CN113721173B - A Fiber-optic SERF Atomic Magnetometer Device Based on Reflective Bidirectional Pumping - Google Patents

Abstract

The invention discloses an optical fiber SERF atomic magnetometer device based on a reflection type bidirectional pump, which relates to the field of optical fiber weak magnetic detection and solves the technical problems that the size of the existing integral structure cannot be further reduced and the structure is difficult to miniaturize; the light source comprises a beam of pumping detection laser and a beam of heating laser, the sensing module comprises a magnetic field coil, an alkali metal atom air chamber, a reflector and a self-focusing lens, and the modulation and demodulation module comprises a photodiode, a transimpedance amplifier and a phase-locked amplifier to realize magnetic field modulation and signal demodulation. The invention avoids the photoelectric conversion near the air chamber in the traditional method, adopts the all-optical structure for detection, avoids the magnetic noise brought by the photoelectric conversion circuit, and improves the detection sensitivity; meanwhile, a reflection type bidirectional pumping structure is adopted, so that the polarizability in the atomic gas chamber is more uniform, and the stability and the accuracy of magnetic field detection are improved.

Description

A Fiber-optic SERF Atomic Magnetometer Device Based on Reflective Bidirectional Pumping

technical field

The invention relates to the field of optical fiber weak magnetic detection, and more particularly to an optical fiber SERF atomic magnetometer device based on reflective bidirectional pumping.

Background technique

The SERF magnetic field measurement device has great application value in the fields of industry, agriculture, medical treatment and scientific research. Compared with other magnetic field detection devices, it has the advantages of ultra-high sensitivity and can be measured close to the surface of the object to be measured. The detection of mineral deposits is essentially the detection of abnormal fields. Different minerals have different magnetic field characteristics. Therefore, the use of SERF magnetic field measurement devices can accurately know the type, scale and location of underground or seabed minerals, which will play an important role in the development of industry and agriculture. Important role in promoting; in medical imaging, SERF magnetic field measurement device does not require an externally enhanced magnetic field, and has the advantages of "dynamic measurement, no damage to the human body, and overall, multi-directional imaging".

At present, a magnetic field detection method based on SERF has been realized, which can detect extremely weak magnetic fields. However, this method usually introduces some circuit parts near the probe, which brings additional interference magnetic field noise and hinders further improvement of sensitivity; at the same time , due to the existence of the circuit part, the overall structure size cannot be further reduced, and it is difficult to realize the structure miniaturization.

SUMMARY OF THE INVENTION

The purpose of the present invention is: in order to solve the above-mentioned technical problems, the present invention provides a kind of optical fiber SERF atomic magnetometer device based on reflection type bidirectional pumping, which is used to improve the magnetic field detection sensitivity, stability, accuracy and make the sensor probe structure miniature. change.

The present invention specifically adopts the following technical solutions in order to achieve the above object:

An optical fiber SERF atomic magnetometer device based on reflective bidirectional pumping, comprising a light source, a sensing module and a modulation and demodulation module, the light source includes a heating light source, a pump detection light source, and a polarization controller; The sensing module includes a circulator, a magnetic field coil, a first optical fiber collimator, an alkali metal atomic gas chamber (7), a reflector, and a second optical fiber collimator; the modulation and demodulation module includes a photodiode, a transimpedance amplifier , lock-in amplifier;

The heating light source is connected with the second fiber collimator, the pump detection light source is connected with the polarization controller, the output end of the polarization controller is connected with the first port of the circulator, and the second port of the circulator is connected with the first fiber collimator, The three ports of the circulator are connected to the photodiode; the reference output end of the lock-in amplifier is connected to the magnetic field coil, the input end of the transimpedance amplifier is connected to the output end of the photodiode, and the output end of the transimpedance amplifier is connected to the lock-in amplifier;

One end of the first optical fiber collimator away from the circulator is sequentially provided with an alkali metal atomic gas chamber and a reflector, a second optical fiber collimator is arranged on the top of the alkali metal atomic gas chamber, and the outgoing light of the second optical fiber collimator is the same as that of the first optical fiber collimator. The outgoing light of the fiber collimator is perpendicular to each other.

