CN111307322A - Distributed optical fiber temperature sensing system based on annular light path - Google Patents
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Abstract
The invention discloses a distributed optical fiber temperature sensing system based on an annular light path, which comprises: the device comprises a pulse laser (1), a wavelength division multiplexer (2), an optical switch (3), a first optical fiber ring (5), a second optical fiber ring (6), a temperature measurement optical fiber (7), a photoelectric detector (8), a data acquisition card (9) and an upper computer (10); the distributed optical fiber temperature sensing system of the annular optical path can perform laser power feedback adjustment and Rayleigh scattering noise compensation for inhibiting nonlinear effects. The invention improves the long-term stability of the distributed optical fiber temperature sensor in the practical application environment; the influence of the Rayleigh scattering light on the temperature demodulation precision is eliminated, so that the direct demodulation of the temperature field information of the sensing optical fiber is realized, the complexity of system debugging is reduced, and the temperature measurement precision and the long-term measurement stability are improved.
Description
Technical Field
The invention belongs to the technical field of optical fiber sensing, and particularly relates to a distributed optical fiber temperature sensing system based on an annular light path.
Background
A distributed optical fiber temperature sensor based on Raman scattering utilizes the principle that Raman scattering light intensity and temperature in a sensing optical fiber are sensitive, and collects backward Raman scattering light of each point on the sensing optical fiber, wherein each point is modulated by temperature, by injecting detection light pulses into the sensing optical fiber. The Raman scattering light comprises an up-shifted anti-Stokes scattering light and a down-shifted Stokes scattering light, and because the light intensity is very weak, the signal to noise ratio of a signal is improved by a high-sensitivity avalanche photodetector and accumulation average processing. The anti-Stokes scattered light is sensitive to temperature and is used for temperature demodulation, and the Stokes scattered light is used for correcting the anti-Stokes scattered light and weakening the influence of light source power fluctuation and sensing optical fiber loss on temperature demodulation performance.
When the Raman is subjected to weak light detection, the signal-to-noise ratio of Raman scattering light can be improved by improving the output power of the laser, but the output power of the laser cannot be infinitely increased in order to avoid the occurrence of stimulated Raman scattering. In practical engineering use, the laser power changes with time, different losses of connecting devices and other factors. Therefore, to maximize the raman scattering signal-to-noise ratio, the output power of the laser needs to be adjusted in real time.
In addition, in practical engineering applications, the performance of the sensor is affected by environmental factors, such as performance changes of the light source and the photodetector due to changes in operating temperature, and nonlinear loss caused by bending or stretching of the sensing optical fiber or erosion of a strong corrosive substance, which all degrade the performance of the sensor, increase temperature demodulation errors, and fail in severe cases.
The external factors acting on the sensing fiber have uncertainty, and the loss degree of the sensing fiber is related to the wavelength, so that the external factors cannot be eliminated or corrected. The annular sensing light path is adopted to collect Raman scattered light of the sensing optical fiber in the positive direction and the negative direction, and optical fiber loss related to the position can be effectively eliminated through geometric average processing, so that the environmental adaptability of the sensor is greatly improved.
The scattered light generated in the optical fiber includes not only raman scattered light but also rayleigh scattered light and brillouin scattered light, and a common method is to select the raman scattered light by using a wavelength division multiplexer. However, since the rayleigh scattered light intensity is high and is about 30dB higher than the raman scattered light intensity, and the isolation of a commercially available wavelength division multiplexer is usually 35dB to 40dB, a large amount of rayleigh scattered light noise exists in the measured raman scattered light. In a small dynamic range (< 100 ℃), rayleigh scattered light has less influence on temperature demodulation errors, but temperature errors gradually deteriorate as the dynamic range increases. Therefore, it is necessary to compensate for rayleigh scattered light noise without changing the device performance.
