CN111896137A - Centimeter-level spatial resolution distributed optical fiber Raman sensing device and method - Google Patents
Centimeter-level spatial resolution distributed optical fiber Raman sensing device and method Download PDFInfo
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Abstract
The invention relates to the field of temperature demodulation in a distributed optical fiber sensing system, and discloses a distributed optical fiber Raman sensing device and method capable of realizing centimeter-level spatial resolution. The device comprises a first pulse laser and a second pulse laser, wherein pulse laser light with different pulse widths generated by the first pulse laser and the second pulse laser is sent to the sensing optical fiber through an optical switch in a time-sharing manner to generate Raman scattering respectively; and after the anti-Stokes light in backward Raman scattering is detected by the avalanche photodetector, the anti-Stokes light is output to a high-speed data acquisition card for acquisition and is sent to a computer for calculation to obtain the temperature information along the sensing optical fiber. The method is based on double-pulse modulation, backward Raman anti-Stokes scattering signals excited in two different pulse width states are collected in a calibration stage and a measurement stage, self-demodulation temperature extraction is carried out, and the spatial resolution of the system can be optimized to the centimeter magnitude on the premise of not influencing the sensing distance.
Description
Technical Field
The invention relates to the field of temperature demodulation in a distributed optical fiber sensing system, in particular to a centimeter-level spatial resolution distributed optical fiber Raman sensing device and method based on double-pulse modulation.
Background
The distributed optical fiber Raman sensing system can continuously measure the distributed temperature characteristic information along the sensing optical fiber. The system demodulates the temperature change along the optical fiber by collecting the back Raman scattering light carrying temperature information generated when the pulse light is transmitted in the optical fiber, and then performs positioning according to the optical time domain reflection technology, thereby realizing distributed continuous measurement of the temperature along the sensing optical fiber. Compared with the traditional electronic temperature sensor, the distributed optical fiber Raman sensing system has the advantages of electromagnetic interference resistance, high voltage resistance, high sensitivity, large temperature detection range and the like, and is widely applied to the temperature safety monitoring fields of electric power, traffic, fire fighting, petrochemical industry, aerospace and the like.
The spatial resolution is a key performance index of the distributed optical fiber Raman sensing technology, can reflect the minimum optical fiber length which can be distinguished by an optical fiber sensing system, and has important significance for the field of industrial temperature safety monitoring by improving the spatial resolution of the system. At present, in a distributed fiber Raman sensing system, all detection signals are pulse signals, the positioning principle is a pulse time flight method, and the spatial resolution of the system is limited within a spatial scale corresponding to half pulse width by the method. Reducing the pulse width of the light source can improve the spatial resolution of the system, but also deteriorates the signal-to-noise ratio of the system, and finally affects the sensing distance of the system. Therefore, the existing distributed fiber raman sensing system has a contradiction that sensing distance and spatial resolution cannot be considered at the same time, and is limited by the pulse width of the light source, so that the spatial resolution is difficult to break through 1 m.
Therefore, a brand new temperature demodulation method needs to be invented to solve the technical problem that the existing distributed optical fiber raman sensor system cannot give consideration to both the sensing distance and the spatial resolution, and the spatial resolution of the existing distributed optical fiber raman sensor is difficult to break through 1m due to the limitation of the pulse width of the light source.
Disclosure of Invention
The distributed optical fiber Raman sensor aims to solve the technical problem that the existing distributed optical fiber Raman sensor system cannot give consideration to both sensing distance and spatial resolution, and the spatial resolution is difficult to break through 1m due to the limitation of the pulse width of a light source. The invention provides a centimeter-level spatial resolution distributed optical fiber Raman sensing device and method.
In order to solve the technical problems, the invention adopts the technical scheme that: a distributed optical fiber Raman sensing device with centimeter-level spatial resolution comprises a first pulse laser, a second pulse laser, an optical switch, a sensing optical fiber, a filter, an avalanche photodetector, a high-speed data acquisition card and a computer, wherein laser output ends of the first pulse laser and the second pulse laser are connected with an input end of the optical switch, an output end of the optical switch is connected with one end of the sensing optical fiber, the first pulse laser and the second pulse laser are respectively used for generating pulse lasers with pulse width difference smaller than 1ns, and the optical switch is used for transmitting the pulse lasers generated by the first pulse laser and the second pulse laser to the sensing optical fiber in a time-sharing manner to generate Raman scattering; the backward Raman scattering light is filtered out by the filter to obtain Raman anti-Stokes light, and then is detected by the avalanche photodetector and then is output to the high-speed data acquisition card, and the high-speed data acquisition card is used for respectively acquiring the light intensity of the Raman anti-Stokes light generated by the laser pulse emitted by the first pulse laser and the second pulse laser at each position in the sensing optical fiber and sending the light intensity to the computer to calculate and obtain the temperature information along the sensing optical fiber.
