A linear optical chiral structure generalized complex phase metasurface design method

Abstract

The application provides a linear optical chiral structure generalized composite phase super-structure design method, which comprises the following steps: 1, designing a super-structure device; the super-structure device comprises a metal reflection layer and a metal structure layer stacked from bottom to top, wherein the metal structure layer comprises a chiral metal unit structure with n-fold rotational symmetry; the chiral metal unit structure comprises three circular arc arms, and each circular arc arm comprises a cuboid and a circular arc; 2, when left-handed circularly polarized LCP light is incident, a phase distribution of Φ LCP =+2nθ is generated, wherein θ is a directional angle of a sub-wavelength structure; and when right-handed circularly polarized LCP light is incident, a phase distribution of Φ RCP =-2nθ+β A is generated, wherein β A is an Aharonov-Bohm AA phase; and 3, by adjusting the circular arc length and the rotation angle θ of the chiral structure, left-handed and right-handed circularly polarized light can be independently controlled. The application can preferably realize independent control of circularly polarized light.

Description

Technical Field

[0001] This invention relates to the field of electromagnetic wave phase and amplitude modulation technology, and more specifically, to a method for designing a linear optical chiral structure generalized composite phase metasurface. Background Technology

[0002] Metasurfaces, by altering the shape and size of their subwavelength structures, flexibly control parameters such as polarization, phase, and amplitude of electromagnetic waves, providing new avenues for the miniaturization and integration of optical systems. They have been widely applied in fields such as holographic displays, vector light field manipulation, and polarization imaging. In nonlinear optics, circular polarization multiplexing is often achieved using multiple rotationally symmetric structures. When left-hand LCP light is incident, it produces a phase of (m-1)θ (where m is the harmonic order and θ is the direction angle), while when RCP light is incident, the corresponding harmonic produces a phase of (m+1)θ. Therefore, circular polarization multiplexing can be easily achieved in nonlinear optics using higher-order harmonics.

[0003] In linear optics, most metasurfaces rely on conventional geometric phase modulation of the wavefront, meaning that when the structural orientation angle θ varies from 0 to 180°, the phase can cover a range of 0 to 360° (satisfying the relationship Φ = ±2θ). However, multi-rotational symmetry structures are generally considered isotropic in linear optics, meaning they lack phase modulation capabilities. Recently, the concept of generalized geometric phase (Φ = ±2nθ) has been proposed for n (where n is odd) multi-rotational symmetry structures, further refining the conventional geometric phase theory. However, due to the spin symmetry of the geometric phase, independent modulation of left- and right-hand circularly polarized light is difficult to achieve in linear optics. To address this issue, circular polarization multiplexing has been achieved using symmetric structures based on the combination of transmission phase and generalized geometric phase. However, this requires designing multiple structural parameters, which is challenging and increases manufacturing complexity. Furthermore, whether chiral structures can achieve independent modulation of LCP and RCP light remains unknown. Therefore, the ability to design generalized composite phase metasurfaces using chiral structures in linear optics has become a pressing problem. Summary of the Invention

[0004] The present invention provides a method for designing a generalized composite phase metasurface with linear optical chiral structure, which can better achieve independent control of circularly polarized light.

[0005] A method for designing a linear optical chiral structure generalized composite phase metasurface according to the present invention includes the following steps:

[0006] I. Design of metasurface devices;

[0007] The super-structured surface device comprises a metal reflection layer and a metal structure layer stacked from bottom to top, wherein the metal structure layer comprises a chiral metal unit structure with n-fold rotational symmetry; the chiral metal unit structure comprises three circular arc arms, and each circular arc arm comprises a cuboid and a circular arc.

[0008] II. When left-handed circularly polarized (LCP) light is incident, a phase distribution of Φ LCP = +2nθ is generated, wherein θ is a directional angle of the sub-wavelength structure, and when right-handed circularly polarized (RCP) light is incident, a phase distribution of Φ RCP = -2nθ+β A is generated, wherein β A is an Aharonov-Annandam (AA) phase;

[0009] III. By adjusting the length of the circular arc and the rotation angle θ of the chiral structure, left-handed and right-handed circularly polarized light can be independently controlled.

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

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

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

[0013] x = (L1-W / 2)cosα

[0014] y = (L1-W / 2)sinα

[0015] In the formula, the value range of α is 0-70°, the center line of the circular arc is translated outward along the radial direction by W / 2 to generate an outer contour line of the circular arc, and is translated inward along the radial direction by W / 2 to generate an inner contour line of the circular arc, the inner and outer contour lines of the circular arc are closed and connected, and finally the circular arc is formed.

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

[0017] Preferably, by combining the generalized geometric phase and the AA phase, when LCP light is incident, the phase is unchanged, and when RCP light is incident, the phase covers a range of 0-360°, thereby realizing independent control of circularly polarized light.

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

[0019] The present application can preferably realize independent control of circularly polarized light, and by controlling the polarization state of incident light, different functions can be realized by using a single super-structured surface device, which is convenient for multi-functional integration and can be used in the fields of polarization imaging, holographic display, information coding and the like. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 Structure schematic diagram of the super-structured surface device in the embodiment;

[0021] Figure 2 Structure schematic diagram of the super-structured surface device in the embodiment;

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

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

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

[0025] Figure 4(b) is an AA phase distribution curve when the circular arc angle α changes in the range of 0-40° when RCP light is incident in the embodiment. DETAILED DESCRIPTION

[0026] In order to further understand the content of the present application, the present application will be described in detail in conjunction with the drawings and embodiments. It should be understood that the embodiments are only used to explain the present application but not to limit the present application.

