Multi-frequency magnetic field communication method and system based on alkali metal atom magnetic field measurement

Abstract

The invention discloses a multi-frequency magnetic field communication method and system based on alkali metal atom magnetic field measurement. The method comprises the following steps: firstly, constructing a multi-frequency physical layer carrier wave; the static magnetic field B0 is used for regulating and controlling atomic energy level splitting; generating at least two groups of discrete magnetic resonance frequencies through optical polarization and alternating magnetic field excitation; wherein mistuned laser is adopted to pump atomic energy levels corresponding to all resonant frequencies at the same time, and the signal-to-noise ratio difference of each frequency channel meets a preset value by regulating and controlling the optical wavelength, the optical power and the polarization elliptic polarization of light; and finally, receiving and transmitting multi-system frequency shift keying communication signals, mapping binary data streams to a carrier frequency combination, and restoring data by a receiving end through a multi-channel synchronous demodulation algorithm. According to the invention, the second-order Zeeman effect of the trona metal isotope or the elementary atom is utilized to realize high-robustness communication in a non-magnetic shielding environment, so that the communication reliability is improved; meanwhile, a single-air-chamber structure is adopted, redundant optical assemblies are saved, and the system integration degree is remarkably optimized.

Description

Technical Field

[0001] The present invention belongs to the field of quantum magnetic perception technology, and in particular relates to a multi-frequency magnetic field communication method and system based on alkali metal atomic magnetic field measurement. Background Art

[0002] In the field of magnetic induction communication in an unshielded environment, the receiver's simultaneous and highly sensitive detection of multi-frequency magnetic fields faces two major challenges: first, environmental magnetic field interference: RF optically pumped atomic magnetometers require a static bias field to set the Larmor frequency, but environmental magnetic field fluctuations (such as geomagnetic disturbances and mobile platform vibrations) cause the resonant frequency to lose lock, and communication reliability plummets (see the literature: Deans et al., Rev. Sci. Instrum. 89, 083111, 2018); second, insufficient multi-frequency compatibility: existing monoisotope OPMs can only respond to a single frequency point and cannot support multi-frequency modulation communications such as BFSK, while the multi-chamber solution significantly increases the system size and power consumption (literature: Dhomridge et al., Phys. Rev. Applied 18, 044052, 2022, Sec. I).

[0003] The paper "High-Sensitivity rf Detection Using an Optically Pumped Co Magnetometer Based on Natural-Abundance Rubidium with Active Ambient-Field Cancellation" (Phys. Rev. Applied 18, 044052, 2022) proposes a co-atomic magnetometer based on natural rubidium isotopes. Its technical solution is as follows: high-sensitivity detection of radio frequency magnetic fields is achieved in an unshielded environment, and the problem of bias field instability is solved by active ambient field compensation. Dual isotope synergy: using natural rubidium vapor ( 85 Rb:72.2%, 87 Rb: 27.8%)) 85 / γ 87 =2 / 3), a dual-frequency atomic magnetometer is constructed in the same gas chamber; function allocation: 87 Rb acts as an "environmental field sensor" to generate an error signal to drive the PID feedback to the three-axis coil to compensate for ≤60Hz interference; 85 Rb acts as an "alternating magnetic field detector" to achieve 21.5kHz RF detection under a stable bias field (Sec.IIA, Fig.2); active compensation: through 87 The transverse slow modulation of Rb (f⊥=1kHz) analyzes the environmental magnetic field vector and performs real-time calibration85 Bias field of Rb (Sec. IIC, Fig. 3). Technical effect: Achieves RF sensitivity of 9fT / √Hz in a shielded environment, with an ambient field compensation bandwidth of 60-96Hz (Table I), providing a path for unshielded applications (Sec. IV).

