Dynamic strain sensing system and method based on time delay double pulse and double wavelength Φ-otdr
By introducing a cascaded sensing method of time-delayed dual pulses and dual wavelengths into a distributed optical fiber sensing system, and combining time-delay differential and wavelength differential, the problem of phase demodulation distortion under large dynamic strain is solved, and accurate measurement of ultra-large dynamic strain is achieved.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- ZHEJIANG BREI COMM ENG CO LTD
- Filing Date
- 2026-04-17
- Publication Date
- 2026-06-12
Smart Images
Figure CN122192199A_ABST
Abstract
Description
Technical Field
[0001] This application relates to the field of distributed optical fiber sensing technology, and in particular to a Φ-OTDR dynamic strain sensing system and method based on time-delayed dual pulses and dual wavelengths. Background Technology
[0002] Distributed fiber optic sensing technology, especially Φ-OTDR-based sensing systems, has significant application value in infrastructure health monitoring, geological exploration, and perimeter security due to its ability to achieve long-distance, high-sensitivity distributed vibration and strain measurements. In Φ-OTDR systems, external disturbances (such as dynamic strain) have a linear relationship with the phase change of the Rayleigh backscattered signal. To quantitatively recover external disturbances, the system typically employs phase demodulation techniques. However, traditional phase demodulation algorithms are constrained by the phase unwinding condition, namely, the absolute value of the phase difference between two adjacent sampling points must be less than π. When the applied dynamic strain amplitude is large (e.g., reaching micro-strain), the induced phase change often exceeds this threshold, leading to phase winding and severely distorting the demodulation results, failing to accurately reflect the actual strain. To address the phase winding problem caused by large dynamic strain, existing technologies primarily focus on reducing the amplitude of the signal to be unwound by "compressing the phase." Currently, two main technical approaches exist: "dual-wavelength detection" and "time-delayed dual-pulse" methods.
[0003] The first type of technology is a phase compression method based on "dual-wavelength detection." This method uses two probe beams of different wavelengths to perform measurements simultaneously. Since different wavelengths have different phase responses to the same strain, an equivalent phase signal can be obtained by calculating the difference between the demodulated phases of the two wavelengths. The equivalent wavelength of this phase is much larger than that of a single wavelength, thereby reducing phase sensitivity and expanding the dynamic range. However, this method has limitations: achieving a large dynamic range extension requires extremely precise wavelength control, which is limited by the tuning range and frequency drift noise of the laser. The phase compression capability of single-dimensional wavelength difference has a physical bottleneck and is difficult to cope with extremely complex strain environments.
[0004] The second type of technique is the phase compression method based on "time-delayed double pulses." This method introduces two probe pulses with a small time delay in the time domain. By differentially analyzing the Rayleigh scattering signals generated by these two pulses, the phase amplitude is compressed using the differential properties of a sinusoidal function. This method is low-cost and can significantly improve the dynamic range. However, this method has a significant problem: the compression effect of the time-delayed double pulse depends on the amount of time delay and the frequency of the disturbance. When the external dynamic strain is very large (e.g., strong seismic waves), even after one time-delay differential analysis, the differential phase may still exceed the π dewinding threshold. In this case, a single time-delay differential dimension is insufficient to meet the demodulation requirements, and the system will still fall into the predicament of phase winding, leading to measurement failure.
[0005] In summary, all single "phase compression" techniques have limitations. Most existing solutions improve the phase signal in only one dimension, either the "time domain" or the "wavelength domain." Currently, there is a lack of a mechanism that can organically combine these two dimensions. If a second dimension could be introduced—that is, by superimposing wavelength difference on top of time delay difference to construct a "dual-difference" architecture—theoretically, secondary phase compression could be achieved. This cascaded approach would further compress the phase signal after time delay difference using the synthesized wavelength, resulting in a multiplier increase in the dynamic strain range that the system can measure.
[0006] Therefore, there is an urgent need in this field for a cascaded sensing method that integrates time-delayed dual-pulse and dual-wavelength detection, which can break through the dynamic range limit of existing technologies through a dual compression mechanism and achieve accurate measurement of ultra-large dynamic strain. Summary of the Invention
[0007] To improve the measurement range of dynamic strain sensing systems, this application provides a Φ-OTDR dynamic strain sensing system and method based on time-delayed dual pulses and dual wavelengths.
