CN110307920B - Optical fiber temperature and stress sensing system based on noise modulation and measuring method - Google Patents
Optical fiber temperature and stress sensing system based on noise modulation and measuring method Download PDFInfo
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- G01K11/00—Measuring temperature based upon physical or chemical changes not covered by groups G01K3/00, G01K5/00, G01K7/00 or G01K9/00
- G01K11/32—Measuring temperature based upon physical or chemical changes not covered by groups G01K3/00, G01K5/00, G01K7/00 or G01K9/00 using changes in transmittance, scattering or luminescence in optical fibres
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- G01K—MEASURING TEMPERATURE; MEASURING QUANTITY OF HEAT; THERMALLY-SENSITIVE ELEMENTS NOT OTHERWISE PROVIDED FOR
- G01K11/00—Measuring temperature based upon physical or chemical changes not covered by groups G01K3/00, G01K5/00, G01K7/00 or G01K9/00
- G01K11/32—Measuring temperature based upon physical or chemical changes not covered by groups G01K3/00, G01K5/00, G01K7/00 or G01K9/00 using changes in transmittance, scattering or luminescence in optical fibres
- G01K11/324—Measuring temperature based upon physical or chemical changes not covered by groups G01K3/00, G01K5/00, G01K7/00 or G01K9/00 using changes in transmittance, scattering or luminescence in optical fibres using Raman scattering
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
- G01L1/00—Measuring force or stress, in general
- G01L1/24—Measuring force or stress, in general by measuring variations of optical properties of material when it is stressed, e.g. by photoelastic stress analysis using infrared, visible light, ultraviolet
- G01L1/242—Measuring force or stress, in general by measuring variations of optical properties of material when it is stressed, e.g. by photoelastic stress analysis using infrared, visible light, ultraviolet the material being an optical fibre
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Abstract
The invention discloses an optical fiber temperature and stress sensing system based on noise modulation, which comprises a semiconductor laser (1), a first electro-optical modulator (2), a 1 x 3 optical fiber coupler (3), a first optical circulator (4), a first bidirectional semiconductor optical amplifier (5), a second electro-optical modulator (6), a second optical circulator (7), a second bidirectional semiconductor optical amplifier (8), a 1 x 2 optical switch (9), a wavelength division multiplexer (10), an avalanche photodetector (11), a first photodetector (12), a second photodetector (13), a data acquisition card (14), a computer (15), a three-core sensing optical fiber (16), a pulse modulator (17), a 20MHz arbitrary waveform generator (18) and a constant temperature bath (19). The invention utilizes the Rayleigh scattering intensity change caused by the loss change of the sensing optical fiber when the stress changes and the characteristic that the Raman scattering light intensity is sensitive to the temperature, and simultaneously realizes the temperature along the optical fiber.
Description
Technical Field
The invention relates to the field of distributed optical fiber sensing systems, in particular to an optical fiber temperature and stress sensing system based on noise modulation and a measuring method.
Background
Since the 70 s of the last century, optical fiber sensing technology has received wide attention from people as a novel sensing technology. The optical fiber sensing technology is a technology for measuring external specific physical quantity by taking an optical fiber as a laser signal transmission medium.
The commonly used distributed fiber sensing technology mainly involves three types of backscattering: rayleigh scattering, brillouin scattering, raman scattering. The Rayleigh scattering intensity is maximum, the detection is easy, and the method is mainly used for detecting the breakpoint of the optical fiber; the frequency shift of the brillouin scattering is sensitive to temperature and stress changes, but because the brillouin scattering is very difficult to accurately distinguish the frequency shift caused by strain from the frequency shift caused by temperature change, the brillouin distributed optical fiber sensor is difficult to be finished and marketed, and the cost is extremely high; the light intensity of Raman scattering is sensitive to temperature, and the device is simple, so that the existing distributed optical fiber Raman temperature measurement technology is mature, the technical indexes such as temperature resolution, spatial resolution and the like can meet the requirements of general industrialization, but the Raman scattering itself is not sensitive to stress change, and the traditional Raman distributed sensing is not applied to stress sensing.
