CN111879366A - Long-distance distributed optical fiber demodulator for measuring absolute temperature and absolute strain - Google Patents
Long-distance distributed optical fiber demodulator for measuring absolute temperature and absolute strain Download PDFInfo
- Publication number
- CN111879366A CN111879366A CN202010936298.2A CN202010936298A CN111879366A CN 111879366 A CN111879366 A CN 111879366A CN 202010936298 A CN202010936298 A CN 202010936298A CN 111879366 A CN111879366 A CN 111879366A
- Authority
- CN
- China
- Prior art keywords
- optical fiber
- optic modulator
- temperature
- acousto
- strain
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Pending
Links
- 239000013307 optical fiber Substances 0.000 title claims abstract description 99
- 230000003287 optical effect Effects 0.000 claims abstract description 54
- 230000010287 polarization Effects 0.000 claims abstract description 20
- 230000007246 mechanism Effects 0.000 claims abstract description 18
- 239000000523 sample Substances 0.000 claims abstract description 13
- 239000000835 fiber Substances 0.000 claims description 46
- 238000004321 preservation Methods 0.000 claims description 12
- 238000005259 measurement Methods 0.000 claims description 6
- 238000005516 engineering process Methods 0.000 abstract description 18
- 238000009529 body temperature measurement Methods 0.000 abstract description 4
- 238000001069 Raman spectroscopy Methods 0.000 description 25
- 238000000034 method Methods 0.000 description 6
- 238000004458 analytical method Methods 0.000 description 5
- 238000012544 monitoring process Methods 0.000 description 5
- 230000005540 biological transmission Effects 0.000 description 4
- 230000008859 change Effects 0.000 description 3
- 239000000463 material Substances 0.000 description 3
- 229910052691 Erbium Inorganic materials 0.000 description 2
- 238000006243 chemical reaction Methods 0.000 description 2
- 230000008878 coupling Effects 0.000 description 2
- 238000010168 coupling process Methods 0.000 description 2
- 238000005859 coupling reaction Methods 0.000 description 2
- 238000001914 filtration Methods 0.000 description 2
- 238000005070 sampling Methods 0.000 description 2
- 230000002269 spontaneous effect Effects 0.000 description 2
- 230000005534 acoustic noise Effects 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 238000010276 construction Methods 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 230000000737 periodic effect Effects 0.000 description 1
- 230000003595 spectral effect Effects 0.000 description 1
- 230000001629 suppression Effects 0.000 description 1
- 230000002277 temperature effect Effects 0.000 description 1
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 1
Images
Classifications
-
- 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
-
- 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
- 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
Landscapes
- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Measuring Temperature Or Quantity Of Heat (AREA)
Abstract
The invention relates to a long-distance distributed optical fiber demodulator for measuring absolute temperature and absolute strain, which belongs to the field of optics and comprises a laser, wherein continuous light generated by the laser is divided into pump light and probe light through an 80:20 polarization maintaining optical fiber coupler, the pump light is connected with a computer through a temperature measuring mechanism, and the pump light and the probe light are connected with the computer through a strain measuring mechanism. The long-distance distributed optical fiber demodulator for respectively measuring absolute temperature and absolute strain combines two technologies in one system, wherein the two technologies share some devices in the system, but can realize respective functions without mutual interference, thereby greatly reducing the cost and simplifying the system; the mode of placing the reference optical fiber in the equipment is adopted, a reference is provided for temperature measurement of the sensing optical cable, and the accuracy of temperature measurement of the sensing optical cable is guaranteed when the equipment is in different temperature environments.
Description
Technical Field
The invention relates to the field of optics, in particular to a long-distance distributed optical fiber demodulator for measuring absolute temperature and absolute strain.
Background
The Brillouin optical time domain analysis technology is a stimulated Brillouin scattering effect, stimulated Brillouin scattering is simultaneously influenced by strain and temperature, when the temperature along the optical fiber changes or axial strain exists, the frequency of back Brillouin scattering light of the optical fiber drifts, and the drift amount of the frequency is in a linear relation with the strain and the temperature of the optical fiber, so that the distribution information of the temperature and the strain of the optical fiber along the line can be obtained by measuring the frequency shift amount of the back Brillouin scattering light in the optical fiber, but the distribution information of the temperature and the strain cannot be separated, and absolute strain and absolute temperature cannot be measured.
