A single-beam NMOR atomic magnetometer based on fiber EOM

Abstract

A single-beam NMOR atomic magnetometer based on fiber EOM utilizes a single laser beam to simultaneously detect the polarization and optical rotation angle signals of alkali metal atoms. Combined with AC modulation of the linearly polarized light intensity by the fiber EOM, this not only enables high-precision magnetic field measurements in geomagnetic environments, but also simplifies system complexity and reduces power consumption, facilitating miniaturization and portable applications of the magnetometer. Furthermore, the Jones matrix is ​​used to derive the differential output signal of the fiber EOM light intensity modulation, enabling intuitive and quantitative analysis of the impact of various modulation parameters on the output signal, providing a theoretical basis for improving sensitivity and other indicators. Furthermore, a lock-in amplifier is used to extract the magnetic field signal, effectively preventing interference from low-frequency noise in the system and improving the magnetometer's sensitivity.

Description

Technical Field

[0001] The present invention relates to the technical field of atomic magnetometers, and in particular to a single-beam NMOR atomic magnetometer based on optical fiber EOM. By simultaneously polarizing and detecting an atomic ensemble with a single laser beam, combined with a compact optical fiber EOM, the intensity of linearly polarized light is modulated. This allows for portable and high-precision detection of weak magnetic field signals in geomagnetic environments, and is widely used in fields such as magnetic anomaly detection, life and health monitoring, and geophysical surveys. Background Art

[0002] Magnetometers are essential tools in many research fields, including biology, geophysics, and medicine, and are indispensable for measuring magnetic signals. In recent years, with the development and application of near-resonant light interactions with atoms in magnetic fields, magnetometers based on the nonlinear magneto-optical rotation (NMOR) effect have become a research hotspot. Compared to superconducting quantum interference devices (SQUIDs) and spin-exchange relaxation-free (SERF) atomic magnetometers, NMOR atomic magnetometers offer advantages such as a wide dynamic range, simple setup, low environmental requirements, and ultrahigh sensitivity, paving the way for compact, economical, and portable ultrasensitive magnetic sensors. Currently, most NMOR atomic magnetometers employ a dual-beam structure, using an acousto-optic modulator (AOM) for modulation. However, the AOM requires a separate acoustic field driver module and consumes significant power. Furthermore, the dual-beam structure complicates the overall system, hindering miniaturization and portability. The NMOR atomic magnetometer with a single-beam structure also uses an acousto-optic modulator (AOM) for modulation and suffers from the same problems mentioned above. Summary of the Invention

[0003] The technical problem solved by the present invention is: to overcome the shortcomings of the existing technology and propose a single-beam NMOR atomic magnetometer based on optical fiber EOM. By simultaneously polarizing and detecting the atomic ensemble with a single laser beam, combined with a compact optical fiber EOM (Electro-optical modulator), the system has low power consumption and a simple structure and can detect weak magnetic field signals with high precision in geomagnetic environments. The system is suitable for weak magnetic field measurement under geomagnetic conditions and can be portable, highly integrated and highly precise.

[0004] The technical solutions of the present invention are as follows:

[0005] A single-beam NMOR atomic magnetometer based on optical fiber EOM is characterized by comprising an atomic polarization system with an optical fiber EOM located on the single-beam incident side of a gas chamber, a differential detection system located on the single-beam exit side of the gas chamber, and a circuit system respectively connected to the atomic polarization system and the differential detection system. The optical fiber EOM modulates a light intensity signal, the atomic polarization system outputs a single beam into the gas chamber to polarize the alkali metal atoms in the gas chamber, the differential detection system obtains an optical rotation angle signal generated by the Larmor precession of the alkali metal atoms in a magnetic field from the single beam exiting the gas chamber, and the circuit system comprises a signal generator and a phase-locked amplifier. The signal generator outputs a DC signal to drive the optical fiber EOM, and the phase-locked amplifier generates a radio frequency signal to modulate the optical fiber EOM, and demodulates the optical rotation angle signal to output magnetic field information, thereby achieving measurement of the magnetic field.

