Reconfigurable terahertz metasurface based on vanadium dioxide

Abstract

The invention relates to a vanadium dioxide-based reconfigurable terahertz metasurface, which comprises a plurality of units arranged in an array, each unit comprises a vanadium dioxide pattern layer, a first polyamide layer, a metal annular layer, a vanadium dioxide film layer, a second polyamide layer and a metal bottom layer which are laminated from top to bottom, the vanadium dioxide pattern layer forms a cross-shaped pattern with a cross-shaped interval in the middle; the metal annular layer is formed by a plurality of nested concentric rings, a first opening part is formed in the outermost ring, a second opening part is formed in the innermost ring, and the center line of the first opening part and the center line of the second opening part are located on the same straight line. The metasurface is based on the phase change characteristic of vanadium dioxide, switching of absorption and polarization conversion functions of the same unit is achieved, the function conversion difficulty is greatly reduced, the metasurface has dynamic adjustability and good flexibility, reconstruction of the metasurface can be achieved through the simple open double rings, and machining is convenient and easy to achieve.

Description

Technical Field

[0001] The present invention belongs to the field of metasurfaces, and particularly relates to a reconfigurable terahertz metasurface based on vanadium dioxide. Background Art

[0002] In many practical applications, it is necessary to be able to adjust the characteristics of the metasurface in real time according to different requirements, such as dynamically regulating the reflection, refraction, absorption and other characteristics of terahertz waves to achieve more flexible functions. In the field of communication, the reconfigurable terahertz metasurface can be used to dynamically regulate the propagation of terahertz waves to achieve high-speed and large-capacity communication; in the field of imaging, the focusing and imaging of terahertz waves can be achieved by reconstructing the metasurface to improve the resolution and contrast of imaging; in the field of sensing, the response characteristics of the metasurface can be adjusted according to different sensing requirements to improve the sensitivity and selectivity of the sensor. Therefore, the reconfigurable technology has become a research hotspot.

[0003] However, once the traditional metasurface is manufactured, its functions and characteristics are fixed, lacking dynamic adjustability and poor flexibility, and the existing metasurfaces have single functions and complex structures, which are not easy to process. Summary of the Invention

[0004] In order to solve the above problems existing in the prior art, the present invention provides a reconfigurable terahertz metasurface based on vanadium dioxide. The technical problems to be solved by the present invention are realized through the following technical solutions:

[0005] An embodiment of the present invention provides a reconfigurable terahertz metasurface based on vanadium dioxide, including: a plurality of units arranged in an array, each unit including a vanadium dioxide pattern layer, a first polyamide layer, a metal ring layer, a vanadium dioxide thin film layer, a second polyamide layer and a metal bottom layer stacked from top to bottom, wherein,

[0006] The vanadium dioxide pattern layer forms a cross-shaped pattern with a cross-shaped interval in the middle;

[0007] The metal ring layer is formed by a plurality of nested concentric rings, and a first opening is provided on the outermost ring, and a second opening is provided on the innermost ring, and the center lines of the first opening and the second opening are located on the same straight line;

[0008] The center of the concentric rings coincides with the center of the cross-shaped pattern, and a preset angle is formed between the straight line and the horizontal line of the cross-shaped pattern.

[0009] In an embodiment of the present invention, the vanadium dioxide pattern layer includes four right-angled figures, wherein,

[0010] Each right-angled figure is formed by connecting two mutually perpendicular right-angled sides, and the right-angled sides of the four right-angled figures are adjacent to each other in pairs and arranged at intervals to form the cross-shaped interval.

[0011] In an embodiment of the present invention, the lengths of the right-angled sides in the four right-angled figures are the same and the widths are the same, and the distances between adjacent two right-angled sides are the same;

[0012] The cross-shaped pattern with a cross-shaped interval in the middle is a centrosymmetric pattern.

[0013] In an embodiment of the present invention, the distance between adjacent right-angled sides is 2.5 μm;

[0014] The length and width of the cross-shaped pattern are both 57 μm;

[0015] The widths of the right-angled sides are all 3.75 μm.

[0016] In an embodiment of the present invention, the plurality of concentric rings include a first ring, a second ring and a third ring, wherein,

[0017] The first ring, the second ring and the third ring are nested in sequence from the outside to the inside and form concentric circles; a first opening is provided on the first ring, and a second opening is provided on the third ring.

