CN105865655B - A kind of temperature based on optical fiber acousto-optic mould interaction and strain while measurement method - Google Patents
A kind of temperature based on optical fiber acousto-optic mould interaction and strain while measurement method Download PDFInfo
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- CN105865655B CN105865655B CN201610352865.3A CN201610352865A CN105865655B CN 105865655 B CN105865655 B CN 105865655B CN 201610352865 A CN201610352865 A CN 201610352865A CN 105865655 B CN105865655 B CN 105865655B
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01K—MEASURING TEMPERATURE; MEASURING QUANTITY OF HEAT; THERMALLY-SENSITIVE ELEMENTS NOT OTHERWISE PROVIDED FOR
- G01K11/00—Measuring temperature based upon physical or chemical changes not covered by groups G01K3/00, G01K5/00, G01K7/00 or G01K9/00
- G01K11/32—Measuring temperature based upon physical or chemical changes not covered by groups G01K3/00, G01K5/00, G01K7/00 or G01K9/00 using changes in transmittance, scattering or luminescence in optical fibres
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B11/00—Measuring arrangements characterised by the use of optical techniques
- G01B11/16—Measuring arrangements characterised by the use of optical techniques for measuring the deformation in a solid, e.g. optical strain gauge
Abstract
The invention discloses a kind of temperature based on optical fiber acousto-optic mould interaction and strain while measurement methods, multimodal brillouin gain spectrum is generated using the interaction between some optical mode excited in optical fiber and more acoustic modes of corresponding excitation, measurement is compared in a certain characteristic quantity that two gain peaks are arbitrarily chosen from multimodal brillouin gain spectrum, or measurement is compared in certain two characteristic quantity of arbitrarily one gain peak of selection, obtain the perception sensitivity coefficient of Brillouin shift and/or brillouin gain coefficient with temperature and strain, constitute coefficient matrix, temperature and strain are obtained by solution matrix equation, it is measured while realizing temperature and strain；Measurement method, without introducing additional measurement mechanism or equipment, has simple structure, strong robustness, the high feature of accuracy of measurement while eliminating temperature and strain cross sensitivity adverse effect simultaneously for temperature provided by the invention and strain.
Description
Technical field
The invention belongs to technical field of optical fiber sensing, more particularly, to a kind of temperature based on optical fiber acousto-optic mould interaction
Degree and strain while measurement method.
Background technology
Distributed Optical Fiber Sensing Techniques use optical fibers as transmission medium and replace a series of intensive dotted sensor arrays, can
The sensings amount such as the temperature of optical fiber everywhere and strain is measured, with high certainty of measurement, accurate positioning and wide range of measurement
Advantage is widely used in the various fields such as material structure and environmental monitoring.Its apply in a key technical problems be as
What to temperature and strain realize simultaneously and mutually independent measurement, exclude cross influence between the two, such as realize exclude temperature shadow
Loud high-precision strain measurement, and exclude the high-resolution hydrocode that strain influences.
The prior art includes：Early stage multiselect is carried out with general single mode fiber, and brillouin effect is combined with other effects
It is measured while into trip temperature and strain, is for example combined using Brillouin scattering and Raman scattering and realizes temperature and strain simultaneously
It measures, or realizes temperature and strain using the brillouin effect and birefringence effect of polarization maintaining optical fibre while measuring.Such methods
It needs the additional birefringent characteristic to Raman scattering signal or optical fiber to measure, increases the difficulty and reality of system building
The complexity of border operation.
The prior art further includes：Survey is compared using multiple and different characteristic quantities of brillouin gain spectrum in brillouin effect
Amount, for example by the Brillouin of the unimodal brillouin gain spectrum generated to single optical mode in single mode optical fiber and single acoustic mode interaction
Two characteristic quantities of frequency displacement and brillouin gain coefficient measure, and achieve the purpose that temperature and strain while measuring, or utilize
Some characteristic quantity for multiple unimodal brillouin gain spectrums that multiple optical modes and single acoustic mode interaction generate in less fundamental mode optical fibre into
Row matching measurement achievees the purpose that temperature and strain while measuring.Some excited in optical fiber is not utilized in such methods
Interaction between optical mode and more acoustic modes of corresponding excitation generates multimodal brillouin gain spectrum, and in such methods for temperature and
The perceptual sensitivity of strain is relatively low, constrains precision and the accuracy of temperature and strain measurement.
Invention content
For the disadvantages described above or Improvement requirement of the prior art, the present invention provides one kind being based on optical fiber acousto-optic mould interaction
Temperature and strain measurement method simultaneously, particularly utilize the more sound of the corresponding excitation of some optical mode excited in optical fiber
Interaction between mould generates multimodal brillouin gain spectrum, and two gain peaks certain is arbitrarily chosen from multimodal brillouin gain spectrum
Measurement is compared in one characteristic quantity, or measurement is compared in certain two characteristic quantity of arbitrarily one gain peak of selection；Its purpose
It is to eliminate the cross jamming between temperature and strain in temperature and strain while in measuring, improves the essence of temperature and strain measurement
Degree and accuracy.
