CN113008302B

CN113008302B - Temperature and acoustic resistance double-parameter sensing method and device based on forward Brillouin scattering

Info

Publication number: CN113008302B
Application number: CN202110222185.0A
Authority: CN
Inventors: 路元刚; 张泽霖; 彭楗钦; 吉正源
Original assignee: Nanjing University of Aeronautics and Astronautics
Current assignee: Nanjing University of Aeronautics and Astronautics
Priority date: 2021-02-28
Filing date: 2021-02-28
Publication date: 2021-11-23
Anticipated expiration: 2041-02-28
Also published as: CN113008302A

Abstract

The invention is based on the fact that temperature and acoustic resistance respectively cause R_0,mThe method and the device for sensing the temperature and the acoustic impedance double parameters based on the forward Brillouin scattering are provided, so that the temperature and the acoustic impedance double parameters can be sensed simultaneously, the method and the device have the advantages of easiness in implementation and simplicity and convenience in operation, compared with the prior art, the method and the device have higher sensing measurement accuracy while realizing a double parameter sensor, and are suitable for popularization and application in related technical fields of chemical engineering, oil and gas storage and detection, tumor detection and the like.

Description

Temperature and acoustic resistance double-parameter sensing method and device based on forward Brillouin scattering

Technical Field

The invention relates to the technical field of optical fiber sensing, in particular to a temperature and acoustic resistance double-parameter sensing method and device based on forward Brillouin scattering, which can be applied to the related fields of chemical engineering, oil gas detection and storage, tumor identification and detection and the like.

Background

In recent years, Forward Brillouin Scattering (FBS) in optical fibers has been fully utilized as a typical acousto-optic interaction in related technologies such as optical frequency comb generation, fiber lasers and microcavity optics. In addition, the forward sound field excited by the forward brillouin scattering can respond to the changes of physical quantities such as temperature, strain and acoustic resistance, and is gradually applied to the field of optical fiber sensing. For example, a temperature/strain sensor based on forward brillouin scattering can realize temperature/strain sensing by measuring the linear change relationship between the temperature/optical fiber axial deformation and the forward sound field central resonance frequency. In addition, the acoustic resistance sensor based on the forward Brillouin scattering utilizes the different reflectivity of the acoustic wave reflection at the fiber cladding-medium boundary under different external medium environments, and can realize external acoustic resistance sensing by measuring the change relationship between the external acoustic resistance and the forward stimulated forward Brillouin scattering spectrum line width.

At present, most of temperature/acoustic resistance sensors based on forward Brillouin scattering are single-parameter sensors, and only single-parameter sensing of temperature/acoustic resistance can be realized. The conventional multi-parameter optical fiber sensor, such as double-parameter sensing based on multi-acoustic waveguide brillouin scattering, double-parameter sensing based on few-mode optical fiber brillouin scattering and double-parameter sensing based on optical fiber brillouin scattering and rayleigh scattering mechanisms, realizes double-parameter measurement of temperature and strain by combining backward brillouin scattering. However, the sound field excited by the backward brillouin scattering is an axial sound field, stable sound wave reflection cannot be formed at the interface of the optical fiber cladding and the external medium to sense the change of the acoustic resistance of the external medium, double-parameter sensing of the acoustic resistance of the medium, temperature and other physical quantities cannot be realized, and the application range of the double-parameter sensing in the fields of chemical engineering, oil-gas detection, storage and the like is limited. Therefore, how to explore a new sensing mechanism to realize high-precision and double-parameter sensing of temperature and acoustic resistance by combining the existing single parameter sensor technology based on temperature/acoustic resistance of forward brillouin scattering and the like is a key problem to be solved urgently.

Disclosure of Invention

Aiming at the defects in the prior art, the invention designs a temperature and acoustic resistance double-parameter sensing method and device based on forward Brillouin scattering aiming at a double-parameter optical fiber sensing technology, and realizes high-precision double-parameter sensing of temperature and external medium acoustic resistance by fully utilizing the linear response characteristics of forward stimulated forward Brillouin scattering spectrum (central frequency/line width) and temperature/acoustic resistance.