[0018] In an embodiment of the present invention, the distance between the first ring and the second ring, and the distance between the second ring and the third ring are equal;

[0019] The width of the first ring and the width of the second ring are the same and less than the width of the third ring;

[0020] The radian of the first opening and the radian of the second opening are equal.

[0021] In an embodiment of the present invention, the radius of the first ring is 16 μm, the radius of the second ring is 21 μm, and the radius of the third ring is 26 μm;

[0022] The width of the first ring is 1 μm, the width of the second ring is 1 μm, and the width of the third ring is 3 μm;

[0023] The radian of the first opening and the radian of the second opening are both 10°;

[0024] The preset included angle is 45°.

[0025] In an embodiment of the present invention, the material of the metal ring-shaped layer includes gold, and the material of the metal bottom layer includes gold.

[0026] In one embodiment of the present invention, the period of the unit is 60 μm;

[0027] The thickness of the vanadium dioxide pattern layer is 0.2 μm, the thickness of the first polyamide layer is 16 μm, the thickness of the metal ring layer is 0.2 μm, the thickness of the vanadium dioxide thin film layer is 0.2 μm, the thickness of the second polyamide layer is 17 μm, and the thickness of the metal bottom layer is 0.3 μm.

[0028] In one embodiment of the present invention, when vanadium dioxide is in the metallic state, the metasurface is a broadband absorber, and the broadband absorber includes a vanadium dioxide pattern layer, a first polyamide layer, and a vanadium dioxide thin film layer;

[0029] When vanadium dioxide is in the insulating state, the metasurface is a cross-polarization converter, and the cross-polarization converter includes a metal ring layer, a second polyamide layer, and a metal bottom layer.

[0030] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0031] In the metasurface of the present invention, each unit is formed by laminating a vanadium dioxide pattern layer, a first polyamide layer, a metal ring layer, a vanadium dioxide thin film layer, a second polyamide layer, and a metal bottom layer. The vanadium dioxide pattern layer has a cross-shaped pattern with a cross-shaped interval in the middle. The metal ring layer is composed of several rings. When vanadium dioxide is in the metallic state, the metasurface is a broadband absorber. When vanadium dioxide is in the insulating state, the metasurface is a cross-polarization converter. Based on the phase change characteristics of vanadium dioxide, the switching of the absorption and polarization conversion functions of the same unit is realized, greatly reducing the difficulty of function conversion, having dynamic adjustability, good flexibility, and using relatively simple open double rings to realize the reconstruction of the metasurface, which is convenient for processing and easy to implement. Description of the Drawings

[0032] Figure 1 It is a schematic structural diagram of a reconfigurable terahertz metasurface based on vanadium dioxide provided by an embodiment of the present invention;

[0033] Figure 2 It is a schematic structural diagram of another reconfigurable terahertz metasurface based on vanadium dioxide provided by an embodiment of the present invention;

[0034] Figure 3 It is a top view of a reconfigurable terahertz metasurface based on vanadium dioxide provided by an embodiment of the present invention;

[0035] Figure 4 It is a schematic diagram of a metal ring layer provided by an embodiment of the present invention;

[0036] Figure 5 It is a schematic diagram of the reflection and absorption spectra of the broadband absorber provided by an embodiment of the present invention;

[0037] Figure 6 This is a schematic diagram of the co-polarized and cross-polarized reflection coefficients of the converter when the incident angle is zero provided by the embodiments of the present invention. Detailed implementation manners

[0038] The present invention will be further described in detail below in conjunction with specific embodiments, but the implementation manners of the present invention are not limited thereto.

[0039] Embodiment 1

[0040] Please refer to Figure 1 and Figure 2 , Figure 1 This is a schematic diagram of the structure of a vanadium dioxide-based reconfigurable terahertz metasurface provided by the embodiments of the present invention, Figure 2 This is another schematic diagram of the structure of a vanadium dioxide-based reconfigurable terahertz metasurface provided by the embodiments of the present invention.

[0041] The vanadium dioxide-based reconfigurable terahertz metasurface in this embodiment includes a plurality of units arranged in an array, and each unit includes a vanadium dioxide pattern layer 1, a first polyamide layer 2, a metal ring layer 3, a vanadium dioxide thin film layer 4, a second polyamide layer 5, and a metal bottom layer 6 stacked from top to bottom.

