Distributed optical fiber vibration monitoring device based on logarithm transformation and optical fiber sensing along-line vibration identification and positioning method

Abstract

The invention discloses a distributed optical fiber vibration monitoring device based on logarithm transformation. Comprising a narrow linewidth laser, an acousto-optic modulator, an optical pulse amplifier, an optical fiber circulator, a verification optical fiber unit, a balanced photoelectric detector, a band-pass filter, a low-noise amplifier, a logarithmic detector, a data acquisition and processing module, an industrial personal computer, a first optical fiber coupler, a second optical fiber coupler and an optical fiber interface. A radio frequency signal is converted into a voltage signal in a logarithmic detection mode, so that the requirements of a subsequent data acquisition and processing module on a sampling rate and high-speed data processing are reduced, and a vibration event along a sensing optical fiber is identified and positioned through gradual difference operation of a time domain logarithmic signal and a normalized threshold calibration algorithm. The distributed optical fiber vibration monitoring device provided by the invention is simple in structure, and the performance requirements of a device based on a traditional scheme on system hardware such as an acousto-optic modulator and a data acquisition and processing module can be greatly reduced.

Description

Technical Field

[0001] The present invention relates to the field of optical fiber sensing technology, and in particular to a distributed optical fiber vibration monitoring device based on logarithmic transformation and a method for identifying and locating vibration along an optical fiber sensing line. Background Art

[0002] Distributed fiber-optic vibration monitoring technology is a real-time dynamic monitoring technology based on fiber-optic sensing. It transforms the entire fiber into a continuously distributed vibration sensor by combining optical time-domain reflectometry with Rayleigh scattered light within the fiber. Its core principle is that external vibrations acting on the fiber alter its refractive index or strain distribution, causing changes in the phase, frequency, or intensity of the backscattered light. By demodulating these changes, vibration events can be located and identified. This technology offers advantages such as electromagnetic interference resistance, corrosion resistance, long monitoring distances (up to tens of kilometers), and high spatial resolution (meter-level). It is widely used in pipeline safety, perimeter security, rail transit, and geological disaster early warning. Distributed fiber-optic vibration monitoring technology detects Rayleigh scattered light using two methods: direct detection and coherent detection. Direct detection has lower sensitivity and a shorter sensing range. While coherent detection offers higher sensitivity, signal extraction and vibration signal analysis are more complex. The coherent detection type of distributed fiber optic vibration device solution uses an acousto-optic modulator to obtain light pulses and shift the optical frequency, so that after optical coherence, a higher-frequency RF signal is output from the balanced photodetector. The frequency of the RF signal corresponds to the frequency shift of the acousto-optic modulator. For example, the more commonly used ones are 40MHz, 80MHz, and 200MHz. The power of the RF signal is subsequently extracted through digital signal processing. This requires the system hardware to be equipped with a high-speed data acquisition card and high-computing power computing resources such as FPGA modules. This undoubtedly increases the complexity of system development and inevitably increases system costs, which is not conducive to technology promotion.

[0003] To address these issues, the invention patent "Fusion-type Fiber-optic Distributed Multi-point Disturbance Detection and Demodulation System and Fault Location Method" (Publication No.: CN119197738 A) employs two light sources, a unidirectional Mach-Zehnder fiber interferometer, a phase-sensitive optical time-domain reflectometer, and a data acquisition and processing module. The phase-sensitive optical time-domain reflectometer acquires the optical signal caused by vibration events along the sensing fiber. The Mach-Zehnder interferometer, combined with a carrier phase demodulation scheme, then demodulates the signal to identify and locate the vibration event. Although this system utilizes a Mach-Zehnder interferometer optical path structure, it still relies on direct detection to extract signal power, resulting in a complex structure and low system sensitivity.