[0004] Although this technology integrates environmental field compensation and RF detection, it is not designed for multi-frequency magnetic field communication needs and has the following key flaws: the design goal is only single-frequency RF detection (21.5kHz), and it does not build multi-frequency parallel demodulation capabilities (Abstract, Sec. I), and cannot support communication modulation such as BFSK; among them, 87 Rb is only used for compensation feedback, 85 Rb only responds to a fixed frequency and does not utilize the dual-frequency response characteristics of the isotope to achieve dual-channel communication (Sec. IIIB); scalability is limited: not optimized 85 Rb / 87 The amplitude / bandwidth balance of Rb dual-frequency signals (Sec. I) leads to an imbalance in the signal-to-noise ratio in communication scenarios; other alkali metal isotopes (such as 133 Cs / 131 Cs, 39 K / 41 K) applicability, insufficient multi-element compatibility (Sec. I). Summary of the Invention

[0005] The present invention aims to solve the problems raised in the background technology and proposes a multi-frequency magnetic field communication method and system based on alkali metal atomic magnetic field measurement.

[0006] To achieve the purpose of the present invention, the present invention discloses a multi-frequency magnetic field communication method based on alkali metal atomic magnetic field measurement, comprising the following steps:

[0007] Step 1: Multi-frequency physical layer carrier construction; using static magnetic field B0 to control atomic spin energy level splitting;

[0008] Step 2: Generate at least two sets of discrete magnetic resonance frequencies {f1, f2, ..., f n};

[0009] Among them, a detuned laser is used to simultaneously pump the atomic energy levels corresponding to all resonant frequencies, and the signal-to-noise ratio difference of each frequency channel meets the preset value by adjusting the light wavelength, light power and light polarization ellipticity.

[0010] Step 3: Multi-level frequency shift keying communication signal transmission and reception, mapping the binary data stream to the carrier frequency combination, and the receiving end restores the data through a multi-channel synchronous demodulation algorithm.

[0011] Furthermore, in step 2, each group of frequencies satisfies:

[0012] f k =γ_{eff}·B0+Δk(k=1,2,...,n)

[0013] where γ_{eff} is the effective gyromagnetic ratio of the atom, and the frequency offset Δ k This is achieved by selecting isotope combinations of alkali metal atoms with different gyromagnetic ratios, or by regulating the optical pumping parameters to excite the nonlinear Zeeman effect of atoms of the same type.

[0014] Furthermore, in step 3, the multi-ary frequency shift keying communication signal is transmitted and received, and the binary data stream is mapped to the carrier frequency combination using M-ary frequency shift keying, and each symbol period T s Internal activation of a set of frequencies {f k}, M≤n; or adopt orthogonal joint modulation to activate two sets of orthogonal frequency combinations {f p ,f q}, p≠q, and the symbols are distinguished by the carrier phase / power ratio.

[0015] Furthermore, step 1 specifically includes the following steps:

[0016] Step 1-1, steam chamber configuration: Place a steam chamber containing natural isotope alkali metal at the center of a triaxial magnetic field coil and fill it with buffer gas to suppress atomic diffusion and relaxation;

[0017] Step 1-2, bias field setting: Apply a constant current to the Z-axis coil to generate a static magnetic field B0 so that the Larmor frequencies of the two isotope atoms meet

[0018] f1=γ1·B0,f2=γ2·B0

[0019] Where γ1,γ2 are the isotope gyromagnetic ratios;

[0020] Frequency design constraint: The difference Δf between f1 and f2 meets the BFSK interval requirement.

[0021] Furthermore, step 2 specifically includes the following steps:

[0022] Step 2-1: Pump light modulation: Use a single elliptically polarized pump laser with a wavelength tuned to the alkali metal D line, covering the transition from the ground state to the excited state of both isotopes at the same time, with a pump power of 0.1–10 mW / cm 2 ;

[0023] Step 2-2, detection light optimization: The wavelength of the single linearly polarized detection laser is set to blue detuning, and the sensitivity balance is improved by enhancing the non-resonant Faraday rotation angle.

