CN113447110A - Distributed optical fiber vibration sensing system and phase carrier demodulation method thereof - Google Patents
Distributed optical fiber vibration sensing system and phase carrier demodulation method thereof Download PDFInfo
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Abstract
The invention discloses a distributed optical fiber vibration sensing system based on Rayleigh backscattering and Mach-Zehnder interference, which comprises a phase-sensitive optical time domain reflectometer, a one-way Mach-Zehnder optical fiber interferometer, a photoelectric detector, a signal processing unit, a signal source and a signal processing unit, wherein the phase-sensitive optical time domain reflectometer, the one-way Mach-Zehnder optical fiber interferometer, the photoelectric detector and the signal processing unit are sequentially connected; the signal processing unit collects the sensing electrical signals transmitted back by the photoelectric detector, and then analyzes and demodulates the received signals, so that amplitude-frequency information of the vibration signals applied to the sensing optical fiber is demodulated. The invention also discloses a phase carrier demodulation method, which can effectively realize the linear demodulation of the vibration signal applied to the sensing optical fiber by using the phase carrier demodulation technology which is not influenced by the interference light intensity and the modulation depth.
Description
Technical Field
The invention belongs to the technical field of sensing and detection, and particularly relates to a distributed optical fiber vibration sensing system based on Rayleigh scattering and Mach-Zehnder interference and a phase carrier demodulation method thereof.
Background
The distributed optical fiber vibration sensing technology can realize continuous multi-point vibration sensing detection along the line by using a single optical fiber link, and the positioning precision of the distributed optical fiber vibration sensing technology can be adjusted by hardware parameters such as an optical path and the like. Compared with the traditional electromagnetic vibration sensing technology, the distributed optical fiber vibration sensing technology has the advantages of simple structure, high sensitivity, electromagnetic interference resistance and the like. The technology is successfully applied to a plurality of application fields such as perimeter security detection, pipeline security detection, submarine cable fault detection, power line fault detection and the like. With the deep application of the distributed optical fiber vibration sensing technology in the above fields, the traditional method of only performing single vibration sensing detection cannot meet the requirements of increasingly detecting and developing. For example, the fault type can be accurately judged through accurate frequency analysis and vibration amplitude analysis of some fault vibration signals. On the other hand, the vibration signal applied to the sensing optical fiber link is subjected to accurate disturbance information demodulation, and accurate characteristic information can be provided for subsequent intelligent vibration mode identification and classification, so that the false alarm rate and the false alarm rate of the distributed optical fiber vibration sensing system are reduced, and the accuracy and the reliability of system detection are improved.
The distributed optical fiber vibration sensing system applied at present can be divided into a scattering type vibration sensing system and an interference type vibration sensing system according to the sensing principle. The scattering type optical fiber vibration sensing system performs analysis of vibration signals by injecting a narrow linewidth pulse light signal with a certain duty ratio into a sensing optical fiber to acquire various scattering signals such as rayleigh scattering, brillouin scattering and the like. The interferometric optical fiber vibration sensing system analyzes the vibration signal by building various types of optical fiber interferometers such as a mach-zehnder optical fiber interferometer, a michelson interferometer and the like. Since the backscattered light interference signal caused by the vibration signal of the scattering type optical fiber vibration sensing system and the applied vibration information are in a nonlinear relationship, it is often necessary to design a complex demodulation structure to perform corresponding linear demodulation such as a coherent detection structure, a chirped pulse modulation structure, and a 3 × 3 linear demodulation structure. The introduction of these structures increases the complexity of the distributed fiber optic vibration sensing system and reduces the real-time nature of the system demodulation to some extent. Although the interference light intensity of the interference type optical fiber vibration sensing system is in a linear relation with the vibration signal applied from the outside, the application of the interference type optical fiber vibration sensing system in the actual field is limited due to the defects that the vibration signal cannot be positioned by using a single interferometer structure, the demodulation dynamic range of the interference signal is small and the like.
In view of the above analysis, the design of the distributed optical fiber vibration sensing system with simple structure, large demodulation dynamic range, high positioning accuracy and high demodulation linearity has important significance and value for further expanding application in the actual vibration sensing detection field.
