CN112378431B - Distributed optical fiber Raman sensing method based on broadband chaotic laser - Google Patents
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- 238000000253 optical time-domain reflectometry Methods 0.000 description 3
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- G01D5/00—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable
- G01D5/26—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light
- G01D5/32—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light
- G01D5/34—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells
- G01D5/353—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre
- G01D5/35338—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre using other arrangements than interferometer arrangements
- G01D5/35354—Sensor working in reflection
- G01D5/35358—Sensor working in reflection using backscattering to detect the measured quantity
- G01D5/35361—Sensor working in reflection using backscattering to detect the measured quantity using elastic backscattering to detect the measured quantity, e.g. using Rayleigh backscattering
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- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B11/00—Measuring arrangements characterised by the use of optical techniques
- G01B11/16—Measuring arrangements characterised by the use of optical techniques for measuring the deformation in a solid, e.g. optical strain gauge
- G01B11/18—Measuring arrangements characterised by the use of optical techniques for measuring the deformation in a solid, e.g. optical strain gauge using photoelastic elements
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- G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
- G01D5/00—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable
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- G01D5/32—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light
- G01D5/34—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells
- G01D5/353—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre
- G01D5/35383—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre using multiple sensor devices using multiplexing techniques
- G01D5/35387—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre using multiple sensor devices using multiplexing techniques using wavelength division multiplexing
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- G01K—MEASURING TEMPERATURE; MEASURING QUANTITY OF HEAT; THERMALLY-SENSITIVE ELEMENTS NOT OTHERWISE PROVIDED FOR
- G01K11/00—Measuring temperature based upon physical or chemical changes not covered by groups G01K3/00, G01K5/00, G01K7/00 or G01K9/00
- G01K11/32—Measuring temperature based upon physical or chemical changes not covered by groups G01K3/00, G01K5/00, G01K7/00 or G01K9/00 using changes in transmittance, scattering or luminescence in optical fibres
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
- G01L1/00—Measuring force or stress, in general
- G01L1/24—Measuring force or stress, in general by measuring variations of optical properties of material when it is stressed, e.g. by photoelastic stress analysis using infrared, visible light, ultraviolet
- G01L1/242—Measuring force or stress, in general by measuring variations of optical properties of material when it is stressed, e.g. by photoelastic stress analysis using infrared, visible light, ultraviolet the material being an optical fibre
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
- G01L1/00—Measuring force or stress, in general
- G01L1/24—Measuring force or stress, in general by measuring variations of optical properties of material when it is stressed, e.g. by photoelastic stress analysis using infrared, visible light, ultraviolet
- G01L1/247—Measuring force or stress, in general by measuring variations of optical properties of material when it is stressed, e.g. by photoelastic stress analysis using infrared, visible light, ultraviolet using distributed sensing elements, e.g. microcapsules
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Abstract
The invention relates to the field of distributed optical fiber sensing, and discloses a millimeter-scale spatial resolution distributed optical fiber sensing method based on broadband chaotic laser, which comprises the following steps of: s1, building a distributed optical fiber Raman sensing system; s2, a calibration stage: at the front end of the sensing optical fiberL 0 The length of the position setting is longer than the laser pulse widthWIs positioned by the optical fiber ring of (a)L 0 The intensity of the anti-stokes scattered light after chromatographic treatment; s3, measuring: performing chromatographic processing and chaotic matched filtering operation on the acquired chaotic Raman anti-Stokes scattered light signals, and calculating to obtain a temperature T of a temperature change position and a temperature T of the temperature change position 1 The method comprises the steps of carrying out a first treatment on the surface of the And carrying out chaotic matched filtering operation on the chaotic pulse reference signal and the chaotic Rayleigh scattering signal to obtain the additional loss of the sensing optical fiber, and further demodulating the stress information received along the sensing optical fiber. The invention realizes millimeter-scale spatial resolution of the distributed optical fiber sensing method and improves measurement accuracy.
Description
Technical Field
The invention relates to the field of distributed optical fiber sensing, in particular to a distributed optical fiber sensing method with millimeter-level spatial resolution based on broadband chaotic laser.
