CN114705239A - Temperature and stress demodulation method, device and system based on Brillouin optical fiber sensing - Google Patents
Temperature and stress demodulation method, device and system based on Brillouin optical fiber sensing Download PDFInfo
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- CN114705239A CN114705239A CN202210273355.2A CN202210273355A CN114705239A CN 114705239 A CN114705239 A CN 114705239A CN 202210273355 A CN202210273355 A CN 202210273355A CN 114705239 A CN114705239 A CN 114705239A
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- 239000013307 optical fiber Substances 0.000 title claims abstract description 68
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- 238000003199 nucleic acid amplification method Methods 0.000 claims description 3
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- 230000003595 spectral effect Effects 0.000 claims description 2
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- 230000010363 phase shift Effects 0.000 claims 1
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- G—PHYSICS
- G01—MEASURING; TESTING
- 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
- G01D21/00—Measuring or testing not otherwise provided for
- G01D21/02—Measuring two or more variables by means not covered by a single other subclass
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- G—PHYSICS
- G01—MEASURING; TESTING
- 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
- 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
Abstract
The invention discloses a demodulation method, a demodulation device and a demodulation system of temperature and stress based on Brillouin optical fiber sensing, which comprise a narrow-spectrum light source; light emitted by the narrow-spectrum light source is output through the coupler 1, one part of light is used as reference light, the other part of light is modulated into pulse light through EOM, the pulse light is amplified through an optical amplifier EDFA1, spontaneous heat radiation noise is filtered by the fiber grating 1 and then is injected into the port 1 of the circulator 2, the pulse light is totally reflected by the fiber grating 2 through the port 2 and is output from the port 3, and then the pulse light enters the sensing optical fiber; the back scattering light generated by the light during propagation is output from the port 4 of the circulator 2, and then is filtered by the optical amplifier EDFA2 and the fiber grating 3 to remove the self-heating radiation noise, and is detected in the photodetector 1 in a coherent manner with the reference light. While the frequencies of the two lasers are continuously adjusted, the frequency difference corresponding to the maximum energy transfer in each small section of the optical fiber can be determined by detecting the power of the continuous light coupled out from one end of the optical fiber, so that the temperature information can be obtained.
Description
Technical Field
The invention relates to the technical field of optical fiber sensing, in particular to a temperature and stress demodulation method, device and system based on Brillouin optical fiber sensing.
Background
The optical fiber sensing technology starts in 1977 and is rapidly developed along with the development of the optical fiber communication technology, and the optical fiber sensing technology is an important mark for measuring the informatization degree of a country; the optical fiber sensing technology is widely applied to the fields of military affairs, national defense, aerospace, industrial and mining enterprises, energy environmental protection, industrial control, medicine and health, metering test, building, household appliances and the like, and has a wide market; there are hundreds of fiber optic sensing technologies in the world, and physical quantities such as temperature, pressure, flow, displacement, vibration, rotation, bending, liquid level, speed, acceleration, sound field, current, voltage, magnetic field and radiation realize sensing with different performances.
The spontaneous Brillouin backscattering signal is very weak and contains a large amount of random noise and phase noise, and the temperature and stress measurement precision and the measurement range which can be achieved by the Brillouin optical fiber sensing system are limited. Therefore, a demodulation method, device and system based on the temperature and stress of the Brillouin optical fiber sensing are provided to solve the problems.
Disclosure of Invention
A demodulation method, a device and a system based on temperature and stress sensed by Brillouin optical fiber comprise a narrow-spectrum light source;
light emitted by the narrow-spectrum light source is output through the coupler 1, one part of light is used as reference light, the other part of light is modulated into pulse light through EOM, the pulse light is amplified through an optical amplifier EDFA1, spontaneous heat radiation noise is filtered by the fiber grating 1 and then is injected into the port 1 of the circulator 2, the pulse light is totally reflected by the fiber grating 2 through the port 2 and is output from the port 3, and then the pulse light enters the sensing optical fiber; the back scattering light generated by the light during the propagation is output from the port 4 of the circulator 2, and then self-heating radiation noise is filtered by the optical amplifier EDFA2 and the fiber grating 3, and is subjected to coherent detection with the reference light in the photoelectric detector 1; in order to ensure that the polarization states of the two paths of light are well matched, the PC is added into a reference light path to disturb the linear polarization state of the light signal, the electric signal output by the photoelectric detector 1 only comprises a Brillouin frequency shift signal, and direct current and second harmonic components are filtered.