[0008] In a first aspect, this application provides a Φ-OTDR dynamic strain sensing system based on time-delayed dual pulses and dual wavelengths, employing the following technical solution: A dynamic strain sensing system based on time-delayed dual-pulse and dual-wavelength Φ-OTDR includes a first DFB laser, a first optical coupler, a second optical coupler, a first acousto-optic modulator, a second DFB laser, a third optical coupler, a fourth optical coupler, a second acousto-optic modulator, a fifth optical coupler, an optical circulator, a sensing fiber, an FBG optical filter, a sixth optical coupler, a seventh optical coupler, a first signal processing module, a second signal processing module, and a data processing module. The first DFB laser is used to generate a first continuous laser of a first wavelength; The first optical coupler is used to split the first continuous laser into a first probe beam and a first reference beam. The first probe beam enters the first input terminal of the second optical coupler, and the first reference beam enters the second input terminal of the sixth optical coupler. The second optical coupler is used to split the first probe light into a first probe splitter and a second probe splitter. The first probe splitter enters the first input terminal of the first acousto-optic modulator, and the second probe splitter enters the first input terminal of the second acousto-optic modulator. The second DFB laser is used to generate a second continuous laser of a second wavelength; The second optical coupler is used to split the second continuous laser into a second probe beam and a second reference beam. The second probe beam enters the first input terminal of the third optical coupler, and the second reference beam enters the second input terminal of the seventh optical coupler. The third optical coupler is used to split the second probe light into a third probe beam and a fourth probe beam. The third probe beam enters the second input terminal of the first acousto-optic modulator, and the fourth probe beam enters the second input terminal of the second acousto-optic modulator. The first acousto-optic modulator is used to modulate the first detection beam into a first pulse at a first modulation frequency, and to modulate the third detection beam into a second pulse at the first modulation frequency; The second acousto-optic modulator is used to modulate the first detection beam into a third pulse at a second modulation frequency, and to modulate the third detection beam into a fourth pulse at a first modulation frequency; The fifth optical coupler is used to amplify the power of the first pulse, the second pulse, the third pulse, and the fourth pulse to obtain a probe light pulse; The optical circulator is used to inject the probe light pulse into the sensing optical fiber and acquire the Rayleigh scattering signal; The FBG optical filter is used to separate the first Rayleigh scattering signal of the first wavelength and the second Rayleigh scattering signal of the second wavelength from the Rayleigh scattering signal. The sixth optical coupler is used to combine the first Rayleigh scattering signal and the first reference light into a first processed signal; The first signal processing module is used to process the first processed signal into a first low-frequency signal of a first frequency and a second low-frequency signal of a second frequency; The seventh optical coupler is used to combine the second Rayleigh scattering signal and the second reference light into a second processed signal; The second signal processing module is used to process the second processed signal into a third low-frequency signal of a first frequency and a fourth low-frequency signal of a second frequency; The data processing module is used to process the first low-frequency signal, the second low-frequency signal, the third low-frequency signal and the fourth low-frequency signal to obtain dynamic strain measurement results.
[0009] By adopting the above technical solution and constructing an optical path structure including dual lasers, dual frequencies, and multiple couplers, the generation and independent detection of four pulsed lights with two wavelengths and two modulation frequencies were achieved. This architecture lays the hardware foundation for subsequent dual differential modulation in the time and wavelength domains, enabling simultaneous time-delay pulse modulation of two wavelengths, facilitating subsequent cascaded phase demodulation, and improving the measurement range of the dynamic strain sensing system.
[0010] Optionally, the data processing module is used to perform IQ demodulation on the first low-frequency signal to obtain a first equivalent phase; and is also used to perform IQ demodulation on the second low-frequency signal to obtain a second equivalent phase, wherein the second equivalent phase has a preset time delay relative to the first equivalent phase; The data processing module is also used to calculate the phase difference between the first equivalent phase and the second equivalent phase to obtain the first differential phase; The data processing module is also used to perform IQ demodulation on the third low-frequency signal to obtain a third equivalent phase; and to perform IQ demodulation on the fourth low-frequency signal to obtain a fourth equivalent phase, wherein the fourth equivalent phase has the preset time delay relative to the third equivalent phase; The data processing module is also used to calculate the phase difference between the third equivalent phase and the fourth equivalent phase to obtain the second differential phase; The data processing module is also used to calculate the difference between the first differential phase and the second differential phase to obtain the second differential phase; The data processing module is also used to generate the dynamic strain measurement results based on the second differential phase.
[0011] By employing the above technical solution, a dual-phase compression mechanism is constructed by demodulating the time-delayed pulses of two wavelengths using IQ modulation and calculating the differential phase, and then performing a second differential division on the two differential phases. This processing method can effectively eliminate the winding phenomenon of single-dimensional differential phases under extreme large strain conditions, achieving accurate restoration of ultra-large dynamic strain signals.
[0012] Optionally, the system further includes an arbitrary waveform generator, which is connected to the first acousto-optic modulator and the second acousto-optic modulator; The arbitrary waveform generator is used to adjust the output waveforms of the first and second acousto-optic modulators. The arbitrary waveform generator is also used to adjust the time delay of the output signals of the first and second acousto-optic modulators to the preset time delay.
[0013] By employing the above technical solution, the output waveforms and time delays of the two acousto-optic modulators are precisely controlled by an arbitrary waveform generator, enabling flexible adjustment of the preset time delay τ. This design ensures that the two pairs of time-delayed pulses at different wavelengths have the same delay, providing a guarantee for the accurate calculation of the subsequent differential phase and improving the system's adjustability and measurement accuracy.
[0014] Optionally, the difference between the first wavelength and the second wavelength is less than a preset wavelength difference.
[0015] By adopting the above technical solution, the phase signal after time delay differential is further compressed, effectively avoiding phase entanglement, thereby greatly expanding the detection range of dynamic strain.
