NV color center fiber magnetometer based on integrated electronic chip

Abstract

The invention discloses an NV color center fiber magnetometer based on an integrated electronic chip, the NV color center fiber magnetometer comprises a circuit part and an optical path part, the circuit part comprises a microcontroller, a microwave chip, a digital radio frequency attenuator, a power amplifier, a constant current source and a multi-way switch power supply, the microcontroller is an STM32 microcontroller, the microcontroller controls the microwave chip to generate microwaves and adjust the output frequency, and the power amplifier is connected with the digital radio frequency attenuator. The power of the microwave is adjusted through the digital radio frequency attenuator, the microwave is amplified through the power amplifier, and the microcontroller controls the constant current source to control the laser output and adjust the laser intensity; the light path part comprises a laser, a dichroscope, an optical fiber coupler, a multimode optical fiber, a diamond sample, a microwave waveguide, a focusing lens and a photoelectric detector, and further comprises a bias magnetic field. The STM32 microcontroller controls the output of the microwave chip and the laser and performs data acquisition, so that the miniaturization of the circuit part of the optical fiber magnetometer is realized, and the production cost is greatly reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field of fiber optic sensors, and particularly relates to an NV center fiber optic magnetometer based on an integrated electronic chip. Background Art

[0002] Weak magnetic field detection refers to the measurement of very weak magnetic fields, whose intensity is usually in the range of nanotesla (nT) or smaller. It has important applications in geological exploration, medical diagnosis, environmental monitoring, etc. The nitrogen-vacancy (NV) center is a point defect in diamond, which has a long quantum coherence time at room temperature and is widely used in quantum sensing. The energy level structure of the NV center includes a triplet excited state 3 E, a triplet ground state 3 A2, and intermediate states. Among them, 3 A2 is composed of m s = 0 and m s = ±1 spin states, and the zero-field splitting is 2.87 GHz. Under the excitation of a 532 nm laser, the NV center is excited to the 3 E state, and then returns to the ground state through radiative and non-radiative transitions. Among them, the NV center in the m s = 0 state can decay back to the m s = 0 state of the electronic ground state through spontaneous emission, while the NV center in the m s = ±1 state can not only return to the m s = ±1 state of the ground state through radiative transition, but also decay to the singlet excited state through an intersystem crossing process, and then decay to the m s = 0 or m s = ±1 state of the ground state. Due to this difference, the fluorescence intensity of the NV center in the m s = 0 state is higher than that of the NV center in the m s = ±1 spin state. If continuous laser excitation is used, all NV centers can be polarized to the m s = 0 spin state. Then, a swept-frequency microwave is applied. When the microwave frequency resonates with the zero-field splitting frequency, the NV center can be resonantly pumped from the m s = 0 state to the m s = ±1 state. At this time, the fluorescence intensity decreases and a valley appears, which is the optically detected magnetic resonance (ODMR) of the diamond NV center. When an external magnetic field is applied, due to the Zeeman effect, the m s = ±1 state will split. When a swept-frequency microwave is applied, two valleys of the 0 → +1 state and the 0 → -1 state will appear. The frequency widths of the two valleys are proportional to the magnitude of the magnetic field, so it can be used for magnetic field detection.

[0003] A fiber optic magnetometer based on diamond NV color centers usually consists of two parts, a circuit part and an optical path part. The circuit part usually uses commercial microwave sources, lasers, and power amplifiers, which results in a very large volume of the device, inconvenient handling, limited application scenarios, and high costs. For the industrial field that pursues cost-effectiveness, there is an urgent need to reduce the volume and cost. Summary of the Invention

[0004] Based on this concept, the present invention provides an NV color center fiber optic magnetometer based on an integrated electronic chip, which uses a microcontroller to control microwaves and lasers, realizing an integrated electronic chip fiber optic magnetometer.

