CN108303197B - Distributed temperature and strain double-parameter sensing device based on backscatter enhanced optical fiber and demodulation method thereof - Google Patents
Distributed temperature and strain double-parameter sensing device based on backscatter enhanced optical fiber and demodulation method thereof Download PDFInfo
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Abstract
The invention discloses a backward scattering enhanced optical fiber based distributed temperature and strain double-parameter sensing device and a demodulation method thereof; the device comprises a narrow-linewidth light source, a coupler, an acousto-optic modulation module, a driver, an erbium-doped fiber amplifier, a circulator, a Raman wavelength division multiplexer, a sensing fiber with a plurality of continuous scattering enhancement points, a filter, a photoelectric detector, a data acquisition card and an upper computer; the realization principle of the double-parameter measurement is based on the characteristics that the phase of a backward Rayleigh scattering light signal in a sensing optical fiber is sensitive to the change of an external environment and the light intensity of Raman scattering light is sensitive to the change of temperature, and an implementation scheme of absolute temperature stress distributed measurement is provided by utilizing an optical time domain reflection technology, a coherent detection technology, a beat frequency signal cross-correlation technology, a phase demodulation technology, a wavelength division multiplexing technology and a temperature stress decoupling technology. The invention can realize the simultaneous measurement of the temperature field and the stress field which are continuously distributed along the optical fiber, and has the advantages of long measurement distance, high spatial resolution, high sensitivity, high response speed and small error.
Description
Technical Field
The invention relates to the technical field of double parameters for optical fiber measurement, and particularly provides a distributed temperature and strain double-parameter sensing device based on a backscattering enhanced optical fiber and a demodulation method thereof.
Background
The development of optical fiber sensing technology has been advanced rapidly in recent years, and the optical fiber sensing technology has advantages which are incomparable with the traditional sensors such as electric sensors, and the main advantages are as follows: the cable is free from electromagnetic interference and has good insulativity; the optical fiber is corrosion resistant and safe to use; has high sensitivity; the optical fiber is portable; the number of measurement objects is large; the influence on the measured substances is small; the reusability is strong; the networking is convenient; the price is low; can be applied to the environment of high temperature, high pressure and high electromagnetism.
The optical fiber sensing technology can be divided into point type optical fiber sensing, quasi-distributed optical fiber sensing and distributed optical fiber sensing according to different working modes. The point type optical fiber sensing can only measure information at a sensing point, and other optical fibers are only used as transmission media of signals, so that although single-point measurement meets performance requirements of high resolution, high sensitivity and the like at the sensing point, information of an external environment at a certain point can only be measured, and the requirements of actual engineering are difficult to meet. The quasi-distributed optical fiber sensor generally comprises an optical fiber sensor array, a plurality of multiplexing optical fiber sensors and the like, and information detection in a certain range is realized through multi-point coverage. With the advent of Optical Time Domain Reflectometry (OTDR) technology, distributed optical fiber sensor technology has been rapidly developed, which can continuously sense measured values (temperature, pressure, stress, etc.) along the length direction of an optical fiber by using the characteristics of light wave transmitted in the optical fiber. And can realize continuous detection, and has higher cost performance and practicability compared with single-point and quasi-distributed optical fiber sensing technologies. With the development of social economy, many engineering projects, such as oil and gas pipelines, dam reservoirs, underground exploration and the like, need to realize the measurement of temperature and other external parameters such as strain, vibration and the like. The current methods for measuring temperature and strain mainly include: (1) the simultaneous measurement of temperature and strain is performed based on the raman scattering and brillouin frequency shift strain modes. The sensing mechanism is that the characteristic that spontaneous Raman scattering is sensitive to temperature only is utilized, temperature information distributed on the optical fiber along the line is measured through a Raman optical fiber sensing system, Brillouin frequency shift containing temperature and strain information is measured through the Brillouin optical fiber sensing system, and then strain information distributed on the optical fiber along the line can be calculated. At present, the temperature measurement precision is +/-1.5 ℃ and the strain measurement precision is +/-50 mu epsilon within the distance range of 25 km. The method has the advantages that the error introduced by the method is small, and the measurement precision is relatively high. However, the structure of the measuring system is complicated, the cost is high, and a double light source is required to replace a single light source for each measurement, so that the stability of the measurement is reduced. (2) A method combining rayleigh scattering and raman scattering measurements. The sensing mechanism is an OTDR technology combining Rayleigh scattering and spontaneous Raman scattering, the method utilizes a laser with narrow line width to provide a coherent light source for an OTDR system, simultaneously, the line width is too narrow to generate a nonlinear effect easily, the nonlinear effect can be effectively avoided by modulating the amplitude of a pulse, and the pulse with higher power can be modulated for the R-OTDR system to improve the signal-to-noise ratio of a Raman scattering signal. When the external temperature and the vibration change are demodulated, the Raman scattering generated by the high-power pulse light is used for temperature demodulation, and the Rayleigh scattering generated by the low-power pulse light is used for vibration demodulation according to the high-power and low-power detection light pulses continuously generated by the acousto-optic modulator. Because the vibration is a dynamic signal which changes rapidly and the temperature is a slowly-changing signal, the repetition frequency of the vibration detection pulse is increased by using the high-low power pulse modulation method at the cost of reducing the repetition frequency of the temperature detection pulse, so that the frequency response range of the vibration measurement is not influenced, and the requirement of the temperature measurement can be met. Vibration measurement with the spatial resolution of 5.8m and the vibration frequency of 1kHz and 10kHz is realized on a 1.2km sensing optical fiber, and temperature measurement with the spatial resolution of 4.8m and the temperature measurement precision of +/-3 ℃ is realized. However, the device is easily affected by modulation pulse, and the signal-to-noise ratio of the acquired signal can be seriously affected by the instability of pulse parameters. In addition, the performance of the method in the aspects of sensitivity, response speed, measurement accuracy, measurement distance and the like needs to be improved. In addition, the method also has dual parameter measurement based on fiber grating, such as fiber grating method, dual wavelength grating method, grating pair method with different cladding diameters, fiber core doping method, and fiber grating F-P cavity method, although the accuracy of measuring the temperature and strain of one point is high, these methods are difficult to realize long distance sensing. The measurement of double parameters is also realized by software, such as genetic algorithm, neural network algorithm, simplex algorithm and the like. But the corresponding speed is slow, the precision is not high enough, and the data demodulation has certain difficulty. A new sensing means is required to achieve the measurement of the dual parameters.
