Optical fiber sensing intensity noise elimination method and system

Abstract

The invention discloses an optical fiber sensing intensity noise elimination method and system, and belongs to the technical field of optical fiber sensing noise suppression. Light intensity fluctuation It output by a light source is artificially enhanced by actively modulating current, and phase noise is introduced, so that discrete points pi formed by three paths of interference signals are obviously distributed in a space elliptical conical curved surface; linear interference of the intensity noise is converted into space geometric parameters through space elliptic cone curved surface fitting, linear components of the intensity noise are peeled off through mapping of a cutting plane, and a discrete point pi only reserves phase information, so that interference of the intensity noise is eliminated; and finally, a vibration signal is demodulated through an ellipse fitting algorithm and a differential cross multiplication algorithm, so that the demodulation error is remarkably reduced, and the demodulation precision is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of optical fiber sensing noise suppression, and in particular to an optical fiber sensing intensity noise elimination method and system. Background Art

[0002] In fiber-optic vibration sensors based on a 3x3 coupler solution, random intensity noise is present in the two-way interference signal output due to random fluctuations in the light source's output power or connection loss. This noise directly affects the accuracy of the ellipse fitting, causing the fitting curve to shift and, in turn, affecting the demodulated output signal.

[0003] Conventional methods for eliminating intensity noise rely on more expensive narrow-linewidth light sources, which only partially suppress high-frequency noise. Intensity division noise reduction, which uses the interference signal divided by the light source intensity fluctuation signal to eliminate intensity noise, is affected by factors such as phase delay, resulting in a noise suppression rate of less than 40% in real-world situations, failing to achieve the desired effect. Existing ellipse fitting algorithms suffer from significant phase demodulation errors when subjected to intensity noise interference. How to simultaneously eliminate the effects of intensity noise and phase delay, while achieving high-precision demodulation of micro-vibration signals using low-cost hardware, has become a pressing technical challenge in the field of high-precision fiber optic sensing. Summary of the Invention

[0004] In order to solve the above problems, a method and system for eliminating intensity noise in optical fiber sensing is provided. The present invention actively modulates the driving current of the light source to enhance the light intensity fluctuation and introduce phase noise. Combining spatial elliptical cone fitting and cutting plane mapping, the intensity noise of the light source is converted into separable spatial geometric parameters, and the discrete points are converted into phase noise through cutting plane mapping. p i Mapping to the elliptical ring formed by the cutting plane realizes the stripping of the linear component of the intensity noise, making the discrete points p i The coordinates retain only phase information, resulting in a pure, closed fitting elliptical ring. Combining the ellipse fitting algorithm with the differential cross-multiplication algorithm eliminates the offset interference of intensity noise on the ellipse fitting, solving the technical problem of intensity noise causing reduced demodulation accuracy in fiber optic vibration sensing, achieving high-precision phase demodulation and significantly improving noise suppression.

[0005] To achieve the above object, the technical solution adopted by the present invention is: a method for eliminating optical fiber sensing intensity noise, comprising the following steps: S1: actively modulating the light source driving current to make the light source output light intensity fluctuate I t Enhance and introduce phase noise , synchronously collect three-way interference signals to form discrete points; S2: Perform spatial elliptic conical surface fitting on the discrete points and solve for the vertex p 0( x 0, y 0, z 0) and the unit vector of the central axis d =( A , B , C ); S3: Select a reference point p a ( x a , y a , z a ) on the central axis, and construct a cutting plane with the unit vector of the central axis d as the normal vector; S4: Project each discrete point p i along the direction of its connection with the vertex p 0 onto the intersection line of the cutting plane and the elliptic conical surface, and calculate the coordinates of the mapped point p j ; S5: Extract the spatial coordinates of any two interfering signals corresponding to the mapped point p j , and calculate the fitting parameters through the ellipse fitting algorithm; S6: Construct an orthogonal signal pair based on the fitting parameters, and demodulate the phase change θ s .

[0006] Preferably, the light source drive current in S1 increases stepwise from the first threshold current to the second threshold current, and the increasing duration is controlled within 0.5 - 2 seconds; the number of discrete points collected synchronously > 3000, and the sampling frequency is set to ≥ 3.0 Ksps.