Disclosure of Invention
The technical problem solved by the invention is as follows: the distributed optical fiber temperature sensing system based on the annular light path is provided, through the annular light path structure, nonlinear loss caused by factors such as bending and corrosion of strong corrosive substances in the optical fiber to Raman scattering light intensity is eliminated, long-term stability of the distributed optical fiber temperature sensor in an actual application environment is improved, and the application field of the distributed optical fiber temperature sensing system is expanded. And (4) passing. Meanwhile, Rayleigh scattered light in the back Raman scattered light is calculated, and the influence of the Rayleigh scattered light on temperature demodulation precision is eliminated, so that the temperature field information of the sensing optical fiber is directly demodulated, the complexity of system debugging is reduced, and the temperature measurement precision and the long-term measurement stability are improved.
The purpose of the invention is realized by the following technical scheme: a distributed optical fiber temperature sensing system based on a ring-shaped optical path comprises: the device comprises a pulse laser, a wavelength division multiplexer, an optical switch, a first optical fiber ring, a second optical fiber ring, a temperature measuring optical fiber, a photoelectric detector, a data acquisition card and an upper computer; the output ends of the pulse laser and the pulse laser are connected with the input end of the wavelength division multiplexer; the common end of the wavelength division multiplexer is connected with the input end of the optical switch; two output ends of the optical switch are respectively connected with the first optical fiber ring and the second optical fiber ring; the output ends of the first optical fiber ring and the second optical fiber ring are respectively connected with two ends of the temperature measuring optical fiber; two output ends of the wavelength division multiplexer are respectively connected with two input ends of the photoelectric detector; two output ends of the photoelectric detector are respectively connected with two input ends of a data acquisition card, and the output end of the data acquisition card is connected with the input end of an upper computer; the first optical fiber ring and the second optical fiber ring are both placed in a temperature measuring device, and the output end of the temperature measuring device is connected with the input end of an upper computer; the distributed optical fiber temperature sensing system of the annular optical path can perform laser power feedback adjustment and Rayleigh scattering noise compensation for inhibiting nonlinear effects.
In the above distributed optical fiber temperature sensing system based on the annular optical path, the laser power feedback adjustment for suppressing the occurrence of the nonlinear effect includes the following steps: the method comprises the following steps: two groups of anti-Stokes scattered light V are acquired by a data acquisition cardas1And Vas2And Stokes scattered light Vs1And Vs2Respectively carrying out geometric mean calculation to obtain VasmAnd Vsm(ii) a Step two: calculating the ratio of the anti-Stokes scattered light to the Stokes scattered light after geometric averaging, VR＝Vasm/VsmAnd calculating the ratio difference DeltaV of the positions of the first optical fiber ring and the second optical fiber ringR＝VR(L0)-VR(L1) Wherein L is0And L1The distances between the positions of the first optical fiber ring and the second optical fiber ring are respectively; step three: starting from 0mA, the pumping current of the pulse laser is gradually increased, and the delta V is observed in real timeRWhen Δ VR>10％×MIN[VR(L0),VR(L1)]Reducing the pumping current of the pulse laser to delta V<1％×MIN[VR(L0),VR(L1)]。
In the above distributed optical fiber temperature sensing system based on the annular optical path, the rayleigh scattering noise compensation includes the following steps: (1) placing the temperature measuring optical fiber, the first optical fiber ring and the second optical fiber ring in the same temperature environment, and keeping the environment temperature stable; acquiring anti-Stokes scattering signals and Stokes scattering signals from forward and backward directions respectively to obtain forward acquired anti-Stokes signals Vas_forWith Stokes scattering signal Vs_forReversely collected anti-stokes signal Vas_backWith Stokes scattering signal Vs_back(ii) a (2) Anti-stokes based on forward acquisitionObtaining optical fiber L from the scattering signals of stokes and stokesnForward anti-stokes scattering signal loss at
Loss of signal associated with forward stokes scattering
And obtaining compensated forward anti-Stokes scattering signal loss
With compensated forward stokes scattering signal loss
(3) Obtaining the optical fiber L according to the reversely collected anti-Stokes and Stokes scattering signalsnLoss of reverse anti-stokes scattering signal
Loss of signal associated with reverse Stokes scattering
And obtaining compensated reverse anti-Stokes scattering signal loss
With compensated reverse Stokes scattering signal loss
(4) Based on compensated forward anti-Stokes scattering signal loss
With compensated forward stokes scattering signal loss
Obtaining compensated forward anti-Stokes scattering signal loss containing Rayleigh scattering noise
With compensated forward stokes scattering signal loss
Based on compensated reverse anti-Stokes scattering signal loss
With compensated reverse Stokes scattering signal loss
Obtaining compensated reverse anti-stokes scattering signal loss containing Rayleigh scattering noise
With compensated reverse Stokes scattering signal loss
In the distributed optical fiber temperature sensing system based on the annular light path, in the step (2), the optical fiber LnOptical fiber L is obtained from anti-Stokes and Stokes scattering signals of forward collectionnForward anti-stokes scattering signal loss at
Loss of signal associated with forward stokes scattering
Respectively expressed as:
wherein m is the number of translation steps of the loss point of the optical fiber.
