Vibration positioning method and vibration positioning device

Abstract

The present invention provides a vibration positioning method and a vibration positioning device, belonging to the field of optical fiber sensing technology. The vibration positioning method includes: in response to a vibration event acting on an optical fiber, obtaining a first phase signal and a second phase signal; dividing the first phase signal and the second phase signal in the time domain according to a preset division rule to obtain n first signal segments and n second signal segments; determining the i-th segment delay difference between the i-th first signal segment and the i-th second signal segment; determining the time delay difference between the first phase signal and the second phase signal based on the n segment delay differences; and determining the position of the vibration event acting on the optical fiber based on the time delay difference between the first phase signal and the second phase signal. The vibration positioning method of the present invention can be applied in long-distance detection scenarios.

Description

Technical Field

[0001] The present invention relates to the field of optical fiber sensing technology, and in particular to an optical fiber-based vibration positioning method and a vibration positioning device. Background Art

[0002] With the continuous advancement of science and technology, the scale of infrastructure continues to expand. Developed since the end of the last century, vibration safety monitoring using fiber optic sensing technology has gradually become a key technology for ensuring the safe construction of infrastructure projects. Distributed fiber optic vibration sensing technology uses light waves as a carrier and optical fiber as a medium to measure external vibration events. Due to its advantages such as high sensitivity, long-distance detection, full regional coverage, and ease of large-scale intelligent network monitoring, it has been applied in pipeline, security, oil and gas, and large-scale building health monitoring.

[0003] The basic principle of distributed fiber-optic vibration sensing technology is that continuous laser light is incident on an optical fiber. When external vibrations act on the fiber, minute changes in the fiber's refractive index or length affect the light's properties. By demodulating these changes, the location and characteristics of the vibration event can be detected in real time. Currently, the most widely used distributed fiber-optic vibration sensing technology is based on optical time-domain reflectometry (Φ-OTDR), which relies primarily on backscattered Rayleigh light. However, backscattered Rayleigh light is very weak compared to the incident light. Furthermore, due to the inhomogeneity of the optical fiber medium, the backscattered light interferes with it, resulting in interference fading, which causes the information about the vibration event carried by the backscattered light to be buried in noise. Furthermore, the backscattered light signal in the fiber exhibits exponential decay with increasing distance. These limitations limit the application of backscattered light in long-distance detection scenarios. Summary of the Invention

[0004] In view of the above problems, at least one embodiment of the present invention provides a vibration positioning method and a vibration positioning device to detect vibration events in long-distance detection scenarios.

[0005] As a first aspect of the present invention, a vibration positioning method is provided, comprising:

[0006] In response to a vibration event acting on the optical fiber, a first phase signal and a second phase signal are obtained, wherein the first phase signal is determined by a phase change of the first detection laser signal before and after transmission through the optical fiber, and the second phase signal is determined by a phase change of the second detection laser signal before and after transmission through the optical fiber; the first detection laser signal and the second detection laser signal are transmitted in opposite directions within the optical fiber;

[0007] According to a preset division rule, the first phase signal and the second phase signal are respectively divided in the time domain to obtain n first signal segments of the first phase signal and n second signal segments of the second phase signal;

[0008] Determine an i-th segment delay difference between an i-th first signal segment and an i-th second signal segment, 1≤i≤n;

[0009] Determine the time delay difference between the first phase signal and the second phase signal according to the n segment time delay differences;

[0010] The position where the vibration event acts on the optical fiber is determined according to the time delay difference between the first phase signal and the second phase signal.

[0011] According to an embodiment of the present invention, determining an i-th segment delay difference between an i-th first signal segment and an i-th second signal segment includes:

[0012] When i>1, the i-th second signal segment is updated according to the i-1-th segment delay difference to obtain an updated i-th second signal segment;

[0013] Determining an i-th updated delay difference between the updated i-th second signal segment and the i-th first signal segment;

[0014] The i-th segment delay difference is obtained according to the i-th updated delay difference and the i-1-th segment delay difference.

[0015] According to an embodiment of the present invention, determining an i-th updated delay difference between an i-th second signal segment and an i-th first signal segment after update includes:

[0016] determining an updated i-th cross-correlation function between the i-th second signal segment and the i-th first signal segment;

[0017] intercepting a preset range of data points on the i-th cross-correlation function, where the preset range includes the data point at the peak of the i-th cross-correlation function;

[0018] Perform quadratic function fitting on the data points in the preset range to obtain the i-th fitting curve;

[0019] The i-th update delay difference is obtained according to the i-th fitting curve.

[0020] According to an embodiment of the present invention, dividing the first phase signal and the second phase signal in the time domain according to a preset division rule includes:

[0021] The first phase signal and the second phase signal are divided according to the sliding window and the preset step size respectively.

[0022] According to an embodiment of the present invention, obtaining a delay difference between a first phase signal and a second phase signal according to n segment delay differences includes:

[0023] The delay differences of the n segments are averaged to obtain the delay difference between the first phase signal and the second phase signal.