The single-mode distributed Raman temperature sensing technology is an optical fiber sensing technology for measuring the spatial temperature field distribution in real time. The single-mode optical fiber is a light transmission medium and a sensing element, and can be used for measuring the temperature distribution condition on the whole optical fiber length based on the fact that anti-Stokes in Raman scattering is a sensitive function of temperature. The temperature field distribution along the fiber can be obtained by the technology without being influenced by strain.
By combining the Brillouin optical time domain analysis technology and the spontaneous Raman scattering technology, the absolute temperature and the absolute strain along the optical cable can be respectively measured. Filed on 28/8/2015, application No.: chinese patent "method for calculating distributed brillouin scattering spectral shift" in cn201510542288.x, and application No. applied at 3/30/2010: CN101806735A, "a device and method for simultaneously detecting stimulated brillouin scattering and raman scattering threshold generated by laser transmission in water". The existing patent technology cannot distinguish absolute strain and absolute temperature sensed by an optical cable on the basis of monitoring a single-mode sensing optical cable.
The temperature distribution of the single-mode optical cable can be accurately monitored by using the single-mode distributed Raman scattering technology, but the temperature distribution is not influenced by strain. The Brillouin optical time domain analysis technology can monitor the distribution information of the temperature and the strain of the whole optical cable. The single-mode distributed Raman scattering technology and the Brillouin optical time domain analysis technology are combined, so that the absolute temperature and the absolute strain of the optical cable can be measured respectively. The distributed optical fiber sensing technology is favorably applied to monitoring of strain and stress in engineering, the construction difficulty is greatly reduced, and the popularity of monitoring application of the distributed optical cable is improved. When the optical cable strain needs to be monitored, the temperature compensation optical cable does not need to be laid. The temperature and strain distribution can be monitored respectively by only arranging one optical cable.
Disclosure of Invention
The present invention is directed to a long-distance distributed fiber optic demodulator for measuring absolute temperature and absolute strain, which solves the above-mentioned problems of the prior art.
In order to achieve the purpose, the invention provides the following technical scheme:
a long-distance distributed optical fiber demodulator for measuring absolute temperature and absolute strain comprises a laser, continuous light generated by the laser is divided into pump light and probe light through an 80:20 polarization maintaining optical fiber coupler, the pump light is connected with a computer through a temperature measuring mechanism, and the pump light and the probe light are connected with the computer through a strain measuring mechanism.
As a further technical scheme of the invention: the strain measuring mechanism comprises an electro-optical modulator, a 90:10 optical fiber coupler, a second erbium-doped optical fiber amplifier, a bipolar isolator and a heat preservation box, wherein the output end of the 90:10 optical fiber coupler is connected with the electro-optical modulator through an automatic control voltage offset plate, the electro-optical modulator is connected with a computer through a microwave source, a reference optical fiber and a thermistor are installed in the heat preservation box, and the bipolar isolator is connected with the reference optical fiber through a sensing optical fiber; the strain measurement mechanism further comprises an acousto-optic modulator, an acousto-optic modulator driver, a first erbium-doped optical fiber amplifier, a band-pass filter, a polarization controller, a circulator, a reference optical fiber, a thermistor, a sensing optical fiber, an electric control optical attenuator, a three-channel avalanche diode photoelectric detector and a three-channel acquisition card, wherein the acousto-optic modulator is connected with the three-channel acquisition card through the acousto-optic modulator driver, the acousto-optic modulator is connected with the circulator through the first erbium-doped optical fiber amplifier, the band-pass filter and the polarization controller in sequence, one end of the circulator is connected with the reference optical fiber, the other end of the circulator is connected with an optical switch, one end of the optical switch is connected with the electric control optical attenuator, the electric control optical attenuator is connected with the three-channel acquisition card through the three-channel.
