System and method for simultaneous sensing of fiber optic temperature and strain using random number encoding of probe light

Abstract

The present application belongs to the field of distributed optical fiber sensing technology, and solves the problem that temperature and strain in Brillouin frequency shift cannot be measured simultaneously. A system and method for simultaneously sensing temperature and strain of optical fiber by random number coding detection are provided. Brillouin scattered light signals and Raman scattered light signals generated by the sensing optical fiber enter a data acquisition card and a data processing flow unit. The data processing flow unit decodes the random number coding sequence, obtains a single pulse system response, realizes the restoration of Brillouin and Raman scattering signals, and obtains temperature and strain demodulation results. The present application constructs a Brillouin-Raman fusion temperature and strain dual-parameter sensing system based on random number coding detection, establishes a temperature and strain dual-parameter demodulation method, realizes the restoration of Brillouin and Raman scattering signals through random number coding sequence decoding, obtains temperature and strain demodulation results, can accurately measure temperature and strain simultaneously, and solves the problem of cross-sensitivity of temperature and strain in the system.

Description

Technical Field

[0001] This invention belongs to the field of distributed optical fiber sensing technology, specifically relating to a system and method for simultaneously sensing optical fiber temperature and strain using random number encoding detection. Background Technology

[0002] Distributed fiber optic sensing technology has advantages such as long-distance measurement, corrosion resistance, and electromagnetic interference resistance, making it widely used in pipeline safety monitoring, cable fault detection, and structural health monitoring.

[0003] In actual measurements of distributed fiber optic sensing, changes in both temperature and strain will cause changes in the Brillouin frequency shift in the fiber. Relying solely on Brillouin frequency shift measurements cannot distinguish whether the frequency shift is caused by temperature or strain. In other words, there is a problem of cross-sensitivity between temperature and strain, making it impossible to measure both temperature and strain simultaneously. This severely restricts the practical application of distributed fiber optic sensing technology. Summary of the Invention

[0004] In order to solve at least one of the above-mentioned technical problems in the prior art, the present invention provides a system and method for simultaneous sensing of fiber optic temperature and strain by random number encoding detection.

[0005] This invention is achieved using the following technical solution: a system for simultaneous sensing of fiber optic temperature and strain using random number encoding detection, comprising a narrow linewidth laser, a sensing fiber, a dual-parameter composite sensing unit, a data acquisition card, and a data processing unit.

[0006] The dual-parameter composite sensing unit includes a first optical coupler, a pulsed light modulator, a pulse signal generator, a pulsed light amplifier, an optical circulator, a wavelength division multiplexer, a continuous optical amplifier, an optical filter, a polarization scrambler, a second optical coupler, a photodetector, a low-noise amplifier, a mixer, a microwave source, and dual photodetectors.

[0007] The light wave of the set wavelength generated by the narrow linewidth laser is split into two outputs by the first optical coupler, including one probe light and one reference light. The probe light enters the pulse light modulator, and the pulse signal generator generates a random number encoded light probe signal which is injected into the pulse light modulator. The pulse light modulator modulates the probe light into a random number encoded sequence of pulse light, which is amplified by the pulse light amplifier and then injected into the sensing fiber through the optical circulator. The Brillouin scattering light signal and the Raman scattering light signal generated by the sensing fiber return to the input end of the wavelength division multiplexer through the optical circulator. The wavelength division multiplexer simultaneously filters out the Brillouin scattering light signal of the first wavelength, the Raman Stokes light signal of the second wavelength, and the Raman anti-Stokes light signal of the third wavelength and outputs them through its three output ends respectively. The Raman Stokes light signal of the second wavelength and the Raman anti-Stokes light signal of the third wavelength enter the dual-path photodetector and are converted into electrical signals, which are then input to the data acquisition card and the data processing unit.

[0008] The Brillouin scattered light signal of the first wavelength is amplified by a continuous optical amplifier and filtered by an optical filter before entering the input of the second optical coupler. The reference light output from the first optical coupler is polarized and fading is eliminated by a polarization scrambler before entering the other input of the second optical coupler and mixing coherently with the Brillouin scattered light signal to obtain a difference frequency light signal containing Brillouin frequency shift information. The difference frequency light signal enters a photodetector and is converted into an electrical signal. The electrical signal is amplified by a low-noise amplifier and then mixed with the output signal of the microwave source in a mixer. The down-frequency electrical signal enters the data acquisition card and data processing unit.

[0009] The data processing unit decodes the random number encoding sequence and demodulates the Brillouin frequency shift, the intensity ratio of the Raman anti-Stokes signal and the Raman Stokes signal. The intensity ratio of the Raman anti-Stokes signal and the Raman Stokes signal is used to determine the temperature information of the sensing fiber, thus realizing temperature measurement. Then, the temperature-induced Brillouin frequency shift is subtracted from the Brillouin frequency shift to determine the strain information of the sensing fiber, thus realizing strain measurement.

