CN113324569B - Dual-wavelength unidirectional ring type distributed optical fiber sensing and positioning system - Google Patents
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Abstract
The invention belongs to the technical field of optical fiber sensing, and particularly relates to a dual-wavelength unidirectional ring type distributed optical fiber sensing positioning system. The system comprises a light source part, a light detection part and a light interference part; the optical interference part comprises an interference unit, two dual-wavelength transceiving modules and two sensing optical cables. The invention realizes distributed optical fiber sensing and positioning by using a dual-wavelength one-way ring interferometer, directly performs cross-correlation operation on two demodulated phase signals to obtain time delay between two paths of signals, thereby calculating the distance between a disturbance occurrence position and a dual-wavelength transceiver module, and judging which sensing optical cable the disturbance occurs on according to the relative relation between the cross-correlation peak position and the central position, thereby finally realizing disturbance positioning. Compared with the traditional interference type long-distance distributed sensing system, the system disclosed by the invention does not need subtraction on signals on a positioning algorithm, so that the similarity of the two signals for cross-correlation calculation is ensured, and the precision of disturbance positioning is improved.
Description
Technical Field
The invention belongs to the technical field of optical fiber sensing, and particularly relates to a dual-wavelength unidirectional ring type distributed optical fiber sensing positioning system and an algorithm.
Background
The distributed optical fiber sensor has the advantages of electromagnetic interference resistance, suitability for severe environments and the like, and can be used in the fields of perimeter security protection, petroleum pipeline leakage monitoring and the like. The disturbance occurring at any point on a sensing line can be positioned by using a distributed optical fiber sensor, and the conventional interferometric distributed optical fiber sensor for positioning the disturbance by using a time delay estimation method generally needs to perform subtraction of two signals in a positioning algorithm, so that a certain error may be introduced into the signals in the subtraction process, and the positioning error is increased. The dual-wavelength unidirectional ring-shaped distributed optical fiber sensing and positioning system provided by the invention ensures that no signal subtraction is needed during disturbance positioning from the optical path structure, thereby improving the positioning accuracy of the interference type long-distance distributed optical fiber sensing system.
Disclosure of Invention
The invention aims to provide a dual-wavelength unidirectional ring-shaped distributed optical fiber sensing and positioning system.
The invention realizes distributed optical fiber sensing and positioning by using a dual-wavelength unidirectional ring interferometer, and provides a sensing and positioning algorithm based on the optical fiber interferometer. The invention can improve the positioning precision of the interference type long-distance distributed optical fiber sensing system and avoid the positioning error caused by the signal subtraction operation in the traditional dual-wavelength optical fiber sensing positioning system.
The structure of the dual-wavelength unidirectional ring-shaped distributed optical fiber sensing and positioning system provided by the invention is shown in figure 1, and the system comprises a light source part, a light detection part and a light interference part; wherein:
the light source section includes: a broad spectrum laser (1), a first optical isolator (2);
the light detection section includes: the device comprises a first wavelength division multiplexer (9), a second wavelength division multiplexer (10), a first photoelectric detector (11), a second photoelectric detector (12), a third photoelectric detector (13) and a fourth photoelectric detector (14);
the light interference section includes: the system comprises an interference unit (3), a first dual-wavelength transceiver module (4), a second dual-wavelength transceiver module (5), a first sensing optical cable (6) and a second sensing optical cable (7); the first sensing cable (6) is connected with the second sensing cable (7) at an intermediate position (8);
the laser emitted by the wide-spectrum laser (1) is isolated by the first optical isolator (2) and then is connected with the interference unit (3) through the light injection interface (15);
the first photoelectric detector (11) and the second photoelectric detector (12) are respectively connected with the first wavelength division multiplexer (9), and the first wavelength division multiplexer (9) is connected with the interference unit (3) through a first optical detection interface (16);
the third photoelectric detector (13) and the fourth photoelectric detector (14) are respectively connected with the second wavelength division multiplexer (10); the second wavelength division multiplexer (10) is connected with the interference unit (3) through a second optical detection interface (17);
a first sensing optical path interface (18) of the interference unit (3) is connected with an inner side interface (20) of the first dual-wavelength transceiving module (4); a second sensing optical path interface (19) of the interference unit (3) is connected with an inner side interface (22) of the second dual-wavelength transceiver module (5);
the other end of the first sensing optical cable (6) is connected with an outer side interface (21) of the first dual-wavelength transceiver module (4), and the other end of the second sensing optical cable (7) is connected with an outer side interface (23) of the second dual-wavelength transceiver module (5); the first sensing optical cable (6) and the second sensing optical cable (7) are the same in length.