In the distributed optical fiber temperature sensing system based on the annular optical path, in the step (2), the compensated forward anti-stokes scattering signal loss
With compensated forward stokes scattering signal loss
Respectively expressed as:
in the above distributed optical fiber temperature sensing system based on the annular optical path, in step (3), the optical fiber LnLoss of reverse anti-stokes scattering signal
Loss of signal associated with reverse Stokes scattering
Respectively expressed as:
in the distributed optical fiber temperature sensing system based on the annular optical path, in the step (3), the compensated reverse anti-stokes scattering signal loss
And after compensationLoss of reverse stokes scattered signal
Respectively expressed as:
in the above distributed optical fiber temperature sensing system based on the annular optical path, in step (4), the compensated forward anti-stokes scattering signal loss containing rayleigh scattering noise
Comprises the following steps:
wherein l is the position distance of a certain point of the optical fiber, h is Planck constant, Deltav is Raman scattering frequency shift in the quartz optical fiber, k is Boltzmann constant, T is the environment temperature of the optical fiber, αasFor the attenuation coefficient of anti-Stokes scattered light in silica fiber, αsThe attenuation coefficient of Stokes' scattered light in a silica optical fiber, αrAttenuation coefficient of Rayleigh scattered light in quartz fiber, AforScattering coefficient of anti-Stokes scattered light obtained for forward detection, BforDetecting Rayleigh scattering coefficient, C, in channel for anti-Stokes scattered lightforScattering coefficient of anti-Stokes scattered light, D, obtained for forward detectionforRayleigh scattering coefficient, A, in a channel for Stokes scattering light detectionbackScattering coefficient of anti-Stokes scattered light obtained for reverse detection, BbackDetecting Rayleigh scattering coefficient, C, in channel for anti-Stokes scattered lightbackStokes scattering coefficient, D, for reverse detectionbackIs reversedRayleigh scattering coefficient in the detection channel of Stokes scattered light to be detected, αr0The attenuation coefficient of Rayleigh scattered light in a forward anti-Stokes detection signal in a quartz optical fiber is detected.
In the above distributed optical fiber temperature sensing system based on the ring optical path, in step (4), the compensated forward stokes scattering signal loss containing rayleigh scattering noise
Comprises the following steps:
wherein l is the position distance of a certain point of the optical fiber, h is Planck constant, Deltav is Raman scattering frequency shift in the quartz optical fiber, k is Boltzmann constant, T is the environment temperature of the optical fiber, αasFor the attenuation coefficient of anti-Stokes scattered light in silica fiber, αsThe attenuation coefficient of Stokes' scattered light in a silica optical fiber, αrAttenuation coefficient of Rayleigh scattered light in quartz fiber, CforScattering coefficient of anti-Stokes scattered light, D, obtained for forward detectionforRayleigh scattering coefficient in the detection channel for Stokes scattered light, αr1The attenuation coefficient of Rayleigh scattered light in a forward Stokes detection signal in a quartz optical fiber is detected.