Disclosure of Invention
Aiming at the defects of the prior art, the invention provides a distributed temperature and strain double-parameter sensing device based on a backscattering enhanced optical fiber, aiming at enhancing a backscattering anti-Stokes optical signal, a Rayleigh scattering optical signal and a Stokes optical signal by utilizing a single-mode optical fiber with a plurality of scattering enhanced points, improving the signal-to-noise ratio of a system and solving the problem of long-distance sensing.
The invention provides a backward scattering-based enhanced optical fiber distributed temperature and strain double-parameter sensing device, which comprises: the device comprises a narrow linewidth light source, a 99:1 coupler, an acousto-optic modulation module, a driver, an erbium-doped fiber amplifier EDFA, a circulator, a Raman wavelength division multiplexer, single-mode fibers with a plurality of scattering enhancement points, a 1550nm filter, a 2 x 2 coupler, a Stokes photodetector APD, an anti-Stokes photodetector APD, a Rayleigh photodetector BPD, a data acquisition card and an upper computer; the output end of the narrow linewidth light source is connected with the input end of a 99:1 coupler, the output end of the 99:1 coupler comprises a first port which accounts for 99% of an optical signal of the input end and a second port which accounts for 1% of the optical signal of the input end, wherein the first port is connected with the input end of the acousto-optic modulation module, and the second port is connected with one end of a 2 x 2 coupler; the output end of the driver is connected with the power supply end of the acousto-optic modulation module, and the input end of the erbium-doped fiber amplifier EDFA is connected with the output end of the acousto-optic modulator; the circulator comprises a first port, a second port and a third port; the first port is connected with the output end of an erbium-doped fiber amplifier (EDFA), the second port is connected with the 1550nm end of the Raman wavelength division multiplexer, and the third port is connected with the input end of the 1550nm filter; the Raman wavelength division multiplexer comprises four ports of 1550nm, 1650nm, 1450nm and COM, an optical pulse signal sent by the second port of the circulator enters the 1550nm port of the Raman wavelength division multiplexer and then is sent out to the sensing optical fiber by the COM port of the Raman wavelength division multiplexer, and the 1650nm port and the 1450nm port of the Raman wavelength division multiplexer are respectively connected with the input end of the Stokes photo detector APD and the input end of the anti-Stokes photo detector APD; the output end of the 1550nm filter and the second end of the 99:1 coupler, which accounts for 1% of the optical signal at the input end, are respectively connected with two input ends of a 2 × 2 coupler, and two output ends of the 2 × 2 coupler are respectively connected with two input ends of a Rayleigh photodetector BPD; the input end of the data acquisition card is connected with the output end of the Rayleigh photodetector BPD, the output end of the Stokes photodetector APD and the output end of the anti-Stokes photodetector APD; the input end of the upper computer is connected with the output end of the data acquisition card.
Further, in operation, the narrow linewidth light source provides an optical signal; the 99:1 coupler divides the optical signal at the input end into two paths of optical signals of 99: 1; the acousto-optic modulation module modulates the narrow-linewidth light source into pulsed light; the driver provides drive for the acousto-optic modulator; the erbium-doped fiber amplifier EDFA amplifies the light source signal; the circulator feeds the light sent by the first port to the second port for output, the light entering the second port is sent to a 1550nm end of the Raman wavelength division multiplexer, then enters the sensing optical fiber from a COM end of the Raman wavelength division multiplexer, backward Stokes light, anti-Stokes light and Rayleigh light scattering are generated in the sensing optical fiber, and the backward scattered light respectively enters a 1650nm port, a 1450nm port and a 1550nm port of the Raman wavelength division multiplexer; rayleigh scattering light which is back-scattered from a 1550 port enters two ports of a circulator and is sent out to three ports of the circulator, light emitted from the three ports of the circulator is sent out to a 1550nm filter for filtering, signal light is emitted out of the 1550nm filter and enters two input ends of a 2 multiplied by 2 coupler in sequence with the 99:1 coupler accounting for 1% of optical signals at the input ends to form coherent light beat frequency signals; two beams of signal light enter a Rayleigh light detector BPD through the output of a 2 multiplied by 2 coupler and are converted into electrical signals; then, the Stokes light and the anti-Stokes light which are scattered back respectively enter a 1650nm port and a 1450nm port of the Raman wavelength division multiplexer, sequentially enter a Stokes photo-detector APD and an anti-Stokes photo-detector APD for light amplification, convert light signals into electric signals, and acquire data of the three beams of light by using a data acquisition card; and processing the data and demodulating the change parameters of the external temperature and the stress through an upper computer.