To achieve the above object, the present invention provides a kind of temperature based on optical fiber acousto-optic mould interaction and strain at the same survey
Amount method, includes the following steps：
(1) it transmits the architectural characteristic of met modal eigenvalue equation and optical fiber in a fiber according to light wave fields, obtains
Allow the mode distributions of number, type and the optical mode of all optical modes of excitation on cross section of optic fibre in optical fiber；
(2) an optical mode is arbitrarily chosen from all optical modes for allowing excitation, being transmitted in a fiber according to acoustic wavefield expires
The modal eigenvalue equation of foot, the number, type and more acoustic modes for obtaining the corresponding more acoustic modes excited of the optical mode are transversal in optical fiber
Mode distributions on face；
(3) transmit met modal eigenvalue equation in a fiber according to the acoustic wavefield, obtain the optical mode with it is corresponding
Multiple Brillouin shifts that more acoustic mode interactions generate；
According to more acoustic modes of mode distributions and the optical mode corresponding excitation of the optical mode on cross section of optic fibre
The mode distributions and brillouin gain coefficient of number, type, more acoustic modes on cross section of optic fibre are coupled with the mould field of acousto-optic mould
The relationship of efficiency obtains multiple brillouin gain coefficients that the optical mode is generated with corresponding more acoustic mode interactions；
And according to the Brillouin shift and brillouin gain coefficient, obtain multimodal brillouin gain spectrum；
(4) according to the refractive index of light wave on cross section of optic fibre and longitudinal rate of sound wave with the pass of temperature and strain variation
System and light wave refractive index and longitudinal rate of sound wave and the relationship of brillouin gain spectrum, obtain the optical mode with it is corresponding more
Acoustic mode interaction generate multimodal brillouin gain spectrum with temperature and strain variation relationship；
(5) two gain peaks are arbitrarily chosen from the multimodal gain spectral that the optical mode is generated with corresponding more acoustic mode interactions
Measurement is compared in some characteristic quantity, or measurement is compared in certain two characteristic quantity of arbitrarily one gain peak of selection, obtains
Brillouin shift variation with temperature coefficientBrillouin shift with strain variation coefficientBrillouin gain coefficient
Variation with temperature coefficientWith brillouin gain coefficient with the variation coefficient of strain
And according to describedWithEstablish Brillouin shift and/or brillouin gain coefficient with
The coefficient matrix relationship of temperature and strain obtains temperature and the strain of optical fiber by solution matrix equation.
Preferably, the above-mentioned temperature based on optical fiber acousto-optic mould interaction and strain while measurement method, light wave fields is in optical fiber
The modal eigenvalue equation of middle transmission is：
The modal eigenvalue equation that acoustic wavefield is transmitted in a fiber is：
Wherein, E refers to mode distributions of the optical mode on cross section of optic fibre, and λ refers to lambda1-wavelength, and n refers to that optical fiber is transversal
Index distribution on face, neffIt refer to the effective refractive index of light field basic mode in a fiber；Wherein, umRefer to m-th of acoustic mode in optical fiber
Mode distributions on cross section, ΩmRefer to the characteristic frequency of sound wave, VlRefer to longitudinal rate distribution of sound wave, the biography of acoustic wave mode
Defeated constant betaac=2 βopt, βopt=2 π neff/ λ is the transmission of light wave pattern.
Preferably, the above-mentioned temperature based on optical fiber acousto-optic mould interaction and strain while measurement method, cross section of optic fibre
The index distribution n of upper light wave is with temperature and the relationship of strain：
N=n0[1+(1×10-3+3×10-6ΔT+1.5×10-7Δε)×ωGe
+(-3.3×10-3+3.6×10-6ΔT+7.5×10-7Δε)×ωF]；
Longitudinal rate distribution V of sound wave on its cross section of optic fibrelIt is with temperature and the relationship of strain：
Vl=Vl0[1-(7.2×10-3-4.7×10-5ΔT-2.1×10-6Δε)×ωGe
-(2.7×10-2-1.8×10-5ΔT-3.8×10-6Δε)×ωF]；
Wherein, n0For the refractive index of fibre cladding, Vl0For longitudinal velocity of sound of fibre cladding, Δ T is temperature variation, Δ ε
For strain variation amount, ωGeFor the doping concentration of Ge, ωFFor the doping concentration of F.
