Single-photon emitter with controllable three-way spin angular momentum and momentum direction and method thereof

Abstract

The present invention discloses a three-way single-photon emitter with controllable spin angular momentum and momentum direction, and a method thereof. The present invention independently controls the spin angular momentum of the emitted photons through the internal structure of each nano-scattering unit, in a scheme that is independent of the scattered light phase; controls the momentum direction of the emitted photons through the position of each nano-scattering unit, in a scheme that is dependent on the scattered light phase. Since these two schemes do not affect each other, the control of the spin angular momentum and momentum direction of the emitted photons can be independently designed; two sets of metasurface structures corresponding to the three-way emitted photons are combined in a set manner to form a three-way single-photon emitter, which can realize three-way single-photon emission, and the spin angular momentum and momentum direction of the photons emitted in each path can be independently controlled; the emission angle can reach a maximum of 53°, and the phase-independent scheme makes the spin angular momentum insensitive to the precise position of the single-photon source relative to the metasurface, eliminating the need for high-precision single-photon source positioning and alignment technology.

Description

Technical Field

[0001] The present invention relates to the field of nanophotonics, and in particular to a single-photon emitter with controllable three-way spin angular momentum and momentum direction and a method for realizing the same. Background Art

[0002] Quantum information science has developed rapidly in recent years and is one of the frontiers of modern physics. Compared with other physical systems, photons interact less strongly with their environment and can maintain good quantum coherence, making them ideal carriers of quantum information. Single-photon sources play an important role in photon-based quantum information technology. In particular, solid-state single-photon sources, such as quantum dots and nitrogen vacancy color centers, are considered to be important basic units for building scalable photon-based quantum information technology. For photons, their energy, momentum, and spin angular momentum are all fundamental degrees of freedom that can be used to carry quantum information and increase information capacity, such as for wavelength multiplexing and momentum multiplexing. Generally, the energy of a photon can be simply controlled by the energy gap of a solid-state single-photon source. However, the photons emitted by solid-state single-photon sources are usually emitted isotropically in space, and the light wave vector corresponds to the momentum direction, that is, the momentum direction is random; at the same time, the polarization state of the photons emitted by solid-state single-photon sources is usually also random, and the polarization state corresponds to the spin angular momentum of the photon, so its spin angular momentum is also random. To achieve control of the momentum direction and spin angular momentum of photons emitted by solid-state single-photon sources, special plans and designs are required.

[0003] The rapid development of metasurface technology provides a very promising platform for controlling light. Metasurfaces are planar optical elements constructed by artificial nanostructures that can control the amplitude, phase and polarization of light on a subwavelength scale. Compared with traditional optical elements, metasurfaces are an ideal platform for miniaturization, integration and multifunctionality of optical devices. They have a wide range of applications, such as beam focusing, polarization state control of light, wavefront shaping, multiplexing and holography. Recently, there have been some studies that have achieved control over the photons emitted by a single-photon source by integrating a properly designed metasurface with a single-photon source. For example, by precisely placing a single-photon source on a metasurface constructed of circular nanoridges with different centers on a silver film, the momentum direction of the emitted photons can be controlled based on phase matching conditions, thereby realizing a single-photon emitter with controllable momentum direction; by preparing a metasurface constructed of dielectric nanoridges with azimuthal widths on a silver film around a nitrogen vacancy color center, the emitted single photons can be controlled at room temperature to have a positive reduced Planck constant + 's spin angular momentum, that is, the emitted photon is in a left-handed circularly polarized state, realizing a circularly polarized single-photon emitter. The total scattering field of the metasurface in free space originates from the coherent superposition of the scattering fields from all nanoscattering units. However, the existing works on the control of the momentum direction and spin angular momentum of the photons are based on the precise control of the phase of the scattered light from the nanoscattering units in the metasurface. This phase-dependent scheme means that the control of the momentum direction and spin angular momentum of the photons is very sensitive to the phase of the scattered light. The positional deviation of the single-photon source and the nanoscattering units in the metasurface will affect the interference results. Therefore, precise mutual positioning between the single-photon source and the nanoscattering units is required. For example, the nitrogen vacancy color center must be placed with a high precision of less than tens of nanometers relative to the metasurface constructed by dielectric nanoridges whose width varies with the azimuthal angle, and the emitted photons can obtain the designed normalized Planck constant + The spin angular momentum of a photon is a left-handed circular polarization state. On the one hand, the position sensitivity caused by the phase sensitivity mentioned above greatly increases the difficulty of manufacturing. On the other hand, the phase sensitivity makes it a huge challenge to simultaneously and independently control the momentum direction and spin angular momentum of the emitted photons. To date, there has been no single-photon emitter that can simultaneously and independently control the momentum direction and spin angular momentum of the emitted photons. There is even less a three-way single-photon emitter that can simultaneously and independently control the momentum direction and spin angular momentum of multiple emitted photons. A three-way single-photon emitter that can simultaneously and independently control the momentum direction and spin angular momentum of three-way emitted photons may find important applications in quantum information fields such as single-photon momentum multiplexing and spin angular momentum multiplexing. Summary of the Invention

[0004] In response to the problems existing in the above-mentioned prior art, the present invention proposes a three-way single-photon emitter with controllable spin angular momentum and momentum direction and an implementation method thereof. At the same time, phase-independent and phase-dependent schemes are used to construct an anisotropic metasurface, and a single-photon source is integrated with the metasurface. The spin angular momentum and momentum direction of the emitted photons are independently controlled by the phase-independent scheme and the phase-dependent scheme, respectively. Since these two schemes do not affect each other, the control of the spin angular momentum and momentum direction of the emitted photons can be independently designed. Furthermore, three sets of metasurface structures corresponding to the three-way emission of photons are structurally combined to form a three-way single-photon emitter, which can realize three-way single-photon emission, and the spin angular momentum and momentum direction of each emitted photon can be independently controlled by the corresponding structure.

[0005] One object of the present invention is to provide a single-photon emitter with controllable three-way spin angular momentum and momentum direction.

[0006] The three-way single-photon emitter with controllable spin angular momentum and momentum direction of the present invention comprises: a metal substrate, a first metasurface structure, a second metasurface structure, a third metasurface structure, a dielectric spacer and a single-photon source; wherein, in a Cartesian coordinate system, the upper surface of the metal substrate is perpendicular to the z-axis; the first metasurface structure, the second metasurface structure and the third metasurface structure are respectively formed on the upper surface of the metal substrate; the first to third metasurface structures are respectively a plurality of nano-scattering units engraved on the upper surface of the metal substrate, each nano-scattering unit comprises two rectangular nano-grooves of the same shape engraved on the upper surface of the metal substrate; the rectangular nano-grooves located in the counterclockwise direction of the radius are the first nano-grooves, and the second nano-grooves located in the counterclockwise direction of the radius are the second nano-grooves. The rectangular nanogroove with a clockwise radius is the second nanogroove. The first and second nanogrooves are on the inner long side and the adjacent vertices are located on the same radius centered on the origin. The vertex belonging to the first nanogroove is the first vertex, and the vertex belonging to the second nanogroove is the second vertex. In the first to third metasurface structures, the angle between the long side and the radius of the first nanogroove is expressed as α1, α2 and α3 as the orientation of the first nanogroove, and the angle between the long side and the radius of the second nanogroove is expressed as β1, β2 and β3 as the orientation of the second nanogroove. The distance from the center of the second nanogroove to the origin minus the distance from the center of the first nanogroove to the origin is taken as the first radial distance s. r1 、s r2 and s r3 The first metasurface structure is located in the first sub-coordinate system x1y1z, the second metasurface structure is located in the second sub-coordinate system x2y2z, and the third metasurface structure is located in the third sub-coordinate system x3y3z. The first to third sub-coordinate systems share the same z-axis and have the same origin. The orientations and radial distances of the first and second nanogrooves of the first to third metasurface structures satisfy the following set of spin angular momentum control equations:

[0007]

[0008]

[0009]

[0010] Where i = 1, 2, 3, k spp is the wave vector of surface plasmon, k0 is the wave vector of vacuum light, is the azimuth angle of the nano-scattering unit of the first metasurface structure in the first sub-coordinate system, is the azimuth angle of the nano-scattering unit of the second metasurface structure in the second sub-coordinate system, is the azimuth angle of the nano-scattering unit of the third metasurface structure in the third sub-coordinate system, that is, the azimuth angle of the radius of the first vertex of the first to third metasurface structures, and the length and width of the rectangular nano-groove are represented by l and w respectively; the nano-scattering unit is structurally anisotropic, that is, the internal structural parameters of the nano-scattering unit at different azimuth angles are different, and it is an anisotropic metasurface; k1 is the light wave vector of the set emission direction of the first metasurface structure, which represents the set emission direction of the first metasurface structure. The set emission direction is in the x1-z plane, and the angle between the set emission direction of the first metasurface structure and the z-axis is the first emission angle θ1; k2 is the light wave vector of the second metasurface structure. The light wave vector of the set emission direction of the surface structure represents the set emission direction. The set emission direction is in the x2-z plane, and the angle between the set emission direction of the second metasurface structure and the z-axis is taken as the second emission angle θ2; k3 is the light wave vector of the set emission direction of the third metasurface structure, which represents the set emission direction of the third metasurface structure. The set emission direction is in the x3-z plane, and the angle between the set emission direction of the third metasurface structure and the z-axis is taken as the third emission angle θ3; Among them, in the third equation of the spin angular momentum control equation group, the right side of the equation takes "﹢" to represent left-handed circular polarization, that is, the spin angular momentum of the photon in the set emission direction is the positive reduced Planck constant + Take “-” to represent right-handed circular polarization, that is, set the spin angular momentum of the photon in the emission direction to the negative reduced Planck constant - The light wave vectors k1, k2 and k3 in the set emission directions of the first to third metasurface structures form an angle of 120° between the projection directions on the metal substrate surface, that is, the angles between the x1 axis, the x2 axis and the x3 axis are 120°;

[0011] The position vectors r1, r2, and r3 of the nano-scattering units of the first to third metasurface structures respectively satisfy the constructive interference conditions in the set emission directions of the first to third metasurface structures:

[0012] k spp r i +δ i -k i ·r i =2m i π+C 0i (4)

[0013] Among them, δ1, δ2 and δ3 are the scattering phases of the nano-scattering units of the first to third metasurface structures, r1, r2 and r3 are the moduli of the position vectors r1, r2 and r3 of the nano-scattering units of the first to third metasurface structures, respectively. The midpoint between the first vertex and the second vertex of the nano-scattering unit is taken as the position of the nano-scattering unit, that is, r1, r2 and r3 are the distances from the midpoint between the first vertex and the second vertex of the first to third metasurface structures to the origin, respectively. C01 、C 02 and C 03 are constants applicable to all nano-scattering units of the first to third metasurface structures, respectively, and m1, m2 and m3 are integers;