In the above distributed optical fiber temperature sensing system based on the ring optical path, in step (4), the compensated reverse anti-stokes scattering signal loss containing rayleigh scattering noise
Comprises the following steps:
wherein l is the position distance of a certain point of the optical fiber, h is Planck constant, Deltav is Raman scattering frequency shift in the quartz optical fiber, k is Boltzmann constant,t is the ambient temperature of the fiber, αasFor the attenuation coefficient of anti-Stokes scattered light in silica fiber, αsThe attenuation coefficient of Stokes' scattered light in a silica optical fiber, αrAttenuation coefficient of Rayleigh scattered light in quartz fiber, AbackScattering coefficient of anti-Stokes scattered light obtained for reverse detection, BbackDetection of Rayleigh scattered light scattering coefficients in a channel for anti-Stokes scattered light, αr2The attenuation coefficient of Rayleigh scattered light in a signal in a quartz fiber is detected for reverse anti-Stokes.
In the above distributed optical fiber temperature sensing system based on the ring optical path, in step (4), the compensated reverse stokes scattering signal loss containing rayleigh scattering noise
Comprises the following steps:
wherein l is the position distance of a certain point of the optical fiber, h is Planck constant, Deltav is Raman scattering frequency shift in the quartz optical fiber, k is Boltzmann constant, T is the environment temperature of the optical fiber, αasFor the attenuation coefficient of anti-Stokes scattered light in silica fiber, αsThe attenuation coefficient of Stokes' scattered light in a silica optical fiber, αrAttenuation coefficient of Rayleigh scattered light in quartz fiber, CbackStokes scattering coefficient, D, for reverse detectionbackRayleigh scattering coefficient in the channel is detected for Stokes scattering light for reverse detection, αr3The attenuation coefficient of Rayleigh scattered light in a signal in a quartz fiber is detected for the reverse Stokes.
Compared with the prior art, the invention has the following beneficial effects:
(1) compared with fixed laser parameters, the pulsed light regulated by feedback control can ensure that the fiber-entering power of the laser is improved as much as possible on the premise of not generating stimulated Raman scattering, thereby ensuring that the signal-to-noise ratio of Raman scattering light intensity is maximized.
(2) Compared with the temperature measurement result without a Rayleigh scattering noise filtering device or a Rayleigh scattering noise compensation algorithm, the Rayleigh scattering noise compensation algorithm can effectively make up the Rayleigh scattering noise influence caused by insufficient isolation of the wavelength division multiplexer. By changing the temperature of the fiber ring, the rayleigh scattering intensity distribution in the sensing fiber can be quickly calculated and subtracted from the demodulation formula.
Drawings
Various other advantages and benefits will become apparent to those of ordinary skill in the art upon reading the following detailed description of the preferred embodiments. The drawings are only for purposes of illustrating the preferred embodiments and are not to be construed as limiting the invention. Also, like reference numerals are used to refer to like parts throughout the drawings. In the drawings:
fig. 1 is a block diagram of a distributed optical fiber temperature sensing system of a ring optical path according to an embodiment of the present invention.
Detailed Description
Exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be embodied in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art. It should be noted that the embodiments and features of the embodiments may be combined with each other without conflict. The present invention will be described in detail below with reference to the embodiments with reference to the attached drawings.
Fig. 1 is a block diagram of a distributed optical fiber temperature sensing system of a ring optical path according to an embodiment of the present invention. As shown in fig. 1, the distributed optical fiber temperature sensing system of the ring-shaped optical path includes: the device comprises a pulse laser 1, a wavelength division multiplexer 2, an optical switch 3, a first optical fiber ring 5, a second optical fiber ring 5, a temperature measuring optical fiber 7, a photoelectric detector 8, a data acquisition card 9 and an upper computer 10; wherein,
the output ends of the pulse laser 1 and the pulse laser 1 are connected with the input end of the wavelength division multiplexer 2; the common end of the wavelength division multiplexer 2 is connected with the input end of the optical switch 3; two output ends of the optical switch 3 are respectively connected with a first optical fiber ring 5 and a second optical fiber ring 6; the output ends of the first optical fiber ring 5 and the second optical fiber ring 6 are respectively connected with two ends of a temperature measuring optical fiber 7; two output ends of the wavelength division multiplexer 2 are respectively connected with two input ends of the photoelectric detector 8; two output ends of the photoelectric detector 8 are respectively connected with two input ends of a data acquisition card 9, and the output end of the data acquisition card is connected with the input end of an upper computer 10; the first optical fiber ring 5 and the second optical fiber ring 6 are both placed in the temperature measuring device 4, and the output end of the temperature measuring device 4 is connected with the input end of the upper computer 10;
the distributed optical fiber temperature sensing system of the annular optical path can perform laser power feedback adjustment and Rayleigh scattering noise compensation for inhibiting nonlinear effects.
