Triangular wave sweep frequency-based temperature drift-resistant optical pump atomic magnetometer and measurement method

Abstract

The invention belongs to the technical field of quantum precision measurement and weak magnetic detection, and particularly discloses a triangular wave sweep frequency-based temperature drift-resistant optical pump atom magnetometer and a measurement method, a half-frequency triangular wave is utilized to drive a VCSEL laser, the time (t1, t2) when an atomic absorption peak appears at the rising edge and the falling edge of the triangular wave is detected in a time domain, and the temperature drift-resistant optical pump atom magnetometer is obtained. Based on a waveform symmetry principle, on one hand, a phase error caused by temperature drift is eliminated by calculating an average value of two moments, and high-precision magnetic field measurement is realized; on the other hand, an error signal is generated by calculating the time difference of two moments to feed back and control direct-current bias, and software locking of the laser center frequency is achieved; according to the invention, no extra lock-in amplifier hardware is needed, high-sensitivity and high-robustness magnetic field measurement can still be realized under the condition of limited temperature control precision, the system hardware is greatly simplified, and the cost is reduced.

Description

Technical Field

[0001] This invention belongs to the field of quantum precision measurement and weak magnetic field detection technology, and particularly relates to a temperature-drifting optical pump atomic magnetometer and measurement method based on triangular wave sweep frequency. Background Technology

[0002] Optically pumped atomic magnetometers (OPMs) utilize the interaction between light and atoms to measure magnetic fields, exhibiting extremely high sensitivity. With the development of microelectromechanical systems (MEMS) technology, chip-scale atomic magnetometers (CSAMs) based on vertical-cavity surface-emitting lasers (VCSELs) have become a research hotspot. However, current atomic magnetometer solutions on the market suffer from the following main problems:

[0003] Laser frequency stabilization systems are complex: the wavelength of VCSEL lasers is highly sensitive to temperature and current. To eliminate light shift and ensure pump efficiency, traditional solutions (such as the Bell-Bloom scheme) typically require building a separate frequency stabilization loop (usually using dual modulation or extremum locking techniques). This necessitates additional lock-in amplifiers and mixer circuits, resulting in large system size, high power consumption, and high cost.

[0004] Weak resistance to temperature drift: In miniaturized portable devices, temperature control accuracy is often limited by power consumption and size. Under these conditions, the laser frequency will drift significantly, causing fluctuations or even disappearance of the magnetic resonance signal amplitude. Moreover, the frequency drift will directly translate into phase noise in the magnetic field measurement, severely affecting the measurement accuracy.

[0005] Simple frequency sweep schemes are inefficient: Although there are simplified schemes that use sawtooth wave frequency sweeps, the pumping efficiency is low due to the asymmetry of unidirectional scanning and the dead zone of retrace. Furthermore, it is impossible to distinguish between temperature drift and magnetic field changes, resulting in high baseline noise. Summary of the Invention

[0006] This invention provides a temperature-drift-resistant optically pumped atomic magnetometer and measurement method based on triangular wave frequency sweep, which solves the problems of existing optically pumped atomic magnetometers that usually use a complex dual-loop frequency locking system to overcome laser frequency drift, resulting in high hardware costs and complex debugging; or use a simple open-loop frequency sweep, resulting in high phase noise and low sensitivity.

[0007] In a first aspect, a temperature-drift optically pumped atomic magnetometer based on triangular wave frequency sweep is provided, the magnetometer comprising:

[0008] Digital signal processing unit, digital-to-analog converter, laser drive circuit, vertical-cavity surface-emitting laser (VCSEL), atomic gas cell, photodetector, and analog-to-digital converter; among which,

[0009] The digital signal processing unit is used to generate a triangular wave and transmit it to the digital-to-analog converter;

[0010] The digital-to-analog converter is used to convert the triangular wave into an analog signal and superimpose a bias DC to form a superimposed signal, which is then transmitted to the laser driving circuit.

[0011] The laser driving circuit is used to convert the superimposed signal into a driving signal to drive the VCSEL;

[0012] The VCSEL is used to generate laser light under the drive of a driving signal and transmit it to the atomic gas chamber;

[0013] The atomic gas chamber is used to interact atoms with the laser to form an atomic beam, which is then transmitted to the photodetector.

[0014] The photodetector is used to detect the atomic beam and transmit it to the analog-to-digital converter;

[0015] The analog-to-digital converter is used to convert the atomic beam into a digital signal and feed it back to the digital signal processing unit. After PID calculation, the signal is superimposed on the driving signal to form a closed-loop control.

