Optical fiber collimator and atomic magnetometer

Abstract

The application relates to an optical fiber collimator and an atomic magnetometer. The optical fiber collimator is used for light beam collimation in the atomic magnetometer and comprises an optical fiber input end, a collimation transition interface, a LOS light coupling microstructure layer, a light beam shaping layer and a collimation output end arranged in sequence along an optical path. The optical fiber input end is used for receiving incident light output by an optical fiber. The collimation transition interface is used for reducing interface reflection loss. The LOS light coupling microstructure layer is a near-plane nanometer period structure, the structure period is 300nm-800nm, the structure height is 100nm-500nm, and the LOS light coupling microstructure layer is used for coupling the optical fiber waveguide mode into a free space propagation light beam. The light beam shaping layer is used for adjusting the light beam divergence angle so that the output light beam approaches a parallel light beam. The collimation output end is used for coupling the collimated light beam to an alkali metal cell of the atomic magnetometer. In a compact integrated structure, low divergence angle, high-quality light beam output close to a plane wave front is realized.

Description

Technical Field

[0001] This invention relates to the technical field of quantum precision measurement equipment, and in particular to an optical fiber collimator and an atomic magnetometer. Background Technology

[0002] Quantum precision measurement technology based on the spin coherence effect of alkali metal atoms has been applied to high-sensitivity detection devices such as spin-free exchange relaxation (SERF) atomic magnetometers, atomic gyroscopes, and atomic accelerometers. These devices achieve high-precision measurement of physical quantities such as extremely weak magnetic fields by optically pumping and resonantly detecting alkali metal atomic vapors, which places extremely high demands on the uniformity of the optical field distribution, the stability of the optical path, and the optical coupling efficiency.

[0003] In multi-chamber atomic magnetometers, incident light needs to undergo multiple reflections within the chambers to prolong the interaction path between the light and the atomic medium. The fiber optic collimator, located outside the chambers, is responsible for efficiently coupling the fiber optic output light into the chambers. In existing technologies, fiber optic collimators often employ traditional spherical lenses or gradient refractive index (GRIN) lens structures.

[0004] However, the above structure has significant shortcomings in multi-chamber applications: the wavefront curvature or divergence angle of the output beam of a traditional collimator is large, making it difficult to meet the high collimation and low aberration requirements for multiple reflections; the coupling structure between the fiber and the collimating lens is highly dependent on the assembly and adjustment accuracy, and the system is prone to optical axis shift under temperature changes or mechanical disturbances; in addition, conventional coupling methods are difficult to balance miniaturization and high stability requirements, which is not conducive to the compact integrated design of multi-chamber systems. Summary of the Invention

[0005] Therefore, it is necessary to address the above problems by providing a fiber collimator and atomic magnetometer that can achieve high-quality collimation output, stable optical axis control, and efficient fiber-to-gas cell coupling in a compact structure.

[0006] This application first provides an optical fiber collimator for beam collimation within an atomic magnetometer, comprising an optical fiber input end, a collimation transition interface, a LOS optical coupling microstructure layer, a beam shaping layer, and a collimation output end arranged sequentially along the optical path; the optical fiber input end is used to receive incident light output from the optical fiber; the collimation transition interface is used to reduce interface reflection loss; the LOS optical coupling microstructure layer is a near-planar nano-periodic structure with a structural period of 300nm–800nm ​​and a structural height of 100nm–500nm, used to couple the optical fiber waveguide mode into a free-space propagating beam; the beam shaping layer is used to adjust the beam divergence angle so that the output beam approaches a parallel beam; the collimation output end is used to couple the collimated beam to the alkali metal gas cell of the atomic magnetometer.

[0007] In one embodiment, the LOS optical coupling microstructure layer is a trapezoidal nanoridge structure, a subwavelength grating structure, a nano-sawtooth structure, or a subwavelength periodic microstructure array; and / or, The beam shaping layer is a microlens array, a planar metasurface lens, or a diffractive optical element; and / or The collimation transition interface is a refractive index matching layer, an optical adhesive layer, or a transparent medium layer.

[0008] In one embodiment, the optical fiber input end includes an optical fiber core and an optical fiber cladding disposed outside the optical fiber core, the optical fiber cladding being used to confine the light beam to propagate within the optical fiber core and prevent light beam leakage.

[0009] In one embodiment, a coupling adjustment component is also included, which is used to adjust the spatial position and tilt angle of the optical fiber input end.

