A multifunctional optically pumped magnetometer based on FPGA and VCSEL

Abstract

The present invention belongs to the technical field of optically pumped magnetometers, and specifically provides a multifunctional optically pumped magnetometer based on FPGA and VCSEL, which is used to meet the weak magnetic detection scenarios in geomagnetic environments and zero magnetic environments. The present invention comprises: a VCSEL laser 1, a polarizer 2, an alkali metal atom gas chamber 3, a photodetection amplifier module 4, a phase-locked system 5, a laser pulse modulation module 6, a circular polarizer 7, a VCSEL directly tunable laser 8, and a digital signal processing module 9. The laser pulse modulation module decodes and outputs the detection light control level and the pump light control level according to a control coding signal. The control coding signal includes an operating mode control bit, a modulation frequency control bit, and a modulation duration control bit, etc., which controls the VCSEL directly tunable laser to output a square wave modulated laser or an unmodulated laser, corresponding to the operating modes of the geomagnetic environment and the zero magnetic environment. The present invention realizes multifunctional magnetic field measurement while also having the advantages of small size, high integration, and low cost, and is suitable for various weak magnetic detection fields.

Description

Technical Field

[0001] The present invention belongs to the technical field of optically pumped magnetometers, and specifically provides a multifunctional optically pumped magnetometer based on FPGA and VCSEL, which is suitable for high-precision measurement of weak magnetic fields in geomagnetic field environments and zero-magnetic environments, and realizes high integration and miniaturization design. Background Art

[0002] As a key branch of magnetic field measurement, weak-field magnetic detection has been extensively researched, and demand continues to grow. It is widely used in medical testing, archaeological exploration, nondestructive testing, and military submarine detection, and has also proven its irreplaceable role in navigation and earthquake early warning. A variety of weak-field magnetic measurement devices exist, including superconducting quantum interferometers (SQUIDs), fluxgate magnetometers, magnetoresistive sensors, and optically pumped magnetometers. Optically pumped magnetometers, with their low cost, small size, and high sensitivity, have seen rapid development over the past two decades.

[0003] Optically pumped magnetometers primarily utilize the Larmor precession of magnetic moments generated by polarized atoms in an external magnetic field to measure magnetic fields. Miniaturization, high integration, and high sensitivity are currently the primary research and development directions for optically pumped magnetometers. Miniaturization and chip-based implementation are key factors in the future development of wearable and mobile electronic devices. Currently, research on optically pumped magnetometers focuses primarily on high sensitivity and single-measurement applications. For example, zero-magnetic SERF magnetometers are unable to operate in complex magnetic field environments. Most research is still in the laboratory stage, and development into ASIC circuits is still in its infancy. Therefore, developing a low-cost, compact, and multifunctional optically pumped magnetometer has high practical and commercial value. Summary of the Invention

[0004] The purpose of the present invention is to provide a multifunctional optically pumped magnetometer based on FPGA and VCSEL for weak magnetic field detection scenarios in geomagnetic environments (complex magnetic fields) and zero magnetic environments (extremely weak magnetic fields), so as to realize multifunctional magnetic field measurement. At the same time, it also has the advantages of small size, high integration and low cost, and is suitable for various weak magnetic detection fields. It has broad application prospects and high commercial value.

[0005] To achieve the above object, the technical solution adopted by the present invention is:

[0006] A multifunctional optically pumped magnetometer based on FPGA and VCSEL, comprising: a VCSEL laser 1, a polarizer 2, an alkali metal atom gas chamber 3, a photoelectric detection amplifier module 4, a phase-locked system 5, a laser pulse modulation module 6, a circularly polarized polarizer 7, a VCSEL directly adjustable laser 8 and a digital signal processing module 9; characterized in that the laser pulse modulation module 6 decodes and outputs a detection light control level and a pump light control level according to a control coding signal, and the control number signal includes an operating mode control bit, a modulation frequency control bit and an operating time control bit; the detection light control level controls the VCSEL laser 1 to output a non-modulated laser, and the laser is converted into a stable laser through the polarizer 2. The linearly polarized light is used as detection light and passes through the alkali metal atom gas chamber 3; the pump light controls the level of the VCSEL directly adjustable laser 8 to output square wave modulated laser or non-modulated laser, and the laser is converted into circularly polarized light by the circular polarizer 7 and used as pump light, and is incident on the alkali metal atom gas chamber 3; the photoelectric detection amplifier module 4 detects the detection light after passing through the alkali metal atom gas chamber 3, and outputs the detection electrical signal to the phase-locked system 5; the phase-locked system 5 demodulates the detection electrical signal into a digital signal and transmits it to the digital signal processing module 9; the digital signal processing module 9 selects the corresponding data processing method according to the control coding signal to process the digital signal and outputs the magnetic field measurement result.