Disclosure of Invention
The invention aims to realize linear demodulation of a distributed optical fiber vibration sensing system, and provides the distributed optical fiber vibration sensing system based on Rayleigh backscattering and Mach-Zehnder interference and a phase carrier demodulation method thereof for more accurately and effectively analyzing vibration information applied to a sensing optical fiber. The linear demodulation of the vibration signal applied to the sensing optical fiber can be effectively realized by utilizing a phase carrier demodulation technology which is not influenced by the interference light intensity and the modulation depth.
Therefore, the invention provides a distributed optical fiber vibration sensing system based on Rayleigh backscattering and Mach-Zehnder interference, which comprises a phase-sensitive optical time domain reflectometer, a one-way Mach-Zehnder optical fiber interferometer, a photoelectric detector, a signal processing unit, a signal source and a signal processing unit, wherein the phase-sensitive optical time domain reflectometer, the one-way Mach-Zehnder optical fiber interferometer, the photoelectric detector and the signal processing unit are sequentially connected;
the phase-sensitive optical time domain reflectometer comprises a light source, a first isolator, a second isolator, an acousto-optic modulator (AOM), a first erbium-doped fiber amplifier, a second erbium-doped fiber amplifier, a circulator and a sensing fiber; the light source adopts an ultra-narrow linewidth continuous laser, the light source is emitted into the first isolator to ensure the unidirectional transmission of continuous optical signals, and the other end of the first isolator is connected with the acousto-optic modulator and is used for modulating the continuous optical signals into pulse laser signals; the other end of the acousto-optic modulator is connected with the first erbium-doped fiber amplifier and is used for carrying out power amplification on pulse optical signals; the other end of the first erbium-doped fiber amplifier is connected with the circulator and is used for coupling pulse light signals into the sensing fiber and reversely transmitting Rayleigh backward scattering light signals generated by the pulse light signals to the second erbium-doped fiber amplifier; one end of the circulator is connected with the sensing optical fiber, and the other end of the circulator is connected with the second erbium-doped optical fiber amplifier and used for carrying out power amplification on Rayleigh backward scattering optical signals; the other end of the sensing optical fiber is connected with a second isolator and used for eliminating Fresnel reflection at the tail end of the optical fiber;
the unidirectional Mach-Zehnder optical fiber interferometer comprises piezoelectric ceramics (PZT) and optical fiber couplers respectively arranged at two ends of the PZT; the piezoelectric ceramic is used for carrying out high-frequency carrier modulation on an optical signal on one sensing arm in the Mach-Zehnder optical fiber interferometer;
a photoelectric detector: the optical fiber interferometer is used for receiving the sensing optical signals output by the one-way Mach-Zehnder optical fiber interferometer and converting the sensing optical signals into sensing electrical signals; one end of the photoelectric detector is connected with the one-way Mach-Zehnder optical fiber interferometer, and the other end of the photoelectric detector is connected with the signal processing unit;
a signal processing unit: the device is used for collecting the sensing electrical signal transmitted back by the photoelectric detector and analyzing and demodulating the received signal so as to demodulate the amplitude-frequency information of the vibration signal applied to the sensing optical fiber;
a signal source: the device is used for generating periodic pulse signals and periodic high-frequency modulation signals required by an acousto-optic modulator, a data acquisition card and piezoelectric ceramics.
Further, the first fiber coupler and the second fiber coupler are fiber couplers with the same splitting ratio.
Furthermore, the outlets of the first erbium-doped fiber amplifier and the second erbium-doped fiber amplifier are respectively connected with a filter for filtering noise signals generated by the amplifiers.
Furthermore, the circulator is externally connected with a third filter for filtering the generated spontaneous emission light for the second time and then entering the sensing optical fiber.
