Chiral light transverse spin separation method based on frequency regulation and control of magneto-optical super atoms

Abstract

The invention discloses a chiral light transverse spin separation method based on frequency regulation of magneto-optical super atoms, and belongs to the field of micro-nano photonics. Carrying out transverse spin separation by adopting a magneto-optical super-atom structure; the magneto-optical super-atom structure comprises an upper magnetic metal material layer, a lower magnetic metal material layer and a middle magneto-optical material layer, a rectangular coordinate system is established based on a magneto-optical super-atom structure, left-hand circularly polarized light and right-hand circularly polarized light are incident in the-y-axis direction, magnetic metal materials on the upper layer and the lower layer apply a static magnetic field to a magneto-optical material on the middle layer in the z-axis direction of the structure, and the magneto-optical effect of the magneto-optical material on the middle layer is excited. And electric and magnetic dipole moments are generated to generate scattering transverse spin separation on the incident left-hand circularly polarized light and right-hand circularly polarized light. The method breaks through traditional fixed frequency limitation, dynamic reversible regulation and control of the separation direction and amplitude are achieved, and forward separation, complete suppression and reverse separation can be continuously switched by adjusting the incident light frequency.

Description

Technical Field

[0001] This invention belongs to the field of micro-nano photonics, specifically relating to a chiral optical transverse spin separation method based on frequency modulation of magneto-optical superatoms. Background Technology

[0002] The photonic spin Hall effect is a fundamental optical phenomenon originating from the spin-orbit interaction of light, in which the spin angular momentum of light couples with the external orbital angular momentum, resulting in left-handed and right-handed circularly polarized light exhibiting lateral shifts in opposite directions during propagation. Due to its potential applications in high-precision optical metrology, polarization-sensitive imaging, and spin-controlled photonic devices, this effect has attracted widespread attention in recent years. However, the inherent photonic spin Hall effect is typically weak, posing a challenge to its practical applications in optical information processing and photonic chip integration. Therefore, enhancing the photonic spin Hall effect has become an important research direction. In recent years, research on realizing the photonic spin Hall effect through the special properties of superatoms has gradually attracted research interest. For example, utilizing the magnetoelectric coupling properties of bi-anisotropic superatoms can significantly enhance the photonic spin Hall effect, achieving obvious lateral spin separation.

[0003] Currently, existing methods for enhancing the photon spin Hall effect using superatomic properties to achieve transverse spin separation are all based on a fixed incident frequency, which can only achieve transverse spin separation in a fixed direction. This greatly limits the freedom and flexibility of spin-controlled light fields. Summary of the Invention

[0004] To address the aforementioned issue of achieving transverse spin separation based on a fixed incident frequency, this invention provides a method that utilizes superatoms of magneto-optical materials to enhance the photon spin Hall effect, thereby achieving significant transverse spin separation of scattered light under incident left- or right-handed circularly polarized light, with the amplitude and direction of the separation being adjustable by the incident frequency.

[0005] This invention provides a chiral optical transverse spin separation method based on frequency modulation of magneto-optical superatoms. The method employs a magneto-optical superatomic structure for transverse spin separation. The magneto-optical superatomic structure comprises upper and lower layers of identical magnetic metal materials and a middle layer of magneto-optical material. A Cartesian coordinate system is established based on the magneto-optical superatomic structure. Left-handed and right-handed circularly polarized light are incident along the -y-axis. The upper and lower magnetic metal materials apply a static magnetic field to the middle layer of magneto-optical material along the z-axis of the structure, exciting the magneto-optical effect of the middle layer and generating electric and magnetic dipole moments that scatter the incident left-handed and right-handed circularly polarized light, resulting in transverse spin separation.

[0006] Furthermore, the magnetic metal material is a nickel-copper-nickel magnet with a magnetic field strength of 1000-2300eO; the magneto-optical material is yttrium iron garnet with a relative permittivity of 14.5.

[0007] Furthermore, the magnetic metal material and the magneto-optical material have a cylindrical structure; the diameter of the magnetic metal material and the magneto-optical material is 4-5 mm.

