Phase modulation depth control method and system of sinusoidal phase modulation interferometer

Abstract

The invention provides a phase modulation depth control method and system for a sinusoidal phase modulation interferometer, and relates to the technical field of phase modulation depth control, and the method comprises the steps: determining an original interference signal of a to-be-measured object through the sinusoidal phase modulation interferometer in combination with a Bessel identical equation and a trigonometric function formula; performing fast Fourier transform on the original interference signal to obtain the sum of component amplitudes of harmonic terms with carrier frequency and harmonic frequency; calculating an attenuation ratio related to the phase modulation depth according to the sum of the component amplitudes of the harmonic terms; determining an actual phase modulation depth according to the attenuation ratio; with approaching of the actual phase modulation depth and the expected phase modulation depth as a target, the actual phase modulation depth is controlled through an incremental PID algorithm, and an expected carrier frequency serving as a driving signal is output; and inputting the driving signal into the sinusoidal phase modulation interferometer to control the actual phase modulation depth. And the phase modulation depth control precision and control efficiency are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of signal demodulation, and in particular to a phase modulation depth control method and system for a sinusoidal phase modulation interferometer. Background Art

[0002] Sinusoidal phase modulation interferometer is an interferometric measurement device based on phase modulation technology. It is usually used in high-precision optical measurement, displacement measurement, vibration analysis and other applications. It uses the phase change of coherent light to generate interference fringes. Phase modulation can improve the sensitivity and measurement accuracy of the system. Sinusoidal phase modulation specifically refers to phase modulation of the interference light signal in the form of a sine wave. Phase modulation depth is a parameter that describes the degree of influence of the modulation signal on the phase shift of the carrier signal during the phase modulation (PM) process. It represents the maximum phase shift of the carrier signal due to the modulation signal.

[0003] The control of the phase modulation depth of the sinusoidal phase modulation interferometer is crucial, as it directly affects the measurement accuracy, sensitivity and stability of the system. Appropriate modulation depth can optimize the response of the system, making it more sensitive to small changes, while avoiding excessive harmonic interference and maintaining the clarity of the signal spectrum. Too small a modulation depth will lead to insufficient sensitivity, while too large a modulation depth will introduce noise and nonlinear effects, affecting the accuracy of signal demodulation. Therefore, reasonable control of the modulation depth is the key to ensuring efficient and stable operation of the interferometer.

[0004] However, the current phase demodulation process does not take into account the error between the actual phase modulation depth and the expected phase modulation depth, and the phase modulation depth cannot be accurately controlled. The phase modulation depth may fluctuate due to small changes such as modulator power instability and changes in electronic component performance, which may lead to significant errors between the demodulated phase to be measured and the actual value. Summary of the invention

[0005] In order to solve the technical problem that the error between the actual phase modulation depth and the expected phase modulation depth is not taken into account in the demodulation process of the phase to be measured in the prior art, and the phase modulation depth cannot be accurately controlled, and the phase modulation depth may fluctuate due to small changes such as unstable modulator power and changes in the performance of electronic components, which leads to a significant error between the demodulated phase to be measured and the actual value, the present invention provides a phase modulation depth control method and system for a sinusoidal phase modulation interferometer.

[0006] The technical solution provided by the embodiment of the present invention is as follows:

[0007] First aspect

[0008] An embodiment of the present invention provides a phase modulation depth control method for a sinusoidal phase modulation interferometer, comprising:

[0009] S1: Combining Bessel's identity and trigonometric function formulas, the original interference signal of the object to be measured is determined by a sinusoidal phase modulation interferometer;

[0010] S2: Perform fast Fourier transform on the original interference signal to obtain the sum of the amplitudes of the harmonic components with carrier frequency and harmonic frequency;

[0011] S3: Calculate the attenuation ratio related to the phase modulation depth according to the sum of the amplitudes of each harmonic component;

[0012] S4: determining the actual phase modulation depth according to the attenuation ratio;

[0013] S5: With the actual phase modulation depth approaching the expected phase modulation depth as the goal, the actual phase modulation depth is controlled by an incremental PID algorithm, and the expected carrier frequency is output as a driving signal;

[0014] S6: Input the driving signal to the sinusoidal phase modulation interferometer to control the actual phase modulation depth.

[0015] Second aspect

[0016] An embodiment of the present invention provides a phase modulation depth control system of a sinusoidal phase modulation interferometer, comprising:

[0017] processor;

[0018] A memory having computer-readable instructions stored thereon, wherein when the computer-readable instructions are executed by the processor, the phase modulation depth control method of the sinusoidal phase modulation interferometer as described in the first aspect is implemented.

[0019] The third aspect

[0020] An embodiment of the present invention provides a computer-readable storage medium, on which a computer program is stored. When the program is executed by a processor, the phase modulation depth control method of the sinusoidal phase modulation interferometer as described in the first aspect is implemented.

[0021] The beneficial effects brought about by the technical solution provided by the embodiment of the present invention include at least:

[0022] In the present invention, the actual phase modulation depth is obtained by fast Fourier transform, and the amplitude of each harmonic component can be directly extracted from the original interference signal of the object to be measured, and the actual phase modulation depth is accurately estimated in combination with the attenuation ratio, which does not rely on complex time domain demodulation algorithms, avoids errors caused by nonlinear effects and noise interference, and retains the high-resolution characteristics of frequency domain analysis, making the calculation of the actual phase modulation depth faster and more stable, suitable for real-time measurement and complex signal analysis. After that, the actual phase modulation depth is controlled by an incremental PID algorithm, which can dynamically adjust the drive signal according to the real-time error, gradually approach the expected phase modulation depth, quickly respond to changes in the modulation depth, reduce the steady-state error of the system, and avoid oscillations caused by over-adjustment, so that the actual phase modulation depth reaches the expected value smoothly and accurately, and ensures the stability and high precision of the control process. The phase modulation depth error caused by various factors is compensated, so that the actual phase modulation depth is stabilized within the acceptable range of the expected phase modulation depth, the phase modulation depth control accuracy is improved, and the signal demodulation accuracy is increased. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings in the following description are only some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying creative work.