[0010] In one embodiment, the collimation output end includes a protective window disposed at the exit end of the beam shaping layer.

[0011] In one embodiment, the packaged housing is also included, wherein the fiber input end, collimation transition interface, LOS optical coupling microstructure layer, beam shaping layer and protective window are integrally packaged within the packaged housing, and the material of the packaged housing is boron nitride.

[0012] In one embodiment, the fiber collimator is a fiber array structure including multiple collimation channels, each collimation channel being arranged side by side, and each collimation channel including the fiber input end, the collimation transition interface, the LOS optical coupling microstructure layer and the beam shaping layer arranged sequentially along the optical path.

[0013] This application also provides an atomic magnetometer, comprising: an alkali metal gas cell; a pump optical path, including a pump source for generating pump light and incident on the alkali metal gas cell to establish atomic spin polarization; a detection optical path, including a detection source and the aforementioned fiber collimator, wherein the detection light generated by the detection source is collimated by the fiber collimator and coupled into the alkali metal gas cell; and a photoelectric detection unit for detecting the polarization state change of the detection light output from the alkali metal gas cell and converting it into an electrical signal.

[0014] In one embodiment, the alkali metal gas chamber is a multi-pass chamber, and a reflector structure is provided in the multi-pass chamber. The reflector structure is used to make the probe light entering the multi-pass chamber propagate back and forth multiple times along a predetermined path to form a multi-path propagation.

[0015] In one embodiment, the reflector structure includes a first Herriott cavity mirror and a second Herriott cavity mirror disposed opposite to each other. The first Herriott cavity mirror or the second Herriott cavity mirror is provided with a light-transmitting hole for the detection light to be incident on and emitted.

[0016] The aforementioned fiber collimator, through the synergistic effect of the LOS microstructure and the beam shaping layer, achieves high-quality beam output with low divergence angle and near-plane wavefront within a compact integrated structure. This effectively meets the high collimation and low aberration requirements of multi-chamber atomic magnetometers for multiple reflections and propagation, enabling the probe light to maintain a stable spot size and propagation trajectory during multi-path propagation. This extends the interaction length between light and the atomic medium, enhances the cumulative effect of Faraday rotation signals, and ultimately improves the system's signal-to-noise ratio and magnetic field measurement sensitivity. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the fiber optic collimator of this application; Figure 2 for Figure 1 Schematic diagram of the LOS optical coupling microstructure layer; Figure 3 This is a schematic diagram of the atomic magnetometer system of this application.

[0018] Reference numerals: 2. Polarization-maintaining fiber; 3. Fiber collimator; 6. Concave lens; 7. Convex lens; 8. First Herriott cavity mirror; 9. Magnetic shielding assembly; 14. Second Herriott cavity mirror; 15. Alkali metal gas chamber; 19. Fiber cladding; 20. Fiber core; 21. Collimation transition interface; 22. LOS optical coupling microstructure layer; 23. Beam shaping layer; 24. Protective window. Detailed Implementation

[0019] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Many specific details are set forth in the following description to provide a thorough understanding of the present invention. However, the present invention can be practiced in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0020] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0021] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0022] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0023] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "over," and "on top" of the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0024] It should be noted that when an element is referred to as being "fixed to" or "set on" another element, it can be directly on the other element or there may be an intervening element. When an element is considered to be "connected to" another element, it can be directly connected to the other element or there may be an intervening element. The terms "vertical," "horizontal," "upper," "lower," "left," "right," and similar expressions used herein are for illustrative purposes only and do not represent the only possible implementation.

[0025] Please combine Figure 1 as well as Figure 2 As shown, this application first provides an optical fiber collimator, including an optical fiber input end, a collimation transition interface 21, an LOS optical coupling microstructure layer 22, a beam shaping layer 23 and a collimation output end arranged sequentially along the optical path; The optical fiber input end is used to receive the incident light output from the optical fiber. The incident light is guided by the external polarization-maintaining fiber 2 into the collimator structure and propagates along the fiber core to the end of the fiber. The collimation transition interface 21 is disposed between the output end face of the fiber input end and the LOS optical coupling microstructure layer 22 to reduce interface reflection loss and realize low-loss transition from fiber guided mode to free space propagation mode. LOS optical coupling microstructure layer 22 is a near-planar nano-periodic structure with finite lateral dimensions. Its period is 300 nm–800 nm, and its height is 100 nm–500 nm. This structure couples fiber waveguide modes into free-space propagating beams by modulating the local optical field distribution, achieving directional light output in the paraxial direction. Due to its finite lateral dimensions, this structure can significantly suppress optical crosstalk generated during lateral light propagation. The beam shaping layer 23 is disposed above the LOS optical coupling microstructure layer 22 and is used to adjust the beam divergence angle, improve the beam collimation and optimize the beam spatial distribution, so that the output beam is close to a parallel beam. The collimation output is used to couple the collimated beam after the above-mentioned processing to the alkali metal gas cell 15 of the atomic magnetometer, forming a collimated output with low divergence angle, high directionality and high beam quality.

