Dual-path spin angular momentum and momentum direction controllable single photon emitter and method thereof

Abstract

The application discloses a kind of two-way spin angular momentum and momentum direction controllable single photon emitter and method thereof.The application independently controls the spin angular momentum of emitting photon by the internal structure of each nano scattering unit, and is irrelevant to the phase of scattered light;The momentum direction of emitting photon is controlled by the position of each nano scattering unit, and is related to the phase of scattered light, two kinds of control do not affect each other, and the control of the spin angular momentum and momentum direction of emitting photon can be independently designed;Two sets of super surface structures corresponding to two emitting photons are combined to form a two-way single photon emitter, and single photon emission is realized, and the spin angular momentum and momentum direction of each emitting photon can be independently controlled by the corresponding super surface structure;The maximum emission angle can reach 53°, and the phase-independent scheme makes the spin angular momentum insensitive to the accurate position of single photon source relative to the super surface, so high-precision single photon source positioning and alignment technology is no longer needed.

Description

Technical Field

[0001] This invention relates to the field of nanophotonics, specifically to a dual-path single-photon emitter with controllable spin angular momentum and momentum direction, and a method for implementing it. Background Technology

[0002] Quantum information science has developed rapidly in recent years and is one of the cutting-edge fields of modern physics. Compared with other physical systems, photons interact weakly 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, especially solid-state single-photon sources, such as quantum dots and nitrogen-vacancy color centers, which are considered important basic units for building scalable photon-based quantum information technology. For photons, energy, momentum, and spin angular momentum are fundamental degrees of freedom, which can be used to carry quantum information and increase information capacity, such as through wavelength multiplexing and momentum multiplexing. Typically, the energy of a photon can be easily controlled by the bandgap of a solid-state single-photon source. However, photons emitted by solid-state single-photon sources are usually spatially isotropic, with the wave vector corresponding to the momentum direction, meaning the momentum direction is random. At the same time, the polarization state of photons emitted by solid-state single-photon sources is also usually random, and the polarization state corresponds to the spin angular momentum of the photon. Therefore, its spin angular momentum is also random. To achieve control over the momentum direction and spin angular momentum of photons emitted by solid-state single-photon sources, specialized schemes and designs are required.

[0003] The rapid development of metasurface technology has provided a promising platform for controlling light. Metasurfaces are planar optical elements constructed from artificial nanostructures, capable of controlling the amplitude, phase, and polarization of light at subwavelength scales. Compared to traditional optical elements, metasurfaces are an ideal platform for miniaturizing, integrating, and multifunctionalizing optical devices, with wide-ranging applications such as beam focusing, polarization control, wavefront shaping, multiplexing, and holography. Recently, some studies have demonstrated the control of photons emitted by single-photon sources by integrating appropriately designed metasurfaces with them. For example, by precisely placing the single-photon source on a metasurface constructed from ring-shaped nanoridges with different centers on a silver film, the momentum direction of the emitted photons can be controlled based on phase-matching conditions, realizing a momentum-direction-controllable single-photon emitter. Furthermore, by fabricating a metasurface on a silver film around nitrogen-vacancy color centers, constructed from dielectric nanoridges with widths varying with azimuth angles, the emitted single photons can be controlled to possess the reduced Planck constant at room temperature. The spin angular momentum, i.e., the emitted photon is in a left-handed circularly polarized state, realizes a circularly polarized single-photon emitter. The total scattering field of the metasurface in free space originates from the coherent superposition of the scattered fields from all nano-scattering units. However, existing works on controlling the photon momentum direction and spin angular momentum rely on precise control of the phase of the scattered light from the nano-scattering units in the metasurface. This phase-dependent approach means that the control of photon momentum direction and spin angular momentum is very sensitive to the phase of the scattered light. The positional deviation between the single-photon source and the nano-scattering units in the metasurface will affect the interference results. Therefore, precise mutual positioning between the single-photon source and the nano-scattering 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 from a medium nanoridge whose width varies with the azimuth angle in order to achieve the designed reduced Planck constant + The spin angular momentum, i.e., the polarization state, is left-handed circularly polarized. On the one hand, the position sensitivity caused by the aforementioned phase sensitivity greatly increases the manufacturing difficulty; on the other hand, the phase sensitivity makes simultaneously and independently controlling the momentum direction and spin angular momentum of the emitted photon a huge challenge. To date, no single-photon emitter has been realized that can simultaneously and independently control the momentum direction and spin angular momentum of the emitted photon; even less so has a dual-path single-photon emitter that can simultaneously and independently control the momentum direction and spin angular momentum of two emitted photons. However, a dual-path single-photon emitter that can simultaneously and independently control the momentum direction and spin angular momentum of two emitted photons has the potential to find important applications in quantum information fields such as momentum multiplexing and spin angular momentum multiplexing of single photons. Summary of the Invention

[0004] To address the problems of the existing technologies, this invention proposes a dual-path single-photon emitter with controllable spin angular momentum and momentum direction, and its implementation method. It utilizes both phase-independent and phase-dependent schemes to construct an anisotropic metasurface, integrating the single-photon source with this metasurface. The spin angular momentum and momentum direction of the emitted photons are independently controlled by the phase-independent and phase-dependent schemes, respectively. Since these two schemes do not interfere with each other, the control of the spin angular momentum and momentum direction of the emitted photons can be designed independently. Furthermore, the two sets of metasurface structures, each corresponding to one of the two emitted photons, are structurally combined to form a dual-path single-photon emitter, enabling dual-path single-photon emission. The spin angular momentum and momentum direction of each emitted photon can be independently controlled through the corresponding structure.

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

[0006] The dual-path spin angular momentum and momentum direction controllable single-photon emitter of the present invention includes: a metal substrate, a first metasurface structure, a second metasurface structure, a dielectric spacer layer, and a single-photon source; wherein, in the Cartesian coordinate system, the upper surface of the metal substrate is perpendicular to the z-axis; the first metasurface structure and the second metasurface structure are respectively formed on the upper surface of the metal substrate; the first metasurface structure and the second metasurface structure are respectively multiple nano-scattering units etched on the upper surface of the metal substrate, each nano-scattering unit including two rectangular nanogrooves of the same shape etched on the upper surface of the metal substrate, the rectangular nanogrooves located in the counterclockwise direction of the radius being the first nanogrooves, and the rectangular nanogrooves located in the clockwise direction of the radius being the second nanogrooves. The rectangular nanogroove in the needle direction is the second nanogroove. The vertices of the first and second nanogrooves, located on their inner long sides and adjacent to each other, lie on the same radius centered at the origin. The vertex belonging to the first nanogroove is designated as the first vertex, and the vertex belonging to the second nanogroove as the second vertex. The angle between the long side and the radius of the first nanogroove of the first metasurface structure is denoted as α1, representing the orientation of the first nanogroove. The angle between the long side and the radius of the second nanogroove of the first metasurface structure is denoted as β1, representing 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 defined as the first radial distance s. r1 The angle between the long side and the radius of the first nanogroove of the second metasurface structure is denoted as α2, representing the orientation of the first nanogroove. The angle between the long side and the radius of the second nanogroove of the second metasurface structure is denoted as β2, representing 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 represented as the second radial distance s. r2 The first metasurface structure is located in the first sub-coordinate system x1y1z, and the second metasurface structure is located in the second sub-coordinate system x2y2z. The first and second sub-coordinate systems share the same z-axis and have the same origin. The orientation and radial distance of the first and second nanogrooves of the first and second metasurface structures satisfy the following set of spin angular momentum control equations:

[0007]

[0008]

[0009]

[0010] Where i = 1 or 2, k spp Let k be the wave vector of the surface plasmon polariton, and k0 be the wave vector of the vacuum light. The azimuth angle of the nano-scattering unit of the first metasurface structure located in the first sub-coordinate system. The azimuth angles of the nano-scattering units of the second metasurface structure located in the second sub-coordinate system are the azimuth angles of the radii of the first vertices of the first and second metasurface structures, respectively. The nano-scattering units are structurally anisotropic, meaning their internal structural parameters differ at different azimuth angles, making them an anisotropic metasurface. k1 is the light wave vector representing the set emission direction of the first metasurface structure, indicating the set emission direction within the x1-z plane. The angle between the set emission direction and the z-axis is taken as the first emission angle θ1. k2 is the light wave vector representing the set emission direction of the second metasurface structure, indicating the set emission direction within the x2-z plane. The angle between the set emission direction and the z-axis is taken as the second emission angle θ2. The length and width of the rectangular nanogroove are represented by l and w, respectively. In the third equation of the spin angular momentum control equation set, taking "+" on the right-hand side indicates left-hand circular polarization, meaning the spin angular momentum of the photon in the set emission direction is the reduced Planck constant + The "-" symbol indicates right-hand circular polarization, meaning the spin angular momentum of the photon in the emission direction is set to the negative reduced Planck constant. Furthermore, the light wave vector k1 of the first metasurface structure and the light wave vector k2 of the second metasurface structure are projected onto the metal substrate surface in opposite directions, that is, the x1 axis and the x2 axis point in opposite directions.

