distributed optical fiber sensing system and method based on multi-pulse and multi-wavelength, belonging to the technical field of distributed optical fiber sensors. The invention uses a plurality of light source combinations, light with n wavelengths is injected in a period T, delay time is controlled through an optical fiber delay line, light pulses are sequentially injected into a sensing optical fiber according to a specific sequence, backward Rayleigh scattering light generated by the n light pulses is separated through gratings with different central reflection wavelengths, enters a photoelectric detector and is subjected to photoelectric conversion, n OTDR curves which are mutually independent are obtained after AD acquisition, n phase information with repetition frequency f is obtained by demodulating the n OTDR curves, and the n demodulated curves are interwoven through an array to form a final result.
Description
Technical Field
The invention belongs to the technical field of distributed optical fiber sensors, and particularly relates to a distributed optical fiber sensing system and method based on multi-pulse and multi-wavelength.
Background
Distributed optical fiber sensing is an important application in the field of optical fiber sensing, compared with point type sensors, the distributed optical fiber sensing has the advantages of obvious advantages, low cost, convenience in processing and the like, has obvious market advantages in the fields of perimeter security, pipeline detection, geological exploration, distributed temperature measurement and the like, can detect physical quantities such as vibration, temperature, strain and the like along an optical cable in real time, and has good market prospect.
At present, the system of distributed measurement is mainly based on the principle of back scattering, and the principle of such system is to utilize the property change of the back scattering light to realize detection, including the phase, polarization state, frequency change and the like of the back scattering light. Common principles include phase-sensitive optical time domain reflectometers (phi-OTDR), polarization-sensitive optical time domain reflectometers (P-OTDR), Brillouin optical time domain reflectometers (B-OTDR), Raman optical time domain reflectometers (R-OTDR). The phase-sensitive optical time domain reflectometer (phi-OTDR) is especially suitable for use occasions with long distance, high spatial resolution and high signal-to-noise ratio. The method can be used in the fields of vibration detection, sound sensing, perimeter security and the like.
The basic principle of Φ -OTDR is to achieve phase demodulation by demodulating the phase change of the backward rayleigh scattered light generated by pulsed light injected in the fiber. When vibration and the like act on the optical fiber, the force changes the refractive index of the optical fiber in the axial direction, further causes the optical phase at the position to change, and a vibration signal can be obtained by analyzing the optical phase change. In the currently common distributed sensing system, common detection demodulation schemes include 3 × 3 coupler demodulation, phase generation carrier demodulation scheme, and digital coherent demodulation scheme, where there is at most one optical pulse injected into the sensing fiber at a time. If more than a plurality of light pulses are injected, the backward rayleigh scattered light generated by the previous light pulse and the rayleigh scattered light generated by the next light pulse are mixed, and a part of the intensity of the backward rayleigh scattered light of the two pulses is repeated, so that the phase of the repeated part cannot be demodulated.
Therefore, as the length of the fiber increases, the maximum repetition rate of the pulses decreases, and the maximum repetition rate is related to the length of the fiber by f 2nl/c, where n is the effective refractive index of the fiber. The optical pulse injected into the optical fiber in the phi-ODTR system is essentially discrete sampling of the position of the individual point on the optical fiber, so that the maximum detection frequency of the system for the vibration signal is nl/c according to the Shannon sampling law. In practical cases, since the vibration signal is almost impossible to be a single frequency signal, the maximum frequency of actual detection is usually nl/2 c. In a 100Km system, the maximum repetition frequency is 1KHz, and the maximum frequency of actual detection without down-sampling is only 250Hz, which cannot be realized for high-frequency vibration and sound wave detection. If the maximum frequency of detection is guaranteed, 10 sets of 10Km systems are needed, which greatly increases the system cost. The power of the single light source is split for N times by using the scheme of combining the single light source with a frequency shifter, a balanced detector, demodulation and the like, and then the power is reduced to
The signal-to-noise ratio will degrade rapidly as N increases. Using N asynchronous signals to control N asynchronous signals simultaneouslyThe co-frequency shifter also increases the complexity and cost of the system, and circuit devices such as a mixer filter and the like are not added. And the full-optical scheme is adopted to combine with multiple light sources, and an optical power distribution device is not used, so that the power of a single pulse cannot be reduced. The combination of the grating and the circulator is used for separating light with different wavelengths in space, and meanwhile, the optical fiber interferometer is used for demodulation.
