A multi-channel microseismic monitoring system and method based on optical fiber sensing

Abstract

The application discloses a kind of multi-channel microseismic monitoring system and method based on optical fiber sensing, belong to optical fiber sensing noise suppression technical field.The application is intermittently outputted symmetric square wave modulation signal and synchronous trigger signal by signal generation module, the modulation signal controls the laser output of three periodic phase states, the trigger signal is synchronously collected three-way interference electric signal in rising edge, combined with intermittent collection, solve the problem of interchannel crosstalk, poor synchronism, high system complexity in multi-channel monitoring, realize the effect of crosstalk-free parallel processing of multi-channel data time division multiplexing.Simultaneously, three-way interference signals of synchronous collection are regarded as spatial discrete points, noise interference is stripped through fitting, translation, rotation and mapping and other space conversion modes, keep pure phase information, solve the technical problem that traditional ellipse fitting fails under weak microvibration signal, significantly improve the robustness and monitoring precision of weak signal demodulation.

Description

TECHNICAL FIELD

[0001] The application relates to the field of optical fiber sensing noise suppression, in particular to a multi-channel microseismic monitoring system and method based on optical fiber sensing. BACKGROUND

[0002] In recent years, optical fiber sensing technology has rapidly developed due to its high sensitivity, wide dynamic range, intrinsic safety and anti-electromagnetic interference, and is widely used in the field of microseismic measurement. It uses light waves as carriers to demodulate external vibrations by sensing the changes of physical parameters such as phase, intensity and wavelength of light in the optical fiber.

[0003] PGC (Phase Generated Carrier) demodulation is one of the most core and classical demodulation schemes in optical fiber interferometer sensors. It actively injects a high-frequency carrier signal into the interferometer, modulates the low-frequency and weak signal to be measured onto the carrier, and then generates a base frequency and a multiple frequency signal synchronized with the carrier signal. After mixing and filtering, a pair of quadrature signals is output, and then the vibration signal is demodulated by DCM or ATAN. This method has high circuit complexity and may also cause carrier phase delay problems. Meanwhile, the phase-frequency characteristics of the filter will affect the orthogonality of the output signal, and further affect the demodulation result.

[0004] The 3x3 coupler demodulation scheme directly outputs signals with fixed phase difference by using the inherent symmetric phase characteristics of the 3x3 coupler, and then constructs quadrature signals by using the ellipse fitting method, and further demodulates the vibration information. This scheme has simple structure and lower cost, and does not need complex active modulation. However, this scheme needs to collect two signals at the same time and perform real-time ellipse fitting operation. When the external vibration signal is too weak, the ellipse may not be closed, which may lead to fitting failure and further demodulation failure. Meanwhile, this scheme is easily affected by low-frequency interference. SUMMARY

[0005] In view of the above problems, the application provides a multi-channel microseismic monitoring system and method based on optical fiber sensing. The application outputs intermittent symmetric square wave modulation signals and synchronous trigger signals through a signal generation module. The modulation signals control the light source to output three periodic phase state lasers. The trigger signals are collected synchronously at the rising edge of the three interference signals. The intermittent collection solves the problems of channel crosstalk, poor synchronization and high system complexity in multi-channel monitoring, and realizes the effect of non-crosstalk parallel processing of multi-channel data time division multiplexing. Meanwhile, the three interference signals collected synchronously are regarded as spatial discrete points. The noise interference is stripped by space conversion methods such as fitting, translation, rotation and mapping, and the pure phase information is retained. The technical problem of fitting failure of the traditional ellipse fitting under weak micro-vibration signal is solved, and the robustness and monitoring accuracy of weak signal demodulation are significantly improved.

[0006] To achieve the above object, the technical scheme adopted by the present application is: a multi-channel microseismic signal demodulation method, comprising the following steps:

[0007] S1: collecting three-way interference signals with fixed phase difference β to form discrete points P i ( x i , y i , z i );

[0008] S2: adjusting the amplitude of the modulation signal to control the phase difference β to be 0 and π respectively, collecting corresponding discrete points P i and fitting a spatial straight line L 1 and L 2;

[0009] S3: calculating the intersection L 0 of the straight lines L 1 and P 2 and the normal vector of the plane where they are located, constructing a spatial straight line x 0 passing through the intersection P 0 and perpendicular to the planes where the two straight lines are located L 0;

[0010] S4: calculating the angle between the straight line L 0 and the Z-axis or Y-axis, constructing a rotation matrix with the X-axis as the rotation axis and the angle as the rotation angle R x ;

[0011] S5: based on the intersection P 0 and the rotation matrix R x , mapping and converting the collected discrete points P i into discrete points P j ( x j , y j , z j ), and extracting orthogonal signals;

[0012] S6: performing differential cross-multiplication operation on the orthogonal signals to demodulate the phase change caused by external vibration .