[0011] The position vectors r1 and r2 of the nano-scattering units of the first and second metasurface structures satisfy the constructive interference condition in the predetermined emission directions of the first and second metasurface structures, respectively:

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

[0013] Where δ1 and δ2 are the scattering phases of the nano-scattering units of the first and second metasurface structures, respectively; r1 and r2 are the moduli of the position vectors r1 and r2 of the nano-scattering units of the first and second metasurface structures, respectively; and the midpoint between the first and second vertices of the nano-scattering unit is taken as the position of the nano-scattering unit, i.e., r1 and r2 are the distances from the midpoint between the first and second vertices of the first and second metasurface structures to the origin, respectively. 01 and C 02 , respectively, are constants for all nano-scattering units applicable to the first and second metasurface structures, where m1 and m2 are integers;

[0014] Polar coordinate positions of nano-scattering units in the first and second metasurface structures Satisfies the momentum direction control equation:

[0015]

[0016] Wherein, the distance r from the starting point of the elliptical helix of the first or second metasurface structure to the origin. 0i =(C 0i / k spp +λ spp ), λ spp λ and λ represent the surface plasmon wavelength and the light wavelength, respectively; m1 and m2 represent the number of turns of the elliptical helix of the first and second metasurface structures, respectively, in the negative directions of x1 and x2 of the first and second sub-coordinate systems, respectively, m1=m2=1,…,N, and in the positive directions of x1 and x2 of the first and second sub-coordinate systems, respectively, m1=m2=N+1,…,M, 3≤N≤M-3, 6≤M≤15, so that the positions of the nano-scattering units of the first and second metasurface structures do not overlap with each other in space;

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

[0018]

[0019] Where θ1 and θ2 are the first and second emission angles, respectively, and σ1 and σ2 represent the photon spins of the first and second metasurface structures, respectively. For left-handed circularly polarized (LCP) light and right-handed circularly polarized (RCP) light, these values ​​are +1 and -1, respectively, corresponding to the reduced Planck constants +1 and -1, respectively. and the negatively reduced Planck constant - According to the momentum direction control equation and the geometric phase equation, the positions of the nano-scattering units are anisotropic. For obliquely emitted LCP and RCP light, the solution to the momentum direction control equation is an elliptical spiral, meaning that the positions of the nano-scattering units are arranged in a multi-turn elliptical spiral, with each turn of the elliptical spiral being confocal and the focal point located at the origin. The spiral directions of the multi-turn elliptical spirals corresponding to LCP and RCP light are opposite. For normally emitted LCP and RCP light, the solution to the momentum direction control equation is an Archimedean spiral.

[0020] A dielectric spacer layer is disposed on a metal substrate with first and second 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 and second metasurface structures.

[0021] An excitation beam illuminates a single-photon source, causing the source to emit photons, which in turn excite surface plasmons on the metal surface. Polariton (SPP), the excited SPP propagates uniformly along the surface of the metal substrate in all radial directions; the SPP encounters the nano-scattering units of the first and second metasurface structures and is scattered to form scattered light. The position vector of each nano-scattering unit satisfies the constructive interference condition in the set emission direction, so 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 along the set emission direction of the first metasurface structure. Similarly, 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 along the set emission direction of the second metasurface structure. The set emission direction corresponds to the momentum direction of the photon. Thus, by setting the arrangement position of each nano-scattering unit of the first and second metasurface structures, the momentum direction of the scattered light of the first and second metasurface structures can be independently controlled, and the momentum direction is phase-dependent with the scattered light from the nano-scattering units. Each nano-scattering unit within the metasurface structure satisfies the spin angular momentum control equations of the first and second metasurfaces. The linearly polarized light scattered from the first and second nano-grooves within a nano-scattering unit to the far field is orthogonal to each other and has equal amplitude on a plane perpendicular to the set emission direction. Simultaneously, the scattered light from the first and second nano-grooves has a phase difference of ±π / 2 in the set emission direction, such that the scattered light from each nano-scattering unit within the first and second metasurface structures has the same circular polarization in the set emission direction of the first and second metasurface structures, i.e., the same target polarization state. The polarization state corresponds to the spin angular momentum of the photon. Thus, by setting the internal structure of the nano-scattering unit of the first and second metasurface structures, the spin angular momentum of the scattered light from the first and second metasurface structures can be independently controlled, and the spin angular momentum is independent of the phase of the scattered light from the nano-scattering unit. The scattered light from the first and second metasurface structures finally propagates to the far field along the set emission direction of the first and second metasurface structures with circularly polarized spin angular momentum, realizing a dual-path single-photon emitter that simultaneously and independently controls the momentum direction and spin angular momentum.

[0022] When the first or second launch angle θ1 or θ2 ≤ 15°, the spin angular momentum control equations 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; the thickness of the metal substrate is ≥300nm. The distance between adjacent nano-scattering units along the angular direction is <1μm, and the spacing between nano-scattering units is ≥50nm; the length of the rectangular nano-grooves is 200nm~300nm, and the width is 50nm~100nm; the depth is related to the length and width, and is calculated by the finite element method to give the nano-scattering units high scattering efficiency and high circular polarization.

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

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

[0029] Another objective of this invention is to propose a method for realizing a single-photon emitter with controllable dual-path spin angular momentum and momentum direction.

[0030] The method for implementing the dual-path spin angular momentum and momentum direction controllable single-photon emitter of the present invention includes the following steps:

[0031] 1) A dielectric spacer layer 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;

[0032] 2) In the Cartesian coordinate system, the upper surface of the metal substrate is the xy plane. A single photon source is placed on the dielectric spacer layer and is located within the multi-ring nano-scattering unit of the first and second metasurface structures. The excitation spot irradiates the single photon source, causing the single photon source to emit photons and excite the surface plasmon polariton (SPP) on the metal surface. The excited SPP propagates uniformly along the surface of the metal substrate in all radial directions.

[0033] 3) SPP is scattered by the nano-scattering units of the first and second metasurface structures, forming scattered light;

[0034] The position vectors r1 and r2 of the nano-scattering units of the first and second metasurface structures satisfy the constructive interference condition in the predetermined emission directions of the first and second metasurface structures, respectively:

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

[0036] Where i = 1 or 2, k spp Let δ1 and δ2 be the wave vectors of the surface plasmons, respectively, and let k1 be the wave vector of the first metasurface structure with a predetermined emission direction, representing the predetermined emission direction of the first metasurface structure. The predetermined emission direction lies in the x1-z plane, and the angle between the predetermined emission direction of the first metasurface structure and the z-axis is taken as the first emission angle θ1. Let k2 be the wave vector of the second metasurface structure with a predetermined emission direction, representing the predetermined emission direction lies in the x2-z plane, and the angle between the predetermined emission direction of the second metasurface structure and the z-axis is taken as the second emission angle θ2. Let r1 and r2 be the magnitudes of the position vectors r1 and r2 of the nano-scattering units of the first and second metasurface structures, respectively. The midpoint between the first and second vertices of the nano-scattering unit is taken as the position of the nano-scattering unit, i.e., r1 and r2 are the distances from the midpoint between the first and second vertices of the first and second metasurface structures to the origin, respectively. 01 and C 02 , respectively, are constants for all nano-scattering units applicable to the first and second metasurface structures, where m1 and m2 are integers;

[0037] Polar coordinate positions of nano-scattering units in the first and second metasurface structures The momentum direction control equation should be satisfied:

[0038]

[0039] Where i = 1 or 2, and r is the distance r from the starting point of the elliptical helix of the first or second metasurface structure to the origin. 0i =(C 0i / k spp +λ spp m1 and m2 represent the number of turns of the elliptical helixes of the first and second metasurface structures, respectively, in the negative directions of x1 and x2 of the first and second sub-coordinate systems, respectively, m1 = m2 = 1, ..., N, and in the positive directions of x1 and x2 of the first and second sub-coordinate systems, respectively, m1 = m2 = N+1, ..., M, 3 ≤ N ≤ M-3, 6 ≤ M ≤ 15, so that the positions of the nano-scattering units of the first and second metasurface structures do not overlap with each other in space;

[0040] The scattering phases δ1 and δ2 of the nano-scattering units of the first and second metasurface structures satisfy the geometric phase equation:

[0041]

[0042] Where θ1 and θ2 are the first and second emission angles, respectively, and σ1 and σ2 represent the photon spins of the first and second metasurface structures, respectively. For left-handed circularly polarized (LCP) light and right-handed circularly polarized (RCP) light, these values ​​are +1 and -1, respectively, corresponding to the reduced Planck constants +1 and -1, respectively. + and the negatively reduced Planck constant - According to the momentum direction control equation and the geometric phase equation, the positions of the nano-scattering units are anisotropic. For tilted LCP and RCP light, the solution to the momentum direction control equation is an elliptical spiral, meaning the positions of the nano-scattering units are arranged in multiple elliptical spirals, with each spiral confocal and its focal point at the origin. The spiral directions of the multiple elliptical spirals corresponding to LCP and RCP light are opposite. For orthogonally emitted LCP 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, thus the scattered light after being scattered by all the nano-scattering units of the first metasurface structure follows the set emission direction of the first metasurface structure. The direction of the scattered light from the first metasurface structure is coherently and constructively generated to form an emission spot, thereby controlling the direction of the scattered light from the first metasurface structure to be along the set emission direction of the first metasurface structure. The scattered light after being scattered by the nano-scattering units of the second metasurface structure is coherently and constructively generated to form an emission spot along the set emission direction of the second metasurface structure, thereby controlling the direction of the scattered light from the second metasurface structure to be along the set emission direction of the second metasurface structure. The set emission direction corresponds to the momentum direction of the photon. Thus, by setting the arrangement position of each nano-scattering unit of the first and second metasurface structures respectively, the momentum direction of the scattered light from the first and second metasurface structures is independently controlled, and the momentum direction is phase-dependent with the scattered light from the nano-scattering unit.

[0043] 4) In each nano-scattering unit, the length and width of the rectangular nano-groove are denoted as l and w, respectively. 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 vertices of the first and second nano-grooves on their 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. The angle between the long side and the radius of the first nano-groove of the first metasurface structure is denoted as α1, and the angle between the long side and the radius of the second nano-groove of the first metasurface structure is denoted as β1, and 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 the first radial distance s.r1 The angle between the long side and the radius of the first nanogroove of the second metasurface structure is denoted as α2, representing the orientation of the first nanogroove. The angle between the long side and the radius of the second nanogroove of the second metasurface structure is denoted as β2, representing 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 represented as the second radial distance s. r2 The first metasurface structure is located in the first sub-coordinate system x1y1z, and the second metasurface structure is located in the second sub-coordinate system x2y2z. The first and second sub-coordinate systems share the same z-axis and have the same origin. The orientation and radial distance of the first and second nanogrooves of the first and second metasurface structures satisfy...