As an optional technical solution, the pump light of the pump detection light source passes through the alkali metal atomic gas cell and is vertically incident on the mirror, and the reflected pump light passes through the alkali metal atomic gas cell again, After passing through the self-focusing lens on the first optical fiber collimator (6), it is coupled into the optical fiber again, and output to the outside of the magnetic shielding barrel to form a passive sensor head structure;

The optical signal is output to the modulation and demodulation module through the circulator outside the magnetic shielding barrel, and photoelectric conversion and data processing are performed in the modulation and demodulation module.

As an optional technical solution, in the sensing module, the pumping light power of the pumping and detecting light source will attenuate with the increase of the propagation distance in the alkali metal atom gas chamber, thereby causing the pumping rate to decrease;

Define the intersection of the pump light and the alkali metal atomic gas chamber as the origin 0, and the pump light propagation direction is the positive direction of the x-axis, then the relationship between the pumping rate R _p1 and the spatial abscissa x in the alkali metal atomic gas chamber is the formula one:

Among them, lambertw() is the Lambert W function, R _r is the relaxation rate, and R _p0 is the pump rate that has not yet decayed at the incident;

After the pump light reaches the mirror, it will be completely reflected and enter the alkali metal atomic gas chamber again, forming a bidirectional pump. The relationship between the second pumping rate R _p2 and the spatial abscissa x in the alkali metal atomic gas chamber is formula 2 :

where x _M is the abscissa of the point where the first pump light is emitted from the atomic gas cell, that is, the length of the atomic gas cell along the light propagation direction;

Further, after bidirectional pumping, the total pumping rate _Rp in the alkali metal atom gas chamber (7) is the sum of the two pumping rates, that is, formula 3:

R _p =R _p1 +R _p2

In formula 3, R _p1 decreases monotonically with the increase of x, so it will cause the inhomogeneity of the pumping rate in the alkali metal atomic gas chamber, while R _p2 increases monotonically with the increase of x, which can compensate for the inhomogeneity of the first term, This results in a more uniform pumping rate.

As an optional technical solution, the atomic polarizability P in the alkali metal atomic gas chamber is formula 4:

As an optional technical solution, the central wavelength of the pump detection light source is 795nm, 894nm or 770nm, corresponding to the D1 line of rubidium atom, cesium atom and potassium atom respectively, and the output laser is linearly polarized light;

The operating wavelengths of the circulator, the first fiber collimator and the photodiode are matched with the central wavelength of the pumping and detecting light source (2).

As an optional technical solution, the output power of the heating light source is more than 150mw, and its power needs to ensure that it can heat the gas chamber so that the alkali metal atoms in the gas chamber can change from solid to gas; the second optical fiber collimator The operating wavelength matches the central wavelength of the heating light source.

As an optional technical solution, the alkali metal atomic gas chamber is attached with an absorption filter on both sides of the light-transmitting surface of the heating light source, and its absorption center wavelength is consistent with the center wavelength of the heating light source, and the output side is The thickness of the filter is thicker than that of the filter on the incident side, so that the light energy absorbed by the two filters is equal, and the air chamber can be heated uniformly from both sides.

As an optional technical solution, the modulation signal generated by the modulation and demodulation module is a sinusoidal signal with a frequency of ω and an amplitude of B ₁ , and the demodulated output signal is

Among them, γe is the gyromagnetic ratio of alkali metal atoms, B ₀ is the amplitude of the magnetic field to be measured, J ₀ is the 0-order Bessel function, J ₁ is the 1-order Bessel function, Q is the nuclear deceleration factor, and R _p is the light pump rate, R _r is the relaxation rate, and P is the atomic polarizability in the gas cell.

The beneficial effects of the present invention are as follows:

1. Compared with the traditional SERF atomic magnetometer device, this method uses a reflector and a self-focusing lens to couple the probe beam into the optical fiber and transmit it to the outside of the magnetic shielding barrel for photoelectric conversion, and the photoelectric conversion circuit on the magnetic sensing probe is removed. And the number of optical fibers is reduced, so that the structure size can be further reduced, which is convenient for integration and array applications.

2. Since the photoelectric conversion circuit near the alkali metal atomic gas chamber is removed, the magnetic field noise brought by this part of the circuit is eliminated.