Preferably, the above-mentioned temperature based on optical fiber acousto-optic mould interaction and strain measurement method simultaneously is right in step (5)
The Brillouin shift of certain two gain peak in the multimodal gain spectral that this optical mode is generated with corresponding more acoustic mode interactions is compared
To measuring, according to the coefficient obtained is measured, the Brillouin shift of the two gain peaks is established with the coefficient matrix of temperature and strain
Relationship：
Wherein, Δ T is temperature variation, and Δ ε is strain variation amount, and Δ BFS1 refers to some in the two gain peaks
The corresponding Brillouin shift variable quantity of gain peak, Δ BFS2 refer in the corresponding cloth of another gain peak in the two gain peaks
Deep frequency displacement variable quantity.
Preferably, the above-mentioned temperature based on optical fiber acousto-optic mould interaction and strain measurement method simultaneously is right in step (5)
The Brillouin shift and Bu Li of some gain peak in the multimodal gain spectral that this optical mode is generated with corresponding more acoustic mode interactions
Measurement is compared in deep gain coefficient, according to the coefficient obtained is measured, establishes the Brillouin shift and Bu Li of this gain peak
Deep gain coefficient with temperature and strain coefficient matrix relationship：
Wherein, Δ T is temperature variation, and Δ ε is strain variation amount, and Δ BFS refers in the corresponding cloth of this gain peak
Deep frequency displacement variable quantity, Δ BGC refer to the corresponding brillouin gain index variation amount of this gain peak.
Preferably, the above-mentioned temperature based on optical fiber acousto-optic mould interaction and strain measurement method simultaneously is right in step (5)
The brillouin gain coefficient of certain two gain peak in the multimodal gain spectral that this optical mode is generated with corresponding more acoustic mode interactions into
Row matching measurement establishes the brillouin gain coefficient of the two gain peaks with temperature and strain according to the coefficient obtained is measured
Coefficient matrix relationship：
Wherein, Δ T is temperature variation, and Δ ε is strain variation amount, and Δ BGC1 refers to some in the two gain peaks
The corresponding brillouin gain index variation amount of gain peak, Δ BGC2 refer to that another gain peak in the two gain peaks is corresponding
Brillouin gain index variation amount.
In general, through the invention it is contemplated above technical scheme is compared with the prior art, can obtain down and show
Beneficial effect：
(1) temperature provided by the invention based on optical fiber acousto-optic mould interaction and strain while the method measured, utilize light
Interaction between more acoustic modes of the corresponding excitation of some optical mode excited in fibre generates multimodal brillouin gain spectrum, from more
Measurement, or one increasing of arbitrary selection is compared in some characteristic quantity that two gain peaks are arbitrarily chosen in peak brillouin gain spectrum
Measurement is compared in certain two characteristic quantity at beneficial peak, obtains Brillouin shift and/or brillouin gain coefficient with temperature and strain
Perception sensitivity coefficient, constitute coefficient matrix, temperature and strain obtained by solution matrix equation, realize the same of temperature and strain
When measure；
(2) temperature provided by the invention and strain while the method measured, are not limited to certain specific optical fiber type, by
In can arbitrarily choose wherein a certain optical mode in all optical modes that optical fiber allows excitation, and in the corresponding more sound of this optical mode
Measurement, or arbitrary choosing is compared in some characteristic quantity that certain two gain peak is arbitrarily chosen in multiple gain peaks caused by mould
Take certain two characteristic quantity of a gain peak to be compared measurement, thus can according to the case where the optical mode and acoustic mode actually encouraged and
Demand, selection is easy to measure or performance more preferably analyzed by pattern when matching measurement, increases the flexibility of measurement；
(3) temperature provided by the invention and the key of strain while measurement method are the acousto-optic mould from fiber medium itself
Interaction mechanism sets out, and utilizes the interaction between more acoustic modes of the corresponding excitation of a certain optical mode so that its Brillouin increases
Characteristic of the benefit spectrum with multimodal, and be used while realizing temperature and strain and survey to the brillouin gain spectrum of this multimodal
Amount, therefore be not intended to limit and which kind of specific device and method to measure brillouin gain spectrum using, no matter using continuous or pulse
Signal light or pump light, it is every to obtain brillouin gain spectrum using the method for direct detection or coherent detection without limitation
Device or method；
On the other hand, other upper effects are combined to realize temperature and the skill that strain measures simultaneously using brillouin effect with existing
Art is compared, and the beneficial effects of the present invention are merely with brillouin effect, a kind of this effect can be realized to temperature and strain
It measures simultaneously, without introducing additional measurement mechanism or equipment, has many advantages, such as simple structure, strong robustness；
On the other hand, with existing temperature is realized using one or more optical modes in brillouin effect and the effect of single acoustic mode
It is compared with the technology of strain while measurement, the beneficial effects of the present invention are by the optimization design to optical fiber structure, be utilized
Interaction in optical fiber between a variety of acoustic modes of the corresponding excitation of a certain optical mode measures to realize while temperature and strain,
Have the advantages that temperature and strain perceptual sensitivity height, high certainty of measurement.