[0008] Furthermore, the incident polarization frequencies of the left-handed and right-handed circularly polarized light are 10–12 GHz.

[0009] Furthermore, the incident electric field with polarization along the x-axis excites the electric dipole moment p in the x-axis direction of the bi-anisotropic structure of the magneto-optical material. x Due to the electromagnetic coupling characteristics of the magneto-optical superatomic structure, the incident magnetic field along the x-axis can simultaneously excite the magnetic dipole moment m along the y-axis in the magneto-optical superatomic structure. y ;p x and m y The phase and amplitude are determined by the polarizability tensor components of the magneto-optical superatomic structure. and Therefore, the cosine of the elevation angle of the centroid position of the scattered light intensity of left-handed and right-handed circularly polarized light is:

[0010]

[0011] in,<cosθ> σ is the cosine function of the elevation angle; σ is the helicity of the incident polarized light. For the polarizability tensor component; These are the components of the magnetic polarization tensor; It is the conjugate of the polarizability tensor component; It is the conjugate of the magnetic polarization tensor component.

[0012] Furthermore, by changing the incident polarized light frequency, the magnetic field strength of the magnetic metal material, and the dimensions of the magnetic metal material and the magneto-optical material, the magnitudes of the polarizability tensor components and the magnetic polarizability tensor components are altered, thereby controlling the amplitude and direction of the separation between left-handed and right-handed circularly polarized light, ultimately achieving the control of transverse spin separation.

[0013] Furthermore, there exists a critical frequency within the incident polarized light frequency range, such that the elevation cosine of the centroid position of the scattered light intensity corresponding to the left-hand circularly polarized light and the right-hand circularly polarized light both approach zero, and no spin-dependent lateral separation occurs at this critical frequency.

[0014] Furthermore, when the incident polarized light frequency is greater than the critical frequency, the elevation cosine of the centroid position of the scattered light intensity of the right-hand circularly polarized light incident is positive, while the elevation cosine of the corresponding left-hand circularly polarized light is negative, resulting in positive transverse spin separation; when the incident polarized light frequency is less than the critical frequency, the elevation cosine of the centroid position of the scattered light intensity of the right-hand circularly polarized light incident is negative, while the elevation cosine of the corresponding left-hand circularly polarized light is positive, resulting in reverse transverse spin separation.

[0015] Furthermore, the greater the magnetic field strength of the magnetic metal material, the higher the critical frequency; the smaller the magnetic field strength of the magnetic metal material, the lower the critical frequency.

[0016] Furthermore, for a given thickness of the magnetic metal material and the magneto-optical material, the larger the diameter, the lower the critical frequency; for a given thickness of the magnetic metal material and the magneto-optical material, the smaller the diameter, the higher the critical frequency.

[0017] The beneficial effects of this invention are as follows:

[0018] This invention employs a unique structure using a magneto-optical superatomic structure, with the upper and lower layers made of magnetic metallic materials and the middle layer made of magneto-optical materials. This structure enables spin separation of polarized light, breaking through the traditional fixed-frequency limitation and achieving dynamic and reversible control of the separation direction and amplitude: by adjusting the incident light frequency, forward separation, complete suppression, and reverse separation can be continuously switched. This spin separation behavior can also achieve frequency control of transverse optical forces.

[0019] This invention combines the non-reciprocal properties of magnetic anisotropy with scattering polarization conversion to decouple the scattering separation direction from the incident light spin. This invention does not rely on dual anisotropy or complex geometric design, and for the first time achieves dynamic reversible control of spin separation through magneto-optical coupling and frequency modulation, providing support for the practical application of spin photonic devices and optical manipulation technologies. Attached Figure Description

[0020] Figure 1 This is a diagram of the magneto-optical superatomic structure of the present invention;

[0021] Figure 2 Figure (a) is a schematic diagram of transverse spin separation without scattering polarization conversion, and Figure (b) is a schematic diagram of reverse transverse spin separation with scattering polarization conversion.

