Terahertz sensor based on graphene Fano resonance and regulation and control method and application thereof

Abstract

The invention discloses a terahertz sensor based on graphene Fano resonance and a regulation and control method and application thereof, and relates to the technical field of sensing devices, the terahertz sensor comprises a substrate layer, a dielectric layer and a graphene layer, the graphene layer comprises at least one unit structure arranged on the dielectric layer, each unit structure comprises two long graphene ribbons arranged in parallel at intervals and four short graphene ribbons arranged between the two long graphene ribbons, the four short graphene ribbons are symmetrically arranged at the two ends of the two long graphene ribbons in pairs, and the outer ends of the short graphene ribbons are flush with the ends of the long graphene ribbons. Fano resonance is combined with the graphene terahertz sensor, electric dipole resonance caused by the action of an electric field and a magnetic field is utilized to generate a Fano resonance phenomenon, radiation loss is effectively reduced and the Q value of the sensor is improved through destructive interference action between a light mode and a dark mode, and the terahertz sensor has good sensing performance and can be used for sensing terahertz waves. The method has important application potential in the aspects of biomedicine and sample detection.

Description

Technical Field

[0001] The present invention relates to the technical field of sensor devices, and in particular to a terahertz sensor based on graphene Fano resonance and a control method and application thereof. Background Art

[0002] Terahertz waves are located in a specific area of ​​the electromagnetic spectrum, with a frequency between infrared light and microwaves and a wavelength between 0.1 mm and 1 mm, which is called the "terahertz gap". In recent years, terahertz waves have important application potential in many fields due to their unique characteristics such as strong penetration, significant interaction with matter, and no ionizing radiation. Metamaterials are artificially synthesized periodic subwavelength structured electromagnetic materials with optical properties beyond the scope of traditional natural materials. Optical devices designed by metamaterials have been widely used in terahertz technology, breaking through the limitation that most traditional materials cannot produce strong electromagnetic responses in the terahertz band, and greatly changing the traditional methods of regulating terahertz waves.

[0003] Graphene is a two-dimensional material composed of a single layer of carbon atoms with excellent electrical and optical properties. Graphene has extremely high transparency in the visible light range, with an absorbance of only 2.3%, which allows the graphene surface to achieve total internal reflection. In addition, graphene can excite surface plasmon resonance (SPR) in the terahertz band, which can enhance the interaction between terahertz waves and graphene, thereby producing a local electromagnetic field enhancement effect. By changing the bias voltage of graphene, the Fermi level of graphene can be adjusted, the frequency of SPR can be changed, and the dynamic tunability of the resonance peak can be achieved. In addition, graphene itself has efficient carrier mobility, which means that it can respond quickly to changes in external electromagnetic fields. Compared with optical devices made of precious metals, graphene has better tunability and lower damping loss, which enables terahertz sensors to achieve higher quality factors, thereby improving sensing performance. These characteristics make graphene have a wide range of application potential in terahertz sensing.

[0004] Some graphene-based terahertz sensors have been disclosed in the prior art, such as the Chinese invention patent with publication number CN117007186A, patent name of dual-frequency terahertz sensor based on graphene metamaterial, and the patent with publication number CN 118258788 A, patent name of a tunable graphene metamaterial triple-frequency terahertz refractive index sensor. However, the sensing performance of terahertz sensors still needs to be further improved.

[0005] Fano resonance is a quantum interference effect caused by the interaction between discrete and continuous states. Two characteristic resonance modes can be excited in the plasma structure: narrowband subradiant (dark state) resonance and broadband superradiant (bright state) resonance mode. Fano line shape can be generated through interference destructive interaction between resonance modes, which leads to resonance enhancement of terahertz waves, transparent window formation and nonlinear optical effects, thereby improving the sensitivity and quality factor of the sensor. In addition, Fano resonance has a local field enhancement response. By sensing the changes in the dielectric environment around the structure and the weak interactions in the sample being measured, the frequency, amplitude or phase of the resonance peak changes. It has unique advantages in designing high-sensitivity terahertz sensors. However, there are few reports in the existing technology on the preparation of terahertz sensors based on graphene and Fano resonance. Summary of the invention

[0006] The present invention aims to provide a terahertz sensor based on graphene Fano resonance and a control method and application thereof, and further improve the sensing performance of the terahertz sensor by combining Fano resonance with the graphene terahertz sensor.

[0007] In order to achieve the above-mentioned purpose, the specific scheme adopted by the present invention is: a terahertz sensor based on graphene Fano resonance, comprising a substrate layer, a dielectric layer and a graphene layer, the graphene layer comprising at least one unit structure arranged on the dielectric layer, the unit structure comprising two long graphene ribbons arranged in parallel and spaced apart and four short graphene ribbons arranged between the two long graphene ribbons, the four short graphenes are symmetrically arranged in pairs at both ends of the two long graphene ribbons, and the outer ends of the short graphene ribbons are flush with the ends of the long graphene ribbons.