Disclosure of Invention
Aiming at the problems in the prior art, the invention provides a distributed optical fiber sensing system and a distributed optical fiber sensing method based on multi-pulse and multi-wavelength; the present invention uses a combination of multiple light sources with slightly different center wavelengths, which injects n wavelengths of light over a period T compared to conventional phi-ODTR systems. The light of each wavelength is controlled by an optical fiber delay line, the light pulses are sequentially injected into a sensing optical fiber according to the sequence by controlling the delay time, backward Rayleigh scattered light generated by the n light pulses is separated by gratings with different central reflection wavelengths, enters a photoelectric detector for photoelectric conversion, and is acquired by AD acquisition to obtain n OTDR curves, the curves are mutually independent and have intervals in time, n pieces of phase information with repetition frequency f are obtained by demodulating the n OTDR curves, the n demodulated curves are interwoven to form a final result through an array, and the maximum frequency of a detection signal of the actual demodulation scheme is improved to n times according to Shannon sampling theorem.
One of the objects of the present invention is to provide a distributed optical fiber sensing system based on multi-pulse and multi-wavelength, comprising
The light source module comprises n narrow linewidth laser light sources with different central wavelengths; n is a natural number greater than 1;
the modulation module comprises n optical fiber optical modulators and a pulse signal generator, wherein the input end of each optical fiber optical modulator is coupled with the light source output terminal of a narrow-linewidth laser light source, and the signal output terminal of the pulse signal generator is electrically connected with the modulation terminals of the n optical fiber optical modulators; the optical fiber light modulator modulates the light source output by the narrow linewidth laser light source into pulse light;
the delay module comprises n-1 optical fiber delay lines; the delay time of each optical fiber delay line is different from one another, and the delay time of each optical fiber delay line is
m is an integer from 0 to n-1; f is the pulse repetition frequency of the pulse signal generator;
the coupling module comprises an n x 1 optical fiber coupler, one output end of the n optical fiber modulators is coupled with one input end of the n x 1 optical fiber coupler through an optical fiber, and the other n-1 output ends of the n optical fiber modulators are respectively coupled with one input end of the n x 1 optical fiber coupler through 1 optical fiber delay line;
the pulse amplification module comprises a pulse optical amplifier, and a signal input terminal of the pulse optical amplifier is connected with a signal output terminal of the n multiplied by 1 optical fiber coupler through an optical fiber;
the pre-amplification module comprises a pre-amplifier, and the signal output terminal of the pulse light amplifier is respectively connected with the sensing optical fiber and the signal input terminal of the pre-amplifier after passing through the polarizer and the circulator A in sequence;
the light splitting system comprises n groups of light splitting modules, each group of light splitting modules comprises a circulator B and a fiber grating, the circulator B and the fiber grating of each group of light splitting modules are connected through optical fibers, the n groups of light splitting modules are sequentially connected in series through the optical fibers, and the central wavelengths reflected by the n fiber gratings are respectively equal to the central wavelengths of the n narrow-linewidth laser light sources; the signal output terminal of the preamplifier is connected with the signal input terminal of the circulator B of the first light splitting module through an optical fiber;
the interference module comprises n optical fiber interference assemblies which correspond to the n circulators B one by one, and each optical fiber interference assembly consists of a2 multiplied by 2 optical fiber coupler, a 3 multiplied by 3 optical fiber coupler and two Faraday rotators to form a Michelson interferometer;
the signal detection module comprises n photoelectric detectors, and each photoelectric detector corresponds to one optical fiber interference component;
and the data processing terminal is used for receiving the output signal of the signal detection module and analyzing and processing the signal.
Further: the bandwidth of the narrow-linewidth laser light source is less than 1 KHZ.
Further: for each fiber optic interferometer assembly: the 2 × 2 optical fiber coupler includes an input terminal a (20), an input terminal B (27), an output terminal a (25), and a butt terminal a; the 3 × 3 optical fiber coupler includes two input terminals C, an input terminal D (28), an output terminal C (24), an output terminal D (26), and a butt terminal B; the butt terminal a and the butt terminal B are connected by an optical fiber, and the input terminal B (27) and the input terminal D (28) are vacant by a connection loss element; the two input terminals C are connected to a Faraday rotator mirror 23.