[0006] The atomic polarization system includes a laser connected to the optical fiber EOM through a first optical fiber, the optical fiber EOM is connected to a fiber collimator through a second optical fiber, the fiber collimator inputs a single light beam into the gas chamber through a Glan prism, and a non-magnetic electric heating device is provided on the periphery of the gas chamber. The differential detection system includes a differential amplification operation circuit, the output end of the differential amplification operation circuit is connected to the differential detection signal input end of the phase-locked amplifier, the negative input end of the differential amplification operation circuit is connected to the output end of the first photodetector, the positive input end of the differential amplification operation circuit is connected to the output end of the second photodetector, the input end of the first photodetector is connected to the transmission end of the polarization beam splitter prism, the input end of the second photodetector is connected to the reflection end of the polarization beam splitter prism, and the input end of the polarization beam splitter prism receives the single light beam emitted from the gas chamber through a half-wave plate.

[0007] The fiber collimator directs the laser light into the optical path with a certain spot size. The Glan prism outputs linearly polarized light with a high extinction ratio. The linearly polarized light enters the gas chamber to polarize the atoms. The fiber EOM outputs light intensity signals of different frequencies and amplitudes according to different RF signals and / or different driving signals.

[0008] The differential output signal P of the differential detection system is:

[0009]

[0010] Among them I pbsT is the intensity of light transmitted through the polarization beam splitter prism, I pbsF is the intensity of light reflected by the polarization beam splitter prism, I0 is the initial intensity of light in the input light path, is the optical rotation angle, u is the modulation signal amplitude, ω m is the modulation signal frequency, U λ / 2 is the half-wave voltage of the fiber EOM, and t is the time.

[0011] Based on the nonlinear optical rotation effect, the optical rotation angle

[0012]

[0013] Where g is the Lande factor, μ is the Bohr magneton, and B is the external magnetic field. is the reduced Planck constant, Γ is the line width, l is the cell length, and l0 is the absorption length.

[0014] The technical effects of the present invention are as follows: The present invention is a single-beam NMOR atomic magnetometer based on optical fiber EOM, which uses a single laser beam to simultaneously detect the polarization and optical rotation angle signals of alkali metal atoms. Combined with the AC modulation of the intensity of linearly polarized light by optical fiber EOM, it can not only realize the magnetic field measurement in the geomagnetic environment with high precision, but also simplify the complexity of the system, reduce the system power consumption, and is conducive to the miniaturization and portable application of the magnetometer. At the same time, the differential output signal of the optical fiber EOM light intensity modulation is derived using the Jones matrix, which can intuitively and quantitatively analyze the influence of each modulation parameter on the output signal, providing a theoretical basis for improving indicators such as sensitivity. In addition, the use of a phase-locked amplifier to extract the magnetic field signal can effectively avoid the interference of low-frequency noise in the system and improve the sensitivity of the magnetometer. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 A schematic structural diagram of a single-beam NMOR atomic magnetometer based on optical fiber EOM is provided for implementing the present invention.

[0016] The meanings of the reference numerals are as follows: 1 is a gas chamber, 2 is a non-magnetic electric heating device, 3 is an atomic polarization system, 4 is a differential detection system, 5 is a circuit system, 31 is a laser, 32 is an optical fiber EOM (Electro-optical modulator), 33 is an optical fiber collimator, 34 is a Glan prism, 41 is a half-wave plate, 42 is a polarization beam splitter prism, 43 is a first photodetector, 44 is a second photodetector, 45 is a differential amplifier circuit, 51 is a signal generator (DC signal output terminal CH1 or CH2), 52 is a phase-locked amplifier (including a magnetic field information output terminal OUT, a differential detection signal input terminal IN, and a radio frequency signal output terminal). DETAILED DESCRIPTION

[0017] Below is the attached figure ( Figure 1 ) and Examples illustrate the present invention.

