A method for online compensation of optical rotation angle detection errors caused by optical polarization fluctuations

Abstract

A method for online compensation of optical rotation angle detection errors caused by optical polarization fluctuations is proposed. Based on the response signal of atomic spin to magnetic or optical field modulation, combined with wavelet analysis data denoising and incremental PID control algorithms, the method achieves rapid real-time compensation of optical rotation angle detection errors by changing the optical axis angle of the quarter-wave plate in the optical path. This method is reasonable, universal, and simple to operate experimentally. It is not limited by the complexity of the optical path and can be applied to various scenarios based on optical rotation angle detection systems.

Description

Technical Field

[0001] This invention relates to the field of optical detection technology for atomic sensors, and more particularly to the field of high-precision optical rotation angle detection. Specifically, it relates to a method for online compensation of optical rotation angle detection errors caused by light polarization fluctuations. This method can achieve precise control and compensation of the degree of laser polarization acting on atomic spin precession, eliminate additional atomic polarization caused by light polarization fluctuations, and thus suppress optical rotation angle detection errors. Background Technology

[0002] Optical rotation angle detection based on far-detuned linearly polarized light is a non-destructive detection method at the atomic level, widely used in cutting-edge physics exploration, quantum storage, medical health monitoring, and daily life. To suppress various low-frequency random noises, optical rotation angle detection is often used in conjunction with high-frequency modulation crystals. Optical rotation angle detection systems containing high-frequency modulators have many optical components and complex optical paths, making them more susceptible to random errors such as installation deviations and environmental noise. This causes unknown changes in the polarization degree of the laser acting on the atomic spin precession, thus affecting the accuracy and sensitivity of the optical rotation angle detection system. Currently, experimental methods to suppress optical rotation angle detection errors caused by light polarization fluctuations employ linearly polarized optical devices with high extinction ratios to ensure the polarization degree of the detection light. However, because the atoms are encapsulated within a closed magnetic shielding system, the polarization degree of the detection light acting on the atoms cannot be accurately determined. Furthermore, maintaining the linear polarization of the detection light using linearly polarized optical devices is an open-loop process, performed before experiments based on atomic spin precession magnetic measurements or inertial measurements, and cannot be performed during operation, nor can it be adjusted in a timely manner for changes in light polarization caused by environmental noise. Summary of the Invention

[0003] This invention addresses the deficiencies or shortcomings of existing technologies by proposing a method for online compensation of optical rotation angle detection errors caused by optical polarization fluctuations. This method can compensate for the polarization degree of the detected light in real time during the optical rotation angle measurement process, thereby stably and effectively suppressing optical rotation angle detection noise caused by the detected light.

[0004] The technical solution of the present invention is as follows:

[0005] A method for online compensation of optical rotation angle detection error caused by optical polarization fluctuations is characterized by utilizing the response signal of atomic spin to magnetic field or optical field modulation in the optical rotation angle detection system, as well as the difference in slope or change of the precession signal, combined with wavelet analysis data denoising and incremental PID control algorithm, to achieve rapid real-time compensation of optical rotation angle detection error by changing the optical axis angle of the 1 / 4 wave plate in the optical path in real time.

[0006] Includes the following steps:

[0007] Step A: Adjustment and calibration before measuring the optical rotation angle;

[0008] Step B: Real-time compensation in optical rotation angle measurement.

[0009] Step A includes:

[0010] Step A1: Turn on the optical rotation angle detection system, block the pump light, and align it with the detection light;

[0011] Step A2: Apply a transverse modulation magnetic field within the atomic gas cell region;

[0012] Step A3, detection and demodulation of photoelectric signals;

[0013] Step A4: Develop a response curve based on the response signal of atomic spin to magnetic field modulation, and then denoise and fit the response curve.

[0014] Step A5: Determine whether the slope of the fitted response curve is equal to zero. If it is, it means that the debugging and calibration before the optical rotation angle measurement has been completed and the process ends. If not, use the PID control module to control the 1 / 4 waveplate in the electronically controlled waveplate holder to rotate the optical axis and then return to step A4.

[0015] The optical rotation angle detection system in step A1 includes a detection laser, a detection beam shaping and intensity stabilization module, a detection linear polarization device, a detection high-frequency modulator, a quarter-wave plate with an electrically controlled waveplate holder, an atomic gas cell, a polarizer, and a photodetector arranged sequentially on the detection beam path. The photodetector is connected to a lock-in amplifier module. One path of the lock-in amplifier module is connected to the electrically controlled waveplate holder via a PID control module, and the other path is connected to the detection high-frequency modulator. The atomic gas cell is located within a non-magnetic heating system, which is located within a magnetic shielding system. The pump laser is connected to the incident side of the pump beam from the atomic gas cell via a circular polarization device, a pump beam intensity control module, and a pump linear polarization device.

