Linear optical chiral structure generalized composite phase metasurface design method

Abstract

The invention provides a linear optical chiral structure generalized composite phase metasurface design method. The method comprises the following steps: 1, designing a metasurface device; the metasurface device comprises a metal reflecting layer and a metal structure layer which are stacked from bottom to top, and the metal structure layer comprises a chiral metal unit structure with n-fold rotational symmetry; each chiral metal unit structure comprises three arc arms, and each arc arm comprises a cuboid and an arc; 2, when the left-hand circular polarization LCP light is incident, phase distribution of phi LCP = + 2n theta is generated, theta is a direction angle of the sub-wavelength structure, when the right-hand circular polarization LCP light is incident, phase distribution of phi RCP =-2n theta + betaA is generated, and betaA is an Ahalonov-Anandan AA phase; and 3, realizing independent regulation and control of the left-handed circularly polarized light and the right-handed circularly polarized light by adjusting the arc length and the rotation angle theta of the chiral structure. According to the invention, independent regulation and control of circularly polarized light can be well realized.

Description

Technical Field

[0001] The present invention relates to the technical field of electromagnetic wave phase and amplitude regulation, and specifically, to a design method for a generalized composite phase metasurface of a linear optical chiral structure. Background Art

[0002] Metasurfaces can flexibly regulate parameters such as the polarization, phase, and amplitude of electromagnetic waves by changing the shape and size of subwavelength structures, providing a new way for the miniaturization and integration development of optical systems, and have been widely used in fields such as holographic display, vector light field regulation, and polarization imaging. In nonlinear optics, multiple rotational symmetry structures are often used to achieve circular polarization multiplexing. When left-handed circularly polarized (LCP) light is incident, a phase of (m - 1)θ (m is the harmonic order, θ is the direction angle) is generated, while when right-handed circularly polarized (RCP) light is incident, the corresponding harmonic generates a phase of (m + 1)θ. Therefore, it is relatively easy to achieve circular polarization multiplexing using high-order harmonics in nonlinear optics.

[0003] In linear optics, most metasurfaces regulate the light wavefront based on traditional geometric phase, that is, when the structure direction angle θ varies in the range of 0 - 180°, the phase can cover the range of 0 - 360° (satisfying the relationship of Φ = ±2θ). And multiple rotational symmetry structures are generally considered isotropic in linear optics, that is, they do not have the ability to regulate phase. Recently, the concept of generalized geometric phase, i.e., Φ = ±2nθ, has been proposed for n (n is odd) - fold rotational symmetry structures, making the traditional geometric phase theory more perfect. However, limited by the spin symmetry of geometric phase, it is difficult to achieve independent regulation of left - and right - handed circularly polarized light in linear optics. To solve this problem, symmetric structures have been used to achieve circular polarization multiplexing based on the compound of transmission phase and generalized geometric phase. However, multiple structural parameters need to be designed, with a large design difficulty and a certain increase in manufacturing complexity. In addition, it is still unknown whether chiral structures can achieve independent regulation of LCP light and RCP light. In linear optics, whether a generalized composite phase metasurface can be designed using chiral structures has become an urgent problem to be solved. Summary of the Invention

[0004] The content of the present invention is to provide a design method for a generalized composite phase metasurface of a linear optical chiral structure, which can preferably achieve independent regulation of circularly polarized light.

[0005] According to a design method for a generalized composite phase metasurface of a linear optical chiral structure of the present invention, the following steps are included:

[0006] 1. Design a metasurface device;

[0007] The metasurface device includes a metal reflection layer and a metal structure layer stacked from bottom to top. Among them, the metal structure layer includes a chiral metal unit structure with n-fold rotational symmetry; the chiral metal unit structure includes three arc arms, and the arc arms include a cuboid and an arc.

[0008] Second, when left-handed circularly polarized LCP light is incident, a phase distribution of Φ LCP = +2nθ is generated, where θ is the direction angle of the sub-wavelength structure. When right-handed circularly polarized LCP light is incident, a phase distribution of Φ RCP = -2nθ + β A is generated, where β A is the Aharonov - Anandan AA phase.

[0009] Third, by adjusting the arc length and rotation angle θ of the chiral structure, independent control of left- and right-handed circularly polarized light is achieved.

[0010] Preferably, in the broadband range of 9 - 12 μm, the thickness t of the bottom metal reflection layer is 1 μm, and the thickness H of the top metal structure layer is 8.2 μm.

