Triple plasma induced transparent graphene metasurface structure based on synergistic effect, preparation method and application thereof

Abstract

The invention provides a triple plasma induced transparent graphene metasurface structure based on a synergistic effect. The triple plasma induced transparent graphene metasurface structure based on the synergistic effect sequentially comprises a Si substrate, a graphene layer and a Si covering layer from bottom to top, the optical characteristics of the metasurface can be effectively changed by changing the Fermi level of graphene, a refractive index sensor with the sensing quality factor of 34.6 RIU <-1 > can be achieved, and meanwhile the metasurface has the excellent performance that the sensitivity is 1.32 THz / RIU. The slow light performance of the metasurface can be well enhanced by changing the carrier mobility of graphene, so that the metasurface has potential application prospects in the aspect of optical storage devices, and the group refractive index reaches up to 1109.

Description

Technical Field

[0001] The present invention belongs to the technical field of all-dielectric metasurface structures, and particularly relates to a graphene metasurface structure with triple plasmon-induced transparency based on a synergistic effect, a preparation method thereof, and an application thereof. Background Technique

[0002] Surface plasmon polaritons (SPPs) are oscillating waves generated by the resonant coupling of photons with free electrons on the surface of a metal medium. Since it can significantly enhance the interaction between light and matter, break through the traditional diffraction limit, and localize the light field at the sub-wavelength scale, it has become a research hotspot in the field of nano-optics [3]. However, the research on traditional SPPs is mainly based on noble metal materials, and its inherent defects such as high ohmic loss and poor dynamic tunability severely limit the practical applications of SPPs. Graphene, as a new two-dimensional material with a hexagonal honeycomb lattice structure, has attracted extensive attention from researchers due to its unique advantages in the optical field. In addition, graphene usually exhibits dynamically tunable characteristics, and its optical properties can be characterized and regulated by changes in conductivity. Compared with noble metals with free electrons, its carrier concentration can be dynamically regulated using voltage and chemical doping, thus showing different optical characteristics in different terahertz bands. Compared with noble metal materials, SPPs supported by graphene have significant advantages. Particularly importantly, the bandwidth of SPPs generated by graphene materials can be dynamically regulated using the Fermi level or carrier mobility. These excellent characteristics have enabled extensive research on various optical devices based on graphene SPPs, such as optical memories, optical switches, sensors, slow light devices, etc.

[0003] The functions of many devices are realized by using the plasmon-induced transparency (PIT) effect, which is generated by the interaction between graphene and SPPs. The emergence of PIT has greatly promoted the development of terahertz optical devices. So far, the application of the PIT effect in optical devices has been dominant: for example, in 2021, Jiang et al. used single PIT generated by a cross-shaped and four-bar graphene to achieve a sensor insensitive to polarized light; in 2022, Fan et al. used single PIT generated by a cross-shaped and circular graphene metasurface to achieve dual-frequency optical switch modulation; in 2023, Yang et al. used double PIT generated by two graphene bars and a graphene block to achieve a good slow light effect with a group refractive index of 380; also in 2024, Wang et al. used double PIT generated by four graphene bars and four graphene rings to achieve a good sensor. However, in practical applications, to meet the requirements of complex functional devices, the functions of many devices are realized using the multi-PIT effect.

[0004] At present, the research on the excitation mechanism of the multi-PIT effect mainly combines the formation process of single PIT and utilizes the coupling between multiple bright and dark modes to achieve the evolution from single PIT to multi-PIT. However, there is an important phenomenon that has been ignored in this evolution process, that is, the synergy effect. Summary of the Invention

[0005] Based on this, the present invention provides a graphene metasurface structure with triple plasmon-induced transparency based on the synergy effect. This structure consists of two longitudinal graphene strips and five transverse graphene bars. Under the excitation of incident light, a triple PIT effect can be generated, and its formation mechanism stems from the synergy effect between two single PITs.

[0006] The present invention provides a graphene metasurface structure with triple plasmon-induced transparency based on the synergy effect. The graphene metasurface structure with triple plasmon-induced transparency based on the synergy effect includes a Si substrate, a graphene layer, a Si capping layer, and an electrode layer from bottom to top in sequence;

[0007] Among them, the graphene layer includes:

[0008] A first transverse graphene strip, which is disposed on the surface of the Si substrate;

[0009] A longitudinal graphene strip, which is disposed at both ends of the first transverse graphene strip and is perpendicular to the first transverse graphene strip; both ends of the first transverse graphene strip are integrally connected to the longitudinal graphene strip;

[0010] Two second transverse graphene strips, which are symmetrically disposed on both sides of the first transverse graphene strip with the first transverse graphene strip as the symmetry axis and are parallel to the first transverse graphene strip;

[0011] Both ends of the second transverse graphene strip are integrally connected to the longitudinal graphene strip;

[0012] In the middle of each second transverse graphene strip, there is a gap, which divides each second transverse graphene strip into two parts.