[0016] Step A1 includes: aligning the detection optical path while blocking the pump light; turning on the detection laser; and aligning the centers of the detection beam shaping and intensity stabilization module, the detection linear polarization device, the detection high-frequency modulator, the quarter-wave plate, the atomic gas cell, the polarizer, and the photodetector according to the position of the detection laser; aligning the optical axis of the detection linear polarization device with the y-direction; aligning the optical axis of the quarter-wave plate with the y-direction and mounting it on the electrically controlled waveplate holder; placing the atomic gas cell at the center of the magnetic shielding system and the non-magnetic heating system; and aligning the optical axis of the polarizer with the z-direction.

[0017] Step A2 includes: applying a sinusoidal modulated magnetic field B of known frequency and amplitude within the atomic gas chamber region. mod =B0sin(ω) modt), the magnetic field direction is aligned with the y-axis or z-axis, the sinusoidal modulated magnetic field is generated by the shimming coil in the magnetic shielding system, and the frequency ω of the modulated magnetic field is... mod 10 -1 The value is in the Hz range, and the amplitude B0 is 10. -8 The order of magnitude is T, where t is time.

[0018] Step A3 includes: when detecting optical polarization fluctuations, extracting the fundamental frequency signal V from the lock-in amplifier module using a reference signal based on the optical rotation angle signal measured on the photodetector. signal :

[0019]

[0020] Where η is the conversion efficiency between the photodetector and the lock-in amplifier, R tot R is the total relaxation rate of atoms in the gas chamber. pr To detect the pumping rate of light on atoms, s pr To detect the spin of a photon, its value is proportional to twice the optical axis angle of the quarter-wave plate. The sine value, i.e. γ is the electron gyromagnetic ratio, B mod To modulate the magnetic field, the reference signal comes from a high-frequency modulator of the detection light, and its frequency is the same as the modulation frequency of the modulator.

[0021] Step A4 includes: extracting the fundamental frequency signal from the lock-in amplifier, and performing signal denoising processing using a wavelet threshold denoising algorithm. The signal denoising process is as follows: selecting an appropriate wavelet basis, performing multi-level decomposition to obtain the corresponding wavelet coefficients and scaling coefficients; selecting an appropriate threshold based on the coefficients of each level of decomposition, and applying a threshold shrinkage function to shrink the wavelet coefficients; reconstructing the signal using approximate scaling coefficients and the processed wavelet coefficients of each level; and reconstructing the signal based on the denoised fundamental frequency signal V′. signal This yields the change in the fundamental frequency signal with respect to the modulation magnetic field amplitude, i.e., the derivative of the fundamental frequency signal with respect to the modulation magnetic field amplitude.

[0022]

[0023] Step A5 includes: inputting the difference between the derivative of the fundamental frequency signal with respect to the amplitude of the modulated magnetic field and the set value into the PID module for incremental PID control algorithm analysis, and the result is converted and output to the rotation angle set value of the electrically controlled waveplate holder; rotating the optical axis of the 1 / 4 waveplate carried in the electrically controlled waveplate holder to achieve debugging and calibration before the optical rotation angle measurement.

[0024] Step B includes:

[0025] Step B1: Turn on the pump light and align it orthogonally with the detection light;

[0026] Step B2: Modulate the intensity of the pump light;

[0027] Step B3, detection and demodulation of photoelectric signals;

[0028] Step B4: Obtain the signal change as pump light changes based on the precession signal modulated by atomic spin on the light field.

[0029] Step B5: Determine if the difference in signal change is zero. If it is, it means that real-time compensation in optical rotation angle measurement has been achieved and the process ends. If not, use the PID control module to control the 1 / 4 waveplate in the electronically controlled waveplate holder to rotate the optical axis and then return to step B4.

[0030] Step B1 includes: turning on the pump laser, aligning the centers of the pump linear polarization device, the pump light intensity control module, the circular polarization device, and the atomic gas cell according to the laser position, and simultaneously aligning the pump light and the detection light orthogonally.

[0031] Step B2 includes: applying a sinusoidal modulation field R of known frequency and amplitude to the pump light. pu =R pu0 ·cosω pu t; the sinusoidal modulation field is generated by the pump light intensity control module; the frequency ω of the modulation field pu 10 0 Hz level, modulation amplitude R pu0 Corresponding to 10 4 On the order of / s.

[0032] Step B3 includes: when detecting optical polarization fluctuations, the optical rotation angle signal measured on the photodetector is used as a reference signal to extract the fundamental frequency signal V within the lock-in amplifier module. signal :

[0033]

[0034] Where η is the conversion efficiency between the photodetector and the lock-in amplifier, J0(R pu0 / ω pu R is the Bessel coefficient. tot R is the total relaxation rate of atoms in the gas chamber. pr To detect the pumping rate of light on atoms, s pr To detect the spin of a photon, its value is proportional to twice the optical axis angle of the quarter-wave plate. The sine value, i.e. The reference signal comes from the detection optical high-frequency modulator, and its frequency is the same as the modulation frequency of the modulator.