[0014] Polar coordinate positions of the nanoscattering units of the first to third metasurface structures Satisfies the momentum direction control equation:

[0015]

[0016] Among them, the distance r from the starting point to the origin of the elliptical spiral lines of the first, second and third metasurface structures is 0i =(C 0i / k spp +λ spp ), λ spp and λ represent the surface plasmon wavelength and light wavelength respectively; m1, m2 and m3 represent the turns of the elliptical spirals of the first to third metasurface structures, respectively, in the first to third sub-coordinate systems, And in the first to third sub-coordinate systems respectively, 3≤N≤M-3, 6≤M≤15, so that the positions of the nano-scattering units of the first to third metasurface structures do not overlap with each other in space;

[0017] The scattering phases δ1, δ2, and δ3 of the nano-scattering units of the first to third metasurface structures satisfy the geometric phase equation:

[0018]

[0019] Among them, θ1, θ2 and θ3 are the first to third emission angles, σ1, σ2 and σ3 are the photon spins of the first to third metasurface structures, respectively. For left-handed circularly polarized (LCP) light and right-handed circularly polarized (RCP) light, they are +1 and -1, respectively. The corresponding photon spin angular momentum is the positive reduced Planck constant + and the negative reduced Planck constant - According to the momentum direction control equation and the geometric phase equation, the position of the nanoscattering unit is anisotropic. For obliquely emitted LCP light and RCP light, the solution to the momentum direction control equation is an elliptical spiral, that is, the position of the nanoscattering unit is arranged in a multi-turn elliptical spiral, each turn of the elliptical spiral is confocal and the focus is at the origin. The spiral directions of the multi-turn elliptical spirals corresponding to the LCP light and RCP light are opposite. For the forward-emitted LCP light and RCP light, the solution to the momentum direction control equation is an Archimedean spiral.

[0020] A dielectric spacer layer is provided on a metal substrate engraved with the first to third metasurface structures to eliminate the fluorescence quenching effect of the single-photon source on the metal surface; a single-photon source is placed on the dielectric spacer layer, and the single-photon source is located within the multi-ring nano-scattering unit of the first to third metasurface structures;

[0021] The excitation light spot is irradiated to the single-photon source, causing the single-photon source to emit photons, exciting surface plasmon polariton (SPP) on the metal surface, and the excited SPP propagates uniformly in all directions along the radial direction along the surface of the metal substrate; the SPP encounters the nano-scattering units of the first to third metasurface structures and is scattered to form scattered light, and the position vectors of each nano-scattering unit respectively meet the constructive interference condition in the set emission direction, so that the scattered light after being scattered by all the nano-scattering units of the first metasurface structure coherently constructively forms an emission light spot along the set emission direction of the first metasurface structure, thereby controlling the direction of the scattered light of the first metasurface structure to be along the set emission direction of the first metasurface structure, and the position vectors of the scattered light after being scattered by all the nano-scattering units of the second metasurface structure are coherently constructive. The scattered light is coherently constructive along the set emission direction of the second metasurface structure to form an emission spot, thereby controlling the direction of the scattered light of the second metasurface structure to be along the set emission direction of the second metasurface structure, and the scattered light after being scattered by all the nano-scattering units of the third metasurface structure is coherently constructive along the set emission direction of the third metasurface structure to form an emission spot, thereby controlling the direction of the scattered light of the third metasurface structure to be along the set emission direction of the third metasurface structure. The set emission direction corresponds to the momentum direction of the photon, thereby independently controlling the first to third metasurface structures by respectively setting the arrangement positions of the respective nano-scattering units of the first to third metasurface structures. The momentum direction of the scattered light is determined, and the momentum direction is phase-related to the scattered light from the nano-scattering unit; each nano-scattering unit located in the first to third metasurface structures satisfies the respective spin angular momentum control equations of the first to third metasurface structures, and the projections of the linearly polarized light scattered to the far field from the first and second nano-grooves in a nano-scattering unit on a plane perpendicular to the set emission direction are orthogonal to each other and have equal amplitudes, and the scattered light from the first and second nano-grooves has a phase difference of ±π / 2 in the set emission direction, so that the scattered light from each nano-scattering unit in the first to third metasurface structures is in the first The nano-scattering units of the first to third metasurface structures have the same circular polarization in the emission direction set by each of them, that is, they have the same target polarization state, and the polarization state corresponds to the spin angular momentum of the photon. Therefore, the spin angular momentum of the scattered light of the first to third metasurface structures can be independently controlled by respectively setting the internal structure of the nano-scattering units of the first to third metasurface structures, and the spin angular momentum is independent of the phase of the scattered light from the nano-scattering units; the scattered light of the first to third metasurface structures finally propagates to the far field along the emission directions set by the first to third metasurface structures respectively with circularly polarized spin angular momentum, realizing a single-photon emitter with three-way simultaneous and independent control of momentum direction and spin angular momentum.

[0022] When the first, second and third emission angles θ i≤15°, the control equations of spin angular momentum are approximately simplified to obtain an approximate analytical solution:

[0023]

[0024]

[0025] The offset of the single photon source from the z-axis is less than 600 nm.

[0026] The metal substrate is made of silver and has a thickness of 300 nm or greater. The distance between angularly adjacent nanoscattering units is less than 1 μm, and the spacing between nanoscattering units is 50 nm or greater. The rectangular nanogrooves have a length of 200 nm to 300 nm and a width of 50 nm to 100 nm. The depth is related to the length and width. Finite element calculations are used to ensure that the nanoscattering units have high scattering efficiency and high circular polarization degree.

[0027] The dielectric spacer layer is made of a dielectric material transparent in the visible light band, such as aluminum oxide, glass or quartz, and has a thickness of 5nm to 20nm.

[0028] The excitation light spot is a focused light spot, and the size of the light spot is the diffraction limit.

[0029] Another object of the present invention is to provide a method for realizing a single-photon emitter with controllable three-way spin angular momentum and momentum direction.

[0030] The method for realizing a single-photon emitter with controllable three-way spin angular momentum and momentum direction of the present invention comprises the following steps:

[0031] 1) providing a dielectric spacer layer on the metal substrate engraved with the first to third metasurface structures to eliminate the fluorescence quenching effect of the single-photon source on the metal surface;

[0032] 2) In a Cartesian coordinate system, the upper surface of the metal substrate is perpendicular to the z-axis, and a single-photon source is placed on the dielectric spacer layer. The single-photon source is located within the multi-ring nano-scattering units of the first to third metasurface structures. The excitation light spot is irradiated onto the single-photon source, causing the single-photon source to emit photons, exciting surface plasmons (SPPs) on the metal surface. The excited SPPs propagate uniformly in all directions along the surface of the metal substrate in a radial direction.

[0033] 3) SPP encounters the nano-scattering units of the first to third metasurface structures and is scattered to form scattered light;

[0034] The position vectors r1, r2, and r3 of the nano-scattering units of the first to third metasurface structures respectively satisfy the constructive interference conditions in the set emission directions of the first to third metasurface structures:

[0035] k spp ri +δ i -k i ·r i =2m i π+C 0i

[0036] Among them, k spp is the wave vector of the surface plasmon, δ1, δ2 and δ3 are the scattering phases of the nano-scattering units of the first to third metasurface structures respectively; k1 is the light wave vector of the set emission direction of the first metasurface structure, indicating the set emission direction of the first metasurface structure, the set emission direction is in the x1-z plane, and the angle between the set emission direction of the first metasurface structure and the z-axis is taken as the first emission angle θ1; k2 is the light wave vector of the set emission direction of the second metasurface structure, indicating the set emission direction, the set emission direction is in the x2-z plane, and the angle between the set emission direction of the second metasurface structure and the z-axis is taken as the second emission angle Angle θ2; k3 is the light wave vector of the set emission direction of the third metasurface structure, which represents the set emission direction of the third metasurface structure. The set emission direction is in the x3-z plane, and the angle between the set emission direction of the third metasurface structure and the z-axis is taken as the third emission angle θ3; r1, r2 and r3 are the moduli of the position vectors r1, r2 and r3 of the nano-scattering units of the first to third metasurface structures, respectively. The midpoint between the first vertex and the second vertex of the nano-scattering unit is taken as the position of the nano-scattering unit, that is, r1, r2 and r3 are the distances from the midpoint of the first vertex and the second vertex of the first to third metasurface structures to the origin, respectively. 01 、C 02 and C 03 are constants applicable to all nano-scattering units of the first to third metasurface structures, respectively, and m1, m2 and m3 are integers;

[0037] Polar coordinate positions of the nanoscattering units of the first to third metasurface structures Satisfies the momentum direction control equation:

[0038]

[0039] Where i = 1, 2, 3, the distance from the starting point to the origin of the elliptical spiral line of the first, second and third metasurface structures is r 0i =(C 0i / k spp +λ spp ), λ spp and λ represent the surface plasmon wavelength and light wavelength respectively; m1, m2 and m3 represent the turns of the elliptical spirals of the first to third metasurface structures, respectively, in the first to third sub-coordinate systems,

[0040] And in the first to third sub-coordinate systems respectively,

[0041] 3≤N≤M-3, 6≤M≤15, so that the positions of the nano-scattering units of the first, second and third metasurface structures do not overlap with each other in space;

[0042] The scattering phases δ1, δ2, and δ3 of the nano-scattering units of the first to third metasurface structures satisfy the geometric phase equation:

[0043]

[0044] Among them, θ1, θ2 and θ3 are the first to third emission angles, σ1, σ2 and σ3 are the photon spins of the first to third metasurface structures, respectively. For left-handed circularly polarized LCP light and right-handed circularly polarized RCP light, they are +1 and -1, respectively. The corresponding photon spin angular momentum is the positive reduced Planck constant + and the negative reduced Planck constant - According to the momentum direction control equation and the geometric phase equation, the position of the nanoscattering unit is anisotropic. For obliquely emitted LCP light and RCP light, the solution to the momentum direction control equation is an elliptical spiral, that is, the position of the nanoscattering unit is arranged in a multi-turn elliptical spiral, each turn of the elliptical spiral is confocal and the focus is at the origin. The spiral directions of the multi-turn elliptical spirals corresponding to the LCP light and RCP light are opposite. For the forward-emitted LCP light and RCP light, the solution to the momentum direction control equation is an Archimedean spiral.