[0022] Figure 3Figure 1 shows the variation of the present invention with incident frequency; wherein, Figure (a) shows the variation of the amplitude of the polarizability tensor of the magneto-optical superatom with incident frequency, Figure (b) shows the variation of the phase of the polarizability tensor of the magneto-optical superatom with incident frequency, Figure (c) shows the variation of the azimuth cosine of the centroid of the scattered light intensity with incident light frequency, and Figure (d) shows the variation of the elevation cosine of the centroid of the scattered light intensity with incident light frequency.

[0023] Figure 4 The figures are two-dimensional far-field amplitude diagrams at different incident frequencies in the embodiments of the present invention; wherein, Figure (a) is a two-dimensional far-field amplitude diagram at 10.9 GHz, corresponding to reverse transverse spin separation, Figure (b) is a two-dimensional far-field amplitude diagram at 11.2 GHz, corresponding to no transverse spin separation, and Figure (c) is a two-dimensional far-field amplitude diagram at 11.4 GHz, corresponding to forward transverse spin separation.

[0024] Figure 5 The figures are three-dimensional far-field amplitude diagrams at different incident frequencies in the embodiments of the present invention; wherein, Figure (a) is a three-dimensional far-field amplitude diagram at 10.9 GHz, corresponding to reverse transverse spin separation, Figure (b) is a three-dimensional far-field amplitude diagram at 11.2 GHz, corresponding to no transverse spin separation, and Figure (c) is a three-dimensional far-field amplitude diagram at 11.4 GHz, corresponding to forward transverse spin separation. Detailed Implementation

[0025] The present invention will now be further described with reference to the accompanying drawings.

[0026] This invention discloses a magneto-optical superatomic structure, which is a three-layer structure comprising a magnetic metal disk and a magneto-optical material disk. The upper and lower layers are nickel-copper-nickel magnetic disks of the same size, and the middle layer is the magneto-optical material yttrium iron garnet (YIG). The magnetic metal disk is a nickel-copper-nickel magnetic disk with a magnetic field strength of 1000oe to 2300oe; the diameters of the magnetic metal disk and the yttrium iron garnet disk are 4 to 5 mm.

[0027] Transverse spin separation is achieved using a magneto-optical superatomic structure. A spatial rectangular coordinate system is established with the center of the three-layer cylinder as the origin and the disk symmetry axis as the z-axis. Left-handed and right-handed circularly polarized light is incident along the -y-axis, and electromagnetic waves excite the electric and magnetic dipole moments in the magneto-optical structure, resulting in transverse spin separation.

[0028] Left-handed and right-handed circularly polarized light propagates along the -y-axis, and the electromagnetic wave excites the electromagnetic dipole moment in the magneto-optical structure. Specifically, the incident electric field with polarization along the x-axis excites the electric dipole moment p in the x-axis direction of the bi-anisotropic structure of the magneto-optical material. x Due to the electromagnetic coupling characteristics of this magneto-optical structure, the incident magnetic field along the x-axis can simultaneously excite the magnetic dipole moment m along the y-axis in the magneto-optical material.y p x and m y The phase and amplitude are determined by the polarizability tensor components of the superatom. and Decide.

[0029] By changing the frequencies of the incident left-handed and right-handed circularly polarized light, the polarizability tensor components can be tuned, thus controlling transverse spin separation. The incident frequencies of the left-handed and right-handed circularly polarized light are 10–12 GHz. Within this incident frequency range, there exists a critical frequency such that the elevation cosine of the centroid position of the scattered light intensity corresponding to the left-handed and right-handed circularly polarized light approaches zero; at this frequency, spin-dependent transverse separation does not occur. When the incident light frequency is greater than the critical frequency, the elevation cosine of the centroid position of the scattered light intensity of the right-handed circularly polarized light is positive, while the elevation cosine of the corresponding left-handed circularly polarized light is negative, resulting in positive transverse spin separation. When the incident light frequency is less than the critical frequency, the elevation cosine of the centroid position of the scattered light intensity of the right-handed circularly polarized light is negative, while the elevation cosine of the corresponding left-handed circularly polarized light is positive, resulting in reverse transverse spin separation.