Distributed optical fiber temperature sensing system based on annular light path includes: the device comprises a pulse laser with the center wavelength of 1550nm, a band-pass wavelength division multiplexer with the center wavelengths of 1450nm and 1661nm, a 1 multiplied by 2 optical switch, an optical fiber ring, a multimode temperature measuring optical fiber with the length of 2km, two optical fiber rings with the length of 100m, a two-channel synchronous acquisition photoelectric detector with the bandwidth of 100MHz, a two-channel data acquisition card of 100MSPS, an upper computer and a PT1000 platinum resistance measuring device.
The laser power feedback regulation for inhibiting the nonlinear effect comprises the following steps:
the method comprises the following steps: two groups of anti-Stokes scattered light (V) are acquired by a data acquisition cardas1And Vas2) And Stokes scattered light (V)s1And Vs2) Respectively carrying out geometric mean calculation to obtain VasmAnd Vsm；
Step two: calculating the ratio of the anti-Stokes scattered light to the Stokes scattered light after geometric averaging, VR＝Vasm/VsmAnd calculating the ratio difference DeltaV of the positions of the first optical fiber ring and the second optical fiber ringR＝VR(L0)-VR(L1) Wherein L is0＝50m，L1＝2150m；
Step three: starting from 20mA, the pumping current of the laser is gradually increased, and the delta V is observed in real timeRWhen Δ VR>10％×MIN[VR(L0),VR(L1)]Reducing the pumping current of the laser to delta V<1％×MIN[VR(L0),VR(L1)]。
This embodiment passes through two optical fiber rings at the annular light path head and end, realizes the real-time supervision to stimulated raman scattering threshold value, and the pumping current of feedback regulation laser instrument realizes injecting pulse optical power maximize under spontaneous raman scattering state, and then promotes sensing system's wholeness ability.
In the invention: the temperature sensing system has a Rayleigh scattering noise compensation function, and the compensation algorithm comprises the following steps:
the method comprises the following steps: and placing the temperature measuring optical fiber, the first optical fiber ring and the second optical fiber ring in an environment at 25 ℃, and keeping the environment temperature stable. Respectively collecting anti-Stokes scattering signals and Stokes scattering signals from positive and negative directions, Vas_for，Vs_for，Vas_backAnd Vs_back。
Step two: and respectively calculating the loss of each point including the optical fiber connector and the optical fiber fusion point for the anti-Stokes and Stokes scattering signals collected in the forward direction. Optical fiber LnThe anti-stokes scattering signal loss and the stokes scattering signal loss at (a) can be expressed as:
wherein m is 5 m. The compensated raman scattering curve is:
wherein L is 2200 m.
Step three: and (3) for the reversely collected anti-Stokes and Stokes scattering signals, obtaining the loss of each point of the optical fiber calculated by the direction data by adopting the same processing method as the step two:
the compensated raman scattering curve should be:
step three: the two-way anti-stokes scattering signal and the stokes scattering signal after loss compensation respectively contain Rayleigh scattering noise with different degrees, and can be represented by the following formulas:
wherein l is the position distance of a certain point of the optical fiber, h is Planck constant, Δ v ═ 13.2THz is Raman scattering frequency shift in the quartz optical fiber, k is Boltzmann constant, T is the ambient temperature of the optical fiber, αasFor the attenuation coefficient of anti-Stokes scattered light in silica fiber, αsThe attenuation coefficient of Stokes' scattered light in a silica optical fiber, αrAttenuation coefficient of Rayleigh scattered light in quartz fiber, AforScattering coefficient of anti-Stokes scattered light obtained for forward detection, BforDetecting Rayleigh scattering coefficient, C, in channel for anti-Stokes scattered lightforScattering coefficient of anti-Stokes scattered light, D, obtained for forward detectionforRayleigh scattering coefficient, A, in a channel for Stokes scattering light detectionbackScattering coefficient of anti-Stokes scattered light obtained for reverse detection, BbackDetecting Rayleigh scattering coefficient, C, in channel for anti-Stokes scattered lightbackStokes scattering coefficient, D, for reverse detectionbackThe rayleigh scattering coefficient in the channel is detected for the stokes scattered light for reverse detection.
