Mirror symmetry-based metasurface for total-space 1-bit phase regulation

Abstract

The invention provides a metasurface for total space 1-bit phase regulation based on mirror symmetry, the metasurface comprises a plurality of structural units, the plurality of structural units comprise a support layer, a reflection assembly and a first position or a second position, the reflection assembly is located on one side surface of the support layer and is located at the first position, when the reflection assembly is located at the first position, a reflection light beam has a first phase, and when the reflection assembly is located at the second position, the reflection light beam has a second phase; when the reflection assembly is located at the second position, the reflected light beam has a second phase; the transmission assembly is located on the surface of the side, away from the reflection assembly, of the supporting layer; a first through hole is formed in the transmission assembly, and the first through hole is located at a third position or a fourth position; when the first through hole is located at the third position, the transmission light beam has a third phase, and when the transmission assembly is located at the fourth position, the transmission light beam has a fourth phase.

Description

Technical Field

[0001] The present invention relates to the field of optics, and particularly to a metasurface for full-space 1-bit phase modulation based on mirror symmetry. Background Art

[0002] As a two-dimensional artificially designed electromagnetic material, the metasurface provides new ideas for the miniaturization and functional integration of terahertz devices by flexibly modulating the amplitude, phase, and polarization state of electromagnetic waves through sub-wavelength-scale structural units. However, it is difficult to fully utilize the transmission space and reflection space of traditional metasurfaces. Therefore, researchers have gradually focused on metasurfaces with full-space modulation capabilities. Currently, full-space metasurfaces mainly achieve modulation goals by means of frequency multiplexing, polarization multiplexing, and incident direction multiplexing. In addition, although there are full-space designs that can achieve full-space wavefront modulation under the conditions of incident light with the same frequency, propagation direction, and polarization state, they cannot truly achieve independent wavefront modulation of the transmission space and reflection space under the same incident conditions. Summary of the Invention

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

[0004] A support layer;

[0005] A reflection component, located on one side surface of the support layer and at a first position or a second position. When the reflection component is at the first position, the projection of the reflection component on a preset plane and the projection of the reflection component on the preset plane when the reflection component is at 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, and 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 on the preset plane. The reflection component is adapted to reflect the received incident light beam to obtain a reflection light beam perpendicular to the polarization direction of the incident light beam. When the reflection component is in the first position, the reflected light has a first phase, and when the reflection component is in the second position, the reflected light beam has a second phase;

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

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

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

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

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

[0011] A first sub-support layer, on which the reflection component is located.

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

[0013] A second sub-support layer, located on a 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, positions of reflection components of the plurality of structural units are determined according to a diffraction order of the reflective grating, a size of the unit structure, and a position of the structural unit.

[0015] When the transmitted light is used as a grating, positions of the first through-holes of the plurality of structural units are determined according to a diffraction order of the transmissive grating, a size of the unit structure, and a 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 reflection components of the respective plurality of structural units are determined according to 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 positions of the first through-holes of the respective plurality of structural units are determined according to the focal length of the transmissive Fresnel lens and the positions of the structural units.

[0018] According to an embodiment of the present invention, when the metasurface is used as a reflective vortex beam generator, the positions of the reflection components of the respective 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;

[0019] When the metasurface is used as a transmissive vortex beam generator, the positions of the first through-holes of the respective plurality of structural units are determined according to the topological number and focal length of the transmissive vortex beam generator and the positions of the structural units.

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

[0021] When the metasurface is used as a transmissive holographic imaging structure, the positions of the first through-holes of the respective plurality of structural units, and the positions of the reflection components of the respective plurality of structural units are determined according to the light intensity distribution of the target holographic image, the size of the structural units, 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 reflection component to be located at the mirror-symmetric first position or the second position, the phase of the reflected beam can be the first phase or the 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 the mirror-symmetric third position or the fourth position, the phase of the transmitted beam can be the third phase or the fourth phase, and the phase difference between the two is 180°.

