Vortex light generation based on metasurfaces and its spin Hall device

Abstract

This invention provides a metasurface-based vortex light generation and spin Hall device, comprising an anisotropic surface plasmon metasurface. The core innovation of this invention lies in fusing two different optical functions into a single metasurface device through phase superposition, enabling the device to operate in a wide visible light band and exhibiting robustness to incident light angles. The optical functions include: converting incident plane waves into vortex beams and the spin Hall effect of the vortex beams; the metasurface is arranged with anisotropic identical superatoms according to a specific coded phase distribution; the coded phase distribution is obtained by superimposing a coded helical gradient phase distribution and a coded linear gradient phase distribution; the superatoms are designed as half-wave plates operating in a wide visible light band.

Description

TECHNICAL FIELD

[0001] The application relates to a visible-band vortex light spin Hall device based on a plasmonic metasurface. BACKGROUND

[0002] So far, the in-plane size of the coded metasurface device is in the range of more than millimeters, which significantly limits their application in nanophotonics and compact optoelectronic devices. This can be solved by extending the coded metasurface to the optical frequency, which can reduce the size of the device to the micron level. And extending from the terahertz band to the visible or near-infrared band has important scientific research significance and practical application value. The main difficulties in extending from other bands to the visible band are the contradiction between the working wavelength, the size of the artificial super atom and the preparation and processing capacity. The shorter the working wavelength, the smaller the size of the artificial super atom, and the more difficult the preparation and processing.

[0003] Another aspect is the difficulty of preparation and processing. Since most of the articles require single crystal materials and very strict geometric size requirements for advanced and powerful functional metasurfaces, in fact, its manufacturing is constantly challenging the limit of current semiconductor process processing, and only a few laboratories in the world can process some single products. For example, the titanium dioxide metasurface lens ranked as one of the top ten scientific and technological breakthroughs in the world in 2016 by the Science magazine, the maximum aspect ratio (width 40 nm, depth 600 nm) of its micro-nano structure is as high as 15 (Science, 2016, 352, 1190-1194), and the traditional semiconductor process cannot guarantee the minimum process error requirement. SUMMARY

[0004] The main technical problem to be solved by the application is to provide a vortex light generation and spin Hall device based on a metasurface, a visible-band vortex light spin Hall device based on a plasmonic metasurface, which can work in the visible light band and has robustness in a large range of incident angles.

[0005] In order to solve the above technical problems, the application provides a vortex light generation and spin Hall device based on a metasurface, which is used for generating a spin Hall effect of vortex light and comprises: an anisotropic surface plasmonic metasurface, the surface of the metasurface is arranged with anisotropic homochiral super atoms according to a certain coding phase distribution; the super atom is a half-wave plate designed to work in a wide-frequency visible light band;

[0006] The homochiral super atom is arranged according to a certain coding geometric phase distribution; the coding geometric phase distribution is a coding spiral gradient phase distribution and a coding linear gradient phase distribution obtained by phase superposition, The representative mutation phase gradient; the super surface capable of realizing the generation of vortex beams corresponding to the spiral gradient phase distribution, and the spin Hall effect of photons corresponding to the linear gradient phase distribution.

[0007] In a preferred embodiment: the super atom includes a substrate and a nanorod disposed on the upper surface of the substrate.

[0008] In a preferred embodiment: the material of the nanorod is one of Au, Ag, Al, and Na.

[0009] In a preferred embodiment: the material of the nanorod is Au, and the corresponding Drude model is:

[0010] The dielectric constant ε ∞ , the plasma frequency ω , and the electron collision frequency γ are respectively set to 12, 1.37×10 16 rad / s, and 1.05×10 14 s -1 .

[0011] In a preferred embodiment: the length, width, and thickness of the nanorod are respectively 190 nm, 60 nm, and 60 nm.

[0012] In a preferred embodiment: the dependence of the incident angle and the reflection angle of light is calculated by the generalized Snell's law:

[0013]

[0014] Where θ r is the reflection angle of the reflected light, θ i is the incident angle of the incident light, is the rotation angle between adjacent super atoms, and k0 is the free space wave vector.

[0015] In a preferred embodiment: the characteristic wavelength of the design element is 632.8 nm, and the period of the super atom is 258 nm.

[0016] In a preferred embodiment: the wavelength range of the incident visible light is 390-780 nm, and the period range of the super atom is 157-314 nm.

[0017] In a preferred embodiment: the size S of the super surface is ≥(17λ) 2 , and λ refers to the wavelength of the incident light. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 is a schematic diagram of a super atom in a preferred embodiment of the present application;

[0019] Figure 2 This is a scanning electron microscope (SEM) image of the metasurface device in a preferred embodiment of the present invention;

[0020] Figure 3 This is a linear gradient phase distribution diagram along the x-direction in a preferred embodiment of the present invention;

[0021] Figure 4 This is a spiral gradient phase distribution diagram in a preferred embodiment of the present invention;

[0022] Figure 5 for Figure 3 and Figure 4 The phase distribution map is obtained by convolving the phase distribution;

[0023] Figure 6 The vortex light spectrum generated by the device under different wavelengths of light excitation when incident perpendicularly (0 degrees angle);

[0024] Vortex light generated at a negative angle is left-handed spiral light (LCP), while vortex light generated at a positive angle is right-handed spiral light (RCP).