[0042] Exemplarily, the shape of each unit is a square, and the period of each unit, that is, the side length of the square, is 60 μm.

[0043] Please refer to Figure 3 , Figure 3 This is a top view of a vanadium dioxide-based reconfigurable terahertz metasurface provided by the embodiments of the present invention.

[0044] In a specific embodiment, the vanadium dioxide pattern layer 1 forms a cross-shaped pattern with a cross-shaped interval in the middle, thereby forming a cross-like figure.

[0045] Specifically, the vanadium dioxide pattern layer 1 includes four right-angled figures 11. Each right-angled figure 11 is formed by connecting two mutually perpendicular right-angled sides 111 and 112. The right-angled sides of the four right-angled figures 11 are adjacent to each other in pairs and arranged at intervals to form a cross-shaped interval. It can be understood that the first right-angled side of the first right-angled figure 11 is adjacent to and arranged at intervals from the first right-angled side of the second right-angled figure 11, the second right-angled side of the second right-angled figure 11 is adjacent to and arranged at intervals from the first right-angled side of the third right-angled figure 11, the second right-angled side of the third right-angled figure 11 is adjacent to and arranged at intervals from the first right-angled side of the fourth right-angled figure 11, and the second right-angled side of the fourth right-angled figure 11 is adjacent to and arranged at intervals from the second right-angled side of the first right-angled figure 11. The intervals between the eight right-angled sides together form a cross-shaped interval, and the cross-shaped interval and the four right-angled figures 11 together form a cross-like figure.

[0046] Specifically, the lengths of the right-angled sides in the four right-angled figures 11 are the same and the widths are the same, and the distances between adjacent right-angled sides are the same. Thus, the cross-shaped pattern with a cross-shaped interval in the middle forms a centrosymmetric pattern, that is, the cross-like figure is a centrosymmetric figure.

[0047] Preferably, the distance between adjacent right-angled sides is d = 2.5 μm; the length and width of the cross-shaped pattern are both L 1 = 57 μm; the widths of the right-angled sides are both w = 3.75 μm.

[0048] Please refer to Figure 4 , Figure 4 which is a schematic diagram of a metal ring layer provided by an embodiment of the present invention. The metal ring layer 3 is formed by a plurality of nested concentric rings Circle, and a first opening θ is provided on the outermost ring 1 ,and a second opening θ is provided on the innermost ring 2 ,the center line of the first opening θ 1 and the center line of the second opening θ 2 are located on the same straight line; the center of the concentric rings coincides with the center of the cross-shaped pattern, and a preset angle is formed between the straight line and the horizontal line of the cross-shaped pattern.

[0049] It can be understood that the cross-shaped pattern with a cross-shaped interval in the middle forms four regions at the four corners. The first opening θ 1 can be located in any region of the cross-shaped pattern. Correspondingly, the second opening θ 2 is located in the diagonal region of this region.

[0050] Specifically, the plurality of concentric rings include a first ring Circle1, a second ring Circle2, and a third ring Circle3, where

[0051] The first ring Circle1, the second ring Circle2, and the third ring Circle3 are nested in sequence from the outside to the inside and form concentric circles; a first opening θ is provided on the first ring. 1 A second opening θ is provided on the third ring. 2 Moreover, the center line of the first opening θ 1 and the center line of the second opening θ 2 are located on the same straight line.

[0052] Furthermore, the distance between the first ring Circle1 and the second ring Circle2, and the distance between the second ring Circle2 and the third ring Circle3 are both equal; the width of the first ring Circle1 and the width of the second ring Circle2 are the same and less than the width of the third ring Circle1; the radian of the first opening θ 1 and the radian of the second opening θ 2 are equal.

[0053] Preferably, the radius of the first ring Circle1 is 16 μm, the radius of the second ring Circle2 is 21 μm, and the radius of the third ring Circle3 is 26 μm, that is, the distance between the first ring Circle1 and the second ring Circle2, and the distance between the second ring Circle2 and the third ring Circle3 are both 5 μm; the width of the first ring is 1 μm, the width of the second ring is 1 μm, and the width of the third ring is 3 μm; the radian of the first opening and the radian of the second opening are both 10°.

[0054] Preferably, the straight line formed by the coincidence of the center line of the first opening θ 1 and the center line of the second opening θ 2 forms a 45° angle with the horizontal line of the cross-shaped pattern.