[0044] The following set of spin angular momentum governing equations:

[0045]

[0046]

[0047]

[0048] Where i = 1 or 2, k spp Let k be the wave vector of the surface plasmon polariton, and k0 be the wave vector of the vacuum light. The azimuth angle of the nano-scattering unit of the first metasurface structure located in the first sub-coordinate system. The azimuth angles of the nano-scattering units of the second metasurface structure located in the second sub-coordinate system are the azimuth angles of the radii of the first vertices of the first and second metasurface structures, respectively. The nano-scattering units are structurally anisotropic, meaning that the internal structural parameters of the nano-scattering units at different azimuth angles are different, making it an anisotropic metasurface. In the third equation of the spin angular momentum governing equations, taking "+" on the right-hand side indicates left-hand circular polarization, i.e., setting the spin angular momentum of the photon in the emission direction to the reduced Planck constant + The "-" symbol indicates right-hand circular polarization, meaning the spin angular momentum of the photon in the emission direction is set to the negative reduced Planck constant. Furthermore, the light wave vector k1 of the first metasurface structure and the light wave vector k2 of the second metasurface structure are projected onto the metal substrate surface in opposite directions, that is, the x1 axis and the x2 axis point in opposite directions.

[0049] Each nano-scattering unit located within the first and second metasurface structures satisfies the respective spin angular momentum control equations of the first and second metasurfaces. The linearly polarized light scattered from the first and second nano-grooves within a nano-scattering unit to the far field is orthogonal to each other and has equal amplitude on a plane perpendicular to the set emission direction. Simultaneously, the scattered light from the first and second nano-grooves has a phase difference of ±π / 2 in the set emission direction, such that the scattered light from each nano-scattering unit within the first and second metasurface structures has the same circular polarization in the set emission direction of the first and second metasurface structures, i.e., the same target polarization state. The polarization state corresponds to the spin angular momentum of the photon. Thus, by setting the internal structure of the nano-scattering unit of the first and second metasurface structures, the spin angular momentum of the scattered light from the first and second metasurface structures can be independently controlled, and the spin angular momentum is independent of the phase of the scattered light from the nano-scattering unit.

[0050] 5) The scattered light from the first and second metasurface structures eventually propagates to the far field with circularly polarized spin angular momentum along the respective emission directions set by the first and second metasurface structures, realizing a dual-path single-photon emitter that can simultaneously and independently control the momentum direction and spin angular momentum.

[0051] Advantages of this invention:

[0052] This invention independently controls the spin angular momentum of emitted photons through the internal structure of each nano-scattering unit, a method independent of the phase of the scattered light; and controls the momentum direction of emitted photons through the position of each nano-scattering unit, a method related to the phase of the scattered light. Since these two methods are independent of each other, the control of the spin angular momentum and momentum direction of the emitted photons can be designed independently. Combining two sets of metasurface structures corresponding to two different emitted photons constitutes a dual-path single-photon emitter, enabling dual-path single-photon emission. The spin angular momentum and momentum direction of each emitted photon can be independently controlled through its corresponding metasurface structure. 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 techniques. Attached Figure Description

[0053] Figure 1 This is a schematic diagram of a metasurface structure in the dual-path spin angular momentum and momentum direction controllable single-photon emitter of the present invention, wherein (a) is a top view of the whole and (b) is a schematic diagram of the internal structure of a nano-scattering unit.

[0054] Figure 2The figure shows the numerical simulation results of far-field emission obtained from an embodiment of a metasurface structure in a dual-path spin angular momentum and momentum direction controllable single-photon emitter according to the present invention. In the figure, (a) is the intensity distribution of far-field scattered light of the single-photon emitter with the single photon source located exactly on the z-axis and polarized along the z-direction; (b) is the distribution of far-field scattered light, where the height in the vertical direction represents the intensity of the scattered field, and the brightness depth represents the chirality of the scattered field; (c) is the integral chirality of the far-field emitted light spot under 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; and (d) is the integral chirality of the far-field emitted light spot under different distances of the single photon source deviating from the z-axis, where the solid line and the dashed line correspond to the results of deviation along the x-direction and the y-direction, respectively.

[0055] Figure 3 This is a schematic diagram of an embodiment of the dual-path spin angular momentum and momentum direction controllable single-photon emitter of the present invention. The first and second metasurface structures correspond to black solid and black hollow rectangular nanogrooves, respectively. The emission angles set for the first and second metasurfaces are θ1=θ2=15°, and the spin angular momentum set for the emitted photons are respectively the reduced Planck constant + and the negatively reduced Planck constant -

[0056] Figure 4 The figure shows the numerical simulation results of far-field emission obtained by embodiment 1 of the dual-path spin angular momentum and momentum direction controllable single-photon emitter according to the present invention, wherein (a) is the intensity distribution of far-field scattered light of the single-photon emitter, (b) is the intensity distribution of LCP light in the far-field scattered light, and (c) is the intensity distribution of RCP light in the far-field scattered light.

[0057] Figure 5 This is a schematic diagram of a second embodiment of the dual-path spin angular momentum and momentum direction controllable single-photon emitter of the present invention. The first and second metasurface structures correspond to black solid and black hollow rectangular nanogrooves, respectively. The emission angles set for the first and second metasurfaces are θ1=θ2=15°, and the spin angular momentum set for the emitted photons is the reduced Planck constant +

[0058] Figure 6 The figure shows the numerical simulation results of far-field emission obtained by Embodiment 2 of the dual-path spin angular momentum and momentum direction controllable single-photon emitter according to the present invention. Among them, (a) is the intensity distribution of far-field scattered light of the single-photon emitter, (b) is the intensity distribution of LCP light in the far-field scattered light, and (c) is the intensity distribution of RCP light in the far-field scattered light.

[0059] Figure 7This is a schematic diagram of Embodiment 3 of the dual-path spin angular momentum and momentum direction controllable single-photon emitter of the present invention. The first and second metasurface structures correspond to black solid and black hollow rectangular nanogrooves, respectively. The emission angles set for the first and second metasurfaces are θ1 = 20° and θ2 = 10°, respectively, and the spin angular momentum set for the emitted photons are respectively the reduced Planck constant + and the negatively reduced Planck constant -

[0060] Figure 8 The figure shows the numerical simulation results of far-field emission obtained by Embodiment 3 of the dual-path spin angular momentum and momentum direction controllable single-photon emitter according to the present invention. Among them, (a) is the intensity distribution of far-field scattered light of the single-photon emitter, (b) is the intensity distribution of LCP light in the far-field scattered light, and (c) is the intensity distribution of RCP light in the far-field scattered light.

[0061] Figure 9 The figures show the experimental results obtained in Embodiment 1 and Embodiment 2 of the dual-path spin angular momentum and momentum direction controllable single-photon emitter according to the present invention. (a) is a scientific complementary metal oxide semiconductor (sCMOS) image of a sample in Embodiment 1 on the sample surface. The left and right images show the results of large-area excitation and selective excitation of a single quantum dot, respectively. (b) is an sCMOS image obtained by far-field detection of a sample in Embodiment 1. The left and right images show the intensity distribution of LCP light and RCP light, respectively. (c) is an sCMOS image obtained by far-field detection of a sample in Embodiment 2. The left and right images show the intensity distribution of LCP light and RCP light, respectively.

[0062] Figure 10 The second-order correlation function g of the emitted light in Embodiment 1 of the dual-path spin angular momentum and momentum direction controllable single-photon emitter of the present invention is... (2) (t) Measurement results, where (a) is the result of measuring the direct emission of light from a quantum dot on the sample surface of a sample, and (b) is the result of measuring the far-field LCP emission spot emitted by the same quantum dot. Detailed Implementation

[0063] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0064] like Figure 1As shown, a metasurface structure is etched on the upper surface of a metal substrate. A single-photon emitter with only one metasurface structure includes: a metal substrate, nano-scattering units, a dielectric spacer layer, and a single-photon source. In Cartesian coordinates, the upper surface of the metal substrate is the xy-plane. The metasurface structure etched on the upper surface of the metal substrate comprises multiple nano-scattering units. Each nano-scattering unit includes two identical rectangular nanogrooves etched on the upper surface of the metal substrate. The first nanogroove is located counterclockwise, and the second nanogroove is located clockwise. The rectangular nanogroove along the needle direction is the second nanogroove. The vertices of the first and second nanogrooves, located on their inner long sides and adjacent to each other, lie on the same radius centered at the origin. The vertex belonging to the first nanogroove is designated as the first vertex, and the vertex belonging to the second nanogroove as the second vertex. The angle between the long side and the radius of the first nanogroove is denoted as α, representing its orientation. The angle between the long side and the radius of the second nanogroove is denoted as β, representing its orientation. The radial distance s is 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. r The orientation and radial distance of the first and second nanogrooves satisfy the following set of spin angular momentum control equations:

[0065]

[0066]

[0067]

[0068] Where, k spp Let k be the wave vector of the surface plasmon polariton, and k0 be the wave vector of the vacuum light. θ represents the azimuth angle of the nano-scattering unit, i.e., the azimuth angle of the radius of the first vertex. The nano-scattering unit is structurally anisotropic, meaning its internal structural parameters differ at different azimuth angles, making it an anisotropic metasurface. k is the light wave vector of the set emission direction, representing the set emission direction, which lies in the xz plane. The angle between the set emission direction and the z-axis is taken as the emission angle θ. The length and width of the rectangular nanogroove are represented by l and w, respectively. In the third equation of the spin angular momentum control equation set, taking "+" on the right-hand side indicates left-hand circular polarization, meaning the spin angular momentum of the photon in the set emission direction is the reduced Planck constant + θ. The "-" symbol indicates right-hand circular polarization, meaning the spin angular momentum of the photon in the emission direction is set to the negative reduced Planck constant. The center of the first nanogroove is closer to the origin and exhibits left-handed circular polarization, while the center of the second nanogroove is closer to the origin and exhibits right-handed circular polarization.

