An optical frequency shift noise suppression device and method for a single-beam atomic magnetometer

Abstract

The application discloses a light frequency shift noise suppression device and method for a single-beam atomic magnetometer, and the device comprises a DBR laser, an NTC thermistor and a TEC integrated in the laser, a laser light field regulation external light path, a digital laser controller, a single-beam atomic magnetometer principle prototype, a magnetometer control and detection unit. The application provides a low-frequency light frequency shift noise suppression method based on precise control of the temperature of the DBR laser, adopts a type III compensation network to improve the stability margin of the temperature control loop according to the frequency response characteristics of the laser temperature control loop, eliminates the low-frequency fluctuation of the temperature of the laser, realizes fine thermal tuning of the laser wavelength, thereby suppressing the low-frequency light frequency shift noise caused by the fluctuation of the temperature of the laser in the single-beam atomic magnetometer, and solves the problem of the deterioration of the low-frequency magnetic field measurement sensitivity of the magnetometer. The application can effectively improve the low-frequency performance of the single-beam atomic magnetometer, and is helpful to the extraction of low-frequency biological weak magnetic information.

Description

Technical Field

[0001] This invention relates to the field of magnetic sensor noise suppression technology, and more specifically, to a device and method for suppressing optical frequency shift noise in a single-beam atomic magnetometer. Background Technology

[0002] Spin-exchange relaxation-free (SERF) atomic magnetometers, by overcoming the contradiction between atomic density and atomic spin relaxation time, are currently the most sensitive magnetic field sensors. In particular, magnetic field imaging instruments composed of arrays of SERF atomic magnetometers have become new tools for medical functional imaging techniques such as magnetocardiography (MCG) and magnetoencephalography (MEG), driving the development of biomagnetism research. However, since biomagnetic signals are concentrated in the low-frequency range, low-frequency sensitivity degradation is a significant factor limiting the clinical application of SERF atomic magnetometers. For single-beam atomic magnetometers, low-frequency optical frequency shift noise caused by laser temperature fluctuations is the main source of sensitivity degradation.

[0003] Previous methods for suppressing optical frequency shift noise typically suffer from two main drawbacks: the introduction of additional optical components and the ability to suppress only static optical frequency shift noise. The former complicates the multi-channel integration of atomic magnetometers, making them inconvenient for use in clinical settings outside the laboratory. As for the latter, it is only effective under the assumption that the optical frequency shift noise remains constant, and its suppression effect is limited by the detection accuracy of atomic spin polarization signals and the generation of compensating magnetic field noise.

[0004] Therefore, it is necessary to conduct in-depth research on the influence mechanism of low-frequency optical frequency shift noise in atomic magnetometers and propose an effective noise suppression method. Summary of the Invention

[0005] In view of this, the present invention proposes an optical frequency shift noise suppression device and method for a single-beam atomic magnetometer, aiming to solve the problem that current optical frequency shift noise suppression methods cannot eliminate low-frequency optical frequency shift noise caused by laser temperature fluctuations, and improve the stability of laser wavelength through precise temperature control, thereby improving the low-frequency sensitivity of the single-beam atomic magnetometer.

[0006] This invention proposes an optical frequency shift noise suppression device for a single-beam atomic magnetometer, comprising:

[0007] The components include a DBR laser, an external optical path for laser field modulation, a digital laser controller, a prototype single-beam atomic magnetometer, a magnetometer detection module, a negative temperature coefficient thermistor integrated within the DBR laser, and a thermoelectric cooler.

[0008] The DBR laser is configured to provide a pump source for pumping atoms for a single-beam atomic magnetometer, and the DBR laser is also configured to provide a detection beam for measuring weak magnetic fields.

[0009] Both the negative temperature coefficient thermistor and the thermoelectric cooler are configured to perform closed-loop control of the temperature of the Bragg grating inside the DBR laser. The negative temperature coefficient thermistor is connected to the temperature reading circuit in the digital laser controller via a coaxial shielded wire. The negative temperature coefficient thermistor is also configured to obtain an accurate actual laser temperature value based on a high-precision voltage reference source. The thermoelectric cooler is also configured to heat or cool the Bragg grating based on the difference from the target temperature, driven by the digital laser controller.

[0010] The external optical path for laser field modulation is configured to limit the laser direction of the DBR laser, and the external optical path for laser field modulation is also configured to adjust the laser polarization state of the DBR laser.

[0011] The digital laser controller is configured to provide current drive and temperature control for the DBR laser;

[0012] The prototype of the single-beam atomic magnetometer is equipped with a photodetector. It is also configured to measure the light absorption signal after the laser passes through the atomic gas cell, and to improve the signal-to-noise ratio based on a preset magnetic field modulation detection scheme.

[0013] The magnetometer detection module is configured to drive and control the gas temperature control unit, magnetic compensation and magnetic modulation coil in the prototype of the single-beam atomic magnetometer; the magnetometer detection module is also configured to preprocess the light absorption signal after improving the signal-to-noise ratio, and determine the magnetic field to be measured based on the preprocessed light absorption signal.

