CN105865655A - Simultaneous temperature and strain measuring method based on interaction between acoustic and optical modes in optical fibers - Google Patents

Abstract

The invention discloses a simultaneous temperature and strain measuring method based on interaction between acoustic and optical modes in optical fibers. A multi-peak Brillouin gain spectrum is generated under the interaction between an optical mode excited in an optical fiber and multiple acoustic modes excited correspondingly, one characteristic quantity of two gain peaks or two characteristic quantities of one gain peak are randomly selected from the multi-peak Brillouin gain spectrum for comparison measurement, perception sensitivity coefficients of Brillouin frequency shift and/or Brillouin gain coefficients along with the temperature and strain are acquired, a coefficient matrix is formed, the temperature and strain are acquired by solving a matrix equation, and simultaneous measurement of the temperature and strain is realized. With the adoption of the simultaneous temperature and strain measuring method, extra measuring mechanism or equipment is not required to be introduced while the adverse effect of temperature and strain cross sensitivity is eliminated, and the method has the characteristics that the structure is simple, the robustness is high and the measurement accuracy is high.

Description

A kind of temperature based on optical fiber acousto-optic mould interaction and strain measuring method simultaneously

Technical field

The invention belongs to technical field of optical fiber sensing, more particularly, to one based on optical fiber acousto-optic mould The temperature of interaction and strain measuring method simultaneously.

Background technology

Distributed Optical Fiber Sensing Techniques uses optical fibers as transmission medium and replaces a series of intensive point-like biography Sense array, can measure sensing amounts such as optical fiber temperature everywhere and strains, have certainty of measurement high, The advantage that accurate positioning is wide with the scope of measurement, is widely used in material structure and environmental monitoring etc. numerous Field.A key technical problems during it is applied is how to realize temperature and strain simultaneously and mutual Independent measurement, gets rid of cross influence between the two, as realized getting rid of the high accuracy strain of temperature impact Measure, and get rid of the high-resolution hydrocode of strain impact.

Prior art includes: in early days select general single mode fibers to carry out more, by brillouin effect and other Effect combines while carrying out temperature and strain and measures, and such as utilizes Brillouin scattering and Raman scattering Combine and realize temperature and strain is measured simultaneously, or utilize the brillouin effect of polarization maintaining optical fibre and two-fold Penetrate effect realize temperature and strain measure simultaneously.This kind of method need extra to Raman scattering signal or The birefringent characteristic of optical fiber measures, and adds the difficulty of system building and the complexity of practical operation Degree.

Prior art also includes: utilize multiple different characteristic amounts of brillouin gain spectrum in brillouin effect Compare measurement, such as by optical mode single in single-mode fiber and single acoustic mode interaction produced Brillouin shift and two characteristic quantities of brillouin gain coefficient of unimodal brillouin gain spectrum measure, Reach temperature and strain the purpose simultaneously measured, or utilizing multiple optical modes and single sound in less fundamental mode optical fibre Some characteristic quantity of multiple unimodal brillouin gain spectrum that mould interaction produces is compared measurement, reaches The purpose simultaneously measured to temperature and strain.This kind of method does not utilize some excited in optical fiber Interaction between optical mode with the corresponding many acoustic modes excited produces multimodal brillouin gain spectrum, and this kind of side In method, the perceptual sensitivity for temperature and strain is on the low side, constrain temperature and strain measurement precision and Accuracy.

Summary of the invention

For disadvantages described above or the Improvement requirement of prior art, the invention provides a kind of based on optical fiber sound The temperature of optical mode interaction and strain simultaneously measuring method, particularly utilize excite in optical fiber a certain Interaction between the corresponding many acoustic modes excited of individual optical mode produces multimodal brillouin gain spectrum, from many Peak brillouin gain spectrum is arbitrarily chosen some characteristic quantities of two gain peak compare measurement, or Arbitrarily choose certain two characteristic quantity of a gain peak to compare measurement；Its object is in temperature and Strain eliminates the cross interference between temperature and strain, raising temperature and strain measurement simultaneously in measuring Precision and accuracy.

For achieving the above object, the invention provides a kind of temperature based on optical fiber acousto-optic mould interaction and Strain measuring method simultaneously, comprises the steps:

(1) met modal eigenvalue equation is transmitted in a fiber according to light wave fields, and the knot of optical fiber Structure characteristic, it is thus achieved that the number of all optical modes, kind and the optical mode that allow excitation in optical fiber are transversal at optical fiber Mode distributions on face；

(2) from all optical modes allowing excitation, an optical mode is arbitrarily chosen, according to acoustic wavefield at optical fiber The modal eigenvalue equation that middle transmission is met, it is thus achieved that the number of the many acoustic modes excited corresponding to this optical mode, Kind, and the mode distributions that many acoustic modes are on cross section of optic fibre；

(3) met modal eigenvalue equation is transmitted in a fiber according to described acoustic wavefield, it is thus achieved that described Multiple Brillouin shifts that optical mode produces with corresponding many acoustic modes interaction；

According to described optical mode mode distributions on cross section of optic fibre, and excite corresponding to described optical mode The number of many acoustic modes, kind, many acoustic modes mode distributions on cross section of optic fibre, and Brillouin The relation of the mould field coupling efficiency of gain coefficient and acousto-optic mould, it is thus achieved that described optical mode is mutual with corresponding many acoustic modes Multiple brillouin gain coefficients that effect produces；

And according to described Brillouin shift and brillouin gain coefficient, it is thus achieved that multimodal brillouin gain spectrum；

(4) according to the refractive index of light wave on cross section of optic fibre and longitudinal speed of sound wave with temperature and strain The relation of change, and the relation of longitudinal speed of the refractive index of light wave and sound wave and brillouin gain spectrum, Obtain multimodal brillouin gain spectrum that described optical mode produces with corresponding many acoustic modes interaction with temperature and strain The relation of change；

(5) from the multimodal gain spectral that described optical mode produces with corresponding many acoustic modes interaction, two are arbitrarily chosen Some characteristic quantity of individual gain peak is compared measurement, or arbitrarily chooses certain two of a gain peak Characteristic quantity is compared measurement, obtains Brillouin shift variation with temperature coefficientBrillouin shift Variation coefficient with strainBrillouin gain coefficient variation with temperature coefficientIncrease with Brillouin Benefit coefficient is with the variation coefficient of strain

And according to describedWithSet up Brillouin shift and/or brillouin gain Coefficient and temperature and the coefficient matrix relation of strain, by solution matrix equation obtain optical fiber temperature and Strain.