[0013] Preferably, the interference signal is represented as:

[0014] ;

[0015] wherein,a 1、 a 2、 a 3 represents the DC bias of the signal, b 1、 b 2、 b 3 represents the AC amplitude, is the phase change caused by the vibration, β is the fixed phase difference.

[0016] Preferably, the spatial straight line L 1 has a parametric equation as follows:

[0017] ;

[0018] Preferably, the spatial straight line L 2 has a parametric equation as follows:

[0019] ;

[0020] wherein, i 1、 i 2、 i 3 is the coordinate corresponding to the directional vector of the straight line L 1; x 1、 y 1、 z 1 is the coordinate corresponding to an arbitrary point on the straight line L 1; j 1、 j 2、 j 3 is the coordinate corresponding to the directional vector of the straight line L 2; x 2、 y 2、 z 2 is the coordinate corresponding to an arbitrary point on the straight line L 2; t is a real number parameter.

[0021] Preferably, the spatial straight line L 0 has:

[0022]

[0023] Meanwhile k 1、 k 2、 k 3 satisfy the following relationship:

[0024] ;

[0025] wherein, x 0, y0, z0 are the coordinates corresponding to the intersection point P 0; k 1、 k 2、 k3 is a straight line L 0 is a direction vector; i 1, i 2, i 3 is a straight line L 1 is a direction vector corresponding to coordinates; j 1, j 2, j 3 is a straight line L 2 is a direction vector corresponding to coordinates.

[0026] Preferably, the straight line L 0 is an angle between the Z axis The sine and cosine values are:

[0027] ;

[0028] Wherein, k 1, k 2, k 3 is a straight line L 0 is a direction vector.

[0029] Preferably, the rotation matrix R x Is expressed as:

[0030] ;

[0031] Wherein, is a straight line L 0 is an angle between the Z axis.

[0032] Preferably, the discrete point P i Mapping transformation into discrete point P j ( x j , y j , z j ) The mapping relationship is:

[0033] ;

[0034] Wherein, is a straight line L 0 is an angle between the Z axis; x 0, y0, z0 is the intersection P 0 corresponding to the coordinates; y j , z j Is an orthogonal signal.

[0035] A multi-channel microseismic monitoring method based on fiber optic sensing includes step 1: outputting an intermittent symmetrical square wave modulation signal and a strictly synchronized intermittent square wave trigger signal through a signal generation module, wherein the modulation signal controls the light source module to output laser light in three periodic phase states;

[0036] Step 2: Distribute the modulated laser to N sensing channels through a 1×N beam splitter;

[0037] Step 3: Each sensing channel converts the phase change caused by external vibration into three paths with a fixed phase difference using an interferometer. β The interference signal is converted into three interference electrical signals by the photoelectric conversion module. The trigger signal controls the data acquisition module to synchronously acquire the three interference electrical signals at the rising edge of each pulse and output them to the signal processing module.

[0038] Step 4: The signal processing module uses the above-mentioned multi-channel micro-vibration signal demodulation method to process the three-channel interference electrical signals acquired by the N sensing channels, and demodulates the phase change caused by external vibration. .

[0039] Preferably, the sensing channel includes a circulator, an interferometer, and a photoelectric conversion module; the interferometer is a Michelson interferometer including a coupler, a mass block, an elastic body, and a Faraday rotator; the time interval for each pulse of the trigger signal to acquire three interference electrical signals is... t 1. Interval duration is t 2.

[0040] A multi-channel microseismic monitoring system based on fiber optic sensing includes a signal generation module for outputting a modulation signal of an intermittent symmetrical square wave and a trigger signal of an intermittent square wave that is strictly synchronized with it, wherein the rising edge of each pulse of the trigger signal is synchronized with the level switching time of the modulation signal; a light source module for receiving the modulation signal and outputting phase-modulated laser light; a beam splitter for splitting the laser light output from the light source into N channels; N sensing channels for converting external vibration signals into three interferometric electrical signals; a data acquisition module for receiving the trigger signal output from the signal processing module and synchronously acquiring the three interferometric electrical signals; and a system for processing the acquired multi-channel three-channel interferometric electrical signals using the above-described multi-channel microseismic monitoring method and demodulating the phase changes. The signal processing module.

[0041] By adopting the above technical solution, the present invention has the following beneficial effects.

