Metasurface based on mirror symmetry for full-space 1-bit phase control

Abstract

The application provides a mirror-symmetry-based full-space 1-bit phase control super surface, which comprises a plurality of structure units, wherein the plurality of structure units comprise: a support layer, a reflection component located on one side surface of the support layer and located at a first position or a second position, wherein the reflected light beam has a first phase when the reflection component is at the first position, and the reflected light beam has a second phase when the reflection component is at the second position; and a transmission component located on the side surface of the support layer away from the reflection component; a first through hole is formed on the transmission component, and the first through hole is located at a third position or a fourth position; the transmitted light beam has a third phase when the first through hole is at the third position, and the transmitted light beam has a fourth phase when the transmission component is at the fourth position.

Description

Technical Field

[0001] This invention relates to the field of optics, and in particular to a metasurface based on mirror symmetry and full-space 1-bit phase modulation. Background Technology

[0002] Metasurfaces, as two-dimensional artificially designed electromagnetic materials, offer new insights for the miniaturization and functional integration of terahertz devices by flexibly controlling the amplitude, phase, and polarization state of electromagnetic waves through subwavelength-level structural units. However, the transmission and reflection spaces of traditional metasurfaces are difficult to fully utilize. Therefore, researchers have increasingly focused on metasurfaces with full-space control capabilities. Currently, full-space metasurfaces mainly achieve control through frequency reuse, polarization reuse, and incident direction reuse. Furthermore, although some full-space designs can achieve full-space wavefront control under incident light conditions of the same frequency, propagation direction, and polarization state, they cannot truly achieve independent wavefront control of the transmission and reflection spaces under the same incident conditions. Summary of the Invention

[0003] In view of this, the present invention provides a metasurface based on mirror symmetry and full-space 1-bit phase modulation, comprising multiple structural units, wherein the multiple structural units include:

[0004] Support layer;

[0005] A reflective component is located on one side surface of the support layer, and is in either a first position or a second position. The projection of the reflective component onto a preset plane when it is in the first position and the projection of the reflective component onto the preset plane when it is in the second position are mirror-symmetrical with respect to a target axis. The preset plane is a plane perpendicular to the height direction of the structural unit. The target axis is a straight line passing through a target point, and the target point is the center point of the projection of the structural unit onto the preset plane. The reflective component is adapted to reflect a received incident light beam to obtain a reflected light beam perpendicular to the polarization direction of the incident light beam. When the reflective component is in the first position, the reflected light has a first phase, and when the reflective component is in the second position, the reflected light beam has a second phase.

[0006] A transmission component is located on the side of the support layer away from the reflective component. A first through-hole is formed on the transmission component. The first through-hole is located in a third position or a fourth position. When the transmission component is located in the third position, its projection on the preset plane and when it is located in the fourth position are mirror-symmetrical with respect to the target axis. The transmission component is adapted to transmit an incident light beam that passes sequentially through the reflective component and the support layer, and obtain a transmitted light beam with a polarization direction opposite to that of the incident light beam. When the first through-hole is located in the third position, the transmitted light beam has a third phase, and when the transmission component is located in the fourth position, the transmitted light beam has a fourth phase.

[0007] According to an embodiment of the present invention, the reflective component includes a U-shaped metal ring and a metal strip, both located on the support layer;

[0008] The first through hole is a U-shaped hole, and the opening direction of the U-shaped metal ring and the U-shaped hole are perpendicular.

[0009] According to an embodiment of the present invention, the two parallel arms of the U-shaped metal ring extend in the same direction as the metal strip.

[0010] According to an embodiment of the present invention, the polarization direction of the incident light is a first direction, and the support layer includes:

[0011] First sub-support layer, the reflective component is located on the first sub-support layer;

[0012] A transmission polarization selection layer is located on the side surface of the first sub-support layer away from the reflective component. A second through-hole extending along the first direction is formed on the transmission polarization selection layer for polarization filtering of the incident light beam passing through the first sub-support layer.

[0013] The second sub-support layer is located on the side surface of the transmission polarization selection layer away from the first sub-support layer.

[0014] According to an embodiment of the present invention, when the metasurface is used as a reflective grating, the positions of the reflective components of each of the plurality of structural units are determined based on the diffraction order of the reflective grating, the size of the unit structure, and the position of the structural unit;

[0015] When the transmitted light is used as a grating, the position of the first through-hole of each of the plurality of structural units is determined according to the diffraction order of the transmission grating, the size of the unit structure, and the position of the structural unit.

[0016] According to an embodiment of the present invention, when the metasurface is used as a reflective Fresnel lens, the positions of the reflective components of each of the plurality of structural units are determined based on the focal length of the reflective Fresnel lens and the positions of the structural units;

[0017] When the metasurface is used as a transmissive Fresnel lens, the position of the first through-hole of each of the plurality of structural units is determined according to the focal length of the transmissive Fresnel lens and the position of the structural unit.

[0018] According to an embodiment of the present invention, when the metasurface is used as a reflective vortex beam generator, the positions of the reflective components of each of the plurality of structural units are determined according to the topology number and focal length of the reflective vortex beam generator and the positions of the structural units;

[0019] When the metasurface is used as a transmissive vortex beam generator, the position of the first through-hole of each of the plurality of structural units is determined according to the topology number and focal length of the transmissive vortex beam generator and the position of the structural unit.

[0020] According to an embodiment of the present invention, when the metasurface is used as a reflective holographic imaging structure, the positions of the reflective components of each of the plurality of structural units are determined based on the light intensity distribution of the target holographic image, the size of the structural unit, and the phase distribution of the target holographic image;

[0021] When the metasurface is used as a transmission holographic imaging structure, the positions of the first through holes of each of the plurality of structural units and the positions of the reflective components of each of the plurality of structural units are determined based on the light intensity distribution of the target holographic image, the size of the structural unit, and the phase distribution of the target holographic image.

[0022] According to an embodiment of the present invention, the incident light is a terahertz wave.

