Forward Brillouin scattering temperature and axial strain double-parameter sensing device and method based on optical fiber direct detection structure

Abstract

The invention discloses a forward Brillouin scattering temperature and axial strain double-parameter sensing device and method based on an optical fiber direct detection structure. A forward Brillouin scattering spectrum which is excited by a torsion-radial acoustic mode and has a narrow line width and a high signal-to-noise ratio is obtained by using an optical polarization controller and an optical polarizer for the first time. The optical polarization controller enhances the optical beat of forward Brillouin scattering corresponding to the pump light and the torsion-radial acoustic mode, and weakens the optical beat of forward Brillouin scattering corresponding to the pump light and the radial acoustic mode. The optical polarizer is used for filtering components perpendicular to the polarization plane of the optical polarizer, and effectively eliminating the influence of signals in other polarization directions on the optical beat signal. Two response coefficients of frequency shift-temperature and frequency shift-axial strain are measured at the same time, and high-precision temperature and axial strain double-parameter measurement can be realized while the problem of temperature cross sensitivity is effectively avoided by using a 2 * 2 coefficient matrix. The sensing device provided by the invention has a simple manufacturing method, and realizes high-precision simultaneous measurement.

Description

Technical Field

[0001] The present invention relates to the field of optical fiber sensing technology, and in particular to a dual-parameter sensing device and method for forward Brillouin scattering temperature and axial strain based on an optical fiber direct detection structure. Background Art

[0002] Since the forward Brillouin scattering spectrum has multiple resonance peaks, the simultaneous detection of multiple parameters in the surrounding environment is one of the most fundamental and challenging problems in the research of forward Brillouin scattering fiber sensors. Among them, temperature and axial strain sensors are very attractive due to their unique ability to monitor infrastructure, structural health monitoring, and various industrial manufacturing processes.

[0003] The forward Brillouin scattering phenomenon in optical fibers has been studied since the mid-1980s. Due to the thermal motion characteristics of the sensing fiber itself, the transverse acoustic field modulates the phase / polarization state of the incident light, resulting in the spontaneous forward Brillouin scattering spectrum excited by the radial acoustic mode and the torsional-radial acoustic mode. So far, a large number of forward Brillouin scattering spectrum measurement methods based on Sagnac ring structures have been studied. These methods have the disadvantages of low signal-to-noise ratio and wide linewidth, which leads to low Lorentz fitting accuracy. Forward Brillouin scattering excited by radial acoustic modes based on Sagnac ring structures has been used for dual-parameter measurements, including strain and temperature, temperature and acoustic impedance, and relative humidity and temperature. In the prior art 1 published by Lu Yuangang et al. (Lu Yuangang, Zhang Zelin, Peng Jianqin, Ji Zhengyuan, Temperature and acoustic impedance dual parameter sensing method and device based on forward Brillouin scattering, application number CN 202110222185.0, invention patent authorized), the two optical polarization controllers in the Sagnac ring structure sensing device discussed increase the complexity of polarization state adjustment of the forward transmitted light wave during the experiment, and half of the output light energy will enter the laser light source, resulting in half of the light energy loss. In the prior art 2 published by Lu Yuangang et al. (Lu Yuangang, Zhang Wujun, He Chongjun, Zhu Meng, Liu Pengkai, Li Mengli, Sun Rui, Forward Brillouin scattering dual parameter sensing device and method based on optical fiber single-end reflection structure, application number CN 202410151319.8, invention patent published), the optical fiber single-end reflection structure discussed has a circulator, an optical polarization controller and a plane reflector, and the light wave passing through the plane reflector cannot be fully reflected, resulting in energy loss. How to further reduce the signal light energy loss and reduce the complexity of the detection system requires further research. At the same time, in previous experimental research and practical applications, some conventional single-mode optical fibers have poor bending resistance, which makes the optical fiber sensor unit unable to bend, affecting the normal monitoring in the project.

[0004] How to build a simple sensing device to generate forward Brillouin scattering spectra excited by the torsional-radial acoustic mode for dual-parameter sensing measurement while overcoming the shortcomings of low signal-to-noise ratio, wide linewidth and poor bending resistance is an important challenge for the simultaneous measurement of high-precision dual parameters of temperature and axial strain. Summary of the invention

[0005] In view of the defects of the existing technology, the present invention provides a dual-parameter sensing device and method of forward Brillouin scattering temperature and axial strain based on an optical fiber direct detection structure, which has the advantages of high measurement accuracy, high sensitivity, strong bending resistance, simple manufacturing method, simple structure, and the ability to eliminate temperature crosstalk.