The pulse widths of the laser output by the first pulse laser and the second pulse laser are more than 10ns, and the pulse width difference is 0.1 ns.
The wavelength of the first pulse laser is 1550nm, the repetition frequency is 8KHz, the wavelength of the second pulse laser is 1550nm, the repetition frequency is 8KHz, the bandwidth of an avalanche photodetector is 100MHz, the spectral response range is 900-1700 nm, the working wavelength of the filter is 1450nm, the number of channels of the high-speed data acquisition card 9 is 2, the sampling rate is 10GS/s, and the bandwidth is 10 GHz; the sensing optical fiber is a refractive index graded multimode optical fiber.
The distributed optical fiber Raman sensing device with centimeter-level spatial resolution further comprises an optical circulator and an amplifier, wherein a first port of the optical circulator is connected with the output end of the optical switch, a second port of the optical circulator is connected with one end of the sensing optical fiber, a third port of the optical circulator is connected with the filter, and the amplifier is arranged between the avalanche photodetector and the high-speed data acquisition card and used for amplifying detection signals of the avalanche photodetector.
The calculation formula of the temperature information along the sensing optical fiber obtained by the computer is as follows:
wherein T represents the measured temperature at the position L in the sensing optical fiber, h is a Planckian constant, Δ v represents the Raman frequency shift, k is a Boltzmann constant, ln represents the logarithm, T represents the set environmental temperature of the sensing optical fiber in the calibration stage, and phias1(L) represents the difference of the backward Raman anti-Stokes scattered light intensity generated by the laser emitted by the first pulse laser and the laser emitted by the second pulse laser in the sensing optical fiber respectively in the measuring stage, phias0And (L) the difference of the light intensity of backward Raman anti-Stokes scattered light generated by the laser light emitted by the first pulse laser and the laser light emitted by the second pulse laser in the sensing optical fiber respectively in the calibration stage.
In addition, the invention also provides a centimeter-level spatial resolution distributed optical fiber Raman sensing method, which is realized based on the centimeter-level spatial resolution distributed optical fiber Raman sensing device and comprises the following steps:
s1, calibration stage: setting the temperature along the sensing fiber to T0The pulse lasers emitted by the first pulse laser and the second pulse laser are respectively transmitted to the sensing optical fiber through the optical switch, and the high-speed data acquisition card is utilized to respectively acquire the light intensity phi of backward Raman anti-Stokes signals generated by the pulse lasers emitted by the first pulse laser at the L position of the sensing optical fiberas10(L) and the light intensity phi of backward Raman anti-Stokes signal generated by the pulse laser emitted by the second pulse laser at the position L of the sensing optical fiberas20(L)；
S2, measurement stage: pulse lasers emitted by the first pulse laser and the second pulse laser are respectively transmitted to the sensing optical fiber through the optical switch, and the light intensity phi of backward Raman anti-Stokes signals generated at the L position of the sensing optical fiber by the pulse lasers emitted by the first pulse laser is respectively collected by the high-speed data collection cardas11(L) and the light intensity phi of backward Raman anti-Stokes signal generated by the pulse laser emitted by the second pulse laser at the L position of the sensing optical fiberas21(L); wherein phi isas10(L)、φas20(L)、φas21(L)、φas11(L) are the superposition sum of half pulse space scale scattering signals at the position L of the sensing optical fiber;
s3, calculating: and (3) sending the light intensity signals measured in the step (S1) and the step (S2) to a computer, and obtaining the temperature information along the sensing optical fiber (5) through the computer, wherein the calculation formula is as follows:
wherein T represents the measured temperature at the position L in the sensing optical fiber, h is a Planckian constant, Δ v is a Raman frequency shift, k is a Boltzmann constant, ln represents logarithm, and T0Set ambient temperature, phi, of the sensing fiber at the calibration stageas1(L) represents measurementThe phase data collection card collects the light intensity difference phi of two backward Raman anti-Stokes scattered lights at the position L in the sensing optical fiberas1(L)＝φas21(L)-φas11(L)，φas0(L) represents the light intensity difference of two backward Raman anti-Stokes scattered lights at the position L in the sensing optical fiber acquired by the calibration stage data set acquisition card, phias0(L)＝φas20(L)-φas10(L)。
Compared with the prior art, the invention has the following beneficial effects: the invention provides a centimeter-level spatial resolution distributed optical fiber Raman temperature sensing device and a centimeter-level spatial resolution distributed optical fiber Raman temperature sensing method, which are realized on the basis of a Raman anti-Stokes light self-demodulation principle of double-pulse modulation, pulse light with the pulse width difference of 0.1ns is respectively injected into a sensing optical fiber through an optical switch by arranging two high-power pulse lasers with different pulse widths, then backward Raman anti-Stokes scattering signals excited in two different pulse width states are collected in a calibration stage and a measurement stage, and self-demodulation temperature adjustment degree extraction is carried out by utilizing anti-Stokes light intensity data of the sensing optical fiber. The invention can ensure that the spatial resolution of the system is optimized to the centimeter magnitude on the premise of not influencing the sensing distance.