[0024] According to an embodiment of the present invention, since the metasurface of the embodiment of the present invention includes a plurality of structural units, by controlling the positions of the respective reflection components and the first through holes of the plurality of structural units of the metasurface, each structural unit can modulate the phases of the respective corresponding reflected light beam and transmitted light beam, thereby realizing the independent control of the wavefronts of the reflected light (including the reflected light beams corresponding to all the structural units respectively) and the transmitted light (including the transmitted light beams corresponding to all the structural units respectively). Through the collaborative design of the reflection components and the transmission components, the wavefront regulation of the transmitted light and the reflected light is completely decoupled, and the two do not interfere with each other, and independent 1-bit phase regulation of the reflected light and the transmitted light of the incident light can be achieved. Description of the Drawings

[0025] Through the following description of the embodiments of the present invention with reference to the drawings, the above and other objects, features, and advantages of the present invention will become clearer. In the drawings:

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

[0027] Figure 2 is a three-dimensional view of a structural unit.

[0028] Figure 3 are the coordinate axes before and after mirror symmetry change according to an embodiment of the present invention.

[0029] Figure 4 are the phase curves of the corresponding reflected light and transmitted light of the basic units "00" and "01" according to an embodiment of the present invention.

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

[0031] Figure 6 are the amplitude curves of the corresponding reflected light and transmitted light of the basic units "00" and "01" according to an embodiment of the present invention.

[0032] Figure 7 are the amplitude curves of the corresponding reflected light and transmitted light of the basic units "00" and "10" according to an embodiment of the present invention.

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

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

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

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

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

[0038] Figure 13 is Figure 11 take intensity curve graph along the z direction.

[0039] Figure 14 is at the main focus position intensity distribution diagram of the plane.

[0040] Figure 15 is for Figure 14 take intensity curve graph along the x direction.

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

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

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

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

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

[0046] Figure 21 is the vortex beam in the reflection space in Example 2 intensity distribution diagram of the plane.

[0047] Figure 22 is the intensity distribution diagram at the holographic image imaging position in the transmission space in Example 2.

[0048] Figure 23 is the optical phase distribution diagram at the holographic image imaging position in the transmission space in Example 2.

[0049] Explanation of reference numerals

[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: Reflection component

[0058] 1121: U - shaped metal ring

[0059] 1122: Metal strip

[0060] 113: Transmission component

[0061] 1131: First through - hole Detailed implementation manners

[0062] To make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the following further elaborates on the present invention in detail with reference to specific embodiments and the accompanying drawings.

[0063] The terms used herein are merely for describing specific embodiments and are not intended to limit the present invention. The terms "including", "comprising", etc. used herein indicate the presence of the described 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 should be interpreted as having a meaning consistent with the context of this specification and should not be interpreted in an idealized or overly rigid manner.

[0065] In the case of using expressions such as "at least one of A, B, and C, etc.", generally, it should be interpreted according to the meaning commonly understood by those skilled in the art. For example, "a system having at least one of A, B, and C" should include, but not be limited to, a system having only A, only B, only C, having A and B, having A and C, having B and C, and / or having A, B, and C, etc. In the case of using expressions such as "at least one of A, B, or C, etc.", generally, it should be interpreted according to the meaning commonly understood by those skilled in the art. For example, "a system having at least one of A, B, or C" should include, but not be limited to, a system having only A, only B, only C, having A and B, having A and C, having B and C, and / or having A, B, and C, etc.

[0066] It should also be noted that the directional terms mentioned in the embodiments, such as "upper", "lower", "front", "rear", "left", "right", etc., are only references to the directions in the accompanying drawings and are not used to limit the protection scope of the present invention. Throughout the accompanying drawings, the same elements are denoted by the same or similar reference numerals. When it may cause confusion in the understanding of the present invention, conventional structures or configurations will be omitted.

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

[0068] As Figure 1 shown, the metasurface 1 includes: a plurality of structural units 110. The plurality of structural units 110 are arranged in an array.

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

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

[0071] According to an embodiment of the present invention, for one of the structural units, by controlling the reflection component to be in the first position or the second position that is mirror-symmetrical, the phase of the reflected light beam can be made the first phase or the 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 in the third position or the fourth position that is mirror-symmetrical, the phase of the transmitted light beam can be the third phase or the fourth phase, and the phase difference between the two is 180°.