[0045] The position vectors of each nano-scattering unit satisfy the constructive interference condition in the set emission direction, so that the scattered light after being scattered by all the nano-scattering units of the first metasurface structure coherently constructively forms an emission spot along the set emission direction of the first metasurface structure, thereby controlling the direction of the scattered light of the first metasurface structure to be along the set emission direction of the first metasurface structure, and the scattered light after being scattered by all the nano-scattering units of the second metasurface structure coherently constructively forms an emission spot along the set emission direction of the second metasurface structure, thereby controlling the direction of the scattered light of the second metasurface structure to be along the set emission direction of the second metasurface structure, and the scattered light after being scattered by all the nano-scattering units of the third metasurface structure coherently constructively forms an emission spot along the set emission direction of the third metasurface structure, thereby controlling the direction of the scattered light of the third metasurface structure to be along the set emission direction of the third metasurface structure. The set emission direction corresponds to the momentum direction of the photon, thereby independently controlling the first to third metasurface structures by respectively setting the arrangement positions of each nano-scattering unit of the first to third metasurface structures.

[0046] The momentum direction of the scattered light of the surface structure is related to the phase of the scattered light from the nano-scattering unit; 4) in each nano-scattering unit, the rectangular nano-groove located in the counterclockwise direction of the radius is the first nano-groove,

[0047] The rectangular nano-groove located in the clockwise direction of the radius is the second nano-groove. The first and second nano-grooves are on the inner long side and the adjacent vertices are located on the same radius centered on the origin. The vertex belonging to the first nano-groove is the first vertex, and the vertex belonging to the second nano-groove is the second vertex. In the first to third metasurface structures, the angles between the long side and the radius of the first nano-groove are expressed as the orientation of the first nano-groove as α1, α2 and

[0048] α3, the angle between the long side of the second nanogroove and the radius is expressed as the orientation of the second nanogroove as β1, β2 and β3, and the distance from the center of the second nanogroove to the origin minus the distance from the center of the first nanogroove to the origin is the first radial distance s r1 、s r2 and s r3 The first metasurface structure is located in the first sub-coordinate system of x1y1z, the second metasurface structure is located in the second sub-coordinate system of x2y2z, and the third metasurface structure is located in the third sub-coordinate system of x3y3z. The first to third sub-coordinate systems share the same z-axis and have the same origin. The first and second nanostructures of the first to third metasurface structures are located in the first sub-coordinate system of x2y2z.

[0049] The orientation and radial distance of the grooves satisfy the following set of governing equations for spin angular momentum:

[0050]

[0051]

[0052]

[0053] Where i = 1, 2, 3, k spp is the wave vector of surface plasmon, k0 is the wave vector of vacuum light, is the azimuth angle of the nano-scattering unit of the first metasurface structure in the first sub-coordinate system, is the azimuth angle of the nano-scattering unit of the second metasurface structure in the second sub-coordinate system, is the azimuth angle of the nanoscattering unit of the third metasurface structure in the third sub-coordinate system, that is, the azimuth angle of the radius of the first vertex of the first to third metasurface structures; the length and width of the rectangular nanogroove are represented by l and w respectively; the nanoscattering unit is structurally anisotropic, that is, the internal structural parameters of the nanoscattering unit at different azimuth angles are different, and it is an anisotropic metasurface; among them, in the third equation of the spin angular momentum control equation group, the right side of the equation is taken as "+" to represent left-handed circular polarization, that is, the spin angular momentum of the photon in the emission direction is set to the normal reduced Planck constant + Take “-” to represent right-handed circular polarization, that is, set the spin angular momentum of the photon in the emission direction to the negative reduced Planck constant - The light wave vectors k1, k2 and k3 of the set emission directions of the first to third metasurface structures are 120 degrees apart from each other in the projection direction of the metal substrate surface.

[0054] The angle between the x1 axis, x2 axis and x3 axis is 120°;

[0055] Each nanoscattering unit respectively located in the first to third metasurface structures satisfies the respective spin angular momentum control equations of the first to third metasurface structures. The projections of the linearly polarized light scattered to the far field by the first and second nanogrooves in a nanoscattering unit on a plane perpendicular to the set emission direction are orthogonal to each other and have equal amplitudes. At the same time, the scattered light from the first and second nanogrooves has a phase difference of ±π / 2 in the set emission direction, so that the scattered light from each nanoscattering unit in the first to third metasurface structures has the same circular polarization in the emission direction set by the first to third metasurface structures, that is, has the same target polarization state. The polarization state corresponds to the spin angular momentum of the photon, so that the spin angular momentum of the scattered light of the first to third metasurface structures is independently controlled by respectively setting the internal structures of the nanoscattering units of the first to third metasurface structures, and the spin angular momentum is independent of the phase of the scattered light from the nanoscattering unit.

[0056] 5) The scattered light from the first to third metasurface structures eventually propagates to the far field along the respective set emission directions of the first to third metasurface structures with circularly polarized spin angular momentum, realizing a single-photon emitter with three-way simultaneous and independent control of momentum direction and spin angular momentum.

[0057] Advantages of the present invention:

[0058] The present invention independently controls the spin angular momentum of emitted photons through the internal structure of each nanoscattering unit, and the scheme is independent of the phase of the scattered light; controls the momentum direction of emitted photons through the position of each nanoscattering unit, and the scheme is related to the phase of the scattered light. Since these two schemes do not affect each other, the control of the spin angular momentum and momentum direction of the emitted photons can be independently designed; three sets of metasurface structures corresponding to three paths of emitted photons are combined in a set manner to form a three-path single-photon emitter, which can realize three-path single-photon emission. The spin angular momentum and momentum direction of the photons emitted in each path can be independently controlled by their respective corresponding metasurface structures; the maximum emission angle can reach 53°, and the phase-independent scheme makes the spin angular momentum insensitive to the precise position of the single-photon source relative to the metasurface, eliminating the need for high-precision single-photon source positioning and alignment technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0059] Figure 1 Schematic diagram of a metasurface structure in the three-way single-photon emitter with controllable spin angular momentum and momentum direction of the present invention, wherein (a) is a top view of the entire structure, and (b) is a schematic diagram of the internal structure of a nano-scattering unit;

[0060] Figure 2 Figure 3 is a numerical simulation result of far-field emission obtained from an embodiment of a metasurface structure in a single-photon emitter with controllable three-way spin angular momentum and momentum direction according to the present invention, wherein (a) is a far-field scattered light intensity distribution diagram of the single-photon emitter, where the single-photon source is located exactly on the z-axis and polarized along the z-direction; (b) is a distribution diagram of the far-field scattered light, where the vertical height represents the intensity of the scattered field, and the brightness represents the chirality of the scattered field; (c) is the integrated chirality of the far-field emission spot at different emission angles θ, where the solid line and the dashed line correspond to the results given by the rigorous numerical solution and the approximate analytical solution, respectively; (d) is the integrated chirality of the far-field emission spot when the single-photon source deviates from the z-axis at different distances, where the solid line and the dashed line correspond to the results of deviation along the x-direction and the y-direction, respectively;

[0061] Figure 3 Schematic diagram of embodiment 1 of the three-way single-photon emitter with controllable spin angular momentum and momentum direction of the present invention, wherein the area between the solid line and the dashed line is the first metasurface structure I, the area between the solid line and the dot-dash line is the second metasurface structure II, and the area between the dot-dash line is the third metasurface structure III. The emission angles set for the first, second, and third metasurface structures are θ1=θ2=θ3=15°, respectively, and the spin angular momentum of the emitted photons is set to the negative reduced Planck constant - Normalized Planck constant + and the normalized Planck constant +

[0062] Figure 4Figures 1 and 2 show the numerical simulation results of far-field emission obtained according to Example 1 of the single-photon emitter with controllable three-way spin angular momentum and momentum direction of the present invention, wherein (a) is the intensity distribution of the far-field scattered light of the single-photon emitter, (b) is the intensity distribution of the LCP light in the far-field scattered light, and (c) is the intensity distribution of the RCP light in the far-field scattered light.

[0063] Figure 5 This is a numerical simulation result of the far-field emission obtained according to the second embodiment of the present invention of the three-way single-photon emitter with controllable spin angular momentum and momentum direction. In the second embodiment, the emission angles set for the first, second, and third metasurface structures are θ1=θ2=θ3=15°, respectively, and the spin angular momentum of the emitted photons is set to be the normalized Planck constant + Among them, (a) is the intensity distribution diagram of the far-field scattered light of the single-photon emitter, (b) is the intensity distribution diagram of the LCP light in the far-field scattered light, and (c) is the intensity distribution diagram of the RCP light in the far-field scattered light;

[0064] Figure 6 These are graphs of experimental results obtained according to Examples 1 and 2 of the three-way single-photon emitter with controllable spin angular momentum and momentum direction according to the present invention, wherein (a) is a scientific-grade complementary metal oxide semiconductor detector (sCMOS) image obtained by far-field detection of a sample of Example 1, and the left and right figures respectively show the intensity distribution diagrams of LCP light and RCP light in the far-field scattered light; (b) is an sCMOS image obtained by far-field detection of a sample of Example 2, and the left and right figures respectively show the intensity distribution diagrams of LCP light and RCP light in the far-field scattered light. DETAILED DESCRIPTION

[0065] The present invention will be further described below through specific embodiments in conjunction with the accompanying drawings.

[0066] like Figure 1As shown, a metasurface structure is engraved on the upper surface of the metal substrate. A single-photon emitter having only one metasurface structure includes: a metal substrate, a nano-scattering unit, a dielectric spacer layer, and a single-photon source; wherein, in a Cartesian coordinate system, the upper surface of the metal substrate is an xy plane; a plurality of nano-scattering units are engraved on the upper surface of the metal substrate, and each nano-scattering unit includes two rectangular nano-grooves of the same shape engraved on the upper surface of the metal substrate, the rectangular nano-groove located in the counterclockwise direction of the radius is the first nano-groove, and the rectangular nano-groove located in the clockwise direction of the radius is the second nano-groove. The nanogroove is the second nanogroove. The first and second nanogrooves are on the inner long side and the adjacent vertices are located on the same radius centered at the origin. The vertex belonging to the first nanogroove is the first vertex, and the vertex belonging to the second nanogroove is the second vertex. The angle between the long side and the radius of the first nanogroove is expressed as α as the orientation of the first nanogroove, and the angle between the long side and the radius of the second nanogroove is expressed as β as the orientation of the second nanogroove. The distance from the center of the second nanogroove to the origin minus the distance from the center of the first nanogroove to the origin is the radial distance s. r The orientation and radial distance of the first and second nanogrooves satisfy the following set of spin angular momentum governing equations:

[0067]

[0068]

[0069]

[0070] Among them, k spp is the wave vector of surface plasmon, k0 is the wave vector of vacuum light, is the azimuth angle of the nanoscattering unit, that is, the azimuth angle of the radius where the first vertex is located; the nanoscattering unit is structurally anisotropic, that is, the internal structural parameters of the nanoscattering unit at different azimuth angles are different, and it is an anisotropic metasurface; k is the light wave vector of the set emission direction, which represents the set emission direction. The set emission direction is in the xz plane, and the angle between the set emission direction and the z-axis is the emission angle θ. l and w are the length and width of the rectangular nanogroove, respectively; among them, in the third equation of the spin angular momentum control equation group, the right side of the equation takes "+" to represent left-handed circular polarization, that is, the spin angular momentum of the photon in the emission direction is set to the normalized Planck constant + Take “-” to represent right-handed circular polarization, that is, set the spin angular momentum of the photon in the emission direction to the negative reduced Planck constant - The center of the first nano-groove is closer to the origin, indicating left-handed circular polarization, and the center of the second nano-groove is closer to the origin, indicating right-handed circular polarization.