Background
The distributed optical fiber Raman sensing system can continuously measure the distributed temperature characteristic information along the sensing optical fiber. In the distributed optical fiber Raman sensing system, the environment temperature along the sensing optical fiber can carry out intensity modulation on Raman scattered light in the optical fiber, and the system can obtain the temperature change condition along the sensing optical fiber through collecting the Raman scattered light carrying temperature information and demodulating the Raman scattered light. The distributed optical fiber Raman sensing system has the advantages of high pressure resistance, electromagnetic interference resistance, small volume, light weight and the like, and is widely applied to the temperature safety monitoring fields of coal mines, oil and gas pipelines, bridges, buildings and the like.
In the distributed optical fiber Raman sensing system, the spatial resolution is a main technical index, and can reflect the minimum length of the temperature measuring system capable of distinguishing the temperature change of the optical fiber. At present, the distributed optical fiber Raman sensing system is positioned based on an Optical Time Domain Reflectometry (OTDR) technology, and because of the limitation of a light source pulse width, the method has contradiction that the spatial resolution and the sensing distance cannot be considered, and the optimal spatial resolution can reach 1m. In addition, the distributed optical fiber Raman sensing system can only monitor the temperature change condition along the optical fiber, and can not extract the stress and strain information along the optical fiber.
Based on the above, a brand new distributed optical fiber sensing method is necessary to be invented, so as to solve the technical problems that the existing distributed optical fiber sensing system cannot detect temperature and strain at the same time, the spatial resolution is limited by the pulse width of a light source, and the spatial resolution is difficult to break through 1m.
Disclosure of Invention
In order to solve the technical problem that the spatial resolution of the existing distributed optical fiber Raman sensing system is limited by an OTDR principle, the technical problem that the existing distributed optical fiber Raman sensing system is difficult to break through 1m is solved, and the system cannot realize continuous distributed measurement of two parameters, namely temperature and strain, at the same time. The invention provides a distributed optical fiber Raman sensing method based on broadband chaos, which can carry out cooperative monitoring on two parameters of temperature and strain along an optical fiber, and finally realize millimeter-level spatial resolution measurement along the optical fiber.
In order to solve the technical problems, the invention adopts the following technical scheme: a distributed optical fiber sensing method based on broadband chaotic laser comprises the following steps:
s1, a distributed optical fiber Raman sensing system is built, pulse laser output by a broadband chaotic laser source is divided into two beams, one beam is used as a detection beam to be incident to a sensing optical fiber, back chaotic Rayleigh scattered light and chaotic Raman anti-Stokes scattered light generated in the sensing optical fiber are respectively detected by a first detector and a second detector after being separated, and the other beam is used as a reference beam to be detected by a third detector; collecting detection signals of the three detectors through a data acquisition card;
s2, a calibration stage: at the front end L of the sensing optical fiber 0 An optical fiber ring with the length longer than the laser pulse width W is arranged at the position, and the temperature of the optical fiber ring is set as T' 0 The ambient temperature of the sensing optical fiber is recorded as T 0 Measuring position L 0 Is subjected to chromatographic treatment to obtain the position L 0 The intensity of the anti-stokes scattered light after chromatographic treatment;
s3, measuring: carrying out chromatographic treatment on the acquired chaotic Raman anti-Stokes scattered light signals to obtain Raman scattered signals after chromatographic treatment; performing chaos matched filtering operation on the chaos pulse reference signal and the chromatography chaos Raman anti-Stokes signal to obtain a matching coefficient of the chaos pulse reference signal and the chromatography chaos Raman anti-Stokes signalCalculating the temperature T of the temperature change position and the temperature change position according to the correlation peak position of the matching coefficient of the chaotic pulse reference signal and the chromatographic processing chaotic Raman anti-Stokes signal 1 The method comprises the steps of carrying out a first treatment on the surface of the The calculation formula is as follows:
wherein c represents the speed of light, n 0 For sensing refractive index of optical fiber, m 1 Representing a first chaotic matching coefficientThe first chaos matching coefficient +.>Is obtained by performing chromatographic processing and chaotic filtering operation on an anti-Stokes optical signal obtained by detecting a first photoelectric detector (16), L 1 Indicating the temperature change position, T 1 Indicating the temperature change position L 1 Temperature at L 0 Indicating the position of the optical fiber ring in the calibration stage, wherein Deltav is Raman frequency shift, h is Planck constant, k is Boltzmann constant, R as Representing the temperature modulation function of anti-Stokes scattered light, I 1 Indicating the position after chromatographic treatment as L 1 Chaotic raman anti-stokes scattered light intensity at temperature change of (I) 0 Indicating the position L after chromatographic treatment obtained in the calibration stage 0 Is a) the intensity of the chaotic raman anti-stokes scattered light, α 0 、α as Respectively representing loss coefficients of incident light and chaotic anti-Stokes light in a unit length of the sensing optical fiber;
performing chaotic matched filtering operation on the chaotic pulse reference signal and the chaotic Rayleigh scattering signal to obtain a matching coefficient of the chaotic pulse reference signal and the chaotic Rayleigh scattering signalAnd calculating the slope of the optical fiber, and obtaining the additional loss of the sensing optical fiber according to the slope, so as to demodulate the stress information received along the sensing optical fiber.