[0035] Step B4 includes: extracting the fundamental frequency signal from the lock-in amplifier and performing signal denoising processing using a wavelet threshold denoising algorithm; the signal denoising process is as follows: selecting an appropriate wavelet basis, performing multi-level decomposition to obtain corresponding wavelet coefficients and scaling coefficients; selecting an appropriate threshold based on the coefficients of each level of decomposition, and applying a threshold shrinkage function to shrink the wavelet coefficients; reconstructing the signal using approximate scaling coefficients and the processed wavelet coefficients of each level; and reconstructing the signal based on the denoised fundamental frequency signal V′. signal The change in the fundamental frequency signal as a function of the pump light was obtained:

[0036] ΔV signal =|V′ signal (N)-V′ signal (N-1)|

[0037] Where ΔV signal It represents the change, N is the series number in the multi-level decomposition, and N is a positive integer.

[0038] Step B5 includes: inputting the difference between the change in the fundamental frequency signal with the pump light and the set value into the PID module for incremental PID control algorithm analysis, and the result is converted and output to the rotation angle set value of the electrically controlled waveplate holder; the optical axis of the 1 / 4 waveplate carried in the electrically controlled waveplate holder rotates to realize real-time compensation in the optical rotation angle measurement.

[0039] The technical effects of this invention are as follows: This invention provides a method for online compensation of optical rotation angle detection errors caused by optical polarization fluctuations. Based on the response signal of atomic spin to magnetic field or optical field modulation, and utilizing the difference in the slope or change of the precession signal, combined with wavelet analysis data denoising and incremental PID control algorithm, the optical axis angle of the quarter-wave plate in the optical path is changed in real time to achieve rapid real-time compensation of optical rotation angle detection errors.

[0040] This invention has the following characteristics: (1) This invention utilizes the magnetic field response of ultra-sensitive atomic spin to feedback and adjust the laser polarization degree, which can achieve high-precision in-situ compensation of the laser polarization degree compared with existing methods. (2) This invention can be operated while the optical rotation angle detection system is in operation. (3) This invention uses a PID control algorithm to control the electric waveplate holder to change the rotation angle, and can control the adjustment of any laser polarization degree in real time in a closed loop. (4) In terms of data processing, this invention adopts filtering and noise reduction processing based on wavelet analysis threshold method, which makes the data input to the PID controller less noisy, the electric waveplate holder more sensitive, and the accuracy higher. (5) The method of this invention is reasonable and universal, the experimental operation is simple, it is not limited by the complexity of the optical path, and it can be applied to various scenarios based on optical rotation angle detection systems. Attached Figure Description

[0041] Figure 1A schematic diagram of the optical rotation angle detection system used to implement the present invention, which is a method for online compensation of optical rotation angle detection errors caused by optical polarization fluctuations.

[0042] Figure 2 This is a schematic diagram of the debugging and calibration process before measuring the optical rotation angle in this invention. Figure 2 The process includes the following steps: Step 1, blocking the pump light and aligning it with the detection light; Step 2, applying a transverse modulation magnetic field in the atomic gas cell region; Step 3, detection and demodulation of photoelectric signals; Step 4, noise reduction processing and signal slope determination; Step 5, PID control of the electronically controlled waveplate (PID: Proportion Integration Differentiation).

[0043] Figure 3 This is a schematic diagram of the real-time compensation process in the optical rotation angle measurement of this invention. Figure 3 The process includes the following steps: Step 1, turn on the pump light and align the pump light and the detection light orthogonally; Step 2, modulate the intensity of the pump light; Step 3, detect and demodulate the photoelectric signal; Step 4, perform noise reduction processing and judge the signal change; Step 5, use PID control to control the electronically controlled wave plate holder.

[0044] The following are the annotations in the figure: 1-Detection laser; 2-Detection beam shaping and intensity stabilization module; 3-Detection linear polarization device; 4-Detection high-frequency modulator; 5-1 / 4 waveplate; 6-Pump laser; 7-Pump linear polarization device; 8-Pump intensity control module; 9-Circular polarization device; 10-Polarizer; 11-Photodetector; 12-Lock-in amplifier module; 13-Atomic gas chamber; 14-Non-magnetic heating system; 15-Magnetic shielding system; 16-PID control module (PID: Proportion-Integration-Differential controller); 17-Electrically controlled waveplate holder. Detailed Implementation

[0045] The following is in conjunction with the attached diagram ( Figures 1-3 The invention will be described in the following sections and examples.

[0046] Figure 1 A schematic diagram of the optical rotation angle detection system used to implement the present invention, which is a method for online compensation of optical rotation angle detection errors caused by optical polarization fluctuations. Figure 2 This is a schematic diagram of the debugging and calibration process before measuring the optical rotation angle in this invention. Figure 3 This is a schematic diagram of the real-time compensation process in the optical rotation angle measurement of this invention. (Reference) Figures 1 to 3As shown, a method for online compensation of optical rotation angle detection errors caused by optical polarization fluctuations includes utilizing the response signals of atomic spins to magnetic or optical field modulation in the optical rotation angle detection system, as well as the difference in the slope or change of the precession signal. This is combined with wavelet analysis data denoising and an incremental PID control algorithm to achieve rapid real-time compensation of the optical rotation angle detection error by changing the optical axis angle of the quarter-wave plate in the optical path. The method includes the following steps: Step A, calibration and adjustment before optical rotation angle measurement; Step B, real-time compensation during optical rotation angle measurement.