[0024] Furthermore, step 3 specifically includes the following steps:

[0025] Step 3-1, transmitter modulation: According to the binary data stream to be transmitted, the BFSK modulator drives the resonant coil to generate a time-varying magnetic field B tx :

[0026] The symbol “0” refers to the magnetic field pulse of carrier frequency f1;

[0027] The symbol “1” refers to the magnetic field pulse of carrier frequency f2;

[0028] Step 3-2, physical layer demodulation at the receiving end: After the detection light passes through the steam chamber, the balanced photodetector outputs a dual-frequency mixed signal V S , separate the f1 / f2 channels by bandpass filtering:

[0029]

[0030] Where t is time, α and β are isotope response amplitudes, are the initial phases of electromagnetic waves with frequencies f1 and f2, respectively. After optimization by S2, |α-β| / avg(α,β)<15%;

[0031] Use non-coherent envelope detection to decide the symbol:

[0032] When ∫|V1(t)|dt>∫|V2(t|dt and the difference exceeds the threshold → it is judged as symbol "0"

[0033] When ∫|V2(t)|dt>∫|V1(t)|dt and the difference exceeds the threshold → it is judged as the symbol "1".

[0034] In order to achieve the purpose of the present invention, the present invention also discloses a multi-frequency magnetic field communication system based on alkali metal atomic magnetic field measurement, characterized in that it includes a transmitting end, a signal receiving end, and a signal demodulation module; the transmitting end is used to perform frequency shift keying modulation on the binary data stream to generate a dual-frequency magnetic field signal, wherein the first frequency f1 maps the symbol "0" and the second frequency f2 maps the symbol "1", and the interval between the two frequency points satisfies Δf>5×Γ ， Where Γ is the atomic magnetic resonance linewidth, defined as the full width at half maximum of the resonance peak; the signal receiving end includes a vapor chamber filled with natural alkali metal isotopes, a weak bias magnetic field coil, and a single-path or multi-path dual-resonance optical detection module, which synchronously senses the f1 and f2 magnetic field components through atomic spin polarization and resonant frequency splitting, and outputs an electrical signal containing dual-frequency information; the signal demodulation module performs dual-channel bandpass filtering separation, envelope energy integration, and differential judgment on the electrical signal at the signal receiving end, outputting the symbol "0" when the integrated energy E1>E2 and the symbol "1" when E2>E1, realizing direct symbol demodulation at the physical layer.

[0035] Furthermore, the transmitting end includes a BFSK modulator and a dual-frequency resonant antenna; the BFSK modulator converts the binary data stream into a dual-frequency magnetic field signal, the symbol "0" maps the carrier frequency f1, and the symbol "1" maps the carrier frequency f2; the dual-frequency resonant antenna is a pair of orthogonal ring coils, which resonate at f1 and f2 respectively, generating direction-controllable BFSK magnetic field waves.

[0036] Furthermore, the signal receiving end is an atomic magnetometer, which includes an alkali metal vapor chamber, a three-axis magnetic field coil, a pump laser, a detection laser and a balanced photodetector; the alkali metal vapor chamber is provided with a cubic gas chamber filled with nitrogen buffer gas; the Z axis of the three-axis magnetic field coil applies a bias field B0 and compensates for disturbances, and the X / Y axis is used to compensate for environmental interference; the pump laser is provided with a polarized light source, which forms circularly polarized light through beam expansion and a 1 / 4 wave plate to synchronously polarize the isotope atoms; the linearly polarized light of the detection laser is incident on the gas chamber through a polarization beam splitter, with a blue shift detuning amount of +0.1–10 GHz; the balanced photodetector is used to detect the polarization rotation angle of the detection light and output a mixed electrical signal containing f1 / f2.

[0037] Furthermore, the signal demodulation module includes a dual-channel bandpass filter, an envelope detector and a symbol decision device; the dual-channel bandpass filter is used to separate the f1 channel and the f2 channel; the envelope detector rectifies and low-pass filters the signal of each channel to extract the amplitudes |V1| and |V2|; the symbol decision device judges it as "0" when |V1|-|V2|>threshold, and "1" otherwise.

