Dual-wavelength phase-shifting high-frequency signal extraction method and device based on VMD noise reduction

Abstract

The invention discloses a dual-wavelength phase-shifting high-frequency signal extraction method and device based on VMD noise reduction, and the method comprises the steps: enabling laser to be coupled through a first wavelength division multiplexer, enabling the laser to pass through a phase modulator, controlling piezoelectric ceramics through a signal generator to generate a high-frequency vibration signal, and enabling the high-frequency vibration signal to act on a signal arm, meanwhile, a phase modulator is controlled to generate a rectangular pulse binary phase modulation signal and a reference signal; the optical signals enter a second wavelength division multiplexer and enter corresponding photoelectric detectors according to different wavelengths, electric signals converted by the photoelectric detectors are received through an FPGA, and two groups of three-step phase shift signals with different wavelengths are obtained; based on the two groups of three-step phase shift signals, obtaining two groups of wrapped phases through a phase shift demodulation algorithm; vMD (variational mode decomposition) is carried out on the two groups of wrapped phases, Fourier transform is carried out on a plurality of mode quantities IMFs to solve total harmonic distortion and a signal-to-noise ratio, an undistorted demodulation standard is defined, and IMF components meeting corresponding conditions are used as finally demodulated high-frequency vibration signals.

Description

Technical Field

[0001] The present invention belongs to the technical field of optical fiber sensing, and particularly relates to a method and device for extracting dual-wavelength phase-shifted high-frequency signals based on VMD noise reduction. Background Technique

[0002] Optical fiber sensors use light waves as information carriers. With their ultra-high sensitivity, strong structural flexibility, and inherent electromagnetic interference resistance, they show unique advantages in the detection of multiple physical quantities such as vibration, displacement, and pressure. This technology has been widely applied in fields such as urban infrastructure prevention and control, monitoring, and geological disaster warning. Among many types of optical fiber sensors, interferometric optical fiber sensors based on the phase modulation principle have become a benchmark technology for precision measurement with nanoscale resolution accuracy and a large dynamic monitoring range. At the same time, the probe forms of this type of sensor are diverse, and with its unique network deployment ability, it performs particularly well in distributed sensing scenarios such as high-precision seismic wave detection and underwater acoustic monitoring systems.

[0003] For interferometric optical fiber sensors, phase detection technology is one of its key technologies. The rectangular pulse binary phase modulation method has the characteristics of simple optical path, low requirements for the hardware system, and fast calculation speed, and is an efficient method suitable for large experimental application systems. For phase detection, when the phase signal to be solved exceeds the range of [-π / 2, π / 2], a phase unwrapping algorithm is required to further process the result. The phase unwrapping algorithm requires that the absolute difference between adjacent phase values is less than π, otherwise unpacking distortion will occur. However, in some specific applications, such as high-sensitivity acceleration sensing systems, fiber optic sensing perimeter intrusion systems, etc., it is necessary to implement phase detection of high-frequency signals. At this time, the absolute difference between adjacent phase values of phase unwrapping will be greater than π, resulting in the inability to obtain the true phase information by unwrapping, affecting the final phase result. Currently, the use of the dual-wavelength method will cause amplification of phase noise, leading to phase demodulation distortion, thus posing higher requirements for the performance of the system laser. Therefore, effectively obtaining high-signal-to-noise-ratio high-frequency vibration signals without increasing hardware costs is a problem that needs to be solved when applying the dual-wavelength method to rectangular pulse binary phase modulation. Summary of the Invention

[0004] Object of the Invention: The object of the present invention is to provide a method and device for extracting dual-wavelength phase-shifted high-frequency signals based on VMD noise reduction.