[0047] Step A includes: Step A1, turning on the optical rotation angle detection system, blocking the pump light, and aligning the detection light; Step A2, applying a transverse modulation magnetic field in the atomic gas cell region; Step A3, detecting and demodulating the photoelectric signal; Step A4, forming a response curve based on the response signal of atomic spin to magnetic field modulation, denoising and fitting the response curve; Step A5, determining whether the slope of the fitted response curve is equal to zero. If it is, it indicates that the debugging and calibration before optical rotation angle measurement has been completed and the process ends. If not, the PID control module is used to control the 1 / 4 waveplate in the electronically controlled waveplate holder to rotate the optical axis and then return to step A4.

[0048] The optical rotation angle detection system in step A1 includes a detection laser 1, a detection beam shaping and intensity stabilization module 2, a detection linear polarization device 3, a detection high-frequency modulator 4, a quarter-wave plate 5 with an electrically controlled waveplate holder 17, an atomic gas cell 13, a polarizer 10, and a photodetector 11 arranged sequentially on the detection beam path. The photodetector 11 is connected to a lock-in amplifier module 12. One path of the lock-in amplifier module 12 is connected to the electrically controlled waveplate holder 17 through a PID control module 16, and the other path is connected to the detection high-frequency modulator 4. The atomic gas cell 13 is located within a non-magnetic heating system 14, which is located within a magnetic shielding system 15. The pump laser 6 is connected to the pump beam incident side of the atomic gas cell 13 sequentially through a circular polarization device 9, a pump beam intensity control module 8, and a pump linear polarization device 7.

[0049] Step A1 includes: aligning the detection optical path while blocking the pump light; turning on the detection laser 1; and aligning the centers of the detection light beam shaping and intensity stabilization module 2, the detection linear polarization device 3, the detection light high-frequency modulator 4, the quarter-wave plate 5, the atomic gas cell 13, the polarizer 10, and the photodetector 11 according to the position of the detection laser; aligning the optical axis of the detection linear polarization device 3 with the y-direction; aligning the optical axis of the quarter-wave plate 5 with the y-direction and mounting it on the electrically controlled waveplate holder 17; placing the atomic gas cell 13 at the center of the magnetic shielding system 15 and the non-magnetic heating system 14; and aligning the optical axis of the polarizer 10 with the z-direction. Step A2 includes: applying a sinusoidal modulated magnetic field B of known frequency and amplitude within the region of the atomic gas cell 13. mod=B0sin(ω) mod t), the magnetic field direction is aligned with the y-axis or z-axis, the sinusoidal modulated magnetic field is generated by the shimming coil in the magnetic shielding system 15, and the frequency ω of the modulated magnetic field is... mod 10 -1 The value is in the Hz range, and the amplitude B0 is 10. -8 The order of magnitude T, where t is time. Step A3 includes: when detecting optical polarization fluctuations, extracting the fundamental frequency signal V from the lock-in amplifier module 12 using a reference signal based on the optical rotation angle signal measured on the photodetector 11. signal :

[0050]

[0051] Where η is the conversion efficiency between the photodetector 11 and the lock-in amplifier 12, R tot R is the total relaxation rate of atoms in atomic gas cell 13. pr To detect the pumping rate of light on atoms, s pr To detect the spin of a photon, its value is proportional to twice the optical axis angle of a quarter-wave plate. The sine value, i.e. γ is the electron gyromagnetic ratio, B mod To modulate the magnetic field, the reference signal comes from the detection optical high-frequency modulator 4, and its frequency is the same as the modulation frequency of the modulator. Step A4 includes: extracting the fundamental frequency signal from the lock-in amplifier module 12, and performing signal denoising processing using a wavelet threshold denoising algorithm. The signal denoising process is as follows: selecting an appropriate wavelet basis, performing multi-level decomposition to obtain corresponding wavelet coefficients and scaling coefficients; selecting an appropriate threshold based on the coefficients of each level of decomposition, and applying a threshold shrinkage function to shrink the wavelet coefficients; reconstructing the signal using approximate scaling coefficients and the processed wavelet coefficients of each level; and reconstructing the signal based on the denoised fundamental frequency signal V′. signal This yields the change in the fundamental frequency signal with respect to the modulation magnetic field amplitude, i.e., the derivative of the fundamental frequency signal with respect to the modulation magnetic field amplitude.

[0052]

[0053] Step A5 includes: inputting the difference between the derivative of the fundamental frequency signal with respect to the amplitude of the modulated magnetic field and the set value into the PID module 16 for incremental PID control algorithm analysis, and the result is converted and output to the rotation angle set value of the electrically controlled waveplate holder 17; the optical axis of the 1 / 4 waveplate 5 carried in the electrically controlled waveplate holder 17 rotates to realize the debugging and calibration before the optical rotation angle measurement.