[0016] Optionally, the first signal processing module includes a first balanced detector, a first bandpass filter, a second balanced detector, and a second bandpass filter; The sixth optical coupler is also used to divide the first processed signal into a first processed sub-signal and a second processed signal. The first balanced detector is used to mix the first processed sub-signal to obtain a first beat frequency signal; The first bandpass filter is used to filter the first beat frequency signal to obtain the first low frequency signal; The second balanced detector is used to mix the second processed sub-signal to obtain the second beat frequency signal; The second bandpass filter is used to filter the first beat frequency signal to obtain the second low-frequency signal.
[0017] By adopting the above technical solution, the Rayleigh scattering signals generated by two time-delayed pulses at the same wavelength can be independently detected, providing an accurate source of phase information for subsequent calculation of the first differential phase.
[0018] Optionally, the second signal processing module includes a third balanced detector, a third bandpass filter, a fourth balanced detector, and a fourth bandpass filter; The seventh optical coupler is also used to divide the second processed signal into a third processed sub-signal and a fourth processed sub-signal; The third balance detector is used to mix the third processing sub-signal to obtain the third beat frequency signal; The third bandpass filter is used to filter the third beat frequency signal to obtain the third low frequency signal; The fourth balance detector is used to mix the fourth processing sub-signal to obtain the fourth beat frequency signal; The fourth bandpass filter is used to filter the fourth beat frequency signal to obtain the fourth low-frequency signal.
[0019] By adopting the above technical solution, independent detection of two time-delayed pulse signals under the second wavelength was achieved. Combined with the output of the first signal processing module, complete four-channel phase data was provided for subsequent dual differential operations.
[0020] Optionally, the system further includes a first EDFA optical amplifier and a second EDFA optical amplifier; The first EDFA optical amplifier is disposed between the fifth optical coupler and the optical circulator; The second EDFA optical amplifier is disposed between the optical circulator and the FBG optical filter.
[0021] By employing the above technical solution, power compensation can be performed on optical pulse signals and Rayleigh scattering signals. This design ensures the signal-to-noise ratio of optical signals during long-distance sensing, avoids the decrease in phase demodulation accuracy due to optical power attenuation, and improves the detection distance and stability of the system.
[0022] Optionally, the modulation frequency of the first acousto-optic modulator is 110MHz, and the modulation frequency of the second acousto-optic modulator is 200MHz.
[0023] Optionally, the difference in output power between the first DFB laser and the second DFB laser is less than a preset difference threshold.
[0024] By employing the above technical solution, it is ensured that the two wavelength probe pulses have similar optical power after being amplified by the EDFA. This design avoids phase demodulation errors caused by power differences, improving the accuracy of dual-wavelength differential operations and the overall measurement precision of the system.
[0025] Secondly, this application provides a Φ-OTDR dynamic strain sensing method based on time-delayed dual pulses and dual wavelengths, employing the following technical solution: A dynamic strain sensing method based on time-delayed dual pulses and dual wavelengths Φ-OTDR is provided, wherein the method is executed by any of the above-mentioned dynamic strain sensing systems based on time-delayed dual pulses and dual wavelengths Φ-OTDR.
[0026] Thirdly, this application provides a smart terminal, which adopts the following technical solution: A smart terminal includes a memory and a processor, wherein the memory stores a computer program that can be loaded by the processor and executed according to the above method.
[0027] Fourthly, this application provides a computer storage medium capable of storing corresponding programs, which facilitates improving the measurement range of the dynamic strain sensing system, and adopts the following technical solution: A computer-readable storage medium storing a computer program that can be loaded by a processor and executed any of the above-mentioned Φ-OTDR dynamic strain sensing methods based on time-delayed dual pulses and dual wavelengths.
[0028] In summary, this application includes at least one of the following beneficial technical effects: 1. By constructing an optical path structure including dual lasers, dual frequencies, and multiple couplers, the generation and independent detection of four pulsed lights with two wavelengths and two modulation frequencies were achieved. This architecture lays the hardware foundation for subsequent dual differential modulation in the time and wavelength domains, enabling simultaneous time-delay pulse modulation of two wavelengths, facilitating subsequent cascaded phase demodulation, and improving the measurement range of the dynamic strain sensing system; 2. By performing IQ demodulation on the time-delayed pulses of two wavelengths and calculating the differential phase, and then performing a second differential division on the two differential phases, a dual-phase compression mechanism is constructed. This processing method can effectively eliminate the winding phenomenon of single-dimensional differential phase under extreme large strain conditions, and achieve accurate restoration of ultra-large dynamic strain signals; 3. By precisely controlling the output waveforms and time delays of the two acousto-optic modulators through an arbitrary waveform generator, flexible adjustment of the preset time delay τ is achieved. This design ensures that the two pairs of time-delayed pulses at different wavelengths have the same delay, providing a guarantee for the accurate calculation of the subsequent differential phase and improving the system's adjustability and measurement accuracy. Attached Figure Description
[0029] Figure 1 This is a schematic diagram of a Φ-OTDR dynamic strain sensing system based on time-delayed dual pulses and dual wavelengths disclosed in an embodiment of this application.
