CN111896136A - Dual-parameter distributed optical fiber sensing device and method with centimeter-level spatial resolution - Google Patents

Dual-parameter distributed optical fiber sensing device and method with centimeter-level spatial resolution Download PDF

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CN111896136A
CN111896136A CN202010604040.2A CN202010604040A CN111896136A CN 111896136 A CN111896136 A CN 111896136A CN 202010604040 A CN202010604040 A CN 202010604040A CN 111896136 A CN111896136 A CN 111896136A
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pulse laser
optical fiber
sensing
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stokes
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CN111896136B (en
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李健
于福浩
张明江
张建忠
许扬
余涛
周新新
乔丽君
王涛
高少华
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Taiyuan University of Technology
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    • 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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Abstract

The invention belongs to the technical field of distributed optical fiber sensing, and discloses a double-parameter distributed optical fiber sensing device and method with centimeter-level spatial resolution. The device comprises a first pulse laser, a second pulse laser, a first optical switch, a wavelength division multiplexer, a second optical switch, a reference optical fiber, a sensing optical fiber, a first avalanche photodetector, a second avalanche photodetector, a high-speed data acquisition card and a computer. The invention is provided with two high-power pulse lasers with different pulse widths, pulse light with the pulse width difference smaller than 1ns is respectively injected into the sensing optical fiber through the optical switch, then forward Raman scattering signals and backward Raman scattering signals excited in two different pulse width states are respectively collected to carry out difference value calculation, and then the sensing optical fiber temperature extraction is carried out by utilizing the loop demodulation principle. 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.

Description

Dual-parameter distributed optical fiber sensing device and method with centimeter-level spatial resolution
Technical Field
The invention relates to the technical field of distributed optical fiber sensing, in particular to a double-parameter distributed optical fiber sensing device and method with centimeter-level spatial resolution.
Background
The distributed optical fiber Raman sensing system can realize continuous distributed temperature monitoring and has the advantages of electromagnetic interference resistance, corrosion resistance, electric insulation, high sensitivity, fire and explosion prevention, good reliability and low cost. In the sensing fiber, the pulsed laser light propagates through the fiber to generate raman scattering signals of two components, stokes light and anti-stokes light. The anti-Stokes signal is sensitive to temperature, so that anti-Stokes light can be extracted for temperature demodulation, and distributed temperature monitoring along the optical fiber is realized.
In recent years, a safety monitoring system for traffic infrastructure such as a highway tunnel requires a distributed optical fiber raman sensor to simultaneously realize cooperative measurement of temperature and structural cracks. However, the raman anti-stokes signal is only sensitive to temperature, and the distributed optical fiber raman sensing system can only realize distributed temperature detection along the optical fiber. Therefore, the existing distributed optical fiber Raman sensing system has the technical problem that structural crack measurement cannot be realized. Furthermore, spatial resolution is one of the important performance indicators in the field of industrial temperature monitoring. However, since the detection signal of the distributed fiber raman sensing system is a pulse signal, the pulse width of the light source limits the spatial resolution performance of the system, and reducing the pulse width of the light source can improve the spatial resolution of the system, but also can affect the signal-to-noise ratio of the system and reduce the sensing distance of the system. Therefore, the spatial resolution of the current distributed fiber raman sensor cannot break through the limit of 1m, limited by the pulse width of the light source.
Therefore, a brand-new distributed optical fiber raman sensing device and method are needed to be invented to solve the technical problems that the existing distributed optical fiber raman sensing system cannot measure temperature and crack simultaneously, and the spatial resolution is difficult to break through 1m due to the limitation of the pulse width of a light source.
Disclosure of Invention
In order to solve the problem that the existing distributed optical fiber Raman sensing system cannot realize simultaneous cooperative monitoring of temperature and structure cracks and is limited by the pulse width of a light source, and the spatial resolution of the system cannot break through 1m, the invention provides a double-parameter distributed optical fiber sensing device and method for measuring the spatial resolution of centimeter magnitude.
In order to solve the technical problems, the invention adopts the technical scheme that: a double-parameter distributed optical fiber sensing device with centimeter-level spatial resolution comprises a first pulse laser, a second pulse laser, a first optical switch, a wavelength division multiplexer, a second optical switch, a reference optical fiber, a sensing optical fiber, a first avalanche photodetector, a second avalanche photodetector, a high-speed data acquisition card and a computer; the laser output ends of the first pulse laser and the second pulse laser are connected with the input end of the first optical switch, the output end of the first optical switch is connected with the input end of the second optical switch after passing through a wavelength division multiplexer, and one output end of the second optical switch is connected with the other output end after sequentially passing through a reference optical fiber and a sensing optical fiber; the first pulse laser and the second pulse laser are respectively used for generating pulse laser with the pulse width difference smaller than 1ns, the first optical switch is used for sequentially sending the pulse laser generated by the first pulse laser or the second pulse laser to the wavelength division multiplexer and the second optical switch, and the second optical switch is used for adjusting the directions of light beams incident to the reference optical fiber and the sensing optical fiber so as to respectively generate backward Raman scattering and forward Raman scattering in the reference optical fiber and the sensing optical fiber; and the high-speed data acquisition card is used for respectively acquiring the light intensity of backward Raman Stokes light, the light intensity of backward Raman anti-Stokes light, the light intensity of forward Raman Stokes light and the light intensity of forward Raman anti-Stokes light generated by laser pulses emitted by the first pulse laser and the second pulse laser at each position in the sensing optical fiber and the light intensity of forward Raman anti-Stokes light, and sending the light intensities to a computer to calculate and obtain the temperature information and the structural crack 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 bandwidths of the first avalanche photodetector and the second avalanche photodetector are 100MHz, the spectral response range is 900-1700 nm, the working wavelength of the wavelength division multiplexer is 1450nm/1550nm/1650nm, the number of channels of the high-speed data acquisition card is 4, 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 double-parameter distributed optical fiber sensing device with the centimeter-level spatial resolution further comprises a first amplifier and a second amplifier, wherein the first amplifier is arranged between the first avalanche photodetector and the high-speed data acquisition card, the second amplifier is arranged between the second avalanche photodetector and the high-speed data acquisition card, and the first amplifier and the second amplifier are respectively used for amplifying detection signals of the first avalanche photodetector and the second avalanche photodetector.
