High-sensitivity magnetic field sensor based on whispering gallery mode modulation

Abstract

The application relates to the technical field of magnetic field sensors, and particularly relates to an echo wall microcavity high-sensitivity magnetic field sensor based on magnetic force modulation frequency locking, which comprises a laser, an isolator, a polarization controller, an attenuator, a sensitive unit, a photoelectric detector, a lock-in amplifier, an oscilloscope, an upper computer, a frequency locking module and a Helmholtz coil. The sensitive unit comprises a tapered optical fiber, an echo wall microcavity and a magnet. The frequency locking module comprises an RF signal source, a mixer, a low-pass filter and a PID controller. The outgoing end of the laser is sequentially connected with the leading end of the tapered optical fiber through the isolator, the polarization controller and the attenuator. The echo wall microcavity is coupled with the tapered region of the tapered optical fiber. The magnet is adhered to the surface of the echo wall microcavity. The trailing end of the tapered optical fiber is connected with the incident end of the photoelectric detector. The application solves the problems of low sensitivity and poor anti-interference capability of the existing magnetic field sensor, and is suitable for the fields of biomedicine, industrial detection, environmental monitoring and the like.

Description

Technical Field

[0001] This invention relates to the field of magnetic field sensor technology, specifically a high-sensitivity magnetic field sensor based on magnetic modulation frequency locking in a whispering-gallery microcavity. Background Technology

[0002] Magnetic field sensors are widely used in biomedicine, industrial detection, and environmental monitoring due to their advantages of small size, light weight, easy integration, and strong reusability. However, in practical applications, existing magnetic field sensors suffer from low sensitivity and poor anti-interference capabilities due to their inherent structural limitations. Specifically, existing magnetic field sensors generally utilize phase modulators for PDH (Pound-Drever-Hall) frequency locking during measurement. This frequency locking method not only has a complex optical path and high implementation cost but also introduces high-frequency noise, resulting in low sensor sensitivity and poor anti-interference capabilities. Therefore, it is necessary to invent a high-sensitivity magnetic field sensor based on magnetic modulation frequency locking using a whispering-gallery microcavity to solve the problems of low sensitivity and poor anti-interference capabilities of existing magnetic field sensors. Summary of the Invention

[0003] To address the problems of low sensitivity and poor anti-interference capability of existing magnetic field sensors, this invention provides a high-sensitivity magnetic field sensor based on magnetic modulation frequency locking in a whispering-gallery microcavity.

[0004] This invention is achieved using the following technical solution:

[0005] A high-sensitivity magnetic field sensor based on magnetic modulation frequency locking for a whispering-gallery microcavity includes a laser, an isolator, a polarization controller, an attenuator, a sensing element, a photodetector, a lock-in amplifier, an oscilloscope, a host computer, a frequency locking module, and a Helmholtz coil; the sensing element includes a tapered optical fiber, a whispering-gallery microcavity, and a magnet; the frequency locking module includes an RF signal source, a mixer, a low-pass filter, and a PID controller.

[0006] The laser's output end is connected to the beginning of a tapered optical fiber via an isolator, a polarization controller, and an attenuator. A whispering-gallery microcavity is coupled to the tapered region of the tapered optical fiber. A magnet is attached to the surface of the whispering-gallery microcavity. The end of the tapered optical fiber is connected to the incident end of a photodetector. The photodetector's signal output is connected to the signal input of a host computer via a lock-in amplifier and an oscilloscope, and also to the first signal input of a mixer. The RF signal source's signal output is connected to the second signal input of the mixer and the signal input of a Helmholtz coil. The mixer's signal output is connected to the laser's control terminal via a low-pass filter and a PID controller. The Helmholtz coil is located beside the magnet.

[0007] Furthermore, the laser is a continuously tunable ultra-narrow linewidth laser; the tapered fiber is a single-mode polarization-maintaining fiber; the whispering-gallery microcavity is a disk-shaped calcium fluoride crystal resonator, a disk-shaped magnesium fluoride crystal resonator, or a disk-shaped barium fluoride crystal resonator; the magnet is a disk-shaped neodymium iron boron magnet, which is adhered to the surface of the whispering-gallery microcavity by UV-curing adhesive; and the low-pass filter is a digital low-pass filter.

[0008] Furthermore, the sensitive unit also includes a U-shaped bracket and a copper pillar; a tapered optical fiber is adhered to the U-shaped bracket; and a sounding wall microcavity is adhered to the copper pillar.

[0009] Furthermore, the tapered optical fiber is adhered to the U-shaped bracket using UV-curable adhesive; the whispering wall microcavity is adhered to the copper pillar using UV-curable adhesive.

