A method and system for monitoring the EIT signal lock-in state of a CPT atomic magnetometer

Abstract

This invention discloses a method and system for monitoring the EIT signal lock-in state of a CPT atomic magnetometer. The method modulates the frequency of the microwave signal injected into the laser and demodulates the optical power signal output by the detector to obtain its second harmonic signal. The amplitude of the EIT signal peak is then calculated. By determining whether the amplitude is less than a set threshold, it is determined whether the CPT atomic magnetometer has lost lock. If it has lost lock, the system re-searches for and locks the EIT signal peak, restoring the magnetic field measurement function. This invention addresses the problem of existing CPT magnetometers being unable to determine the EIT signal peak lock-in state; the device can automatically find the EIT signal peak and restore the lock-in state, improving the equipment's engineering applicability.

Description

Technical Field

[0001] This invention relates to a method and system for monitoring the EIT signal lock-in state of a CPT atomic magnetometer, and pertains to the field of CPT atomic magnetometer technology. Background Technology

[0002] The CPT (coherent population trapping) magnetometer is a scalar atomic magnetometer that measures magnetic fields by measuring the Zeeman level splitting interval of atomic energy levels in a magnetic field. The CPT atomic magnetometer is characterized by its miniaturization, absence of directional blind zones, and high precision, and can be applied to fields such as space magnetic field measurement and underwater target detection.

[0003] When the CPT atomic magnetometer is working normally, its microwave signal frequency is locked to the EIT signal peak. When the external magnetic field value changes, the microwave signal frequency locked to the EIT signal peak also changes. By detecting the amount of change in microwave frequency, the external magnetic field value can be obtained. Because the linewidth of the EIT signal is narrow, if the external magnetic field undergoes a step change, causing the microwave signal to be unable to track the EIT signal, the CPT magnetometer will experience a loss of lock. In this case, the magnetic field value output by the CPT magnetometer will be incorrect, which is an erroneous operating mode. Summary of the Invention

[0004] The technical problem solved by this invention is to overcome the shortcomings of the prior art and propose a method and system for monitoring the EIT signal lock-in state of a CPT atomic magnetometer. Existing methods cannot determine the EIT signal peak lock-in state of a CPT magnetometer. By frequency modulation and demodulation of the microwave frequency, the amplitude signal of the EIT signal is obtained. By judging whether the amplitude signal is lower than a set threshold, it is determined whether the CPT magnetometer is in a locked state. If the magnetometer is unlocked, the device can automatically find the EIT signal peak to restore the locked state, improving the engineering applicability of the device.

[0005] The objective of this invention is achieved through the following technical solutions:

[0006] This invention discloses a method for monitoring the EIT signal lock-in state of a CPT atomic magnetometer, comprising:

[0007] The signal with frequency f2 generated by the first signal generator 12 and the microwave signal with frequency f0 generated by the microwave source 10 are injected into the IQ modulator 8 to achieve single-sideband modulation. The IQ modulator 8 outputs a signal with frequency f0+f2 and sends it to the laser 1.

[0008] The second signal generator 11 generates a frequency of 2f. M The signal, after being divided by a frequency divider, yields a frequency of f. MThe signal is injected into the first signal generator 12, and the signal generated by the first signal generator 12 at frequency f1 is modulated so that the first signal generator 12 outputs a signal at frequency f2.

[0009] The microwave signal output by the IQ modulator 8 is injected into the laser 1 to achieve high-frequency modulation of the laser 1. The generated laser light is converted into circularly polarized light by the polarizer 2 and the quarter-wave plate 3, and enters the atomic gas cell 4 to achieve the CPT effect. The light passing through the atomic gas cell 4 is received by the photodetector 5, and converted into a voltage signal describing the change of optical power by the driving circuit 6, and output to the phase-locked loop amplifier 7.

[0010] The frequency 2f output by the second signal generator 11 M Using the signal as a reference signal and the signal output from the drive circuit 6 as the input signal, the two signals are phase-sensitively detected by the lock-in amplifier 7 to obtain the amplitude signal of the EIT signal peak.

[0011] Set a lockout threshold. If the peak amplitude of the EIT signal output by the lockout amplifier 7 is lower than the lockout threshold for a continuous period of time t, it is determined to be in an unlocked state; otherwise, it is in a locked state.

[0012] In the above-described locking state monitoring method, the frequency of the frequency modulation signal input to the first signal generator 12 is half the frequency of the reference signal input to the lock-in amplifier 7.

[0013] In the above-described lockout monitoring method, the value of f2 is f1 + A. M cos2πf M t, where A M For frequency modulation depth.

