Echo wall microcavity high-sensitivity magnetic field sensor based on magnetic modulation frequency locking

Abstract

The invention relates to the technical field of magnetic field sensors, in particular to an echo wall microcavity high-sensitivity magnetic field sensor based on magnetic modulation frequency locking, which comprises a laser, an isolator, a polarization controller, an attenuator, a sensing unit, a photoelectric detector, a lock-in amplifier, an oscilloscope, an upper computer, a frequency locking module and a Helmholtz coil, the sensing unit comprises a conical optical fiber, an echo wall microcavity and a magnet, the frequency locking module comprises a radio-frequency signal source, a frequency mixer, a low-pass filter and a PID controller, the emergent end of the laser is connected with the head end of the conical optical fiber through an isolator, a polarization controller and an attenuator in sequence, and the echo wall microcavity is coupled with a conical region of the conical optical fiber. The magnet adheres to the surface of the echo wall microcavity, and the tail end of the conical optical fiber is connected with the incident end of the photoelectric detector. The problems that an existing magnetic field sensor is low in sensitivity and poor in anti-interference capacity are solved, and the magnetic field sensor is suitable for the fields of biomedicine, industrial detection, environment monitoring and the like.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of magnetic field sensors, in particular to an echo wall microcavity high-sensitivity magnetic field sensor based on magnetic force modulation frequency locking. BACKGROUND

[0002] Magnetic field sensors are widely used in biomedical, industrial detection, environmental monitoring and other fields due to their small size, light weight, easy integration and strong multiplicity. However, in practical applications, the existing magnetic field sensors have the problems of low sensitivity and poor anti-interference ability due to their own structure. Specifically, the existing magnetic field sensors generally use a phase modulator 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, thereby resulting in low sensitivity and poor anti-interference ability of the sensor. Therefore, it is necessary to invent an echo wall microcavity high-sensitivity magnetic field sensor based on magnetic force modulation frequency locking to solve the problems of low sensitivity and poor anti-interference ability of the existing magnetic field sensors. SUMMARY

[0003] The present application provides an echo wall microcavity high-sensitivity magnetic field sensor based on magnetic force modulation frequency locking to solve the problems of low sensitivity and poor anti-interference ability of the existing magnetic field sensors.

[0004] The present application is implemented by adopting the following technical solutions: The echo wall microcavity high-sensitivity magnetic field sensor based on magnetic force modulation frequency locking comprises a laser, an isolator, a polarization controller, an attenuator, a sensitive unit, a photodetector, a lock-in amplifier, an oscilloscope, an upper computer, a frequency locking module and a Helmholtz coil. The outgoing end of the laser is connected with the first end of the tapered optical fiber through the isolator, the polarization controller and the attenuator in sequence. 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 tail end of the tapered optical fiber is connected with the incident end of the photodetector. The signal output end of the photodetector is connected with the signal input end of the upper computer through the lock-in amplifier and the oscilloscope in sequence on one hand, and is connected with the first signal input end of the mixer on the other hand. The signal output end of the radio frequency signal source is connected with the second signal input end of the mixer on one hand, and is connected with the signal input end of the Helmholtz coil on the other hand. The signal output end of the mixer is connected with the control end of the laser through the low-pass filter and the PID controller in sequence. The Helmholtz coil is located beside the magnet.

[0005] Further, the laser adopts a continuous tunable ultra-narrow linewidth laser; the tapered fiber adopts a single-mode polarization maintaining fiber; the whispering gallery microcavity adopts a disc-shaped calcium fluoride crystal resonant cavity or a disc-shaped magnesium fluoride crystal resonant cavity or a disc-shaped barium fluoride crystal resonant cavity; the magnet adopts a disc-shaped neodymium-iron-boron magnet which is adhered to the surface of the whispering gallery microcavity through ultraviolet curing glue; and the low-pass filter adopts a digital low-pass filter.

[0006] Further, the sensitive unit further comprises a U-shaped bracket and a copper column; the tapered fiber is adhered to the U-shaped bracket; and the whispering gallery microcavity is adhered to the copper column.

[0007] Further, the tapered fiber is adhered to the U-shaped bracket through ultraviolet curing glue; and the whispering gallery microcavity is adhered to the copper column through ultraviolet curing glue.