[0024] Figure 1 A schematic flow chart of a phase modulation depth control method for a sinusoidal phase modulation interferometer provided in an embodiment of the present invention;

[0025] Figure 2 A schematic diagram of the structure of a sinusoidal phase modulation interferometer for measuring an original interference signal provided by an embodiment of the present invention;

[0026] Figure 3 A schematic diagram of a flow chart of a DCM algorithm for demodulating a phase to be measured provided by an embodiment of the present invention;

[0027] Figure 4 A schematic diagram of the relationship between phase modulation depth and attenuation ratio provided in an embodiment of the present invention;

[0028] Figure 5 A schematic diagram of a process for measuring phase modulation depth provided by an embodiment of the present invention;

[0029] Figure 6 A schematic diagram of a flow chart of controlling the actual phase modulation depth using an incremental PID algorithm provided in an embodiment of the present invention;

[0030] Figure 7A schematic diagram of the structure of an experimental system for testing phase modulation depth provided by an embodiment of the present invention;

[0031] Figure 8 A schematic structural diagram of a phase modulation depth control system of a sinusoidal phase modulation interferometer provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0032] The technical solution of the present invention is described below in conjunction with the accompanying drawings.

[0033] In the embodiments of the present invention, words such as "exemplarily" and "for example" are used to indicate examples, illustrations or explanations. Any embodiment or design described as "example" in the present invention should not be interpreted as being more preferred or more advantageous than other embodiments or designs. Specifically, the use of the word "example" is intended to present the concept in a specific way. In addition, in the embodiments of the present invention, the meaning expressed by "and / or" can be both, or it can be either of the two.

[0034] In order to make the technical problems, technical solutions and advantages to be solved by the present invention more clear, a detailed description will be given below with reference to the accompanying drawings and specific embodiments.

[0035] Reference Manual Attached Figure 1 , shows a flow chart of a phase modulation depth control method of a sinusoidal phase modulation interferometer provided in an embodiment of the present invention.

[0036] An embodiment of the present invention provides a phase modulation depth control method for a sinusoidal phase modulation interferometer, which can be implemented by a phase modulation depth control device for a sinusoidal phase modulation interferometer, and the phase modulation depth control device for a sinusoidal phase modulation interferometer can be a terminal or a server. The processing flow of the phase modulation depth control method for a sinusoidal phase modulation interferometer can include the following steps:

[0037] Reference Manual Attached Figure 2 , showing a structural schematic diagram of a sinusoidal phase modulation interferometer for measuring an original interference signal provided by an embodiment of the present invention.

[0038] Figure 2In the process, the laser beam output by the narrow-linewidth frequency-stabilized helium-neon laser passes through the polarizer and the quarter-wave plate and enters the beam splitter. The laser is divided into two paths on the beam splitter to form mutually perpendicular detection light and reference light. The detection light is incident on the acrylic plate, and the sound waves emitted by the speaker produce surface micro-vibrations of the same frequency on the acrylic plate. At this time, the phase of the detection light is modulated by the vibration. After the reference light is modulated by the electro-optical phase modulator, its phase generates a high-frequency carrier, which is incident on the plane reflector 2 and then returns. The detection light and the reference light meet again at the beam splitter, and optical mixing occurs to produce interference. The interference light is received by the photodetector, and the interference optical signal is converted into an electrical signal, that is, the original interference signal. The signal data is substituted into the PGC demodulation algorithm for calculation, and the result can be filtered to solve the acoustic wave vibration signal on the surface of the acrylic plate. In the entire optical path system, the main function of the polarizer and the quarter-wave plate is to prevent the reflected light from returning to the laser and avoid the return light from causing the laser power to be unstable.

[0039] S1: Combining Bessel's identity and trigonometric function formulas, the original interference signal of the object to be measured is determined by a sinusoidal phase modulation interferometer.

[0040] Among them, the Bessel function is the expansion form of the modulated signal in the Fourier series, which is used to describe the different harmonic components in the modulated signal. For example, the frequency spectrum of the modulated signal can be accurately described by the Bessel function in frequency modulation (FM) and phase modulation (PM) signals. Trigonometric function formulas such as sine and cosine formulas describe the periodic changes of fluctuations and are usually used to analyze the phase relationship of interference signals. In the interferometer, the sine and cosine function relationship of the interference signal reflects the phase difference of the light wave, which is crucial for the analysis of interference fringes and phase modulation. The advantage of combining the Bessel identity and the trigonometric function formula to obtain the original interference signal is that this method can accurately decompose the harmonic components in the interference signal, thereby effectively extracting the phase information in the interference fringes, providing a comprehensive analysis and high-precision measurement of the modulation depth, while avoiding signal distortion or spectrum confusion.

[0041] In a possible implementation, S1 specifically includes:

[0042] S101: Based on the basic principle of Michael interferometer, the interference signal is determined by sinusoidal phase modulation interferometer:

[0043] S(t)=A0+A1cos[Ccos(ω c t)+ψ(t)]

[0044] ψ(t)=2kX l sin(ω l t+ψ l )+ψ(0)

[0045] Where S(t) represents the interference signal related to time t, A0 represents the DC component amplitude related to the light intensity, A1 represents the AC component amplitude related to the optical power intensity of the reference light and the measurement light, C represents the phase modulation depth, ω c represents the sine wave carrier frequency, ψ(t) represents the phase to be measured, k represents the wave number, X l represents the disturbance amplitude of the interference signal, ω l represents the interference signal disturbance angular frequency, ψ l represents the initial phase of the interference signal disturbance, ψ(0) represents the phase difference caused by the initial optical path difference between the reference arm and the measurement arm, sin and cos represent the sine function and cosine function, respectively.

[0046] S102: Using the Bessel identity and trigonometric function formula, the interference signal is further decomposed, and the decomposed interference signal is output as the original interference signal:

[0047]

[0048] Where S'(t) represents the original interference signal, J represents the first kind of Bessel function, J0, J 2α , J 2α-1 They represent the 0th-order Bessel function, the 2αth-order Bessel function, and the 2α-1th-order Bessel function, respectively.