[0023] According to an embodiment of the present invention, for one of the structural units, by controlling the reflective component to be located at a mirror-symmetrical first position or a second position, the phase of the reflected beam can be either a first phase or a second phase, and the phase difference between the first phase and the second phase is 180°. By controlling the first through-hole of the transmission component to be located at a mirror-symmetrical third position or a fourth position, the phase of the transmitted beam can be either a third phase or a fourth phase, and the phase difference between the two phases is 180°.

[0024] According to an embodiment of the present invention, since the metasurface of the present invention comprises multiple structural units, by controlling the positions of the reflective components and the first through-holes of each of the multiple structural units of the metasurface, each structural unit can modulate the phase of its corresponding reflected beam and transmitted beam, thereby achieving individual control of the wavefronts of the reflected light (including the reflected beams corresponding to each of all structural units) and the transmitted light (including the transmitted beams corresponding to each of all structural units). By utilizing the collaborative design of the reflective and transmitted components, the wavefront modulation of the transmitted light and the reflected light is completely decoupled, and the two do not interfere with each other, thus achieving independent 1-bit phase modulation of the incident light's reflected and transmitted light. Attached Figure Description

[0025] The above and other objects, features and advantages of the present invention will become more apparent from the following description of embodiments of the invention with reference to the accompanying drawings, in which:

[0026] Figure 1 This is a three-dimensional view of a metasurface based on mirror symmetry and full-space 1-bit phase modulation, provided according to an embodiment of the present invention.

[0027] Figure 2 It is a three-dimensional diagram of the structural unit.

[0028] Figure 3 These are the coordinate axes before and after the mirror-symmetric transformation provided in the embodiments of the present invention.

[0029] Figure 4 These are the phase curves of the reflected and transmitted light corresponding to the basic units "00" and "01" provided in the embodiments of the present invention.

[0030] Figure 5 These are the phase curves of reflected and transmitted light of the basic units "00" and "10" provided according to embodiments of the present invention.

[0031] Figure 6 This is an amplitude curve diagram of reflected light and transmitted light corresponding to the basic units "00" and "01" provided in the embodiments of the present invention.

[0032] Figure 7 This is an amplitude curve diagram of reflected light and transmitted light corresponding to the basic units "00" and "10" provided in the embodiments of the present invention.

[0033] Figure 8 This is the phase arrangement diagram of the reflection space in Example 1.

[0034] Figure 9 This is a schematic diagram of the Fresnel lens principle.

[0035] Figure 10 This is the phase arrangement diagram of the transmission space in Example 1.

[0036] Figure 11 The elevation angle of the grating in the reflection space in Example 1. and azimuth The relationship diagram.

[0037] Figure 12 It is the Fresnel lens in the transmission space of Example 1. Light intensity distribution diagram of a plane.

[0038] Figure 13 yes Figure 11 Pick Light intensity curve along the z-direction.

[0039] Figure 14 It is the main focal point. Light intensity distribution diagram of a plane.

[0040] Figure 15 Yes Figure 14 Pick Light intensity curve along the x-direction.

[0041] Figure 16 This is the phase arrangement diagram of the reflection space of the metasurface in Example 2.

[0042] Figure 17 This is the light intensity distribution map of the target holographic image in Example 2.

[0043] Figure 18 This is the phase arrangement diagram of the transmission space of the metasurface in Example 2.

[0044] Figure 19 This is a light intensity distribution diagram at the focal point of the vortex beam in the reflection space in Example 2.

[0045] Figure 20 This is a diagram showing the optical phase distribution at the focal point of the vortex beam in the reflection space in Example 2.

[0046] Figure 21 It is the vortex beam in the reflected space in Example 2. Light intensity distribution diagram of a plane.

[0047] Figure 22 This is the light intensity distribution at the holographic image imaging location in the transmission space in Example 2.

[0048] Figure 23 This is the light phase distribution map at the imaging position of the holographic image in the transmission space in Example 2.

[0049] Explanation of reference numerals in the attached figures

[0050] 1: Metasurface

[0051] 110: Structural Unit

[0052] 111: Support layer

[0053] 1111: First Sub-Support Layer

[0054] 1112: Transmission polarization selection layer

[0055] 1112-1: Second through hole

[0056] 1113: Second Sub-support Layer

[0057] 112: Reflective component

[0058] 1121: U-shaped metal ring

[0059] 1122: Metal strip

[0060] 113: Transmission Component

[0061] 1131: First through hole Detailed Implementation

[0062] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to specific embodiments and accompanying drawings.

[0063] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the invention. The terms “comprising,” “including,” etc., as used herein indicate the presence of the stated features, steps, operations, and / or components, but do not exclude the presence or addition of one or more other features, steps, operations, or components.

[0064] All terms used herein, including technical and scientific terms, have the meanings commonly understood by those skilled in the art, unless otherwise defined. It should be noted that the terms used herein are to be interpreted in a manner consistent with the context of this specification, and not in an idealized or overly rigid way.

[0065] When using expressions such as "at least one of A, B, and C," the meaning should generally be interpreted according to the understanding of someone skilled in the art. For example, "a system having at least one of A, B, and C" should include, but is not limited to, systems having A alone, having B alone, having C alone, having A and B, having A and C, having B and C, and / or having A, B, and C. Similarly, when using expressions such as "at least one of A, B, or C," the meaning should generally be interpreted according to the understanding of someone skilled in the art. For example, "a system having at least one of A, B, or C" should include, but is not limited to, systems having A alone, having B alone, having C alone, having A and B, having A and C, having B and C, and / or having A, B, and C.

[0066] It should also be noted that the directional terms mentioned in the embodiments, such as "up," "down," "front," "back," "left," and "right," are only for reference to the directions in the accompanying drawings and are not intended to limit the scope of protection of the present invention. Throughout the accompanying drawings, the same elements are represented by the same or similar reference numerals. Conventional structures or constructions will be omitted where they may cause confusion in understanding the present invention.

[0067] Figure 1 This is a three-dimensional view of a metasurface based on mirror symmetry and full-space 1-bit phase modulation, provided according to an embodiment of the present invention.