[0008] The method is realized based on the high-sensitivity magnetic field sensor for the whispering gallery microcavity based on magnetic force modulation lock frequency, and is realized by the following steps: First, the sensor is controlled to enter a working mode; the working mode is specifically that: a laser outputs an optical signal; the optical signal is sequentially incident on a photodetector through an isolator, a polarization controller, an attenuator, a tapered fiber, a whispering gallery microcavity and another tapered fiber; then the photodetector is converted into an electrical signal; the electrical signal is transmitted to a mixer on one hand and is transmitted to an oscilloscope through a lock-in amplifier on the other hand, and is converted into a transmission spectrum by the oscilloscope; the transmission spectrum is displayed on the oscilloscope on one hand and is transmitted to an upper computer on the other hand; a radio frequency signal source outputs a radio frequency signal; the radio frequency signal is transmitted to the mixer on one hand and is transmitted to a Helmholtz coil on the other hand, and is converted into a modulated magnetic field by the Helmholtz coil; the modulated magnetic field acts on the sensitive unit, so that the whispering gallery microcavity is disturbed, and thus the electrical signal has disturbance information; the radio frequency signal and the electrical signal with disturbance information are mixed by the mixer and then transmitted to a low-pass filter, and an error signal is extracted by the low-pass filter; 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, so that the output frequency of the laser is consistent with the resonance frequency of the whispering gallery microcavity, thereby locking the output frequency of the laser at the resonance frequency of the whispering gallery microcavity. In the working mode, when a to-be-measured magnetic field acts on the sensitive unit, the resonance frequency of the whispering gallery microcavity changes, so that the voltage amplitude of the transmission spectrum changes; the upper computer monitors the voltage amplitude change of the transmission spectrum in real time, and calculates the strength of the to-be-measured magnetic field according to the voltage amplitude change of the transmission spectrum.

[0009] Compared with the prior art, the present application does not use a phase modulator for PDH frequency locking, but uses a radio frequency signal source and a Helmholtz coil to introduce a modulation magnetic field, cooperates with a mixer, a low-pass filter and a PID controller to perform frequency locking, so that the optical path is simplified, the implementation cost is reduced, high-frequency noise is avoided, the sensor sensitivity is higher and the anti-interference ability is stronger.

[0010] The present application effectively solves the problems of low sensitivity and poor anti-interference ability of the prior art magnetic field sensor, and is suitable for the fields of biomedicine, industrial detection and environmental monitoring. BRIEF DESCRIPTION OF DRAWINGS

[0011] Figure 1 is a structural schematic diagram of the present application.

[0012] Figure 2 is a structural schematic diagram of the sensitive unit in the present application.

[0013] Figure 3 is a top view of Figure 2 .

[0014] Figure 4 is a bottom view of Figure 2 .

[0015] In the figure: 1-laser, 2-isolator, 3-polarization controller, 4-attenuator, 5.1-tapered optical fiber, 5.2-echo wall microcavity, 5.3-magnet, 5.4-U-shaped bracket, 5.5-copper column, 6-optoelectronic detector, 7-phase-locked amplifier, 8-oscilloscope, 9-upper computer, 10.1-radio frequency signal source, 10.2-mixer, 10.3-low-pass filter, 10.4-PID controller, 11-Helmholtz coil. DETAILED DESCRIPTION

[0016] The echo wall microcavity high-sensitivity magnetic field sensor based on magnetic force modulation frequency locking comprises a laser 1, an isolator 2, a polarization controller 3, an attenuator 4, a sensitive unit, an optoelectronic detector 6, a phase-locked amplifier 7, an oscilloscope 8, an upper computer 9, a frequency locking module and a Helmholtz coil 11; the sensitive unit comprises a tapered optical fiber 5.1, an echo wall microcavity 5.2 and a magnet 5.3; the frequency locking module comprises a radio frequency signal source 10.1, a mixer 10.2, a low-pass filter 10.3 and a PID controller 10.4. The exit end of the laser 1 is connected with the first end of the taper fiber 5.1 through the isolator 2, the polarization controller 3 and the attenuator 4 in sequence; the echo wall microcavity 5.2 is coupled with the taper region of the taper fiber 5.1; the magnet 5.3 is adhered to the surface of the echo wall microcavity 5.2; the tail end of the taper fiber 5.1 is connected with the entrance end of the photoelectric detector 6; the signal output end of the photoelectric detector 6 is connected with the signal input end of the upper computer 9 through the lock-in amplifier 7 and the oscilloscope 8 in sequence on one hand, and is connected with the first signal input end of the frequency mixer 10.2 on the other hand; the signal output end of the radio frequency signal source 10.1 is connected with the second signal input end of the frequency mixer 10.2 on one hand, and is connected with the signal input end of the Helmholtz coil 11 on the other hand; the signal output end of the frequency mixer 10.2 is connected with the control end of the laser 1 through the low-pass filter 10.3 and the PID controller 10.4 in sequence; the Helmholtz coil 11 is located beside the magnet 5.3.