[0026] In some embodiments, the LOS optical coupling microstructure layer 22 may adopt one of the following forms: a trapezoidal nanoridge structure, a subwavelength grating structure, a nano-sawtooth structure, or a subwavelength periodic microstructure array; all of the above structures are formed based on periodic micro-nano fabrication at the subwavelength scale, and by adjusting parameters such as the structural period, duty cycle, and groove depth, precise control of the wavefront and propagation direction of the emitted light field can be achieved. Among them, the trapezoidal nanoridge structure has a wider process tolerance; the subwavelength grating structure can provide higher diffraction efficiency; the nano-sawtooth structure is conducive to achieving a wide-band response; and the subwavelength periodic microstructure array facilitates multi-channel parallel fabrication and integration.

[0027] The beam shaping layer 23 can employ one of the following elements: a microlens array, a planar metasurface lens, or a diffractive optical element (DOE). The microlens array achieves overall wavefront planarization by independently focusing and phase-tuning the light waves within each sub-aperture; the planar metasurface lens utilizes the phase accumulation effect of subwavelength structural units to achieve the focusing and collimation functions of a traditional spherical lens within an extremely thin planar layer; the diffractive optical element introduces controlled phase delay through etched relief-type microstructures, achieving beam shaping and divergence angle compression.

[0028] The collimation transition interface 21 can adopt one of the following structures: a refractive index matching layer, an optical adhesive layer, or a transparent dielectric layer. The refractive index matching layer reduces Fresnel reflection loss by selecting a material with a refractive index similar to that of the fiber core and adjacent functional layers; the optical adhesive layer achieves refractive index matching while also providing bonding and fixation; and the transparent dielectric layer provides a flat processing substrate for subsequent functional layers.

[0029] Please refer to Figure 1 As shown, in some embodiments, the optical fiber input end includes an optical fiber core 20 and an optical fiber cladding 19 disposed outside the optical fiber core 20; the optical fiber core 20 is used to conduct a linearly polarized beam from a laser source; the optical fiber cladding 19 is used to confine the beam within the optical fiber core 20 and prevent the beam from leaking into the external environment.

[0030] In one specific embodiment, the optical fiber may be polarization-maintaining fiber 2 to maintain the stability of the polarization state of the probe light and meet the polarization baseline requirements of Faraday rotation detection.

[0031] In some embodiments, the fiber collimator further includes a coupling adjustment component to further improve coupling efficiency and optical axis alignment accuracy. The coupling adjustment component is used to adjust the spatial position and tilt angle of the fiber input end to achieve optical center alignment between the fiber output optical axis and the subsequent LOS optical coupling microstructure layer 22 and beam shaping layer 23.

[0032] In one specific embodiment, the coupling adjustment component may employ a precision threaded adjustment structure, a piezoelectrically driven micro-displacement platform, or an elastic hinge-type adjustment mechanism to adjust along the three translational degrees of freedom (X, Y, Z) and the two rotational degrees of freedom (pitch, yaw).

[0033] Please refer to Figure 1As shown, in some embodiments, the collimated output end includes a protective window 24, which is disposed at the exit end of the beam shaping layer 23. The protective window 24 is formed of an optically grade transparent material, serving both as an output window for the beam and providing mechanical protection and hermetically sealed isolation for the internal functional layers. Specifically, the collimated beam, after being processed by the LOS coupling structure and the beam shaping layer 23, is output from the protective window 24, forming a collimated output beam with low divergence angle, high directionality, low crosstalk, and high beam quality, and is directly coupled to the alkali metal gas chamber 15.

[0034] In some embodiments, the fiber collimator further includes a housing, in which the fiber input end, collimation transition interface 21, LOS optical coupling microstructure layer 22, beam shaping layer 23, and protective window 24 are integrally encapsulated to improve the optical axis stability of the system under temperature changes and mechanical disturbances. Specifically, the components can be integrated or quasi-integrated assembled by means of optical bonding, eutectic bonding, or laser welding.