[0007] Preferably, the first threshold current is 90 mA, the second threshold current is 120 mA; the number of discrete points is 3200, and the sampling frequency is set to 3.2 Ksps.

[0008] Preferably, the three interfering signals in S1 are: ; Among them, a 1( I t ), a 2( I t ), a 3(I t ) is the DC bias of the three-path interference signal; b 1( I t )、 b 2( I t )、 b 3( I t ) are the AC biases of the three-path interference signals; I t is the light intensity fluctuation, θ s is the phase change; β is the fixed phase difference, is the introduced phase noise.

[0009] Preferably, the point-normal equation of the cutting plane in S3 is: ; where, A , B , C are the corresponding coordinate values of the unit vector of the central axis d ; x 0, y 0, z 0 are the corresponding coordinate values of the vertex p 0.

[0010] Preferably, the parametric equation of the straight line formed by the discrete points p i in S4 along their connection line with the vertex p 0 is: ; where t is the equation parameter, and the simultaneous solution of the parametric equation and the point-normal equation of the cutting plane gives: ; where, A , B , C are the corresponding coordinate values of the unit vector of the central axis d ; x , y , z are the corresponding coordinate values of the vertex p ; x a , y a , z a are the corresponding coordinate values of the reference point p a selected on the central axis;x i and y i and z i are the corresponding coordinate values of each discrete point p i .

[0011] Preferably, the mapping relationship of the mapping point p j in S4 satisfies: ; wherein, x j and y j and z j are the corresponding coordinate values of the mapping point p j ; x 0, y 0, z 0 are the corresponding coordinate values of the vertex p 0; x i and y i and z i are the corresponding coordinate values of each discrete point p i .

[0012] Preferably, the formula for the pair of orthogonal signals and in S6 is: ; wherein, a 1, a 2 are the DC biases of any two interference signals; b 1, b 2 are the AC biases of any two interference signals; θ s is the phase change; β is the fixed phase difference; V 1, V 1 are any two interference signals.

[0013] Preferably, the formula for the differential cross - multiplication algorithm in S6 is: ; wherein, and are the pair of orthogonal signals, θ s is the phase change.

[0014] An optical fiber sensing intensity noise cancellation system includes a light source driving module for outputting an adjustable light source driving current, an optical interference unit for sensing an external vibration signal and outputting three interference signals, a circulator, a signal acquisition unit for acquiring the three interference signals, and a signal processing unit; the optical interference unit includes a 3×3 coupler, a Faraday rotator mirror, a reference arm and a sensing arm wound around a mass block and an elastic body respectively; the signal processing unit sets the light source driving module to output a linearly increasing light source driving current to the light source, the light source outputs a laser, which enters the 3×3 coupler through the circulator and is split into sensing light, reference light and a third light, the third light is subjected to anti-reflection processing, the sensing light and the reference light respectively pass through the elastic body and the mass block and are output to the Faraday rotator mirror, and after reflection, they return along the original path to the 3×3 coupler to generate interference and output three interference signals, which are collected by the signal acquisition unit and then output to the signal processing unit, and the signal processing unit demodulates the phase change by using the intensity noise cancellation method θ s 。

[0015] Due to the above technical solutions, the present invention has the following beneficial effects

[0016] (1) The present invention actively modulates the light source driving current to enhance the light intensity fluctuation and introduce phase noise, combines spatial ellipsoidal cone surface fitting and cutting plane mapping, converts the intensity noise of the light source into separable spatial geometric parameters, and maps the discrete points p i to the elliptical ring formed by the cutting plane through cutting plane mapping, realizes the stripping of the linear component of the intensity noise, makes the discrete points p i coordinates only retain the phase information, and obtain a pure and closed fitting elliptical ring. Then, combined with the elliptical fitting algorithm and the differential cross-multiplication algorithm, the offset interference of the intensity noise on the elliptical fitting is eliminated, the technical problem of the decrease in the demodulation accuracy caused by the intensity noise in the optical fiber vibration sensing is solved, and the high-precision phase demodulation and the significant improvement of the noise suppression rate are realized

[0017] (2) The present invention actively modulates the light source driving current to artificially enhance the light intensity fluctuation of the light source output I t and introduce phase noise , so that the discrete points formed by the three interference signals p i show a significant spatial ellipsoidal cone surface distribution in space; through spatial ellipsoidal cone surface fitting, the linear interference of the intensity noise is converted into spatial geometric parameters, and the linear component of the intensity noise is stripped through the mapping of the cutting plane, so that the discrete points p iOnly the phase information is retained to eliminate the offset distortion of traditional ellipse fitting; finally, the interference of intensity noise is eliminated through the ellipse fitting algorithm and the differential cross - multiplication algorithm, significantly reducing the demodulation error and improving the demodulation accuracy.