[0068] like Figure 1 As shown, the metasurface 1 includes multiple structural units 110. The multiple structural units 110 are arranged in an array.

[0069] Figure 2 It is a three-dimensional diagram of the structural unit.

[0070] like Figure 2 As shown, each structural unit 110 includes: a support layer 111, a reflective component 112, and a transmission component 113. The reflective component 112 is located on one side surface of the support layer 111 and is located in either a first position or a second position. The projection of the reflective component 112 onto a preset plane when it is in the first position and the projection of the reflective component 112 onto the preset plane when it is in the second position are mirror-symmetrical with respect to the target axis. The preset plane is a plane perpendicular to the height direction of the structural unit 110, the target axis is a straight line passing through a target point, and the target point is the center point of the projection of the structural unit onto the preset plane. The reflective component 112 is adapted to reflect the received incident light beam to obtain a reflected light beam perpendicular to the polarization direction of the incident light beam. When the reflective component 112 is in the first position, the reflected light beam has a first phase, and when the reflective component 112 is in the second position, the reflected light beam has a second phase. The transmission component 113 is located on the surface of the support layer 111 away from the reflective component 112. A first through-hole 1131 is formed on the transmission component 113. The first through-hole 1131 is located in a third position or a fourth position. When the transmission component 113 is located in the third position, its projection onto a preset plane is mirror-symmetrical with respect to the target axis as it is located in the fourth position. The transmission component 113 is suitable for transmitting an incident light beam that passes sequentially through the reflective component 112 and the support layer 111, and obtaining a transmitted light beam with a polarization direction opposite to that of the incident light beam. When the first through-hole 1131 is located in the third position, the transmitted light beam has a third phase, and when the transmission component 113 is located in the fourth position, the transmitted light beam has a fourth phase.

[0071] According to an embodiment of the present invention, for one of the structural units, by controlling the reflective component to be located in a mirror-symmetrical first or second position, the phase of the reflected beam can be either a first phase or a second phase, and the phase difference between the first phase and the second phase is 180°. By controlling the first through-hole 1131 of the transmission component to be located in a mirror-symmetrical third or fourth position, the phase of the transmitted beam can be either a third phase or a fourth phase, and the phase difference between the two phases is 180°.

[0072] According to an embodiment of the present invention, since the metasurface 1 includes multiple structural units 110, by controlling the positions of the reflective components 112 and the first through-hole 1131 of each of the multiple structural units 110 of the metasurface 1, each structural unit can modulate the phase of its corresponding reflected beam and transmitted beam, thereby achieving individual control of the wavefronts of the reflected light (including the reflected beams corresponding to each of all structural units) and the transmitted light (including the transmitted beams corresponding to each of all structural units). By utilizing the collaborative design of the reflective and transmitted components, the wavefront modulation of the transmitted and reflected light is completely decoupled, and the two do not interfere with each other, thus achieving independent 1-bit phase modulation of the incident light's reflected and transmitted light.

[0073] According to embodiments of the present invention, the following is combined with Figure 3 The principle is explained in detail: when the position of the reflecting component or the first through-hole changes symmetrically, the phase difference between the emitted beam (reflected beam or transmitted beam) is 180°. This principle explanation applies to both reflected and transmitted beams. In this principle explanation, the reflecting component 112 and the first through-hole 1131, whose positions change symmetrically in the structural unit, are collectively referred to as the conversion structure.

[0074] Figure 3 These are the coordinate axes before and after the mirror-symmetric transformation provided in the embodiments of the present invention.

[0075] like Figure 3 As shown, the transformation structure in structural unit 110 is mirror-symmetric before employing... Figure 1 We will study it using the xoy coordinate system. In the xoy coordinate system, the incident beam... The phase change after structural transformation can be represented by the Jones matrix. This indicates the emitted beam (reflected beam or transmitted beam) of the structural unit. It can be expressed as equation (1).

[0076]

[0077] in, , These are the incident beams Complex amplitude in the x and y directions; , These are the emitted beams Complex amplitude in the x and y directions.

[0078] Next, consider the transformation structure with respect to any rotation angle as... The change in the emitted beam after mirroring the target axis. Along Figure 3 Let the axis after mirroring the dashed axis in the coordinate system be x'oy'. In the x'oy' coordinate system, the Jones matrix corresponding to the transformed structure after mirroring is... Then the outgoing beam of the conversion structure at this time With the incident beam The relationship can be expressed as equation (2).

[0079]

[0080] Note that the spatial coordinates of the transformed structure after mirror symmetry in the x'oy' coordinate system are the same as the spatial coordinates of the transformed structure before mirror symmetry in the xoy coordinate system. Therefore, we have:

[0081]

[0082] Since we need to study the transformation structure before and after mirror symmetry in the same coordinate system, we first determine the coordinate transformation matrix between the xoy and x'oy' coordinate systems based on geometric relationships:

[0083]

[0084] therefore and , and The following transformation relationship exists:

[0085] According to formula (5), the output beam of the mirror-symmetric transformation structure in the xoy coordinate system can be obtained. With the incident beam Relationship:

[0086]

[0087] , These are the emitted beams Complex amplitudes of the x and y components.

[0088] Expanding formula (6), we obtain the expression for the outgoing beam of the mirror-symmetric structure in the xoy coordinate system as follows:

[0089]

[0090] In this invention, the incident beam can be Linearly polarized light, i.e. At the same time, the target axis that makes the transformation structure mirror-symmetric is horizontal, i.e. Then formula (1) can be simplified to:

[0091]

[0092] Formula (7) can be simplified to:

[0093]

[0094] Comparing formulas (8) and (9), we can conclude that:

[0095]

[0096] The above explains the phase difference between the cross-polarized output light of the structural unit after mirroring and that before symmetry. Meanwhile, the phase of co-polarized light remains unchanged. Furthermore, since there is [a certain characteristic] at every frequency... Therefore, this conclusion holds true across the entire frequency band.