[0010] Preferably, the data processing unit includes a Brillouin and Raman scattering signal module, an operator module, a random number encoded probe pulse sequence module, a decoding curve module, a single-pulse system response module, and a temperature and strain demodulation result module.

[0011] The Brillouin and Raman scattering signals in the Brillouin and Raman scattering signal module and the random number encoded probe pulse sequence in the random number encoded probe pulse sequence module are correlated through the operator module to obtain the decoding curve. The decoding curve in the decoding curve module is accumulated and averaged to calculate the single-pulse system response, realizing the reconstruction of the Brillouin and Raman scattering signals and obtaining the temperature and strain demodulation results. Based on the Brillouin frequency shift and the intensity ratio of the Raman anti-Stokes signal to the Raman Stokes signal in the temperature and strain demodulation result module, the strain and temperature information along the sensing fiber are calculated.

[0012] Preferably, the wavelength of the first wavelength Brillouin scattering light signal is 1550 nm, the wavelength of the second wavelength Raman-Stokes light signal is 1450 nm, and the wavelength of the third wavelength Raman-anti-Stokes light signal is 1660 nm.

[0013] The present invention also provides a method for simultaneous sensing of fiber temperature and strain by random number encoded detection, comprising the following steps: S1: the probe light output from the first optical coupler enters the pulse light modulator, the pulse signal generator generates a random number encoded light probe signal and injects it into the pulse light modulator, the pulse light modulator modulates the probe light input from the first optical coupler into a random number encoded sequence pulse light, which is amplified by the pulse light amplifier and then injected into the sensing fiber through the optical circulator.

[0014] S2: The Brillouin scattering and Raman scattering signals generated by the sensing fiber enter the data acquisition card and data processing unit. The data processing unit performs random number encoding sequence decoding to obtain the single-pulse system response, realizes the restoration of Brillouin and Raman scattering signals, and obtains temperature and strain demodulation results.

[0015] S3: Based on the Brillouin frequency shift and the intensity ratio of the Raman anti-Stokes signal to the Raman Stokes signal in the temperature and strain demodulation results, the strain and temperature signal changes along the sensing fiber are calculated using the Brillouin-Raman fusion temperature and strain dual-parameter simultaneous demodulation principle, thus obtaining the strain and temperature information along the sensing fiber.

[0016] Preferably, the data processing unit performs random number encoding sequence decoding to restore the Brillouin and Raman scattering signals, obtaining the temperature and strain demodulation results as follows:

[0017] The Brillouin and Raman scattering signals f(t) in the sensing fiber can be expressed as:

[0018] f(t) = p(t) * P(t);

[0019] In the formula: * represents convolution operation, p(t) represents random number encoded probe pulse sequence, and P(t) represents single pulse system response of dual-parameter composite sensing unit when single pulse light is injected;

[0020] M groups of random numbers of length L are used to encode the probe pulse sequences p1(t), p2(t), ... p1(t). n (t) is injected into the sensing fiber to obtain M sets of corresponding Brillouin and Raman scattering signals f1(t), f2(t), ... f M (t):

[0021]

[0022] In the formula: f i (t) represents the i-th group of Brillouin and Raman scattering signals in the sensing fiber, p i (t) represents the i-th set of random number encoded probe pulse sequences, m j It is the j-th element of the random number-coded probe pulse sequence, τ j It is the time delay between the j-th "1" code in the random number encoded probe pulse sequence and the start of the sequence;

[0023] As can be seen from the above formula, the scattering time-domain curve corresponding to each group of coded pulse sequences is actually the result of superimposing the system's single-pulse response according to the coded pulse rules after a delay.

[0024] f i (t) and its corresponding p iThe decoding curve S can be obtained by performing cross-correlation operation on (t). i (t), the expression is:

[0025]

[0026] In the formula: (representing the relevant operators), p i The mean of (t);

[0027] The obtained S i (t) The cumulative average is obtained as follows:

[0028]

[0029] In the formula: M represents the number of groups of random number encoded probe pulse sequences, and S(t) represents the cumulative average result of Si(t);

[0030] The expression for the low-sidelobe impulse function of a random number-coded probe pulse sequence is:

[0031]

[0032] In the formula: η(t) represents a low-sidelobe impulse function, δ(t) represents the impulse function; L is the length of the random number encoding sequence;

[0033] Combined:

[0034]

[0035]

[0036]

[0037]

[0038] Decoding yields the single-pulse system response of the dual-parameter composite sensing unit under single-pulse light injection:

[0039]

[0040] Preferably, the process of calculating the strain and temperature signal changes along the sensing fiber (18) using the Brillouin-Raman fusion temperature and strain dual-parameter simultaneous demodulation principle is as follows:

[0041] The expression for the change in fiber Brillouin frequency shift is:

[0042] ΔV B =C ε Δε+C T ΔT;

[0043] Where: ΔVB C represents the Brillouin frequency shift variation. ε C T ε and ΔT are the strain coefficient and temperature coefficient of the Brillouin frequency shift, respectively, and Δε and ΔT are the strain change and temperature change, respectively.