Preferably, above-mentioned temperature based on optical fiber acousto-optic mould interaction and strain measuring method, light simultaneously The modal eigenvalue equation that wave field transmits in a fiber is:

${\▿}_{\⊥}^{2}E+{\left(\frac{2\mathrm{\π}}{\mathrm{\λ}}\right)}^2(n^2-n_{eff}^2)E=0;$

The modal eigenvalue equation that acoustic wavefield is transmitted in a fiber is:

${\▿}_{\⊥}^2{u}_m+(\frac{{\mathrm{\Ω}}_m^2}{{V_l}^2}-{\mathrm{\β}}_{ac}^2)u_m=0;$

Wherein, E refers to optical mode mode distributions on cross section of optic fibre, and λ refers to that lambda1-wavelength, n are Refer to index distribution on cross section of optic fibre, n_effRefer to light field basic mode effective refractive index in a fiber；Its In, u_mRefer to m-th acoustic mode mode distributions on cross section of optic fibre, Ω_mRefer to the feature of sound wave Frequency, V_lRefer to longitudinal rate distribution of sound wave, transmission β of acoustic wave mode_ac=2 β_opt, β_opt=2 π n_eff/ λ is the transmission of light wave mode.

Preferably, above-mentioned temperature based on optical fiber acousto-optic mould interaction and strain measuring method simultaneously, its On cross section of optic fibre, index distribution n of light wave with the relation of temperature and strain is:

N=n₀[1+(1×10^-3+3×10^-6ΔT+1.5×10^-7Δε)×ω_Ge

+(-3.3×10^-3+3.6×10^-6ΔT+7.5×10^-7Δε)×ω_F]；

Longitudinal rate distribution V of sound wave on its cross section of optic fibre_lWith the relation of temperature and strain it is:

V_l=V_l0[1-(7.2×10^-3-4.7×10^-5ΔT-2.1×10^-6Δε)×ω_Ge

-(2.7×10^-2-1.8×10^-5ΔT-3.8×10^-6Δε)×ω_F]；

Wherein, n₀For the refractive index of fibre cladding, V_l0For longitudinal velocity of sound of fibre cladding, Δ T is that temperature becomes Change amount, Δ ε is strain variation amount, ω_GeFor the doping content of Ge, ω_FDoping content for F.

Preferably, above-mentioned temperature based on optical fiber acousto-optic mould interaction and strain measuring method simultaneously, step Suddenly in (5), certain two in the multimodal gain spectral that this optical mode is produced with corresponding many acoustic modes interaction The Brillouin shift of gain peak is compared measurement, according to measuring the coefficient obtained, sets up the two and increases The Brillouin shift at benefit peak is with the coefficient matrix relation of temperature and strain:

$\left[\begin{array}{c}\mathrm{\Δ}BFS1\\ \mathrm{\Δ}BFS2\end{array}\right]=\left[\begin{array}{cc}{C}_{\mathrm{\μ}\mathrm{\ϵ}}^{BFS1}& C_T^{BFS1}\\ C_{\mathrm{\μ}\mathrm{\ϵ}}^{BFS2}& C_T^{BFS2}\end{array}\right]\left[\begin{array}{c}\mathrm{\Δ}\mathrm{\ϵ}\\ \mathrm{\Δ}T\end{array}\right];$

Wherein, Δ T is temperature variation, and Δ ε is strain variation amount, and Δ BFS1 refers in the two gain peak Brillouin shift variable quantity corresponding to some gain peak, Δ BFS2 refers in the two gain peak The Brillouin shift variable quantity that another gain peak is corresponding.

Preferably, above-mentioned temperature based on optical fiber acousto-optic mould interaction and strain measuring method simultaneously, step Suddenly some in (5), in the multimodal gain spectral that this optical mode is produced with corresponding many acoustic modes interaction The Brillouin shift of gain peak and brillouin gain coefficient are compared measurement, according to measure obtain be Number, set up the Brillouin shift of this gain peak and brillouin gain coefficient with temperature and strain Coefficient matrix relation:

$\left[\begin{array}{c}\mathrm{\Δ}BFS\\ \mathrm{\Δ}BGC\end{array}\right]=\left[\begin{array}{cc}{C}_{\mathrm{\μ}\mathrm{\ϵ}}^{BFS}& C_T^{BFS}\\ C_{\mathrm{\μ}\mathrm{\ϵ}}^{BGC}& C_T^{BGC}\end{array}\right]\left[\begin{array}{c}\mathrm{\Δ}\mathrm{\ϵ}\\ \mathrm{\Δ}T\end{array}\right];$

Wherein, Δ T is temperature variation, and Δ ε is strain variation amount, and Δ BFS refers to this gain peak correspondence Brillouin shift variable quantity, Δ BGC refers to that brillouin gain coefficient corresponding to this gain peak becomes Change amount.