[0011] Preferably, the length L1 of the cuboid is 2.5 μm, and the width W is 1 μm.

[0012] Preferably, the coordinates of the center O1 corresponding to the arc are (-W / 2, 0), and the calculation formula for the arc center line is as follows:

[0013] x = L1cosα

[0014] y = L1sinα

[0015] In the formula, the value range of α is 0 - 70°. Translating the arc center line along the positive y-axis by W / 2 generates the outer contour line of the arc, and translating it along the negative y-axis by W / 2 forms the inner contour line of the arc. Closing and connecting the inner and outer contour lines of the arc finally forms the arc.

[0016] Preferably, the materials of the metal reflection layer and the metal structure layer are gold, silver, chromium, or copper.

[0017] Preferably, through the combination of the generalized geometric phase and the AA phase, when LCP light is incident, the phase remains unchanged, while when RCP light is incident, the phase covers the range of 0 - 360°, realizing independent control of circularly polarized light.

[0018] The beneficial effects of the present invention are as follows:

[0019] The present invention can preferably achieve independent control of circularly polarized light. Using a single metasurface device, different functions can be realized by controlling the polarization state of the incident light, which is convenient for multi-functional integration and can be used in fields such as polarization imaging, holographic display, and information coding. Description of the Drawings

[0020] Figure 1 It is a schematic structural diagram of the metasurface device in the embodiment;

[0021] Figure 2 It is a top-view structural schematic diagram of the metasurface device in the embodiment;

[0022] Figure 3(a) is a curve graph of the generalized geometric phase distribution of the structure when LCP light is incident in the embodiment and θ varies in the range of 0 - 50°;

[0023] Figure 3(b) is a curve graph of the generalized geometric phase distribution of the structure when RCP light is incident in the embodiment and θ varies in the range of 0 - 50°;

[0024] Figure 4(a) is the AA phase distribution curve when LCP light is incident in the embodiment and the circular arc angle α varies in the range of 0 - 40°;

[0025] Figure 4(b) is the AA phase distribution curve when RCP light is incident in the embodiment and the circular arc angle α varies in the range of 0 - 40°. Detailed implementation manners

[0026] To further understand the content of the present invention, the present invention will be described in detail with reference to the accompanying drawings and embodiments. It should be understood that the embodiments are only for explaining the present invention rather than limiting it.

[0027] Embodiment

[0028] This embodiment provides a design method for a generalized composite phase metasurface of a linear optical chiral structure, which includes the following steps:

[0029] 1. Design the metasurface device;

[0030] As shown in Figure 1 and Figure 2 , the metasurface device includes a metal reflection layer and a metal structure layer stacked from bottom to top. Among them, the metal structure layer includes a chiral metal unit structure with n-fold rotational symmetry; the chiral metal unit structure includes three circular arc arms, and the circular arc arms include a cuboid and a circular arc. Figure 1 and Figure 2 , the metal reflection layer is a cube with a side length of P and a height of t.

[0031] In the broadband range of 9 - 12 μm, the thickness t of the bottom metal reflection layer is 1 μm, and the thickness H of the top metal structure layer is 8.2 μm. The length L1 of the cuboid is 2.5 μm, and the width W is 1 μm. The coordinates of the center O1 corresponding to the circular arc are (-W / 2, 0), and the calculation formula of the circular arc center line (dotted line) is as follows:

[0032] x = L1cosα

[0033] y = L1sinα

[0034] In the formula, the value range of α is 0 - 70°. Translating the center line of the arc along the positive y-axis by W / 2 generates the outer contour line of the arc, and translating it along the negative y-axis by W / 2 forms the inner contour line of the arc. The inner and outer contour lines of the arc are closed and connected to finally form the arc.

[0035] Rotate the arc arm composed of 1 cuboid and 1 arc counterclockwise around the center O by 120° and 240° and copy and stack them to make a single C3 chiral structure (n = 3). In addition, further rotation can form multiple rotation symmetry (Cn) structures such as C5 and C7. The materials of the bottom metal reflection layer and the top structure layer of the chiral structure are both gold (Au). The material parameters can be found in the Palik material handbook, and the material can be replaced with metals such as silver, chromium, and copper. Among them, the arc can be replaced with a cuboid, a spiral shape, or other shapes to form the chiral structure.