[0044] When a random number-coded sequence pulse light is injected into the sensing fiber (18), Raman-Stokes light and Raman-anti-Stokes scattered light are generated, and their intensities are expressed as follows:

[0045] φ s =K s SV s 4 φ e {1-exp[-hΔv / (kT)]} -1 exp[-(α0+α s )L];

[0046] φ a =K a SV a 4 φ e {exp[hΔv / (kT)]-1} -1 exp[-(α0+α a )L];

[0047] Where: φ s For Ramanstokes light, φ a For Raman anti-Stokes light, φ e Let S be the intensity of the incident light, S be the scattering cross section, and K be the intensity of the incident light. s K a These are coefficients related to the Raman-Stokes scattering cross section and the Raman-anti-Stokes scattering cross section, respectively, V s V a The frequencies of the Raman-Stokes and Raman-anti-Stokes beams are respectively given, where h is Planck's constant, Δv is the frequency shift of the Raman scattered light, k is Boltzmann's constant, T is the thermodynamic temperature, and α0 and α... s α a The propagation losses of incident light, Raman-Stokes light and Raman-anti-Stokes light in the sensing fiber are respectively defined, where G is the length of the sensing fiber.

[0048] Since Raman anti-Stokes light is sensitive to temperature changes, while Raman Stokes light is not, temperature information can be demodulated by comparing the intensity ratio of the Raman anti-Stokes signal to that of the Raman Stokes signal.

[0049]

[0050] To determine the optical power ratio reference A0 at temperature T0, the temperature of the sensing fiber must first be calibrated by maintaining the temperature at the reference value T0; then, the temperature information T of the sensing fiber is demodulated by comparing the optical power ratio A at temperature T with the optical power ratio reference A0.

[0051]

[0052] With equation ΔV B =C ε Δε+C T The strain change Δε of the sensing fiber can be obtained by combining ΔT and ΔT:

[0053]

[0054] According to the above formula, by measuring the temperature information of the sensing fiber through Raman scattering and subtracting the Brillouin frequency shift caused by temperature from the Brillouin frequency shift, the strain information of the sensing fiber can be determined.

[0055] Compared with the prior art, the beneficial effects of the present invention are:

[0056] This invention proposes a random number encoding detection method based on the traditional Brillouin-Raman fusion temperature and strain dual-parameter measurement system. This method can improve the accuracy of temperature and strain measurement of the system. At the same time, by utilizing the characteristics of random number encoding detection, the system can simultaneously detect Brillouin scattering signals and Raman scattering signals using only a single laser and a single-mode fiber. By decoding the random number encoding sequence, the Brillouin and Raman scattering signals can be restored, and the temperature and strain demodulation results can be obtained, realizing the simultaneous measurement of temperature and strain.

[0057] This invention constructs a Brillouin-Raman fusion temperature and strain dual-parameter sensing system based on random number encoded detection, establishes a temperature and strain dual-parameter demodulation method, and realizes the reconstruction of Brillouin and Raman scattering signals through random number encoded sequence decoding to obtain temperature and strain demodulation results. It can simultaneously and accurately measure temperature and strain, and solve the problem of cross-sensitivity between temperature and strain in the system. Attached Figure Description

[0058] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. 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 effort.

[0059] Figure 1 This is a schematic diagram of the system module connection structure of the present invention;

[0060] Figure 2 This is a schematic diagram of the modular structure of the data processing flow unit of the present invention.