[0069] When the launch angle θ ≤ 15°, the spin angular momentum control equations can be approximately simplified to obtain an approximate analytical solution:

[0070]

[0071]

[0072] Each nano-scattering unit satisfies the spin angular momentum control equations. The linearly polarized light scattered from the first and second nano-grooves within a nano-scattering unit to the far field is orthogonal to each other and has equal amplitude on a plane perpendicular to the set emission direction. At the same time, 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 the nano-scattering unit has the same circular polarization in the set emission direction, that is, it has the same target polarization state. The polarization state corresponds to the spin angular momentum of the photon. Thus, the spin angular momentum of the scattered light can be independently controlled through the internal structure of the nano-scattering unit, and the spin angular momentum is independent of the phase of the scattered light from the nano-scattering unit.

[0073] To control the momentum direction of emitted photons, i.e., to control the emission direction of 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 units satisfies the constructive interference condition in the set emission direction:

[0074] k spp r+δ-k·r=2mπ+C0

[0075] Where δ is the scattering phase of the nano-scattering unit, r is the magnitude of the position vector r of the nano-scattering unit, the midpoint between the first and second vertices of the nano-scattering unit is taken as the position of the nano-scattering unit, that is, r is the distance from the midpoint between the first and second vertices to the origin, C0 is a constant applicable to all nano-scattering units, and m is an integer.

[0076] Polar coordinate position of nano-scattering unit The momentum direction control equation should be satisfied:

[0077]

[0078] Wherein, the distance r0 from the starting point of the elliptical spiral to the origin is (C0 / k spp +λ spp m = 1, 2, 3, 4, 5;

[0079] The scattering phase δ of the nano-scattering unit satisfies the geometric phase equation:

[0080]

[0081] Where θ is the emission angle, and σ represents the photon spin, taking values ​​of +1 and -1 for left-handed circularly polarized (LCP) and right-handed circularly polarized (RCP) light, respectively. The corresponding photon spin angular momentum are respectively the reduced Planck constant +... and the negatively reduced Planck constant - According to the momentum direction control equation and the geometric phase equation, the position of the nano-scattering unit is anisotropic; for obliquely emitted LCP and RCP light, the solution of the momentum direction control equation is an elliptical spiral, that is, the position of the nano-scattering unit is arranged in a multi-turn elliptical spiral with opposite spiral directions, the elliptical spirals are confocal and the focal point is located at the origin, and the spiral directions of the multi-turn elliptical spirals corresponding to LCP and RCP light are opposite; for normally emitted LCP and RCP light, the solution of the position equation is an Archimedean spiral.

[0082] A dielectric spacer layer 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; the single photon source is placed on the dielectric spacer layer with an offset of less than 600 nm from the z-axis.

[0083] An excitation spot illuminates a single-photon source, causing the source to emit photons and excite surface plasmon polaritons (SPPs) on the metal surface. The excited SPPs propagate uniformly radially along the metal substrate surface. When the SPPs encounter nano-scattering units, they are scattered, forming scattered light. The position vector *r* of each nano-scattering unit satisfies the constructive interference condition in the predetermined emission direction. Therefore, the scattered light, after being scattered by all nano-scattering units, coherently and constructively forms an emission spot along the predetermined emission direction. The direction of the scattered light is along the predetermined emission direction, which corresponds to the momentum direction of the photons. Thus, the momentum direction is independently controlled by the arrangement of each nano-scattering unit, and the momentum direction is phase-dependent with the scattered light from the nano-scattering units. Each nano-scattering unit satisfies the spin angular momentum control equations. From the first and second... The linearly polarized light scattered from the nano-grooves to the far field is projected onto a plane perpendicular to the set emission direction and is orthogonal to each other with equal amplitude. Meanwhile, 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 the nano-scattering unit has the same circular polarization in the set emission direction, that is, it has the same target polarization state. The polarization state corresponds to the spin angular momentum of the photon. Thus, the spin angular momentum of the scattered light can be independently controlled by the internal structure of the nano-scattering unit, and the spin angular momentum is independent of the phase of the scattered light from the nano-scattering 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 that simultaneously and independently controls the momentum direction and spin angular momentum.

[0084] The internal structure of the nano-scattering units is designed to scatter light with the same target spin angular momentum in a predetermined emission direction. This process ensures that the spin angular momentum of the total scattered field in the far field is almost independent of the phase of the scattered light from the nano-scattering units, and is insensitive to the precise positional relationship between the single-photon source and the nano-scattering units—a phase-independent mechanism. The momentum direction is controlled by precisely positioning the nano-scattering units within the metasurface, thereby obtaining the desired scattered light phase to ensure constructive interference between the scattered light from all nano-scattering units in the predetermined emission direction—a phase-dependent mechanism. The specific structure of the nano-scattering units varies depending on the spin angular momentum and momentum direction.

[0085] To verify this invention, numerical simulations were performed using the finite element software COMSOL Multiphysics. In the simulation, a single-photon source was represented by an electric dipole located 20 nm above a metal substrate, with the x and y coordinates equal to 0. The wavelength of the light emitted by the single-photon source under excitation by the excitation spot was λ = 623 nm. The metal substrate was made of silver with an effective refractive index of 0.0363 + 3.13i. Each nanogroove etched into the metal substrate had a length of 250 nm, a width of 100 nm, and a depth of 70 nm. An elliptical helix had 5 turns, with m = 1, 2, 3, 4, 5, and 70 nano-scattering units in each turn. The starting point r0 of the elliptical helix was set to 7.5 μm. A typical example was taken with an emission angle θ = 15° and emitted photon polarization of LCP. These conditions correspond to a designed emitted photon momentum of... (sin15°, 0, cos15°), spin angular momentum is + Different azimuth angles The anisotropic orientation angle and radial distance of the nanogrooves in the nano-scattering unit are determined by the spin angular momentum governing equations, and the position of the nano-scattering unit in the metasurface is determined by the coherent constructive condition and the geometric phase equation. Therefore, the internal structure and position of the nano-scattering unit can be designed independently.

[0086] In the far field, the intensity distribution of scattered light from 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° was obtained. The simulated emission angle was 14.7°, which is very close to the design value of emission angle θ = 15°. The small difference is attributed to the additional loss and phase shift of SPP propagation on the nano-scattering unit. Figure 2 (b) The far-field scattered light distribution is further shown in a three-dimensional plot. The vertical height represents the intensity of the scattered field, while the brightness level indicates the chirality of the scattered field. Here, the circular polarization of the far-field scattered light is characterized by chirality C, defined as C = (I... L –I R ) / (I L +I R ), where I L and I R Let C = 1 and C = -1 represent the intensity of LCP and RCP light in a specific direction, respectively. Thus, C = 1 and C = -1 represent ideal LCP and RCP light, respectively. It can be seen that the far-field scattering pattern exhibits a sharp single-peak structure, indicating that the scattered light is well collimated to the far field. Furthermore, this peak is almost completely black, indicating high-purity LCP light. To further quantitatively describe the chirality of the far-field emitted light spot, the integral chirality C is used. int Defined as C int =(I Lint –I Rint) / (I Lint +I Rint ), where I Lint and I Rint These are the integrated intensities of the LCP and RCP light in the far-field emission spot, respectively. Integration is performed with the location of maximum intensity in the far-field emission spot as the center and the full width at half maximum (FWHM) of the peak as the radius, thus encompassing most of the far-field emission spot intensity. Calculation results show that the integral chirality C... int Reaching 0.91 indicates that the far-field emitted light spot is high-purity LCP light in the set emission direction, meaning the spin angular momentum of the emitted photons in the set emission direction is + These numerical simulation results provide a good validation of the proposed design. Furthermore, the simulations show that the scattered light from the SPP excited by the single-photon source and the nano-scattering units to the far field accounts for 71% and 49% of the total power of the single-photon source, respectively.

[0087] The integral chirality of the far-field emitted light spot was further simulated under different emission angles θ, and the results are as follows: Figure 2 As shown by the dashed line in (c), it can be observed that when the emission angle θ ≤ 15°, the integrated chirality of the simulated far-field emission spot remains high (≥ 0.91). For larger emission angles θ, the integrated chirality of the simulated far-field emission spot decreases rapidly. This is because the simulation directly uses the approximate analytical solution, which is the internal structural parameters of the nano-scattering unit given in the approximate analytical solution obtained by approximating the circular polarization geometric parameter equations. This approximation will cause a large deviation when the emission angle θ is large. In this case, the performance of the metasurface can be improved by using the precise numerical solution, and the orientation angles α, β and radial distance s of the nanogrooves can be obtained through the precise numerical solution. r The parameters, obtained from simulations using the internal structural parameters of the nano-scattering unit given by the exact numerical solution, are as follows: Figure 2As shown by the solid line in (c), it can be seen that at large emission angles θ, the metasurface performance given by the exact numerical solution is significantly better than that of the approximate analytical solution. When the emission angle θ ≤ 53°, the collection angle of 53° corresponds to a numerical aperture (NA) of 0.8 for the objective lens used in the experiment, and the integral chirality of the far-field emission spot remains at a high value (≥ 0.92). In previous work, the maximum emission angle θ only reached 20°, which is much smaller than the maximum emission angle θ = 53° achieved here. That is, by changing the emission angle θ in the spin angular momentum control equations, momentum direction control equations, and geometric phase equations, the corresponding metasurface structure parameters can be obtained, thereby controlling the angle between the emission direction of the designed single-photon generator and the z-axis over a wide range. In addition, for a set emission angle θ, the orientation of the emission direction of the single-photon generator 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, and the projection of the momentum direction of the emitted photon in the xy plane can also be rotated by the same angle around the z-axis.