The technical scheme provided by the invention is as follows:

a temperature and acoustic resistance double-parameter sensing method based on forward Brillouin scattering is characterized in that the temperature and acoustic resistance linear response characteristics of a sensing optical fiber are obtained through the following steps:

step S1: solving for temperature and acoustic resistance parameters using equations (1) and (2)

Acquiring a forward Brillouin scattering spectrogram excited by a radial acoustic mode of the sensing optical fiber in an initial state, wherein the frequency spectrum of an mth scattering peak is R_0,mExcited forward Brillouin scattering spectrum, said R_0,mThe center frequency of the excited forward Brillouin scattering spectrum is ν, and the line width is Γ, then:

ν＝ν_O+C_ν-T·ΔT+C_ν-Z·ΔZ (1)

Γ＝Γ_O+C_Γ-T·ΔT+C_Γ-Z·ΔZ (2)

wherein, v_oAnd r_oAre respectively R in the initial state_0,mExciting the central frequency and the line width of the forward Brillouin scattering spectrum; c_ν-TAnd C_ν-ZAre each R_0,mExciting a frequency shift-temperature and frequency shift-acoustic resistance linear response coefficient of a forward Brillouin scattering spectrum; c_Г-TAnd C_Г-ZAre each R_0,mExciting a line width-temperature coefficient and a line width-acoustic resistance linear response coefficient of a forward Brillouin scattering spectrum; Δ T and Δ Z represent the change values of the external ambient temperature and the acoustic resistance, respectively, compared to the initial state;

step S2: solving for measurement uncertainty of temperature and acoustic resistance parameters using equations (3) through (6)

Let R_0,mThe measurement uncertainties of the center frequency and the line width of the excited forward Brillouin scattering spectrum are respectively delta ν and delta Γ, and then:

δν＝C_ν-T·δT+C_ν-Z·δZ (3)

δΓ＝C_Γ-T·δT+C_Γ-Z·δZ (4)

wherein δ T and δ Z are the measurement uncertainties of the temperature and acoustic resistance of the detection environment, respectively, and are expressed as:

preferably, m is 8.

A sensing device for implementing the dual parameter sensing method as described above, comprising a light source, a fiber sagnac loop, a photodetector and a data acquisition and processing system;

the optical fiber Sagnac ring consists of a coupler, a polarization controller and a sensing optical fiber;

the data acquisition and processing system comprises a frequency spectrograph;

in the optical fiber sagnac loop, aiming at the light wave signal entering the sensing optical fiber through the input end of the coupler, the polarization controller inhibits the forward Brillouin scattering signal excited by the torsion radial acoustic mode in the optical fiber, and at the output end of the coupler, the light wave signal subjected to acousto-optic phase modulation is converted into an electric signal through the photoelectric detector and is sent to the data acquisition and processing system, and then the analysis of the signal spectrum is completed in the data acquisition and processing system.

On the basis of the above scheme, a further improved or preferred scheme further comprises:

further, an optical isolator and an optical attenuator are arranged between the light source and the input end of the optical fiber sagnac loop, and light wave signals emitted by the light source are adjusted by the optical isolator and the optical attenuator and then enter the input end of the optical fiber sagnac loop.

Preferably, the sensing optical fiber is a large-effective-area optical fiber with a coating layer removed.

Preferably, the large effective area fiber has a length of 11.5m, a core diameter and a cladding outer diameter of 8.9 μm and 124.3 μm, respectively, and an effective mode field area of 92 μm²The effective refractive index and transmission loss in the 1550nm band were 1.467 and 0.2dB/km, respectively.

Preferably, the light source used is a narrow linewidth single frequency laser centered at 1550.12nm and the output laser linewidth is 5 kHz.

Has the advantages that:

the invention is based on the fact that the temperature and the medium acoustic resistance respectively cause R_0,mThe linear change of the line width and the central frequency shift of the forward Brillouin scattering spectrum excited by the sound field provides a temperature and acoustic resistance double-parameter sensing method and a sensing test system based on the forward Brillouin scattering, realizes the double-parameter sensing of the temperature and the acoustic resistance, has the advantages of easy realization and simple and convenient operation, and compared with the prior art, realizes the double-parameter sensingThe device also has higher sensing measurement accuracy, and is suitable for popularization and use in related technical fields such as chemical engineering, oil gas storage and detection, tumor detection and the like.

