Sinusoidal phase modulation interferometer pgc demodulation method, system, device and storage medium

Abstract

The application provides a sine phase modulation interferometer PGC demodulation method, system, device and storage medium, which comprises the following steps: obtaining a sine phase modulation interferometer original interference signal; low-pass filtering the original interference signal to obtain an in-phase interference signal component with a direct current bias; mixing the carrier signal with the original interference signal, and low-pass filtering to obtain a quadrature interference signal component; based on the quadrature interference signal composed of the in-phase interference signal component and the quadrature interference signal component, performing Lissajous ellipse fitting according to the least square principle to obtain the I-axis coordinate value of the center point of the ellipse, the radius of the ellipse on the I-axis, and the radius of the ellipse on the Q-axis; performing normalization processing on the quadrature interference signal pair by using the I-axis coordinate value of the center point of the ellipse, the radius of the ellipse on the I-axis, and the radius of the ellipse on the Q-axis obtained by the Lissajous ellipse fitting; and after completing the amplitude normalization of the quadrature interference signal pair, demodulating the phase of the interference signal.

Description

Technical Field

[0001] This invention relates to the field of laser interferometry technology, specifically to a sinusoidal phase modulation interferometer (PGC) demodulation method, system, device, and storage medium. Background Technology

[0002] In recent years, sinusoidal phase modulation interferometers have been increasingly used in the measurement of weak displacement quantities such as sound waves and mechanical strain. To achieve the measurement of these weak displacement quantities, phase demodulation of the interference signal is essential. Sinusoidal phase modulation interferometers employ a PGC demodulation scheme to achieve phase demodulation of the interference signal.

[0003] There are two implementation paths for PGC demodulation schemes: the Arctangent algorithm and the DCM algorithm. Each algorithm has its advantages. The Arctangent algorithm is unaffected by fringe visibility, but its demodulation results have relatively high harmonic distortion. The DCM algorithm has low harmonic distortion, but is more sensitive to factors such as light intensity disturbances. PGC demodulation schemes often introduce nonlinear errors due to variations in laser interference signal parameters, such as interference fringe visibility, light intensity disturbances, instability in carrier modulation depth, and carrier phase delay.

[0004] To address the aforementioned issues, existing technologies have proposed a series of effective improved algorithms to eliminate phase demodulation errors based on conventional PGC demodulation algorithms, such as PGC-RCM, PGC-DSM-Atan, PGC-DCM-Atan, PGC-DSMI, PGC-Elim-B, etc.

[0005] Both conventional PGC demodulation algorithms and various improved demodulation algorithms first use first and second harmonic carrier signals to mix with the interference signal and perform low-pass filtering to obtain in-phase and quadrature interference components. For the PGC-DCM algorithm, the optimal value of the phase modulation depth C of the interference signal is 2.37 rad, which makes the product of the Bessel function values ​​J1(C)*J2(C) reach its maximum value of 0.2243, thus achieving the best signal-to-noise ratio for phase demodulation. For the PGC-Arctan algorithm, the phase modulation depth of the interference signal is required to be 2.63 rad, so that the Bessel function value J1(C) is exactly equal to J2(C), to ensure that the two quadrature interference components have the same amplitude as much as possible.

[0006] However, for sinusoidal phase modulation interferometers, since the carrier frequency is usually large, achieving a phase modulation depth of 2.37 rad or 2.63 rad would incur high equipment costs. For example, for electro-optic modulation methods, generating such a deep phase carrier for the interference signal requires expensive high-voltage amplifier drivers. In the PGC demodulation method, the in-phase component of the interference signal needs to be obtained by mixing and filtering the second-harmonic carrier signal with the original interference signal. However, the frequency doubling of the carrier signal increases the system cost and also generates some phase noise. Summary of the Invention

[0007] (a) Technical problems to be solved

[0008] To address the shortcomings of existing technologies, this invention provides a method, system, device, and storage medium for demodulating a sinusoidal phase modulation interferometer (PGC). This solves the problem mentioned in the background art, where the in-phase component of the interference signal in the PGC demodulation method for a sinusoidal phase modulation interferometer requires mixing and filtering with a second-harmonic carrier signal to obtain the original interference signal. However, the frequency doubling of the carrier signal increases system costs and also generates phase noise.