[0049] It should be noted that the advantage of obtaining the original interference signal by using the Bessel identity and trigonometric function formula is that it can accurately decompose the various harmonic components in the interference signal and retain the key information related to the phase modulation depth. This not only ensures the accuracy of the signal, but also improves the efficiency of signal processing, and provides a stable foundation for the subsequent phase modulation depth calculation, thereby effectively avoiding the influence of interference noise.

[0050] Reference Manual Attached Figure 3 , shows a schematic diagram of a process of demodulating a phase to be measured using a DCM algorithm provided by an embodiment of the present invention.

[0051] After obtaining the original interference signal, in order to accurately demodulate the phase to be measured, it is necessary to solve the accurate interference signal pair. The original interference signal is filtered out by the AC coupling sampling method to remove the DC component in the interference signal, and then mixed with the one-fold carrier signal cos(ω c t) and the double frequency carrier signal cos(2ω c t) for mixing. Therefore, after low-pass filtering, ignoring the carrier phase delay (the carrier phase delay can be eliminated by adjusting the initial phase of the carrier sampling signal), the orthogonal interference signal pair required for PGC demodulation is finally obtained:

[0052]

[0053] In the formula, to achieve the demodulation of phase ψ(t), the orthogonal signal pair needs to be processed. The processing methods can be divided into two types: PGC-DCM and PGC-Arctan. Figure 3 As shown in , the demodulation result of the DCM algorithm has a coefficient term in addition to the phase ψ(t) to be measured. The DCM demodulation of the interference signal pair is performed, and the result is:

[0054] DCM(Q,I)=A1 2 J1(C)J2(C)ψ(t)

[0055] The DCM de-phased result contains coefficients related to A1, J1(C) and J2(C) in the amplitude of the orthogonal signal pair. When the phase modulation depth C is equal to 2.37rad, the product of J1(C)J2(C) reaches the maximum value. At this time, the DCM demodulation result has the best signal-to-noise ratio.

[0056] The demodulation formula of the Arctan algorithm is:

[0057]

[0058] When the phase modulation depth C is controlled, That is, when J1(C) is exactly equal to J2(C), for example, when C is equal to 2.63 rad, the division result is subjected to an inverse tangent operation to demodulate the phase ψ(t) to be measured.

[0059] From the two demodulation algorithms, PGC-DCM and PGC-Arctan, it can be seen that in order to demodulate the phase to be measured with the best effect, the phase modulation depth C must be kept at a certain value. The DCM algorithm needs to keep C at 2.37rad to obtain the best signal-to-noise ratio. The Arctan algorithm needs to keep C at 2.63rad to make J1(C) exactly equal to J2(C) to eliminate the amplitude coefficient. Since the phase modulation depth C may fluctuate due to small changes such as modulator power instability and changes in electronic component performance, there may be significant errors between the demodulated phase to be measured and the actual value. To ensure the accuracy of demodulation, the phase modulation depth must be precisely controlled. In phase modulation technology, there is usually a nonlinear relationship between the phase modulation depth C and the high-frequency carrier drive voltage, and the relationship between the two is a complex positive correlation. The larger the high-frequency carrier voltage, the stronger the influence of the modulation signal on the phase of the interference signal, and the larger the modulation depth C value. Since it is difficult to achieve a one-to-one correspondence between the phase modulation depth and the high-frequency carrier voltage, and the voltage of the high-frequency carrier is affected by the direct digital synthesis (DDS) signal amplitude and the signal amplifier power and fluctuates, an effective control method is needed to stabilize the phase modulation depth C at a specific value under any external conditions. By calculating the real-time error between the actual phase modulation depth and the target phase modulation depth, when the C value deviates from the expected value, the amplitude A of the high-frequency carrier is adjusted. c size, and implements calculation tracking of C to stabilize C at a specific value.

[0060] S2: Perform fast Fourier transform on the original interference signal to obtain the sum of the amplitudes of the harmonic components with the carrier frequency and the harmonic frequency.

[0061] Among them, the Fast Fourier Transform (FFT) is an efficient algorithm for converting time domain signals into frequency domain signals. It decomposes complex time domain signals into multiple frequency components by calculating the Discrete Fourier Transform (DFT), so that we can analyze the spectral characteristics of the signal, which is much faster than directly calculating the DFT. The carrier frequency is the basic frequency in the modulated signal, usually the frequency of the unmodulated signal. It is a high-frequency signal used to carry the modulation information. In phase modulation and frequency modulation, the phase or frequency of the carrier frequency will change with the change of the modulating signal. The harmonic frequency is an integer multiple frequency of the carrier frequency. In the modulation or interference process of the signal, the harmonic frequency is the frequency component generated by the modulation or nonlinear effect. The harmonic frequency can reflect the complex frequency structure in the signal. Especially in phase modulation, the interference signal will produce multi-order harmonic frequency components. The amplitude of the harmonic component represents the signal strength or amplitude corresponding to each harmonic frequency. Through FFT, we can extract the amplitude of each frequency component, especially the harmonic components of the carrier frequency and its multiples. These amplitudes reflect the energy distribution of the signal at each frequency. Combining the frequency domain information and the characteristics of the Bessel function, the accuracy of the modulation depth calculation is improved, which can effectively avoid the interference of time domain noise and ensure the stability of the results.

[0062] In a possible implementation manner, the amplitude of the harmonic component includes the amplitude of the first harmonic component and the amplitude of the third harmonic component.

[0063] In a possible implementation, S2 specifically includes:

[0064] S201: Perform fast Fourier transform on the original interference signal to obtain the amplitude of the first harmonic component and the amplitude of the third harmonic component.

[0065]

[0066] Among them, I(Mω l +ω c ) indicates that the frequency of the interference signal is Mω l +ω c The harmonic component amplitude is the first harmonic component amplitude, I(Mω l +3ω c ) indicates that the frequency of the interference signal is Mω l +3ω c The harmonic component amplitude is the third harmonic component amplitude, M represents the integer frequency multiplication coefficient, π represents pi, ψ(0) represents the phase difference caused by the initial optical path difference between the reference arm and the measurement arm, C l represents the phase modulation depth of a given disturbance in the interference signal, where C l =2kX l , k represents the wave number, X lrepresents the disturbance amplitude of the interference signal, J1(C) represents the Bessel function with order 1 and phase modulation C as the independent variable, J M (C l ) indicates that the order is M and the phase modulation depth is C l is the Bessel function of the independent variable, || means taking the absolute value.