In the present invention, one structure of the interference unit (3) is as shown in fig. 2, and includes a 3 × 3 optical fiber coupler (24), an optical fiber delay line (25), and a 2 × 2 optical fiber coupler (26) connected in sequence.
In the present invention, one structure of the dual-wavelength transceiver module is shown in fig. 3, wherein the first dual-wavelength transceiver module (4) includes a third wavelength division multiplexer (27), a second optical isolator (28), and a fourth wavelength division multiplexer (29) connected in sequence; the second dual-wavelength transceiving module (5) comprises a fifth wavelength division multiplexer (30), a third optical isolator (31) and a sixth wavelength division multiplexer (32) which are connected in sequence.
In the double-wavelength unidirectional ring-shaped distributed optical fiber sensing and positioning system, the optical isolator (2) is added at the light-emitting position of the laser (1) to prevent the back scattered light of the sensing optical fiber and the reflected signal light from entering the wide-spectrum laser and influencing the working state of the laser.
The double-wavelength unidirectional ring type distributed optical fiber sensing and positioning system comprises a first unidirectional ring type interferometer and a second unidirectional ring type interferometer, wherein the two unidirectional ring type interferometers are symmetrical in structure, sensing light used by the two unidirectional ring type interferometers respectively occupies two different wave bands, and paths are distinguished through a wavelength division multiplexer. Wherein the first one-way ring interferometer occupies λ1And in the waveband, unidirectional transmission is carried out in the optical interference part according to the sequence of a second dual-wavelength transceiver module (5), a second sensing optical cable (7), a first sensing optical cable (6) and a first dual-wavelength transceiver module (4), and a first photoelectric detector (11) and a third photoelectric detector (13) are used in the optical detection part. Occupancy of the second one-way ring interferometer by λ2A first dual-wavelength transceiver module in the optical interference part(4) The first sensing optical cable (6), the second sensing optical cable (7) and the second dual-wavelength transceiver module (5) are sequentially transmitted in a one-way mode, and the second photoelectric detector (12) and the fourth photoelectric detector (14) are used in the optical detection portion. The distributed vibration sensing and disturbance positioning can be realized by laying the sensing optical cable in an area to be monitored.
In the dual-wavelength unidirectional ring-shaped distributed optical fiber sensing and positioning system, phase difference signals generated by disturbance are demodulated through a phase demodulation algorithm to obtain two paths of disturbance signals with time delay, the two paths of signals are subjected to cross-correlation operation to find the peak value of a cross-correlation function, the time delay related to the disturbance position can be obtained, and the occurrence position of the disturbance can be calculated.
In the dual-wavelength unidirectional ring type distributed optical fiber sensing and positioning system, the dual-wavelength transceiver module is used for transmitting light with one wavelength to the sensing optical path and receiving light with the other wavelength from the sensing optical path. They ensure that light of each wavelength is transmitted in one direction in the annular sensing optical path. The two dual-wavelength transceiver modules are functionally symmetrical, one for receiving lambda1Wavelength, transmission lambda2Wavelength, then another implementation receives λ2Wavelength, transmission lambda1Wavelength.
In the distributed optical fiber sensing positioning system based on the asymmetric fusion interferometer, the positioning algorithm is as follows:
the two detected interference signals of the first one-way ring type interferometer are respectively as follows:
wherein E is01And E03Is the amplitude of the light, and,
is the phase change caused by the perturbation, psi is the fixed initial phase difference of the 3 x 3 coupler.
The two detected interference signals of the second one-way ring type interferometer are respectively as follows:
wherein E is02And E04Is the amplitude of the light, and,
is the phase change caused by the perturbation, psi is the fixed initial phase difference of the 3 x 3 coupler.
If a disturbance occurs on the first sensing cable, the same disturbance causes a phase change of the two interferometers
And
respectively as follows:
wherein L isdThe length of the optical fiber delay line is L, and the length of the first sensing optical cable and the length of the second sensing optical cable are Ls，LxIs the distance (L) from the disturbance occurrence location to the first dual-wavelength transceiver modules≥Lx) And c is the speed of light in vacuum and n is the refractive index of the fiber.