[0005] Technical solution: The dual-wavelength phase-shifting high-frequency signal extraction method based on VMD noise reduction of the present invention constructs a dual-wavelength phase-shifting interference system using two lasers with different wavelengths, and demodulates the initial high-frequency vibration signal through the virtual synthetic wavelength constructed by the two different wavelengths. The upper computer software performs modal decomposition on the demodulated initial high-frequency vibration signal through the VMD algorithm, and selects the qualified mode as the final high-frequency vibration signal based on a 30 dB SINAD ratio as the judgment basis, specifically as follows:

[0006] A dual-wavelength phase-shifting high-frequency signal extraction method based on VMD noise reduction includes the following steps:

[0007] Step 1: Turn on the first laser and the second laser. After the laser is coupled through the first wavelength division multiplexer, it passes through the phase modulator, coupler and enters the signal arm, reference arm, and Faraday rotator. The signal generator controls the piezoelectric ceramic to generate a high-frequency vibration signal acting on the signal arm, and at the same time controls the phase modulator to generate a rectangular pulse binary phase modulation signal and a reference signal;

[0008] Step 2: The laser enters the signal arm, reference arm, and Faraday rotator through the coupler; after being reflected by the Faraday rotator, the optical signal carrying the high-frequency vibration information returns through the coupler and enters the second wavelength division multiplexer and then enters the corresponding photodetector according to different wavelengths. The FPGA receives the electrical signal converted by the photodetector, extracts the light intensity, and then transmits the high-frequency phase-shifting interference signal to the upper computer software to obtain two groups of three-step phase-shifting signals with different wavelengths. The three-step phase-shifting signals are positioned through the reference signal for subsequent signal extraction and demodulation;

[0009] Step 3: Based on the two groups of three-step phase-shifting signals, two groups of wrapped phases are obtained through the phase-shifting demodulation algorithm;

[0010] Step 4: Perform variational mode decomposition (VMD) on the two groups of wrapped phases to obtain multiple modal components IMFs;

[0011] Step 5: Perform Fourier transform on the multiple modal components IMFs to solve the total harmonic distortion and SINAD ratio, and define the distortionless demodulation standard. The IMF components that meet the corresponding conditions are the final demodulated high-frequency vibration signals.

[0012] Further, in step 1, the wavelength of the first laser is λ1, and the wavelength of the second laser is λ2, satisfying λ1 > λ2. The laser generates a rectangular binary phase modulation signal through the phase modulator, and the phase modulation amount generated by the phase modulator is [π / 2, 0]; at the same time, the phase modulator generates a reference pulse with the same frequency as the phase modulation signal for subsequent signal extraction and demodulation.

[0013] Further, in step 1, the generated rectangular pulse binary phase modulation signal is expressed as:

[0014]

[0015] where k is an integer, T is the modulation signal period, and τ p is the pulse width of the phase modulation signal, satisfying τ p ≤ T / 3.

[0016] Further, in step 2, the two groups of three-step phase shift signals are expressed as:

[0017]

[0018] where A a and A b and B a and B b are proportional to the input optical intensity, and B = κA, where κ ≤ 1 is the interference fringe visibility; θ a (t) and θ b (t) are the phase changes of the high-frequency vibration signal.

[0019] Further, step 3 is specifically: obtaining two groups of wrapped phases through a phase shift demodulation algorithm as follows:

[0020]

[0021] Subtracting the wrapped phases to obtain the virtual synthetic wavelength wrapped phase:

[0022] θ s (t) wrap = θ a (t) wrap - θ b (t) wrap (5)

[0023] Unwrapping θ s (t) wrap to obtain the phase θ s (t), and calculating the phase θ(t) corresponding to a single wavelength:

[0024] θ(t) = θ s (t)·λ1 / (λ1 - λ2) (6)

[0025] where the wavelength of the first laser is λ1 and the wavelength of the second laser is λ2.

[0026] Further, step 5 is specifically: performing a Fourier transform on multiple modal IMFs to solve for the total harmonic distortion and the signal-to-noise-and-distortion ratio, and defining a distortionless demodulation standard: the total harmonic distortion THD is not higher than 8%; at the same time, the signal-to-noise-and-distortion ratio SINAD reaches at least 30 dB, and the IMF component meeting the corresponding conditions is the final demodulated phase:

[0027] u k u(t) = A k (t) cos(φ k (t)) (7)

[0028] where A k (t) is the envelope value of the signal u k (t), and φ k (t) is the instantaneous phase. The modal quantity u k (t) that meets the conditions is used as the high-frequency vibration signal for the final demodulation.