Further: the pulse frequency f is in the range of 1 muHz to 10Mhz, and the pulse duration is less than
Further, the data processing terminal comprises an analog-to-digital conversion module and a demodulation analyzer.
The invention also aims to provide a method for a distributed optical fiber sensing system based on multi-pulse and multi-wavelength, which at least comprises the following steps:
the method comprises the following steps: n narrow linewidth laser light sources emit n central wavelengths which are lambda in sequence1,λ2…λnEach light source is connected with one optical fiber light modulator, the n optical fiber light modulators are connected with the same pulse signal generator, and the pulse signal generator and the optical fiber light modulators modulate continuous light into pulse light;
step two: dividing by lambda under the action of delay module1Other n-1 pulse lights pass through different fiber delay lines to generate different time delays lambda1,λ2…λnDelay respectively
Step three: after being delayed, the n pulse lights enter a pulse amplifier through an n multiplied by 1 coupler to carry out pulse power amplification;
step four: the n amplified pulse lights are changed into linearly polarized lights through a polarizer and then injected into the sensing optical fiber through a circulator A;
step five: backward Rayleigh scattered light returning from the third port of the circulator A enters a preamplifier, and the preamplifier amplifies the backward Rayleigh scattered light;
step six: the amplified backward Rayleigh scattered light enters an optical splitting system, each optical splitting module in the optical splitting system reflects light waves with a specific central wavelength and transmits other light waves, and then the light with different central wavelengths is split;
step seven: the separated Rayleigh scattering light with each central wavelength enters the optical fiber interference components, and each optical fiber interference component outputs three paths of interference signals with phase difference of 120 degrees;
step eight: the signal detection module converts interference ripple signals formed by the three interference signals of each optical fiber interference component into electric signals;
and step nine, the data processing terminal performs digital-to-analog conversion and real-time or off-line demodulation on the received signals at the same time to obtain phi-OTDR demodulation results of n different wavelengths, and performs data interleaving on the results.
In summary, the advantages and positive effects of the invention are:
the invention adopts the multiplexing and demultiplexing of multi-wavelength multi-pulse light formed by an optical delay system, simultaneously uses a pure optical beam splitting system and an interferometer demodulation scheme to respectively interleave processed OTDR curves with different wavelengths, so that the detection bandwidth of the system is increased to n times, and the detection bandwidth of the system to vibration signals is effectively increased. Meanwhile, the signal-to-noise ratio of the system can be improved by combining methods such as average down sampling and the like on the premise of sacrificing a certain system bandwidth. And the light source and the light splitting system can be flexibly configured according to the requirement, and an all-optical scheme is used, so that the introduction of devices such as an electric mixer, an analog circuit filter and the like is avoided, and the electromagnetic radiation resistance of the system is improved.
Drawings
FIG. 1 is a block diagram of the preferred embodiment of the present invention;
FIG. 2 is a block diagram of a fiber optic interference assembly in accordance with a preferred embodiment of the present invention;
FIG. 3 is an OTDR curve of n wavelengths generated under a pulse signal according to a preferred embodiment of the present invention
FIG. 4 is a chart of the phi-OTDR demodulation results for each pulse for each single pulse of light prior to data interleaving
Fig. 5 shows the demodulation result of up-sampling after interleaving the demodulation data of a plurality of pulsed lights with a plurality of wavelengths.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail with reference to the following embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
As shown in fig. 1 and 2, a distributed optical fiber sensing system based on multiple pulses and multiple wavelengths is provided with n narrow linewidth laser light source modules with different central wavelengths, an n × 1 optical fiber coupler, an optical fiber optical modulator, an optical fiber polarizer, a grating, an optical fiber delay line, an optical amplification module, a2 × 2 optical fiber coupler, a 3 × 3 optical fiber coupler, a faraday rotator, an optical fiber circulator, a photodetector, a pulse signal generator, a digital-to-analog conversion collector, and a demodulation analyzer. The bandwidth of the narrow-linewidth laser light source is less than 1 KHZ.