[0035] In addition, the encapsulation housing is made of boron nitride, which has a low coefficient of thermal expansion and excellent dimensional stability, effectively reducing alignment mismatch caused by temperature drift and meeting the requirements for long-term stable operation of the atomic magnetometer; of course, in some other embodiments, the encapsulation housing may also be made of other low thermal expansion materials.

[0036] Because the LOS optical coupling microstructure layer 22 has a significant suppression effect on lateral propagation, no obvious optical crosstalk is generated between adjacent collimating channels. Based on this characteristic, in some embodiments, the fiber collimator can be extended into a fiber array structure containing multiple collimating channels, with each collimating channel arranged side by side on the same substrate. Each collimating channel includes a fiber input end, a collimation transition interface 21, an LOS optical coupling microstructure layer 22, and a beam shaping layer 23 arranged sequentially along the optical path. This multi-channel structure can be applied to high-density optical detection arrays, multi-channel quantum magnetometer optical systems, or optical microscopy imaging systems to achieve high-density parallel beam collimation and coupling.

[0037] Please refer to Figure 3 As shown, the present invention also provides a dual-beam spin-exchange-relaxation (SERF) atomic magnetometer, including an alkali metal gas chamber 15, a pump optical path, a probe optical path, and a photoelectric detection unit.

[0038] The alkali metal gas chamber 15 is the core functional unit of the atomic magnetometer, made of non-magnetic optical glass material, preferably borosilicate glass or aluminosilicate glass. In this embodiment, the gas chamber is a cubic encapsulation structure made of borosilicate material, with an inner side length of approximately 10 mm and a wall thickness of approximately 1 mm. The gas chamber is encapsulated with an alkali metal atom layer rich in 87Rb and filled with nitrogen gas of approximately 750 Torr as a buffer gas to improve atomic polarization efficiency and reduce relaxation between atoms and the gas chamber wall.

[0039] The pump optical path includes a pump light source, which generates pump light and incident it into the alkali metal gas cell 15 to establish atomic spin polarization. The wavelength of the pump light corresponds to the D1 or D2 line resonant transition of the alkali metal atom, and the alkali metal atom achieves a high degree of electronic spin polarization through optical pumping.

[0040] The detection optical path includes a detection light source and an optical fiber collimator as described in any of the preceding embodiments. The detection light generated by the detection light source is wavefront shaped and collimated by the optical fiber collimator to form a beam with a low divergence angle and approximately a plane wave, which is coupled into the alkali metal gas chamber 15 according to preset incident conditions. Under the action of a weak magnetic field, the spins of the alkali metal atoms precess, causing changes in the optical properties of the atomic medium, and the polarization state of the detection light undergoes Faraday rotation.

[0041] The photoelectric detection unit is used to detect the change in polarization state of the probe light output from the alkali metal gas cell 15 and convert it into an electrical signal. In this embodiment, the photoelectric detection unit includes a polarizing beam splitter, a photodetector, and a transimpedance amplifier. It extracts the Faraday rotation signal through differential detection to measure the external magnetic field.

[0042] Furthermore, in some embodiments, the alkali metal gas chamber 15 is a multi-pass chamber, and a reflector structure is provided inside the multi-pass chamber. The reflector structure is used to allow the probe light entering the multi-pass chamber to propagate back and forth multiple times along a predetermined path, forming a multi-path propagation path. The collimated beam maintains a stable spot size and propagation direction during the multi-path propagation process, so as to extend the interaction length between the light and the alkali metal atomic medium, and allow the Faraday rotation signal to be accumulated and amplified during the multi-path reflection process, thereby improving the detection signal strength and the system signal-to-noise ratio.

[0043] Since the fiber collimator of this invention can output a high-quality collimated beam near the plane wavefront, the probe light can effectively suppress the beam spread and phase distortion during multi-path reflection, ensuring that the beam distribution and propagation trajectory are highly consistent after each reflection. This is a key prerequisite for achieving effective accumulation and amplification of Faraday rotation signals.

[0044] Please refer to Figure 3As shown, further, in some embodiments, the reflector structure includes a first Herriott cavity mirror 8 and a second Herriott cavity mirror 14 disposed opposite to each other. The first Herriott cavity mirror 8 or the second Herriott cavity mirror 14 is provided with a light-transmitting aperture for the incident and emitted probe light. Both the first Herriott cavity mirror 8 and the second Herriott cavity mirror 14 are high-reflectivity optical mirrors, with optimized mirror curvature and spacing, enabling the probe light to propagate along a closed loop path between the two cavity mirrors, achieving dozens to hundreds of round-trip reflections, thereby extending the effective optical path by one to two orders of magnitude.