[0030] Figure 2 This is a differential phase comparison diagram obtained from a time-delayed double-pulse system under different strain amplitudes, as disclosed in an embodiment of this application.
[0031] Figure 3 This is a strain comparison diagram obtained by demodulating a time-delayed dual-pulse system under different strain amplitudes, as disclosed in an embodiment of this application.
[0032] Figure 4 This is a differential phase map obtained by a cascaded detection system under large strain as disclosed in an embodiment of this application.
[0033] Figure 5 This is a dynamic strain map obtained by demodulation of a cascaded detection system under large strain, as disclosed in an embodiment of this application.
[0034] Explanation of reference numerals in the attached figures: 1. First DFB laser; 2. First optical coupler; 3. Second optical coupler; 4. First acousto-optic modulator; 5. Second DFB laser; 6. Third optical coupler; 7. Fourth optical coupler; 8. Second acousto-optic modulator; 9. Arbitrary waveform generator; 10. Fifth optical coupler; 11. First EDFA optical amplifier; 12. Optical circulator; 13. Sensing fiber; 14. Second EDFA optical amplifier; 15. FBG optical filter; 16. Sixth optical coupler; 17. First balanced detector; 18. First bandpass filter; 19. Second balanced detector; 20. Second bandpass filter; 21. Seventh optical coupler; 22. Third balanced detector; 23. Third bandpass filter; 24. Fourth balanced detector; 25. Fourth bandpass filter; 26. Data processing module. Detailed Implementation
[0035] To make the purpose, technical solution, and advantages of this application clearer, the following description is provided in conjunction with the appendix. Figures 1 to 5 The present application will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are for illustrative purposes only and are not intended to limit the scope of the application.
[0036] This application discloses a Φ-OTDR dynamic strain sensing system based on time-delayed dual pulses and dual wavelengths. (Refer to...) Figure 1 The system includes a first DFB laser 1, a first optical coupler 2, a second optical coupler 3, a first acousto-optic modulator 4, a second DFB laser 5, a third optical coupler 6, a fourth optical coupler 7, a second acousto-optic modulator 8, an arbitrary waveform generator 9, a fifth optical coupler 10, a first EDFA optical amplifier 11, an optical circulator 12, a sensing fiber 13, a second EDFA optical amplifier 14, an FBG optical filter 15, a sixth optical coupler 16, a first balanced detector 17, a first bandpass filter 18, a second balanced detector 19, a second bandpass filter 20, a seventh optical coupler 21, a third balanced detector 22, a third bandpass filter 23, a fourth balanced detector 24, a fourth bandpass filter 25, and a data processing module 26.
[0037] The first DFB laser 1 is used to generate a first continuous laser beam with a first wavelength. For example, the first DFB laser 11 generates a laser beam with a center wavelength of... A narrow-linewidth continuous-wave laser with a wavelength of 1550.3 nm and a linewidth < 1 kHz is used. This continuous-wave laser is split into two paths by a first optical coupler 22, with a power ratio of 90%:10%. The first optical coupler 2 is used to split the first continuous-wave laser into a first probe beam and a first reference beam. The first probe beam enters the first input terminal of a second optical coupler 3, and the first reference beam enters the second input terminal of a sixth optical coupler 16. Specifically, the first path, with 90% of the laser's power, serves as the probe beam and enters the first input terminal of the second optical coupler 33. The second path, with 10% of the laser's power, serves as the reference beam and enters the second input terminal of the sixth optical coupler 16.
[0038] The second optical coupler 3 is used to split the first probe light into a first probe splitter and a second probe splitter. The first probe splitter enters the first input terminal of the first acousto-optic modulator 4, and the second probe splitter enters the first input terminal of the second acousto-optic modulator 8. Specifically, the second optical coupler 33 splits the wavelength of the first probe light into two beams at a ratio of 50%:50%. The laser beam is split into two beams. The first beam enters the first input terminal of the first acousto-optic modulator 4; the second beam enters the first input terminal of the second acousto-optic modulator 8.
[0039] The first acousto-optic modulator 4 is used to modulate the first probe beam into a first pulse at a first modulation frequency, and the second acousto-optic modulator 8 is used to modulate the first probe beam into a third pulse at a second modulation frequency. Specifically, under the control of the output radio frequency signal of the arbitrary waveform generator 9, the first acousto-optic modulator 4 modulates the first probe beam into a third pulse at a second modulation frequency. The continuous light is modulated into pulsed light with a repetition frequency of . The second acousto-optic modulator 8 will have a wavelength of The continuous light is modulated into pulsed light with a repetition frequency of . The frequency is The pulse has an adjustable delay (τ) on the order of microseconds relative to the pulse with frequency . The two pulses enter the first and second input terminals of the fifth optical coupler 10, respectively.