[0009] (II) Technical Solution

[0010] To achieve the above objectives, the present invention provides the following technical solution:

[0011] A sinusoidal phase modulation interferometer (PGC) demodulation method includes:

[0012] Acquire the original interference signal from the sinusoidal phase-modulated interferometer;

[0013] The original interference signal is low-pass filtered to obtain in-phase interference signal components with DC bias;

[0014] Orthogonal interference signal components are obtained by mixing the carrier signal with the original interference signal and low-pass filtering.

[0015] Based on the orthogonal interference signal pair composed of in-phase interference signal components and orthogonal interference signal components, Lissajous ellipse fitting is performed according to the least squares principle to obtain the I-axis coordinates of the center point of the ellipse, the radius of the ellipse on the I-axis, and the radius on the Q-axis.

[0016] The center point I-axis coordinates of the ellipse obtained by Lissajous ellipse fitting, the radius of the ellipse on the I-axis, and the radius of the ellipse on the Q-axis are normalized to the orthogonal interference signal pairs.

[0017] After normalizing the amplitude of the orthogonal interference signal pairs, demodulation of the interference signal phase is performed.

[0018] Preferably, the step of low-pass filtering the original interference signal to obtain in-phase interference signal components with DC bias; and using the carrier signal to mix and low-pass filter the original interference signal to obtain orthogonal interference signal components; includes:

[0019] Suppose the driving signal of the phase modulator has the form of a sine wave with a frequency of ω. c If the phase is θ, then the phase of the interference signal will generate a frequency ω. c Sine wave carrier;

[0020] Let the measured displacement be d(t), then the interference signal S(t) has the following form:

[0021]

[0022] In the formula, S0 is the DC bias of the interference signal, S1 is the amplitude of the AC component; C is the phase modulation depth related to the driving intensity of the phase modulator; k is the wave number, k=2π / λ, and λ is the wavelength of the laser beam; The initial phase caused by the initial optical path difference between the measuring arm and the reference arm;

[0023] Let the demodulated phase be By using the identity of the first-order Bessel function and related trigonometric formulas, the interference signal (1) is decomposed into the sum of each harmonic term, thus obtaining the decomposed interference signal:

[0024]

[0025] In the formula, J n This represents an nth-order Bessel function of the first kind, where n is a positive integer; the decomposed interference signal already contains in-phase components. The in-phase component can be extracted directly from the original interference signal using filtering methods;

[0026] Orthogonal components are obtained by mixing and filtering the carrier signal with the original interference signal, resulting in orthogonal interference signal component pairs:

[0027]

[0028] In the formula, α0, α1, and α2 are the low-pass filter gain coefficients, I(t) is the in-phase interference signal component, and Q(t) is the orthogonal interference signal component.

[0029] Preferably, the orthogonal interference signal pair composed of in-phase interference signal components and orthogonal interference signal components is fitted with a Lissajous ellipse according to the least squares principle to obtain the coordinates of the center point on the I-axis, the radius of the ellipse on the I-axis, and the radius on the Q-axis; including:

[0030] The in-phase interference signal component I(t) is used as the abscissa value of the Lissajous figure point, and the orthogonal interference signal component Q(t) is used as the ordinate value of the Lissajous figure point;

[0031] Within an observation time of N s, after sampling at a sampling frequency of fs Hz, the resulting orthogonal interference signal pairs can form Nf s A point of Lisaru;

[0032] Let the k-th point P k The coordinates are (i k ,q k );

[0033] In a two-dimensional coordinate system (let the abscissa be i and the ordinate be q), the ellipse has the following equation:

[0034] i 2 +Aiq+Bq 2 +Ci+Dq+E=0 (6)

[0035] In the formula, A, B, C, D, and E are real coefficients. For Nf s Given ∑ Lissajous points, and according to the least squares principle, let the objective function for least squares fitting be:

[0036]

[0037] For function F to reach its minimum value, the solutions A, B, C, D, and E must satisfy the following:

[0038]

[0039] After obtaining the values ​​of A, B, C, D, and E, the complete equation of the Lissajous ellipse can be obtained. Then, the abscissa offset I of the Lissajous ellipse parameter... c ellipse I-axis radius r i and Q-axis radius r q The calculation formula is as follows:

[0040]

[0041] Preferably, the normalization of the orthogonal interference signal pairs using the center point I-axis coordinates of the ellipse obtained by Lissajous ellipse fitting, the radius of the ellipse on the I-axis, and the radius on the Q-axis includes:

[0042] The Lissajous ellipse is translated by coordinates, and then the coordinates of each point are multiplied by the correction factor to scale its major and minor axes to 1. Finally, the Lissajous figure of the orthogonal interference signal pair is corrected to a perfect circle. The normalization calculation formula is shown in Equation (5).

[0043]

[0044] Preferably, the demodulation of the phase of the interference signal after the amplitude normalization of the orthogonal interference signal pair is completed includes: after the amplitude normalization of the orthogonal interference signal pair is completed, demodulation of the phase of the interference signal is achieved by using Arctangent or differential cross multiplication.

[0045] The present invention also provides a sinusoidal phase modulation interferometer PGC demodulation system, comprising:

[0046] Raw interference signal acquisition module: used to acquire the raw interference signal of the sinusoidal phase modulation interferometer;

[0047] Orthogonal interference signal pair calculation module: used to low-pass filter the original interference signal to obtain in-phase interference signal components with DC bias;

[0048] Orthogonal interference signal components are obtained by mixing the carrier signal with the original interference signal and low-pass filtering.

[0049] Lissajous ellipse fitting module: used to perform Lissajous ellipse fitting based on the least squares principle on orthogonal interference signal pairs composed of in-phase interference signal components and orthogonal interference signal components, to obtain the I-axis coordinates of the center point of the ellipse, the radius of the ellipse on the I-axis, and the radius of the ellipse on the Q-axis.

[0050] The center point I-axis coordinates of the ellipse obtained by Lissajous ellipse fitting, the radius of the ellipse on the I-axis, and the radius of the ellipse on the Q-axis are normalized to the orthogonal interference signal pairs.

[0051] Phase demodulation module: Used to demodulate the phase of the interference signal after the amplitude of the orthogonal interference signal pair is normalized.

[0052] The present invention also provides a sinusoidal phase modulation interferometer PGC demodulation device, comprising: a memory and a processor, characterized in that the memory stores a computer program, and the processor is configured to execute the method as described in any of the preceding claims through the computer program.

[0053] The present invention also provides a computer-readable storage medium comprising a stored program, wherein the program, when executed, performs the method as described in any of the preceding claims.

[0054] Beneficial effects

[0055] This invention provides a method, system, device, and storage medium for demodulating a sinusoidal phase modulation interferometer (PGC). It offers the following advantages:

[0056] This invention proposes a simpler phase-generating carrier signal demodulation scheme for sinusoidal phase-modulated laser interferometers. It eliminates the need for the second harmonic signal of the carrier wave in demodulation and is considered to have lower implementation cost and higher signal-to-noise ratio. Unlike conventional PGC demodulation schemes, this scheme obtains in-phase interference signal components with DC bias by low-pass filtering the original SPMI interference signal. Orthogonal interference signal components are obtained by mixing the carrier signal and the interference signal and then low-pass filtering. The Lissajous figures formed by these two orthogonal interference signal components are ellipses centered outside the origin. Fitting this ellipse is used to translate and normalize the amplitude of the orthogonal interference signal pairs. Finally, phase demodulation of the interference signal is achieved using the Arctangent algorithm or differential cross-multiplication. Attached Figure Description

[0057] Figure 1 This is a schematic diagram of a sinusoidal phase modulation interferometer.