As a further technical scheme of the invention: the temperature measuring mechanism comprises an acousto-optic modulator, an acousto-optic modulator driver, a first erbium-doped optical fiber amplifier, a band-pass filter, a polarization controller, a circulator, a reference optical fiber, a heat preservation box, a thermistor, a sensing optical fiber, a 50:50 optical fiber coupler, a 1450nm wavelength division multiplexer, a 1450nm filter, a three-channel avalanche diode photoelectric detector and a three-channel acquisition card, wherein the acousto-optic modulator is connected with the three-channel acquisition card through the acousto-optic modulator driver, the acousto-optic modulator is connected with the circulator through the first erbium-doped optical fiber amplifier, the band-pass filter and the polarization controller in sequence, one end of the circulator is connected with the reference optical fiber, the other end of the circulator is connected with an optical switch, one end of the 50:50 optical fiber coupler is connected with the three-channel avalanche diode photoelectric detector through the 1450nm wavelength division optical fiber amplifier and the 1450nm filter, and the other end of the 50, and the three-channel avalanche diode photoelectric detector is connected with the optical switch.
As a further technical scheme of the invention: and the thermistor is connected with the three-channel acquisition card.
As a further technical scheme of the invention: the laser is a tunable fiber laser.
As a further technical scheme of the invention: the laser produces a continuous wavelength of 1.55 μm.
As a further technical scheme of the invention: the microwave source is replaced by a single sideband modulator.
Compared with the prior art, the invention has the beneficial effects that:
1. the long-distance distributed optical fiber demodulator for respectively measuring absolute temperature and absolute strain combines two technologies in a system, wherein the two technologies share some devices in the system, but can realize respective functions without mutual interference, thereby greatly reducing the cost and simplifying the system.
2. The mode of placing the reference optical fiber in the equipment is adopted, a reference is provided for temperature measurement of the sensing optical cable, and the accuracy of temperature measurement of the sensing optical cable is guaranteed when the equipment is in different temperature environments.
3. The temperature of the optical cable can be accurately measured by using the Raman scattering system, but the temperature is not influenced by strain, the absolute temperature can be measured, the Brillouin scattering system can accurately measure the temperature and the strain of the optical cable, but the influence of which factor is the temperature and the strain can not be distinguished, the Brillouin frequency shift quantity measured by the Brillouin scattering system is subtracted from the Brillouin frequency shift quantity caused by the temperature measured by the Raman scattering system, and the Brillouin frequency shift quantity caused by the strain of the optical cable can be measured, so that the absolute strain is calculated.
4. Three channels of the same acquisition card are adopted. The consistency of the sampling rates of the Brillouin scattering system and the Raman scattering system can be ensured. Strain values can be derived by simply subtracting the corresponding points.
5. Only one monitoring optical cable is adopted, the absolute temperature and the absolute strain information along the sensing optical cable can be measured simultaneously, the problem that a temperature compensation optical cable needs to be arranged when a Brillouin scattering system is used is avoided, and the practicability of engineering application is greatly improved.
6. The method has the advantages of long sensing distance, high spatial resolution, high measurement precision and the like, and compared with a single sensing technology, the method has wider application field.
Drawings
Fig. 1 is a schematic structural diagram of a long-distance distributed optical fiber demodulator for measuring absolute temperature and absolute strain.
In the figure: 1-laser, 2-80:20 polarization maintaining fiber coupler, 3-acousto-optic modulator, 4-acousto-optic modulator driver, 5-erbium doped fiber amplifier, 6-band pass filter, 7-polarization controller, 8-circulator, 9-reference fiber, 10-heat preservation box, 11-thermistor, 12-sensing fiber, 13-electro-optic modulator, 14-microwave source, 15-automatic control voltage bias board, 16-90:10 fiber coupler, 17-erbium doped fiber amplifier, 18-bipolar isolator, 19-optical switch, 20-electric control optical attenuator, 21-50:50 fiber coupler, 22-1450nm wavelength division multiplexer, 23-1663nm wavelength division multiplexer, 24-1450nm filter, 25-1663nm filter, 26-three-channel avalanche diode photodetector, 27-three-channel acquisition card and 28-computer.
Detailed Description
The technical solution in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention.