[0097] According to an embodiment of the present invention, the reflective component 112 includes a U-shaped metal ring 1121 and a metal strip 1122 both located on the support layer 111. The first through hole 1131 of the transmission component 113 is a U-shaped hole, and the opening directions of the U-shaped metal ring and the U-shaped hole are perpendicular. The U-shaped hole of the transmission component is perpendicular to the opening direction of the U-shaped metal ring of the reflective component, which can avoid electromagnetic field interference in the reflective component and effectively achieve decoupling of the phase of the reflected light and the phase of the transmitted light. This ensures independent 1-bit phase control of the reflected light and the transmitted light.

[0098] According to an embodiment of the present invention, the size of the U-shaped hole is the same as the size of the U-shaped metal ring.

[0099] According to an embodiment of the present invention, the two parallel arms of the U-shaped metal ring extend in the same direction as the metal strip. This allows for a larger amplitude of the generated reflected light.

[0100] According to an embodiment of the present invention, the projection of the structural unit onto a predetermined plane is square. The wavelength of the incident light... The side length of the structural unit projected onto the preset plane It is approximately a subwavelength scale.

[0101] According to an embodiment of the present invention, the polarization direction of the incident light beam is a first direction (e.g., the Y direction). The support layer 111 includes: a first sub-support layer 1111, with a reflective component 112 located on the first sub-support layer; a transmission polarization selection layer 1112 located on the side of the first sub-support layer 1111 away from the reflective component 112, wherein a second through-hole 1112-1 extending along the first direction is formed on the transmission polarization selection layer 1112 for polarization filtering of the incident light beam passing through the first sub-support layer 1111, thereby filtering out components with polarization directions different from the incident light beam, so that the polarization direction of the light entering the transmission component is always the first direction. A second sub-support layer 1113 is located on the side of the transmission polarization selection layer 1112 away from the first sub-support layer 1111.

[0102] According to an embodiment of the present invention, the incident light can be, for example, a terahertz wave, and the materials of the first sub-support layer and the second sub-support layer can be, for example, polyimide (PI) with a dielectric constant of 2.96. The three layers of the reflective component 112, the transmission component, and the transmission polarization selection layer can be made of aluminum with a dielectric constant of 3.56.

[0103] For example, the side length of the projection of a structural unit (i.e., the side length of the unit structure). μm; metal strip width μm; metal strip length μm; length of the two parallel sidewalls of the U-shaped metal ring The length of the bottom straight section between the two parallel sidewalls satisfy μm. The width of the parallel sidewalls and the width of the straight section are the same as the width of the metal strip. When the U-shaped metal ring and the metal strip are in the first position, the horizontal displacement of the projection of the center of the solid U-shaped metal ring onto the preset plane relative to the projection of the center of the structural unit onto the preset plane is... μm, vertical displacement is μm. In this embodiment of the invention, the projection of the metal strip onto the preset plane follows the line connecting the midpoints of the two opposite sides of the square, and the extension direction of the metal strip is the direction of the target axis. The second through-hole of the transmission polarization selective layer is a strip-shaped through-hole with the same size as the metal strip. The spatial position of the U-shaped hole is obtained by rotating the U-shaped metal strip counterclockwise by 90°, that is... μm and μm. Thickness of the transmission polarization selection layer 1112. μm; the thickness of the PI adhesive used to connect the layers. μm. This indicates the horizontal displacement (i.e., the displacement along the x-direction) of the projection of the center of the U-shaped hole onto the preset plane relative to the projection of the center of the structural unit onto the preset plane. This represents the vertical displacement (i.e., the displacement along the y-direction) of the projection of the center of the U-shaped hole onto the preset plane relative to the projection of the center of the structural unit onto the preset plane.

[0104] In the metasurface structure designed in this paper, the first-layer reflective component 112 uses a solid U-shaped metal ring and metal strips; the third-layer transmission polarization selection layer 1112 uses a hollow metal strip complementary structure (perpendicular to the extension direction of the metal strips); and the fifth-layer transmission component uses a hollow U-shaped through-hole, a complementary structure of the solid U-shaped metal ring. Different positions of the first-layer U-shaped metal ring and the fifth-layer U-shaped through-hole are used to independently control the electromagnetic response of the reflection and transmission spaces. By rotating the fifth-layer U-shaped through-hole structure 90° relative to the first-layer U-shaped metal ring, the decoupling of the reflection and transmission phases can be effectively achieved. The middle third layer functions to transmit waves perpendicular to the metal strip polarization and block waves parallel to the metal strip polarization. Specifically, when a y-polarized beam is incident on the reflective component 112, a reflected beam with an x-polarized component is generated, while some light is transmitted. After processing by the third-layer structure, the x-polarized component of the transmitted beam is reflected, allowing only the y-polarized beam to transmit and be incident on the fifth-layer transmission component 113, ultimately converting it into x-polarized light for transmission output.

[0105] In order to analyze the influence of the reflective component 112 or the first through hole 1131 on the phase of reflected or transmitted light at different positions, this embodiment of the invention uses CST Microwave Studio electromagnetic simulation software to perform unit structure simulation.

[0106] During the simulation, Unit Cell boundary conditions were applied to the structural units in the x and y directions, while Open boundary conditions were set in the z direction (perpendicular to the x and y directions). The simulation frequency range was from 0.4 THz to 1.3 THz. This embodiment of the invention is illustrated using 0.7 THz as a representative value. At 0.7 THz, to illustrate the 1-bit phase modulation method at the transmission and reflection ends, this embodiment of the invention uses four basic units, named "00", "01", "10", and "11" respectively. The first code of each of the four basic units represents the phase of the transmitted light, and the second code represents the phase of the reflected light.

[0107] Figure 4 These are the phase curves of the reflected and transmitted light corresponding to the basic units "00" and "01" provided in the embodiments of the present invention.

[0108] Figure 5 These are the phase curves of reflected and transmitted light of the basic units "00" and "10" provided according to embodiments of the present invention.