[0072] According to an embodiment of the present invention, since the metasurface 1 includes a plurality of structural units 110, by controlling the positions of the respective reflection components 112 and the first through-holes 1131 of the plurality of structural units 110 of the metasurface 1, each structural unit can modulate the phases of the respective corresponding reflected light beam and transmitted light beam, and thus realize the individual control of the wavefronts of the reflected light (including the reflected light beams corresponding to all the structural units) and the transmitted light (including the transmitted light beams corresponding to all the structural units). By using the collaborative design of the reflection component and the transmission component, the wavefront regulation of the transmitted light and the reflected light is completely decoupled, and the two do not interfere with each other, and independent 1-bit phase regulation of the reflected light and the transmitted light of the incident light can be achieved.

[0073] According to an embodiment of the present invention, the following combines Figure 3 and theoretically explains that when the position of the reflection component or the first through-hole changes before and after mirror symmetry, the phase of the outgoing light beam (reflected light beam or transmitted light beam) differs by 180°. This theoretical explanation applies to both the reflected light beam and the transmitted light beam. In this theoretical explanation, the reflection component 112 and the first through-hole 1131 whose positions in the structural unit will change in mirror symmetry are collectively referred to as the conversion structure.

[0074] Figure 3 are the coordinate axes before and after the mirror symmetry change provided according to an embodiment of the present invention.

[0075] As Figure 3 shown, the xoy coordinate system is used to study the conversion structure in the structural unit 110 before mirror symmetry. In the xoy coordinate system, the phase change amount of the incident light beam Figure 1 after passing through the conversion structure of the structural unit can be represented by the Jones matrix

[0076]

[0077] wherein, are the complex amplitudes of the incident light beam in the x and y directions respectively; , are the complex amplitudes of the output beam in the x and y directions respectively.

[0078] Next, consider the change in the output beam after the conversion structure is mirror-symmetric about the target axis with an arbitrary rotation angle of . After mirror-symmetry along the dashed axis in Figure 3 , the coordinate axes are set as x'oy'. In the x'oy' coordinate system, the Jones matrix corresponding to the mirror-symmetric conversion structure is . Then, the relationship between the output beam of the conversion structure at this time and the input beam can be expressed by Equation (2).

[0079]

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

[0081]

[0082] Since it is necessary to study the conversion structure before and after mirror-symmetry in the same coordinate system, the coordinate transformation matrix between the xoy and x'oy' coordinate systems is first determined according to the geometric relationship as:

[0083]

[0084] Therefore and , and have the following transformation relationships:

[0085] According to Equation (5), the relationship between the output beam of the conversion structure after mirror-symmetry in the xoy coordinate system and the input beam can be obtained:

[0086]

[0087] , are the complex amplitudes of the components of the output beam in the x and y directions respectively.

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

[0089]

[0090] In the present invention, the incident light beam can be linearly polarized light, that is . At the same time, the target axis that makes the conversion structure mirror-symmetrical is horizontal, that is . Then, formula (1) can be simplified to:

[0091]

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

[0093]

[0094] By comparing formula (8) and formula (9), it can be obtained that:

[0095]

[0096] The above can illustrate that the phase of the cross-polarized output light of the structural unit after mirror symmetry is different from that before symmetry by , and the phase of the co-polarized light remains unchanged. Moreover, since there is at each frequency, this conclusion holds in the entire frequency band.

[0097] According to an embodiment of the present invention, the reflection component 112 includes a U-shaped metal ring 1121 and a metal strip 1122 that are 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 reflection component, which can avoid the electromagnetic field in the reflection component from interfering with the transmission phase regulation and effectively realize the decoupling of the phase of the reflected light and the phase of the transmitted light. Furthermore, it ensures the independent 1-bit phase regulation 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 extension directions of the two parallel arms of the U-shaped metal ring are the same as the extension direction of the metal strip. This can make the amplitude of the generated reflected light larger.