Description of the drawings
Fig. 1 is provided by the present invention based on the temperature of acousto-optic mould interaction in optical fiber and strain while the stream of measurement method
Cheng Tu；
Fig. 2 is the field pattern for allowing the optical mode encouraged in the embodiment of the present invention in optical fiber in cross section taken in correspondence；Wherein,
Fig. 2 (a) is field patterns of the optical mode LP01 on cross section of optic fibre, and Fig. 2 (b) is fields of the optical mode LP11 on cross section of optic fibre point
Butut；
Fig. 3 is the field in acoustic mode A0m, the A1m and A2m races cross section taken in correspondence for allow in optical fiber in the embodiment of the present invention excitation
Distribution map；
Fig. 4 is more acoustic mode interactions of the corresponding excitation of optical mode when choosing LP01 or LP11 optical modes in the embodiment of the present invention
With the multimodal brillouin gain spectrum of generation；Wherein, Fig. 4 (a) is corresponding multimodal brillouin gain spectrum, figure when choosing LP01 optical modes
4 (b) is corresponding multimodal brillouin gain spectrum when choosing LP11 optical modes；
Fig. 5 is when choosing LP11 optical modes in the embodiment of the present invention, and more acoustic mode interactions of the corresponding excitation of optical mode generate
Multimodal brillouin gain spectrum with temperature and strain variation relation figure；Wherein, Fig. 5 (a) is multimodal brillouin gain spectrum with answering
The variation relation figure of change, Fig. 5 (b) are multimodal brillouin gain spectrum variation with temperature relational graphs；
Fig. 6 be the embodiment of the present invention in choose LP11 optical modes when, multiple Brillouin shifts of multimodal brillouin gain spectrum and
Brillouin gain coefficient with temperature and strain variation relation figure；Wherein, Fig. 6 (a) is change of multiple Brillouin shifts with strain
Change relational graph, Fig. 6 (b) is multiple Brillouin shift variation with temperature relational graphs, and Fig. 6 (c) is multiple brillouin gain coefficients
With the variation relation figure of strain, Fig. 6 (d) is multiple brillouin gain coefficient variation with temperature relational graphs.
Specific implementation mode
In order to make the purpose , technical scheme and advantage of the present invention be clearer, with reference to the accompanying drawings and embodiments, right
The present invention is further elaborated.It should be appreciated that described herein, specific examples are only used to explain the present invention, not
For limiting the present invention.As long as in addition, technical characteristic involved in the various embodiments of the present invention described below that
Conflict is not constituted between this to can be combined with each other.
It is provided in an embodiment of the present invention a kind of based on acousto-optic in optical fiber for the disadvantages described above or Improvement requirement of the prior art
The temperature of mould interaction and strain while measurement method, flow is as shown in Figure 1, specifically comprise the following steps：
(1) the concrete structure characteristic of met modal eigenvalue equation and optical fiber is transmitted in a fiber according to light wave fields,
Obtain number, type and its mode distributions on cross section of optic fibre of all optical modes for allowing excitation in optical fiber；
(2) some arbitrary optical mode is chosen from all optical modes for allowing excitation, is transmitted in a fiber according to acoustic wavefield
The modal eigenvalue equation met obtains number, type and its cross section of optic fibre of the corresponding more acoustic modes excited of this optical mode
On mode distributions；
(3) transmit met modal eigenvalue equation in a fiber according to the acoustic wavefield, obtain this optical mode with it is corresponding
Multiple Brillouin shifts that more acoustic mode interactions generate；According to the number of this described optical mode and its more acoustic modes of corresponding excitation,
The pass of mode distributions and brillouin gain coefficient and the mould field coupling efficiency of acousto-optic mould in type and its cross section of optic fibre
System obtains multiple brillouin gain coefficients that this optical mode is generated with corresponding more acoustic mode interactions；And according to the brillouin frequency
It moves and brillouin gain coefficient, acquisition multimodal brillouin gain spectrum；
(4) according to the refractive index of light wave on cross section of optic fibre and longitudinal rate of sound wave with the pass of temperature and strain variation
System and light wave refractive index and longitudinal rate of sound wave and the relationship of brillouin gain spectrum, obtain this optical mode with it is corresponding more
Acoustic mode interaction generate multimodal brillouin gain spectrum with temperature and strain variation relationship；
(5) two gain peaks are arbitrarily chosen from the multimodal gain spectral that this optical mode is generated with corresponding more acoustic mode interactions
Measurement is compared in some characteristic quantity, or measurement is compared in certain two characteristic quantity of arbitrarily one gain peak of selection, obtains
Brillouin shift variation with temperature coefficientBrillouin shift with strain variation coefficientBrillouin gain coefficient
Variation with temperature coefficientWith brillouin gain coefficient with the variation coefficient of strainAnd according to describedWithEstablish the coefficient square of Brillouin shift and/or brillouin gain coefficient and temperature and strain
Battle array relationship obtains temperature and the strain of optical fiber by solution matrix equation.