[0071] When the launch angle θ≤15°, the control equations of spin angular momentum are approximately simplified to obtain an approximate analytical solution:

[0072]

[0073]

[0074] Each nanoscattering unit satisfies a set of spin angular momentum control equations. The projections of linearly polarized light scattered from the first and second nanogrooves within a nanoscattering unit into the far field on a plane perpendicular to a set emission direction are orthogonal to each other and have equal amplitudes. At the same time, the scattered light from the first and second nanogrooves has a phase difference of ±π / 2 in the set emission direction, so that the scattered light from the nanoscattering unit has the same circular polarization in the set emission direction, that is, the same target polarization state. The polarization state corresponds to the spin angular momentum of the photon. Therefore, the spin angular momentum of the scattered light is independently controlled by the internal structure of the nanoscattering unit, and the spin angular momentum is independent of the phase of the scattered light from the nanoscattering unit.

[0075] In order to control the momentum direction of the emitted photons, that is, to control the emission direction of the emitted photons, the positions of the nano-scattering units are arranged based on the constructive interference condition. The position vector r of the nano-scattering unit satisfies the constructive interference condition in the set emission direction:

[0076] k spp r+δ-k·r=2mπ+C0

[0077] Wherein, δ is the scattering phase of the nanoscattering unit, r is the modulus of the position vector r of the nanoscattering unit, the midpoint between the first vertex and the second vertex of the nanoscattering unit is taken as the position of the nanoscattering unit, that is, r is the distance from the midpoint between the first vertex and the second vertex to the origin, C0 is a constant applicable to all nanoscattering units, and m is an integer;

[0078] Polar coordinate position of the nanoscattering unit Satisfies the momentum direction control equation:

[0079]

[0080] The distance from the starting point of the elliptical spiral to the origin is r0 = (C0 / k spp +λ spp ); m=1,2,3,4,5;

[0081] The scattering phase δ of the nanoscattering unit satisfies the geometric phase equation:

[0082]

[0083] Where θ is the emission angle, which is the angle between the set emission direction and the z-axis. σ represents the photon spin, which is +1 for left-handed circularly polarized (LCP) light and -1 for right-handed circularly polarized (RCP) light, and the corresponding photon spin angular momentum is the positive reduced Planck constant + and the negative reduced Planck constant - According to the momentum direction control equation and the geometric phase equation, the position of the nanoscattering unit is anisotropic. For obliquely emitted LCP light and RCP light, the solution to the momentum direction control equation is an elliptical spiral, that is, the position of the nanoscattering unit is arranged in a multi-turn elliptical spiral with opposite spiral directions. Each turn of the elliptical spiral is confocal and the focus is at the origin. The spiral directions of the multi-turn elliptical spirals corresponding to the LCP light and RCP light are opposite. For the positively emitted LCP light and RCP light, the solution to the position equation is an Archimedean spiral.

[0084] A dielectric spacer is set on the metal substrate of the nano-scattering unit to eliminate the fluorescence quenching effect of the single-photon source on the metal surface; a single-photon source is placed on the dielectric spacer, and the offset of the single-photon source from the coordinate z-axis is less than 600nm.

[0085] The excitation spot is irradiated to the single-photon source, causing the single-photon source to emit photons, exciting surface plasmon polariton (SPP) on the metal surface. The excited SPP propagates uniformly in all directions along the radial direction along the surface of the metal substrate; the SPP encounters the nano-scattering unit and is scattered to form scattered light. The position vector r of each nano-scattering unit satisfies the constructive interference condition in the set emission direction, so that the scattered light scattered by all the nano-scattering units coherently constructively forms an emission spot along the set emission direction, so that the direction of the scattered light is along the set emission direction. The set emission direction corresponds to the momentum direction of the photon, so that the momentum direction is independently controlled by the arrangement position of each nano-scattering unit, and the momentum direction is related to the phase of the scattered light from the nano-scattering unit; each nano-scattering unit satisfies the spin angular momentum control equation group, and the first and second phases within a nano-scattering unit are obtained. The projections of the linearly polarized light scattered by the nanogrooves into the far field on a plane perpendicular to the set emission direction are orthogonal to each other and have equal amplitudes. At the same time, the scattered light from the first and second nanogrooves has a phase difference of ±π / 2 in the set emission direction, so that the scattered light from the nanoscattering unit has the same circular polarization in the set emission direction, that is, has the same target polarization state. The polarization state corresponds to the spin angular momentum of the photon, so that the spin angular momentum of the scattered light is independently controlled by the internal structure of the nanoscattering unit, and the spin angular momentum is independent of the phase of the scattered light from the nanoscattering unit; the scattered light finally propagates to the far field along the set emission direction with circularly polarized spin angular momentum, realizing a single-photon emitter with simultaneous and independent control of momentum direction and spin angular momentum.

[0086] The internal structure of the nanoscattering unit is designed to scatter light with the same target spin angular momentum in the set emission direction. This process makes the spin angular momentum of the total scattered field in the far field almost independent of the phase of the scattered light from the nanoscattering unit, and is insensitive to the precise positional relationship between the single-photon source and the nanoscattering unit. This is a phase-independent mechanism. The control of the momentum direction is achieved by reasonably controlling the position of the nanoscattering unit in the metasurface, thereby obtaining the required phase of the scattered light to ensure that the scattered light from all nanoscattering units in the set emission direction constructively interferes with each other. This is a phase-dependent mechanism. The specific structure of the nanoscattering unit is different for different spin angular momenta and momentum directions.

[0087] In order to verify the present invention, numerical simulation was performed using the finite element software COMSOL Multiphysics. In the simulation, an electric dipole located 20 nm above the metal substrate is used to represent the single-photon source, and the x and y coordinates of the single-photon source are equal to 0. The wavelength of light emitted by the single-photon source under the excitation of the excitation spot is λ = 623 nanometers. The metal substrate is made of silver, and the effective refractive index is 0.0363 + 3.13i. Each nano-groove etched into the metal substrate has a length of 250 nm, a width of 100 nm and a depth of 70 nm. The elliptical spiral has 5 turns, with m = 1, 2, 3, 4, 5, and there are 70 nano-scattering units in each turn. The value of the starting point r0 of the elliptical spiral is set to 7.5 μm. Take the emission angle θ = 15° and the polarization of the emitted photons as LCP as a typical example. These conditions correspond to the design of the emitted photon momentum of (sin15°, 0, cos15°), the spin angular momentum is + Different azimuths The anisotropic orientation angle and radial spacing of the nanogrooves in the nanoscattering units are determined by the governing equations for spin angular momentum, while the positions of the nanoscattering units within the metasurface are determined by the coherent constructive conditions and the geometric phase equation. Therefore, the internal structure and positions of the nanoscattering units can be independently designed.

[0088] In the far field, the scattered light intensity distribution of a single photon emitter is as follows: Figure 2 As shown in (a), a well-collimated emission spot with a divergence angle of only 2.7° is obtained. The simulated emission angle is 14.7°, which is very close to the design value of emission angle θ = 15°. The slight difference is attributed to the additional loss and phase shift when the SPP propagates on the nanoscattering unit. Figure 2 (b) The far-field scattered light distribution is further shown in a three-dimensional graph. The vertical height in the graph represents the intensity of the scattered field, while the brightness depth represents the chirality of the scattered field. Here, the circular polarization degree of the far-field scattered light is characterized by the chirality C, which is defined as C = (I L –I R ) / (I L +I R ), where I L and I R Represents the intensity of LCP light and RCP light in a specific direction. Thus, C = 1 and -1 represent ideal LCP light and ideal RCP light, respectively. It can be seen that the far-field scattering pattern shows a sharp single-peak structure, indicating that the scattered light is well collimated to the far field. At the same time, this peak is almost completely black, indicating that it is high-purity LCP light. In order to further quantitatively describe the chirality of the far-field emission spot, the integrated chirality C is used. int , defined as C int =(I Lint –I Rint) / (I Lint +I Rint ), where I Lint and I Rint are the integrated light intensities of the LCP light and the RCP light in the far-field emission spot, respectively. When integrating, the maximum light intensity position of the far-field emission spot is taken as the center and the full width at half maximum of the peak is taken as the radius, thus including most of the far-field emission spot intensity. The calculation results show that the integrated chirality C int It reaches 0.91, which indicates that the far-field emission spot is high-purity LCP light in the set emission direction, that is, the spin angular momentum of the emitted photon in the set emission direction is + These numerical simulation results well validate the proposed design. In addition, the simulations also show that the SPPs excited by the single-photon source and the scattered light from the nanoscattering unit to the far field account for 71% and 49% of the total power of the single-photon source, respectively.