In the step S2 and the step S3, the specific method of the chromatographic treatment is as follows: the amplitude of the sampled signal at the previous instant is subtracted from the amplitude of the sampled signal at the subsequent instant of the adjacent instants.
The chaotic pulse reference signal and the chromatography-processed chaotic Raman anti-Stokes signal are matchedCoefficient of matchThe calculation formula of (2) is as follows:
matching coefficient of chaotic pulse reference signal and chaotic Rayleigh scattering signalThe calculation formula of (2) is as follows:
wherein ,xn+m Represents the chaotic reference signal of the nth sampling point when the delay time is m, N represents the total number of the sampling points,the intensity of the Raman anti-Stokes light representing the nth sample point after chromatography treatment,/->Representing the rayleigh scattering intensity at the nth sample point.
During strain demodulation, the calculation formula of the position where the strain occurs is as follows: wherein ,L2 Indicating the location where the strain occurs, m 2 Matching coefficient for representing chaotic pulse reference signal and chaotic Rayleigh scattering signal>Corresponding delay time when slope changes in image, c represents light speed, n 0 Is the refractive index of the sensing fiber.
In the step S1, the built distributed optical fiber raman sensing system includes: the device comprises a broadband chaotic laser generator, an isolator, an acousto-optic modulator, a pulse signal generator, an optical fiber coupler, a wavelength division multiplexer, a sensing optical fiber, a first erbium-doped optical fiber amplifier, a first photoelectric detector, a second erbium-doped optical fiber amplifier, a second photoelectric detector, a third photoelectric detector, an acquisition card and a computer;
the broadband chaotic laser generator emits laser signals, the laser signals are changed into pulse signals after passing through the isolator and the acousto-optic modulator, the pulse signals are divided into two beams by the optical fiber coupler, one beam is used as a detection beam to be incident into the sensing optical fiber after passing through the wavelength division multiplexer, the back chaotic Rayleigh scattered light and the chaotic Raman anti-Stokes scattered light generated in the sensing optical fiber are separated by the wavelength division multiplexer and are respectively detected by the first detector and the second detector after being amplified by the first erbium-doped optical fiber amplifier and the second erbium-doped optical fiber amplifier, and the other beam is used as a reference beam to be detected by the third detector; and acquiring detection signals of the three detectors through the acquisition card and sending the detection signals to the computer.
Compared with the prior art, the invention has the following beneficial effects: according to the method, chaos pulse reference signals and chaos Raman scattering signals which are scattered back along the optical fibers and subjected to chromatography processing are subjected to chaos matched filtering processing, the positions of temperature change areas of sensing optical fibers are positioned, and the positioning accuracy can reach millimeter-level spatial resolution. In addition, the ratio demodulation is carried out on the chaotic Raman scattering signal and the chaotic pulse reference signal to obtain detailed temperature information of a temperature change region; and finally, the detailed strain information along the optical fiber is obtained through chaos matched filtering demodulation of the chaos pulse reference signal and the chaos Rayleigh signal, so that the accuracy of the distributed Raman sensing method is improved.
