Structure based on graphene metamaterial, preparation method and application

Abstract

A structure based on a graphene metamaterial is a matrix formed by a plurality of repetitive modules, each repetitive module is formed by arranging a plurality of elements in a certain geometrical shape, and each element is of a multi-layer structure and sequentially comprises a silicon substrate layer, a graphene layer, a silicon covering layer and an electrode layer from bottom to top; wherein the electrode layer and the graphene layer are externally connected with a power supply to form a loop; each repeating module is arranged in a specific geometric pattern on the matrix. Due to complete isolation processing between the element patterns D1, D2,..., Dc-1, Dc + 1, Dc + 2,..., Dn, and between Dc and Dd, the device has the advantages that the function effect of the device can be enhanced, diversified control can be realized, and the device can realize different functions by modulating the electrode assemblies in different areas.

Description

Technical Field

[0001] The present invention relates to the field of graphene-related structures, and in particular to a structure based on graphene metamaterials and a preparation method and application thereof. Background Art

[0002] Surface plasmons (Sps) are generated by the interaction between conduction electrons on the surface of metal media and photons in light waves. Researchers divide plasmons into two main types according to the way they are generated: one is surface plasmons (LSPs) propagating on the medium, and the other is bound localized surface plasmons (Spps). Both can localize electromagnetic waves within the subwavelength range and enhance local electric and magnetic fields. Due to its ability to break through the limits of traditional optical diffraction and propagate within the subwavelength range, various terahertz devices based on SPPs have been widely studied, such as optical switches, perfect absorbers, modulators, etc. However, there are two significant problems with this type of traditional optical devices: first, most of them use metal media as the main structure of the device, and the active tunability is poor; second, the ohmic and radiation losses of metals are relatively serious. As a new type of two-dimensional material, graphene is a hexagonal honeycomb structure composed of a single layer of carbon atoms. Since it was discovered by two professors from the University of Manchester in the UK, it has attracted widespread attention. Surprisingly, related studies have found that graphene also has certain properties of metal media, such as negative dielectric constant and high carrier mobility, which allows it to excite and propagate SPPs like metals. Moreover, compared with integrated optical devices with metal media as the architecture, various devices composed of graphene have incomparable advantages, such as the ability to dynamically control devices by changing the Fermi level of graphene, lower ohmic transmission loss, and mature preparation methods, which have begun to replace metal media as the main architecture of various optical devices. At the same time, researchers have also found that graphene has many interesting phenomena, such as stronger compression ability of light waves, stronger local characteristics than metals, and better plasmon-induced transparency (PIT) effect.

[0003] The PIT effect is the key to improving nano-optical devices. It enhances the interaction between light and matter to achieve higher coupling efficiency. Compared with EIT, PIT is generated by the interaction of near-field coupling modes. It is not subject to strict experimental conditions and restrictions. Its strong practical value makes it have an important impact on the application of optical devices. There are two ways to generate PIT: one is the mutual coupling between the bright mode that can be directly excited by the incident light and the dark mode that is indirectly excited, thereby generating destructive interference; the other is the weak coupling between the two bright modes, thereby generating a transmission valley in the transmission spectrum. At present, the technology of using the PIT effect to study nano-optical devices is relatively mature: in 2021, Jiang et al. used the single PIT effect to realize a multifunctional sensor, and in 2024, Lei et al. used a single PIT generated by a cross-shaped graphene pattern to realize an optical switch device that is insensitive to polarized light. Moreover, the regulation of many devices is no longer limited to a single PIT. Various optical devices based on dual PIT, triple PIT, and even quadruple PIT have been widely studied and applied. However, most of the multi-PIT effects are produced using two common methods: one is to simply use the coupling between dark modes and multiple bright modes on a single-layer pattern, so that the combination structure of graphene per unit area becomes complex; the other is to adopt a multi-layer graphene combination architecture, which leads to the complexity of device design and increased manufacturing difficulty, bringing challenges to the practical application of the device.