[0006] To achieve the above object, the technical solution of the present invention is:

[0007] A dual-parameter sensing device for forward Brillouin scattering temperature and axial strain based on an optical fiber direct detection structure, comprising a laser light source, an optical isolator, a sensing optical fiber, an optical polarization controller, an optical polarizer, a photodetector and a data processing module, wherein the laser light source, the optical isolator, the sensing optical fiber, the optical polarization controller, the optical polarizer and the photodetector are arranged in sequence along the propagation direction of light, and the entire sensing system structure is in a "single line" form. Compared with the Sagnac ring structure and the single-end reflection structure, this "single line" morphological structure is simpler in structure and has a smaller energy loss of signal light. The polarization state passing direction of the optical polarizer is set to the x direction, and when the vibration directions of the three light waves of the pump light, the forward Brillouin scattering light corresponding to the radial acoustic mode, and the forward Brillouin scattering light corresponding to the torsion-radial acoustic mode are all along the x-axis, the initial state of the polarization controller is the state with the least influence on the light wave intensity. Slowly adjust the first and second rotating wave plates of the optical polarization controller, and observe the optical beat effect between the pump light and the forward Brillouin scattered light corresponding to the torsion-radial acoustic mode at the same time, and determine a position that makes the polarization states of the pump light and the forward Brillouin scattered light corresponding to the torsion-radial acoustic mode as similar as possible (that is, the directions of their electric field vectors in polarization space are as consistent as possible, usually the x-axis). This will obtain the optical beat amplitude enhancement between the pump light and the forward Brillouin scattered light corresponding to the torsion-radial acoustic mode. While maintaining the optical beat enhancement between the pump light and the forward Brillouin scattered light corresponding to the torsion-radial acoustic mode, adjust the position of the third rotating wave plate of the polarization controller to change the polarization state of the forward Brillouin scattered light corresponding to the radial acoustic mode, so that it is as different as possible from the polarization state of the pump light to weaken the optical beat of the forward Brillouin scattered light corresponding to the pump light and the radial acoustic mode. The polarizer is used to filter out the component perpendicular to its polarization plane, effectively eliminating the influence of other polarization direction signals on the beat frequency signal.

[0008] Optionally, the laser light source includes a narrow linewidth single-frequency laser.

[0009] Optionally, the sensing optical fiber is a BI 1011-A single-mode optical fiber with a high bending resistance coating.

[0010] The present invention also provides a dual-parameter sensing method of forward Brillouin scattering temperature and axial strain based on an optical fiber direct detection structure, which is applied to the dual-parameter sensing device of forward Brillouin scattering temperature and axial strain based on an optical fiber direct detection structure, and comprises:

[0011] Step S1, using different temperatures and axial strains to change the acoustic properties of the sensing optical fiber so that the frequency shift of its spectral resonance peak has different response characteristics, and obtaining the frequency shift response coefficient of the frequency shift to the temperature and axial strain;

[0012] Step S2, by simultaneously measuring the frequency shift changes corresponding to the two resonance peaks, solving the measurement results, the measurement results including the temperature change and the axial strain change;

[0013] Step S3, calculating the uncertainty of the measurement result for verification;

[0014] Step S4: If the obtained measurement uncertainty exceeds the theoretical calculated value excessively, return to step S1 to reselect two torsional-radial acoustic modes and execute subsequent steps until the measurement uncertainty reaches the ideal value.

[0015] Furthermore, in the step S1, the temperature around the sensing optical fiber and the axial strain applied to the sensing optical fiber are controlled to change multiple times, and the forward Brillouin scattering spectra of the temperature and axial strain of the sensing optical fiber in various states during the change process are obtained; and the resonance peaks of the two torsional-radial acoustic modes in the various states are Lorentz fitted to obtain the corresponding frequency shift changes; then the frequency shift changes are linearly fitted with the temperature and axial strain changes in the various states to obtain the frequency shift response coefficient of the frequency shift to the temperature and axial strain.