Drawings
Fig. 1 is a schematic structural diagram of a distributed optical fiber raman sensor device according to an embodiment of the present invention;
in the figure: the device comprises a 1-broadband chaotic laser generator, a 2-isolator, a 3-acousto-optic modulator, a 4-pulse signal generator, a 5-optical fiber coupler, a 6-wavelength division multiplexer, a 7-sensing optical fiber, an 8-first erbium-doped optical fiber amplifier, a 9-first photoelectric detector, a 10-second erbium-doped optical fiber amplifier, a 11-second photoelectric detector, a 12-third photoelectric detector, a 13-acquisition card and a 14-computer.
Detailed Description
For the purpose of making the objects, technical solutions and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below, and it is apparent that the described embodiments are some embodiments of the present invention, but not all embodiments; all other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
The embodiment of the invention provides a distributed optical fiber sensing method based on broadband chaotic laser, which has millimeter-scale spatial resolution, is positioned based on a chaotic matched filtering method, can sense and position the temperature and the stress along the optical fiber, and specifically comprises the following steps:
step one: and constructing a distributed optical fiber Raman sensing system based on a chaos matched filtering method.
The specific method comprises the following steps: the method comprises the steps that pulse laser output by a broadband chaotic laser source is divided into two beams, one beam is used as a detection beam to be incident to a sensing optical fiber, and the back chaotic Rayleigh scattered light and the chaotic Raman anti-Stokes scattered light generated in the sensing optical fiber are respectively detected by a first detector and a second detector after being divided, and the other beam is used as a reference beam to be detected by a third detector; collecting detection signals of the three detectors through a data acquisition card;
as shown in fig. 1, the distributed optical fiber raman sensing system constructed in the present embodiment comprises a broadband chaotic laser generator 1, an isolator 2, an acousto-optic modulator 3, a pulse signal generator 4, an optical fiber coupler 5, a wavelength division multiplexer 6, a sensing optical fiber 7, a first erbium-doped optical fiber amplifier 8, a first photoelectric detector 9, a second erbium-doped optical fiber amplifier 10, a second photoelectric detector 11, a third photoelectric detector 12, a high-speed data acquisition card 13 and a computer 14. The output end of the broadband chaotic laser 1 is connected with the input end of the isolator 2; the output end of the isolator 2 is connected with the input end of the acousto-optic modulator 3, the pulse signal generator 4 is connected with the acousto-optic modulator 3, and the output end of the acousto-optic modulator 3 is connected with the port a of the optical fiber coupler 5; the wavelength division multiplexer 6 and the third photoelectric detector 12 are respectively connected with the port b and the port c of the optical fiber coupler 5; the b port, the c port and the d port of the wavelength division multiplexer 6 are respectively connected with the sensing optical fiber 7, the second erbium-doped optical fiber amplifier 10 and the first erbium-doped optical fiber amplifier 8; the output end of the second erbium-doped fiber amplifier 10 is connected with the second photoelectric detector 11, and the output end of the first erbium-doped fiber amplifier 8 is connected with the first photoelectric detector 9; the output ends of the first photoelectric detector 9, the second photoelectric detector 11 and the third photoelectric detector 12 are connected with a high-speed data acquisition card 13; the high-speed data acquisition card 13 is connected with a 14 computer.
The broadband chaotic laser generator 1 emits laser signals, the laser signals become pulse signals after passing through the isolator 2 and the acousto-optic modulator 3, the pulse signals are divided into two beams by the optical fiber coupler 5, one beam is used as a detection beam, the detection beam enters the sensing optical fiber 7 after passing through the wavelength division multiplexer 6, the back chaotic Rayleigh scattered light and the chaotic Raman anti-Stokes scattered light generated in the sensing optical fiber 7 are separated by the wavelength division multiplexer 6 and are respectively detected by the first erbium-doped optical fiber amplifier 8 and the second erbium-doped optical fiber amplifier 10 after being amplified by the first detector and the second detector, and the other beam is used as a reference beam to be detected by the third detector; and acquiring detection signals of the three detectors through a data acquisition card and sending the detection signals to the computer.
Further, the working wavelength of the broadband chaotic laser 1 is 1550nm, and the pulse laser passing branch ratio is 1:99, the optical fiber coupler 3 is divided into a reference path and a detection path; the chaotic pulse laser of the detection path enters the sensing optical fiber after passing through the wavelength division multiplexer, and the back chaotic Rayleigh scattered light and the chaotic Raman anti-Stokes scattered light are generated in the sensing optical fiber. The chaotic back Rayleigh scattered light and the chaotic Raman anti-Stokes scattered light are split by the wavelength division multiplexer and respectively emitted from 1550nm (c) and 1450nm (d) ports of the wavelength division multiplexer.