[0013] Further, the length L of the longitudinal graphene strip y is 3 - 4 μm, and the width is 1.1 - 1.3 μm.

[0014] Further, the length m1 of the first transverse graphene strip is 2 - 3 μm, and the width is 0.7 - 0.9 μm.

[0015] Further, the length w1 of the gap is 0.3 - 0.5 μm.

[0016] Further, the distances h1 and h2 between the side of the second transverse graphene strip opposite to the first transverse graphene strip are 0.2 - 0.4 μm.

[0017] Further, the length w2 of the second transverse graphene strip is 1 - 2 μm, and the width is 0.7 - 0.9 μm.

[0018] Further, the width of the SiO2 substrate is 4 - 6 μm, the length is 4 - 6 μm, and the thickness is 15 - 25 nm.

[0019] Further, the thickness of the graphene layer is 0.01 - 0.05 nm.

[0020] Further, the thickness of the Si covering layer is 5 - 15 nm.

[0021] Further, the thickness of the electrode layer is 0.1 - 0.5 μm.

[0022] Further, the material of the electrode layer is selected from one or more of gold and silver.

[0023] Further, the Fermi level E of the graphene material in the graphene layer f is 0.8 - 1.2 eV.

[0024] Further, the carrier mobility of the graphene material in the graphene layer is 1.0 - 3.0 m 2 / (V·s).

[0025] Further, the relative dielectric constant of the silicon material of the Si covering layer and the Si substrate is 11 - 12.

[0026] Further, an electrode layer is further provided on the upper surface of the Si covering layer at one end of the longitudinal graphene strip, and the electrode layer and the graphene layer are connected by an external power supply;

[0027] Wherein, the Fermi level of the graphene material in the graphene layer is adjusted by adjusting the voltage of the external power supply.

[0028] Further, the voltage of the external power supply is 6.4 - 14.4 V.

[0029] Further, the preparation method of the graphene metasurface structure with triple plasmon-induced transparency based on the synergy effect includes the following steps: coating a layer of graphene on the Si substrate, etching the graphene to form a graphene layer, coating a Si covering layer on the graphene layer, coating an electrode layer on the Si covering layer, and connecting the graphene layer and the electrode layer with an external power supply to form a circuit, thereby obtaining the graphene metasurface structure with triple plasmon-induced transparency based on the synergy effect.

[0030] The present invention also provides a graphene metasurface structure array, the structure of which is as Figure 1 (a) shown. One end of the upper surface of the graphene metasurface structure array is provided with an electrode layer, and the graphene metasurface structure array includes a plurality of the graphene metasurface structures with triple plasmon-induced transparency based on the synergy effect arranged in a periodic array;

[0031] Among them, the electrode layer is arranged on the upper surface of the Si covering layer, and the electrode layer and the graphene layer are connected by an external power supply.

[0032] The present invention also provides the application of the graphene metasurface structure with triple plasmon-induced transparency based on the synergy effect in biosensing.

[0033] The graphene metasurface structure with triple plasmon-induced transparency based on the synergy effect and the application provided by the present invention have the following beneficial effects:

[0034] The present invention excites a graphene metasurface structure with triple PIT effect through the synergy effect between two single PITs of the graphene structure, and then compares the measured numerical results with the results of the coupled mode theory. The two results are highly consistent, verifying the accuracy of the results. Research shows that by changing the Fermi level of graphene, the optical properties of the metasurface can be effectively changed, and a refractive index sensor with a sensing quality factor of 34.6 RIU -1 can be realized, and it also has excellent performance with a sensitivity of 1.32 THz / RIU. In addition, by changing the carrier mobility of graphene, the slow light performance of the metasurface can be well enhanced, making it have potential application prospects in the application of optical storage devices, and the group refractive index is as high as 1109. Therefore, this graphene metasurface is expected to provide ideas for the design of refractive index sensors and optical storage with excellent performance. Description of the Drawings

[0035] Figure 1 (a) is a full view of an array composed of a plurality of graphene metasurface structures of the present invention;

[0036] [[ID=2,8]] Figure 1 (b) is a detailed view of the graphene layer in the graphene metasurface structure;

[0037] Figure 1 (c) is a side view of the graphene metasurface structure;

[0038] Figure 1 (d) is a schematic diagram of the coupled-mode theory;

[0039] Figure 2 (a) is a schematic diagram of the formation mechanism of PIT1;