[0014] In the above-described locking status monitoring method, the signals generated by the first signal generator 12 and the second signal generator 11 are sinusoidal signals or square wave signals.

[0015] In the above-mentioned locked state monitoring method, the frequency of the microwave signal generated by the microwave source 10 is f0 = 3417.344 ± 10 MHz;

[0016] In the above-mentioned locked state monitoring method, f0+f2 is 3417.344MHz±nγB, where γ is the gyromagnetic ratio of alkali metal atoms, B is the magnetic field value of the environment to be measured, n is the locked EIT signal peak, and n is 0, ±1, ±2 or ±3.

[0017] In the above-mentioned locked state monitoring method, the magnetic field value B of the environment to be measured is 100 to 100000 nT.

[0018] In the above-mentioned method for monitoring locked states, the time t is greater than 1 second.

[0019] In the above-mentioned locked state monitoring method, the frequency of the microwave signal is f0 = 3417.344 ± 10 MHz.

[0020] This invention discloses a CPT atomic magnetometer EIT signal lock-in status monitoring system, comprising:

[0021] Microwave source 10: generates a microwave signal with a frequency of f0;

[0022] First signal generator 12: Generates a signal with frequency f1, and receives a signal with frequency f1 sent by frequency divider 9. M After the signal is received, the signal with frequency f1 is modulated to output a signal with frequency f2, which is then sent to the IQ modulator 8.

[0023] IQ modulator 8: Receives a signal with frequency f2 generated by the first signal generator 12 and a microwave signal with frequency f0 generated by the microwave source 10, modulates it, outputs a signal with frequency f0+f2, and sends it to laser 1;

[0024] Second signal generator 11: generates a frequency of 2f M The signal output is sent to the phase-locked loop amplifier 7 and simultaneously sent to the frequency divider 9;

[0025] Frequency divider 9: Receives the frequency 2f transmitted by the second signal generator 11. M The signal, after frequency division, generates a frequency of f. M The signal is sent to the first signal generator 12;

[0026] Laser 1: Receives a signal with a frequency of f0+f2 input from IQ modulator 8. After high-frequency modulation, the generated laser signal is converted into circularly polarized light by polarizer 2 and quarter-wave plate 3 and enters atomic gas cell 4.

[0027] Photodetector 5: Receives circularly polarized light passing through atomic gas cell 4, converts the circularly polarized light into an electrical signal, and sends it to drive circuit 6;

[0028] Drive circuit 6: Converts the electrical signal sent by photodetector 5 into a voltage signal describing the change in optical power, and outputs it to phase-locked loop amplifier 7;

[0029] Phase-locked loop amplifier 7: Converts the frequency 2f output from the second signal generator 11 M Using the signal as a reference signal, the voltage signal output by the drive circuit 6 is used as the input signal for phase-sensitive detection to obtain the amplitude signal of the EIT signal peak.

[0030] Compared with the prior art, the present invention has the following advantages:

[0031] 1. This invention modulates the microwave frequency and uses a second harmonic of the modulation frequency for phase-sensitive detection to obtain its second harmonic signal, thereby obtaining the amplitude signal of the current EIT signal, which can improve the signal detection rate.

[0032] 2. This invention provides that when the magnetometer is normally locked, the signal demodulated by the second harmonic exceeds a set threshold, which can identify that the current state is locked. When the magnetometer is unlocked, the signal demodulated by the second harmonic is zero and lower than the set threshold, which can be used to determine that the magnetometer is unlocked. The current locked state of the magnetometer can be identified. If the magnetometer is unlocked, the locked state can be quickly restored, which has high engineering applicability. Attached Figure Description

[0033] Figure 1 This is a flowchart of the monitoring method of the present invention;

[0034] Figure 2 This is an illustration of the EIT signal lock-in state of the present invention;

[0035] Figure 3 This is a diagram illustrating the EIT signal loss-of-lock state of the present invention. Detailed Implementation

[0036] The following is a detailed explanation with reference to the accompanying drawings.

[0037] like Figure 1 As shown, this invention discloses a method for monitoring the EIT signal lock-in state of a CPT atomic magnetometer, comprising:

[0038] The signal with frequency f2 generated by the first signal generator 12 and the microwave signal with frequency f0 generated by the microwave source 10 are injected into the IQ modulator 8 to achieve single-sideband modulation. The IQ modulator 8 outputs a signal with frequency f0+f2 and sends it to the laser 1; the value of f2 is f1+A. M cos2πf M t, where A M The frequency modulation depth is defined as follows: The microwave signal frequency generated by microwave source 10 is f0 = 3417.344 ± 10 MHz. The frequency of the microwave signal is f0 = 3417.344 ± 10 MHz. The frequency of the frequency-modulated signal input to the first signal generator 12 is half the frequency of the reference signal input to the lock-in amplifier 7. The signals generated by the first signal generator 12 and the second signal generator 11 are sinusoidal or square wave signals. Signal generator 12 generates a signal with frequency f1, such that the sum of f0 and f1 is 3417.344 MHz ± nγB, where γ is the gyromagnetic ratio of the alkali metal atom, B is the magnetic field value of the environment to be measured, and n is the locked EIT signal peak, which can be 0, ±1, ±2, or ±3. The magnetic field value B of the environment to be measured is 100 to 100000 nT.