Example 1
The long-distance distributed fiber demodulation instrument for measuring absolute temperature and absolute strain as shown in fig. 1 comprises a laser 1, wherein continuous light generated by the laser 1 is divided into pump light and probe light through an 80:20 polarization maintaining fiber coupler 2, the pump light is connected with a computer 28 through a temperature measuring mechanism, the pump light and the probe light are connected with the computer 28 through a strain measuring mechanism, namely, the pump light and the probe light are divided into two paths through the 80:20 polarization maintaining fiber coupler 2, 80% of the light is used as the pump light, 20% of the light is used as the probe light, then the absolute temperature and the absolute strain are measured, specifically, the strain measuring mechanism comprises an electro-optical modulator 13, a 90:10 fiber coupler 16, a second erbium-doped fiber amplifier 17, a bipolar isolator 18 and a heat preservation box 10, the output end of the 90:10 fiber coupler 16 is connected with the electro-optical modulator 13 through an automatic control voltage bias board 15, the electro-optical modulator 13 is connected with a computer 28 through a microwave source 14, a reference optical fiber 9 and a thermistor 11 are installed in the heat preservation box 10, the bipolar isolator 18 is connected with the reference optical fiber 9 through a sensing optical fiber 12, the computer 28 controls the microwave source 14 through a serial port line to control the frequency shift amount of the microwave source 14, 20% of output ports are connected with an input port of the electro-optical modulator 13, the microwave source 14 is loaded on the electro-optical modulator 13 and used for shifting the frequency of continuous light generated by the laser 1, and the output ports of the electro-optical modulator 13 are connected with 90:10 input port connection of the fiber coupler 16, 90: 10% of output light of the optical fiber coupler 13 is connected with an automatic control voltage bias board 15, the automatic control voltage bias board 15 is connected with a piezoelectric control port of the electro-optical modulator 13, and is used for controlling the stability of frequency shift quantity, and 90: the 10 optical fiber coupler 16 has 90% of output light connected to the input port of the second erbium-doped fiber amplifier 17 for amplifying the probe light, the output port of the second erbium-doped fiber amplifier 17 is connected to the input port of the bipolar isolator 18 for preventing the pulse light from being transmitted into the probe light link, the output port of the bipolar isolator 18 is connected to the other port of the sensing optical fiber 12 for injecting the probe light into the sensing optical fiber 12 and the reference optical fiber 9; the strain measuring mechanism further comprises an acousto-optic modulator 3, an acousto-optic modulator driver 4, a first erbium-doped optical fiber amplifier 5, a band-pass filter 6, a polarization controller 7, a circulator 8, a reference optical fiber 9, a thermistor 11, a sensing optical fiber 12, an electronic control optical attenuator 20, a three-channel avalanche diode photoelectric detector 26 and a three-channel acquisition card 27, wherein the acousto-optic modulator 3 is connected with the three-channel acquisition card 27 through the acousto-optic modulator driver 4, the acousto-optic modulator 3 is connected with the circulator 8 through the first erbium-doped optical fiber amplifier 5, the band-pass filter 6 and the polarization controller 7 in sequence, one end of the circulator 8 is connected with the reference optical fiber 9, the other end of the circulator is connected with an optical switch 19, one end of the optical switch 19 is connected with the electronic controller 20, the electronic control optical attenuator 20 is connected with the three-channel acquisition card 27 through, the three-channel acquisition card 27 is connected with a computer 28.