[0004] In the prior art, CN117406470A and CN116154484A both report devices related to plasma induced transparency, which have excellent optical properties and can be used in related optical instrument application fields. However, the above two plasma induced transparent devices have certain shortcomings, such as the integrated connection adopted in the structure, all controls can only be determined by one electrode, and the lack of diversified control limits them in certain application occasions. Therefore, it is necessary to further optimize the prior art. Summary of the invention

[0005] Based on this, this paper constructs a new type of single-layer graphene metamaterial structure, which uses the interaction between three graphene blocks and one graphene strip to produce two single PITs. The two single PITs can produce a tunable triple PIT effect at terahertz frequencies through a synergistic effect, such as Figure 1As shown. The actual experimental phenomenon observation and related test data show that the results shown by the device are in line with expectations. The structure can use the voltage change on the electrode to achieve the regulation of the graphene Fermi level, without the need to change the device's geometric model like some structural designs. In addition, the influence of different polarization angles of external polarized light on the device performance is also studied. The results show that when the polarization angle changes between -20° and 20°, the structure can still maintain a stable transmission spectrum, which solves the problem that the polarized light cannot meet the theoretical situation in practice, resulting in functional failure, and greatly improves the practicality. Through further research, by changing the carrier mobility and Fermi level of graphene, a six-frequency asynchronous optical switch with excellent performance of 99.3%, 3.16 dephasing time and 0.039dB can be achieved. Moreover, the graphene metasurface structure has excellent slow light characteristics, and its slow light coefficient is as high as 1212, which surpasses most traditional slow light devices. The graphene metamaterial structure proposed in the present invention can provide corresponding theoretical guidance for various optical switches and slow light devices with excellent performance.

[0006] An object of the present invention is to disclose a structure based on graphene metamaterials, wherein the structure is a matrix composed of a plurality of repeating modules, wherein the repeating modules are composed of a plurality of primitives arranged in a certain geometric shape,

[0007] Each unit cell has a multi-layer structure, which consists of a silicon base layer, a graphene layer, a silicon cover layer, and an electrode layer from bottom to top. The electrode layer and the graphene layer are connected to an external power source to form a loop.

[0008] Each repeating module is arranged in the following geometric pattern on the matrix:

[0009] Adjacent repeating modules, primitive pattern D in the longitudinal direction d Connected to each other, they form a straight line pattern arrangement;

[0010] From the primitive pattern D in each repeating module d The center position of is the endpoint, and a primitive pattern is extended in the horizontal direction, set as D c ;

[0011] D c is the axis of symmetry, at D c On the left and right sides of the , n primitive patterns are laid in the horizontal direction, denoted as D1, D2, ... D c-1 ; and D c+1 , D c+2 ......D n ;D c The primitive patterns on the left and right sides are axially symmetrical;

[0012] D1, D2...Dc-1 , and D c+1 , D c+2 ......D n , all of them are connected to the primitive patterns in the longitudinal direction, and there is no other primitive pattern connected to them, and the distance is S1;

[0013] D1, D2...D c-1 , and D c+1 , D c+2 ......D n , there are no other primitive patterns connected to the adjacent primitive patterns in the lateral direction, and the distance is S2.

[0014] Furthermore, the number of n is an even number.

[0015] Furthermore, in the primitive pattern, D d The width m3 is 0.1-0.6um; the width w1 is 0.5-1um.

[0016] Furthermore, in the primitive pattern, D c The length m2 is 1.5-3um.

[0017] Furthermore, in the primitive pattern, D1, D2...D c-1 , and D c+1 , D c+2 ......D n , length m1 is 1.5-3um; width w2 is 0.5-1um.

[0018] Furthermore, the value range of S1 and S2 is 0.2-0.8um.

[0019] Another object of the present invention is to disclose a method for preparing the structure based on graphene metamaterial, wherein the method comprises the following steps:

[0020] S1, coating a graphene layer on the silicon substrate layer;

[0021] S2, coating a silicon cover layer on the graphene layer;

[0022] S3, coating an electrode layer on the silicon cover layer;

[0023] S4. Connect the graphene layer and the electrode layer to an external power source to form a circuit.

[0024] Furthermore, an adjustable resistor is also provided in the loop.

[0025] Furthermore, polarized light is applied to the graphene metamaterial to adjust the polarization angle.

[0026] Another object of the present invention is to disclose the application of the above-mentioned graphene metamaterial-based structure in optical instruments.

[0027] Specifically, in a primitive pattern, D d It is not directly excited by incident light, which is called dark mode; D c , D c-1