If a disturbance occurs on the second sensing cable, the same disturbance causes a phase change of both interferometers
And
respectively as follows:
wherein L isd、LsC and n are as defined above, and LxIs the distance (L) from the location of the disturbance to the second dual-wavelength transceiver modules≥Lx)。
The two groups are
And
symmetrical in form, whether the disturbance occurs on the first sensing cable or the second sensing cable,
and
all have a time difference tau betweenxIt contains information of the disturbance position, and the expression is:
τx＝2n(Ls-Lx)/c
by pairs
And
making a cross-correlation function, wherein the cross-correlation function is expressed as:
the cross-correlation function is searched for the peak, and the time delay tau can be obtained by the difference between the peak position and the center position of the cross-correlation functionxThus, the disturbance position can be obtained, and the calculation formula is as follows:
Lx＝Ls-c·τx/2n
the mode of judging which sensing optical cable the disturbance occurs in is as follows:
judging the left-right relation of the peak position of the cross-correlation function relative to the central position, if the peak position of the cross-correlation function is at the right side of the central position (namely the abscissa of the peak position is larger than the abscissa of the central position), proving that the peak position of the cross-correlation function is at the right side of the central position
Is delayed at
Where the disturbance occurs on the first sensing cable. If the peak position of the cross-correlation function is to the left of the center position (i.e., the abscissa of the peak position is smaller than the abscissa of the center position), it turns out that
Is delayed at
Where the disturbance occurs on the second sensing cable.
Determination by sensing optical cable and LxThe specific position of the disturbance can be obtained by calculation, and sensing and disturbance positioning are realized.
The system realizes distributed optical fiber sensing and positioning by using the dual-wavelength unidirectional ring-shaped optical fiber interferometer, provides a sensing and positioning demodulation algorithm based on the system, and compared with the traditional interferometric long-distance distributed sensing system, the system does not need subtraction on signals in the positioning algorithm, ensures the similarity of the two signals for cross-correlation calculation, and improves the precision of disturbance positioning.
Drawings
FIG. 1 is a structural diagram of a dual-wavelength unidirectional ring-type distributed optical fiber sensing and positioning system of the present invention.
FIG. 2 is a diagram showing a structure of an interference unit used in the dual-wavelength unidirectional ring distributed optical fiber sensing and positioning system of the present invention.
Fig. 3 is a structure of a dual-wavelength transceiver module in the dual-wavelength unidirectional ring distributed optical fiber sensing and positioning system of the present invention.
FIG. 4 is a flow chart of a positioning algorithm in the dual-wavelength unidirectional ring-shaped distributed optical fiber sensing positioning system of the present invention.
FIG. 5 is a diagram of a dual-wavelength unidirectional ring-shaped distributed optical fiber sensing and positioning system according to the present invention, which is obtained by phase demodulation when disturbance occurs in the first sensing optical cable
And
fig. 6 is a cross-correlation function obtained through cross-correlation operation when disturbance occurs in the first sensing optical cable in the dual-wavelength unidirectional ring-shaped distributed optical fiber sensing and positioning system of the present invention.
FIG. 7 is a diagram of a dual-wavelength unidirectional ring-shaped distributed optical fiber sensing and positioning system according to the present invention, which is obtained by phase demodulation when disturbance occurs in the second sensing optical cable
And
fig. 8 is a cross-correlation function obtained through cross-correlation operation when disturbance occurs in the second sensing optical cable in the dual-wavelength unidirectional ring-shaped distributed optical fiber sensing and positioning system of the present invention.
Reference numbers in the figures: 1. a broad spectrum laser; 2. a first optical isolator; 3. an interference unit; 4. a first dual-wavelength transceiver module; 5. a second dual-wavelength transceiver module; 6. a first sensing cable; 7. a second sensing cable; 8. sensing the middle position of the optical cable; 9. a first wavelength division multiplexer; 10. a second wavelength division multiplexer; 11. a first photodetector; 12. a second photodetector; 13. a third photodetector; 14. a fourth photodetector; 15. a light injection interface; 16. a first optical detection interface; 17. a second optical detection interface; 18. a first sensing optical path interface; 19. a second sensing optical path interface; 20. an inner side interface of the first dual-wavelength transceiver module; 21. a first dual-wavelength transceiver module outer interface; 22. an inner side interface of the second dual-wavelength transceiver module; 23. a second dual-wavelength transceiver module outer interface; 24. a 3 × 3 fiber coupler; 25. an optical fiber delay line; 26. a 2 × 2 fiber coupler; 27. a third wavelength division multiplexer; 28. a second optical isolator; 29. a fourth wavelength division multiplexer; 30. a fifth wavelength division multiplexer; 31. a third optical isolator; 32. and a sixth wavelength division multiplexer.
Detailed Description
The following further describes embodiments of the present invention with reference to the drawings.