Drawings
Fig. 1 is a schematic structural diagram of a distributed optical fiber raman sensing device with centimeter-level spatial resolution according to an embodiment of the present invention.
In the figure: 1-a first pulse laser, 2-a second pulse laser, 3-an optical switch, 4-a circulator, 5-a sensing optical fiber, 6-a filter, 7-an avalanche photodetector, 8-an amplifier, 9-a high-speed data acquisition card and 10-a computer.
Detailed Description
In order to make the objects, technical solutions and advantages 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, and it is obvious that the described embodiments are 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.
As shown in fig. 1, an embodiment of the present invention provides a centimeter-level spatial resolution distributed optical fiber raman sensing device, including a first pulse laser 1, a second pulse laser 2, an optical switch 3, an optical circulator 4, a sensing optical fiber 5, a filter 6, an avalanche photodetector 7, an amplifier 8, a high-speed data acquisition card 9, and a computer 10, where laser output ends of the first pulse laser 1 and the second pulse laser 2 are connected to an input end of the optical switch 3, an output end of the optical switch 3 is connected to a first port a of the optical circulator 4, a second port b of the optical circulator 4 is connected to one end of the sensing optical fiber 5, and a third port c of the optical circulator 4 is connected to the filter 6; the first pulse laser 1 and the second pulse laser 2 are respectively used for generating pulse laser with pulse width difference smaller than 1ns, and the optical switch 3 is used for transmitting the pulse laser generated by the first pulse laser 1 and the second pulse laser 2 to the sensing optical fiber 5 in a time-sharing manner after passing through the optical circulator 4 to generate Raman scattering; backward Raman scattered light generated in the sensing optical fiber 5 is filtered out of Raman anti-Stokes light through the filter 6, then is detected by the avalanche photodetector 7 and is amplified by the amplifier 8, and then is output to the high-speed data acquisition card 9, and the high-speed data acquisition card 9 is used for acquiring the superposition sum of scattered signals of half pulse space scale in the sensing optical fiber and sending the superposition sum to the computer 10 to calculate and obtain the distributed temperature field information along the sensing optical fiber 5.
Specifically, in this embodiment, the pulse widths of the laser light output by the first pulse laser 1 and the laser light output by the second pulse laser 2 are 100ns and 100.1ns, respectively, and the pulse width difference is 0.1 ns.
Specifically, in this embodiment, the wavelength of the first pulse laser 1 is 1550nm, the repetition frequency is 8KHz, the wavelength of the second pulse laser 2 is 1550nm, the repetition frequency is 8KHz, the bandwidth of the avalanche photodetector 8 is 100MHz, the spectral response range is 900-1700 nm, the working wavelength of the filter 6 is 1450nm, the number of channels of the high-speed data acquisition card 9 is 2, the sampling rate is 10GS/s, and the bandwidth is 10 GHz; the sensing fiber 5 is a graded-index multimode fiber.
The measurement principle of the embodiment of the present invention is described below.