[0109] exist Figure 4 and Figure 5 In the first position, before the reflective component is mirror-symmetrical, the phase of the reflected beam is 18.14°, denoted as "0" for the reflected beam phase. After the reflective component is mirror-symmetrical (in the second position), the phase of the reflected beam is 162.56°, denoted as "1" for the reflected beam phase. Before the first through-hole 1131 is mirror-symmetrical (in the third position), the phase of the transmitted beam is 118.23°, denoted as "0" for the transmitted beam phase. After the first through-hole 1131 is mirror-symmetrical (in the fourth position), the phase of the transmitted beam is 62.51°, denoted as "1" for the transmitted beam phase. Figure 4 and Figure 5 As shown in the figure. and (u, v = 0, 1) represent the phases of the reflected and transmitted beams corresponding to the basic unit "uv", respectively. Observe... Figure 4 and Figure 5 It can be seen that the mirror symmetry of the reflective component only causes the phase difference of the reflected beam to be 180°, while the phase of the transmitted beam remains unchanged; the mirror symmetry of the first through-hole of the transmission component only causes the phase difference of the transmitted beam to be 180°, while the phase of the reflected beam remains unchanged.

[0110] Through simulation, the phase changes of the first through-hole of the reflective and transmissive components of the structural unit before and after mirror symmetry were obtained. In addition, the amplitudes of the reflected and transmitted beams before and after mirror symmetry of the first through-hole of the reflective and transmissive components were also obtained through simulation.

[0111] Figure 6 This is an amplitude curve diagram of the reflected beam and the transmitted beam corresponding to the basic units "00" and "01" provided in the embodiments of the present invention.

[0112] Figure 7 This is an amplitude curve diagram of the reflected beam and the transmitted beam corresponding to the basic units "00" and "10" provided in the embodiments of the present invention.

[0113] In the picture and (u, v = 0, 1) represent the reflection and transmission amplitudes of the basic unit "uv", respectively. By comparison... Figure 6 of and The transmission phase (i.e., the phase of the transmitted beam) is generated. The phase abrupt change does not affect the reflection amplitude of the basic unit; similarly, in contrast... Figure 7 of and The reflection phase (i.e., the phase of the reflected beam) is generated. The phase abrupt change does not affect the transmission amplitude of the basic unit. Based on this, it can be proven that the design can achieve independent 1-bit phase control throughout the entire space. Figures 4-7 Specific information at 0.7THz is shown in Table 1.

[0114] Table 1

[0115]

[0116] The metasurface provided in this embodiment of the invention can achieve different functions in the reflection space (the space where the reflected beam is located) by adjusting the position of the reflective components in each structural unit. Similarly, the metasurface provided in this embodiment of the invention can achieve different functions in the transmission space (the space where the transmitted beam is located) by adjusting the position of the first through hole in each structural unit.

[0117] According to an embodiment of the present invention, when the metasurface 1 is used as a reflective grating (i.e., realizing the function of a grating in the reflection space), the positions of the reflective components of each of the plurality of structural units 110 are determined based on the diffraction order of the reflective grating, the size of the unit structure, and the position of the structural unit. When the metasurface is used as a transmissive grating (i.e., realizing the function of a grating in the transmission space), the positions of the first through-holes of each of the plurality of structural units are determined based on the diffraction order of the transmissive grating, the size of the unit structure, and the position of the structural unit.

[0118] According to an embodiment of the present invention, when the metasurface 1 is used as a reflective Fresnel lens (i.e., the function of a Fresnel lens is realized in the reflection space), the position of the reflective component of each of the plurality of structural units 110 is determined according to the focal length of the reflective Fresnel lens and the position of the structural unit; when the metasurface is used as a transmissive Fresnel lens, the position of the first through hole of each of the plurality of structural units is determined according to the focal length of the transmissive Fresnel lens and the position of the structural unit.

[0119] According to an embodiment of the present invention, when the metasurface 1 is used as a reflective vortex beam generator (i.e., to realize the function of a reflective vortex beam generator in the reflection space), the positions of the reflective components of each of the plurality of structural units 110 are determined according to the topological number and focal length of the reflective vortex beam generator and the positions of the structural units; when the metasurface is used as a transmissive vortex beam generator (i.e., to realize the function of a reflective vortex beam generator in the transmission space), the positions of the first through holes of each of the plurality of structural units are determined according to the topological number and focal length of the reflective vortex beam generator and the positions of the structural units.

[0120] According to an embodiment of the present invention, when the metasurface 1 is used as a reflective holographic imaging structure (i.e., to realize holographic imaging in the reflection space), the positions of the reflective components of each of the plurality of structural units 110 are determined according to the amplitude of the target holographic image, the size of the structural unit, and the pixel size of the target holographic image; when the metasurface is used as a transmissive Fresnel lens (i.e., to realize holographic imaging in the transmission space), the positions of the first through holes of each of the plurality of structural units and the positions of the reflective components of each of the plurality of structural units are determined according to the amplitude of the target holographic image, the size of the structural unit, and the pixel size of the target holographic image.

[0121] To verify the effectiveness of different functions achieved by different spaces of a metasurface, Examples 1 and 2 of this invention respectively designed two types of multifunctional metasurface devices with full-space integration of the same or different functions in the electromagnetic wave reflection and transmission spaces. A first-order diffraction grating structure can be designed in the metasurface reflection space (the space where the reflected beam is located), while a Fresnel lens is constructed in the transmission space (the space where the transmitted beam is located) to achieve focusing. Alternatively, a topological charge-carrying device can be generated in the metasurface reflection space. The device generates a vortex beam and simultaneously achieves computational holographic imaging of the letter "T" in its transmission space through phase encoding. This fully independent control design breaks through the functional limitations of traditional metasurface devices, realizing differentiated electromagnetic responses in the reflection and transmission spaces on the same device. Both metasurfaces demonstrate the ability of the designed unit structure to control the wavefront across the entire space, showing broad application prospects in multifunctional integrated optical devices.

[0122] Example 1: A full-space device integrating grating and lens functions.

[0123] This example demonstrates a grating function that can achieve ±1 order beam deflection in the reflection space and a focusing function at 10 mm in the transmission space.