The calculation formula of the temperature information along the sensing optical fiber obtained by the computer is as follows:
Figure BDA0002560258510000021
where T represents the temperature at L in the sensing fiber, TrDenotes the temperature of the reference fiber, h is the Planck constant, Δ v denotes the Raman frequency shift, k is the Boltzmann constant, ln denotes the logarithm, φas1(L) the difference phi between the backward Raman anti-Stokes scattered light intensities generated by the pulse lasers emitted by the first pulse laser and the second pulse laser respectively at the position L in the sensing optical fiber and acquired by the data acquisition cards1(L) the difference phi between the backward Raman Stokes scattered light intensities generated by the pulse lasers emitted by the first pulse laser and the second pulse laser respectively at the position L in the sensing optical fiber and acquired by the data acquisition cardas1f(L) the difference phi between the forward Raman anti-Stokes scattered light intensities generated by the pulse lasers emitted by the first pulse laser and the second pulse laser respectively at the position L in the sensing optical fiber and acquired by the data acquisition cards1f(L) the difference of the forward Raman Stokes scattered light intensities generated by the pulse lasers emitted by the first pulse laser and the second pulse laser respectively at the position L in the sensing optical fiber and acquired by the data acquisition card,
Figure BDA0002560258510000031
and
Figure BDA0002560258510000032
respectively representing backward Raman Stokes scattered light intensity and backward Raman Stokes scattered light intensity generated by the pulse laser emitted by the first pulse laser and the second pulse laser which are acquired by the data acquisition card at the position L in the reference optical fiber,
Figure BDA0002560258510000033
and
Figure BDA0002560258510000034
respectively representing the forward Raman Stokes scattered light intensity and the backward Raman anti-Stokes scattered light intensity of the pulse laser emitted by the first pulse laser and the second pulse laser which are acquired by the data acquisition card and respectively generated at the position L in the reference optical fiber;
the calculation formula of the structural crack along the line of the sensing optical fiber calculated by the computer is as follows:
Figure BDA0002560258510000035
s (L) represents a modulation factor influenced by the transverse tension of the optical fiber at the position L in the sensing optical fiber obtained by measurement;
Figure BDA0002560258510000036
indicating sensing fiber temperature setting ToAnd measuring the difference of the backward Raman Stokes scattered light intensities generated by the pulse laser emitted by the first pulse laser and the pulse laser emitted by the second pulse laser at the position L in the sensing optical fiber in the calibration stage.
In addition, the invention also provides a double-parameter distributed optical fiber sensing method with centimeter-level spatial resolution, which is realized based on the double-parameter distributed optical fiber sensing device with centimeter-level spatial resolution and comprises the following steps:
s1, calibration stage: setting the temperature along the sensing fiber to T0The sensing optical fiber is kept loose, the pulse lasers emitted by the first pulse laser and the second pulse laser are respectively sent to the sensing optical fiber through the first optical switch, the second optical switch is controlled to be switched on, the first channel of the second optical switch is switched on, and the backward Raman Stokes scattered light intensity phi generated by the pulse lasers emitted by the first pulse laser and the second pulse laser at the position L in the sensing optical fiber is respectively collected by the high-speed data collection cards11To(L) and phis21To(L)；
S2, measurement stage: the first channel of the second optical switch is switched on, so that the pulse lasers emitted by the first pulse laser and the second pulse laser respectively pass through the first lightA switch for respectively collecting the light intensity phi of backward Raman anti-Stokes signals generated by the pulse laser emitted by the first and second pulse lasers at the L position of the sensing fiber by using a high-speed data acquisition cardas11(L) and phias21(L) and the light intensity phi of backward Raman Stokes signals generated at the position L of the sensing optical fiber by the pulse lasers emitted by the first pulse laser and the second pulse lasers11(L) and phis21(L), simultaneously, respectively collecting the light intensity difference of backward Raman anti-Stokes signals of the pulse laser emitted by the first pulse laser and the second pulse laser at any position of the reference fiber by using a high-speed data acquisition card
Figure BDA0002560258510000041
Light intensity difference with backward Raman Stokes signal
Figure BDA0002560258510000042
Then, a second channel of the second optical switch is switched on, pulse lasers emitted by the first pulse laser and the second pulse laser respectively pass through the first optical switch, and the light intensity phi of forward Raman anti-Stokes signals, which are generated at the L position of the sensing optical fiber by the pulse lasers emitted by the first pulse laser and the second pulse laser, is respectively collected by a high-speed data acquisition cardas11f(L) and phias21f(L) and the light intensity phi of the forward Raman anti-Stokes signal generated at the position L of the sensing optical fiber by the pulse laser emitted by the first pulse laser and the second pulse lasers21f(L) and phis11f(L); meanwhile, the light intensity difference of forward Raman anti-Stokes signals generated by the pulse laser emitted by the first pulse laser and the pulse laser emitted by the second pulse laser at any position of the reference optical fiber is respectively collected by using a high-speed data acquisition card
Figure BDA0002560258510000043
Light intensity difference with forward Raman Stokes signal
Figure BDA0002560258510000044
S3, calculation stage: and (4) sending the light intensity signals measured in the steps S1 and S2 to a computer, and obtaining the temperature information and the structural crack information along the sensing optical fiber through the computer, wherein the calculation formula is as follows:
Figure BDA0002560258510000045
Figure BDA0002560258510000046