[0028] , D c+1 It will be directly excited by the incident light, which is called bright mode. d and D c There will be destructive interference between them, thus stimulating a single PIT_1, and D c and D c-1 , D c+1 The three will be weakly coupled to stimulate a single PIT_2 with the same properties as single PIT_1, but with frequency shift. Then PIT_1 and PIT_2 will produce a triple PIT effect with three transparent windows under the synergistic effect. The dispersion characteristics and transparent window offset effects produced in this coupling state are excellent. We can use the dispersion characteristics to study the slow light characteristics of the device. The most important indicator is the group refractive index. The larger the group refractive index, the better the slow light characteristics. In the experiment, we prepared graphene pattern structures with different mobilities, and the corresponding mobilities are μ = 1.0m 2 ·(V·s) -1 、μ=2.0m 2 ·(V·s) -1 、μ=3.0m 2 ·(V·s) -1 When we control the voltage on the electrode, we finally get the experimental data and find that its group refraction can reach 1200, which has a very excellent slow light effect. The different offset degrees of the transparent window can be used to make corresponding optical switches according to needs. During the experiment, we controlled the carrier mobility at μ = 3.0m 2 ·(V·s) -1 The operation of an optical switch is achieved by adjusting the voltage value at different incident light frequency points. The performance parameters of the optical switch are mainly determined by the insertion loss and modulation depth, which are 0.03dB and 99.31% respectively. Relatively speaking, the performance is very excellent.

[0029] The present invention has the following beneficial effects: the present invention can perform corresponding regulation without changing the structural parameters. In addition, the structure can be adjusted accordingly according to different requirements of actual application. c-1 , and D c+1 , D c+2 ......Dn The primitive patterns are related to each other and to D c , D d The complete isolation between them has the following advantages: first, it can enhance the functional effect of the device; second, it can achieve diversified control by modulating the electrode components in different areas to enable the device to achieve different functions.

[0030] Specifically, for slow light applications, our device design has three structures parallel to the x-direction, and have a certain length. They are isolated from each other and maintain a certain distance, which is used to enhance the coupling between graphenes and thus enhance the binding of light, so that the slow light effect is more obvious; for optical switch applications, the layout of graphene is mostly oriented along the incident direction of light and maintains a certain distance so that the graphene along the y-direction can be coordinated and coupled with the graphene in the x-direction, thereby enhancing the coupling efficiency. In addition, the distance between the graphene in the x-direction is relatively close, and near-field coupling can be used to further enhance the binding and resonance of light, making the transmission peak stronger, and both states of the optical switch can be better displayed. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 The spectra produced by different structural parts of graphene are shown, where (a) is formed by The G_1 and The G_2

[0032]

[0033] (Ef=1eV,μ=1.0m 2 / (Vs)).

[0034] Figure 2 (a) shows a top view of the overall structure of the graphene metamaterial of Examples 1-3;

[0035] Figure 2 (b) shows a multilayer structure diagram of a single repeating module of Examples 1-3;

[0036] Figure 2 (c) shows the size parameters of each primitive pattern on a single repeating module of Examples 1-3;

[0037] Figure 2 (d) shows a flow chart for the preparation of a single repeating module of Examples 1-3.

[0038] Figure 3 A device structure diagram of a comparative example is shown.

[0039] Among them, 2 is an arbitrary repeating module; 31 is the primitive pattern D d 32 and 33 are primitive patterns D c .

[0040] Figure 4 The graphs showing the variation of group refractive index and phase shift with frequency for the Fermi level (a) Ef = 0.9 eV, (b) Ef = 1.0 eV, (c) Ef = 1.1 eV and (d) Ef = 1.2 eV are shown respectively.

[0041] Figure 5 It shows the six-frequency optical switch modulation when the Fermi level is at 0.8eV, 1.2eV and the mobility μ=3.0m2 / (Vs).

[0042] Figure 6 The transmission spectrum changes at different polarization angles. (a) The transmission spectrum generated when the polarization angle changes between -20° and 20°; (b) The evolution of the transmission spectrum as the polarization angle of the incident light changes. DETAILED DESCRIPTION

[0043] Example

[0044] The following examples prepare graphene metamaterial structures based on graphene metamaterials of different sizes. The relevant sizes are shown in Table 1 below. Here, we take n=2; the number of repeating modules is 9. That is, the structure of the graphene metamaterial is a matrix composed of 9 repeating modules.

[0045] Table 1 A series of graphene metamaterial-based structures of different sizes

[0046] Example 1 Example 2 Example 3 <![CDATA[m1(um)]]> 2.2 2.0 1.8 <![CDATA[m2(um)]]> 2.3 2.2 2.1 <![CDATA[m3(um)]]> 1.2 1.1 1.0 <![CDATA[S1(um)]]> 0.4 0.4 0.4 <![CDATA[S2(um)]]> 0.25 0.25 0.25 <![CDATA[W1(um)]]> 0.8 0.8 0.8 <![CDATA[W2(um)]]> 0.6 0.5 0.4 <![CDATA[L x (one)]]> 4 4 4 <![CDATA[L y (one)]]> 4 4 4

