System for simultaneously measuring temperature and pressure based on forward Brillouin scattering in multi-core optical fiber

Abstract

The invention discloses a system for simultaneously measuring temperature and pressure based on forward Brillouin scattering in a multi-core optical fiber, which relates to the technical field of optical fiber temperature and pressure double-parameter sensors, and is characterized in that light emitted by a pump light source enters a polarization controller after being modulated by a pump light modulation system, and then enters an erbium-doped optical fiber amplifier; one part is injected into a Sagnac ring, and the other part excites a high-order torsion-radial mode through a multi-core optical fiber; light emitted by the detection light source is divided into light beams transmitted in the clockwise direction and the anticlockwise direction through the coupler, and the light beams are injected into the Sagnac ring; the spectrum analyzer captures the frequency shift of the Brillouin scattering signal; the signal processing unit processes the frequency shift of the Brillouin scattering signal and inverts temperature and strain data; and the data analysis and feedback system is combined with machine learning to optimize temperature and strain data. According to the invention, high-sensitivity temperature and strain sensing is realized.

Description

Technical Field

[0001] The present invention relates to the technical field of optical fiber temperature and pressure dual-parameter sensors, and in particular to a temperature and pressure simultaneous measurement system based on forward Brillouin scattering in a multi-core optical fiber. Background Art

[0002] In fields such as industry, construction, and medicine, the simultaneous measurement of temperature and pressure is of great significance for structural health monitoring and safety assessment. Current measurement methods mostly rely on the detection of a single parameter, making it difficult to obtain temperature and pressure information simultaneously. Existing fiber-based temperature and pressure sensing methods include fiber Bragg gratings, backward Brillouin scattering, microcavities, and Fabry-Perot interferometers. Sensors based on the above methods can effectively achieve simultaneous measurement of temperature and pressure, but there are still certain defects that limit their practical application. For example, sensing methods based on fiber Bragg gratings usually require at least two sensors to achieve simultaneous measurement, sensing methods based on microcavities usually have a relatively narrow measurement range, and sensing methods based on backward Brillouin scattering have problems such as high signal frequency, high cost, and complex data processing. Measurement technology based on multi-core fiber forward Brillouin scattering has gradually attracted attention due to its advantages such as space separation characteristics, high sensitivity, and resistance to electromagnetic interference.

[0003] Multi-core fiber optic sensing technology has become an ideal choice for temperature and pressure measurement due to its space separation characteristics, high sensitivity, anti-electromagnetic interference and long-distance transmission capabilities. Brillouin scattering is one of the important scattering mechanisms. It uses the characteristics of the interaction between light and phonons to measure the temperature and pressure in the environment with high precision. Brillouin scattering can be divided into forward Brillouin scattering (FBS) and backward Brillouin scattering according to the propagation direction of Stokes scattered light. Forward Brillouin scattering has unique advantages in practical applications due to its low signal frequency, multiple acoustic modes and large measurement range. The introduction of multi-core optical fiber can stimulate forward Brillouin scattering, further improving the performance of Brillouin scattering technology and showing a broader application prospect in temperature and pressure measurement.

[0004] Currently, the methods for simultaneous measurement of temperature and pressure based on optical fibers mainly include fiber Bragg gratings, microcavities, back-Brillouin scattering, and Fabry-Perot interferometers. However, there are problems that need to be solved, such as a large number of sensors, a small sensing range, low sensing accuracy, and high cost. Summary of the Invention

[0005] The embodiment of the present invention provides a simultaneous temperature and pressure measurement system based on forward Brillouin scattering in a multi-core optical fiber, which realizes high-sensitivity temperature and strain sensing.

[0006] In a first aspect, the present invention provides a simultaneous temperature and pressure measurement system based on forward Brillouin scattering in a multi-core optical fiber, comprising: a pump light source, a pump light modulation system, a polarization controller, an erbium-doped fiber amplifier, a multi-core optical fiber, a detection light source, a Sagnac ring, a spectrum analyzer, an oscilloscope, a signal processing unit, and a data analysis and feedback system;

[0007] The light emitted by the pump light source is modulated by the pump light modulation system and then enters the polarization controller to increase the gain of the high-order twist-radial mode. After passing through the polarization controller and entering the erbium-doped fiber amplifier, a portion of the light is injected into the Sgnac ring, and the other portion excites the high-order twist-radial mode through the multi-core optical fiber;

[0008] The light emitted by the detection light source is divided into two beams transmitted in clockwise and counterclockwise directions by a coupler and injected into the Sagnac ring, and changes in temperature and external pressure are simultaneously applied to the multi-core optical fiber;

[0009] The spectrum analyzer is used to capture the frequency shift of the Brillouin scattering signal;

[0010] The oscilloscope is used to collect time domain signals;

[0011] The signal processing unit is used to process the frequency shift of the Brillouin scattering signal, obtain a spectrum distribution after Fourier transforming the time domain signal, extract the mode linewidth, and invert the temperature and strain data;

[0012] The data analysis and feedback system is used to optimize temperature and strain data in combination with machine learning.