According to formula (1) and formula (2), the time when the first fiber loop (l) is recorded0) And a second optical fiber ring (l)1) Are respectively at a temperature T030 ℃ and T1Intensity of bidirectional raman scattered light at 80 ℃:
where L2100 m is the fiber length between the first fiber loop and the second fiber loop. A is calculated by the formula (5) and the formula (6)forAnd BforAnd the data are substituted into the formula (7) and the formula (8), and the formula (8) is subtracted from the formula (7) to calculate αr0。
C can be calculated from the formula (9), the formula (10), the formula (11) and the formula (12) by the same method as described abovefor、DforAnd αr1。
Similarly, A for reverse detection of anti-Stokes scattered light and Stokes scattered light can be calculatedfor、Bfor、Cfor、Dfor、αr2And αr3。
Wherein, αrGet αr0、αr1、αr2And αr3Average value of (a).
The signal after forward and backward raman scattering with rayleigh scattering noise removed can be expressed as:
geometric mean processing is performed on the formulas (13) and (15), and the formulas (14) and (16), so that:
in this case, equations (17) and (18) are related only to the temperature T at each position of the optical fiber, and not to the distance.
Dividing equation (17) by equation (18) yields:
selecting the intensity of the scattering signal of the first optical fiber ring or the second optical fiber ring and the real-time environment temperature where the scattering signal is located as a reference temperature, and obtaining:
dividing equation (19) by equation (20) yields:
the nonlinear loss caused by factors such as bending and corrosion of strong corrosive substances to the Raman scattering light intensity in the optical fiber is eliminated through the annular light path structure, the long-term stability of the distributed optical fiber temperature sensor in the practical application environment is improved, and the application field of the distributed optical fiber temperature sensor is expanded. And (4) passing. Meanwhile, Rayleigh scattered light in the back Raman scattered light is calculated, and the influence of the Rayleigh scattered light on temperature demodulation precision is eliminated, so that the temperature field information of the sensing optical fiber is directly demodulated, the complexity of system debugging is reduced, and the temperature measurement precision and the long-term measurement stability are improved.
Although the present invention has been described with reference to the preferred embodiments, it is not intended to limit the present invention, and those skilled in the art can make variations and modifications of the present invention without departing from the spirit and scope of the present invention by using the methods and technical contents disclosed above.
Claims (11)
1. A distributed optical fiber temperature sensing system based on an annular light path is characterized by comprising: the device comprises a pulse laser (1), a wavelength division multiplexer (2), an optical switch (3), a first optical fiber ring (5), a second optical fiber ring (6), a temperature measurement optical fiber (7), a photoelectric detector (8), a data acquisition card (9) and an upper computer (10); wherein,
the output ends of the pulse laser (1) and the pulse laser (1) are connected with the input end of the wavelength division multiplexer (2); the common end of the wavelength division multiplexer (2) is connected with the input end of the optical switch (3); two output ends of the optical switch (3) are respectively connected with the first optical fiber ring (5) and the second optical fiber ring (6); the output ends of the first optical fiber ring (5) and the second optical fiber ring (6) are respectively connected with the two ends of the temperature measuring optical fiber (7); two output ends of the wavelength division multiplexer (2) are respectively connected with two input ends of the photoelectric detector (8); two output ends of the photoelectric detector (8) are respectively connected with two input ends of a data acquisition card (9), and the output end of the data acquisition card is connected with the input end of an upper computer (10); the first optical fiber ring (5) and the second optical fiber ring (6) are both placed in the temperature measuring device 4, and the output end of the temperature measuring device 4 is connected with the input end of the upper computer (10);
the distributed optical fiber temperature sensing system of the annular optical path can perform laser power feedback adjustment and Rayleigh scattering noise compensation for inhibiting nonlinear effects.