Step two: and (3) a scaling stage.
At the front end L of the sensing optical fiber 0 An optical fiber ring with the length longer than the laser pulse width W is arranged at the position, and the temperature of the optical fiber ring is set as T' 0 Ambient temperature at which the sensing fiber is locatedDenoted as T 0 Measuring position L 0 Is subjected to chromatographic treatment to obtain the position L 0 The intensity of the anti-stokes scattered light after chromatographic treatment;
step three: and (3) a measuring stage.
Carrying out chromatographic treatment on the acquired chaotic Raman anti-Stokes scattered light signals to obtain Raman scattered signals after chromatographic treatment; performing chaos matched filtering operation on the chaos pulse reference signal and the chromatography chaos Raman anti-Stokes signal to obtain a matching coefficient of the chaos pulse reference signal and the chromatography chaos Raman anti-Stokes signalCalculating the temperature T of the temperature change position and the temperature change position according to the correlation peak position of the matching coefficient of the chaotic pulse reference signal and the chromatographic processing chaotic Raman anti-Stokes signal 1 。
Performing chaotic matched filtering operation on the chaotic pulse reference signal and the chaotic Rayleigh scattering signal to obtain a matching coefficient of the chaotic pulse reference signal and the chaotic Rayleigh scattering signalAnd calculating the slope of the optical fiber, and obtaining the additional loss of the sensing optical fiber according to the slope, so as to demodulate the stress information received along the sensing optical fiber.
The demodulation and positioning principle for temperature and stress measurement in the embodiment of the present invention is described below.
1. Chaotic pulse reference signal and chaotic Raman anti-Stokes signal light intensity processing
(1) Acquisition and processing of chaotic raman anti-stokes signals
In temperature demodulation, let the laser pulse width be W, the backward Raman anti-Stokes scattering signal (anti-Stokes) intensity at the position of the sensing fiber L is:
wherein P is the incident power of the pulse laser, K as Representing the coefficient related to the raman anti-stokes backscattering cross section, S being the backscattering factor of the fiber, v as Is the frequency of the raman anti-stokes scattering signal, phi e Representing the pulse laser light flux, alpha, coupled into the fiber 0 、α as The loss coefficients of incident light and anti-Stokes light in the sensing optical fiber per unit length are respectively L is the length of the sensing light, R as (T) is the temperature modulation function of the anti-stokes scattered light:
Δν is raman shift, h is planck constant, k is boltzmann constant, and T is sensing fiber temperature.
In fact, in the distributed optical fiber raman sensing system, the detection signal is a pulse signal, so that the information collected by the high-speed data collection card at a certain moment is not the light intensity information of one point at the position of the optical fiber L, but the superposition of the light intensity information of a section of optical fiber with the sensing distance equal to half pulse width of the whole pulse signal. The detection signal used in the millimeter-scale spatial resolution distributed optical fiber Raman sensing method based on the chaotic matched filtering method is a chaotic pulse signal, and the power of the whole pulse signal is in a random fluctuation state. Therefore, when the chaotic pulse sequence with the pulse width W of the detection signal is adopted, the chaotic Raman anti-Stokes signal intensity at the position of the sensing optical fiber L is acquired by the high-speed data acquisition card and can be expressed as follows:
in the formula ,the light intensity accumulation information of the chaos anti-Stokes scattering signal collected by the high-speed data collection card at the position of the sensing optical fiber L is shown,c is the speed of light and n is the refractive index of the sensing fiber. When the pulse width is W, L i The light intensity information collected by the high-speed data collection card at the L position comes from the sensing optical fibers [ (L-Wc/2 n) to L]Is a position interval of the (c). P (P) i Representing the optical power of the pulsed chaotic signal.
(2) And (5) acquisition and processing of chaotic pulse reference signals.
Pulse laser emitted by the 1-broadband chaotic laser passes through a c port of the 5-optical fiber coupler and is collected by the 13-acquisition card to obtain a reference signal I c ＝P i 。
(3) And (3) chromatographic processing of the chaotic Raman anti-Stokes signal.