[0014] The magnetometer detection module preprocesses the light absorption signal after improving the signal-to-noise ratio by filtering, amplifying, and demodulating the light absorption signal.

[0015] Furthermore, the external optical path for laser light field modulation includes:

[0016] An optical isolator, equipped with a magneto-optical crystal based on the Faraday effect, limits the laser trajectory of the DBR laser;

[0017] The optical polarization state adjustment module is equipped with a half-wave plate and a polarization beam splitter prism. The optical polarization state adjustment module is configured to adjust the laser emitted by the DBR laser to a linear polarization state.

[0018] Furthermore, the DBR laser is also configured to output 795nm band laser corresponding to the D1 line transition of rubidium atoms.

[0019] Furthermore, the negative temperature coefficient thermistor is specifically a surface-mount package, and the negative temperature coefficient thermistor is also configured to have a resistance tolerance of ±10% at 25°C.

[0020] Furthermore, the driving force of the thermoelectric cooler is configured to be >1A.

[0021] Furthermore, the isolation of the optical isolator is configured to be >60dB, and the external optical path for laser field modulation is configured to use polarization-maintaining fiber to transmit the laser emitted by the DBR laser tube to the prototype of the single-beam atomic magnetometer.

[0022] Furthermore, the digital laser controller includes a current source module and a temperature control module, both of which are equipped with a 16-bit low-noise DAC to set the target value; wherein,

[0023] The current source module is equipped with a voltage reference chip, which is configured to provide a voltage reference to the DAC in the current source module.

[0024] The temperature control module is equipped with a TEC integrated control chip, which is configured to provide a voltage reference to the DAC in the temperature control module, wherein:

[0025] The TEC integrated control chip is configured to drive the TEC according to the PWM wave, and the TEC integrated control chip is also configured to filter out high-frequency noise in the drive current based on the LC network.

[0026] The temperature control module is also configured to use a Type III analog compensation network as the control law for the temperature control loop, and the temperature control module is also configured to tune the resistance and capacitance parameters of the network according to the preset TEC frequency characteristics.

[0027] Furthermore, the prototype of the single-beam atomic magnetometer is equipped with an optical fiber collimator, a combined polarization prism, a rubidium atomic gas cell, a non-magnetic heating film attached to the outer wall of the gas cell, a platinum resistance thermometer for measuring the temperature of the gas cell, a triaxial magnetic compensation and magnetic modulation miniature coil, and a photodetector.

[0028] The prototype of the single-beam atomic magnetometer is set in the central area of ​​the four-layer magnetic shielding barrel. The prototype of the single-beam atomic magnetometer is also configured to perform active magnetic compensation based on micro coil drive.

[0029] The fiber collimator, combined polarization prism, rubidium atom gas cell, and photodetector are located on the same axis, and the laser light introduced by the fiber passes through each component in sequence.

[0030] Furthermore, the magnetometer detection module includes:

[0031] The control module is configured to provide sinusoidal drive to the non-magnetic heating film and magnetic modulation coil in the gas chamber;

[0032] The detection module is configured with a transimpedance amplifier, a lock-in amplifier, and a data acquisition submodule, wherein:

[0033] The transimpedance amplifier is configured with 10 5 Fixed gain of V / A;

[0034] The lock-in amplifier is equipped with a demodulation frequency of 1 kHz, which is the same as the magnetic field modulation frequency.

[0035] The data acquisition submodule is configured with a sampling rate of 200Hz.

[0036] Compared with existing technologies, the advantages of this invention are as follows: The DBR laser serves as both the pump source for a single-beam atomic magnetometer and a source for detecting weak magnetic fields. This dual-function setup allows the laser to directly provide a high-quality beam, meeting the magnetometer's stringent light source requirements. Furthermore, stable single-beam laser transmission reduces system complexity and improves the signal-to-noise ratio. Secondly, through a closed-loop temperature control design using a negative temperature coefficient thermistor (NTC) and thermoelectric cooler (TEC), the device enables precise adjustment of the temperature of the Bragg grating inside the DBR laser. Specifically, the NTC is connected to the temperature reading circuit of the digital laser controller via a coaxial shielded wire and relies on a high-precision voltage reference source to accurately obtain the actual temperature value. The TEC uses the drive signal provided by the digital laser controller to adjust the temperature difference in real time, ensuring the temperature of the laser's Bragg grating remains stable at the set value, thereby suppressing laser wavelength drift caused by temperature fluctuations. This temperature control mechanism significantly improves the stability of the laser frequency, enabling long-term low-noise operation. In addition, the external optical path for laser field modulation further enhances optical transmission stability. This optical path includes not only an optical isolator to prevent interference from backlighting, but also a polarization adjustment module. By adjusting the laser polarization direction, it makes the light transmission in the optical fiber more stable. This optical field modulation design ensures that the laser beam output has good polarization consistency during transmission, thus providing stable and reliable light source conditions for magnetic field detection. Finally, in terms of signal processing, the magnetometer detection module is equipped with units for controlling the gas chamber temperature, magnetic field compensation, and magnetic field modulation. Through filtering, amplification, and demodulation of the light absorption signal, it ensures high accuracy and low noise output of the final signal. Through the regulation of this module, it is possible not only to compensate for the interference of environmental factors on magnetic field measurement, but also to optimize the signal-to-noise ratio through signal modulation technology, making magnetic field measurement more sensitive and accurate.