Drawings

FIG. 1 is a schematic structural diagram of a sensing device according to the present invention;

FIG. 2 is a forward Brillouin scattering spectrum of an actually measured large effective area optical fiber;

FIG. 3 shows R at different temperatures_0,8Exciting a forward Brillouin scattering spectrogram and frequency shift-temperature response and line width-temperature response thereof;

FIG. 3(a) shows R at different temperatures_0,8Exciting a forward Brillouin scattering spectrum;

FIG. 3(b) shows R at a temperature of 0 ℃ to 60 ℃_0,8A frequency shift-temperature response and a line width-temperature response graph of the excited forward Brillouin scattering spectrum;

FIG. 4 shows R in different concentrations of sucrose solutions_0,8Exciting a forward Brillouin scattering spectrogram and frequency shift-acoustic resistance and line width-acoustic resistance response thereof;

FIG. 4(a) shows R in different sucrose solutions_0,8Exciting a forward Brillouin scattering spectrum;

FIG. 4(b) is a graph showing that when the external medium acoustic resistance is less than 2.02 kg/(s.mm)²) When R is_0,8Exciting a frequency shift-acoustic resistance response and a line width-acoustic resistance response graph of a forward Brillouin scattering spectrum;

FIG. 5 shows R in states 1 and 2_0,8Exciting a forward Brillouin scattering spectrum;

FIG. 5(a) shows R in State 1_0,8Exciting a forward Brillouin scattering spectrum;

FIG. 5(b) shows R in State 2_0,8Exciting a forward brillouin scattering spectrum.

Detailed Description

The invention designs a temperature and acoustic resistance double-parameter sensing method and device based on forward Brillouin scattering by using an optical fiber sensing technology.

In a single mode fiber, due to different acoustic field displacement equations participating in forward brillouin scattering, a radial acoustic mode (R) is excited in the lateral direction of the fiber_0,m) And torsionRadial acoustic mode (TR)_2,m) Each acoustic mode (acoustic mode) corresponds to a respective resonant frequency and line width. And TR_2,mAcoustic modal phase ratio, R_0,mThe acoustic mode has stronger scattering efficiency and utilizes R_0,mSensing in the acoustic mode can achieve a stronger probe response. Therefore, the forward Brillouin scattering-based optical fiber sensor can use R_0,mThe acoustic model senses the external physical quantity change. In general, a temperature sensor based on forward brillouin scattering can be used to determine R_0,mAnd exciting a linear relation between the frequency shift of the forward Brillouin scattering spectrum center and the temperature change to realize temperature sensing. However, with respect to temperature change vs. R_0,mThe influence of the line width of the excited forward Brillouin scattering spectrum is not reported in corresponding experiments. In addition, although by measuring R_0,mAcoustic resistance sensing can also be realized by linear change relation between excited forward Brillouin scattering spectrum line width and external medium acoustic resistance, but R is related to_0,mThe change rule of the center frequency of the excited forward Brillouin scattering spectrum and the acoustic resistance is not reported.

The invention utilizes the structure of the optical fiber Sagnac ring to respectively align R in quartz single-mode optical fiber_0,mThe temperature response and the acoustic resistance response of the excited forward brillouin spectrum were tested. In the temperature response test, it was found that: within a certain temperature range, the change of the external temperature can not only cause R_0,mThe line width of the excited forward Brillouin scattering spectrum changes linearly with the change of temperature. In addition, in the acoustic resistance response test, it was found that: change of acoustic resistance of external medium except for causing R_0,mWhen the linewidth of the excited forward Brillouin scattering spectrum is not linearly changed and is less than a certain acoustic resistance_0,mThe center frequency of the excited forward brillouin spectrum also varies linearly with acoustic resistance. On the basis of the discovery, the invention combines the existing single parameter sensing mechanism of the forward Brillouin scattering temperature/acoustic resistance of the optical fiber, and provides possibility for the simultaneous sensing of double parameters of the temperature and the acoustic resistance.

The sensing method and apparatus of the present invention will be described in detail below with reference to specific embodiments and the accompanying drawings.