[0018] Figure 1 A schematic diagram of the structure of a single-beam NMOR atomic magnetometer based on fiber EOM is provided for the implementation of the present invention. Figure 1As shown, a single-beam NMOR atomic magnetometer based on optical fiber EOM includes an atomic polarization system 3 with an optical fiber EOM 32 located on the single-beam incident side of a gas cell 1, a differential detection system 4 located on the single-beam exit side of the gas cell 1, and a circuit system 5 respectively connected to the atomic polarization system 3 and the differential detection system 4. The optical fiber EOM 32 modulates a light intensity signal, and the atomic polarization system 3 outputs a single beam into the gas cell 1 to polarize the alkali metal atoms in the gas cell 1. The differential detection system 4 obtains an optical rotation angle signal generated by the Larmor precession of the alkali metal atoms in the magnetic field from the single beam emitted from the gas cell 1. The circuit system 5 includes a signal generator 51 and a phase-locked amplifier 52. The signal generator 51 outputs a DC signal to drive the optical fiber EOM 32. The phase-locked amplifier 52 generates a radio frequency signal to modulate the optical fiber EOM 32, and demodulates the optical rotation angle signal to output magnetic field information to achieve measurement of the magnetic field.

[0019] The atomic polarization system 3 includes a laser 31 connected to the optical fiber EOM 32 through a first optical fiber, the optical fiber EOM 32 is connected to the optical fiber collimator 33 through a second optical fiber, the optical fiber collimator 33 inputs a single light beam into the gas chamber 1 through a Glan prism 34, and a non-magnetic electric heating device 2 is provided on the periphery of the gas chamber 1. The differential detection system 4 includes a differential amplifier circuit 45, the output end of the differential amplifier circuit 45 is connected to the differential detection signal input end (IN) of the phase-locked amplifier 52, the negative input end (-) of the differential amplifier circuit 45 is connected to the output end of the first photodetector 43, and the positive input end (-) of the differential amplifier circuit 45 is connected to the output end of the first photodetector 43. The end (+) is connected to the output end of the second photodetector 44, the input end of the first photodetector 43 is connected to the transmission end of the polarization beam splitting prism 42, and the input end of the second photodetector 44 is connected to the reflection end of the polarization beam splitting prism 42. The input end of the polarization beam splitting prism 42 receives the single light beam emitted by the gas cell 1 through the half wave plate 41. The optical fiber collimator 33 guides the light output by the laser 31 into the optical path with a certain spot size. The Glan prism 34 outputs linearly polarized light with a high extinction ratio. The linearly polarized light enters the gas cell 1 to polarize the atoms. The optical fiber EOM 32 outputs light intensity signals of different frequencies and amplitudes according to different radio frequency signals and / or different driving signals.

[0020] The differential output signal P of the differential detection system 4 is:

[0021]

[0022] Among them I pbsT is the intensity of light transmitted through the polarization beam splitter prism, I pbsF is the intensity of light reflected by the polarization beam splitter prism, I0 is the initial intensity of light in the input light path, is the optical rotation angle, u is the modulation signal amplitude, ω mis the modulation signal frequency, U λ / 2 is the half-wave voltage of the fiber EOM, and t is the time.

[0023] Based on the nonlinear optical rotation effect, the optical rotation angle signal

[0024]

[0025] Where g is the Lande factor, μ is the Bohr magneton, and B is the external magnetic field. is the reduced Planck constant, Γ is the line width, l is the cell length, and l0 is the absorption length.

[0026] A single-beam NMOR atomic magnetometer based on an optical fiber EOM includes a gas chamber, a non-magnetic electric heating device, an optical path system, a differential detection system, and a circuit system. The gas chamber is filled with elemental alkali metal atoms and a buffer gas, wherein the alkali metal atoms serve as a sensitive medium and the buffer gas prevents collisions between the alkali metal atoms and the gas chamber walls. The non-magnetic electric heating device provides a constant temperature for the gas chamber. The optical path system generates linearly polarized light to polarize the atoms. The differential detection system detects the optical rotation angle signal to detect the magnetic field. The circuit system includes a signal generator and a phase-locked amplifier. The signal generator outputs a DC signal to drive the optical fiber EOM. The phase-locked amplifier generates a radio frequency signal to modulate the optical fiber EOM and demodulates the differential detection signal to output magnetic field information. The present invention utilizes the optical fiber EOM for light intensity modulation to achieve single-beam NMOR magnetometer measurements under geomagnetic conditions. The present invention has the advantages of simple device, high precision, wide dynamic range, small size, and easy integration. It is of great significance for the application of high-precision and miniaturized atomic magnetometers in geomagnetic environments.