[0037] On the other hand, this application also provides a method for suppressing optical frequency shift noise in a single-beam atomic magnetometer, comprising:

[0038] Step S1: Using the light absorption signal detected by the single-beam atomic magnetometer, adjust the current and temperature values ​​of the DBR laser and set the laser to the optimal static operating point so that the atomic magnetometer reaches the optimal response state.

[0039] Step S2: Disconnect the temperature control closed loop, apply a set of frequency-scanning constant-amplitude sinusoidal perturbations to the TEC drive current using the digital controller, record the dynamic response of the laser temperature, plot the frequency response curve of the controlled object in the temperature control loop, and establish the transfer function model of the controlled object near the static operating point of the magnetometer based on the frequency response curve.

[0040] Step S3: Based on the characteristics of the transfer function of the controlled object, a type III network with two additional zeros is used for loop compensation. By adjusting the values ​​of R2 and C1, the position of the first zero z1 of the type III network is determined so that the loop can obtain sufficient DC gain. z1 is set between the two poles of the controlled object.

[0041] Step S4: By adjusting R2, C1, and C3, the crossover frequency of the temperature control loop is increased to 20Hz. Positive phase compensation is introduced into the temperature control loop based on the second zero point z2 of the type III network controlled by R1 and C3, so that the loop can obtain sufficient phase margin at the crossover frequency. The values ​​of R1 and C3 are determined respectively.

[0042] Step S5: The zero points z1 and z2 are set and canceled out by the pole p1 at 40Hz and the pole p2 at 80Hz, respectively, so that the Type III network provides positive phase compensation in the low frequency band of the temperature control loop, and the values ​​of R3 and C2 are determined.

[0043] Step S6: Perform a step response test on the compensated laser temperature control system, and comprehensively evaluate the compensation effect of the Type III network based on the settling time, overshoot, and steady-state error parameters. If the compensation effect is lower than the preset compensation effect, then repeat steps S3-S5 to adjust the RC parameters of the Type III network.

[0044] It is understood that the optical frequency shift noise suppression device and method for a single-beam atomic magnetometer in the above embodiments have the same beneficial effects, and will not be described in detail here. Attached Figure Description

[0045] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings:

[0046] Figure 1 This is a functional structural diagram of an optical frequency shift noise suppression device for a single-beam atomic magnetometer provided in an embodiment of the present invention;

[0047] Figure 2 This is a control block diagram of the temperature control module in a digital laser controller provided in an embodiment of the present invention;

[0048] Figure 3 A Bode plot of the total controlled object provided in an embodiment of the present invention;

[0049] Figure 4 The circuit schematic diagram of the Type III compensation network provided in the embodiment of the present invention;

[0050] Figure 5 This is a flowchart illustrating a method for suppressing optical frequency shift noise in a single-beam atomic magnetometer, as provided in an embodiment of the present invention. Detailed Implementation

[0051] Exemplary embodiments of the present disclosure will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided to enable a more thorough understanding of the present disclosure and to fully convey the scope of the disclosure to those skilled in the art. It should be noted that, unless otherwise specified, embodiments and features in the embodiments of the present invention can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0052] like Figure 1 As shown in some embodiments of this application, this embodiment provides an optical frequency shift noise suppression device for a single-beam atomic magnetometer, including: a DBR laser, an NTC thermistor and TEC integrated in the laser, an external optical path for laser optical field modulation, a digital laser controller, a prototype of a single-beam atomic magnetometer, and a magnetometer control and detection unit.