Further, the signal processing unit includes:
a data acquisition module: the industrial personal computer is used for acquiring a sensing electric signal transmitted back by the photoelectric detector and then outputting data to the industrial personal computer in an alternating current coupling mode;
a direct current filtering module: carrying out direct-current component filtering processing on the input interference signal;
the carrier signal processing module: multiplying the input sensing signal by a first harmonic and a second harmonic high-frequency carrier signal respectively to separate a vibration signal to be detected from the carrier signal; converting the interference signal into a trigonometric function including a sine term and a cosine term;
a low-pass filter: the device is used for filtering direct current components, carrier signal components and high-order sub-carrier signal components corresponding to the direct current components and the carrier signal components which are generated after the original interference sensing signals are multiplied by the primary carrier signals and the secondary carrier signals;
an arithmetic unit: the low-pass filter is used for performing differential operation on a sine item and a cosine item which are generated by the low-pass filter and contain vibration signal information to be detected so as to complete conversion on a trigonometric function containing a sensing signal, and then performing inverse phase and arc tangent operation on the converted signal;
a high-pass filter: and the low-frequency noise filter is used for filtering out the low-frequency noise in the demodulated vibration signal to be detected.
A phase carrier demodulation method of a distributed optical fiber vibration sensing system based on Rayleigh backscattering and Mach-Zehnder interference comprises the following steps:
a light source enters a phase-sensitive optical time domain reflectometer, a connecting laser signal is subjected to pulse modulation by using the acousto-optic modulator, is subjected to power amplification by the first erbium-doped fiber amplifier and then enters the sensing fiber through the circulator to generate a corresponding backward Rayleigh scattering light signal so as to sense a vibration signal along the sensing fiber;
backward Rayleigh scattering light signals carrying vibration information are subjected to power amplification again through the second erbium-doped optical fiber amplifier by the circulator and then enter the one-way optical fiber Mach-Zehnder interferometer to perform corresponding high-frequency modulation and interference on the backward Rayleigh scattering light signals;
the interfered backward Rayleigh scattering optical signal enters a photoelectric detector to be converted into a sensing electric signal and then enters a signal processing unit to be subjected to phase carrier demodulation;
wherein the phase carrier demodulation comprises the following steps:
collecting a sensing electric signal with vibration information transmitted by the photoelectric detector by using a data acquisition card, and outputting the data to an industrial personal computer in an alternating current coupling mode;
since vibration causes signal phase change, the phase change introduced by the vibration signal is used for expressing the interference signal;
the industrial personal computer multiplies the input interference signal by a first harmonic and a second harmonic high-frequency carrier signal respectively to complete the separation of the vibration signal to be detected and the carrier signal; converting the interference signal into a trigonometric function including a sine term and a cosine term;
then, obtaining information containing the vibration signal to be detected after passing through a low-pass filter, wherein the information is information of filtering out direct current components, carrier signal components and corresponding high-order sub-carrier signal components;
then, performing differential operation on a sine term and a cosine term in the information passing through the low-pass filter, and converting a trigonometric function containing the sensing signal;
and finally, after the inversion and arc tangent operation is carried out on the converted signal, the high-pass filter is used for filtering out the low-frequency noise in the demodulated vibration signal to be detected, so that the amplitude-frequency information of the vibration signal applied to the sensing optical fiber is demodulated.
Compared with the prior art, the invention has the beneficial effects and remarkable progresses that:
different from a linear demodulation structure of a traditional distributed optical fiber vibration sensing system, the invention adopts the mode that the tail end of a phase sensitive optical time domain reflectometer is connected to a one-way Mach-Zehnder interferometer to realize the interference and high-frequency carrier modulation of vibration sensing optical signals, and finally, the amplitude-frequency information of the vibration signals to be detected can be linearly demodulated by adopting a phase carrier demodulation method irrelevant to the light source intensity and the modulation depth to realize the linear demodulation of vibration sensing. On the one hand, the method can improve the stability of the demodulation result, namely, the demodulation result is not influenced by the interference intensity and the modulation depth. On the other hand, compared with the traditional linear demodulation structure, the method has a simple optical path structure, and does not need complex optical path structures such as coherent detection, chirp pulse modulation and the like.
Drawings
FIG. 1 is a block diagram of a distributed optical fiber vibration sensing system according to the present invention;
fig. 2 is a schematic diagram of a phase carrier demodulation method according to the present invention.