[0100] According to an embodiment of the present invention, the projection of the structural unit on the preset plane is square. The wavelength of the incident light and the side length of the projection of the structural unit on the preset plane

[0101] According to an embodiment of the present invention, the polarization direction of the incident light beam is the first direction (for example, it can be the Y direction). The support layer 111 includes: a first sub-support layer 1111, on which the reflection component 112 is located; a transmissive polarization selection layer 1112 located on the surface of the first sub-support layer 1111 away from the reflection component 112. A second through hole 1112-1 extending in the first direction is formed on the transmissive polarization selection layer 1112, which is used to perform polarization filtering on the incident light beam passing through the first sub-support layer 1111, so as to filter out the components with different polarization directions from the incident light beam, so that the polarization directions of the light entering the transmissive component are all the first direction. A second sub-support layer 1113 is located on the surface of the transmissive 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. The materials of the first sub-support layer and the second sub-support layer can be, for example, polyimide (PI), and its dielectric constant is 2.96. The three layers of the reflection component 112, the transmissive component and the transmissive polarization selection layer can adopt an aluminum material with a dielectric constant of 3.56.

[0103] Exemplarily, the side length of the projection of the structural unit (i.e., the side length of the unit structure) μm; the width of the metal strip μm; the length of the metal strip μm; the length of the two parallel side walls of the U-shaped metal ring and the length of the straight section at the bottom between the two parallel side walls Satisfy μm. The widths of the parallel side walls and 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 on the preset plane relative to the projection of the center of the structural unit on the preset plane μm, and the vertical displacement is μm. In the embodiment of the present invention, the projection of the metal strip on the preset plane is along the midpoint connection line of 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 transmissive polarization selection layer is a strip-shaped through hole, and its size is the same as that of 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. The thickness of the transmissive polarization selection layer 1112 μm; the thickness of the PI glue used to connect the layers μm. Represents the horizontal displacement of the projection of the center of the U-shaped hole on the preset plane relative to the projection of the center of the structural unit on the preset plane (i.e., the displacement along the x direction). It represents the vertical displacement (i.e., the displacement along the y direction) of the center of the U-shaped hole in the projection on the preset plane relative to the projection of the center of the structural unit on the preset plane.

[0104] In the metasurface structure designed in this paper, the reflection component 112 as the first layer adopts a solid U-shaped metal ring and metal strips. The transmission polarization selection layer 1112 as the third layer adopts a complementary structure of hollow metal strips (perpendicular to the extension direction of the metal strips). The transmission component as the fifth layer adopts a complementary structure of a solid U-shaped metal ring, that is, a hollow U-shaped through hole. Different positions of the U-shaped metal ring in the first layer and different positions of the U-shaped through hole in the fifth layer are respectively used to independently control the electromagnetic responses of the reflection space and the transmission space. By rotating the U-shaped through hole structure in the fifth layer by 90° in space relative to the U-shaped metal ring in the first layer, the decoupling of the reflection and transmission phases can be effectively realized. The middle third layer undertakes the function of transmitting the polarization wave perpendicular to the metal strip and blocking the polarization wave parallel to the metal strip. Specifically, when a y-polarized light beam is incident on the reflection component 112, a reflected light beam with an x-polarization component will be generated, and at the same time, part of the light is transmitted. After being processed by the third-layer structure, the x-polarization component in the transmitted light beam is reflected, and only the y-polarized light beam is allowed to be transmitted and incident on the fifth-layer transmission component 113, and finally is converted into an x-polarized light and transmitted out.

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

[0106] During the simulation process, the Unit Cell boundary condition is adopted for the structural unit in the x and y directions, and the Open boundary condition is set in the z direction (perpendicular to the x and y directions). The simulation frequency range is from 0.4 THz to 1.3 THz. The embodiments of the present invention are described by taking 0.7 THz as an example. At 0.7 THz, in order to illustrate the 1-bit phase modulation method at the transmission end and the reflection end, the embodiments of the present invention adopt four basic units, which are respectively named "00", "01", "10", and "11". Among them, the first code of each basic unit in 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 are the phase curves of the reflected light and the transmitted light corresponding to the basic units "00" and "01" provided by the embodiments of the present invention.

