A visible band vortex beam generation device based on plasmonic metasurface

Abstract

The application provides a visible band vortex beam generation device based on a plasmonic metasurface, comprising: an anisotropic metasurface, which is designed according to a PB geometric phase principle; the metasurface is divided into N regions around a geometric center of the metasurface, and each region is arranged with anisotropic allotropic superatoms in a specific direction; the superatoms are designed to have the function of a half-wave plate; the included angle of allotropic superatoms of two adjacent regions is π / N, and the geometric phase increment is 2π / N, so that the metasurface generates a spiral gradient phase distribution around the geometric center for a plane wave; when the metasurface is irradiated by circularly polarized visible light vertically, due to the spiral gradient phase distribution and the half-wave plate function of each superatom, the reflected light of left-handed or right-handed light is converted into right-handed or left-handed vortex light.

Description

Technical Field

[0001] This invention relates to a visible-band vortex beam generating device based on a plasma metasurface. Background Technology

[0002] To date, the in-plane dimensions of coded metasurface devices are in the range of millimeters and above, significantly limiting their application in nanophotonics and compact optoelectronic devices. This limitation can be addressed by extending coded metasurfaces to optical frequencies, which can reduce device size to the micrometer scale. Furthermore, extending from the terahertz band to the visible or near-infrared bands has significant scientific research and practical application value. Extending from other bands to the visible band mainly faces several challenges, such as the trade-off between operating wavelength, artificial metamaterial atomic size, and fabrication capabilities. The shorter the operating wavelength, the smaller the artificial metamaterial atomic size, and the more difficult the fabrication becomes. Summary of the Invention

[0003] The main technical problem to be solved by this invention is to provide a vortex beam generating device based on a plasma metasurface that can operate in the visible light band.

[0004] To address the aforementioned technical problems, this invention provides a visible-band vortex beam generating device based on a plasma metasurface, comprising: an anisotropic metasurface designed according to the PB geometric phase principle; N regions surrounding the geometric center of the metasurface, each region arranging anisotropic identical superatoms in a specific direction; the superatoms being designed to function as half-wave plates; the angle between two adjacent identical superatoms in the region being π / N, and the geometric phase increment being 2π / N, thereby enabling the metasurface to generate a spiral gradient phase distribution around the geometric center for plane waves; when the metasurface is irradiated by perpendicularly incident circularly polarized visible light, due to the spiral gradient phase distribution and the half-wave plate function of each superatom, the reflected light of left-handed or right-handed spiral light is transformed into right-handed or left-handed spiral light.

[0005] In a preferred embodiment: the superatoms include a substrate and nanorods disposed on the upper surface of the substrate.

[0006] In a preferred embodiment, the nanorods are made of one of Au, Ag, Al, and Na.

[0007] In a preferred embodiment: the nanorod is made of Au, and the corresponding Drude model is:

[0008] 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 × 1014 s -1 .

[0009] In a preferred embodiment, the length, width, and thickness of the nanorod are 190 nm, 60 nm, and 60 nm, respectively.

[0010] In a preferred embodiment: the characteristic wavelength of the device is 632.8 nm, and the period of the superatom is 258 nm.

[0011] In a preferred embodiment: the wavelength range of the incident visible light is 390-780 nm, and the period range of the superatom is 157-314 nm.

[0012] In a preferred embodiment: the size S of the metasurface is ≥ (17λ). 2 λ refers to the wavelength of the incident light.

[0013] In a preferred embodiment: the spiral gradient phase distribution is expressed as:

[0014] 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. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the superatoms in a preferred embodiment of the present invention;

[0016] Figure 2 This is a scanning electron microscope (SEM) image of the metasurface in a preferred embodiment of the present invention;

[0017] Figure 3 for Figure 2 Phase distribution diagram of metasurface;

[0018] Figure 4 The circularly polarized vortex light spectrum generated by the device under normal incidence of light of different wavelengths; (left: left-handed vortex light incidence, right: right-handed vortex light incidence);

[0019] Figure 5 This is a schematic diagram of the interference between left-handed vortex light generated by the device and linearly polarized light when the light wavelength is 632.8 nm.

[0020] Figure 6 This is a schematic diagram of the interference between right-handed vortex light generated by the device and linearly polarized light when the light wavelength is 632.8 nm.