[0013] In some examples, the pump light modulation system includes: a semiconductor amplifier, an electro-optical modulator, and an arbitrary waveform generator;

[0014] The pump light emitted by the pump light source is modulated by the semiconductor amplifier, the electro-optical modulator and the arbitrary waveform generator.

[0015] In some examples, the signal processing unit is configured to filter the frequency shift of the Brillouin scattering signal to remove noise, extract the frequency shift value through Fourier transform, and calculate the temperature and strain values in real time by combining the difference in the frequency shifts of the forward and backward scattered signals with known temperature coefficients and gauge coefficients;

[0016] At the same time, the spectrum distribution is obtained by Fourier transforming the time domain signal, and the mode linewidth characteristic parameters are extracted to further demodulate the temperature and pressure changes.

[0017] In some examples, the data analysis and feedback system is trained through an artificial neural network to automatically identify error sources and correct the inverted temperature and strain data, thereby optimizing the inversion accuracy of temperature and strain.

[0018] In some examples, the system further comprises: an output unit;

[0019] The output unit is used to output the optimized temperature and strain data in real time.

[0020] In general, the above technical solutions conceived by the present invention can achieve the following beneficial effects compared with the prior art:

[0021] By exciting the off-axis outer core in a multi-core optical fiber to generate a stimulated high-order torsional-radial mode, and using a single stimulated acoustic mode to simultaneously monitor the resonant frequency and mode linewidth of the forward Brillouin scattering signal, both temperature and pressure parameters can be measured simultaneously with high precision and high sensitivity. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative work.

[0023] Figure 1 Schematic diagram of the multi-core optical fiber structure provided by an embodiment of the present invention;

[0024] Figure 2 1 is a simulation principle diagram of temperature measurement using forward Brillouin scattering provided by an embodiment of the present invention, wherein (a) shows the relationship between frequency shift and pressure, (b) shows the relationship between line width and temperature, and (c) shows the relationship between frequency shift and temperature.

[0025] Figure 3 Schematic diagram of a temperature and pressure measurement system provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0026] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without making any creative efforts shall fall within the scope of protection of the present invention.

[0027] In the following description, specific embodiments of the present invention will be described with reference to steps and symbols performed by one or more computers, unless otherwise specified. Therefore, these steps and operations will be mentioned several times as being performed by a computer, and computer execution as referred to herein includes operations by a computer processing unit that represents electronic signals of data in a structured form. This operation converts the data or maintains it at a location in the computer's memory system, which can be reconfigured or otherwise change the operation of the computer in a manner familiar to testers in the field. The data structure in which the data is maintained is a physical location in the memory, which has specific characteristics defined by the data format. However, the principles of the present invention are described in the above text, which does not represent a limitation, and testers in the field will understand that the various steps and operations below can also be implemented in hardware.

[0028] As used herein, the terms "module" or "unit" may be considered software objects executed on the computing system. The various components, modules, engines, and services herein may be considered implementation objects on the computing system. While the devices and methods herein are preferably implemented in software, they may also be implemented in hardware and remain within the scope of protection of the present invention.

[0029] It will be understood by those skilled in the art that, unless expressly stated otherwise, the singular forms "a", "an", and "the" used herein may also include the plural forms. It should be further understood that the term "comprising" used in the specification of the present invention refers to the presence of features, integers, steps, operations, elements and / or components, but does not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or groups thereof. It should be understood that when we refer to an element as being "connected" or "coupled" to another element, it may be directly connected or coupled to the other element, or there may be intermediate elements. In addition, "connected" or "coupled" as used herein may include wireless connections or wireless couplings. The term "and / or" used herein includes all or any unit and all combinations of one or more associated listed items.

[0030] This paper proposes a novel temperature and strain measurement system based on the principle of forward Brillouin scattering. By leveraging the inter-core phase modulation characteristics caused by forward Brillouin scattering in multi-core optical fibers and their relationship to temperature and strain, combined with high-precision spectral analysis techniques and advanced data processing algorithms, highly sensitive temperature and strain sensing is achieved.