Further, the sensing fiber is a single mode fiber with backscattering enhancement; the ultraviolet light is utilized to carry out continuous exposure treatment on the single-mode optical fiber to form a plurality of scattering enhancement points, and the enhancement points enable anti-Stokes light signals, Rayleigh scattering light signals and Stokes light signals which are scattered backwards by the optical fiber to have an enhanced effect, so that the signal-to-noise ratio of the system is improved.
The intensity or phase of the backscattered light generated according to any point in the optical fiber is related to the strain or temperature variation at the point, that is, the backscattered light at the points carries the information amount of the external temperature or strain at the point, and the scattering points are located at different positions on the optical fiber.
The invention also provides a demodulation method based on the backscatter enhanced optical fiber distributed temperature and strain double-parameter sensing device, which comprises the following steps of:
(1) collecting the light intensity data of Stokes light and anti-Stokes light in the backward scattering light generated by any position point in the sensing optical fiber, and respectively measuring the known temperature T0Lower anti-stokes light intensity to stokes light intensity ratio Fas-s(T0) And the ratio F of the anti-Stokes light intensity to the Stokes light intensity at the pointas-s(T), and then Fas-s(T) and Fas-s(T0) Dividing, and obtaining the measured temperature T through mathematical transformation;
(2) obtaining an external temperature variation according to the measured temperature and the initial temperature of the sensing optical fiber at the position, and obtaining a phase variation caused only by the temperature variation according to the external temperature variation and a backward Rayleigh scattering light phase temperature coefficient;
(3) the Rayleigh scattering light in the backward scattering light generated by each point in the sensing optical fiber is sequentially coherent with intrinsic light accounting for 1% of the total light source to form a coherent light beat frequency signal, and the beat frequency signals corresponding to the backward Rayleigh scattering light signals of two adjacent points in the optical fiber are subjected to cross-correlation operation to obtain the displacement of the position of a correlation peak on a time domain; obtaining the total phase change of the backward Rayleigh scattering light signal under the combined action of the outside temperature and the strain according to the position displacement of the correlation peak on the time domain;
(4) the total phase change of the backward Rayleigh scattering light signal caused by the combined action of the outside temperature and the strain by adopting phase decoupling
Subtracting the phase change of the backward Rayleigh scattering light signal caused only by the temperature change
Obtaining the variation of the phase of the backward Rayleigh scattering light signal at the point caused by the strain only
Solving the external strain according to the corresponding relation between the external strain and the phase change amount; and finally, realizing the distributed measurement of the absolute temperature stress double parameters.
Further, in step (1), the measured temperature T is represented by the following formula
Obtaining; wherein T is the measured temperature, T0For known temperature, k is Boltzmann constant, h is Planck constant, c is speed of light, Δ ν Raman frequency shift, Fas-s(T) is the ratio of the anti-Stokes light intensity to the Stokes light intensity at the measured temperature T, Fas-s(T0) Is a known temperature T0Lower anti-stokes light intensity andstokes light intensity ratio; since the light intensity of the anti-stokes light is sensitive to the temperature change of the external environment and is not basically influenced by the stress change, the temperature T at the point is demodulated to be the absolute temperature.
Further, in step (2), the outside temperature change amount Δ T ═ T-TFirst stageAmount of phase change
Wherein, Delta T is the variation of the outside temperature, TFirst stageTo sense the initial temperature at this point of the fiber, T is the measured temperature,
for the phase change caused only by the temperature change, epsilonTIs the phase temperature coefficient of the backward Rayleigh scattering light.
Further, in step (3), the amount of displacement of the position of the correlation peak in the time domain
Total phase change of backward Rayleigh scattering light signal
Where Δ t is the displacement of the correlation peak position, f is the frequency of the coherent optical beat signal, εT,εεThe phase temperature coefficient and the phase strain coefficient of the backward Rayleigh scattering light are respectively, and the delta T and the delta epsilon are respectively the external temperature variation and the external strain.
Further, in step (4), the phase decoupling formula
Wherein
Is the amount of phase change caused only by the amount of temperature change.
Further, in step (4), the corresponding relationship between the external strain and the phase change amount is:
wherein,
for the phase change of the back-Rayleigh scattered light caused only by external strain, ∈εThe phase strain coefficient of the backward Rayleigh scattering light is shown, and delta epsilon is the external strain quantity.