[0005] The object of the present invention is achieved by the following technical solutions: An NV color center fiber optic magnetometer based on an integrated electronic chip, comprising a circuit part and an optical path part. The circuit part includes a microcontroller, a microwave chip, a digital RF attenuator, a power amplifier, a constant current source, and a multi-channel switching power supply. The multi-channel switching power supply supplies power to the digital RF attenuator, the microwave chip, the constant current source, and the power amplifier respectively. The microcontroller is an STM32 microcontroller, which controls the microwave chip to generate microwaves and adjust the output frequency. The output microwave is adjusted in power by the digital RF attenuator and then amplified by the power amplifier. The microcontroller controls the switch and current magnitude of the constant current source to control the laser output and the adjustment of the laser intensity. The optical path part includes a laser, a dichroic mirror, an optical fiber coupler, a multimode optical fiber, a diamond sample, a microwave waveguide, a long-pass filter, a focusing lens, and a photodetector, and also includes a bias magnetic field. The beam emitted by the laser is reflected by the dichroic mirror and enters the optical fiber coupler, is coupled into the multimode optical fiber. The diamond sample is adhered to the head of the multimode optical fiber. The head of the multimode optical fiber is wound around the microwave waveguide and connected to the microwave chip to apply microwaves. The fluorescence emitted by the NV color centers of the diamond sample is collected and transmitted through the multimode optical fiber, and the stray light generated by non-NV color centers is filtered by the dichroic mirror and the filter and focused onto the photodetector through the focusing lens. The collected data is transmitted into the microcontroller through a BNC interface. The bias magnetic field is placed under the diamond sample.

[0006] For the above NV color center fiber optic magnetometer based on an integrated electronic chip, the microwave chip is an ADF4351 microwave chip.

[0007] For the above NV color center fiber optic magnetometer based on an integrated electronic chip, the diamond sample is adhered to the head of the multimode optical fiber using ultraviolet curable glue.

[0008] Compared with the prior art, the present invention has the following technical effects: The present invention uses an STM32 microcontroller as the control system to control the output of the microwave chip and the laser, and perform data acquisition, realizing the miniaturization of the circuit part of the fiber optic magnetometer, with an overall size of 40*20*10 cm 3 , small in size and portable; the cost of the circuit part is only 750 yuan, significantly reducing the production cost. Quasi-real-time magnetic field sensing is achieved, and its sensitivity can reach . BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 is the structural block diagram of the present invention.

[0010] Figure 2 is the schematic diagram of the diamond probe of the present invention.

[0011] Figure 3 is the circuit schematic diagram of the present invention.

[0012] Figure 4 is the schematic diagram of magnetic field sensing of the present invention.

[0013] Figure 5 is the schematic diagram of quasi-real-time magnetic field sensing of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0014] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention.

[0015] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", etc. indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation to the present invention.

[0016] An NV color center fiber optic magnetometer based on an integrated electronic chip, as Figure 1As shown, it includes a circuit part and an optical path part. The circuit part includes a microcontroller, a microwave chip, a digital RF attenuator, a power amplifier, a constant current source, and a multi-channel switching power supply. The multi-channel switching power supply supplies power to the digital RF attenuator, the microwave chip, the constant current source, and the power amplifier respectively. The microcontroller is an STM32 microcontroller. The microcontroller controls the microwave chip to generate microwaves and adjust the output frequency. The output microwaves are used to adjust the power of the microwaves through the digital RF attenuator, and then amplified through the power amplifier. The microcontroller controls the switch and current magnitude of the constant current source to control the laser output and adjust the laser intensity. The optical path part includes a laser 1, a dichroic mirror 2, an optical fiber coupler 3, a multimode optical fiber 4, a diamond sample 5, a microwave waveguide 9, a long-pass filter 6, a focusing lens 7, and a photodetector 8. It also includes a bias magnetic field 10. The beam emitted by the laser 1 is reflected by the dichroic mirror 2 and enters the optical fiber coupler 3, where it is coupled into the multimode optical fiber 4. The diamond sample 5 is glued to the head of the multimode optical fiber. The head of the multimode optical fiber is wound around the microwave waveguide 9 and connected to the microwave chip to apply microwaves. The fluorescence emitted by the NV centers of the diamond sample is collected and transmitted through the multimode optical fiber 4, and the stray light generated by non-NV centers is filtered by the dichroic mirror 2 and the filter 6 and focused onto the photodetector 8 through the focusing lens 7. The collected data is transmitted into the microcontroller through a BNC interface. The bias magnetic field 10 is placed under the diamond sample.