[0031] like Figure 3 As shown in the figure, pump light, detection light source, modulation unit, multi-core optical fiber, temperature and pressure application device, detection and data processing unit, etc. are shown. The sensing system of the present invention mainly consists of the following parts:

[0032] Pump light source: A laser source with a wavelength of 1553 nm and an output power of 10 mW.

[0033] Pump light modulation system: Utilizing a semiconductor amplifier, electro-optical modulator, and arbitrary waveform generator, the pump light is modulated into pulses with a period of 1μs and a duration of 0.5ns. The semiconductor amplifier provides a high modulation extinction ratio, unattainable with electro-optical modulators, but cannot support short pulses. A pulse with a duration of 5ns and a period of 1μs is first generated in the semiconductor amplifier and then further modulated by the electro-optical modulator into a pulse with a duration of 0.5ns and a period of 1μs.

[0034] Polarization controller: Repeatedly adjust the polarization controller to maximize the depth of modulation of the probe light by a specific acoustic mode, that is, to increase the gain of the high-order torsional-radial mode TR18,8.

[0035] Erbium-doped fiber amplifier: The pump light power modulated by the pump light modulation system is amplified to a level between 20mW and 60mW and injected into the Sgnac ring.

[0036] In an embodiment of the present invention, a Sagnac loop is an optical device based on the light wave interference effect, which has high sensitivity and good stability. Monochromatic light emitted by a light source is divided into two beams, which propagate in opposite directions along a loop formed by the same optical fiber, forming a Sagnac loop, resulting in a slight phase change, which is the information of the forward Brillouin scattered light carried by the probe light. This method modulates the pump light into a short pulse and injects it into an off-axis outer core of a multi-core optical fiber in the same direction as the probe light to excite a high-gain high-order torsional-radial mode TR18,8. Temperature and external pressure changes are simultaneously applied to the optical fiber under test. A bandpass filter is added to the Sagnac loop to filter out the pump light signal, retaining only the probe light. The signal is received by a photodetector at the output end, analyzed by a spectrometer, and then subjected to wavelet transform noise reduction processing.

[0037] Multi-core fiber: 30m long commercial seven-core fiber is used, and its cross section is shown in Figure 1 , pump light is injected into an off-axis outer core of a seven-core fiber to excite high-order twist-radial modes. Figure 1 The arrangement of the cores of a multi-core optical fiber is demonstrated; the embodiment of the present invention uses a seven-core optical fiber, with the central inner core located in the middle and the off-axis outer cores evenly distributed in a regular hexagon. The diameter of all cores is r1=r2=9μm, the cladding diameter is 125μm, and the core spacing is d=35μm.

[0038] In an embodiment of the present invention, a seven-core optical fiber structure is adopted, which embeds seven independent optical fiber cores in the cladding of a single optical fiber. These optical fiber cores are arranged in a central core surrounded by six off-axis cores to form a hexagonal symmetrical structure with a core spacing of 35μm, a core diameter of 9μm, and a cladding diameter of 125μm. Each core can transmit optical signals independently, avoiding mutual interference between signals. Each core receives and transmits optical signals independently, thereby improving signal strength and measurement accuracy. The use of multi-core optical fiber can not only increase signal strength, but also inject pump light into the off-axis core to excite high-order torsional-radial modes to improve the measurement accuracy and sensitivity of temperature and pressure.

[0039] Forward Brillouin scattering: Forward Brillouin scattering is a key fiber nonlinear effect in fiber optic sensing technology. When the probe light propagates through the fiber, it interacts with the acoustic field excited by the pump wave, causing part of the light signal to scatter along the fiber's propagation direction and produce a frequency shift. This frequency shift is caused by the exchange of momentum and energy between light and phonons. The amount of the frequency shift is related to the speed of sound in the medium, which is in turn affected by temperature and pressure. Therefore, by detecting the frequency shift of the forward Brillouin scattering signal, it is possible to accurately measure the temperature and pressure of the fiber's environment.