[0055] In a specific embodiment, the material of the metal ring layer 3 includes gold, and the material of the metal bottom layer 6 includes gold.

[0056] Preferably, the thickness of the vanadium dioxide pattern layer 1 is 0.2 μm, the thickness of the first polyamide layer 2 is 16 μm, the thickness of the metal ring layer 3 is 0.2 μm, the thickness of the vanadium dioxide thin film layer 4 is 0.2 μm, the thickness of the second polyamide layer 5 is 17 μm, and the thickness of the metal bottom layer 6 is 0.3 μm. The length and width of the first polyamide layer 2, the length and width of the vanadium dioxide thin film layer 4, the length and width of the second polyamide layer 5, and the length and width of the metal bottom layer 6 are all 60 μm.

[0057] The working principle of the reconfigurable terahertz metasurface based on vanadium dioxide in this embodiment is:

[0058] When vanadium dioxide is in the metallic state, this metasurface is a broadband absorber, which mainly consists of a cross-like vanadium dioxide pattern layer 1, a first polyamide layer 2, and a vanadium dioxide thin film layer 4. Absorptivity is an important parameter reflecting the absorption device. The absorptivity of the absorber can be expressed as: A = 1 - |s 11 | 2 - |s 21 | 2 where s 11 and s 21 represent the reflection coefficient and the transmission coefficient, which are generated by the incident wave incident on the absorber. Since the thickness of the vanadium dioxide thin film is much larger than its skin depth, there is almost no transmitted wave generated. The absorptivity can be simplified to A = 1 - |s 11 | 2 . Please refer to Figure 5 , Figure 5 which is the schematic diagram of the reflection and absorption spectra of the broadband absorber provided by the embodiment of the present invention. In the range of 1.28 Thz - 3.07 Thz, the absorptivity of the designed absorber exceeds 90%. The transmitted energy is almost zero, so the reflection and absorption curves are complementary.

[0059] When vanadium dioxide is in the insulating state, this metasurface is a cross-polarization converter, which consists of a metal ring layer 3, a second polyamide layer 5, and a metal bottom layer 6. Even if the incident field has only one component, the reflected field usually consists of two components in the x and y directions. There is a phase difference of ±π / 2 or ±π between two resonances in different directions, resulting in circular polarization conversion or cross-linear polarization conversion. The co-polarization reflection coefficients of broadband LTX polarization conversion and LTC polarization conversion are defined as r xx = |E rx | / |E ix | and r yy = |E ry | / |E iy |, where r xx represents that both the incident wave and the reflected wave are x-polarized, and r yy represents that both the incident wave and the reflected wave are y-polarized. The cross-polarization reflection coefficients are defined as r yx = |E ry | / |E ix | and r xy = |E rx | / |E iy |, where r yx represents that the incident wave is x-polarized and the reflected wave is y-polarized, and r xy represents that the incident wave is y-polarized and the reflected wave is x-polarized. Please refer to Figure 6 , Figure 6Schematic diagram of the co-polarization and cross-polarization reflection coefficients of the converter when the incident angle is zero provided by the embodiment of the present invention. As can be seen from the figure, the co-polarization and cross-polarization reflection coefficients of the converter are basically the same when the incident angle is zero.

[0060] In summary, for the reconfigurable terahertz metasurface based on vanadium dioxide in this embodiment, when vanadium dioxide is in the metallic state, the device is a broadband absorber, with an absorption rate exceeding 90% from 1.28 Thz to 3.07 Thz, and the broadband absorption performance is insensitive to the oblique incident angle and polarization. When vanadium dioxide is in the insulating state, the device acts as a polarization converter, having two linear-to-cross-polarization functions, linear-to-circular polarization conversion. The polarization conversion efficiency of the linear-to-cross-polarization conversion reaches over 90% from 1.46 Thz to 2.28 Thz. The designed multifunctional metasurface has the advantages of broadband and multifunctionality, integrating multiple functions into one device, and has great potential in terahertz device applications.

[0061] The metasurface of this embodiment is based on the phase change characteristics of vanadium dioxide, realizing the switching of the absorption and polarization conversion functions of the same unit, greatly reducing the difficulty of function conversion, having dynamic adjustability, good flexibility, and using a relatively simple split double-ring to achieve the reconfiguration of the metasurface, which is convenient to process and easy to implement.