2. The distributed optical fiber temperature sensing system based on the annular optical path as claimed in claim 1, wherein: the laser power feedback regulation for inhibiting the nonlinear effect comprises the following steps:
the method comprises the following steps: two groups of anti-Stokes scattered light V are acquired by a data acquisition card (9)as1And Vas2And Stokes scattered light Vs1And Vs2Respectively carrying out geometric mean calculation to obtain VasmAnd Vsm；
Step two: calculating the ratio of the anti-Stokes scattered light to the Stokes scattered light after geometric averaging, VR＝Vasm/VsmAnd calculating the difference DeltaV of the ratio of the positions of the first optical fiber ring (5) and the second optical fiber ring (6)R＝VR(L0)-VR(L1) Wherein L is0And L1The positions of the first optical fiber ring (5) and the second optical fiber ring (6) are respectively distant;
step three: starting from 0mA, the pumping current of the pulse laser (1) is gradually increased, and the delta V is observed in real timeRWhen Δ VR>10％×MIN[VR(L0),VR(L1)]The pumping current of the pulse laser (1) is reduced to delta V<1％×MIN[VR(L0),VR(L1)]。
3. The distributed optical fiber temperature sensing system based on the annular optical path as claimed in claim 1, wherein: the rayleigh scattering noise compensation comprises the steps of:
(1) placing the temperature measuring optical fiber (7), the first optical fiber ring (5) and the second optical fiber ring (6) in the same temperature environment, and keeping the environment temperature stable; collecting anti-Stokes scattering signals from positive and negative directions respectivelyObtaining a forward-collected anti-Stokes signal V from a Stokes scattering signalas_forWith Stokes scattering signal Vs_forReversely collected anti-stokes signal Vas_backWith Stokes scattering signal Vs_back；
(2) Obtaining optical fiber L according to forward collected anti-Stokes and Stokes scattering signalsnForward anti-stokes scattering signal loss at
Loss of signal associated with forward stokes scattering
And obtaining compensated forward anti-Stokes scattering signal loss
With compensated forward stokes scattering signal loss
(3) Obtaining the optical fiber L according to the reversely collected anti-Stokes and Stokes scattering signalsnLoss of reverse anti-stokes scattering signal
Loss of signal associated with reverse Stokes scattering
And obtaining compensated reverse anti-Stokes scattering signal loss
With compensated reverse Stokes scattering signal loss
(4) Based on compensated forward anti-Stokes scattering signal loss
With compensated forward stokes scattering signal loss
Obtaining compensated forward anti-Stokes scattering signal loss containing Rayleigh scattering noise
With compensated forward stokes scattering signal loss
Based on compensated reverse anti-Stokes scattering signal loss
With compensated reverse Stokes scattering signal loss
Obtaining compensated reverse anti-stokes scattering signal loss containing Rayleigh scattering noise
With compensated reverse Stokes scattering signal loss
4. The distributed optical fiber temperature sensing system based on the annular optical path as claimed in claim 3, wherein: in step (2), the optical fiber LnForward acquired anti-stokes and stokes scattered signalsTo obtain an optical fiber LnForward anti-stokes scattering signal loss at
Loss of signal associated with forward stokes scattering
Respectively expressed as:
wherein m is the number of translation steps of the loss point of the optical fiber.