[0042] (1) The application outputs intermittent symmetrical square wave modulation signals and synchronous trigger signals through a signal generating module, the modulation signals control the light source to output three periodic phase state lasers, the trigger signals synchronously collect three interference electric signals at the rising edge, solve the problems of channel crosstalk, poor synchronization and high system complexity in multi-channel monitoring, realize multi-channel high-precision synchronous monitoring, and the system structure is simple, easy to expand and maintain.

[0043] (2) The application constructs spatial discrete points by collecting three interference signals with a fixed phase difference beta, adjusts the amplitude of the modulation signal to make the phase difference β 0 and pi respectively, fits the spatial straight lines L 1 and L 2, calculates the normal vector of the plane where the intersection P 0 and the plane is located, constructs the vertical spatial straight line L 0, and constructs the rotation matrix L 0 by calculating the angle between the straight line R x , based on the intersection P 0 and the rotation matrix R x The collected discrete points are mapped by translation and rotation, and the orthogonal signals are directly extracted. Thus, noise interference is converted into geometric parameters, noise is stripped through spatial transformation, pure phase information is retained, the robustness of weak signal demodulation is improved, the problems of signal distortion and non-orthogonality caused by light source fluctuation and environmental interference are solved, orthogonalization processing of the signals is realized, a high-quality orthogonal signal pair is provided for subsequent DCM demodulation, and finally the differential cross multiplication (DCM) algorithm is used to demodulate the orthogonal signals.

[0044] (3) The application realizes high-precision synchronous monitoring of multi-channel microseismic signals through intermittent modulation signals (three levels) and strictly synchronous trigger signals, time sequence control precision reaches nanosecond level, and a multi-channel architecture that combines a 1xN optical splitter to distribute laser to N independent sensing channels is used, each channel picks up external vibration signals through a Michelson interferometer, and through accurate matching of multi-channel laser distribution and collection time sequence, the high-precision synchronous monitoring of multi-channel microseismic signals is realized.

[0045] (4) The application regards three interference signals as spatial discrete points, replaces traditional ellipse fitting with translation and rotation projection, solves the problem of fitting failure under weak signals, realizes the non-crosstalk parallel processing effect of time division multiplexing of multi-channel data through strict synchronization of modulation signals and trigger signals and intermittent collection (time length t 2), and through the spatial geometric demodulation model and the synchronous time-sharing multi-channel architecture, the problems of weak signal demodulation failure, noise interference and high system complexity are solved, and a high-reliability solution is provided for geological disaster warning. BRIEF DESCRIPTION OF DRAWINGS

[0046] The following discussion of the preferred embodiment of the application now will be made with reference to the accompanying drawings. But it is to be understood that numerous specific details can be used, and changes can be made in the preferred embodiment of the application set forth in the accompanying description which should not be read as a limitation of the application. Rather, these details are included to provide what is believed to be the best representation of the embodiments of the application.

[0047] Figure 1 The distribution of discrete points in the Cartesian coordinate system of the application.

[0048] Figure 2 The distribution of discrete points in the Cartesian coordinate system of the application after mapping.

[0049] Figure 3 The structure of the application.

[0050] Figure 4 The timing diagram of the modulation signal and the trigger signal of the application. DETAILED DESCRIPTION

[0051] The following discussion of the preferred embodiment of the application now will be made with reference to the accompanying drawings. But it is to be understood that numerous specific details can be used, and changes can be made in the preferred embodiment of the application set forth in the accompanying description which should not be read as a limitation of the application. Rather, these details are included to provide what is believed to be the best representation of the embodiments of the application.

[0052] The application regards three-way interference signals as spatial discrete points, replaces traditional ellipse fitting with translation and rotation projection, solves the fitting failure problem under weak signal; through strict synchronization of modulation signal and trigger signal, combined with intermittent acquisition (time length t 2), realizes the non-crosstalk parallel processing effect of multi-channel data time division multiplexing.

[0053] A multi-channel microseismic signal demodulation method, comprising the following steps: S1: acquiring three-way interference signal groups with fixed phase difference β to form discrete points P i ( x i , y i , z i ), the interference signal is represented as:

[0054] ;

[0055] wherein, a 1、 a 2、 a 3 represents the direct current bias of the signal, b 1、b 2、 b 3 represents the AC amplitude, is the phase change caused by vibration, β is the fixed phase difference.

[0056] S2: Control the phase difference by adjusting the amplitude of the modulation signal β respectively 0 and π, collect the corresponding discrete points P i and fit the spatial straight line L 1 and L 2; the parametric equation of the spatial straight line L 1 is:

[0057] .

[0058] The parametric equation of the spatial straight line L 2 is:

[0059] ;

[0060] where, i 1, i 2, i 3 is the directional vector of straight line L 1 corresponding to the coordinates; x 1, y 1, z 1 is the coordinates of any point on straight line L 1; j 1, j 2, j 3 is the directional vector of straight line L 2 corresponding to the coordinates; x 2, y 2, z 2 is the coordinates of any point on straight line L 2; t is a real parameter.