[0027] Embodiment

[0028] The present embodiment provides a linear optical chiral structure generalized complex phase super-structured surface design method, which comprises the following steps:

[0029] I. Designing a super-structured surface device;

[0030] As shown in Figure 1 and Figure 2 , the super-structured surface device comprises a metal reflection layer and a metal structure layer stacked from bottom to top, wherein the metal structure layer comprises a chiral metal unit structure with n-fold rotational symmetry; the chiral metal unit structure comprises three circular arc arms, and the circular arc arm comprises a cuboid and a circular arc. Figure 1 and Figure 2 In and, the metal reflection layer is a square with a side length of P and a height of t.

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

[0032] x = (L1-W / 2)cosα

[0033] y = (L1-W / 2)sin a

[0034] In the formula, the value range of a is 0-70°, the middle line of the circular arc is translated outward along the radial direction by W / 2 to generate the outer contour line of the circular arc, and is translated inward along the radial direction by W / 2 to generate the inner contour line of the circular arc, the inner and outer contour lines of the circular arc are connected to form a circular arc.

[0035] The circular arc arm composed of one cuboid and one circular arc is rotated counterclockwise by 120° and 240° around the center O and is copied and superimposed to form a single C3 chiral structure (n=3). In addition, rotation can further constitute C5, C7 and other multiple rotational symmetries (Cn) structures. The bottom metal reflection layer and the top structure layer material of the chiral structure are both gold (Au), and the material parameters are shown in the Palik Material Handbook. The material can be replaced by silver, chromium, copper and other metals. Among them, the circular arc can be replaced by a cuboid, a helical shape, or other shapes to form a chiral structure.

[0036] II. When left-handed circularly polarized (LCP) light is incident, a phase distribution of Φ LCP =+2nθ is generated, where θ is the directional angle of the subwavelength structure, and 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.

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

[0038] Φ LCP =6θ

[0039] Φ RCP =-6θ+β A

[0040] Where ±6θ is the generalized geometric phase generated by changing the structure rotation angle θ (0-60° range), as shown in FIG. 3(a) and FIG. 3(b); and β A By changing the length of the circular arc, i.e. adjusting the angle a, when a changes in the range of 0-40°, β A is basically unchanged when LCP light is incident, as shown in FIG. 4(a). When RCP light is incident, β A can cover the range of 0-360°, i.e. the AA phase is generated, as shown in FIG. 4(b), and the combination of the two can realize independent control of circularly polarized light. The results show that in linear optics, by combining the generalized geometric phase and the AA phase, different phase controls of LCP light and RCP light can be achieved by using the structure, and circular polarization multiplexing is realized.

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

[0042] The above describes the present application and its embodiments in a schematic manner, which is not restrictive, and the embodiments shown in the drawings are only one of the embodiments of the present application, and the actual structure is not limited thereto. Therefore, if a person skilled in the art is inspired by it, without departing from the purpose of the present application, similar structural modes and embodiments are not creatively designed, which should belong to the protection scope of the present application.

Claims

1. A method for designing a generalized complex phase metasurface with linear optical chiral structures, characterized in that: Comprising the following steps: I. Designing a metasurface device; The metasurface device comprises a metal reflection layer and a metal structure layer stacked from bottom to top, wherein the metal structure layer comprises a chiral metal unit structure with n-fold rotational symmetry; the chiral metal unit structure comprises three circular arc arms, and the circular arc arm comprises a cuboid and a circular arc; The circular arc corresponds to the coordinate (-W / 2, 0) of the center O1, and the center line of the circular arc is calculated as follows: x=(L1-W / 2)cosα y=(L1-W / 2)sinα In the formula, L1 and W are the length and width of the cuboid, and the value range of α is 0-70°; the center line of the circular arc is translated outward along the radial direction by W / 2 to generate the outer contour line of the circular arc, and is translated inward along the radial direction by W / 2 to generate the inner contour line of the circular arc; the inner and outer contour lines of the circular arc are closed and connected, and finally the circular arc is formed; II. When left-handed circularly polarized (LCP) light is incident, a phase distribution of Φ = +2nθ is produced, where θ is the azimuthal angle of the subwavelength structure LCP ; and when right-handed circularly polarized (RCP) light is incident, a phase distribution of Φ = -2nθ + β RCP is produced, where β A is the Aharonov- Anatdan (AA) phase A . III. By adjusting the circular arc length and rotation angle θ of the chiral structure, the independent regulation of left and right circularly polarized light is realized.

2. The method of claim 1, wherein the linear optical chiral structure generalized complex phase meta-surface design method is characterized by: In the broadband range of 9-12 μm, the thickness of the bottom metal reflection layer is t=1 μm, and the thickness of the top metal structure layer is H=8.2 μm.

3. The method of claim 2, wherein the linear optical chiral structure generalized complex phase meta-surface design method is characterized by: The length of the cuboid L1 is 2.5 μm, and the width W is 1 μm.

4. The method of claim 3, wherein the linear optical chiral structure generalized complex phase meta-surface design method is characterized by: The materials of the metal reflection layer and the metal structure layer are gold, silver, chromium or copper.

5. The method of claim 4, wherein the generalized complex phase metasurface design is a linear optical chiral structure. 5 By combining the generalized geometric phase and the AA phase, when LCP light is incident, the phase remains unchanged, and when RCP light is incident, the phase covers the range of 0-360°, realizing independent regulation of circularly polarized light.

Images