[0045] Please refer to Figure 3 As shown, in some embodiments, the atomic magnetometer further includes an optical beam expander located between the fiber collimator 3 and the anti-alkali metal gas cell 15. The optical beam expander includes a concave lens 6 and a convex lens 7 arranged sequentially along the optical axis, which together form a Galilean beam expander structure. The pump light passes through the concave lens and the convex lens in sequence to expand the beam so that the expanded light spot covers the gas cell region, thereby improving the spatial uniformity of atomic polarization.

[0046] In some embodiments, during the operation of the dual-beam SERF atomic magnetometer, the pump light and probe light are configured with independent optical paths. Please refer to... Figure 3 As shown, the working principle of the atomic magnetometer is as follows: Pump light is incident on the alkali metal gas chamber 15 to optically pump the alkali metal atoms, thereby establishing a stable atomic spin polarization state. After the probe light is output from the optical fiber, it undergoes wavefront shaping and collimation processing by the optical fiber collimator of this invention to form a beam with a low divergence angle and approximately a plane wave, and is coupled into the multi-pass gas chamber according to the preset incident conditions.

[0047] When a weak magnetic field exists in the external environment, the atomic spins precess under the influence of the magnetic field, causing changes in the optical properties of the atomic medium. During the multi-path propagation, the probe light interacts with the atoms, causing a slight rotation in its polarization state, i.e., the Faraday rotation effect. This rotation signal interacts with the atomic medium multiple times during the multi-path propagation, resulting in cumulative amplification, thereby improving the detection signal strength and the system signal-to-noise ratio. The probe light output from the gas cell is guided to the photoelectric detection unit, where its polarization change is detected and converted into an electrical signal, realizing the measurement of the external magnetic field.

[0048] Under extremely weak magnetic fields and high alkali metal atom number density, the spin exchange rate between atoms is much higher than their spin precession frequency; at this point, the system rapidly reaches a quasi-equilibrium state, and its density matrix can be approximately described by the spin temperature distribution; the ground-state electron spin polarization behavior can be characterized by the spin-free exchange relaxation (SERF) mechanism and can be effectively described by the Bloch equation. , Where D is the spin diffusion coefficient; P represents the electron spin polarization vector of the alkali metal atom; γ is the electron gyromagnetic ratio; B is the magnetic field vector; s is the photon polarization direction vector of the pump light; R is the pump rate; and Q is the deceleration factor, the value of which is related to the nuclear spin and the degree of atomic polarization. This is the relaxation time.

[0049] Since the pump light and probe light are configured with independent optical paths, optical crosstalk between them can be effectively reduced. At the same time, the probe light has less disturbance to the atomic spin polarization after being shaped by the LOS fiber collimator, which helps to reduce additional relaxation effects and maintain a high degree of polarization. By adjusting the power, polarization and incident direction of the pump light and probe light respectively, the optical path can be independently optimized, improving the system's adjustment flexibility.

[0050] In some embodiments, the atomic magnetometer further includes a magnetic shielding component 9, which is arranged around the alkali metal gas chamber 15 to reduce the influence of the external magnetic field on the measurement system. The magnetic shielding component 9 includes a cylindrical conductive shielding layer and multiple layers of high magnetic permeability material shielding layers, which are nested to form a multi-level magnetic field attenuation structure.

[0051] Specifically, the quasi-static shielding coefficient of the magnetic shielding component 9 can be greater than 105, thereby attenuating the ambient magnetic field to the nanotesla level and providing a low magnetic noise working environment for atomic magnetic measurements; the alkali metal gas chamber 15 is supported and positioned at the center of the working area of ​​the magnetic shielding component 9 by a non-magnetic fixing structure. The fixing structure can be integrally formed by three-dimensional printing to reduce magnetic interference and improve assembly stability.

[0052] In some embodiments, the fiber optic collimator can be arranged coaxially with or at a predetermined angle to the multi-chamber optical path system, allowing the probe light to enter the chamber under set incident conditions and form a multi-path propagation path under the action of the mirror structure. During this process, the probe light, after being processed by the near-plane optical coupling structure, can maintain a stable spot size and propagation direction during multiple reflections, thereby significantly increasing the interaction length between the light and the alkali metal atomic medium and enhancing the cumulative effect of the Faraday rotation signal.