Light intensity processing of Raman anti-Stokes signals
In conventional temperature demodulation, the optical intensity of the back-raman anti-stokes scattering signal excited at the location of the sensing fiber L is:
in fact, in the distributed fiber raman sensing system, the detection signal is a pulse signal, the positioning principle is a pulse time flight method, and the demodulation method enables the information acquired by the high-speed data acquisition card at any time not to be the light intensity information of one point at the position of the optical fiber L, but to be the superposition of a section of raman anti-stokes light intensity information within the fiber sensing distance equal to half pulse time scale. For example, when the pulse width of the detection signal is W, the light intensity of the backward raman anti-stokes signal acquired by the high-speed data acquisition card at the position corresponding to the optical fiber L is actually:
in the formula, phias(Li) Indicating sensing optical fiber LiThe intensity of the back-raman anti-stokes scattering signal excited at the location,
the light intensity accumulated sum of the data acquisition card acquired at the position of the sensing optical fiber L is represented, and when the pulse width is W, the accumulated length is [ L-Wc/2 n-L%]C is the speed of light, n is the refractive index of the fiber, P is the incident power of the pulsed laser, KasRepresenting coefficients relating to the backscattering cross-section of the Raman anti-Stokes signal, S being the backscattering factor of the fibre, vasRepresenting the frequency, phi, of the Raman anti-Stokes scattered signaleIndicating the flux of the pulsed laser coupled into the fiber, Δ v being the Raman frequency shift, h being the Planckian constant, k being the Boltzmann constant, T being the temperature of the sensing fiber, α0、αasThe loss coefficients of the incident light and the anti-stokes light, respectively, per unit length in the sensing fiber.
Second, in the calibration stage, the pulse laser collects the anti-Stokes signals excited by the sensing optical fiber
The first pulse laser 1 emits laser pulses with a pulse width W, and the laser pulses are incident into the sensing fiber 5 through the optical switch 3 and the circulator 4. The incident light and molecules in the optical fiber are subjected to inelastic collision to generate spontaneous Raman scattering, so that Raman scattering light is generated at each position of the sensing optical fiber 5, and the backward Raman scattering light enters the filter 6 through the second port b and the third port c of the circulator 4; the filter 6 separates out Raman anti-Stokes light (1450nm) which is sensitive to temperature, then the Raman anti-Stokes light sequentially enters the high-speed data acquisition card 9 through the avalanche photodetector 7 and the amplifier 8, signals received by the high-speed data acquisition card 9 are superposition sum of scattered signals in a half pulse space scale (Wc/2n) of the sensing optical fiber at the moment, and the high-speed data acquisition card 9 performs analog-to-digital conversion on the received Raman anti-Stokes light, so that the position and light intensity information of the Raman anti-Stokes light is obtained.
Setting the environmental temperature of the whole sensing optical fiber at the calibration stage as T0The light intensity of the backward raman anti-stokes scattered light of the sensing fiber 5 at the L position, which is acquired by the high-speed data acquisition card 9, can be expressed as:
φas10(Li) Indicating the pulse laser emitted by the first pulse laser 1 in the calibration stage on the sensing fiber LiThe intensity of the back-raman anti-stokes scattering signal excited at the location. Phi is aas10And (L) represents the distributed light intensity accumulation information of the backward Raman anti-Stokes scattered light obtained by the data acquisition card at the position L of the sensing optical fiber 5 under the pulse width of W, namely the superposition sum of scattered signals within a half pulse space scale.
The second pulse laser 2 emits pulse laser with pulse width W +0.1nsThe laser pulses inelastically collide with the molecules in the fiber, producing spontaneous raman scattering. The high-speed data acquisition card 10 acquires the Raman anti-Stokes signals in the sensing fiber 5 to obtain the position and light intensity information of the Raman anti-Stokes signals. The signal received by the high-speed data acquisition card 10 at each moment is a sensing optical fiber half pulse space scale L- (W+0.1)cThe sum of the scatter signals within/2 n.
The environmental temperature of the sensing fiber 5 in the calibration stage is set to T0The light intensity of the anti-stokes signal of the sensing fiber 5 acquired by the data acquisition card is expressed as:
φas20(Li) Indicating the pulse laser emitted by the first pulse laser 1 in the sensing fiber LiThe intensity of the back-raman anti-stokes scattering signal excited at the location. Phi is aas20And (L) represents the distributed light intensity accumulation information of the backward Raman anti-Stokes scattered light obtained by the data acquisition card at the L position of the sensing optical fiber 5 under the pulse width of W +0.1, namely the superposition sum of the scattered signals within a half pulse space scale.