Preferably, above-mentioned temperature based on optical fiber acousto-optic mould interaction and strain measuring method simultaneously, step Suddenly in (5), certain two in the multimodal gain spectral that this optical mode is produced with corresponding many acoustic modes interaction The brillouin gain coefficient of gain peak is compared measurement, according to measuring the coefficient obtained, set up this two The brillouin gain coefficient of individual gain peak is with the coefficient matrix relation of temperature and strain:

$\left[\begin{array}{c}\mathrm{\Δ}BGC1\\ \mathrm{\Δ}BGC2\end{array}\right]=\left[\begin{array}{cc}{C}_{\mathrm{\μ}\mathrm{\ϵ}}^{BGC1}& C_T^{BGC1}\\ C_{\mathrm{\μ}\mathrm{\ϵ}}^{BGC2}& C_T^{BGC2}\end{array}\right]\left[\begin{array}{c}\mathrm{\Δ}\mathrm{\ϵ}\\ \mathrm{\Δ}T\end{array}\right];$

Wherein, Δ T is temperature variation, and Δ ε is strain variation amount, and Δ BGC1 refers in the two gain peak Brillouin gain index variation amount corresponding to some gain peak, Δ BGC2 refers to the two gain peak In brillouin gain index variation amount corresponding to another gain peak.

In general, by the contemplated above technical scheme of the present invention compared with prior art, it is possible to Obtain following beneficial effect:

(1) side that the temperature based on optical fiber acousto-optic mould interaction that the present invention provides is measured with strain simultaneously Method, utilizes the interaction between the corresponding many acoustic modes excited of some optical mode excited in optical fiber to produce Raw multimodal brillouin gain spectrum, arbitrarily chooses a certain of two gain peak from multimodal brillouin gain spectrum Individual characteristic quantity is compared measurement, or certain two characteristic quantity arbitrarily choosing a gain peak are compared Measure, obtain Brillouin shift and/or the brillouin gain coefficient perception sensitivity coefficient with temperature and strain, Constitute coefficient matrix, obtain temperature and strain by solution matrix equation, it is achieved temperature and strain same Time measure；

(2) method that the temperature that the present invention provides is measured with strain simultaneously, is not limited to certain specific Optical fiber kind, owing to can arbitrarily choose wherein a certain light in optical fiber allows all optical modes of excitation Mould, and arbitrarily choose certain two increasings in multiple gain peak produced by many acoustic modes corresponding to this optical mode Some characteristic quantity at benefit peak is compared measurement, or arbitrarily chooses certain two feature of a gain peak Measure measurement of comparing, therefore can choose according to the optical mode of reality excitation and the situation of acoustic mode and demand Easily record or performance is more excellent during matching measurement pattern is analyzed, add the motility of measurement；

(3) temperature of present invention offer and it is critical only that from fiber medium originally of strain measuring method simultaneously The acousto-optic mould interaction mechanism of body sets out, and utilizes between many acoustic modes of a certain corresponding excitation of optical mode Interaction so that its brillouin gain spectrum has the characteristic of multimodal, and the Brillouin to this multimodal Gain spectral is used while realizing temperature and strain and measures, and is therefore not limiting as which kind of uses concrete Apparatus and method measure brillouin gain spectrum, no matter use continuously or the flashlight of pulse or pumping Light, the method using direct detection or coherent detection is all unrestricted, every can obtain brillouin gain spectrum Device or method；

On the other hand, with existing utilize brillouin effect be combined other effects realize temperature and strain with Time the technology measured compare, the beneficial effects of the present invention is, merely with this kind of effect of brillouin effect Should realize measuring while temperature and strain, it is not necessary to introduce extra measurement mechanism or equipment, There is the advantage such as simple structure, strong robustness；

On the other hand, one or more optical modes and single acoustic mode effect in brillouin effect are utilized with existing Realize temperature and compare with straining the technology measured simultaneously, the beneficial effects of the present invention is, by right The optimization design of optical fiber structure, make use of the multiple acoustic mode of a certain corresponding excitation of optical mode in optical fiber Between interaction be used for realize temperature and strain while measure, have temperature and strain perceptual sensitivity The advantage high, certainty of measurement is high.

Accompanying drawing explanation

Fig. 1 be provided by the present invention based on the temperature of acousto-optic mould interaction in optical fiber and strain survey simultaneously The flow chart of metering method；

Fig. 2 is that the optical mode allowing excitation in the embodiment of the present invention in optical fiber field in cross section taken in correspondence is divided Butut；Wherein, Fig. 2 (a) is optical mode LP01 field pattern on cross section of optic fibre, Fig. 2 (b) It it is optical mode LP11 field pattern on cross section of optic fibre；

Fig. 3 is acoustic mode A0m, A1m and A2m race allowing excitation in the embodiment of the present invention in optical fiber Field pattern in cross section taken in correspondence；

When Fig. 4 is to choose LP01 or LP11 optical mode in the embodiment of the present invention, the corresponding excitation of optical mode The interaction of many acoustic modes produce multimodal brillouin gain spectrum；Wherein, Fig. 4 (a) is to choose LP01 Multimodal brillouin gain spectrum corresponding during optical mode, Fig. 4 (b) chooses during LP11 optical mode corresponding many Peak brillouin gain spectrum；

When Fig. 5 is to choose LP11 optical mode in the embodiment of the present invention, many acoustic modes of the corresponding excitation of optical mode The multimodal brillouin gain spectrum that interaction produces is with the variation relation figure of temperature and strain；Wherein, Fig. 5 A () is the multimodal brillouin gain spectrum variation relation figure with strain, Fig. 5 (b) is that multimodal Brillouin increases Benefit spectrum variation with temperature graph of a relation；

When Fig. 6 is to choose LP11 optical mode in the embodiment of the present invention, multiple cloth of multimodal brillouin gain spectrum In deep pool frequency displacement and brillouin gain coefficient with the variation relation figure of temperature and strain；Wherein, Fig. 6 (a) Being multiple Brillouin shift variation relation figure with strain, Fig. 6 (b) is that multiple Brillouin shift is with temperature The variation relation figure of degree, Fig. 6 (c) is multiple brillouin gain coefficient variation relation figure with strain, Fig. 6 (d) is multiple brillouin gain coefficient variation with temperature graphs of a relation.