[0067] S202: Determine the effective frequency component at the preset phase modulation depth, and calculate the sum of the amplitude of the first harmonic component and the amplitude of the third harmonic component in the effective frequency component, and obtain the sum of the amplitude of each harmonic term component:

[0068]

[0069] Among them, M f Indicates the number of effective frequency components.

[0070] It should be noted that by extracting the component amplitudes of the first and third harmonics through fast Fourier transform (FFT), the different frequency components in the interference signal can be accurately decomposed, and the interference of noise and errors can be effectively eliminated by calculating the sum of the effective frequency components, which makes the calculation of the phase modulation depth more accurate. At the same time, the sum of the amplitudes of each harmonic provides a stable and reliable frequency domain analysis basis, which improves the system's anti-interference and measurement accuracy.

[0071] Reference Manual Attached Figure 4 , showing a schematic diagram of the relationship between a phase modulation depth and an attenuation ratio provided in an embodiment of the present invention.

[0072] Reference Manual Attached Figure 5 , shows a schematic diagram of a process for measuring phase modulation depth provided by an embodiment of the present invention.

[0073] Figure 4 In the function R, there is a correlation between the attenuation ratio and the phase modulation depth. The modulation depth can be solved according to the attenuation ratio. That is, after the carrier frequency shift, the amplitude of the low-frequency component contained in the interference signal will be enhanced or attenuated according to a specific rule, and the trend of this change depends on the phase modulation depth. Function R a It is not a monotonically increasing function over the entire domain, but in the commonly used modulation depth range (0,3.8320], R a Has an inverse function, since the function R a The inverse function of is difficult to express in analytical form, so this paper uses a lookup table method to determine the value of the modulation depth C under a specific attenuation ratio.

[0074] The Fast Fourier Transform (FFT) algorithm is used to solve the amplitude of different frequency components in the interference signal, and Ra is calculated by looking up the modulation depth C and the attenuation ratio R. a The corresponding numerical table can estimate the modulation depth C. In summary, the phase modulation depth measurement algorithm is as follows Figure 5 As shown. A divider is an electronic or digital circuit element used to perform division operations between two input signals. In a phase modulation depth control system, a divider is usually used to calculate the ratio of two physical quantities. This ratio may be the amplitude of a frequency component, the amplitude of a harmonic component, etc., which is used to further determine the modulation depth or other related parameters of the system. The amplitude of each frequency component is obtained by the FFT algorithm, and the effective low-frequency components of the interference signal are extracted according to the threshold. The sum of the amplitudes of the low-frequency components of the interference signal can be calculated, and the calculation results are Mω. l +ω c and Mω l +3ω c , then the attenuation ratio is obtained, and then the corresponding phase modulation depth is calculated. The phase modulation depth that can be detected by this measurement method ranges from 0 to 3.8320 rad, and the measurement range fully meets the actual application requirements.

[0075] S3: Calculate the attenuation ratio related to the phase modulation depth based on the sum of the amplitudes of the harmonic components.

[0076] Among them, the attenuation ratio is used to describe the ratio between the amplitudes of different frequency components (such as harmonic components) in signal processing. Specifically in phase modulation, the attenuation ratio usually refers to the amplitude ratio of harmonic terms of different orders (such as the first harmonic and the third harmonic). It is related to the phase modulation depth. Through the attenuation ratio, the relative attenuation of each harmonic component in the signal can be quantitatively described, thereby reflecting the magnitude of the modulation depth. By calculating the attenuation ratio of the amplitude of each harmonic component, the change in the phase modulation depth can be accurately reflected. This method uses frequency domain information to avoid time domain noise interference, and combines the characteristics of the Bessel function to make the calculation of the phase modulation depth more accurate and fast, effectively improving the measurement sensitivity and stability of the system.

[0077] In a possible implementation, S3 is specifically:

[0078] The attenuation ratio is obtained by calculating the ratio of the sum of the harmonic component amplitudes corresponding to the third harmonic component amplitude to the sum of the harmonic component amplitudes corresponding to the first harmonic component amplitude:

[0079]

[0080] Among them, J1(C) represents a Bessel function with an order of 1 and a phase modulation C as an independent variable, and J3(C) represents a Bessel function with an order of 3 and a phase modulation C as an independent variable.

[0081] It should be noted that the advantage of calculating the attenuation ratio by the ratio of the sum of the amplitudes of the third harmonic and the first harmonic components is that it can accurately reflect the change in the phase modulation depth, directly associate different-order Bessel functions, and avoid the complex time domain demodulation process. In addition, this method can effectively reduce the impact of noise on the measurement results, ensure the stability and accuracy of signal processing, and thus improve the estimation accuracy and real-time performance of the phase modulation depth.

[0082] S4: Determine the actual phase modulation depth according to the attenuation ratio.

[0083] Among them, the actual phase modulation depth refers to the size of the carrier phase offset actually caused by the modulated signal in the phase modulation system. It reflects the actual degree of change in the phase of the signal due to modulation during the modulation process. The actual phase modulation depth is usually obtained by measurement or calculation, and may deviate from the ideal desired modulation depth, which is affected by environmental noise, device performance, etc. The actual phase modulation depth is determined by the attenuation ratio. This method can provide high-precision modulation depth estimation through frequency domain calculation while avoiding the complexity of direct measurement, so that the system can be automatically calibrated to ensure the stability and accuracy of the measurement process.

[0084] In a possible implementation manner, S4 is specifically:

[0085] Based on the attenuation ratio, the actual phase modulation depth is obtained by looking up the table.

[0086] Reference Manual Attached Figure 6 , shows a schematic flow chart of controlling the actual phase modulation depth using an incremental PID algorithm provided in an embodiment of the present invention.