It is described in detail below in conjunction with specific embodiment：
Light wave fields transmits the modal eigenvalue equation respectively met with acoustic wavefield and is shown below respectively in a fiber：
Wherein, E refers to mode distributions of the optical mode on cross section of optic fibre, and λ refers to lambda1-wavelength, and n refers to that optical fiber is transversal
Index distribution on face, neffIt refer to the effective refractive index of light field basic mode in a fiber；Wherein, umRefer to m-th of acoustic mode in optical fiber
Mode distributions on cross section, ΩmRefer to the characteristic frequency of sound wave, VlRefer to longitudinal rate distribution of sound wave, the biography of acoustic wave mode
Defeated constant betaac=2 βopt, βopt=2 π neff/ λ is the transmission of light wave pattern.
When by regulating and controlling specific optical fiber structure parameter, such as its relative fefractive index difference, core material, core diameter and packet
Layer structure etc. calculates by bringing index distribution n (x, y) in light wavelength lambda and cross section of optic fibre in formula (1) into and obtains light
Allow mode distributions E (x, y) and its corresponding effective refractive index n of all optical modes of excitation on cross section of optic fibre in fibreeff；
Some arbitrary optical mode is chosen from all optical modes for allowing excitation, by the corresponding effective refractive index n of this optical modeeffIt brings into
In formula (2), mould field of all acoustic modes for obtaining this optical mode correspondence excitation in optical fiber on cross section of optic fibre is further calculated
It is distributed um(x, y) and its corresponding Brillouin shift
In embodiments of the present invention, it is illustrated with the less fundamental mode optical fibre of a certain graded index structure to measure, wherein
Existing optical mode is allowed there are LP01 and LP11 patterns.When the optical mode of selection is LP01 patterns, the acoustic mode for being primarily involved in effect is
A0m races；When the optical mode of selection is LP11 patterns, the acoustic mode for being primarily involved in effect is A0m and A2m races.
Each conduction acoustic mode indicates that wherein k indicates the number for the entire standing wave that field amount is along the circumferential direction distributed with Akm,
Also illustrate that the exponent number of Bessel function, m indicate field amount along the number of radial direction maximum value, k and m determine corresponding modes in cross
Field distribution on section.
Fig. 2 is to allow the field in cross section taken in correspondence point optical mode LP01, LP11 for encouraging in optical fiber in the embodiment of the present invention
Butut, wherein LP01 optical modes are the symmetrical mode distributions of circle, and LP11 optical modes are not rounded symmetrical mode distributions, thus can arbitrarily choose it
In a kind of optical mode carry out subsequent analysis.
Fig. 3 is to allow in optical fiber in acoustic mode A0m, the A1m and A2m races cross section taken in correspondence encouraged in the embodiment of the present invention
Field pattern, wherein A01 races acoustic mode are the symmetrical mode distributions of circle, A1m and A2m races acoustic mode is not rounded symmetrical mode distributions, specifically
Existing acoustic mode has A01, A02, A03 of A0m races, A21, A22, A23 etc. of A11, A12, A13 and A2m race of A1m races.
For the stimulated Brillouin effect that multiple acoustic modes participate in, the acoustic-optio coupling coefficient I of each acoustic wave modeaoIt can indicate
For：
The effective core area A of light fieldeffIt can be expressed as：
Wherein, E1And E2The respectively mode distributions of signal light and pump light, AaoIndicate acousto-optic mould interaction effective area,
The effective core area A of itself and light fieldeffBetween relationship be Aao=Aeff/Iao, then brillouin gain coefficient can be expressed as：
The relationship of effective area is overlapped according to the mould field of the above brillouin gain coefficient and acousto-optic mould, you can obtain this
The brillouin gain coefficient that more acoustic mode interactions of the corresponding excitation of optical mode generate is constituted in conjunction with Brillouin shift in multimodal cloth
Deep gain spectral.
Brillouin gain spectrum and the relationship of Brillouin shift and brillouin gain coefficient are shown below：
Wherein, NacIt is the number for the acoustic mode that this optical mode corresponds to excitation, Δ νBIt is the unimodal spectrum width of each gain, GmWith
BFSmIt is the brillouin gain coefficient and Brillouin shift that m-th of acoustic mode effect generates respectively.
When Fig. 4 is selection LP01 provided by the invention or LP11 optical modes, a kind of this more acoustic mode of the corresponding excitation of optical mode
The multimodal brillouin gain spectrum that interaction generates.When choosing LP01 optical modes, brillouin gain spectrum includes that three gains are unimodal, point
It is not generated by acoustic mode A01, A02 and A03 effect；When choosing LP11 optical modes, brillouin gain spectrum includes that four gains are unimodal, point
It is not generated by acoustic mode A01, A02, A03 and A21, A22, A23 effect, the gain that wherein A02 and A21, A03 and A22 effects generate
It is unimodal overlapped, therefore constitute four peak brillouin gain spectrums.