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

[0109] At Figure 4 andFigure 5 , before the reflective component is mirror-symmetrical (located at the first position), the phase of the reflected light beam is 18.14°, which is recorded as the phase "0" of the reflected light; after the reflective component is mirror-symmetrical (located at the second position), the phase of the reflected light beam is 162.56°, which is recorded as the phase "1" of the reflected light beam. Before the first through hole 1131 is mirror-symmetrical (located at the third position), the phase of the transmitted light beam is 118.23°, which is recorded as the phase "0" of the transmitted light beam; after the first through hole 1131 is mirror-symmetrical (located at the fourth position), the phase of the transmitted light beam is 62.51°, which is recorded as the phase "1" of the transmitted light beam. Figure 4 and Figure 5 As shown in the figure. and (u, v = 0, 1) represent the phase of the reflected beam and the phase of the transmitted beam corresponding to the basic unit "uv" respectively. Figure 4 and Figure 5 It can be seen that the mirror symmetry of the reflective component only causes the phase of the reflected light beam to differ by 180°, while the phase of the transmitted light beam does not change; the mirror symmetry of the first through hole of the transmissive component only causes the phase of the transmitted light beam to differ by 180°, while the phase of the reflected light beam does not change.

[0110] Through simulation, the phase changes before and after the first through-holes of the reflective component and the transmissive component of the structural unit are obtained. In addition, the amplitudes of the reflected light beam and the transmitted light beam before and after the first through-holes of the reflective component and the transmissive component are also obtained through simulation.

[0111] Figure 6 1 is an amplitude curve diagram of the reflected light beam and the transmitted light beam corresponding to the basic units “00” and “01” provided according to an embodiment of the present invention.

[0112] Figure 7 1 is an amplitude curve diagram of a reflected light beam and a transmitted light beam corresponding to the basic units “00” and “10” provided according to an embodiment of the present invention.

[0113] In the picture and (u, v = 0, 1) represent the reflection amplitude and transmission amplitude of the basic unit "uv" respectively. By comparing Figure 6 of and , the transmission phase (i.e. the phase of the transmitted light beam) produces The phase mutation of the basic unit is not affected; similarly, compared Figure 7 of and , the reflection phase (i.e. the phase of the reflected beam) produces The transmission amplitude of the basic unit is not affected by the phase mutation. This proves that the design can achieve independent 1-bit phase control in the entire space.Figures 4 - 7 The specific information at 0.7 THz is shown in Table 1.

[0114] Table 1

[0115]

[0116] The metasurface provided by the embodiment of the present invention can achieve different functions in the reflection space (the space where the reflected light beam is located) by adjusting the positions of the reflection components in each structural unit. Similarly, the metasurface provided by the embodiment of the present invention can achieve different functions in the transmission space (the space where the transmitted light beam is located) by adjusting the positions of the first through-holes 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., achieving the function of a grating in the reflection space), the positions of the reflection components of each of the plurality of structural units 110 are determined according to 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., achieving 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 according to 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., achieving the function of a Fresnel lens in the reflection space), the positions of the reflection components of each of the plurality of structural units 110 are 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 positions of the first through-holes of each of the plurality of structural units are 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., achieving the function of a reflective vortex beam generator in the reflection space), the positions of the reflection 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 position of the structural unit; when the metasurface is used as a transmissive vortex beam generator (i.e., achieving 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 position of the structural unit.

[0120] According to an embodiment of the present invention, when the metasurface 1 is used as a reflective holographic imaging structure (i.e., to achieve the function of holographic imaging in the reflection space), the positions of the reflection components of the respective 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 achieve the function of holographic imaging in the transmission space), the positions of the first through holes of the respective structural units and the positions of the reflection components of the respective 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 spaces of the metasurface in achieving different functions, Examples 1 and 2 of the present invention respectively designed two full-space multifunctional metasurface devices, integrating the same or different functions in the reflection and transmission spaces of electromagnetic waves. The reflection space of the metasurface (the space where the reflected light beam is located) can be designed as a first-order diffraction grating structure, and at the same time, a Fresnel lens can be constructed in the transmission space (the space where the transmitted light beam is located) to achieve the focusing function. Or, a vortex beam carrying a topological charge can be generated in the reflection space of the metasurface. At the same time, in its transmission space, computational holographic imaging of the dot matrix letter "T" is realized through phase encoding. This full-space independent control design breaks through the limitation of the single function of traditional metasurface devices, and realizes the differential electromagnetic response of the reflection space and the entire transmission space on the same device. Both of these metasurfaces demonstrate the ability of the designed unit structure to control the wavefront of 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 principle