[0030] Within the range of 1000–2300 oE in magnetic field, decreasing the magnetic field results in a lower critical frequency; increasing the magnetic field results in a higher critical frequency.

[0031] Within the diameter range of 4 to 5 mm, decreasing the diameter results in a higher critical frequency; increasing the diameter results in a lower critical frequency.

[0032] Example 1

[0033] A magneto-optical superatomic structure consists of three cylindrical layers, such as Figure 1 As shown, the top and bottom layers are both made of nickel-copper-nickel magnet material, with a thickness of h2 = 1 mm and a diameter of w = 4.4 mm. The middle layer is a magneto-optical material YIG, with a thickness of h2 = 0.9 mm and the same diameter as the top and bottom layers (w = 4.4 mm). The relative permittivity of YIG is 14.5. The magnetic metal materials of the top and bottom layers apply a static magnetic field of 2200 Oersted (Oe) to the YIG middle layer along the structural axis (z-direction) to excite the magneto-optical effect. The YIG layer that excites the magneto-optical effect scatters incident left- and right-handed electromagnetic waves, resulting in transverse spin separation.

[0034] YIG is a cubic crystal with intrinsic isotropic properties. However, when an external magnetic field is applied, YIG exhibits magnetic anisotropy due to its magneto-optical properties. Under magnetic bias, the polarizability tensor of the magneto-optical superatom is as follows:

[0035]

[0036] in, for; for; For the polarizability tensor component; These are the components of the magnetic polarization tensor;

[0037] The incident light field propagates along the -y axis, and its incident plane is defined as the x–y plane. The expression for the incident field is:

[0038]

[0039]

[0040] Among them, E in H is the incident electric field; in σ is the incident magnetic field; i is the imaginary number; k0 is the wave number in vacuum; σ is the helicity of the incident electromagnetic wave, with values ​​of 0, 1, and -1 defined as linear polarization, right-hand circular polarization, and left-hand circular polarization, respectively; E0 is the amplitude of the incident electric field; H0 is the amplitude of the incident magnetic field. and This is the unit vector in the corresponding direction.

[0041] This invention studies the photon spin Hall effect by analyzing the centroid of the scattered light intensity. In spherical coordinates, the position of the centroid of intensity can be characterized by a cosine function of the azimuth and elevation angles:

[0042]

[0043] Among them, S r The radial component represents the time-averaged intensity of the scattered light; after derivation, the following expression can be obtained:

[0044]

[0045] in,<cosθ> It is the cosine function of the elevation angle; It is the cosine function of the azimuth angle; It is the conjugate of the polarizability tensor component; It is the conjugate of the magnetic polarization tensor component;

[0046] Since the above equation clearly shows that, due to the introduction of bi-anisotropy, the elevation angle cosine function<cosθ> It is strongly dependent on the helicity σ of the incident beam. This means that for incident right-handed circularly polarized light (σ = 1) and left-handed circularly polarized light (σ = -1), the elevation cosine function of the centroid of the light intensity is...<cosθ> The opposite signs indicate that transverse spin separation has occurred. The azimuth cosine function of the centroid of intensity of incident left- and right-handed circularly polarized light... They have the same form. Elevation cosine function<cosθ> Medium magnetic polarization tensor components The magneto-optical superatomic structure of this invention is generated after incident polarized light, and its size is jointly determined by the magnetic field of the magnetic metal material in the magneto-optical superatomic structure, the frequency of the incident polarized light, and the dimensions of the magneto-optical superatomic structure; the elevation angle cosine function equation reveals the polarizability tensor component. With magnetic polarization tensor components The amplitude-phase relationship between the incident polarized light and the incident beam fundamentally determines the scattering intensity and direction of the incident polarized light along the elevation angle (i.e., the z-axis). This is determined by the helicity and polarizability components of the incident beam. and Phase difference calculation of elevation angle cosine function<cosθ> For example, in the case of right-handed circularly polarized light (σ = 1) incident, when the phase difference is... hour,<cosθ> It is negative; when the phase difference is hour,<cosθ> The value is positive. This characteristic highlights the central role of relative phase in controlling the electromagnetic response of the system, indicating that the proposed structure can not only achieve spin separation with a fixed scattering direction by the spin state, but also... Figure 2 (a) Furthermore, by adjusting the phase relationship of the polarizability tensor components, two opposite spin-separation modes can be switched, corresponding to... Figure 2 (b) Due to the intrinsic asymmetry of the structure, the propagation directions of scattered left-handed and right-handed circularly polarized light have inherent directionality: scattered left-handed circularly polarized light always propagates along the +z direction, while scattered right-handed circularly polarized light propagates along the -z direction. This behavior originates from the non-reciprocal magneto-optical response characteristics of the magneto-optical material, which couples the spin angular momentum of light with the propagation direction. After scattering, the incident circularly polarized light is converted to opposite chirality, resulting in a reversal of the spin deflection direction and producing anti-lateral spin separation.