[0087] Figure 6In the figure, PMDMA (Phase Modulation Depth Measurement Algorithm): This is a phase modulation depth measurement module, which extracts the actual phase modulation depth from the modulated signal. SPMI (Signal Processing and Measurement Interface): Signal processing and measurement interface module, responsible for collecting the modulated signal and inputting it into the PMDMA module for analysis. Carrier represents the output carrier signal. The microcontroller feeds back the control quantity to the digital signal generator (DDS) to output the adjusted drive signal. The incremental PID algorithm has two parameter inputs: one is the actual value of the current phase modulation depth Cr, and the other is the expected value of the phase modulation depth Ct. The control algorithm hopes that after the phase modulation depth is controlled by PID, Cr approaches Ct, that is, the value approaches 0, so that C is stable near the expected value. The whole process is a typical closed-loop control system, which gradually approaches the target phase modulation depth by adjusting the error through the PID controller. The error gradually decreases with the measurement and adjustment of the feedback path, and finally the actual phase modulation depth matches the expected phase modulation depth.

[0088] S5: With the actual phase modulation depth approaching the expected phase modulation depth as the goal, the actual phase modulation depth is controlled by an incremental PID algorithm, and the expected carrier frequency is output as a driving signal.

[0089] Among them, the incremental PID algorithm is an algorithm that controls the system output by adjusting the proportion (P), integral (I), and differential (D). Unlike conventional PID, the incremental PID is adjusted by calculating the difference in the control quantity between two adjacent moments, avoiding the cumulative error of the control signal. The drive signal is a signal used to control the operation of the actuator (such as a modulator, oscillator, etc.) in the system. In a phase modulation system, the drive signal is usually a signal applied to a phase modulator or a carrier signal generator, which determines the output phase or carrier frequency of the modulator. The expected carrier frequency refers to the ideal carrier frequency calculated by control. It is the carrier signal frequency required by the system to achieve the target phase modulation depth. By adjusting the carrier frequency, the output phase of the system can be adjusted to ensure that the phase modulation depth approaches the expected value.

[0090] It should be noted that by dynamically adjusting the carrier frequency, the desired phase modulation depth can be approached quickly and flexibly. At the same time, the incremental PID algorithm avoids system instability caused by cumulative errors, has good real-time and anti-interference capabilities, and ensures high-precision control during phase modulation.

[0091] In one possible manner, S5 specifically includes:

[0092] S501: Calculate the phase modulation depth error between the actual phase modulation depth and the expected phase modulation depth:

[0093] ΔC=C r -C t

[0094] Among them, C r Indicates the actual phase modulation depth, C t represents the desired phase modulation depth, and ΔC represents the phase modulation depth error.

[0095] S502: Calculate the driving signal control amount through an incremental PID control algorithm according to the phase modulation depth error.

[0096] In a possible implementation, S502 specifically includes:

[0097] The drive signal amplitude is calculated using the incremental PID algorithm:

[0098] X c =K p (E0-E1)+K i E0+K d (E0-2E1+E2)

[0099] Among them, X c Represents the driving signal, K p , K i , K d They represent the proportional coefficient, integral coefficient and differential coefficient respectively, E0 represents the current phase modulation depth error, E1 represents the phase modulation depth error one sampling cycle ago, and E2 represents the phase modulation depth error two sampling cycles ago.

[0100] It should be noted that the incremental PID algorithm dynamically adjusts the amplitude of the drive signal by calculating the current and historical errors, ensuring real-time and stability in the control process. It effectively reduces the impact of cumulative errors and avoids over-adjustment, ensuring that the system can still maintain precise control and response in complex situations, and is suitable for high-precision phase modulation depth adjustment.

[0101] S503: Feedback the driving signal control amount to the digital signal generator for signal conversion, and output the driving signal, that is, the desired carrier frequency.

[0102] S504: Output a driving signal so that the actual phase modulation depth approaches the expected phase modulation depth.

[0103] It should be noted that the incremental PID algorithm can accurately calculate the phase modulation depth error and generate a drive signal, which can dynamically adjust the carrier frequency in real time so that the actual phase modulation depth gradually approaches the expected value. This process quickly responds to error changes, reduces steady-state errors and oscillations, ensures the stability and accuracy of the modulation process, and is suitable for high-precision phase modulation control systems.

[0104] S6: Input the driving signal to the sinusoidal phase modulation interferometer to control the actual phase modulation depth.

[0105] Reference Manual Attached Figure 7 , showing a schematic diagram of the structure of an experimental system for testing phase modulation depth provided by an embodiment of the present invention.

[0106] Figure 7 In the experimental system, the DDS module controlled by STM32 outputs a high-frequency sine wave of a specific amplitude, which is amplified by the signal amplifier and the high-voltage amplifier in two stages, and then drives the electro-optic phase modulator, so that the phase of the reference light generates a high-frequency carrier of a specific amplitude. The data acquisition card collects the interference signal detected by the photodetector and the drive signal output by the high-voltage amplifier, and transmits them to the computer for subsequent processing. The signal generator DDS module has four independent output channels, its DAC resolution is 14 bits, the output amplitude range that can be set is 0-750mV, and the amplitude resolution is 0.046mV. The first-level signal amplifier uses the AD623 module, the amplification factor is set to 4 times, and the second-level power amplifier gain is set to 100 times. The laser source uses a narrow-linewidth stabilized laser (Thorlab, 632.8nm) with a wavelength of 632.8nm. The modulation frequency of the electro-optic phase modulator (EO-PM-PR-C1, Thorlabs) is 30kHz. The sampling rate of the high-precision data acquisition card (USB-61210, JYTEK) is 1MHz. In the experimental system, the collected interference signal is transmitted to the computer, and the corresponding phase modulation depth C is solved using the measurement algorithm PMDMA described in this article. The data is sent to STM32 in the form of a string at a specific frequency through the RS232 serial port. The single-chip microcomputer detects in real time whether new data is received, and processes the received new data with the PID algorithm to calculate the corresponding control quantity, thereby controlling the DDS to output the actual required sinusoidal drive signal. The drive signal is amplified in the second stage and loaded into the electro-optical phase modulator to modulate the interference signal, so that the phase modulation depth of the interference signal tends to stabilize at a specific value, realizing the closed-loop operation of the entire SPMI phase modulation depth. In order to ensure the stability of the phase modulation depth calculation, a low-frequency disturbance with a frequency of 1Hz is superimposed on the signal output by the DDS.