A temperature and acoustic resistance double-parameter optical fiber sensing method based on forward Brillouin scattering obtains the temperature and acoustic resistance linear response characteristics of a sensing optical fiber through the following steps, and comprises the following steps:

ν＝ν_O+C_ν-T·ΔT+C_ν-Z·ΔZ (1)

Γ＝Γ_O+C_Γ-T·ΔT+C_Γ-Z·ΔZ (2)

δν＝C_ν-T·δT+C_ν-Z·δZ (3)

δΓ＝C_Γ-T·δT+C_Γ-Z·δZ (4)

in the above step, said C_ν-T、C_ν-Z、C_Г-TAnd C_Г-ZThe coefficients can be measured separately by the sensing device under preset test conditions.

The sensing device shown in fig. 1 includes a light source, an optical isolator, a variable optical attenuator, an optical fiber sagnac loop, a photodetector, and a data acquisition and processing system, where the optical fiber sagnac loop includes a coupler, a polarization controller, and a sensing fiber. After being regulated by the optical isolator and the adjustable optical attenuator, light wave signals emitted by the light source are incident into an optical fiber Sagnac ring consisting of the coupler, the polarization controller and the sensing optical fiber. In the sagnac loop, the light wave incident into the sensing fiber excites the forward acoustic field and generates forward brillouin scattering. In the embodiment, a large-effective-area fiber (quartz single-mode large-effective-area fiber) with a coating layer removed is used as a sensing fiber, the sensing fiber is placed in an environment with temperature and acoustic resistance change, and the change of the temperature and the external medium acoustic resistance is sensed by utilizing a forward sound field. In large effective area fibers, radial acoustic modes (R) are excited in the fiber transverse direction due to electrostrictive effects_0,m) And torsional radial acoustic mode (TR)_2,m). By fine tuning of the polarization controller, the TR can be adjusted_2,mThe forward brillouin scattering of the acoustic mode excitation is suppressed as much as possible. In the optical fiber sagnac loop, R_0,mThe phase modulation introduced by the acoustic mode can be converted into an intensity modulation of the optical wave by causing a periodic variation of the refractive index. At the output end of the Sagnac loop, the modulated light wave signal is converted into an electric signal by a photoelectric detector, and the signal is subjected to spectrum processing and analysis by a data acquisition and processing system.

The testing process comprises the following steps:

in this embodiment, sucrose solutions with different concentrations and temperatures are used as the environment where the temperature and the medium acoustic resistance change, and the coefficient and the measurement accuracy of the sensing method are tested.

The specific parameters of the sensing device include:

the length of the large-effective-area optical fiber is 11.5m, the diameters of the fiber core and the cladding are respectively 8.9 μm and 124.3 μm, and the effective mode field area is 92 μm²The effective refractive index and transmission loss at 1550nm band are 1.467 and 0.2dB/km, respectively;

the light source is a narrow linewidth single-frequency laser with the central wavelength of 1550.12nm, the linewidth of output laser is 5kHz, and after passing through an optical isolator and a variable optical attenuator, light waves with the power of 9.6dBm are incident into the optical fiber sagnac loop.

The actually measured forward brillouin scattering spectrum of the large effective area optical fiber is shown in fig. 2. It can be seen that adjacent R_0,mThe scattering peaks have equal frequency spacing between them, with a frequency spacing of 47.9 MHz. Considering R_0,mThe intensity of the excited forward brillouin spectrum and its frequency shift-temperature response (despite some lower order R)_0,mExcited forward brillouin spectrum has higher signal-to-noise ratio but has poor frequency shift-temperature response), so the invention selects R_0,8The stimulated forward Brillouin scattering spectrum is used as a research object to research the temperature and acoustic resistance response of the forward Brillouin scattering spectrum.

Fig. 3 and 4 show the results of single parameter variation test of temperature and sucrose solution concentration (medium acoustic resistance), respectively:

as shown in FIG. 3(a), as the temperature increases, R_0,8The central frequency of the excited forward Brillouin scattering spectrum correspondingly moves to the high-frequency direction; as shown in FIG. 3(b), R_0,8Frequency shift-temperature linear response coefficient (C) of excited forward Brillouin scattering spectrum_ν-T) 27.6 kHz/DEG C; in addition, a new physical phenomenon was discovered by temperature testing: in the temperature range of 0-60 ℃, R increases along with the temperature_0,8The linewidth of the excited forward Brillouin scattering spectrum has a trend along with the temperature, is opposite to the central frequency shift, shows a reduced change, and has a linear response coefficient (C) of the linewidth and the temperature_Г-T) Is-2.4 kHz/DEG C.