Compared with the prior art, the technical scheme of the invention has the advantages that the single-mode optical fiber is continuously exposed by utilizing ultraviolet light, so that the sensing optical fiber has a plurality of scattering enhancement points, and the enhancement points enable anti-Stokes optical signals, Rayleigh scattering optical signals and Stokes optical signals which are backscattered by the optical fiber to have an enhanced effect, thereby improving the signal-to-noise ratio of the system. The beneficial effect of long-distance sensing can be achieved. Because the intensity or the phase of the back scattering light generated at any point in the sensing optical fiber is related to the strain or the temperature variation at the point, namely the back scattering light generated at any point in the sensing optical fiber carries the information quantity of the external temperature and the strain at the point, and the scattering light signals are distinguished in the time domain, the strain point or the temperature variation point on the sensing optical fiber can be positioned in space according to the optical time domain reflection technology, and the beneficial effect of high spatial resolution can be achieved. The advantage of high temperature sensitivity can be obtained because the anti-stokes light intensity at a certain point in the sensing optical fiber is only influenced by the temperature change at the point and is not influenced by the stress change basically, namely, the ratio of the anti-stokes light intensity to the stokes light intensity at the point is only related to the temperature change amount at the point, and the absolute temperature of the point is solved by the ratio of the anti-stokes light intensity to the stokes light intensity at the point and the ratio of the anti-stokes light intensity to the stokes light intensity under the determined temperature. Due to the wavelength division multiplexing technology, the Rayleigh scattering light signals and Stokes light signals which are back scattered can be quickly and accurately distinguished from each other, and the beneficial effect of high response speed can be achieved. Due to the temperature strain decoupling technology, the phase change caused by temperature action and the phase change caused by strain can be effectively distinguished, the measurement of temperature stress double parameters is realized, and the beneficial effect of small measurement error can be obtained.
Drawings
Fig. 1 is a schematic structural diagram of a distributed temperature and strain bi-parametric sensing device according to an embodiment of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
The single-mode optical fiber is subjected to ultraviolet continuous exposure treatment to form a plurality of scattering enhancement points, and the enhancement points enable anti-Stokes light signals, Rayleigh scattering light signals and Stokes light signals which are scattered backwards by the optical fiber to have an enhanced effect, so that the signal-to-noise ratio of the system is improved. Therefore, the problem of long-distance sensing can be solved; the intensity or phase of the backscattered light generated at any point in the sensing optical fiber is related to the strain or temperature variation at the point, that is, the backscattered light generated at any point in the sensing optical fiber carries the information quantity of the external temperature and the strain at the point, that is, the backscattered light at the points carries the information quantity of the external temperature or the strain at the point, and the scattering points are located at different positions on the optical fiber, so that the backscattered light has time difference, the collected scattered light signals do not interfere with each other in a time domain and correspond to the scattering points on the optical fiber, and the strain point or the temperature variation point outside the optical fiber can be spatially located according to an optical time domain reflection technology.
And demodulating the external absolute temperature of a certain point by utilizing the ratio of the anti-Stokes light intensity to the Stokes light intensity at the certain point in the sensing optical fiber and the ratio of the anti-Stokes light intensity to the Stokes light intensity at the certain temperature, and calculating the phase change only corresponding to the temperature change according to the sensitivity of the phase of backward Rayleigh scattering light to the temperature to obtain the phase change amount only caused by the temperature change amount. The reference light accounting for 1% of the total light source intensity and the signal light backscattered from any position in the sensing optical fiber are coherent by a 2 x 2 coupler to form coherent light beat frequency signals, and the peak value of the signal intensity after each coherent light beat frequency can be obtained in a BPD detector through a coherent detection technology. And then performing cross-correlation operation on beat signals corresponding to the backscattered light signals of two adjacent points, wherein the position of a correlation peak generates certain displacement along with the change of external temperature or stress, calculating the displacement of the position of the correlation peak to obtain the total phase change amount of the optical signal caused by the combined action of temperature and strain, and according to the temperature strain decoupling technology, subtracting the phase change amount of the optical signal caused by the temperature change amount before by using the total phase change amount to obtain the phase change amount caused by the strain at the point. And finally, realizing the distributed measurement of the absolute temperature stress double parameters. Compared with the traditional temperature measuring instrument and the traditional strain measuring instrument, the strain gauge has the characteristics of long measuring distance, high spatial resolution, high sensitivity, high response speed, small error, higher cost performance and the like.