where T represents the temperature at L in the sensing fiber, TrDenotes the temperature of the reference fiber, h is the Planck constant, Δ ν denotes the Raman frequency shift, k is the Boltzmann constant, ln denotes the logarithm, φas1(L) the difference phi between the backward Raman anti-Stokes scattered light intensities generated by the pulse lasers emitted by the first pulse laser and the second pulse laser respectively at the position L in the sensing optical fiber and acquired by the data acquisition cards1(L) the difference phi between the backward Raman Stokes scattered light intensities generated by the pulse lasers emitted by the first pulse laser and the second pulse laser respectively at the position L in the sensing optical fiber and acquired by the data acquisition cardas1f(L) the difference phi between the forward Raman anti-Stokes scattered light intensities generated by the pulse lasers emitted by the first pulse laser and the second pulse laser respectively at the position L in the sensing optical fiber and acquired by the data acquisition cards1f(L) the difference of the forward Raman Stokes scattered light intensities generated by the pulse lasers emitted by the first pulse laser and the second pulse laser respectively at the position L in the sensing optical fiber and acquired by the data acquisition card,
Figure BDA0002560258510000047
and
Figure BDA0002560258510000048
respectively indicating the middle positions of the pulse lasers emitted by the first pulse laser and the second pulse laser which are acquired by the data acquisition card in the reference optical fiberThe backward Raman Stokes scattered light intensity generated at the position L and the backward Raman Stokes scattered light intensity,
Figure BDA0002560258510000049
and
Figure BDA00025602585100000410
respectively representing the forward Raman Stokes scattered light intensity and the backward Raman anti-Stokes scattered light intensity of the pulse laser emitted by the first pulse laser and the second pulse laser which are acquired by the data acquisition card and respectively generated at the position L in the reference optical fiber; s (L) represents a modulation factor influenced by the transverse tension of the optical fiber at the position L in the measured sensing optical fiber;
Figure BDA0002560258510000051
indicating sensing fiber temperature setting ToThe calibration stage of the optical fiber laser device measures the difference of the backward Raman Stokes scattered light intensities generated by the pulse laser emitted by the first pulse laser device and the second pulse laser device at the position L in the sensing optical fiber respectively,
Figure BDA0002560258510000052
compared with the prior art, the invention has the following beneficial effects: the invention provides a double-parameter distributed optical fiber sensing device and method with centimeter-level spatial resolution, which are realized based on a loop demodulation principle of modulating anti-Stokes light by Stokes light. 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. In addition, the invention also can realize the cooperative monitoring of temperature and structural crack by utilizing the loss characteristic of Raman Stokes light.
Drawings
Fig. 1 is a schematic diagram of a dual-parameter distributed optical fiber sensing device for centimeter-level spatial resolution measurement according to an embodiment of the present invention.
In the figure: 1-a first pulse laser, 2-a second pulse laser, 3-a first optical switch, 4-a wavelength division multiplexer (1450nm/1550nm/1650nm), 5-a second optical switch, 6-a reference optical fiber, 7-a sensing optical fiber (62.5/125 multimode sensing optical fiber), 8-a first avalanche photodetector, 9-a second avalanche photodetector, 10-a first amplifier, 11-a second amplifier, 12-a high-speed data acquisition card and 13-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 dual-parameter distributed optical fiber sensing apparatus with centimeter-level spatial resolution, which includes a first pulse laser 1, a second pulse laser 2, a first optical switch 3, a wavelength division multiplexer 4, a second optical switch 5, a reference optical fiber 6, a sensing optical fiber 7, a first avalanche photodetector 8, a second avalanche photodetector 9, a first amplifier 10, a second amplifier 11, a high-speed data acquisition card 12, and a computer 13; the laser output ends of the first pulse laser 1 and the second pulse laser 2 are respectively connected with two input ends of the first optical switch 3, the output end of the first optical switch 3 is connected with the input end of the second optical switch 5 after passing through a wavelength division multiplexer 4, and one output end of the second optical switch 5 is connected with the other output end after sequentially referring to an optical fiber 6 and a sensing optical fiber 7; the first pulse laser 1 and the second pulse laser 2 are respectively used for generating pulse laser with the pulse width difference smaller than 1ns, the first optical switch 3 is used for sequentially sending the pulse laser generated by the first pulse laser 1 or the second pulse laser 2 to the wavelength division multiplexer 4 and the second optical switch 5, and the second optical switch 5 is used for adjusting the directions of light beams incident to the reference optical fiber 6 and the sensing optical fiber 7 so as to respectively generate backward Raman scattering and forward Raman scattering in the reference optical fiber 6 and the sensing optical fiber 7; the forward Raman scattered light and the backward Raman scattered light respectively pass through a second optical switch 5, and then are separated into Raman Stokes light and Raman anti-Stokes light by a wavelength division multiplexer 4, the Raman Stokes light and the Raman anti-Stokes light are respectively detected by a first avalanche photodetector 7 and a second avalanche photodetector 8 and then are output to a high-speed data acquisition card 12, and the high-speed data acquisition card 12 is used for respectively acquiring the light intensity of the backward Raman Stokes light, the light intensity of the backward Raman anti-Stokes light, the light intensity of the forward Raman Stokes light and the light intensity of the forward Raman anti-Stokes light which are generated at each position in the sensing optical fiber by the laser pulses sent by the first pulse laser 1 and the second pulse laser 2, and sending the light intensities to a computer 13 to calculate and obtain the temperature information and the structural crack information along the sensing optical fiber 5.
Specifically, in the embodiment of the present invention, the pulse widths of the output laser light 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. Specifically, the pulse widths of the output laser light of the first pulse laser 1 and the second pulse laser 2 are 100ns and 100.1ns, respectively.
Further, 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 bandwidths of the first avalanche photodetector 8 and the second avalanche photodetector 9 are 100MHz, the spectral response range is 900-1700 nm, the working wavelength of the wavelength division multiplexer 4 is 1450nm/1550nm/1650nm, the number of channels of the high-speed data acquisition card 12 is 4, the sampling rate is 10GS/s, and the bandwidth is 10 GHz; the sensing optical fiber 7 is a graded-index multimode optical fiber.
