阅读说明：本技术 一种基于反射式双向泵浦的光纤serf原子磁力仪装置 (Optical fiber SERF atomic magnetometer device based on reflection type bidirectional pumping ) 是由 欧中华 张洋 何孟阳 任博康 岳慧敏 于 2021-09-02 设计创作，主要内容包括：本发明公开了一种基于反射式双向泵浦的光纤SERF原子磁力仪装置,涉及光纤弱磁探测领域,解决现有整体结构尺寸不能进一步缩小,难以实现结构微型化的技术问题,包括光源,传感模块,调制、解调模块；所述的光源包括一束泵浦探测激光,一束加热激光,传感模块包括磁场线圈、碱金属原子气室、反射镜和自聚焦透镜,调制、解调模块包括光电二极管、跨阻放大器、锁相放大器实现对磁场调制以及对信号解调。本发明避免了传统方法中在气室附近进行光电转换,采用全光结构进行探测,避免了光电转换电路带来的磁噪声,提高了探测灵敏度；同时采用反射式双向泵浦结构,使原子气室内的极化率更加均匀,有助于提高磁场探测的稳定性、准确性。(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 realize miniaturization; 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 trans-impedance 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.)

1. An optical fiber SERF atomic magnetometer device based on reflection type bidirectional pumping comprises a light source, a sensing module, a modulation module and a demodulation module, and is characterized in that the light source comprises a heating light source (1), a pumping detection light source (2) and a polarization controller (3); the sensing module comprises a circulator (4), a magnetic field coil (5), a first optical fiber collimator (6), an alkali metal atom air chamber (7), a reflector (8) and a second optical fiber collimator (9); the modulation and demodulation module comprises a photodiode (10), a trans-impedance amplifier (11) and a phase-locked amplifier (12);

the heating light source (1) is connected with an optical fiber collimator (9), the pumping detection light source (2) is connected with a polarization controller (3), the output end of the polarization controller (3) is connected with one port of a circulator (4), the second port of the circulator (4) is connected with a first optical fiber collimator (6), and the third port of the circulator (4) is connected with a photodiode (10); the reference output end of the phase-locked amplifier (12) is connected with the magnetic field coil (5), the input end of the trans-impedance amplifier (11) is connected with the output end of the photodiode (10), and the output end of the trans-impedance amplifier (11) is connected with the phase-locked amplifier (12);

one end of the first optical fiber collimator (6) far away from the circulator (4) is sequentially provided with an alkali metal atom air chamber (7) and a reflector (8), the top of the alkali metal atom air chamber (7) is provided with a second optical fiber collimator (9), and emergent light of the second optical fiber collimator (9) is perpendicular to emergent light of the first optical fiber collimator (6).

2. The optical fiber SERF atomic magnetometer device based on the reflective bidirectional pumping of claim 1, wherein the pump light of the pump detection light source (2) vertically enters the reflector (8) after passing through the alkali metal atom gas chamber (7), and the reflected pump light passes through the alkali metal atom gas chamber (7) again, passes through the self-focusing lens on the first optical fiber collimator (6), is coupled into the optical fiber again, and is output to the outside of the magnetic shielding barrel to form a passive sensing head structure;

the optical signal is output to the modulation and demodulation module through the circulator (4) outside the magnetic shielding barrel, and the modulation and demodulation module carries out photoelectric conversion and data processing.

3. The optical fiber SERF atomic magnetometer device based on the reflective bidirectional pumping according to claim 1, wherein in the sensing module, the pump light power of the pump detection light source (2) will be attenuated as the propagation distance in the alkali metal atom gas chamber (7) increases, thereby causing the pump rate to decrease;

define the gas chamber of the alkali metal atom when the pump light is incident(7) The intersection point of the two is the origin O, the propagation direction of the pump light is the positive direction of the x axis, and then the pumping rate R_p1The relation with the space abscissa x in the alkali metal atom gas chamber (7) is shown as formula I:

wherein lambertiw () is the lambertian W function, R_rFor relaxation rate, R_p0Pump rate at incidence that has not yet attenuated;

after reaching the reflector (8), the pumping light is totally reflected and enters the alkali metal atom gas chamber (7) again to form bidirectional pumping with a second pumping rate R_p2The relation with the space abscissa x in the alkali metal atom gas chamber (7) is shown as a formula II:

wherein x_MThe abscissa of the point of the first-time pump light emergent from the atomic gas chamber represents the length of the atomic gas chamber along the light propagation direction;

further, the total pumping rate R in the alkali metal atom air chamber (7) after bidirectional pumping_pIs the sum of two pumping rates, namely formula three:

R_p＝R_p1+R_p2

in formula III, R_p1Monotonically decreases as x increases, thereby causing non-uniformity in pumping rate in the gas chamber of alkali metal atoms, and R_y2The non-uniformity of the first term can be compensated for by a monotonic increase with increasing x, resulting in a more uniform pumping rate.

4. The fiber SERF atomic magnetometer device based on the reflective bidirectional pumping of claim 1, wherein the atomic polarizability P in the alkali metal atom gas chamber (7) is the formula four:

5. the optical fiber SERF atom magnetometer device based on the reflection type bidirectional pumping according to the claim 1, characterized in that the central wavelength of the pumping detection light source (2) is 795nm, 894nm or 770nm, which respectively corresponds to the D1 line of rubidium atom, cesium atom and potassium atom, and the output laser light is linearly polarized light;

the working wavelengths of the circulator (4), the first optical fiber collimator (6) and the photodiode (10) are matched with the central wavelength of the pump detection light source (2).

6. The fiber SERF atomic magnetometer device based on the reflective bidirectional pumping according to claim 1, wherein the output power of the heating light source (1) is above 150mw, and the power is required to ensure that the gas chamber can be heated to change the alkali metal atoms in the gas chamber from a solid state to a gas state; the working wavelength of the second optical fiber collimator (9) is matched with the central wavelength of the heating light source (1).

7. The optical fiber SERF atomic magnetometer device based on the reflective bidirectional pumping of claim 1, wherein the alkali metal atom gas chamber (7) is attached with an absorption filter on both sides of the light-passing surface of the heating source (1), the absorption center wavelength of the absorption filter is consistent with the center wavelength of the heating light source (1), and the thickness of the filter on the outgoing side is thicker than that of the filter on the incoming side.

8. The fiber SERF atomic magnetometer device based on reflective bidirectional pumping of claim 1, wherein the modulation signal generated by the modulation and demodulation module is frequency ω and amplitude B₁Of the demodulated output signal of

Wherein, γ_eIs the alkali metal atom gyromagnetic ratio, B₀For the amplitude of the magnetic field to be measured, J₀Is a Bessel function of order 0, J₁Is a Bessel function of order 1, Q is a nuclear slowdown factor, R_pFor optical pumping rate, R_rFor relaxation, P is the atomic polarizability in the gas cell.

Technical Field

The invention relates to the field of optical fiber weak magnetic detection, in particular to an optical fiber SERF atomic magnetometer device based on reflection type bidirectional pumping.

Background

The SERF magnetic field measuring device has great application value in the fields of industry, agriculture, medical treatment, scientific research and the like, and has the advantages of ultrahigh sensitivity, capability of being tightly attached to the surface of a measured object for measurement and the like compared with other magnetic field detecting devices. The mineral deposit detection is carried out, essentially, the detection of an abnormal field is carried out, and different mineral products have different magnetic field characteristics, so that the type, scale and position of underground or seabed mineral products can be accurately known by utilizing the SERF magnetic field measuring device, and the method plays an important role in promoting the development of industry and agriculture; in the aspect of medical imaging, the SERF magnetic field measuring device does not need an external strong magnetic field, and has the advantages of passive 'dynamic measurement, no damage to a human body, integral and multi-azimuth imaging' and the like.

At present, a magnetic field detection method based on a SERF (magnetic field resonance) is realized, the method can detect an extremely weak magnetic field, however, the method usually introduces some circuit parts near a probe, thereby bringing additional interference magnetic field noise to prevent the sensitivity from being further improved; meanwhile, due to the existence of the circuit part, the size of the whole structure cannot be further reduced, and the miniaturization of the structure is difficult to realize.