[0053] Specifically, the DBR laser provides both the pump source and the detection beam for a single-beam atomic magnetometer, employing a butterfly-shaped packaged laser tube with an integrated thermistor and TEC. The laser tube contains a Bragg grating structure located outside the active region. This Bragg grating structure selects a single longitudinal mode as the laser mode, achieving single-frequency laser output. The laser mode is controlled by the applied current and temperature and tuned to the 795nm wavelength required for the atomic magnetometer's operation. The integrated NTC thermistor and TEC are attached to the surface of the Bragg grating, forming a precise temperature control system for the grating, thereby achieving fine thermal tuning of the output laser wavelength. The NTC thermistor uses a gold-terminated surface-mount package with a temperature range of -40℃ to 125℃. The TEC's maximum drive current... The laser's external optical route for optical field modulation consists of an optical isolator, a half-wave plate, a polarizing beam splitter, a mirror, and an optical fiber coupler. The optical isolator is used to prevent reverse laser light from returning to the laser. The polarizing beam splitter adjusts the laser to a linear polarization state, improving the stability of laser transmission in the optical fiber. The digital laser controller sets the target values ​​for the drive current and operating temperature of the DBR laser and provides energy. It consists of a current source module and a temperature control module. The current source module uses a 16-bit DAC chip AD5541 based on an external reference voltage to set the laser drive current and communicates with the STM32 main control unit via the SPI protocol. The temperature control module uses a 16-bit low-noise DAC chip DAC8830, and the external reference is provided by the TEC integrated control chip MAX1978.A 5V reference voltage is used. The TEC integrated control chip MAX1978 contains a two-stage amplification system: an instrumentation amplifier and an integrating amplifier. The instrumentation amplifier calculates the difference between the target temperature set by the DAC and the actual temperature read back by the NTC and amplifies it by 50 times, outputting the resulting temperature error signal to the integrating amplifier. The integrating amplifier, in conjunction with resistors and capacitors, forms a type III analog compensation network. Based on the input temperature error signal, it calculates the control voltage of the TEC and transmits it to the built-in power MOSFET for power amplification. The built-in power MOSFET drives the TEC using a 500kHz PWM wave. The prototype of the single-beam atomic magnetometer includes an optical fiber collimator, a combined polarization prism, a rubidium atomic gas cell, a non-magnetic heating film attached to the outer wall of the gas cell, a platinum resistance thermometer for measuring the temperature of the gas cell, triaxial magnetic compensation, and magnetic modulation. The system comprises a miniature coil and a photodetector; the prototype of the single-beam atomic magnetometer is placed in the central region of a four-layer magnetic shielding barrel; the miniature coil actively compensates for the residual magnetism around the prototype, enabling it to operate in a zero-magnetic environment; the fiber optic collimator, combined polarization prism, rubidium atomic gas cell, and photodetector are located on the same axis; the laser is guided and collimated by the fiber optic collimator before passing through each component in sequence; the photodetector detects the light absorption signal after the laser passes through the gas cell, thereby inferring the weak magnetic field to be measured; the magnetometer control and detection unit includes a control module and a detection module; the control module provides sinusoidal drive for the non-magnetic heating film and magnetic modulation coil of the gas cell; the detection module consists of a transimpedance amplifier, a lock-in amplifier, and a data acquisition submodule; the transimpedance amplifier has a 10... 5 The fixed gain of V / A; the reference frequency for demodulation of the lock-in amplifier is the same as the magnetic field modulation frequency, which is 1kHz; the data acquisition submodule is set to a sampling rate of 200Hz.

[0054] As can be seen, the optical frequency shift noise suppression device of the single-beam atomic magnetometer in this invention achieves low-frequency optical frequency shift noise suppression in the precise measurement of weak magnetic fields through the coordinated operation of multiple sub-modules. The DBR laser provides the pump source and detection beam, and selects the single longitudinal mode laser output through a built-in Bragg reflection grating, thereby ensuring the stability of the 795nm single-frequency laser. The NTC thermistor and TEC within the laser work together to form a precise temperature control system. Through bidirectional temperature control driven by the NTC temperature measurement and TEC, and utilizing a Type III compensation network based on an integrating amplifier, closed-loop regulation is provided to finely control the laser wavelength. The external optical path for laser field modulation adjusts the polarization state and direction of laser transmission through optical isolators, polarizing beam splitters, and other optical components to ensure its stability during transmission in the optical fiber. The prototype of the single-beam atomic magnetometer uses a micro-coil for magnetic compensation to create a zero-magnetic-field environment and uses a photodetector to capture the light absorption signal after the laser passes through the rubidium atomic gas cell. The transimpedance amplification, lock-in amplification, and data acquisition modules in the magnetometer's control and detection unit amplify, demodulate, and sample the detected signal to accurately measure weak magnetic fields. This design effectively suppresses low-frequency optical frequency shift noise in the magnetometer through closed-loop precise temperature control of the laser, achieving a high signal-to-noise ratio and high sensitivity in magnetic field measurements.