[0053] In some embodiments, the lateral dimension of the LOS optical coupling microstructure layer 22 is smaller than the aperture of the alkali metal gas chamber 15 to ensure that the effective light transmission area of ​​the collimated beam is within the aperture range of the gas chamber, thereby avoiding the influence of edge diffraction and cutoff loss on the beam quality.

[0054] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0055] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A fiber optic collimator for beam collimation within an atomic magnetometer, characterized in that, It includes an optical fiber input end, a collimation transition interface (21), an LOS optical coupling microstructure layer (22), a beam shaping layer (23), and a collimation output end arranged sequentially along the optical path; The optical fiber input end is used to receive the incident light output from the optical fiber; The collimation transition interface (21) is used to reduce interface reflection loss; The LOS optical coupling microstructure layer (22) is a near-planar nano-periodic structure with a structural period of 300nm to 800nm ​​and a structural height of 100nm to 500nm. It is used to couple the fiber waveguide mode into a free-space propagating beam. The LOS optical coupling microstructure layer (22) has a limited lateral dimension to suppress optical crosstalk generated during the lateral propagation of light. The beam shaping layer (23) is used to adjust the beam divergence angle so that the output beam approaches a parallel beam; The collimation output terminal is used to couple the collimated beam to the alkali metal gas cell (15) of the atomic magnetometer.

2. The fiber optic collimator according to claim 1, characterized in that, The LOS optical coupling microstructure layer (22) is a trapezoidal nanoridge structure, a subwavelength grating structure, a nano-sawtooth structure, or a subwavelength periodic microstructure array; and / or, The beam shaping layer (23) is a microlens array, a planar metasurface lens, or a diffractive optical element; and / or, The collimation transition interface (21) is a refractive index matching layer, an optical adhesive layer, or a transparent medium layer.

3. The fiber optic collimator according to claim 1, characterized in that, The optical fiber input end includes an optical fiber core (20) and an optical fiber cladding (19) sleeved on the outside of the optical fiber core (20). The optical fiber cladding (19) is used to confine the light beam to propagate within the optical fiber core (20) and prevent the light beam from leaking out.

4. The fiber optic collimator according to claim 1, characterized in that, It also includes a coupling adjustment component, which is used to adjust the spatial position and tilt angle of the optical fiber input end.

5. The fiber optic collimator according to claim 1, characterized in that, The collimation output end includes a protective window (24), which is disposed at the output end of the beam shaping layer (23).

6. The fiber optic collimator according to claim 5, characterized in that, It also includes a packaging housing, in which the optical fiber input end, collimation transition interface (21), LOS optical coupling microstructure layer (22), beam shaping layer (23) and protective window (24) are integrally packaged within the packaging housing, and the material of the packaging housing is boron nitride.

7. The fiber optic collimator according to any one of claims 1 to 6, characterized in that, The fiber collimator is a fiber array structure including multiple collimation channels, each collimation channel is arranged side by side, and each collimation channel includes the fiber input end, the collimation transition interface (21), the LOS optical coupling microstructure layer (22) and the beam shaping layer (23) arranged sequentially along the optical path.

8. An atomic magnetometer, characterized in that, include: Alkali metal gas chamber (15); The pump optical path includes a pump light source for generating pump light and incident it onto the alkali metal gas cell (15) to establish atomic spin polarization; The detection optical path includes a detection light source and an optical fiber collimator as described in any one of claims 1 to 7, wherein the detection light generated by the detection light source is collimated by the optical fiber collimator and then coupled into the alkali metal gas cell (15); and The photoelectric detection unit is used to detect the change in polarization state of the probe light output through the alkali metal gas cell (15) and convert it into an electrical signal.

9. The atomic magnetometer according to claim 8, characterized in that, The alkali metal gas chamber (15) is a multi-pass chamber. The multi-pass chamber is equipped with a reflector structure. The reflector structure is used to make the probe light entering the multi-pass chamber propagate back and forth multiple times along a predetermined path to form a multi-path propagation.

10. The atomic magnetometer according to claim 9, characterized in that, The reflector structure includes a first Herriott cavity mirror (8) and a second Herriott cavity mirror (14) arranged opposite to each other. The first Herriott cavity mirror (8) or the second Herriott cavity mirror (14) is provided with a light-transmitting hole for the detection light to be incident and emitted.

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