According to longitudinal rate distribution V of the index distribution n of light wave on cross section of optic fibre and sound wavelBy thermo-optic effect and
Elasto-optical effect and with temperature and strain changed relationship, establish relationship of the multimodal brillouin gain spectrum with temperature and strain,
Longitudinal rate distribution V of the index distribution n of light wave and sound wave wherein on cross section of optic fibrelWith the relational expression of temperature and strain
For：
Wherein, n0And Vl0Respectively the refractive index of fibre cladding and longitudinal velocity of sound, Δ T are temperature variation, and Δ ε is strain
Variable quantity, ωGeAnd ωFThe dopant concentration of Ge and F is indicated respectively.
With longitudinal rate distribution V of the index distribution n (x, y) of light wave on cross section of optic fibre and sound wavelThe change of (x, y)
Change, allows the mode distributions of existing optical mode and acoustic mode also to change therewith in optical fiber, so as to cause Brillouin shift and Brillouin
The variation of gain coefficient.
When Fig. 5 is selection LP11 optical modes provided by the invention, a kind of this more acoustic mode interaction of the corresponding excitation of optical mode
The multimodal brillouin gain spectrum of generation with temperature and strain variation relation figure, the case where when choosing LP01 optical modes with etc
Seemingly, details are not described herein.
Fig. 5 (a) is when choosing LP11 optical modes, in the multimodal cloth that this optical mode is generated with more acoustic mode interactions of corresponding excitation
Deep gain spectral is with the variation relation figure of strain, the visible gradual increase with strain from the figure, multimodal brillouin gain spectrum to
High frequency direction movement, the brillouin gain coefficient of each gain peak also increases or reduces therewith；
Fig. 5 (b) is when choosing LP11 optical modes, in the multimodal cloth that this optical mode is generated with more acoustic mode interactions of corresponding excitation
Deep gain spectral variation with temperature relational graph, the visible gradual increase with temperature from the figure, multimodal brillouin gain spectrum
It is moved towards high frequency direction, the brillouin gain coefficient of each gain peak also increases or reduces therewith, the specific knot of this and optical fiber
The field distribution of structure parameter and the optical mode and acoustic mode of participation effect has relationship.
By changing fibre strain under conditions of temperature-resistant, and change fiber optic temperature under conditions of should become zero,
Choose multiple brillouin frequencies of the multimodal brillouin gain spectrum generated under the acoustic mode interaction of the corresponding excitation of a certain optical mode
It moves and multiple brillouin gain coefficients is with the relationship of temperature and strain, obtain Brillouin shift variation with temperature coefficient
Brillouin shift with strain variation coefficientBrillouin gain coefficient variation with temperature coefficientAnd brillouin gain
Coefficient with strain variation coefficient
When Fig. 6 is selection LP11 optical modes provided by the invention, the multiple Brillouin shifts and cloth of multimodal brillouin gain spectrum
In deep gain coefficient with the variation relation figure of temperature and strain, wherein Fig. 6 (a) is four gain peaks in multimodal brillouin gain spectrum
Brillouin shift with the variation relation figure of strain, Fig. 6 (b) is the brillouin frequency of four gain peaks in multimodal brillouin gain spectrum
Variation with temperature relational graph is moved, Fig. 6 (c) is the brillouin gain coefficient of four gain peaks in multimodal brillouin gain spectrum with answering
The variation relation figure of change, Fig. 6 (d) are the brillouin gain coefficients of four gain peaks in multimodal brillouin gain spectrum with the change of temperature
Change relational graph.
Learn that the multiple Brillouin shifts and brillouin gain coefficient of multimodal brillouin gain spectrum are with temperature by Fig. 6 analyses
Linear relationship is presented in variation with strain, and some optical mode corresponds in the cloth that the multiple and different acoustic modes effects encouraged generate
Deep frequency displacement and brillouin gain coefficient are all different with temperature or the variation coefficient of strain, therefore can be by establishing brillouin frequency
The coefficient matrix relationship with temperature and strain with brillouin gain coefficient is moved, while solution matrix equation realizes temperature and strain
It measures, the cross influence of separation temperature and strain.
Specifically, according to the difference of characteristic quantity is measured in the brillouin gain spectrum of selection, and three kinds of differences can be subdivided into
Measurement of comparison method：
(1) cloth of certain two gain peak in the multimodal gain spectral that this optical mode is generated with corresponding more acoustic mode interactions is chosen
In deep frequency displacement measurements is compared, that is, establish the Brillouin shift of the two gain peaks with temperature and the coefficient matrix of strain public affairs
Formula：
Wherein, Δ T is temperature variation, and Δ ε is strain variation amount, and Δ BFS1 refers to some in the two gain peaks
The corresponding Brillouin shift variable quantity of gain peak, Δ BFS2 refer in the corresponding cloth of another gain peak in the two gain peaks
Deep frequency displacement variable quantity.