[0107] In practical applications, the phase modulation depth of the sinusoidal phase modulation interferometer is easily affected by many factors. The phase modulation depth is measured in real time using FFT transform, and the C value is controlled by incremental PID algorithm. The phase modulation depth measurement calculation model and PID control algorithm model are established. The accuracy of the proposed phase modulation depth measurement method is verified by numerical simulation. First, the actual phase modulation depth C value is nonlinearly positively correlated with the driving signal amplitude, and under the PID closed-loop control condition, the C value can be stabilized within a specific range. When the target value is 2.63rad, the average steady-state error is 0.003rad. The PGC demodulation performance shows obvious differences when the phase modulation depth is turned on or off under the PID closed-loop control state. Secondly, by comparing the signal-to-receive / distortion ratio of the demodulation results, it can be seen that the precise control of the phase modulation depth can significantly improve the performance of the phase demodulation. Through surface micro-vibration measurement tests of different intensities, it can be seen that under the closed-loop control condition of the phase modulation depth, the signal-to-receive / distortion ratio of the vibration signal demodulation is better than 99.85%.

[0108] The beneficial effects brought about by the technical solution provided by the embodiment of the present invention include at least:

[0109] In the present invention, the actual phase modulation depth is obtained by fast Fourier transform, and the amplitude of each harmonic component can be directly extracted from the original interference signal of the object to be measured, and the actual phase modulation depth is accurately estimated in combination with the attenuation ratio, which does not rely on complex time domain demodulation algorithms, avoids errors caused by nonlinear effects and noise interference, and retains the high-resolution characteristics of frequency domain analysis, making the calculation of the actual phase modulation depth faster and more stable, suitable for real-time measurement and complex signal analysis. After that, the actual phase modulation depth is controlled by an incremental PID algorithm, which can dynamically adjust the drive signal according to the real-time error, gradually approach the expected phase modulation depth, quickly respond to changes in the modulation depth, reduce the steady-state error of the system, and avoid oscillations caused by over-adjustment, so that the actual phase modulation depth reaches the expected value smoothly and accurately, and ensures the stability and high precision of the control process. The phase modulation depth error caused by various factors is compensated, so that the actual phase modulation depth is stabilized within the acceptable range of the expected phase modulation depth, the phase modulation depth control accuracy is improved, and the signal demodulation accuracy is increased.

[0110] Reference Manual Attached Figure 8 , showing a structural schematic diagram of a phase modulation depth control system of a sinusoidal phase modulation interferometer provided by the present invention.

[0111] The present invention further provides a phase modulation depth control system 20 for a sinusoidal phase modulation interferometer, which is applied to the phase modulation depth control method of the above-mentioned sinusoidal phase modulation interferometer, comprising:

[0112] Processor 201.

[0113] The memory 202 stores computer-readable instructions. When the computer-readable instructions are executed by the processor 201, the phase modulation depth control method of the sinusoidal phase modulation interferometer in the method embodiment is implemented.

[0114] The phase modulation depth control system 20 of the sinusoidal phase modulation interferometer provided by the present invention can execute the above-mentioned phase modulation depth control method of the sinusoidal phase modulation interferometer and achieve the same or similar technical effects. To avoid repetition, the present invention will not go into details.

[0115] The beneficial effects brought about by the technical solution provided by the embodiment of the present invention include at least:

[0116] In the present invention, the actual phase modulation depth is obtained by fast Fourier transform, and the amplitude of each harmonic component can be directly extracted from the original interference signal of the object to be measured, and the actual phase modulation depth is accurately estimated in combination with the attenuation ratio, which does not rely on complex time domain demodulation algorithms, avoids errors caused by nonlinear effects and noise interference, and retains the high-resolution characteristics of frequency domain analysis, making the calculation of the actual phase modulation depth faster and more stable, suitable for real-time measurement and complex signal analysis. After that, the actual phase modulation depth is controlled by an incremental PID algorithm, which can dynamically adjust the drive signal according to the real-time error, gradually approach the expected phase modulation depth, quickly respond to changes in the modulation depth, reduce the steady-state error of the system, and avoid oscillations caused by over-adjustment, so that the actual phase modulation depth reaches the expected value smoothly and accurately, and ensures the stability and high precision of the control process. The phase modulation depth error caused by various factors is compensated, so that the actual phase modulation depth is stabilized within the acceptable range of the expected phase modulation depth, the phase modulation depth control accuracy is improved, and the signal demodulation accuracy is increased.

[0117] It should be understood that the processor in the embodiment of the present invention may be a central processing unit (CPU), and the processor may also be other general-purpose processors, digital signal processors (DSP), application specific integrated circuits (ASIC), field programmable gate arrays (FPGA) or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. The general-purpose processor may be a microprocessor or the processor may also be any conventional processor, etc.

[0118] It should also be understood that the memory in the embodiments of the present invention may be a volatile memory or a non-volatile memory, or may include both volatile and non-volatile memories. Among them, the non-volatile memory may be a read-only memory (ROM), a programmable read-only memory (PROM), an erasable programmable read-only memory (EPROM), an electrically erasable programmable read-only memory (EEPROM), or a flash memory. The volatile memory may be a random access memory (RAM), which is used as an external cache. By way of example and not limitation, many forms of random access memory (RAM) are available, such as static RAM (SRAM), dynamic random access memory (DRAM), synchronous DRAM (SDRAM), double data rate synchronous dynamic random access memory (DDR SDRAM), enhanced synchronous dynamic random access memory (ESDRAM), synchronous link DRAM (SLDRAM), and direct rambus RAM (DR RAM).