[0016] Further, the method of controlling the temperature around the sensing optical fiber and the axial strain applied to the sensing optical fiber to change multiple times includes:

[0017] The sensing optical fiber is fixed on a heating platform, and the sensing optical fiber is in a relaxed and strain-free state, and the temperature around the sensing optical fiber is changed;

[0018] Fixing a portion of the sensing optical fiber on a heating platform, fixing another portion of the sensing optical fiber on a micro-displacement platform, and changing the axial strain applied to the other portion of the sensing optical fiber by adjusting the micro-displacement platform at room temperature;

[0019] The temperature and axial strain parameters are changed according to the set values. Each time a parameter is kept unchanged, the other parameter is controlled to change, and each parameter changes at least 8 times at equal intervals to complete the control of the temperature and axial strain parameters respectively.

[0020] Further, in the step S2, the forward Brillouin scattering spectrum of the temperature and axial strain of the sensing optical fiber in a certain state is obtained, and the forward Brillouin scattering spectrum in the state is used as the reference state; the forward Brillouin scattering spectrum of the temperature and axial strain of the sensing optical fiber in another state is obtained, and the forward Brillouin scattering spectrum in the state is used as the state to be measured; the forward Brillouin scattering spectra of the sensing optical fiber in the two states are compared to obtain the frequency shift changes of the two torsional-radial acoustic modes in the two states, and the measurement results are calculated according to the frequency shift changes in the two states and the frequency shift response coefficient obtained in step S1, and the measurement results include the temperature change and the axial strain change, and the expression is as follows:

[0021]

[0022] Where: ΔT is the temperature change, Δε is the axial strain change; Δv i and Δv j are the frequency shift changes of two torsional-radial acoustic modes of different orders, i-th and j-th; is the frequency shift-temperature coefficient of the i-th order, is the i-th order frequency shift-axial strain coefficient, is the j-th order frequency shift-temperature coefficient, is the j-th order frequency shift-axial strain coefficient; i and j are any two mode orders in different torsional-radial acoustic modes.

[0023] Furthermore, in the step S3, the forward Brillouin scattering spectrum of the temperature and the axial strain of the sensing optical fiber in a certain state is obtained, and the state is used as a reference state; the temperature around the sensing optical fiber and the axial strain applied to the sensing optical fiber are controlled to change at the same time, and this state is used as a state to be measured, and the forward Brillouin scattering spectrum of the sensing optical fiber in the state to be measured is collected; the forward Brillouin scattering spectrum of the sensing optical fiber in the reference state and the forward Brillouin scattering spectrum of the sensing optical fiber in the state to be measured are compared to obtain the frequency shift change of the torsional-radial acoustic mode in the two states, and the frequency shift measurement error of the forward Brillouin scattering excited by the two torsional-radial acoustic modes is obtained by multiple measurements in a fixed state.

[0024] Furthermore, in step S3, the measurement uncertainty of the measurement result is calculated by the following formula:

[0025]

[0026] Among them, δv i and δv j are the frequency shift measurement errors of forward Brillouin scattering excited by two torsional-radial acoustic modes, which are obtained by the standard deviation of multiple sets of data collected by the corresponding two torsional-radial acoustic modes under a certain state; δT is the measurement uncertainty of temperature, and δε is the measurement uncertainty of axial strain.

[0027] Beneficial effect: The optical fiber direct detection structure constructed by the present invention includes a laser light source, an optical isolator, an optical polarization controller, an optical polarizer, a photodetector and a data processing module. The use of an optical polarization controller makes the sensing device simple. Different forward Brillouin scattering spectrum resonance peaks have frequency response characteristics of different temperatures and axial strains, realizing the simultaneous measurement of temperature and axial strain dual parameters. Compared with the existing single-parameter optical fiber sensor of forward Brillouin scattering spectrum, the scheme of the present invention can realize the effective measurement of dual parameters; compared with the existing structure based on traditional Sagnac ring, the scheme of the present invention can effectively suppress radial acoustic mode and reduce energy loss, stimulate forward Brillouin scattering spectrum of torsion-radial acoustic mode with high signal-to-noise ratio, narrow linewidth and more resonance peaks in the same frequency range, and obtain higher measurement accuracy; compared with the single-end reflection structure of optical fiber, the sensing device of the scheme of the present invention is simple and has increased energy transmittance; compared with the biological or chemical optical fiber sensor of dual-parameter simultaneous measurement based on microstructure, the scheme of the present invention has the advantages of simple manufacturing method, low cost and high manufacturing success rate; the selection of special single-mode optical fiber in the specific embodiment makes the optical fiber sensor have higher bending resistance, which can be applied to more engineering applications, effectively avoids the problem of temperature cross-sensitivity and can realize high-precision simultaneous measurement of dual parameters.