Further, light emitted by the wide-spectrum light source is transmitted by the fiber grating 2, then is output from the port 3 of the circulator 2, and is injected into the sensing fiber through the coupler 2, and rayleigh scattered light is reflected by the splitting ratio of 95: the coupler 2 of 5 enters the photoelectric detector 2, and the signal is analyzed and processed by using a data acquisition and processing unit.
Further, by measuring the frequency shift and intensity of the brillouin scattered light along the length direction of the optical fiber, temperature and strain information of the optical fiber can be obtained, and the changes of brillouin frequency shift and intensity caused by temperature and strain can be expressed by a matrix as follows:
in the formula, VVB represents the frequency shift of brillouin scattering, VPB represents the intensity of brillouin scattering, CvBz and CvBT are respectively the strain and temperature coefficient of brillouin scattering frequency shift, CPBz and CPBT are respectively the strain and temperature coefficient of brillouin scattering intensity, Vz represents the strain suffered by the optical fiber, and VT represents the temperature of the optical fiber.
Further, the intensity of brillouin scattering light is also affected by temperature and strain, and is given by the following formula:
wherein, Δ PB; the change of the Brillouin intensity is shown as delta T, the change of the temperature is shown as delta epsilon, the change of the strain is shown as delta epsilon, the strain coefficient of the Brillouin intensity is shown as CP epsilon, and the temperature coefficient of the Brillouin intensity is shown as CPT.
Further, the quantitative and qualitative relations between the frequency shift, the intensity, the temperature and the strain of the brillouin scattering are established as follows:
vB＝vB0+CvTΔT+CvεΔε
PB＝PB0+CPT△T+CPεΔε
wherein VBO and PBO are respectively brillouin shift and power at a reference temperature and strain; Δ T and Δ ∈ are the amount of change in temperature and strain, respectively; CVT, CV epsilon, CPT and CP epsilon are respectively the temperature and strain coefficients of Brillouin frequency shift and power.
Further, in OTDR, when pulsed light is transmitted in an optical fiber, backscattered light generated by rayleigh scattering can be detected at a pulsed light transmitting end of the optical fiber, a time delay between the backscattered light and the pulsed light providing a measure of the optical fiber position information, and an intensity of the backscattered light providing a measure of the optical fiber attenuation.
Furthermore, the tunable laser at both ends of the optical fiber respectively injects a pulse light (pump light) and a continuous light (probe light) into the sensing optical fiber, when the frequency difference between the pump light and the probe light is equal to the brillouin frequency shift in a certain region of the optical fiber, a brillouin amplification effect, i.e., stimulated brillouin effect (SBS), is generated in the region, and the two light beams are energy-transferred with each other.
Further, the EOM is optically modulated by an electro-optic modulator.
Further, the PC is a polarization controller.
Further, signals of different frequency components of the brillouin spectrum sequentially pass through the band-pass filter, lorentz fitting is carried out on the signals of different frequencies output by the down converter, the frequency corresponding to the maximum point of the spectrum amplitude is brillouin frequency shift of the scattering point, and brillouin scattering intensity is obtained through spectrum integration.
Through the embodiment of the invention, the temperature and the strain are simultaneously measured by measuring the Brillouin frequency shift and the strength, and because the Brillouin frequency shift and the small-range temperature change have a linear relation, the frequency of the two lasers is continuously adjusted, and meanwhile, the frequency difference corresponding to the maximum energy transfer on each small section of the optical fiber can be determined by detecting the power of the continuous light coupled from one end of the optical fiber, so that the temperature information is obtained, and the distributed measurement is realized.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to these drawings without inventive exercise.