[0055] Understandably, the DBR laser, as the core component of the pump source and detection beam, outputs a stable single-frequency laser through its built-in Bragg grating structure. This Bragg grating structure utilizes single longitudinal mode characteristics to stabilize the laser mode at the target wavelength of 795nm, thereby improving the magnetometer's sensitivity under specific light source conditions. To ensure laser frequency stability, the DBR laser integrates a negative temperature coefficient thermistor (NTC) and a thermoelectric cooler (TEC), forming a closed-loop temperature control system for the Bragg grating. This ensures that the laser's frequency output matches the required light source operating conditions of the magnetometer. Furthermore, the laser's internal temperature control system monitors the Bragg grating temperature in real time via the NTC, transmitting the detected temperature information to the digital laser controller for accurate temperature feedback. The TEC, based on the temperature difference signal fed back from the thermistor, appropriately heats or cools the Bragg grating to maintain laser frequency stability. The temperature control module employs a Type III compensation network, introducing two zeros and a high-frequency pole to achieve positive phase compensation for the temperature control loop. This ensures sufficient phase margin at cross-frequency points, reducing the impact of high-frequency noise and improving the accuracy and speed of temperature control response. This structural design significantly enhances the stability of the laser wavelength, avoiding the adverse effects of temperature fluctuations on the laser frequency. Furthermore, the external optical path for laser field control further stabilizes laser transmission through a series of optical components. An optical isolator, based on the Faraday effect, allows only unidirectional laser transmission, blocking interference from reverse laser beams and ensuring laser output quality. A polarizing beam splitter and a half-wave plate adjust the laser to a linear polarization state, making laser transmission in the optical fiber more stable and reducing the impact of environmental disturbances. The overall optical path design gives the laser field control system high anti-interference capability and strong environmental adaptability, providing a low-noise, highly stable light source input for the atomic magnetometer. Meanwhile, the prototype single-beam atomic magnetometer constructs a compact detection optical path using components such as an optical fiber collimator, a combined polarization prism, and a rubidium atomic gas cell. The rubidium atomic gas cell is placed within a four-layer magnetic shield and provided with triaxial magnetic compensation by a miniature coil, ensuring a zero-magnetic environment around the gas cell. The optical signal generated after the laser is absorbed by the gas cell is collected by a photodetector and sent to the control and detection unit for signal processing. A transimpedance amplifier, a lock-in amplifier, and a data acquisition submodule together constitute the detection module. Through fixed-gain amplification and lock-in demodulation, the weak magnetic field signal is extracted and amplified, ultimately obtaining high-precision magnetic field measurement data. Finally, this integrated optical frequency shift noise suppression system, through the combination of precise temperature control, optical modulation, and signal detection technology, achieves higher detection sensitivity and signal-to-noise ratio, enabling the device to maintain excellent measurement accuracy under complex environmental conditions.

[0056] like Figure 2As shown, the temperature control module in the digital laser controller includes four components: a temperature-sensing NTC thermistor, a Type III compensation network, a TEC driver amplifier, and the overall controlled object consisting of the TEC and the laser tube. The temperature-sensing NTC thermistor reads the temperature of the Bragg grating inside the DBR laser in real time, converts it into a voltage signal, and calculates the difference between this signal and the target value set by the DAC chip DAC8830 in the digital controller to obtain a temperature error signal. The Type III compensation network uses the temperature error signal as an input parameter to calculate and output the control voltage of the TEC. The TEC driver amplifier is a power MOSFET built into the MAX1978 integrated TEC control chip, which adjusts the TEC drive current according to the TEC control voltage provided by the Type III compensation network. The overall controlled object, consisting of the TEC and the laser tube, is considered as a whole in the temperature control system.

[0057] The precise temperature control mechanism of the temperature control module in a digital laser controller is understandable. This module comprises four main components: a temperature-sensing NTC thermistor, a Type III compensation network, a TEC driver amplifier, and the overall controlled object consisting of the TEC and the laser tube. During control, the NTC thermistor on the surface of the Bragg grating first monitors the internal temperature change of the laser in real time, converting it into a voltage signal. This signal reflects the actual temperature of the Bragg grating. The temperature signal is then processed by the digital controller and differentially analyzed with the target temperature value set by the DAC chip DAC8830 to obtain a temperature error signal, indicating the deviation of the current temperature from the target value. Next, this temperature error signal is processed by the Type III compensation network. As the regulator in the temperature control loop, the Type III compensation network's task is to generate a suitable control voltage output to the TEC based on the error signal, enhancing the overall temperature control response characteristics. Compared to traditional compensation networks, the Type III compensation network has multiple adjustment points, allowing for more flexible adjustment of the frequency response. It provides high gain to reduce steady-state error and phase compensation over a wider frequency range, significantly improving the bandwidth and phase margin of the temperature control system and ensuring a stable dynamic response. Subsequently, the TEC driver amplifier (composed of power MOSFETs integrated into the MAX1978 integrated control chip) regulates the drive current based on the control voltage output from the Type III compensation network. Through the precise control of the built-in power MOSFETs, the TEC can quickly switch between heating and cooling modes, ultimately stabilizing the temperature at the target setpoint. The chip's amplifier output uses a high-frequency PWM waveform to improve the TEC's driving efficiency. The TEC and the laser tube together constitute the overall controlled object for temperature control, treating them as a single unit for control. This design, through closed-loop feedback control, can accurately maintain the set temperature after it is reached. In this way, temperature fluctuations in the Bragg grating inside the laser are significantly suppressed, effectively controlling the laser frequency stability to meet the application requirements of single-beam atomic magnetometers, thus laying a stable light source foundation for high-precision magnetic field measurements.