[0058] Figure 2 A flowchart of a sinusoidal phase modulation interferometer PGC demodulation method is provided for this invention;

[0059] Figure 3 A schematic diagram of a sinusoidal phase modulation interferometer PGC demodulation system is provided for this invention;

[0060] Figure 4 The Lissajous figures of the orthogonal interference signal components before and after normalization;

[0061] Figure 5 (a) and (b) show the phase demodulation results of the PGC-Arctan algorithm, and (c) and (d) show the phase demodulation results of the PGC-DCM algorithm. Detailed Implementation

[0062] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention.

[0063] Regardless of whether it uses an all-fiber structure or a discrete component structure, the measurement principle of a sinusoidal phase-modulated interferometer is the same. A typical sinusoidal phase-modulated interferometer structure is as follows: Figure 1 As shown:

[0064] The frequency-stabilized laser beam emitted by the He-Ne laser becomes linearly polarized light after passing through polarizer P. This linearly polarized light is then split into measurement light and reference light by beam splitter BS. The measurement light returns to the beam splitter after passing through the moving measurement mirror M2, while the reference light is modulated by phase modulator PM and returns to the beam splitter after passing through mirror M1. The two beams interact and produce light interference. The photodetector converts the optical interference signal into an electrical signal.

[0065] This invention provides a method for demodulating a sinusoidal phase modulation interferometer (PGC), comprising:

[0066] S1 acquires the original interference signal from the sinusoidal phase-modulated interferometer;

[0067] Suppose the driving signal of the phase modulator has the form of a sine wave with a frequency of ω. c If the phase is θ, then the phase of the interference signal will generate a frequency ω. c Sinusoidal carrier wave. Let the measured displacement be d(t), then the interference signal S(t) has the following form:

[0068]

[0069] In the formula, S0 is the DC bias of the interference signal, S1 is the amplitude of the AC component; C is the phase modulation depth related to the driving intensity of the phase modulator; k is the wave number, k=2π / λ, and λ is the wavelength of the laser beam; The initial phase is caused by the initial optical path difference between the measuring arm and the reference arm.

[0070] To measure displacement, the AC component of the interference signal must be demodulated in phase. Obtaining orthogonal interference signal pairs is key to achieving phase demodulation. Let the demodulated phase be... And by using the identity of the first-order Bessel function and related formulas of trigonometric functions, the interference signal (1) is decomposed into the sum of each harmonic term, then:

[0071]

[0072] In the formula, J n Let represent the nth-order Bessel function of the first kind, where n is a positive integer. By mixing the first and second harmonic carrier signals with an amplitude of 1V and the interference signal S(t), and then passing the mixture through a low-pass filter, the following two orthogonal interference signal components can be obtained (assuming the filter has ideal filtering performance):

[0073]

[0074] In the formula, Δθ represents the carrier phase delay, which is the phase difference between the carrier signal and the phase carrier of the interference signal involved in the mixing calculation, and α is a coefficient related to the amplitude of the carrier signal and the performance of the filter.

[0075] S2 performs low-pass filtering on the original interference signal to obtain in-phase interference signal components with DC bias;

[0076] S3 uses the carrier signal and the original interference signal to perform frequency mixing and low-pass filtering to obtain orthogonal interference signal components;

[0077] Preferably, the step of low-pass filtering the original interference signal to obtain in-phase interference signal components with DC bias; and using the carrier signal to mix and low-pass filter the original interference signal to obtain orthogonal interference signal components; includes:

[0078] Suppose the driving signal of the phase modulator has the form of a sine wave with a frequency of ω. c If the phase is θ, then the phase of the interference signal will generate a frequency ω. c Sine wave carrier;

[0079] Let the measured displacement be d(t), then the interference signal S(t) has the following form:

[0080]

[0081] In the formula, S0 is the DC bias of the interference signal, S1 is the amplitude of the AC component; C is the phase modulation depth related to the driving intensity of the phase modulator; k is the wave number, k=2π / λ, and λ is the wavelength of the laser beam; The initial phase caused by the initial optical path difference between the measuring arm and the reference arm;