[0061] S3: Calculate the intersection point L 0 of straight lines L 1 and P 2 x 0, y0, z0) and its normal vector, construct a spatial straight line P 0 passing through the intersection point L 0 and perpendicular to the plane where the two straight lines lie; the spatial straight line L 0 is:

[0062]

[0063] At the same time k 1, k 2,k 3 satisfies the following relationship:

[0064] ;

[0065] wherein, x 0, y0, z0 are coordinates of the intersection point P 0 corresponding to the intersection point; k 1, k 2, k 3 is a direction vector of the straight line L 0. i 1, i 2, i 3 is a direction vector of the straight line L 1 corresponding to the straight line j 1, j 2, j 3 is a direction vector of the straight line L 2 corresponding to the straight line

[0066] S4: calculating an angle between the straight line L 0 and the Z-axis or the Y-axis, and constructing a rotation matrix with the X-axis as a rotation axis and the angle as a rotation angle R x ; the embodiment adopts an angle between the straight line L 0 and the Z-axis. The sine value and the cosine value of the angle between the straight line L 0 and the Z-axis are:

[0067] ;

[0068] wherein, k 1, k 2, k 3 is a direction vector of the straight line L 0.

[0069] The rotation matrix R x is expressed as:

[0070] ;

[0071] wherein, is an angle between the straight line L 0 and the Z-axis.

[0072] S5: based on the intersection point P 0 and the rotation matrix R x mapping the collected discrete points P i into discrete points P j ( x j ​, y j , z j ), and extracts the quadrature signal; the discrete point P i mapping transformation into a discrete point P j ( x j , y j , z j ) mapping relationship is:

[0073] ;

[0074] wherein, is the angle between the straight line L 0 and the Z axis; x 0, y0, z0 are the coordinates of the intersection point P 0 corresponding to; y j , z j is the quadrature signal.

[0075] S6: differential cross-multiplication operation is performed on the quadrature signal, and the phase change caused by external vibration is demodulated .

[0076] A multi-channel microseismic monitoring method based on optical fiber sensing, comprising the following steps: 1: outputting an intermittent symmetrical square wave modulation signal and an intermittent square wave trigger signal strictly synchronized therewith through a signal generation module, the modulation signal controlling a light source module to output laser light of three periodic phase states.

[0077] Step 2: distribute the modulated laser light to N sensing channels through a 1×N optical splitter.

[0078] Step 3: each sensing channel converts the phase change caused by external vibration into three interference signals with a fixed phase difference β of 120 degrees through an interferometer, and after the three interference electrical signals are converted by a photoelectric conversion module, the trigger signal controls a data acquisition module to synchronously acquire the three interference electrical signals at the rising edge of each pulse and output them to a signal processing module.

[0079] Step 4: the signal processing module processes the three interference electrical signals acquired by the N sensing channels using the above multi-channel microseismic signal demodulation method, and demodulates the phase change caused by external vibration .

[0080] The sensing channel comprises a circulator, an interferometer and a photoelectric conversion module; the interferometer adopts a Michelson interferometer comprising a coupler, a mass block, an elastomer and a Faraday rotating mirror; the time interval for the trigger signal to acquire three interference electrical signals for each pulse ist 1, the intermittent length is t 2.

[0081] A multi-channel microseismic monitoring system based on optical fiber sensing includes a signal generation module for outputting an intermittent symmetrical square wave modulation signal and an intermittent square wave trigger signal strictly synchronized therewith, each pulse rising edge of the trigger signal is synchronized with the level switching moment of the modulation signal; an optical source module for receiving the modulation signal and outputting phase-modulated laser; an optical splitter for splitting the laser output by the optical source into N paths; N sensing channels for converting external vibration signals into three-path interference electric signals; a data acquisition module for receiving the trigger signal output by the signal processing module and synchronously acquiring three-path interference electric signals; and a signal processing module for processing the acquired multi-channel three-path interference electric signals and demodulating the phase change .

[0082] Further elaborated below in conjunction with the accompanying Figures 1-4 The present application comprises a Michelson interferometer on an optical path through a 1x2 coupler and a Faraday rotating mirror, the sensing arm of the interferometer is wound on an elastomer, the reference arm is directly connected to the Faraday rotating mirror, so that the two arms have a certain arm length difference. When the interferometer senses external vibration, the optical path difference of the two arms will change, after reflection by the Faraday rotating mirror, it returns to the coupler, converges and interferes, and the vibration signal is modulated into the phase of the interference light.