In this embodiment, a 1550nm first pulse laser 1 and a 1550nm second pulse laser 2 are respectively connected to two ports a and b of a first optical switch 3, a port c of the first optical switch 3 is connected to a port d of a wavelength division multiplexer 4, the first optical switch 3 is configured to switch a light source, so that the first pulse laser 1 and the second pulse laser 2 are respectively output to the wavelength division multiplexer 4, a port h of the wavelength division multiplexer 4 is connected to a port i of the second optical switch, a port j of the second optical switch 5 is connected to one end of a reference optical fiber 6, the other end of the reference optical fiber 6 is connected to a port k of the second optical switch 5 of the wavelength division multiplexer 4 through a sensing optical fiber 7, and a port e and a port f of the wavelength division multiplexer 4 are respectively connected to a first avalanche photodetector 8 and a second photodetector 9. Laser output by a port c of the first optical switch 3 enters the wavelength division multiplexer 4 through a port d and then is output to the second optical switch 5 from a port h, when a first channel of the first optical switch 5 is switched on, pulse laser enters the reference optical fiber 6 and the sensing optical fiber 7 from a port j of the second optical switch 5 to generate Raman scattering, backward scattering light returns to the second optical switch 5 from the port j, then is output to the port h of the wavelength division multiplexer through a port i, and finally, anti-stokes light (1650nm) and stokes light (1450nm) are respectively output from a port e and a port f of the wavelength division multiplexer; when the second channel of the first optical switch 5 is switched on, pulse laser enters the sensing fiber 7 and the reference fiber 6 from the port k of the second optical switch 5 to generate raman scattering, forward scattered light returns to the second optical switch 5 from the port k, then is output to the port h of the wavelength division multiplexer through the port i, and finally, anti-stokes light and stokes light are respectively output from the port e and the port f of the wavelength division multiplexer.
The measurement principle of the embodiment of the present invention is described below.
First, sensing optical fiber Raman scattering signal processing
In conventional temperature demodulation, the light intensity of the back raman anti-stokes scattered signal excited at the location of the sensing fiber L is:
Figure BDA0002560258510000071
in fact, in the distributed optical 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 moment not to be the light intensity information of one point at the position of the optical fiber L, but the optical fiber sensing distance is equal to that of the optical fiber LAnd (3) superposition of a section of Raman anti-Stokes light intensity information within a half pulse time scale. For example, when the pulse width of the detection signal is
Figure BDA0002560258510000072
In the time, the light intensity of the raman anti-stokes signal collected by the high-speed data collection card at the position corresponding to the sensing optical fiber L is actually:
Figure BDA0002560258510000073
in the formula, phias(L) represents the light intensity accumulated sum collected by the data acquisition card 12 at the position of the sensing optical fiber L, when the pulse width is
Figure BDA0002560258510000076
Then, it has a cumulative length of
Figure BDA0002560258510000075
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 pulse laser coupled into the fiber, Deltav being the Raman frequency shift, h being the Planckian constant, k being the Boltzmann constant, T being the temperature of the sensing fiber, alpha0、αasThe loss coefficients of the incident light and the anti-stokes light, respectively, per unit length in the sensing fiber. Similarly, the actual light intensity of the raman stokes signal collected by the high-speed data collection card at the position corresponding to the optical fiber L is as follows:
Figure BDA0002560258510000074
in the formula, KsRepresenting the coefficient relating to the backscattering cross-section of the Raman Stokes signal, vsIs the frequency, alpha, of the Raman Stokes scattered signalsIs loss system of Stokes light in unit length of sensing optical fiberAnd (4) counting.
Backward Raman anti-Stokes and Stokes signal acquisition
The first pulse laser 1 emits laser pulses with pulse width w, and the laser pulses are injected into the sensing optical fiber through the first optical switch (a port), the wavelength division multiplexer, the second optical switch (j port) and the reference optical fiber to generate backward Raman scattering light. And then the backward Raman anti-Stokes and Stokes scattered light at the position of the sensing optical fiber is received by the high-speed data acquisition card (the temperature and the position along the sensing optical fiber are respectively represented by T and L). At the moment, the signal received by the high-speed data acquisition card is a sensing optical fiber half pulse space scale
Figure BDA0002560258510000081
And (3) superposing internal scattering signals, and performing analog-to-digital conversion on the received Raman anti-Stokes light by using a high-speed data acquisition card to obtain the position and light intensity information of the Raman anti-Stokes light, wherein the light intensity can be expressed as:
Figure BDA0002560258510000082
Figure BDA0002560258510000083
and (II) the second pulse laser 2 emits laser pulses with the pulse width of w +0.1ns, and the laser pulses are injected into the sensing optical fiber through the first optical switch (a port b), the wavelength division multiplexer, the second optical switch (a port j) and the reference optical fiber to generate backward Raman scattering light. The high-speed data acquisition card 1 receives backward Raman anti-Stokes and Stokes scattered light of the sensing optical fiber 7, and the light intensity is expressed as:
Figure BDA0002560258510000084
Figure BDA0002560258510000085
(III) calculating the difference of Raman light intensity signals generated by the two different pulse width pulse lasers to obtain:
Figure BDA0002560258510000086
Figure BDA0002560258510000087
wherein phi isas1(L) represents the difference phi between the backward Raman anti-Stokes scattered light intensities generated by the pulse lasers emitted by the first pulse laser (1) and the second pulse laser (2) respectively at the position L in the sensing optical fiber (7) and acquired by the data acquisition card (12)s1And (L) represents the difference of the backward Raman Stokes scattered light intensity generated by the pulse laser emitted by the first pulse laser (1) and the pulse laser emitted by the second pulse laser (2) at the position L in the sensing optical fiber (7) and acquired by the data acquisition card (12).