Detailed description of the invention

In order to make the purpose of the present invention, technical scheme and advantage clearer, below in conjunction with accompanying drawing And embodiment, the present invention is further elaborated.Should be appreciated that described herein specifically Embodiment only in order to explain the present invention, is not intended to limit the present invention.Additionally, basis disclosed below As long as it is the most permissible that the technical characteristic involved by inventing in each embodiment does not constitutes conflict each other It is mutually combined.

For disadvantages described above or the Improvement requirement of prior art, the one that the embodiment of the present invention provides based on The temperature of acousto-optic mould interaction and strain simultaneously measuring method in optical fiber, its flow process is as it is shown in figure 1, concrete Comprise the steps:

(1) met modal eigenvalue equation is transmitted in a fiber according to light wave fields, and the tool of optical fiber Body architectural characteristic, it is thus achieved that allow the number of all optical modes of excitation, kind and horizontal at optical fiber in optical fiber Mode distributions on cross section；

(2) from all optical modes allowing excitation, choose some optical mode arbitrary, exist according to acoustic wavefield Optical fiber transmits the modal eigenvalue equation met, it is thus achieved that the many acoustic modes excited corresponding to this optical mode Mode distributions on number, kind and cross section of optic fibre thereof；

(3) met modal eigenvalue equation is transmitted in a fiber according to described acoustic wavefield, it is thus achieved that this Multiple Brillouin shifts that optical mode produces with corresponding many acoustic modes interaction；According to this optical mode described and The mode distributions on the number of many acoustic modes, kind and cross section of optic fibre thereof that correspondence excites, and background of cloth The relation of the mould field coupling efficiency of deep pool gain coefficient and acousto-optic mould, it is thus achieved that this optical mode and corresponding many acoustic modes Multiple brillouin gain coefficients that interaction produces；And according to described Brillouin shift and brillouin gain Coefficient, it is thus achieved that multimodal brillouin gain spectrum；

(4) according to the refractive index of light wave on cross section of optic fibre and longitudinal speed of sound wave with temperature and strain The relation of change, and the relation of longitudinal speed of the refractive index of light wave and sound wave and brillouin gain spectrum, Obtain multimodal brillouin gain spectrum that this optical mode produces with corresponding many acoustic modes interaction with temperature and strain The relation of change；

(5) from the multimodal gain spectral that this optical mode produces with corresponding many acoustic modes interaction, two are arbitrarily chosen Some characteristic quantity of individual gain peak is compared measurement, or arbitrarily chooses certain two of a gain peak Characteristic quantity is compared measurement, obtains Brillouin shift variation with temperature coefficientBrillouin shift Variation coefficient with strainBrillouin gain coefficient variation with temperature coefficientIncrease with Brillouin Benefit coefficient is with the variation coefficient of strainAnd according to describedWithSet up Brillouin shift and/or brillouin gain coefficient and temperature and the coefficient matrix relation of strain, by solving Matrix equation obtains temperature and the strain of optical fiber.

It is described in detail below in conjunction with specific embodiment:

Light wave fields and acoustic wavefield transmit the modal eigenvalue equation each met in a fiber respectively such as following formula Shown in:

${\▿}_{\⊥}^{2}E+{\left(\frac{2\mathrm{\π}}{\mathrm{\λ}}\right)}^2(n^2-n_{eff}^2)E=0---\left(1\right)$

${\▿}_{\⊥}^2{u}_m+(\frac{{\mathrm{\Ω}}_m^2}{{V_l}^2}-{\mathrm{\β}}_{ac}^2)u_m=0---\left(2\right)$

Wherein, E refers to optical mode mode distributions on cross section of optic fibre, and λ refers to that lambda1-wavelength, n are Refer to index distribution on cross section of optic fibre, n_effRefer to light field basic mode effective refractive index in a fiber；Its In, u_mRefer to m-th acoustic mode mode distributions on cross section of optic fibre, Ω_mRefer to the feature of sound wave Frequency, V_lRefer to longitudinal rate distribution of sound wave, transmission β of acoustic wave mode_ac=2 β_opt, β_opt=2 π n_eff/ λ is the transmission of light wave mode.

When by regulating and controlling concrete optical fiber structure parameter, such as its refractive index contrast, core material, Core diameter and cladding structure etc., by by index distribution in light wavelength lambda and cross section of optic fibre (x, y) brings in formula (1) n, calculates and allows all optical modes encouraged transversal at optical fiber in acquisition optical fiber Mode distributions E on face (x, y) and the effective refractive index n of correspondence_eff；From all light allowing excitation Mould is chosen some optical mode arbitrary, by effective refractive index n corresponding for this optical mode_effBring formula (2) into In, during calculating obtains optical fiber further, all acoustic modes of this optical mode correspondence excitation are on cross section of optic fibre Mode distributions u_m(x, y) and the Brillouin shift of correspondence

In embodiments of the present invention, carry out with the less fundamental mode optical fibre citing of a certain graded index structure Measure, wherein allow the optical mode existed to have LP01 and LP11 pattern.When the optical mode chosen is LP01 During pattern, the acoustic mode being primarily involved in effect is A0m race；When the optical mode chosen is LP11 pattern, The acoustic mode being primarily involved in effect is A0m and A2m race.

Each conduction acoustic mode Akm represents, wherein k represent field amount be along the circumferential direction distributed whole The number of standing wave, also illustrates that the exponent number of Bessel function, and m represents that field is measured along radial direction maximum Number, k and m determines corresponding modes field distribution on cross section.

Fig. 2 is in the embodiment of the present invention, allows optical mode LP01, LP11 of excitation corresponding horizontal in optical fiber Field pattern on cross section, wherein LP01 optical mode is circle symmetric mode field distribution, and LP11 optical mode is not rounded Symmetric mode field distribution, thus can arbitrarily choose a kind of optical mode therein and carry out subsequent analysis.

