A reconfigurable terahertz metasurface based on vanadium dioxide

Abstract

The application relates to a reconfigurable terahertz super surface based on vanadium dioxide, comprising: a plurality of units arranged in an array, each unit comprising, from top to bottom, 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, wherein the vanadium dioxide pattern layer forms a cross-shaped pattern with a cross-shaped interval in the middle; the metal ring layer is formed by a plurality of concentric circular rings, a first opening part is arranged on the outermost circular ring, a second opening part is arranged on the innermost circular 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 super surface is based on the phase change characteristic of vanadium dioxide, realizes switching of the absorption and polarization conversion functions of the same unit, greatly reduces the function conversion difficulty, has dynamic adjustability, is good in flexibility, and realizes the reconfiguration of the super surface by using a relatively simple open double circular ring, and is convenient to process and easy to realize.

Description

TECHNICAL FIELD

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

[0002] In many practical applications, it is necessary to adjust the characteristics of the metasurface in real time according to different needs, such as dynamically regulating the reflection, refraction, absorption and other characteristics of the terahertz wave, so as to realize more flexible functions. In the field of communication, the reconfigurable terahertz metasurface can be used to dynamically regulate the propagation of the terahertz wave, realize high-speed and high-capacity communication; in the field of imaging, the focusing and imaging of the terahertz wave can be realized by reconfiguring the metasurface, so as to improve the resolution and contrast of the imaging; in the field of sensing, the response characteristics of the metasurface can be adjusted according to different sensing needs, so as 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 function and characteristics are fixed, lacking dynamic adjustability and poor flexibility, and the existing metasurface has single function and complex structure, which is not easy to process. SUMMARY

[0004] In order to solve the above problems existing in the prior art, the present application provides a reconfigurable terahertz metasurface based on vanadium dioxide. The technical problem to be solved by the present application is solved by the following technical scheme:

[0005] The present application provides a reconfigurable terahertz metasurface based on vanadium dioxide, comprising: a plurality of units 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,

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

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

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

[0009] In an embodiment of the present application, the vanadium dioxide pattern layer comprises four right-angled patterns, wherein,

[0010] Each of the right-angle figures is formed by two mutually perpendicular right-angle edges, and the right-angle edges of the four right-angle figures are alternately adjacent and spaced to form the cross-shaped spacing.

[0011] In an embodiment of the present application, the length and the width of the right-angle edges in the four right-angle figures are the same, and the spacing between the adjacent right-angle edges is the same.

[0012] The cross-shaped pattern with the cross-shaped spacing in the middle is a central symmetric pattern.

[0013] In an embodiment of the present application, the spacing between the adjacent right-angle edges is 2.5 μm.

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

[0015] The width of the right-angle edges is 3.75 μm.

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

[0017] The first circular ring, the second circular ring and the third circular ring are sequentially nested from outside to inside and form concentric circles; the first circular ring is provided with a first opening portion, and the third circular ring is provided with a second opening portion.

[0018] In an embodiment of the present application, 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.

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

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

[0021] In an embodiment of the present application, 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.

[0022] 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.

[0023] The arc of the first opening portion and the arc of the second opening portion are both 10°.

[0024] The preset included angle is 45°.

[0025] In an embodiment of the present application, the material of the metal annular layer comprises gold, and the material of the metal bottom layer comprises gold.

[0026] In an embodiment of the present application, 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 annular 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.

[0028] In an embodiment of the present application, when the vanadium dioxide is in a metal state, the metasurface is a broadband absorber, and the broadband absorber comprises the vanadium dioxide pattern layer, the first polyamide layer, and the vanadium dioxide film layer.

[0029] When the vanadium dioxide is in an insulator state, the metasurface is a cross-polarization converter, and the cross-polarization converter comprises the metal annular layer, the second polyamide layer, and the metal bottom layer.