[0028] In order to make the above features and advantages of the invention more obvious and easy to understand, embodiments are given below and described in detail with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a structural schematic diagram of the forward Brillouin scattering temperature and axial strain dual parameter measurement sensing device based on the optical fiber direct detection structure of the present invention.

[0030] Figure 2 The present invention is a flow chart of the forward Brillouin scattering temperature and axial strain dual parameter measurement sensing method based on the optical fiber direct detection structure.

[0031] Figure 3 It is a forward Brillouin scattering spectrum of the sensing optical fiber excited by the torsional-radial acoustic mode at room temperature in a specific embodiment.

[0032] Figure 4(a) shows two torsional-radial acoustic modes (TR 2,23 and TR2,29 ) corresponds to the frequency shift-temperature coefficient (C ν-T ) Experimental measurement linear fitting results.

[0033] Figure 4(b) shows two torsional-radial acoustic modes (TR 2,23 and TR 2,29 ) corresponding to the frequency shift-axial strain coefficient (C ν-ε ) Experimental measurement linear fitting results

[0034] Figure 5(a) shows the torsional-radial acoustic mode (TR 2,23 and TR 2,29 ) forward Brillouin scattering spectrum excited by the electron beam.

[0035] Figure 5(b) shows the torsional-radial acoustic mode (TR 2,23 and TR 2,29 ) forward Brillouin scattering spectrum excited by . DETAILED DESCRIPTION

[0036] In order to make the purpose and technical solution of the embodiment of the present invention clearer, the technical solution of the embodiment of the present invention will be clearly and completely described below in conjunction with the drawings of the embodiment of the present invention. Obviously, the described embodiment is a part of the embodiment of the present invention, not all of the embodiments. Based on the described embodiment of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0037] Figure 1 The schematic diagram of the structure of a dual-parameter sensor device for forward Brillouin scattering temperature and axial strain based on a fiber direct detection structure is shown, and the dual-parameter sensor device for forward Brillouin scattering temperature and axial strain based on a fiber direct detection structure comprises a laser light source 1, an optical isolator 2, a sensing optical fiber 3, an optical polarization controller 4, an optical polarizer 5, a photodetector 6 and a data processing module 7. The laser light source 1, the optical isolator 2, the sensing optical fiber 3, the optical polarization controller 4, the optical polarizer 5 and the photodetector 6 are arranged in sequence along the propagation direction of light, and the entire sensing system structure is in a "single line" form.

[0038] More specifically, the laser emitted by the laser light source 1 passes through the optical isolator 2 and then enters the sensing optical fiber 3 for transmission. The sensing optical fiber 3 is used to sense changes in temperature and axial strain in the external environment. Changes in the temperature and the axial strain will cause changes in the laser spectrum passing through the sensing optical fiber 3. The optical polarization controller 4 and the optical polarizer 5 perform phase / polarization state modulation on the laser passing through the sensing optical fiber 3 to generate a beat frequency signal of the forward Brillouin scattered light excited by the pump light and the torsional-radial acoustic mode. The photodetector 6 converts the beat frequency signal into a corresponding electrical signal and sends it to the data processing module 7. The data processing module 7 collects and analyzes the spectrum of the electrical signal to obtain forward Brillouin scattering spectrum characteristic information, and calculates the values ​​of the temperature and the axial strain based on the forward Brillouin scattering spectrum characteristic information.

[0039] Optionally, the laser light source 1 includes a narrow-linewidth single-frequency laser; the narrow-linewidth single-frequency laser has an output laser linewidth of 5 kHz, a maximum output power of 14.5 dBm, and a central wavelength of 1550.12 nm.

[0040] Furthermore, the optical isolator 2 is used to prevent the pump light signal emitted by the laser light source 1 from being reflected and damaging the laser light source 1 .