Fig. 1 is a flow chart of a brillouin optical fiber sensing system according to an embodiment of the present invention;
fig. 2 is a basic block diagram of an optical fiber sensing system according to an embodiment of the present invention.
Detailed Description
In order to make the technical solutions of the present invention better understood, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
It should be noted that the terms "first," "second," and the like in the description and claims of the present invention and in the drawings described above are used for distinguishing between similar elements and not necessarily for describing a particular sequential or chronological order. It is to be understood that the data so used may be interchanged under appropriate circumstances in order to facilitate the description of the embodiments of the invention herein. Furthermore, the terms "comprises," "comprising," and "having," and any variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, system, article, or apparatus that comprises a list of steps or elements is not necessarily limited to those steps or elements expressly listed, but may include other steps or elements not expressly listed or inherent to such process, method, article, or apparatus.
In the present invention, the terms "upper", "lower", "left", "right", "front", "rear", "top", "bottom", "inner", "outer", "center", "vertical", "horizontal", "lateral", "longitudinal", and the like indicate an orientation or positional relationship based on the orientation or positional relationship shown in the drawings. These terms are used primarily to better describe the invention and its embodiments and are not intended to limit the indicated devices, elements or components to a particular orientation or to be constructed and operated in a particular orientation.
Moreover, some of the above terms may be used to indicate other meanings besides the orientation or positional relationship, for example, the term "on" may also be used to indicate some kind of attachment or connection relationship in some cases. The specific meanings of these terms in the present invention can be understood by those skilled in the art as appropriate.
Furthermore, the terms "mounted," "disposed," "provided," "connected," and "sleeved" are to be construed broadly. For example, it may be a fixed connection, a removable connection, or a unitary construction; can be a mechanical connection, or an electrical connection; may be directly connected, or indirectly connected through intervening media, or may be in internal communication between two devices, elements or components. The specific meanings of the above terms in the present invention can be understood by those of ordinary skill in the art according to specific situations.
It should be noted that the embodiments and features of the embodiments may be combined with each other without conflict. The present invention will be described in detail below with reference to the embodiments with reference to the attached drawings.
Referring to fig. 1-2, a demodulation method, apparatus and system based on temperature and stress sensed by a brillouin optical fiber includes a narrow spectrum light source;
light emitted by the narrow-spectrum light source is output through the coupler 1, one part of light is used as reference light, the other part of light is modulated into pulse light through EOM, the pulse light is amplified through an optical amplifier EDFA1, spontaneous heat radiation noise is filtered by the fiber grating 1 and then is injected into the port 1 of the circulator 2, the pulse light is totally reflected by the fiber grating 2 through the port 2 and is output from the port 3, and then the pulse light enters the sensing optical fiber; the back scattering light generated by the light during the propagation is output from the port 4 of the circulator 2, and then self-heating radiation noise is filtered by the optical amplifier EDFA2 and the fiber grating 3, and is subjected to coherent detection with the reference light in the photoelectric detector 1; in order to ensure that the polarization states of the two paths of light are well matched, the PC is added into a reference light path to disturb the linear polarization state of the light signal, the electric signal output by the photoelectric detector 1 only comprises a Brillouin frequency shift signal, and direct current and second harmonic components are filtered.
Further, light emitted by the wide-spectrum light source is transmitted by the fiber grating 2, then is output from the port 3 of the circulator 2, is injected into the sensing fiber through the coupler 2, rayleigh scattered light enters the photoelectric detector 2 through the coupler 2 with the spectral ratio of 95:5, and a data acquisition and processing unit is used for analyzing and processing signals.
Further, by measuring the frequency shift and intensity of the brillouin scattered light along the length direction of the optical fiber, temperature and strain information of the optical fiber can be obtained, and the changes of brillouin frequency shift and intensity caused by temperature and strain can be expressed by a matrix as follows:
in the formula, VVB represents the frequency shift of brillouin scattering, VPB represents the intensity of brillouin scattering, CvBz and CvBT are respectively the strain and temperature coefficient of brillouin scattering frequency shift, CPBz and CPBT are respectively the strain and temperature coefficient of brillouin scattering intensity, Vz represents the strain suffered by the optical fiber, and VT represents the temperature of the optical fiber.