[0061] In the diagram: 1-Narrow linewidth laser; 2-First optical coupler; 3-Pulse light modulator; 4-Pulse signal generator; 5-Pulse light amplifier; 6-Optical circulator; 7-Wavelength division multiplexer; 8-Continuous optical amplifier; 9-Optical filter; 10-Polarization scrambler; 11-Second optical coupler; 12-Photodetector; 13-Low noise amplifier; 14-Mixer; 15-Microwave source; 16-Data acquisition card; 17-Dual-channel photodetector; 18-Sensing fiber; 201-Brillouin and Raman scattering signal module; 202-Arithmetic operator module; 203-Random number encoded probe pulse sequence module; 204-Decoding curve module; 205-Single pulse system response module; 206-Temperature and strain demodulation results module. Detailed Implementation

[0062] The technical solutions of the embodiments of the present invention will be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other implementation methods obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0063] It should be noted that the structures, proportions, sizes, etc., shown in the accompanying drawings of this specification are only for the purpose of assisting those skilled in the art in understanding and reading the content disclosed in the specification, and are not intended to limit the conditions under which the present invention can be implemented. Therefore, they have no substantial technical significance. Any modifications to the structure, changes in the proportional relationships, or adjustments to the size, without affecting the effects and objectives that the present invention can produce, should fall within the scope of the technical content disclosed in the present invention. It should be noted that in this specification, relational terms such as "first" and "second" are only used to distinguish one entity from several other entities, and do not necessarily require or imply any actual relationship or order between these entities.

[0064] This invention provides an embodiment:

[0065] like Figure 1 , Figure 2 As shown, a system for simultaneous sensing of fiber optic temperature and strain using random number encoding detection includes a narrow linewidth laser 1, a sensing fiber optic cable 18, a dual-parameter composite sensing unit, a data acquisition card 16, and a data processing unit.

[0066] The dual-parameter composite sensing unit includes a first optical coupler 2, a pulsed light modulator 3, a pulse signal generator 4, a pulsed light amplifier 5, an optical circulator 6, a wavelength division multiplexer 7, a continuous optical amplifier 8, an optical filter 9, a polarization scrambler 10, a second optical coupler 11, a photodetector 12, a low-noise amplifier 13, a mixer 14, a microwave source 15, and a dual-channel photodetector 17.

[0067] The output of the narrow linewidth laser 1 is connected to the input of the first optical coupler 2. The first output of the first optical coupler 2 is connected to the input of the pulsed light modulator 3. The output of the pulse signal generator 4 is connected to the input of the pulsed light modulator 3. The output of the pulsed light modulator 3 is connected to the input of the pulsed light amplifier 5. The output of the pulsed light amplifier 5 is connected to the input of the optical circulator 6. The output of the optical circulator 6 is connected to the sensing fiber 18. The return end of the optical circulator 6 is connected to the input of the wavelength division multiplexer 7. The first output of the wavelength division multiplexer 7 is connected to the input of the continuous optical amplifier 8. The output of the continuous optical amplifier 8 is connected to the input of the optical filter 9. The output of the optical filter 9 is connected to the first input of the second optical coupler 11. The first optical coupler 2... The second output terminal is connected to the input terminal of the polarization scrambler 10. The output terminal of the polarization scrambler 10 is connected to the second input terminal of the second optocoupler 11. The output terminal of the second optocoupler 11 is connected to the input terminal of the photodetector 12. The output terminal of the photodetector 12 is connected to the input terminal of the low-noise amplifier 13. The output terminal of the low-noise amplifier 13 is connected to the input terminal of the mixer 14. The output terminal of the microwave source 15 is connected to the input terminal of the mixer 14. The output terminal of the mixer 14 is connected to the first acquisition port of the data acquisition card 16. The second and third output terminals of the wavelength division multiplexer 7 are connected to the first and second input terminals of the dual-channel photodetector 17. The first and second output terminals of the dual-channel photodetector 17 are connected to the second and third acquisition ports of the data acquisition card 16.

[0068] The light wave of the set wavelength generated by the narrow linewidth laser 1 is split into two outputs by the first optical coupler 2, including one probe light and one reference light. The probe light enters the pulse light modulator 3, and the pulse signal generator 4 generates a random number encoded light probe signal which is injected into the pulse light modulator 3. The pulse light modulator 3 modulates the probe light into a random number encoded sequence pulse light, which is amplified by the pulse light amplifier 5 and then injected into the sensing fiber 18 through the optical circulator 6. The Brillouin scattering light signal and the Raman scattering light signal generated by the sensing fiber 18 are returned to the input end of the wavelength division multiplexer 7 through the optical circulator 6. The wavelength division multiplexer 7 simultaneously filters out the Brillouin scattering light signal of the first wavelength, the Raman Stokes light signal of the second wavelength, and the Raman anti-Stokes light signal of the third wavelength and outputs them through its three output ends respectively. The Raman Stokes light signal of the second wavelength and the Raman anti-Stokes light signal of the third wavelength enter the dual-path photodetector 17 and are converted into electrical signals, which are then input to the data acquisition card 16 and the data processing unit.