[0088] Based on the above design principles, this invention independently controls the spin angular momentum of emitted photons by designing the internal structure of the nano-scattering unit. For example, by changing the "+" on the right side of the third equation in the spin angular momentum control equation set to "-", the spin angular momentum of the emitted photon can be controlled from the reduced Planck constant + Switch to negatively reduced Planck constant - This is manifested in the structure by exchanging the radial positions of the two nanogrooves in each nano-scattering unit, while the spiral direction of the elliptical spiral needs to be reversed according to the momentum direction control equation and the geometric phase equation.

[0089] A key advantage of the proposed single-photon emitter is that the spin angular momentum of the emitted photon is insensitive to the precise position of the single-photon source relative to the metasurface. This is because the spin angular momentum control of the emitted photon employs a phase-independent design. 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 along the x and y directions, respectively. When the offset is less than 600 nm (≈λ), the integrated chirality of the far-field emission spot decreases only slightly (remaining ≥0.87). This phenomenon was not 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.

[0090] In the above analysis, only single-photon sources polarized in the z-direction were considered because the energy of a single-photon source coupled into the SPP mode is proportional to the coupling strength between the electric dipole and the SPP field. Since the z-component of the SPP field is much stronger than the x and y components, the coupling strength between the z-direction electric dipole and the SPP is much greater than that between the x and y-direction electric dipoles. 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. Considering the random polarization direction of the single-photon source's own emission, this fact implies that the signal detected in actual experiments mainly comes from the z-polarization contribution of the single-photon source, while the contributions from x and y-direction polarization are negligible.

[0091] like Figure 3 As shown, a dual-path single-photon emitter with controllable spin angular momentum and momentum direction includes: a metal substrate, a first metasurface structure, a second metasurface structure, a dielectric spacer layer, and a single-photon source; wherein, in the Cartesian coordinate system, the upper surface of the metal substrate is perpendicular to the z-axis; the first metasurface structure and the second metasurface structure are formed on the upper surface of the metal substrate; the first metasurface structure and the second metasurface structure are multiple nano-scattering units etched on the upper surface of the metal substrate, each nano-scattering unit including two rectangular nanogrooves of the same shape etched on the upper surface of the metal substrate, the length and width of the rectangular nanogrooves being represented by l and w, respectively, and the rectangular nanogroove located in the counterclockwise direction of the radius being the first nano-scattering unit. The first nano-groove is a rectangular nano-groove located clockwise from the radius. The vertices of the first and second nano-grooves, located on their inner long sides and adjacent to each other, lie on the same radius centered at the origin. The vertex belonging to the first nano-groove is designated as the first vertex, and the vertex belonging to the second nano-groove as the second vertex. The angle between the long side and the radius of the first nano-groove of the first metasurface structure is denoted as α1, and the angle between the long side and the radius of the second nano-groove of the first metasurface structure is denoted as β1. 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 designated as the first radial distance s. r1 The angle between the long side and the radius of the first nanogroove of the second metasurface structure is denoted as α2, representing the orientation of the first nanogroove. The angle between the long side and the radius of the second nanogroove of the second metasurface structure is denoted as β2, representing 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 represented as the second radial distance s. r2The first metasurface structure is located in the first sub-coordinate system x1y1z, and the second metasurface structure is located in the second sub-coordinate system x2y2z. The first and second sub-coordinate systems share the same z-axis and have the same origin. The orientation and radial distance of the first and second nanogrooves of the first and second metasurface structures satisfy the following set of spin angular momentum control equations:

[0092]

[0093]

[0094]

[0095] Where i = 1 or 2, k spp Let k be the wave vector of the surface plasmon polariton, and k0 be the wave vector of the vacuum light. The azimuth angle of the nano-scattering unit of the first metasurface structure located in the first sub-coordinate system. The azimuth angles of the nano-scattering units of the second metasurface structure located in the second sub-coordinate system are the azimuth angles of the radii of the first vertices of the first and second metasurface structures, respectively. The nano-scattering units are structurally anisotropic, meaning their internal structural parameters differ at different azimuth angles, making them an anisotropic metasurface. k1 is the light wave vector representing the set emission direction of the first metasurface structure, indicating the set emission direction within the x1-z plane. The angle between the set emission direction and the z-axis is taken as the first emission angle θ1. k2 is the light wave vector representing the set emission direction of the second metasurface structure, indicating the set emission direction within the x2-z plane. The angle between the set emission direction and the z-axis is taken as the second emission angle θ2. In the third equation of the spin angular momentum control equation set, taking "+" on the right-hand side indicates left-hand circular polarization, meaning the spin angular momentum of the photon in the set emission direction is the reduced Planck constant + The "-" symbol indicates right-hand circular polarization, meaning the spin angular momentum of the photon in the emission direction is set to the negative reduced Planck constant. Furthermore, the light wave vector k1 of the first metasurface structure and the light wave vector k2 of the second metasurface structure are projected onto the metal substrate surface in opposite directions, that is, the x1 axis and the x2 axis point in opposite directions.

[0096] The position vectors r1 and r2 of the nano-scattering units of the first and second metasurface structures satisfy the constructive interference condition in the predetermined emission directions of the first and second metasurface structures, respectively:

[0097] k spp r i +δ i -k i·r i =2m i π+C 0i

[0098] Where δ1 and δ2 are the scattering phases of the nano-scattering units of the first and second metasurface structures, respectively; r1 and r2 are the moduli of the position vectors r1 and r2 of the nano-scattering units of the first and second metasurface structures, respectively; and the midpoint between the first and second vertices of the nano-scattering unit is taken as the position of the nano-scattering unit, i.e., r1 and r2 are the distances from the midpoint between the first and second vertices of the first and second metasurface structures to the origin, respectively. 01 and C 02 , respectively, are constants for all nano-scattering units applicable to the first and second metasurface structures, where m1 and m2 are integers;

[0099] Polar coordinate positions of nano-scattering units in the first and second metasurface structures Satisfies the momentum direction control equation:

[0100]

[0101] Wherein, the distance r from the starting point of the elliptical helix of the first or second metasurface structure to the origin. 0i =(C 0i / k spp +λ spp ), λ spp λ and λ represent the surface plasmon wavelength and the light wavelength, respectively; m1 and m2 represent the number of turns of the elliptical helix of the first and second metasurface structures, respectively, in the negative directions of x1 and x2 of the first and second sub-coordinate systems, m1 = m2 = 1, 2, 3, 4, 5, and in the positive directions of x1 and x2 of the first and second sub-coordinate systems, m1 = m2 = 6, 7, 8, 9, 10, respectively, so that the positions of the nano-scattering units of the first and second metasurface structures do not overlap with each other in space;

[0102] The scattering phases δ1 and δ2 of the nano-scattering units of the first and second metasurface structures satisfy the geometric phase equation:

[0103]

[0104] Where θ1 and θ2 are the first and second emission angles, respectively, and σ1 and σ2 represent the photon spins of the first and second metasurface structures, respectively. For left-handed circularly polarized (LCP) light and right-handed circularly polarized (RCP) light, these values ​​are +1 and -1, respectively, corresponding to the reduced Planck constants +1 and -1, respectively. + and the negatively reduced Planck constant - According to the momentum direction governing equation and the geometric phase equation, the position of the nano-scattering unit is anisotropic; for obliquely emitted LCP and RCP light, the solution to the momentum direction governing equation is an elliptical spiral, that is, the position of the nano-scattering unit is arranged with multiple turns of elliptical spirals, each turn of the elliptical spiral is confocal and the focal point is located at the origin, and the spiral directions of the multiple turns of elliptical spirals corresponding to LCP and RCP light are opposite; for normally emitted LCP and RCP light, the solution to the momentum direction governing equation is an Archimedean spiral.

[0105] A dielectric spacer layer is disposed on a metal substrate with first and second 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 and second metasurface structures.

[0106] An excitation beam illuminates a single-photon source, causing the source to emit photons, which in turn excite surface plasmons on the metal surface. Polariton (SPP), the excited SPP propagates uniformly along the surface of the metal substrate in all radial directions; the SPP encounters the nano-scattering units of the first and second metasurface structures and is scattered to form scattered light. The position vector of each nano-scattering unit satisfies the constructive interference condition in the set emission direction, so 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 along the set emission direction of the first metasurface structure. Similarly, 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 along the set emission direction of the second metasurface structure. The set emission direction corresponds to the momentum direction of the photon. Thus, by setting the arrangement position of each nano-scattering unit of the first and second metasurface structures, the momentum direction of the scattered light of the first and second metasurface structures can be independently controlled, and the momentum direction is phase-dependent with the scattered light from the nano-scattering units. Each nano-scattering unit within the metasurface structure satisfies the spin angular momentum control equations of the first and second metasurfaces. The linearly polarized light scattered from the first and second nano-grooves within a nano-scattering unit to the far field is orthogonal to each other and has equal amplitude on a plane perpendicular to the set emission direction. Simultaneously, the scattered light from the first and second nano-grooves has a phase difference of ±π / 2 in the set emission direction, such that the scattered light from each nano-scattering unit within the first and second metasurface structures has the same circular polarization in the set emission direction of the first and second metasurface structures, i.e., the same target polarization state. The polarization state corresponds to the spin angular momentum of the photon. Thus, by setting the internal structure of the nano-scattering unit of the first and second metasurface structures, the spin angular momentum of the scattered light from the first and second metasurface structures can be independently controlled, and the spin angular momentum is independent of the phase of the scattered light from the nano-scattering unit. The scattered light from the first and second metasurface structures finally propagates to the far field along the set emission direction of the first and second metasurface structures with circularly polarized spin angular momentum, realizing a dual-path single-photon emitter that simultaneously and independently controls the momentum direction and spin angular momentum.