[0036] II. When left-handed circularly polarized LCP light is incident, Φ LCP = +2nθ phase distribution is generated, where θ is the direction angle of the sub-wavelength structure. When right-handed circularly polarized LCP light is incident, Φ RCP = -2nθ + β A phase distribution is generated, where β A is the Aharonov - Anandan AA phase.

[0037] Specifically, when LCP light and RCP light are incident, different phase distributions can be obtained by designing the structure rotation angle and the arc arm size (achieved by changing α) as follows:

[0038] Φ LCP = 6θ

[0039] Φ RCP = -6θ + β A

[0040] Among them, ±6θ is the generalized geometric phase, which is generated by changing the structure rotation angle θ (varying in the range of 0 - 60°), as shown in Figures 3(a) and 3(b); and β A is achieved by changing the arc length, that is, adjusting the angle α. When α varies in the range of 0 - 40°, when LCP light is incident, β A is basically unchanged, as shown in Figure 4(a). When RCP light is incident, β A can cover the range of 0 - 360°, that is, the AA phase is generated, as shown in Figure 4(b). The combination of the two can achieve independent control of circularly polarized light. The results show that in linear optics, through the combination of the generalized geometric phase and the AA phase, different phase controls of LCP light and RCP light can be achieved using this structure, realizing circular polarization multiplexing.

[0041] III. By adjusting the arc length and rotation angle θ of the chiral structure, independent control of left- and right-handed circularly polarized light can be achieved. Through the combination of the generalized geometric phase and the AA phase, when LCP light is incident, the phase remains unchanged, while when RCP light is incident, the phase covers the range of 0 - 360°, realizing independent control of circularly polarized light.

[0042] The above has schematically described the present invention and its implementation manners. This description is not restrictive, and only one of the implementation manners of the present invention is shown in the drawings. The actual structure is not limited thereto. Therefore, if those of ordinary skill in the art are inspired by it and, without departing from the gist of the present invention, design similar structural manners and embodiments to this technical solution without creative efforts, they shall fall within the protection scope of the present invention.

Claims

1. A design method for a generalized composite phase metasurface of a linear optical chiral structure, characterized in that: It includes the following steps:

1. Design a metasurface device; The metasurface device includes a metal reflection layer and a metal structure layer stacked from bottom to top. Among them, the metal structure layer includes a chiral metal unit structure with n-fold rotational symmetry; the chiral metal unit structure includes three arc arms, and the arc arms include a cuboid and an arc; II. When left-handed circularly polarized (LCP) light is incident, a phase distribution of Φ LCP = +2nθ is generated, where θ is the direction angle of the sub-wavelength structure. When right-handed circularly polarized (RCP) light is incident, a phase distribution of Φ RCP = -2nθ + β A is generated, where β A is the Aharonov - Anandan (AA) phase; 3. By adjusting the arc length and rotation angle θ of the chiral structure, independent control of left- and right-handed circularly polarized light is achieved.

2. The design method of a generalized composite-phase metasurface with a linear optical chiral structure according to claim 1, characterized in that: In the broadband range of 9 - 12 μm, the thickness t of the bottom metal reflection layer is 1 μm, and the thickness H of the top metal structure layer is 8.2 μm.

3. A design method for a generalized composite-phase metasurface of a linear optical chiral structure according to claim 2, characterized in that: The length L1 of the cuboid is 2.5 μm, and the width W is 1 μm.

4. A design method of a generalized composite-phase metasurface with a linear optical chiral structure according to claim 3, characterized in that: The coordinates of the center O1 corresponding to the arc are (-W / 2, 0), and the calculation formula for the arc center line is as follows: x = L1cosα y = L1sinα In the formula, the value range of α is 0 - 70°. Translate the arc center line along the positive y-axis by W / 2 to generate the outer contour line of the arc, and translate it along the negative y-axis by W / 2 to form the inner contour line of the arc. Connect the inner and outer contour lines of the arc to form the arc.

5. A design method for a generalized composite-phase metasurface of a linear optical chiral structure according to claim 4, characterized in that: The materials of the metal reflection layer and the metal structure layer are gold, silver, chromium or copper.

6. A design method of a generalized composite-phase metasurface with a linear optical chiral structure according to claim 5, characterized in that: Through the combination of generalized geometric phase and AA phase, when LCP light is incident, the phase remains unchanged, while when RCP light is incident, the phase covers the range of 0 - 360°, realizing independent control of circularly polarized light.

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