[0021] Figure 7 This is a schematic diagram of the vortex light generated by the device when the light is incident perpendicularly (0 degrees angle). Detailed Implementation

[0022] 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.

[0023] 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.

[0024] 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.

[0025] refer to Figures 1-6 This embodiment provides a visible-band vortex beam generating device based on a plasma metasurface, comprising: an anisotropic metasurface, wherein the metasurface is designed according to the PB geometric phase principle;

[0026] like Figure 2 As shown, the surface is divided into N regions around the geometric center of the metasurface, and each region is arranged with anisotropic and identical superatoms in a specific direction; the superatoms are designed to function as half-wave plates.

[0027] The angle between two adjacent regions of identical superatoms is π / N, and the geometric phase increment is 2π / N, which causes the metasurface to generate a spiral gradient phase distribution around the geometric center for plane waves.

[0028] When the metasurface is irradiated with perpendicularly incident circularly polarized visible light, due to the helical gradient phase distribution and the half-wave plate function of each superatom, the reflected light from left-handed or right-handed spiral light is transformed into right-handed or left-handed spiral light, such as... Figure 7 As shown.

[0029] like Figure 3As shown, in order to form the above-mentioned spiral gradient phase distribution, the spiral gradient phase distribution is expressed as:

[0030] 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.

[0031] Figure 4 The circularly polarized vortex light spectra generated by the device under normal incidence of light of different wavelengths are presented; the left side represents left-handed vortex light incidence, and the right side represents right-handed vortex light incidence. Figures 5-6 Furthermore, a schematic diagram is given showing the interference between the left-handed or right-handed vortex light generated by the device and the linearly polarized light when the light wavelength is 632.8 nm.

[0032] In this embodiment, as Figure 1 As shown, 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 .

[0033] 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.

[0034] As a simple alternative to this embodiment, the nanorods can also be made of one of Ag, Al, or Na. The Au layer can be made of TiO2, Si, or GST.

[0035] To achieve the vortex light effect, the size of the metasurface is S ≥ (17λ). 2 λ refers to the wavelength of the incident light.

[0036] 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 visible-band vortex beam generating device based on a plasmonic metasurface, comprising: An anisotropic metasurface, designed based on the PB geometric phase principle; The surface is divided into N regions around its geometric center, and each region is arranged with anisotropic and identical superatoms in a specific orientation. The superatom includes a substrate and nanorods disposed on the upper surface of the substrate; the superatom is designed to function as a half-wave plate. The angle between two identical superatoms in adjacent regions is Geometric phase increment is This causes the metasurface to produce a spiral gradient phase distribution around the geometric center for plane waves; When the metasurface is irradiated with vertically incident circularly polarized visible light, due to the spiral gradient phase distribution and the half-wave plate function of each superatom, the reflected light of left-handed or right-handed spiral light is transformed into right-handed or left-handed spiral light.

2. The visible-band vortex beam generating device based on a plasma metasurface according to claim 1, characterized in that: The nanorods are made of one of the following materials: Au, Ag, Al, and Na.

3. The visible-band vortex beam generating device based on a plasma metasurface according to claim 2, characterized in that: The nanorods are made of Au, and the corresponding Drude model is: ; The dielectric constant plasma frequency The electron collision frequencies γ were set to 12 and 1.37, respectively. 10 16 rad / s, and 1.05 10 14 s -1 .

4. The visible-band vortex beam generating device based on a plasma metasurface according to claim 3, characterized in that: The length, width, and thickness of the nanorod are 190 nm, 60 nm, and 60 nm, respectively.

5. The visible-band vortex beam generating device based on a plasma metasurface according to claim 1, characterized in that: The device is designed with a characteristic wavelength of 632.8 nm and the superatom has a period of 258 nm.

6. The visible-band vortex beam generating device based on a plasma metasurface 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.

7. The visible-band vortex beam generating device based on a plasma metasurface according to claim 1, characterized in that: The dimensions of the metasurface λ refers to the wavelength of the incident light.

8. The visible-band vortex beam generating device based on a plasma metasurface according to claim 1, characterized in that: The spiral gradient phase distribution is expressed as: Φ(𝑥, 𝑦) = l𝜑 = larctan(𝑥, 𝑦), 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.

Images