[0018] (3) The present invention enhances the light intensity fluctuation by modulating the driving current of the light source and introduces phase noise, combines the linear components of the spatial geometry to separate the intensity noise, and realizes the suppression of the intensity noise in the full frequency band; through discrete points p i mapped onto the cutting plane to strip the linear components of the intensity noise, combines the ellipse fitting algorithm and the differential cross - multiplication algorithm to convert the intensity noise into separable spatial variables, saves the need for a narrow line - width light source, and realizes the low - cost and high - precision of fiber optic sensing. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The following details the fabrication and application of the preferred embodiments of the present invention. It should be understood that the present invention provides many applicable inventive concepts, which can be embodied in various specific environments. The specific embodiments discussed are only for illustrating the specific ways of manufacturing and using the present invention and do not limit the scope of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0020] Figure 1 It is the distribution diagram of the discrete points of the present invention on the space rectangular coordinate system.

[0021] Figure 2 It is the mapping schematic diagram of the present invention in the space rectangular coordinate system.

[0022] Figure 3 It is the structural schematic diagram of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0023] The following details the fabrication and application of the preferred embodiments of the present invention. It should be understood that the present invention provides many applicable inventive concepts, which can be embodied in various specific environments. The specific embodiments discussed are only for illustrating the specific ways of manufacturing and using the present invention and do not limit the scope of the present invention.

[0024] The present invention artificially enhances the light intensity fluctuation output by the light source by actively modulating the driving current of the light source I t and introduces phase noise , so that the discrete points composed of the three - path interference signals p i present a significant spatial elliptical conical surface distribution in space; through the fitting of the spatial elliptical conical surface, the linear interference of the intensity noise is converted into spatial geometric parameters, and the linear components of the intensity noise are stripped through the mapping of the cutting plane, so that the discrete points pi Only the phase information is retained to eliminate the offset distortion of traditional ellipse fitting; finally, the interference of intensity noise is eliminated through the ellipse fitting algorithm and the differential cross - multiplication algorithm, significantly reducing the demodulation error and improving the demodulation accuracy.

[0025] A novel method and system for eliminating intensity noise in fiber optic sensing. A balanced Michelson interferometer is formed by a 3x3 coupler and a Faraday rotator mirror on the interference optical path. The sensing arm and the reference arm of the interferometer are respectively wound around an elastomer and a mass block. When the interferometer senses external vibrations, it will cause a change in the optical path difference between the sensing arm and the reference arm. After the two beams of light are reflected by the Faraday rotator mirror, they return along the original path and converge in the 3x3 coupler to interfere. The vibration signal will be modulated into the phase of the interference light and three interference signals with a fixed phase difference β =2 π / 3 are output from the 3x3 coupler. They are respectively converted into electrical signals by photodetectors and output to the signal processing unit through the signal acquisition unit for demodulation operations by the signal processing unit. The three interference signals with a fixed phase difference can be expressed as: ; Where, a 1( I t ), a 2( I t ), a 3( I t ) are the DC biases of the three interference signals; b 1( I t ), b 2( I t ), b 3( I t ) are the AC biases of the three interference signals; I t is the light intensity fluctuation, θ s is the phase change; β is the fixed phase difference. Among them, the DC bias and the AC amplitude are both linearly related to the light intensity.

[0026] A method for eliminating intensity noise in fiber optic sensing includes the following steps: S1: Actively modulate the driving current of the light source to make the light source output light intensity fluctuation I t Enhance and introduce phase noise , and synchronously collect three interference signals to form discrete points. The three interference signals are: ; Among them, a 1( I t ), a 2( I t ), a 3( I t ) are the DC biases of the three-path interference signals; b 1( I t ), b 2( I t ), b 3( I t ) are the AC biases of the three-path interference signals; I t is the light intensity fluctuation, θ s is the phase change; β is the fixed phase difference, is the introduced phase noise. And a series of discrete points p i ( x i , y i , z i ) are distributed in the space rectangular coordinate system as Figure 1 shown.