[0083] In addition, the present application uses a signal generation module to generate a phase modulation signal and a synchronous trigger acquisition signal of a specific waveform, and combines time division separation technology to acquire a set of discrete signals with fixed phase difference, and the voltage values of the three signals are taken as the coordinate values of a single point in space, so that they are distributed in the space rectangular coordinate system, and finally a pair of orthogonal signals are constructed after translation, rotation and projection, and then the conventional DCM demodulation algorithm is used to realize high-precision demodulation of vibration information.

[0084] The three-path interference signal with fixed phase difference β is expressed as:

[0085] ;

[0086] Among them, a 1, a 2, a 3 represent the direct current bias of the signal, b 1, b 2, b 3 represent the alternating current amplitude, is the phase change caused by vibration, β is the fixed phase difference. Among them, the fixed phase difference βThe value is adjusted by the amplitude of the modulation signal applied to the light source.

[0087] A series of discrete points collected synchronously by the data acquisition module P i ( x i y i , z i The distribution of ) in a spatial rectangular coordinate system is as follows Figure 1 As shown. Wherein, when the phase difference... β =0 and β= When π, discrete points P i ( x i y i , z i The distribution in a spatial rectangular coordinate system consists of two intersecting straight lines, while when 0 < β When <π, discrete points P i ( x i y i , z i The distribution of these elements in a Cartesian coordinate system presents as elliptical rings of varying shapes and sizes.

[0088] A multi-channel microseismic signal demodulation method includes the following steps: Step 1: Controlling the phase difference by adjusting the amplitude of the modulation signal to zero. β =0. At this point, after collecting a series of discrete points, the direction vector can be obtained using a spatial line fitting algorithm. and any point on the line P 1( x 1, y 1, z 1), then the parametric equation of the line is expressed as:

[0089] ;

[0090] in, i 1. i 2. i 3 is a straight line L The direction vector of 1 corresponds to the coordinates; x 1. y 1. z 1 is a straight line L The coordinates of any point on 1; t The parameter is a real number.

[0091] Step 2: Adjust the amplitude of the modulation signal to control the phase difference. β= π, at this time, a series of discrete points are collected, and the direction vector of the straight line is obtained by using a spatial straight line fitting algorithm Any point on the straight line P 2( x 2, y 2, z 2) is represented by the parametric equation of the straight line as follows:

[0092] ;

[0093] Wherein, j 1, j 2, j 3 is the direction vector of the straight line L 2 corresponding to the coordinates; x 2, y 2, z 2 is the coordinates of any point on the straight line L 2; t is a real number parameter.

[0094] Step 3: the intersection point L 0( L 0, y0, z0) of the straight line P 1 and the straight line x 2 can be calculated by simultaneously solving the equations of the two straight lines in step 1 and step 2, in addition, the normal vector of the plane on which the straight line L 1 and the straight line L 2 lie can be calculated by the cross product, and the calculation formula is as follows:

[0095]

[0096] Wherein, i 1, i 2, i 3 is the direction vector of the straight line L 1 corresponding to the coordinates; j 1, j 2, j 3 is the direction vector of the straight line L 2 corresponding to the coordinates.

[0097] Therefore, Figure 1 the straight line L 0 which is perpendicular to the plane on which the straight line L 1 and the straight line P 2 lie and passes through the intersection point x 0( L 0, y0, z0) constructed in is represented as:

[0098] ;

[0099] Wherein, x0, y0, z0 is the intersection point P 0 corresponds to the coordinate; k 1, k 2, k 3 is a straight line L 0 direction vector.

[0100] And the straight line L 0 direction vector can be expressed as:

[0101] ;

[0102] wherein, i 1, i 2, i 3 is a straight line L 1 direction vector corresponds to the coordinate; j 1, j 2, j 3 is a straight line L 2 direction vector corresponds to the coordinate.

[0103] Step 4: in the rectangular coordinate system Z The direction vector of the coordinate axis can be expressed as (0, 0, 1), and according to the included angle formula, the sine value and the cosine value of the included angle between the straight line L 0 and the coordinate axis can be calculated: Z

[0104] ;

[0105] wherein, k 1, k 2, k 3 is a straight line L 0 direction vector.

[0106] Step 5: construct a rotation matrix with the X axis as the rotation axis and the included angle as the rotation angle R x :

[0107] ;

[0108] wherein, is a straight line L 0 and the included angle between the Z axis. After obtaining the rotation matrix R x and the intersection point P 0 x (y0, z0), the amplitude of the modulation signal is set so that 0 < a < π, at this time the discrete points β P i x ​​​​i , y i , z i ) in the spatial rectangular coordinate system presents different shapes and sizes of elliptical ring.