[0024] As a second aspect of the present invention, a vibration positioning device is also provided, comprising:

[0025] A laser, adapted to emit an initial laser signal;

[0026] A beam splitting module, adapted to split the initial laser signal into a first detection laser signal, a second detection laser signal, a first local oscillator laser signal, and a second local oscillator laser signal;

[0027] an optical fiber adapted to respond to a vibration event and receive a first detection laser signal and a second detection laser signal, wherein the first detection laser signal and the second detection laser signal propagate in opposite directions in the optical fiber;

[0028] a phase determination module adapted to obtain a first phase signal based on the second local oscillator laser signal and the first detection laser signal transmitted via the optical fiber, and to obtain a second phase signal based on the first local oscillator laser signal and the second detection laser signal transmitted via the optical fiber;

[0029] The processing module is adapted to obtain the position where the vibration event acts on the optical fiber according to the first phase signal and the second phase signal based on the above-mentioned vibration positioning method.

[0030] According to an embodiment of the present invention, the phase determination module includes:

[0031] Frequency shifting unit, including:

[0032] A first frequency shifting component is adapted to perform a first frequency shift on the first detection laser signal output by the beam splitting module, and transmit the first detection laser signal after the first frequency shift to the first port of the optical fiber;

[0033] a second frequency shifting component, performing a first frequency shift on the second detection laser signal output by the beam splitting module, and transmitting the second detection laser signal after the first frequency shift to the second port of the optical fiber;

[0034] The first frequency shifting component is further adapted to perform a second frequency shift on the second detection laser output from the second port, and the second frequency shifting component is further adapted to perform a second frequency shift on the first detection laser output from the first port;

[0035] The first photoelectric detection unit is adapted to generate a first beat frequency between the first local oscillator laser signal and the second detection laser signal after the second frequency shift, and convert the optical signal obtained after the first beat frequency into a first electrical signal;

[0036] The second photoelectric detection unit is adapted to generate a second beat frequency between the second local oscillator laser signal and the first detection laser signal after the second frequency shift, and convert the optical signal obtained after the second beat frequency into a second electrical signal;

[0037] The data acquisition card is adapted to perform quadrature demodulation processing, low-pass filtering processing, phase inverse tangent processing, and de-wrapping processing on the first electrical signal to obtain the second phase signal, and to perform quadrature demodulation processing, low-pass filtering processing, phase inverse tangent processing, and de-wrapping processing on the second electrical signal to obtain the first phase signal.

[0038] According to an embodiment of the present invention, the beam splitting module includes:

[0039] a first coupler adapted to split the initial laser signal into a first sub-laser signal and a second sub-laser signal;

[0040] a second coupler adapted to split the first sub-laser signal into a first detection laser signal and a first local oscillator laser signal;

[0041] The third coupler is adapted to split the second sub-laser signal into a second detection laser signal and a second local oscillator laser signal.

[0042] According to an embodiment of the present invention, the phase determination module further includes:

[0043] Driver component, suitable for synchronizing the clock between the frequency shift unit and the data acquisition card.

[0044] According to an embodiment of the present invention, the amount of frequency shift applied by the first frequency shifting component is different from the amount of frequency shift applied by the second frequency shifting component.

[0045] According to the vibration positioning method of an embodiment of the present invention, bidirectionally transmitted forward detection light (i.e., a first detection laser signal and a second detection laser signal) is used for vibration positioning, taking advantage of the low attenuation characteristics of the forward light, and is therefore suitable for long-distance vibration positioning scenarios.

[0046] According to the vibration positioning method of an embodiment of the present invention, the first phase signal and the second phase signal are divided into n segments for processing respectively, and the segment delay difference is calculated independently for each corresponding signal segment (the i-th first signal segment and the i-th second signal segment). The final signal delay difference is determined based on the statistical analysis of the n segment delay differences, so that the vibration event can be accurately positioned. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 A flow chart of a vibration positioning method according to an embodiment of the present invention is shown;

[0048] Figure 2A schematic diagram of a vibration positioning device according to an embodiment of the present invention is shown.

[0049] Description of Reference Numerals

[0050] 1-laser; 2-beam splitting module; 3-optical fiber; 4-phase determination module; 5-processing module; 21-first coupler; 22-second coupler; 23-third coupler; 31-first port; 32-second port; 41-frequency shift unit; 42-first photodetection unit; 43-second photodetection unit; 44-data acquisition card; 45-drive component; 411-first acousto-optic crystal; 412-first acousto-optic driver; 413-first circulator; 414-second acousto-optic driver; 415-second acousto-optic crystal; 416-second circulator; 421-fourth coupler; 422-first photodetector; 431-fifth coupler; 432-second photodetector. DETAILED DESCRIPTION

[0051] During the implementation of this invention, it was discovered that distributed fiber-optic vibration sensing technology based on forward light transmission (light signals propagating along the transmission direction of an optical fiber) has become a research hotspot in recent years. This technology directly senses external disturbances through forward light transmission, offering advantages such as long detection range. However, due to factors such as algorithm accuracy, sampling rate, and noise, the use of forward light transmission for vibration event detection still has certain limitations, such as insufficient positioning accuracy. Therefore, the development of a vibration positioning method based on forward light transmission is of great significance.

[0052] Figure 1 A flow chart of a vibration positioning method according to an embodiment of the present invention is shown.