[0038] Compared with the existing technology, the significant progress of the present invention is: 1) Improved communication reliability; in a non-magnetic shielding environment, the sensitivity of the atomic magnetometer as a receiver reaches tens of pT / √Hz (dual-frequency average). This advantage is due to the inherent noise suppression characteristics of the isotope dual-frequency response; dual-channel balance: through the optimization of the double-transition excitation of the pump light and the blue detuning of the detection light, the 85 Rb and 87 The sensitivity difference of Rb is compressed to <20%, ensuring the symmetry of the "0" and "1" symbol error rates of BFSK; anti-interference is enhanced: f1 and f2 show synchronous drift characteristics in response to environmental magnetic field fluctuations, and common-mode noise suppression of ≥10dB is achieved through differential demodulation algorithm; 2) system integration is significantly optimized; a single gas chamber structure is adopted to reduce the volume of the receiver to a maximum single side of 13cm (including the laser, coil, gas chamber, gas chamber heating device and photodetector), and more gas chamber atomic magnetometer solutions are used to save redundant optical components, and use the same pump light to synchronously excite dual isotopes (such as 780nm laser covering Rb's D2 line F=3→F' and F=2→F' transitions), and the physical layer directly outputs BFSK symbols, eliminating traditional I / Q modulation and demodulation circuits and saving FPGA logic resources.

[0039] In order to more clearly illustrate the functional characteristics and structural parameters of the present invention, further description is given below with reference to the accompanying drawings and specific embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] The drawings described herein are used to provide a further understanding of the present invention and constitute a part of this application. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0041] Figure 1 This is a structural diagram of a multi-frequency magnetic field communication system based on alkali metal atomic magnetic field measurement. DETAILED DESCRIPTION

[0042] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments; based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0043] To address the core technical bottleneck of existing magnetic induction communication systems, where receivers cannot synchronously demodulate multi-frequency signals in an unshielded environment, the present invention provides a magnetic field communication method based on the multi-peak atomic magnetic resonance and dual-frequency resonance characteristics brought about by alkali metal isotope atoms or the nonlinear Zeeman effect, achieving the following innovations in communication methods:

[0044] Atomic-level physical layer multi-frequency demodulation architecture: using natural alkali metal isotopes ( 85 Rb / 87 Rb, 133 Cs / 131 Cs, etc.), or the second-order Zeeman effect of a single atom, generates dual Larmor frequencies (f1 / f2) under the same bias field (also called the main magnetic field). The two frequencies are directly mapped to the "0" and "1" symbol bits of binary frequency shift keying (BFSK or 2FSK), realizing the direct physical layer conversion of atomic spin state to communication symbol (without the need for additional modulation circuitry).

[0045] Achieve highly robust communication in a non-magnetic shielding environment: Based on the common-mode noise suppression characteristics of the isotope dual-frequency signal (environmental interference causes synchronous drift of f1 / f2), an anti-interference BFSK demodulation algorithm is constructed to suppress interference caused by environmental fluctuations such as geomagnetic field.

[0046] like Figure 1As shown, a multi-frequency magnetic field communication system based on alkali metal atomic magnetic field measurement includes a transmitter, a signal receiver, and a signal demodulation module; the transmitter is used to perform frequency shift keying modulation on a binary data stream to generate a dual-frequency magnetic field signal, where the first frequency f1 maps the symbol "0" and the second frequency f2 maps the symbol "1", and the interval between the two frequency points satisfies Δf>5×Γ ， Where Γ is the atomic magnetic resonance line width, defined as the full width at half maximum of the resonance peak; the signal receiving end contains a natural alkali metal isotope filled (such as 85 Rb / 87 Rb or 133 Cs / 131 Cs, etc.), a weak bias magnetic field coil, and a single- or multi-path dual-resonance optical detection module synchronously sense the f1 and f2 magnetic field components through atomic spin polarization and resonant frequency splitting, and output an electrical signal containing dual-frequency information; the signal demodulation module performs dual-channel bandpass filtering separation, envelope energy integration, and differential judgment on the electrical signal at the signal receiving end, and outputs the symbol "0" when the integrated energy E1>E2, and outputs the symbol "1" when E2>E1, realizing direct symbol demodulation at the physical layer.