[0119] The above embodiments can be implemented in whole or in part by software, hardware (such as circuits), firmware or any other combination. When implemented using software, the above embodiments can be implemented in whole or in part in the form of a computer program product. The computer program product includes one or more computer instructions or computer programs. When a computer instruction or computer program is loaded or executed on a computer, a process or function according to an embodiment of the present invention is generated in whole or in part. The computer can be a general-purpose computer, a special-purpose computer, a computer network, or other programmable device. Computer instructions can be stored in a computer-readable storage medium, or transmitted from one computer-readable storage medium to another computer-readable storage medium. For example, computer instructions can be transmitted from one website, computer, server or data center to another website, computer, server or data center by wired (such as infrared, wireless, microwave, etc.). The computer-readable storage medium can be any available medium that can be accessed by a computer or a data storage device such as a server or data center that contains one or more available media sets. The available medium can be a magnetic medium (for example, a floppy disk, a hard disk, a tape), an optical medium (for example, a DVD), or a semiconductor medium. The semiconductor medium can be a solid-state hard disk.

[0120] It should be understood that the term "and / or" in this article is only a description of the association relationship of associated objects, indicating that there can be three relationships. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. A and B can be singular or plural. In addition, the character " / " in this article generally indicates that the associated objects before and after are in an "or" relationship, but it may also indicate an "and / or" relationship. Please refer to the context for specific understanding.

[0121] In the present invention, "at least one" means one or more, and "more than one" means two or more. "At least one of the following" or similar expressions refers to any combination of these items, including any combination of single or plural items. For example, at least one of a, b, or c can be represented by: a, b, c, ab, ac, bc, or abc, where a, b, c can be single or multiple.

[0122] It should be understood that in various embodiments of the present invention, the size of the serial numbers of the above-mentioned processes does not mean the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present invention.

[0123] Those skilled in the art will appreciate that the units and algorithm steps of each example described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are performed in hardware or software depends on the specific application and design constraints of the technical solution. Professional and technical personnel can use different methods to implement the described functions for each specific application, but such implementation should not be considered to be beyond the scope of the present invention.

[0124] Those skilled in the art can clearly understand that, for the convenience and brevity of description, the specific working processes of the above-described equipment, devices and units can refer to the corresponding processes in the aforementioned method embodiments and will not be repeated here.

[0125] In the several embodiments provided by the present invention, it should be understood that the disclosed devices, apparatuses and methods can be implemented in other ways. For example, the device embodiments described above are only schematic, for example, the division of units is only a logical function division, and there may be other division methods in actual implementation, such as multiple units or components can be combined or integrated into another device, or some features can be ignored or not executed. Another point is that the mutual coupling or direct coupling or communication connection shown or discussed can be through some interfaces, indirect coupling or communication connection of devices or units, which can be electrical, mechanical or other forms.

[0126] The units described as separate components may or may not be physically separated, and the components shown as units may or may not be physical units, that is, they may be located in one place or distributed on multiple network units. Some or all of the units may be selected according to actual needs to achieve the purpose of the solution of this embodiment.

[0127] In addition, each functional unit in each embodiment of the present invention may be integrated into one processing unit, or each unit may exist physically separately, or two or more units may be integrated into one unit.

[0128] If the function is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention, or the part that contributes to the prior art, or the part of the technical solution, can be embodied in the form of a software product. The computer software product is stored in a storage medium, including several instructions for a computer device (which can be a personal computer, server, or network device, etc.) to perform all or part of the steps of the methods of various embodiments of the present invention. The aforementioned storage medium includes: U disk, mobile hard disk, read-only memory (ROM), random access memory (RAM), disk or optical disk, etc., various media that can store program codes.

[0129] An embodiment of the present invention provides a computer-readable storage medium having a computer program stored thereon. When the program is executed by a processor, a phase modulation depth control method for a sinusoidal phase modulation interferometer as described in a method embodiment is implemented.

[0130] A computer-readable storage medium provided by the present invention can implement the steps and effects of the phase modulation depth control method of the sinusoidal phase modulation interferometer of the above method embodiment. To avoid repetition, the present invention will not go into details.

[0131] The beneficial effects brought about by the technical solution provided by the embodiment of the present invention include at least:

[0132] In the present invention, the actual phase modulation depth is obtained by fast Fourier transform, and the amplitude of each harmonic component can be directly extracted from the original interference signal of the object to be measured, and the actual phase modulation depth is accurately estimated in combination with the attenuation ratio, which does not rely on complex time domain demodulation algorithms, avoids errors caused by nonlinear effects and noise interference, and retains the high-resolution characteristics of frequency domain analysis, making the calculation of the actual phase modulation depth faster and more stable, suitable for real-time measurement and complex signal analysis. After that, the actual phase modulation depth is controlled by an incremental PID algorithm, which can dynamically adjust the drive signal according to the real-time error, gradually approach the expected phase modulation depth, quickly respond to changes in the modulation depth, reduce the steady-state error of the system, and avoid oscillations caused by over-adjustment, so that the actual phase modulation depth reaches the expected value smoothly and accurately, and ensures the stability and high precision of the control process. The phase modulation depth error caused by various factors is compensated, so that the actual phase modulation depth is stabilized within the acceptable range of the expected phase modulation depth, the phase modulation depth control accuracy is improved, and the signal demodulation accuracy is increased.

[0133] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art can easily think of changes or substitutions within the technical scope disclosed by the present invention, which should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

[0134] There are a few points to note:

[0135] (1) The drawings of the embodiments of the present invention only relate to the structures related to the embodiments of the present invention, and other structures may refer to the general design.

[0136] (2) For the sake of clarity, in the drawings used to describe the embodiments of the present invention, the thickness of the layers or regions is exaggerated or reduced, that is, these drawings are not drawn according to the actual scale. It is understood that when an element such as a layer, film, region or substrate is referred to as being "on" or "under" another element, the element may be "directly" "on" or "under" the other element or there may be intermediate elements.

[0137] (3) In the absence of conflict, the embodiments of the present invention and the features therein may be combined with each other to obtain new embodiments.

[0138] The above are only specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. The protection scope of the present invention shall be based on the protection scope of the claims.