As can be seen from the above description, the conventional distributed sensing system mainly faces the following problems when measuring temperature changes and stress changes simultaneously: firstly, brillouin scattering is sensitive to temperature and stress changes, and brillouin scattering frequency shift is generated, but the frequency shift caused by strain and the frequency shift caused by temperature change are difficult to distinguish in practical situations, so brillouin distributed sensing still faces a large problem in measurement; secondly, although the raman scattering is sensitive to temperature change, it is not sensitive to stress change, and it is difficult to simultaneously measure temperature and stress. Therefore, in practical applications, a method which has a simple structure and can realize simultaneous measurement of temperature and stress is required.
Disclosure of Invention
The invention aims to provide an optical fiber temperature and stress sensing system and a measuring method based on noise modulation, which are used for solving the problems that the temperature and stress changes are difficult to be measured simultaneously and chaotic signals cannot be simultaneously realized at long distance and high precision in the conventional distributed optical fiber stress sensing system.
The invention is realized by adopting the following technical scheme:
an optical fiber temperature and stress sensing system based on noise modulation comprises a semiconductor laser, a first electro-optic modulator, a 1 x 3 optical fiber coupler, a first optical circulator, a first bidirectional semiconductor optical amplifier, a second electro-optic modulator, a second optical circulator, a second bidirectional semiconductor optical amplifier, a 1 x 2 optical switch, a wavelength division multiplexer, an avalanche photodetector, a first photodetector, a second photodetector, a data acquisition card, a computer, a three-core sensing optical fiber, a pulse modulator, a 20MHz arbitrary waveform generator and a thermostatic bath.
The output end of the semiconductor laser is connected with the input end of a first electro-optical modulator through a common single-mode jumper, the modulation end of the first electro-optical modulator is connected with the output end of a 20MHz arbitrary waveform generator, the output end of the first electro-optical modulator is connected with the input end of a 1 × 3 optical fiber coupler through the common single-mode jumper, the first output end of the 1 × 3 optical fiber coupler is connected with the input end of a first photoelectric detector through the common single-mode jumper, and the output end of the first photoelectric detector is connected with a data acquisition card through a coaxial cable; the second output end of the 1 x 3 optical fiber coupler is connected with one end of a first optical circulator through a common single-mode jumper, the other end of the first optical circulator is connected with one end of a first bidirectional semiconductor optical amplifier through the common single-mode jumper, and the other end of the first bidirectional semiconductor optical amplifier is connected with one of fiber cores in the three-core sensing optical fiber through the common single-mode jumper; the third end of the first optical circulator is connected with the input end of a second photoelectric detector through a common single-mode jumper, and the output end of the second photoelectric detector is connected with a data acquisition card through a coaxial cable; the third output end of the 1 × 3 optical fiber coupler is connected with the input end of a second electro-optical modulator through a common single-mode jumper, the modulation end of the second electro-optical modulator is connected with the pulse modulator, the output end of the second electro-optical modulator is connected with one end of a second optical circulator through a common single-mode jumper, the other end of the second optical circulator is connected with one end of a second bidirectional semiconductor optical amplifier through a common single-mode jumper, the other end of the second bidirectional semiconductor optical amplifier is connected with one end of a 1 × 2 optical switch, the other two ends of the 1 × 2 optical switch are respectively connected with one ends of the other two fiber cores in the three-core sensing optical fiber, one of the two fiber cores is placed in a thermostatic bath for thermostatic control and serves as a calibration fiber, and the other ends of the two fiber cores are connected through a jumper to form a closed loop; the third end of the second optical circulator is connected with the input end of the wavelength division multiplexer through a common single-mode jumper, the other end of the wavelength division multiplexer is connected with the input end of the avalanche photodetector through a common single-mode jumper, and the output end of the avalanche photodetector is connected with the data acquisition card through a coaxial cable; the output end of the data acquisition card is connected with the computer.
The optical fiber temperature and stress measurement method based on the sensing system has the following specific working processes:
(1) continuous light generated by the semiconductor laser is subjected to noise signal modulation through the first electro-optical modulator, and the arbitrary waveform generator with the frequency of 20MHz is used as a noise signal source for modulating Gaussian white noise optical signals required by the sensing system.