[0007] Furthermore, in the control coding signal, the working mode control bit is 1, indicating that the optically pumped magnetometer operates in a geomagnetic environment, and the decoded pump light control level controls the VCSEL directly adjustable laser 8 to output a square wave modulated laser; the working mode control bit is 0, indicating that the optically pumped magnetometer operates in a zero magnetic environment, and the decoded pump light control level controls the VCSEL directly adjustable laser 8 to output a non-modulated laser.

[0008] Furthermore, the laser pulse modulation module 6 and the digital signal processing module 9 are implemented based on an FPGA board.

[0009] Based on the above technical solution, the beneficial effects of the present invention are:

[0010] The present invention provides a multifunctional optically pumped magnetometer based on FPGA and VCSEL. The core technologies of FPGA encoding, decoding, synchronous control, and level output control are adopted to realize high-precision modulation control output of laser signals, rapid function switching, and digital signal processing of the optically pumped magnetometer. Combined with a small-volume VCSEL laser and a highly integrated optical circuit design, the optically pumped magnetometer can not only complete real-time and accurate measurement of weak magnetic fields, but also realize rapid switching between different operating modes under two magnetic environments: geomagnetic and zero magnetic fields. The optically pumped magnetometer has the advantages of small size, low cost, and a wide range of applications. It provides a new direction for the development of optically pumped magnetometers into wearable devices and mobile electronic devices. It has good development prospects in medicine, aviation magnetometry, geological exploration, and ocean exploration, and has high research and commercial value. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 This is a structural diagram of the multifunctional optically pumped magnetometer based on FPGA and VCSEL in the present invention, wherein 1 is the VCSEL laser, 2 is the polarizer, 3 is the alkali metal atom gas chamber, 4 is the photoelectric detection and amplification module, 5 is the phase-locked system, 6 is the laser pulse modulation module, 7 is the circular polarization polarizer, 8 is the VCSEL directly tunable laser, and 9 is the digital signal processing module (DSP).

[0012] Figure 2 This is a measurement principle diagram of the multifunctional optically pumped magnetometer based on FPGA and VCSEL in the present invention.

[0013] Figure 3 This is a diagram showing the measurement principle and time process of the multifunctional optically pumped magnetometer based on FPGA and VCSEL in the present invention in a geomagnetic environment. DETAILED DESCRIPTION

[0014] In order to make the purpose, technical solutions and beneficial effects of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments.

[0015] This embodiment provides a multifunctional optical pump magnetometer based on FPGA and VCSEL, whose structure is as follows: Figure 1As shown; it mainly includes: a 780nm VCSEL laser 1, a polarizer 2, an alkali metal atom gas chamber 3, a photoelectric detection amplifier module 4, a phase-locked system 5, a laser pulse modulation module 6, a circular polarization polarizer 7, a 795nm VCSEL directly tunable laser 8, and a digital signal processing module 9; wherein, the laser pulse modulation module 6 decodes and outputs a detection light control level and a pump light control level according to the control coding signal, and the control number signal includes a working mode control bit, a modulation frequency control bit, and a working time control bit. The working mode control bit is 1, indicating that the optical pump magnetometer works in a geomagnetic environment, and the working mode control bit is 0, indicating that the optical pump magnetometer works in a zero magnetic environment; the detection light control level controls the 780nm VCSEL laser 1 to output a 780nm non-modulated laser, which is generated by the starting After the polarizer 2 changes the light into stable linear polarized light, it serves as detection light and passes through the alkali metal atom gas chamber 3; the pump light control level controls the 795nm VCSEL directly adjustable laser 8 to output square wave modulated laser (corresponding to the optical pump magnetometer working in the geomagnetic environment) or non-modulated laser (corresponding to the optical pump magnetometer working in the zero magnetic environment), and the laser passes through the circular polarizer 7 to change the light into circular polarized light and serves as pump light, and is incident on the alkali metal atom gas chamber 3; the photoelectric detection amplifier module 4 detects the detection light after passing through the alkali metal atom gas chamber 3, and outputs the detection electrical signal to the phase-locked system 5; the phase-locked system 5 demodulates the detection electrical signal into a digital signal and transmits it to the digital signal processing module 9; the digital signal processing module 9 selects the corresponding data processing method according to the control coding signal to process the digital signal and outputs the magnetic field measurement result.