[0047] Figure 3 (a) is a graph showing the variation of the polarizability tensor of magneto-optical superatoms with incident frequency; Figure 3 (b) is a graph showing the phase of the polarizability tensor of the magneto-optical superatom as a function of the incident frequency;

[0048] As can be seen at 11.2GHz, and The phase difference is 0, spin separation is suppressed at this frequency, and left-handed and right-handed circularly polarized light have similar scattered field amplitude distributions when incident, corresponding to... Figure 4 (b) and Figure 5 (b)

[0049] When the frequency is less than 11.2 GHz, the phase difference is positive, corresponding to reverse transverse spin separation, and the separation reaches its maximum value at an input RF frequency of 10.9 GHz. Figure 4 (a) and Figure 5 (a). Figure 5 (a) shows that the scattering underwent a polarization conversion, resulting in reverse spin separation.

[0050] When the frequency is greater than 11.2 GHz, the phase difference is negative, corresponding to positive transverse spin separation, and the separation reaches its maximum value at an input RF frequency of 11.4 GHz. Figure 4 (c) and Figure 5 (c) Figure 2 (b) is a graph showing the change of the elevation cosine of the centroid of the scattered light intensity with the incident light frequency, demonstrating the effect of frequency change on the direction and magnitude of spin separation.

[0051] Within the magnetic field range of 1000–2300 oE, decreasing the magnetic field will lower the critical frequency below 11.2 GHz, while increasing the magnetic field will raise the critical frequency above 11.2 GHz.

[0052] Within a diameter range of 4–5 mm, decreasing the diameter results in a critical frequency higher than 11.2 GHz, while increasing the diameter results in a critical frequency lower than 11.2 GHz.

[0053] The above description is merely an exemplary embodiment of the present invention and should not be construed as limiting the scope of the invention. Any equivalent changes and modifications made in accordance with the teachings of this invention are still within the scope of this invention. Those skilled in the art will readily conceive of embodiments of the invention upon considering the specification and practicing the disclosure herein. This invention is intended to cover any variations, uses, or adaptations of the invention that follow the general principles of the invention and include common knowledge or customary techniques in the art not described herein. The specification and embodiments are to be considered exemplary only, and the scope and spirit of the invention are defined by the claims.

Claims

1. A chiral optical transverse spin separation method based on frequency modulation of magneto-optical superatoms, characterized in that, Lateral spin separation is achieved using a magneto-optical superatomic structure. The magneto-optical superatomic structure comprises two layers of magnetic metal materials of the same size and a middle layer of magneto-optical material. A rectangular coordinate system is established based on the magneto-optical superatomic structure. Left-handed and right-handed circularly polarized light are incident along the -y-axis. The magnetic metal materials of the upper and lower layers apply a static magnetic field to the magneto-optical material of the middle layer along the z-axis of the structure, which excites the magneto-optical effect of the magneto-optical material of the middle layer. This generates electric and magnetic dipole moments that scatter the incident left-handed and right-handed circularly polarized light, resulting in lateral spin separation.