As shown in fig. 1, the present invention provides a distributed temperature/strain dual-parameter sensing device based on a backscattering enhanced optical fiber, comprising: a narrow linewidth light source 2, a 99:1 coupler 3, an acousto-optic modulation module (AOM)4, a driver 5, an erbium-doped fiber amplifier EDFA6, a circulator 7, a Raman wavelength division multiplexer 8, a sensing fiber 9 with continuous scattering enhancing points, a 1550nm filter 10, a 2 x 2 coupler 11, a Stokes photodetector APD12, an anti-Stokes photodetector APD13, a Rayleigh photodetector BPD14, a data acquisition card 15 and an upper computer 16; the output end of the narrow linewidth light source 2 is connected with the input end of the 99:1 coupler 3, and the narrow linewidth light source 2 is used for providing an optical signal; the output end of the 99:1 coupler 3 comprises a first port which accounts for 99% of the optical signal at the input end and a second port which accounts for 1% of the optical signal at the input end, wherein the first port is connected with the input end of the acousto-optic modulation module 4, the second port is connected with one end of the 2 x 2 coupler 11, and the 99:1 coupler 3 is used for dividing the optical signal at the input end into two paths of optical signals of 99: 1; the acousto-optic modulation module 4 is used for modulating the narrow linewidth light source 2 into pulsed light; the output end of the driver 5 is connected with the power supply end of the acousto-optic modulation module 4, and the driver 5 is used for driving the acousto-optic modulator 4; the input end of the erbium-doped fiber amplifier EDFA6 is connected to the output end of the acousto-optic modulator 4, and the erbium-doped fiber amplifier EDFA6 is used for amplifying light source signals; the circulator 7 includes a first port, a second port, and a third port; the first port is connected with the output end of an erbium-doped fiber amplifier EDFA6, the second port of the circulator is connected with the 1550nm end of the Raman wavelength division multiplexer 8, the third port of the circulator 7 is connected with the input end of the 1550nm filter 10, the circulator 7 is used for feeding light sent in by the first port to the second port for output, and light sent in by the second port is sent to the third port and sent out to the filter 10; the raman wavelength division multiplexer 8 comprises four ports of 1550nm, 1650nm, 1450nm and COM, an optical pulse signal sent by the second port of the circulator 7 enters the 1550nm port of the raman wavelength division multiplexer and then is sent out to the sensing optical fiber 9 by the COM port of the raman wavelength division multiplexer 8, and the 1650nm port and the 1450nm port are respectively connected with the input end of the stokes photo detector APD12 and the input end of the anti-stokes photo detector APD 13. The output end of the filter 10 and one end of the 99:1 coupler 3, which accounts for 1% of the optical signal at the input end, are respectively connected with two input ends of the 2 × 2 coupler 11, two output ends of the 2 × 2 coupler 11 are respectively connected with two input ends of a rayleigh photodetector BPD14, and the rayleigh photodetector BPD14 is used for converting the optical signal into an electrical signal. The input end of the data acquisition card 15 is connected with the output end of the Rayleigh photodetector BPD14, the output end of the Stokes photodetector APD12 and the output end of the anti-Stokes photodetector APD 13; for data acquisition. The input end of the upper computer 16 is connected with the output end of the data acquisition card 15; the device is used for processing data and demodulating the change parameters of the external temperature and the stress.
In the embodiment of the invention, the sensing fiber 9 with the continuous scattering enhancing point is a single-mode fiber with ultraviolet sensitization; the ultraviolet light is utilized to carry out continuous exposure treatment on the single-mode optical fiber to form a plurality of scattering enhancement points, and the enhancement points enable anti-Stokes light signals, Rayleigh scattering light signals and Stokes light signals which are scattered backwards by the optical fiber to have an enhanced effect, so that the signal-to-noise ratio of the system is improved.
In the embodiment of the invention, a narrow linewidth pulse signal with the wavelength of 1550nm is sent out by the raman wavelength division multiplexer 8 to the sensing optical fiber 9 with the continuous scattering enhancement point, and backward rayleigh scattering, stokes light and anti-stokes light are generated in the sensing optical fiber 9. Since the central wavelengths of the three scattered lights are 1550nm, 1650nm and 1450nm, the three scattered lights can be separated by 1550nm port, 1650nm port and 1450nm port of the raman wavelength division multiplexer 8, the stokes light and the anti-stokes light are received by the APD detectors 12 and 13, the backward rayleigh scattered light is received by the BPD detector 14, and the three scattered light signals are collected and received at the same time.
In the embodiment of the present invention, the intensity or phase of the backscattered light generated at any point in the sensing fiber 9 is related to the strain or the change amount of the temperature at the point, that is, the backscattered light at the point carries the information amount of the temperature or the strain at the point, and since the scattered light signals backscattered from each point are distinguished in the time domain, the strain point or the temperature change point on the sensing fiber 9 can be spatially located according to the optical time domain reflection technique; the temperature is measured by utilizing a Stokes light detector APD12 and an anti-Stokes light detector APD13 to respectively carry out light amplification on Stokes light and anti-Stokes light scattered back by a sensing optical fiber and convert optical signals into electric signals, because the intensity of the anti-Stokes light is sensitive to the temperature change of the external environment, the absolute temperature of the external environment of a certain point in the sensing optical fiber is demodulated by utilizing the ratio of the anti-Stokes light intensity to the Stokes light intensity of the point and determining the ratio of the anti-Stokes light intensity to the Stokes light intensity under the temperature, the phase change corresponding to the temperature change is calculated according to the sensitivity of the phase of the backward Rayleigh scattering light to the temperature, and the phase change of the backward Rayleigh scattering light caused only by the temperature change is obtained. Light which is 1% of the total light source and is separated from the narrow-linewidth light source 2 by the 2 x 2 coupler 11 is coherent with backward Rayleigh scattering light at any position in the sensing optical fiber 9 to form coherent light beat frequency signals, and the peak value of the signal intensity after each coherent light beat frequency can be obtained in the BPD detector 14 through a coherent detection technology. When strain and temperature change exist between any two points in the sensing optical fiber 9, cross-correlation operation is performed by using beat signals corresponding to backward Rayleigh scattering light signals of the two points, the position of a correlation peak generates certain displacement along with external strain and temperature change, the displacement of the position of the correlation peak is calculated to obtain the total change amount of the backward Rayleigh scattering light phase under the action of the external temperature and the strain, the phase change caused by temperature action is distinguished from the phase change caused by strain by a decoupling method, the phase change caused only by the temperature change before is subtracted from the total phase change to obtain the phase change caused only by the external strain action, therefore, the change of the optical signal phase caused by the external temperature change can be regarded as zero, and the external strain is solved according to the corresponding relation between the external strain and the optical phase change. And finally, realizing the distributed measurement of the absolute temperature stress double parameters.