[0107] When the first or second launch angle θ1 or θ2 ≤ 15°, the spin angular momentum control equations are approximately simplified to obtain an approximate analytical solution:

[0108]

[0109]

[0110] Since the anisotropic metasurface of the present invention can achieve independent control of the spin angular momentum and momentum direction of the emitted photons, it is possible to combine metasurface structures corresponding to two different emission spots to realize a single-photon emitter with controllable spin angular momentum and momentum direction.

[0111] Example 1

[0112] Figure 3 This is a schematic diagram of an embodiment of the dual-path spin angular momentum and momentum direction controllable single-photon emitter of the present invention. The first and second metasurface structures correspond to black solid and black hollow rectangular nanogrooves, respectively. The emission angles set for the first and second metasurfaces are θ1=θ2=15°, and the spin angular momentum set for the emitted photons are respectively the reduced Planck constant + and the negatively reduced Planck constant - The nano-scattering units of the first and second metasurface structures are distributed along multiple turns of an elliptical helix. In the negative directions of x1 and x2 of the first and second sub-coordinate systems, m1 = m2 = 1, 2, 3, 4, 5; in the positive directions of x1 and x2 of the first and second sub-coordinate systems, m1 = m2 = 6, 7, 8, 9, 10. This selection of turns ensures that the positions of the nano-scattering units of the first and second metasurface structures do not overlap in space, while maintaining the overall symmetry and integrity of the elliptical helix structure, thus ensuring that the collimation of the emitted light spot remains good. Figure 4 The figure shows the numerical simulation results of far-field emission obtained according to Example 1, wherein, Figure 4 (a) shows the intensity distribution of the far-field scattered light from the single-photon emitter. The two emitted light spots are clearly visible, and their emission angles are θ1 = θ2 = 15.2°, which is very close to the design value of θ1 = θ2 = 15°. The divergence angles of the two emitted light spots are both 2.7°, which still exhibits good collimation characteristics. Figure 4 (b) and (c) are the intensity distribution diagrams of LCP and RCP light in the far-field scattered light, respectively. The light spot on the left appears as a bright spot in the intensity distribution diagram of LCP light, but disappears in the intensity distribution diagram of RCP light. This indicates that the polarization of the light spot on the left is LCP, that is, the photon spin angular momentum of this light spot is the reduced Planck constant + Conversely, the right-hand spot appears as a bright spot in the RCP light intensity distribution diagram, but disappears in the LCP light intensity distribution diagram. This indicates that the polarization of the right-hand spot is RCP, meaning that the photon spin angular momentum of this spot is a negative reduced Planck constant. The simulation results are consistent with the design. The integrated chirality of the emitted light spots of LCP and RCP light are 0.89 and -0.89, respectively, which are only slightly smaller than the integrated chirality of 0.91 in the single-path emission case.

[0113] Example 2

[0114] Figure 5 This is a schematic diagram of a second embodiment of the dual-path spin angular momentum and momentum direction controllable single-photon emitter of the present invention. The first and second metasurface structures correspond to black solid and black hollow rectangular nanogrooves, respectively. The emission angles set for the first and second metasurfaces are θ1=θ2=15°, and the spin angular momentum set for the emitted photons is the reduced Planck constant + Figure 6 The figure shows the numerical simulation results of far-field emission obtained according to Example 2, wherein, Figure 6 (a) shows the intensity distribution of far-field scattered light from the single-photon emitter, with two emission spots clearly visible. Figure 6 (b) and (c) are the intensity distribution diagrams of LCP and RCP light in the far-field scattered light, respectively. The light spots on both sides appear as bright spots in the LCP component intensity distribution diagram, but are extinct in the RCP light intensity distribution diagram. This indicates that the polarization of both light spots is LCP, meaning that the photon spin angular momentum of both light spots is the reduced Planck constant + 0. The results of Examples 1 and 2 show that the present invention can independently control the spin angular momentum of emitted photons from two emission spots, a function that cannot be achieved by using previous metasurfaces, where the spin angular momentum of the two emission spots is independent of each other.

[0115] Example 3

[0116] Figure 7 This is a schematic diagram of Embodiment 3 of the dual-path spin angular momentum and momentum direction controllable single-photon emitter of the present invention. The first and second metasurface structures correspond to black solid and black hollow rectangular nanogrooves, respectively. The emission angles set for the first and second metasurfaces are θ1 = 20° and θ2 = 10°, respectively, and the spin angular momentum set for the emitted photons are respectively the reduced Planck constant + and the negatively reduced Planck constant - Figure 8 The figure shows the numerical simulation results of far-field emission obtained according to Example 3, where, Figure 8 (a) shows the intensity distribution of far-field scattered light from the single-photon emitter. The two emitted light spots are clearly visible, with emission angles of θ1 = 20° and θ2 = 10°, respectively. Figure 8 (b) and (c) are the intensity distribution diagrams of LCP and RCP light in the far-field scattered light, respectively. The results show that the polarization of the emitted light spots on the first and second metasurfaces are LCP and RCP, respectively, that is, the photon spin angular momentum is the reduced Planck constant + and the negatively reduced Planck constant - The results of Example 3 show that the present invention can also independently control the momentum direction of emitted photons from two emission spots.

[0117] To experimentally verify the scheme of the present invention, a 400 nm thick silver film was first deposited on a glass substrate. Since the thickness of the remaining portion 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 to be optically equivalent to infinite thickness. Next, first and second metasurface structures were etched on the silver surface using focused ion beam etching, and a 10 nm thick layer of Al₂O₃ was 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 have good single-photon emission performance. The CdSe colloidal quantum dot solution was spin-coated onto the sample surface, so that the CdSe colloidal quantum dots were randomly distributed on the sample surface. The concentration of the CdSe colloidal quantum dot solution was adjusted to adjust the density of CdSe colloidal quantum dots on the sample surface. An appropriate concentration was selected so that the average distance between CdSe colloidal quantum dots was about 2 μm. This average distance is greater than the spot diameter of the tightly focused excitation light, which is 1 μm, and can ensure that the tightly focused excitation light can excite only one single photon source each time.

[0118] Two excitation methods were employed in the experiment. One method involved using a large laser spot of approximately 70 μm incident at a 30-degree angle onto the sample, simultaneously exciting multiple single-photon sources within a relatively large sample region. The center wavelength of the single-photon source emission was 623 nm, and the fluorescence spectral width was only 15 nm, approximately considered quasi-monochromatic. The fluorescence signal emitted by the single-photon source was collected by a high-magnification objective lens with 100x magnification and a numerical aperture (NA) of 0.8, and imaged onto a scientific-grade complementary metal-oxide-semiconductor (sCMOS) detector for detection. Figure 9 The left image of (a) is an sCMOS image of a sample from Example 1 under large-area excitation, showing the nano-scattering unit structure and many randomly distributed single-photon sources. Another excitation method is to focus a 405nm pulsed laser into a tightly focused spot with a diameter of about 1μm through a 100x high-magnification objective lens, and then selectively excite only a single single-photon source. Figure 9 The right image in (a) is an sCMOS image of a sample from Example 1 when only one single-photon source is excited. In this case, only one single-photon source near the origin is excited; other single-photon sources on the metal substrate surface are hardly effectively excited because their absorption at their own fluorescence emission wavelength is very weak. Since the structure composed of nano-scattering units has a relatively large area, and the emission of a single single-photon source is relatively weak, Figure 9In the right-hand figure of (a), no obvious scattered light signal can be observed. However, the scattered light signal is observable in the far field because it is collimated and emitted into a smaller divergence angle. By inserting a focusing lens into the probe optical path, and ensuring that the distance between the focusing lens and the sCMOS detector is 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, which is the spatial spectral plane of the sample. At this point, the sCMOS detector detects the far-field distribution of the scattered light. Adding a quarter-wave plate and a polarizer before the focusing lens in the probe optical path, and changing the angle of the polarizer, allows for the separate detection of LCP and RCP light in the far-field scattered light.

[0119] First, a sample from Example 1 was measured. Figure 9(b) shows the left and right images of LCP and RCP light intensity distributions in the far-field scattered light measured in the experiment. The emission spot on the right is only visible in the intensity distribution image of LCP light, while the emission spot on the left is only visible in the intensity distribution image of RCP light. This phenomenon indicates that the polarization states of the emission spots on the right and left are LCP and RCP, respectively, which is consistent with the design. Consistent with the processing method in the numerical simulation, the integral chirality of the far-field emission spot in the experiment was also calculated. Similarly, the signal within the radius of the full width at half maximum (FWHM) of the spot was integrated, and the contribution of the uniform background signal in the integration region was removed to obtain the integral intensities of LCP and RCP light, respectively. Then, the integral chirality of the experimental light was obtained by dividing the difference between the integral intensities of LCP and RCP light by the sum of the integral intensities of LCP and RCP light. The results showed that the integral chirality of LCP light on the right reached 0.76, and the integral chirality of RCP light on the left reached -0.89, both showing good circular polarization characteristics. The measured divergence angles of the two emission spots were 2.6° and 3.0°, respectively. These results are close to those of the numerical simulations. The discrepancy between the experimental and simulation results is mainly due to imperfections in sample fabrication; for example, the actual sample fabrication resulted in non-uniform length, width, and depth of the rectangular nanogrooves. The measured emission angles of the two emission spots were θ1 = 11.3° and θ2 = 19.7°, which deviate from the design value θ1 = θ2 = 15° by approximately 4°–5°. This is primarily attributed to the quantum dot position deviating from the z-axis. Previous simulations indicated that a 600 nm quantum dot position offset would result in approximately a 4° change in the emission angle. Nevertheless, the two emission spots in the far field remain well-collimated circularly polarized emission spots, with a separation angle of 31°, close to the simulation prediction of 30°. The actual separation angle is much larger than the divergence angle of the two spots, a phenomenon beneficial for achieving photon momentum or spatial multiplexing between the two emission spots. The experimental results also verify that the designed metasurface has high robustness in the placement of single-photon sources, which enables room-temperature dual-path single-photon circularly polarized light collimation emission with a simpler sample fabrication process.