Fig. 3 is in the embodiment of the present invention, allows acoustic mode A0m, A1m and A2m of excitation in optical fiber Field pattern in race's cross section taken in correspondence, wherein A01 race acoustic mode for circle symmetric mode field distribution, A1m and A2m race acoustic mode is not rounded symmetric mode field distribution, the concrete acoustic mode existed have the A01 of A0m race, A02, A21, A22, A23 etc. of A11, A12, A13 and A2m race of A03, A1m race.

The stimulated Brillouin effect that multiple acoustic modes are participated in, the acoustic-optio coupling coefficient of each acoustic wave mode I^aoCan be expressed as:

$I^{ao}=\frac{{(\∫\∫E_1\·E_2\·u_{m}dxdy)}^2}{\∫\∫E_1^2\·E_2^{2}dxdy\·\∫\∫u_m^2}---\left(3\right)$

The effective core area A of light field_effCan be expressed as:

$A_{eff}=\frac{\∫\∫E_1^{2}dxdy\·\∫\∫E_2^{2}dxdy}{\∫\∫E_1^2\·E_2^{2}dxdy\·}---\left(4\right)$

Wherein, E₁And E₂It is respectively the mode distributions of flashlight and pump light, A^aoRepresent that acousto-optic mould interaction has Effect area, itself and the effective core area A of light field_effBetween relation be A^ao=A_eff/I^ao, then Brillouin Gain coefficient can be expressed as:

$g_m=\frac{I_{ao}}{A_{eff}}=\frac{1}{A^{ao}}=\frac{{(\∫\∫E_1\·E_2\·u_{m}dxdy)}^2}{\∫\∫E_1^{2}dxdy\·\∫\∫E_2^{2}dxdy\·\∫\∫u_m^{2}dxdy}---\left(5\right)$

Mould field according to above brillouin gain coefficient Yu acousto-optic mould overlaps the relation of effective area, Obtain the brillouin gain coefficient that many acoustic modes interaction of the corresponding excitation of this optical mode produces, knot Close Brillouin shift and constitute multimodal brillouin gain spectrum.

Brillouin gain spectrum is shown below with the relation of Brillouin shift and brillouin gain coefficient:

$BGS\left(v\right)={\Σ}_{m=1}^{N_{ac}}{G}^m\frac{{({\mathrm{\Δv}}_B/2)}^2}{{({\mathrm{\Δv}}_B/2)}^2+{(v-{\mathrm{BFS}}^m)}^2}---\left(6\right)$

Wherein, N_acIt is the number of the acoustic mode of this optical mode correspondence excitation, Δ ν_BIt is the unimodal spectrum width of each gain, G^mAnd BFS^mIt is brillouin gain coefficient and the Brillouin shift of m-th acoustic mode effect generation respectively.

Fig. 4 for the present invention provide when choosing LP01 or LP11 optical mode, this kind of optical mode is corresponding The multimodal brillouin gain spectrum that many acoustic modes interaction of excitation produces.When choosing LP01 optical mode, background of cloth It is unimodal that deep pool gain spectral comprises three gains, is produced by acoustic mode A01, A02 and A03 effect respectively；When When choosing LP11 optical mode, it is unimodal that brillouin gain spectrum comprises four gains, respectively by acoustic mode A01, A02, A03 and A21, A22, A23 effect produce, and wherein A02 and A21, A03 and A22 effect are produced Raw gain is unimodal overlapped, therefore constitutes four peak brillouin gain spectrum.

According to index distribution n of light wave on cross section of optic fibre and longitudinal rate distribution V of sound wave_lIt is subject to Thermo-optic effect and elasto-optical effect and the relation that changes with temperature and strain, set up multimodal Brillouin and increase Benefit spectrum with temperature and the relation of strain, wherein index distribution n of light wave and sound wave on cross section of optic fibre Longitudinal rate distribution V_lWith the relational expression of temperature and strain it is:

$\begin{array}{c}n=n_0[1+(1\×{10}^{-3}+3\×{10}^{-6}\mathrm{\ΔT}+1.5\×{10}^{-7}\mathrm{\Δ\ϵ})\×{\mathrm{\ω}}_{\mathrm{Ge}}\\ +(-3.3\×{10}^{-3}+3.6\×{10}^{-6}\mathrm{\ΔT}+7.5\×{10}^{-7}\mathrm{\Δ\ϵ})\×{\mathrm{\ω}}_F]\end{array}---\left(7\right)$

$\begin{array}{c}{V}_l=V_{l0}[1-(7.2\×{10}^{-3}-4.7\×{10}^{-5}\mathrm{\ΔT}-2.1\×{10}^{-6}\mathrm{\Δ\ϵ})\×{\mathrm{\ω}}_{\mathrm{Ge}}\\ -(2.7\×{10}^{-2}-1.8\×{10}^{-5}\mathrm{\ΔT}-3.8\×{10}^{-6}\mathrm{\Δ\ϵ})\×{\mathrm{\ω}}_F]\end{array}---\left(8\right)$

Wherein, n₀And V_l0Being respectively the refractive index of fibre cladding and longitudinal velocity of sound, Δ T is temperature variation, Δ ε For strain variation amount, ω_GeAnd ω_FRepresent the dopant concentration of Ge and F respectively.

Along with on cross section of optic fibre light wave index distribution n (x, y) and longitudinal rate distribution of sound wave V_l(x, change y), allow the mode distributions of optical mode and the acoustic mode existed to change the most therewith in optical fiber, from And cause Brillouin shift and the change of brillouin gain coefficient.

Fig. 5 for the present invention provide when choosing LP11 optical mode, this corresponding excitation of a kind of optical mode is many The multimodal brillouin gain spectrum that acoustic mode interaction produces is with the variation relation figure of temperature and strain, when choosing Situation during LP01 optical mode is similar to therewith, does not repeats them here.