The n light sources emit laser with n central wavelengths, each light source is connected with a modulator, and the n modulators are connected with the same pulse signal generator. After the modulator modulates continuous light into pulse light, the other n-1 light sources except the first light source are connected with different optical fiber delay lines after passing through the modulator, and each delay line is set with different delay time, lambda1,λ2…λnThe delay time of the delay line corresponding to the light source is respectively
Where f is the pulse repetition frequency of the pulse signal generator. Then, the n paths of light are converged into a beam through an n x 1 optical fiber coupler in one period
Within, there are n light pulses in time sequence, the wavelengths corresponding to lambda1,λ2…λn. The input of the n multiplied by 1 optical fiber coupler is connected with a pulse optical amplifier, the amplified pulse optical amplifier enters the circulator, and the other port of the circulator is respectively connected with the long-distance sensing optical fiber and the preamplifier. The preamplifier amplifies the backward Rayleigh scattered light, and then the amplified light enters a light splitting system consisting of n circulators and fiber gratings, and the reflection peak value of each grating corresponds to lambda1,λ2…λnAnd for other wavelength light transmission, separating different wavelength backward Rayleigh light on space and then respectively entering n optical fiber interferometers formed by 3 x 3 optical fiber couplers and 2 x 2 optical fiber couplers, wherein the interferometers are connected with photoelectric detectors and then connected with analog-to-digital conversion collectors, and the light is analyzed by a digital signal processing method through a demodulation analyzer.
The central wavelengths of the n narrow linewidth laser light sources are respectively lambda1,λ2…λn。
The modulator used in the present invention is of the intensity modulation type, and functions to convert a continuous light output into a pulsed light.
The optical fiber delay line used in the invention can make the optical pulse generate time delay.
The invention uses an n x 1 fiber coupler acting to couple lambda1,λ2…λnIs coupled into the optical fiber with equal power.
The pulse signal generator used in the invention has the function of generating periodic pulse signals, the pulse frequency f can be set from 1 mu Hz to 10Mhz, and the pulse duration is set to be far less than
Any waveform generator may be used.
The light amplification module is used in the invention to amplify the modulated pulse light intensity.
The circulator adopted in the invention emits pulse light into the sensing optical fiber, and receives backward Rayleigh scattered light at the other port.
The preamplifier adopted in the invention is used for amplifying the backward Rayleigh scattered light received by the circulator again.
The light splitting system comprises an optical circulator and gratings, wherein the centers of n gratings correspond to lambda1,λ2…λnIts function is to reflect back selectively to lambda1,λ2…λnCorresponding rayleigh light while transmitting other wavelength bands.
The optical fiber interferometer used in the invention is a Michelson interferometer composed of a2 × 2 optical fiber coupler, a 3 × 3 optical fiber coupler and a Faraday rotator mirror. The output is interference signals with phase difference of 120 degrees. (ii) a
As shown in fig. 2: for each fiber optic interferometer assembly: the 2 × 2 optical fiber coupler 21 includes an input terminal a20, an input terminal B27, an output terminal a25, and a butt terminal a; the 3 × 3 optical fiber coupler comprises two input terminals C, an input terminal D28, an output terminal C24, an output terminal D26 and a butt terminal B; the butt terminal a and the butt terminal B are connected by an optical fiber, and the input terminal B27 and the input terminal D28 are left vacant by a connection loss element; one faraday rotator 23 is connected to each of the two input terminals C.
That is, the right end of the 2 × 2 optical fiber coupler 21 is connected to the left end of the 3 × 3 optical fiber coupler 22, and the input terminal B27 of the 2 × 2 optical fiber coupler is left vacant by a connection loss device. The 3 x 3 fiber coupler is then connected across faraday rotator mirror 23 with input terminal D28 left free by the connection loss device. Then, the output result of the 2 × 2 optical fiber coupler output terminal a25, the 3 × 3 optical fiber coupler output terminal C24 and the 3 × 3 optical fiber coupler output terminal D26 is 3 interference signals with a phase difference of 120 ° between two signals.
The photoelectric detectors adopted in the invention are high-sensitivity type, each photoelectric detector is provided with three photoelectric detection diodes with the same characteristics, and the photoelectric detectors have a low-noise signal amplification function.
The analog-to-digital conversion collector used in the present invention functions to convert analog voltage/current signals into digital signals.
The demodulation analyzer of the invention analyzes and processes the collected signals to obtain n OTDR curve demodulation results, and then interweaves the n ODTR curve demodulation results, which can be realized by a computer or an FPGA, a DSP, an ARM embedded platform and the like.