[0053] like Figure 1 As shown, the vibration positioning method includes operations S1 to S5.

[0054] In operation S1, in response to a vibration event acting on an optical fiber, a first phase signal and a second phase signal are determined, wherein the first phase signal is determined by a phase change of the first probe laser signal before and after transmission through the optical fiber, and the second phase signal is determined by a phase change of the second probe laser signal before and after transmission through the optical fiber; the first probe laser signal and the second probe laser signal are transmitted in opposite directions within the optical fiber. Illustratively, the first probe laser signal is input from a first port of the optical fiber and output from a second port of the optical fiber, and the second probe laser signal is input from the second port of the optical fiber and output from the first port of the optical fiber.

[0055] In operation S2, the first phase signal and the second phase signal are respectively divided in the time domain according to a preset division rule to obtain n first signal segments of the first phase signal and n second signal segments of the second phase signal.

[0056] In operation S3 , the i-th segment delay difference between the i-th first signal segment and the i-th second signal segment is determined, where 1≤i≤n.

[0057] In operation S4, a delay difference between the first phase signal and the second phase signal is determined according to the n segment delay differences.

[0058] In operation S5 , a position where a vibration event acts on the optical fiber is determined according to a time delay difference between the first phase signal and the second phase signal.

[0059] According to an embodiment of the present invention, the first detection laser signal and the second detection laser signal propagate in opposite directions in the optical fiber. When an external vibration event acts on the optical fiber, a vibration point (the point where vibration occurs) is generated on the optical fiber. When the first detection laser signal and the second detection laser signal pass through the vibration point, the vibration point simultaneously modulates the phase of the first detection laser signal and the second detection laser signal to form a phase change signal related to the vibration point, so as to obtain the first phase signal and the second phase signal.

[0060] According to the vibration localization method of an embodiment of the present invention, two probe laser signals propagate in opposite directions within an optical fiber. After passing the vibration point, the two probe laser signals propagate along their respective remaining paths within the fiber until they are respectively output from the fiber. Both probe laser signals are detected after propagating the same distance outside the fiber. The difference in the length of the remaining paths of the two probe laser signals within the fiber results in different detection times for the first and second phase signals, which in turn results in a time delay difference between the first and second phase signals. This time delay difference can be calculated to determine the specific location of the vibration event on the fiber.

[0061] It is understandable that when a vibration event acts on the middle position of the optical fiber, the time delay difference between the first phase signal and the second phase signal is 0. In this case, vibration positioning can also be performed according to the method of the embodiment of the present invention.

[0062] According to an embodiment of the present invention, the first phase signal and the second phase signal are divided into n segments for processing, and the segment delay difference is independently calculated for each corresponding pair of signal segments (the i-th first signal segment and the i-th second signal segment). When the delay difference between the first phase signal and the second phase signal is determined based on the statistical analysis of the n segment delay differences, accurate positioning of the vibration event can be achieved.

[0063] According to the vibration positioning method of an embodiment of the present invention, bidirectionally transmitted forward detection light is adopted, that is, a first detection laser signal and a second detection laser signal are adopted for vibration positioning, and the low attenuation characteristics of the forward light are utilized, so it is suitable for long-distance vibration positioning scenarios.

[0064] According to an embodiment of the present invention, in operation S2, the first phase signal and the second phase signal are respectively divided in the time domain according to a preset division rule, including: dividing the first phase signal and the second phase signal according to a sliding window and a preset step size. Specifically, the sliding window is caused to slide at a preset step size from the starting point of the first phase signal and the starting point of the second phase signal, respectively. Based on the position of the sliding window during the a-th sliding of the sliding window on the first phase signal, the a+1-th first signal segment is obtained, where 0≤a≤n-1. Based on the position of the sliding window during the b-th sliding of the sliding window on the second phase signal, the b+1-th second signal segment is obtained, where 0≤b≤n-1.

[0065] It will be appreciated that, since both the first and second phase signals are signals in the time domain, the positions on the first and second phase signals referred to in the embodiments of the present invention refer to time positions. In other words, the position corresponding to the a-th sliding of the sliding window on the first phase signal, and the position of the a+1-th first signal segment determined thereby, are both divided based on the time dimension. Similarly, the above principles also apply to related operations on the second phase signal.

[0066] The first phase signal and the second phase signal are expressed as equations (1) and (2).

[0067] (1);

[0068] (2).

[0069] in, represents the first phase signal, represents the second phase signal, Indicates time, represents the time delay of the first detection laser signal, represents the time delay of the second detection laser signal, c is the speed of light in vacuum, is the refractive index of the fiber core, is the total length, is the distance the second detection laser signal travels from the vibration point on the optical fiber to the point where it is detected. is the distance the first detection laser signal travels from the vibration point on the optical fiber to the point where it is detected. For the convenience of expression, Abbreviated as , Abbreviated as .