[0039] The second signal generator 11 generates a frequency of 2f. M The signal, after being divided by a frequency divider, yields a frequency of f. M The signal is injected into the first signal generator 12, and the signal generated by the first signal generator 12 at frequency f1 is modulated so that the first signal generator 12 outputs a signal at frequency f2.

[0040] The microwave signal output by the IQ modulator 8 is injected into the laser 1 to achieve high-frequency modulation of the laser 1. The generated laser light is converted into circularly polarized light by the polarizer 2 and the quarter-wave plate 3, and enters the atomic gas cell 4 to achieve the CPT effect. The light passing through the atomic gas cell 4 is received by the photodetector 5, and converted into a voltage signal describing the change of optical power by the driving circuit 6, and output to the phase-locked loop amplifier 7.

[0041] The frequency 2f output by the second signal generator 11 M Using the signal as a reference signal and the signal output from the drive circuit 6 as the input signal, the two signals are phase-sensitively detected by the lock-in amplifier 7 to obtain the amplitude signal of the EIT signal peak.

[0042] A lockout threshold is set. If the peak amplitude of the EIT signal output by the lock-in amplifier 7 is lower than the lockout threshold for a continuous period of time t, it is determined to be in an unlocked state (e.g., ...). Figure 3 (as shown), otherwise it is in a locked state (as shown). Figure 2 (As shown). Time t is greater than 1 second.

[0043] This invention discloses a CPT atomic magnetometer EIT signal lock-in status monitoring system, comprising:

[0044] Microwave source 10: generates a microwave signal with a frequency of f0;

[0045] First signal generator 12: Generates a signal with frequency f1, and receives a signal with frequency f1 sent by frequency divider 9. M After the signal is received, the signal with frequency f1 is modulated to output a signal with frequency f2, which is then sent to the IQ modulator 8.

[0046] IQ modulator 8: Receives a signal with frequency f2 generated by the first signal generator 12 and a microwave signal with frequency f0 generated by the microwave source 10, modulates it, outputs a signal with frequency f0+f2, and sends it to laser 1;

[0047] Second signal generator 11: generates a frequency of 2f M The signal output is sent to the phase-locked loop amplifier 7 and simultaneously sent to the frequency divider 9;

[0048] Frequency divider 9: Receives the frequency 2f transmitted by the second signal generator 11. MThe signal, after frequency division, generates a frequency of f. M The signal is sent to the first signal generator 12;

[0049] Laser 1: Receives a signal with a frequency of f0+f2 input from IQ modulator 8. After high-frequency modulation, the generated laser signal is converted into circularly polarized light by polarizer 2 and quarter-wave plate 3 and enters atomic gas cell 4.

[0050] Photodetector 5: Receives circularly polarized light passing through atomic gas cell 4, converts the circularly polarized light into an electrical signal, and sends it to drive circuit 6;

[0051] Drive circuit 6: Converts the electrical signal sent by photodetector 5 into a voltage signal describing the change in optical power, and outputs it to phase-locked loop amplifier 7;

[0052] Phase-locked loop amplifier 7: Converts the frequency 2f output from the second signal generator 11 M Using the signal as a reference signal, the voltage signal output by the drive circuit 6 is used as the input signal for phase-sensitive detection to obtain the amplitude signal of the EIT signal peak.

[0053] Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make possible changes and modifications to the technical solutions of the present invention by utilizing the methods and techniques disclosed above without departing from the spirit and scope of the present invention. Therefore, any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solutions of the present invention shall fall within the protection scope of the technical solutions of the present invention.