[0017] The laser 1 adopts a continuous tunable ultra-narrow linewidth laser; the taper fiber 5.1 adopts a single-mode polarization maintaining optical fiber; the echo wall microcavity 5.2 adopts a disc-shaped calcium fluoride crystal resonant cavity or a disc-shaped magnesium fluoride crystal resonant cavity or a disc-shaped barium fluoride crystal resonant cavity; the magnet 5.3 adopts a disc-shaped neodymium-iron-boron magnet which is adhered to the surface of the echo wall microcavity 5.2 through ultraviolet curing glue; and the low-pass filter 10.3 adopts a digital low-pass filter.

[0018] The sensitive unit further comprises a U-shaped bracket 5.4 and a copper column 5.5; the taper fiber 5.1 is adhered to the U-shaped bracket 5.4; and the echo wall microcavity 5.2 is adhered to the copper column 5.5.

[0019] The taper fiber 5.1 is adhered to the U-shaped bracket 5.4 through ultraviolet curing glue; and the echo wall microcavity 5.2 is adhered to the copper column 5.5 through ultraviolet curing glue.

[0020] The echo wall microcavity high-sensitivity magnetic field measurement method based on magnetic force modulation lock frequency is realized based on the echo wall microcavity high-sensitivity magnetic field sensor based on magnetic force modulation lock frequency, and is realized by the following steps: Firstly, the sensor is controlled to enter a working mode; the working mode is specifically as follows: the laser 1 outputs an optical signal, the optical signal is sequentially incident to a photodetector 6 through an isolator 2, a polarization controller 3, an attenuator 4, a tapered optical fiber 5.1, a whispering gallery microcavity 5.2, the tapered optical fiber 5.1, and then is converted into an electrical signal by the photodetector 6; the electrical signal is transmitted to a mixer 10.2 on one hand and is transmitted to an oscilloscope 8 through a 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 is transmitted to an upper computer 9 on the other hand; a 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 is converted into a modulated magnetic field by a Helmholtz coil 11 on the other hand; the modulated magnetic field acts on a sensitive unit, so that the whispering gallery microcavity 5.2 is disturbed, thereby the electrical signal has disturbance information; the radio frequency signal and the electrical signal having the disturbance information are mixed by the mixer 10.2 and then are transmitted to a low-pass filter 10.3, and an 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, so that the output frequency of the laser 1 is consistent with the resonance frequency of the whispering gallery microcavity 5.2, thereby the output frequency of the laser 1 is locked on the resonance frequency of the whispering gallery microcavity 5.2; In the working mode, when a to-be-measured magnetic field acts on the sensitive unit, the resonance frequency of the whispering gallery microcavity 5.2 changes, so that the voltage amplitude of the transmission spectrum changes; the upper computer 9 monitors the voltage amplitude change amount of the transmission spectrum in real time, and calculates the strength of the to-be-measured magnetic field according to the voltage amplitude change amount of the transmission spectrum.

[0021] In specific implementation, the center wavelength of the laser 1 is 1550 nm, and the line width is less than or equal to 10 kHz; the tapered optical fiber 5.1 is processed by a fusion taper method, and the length is 3 cm; the whispering gallery microcavity 5.2 is processed by a single-point diamond cutting process and a hand precision grinding and polishing process, and the roughness is less than nm order, and the Q value is greater than 5*10 8 The diameter of the copper column 5.5 is 3 mm.

[0022] Although the specific embodiments of the present application are described above, those skilled in the art should understand that these are only illustrative, and the protection scope of the present application 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 application, and these changes and modifications all fall within the protection scope of the present application.

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) in turn. The output terminal of the mixer (10.2) is connected to the control terminal of the laser (1) in sequence through the low-pass filter (10.3) and the PID controller (10.4). The Helmholtz coil (11) is located next to the magnet (5.3).

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: 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).

4. The high-sensitivity magnetic field sensor for a whispering-gallery microcavity based on magnetic modulation frequency locking according to claim 3, 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.

5. 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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