[0016] Secondly, a method for measuring temperature-drift optically pumped atomic magnetometers based on triangular wave frequency sweep is provided, the method comprising:

[0017] Step S10: System initialization and waveform generation;

[0018] Step S20: Optical pumping and signal acquisition;

[0019] Step S30: Temporal feature point extraction;

[0020] Step S40: Magnetic field phase calculation;

[0021] Step S50: Laser frequency closed-loop locking;

[0022] Step S60: Output magnetic field value.

[0023] The present invention provides a temperature-drift-resistant optically pumped atomic magnetometer and measurement method based on triangular wave frequency sweep, which has the following advantages:

[0024] Reduced temperature control requirements: By utilizing the differential complementary principle, the system can still eliminate most of the magnetic field measurement noise caused by temperature drift even under low-precision temperature control conditions.

[0025] Extremely simple hardware: It eliminates the expensive analog lock-in amplifier and mixer in traditional solutions, and uses digital logic to achieve soft locking, reducing size and cost;

[0026] Good pump continuity: Compared with sawtooth waves, triangular waves have no backsweep dead zone. Combined with half-frequency drive, it ensures the continuity of atomic spin polarization and the signal quality is better than simple frequency sweep schemes.

[0027] It is a technology that uses the optical pumping effect to detect magnetic fields, and it plays an irreplaceable role in fields such as geomagnetic navigation, mineral exploration, emergency rescue, archaeology, unexploded ordnance detection, and biomagnetic measurement.

[0028] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention may be realized and obtained by means of the structures particularly pointed out in the written description, claims, and drawings. Attached Figure Description

[0029] The accompanying drawings, which are included to provide a further understanding of the invention and form part of this invention, illustrate exemplary embodiments of the invention and are used to explain the invention, but do not constitute an undue limitation of the invention. In the drawings:

[0030] Figure 1 A schematic diagram of a temperature-drifting optical pump atomic magnetometer based on a triangular wave sweep frequency according to an embodiment of the present invention;

[0031] Figure 2 A schematic diagram illustrating the implementation process of a temperature-drifting optical pump atomic magnetometer measurement method based on triangular wave frequency sweep according to an embodiment of the present invention;

[0032] Figure 3 This is a schematic diagram illustrating the timing relationship between the triangular wave driving signal and the photoelectric detection signal, as well as the extraction of t1 and t2, according to an embodiment of the present invention. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of this specification clearer, the technical solutions of this specification will be clearly and completely described below in conjunction with specific embodiments and corresponding drawings. Obviously, the described embodiments are only a part of the embodiments of this specification, and not all of them. Based on the embodiments in this specification, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of this specification.

[0034] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of the invention described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover a non-exclusive inclusion; for example, a process, method, apparatus, product, or device that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or devices.

[0035] The technical solutions provided in the various embodiments of this specification are described in detail below with reference to the accompanying drawings.

[0036] To achieve high-precision magnetic field measurement using an atomic magnetometer, this invention provides a temperature-drifting optical pump atomic magnetometer and measurement method based on triangular wave frequency sweep.

[0037] Figure 1 A schematic diagram of a temperature-drift-resistant optical pump atomic magnetometer based on a triangular wave sweep frequency according to an embodiment of the present invention is provided. See also: Figure 1 The magnetometer includes:

[0038] Digital signal processing unit, digital-to-analog converter, laser drive circuit, vertical-cavity surface-emitting laser (VCSEL), atomic gas cell, photodetector, and analog-to-digital converter; among which,

[0039] The digital signal processing unit is used to generate a triangular wave and transmit it to the digital-to-analog converter;

[0040] The digital-to-analog converter is used to convert the triangular wave into an analog signal and superimpose a bias DC to form a superimposed signal, which is then transmitted to the laser driving circuit.

[0041] The laser driving circuit is used to convert the superimposed signal into a driving signal to drive the VCSEL;

[0042] The VCSEL is used to generate laser light under the drive of a driving signal and transmit it to the atomic gas chamber;

[0043] The atomic gas chamber is used to interact atoms with the laser to form an atomic beam, which is then transmitted to the photodetector.

[0044] The photodetector is used to detect the atomic beam and transmit it to the analog-to-digital converter;

[0045] The analog-to-digital converter is used to convert the atomic beam into a digital signal and feed it back to the digital signal processing unit. After PID calculation, the signal is superimposed on the driving signal to form a closed-loop control.