[0069] The Brillouin scattered light signal of the first wavelength is amplified by the continuous optical amplifier 8 and filtered by the optical filter 9, and then enters the input of the second optical coupler 11. The reference light output from the first optical coupler 2 is polarized and fading is eliminated by the polarization scrambler 10. After entering the other input of the second optical coupler 11, it is mixed and coherently mixed with the Brillouin scattered light signal to obtain a difference frequency light signal containing Brillouin frequency shift information. The difference frequency light signal enters the photodetector 12 and is converted into an electrical signal. The electrical signal is amplified by the low noise amplifier 13 and then mixed with the output signal of the microwave source 15 in the mixer 14. The down-frequency electrical signal enters the data acquisition card 16 and the data processing flow unit.

[0070] The data processing unit decodes the random number encoding sequence and demodulates the Brillouin frequency shift, the intensity ratio of the Raman anti-Stokes signal and the Raman Stokes signal. The intensity ratio of the Raman anti-Stokes signal and the Raman Stokes signal is used to determine the temperature information of the sensing fiber, thus realizing temperature measurement. Then, the temperature-induced Brillouin frequency shift is subtracted from the Brillouin frequency shift to determine the strain information of the sensing fiber, thus realizing strain measurement.

[0071] The data processing unit includes a Brillouin and Raman scattering signal module 201, an operator module 202, a random number encoded probe pulse sequence module 203, a decoding curve module 204, a single pulse system response module 205, and a temperature and strain demodulation result module 206.

[0072] The Brillouin and Raman scattering signals in module 201 and the random number encoded probe pulse sequence in module 203 are correlated by operator module 202 to obtain the decoding curve. The decoding curve in module 204 is accumulated and averaged to calculate the single-pulse system response, thereby restoring the Brillouin and Raman scattering signals and obtaining the temperature and strain demodulation results. Based on the Brillouin frequency shift and the intensity ratio of the Raman anti-Stokes signal to the Raman Stokes signal in module 206, the strain and temperature information along the sensing fiber 18 are calculated.

[0073] The wavelength of the first wavelength Brillouin scattering light signal is 1550 nm, the wavelength of the second wavelength Raman-Stokes light signal is 1450 nm, and the wavelength of the third wavelength Raman-anti-Stokes light signal is 1660 nm.

[0074] A method for simultaneous sensing of temperature and strain in optical fiber using random number encoding detection includes the following steps:

[0075] S1: The probe light output from the first optical coupler 2 enters the pulse light modulator 3. The pulse signal generator 4 generates a random number encoded light probe signal and injects it into the pulse light modulator 3. The pulse light modulator 3 modulates the probe light input from the first optical coupler 2 into a random number encoded sequence pulse light. After being amplified by the pulse light amplifier 5, it is injected into the sensing fiber 18 through the optical circulator 6.

[0076] S2: The Brillouin scattering light signal and Raman scattering light signal generated by the sensing fiber 18 enter the data acquisition card 16 and the data processing flow unit. The data processing flow unit performs random number encoding sequence decoding to obtain the single pulse system response, realizes the restoration of Brillouin and Raman scattering signals, and obtains temperature and strain demodulation results.

[0077] S3: Based on the Brillouin frequency shift and the intensity ratio of the Raman anti-Stokes signal to the Raman Stokes signal in the temperature and strain demodulation results, the strain and temperature signal changes along the sensing fiber are calculated using the Brillouin-Raman fusion temperature and strain dual-parameter simultaneous demodulation principle, thus obtaining the strain and temperature information along the sensing fiber.

[0078] The data processing unit decodes the random number encoding sequence to restore the Brillouin and Raman scattering signals, obtaining the temperature and strain demodulation results as follows:

[0079] The Brillouin and Raman scattering signals f(t) in the sensing fiber can be expressed as:

[0080] f(t) = p(t) * P(t);

[0081] In the formula: * represents convolution operation, p(t) represents random number encoded probe pulse sequence, and P(t) represents single pulse system response of dual-parameter composite sensing unit when single pulse light is injected;

[0082] M groups of random numbers of length L are used to encode the probe pulse sequences p1(t), p2(t), ... p1(t). n (t) is injected into sensing fiber 18 to obtain M sets of corresponding Brillouin and Raman scattering signals f1(t), f2(t)...f M (t):

[0083]

[0084] In the formula: f i (t) represents the i-th group of Brillouin and Raman scattering signals in the sensing fiber, p i (t) represents the i-th set of random number encoded probe pulse sequences, m j It is the j-th element of the random number-coded probe pulse sequence, τ j It is the time delay between the j-th "1" code in the random number encoded probe pulse sequence and the start of the sequence;

[0085] As can be seen from the above formula, the scattering time-domain curve corresponding to each group of coded pulse sequences is actually the result of superimposing the system's single-pulse response according to the coded pulse rules after a delay.