[0125] Embodiments of the present invention realize the abnormal deflection control of light waves based on the metasurface phase modulation mechanism, and its physical essence can be described by the generalized Snell's law. When the incident light is incident on the metasurface with angle and has phase gradient distribution, it will trigger the wavefront control effect of abnormal deflection: respectively generating abnormal reflection with a reflection angle and abnormal transmission with a refraction angle , and the angular relationship breaks through the constraints of the traditional refraction law. Based on the extreme optical path condition in Fermat's principle, the mathematical expressions of the generalized refraction / reflection law can be deduced:

[0126]

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

[0128] Combining the generalized Snell's law and the grating equation, in the reflection space, for the design of the grating diffraction function. The phase distribution of the metasurface of a one-dimensional grating can be set as:

[0129]

[0130] Where is the diffraction order, is the grating period. Since the period of the unit structure designed in this paper is less than half of the wavelength, there will be a diffraction effect affecting the modulation effect. Therefore, in the design of the grating structure, we take q unit structures with the same phase as a phase unit, then .

[0131] Since , due to the independence of the direction, it is easy to generalize Equation (12) to the two-dimensional diffraction case, that is

[0132]

[0133] Where are the diffraction orders in the directions of, respectively. In the two-dimensional case, the elevation angle and the azimuth angle in the polar coordinate system can be used to better describe the deflection of the beam. According to the following relationship:

[0134]

[0135] The elevation angle is defined as the angle between the wave vector and the z-axis. According to the geometric relationship, it can be known that:

[0136]

[0137] Where , which is the modulus of the wave vector.

[0138] The azimuth angle is defined as the angle between the wave vector in the plane and the x-axis. According to the geometric relationship, it can be known that:

[0139]

[0140] According to formula (1516), it can be deduced that in the case of two-dimensional phase gradient, the elevation angle and azimuth angle of the first-order grating are calculated as follows:

[0141]

[0142] In this work, the structural parameters of are selected. At this time, the beam deflection angle is small and the energy is high, which is convenient for measurement and research. The corresponding metasurface units are periodically distributed as "000111" in both the x and y directions.

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

[0144] As Figure 8 shown, the grating period . According to the theoretical calculation of formula (17), taking the incidence of 0.7 THz light as an example, the theoretically predicted value of the elevation angle θ is ±42.33°, and the theoretically predicted values of the azimuth angle are 45°, 135°, 225°, and 315°.

[0145] 2) Functional design principle of Fresnel lens

[0146] In the transmission space, the metasurface is designed to realize the function of a Fresnel lens. The traditional lens realizes wavefront regulation through the phase accumulation caused by the propagation of light in the glass medium, so as to converge the light beam at the focus. This volume phase regulation method results in a relatively large thickness of the device, and due to the processing technology limitations, a spherical configuration is usually adopted, making it difficult to avoid the inherent spherical aberration problem. The Fresnel lens is formed by a structure that blocks an even or odd number of half-wave zones. The Fresnel lens eliminates the coherent cancellation between adjacent two half-wave zones of the ordinary zone plate, making the intensity of the outgoing light beam equal to the square of the sum of the amplitudes transmitted through each slit, thus significantly enhancing the light intensity and also reducing the thickness to a certain extent. The introduction of the metasurface further reduces the volume of the lens. By precisely designing the phase distribution of the converging spherical wave, spherical aberration is eliminated in principle, and it has the advantages of extremely thin structure, uniform thickness, and large focusing intensity.

[0147] This paper designs based on the principle of the phase-type Fresnel lens. Based on this principle, the focusing phase distribution of the metasurface is analyzed.

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

[0149] As Figure 9As shown, the incident electromagnetic wave is focused on the focal point F after being regulated by the metasurface. The origin of the metasurface is O. Consider a point P with coordinates ( ) on the metasurface. When 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 the metasurface with 1-bit phase regulation, the phase difference between point O and point P can be described as . Combining formula (19), the phase design formula for the 1-bit focusing lens can be obtained:

[0153]

[0154] where is the working wavelength, is the distance between a point on the metasurface and the origin O. According to formula (19), we construct the required lens phase distribution under the conditions of focal length and incident light frequency of 0.7 THz.