[0010] A high-sensitivity magnetic field measurement method for whispering-gallery microcavities based on magnetic modulation frequency locking, which is based on the high-sensitivity magnetic field sensor for whispering-gallery microcavities described in this invention, is implemented through the following steps:

[0011] First, the control sensor enters its operating mode. Specifically, the laser outputs an optical signal, which sequentially passes through an isolator, polarization controller, attenuator, tapered fiber, whispering-gallery microcavity, and tapered fiber before reaching a photodetector. The photodetector then converts this signal into an electrical signal. This electrical signal is transmitted to a mixer and, via a lock-in amplifier, to an oscilloscope, where it is converted into a transmission spectrum. The transmission spectrum is displayed on the oscilloscope and transmitted to the host computer. The radio frequency (RF) signal source outputs an RF signal, which is transmitted to both the mixer and a Helmholtz converter. The laser is fed into a coil and converted into a modulation magnetic field by a Helmholtz coil. The modulation magnetic field acts on the sensitive unit, causing a disturbance in the whispering-gallery microcavity, which in turn causes the electrical signal to carry disturbance information. The radio frequency signal and the electrical signal with disturbance information are mixed by a mixer and then transmitted to a low-pass filter, where the error signal is extracted. The error signal is transmitted to a PID controller. The PID controller adjusts the output frequency of the laser in real time according to the error signal, thereby making the output frequency of the laser consistent with the resonant frequency of the whispering-gallery microcavity, thus locking the output frequency of the laser at the resonant frequency of the whispering-gallery microcavity.

[0012] In the working mode, when the magnetic field to be measured acts on the sensitive unit, the resonant frequency of the whispering galvanic microcavity changes, causing the voltage amplitude of the transmission spectrum to change. The host computer monitors the change in voltage amplitude of the transmission spectrum in real time and calculates the strength of the magnetic field to be measured based on the change in voltage amplitude of the transmission spectrum.

[0013] Compared with existing magnetic field sensors, this invention no longer uses a phase modulator for PDH frequency locking. Instead, it uses an RF signal source and a Helmholtz coil to introduce a modulated magnetic field, and then uses a mixer, low-pass filter, and PID controller to lock the frequency. This frequency locking method not only simplifies the optical path and reduces the implementation cost, but also avoids the introduction of high-frequency noise, thereby making the sensor more sensitive and more resistant to interference.

[0014] This invention effectively solves the problems of low sensitivity and poor anti-interference ability of existing magnetic field sensors, and is applicable to fields such as biomedicine, industrial detection, and environmental monitoring. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the structure of the present invention.

[0016] Figure 2 This is a schematic diagram of the structure of the sensitive unit in this invention.

[0017] Figure 3 yes Figure 2 Top view.

[0018] Figure 4 yes Figure 2 A bottom view.

[0019] In the diagram: 1-Laser, 2-Isolator, 3-Polarization controller, 4-Attenuator, 5.1-Tapered fiber, 5.2-Speaking-gallery microcavity, 5.3-Magnet, 5.4-U-shaped bracket, 5.5-Copper pillar, 6-Photodetector, 7-Lock-in amplifier, 8-Oscilloscope, 9-Host computer, 10.1-RF signal source, 10.2-Mixer, 10.3-Low-pass filter, 10.4-PID controller, 11-Helmholtz coil. Detailed Implementation

[0020] A high-sensitivity magnetic field sensor based on magnetic modulation frequency locking for a whispering-gallery microcavity includes a laser 1, an isolator 2, a polarization controller 3, an attenuator 4, a sensing unit, a photodetector 6, a lock-in amplifier 7, an oscilloscope 8, a host computer 9, a frequency locking module, and a Helmholtz coil 11. The sensing unit includes a tapered optical fiber 5.1, a whispering-gallery microcavity 5.2, and a magnet 5.3. The frequency locking module includes an RF signal source 10.1, a mixer 10.2, a low-pass filter 10.3, and a PID controller 10.4.

[0021] The output end of laser 1 is connected to the beginning of tapered fiber 5.1 via isolator 2, polarization controller 3, and attenuator 4 in sequence; whispering-gallery microcavity 5.2 is coupled to the tapered region of tapered fiber 5.1; magnet 5.3 is attached to the surface of whispering-gallery microcavity 5.2; the tail end of tapered fiber 5.1 is connected to the incident end of photodetector 6; the signal output end of photodetector 6 is connected to the signal input end of host computer 9 via lock-in amplifier 7 and oscilloscope 8 in sequence, and to the first signal input end of mixer 10.2 in sequence; the signal output end of radio frequency signal source 10.1 is connected to the second signal input end of mixer 10.2 in sequence, and to the signal input end of Helmholtz coil 11 in sequence; the signal output end of mixer 10.2 is connected to the control end of laser 1 via low-pass filter 10.3 and PID controller 10.4 in sequence; Helmholtz coil 11 is located next to magnet 5.3.