Forward Raman anti-stokes and stokes signal acquisition
The first pulse laser 1 emits laser pulses with a pulse width of 100ns, and the laser pulses are injected into the sensing optical fiber through the first optical switch (a port), the wavelength division multiplexer and the second optical switch (k port) to generate forward Raman scattering light. Then the forward Raman anti-Stokes and Stokes scattered light at the position of the sensing optical fiber is received by the high-speed data acquisition card (the temperature and the position along the sensing optical fiber are respectively represented by T and L, I is the total length of the sensing optical fiber), and the light intensity can be represented as follows:
Figure BDA0002560258510000091
Figure BDA0002560258510000092
the second pulse laser 2 emits laser pulses with the pulse width of 100.1ns, and the laser pulses are injected into the sensing optical fiber through the first optical switch (b port), the wavelength division multiplexer and the second optical switch (k port) to generate forward Raman scattering light. The high-speed data acquisition card 12 receives forward raman anti-stokes and stokes scattered light of the sensing optical fiber, and the light intensity is expressed as:
Figure BDA0002560258510000093
Figure BDA0002560258510000094
(III) calculating the difference of Raman light intensity signals generated by the two different pulse width pulse lasers to obtain:
Figure BDA0002560258510000095
Figure BDA0002560258510000096
wherein phi isas1f(L) represents the difference phi between the forward Raman anti-Stokes scattered light intensities generated by the pulse lasers emitted by the first pulse laser (1) and the second pulse laser (2) respectively at the position L in the sensing optical fiber (7) and acquired by the data acquisition card (12)s1fAnd (L) represents the difference of the forward Raman Stokes scattered light intensity generated by the pulse laser emitted by the first pulse laser (1) and the pulse laser emitted by the second pulse laser (2) at the position L in the sensing optical fiber (7) and acquired by the data acquisition card (12).
Distributed temperature extraction processing process based on Raman loop demodulation device
As can be seen from equations (8) and (9), after the difference operation, the ratio of the backward raman anti-stokes light difference value to the stokes light difference value in the sensing fiber can be represented as:
Figure BDA0002560258510000101
as can be seen from equations (14) and (15), after the difference operation, the ratio of the forward raman anti-stokes light difference value to the stokes light difference value in the sensing fiber can be represented as:
Figure BDA0002560258510000102
since the sampling rate of the high-speed data acquisition card 12 used in this embodiment is 10GS/s, the number of acquisition points in the equations (16) and (17) is 1. Thus, equations (16) and (17) can be solved as:
Figure BDA0002560258510000103
Figure BDA0002560258510000104
the following equations (18) and (19) are calculated:
Figure BDA0002560258510000105
after the difference operation, the ratio of the backward anti-stokes light intensity difference in the reference fiber to the stokes light intensity difference can be expressed as:
Figure BDA0002560258510000106
in the formula, TrIndicating the temperature of the reference fiber. After the difference operation, the ratio of the forward stokes light intensity difference to the anti-stokes light intensity difference in the reference fiber can be expressed as:
Figure BDA0002560258510000107
calculated by the formulas (21) and (22):
Figure BDA0002560258510000108
fifth, the loss information acquisition of the fiber Raman Stokes signal
And (I) before the structural crack is measured, the sensing optical fiber is kept in a relaxed state, and the system carries out calibration treatment. In the calibration stage, the raman stokes light intensity after the difference processing of the first pulse laser and the second pulse laser can be expressed as:
Figure BDA0002560258510000111
Tothe temperature of the fiber is sensed for the calibration phase.
In the measurement stage, the sensing optical fiber generates a transverse tension due to the structural crack, so that the local loss information of the optical fiber at the point is changed, and therefore, distributed structural crack monitoring can be carried out by measuring the local attenuation information of the optical fiber. In the measurement stage, the raman stokes light intensity after the difference processing of the first pulse laser and the second pulse laser can be expressed as:
Figure BDA0002560258510000112
wherein S (L) is a modulation factor influenced by the transverse tension of the optical fiber on the Stokes signal.
Sixthly, double-parameter distributed optical fiber demodulation processing capable of realizing high spatial resolution measurement
Distributed temperature information along the sensing optical fiber can be obtained through calculation of formulas (20) and (23):
Figure BDA0002560258510000113
the modulation factor capable of reflecting the structural crack information influenced by the transverse tension of the optical fiber along the sensing optical fiber can be obtained by calculation through formulas (24) and (25), and the calculation formula is as follows:
Figure BDA0002560258510000114
thus, a passing formula(26) And the equation (27) can demodulate and obtain the temperature information and the structural crack information along the sensing optical fiber 7. Where T represents the temperature at L in the sensing fiber 7, TrDenotes the temperature of the reference fiber, h is the Planck constant, Δ v denotes the Raman frequency shift, k is the Boltzmann constant, ln denotes the logarithm, φas1(L) represents the difference of the backward Raman anti-Stokes scattered light intensity generated by the pulse laser emitted by the first pulse laser 1 and the second pulse laser 2 respectively at the position L in the sensing optical fiber 7 and acquired by the data acquisition card 12, phis1(L) represents the difference of the backward Raman Stokes scattered light intensity generated by the pulse laser emitted by the first pulse laser 1 and the second pulse laser 2 respectively at the position L in the sensing optical fiber 7 and acquired by the data acquisition card 12, phias1f(L) represents the difference of the forward Raman anti-Stokes scattered light intensity generated by the pulse laser emitted by the first pulse laser 1 and the pulse laser emitted by the second pulse laser 2 respectively at the position L in the sensing optical fiber 7 and acquired by the data acquisition card 12, phis1f(L) represents the difference of the forward Raman Stokes scattered light intensities generated by the pulse lasers emitted by the first pulse laser 1 and the second pulse laser 2 respectively at the position L in the sensing optical fiber 7 and acquired by the data acquisition card 12,
Figure BDA0002560258510000121
and
Figure BDA0002560258510000122
respectively represents the backward Raman Stokes scattered light intensity and the backward Raman Stokes scattered light intensity generated at the position L in the reference fiber 6 by the pulse laser emitted by the first pulse laser 1 and the second pulse laser 2 collected by the data acquisition card 12,
Figure BDA0002560258510000123
and
Figure BDA0002560258510000124
respectively shows that the pulse lasers emitted by the first pulse laser 1 and the second pulse laser 2 acquired by the data acquisition card 12 are respectively in the pulse laserThe forward Raman Stokes scattered light intensity and the backward Raman anti-Stokes scattered light intensity generated at the position L in the optical fiber 6 are considered; s (L) represents a modulation factor influenced by the transverse tension of the optical fiber at the position L in the sensing optical fiber 7 obtained by measurement;
Figure BDA0002560258510000125
indicating that the temperature of the sensing fiber 7 is set to ToThe calibration stage of the optical fiber laser device measures the difference of the backward Raman Stokes scattered light intensities generated by the pulse laser light emitted by the first pulse laser device 1 and the second pulse laser device 2 at the position L in the sensing optical fiber 7 respectively,
Figure BDA0002560258510000126
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； (28)
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 (28)-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.