[0030] Compared with the prior art, the present application has the following beneficial effects:

[0031] In the metasurface of the present application, each unit is stacked by the vanadium dioxide pattern layer, the first polyamide layer, the metal annular layer, the vanadium dioxide film layer, the second polyamide layer, and the metal bottom layer, and the vanadium dioxide pattern layer has a cross-shaped pattern with a cross-shaped space in the middle. The metal annular layer is composed of a plurality of annular rings. When the vanadium dioxide is in a metal state, the metasurface is a broadband absorber. When the vanadium dioxide is in an insulator 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, the functional conversion difficulty is greatly reduced, the dynamic adjustability is good, the flexibility is good, and the reconstruction of the metasurface can be realized by using a relatively simple open double annular ring, which is convenient to process and easy to realize. BRIEF DESCRIPTION OF DRAWINGS

[0032] Figure 1 A structure diagram of a reconfigurable terahertz metasurface based on vanadium dioxide is provided for an embodiment of the present application.

[0033] Figure 2 Another structure diagram of a reconfigurable terahertz metasurface based on vanadium dioxide is provided for an embodiment of the present application.

[0034] Figure 3 A top view of a reconfigurable terahertz metasurface based on vanadium dioxide is provided for an embodiment of the present application.

[0035] Figure 4 A schematic diagram of a metal annular layer is provided for an embodiment of the present application.

[0036] Figure 5 A reflection and absorption spectrum diagram of a broadband absorber is provided for an embodiment of the present application.

[0037] Figure 6 A schematic diagram of co-polarization and cross-polarization reflection coefficients of the transformer when the incidence angle is zero is provided for the embodiments of the present application. DETAILED DESCRIPTION

[0038] The present application will be further described below in connection with specific embodiments, but the embodiments of the present application are not limited thereto.

[0039] Embodiment One

[0040] See Figure 1 and Figure 2 , Figure 1 A schematic diagram of a structure of a reconfigurable terahertz metasurface based on vanadium dioxide is provided for the embodiments of the present application. Figure 2 A schematic diagram of another structure of a reconfigurable terahertz metasurface based on vanadium dioxide is provided for the embodiments of the present application.

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

[0042] For example, the shape of each unit is a square, and the period of each unit, i.e., the side length of the square, is 60 μm.

[0043] See Figure 3 , Figure 3 A top view of a reconfigurable terahertz metasurface based on vanadium dioxide is provided for the embodiments of the present application.

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

[0045] Specifically, the vanadium dioxide pattern layer 1 includes four right-angled patterns 11. Each of the right-angled patterns 11 is formed by two mutually perpendicular right-angled sides 111, 112. The right-angled sides of the four right-angled patterns 11 are arranged alternately and spaced apart to form a cross-shaped space. It can be understood that the first right-angled side of the first right-angled pattern 11 is adjacent to and spaced apart from the first right-angled side of the second right-angled pattern 11, the second right-angled side of the second right-angled pattern 11 is adjacent to and spaced apart from the first right-angled side of the third right-angled pattern 11, the second right-angled side of the third right-angled pattern 11 is adjacent to and spaced apart from the first right-angled side of the fourth right-angled pattern 11, the second right-angled side of the fourth right-angled pattern 11 is adjacent to and spaced apart from the second right-angled side of the first right-angled pattern 11, and the spaces between the eight right-angled sides form a cross-shaped space together, and the cross-shaped space and the four right-angled patterns 11 form a cross-like pattern together.

[0046] Specifically, the lengths of the right-angled sides of the four right-angled patterns 11 are the same, the widths of the right-angled sides are the same, and the distances between the adjacent right-angled sides are the same, so that the cross-shaped pattern with the cross-shaped space forms a central symmetric pattern, that is, the cross-like pattern is a central symmetric pattern.

[0047] Preferably, the distance between the adjacent right-angled sides is d = 2.5 μm, the length and width of the cross-shaped pattern are L1 = 57 μm, and the width of the right-angled side is w = 3.75 μm.