[0017] In the NV - center fiber magnetometer based on an integrated electronic chip according to the present invention, the microwave chip is an ADF4351 microwave chip.

[0018] In the NV - center fiber magnetometer based on an integrated electronic chip according to the present invention, the diamond sample 5 is glued to the head of the multimode optical fiber using ultraviolet - curable adhesive.

[0019] The overall size of the device of the present invention: 40 * 20 * 10 cm 3 , including a circuit part and an optical part.

[0020] Circuit part: The device uses a microcontroller (STM32) as the control system to control the microwave chip to generate microwaves and adjust the output frequency. The output microwaves are used to adjust the power of the microwaves through the digital RF attenuator, and then amplified through the power amplifier. Finally, they are applied to the diamond sample through the microwave waveguide. The control system controls the switch and current magnitude of the constant current source to achieve the adjustment of laser output and laser intensity. The entire circuit system is powered by a multi - channel switching power supply. The photodetector detects the voltage signal formed by the fluorescence intensity, which is collected by the control system and the data is processed, such as Figure 1 shown; Optical path part: The beam emitted by the laser 1 is reflected by the dichroic mirror 2 and enters the fiber coupler 3, where it is coupled into the multimode fiber 4. The diamond sample 5 is glued to the fiber head using ultraviolet curing adhesive, and the fiber head is wound with a microwave waveguide 9 which is connected to the microwave chip to apply microwaves, as Figure 2 shown. The fluorescence emitted by the NV color centers is collected and transmitted through the multimode fiber. The dichroic mirror 2 and the filter 6 are used to filter out the stray light generated by non-NV color centers and focus it onto the photodetector 8 through the focusing lens 7. The collected data is transmitted into the microcontroller through the BNC interface. We place a bias magnetic field 10 below the sample, and by adjusting the height of the sample, the magnetic field around the sample can be changed to achieve quasi-real-time magnetic field detection, as Figure 4 and Figure 5 shown.

[0021] The specific selection and cost of the circuit part of the present invention are as follows: Circuit part (1) Control module: The device uses STM32 as the main control system, which supports multiple communication interfaces such as SPI, I2C, USART, etc., to achieve data exchange and communication with other devices. It also includes multiple general-purpose input / output pins for connecting external devices and sensors. The chip is also equipped with an analog-to-digital converter and a digital-to-analog converter, which can collect the voltage signal converted from the fluorescence intensity detected by the photodetector and then process the data; Size: 10*5*1 cm 3 ; Cost: 70 yuan.

[0022] (2) Microwave chip: The device uses the ADF4351 microwave chip, which can generate microwave signals with a continuous frequency range from 35 MHz to 4400 MHz, with a frequency step of 0.1 MHz. It has many advantages such as wide frequency band, high precision, fast tuning, low noise, and multi-functional modulation. While ensuring that the functions are fully sufficient, it can also reduce the volume and cost of the device.

[0023] Size: 5*5*1 cm 3 ; Cost: 100 yuan.

[0024] (3) Digital RF attenuator module: The ADF4351 can only achieve power adjustment in 4 steps. The device uses a digital RF attenuator (HMC624A) which can achieve a step size of 0.5 dB and a maximum attenuation of 31.75 dB in intensity, enabling multi-power adjustment.

[0025] Size: 5*5*1 cm 3 ; Cost: 115 yuan.

[0026] (4) Power amplifier: In order to increase the intensity of the microwave signal, we use a power amplifier with a gain of 40 dBm.

