CN114111860B - Distributed phi-OTDR sensing method and system based on multi-frequency pulse coding - Google Patents
Distributed phi-OTDR sensing method and system based on multi-frequency pulse coding Download PDFInfo
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- 238000000253 optical time-domain reflectometry Methods 0.000 title claims abstract description 61
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- 239000013307 optical fiber Substances 0.000 claims abstract description 81
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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
Abstract
The invention discloses a distributed phi-OTDR sensing method and system based on multi-frequency pulse coding, and relates to the technical field of distributed optical fiber sensing. The method comprises the following steps: the sending unit outputs optical signals to a first coupler, and the first coupler divides the optical signals into a first path of optical signals and a second path of optical signals; inputting the first path of optical signal to a modulation unit to obtain a modulated optical signal; inputting the second path of optical signal to a receiving unit; the modulated optical signal is input to a sensing optical fiber after passing through an erbium-doped optical fiber amplifier; after being disturbed by the disturbance simulation unit, the sensing optical fiber returns a backward Rayleigh scattering optical signal carrying disturbance information to the erbium-doped optical fiber amplifier, and then the backward Rayleigh scattering optical signal is input to the receiving unit; and the receiving unit mixes the received second path of optical signals and the backward Rayleigh scattering optical signals carrying the disturbance information and sends the mixed signals to the processing unit to obtain disturbance signal information. The invention can solve the problem of the limit of the distance, the signal amplitude and the frequency of the detection disturbance signal in the prior art, and can improve the system performance.
Description
Technical Field
The invention relates to the technical field of distributed optical fiber sensing, in particular to a distributed phi-OTDR sensing method and system based on multi-frequency pulse coding.
Background
Under the current era background of vigorous engineering construction, the scale of infrastructure construction and large-scale engineering construction is gradually enlarged, so the method is also particularly important for monitoring the structural health of various large buildings, bridges and oil and gas pipelines. In long-distance disturbance monitoring of large-scale engineering, compared with a traditional electronic sensor, the distributed sensing network based on the optical fiber has the advantages of low power consumption, capability of completing measurement in a severe environment and the like.
In the prior art, a heterodyne I/Q coherent detection technique of a distributed Φ -OTDR (Phase-Sensitive Optical Time-Domain reflectometer) system based on a single-frequency unipolar Golay code is disclosed. In such a Φ -OTDR system, a continuous laser beam is generally modulated into an optical pulse by using an AOM (Acousto-optic modulator). Because negative value modulation cannot be realized in intensity modulation, each group of bipolar sequences is subjected to single polarization treatment and is divided into two paths of injection optical fibers. Therefore, four pulses are required to be respectively injected into the optical fiber for detecting each disturbance, the time required for detection is prolonged, and the influence of system noise is larger. And because of the time difference of the multi-pulse injection optical fiber, the technology has limits on the amplitude and the frequency of the disturbance signal.
In the second prior art, a distributed phi-OTDR system heterodyne I/Q coherent detection technology based on single-frequency bipolar Golay codes. The phi-OTDR system cannot adopt a direct detection technology at a receiving end, needs to recover the phase by coherent detection, and directly receives a vector light field through an optical mixer. Compared with a unipolar code, the sensitivity is improved, the measurement time is halved, and the problems of amplitude limitation and frequency limitation of a disturbance signal caused by detection time difference still exist.
The phi-OTDR adopts a highly coherent narrow linewidth laser as a transmitting end light source, and detects the position, amplitude and frequency of a disturbance signal by utilizing the intensity and phase of backward Rayleigh scattering light. The spatial resolution of single pulse light based Φ -OTDR systems is limited by the pulse width, but reducing the pulse width again results in a too low signal-to-noise ratio. Although the phi-OTDR system based on single-frequency pulse coding effectively solves the problem, the system inevitably limits the detection distance, the amplitude of the disturbance signal and the frequency of the disturbance signal due to a certain time difference of a multi-path pulse injection optical fiber.
In summary, in the prior art, single-frequency optical pulse codes are mostly used for detecting the disturbance, so that the disturbance signals detected by multiple paths of pulses are not completely consistent, and therefore, the detection length, the disturbance signal amplitude and the disturbance signal frequency are limited to a certain extent, and a further improvement space is provided, so that the problem that how to solve the problem that a distributed phi-OTDR sensing system based on single-frequency pulse codes is limited in detecting the disturbance signal amplitude and phase in the prior art exists.
Disclosure of Invention
The invention provides a distributed phi-OTDR sensing system based on single-frequency pulse coding, which aims at solving the problem that the amplitude and the phase of a detected disturbing signal are limited in the prior art.
In order to solve the technical problems, the invention provides the following technical scheme:
on one hand, the invention provides a distributed phi-OTDR sensing method based on multi-frequency pulse coding, which is realized by a distributed phi-OTDR sensing system based on multi-frequency pulse coding, wherein the distributed phi-OTDR sensing system based on multi-frequency pulse coding comprises a sending unit, a first coupler, a modulating unit, an erbium-doped fiber amplifier, a sensing fiber, a disturbance simulating unit, a receiving unit and a processing unit; wherein the receiving unit comprises a balanced photodetector BPD or an integrated coherent receiver ICR.
The method comprises the following steps:
s1, the sending unit outputs the optical signal to the first coupler, and the first coupler divides the optical signal into a first path of optical signal and a second path of optical signal; inputting the first path of optical signal to a modulation unit to obtain a modulated optical signal; the second optical signal is input to the receiving unit.
S2, inputting the modulated optical signal to a sensing optical fiber after passing through an erbium-doped optical fiber amplifier; the sensing optical fiber returns backward Rayleigh scattering optical signals carrying disturbance information to the erbium-doped optical fiber amplifier after being disturbed by the disturbance simulation unit, and the backward Rayleigh scattering optical signals are input to the receiving unit after passing through the erbium-doped optical fiber amplifier.
And S3, the receiving unit mixes the received second path of optical signal with the backward Rayleigh scattering optical signal carrying the disturbance information and sends the mixed signal to the processing unit to obtain the disturbance signal information.
Optionally, the transmitting unit in S1 is a narrow linewidth laser.
The first coupler is 99: 1.
The disturbance simulation unit is a piezoelectric ceramic oscillator PZT.
Optionally, the modulation unit in S1 includes a beam splitter, four different-frequency fiber acousto-optic modulators AOM, an arbitrary waveform generator AWG, and a second coupler.
Alternatively, the modulation unit comprises an I/Q modulator, an arbitrary waveform generator AWG.
Optionally, the modulation unit in S1 includes a beam splitter, four different-frequency fiber acousto-optic modulators AOM, an arbitrary waveform generator AWG, and a second coupler.