[0058] like Figure 3 As shown, the Bode plot of the total controlled object is obtained by frequency response testing, and the transfer function of the total controlled object is established based on the fitted curve. Specifically, the digital controller applies a set of frequency-scanning, constant-amplitude sinusoidal perturbations to the static operating point of the TEC drive current, while simultaneously recording the dynamic response of the laser temperature to obtain the Bode plot of the total controlled object; the transfer function of the total controlled object has two low-frequency poles.

[0059] Understandably, when the laser operates at its static temperature control point, a frequency-scanning, constant-amplitude sinusoidal perturbation is applied to the TEC drive current via a digital controller, introducing a small perturbation signal within a specific frequency band. This causes the system to respond, allowing observation of changes in the laser temperature. Since this frequency-scanning perturbation signal covers different frequency bands, the response behavior can be recorded over a wide frequency range, resulting in a Bode plot characterizing the system's frequency characteristics. This plot directly shows the gain and phase response of the controlled object to perturbations at different frequencies, aiding in the analysis of the system's dynamic characteristics. By fitting the curve of this Bode plot, a mathematical model of the entire controlled object can be established, describing the system's response to temperature changes, i.e., the system's transfer function. This transfer function reveals the system's frequency characteristics, showing the existence of two low-frequency poles. These low-frequency poles often correspond to system response delays or some inertial characteristics. Specifically, these poles have an effect in the low-frequency range, causing a slower response under low-frequency conditions. This dynamic characteristic provides important basis for subsequent design, helping designers incorporate appropriate parameters into the compensation network design to improve response speed while maintaining system stability. In further compensation network design, the pole characteristics in the transfer function guide the setting of zero locations in the compensation network to offset or mitigate the adverse effects of poles. For example, the Type III compensation network, by introducing appropriate zero configuration, achieves sufficient gain and phase margin at the operating frequency. This design not only improves the response speed of the temperature control loop but also effectively suppresses the amplification effect of high-frequency noise, ensuring optimal dynamic performance and anti-interference capability in actual operation.

[0060] like Figure 4 As shown, the Type III compensation network consists of an integrator amplifier and surrounding resistors and capacitors within the TEC integrated control chip MAX1978, and its transfer function is:

[0061]

[0062] D(s) has two zeros, denoted as z1 and z2, and two poles, denoted as p1 and p2. The two zeros add positive phase compensation to the temperature control loop, improving low-frequency gain and crossover frequency, and expanding the phase margin. Simultaneously, the two poles are used to terminate newly added zeros, preventing the introduction of amplified high-frequency noise. In practical applications, the approximate conditions R1 >> R3 and C1 << C2 are usually used to simplify the design. In this case, the frequencies of the two zeros are:

[0063]

[0064]

[0065] The frequencies of the two poles are:

[0066]

[0067]

[0068] Understandably, configuring the zeros (z1 and z2) of the compensation network to provide positive phase compensation in the low-frequency range of the temperature control loop not only improves the low-frequency gain of the system but also extends the system's crossover frequency, thereby enhancing the phase margin of the temperature control. This design helps the system obtain sufficient response bandwidth in the low-frequency band, effectively reducing steady-state error, thus enabling the temperature control to maintain fast response and precise adjustment characteristics at lower frequencies. This plays a crucial role in ensuring that the laser temperature can still be accurately controlled to the target value when disturbed. On the other hand, to avoid the amplification effect of the added zeros on high-frequency noise, the Type III compensation network introduces two poles (p1 and p2) in the high-frequency band. These poles are used to "terminate" the gain boost effect of the zeros in the compensation network, limiting the gain increase trend of the compensation network in the high-frequency band. This design is very important for the system's noise suppression capability in the high-frequency band. By setting the pole frequencies in a sufficiently high band, it is ensured that the phase compensation provided by the compensation network in the low-frequency range is not affected, while avoiding high-frequency noise amplification, thereby improving the system's anti-interference capability. In practical design, to simplify the adjustment process of zeros and poles, the values ​​of resistors and capacitors are usually set to ensure that the compensation network satisfies the approximate conditions R1 >> R3 and C1 << C2. Under this configuration, the zero and pole frequencies can be approximated by relatively simple calculation formulas, facilitating rapid parameter adjustment and optimization by designers. This simplified design not only reduces the complexity of the compensation network but also ensures the response speed and stability of the temperature control loop, optimizes the operating state of the DBR laser, and achieves robust performance of the temperature control system under different operating conditions. Finally, through the design of the aforementioned Type III compensation network, the temperature control not only possesses high sensitivity to low-frequency errors but also takes into account the suppression capability of high-frequency noise, thus optimizing the overall temperature control performance of the DBR laser. This design ensures that the laser can maintain the stability of the laser mode even when the external environment or operating conditions change.