The dual-wavelength unidirectional ring-shaped distributed optical fiber sensing and positioning system adopts a wide-spectrum light source of a superluminescent light emitting diode (SLD) and has a central wavelength of 1550nm as shown in figure 1. The first opto-isolator eliminates optical reflections and four photodetectors are used for photoelectric conversion. The interference unit is used for making light generate interference therein, and converting the light phase change in the sensing optical path into light intensity change, and one possible structure of the interference unit is shown in fig. 2, the interior of the interference unit is composed of a 3 × 3 optical fiber coupler, an optical fiber delay line and a 2 × 2 optical fiber coupler, a light injection interface of the interference unit is used for connecting a laser, two light detection interfaces are used for connecting a photoelectric detector, and two sensing optical path interfaces are used for connecting a subsequent dual-wavelength transceiver module. Inside interface connection interference of dual-wavelength transceiver moduleThe sensing optical path interface of the unit and the outer side interface of the dual-wavelength transceiving module are connected with a sensing optical cable. One implementation of a dual-wavelength transceiver module is a combination of a wavelength division multiplexer and an optical isolator as shown in fig. 3, which separates the two wavelengths of the two single-ring interferometers to a wavelength λ1The light is transmitted in a single direction along the counterclockwise direction in the annular sensing optical path, so that the wavelength is lambda2The light of (a) is transmitted in a clockwise direction in the annular sensing optical path. The phases of the sensing light with two wavelengths can be modulated by the same disturbing signal, and the time for the two phase disturbing signals to reach the two groups of photoelectric detectors is related to the disturbing position, so that the position of the disturbance can be calculated according to the time difference between the two phase disturbing signals. The computer with data acquisition card is used to collect the photoelectric signal, and the detection and positioning of the disturbance can be realized by the algorithm in the flow chart of fig. 4. Taking a sampling rate of 500kSa/s as an example, when a disturbance occurs in the first sensing cable, the phase change signal is as shown in FIG. 5, and the cross-correlation function is as shown in FIG. 6, where the peak of the cross-correlation function is to the right of the center position (500000). When a disturbance occurs in the second sensing cable, the phase change signal is as shown in FIG. 7 and the cross-correlation function is as shown in FIG. 8, with the peak of the cross-correlation function to the left of the center position (500000). And disturbance positioning can be realized according to the relative position and difference value of the peak value and the center of the cross-correlation function.
Claims (4)
1. A dual-wavelength unidirectional ring-shaped distributed optical fiber sensing and positioning system is characterized by comprising a light source part, a light detection part and a light interference part; wherein:
the light source section includes: a broad spectrum laser (1), a first optical isolator (2);
the light detection section includes: the device comprises a first wavelength division multiplexer (9), a second wavelength division multiplexer (10), a first photoelectric detector (11), a second photoelectric detector (12), a third photoelectric detector (13) and a fourth photoelectric detector (14);
the light interference section includes: the system comprises an interference unit (3), a first dual-wavelength transceiver module (4), a second dual-wavelength transceiver module (5), a first sensing optical cable (6) and a second sensing optical cable (7); the first sensing cable (6) is connected with the second sensing cable (7) at an intermediate position (8);
the laser emitted by the wide-spectrum laser (1) is isolated by the first optical isolator (2) and then is connected with the interference unit (3) through the light injection interface (15);
the first photoelectric detector (11) and the second photoelectric detector (12) are respectively connected with the first wavelength division multiplexer (9), and the first wavelength division multiplexer (9) is connected with the interference unit (3) through a first optical detection interface (16);
the third photoelectric detector (13) and the fourth photoelectric detector (14) are respectively connected with the second wavelength division multiplexer (10); the second wavelength division multiplexer (10) is connected with the interference unit (3) through a second optical detection interface (17);
a first sensing optical path interface (18) of the interference unit (3) is connected with an inner side interface (20) of the first dual-wavelength transceiving module (4); a second sensing optical path interface (19) of the interference unit (3) is connected with an inner side interface (22) of the second dual-wavelength transceiver module (5);
the other end of the first sensing optical cable (6) is connected with an outer side interface (21) of the first dual-wavelength transceiver module (4), and the other end of the second sensing optical cable (7) is connected with an outer side interface (23) of the second dual-wavelength transceiver module (5); the first sensing optical cable (6) and the second sensing optical cable (7) have the same length;