In addition, an embodiment of the present invention further provides a dual-parameter distributed optical fiber sensing method with a centimeter-level spatial resolution, which is implemented based on the dual-parameter distributed optical fiber sensing device with a centimeter-level spatial resolution shown in fig. 1, and includes the following steps:
s1, calibration stage: setting the temperature along the sensing fiber 7 to T0The sensing optical fiber is kept loose, and the pulse laser beams emitted by the first pulse laser 1 and the second pulse laser 2 are respectively transmitted to the first optical switch 3A sensing optical fiber 5 for controlling the second optical switch 5 to switch on the first channel, and respectively collecting backward Raman Stokes scattered light intensity phi generated by the pulse laser emitted by the first pulse laser 1 and the second pulse laser 2 at the position L in the sensing optical fiber 7 by using a high-speed data acquisition card 12s11To(L) and phis21To(L)；
S2, measurement stage: the first channel of the second optical switch 5 is connected, the pulse lasers emitted by the first pulse laser 1 and the second pulse laser 2 respectively pass through the first optical switch 3, and the high-speed data acquisition card 12 is used for respectively acquiring the light intensity phi of backward Raman anti-Stokes signals generated by the pulse lasers emitted by the first pulse laser 1 and the second pulse laser 2 at the L position of the sensing optical fiber 7as11(L) and phias21(L) and the light intensity phi of backward Raman Stokes signals generated at the position L of the sensing fiber 7 by the pulse laser emitted by the first pulse laser 1 and the second pulse laser 2s11(L) and phis21(L), simultaneously, respectively collecting the light intensity difference of backward Raman anti-Stokes signals generated by the pulse laser emitted by the first pulse laser 1 and the second pulse laser 2 at any position of the reference optical fiber 6 by using a high-speed data acquisition card 12
Figure BDA0002560258510000131
Light intensity difference with backward Raman Stokes signal
Figure BDA0002560258510000132
Then, the second channel of the second optical switch 5 is turned on, the pulse lasers emitted by the first pulse laser 1 and the second pulse laser 2 respectively pass through the first optical switch 3, and the light intensity phi of the forward raman anti-stokes signal generated at the L position of the sensing optical fiber 5 by the pulse lasers emitted by the first pulse laser 1 and the second pulse laser 2 is respectively collected by the high-speed data acquisition card 12as11f(L) and phias21f(L) and the light intensity phi of the forward Raman anti-Stokes signal generated at the L position of the sensing fiber 5 by the pulse laser emitted by the first pulse laser 1 and the second pulse laser 2s21f(L) and phis11f(L); meanwhile, the light intensity difference of forward Raman anti-Stokes signals generated by the pulse laser emitted by the first pulse laser 1 and the second pulse laser 2 at any position of the reference fiber 6 is respectively collected by the high-speed data acquisition card 12
Figure BDA0002560258510000133
Light intensity difference with forward Raman Stokes signal
Figure BDA0002560258510000134
S3, calculation stage: and sending the light intensity signals measured in the steps S1 and S2 to the computer 12, and obtaining the temperature information and the structural crack information along the sensing optical fiber 5 through calculation of the computer 12, wherein the calculation formulas are the formula (26) and the formula (27).
In summary, the present invention provides a dual-parameter distributed optical fiber sensing device and method with centimeter-level spatial resolution, which are implemented based on the loop demodulation principle of stokes light demodulation and anti-stokes light demodulation, and the present invention provides two high-power pulse lasers with different pulse widths, and injects pulse widths of
Figure BDA0002560258510000135
The pulse light is then respectively collected and the difference value of the forward Raman scattering signal and the backward Raman scattering signal excited under two different pulse width states is calculated, and then the temperature of the sensing optical fiber is extracted by utilizing the loop demodulation principle. 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. In addition, the invention also can realize the cooperative monitoring of temperature and structural crack by utilizing the loss characteristic of Raman Stokes light.
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 double-parameter distributed optical fiber sensing device with centimeter-level spatial resolution is characterized by comprising a first pulse laser (1), a second pulse laser (2), a first optical switch (3), a wavelength division multiplexer (4), a second optical switch (5), a reference optical fiber (6), a sensing optical fiber (7), a first avalanche photodetector (8), a second avalanche photodetector (9), a high-speed data acquisition card (12) and a computer (13); the laser output ends of the first pulse laser (1) and the second pulse laser (2) are connected with the input end of the first optical switch (3), the output end of the first optical switch (3) is connected with the input end of the second optical switch (5) after passing through a wavelength division multiplexer (4), and one output end of the second optical switch (5) is connected with the other output end after sequentially passing through a reference optical fiber (6) and a sensing optical fiber (7); the first pulse laser (1) and the second pulse laser (2) are respectively used for generating pulse laser with the pulse width difference smaller than 1ns, the first optical switch (3) is used for sequentially sending the pulse laser generated by the first pulse laser (1) or the second pulse laser (2) to the wavelength division multiplexer (4) and the second optical switch (5), and the second optical switch (5) is used for adjusting the beam direction of light entering the reference optical fiber (6) and the sensing optical fiber (7) so as to respectively generate backward Raman scattering and forward Raman scattering in the reference optical fiber (6) and the sensing optical fiber (7); the forward Raman scattered light and the backward Raman scattered light respectively pass through a second optical switch (5), then Raman Stokes light and Raman anti-Stokes light are separated by a wavelength division multiplexer (4), the Raman Stokes light and the Raman anti-Stokes light are respectively detected by a first avalanche photodetector (7) and a second avalanche photodetector (8) and then output to a high-speed data acquisition card (12), the high-speed data acquisition card (12) is used for respectively acquiring the light intensity of the backward Raman Stokes light, the light intensity of the backward Raman anti-Stokes light, the light intensity of the forward Raman Stokes light and the light intensity of the forward Raman anti-Stokes light which are generated at each position in the sensing optical fiber by laser pulses sent by a first pulse laser (1) and a second pulse laser (2), and the temperature information and the structural crack information along the sensing optical fiber (5) are calculated and obtained by sending the information to a computer (13).