When Fig. 5 (a) is to choose LP11 optical mode, this optical mode produces with many acoustic modes interaction of corresponding excitation Raw multimodal brillouin gain spectrum with the variation relation figure of strain, from this figure visible along with strain by Cumulative multimodal brillouin gain spectrum moves towards high frequency direction greatly, the brillouin gain of each gain peak Coefficient increases the most therewith or reduces；

When Fig. 5 (b) is to choose LP11 optical mode, many acoustic modes interaction of this optical mode and corresponding excitation The multimodal brillouin gain spectrum variation with temperature graph of a relation produced, visible along with temperature from this figure Being gradually increased, multimodal brillouin gain spectrum also moves towards high frequency direction, the Brillouin of each gain peak Gain coefficient increases the most therewith or reduces, this and the concrete structure parameter of optical fiber and the light of participation effect The field distribution of mould and acoustic mode all has relation.

By changing fibre strain under conditions of temperature-resistant, and change under conditions of answering vanishing Fiber optic temperature, chooses the multimodal background of cloth produced under the acoustic mode interaction of a certain corresponding excitation of optical mode Deep pool multiple Brillouin shifts of gain spectral and multiple brillouin gain coefficient with temperature and the relation of strain, Obtain Brillouin shift variation with temperature coefficientBrillouin shift is with the variation coefficient of strain Brillouin gain coefficient variation with temperature coefficientWith brillouin gain coefficient with the change system strained Number

Fig. 6 for the present invention provide when choosing LP11 optical mode, multiple background of cloth of multimodal brillouin gain spectrum Deep pool frequency displacement and brillouin gain coefficient are with the variation relation figure of temperature and strain, and wherein Fig. 6 (a) is many In peak brillouin gain spectrum, the Brillouin shift of four gain peak is with the variation relation figure of strain, Fig. 6 (b) It is the Brillouin shift variation with temperature graph of a relation of four gain peak in multimodal brillouin gain spectrum, Fig. 6 C () is that the brillouin gain coefficient of four gain peak in multimodal brillouin gain spectrum closes with the change of strain System's figure, Fig. 6 (d) is that the brillouin gain coefficient of four gain peak in multimodal brillouin gain spectrum is with temperature The variation relation figure of degree.

Learnt by Fig. 6 analysis, multiple Brillouin shifts of multimodal brillouin gain spectrum and brillouin gain Coefficient all presents linear relationship with the change of temperature and strain, and the excitation of some optical mode correspondence is multiple The Brillouin shift of different acoustic mode effect generations and brillouin gain coefficient are with temperature or the change of strain Coefficient all differs, therefore, it is possible to by set up Brillouin shift and brillouin gain coefficient with temperature and The coefficient matrix relation of strain, solution matrix equation is measured while realizing temperature and strain, is separated temperature Degree and the cross influence of strain.

Specifically, the brillouin gain spectrum according to selection is measured the difference of characteristic quantity, can segment again It is three kinds of different measurement of comparison methods:

(1) certain two in the multimodal gain spectral that this optical mode produces are chosen with corresponding many acoustic modes interaction The Brillouin shift of gain peak is compared measurement, i.e. set up the Brillouin shift of the two gain peak with The coefficient matrix formula of temperature and strain:

$\left[\begin{array}{c}\mathrm{\Δ}BFS1\\ \mathrm{\Δ}BFS2\end{array}\right]=\left[\begin{array}{cc}{C}_{\mathrm{\μ}\mathrm{\ϵ}}^{BFS1}& C_T^{BFS1}\\ C_{\mathrm{\μ}\mathrm{\ϵ}}^{BFS2}& C_T^{BFS2}\end{array}\right]\left[\begin{array}{c}\mathrm{\Δ}\mathrm{\ϵ}\\ \mathrm{\Δ}T\end{array}\right]---\left(9\right)$

Wherein, Δ T is temperature variation, and Δ ε is strain variation amount, and Δ BFS1 refers in the two gain peak Brillouin shift variable quantity corresponding to some gain peak, Δ BFS2 refers in the two gain peak The Brillouin shift variable quantity that another gain peak is corresponding.

(2) some in the multimodal gain spectral that this optical mode produces is chosen with corresponding many acoustic modes interaction The Brillouin shift of gain peak and brillouin gain coefficient are compared measurement, i.e. set up this gain The Brillouin shift at peak and brillouin gain coefficient are with the coefficient matrix formula of temperature and strain:

$\left[\begin{array}{c}\mathrm{\Δ}BFS\\ \mathrm{\Δ}BGC\end{array}\right]=\left[\begin{array}{cc}{C}_{\mathrm{\μ}\mathrm{\ϵ}}^{BFS}& C_T^{BFS}\\ C_{\mathrm{\μ}\mathrm{\ϵ}}^{BGC}& C_T^{BGC}\end{array}\right]\left[\begin{array}{c}\mathrm{\Δ}\mathrm{\ϵ}\\ \mathrm{\Δ}T\end{array}\right]---\left(10\right)$

Wherein, Δ T is temperature variation, and Δ ε is strain variation amount, and Δ BFS refers to this gain peak pair The Brillouin shift variable quantity answered, Δ BGC refers to the brillouin gain coefficient that this gain peak is corresponding Variable quantity.

(3) certain two in the multimodal gain spectral that this optical mode produces are chosen with corresponding many acoustic modes interaction The brillouin gain coefficient of gain peak is compared measurement, and the Brillouin i.e. setting up the two gain peak increases Benefit coefficient is with the coefficient matrix formula of temperature and strain:

$\left[\begin{array}{c}\mathrm{\Δ}BGC1\\ \mathrm{\Δ}BGC2\end{array}\right]=\left[\begin{array}{cc}{C}_{\mathrm{\μ}\mathrm{\ϵ}}^{BGC1}& C_T^{BGC1}\\ C_{\mathrm{\μ}\mathrm{\ϵ}}^{BGC2}& C_T^{BGC2}\end{array}\right]\left[\begin{array}{c}\mathrm{\Δ}\mathrm{\ϵ}\\ \mathrm{\Δ}T\end{array}\right]---\left(11\right)$

Wherein, Δ T is temperature variation, and Δ ε is strain variation amount, and Δ BGC1 refers to the two gain peak In brillouin gain index variation amount corresponding to some gain peak, Δ BGC2 refers to the two gain The brillouin gain index variation amount that another gain peak in peak is corresponding.