[0040] Figure 2 (b) is a schematic diagram of the formation mechanism of PIT2;

[0041] Figure 2 (c) is the triple PIT transmission spectrum (E f = 1eV, μ = 1.0m 2 / (V·s)) formed by the graphene metasurface structure;

[0042] Figure 2 (d) is the normalized electric field map of the resonance valley;

[0043] Figure 3 (a) is the transmission diagram of theoretical coupling and numerical coupling at different Fermi levels;

[0044] Figure 3 (b) is the variation of the effective refractive index with the Fermi level;

[0045] Figure 3 (c) is the variation of Re(n eff ) with frequency at different Fermi levels;

[0046] Figure 4 (a) is the transmission spectrum at different medium refractive indices;

[0047] Figure 4 (b) is the sensitivity of different transmission valleys;

[0048] Figure 4 (c) is the sensing quality factor when the medium refractive index is equal to n = 1.1 (E f = 1.0eV);

[0049] Figure 4 (d) is the sensing quality factor when the medium refractive index is equal to n = 1.2 (E f = 1.0eV);

[0050] Figure 4 (e) is the sensing quality factor when the medium refractive index is equal to n = 1.3 (E f = 1.0eV);

[0051] Figure 4(f) is the sensing quality factor (E f = 1.0 eV) when the refractive index of the medium is n = 1.4;

[0052] Figure 5 (a) is the transmittance diagram under different carriers;

[0053] Figure 5 (b) is the sensitivity numerical diagram under different carriers;

[0054] Figure 6 (a)-(d) are respectively the diagrams of the change magnitude of the optical storage value under different carrier mobilities;

[0055] Figure 7 is the top view of the graphene metasurface structure.

[0056] In the figure: 1, Si substrate; 2, graphene layer; 21, first transverse graphene strip; 22, longitudinal graphene strip; 23, second transverse graphene strip; 3, Si capping layer; 4, electrode layer. Detailed implementation manners

[0057] To more clearly illustrate the technical solution of the present invention, the following examples are listed. The raw materials, reactions, and post-treatment means appearing in the examples are all common raw materials on the market and technical means well-known to those skilled in the art, unless otherwise specified.

[0058] Example 1

[0059] A graphene metasurface structure based on triple plasmon-induced transparency with a synergistic effect, as shown in Figure 1 (b)-(c) and Figure 7 shown, the graphene metasurface structure based on triple plasmon-induced transparency with a synergistic effect sequentially includes an Si substrate 1 (20 nm), a graphene layer 2 (0.01 nm), an Si capping layer 3 (10 nm), and an electrode layer 4 (gold, 0.1 nm) from bottom to top;

[0060] Among them, the graphene layer 2 includes:

[0061] A first transverse graphene strip 21, and the first transverse graphene strip 21 is disposed on the surface of the Si substrate 1;

[0062] A longitudinal graphene strip 22, and the longitudinal graphene strip 22 is disposed at both ends of the first transverse graphene strip 21 and is perpendicular to the first transverse graphene strip 21; both ends of the first transverse graphene strip 21 are integrally connected to the longitudinal graphene strip 22;

[0063] The second transverse graphene strip 23, the number of the second transverse graphene strips 23 is two, and they are respectively arranged on both sides of the first transverse graphene strip 21 with the first transverse graphene strip 21 as the axis of symmetry, and are parallel to the first transverse graphene strip 21;

[0064] Both ends of the second transverse graphene strip 23 are integrally connected to the longitudinal graphene strip 22;

[0065] In the middle of each second transverse graphene strip 23, there is a gap, which divides each second transverse graphene strip 23 into two parts, and the gap (w1) = 0.4 μm;

[0066] The electrode layer 4 is arranged on the upper surface of the Si covering layer 3 at one end of the longitudinal graphene strip 22, and the electrode layer 4 and the graphene layer 2 are connected by an external power supply;

[0067] The width (L x ) of the Si substrate 1 = the length (L y ) = 4 μm;

[0068] The length (m1) of the first transverse graphene strip 21 = 2.6 μm, and the width is 0.8 μm;

[0069] The length of the longitudinal graphene strip 22 is the same as the length of the Si substrate 1, and the width of the longitudinal graphene strip 22 is 1.2 μm;

[0070] The length (w2) of the second transverse graphene strip = 1.1 μm, and the width is 0.8 μm;

[0071] The distance h1 = h2 = 0.27 μm between the side of the second transverse graphene strip 23 opposite to the first transverse graphene strip 21;

[0072] The distance (h3) from the side of the second transverse graphene strip 23 far from the first transverse graphene strip 21 to the edge of the Si substrate 1 = 0.73 μm;

[0073] The distance (m2) between the opposite sides of the two longitudinal graphene strips = 3.8 μm.