Disclosure of Invention

The invention aims to: in order to solve the technical problems, the invention provides an optical fiber SERF atomic magnetometer device based on a reflection type bidirectional pump, which is used for improving the sensitivity, stability and accuracy of magnetic field detection and miniaturizing the structure of a sensing probe.

The invention specifically adopts the following technical scheme for realizing the purpose:

an optical fiber SERF atomic magnetometer device based on reflection type bidirectional pumping comprises a light source, a sensing module, a modulation module and a demodulation module, wherein the light source comprises a heating light source, a pumping detection light source and a polarization controller; the sensing module comprises a circulator, a magnetic field coil, a first optical fiber collimator, an alkali metal atom air chamber (7), a reflector and a second optical fiber collimator; the modulation and demodulation module comprises a photodiode, a trans-impedance amplifier and a phase-locked amplifier;

the heating light source is connected with the optical fiber collimator, the pumping detection light source is connected with the polarization controller, the output end of the polarization controller is connected with one port of the circulator, the second port of the circulator is connected with the first optical fiber collimator, and the third port of the circulator is connected with the photodiode; the reference output end of the phase-locked amplifier is connected with the magnetic field coil, the input end of the transimpedance amplifier is connected with the output end of the photodiode, and the output of the transimpedance amplifier is connected with the phase-locked amplifier;

one end of the first optical fiber collimator, which is far away from the circulator, is sequentially provided with an alkali metal atom air chamber and a reflector, the top of the alkali metal atom air chamber is provided with a second optical fiber collimator, and emergent light of the second optical fiber collimator is perpendicular to that of the first optical fiber collimator.

As an optional technical scheme, the pump light of the pump detection light source vertically enters the reflector after passing through the alkali metal atom gas chamber, passes through the alkali metal atom gas chamber again after being reflected, is coupled into the optical fiber again after passing through the self-focusing lens on the first optical fiber collimator (6), and is output to the outside of the magnetic shielding barrel to form a passive sensing head structure;

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

As an optional technical solution, in the sensing module, the pump light power of the pump detection light source will be attenuated as the propagation distance in the alkali metal atom gas chamber increases, thereby causing the pump rate to decrease;

defining the intersection point of the pump light and the alkali metal atom gas chamber when the pump light is incident as the origin O, and the propagation direction of the pump light as the positive direction of the x axis, then the pumping rate R_p1The relationship with the horizontal coordinate x of the space in the alkali metal atom gas chamber is shown as formula one:

wherein lambertiw () is the lambertian W function, R_rFor relaxation rate, R_p0Pump rate at incidence that has not yet attenuated;

after the pump light reaches the reflector, the pump light is totally reflected and enters the alkali metal atom gas chamber again to form a two-way pump, and the second pumping rate R is_p2The relation with the horizontal coordinate x of the space in the alkali metal atom gas chamber is shown as a formula II:

wherein x_MThe abscissa of the point of the first-time pump light emergent from the atomic gas chamber represents the length of the atomic gas chamber along the light propagation direction;

further, the total pumping rate R in the alkali metal atom gas chamber after the bidirectional pumping_pIs the sum of two pumping rates, namely formula three:

R_p＝R_p1+R_p2

in formula III, R_p1Monotonically decreases as x increases, thereby causing non-uniformity in pumping rate in the gas chamber of alkali metal atoms, and R_p2The non-uniformity of the first term can be compensated for by a monotonic increase with increasing x, resulting in a more uniform pumping rate.

As an optional technical solution, the atomic polarizability P in the alkali metal atom gas chamber is represented by formula four:

as an optional technical solution, the central wavelength of the pump detection light source is 795nm, 894nm or 770nm, which respectively corresponds to the D1 lines of rubidium atoms, cesium atoms and potassium atoms, and the output laser light thereof is linearly polarized light;

the working wavelengths of the circulator, the first optical fiber collimator and the photodiode are matched with the central wavelength of the pump detection light source (2).

As an optional technical solution, the output power of the heating light source is above 150mw, and the power is required to ensure that the gas chamber can be heated so that the alkali metal atoms in the gas chamber can be changed from a solid state to a gas state; the working wavelength of the second optical fiber collimator is matched with the central wavelength of the heating light source.