2. The dual-parameter distributed optical fiber sensing device with spatial resolution of centimeter level according to claim 1, wherein the pulse width of the output laser of the first pulse laser (1) and the pulse width of the output laser of the second pulse laser (2) are more than 10ns, and the difference between the pulse widths is 0.1 ns.
3. The dual-parameter distributed optical fiber sensing device with spatial resolution of centimeter magnitude 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 bandwidths of the first avalanche photodetector (8) and the second avalanche photodetector (9) are 100MHz, the spectral response range is 900-1700 nm, the operating wavelength of the wavelength division multiplexer (4) is 1450nm/1550nm/1650nm, the number of channels of the high speed data acquisition card (12) is 4, the sampling rate is 10GS/s, and the bandwidth is 10 GHz; the sensing optical fiber (7) is a refractive index graded multi-mode optical fiber.
4. A dual parameter distributed optical fiber sensing apparatus with a spatial resolution on the order of centimeters as claimed in claim 1, further comprising a first amplifier (10) and a second amplifier (11), wherein the first amplifier (10) is disposed between the first avalanche photodetector (8) and the high speed data acquisition card (12), the second amplifier (11) is disposed between the second avalanche photodetector (9) and the high speed data acquisition card (12), and the first amplifier (10) and the second amplifier (11) are respectively used for amplifying the detection signals of the first avalanche photodetector (8) and the second avalanche photodetector (9).
5. The dual-parameter distributed optical fiber sensing device with centimeter-level spatial resolution according to claim 1, wherein the calculation formula of the computer (13) for calculating the temperature information along the sensing optical fiber is as follows:
Figure DEST_PATH_IMAGE001
；
wherein T represents the temperature at L in the sensing fiber (7),
Figure 978959DEST_PATH_IMAGE002
which is indicative of the temperature of the reference fiber,his the constant of the planck, and is,
Figure DEST_PATH_IMAGE003
which is indicative of the raman shift, is,kis boltzmann's constant, ln denotes taking the logarithm,
Figure 339533DEST_PATH_IMAGE004
the position of the pulse laser emitted by the first pulse laser (1) and the position of the pulse laser emitted by the second pulse laser (2) which are acquired by the data acquisition card (12) are respectively shown in the sensing optical fiber (7)LThe difference of the intensity of the backward Raman anti-Stokes scattered light generated at the position,
Figure DEST_PATH_IMAGE005
the position of the pulse laser emitted by the first pulse laser (1) and the position of the pulse laser emitted by the second pulse laser (2) which are acquired by the data acquisition card (12) are respectively shown in the sensing optical fiber (7)LThe difference of the intensity of the backward raman stokes scattered light generated at the position,
Figure 664335DEST_PATH_IMAGE006
the position of the pulse laser emitted by the first pulse laser (1) and the position of the pulse laser emitted by the second pulse laser (2) which are acquired by the data acquisition card (12) are respectively shown in the sensing optical fiber (7)LAt the intensity of the generated forward Raman anti-Stokes scattered lightThe difference is that the number of the first and second,
Figure DEST_PATH_IMAGE007
the position of the pulse laser emitted by the first pulse laser (1) and the position of the pulse laser emitted by the second pulse laser (2) which are acquired by the data acquisition card (12) are respectively shown in the sensing optical fiber (7)LThe difference of the intensity of forward raman stokes scattered light generated at the position,
Figure 34137DEST_PATH_IMAGE008
and
Figure DEST_PATH_IMAGE009
respectively representing the positions of the pulse lasers emitted by the first pulse laser (1) and the second pulse laser (2) acquired by the data acquisition card (12) in the reference optical fiber (6)LThe generated backward Raman Stokes scattered light intensity and the backward Raman Stokes scattered light intensity,
Figure 355091DEST_PATH_IMAGE010
and
Figure DEST_PATH_IMAGE011
respectively representing the positions of the pulse lasers emitted by the first pulse laser (1) and the second pulse laser (2) acquired by the data acquisition card (12) in the reference optical fiber (6)LThe forward Raman Stokes scattered light intensity and the backward Raman anti-Stokes scattered light intensity are generated;
the calculation formula of the crack of the sensing optical fiber along the line structure calculated by the computer (13) is as follows:
Figure 89829DEST_PATH_IMAGE012
；
wherein the content of the first and second substances,
Figure DEST_PATH_IMAGE013
indicating the measured light-receiving fiber at position L in the sensing fiber (7)Modulation factor of the lateral tension effect;
Figure 698665DEST_PATH_IMAGE014
indicating the sensing fiber (7) temperature setting
Figure DEST_PATH_IMAGE015
The positions of the pulse lasers emitted by the first pulse laser (1) and the second pulse laser (2) which are obtained by measurement in the calibration stage are respectively arranged in the sensing optical fiber (7)LThe difference of the intensity of the backward raman stokes scattered light generated at the position.