[0040] The solution of the characteristic equation obtained by the boundary condition of no radial pressure at the surface of the silica cladding at r = a can obtain the vibration frequency fnm of the forward Brillouin scattering sound field. The characteristic equation can be expressed as:

[0041] Det(M)=0 (1)

[0042] The components of the M matrix are:

[0043]

[0044] Where n and m are integers, representing the order and mode number of the forward Brillouin scattering sound field mode, respectively; a is the fiber cladding radius; vs represents the shear velocity of the sound wave in the fiber medium; vd represents the longitudinal velocity of the sound wave in the fiber medium; α = vs / vd represents the velocity ratio; and Jn(x) is the nth-order first-kind Bessel function. The solution of equation (1) is ym = Ωn, where m*a / vs is a real number. The resonant frequency of the nth-order torsional-radial mode, i.e., the Brillouin frequency, can be obtained as:

[0045]

[0046] The speed of sound vs varies approximately linearly with the temperature and pressure of the material:

[0047] v s =v s0 (1+α(ε-ε0)+β(T-T0)) (4)

[0048] Where α and β represent the pressure coefficient and temperature coefficient, respectively. The Brillouin frequency shift, or the resonant frequency of each acoustic mode, is approximately linearly related to temperature and pressure:

[0049] f n，m =f n，m0 +αΔε+βΔT (5)

[0050] In addition, to distinguish whether the Brillouin frequency shift is caused by temperature change or pressure change, the present invention uses an oscilloscope in the device to collect a 10μs time domain signal, obtains the spectrum distribution after Fourier transform, extracts its 3dB bandwidth as the mode linewidth characteristic parameter, and introduces the mode linewidth to further demodulate temperature and pressure changes. The acoustic mode linewidth of forward Brillouin scattering can be expressed as:

[0051] Γ m =Γ inhomo +Γ τ (6)

[0052] Among them, Γ inhomo is related to the change in fiber diameter, which is negligible with temperature and pressure changes, while is the viscous damping term, which is inversely proportional to the phonon lifetime τ of the acoustic field. As the temperature increases, the viscosity increases, the phonon lifetime τ and the forward Brillouin scattering efficiency increase, which leads to the narrowing of the mode linewidth. It is found that the linewidth change decreases approximately linearly and is independent of the pressure change:

[0053] ΔΓ m =γΔT (7)

[0054] Therefore, the present invention monitors the resonance frequency f of the forward Brillouin acoustic mode signal. n,m and mode linewidth Γ m , that is, the temperature and pressure information can be demodulated, such as Figure 2 As shown, the simulation results show good linear relationships between forward Brillouin frequency shift and pressure, line width and temperature, and frequency shift and temperature.

[0055] Probe Light Source: A 1550nm wavelength laser with a 10kHz linewidth is used. A coupler splits the probe light into two beams, one propagating in clockwise and the other in counterclockwise directions, and injects them into the Sagnac loop. The clockwise light propagates in the same direction as the pump light. Because the phase matching condition for forward Brillouin scattering is met, the inter-core phase modulation caused by forward Brillouin scattering in the clockwise probe light accumulates over the entire fiber length. The nonlinear phase perturbation of the counterclockwise probe light is negligible.

[0056] Spectrum analyzer: used to accurately capture the frequency shift of the Brillouin scattering signal and can obtain the scattered signal of each core with high precision.

[0057] Signal processing unit: collects data through a spectrum analyzer or real-time acquisition oscilloscope, and then uses signal processing software to process the Brillouin scattering signal collected in the optical fiber sensor and invert the temperature and strain data.

[0058] In the embodiments of the present invention, the optical signal directly obtained in the experiment usually contains a lot of interfering noise signals. Therefore, the wavelet transform method is used to reduce noise and extract features from the time domain signal, thereby obtaining the frequency and linewidth information of the forward Brillouin scattering signal. First, a suitable mother wavelet is selected, such as the Daubechies wavelet. Second, the Brillouin scattering signal is decomposed into wavelet coefficients of different scales. The discrete wavelet transform is used to decompose the signal into low-frequency components (approximation coefficients) and high-frequency components (detail coefficients). Then, a threshold is set, and coefficients below the threshold are set to zero, and coefficients above the threshold are subtracted from the threshold. Next, feature extraction is performed. The changes in the denoised wavelet coefficients reflect the characteristics of the signal. By extracting these changes, Brillouin scattering information can be obtained. Finally, an inverse wavelet transform is performed on the denoised wavelet coefficients to reconstruct the signal.

[0059] Data analysis and feedback system: Combines machine learning algorithms and physical models to process data, optimize measurement accuracy, and achieve system adaptive adjustment.

[0060] Specific implementation steps and operation procedures

[0061] 1. Experimental preparation and system configuration:

[0062] Before implementation, system components must be configured according to the application environment. The light source used is a 1550nm laser, which is transmitted to the sensor via optical fiber. When deploying the fiber optic sensor, the sensor must be placed in the area to be monitored based on the measurement requirements.