As an optional technical solution, the alkali metal atom gas chamber is attached with absorption filters at two sides of the light-passing surface of the heating source, the absorption center wavelength of the absorption filters is consistent with the center wavelength of the heating light source, and the thickness of the filter at the emergent side is thicker than that of the filter at the incident side, so that the light energy absorbed by the two filters is equal, and the gas chamber can be uniformly heated from two sides.

As an optional technical solution, the modulation signal generated by the modulation and demodulation module has a frequency of ω and an amplitude of B₁Of the demodulated output signal of

Wherein, γ_eIs the alkali metal atom gyromagnetic ratio, B₀For the amplitude of the magnetic field to be measured, J₀Is a Bessel function of order 0, J₁Is a Bessel function of order 1, Q is a nuclear slowdown factor, R_pFor optical pumping rate, R_rFor relaxation, P is the atomic polarizability in the gas cell.

The invention has the following beneficial effects:

1. compared with the traditional SERF atomic magnetometer device, the method utilizes the reflector and the self-focusing lens to couple the detection light beam into the optical fiber to be transmitted to the outside of the magnetic shielding barrel for photoelectric conversion, removes a photoelectric conversion circuit on the magnetic sensing probe and reduces the number of the optical fibers, so that the structural size can be further reduced, and the integration and array application are facilitated.

2. The photoelectric conversion circuit near the gas chamber of the alkali metal atoms is removed, so that the magnetic field noise caused by the circuit is eliminated.

3. After the reflector is used for bidirectional pumping, the uniformity of the pumping rate in the alkali metal atom gas chamber is improved, so that the uniformity of the polarizability is also improved, and the stability and the accuracy of system measurement are improved.

4. By adopting the reflective optical coupling structure, the quantity of optical fibers and optical components in the weak magnetic sensing probe can be reduced, thereby reducing the size and volume of the sensing head and improving the reliability of the sensing head

Drawings

FIG. 1 is a schematic diagram of the system of the present invention;

reference numerals: the device comprises a 1-laser, a 2-laser, a 3-polarization controller, a 4-three-port circulator, a 5-magnetic field coil, a 6-optical fiber collimator, a 7-alkali metal atom air chamber, an 8-reflector, a 9-optical fiber collimator, a 10-photodiode, an 11-transimpedance amplifier and a 12-phase-locked amplifier.

Detailed Description

In order to make the objects, 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 drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all, embodiments of the present invention. The components of embodiments of the present invention generally described and illustrated in the figures herein may be arranged and designed in a wide variety of different configurations.

Thus, the following detailed description of the embodiments of the present invention, presented in the figures, is not intended to limit the scope of the invention, as claimed, but is merely representative of selected embodiments of the invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

Example 1

As shown in fig. 1, rubidium atoms, cesium atoms and potassium atoms can be used as the alkali metal atom cells 7, and rubidium atom cells are preferred in this embodiment 1; the invention discloses an optical fiber SERF atomic magnetometer device based on a reflection type bidirectional pump, which comprises a light source, a sensing module and a modulation and demodulation module. The light source comprises a beam of 1550nm laser and a beam of 795nm laser, the 1550nm laser heats the rubidium atom air chamber, the output power of the laser is required to be larger than 150mw, the laser is enabled to be output from the second optical collimator 9 and then to hit the rubidium atom air chamber, and the rubidium atom air chamber can be heated to about 150 ℃. The 795nm light source outputs linearly polarized light, the linearly polarized light is changed into left-handed circularly polarized light after passing through the polarization controller 3, the left-handed circularly polarized light is input from one port of the circulator 4 and output from two ports, the linearly polarized light is emitted on the rubidium atom air chamber through the first optical collimator 6 and vertically hits on the reflector 8 after passing through the rubidium atom air chamber, reflected light is reflected back to enter the rubidium atom air chamber again, and the reflected light enters the optical fiber through the coupling of the self-focusing lens on the first optical collimator 6 at the emitting end and is transmitted to the outside of the magnetic shielding barrel, and meanwhile, a magnetic field coil inside the magnetic shielding barrel is driven by the reference output of the phase-locked amplifier 12 to generate a modulation magnetic field with certain frequency. Outside the magnetic shielding barrel, a measured optical signal is output from three ports of the circulator 4, the optical signal is converted into a current signal by the photodiode 10, and then the current signal is amplified by the trans-impedance amplifier 11 by a certain multiple and converted into a voltage signal, and then the voltage signal is transmitted to the phase-locked amplifier 12 for demodulation processing.