[0054] Step B includes: Step B1, turning on the pump light and aligning it orthogonally with the detection light; Step B2, modulating the intensity of the pump light; Step B3, detecting and demodulating the photoelectric signal; Step B4, obtaining the signal change amount as the pump light changes based on the precession signal of the light field modulation by atomic spin; Step B5, determining whether the difference in signal change amount is zero. If it is, it indicates that real-time compensation in the optical rotation angle measurement has been achieved and the process ends. If not, the PID control module is used to control the 1 / 4 waveplate in the electronically controlled waveplate holder to rotate the optical axis and then return to step B4.

[0055] Step B1 includes: turning on the pump laser 6, and aligning the centers of the pump linear polarization device 7, the pump light intensity control module 8, the circular polarization device 9, and the atomic gas cell 13 according to the laser position, while simultaneously aligning the pump light orthogonally with the detection light. Step B2 includes: applying a sinusoidal modulation field R with a known frequency and amplitude to the pump light. pu =R pu0 ·cosω pu t; the sinusoidal modulation field is generated by the pump light intensity control module 8; the frequency ω of the modulation field pu 10 0 Hz level, modulation amplitude R pu0 Corresponding to 10 4 The value is on the order of / s. Step B3 includes: when detecting optical polarization fluctuations, the optical rotation angle signal measured on the photodetector 11 is used as a reference signal to extract the fundamental frequency signal V in the lock-in amplifier module 12. signal :

[0056]

[0057] Where η is the conversion efficiency between the photodetector 11 and the lock-in amplifier 12, J0(R pu0 / ω pu R is the Bessel coefficient. tot R is the total relaxation rate of atoms in atomic gas cell 13. pr To detect the pumping rate of light on atoms, s pr To detect the spin of a photon, its value is proportional to twice the optical axis angle of a quarter-wave plate. The sine value, i.e. The reference signal comes from the detection optical high-frequency modulator 4, and its frequency is the same as the modulation frequency of the modulator. Step B4 includes: extracting the fundamental frequency signal from the lock-in amplifier module 12, and performing signal denoising processing using a wavelet threshold denoising algorithm; the signal denoising process is as follows: selecting an appropriate wavelet basis, performing multi-level decomposition to obtain corresponding wavelet coefficients and scaling coefficients; selecting an appropriate threshold based on the coefficients of each level of decomposition, and applying a threshold shrinkage function to shrink the wavelet coefficients; reconstructing the signal using approximate scaling coefficients and the processed wavelet coefficients of each level; and reconstructing the signal based on the denoised fundamental frequency signal V′. signal The change in the fundamental frequency signal as a function of the pump light was obtained:

[0058] ΔV signal =|V′ signal (N)-V′ signal (N-1)|

[0059] Where ΔV signal N is the change, and N is the series number in the multi-level decomposition. N is a positive integer. Step B5 includes: inputting the difference between the change in the fundamental frequency signal with the pump light and the set value into the PID module 16 for incremental PID control algorithm analysis, and the result is converted and output to the rotation angle set value of the electrically controlled waveplate holder 17; the optical axis of the 1 / 4 waveplate 5 carried in the electrically controlled waveplate holder 17 rotates to realize real-time compensation in the optical rotation angle measurement.

[0060] A method for online compensation of optical rotation angle detection error caused by optical polarization fluctuations includes two parts: (1) debugging and calibration before optical rotation angle measurement, and (2) real-time compensation during optical rotation angle measurement.

[0061] The content (1) includes five steps for debugging and calibration before measuring the optical rotation angle: Step 1, blocking the pump light and aligning the detection light; Step 2, applying a transverse modulation magnetic field in the atomic gas cell region; Step 3, detection and demodulation of photoelectric signals; Step 4, noise reduction processing and signal slope judgment; Step 5, PID control of the electronically controlled wave plate holder.

[0062] The content (2) Real-time compensation in optical rotation angle measurement includes 5 steps: Step 1, turn on the pump light and align the pump light and the detection light orthogonally; Step 2, modulate the intensity of the pump light; Step 3, detect and demodulate the photoelectric signal; Step 4, noise reduction and signal change judgment; Step 5, PID control of the electronically controlled wave plate frame.

[0063] A method for online compensation of optical rotation angle detection errors caused by optical polarization fluctuations is proposed. Based on the response signal of atomic spin to magnetic or optical field modulation, combined with wavelet analysis data denoising and incremental PID control algorithms, the method achieves rapid real-time compensation of optical rotation angle detection errors by changing the optical axis angle of the quarter-wave plate in the optical path. This method is reasonable, universal, and simple to operate experimentally. It is not limited by the complexity of the optical path and can be applied to various scenarios based on optical rotation angle detection systems.

[0064] refer to Figures 1 to 3 A method for online compensation of optical rotation angle detection error caused by optical polarization fluctuations includes two parts: (1) debugging and calibration before optical rotation angle measurement, and (2) real-time compensation during optical rotation angle measurement.