[0082] Let the demodulated phase be By using the identity of the first-order Bessel function and related trigonometric formulas, the interference signal (1) is decomposed into the sum of each harmonic term, thus obtaining the decomposed interference signal:

[0083]

[0084] In the formula, J n This represents an nth-order Bessel function of the first kind, where n is a positive integer; the decomposed interference signal already contains in-phase components. The in-phase component can be extracted directly from the original interference signal using filtering methods;

[0085] Orthogonal components are obtained by mixing and filtering the carrier signal with the original interference signal, resulting in orthogonal interference signal component pairs:

[0086]

[0087] In the formula, α0, α1, and α2 are the low-pass filter gain coefficients, I(t) is the in-phase interference signal component, and Q(t) is the orthogonal interference signal component.

[0088] As shown in equation (4), the in-phase interference signal component also includes a DC bias α0S0. Furthermore, due to factors such as the different frequency response coefficients of the filters, the phase modulation depth C not being precisely equal to 1.4348 rad leading to J0(C) not being precisely equal to J1(C), and the carrier phase delay Δθ, the amplitude of the in-phase interference signal component generated by the aforementioned method will not be equal to the amplitude of the orthogonal interference signal component. Therefore, the Lissajous figure drawn using these two orthogonal interference signal components will be an ellipse with its center deviating from the origin.

[0089] S4 uses the orthogonal interference signal pair composed of in-phase interference signal components and orthogonal interference signal components to perform Lissajous ellipse fitting according to the least squares principle, and obtains the I-axis coordinates of the center point of the ellipse, the radius of the ellipse on the I-axis, and the radius on the Q-axis.

[0090] S5 uses the I-axis coordinates of the center point of the ellipse obtained by Lissajous ellipse fitting, the radius of the ellipse on the I-axis, and the radius of the ellipse on the Q-axis to normalize the orthogonal interference signal pairs.

[0091] After S6 completes the amplitude normalization of the orthogonal interference signal pairs, it demodulates the phase of the interference signals.

[0092] Preferably, the orthogonal interference signal pair composed of in-phase interference signal components and orthogonal interference signal components is fitted with a Lissajous ellipse according to the least squares principle to obtain the coordinates of the center point on the I-axis, the radius of the ellipse on the I-axis, and the radius on the Q-axis; including:

[0093] The in-phase interference signal component I(t) is used as the abscissa value of the Lissajous figure point, and the orthogonal interference signal component Q(t) is used as the ordinate value of the Lissajous figure point;

[0094] Within an observation time of N s, after sampling at a sampling frequency of fs Hz, the resulting orthogonal interference signal pairs can form Nf s A point of Lisaru;

[0095] Let the k-th point P k The coordinates are (i k ,q k );

[0096] In a two-dimensional coordinate system (let the abscissa be i and the ordinate be q), the ellipse has the following equation:

[0097] i 2 +Aiq+Bq 2 +Ci+Dq+E=0 (6)

[0098] In the formula, A, B, C, D, and E are real coefficients. For Nf sGiven ∑ Lissajous points, and according to the least squares principle, let the objective function for least squares fitting be:

[0099]

[0100] For function F to reach its minimum value, the solutions A, B, C, D, and E must satisfy the following:

[0101]

[0102] After obtaining the values ​​of A, B, C, D, and E, the complete equation of the Lissajous ellipse can be obtained. Then, the abscissa offset I of the Lissajous ellipse parameter... c ellipse I-axis radius r i and Q-axis radius r q The calculation formula is as follows:

[0103]

[0104] Preferably, the normalization of the orthogonal interference signal pairs using the center point I-axis coordinates of the ellipse obtained by Lissajous ellipse fitting, the radius of the ellipse on the I-axis, and the radius on the Q-axis includes:

[0105] The Lissajous ellipse is translated by coordinates, and then the coordinates of each point are multiplied by the correction factor to scale its major and minor axes to 1. Finally, the Lissajous figure of the orthogonal interference signal pair is corrected to a perfect circle. The normalization calculation formula is shown in Equation (5).