[0040] The second DFB laser 5 is used to generate a second continuous laser with a second wavelength, the difference between the first wavelength and the second wavelength being less than a preset wavelength difference. For example, the second DFB laser 5 generates a laser with a center wavelength of... A narrow-linewidth continuous-wave laser with a wavelength of 1530.3 nm and a linewidth < 1 kHz. The laser beam is split into two paths after passing through the third optical coupler 6, with a power ratio of 90%:10%. The second optical coupler 3 is used to split the second continuous laser beam into a second probe beam and a second reference beam. The second probe beam enters the first input terminal of the third optical coupler 6, and the second reference beam enters the second input terminal of the seventh optical coupler 21. The first path, with 90% power, serves as the probe beam and enters the first input terminal of the third optical coupler 6. The second path, with 10% power, serves as the reference beam and enters the second input terminal of the seventh optical coupler 21.
[0041] The third optical coupler 6 is used to split the second probe light into a third probe splitter and a fourth probe splitter. The third probe splitter enters the second input terminal of the first acousto-optic modulator 4, and the fourth probe splitter enters the second input terminal of the second acousto-optic modulator 8. Specifically, the third optical coupler 6 splits the wavelength of the second probe light into two beams in a 50%:50% ratio. The laser beam is split into two beams. The first beam enters the second input terminal of the first acousto-optic modulator 4; the second beam enters the second input terminal of the second acousto-optic modulator 8.
[0042] The first acousto-optic modulator 4 is used to modulate the third probe beam to a second pulse at a first modulation frequency, and the second acousto-optic modulator 8 is used to modulate the third probe beam to a fourth pulse at the first modulation frequency. Specifically, under the control of the output radio frequency signal of the arbitrary waveform generator 9, the first acousto-optic modulator 4 modulates the third probe beam to a fourth pulse at a wavelength of... The continuous light is modulated into pulsed light with a repetition frequency of . The second acousto-optic modulator 8 will have a wavelength of The continuous light is modulated into pulsed light with a repetition frequency of . The frequency is The pulse relative to the frequency is The pulse has an adjustable delay on the order of microseconds, the magnitude of which is related to the wavelength. The two light pulses have the same time delay. The wavelength is... The two pulses of light enter the first and second input terminals of the fifth optical coupler 10, respectively.
[0043] In summary, the wavelength is The repetition frequency is The pulse and wavelength are The repetition frequency is also the same. The pulse simultaneously enters the first input terminal of the fifth optocoupler 10. The wavelength is... The repetition frequency is The pulse and wavelength are The repetition frequency is also the same. The pulse simultaneously enters the second input terminal of the fifth optocoupler 10.
[0044] The output of the fifth optical coupler 10 is connected to the input of the first EDFA optical amplifier 11, amplifying the power of the four photodetector pulses. The first EDFA optical amplifier 11 operates at a wavelength... and The two wavelengths of light pulses have similar gain, ensuring that they have similar optical power.
[0045] The first EDFA optical amplifier 11 is positioned between the fifth optical coupler 10 and the optical circulator 12. The input terminal of the first EDFA optical amplifier 11 is connected to the first input terminal of the optical circulator 12. The probe light pulse is emitted from the first output terminal of the optical circulator 12 and injected into the sensing fiber 13. Due to the microscopic random fluctuations in the refractive index of the fiber core, each light pulse undergoes Rayleigh backscattering during propagation in the sensing fiber 13, and the phase change of the scattered light reflects the information of the dynamic strain acting on the fiber.
[0046] Rayleigh scattering signal is emitted from the second output terminal of optical circulator 12 and enters the second EDFA optical amplifier 14 for optical power amplification.
[0047] The second EDFA optical amplifier 14 is positioned between the optical circulator 12 and the FBG optical filter 5. The outgoing light from the second EDFA optical amplifier 14 enters the FBG optical filter 15. The center operating wavelength of the FBG optical filter 15 is... At wavelength It has high reflectivity, therefore it is suitable for wavelengths of The light pulse is reflected, and the wavelength is... The light pulse is transmitted, thereby separating the Rayleigh scattering signals of the two wavelengths.
[0048] The sixth optical coupler 16 is used to combine the first Rayleigh scattering signal and the first reference light into a first processed signal, and the sixth optical coupler 16 is also used to divide the first processed signal into a first processed sub-signal and a second processed sub-signal. The first signal processing module is used to process the first processed signal into a first low-frequency signal of a first frequency and a second low-frequency signal of a second frequency. For example, the first signal processing module includes a first balanced detector 17, a first bandpass filter 18, a second balanced detector 19, and a second bandpass filter 20. The wavelength is... The Rayleigh scattering signal enters the first input terminal of the sixth optical coupler 16 and interacts with the first optical coupler. The output wavelengths are the same. The reference light is combined into a single beam. The sixth optical coupler 16 will combine the wavelengths... The light is divided into two beams with a power ratio of 50%:50%, and injected into the first balanced detector 17 and the second balanced detector 19 respectively.
[0049] The Rayleigh scattering signal with wavelength λ is mixed with reference light of the same wavelength in the first balanced detector 17, generating frequencies of 2λ and 2λ respectively. + and Two beat frequency signals. It is the center operating frequency of the first DFB laser 1. This is the modulation frequency of the first acoustic-optic modulator 4. The output signal of the first balanced detector 17 is filtered by the first bandpass filter 18, retaining only the frequency of . The first low-frequency signal.