And collecting the obtained chaotic Raman anti-Stokes scattered light signals, wherein each sampling point is the superposition of light intensity information of the whole chaotic pulse sequence in the length of an optical fiber with half pulse width. And performing chromatographic processing on the sampling signal, namely subtracting the amplitude of the sampling signal at the previous moment from the amplitude of the sampling signal at the next moment in the adjacent moments, wherein the expression is as follows:
in the formula Pi Representing the optical power of each point of the pulse chaotic signal, T 1 Representing the temperature of the position of the sensing optical fiber where the sampling signal is located at the later moment, T 0 For the temperature of the sensing optical fiber position where the sampling signal is located at the previous moment, L 1 Indicating the position of the sensing fiber.
2. Position location using chaotic matched filtering
And performing chaotic matched filtering operation on the chaotic pulse reference signal and the chromatographic processing chaotic Raman anti-Stokes signal, wherein the operation mode is as follows:
wherein Represents the matching coefficient of the chaotic pulse reference signal and the chromatographic processing chaotic Raman anti-Stokes signal, x n+m The chaotic reference signal of the nth sampling point is represented when the delay time is m, N represents the total number of the sampling points, < >>The raman anti-stokes intensity representing the nth sample point after chromatography is substantially equal to I 1 ，/>Representing the rayleigh scattering intensity at the nth sample point.
The intensity of the Raman anti-Stokes signal processed by chromatography is close to 0 in the non-temperature-changing area of the optical fiber, and the intensity of the signal in the temperature-changing area depends on the temperature of the temperature-changing area. Therefore, the reference signal and the chromatographic-processed Raman anti-Stokes signal are subjected to chaos matched filtering operation, and the relative peak position is the position information of the corresponding temperature change of the sensing optical fiber. When the delay time is m 1 The temperature change area is positioned at the time scale as followsThe temperature change area position under the spatial scale is as follows:
wherein c represents the speed of light, n 0 Is the refractive index of the sensing fiber. The system can obtain the specific position information of the optical fiber along the line through the delay time after calculation.
3. Demodulation temperature by chaos ratio method
(1) Calibration stage
At the front end L of the sensing optical fiber 0 An optical fiber ring with the length longer than the laser pulse width W is arranged at the position, and the temperature of the optical fiber ring is set as T' 0 The ambient temperature of the sensing optical fiber is recorded as T 0 Position L after chromatographic treatment 0 The anti-stokes scattered light intensity is:
I 0 ＝K·[R as (T 0 ′)-R as (T 0 )]·exp[-(α 0 +α as )L 0 ]·P i ； (7)
(2) Stage of measurement
Set up sensing optic fibre L 1 The position generates temperature change, the temperature is T 1 L is then 1 The intensity of the anti-stokes scattering light is:
I 1 ＝K·[R as (T 1 )-R as (T 0 )]·exp[-(α 0 +α as )L 1 ]·P i ； (8)
and (3) carrying out ratio demodulation by the two formulas (1) and (2), so as to obtain:
the temperature T of the temperature change area is obtained by the arrangement of (9) 1 The method comprises the following steps:
wherein ,L1 Indicating the temperature change position, T 1 Indicating the temperature change position L 1 Temperature at L 0 Indicating the position of the optical fiber ring in the calibration stage, wherein Deltav is Raman frequency shift, h is Planck constant, k is Boltzmann constant, R as Representing the temperature modulation function of anti-Stokes scattered light, I 1 Indicating the position after chromatographic treatment as L 1 Chaotic raman anti-stokes scattered light intensity at temperature change of (I) 0 Indicating the position L after chromatographic treatment obtained in the calibration stage 0 Is a) the intensity of the chaotic raman anti-stokes scattered light, α 0 、α as Respectively representing loss coefficients of incident light and chaotic anti-Stokes light in a unit length of the sensing optical fiber; thus, the fiber can be temperature demodulated and positioned along the line by the formula (10) and the formula (6).