[0070] For example, you can use the calculation software to and Segment processing. For example, we can use the sliding window to first The time domain is divided into n segments. The length of each segment can be set to 50T (where T is the period of the vibration source that generates the vibration event. For example, when the vibration source is a 100Hz sine signal, T=0.01s, then each signal segment contains 0.5s of time domain phase data). When processing in segments, a step-by-step segment interception method can be used to As the starting time of the 1st first signal segment, the starting time (or starting position) of the ith first signal segment can be Based on the starting point, increase , where 1≤i≤n. The second phase The segmented processing method of is similar to that of the first phase signal, except that The starting point of the first second signal segment is taken as the starting time of the first second signal segment, and the starting time of the i-th second signal segment can be sequentially Based on the starting point, The two adjacent segments of the same phase signal obtained by this segmentation method have overlapping areas, which can further improve the detection accuracy.

[0071] According to an embodiment of the present invention, in operation S3, the step of determining the i-th segment delay difference between the i-th first signal segment and the i-th second signal segment includes a case where i=1 and a case where i>1.

[0072] In the case of i=1, a method for determining the first segment delay difference between the first first signal segment and the first second signal segment is as follows.

[0073] The first signal segment is represented as , the first second signal segment is expressed as ,right and By sequentially performing the steps of time difference, integration, filtering, and cross-correlation, we can obtain and The cross-correlation function between . and The cross-correlation function between It is expressed as formula (3).

[0074] (3).

[0075] In formula (3), represents the signal delay difference between the first phase signal and the second phase signal, Indicates Delay .

[0076] The cross-correlation function is a function that describes how the similarity between two signals changes with time delay. The data points in a specific range are intercepted and fitted with a quadratic function. The peak point (i.e., the intercepted cross-correlation function The first fitting curve is obtained by fitting the data points with appropriate width around the upper peak point, and the delay value corresponding to the symmetry axis of the first fitting curve is taken as and The delay difference is recorded as Among them, the quadratic function is expressed as formula (4), the delay difference It is expressed as formula (5).

[0077] (4);

[0078] (5).

[0079] In formula (4), A, B, and C are all fitting parameters, x represents the horizontal coordinate of the data point for quadratic function fitting, and y represents the vertical coordinate of the data point for quadratic function fitting.

[0080] According to an embodiment of the present invention, the process of determining the first phase signal and the second phase signal needs to be carried out in the data acquisition card. The first phase signal obtained by the data acquisition card can reflect the phase change of the first detection laser signal before and after the optical fiber transmission in the actual process. Similarly, the second phase signal obtained by the data acquisition card can reflect the phase change of the second detection laser signal before and after the optical fiber transmission in the actual process. However, due to the working principle of the data acquisition card, the first phase signal and the second phase signal detected by it are discrete in the time domain, and even at a high sampling rate, there is still a time interval between the sampling points of the first phase signal and the second phase signal, and there is a difference in accuracy with the phase change of the laser signal before and after the optical fiber transmission in the actual process. This results in the positioning accuracy of the cross-correlation operation being limited, and directly and When performing a cross-correlation operation, the peak delay value obtained cannot meet the requirements of high-precision positioning. This embodiment of the present invention effectively compensates for the impact on delay difference measurement accuracy caused by the sampling rate limitation of the data acquisition card by using a quadratic function to fit the local curve near the peak point of the cross-correlation function. By leveraging the local approximation characteristics of the quadratic function, the measurement accuracy of the delay difference can be significantly improved.

[0081] According to an embodiment of the present invention, when i>1, determining the delay difference of the i-th segment includes operations S31 to S33.

[0082] In operation S31, the position of the i-th second signal segment is updated according to the i-1-th segment delay difference to obtain an updated i-th second signal segment.

[0083] In operation S32, an i-th updated delay difference between the updated i-th second signal segment and the i-th first signal segment is determined.

[0084] In operation S33, the i-th segment delay difference is obtained according to the i-th updated delay difference and the i-1-th segment delay difference. The i-th segment delay difference is equal to the sum of the i-th updated delay difference and the i-1-th segment delay difference.

[0085] According to an embodiment of the present invention, for example, the delay difference of the i-1th segment can be expressed as , the i-th first signal segment and the i-th second signal segment The delay difference of the i-th segment is expressed as , the i-th update delay difference is expressed as , the relationship between the three is expressed as formula (6).

[0086] (6)

[0087] According to the above rules, the delay difference of the nth segment It is expressed as formula (7).

[0088] (7)

[0089] When the i-1th segment delay difference is used to update the i-th second signal segment (update the position of the i-th second signal segment on the second phase signal), the i-1th segment delay difference needs to be used The starting position (time) of the i-th second signal segment is compensated so that the i-th first signal segment is aligned with the updated i-th second signal segment in the time domain, thereby reducing the problem of weakening of the mutual correlation between the i-th first signal segment and the i-th second signal segment due to the time domain inconsistency of the phase signals of the i-th first signal segment and the i-th second signal segment, thereby affecting the accuracy of the signal delay difference.

[0090] According to an embodiment of the present invention, in operation S32 , determining the i th updated delay difference between the updated i th second signal segment and the i th first signal segment includes: operations S321 to S324 .

[0091] In operation S321 , an i-th cross-correlation function between the updated i-th second signal segment and the i-th first signal segment is determined.

[0092] In operation S322 , a preset range of data points is intercepted on the i-th cross-correlation function, where the preset range of data points includes a data point at a peak of the i-th cross-correlation function.

[0093] In operation S323 , a quadratic function is fitted to the data points in a preset range to obtain an i-th fitting curve.