It is important to note that in inventive embodiments, can be in optical fiber allows the multiple optical mode of excitation Arbitrarily choose wherein a certain optical mode to be analyzed, from many acoustic modes of the corresponding excitation of this optical mode Some characteristic quantity arbitrarily choosing two gain peak in the multimodal brillouin gain spectrum that interaction produces enters Row matching measurement, or certain two characteristic quantity arbitrarily choosing a gain peak compare measurement, the most not The optical mode of low order only can be utilized to produce multimodal brillouin gain spectrum with the interaction of corresponding many acoustic modes, also The optical mode of high-order can be utilized to produce multimodal brillouin gain spectrum with the interaction of corresponding many acoustic modes.

Interaction in the embodiment of the present invention, between many acoustic modes of this corresponding excitation of a kind of optical mode In the multimodal brillouin gain spectrum produced, the frequency interval (about 140MHz) of adjacent two gain peak is remote The gain spectrum width (about 35MHz) unimodal more than each gain, the most different acoustic mode participation effects is produced Raw gain is unimodal will not be overlapped on frequency spectrum, thus forms distinguishable multimodal gain spectral spectral pattern.

Interaction in the embodiment of the present invention, between many acoustic modes of this kind of optical mode and corresponding excitation thereof In the multimodal brillouin gain spectrum produced, the difference of the peak gain coefficient of adjacent two gain peak all exists Within 10dB, be conducive to improving Brillouin shift and brillouin gain coefficient during reality is measured Accuracy of measurement.

It should be strongly noted that the present embodiment explanation made for the present invention is descriptively rather than limit Qualitatively, such as Fig. 2 and Fig. 3 allow the optical mode of excitation and the kind of acoustic mode to be only not limited to LP01, LP11 and A01, A0m, A2m race, according to the difference of optical fiber structure design, wherein allow The optical mode of excitation can corresponding change to acoustic mode kind.The a certain corresponding excitation of optical mode in Fig. 4 The spectral pattern of multimodal brillouin gain spectrum that produces of many acoustic modes interaction, specifically include gain peak number, Frequency interval etc. between gain coefficient and the different gains peak of each gain peak can change accordingly Become.

By the method for the invention, utilize many acoustic modes of a certain corresponding excitation of optical mode in optical fiber Between interaction produce multimodal brillouin gain spectrum, from multimodal brillouin gain spectrum, arbitrarily choose two Some characteristic quantity of individual gain peak is compared measurement, or arbitrarily chooses certain two of a gain peak Characteristic quantity is compared measurement, it is possible to achieve measures while temperature and strain, eliminates temperature and strain The adverse effect of cross sensitivity, and without introducing extra measurement mechanism or equipment, there is structure letter Easily, strong robustness, accuracy of measurement advantages of higher.

As it will be easily appreciated by one skilled in the art that and the foregoing is only presently preferred embodiments of the present invention, Not in order to limit the present invention, all made within the spirit and principles in the present invention any amendment, etc. With replacement and improvement etc., should be included within the scope of the present invention.

Claims (6)

1. temperature based on an optical fiber acousto-optic mould interaction and strain measuring method simultaneously, its feature exists In, comprise the steps:

(1) met modal eigenvalue equation is transmitted in a fiber according to light wave fields, and the knot of optical fiber Structure characteristic, it is thus achieved that the number of all optical modes, kind and the optical mode that allow excitation in optical fiber are transversal at optical fiber Mode distributions on face；

(2) from all optical modes allowing excitation, an optical mode is arbitrarily chosen, according to acoustic wavefield at optical fiber The modal eigenvalue equation that middle transmission is met, it is thus achieved that the number of the many acoustic modes excited corresponding to described optical mode, Kind, and the mode distributions that many acoustic modes are on cross section of optic fibre；

(3) met modal eigenvalue equation is transmitted in a fiber according to described acoustic wavefield, it is thus achieved that described Multiple Brillouin shifts that optical mode produces with corresponding many acoustic modes interaction；

According to described optical mode mode distributions on cross section of optic fibre, and excite corresponding to described optical mode The number of many acoustic modes, kind, many acoustic modes mode distributions on cross section of optic fibre, and Brillouin The relation of the mould field coupling efficiency of gain coefficient and acousto-optic mould, it is thus achieved that described optical mode is mutual with corresponding many acoustic modes Multiple brillouin gain coefficients that effect produces；

And according to described Brillouin shift and brillouin gain coefficient, it is thus achieved that multimodal brillouin gain spectrum；

(4) according to the refractive index of light wave on cross section of optic fibre and longitudinal speed of sound wave with temperature and strain The relation of change, and the relation of longitudinal speed of the refractive index of light wave and sound wave and brillouin gain spectrum, Obtain multimodal brillouin gain spectrum that described optical mode produces with corresponding many acoustic modes interaction with temperature and strain The relation of change；

(5) from the multimodal gain spectral that described optical mode produces with corresponding many acoustic modes interaction, two are arbitrarily chosen Some characteristic quantity of individual gain peak is compared measurement, or arbitrarily chooses certain two of a gain peak Characteristic quantity is compared measurement, obtains Brillouin shift variation with temperature coefficientBrillouin shift Variation coefficient with strainBrillouin gain coefficient variation with temperature coefficientIncrease with Brillouin Benefit coefficient is with the variation coefficient of strain

And according to describedWithSet up Brillouin shift and/or brillouin gain Coefficient and temperature and the coefficient matrix relation of strain, by solution matrix equation obtain optical fiber temperature and Strain.

