A visible band photonic spin hall device based on plasmonic metasurface

Abstract

The application provides a visible band photonic spin Hall device based on a plasmonic metasurface, which comprises: an anisotropic metasurface, which is designed based on a PB geometric phase principle and is formed by periodic arrangement of supercells; the supercells are arranged by homochiral superatoms every interval p and rotation angle by turns, so that the last superatom of each supercell rotates 180 DEG relative to the first superatom; the superatom is a half-wave plate working in a wide frequency visible light band, that is, when left-handed or right-handed circularly polarized light is incident on the superatom, the reflected light is converted into right-handed or left-handed circularly polarized light; under parallel circularly polarized light incidence, the reflected circularly polarized light of the metasurface device follows the generalized Snell law, and left-handed light and right-handed light are reflected towards opposite directions respectively, that is, a photonic spin Hall effect is generated.

Description

TECHNICAL FIELD

[0001] The application relates to a visible band photonic 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 millimeter, 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 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 functions of the metasurface, in fact, its manufacture is constantly challenging the limit of current semiconductor process, 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 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 photonic spin Hall device based on a plasmonic metasurface, which can work in the visible light band, and the device has robustness to the incident angle of the incident light, that is, the device can work normally when the incident light is incident within the angle range of ±40° relative to the normal direction of the device.

[0005] In order to solve the above technical problems, the application provides a visible band photonic spin Hall device based on a plasmonic metasurface, comprising: an anisotropic metasurface, which is designed based on the PB geometric phase principle and is periodically arranged by supercell;

[0006] The supercell is arranged by homochiral superatoms every interval p and rotated by an angle of 180° relative to the first superatom; the superatom is a half-wave plate working in a broadband visible light band, that is, when left-handed or right-handed circularly polarized light is incident on the superatom, the reflected light is converted into right-handed or left-handed circularly polarized light;

[0007] The metasurface device reflects circularly polarized light in accordance with the generalized Snell's law when parallel circularly polarized light is incident, and left-handed and right-handed light is reflected in opposite directions, i.e., a spin Hall effect of photons is generated.

[0008] In a preferred embodiment: the superatom is composed of a three-layer structure and is placed on a silicon substrate, from top to bottom, a rectangular nanorod, a silicon dioxide layer, and a gold layer;

[0009] In a preferred embodiment: the material of the nanorod is one of Au, Ag, Al, and Na.

[0010] In a preferred embodiment: the material of the nanorod is Au, and the corresponding Drude model is:

[0011] The dielectric constant ε ∞ , the plasma frequency ω p , and the electron collision frequency γ are set to 12, 1.37×10 16 rad / s, and 1.05×10 14 s -1 , respectively.

[0012] In a preferred embodiment: the length, width, and thickness of the nanorod are 190 nm, 60 nm, and 60 nm, respectively.

[0013] In a preferred embodiment: the incidence and reflection laws of the metasurface are calculated by the generalized Snell's law:

[0014]

[0015] where θ r is the reflection angle of the reflected light, θ i is the incidence angle 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 arrangement.

[0016] When the phase of the first superatom is 0, the phase of the second superatom is The phase of the n-th superatom is

[0017] In a preferred embodiment: the metasurface device is designed according to a center wavelength of 632.8 nm, and the period of the superatom is 258 nm.

[0018] 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.

[0019] In a preferred embodiment: the size of the superatom S≥(17λ) 2 λ refers to the wavelength of the incident light. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 is a schematic diagram of a superatom in a preferred embodiment of the present application;

[0021] Figure 2 is a scanning electron microscope (SEM) image of a superatom in a preferred embodiment of the present application;

[0022] Figure 3 is a schematic diagram of the incident light and the reflected light in a preferred embodiment of the present application;

[0023] Figure 4 In a preferred embodiment:

[0024] a is a schematic diagram of the normalized reflection amplitudes of the x-polarized light and the y-polarized light after the linearly polarized light is incident on the superatom in a preferred embodiment of the present application;

[0025] b is a schematic diagram of the phases of the x-polarized light and the y-polarized light and the phase difference between them in a preferred embodiment of the present application;

[0026] c is a diagram of the rotation angle of each superatom and the corresponding PB phase in a period in a preferred embodiment of the present application;

[0027] Figure 5 is an angularly resolved spectrum observed in an experiment;

[0028] Figure 6 is a numerical simulation diagram;

[0029] Figure 7 is a schematic diagram of the distribution of left-handed light and right-handed light when the incident wavelength is 632.8 nm and the incident angle ranges from -40° to +40°. DETAILED DESCRIPTION

[0030] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the scope of protection of the present application.

[0031] In the description of the present application, it should be noted that the terms "upper", "lower", "inner", "outer", "top / bottom end" and the like indicate the orientation or positional relationship shown in the drawings, which is only for the convenience of describing the present application and simplifying the description, and does not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application. In addition, the terms "first", "second" are only for descriptive purposes and cannot be understood as indicating or implying relative importance.

[0032] In the description of the present application, it should be noted that unless otherwise explicitly specified and limited, the terms "mounting", "provided with", "sleeved / connected", "connected" and the like should be broadly understood, for example, "connected" can be wall-mounted connection, can also be detachable connection, or integral connection, can be mechanical connection, can also be electrical connection, can be directly connected, can also be indirectly connected through an intermediate medium, can be internal communication of two elements, and those skilled in the art can understand the specific meaning of the above terms in the present application according to the specific circumstances.