[0063] 2. Signal acquisition and Brillouin frequency shift analysis:

[0064] After the system is activated, the laser signal is transmitted through the optical fiber. As it passes through each fiber core, changes in temperature or strain cause a forward Brillouin scattering frequency shift. The spectrum analyzer collects this forward frequency shift information in real time.

[0065] 3. Data processing and temperature strain calculation:

[0066] The collected Brillouin scattering signal frequency shift data is processed by the signal processing unit and then analyzed using advanced algorithms to calculate temperature and strain. The data is first filtered to remove noise, and then the frequency shift value is extracted using methods such as Fourier transform. The temperature and strain values are calculated in real time by combining the difference in the forward and backward scattered signal frequency shifts with the known temperature coefficient and gauge coefficient.

[0067] 4. Machine Learning Optimization and Feedback:

[0068] To further improve system stability and data accuracy, this paper introduces a machine learning algorithm, specifically an artificial neural network (ANN), for data training and optimization. By learning from a large amount of experimental data, the algorithm can automatically identify error sources and correct the data, thereby optimizing the inversion accuracy of temperature and strain.

[0069] 5. Result output and system feedback:

[0070] After data processing is complete, temperature and strain measurement results are displayed in real time on a display screen or remote terminal, providing information to the user or control system. This data feedback allows the system to adjust parameters and models based on the real-time measurement results, improving measurement accuracy. In practical applications, this system can monitor and adapt to temperature and strain changes in real time under various conditions, finding widespread application in industries such as industrial and structural monitoring.

[0071] This invention successfully achieves real-time, high-precision measurement of temperature and strain by leveraging the principle of multi-core fiber forward Brillouin scattering, combined with high-precision spectrum analysis and machine learning optimization. The system's excellent performance and broad application potential make it valuable for practical applications in a variety of fields.

[0072] The above is a detailed introduction to a simultaneous temperature and pressure measurement system based on forward Brillouin scattering in a multi-core optical fiber provided by an embodiment of the present invention. Specific examples are used herein to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only used to help understand the method of the present invention and its core idea. At the same time, for those skilled in the art, according to the ideas of the present invention, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting the present invention.

Claims

1. A simultaneous temperature and pressure measurement system based on forward Brillouin scattering in a multi-core optical fiber, characterized in that: include: Pump light source, pump light modulation system, polarization controller, erbium-doped fiber amplifier, multi-core optical fiber, detection light source, Sagnac loop, spectrum analyzer, oscilloscope, signal processing unit and data analysis and feedback system; The light emitted by the pump light source is modulated by the pump light modulation system and then enters the polarization controller to increase the gain of the high-order twist-radial mode. After passing through the polarization controller and entering the erbium-doped fiber amplifier, a portion of the light is injected into the Sgnac ring, and the other portion excites the high-order twist-radial mode through the multi-core optical fiber; The light emitted by the detection light source is divided into two beams transmitted in clockwise and counterclockwise directions by a coupler and injected into the Sagnac ring, and changes in temperature and external pressure are simultaneously applied to the multi-core optical fiber; The spectrum analyzer is used to capture the frequency shift of the Brillouin scattering signal; The oscilloscope is used to collect time domain signals; The signal processing unit is used to process the frequency shift of the Brillouin scattering signal, obtain a spectrum distribution after Fourier transforming the time domain signal, extract the mode linewidth, and invert the temperature and strain data; The data analysis and feedback system is used to optimize temperature and strain data in combination with machine learning.

2. The system according to claim 1, wherein: The pump light modulation system includes: a semiconductor amplifier, an electro-optical modulator and an arbitrary waveform generator; The pump light emitted by the pump light source is modulated by the semiconductor amplifier, the electro-optical modulator and the arbitrary waveform generator.

3. The system according to claim 2, characterized in that The signal processing unit is used to filter the frequency shift of the Brillouin scattering signal to remove noise, then extract the frequency shift value through Fourier transform, and calculate the temperature and strain values in real time by combining the difference in the frequency shift of the forward and backward scattered signals with the known temperature coefficient and gauge coefficient; At the same time, the spectrum distribution is obtained by Fourier transforming the time domain signal, and the mode linewidth characteristic parameters are extracted to further demodulate the temperature and pressure changes.

4. The system according to claim 3, characterized in that The data analysis and feedback system is trained through an artificial neural network to automatically identify error sources and correct the inverted temperature and strain data, thereby optimizing the inversion accuracy of temperature and strain.

5. The system according to claim 4, characterized in that The system further includes: an output unit; The output unit is used to output the optimized temperature and strain data in real time.

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