[0050] Similarly, the wavelength is The Rayleigh scattering signal and the reference light of the same wavelength are mixed in the second balanced detector 19, producing frequencies of 2... + and Two beat frequency signals. This is the modulation frequency of the second audio-visual modulator 8. Modulation frequency and The frequency difference is greater than 50MHz to allow for independent detection of the Rayleigh scattering signals generated by the two pulses. The output signal of the second balanced detector 19, after being filtered by the second bandpass filter 20, also retains only the frequency of... The second low-frequency signal.
[0051] The seventh optical coupler 21 is used to combine the second Rayleigh scattering signal and the second reference light into a second processed signal, and also to divide the second processed signal into a third processed sub-signal and a fourth processed sub-signal. The second signal processing module is used to process the second processed signal into a third low-frequency signal of a first frequency and a fourth low-frequency signal of a second frequency. For example, the second signal processing module includes a third balanced detector 22, a third bandpass filter 23, a fourth balanced detector 24, and a fourth bandpass filter 25. The wavelength is... The Rayleigh scattering signal enters the first input terminal of the seventh optical coupler 21, and has the same wavelength as the output of the third optical coupler 6. The reference light is combined into a single beam. The seventh optical coupler 21 combines the wavelengths of... The light is divided into two beams with a power ratio of 50%:50%, and injected into the third balanced detector 22 and the fourth balanced detector 24 respectively.
[0052] The Rayleigh scattering signal with wavelength λ2 is mixed with the reference light of the same wavelength in the third balanced detector 22, producing frequencies of 2 and 2. + and Two beat frequency signals. This is the center operating frequency of the second DFB laser 5. The output signal of the third balanced detector 22 is filtered by the third bandpass filter 23, retaining only the frequency of... The third low-frequency signal.
[0053] Similarly, the wavelength is The Rayleigh scattering signal and the reference light of the same wavelength are mixed in the fourth balanced detector 24, producing frequencies of 2... + and The two beat frequency signals. After the output signal of the fourth balanced detector 24 is filtered by the fourth bandpass filter 25, only the frequency of is retained. The fourth low-frequency signal.
[0054] The data processing module 26 processes four low-frequency signals from the first bandpass filter 18, the second bandpass filter 20, the third bandpass filter 23, and the fourth bandpass filter 25, respectively.
[0055] The signal generated by the first bandpass filter 18 is demodulated using IQ to obtain a wavelength of The modulation frequency is equivalent phase of Rayleigh signal The signal generated by the second bandpass filter 20 is demodulated using IQ modulation to obtain a wavelength of... The modulation frequency is equivalent phase of Rayleigh signal Arbitrary waveform generator 9 sends a control signal to adjust the phase. Compared to It has a time delay (τ), that is The difference between the two phases, i.e., the differential phase, is... . This refers to the dynamic strain acting on the sensing fiber.
[0056] Similarly, the signal generated by the third bandpass filter 23 is IQ demodulated to obtain a wavelength of The modulation frequency is equivalent phase of Rayleigh signal The signal generated by the fourth bandpass filter 25 is demodulated using IQ modulation to obtain a wavelength of... The modulation frequency is equivalent phase of Rayleigh signal The difference phase between the two phases is .
[0057] The results of the differential phase analysis show that the differential phase obtained by the time-delay pulse scheme is... Proportional to strain The change in time delay (τ). If the time delay (τ) is very small, it may be possible to differentiate the phase. Limited to Within the interval, this avoids the phase winding problem of the Rayleigh signal. Then, through time-domain integration, the differential phase can be obtained. The equivalent phase of the Rayleigh scattering signal is obtained through inversion, ultimately accurately reconstructing the dynamic strain information. However, for dynamic strains with high-frequency changes or drastic fluctuations, even after one time-delay differential, the differential phase may still exceed the ±π dewinding threshold. In this case, a single time-delay differential dimension is insufficient to meet the demodulation requirements. Figure 2 and Figure 3 The results of differential phase and demodulated strain were compared when dynamic strain of different amplitudes was applied. For example... Figure 2 As shown in (a), when the strain amplitude is small (e.g., When the differential phase does not coil, the strain obtained by demodulation is completely consistent with the actual applied strain. Figure 3 (a)). However, when the strain is increased to At that time, the differential phase exceeded The unwinding threshold was exceeded, and winding occurred. Therefore, strain information could not be accurately recovered. Figure 3 (b)).
[0058] To address the winding problem of differential phases in time-delay pulse schemes and further increase the strain detection range, the two differential phases... and Perform a second difference. Due to the different wavelengths, the phase result of the second difference is as follows: .