[0022] The laser 1 is a continuously tunable ultra-narrow linewidth laser; the tapered fiber 5.1 is a single-mode polarization-maintaining fiber; the whispering-gallery microcavity 5.2 is a disk-shaped calcium fluoride crystal resonator, a disk-shaped magnesium fluoride crystal resonator, or a disk-shaped barium fluoride crystal resonator; the magnet 5.3 is a disk-shaped neodymium iron boron magnet, which is adhered to the surface of the whispering-gallery microcavity 5.2 by UV-curing adhesive; and the low-pass filter 10.3 is a digital low-pass filter.

[0023] The sensitive unit also includes a U-shaped bracket 5.4 and a copper pillar 5.5; a tapered optical fiber 5.1 is attached to the U-shaped bracket 5.4; and a sounding wall microcavity 5.2 is attached to the copper pillar 5.5.

[0024] The tapered optical fiber 5.1 is adhered to the U-shaped bracket 5.4 using UV-curable adhesive; the sounding wall microcavity 5.2 is adhered to the copper pillar 5.5 using UV-curable adhesive.

[0025] A high-sensitivity magnetic field measurement method for whispering-gallery microcavities based on magnetic modulation frequency locking, which is based on the high-sensitivity magnetic field sensor for whispering-gallery microcavities described in this invention, is implemented through the following steps:

[0026] First, the control sensor enters the working mode. Specifically, the working mode is as follows: Laser 1 outputs an optical signal, which sequentially passes through isolator 2, polarization controller 3, attenuator 4, tapered fiber 5.1, whispering-gallery microcavity 5.2, and tapered fiber 5.1 before being incident on photodetector 6. Photodetector 6 then converts the signal into an electrical signal. This electrical signal is transmitted to mixer 10.2 and, via lock-in amplifier 7, to oscilloscope 8, where it is converted into a transmission spectrum. The transmission spectrum is displayed on oscilloscope 8 and transmitted to host computer 9. Radio frequency (RF) signal source 10.1 outputs an RF signal, which is transmitted to mixer 10.2 and Helmholtz coil. 11, and converted into a modulation magnetic field by Helmholtz coil 11; the modulation magnetic field acts on the sensitive unit, causing disturbance in the whispering-gallery microcavity 5.2, thereby making the electrical signal carry disturbance information; the radio frequency signal and the electrical signal with disturbance information are mixed by mixer 10.2 and then transmitted to low-pass filter 10.3, and the error signal is extracted by low-pass filter 10.3; the error signal is transmitted to PID controller 10.4; PID controller 10.4 adjusts the output frequency of laser 1 in real time according to the error signal, thereby making the output frequency of laser 1 consistent with the resonant frequency of whispering-gallery microcavity 5.2, thereby locking the output frequency of laser 1 at the resonant frequency of whispering-gallery microcavity 5.2;

[0027] In the working mode, when the magnetic field to be measured acts on the sensitive unit, the resonant frequency of the whispering galvanic microcavity 5.2 changes, causing the voltage amplitude of the transmission spectrum to change; the host computer 9 monitors the change in voltage amplitude of the transmission spectrum in real time and calculates the strength of the magnetic field to be measured based on the change in voltage amplitude of the transmission spectrum.

[0028] In specific implementation, the center wavelength of laser 1 is 1550nm, and its linewidth is less than or equal to 10kHz; the tapered optical fiber 5.1 is fabricated using the fused taper method, and its length is 3cm; the whispering-gallery microcavity 5.2 is fabricated using single-point diamond cutting and manual precision grinding and polishing processes, and its roughness is less than the nm order of magnitude, with a Q value greater than 5×10⁻⁶. 8 The diameter of the copper pillar 5.5 is 3mm.

[0029] While specific embodiments of the present invention have been described above, those skilled in the art should understand that these are merely illustrative examples, and the scope of protection of the present invention is defined by the appended claims. Those skilled in the art can make various changes or modifications to these embodiments without departing from the principles and essence of the present invention, but all such changes and modifications fall within the scope of protection of the present invention.