[0120] A sample from Example 2 was also measured. Figure 9(c) shows the left and right images of the far-field scattered light intensity distribution measured in the experiment, representing LCP and RCP light, respectively. The emission spots on the left and right are very bright in the LCP light image but almost invisible in the RCP light image, indicating that the polarization state of both spots is LCP. The measured integral chirality of the two spots is 0.88 and 0.74, respectively; the emission angles are 20.7° and 11.5°, respectively; and the divergence angles are 4.2° and 2.4°, respectively. In contrast, the simulated integral chirality, emission angle, and divergence angle of the two spots are 0.90, 15.2°, and 2.7°, respectively. The measured results are basically consistent with the simulated results, and the small difference between them is mainly attributed to the quantum dot position deviating from the origin and imperfect sample fabrication.

[0121] This invention also verifies the experimental single-photon nature of the emitted light, specifically by using the experimental scheme proposed by Hanbury Brown and Twiss to measure the second-order correlation function g of the emitted light. (2) (t). Figure 10 (a) shows typical results from direct measurements of radiation from a single-photon source in a sample from Example 1, with curve fitting results indicating g (2) (0) = 0.23, which is significantly less than the critical value of 0.5 corresponding to the single-photon state, indicating that the direct emission light from the single-photon source is in a very good single-photon state. Figure 10 (b) is the second-order correlation function obtained by measuring a far-field LCP emission spot emitted from the same quantum dot in the experiment. The fitting results of the curve show that g (2) (0) = 0.29, which is still less than the critical value of 0.5 corresponding to the single-photon state. This indicates that the far-field emission spot of the single-photon source still satisfies the single-photon state, but the single-photon property is partially reduced compared to the direct emission light of the single-photon source. This is due to the contribution of the background signal. It is not difficult to see that... Figure 10 (a) The background signal of the curve is stronger than Figure 10 (b) Background signal of the curve.

[0122] Finally, it should be noted that the purpose of disclosing the embodiments is to help further understand the present invention. However, those skilled in the art will understand 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 content disclosed in the embodiments, and the scope of protection of the present invention is defined by the claims.

Claims

1. A dual-path single-photon emitter with controllable spin angular momentum and momentum direction, characterized in that, The dual-path spin angular momentum and momentum direction controllable single-photon emitter includes: a metal substrate, a first metasurface structure, a second metasurface structure, a dielectric spacer layer, and a single-photon source; wherein, in Cartesian coordinates, the upper surface of the metal substrate is perpendicular to the z-axis; the first metasurface structure and the second metasurface structure are respectively formed on the upper surface of the metal substrate; the first metasurface structure and the second metasurface structure are multiple nano-scattering units etched on the upper surface of the metal substrate, each nano-scattering unit including two rectangular nanogrooves of the same shape etched on the upper surface of the metal substrate, the rectangular nanogrooves located in the counterclockwise direction of the radius are the first nanogrooves, and the rectangular nanogrooves located in the clockwise direction of the radius are the second nanogrooves, the vertices of the first and second nanogrooves on their inner long sides and adjacent vertices are located on the same radius centered at the origin, the vertex belonging to the first nanogrooves is the first vertex, the vertex belonging to the second nanogrooves is the second vertex, and the angle between the long side and the radius of the first nanogrooves of the first metasurface structure is used as the orientation of the first nanogrooves. The angle between the long side and the radius of the second nanogroove in the first metasurface structure is represented as the orientation of the second nanogroove. The first radial distance is the distance from the center of the second nanogroove of the first metasurface structure to the origin minus the distance from the center of the first nanogroove to the origin. The angle between the long side and the radius of the first nanogroove in the second metasurface structure is represented as the orientation of the first nanogroove. The angle between the long side and the radius of the second nanogroove of the second metasurface structure is represented as the orientation of the second nanogroove as follows: The second radial distance is calculated by subtracting the distance from the center of the first nanogroove to the origin from the distance from the center of the second nanogroove in the second metasurface structure. The first metasurface structure is located in In the first sub-coordinate system, the second metasurface structure is located In the second sub-coordinate system, the first and second sub-coordinate systems share the same z-axis and have the same origin; the orientation and radial distance of the first and second nanogrooves of the first and second metasurface structures satisfy the following set of spin angular momentum control equations: （1） （2） Where i = 1 or 2, Let the wave vector be a surface plasmon polaron. For vacuum light wave vector, The azimuth angle of the nano-scattering unit of the first metasurface structure located in the first sub-coordinate system. 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 radius of the first vertex of the first and second metasurface structures, 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, which is an anisotropic metasurface. Let the light wave vector be the light wave vector of the predetermined emission direction of the first metasurface structure, representing the predetermined emission direction of the first metasurface structure. In the -z plane, the angle between the emission direction of the first metasurface structure and the z-axis is taken as the first emission angle. ; The light wave vector representing the emission direction set for the second metasurface structure indicates the set emission direction, where the set emission direction is in... In the -z plane, the angle between the emission direction of the second metasurface structure and the z-axis is used as the second emission angle. The length and width of the rectangular nanogrooves are respectively expressed as and In the third equation of the spin angular momentum governing equations, taking "+" on the right-hand side indicates left-hand circular polarization, meaning that the spin angular momentum of the photon in the emission direction is set to the reduced Planck constant. The "-" sign indicates right-handed circular polarization, meaning that the spin angular momentum of the photon in the emission direction is set to the negative reduced Planck constant. Furthermore, the light wave vector of the emission direction set by the first metasurface structure The light wave vector of the emission direction set by the second metasurface structure The projection direction on the surface of the metal substrate is opposite, that is shaft and The axes point in opposite directions; Position vectors of nano-scattering units in the first and second metasurface structures and The constructive interference condition is satisfied in the designated emission directions of the first and second metasurface structures, respectively: （4） in, and These represent the scattering phases of the nano-scattering units of the first and second metasurface structures, respectively. and The position vectors of the nano-scattering units of the first and second metasurface structures are respectively. and The modulus is such that the midpoint between the first and second vertices of the nano-scattering unit is taken as the position of the nano-scattering unit, i.e. and , respectively, are the distances from the midpoints of the first and second vertices of the first and second metasurface structures to the origin. and , respectively, are constants for all nano-scattering units applicable to the first and second metasurface structures. and It is an integer; Polar coordinate positions of the nano-scattering units of the first and second metasurface structures ( , Satisfies the momentum direction control equation: （5） The distance from the starting point of the elliptical helix of the first or second metasurface structure to the origin. , λ and λ represent the surface plasmon wavelength and the light wavelength, respectively; and These represent the number of turns of the elliptical helixes in the first and second metasurface structures, respectively, and are located in the first and second sub-coordinate systems. and In the negative direction, =1,…,N, and respectively in the first and second sub-coordinate systems. and positive direction =N+1,…,M,3≤N≤M-3,6≤M≤15,so that the positions of the nano-scattering units of the first and second metasurface structures do not overlap with each other in space; Scattering phase of nano-scattering units in the first and second metasurface structures and Satisfies the geometric phase equation: （6） in, and These are the first and second launch angles, respectively. and Let +1 and +1 represent the photon spins of the first and second metasurface structures, respectively, for left-hand circularly polarized LCP light and right-hand circularly polarized RCP light. The corresponding photon spin angular momentum are respectively the reduced Planck constants. and the negatively reduced Planck constant According to the momentum direction governing equation and the geometric phase equation, the positions of the nano-scattering units are anisotropic. For obliquely emitted LCP and RCP light, the solution to the momentum direction governing equation is an elliptical spiral, meaning that the positions of the nano-scattering units are arranged in a multi-turn elliptical spiral, with each turn of the elliptical spiral being confocal and the focal point located at the origin. The spiral directions of the multi-turn elliptical spirals corresponding to LCP and RCP light are opposite. For orthogonally emitted LCP and RCP light, the solution to the momentum direction governing equation is an Archimedean spiral. A dielectric spacer layer is disposed on a metal substrate with first and second 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 and second metasurface structures. An excitation spot illuminates a single-photon source, causing the source to emit photons and excite surface plasmon polaritons (SPPs) on the metal surface. The excited SPPs propagate uniformly radially along the surface of the metal substrate. When the SPPs encounter nano-scattering units of the first and second metasurface structures, they are scattered, forming scattered light. The position vectors of each nano-scattering unit satisfy constructive interference conditions in their respective emission directions. Thus, the scattered light from all the nano-scattering units of the first metasurface structure coherently and constructively interacts along the predetermined emission direction, forming an emission spot. This controls the direction of the scattered light from the first metasurface structure to follow its predetermined emission direction. Similarly, the scattered light from all the nano-scattering units of the second metasurface structure coherently and constructively interacts along its predetermined emission direction, forming an emission spot. This controls the direction of the scattered light from the second metasurface structure to follow its predetermined emission direction. The predetermined emission direction corresponds to the momentum direction of the photons. Therefore, by independently setting the arrangement positions of the nano-scattering units of the first and second metasurface structures, the momentum direction of the scattered light from both structures is controlled, and the momentum direction is in phase with the scattered light from the nano-scattering units. Relatedly, each nano-scattering unit located within the first and second metasurface structures satisfies the respective spin angular momentum control equations of the first and second metasurfaces. The linearly polarized light scattered from the first and second nano-grooves within a nano-scattering unit to the far field is orthogonal to each other and has equal amplitude on a plane perpendicular to the set emission direction. Simultaneously, the scattered light from the first and second nano-grooves has a phase difference of ±π / 2 in the set emission direction, such that the scattered light from each nano-scattering unit within the first and second metasurface structures has the same circular polarization in the set emission direction of the first and second metasurface structures, i.e., the same target polarization state. The polarization state corresponds to the spin angular momentum of the photon. Thus, by setting the internal structure of the nano-scattering unit of the first and second metasurface structures, the spin angular momentum of the scattered light from the first and second metasurface structures can be independently controlled, and the spin angular momentum is independent of the phase of the scattered light from the nano-scattering unit. The scattered light from the first and second metasurface structures finally propagates to the far field along the respective set emission directions of the first and second metasurface structures with circularly polarized spin angular momentum, realizing a dual-path single-photon emitter that simultaneously and independently controls the momentum direction and spin angular momentum.