[0047] Specifically, in one embodiment, the transmitting end includes a BFSK modulator and a dual-frequency resonant antenna; the BFSK modulator converts a binary data stream into a dual-frequency magnetic field signal, the symbol "0" maps the carrier frequency f1, and the symbol "1" maps the carrier frequency f2; the dual-frequency resonant antenna is a pair of orthogonal ring coils, which resonate at f1 and f2 respectively, generating a direction-controllable BFSK magnetic field wave.

[0048] Specifically, in one embodiment, the signal receiving end is an atomic magnetometer, which includes an alkali metal vapor chamber, a three-axis magnetic field coil, a pump laser, a detection laser and a balanced photodetector; the alkali metal vapor chamber is provided with a cubic gas chamber, for example, 85 Rb / 87 Rb or 133 Cs / 131 A cubic gas cell of Cs (usually 1–20 mm in side length, but also spherical, cylindrical, etc.) is filled with a buffer gas (usually nitrogen or an inert gas, with a pressure range of tens of torr to several atmospheres atm); the Z axis of the three-axis magnetic field coil applies a bias field B0 (1–1000 μT) and compensates for disturbances, while the X / Y axes are used to compensate for environmental interference; the pump laser is equipped with a polarized light source, which (for example, the D1 line of 795 nm rubidium atoms) is expanded and combined with a quarter-wave plate to form elliptically polarized light, synchronously polarizing the isotope atoms; the linearly polarized light of the detection laser (orthogonal to the propagation direction of the pump light) is incident on the gas cell through a polarization beam splitter, with a blue shift detuning amount of +0.1–10 GHz; a balanced photodetector is used to detect the polarization rotation angle of the detection light and output a mixed electrical signal containing f1 / f2.

[0049] Specifically, in one embodiment, the signal demodulation module includes a dual-channel bandpass filter, an envelope detector and a symbol decider; the dual-channel bandpass filter is used to separate the f1 channel and the f2 channel; the envelope detector rectifies and low-pass filters the signal of each channel to extract the amplitudes |V1| and |V2|; the symbol decider judges it as "0" when |V1|-|V2|>threshold, and "1" otherwise.

[0050] In order to achieve the purpose of the present invention, the present invention also discloses a multi-frequency magnetic field communication method based on alkali metal atomic magnetic field measurement, comprising the following steps:

[0051] Step 1: Multi-frequency physical layer carrier construction; using static magnetic field B0 to control atomic spin energy level splitting;

[0052] Step 2: Generate at least two sets of discrete magnetic resonance frequencies {f1, f2, ..., f n};

[0053] Among them, a detuned laser is used to simultaneously pump the atomic energy levels corresponding to all resonant frequencies, and the signal-to-noise ratio difference of each frequency channel meets the preset value by adjusting the light wavelength, light power and light polarization ellipticity.

[0054] Atomic magnetometers mainly rely on the Zeeman effect to create discrete atomic ground state sub-levels, then use optical pumping to polarize the atomic populations at different energy levels, and then use optical modulation or magnetic field to produce transitions.

[0055] The radio frequency atomic magnetometer applies an oscillating field at the Larmor frequency to induce atomic transitions, causing changes in the probability distribution of atoms at different energy levels. By measuring the changes in this probability distribution, the magnetic field to be measured is detected. It should be pointed out that in the context of atomic magnetometers, "radio frequency" means that the atomic transitions are triggered by an alternating magnetic field. This is a concept relative to all-optical atomic magnetometers and is different from the connotation of "radio frequency" in the communications field.

[0056] Step 3: Multi-level frequency shift keying communication signal transmission and reception, mapping the binary data stream to the carrier frequency combination, and the receiving end restores the data through a multi-channel synchronous demodulation algorithm.