A method for using a large-bandwidth distributed optical fiber sensing system with multi-pulse and multi-wavelength light comprises the following specific implementation steps:
the method comprises the following steps: n light sources emit n central wavelength laser lambda1,λ2…λnEach light source is connected with a modulator, and the n modulators are connected with the same pulse signal generator. The modulator modulates continuous light into pulsed light under the input of an external signal.
Step two: except for lambda1The outer n-1 pulse lights pass through different optical fiber delay lines to generate different time delays, lambda1,λ2…λnDelay respectively
Step three: the n pulse lights are delayed, pass through the n multiplied by 1 coupler and then enter the pulse amplifier for pulse power amplification.
Step four: and the amplified pulse light is converted into linearly polarized light through a polarizer and then is injected into the sensing optical fiber through the circulator.
Step five: the backward rayleigh scattered light returned from the port of the circulator 3 enters a preamplifier, and the amplifier amplifies the backward rayleigh scattered light.
Step six: the amplified backward Rayleigh scattering light enters an optical splitting system, each grating of the optical splitting system reflects the central wavelength corresponding to the central wavelength of the light source, selectively reflects the corresponding wavelength, transmits other wavelengths, and then separates the light with different central wavelengths.
Step seven: the separated Rayleigh scattered light with each wavelength enters the optical fiber interferometer and outputs three paths of interference signals with phase difference of 120 degrees.
Step eight: the n three-path interference signals are input into the photoelectric detector and then enter the analog-to-digital converters, the analog-to-digital converters work in a delay triggering mode, different delays are set for the analog-to-digital converters corresponding to each optical splitting system so as to achieve synchronization of the final OTDR curves, and data are sent to an upper computer after analog-to-digital conversion and collection.
Step nine: the upper computer demodulates the acquired data in real time or off line to obtain phi-OTDR demodulation results of n different wavelengths, and the results are interleaved to obtain the result of increasing the sampling rate by n times.
In FIG. 3, λ1，λ2，λ3…λnThe corresponding curves are respectively acquired before demodulation OTDR intensity curves after being divided by the light splitting system, and it can be seen that the time intervals of each curve are the same and are periodically arranged in time.
In fig. 4, taking 4 wavelengths as an example, the line widths of the 4 light sources are 1khz, with the central wavelengths of the 4 light sources being 1550.1nm, 1550.3nm, 1550.5nm and 1550.7nm, respectively. The four curves are phase diagrams of the vibration position phi-ODTR after being respectively and independently used and demodulated, and it can be seen that the real vibration signal cannot be reproduced under the condition of insufficient sampling rate.
Fig. 5 is a vibration curve depicted after data interleaving of the curve in fig. 4, and after the system improves sampling, high-frequency components are greatly improved, and a vibration signal can be reproduced.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents and improvements made within the spirit and principle of the present invention are intended to be included within the scope of the present invention.
Claims (6)
1. A distributed optical fiber sensing system based on multi-pulse and multi-wavelength is characterized in that: at least comprises the following steps:
the light source module comprises n narrow linewidth laser light sources with different central wavelengths; n is a natural number greater than 1;
the modulation module comprises n optical fiber optical modulators and a pulse signal generator, wherein the input end of each optical fiber optical modulator is coupled with the light source output terminal of a narrow-linewidth laser light source, and the signal output terminal of the pulse signal generator is electrically connected with the modulation terminals of the n optical fiber optical modulators; the optical fiber light modulator modulates the light source output by the narrow linewidth laser light source into pulse light;
the delay module comprises n-1 optical fiber delay lines; the delay time of each optical fiber delay line is different from one another, and the delay time of each optical fiber delay line is
m is an integer from 0 to n-1; f is the pulse repetition frequency of the pulse signal generator;
the coupling module comprises an n x 1 optical fiber coupler, one output end of the n optical fiber modulators is coupled with one input end of the n x 1 optical fiber coupler through an optical fiber, and the other n-1 output ends of the n optical fiber modulators are respectively coupled with one input end of the n x 1 optical fiber coupler through 1 optical fiber delay line;
the pulse amplification module comprises a pulse optical amplifier, and a signal input terminal of the pulse optical amplifier is connected with a signal output terminal of the n multiplied by 1 optical fiber coupler through an optical fiber;