(III) calculating the difference value of Raman anti-Stokes light intensity signals generated by the two pulse lasers with different pulse widths to obtain:
φas0and (L) represents the light intensity difference of the two backward Raman anti-Stokes scattered lights collected by the calibration stage data collection card.
Thirdly, a measurement stage: anti-stokes signal acquisition excited by sensing optical fiber by pulse laser
The first pulse laser 1 emits laser pulses with pulse width W, the temperature and the position along the sensing optical fiber 5 are respectively represented by T and L, the backward Raman anti-Stokes scattered light at the position of the sensing optical fiber 5 is received by the high-speed data acquisition card 9, and the light intensity is represented as:
φas1(Li) Indicating the pulse laser emitted by the first pulse laser 1 in the sensing optical fiber L in the measuring stageiThe intensity of the back-raman anti-stokes scattering signal excited at the location. Phi is aas11And (L) the light intensity of a backward Raman anti-Stokes signal generated at the position L of the sensing optical fiber 5 by the pulse laser emitted by the first pulse laser 1 and acquired by the data acquisition card in the measurement stage.
(II) the second pulse laser 2 emits laser pulse with pulse width W +0.1, the temperature and position of the sensing fiber 5 are respectively represented by T and L, the high-speed data acquisition card 9 receives backward Raman anti-Stokes scattered light of the sensing fiber 5, and the light intensity is represented as:
φas21(Li) Indicating the pulse laser emitted by the second pulse laser 2 in the sensing optical fiber L in the measuring stageiThe intensity of the back-raman anti-stokes scattering signal excited at the location. Phi is aas21And (L) the light intensity of a backward Raman anti-Stokes signal generated at the position L of the sensing optical fiber 5 by the pulse laser emitted by the second pulse laser 2 and acquired by the data acquisition card in the measurement stage.
(III) calculating the difference value of Raman anti-Stokes light intensity signals generated by the two pulse lasers with different pulse widths to obtain:
φas1and (L) represents the light intensity difference of the two backward Raman anti-Stokes scattered lights collected by the data collection and collection card in the measuring stage.
Centimeter-level Raman emission Stokes light self-demodulation processing process based on double-pulse modulation
And (5) performing simultaneous calculation according to the formulas (8) and (5) to obtain distributed temperature information along the sensing optical fiber 5:
equation (9) is a calculation equation of the temperature information along the sensing optical fiber, and the computer 10 can calculate the distributed temperature field information along the sensing optical fiber 5 by using equation (9). Wherein T represents the measured temperature at the position L in the sensing optical fiber, h is a Planckian constant, Δ v is a Raman frequency shift, k is a Boltzmann constant, ln represents logarithm, and T0Set ambient temperature, phi, of the sensing fiber at the calibration stageas1(L) represents the difference of the intensity of the backward Raman anti-Stokes scattered light generated by the laser light emitted by the first pulse laser 1 and the second pulse laser 2 in the sensing optical fiber 5 respectively in the pulse in the measuring stage, phias0And (L) represents the difference of the intensities of the backward raman anti-stokes scattered lights generated by the laser lights emitted by the first pulse laser 1 and the second pulse laser 2 in the sensing fiber 5 respectively in the calibration stage.
In this embodiment, since the acquisition time of the raman scattered light at the position L in the sensing fiber is half the pulse width time, and the light intensities acquired by the two pulse lasers are subtracted from each other, the flight distance of the laser within the time scale of the pulse width difference between the two pulse lasers is obtained, and therefore, the resolution expression is as follows:
ΔL＝Δt·c/2n； (10)
where Δ L denotes a resolution of the system, Δ t denotes a pulse width difference between two pulsed laser beams, c denotes a light speed, and n denotes a refractive index, and when the pulse width difference between two pulsed laser beams is 0.1ns, the resolution Δ L ═ Δ t · c/2n ═ 0.1 × 10 can be calculated from equation (10)-9·3×108The/2.1.57 is approximately equal to 0.01m, so that the invention can realize the resolution of centimeter magnitude under the condition of the pulse width difference of 0.1-1 ns.