The temperature measuring mechanism comprises an acousto-optic modulator 3, an acousto-optic modulator drive 4, a first erbium-doped fiber amplifier 5, a band-pass filter 6, a polarization controller 7, a circulator 8, a reference fiber 9, a heat preservation box 10, a thermistor 11, a sensing fiber 12, a 50:50 fiber coupler 21, a 1450nm wavelength division multiplexer 22, a 1450nm filter 24, a three-channel avalanche diode photodetector 26 and a three-channel acquisition card 27, wherein the acousto-optic modulator 3 is connected with the three-channel acquisition card 27 through the acousto-optic modulator drive 4, the acousto-optic modulator 3 is connected with the circulator 8 through the first erbium-doped fiber amplifier 5, the band-pass filter 6 and the polarization controller 7 in sequence, one end of the circulator 8 is connected with the reference fiber 9, the other end of the circulator is connected with an optical switch 19, one end of the 50:50 fiber coupler 21 is connected with the three-channel diode photodetector 26 through the 1450nm wavelength division multiplexer 22 and the 1450nm filter 24, the other end is connected with a three-channel avalanche diode photoelectric detector 26 through a 1663nm wavelength division multiplexer 23 and a 1663nm filter 25, the three-channel avalanche diode photoelectric detector 26 is connected with an optical switch 19, a three-channel acquisition card 27 is connected with the acousto-optic modulator driver 4 to provide an electric pulse signal for the acousto-optic modulator driver 4, the acousto-optic modulator driver 4 is loaded on the acousto-optic modulator 3 to drive, and 80: 80% of output ports of the 20 polarization-maintaining fiber coupler 2 are connected with the input port of the acousto-optic modulator 3, and the continuous light is modulated into pulse light; the output port of the acousto-optic modulator 13 is connected with the input port of the first erbium-doped fiber amplifier 5 and is used for amplifying the pulse light; the output port of the first erbium-doped fiber amplifier 5 is connected with the input port of the band-pass filter 6 and is used for filtering noise outside a bandwidth and improving the signal-to-noise ratio; the output port of the band-pass filter 6 is connected with the input port of the polarization controller 7 and is used for controlling the polarization state in the optical fiber; an output port of the polarization controller 7 is connected with a first port of the circulator 8, a second port of the circulator 8 is connected with an input port of a reference optical fiber 9, and the amplified pulse light is transmitted to the reference optical fiber 9; the reference optical fiber 9 is placed in a heat preservation box 10, and a thermistor 11 is placed in the heat preservation box 10 and used for accurately measuring the temperature of the reference optical fiber 9; the output port of the reference fiber 9 is connected with one end of the sensing fiber 12, and the pulse light is injected into the sensing fiber 12; a third port of the circulator 8 is connected with an input port of an optical switch 19, and a first output port of the optical switch 19 is connected with an electrically controlled optical attenuator 20 and is used for attenuating light entering the detector; the output end of the electrically controlled optical attenuator 20 is connected with the first port of the three-channel avalanche diode photodetector 26, and is used for performing photoelectric conversion, and only the stokes light of brillouin scattering can be monitored due to the limitation of the bandwidth of the first port of the three-channel avalanche diode photodetector 26; the second output port of the optical switch 19 is connected with the input port of the 50:50 optical fiber coupler 21, and the two output ports of the 50:50 optical fiber coupler are respectively connected with the input ports of the 1450nm wavelength division multiplexer 22 and the 1663nm wavelength division multiplexer 23 and are used for separating out Stokes light and Anti-Stokes light; the 1450nm wavelength division multiplexer 22 and the 1663nm wavelength division multiplexer 23 are respectively connected with the input end of the 1450nm filter 24 and the input end of the 1663nm filter 25, and are used for filtering white noise of Stokes light and Anti-Stokes light Anti-Stokes, and improving the sideband suppression ratio; the output ports of the 1450nm filter 24 and the 1663nm filter 25 are respectively connected with the input ports of the second port and the third port of the three-channel avalanche diode photodetector 26, and are used for converting optical signals into electrical signals; the output end of the three-channel avalanche diode photoelectric detector 26 is correspondingly connected with the input end of a three-channel acquisition card 27 and is used for acquiring stimulated Brillouin scattering and spontaneous Raman scattering electric signals; the three-channel acquisition card 27 is connected with the optical switch 19 and used for controlling the switching of the optical switch 19, preferably, the thermistor 11 is connected with the three-channel acquisition card 27, that is, the three-channel acquisition card 27 is connected with the thermistor 11 and used for monitoring the temperature of the reference optical fiber 9; the three-channel acquisition card 27 is connected with the computer 28 through a network cable for data transmission, and then the computer 28 controls the microwave source 14 through a serial line so as to control the frequency shift amount of the microwave source 14.
Further, the laser 1 is a tunable fiber laser, and preferably, the continuous light generated by the laser 1 has a wavelength of 1.55 μm.