[0004] The invention patent "Power Optical Fiber Communication Line Fault Monitoring Device" (authorization announcement number: CN106533547B) discloses a power optical fiber communication line fault monitoring device, which uses optical time domain reflectometry technology to extract the distributed Rayleigh scattering optical signal of the power optical fiber communication line, adopts a coherent detection method to improve the detection sensitivity, uses logarithmic detection and averaging methods to improve the extraction efficiency of the detection signal, and uses a laser frequency hopping scheme based on pulse counting to reduce the fading noise on the optical time domain reflectance curve. The optical polarization scrambler and laser frequency hopping scheme in its system structure eliminate the possible polarization noise and Rayleigh fading noise, and finally make the optical time domain reflectance curve very smooth to identify the fault (attenuation) events along the sensing optical fiber. This scheme eliminates the power fluctuation problem caused by the phase change of the Rayleigh scattering signal (makes the optical time domain reflectance curve smoother) in principle and cannot be used to measure the vibration events along the sensing optical fiber. Summary of the Invention

[0005] Object of the Invention: To overcome the deficiencies of the background art, the first object of the present invention is to disclose a distributed optical fiber vibration monitoring device based on logarithmic transformation; the device uses a coherent detection method to improve the sensitivity of the device, uses a logarithmic detection method to extract the power information of the radio frequency signal and restores the Rayleigh scattering signal power through logarithmic transformation, and combines the fluctuation ratio of the signal power in adjacent two measurement periods at the sensing position to establish a normalized vibration time discrimination threshold, so as to ensure that the device has high sensitivity and measurement accuracy; The second object is to disclose a method for identifying and positioning the vibration along the optical fiber sensing based on the above-mentioned distributed optical fiber vibration monitoring device based on logarithmic transformation.

[0006] Technical Solution: The distributed optical fiber vibration monitoring device based on logarithmic transformation disclosed by the present invention includes: a narrow linewidth laser, an acousto-optic modulator, an optical pulse amplifier, an optical fiber circulator, a calibration optical fiber unit, a balanced photodetector, a band-pass filter, a low-noise amplifier, a logarithmic detector, a data acquisition and processing module, an industrial control computer, a first optical fiber coupler, a second optical fiber coupler, and an optical fiber interface; The narrow linewidth laser outputs continuous light, which is divided into two paths by the first optical fiber coupler. One path is connected to the acousto-optic modulator and modulated into optical pulses for output. The optical pulses enter the optical pulse amplifier to increase the peak power, and then are connected to port 1 of the optical fiber circulator and enter the calibration optical fiber unit from port 2 of the optical fiber circulator, and then are injected into the sensing optical fiber through the optical fiber interface; The data acquisition and processing module issues an electrical pulse to drive the acousto-optic modulator to output optical pulses; The backward Rayleigh scattering light generated by the optical pulses transmitted along the sensing optical fiber enters one input end of the second optical fiber coupler in sequence through the optical fiber interface, the calibration optical fiber unit, port 2 of the optical fiber circulator, and port 3 of the optical fiber circulator; The other path of light separated by the first optical fiber coupler directly enters the other input end of the second optical fiber coupler and is used as local oscillator light; The backward Rayleigh scattered light entering the second optical fiber coupler converges with the local oscillator light to produce an optical coherence effect, and then enters the balanced photodetector. The balanced photodetector converts the optical coherence envelope signal into a radio frequency signal; After the radio frequency signal is filtered and denoised by the band-pass filter and its power is boosted by the low-noise amplifier, the logarithmic detector converts the radio frequency signal into a DC voltage signal; The data acquisition and processing module acquires the DC voltage signal, obtains the optical time domain reflectance signal data, and identifies and locates the vibration events along the sensing optical fiber through a vibration signal extraction algorithm, and transmits the data to the industrial control computer.

[0007] Further, the calibration optical fiber unit is composed of an optical fiber with a length of 50 to 100 meters and a packaging box. The packaging box fixes the optical fiber inside it using a shock-proof gasket.

[0008] Further, the line width of the narrow line width laser is less than 50 kHz.

[0009] Further, the optical pulse amplifier uses an erbium-doped fiber amplifier.

[0010] Further, the optical pulse amplifier uses a semiconductor optical amplifier.

[0011] Further, the second optical fiber coupler selects an X-type optical fiber coupler with a splitting ratio of 50:50.

[0012] Further, the logarithmic detector uses AD8310 of ANALOG DEVICES.