[0027] Dimensions: 3.3 * 2.5 * 1 cm 3 ; Cost: 35 yuan

[0028] (5) Laser: A small semiconductor laser, and the output power of the laser can be controlled by controlling the input current.

[0029] Dimensions: radius 1 cm, length 6 cm; Cost: 250 yuan

[0030] (6) Micro constant current source: The device uses a constant current source (KW-VCCS1000) to change the input current of the laser and control the laser intensity.

[0031] Dimensions: 4 * 4 * 3 cm 3 ; Cost: 100 yuan

[0032] (7) Multi-channel switching power supply: The device uses a multi-channel switching power supply to provide 5 - 40 V voltage to power each module.

[0033] Dimensions: 9.6 * 7.2 * 2 cm 3 ; Cost: 42 yuan

[0034] Optical path part 1. Laser; 2. Dichroic mirror; 3. Fiber optic coupler; 4. Multimode fiber; 5. Diamond sample; 6. Filter; 7. Focusing lens; 8. Photoelectric detector; 9. Microwave waveguide; 10. Permanent magnet (1) Laser: Used to generate laser; (2) Dichroic mirror: Transmits light with a wavelength above 650 nm and reflects light with a wavelength below 650 nm, so that the laser is reflected and the fluorescence generated by the diamond NV center passes through; (3) Fiber optic coupler: Can couple the laser into the multimode fiber; (5) Multimode fiber: Used to transmit laser and fluorescence; (5) Diamond sample: Diamond containing NV centers; (6) Filter: A 650 nm long-pass filter is used to filter out stray light; (7) Focusing lens: Focuses the divergent fluorescence of the diamond NV center to a point; (8) Photoelectric detector: Collects the fluorescence of the NV center and converts it into a voltage value; (9) Microwave waveguide: Used to transmit microwaves; (10) Permanent magnet: Used to apply a bias magnetic field.

[0035] The circuit principle of the present invention is as follows: STM32 controls the microwave chip (ADF4351): To achieve the control of the microwave chip, this system uses an STM32 microcontroller to complete the register configuration by simulating the serial peripheral interface (SPI) protocol through the general-purpose input / output (GPIO).

[0036] Hardware connection: The PC9, PC10, PC11, and PC12 pins of STM32 are respectively connected to the LE (latch enable), DATA (data input), CLK (clock), and CE (enable) of ADF4351 to form a custom SPI communication, as Figure 3 .

[0037] Control logic: After the user sets the specified frequency, STM32 configures the internal registers of the chip through a three-wire serial interface to directly set the operating frequency band of the voltage-controlled oscillator and the parameters of the frequency divider. A continuous frequency output from 35 MHz to 4400 MHz is achieved, with a step accuracy of 0.1 MHz.

[0038] STM32 controls the digital RF attenuator (HMC624A): To achieve the adjustment of microwave power, the control module of the HMC624A digital RF attenuator is designed based on the STM32 microcontroller in this system.

[0039] Hardware connection: The PC6, PC7, and PC8 pins of STM32 are respectively connected to the LE, DATA, and CLK interfaces of HMC624A, and the attenuation value is defined by simulating the SPI protocol through GPIO, as Figure 3 .

[0040] Control logic: After the user sets the attenuation value, the system converts it into a 6-bit binary code, adapts to the input specification of HMC624A, and writes the value of the shift register into the attenuation control unit. An attenuation of 0–31.5 dB is achieved, with a step accuracy of 0.5 dB.

[0041] STM32 controls the constant current source: To achieve the control of laser power, the constant current source control module is designed based on the STM32 microcontroller in this system.

[0042] Hardware connection: The PA5 pin of STM32 outputs an analog signal, which is connected to the input end of the constant current source module to adjust the drive current of the laser.

[0043] Control logic: After the user sets the target current value, the system converts it into a 12-bit DAC output value, which is transmitted to the DAC register through DMA (direct memory access) to achieve precise control of the laser power, with an adjustment accuracy better than ±0.1 mA.