[0033] Reference Figures 1-4 The embodiment provides a visible band photonic spin Hall device based on a plasmonic super surface, which comprises: an anisotropic super surface, which is designed based on a PB geometric phase principle and is formed by periodic arrangement of super cells;

[0034] The super cells are arranged by homochiral super atoms every interval p and rotated by an angle of 20° in sequence, so that the last super atom of each super cell rotates 180° relative to the first super atom; the super atom is a half-wave plate working in a wide-frequency visible light band, that is, when left-handed or right-handed circularly polarized light is incident on the super atom, the reflected light changes into right-handed or left-handed circularly polarized light;

[0035] The super surface device reflects circularly polarized light in accordance with the generalized Snell's law under parallel circularly polarized light incidence, and left-handed light and right-handed light are reflected in opposite directions, that is, the photonic spin Hall effect is generated.

[0036] In the embodiment, the number of super atoms in a super cell is 9, and the rotation angle between adjacent two super atoms is 20°. Figure 4 As can be seen from c, by continuously rotating the nanorods at the top of the super atoms at different positions, each time by 20°, a total of 9 times, the super cells of the super surface are formed, is the rotation angle between adjacent super atoms, and the numbers 0-8 represent the phase coding. As can be seen from Figure 4 , under normal incidence of left-handed and right-handed light, the relationship between the rotation angle and the phase response is: that is, every rotation of the super atom will produce The additional phase is the PB phase.

[0037] Therefore, after incident visible circularly polarized light is reflected by anisotropic superatoms, the resulting reflected light acquires an additional geometric phase to form left-circularly polarized light and right-circularly polarized light, thereby achieving the effect of photon spin.

[0038] Further reference Figure 5 , Figure 5 The angle-resolved spectrum obtained in the experiment shows that the circular polarization is reflected in the broad visible light range from 600 nm to 800 nm. Left-handed and right-handed light are reflected in different directions, and the circular polarization is close to 100%, which proves that the effect of photon spin can indeed be obtained.

[0039] Using the formula for calculating the degree of circular polarization:

[0040] (I LCP –I RCP ) / (I LCP +I RCP )

[0041] RCP: Right-hand circular polarization, LCP: Left-hand circular polarization, I LCP Intensity of left-handed circularly polarized light, I RCP The intensity of right-handed circularly polarized light can be used to... Figure 5 The experimental environment shown was simulated and the results obtained are as follows. Figure 6 As shown in the figure. The simulation results agree well with the experimental results.

[0042] Figure 7 When light with an incident wavelength of 632.8 nm is incident at different angles (-40° to +40°) on the metasurface, the photonic spin Hall device functions normally. Therefore, the metasurface device exhibits robustness over a wide range of incident angles, meaning that the device functions normally even when parallel light is incident within a range of ±40° in the experiment.

[0043] 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 .

[0044] 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. As a simple alternative to this embodiment, within the visible light frequency range, the generalized Snell's law can be applied. The incident and reflection characteristics of the metasurface are calculated: 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 superatomic arrangement.

[0045] The result is: when the first superatom phase is 0, the second superatom phase is... The nth superatomic phase is For period p, with a fixed incident angle of 0°, a reflection angle of 16°, and an adjacent rotation angle of 20°, the size of period p varies from 157 to 314 nm across the entire visible light range (390-780).

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

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

[0048] As described above, these are merely preferred embodiments 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 are considered acts that infringe upon the protection scope of the present invention.

Claims

1. A visible-wavelength photonic spin Hall device based on a plasmonic metasurface, comprising: An anisotropic metasurface, designed based on the PB geometric phase principle, is composed of periodically arranged supercells; The supercell is composed of identical superatoms spaced at intervals p, and rotated sequentially. The superatoms are arranged at angles such that the last superatom of each supercell rotates 180° relative to the first superatom; the superatom is a half-wave plate that operates in the broadband visible light band, that is, when left-handed or right-handed circularly polarized light is incident on the superatom, the reflected light is converted into right-handed or left-handed circularly polarized light. When parallel circularly polarized light is incident on the metasurface device, the reflected circularly polarized light follows the generalized Snell's law, with left-handed and right-handed light being reflected in opposite directions, thus generating the spin Hall effect of photons.

2. The visible-wavelength photonic spin Hall device based on a plasmonic metasurface according to claim 1, characterized in that: The superatoms consist of a three-layer structure placed on a silicon substrate, consisting of a rectangular nanorod, a silicon dioxide layer, and a gold layer from top to bottom.

3. The visible-wavelength photonic spin Hall device based on a plasmonic metasurface according to claim 2, characterized in that: The nanorods are made of one of the following materials: Au, Ag, Al, and Na.

4. A visible-wavelength photonic spin Hall device based on a plasmonic metasurface according to claim 3, characterized in that: The nanorods are 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 .

5. A visible-wavelength photonic spin Hall device based on a plasmonic metasurface 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. A visible-wavelength photonic spin Hall device based on a plasmonic metasurface according to claim 1, characterized in that: The incident and reflection laws of the metasurface are 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 superatomic arrangement; When the first superatom phase is 0, the second superatom phase is The nth superatomic phase is 7. A visible-wavelength photonic spin Hall device based on a plasmonic metasurface according to claim 1, characterized in that: The metasurface device is designed with a center wavelength of 632.8 nm, and the period of the superatoms is 258 nm.

8. A visible-wavelength photonic spin Hall device based on a plasmonic 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.

9. A visible-wavelength photonic spin Hall device based on a plasmonic metasurface according to claim 1, characterized in that: The size of the metasurface is S≥(17λ). 2 λ refers to the wavelength of the incident light.

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