[0089] We further simulated the changes in the integrated chirality of the far-field emission spot at different emission angles θ, and the results are as follows: Figure 2 As shown by the dotted line in (c). It can be observed that when the emission angle θ≤15°, the simulated integrated chirality of the far-field emission spot remains relatively high (≥0.91). For larger emission angles θ, the simulated integrated chirality of the far-field emission spot decreases rapidly. The reason is that the above simulation directly uses an approximate analytical solution, that is, the circular polarization geometric parameter equations are approximately simplified to obtain the internal structural parameters of the nano-scattering unit given in the approximate analytical solution. The above approximation will cause a large deviation when the emission angle θ is large. At this time, the performance of the metasurface can be improved by using an accurate numerical solution, and the orientation angles α, β and radial distance s of the nano-grooves can be obtained through the accurate numerical solution. r The simulation results obtained under the internal structural parameters of the nano-scattering unit given by the exact numerical solution are as follows Figure 2The solid line in (c) shows that at large emission angles θ, the metasurface performance given by the exact numerical solution is significantly superior to the approximate analytical solution. When the emission angle θ is ≤ 53°, and the collection angle of 53° corresponds to a numerical aperture (NA) of 0.8 for the objective lens used in the experiment, the integrated chirality of the far-field emission spot remains consistently high (≥ 0.92). In previous work, the maximum emission angle θ only reached 20°, far less than the maximum emission angle θ = 53° achieved here. This means that by varying the emission angle θ in the control equations for spin angular momentum, momentum direction, and geometric phase, the corresponding metasurface structural parameters can be obtained, allowing the angle of the emission direction of the designed single-photon generator relative to the z-axis to be controlled over a wide range. Furthermore, for a set emission angle θ, the orientation of the single-photon generator's emission direction in the xy plane can be rotated by the same angle around the z-axis by simply rotating the entire metasurface structure around the z-axis. This also causes the projection of the emitted photon's momentum direction in the xy plane to rotate by the same angle around the z-axis.

[0090] Based on the above design principles, the present invention independently controls the spin angular momentum of the emitted photons by designing the internal structure of the nano-scattering unit. For example, the "+" on the right side of the third equation in the spin angular momentum control equation group is changed to "-", and the spin angular momentum of the emitted photons can be changed from the normalized Planck constant + Switch to negative reduced Planck constant - Structurally, this is achieved by exchanging the radial positions of the two nanogrooves in each nanoscattering unit. At the same time, according to the momentum direction control equation and the geometric phase equation, the spiral direction of the elliptical helix needs to be reversed.

[0091] A particular advantage of the proposed single-photon emitter is that the spin angular momentum of the emitted photons is insensitive to the precise position of the single-photon source relative to the metasurface, due to the phase-independent design scheme used to control the spin angular momentum of the emitted photons. Figure 2 The solid and dashed lines in (d) show the integrated chirality of the far-field emission spot when the single-photon source deviates from the z-axis by different distances in the x-direction and y-direction, respectively. When the offset does not exceed 600nm (≈λ), the integrated chirality of the far-field emission spot decreases only slightly (maintaining ≥0.87). This phenomenon could not be observed in previous work based on phase correlation schemes. This positional robustness of the single-photon source allows for sample preparation and experiments using relatively simple sample preparation processes, eliminating the need for high-precision single-photon source positioning and alignment techniques.

[0092] In the above analysis, only single-photon sources with z-polarization were considered. The reason is that the energy coupled into the SPP mode by a single-photon source is proportional to the coupling strength between the electric dipole and the SPP field. The z component of the SPP field is much stronger than the x and y components. Therefore, the coupling strength between the z-direction electric dipole and the SPP is much greater than the coupling strength between the x- and y-direction electric dipoles and the SPP. Numerical simulations show that the SPP power excited by an x- or y-direction electric dipole is only about one twentieth of the SPP power excited by a z-direction electric dipole. Given the random polarization of the single-photon source itself, this fact means that the signal detected in the actual experiment mainly comes from the z-polarization contribution of the single-photon source, while the contributions from the x- and y-directions are negligible.

[0093] Since the anisotropic metasurface of the present invention can achieve independent control of the spin angular momentum and momentum direction of the emitted photons, the metasurface structures corresponding to the emission spots in three different directions are structurally combined to realize a single-photon emitter with controllable three-way spin angular momentum and momentum direction.

[0094] A single-photon emitter with controllable three-way spin angular momentum and momentum direction includes: a metal substrate, a first metasurface structure, a second metasurface structure, a third metasurface structure, a dielectric spacer and a single-photon source; wherein, in a Cartesian coordinate system, the upper surface of the metal substrate is perpendicular to the z-axis; a first metasurface structure, a second metasurface structure and a third metasurface structure are respectively formed on the upper surface of the metal substrate; the first to third metasurface structures are respectively a plurality of nano-scattering units engraved on the upper surface of the metal substrate, each nano-scattering unit includes two rectangular nano-grooves of the same shape engraved on the upper surface of the metal substrate; the rectangular nano-groove located in the counterclockwise direction of the radius is the first nano-groove, and the rectangular nano-groove located in the counterclockwise direction of the radius is the second nano-groove. The rectangular nanogroove in the clockwise direction is the second nanogroove. The first and second nanogrooves are on the inner long side and the adjacent vertices are located on the same radius centered on the origin. The vertex belonging to the first nanogroove is the first vertex, and the vertex belonging to the second nanogroove is the second vertex. In the first to third metasurface structures, the angle between the long side and the radius of the first nanogroove is expressed as α1, α2 and α3 as the orientation of the first nanogroove, and the angle between the long side and the radius of the second nanogroove is expressed as β1, β2 and β3 as the orientation of the second nanogroove. The distance from the center of the second nanogroove to the origin minus the distance from the center of the first nanogroove to the origin is taken as the first radial distance s. r1 、s r2 and s r3The first metasurface structure is located in the first sub-coordinate system x1y1z, the second metasurface structure is located in the second sub-coordinate system x2y2z, and the third metasurface structure is located in the third sub-coordinate system x3y3z. The first to third sub-coordinate systems share the same z-axis and have the same origin. The orientations and radial distances of the first and second nanogrooves of the first to third metasurface structures satisfy the following set of spin angular momentum control equations:

[0095]

[0096]

[0097]

[0098] Where i = 1, 2, 3, k spp is the wave vector of surface plasmon, k0 is the wave vector of vacuum light, is the azimuth angle of the nano-scattering unit of the first metasurface structure in the first sub-coordinate system, is the azimuth angle of the nano-scattering unit of the second metasurface structure in the second sub-coordinate system, is the azimuth angle of the nano-scattering unit of the third metasurface structure in the third sub-coordinate system, that is, the azimuth angle of the radius of the first vertex of the first to third metasurface structures, and the length and width of the rectangular nano-groove are represented by l and w respectively; the nano-scattering unit is structurally anisotropic, that is, the internal structural parameters of the nano-scattering unit at different azimuth angles are different, and it is an anisotropic metasurface; k1 is the light wave vector of the set emission direction of the first metasurface structure, which represents the set emission direction of the first metasurface structure. The set emission direction is in the x1-z plane, and the angle between the set emission direction of the first metasurface structure and the z-axis is the first emission angle θ1; k2 is the light wave vector of the second metasurface structure. The light wave vector of the set emission direction of the surface structure represents the set emission direction. The set emission direction is in the x2-z plane, and the angle between the set emission direction of the second metasurface structure and the z-axis is taken as the second emission angle θ2; k3 is the light wave vector of the set emission direction of the third metasurface structure, which represents the set emission direction of the third metasurface structure. The set emission direction is in the x3-z plane, and the angle between the set emission direction of the third metasurface structure and the z-axis is taken as the third emission angle θ3; Among them, in the third equation of the spin angular momentum control equation group, the right side of the equation takes "﹢" to represent left-handed circular polarization, that is, the spin angular momentum of the photon in the set emission direction is the positive reduced Planck constant + Take “-” to represent right-handed circular polarization, that is, set the spin angular momentum of the photon in the emission direction to the negative reduced Planck constant - The light wave vectors k1, k2 and k3 in the set emission directions of the first to third metasurface structures form an angle of 120° between the projection directions on the metal substrate surface, that is, the angles between the x1 axis, the x2 axis and the x3 axis are 120°;

[0099] When the first, second and third emission angles θ i ≤15°, the control equations of spin angular momentum are approximately simplified to obtain an approximate analytical solution:

[0100]

[0101]

[0102] The position vectors r1, r2, and r3 of the nano-scattering units of the first to third metasurface structures respectively satisfy the constructive interference conditions in the set emission directions of the first to third metasurface structures:

[0103] k spp r i +δ i -k i ·r i =2m i π+C 0i

[0104] Among them, δ1, δ2 and δ3 are the scattering phases of the nano-scattering units of the first to third metasurface structures, r1, r2 and r3 are the moduli of the position vectors r1, r2 and r3 of the nano-scattering units of the first to third metasurface structures, respectively. The midpoint between the first vertex and the second vertex of the nano-scattering unit is taken as the position of the nano-scattering unit, that is, r1, r2 and r3 are the distances from the midpoint between the first vertex and the second vertex of the first to third metasurface structures to the origin, respectively. C 01 、C 02 and C 03 are constants applicable to all nano-scattering units of the first to third metasurface structures, respectively, and m1, m2 and m3 are integers;

[0105] Polar coordinate positions of the nanoscattering units of the first to third metasurface structures Satisfies the momentum direction control equation:

[0106]

[0107] Among them, the distance r from the starting point to the origin of the elliptical spiral lines of the first, second and third metasurface structures is 0i =(C 0i / k spp +λ spp ), λ sppand λ represent the surface plasmon wavelength and light wavelength respectively; m1, m2 and m3 represent the turns of the elliptical spirals of the first to third metasurface structures, respectively, in the first to third sub-coordinate systems, And in the first to third sub-coordinate systems respectively, 3≤N≤M-3, 6≤M≤15, so that the positions of the nano-scattering units of the first to third metasurface structures do not overlap with each other in space;

[0108] The scattering phases δ1, δ2, and δ3 of the nano-scattering units of the first to third metasurface structures satisfy the geometric phase equation:

[0109]

[0110] Among them, θ1, θ2 and θ3 are the first to third emission angles, σ1, σ2 and σ3 are the photon spins of the first to third metasurface structures, respectively. For left-handed circularly polarized (LCP) light and right-handed circularly polarized (RCP) light, they are +1 and -1, respectively. The corresponding photon spin angular momentum is the positive reduced Planck constant + and the negative reduced Planck constant - According to the momentum direction control equation and the geometric phase equation, the position of the nanoscattering unit is anisotropic. For obliquely emitted LCP light and RCP light, the solution to the momentum direction control equation is an elliptical spiral, that is, the position of the nanoscattering unit is arranged in a multi-turn elliptical spiral, each turn of the elliptical spiral is confocal and the focus is at the origin. The spiral directions of the multi-turn elliptical spirals corresponding to the LCP light and RCP light are opposite. For the forward-emitted LCP light and RCP light, the solution to the momentum direction control equation is an Archimedean spiral.