[0027] A single-beam NMOR atomic magnetometer based on optical fiber EOM mainly consists of an air chamber (1), a non-magnetic electric heating device (2), an atomic polarization system (3), a differential detection system (4) and a circuit system (5); the air chamber (1) is filled with alkali metal atoms as a sensitive medium and a buffer gas; the non-magnetic electric heating device (2) provides a constant temperature for the air chamber; the atomic polarization system (3) consists of a laser (31), an optical fiber EOM (32), an optical fiber collimator (33) and a Glan prism (34), and generates a beam of linearly polarized light to polarize atoms; the differential detection system (4) consists of a half-wave plate (41), a polarization beam splitter prism (42), a photodetector 1 (43), a photodetector 2 (44) and a differential operational amplifier circuit (45), and detects a light intensity signal passing through the air chamber to realize magnetic field detection; the circuit system (5) consists of a signal generator (51) and a phase-locked amplifier (52).

[0028] The laser (31) outputs laser light into the optical fiber EOM (32). The optical fiber EOM (32) receives the radio frequency modulation signal of the phase-locked amplifier to modulate the input laser light intensity signal, thereby expanding the magnetic field measurement range and realizing the measurement of magnetic fields of any size from zero magnetic field to geomagnetic field. The optical fiber collimator (33) introduces the laser light into the optical system with a specific spot size. After being polarized by the Glan prism (34), a beam of linearly polarized light with a high extinction ratio passes through the gas chamber (1) to polarize the alkali metal atoms. At the same time, after the linearly polarized light passes through the gas chamber (1), the polarization plane rotates to generate an optical rotation angle. The differential detection system (4) detects the light signal passing through the gas chamber, thereby realizing the detection of the optical rotation angle. The signal generator (51) in the circuit system (5) outputs a DC signal to drive the optical fiber EOM (32). The phase-locked amplifier (52) outputs magnetic field information by demodulating the optical rotation angle signal, thereby realizing the measurement of the magnetic field.

[0029] An optical fiber EOM (32) is used to modulate a light intensity signal, and a single beam linearly polarized laser is used to realize the polarization and detection process of an alkali metal, thereby forming a single beam self-oscillation mode modulated by the optical fiber EOM, thereby realizing the measurement of a magnetic field.

[0030] The Jones matrix is ​​used to derive the differential output signal of the fiber EOM linearly polarized light intensity modulation:

[0031]

[0032] Among them, I pbsT is the intensity of light transmitted through the polarization beam splitter prism, I pbsT is the intensity of light reflected by the polarization beam splitter prism, I0 is the initial intensity of light in the input light path, is the optical rotation angle, u is the modulation signal amplitude, ω m is the modulation signal frequency, U λ / 2 is the half-wave voltage of the fiber EOM, and t is the time.

[0033] According to the nonlinear optical rotation effect, the optical rotation angle signal It can be expressed as:

[0034]

[0035] g is the Lande factor, μ is the Bohr magneton, B is the external magnetic field, is the reduced Planck constant, Γ is the line width, l is the cell length, and l0 is the absorption length.

[0036] Furthermore, the atomic polarization system consists of a laser, an optical fiber EOM, an optical fiber collimator and a Glan prism, which generate the linearly polarized light required to polarize atoms. The optical fiber collimator directs the light output by the laser into the optical path with a specific spot size; the Glan prism outputs linearly polarized light with a high extinction ratio; the linearly polarized light passes through the gas chamber to polarize the atoms; the optical fiber EOM is used to modulate the intensity of the input light. According to different RF drive signals, the optical fiber EOM can output light intensity signals of different frequencies and amplitudes.

[0037] Furthermore, in the differential detection system, a half-wave plate and a polarization beam splitter prism split the light passing through the gas chamber into two beams of orthogonal polarized light. The two detected light intensity signals are operated on by a photodetector and a differential amplification circuit to obtain the optical rotation angle signal generated by the Larmor precession of atoms in the magnetic field, thereby realizing the detection of the magnetic field.

[0038] Furthermore, the phase-locked amplifier demodulates the signal output by the differential detection system, outputs a sinusoidal wave signal of corresponding frequency to drive the optical fiber EOM, and outputs frequency information through a phase-locked loop to obtain the magnetic field to be measured through calculation.