6. A double-parameter distributed optical fiber sensing method with centimeter-level spatial resolution is realized based on the double-parameter distributed optical fiber sensing device with centimeter-level spatial resolution of claim 1, and is characterized by comprising the following steps:
s1, calibration stage: setting the temperature along the sensing fiber (7) to beT 0 Keeping the sensing optical fiber loose, respectively sending pulse lasers emitted by the first pulse laser (1) and the second pulse laser (2) to the sensing optical fiber (5) through the first optical switch (3), controlling the second optical switch (5) to switch on a first channel, and respectively collecting the pulse lasers emitted by the first pulse laser (1) and the second pulse laser (2) in the sensing optical fiber (7) through the high-speed data acquisition card (12)LIntensity of backward Raman Stokes scattered light generated by the light source
Figure 809840DEST_PATH_IMAGE016
And
Figure DEST_PATH_IMAGE017
；
s2, measurement stage: the first channel of the second optical switch (5) is switched on, the pulse lasers emitted by the first pulse laser (1) and the second pulse laser (2) respectively pass through the first optical switch (3), and the high-speed data acquisition card (12) is used for respectively acquiring the first pulse lasersThe pulse laser emitted by the optical device (1) and the second pulse laser (2) is arranged on the sensing optical fiber (7)LLight intensity of backward Raman anti-Stokes signal occurring at a location
Figure 820522DEST_PATH_IMAGE018
And
Figure DEST_PATH_IMAGE019
and the pulse laser emitted by the first pulse laser (1) and the second pulse laser (2) is arranged on the sensing optical fiber (7)LLight intensity of backward Raman Stokes signal occurring at a location
Figure 726161DEST_PATH_IMAGE020
And
Figure DEST_PATH_IMAGE021
simultaneously, a high-speed data acquisition card (12) is used for respectively acquiring the light intensity difference of backward Raman anti-Stokes signals generated by the pulse laser emitted by the first pulse laser (1) and the second pulse laser (2) at any position of the reference fiber (6)
Figure 258511DEST_PATH_IMAGE022
Light intensity difference with backward Raman Stokes signal
Figure DEST_PATH_IMAGE023
；
Then, a second channel of a second optical switch (5) is switched on, pulse laser emitted by the first pulse laser (1) and the second pulse laser (2) respectively pass through the first optical switch (3), and pulse laser emitted by the first pulse laser (1) and the second pulse laser (2) is respectively collected on a sensing optical fiber (5) by a high-speed data acquisition card (12)LLight intensity of forward Raman anti-Stokes signal occurring at a location
Figure 970115DEST_PATH_IMAGE024
And
Figure DEST_PATH_IMAGE025
and the pulse laser emitted by the first pulse laser (1) and the second pulse laser (2) is arranged on the sensing optical fiber (5)LLight intensity of forward Raman anti-Stokes signal occurring at a location
Figure 772986DEST_PATH_IMAGE026
And
Figure DEST_PATH_IMAGE027
(ii) a Meanwhile, a high-speed data acquisition card (12) is used for respectively acquiring the light intensity difference of forward Raman anti-Stokes signals generated by the pulse laser emitted by the first pulse laser (1) and the second pulse laser (2) at any position of the reference optical fiber (6)
Figure 911843DEST_PATH_IMAGE011
Light intensity difference with forward Raman Stokes signal
Figure 432954DEST_PATH_IMAGE010
；
S3, calculation stage: and (3) sending the light intensity signals measured in the steps S1 and S2 to a computer (12), and calculating the temperature information and the structural crack information along the sensing optical fiber (5) by the computer (12), wherein the calculation formula is as follows:
Figure 682670DEST_PATH_IMAGE001
；
Figure 667944DEST_PATH_IMAGE028
；
wherein the content of the first and second substances,Tindicating the temperature at L in the sensing fiber (7),
Figure DEST_PATH_IMAGE029
indicating a reference fibreThe temperature of (a) is set to be,his the constant of the planck, and is,
Figure 915385DEST_PATH_IMAGE003
which is indicative of the raman shift, is,kis boltzmann's constant, ln denotes taking the logarithm,
Figure 986110DEST_PATH_IMAGE030
the position of the pulse laser emitted by the first pulse laser (1) and the position of the pulse laser emitted by the second pulse laser (2) which are acquired by the data acquisition card (12) are respectively shown in the sensing optical fiber (7)LThe difference of the intensity of the backward Raman anti-Stokes scattered light generated at the position,
Figure 39516DEST_PATH_IMAGE005
the position of the pulse laser emitted by the first pulse laser (1) and the position of the pulse laser emitted by the second pulse laser (2) which are acquired by the data acquisition card (12) are respectively shown in the sensing optical fiber (7)LThe difference of the intensity of the backward raman stokes scattered light generated at the position,
Figure 879296DEST_PATH_IMAGE006
the position of the pulse laser emitted by the first pulse laser (1) and the position of the pulse laser emitted by the second pulse laser (2) which are acquired by the data acquisition card (12) are respectively shown in the sensing optical fiber (7)LThe difference of the light intensity of the forward raman anti-stokes scattered light generated at the position,
Figure 796174DEST_PATH_IMAGE007
the position of the pulse laser emitted by the first pulse laser (1) and the position of the pulse laser emitted by the second pulse laser (2) which are acquired by the data acquisition card (12) are respectively shown in the sensing optical fiber (7)LThe difference of the intensity of forward raman stokes scattered light generated at the position,
Figure 88615DEST_PATH_IMAGE008
and
Figure DEST_PATH_IMAGE031
respectively representing the positions of the pulse lasers emitted by the first pulse laser (1) and the second pulse laser (2) acquired by the data acquisition card (12) in the reference optical fiber (6)LThe generated backward Raman Stokes scattered light intensity and the backward Raman Stokes scattered light intensity,
Figure 883396DEST_PATH_IMAGE010
and
Figure 577683DEST_PATH_IMAGE011
respectively representing the positions of the pulse lasers emitted by the first pulse laser (1) and the second pulse laser (2) acquired by the data acquisition card (12) in the reference optical fiber (6)LThe forward Raman Stokes scattered light intensity and the backward Raman anti-Stokes scattered light intensity are generated;
Figure 229244DEST_PATH_IMAGE032
the measured modulation factor influenced by the transverse tension of the optical fiber at the position L in the sensing optical fiber (7) is represented;
Figure DEST_PATH_IMAGE033
indicating the sensing fiber (7) temperature setting
Figure 212243DEST_PATH_IMAGE015
The positions of the pulse lasers emitted by the first pulse laser (1) and the second pulse laser (2) which are obtained by measurement in the calibration stage are respectively arranged in the sensing optical fiber (7)LThe difference of the intensity of the backward raman stokes scattered light generated at the position,
Figure 607453DEST_PATH_IMAGE034
。
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