Therefore, an embodiment of the present invention further provides a distributed optical fiber raman sensing method capable of implementing centimeter-level spatial resolution, which is implemented based on the distributed optical fiber raman sensing apparatus with centimeter-level spatial resolution shown in fig. 1, and includes the following steps:
s1, calibration stage: setting the temperature along the sensing fiber 5 to T0The pulse lasers emitted by the first pulse laser 1 and the second pulse laser 2 are respectively transmitted to the sensing optical fiber 5 through the optical switch 3, and the light intensity phi of backward Raman anti-Stokes signals generated at the L position of the sensing optical fiber 5 by the pulse lasers emitted by the first pulse laser 1 is respectively collected by the high-speed data acquisition card 9as10(L) and the light intensity phi of backward Raman anti-Stokes signal generated by the pulse laser emitted by the second pulse laser 2 at the position L of the sensing fiber 5as20(L)；
S2, measurement stage: the pulse lasers emitted by the first pulse laser 1 and the second pulse laser 2 are respectively transmitted to the sensing optical fiber 5 through the optical switch 3, and the light intensity phi of backward Raman anti-Stokes signals generated at the L position of the sensing optical fiber 5 by the pulse lasers emitted by the first pulse laser 1 is respectively collected by the high-speed data acquisition card 9as21(L) and the light intensity phi of backward Raman anti-Stokes signal generated by the pulse laser emitted by the second pulse laser 2 at the L position of the sensing fiber 5as11(L); wherein phi isas10(L)、φas20(L)、φas21(L)、φas11(L) are the superposition sum of half pulse space scale scattering signals at the position L of the sensing optical fiber;
s3, calculating: the light intensity signals measured in step S1 and step S2 are sent to the computer 10, and the information of the temperature field distributed along the sensing fiber 5 is obtained by the computer 10 through the formula (9).
In summary, the invention provides a centimeter-level spatial resolution distributed optical fiber Raman temperature sensing device and method, which are realized based on a Raman anti-Stokes light self-demodulation principle of double-pulse modulation, and the device and method are characterized in that two high-power pulse lasers with different pulse widths are arranged, pulsed light with pulse widths of W (more than or equal to 10ns) and W +0.1ns is respectively injected into a sensing optical fiber through an optical switch, then backward Raman anti-Stokes scattering signals excited in two different pulse width states are collected through a calibration stage and a measurement stage, and self-demodulation thermoregulation degree extraction is carried out by utilizing anti-Stokes light intensity data of the sensing optical fiber. The invention can ensure that the spatial resolution of the system is optimized to the centimeter magnitude on the premise of not influencing the sensing distance.
Finally, it should be noted that: the above embodiments are only used to illustrate the technical solution of the present invention, and not to limit the same; while the invention has been described in detail and with reference to the foregoing embodiments, it will be understood by those skilled in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some or all of the technical features may be equivalently replaced; and the modifications or the substitutions do not make the essence of the corresponding technical solutions depart from the scope of the technical solutions of the embodiments of the present invention.
Claims (6)
1. A distributed optical fiber Raman sensing device with centimeter-level spatial resolution is characterized by comprising a first pulse laser (1), a second pulse laser (2), an optical switch (3), a sensing optical fiber (5), a filter (6), an avalanche photodetector (7), a high-speed data acquisition card (9) and a computer (10), the laser output ends of the first pulse laser (1) and the second pulse laser (2) are connected with the input end of the optical switch (3), the output end of the optical switch (3) is connected with one end of the sensing optical fiber (5), the first pulse laser (1) and the second pulse laser (2) are respectively used for generating pulse laser with the pulse width difference less than 1ns, the optical switch (3) is used for transmitting the pulse laser generated by the first pulse laser (1) and the second pulse laser (2) to the sensing optical fiber (5) in a time-sharing manner to generate Raman scattering; the backward Raman scattering light is filtered out to be Raman anti-Stokes light through the filter (6), then the Raman anti-Stokes light is detected by the avalanche photodetector (7) and then output to the high-speed data acquisition card (9), the high-speed data acquisition card (9) is used for respectively acquiring the light intensity of the Raman anti-Stokes light generated by the laser pulse emitted by the first pulse laser (1) and the second pulse laser (2) at each position in the sensing optical fiber, and the light intensity is sent to the computer (10) to calculate and obtain the temperature information along the sensing optical fiber (5).
2. The distributed fiber Raman sensing device with centimeter-level spatial resolution according to claim 1, wherein the pulse widths of the output laser of the first pulse laser (1) and the second pulse laser (2) are greater than 10ns, and the pulse width difference is 0.1 ns.