3. After bidirectional pumping with mirrors, the uniformity of the pumping rate in the alkali metal atomic gas chamber is improved, thereby also improving the uniformity of the polarizability, which is beneficial to improve the stability and accuracy of the system measurement.

4. The use of reflective optical coupling structure can reduce the number of optical fibers and optical components in the weak magnetic sensor probe, thereby reducing the size and volume of the sensor head and improving the reliability of the sensor head

Description of drawings

Fig. 1 is the system schematic diagram of the present invention;

Reference signs: 1-heating light source, 2-laser, 3-polarization controller, 4-three-port circulator, 5-magnetic field coil, 6-first fiber collimator, 7-alkali metal atomic gas cell, 8- Mirror, 9-second fiber collimator, 10-photodiode, 11-transimpedance amplifier, 12-lock-in amplifier.

Detailed ways

In order to make the purposes, 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. Obviously, the described embodiments These are some embodiments of the present invention, but not all embodiments. The components of the embodiments of the invention generally described and illustrated in the drawings herein may be arranged and designed in a variety of different configurations.

Thus, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the invention as claimed, but is merely representative of selected embodiments of the invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

Example 1

As shown in Figure 1, the alkali metal atomic gas chamber 7 can adopt rubidium atom, cesium atom, potassium atom, the present embodiment 1 is preferably a rubidium atomic gas chamber; a kind of optical fiber SERF atomic magnetic force based on reflection type bidirectional pumping of the present invention The instrument device includes a light source, a sensing module, a modulation and demodulation module. The light source includes a beam of 1550nm laser and a beam of 795nm laser. The 1550nm laser heats the rubidium atomic gas chamber, and the output power of the laser needs to be greater than 150mw, so that it is output from the second fiber collimator 9 and hits the rubidium atomic gas. On the chamber, the rubidium atomic gas chamber can be heated to about 150°C. The 795nm light source outputs linearly polarized light, which becomes left-handed circularly polarized light after passing through the polarization controller 3, which is input from the first port of the circulator 4 and output from the second port, and then exits on the rubidium atomic gas chamber through the first fiber collimator 6. After passing through the rubidium atomic gas chamber, it hits the reflector 8 vertically, and the reflected light is reflected back and enters the rubidium atomic gas chamber again. Outside the shielding barrel, the magnetic field coil inside the magnetic shielding barrel is driven by the reference output of the lock-in amplifier 12 to generate a modulated magnetic field with a certain frequency. Outside the magnetic shielding barrel, the measured optical signal is output from the three ports of the circulator 4, and the optical signal is converted into a current signal by the photodiode 10, and then amplified by a certain multiple of the transimpedance amplifier 11 and converted into a voltage signal, and then transmitted to the lock-in amplifier. 12 Perform demodulation processing.

Example 2

Further, include the following steps:

Step 1: The output laser of the laser 1 is a 1550nm laser, and its output power needs to be greater than 150mW so as to be able to heat the alkali metal atomic gas chamber at about 7 to 150°C. The laser 2 outputs 795nm linearly polarized light, which is converted by the polarization controller 3 For left-handed circularly polarized light, the two laser beams are orthogonally emitted and hit on the alkali metal atomic gas chamber 7 . The relationship between the first pumping rate Rp1 and the spatial abscissa x in the alkali metal atom gas cell 7 is formula 1:

Among them, lambertw() is the Lambert W function, R _r is the relaxation rate, and R _p0 is the pump rate that has not yet decayed at the time of incidence.

After passing through the mirror, the pump light enters the alkali metal atomic gas chamber 7 again to form bidirectional pumping. The relationship between the second pumping rate Rp2 and x is formula 2:

where x _M is the abscissa of the point where the first pump light is emitted from the atomic gas cell, that is, the length of the atomic gas cell along the light propagation direction;

Further, after bidirectional pumping, the total pumping rate _Rp in the alkali metal atom gas chamber (7) is the sum of the two pumping rates, that is, formula 3:

R _p =R _p1 +R _p2

Further, the atomic polarizability P in the alkali metal atomic gas chamber 7 is the formula 4:

In Equation 4, the first term R _p1 on the right side decreases monotonically with the increase of x, which will cause the inhomogeneity of the pumping rate in the alkali metal atomic gas chamber, while the second term R _p2 increases monotonically with the increase of x, which can be used for the first term. The inhomogeneity is compensated to obtain a relatively uniform pump rate, which also improves the uniformity of the polarizability.