[0027] The light source drive current increases step by step from the first threshold current to the second threshold current, and the increasing duration is controlled within 0.5 - 2 seconds; the number of synchronously collected discrete points > 3000, and the sampling frequency is set to ≥ 3.0 Ksps. In this embodiment, the first threshold current is 90 mA, the second threshold current is 120 mA; the number of discrete points is 3200, and the sampling frequency is set to 3.2 Ksps.

[0028] S2: Use the above discrete points to perform an ellipsoidal cone surface fitting in the space rectangular coordinate system, that is, perform a space ellipsoidal cone surface fitting on the discrete points, and the vertex p 0( x 0, y 0, z 0) and the unit vector of the central axis d =( A , B , C ) can be solved; S3: Select a reference point p a ( xa , y a , z a ), with the central axis unit vector d Construct a cutting plane for the normal vector, the point normal equation of the cutting plane is: ; in, A 、 B 、 C is the central axis unit vector d The corresponding coordinate values of ; x 0. y 0. z 0 is the vertex p The corresponding coordinate value of 0. The intersection line of the elliptical cone surface and the cutting plane forms an elliptical ring.

[0029] S4: Each discrete point p i Along the vertex p 0 The direction of the line is projected onto the intersection of the cutting plane and the elliptical conic surface, and the mapping point is calculated. p j Coordinates. The discrete points p i Along the vertex p 0 The parametric equation of the straight line formed by the lines is: ; in, t is the equation parameter, and the parametric equation and the point normal equation of the cutting plane are combined to obtain: ; in, A 、 B 、 C is the central axis unit vector d The corresponding coordinate values of ; x 0. y 0. z 0 is the vertex p The corresponding coordinate value of 0; x a 、 y a 、 z a Pick a reference point for the central axis p a The corresponding coordinate values of ; x i 、 y i 、 zi For each discrete point p i The corresponding coordinate values

[0030] The values obtained using the above formula t Can map the collected discrete points p i ( x i , y i , z i ) onto the elliptical ring, and the mapping relationship of the mapping points p j Satisfies: ; Where x j , y j , z j Are the corresponding coordinate values of the mapping point p j ; x 0, y 0, z 0 Are the corresponding coordinate values of the vertex p 0; x i , y i , z i Are the corresponding coordinate values of each discrete point p i . After completing the above mapping, a series of points p i ( x i , y i , z i ) Are distributed on the elliptical ring formed by the elliptical conical surface and the cutting plane, as shown in Figure 2 Shown

[0031] S5: Extract the spatial coordinates of any two interfering signals corresponding to the mapping point p j , and calculate the fitting parameters through the ellipse fitting algorithm. The any two interfering signals satisfy the formula: ; Where a 1 and a 2 Represent the DC biases of the two signals, b 1 and b 2 Are the AC amplitudesθ s is the phase change caused by vibration, β is the fixed phase difference.

[0032] Due to the fixed phase difference output by the 3x3 coupler β = 2 π / 3, it cannot be directly solved. And V 1 and V 2 satisfy the general equation of the ellipse: .

[0033] According to the two sets of data of V 1 and V 2 obtained by mapping conversion, using the ellipse fitting algorithm, the A , B , C , D , E these 5 coefficients of the general equation can be obtained, and then a 1, a 2, b 1, b 2, cos β , sin β these 6 fitting parameters can be obtained.

[0034] S6: Based on the fitting parameters, a pair of orthogonal signal pairs containing the phase information to be measured can be constructed, and the phase change can be demodulated through the differential cross multiplication algorithm θ s .

[0035] Through the above fitting parameters and the two-path interference signal formula, a pair of orthogonal signal pairs containing the phase information to be measured can be constructed. The formula of the orthogonal signal pair and is: ; wherein, a 1, a 2 are the DC biases of any two-path interference signals; b 1, b 2 are the AC biases of any two-path interference signals; θ s is the phase change; β is the fixed phase difference; V 1, V 1 are any two-path interference signals.