[0111] A dielectric spacer layer is provided on a metal substrate engraved with the first to third metasurface structures to eliminate the fluorescence quenching effect of the single-photon source on the metal surface; a single-photon source is placed on the dielectric spacer layer, and the single-photon source is located within the multi-ring nano-scattering unit of the first to third metasurface structures;

[0112] The excitation light spot is irradiated to the single-photon source, causing the single-photon source to emit photons, exciting surface plasmon polariton (SPP) on the metal surface, and the excited SPP propagates uniformly in all directions along the radial direction along the surface of the metal substrate; the SPP encounters the nano-scattering units of the first to third metasurface structures and is scattered to form scattered light, and the position vectors of each nano-scattering unit respectively meet the constructive interference condition in the set emission direction, so that the scattered light after being scattered by all the nano-scattering units of the first metasurface structure coherently constructively forms an emission light spot along the set emission direction of the first metasurface structure, thereby controlling the direction of the scattered light of the first metasurface structure to be along the set emission direction of the first metasurface structure, and the position vectors of the scattered light after being scattered by all the nano-scattering units of the second metasurface structure are coherently constructive. The scattered light is coherently constructive along the set emission direction of the second metasurface structure to form an emission spot, thereby controlling the direction of the scattered light of the second metasurface structure to be along the set emission direction of the second metasurface structure, and the scattered light after being scattered by all the nano-scattering units of the third metasurface structure is coherently constructive along the set emission direction of the third metasurface structure to form an emission spot, thereby controlling the direction of the scattered light of the third metasurface structure to be along the set emission direction of the third metasurface structure. The set emission direction corresponds to the momentum direction of the photon, thereby independently controlling the first to third metasurface structures by respectively setting the arrangement positions of the respective nano-scattering units of the first to third metasurface structures. The momentum direction of the scattered light is determined, and the momentum direction is phase-related to the scattered light from the nano-scattering unit; each nano-scattering unit located in the first to third metasurface structures satisfies the respective spin angular momentum control equations of the first to third metasurface structures, and the projections of the linearly polarized light scattered to the far field from the first and second nano-grooves in a nano-scattering unit on a plane perpendicular to the set emission direction are orthogonal to each other and have equal amplitudes, and the scattered light from the first and second nano-grooves has a phase difference of ±π / 2 in the set emission direction, so that the scattered light from each nano-scattering unit in the first to third metasurface structures is in the first The nano-scattering units of the first to third metasurface structures have the same circular polarization in the emission direction set by each of them, that is, they have the same target polarization state, and the polarization state corresponds to the spin angular momentum of the photon. Therefore, the spin angular momentum of the scattered light of the first to third metasurface structures can be independently controlled by respectively setting the internal structure of the nano-scattering units of the first to third metasurface structures, and the spin angular momentum is independent of the phase of the scattered light from the nano-scattering units; the scattered light of the first to third metasurface structures finally propagates to the far field along the emission directions set by the first to third metasurface structures respectively with circularly polarized spin angular momentum, realizing a single-photon emitter with three-way simultaneous and independent control of momentum direction and spin angular momentum.

[0113] Example 1

[0114] Figure 3This is a schematic diagram of Example 1 of a three-way single-photon emitter with controllable spin angular momentum and momentum direction according to the present invention, wherein the area between the solid line and the dashed line is the first metasurface structure I, the area between the solid line and the dot-dash line is the second metasurface structure II, and the area between the dashed line and the dot-dash line is the third metasurface structure III. The emission angles set for the first, second, and third metasurface structures are θ1=θ2=θ3=15°, respectively, and the spin angular momentum of the emitted photons is set to be the negative reduced Planck constant - Normalized Planck constant + and the normalized Planck constant + The positions of the nano-scattering units of the first, second and third metasurface structures are distributed on a multi-turn elliptical spiral. In the first to third sub-coordinate systems, And in the first to third sub-coordinate systems respectively, This circle selection method ensures that the positions of the nano-scattering units of the first, second and third metasurface structures do not overlap with each other in space, thereby avoiding mutual interference in the scattering process. Figure 4 : is a numerical simulation result diagram of far-field emission obtained according to Example 1, wherein: Figure 4 (a) shows the far-field scattered light intensity distribution of the single-photon emitter. The three emission spots are clearly visible, with the emission angles of θ1 = θ2 = θ3 = 15.1°, very close to the design value of θ1 = θ2 = θ3 = 15°. The divergence angles of the three emission spots are all 2.9°, maintaining good collimation. Figure 4 (b) and (c) are the intensity distribution diagrams of LCP light and RCP light in the far-field scattered light, respectively. The light spot on the right appears as a bright spot in the intensity distribution diagram of RCP light, but is extinct in the intensity distribution diagram of LCP light, indicating that the polarization of the light spot on the right is RCP, that is, the photon spin angular momentum of the light spot is the negative reduced Planck constant - In contrast, the two light spots on the left appear as bright spots in the intensity distribution diagram of LCP light, but are extinguished in the intensity distribution diagram of RCP component, indicating that the polarization of the two light spots on the left is LCP, that is, the photon spin angular momentum of these two light spots is the positive reduced Planck constant + The simulation results are consistent with the design. The integrated chirality of the two LCP light emission spots on the left is +0.93, while the integrated chirality of the RCP emission spot on the right is -0.93, both showing good chiral characteristics.

[0115] Example 2

[0116] Figure 5This is a numerical simulation result of the far-field emission obtained in Example 2 of the single-photon emitter with three-way controllable spin angular momentum and momentum direction according to the present invention. In Example 2, the emission angles set for the first, second, and third metasurface structures are still θ1=θ2=θ3=15°, but the spin angular momentum of the emitted photons is set to the normalized Planck constant + in, Figure 5 Figure a is the intensity distribution of the far-field scattered light of the single-photon emitter, and the three emission spots are clearly visible. Figures (b) and (c) are the intensity distribution of the LCP light and RCP light in the far-field scattered light, respectively. The three emission spots all appear as bright spots in the intensity distribution of the LCP light, but are all extinct in the intensity distribution of the RCP light, indicating that the polarization of the three emission spots is LCP, that is, the photon spin angular momentum of the three emission spots is the normalized Planck constant + The results of Example 1 and Example 2 show that the present invention can independently control the spin angular momentum of the emitted photons of each emission spot.

[0117] To experimentally verify the present invention's approach, a 400nm-thick silver film was first vapor-deposited on a glass substrate. Because the remaining thickness of the silver film after subtracting the depth of the rectangular nanogrooves is much greater than the skin depth of visible light in silver, the silver film is approximately considered optically equivalent to infinite thickness. Next, the first, second, and third metasurface structures were etched onto the silver surface using focused ion beam etching, and a 10nm-thick layer of Al2O3 was vapor-deposited as a dielectric spacer to reduce the fluorescence quenching effect of the single-photon source on the silver surface. The single-photon source used in the experiment was CdSe colloidal quantum dots, which exhibit excellent single-photon emission performance. A CdSe colloidal quantum dot solution was spin-coated onto the sample surface, resulting in a random distribution of the CdSe colloidal quantum dots. The concentration of the CdSe colloidal quantum dot solution is adjusted to adjust the density of the CdSe colloidal quantum dots on the sample surface. The appropriate concentration is selected so that the average distance between the CdSe colloidal quantum dots is about 2μm. This average distance is larger than the spot diameter of the tightly focused excitation light of 1μm, which can ensure that the tightly focused excitation light can only excite one single photon source at a time.

[0118] Two excitation methods were used in the experiment. One method used a large laser spot of approximately 70 μm incident on the sample at a 30-degree oblique angle, simultaneously exciting numerous single-photon sources within a relatively large sample area. The single-photon source emits light with a central wavelength of 623 nm, and the fluorescence spectrum is only 15 nm wide, making it approximately quasi-monochromatic. The fluorescence signal emitted by the single-photon source was collected by a high-magnification objective lens with a 100x magnification and a numerical aperture (NA) of 0.8, and imaged onto a scientific-grade complementary metal oxide semiconductor (sCMOS) detector for detection. This large-area excitation method enabled the identification of metasurface structures and single-photon sources on the sample surface. Another excitation method used a 405 nm pulsed laser focused by a 100x high-magnification objective lens into a tightly focused spot of approximately 1 μm in diameter, which then selectively excited a single single-photon source. At this point, only one single-photon source close to the origin is excited, and other single-photon sources on the metal substrate surface are hardly effectively excited because the single-photon source absorbs light very weakly at its own fluorescence emission wavelength. By inserting a focusing lens into the detection light path and making the distance from the focusing lens to the sCMOS detector exactly equal to the focal length of the focusing lens, the detection position of the sCMOS detector can be switched from the sample surface to the back focal plane of the 100x high-magnification objective lens, that is, the spatial spectrum plane of the sample. At this time, the sCMOS detects the far-field distribution of the scattered light. A quarter-wave plate and a polarizer are then added before the focusing lens in the detection light path. By changing the angle of the polarizer, the LCP light and RCP light in the far-field scattered light can be detected separately.

[0119] First, a sample of Example 1 was measured. Figure 6The left and right figures of (a) show the images of LCP light and RCP light in the far-field scattered light intensity distribution measured in the experiment, respectively. The emission spot on the right is only visible in the intensity distribution diagram of RCP light, while the two emission spots on the left are only visible in the intensity distribution diagram of LCP light. This phenomenon indicates that the polarization state of the emission spot on the right is RCP, while the polarization state of the two emission spots on the left are both LCP. This experimental result is consistent with the design. Consistent with the processing method in the numerical simulation, the integrated chirality of the experimental far-field emission spot is also calculated. The signal within the radius is also integrated with the half-height full width of the spot as the radius, and the contribution of the uniform background signal in the integration area is removed to obtain the integrated intensities of LCP light and RCP light respectively. The experimental integrated chirality is then obtained by dividing the difference between the integrated intensities of LCP light and RCP light by the sum of the integrated intensities of LCP light and RCP light. The measured integrated chirality of the RCP light on the right reached -0.85, while the integrated chirality of the two LCP lights on the left was 0.96 and 0.88, respectively, demonstrating good circular polarization characteristics. These results are consistent with numerical simulations. The discrepancy between the experimental and simulation results is primarily due to imperfect sample fabrication. For example, the length, width, and depth of the rectangular nanogrooves produced in the actual sample are somewhat non-uniform. The measured emission angles of the three emission spots are θ1 = 13.4°, θ2 = 16.8°, and θ3 = 13.4°. These three angles deviate by approximately 2° from the designed values ​​of θ1 = θ2 = θ3 = 15°, primarily due to the quantum dot position offset from the z-axis. Previous simulations have shown that a 600nm quantum dot position offset results in a roughly 4° variation in emission angle. Despite this, the three emission spots in the far field remain well-collimated circularly polarized, and the separation angle between any two spots is much larger than the divergence angle of the spots, a phenomenon that facilitates the photon momentum or spatial multiplexing of the three emission spots. The above experimental results also verify that the designed metasurface has high single-photon source placement robustness, which enables the realization of three-way single-photon circularly polarized light collimated emission at room temperature with a simpler sample manufacturing process.