[0013] Correspondingly, a method for identifying and locating vibrations along an optical fiber sensor of the distributed optical fiber vibration monitoring device based on the above logarithmic transformation is disclosed. The data acquisition and processing module uses a vibration signal extraction algorithm to identify and locate vibration events along the sensing optical fiber, including the following steps: S1. The data acquisition and processing module acquires the optical time domain reflectance signal voltage data corresponding to 100 consecutive measurement periods; S2. Subtract the optical time domain reflectance signal voltage data of the latter measurement period from that of the previous measurement period in sequence, then divide by 10 times the conversion coefficient of the radio frequency logarithm power and voltage of the logarithmic detector, and finally take the exponent of 10; thereby normalizing the vibration signal power to obtain the optical time domain reflectance signal fluctuation amplitude ratio corresponding to each position along the optical fiber; take the maximum value of the optical time domain reflectance signal fluctuation amplitude ratio corresponding to each position along the optical fiber; S3. Set the vibration event judgment threshold. When the fluctuation amplitude of the optical time domain reflectance (OTDR) signal greater than the threshold is in the fiber area corresponding to the calibration fiber unit compared to the position corresponding to the maximum value, it is determined as a system fault. The system starts self-check, and the industrial control computer records the operating parameters of the narrow linewidth laser and the optical pulse amplifier. When the operating parameters of the narrow linewidth laser or the optical pulse amplifier are abnormal, a system fault is reported. When the position corresponding to the maximum value of the fluctuation amplitude ratio of the OTDR signal greater than the threshold is in the area corresponding to the sensing fiber, mark the corresponding position as the vibration event position. S4. Repeat the operations of S1 to S3.

[0014] Further, the vibration positioning judgment threshold is selected as 0.3.

[0015] Beneficial effects: The distributed fiber vibration monitoring device based on logarithmic transformation of the present invention uses a coherent detection method to improve the sensitivity of capturing Rayleigh scattering optical signals, uses a logarithmic detection method to reduce the requirements for high sampling rate and high-speed data processing computing power in traditional digital signal processing solutions, and specifically uses a logarithmic transformation method to finally establish a normalized signal fluctuation threshold to distinguish vibration events along the sensing fiber. Compared with traditional or existing distributed fiber vibration monitoring technical solutions, its signal extraction scheme is simpler and more sensitive. The sampling rate for data acquisition is not affected by the frequency shift of the acousto-optic modulator and the coherent intermediate frequency, and only needs to meet twice the frequency corresponding to the optical pulse width. Moreover, the signal fluctuation amplitude ratio is normalized to the threshold, which is more general for the discrimination of vibration events. Brief Description of the Drawings

[0016] Figure 1 It is a schematic diagram of the device structure of the present invention; Figure 2 It is a schematic diagram of the calibration fiber unit; Figure 3 It is a schematic diagram of the OTDR voltage data corresponding to 100 consecutive measurement periods; Figure 4 It is a schematic diagram of the process of obtaining the fluctuation amplitude ratio by transforming the OTDR voltage data corresponding to two adjacent measurement periods; Figure 5 For Figure 4 It is a schematic diagram of taking the maximum value according to the fiber position of the two-dimensional numerical matrix corresponding to the fluctuation amplitude ratio of; Figure 6 It is a schematic diagram of system fault discrimination; Figure 7 It is a schematic diagram of vibration event discrimination and positioning. Detailed Embodiments

[0017] The technical solution of the present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0018] As Figure 1 shown, the distributed optical fiber vibration monitoring device based on logarithmic transformation includes: a narrow linewidth laser 101, an acousto-optic modulator 102, an optical pulse amplifier 103, an optical fiber circulator 104, a calibration optical fiber unit 105, a balanced photodetector 106, a bandpass filter 107, a low-noise amplifier 108, a logarithmic detector 109, a data acquisition and processing module 110, an industrial control computer 111, a first optical fiber coupler 201, a second optical fiber coupler 202, and an optical fiber interface 301; The narrow linewidth laser 101 outputs continuous light, which is split into two paths by the first optical fiber coupler 201. One of the paths is connected to the acousto-optic modulator 102 and modulated into optical pulses for output. The optical pulses enter the optical pulse amplifier 103 to increase the peak power, and then are connected to port 1 of the optical fiber circulator 104 and enter the calibration optical fiber unit 105 from port 2 of the optical fiber circulator 104, and then are injected into the sensing optical fiber through the optical fiber interface 301.

[0019] The data acquisition and processing module 110 issues electrical pulses to drive the acousto-optic modulator 102 to output optical pulses.

[0020] The backward Rayleigh scattered light generated by the optical pulses propagating along the sensing optical fiber sequentially enters one input end of the second optical fiber coupler 202 through the optical fiber interface 301, the calibration optical fiber unit 105, port 2 of the optical fiber circulator 104, and port 3 of the optical fiber circulator 104.