[0069] In the above embodiments, the DBR laser serves as both the pump source for a single-beam atomic magnetometer and a source for detecting weak magnetic fields. This dual-purpose configuration allows the laser to directly provide a high-quality beam, meeting the magnetometer's stringent light source requirements. Furthermore, stable single-beam laser transmission reduces system complexity and improves the signal-to-noise ratio. Secondly, a closed-loop temperature control design using a negative temperature coefficient thermistor (NTC) and thermoelectric cooler (TEC) enables precise temperature adjustment of the Bragg grating inside the DBR laser. Specifically, the NTC is connected to the temperature reading circuit of the digital laser controller via a coaxial shielded wire and relies on a high-precision voltage reference source to accurately obtain the actual temperature value. The TEC uses the drive signal provided by the digital laser controller to adjust the temperature difference in real time, ensuring the temperature of the laser's Bragg grating remains stable at the set value, thereby suppressing laser wavelength drift caused by temperature fluctuations. This temperature control mechanism significantly improves laser frequency stability, enabling long-term low-noise operation. In addition, the external optical path for laser field modulation further enhances optical transmission stability. This optical path includes not only an optical isolator to prevent interference from backlighting, but also a polarization adjustment module. By adjusting the laser polarization direction, it makes the light transmission in the optical fiber more stable. This optical field control design ensures that the laser beam output has good polarization consistency during transmission, reducing the impact of optical field interference on the magnetometer, thus providing stable and reliable light source conditions for magnetic field detection. Finally, in terms of signal processing, the magnetometer detection module is equipped with units for controlling the gas chamber temperature, magnetic field compensation, and magnetic field modulation. Through filtering, amplification, and demodulation of the light absorption signal, it ensures high accuracy and low noise output of the final signal. Through the control of this module, it is possible not only to compensate for the interference of environmental factors on magnetic field measurement, but also to optimize the signal-to-noise ratio through signal modulation technology, making magnetic field measurement more sensitive and accurate.

[0070] In another preferred embodiment based on the above embodiments, such as Figure 5 As shown, this embodiment provides a method for suppressing optical frequency shift noise in a single-beam atomic magnetometer, including:

[0071] S1. Using the light absorption signal detected by the single-beam atomic magnetometer, adjust the current and temperature values ​​of the DBR laser and set the laser to the optimal static operating point so that the atomic magnetometer can reach the optimal response state.

[0072] S2. Disconnect the temperature control closed loop, apply a set of frequency-scanning constant-amplitude sinusoidal perturbations to the TEC drive current using the digital controller, record the dynamic response of the laser temperature, plot the frequency response curve of the controlled object in the temperature control loop, and establish the transfer function model of the controlled object near the static operating point of the magnetometer based on the frequency response curve.

[0073] S3. Based on the characteristics of the transfer function of the controlled object, a type III network with two additional zeros is used for loop compensation. By adjusting the values ​​of R2 and C1, the position of the first zero z1 of the type III network is determined so that the loop can obtain sufficient DC gain. z1 is set between the two poles of the controlled object.

[0074] S4. By adjusting R2, C1 and C3, the crossover frequency of the temperature control loop is increased to 20Hz. Based on the second zero point z2 of the type III network controlled by R1 and C3, positive phase compensation is introduced into the temperature control loop to ensure that the loop has sufficient phase margin at the crossover frequency. The values ​​of R1 and C3 are determined respectively.

[0075] S5. The zeros z1 and z2 are set and canceled out by the pole p1 at 40Hz and the pole p2 at 80Hz, respectively, so that the Type III network provides positive phase compensation in the low frequency band of the temperature control loop, and the values ​​of R3 and C2 are determined.

[0076] S6. Perform a step response test on the compensated laser temperature control system, and comprehensively evaluate the compensation effect of the Type III network based on the settling time, overshoot, and steady-state error parameters, where:

[0077] If the compensation effect is lower than the preset compensation effect, then it is determined that steps S3-S5 will be repeated to adjust the RC parameters of the Type III network.

[0078] It is understood that the optical frequency shift noise suppression device and method for a single-beam atomic magnetometer in the above embodiments have the same beneficial effects, and will not be described in detail here.