[0025] Figure 7 When 632.8nm light is incident from different incident angles, the device generates left-handed and right-handed vortex light;

[0026] Figure 8 The diagram shows the interference between left-handed vortex light and linearly polarized light generated by the device at a wavelength of 632.8 nm. In the diagram, the red dashed circle represents the incident light, with left-handed vortex light to the left of the incident light and right-handed vortex light to the right.

[0027] Figure 9 The image shows the interference pattern of right-handed vortex light and linearly polarized light generated by the device at a wavelength of 632.8 nm.

[0028] Figure 10 The images show left-handed and right-handed vortex beams measured in the far field under normal incidence of linearly polarized light at 632.8 nm, where a is a side view and b is a top view.

[0029] Figure 11 This is a schematic diagram of the left-hand and right-hand vortex beams generated when the light is incident perpendicularly (0 degrees angle) in a preferred embodiment of the present invention. Detailed Implementation

[0030] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0031] In the description of this invention, it should be noted that the terms "upper," "lower," "inner," "outer," "top / bottom," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0032] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installed", "equipped", "sleeved / connected", "connected", etc., should be interpreted broadly. For example, "connection" can be a wall-mounted connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium; it can be a connection within two components. For those skilled in the art, the specific meaning of the above terms in this invention can be understood according to the specific circumstances.

[0033] refer to Figures 1-10 This embodiment provides a metasurface-based vortex beam generation and its spin Hall device, which simultaneously possesses two functions: spin-dependent vortex beam generation and the spin Hall effect that generates the vortex beam. The device includes: an anisotropic metasurface, the surface of which is arranged with anisotropic identical superatoms according to a certain coded phase distribution; the coded phase distribution is obtained by convolving a coded helical gradient phase distribution and a coded linear gradient phase distribution.

[0034] In this embodiment, the superatoms are arranged according to a phase distribution obtained by convolving the encoded helical gradient phase distribution and the encoded linear gradient phase distribution. Theoretically, the far-field scattering mode f(sinθ) of the metasurface can be obtained using the near-field encoded mode f(x). λ It is obtained through Fourier transform:

[0035]

[0036] in Where θ is the electric length and θ is the angle relative to the normal direction. According to convolution theory, this Fourier transform relationship also applies to the superposition of two scattering modes, i.e.:

[0037]

[0038] That is, the convolution f(sinθ)*g(sinθ) of the two far-field scattering modes can be passed through their near-field counterparts f(x) λ )·g(x λIt is obtained through Fourier transform.

[0039] Therefore, considering the exponential relationship between the field distribution and the phase distribution, theoretically, only a linear gradient phase distribution capable of realizing the photon spin Hall effect is needed, such as... Figure 3 As shown, the superposition can achieve the spiral gradient phase distribution generated by the vortex beam, such as... Figure 4 As shown, the phase distribution of the metasurface in this invention can be obtained. Figure 5 Such a phase distribution can generate both spin-dependent vortex light and the spin Hall effect of vortex light.

[0040] The encoded phase distribution is obtained through an encoded spiral gradient phase distribution on a metasurface capable of generating vortex beams. Encoded linear gradient phase distribution of metasurfaces capable of realizing the photonic spin Hall effect Obtained through phase superposition φ represents the abrupt phase gradient, where x and y are the distances along the x and y axes of the metasurface, l is the topological charge number, and φ is the azimuth angle.

[0041] The metasurface device of this invention is formed by arranging superatoms according to the phase distribution after phase superposition, such as... Figure 2 As shown, when linearly polarized parallel visible light is incident perpendicularly (at a 0-degree angle) onto the metasurface, left-handed polarized LCP vortex light and right-handed polarized RCP vortex light are generated and reflected in opposite directions (negative and positive angles). This means that both spin-dependent vortex light and the spin Hall effect of vortex light can be generated, as shown in the diagram. Figure 11 As shown, the metasurface device is robust to a wide range of incident angles, meaning that it can function normally when parallel light is incident within a range of ±40°.

[0042] The encoding of linear gradient phase distributions within the visible light frequency range can be expressed by the generalized Snell's law. Perform the calculation, where θ r It is the angle of reflection of the reflected light, θ i It is the angle of incidence of the incident light. is the rotation angle between adjacent superatoms, k0 is the free space wave vector, and p is the period of the superatom.