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

[0156] According to the phase distribution diagrams of the reflection space and the transmission space ( Figure 8 and Figure 10 ), a metasurface with the functions of a two-dimensional grating and a Fresnel lens in the reflection space and the transmission space respectively can be built. In the CST Microwave Studio time-domain solver, a 0.7 THz polarized Gaussian beam is used as the excitation source to simulate this device. In the reflection space, by setting up a reflection space electric field monitor to record the frequency-domain data and performing a two-dimensional discrete space Fourier transform on it, the grating diffraction spectrum in the cross-section direction is obtained. After analyzing and calculating the spectrum, the relationship diagram of the elevation angle and the azimuth angle is obtained.

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

[0158] As Figure 10 shown, where the simulation value is ±42.2°, The simulated values of 45.1°, 135.1°, 225.1°, and 315.1° are in good agreement with the theoretical predicted values, fully verifying the effectiveness of the reflection space design method. In the transmission space, by obtaining plane the light intensity distribution in the direction.

[0159] Figure 12 is the Fresnel lens in the transmission space in Example 1 light intensity distribution map of the plane.

[0160] As Figure 12 shown, it can be observed that the metalens exhibits a significant focusing effect. To quantitatively characterize the focusing characteristics, the longitudinal light intensity distribution on the Figure 11 axis in is further extracted.

[0161] Figure 13 is Figure 11 taking light intensity curve along the z direction.

[0162] As Figure 13 shown, the light intensity curve clearly shows the intensity distribution of the focus, and at the same time, the actual focusing position can be quantitatively measured as 9570 μm, with a relative deviation of only -4.30% from the theoretical design value. To deeply evaluate the focusing performance of the Fresnel lens, the plane can be intercepted at the main focus position for light field intensity analysis.

[0163] Figure 14 is the light intensity distribution map of the plane at the main focus position.

[0164] As Figure 14 shown, by extracting the transverse light intensity distribution curve on the Figure 14 axis in and plotting it as Figure 15 .

[0165] Figure 15 is for Figure 14 taking light intensity curve along the x direction.

[0166] As Figure 15 shown, the full width at half maximum of the focused spot is 0.242 mm, showing 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 focusing vortex beam at a position of 10 mm in the reflection space and a holographic function of a dot-shaped "T" in the transmission space.

[0169] 1) Design principle of vortex beam

[0170] In the reflection space, the metasurface is designed as a vortex beam generator structure. It shows a phase change along the angular direction in terms of phase, and the change amount is usually an integer multiple of 2π. Due to the phase change along the angular direction, the phase at the center point of the vortex light cannot be defined, forming a singularity, resulting in an intensity pattern presenting a spiral arm shape with a hole in the center. Therefore, when Gaussian light is incident on the metasurface with the following phase distribution, a focused vortex beam can be generated.

[0171]

[0172] where is the topological number of the vortex beam. The second term of the above formula is deformed from formula (18) of the Fresnel lens part mentioned above, which means that the metasurface can not only generate vortex beams, but also focus the vortex beams to the focal length position designed by us, facilitating its measurement and research.

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

[0174]

[0175] Combining formula (20) and formula (21), taking the topological number and the focal length , when the 0.7 THz light is incident, the phase arrangement of the metasurface as shown in Figure 16 can be obtained.

[0176] 2) Design principle of holographic imaging

[0177] In the transmission space, the metasurface is designed as a holographic imaging structure. In the process of hologram design in this paper, the Rayleigh - Sommerfeld (RS) diffraction formula and the Gerchberg - Saxton (GS) iterative algorithm are combined. According to the principle of optical path reversibility, first, the amplitude and phase distributions of the metasurface are constructed by inverse diffraction based on the light intensity distribution and amplitude distribution 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 approximately regarded as a diffraction process between two planes in free space, the RS diffraction formula can be used to calculate the amplitude and phase distributions of the metasurface:

[0178]

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

[0180]

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

[0182] When obtaining the distribution of the reconstructed image according to the holographic metasurface, the inverse transformation of the above formula is used, that is:

[0183]

[0184] In the formula, represents the electric field at point r1 on the reconstructed image; is the electric field at point R0 on the metasurface after discretization; is the range of the metasurface. Due to the change in the light transmission direction, the sign of the exponential term is opposite.

[0185] Since the target holographic image has an arbitrary initial phase in the above process, it is difficult to achieve an ideal holographic imaging effect in a single reconstruction. The embodiment of the present 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 (the amplitude remains unchanged), and then the target holographic image is used to enter the above process for the second reconstruction, and so on iteratively.