Fourth, the method comprises the following steps: strain measurement for distributed fiber raman sensing systems
(1) Collecting chaotic Rayleigh scattering signals
The pulse signal sent by the chaotic pulse laser source is transmitted into the sensing optical fiber through the wavelength division multiplexer, and the Rayleigh scattering signal intensity acquired by the acquisition card is as follows:
I Ray ＝I 0 ·ν 0 4 exp(-2α 0 L)； (11)
in the formula ,I0 For the light intensity incident on the sensing optical fiber, L is the position of the sensing optical fiber, v 0 For the frequency of incident light, alpha 0 Is the loss of incident light propagating in the fiber.
(2) Chaotic matching filtering processing for chaotic Rayleigh scattering signal and chaotic pulse reference signal
And carrying out chaotic matched filtering operation on the chaotic pulse reference signal and the chaotic Rayleigh scattering signal, wherein the operation mode is as follows:
in the formula ,xn+m Represents the chaotic reference signal of the nth sampling point when the delay time is m, N represents the total number of the sampling points,representing the Rayleigh scattering intensity at the nth sample point, which is equal to the Rayleigh scattering signal I collected above Ray ；And the matching coefficient of the chaotic pulse reference signal and the Rayleigh scattering signal is represented.
Carrying out chaos matching filtering operation on the chaos pulse reference signal and the Rayleigh scattering signal to obtain a chaos matching coefficientThe slope of the image of (a) represents the attenuation coefficient of the sensing fiber and the Rayleigh scattering signal loss from the unstrained region of the sensing fiberThe consumption coefficient is alpha 0 Rayleigh scattering signal loss factor from strained region is alpha 1 ＝α 0 +Δα, where Δα is the strain-induced parasitic loss. The position of the sensing optical fiber where the strain occurs can be obtained through the chaos matching coefficient, and the additional loss value delta alpha caused by the strain can be obtained. During strain demodulation, the calculation formula of the position where the strain occurs is as follows: /> wherein ,L2 Indicating the location where the strain occurs, m 2 Representing chaos matching coefficient->Corresponding delay time when slope changes in image, c represents light speed, n 0 Is the refractive index of the sensing fiber. And the additional loss of the sensing optical fiber is in a positive linear relation with the stress strain to which the optical fiber is subjected. Based on this, strain information along the fiber can be demodulated.
Finally, it should be noted that: the above embodiments are only for illustrating the technical solution of the present invention, and not for limiting the same; although the invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical scheme described in the foregoing embodiments can be modified or some or all of the technical features thereof can be replaced by equivalents; such modifications and substitutions do not depart from the spirit of the invention.
Claims (5)
1. The distributed optical fiber sensing method based on the broadband chaotic laser is characterized by comprising the following steps of:
s1, a distributed optical fiber Raman sensing system is built, pulse laser output by a broadband chaotic laser source is divided into two beams, one beam is used as a detection beam to be incident to a sensing optical fiber, back chaotic Raman anti-Stokes scattered light and chaotic Rayleigh scattered light generated in the sensing optical fiber are respectively detected by a first photoelectric detector and a second photoelectric detector after being separated, and the other beam is used as a reference beam to be detected by a third photoelectric detector; collecting detection signals of the three detectors through a data acquisition card;
s2, a calibration stage: at the front end of the sensing optical fiberL 0 The length of the position setting is longer than the laser pulse widthWThe temperature of the optical fiber ring is set asT 0 ’The ambient temperature of the sensing optical fiber is recorded asT 0 Measuring positionL 0 Is subjected to chromatographic treatment to obtain the positionL 0 The intensity of the anti-stokes scattered light after chromatographic treatment;
s3, measuring: carrying out chromatographic treatment on the acquired chaotic Raman anti-Stokes scattered light signals to obtain Raman scattered signals after chromatographic treatment; performing chaos matched filtering operation on the chaos pulse reference signal and the chromatography chaos Raman anti-Stokes signal to obtain a matching coefficient of the chaos pulse reference signal and the chromatography chaos Raman anti-Stokes signalCalculating a temperature T of a temperature change position and a temperature change position according to the relative peak positions of the matching coefficients of the chaotic pulse reference signal and the chromatographic processing chaotic Raman anti-Stokes signal 1 The method comprises the steps of carrying out a first treatment on the surface of the The calculation formula is as follows:
；
；