[0041] Furthermore, all the light passing through the optical polarizer 5 is converted into linearly polarized light having a specific direction.

[0042] Optionally, the sensing optical fiber 3 comprises a BI 1011-A single-mode optical fiber with a coating layer and high bending resistance.

[0043] Optionally, the sensing optical fiber 3 is 30 m long, the cladding diameter and the coating diameter are 125 μm and 250 μm respectively, and the transmission loss in the 1550 nm band is 0.21 dB / km.

[0044] Further, in the optical fiber direct detection structure of the present invention, the thermal vibration in the sensing optical fiber causes the phase / polarization state modulation of the incident light through the transverse acoustic field. Therefore, this phase / polarization state modulation triggers the forward Brillouin scattering spectrum excited by the radial acoustic mode and the torsion-radial acoustic mode. Due to the birefringence in the sensing optical fiber, the forward propagating light wave has a high probability of being elliptically polarized light, and the forward propagating light wave includes pump light and forward Brillouin scattered light excited by the radial acoustic mode and the torsion-radial acoustic mode. The spatial polarization mode interaction caused by the random birefringence of the non-polarization-maintaining optical fiber will change the electric field distribution of the optical fiber along its two main axes, thereby causing the light beat phenomenon between the projections of the light beams projected along the x and y axes of the optical fiber coordinate system. Without loss of generality, it is assumed that the intensities of the forward Brillouin scattered light excited by the radial acoustic mode and the torsion-radial acoustic mode are equal, and it is defined that their electric field vectors in the x direction are greater than the electric field vectors in the y direction. In order to explain more clearly, the linear polarization direction of the forward propagating light wave through the optical polarizer 5 is defined as the x axis.

[0045] By carefully adjusting the position of the rotatable wave plate of the optical polarization controller 4, the optical beat between the forward Brillouin scattered light excited by the torsion-radial acoustic mode and the pump light is enhanced, and the optical beat between the forward Brillouin scattered light excited by the radial acoustic mode and the pump light is weakened. The first and second rotating wave plates of the optical polarization controller are slowly adjusted, and the optical beat effect between the pump light and the forward Brillouin scattered light corresponding to the torsion-radial acoustic mode is observed at the same time, and a position is determined so that the polarization states of the pump light and the forward Brillouin scattered light corresponding to the torsion-radial acoustic mode are as similar as possible (that is, the directions of their electric field vectors in the polarization space are as consistent as possible, usually the x-axis). This will obtain an enhancement in the optical beat amplitude between the pump light and the forward Brillouin scattered light corresponding to the torsion-radial acoustic mode. While maintaining the enhancement in the optical beat between the pump light and the forward Brillouin scattered light corresponding to the torsion-radial acoustic mode, the position of the third rotating wave plate of the polarization controller is adjusted to change the polarization state of the forward Brillouin scattered light corresponding to the radial acoustic mode, so that it is as different as possible from the polarization state of the pump light to weaken the optical beat of the forward Brillouin scattering corresponding to the pump light and the radial acoustic mode. After the light passing through the optical polarization controller 4 passes through the optical polarizer 5, only the projection component of the pump light on the x-axis and the projection component of the radial acoustic mode on the x-axis are present, indicating that the optical polarizer 5 has filtered out all y-axis components. Assuming that the insertion loss in the optical polarizer 5 is negligible, the light wave propagating forward through the optical polarization controller 4 and the optical polarizer 5 maintains the same projection component along the x-axis. The light wave signal after the acoustic-optical interaction is converted into an electrical signal by the photodetector 6, and then sent to the data processing module 7 to analyze and collect the spectrum of the electrical signal.

[0046] like Figure 2As shown, the dual parameter sensing method of forward Brillouin scattering temperature and axial strain based on the optical fiber direct detection structure specifically includes the following steps:

[0047] Step S1, using different temperatures and axial strains to change the acoustic properties of the sensing optical fiber so that the frequency shift of its spectral resonance peak has different response characteristics, and obtaining the frequency shift response coefficient of the frequency shift to temperature and axial strain.