[0109] Step 6: the collected discrete points P i ( x i , y i , z i ) can be obtained after translation and rotation one-to-one mapping discrete points P j ( x j , y j , z j ) after mapping in the spatial rectangular coordinate system, the discrete points P i ( x i , y i , z i ) obtained after mapping in the spatial rectangular coordinate system, the distribution of the discrete points P j ( x j , y j , z j ) is shown in Figure 2 , and the mapping relationship is:

[0110] ;

[0111] wherein, is the angle between the straight line L 0 and the Z axis; x 0, y0, z0 are the coordinates of the intersection point P 0. y j , z j are orthogonal signals.

[0112] Step 7: the phase change caused by the interferometer due to external vibration can be directly solved by using the conventional differential cross multiplication operation (DCM demodulation algorithm) :

[0113] ;

[0114] wherein, C 0 is a fixed coefficient.

[0115] The complete hardware system optical structure is shown in Figure 3, a multi-channel microseismic monitoring system based on optical fiber sensing, comprising a signal generation module for outputting an intermittent symmetrical square wave modulation signal and an intermittent square wave trigger signal strictly synchronized therewith, each pulse rising edge of the trigger signal is synchronized with the level switching moment of the modulation signal; an optical source module for receiving the modulation signal and outputting phase-modulated laser; an optical splitter for splitting the laser output by the optical source into N paths; N sensing channels for converting external vibration signals into three-path interference electric signals; a data acquisition module for receiving the trigger signal output by the signal processing module and synchronously acquiring three-path interference electric signals; and a signal processing module for processing the acquired multi-channel three-path interference electric signals and demodulating the phase change of the signals.

[0116] The sensing channel comprises a circulator, a coupler, an optoelectronic conversion module, a mass block, an elastic body and a Faraday rotating mirror, and the coupler, the mass block, the elastic body and the Faraday rotating mirror constitute a Michelson interferometer; when external vibration causes the Michelson interferometer of the sensing channel of the plurality of channels to change in phase, the sensitive optical fiber wound on the mass block and the elastic body can pick up the vibration signal.

[0117] The working process and principle of the entire hardware system are as follows: the signal generation module outputs an intermittent symmetrical square wave modulation signal and an intermittent square wave trigger signal strictly synchronized therewith, the modulation signal controls the optical source module to output laser with three periodic phase states, the laser is distributed to N sensing channels after passing through a 1xN optical splitter, the split laser is split into sensing light and reference light after passing through the circulator and the coupler of each sensing channel in turn, and is output to the Faraday rotating mirror through the sensing arm and the reference arm of the interferometer respectively, and after being reflected by the Faraday rotating mirror, it returns to the coupler along the original route, and interference occurs in the coupler to form an interference signal.

[0118] As Figure 4 shown is the timing diagram of the modulation signal and the trigger signal of the application, since the intermittent symmetrical square wave modulation signal intermittently generates three kinds of level signals, and the voltage value can be adjusted within a certain range, the modulation signal can make the three-path interference signals output by the Michelson interferometer of each sensing channel generate 0, β and β three kinds of modulation phases, and β the value is determined by the voltage value of the modulation signal level V 0, Figure 4 The trigger signal of the application is intermittently generated in synchronization with the modulation signal, and the intermittent duration is t 2, the data acquisition module acquires interference signal data at the rising edge of the trigger signal, the time interval of continuously acquiring 3 points is t 1, and it is required that t1 < 1µs. Due to the strict matching between the modulation signal and the synchronization trigger signal, the above interference signal can output three symmetrical phase changes with a fixed phase difference. β Interference signals.

[0119] The interference signal is converted into three interference electrical signals by the photoelectric conversion module. At the rising edge of each pulse, the trigger signal controls the data acquisition module to synchronously acquire the three interference electrical signals and output them to the signal processing module. The signal processing module uses the aforementioned multi-channel micro-vibration signal demodulation method to process the three interference electrical signals acquired by the N sensing channels, demodulating the phase changes caused by external vibrations. .

[0120] The specific execution process of this invention is as follows: S1: The system is powered on, and the system waits for the light source module to start and output a laser signal with stable power for 10 seconds.

[0121] S2: Set the signal generation module to output a modulation signal and a trigger signal, and set the time interval for the level change of the modulation signal. t 1 = 0.25us, intermittent time interval t 2 = 20us.

[0122] S3: Set the voltage value of the modulation signal output by the signal generation module. V 0 = 0, that is, at this time β =0. Under the condition that the interferometer is subjected to external excitation, the data acquisition module is triggered to collect 1000 sets of discrete points. P i ( x i y i , z i A spatial line fitting algorithm is executed in a spatial rectangular coordinate system to calculate the direction vector of the line. and any point on the line P 1( x 1, y 1, z 1).