Wherein:
1: light source 2: first isolator 3: acousto-optic modulator
4: first erbium-doped fiber amplifier 5: first filter 6: ring-shaped device
7: third filter 8: second erbium-doped fiber amplifier 9: second filter
10: the signal source 11: first fiber coupler 12: second optical fiber coupler
13: the photodetector 14: a data acquisition card 15: industrial control machine
16: second isolator 17: the sensing optical fiber 18: piezoelectric ceramics
Detailed Description
In order to make the objects, technical solutions, advantages and significant progress of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings provided in the embodiments of the present invention, and it is obvious that all of the described embodiments are only some embodiments of the present invention, but not all embodiments; all other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
In the present invention, unless otherwise explicitly specified or limited, the terms "mounted," "fixed," "connected," and the like are to be understood broadly, and for example, may be fixedly connected, detachably connected or movably connected, or may be integrated; the connection can be direct connection, indirect connection through an intermediate medium or invisible signal connection, and can be the communication inside two elements or the interaction relation of the two elements; unless otherwise specifically defined, specific meanings of the above terms in the present invention can be understood as specific conditions by those of ordinary skill in the art.
It should be noted that the terms "first", "second", "third", etc. in the description and claims of the present invention are used for distinguishing different objects, and are not used for describing a specific order.
Fig. 1 shows that the high-stability distributed optical fiber vibration sensing system is based on rayleigh backscattering and unidirectional mach-zehnder interference principles, adopts a phase carrier modulation and demodulation technology, realizes high-frequency carrier modulation on a backward rayleigh scattered light signal transmitted in the unidirectional mach-zehnder optical fiber interferometer by utilizing piezoelectric ceramic PZT, and then realizes linear demodulation of a vibration sensing signal by a phase carrier demodulation method which is not influenced by interference light intensity and modulation depth. In the invention, a phase-sensitive optical time domain reflectometer formed by pulse light entering a sensing optical fiber and a one-way Mach-Zehnder optical fiber interferometer for Rayleigh scattering light entering the sensing optical fiber jointly form the whole optical fiber vibration sensing system.
As shown in fig. 1, a high-stability distributed optical fiber vibration sensing system includes a phase-sensitive optical time domain reflectometer, a one-way mach-zehnder optical fiber interferometer, a photodetector 13, a signal processing unit, and a signal source 10 for generating a periodic pulse signal and a periodic high-frequency modulation signal. Wherein the phase sensitive optical time domain reflectometer comprises:
light source 1: the distributed feedback laser (DFB) with ultra-narrow bandwidth and wavelength near 1550nm is used for generating continuous laser signals and realizing distributed optical fiber vibration sensing;
first isolator 2: the device is used for ensuring the unidirectional transmission of continuous laser signals output by the light source 1 and avoiding reverse light from entering and damaging the light source 1; one end of the first isolator 2 is connected with the light source 1, and the other end of the first isolator is connected with the AOM 3;
AOM 3: for modulating the continuous laser signal into a pulsed laser signal for generating a corresponding rayleigh backscatter signal within the sensing fiber 17; one end of the AOM3 is connected with the first isolator 2, and the other end is connected with the first erbium-doped fiber amplifier 4;
second isolator 16: the Fresnel reflection sensor is connected with the tail end of the sensing optical fiber 17 and is used for eliminating Fresnel reflection at the tail end of the optical fiber;
first erbium-doped fiber amplifier 4: the first erbium-doped fiber amplifier 4 is used for amplifying the power of the pulse light signal, and generates a plurality of spontaneous radiation light signals which can be effectively filtered by a first filter 5 connected with the first erbium-doped fiber amplifier while amplifying the pulse light signal; one end of the first erbium-doped fiber amplifier 4 is connected with the AOM3, and the other end of the first erbium-doped fiber amplifier is connected with the first filter 5;
first filter 5: for filtering the noise signal generated by the first erbium-doped fiber amplifier 4 during power amplification;
a circulator 6: the second erbium-doped fiber amplifier 8 is used for coupling the pulse light signal emitted by the light source 1 into the sensing fiber 17 and reversely transmitting a Rayleigh backward scattering light signal generated by the pulse light signal to the second erbium-doped fiber amplifier;
second erbium-doped fiber amplifier 8: the power amplifier is used for amplifying power of Rayleigh backward scattering light signals, and spontaneous radiation light of other wave bands can be generated while the power is amplified, and can be effectively filtered by the second filter 8;
the second filter 9: for filtering the noise signal generated by the second erbium-doped fiber amplifier 8 during power amplification; and
a sensing optical fiber: and a G.652D communication optical cable is adopted for transmitting vibration signals along the sensor to a sensing optical path structure.