The first path of optical signal in S1 is input to the modulation unit, and obtaining the modulated optical signal includes:
the first path of optical signal is input into the beam splitter and then is divided into four paths of optical signals, and the four paths of optical signals pass through the arbitrary waveform generator to obtain four paths of different pulse codes; four paths of different pulse codes are respectively modulated by four different-frequency optical fiber acousto-optic modulators AOM.
The modulated four optical signals are combined into one optical signal, namely the modulated optical signal, through the second coupler.
Optionally, the receiving unit is a balanced photodetector BPD.
The receiving unit mixes the received second path of optical signal with the backward Rayleigh scattering optical signal carrying the disturbance information, and sends the mixed signal to the processing unit, and the obtaining of the disturbance signal information comprises the following steps:
and the balance photoelectric detector mixes the received second path of optical signals and the backward Rayleigh scattering optical signals carrying the disturbance information, converts the mixed signals into electric signals, and extracts and analyzes the electric signals through the processing unit to obtain disturbance signal information.
Optionally, the modulation unit in S1 includes an I/Q modulator, an arbitrary waveform generator AWG.
The first path of optical signal in S1 is input to the modulation unit, and obtaining the modulated optical signal includes:
the first path of optical signal is input to an arbitrary waveform generator AWG for pulse coding and then input to an I/Q modulator to obtain a path of pulse coding signal, namely a modulated optical signal; the modulated optical signals include optical signals with positive and negative modulation frequencies and optical signals with positive modulation frequencies.
Optionally, when the modulated optical signal is an optical signal with a modulation frequency of positive and negative frequencies, the receiving unit is an integrated coherent receiver ICR.
The receiving unit mixes the received second path of optical signal with the backward Rayleigh scattering optical signal carrying the disturbance information, and sends the mixed signal to the processing unit, and the obtaining of the disturbance signal information comprises the following steps:
and the second path of optical signal and the backward Rayleigh scattering optical signal carrying the disturbance information are converted into electric signals through the BPD after passing through the Hybrid of the optical mixer, the I path of signal and the Q path of signal are converted into complex signals, and the complex signals are extracted and analyzed by the processing unit to obtain disturbance signal information.
Optionally, when the modulated optical signal is an optical signal whose modulation frequencies are all positive frequencies, the receiving unit is a balanced photodetector BPD.
The receiving unit mixes the received second path of optical signal with the backward Rayleigh scattering optical signal carrying the disturbance information, and sends the mixed signal to the processing unit, and the obtaining of the disturbance signal information comprises the following steps:
and the balance photoelectric detector mixes the received second path of optical signals and the backward Rayleigh scattering optical signals carrying the disturbance information, converts the mixed signals into electric signals, and extracts and analyzes the electric signals through the processing unit to obtain disturbance signal information.
On the other hand, the invention provides a distributed phi-OTDR sensing system based on multi-frequency pulse coding, which is used for realizing a distributed phi-OTDR sensing method based on multi-frequency pulse coding, and comprises a sending unit, a first coupler, a modulating unit, an erbium-doped fiber amplifier, a sensing fiber, a disturbance simulating unit, a receiving unit and a processing unit; the receiving unit comprises a Balanced Photoelectric Detector (BPD) and an Integrated Coherent Receiver (ICR);
wherein:
and the transmitting unit is used for outputting the optical signal to the first coupler.
The first coupler is used for dividing the optical signal into a first path of optical signal and a second path of optical signal.
And the modulation unit is used for obtaining the modulated optical signal.
And the erbium-doped fiber amplifier is used for inputting the modulated optical signal to the sensing fiber after passing through the erbium-doped fiber amplifier.
And the sensing optical fiber is used for returning a backward Rayleigh scattering optical signal carrying disturbance information after being disturbed by the disturbance simulation unit.
And the disturbance simulation unit is used for disturbing the sensing optical fiber.
And the receiving unit is used for mixing the received second path of optical signals and the backward Rayleigh scattering optical signals carrying the disturbance information and sending the mixed signals to the processing unit.
And the processing unit is used for obtaining the disturbance signal information.
Optionally, the transmitting unit is a narrow linewidth laser.
The first coupler is 99: 1.
The disturbance simulation unit is a piezoelectric ceramic oscillator PZT.
Optionally, the modulation unit includes a beam splitter, four different-frequency fiber acousto-optic modulators AOMs, an arbitrary waveform generator AWG, and a second coupler.
Alternatively, the modulation unit comprises an I/Q modulator, an arbitrary waveform generator AWG.
Optionally, the modulation unit in S1 includes a beam splitter, four different-frequency fiber acousto-optic modulators AOM, an arbitrary waveform generator AWG, and a second coupler.
Optionally, the modulation unit is further configured to:
the first path of optical signal is input into a beam splitter and then is divided into four paths of optical signals, and the four paths of optical signals pass through an arbitrary waveform generator to obtain four paths of different pulse codes; four paths of different pulse codes are respectively modulated by four different-frequency optical fiber acousto-optic modulators AOM.
The modulated four optical signals are combined into one optical signal, namely the modulated optical signal, through the second coupler.
Optionally, the receiving unit is a balanced photodetector BPD.
A receiving unit, further configured to:
and the balance photoelectric detector mixes the received second path of optical signals and the backward Rayleigh scattering optical signals carrying the disturbance information, converts the mixed signals into electric signals, and extracts and analyzes the electric signals through the processing unit to obtain disturbance signal information.
Optionally, the modulation unit in S1 includes an I/Q modulator, an arbitrary waveform generator AWG.
Optionally, the modulation unit is further configured to:
the first path of optical signal is input to an arbitrary waveform generator AWG for pulse coding and then is input to an I/Q modulator to obtain a path of pulse coding signal, namely a modulated optical signal; the modulated optical signals include optical signals with positive and negative modulation frequencies and optical signals with positive modulation frequencies.
Optionally, when the modulated optical signal is an optical signal with a modulation frequency of positive and negative frequencies, the receiving unit is an integrated coherent receiver ICR.
A receiving unit, further configured to:
and the second path of optical signal and the backward Rayleigh scattering optical signal carrying the disturbance information are converted into electric signals through the BPD after passing through the Hybrid of the optical mixer, the I path of signal and the Q path of signal are converted into complex signals, and the complex signals are extracted and analyzed by the processing unit to obtain disturbance signal information.
Optionally, when the modulated optical signal is an optical signal whose modulation frequencies are all positive frequencies, the receiving unit is a balanced photodetector BPD.