Finally, LabVIEW software is used on the upper computer 16 to respectively perform corresponding programming processing on a Stokes light intensity and anti-Stokes light intensity ratio demodulation temperature method, a backward Rayleigh scattering light coherent detection method, beat frequency signal cross-correlation operation, phase demodulation and temperature strain decoupling technology, so that the processing of signals is realized, and finally, distributed measurement of absolute temperature stress double parameters can be achieved.
The invention also provides a demodulation method based on the backscatter enhanced optical fiber distributed temperature and strain double-parameter sensing device, which comprises the following steps of:
(1) collecting the light intensity data of Stokes light and anti-Stokes light in the backward scattering light generated by any position point in the sensing optical fiber, and respectively measuring the known temperature T0Lower anti-stokes light intensity to stokes light intensity ratio Fas-s(T0) And the ratio F of the anti-Stokes light intensity to the Stokes light intensity at the pointas-s(T), and then Fas-s(T) and Fas-s(T0) Dividing, and obtaining the measured temperature T through mathematical transformation;
wherein the measured temperature T is represented by the following formula
Obtaining; t is the measured temperature, T0For known temperature, k is Boltzmann constant, h is Planck constant, c is speed of light, Δ ν Raman frequency shift, Fas-s(T) is the ratio of the anti-Stokes light intensity to the Stokes light intensity at the measured temperature T, Fas-s(T0) Is a known temperature T0The ratio of lower anti-stokes light intensity to stokes light intensity; since the light intensity of the anti-stokes light is sensitive to the temperature change of the external environment and is not basically influenced by the stress change, the temperature T at the point is demodulated to be the absolute temperature.
(2) Obtaining an external temperature variation according to the measured temperature and the initial temperature of the sensing optical fiber at the position, and obtaining a phase variation caused only by the temperature variation according to the external temperature variation and a backward Rayleigh scattering light phase temperature coefficient;
external temperature variation delta T ═ T-TFirst stageAmount of phase change
Wherein, Delta T is the variation of the outside temperature, TFirst stageTo sense the initial temperature at this point of the fiber, T is the measured temperature,
for the phase change caused only by the temperature change, epsilonTIs the phase temperature coefficient of the backward Rayleigh scattering light.
(3) The Rayleigh scattering light in the backward scattering light generated by each point in the sensing optical fiber is sequentially coherent with intrinsic light accounting for 1% of the total light source to form a coherent light beat frequency signal, and the beat frequency signals corresponding to the backward Rayleigh scattering light signals of two adjacent points in the optical fiber are subjected to cross-correlation operation to obtain the displacement of the position of a correlation peak on a time domain; obtaining the total phase change of the backward Rayleigh scattering light signal under the combined action of the outside temperature and the strain according to the position displacement of the correlation peak on the time domain;
displacement of correlation peak position in time domain
Total phase change of backward Rayleigh scattering light signal
Where Δ t is the displacement of the correlation peak position, f is the frequency of the coherent optical beat signal, εT,εεThe phase temperature coefficient and the phase strain coefficient of the backward Rayleigh scattering light are respectively, and the delta T and the delta epsilon are respectively the external temperature variation and the external strain.
(4) The total phase change of the backward Rayleigh scattering light signal caused by the combined action of the outside temperature and the strain by adopting phase decoupling
Subtracting the phase change of the backward Rayleigh scattering light signal caused only by the temperature change
Obtaining the variation of the phase of the backward Rayleigh scattering light signal at the point caused by the strain only
Then, the external strain is solved; and realizing distributed measurement of double parameters of absolute temperature stress.
Wherein, the phase decoupling formula
Wherein
The phase change of the backward rayleigh scattered light signal is caused only by the temperature change,
in order to cause the phase change of the backward rayleigh scattering light only by the external strain, the corresponding relationship between the external strain and the phase change amount is:
εεthe phase strain coefficient of the backward Rayleigh scattering light is shown, and delta epsilon is the external strain quantity.
It will be understood by those skilled in the art that the foregoing is only a preferred embodiment of the present invention, and is not intended to limit the invention, and that any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the present invention.