Further, the intensity of brillouin scattering light is also affected by temperature and strain, and is given by the following formula:
wherein, Δ PB; the change of the Brillouin intensity is shown as delta T, the change of the temperature is shown as delta epsilon, the change of the strain is shown as delta epsilon, the strain coefficient of the Brillouin intensity is shown as CP epsilon, and the temperature coefficient of the Brillouin intensity is shown as CPT.
Further, the quantitative and qualitative relations between the frequency shift, the intensity, the temperature and the strain of the brillouin scattering are established as follows:
vB＝vB0+CvTΔT+CvεΔε
PB＝PB0+CPTΔT+CPεΔε
wherein VBO and PBO are respectively brillouin shift and power at a reference temperature and strain; Δ T and Δ ∈ are the amount of change in temperature and strain, respectively; CVT, CV epsilon, CPT and CP epsilon are respectively the temperature and strain coefficients of Brillouin frequency shift and power.
Further, in OTDR, when pulsed light is transmitted in an optical fiber, backscattered light generated by rayleigh scattering can be detected at a pulsed light transmitting end of the optical fiber, a time delay between the backscattered light and the pulsed light providing a measure of the optical fiber position information, and an intensity of the backscattered light providing a measure of the optical fiber attenuation.
Furthermore, the tunable laser at both ends of the optical fiber injects a pulse light (pump light) and a continuous light (probe light) into the sensing optical fiber, and when the frequency difference between the pump light and the probe light is equal to the brillouin frequency shift in a certain region of the optical fiber, a brillouin amplification effect, i.e., stimulated brillouin effect (SBS), is generated in the region, and energy transfer occurs between the two light beams.
Further, the EOM is optically modulated by an electro-optic modulator.
Further, the PC is a polarization controller.
Further, signals of different frequency components of the brillouin spectrum sequentially pass through the band-pass filter, lorentz fitting is carried out on the signals of different frequencies output by the down converter, the frequency corresponding to the maximum point of the spectrum amplitude is brillouin frequency shift of the scattering point, and brillouin scattering intensity is obtained through spectrum integration.
The invention has the advantages that: the invention realizes the simultaneous measurement of temperature and strain by measuring the Brillouin frequency shift and the strength, and because the Brillouin frequency shift has a linear relation with the small-range temperature change, the frequency of the two lasers is continuously adjusted, and the frequency difference corresponding to the maximum energy transfer on each small section of area of the optical fiber can be determined by detecting the power of continuous light coupled from one end of the optical fiber, thereby obtaining temperature information and realizing the distributed measurement.
The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (10)
1. A demodulation method, a device and a system based on temperature and stress of Brillouin optical fiber sensing are characterized in that: comprises a narrow-spectrum light source;
light emitted by the narrow-spectrum light source is output through the coupler 1, one part of light is used as reference light, the other part of light is modulated into pulse light through EOM, the pulse light is amplified through an optical amplifier EDFA1, spontaneous heat radiation noise is filtered by the fiber grating 1 and then is injected into the port 1 of the circulator 2, the pulse light is totally reflected by the fiber grating 2 through the port 2 and is output from the port 3, and then the pulse light enters the sensing optical fiber; the back scattering light generated by the light during the propagation is output from the port 4 of the circulator 2, and then self-heating radiation noise is filtered by the optical amplifier EDFA2 and the fiber grating 3, and is subjected to coherent detection with the reference light in the photoelectric detector 1; in order to ensure that the polarization states of the two paths of light are well matched, the PC is added into a reference light path to disturb the linear polarization state of the light signal, the electric signal output by the photoelectric detector 1 only comprises a Brillouin frequency shift signal, and direct current and second harmonic components are filtered.