Claims

1. A high-sensitivity magnetic field sensor for a whispering-gallery microcavity based on magnetic modulation frequency locking, characterized in that: The system includes a laser (1), an isolator (2), a polarization controller (3), an attenuator (4), a sensing unit, a photodetector (6), a lock-in amplifier (7), an oscilloscope (8), a host computer (9), a frequency locking module, and a Helmholtz coil (11); the sensing unit includes a tapered optical fiber (5.1), a whispering-gallery microcavity (5.2), and a magnet (5.3); the frequency locking module includes a radio frequency signal source (10.1), a mixer (10.2), a low-pass filter (10.3), and a PID controller (10.4). The output end of the laser (1) is connected to the head end of the tapered optical fiber (5.1) in sequence through an isolator (2), a polarization controller (3), and an attenuator (4); the whispering-gallery microcavity (5.2) is coupled to the tapered region of the tapered optical fiber (5.1); a magnet (5.3) is attached to the surface of the whispering-gallery microcavity (5.2); the tail end of the tapered optical fiber (5.1) is connected to the incident end of the photodetector (6); the signal output end of the photodetector (6) is connected to the signal output of the host computer (9) in sequence through a lock-in amplifier (7) and an oscilloscope (8). The input terminal is connected to the mixer (10.2), and the output terminal of the radio frequency signal source (10.1) is connected to the second signal input terminal of the mixer (10.2) and the signal input terminal of the Helmholtz coil (11) on the other hand; the output terminal of the mixer (10.2) is connected to the control terminal of the laser (1) through a low-pass filter (10.3) and a PID controller (10.4) in sequence; the Helmholtz coil (11) is located next to the magnet (5.3); The sensitive unit also includes a U-shaped bracket (5.4) and a copper pillar (5.5); a tapered optical fiber (5.1) is attached to the U-shaped bracket (5.4); and a sounding wall microcavity (5.2) is attached to the copper pillar (5.5).

2. The high-sensitivity magnetic field sensor for whispering-gallery microcavities based on magnetic modulation frequency locking according to claim 1, characterized in that: The laser (1) is a continuously tunable ultra-narrow linewidth laser; the tapered fiber (5.1) is a single-mode polarization-maintaining fiber; the whispering wall microcavity (5.2) is a disk-shaped calcium fluoride crystal resonator, a disk-shaped magnesium fluoride crystal resonator, or a disk-shaped barium fluoride crystal resonator; the magnet (5.3) is a disk-shaped neodymium iron boron magnet, which is adhered to the surface of the whispering wall microcavity (5.2) by UV-curing adhesive; the low-pass filter (10.3) is a digital low-pass filter.

3. The high-sensitivity magnetic field sensor for a whispering-gallery microcavity based on magnetic modulation frequency locking according to claim 1, characterized in that: Tapered optical fiber (5.1) is adhered to U-shaped bracket (5.4) by UV-curing adhesive; whispering wall microcavity (5.2) is adhered to copper column (5.5) by UV-curing adhesive.

4. A method for measuring the high-sensitivity magnetic field of a whispering-gallery microcavity based on magnetic modulation frequency locking, wherein the method is based on the high-sensitivity magnetic field sensor of a whispering-gallery microcavity based on magnetic modulation frequency locking as described in claim 1, characterized in that: This method is implemented using the following steps: First, the control sensor enters the working mode; the working mode is as follows: the laser (1) outputs an optical signal, which is sequentially incident on the photodetector (6) through the isolator (2), polarization controller (3), attenuator (4), tapered fiber (5.1), whispering-gallery microcavity (5.2), and tapered fiber (5.1), and then converted into an electrical signal by the photodetector (6); the electrical signal is transmitted to the mixer (10.2) on one hand, and to the oscilloscope (8) through the lock-in amplifier (7) on the other hand, and is converted into a transmission spectrum by the oscilloscope (8); the transmission spectrum is displayed on the oscilloscope (8) on one hand, and transmitted to the host computer (9) on the other hand; the radio frequency signal source (10.1) outputs a radio frequency signal; the radio frequency signal is transmitted to the mixer (10.2) on one hand, and to the Helmholtz resonator on the other hand. A Helmholtz coil (11) is used to convert the signal into a modulation magnetic field. The modulation magnetic field acts on the sensitive unit, causing the whispering wall microcavity (5.2) to be disturbed, thereby making the electrical signal carry disturbance information. The radio frequency signal and the electrical signal with disturbance information are mixed by a mixer (10.2) and then transmitted to a low-pass filter (10.3), and the error signal is extracted by the low-pass filter (10.3). The error signal is transmitted to a PID controller (10.4). The PID controller (10.4) adjusts the output frequency of the laser (1) in real time according to the error signal, thereby making the output frequency of the laser (1) consistent with the resonant frequency of the whispering wall microcavity (5.2), thereby locking the output frequency of the laser (1) at the resonant frequency of the whispering wall microcavity (5.2). In the working mode, when the magnetic field to be measured acts on the sensitive unit, the resonant frequency of the whispering galvanic cavity (5.2) changes, causing the voltage amplitude of the transmission spectrum to change; the host computer (9) monitors the change in voltage amplitude of the transmission spectrum in real time and calculates the strength of the magnetic field to be measured based on the change in voltage amplitude of the transmission spectrum.

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