(2) cloth of some gain peak in the multimodal gain spectral that this optical mode is generated with corresponding more acoustic mode interactions is chosen
In deep frequency displacement and brillouin gain coefficient measurements is compared, that is, establish Brillouin shift and the Brillouin's increasing of this gain peak
Beneficial coefficient with temperature and strain coefficient matrix formula：
Wherein, Δ T is temperature variation, and Δ ε is strain variation amount, and Δ BFS refers in the corresponding cloth of this gain peak
Deep frequency displacement variable quantity, Δ BGC refer to the corresponding brillouin gain index variation amount of this gain peak.
(3) cloth of certain two gain peak in the multimodal gain spectral that this optical mode is generated with corresponding more acoustic mode interactions is chosen
In deep gain coefficient measurement is compared, that is, establish the brillouin gain coefficient of the two gain peaks with the coefficient of temperature and strain
Matrix Formula：
Wherein, Δ T is temperature variation, and Δ ε is strain variation amount, and Δ BGC1 refers to some in the two gain peaks
The corresponding brillouin gain index variation amount of gain peak, Δ BGC2 refer to that another gain peak in the two gain peaks is corresponding
Brillouin gain index variation amount.
It is important to note that in inventive embodiments, it can be arbitrarily chosen in a variety of optical modes that optical fiber allows excitation
Middle a certain kind optical mode is analyzed, and the multimodal Brillouin generated from the interaction of more acoustic modes of the corresponding excitation of this optical mode increases
Some characteristic quantity that two gain peaks are arbitrarily chosen in benefit spectrum is compared measurements, or arbitrary one gain peak of selection certain two
Measurement is compared in a characteristic quantity, i.e., not only the optical mode of low order can be utilized to be generated in multimodal cloth with the interaction of corresponding more acoustic modes
Deep gain spectral can also utilize the optical mode of high-order to generate multimodal brillouin gain spectrum with the interaction of corresponding more acoustic modes.
In the embodiment of the present invention, multimodal that the interaction between a kind of this more acoustic mode of the corresponding excitation of optical mode generates
In brillouin gain spectrum, the frequency interval (about 140MHz) of two neighboring gain peak is much larger than the unimodal gain spectral of each gain
Wide (about 35MHz), thus gain is unimodal caused by different acoustic mode participation effects will not be overlapped on frequency spectrum, to shape
At distinguishable multimodal gain spectral spectral pattern.
In the embodiment of the present invention, the multimodal of the interaction generation between a kind of this optical mode and its more acoustic modes of corresponding excitation
In brillouin gain spectrum, the difference of the peak gain coefficient of two neighboring gain peak is conducive within 10dB in practical measurement
The accuracy of measurement to Brillouin shift and brillouin gain coefficient is improved in the process.
It should be strongly noted that the present embodiment explanation made for the present invention is descriptively rather than limited, example
As allowed the optical mode of excitation and the type of acoustic mode to be not limited to only LP01, LP11 and A01, A0m, A2m race in Fig. 2 and Fig. 3,
According to the difference that optical fiber structure designs, wherein the optical mode of excitation is allowed corresponding to change to acoustic mode type.It is a certain in Fig. 4
The spectral pattern for the multimodal brillouin gain spectrum that more acoustic mode interactions of the corresponding excitation of optical mode generate specifically includes of gain peak
Frequency interval etc. between the gain coefficient and different gains peak of several, each gain peak can accordingly change.
The method through the invention utilizes the interaction between more acoustic modes of the corresponding excitation of a certain optical mode in optical fiber
With multimodal brillouin gain spectrum is generated, arbitrarily chosen from multimodal brillouin gain spectrum some characteristic quantities of two gain peaks into
Measurement is compared in row matching measurement, or certain two characteristic quantity of arbitrarily one gain peak of selection, and temperature and strain may be implemented
While measure, eliminate temperature and strain the adverse effect of cross sensitivity, and without introducing additional measurement mechanism or equipment,
Have many advantages, such as that simple structure, strong robustness, accuracy of measurement are high.
As it will be easily appreciated by one skilled in the art that the foregoing is merely illustrative of the preferred embodiments of the present invention, not to
The limitation present invention, all within the spirits and principles of the present invention made by all any modification, equivalent and improvement etc., should all include
Within protection scope of the present invention.