(2) The output noise optical signal is firstly divided into three paths of light by a 1 x 3 optical fiber coupler, wherein a first path of light source is used as reference light, is converted into an electric signal by a first photoelectric detector and then is input into a data acquisition card; a second path of optical signal is used as a path of pump light, directly enters a first optical circulator, passes through a first bidirectional semiconductor amplifier, finally enters one fiber core in the three-core sensing optical fiber, generates backward scattering light at each point of the optical fiber, outputs the backward scattering light of the optical fiber through a reflecting end of the first optical circulator, is converted into an electric signal through a second photoelectric detector, and then is input into a data acquisition card; and finally, inputting the signals acquired by the data acquisition card into a computer after A/D conversion. When the sensing fiber is subjected to stress strain, the cross-sectional diameter of the fiber changes (the scattering cross-section changes), resulting in a change in the rayleigh scattering intensity at that location of the fiber, specifically in a decrease in the scattering intensity at that point. And processing the electric signals of the pump light and the reference light collected by the photoelectric detector by adopting a cross-correlation method to obtain scattered light intensity information at any position of the optical fiber.
Wherein f is1(t) is the light intensity emitted by the light source as a function of time, f2And (t) is the relation between the Rayleigh scattering light intensity received by the detector and the time function, L is the backward scattering position (length) of the sensing optical fiber light, and C is the propagation speed of the light in the sensing optical fiber. The real-time stress change conditions of the optical fiber at different positions can be calculated by the formula.
(3) The third path of optical signal is used as the other path of pump light, enters a second photoelectric modulator through a 1 x 3 optical fiber coupler for pulse modulation, then the pulse light passes through the second optical circulator, is amplified through a second bidirectional semiconductor optical amplifier, enters a 1 x 2 optical switch, enters a loop configured by the three-core sensing optical fiber, generates backward scattering light at each point of the optical fiber, then the backward scattering light of the optical fiber is output through a reflection end of the second optical circulator, a Raman scattering signal is filtered out through a wavelength division multiplexer, the filtered Stokes light and the anti-Stokes light are output from an output end of the wavelength division multiplexer, enter an avalanche photoelectric detector to convert the optical signal into an electric signal, and finally the signal collected through a data collection card is input into a computer after A/D conversion; the temperature information at any position of the optical fiber is obtained by processing with the temperature sensitive characteristics of the intensity of the Stokes light and the anti-Stokes light.
The twice acquired backscatter data is demodulated according to the following formula to obtain the corresponding temperature. Because the intensity of the Stokes light and the anti-Stokes light has a correlation with the temperature of the environment, the relationship between the Stokes light intensity and the anti-Stokes light intensity is as the following formula,
wherein, KsAnd KaIs the Stokes light and the anti-Stokes lightScattering cross section in the fiber, vsAnd vaIs the central wavelength of the Stokes light and the anti-Stokes light, alphaaAnd alphaSIs the attenuation coefficient of the optical fiber.
Wherein R isLoop(T, L) is a temperature modulation function of Raman scattering intensity, RLoop(T0，L0) Temperature modulation function of Raman scattering intensity in order to calibrate temperature, T0For calibrating temperature, T is measured temperature, h is Planck constant, k is Boltzmann constant, L is sensing fiber light backscattering position, L is measured temperature, and0to scale the position of the fiber. The temperature of the corresponding sensing point position of the optical fiber can be calculated through the formula.
Based on the process, compared with the traditional distributed sensing system, the optical fiber temperature and stress sensing system based on noise modulation and the measuring method have the following advantages:
1. compared with the traditional distributed optical fiber sensing device, the invention utilizes the characteristics that Rayleigh scattering intensity change caused by loss change of the sensing optical fiber during stress change is used for detection and Raman scattering light intensity is sensitive to temperature, simultaneously realizes real-time measurement of temperature and stress along the optical fiber, and effectively avoids the problem that frequency shift caused by stress change and frequency shift caused by temperature change are difficult to distinguish in the application process of Brillouin distributed sensing.
2. Compared with the traditional distributed optical fiber sensing device, the sensing system adopts the Gaussian white noise modulation optical signal as the sensing optical signal, and effectively improves the spatial resolution of the sensing system by means of cross-correlation calculation of Rayleigh scattering of reference light and pump light.