The unidirectional Mach-Zehnder fiber optic interferometer includes:
first fiber coupler 11: a 1:2 spectral coupler with the central wavelength of 1550nm and the spectral ratio of 50: 50; the optical fiber interferometer is used for coupling the Rayleigh backward scattering optical signals filtered by the second filter 9 into the one-way Mach-Zehnder optical fiber interferometer; one end of the first optical fiber coupler is connected with the second filter 9, and the other end of the first optical fiber coupler is connected with the piezoelectric ceramic 18;
piezoelectric ceramic (PZT) 18: the optical signal on one sensing arm in the Mach-Zehnder fiber optic interferometer is subjected to high-frequency carrier modulation; and
second fiber coupler 12: a 2:1 spectral coupler with the central wavelength of 1550nm and the spectral ratio of 50: 50; the signal processing device is used for interfering the modulated high-frequency carrier signal with the other path of signal corresponding to the modulated high-frequency carrier signal; one end of the second optical fiber coupler 12 is connected with the piezoelectric ceramic 18, and the other end is connected with the photoelectric detector 13.
The optical fiber vibration sensing system further comprises a photoelectric detector, a signal processing unit and a signal source. Wherein:
a photoelectric detector: an avalanche photodetector is used for receiving backward Rayleigh scattering optical signals generated in the sensing optical fiber by pulse light with the wavelength of 1550 nm. One end of the photoelectric detector is connected with the one-way Mach-Zehnder optical fiber interferometer, and the other end of the photoelectric detector is connected with the signal processing unit;
a signal source: the device is used for generating periodic pulse signals and periodic high-frequency modulation signals required by an acousto-optic modulator, a data acquisition card and piezoelectric ceramics.
A signal processing unit: the device is used for collecting the sensing electrical signal transmitted back by the photoelectric detector and then analyzing and demodulating the received signal, thereby demodulating the amplitude-frequency information of the vibration signal applied to the sensing optical fiber.
The signal processing unit includes:
a data acquisition module: the system comprises a high-speed data acquisition card with a sampling rate of more than 50MSPS and a hardware accumulation function, wherein the high-speed data acquisition card is used for acquiring sensing electric signals transmitted back by a photoelectric detector, and then outputting data to an industrial personal computer in an alternating current coupling mode for acquiring the sensing electric signals transmitted back by the photoelectric detector;
the carrier signal processing module: multiplying the input sensing signal by a first harmonic and a second harmonic high-frequency carrier signal respectively to separate a vibration signal to be detected from the carrier signal; converting the interference signal into a trigonometric function including a sine term and a cosine term;
a low-pass filter: the device is used for filtering direct current components, carrier signal components and high-order sub-carrier signal components corresponding to the direct current components and the carrier signal components which are generated after the original interference sensing signals are multiplied by the primary carrier signals and the secondary carrier signals;
an arithmetic unit: the low-pass filter is used for performing differential operation on a sine item and a cosine item which are generated by the low-pass filter and contain vibration signal information to be detected so as to complete conversion on a trigonometric function containing a sensing signal, and then performing inverse phase and arc tangent operation on the converted signal;
a high-pass filter: and the low-frequency noise filter is used for filtering out the low-frequency noise in the demodulated vibration signal to be detected.