[0065] The calibration and adjustment process before measuring the optical rotation angle (1) includes the following steps:

[0066] Step 1, with the pump laser 6 off, align the detection optical path: Turn on the detection laser 1, and align the centers of the detection beam shaping and intensity stabilization module 2, the detection linear polarization device 3, the detection high-frequency modulator 4, the quarter-wave plate 5, the atomic gas cell 13, the polarizer 10, and the photodetector 11 according to the position of the detection laser. The optical axis of the detection linear polarization device 3 is aligned with the y-direction. The optical axis of the quarter-wave plate 5 is aligned with the y-direction and mounted on the electrically controlled waveplate holder 17. The atomic gas cell 13 is placed at the center of the magnetic shielding system 15 and the non-magnetic heating system 14. The optical axis of the polarizer 10 is aligned with the z-direction.

[0067] Step 2, apply a transverse modulation magnetic field within the atomic gas chamber 13: Apply a sinusoidal modulation magnetic field B with a known frequency and amplitude within the atomic gas chamber 13. mod =B0sin(ω) mod The magnetic field direction can be aligned with either the y-axis or the z-axis. The sinusoidal modulated magnetic field is generated by the shimming coil in the magnetic shielding system 15. The frequency ω of the modulated magnetic field... mod 10 -1 The value is in the Hz range, and the amplitude B0 is 10. -8 On the order of terabytes (T).

[0068] Step 3, Measurement and Demodulation of Photoelectric Signal: When detecting light polarization fluctuations, the optical rotation angle signal measured on the photodetector 11 is used as a reference signal to extract the fundamental frequency signal V in the lock-in amplifier module 12. signal for:

[0069]

[0070] Where η is the conversion efficiency between the photodetector 11 and the lock-in amplifier 12, R tot R is the total relaxation rate of atoms in the gas chamber. prTo detect the pumping rate of light on atoms, s pr To detect the spin of a photon, its value is proportional to twice the 5-axis angle of the quarter-wave plate. sine value γ is the electron gyromagnetic ratio, B mod The magnetic field is modulated. The reference signal comes from the detection optical high-frequency modulator 4, and its frequency is the same as the modulation frequency of the modulator.

[0071] Step 4, Noise Reduction and Signal Slope Determination: The fundamental frequency signal extracted by the lock-in amplifier 12 is denoised using a wavelet threshold denoising algorithm. The denoising process involves: selecting an appropriate wavelet basis and performing multi-level decomposition to obtain corresponding wavelet coefficients and scaling coefficients; selecting an appropriate threshold based on the coefficients of each decomposition level and applying a threshold shrinkage function to shrink the wavelet coefficients; reconstructing the signal using approximate scaling coefficients and the processed wavelet coefficients of each level. The denoised fundamental frequency signal V′ is then used as the basis for the signal denoising. signal This yields the change in the fundamental frequency signal with respect to the modulation magnetic field amplitude, i.e., the derivative of the fundamental frequency signal with respect to the modulation magnetic field amplitude.

[0072]

[0073] Step 5, PID control of the electrically controlled waveplate holder 17: The difference between the derivative of the fundamental frequency signal with respect to the amplitude of the modulated magnetic field and the set value is input into the PID module 16 for incremental PID control algorithm analysis. The result is converted and output to the rotation angle set value of the electrically controlled waveplate holder 17. The optical axis of the quarter-wave plate 5 carried in the electrically controlled waveplate holder 17 rotates to achieve debugging and calibration before the optical rotation angle measurement.

[0074] The real-time compensation process in the optical rotation angle measurement (2) includes the following steps:

[0075] Step 1, turn on the pump light and align the pump light and the detection light orthogonally: turn on the pump laser 6, and align the centers of the pump linear polarization device 7, the pump light intensity control module 8, the circular polarization device 9, and the atomic gas cell 13 according to the laser position, while aligning the pump light and the detection light orthogonally.

[0076] Step 2, modulate the pump light intensity: Apply a sinusoidal modulation field R with known frequency and amplitude to the pump light. pu =R pu0 ·cosω pu The sinusoidal modulation field is generated by the pump light intensity control module 8. The frequency ω of the modulation field is... pu 10 0 The frequency range is in the Hz range, and the modulation amplitude corresponds to R. pu0 ~10 4 On the order of / s.

[0077] Step 3, Measurement and Demodulation of Photoelectric Signal: When detecting light polarization fluctuations, the optical rotation angle signal measured on the photodetector 11 is used as a reference signal to extract the fundamental frequency signal V in the lock-in amplifier module 12. signal for:

[0078]

[0079] Where η is the conversion efficiency between the photodetector 11 and the lock-in amplifier 12, J0(R pu0 / ω pu R is the Bessel coefficient. tot R is the total relaxation rate of atoms in the gas chamber. pr To detect the pumping rate of light on atoms, s pr To detect the spin of a photon, its value is proportional to twice the 5-axis angle of the quarter-wave plate. sine value The reference signal comes from the detection optical high-frequency modulator 4, and its frequency is the same as the modulation frequency of the modulator.