3. Compared with the sensing system adopting chaotic laser in recent years, the invention has the greatest characteristic of overcoming the time delay characteristic of the chaotic laser, and can still ensure that the sensing distance is not influenced while the resolution is improved.
The invention has reasonable design and good popularization and application value.
Drawings
Fig. 1 shows a schematic structural diagram of a fiber temperature and stress sensing system based on noise modulation according to the present invention.
In the figure: 1-a semiconductor laser, 2-a first electro-optical modulator, 3-1 x 3 optical fiber coupler, 4-a first optical circulator, 5-a first bidirectional semiconductor optical amplifier, 6-a second electro-optical modulator, 7-a second optical circulator, 8-a second bidirectional semiconductor optical amplifier, 9-1 x 2 optical switch, 10-a wavelength division multiplexer, 11-an avalanche photodetector, 12-a first photodetector, 13-a second photodetector, 14-a data acquisition card, 15-a computer, 16-a three-core sensing optical fiber, 17-a pulse modulator, an 18-20MHz arbitrary waveform generator and 19-a constant temperature bath.
Detailed Description
The following detailed description of specific embodiments of the invention refers to the accompanying drawings.
An optical fiber temperature and stress sensing system based on noise modulation comprises a semiconductor laser 1, a first electro-optical modulator 2, a 1 x 3 optical fiber coupler 3, a first optical circulator 4, a first bidirectional semiconductor optical amplifier 5, a second electro-optical modulator 6, a second optical circulator 7, a second bidirectional semiconductor optical amplifier 8, a 1 x 2 optical switch 9, a wavelength division multiplexer 10, an avalanche photodetector 11, a first photodetector 12, a second photodetector 13, a data acquisition card 14, a computer 15 and a three-core sensing optical fiber 16.
As shown in fig. 1, the output end of the semiconductor laser 1 is connected to the input end of the first electro-optical modulator 2 through a common single-mode jumper, the modulation end of the first electro-optical modulator 2 is connected to the output end of the arbitrary waveform generator 18 of 20MHz, the output end of the first electro-optical modulator 2 is connected to the input end of the 1 × 3 optical fiber coupler 3 through a common single-mode jumper, the first output end of the 1 × 3 optical fiber coupler 3 is connected to the input end of the first photodetector 12 through a common single-mode jumper, and the output end of the first photodetector 12 is connected to the data acquisition card 14 through a coaxial cable; a second output end of the 1 × 3 optical fiber coupler 3 is connected with one end of a first optical circulator 4 through a common single-mode jumper, the other end of the first optical circulator 4 is connected with one end of a first bidirectional semiconductor optical amplifier 5 through a common single-mode jumper, and the other end of the first bidirectional semiconductor optical amplifier 5 is connected with one of fiber cores in the three-core sensing optical fiber 16 through a common single-mode jumper; the third end of the first optical circulator 4 is connected with the input end of a second photoelectric detector 13 through a common single-mode jumper, and the output end of the second photoelectric detector 13 is connected with a data acquisition card 14 through a coaxial cable; a third output end of the 1 × 3 optical fiber coupler 3 is connected with an input end of a second electro-optical modulator 6 through a common single-mode jumper, a modulation end of the second electro-optical modulator 6 is connected with a pulse modulator 17, an output end of the second electro-optical modulator 6 is connected with one end of a second optical circulator 7 through a common single-mode jumper, the other end of the second optical circulator 7 is connected with one end of a second bidirectional semiconductor optical amplifier 8 through a common single-mode jumper, the other end of the second bidirectional semiconductor optical amplifier 8 is connected with one end of a 1 × 2 optical switch 9, the other two ends of the 1 × 2 optical switch 9 are respectively connected with one ends of the other two fiber cores in the three-core sensing optical fiber 16, one of the other two fiber cores is placed in a thermostatic bath 19 to be subjected to thermostatic control to serve as a calibration fiber, and the other ends of the two fiber cores are connected through a jumper to form a closed loop; the third end of the second optical circulator 7 is connected with the input end of the wavelength division multiplexer 10 through a common single mode jumper, the other end of the wavelength division multiplexer 10 is connected with the input end of the avalanche photodetector 11 through a common single mode jumper, and the output end of the avalanche photodetector 11 is connected with the data acquisition card 14 through a coaxial cable; the output of the data acquisition card 14 is connected to a computer 15.