3. The distributed optical fiber Raman sensing device with centimeter-level spatial resolution according to claim 1, wherein the wavelength of the first pulse laser (1) is 1550nm, the repetition rate is 8KHz, the wavelength of the second pulse laser (2) is 1550nm, the repetition rate is 8KHz, the bandwidth of the avalanche photodetector (8) is 100MHz, the spectral response range is 900-1700 nm, the operating wavelength of the filter (6) is 1450nm, the number of channels of the high-speed data acquisition card (9) is 2, the sampling rate is 10GS/s, and the bandwidth is 10 GHz; the sensing optical fiber (5) is a refractive index graded multi-mode optical fiber.
4. The distributed fiber Raman sensing device with centimeter-level spatial resolution according to claim 1, further comprising an optical circulator (4) and an amplifier (8), wherein a first port of the optical circulator (4) is connected with an output end of the optical switch (3), a second port is connected with one end of the sensing fiber (5), a third port is connected with the filter (6), and the amplifier (8) is arranged between the avalanche photodetector (7) and the high-speed data acquisition card (9) and is used for amplifying a detection signal of the avalanche photodetector (7).
5. The distributed optical fiber Raman sensing device with centimeter-level spatial resolution according to claim 1, wherein the calculation formula of the computer (10) for calculating the temperature information along the sensing optical fiber is as follows:
wherein the content of the first and second substances,Tindicating the position of the measured sensing fiber in the sensing fiberLThe temperature of the (c) is,his the constant of the planck, and is,
which is indicative of the raman shift, is,kis boltzmann's constant, ln denotes taking the logarithm,T 0 indicating the set ambient temperature of the sensing fiber during the calibration phase,
representing the difference of the intensity of backward Raman anti-Stokes scattered light generated by the laser light emitted by the first pulse laser (1) and the second pulse laser (2) in the sensing optical fiber (5) respectively in the measuring stage,
and the difference of the backward Raman anti-Stokes scattered light intensity of the laser light emitted by the first pulse laser (1) and the laser light emitted by the second pulse laser (2) in the calibration stage in the sensing optical fiber (5) is shown.
6. A centimeter-level spatial resolution distributed optical fiber Raman sensing method is realized based on the centimeter-level spatial resolution distributed optical fiber Raman sensing device in claim 1, and is characterized by comprising the following steps:
s1, calibration stage: setting the temperature along the sensing fiber (5) to beT 0 Pulse lasers emitted by the first pulse laser (1) and the second pulse laser (2) are respectively transmitted to the sensing optical fiber (5) through the optical switch (3), and the pulse lasers emitted by the first pulse laser (1) are respectively collected on the sensing optical fiber (5) by the high-speed data collection card (9)LLight intensity of backward Raman anti-Stokes signal occurring at a location
And the pulse laser emitted by the second pulse laser (2) is arranged on the sensing optical fiber (5)LLight intensity of backward Raman anti-Stokes signal occurring at a location
；
S2, measurement stage: pulse lasers emitted by the first pulse laser (1) and the second pulse laser (2) are respectively sent to the sensing optical fiber (5) through the optical switch (3), and the pulse lasers emitted by the first pulse laser (1) are respectively collected on the sensing optical fiber (5) by the high-speed data collection card (9)LLight intensity of backward Raman anti-Stokes signal occurring at a location
And the pulse laser emitted by the second pulse laser (2) is arranged on the sensing optical fiber (5)LLight intensity of backward Raman anti-Stokes signal occurring at a location
(ii) a Wherein the content of the first and second substances,
、
、
、
the scattering signals are the superposition sum of half pulse space scale scattering signals at the position L of the sensing optical fiber;
s3, calculating: and (3) sending the light intensity signals measured in the steps S1 and S2 to a computer (10), and calculating the temperature information along the sensing optical fiber (5) by the computer (10), wherein the calculation formula is as follows:
wherein the content of the first and second substances,Tthe measured temperature of the position L in the sensing optical fiber is shown, h is a Planck constant,
in order to be the raman shift frequency,kis boltzmann's constant, ln denotes taking the logarithm,T 0the calibration stage senses the set ambient temperature of the fiber,
indicating the position in the sensing optical fiber (5) acquired by the data acquisition card in the measurement phaseLThe difference in the light intensity of the two back-raman anti-stokes scattered lights,
，
the position in the sensing optical fiber (5) acquired by the data acquisition card in the calibration stage is shownLThe difference in the light intensity of the two back-raman anti-stokes scattered lights,
。
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