[0094] In operation S324, an i-th updated delay difference is obtained according to the data point at the symmetry axis of the i-th fitting curve. The delay value at the symmetry axis of the i-th fitting curve is the i-th updated delay difference.

[0095] According to an embodiment of the present invention, the symmetry axis of the fitting curve can fall on a non-integer sampling point position of the data acquisition card, breaking through the sampling interval limitation of the data acquisition card on the first detection laser signal and the second detection laser signal, and can further improve the positioning accuracy.

[0096] According to an embodiment of the present invention, in operation S4, the delay difference between the first phase signal and the second phase signal is obtained based on the n segment delay differences, including: averaging the n segment delay differences to obtain the delay difference between the first phase signal and the second phase signal. The signal delay difference between the first phase signal and the second phase signal The calculation formula is expressed as formula (8).

[0097] (8).

[0098] Formula (8) is simplified to formula (9).

[0099] (9).

[0100] According to the embodiments of the present invention, the delay measurement of a single segment may be affected by noise, jitter or transient interference. By averaging multiple independent measurement results, random errors can be effectively reduced and the statistical reliability of the delay difference can be improved.

[0101] According to an embodiment of the present invention, in operation S5, the position where the vibration event acts on the optical fiber (ie, the position of the vibration point on the optical fiber) may be determined using formula (10).

[0102] (10).

[0103] In formula (10), c is the speed of light, is the refractive index of the fiber core. For example, the direction of the second detection laser signal transmission is recorded as the positive direction. hour, is positive; is negative.

[0104] According to embodiments of the present invention, all or part of the above-described processes can be completed by instructing relevant hardware (e.g., a processor, a controller, etc.) through a computer program. The computer program can be stored in a computer-readable storage medium. When executed, the computer program can include the processes of the above-described method embodiments. The computer-readable storage medium can be a memory, a magnetic disk, or an optical disk.

[0105] Figure 2 A schematic diagram of a vibration positioning device according to an embodiment of the present invention is shown.

[0106] like Figure 2 As shown, the vibration positioning device includes a laser 1, a beam splitting module 2, an optical fiber 3, a phase determination module 4, and a processing module 5.

[0107] Laser 1 is adapted to emit an initial laser signal. Laser 1 may be, for example, a semiconductor laser capable of emitting continuous laser light with a central wavelength of 1550.12 nm. The laser energy output of laser 1 can be controlled by adjusting the current. Beam splitting module 2 is adapted to split the initial laser signal into a first detection laser signal, a second detection laser signal, a first local oscillator laser signal, and a second local oscillator laser signal. Optical fiber 3 is adapted to respond to a vibration event and receive the first detection laser signal and the second detection laser signal, wherein the first detection laser signal and the second detection laser signal propagate in opposite directions within optical fiber 3. For example, the first detection laser signal is input from the first port 31 of optical fiber 3 and output from the second port 32 of optical fiber 3, while the second detection laser signal is input from the second port 32 of optical fiber 3 and output from the first port 31 of optical fiber 3. Phase determination module 4 is adapted to derive a first phase signal from the second local oscillator laser signal and the first detection laser signal after transmission through the optical fiber, and to derive a second phase signal from the first local oscillator laser signal and the second detection laser signal after transmission through the optical fiber. Processing module 5 is adapted to utilize the above-described vibration positioning method to determine the position of the vibration event on the optical fiber based on the first phase signal and the second phase signal.

[0108] According to an embodiment of the present invention, the beam splitting module 2 includes a first coupler 21, a second coupler 22 and a third coupler 23. The first coupler 21 is suitable for splitting the initial laser signal into a first sub-laser signal and a second sub-laser signal. The optical power ratio of the first sub-laser signal and the second sub-laser signal can be, for example, 1:1. The second coupler 22 is suitable for splitting the first sub-laser signal into a first detection laser signal and a first local oscillator laser signal, and the optical power ratio of the first detection laser signal and the first local oscillator laser signal can be, for example, 1:1. The third coupler 23 is suitable for splitting the second sub-laser signal into a second detection laser signal and a second local oscillator laser signal. The optical power ratio of the second detection laser signal and the second local oscillator laser signal can be, for example, 1:1.

[0109] According to an embodiment of the present invention, optical fiber 3 is a standard single-mode optical fiber, which is used to sense external vibrations, trigger characteristic changes of two detection light signals, and serve as a transmission channel for the two detection light signals to achieve long-distance distributed vibration monitoring and positioning.

[0110] According to an embodiment of the present invention, the phase determination module 4 includes a frequency shift unit 41 , a first photodetection unit 42 , a second photodetection unit 43 , and a data acquisition card 44 .

[0111] The frequency shifting unit 41 includes a first frequency shifting component and a second frequency shifting component. The first frequency shifting component is adapted to perform a first frequency shift on the first detection laser signal output by the beam splitting module 2, and transmit the first detection laser signal after the first frequency shift to the first port 31 of the optical fiber 3. The second frequency shifting component is adapted to perform a first frequency shift on the second detection laser signal output by the beam splitting module 2, and transmit the second detection laser signal after the first frequency shift to the second port 32 of the optical fiber 3. The first frequency shifting component is also adapted to perform a second frequency shift on the first detection laser signal output from the second port 32, and the second frequency shifting component is also adapted to perform a second frequency shift on the first detection laser signal output from the first port 31.