[0039] The principle of the present invention is: a single-beam NMOR magnetometer based on an optical fiber EOM, based on the nonlinear magneto-optical rotation effect. Its principle can be divided into the following three steps: First, linearly polarized light passes through an alkali metal gas chamber, polarizing the atoms, thereby generating a precession of the quadrupole moment (called "alignment"). Second, under the influence of an external magnetic field, the polarized atoms undergo ground-state Zeeman splitting, forming an energy level difference between the energy levels, and the polarization moment undergoes Larmor precession in the magnetic field. At this time, the alkali metal atoms act as an optical rotation element. Third, the linearly polarized light passes through the gas chamber, causing the polarization plane to rotate, thereby generating an optical rotation angle signal related to the magnetic field. However, the magnetic field measurement range of the above method is relatively narrow. Therefore, a method of light intensity modulation is adopted. The optical fiber EOM modulates the linearly polarized light intensity at a near-resonance frequency (twice the Larmor precession frequency), which can expand the magnetic field measurement range to the geomagnetic range. At this time, a differential detection system detects the optical rotation angle signal and inputs the signal into a phase-locked amplifier. The phase-locked amplifier demodulates the signal to obtain the modulation frequency, thereby achieving magnetic field measurement.

[0040] Linearly polarized light passes through the gas chamber 1 to polarize the atoms. The polarized atoms undergo Larmor precession under the influence of the ambient magnetic field. The corresponding precession frequency is called the Larmor precession frequency ω L , when the external magnetic field changes, the Larmor precession frequency will also change. The relationship between the magnetic field and the Larmor precession frequency can be expressed as:

[0041] ω L =γB

[0042] Among them, γ is the gyromagnetic ratio, which serves as the conversion factor between frequency and field strength, and B is the ambient magnetic field.

[0043] During the detection process, the lock-in amplifier outputs a frequency-variable AC sinusoidal wave to modulate the optical fiber EOM. The output sinusoidal modulation signal U(t) can be expressed as:

[0044] U(t)=u sinω m t

[0045] Where u is the modulation signal amplitude, ω m is the modulation signal frequency, and t represents time.

[0046] When the light modulation frequency ω m and Larmor precession frequency ω L When the double of coincides, that is, ω m =2ω L When the phase-locked loop is used to track the position of the phase zero point, that is, the resonant frequency position, a strong resonance curve can be observed. At this time, the differential detection system detects the modulated signal and uses it as the input signal of the phase-locked amplifier. The phase-locked amplifier demodulates the frequency signal, and then calculates the magnetic field signal to achieve magnetic field measurement.

[0047] Figure 1 The single-beam NMOR atomic magnetometer based on fiber EOM is shown, characterized in that: the atomic polarization system 3 consists of a laser 31, a fiber EOM 32, a fiber collimator 33 and a Glan prism 34, which generates the linearly polarized light required to polarize atoms. The fiber collimator 33 directs the light output by the laser 31 into the optical path with a specific spot size; the Glan prism 36 outputs linearly polarized light with a high extinction ratio; the linearly polarized light passes through the gas chamber 1 to polarize the atoms; the fiber EOM 32 is used to modulate the intensity of the input light. According to different RF drive signals, the fiber EOM 32 can output light intensity signals of different frequencies and amplitudes.

[0048] Figure 1 The single-beam NMOR atomic magnetometer based on optical fiber EOM shown in the figure is characterized in that: the half-wave plate 41 and polarization beam splitter prism 42 split the light passing through the gas chamber 1 into two beams of orthogonal polarization light, and the two detected light intensity signals are calculated by the photodetector and differential amplifier circuit 45 to obtain the optical rotation angle signal generated by the Larmor precession of atoms in the magnetic field, thereby realizing the detection of the magnetic field.

[0049] Figure 1The single-beam NMOR atomic magnetometer based on optical fiber EOM shown in the figure is characterized in that: the phase-locked amplifier 52 demodulates the signal output by the differential detection system 4, on the one hand outputs a sinusoidal wave signal of the corresponding frequency to drive the optical fiber EOM 32, and on the other hand outputs frequency information through the phase-locked loop, and obtains the magnetic field to be measured through calculation.