[0120] A sample of Example 2 was also measured experimentally. Figure 6The left and right panels of (b) show the experimentally measured far-field scattered light intensity distributions for LCP and RCP light, respectively. The three emission spots appear bright in the LCP image but are barely visible in the RCP image, indicating that the polarization state of all three spots is LCP. The measured integrated chirality of the emission spots for the first, second, and third metasurface structures is 0.87, 0.89, and 0.96, respectively, with emission angles of θ1 = 14.6°, θ2 = 16.8°, and θ3 = 15.9°, respectively. The measured results are generally consistent with the simulated results, with minor discrepancies primarily attributable to the quantum dot's positional deviation from the origin and imperfect sample fabrication.

[0121] Finally, it should be noted that the purpose of disclosing the embodiments is to facilitate a further understanding of the present invention. However, those skilled in the art will appreciate that various substitutions and modifications are possible without departing from the spirit and scope of the present invention and the appended claims. Therefore, the present invention should not be limited to the contents disclosed in the embodiments; the scope of protection claimed by the present invention shall be determined by the scope defined in the claims.

Claims

1. A single-photon emitter with three-way controllable spin angular momentum and momentum direction, characterized in that: The three-way single-photon emitter with controllable spin angular momentum and momentum direction includes: a metal substrate, a first metasurface structure, a second metasurface structure, a third metasurface structure, a dielectric spacer and a single-photon source; wherein, in a Cartesian coordinate system, the upper surface of the metal substrate is perpendicular to the z-axis; the first metasurface structure, the second metasurface structure and the third metasurface structure are respectively formed on the upper surface of the metal substrate; the first to third metasurface structures are respectively a plurality of nano-scattering units engraved on the upper surface of the metal substrate, each nano-scattering unit includes two rectangular nano-grooves of the same shape engraved on the upper surface of the metal substrate; the rectangular nano-grooves located in the counterclockwise direction of the radius are the first nano-grooves, and the rectangular nano-grooves located in the semi-clockwise direction of the radius are the second nano-grooves. The rectangular nanogroove in the clockwise direction is the second nanogroove, the first and second nanogrooves are on the inner long side and the adjacent vertices are located on the same radius centered on the origin, the vertex belonging to the first nanogroove is the first vertex, and the vertex belonging to the second nanogroove is the second vertex; in the first to third supersurface structures, the angle between the long side and the radius of the first nanogroove is expressed as α1, α2 and α3 as the orientation of the first nanogroove, the angle between the long side and the radius of the second nanogroove is expressed as β1, β2 and β3 as the orientation of the second nanogroove, and the distance from the center of the second nanogroove to the origin minus the distance from the center of the first nanogroove to the origin is taken as the first radial distance s r1 、s r2 and s r3 The first metasurface structure is located in the first sub-coordinate system x1y1z, the second metasurface structure is located in the second sub-coordinate system x2y2z, and the third metasurface structure is located in the third sub-coordinate system x3y3z. The first to third sub-coordinate systems share the same z-axis and have the same origin. The orientations and radial distances of the first and second nanogrooves of the first to third metasurface structures satisfy the following set of spin angular momentum control equations: Where i = 1, 2, 3, k spp is the wave vector of surface plasmon, k0 is the wave vector of vacuum light, is the azimuth angle of the nano-scattering unit of the first metasurface structure in the first sub-coordinate system, is the azimuth angle of the nano-scattering unit of the second metasurface structure in the second sub-coordinate system, is the azimuth angle of the nano-scattering unit of the third metasurface structure in the third sub-coordinate system, that is, the azimuth angle of the radius of the first vertex of the first to third metasurface structures, and the length and width of the rectangular nano-groove are represented by l and w respectively; the nano-scattering unit is structurally anisotropic, that is, the internal structural parameters of the nano-scattering unit at different azimuth angles are different, and it is an anisotropic metasurface; k1 is the light wave vector of the set emission direction of the first metasurface structure, which represents the set emission direction of the first metasurface structure. The set emission direction is in the x1-z plane, and the angle between the set emission direction of the first metasurface structure and the z-axis is the first emission angle θ1; k2 is the light wave vector of the second metasurface structure. The light wave vector of the set emission direction of the surface structure represents the set emission direction. The set emission direction is in the x2-z plane, and the angle between the set emission direction of the second metasurface structure and the z-axis is used as the second emission angle θ2; k3 is the light wave vector of the set emission direction of the third metasurface structure, representing the set emission direction of the third metasurface structure. The set emission direction is in the x3-z plane, and the angle between the set emission direction of the third metasurface structure and the z-axis is used as the third emission angle θ3; wherein, in the third equation of the spin angular momentum control equation group, the right side of the equation takes "+" to represent left-handed circular polarization, that is, the spin angular momentum of the photon in the set emission direction is set to the normalized Planck constant "-" represents right-handed circular polarization, that is, the spin angular momentum of the photon in the emission direction is set to the negative reduced Planck constant The light wave vectors k1, k2 and k3 in the set emission directions of the first to third metasurface structures form an angle of 120° between the projection directions on the metal substrate surface, that is, the angles between the x1 axis, the x2 axis and the x3 axis are 120°; The position vectors r1, r2, and r3 of the nano-scattering units of the first to third metasurface structures respectively satisfy the constructive interference conditions in the set emission directions of the first to third metasurface structures: k spp r i +δ i -k i ·r i =2m i π+C 0i (4) Among them, δ1, δ2 and δ3 are the scattering phases of the nano-scattering units of the first to third metasurface structures, r1, r2 and r3 are the moduli of the position vectors r1, r2 and r3 of the nano-scattering units of the first to third metasurface structures, respectively. The midpoint between the first vertex and the second vertex of the nano-scattering unit is taken as the position of the nano-scattering unit, that is, r1, r2 and r3 are the distances from the midpoint between the first vertex and the second vertex of the first to third metasurface structures to the origin, respectively. C 01 、C 02 and C 03 are constants applicable to all nano-scattering units of the first to third metasurface structures, respectively, and m1, m2 and m3 are integers; Polar coordinate positions of the nanoscattering units of the first to third metasurface structures Satisfies the momentum direction control equation: Among them, the distance r from the starting point to the origin of the elliptical spiral lines of the first, second and third metasurface structures is 0i =(C 0i / k spp +λ spp ), λ spp and λ represent the surface plasmon wavelength and light wavelength respectively; m1, m2 and m3 represent the turns of the elliptical spirals of the first to third metasurface structures, respectively, in the first to third sub-coordinate systems, m1=m2=m3=1,…,N, and in the first to third sub-coordinate systems respectively, m1=m2=m3=N+1,…,M, 3≤N≤M-3, 6≤M≤15, so that the positions of the nano-scattering units of the first to third metasurface structures do not overlap with each other in space; The scattering phases δ1, δ2, and δ3 of the nano-scattering units of the first to third metasurface structures satisfy the geometric phase equation: Among them, θ1, θ2 and θ3 are the first to third emission angles respectively, σ1, σ2 and σ3 represent the photon spins of the first to third metasurface structures respectively, and for left-handed circularly polarized LCP light and right-handed circularly polarized RCP light, they are +1 and -1 respectively, and the corresponding photon spin angular momentum is the positive reduced Planck constant and the negative reduced Planck constant According to the momentum direction control equation and the geometric phase equation, the position of the nanoscattering unit is anisotropic. For obliquely emitted LCP light and RCP light, the solution to the momentum direction control equation is an elliptical spiral, that is, the position of the nanoscattering unit is arranged in a multi-turn elliptical spiral, each turn of the elliptical spiral is confocal and the focus is at the origin. The spiral directions of the multi-turn elliptical spirals corresponding to the LCP light and RCP light are opposite. For the forward-emitted LCP light and RCP light, the solution to the momentum direction control equation is an Archimedean spiral. A dielectric spacer layer is provided on a metal substrate engraved with the first to third metasurface structures to eliminate the fluorescence quenching effect of the single-photon source on the metal surface; a single-photon source is placed on the dielectric spacer layer, and the single-photon source is located within the multi-ring nano-scattering unit of the first to third metasurface structures; The excitation light spot is irradiated to the single-photon source, causing the single-photon source to emit photons, exciting the surface plasmons SPP on the metal surface, and the excited SPP propagates uniformly in all directions along the radial direction along the surface of the metal substrate; the SPP encounters the nano-scattering units of the first to third metasurface structures and is scattered to form scattered light, and the position vectors of each nano-scattering unit respectively meet the constructive interference conditions in the set emission direction, so that the scattered light after being scattered by the nano-scattering units of all the first metasurface structures coherently constructively forms an emission light spot along the set emission direction of the first metasurface structure, thereby controlling the direction of the scattered light of the first metasurface structure to be along the set emission direction of the first metasurface structure, and passing through all The scattered light after being scattered by the nano-scattering units of the second metasurface structure coherently constructively forms an emission spot along the set emission direction of the second metasurface structure, thereby controlling the direction of the scattered light of the second metasurface structure to be along the set emission direction of the second metasurface structure, and the scattered light after being scattered by the nano-scattering units of all the third metasurface structures coherently constructively forms an emission spot along the set emission direction of the third metasurface structure, thereby controlling the direction of the scattered light of the third metasurface structure to be along the set emission direction of the third metasurface structure, and the set emission direction corresponds to the momentum direction of the photon, so that the arrangement positions of the respective nano-scattering units of the first to third metasurface structures are independently set. The momentum direction of the scattered light of the first to third metasurface structures is controlled, and the momentum direction is related to the phase of the scattered light from the nanoscattering unit; each nanoscattering unit located in the first to third metasurface structures satisfies the spin angular momentum control equations of the first to third metasurface structures respectively, and the projections of the linearly polarized light scattered to the far field from the first and second nanogrooves in a nanoscattering unit on a plane perpendicular to the set emission direction are orthogonal to each other and have equal amplitudes, and the scattered light from the first and second nanogrooves has a phase difference of ±π / 2 in the set emission direction, so that the scattered light from each nanoscattering unit in the first to third metasurface structures is The scattered light has the same circular polarization in the emission directions set by the first to third metasurface structures, that is, it has the same target polarization state, and the polarization state corresponds to the spin angular momentum of the photon. Therefore, the spin angular momentum of the scattered light of the first to third metasurface structures can be independently controlled by respectively setting the internal structures of the nanoscattering units of the first to third metasurface structures, and the spin angular momentum is independent of the phase of the scattered light from the nanoscattering units; the scattered light of the first to third metasurface structures finally propagates to the far field with circularly polarized spin angular momentum along the emission directions set by the first to third metasurface structures, thereby realizing a single-photon emitter with three-way simultaneous and independent control of momentum direction and spin angular momentum.