[0046] In one specific implementation,

[0047] The digital signal processing unit can be either an FPGA or an MCU; by using the digital logic resources of an FPGA or MCU to replace the expensive analog lock-in amplifier, the system cost and size are greatly reduced.

[0048] The digital signal processing unit includes:

[0049] The system includes a triangular wave generator, a time-domain feature extraction module, a magnetic field phase calculation module, and a PID controller.

[0050] Based on the same inventive concept, this invention also provides a measurement method for a temperature-drifting optically pumped atomic magnetometer based on triangular wave frequency sweeping, see [link to relevant documentation]. Figure 2 The method includes:

[0051] Step S10: System initialization and waveform generation;

[0052] Step S20: Optical pumping and signal acquisition;

[0053] Step S30: Temporal feature point extraction;

[0054] Step S40: Magnetic field phase calculation;

[0055] Step S50: Laser frequency closed-loop locking;

[0056] Step S60: Output magnetic field value.

[0057] In one specific implementation, step S10: system initialization and waveform generation specifically includes:

[0058] The digital signal processing unit generates a triangular wave modulated signal through a digital-to-analog converter.

[0059] In one specific implementation,

[0060] The frequency of the triangular wave modulation signal is equal to half of the Larmor precession frequency corresponding to the magnetic field under test;

[0061] The amplitude of the triangular wave in the triangular wave modulation signal is such that its corresponding laser frequency scanning range is slightly larger than the absorption linewidth of the atom (e.g., covering 1-2 GHz) to adapt to the pressure broadening characteristics of the buffer gas chamber.

[0062] In one specific embodiment, step S20: optical pumping and signal acquisition specifically includes:

[0063] The triangular wave modulation signal is superimposed on the DC bias current DC to drive the VCSEL. The laser passes through the atomic gas cell and is received by the photodetector PD. Since the triangular wave is symmetrical, within one period T, the laser frequency will pass through the central absorption frequency of the atom twice, from low to high and then from high to low. Therefore, the photodetector will output a signal containing two absorption valleys Dip.

[0064] In one specific implementation, see Figure 3 Step S30: Temporal feature point extraction, specifically includes:

[0065] The digital signal processing unit acquires PD signals at high speed through an analog-to-digital converter. Using a peak search algorithm or a threshold detection algorithm, it identifies the times corresponding to the two absorption valleys within one modulation period, which are denoted as the rising edge absorption time t1 and the falling edge absorption time t2, respectively.

[0066] In one specific embodiment, step S40: magnetic field phase calculation (anti-temperature drift processing) specifically includes:

[0067] Calculate the magnetic field phase reference point tp = (t1 + t2) / 2;

[0068] Calculation principle: When the laser temperature drifts slightly, the laser center wavelength shifts. Assuming a redshift, this will cause the resonance time t1 of the rising edge to advance, while the resonance time t2 of the falling edge will lag behind, or vice versa. It depends on the relationship between wavelength and current. The absolute values ​​of the changes of the two are approximately equal. Therefore, taking the average value tp can effectively offset the time error introduced by temperature drift, thereby obtaining the true phase information that is only related to the precession of the magnetic field.

[0069] In one specific embodiment, step S50: laser frequency closed-loop locking specifically includes:

[0070] Calculate the frequency error Ef = (t2 - t1) - dT, where dT is the ideal time interval (usually T / 2) when the laser is aligned with the center.

[0071] The error value Ef is input into the digital PID controller, which outputs a correction voltage and superimposes the adjusted DC bias current DC of the VCSEL.

[0072] Calculation principle: If the interval between t1 and t2 deviates from the set value (i.e., asymmetry), it means that the center of the laser scan deviates from the atomic absorption peak. By adjusting the DC current through feedback, the waveform is forced back to a symmetrical state, thereby achieving laser frequency locking.

[0073] In one specific embodiment, step S60: magnetic field numerical output, specifically includes:

[0074] Based on the phase information obtained in step S40, combined with the current driving frequency, the accurate Larmor frequency is calculated, converted into magnetic field strength according to the gyromagnetic ratio, and output through the data interface.

[0075] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of the invention.