[0050] Figure 1 The main light intensity modulation process of a single-beam NMOR atomic magnetometer based on fiber EOM is shown as follows:

[0051] The Jones matrix is ​​used to derive the differential detection signal modulated by the optical fiber EOM 32.

[0052] (1) Assume that the light propagation direction is along the z-axis, the polarization direction of the laser output linear polarized light is along the y-axis, and the laser output laser amplitude is A, corresponding to the initial light intensity I0 = A 2 , then the Jones vector E of the path polarized light can be expressed as:

[0053]

[0054] (2) The fiber EOM consists of a polarizer, a lithium niobate crystal, a quarter-wave plate, and an analyzer. The lithium niobate crystal and the quarter-wave plate are placed between the polarizer and the analyzer, and the quarter-wave plate can be placed before or after the lithium niobate crystal. Therefore, the Jones matrix of the fiber EOM can be obtained by multiplying the Jones matrices of the four polarization elements. Among them, the transmission axis of the polarizer is along the y-axis direction, and the transmission axis of the analyzer is perpendicular to the polarizer and along the x-axis direction; the induction principal axes x' and y' of the crystal are 45° to the two main vibration directions x and y of the crystal when no electric field is applied, and are at a 45° angle to the transmission axis of the polarizer. The fast and slow axes of the quarter-wave plate are consistent with the induction principal axes of the crystal and are at a 45° angle to the transmission axis of the polarizer.

[0055] The transmission axis of the polarizer is along the y-axis, and the Jones matrix of the polarizer G p Expressed as:

[0056]

[0057] Lithium niobate crystal acts like a wave plate under the action of an external electric field, playing the role of phase delay. The Jones matrix G of lithium niobate crystal is N It can be expressed as:

[0058]

[0059] Where i is the imaginary unit and δ is the phase difference caused by the birefringence of the crystal, expressed as:

[0060]

[0061] Where λ is the wavelength of the input light in vacuum, U is the applied voltage, and U λ / 2 is the half-wave voltage of the lithium niobate crystal, n o It is the refractive index of o light (a beam of polarized light includes o light and e light).

[0062] The fast and slow axes of the quarter-wave plate are at a 45° angle to the x-axis, and the Jones matrix of the quarter-wave plate G λ / 4 Expressed as:

[0063]

[0064] The transmittance axis of the polarizer is along the x-axis, and the Jones matrix of the polarizer G A Expressed as:

[0065]

[0066] Then the light vector E output by the fiber EOM is EOM for:

[0067]

[0068] According to the light vector E EOM And the sinusoidal modulation signal U(t) is used to get the output light intensity I EOM The formula is:

[0069]

[0070] (3) The modulated light output by the fiber EOM enters the gas chamber through the Glan prism and polarizes the alkali metal atoms. The transmission axis of the Glan prism is along the x-axis, and the Glan prism Jones matrix G GT Expressed as:

[0071]

[0072] According to the birefringence principle and coherence effect, the alkali metal atoms in the gas chamber rotate the polarization plane of the detection light passing through the gas chamber under the action of linear polarized light and external magnetic field, generating an optical rotation angle Then the Jones matrix of the gas cell can be obtained from the Jones matrix G of the optical rotator cell express:

[0073]

[0074] The fast axis of the half-wave plate forms an angle of 22.5° with the x-axis, ensuring that the optical rotation angle output is zero when the atom is not polarized. The Jones matrix of the half-wave plate G λ / 2 Expressed as:

[0075]

[0076] where i is the imaginary unit.

[0077] The transmission direction and reflection direction of the polarization beam splitter prism are equivalent to two polarizers, which are the same as the polarizer and analyzer. The Jones matrix E of the polarization beam splitter prism in the transmission direction is pbsT and the reflection direction Jones matrix E pbsF They can be expressed as:

[0078]

[0079] Light vector E in the transmission direction pbsT It can be expressed as:

[0080]

[0081] Output light intensity in transmission direction I pbsF It can be expressed as:

[0082]

[0083] Light vector E in the reflected direction pbsF It can be expressed as:

[0084]

[0085] Output light intensity in the reflected direction I pbsF It can be expressed as:

[0086]

[0087] Finally, the differential signal can be represented by the difference between the light intensity in the transmission direction and the light intensity in the reflection direction:

[0088]

[0089] Among them, it can be seen from the nonlinear optical rotation effect that the optical rotation angle It can be expressed as:

[0090]

[0091] Among them, g is the Lande factor, μ is the Bohr magneton, B is the external magnetic field, is the reduced Planck constant, Γ is the line width, l is the cell length, and l0 is the absorption length.