Example 2
This embodiment is different from embodiment 1 in that the microwave source 14 is replaced by a single-sideband modulator, i.e. sideband light is generated by the single-sideband modulator, and in addition, the coupling ratio of the 80:20 polarization-maintaining fiber coupler 2 can also be set to 90:10 or 60: 40.
The working principle is as follows:
the brillouin optical time domain analysis technique (BOTDA) is a technique in which stimulated brillouin scattering occurs due to a change in refractive index of an optical fiber material caused by acoustic noise generated by brownian heat running of molecules of the optical fiber material. The optical fiber refractive index shows periodic change due to the propagation of the acoustic wave in the optical fiber material, so that the frequency of the scattered light generates Doppler shift relative to the transmitted light, and the Brillouin scattered light has Stokes light and anti-Stokes light, which have smaller functions. The Brillouin scattering is affected by strain and temperature at the same time, when the temperature along the optical fiber changes or axial strain exists, the frequency of the back Brillouin scattering light of the optical fiber shifts, and the shift amount of the frequency is in a linear relation with the strain and the temperature of the optical fiber, so that the distribution information of the temperature and the strain along the optical fiber can be obtained by measuring the frequency shift amount of the back Brillouin scattering light in the optical fiber.
Brillouin frequency shift increases with increasing temperature and strain
Temperature coefficient:
strain coefficient:
temperature effect of fiber raman backscattering:
stokes raman backscattered photon count:
Anti-Stokes raman backscattered photon count:
in the above formulas, the number of photons included in each laser pulse incident on the optical fiber; respectively, coefficients related to the optical fiber Stokes and Anti-Stokes Raman scattering cross sections and the like; s is a backscattering factor of the optical fiber; stokes and Anti-Stokes Raman photon frequencies, respectively, incident photon frequency; average transmission loss of incident photons for Stokes and Anti-Stokes Raman scattered photons in the fiber; l is the length of the optical fiber; the population numbers of the upper and lower molecular energy levels related to the Raman scattering of the optical fiber molecules respectively are related to the temperature, and the population numbers of the molecular energy levels are
Wherein is the raman phonon frequency; h is Planckian constant and k is Boltzmann constant. When the temperature at the local position of the optical fiber changes, the photon number of the optical fiber Raman scattering, namely the temperature modulation mechanism of the optical fiber Raman backscattering, is modulated.
The ratio of Anti-Stokes Raman scattering to Rayleigh scattering photons number is
In actual measurement, the temperature of each point of the fiber is determined by the above formula when the starting temperature is known, i.e. the temperature is measured
In the actual measurement, the ratio of the number of photons is not directly measured, but the ratio of the signal level after photoelectric conversion. The ratio of the signal levels corresponding to the ratio of the number of photons in the above equation can be determined experimentally, and the temperature T at each point on the fiber can be determined from the above equation if the starting temperature is known.
The strain technology is demodulated by adopting Raman scattering and Brillouin scattering coupling: raman scattering is only sensitive to temperature and brillouin scattering is affected by both strain and temperature. In order to demodulate the strain well, the temperature change measured by the raman scattering needs to be subtracted from the brillouin frequency shift measured by the brillouin scattering, so that the value of the strain can be obtained. Since the sampling rates of raman scattering and brillouin scattering are 250MSample/s, strain values can be obtained by simply subtracting the values of the corresponding points in distance.
It will be evident to those skilled in the art that the invention is not limited to the details of the foregoing illustrative embodiments, and that the present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein. Any reference sign in a claim should not be construed as limiting the claim concerned.
Furthermore, it should be understood that although the present description refers to embodiments, not every embodiment may contain only a single embodiment, and such description is for clarity only, and those skilled in the art should integrate the description, and the embodiments may be combined as appropriate to form other embodiments understood by those skilled in the art.
Claims (7)
1. A long distance distributed fiber optic demodulator for measuring absolute temperature and absolute strain, comprising a laser (1), characterized in that: continuous light generated by the laser (1) is divided into pump light and probe light through an 80:20 polarization-maintaining optical fiber coupler (2), the pump light is connected with a computer (28) through a temperature measuring mechanism, and the pump light and the probe light are connected with the computer (28) through a strain measuring mechanism.