[0021] The other path separated by the first optical fiber coupler 201 directly enters the other input end of the second optical fiber coupler 202 and is used as the local oscillator light.

[0022] The backward Rayleigh scattered light entering the second optical fiber coupler 202 converges with the local oscillator light to produce an optical coherence effect, and then enters the balanced photodetector 106. The balanced photodetector 106 converts the optical coherence envelope signal into a radio frequency signal.

[0023] After the radio frequency signal is filtered and noise-reduced by the bandpass filter 107 and its power is increased by the low-noise amplifier 108, the logarithmic detector 109 converts the radio frequency signal into a DC voltage signal.

[0024] The data acquisition and processing module 110 acquires the DC voltage signal, obtains the optical time domain reflectance signal data, identifies and locates the vibration events along the sensing optical fiber through the vibration signal extraction algorithm, and transmits the data to the industrial control computer 111.

[0025] AsFigure 2 As shown, the calibration optical fiber unit 105 is composed of an optical fiber with a length of 50 meters to 100 meters and a packaging box. The packaging box uses shock pads to fix the optical fiber inside it.

[0026] Among them, the narrow linewidth laser 101 is a distributed Bragg emission laser with a linewidth less than 50 kHz.

[0027] The optical pulse amplifier 103 uses an erbium-doped fiber amplifier or a semiconductor optical amplifier.

[0028] The second optical fiber coupler 202 selects an X-type optical fiber coupler with a splitting ratio of 50:50.

[0029] The logarithmic detector 109 uses the AD8310 of ANALOG DEVICES.

[0030] The data acquisition and processing module 109 uses a vibration signal extraction algorithm to identify and locate vibration events along the sensing optical fiber, including the following steps: S1. The data acquisition and processing module 109 acquires the optical time domain reflectometry signal voltage data corresponding to 100 consecutive measurement periods, as Figure 3 shown; S2. Subtract the optical time domain reflectometry signal voltage data of the latter measurement period from that of the previous measurement period in turn, then divide by 10 times the conversion coefficient K of the radio frequency logarithmic power and voltage of the logarithmic detector, and finally take the exponent of 10; thereby normalizing the vibration signal power to obtain the optical time domain reflectometry signal fluctuation amplitude ratio corresponding to each position along the optical fiber, that is, a new two-dimensional numerical matrix, as Figure 4 shown; take the maximum value of the optical time domain reflectometry signal fluctuation amplitude ratio corresponding to each position along the optical fiber, as Figure 5 shown; S3. Set the vibration event judgment threshold to 0.3. When the position corresponding to the maximum value of the optical time domain reflectometry signal fluctuation amplitude ratio greater than the threshold is in the optical fiber area corresponding to the calibration optical fiber unit, as Figure 6 shown, it is judged as a system fault, the system starts self-checking, and the working parameters of the narrow linewidth laser and the optical pulse amplifier are recorded by the industrial control computer; when the working parameters of the narrow linewidth laser 101 or the optical pulse amplifier 103 are abnormal, a system fault is reported; When the position corresponding to the maximum value of the optical time domain reflectometry signal fluctuation amplitude ratio greater than the threshold is in the area corresponding to the sensing optical fiber, mark the corresponding position as the vibration event position, as Figure 7 shown; S4. Repeat the operations of S1 to S3.