[0016] In this embodiment, the laser pulse modulation module 6 and the digital signal processing module 9 are implemented based on the FPGA board. The control coding signal adopts 32-bit coding information. The corresponding coding instructions are transmitted to the FPGA board through the host computer and the serial port. Then, the input 32-bit coding information is decoded using the three-stage pipeline of instruction acquisition-instruction decoding-instruction execution to obtain the corresponding key information such as the working mode, modulation frequency and modulation duration. The entire process operates under the main frequency of 100MHz, and only three clock cycles are needed to obtain the corresponding modulation information. Then, the corresponding level is output according to the corresponding information to drive the VCSEL directly adjustable laser to output modulated (or non-modulated) light; the multifunctional optically pumped magnetometer is based on programmable logic devices and optical magnetometers, which can realize multifunctional magnetic field measurement, is suitable for various weak magnetic measurement fields, and is compact and easy to carry, providing a new direction for the miniaturization and chipization of weak magnetic sensors. In a geomagnetic environment (complex magnetic field), a simple square wave modulation method is used. The pump light is first turned on and then off within a cycle. After the pump light is turned off, the angle of the linearly polarized detection light oscillates and decays at the Larmor frequency. Measuring the frequency of this oscillation can measure the magnetic field information. This method does not require frequency sweeping, making the measurement faster and more convenient. In a zero-field (extremely weak magnetic) environment, a spin-exchange relaxation-free (SERF) optically pumped magnetometer can be realized. Under high-frequency magnetic field modulation, the detection light is directly pumped with unmodulated light and then the optical rotation angle is measured, which can be demodulated to obtain the extremely weak magnetic field in the zero-field environment. Furthermore, all electrical and optical components are located on the same plane, resulting in a compact overall structure and all soldered to a PCB circuit board. This facilitates high integration and ASIC design. Further reducing the size of the ASIC circuit to achieve large-scale mass production will significantly reduce costs.

[0017] The working principle of the present invention is:

[0018] The measurement principle of the multifunctional optical pump magnetometer based on FPGA and VCSEL in the present invention is as follows: Figure 2 As shown, alkali metal atoms are polarized under the action of pump light, and the polarization measurement is achieved by measuring the change in the intensity of the detection light, thereby achieving magnetic field measurement.

[0019] In a geomagnetic environment (complex magnetic field), when the frequency of the pump light is consistent with the Larmor precession frequency of the alkali metal atoms, optical magnetic resonance occurs, and the resonance frequency is expressed as:

[0020] ω=γB,

[0021] Among them, γ is the gyromagnetic ratio of the alkali metal atom, is a constant value, and B is the magnitude of the magnetic field. The magnitude of the magnetic field can be measured by measuring the resonance frequency ω. At this time, the magnetometer works in a complex environmental magnetic field such as the geomagnetic field.