[0048] Please refer to Figure 4 , Figure 4 A schematic diagram of a metal annular layer provided by an embodiment of the present application is shown in FIG. 3. The metal annular layer 3 is formed by a plurality of concentric circular rings Circle, and a first opening θ1 is formed on the outermost circular ring and a second opening θ2 is formed on the innermost circular ring. The center line of the first opening θ1 and the center line of the second opening θ2 are located on the same straight line. The center of the concentric circular ring coincides with the center of the cross-shaped pattern, and a preset included 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 the cross-shaped space forms four regions at the four corners, and the first opening θ1 can be located in any region of the cross-shaped pattern, and correspondingly, the second opening θ2 is located in the diagonal region of the region.

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

[0051] The first circular ring Circle1, the second circular ring Circle2 and the third circular ring Circle3 are nested from outside to inside and form concentric circles; the first opening part θ1 is arranged on the first circular ring, the second opening part θ2 is arranged on the third circular ring, and the center lines of the first opening part θ1 and the second opening part θ2 are located on the same straight line.

[0052] Further, the distance between the first circular ring Circle1 and the second circular ring Circle2 and the distance between the second circular ring Circle2 and the third circular ring Circle3 are equal; the width of the first circular ring Circle1 and the width of the second circular ring Circle2 are the same and less than the width of the third circular ring Circle1; the arc of the first opening part θ1 and the arc of the second opening part θ2 are equal.

[0053] Preferably, the radius of the first circular ring Circle1 is 16 μm, the radius of the second circular ring Circle2 is 21 μm, and the radius of the third circular ring Circle3 is 26 μm, that is, the distance between the first circular ring Circle1 and the second circular ring Circle2 and the distance between the second circular ring Circle2 and the third circular ring Circle3 are both 5 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 arc of the first opening part and the arc of the second opening part are both 10°.

[0054] Preferably, the center lines of the first opening part θ1 and the second opening part θ2 coincide to form a straight line, and the straight line and the horizontal line of the cross-shaped pattern form an included angle of 45°.

[0055] In one 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 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 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 as follows:

[0058] When the vanadium dioxide is in a metal state, the metasurface is a broadband absorber, which mainly includes the cross-like vanadium dioxide pattern layer 1, the first polyamide layer 2 and the vanadium dioxide film layer 4. Absorptivity is an important parameter of the absorber, and the absorptivity of the absorber can be calculated as follows: A = 1 - |s 11 |2 -|s 21 | 2 where s 11 and s 21 represent the reflection and transmission coefficients, which are generated by the incident wave incident on the absorber. Since the thickness of the vanadium dioxide film is much larger than its skin depth, almost no transmission wave is generated. The absorption can be simplified as A = 1 - |s 11 | 2 . Please refer to Figure 5 , Figure 5 The schematic diagram of the reflection and absorption spectrum of the broadband absorber provided by the embodiment of the present application is shown in the figure. In the range of 1.28 Thz-3.07 Thz, the designed absorber has an absorbance of more than 90%. The transmission energy is almost zero, so the reflection and absorption curves are complementary.

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

[0060] In summary, the embodiment is based on a reconfigurable terahertz metasurface of vanadium dioxide. When vanadium dioxide is in a metallic state, the device is a broadband absorber with an absorption rate of over 90% from 1.28 Thz to 3.07 Thz. The broadband absorption performance is insensitive to the oblique incidence angle and polarization. When vanadium dioxide is in an insulating state, the device behaves as a polarization transformer with two linear-to-cross-polarization functions, linear-to-circular polarization conversion. The polarization conversion efficiency of linear-to-cross-polarization conversion reaches more than 90% from 1.46 Thz to 2.28 Thz. The designed multifunctional metasurface has the advantages of wideband and multifunction, and multiple functions are concentrated into one device, which has great potential in terahertz device applications.

[0061] The metasurface of the embodiment is based on the phase transition characteristics of vanadium dioxide, which realizes the switching of the absorption and polarization conversion functions of the same unit, greatly reduces the difficulty of function conversion, has dynamic adjustability, good flexibility, and uses a relatively simple open double circular ring to realize the reconstruction of the metasurface, which is convenient to process and easy to realize.