[0076] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A temperature-drifting optically pumped atomic magnetometer based on triangular wave frequency sweep, characterized in that, The magnetometer includes: Digital signal processing unit, digital-to-analog converter, laser drive circuit, vertical-cavity surface-emitting laser (VCSEL), atomic gas cell, photodetector, and analog-to-digital converter; among which, The digital signal processing unit is used to generate a triangular wave and transmit it to the digital-to-analog converter; The digital-to-analog converter is used to convert the triangular wave into an analog signal and superimpose a bias DC to form a superimposed signal, which is then transmitted to the laser driving circuit. The laser driving circuit is used to convert the superimposed signal into a driving signal to drive the VCSEL; The VCSEL is used to generate laser light under the drive of a driving signal and transmit it to the atomic gas chamber; The atomic gas chamber is used to interact atoms with the laser to form an atomic beam, which is then transmitted to the photodetector. The photodetector is used to detect the atomic beam and transmit it to the analog-to-digital converter; The analog-to-digital converter is used to convert the atomic beam into a digital signal and feed it back to the digital signal processing unit. After PID calculation, the signal is superimposed on the driving signal to form a closed-loop control.

2. The magnetometer according to claim 1, characterized in that, The digital signal processing unit can be either an FPGA or an MCU. The digital signal processing unit includes: The system includes a triangular wave generator, a time-domain feature extraction module, a magnetic field phase calculation module, and a PID controller.

3. A measurement method for a temperature-drifting optically pumped atomic magnetometer based on triangular wave frequency sweep, characterized in that, The method applied to the temperature-drift-resistant optically pumped atomic magnetometer based on triangular wave sweep frequency as described in any one of claims 1 to 2, the method comprising: Step S10: System initialization and waveform generation; Step S20: Optical pumping and signal acquisition; Step S30: Temporal feature point extraction; Step S40: Magnetic field phase calculation; Step S50: Laser frequency closed-loop locking; Step S60: Output magnetic field value.

4. The method according to claim 1, characterized in that, Step S10: System initialization and waveform generation, specifically includes: The digital signal processing unit generates a triangular wave modulated signal through a digital-to-analog converter.

5. The method according to claim 4, characterized in that, The frequency of the triangular wave modulation signal is equal to half of the Larmor precession frequency corresponding to the magnetic field under test; The amplitude of the triangular wave in the triangular wave modulation signal is such that its corresponding laser frequency scanning range is slightly larger than the absorption linewidth of the atom, in order to adapt to the pressure broadening characteristics of the buffer gas chamber.

6. The method according to claim 5, characterized in that, Step S20: Optical pumping and signal acquisition, specifically includes: The triangular wave modulation signal is superimposed on the DC bias current DC to drive the VCSEL. The laser passes through the atomic gas cell and is received by the photodetector PD. Since the triangular wave is symmetrical, within one period T, the laser frequency will pass through the central absorption frequency of the atom twice, from low to high and then from high to low. Therefore, the photodetector will output a signal containing two absorption valleys Dip.

7. The method according to claim 6, characterized in that, Step S30: Temporal feature point extraction specifically includes: The digital signal processing unit acquires PD signals at high speed through an analog-to-digital converter. Using a peak search algorithm or a threshold detection algorithm, it identifies the times corresponding to the two absorption valleys within one modulation period, which are denoted as the rising edge absorption time t1 and the falling edge absorption time t2, respectively.

8. The method according to claim 7, characterized in that, Step S40: Magnetic field phase calculation, specifically includes: Calculate the magnetic field phase reference point tp = (t1 + t2) / 2; Calculation principle: When the laser temperature drifts slightly, the laser center wavelength shifts. Assuming a redshift, this will cause the resonance time t1 of the rising edge to advance, while the resonance time t2 of the falling edge will lag behind, or vice versa. It depends on the relationship between wavelength and current. The absolute values ​​of the changes of the two are approximately equal. Therefore, taking the average value tp can effectively offset the time error introduced by temperature drift, thereby obtaining the true phase information that is only related to the precession of the magnetic field.

9. The method according to claim 8, characterized in that, Step S50: Laser frequency closed-loop locking, specifically includes: Calculate the frequency error Ef = (t2 - t1) - dT, where dT is the ideal time interval when the laser is aligned with the center; The error value Ef is input into the digital PID controller, which outputs a correction voltage and superimposes the adjusted DC bias current DC of the VCSEL. Calculation principle: If the interval between t1 and t2 deviates from the set value, it means that the center of the laser scan deviates from the atomic absorption peak. By adjusting the DC current through feedback, the waveform is forced back to a symmetrical state, thereby achieving laser frequency locking.

10. The method according to claim 9, characterized in that, Step S60: Magnetic field numerical output, specifically includes: Based on the phase information obtained in step S40, combined with the current driving frequency, the accurate Larmor frequency is calculated, converted into magnetic field strength according to the gyromagnetic ratio, and output through the data interface.

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