[0022] However, in a zero-magnetic environment (extremely weak magnetic field), high-resolution resonance frequency or optical rotation angle measurement cannot be achieved due to the small magnetic field. Therefore, it is necessary to measure its macroscopic polarization P to achieve magnetic field measurement. Taking advantage of the easy polarization characteristics of alkali metal atoms, its macroscopic polarization P can be described by the Bloch equation:

[0023]

[0024] Where D is the diffusion coefficient, s is the pump ellipticity, R p is the pumping rate, R sd is the relaxation rate, Q is the attenuation coefficient, and γ is the gyromagnetic ratio;

[0025] Based on the different measurement principles in the above-mentioned geomagnetic environment and zero magnetic environment, at present, facing the two measurement environments, it is necessary to build two optical pumping magnetometer systems, that is, the existing optical pumping magnetometer has only a single function. In response to this problem, the present invention provides a multifunctional optical pumping magnetometer based on FPGA and VCSEL. Through the design of the laser pulse modulation module 6 based on FPGA, the laser pulse modulation module outputs a coded signal including a working mode control bit, a modulation frequency control bit and a working time control bit. The working mode control bit is 1, indicating that the optical pumping magnetometer works in the geomagnetic environment, and the working mode control bit is 0, indicating that the optical pumping magnetometer works in the zero magnetic environment. In the geomagnetic environment, the laser pulse modulation module 6 controls the VCSEL directly adjustable laser 8 to output square wave modulated light, and performs two processes of pumping and measuring the alkali metal atomic gas chamber in one cycle. After the output signal stabilizes, the pumping light is turned off, and the macroscopic polarization will oscillate and decay at the Larmor precession frequency. By measuring the time interval between the two passages of the detection light through the equilibrium point, the magnitude of the magnetic field in the oscillation time period can be obtained. The pumping and measurement processes are shown in the attached figure. Figure 3 As shown; in a zero-magnetic environment, the laser pulse modulation module 6 controls the VCSEL directly tunable laser 8 to output non-modulated light, and the corresponding magnetic field information is obtained by directly measuring the optical rotation angle of the detection light. At this time, an additional magnetic shielding environment and a magnetic modulation coil are required; the two working modes can be flexibly switched, and the switching delay only requires seven to ten working clock cycles, one measurement cycle and the corresponding transmission delay. This delay is very short, which can realize rapid switching of the measurement mode, that is, a multifunctional optically pumped magnetometer is obtained.

[0026] The above description is only a specific embodiment of the present invention. Any feature disclosed in this specification, unless otherwise stated, can be replaced by other equivalent or alternative features with similar purposes; all disclosed features, or all steps in the methods or processes, except for mutually exclusive features and / or steps, can be combined in any way.

Claims

1. A multifunctional optically pumped magnetometer based on FPGA and VCSEL, comprising: VCSEL laser (1), polarizer (2), alkali metal atom gas chamber (3), photoelectric detection amplifier module (4), phase-locked system (5), laser pulse modulation module (6), circular polarization polarizer (7), VCSEL directly adjustable laser (8) and digital signal processing module (9); characterized in that the laser pulse modulation module (6) decodes and outputs detection light control level and pump light control level according to the control coding signal, and the control number signal includes an operating mode control bit, a modulation frequency control bit and an operating time control bit; the detection light control level controls the VCSEL laser (1) to output non-modulated laser light, and the laser light is converted into stable linear polarized light through the polarizer (2) and serves as detection light. and passes through the alkali metal atom gas chamber (3); the pump light controls the level of the VCSEL directly adjustable laser (8) to output a square wave modulated laser or a non-modulated laser, and the laser is converted into circularly polarized light by the circular polarizer (7) as pump light and incident on the alkali metal atom gas chamber (3); the photoelectric detection amplifier module (4) detects the detection light after passing through the alkali metal atom gas chamber (3), and outputs the detection electrical signal to the phase-locked system (5); the phase-locked system (5) demodulates the detection electrical signal into a digital signal and transmits it to the digital signal processing module (9); the digital signal processing module (9) selects the corresponding data processing method according to the control coding signal to perform signal processing on the digital signal and outputs the magnetic field measurement result; In the control number signal, the operating mode control bit is 1, indicating that the optical pump magnetometer operates in a geomagnetic environment, and the decoded pump light control level controls the VCSEL directly adjustable laser (8) to output square wave modulated laser; the operating mode control bit is 0, indicating that the optical pump magnetometer operates in a zero magnetic environment, and the decoded pump light control level controls the VCSEL directly adjustable laser (8) to output non-modulated laser.

2. The multifunctional optically pumped magnetometer based on FPGA and VCSEL according to claim 1, characterized in that: The laser pulse modulation module (6) and the digital signal processing module (9) are implemented based on an FPGA board.

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