The optical fiber temperature and stress sensing measurement method based on noise modulation comprises the following steps:
1. continuous light generated by the DFB semiconductor laser 1 is subjected to noise signal modulation through the first electro-optical modulator 2, and the arbitrary waveform generator 18 with 20MHz is used as a noise signal source for modulating Gaussian white noise optical signals required by a sensing system.
2. Optical fiber stress detection along a line
The output Gaussian white noise optical signal is firstly divided into three paths of light by a 1 x 3 optical fiber coupler 3, wherein the first path of light source is used as reference light, is converted into an electric signal by a first photoelectric detector 12 and then is input into a data acquisition card 14; the second optical signal is used as a pump light, directly enters the first optical circulator 4, passes through the first bidirectional semiconductor amplifier 5, finally enters one of the fiber cores in the three-core sensing optical fiber 16, generates backward scattering light at each point of the optical fiber, then the backward scattering light of the optical fiber is output through the reflection end of the first optical circulator 4, is converted into an electric signal through the second photoelectric detector 13, then is input into the data acquisition card 14, and finally the signal acquired through the data acquisition card 14 is input into the computer 15 after being subjected to A/D conversion.
When the sensing optical fiber is subjected to stress strain, the cross-sectional diameter of the optical fiber changes (the scattering section changes), so that the rayleigh scattering intensity at the position of the optical fiber changes, and the scattering intensity at the position becomes low. And processing the electric signals of the pump light and the reference light collected by the photoelectric detector by adopting a cross-correlation method to obtain scattered light intensity information at any position of the optical fiber.
Wherein f is1(t) is the light intensity emitted by the light source as a function of time, f2And (t) is the relation between the Rayleigh scattering light intensity received by the detector and the time function, L is the backward scattering position (length) of the sensing optical fiber light, and C is the propagation speed of the light in the sensing optical fiber. The intensity of the scattered light and the change of the stress are in a linear relation in the bearable range of the optical fiber, and the real-time stress change conditions of the optical fiber at different positions can be calculated by the formula.
(3) Optical fiber line temperature detection
The third optical signal as the other pump light enters the second photoelectric modulator 6 through the 1 x 3 optical fiber coupler 3 for pulse modulation, then the pulse light passes through a second optical circulator 7, is amplified by a second bidirectional semiconductor optical amplifier 8, passes through a 1 multiplied by 2 optical switch 9, enters a closed loop formed by a three-core sensing optical fiber 16, when one of the 1 x 2 optical switches 9 is open, the light produces backscattered light at each point of the fiber, then the optical fiber backward scattering light is output through the reflection end of the second optical circulator 7, the wavelength division multiplexer 10 filters out the raman scattering signal, the filtered stokes light and the anti-stokes light are output from the output end of the wavelength division multiplexer 10, enter the avalanche photodetector 11 to convert the optical signal into an electrical signal, and finally the signal collected by the data collection card 14 is input into the computer 15 after being subjected to a/D conversion. When the other path of the 1 × 2 optical switch 9 is opened, light enters from the other end of the loop, generated backscattering returns to the second optical circulator 7 through the 1 × 2 optical switch 9, a raman scattering signal is filtered out through the wavelength division multiplexer 10, the filtered stokes light and the anti-stokes light are output from the output end of the wavelength division multiplexer 10, enter the avalanche photodetector 11 to convert an optical signal into an electrical signal, and finally, the signal collected through the data acquisition card 14 is input into the computer 15 after being subjected to a/D conversion.
Finally, the backscattering data acquired twice are demodulated according to the following formula to obtain the corresponding temperature; since the intensity of the Stokes light and the anti-Stokes light is related to the temperature of the environment, the Stokes light intensity and the anti-Stokes light intensity are related by the following formula:
wherein, KsAnd KaV is the scattering cross section of Stokes light and anti-Stokes light in the optical fibersAnd vaIs the central wavelength of the Stokes light and the anti-Stokes light, alphaaAnd alphaSIs the attenuation coefficient of the optical fiber.