[0106]

[0107] Preferably, the demodulation of the phase of the interference signal after the amplitude normalization of the orthogonal interference signal pair is completed includes: after the amplitude normalization of the orthogonal interference signal pair is completed, demodulation of the phase of the interference signal is achieved by using Arctangent or differential cross multiplication.

[0108] The present invention also provides a sinusoidal phase modulation interferometer PGC demodulation system, comprising:

[0109] Raw interference signal acquisition module: used to acquire the raw interference signal of the sinusoidal phase modulation interferometer;

[0110] Orthogonal interference signal pair calculation module: used to low-pass filter the original interference signal to obtain in-phase interference signal components with DC bias;

[0111] Orthogonal interference signal components are obtained by mixing the carrier signal with the original interference signal and low-pass filtering.

[0112] Lissajous ellipse fitting module: used to perform Lissajous ellipse fitting based on the least squares principle on orthogonal interference signal pairs composed of in-phase interference signal components and orthogonal interference signal components, to obtain the I-axis coordinates of the center point of the ellipse, the radius of the ellipse on the I-axis, and the radius of the ellipse on the Q-axis.

[0113] The center point I-axis coordinates of the ellipse obtained by Lissajous ellipse fitting, the radius of the ellipse on the I-axis, and the radius of the ellipse on the Q-axis are normalized to the orthogonal interference signal pairs.

[0114] Phase demodulation module: Used to demodulate the phase of the interference signal after the amplitude of the orthogonal interference signal pair is normalized.

[0115] The present invention also provides a sinusoidal phase modulation interferometer PGC demodulation device, comprising: a memory and a processor, characterized in that the memory stores a computer program, and the processor is configured to execute the method as described in any of the preceding claims through the computer program.

[0116] The present invention also provides a computer-readable storage medium comprising a stored program, wherein the program, when executed, performs the method as described in any of the preceding claims.

[0117] It can be observed from the decomposed interference signal (2) that the interference signal (2) already contains in-phase components. This component can be clearly distinguished from other high-frequency components. Therefore, the in-phase component can be directly extracted from the original interference signal using filtering methods. Orthogonal components can be obtained by mixing and filtering the carrier signal with the original interference signal. Thus, the orthogonal interference signal component pairs can be obtained, as shown in equation (4).

[0118]

[0119] In the formula, α0, α1, and α2 are the low-pass filter gain coefficients. From equation (4), it can be seen that the in-phase interference signal component also includes a DC bias α0S0. Furthermore, due to the different frequency response coefficients of the filters, the phase modulation depth C not being precisely equal to 1.4348 rad leading to J0(C) not being precisely equal to J1(C), and the carrier phase delay Δθ, the amplitude of the in-phase interference signal component generated by the aforementioned method will not be equal to the amplitude of the orthogonal interference signal component. Therefore, the Lissajous figure drawn using these two orthogonal interference signal components will be an ellipse with its center deviating from the origin. Fitting this ellipse, the coordinate value of the center point I-axis of the ellipse is I... c The radius of the ellipse on the I-axis is r i The radius on the Q-axis is r qThe three parameters of the Lissajous ellipse can be used to normalize the orthogonal interference signal pairs. First, the coordinates of the Lissajous ellipse are translated, and then the coordinates of each point are multiplied by the correction coefficient to scale its major and minor axes to 1, thus correcting the Lissajous figure of the orthogonal interference signal pairs to a perfect circle. The normalization calculation formula is shown in Equation (5).

[0120]

[0121] To verify the accuracy of the proposed PGC phase demodulation mechanism and normalization algorithm, numerical simulation studies were conducted. Assuming the measured displacement d(t) is a sinusoidally varying displacement, the design values ​​of the relevant parameters of the interference signal in the numerical simulation are shown in Table 1.

[0122] Table 1 Main Simulation Parameters

[0123]

[0124] The simulated interference signal is constructed using equation (1), and the orthogonal interference signal components I(t) and Q(t) are obtained using the sinusoidal phase modulation interferometer PGC demodulation method provided in this invention. Finally, the amplitude normalization of the orthogonal interference signal components is achieved by using Lissajous ellipse fitting.