[0036] The formula of the differential cross multiplication algorithm is: ; wherein, and is an orthogonal signal pair, θ s is the phase change.

[0037] Such as Figure 3 A fiber optic sensing intensity noise cancellation system as shown, including a light source driving module for outputting an adjustable light source driving current, an optical interference unit for sensing an external vibration signal and outputting three interference signals, a circulator, a signal acquisition unit for collecting the three interference signals, and a signal processing unit; the optical interference unit includes a 3×3 coupler, a Faraday rotator mirror, a reference arm and a sensing arm respectively wound around a mass block and an elastic body; in this embodiment, the signal acquisition unit uses an ADC, and the signal processing unit uses an SOC.

[0038] The SOC sets the light source driving module to output a linearly increasing light source driving current to the light source. The light source outputs a laser, which enters the 3×3 coupler through the circulator and is split into sensing light, reference light, and a third light. The third light is subjected to anti-reflection processing. The sensing light and the reference light respectively pass through the elastic body and the mass block and are output to the Faraday rotator mirror. After reflection, they return along the original path to the 3×3 coupler to interfere and output three interference signals. The first interference signal enters the photodetector 1 through the circulator, and the second and third interference signals are respectively output to the photodetector 2 and the photodetector 3. The three interference signals are converted into electrical signals by the photodetector 1, the photodetector 2, and the photodetector 3 and then output to the ADC. After being collected by the ADC, they are output to the SOC, and the SOC uses the intensity noise cancellation method to demodulate the phase change θ s .

[0039] The specific implementation process of the intensity noise cancellation of the present invention is as follows: Step 1: The system is powered on. Through the SOC, a stable 120 mA current is set for the light source driving output, and wait for the light source to output a stable laser. The waiting duration is 3 seconds.

[0040] Step 2: Through the SOC, set the light source driving current output by the light source driving, which gradually increases linearly from 90 mA to 120 mA. The duration of the light source driving current change is 0.5 - 2 seconds. In this embodiment, the duration is 1 second. At the same time, set the sampling rate of the ADC to ≥3.0 Ksps. In this embodiment, the sampling rate of the ADC is set to 3.2 Ksps, and start the ADC to synchronously collect the voltage values output by the 3 photodetectors. After the current change stops, turn off the ADC collection.

[0041] Step 3: Fit the 3200 discrete numerical points collected by the ADC to an elliptic cone surface in a three-dimensional rectangular coordinate system, and calculate the vertex of the elliptic cone surface p 0( x 0, y0, z 0) and the unit vector in the direction of the central axis d =( A , B , C ).

[0042] Step 4: Select the distance vertex on the center axis p 0 is the reference point of 2 p a ( x a , y a , z a ).

[0043] Step 5: Unit vector of the central axis d Construct a cutting plane for the normal vector, the point normal equation of the cutting plane is: ; in, A 、 B 、 C is the central axis unit vector d The corresponding coordinate values of ; x 0. y 0. z 0 is the vertex p The corresponding coordinate value of 0. The intersection line of the elliptical cone surface and the cutting plane forms an elliptical ring.

[0044] Step 6: Disperse the points p i Along the vertex p 0 The direction of the line is projected onto the intersection of the cutting plane and the elliptical conic surface, and the mapping point is calculated. p j Coordinates. The discrete points p i Along the vertex p 0 The parametric equation of the straight line formed by the lines is: ; in, t is the equation parameter, and the parametric equation and the point normal equation of the cutting plane are combined to obtain: ; in, A 、 B 、 C is the central axis unit vector d The corresponding coordinate values of ; x 0. y 0.z 0 is the vertex p The corresponding coordinate value of 0; x a 、 y a 、 z a are reference points selected on the central axis p a The corresponding coordinate value of; x i 、 y i 、 z i are each discrete point p i The corresponding coordinate value of.

[0045] The t value obtained using the above formula can map the collected discrete points p i ( x i , y i , z i ) to the elliptical ring, and the mapping relationship of the mapping point p j satisfies: ; Among them, x j 、 y j 、 z j are the corresponding coordinate values of the mapping point p j ; x 0, y 0, z 0 is the vertex p The corresponding coordinate value of 0; x i 、 y i 、 z i are each discrete point p i The corresponding coordinate value of. After completing the above mapping, a series of points p i ( x i , y i , z i ) are distributed on the elliptical ring formed by the elliptic conical surface and the cutting plane, as shown in Figure 2As shown, that is, according to the collected discrete points p i , calculate 3,200 mapping points one by one p j ( x j , y j , z j ) coordinates.