[0059] This result introduces an additional wavelength-dependent compression factor compared to the time delay difference at a single wavelength. When the operating wavelengths of two DFB lasers are close, the compression factor... Much less than 1. For example... Figure 4 As shown, compared to the differential phase of the time-delay pulse, the cascaded differential phase after wavelength differentiation is further reduced, effectively avoiding phase winding. Figure 5 The results show that the differential phase obtained by the time-delayed double pulse and dual-wavelength cascade scheme accurately restored the phase. The large strain greatly improves the measurement range of dynamic strain. At the same time, by adopting time delay differential with the same wavelength, common-mode noise between the light source and the detector is effectively eliminated, improving the detection signal-to-noise ratio.
[0060] Preferably, the difference in output power between the first DFB laser 1 and the second DFB laser 5 is less than a preset difference threshold.
[0061] Preferably, the modulation frequency of the first acousto-optic modulator 4 =110MHz.
[0062] Preferably, the modulation frequency of the second acousto-optic modulator 8 =200MHz.
[0063] Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the above-described division of functional modules is used as an example. In practical applications, the above functions can be assigned to different functional modules as needed, that is, the internal structure of the device can be divided into different functional modules to complete all or part of the functions described above. The specific working process of the system, device, and unit described above can be referred to the corresponding process in the foregoing method embodiments, and will not be repeated here.
[0064] This application provides a computer-readable storage medium storing a computer program that can be loaded and executed by a processor using a Φ-OTDR dynamic strain sensing method based on time-delayed dual pulses and dual wavelengths.
[0065] Computer storage media include, for example, USB flash drives, portable hard drives, read-only memory (ROM), random access memory (RAM), magnetic disks, optical disks, and other media that can store program code.
[0066] Based on the same inventive concept, embodiments of this application provide a smart terminal, including a memory and a processor. The memory stores a computer program that can be loaded and executed by the processor using a Φ-OTDR dynamic strain sensing method based on time-delayed dual pulses and dual wavelengths.
[0067] Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the above-described division of functional modules is used as an example. In practical applications, the above functions can be assigned to different functional modules as needed, that is, the internal structure of the device can be divided into different functional modules to complete all or part of the functions described above. The specific working process of the system, device, and unit described above can be referred to the corresponding process in the foregoing method embodiments, and will not be repeated here.
[0068] The above are all preferred embodiments of this application and are not intended to limit the scope of protection of this application. Any feature disclosed in this specification (including the abstract and drawings) may be replaced by other equivalent or similar features unless specifically stated otherwise. That is, unless specifically stated otherwise, each feature is only one example of a series of equivalent or similar features.
Claims
1. A Φ-OTDR dynamic strain sensing system based on time-delayed dual-pulse and dual-wavelength, characterized in that, It includes a first DFB laser (1), a first optical coupler (2), a second optical coupler (3), a first acousto-optic modulator (4), a second DFB laser (5), a third optical coupler (6), a fourth optical coupler (7), a second acousto-optic modulator (8), a fifth optical coupler (10), an optical circulator (12), a sensing fiber (13), an FBG optical filter (15), a sixth optical coupler (16), a seventh optical coupler (21), a first signal processing module, a second signal processing module, and a data processing module (26). The first DFB laser (1) is used to generate a first continuous laser of a first wavelength; The first optical coupler (2) is used to split the first continuous laser into a first probe light and a first reference light. The first probe light enters the first input end of the second optical coupler (3), and the first reference light enters the second input end of the sixth optical coupler (16). The second optical coupler (3) is used to split the first probe light into a first probe splitter and a second probe splitter. The first probe splitter enters the first input terminal of the first acousto-optic modulator (4), and the second probe splitter enters the first input terminal of the second acousto-optic modulator (8). The second DFB laser (5) is used to generate a second continuous laser of a second wavelength; The second optical coupler (3) is used to split the second continuous laser into a second probe beam and a second reference beam. The second probe beam enters the first input end of the third optical coupler (6), and the second reference beam enters the second input end of the seventh optical coupler (21). The third optical coupler (6) is used to split the second probe light into a third probe beam and a fourth probe beam. The third probe beam enters the second input terminal of the first acousto-optic modulator (4), and the fourth probe beam enters the second input terminal of the second acousto-optic modulator (8). The first acousto-optic modulator (4) is used to modulate the first detection beam into a first pulse at a first modulation frequency, and to modulate the third detection beam into a second pulse at the first modulation frequency; The second acousto-optic modulator (8) is used to modulate the first detection beam into a third pulse at a second modulation frequency, and to modulate the third detection beam into a fourth pulse at a first modulation frequency; The fifth optical coupler (10) is used to amplify the power of the first pulse, the second pulse, the third pulse and the fourth pulse to obtain a probe light pulse; The optical circulator (12) is used to inject the probe light pulse into the sensing optical fiber (13) and acquire the Rayleigh scattering signal; The FBG optical filter (15) is used to separate the first Rayleigh scattering signal of the first wavelength and the second Rayleigh scattering signal of the second wavelength in the Rayleigh scattering signal; The sixth optical coupler (16) is used to combine the first Rayleigh scattering signal and the first reference light into a first processed signal; The first signal processing module is used to process the first processed signal into a first low-frequency signal of a first frequency and a second low-frequency signal of a second frequency; The seventh optical coupler (21) is used to combine the second Rayleigh scattering signal and the second reference light into a second processed signal; The second signal processing module is used to process the second processed signal into a third low-frequency signal of a first frequency and a fourth low-frequency signal of a second frequency; The data processing module (26) is used to process the first low-frequency signal, the second low-frequency signal, the third low-frequency signal and the fourth low-frequency signal to obtain dynamic strain measurement results.