[0086] f i (t) and its corresponding p i The decoding curve S can be obtained by performing cross-correlation operation on (t). i (t), the expression is:

[0087]

[0088] In the formula: (representing the relevant operators), p i The mean of (t);

[0089] The obtained S i (t) The cumulative average is obtained as follows:

[0090]

[0091] In the formula: M represents the number of groups of random number encoded probe pulse sequences, and S(t) represents the cumulative average result of Si(t);

[0092] The autocorrelation characteristic of the random number-coded probe pulse sequence, possessing a low sidelobe-like impulse function, is a crucial basis for the random number encoding and decoding process in a distributed fiber optic dual-parameter composite sensing system. The expression for the low sidelobe-like impulse function of the random number-coded probe pulse sequence is as follows:

[0093]

[0094] In the formula: η(t) represents a low-sidelobe impulse function, δ(t) represents the impulse function; L is the length of the random number encoding sequence;

[0095] Combined:

[0096]

[0097]

[0098]

[0099]

[0100] Decoding yields the single-pulse system response of the dual-parameter composite sensing unit under single-pulse light injection:

[0101]

[0102] The process of calculating the strain and temperature signal changes along the sensing fiber (18) using the Brillouin-Raman fusion dual-parameter demodulation principle is as follows:

[0103] Based on the elasto-optical and thermo-optical effects of optical fibers, changes in temperature and strain will alter the refractive index and length of the fiber, thereby causing a change in the Brillouin frequency shift. The expression for the change in the Brillouin frequency shift is:

[0104] ΔV B =C ε Δε+C T ΔT;

[0105] Where: ΔV B C represents the Brillouin frequency shift variation. ε C T ε and ΔT are the strain coefficient and temperature coefficient of the Brillouin frequency shift, respectively, and Δε and ΔT are the strain change and temperature change, respectively.

[0106] Injecting a random number-coded sequence of pulsed light into a sensing fiber will generate Raman-Stokes light and Raman-anti-Stokes scattered light, the intensities of which are expressed as follows:

[0107] φ s =K s SV s 4 φ e {1-exp[-hΔv / (kT)]} -1 exp[-(α0+α s )L];

[0108] φ a =K a SV a 4 φ e {exp[hΔv / (kT)]-1} -1 exp[-(α0+α a )L];

[0109] Where: φ s For Ramanstokes light, φ a For Raman anti-Stokes light, φ e Let S be the intensity of the incident light, S be the scattering cross section, and K be the intensity of the incident light. s K a These are coefficients related to the Raman-Stokes scattering cross section and the Raman-anti-Stokes scattering cross section, respectively, V s V a The frequencies of the Raman-Stokes and Raman-anti-Stokes beams are respectively given, where h is Planck's constant, Δv is the frequency shift of the Raman scattered light, k is Boltzmann's constant, T is the thermodynamic temperature, and α0 and α...s α a The propagation losses of incident light, Raman-Stokes light and Raman-anti-Stokes light in the sensing fiber are respectively defined, where G is the length of the sensing fiber.

[0110] Since Raman anti-Stokes light is sensitive to temperature changes, while Raman Stokes light is not, temperature information can be demodulated by comparing the intensity ratio of the Raman anti-Stokes signal to that of the Raman Stokes signal.

[0111]

[0112] To determine the optical power ratio reference A0 at temperature T0, the temperature of the sensing fiber must first be calibrated by maintaining the temperature at the reference value T0; then, the temperature information T of the sensing fiber is demodulated by comparing the optical power ratio A at temperature T with the optical power ratio reference A0.

[0113]

[0114] With equation ΔV B =C ε Δε+C T The strain change Δε of the sensing fiber can be obtained by combining ΔT and ΔT:

[0115]

[0116] According to the above formula, by measuring the temperature information of the sensing fiber through Raman scattering and subtracting the Brillouin frequency shift caused by temperature from the Brillouin frequency shift, the strain information of the sensing fiber can be determined.