[0074] The relative dielectric constant of the silicon material of the Si covering layer and the Si substrate is 11.7. Having a consistent dielectric constant can ensure the stability and consistency of the overall structure;

[0075] The Fermi level of graphene in the graphene layer is E f = 1.0 eV.

[0076] In this system, the working temperature T = 300K, and its surface conductivity can be expressed by the following formula:

[0077]

[0078] In the above formula, e represents the electron charge, E F represents the Fermi level, h is the reduced Planck constant, and ω is the angular frequency of the incident light. Among them, τ = μE F / (eV F ) 2 represents the carrier relaxation time, μ represents the carrier mobility, and V F represents the Fermi velocity. The propagation constant β of the SPPs on the graphene surface can be expressed as:

[0079]

[0080] Among them, k0 represents the wave vector, ε0, ε1, and ε2 represent the vacuum permittivity, the air permittivity, and the relative permittivity of silicon respectively. From this, the calculation formula for the effective refractive index is obtained: n eff = β / k0.

[0081] When the incident light is incident on the graphene structure along the z-axis, due to the interaction between the graphene and the incident light, triple PIT will be excited.

[0082] The preparation method of the above graphene metasurface structure with triple plasmon-induced transparency based on the synergistic effect is as follows:

[0083] Coat a layer of graphene on the Si substrate, then use plasma etching to etch the graphene to form a graphene layer, then coat a Si covering layer on the graphene layer, coat an electrode layer on the Si covering layer, and use an external power supply to connect the graphene layer and the electrode layer to form a circuit, obtaining the graphene metasurface structure with triple plasmon-induced transparency based on the synergistic effect;

[0084] Among them, the voltage of the external power supply is 6.4 - 14.4V.

[0085] Preparation Example 1 (Gra1)

[0086] A dielectric metasurface structure. Compared with Example 1, the difference in this preparation example is that: only longitudinal graphene strips 22 are provided in the graphene layer 2 of the metasurface structure, and the rest of the structure is the same as that in Example 1.

[0087] Preparation Example 2 (Gra2)

[0088] A dielectric metasurface structure. Compared with Example 1, the difference of this preparation example lies in that: only the first transverse graphene strip 21 is provided in the graphene layer 2 of the metasurface structure, and the rest of the structure is the same as that of Example 1.

[0089] Preparation Example 3 (PIT1)

[0090] A dielectric metasurface structure. Compared with Example 1, the difference of this preparation example lies in that: only the first transverse graphene strip 21 and the longitudinal graphene strip 22 are provided in the graphene layer 2 of the metasurface structure, and the rest of the structure is the same as that of Example 1.

[0091] Preparation Example 4 (Gra3)

[0092] A dielectric metasurface structure. Compared with Example 1, the difference of this preparation example lies in that: only the second transverse graphene strip 23 is provided in the graphene layer 2 of the metasurface structure, and the rest of the structure is the same as that of Example 1.

[0093] Preparation Example 5 (PIT2)

[0094] A dielectric metasurface structure. Compared with Example 1, the difference of this preparation example lies in that: only the longitudinal graphene strip 22 and the second transverse graphene strip 23 are provided in the graphene layer 2 of the metasurface structure, and the rest of the structure is the same as that of Example 1.

[0095] Test Example 1

[0096] To clearly understand the formation mechanism of this triple PIT system, we set Preparation Examples 1-5 for each region of the graphene structure, and analyze the excitation transmission spectra of Preparation Examples 1-5, as Figure 2 (a)-(d) shown.

[0097] In the figure, Example 1 is the Triple PIT curve; Preparation Example 1 is the Gra1 curve, Preparation Example 2 is the Gra2 curve, Preparation Example 3 is the PIT1 curve, Preparation Example 4 is the Gra3 curve, and Preparation Example 5 is the PIT2 curve;

[0098] From Figure 2 (a), it can be seen that Gra2 and Gra3 can generate two different Lorentz resonance modes. Since they can be directly excited by x-polarized light, they appear as bright modes. However, Gra1 lacks a vertical magnetic field component in its central axis direction, so it cannot be directly coupled with x-polarized light, but it can interact with the local field generated by the coupling of the bright mode and x-polarized light, and thus be indirectly excited, so it appears as a dark mode. During the formation of PIT1, Gra1 and Gra2 undergo coherent coupling to form destructive interference, thus generating a golden single PIT curve.