[0047] The preparation method of the graphene metamaterial-based structure of the above-mentioned embodiments 1-3 is as follows:

[0048] S1. First, a graphene layer is grown on a copper foil at 1000°C by chemical vapor deposition, and then the prepared graphene layer is transferred to a silicon substrate by dry and wet transfer techniques, and then the graphene layer is etched by plasma etching to obtain the following Figure 2 Patterned graphene strips on a silicon substrate are shown;

[0049] S2. Using a mask, a vacuum thermal evaporation system will have Figure 2 The specific pattern shown is a 0.01um thick copper film electrode deposited on the graphene strip and silicon surface;

[0050] S3, connecting the graphene layer and the electrode layer to an external power source and a resistor using a wire to form a loop, and regulating the device by changing the resistance value of the resistor or the voltage value of the power source;

[0051] S4, external polarization device. The obtained device structure is as follows Figure 2 shown.

[0052] Comparative Example

[0053] Here, we introduce the device structure in CN116154484A for comparison. Its relevant dimensions are as follows Figure 2 shown.

[0054] The multilayer structure of the comparative example is consistent with the preparation method and size of Example 1.

[0055] The design of the above comparative example has disadvantages in that: for the application of slow light, there is only one graphene parallel to the x direction and its area is small, and the near-field coupling between the graphenes is weak, so the binding effect on the x-polarized light is small, making its slow light effect not obvious; for the application of optical switches, because its structure adopts an "I" shape, when the incident light is irradiated, it will be weakened by the near-field coupling of different graphene directions, resulting in the weakening of the transmission peak, which makes many performances of the optical switch poor, such as modulation depth, insertion loss, etc.

[0056] Test Case

[0057] The following test example tests the characteristics of the graphene metamaterial structure of the size of Example 1. By adjusting the voltage on the corresponding structure electrode, the Fermi level is modulated.

[0058] We use polarized lasers to generate two polarized lights, one of which is irradiated on the graphene structure; the other is used as reference light. The transmitted light signal is received by an optical detector and sent to an oscilloscope. The output signal is then compared with the reference signal. By comparing the delay and phase shift between the two output light signals, the slow light effect of the device can be calculated. Combined with the experimental observations, we analyzed a type of slow light under carrier mobility. First, the carrier mobility of the graphene structure is fixed to μ = 3.0 m 2 / (V·s), analyze the phase shift when the Fermi level is 0.9eV, 1.0eV, 1.1eV, and 1.2eV, and use MATLAB according to the formula The phase shift data obtained is converted into the change data of the group refractive index. When the mobility is controlled at μ = 3.0 m 2 / (V·s), the group refractive index result is as follows Figure 4 As shown in (a)-(d). As shown in the figure, when the Fermi level is set to 0.8eV, its group refractive index is 812, such as Figure 4 As shown in (a), when the Fermi level is 1.2 eV, its group refractive index is as high as 1212, indicating that it is a graphene device with excellent slow light performance.

[0059] Furthermore, the modulation characteristics of the optical switch of Example 1 were tested, and the relevant parameters were designed and controlled according to the theoretically estimated model, as shown in Table 2 below.

[0060] Table 2 Results of modulation characteristics of the relevant optical switches of Example 1

[0061] Example 1 Insertion loss(dB) 0.03 Dephase time (ps) 3.16 Modulation Depth(%) 99.3

[0062] Then, the polarized laser is used to control the corresponding frequency for incidence, and the voltage is controlled by using the electrodes on the structure. The corresponding switching state of Example 1 can be obtained according to different frequency points, as shown in Table 3. Figure 5 shown.

[0063] Table 3 Corresponding switch states of Example 1

[0064]

[0065] For example, at 5.3206 Thz, when the voltage on the electrode controls the Fermi level to 0.8 eV, the photodetector detects that the light transmittance of the device is weak, indicating that the device is in the closed state; and when the voltage control makes the Fermi level 1.2 eV, the light transmittance of the device is detected to be very strong, indicating that the device is in the open state.

[0066] Then, the incident frequency was changed to test the switching effects of other frequency points one by one, and it was found that it could realize the basic functions of the optical switch. Then, a comparative functional test was carried out, and it was found that all of them could achieve the expected results. Then, based on the experimental data, the modulation depth (MD), dephasing time (MD), and insertion loss (IL) were sorted out to evaluate the characteristics of the optical switch. The modulation depth is the maximum and minimum values ​​of the light transmittance of the device detected by the photodetector for comparison. The insertion loss is the loss coefficient of the optical switch, which is usually calculated by taking the logarithm of the maximum value of the light transmittance, and the dephasing time is obtained by using the half-height width on the oscilloscope. The corresponding formulas are:

[0067] IL = -10 × log(T max ),

[0068] By sorting out the experimental data, it is found that its modulation depth, dephasing time, and insertion loss are 99.31%, 3.16ps, and 0.03dB respectively. Such data can meet the requirements of excellent optical switches.