Claims (4)
1. A distributed temperature and strain dual-parameter sensing device based on a backscattering enhanced optical fiber is characterized by comprising: the device comprises a narrow linewidth light source (2), a 99:1 coupler (3), an acousto-optic modulation module (4), a driver (5), an erbium-doped fiber amplifier (EDFA) (6), a circulator (7), a Raman wavelength division multiplexer (8), a sensing fiber (9), a 1550nm filter (10), a 2 multiplied by 2 coupler (11), a Stokes photo detector (APD) (12), an anti-Stokes photo detector APD (13), a Rayleigh photo detector BPD (14), a data acquisition card (15) and an upper computer (16);
the output end of the narrow-linewidth light source (2) is connected with the input end of the 99:1 coupler (3), the output end of the 99:1 coupler (3) comprises a first end and a second end, the first end accounts for 99% of an optical signal of the input end, the second end accounts for 1% of the optical signal of the input end, the first end is connected with the input end of the acousto-optic modulation module (4), and the second end is connected with one end of the 2 x 2 coupler (11); the output end of the driver (5) is connected with the power supply end of the acousto-optic modulation module (4), and the input end of the erbium-doped fiber amplifier EDFA (6) is connected with the output end of the acousto-optic modulator (4);
the circulator (7) comprises a first port, a second port and a third port; the first port is connected with the output end of the erbium-doped fiber amplifier EDFA (6), the second port is connected with the 1550nm end of the Raman wavelength division multiplexer (8), and the third port is connected with the input end of a 1550nm filter (10);
the Raman wavelength division multiplexer (8) comprises four ports of 1550nm, 1650nm, 1450nm and COM, an optical pulse signal sent by the second port of the circulator (7) enters the 1550nm port of the Raman wavelength division multiplexer (8) and is sent out to the sensing optical fiber (9) from the COM port of the Raman wavelength division multiplexer (8), and the 1650nm port and the 1450nm port of the Raman wavelength division multiplexer (8) are respectively connected with the input end of the Stokes photo detector APD (12) and the input end of the anti-Stokes photo detector APD (13);
the output end of the 1550nm filter (10) and the second end of the 99:1 coupler (3) which accounts for 1% of the optical signal at the input end are respectively connected with two input ends of a 2 x 2 coupler (11), and two output ends of the 2 x 2 coupler (11) are respectively connected with two input ends of a Rayleigh optical detector BPD (14);
the input end of the data acquisition card (15) is connected with the output end of a Rayleigh photodetector BPD (14), the output end of a Stokes photodetector APD (12) and the output end of an anti-Stokes photodetector APD (13); the input end of the upper computer (16) is connected with the output end of the data acquisition card (15);
the sensing optical fiber (9) is a single-mode optical fiber with backscattering enhancement, and the single-mode optical fiber is continuously exposed by ultraviolet light to form a plurality of scattering enhancement points;
the device adopts the following demodulation method:
(1) collecting the light intensity data of Stokes light and anti-Stokes light in the backward scattering light generated by any position point in the sensing optical fiber, and respectively measuring the ratio F of the anti-Stokes light intensity to the Stokes light intensity at the known temperature T0as-s(T0) And the ratio F of the anti-Stokes light intensity to the Stokes light intensity at the pointas-s(T), and then Fas-s(T) and Fas-s(T0) Dividing, and obtaining the measured temperature T through mathematical transformation;
(2) obtaining an external temperature variation according to the measured temperature and the initial temperature of the sensing optical fiber at the position, and obtaining a phase variation caused only by the temperature variation according to the external temperature variation and a backward Rayleigh scattering light phase temperature coefficient;
(3) the Rayleigh scattering light in the backward scattering light generated by each point in the sensing optical fiber is sequentially coherent with intrinsic light accounting for 1% of the total light source to form coherent light beat frequency signals, and the beat frequency signals corresponding to the backward Rayleigh scattering light signals of two adjacent points in the optical fiber are subjected to cross-correlation operation to obtain the displacement of a correlation peak on the position of a time domain; obtaining the total phase change of the backward Rayleigh scattering light signal under the combined action of the outside temperature and the strain according to the position displacement of the correlation peak on the time domain;
wherein the position of the correlation peak in the time domain is shifted by an amount
Total phase change of backward Rayleigh scattering light signal
Where Δ t is the displacement of the correlation peak position, f is the frequency of the coherent optical beat signal, εT,εεRespectively are backward Rayleigh scattering light phase temperature coefficient and backward Rayleigh scattering light phase strain coefficient, and respectively are outside temperature variation and outside strain
(4) The total phase change of the backward Rayleigh scattering light signal caused by the combined action of the outside temperature and the strain by adopting phase decoupling
Subtracting the phase change of the backward Rayleigh scattering light signal caused only by the temperature change
Obtaining the variation of the phase of the backward Rayleigh scattering light signal at the point caused by the strain only
Solving the external strain according to the corresponding relation between the external strain and the phase change amount; and finally, realizing the distributed measurement of the absolute temperature stress double parameters.