[0123] S4: Gradually adjust the voltage value of the modulation signal output by the signal generation module. V 0, making the phase of the interference signal... β =π, under the condition that the interferometer is subjected to external excitation, the data acquisition module is triggered to collect 1000 sets of discrete points. P i ( x i y i , z i A spatial line fitting algorithm is executed in a spatial rectangular coordinate system to calculate the direction vector of the line. and any point on the straight line P 2 x 2, y 2, z 2).

[0124] S5: simultaneously solving the equations of the straight lines L 1 and L 2, to calculate the coordinates of the intersection point of the two straight lines P 0 x 0, y0, z0) saved in the signal processing module.

[0125] S6: using the direction vectors of the straight lines L 1 and L 2, to calculate the direction vector of the constructed straight line L 0 , then the spatial straight line L 0 is:

[0126]

[0127] Meanwhile k 1, k 2, k 3 satisfy the following relationship:

[0128] ;

[0129] wherein x 0, y0, z0 are the coordinates corresponding to the intersection point P 0; k 1, k 2, k 3 are the direction vectors of the straight line L 0; i 1, i 2, i 3 are the coordinates corresponding to the direction vectors of the straight line L 1. j 1, j 2, j 3 are the coordinates corresponding to the direction vectors of the straight line L 2.

[0130] S7: calculating the angle between the straight line L 0 and the Z-axis or the Y-axis, to construct a rotation matrix with the X-axis as the rotation axis and the angle as the rotation angle R x ; this embodiment adopts the angle between the straight line L 0 and the Z-axis. The sine value and the cosine value of the angle between the straight line L 0 and the Z-axis are:

[0131] ​ ;

[0132] wherein, k 1、 k 2、 k 3 is a direction vector of a straight line. L 0.

[0133] The rotation matrix R x is expressed as:

[0134] ;

[0135] wherein, is an angle between the straight line L 0 and the Z axis.

[0136] S8: Adjusting the voltage value of the modulation signal output by the signal generation module V 0 so that the interference signal 0 < x < π. β P i ( x i , y i , z i ), combined with the intersection coordinates P 0( x 0, y0, z0) and the rotation matrix R x based on the intersection P 0 and the rotation matrix R x The collected discrete points P i are mapped and converted into discrete points P j ( x j , y j , z j ), and the orthogonal signals are extracted; the mapping relationship of the discrete points P i is mapped and converted into discrete points P j ( x j , y j , z j ) is:

[0137] ;

[0138] wherein, is an angle between the straight line L 0 and the Z axis. x ​0, y0, z0 is the intersection point P 0 corresponding coordinate; y j , z j is the quadrature signal.

[0139] S9: take out the mapped discrete points P j x j , y j , z j ) Y-axis and Z-axis coordinate values, and using differential cross multiplication operation (DCM demodulation algorithm) to demodulate the above quadrature signal y j , z j (Y and Z-axis coordinate values of discrete points P j ) caused by external vibration phase change, the expression of the differential cross multiplication operation (DCM demodulation algorithm) is:

[0140] ;

[0141] Wherein, C 0 is a fixed coefficient.

[0142] The present application regards three-way interference signal as a spatial discrete point, replaces the traditional ellipse fitting by translation and rotation projection, solves the fitting failure problem under weak signal; through strict synchronization of modulation signal and trigger signal, combined with intermittent acquisition (time length t 2), realize the non-crosstalk parallel processing effect of multi-channel data time division multiplexing. Through the spatial geometric demodulation model and synchronous time-sharing multi-channel architecture, the present application solves the industry problems of weak signal demodulation failure, noise interference and high system complexity, and provides a high reliability solution for geological disaster warning.

[0143] Although the specification has been described in detail, it should be understood that various changes, substitutions and modifications can be made without departing from the spirit and scope of the present application as defined by the appended claims. In addition, the specific embodiments described are not intended to limit the scope of the present application, and those skilled in the art can easily understand that the existing or later developed processes, machines, manufactures, compositions of matter, means, methods or steps can perform substantially the same function or obtain substantially the same result as the embodiments of the present application. Therefore, the appended claims are intended to include such processes, machines, manufactures, compositions of matter, means, methods or steps within their scope.​