2. temperature as claimed in claim 1 and strain measuring method simultaneously, it is characterised in that light wave The modal eigenvalue equation that field is transmitted in a fiber is:

${\▿}_{\⊥}^{2}E+{\left(\frac{2\mathrm{\π}}{\mathrm{\λ}}\right)}^2(n^2-n_{eff}^2)E=0;$

The modal eigenvalue equation that acoustic wavefield is transmitted in a fiber is:

${\▿}_{\⊥}^2{u}_m+(\frac{{\mathrm{\Ω}}_m^2}{V_l^2}-{\mathrm{\β}}_{ac}^2)u_m=0;$

Wherein, E refers to optical mode mode distributions on cross section of optic fibre, and λ refers to that lambda1-wavelength, n are Refer to index distribution on cross section of optic fibre, n_effRefer to light field basic mode effective refractive index in a fiber；Its In, u_mRefer to m-th acoustic mode mode distributions on cross section of optic fibre, Ω_mRefer to the feature of sound wave Frequency, V_lRefer to longitudinal rate distribution of sound wave, transmission β of acoustic wave mode_ac=2 β_opt, β_opt=2 π n_eff/ λ is the transmission of light wave mode.

Temperature the most as claimed in claim 1 or 2 and strain measuring method simultaneously, it is characterised in that On described cross section of optic fibre, index distribution n of light wave with the relation of temperature and strain is:

N=n₀[1+(1×10^-3+3×10^-6ΔT+1.5×10^-7Δε)×ω_Ge

+(-3.3×10^-3+3.6×10^-6ΔT+7.5×10^-7Δε)×ω_F]；

Longitudinal rate distribution V of sound wave on described cross section of optic fibre_lWith the relation of temperature and strain it is:

V_l=V_l0[1-(7.2×10^-3-4.7×10^-5ΔT-2.1×10^-6Δε)×ω_Ge

-(2.7×10^-2-1.8×10^-5ΔT-3.8×10^-6Δε)×ω_F]；

Wherein, n₀For the refractive index of fibre cladding, V_l0For longitudinal velocity of sound of fibre cladding, Δ T is that temperature becomes Change amount, Δ ε is strain variation amount, ω_GeFor the doping content of Ge, ω_FDoping content for F.

4. temperature as claimed in claim 1 and strain measuring method simultaneously, it is characterised in that step (5) particularly as follows: in the multimodal gain spectral that described optical mode is produced with corresponding many acoustic modes interaction certain two The Brillouin shift of individual gain peak is compared measurement, according to measuring the coefficient obtained WithSet up the Brillouin shift of said two gain peak with temperature and the coefficient matrix of strain Relation:

$\left[\begin{array}{c}\mathrm{\Δ}BFS1\\ \mathrm{\Δ}BFS2\end{array}\right]=\left[\begin{array}{cc}{C}_{\mathrm{\μ}\mathrm{\ϵ}}^{BFS1}& C_T^{BFS1}\\ C_{\mathrm{\μ}\mathrm{\ϵ}}^{BFS2}& C_T^{BFS2}\end{array}\right]\left[\begin{array}{c}\mathrm{\Δ}\mathrm{\ϵ}\\ \mathrm{\Δ}T\end{array}\right];$

Wherein, Δ T is temperature variation, and Δ ε is strain variation amount, and Δ BFS1 refers to said two gain peak In Brillouin shift variable quantity corresponding to some gain peak, Δ BFS2 refers to said two gain peak In Brillouin shift variable quantity corresponding to another gain peak.

5. temperature as claimed in claim 1 and strain measuring method simultaneously, it is characterised in that step (5) particularly as follows: certain in the multimodal gain spectral that described optical mode is produced with corresponding many acoustic modes interaction The Brillouin shift of gain peak and brillouin gain coefficient are compared measurement, according to measure obtain be NumberWithSet up Brillouin shift and the brillouin gain system of described gain peak Number is with the coefficient matrix relation of temperature and strain:

$\left[\begin{array}{c}\mathrm{\Δ}BFS\\ \mathrm{\Δ}BGC\end{array}\right]=\left[\begin{array}{cc}{C}_{\mathrm{\μ}\mathrm{\ϵ}}^{BFS}& C_T^{BFS}\\ C_{\mathrm{\μ}\mathrm{\ϵ}}^{BGC}& C_T^{BGC}\end{array}\right]\left[\begin{array}{c}\mathrm{\Δ}\mathrm{\ϵ}\\ \mathrm{\Δ}T\end{array}\right];$

Wherein, Δ T is temperature variation, and Δ ε is strain variation amount, and Δ BFS refers to that described gain peak is corresponding Brillouin shift variable quantity, Δ BGC refers to the brillouin gain index variation that described gain peak is corresponding Amount.

6. temperature as claimed in claim 1 and strain measuring method simultaneously, it is characterised in that step (5) particularly as follows: in the multimodal gain spectral that described optical mode is produced with corresponding many acoustic modes interaction certain two The brillouin gain coefficient of individual gain peak is compared measurement, according to measuring the coefficient obtained WithSet up the brillouin gain coefficient of said two gain peak with temperature and the coefficient of strain Matrix relationship:

$\left[\begin{array}{c}\mathrm{\Δ}BGC1\\ \mathrm{\Δ}BGC2\end{array}\right]=\left[\begin{array}{cc}{C}_{\mathrm{\μ}\mathrm{\ϵ}}^{BGC1}& C_T^{BGC1}\\ C_{\mathrm{\μ}\mathrm{\ϵ}}^{BGC2}& C_T^{BGC2}\end{array}\right]\left[\begin{array}{c}\mathrm{\Δ}\mathrm{\ϵ}\\ \mathrm{\Δ}T\end{array}\right];$

Wherein, Δ T is temperature variation, and Δ ε is strain variation amount, and Δ BGC1 refers to said two gain peak In brillouin gain index variation amount corresponding to some gain peak, Δ BGC2 refers to that said two increases Brillouin gain index variation amount corresponding to another gain peak in benefit peak.