As shown in FIG. 4(a), the concentration of sucrose solution (C) was variedDielectric acoustic resistance) increase, R_0,8The linewidth of the excited forward Brillouin scattering spectrum is correspondingly widened; as shown in FIG. 4(b), R_0,8Linear response coefficient (C) of excited forward Brillouin scattering spectral line width and acoustic resistance_Г-Z) 1.3MHz/[ kg/(s.mm)²)](ii) a In addition, a new physical law is discovered through an acoustic resistance test: when the external medium acoustic resistance is less than 2.02 kg/(s.mm)²) When, as the acoustic resistance of the medium increases, R_0,8The center frequency of the excited forward Brillouin scattering spectrum shifts to the high frequency direction, and the frequency shift and the linear response coefficient (C) of the acoustic resistance_ν-Z) Is 0.302MHz/[ kg/(s.mm)²)]。

FIG. 5 shows the results of the test of the temperature and acoustic resistance:

in the temperature and acoustic impedance double-parameter test, distilled water at 40 ℃ and 20% of sucrose solution are respectively selected as a State 1(State 1, initial State) and a State 2(State 2). In the two states, the reference values of temperature and acoustic resistance are respectively T_O＝39.8℃、T_R19.9 ℃ and Z_O＝1.505kg/(s·mm²)、Z_R＝1.690kg/(s·mm²)。

As in FIG. 5, FIGS. 5(a) and 5(b) show R in State 1 and State 2, respectively_0,8Exciting a forward brillouin scattering spectrum. In state 1, R_0,8Center frequency (v) of excited forward Brillouin scattering spectrum_o) And line width (r)_o) 369.612MHz and 4.074MHz respectively; in state 2, R_0,8Center frequency (v) of excited forward Brillouin scattering spectrum_R) And line width (r)_R) 369.121MHz and 4.352MHz respectively. In the test procedure, the frequency Resolution Bandwidth (RBW) of the spectrometer was set to 1kHz, the average number of spectral measurements per time was 1000, R_0,8The measurement uncertainties of the center frequency and the line width of the excited forward brillouin scattering spectrum are respectively δ ν ═ 0.002MHz and δ Γ ═ 0.005 MHz.

Measuring R in two states_0,8Substituting the central frequency and the line width of the excited forward Brillouin scattering spectrum into the formulas (1) and (2), taking the temperature and the acoustic resistance parameter of the state 1 as the known initial state parameters, and based on the pre-measured C_ν-T、C_ν-Z、C_Г-TAnd C_Г-ZCoefficient, the measured values of temperature and acoustic resistance in the state 2 are respectively T_{R_e}20.03 ℃ and Z_{R_e}＝1.689kg/(s·mm²). Uncertainty of measurement (delta T) of measured temperature and acoustic resistance compared to reference value_e＝|T_R__e-T_RI and delta Z_e＝|Z_R__e-Z_RI) are respectively 0.13 ℃ and 0.006 kg/(s.mm)²) The corresponding relative percentages of measurement uncertainty are 0.7% and 0.3%, respectively. In addition, by solving equations (3) - (6), theoretical values of uncertainty of temperature and acoustic resistance measurements can be obtained as δ T_t0.10 ℃ and δ Z_t＝0.0039kg/s·mm²The corresponding relative percentages of measurement uncertainty are 0.5% and 0.23%, respectively. It can be seen that the theoretical values and the measured values are well matched, and the deviation may be derived from the linear coefficient estimation error and the temperature fluctuation brought by the temperature control system (<0.1 deg.C). Compared with the accuracy (1%) of the existing temperature/acoustic resistance single parameter sensor based on forward Brillouin scattering, the invention can improve the sensing accuracy by more than 30%, and is the lowest value of the currently known reported measurement error. By means of the double-parameter and high-precision sensing characteristics, the method can be effectively applied to the related technical fields of chemical engineering, oil-gas storage and detection, tumor detection and the like.