Claims

1. A phase modulation depth control method for a sinusoidal phase modulation interferometer, characterized in that: include: S1: combining Bessel's identity and trigonometric function formulas, determining the original interference signal of the object to be measured through the sinusoidal phase modulation interferometer; S2: Performing a fast Fourier transform on the original interference signal to obtain the sum of the amplitudes of the harmonic components having the carrier frequency and the harmonic frequency; S3: Calculating the attenuation ratio related to the phase modulation depth according to the sum of the amplitudes of the harmonic components; S4: determining an actual phase modulation depth according to the attenuation ratio; S5: taking the actual phase modulation depth approaching the expected phase modulation depth as a goal, controlling the actual phase modulation depth through an incremental PID algorithm, and outputting an expected carrier frequency as a driving signal; S6: Input the driving signal to the sinusoidal phase modulation interferometer to control the actual phase modulation depth.

2. The phase modulation depth control method of the sinusoidal phase modulation interferometer according to claim 1, characterized in that: The S1 specifically includes: S101: Based on the basic principle of Michael interferometer, the interference signal is determined by sinusoidal phase modulation interferometer: S(t)=A0+A1cos[Ccos(ω c t)+ψ(t)] ψ(t)=2kX l sin(ω l t+ψ l )+ψ(0) Where S(t) represents the interference signal related to time t, A0 represents the DC component amplitude related to the light intensity, A1 represents the AC component amplitude related to the optical power intensity of the reference light and the measurement light, C represents the phase modulation depth, ω c represents the sine wave carrier frequency, ψ(t) represents the phase to be measured, k represents the wave number, X l represents the disturbance amplitude of the interference signal, ω l represents the interference signal disturbance angular frequency, ψ l represents the initial phase of the interference signal disturbance, ψ(0) represents the phase difference caused by the initial optical path difference between the reference arm and the measurement arm, sin and cos represent the sine function and cosine function respectively; S102: Using Bessel's identity and trigonometric function formulas, further decompose the interference signal, and output the decomposed interference signal as the original interference signal: Where S'(t) represents the original interference signal, J represents the first kind of Bessel function, J0, J 2α , J 2α-1 They represent the 0th-order Bessel function, the 2αth-order Bessel function, and the 2α-1th-order Bessel function, respectively.

3. The phase modulation depth control method of the sinusoidal phase modulation interferometer according to claim 1, characterized in that: The harmonic component amplitudes include a first harmonic component amplitude and a third harmonic component amplitude.

4. The phase modulation depth control method of the sinusoidal phase modulation interferometer according to claim 3, characterized in that: The S2 specifically includes: S201: performing a fast Fourier transform on the original interference signal to obtain the amplitude of the first harmonic component and the amplitude of the third harmonic component; Among them, I(Mω l +ω c ) indicates that the frequency of the interference signal is Mω l +ω c The harmonic component amplitude is the first harmonic component amplitude, I(Mω l +3ω c ) indicates that the frequency of the interference signal is Mω l +3ω c The harmonic component amplitude is the third harmonic component amplitude, M represents the integer frequency multiplication coefficient, π represents pi, ψ(0) represents the phase difference caused by the initial optical path difference between the reference arm and the measurement arm, C l represents the phase modulation depth of a given disturbance in the interference signal, where C l =2kX l , k represents the wave number, X l represents the disturbance amplitude of the interference signal, J1(C) represents the Bessel function with order 1 and phase modulation C as the independent variable, J M (C l ) indicates that the order is M and the phase modulation depth is C l is the Bessel function of the independent variable, || means taking the absolute value; S202: Determine the effective frequency component at a preset phase modulation depth, and respectively calculate the sum of the amplitude of the first harmonic component and the amplitude of the third harmonic component within the effective frequency component to obtain the sum of the amplitudes of each harmonic term component: Among them, M f Indicates the number of effective frequency components.

5. The phase modulation depth control method of the sinusoidal phase modulation interferometer according to claim 4, characterized in that: The S3 is specifically: The attenuation ratio is obtained by calculating the ratio of the sum of the harmonic component amplitudes corresponding to the amplitude of the third harmonic component to the sum of the harmonic component amplitudes corresponding to the amplitude of the first harmonic component: Among them, J1(C) represents a Bessel function with an order of 1 and a phase modulation C as an independent variable, and J3(C) represents a Bessel function with an order of 3 and a phase modulation C as an independent variable.

6. The phase modulation depth control method of the sinusoidal phase modulation interferometer according to claim 1, characterized in that: The S4 is specifically: Based on the attenuation ratio, the actual phase modulation depth is obtained by a table lookup method.

7. The phase modulation depth control method of the sinusoidal phase modulation interferometer according to claim 1, characterized in that: The S5 specifically includes: S501: Calculate the phase modulation depth error between the actual phase modulation depth and the expected phase modulation depth: ΔC=C r -C t Among them, C r Indicates the actual phase modulation depth, C t represents the desired phase modulation depth, ΔC represents the phase modulation depth error; S502: Calculating a driving signal control amount through the incremental PID control algorithm according to the phase modulation depth error; S503: Feeding back the driving signal control amount to a digital signal generator for signal conversion, and outputting the driving signal, i.e., the desired carrier frequency; S504: Output the driving signal so that the actual phase modulation depth approaches the expected phase modulation depth.

8. The phase modulation depth control method of the sinusoidal phase modulation interferometer according to claim 7, characterized in that: The S502 specifically includes: The drive signal amplitude is calculated by the incremental PID algorithm: X c =K p (E0-E1)+K i E0+K d (E0-2E1+E2) Among them, X c Represents the driving signal, K p , K i , K d They represent the proportional coefficient, integral coefficient and differential coefficient respectively, E0 represents the current phase modulation depth error, E1 represents the phase modulation depth error one sampling cycle ago, and E2 represents the phase modulation depth error two sampling cycles ago.

9. A phase modulation depth control system of a sinusoidal phase modulation interferometer, characterized in that: include: processor; A memory having computer-readable instructions stored thereon, wherein when the computer-readable instructions are executed by the processor, the phase modulation depth control method of the sinusoidal phase modulation interferometer as described in any one of claims 1 to 8 is implemented.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the program is executed by a processor, the phase modulation depth control method of the sinusoidal phase modulation interferometer according to any one of claims 1 to 8 is implemented.

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