A receiving unit, further configured to:
and the balance photoelectric detector mixes the received second path of optical signals and the backward Rayleigh scattering optical signals carrying the disturbance information, converts the mixed signals into electric signals, and extracts and analyzes the electric signals through the processing unit to obtain disturbance signal information.
The technical scheme provided by the embodiment of the invention has the beneficial effects that at least:
in the scheme, based on the existing application of a single-frequency optical pulse coding technology to a distributed phi-OTDR system, the single-frequency optical pulse coding is replaced by the multi-frequency optical pulse coding. A distributed phi-OTDR sensing method and system based on multi-frequency pulse coding are provided, signals are modulated through an acousto-optic modulator or an I/Q modulator, then are combined into a path of optical signal to be injected into a sensing optical fiber, coherent detection is carried out at a receiving end, relevant information of the intensity and the phase of a return pulse can be detected, the pulse coding has no time difference for detecting the position, the intensity and the phase of a disturbance signal, and the limitation of the original single-frequency pulse coding on the length, the amplitude and the frequency of the disturbance signal can be effectively reduced. The multi-channel pulse coding signals are modulated into the multi-frequency one-channel signal light to be injected into the optical fiber by using the acousto-optic modulator or the I/Q modulator, so that the detection distance is prolonged, the limits on the amplitude, the frequency and the like of the disturbance signals are reduced, and the system performance is further improved.
The invention can solve the problem of the limit of the detection distance, the signal amplitude and the frequency of the disturbance signal when the single-frequency pulse code is applied to the distributed phi-OTDR sensing system, and greatly improves the system performance. The distributed phi-OTDR sensing method and system based on multi-frequency pulse coding is expected to become an implementation scheme for improving the signal-to-noise ratio, sensitivity and sensing distance of a future distributed phi-OTDR optical fiber sensing system.
Drawings
In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required to be used in the description of the embodiments are briefly introduced below, and it is obvious that the drawings in the description below are only some embodiments of the present invention, and it is obvious for those skilled in the art that other drawings can be obtained according to the drawings without creative efforts.
FIG. 1 is a schematic flow diagram of a distributed phi-OTDR sensing method based on multi-frequency pulse encoding according to the present invention;
FIG. 2 is a schematic flow chart of a distributed phi-OTDR sensing method based on multi-frequency pulse encoding according to the present invention;
FIG. 3 is a block diagram of a distributed phi-OTDR sensing system based on multi-frequency pulse encoding according to the present invention;
FIG. 4 is a four-frequency unipolar spectrum diagram of the present invention;
FIG. 5 is a diagram illustrating a time-domain waveform of a perturbation signal based on multi-pulse coding and a detected signal of each pulse coding signal according to the present invention;
FIG. 6 is a schematic diagram of a single pulse code-based time domain waveform of a disturbance signal and a detected signal of each pulse code signal according to the present invention;
FIG. 7 is a diagram of a comparison of a single frequency pulse encoded signal phi-OTDR system of the present invention and a modified multiple frequency pulse encoded signal phi-OTDR system;
FIG. 8 is a schematic flow chart of a distributed phi-OTDR sensing method based on multi-frequency pulse encoding according to the present invention;
FIG. 9 is a block diagram of a distributed phi-OTDR sensing system based on multi-frequency pulse encoding according to the present invention;
FIG. 10 is a schematic diagram of dual-frequency bipolar spectrum of the present invention;
FIG. 11 is a schematic flow chart of a distributed phi-OTDR sensing method based on multi-frequency pulse encoding according to the present invention;
FIG. 12 is a block diagram of a distributed phi-OTDR sensing system based on multi-frequency pulse encoding according to the present invention;
FIG. 13 is a schematic diagram of dual-frequency bipolar spectrum of the present invention;
fig. 14 is a block diagram of a distributed phi-OTDR sensing system based on multi-frequency pulse encoding according to the present invention.
Detailed Description
In order to make the technical problems, technical solutions and advantages of the present invention more apparent, the following detailed description is given with reference to the accompanying drawings and specific embodiments.
As shown in fig. 1, an embodiment of the present invention provides a distributed Φ -OTDR sensing method based on multi-frequency pulse coding, where the method may be implemented by a distributed Φ -OTDR sensing system based on multi-frequency pulse coding, where the distributed Φ -OTDR sensing system based on multi-frequency pulse coding includes a sending unit, a first coupler, a modulation unit, an erbium-doped fiber amplifier, a sensing fiber, a disturbance simulation unit, a receiving unit, and a processing unit; wherein the receiving unit comprises a balanced photodetector BPD and an integrated coherent receiver ICR. As shown in fig. 1, a flow chart of a distributed Φ -OTDR sensing method based on multi-frequency pulse coding, a processing flow of the method may include the following steps:
s11, the sending unit outputs the optical signal to the first coupler, and the first coupler divides the optical signal into a first path of optical signal and a second path of optical signal; inputting the first path of optical signal to a modulation unit to obtain a modulated optical signal; the second optical signal is input to the receiving unit.
S12, inputting the modulated optical signal to a sensing optical fiber after passing through an erbium-doped optical fiber amplifier; the sensing optical fiber returns backward Rayleigh scattering optical signals carrying disturbance information to the erbium-doped optical fiber amplifier after being disturbed by the disturbance simulation unit, and the backward Rayleigh scattering optical signals are input to the receiving unit after passing through the erbium-doped optical fiber amplifier.
And S13, the receiving unit mixes the received second path of optical signal with the backward Rayleigh scattering optical signal carrying the disturbance information, and sends the mixed signal to the processing unit to obtain disturbance signal information.
Optionally, the transmitting unit in S11 is a narrow linewidth laser.
The first coupler is 99: 1.
The disturbance simulation unit is a piezoelectric ceramic oscillator PZT.
Optionally, the modulation unit in S11 includes a beam splitter, four different-frequency fiber acousto-optic modulators AOM, an arbitrary waveform generator AWG, and a second coupler.
Alternatively, the modulation unit comprises an I/Q modulator, an arbitrary waveform generator AWG.
Optionally, the modulation unit in S11 includes a beam splitter, four different-frequency fiber acousto-optic modulators AOM, an arbitrary waveform generator AWG, and a second coupler.
The first path of optical signal in S11 is input to the modulation unit, and obtaining the modulated optical signal includes:
the first path of optical signal is input into the beam splitter and then is divided into four paths of optical signals, and the four paths of optical signals pass through the arbitrary waveform generator to obtain four paths of different pulse codes; four paths of different pulse codes are respectively modulated by four different-frequency optical fiber acousto-optic modulators AOM.
The modulated four optical signals are combined into one optical signal, namely the modulated optical signal, through the second coupler.