2. The dual-path spin angular momentum and momentum direction controllable single-photon emitter as described in claim 1, characterized in that, When the first or second launch angle or For spin angular momentum ≤15°, the governing equations are simplified to obtain an approximate analytical solution: （7） （8）。 3. The dual-path spin angular momentum and momentum direction controllable single-photon emitter as described in claim 1, characterized in that, The offset of the single-photon source from the z-axis is less than 600 nm.

4. The dual-path spin angular momentum and momentum direction controllable single-photon emitter as described in claim 1, characterized in that, The thickness of the metal substrate is ≥300 nm.

5. The dual-path spin angular momentum and momentum direction controllable single-photon emitter as described in claim 1, characterized in that, The distance between adjacent nano-scattering units along the angular direction is <1 μm, and the spacing between nano-scattering units is ≥50 nm.

6. The dual-path spin angular momentum and momentum direction controllable single-photon emitter as described in claim 1, characterized in that, The rectangular nanogrooves have a length of 200 nm to 300 nm and a width of 50 nm to 100 nm.

7. The dual-path spin angular momentum and momentum direction controllable single-photon emitter as described in claim 1, characterized in that, The dielectric spacer layer is made of a transparent dielectric material in the visible light band, with a thickness of 5 nm to 20 nm.

8. A method for implementing a dual-path spin angular momentum and momentum direction controllable single-photon emitter as described in claim 1, characterized in that, The implementation method includes the following steps: 1) A dielectric spacer layer 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; 2) In the Cartesian coordinate system, the upper surface of the metal substrate is the xy plane. A single photon source is placed on the dielectric spacer layer and is located within the multi-ring nano-scattering unit of the first and second metasurface structures. The excitation spot irradiates the single photon source, causing the single photon source to emit photons and excite the surface plasmon polaritons (SPPs) on the metal surface. The excited SPPs propagate uniformly along the surface of the metal substrate in all radial directions. 3) SPP is scattered by the nano-scattering units of the first and second metasurface structures, forming scattered light; Position vectors of nano-scattering units in the first and second metasurface structures and The constructive interference condition is satisfied in the designated emission directions of the first and second metasurface structures, respectively: Where i = 1 or 2, Let the wave vector be a surface plasmon polaron. and These represent the scattering phases of the nano-scattering units of the first and second metasurface structures, respectively. Let the light wave vector be the light wave vector of the predetermined emission direction of the first metasurface structure, representing the predetermined emission direction of the first metasurface structure. In the -z plane, the angle between the emission direction of the first metasurface structure and the z-axis is taken as the first emission angle. ; The light wave vector representing the emission direction set for the second metasurface structure indicates the set emission direction, where the set emission direction is in... In the -z plane, the angle between the emission direction of the second metasurface structure and the z-axis is used as the second emission angle. ; and The position vectors of the nano-scattering units of the first and second metasurface structures are respectively. and The modulus is such that the midpoint between the first and second vertices of the nano-scattering unit is taken as the position of the nano-scattering unit, i.e. and , respectively, are the distances from the midpoints of the first and second vertices of the first and second metasurface structures to the origin. and , respectively, are constants for all nano-scattering units applicable to the first and second metasurface structures. and They are integers respectively; Polar coordinate positions of the nano-scattering units of the first and second metasurface structures ( , The momentum direction control equation should be satisfied: Where i = 1 or 2, is the distance from the origin to the starting point of the elliptical helix of the first or second metasurface structure. ; and These represent the number of turns of the elliptical helixes in the first and second metasurface structures, respectively, and are located in the first and second sub-coordinate systems. and In the negative direction, =1,…,N, and respectively in the first and second sub-coordinate systems. and positive direction =N+1,…,M,3≤N≤M-3,6≤M≤15,so that the positions of the nano-scattering units of the first and second metasurface structures do not overlap with each other in space; Scattering phase of nano-scattering units in the first and second metasurface structures and Satisfies the geometric phase equation: in, and These are the first and second launch angles, respectively. and Let +1 and +1 represent the photon spins of the first and second metasurface structures, respectively, for left-hand circularly polarized LCP light and right-hand circularly polarized RCP light. The corresponding photon spin angular momentum are respectively the reduced Planck constants. and the negatively reduced Planck constant According to the momentum direction control equation and the geometric phase equation, the position of the nano-scattering unit is anisotropic. For LCP and RCP light emitted at an angle, the solution to the momentum direction control equation is an elliptical spiral, meaning that the position of the nano-scattering unit is arranged with multiple turns of elliptical spirals, all of which are confocal with the focal point at the origin. The spiral directions of the multiple turns of elliptical spirals corresponding to LCP and RCP light are opposite. For LCP and RCP light emitted at the center, 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. Thus, the scattered light after being scattered by all the nano-scattering units of the first metasurface structure coherently and 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. Similarly, the scattered light after being scattered by all the nano-scattering units of the second metasurface structure coherently and 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. The set emission direction corresponds to the momentum direction of the photon. Thus, by setting the arrangement position of each nano-scattering unit of the first and second metasurface structures, the momentum direction of the scattered light of the first and second metasurface structures can be independently controlled, and the momentum direction is phase-dependent with the scattered light from the nano-scattering unit. 4) The length and width of the rectangular nanogroove in each nano-scattering unit are respectively expressed as: and The rectangular nanogroove located counterclockwise is designated as the first nanogroove, and the rectangular nanogroove located clockwise is designated as the second nanogroove. The vertices of the first and second nanogrooves, located on their inner long sides and adjacent to each other, lie on the same radius centered at the origin. The vertex belonging to the first nanogroove is designated as the first vertex, and the vertex belonging to the second nanogroove as the second vertex. The angle between the long side and the radius of the first nanogroove in the first metasurface structure is used to represent the orientation of the first nanogroove. The angle between the long side and the radius of the second nanogroove in the first metasurface structure is represented as the orientation of the second nanogroove. The first radial distance is the distance from the center of the second nanogroove of the first metasurface structure to the origin minus the distance from the center of the first nanogroove to the origin. The angle between the long side and the radius of the first nanogroove in the second metasurface structure is represented as the orientation of the first nanogroove. The angle between the long side and the radius of the second nanogroove of the second metasurface structure is represented as the orientation of the second nanogroove as follows: The second radial distance is calculated by subtracting the distance from the center of the first nanogroove to the origin from the distance from the center of the second nanogroove in the second metasurface structure. The first metasurface structure is located in In the first sub-coordinate system, the second metasurface structure is located In the second sub-coordinate system, the first and second sub-coordinate systems share the same z-axis and have the same origin; the orientation and radial distance of the first and second nanogrooves of the first and second metasurface structures satisfy the following set of spin angular momentum control equations: Where i = 1 or 2, Let the wave vector be a surface plasmon polaron. For vacuum light wave vector, The azimuth angle of the nano-scattering unit of the first metasurface structure located in the first sub-coordinate system. The azimuth angles of the nano-scattering units of the second metasurface structure located in the second sub-coordinate system are the azimuth angles of the radii of the first vertices of the first and second metasurface structures, respectively. The nano-scattering units are structurally anisotropic, meaning that the internal structural parameters of the nano-scattering units at different azimuth angles are different, making it an anisotropic metasurface. In the third equation of the spin angular momentum governing equations, taking "+" on the right-hand side indicates left-hand circular polarization, meaning that the spin angular momentum of the photon in the emission direction is set to the reduced Planck constant. The "-" sign indicates right-handed circular polarization, meaning that the spin angular momentum of the photon in the emission direction is set to the negative reduced Planck constant. Furthermore, the light wave vector of the emission direction set by the first metasurface structure The light wave vector of the emission direction set by the second metasurface structure The projection direction on the surface of the metal substrate is opposite, that is shaft and The axes point in opposite directions; Each nano-scattering unit located within the first and second metasurface structures satisfies the respective spin angular momentum control equations of the first and second metasurfaces. The linearly polarized light scattered from the first and second nano-grooves within a nano-scattering unit to the far field is orthogonal to each other and has equal amplitude on a plane perpendicular to the set emission direction. Simultaneously, the scattered light from the first and second nano-grooves has a phase difference of ±π / 2 in the set emission direction, such that the scattered light from each nano-scattering unit within the first and second metasurface structures has the same circular polarization in the set emission direction of the first and second metasurface structures, i.e., the same target polarization state. The polarization state corresponds to the spin angular momentum of the photon. Thus, by setting the internal structure of the nano-scattering unit of the first and second metasurface structures, the spin angular momentum of the scattered light from the first and second metasurface structures can be independently controlled, and the spin angular momentum is independent of the phase of the scattered light from the nano-scattering unit. The scattered light from the first and second metasurface structures eventually propagates to the far field with circularly polarized spin angular momentum along the respective emission directions set by the first and second metasurface structures, realizing a dual-path single-photon emitter that can simultaneously and independently control the momentum direction and spin angular momentum.

Images