[0112] According to an embodiment of the present invention, the first frequency-shifting component includes a first acousto-optic crystal 411, a first acousto-optic driver 412, and a first circulator 413. The first circulator 413 is used to transmit the first detection laser signal output by the second coupler 22 to the first acousto-optic crystal 411, and the first acousto-optic crystal is connected to the first port 31 of the optical fiber 3. Under the action of the first acousto-optic driver 412, the first acousto-optic crystal 411 is used to frequency-shift the detection light signal it receives. Specifically, the first acousto-optic crystal is used to frequency-shift the first detection laser signal output by the second coupler 22 by A MHz, and is also suitable for frequency-shifting the second detection laser signal output by the optical fiber 3 by A MHz.

[0113] The second frequency shifting component includes a second acousto-optic crystal 415, a second acousto-optic driver 414 and a second circulator 416. The second circulator 416 is used to transmit the second detection laser output by the third coupler 23 to the second acousto-optic crystal 415. Under the action of the second acousto-optic driver 414, the second acousto-optic crystal 415 is used to frequency-shift the detection light signal it receives. Specifically, the second acousto-optic crystal 415 is used to frequency-shift the second detection laser signal output by the third coupler 23 by B MHz, and is also suitable for frequency-shifting the first detection laser signal output by the optical fiber 3 by B MHz. The frequency shift of the first detection laser signal after two frequency shifts is (A+B) MHz, and the frequency shift of the second detection laser signal after two frequency shifts is also (A+B) MHz. The frequency shifts applied by the first acousto-optic crystal 411 and the second acousto-optic crystal 415 are different, that is, A≠B.

[0114] Each acousto-optic crystal has a positive frequency shift (i.e., A>0, B>0) and uses a fixed carrier frequency, but the center frequency varies. The frequency shift applied by each acousto-optic crystal is uniquely determined by its corresponding drive frequency and is independent of the spatial position of the two detection laser signals in the optical path. Furthermore, the first circulator 413 is also adapted to transmit the second detection laser signal output by the first acousto-optic crystal 411, and the second circulator 416 is also adapted to transmit the first detection laser signal output by the second acousto-optic crystal 415.

[0115] The optical field of the first local oscillator laser signal , the light field of the second local oscillator laser signal , the light field of the first detection laser signal after the second frequency shift , the light field of the second detection laser signal after the second frequency shift They are expressed as formula (11) to formula (14) respectively.

[0116] (11);

[0117] (12);

[0118] (13);

[0119] (14).

[0120] in, is the light intensity amplitude of the first local oscillator laser signal, is the light intensity amplitude of the second local oscillator laser signal, is the light intensity amplitude of the first detection laser signal, is the light intensity amplitude of the second detection laser signal; is the frequency of the initial laser; is the cumulative frequency shift of the two AOMs, such as (A+B) MHz. is the phase of the first detection laser signal at time t, is the phase of the second detection laser signal at time t, is the phase of the first local oscillator laser signal at time t, is the phase of the second local oscillator laser signal at time t.

[0121] The first photodetection unit 42 is adapted to cause a first beat frequency between the first local oscillator laser signal and the second detection laser signal after the second frequency shift, and to convert the optical signal obtained after the first beat frequency into a first electrical signal. The first photodetection unit 42 includes a fourth coupler 421 and a first photodetector 422. The fourth coupler 421 is connected to the second coupler 22 and the first circulator 413, and is adapted to couple the first local oscillator laser signal from the second coupler and the second detection laser signal from the first circulator to obtain a first coupled signal. The first photodetector 422 is adapted to cause a first beat frequency between the first coupled signal and to convert the optical signal obtained after the first beat frequency into a first electrical signal. The fourth coupler may be, for example, a 2×2 coupler.

[0122] The second photodetection unit 43 is suitable for causing the second local oscillator laser signal and the first detection laser signal after the second frequency shift to generate a second beat frequency, and converting the optical signal obtained after the second beat frequency into a second electrical signal. The second photodetection unit 43 includes a fifth coupler 431 and a second photodetector 432. The fifth coupler 431 is connected to the third coupler 23 and the second circulator 416, and is used to couple the second local oscillator laser signal from the third coupler and the first detection laser signal from the second circulator 416 to obtain a second coupled signal. The second photodetector 432 is used to cause the second coupled signal to generate a second beat frequency, and convert the optical signal obtained after the second beat frequency into a second electrical signal. The fifth coupler can be, for example, a 2×2 coupler. The first photodetector 422 and the second photodetector 432 can both be balanced detectors.

[0123] According to an embodiment of the present invention, when a vibration event acts on the optical fiber, the first electrical signal detected by the first photodetector is It can be expressed as formula (15), the second electrical signal detected by the second photodetector is It can be expressed as formula (16).

[0124] (15).

[0125] (16).