Fig. 2 shows a schematic diagram of a phase carrier demodulation method. As shown in fig. 1-2, the phase carrier demodulation method includes:
the continuous optical signal emitted by the light source 1 is transmitted to the AOM3 through the first isolator 2, the continuous laser signal is modulated into a periodic pulse optical signal with a certain duty ratio, and then the pulse optical signal is power-amplified by the first erbium-doped fiber amplifier 4 and spontaneous radiation light generated by the pulse optical signal is filtered by the first filter 5. The amplified optical pulse signal is connected to a third filter 7 through a circulator 6 for secondary filtering of spontaneous emission light and then enters the sensing optical fiber. The pulsed light signal transmitted in the sensing fiber 17 generates a corresponding backward rayleigh scattering curve along with the transmission of the fiber. When a certain point on the sensing fiber 17 is subjected to an external force, the refractive index of the sensing fiber 17 at the corresponding position is changed, so that the interference light intensity corresponding to the corresponding rayleigh backscattering curve is changed. The backward Rayleigh scattering signal carrying the external vibration sensing information is transmitted to the second erbium-doped fiber amplifier 8 again through the circulator 6 for continuous RayleighThe scattered light signal is amplified and then the spontaneous emission light signal generated by the scattered light signal is filtered again by a second filter 9. The amplified backward rayleigh scattered light signal enters the unidirectional mach-zehnder optical fiber interferometer through the first optical fiber coupler 11, wherein one path of sensing signal carries out high-frequency phase carrier modulation on the signal transmitted in the unidirectional mach-zehnder optical fiber interferometer through the piezoelectric ceramic PZT18, and then the interference of the final modulation signal is carried out through the second optical fiber coupler 12. Let Ccosw be the high-frequency carrier signal applied to the piezoelectric ceramic 180t, where C is the modulation depth, w0Is the modulation signal angular frequency. The interference signal generated at the second fiber coupler 12 can be expressed as:
wherein A is a direct current component, B is an interference intensity,
phase information introduced for the vibration signal. After the photoelectric detection and data acquisition are carried out on the formula (1) by using the data acquisition module, the data are sent to an industrial personal computer IPC in an alternating current coupling mode and are demodulated by adopting a phase carrier demodulation method shown in the attached figure 2.
The separation of the vibration signal to be measured and the carrier signal is finished by respectively multiplying the input interference signal I (t) by a first harmonic and a second harmonic high-frequency carrier signal by utilizing a carrier signal processing module and a low-pass filter, and the separation can be obtained after the separation passes through the low-pass filter:
subsequently, using the operator pair I1(t) and I2(t) direct division can be carried out to obtain:
to I1(t) and I2(t) the differential self-multiplication products are simultaneously performed, respectively, to obtain:
the division operation is performed on the above equation (4) and the sign inversion is performed to obtain:
I5(t) dividing the root mean square root of the above equation (5) to obtain:
last pair of I5(t) performing an arctangent operation and performing high-pass filtering using a high-pass filter to obtain:
phase change due to vibration signal
Can be expressed as
Where D is the amplitude of the vibration signal application, fsIs the frequency at which the vibration signal is applied. Therefore, as can be seen from the formula (7), the amplitude-frequency information of the vibration signal applied to the sensing optical fiber can be accurately demodulated by the device and the method of the invention, so that the accurate and linear analysis of the vibration signal is realized.
Although the present invention has been described in detail with reference to the foregoing embodiments, it should be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made on the technical solutions described in the foregoing embodiments, or some or all of the technical features of the embodiments can be replaced with equivalents, without departing from the scope of the embodiments of the present invention, and the technical solutions can not be modified or replaced by the modifications, the modifications and the substitutions in the non-essential scope of the present invention.