the first dual-wavelength transceiving module (4) comprises a third wavelength division multiplexer (27), a second optical isolator (28) and a fourth wavelength division multiplexer (29), wherein one path of the third wavelength division multiplexer, the second optical isolator and the fourth wavelength division multiplexer are sequentially connected, and the other path of the first dual-wavelength transceiving module is connected with the third wavelength division multiplexer (27) and the fourth wavelength division multiplexer (29);
the second dual-wavelength transceiving module (5) comprises a fifth wavelength division multiplexer (30), a third optical isolator (31) and a sixth wavelength division multiplexer (32), wherein one path of the fifth wavelength division multiplexer, the third optical isolator and the sixth wavelength division multiplexer are sequentially connected, and the other path of the second dual-wavelength transceiving module is connected with the fifth wavelength division multiplexer (30) and the sixth wavelength division multiplexer (32);
the system comprises a first one-way ring-type interferometer and a second one-way ring-type interferometer, wherein the two one-way ring-type interferometers are symmetrical in structure, sensing light used by the two one-way ring-type interferometers respectively occupies two different wave bands, and paths are distinguished through a wavelength division multiplexer; wherein the first one-way ring interferometer occupies λ1Wave band in lightThe interference part carries out unidirectional transmission according to the sequence of a second dual-wavelength transceiver module (5), a second sensing optical cable (7), a first sensing optical cable (6) and a first dual-wavelength transceiver module (4), and a first photoelectric detector (11) and a third photoelectric detector (13) are used in the optical detection part; occupancy of the second one-way ring interferometer by λ2The optical interference part carries out unidirectional transmission according to the sequence of a first dual-wavelength transceiver module (4), a first sensing optical cable (6), a second sensing optical cable (7) and a second dual-wavelength transceiver module (5), and the optical detection part uses a second photoelectric detector (12) and a fourth photoelectric detector (14); the distributed vibration sensing and disturbance positioning can be realized by laying the sensing optical cable in an area to be monitored.
2. The dual-wavelength unidirectional ring type distributed optical fiber sensing and positioning system according to claim 1, wherein the interference unit (3) comprises a 3 × 3 optical fiber coupler (24), an optical fiber delay line (25), and a 2 × 2 optical fiber coupler (26) connected in sequence, and the other route 3 × 3 optical fiber coupler (24) is connected with the 2 × 2 optical fiber coupler (26).
3. The dual wavelength unidirectional ring type distributed optical fiber sensing positioning algorithm based on the system of claim 2 is characterized by comprising the following specific steps:
the two detected interference signals of the first one-way ring type interferometer are respectively as follows:
wherein E is01And E03Is the amplitude of the light, and,
is a phase change caused by a disturbance,. phi.A fixed initial phase difference of the combiner;
the two detected interference signals of the second one-way ring type interferometer are respectively as follows:
wherein E is02And E04Is the amplitude of the light, and,
is the phase change caused by the disturbance, psi is the fixed initial phase difference of the 3 × 3 coupler;
when disturbance occurs on the first sensing optical cable, the phase change of the two interferometers caused by the same disturbance
And
respectively as follows:
wherein L isdThe length of the optical fiber delay line is L, and the length of the first sensing optical cable and the length of the second sensing optical cable are Ls，LxIs the distance, L, from the location of the disturbance to the first dual-wavelength transceiver modules≥LxC is the speed of light in vacuum, n is the refractive index of the fiber;
when disturbance occurs on the second sensing cable, the phase change of the two interferometers caused by the same disturbance
And
respectively as follows:
wherein L isd、LsC and n are as defined above, and LxIs the distance, L, from the location of the disturbance to the second dual-wavelength transceiver modules≥Lx；
The two groups are
And
symmetrical in form, whether the disturbance occurs on the first sensing cable or the second sensing cable,
and
all have a time difference tau betweenxIt contains information of the disturbance position, and the expression is:
τx＝2n(Ls-Lx)/c；
by pairs
And
making a cross-correlation function, wherein the cross-correlation function is expressed as:
the cross-correlation function is searched for the peak, and the time delay tau is obtained by the difference between the peak position and the center position of the cross-correlation functionxThus, the disturbance position is obtained, and the calculation formula is as follows:
Lx＝Ls-c·τx/2n。
4. the dual wavelength unidirectional ring distributed optical fiber sensing and positioning algorithm of claim 3, wherein the manner of determining which sensing cable the disturbance occurs in is as follows:
judging the left-right relation of the peak position of the cross-correlation function relative to the central position, if the peak position of the cross-correlation function is at the right side of the central position, namely the abscissa of the peak position is larger than the abscissa of the central position, explaining
Is delayed at
At this time, disturbance occurs on the first sensing optical cable; if the peak position of the cross-correlation function is to the left of the center position, i.e. the abscissa of the peak position is smaller than the abscissa of the center position, this indicates that
Is delayed at
Where the disturbance occurs on the second sensing cable.
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