[0062] The above is a further detailed description of the present application in combination with specific preferred embodiments, and the specific implementation of the present application cannot be limited to these descriptions. For ordinary skilled persons in the technical field to which the present application belongs, a number of simple deductions or substitutions can be made without departing from the concept of the present application, and all of them should be regarded as falling within the protection scope of the present application.

Claims

1. A reconfigurable terahertz metasurface based on vanadium dioxide, characterized in that, The application relates to a super surface, which comprises: a plurality of units arranged in an array, each unit comprising, from top to bottom, 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, wherein the vanadium dioxide pattern layer forms a cross-shaped pattern with a cross-shaped gap in the middle, the cross-shaped pattern with the cross-shaped gap in the middle is a central symmetric pattern; the vanadium dioxide pattern layer comprises four right-angled figures, each right-angled figure being formed by two mutually perpendicular right-angled edges, and the right-angled edges of the four right-angled figures are arranged in pairs and spaced apart to form the cross-shaped gap; the metal ring layer comprises a first circular ring, a second circular ring and a third circular ring, the first circular ring, the second circular ring and the third circular ring are nested in sequence from outside to inside and form concentric circular rings, a first opening part is formed in the first circular ring, a second opening part is formed in the third circular ring, the center line of the first opening part and the center line of the second opening part are located on the same straight line, and the first opening part and the second opening part are different in direction, and 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 center of the concentric circular ring coincides with the center of the cross-shaped pattern, and a preset included angle is formed between the straight line and the horizontal line of the cross-shaped pattern.

2. The reconfigurable terahertz metasurface based on vanadium dioxide according to claim 1, wherein, the lengths of the right-angled edges in the four right-angled figures are the same, the widths of the right-angled edges are the same, and the spacings between the adjacent right-angled edges are the same.

3. The reconfigurable terahertz metasurface based on vanadium dioxide of claim 1, wherein, the spacing between the adjacent right-angled edges is 2.5 mu m; the length and the width of the cross-shaped pattern are both 57 mu m; the width of the right-angled edge is 3.75 mu m.

4. The reconfigurable terahertz metasurface based on vanadium dioxide of claim 1, wherein, 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 arc of the first opening part is equal to the arc of the second opening part.

5. The reconfigurable terahertz metasurface based on vanadium dioxide of claim 4, wherein, the radius of the first circular ring is 16 mu m, the radius of the second circular ring is 21 mu m, and the radius of the third circular ring is 26 mu m; the width of the first circular ring is 1 mu m, the width of the second circular ring is 1 mu m, and the width of the third circular ring is 3 mu m; the arc of the first opening part and the arc of the second opening part are both 10 degrees; the preset included angle is 45 degrees.

6. The reconfigurable terahertz metasurface based on vanadium dioxide of claim 1, wherein, the material of the metal ring layer comprises gold, and the material of the metal bottom layer comprises gold.

7. The reconfigurable terahertz metasurface based on vanadium dioxide of claim 1, wherein, the period of the unit is 60 mu m; the thickness of the vanadium dioxide pattern layer is 0.2 mu m, the thickness of the first polyamide layer is 16 mu m, the thickness of the metal ring layer is 0.2 mu m, the thickness of the vanadium dioxide film layer is 0.2 mu m, the thickness of the second polyamide layer is 17 mu m, and the thickness of the metal bottom layer is 0.3 mu m. 8.The reconfigurable terahertz metasurface based on vanadium dioxide of claim 1, wherein, when the vanadium dioxide is in a metal state, the super surface is a broadband absorber, the broadband absorber comprising a vanadium dioxide pattern layer, a first polyamide layer and a vanadium dioxide film layer; when the vanadium dioxide is in an insulator state, the super surface is a cross-polarization converter, the cross-polarization converter comprising a metal ring layer, a second polyamide layer and a metal bottom layer.

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