2. The single-photon emitter with controllable three-way spin angular momentum and momentum direction according to claim 1, characterized in that: When the first, second and third emission angles θ i ≤15°, the control equations of spin angular momentum are approximately simplified to obtain an approximate analytical solution:

3. The single-photon emitter with controllable three-way spin angular momentum and momentum direction according to claim 1, characterized in that: The offset of the single photon source from the z-axis is less than 600 nm.

4. The single-photon emitter with controllable three-way spin angular momentum and momentum direction according to claim 1, characterized in that: The thickness of the metal substrate is ≥300 nm.

5. The single-photon emitter with controllable three-way spin angular momentum and momentum direction as claimed in claim 1, characterized in that: The length of the rectangular nano-groove is 200nm to 300nm, and the width is 50nm to 100nm.

6. The single-photon emitter with controllable three-way spin angular momentum and momentum direction according to claim 1, characterized in that: The dielectric spacer layer is made of a dielectric material transparent in the visible light band and has a thickness of 5nm to 20nm.

7. A method for realizing a single-photon emitter with controllable three-way spin angular momentum and momentum direction as claimed in claim 1, characterized in that: The implementation method comprises the following steps: 1) providing a dielectric spacer layer on the metal substrate engraved with the first to third metasurface structures to eliminate the fluorescence quenching effect of the single-photon source on the metal surface; 2) In a Cartesian coordinate system, the upper surface of the metal substrate is perpendicular to the z-axis, and a single-photon source is placed on the dielectric spacer layer. The single-photon source is located within the multi-ring nano-scattering units of the first to third metasurface structures. The excitation light spot is irradiated onto the single-photon source, causing the single-photon source to emit photons, exciting surface plasmons (SPPs) on the metal surface. The excited SPPs propagate uniformly in all directions along the surface of the metal substrate in a radial direction. 3) SPP encounters the nano-scattering units of the first to third metasurface structures and is scattered to form scattered light; The position vectors r1, r2, and r3 of the nano-scattering units of the first to third metasurface structures respectively satisfy the constructive interference conditions in the set emission directions of the first to third metasurface structures: k spp r i +δ i -k i ·r i =2m i π+C 0i Among them, k spp is the wave vector of the surface plasmon, δ1, δ2 and δ3 are the scattering phases of the nano-scattering units of the first to third metasurface structures respectively; k1 is the light wave vector of the set emission direction of the first metasurface structure, indicating the set emission direction of the first metasurface structure, the set emission direction is in the x1-z plane, and the angle between the set emission direction of the first metasurface structure and the z-axis is taken as the first emission angle θ1; k2 is the light wave vector of the set emission direction of the second metasurface structure, indicating the set emission direction, the set emission direction is in the x2-z plane, and the angle between the set emission direction of the second metasurface structure and the z-axis is taken as the second emission angle Angle θ2; k3 is the light wave vector of the set emission direction of the third metasurface structure, which represents the set emission direction of the third metasurface structure. The set emission direction is in the x3-z plane, and the angle between the set emission direction of the third metasurface structure and the z-axis is taken as the third emission angle θ3; r1, r2 and r3 are the moduli of the position vectors r1, r2 and r3 of the nano-scattering units of the first to third metasurface structures, respectively. The midpoint between the first vertex and the second vertex of the nano-scattering unit is taken as the position of the nano-scattering unit, that is, r1, r2 and r3 are the distances from the midpoint of the first vertex and the second vertex of the first to third metasurface structures to the origin, respectively. 01 、C 02 and C 03 are constants applicable to all nano-scattering units of the first to third metasurface structures, respectively, and m1, m2 and m3 are integers; Polar coordinate positions of the nanoscattering units of the first to third metasurface structures Satisfies the momentum direction control equation: Where i = 1, 2, 3, the distance from the starting point to the origin of the elliptical spiral line of the first, second and third metasurface structures is r 0i =(C 0i / k spp +λ spp ), λ spp and λ represent the surface plasmon wavelength and light wavelength respectively; m1, m2 and m3 represent the turns of the elliptical spirals of the first to third metasurface structures, respectively, in the first to third sub-coordinate systems, m1=m2=m3=1,…,N, and in the first to third sub-coordinate systems respectively, m1=m2=m3=N+1,…,M, 3≤N≤M-3, 6≤M≤15, so that the positions of the nano-scattering units of the first, second and third metasurface structures do not overlap with each other in space; The scattering phases δ1, δ2, and δ3 of the nano-scattering units of the first to third metasurface structures satisfy the geometric phase equation: Among them, θ1, θ2 and θ3 are the first to third emission angles respectively, σ1, σ2 and σ3 represent the photon spins of the first to third metasurface structures respectively, and for left-handed circularly polarized LCP light and right-handed circularly polarized RCP light, they are +1 and -1 respectively, and the corresponding photon spin angular momentum is the positive reduced Planck constant and the negative reduced Planck constant According to the momentum direction control equation and the geometric phase equation, the position of the nanoscattering unit is anisotropic. For obliquely emitted LCP light and RCP light, the solution to the momentum direction control equation is an elliptical spiral, that is, the position of the nanoscattering unit is arranged in a multi-turn elliptical spiral, each turn of the elliptical spiral is confocal and the focus is at the origin. The spiral directions of the multi-turn elliptical spirals corresponding to the LCP light and RCP light are opposite. For the forward-emitted LCP light and RCP light, the solution to the momentum direction control equation is an Archimedean spiral. The position vectors of each nano-scattering unit satisfy the constructive interference condition in the set emission direction, so that the scattered light after being scattered by all the nano-scattering units of the first metasurface structure coherently constructively forms an emission spot along the set emission direction of the first metasurface structure, thereby controlling the direction of the scattered light of the first metasurface structure to be along the set emission direction of the first metasurface structure, and the scattered light after being scattered by all the nano-scattering units of the second metasurface structure coherently constructively forms an emission spot along the set emission direction of the second metasurface structure, thereby controlling the direction of the scattered light of the second metasurface structure to be along the set emission direction of the second metasurface structure, and the scattered light after being scattered by all the nano-scattering units of the third metasurface structure coherently constructively forms an emission spot along the set emission direction of the third metasurface structure, thereby controlling the direction of the scattered light of the third metasurface structure to be along the set emission direction of the third metasurface structure, and the set emission direction corresponds to the momentum direction of the photon, so that the momentum direction of the scattered light of the first to third metasurface structures is independently controlled by respectively setting the arrangement positions of each nano-scattering unit of the first to third metasurface structures, and the momentum direction is related to the phase of the scattered light from the nano-scattering unit; 4) In each nano-scattering unit, the rectangular nano-groove located in the counterclockwise direction of the radius is the first nano-groove, and the rectangular nano-groove located in the clockwise direction of the radius is the second nano-groove. The adjacent vertices of the first and second nano-grooves on the inner long sides are located on the same radius centered on the origin. The vertex belonging to the first nano-groove is the first vertex, and the vertex belonging to the second nano-groove is the second vertex. In the first to third metasurface structures, respectively, the angle between the long side of the first nano-groove and the radius is expressed as α1, α2 and α3 as the orientation of the first nano-groove, and the angle between the long side of the second nano-groove and the radius is expressed as β1, β2 and β3 as the orientation of the second nano-groove. The distance from the center of the second nano-groove to the origin minus the distance from the center of the first nano-groove to the origin is taken as the first radial distance s. r1 、s r2 and s r3 The first metasurface structure is located in the first sub-coordinate system x1y1z, the second metasurface structure is located in the second sub-coordinate system x2y2z, and the third metasurface structure is located in the third sub-coordinate system x3y3z. The first to third sub-coordinate systems share the same z-axis and have the same origin. The orientations and radial distances of the first and second nanogrooves of the first to third metasurface structures satisfy the following set of spin angular momentum control equations: Where i = 1, 2, 3, k spp is the wave vector of surface plasmon, k0 is the wave vector of vacuum light, is the azimuth angle of the nano-scattering unit of the first metasurface structure in the first sub-coordinate system, is the azimuth angle of the nano-scattering unit of the second metasurface structure in the second sub-coordinate system, is the azimuth angle of the nanoscattering unit of the third metasurface structure in the third sub-coordinate system, that is, the azimuth angle of the radius of the first vertex of the first to third metasurface structures; the length and width of the rectangular nanogroove are represented by l and w respectively; the nanoscattering unit is structurally anisotropic, that is, the internal structural parameters of the nanoscattering unit at different azimuth angles are different, and it is an anisotropic metasurface; among them, in the third equation of the spin angular momentum control equation group, the right side of the equation is "+" to represent left-handed circular polarization, that is, the spin angular momentum of the photon in the emission direction is set to the normalized Planck constant "-" represents right-handed circular polarization, that is, the spin angular momentum of the photon in the emission direction is set to the negative reduced Planck constant The light wave vectors k1, k2 and k3 in the set emission directions of the first to third metasurface structures form an angle of 120° between the projection directions on the metal substrate surface, that is, the angles between the x1 axis, the x2 axis and the x3 axis are 120°; Each nanoscattering unit respectively located in the first to third metasurface structures satisfies the respective spin angular momentum control equations of the first to third metasurface structures. The projections of the linearly polarized light scattered to the far field by the first and second nanogrooves in a nanoscattering unit on a plane perpendicular to the set emission direction are orthogonal to each other and have equal amplitudes. At the same time, the scattered light from the first and second nanogrooves has a phase difference of ±π / 2 in the set emission direction, so that the scattered light from each nanoscattering unit in the first to third metasurface structures has the same circular polarization in the emission direction set by the first to third metasurface structures, that is, has the same target polarization state. The polarization state corresponds to the spin angular momentum of the photon, so that the spin angular momentum of the scattered light of the first to third metasurface structures is independently controlled by respectively setting the internal structures of the nanoscattering units of the first to third metasurface structures, and the spin angular momentum is independent of the phase of the scattered light from the nanoscattering unit. 5) The scattered light from the first to third metasurface structures eventually propagates to the far field along the respective set emission directions of the first to third metasurface structures with circularly polarized spin angular momentum, realizing a single-photon emitter with three-way simultaneous and independent control of momentum direction and spin angular momentum.

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