[0099] Similarly, asFigure 2 (b), the shown Gra1 acts as a dark mode, and destructive interference with the bright mode Gra3 generates a single-PIT blue curve, labeled as PIT2. Surprisingly, a triple-PIT effect is generated under the interaction of two single-PITs;

[0100] As Figure 2 shown by the black curve in (c). The formation of this triple-PIT effect can be explained using the coupled-mode theory: Under normal circumstances, a single-PIT has two resonance modes, and two PITs will have three resonance modes because two adjacent modes will disappear due to coupling and generate a new resonance mode. If there is a certain phase difference between two adjacent resonance modes, then coupling will not occur, thus maintaining four resonance modes and ultimately forming the three-PIT effect.

[0101] To further elaborate on the essence of the synergistic effect, the normalized electric field distributions in the x-y plane at four resonance frequencies are plotted, as Figure 2 shown in (d). The electric field of the transmission valley (Dip1) on the left side of PIT1, where the value of the curve is the lowest, is mainly localized at the outer edge of graphene Gra1. This distribution characteristic indicates that the formation of Dip1 is due to the contribution of graphene Gra1. The electric field of the transmission valley Dip3 on the right side is mainly localized on the surfaces and both sides of the graphene structures Gra1 and Gra2, indicating that the formation of Dip3 is the result of the combined action of Gra1 and Gra2. For PIT2, the electric field is mainly localized on the surfaces and near-field regions of Gra1 and Gra3, indicating that Gra1 and Gra3 are simultaneously excited. The electric field characteristics of the left transmission valley Dip2 are mainly localized between Gra3 and the near-field, indicating that the formation of Dip2 is mainly contributed by Gra3. The electric field of the right Dip4 is distributed across the entire graphene surface, indicating that the formation of the transmission valley Dip4 is mainly due to the combined action between Gra1 and Gra3. Therefore, combining the electric field distributions before and after the formation of the triple-PIT can prove the physical mechanism analyzed above. Among them, dip1 is similar to Dip1, dip2 is similar to Dip2, and dip3 is similar to Dip3, indicating that the formation of dip1, dip2, and dip3 is due to the incoherent coupling of Dip1, Dip2, and Dip3. The electric field distribution of dip4 is similar to that of Dip4, and the appearance of Gra2 further enhances the electric field. This indicates that the formation of dip4 is due to the incoherent coupling of Dip4 with the bright mode Gra2.

[0102] In summary, Dip1, Dip2, and Dip3 generate dip1, dip2, and dip3 through incoherent coupling. Dip4 and Gra2 undergo incoherent coupling to produce dip4, and ultimately, the best triple PIT effect is generated through the synergistic effect between PIT1 and PIT2.

[0103] Test Example 2

[0104] To study the coupling effect between various combinations of graphene, we adopted the coupled-mode theory. Figure 1 (d) Schematic diagram of the coupled-mode theory showing the triple PIT effect. Here, A, B, C, and D correspond to four different resonant modes, "in" and "out" represent the input and output of the incident light, and "+" and "-" are the propagation directions of the incident light. The intrinsic loss coefficients between the modes are represented by γ i(n) (n = 1, 2, 3, 4), and the external loss coefficient is represented by γ o(n) (n = 1, 2, 3, 4). μm n (m, n = 1, 2, 3, 4 and m ≠ n) are the coupling coefficients between the four coupled modes, and the coupling relationship of the four modes satisfies the following expressions:

[0105]

[0106] Here, γ n = (iω - iω n - γ in - γ on )(n = 1, 2, 3, 4), and γ in = ω n / (2Q in ), γ on = ω n / (2Q on ). ω represents the angular frequency of the incident light, ω n represents the angular frequency of the nth resonant mode, Q on and Q in represent the external quality factor and the internal quality factor of the nth mode, respectively. Q tn represents the total quality factor, and it and Q on , Q in satisfy the expression: 1 / Q tn = 1 / Q on + 1 / Q in , and it can also be calculated using the expression Q tn = f / Δf (f and Δf are the resonance frequency and the full width at half maximum of the nth resonant mode, respectively). The calculation method of the internal loss factor is: Q in = Re(n eff ) / Im(n eff )(Re(neff ) and Im(n eff ) are the real part and the imaginary part of the effective refractive index respectively). According to the law of conservation of energy, the energy relationship of the four resonant modes satisfies the following equation:

[0107]

[0108] where are the phase differences between different resonant modes respectively. Since the four resonant modes are in the same plane, the phase differences between them The transmission coefficient t can be simplified as:

[0109]

[0110] where K n (n = 1, 2, 3, 4) can be obtained by the following formula:

[0111]

[0112]

[0113] Finally, the transmittance T of the triple PIT system can be obtained from T = t 2 obtained.