The foregoing shows and describes the general principles, essential features, and advantages of the invention. It will be understood by those skilled in the art that the present invention is not limited to the embodiments described above, which are described in the foregoing description only for the purpose of illustrating the principles of the present invention, but that various changes and modifications may be made therein without departing from the spirit and scope of the invention as defined by the appended claims, specification, and equivalents thereof.

Claims

1. a temperature and acoustic resistance dual-parameter sensing method based on forward Brillouin scattering, is characterized in that, obtains the temperature and acoustic resistance linear response characteristic of sensing fiber through the following steps, comprising:

Step S1: Use formula (1) and formula (2) to solve the temperature and acoustic resistance parameters

Obtain the forward Brillouin scattering spectrum excited by the radial acoustic mode of the sensing fiber in the initial state, and set the spectrum of the mth scattering peak to be R _0,m excited forward Brillouin scattering spectrum, so The center frequency of the forward Brillouin scattering spectrum excited by R _0,m is ν and the line width is Г, then:

ν=ν _O +C _ν-T ·ΔT+C _ν-Z ·ΔZ (1)

Γ=Γ _O +C _Γ-T ·ΔT+C _Γ-Z ·ΔZ (2)

Among them, ν _o and Г _o are the center frequency and linewidth of the forward Brillouin scattering spectrum of the R _0,m excitation in the initial state, respectively; C _ν-T and C _ν-Z are the forward distribution of the R _0,m excitation, respectively Frequency-shift-temperature and frequency-shift-resistance linear response coefficients of Brillouin scattering spectra; C _Г-T and C _Г-Z are the linewidth-temperature coefficients and lines of forward Brillouin scattering spectra excited by R _0,m, respectively Wide-acoustic resistance linear response coefficient; ΔT and ΔZ represent the changes in external ambient temperature and acoustic resistance compared with the initial state, respectively;

Step S2: Use formula (3) to formula (6) to solve the measurement uncertainty of temperature and acoustic resistance parameters

Assuming that the measurement uncertainty of the center frequency and linewidth of the forward Brillouin scattering spectrum excited by R _0,m is δν and δГ, respectively, we have:

δν=C _ν-T δT+C _ν-Z δZ (3)

δΓ＝C _Γ-T ·δT+C _Γ-Z ·δZ (4)

Among them, δT and δZ are the measurement uncertainty of the temperature and acoustic resistance of the detection environment, respectively, which are expressed as:

.

2 . The forward Brillouin scattering-based dual-parameter sensing method for temperature and acoustic resistance according to claim 1 , wherein the value of m is 8. 3 .

3. A sensing device for implementing the dual-parameter sensing method according to claim 1 or 2, characterized in that, comprising a light source, an optical fiber Sagnac ring, a photodetector and a data acquisition and processing system;

The fiber Sagnac ring consists of a coupler, a polarization controller and a sensing fiber;

The data acquisition and processing system includes a spectrum analyzer;

In the fiber Sagnac ring, for the light wave signal entering the sensing fiber through the input end of the coupler, the forward Brillouin scattering signal excited by the twisted radial acoustic mode in the fiber is suppressed by the polarization controller. At the output end of the acousto-optic phase-modulated light wave signal is converted into an electrical signal by a photodetector and sent to the data acquisition and processing system, and then completes the analysis of the signal spectrum in the data acquisition and processing system.

4. The sensing device according to claim 3, wherein an optical isolator and an optical attenuator are also provided between the light source and the input end of the optical fiber Sagnac ring, and the light wave signal emitted by the light source passes through the optical isolator After the adjustment of the optical attenuator and the optical attenuator, it is incident on the input end of the fiber Sagnac ring.

5 . The sensing device according to claim 3 , wherein the sensing optical fiber adopts a large effective area optical fiber with a coating layer removed. 6 .

6 . The sensing device according to claim 5 , wherein the large effective area optical fiber has a length of 11.5 m, a core diameter and a cladding outer diameter of 8.9 μm and 124.3 μm, respectively, and an effective mode field area of 92 μm. 7 . ² , the effective refractive index and transmission loss in the 1550nm band are 1.467 and 0.2dB/km, respectively.

7. The sensing device according to claim 5 or 6, wherein the light source used is a narrow linewidth single-frequency laser with a center wavelength of 1550.12 nm, and the output laser linewidth is 5 kHz.