[0080] Step 4, Noise Reduction and Signal Change Judgment: The fundamental frequency signal extracted by the lock-in amplifier 12 is denoised using a wavelet threshold denoising algorithm. The denoising process is as follows: An appropriate wavelet basis is selected, and multi-level decomposition is performed to obtain the corresponding wavelet coefficients and scaling coefficients; based on the coefficients of each decomposition level, an appropriate threshold is selected, and a threshold shrinkage function is applied to shrink the wavelet coefficients; the signal is reconstructed using approximate scaling coefficients and the processed wavelet coefficients of each level. Based on the denoised fundamental frequency signal V... si ′ gnal The change in the fundamental frequency signal as a function of the pump light was obtained:

[0081] △V signal =V si ′ gnal (N)-V si ′ gnal (N-1)

[0082] Step 5, PID control of the electrically controlled waveplate holder 17: The difference between the change in the fundamental frequency signal with the pump light and the set value is input into the PID module 16 for incremental PID control algorithm analysis. The result is converted and output to the rotation angle set value of the electrically controlled waveplate holder 17. The optical axis of the quarter-wave plate 5 carried in the electrically controlled waveplate holder 17 rotates, realizing real-time compensation in the optical rotation angle measurement.

[0083] Contents not described in detail in this specification are prior art known to those skilled in the art. It is hereby indicated that the above description is intended to help those skilled in the art understand this invention, but does not limit the scope of protection of this invention. Any equivalent substitutions, modifications, improvements, and / or simplifications of the above descriptions that do not depart from the essential content of this invention fall within the scope of protection of this invention.

Claims

1. A method for online compensation of optical rotation angle detection errors caused by optical polarization fluctuations, characterized in that, This includes utilizing the response signal of atomic spin to magnetic or optical field modulation in the optical rotation angle detection system, as well as the difference in the slope or change of the precession signal, combined with wavelet analysis data denoising and incremental PID control algorithm, to achieve rapid real-time compensation of optical rotation angle detection error by changing the optical axis angle of the 1 / 4 wave plate in the optical path in real time; Includes the following steps: Step A: Adjustment and calibration before measuring the optical rotation angle; Step B, real-time compensation in optical rotation angle measurement; Step A includes: Step A1: Turn on the optical rotation angle detection system, block the pump light, and align it with the detection light; Step A2: Apply a transverse modulation magnetic field within the atomic gas cell region; Step A3, detection and demodulation of photoelectric signals; Step A4: Develop a response curve based on the response signal of atomic spin to magnetic field modulation, and then denoise and fit the response curve. Step A5: Determine whether the slope of the fitted response curve is equal to zero. If it is, it means that the debugging and calibration before the optical rotation angle measurement has been completed and the process ends. If not, use the PID control module to control the 1 / 4 waveplate in the electronically controlled waveplate holder to rotate the optical axis and then return to step A4. Step B includes: Step B1: Turn on the pump light and align it orthogonally with the detection light; Step B2: Modulate the pump light intensity; Step B3, detection and demodulation of photoelectric signals; Step B4: Obtain the signal change as pump light changes based on the precession signal modulated by atomic spin on the light field. Step B5: Determine if the difference in signal change is zero. If it is, it means that real-time compensation in optical rotation angle measurement has been achieved and the process ends. If not, use the PID control module to control the 1 / 4 waveplate in the electronically controlled waveplate holder to rotate the optical axis and then return to step B4.

2. The method for online compensation of optical rotation angle detection error caused by optical polarization fluctuations according to claim 1, characterized in that, The optical rotation angle detection system in step A1 includes a detection laser, a detection beam shaping and intensity stabilization module, a detection linear polarization device, a detection high-frequency modulator, a quarter-wave plate with an electrically controlled waveplate holder, an atomic gas cell, a polarizer, and a photodetector arranged sequentially on the detection beam path. The photodetector is connected to a lock-in amplifier module. One path of the lock-in amplifier module is connected to the electrically controlled waveplate holder via a PID control module, and the other path is connected to the detection high-frequency modulator. The atomic gas cell is located within a non-magnetic heating system, which is located within a magnetic shielding system. The pump laser is connected to the incident side of the pump beam from the atomic gas cell via a circular polarization device, a pump beam intensity control module, and a pump linear polarization device.

3. The method for online compensation of optical rotation angle detection error caused by optical polarization fluctuations according to claim 1, characterized in that, Step A1 includes: aligning the detection optical path while blocking the pump light; turning on the detection laser; and aligning the centers of the detection beam shaping and intensity stabilization module, the detection linear polarization device, the detection high-frequency modulator, the quarter-wave plate, the atomic gas cell, the polarizer, and the photodetector according to the position of the detection laser; aligning the optical axis of the detection linear polarization device with the y-direction; aligning the optical axis of the quarter-wave plate with the y-direction and mounting it on the electrically controlled waveplate holder; placing the atomic gas cell at the center of the magnetic shielding system and the non-magnetic heating system; and aligning the optical axis of the polarizer with the z-direction. Step A2 includes: applying a sinusoidal modulated magnetic field of known frequency and amplitude within the atomic gas chamber region. The magnetic field direction is aligned with the y-axis or z-axis. The sinusoidal modulated magnetic field is generated by the shimming coil in the magnetic shielding system, and the frequency of the modulated magnetic field is... 10 -1 Hz level, amplitude 10 -8 The order of magnitude is T, where t is time.