[0114] Test Example 3

[0115] By changing the voltage on the electrode in Example 1, the dynamic regulation of graphene can be realized to adjust the Fermi level of graphene. The specific regulation relationship satisfies the following expression:

[0116]

[0117] where v F is the Fermi velocity, e is the electron charge, d is the distance between the graphene layer and the electrode, and ε0 and ε Si are the vacuum permittivity and the permittivity of silicon respectively.

[0118] The test results are as shown in Figure 3 (a). The blue solid line and the red dashed line are the experimental data and the results of theoretical calculation respectively, and the two results are in good agreement.

[0119] In addition, with the increase of the Fermi level, the low-frequency transmission valley hardly changes with the increase of the Fermi level, while the high-frequency transmission valley continuously blueshifts, as shown in Figure 3 (a). The generation of this phenomenon is mainly related to the change of the effective refractive index Re(n eff ) of the device.

[0120] From Figure 3(b) It can be seen that by controlling the voltage of the external power supply in the range of 6.4 - 14.4 V, the Fermi level E f is adjusted to the range of 0.8 - 1.2 eV, and the effective refractive index Re(n eff ) will decrease as the Fermi level increases. The resonance frequency of the resonance mode is also inversely proportional to the effective refractive index Re(n eff ). Thus, the resonance frequency will increase as the Fermi level increases, resulting in a blue shift of the transmission valley. However, the value of Re(n eff ) at dip1 in the low-frequency region is almost a horizontal line, so that the resonance frequency of dip1 is almost unchanged, and this phenomenon is more obvious at high frequencies, as shown in Figure 3 (c). At the same time, it can be seen that dip1 and dip2 have small transmission values and narrow transmission spectra. Therefore, this device is very sensitive to changes in the surrounding environment, and this characteristic can be used to realize the application of a refractive index sensor.

[0121] The sensing figure of merit (FOM) is an important parameter for evaluating the sensing performance, and the calculation formula is:

[0122]

[0123] where T(f, n + Δn) and T(f, n) are the transmittances at a frequency of f with refractive indices of n and n + Δn, respectively. The sensitivity is also an important parameter for measuring the sensing performance, usually defined as S = Δf / Δn. Here, Δf is the shift of the resonance frequency of the transmission valley when the refractive index changes by Δn. Through research, it is found that when the refractive index of the medium changes from 1.0 to 1.4, the transmission valley produces a large displacement as the refractive index increases, as shown in Figure 4 (a). The FOM results calculated according to the formula are shown in Figure 4 (c)-(f). The sensing figure of merit FOM shows a very steep peak at dip2, up to 34.6 RIU -1 , while the values at other positions are relatively small. The main reason for this phenomenon is that the transmission value when the refractive index n is 1.0 is close to 0. In addition, a numerical change relationship diagram of the sensitivity with respect to the change in the refractive index is plotted through calculation, as shown in Figure 4 (b), and it can be seen that the sensitivity is as high as 1.32 Thz / RIU;

[0124] In addition, in order to intuitively reflect the excellent performance of this refractive index sensor, we also set a sensor in the prior art as a comparative example and made a series of comparisons with the relevant parameters of the sensor in Embodiment 1 of the present invention.

[0125] The test results are shown in Table 1.

[0126] Table 1 Performance Comparison of Different Refractive Index Sensors

[0127]

[0128] As can be seen from Table 1, the refractive index sensor of the present invention has excellent sensing quality factors and sensitivity.

[0129] Among them, the refractive index sensors of Comparative Examples 1-10 were prepared with reference to the following documents:

[0130] Comparative Example 1:

[0131] He Zhihui, Cui Wei, Ren Xincheng, Li Chunjiang, Li Zhenxiong, Xue Weiwei, Zhang Bohang, Zhao Renman, Ultra-high sensitivity sensing based on tunable plasmon-induced transparency in graphene metamaterials in terahertz, optical materials, 108(2020)110221. (Ultra-high sensitivity sensing based on tunable plasmon-induced transparency).

[0132] Comparative Example 2:

[0133] Ge Jiahao, You Chenglong, Feng He, Li Xiaoman, Wang Mei, Dong Lifeng, Veronis Georgios, Yun Maojin, Tunable dual plasmon-induced transparency based on a monolayer graphene metamaterial and its terahertz sensing performance, Optics Express, 28(21)(2020)31781-31795. (Tunable dual plasmon-induced transparency based on a monolayer graphene metamaterial and its terahertz sensing performance). Comparative Example 3:

[0134] Jiang Weijie, Chen Tao, A terahertz graphene metamaterial based on polarization-insensitive plasmon-induced transparency for sensing application, Diamond and Related Materials 118(2021)108531. (A sensing application of a terahertz graphene metamaterial based on polarization-insensitive plasmon-induced transparency).