wherein ,cthe speed of light is indicated as being the speed of light,n 0 in order to sense the refractive index of the optical fiber,m 1 representing a first chaotic matching coefficientThe first chaos matching coefficient +.>Is obtained by performing chromatographic processing and chaotic filtering operation on an anti-Stokes optical signal detected by a first photoelectric detector, L 1 Indicating the temperature change position, T 1 Indicating the temperature change position L 1 The temperature at which the temperature is to be maintained,L 0 indicating the position of the fiber loop during the calibration phase,Δνfor the raman shift of the light,his a constant of planck, which is set to be the planck's constant,kis Boltzmann constant, & gt>Temperature modulation function representing anti-Stokes scattered light,/->Indicating the position after chromatographic treatment as L 1 Chaotic raman anti-stokes scattered light intensity at temperature change of>Representing the position after chromatographic processing obtained in the calibration stage asL 0 Is a chaotic raman anti-stokes scattered light intensity,α 0 、α as respectively representing loss coefficients of incident light and chaotic anti-Stokes light in a unit length of the sensing optical fiber;
performing chaotic matched filtering operation on the chaotic pulse reference signal and the chaotic Rayleigh scattering signal to obtain a matching coefficient of the chaotic pulse reference signal and the chaotic Rayleigh scattering signalAnd calculating the slope of the optical fiber, and obtaining the additional loss of the sensing optical fiber according to the slope, so as to demodulate the stress information received along the sensing optical fiber.
2. The distributed optical fiber sensing method based on the broadband chaotic laser according to claim 1, wherein in the step S2 and the step S3, the specific method of the chromatographic treatment is as follows: the amplitude of the sampled signal at the previous instant is subtracted from the amplitude of the sampled signal at the subsequent instant of the adjacent instants.
3. The distributed optical fiber sensing method based on broadband chaotic laser according to claim 1, wherein the matching coefficient of the chaotic pulse reference signal and the chromatographic processing chaotic Raman anti-Stokes signalThe calculation formula of (2) is as follows:
；
matching coefficient of chaotic pulse reference signal and chaotic Rayleigh scattering signalThe calculation formula of (2) is as follows:
；
wherein ,the chaotic reference signal of the nth sampling point is represented when the delay time is m, N represents the total number of the sampling points, and +.>The intensity of the Raman anti-Stokes light representing the nth sample point after chromatography treatment,/->Representing the rayleigh scattering intensity at the nth sample point.
4. The distributed optical fiber sensing method based on broadband chaotic laser according to claim 1, wherein a calculation formula of a position where strain occurs during strain demodulation is as follows:； wherein ,L2 Indicating the location where the strain occurs, m 2 Matching coefficient for representing chaotic pulse reference signal and chaotic Rayleigh scattering signal>The corresponding delay time when the slope in the image changes,cthe speed of light is indicated as being the speed of light,n 0 is the refractive index of the sensing fiber.
5. The distributed optical fiber sensing method based on the broadband chaotic laser according to claim 1, wherein in the step S1, the built distributed optical fiber raman sensing system comprises: the device comprises a broadband chaotic laser generator (1), an isolator (2), an acousto-optic modulator (3), a pulse signal generator (4), an optical fiber coupler (5), a wavelength division multiplexer (6), a sensing optical fiber (7), a first erbium-doped optical fiber amplifier (8), a first photoelectric detector (9), a second erbium-doped optical fiber amplifier (10), a second photoelectric detector (11), a third photoelectric detector (12), an acquisition card (13) and a computer (14);
the broadband chaotic laser generator (1) emits laser signals, the laser signals are changed into pulse signals after passing through the isolator (2) and the acousto-optic modulator (3), the pulse signals are then divided into two beams by the optical fiber coupler (5), one beam is used as a detection beam to enter the sensing optical fiber (7) after passing through the wavelength division multiplexer (6), the backward chaotic Rayleigh scattered light and the chaotic Raman anti-Stokes scattered light generated in the sensing optical fiber (7) are separated by the wavelength division multiplexer (6), and are respectively amplified by the first erbium-doped optical fiber amplifier (8) and the second erbium-doped optical fiber amplifier (10) and are respectively detected by the first photoelectric detector (9) and the second photoelectric detector (11), and the other beam is used as a reference beam to be detected by the third photoelectric detector (12); and detecting signals of the three photoelectric detectors are collected through a collecting card (13) and sent to the computer.
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