Example 2

Further, the method comprises the following steps:

the method comprises the following steps: the output laser of the laser 1 is 1550nm laser, the output power of the laser needs to be more than 150mW, so that the alkali metal atom air chamber 7 can be heated to about 150 ℃, the laser 2 outputs 795nm linear polarized light, the linear polarized light is converted into left-handed circular polarized light through the polarization controller 3, and two beams of laser are orthogonally emitted and hit on the alkali metal atom air chamber 7. The first pumping rate Rp1 is related to the abscissa x of the space in the alkali metal atom gas cell 7 by the formula one:

wherein lambertiw () is Lambor W function, Rr is relaxation rate, R_p0Is the pump rate at incidence that has not yet attenuated.

After passing through the reflector, the pump light enters the alkali metal atom air chamber 7 again to form a bidirectional pump, and the relationship between the second pumping rate Rp2 and x is expressed as formula two:

wherein x_MIs the point of the first pumping light emergent from the alkali metal atom gas chamber 7Abscissa of (a), x_MAlso representing the length of the alkali metal atom cell 7 in the direction of light propagation.

Further, after the bidirectional pumping, the pumping rate R of the alkali metal atom gas chamber 7 is at this time_pIs the sum of two pumping rates, i.e. formula three

R_p＝R_p1+R_p2

Further, the atomic polarizability P in the alkali metal atom gas cell 7 is given by the formula four:

in formula four, the first term R on the right_p1Monotonically decreases as x increases, thereby causing non-uniformity in the pumping rate in the alkali metal atom gas cell, and the second term R_p2The first term non-uniformity can be compensated for by a monotonic increase with increasing x, resulting in a relatively uniform pumping rate and thus also an improved uniformity of the polarizability.

Step two: the phase-locked amplifier 12 is connected with a reference output of the magnetic field coil 5 and generates a modulation magnetic field B with the frequency of omega and the amplitude of B1₁cosωt。

Step three: 795nm is emitted from the air chamber again, and then is coupled into the optical fiber through a self-focusing lens on the optical fiber collimator 6, and then is transmitted out of the magnetic shielding barrel, and is subjected to photoelectric conversion by the photodiode 10.

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

wherein, γ_eIs the alkali metal atom gyromagnetic ratio, B₀For the amplitude of the magnetic field to be measured, omega for the frequency of the modulated magnetic field, B₁For modulating the magnetic field amplitude, J₀Is a Bessel function of order 0, J₁Is a Bessel function of order 1, Q is a nuclear slowdown factor, R_pFor optical pumping rate, R_rFor relaxation rate, P is in the gas cellAtomic polarizability.

Step four: the weak magnetic signal B0 to be detected can be extracted from noise by performing phase-locked amplification on the first harmonic term by using the phase-locked amplifier 12, and the expression can be approximated to formula six in the zero field range:

further, since parameters such as the photoelectric conversion coefficient k, the modulation amplitude B1, the modulation frequency ω, the pumping rate Rp, the relaxation rate Rr, the gyromagnetic ratio re, and the like are not changed after being adjusted and stabilized, linear output can be realized.

Through the steps one to four, the space uniformity of the atomic polarizability in the atomic gas chamber is improved due to the mode of the reflective bidirectional pumping, so that the stability and the reliability of a detection result are improved, the photoelectric conversion is avoided near the alkali metal atomic gas chamber 7 by adopting a space optical coupling mode, an additional magnetic field caused by a photoelectric conversion circuit is avoided, the magnetic noise is further reduced, the device has higher detection sensitivity, and meanwhile, the structure of the sensing probe can be further miniaturized due to the fact that the number of the photoelectric conversion circuit and the number of optical fibers on the sensing probe are reduced, and the integration and array application are facilitated.

The above description is only for the purpose of illustrating the preferred embodiments of the present invention and should not be taken as limiting the scope of the present invention, and any modifications, equivalents and improvements made by those skilled in the art within the spirit and principle of the present invention should be included in the scope of the present invention.