[0048] More specifically, the temperature around the sensing optical fiber and the axial strain applied to the sensing optical fiber are controlled to change multiple times, and the forward Brillouin scattering spectra of the temperature and axial strain of the sensing optical fiber in various states during the change process are obtained; and the resonance peaks of the two torsional-radial acoustic modes in the various states are Lorentz fitted to obtain the corresponding frequency shift changes; then the frequency shift changes are linearly fitted with the temperature and axial strain changes in the various states to obtain the frequency shift response coefficient of the frequency shift to the temperature and axial strain.

[0049] Furthermore, the method of controlling the temperature around the sensing optical fiber 3 and the axial strain applied to the sensing optical fiber 3 to change multiple times includes:

[0050] The sensing optical fiber 3 is fixed on the heating platform, and the sensing optical fiber 3 is in a relaxed and strain-free state, and the temperature around the sensing optical fiber 3 is changed.

[0051] A portion of the sensing optical fiber 3 is fixed on the heating platform, and another portion of the sensing optical fiber 3 is fixed on the micro-displacement platform. The axial strain applied to the other portion of the sensing optical fiber is changed by adjusting the micro-displacement platform at room temperature.

[0052] The temperature and axial strain parameters are changed according to the set values. Each time a parameter is kept unchanged, the other parameter is controlled to change, and each parameter changes at least 8 times at equal intervals to complete the control of the temperature and axial strain parameters respectively.

[0053] Step S2, by simultaneously measuring the frequency shift changes corresponding to the two resonance peaks, a measurement result is obtained, wherein the measurement result includes a temperature change and an axial strain change.

[0054] More specifically, the forward Brillouin scattering spectrum of the temperature and axial strain of the sensing optical fiber in a certain state is obtained, and the forward Brillouin scattering spectrum in the state is used as the reference state; the forward Brillouin scattering spectrum of the temperature and axial strain of the sensing optical fiber in another state is obtained, and the forward Brillouin scattering spectrum in the state is used as the state to be measured; the forward Brillouin scattering spectra of the sensing optical fiber in the two states are compared to obtain the frequency shift changes of the two torsional-radial acoustic modes in the two states, and the measurement results are calculated according to the frequency shift changes in the two states and the frequency shift response coefficient obtained in step S1, and the measurement results include the temperature change and the axial strain change, and the expression is as follows:

[0055]

[0056] Where: ΔT is the temperature change, Δε is the axial strain change; Δv i and Δv j are the frequency shift changes of two torsional-radial acoustic modes of different orders, i-th and j-th; is the frequency shift-temperature coefficient of the i-th order, is the i-th order frequency shift-axial strain coefficient, is the j-th order frequency shift-temperature coefficient, is the j-th order frequency shift-axial strain coefficient; i and j are any two mode orders in different torsional-radial acoustic modes.

[0057] Step S3, calculating the uncertainty of the measurement result for verification.

[0058] More specifically, the forward Brillouin scattering spectrum of the temperature and axial strain of the sensing optical fiber in a certain state is obtained, and this state is used as a reference state; the temperature around the sensing optical fiber and the axial strain applied to the sensing optical fiber are controlled to change simultaneously, and this state is used as a state to be measured, and the forward Brillouin scattering spectrum of the sensing optical fiber in the state to be measured is collected; the forward Brillouin scattering spectrum of the sensing optical fiber in the reference state and the forward Brillouin scattering spectrum of the sensing optical fiber in the state to be measured are compared to obtain the frequency shift change of the torsional-radial acoustic mode in the two states, and the frequency shift measurement error of the forward Brillouin scattering excited by the two torsional-radial acoustic modes is obtained by multiple measurements in a fixed state.

[0059] Furthermore, the measurement uncertainty of the measurement result is calculated by the following formula:

[0060]

[0061] Among them, δv i and δv jare the frequency shift measurement errors of forward Brillouin scattering excited by two torsional-radial acoustic modes, which are obtained by the standard deviation of multiple sets of data collected by the corresponding two torsional-radial acoustic modes under a certain state; δT is the measurement uncertainty of temperature, and δε is the measurement uncertainty of axial strain.

[0062] Step S4: If the obtained measurement uncertainty exceeds the theoretical calculated value excessively, return to step S1 to reselect two torsional-radial acoustic modes and execute subsequent steps until the measurement uncertainty reaches the ideal value.