[0117] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A system for simultaneous sensing of fiber optic temperature and strain using random number encoding detection, characterized in that: It includes a narrow linewidth laser (1), a sensing fiber (18), a dual-parameter composite sensing unit, a data acquisition card (16), and a data processing flow unit; The dual-parameter composite sensing unit includes a first optical coupler (2), a pulsed light modulator (3), a pulse signal generator (4), a pulsed light amplifier (5), an optical circulator (6), a wavelength division multiplexer (7), a continuous optical amplifier (8), an optical filter (9), a polarization scrambler (10), a second optical coupler (11), a photodetector (12), a low-noise amplifier (13), a mixer (14), a microwave source (15), and a dual-path photodetector (17). The light wave of the set wavelength generated by the narrow linewidth laser (1) is split into two outputs by the first optical coupler (2), including one probe light and one reference light. The probe light enters the pulse light modulator (3), and the pulse signal generator (4) generates a random number encoded light probe signal which is injected into the pulse light modulator (3). The pulse light modulator (3) modulates the probe light into a random number encoded sequence pulse light, which is amplified by the pulse light amplifier (5) and then injected into the sensing fiber (18) through the optical circulator (6). The Brillouin scattering light signal generated by the sensing fiber (18) The Raman scattered light signal returns to the input of the wavelength division multiplexer (7) through the optical circulator (6). The wavelength division multiplexer (7) simultaneously filters out the first wavelength Brillouin scattered light signal, the second wavelength Raman Stokes light signal, and the third wavelength Raman anti-Stokes light signal and outputs them through its three output terminals respectively. The second wavelength Raman Stokes light signal and the third wavelength Raman anti-Stokes light signal enter the dual-path photodetector (17) and are converted into electrical signals, which are then input to the data acquisition card (16) and the data processing unit. The Brillouin scattered light signal of the first wavelength is amplified by the continuous optical amplifier (8) and filtered by the optical filter (9) and then enters the input end of the second optical coupler (11). The reference light output from the first optical coupler (2) is depolarized by the polarization scrambler (10) and then enters the other input end of the second optical coupler (11) to mix and coherently with the Brillouin scattered light signal to obtain a difference frequency light signal containing Brillouin frequency shift information. The difference frequency light signal enters the photodetector (12) and is converted into an electrical signal. The electrical signal is amplified by the low noise amplifier (13) and then mixed with the output signal of the microwave source (15) in the mixer (14). The down-frequency electrical signal enters the data acquisition card (16) and the data processing flow unit. The data processing unit decodes the random number encoding sequence and demodulates the Brillouin frequency shift, the intensity ratio of the Raman anti-Stokes signal and the Raman Stokes signal. The intensity ratio of the Raman anti-Stokes signal and the Raman Stokes signal is used to determine the temperature information of the sensing fiber, thus realizing temperature measurement. Then, the temperature-induced Brillouin frequency shift is subtracted from the Brillouin frequency shift to determine the strain information of the sensing fiber, thus realizing strain measurement.

2. The system for simultaneous sensing of fiber optic temperature and strain using random number encoding detection according to claim 1, characterized in that: The data processing flow unit includes a Brillouin and Raman scattering signal module (201), an operation symbol module (202), a random number encoded probe pulse sequence module (203), a decoding curve module (204), a single pulse system response module (205), and a temperature and strain demodulation result module (206). The Brillouin and Raman scattering signals in the Brillouin and Raman scattering signal module (201) and the random number encoded probe pulse sequence in the random number encoded probe pulse sequence module (203) are correlated by the operation module (202) to obtain the decoding curve; the decoding curve in the decoding curve module (204) is accumulated and averaged to calculate the single pulse system response, realize the restoration of the Brillouin and Raman scattering signals, and obtain the temperature and strain demodulation results; the strain and temperature information along the sensing fiber (18) are calculated based on the Brillouin frequency shift, the intensity ratio of the Raman anti-Stokes signal to the Raman Stokes signal in the temperature and strain demodulation result module (206).

3. The system for simultaneous sensing of fiber optic temperature and strain using random number encoding detection according to claim 2, characterized in that: The wavelength of the first wavelength Brillouin scattering light signal is 1550 nm, the wavelength of the second wavelength Raman-Stokes light signal is 1450 nm, and the wavelength of the third wavelength Raman-anti-Stokes light signal is 1660 nm.

4. A method for simultaneous sensing of fiber optic temperature and strain using random number encoding, based on the system for simultaneous sensing of fiber optic temperature and strain using random number encoding as described in any one of claims 1 to 3, characterized in that... This includes the following steps: S1: The probe light output from the first optical coupler (2) enters the pulse light modulator (3). The pulse signal generator (4) generates a random number encoded light probe signal and injects it into the pulse light modulator (3). The pulse light modulator (3) modulates the probe light input from the first optical coupler (2) into a random number encoded sequence pulse light. After being amplified by the pulse light amplifier (5), it is injected into the sensing fiber (18) through the optical circulator (6). S2: The Brillouin scattering light signal and Raman scattering light signal generated by the sensing fiber (18) enter the data acquisition card (16) and the data processing flow unit. The data processing flow unit performs random number encoding sequence decoding to obtain the single pulse system response, realizes the restoration of Brillouin and Raman scattering signals, and obtains temperature and strain demodulation results. S3: Based on the Brillouin frequency shift and the intensity ratio of the Raman anti-Stokes signal to the Raman Stokes signal in the temperature and strain demodulation results, the strain and temperature signal changes along the sensing fiber are calculated using the Brillouin-Raman fusion temperature and strain dual-parameter simultaneous demodulation principle, thus obtaining the strain and temperature information along the sensing fiber.