Step 2: The reference output of the lock-in amplifier 12 is connected to the magnetic field coil 5 to generate a modulated magnetic field B ₁ cosωt with a frequency of ω and an amplitude of B1.

Step 3: After 795 nm is emitted from the air chamber again, it is coupled into the optical fiber through the self-focusing lens on the optical fiber collimator 6, and then transmitted out of the magnetic shielding barrel, where the photodiode 10 performs photoelectric conversion.

The light intensity signal Sx detected by the photodiode 10 is proportional to the polarization component Px, and its first harmonic term is formula 5:

Among them, γe is the gyromagnetic ratio of alkali metal atoms, B ₀ is the amplitude of the magnetic field to be measured, J ₀ is the 0-order Bessel function, J ₁ is the 1-order Bessel function, Q is the nuclear deceleration factor, and R _p is the light pump rate, R _r is the relaxation rate, and P is the atomic polarizability in the gas cell.

Step 4: Use the lock-in amplifier 12 to lock-in and amplify the first harmonic term to extract the field-weakening signal B0 to be measured from the noise. In the zero-field range, the expression can be approximated as formula 6:

Further, since parameters such as photoelectric conversion coefficient k, modulation amplitude B1, modulation frequency ω, pump rate Rp, relaxation rate Rr, and gyromagnetic ratio re will not change after adjustment and stabilization, linear output can be achieved.

Through the above steps 1 to 4, thanks to the reflective bidirectional pumping method, the spatial uniformity of the atomic polarizability in the atomic gas chamber is improved, thereby improving the stability and reliability of the detection results. The method avoids photoelectric conversion near the alkali metal atomic gas chamber 7 and avoids the additional magnetic field brought by the photoelectric conversion circuit, thereby further reducing the magnetic noise and making the device have higher detection sensitivity. The photoelectric conversion circuit and the number of optical fibers on the sensing probe make the structure of the sensing probe further miniaturized, which is convenient for integration and array applications.

The above are only preferred embodiments of the present invention, and are not intended to limit the protection scope of the present invention. Any modifications, equivalent replacements and improvements made by any person skilled in the art within the spirit and principles of the present invention, etc. , should be included within the protection scope of the present invention.

Claims (7)

1. a kind of optical fiber SERF atomic magnetometer device based on reflective bidirectional pumping, comprises light source, sensing module and modulation, demodulation module, it is characterized in that, described light source comprises heating light source (1), pump detection light source (2), a polarization controller (3); the sensing module includes a circulator (4), a magnetic field coil (5), a first optical fiber collimator (6), an alkali metal atomic gas chamber (7), a reflection a mirror (8), a second fiber collimator (9); the modulation and demodulation module includes a photodiode (10), a transimpedance amplifier (11), and a lock-in amplifier (12); The heating light source (1) is connected with the second fiber collimator (9), the pump detection light source (2) is connected with the polarization controller (3), and the output end of the polarization controller (3) is connected with the circulator (4). ) one port is connected, the second port of the circulator (4) is connected to the first fiber collimator (6), and the three ports of the circulator (4) are connected to the photodiode (10); the lock-in amplifier (12) refers to the output end is connected with the magnetic field coil (5), the input end of the transimpedance amplifier (11) is connected with the output end of the photodiode (10), and the output end of the transimpedance amplifier (11) is connected with the lock-in amplifier (12); One end of the first optical fiber collimator (6) away from the circulator (4) is sequentially provided with an alkali metal atomic gas chamber (7) and a reflector (8), and the top of the alkali metal atomic gas chamber (7) is provided with a second optical fiber collimator device (9), and the outgoing light of the second optical fiber collimator (9) and the outgoing light of the first optical fiber collimator (6) are perpendicular to each other; In the sensing module, the pumping light power of the pumping and detecting light source (2) will attenuate as the propagation distance in the alkali metal atom gas chamber (7) increases, thereby causing the pumping rate to decrease; Define the point of intersection of the pump light and the alkali metal atom gas cell (7) as the origin O, and the pump light propagation direction is the positive direction of the x-axis, then the pump rate R _p1 and the space in the alkali metal atom gas cell (7) The relationship between the abscissa x is formula 1:

Among them, lambertw() is the Lambert W function, R _r is the relaxation rate, and R _p0 is the pump rate that has not yet decayed at the incident; After the pump light reaches the mirror (8), it will all be reflected and enter the alkali metal atomic gas chamber (7) again, forming a bidirectional pump. The second pumping rate R _p2 and the alkali metal atomic gas chamber (7) The relationship between the spatial abscissa x of , is formula 2:

where x _M is the abscissa of the point where the first pump light is emitted from the atomic gas cell, that is, the length of the atomic gas cell along the light propagation direction; Further, after bidirectional pumping, the total pumping rate _Rp in the alkali metal atom gas chamber (7) is the sum of the two pumping rates, that is, formula 3: R _p =R _p1 +R _p2 In formula 3, R _p1 decreases monotonically with the increase of x, so it will cause the inhomogeneity of the pumping rate in the alkali metal atomic gas chamber, while R _p2 increases monotonically with the increase of x, which can compensate for the inhomogeneity of the first term, This results in a more uniform pumping rate. 2. a kind of optical fiber SERF atomic magnetometer device based on reflection type bidirectional pumping according to claim 1, is characterized in that, the pump light of described pump detection light source (2) passes through alkali metal atom gas chamber ( 7) and then vertically incident on the mirror (8), the reflected pump light passes through the alkali metal atomic gas chamber (7) again, and is coupled again after passing through the self-focusing lens on the first fiber collimator (6). Enter the optical fiber and output to the outside of the magnetic shielding barrel to form a passive sensor head structure; The optical signal is output to the modulation and demodulation module through the circulator (4) outside the magnetic shielding barrel, and photoelectric conversion and data processing are performed in the modulation and demodulation module. 3. a kind of optical fiber SERF atomic magnetometer device based on reflection type bidirectional pumping according to claim 1, is characterized in that, atomic polarizability P in alkali metal atom gas chamber (7) is formula four:

4. a kind of optical fiber SERF atomic magnetometer device based on reflective bidirectional pumping according to claim 1, is characterized in that, the central wavelength of described pump detection light source (2) is 795nm, 894nm or 770nm, corresponding to respectively The D1 line of rubidium atom, cesium atom and potassium atom, and its output laser is linearly polarized light; The operating wavelengths of the circulator (4), the first fiber collimator (6) and the photodiode (10) are matched with the central wavelength of the pumping and detecting light source (2). 5. a kind of optical fiber SERF atomic magnetometer device based on reflective bidirectional pumping according to claim 1, is characterized in that, the output power of described heating light source (1) is more than 150mw, and its power needs to guarantee that can heat The gas chamber enables the alkali metal atoms in the gas chamber to change from a solid state to a gaseous state; the working wavelength of the second optical fiber collimator (9) matches the central wavelength of the heating light source (1). 6. a kind of optical fiber SERF atomic magnetometer device based on reflective bidirectional pumping according to claim 1, is characterized in that, described alkali metal atomic gas chamber (7) is on the two sides of the light passing surface of heating light source (1). An absorption filter is affixed on the side, the absorption center wavelength of which is consistent with the center wavelength of the heating light source (1), and the thickness of the filter on the output side is thicker than that on the incident side. 7. a kind of optical fiber SERF atomic magnetometer device based on reflection type bidirectional pumping according to claim 1, is characterized in that, the modulation signal that described modulation, demodulation module produces is that frequency is ω, and amplitude is B ₁ sinusoidal signal, the demodulated output signal is

Among them, γ _e is the gyromagnetic ratio of alkali metal atoms, B ₀ is the amplitude of the magnetic field to be measured, J ₀ is the zero-order Bessel function, J ₁ is the first-order Bessel function, Q is the nuclear deceleration factor, and R _p is the optical pumping rate, R _r is the relaxation rate, and P is the atomic polarizability in the gas cell.

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