[0135] Comparative Example 4:

[0136] He Zhihui, Li Lingqiao, Ma Huqiang, Pu Lihui, Xu Hui, Zao Yi, Cao Xinliang, Cui Wei, Graphene-based metasurface sensing applications in terahertz band, Results in Physics, 21(2021)103795. (Graphene-based metasurface sensing applications in the terahertz band).

[0137] Comparative Example 5:

[0138] Chen Tao, Liang Dihan, Jiang Weijie, A tunable terahertz graphene metamaterial sensor based on dual polarized plasmon-induced transparency, IEEE Sensors Journal, 22(14)(2022)14084 - 14090. (A tunable terahertz graphene metamaterial sensor based on dual polarized plasmon-induced transparency).

[0139] Comparative Example 6:

[0140] Wang Yixuan, Chang Baosheng, Xue Jingjing, Cao Xinliang, He Hui, Cui Wei, He Zhihui, Sensing and slow light applications based on graphene metasurface in terahertz, Diamond and Related Materials, 123(2022)108881. (Based on terahertz graphene metasurface sensing and slow light applications).

[0141] Comparative Example 7:

[0142] Chen Tao, Wang Juncheng, Liang Dihan, A polarization-insensitive dual plasmon-induced transparency terahertz sensor based on graphene metamaterial, Optics Communications, 544(2023)129622. (A polarization-insensitive dual plasmon-induced transparency terahertz sensor based on graphene metamaterial).

[0143] Comparative Example 8:

[0144] Zhu Aijun, Bu Pengcheng, Cheng Lei, Hu Cong, Mahapatra Babi, High-sensitivity sensor based on diametrical graphene strip plasma-induced transparency, Photonics.MDPI, 10(7)(2023)830. (High-sensitivity sensor based on diametrical graphene strip plasma-induced transparency).

[0145] Comparative Example 9:

[0146] Wu Xiongxiong, Chen Jiani, Wang Shaolong, Ren Yang, Yang Yanning, He Zhihui, Sensing based on plasmon-induced transparency in H-shaped graphene-based metamaterials, Nanomaterials, 14(12)(2024)997. (Sensing based on plasmon-induced transparency of H-shaped graphene-based metamaterials).

[0147] Comparative Example 10:

[0148] Pan Yizhao, Chen Fang, Li Yuchang, Yang Wenxing, Sun Lihui, Yi Zao, A carbon nanotube metamaterial sensor showing slow light properties based on double plasmon-induced transparency, Physical Chemistry Chemical Physics, (2024). (A carbon nanotube metamaterial sensor showing slow light properties based on double plasmon-induced transparency).

[0149] In addition, by using the chemical doping method to change the carrier mobility of graphene in Example 1 to the range of 1.0 - 3.0 m 2 / (V·s), it can be seen that the change of carrier mobility can also achieve the regulation of the transmission spectrum. To study this property more accurately, the Fermi level of graphene is fixed at E f = 1.0 eV, and the carrier change increment is 0.5 m 2 / (V·s).

[0150] The test results are as shown in Figure 5 (a)-(b). The results show that with the increase of carrier mobility, the transmission spectrum has a slight red shift. The reason for this phenomenon is that Re(neff) increases with the increase of carrier mobility, and this phenomenon is more obvious at high frequencies, resulting in the decrease of the resonance frequency and the compression of the spectrum, generating a red shift.

[0151] The compression of the spectrum will narrow the full width at half maximum of the transmission valley, resulting in strong dispersion and high group attenuation of the triple PIT system, showing excellent slow light effects. Using this property, optical storage can be achieved. The variation of group attenuation and phase shift with frequency at different carrier mobilities is as shown in Figure 6(a)-(d) as shown. Among them, the group refractive index n g is a parameter to measure the slow light effect, and its magnitude depends on the resonance peak of the high quality factor. The group refractive index of the system can be obtained by the following formula:

[0152]

[0153] where c is the speed of light in vacuum, θ(ω) = arg(t) is the transmission phase shift, ω is the angular frequency, l is the thickness of the structured silicon substrate, and k is the wave vector of light.

[0154] When the carrier mobility increases at a rate of 0.5 m 2 / (V·s), the group refractive index will increase with the increase of the carrier mobility. When μ = 3.0 m 2 / (V·s), the maximum group refractive index is 1109. Compared with other optical storage devices, the performance exhibited by this device is very excellent.