Claims

1. A method for demodulating multi-channel microseismic signals, characterized in that: The method comprises the following steps: S1: collect three paths of interference signals with fixed phase difference β to form discrete points P i (x i , y i , z i ); S2: Collect the discrete points P corresponding to the phase difference β of 0 and π by adjusting the amplitude of the modulation signal i And fit the spatial straight lines L1 and L2; S3: calculating the intersection point P0(x0, y0, z0) of the straight lines L1 and L2 and the normal vector of the plane where the intersection point P0 is located, and constructing a spatial straight line L0 passing through the intersection point P0 and being perpendicular to the plane where the two straight lines are located; S4: calculate the angle between the straight line L0 and the Z-axis or the Y-axis, and construct a rotation matrix R with the X-axis as the rotation axis and the angle as the rotation angle x ; S5: based on the intersection point P0 and the rotation matrix R x The collected discrete points P i Mapping is converted into discrete points P j (x j , y j , z j ), and the orthogonal signal is extracted; S6: performing differential cross-multiplication operation on the quadrature signal to demodulate the phase change caused by the external vibration 2. The method of claim 1, wherein: The interference signal in the S1 is represented as: wherein a1, a2, a3 represent the DC bias of the signal, b1, b2, b3 represent the AC amplitude, for the phase change caused by the vibration, and β is a fixed phase difference.

3. The method of claim 1, wherein: The parametric equation of the spatial straight line L1 in the S2 is: The parametric equation of the spatial straight line L2 is: Wherein, i1, i2, i3 are the coordinates corresponding to the direction vector of the straight line L1; x1, y1, z1 are the coordinates corresponding to any point on the straight line L1; j1, j2, j3 are the coordinates corresponding to the direction vector of the straight line L2; x2, y2, z2 are the coordinates corresponding to any point on the straight line L2; t is a real number parameter.

4. The method of claim 1, wherein: The spatial straight line L0 of the S3 is: Meanwhile, k1, k2, k3 satisfy the following relationship: Wherein, x0, y0, z0 are the coordinates corresponding to the intersection point P0; k1, k2, k3 are the direction vector of the straight line L0; i1, i2, i3 are the coordinates corresponding to the direction vector of the straight line L1; j1, j2, j3 are the coordinates corresponding to the direction vector of the straight line L2; t is a real number parameter.

5. The method of claim 4, wherein: The sine and cosine values of the angle θ between the straight line L0 and the Z axis are: Wherein, k1, k2, k3 are the direction vector of the straight line L0.

6. The method of claim 1, wherein: The rotation matrix R x is expressed as: Wherein, θ is the angle between the straight line L0 and the Z axis.

7. The method of claim 1, wherein: The discrete point P i The mapping is converted into a discrete point P j (x j , y j , z j ) mapping relationship is: Wherein, θ is the angle between straight line L0 and Z axis; x0, y0, z0 are the coordinates corresponding to intersection point P0; y j , z j are orthogonal signals.

8. A multi-channel microseismic monitoring method based on optical fiber sensing, characterized in that: Step 1: outputting a modulating signal of an intermittent symmetrical square wave and a strictly synchronous intermittent square wave trigger signal through a signal generating module, wherein the modulating signal controls a light source module to output laser with three periodic phase states; Step 2: distributing the modulated laser to N sensing channels through a 1×N optical splitter; Step 3: each sensing channel converts the phase change caused by external vibration into three interference signals with a fixed phase difference β through an interferometer, and then converts the three interference signals into three interference electric signals through a photoelectric conversion module, and then controls the data acquisition module to synchronously collect the three interference electric signals at the rising edge of each pulse of the trigger signal and outputs the three interference electric signals to a signal processing module; Step 4: The signal processing module uses the multi-channel microseismic signal demodulation method as claimed in any one of claims 1-7 to process the three-way interference electric signals collected by N sensing channels, and demodulates the phase changes caused by external vibration 9. The multi-channel microseismic monitoring method based on fiber optic sensing of claim 8, wherein: The sensing channel comprises a circulator, an interferometer and a photoelectric conversion module; the interferometer adopts a Michelson interferometer comprising a coupler, a mass block, an elastic body and a Faraday rotating mirror; the time interval for collecting three interference electric signals at each pulse of the trigger signal is t1, and the intermittent time is t2.

10. A multi-channel microseismic monitoring system based on fiber optic sensing, characterized by: The signal generating module comprises a signal generating module for outputting a modulating signal of an intermittent symmetrical square wave and a strictly synchronous intermittent square wave trigger signal, wherein the rising edge of each pulse of the trigger signal is synchronous with the level switching time of the modulating signal; a light source module for receiving the modulating signal and outputting phase-modulated laser; an optical splitter for splitting the laser output by the light source into N paths; and N sensing channels for converting external vibration signals into three interference electric signals. The data acquisition module is used for receiving a trigger signal output by the signal processing module and synchronously collecting three-path interference electric signals. The signal processing module is used for processing the collected multi-channel three-path interference electric signals and demodulating phase change signals.

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