[0124] 1) Grating Design Principles

[0125] This invention achieves anomalous light wave deflection manipulation based on a metasurface phase modulation mechanism, the physical essence of which can be described by the generalized Snell's law. When the incident light... Angular incidence to having When a metasurface with a phase gradient distribution is used, it will induce a wavefront manipulation effect of anomalous deflection: generating reflection angles respectively. Anomalous reflection and refraction angles The anomalous transmission phenomenon exhibits angular relationships that defy the constraints of traditional refraction laws. Based on the extreme value condition of optical path in Fermat's principle, the mathematical expression of the generalized law of refraction / reflection can be derived:

[0126]

[0127] in, Let be the refractive indices of the materials in the incident (reflection) space and the transmission space, respectively. It is evident from equation (11) that reflected and refracted beams can be designed to have arbitrary directions, provided that a suitable, constant, and non-zero phase gradient is introduced. In this case, the usual laws of refraction and reflection are restored, which means the continuity of the wave vector at the interface.

[0128] Combining the generalized Snell's law and the grating equations, in the design of the grating to achieve diffraction in reflection space, the metasurface phase distribution of a one-dimensional grating can be set as:

[0129]

[0130] in For diffraction orders, Let q be the grating period. Since the period of the unit structure designed in this paper is less than half the wavelength, diffraction effects will affect the modulation effect. Therefore, in the design of the grating structure, we consider q unit structures with the same phase as a single phase unit. .

[0131] because , The independence of direction makes it easy to extend equation (12) to the case of two-dimensional diffraction, that is...

[0132]

[0133] in They are respectively The diffraction order in the direction. In the two-dimensional case, it can be represented by the elevation angle in polar coordinates. and azimuth To better describe the deflection of the light beam, based on the following relationship:

[0134]

[0135] Angle of elevation Defined as wave vector The angle with the z-axis can be determined geometrically as follows:

[0136]

[0137] in , is the modulus of the wave vector.

[0138] Azimuth Defined as wave vector exist The angle between the plane and the x-axis can be determined geometrically as follows:

[0139]

[0140] According to formula (1516), the elevation angle of a first-order grating in the case of a two-dimensional phase gradient can be derived. and azimuth The calculation formula is:

[0141]

[0142] This work selects The structural parameters are such that the beam deflection angle is small and the energy is high, making it convenient for measurement and research. The corresponding metasurface units are arranged in a periodic distribution of "000111" in both the x and y directions.

[0143] Figure 8 This is the phase arrangement diagram of the reflection space in Example 1.

[0144] like Figure 8 As shown, grating period Theoretical calculations were performed based on equation (17), using 0.7 THz light incidence as an example. The theoretical predicted elevation angle θ was ±42.33°, and the azimuth angle was... The theoretical predicted values ​​are 45°, 135°, 225° and 315°.

[0145] 2) Functional design principle of Fresnel lens

[0146] In transmission space, metasurfaces are designed to function as Fresnel lenses. Traditional lenses achieve wavefront modulation through phase accumulation caused by light propagation in a glass medium, thus focusing the beam to a focal point. This volumetric phase modulation method results in a relatively large device thickness, and due to manufacturing limitations, they are usually spherical in shape, making it difficult to avoid inherent spherical aberration. Fresnel lenses are formed by blocking an even or odd number of half-wave zones. Fresnel lenses eliminate the coherent destructive phases between adjacent half-wave zones of ordinary zone plates, making the intensity of the outgoing beam equal to the square of the sum of the amplitudes transmitted through each slit, thereby significantly enhancing light intensity while also reducing thickness to some extent. The introduction of metasurfaces further reduces the size of the lens. By precisely designing the phase distribution of the converging spherical wave, spherical aberration is eliminated in principle, resulting in advantages such as extremely thin structure, uniform thickness, and high focusing intensity.

[0147] This paper presents a design based on the principle of phase-type Fresnel lenses. Based on this principle, the focusing phase distribution of the metasurface is analyzed.

[0148] Figure 9 This is a schematic diagram of the Fresnel lens principle.

[0149] like Figure 9As shown, the incident electromagnetic wave is focused at the focal point F after being modulated by the metasurface. The origin of the metasurface is O. Consider a point on the metasurface with coordinates ( Point P is a point on the metasurface. After light passes through the metasurface, the phase difference between the light from point P to the focal point F and the light from the origin O to the focal point F is:

[0150]

[0151] In the above description, f is the focal length of the Fresnel lens. Due to the arbitrariness of point P, formula (18) applies to every point on the metasurface.

[0152] In a metasurface employing 1-bit phase modulation, the phase difference between point O and point P can be described as... Combining formula (19), the phase design formula for a 1-bit focusing lens can be derived:

[0153]

[0154] in For the operating wavelength, Let be the distance between a point on the hypersurface and the origin O. According to formula (19), we find the focal length... Under the condition that the incident light frequency is 0.7 THz, construct the required lens phase distribution.

[0155] Figure 10 This is the phase arrangement diagram of the transmission space in Example 1.

[0156] Based on the phase distribution diagrams of the reflection space and the transmission space ( Figure 8 and Figure 10 This allows the construction of metasurfaces with two-dimensional gratings in reflection space and Fresnel lenses in transmission space. In the CST Microwave Studio time-domain solver, a 0.7 THz... The device was simulated using a polarized Gaussian beam as the excitation source. In the reflection space, frequency domain data was recorded by setting up an electric field monitor, and a two-dimensional discrete-space Fourier transform was performed to obtain the grating diffraction spectrum along the cross-section. The elevation angle was then calculated through spectrum analysis. and azimuth The relationship diagram.

[0157] Figure 11 The elevation angle of the grating in the reflection space in Example 1. and azimuth The relationship diagram.

[0158] like Figure 10 As shown, where The simulated value is ±42.2°. The simulated values ​​of 45.1°, 135.1°, 225.1°, and 315.1° are in good agreement with the theoretical predictions, fully validating the effectiveness of the reflection space design method. In the transmission space, by obtaining... flat Light intensity distribution in a specific direction.

[0159] Figure 12 It is the Fresnel lens in the transmission space of Example 1. Light intensity distribution diagram of a plane.