[0044] STM32 reads the voltage signal: To achieve the reading of the voltage signal output by the photodetector, the ADC control module is designed based on the STM32 microcontroller in this system.

[0045] Hardware connection: The PC1 pin of STM32 is connected to channel 11 of the ADC, and the GPIO is configured as the analog input mode.

[0046] Control logic: The system first enables the ADC clock and configures the ADC operating mode, triggers the acquisition, waits for the conversion to complete, reads the conversion result, and converts the digital signal into the actual voltage value.

[0047] The specific experiments are as follows: According to the background introduction, it can be known that the splitting width of the NV - color - center spin state increases with the increase of the external magnetic field, and the splitting width of the spin state can be demonstrated by optically detected magnetic resonance (ODMR). In the experiment, a permanent magnet is placed under the diamond sample and the height of the diamond sample is adjusted to change the magnetic field magnitude felt by the diamond sample, and then the ODMR at different distances is measured. As Figure 4 shown, it can be calculated that with the change in the position of the diamond sample, the magnetic field intensity measured by the NV - color - center increases from 18 G to 45 G.

[0048] Based on the above experiments, the present invention further modifies the program to achieve quasi - real - time magnetic field sensing. In the first 30 s, the diamond sample is adjusted to move away from the magnetic field, and the splitting width gradually decreases, as Figure 5 shown by the red dots. The magnetic field intensity decreases from 40 G to 25 G. In the next 30 s, the diamond sample is adjusted to move closer to the magnet, and a trend opposite to that of the decreasing magnetic field is obtained, thus achieving quasi - continuous real - time magnetic field detection. According to the calculation, the sensitivity of the magnetic field detection can reach .

[0049] The above - mentioned are only the preferred embodiments of the present invention. It should be pointed out that for those skilled in the art, without departing from the overall concept of the present invention, several changes and improvements can still be made, and these should also be regarded as the protection scope of the present invention.

Claims

1. An NV - center fiber optic magnetometer based on an integrated electronic chip, comprising a circuit part and an optical path part, characterized in that: The circuit part includes a microcontroller, a microwave chip, a digital RF attenuator, a power amplifier, a constant current source, and a multi-channel switching power supply; the multi-channel switching power supply supplies power to the digital RF attenuator, the microwave chip, the constant current source, and the power amplifier respectively. The microcontroller is an STM32 microcontroller. The microcontroller controls the microwave chip to generate microwaves and adjust the output frequency. The output microwaves are adjusted in power by the digital RF attenuator and then amplified by the power amplifier. The microcontroller controls the switch and current magnitude of the constant current source to achieve the adjustment of laser output and laser intensity; the optical path part includes a laser (1), a dichroic mirror (2), an optical fiber coupler (3), a multimode optical fiber (4), a diamond sample (5), a long-pass filter (6), a microwave waveguide (9), a focusing lens (7), and a photodetector (8), and also includes a bias magnetic field (10); the beam emitted by the laser (1) is reflected by the dichroic mirror (2) and enters the optical fiber coupler (3), is coupled into the multimode optical fiber (4). The diamond sample (5) is glued to the head of the multimode optical fiber. The head of the multimode optical fiber is wound around the microwave waveguide (9) and connected to the microwave chip to apply microwaves. The fluorescence emitted by the NV center of the diamond sample is collected and transmitted through the multimode optical fiber (4), and the stray light generated by non-NV centers is filtered by the dichroic mirror (2) and the filter (6) and focused onto the photodetector (8) through the focusing lens (7). The collected data is transmitted into the microcontroller through the BNC interface. The bias magnetic field (10) is placed under the diamond sample.

2. The NV - center fiber optic magnetometer based on an integrated electronic chip according to claim 1, wherein: The microwave chip is an ADF4351 microwave chip.

3. The NV - color - center fiber optic magnetometer based on an integrated electronic chip according to claim 1, wherein: The diamond sample (5) is glued to the head of the multimode optical fiber using ultraviolet curable glue.

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