2. The distributed temperature and strain bi-parametric sensing device based on backscattering enhanced fiber as claimed in claim 1, wherein in operation, the narrow linewidth light source (2) provides an optical signal; the 99:1 coupler (3) divides an optical signal at an input end into two paths of optical signals of 99: 1; the acousto-optic modulation module (4) modulates the narrow linewidth light source (2) into pulsed light; the driver (5) provides drive for the acousto-optic modulation module (4); the erbium-doped fiber amplifier EDFA (6) optically amplifies the light source signal; the circulator (7) feeds the light sent by the first port to the second port for output, the light sent by the second port is sent to a 1550nm port of the Raman wavelength division multiplexer (8), and then is sent to the sensing optical fiber (9) from the COM port, backward Stokes light, anti-Stokes light and Rayleigh light scattering occur in the sensing optical fiber (9), and the backward scattered light respectively enters a 1650nm port, a 1450nm port and a 1550nm port of the Raman wavelength division multiplexer; rayleigh scattering light which is back scattered from a 1550nm port enters a two port of a circulator (7) and is sent out to a three port of the circulator (7), light emitted from the three port of the circulator is sent out to a 1550nm filter (10) to be filtered, signal light is emitted from the 1550nm filter (10), and the signal light and a second end, which accounts for 1% of an optical signal at an input end, of a 99:1 coupler (3) sequentially enter two input ends of a 2 x 2 coupler (11) to be coherent to form a coherent light beat frequency signal; two beams of signal light are output through a 2 x 2 coupler (11) to enter a Rayleigh light detector BPD (14) and optical signals are converted into electric signals; then, the Stokes light and the anti-Stokes light which are scattered back respectively enter a 1650nm port and a 1450nm port of the Raman wavelength division multiplexer, sequentially enter a Stokes photo-detector APD (12) and an anti-Stokes photo-detector APD (13) for light amplification, convert light signals into electric signals, and acquire data of the three beams of light by using a data acquisition card (15); the data are processed and the change parameters of the external temperature and the stress are demodulated through an upper computer (16).
3. The distributed temperature and strain bi-parametric sensing device based on backscattering enhanced optical fiber as claimed in claim 2, wherein the intensity or phase of the backscattering light generated at any point in the sensing optical fiber (9) is related to the strain or temperature variation at the point, that is, the backscattering light at the points carries the information of the external temperature or strain at the point, and the scattering points are located at different positions on the optical fiber, and due to the time difference of the backscattering scattered light, the collected scattered light signals do not interfere with each other in the time domain and correspond to the scattering points on the optical fiber, so that the strain point or temperature variation point outside the optical fiber can be spatially located.
4. A method for demodulating a backscatter enhanced fiber distributed temperature and strain bi-parametric sensing device according to any one of claims 1 to 3, comprising the steps of:
(1) collecting the light intensity data of Stokes light and anti-Stokes light in the backward scattering light generated by any position point in the sensing optical fiber, and respectively measuring the known temperature T0Lower anti-stokes light intensity to stokes light intensity ratio Fas-s(T0) And the ratio F of the anti-Stokes light intensity to the Stokes light intensity at the pointas-s(T), and then Fas-s(T) and Fas-s(T0) Dividing, and obtaining the measured temperature T through mathematical transformation;
(2) obtaining an external temperature variation according to the measured temperature and the initial temperature of the sensing optical fiber at the position, and obtaining a phase variation caused only by the temperature variation according to the external temperature variation and a backward Rayleigh scattering light phase temperature coefficient;
(3) the Rayleigh scattering light in the backward scattering light generated by each point in the sensing optical fiber is sequentially coherent with intrinsic light accounting for 1% of the total light source to form coherent light beat frequency signals, and the beat frequency signals corresponding to the backward Rayleigh scattering light signals of two adjacent points in the optical fiber are subjected to cross-correlation operation to obtain the displacement of a correlation peak on the position of a time domain; obtaining the total phase change of the backward Rayleigh scattering light signal under the combined action of the outside temperature and the strain according to the position displacement of the correlation peak on the time domain;
(4) the total phase change of the backward Rayleigh scattering light signal caused by the combined action of the outside temperature and the strain by adopting phase decoupling
Subtracting the phase change of the backward Rayleigh scattering light signal caused only by the temperature change
Obtaining the variation of the phase of the backward Rayleigh scattering light signal at the point caused by the strain only
Solving the external strain according to the corresponding relation between the external strain and the phase change amount; finally realizing distributed measurement of double parameters of absolute temperature stress;
in step (1), the measured temperature T is represented by the following formula
Obtaining; wherein T is the measured temperature, T0For known temperature, k is Boltzmann constant, h is Planck constant, c is speed of light, Δ ν Raman frequency shift, Fas-s(T) is the ratio of the anti-Stokes light intensity to the Stokes light intensity at the measured temperature T, Fas-s(T0) Is a known temperature T0The ratio of lower anti-stokes light intensity to stokes light intensity; the light intensity of the anti-Stokes light is sensitive to the temperature change of the external environment and basically not influenced by the stress change, so that the temperature T of the point is demodulated to be absolute temperature;
in step (2), the variation Δ T of the outside temperature is | T-TFirst stageAmount of phase change
Wherein, Delta T is the variation of the outside temperature, TFirst stageTo sense the initial temperature at this point of the fiber, T is the measured temperature,
for the phase change caused only by the temperature change, epsilonTIs the phase temperature coefficient of the backward Rayleigh scattering light;
in step (3), the amount of displacement of the position of the correlation peak in the time domain
Total phase change of backward Rayleigh scattering light signal
Where Δ t is the displacement of the correlation peak position, f is the frequency of the coherent optical beat signal, εT,εεRespectively representing backward Rayleigh scattering light phase temperature coefficient and backward Rayleigh scattering light phase strain coefficient, wherein delta T and delta epsilon respectively represent external temperature variation and external strain;
in step (4), the phase decoupling formula
Wherein
Is a phase change amount caused only by a temperature change amount;
the corresponding relation between the external strain and the phase change amount is as follows:
wherein,
for the phase change of the back-Rayleigh scattered light caused only by external strain, ∈εThe phase strain coefficient of the backward Rayleigh scattering light is shown, and delta epsilon is the external strain quantity.
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