[0063] In summary, the present invention discloses a dual-parameter sensing device and method of forward Brillouin scattering temperature and axial strain based on an optical fiber direct detection structure. The sensing device (optical fiber direct detection structure) used includes a laser light source, an optical isolator, an optical polarization controller, an optical polarizer, a photodetector and a data processing module, wherein the optical polarization controller and the optical polarizer modulate the polarization state of the forward transmission light wave. The torsional-radial acoustic mode caused by the acoustic-optical interaction of the sensing optical fiber excites a forward Brillouin scattering spectrum with a narrow linewidth and a high signal-to-noise ratio. The acoustic properties of the sensing optical fiber are changed by different temperatures and axial strains so that the frequency shift of its spectral resonance peak has different response characteristics, and the frequency shift response coefficient of the frequency shift to temperature and axial strain is obtained. By simultaneously measuring the frequency shift changes corresponding to the two resonance peaks, the temperature change and the axial strain change are solved using a 2x2 coefficient matrix, which effectively avoids the problem of temperature cross-sensitivity and can achieve high-precision dual-parameter measurement of temperature and axial strain. The sensing device of the present invention has a simple manufacturing method and is expected to become a high-precision sensing method for simultaneously measuring temperature and axial strain with high sensitivity, light weight, strong anti-electromagnetic interference ability, and strong anti-bending ability. It has potential application prospects in the fields of infrastructure, structural health monitoring, and various industrial manufacturing processes.

[0064] refer to Figure 3 to Figure 5(b) In one embodiment, according to the mode selection criteria, the torsional-radial acoustic mode selected is TR 2,23 and TR 2,29 , the temperature measurement error and axial strain measurement error of the sensing optical fiber are 0.17℃ and 21με respectively in the temperature range of 28.8~63.1℃ and the axial strain range of 0~1400με. It can be seen that the dual-parameter sensing device and method of forward Brillouin scattering temperature and axial strain based on the optical fiber direct detection structure of the present invention has high measurement accuracy and can meet the requirements of high-precision dual-parameter sensing measurement.

[0065] Although the present invention has been disclosed as above by way of embodiments, it is not intended to limit the present invention. Any person having ordinary knowledge in the technical field may make some changes and modifications without departing from the spirit and scope of the present invention. Therefore, the protection scope of the present invention shall be determined by the scope of the attached patent application.

Claims

1. A dual-parameter sensing device for forward Brillouin scattering temperature and axial strain based on an optical fiber direct detection structure, characterized in that: The invention comprises a laser light source, an optical isolator, a sensing optical fiber, a light polarization controller, a light polarizer, a photodetector and a data processing module. The laser light source, the optical isolator, the sensing optical fiber, the light polarization controller, the light polarizer and the photodetector are arranged in sequence along the propagation direction of light, and the structure of the whole sensing system is in a "single line" form.

2. A dual parameter sensing device for forward Brillouin scattering temperature and axial strain based on an optical fiber direct detection structure as claimed in claim 1, characterized in that: The laser light source includes a narrow linewidth single-frequency laser.

3. A dual parameter sensing device for forward Brillouin scattering temperature and axial strain based on an optical fiber direct detection structure as claimed in claim 1, characterized in that: The sensing fiber comprises a BI 1011-A single mode optical fiber with a highly bend-resistant coating.

4. A dual-parameter sensing method of forward Brillouin scattering temperature and axial strain based on an optical fiber direct detection structure, applied to a dual-parameter sensing device of forward Brillouin scattering temperature and axial strain based on an optical fiber direct detection structure as claimed in any one of claims 1 to 3, characterized in that: include: Step S1, using different temperatures and axial strains to change the acoustic properties of the sensing optical fiber so that the frequency shift of its spectral resonance peak has different response characteristics, and obtaining the frequency shift response coefficient of the frequency shift to the temperature and axial strain; Step S2, by simultaneously measuring the frequency shift changes corresponding to the two resonance peaks, solving the measurement results, the measurement results including the temperature change and the axial strain change; Step S3, calculating the uncertainty of the measurement result for verification; Step S4: If the obtained measurement uncertainty exceeds the theoretical calculated value excessively, return to step S1 to reselect two torsional-radial acoustic modes and execute subsequent steps until the measurement uncertainty reaches the ideal value.