2. The long distance distributed optical fiber demodulator for measuring absolute temperature and absolute strain according to claim 1, wherein: the strain measurement mechanism comprises an electro-optic modulator (13), a 90:10 optical fiber coupler (16), a second erbium-doped optical fiber amplifier (17), a bipolar isolator (18) and a heat preservation box (10), wherein the output end of the 90:10 optical fiber coupler (16) is connected with the electro-optic modulator (13) through an automatic control voltage bias board (15), the electro-optic modulator (13) is connected with a computer (28) through a microwave source (14), a reference optical fiber (9) and a thermistor (11) are installed in the heat preservation box (10), and the bipolar isolator (18) is connected with the reference optical fiber (9) through a sensing optical fiber (12); the strain measurement mechanism further comprises an acousto-optic modulator (3), an acousto-optic modulator driver (4), a first erbium-doped optical fiber amplifier (5), a band-pass filter (6), a polarization controller (7), a circulator (8), a reference optical fiber (9), a thermistor (11), a sensing optical fiber (12), an electronic control optical attenuator (20), a three-channel avalanche diode photoelectric detector (26) and a three-channel acquisition card (27), wherein the acousto-optic modulator (3) is connected with the three-channel acquisition card (27) through the acousto-optic modulator driver (4), the acousto-optic modulator (3) is connected with the circulator (8) through the first erbium-doped optical fiber amplifier (5), the band-pass filter (6) and the polarization controller (7) in sequence, one end of the circulator (8) is connected with the reference optical fiber (9), the other end of the circulator is connected with an optical switch (19), one end of the optical switch (19) is connected with the electronic control optical attenuator (20), the electric control optical attenuator (20) is connected with a three-channel acquisition card (27) through a three-channel avalanche diode photoelectric detector (26), and the three-channel acquisition card (27) is connected with a computer (28).
3. The long distance distributed optical fiber demodulator for measuring absolute temperature and absolute strain according to claim 2, wherein: the temperature measuring mechanism comprises an acousto-optic modulator (3), an acousto-optic modulator driver (4), a first erbium-doped fiber amplifier (5), a band-pass filter (6), a polarization controller (7), a circulator (8), a reference fiber (9), a heat preservation box (10), a thermistor (11), a sensing fiber (12), a 50:50 fiber coupler (21), a 1450nm wavelength division multiplexer (22), a 1450nm filter (24), a three-channel avalanche diode photoelectric detector (26) and a three-channel acquisition card (27), wherein the acousto-optic modulator (3) is connected with the three-channel acquisition card (27) through the acousto-optic modulator driver (4), the acousto-optic modulator (3) is connected with the circulator (8) through the first erbium-doped fiber amplifier (5), the band-pass filter (6) and the polarization controller (7) in sequence, one end of the circulator (8) is connected with the reference fiber (9), the other end of the 50:50 optical fiber coupler (21) is connected with an optical switch (19), one end of the 50:50 optical fiber coupler is connected with a three-channel avalanche diode photoelectric detector (26) through a 1450nm wavelength division multiplexer (22) and a 1450nm filter (24), the other end of the 50:50 optical fiber coupler is connected with the three-channel avalanche diode photoelectric detector (26) through a 1663nm wavelength division multiplexer (23) and a 1663nm filter (25), and the three-channel avalanche diode photoelectric detector (26) is connected with the optical switch (19).
4. The long distance distributed optical fiber demodulator for measuring absolute temperature and absolute strain according to claim 3, wherein: the thermistor (11) is connected with a three-channel acquisition card (27).
5. The long distance distributed optical fiber demodulator for measuring absolute temperature and absolute strain according to claim 1, wherein: the laser (1) is a tunable fiber laser.
6. The long distance distributed optical fiber demodulator for measuring absolute temperature and absolute strain according to claim 5, wherein: the continuous light generated by the laser (1) has a wavelength of 1.55 μm.