[0057] Specifically, in step 2, each group of frequencies satisfies:

[0058] f k =γ_{eff}·B0+Δk(k=1,2,...,n)

[0059] where γ_{eff} is the effective gyromagnetic ratio of the atom, and the frequency offset Δ k This is achieved by selecting isotope combinations of alkali metal atoms with different gyromagnetic ratios, or by regulating the optical pumping parameters to excite the nonlinear Zeeman effect of atoms of the same type.

[0060] Specifically, in step 3, the multi-level frequency shift keying communication signal is transmitted and received, and the binary data stream is mapped to the carrier frequency combination using M-level frequency shift keying (M-FSK, including BFSK / QFSK), and each symbol period T s Internal activation of a set of frequencies {f k}, M≤n; or adopt orthogonal joint modulation (QPSK implementation basis; the magnetic resonance signal of the radio frequency atomic magnetometer has two components, one in phase with the excitation magnetic field and one out of phase, also called orthogonal), and simultaneously activate two sets of orthogonal frequency combinations {f p ,f q}, p≠q, and the symbols are distinguished by the carrier phase / power ratio.

[0061] Specifically, in one embodiment, step 1 specifically includes the following steps:

[0062] Step 1-1, steam chamber configuration: add natural isotope alkali metal (such as 85 Rb / 87 Rb, 133 Cs / 131 Cs or 39 K / 41 The vapor chamber K) is placed at the center of the triaxial magnetic field coil and filled with a buffer gas (N2 or an inert gas) to suppress atomic diffusion relaxation (in one embodiment, an anti-relaxation coating can be performed);

[0063] Step 1-2, bias field setting: Apply a constant current to the Z-axis coil to generate a static magnetic field B0 so that the Larmor frequencies of the two isotope atoms meet

[0064] f1=γ1·B0,f2=γ2·B0

[0065] Where γ1 and γ2 are the isotope gyromagnetic ratios; Example: 85 Rbγ 85 ≈4.67Hz / nT, 87 Rbγ 87 ≈7.00Hz / nT;

[0066] Frequency design constraint: The difference Δf between f1 and f2 meets the BFSK symbol interval requirement (usually Δf ≥ 2 × the symbol rate of the communication).

[0067] Specifically, in one embodiment, step 2 specifically includes the following steps:

[0068] Step 2-1, Pump (also called pumping) light modulation: Use a single elliptically polarized pump laser, with the wavelength tuned to the alkali metal D line (such as Rb: 795nm D1 line or 780nm D2 line, the D1 line and D2 line of rubidium atoms can both achieve the phenomenon, only the efficiency is different), and simultaneously cover the transition from the ground state to the excited state of two isotopes (such as Rb D2 line: 85 Rb's F=3→F'=4 and 87 Rb's F = 2 → F' = 3), pump power 0.1–10 mW / cm 2 ;

[0069] Step 2-2, probe light (also called detection) optimization: The wavelength of a single linearly polarized probe laser is set to blue detuned (relative to the pump light frequency offset +0.1–5 GHz), and the sensitivity balance is improved by enhancing the non-resonant Faraday rotation angle (measured 85 Rb and 87 Rb sensitivity difference <15%).

[0070] Specifically, in one embodiment, step 3 specifically includes the following steps:

[0071] Step 3-1, transmitter modulation: According to the binary data stream to be transmitted, the BFSK modulator drives the resonant coil to generate a time-varying magnetic field B tx :

[0072] Symbol “0” → magnetic field pulse with carrier frequency f1 (amplitude 0.1–10nT, pulse width ≥ 2 / Δf)

[0073] Symbol "1" → magnetic field pulse with carrier frequency f2 (amplitude range is the same as f1)

[0074] Step 3-1, physical layer demodulation at the receiving end: After the detection light passes through the steam chamber, the balanced photodetector outputs a dual-frequency mixed signal V S , separate the f1 / f2 channels by bandpass filtering:

[0075]

[0076] Where t is time, α and β are isotope response amplitudes, are the initial phases of electromagnetic waves with frequencies f1 and f2, respectively. After optimization by S2, |α-β| / avg(α,β)<15%;

[0077] Use non-coherent envelope detection to decide the symbol:

[0078] When ∫|V1(t)|dt>∫|V2(t|dt and the difference exceeds the threshold → it is judged as symbol "0"

[0079] When ∫|V2(t)|dt>∫|V1(t)|dt and the difference exceeds the threshold → it is judged as the symbol "1".