2. The Φ-OTDR dynamic strain sensing system based on time-delayed dual pulses and dual wavelengths according to claim 1, characterized in that, The data processing module (26) is used to perform IQ demodulation on the first low-frequency signal to obtain a first equivalent phase; it is also used to perform IQ demodulation on the second low-frequency signal to obtain a second equivalent phase, wherein the second equivalent phase has a preset time delay relative to the first equivalent phase; The data processing module (26) is also used to calculate the phase difference between the first equivalent phase and the second equivalent phase to obtain the first differential phase; The data processing module (26) is also used to perform IQ demodulation on the third low-frequency signal to obtain a third equivalent phase; and to perform IQ demodulation on the fourth low-frequency signal to obtain a fourth equivalent phase, wherein the fourth equivalent phase has the preset time delay relative to the third equivalent phase; The data processing module (26) is also used to calculate the phase difference between the third equivalent phase and the fourth equivalent phase to obtain the second differential phase; The data processing module (26) is also used to calculate the difference between the first differential phase and the second differential phase to obtain the second differential phase; The data processing module (26) is also used to generate the dynamic strain measurement result based on the second differential phase.
3. The Φ-OTDR dynamic strain sensing system based on time-delayed dual pulses and dual wavelengths according to claim 2, characterized in that, The system also includes an arbitrary waveform generator (9), which is connected to the first acousto-optic modulator (4) and the second acousto-optic modulator (8); The arbitrary waveform generator (9) is used to adjust the output waveforms of the first acoustic-optic modulator (4) and the second acoustic-optic modulator (8); The arbitrary waveform generator (9) is also used to adjust the time delay of the output signals of the first acoustic-optic modulator (4) and the second acoustic-optic modulator (8) to the preset time delay.
4. The Φ-OTDR dynamic strain sensing system based on time-delayed dual pulses and dual wavelengths according to claim 2, characterized in that, The difference between the first wavelength and the second wavelength is less than a preset wavelength difference.
5. The Φ-OTDR dynamic strain sensing system based on time-delayed dual pulses and dual wavelengths according to claim 1, characterized in that, The first signal processing module includes a first balanced detector (17), a first bandpass filter (18), a second balanced detector (19), and a second bandpass filter (20). The sixth optical coupler (16) is also used to divide the first processed signal into a first processed sub-signal and a second processed sub-signal. The first balanced detector (17) is used to mix the first processing sub-signal to obtain the first beat frequency signal; The first bandpass filter (18) is used to filter the first beat frequency signal to obtain the first low frequency signal; The second balance detector (19) is used to mix the second processing sub-signal to obtain the second beat frequency signal; The second bandpass filter (20) is used to filter the first beat frequency signal to obtain the second low frequency signal.
6. The Φ-OTDR dynamic strain sensing system based on time-delayed dual pulses and dual wavelengths according to claim 1, characterized in that, The second signal processing module includes a third balanced detector (22), a third bandpass filter (23), a fourth balanced detector (24), and a fourth bandpass filter (25). The seventh optical coupler (21) is also used to divide the second processed signal into a third processed sub-signal and a fourth processed sub-signal; The third balance detector (22) is used to mix the third processing sub-signal to obtain the third beat frequency signal; The third bandpass filter (23) is used to filter the third beat frequency signal to obtain the third low frequency signal; The fourth balance detector (24) is used to mix the fourth processing sub-signal to obtain the fourth beat frequency signal; The fourth bandpass filter (25) is used to filter the fourth beat frequency signal to obtain the fourth low frequency signal.
7. The Φ-OTDR dynamic strain sensing system based on time-delayed dual pulses and dual wavelengths according to claim 1, characterized in that, The system also includes a first EDFA optical amplifier (11) and a second EDFA optical amplifier (14). The first EDFA optical amplifier (11) is disposed between the fifth optical coupler and the optical circulator (12); The second EDFA optical amplifier (14) is disposed between the optical circulator (12) and the FBG optical filter (15).
8. The Φ-OTDR dynamic strain sensing system based on time-delayed dual pulses and dual wavelengths according to claim 1, characterized in that, The modulation frequency of the first acousto-optic modulator (4) is 110MHz, and the modulation frequency of the second acousto-optic modulator (8) is 200MHz.
9. The Φ-OTDR dynamic strain sensing system based on time-delayed dual pulses and dual wavelengths according to claim 1, characterized in that, The difference in output power between the first DFB laser (1) and the second DFB laser (5) is less than a preset difference threshold.
10. A dynamic strain sensing method based on time-delayed dual-pulse and dual-wavelength Φ-OTDR, characterized in that, The method is performed by the Φ-OTDR dynamic strain sensing system based on time-delayed dual pulses and dual wavelengths as described in claim 1.