5. The distributed optical fiber temperature sensing system based on the annular optical path as claimed in claim 3, wherein: in step (2), the compensated forward anti-Stokes scattering signal loss
With compensated forward stokes scattering signal loss
Respectively expressed as:
6. the distributed optical fiber temperature sensing system based on the annular optical path as claimed in claim 5, wherein: in thatIn step (3), the optical fiber LnLoss of reverse anti-stokes scattering signal
Loss of signal associated with reverse Stokes scattering
Respectively expressed as:
7. the distributed optical fiber temperature sensing system based on the annular optical path as claimed in claim 6, wherein: in step (3), the compensated reverse anti-Stokes scattering signal loss
With compensated reverse Stokes scattering signal loss
Respectively expressed as:
8. the distributed optical fiber temperature sensing system based on the annular optical path as claimed in claim 7, wherein: in step (4), the compensated forward inverse gaussian noise including the rayleigh scattering noise is includedLoss of Thauss scattering signal
Comprises the following steps:
wherein l is the position distance of a certain point of the optical fiber, h is Planck constant, Deltav is Raman scattering frequency shift in the quartz optical fiber, k is Boltzmann constant, T is the environment temperature of the optical fiber, αasFor the attenuation coefficient of anti-Stokes scattered light in silica fiber, αsThe attenuation coefficient of Stokes' scattered light in a silica optical fiber, αrAttenuation coefficient of Rayleigh scattered light in quartz fiber, AforScattering coefficient of anti-Stokes scattered light obtained for forward detection, BforDetecting Rayleigh scattering coefficient, C, in channel for anti-Stokes scattered lightforScattering coefficient of anti-Stokes scattered light, D, obtained for forward detectionforRayleigh scattering coefficient, A, in a channel for Stokes scattering light detectionbackScattering coefficient of anti-Stokes scattered light obtained for reverse detection, BbackDetecting Rayleigh scattering coefficient, C, in channel for anti-Stokes scattered lightbackStokes scattering coefficient, D, for reverse detectionbackRayleigh scattering coefficient in the channel is detected for Stokes scattering light for reverse detection, αr0The attenuation coefficient of Rayleigh scattered light in a forward anti-Stokes detection signal in a quartz optical fiber is detected.
9. The distributed optical fiber temperature sensing system based on the annular optical path as claimed in claim 7, wherein: in step (4), the compensated forward stokes scattering signal loss containing rayleigh scattering noise
Comprises the following steps:
wherein l is the position distance of a certain point of the optical fiber, h is Planck constant, Deltav is Raman scattering frequency shift in the quartz optical fiber, k is Boltzmann constant, T is the environment temperature of the optical fiber, αasFor the attenuation coefficient of anti-Stokes scattered light in silica fiber, αsThe attenuation coefficient of Stokes' scattered light in a silica optical fiber, αrAttenuation coefficient of Rayleigh scattered light in quartz fiber, CforScattering coefficient of anti-Stokes scattered light, D, obtained for forward detectionforRayleigh scattering coefficient in the detection channel for Stokes scattered light, αr1The attenuation coefficient of Rayleigh scattered light in a forward Stokes detection signal in a quartz optical fiber is detected.
10. The distributed optical fiber temperature sensing system based on the annular optical path as claimed in claim 7, wherein: in step (4), the compensated anti-Stokes scattering signal loss containing Rayleigh scattering noise
Comprises the following steps:
wherein l is the position distance of a certain point of the optical fiber, h is Planck constant, Deltav is Raman scattering frequency shift in the quartz optical fiber, k is Boltzmann constant, T is the environment temperature of the optical fiber, αasFor the attenuation coefficient of anti-Stokes scattered light in silica fiber, αsThe attenuation coefficient of Stokes' scattered light in a silica optical fiber, αrAttenuation coefficient of Rayleigh scattered light in quartz fiber, AbackScattering coefficient of anti-Stokes scattered light obtained for reverse detection, BbackDetection of Rayleigh scattered light scattering coefficients in a channel for anti-Stokes scattered light, αr2The attenuation coefficient of Rayleigh scattered light in a signal in a quartz fiber is detected for reverse anti-Stokes.
11. The distributed optical fiber temperature sensing system based on the annular optical path as claimed in claim 7, wherein: in step (4), the compensated reverse Stokes scattering signal loss containing Rayleigh scattering noise
Comprises the following steps:
wherein l is the position distance of a certain point of the optical fiber, h is Planck constant, Deltav is Raman scattering frequency shift in the quartz optical fiber, k is Boltzmann constant, T is the environment temperature of the optical fiber, αasFor the attenuation coefficient of anti-Stokes scattered light in silica fiber, αsThe attenuation coefficient of Stokes' scattered light in a silica optical fiber, αrAttenuation coefficient of Rayleigh scattered light in quartz fiber, CbackStokes scattering coefficient, D, for reverse detectionbackRayleigh scattering coefficient in the channel is detected for Stokes scattering light for reverse detection, αr3The attenuation coefficient of Rayleigh scattered light in a signal in a quartz fiber is detected for the reverse Stokes.
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