Optionally, the receiving unit is a balanced photodetector BPD.
The receiving unit mixes the received second path of optical signal with the backward Rayleigh scattering optical signal carrying the disturbance information, and sends the mixed signal to the processing unit, and the obtaining of the disturbance signal information comprises the following steps:
and the balance photoelectric detector mixes the received second path of optical signals and the backward Rayleigh scattering optical signals carrying the disturbance information, converts the mixed signals into electric signals, and extracts and analyzes the electric signals through the processing unit to obtain disturbance signal information.
Optionally, the modulation unit in S11 includes an I/Q modulator, an arbitrary waveform generator AWG.
The first path of optical signal in S11 is input to the modulation unit, and obtaining the modulated optical signal includes:
the first path of optical signal is input to an arbitrary waveform generator AWG for pulse coding and then input to an I/Q modulator to obtain a path of pulse coding signal, namely a modulated optical signal; the modulated optical signals include optical signals with positive and negative modulation frequencies and optical signals with positive modulation frequencies.
Optionally, when the modulated optical signal is an optical signal with a modulation frequency of positive and negative frequencies, the receiving unit is an integrated coherent receiver ICR.
The receiving unit mixes the received second path of optical signal with the backward Rayleigh scattering optical signal carrying the disturbance information, and sends the mixed signal to the processing unit, and the obtaining of the disturbance signal information comprises the following steps:
and the second path of optical signal and the backward Rayleigh scattering optical signal carrying the disturbance information are converted into electric signals through the BPD after passing through the Hybrid of the optical mixer, the I path of signal and the Q path of signal are converted into complex signals, and the complex signals are extracted and analyzed by the processing unit to obtain disturbance signal information.
Optionally, when the modulated optical signal is an optical signal whose modulation frequencies are all positive frequencies, the receiving unit is a balanced photodetector BPD.
The receiving unit mixes the received second path of optical signal with the backward Rayleigh scattering optical signal carrying the disturbance information, and sends the mixed signal to the processing unit, and the obtaining of the disturbance signal information comprises the following steps:
and the balance photoelectric detector mixes the received second path of optical signals and the backward Rayleigh scattering optical signals carrying the disturbance information, converts the mixed signals into electric signals, and extracts and analyzes the electric signals through the processing unit to obtain disturbance signal information.
In the embodiment of the invention, based on the existing application of a single-frequency optical pulse coding technology to a distributed phi-OTDR system, the single-frequency optical pulse coding is replaced by the multi-frequency optical pulse coding. A distributed phi-OTDR sensing method and system based on multi-frequency pulse coding are provided, signals are modulated through an acousto-optic modulator or an I/Q modulator, then are combined into a path of optical signal to be injected into a sensing optical fiber, coherent detection is carried out at a receiving end, relevant information of the intensity and the phase of a return pulse can be detected, the pulse coding has no time difference for detecting the position, the intensity and the phase of a disturbance signal, and the limitation of the original single-frequency pulse coding on the length, the amplitude and the frequency of the disturbance signal can be effectively reduced. The multi-channel pulse coding signals are modulated into the multi-frequency one-channel signal light to be injected into the optical fiber by using the acousto-optic modulator or the I/Q modulator, so that the detection distance is prolonged, the limits on the amplitude, the frequency and the like of the disturbance signals are reduced, and the system performance is further improved.
The invention can solve the problem of the limit of the detection distance, the signal amplitude and the frequency of the disturbance signal when the single-frequency pulse code is applied to the distributed phi-OTDR sensing system, and greatly improves the system performance. The distributed phi-OTDR sensing method and system based on multi-frequency pulse coding is expected to become an implementation scheme for improving the signal-to-noise ratio, sensitivity and sensing distance of a future distributed phi-OTDR optical fiber sensing system.
As shown in fig. 2, an embodiment of the present invention provides a distributed Φ -OTDR sensing method based on multi-frequency pulse coding, where the method may be implemented by the distributed Φ -OTDR sensing system based on multi-frequency pulse coding as shown in fig. 3, and in the embodiment of the present invention, a modulation unit may include a beam splitter, four different-frequency fiber acousto-optic modulators, an arbitrary waveform generator, and a second coupler; the receiving unit may be a BPD (Balanced Photo Detector). As shown in fig. 2, a flowchart of a distributed Φ -OTDR sensing method based on multi-frequency pulse encoding, a processing flow of the method may include the following steps:
s21, outputting the optical signal to 99 by the narrow linewidth laser: 1 coupler, 99: the coupler of 1 divides the optical signal into a first optical signal and a second optical signal.
In one possible embodiment, the ratio of 99: the coupler of 1 divides the signal into two paths, wherein 99% of laser is used as signal light, and the other 1% is used as local oscillator light.
And S22, inputting the first path of optical signal into a modulation unit to obtain a modulated optical signal.
Optionally, the first optical signal is input into the beam splitter and then split into four optical signals, and the four optical signals pass through an AWG (Arbitrary Function Generator) to obtain four different pulse codes; four different pulse codes are respectively modulated by four different-frequency optical fiber acousto-optic modulators.
In one possible embodiment, the four-frequency unipolar pulse coding uses different pulse coding of the signal light, and the coded signals are four-way unipolar sequences a1(t), a2(t), B1(t), and B2 (t). The four different-frequency optical fiber acousto-optic modulators are used for modulation, and the generated signal frequency spectrum is shown in the attached figure 4.
The four paths of unipolar sequences generated by performing different pulse codes on the signal light have multiple arrangement modes, and one possible implementation mode is that the generated four paths of unipolar sequences correspond to four different-frequency optical fiber acousto-optic modulators one by one, namely, the first path of unipolar sequence is input into the first optical fiber acousto-optic modulator, and the second to fourth paths of unipolar sequences are sequentially input into the second to fourth optical fiber acousto-optic modulators.
And then, the four paths of signal light are combined into a path of four-frequency unipolar pulse coding signal by using a coupler, and the four paths of signal light are injected into the sensing optical fiber after passing through the erbium-doped optical fiber amplifier.
Optionally, the modulated four optical signals are combined into one optical signal, that is, the modulated optical signal, by the second coupler.
S23, inputting the modulated optical signal to a sensing optical fiber after passing through an erbium-doped optical fiber amplifier; the sensing optical fiber returns backward Rayleigh scattering optical signals carrying disturbance information to the erbium-doped optical fiber amplifier after being disturbed by the disturbance simulation unit, and the backward Rayleigh scattering optical signals are input to the receiving unit after passing through the erbium-doped optical fiber amplifier.