[0069] Furthermore, in actual use, changing the polarization angle of the incident light will inevitably make the incident light unable to satisfy the polarization in a single direction due to special reasons, and many devices will fail due to failure to meet the theoretical requirements. Therefore, in the experiment, the polarization angle of the incident light was changed to observe the changes in the device transmission spectrum. It was found that when the polarization angle changes between -20° and +20°, the device transmission spectrum can remain stable. At the same time, the characteristics of the graphene material were tested at different polarization angles. The results show that it can stably meet the requirements when used in slow light devices and optical switch devices, and can better avoid the problem of device unusability in actual use. The results are as follows: Figure 6 As shown in (a) and (b).

[0070] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above and that the present invention can be implemented in other specific forms without departing from the spirit or essential features of the present invention. Therefore, the embodiments should be considered exemplary and non-restrictive in all respects, and the scope of the present invention is defined by the appended claims rather than the above description, and it is intended that all changes falling within the meaning and scope of the equivalent elements of the claims be included in the present invention.

[0071] In addition, it should be understood that although the present specification is described according to implementation modes, not every implementation mode contains only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

Claims

1. A structure based on graphene metamaterial, characterized in that: The graphene metamaterial-based structure is a matrix composed of a plurality of repeating modules, wherein the repeating modules are composed of a plurality of primitives arranged in a certain geometric shape. Each unit cell has a multi-layer structure, which consists of a silicon base layer, a graphene layer, a silicon cover layer, and an electrode layer from bottom to top. The electrode layer and the graphene layer are connected to an external power source to form a loop. Each repeating module is arranged in the following geometric pattern on the matrix: Adjacent repeating modules, primitive pattern D in the longitudinal direction d Connected to each other, they form a straight line pattern arrangement; From the primitive pattern D in each repeating module d The center position of is the endpoint, and a primitive pattern is extended in the horizontal direction, set as D c ; D c is the axis of symmetry, at D c On the left and right sides of the , n primitive patterns are laid in the horizontal direction, denoted as D1, D2, ... D c-1 ; and D c+1 , D c+2 ......D n ;D c The primitive patterns on the left and right sides are axially symmetrical; D1, D2...D c-1 , and D c+1 , D c+2 ......D n , all of them are connected to the primitive patterns in the longitudinal direction, and there is no other primitive pattern connected to them, and the distance is S1; D1, D2...D c-1 , and D c+1 , D c+2 ......D n , there are no other primitive patterns connected to the adjacent primitive patterns in the lateral direction, and the distance is S2.

2. The structure based on graphene metamaterial according to claim 1, characterized in that: The number of n is an even number.

3. The structure based on graphene metamaterial according to claim 1, characterized in that: In the primitive pattern, D d The width m3 is 0.1-0.6um; the width w1 is 0.5-1um.

4. The structure based on graphene metamaterial according to claim 1, characterized in that: In the primitive pattern, D c The length m2 is 1.5-3um.

5. The structure based on graphene metamaterial according to claim 1, characterized in that: In the primitive pattern, D1, D2...D c-1 , and D c+1 , D c+2 ......D n , length m1 is 1.5-3um; width w2 is 0.5-1um.

6. The structure based on graphene metamaterial according to claim 1, characterized in that: The value range of S1 and S2 is 0.2-0.8um.

7. The method for preparing a structure based on graphene metamaterial according to any one of claims 1 to 6, characterized in that: The method for preparing the structure based on graphene metamaterial comprises the following steps: S1, coating a graphene layer on the silicon substrate layer; S2, coating a silicon cover layer on the graphene layer; S3, coating an electrode layer on the silicon cover layer; S4. Connect the graphene layer and the electrode layer to an external power source to form a circuit.

8. The method for preparing a structure based on graphene metamaterial according to claim 7, characterized in that: An adjustable resistor is also arranged in the loop.

9. The method for preparing a structure based on graphene metamaterial according to claim 7, characterized in that: Polarized light is applied to the graphene metamaterial to adjust the polarization angle.

10. Application of the graphene metamaterial-based structure according to any one of claims 1 to 6 in an optical instrument.

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