the pre-amplification module comprises a pre-amplifier, and the signal output terminal of the pulse light amplifier is respectively connected with the sensing optical fiber and the signal input terminal of the pre-amplifier after passing through the polarizer and the circulator A in sequence;
the light splitting system comprises n groups of light splitting modules, each group of light splitting modules comprises a circulator B and a fiber grating, the circulator B and the fiber grating of each group of light splitting modules are connected through optical fibers, the n groups of light splitting modules are sequentially connected in series through the optical fibers, and the central wavelengths reflected by the n fiber gratings are respectively equal to the central wavelengths of the n narrow-linewidth laser light sources; the signal output terminal of the preamplifier is connected with the signal input terminal of the circulator B of the first light splitting module through an optical fiber;
the interference module comprises n optical fiber interference assemblies which correspond to the n circulators B one by one, and each optical fiber interference assembly consists of a2 multiplied by 2 optical fiber coupler, a 3 multiplied by 3 optical fiber coupler and two Faraday rotators to form a Michelson interferometer;
the signal detection module comprises n photoelectric detectors, and each photoelectric detector corresponds to one optical fiber interference component;
and the data processing terminal is used for receiving the output signal of the signal detection module and analyzing and processing the signal.
2. The multi-pulse multi-wavelength based distributed optical fiber sensing system of claim 1, wherein: the bandwidth of the narrow-linewidth laser light source is less than 1 KHZ.
3. The multi-pulse multi-wavelength based distributed optical fiber sensing system of claim 1, wherein: for each fiber optic interferometer assembly: the 2 × 2 optical fiber coupler includes an input terminal a (20), an input terminal B (27), an output terminal a (25), and a butt terminal a; the 3 × 3 optical fiber coupler includes two input terminals C, an input terminal D (28), an output terminal C (24), an output terminal D (26), and a butt terminal B; the butt terminal a and the butt terminal B are connected by an optical fiber, and the input terminal B (27) and the input terminal D (28) are vacant by a connection loss element; the two input terminals C are connected to a Faraday rotator mirror 23.
4. The multi-pulse multi-wavelength based distributed optical fiber sensing system of claim 1, wherein: the pulse frequency f is in the range of 1 muHz to 10Mhz, and the pulse duration is less than
5. The multi-pulse multi-wavelength based distributed optical fiber sensing system of claim 1, wherein said data processing terminal comprises an analog-to-digital conversion module and a demodulation analyzer.
6. A method of a distributed optical fiber sensing system based on multi-pulse and multi-wavelength is characterized by at least comprising the following steps:
the method comprises the following steps: n number ofN central wavelengths emitted by narrow linewidth laser light source are lambda in sequence1,λ2…λnEach light source is connected with one optical fiber light modulator, the n optical fiber light modulators are connected with the same pulse signal generator, and the pulse signal generator and the optical fiber light modulators modulate continuous light into pulse light;
step two: dividing by lambda under the action of delay module1Other n-1 pulse lights pass through different fiber delay lines to generate different time delays lambda1,λ2…λnDelay respectively
Step three: after being delayed, the n pulse lights enter a pulse amplifier through an n multiplied by 1 coupler to carry out pulse power amplification;
step four: the n amplified pulse lights are changed into linearly polarized lights through a polarizer and then injected into the sensing optical fiber through a circulator A;
step five: backward Rayleigh scattered light returning from the third port of the circulator A enters a preamplifier, and the preamplifier amplifies the backward Rayleigh scattered light;
step six: the amplified backward Rayleigh scattered light enters an optical splitting system, each optical splitting module in the optical splitting system reflects light waves with a specific central wavelength and transmits other light waves, and then the light with different central wavelengths is split;
step seven: the separated Rayleigh scattering light with each central wavelength enters the optical fiber interference components, and each optical fiber interference component outputs three paths of interference signals with phase difference of 120 degrees;
step eight: the signal detection module converts interference ripple signals formed by the three interference signals of each optical fiber interference component into electric signals;
and step nine, the data processing terminal performs digital-to-analog conversion and real-time or off-line demodulation on the received signals at the same time to obtain phi-OTDR demodulation results of n different wavelengths, and performs data interleaving on the results.
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