In a possible implementation, the sensing optical fiber can be laid in a scene needing monitoring, such as a large building, an oil and gas pipeline, a large bridge and other structures. In a laboratory scenario, the disturbance simulation unit may be PZT (Piezoelectric ceramic oscillator), modulated optical signals are input to the sensing fiber after passing through the erbium-doped fiber amplifier, a signal is applied to a certain position of the sensing fiber by using the Piezoelectric ceramic oscillator to simulate disturbance, and the sensing fiber returns backward rayleigh scattered light signals carrying disturbance information to the erbium-doped fiber amplifier after being disturbed.
When a balanced photodetector is used for receiving, two photocurrents in the system enter a subtracter, and the obtained signal is shown as the following formula (1):
wherein R is the response coefficient of the detector, A S (t) and A l0 (t) complex amplitudes of the received signal light and the local oscillator light,
and
the phase information of the received signal light and the local oscillator light, respectively.
In a feasible implementation manner, the pulse coding signal is improved by using the above scheme, and the received return signal is a disturbance signal monitored at the same time, as shown in fig. 5, compared with the disturbance signal shown in fig. 6 in the prior art, there is no time difference between the signals, so that the problem that the sensing distance, the amplitude and the phase of the disturbance signal are limited is solved.
And S24, mixing the received second path of optical signal and the backward Rayleigh scattering optical signal carrying the disturbance information by the balanced photoelectric detector, converting the mixed signals into electric signals, and extracting and analyzing the electric signals by the processing unit to obtain disturbance signal information.
In a possible implementation manner, the processing unit may extract and analyze the information of the disturbance signal by using data acquisition, signal processing, and the like.
The digital signal processing process is similar to the prior art single frequency. Firstly, the band-pass filtering processing is carried out on the received signals, the low-frequency intersymbol interference is filtered, and the signals with different frequencies are distinguished. And extracting trace, performing correlation operation, further calculating a trace power difference to determine a disturbance position, and calculating a difference value of a trace phase along a fast time axis to analyze specific information of the disturbance signal.
Fig. 7 shows a Φ -OTDR system of a single-frequency pulse encoded signal in the prior art, a two-dimensional graph of an electrical domain-photocurrent spectrum, a trace power difference/phase difference with distance variation, and a comparison graph of demodulation results.
The scene is the line width of 50Hz, the sensing distance of 5km, the strain frequency of 500Hz, the strain intensity of 10 and the encoding bit number of 8 bit.
In the embodiment of the invention, based on the existing application of a single-frequency optical pulse coding technology to a distributed phi-OTDR system, the single-frequency optical pulse coding is replaced by the multi-frequency optical pulse coding. A distributed phi-OTDR sensing method and system based on multi-frequency pulse coding are provided, signals are modulated through an acousto-optic modulator or an I/Q modulator, then are combined into a path of optical signal to be injected into a sensing optical fiber, coherent detection is carried out at a receiving end, relevant information of the intensity and the phase of a return pulse can be detected, the pulse coding has no time difference for detecting the position, the intensity and the phase of a disturbance signal, and the limitation of the original single-frequency pulse coding on the length, the amplitude and the frequency of the disturbance signal can be effectively reduced. The multi-channel pulse coding signals are modulated into the multi-frequency one-channel signal light to be injected into the optical fiber by using the acousto-optic modulator or the I/Q modulator, so that the detection distance is prolonged, the limits on the amplitude, the frequency and the like of the disturbance signals are reduced, and the system performance is further improved.
The invention can solve the problem of the limit of the detection distance, the signal amplitude and the frequency of the disturbance signal when the single-frequency pulse code is applied to the distributed phi-OTDR sensing system, and greatly improves the system performance. The distributed phi-OTDR sensing method and system based on multi-frequency pulse coding is expected to become an implementation scheme for improving the signal-to-noise ratio, sensitivity and sensing distance of a future distributed phi-OTDR optical fiber sensing system.
As shown in fig. 8, an embodiment of the present invention provides a distributed Φ -OTDR sensing method based on multi-frequency pulse coding, where the method may be implemented by the distributed Φ -OTDR sensing system based on multi-frequency pulse coding as shown in fig. 9, and in the embodiment of the present invention, a modulation unit may include an I/Q modulator and an arbitrary waveform generator; the modulated optical signal can be an optical signal with positive and negative modulation frequencies; the receiving unit may be an Integrated Coherent Receiver (ICR). As shown in fig. 8, a flowchart of a distributed Φ -OTDR sensing method based on multi-frequency pulse encoding, a processing flow of the method may include the following steps:
s31, outputting the optical signal to 99 by the narrow linewidth laser: 1 coupler, 99: the coupler of 1 divides the optical signal into a first optical signal and a second optical signal.
And S32, inputting the first path of optical signal into a modulation unit to obtain a modulated optical signal.
The first path of optical signal is input into an arbitrary waveform generator for pulse coding and then input into an I/Q modulator to obtain a path of pulse coding signal, namely a modulated optical signal; the modulated optical signal is an optical signal whose modulation frequency is positive and negative, as shown in fig. 10.
In one possible embodiment, the I/Q modulator is used for modulation, and the multi-frequency pulse coded signal is generated in the digital domain without passing through a beam splitter.
S33, inputting the modulated optical signal to a sensing optical fiber after passing through an erbium-doped optical fiber amplifier; the sensing optical fiber returns backward Rayleigh scattering optical signals carrying disturbance information to the erbium-doped optical fiber amplifier after being disturbed by the disturbance simulation unit, and the backward Rayleigh scattering optical signals are input to the receiving unit after passing through the erbium-doped optical fiber amplifier.
And S34, the integrated coherent receiver mixes the received second path of optical signal with the backward Rayleigh scattering optical signal carrying the disturbance information and sends the mixed signal to the processing unit to obtain the disturbance signal information.
In a feasible implementation manner, the second path of optical signal and the backward rayleigh scattering optical signal carrying the disturbance information are converted into electrical signals through a 90 ° optical mixer Hybrid, and then converted into complex signals through a BPD, and the I path and the Q path of signals are converted into complex signals, and the complex signals are extracted and analyzed by a processing unit to obtain disturbance signal information, as shown in the following formula (1):
wherein R is the response coefficient of the detector, A S (t) and A l0 (t) the complex amplitudes of the received signal light and the local oscillator light respectively,
and
respectively receiving phase information of the signal light and the local oscillator light; i represents an imaginary unit.