[0160] like Figure 12 As shown, the superlens exhibits a significant focusing effect. To quantitatively characterize the focusing properties, further extraction... Figure 11 middle Longitudinal light intensity distribution along the axis.

[0161] Figure 13 yes Figure 11 Pick Light intensity curve along the z-direction.

[0162] like Figure 13 As shown, the light intensity curve clearly displays the intensity distribution at the focal point, and the actual focal position can be quantitatively measured to be 9570 μm, with a relative deviation of only -4.30% from the theoretical design value. To further evaluate the focusing performance of the Fresnel lens, a section can be taken at the principal focal point. Light field intensity analysis is performed on a plane.

[0163] Figure 14 It is the main focal point. Light intensity distribution diagram of a plane.

[0164] like Figure 14 As shown, by extracting Figure 14 middle The transverse light intensity distribution curve of the axis is plotted as follows. Figure 15 .

[0165] Figure 15 Yes Figure 14 Pick Light intensity curve along the x-direction.

[0166] like Figure 15 As shown, the full width at half maximum (FWHM) of the focused spot is 0.242 mm, demonstrating a good focusing effect.

[0167] Example 2: A full-space device integrating focusing vortex and holographic functions

[0168] This example demonstrates a full-space device that can achieve a second-order focused vortex beam at a position of 10mm in the reflection space and a point-shaped "T" holographic function in the transmission space.

[0169] 1) Design principle of vortex beam

[0170] In reflection space, the metasurface is designed as a vortex beam generator structure. Its phase exhibits an angular phase variation, typically an integer multiple of 2π. Because the phase varies angularly, the phase of the vortex beam at its center cannot be defined, forming a singularity, resulting in an intensity pattern with a centrally hollow spiral arm shape. Therefore, when Gaussian light is incident on a metasurface with this phase distribution, a focused vortex beam can be generated.

[0171]

[0172] in Let be the topological number of the vortex beam. The second term of the above equation is derived from formula (18) of the Fresnel lens section above, which means that the metasurface can not only generate vortex beams, but also focus the vortex beams to the focal length position we designed, so as to facilitate its measurement and research.

[0173] Furthermore, since the unit structure designed in this paper only has two phase states, 0 and π, the metasurface phase distribution represented by formula (20) should be quantified as:

[0174]

[0175] Combining formulas (20) and (21), the topological number is obtained. and focal length Under 0.7 THz light incidence, the following can be obtained: Figure 16 The metasurface phase arrangement is shown.

[0176] 2) Holographic Imaging Design Principles

[0177] In transmission space, the metasurface is designed as a holographic imaging structure. This paper combines the Rayleigh-Sommerfeld (RS) diffraction formula and the Gerchberg-Saxton (GS) iterative algorithm during the hologram design process. Based on the principle of optical path reversibility, the amplitude and phase distribution of the metasurface are first constructed through inverse diffraction based on the intensity and amplitude distributions of the target holographic image. Let the imaging distance between the target holographic image and the metasurface be d. Since the propagation path between the target holographic image and the metasurface can be approximated as a diffraction process between two planes in free space, the RS diffraction formula can be used to calculate the amplitude and phase distribution of the metasurface.

[0178]

[0179] Where U(r0) represents the electric field at point R0 on the metasurface, U(r1) represents the electric field at point R1 on the image plane; S is the region of the target holographic image; λ is the working wavelength; It is a vector perpendicular to the plane of the target holographic image; r 01 It is the distance between R0 and R1; It is the tilt factor, that is Assume the amplitude (light intensity distribution) A of the target holographic image is arbitrary with respect to the initial phase. Then there is Considering the size of the unit structure and the discreteness of the pixel data in the target holographic image, it is difficult to obtain continuous integral data for analytically solving the electric field distribution in both the target holographic image and the metasurface. Therefore, in the actual calculation process, the integral over the target holographic image is converted into a point source superposition of information from each pixel unit, thus obtaining a discrete form of the electric field calculation expression:

[0180]

[0181] Where S represents the region where the target holographic image is located; The dimensions of the discrete structural unit.

[0182] When obtaining the distribution of the reconstructed image based on the holographic metasurface, the inverse transform of the above formula is used, namely:

[0183]

[0184] In the formula, This represents the electric field at point r1 in the reconstructed image; It is the electric field at point R0 on the discretized hypersurface; This refers to the extent of the metasurface. Due to the change in the direction of light transmission, the sign of the exponent is reversed.

[0185] Because the target holographic image has an arbitrary initial phase in the above process, it is difficult to achieve the ideal holographic imaging effect in a single reconstruction. This invention introduces the Gerchberg-Saxton (GS) iterative algorithm to optimize the holographic reconstruction process: after obtaining the reconstructed holographic image, the phase distribution of the target holographic image is replaced with the phase distribution of the reconstructed holographic image (amplitude remains unchanged), and then the target holographic image is used again to enter the above process for a second reconstruction, and so on iteratively.

[0186] Figure 17 This is the light intensity distribution map of the target holographic image in Example 2.

[0187] like Figure 17 As shown, the initial phase position is 0. After multiple rounds of GS iteration calculations, the optimized phase of the metasurface is finally obtained.

[0188] Figure 18 This is the phase arrangement diagram of the transmission space of the metasurface in Example 2.

[0189] Based on the phase distribution diagrams of the transmission and reflection spaces ( Figure 18 and Figure 16 This allows for the construction of metasurfaces with focusing vortex beams in reflection space and holographic imaging capabilities in transmission space. The metasurface was simulated using a 0.7 THz y-polarized Gaussian beam in the CST Microwave Studio time-domain solver. In reflection space, the intensity and phase distribution of the vortex beam were obtained by setting an electric field monitor at the focusing position, as shown below. Figure 19 and Figure 20 As shown.

[0190] Figure 19 This is a light intensity distribution diagram at the focal point of the vortex beam in the reflection space in Example 2.

[0191] Figure 20 This is a diagram showing the optical phase distribution at the focal point of the vortex beam in the reflection space in Example 2.