[0043] Figure 6 A schematic diagram of vortex light generated by a spin Hall device under excitation with different wavelengths of light when incident vertically (0 degrees angle) is shown. Figure 7 The diagram shows the generation of left-handed and right-handed vortex light by a spin Hall effect device when 632.8nm light is incident from different angles. The red dashed circles in the diagram represent the angular positions of the incident light. The right-handed polarized vortex light is located to the left of the incident light, and the left-handed vortex light is located to the right of the incident light. Figure 8The interference pattern of left-handed vortex light and linearly polarized light generated by the vortex spin Hall device at a wavelength of 632.8 nm is further shown. Figure 9 The interference pattern of right-handed vortex light and linearly polarized light generated by the device at a wavelength of 632.8 nm is further shown. Figure 8 and Figure 9 The fact that the tuning forks in the interference fringes are oriented in opposite directions indicates that their topological charge signs are opposite; the fact that there are two tuning forks indicates that the topological charge is 1. Figure 10 The diagram shows the left-handed and right-handed vortex lights measured in the far field under normal incidence of linearly polarized light at 632.8 nm, where a is a side view and b is a top view.

[0044] In this embodiment, the superatoms include a substrate and nanorods disposed on the upper surface of the substrate, wherein the substrate consists of an Au layer and a SiO2 layer disposed sequentially from bottom to top along the thickness direction. The nanorods are also made of Au, and the corresponding Drude model is: The dielectric constant ε ∞ Plasma frequency ω p The electron collision frequencies γ were set to 12 and 1.37 × 10⁻⁶, respectively. 16 rad / s, and 1.05 × 10 14 s -1 .

[0045] The nanorods have a length, width, and thickness of 190 nm, 60 nm, and 60 nm, respectively. The SiO2 and Au layers have thicknesses of 70 nm and 100 nm, respectively, resulting in a superatom with a period of 258 nm and a center wavelength of 632.8 nm.

[0046] As a simple alternative to this embodiment, the material of the nanorods can also be replaced with one of Ag, Al, or Na. As a transmission metasurface, the materials of the Au nanorods and the Au layer can be replaced with TiO2, Si, or SiO2.

[0047] To achieve the effect of vortex optical spin, the size of the metasurface is S≥(17λ). 2 λ refers to the wavelength of the incident light.

[0048] The above description is merely a preferred embodiment of the present invention, but the design concept of the present invention is not limited thereto. Any non-substantial modifications made to the present invention by those skilled in the art within the scope of the technology disclosed in the present invention using this concept shall be deemed as an infringement of the protection scope of the present invention.

Claims

1. A metasurface-based vortex light generation and its spin Hall device, used to generate vortex light using the spin Hall effect, characterized in that... include: An anisotropic surface plasmon metasurface, wherein the surface of the metasurface is arranged with anisotropic identical superatoms according to a certain coded phase distribution; The superatom is a half-wave plate designed to operate in a broadband visible light band. The identical superatoms are arranged according to a certain coded geometric phase distribution; the coded geometric phase distribution is processed by the coded spiral gradient phase distribution Φ(𝑥, 𝑦) = l𝜑 = larctan(𝑥, 𝑦) and the coded linear gradient phase distribution. Obtained through phase superposition The phase gradient represents abrupt changes; the metasurface energy corresponding to the spiral gradient phase distribution enables the generation of vortex beams, while the metasurface energy corresponding to the linear gradient phase distribution enables the spin Hall effect of photons.

2. The metasurface-based vortex light generation and its spin Hall device according to claim 1, characterized in that: The superatoms include a substrate and nanorods disposed on the upper surface of the substrate.

3. The metasurface-based vortex light generation and its spin Hall device according to claim 2, characterized in that: The nanorods are made of one of the following materials: Au, Ag, Al, and Na.

4. The metasurface-based vortex light generation and its spin Hall device according to claim 3, characterized in that: The nanorods are made of Au, and the corresponding Drude model is: ; The dielectric constant plasma frequency Electron collision frequency Set them to 12 and 1.37 respectively. 10 16 rad / s, and 1.05 10 14 s -1 .

5. The metasurface-based vortex light generation and its spin Hall device according to claim 4, characterized in that: The length, width, and thickness of the nanorod are 190 nm, 60 nm, and 60 nm, respectively.

6. The metasurface-based vortex light generation and its spin Hall device according to claim 1, characterized in that: The dependence of the angle of incidence and the angle of reflection on light is calculated using the generalized Snell's law: = ； Where θ r It is the angle of reflection of the reflected light, θ i It is the angle of incidence of the incident light. is the rotation angle between adjacent superatoms, k0 is the free space wave vector, and p is the period of the superatom.

7. The metasurface-based vortex light generation and its spin Hall device according to claim 1, characterized in that: The device is designed with a characteristic wavelength of 632.8 nm and a period of 258 nm for the superatom.

8. The metasurface-based vortex light generation and its spin Hall device according to claim 1, characterized in that: The wavelength range of the incident visible light is 390-780 nm, and the period range of the superatoms is 157-314 nm.

9. The metasurface-based vortex light generation and its spin Hall device according to claim 1, characterized in that: The dimensions of the metasurface λ refers to the wavelength of the incident light.

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