2. The chiral optical transverse spin separation method based on frequency modulation of magneto-optical superatoms according to claim 1, characterized in that, The magnetic metal material is a nickel-copper-nickel magnet with a magnetic field strength of 1000-2300oe; the magneto-optical material is yttrium iron garnet with a relative permittivity of 14.

5.

3. The chiral optical transverse spin separation method based on frequency modulation of magneto-optical superatoms according to claim 1, characterized in that, The magnetic metal material and the magneto-optical material have a cylindrical structure; the diameter of the magnetic metal material and the magneto-optical material is 4-5 mm.

4. The chiral optical transverse spin separation method based on frequency modulation of magneto-optical superatoms according to claim 1, characterized in that, The incident polarization frequencies of the left-handed and right-handed circularly polarized light are 10–12 GHz.

5. The chiral optical transverse spin separation method based on frequency modulation of magneto-optical superatoms according to claim 1, characterized in that, An incident electric field with polarization along the x-axis excites the electric dipole moment p along the x-axis in the bi-anisotropic structure of the magneto-optical material. x Due to the electromagnetic coupling characteristics of the magneto-optical superatomic structure, the incident magnetic field along the x-axis can simultaneously excite the magnetic dipole moment m along the y-axis in the magneto-optical superatomic structure. y ;p x and m y The phase and amplitude are determined by the polarizability tensor components of the magneto-optical superatomic structure. and Therefore, the cosine of the elevation angle of the centroid position of the scattered light intensity of left-handed and right-handed circularly polarized light is: in,<cosθ> σ is the cosine function of the elevation angle; σ is the helicity of the incident polarized light. For the polarizability tensor component; These are the components of the magnetic polarization tensor; It is the conjugate of the polarizability tensor component; It is the conjugate of the magnetic polarization tensor component.

6. The chiral optical transverse spin separation method based on frequency modulation of magneto-optical superatoms according to claim 5, characterized in that, By changing the incident polarized light frequency, the magnetic field strength of the magnetic metal material, and the dimensions of the magnetic metal material and the magneto-optical material, the magnitudes of the polarizability tensor components and the magnetic polarizability tensor components are altered, thereby controlling the amplitude and direction of the separation between left-handed and right-handed circularly polarized light, ultimately achieving the control of transverse spin separation.

7. The chiral optical transverse spin separation method based on frequency modulation of magneto-optical superatoms according to claim 6, characterized in that, There exists a critical frequency within the incident polarized light frequency range, such that the elevation cosine of the centroid position of the scattered light intensity corresponding to the left-hand circularly polarized light and the right-hand circularly polarized light both approach zero, and no spin-dependent lateral separation occurs at this critical frequency.

8. The chiral optical transverse spin separation method based on frequency modulation of magneto-optical superatoms according to claim 7, characterized in that, When the incident polarized light frequency is greater than the critical frequency, the elevation cosine of the centroid of the scattered light intensity of the right-hand circularly polarized light is positive, while the elevation cosine of the left-hand circularly polarized light is negative, resulting in positive transverse spin separation. When the incident polarized light frequency is less than the critical frequency, the elevation cosine of the centroid of the scattered light intensity of the right-hand circularly polarized light is negative, while the elevation cosine of the left-hand circularly polarized light is positive, resulting in reverse transverse spin separation.

9. The chiral optical transverse spin separation method based on frequency modulation of magneto-optical superatoms according to claim 7, characterized in that, The greater the magnetic field strength of the magnetic metal material, the higher the critical frequency; the smaller the magnetic field strength of the magnetic metal material, the lower the critical frequency.

10. The chiral optical transverse spin separation method based on frequency modulation of magneto-optical superatoms according to claim 7, characterized in that, For a given thickness of the magnetic metal material and the magneto-optical material, the larger the diameter, the lower the critical frequency; conversely, for a given thickness of the magnetic metal material and the magneto-optical material, the smaller the diameter, the higher the critical frequency.

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