Claims

1. A distributed optical fiber vibration monitoring device based on logarithmic transformation, characterized in that: Including: A narrow linewidth laser (101), an acousto-optic modulator (102), an optical pulse amplifier (103), an optical fiber circulator (104), a calibration optical fiber unit (105), a balanced photodetector (106), a bandpass filter (107), a low-noise amplifier (108), a logarithmic detector (109), a data acquisition and processing module (110), an industrial control computer (111), a first optical fiber coupler (201), a second optical fiber coupler (202), and an optical fiber interface (301); The narrow linewidth laser (101) outputs continuous light, which is split into two paths by the first optical fiber coupler (201). One of the paths is connected to the acousto-optic modulator (102) and modulated into optical pulses for output. The optical pulses enter the optical pulse amplifier (103) to increase the peak power, then are connected to port 1 of the optical fiber circulator (104), and enter the calibration optical fiber unit (105) from port 2 of the optical fiber circulator (104), and are then injected into the sensing optical fiber through the optical fiber interface (301); The data acquisition and processing module (110) issues an electrical pulse to drive the acousto-optic modulator (102) to output optical pulses; The backward Rayleigh scattered light generated by the optical pulses propagating along the sensing optical fiber sequentially passes through the optical fiber interface (301), the calibration optical fiber unit (105), port 2 of the optical fiber circulator (104), and port 3 of the optical fiber circulator (104) and enters one input end of the second optical fiber coupler (202); The other path separated by the first optical fiber coupler (201) directly enters the other input end of the second optical fiber coupler (202) and is used as local oscillator light; The backward Rayleigh scattered light entering the second optical fiber coupler (202) converges with the local oscillator light to produce an optical coherence effect, and then enters the balanced photodetector (106). The balanced photodetector (106) converts the optical coherence envelope signal into a radio frequency signal; The radio frequency signal is filtered and noise-reduced by the bandpass filter (107), and the power is increased by the low-noise amplifier (108), and then the logarithmic detector (109) converts the radio frequency signal into a direct current voltage signal; The data acquisition and processing module (110) acquires the direct current voltage signal, obtains the optical time domain reflectometry signal data, and identifies and locates the vibration events along the sensing optical fiber through a vibration signal extraction algorithm, and transmits the data to the industrial control computer (111).

2. The distributed optical fiber vibration monitoring device based on logarithmic transformation according to claim 1, characterized in that: The calibration optical fiber unit (105) consists of a section of optical fiber with a length of 50 to 100 meters and a packaging box. The packaging box uses shock-proof gaskets to fix the optical fiber inside.

3. The distributed optical fiber vibration monitoring device based on logarithmic transformation according to claim 1, characterized in that: The linewidth of the narrow linewidth laser (101) is less than 50 kHz.

4. The distributed optical fiber vibration monitoring device based on logarithmic transformation according to claim 1, characterized in that: The optical pulse amplifier (103) uses an erbium-doped optical fiber amplifier.

5. The distributed optical fiber vibration monitoring device based on logarithmic transformation according to claim 1, characterized in that: The optical pulse amplifier (103) uses a semiconductor optical amplifier.

6. The distributed optical fiber vibration monitoring device based on logarithmic transformation according to claim 1, wherein: The second optical fiber coupler (202) selects an X-type optical fiber coupler with a splitting ratio of 50:

50.

7. The distributed optical fiber vibration monitoring device based on logarithmic transformation according to claim 1, characterized in that: The logarithmic detector (109) uses the AD8310 of ANALOG DEVICES.

8. The fiber-optic sensing along-line vibration identification and positioning method of the distributed fiber-optic vibration monitoring device based on logarithmic transformation according to claim 1, characterized in that: The data acquisition and processing module (109) uses a vibration signal extraction algorithm to identify and locate vibration events along the sensing optical fiber, including the following steps: S1. The data acquisition and processing module (109) acquires the optical time domain reflectometry (OTDR) signal voltage data corresponding to 100 consecutive measurement cycles; S2. Subtract the OTDR signal voltage data of the subsequent measurement cycle from that of the previous measurement cycle in sequence, then divide the result by 10 times the conversion coefficient of the radio frequency logarithmic power and voltage of the logarithmic detector (109), and finally take the exponent of 10; thereby normalizing the vibration signal power to obtain the OTDR signal fluctuation amplitude ratio corresponding to each position along the optical fiber; take the maximum value of the OTDR signal fluctuation amplitude ratio corresponding to each position along the optical fiber; S3. Set a vibration event judgment threshold. When the position corresponding to the maximum value of the OTDR signal fluctuation amplitude ratio greater than the threshold is in the optical fiber area corresponding to the calibration optical fiber unit (105), it is judged as a system fault, the system starts self-check, and the industrial control computer (111) records the operating parameters of the narrow linewidth laser (101) and the optical pulse amplifier (103); when the operating parameters of the narrow linewidth laser (101) or the optical pulse amplifier (103) are abnormal, report a system fault; When the position corresponding to the maximum value of the OTDR signal fluctuation amplitude ratio greater than the threshold is in the area corresponding to the sensing optical fiber, mark the corresponding position as the vibration event position; S4. Repeat the operations of S1 to S3.

9. The optical fiber sensing along-line vibration identification and positioning method according to claim 8, characterized in that: The vibration positioning judgment threshold is selected as 0.3.

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