[0062] The above content is a further detailed description of the present invention in combination with specific preferred embodiments, and it cannot be determined that the specific implementation of the present invention is only limited to these descriptions. For those of ordinary skill in the technical field to which the present invention belongs, without departing from the concept of the present invention, several simple deductions or substitutions can still be made, and all should be regarded as belonging to the protection scope of the present invention.

Claims

1. A reconfigurable terahertz metasurface based on vanadium dioxide, characterized in that: include: A plurality of units are arranged in an array, each unit comprising a vanadium dioxide pattern layer, a first polyamide layer, a metal ring layer, a vanadium dioxide film layer, a second polyamide layer and a metal bottom layer stacked from top to bottom, wherein: The vanadium dioxide pattern layer forms a cross-shaped pattern with a cross-shaped interval in the middle; The metal annular layer is formed by a plurality of nested concentric rings, and a first opening is formed on the outermost ring, and a second opening is formed on the innermost ring, and a center line of the first opening and a center line of the second opening are located on the same straight line; The centers of the concentric circles coincide with the center of the cross pattern, and a preset angle is formed between the straight line and the horizontal line of the cross pattern.

2. The vanadium dioxide-based reconfigurable terahertz metasurface according to claim 1, characterized in that: The vanadium dioxide pattern layer includes four right-angle patterns, wherein: Each right-angle figure is formed by connecting two right-angle sides that are perpendicular to each other, and the right-angle sides of the four right-angle figures are adjacent to each other in pairs and are arranged at intervals to form the cross-shaped interval.

3. The vanadium dioxide-based reconfigurable terahertz supersurface according to claim 2, characterized in that: The lengths and widths of the right-angled sides of the four right-angled figures are all the same, and the spacing between two adjacent right-angled sides is the same; The cross-shaped pattern with a cross-shaped interval in the middle is a centrally symmetrical pattern.

4. The vanadium dioxide-based reconfigurable terahertz metasurface according to claim 2, characterized in that: The spacing between adjacent right-angle edges is 2.5 μm; The length and width of the cross pattern are both 57 μm; The width of the right-angle sides is 3.75 μm.

5. The vanadium dioxide-based reconfigurable terahertz metasurface according to claim 1, characterized in that: The plurality of concentric rings include a first ring, a second ring and a third ring, wherein: The first circular ring, the second circular ring and the third circular ring are nested in sequence from outside to inside to form concentric circles; the first circular ring is provided with a first opening, and the third circular ring is provided with a second opening.

6. The vanadium dioxide-based reconfigurable terahertz supersurface according to claim 5, characterized in that: The distance between the first circular ring and the second circular ring, and the distance between the second circular ring and the third circular ring are equal; The width of the first circular ring is the same as the width of the second circular ring and is smaller than the width of the third circular ring; The curvature of the first opening is equal to the curvature of the second opening.

7. The vanadium dioxide-based reconfigurable terahertz supersurface according to claim 6, characterized in that: The radius of the first circular ring is 16 μm, the radius of the second circular ring is 21 μm, and the radius of the third circular ring is 26 μm; The width of the first circular ring is 1 μm, the width of the second circular ring is 1 μm, and the width of the third circular ring is 3 μm; The curvature of the first opening and the curvature of the second opening are both 10°; The preset angle is 45°.

8. The vanadium dioxide-based reconfigurable terahertz metasurface according to claim 1, characterized in that: The material of the metal ring layer includes gold, and the material of the metal bottom layer includes gold.

9. The vanadium dioxide-based reconfigurable terahertz metasurface according to claim 1, characterized in that: The period of the unit is 60 μm; The thickness of the vanadium dioxide pattern layer is 0.2 μm, the thickness of the first polyamide layer is 16 μm, the thickness of the metal ring layer is 0.2 μm, the thickness of the vanadium dioxide film layer is 0.2 μm, the thickness of the second polyamide layer is 17 μm, and the thickness of the metal bottom layer is 0.3 μm.

10. The vanadium dioxide-based reconfigurable terahertz metasurface according to claim 1, characterized in that: When vanadium dioxide is in a metallic state, the metasurface is a broadband absorber, and the broadband absorber includes a vanadium dioxide pattern layer, a first polyamide layer, and a vanadium dioxide thin film layer; When vanadium dioxide is in an insulating state, the metasurface is an alternating polarization converter, which includes a metal annular layer, a second polyamide layer and a metal bottom layer.

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