Wherein R isLoop(T, L) is a temperature modulation function of Raman scattering intensity, RLoop(T0，L0) Temperature modulation function of Raman scattering intensity in order to calibrate temperature, T0For calibrating temperature, T is measured temperature, h is Planck constant, k is Boltzmann constant, L is sensing fiber light backscattering position, L is measured temperature, and0to scale the position of the fiber. The temperature of the corresponding sensing point position of the optical fiber can be calculated through the formula.
In the specific implementation: the central wavelength of the semiconductor laser 1 adopts 1550 nm; the avalanche detector 11 is an avalanche photodetector of the Fby photoelectric, DTS1550-DA-MM type.
Finally, it should be noted that the above embodiments are only for illustrating the technical solutions of the present invention and not for limiting, and although the detailed description is made with reference to the embodiments of the present invention, it should be understood by those skilled in the art that modifications or equivalent substitutions may be made on the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, which should be covered by the protection scope of the claims of the present invention.
Claims (2)
1. An optical fiber temperature and stress sensing system based on noise modulation is characterized in that: the photoelectric detector comprises a semiconductor laser (1), a first electro-optical modulator (2), a 1 x 3 optical fiber coupler (3), a first optical circulator (4), a first bidirectional semiconductor optical amplifier (5), a second electro-optical modulator (6), a second optical circulator (7), a second bidirectional semiconductor optical amplifier (8), a 1 x 2 optical switch (9), a wavelength division multiplexer (10), an avalanche photodetector (11), a first photodetector (12), a second photodetector (13), a data acquisition card (14), a computer (15), a three-core sensing optical fiber (16), a pulse modulator (17), a 20MHz arbitrary waveform generator (18) and a constant temperature tank (19);
the output end of the semiconductor laser (1) is connected with the input end of a first electro-optical modulator (2) through a common single-mode jumper, the modulation end of the first electro-optical modulator (2) is connected with the output end of a 20MHz arbitrary waveform generator (18), the output end of the first electro-optical modulator (2) is connected with the input end of a 1 x 3 optical fiber coupler (3) through the common single-mode jumper, the first output end of the 1 x 3 optical fiber coupler (3) is connected with the input end of a first photoelectric detector (12) through the common single-mode jumper, and the output end of the first photoelectric detector (12) is connected with a data acquisition card (14) through a coaxial cable; the second output end of the 1 x 3 optical fiber coupler (3) is connected with one end of a first optical circulator (4) through a common single-mode jumper, the other end of the first optical circulator (4) is connected with one end of a first bidirectional semiconductor optical amplifier (5) through a common single-mode jumper, and the other end of the first bidirectional semiconductor optical amplifier (5) is connected with one fiber core in a three-core sensing optical fiber (16) through a common single-mode jumper; the third end of the first optical circulator (4) is connected with the input end of a second photoelectric detector (13) through a common single-mode jumper, and the output end of the second photoelectric detector (13) is connected with a data acquisition card (14) through a coaxial cable; the third output end of the 1 x 3 optical fiber coupler (3) is connected with the input end of a second electro-optical modulator (6) through a common single-mode jumper, the modulation end of the second electro-optical modulator (6) is connected with a pulse modulator (17), the output end of the second electro-optical modulator (6) is connected with one end of a second optical circulator (7) through a common single-mode jumper, the other end of the second optical circulator (7) is connected with one end of a second bidirectional optical semiconductor amplifier (8) through a common single-mode jumper, the other end of the second bidirectional semiconductor optical amplifier (8) is connected with one end of a 1 x 2 optical switch (9), the other two ends of the 1 x 2 optical switch (9) are respectively connected with one ends of the other two fiber cores in a three-core sensing optical fiber (16), one of the fiber cores is placed in a thermostatic bath (19) to be subjected to thermostatic control to be used as a calibration fiber, and the other ends of the two fiber cores are connected through a jumper, forming a closed loop; the third end of the second optical circulator (7) is connected with the input end of the wavelength division multiplexer (10) through a common single mode jumper, the other end of the wavelength division multiplexer (10) is connected with the input end of the avalanche photodetector (11) through a common single mode jumper, and the output end of the avalanche photodetector (11) is connected with the data acquisition card (14) through a coaxial cable; the output end of the data acquisition card (14) is connected with a computer (15).