[0079] Those skilled in the art will understand that embodiments of this application can be provided as methods, systems, or computer program goods. Therefore, this application can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, this application can take the form of a computer program goods embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0080] This application is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program goods according to embodiments of this application. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart... Figure 1One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0081] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0082] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0083] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A device for suppressing optical frequency shift noise in a single-beam atomic magnetometer, characterized in that, include: The components include a DBR laser, an external optical path for laser field modulation, a digital laser controller, a prototype single-beam atomic magnetometer, a magnetometer detection module, a negative temperature coefficient thermistor integrated within the DBR laser, and a thermoelectric cooler. The DBR laser is configured to provide a pump source for pumping atoms for a single-beam atomic magnetometer, and the DBR laser is also configured to provide a detection beam for measuring weak magnetic fields. Both the negative temperature coefficient thermistor and the thermoelectric cooler are configured to perform closed-loop control of the temperature of the Bragg grating inside the DBR laser. The negative temperature coefficient thermistor is connected to the temperature reading circuit in the digital laser controller via a coaxial shielded wire. The negative temperature coefficient thermistor is also configured to obtain an accurate actual laser temperature value based on a high-precision voltage reference source. The thermoelectric cooler is also configured to heat or cool the Bragg grating based on the difference from the target temperature, driven by the digital laser controller. The external optical path for laser field modulation is configured to limit the laser direction of the DBR laser, and the external optical path for laser field modulation is also configured to adjust the laser polarization state of the DBR laser. The digital laser controller is configured to provide current drive and temperature control for the DBR laser; the digital laser controller includes a current source module and a temperature control module, both of which are equipped with a 16-bit low-noise DAC to set target values; wherein... The current source module is equipped with a voltage reference chip, which is configured to provide a voltage reference to the DAC in the current source module. The temperature control module is equipped with a TEC integrated control chip, which is configured to provide a voltage reference to the DAC in the temperature control module, wherein: The TEC integrated control chip is configured to drive the TEC according to the PWM wave, and the TEC integrated control chip is also configured to filter out high-frequency noise in the drive current based on the LC network. The temperature control module is also configured to use a type III analog compensation network as the control law for the temperature control loop, and the temperature control module is also configured to adjust the resistance and capacitance parameters of the network according to the preset TEC frequency characteristics. The prototype of the single-beam atomic magnetometer is equipped with a photodetector. It is also configured to measure the light absorption signal after the laser passes through the atomic gas cell, and to improve the signal-to-noise ratio based on a preset magnetic field modulation detection scheme. The magnetometer detection module is configured to drive and control the gas temperature control unit, magnetic compensation and magnetic modulation coil in the prototype of the single-beam atomic magnetometer; the magnetometer detection module is also configured to preprocess the light absorption signal after improving the signal-to-noise ratio, and determine the magnetic field to be measured based on the preprocessed light absorption signal. The magnetometer detection module preprocesses the light absorption signal after improving the signal-to-noise ratio by filtering, amplifying, and demodulating the light absorption signal.

2. The optical frequency shift noise suppression device for a single-beam atomic magnetometer as described in claim 1, characterized in that, The external optical path for laser field modulation includes: An optical isolator, equipped with a magneto-optical crystal based on the Faraday effect, limits the laser trajectory of the DBR laser; The optical polarization state adjustment module is equipped with a half-wave plate and a polarization beam splitter prism. The optical polarization state adjustment module is configured to adjust the laser emitted by the DBR laser to a linear polarization state.

3. The optical frequency shift noise suppression device for a single-beam atomic magnetometer as described in claim 1, characterized in that, The DBR laser is also configured to output 795nm band laser corresponding to the D1 line transition of rubidium atoms.

4. The optical frequency shift noise suppression device for a single-beam atomic magnetometer as described in claim 1, characterized in that, The negative temperature coefficient thermistor is specifically a surface-mount package, and the negative temperature coefficient thermistor is also configured to have a resistance tolerance of ±10% at 25°C.

5. The optical frequency shift noise suppression device for a single-beam atomic magnetometer as described in claim 1, characterized in that, The driving force of the thermoelectric cooler is configured to be >1A.

6. The optical frequency shift noise suppression device for a single-beam atomic magnetometer as described in claim 2, characterized in that, The isolation of the optical isolator is configured to be >60dB, and the external optical path for laser field modulation is configured to use polarization-maintaining fiber to transmit the laser emitted by the DBR laser tube to the prototype of the single-beam atomic magnetometer.

7. The optical frequency shift noise suppression device for a single-beam atomic magnetometer as described in claim 1, characterized in that, The prototype of the single-beam atomic magnetometer is equipped with an optical fiber collimator, a combined polarization prism, a rubidium atomic gas cell, a non-magnetic heating film attached to the outer wall of the gas cell, a platinum resistance thermometer for measuring the temperature of the gas cell, a triaxial magnetic compensation and magnetic modulation miniature coil, and a photodetector. The prototype of the single-beam atomic magnetometer is set in the central area of ​​the four-layer magnetic shielding barrel. The prototype of the single-beam atomic magnetometer is also configured to perform active magnetic compensation based on micro coil drive. The fiber collimator, combined polarization prism, rubidium atom gas cell, and photodetector are located on the same axis, and the laser light introduced by the fiber passes through each component in sequence.

8. The optical frequency shift noise suppression device for a single-beam atomic magnetometer as described in claim 7, characterized in that, The magnetometer detection module includes: The control module is configured to provide sinusoidal drive for the non-magnetic heating film in the air chamber and the magnetic modulation coil; The detection module is configured with a transimpedance amplifier, a lock-in amplifier, and a data acquisition submodule, wherein: The transimpedance amplifier is configured with 10 5 Fixed gain of V / A; The lock-in amplifier is equipped with a demodulation frequency of 1 kHz, which is the same as the magnetic field modulation frequency. The data acquisition submodule is configured with a sampling rate of 200Hz.

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