5. A dual parameter sensing method of forward Brillouin scattering temperature and axial strain based on an optical fiber direct detection structure as claimed in claim 4, characterized in that: In the step S1, the temperature around the sensing optical fiber and the axial strain applied to the sensing optical fiber are controlled to change multiple times, and the forward Brillouin scattering spectra of the temperature and axial strain of the sensing optical fiber in various states during the change process are obtained; and the resonance peaks of the two torsional-radial acoustic modes in various states are subjected to Lorentz fitting to obtain the corresponding frequency shift variation; then the frequency shift variation is linearly fitted with the temperature and axial strain variation in various states to obtain the frequency shift response coefficient of the frequency shift to the temperature and axial strain.

6. A dual parameter sensing method of forward Brillouin scattering temperature and axial strain based on an optical fiber direct detection structure as claimed in claim 5, characterized in that: Methods for controlling the temperature around the sensing fiber and the axial strain applied to the sensing fiber to undergo multiple changes include: The sensing optical fiber is fixed on a heating platform, and the sensing optical fiber is in a relaxed and strain-free state, and the temperature around the sensing optical fiber is changed; Fixing a portion of the sensing optical fiber on a heating platform, fixing another portion of the sensing optical fiber on a micro-displacement platform, and changing the axial strain applied to the other portion of the sensing optical fiber by adjusting the micro-displacement platform at room temperature; The temperature and axial strain parameters are changed according to the set values. Each time a parameter is kept unchanged, the other parameter is controlled to change, and each parameter changes at least 8 times at equal intervals to complete the control of the temperature and axial strain parameters respectively.

7. A dual parameter sensing method of forward Brillouin scattering temperature and axial strain based on an optical fiber direct detection structure as claimed in claim 6, characterized in that: In the step S2, the forward Brillouin scattering spectrum of the temperature and axial strain of the sensing optical fiber in a certain state is obtained, and the forward Brillouin scattering spectrum in the state is used as a reference state; Then obtain the forward Brillouin scattering spectrum of the temperature and axial strain of the sensing optical fiber in another state, and use the forward Brillouin scattering spectrum in this state as the state to be measured; compare the forward Brillouin scattering spectra of the sensing optical fiber in the two states, obtain the frequency shift changes of the two torsional-radial acoustic modes in the two states, and calculate the measurement results according to the frequency shift changes in the two states and the frequency shift response coefficient obtained in step S1, wherein the measurement results include the temperature change and the axial strain change, and the expression is as follows: Where: ΔT is the temperature change, Δε is the axial strain change; Δν i and Δν j are the frequency shift changes of two torsional-radial acoustic modes of different orders, i-th and j-th; is the frequency shift-temperature coefficient of the i-th order, is the i-th order frequency shift-axial strain coefficient, is the j-th order frequency shift-temperature coefficient, is the j-th order frequency shift-axial strain coefficient; i and j are any two mode orders in different torsional-radial acoustic modes.

8. A dual parameter sensing method of forward Brillouin scattering temperature and axial strain based on an optical fiber direct detection structure as claimed in claim 7, characterized in that: In the step S3, the forward Brillouin scattering spectrum of the temperature and axial strain of the sensing optical fiber in a certain state is obtained, and the state is used as a reference state; The temperature around the sensing optical fiber and the axial strain applied to the sensing optical fiber are controlled to change simultaneously, and this state is used as a test state to collect the forward Brillouin scattering spectrum of the sensing optical fiber in the test state; By comparing the forward Brillouin scattering spectrum of the sensing optical fiber in the reference state and the forward Brillouin scattering spectrum in the test state, the frequency shift change of the torsion-radial acoustic mode in the two states is obtained, and multiple measurements are made in a fixed state to obtain the frequency shift measurement error of the forward Brillouin scattering excited by the two torsion-radial acoustic modes.

9. A dual parameter sensing method of forward Brillouin scattering temperature and axial strain based on an optical fiber direct detection structure as claimed in claim 8, characterized in that: In step S3, the measurement uncertainty of the measurement result is calculated by the following formula: Among them, δv i and δv j are the frequency shift measurement errors of forward Brillouin scattering excited by two torsional-radial acoustic modes, which are obtained by the standard deviation of multiple sets of data collected by the corresponding two torsional-radial acoustic modes under a certain state; δT is the measurement uncertainty of temperature, and δε is the measurement uncertainty of axial strain.

Images