5. The method for simultaneous sensing of fiber optic temperature and strain by random number encoding detection according to claim 4, characterized in that: The data processing unit decodes the random number encoding sequence to restore the Brillouin and Raman scattering signals, obtaining the temperature and strain demodulation results as follows: The Brillouin and Raman scattering signals f(t) in the sensing fiber can be expressed as: f(t) = p(t) * P(t); In the formula: * represents convolution operation, p(t) represents random number encoded probe pulse sequence, and P(t) represents single pulse system response of dual-parameter composite sensing unit when single pulse light is injected; M groups of random numbers of length L are used to encode the probe pulse sequences p1(t), p2(t), ... p1(t). n (t) is injected into the sensing fiber (18) to obtain M sets of corresponding Brillouin and Raman scattering signals f1(t), f2(t)...f M (t): In the formula: f i (t) represents the i-th group of Brillouin and Raman scattering signals in the sensing fiber, p i (t) represents the i-th set of random number encoded probe pulse sequences, m j It is the j-th element of the random number-coded probe pulse sequence, τ j It is the time delay between the j-th "1" in the random number encoded probe pulse sequence and the start of the sequence; As can be seen from the above formula, the scattering time-domain curve corresponding to each group of coded pulse sequences is actually the result of superimposing the system's single-pulse response according to the coded pulse rules after a delay. f i (t) and its corresponding p i The decoding curve S can be obtained by performing cross-correlation operation on (t). i (t), the expression is: In the formula: (representing the relevant operators), Let pi(t) represent the mean. The obtained S i (t) The cumulative average is obtained as follows: In the formula: M represents the number of groups of random number encoded probe pulse sequences, and S(t) represents the cumulative average result of Si(t); The expression for the low-sidelobe impulse function of a random number-coded probe pulse sequence is: In the formula: η(t) represents a low-sidelobe impulse function, δ(t) represents the impulse function; L is the length of the random number encoding sequence; Combined: The single-pulse system response of the dual-parameter composite sensing unit during single-pulse light injection is obtained through decoding:

6. The method for simultaneous sensing of fiber optic temperature and strain by random number encoding detection according to claim 5, characterized in that: The process of calculating the strain and temperature signal changes along the sensing fiber (18) using the Brillouin-Raman fusion dual-parameter demodulation principle is as follows: The expression for the change in fiber Brillouin frequency shift is: ΔV B =C ε No+C T ΔT; Where: ΔV B C represents the Brillouin frequency shift variation. ε C T ε and ΔT are the strain coefficient and temperature coefficient of the Brillouin frequency shift, respectively, and Δε and ΔT are the strain change and temperature change, respectively. When a random number-coded sequence pulse light is injected into the sensing fiber (18), Raman-Stokes light and Raman-anti-Stokes scattered light are generated, and their intensities are expressed as follows: f s =K s SV s 4 f e {1-exp[-hΔv / (kT)]} -1 exp[-(α0+α s )L]; f a =K a SV a 4 f e {exp[hΔv / (kT)]-1} -1 exp[-(α0+α a )L]; Where: φ s For Ramanstokes light, φ a For Raman anti-Stokes light, φ e Let S be the intensity of the incident light, S be the scattering cross section, and K be the intensity of the incident light. s K a These are coefficients related to the Raman-Stokes scattering cross section and the Raman-anti-Stokes scattering cross section, respectively, V s V a The frequencies of the Raman-Stokes and Raman-anti-Stokes beams are respectively given, where h is Planck's constant, Δv is the frequency shift of the Raman scattered light, k is Boltzmann's constant, T is the thermodynamic temperature, and α0 and α... s α a The propagation losses of incident light, Raman-Stokes light and Raman-anti-Stokes light in the sensing fiber are respectively defined, where G is the length of the sensing fiber. Since Raman anti-Stokes light is sensitive to temperature changes, while Raman Stokes light is not, temperature information can be demodulated by comparing the intensity ratio of the Raman anti-Stokes signal to that of the Raman Stokes signal. To determine the optical power ratio reference A0 at temperature T0, the temperature of the sensing fiber must first be calibrated by maintaining the temperature at the reference value T0; then, the temperature information T of the sensing fiber is demodulated by comparing the optical power ratio A at temperature T with the optical power ratio reference A0. With equation ΔV B =C ε Δε+C T The strain change Δε of the sensing fiber can be obtained by combining ΔT and ΔT: According to the above formula, by measuring the temperature information of the sensing fiber through Raman scattering and subtracting the Brillouin frequency shift caused by temperature from the Brillouin frequency shift, the strain information of the sensing fiber can be determined.

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