[0126] In formula (15) to formula (16), is a parameter related to the optical power of the first local oscillator laser signal and the second detection laser signal, is a parameter related to the optical power of the second local oscillator laser signal and the first detection laser signal, is the phase change of the second detection laser signal before and after transmission through the optical fiber, is the phase change of the first detection laser signal before and after transmission through the optical fiber, is the initial phase introduced by the fourth coupler 421, is the initial phase introduced by the fifth coupler 431.

[0127] According to an embodiment of the present invention, the data acquisition card 44 is suitable for performing orthogonal demodulation processing, low-pass filtering processing, phase inverse tangent processing and dewrapping processing on the first electrical signal to obtain a second phase signal, and performing orthogonal demodulation processing, low-pass filtering processing, phase inverse tangent processing and dewrapping processing on the second electrical signal to obtain a first phase signal.

[0128] According to an embodiment of the present invention, when optical fiber 3 is long, each probe laser generates strong noise during fiber transmission. This noise, for example, is caused by backscattered noise during fiber transmission and by incomplete connection of link components. Therefore, the probe laser output from the optical fiber may contain parasitic noise bands. In this embodiment of the present invention, two frequency-shifting components are first used to perform two frequency shifts on each of the two probe lasers. When the first and second electrical signals are input to the data acquisition card, the card first performs quadrature demodulation on the first and second signals with the target frequency to generate a mixed signal. The target frequency is the sum of the frequency shifts of the two frequency-shifting components, i.e., (A + B) MHz. Next, low-pass filtering is used to digitally filter the quadrature mixed signal to extract the baseband DC signal. While ensuring no frequency aliasing, noise in unnecessary frequency bands is filtered out, effectively suppressing the impact of a low signal-to-noise ratio on the detection signal transmission and ensuring high-quality signal transmission. Because the backscattered signal and the corresponding detection laser signal travel in opposite directions, their frequency shifts differ. Orthogonal demodulation relative to the target frequency and low-pass filtering can be used to filter out noise, including the backscattered signal. This orthogonal demodulation and low-pass filtering effectively suppress the effects of a low signal-to-noise ratio, enhancing the stability and accuracy of the positioning device. Finally, the signals are processed using methods such as phase inverse tangent solution and unwrapping, ultimately yielding first and second phase signals with highly similar waveforms in the time domain but a certain time delay difference. If only a single acousto-optic crystal were used to frequency-shift the first and second detection light signals, unshifted optical signal components might remain in the backscattered signal, resulting in baseband noise in the first and second phase signals. By applying different frequency shifts using two acousto-optic crystals, the backscattered light can have a different frequency shift than the two detection lights. Subsequent low-pass filtering effectively filters the backscattered signal.

[0129] According to an embodiment of the present invention, the phase determination module further includes a driving component 45, which is adapted to drive the first acousto-optic driver 412 in the first frequency-shifting component and the second acousto-optic driver 414 in the second frequency-shifting component, and is further adapted to synchronize the clocks of the frequency-shifting unit 41 and the data acquisition card 44. The driving component 45 may be, for example, an arbitrary waveform generator.

[0130] According to an embodiment of the present invention, after obtaining the first phase signal and the second phase signal, the processing module 5 can obtain the position acting on the optical fiber according to the above positioning method. The processing module 5 can be, for example, a computer.

[0131] The vibration localization method provided by the present invention performs a quadratic fit on a preset range of data points on both sides of the peak of the cross-correlation function and uses the corresponding delay at the axis of symmetry as the precise delay difference. This method can compensate for the sampling accuracy limitations imposed by the data acquisition card's sampling rate, improving the accuracy of the delay difference without increasing the acquisition card's cost.

[0132] According to the vibration positioning method provided by an embodiment of the present invention, the i-1th segment delay difference is used to perform feedback compensation on the starting position of the i-th second signal segment, so that the i-th first signal segment and the updated i-th second signal segment are aligned in the time domain, reducing the weakening of the cross-correlation caused by the time domain inconsistency of the phase signals between the i-th first signal segment and the i-th second signal segment, thereby reducing the problem of affecting the accuracy of the delay difference.

[0133] Compared with traditional positioning devices, the vibration positioning device provided by the embodiment of the present invention uses forward transmitted light instead of backscattered light, is suitable for long-distance vibration positioning scenarios, has a higher signal-to-noise ratio and does not require the use of an optical amplifier.

[0134] The vibration positioning device provided by the embodiment of the present invention combines a dual acousto-optic modulator with digital filtering, significantly suppressing noise and thus achieving a high signal-to-noise ratio. The vibration positioning device of the embodiment of the present invention has relatively precise vibration positioning performance and high system stability.

[0135] The above describes embodiments of the present invention. However, these embodiments are for illustrative purposes only and are not intended to limit the scope of the present invention. Although each embodiment has been described separately above, this does not mean that the measures in each embodiment cannot be advantageously used in combination. The scope of the present invention is defined by the appended claims and their equivalents. Without departing from the scope of the present invention, those skilled in the art may make various substitutions and modifications, which are intended to fall within the scope of the present invention.