[0192] Figure 19 The beam exhibits obvious vortex characteristics, presenting a typical ring structure, with the central region having zero light intensity due to a phase singularity. Figure 20 The exhibited spiral phase structure indicates that the beam carries orbital angular momentum. This is visible in the phase diagram. The corresponding two phase branches have phase values ​​from arrive There is a jump along the azimuth angle. Simultaneously, a phase singularity can be observed in the central region. Furthermore, this is achieved by acquiring the vortex beam. Light intensity distribution along the xoz direction of the plane.

[0193] Figure 21 It is the vortex beam in the reflected space in Example 2. Light intensity distribution diagram of a plane.

[0194] like Figure 21 As shown, the intensity distribution of the vortex beam along the z-axis can be observed. The focusing position of the vortex beam is 9.73 mm, which is basically consistent with the 10 mm focusing position designed in this embodiment. In the transmission space, by setting an electric field monitor at a preset imaging distance, the intensity and phase distribution of the holographic image were obtained. See below for details. Figure 22 and Figure 23 As shown.

[0195] Figure 22 It is a light intensity distribution map at the imaging position of the holographic image in the transmission space.

[0196] Figure 23 It is a light phase distribution map at the imaging position of a holographic image in the transmission space.

[0197] Figure 22 , Figure 23 The clear dot matrix "T" is displayed, indicating that the device has a good ability to obtain transmission holograms.

[0198] The embodiments of the present invention have been described above. However, these embodiments are merely illustrative and not intended to limit the scope of the invention. Although various embodiments have been described above, this does not mean that the measures in the various embodiments cannot be used advantageously in combination. The scope of the invention is defined by the appended claims and their equivalents. Various substitutions and modifications can be made by those skilled in the art without departing from the scope of the invention, and all such substitutions and modifications should fall within the scope of the invention.

Claims

1. A metasurface based on mirror symmetry and full-space 1-bit phase modulation, characterized in that, include: Multiple structural units, the multiple structural units including: Support layer A reflective component is located on one side surface of the support layer, and is located in either a first position or a second position. When the reflective component is located in the first position, its projection onto a preset plane is mirror-symmetrical with respect to a target axis as when the reflective component is located in the second position. The preset plane is a plane perpendicular to the height direction of the structural unit. The target axis is a straight line passing through a target point, and the target point is the center point of the projection of the structural unit onto the preset plane. The reflective component is adapted to reflect a received incident light beam to obtain a reflected light beam perpendicular to the polarization direction of the incident light beam. When the reflective component is in the first position, the reflected light beam has a first phase, and when the reflective component is in the second position, the reflected light beam has a second phase. A transmission component is located on the side of the support layer away from the reflective component. A first through-hole is formed on the transmission component. The first through-hole is located in a third position or a fourth position. When the transmission component is located in the third position, its projection on the preset plane is mirror-symmetrical with respect to the target axis as is the projection of the transmission component on the preset plane when it is located in the fourth position. The transmission component is adapted to transmit an incident light beam that passes sequentially through the reflective component and the support layer, and obtain a transmitted light beam with a polarization direction opposite to that of the incident light beam. When the first through-hole is located in the third position, the transmitted light beam has a third phase, and when the transmission component is located in the fourth position, the transmitted light beam has a fourth phase.

2. The metasurface according to claim 1, wherein, The reflective component includes a U-shaped metal ring and a metal strip, both located on the support layer.

3. The metasurface according to claim 2, wherein, The first through hole is a U-shaped hole, and the opening direction of the U-shaped metal ring and the U-shaped hole are perpendicular.

4. The metasurface according to claim 2, wherein, The two parallel arms of the U-shaped metal ring extend in the same direction as the metal strip.

5. The metasurface according to claim 1, wherein, The polarization direction of the incident light is a first direction, and the support layer includes: First sub-support layer, the reflective component is located on the first sub-support layer; A transmission polarization selection layer is located on the side surface of the first sub-support layer away from the reflective component. A second through-hole extending along the first direction is formed on the transmission polarization selection layer for polarization filtering of the incident light beam passing through the first sub-support layer. The second sub-support layer is located on the side surface of the transmission polarization selection layer away from the first sub-support layer.

6. The metasurface according to claim 1, wherein, When the metasurface is used as a reflective grating, the positions of the reflective components of each of the plurality of structural units are determined based on the diffraction order of the reflective grating, the size of the structural unit, and the position of the structural unit. When the transmitted light is used as a grating, the position of the first through-hole of each of the plurality of structural units is determined according to the diffraction order of the transmission grating, the size of the structural unit, and the position of the structural unit.

7. The metasurface according to claim 1, wherein, When the metasurface is used as a reflective Fresnel lens, the positions of the reflective components of each of the plurality of structural units are determined according to the focal length of the reflective Fresnel lens and the positions of the structural units. When the metasurface is used as a transmissive Fresnel lens, the position of the first through-hole of each of the plurality of structural units is determined according to the focal length of the transmissive Fresnel lens and the position of the structural unit.

8. The metasurface according to claim 1, wherein, When the metasurface is used as a reflective vortex beam generator, the positions of the reflective components of each of the plurality of structural units are determined according to the topology number and focal length of the reflective vortex beam generator and the positions of the structural units. When the metasurface is used as a transmissive vortex beam generator, the position of the first through-hole of each of the plurality of structural units is determined according to the topology number and focal length of the transmissive vortex beam generator and the position of the structural unit.

9. The metasurface according to claim 1, wherein, When the metasurface is used as a reflective holographic imaging structure, the positions of the reflective components of each of the plurality of structural units are determined according to the light intensity distribution of the target holographic image, the size of the structural unit, and the phase distribution of the target holographic image; When the metasurface is used as a transmission holographic imaging structure, the positions of the first through holes of each of the plurality of structural units and the positions of the reflective components of each of the plurality of structural units are determined based on the light intensity distribution of the target holographic image, the size of the structural unit, and the phase distribution of the target holographic image.

10. The metasurface according to claim 1, wherein, The incident light is a terahertz wave.

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