[0046] Step 7: Extract the spatial coordinates of any two interfering signals corresponding to the mapping points, and calculate the fitting parameters through the ellipse fitting algorithm. The any two interfering signals satisfy the formula: p j ; ; where a 1 and a 2 represent the DC offsets of the two signals, b 1 and b 2 are the AC amplitudes, θ s is the phase change caused by vibration, β is the fixed phase difference.

[0047] Due to the fixed phase difference β = 2 π / 3 output by the 3x3 coupler, it cannot be directly solved. And V 1 and V 2 satisfy the general equation of the ellipse: .

[0048] According to the V 1 and V 2 sets of data obtained by mapping conversion, using the ellipse fitting algorithm, the A , B , C , D , E of the general equation can be obtained. After these 5 coefficients, the a 1, a 2, b 1, b 2, cos β , sin β these 6 fitting parameters can be obtained.

[0049] Step 8: Save the vertices of the elliptic conical surface mentioned above p 0 , the unit vector of the central axis d , the reference point selected on the central axis p a, and after obtaining the six fitting parameters by ellipse fitting, set the ADC sampling rate to 32 Ksps and start the ADC to collect three-channel interference signals in real time.

[0050] Step 9: The ADC collects 320 data points every 10 ms as a frame of data. The SOC calculates a frame of mapping points according to the relevant formula of the above-mentioned optical fiber sensing intensity noise elimination method. p j ( x j , y j , z j ).

[0051] Step 10: Take any two channels of data from this frame of data and combine the six fitting parameters obtained by ellipse fitting to construct an orthogonal signal pair, and then use the differential cross-multiplication algorithm to demodulate the phase change. θ s . That is, through the above-mentioned fitting parameters and the two-channel interference signal formula, a pair of orthogonal signal pairs containing the phase information to be measured can be constructed. The orthogonal signal pair and The formula is: ; Among them, a 1, a 2 are the DC biases of any two-channel interference signals; b 1, b 2 are the AC biases of any two-channel interference signals; θ s is the phase change; β is the fixed phase difference; V 1, V 1 are any two-channel interference signals.

[0052] The formula of the differential cross-multiplication algorithm is: ; Among them, and are the orthogonal signal pair, θ s is the phase change.

[0053] The present invention suppresses the intensity noise in the full frequency band by modulating the driving current of the light source to enhance the light intensity fluctuation and introducing phase noise, and combining the linear component of the spatial geometric separation intensity noise; through discrete points p iMap to the cutting plane to strip the linear component of the intensity noise. Combine the ellipse fitting algorithm and the differential cross-multiplication algorithm to convert the intensity noise into separable spatial variables, reduce the requirement for a narrow linewidth light source, and achieve low cost and high precision in fiber optic sensing.

[0054] Although the specification has been described in detail, it should be understood that various changes, substitutions, and alterations can be made without departing from the spirit and scope of the invention as defined by the appended claims. In addition, the specific embodiments described do not limit the scope of the invention. Those of ordinary skill in the art can easily understand based on the present invention that currently existing or later to be developed processes, machines, manufactures, compositions of matter, means, methods, or steps can perform functions substantially the same as those of the embodiments of the present invention or obtain results substantially the same as those of the embodiments of the present invention. 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 eliminating intensity noise of fiber optic sensing, characterized in that: including the following steps: S1: Actively modulate the driving current of the light source to cause fluctuations in the output light intensity of the light source I t Enhance and introduce phase noise , synchronously collect three interference signals to form discrete points; S2: Perform spatial elliptic conical surface fitting on the discrete points to solve for the vertex p 0( x 0, y 0, z 0) and the unit vector of the central axis d =( A , B , C ); S3: Select a reference point on the central axis p a ( x a , y a , z a ), construct a cutting plane with the unit vector of the central axis d as the normal vector; S4: Project each discrete point p i along the direction of its connection line with the vertex p 0 onto the intersection line of the cutting plane and the elliptic conical surface, and calculate the coordinates of the mapped point p j ; S5: Extract mapping points p j The spatial coordinates of any two corresponding interference signals are used to calculate the fitting parameters by an ellipse fitting algorithm; S6: Construct an orthogonal signal pair based on the fitting parameters, and demodulate the phase change through the differential cross-multiplication algorithm θ s 。 2. The fiber optic sensing intensity noise elimination method according to claim 1, wherein: The light source drive current of S1 increases step by step from the first threshold current to the second threshold current, and the increasing duration is controlled within 0.5 - 2 seconds; the number of discrete points collected synchronously > 3000, and the sampling frequency is set to ≥ 3.0Ksps.