In the embodiment of the invention, based on the existing application of a single-frequency optical pulse coding technology to a distributed phi-OTDR system, the single-frequency optical pulse coding is replaced by the multi-frequency optical pulse coding. A distributed phi-OTDR sensing method and system based on multi-frequency pulse coding are provided, signals are modulated through an acousto-optic modulator or an I/Q modulator, then are combined into a path of optical signal to be injected into a sensing optical fiber, coherent detection is carried out at a receiving end, relevant information of the intensity and the phase of a return pulse can be detected, the pulse coding has no time difference for detecting the position, the intensity and the phase of a disturbance signal, and the limitation of the original single-frequency pulse coding on the length, the amplitude and the frequency of the disturbance signal can be effectively reduced. The multi-channel pulse coding signals are modulated into the multi-frequency one-channel signal light to be injected into the optical fiber by using the acousto-optic modulator or the I/Q modulator, so that the detection distance is prolonged, the limits on the amplitude, the frequency and the like of the disturbance signals are reduced, and the system performance is further improved.
The invention can solve the problem of the limit of the detection distance, the signal amplitude and the frequency of the disturbance signal when the single-frequency pulse code is applied to the distributed phi-OTDR sensing system, and greatly improves the system performance. The distributed phi-OTDR sensing method and system based on multi-frequency pulse coding is expected to become an implementation scheme for improving the signal-to-noise ratio, sensitivity and sensing distance of a future distributed phi-OTDR optical fiber sensing system.
As shown in fig. 11, an embodiment of the present invention provides a distributed Φ -OTDR sensing method based on multi-frequency pulse coding, where the method may be implemented by the distributed Φ -OTDR sensing system based on multi-frequency pulse coding as shown in fig. 12, and in the embodiment of the present invention, a modulation unit may include an I/Q modulator and an arbitrary waveform generator; the modulated optical signal can be an optical signal of which the modulation frequencies are all positive frequencies; the receiving unit may be a balanced photodetector. As shown in fig. 11, a flowchart of a distributed Φ -OTDR sensing method based on multi-frequency pulse encoding, a processing flow of the method may include the following steps:
s41, outputting the optical signal to 99 by the narrow linewidth laser: 1 coupler, 99: the coupler of 1 divides the optical signal into a first optical signal and a second optical signal.
And S42, inputting the first path of optical signal into a modulation unit to obtain a modulated optical signal.
The first path of optical signal is input into an arbitrary waveform generator for pulse coding and then is input into an I/Q modulator to obtain a path of pulse coding signal, namely a modulated optical signal; the modulated optical signals are optical signals whose modulation frequencies are all positive frequencies, as shown in fig. 13.
S43, inputting the modulated optical signal to a sensing optical fiber after passing through an erbium-doped optical fiber amplifier; the sensing optical fiber returns backward Rayleigh scattering optical signals carrying disturbance information to the erbium-doped optical fiber amplifier after being disturbed by the disturbance simulation unit, and the backward Rayleigh scattering optical signals are input to the receiving unit after passing through the erbium-doped optical fiber amplifier.
And S44, mixing the received second path of optical signal and the backward Rayleigh scattering optical signal carrying the disturbance information by the balanced photoelectric detector, converting the mixed signals into electric signals, and extracting and analyzing the electric signals by the processing unit to obtain disturbance signal information.
In a possible embodiment, taking dual-frequency bipolar pulse encoding as an example, the encoded signal is two bipolar sequences a (t) and b (t). After A (t) and B (t) are directly adjusted to different frequencies in a digital domain, the signals become a path of dual-frequency bipolar pulse coding signals through an I/Q modulator and are injected into a sensing optical fiber.
Using AWG to generate frequency f based on A (t) and B (t) A 、f B The pulse code signal of (1). Modulating the generated multi-frequency pulse coding signal by an I/Q modulator, wherein output signals of the multi-frequency pulse coding signal are as the following formulas (1) and (2):
wherein E is in For 99% of the signal light entering the I/Q modulator from the coupler, V π Is a half-wave voltage, namely a driving voltage when the phase shift is pi is obtained in the upper and lower arms; exp is an exponential function; i represents an imaginary unit.
The AWG can be used to give the same u (t) signal to I, Q in two paths, as shown in the following formula (3):
u I (t)＝u Q (t)＝u(t) (3)
when the output signal is injected into the sensing optical fiber, the coded detection signal m (t) is expressed as the following formulas (4), (5) and (6):
m(t)＝m A (t)+m B (t) (6)
wherein M is the total number of the code words; exp is an exponential function; t is the disturbance signal time; tau is A 、τ B Separately representing A, B the pulse width of each codeword in the sequence; f. of A 、f B Represents a modulation frequency; CA p 、CB p Represents the p-th code word in the code sequence; rect is a rectangular function; i represents an imaginary unit.
In the embodiment of the invention, based on the existing application of a single-frequency optical pulse coding technology to a distributed phi-OTDR system, the single-frequency optical pulse coding is replaced by the multi-frequency optical pulse coding. A distributed phi-OTDR sensing method and system based on multi-frequency pulse coding are provided, signals are modulated through an acousto-optic modulator or an I/Q modulator, then are combined into a path of optical signal to be injected into a sensing optical fiber, coherent detection is carried out at a receiving end, relevant information of the intensity and the phase of a return pulse can be detected, the pulse coding has no time difference for detecting the position, the intensity and the phase of a disturbance signal, and the limitation of the original single-frequency pulse coding on the length, the amplitude and the frequency of the disturbance signal can be effectively reduced. The multi-channel pulse coding signals are modulated into the multi-frequency one-channel signal light to be injected into the optical fiber by using the acousto-optic modulator or the I/Q modulator, so that the detection distance is prolonged, the limits on the amplitude, the frequency and the like of the disturbance signals are reduced, and the system performance is further improved.
The invention can solve the problem of the limit of the detection distance, the signal amplitude and the frequency of the disturbance signal when the single-frequency pulse code is applied to the distributed phi-OTDR sensing system, and greatly improves the system performance. The distributed phi-OTDR sensing method and system based on multi-frequency pulse coding is expected to become an implementation scheme for improving the signal-to-noise ratio, sensitivity and sensing distance of a future distributed phi-OTDR optical fiber sensing system.
As shown in fig. 14, the present invention provides a distributed Φ -OTDR sensing system based on multi-frequency pulse coding, which is used for implementing a distributed Φ -OTDR sensing method based on multi-frequency pulse coding, and the distributed Φ -OTDR sensing system based on multi-frequency pulse coding includes a sending unit, a first coupler, a modulation unit, an erbium-doped fiber amplifier, a sensing fiber, a disturbance simulation unit, a receiving unit, and a processing unit; wherein, the receiving unit comprises a balanced photoelectric detector and an integrated coherent receiver;
wherein:
a transmitting unit 1401 for outputting the optical signal to the first coupler.
The first coupler 1402 is configured to split the optical signal into a first optical signal and a second optical signal.