[0125] like Figure 4 The figure shows the Lissajous figures of the orthogonal interference signal components before and after normalization. Before normalization, the Lissajous figure of the orthogonal interference signal components is an ellipse with its center off from the origin. After normalization, the Lissajous figure is a perfect circle with its center at the origin and a radius of 1.

[0126] Phase demodulation is performed using the normalized orthogonal interference signal components, such as... Figure 5 (a) and (b) show the phase demodulation results of the PGC-Arctan algorithm. Figure 5 (c) and (d) show the phase demodulation results of the PGC-DCM algorithm. Figure 5 It can be seen that, apart from the different operating points of the interference signals, both algorithms can accurately demodulate the measured displacement. Furthermore, after normalizing the orthogonal interference signal components, the phase demodulation result of the PGC-DCM algorithm no longer requires gain coefficient calibration. Simulation results verify the accuracy of the method described in this invention.

[0127] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method of demodulating a sinusoidal phase modulation interferometer (PGC), characterized in that, The method comprises the following steps: obtaining a sinusoidal phase modulation interferometer original interference signal; low-pass filtering the original interference signal to obtain an in-phase interference signal component with a direct current bias; mixing the carrier signal with the original interference signal, and low-pass filtering to obtain a quadrature interference signal component, comprising: Let the driving signal of the phase modulator have the form of a sinusoidal wave with a frequency of ω c and a phase of θ, then in the phase of the interference signal a sinusoidal carrier wave with a frequency of ω c will be generated; Let the measured displacement be d(t), and the interference signal S(t) has the following form: In the formula, S0 is the direct current bias of the interference signal, S1 is the amplitude of the alternating current component; C is the phase modulation depth related to the driving strength of the phase modulator; k is the wave number, k = 2π / λ, λ is the wavelength of the laser beam; is the initial phase caused by the initial optical path difference of the measurement arm and the reference arm; Let the demodulated phase be And using the identity of the first kind of Bessel function and the trigonometric function correlation formula, the interference signal (1) is decomposed into the sum of each harmonic term, and the decomposed interference signal is obtained: In the formula, J n denotes the n-th order first kind Bessel function, n is a positive integer; the in-phase component has been contained in the decomposed interference signal The in-phase component is directly extracted from the original interference signal by using a filtering method. Mixing the carrier signal with the original interference signal, and filtering to obtain a quadrature component, obtaining a quadrature interference signal component pair: In the formula, α0, α1, α2 are low-pass filter gain coefficients, the in-phase interference signal component I(t), the quadrature interference signal component Q(t); Based on the quadrature interference signal pair composed of the in-phase interference signal component and the quadrature interference signal component, Lissajous ellipse fitting is performed according to the least square principle to obtain the I-axis coordinate value of the center point of the ellipse, the radius of the ellipse on the I-axis, and the radius of the ellipse on the Q-axis; The I-axis coordinate value of the center point of the ellipse, the radius of the ellipse on the I-axis, and the radius of the ellipse on the Q-axis obtained by Lissajous ellipse fitting are used to normalize the quadrature interference signal pair; After completing the amplitude normalization of the quadrature interference signal pair, the phase demodulation of the interference signal is performed.

2. A method of demodulating a PGC of a sinusoidal phase modulation interferometer according to claim 1, characterized in that, The method comprises the following steps: In the formula, α0, α1, α2 are low-pass filter gain coefficients, the in-phase interference signal component I(t), the quadrature interference signal component Q(t); After sampling, the orthogonal interference signal pair obtained after processing can constitute Nf s Lissajous points; Let the coordinates of the kth point P k be (i k , q k ) In the two-dimensional coordinate system, let the horizontal coordinate be i and the vertical coordinate be q, and the ellipse has the following equation: i 2 + Aiq + Bq 2 + Ci + Dq + E = 0 (6) In the formula, A, B, C, D, E are real coefficients, for Nf s For Nf Lissajous points, according to the least square principle, the objective function of the least square fitting is: In order to make the function F obtain the minimum value, the solutions of A, B, C, D, and E must satisfy: After obtaining the values of A, B, C, D, and E, the complete Lissajous ellipse equation can be obtained, and the calculation formulas of the Lissajous ellipse parameters, the horizontal coordinate offset I c , the radius r i of the I-axis of the ellipse, and the radius r q of the Q-axis are as follows:

3. A method of demodulating a PGC of a sinusoidal phase modulation interferometer according to claim 2, characterized in that, The I-axis coordinate value of the center point of the ellipse, the radius of the ellipse on the I-axis, and the radius of the ellipse on the Q-axis obtained by Lissajous ellipse fitting are used to normalize the quadrature interference signal pair, comprising: The Lissajous ellipse is translated in coordinates, and then the coordinates of each point are multiplied by a correction coefficient to scale the major and minor axes to 1, so that the Lissajous figure of the quadrature interference signal pair is corrected to a perfect circle, and the normalization calculation formula is shown in formula (5).

4. A method of demodulating a PGC of a sinusoidal phase modulation interferometer according to claim 3, characterized in that, After completing the amplitude normalization of the quadrature interference signal pair, the phase demodulation of the interference signal is performed, comprising:

5. A sinusoidal phase modulation interferometer (PGC) demodulation system, characterized by, The method comprises the following steps: An original interference signal acquisition module is configured to obtain a sinusoidal phase modulation interferometer original interference signal; A quadrature interference signal pair calculation module is configured to low-pass filter the original interference signal to obtain an in-phase interference signal component with a direct current bias; Mixing the carrier signal with the original interference signal, and low-pass filtering to obtain a quadrature interference signal component, comprising: Let the driving signal of the phase modulator have the form of a sinusoidal wave with a frequency of ω c and a phase of θ, then in the phase of the interference signal a sinusoidal carrier with a frequency of ω c will be generated. Let the measured displacement be d(t), and the interference signal S(t) has the following form: In the formula, S0 is the direct current bias of the interference signal, S1 is the amplitude of the alternating current component; C is the phase modulation depth related to the driving strength of the phase modulator; k is the wave number, k = 2π / λ, λ is the wavelength of the laser beam; is the initial phase caused by the initial optical path difference of the measurement arm and the reference arm; Let the demodulated phase be And using the identity of the first kind of Bessel function and the trigonometric function correlation formula, the interference signal (1) is decomposed into the sum of each harmonic term, and the decomposed interference signal is obtained: In the formula, J n denotes the n-th order first kind Bessel function, n is a positive integer; the in-phase component has been contained in the decomposed interference signal The in-phase component is directly extracted from the original interference signal by using a filtering method. Mixing the carrier signal with the original interference signal, and filtering to obtain a quadrature component, obtaining a quadrature interference signal component pair: In the formula, a0, a1, a2 are low-pass filter gain coefficients, I(t) is an in-phase interference signal component, Q(t) is a quadrature interference signal component; A Lissajous ellipse fitting module is configured to perform Lissajous ellipse fitting on the quadrature interference signal pair composed of the in-phase interference signal component and the quadrature interference signal component according to a least square principle, to obtain an I-axis coordinate value of a center point of the ellipse, a radius of the ellipse on the I-axis, and a radius of the ellipse on the Q-axis; The I-axis coordinate value of the center point of the ellipse, the radius of the ellipse on the I-axis, and the radius of the ellipse on the Q-axis obtained by the Lissajous ellipse fitting are used to perform normalization processing on the quadrature interference signal pair; A phase demodulation module is configured to complete amplitude normalization of the quadrature interference signal pair and then perform interference signal phase demodulation.

6. A sinusoidal phase modulation interferometer (PGC) demodulation device, characterized by The method comprises: A memory and a processor, wherein the memory stores a computer program, and the processor is configured to execute the method according to any one of claims 1 to 4 by using the computer program.

7. A computer readable storage medium, characterized in that, The computer readable storage medium comprises a stored program, wherein the program is executed to perform the method according to any one of claims 1 to 4.

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