[0092] From the above formula, we can see that the differential detection signal contains magnetic field information. When the external magnetic field B changes, the Larmor precession frequency ω L (ω m half of the optical rotation angle According to the differential detection signal demodulated by the phase-locked amplifier, the phase-locked loop can track the modulation frequency ω under different magnetic fields in real time. m , according to the formula mentioned above, the modulation frequency ωm The formula with the external magnetic field B can be used according to the output modulation frequency ω m The corresponding external magnetic field B is solved to achieve the measurement of the external magnetic field.

[0093] Any content not described in detail in this specification is prior art known to those skilled in the art. It should be noted that the above description is intended to help those skilled in the art understand the present invention, but does not limit the scope of protection of the present invention. Any equivalent substitution, modification, improvement, and / or simplification of the above description that does not depart from the essence of the present invention shall fall within the scope of protection of the present invention.

Claims

1. A single-beam NMOR atomic magnetometer based on fiber EOM, characterized in that: The invention comprises an atomic polarization system with an optical fiber EOM located on the single-beam incident side of the gas chamber, a differential detection system located on the single-beam exit side of the gas chamber, and a circuit system respectively connected to the atomic polarization system and the differential detection system. The optical fiber EOM modulates a light intensity signal. The atomic polarization system outputs a single light beam into the gas chamber to polarize the alkali metal atoms in the gas chamber. The differential detection system obtains an optical rotation angle signal generated by Larmor precession of the alkali metal atoms in a magnetic field from the single light beam exiting the gas chamber. The circuit system comprises a signal generator and a phase-locked amplifier. The signal generator outputs a DC signal to drive the optical fiber EOM. The phase-locked amplifier generates a radio frequency signal to modulate the optical fiber EOM and demodulates the optical rotation angle signal to output magnetic field information, thereby achieving measurement of the magnetic field. The atomic polarization system includes a laser connected to the fiber EOM via a first optical fiber, the fiber EOM is connected to a fiber collimator via a second optical fiber, and the fiber collimator inputs a single beam into the gas chamber via a Glan prism; The fiber collimator directs the laser light into the optical path with a certain spot size. The Glan prism outputs linearly polarized light with a high extinction ratio. The linearly polarized light enters the gas chamber to polarize the atoms. The fiber EOM outputs light intensity signals of different frequencies and amplitudes according to different radio frequency signals and / or different driving signals. The differential output signal P of the differential detection system is: Among them I pbsT is the intensity of light transmitted through the polarization beam splitter prism, I pbsF is the intensity of light reflected by the polarization beam splitter prism, I0 is the initial light intensity of the input light path, is the optical rotation angle, u is the modulation signal amplitude, ω m is the modulation signal frequency, U λ / 2 is the half-wave voltage of the fiber EOM, and t is the time; Based on the nonlinear optical rotation effect, the optical rotation angle : where g is the Lande factor, μ is the Bohr magneton, B is the external magnetic field, h is the reduced Planck constant, Γ is the line width, l is the gas cell length, and l0 is the absorption length.

2. The single-beam NMOR atomic magnetometer based on optical fiber EOM according to claim 1, characterized in that: A non-magnetic electric heating device is provided on the periphery of the gas chamber. The differential detection system includes a differential amplification operational circuit, the output end of the differential amplification operational circuit is connected to the differential detection signal input end of the phase-locked amplifier, the negative input end of the differential amplification operational circuit is connected to the output end of the first photodetector, the positive input end of the differential amplification operational circuit is connected to the output end of the second photodetector, the input end of the first photodetector is connected to the transmission end of the polarization beam splitter prism, the input end of the second photodetector is connected to the reflection end of the polarization beam splitter prism, and the input end of the polarization beam splitter prism receives the single light beam emitted from the gas chamber through a half-wave plate.

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