[0029] The present invention also discloses a dual-wavelength phase-shifted high-frequency signal extraction device based on VMD noise reduction. The device includes a first laser, a second laser, a first wavelength division multiplexer, a phase modulator, a signal generator, a coupler, a piezoelectric ceramic, a signal arm, a reference arm, a Faraday rotator, a second wavelength division multiplexer, a photodetector, an FPGA, and upper computer software. The first laser and the second laser are respectively connected to the first wavelength division multiplexer and the phase modulator through optical fibers. The phase modulator is connected to the signal arm, the reference arm, and the Faraday rotator through a coupler. The second wavelength division multiplexer is connected to the coupler through an optical fiber. The second wavelength division multiplexer is connected to the photodetector through an optical fiber. The photodetector, the FPGA, and the upper computer software are connected.

[0030] The laser beams emitted by the first laser and the second laser are coupled through the first wavelength division multiplexer, enter the signal arm, the reference arm, and the Faraday rotator through the phase modulator and the coupler. The signal generator controls the piezoelectric ceramic to generate a high-frequency vibration signal acting on the signal arm. The signal generator controls the phase modulator to generate a rectangular pulse binary phase modulation signal and a reference signal, which enter the signal arm, the reference arm, and the Faraday rotator through the coupler. After being reflected by the Faraday rotator, the optical signal carrying the high-frequency vibration information returns through the coupler and enters the second wavelength division multiplexer. According to different wavelengths, it enters the corresponding photodetector for photoelectric conversion. The high-frequency phase-shifted interference signal is transmitted to the upper computer software by collecting the electrical signal through the FPGA. The upper computer software first unpacks according to the algorithm, and then performs modal decomposition through the VMD algorithm to realize the unpacking of the high-frequency signal and ensure that the demodulated signal is not distorted.

[0031] The present invention also discloses a computer device, including a memory, a processor, and a computer program stored on the memory. The processor executes the computer program to implement the steps of the method of the present invention.

[0032] The present invention also discloses a computer-readable storage medium, on which a computer program / instructions are stored. When the computer program / instructions are executed by the processor, the steps of the method of the present invention are implemented.

[0033] Beneficial effects: Compared with the prior art, the present invention has the following remarkable advantages: The present invention uses the VMD algorithm to perform variational mode decomposition, compares the demodulation result with the demodulation standard, adaptively adjusts the corresponding parameters in the VMD algorithm, and obtains a high-frequency vibration signal with low total harmonic distortion and high SINAD, while effectively reducing the requirements for the performance of the laser. The present invention reduces the noise appearing in the synthetic wavelength through data processing, and effectively improves the quality of the recovered signal. Brief Description of the Drawings

[0034] Figure 1 It is a schematic structural diagram of a method and device for extracting a dual-wavelength phase-shifted high-frequency signal based on VMD noise reduction according to the present invention.

[0035] Figure 2 It is a flow chart for extracting a dual-wavelength phase-shifted high-frequency signal based on VMD noise reduction according to the present invention.

[0036] Figure 3 It is a time-domain signal diagram returned by a single wavelength in the method for extracting a dual-wavelength phase-shifted high-frequency signal based on VMD noise reduction according to the present invention.

[0037] Figure 4 It is the interference light intensity signals I a1 , I a2 , I a3 and I b1 , I b2 , I b3 .

[0038] Figure 5 It is the unwrapped phases θ a (t) and θ b (t) corresponding to two groups after passing through the second wavelength division multiplexer in the method for extracting a dual-wavelength phase-shifted high-frequency signal based on VMD noise reduction according to the present invention.

[0039] Figure 6 It is the single-wavelength phase signal θ(t) recovered from the virtual synthetic wavelength obtained in the signal of the method for extracting a dual-wavelength phase-shifted high-frequency signal based on VMD noise reduction according to the present invention.

[0040] Figure 7 It is the phase signal decomposed by the VMD algorithm in the signal of the method for extracting a dual-wavelength phase-shifted high-frequency signal based on VMD noise reduction according to the present invention.

[0041] Figure 8 It is the spectrum diagrams of θ a (t), θ(t) and the phase signal decomposed by the VMD algorithm in the signal of the method for extracting a dual-wavelength phase-shifted high-frequency signal based on VMD noise reduction according to the present invention. Detailed implementation mode

[0042] The technical solution of the present invention will be further described below in conjunction with the accompanying drawings.