[0080] It should be noted that, in this document, relational terms such as first and second, etc., are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that includes a list of elements includes not only those elements but also other elements not explicitly listed, or elements inherent to such process, method, article, or apparatus.

[0081] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A multi-frequency magnetic field communication method based on alkali metal atomic magnetic field measurement, characterized in that: The following steps are involved: Step 1: Multi-frequency physical layer carrier construction; using static magnetic field B0 to control atomic spin energy level splitting; Step 2: Generate at least two sets of discrete magnetic resonance frequencies {f1, f2, ..., f n }; Among them, a detuned laser is used to simultaneously pump the atomic energy levels corresponding to all resonant frequencies, and the signal-to-noise ratio difference of each frequency channel meets the preset value by adjusting the light wavelength, light power and light polarization ellipticity. Step 3: Multi-level frequency shift keying communication signal transmission and reception, mapping the binary data stream to the carrier frequency combination, and the receiving end restores the data through a multi-channel synchronous demodulation algorithm.

2. The multi-frequency magnetic field communication method based on alkali metal atomic magnetic field measurement according to claim 1, characterized in that: In step 2, each frequency group satisfies: f k =γ_{eff}·B0+Δk(k=1,2,...,n) where γ_{eff} is the effective gyromagnetic ratio of the atom, and the frequency offset Δ k This is achieved by selecting isotope combinations of alkali metal atoms with different gyromagnetic ratios, or by regulating the optical pumping parameters to excite the nonlinear Zeeman effect of atoms of the same type.

3. The multi-frequency magnetic field communication method based on alkali metal atomic magnetic field measurement according to claim 2, characterized in that: In step 3, the multi-level frequency shift keying communication signal is transmitted and received, and the binary data stream is mapped to the carrier frequency combination using M-level frequency shift keying. s Internal activation of a set of frequencies {f k }, M≤n; or adopt orthogonal joint modulation to activate two sets of orthogonal frequency combinations {f p ,f q }, p≠q, and the symbols are distinguished by the carrier phase / power ratio.

4. The multi-frequency magnetic field communication method based on alkali metal atomic magnetic field measurement according to claim 1, characterized in that: Step 1 specifically includes the following steps: Step 1-1, steam chamber configuration: Place a steam chamber containing natural isotope alkali metal at the center of a triaxial magnetic field coil and fill it with buffer gas to suppress atomic diffusion and relaxation; Step 1-2, bias field setting: Apply a constant current to the Z-axis coil to generate a static magnetic field B o , so that the Larmor frequencies of the two isotope atoms satisfy f1=γ1·B0,f2=γ2·B0 Where γ1,γ2 are the isotope gyromagnetic ratios; Frequency design constraint: The difference Δf between f1 and f2 meets the BFSK symbol interval requirement.

5. The multi-frequency magnetic field communication method based on alkali metal atomic magnetic field measurement according to claim 1, characterized in that: Step 2 specifically includes the following steps: Step 2-1: Pump light modulation: Use a single elliptically polarized pump laser with a wavelength tuned to the alkali metal D line, covering the transition from the ground state to the excited state of both isotopes at the same time, with a pump power of 0.1–10 mW / cm 2 ; Step 2-2, detection light optimization: The wavelength of the single linearly polarized detection laser is set to blue detuning, and the sensitivity balance is improved by enhancing the non-resonant Faraday rotation angle.