4. The method for online compensation of optical rotation angle detection error caused by optical polarization fluctuations according to claim 1, characterized in that, Step A3 includes: when detecting optical polarization fluctuations, extracting the fundamental frequency signal within the lock-in amplifier module based on the optical rotation angle signal measured on the photodetector and using a reference signal. : ， in The conversion efficiency between the photodetector and the lock-in amplifier. The total relaxation rate of atoms in the gas chamber. To detect the pumping rate of light on atoms, To detect the spin of a photon, its value is proportional to twice the optical axis angle of the quarter-wave plate. The sine value, i.e. , Electron gyromagnetic ratio, To modulate the magnetic field, the reference signal comes from a high-frequency modulator of the detection light, and its frequency is the same as the modulation frequency of the modulator.

5. The method for online compensation of optical rotation angle detection error caused by optical polarization fluctuations according to claim 1, characterized in that, Step A4 includes: extracting the fundamental frequency signal from the lock-in amplifier, and performing signal denoising processing using a wavelet threshold denoising algorithm. The signal denoising process is as follows: selecting an appropriate wavelet basis, performing multi-level decomposition to obtain the corresponding wavelet coefficients and scaling coefficients; selecting an appropriate threshold based on the coefficients of each level of decomposition, and applying a threshold shrinkage function to shrink the wavelet coefficients; reconstructing the signal using approximate scaling coefficients and the processed wavelet coefficients of each level; and reconstructing the signal based on the denoised fundamental frequency signal. This yields the change in the fundamental frequency signal with respect to the modulation magnetic field amplitude, i.e., the derivative of the fundamental frequency signal with respect to the modulation magnetic field amplitude. 。 6. The method for online compensation of optical rotation angle detection error caused by optical polarization fluctuations according to claim 1, characterized in that, Step A5 includes: inputting the difference between the derivative of the fundamental frequency signal with respect to the amplitude of the modulated magnetic field and the set value into the PID module for incremental PID control algorithm analysis, and the result is converted and output to the rotation angle set value of the electrically controlled waveplate holder; rotating the optical axis of the 1 / 4 waveplate carried in the electrically controlled waveplate holder to achieve debugging and calibration before the optical rotation angle measurement.

7. The method for online compensation of optical rotation angle detection error caused by optical polarization fluctuations according to claim 1, characterized in that, Step B1 includes: turning on the pump laser, aligning the centers of the pump linear polarization device, the pump light intensity control module, the circular polarization device, and the atomic gas cell according to the laser position, and simultaneously aligning the pump light and the detection light orthogonally. Step B2 includes: applying a sinusoidal modulation field R of known frequency and amplitude to the pump light. pu =R pu0· cosω pu t; the sinusoidal modulation field is generated by the pump light intensity control module; the frequency of the modulation field 10 0 Hz level, modulation amplitude R pu0 Corresponding to 10 4 On the order of / s; Step B3 includes: when detecting optical polarization fluctuations, the optical rotation angle signal measured on the photodetector is used as a reference signal to extract the fundamental frequency signal within the lock-in amplifier module. : in The conversion efficiency between the photodetector and the lock-in amplifier. These are the Bessel coefficients. The total relaxation rate of atoms in the gas chamber. To detect the pumping rate of light on atoms, To detect the spin of a photon, its value is proportional to twice the optical axis angle of the quarter-wave plate. The sine value, i.e. The reference signal comes from the detection optical high-frequency modulator, and its frequency is the same as the modulation frequency of the modulator. Step B4 includes: extracting the fundamental frequency signal from the lock-in amplifier and performing signal denoising processing using a wavelet threshold denoising algorithm; the signal denoising process is as follows: selecting an appropriate wavelet basis, performing multi-level decomposition to obtain corresponding wavelet coefficients and scaling coefficients; selecting an appropriate threshold based on the coefficients of each level of decomposition, and applying a threshold shrinkage function to shrink the wavelet coefficients; reconstructing the signal using approximate scaling coefficients and the processed wavelet coefficients of each level; and based on the denoised fundamental frequency signal... The change in the fundamental frequency signal as a function of the pump light was obtained: ； in It is the change, N is the series number in the multi-level decomposition, and N is a positive integer; Step B5 includes: inputting the difference between the change in the fundamental frequency signal with the pump light and the set value into the PID module for incremental PID control algorithm analysis, and the result is converted and output to the rotation angle set value of the electrically controlled waveplate holder; the optical axis of the 1 / 4 waveplate carried in the electrically controlled waveplate holder rotates to realize real-time compensation in the optical rotation angle measurement.

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