[0155] In summary, we propose that the graphene metasurface can excite the triple PIT effect through the cooperative effect between two single PITs. Then, the numerical results are compared with the results of the coupled mode theory, and the two results are in good agreement, verifying the accuracy of the results. The research shows that by changing the Fermi level of graphene, the optical properties of the metasurface can be effectively changed, and a refractive index sensor with a sensing quality factor of 34.6 RIU -1 can be realized, and it also has excellent performance with a sensitivity of 1.32 THz / RIU. In addition, by changing the carrier mobility of graphene, the slow light performance of the metasurface can be well enhanced, making it have potential application prospects in the field of optical storage devices, and the group refractive index is as high as 1109. Therefore, this graphene metasurface is expected to provide ideas for the design of refractive index sensors and optical storage with excellent performance.

[0156] For those skilled in the art, it is obvious that the present invention is not limited to the details of the above exemplary embodiments, and the present invention can be implemented in other specific forms without departing from the spirit or basic characteristics of the present invention. Therefore, from any point of view, the embodiments should be regarded as exemplary and non-limiting. The scope of the present invention is defined by the appended claims rather than the above description. Therefore, all changes falling within the meaning and scope of the equivalent elements of the claims are intended to be encompassed by the present invention.

[0157] In addition, it should be understood that although this specification is described according to embodiments, not every embodiment only contains an independent technical solution. The narrative way of this specification is only for clarity. Those skilled in the art should regard the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A graphene metasurface structure with triple plasmon-induced transparency based on synergy effects, characterized in that, The graphene metasurface structure based on the triple plasmon-induced transparency with synergy effect includes an Si substrate, a graphene layer, and an Si covering layer from bottom to top in sequence; Among them, the graphene layer includes: A first transverse graphene strip, which is disposed on the surface of the Si substrate; A longitudinal graphene strip, which is disposed at both ends of the first transverse graphene strip and is perpendicular to the first transverse graphene strip; both ends of the first transverse graphene strip are integrally connected to the longitudinal graphene strip; Second transverse graphene strips, with two in number, symmetrically arranged on both sides of the first transverse graphene strip with the first transverse graphene strip as the axis of symmetry and parallel to the first transverse graphene strip; Both ends of the second transverse graphene strip are integrally connected to the longitudinal graphene strip; In the middle of each of the second transverse graphene strips, there is a gap, which divides each of the second transverse graphene strips into two parts.

2. The triple-plasmon-induced-transparency graphene metasurface structure based on the synergy effect according to claim 1, characterized in that, The length of the first transverse graphene strip is 2 - 3 μm, and the width is 0.7 - 0.9 μm; The length of the longitudinal graphene strip is 3 - 4 μm, and the width is 1.1 - 1.3 μm; The length of the second transverse graphene strip is 1 - 2 μm, and the width is 0.7 - 0.9 μm.

3. The triple-plasmon-induced-transparency graphene metasurface structure based on synergy according to claim 1, characterized in that, The length of the gap is 0.3 - 0.5 μm.

4. The graphene metasurface structure based on triple plasmon-induced transparency with synergy according to claim 1, wherein The carrier mobility of the graphene material in the graphene layer is 1.0 - 3.0 m 2 / (V·s).

5. The triple plasmon-induced transparency graphene metasurface structure based on the synergy effect according to claim 1, characterized in that, The Fermi level of the graphene material in the graphene layer is 0.8 - 1.2 eV.

6. The triple plasmon-induced transparency graphene metasurface structure based on the synergy effect according to claim 1, characterized in that, The relative dielectric constant of the Si covering layer and the silicon material of the Si substrate is 11 - 12.

7. The graphene metasurface structure based on the triple plasmon-induced transparency with synergy according to claim 1, characterized in that, On the upper surface of the Si covering layer at one end of the longitudinal graphene strip, there is also an electrode layer, and the electrode layer and the graphene layer are connected through an external power supply; Among them, the Fermi level of the graphene material in the graphene layer is adjusted by adjusting the voltage of the external power supply.

8. The triple plasmon-induced transparency graphene metasurface structure based on synergy according to claim 7, characterized in that, The voltage of the external power supply is 6.4 - 14.4 V.

9. The preparation method of the graphene metasurface structure with triple plasmon-induced transparency based on synergy effect according to any one of claims 1-6, characterized in that, It includes the following steps: coating a layer of graphene on the Si substrate, then etching the graphene to form a graphene layer, then coating an Si covering layer on the graphene layer, coating an electrode layer on the Si covering layer, and using an external power supply to connect the graphene layer and the electrode layer to form a circuit, obtaining the graphene metasurface structure based on the triple plasmon-induced transparency with synergy effect.

10. A graphene metasurface structure array, including a plurality of the graphene metasurface structures based on the triple plasmon-induced transparency with synergy effect according to any one of claims 1 - 7 arranged in a periodic array.

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