A modulation unit 1403, configured to obtain the modulated optical signal.
The erbium-doped fiber amplifier 1404 is configured to input the modulated optical signal to the sensing fiber after passing through the erbium-doped fiber amplifier.
And the sensing optical fiber 1405 is used for returning a backward Rayleigh scattering optical signal carrying disturbance information after being disturbed by the disturbance simulation unit.
And a disturbance simulation unit 1406 for disturbing the sensing fiber.
The receiving unit 1407 is configured to mix the received second optical signal and the backward rayleigh scattered light signal carrying the disturbance information, and send the mixed signal to the processing unit.
A processing unit 1408 for obtaining the disturbing signal information.
Optionally, the transmitting unit is a narrow linewidth laser.
The first coupler is 99: 1.
The disturbance simulation unit is a piezoelectric ceramic oscillator.
Optionally, the modulation unit 1403 includes a beam splitter, four different-frequency fiber acousto-optic modulators, an arbitrary waveform generator, and a second coupler.
Alternatively, the modulation unit 1403 includes an I/Q modulator, an arbitrary waveform generator.
Optionally, the modulation unit 1403 is further configured to:
the first path of optical signal is input into the beam splitter and then is divided into four paths of optical signals, and the four paths of optical signals pass through the arbitrary waveform generator to obtain four paths of different pulse codes; four different pulse codes are respectively modulated by four different-frequency optical fiber acousto-optic modulators.
The modulated four optical signals are combined into one optical signal, namely the modulated optical signal, through the second coupler.
Optionally, the receiving unit 1407 is a balanced photodetector.
The receiving unit 1407 is further configured to:
and the balance photoelectric detector mixes the received second path of optical signals and the backward Rayleigh scattering optical signals carrying the disturbance information, converts the mixed signals into electric signals, and extracts and analyzes the electric signals through the processing unit to obtain disturbance signal information.
Optionally, the modulation unit 1403 is further configured to:
the first path of optical signal is input into an arbitrary waveform generator for pulse coding and then is input into an I/Q modulator to obtain a path of pulse coding signal, namely a modulated optical signal; the modulated optical signals include optical signals with positive and negative modulation frequencies and optical signals with positive modulation frequencies.
Optionally, when the modulated optical signal is an optical signal with a modulation frequency of positive and negative frequencies, the receiving unit is an integrated coherent receiver.
The receiving unit 1407 is further configured to:
and the second path of optical signal and the backward Rayleigh scattering optical signal carrying the disturbance information are converted into electric signals through the BPD after passing through the Hybrid of the optical mixer, the I path of signal and the Q path of signal are converted into complex signals, and the complex signals are extracted and analyzed by the processing unit to obtain disturbance signal information.
Optionally, when the modulated optical signal is an optical signal whose modulation frequencies are all positive frequencies, the receiving unit is a balanced photodetector.
The receiving unit 1407 is further configured to:
and the balance photoelectric detector mixes the received second path of optical signals and the backward Rayleigh scattering optical signals carrying the disturbance information, converts the mixed signals into electric signals, and extracts and analyzes the electric signals through the processing unit to obtain disturbance signal information.
In the embodiment of the invention, based on the existing application of a single-frequency optical pulse coding technology to a distributed phi-OTDR system, the single-frequency optical pulse coding is replaced by the multi-frequency optical pulse coding. A distributed phi-OTDR sensing method and system based on multi-frequency pulse coding are provided, signals are modulated through an acousto-optic modulator or an I/Q modulator, then are combined into a path of optical signal to be injected into a sensing optical fiber, coherent detection is carried out at a receiving end, relevant information of the intensity and the phase of a return pulse can be detected, the pulse coding has no time difference for detecting the position, the intensity and the phase of a disturbance signal, and the limitation of the original single-frequency pulse coding on the length, the amplitude and the frequency of the disturbance signal can be effectively reduced. The multi-channel pulse coding signals are modulated into the multi-frequency one-channel signal light to be injected into the optical fiber by using the acousto-optic modulator or the I/Q modulator, so that the detection distance is prolonged, the limits on the amplitude, the frequency and the like of the disturbance signals are reduced, and the system performance is further improved.
The invention can solve the problem of the limit of the detection distance, the signal amplitude and the frequency of the disturbance signal when the single-frequency pulse code is applied to the distributed phi-OTDR sensing system, and greatly improves the system performance. The distributed phi-OTDR sensing method and system based on multi-frequency pulse coding is expected to become an implementation scheme for improving the signal-to-noise ratio, sensitivity and sensing distance of a future distributed phi-OTDR optical fiber sensing system.
It will be understood by those skilled in the art that all or part of the steps for implementing the above embodiments may be implemented by hardware, or may be implemented by a program instructing relevant hardware, where the program may be stored in a computer-readable storage medium, and the above-mentioned storage medium may be a read-only memory, a magnetic disk or an optical disk, etc.
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, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.
Claims (6)
1. A distributed phi-OTDR sensing method based on multi-frequency pulse coding is characterized in that the method is realized by a distributed phi-OTDR sensing system based on multi-frequency pulse coding, and the distributed phi-OTDR sensing system based on multi-frequency pulse coding comprises a sending unit, a first coupler, a modulating unit, an erbium-doped fiber amplifier, a sensing fiber, a disturbance simulating unit, a receiving unit and a processing unit; wherein the receiving unit comprises a balanced photodetector BPD or an integrated coherent receiver ICR;
the method comprises the following steps:
s1, the sending unit outputs an optical signal to the first coupler, and the first coupler splits the optical signal into a first optical signal and a second optical signal; the first path of optical signal is input to the modulation unit to obtain a modulated optical signal; the second path of optical signal is input to the receiving unit;
s2, inputting the modulated optical signal to the sensing optical fiber after passing through the erbium-doped optical fiber amplifier; after the sensing optical fiber is disturbed by the disturbance simulation unit, backward Rayleigh scattering optical signals carrying disturbance information are returned to the erbium-doped optical fiber amplifier, and are input to the receiving unit after passing through the erbium-doped optical fiber amplifier;
s3, the receiving unit mixes the received second path of optical signal with the backward Rayleigh scattering optical signal carrying the disturbance information and sends the mixed signal to the processing unit to obtain disturbance signal information;
the modulation unit in S1 includes a beam splitter, four different-frequency fiber acousto-optic modulators AOM, an arbitrary waveform generator AWG, and a second coupler;
or the modulation unit comprises an I/Q modulator and an AWG (arbitrary waveform generator);
the inputting of the first optical signal in S1 to the modulation unit to obtain a modulated optical signal includes:
the first path of optical signal is divided into four paths of optical signals after being input into the beam splitter, and the four paths of optical signals pass through an arbitrary waveform generator to obtain four paths of different pulse codes; the four paths of different pulse codes are respectively modulated by the four different-frequency optical fiber acousto-optic modulators AOM;
the modulated four paths of optical signals are combined into one path of optical signal through the second coupler, namely the modulated optical signal;
or, the inputting of the first optical signal in S1 to the modulation unit to obtain the modulated optical signal includes:
the first path of optical signal is input to the arbitrary waveform generator AWG to carry out two paths of pulse coding and simultaneously generate two paths of different pulse coding signals in a digital domain, and then the two paths of different pulse coding signals are simultaneously input to the I/Q modulator to obtain a path of pulse coding signal, namely a modulated optical signal; the modulated optical signals comprise optical signals with positive and negative modulation frequencies or optical signals with positive modulation frequencies.