Claims

1. A method for monitoring the EIT signal lock-in state of a CPT atomic magnetometer, characterized in that, include: The signal with frequency f2 output from the first signal generator (12) and the microwave signal with frequency f0 generated by the microwave source (10) are injected into the IQ modulator (8) to achieve single-sideband modulation. The IQ modulator (8) outputs a signal with frequency f0+f2 and sends it to the laser (1). The second signal generator (11) generates a frequency of 2f M The signal, after being divided by a frequency divider, yields a frequency of f. M The signal is injected into the first signal generator (12) to modulate the signal generated by the first signal generator (12) at a frequency of f1, so that the first signal generator (12) outputs a signal at a frequency of f2. The microwave signal output by the IQ modulator (8) is injected into the laser (1) to achieve high-frequency modulation of the laser (1). The generated laser light is converted into circularly polarized light by the polarizer (2) and the quarter-wave plate (3), and enters the atomic gas cell (4) to achieve the CPT effect. The light passing through the atomic gas cell (4) is received by the photodetector (5), converted into a voltage signal describing the change of optical power by the driving circuit (6), and output to the phase-locked loop amplifier (7). The frequency 2f output by the second signal generator (11) M The signal is used as a reference signal, and the signal output by the driving circuit (6) is used as the input signal. The two signals are phase-sensitively detected by the lock-in amplifier (7) to obtain the amplitude signal of the EIT signal peak. Set a lockout threshold. If the peak amplitude of the EIT signal output by the lockout amplifier (7) is lower than the lockout threshold for a continuous period of time t, it is determined to be in a state of unlocking; otherwise, it is in a state of locking.

2. The method for monitoring the EIT signal lock-in state of a CPT atomic magnetometer according to claim 1, characterized in that: The frequency of the frequency modulation signal input to the first signal generator (12) is half the frequency of the reference signal input to the lock-in amplifier (7).

3. The method for monitoring the EIT signal lock-in state of a CPT atomic magnetometer according to claim 1, characterized in that: The value of f2 is f1 + A M cos(2πf M t), where A M For frequency modulation depth.

4. The method for monitoring the EIT signal lock-in state of a CPT atomic magnetometer according to claim 1, characterized in that: The signals generated by the first signal generator (12) and the second signal generator (11) are sinusoidal signals or square wave signals.

5. The method for monitoring the EIT signal lock-in state of a CPT atomic magnetometer according to claim 1, characterized in that: The microwave signal frequency generated by the microwave source (10) is f0 = 3417.344 ± 10 MHz.

6. The method for monitoring the EIT signal lock-in state of a CPT atomic magnetometer according to claim 1, characterized in that: f0+f2 is 3417.344MHz±nγB, where γ is the gyromagnetic ratio of the alkali metal atom, B is the magnetic field value of the environment to be measured, and n is the locked EIT signal peak, which can be 0, ±1, ±2 or ±3.

7. The method for monitoring the EIT signal lock-in state of a CPT atomic magnetometer according to claim 6, characterized in that: The magnetic field value B of the environment to be tested is 100 to 100,000 nT.

8. The method for monitoring the EIT signal lock-in state of a CPT atomic magnetometer according to claim 1, characterized in that: The time t is greater than 1 second.

9. A method for monitoring the EIT signal lock-in state of a CPT atomic magnetometer according to claim 1, characterized in that: The frequency of the microwave signal is f0 = 3417.344 ± 10 MHz.

10. A CPT atomic magnetometer EIT signal lock-up status monitoring system, characterized in that, include: Microwave source (10): generates a microwave signal with a frequency of f0; First signal generator (12): generates a signal with frequency f1 and receives a signal with frequency f1 sent by the frequency divider (9). M After the signal is modulated, the signal with frequency f1 is modulated and the signal with frequency f2 is output and sent to the IQ modulator (8); IQ modulator (8): Receives the signal with frequency f2 output from the first signal generator (12) and the microwave signal with frequency f0 generated by the microwave source (10), modulates it, outputs a signal with frequency f0+f2, and sends it to the laser (1); Second signal generator (11): generates a frequency of 2f M The signal output is sent to the phase-locked loop amplifier (7) and simultaneously sent to the frequency divider (9); Frequency divider (9): Receives the frequency 2f sent by the second signal generator (11). M The signal, after frequency division, generates a frequency of f. M The signal is sent to the first signal generator (12); Laser (1): Receives a signal with a frequency of f0+f2 input from the IQ modulator (8), and after high-frequency modulation, the generated laser signal is converted into circularly polarized light by the polarizer (2) and the quarter-wave plate (3) and enters the atomic gas cell (4); Photodetector (5): Receives circularly polarized light passing through the atomic gas cell (4), converts the circularly polarized light into an electrical signal, and sends it to the drive circuit (6); Drive circuit (6): Converts the electrical signal sent by photodetector (5) into a voltage signal describing the change in optical power and outputs it to phase-locked loop amplifier (7); Phase-locked loop amplifier (7): The frequency 2f output by the second signal generator (11) M Using the signal as a reference signal, the voltage signal output by the driving circuit (6) is used as the input signal to perform phase-sensitive detection and obtain the amplitude signal of the EIT signal peak.

Images