[0043] Combined with Figure 1 , a dual-wavelength phase-shifting high-frequency signal extraction method and device based on VMD noise reduction, the method steps are as follows:

[0044] Step 1: Turn on the first laser and the second laser. The laser beams emitted by the first laser and the second laser are coupled through the first wavelength division multiplexer, and then enter the signal arm, reference arm, and Faraday rotator through the phase modulator and coupler. The signal generator controls the piezoelectric ceramic to generate a high-frequency vibration signal acting on the signal arm, and the signal generator controls the phase modulator to generate a rectangular pulse binary phase modulation signal and a reference signal, which can be expressed as:

[0045]

[0046] Step 2: Enter the signal arm, reference arm, and Faraday rotator through the coupler. After being reflected by the Faraday rotator, the optical signal carrying the high-frequency vibration information returns through the coupler and enters the second wavelength division multiplexer. According to different wavelengths, it enters the corresponding photodetector. The FPGA receives the electrical signal converted by the photodetector, extracts the light intensity, and then transmits the high-frequency phase-shifting interference signal to the host computer software. The host computer software obtains two groups of three-step phase-shifted signals with different wavelengths. At this time, I can be decomposed into:

[0047]

[0048]

[0049] Among them, A a , A b and B a , B b are proportional to the input light intensity, and B = κA, where κ ≤ 1 is the interference fringe visibility. θ a (t) and θ b (t) are the phase changes of the high-frequency vibration signal.

[0050] Step 3: The host computer software (14) obtains the two groups of wrapped phases through the phase-shifting demodulation algorithm as follows:

[0051]

[0052] Subtract the wrapped phases and perform unwrapping to obtain the virtual synthetic wavelength phase:

[0053] θ s (t) wrap = θ a (t) wrap - θ b(t) wrap (5)

[0054] For θ s (t) wrap Unwrap to obtain the phase θ s (t), and calculate the phase θ(t) corresponding to a single wavelength:

[0055] θ(t) = θ s (t)·λ1 / (λ1 - λ2) (6)

[0056] Step 4: The host computer software performs variational mode decomposition (VMD) on θ(t) to obtain multiple modal quantities. Fourier transform the multiple modal quantities (IMFs) to solve for the total harmonic distortion and the signal-to-noise ratio, and define the distortion-free demodulation criteria: (1) The total harmonic distortion (THD) is not higher than 8%. (2) The signal-to-noise ratio (SINAD) reaches at least 30 dB. The IMF component that meets the corresponding conditions is the final demodulated phase:

[0057] u k (t) = A k (t)cos(φ k (t)) (7)

[0058] where A k (t) is the envelope value of the signal u k (t), and φ k (t) is the instantaneous phase. The modal quantity u k (t) that meets the conditions is used as the high-frequency vibration signal for the final demodulation.

[0059] Example 1

[0060] In the example, the wavelength λ1 of the first laser is 1560 nm, and the wavelength λ2 of the second laser is 1540 nm. A piezoelectric ceramic is placed at the 5-meter position of the sensing optical fiber, and a high-frequency vibration signal is applied. The corresponding device is as Figure 1 shown. At the same time, the corresponding method processing flow of the device is as Figure 2 shown.

[0061] The FPGA receives the time-domain signals returned at different wavelengths as Figure 3 shown. The signal generator controls the piezoelectric ceramic to generate a high-frequency vibration signal. The signal vibration frequency is set to 3 kHz, and the voltage is ±1.5 Vpp. The host computer software extracts two groups of three-step phase-shifted signals I a1 , I a2 , I a3 and I b1 , I b2 , I b3 with different wavelengths, as Figure 4As shown. After being separated by wavelength through the second wavelength division multiplexer, the two wavelengths are unpacked to obtain θ a (t) and θ b (t), as Figure 5 shown. The host computer software obtains the dual-wavelength phase-shifted high-frequency interference signal through the FPGA for demodulation, subtracts the two groups of wrapped phases, obtains the wrapped phase of the virtual synthetic wavelength, and then calculates the phase corresponding to a single wavelength through calculation, as Figure 6 shown. Through calculation, its total harmonic distortion is 10.14% and the signal-to-noise and distortion ratio is 9.52 dB, and the unpacking result has serious distortion. The host computer software performs variational mode decomposition (VMD) on θ(t). In the VMD algorithm, the initial inertia factor is set to 1500, the soft constraint and the DC component are 0, the number of modes is set to 6, and the convergence accuracy is 1e-06 to obtain 6 mode quantities. The Fourier transform is performed on the 6 mode quantities (IMFs) to solve the total harmonic distortion and the signal-to-noise and distortion ratio, and the defined demodulation standard is introduced for threshold judgment. If the demodulation result does not meet the demodulation standard, the VMD algorithm adaptively adjusts the parameters until it meets the demodulation standard to obtain u k (t) as Figure 7 shown. By performing the Fourier transform on θ a (t), θ(t) and the decomposed IMFs, as Figure 8 shown. After inspection, the VMD adaptive algorithm can successfully demodulate the applied signal, which is consistent with the applied conditions. Finally, the total harmonic distortion is 3.92% and the SINAD is 33.53 dB