2. The method according to claim 1, wherein the transmitting unit in S1 is a narrow linewidth laser;
the first coupler is 99: 1, a coupler;
the disturbance simulation unit is a piezoelectric ceramic oscillator PZT.
3. The method according to claim 1, wherein when the modulation unit in S1 comprises a beam splitter, four different frequency fiber acousto-optic modulators AOM, an arbitrary waveform generator AWG, a second coupler, the receiving unit is a balanced photodetector BPD;
the receiving unit mixes the received second path of optical signal with a backward Rayleigh scattering optical signal carrying disturbance information, and sends the mixed signal to the processing unit, and obtaining disturbance signal information comprises:
and the balance photoelectric detector mixes the received second path of optical signal and the backward Rayleigh scattering optical signal carrying the disturbance information and converts the mixed signals into electric signals, and the electric signals are extracted and analyzed by the processing unit to obtain disturbance signal information.
4. The method according to claim 1, wherein when the modulated optical signal is an optical signal with a modulation frequency of positive and negative frequencies, the receiving unit is an integrated coherent receiver ICR;
the receiving unit mixes the received second path of optical signal with a backward Rayleigh scattering optical signal carrying disturbance information, and sends the mixed signal to the processing unit, and obtaining disturbance signal information comprises:
and the second path of optical signal and the backward Rayleigh scattering optical signal carrying the disturbance information are converted into electric signals through a BPD after passing through an optical mixer Hybrid, the two paths of signals of the I path and the Q path are converted into complex signals, and the complex signals are extracted and analyzed by the processing unit to obtain disturbance signal information.
5. The method according to claim 1, wherein when the modulated optical signal is an optical signal whose modulation frequencies are all positive frequencies, the receiving unit is a balanced photodetector BPD;
the receiving unit mixes the received second path of optical signal with a backward Rayleigh scattering optical signal carrying disturbance information, and sends the mixed signal to the processing unit, and obtaining disturbance signal information comprises:
and the balance photoelectric detector mixes the received second path of optical signal and the backward Rayleigh scattering optical signal carrying the disturbance information and converts the mixed signals into electric signals, and the electric signals are extracted and analyzed by the processing unit to obtain disturbance signal information.
6. A distributed phi-OTDR sensing system based on multi-frequency pulse coding is characterized in that the system is used for realizing a distributed phi-OTDR sensing method based on multi-frequency pulse coding, and the distributed phi-OTDR sensing system based on multi-frequency pulse coding comprises a sending unit, a first coupler, a modulating unit, an erbium-doped fiber amplifier, a sensing fiber, a disturbance simulating unit, a receiving unit and a processing unit; wherein the receiving unit comprises a balanced photodetector BPD or an integrated coherent receiver ICR; wherein:
a transmitting unit for outputting an optical signal to the first coupler;
the first coupler is used for dividing the optical signal into a first path of optical signal and a second path of optical signal;
a modulation unit for obtaining a modulated optical signal;
the erbium-doped fiber amplifier is used for inputting the modulated optical signal to the sensing fiber after passing through the erbium-doped fiber amplifier;
the sensing optical fiber is used for returning a backward Rayleigh scattering optical signal carrying disturbance information after being disturbed by the disturbance simulation unit;
the disturbance simulation unit is used for disturbing the sensing optical fiber;
the receiving unit is used for mixing the received second path of optical signals and backward Rayleigh scattering optical signals carrying disturbance information and sending the mixed signals to the processing unit;
the processing unit is used for obtaining disturbance signal information;
the modulation unit comprises a beam splitter, four different-frequency optical fiber acousto-optic modulators (AOM), an Arbitrary Waveform Generator (AWG) and a second coupler;
or the modulation unit comprises an I/Q modulator and an AWG (arbitrary waveform generator);
the first path of optical signal is input to the modulation unit, and obtaining the modulated optical signal comprises:
the first path of optical signal is divided into four paths of optical signals after being input into the beam splitter, and the four paths of optical signals pass through an arbitrary waveform generator to obtain four paths of different pulse codes; the four different pulse codes are respectively modulated by the four different-frequency optical fiber acousto-optic modulators (AOM);
the modulated four paths of optical signals are combined into one path of optical signal through the second coupler, namely the modulated optical signal;
or, the inputting of the first optical signal to the modulation unit to obtain the modulated optical signal includes:
the first path of optical signal is input to the arbitrary waveform generator AWG to carry out two paths of pulse coding and simultaneously generate two paths of different pulse coding signals in a digital domain, and then the two paths of different pulse coding signals are simultaneously input to the I/Q modulator to obtain a path of pulse coding signal, namely a modulated optical signal; the modulated optical signals comprise optical signals with positive and negative modulation frequencies or optical signals with positive modulation frequencies.
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| Interference-Fading-Suppressed Pulse-Coding Φ-OTDR Using Spectrum Extraction and Rotated-Vector-Sum Method;Kexin Cui; Fei Liu; Kuiru Wang; Xiaojun Liu; Jinhui Yuan; Binbin;《IEEE PHOTONICS JOURNAL》;20211019;第13卷(第6期);全文 * |
| Kun Zhu ; Xian Zhou ; Chao Shang ; Wenghong Chung ; Hua-Yaw Tam ; Chao Lu.Dual-Path Phase-Sensitive OTDR for Simultaneously Individual Vibration Monitoring.《2019 Asia Communications and Photonics Conference (ACP)》.2020,1-3. * |
| 光纤瑞利散射传感抗干涉衰落技术研究进展;林圣淘,王子南,熊吉,吴悦,饶云江;《激光与光电子学进展》;20210710;第58卷(第13期);全文 * |
| 用I/Q调制器产生常用模拟通信信号;杨淑莉;《科技信息》;20100615(第17期);全文 * |
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