2. An optical fiber temperature and stress sensing measurement method based on noise modulation is characterized in that: the method comprises the following steps:
(1) continuous light generated by the semiconductor laser (1) is subjected to noise signal modulation through the first electro-optical modulator (2), and finally a Gaussian white noise optical signal required by the sensing system is generated;
(2) optical fiber line stress detection
The output Gaussian white noise optical signal is firstly divided into three paths of light by a 1 x 3 optical fiber coupler (3), wherein the first path of light source is used as reference light, is converted into an electric signal by a first photoelectric detector (12), and then is input into a data acquisition card (14); a second path of optical signal is used as a path of pump light, directly enters a first optical circulator (4), then enters one fiber core in a three-core sensing optical fiber (16) through a first bidirectional semiconductor amplifier (5), finally enters one fiber core, generates backward scattering light at each point of the optical fiber, then the backward scattering light of the optical fiber is output through a reflection end of the first optical circulator (4), is converted into an electric signal through a second photoelectric detector (13), then is input into a data acquisition card (14), and finally is input into a computer (15) after being subjected to A/D conversion through the data acquisition card (14);
when the sensing optical fiber is subjected to stress strain, the diameter of the cross section of the optical fiber changes, so that the Rayleigh scattering intensity of the position of the optical fiber changes, and the specific phenomenon is that the scattering intensity of the point becomes low; processing the electric signals of the pump light and the reference light collected by the photoelectric detector by adopting a cross-correlation method to obtain scattered light intensity information at any position of the optical fiber, wherein the intensity of the scattered light and the change of the stress borne by the optical fiber form a linear relation in a bearable range of the optical fiber, so that the real-time stress change conditions of the optical fiber at different positions are calculated;
(3) optical fiber line temperature detection
A third optical signal serving as another pump light enters a second photoelectric modulator (6) through a 1 x 3 optical fiber coupler (3) for pulse modulation, then the pulse light passes through a second optical circulator (7), is amplified through a second bidirectional semiconductor optical amplifier (8), then passes through a 1 x 2 optical switch (9) and enters a closed loop formed by a three-core sensing optical fiber (16), when one of the 1 x 2 optical switches (9) is opened, light generates backward scattering light at each point of the optical fiber, then the backward scattering light of the optical fiber is output through a reflection end of the second optical circulator (7), a Raman scattering signal is filtered out through a wavelength division multiplexer (10), the filtered Stokes avalanche light and anti-Stokes light are output from an output end of the wavelength division multiplexer (10), the filtered Stokes avalanche light and anti-Stokes light enter a photoelectric detector (11) to convert the optical signal into an electric signal, and finally the signal collected through a data collection card (14) is input into a calculation after A/D conversion In the machine (15); when the other path of the 1 × 2 optical switch (9) is opened, light enters from the other end of the loop, generated backscattering returns to the second optical circulator (7) through the 1 × 2 optical switch (9), a Raman scattering signal is filtered out through the wavelength division multiplexer (10), the filtered Stokes light and the anti-Stokes light are output from the output end of the wavelength division multiplexer (10), enter the avalanche photodetector (11) to convert an optical signal into an electric signal, and finally, the signal acquired through the data acquisition card (14) is input into the computer (15) after being subjected to A/D conversion; and finally, because the intensity of the Stokes light and the anti-Stokes light has a correlation with the temperature of the environment, the temperature of the corresponding sensing point position of the optical fiber can be calculated according to the back scattering data acquired twice.
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
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| CN111307322B (en) * | 2019-12-09 | 2021-12-07 | 北京航天控制仪器研究所 | Distributed optical fiber temperature sensing system based on annular light path |
| CN111307188B (en) * | 2020-02-22 | 2021-09-14 | 太原理工大学 | Exempt from frequency sweep BOTDA device based on noise modulation |
| CN111896136B (en) * | 2020-06-29 | 2021-11-09 | 太原理工大学 | Dual-parameter distributed optical fiber sensing device and method with centimeter-level spatial resolution |
| CN112378432B (en) * | 2020-10-29 | 2023-08-15 | 太原理工大学 | Distributed optical fiber Raman sensing device and method based on noise matched filtering |
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