[0062] It can be seen from this that through the above method, the extraction of dual-wavelength phase-shifted high-frequency signals with VMD noise reduction is realized. Compared with the prior art, the significant advantage of the present invention is that it uses the VMD algorithm to perform variational mode decomposition, compares the demodulation result with the demodulation standard, adaptively adjusts the corresponding parameters in the VMD algorithm, obtains high-frequency vibration signals with low total harmonic distortion and high signal-to-noise and distortion ratio, and at the same time effectively reduces the requirements for the performance of the laser.

Claims

1. A dual-wavelength phase-shifting high-frequency signal extraction method based on VMD noise reduction, characterized in that It includes the following steps: Step 1: Turn on the first laser and the second laser. After the laser is coupled through the first wavelength division multiplexer, it passes through a phase modulator, a coupler and enters the signal arm, the reference arm, and the Faraday rotator. The signal generator controls the piezoelectric ceramic to generate a high-frequency vibration signal acting on the signal arm, and at the same time controls the phase modulator to generate a rectangular pulse binary phase modulation signal and a reference signal; Step 2: The laser enters the signal arm, the reference arm, and the Faraday rotator through the coupler; after being reflected by the Faraday rotator, the optical signal carrying the high-frequency vibration information returns through the coupler and enters the second wavelength division multiplexer and then enters the corresponding photodetector according to different wavelengths. The FPGA receives the electrical signal converted by the photodetector, extracts the light intensity, and then transmits the high-frequency phase-shifted interference signal to the host computer software to obtain two groups of three-step phase-shifted signals with different wavelengths. The three-step phase-shifted signals are positioned by the reference signal for subsequent signal extraction and demodulation; Step 3: Based on the two groups of three-step phase-shifted signals, two groups of wrapped phases are obtained through a phase-shift demodulation algorithm; Step 4: Perform variational mode decomposition (VMD) on the two groups of wrapped phases to obtain multiple modal components IMFs; Step 5: Perform Fourier transform on the multiple modal components IMFs to solve the total harmonic distortion and the signal-to-noise and distortion ratio (SINAD), and define a distortion-free demodulation standard. The IMF component that meets the corresponding conditions is the finally demodulated high-frequency vibration signal.

2. The dual-wavelength phase-shifted high-frequency signal extraction method based on VMD noise reduction according to claim 1, wherein In Step 1, the wavelength of the first laser is λ1, and the wavelength of the second laser is λ2, satisfying λ1 > λ2. The laser generates a rectangular binary phase modulation signal through the phase modulator, and the phase modulation amount generated by the phase modulator is [π / 2, 0]; at the same time, the phase modulator generates a reference pulse with the same frequency as the phase modulation signal for subsequent signal extraction and demodulation.

3. A dual-wavelength phase-shifted high-frequency signal extraction method based on VMD noise reduction according to claim 1, characterized in that In Step 1, the rectangular pulse binary phase modulation signal is generated and expressed as: where k is an integer, T is the modulation signal period, and τ p is the pulse width of the phase modulation signal, satisfying τ p ≤ T / 3.

4. A dual-wavelength phase-shifted high-frequency signal extraction method based on VMD noise reduction according to claim 1, characterized in that, In Step 2, the two groups of three-step phase-shifted signals are expressed as: Among which A a 、A b and B a 、B b are proportional to the input light intensity, and B = κA, where κ ≤ 1 is the visibility of the interference fringes; θ a (t) and θ b (t) are the phase changes of the high-frequency vibration signal.