Claims (6)
1. A distributed optical fiber vibration sensing system is characterized by comprising a phase-sensitive optical time domain reflectometer, a one-way Mach-Zehnder optical fiber interferometer, a photoelectric detector (13), a signal processing unit and a signal source (10) for generating a periodic pulse signal and a periodic high-frequency modulation signal, wherein the phase-sensitive optical time domain reflectometer, the one-way Mach-Zehnder optical fiber interferometer, the photoelectric detector and the signal processing unit are sequentially connected;
the phase-sensitive optical time domain reflectometer comprises a light source (1), a first isolator (2), a second isolator (16), an acousto-optic modulator (3), a first erbium-doped fiber amplifier (4), a second erbium-doped fiber amplifier (8), a circulator (6) and a sensing fiber (17); the light source (1) adopts an ultra-narrow linewidth continuous laser, the light source (1) emits into the first isolator (2), and the other end of the first isolator (2) is connected with the acousto-optic modulator (3) and is used for modulating a continuous optical signal into a pulse laser signal; the other end of the acousto-optic modulator (3) is connected with the first erbium-doped fiber amplifier (4) and is used for carrying out power amplification on pulse optical signals; the other end of the first erbium-doped fiber amplifier (4) is connected with the circulator (6) and is used for coupling pulse light signals into the sensing fiber (17) and reversely transmitting Rayleigh backward scattering light signals generated by the pulse light signals to the second erbium-doped fiber amplifier (8); one end of the circulator (6) is connected with a sensing optical fiber (17), and the other end of the circulator is connected with a second erbium-doped optical fiber amplifier (8) for amplifying power of Rayleigh backward scattering optical signals; the other end of the sensing optical fiber (17) is connected with a second isolator (16) and used for eliminating Fresnel reflection at the tail end of the optical fiber;
the one-way Mach-Zehnder optical fiber interferometer comprises piezoelectric ceramics (18) and optical fiber couplers respectively arranged at two ends of the piezoelectric ceramics; the piezoelectric ceramic is used for carrying out high-frequency carrier modulation on an optical signal on one sensing arm in the Mach-Zehnder optical fiber interferometer;
photodetector (13): the optical fiber interferometer is used for receiving the sensing optical signals output by the one-way Mach-Zehnder optical fiber interferometer and converting the sensing optical signals into sensing electrical signals; one end of the photoelectric detector (13) is connected with the one-way Mach-Zehnder optical fiber interferometer, and the other end of the photoelectric detector is connected with the signal processing unit;
a signal processing unit: the device is used for collecting the sensing electrical signal transmitted back by the photoelectric detector and then analyzing and demodulating the received signal, thereby demodulating the amplitude-frequency information of the vibration signal applied to the sensing optical fiber.
2. A distributed fibre optic vibration sensing system according to claim 1, wherein the first (11) and second (12) fibre optic couplers are fibre optic couplers of the same splitting ratio.
3. A distributed optical fiber vibration sensing system according to claim 1, wherein the outlets of said first (4) and second (8) erbium doped fiber amplifiers are each connected to a filter for filtering the noise signal generated by the amplifier.
4. The distributed optical fiber vibration sensing system according to claim 1, wherein said circulator (6) is externally connected with a third filter (7) for secondarily filtering the generated spontaneous emission light and then entering the sensing optical fiber.
5. A distributed optical fiber vibration sensing system according to claim 1, wherein said signal processing unit comprises:
a data acquisition module: the industrial personal computer is used for acquiring a sensing electric signal transmitted back by the photoelectric detector and then outputting data to the industrial personal computer in an alternating current coupling mode;
the carrier signal processing module: multiplying the input sensing signal by a first harmonic and a second harmonic high-frequency carrier signal respectively to separate a vibration signal to be detected from the carrier signal; converting the interference signal into a trigonometric function including a sine term and a cosine term;
a low-pass filter: the device is used for filtering direct current components, carrier signal components and high-order sub-carrier signal components corresponding to the direct current components and the carrier signal components which are generated after the original interference sensing signals are multiplied by the primary carrier signals and the secondary carrier signals;
an arithmetic unit: the low-pass filter is used for performing differential operation on a sine item and a cosine item which are generated by the low-pass filter and contain vibration signal information to be detected so as to complete conversion on a trigonometric function containing a sensing signal, and then performing inverse phase and arc tangent operation on the converted signal;
a high-pass filter: and the low-frequency noise filter is used for filtering out the low-frequency noise in the demodulated vibration signal to be detected.