Claims

1. A vibration positioning method, characterized in that: The vibration positioning method comprises: In response to a vibration event acting on the optical fiber, a first phase signal and a second phase signal are acquired, wherein the first phase signal is determined by a phase change of the first probe laser signal before and after transmission through the optical fiber, and the second phase signal is determined by a phase change of the second probe laser signal before and after transmission through the optical fiber; the first probe laser signal and the second probe laser signal have opposite transmission directions within the optical fiber; Dividing the first phase signal and the second phase signal in the time domain according to a preset division rule to obtain n first signal segments of the first phase signal and n second signal segments of the second phase signal; Determine an i-th segment delay difference between an i-th first signal segment and an i-th second signal segment, 1≤i≤n; Determining a time delay difference between the first phase signal and the second phase signal according to the n segment time delay differences; The position where the vibration event acts on the optical fiber is determined according to the time delay difference between the first phase signal and the second phase signal.

2. The vibration positioning method according to claim 1, characterized in that: The determining the i-th segment delay difference between the i-th first signal segment and the i-th second signal segment includes: When i>1, the i-th second signal segment is updated according to the i-1-th segment delay difference to obtain an updated i-th second signal segment; Determining an i-th updated delay difference between the updated i-th second signal segment and the i-th first signal segment; The i-th segment delay difference is obtained according to the i-th updated delay difference and the i-1-th segment delay difference.

3. The vibration positioning method according to claim 2, characterized in that: Determining an i-th updated delay difference between the updated i-th second signal segment and the i-th first signal segment includes: determining an i-th cross-correlation function between the updated i-th second signal segment and the i-th first signal segment; intercepting a preset range of data points on the i-th cross-correlation function, where the preset range includes data points at a peak of the i-th cross-correlation function; Performing quadratic function fitting on the data points in the preset range to obtain an i-th fitting curve; The i-th updated delay difference is obtained according to the i-th fitting curve.

4. The vibration positioning method according to claim 1, characterized in that: The first phase signal and the second phase signal are divided in the time domain according to a preset division rule, including: The first phase signal and the second phase signal are divided according to the sliding window and the preset step size respectively.

5. The vibration positioning method according to claim 1, characterized in that: Obtaining a time delay difference between a first phase signal and a second phase signal according to the n segment time delay differences includes: The delay differences of the n segments are averaged to obtain the delay difference between the first phase signal and the second phase signal.

6. A vibration positioning device, characterized in that: The vibration positioning device comprises: A laser, adapted to emit an initial laser signal; A beam splitting module, adapted to split the initial laser signal into a first detection laser signal, a second detection laser signal, a first local oscillator laser signal, and a second local oscillator laser signal; an optical fiber adapted to respond to a vibration event and receive the first detection laser signal and the second detection laser signal, wherein the first detection laser signal and the second detection laser signal propagate in opposite directions in the optical fiber; a phase determination module, adapted to obtain the first phase signal based on the second local oscillator laser signal and the first detection laser signal transmitted through the optical fiber, and to obtain the second phase signal based on the first local oscillator laser signal and the second detection laser signal transmitted through the optical fiber; A processing module is adapted to obtain the position of the vibration event acting on the optical fiber based on the first phase signal and the second phase signal based on the vibration positioning method according to any one of claims 1 to 5.

7. The vibration positioning device according to claim 6, characterized in that: The phase determination module includes: Frequency shifting unit, including: a first frequency shifting component, adapted to perform a first frequency shift on the first detection laser signal output by the beam splitting module, and transmit the first detection laser signal after the first frequency shift to the first port of the optical fiber; a second frequency shifting component, performing a first frequency shift on the second detection laser signal output by the beam splitting module, and transmitting the second detection laser signal after the first frequency shift to the second port of the optical fiber; The first frequency shifting component is further adapted to perform a second frequency shift on the second detection laser signal output from the second port, and the second frequency shifting component is further adapted to perform a second frequency shift on the first detection laser signal output from the first port; a first photoelectric detection unit, adapted to generate a first beat frequency between the first local oscillator laser signal and the second detection laser signal after the second frequency shift, and convert the optical signal obtained after the first beat frequency into a first electrical signal; a second photoelectric detection unit adapted to cause the second local oscillator laser signal and the first detection laser signal after the second frequency shift to generate a second beat frequency, and convert the optical signal obtained after the second beat frequency into a second electrical signal; The data acquisition card is adapted to perform quadrature demodulation processing, low-pass filtering processing, phase inverse tangent processing, and dewrapping processing on the first electrical signal to obtain the second phase signal, and to perform quadrature demodulation processing, low-pass filtering processing, phase inverse tangent processing, and dewrapping processing on the second electrical signal to obtain the first phase signal.

8. The vibration positioning device according to claim 6, characterized in that: The beam splitting module includes: a first coupler adapted to split the initial laser signal into a first sub-laser signal and a second sub-laser signal; a second coupler, adapted to split the first sub-laser signal into the first detection laser signal and the first local oscillator laser signal; The third coupler is adapted to split the second sub-laser signal into the second detection laser signal and the second local oscillator laser signal.

9. The vibration positioning device according to claim 7, characterized in that: The phase determination module also includes: The driving component is adapted to synchronize the clocks of the frequency shift unit and the data acquisition card.

10. The vibration positioning device according to claim 7, characterized in that: The amount of frequency shift applied by the first frequency shifting component is different from the amount of frequency shift applied by the second frequency shifting component.

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