5. A dual-wavelength phase-shifted high-frequency signal extraction method based on VMD noise reduction according to claim 4, characterized in that Step 3 is specifically: Two groups of wrapped phases are obtained through a phase-shift demodulation algorithm as follows: The wrapped phases are subtracted to obtain the virtual synthetic wavelength wrapped phase: θ s (t) wrap = θ a (t) wrap - θ b (t) wrap (5) For θ s (t) wrap unwrap it to obtain the phase θ s (t), and calculate the phase θ(t) corresponding to a single wavelength: θ(t) = θ s (t)·λ1 / (λ1 - λ2) (6) Among them, the wavelength of the first laser is λ1, and the wavelength of the second laser is λ2.

6. A dual-wavelength phase-shifted high-frequency signal extraction method based on VMD noise reduction according to claim 1, characterized in that Step 5 is specifically: Perform Fourier transform on the multiple modal components IMFs to solve the total harmonic distortion and the signal-to-noise and distortion ratio (SINAD), and define a distortion-free demodulation standard: the total harmonic distortion (THD) is not higher than 8%; at the same time, the signal-to-noise and distortion ratio (SINAD) reaches at least 30 dB. The IMF component that meets the corresponding conditions is the finally demodulated phase: u k u(t) = A k u(t) cos(φ k u(t)) (7) Among which A k (t) is the envelope value of the signal u k (t), and φ k (t) is the instantaneous phase. The modal quantity u k (t) that meets the conditions is used as the high-frequency vibration signal for the final demodulation.

7. A dual-wavelength phase-shifting high-frequency signal extraction transposition based on VMD noise reduction is used to implement the method described in claim 1, characterized in that, It includes: The first laser (1), the second laser (2), the first wavelength division multiplexer (3), the phase modulator (4), the signal generator (5), the coupler (6), the piezoelectric ceramic (7), the signal arm (8), the reference arm (9), the Faraday rotator (10), the second wavelength division multiplexer (11), the photodetector (12), the FPGA (13), the host computer software (14); wherein the first laser (1) and the second laser (2) are respectively connected to the first wavelength division multiplexer (3) and the phase modulator (4) through optical fibers, the phase modulator (4) is connected to the signal arm (8), the reference arm (9), and the Faraday rotator (10) through the coupler (6), the second wavelength division multiplexer (11) is connected to the coupler (6) through an optical fiber, the second wavelength division multiplexer (11) is connected to the photodetector (12) through an optical fiber, and the photodetector (12), the FPGA (13) are connected to the host computer software (14).

8. The transposition for extracting a dual-wavelength phase-shifted high-frequency signal based on VMD noise reduction according to claim 7, wherein, The laser beams emitted by the first laser (1) and the second laser (2) are coupled through the first wavelength division multiplexer (3), enter the signal arm (8), the reference arm (9), and the Faraday rotator (10) through the phase modulator (4) and the coupler (6). The signal generator (5) controls the piezoelectric ceramic (7) to generate a high-frequency vibration signal acting on the signal arm (8). The signal generator (5) controls the phase modulator (4) to generate a rectangular pulse binary phase modulation signal and a reference signal, which enter the signal arm (8), the reference arm (9), and the Faraday rotator (10) through the coupler (6). After being reflected by the Faraday rotator, the optical signal carrying the high-frequency vibration information returns through the coupler (6) and enters the second wavelength division multiplexer (7). According to different wavelengths, it enters the corresponding photodetector (12) to achieve photoelectric conversion. The FPGA (13) transmits the high-frequency phase-shifted interference signal to the host computer software (14) by collecting the electrical signal. The host computer software (14) performs threshold judgment, and the VMD algorithm adaptively adjusts the corresponding parameters.

9. A computer device, comprising a memory, a processor, and a computer program stored on the memory, characterized in that, The processor executes the computer program to implement the steps of the method recited in claim 1.

10. A computer-readable storage medium having computer programs / instructions stored thereon, characterized in that, When the computer program / instructions are executed by the processor, the steps of the method recited in claim 1 are implemented.

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