Claims (3)
1. a kind of temperature based on optical fiber acousto-optic mould interaction and strain while measurement method, which is characterized in that including walking as follows
Suddenly：
(1) it transmits the architectural characteristic of met modal eigenvalue equation and optical fiber in a fiber according to light wave fields, obtains optical fiber
The middle mode distributions for allowing number, type and the optical mode of all optical modes encouraged on cross section of optic fibre；
(2) it arbitrarily chooses an optical mode from all optical modes for allowing excitation, is transmitted and met in a fiber according to acoustic wavefield
Modal eigenvalue equation obtains number, type and the more acoustic modes of the corresponding more acoustic modes excited of the optical mode in cross section of optic fibre
On mode distributions；
(3) it transmits met modal eigenvalue equation in a fiber according to the acoustic wavefield, obtains the optical mode and corresponding more sound
Multiple Brillouin shifts that mould interaction generates；
According to of mode distributions and the optical mode corresponding more acoustic modes that excite of the optical mode on cross section of optic fibre
The mode distributions and brillouin gain coefficient of number, type, more acoustic modes on cross section of optic fibre couple effect with the mould field of acousto-optic mould
The relationship of rate obtains multiple brillouin gain coefficients that the optical mode is generated with corresponding more acoustic mode interactions；
And according to the Brillouin shift and brillouin gain coefficient, obtain multimodal brillouin gain spectrum；
(4) according to the refractive index of light wave on cross section of optic fibre and longitudinal rate of sound wave with the relationship of temperature and strain variation, with
And the refractive index and longitudinal rate of sound wave and the relationship of brillouin gain spectrum of light wave, it obtains the optical mode and corresponding more acoustic modes is mutual
The multimodal brillouin gain spectrum of generation is acted on the relationship of temperature and strain variation；
(5) arbitrarily chosen from the multimodal gain spectral that the optical mode is generated with corresponding more acoustic mode interactions gain peak certain two
Measurement is compared in a characteristic quantity, obtains Brillouin shift variation with temperature coefficientBrillouin shift with strain change
Change coefficientBrillouin gain coefficient variation with temperature coefficientWith brillouin gain coefficient with the variation coefficient of strain
And according to describedWithIt establishes Brillouin shift and brillouin gain number and temperature and answers
The coefficient matrix relationship of change obtains temperature and the strain of optical fiber by solution matrix equation；
Step (5) is specially：Some gain peak in the multimodal gain spectral generated with corresponding more acoustic mode interactions to the optical mode
Brillouin shift and brillouin gain coefficient measurement is compared, according to measure obtain coefficient
WithEstablish the gain peak Brillouin shift and brillouin gain coefficient with temperature and strain coefficient matrix relationship：
Wherein, Δ T is temperature variation, and Δ ε is strain variation amount, and Δ BFS refers to the corresponding Brillouin shift of the gain peak
Variable quantity, Δ BGC refer to the corresponding brillouin gain index variation amount of the gain peak.
2. temperature as described in claim 1 and strain while measurement method, which is characterized in that light wave fields transmitted in a fiber
Modal eigenvalue equation is：
The modal eigenvalue equation that acoustic wavefield is transmitted in a fiber is：
Wherein, E refers to mode distributions of the optical mode on cross section of optic fibre, and λ refers to lambda1-wavelength, and n refers on cross section of optic fibre
Index distribution, neffIt refer to the effective refractive index of light field basic mode in a fiber；Wherein, umRefer to that m-th of acoustic mode is transversal in optical fiber
Mode distributions on face, ΩmRefer to the characteristic frequency of sound wave, VlRefer to longitudinal rate distribution of sound wave, the transmission of acoustic wave mode is normal
Number βac=2 βopt, βopt=2 π neff/ λ is the transmission of light wave pattern.
3. temperature as claimed in claim 1 or 2 and strain while measurement method, which is characterized in that the cross section of optic fibre
The index distribution n of upper light wave is with temperature and the relationship of strain：
N=n0[1+(1×10-3+3×10-6ΔT+1.5×10-7Δε)×ωGe
+(-3.3×10-3+3.6×10-6ΔT+7.5×10-7Δε)×ωF]；
Longitudinal rate distribution V of sound wave on the cross section of optic fibrelIt is with temperature and the relationship of strain：
Vl=Vl0[1-(7.2×10-3-4.7×10-5ΔT-2.1×10-6Δε)×ωGe
-(2.7×10-2-1.8×10-5ΔT-3.8×10-6Δε)×ωF]；
Wherein, n0For the refractive index of fibre cladding, Vl0For longitudinal velocity of sound of fibre cladding, Δ T is temperature variation, and Δ ε is to answer
Become variable quantity, ωGeFor the doping concentration of Ge, ωFFor the doping concentration of F.
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| US10401563B2 (en) * | 2017-12-14 | 2019-09-03 | Ofs Fitel, Llc | Optical fibers for simultaneous measurement of temperature and strain |
| CN109085676B (en) * | 2018-08-13 | 2020-03-10 | 南京航空航天大学 | Graded-index optical fiber with similar-strength multi-peak Brillouin gain spectrum |
| CN113310423B (en) * | 2021-04-25 | 2023-03-24 | 东南大学 | Crack sensing system and method based on distributed short-gauge-length optical fiber strain sensor |
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