3. A method for eliminating intensity noise of fiber optic sensing according to claim 2, characterized in that: The first threshold current is 90 mA, and the second threshold current is 120 mA; the number of discrete points is 3200, and the sampling frequency is set to 3.2Ksps.

4. A method for eliminating intensity noise of fiber optic sensing according to claim 1, characterized in that: The three interference signals of S1 are: Among them, a 1( I t )、 a 2( I t )、 a 3( I t ) are the DC biases of the three-path interference signals; b 1( I t )、 b 2( I t )、 b 3( I t ) are the AC biases of the three-path interference signals; I t is the light intensity fluctuation, θ s is the phase change; β is the fixed phase difference, is the introduced phase noise.

5. A method for eliminating intensity noise of fiber optic sensing according to claim 1, characterized in that: The point - normal equation of the cutting plane in S3 is: Among them, A , B , C are the corresponding coordinate values of the central axis unit vector d ; x 0, y 0, z 0 are the corresponding coordinate values of the vertex p 0.

6. The fiber optic sensing intensity noise cancellation method according to claim 1, wherein: Each discrete point in S4 p i along its connection line with the vertex p 0 the parametric equation of the straight line formed is: in, t is the equation parameter, and the parametric equation and the point normal equation of the cutting plane are combined to obtain: Among them, A , B , C are the corresponding coordinate values of the central axis unit vector d ; x 0, y 0, z 0 are the corresponding coordinate values of the vertex p 0; x a , y a , z a are the corresponding coordinate values of the reference point p a selected on the central axis; x i , y i , z i are the corresponding coordinate values of each discrete point p i .

7. A method for eliminating intensity noise of fiber optic sensing according to claim 1, characterized in that: The mapping points in S4 p j The mapping relationship satisfies: Among them, x j , y j , z j are the corresponding coordinate values of the mapping points; p j are the corresponding coordinate values of the vertex x 0, y 0, z 0; p are the corresponding coordinate values of vertex x i , y i , z i are the corresponding coordinate values of each discrete point p i .

8. A method for eliminating intensity noise of fiber optic sensing according to claim 1, characterized in that: The orthogonal signal pair in S6 and has the formula as follows: Among them, a 1. a 2 is the DC bias of any two interference signals; b 1. b 2 is the AC bias of any two interference signals; θ s is the phase change; β is the fixed phase difference; V 1. V 1 is any two interference signals.

9. The method for eliminating intensity noise of fiber optic sensing according to claim 1, wherein: The formula of the differential cross - multiplication algorithm in S6 is: Among them, and are an orthogonal signal pair, θ s is a phase change.

10. An optical fiber sensing intensity noise cancellation system, characterized in that: It includes a light source driving module for outputting an adjustable light source driving current, an optical interference unit for sensing an external vibration signal and outputting three interference signals, a circulator, a signal acquisition unit for acquiring the three interference signals, and a signal processing unit; the optical interference unit includes a 3×3 coupler, a Faraday rotator mirror, a reference arm and a sensing arm wound around a mass block and an elastic body respectively; the signal processing unit sets the light source driving module to output a linearly increasing light source driving current to the light source, the light source outputs laser light, which enters the 3×3 coupler through the circulator and is split into sensing light, reference light and a third light path, the third light path is subjected to antireflection processing, the sensing light and the reference light are respectively output to the Faraday rotator mirror through the elastic body and the mass block, and after being reflected, they return along the original path to the 3×3 coupler to interfere and output three interference signals, which are collected by the signal acquisition unit and then output to the signal processing unit, and the signal processing unit demodulates the phase change by using the intensity noise elimination method described in any one of claims 1-9 θ s 。

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