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

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

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

[0189] According to the phase distribution diagram of transmission space and reflection space ( Figure 18 and Figure 16 ), a metasurface with focused vortex beam and holographic imaging functions in the reflection space and transmission space can be constructed. In the CST Microwave Studio time domain solver, a 0.7THz y-polarized Gaussian beam is used to simulate the metasurface. In the reflection space, by setting an electric field monitor at the focus position, the intensity and phase distribution of the vortex beam are obtained, as shown in Figure 2. Figure 19 and Figure 20 shown.

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

[0191] Figure 20 This is the light phase distribution diagram at the focal position of the vortex beam in the reflection space in Example 2.

[0192] Figure 19 It can be seen that the light beam has obvious vortex characteristics and presents a typical ring structure. The light intensity in the central area is zero due to the phase singularity. Figure 20 The spiral phase structure shown indicates that the beam carries orbital angular momentum. The corresponding two phase branches, the phase value is from arrive There is a jump along the azimuth angle. At the same time, the existence of phase singularity can also be observed in the central area. Further, by obtaining the vortex beam Light intensity distribution in the xoz direction of the plane.

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

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

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

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

[0197] Figure 22 , Figure 23 shows a clear dot matrix "T", indicating that the device has good transmission holographic ability.

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

Claims

1. A metasurface for full-space 1-bit phase modulation based on mirror symmetry, characterized in that Comprising: A plurality of structural units, the plurality of structural units comprising: A support layer, A reflection component, located on one side surface of the support layer and at a first position or a second position. When the reflection component is at the first position, the projection of the reflection component on a preset plane is mirror-symmetrical with respect to a target axis to the projection of the reflection component on the preset plane when the reflection component is at the second position. The preset plane is a plane perpendicular to the height direction of the structural unit, and the target axis is a straight line passing through a target point. The target point is the center point of the projection of the structural unit on the preset plane. The reflection component is adapted to reflect the received incident light beam to obtain a reflection light beam perpendicular to the polarization direction of the incident light beam. When the reflection component is in the first position, the reflection light beam has a first phase, and when the reflection component is in the second position, the reflection light beam has a second phase; A transmission component, located on the side surface of the support layer away from the reflection component. A first through hole is formed in the transmission component, and the first through hole is at a third position or a fourth position. When the transmission component is at the third position, the projection of the transmission component on the preset plane is mirror-symmetrical with respect to the target axis to the projection of the transmission component on the preset plane when the transmission component is at the fourth position; The transmission component is adapted to transmit the incident light beam that sequentially passes through the reflection component and the support layer and obtain a transmission light beam with a polarization direction opposite to that of the incident light beam; When the first through hole is at the third position, the transmission light beam has a third phase, and when the transmission component is at the fourth position, the transmission light beam has a fourth phase.

2. The metasurface according to claim 1, wherein The reflection 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 directions of the U-shaped metal ring and the U-shaped hole are perpendicular.

4. The metasurface according to claim 2, wherein The extending directions of the two parallel arms of the U-shaped metal ring are the same as the extending direction of 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: A first sub-support layer, on which the reflection component is located; A transmission polarization selection layer, located on the side surface of the first sub-support layer away from the reflection component. A second through hole extending along the first direction is formed in the transmission polarization selection layer for performing polarization filtering on the incident light beam passing through the first sub-support layer; A second sub-support layer, 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 reflection components of the respective plurality of structural units are determined according to the diffraction order of the reflective grating, the size of the unit structure, and the position of the structural unit; When the transmitted light is used as a grating, the positions of the first through holes of the respective plurality of structural units are determined according to the diffraction order of the transmissive grating, the size of the unit structure, 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 reflection components of the respective plurality of structural units are 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 positions of the first through-holes of the plurality of structural units are determined according to the focal length of the transmissive Fresnel lens and the positions of the structural units.

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

9. The metasurface according to claim 1, wherein, When the metasurface is used as a reflective holographic imaging structure, the positions of the reflection components 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 transmissive holographic imaging structure, the positions of the first through-holes of the plurality of structural units and the positions of the reflection components 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.

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

Images