6. A phase carrier demodulation method using the distributed optical fiber vibration sensing system according to claim 1, wherein the demodulation method comprises:
a light source enters a phase-sensitive optical time domain reflectometer, a connecting laser signal is subjected to pulse modulation by using the acousto-optic modulator, is subjected to power amplification by the first erbium-doped fiber amplifier and then enters the sensing fiber through the circulator to generate a corresponding backward Rayleigh scattering light signal so as to sense a vibration signal along the sensing fiber;
backward Rayleigh scattering light signals carrying vibration information are subjected to power amplification again through the second erbium-doped optical fiber amplifier by the circulator and then enter the one-way optical fiber Mach-Zehnder interferometer to perform corresponding high-frequency modulation and interference on the backward Rayleigh scattering light signals;
the interfered backward Rayleigh scattering optical signal enters a photoelectric detector to be converted into a sensing electric signal and then enters a signal processing unit to be subjected to phase carrier demodulation;
wherein the phase carrier demodulation comprises the following steps:
collecting a sensing electric signal with vibration information transmitted by the photoelectric detector by using a data acquisition card, and outputting the data to an industrial personal computer in an alternating current coupling mode;
since vibration causes signal phase change, the phase change introduced by the vibration signal is used for expressing the interference signal;
the industrial personal computer multiplies the input interference signal by a first harmonic and a second harmonic high-frequency carrier signal respectively to complete the separation of the vibration signal to be detected and the carrier signal; converting the interference signal into a trigonometric function including a sine term and a cosine term;
then, obtaining information containing the vibration signal to be detected after passing through a low-pass filter, wherein the information is information of filtering out direct current components, carrier signal components and corresponding high-order sub-carrier signal components;
then, performing differential operation on a sine term and a cosine term in the information passing through the low-pass filter, and converting a trigonometric function containing the sensing signal;
and finally, after the inversion and arc tangent operation is carried out on the converted signal, the high-pass filter is used for filtering out the low-frequency noise in the demodulated vibration signal to be detected, so that the amplitude-frequency information of the vibration signal applied to the sensing optical fiber is demodulated.
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| CN114923559A (en) * | 2022-04-19 | 2022-08-19 | 北京理工大学 | Distributed optical fiber sound wave measuring method based on phase demodulation optical frequency domain reflectometer |
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| CN115913378A (en) * | 2022-11-10 | 2023-04-04 | 西南交通大学 | Same-frequency shared optical fiber communication perception integrated system |
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| CN117968823A (en) * | 2024-04-01 | 2024-05-03 | 杭州声飞光电技术有限公司 | Distributed optical fiber sound sensing device and sound detection method |
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| CN114485903A (en) * | 2022-01-17 | 2022-05-13 | 武汉地震工程研究院有限公司 | System and method for measuring high-frequency vibration of long-distance distributed optical fiber |
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| CN114593812A (en) * | 2022-03-11 | 2022-06-07 | 聊城大学 | Monitoring system based on distributed optical fiber vibration sensing and implementation method |
| CN114923559A (en) * | 2022-04-19 | 2022-08-19 | 北京理工大学 | Distributed optical fiber sound wave measuring method based on phase demodulation optical frequency domain reflectometer |
| CN115913378B (en) * | 2022-11-10 | 2024-04-05 | 西南交通大学 | Common-frequency shared optical fiber communication sensing integrated system |
| CN115913378A (en) * | 2022-11-10 | 2023-04-04 | 西南交通大学 | Same-frequency shared optical fiber communication perception integrated system |
| CN115622626A (en) * | 2022-12-20 | 2023-01-17 | 山东省科学院激光研究所 | Distributed sound wave sensing voice information recognition system and method |
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| CN116399379A (en) * | 2023-06-07 | 2023-07-07 | 山东省科学院激光研究所 | Distributed optical fiber acoustic wave sensing system and measuring method thereof |
| CN116399379B (en) * | 2023-06-07 | 2023-11-03 | 山东省科学院激光研究所 | Distributed optical fiber acoustic wave sensing system and measuring method thereof |
| CN117968823A (en) * | 2024-04-01 | 2024-05-03 | 杭州声飞光电技术有限公司 | Distributed optical fiber sound sensing device and sound detection method |
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