2. The brillouin optical fiber sensing-based temperature and stress demodulation method, apparatus and system according to claim 1, characterized in that:
light emitted by the wide-spectrum light source is transmitted by the fiber grating 2, then is output from the port 3 of the circulator 2, is injected into the sensing fiber through the coupler 2, rayleigh scattered light enters the photoelectric detector 2 through the coupler 2 with the spectral ratio of 95:5, and a data acquisition and processing unit is used for analyzing and processing signals.
3. The brillouin optical fiber sensing-based temperature and stress demodulation method, apparatus and system according to claim 1, characterized in that:
temperature and strain information of the optical fiber can be obtained by measuring the frequency shift and intensity of the brillouin scattered light along the length direction of the optical fiber, and the changes of brillouin frequency shift and intensity caused by temperature and strain can be expressed by a matrix as follows:
in the formula, VVB represents the frequency shift of brillouin scattering, VPB represents the intensity of brillouin scattering, CvBz and CvBT are respectively the strain and temperature coefficient of brillouin scattering frequency shift, CPBz and CPBT are respectively the strain and temperature coefficient of brillouin scattering intensity, Vz represents the strain suffered by the optical fiber, and VT represents the temperature of the optical fiber.
4. The brillouin optical fiber sensing-based temperature and stress demodulation method, apparatus and system according to claim 3, characterized in that:
the intensity of brillouin scattered light is also affected by temperature and strain and is given by:
wherein, Δ PB; for changes in brillouin intensity, Δ T is the temperature change, Δ ∈ is the strain change, CP ∈ is the brillouin intensity strain coefficient, and CPT is the brillouin intensity temperature coefficient.
5. The brillouin optical fiber sensing-based temperature and stress demodulation method, apparatus and system according to claim 1, wherein:
the quantitative and qualitative relations among the frequency shift, the intensity, the temperature and the strain of the Brillouin scattering are established as follows:
vB＝vBO+CvTΔT+CvεΔε
PB＝PBO+CPTΔT+CPεΔε
wherein VBO and PBO are respectively brillouin shift and power at a reference temperature and strain; Δ T and Δ ∈ are the amount of change in temperature and strain, respectively; CVT, CV epsilon, CPT and CP epsilon are respectively the temperature and strain coefficients of Brillouin frequency shift and power.
6. The brillouin optical fiber sensing-based temperature and stress demodulation method, apparatus and system according to claim 1, characterized in that:
in OTDR, backscattered light generated by rayleigh scattering can be detected at the pulse light transmitting end of the optical fiber while the pulsed light is transmitted in the optical fiber, the time delay between the backscattered light and the pulsed light providing a measure of the position information of the optical fiber, the intensity of the backscattered light providing a measure of the attenuation of the optical fiber.
7. The brillouin optical fiber sensing-based temperature and stress demodulation method, apparatus and system according to claim 1, characterized in that:
the tunable laser at two ends of the optical fiber respectively injects a pulse light (pumping light) and a continuous light (probe light) into the sensing optical fiber, when the frequency difference between the pumping light and the probe light is equal to the Brillouin frequency phase shift of a certain region in the optical fiber, a Brillouin amplification effect, namely a stimulated Brillouin effect (SBS), is generated in the region, and the two light beams are subjected to energy transfer with each other.
8. The brillouin optical fiber sensing-based temperature and stress demodulation method, apparatus and system according to claim 1, characterized in that:
the EOM is optically modulated by an electro-optic modulator.
9. The brillouin optical fiber sensing-based temperature and stress demodulation method, apparatus and system according to claim 1, characterized in that:
the PC is a polarization controller.
10. The brillouin optical fiber sensing-based temperature and stress demodulation method, apparatus and system according to claim 1, characterized in that:
signals of different frequency components of the Brillouin spectrum sequentially pass through the band-pass filter, Lorentz fitting is carried out on the signals of different frequencies output by the down converter, the frequency corresponding to the maximum point of the spectrum amplitude is Brillouin frequency shift of the scattering point, and the Brillouin scattering intensity is obtained through spectrum integration.
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