7. The long distance distributed optical fiber demodulator for measuring absolute temperature and absolute strain according to claim 2, wherein: the microwave source (14) is replaced by a single sideband modulator.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202010936298.2A CN111879366A (en) | 2020-09-08 | 2020-09-08 | Long-distance distributed optical fiber demodulator for measuring absolute temperature and absolute strain |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202010936298.2A CN111879366A (en) | 2020-09-08 | 2020-09-08 | Long-distance distributed optical fiber demodulator for measuring absolute temperature and absolute strain |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CN111879366A true CN111879366A (en) | 2020-11-03 |
Family
ID=73199053
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CN202010936298.2A Pending CN111879366A (en) | 2020-09-08 | 2020-09-08 | Long-distance distributed optical fiber demodulator for measuring absolute temperature and absolute strain |
Country Status (1)
| Country | Link |
|---|---|
| CN (1) | CN111879366A (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN114136363A (en) * | 2021-10-22 | 2022-03-04 | 陕西电器研究所 | Distributed optical fiber strain and temperature measuring device based on BOTDA |
-
2020
- 2020-09-08 CN CN202010936298.2A patent/CN111879366A/en active Pending
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN114136363A (en) * | 2021-10-22 | 2022-03-04 | 陕西电器研究所 | Distributed optical fiber strain and temperature measuring device based on BOTDA |
| CN114136363B (en) * | 2021-10-22 | 2023-11-07 | 陕西电器研究所 | BOTDA-based distributed optical fiber strain and temperature measuring device |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| CN102759371B (en) | COTDR (coherent detection based optical time-domain reflectometry) fused long-distance coherent detection brilouin optical time-domain analyzer | |
| Horiguchi et al. | Development of a distributed sensing technique using Brillouin scattering | |
| KR100930342B1 (en) | Distribution fiber optic sensor system | |
| US9804001B2 (en) | Brillouin optical distributed sensing device and method with improved tolerance to sensor failure | |
| US9599460B2 (en) | Hybrid Raman and Brillouin scattering in few-mode fibers | |
| CN107917738A (en) | A kind of while measurement temperature, strain and the distributed optical fiber sensing system of vibration | |
| BRPI0718599A2 (en) | DETECTION OF A LIGHT PHASE DISTURBATION PROPAGATING IN AN OPTICAL WAVE GUIDE. | |
| CN108844614B (en) | Chaotic Brillouin optical correlation domain analysis system and method based on phase spectrum measurement | |
| CN107238412A (en) | It is a kind of while monitoring vibration, stress, the distributed fiberoptic sensor of temperature | |
| CN103616091A (en) | Distributed optical fiber temperature and stress sensing device | |
| CN110243493A (en) | Brillouin optical time-domain reflectometer device and method based on super continuous spectrums | |
| CN108917804A (en) | Quick long-distance distributed Brillouin light fiber sensing equipment based on chirp chain | |
| CN203310428U (en) | Distributed Brillouin optical fiber sensing system based on coherent detection | |
| CN103115695A (en) | Double-sideband distributed type optical fiber sensing system parameter measuring device | |
| CN108801305B (en) | Method and device of Brillouin optical time domain reflectometer based on step pulse self-amplification | |
| CN111780859A (en) | Distributed optical fiber sensing detection system | |
| CN104729750A (en) | Distributed optical fiber temperature sensor based on Brillouin scattering | |
| CN111879366A (en) | Long-distance distributed optical fiber demodulator for measuring absolute temperature and absolute strain | |
| CN107727122B (en) | Double-end detection combined Raman and Brillouin scattering distributed optical fiber sensing device | |
| CN104729751A (en) | Distributed optical fiber temperature and stress sensor based on Brillouin scattering | |
| KR20180010049A (en) | Spatially-selective brillouin distributed optical fiber sensor with increased effective sensing points and sensing method using brillouin scattering | |
| CN213021690U (en) | Long-distance distributed optical fiber demodulator for measuring absolute temperature and absolute strain | |
| CN216524011U (en) | Long-distance Brillouin optical time domain reflectometer monitoring device | |
| CN207636092U (en) | A kind of distributed fiber optic temperature and strain sensing device | |
| CN111473952B (en) | Optical fiber sensing device |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PB01 | Publication | ||
| PB01 | Publication | ||
| SE01 | Entry into force of request for substantive examination | ||
| SE01 | Entry into force of request for substantive examination |