6. The multi-frequency magnetic field communication method based on alkali metal atomic magnetic field measurement according to claim 1, characterized in that: Step 3 specifically includes the following steps: Step 3-1, transmitter modulation: According to the binary data stream to be transmitted, the BFSK modulator drives the resonant coil to generate a time-varying magnetic field B tx : The symbol "0" refers to the magnetic field pulse of carrier frequency f1; Symbol "1" refers to the magnetic field pulse of carrier frequency f2; Step 3-2, physical layer demodulation at the receiving end: After the detection light passes through the steam chamber, the balanced photodetector outputs a dual-frequency mixed signal V S , separate the f1 / f2 channels by bandpass filtering: Where t is time, α and β are isotope response amplitudes, are the initial phases of electromagnetic waves with frequencies f1 and f2, respectively. After optimization by S2, |α-β| / avg(α,β)<15%; Use non-coherent envelope detection to decide the symbol: When ∫|V1(t)|dt>∫|V2(t|dt and the difference exceeds the threshold → it is judged as symbol "0" When ∫|V2(t)|dt>∫|V1(t)|dt and the difference exceeds the threshold → it is judged as symbol "1".

7. A multi-frequency magnetic field communication system based on alkali metal atomic magnetic field measurement, characterized in that: It includes a transmitter, a signal receiver, and a signal demodulation module; the transmitter is used to perform frequency shift keying modulation on the binary data stream to generate a dual-frequency magnetic field signal, where the first frequency f1 maps the symbol "0" and the second frequency f2 maps the symbol "1", and the interval between the two frequencies satisfies Δf>5×Γ ， Wherein Γ is the atomic magnetic resonance linewidth, defined as the full width at half maximum of the resonance peak; the signal receiving end comprises a vapor chamber filled with natural alkali metal isotopes, a weak bias magnetic field coil, and a single-path or multi-path dual-resonance optical detection module, which synchronously senses the f1 and f2 magnetic field components through atomic spin polarization and resonant frequency splitting, and outputs an electrical signal containing dual-frequency information; the signal demodulation module performs dual-channel bandpass filtering separation, envelope energy integration, and differential judgment on the electrical signal at the signal receiving end, outputting a symbol "0" when the integrated energy E1>E2 and a symbol "1" when E2>E1, thereby realizing direct symbol demodulation at the physical layer.

8. The multi-frequency magnetic field communication system based on alkali metal atomic magnetic field measurement according to claim 7, characterized in that: The transmitting end includes a BFSK modulator and a dual-frequency resonant antenna; the BFSK modulator converts a binary data stream into a dual-frequency magnetic field signal, with the symbol "0" mapping to the carrier frequency f1 and the symbol "1" mapping to the carrier frequency f2; the dual-frequency resonant antenna is a pair of orthogonal ring coils, which resonate at f1 and f2 respectively, generating a direction-controllable BFSK magnetic field wave.

9. The multi-frequency magnetic field communication system based on alkali metal atomic magnetic field measurement according to claim 7, characterized in that: The signal receiving end is an atomic magnetometer, which includes an alkali metal vapor chamber, a three-axis magnetic field coil, a pump laser, a detection laser and a balanced photodetector; the alkali metal vapor chamber is provided with a cubic gas chamber filled with nitrogen buffer gas; the Z axis of the three-axis magnetic field coil applies a bias field B0 and compensates for disturbances, and the X / Y axes are used to compensate for environmental interference; the pump laser is provided with a polarized light source, which forms circularly polarized light through beam expansion and a 1 / 4 wave plate to synchronously polarize isotope atoms; the linearly polarized light of the detection laser is incident on the gas chamber through a polarization beam splitter, with a blue shift detuning amount of +0.1-10GHz; the balanced photodetector is used to detect the polarization rotation angle of the detection light and output a mixed electrical signal containing f1 / f2.

10. The multi-frequency magnetic field communication system based on alkali metal atomic magnetic field measurement according to claim 7, characterized in that: The signal demodulation module includes a dual-channel bandpass filter, an envelope detector, and a symbol decision device. The dual-channel bandpass filter is used to separate the f1 channel and the f2 channel. The envelope detector rectifies and low-pass filters the signal of each channel to extract the amplitudes |V1| and |V2|. The symbol decision device judges the signal as "0" when |V1|-|V2|>threshold, and "1" otherwise.

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