[0008] As a further optimization of the above technical solution, the number of the unit structures is multiple, and the surface of the dielectric layer is divided into multiple array-distributed graphene ribbon setting areas along the X and Y directions, each graphene ribbon setting area is a square, and each graphene ribbon setting area is provided with one unit structure, and the long graphene ribbons of all unit structures are distributed in the same direction.

[0009] As a further optimization of the above technical solution, the number of the unit structures is 4, and they are distributed in an array along the X and Y directions on the surface of the dielectric layer, and the long graphene strips of the two unit structures arranged along the length direction of the long graphene strip are continuous.

[0010] As a further optimization of the above technical solution, the Fermi level of graphene is 0.3ev~1.0ev.

[0011] As a further optimization of the above technical solution, the material of the substrate layer is a metal film.

[0012] As a further optimization of the above technical solution, the material of the dielectric layer is polycycloolefin copolymer.

[0013] A control method for a terahertz sensor based on graphene Fano resonance, which adjusts the absorption frequency of the sensor to terahertz waves by changing the structural parameters of long graphene strips and short graphene strips, or by changing the Fermi level of graphene by applying a bias voltage.

[0014] The structural parameters include: the length L1 of the long graphene ribbon, the width L2 of the short graphene ribbon, the distance S1 between the long graphene ribbon and the center point, the distance S2 between the short graphene ribbon and the center point, and the spacing g between the short graphene ribbons.

[0015] A method for regulating a graphene Fano resonance terahertz sensor adjusts the absorption spectrum and sensing performance of the sensor by changing the thickness of an object to be measured and / or using objects to be measured with different refractive indices.

[0016] A method for evaluating the sensing performance of a terahertz sensor based on graphene Fano resonance, wherein the sensing performance includes quality factor (Quality, Q), sensitivity (S) and figure of merit (FOM);

[0017] The quality factor is expressed as formula (1):

[0018]

[0019] Wherein, f represents the resonance frequency of the resonance peak, and FWHM represents the full width at half maximum of the resonance peak;

[0020] The sensitivity is expressed as formula (2):

[0021]

[0022] Wherein, Δf is the frequency shift of the resonance peak; Δn is the change of the refractive index, the unit is THz / RIU (Refractive Index Unit, RIU);

[0023] Combining formulas (1) and (2), we get the quality factor FOM value, which is expressed as formula (3):

[0024]

[0025] A terahertz sensor based on graphene Fano resonance is used in detecting biological molecules, where the object to be tested is smeared on the surface of a graphene strip.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] The present invention combines Fano resonance with a graphene terahertz sensor, utilizes the electric dipole resonance caused by the action of electric and magnetic fields to generate the Fano resonance phenomenon, and effectively reduces radiation loss and improves the Q value of the sensor through the destructive interference between bright and dark modes.

[0028] The terahertz sensor of the present invention generates two narrow-band absorption peaks in the frequency range of 3 to 9 THz, achieving the sensing effect of terahertz waves. The terahertz sensor has a simple structure, can be actively tuned, has a wide control range, has good sensing performance, and has important application potential in biomedicine and sample detection.

[0029] The present invention can enhance the flexibility and application range of the sensor by regulating the graphene Fermi level.

[0030] The maximum sensing sensitivity of the present invention can reach 1.548THz / RIU, which effectively solves the problem of low sensitivity compared with the existing terahertz metamaterial refractive index sensor. The sensor proposed by the present invention not only has superior performance, but also can reduce detection costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 is a schematic diagram of the three-dimensional structure of the terahertz sensor in Example 1 of the present invention;

[0032] Figure 2 is a top view schematic diagram of a unit structure in the present invention;

[0033] Figure 3 is a schematic diagram of the three-dimensional structure of the terahertz sensor in Example 2 of the present invention;

[0034] Figure 4 It is an absorption spectrum diagram of a terahertz sensor based on graphene Fano resonance under different polarizations of the present invention;

[0035] Figure 5 It is a schematic diagram of the electric field and current of a terahertz sensor based on graphene Fano resonance at a terahertz frequency of 6.1 THz according to the present invention;

[0036] Figure 6 It is an absorption spectrum diagram of a terahertz sensor based on graphene Fano resonance at different Fermi levels of the present invention;

[0037] Figure 7 It is an absorption spectrum diagram of a terahertz sensor based on graphene Fano resonance under different structural parameters of the present invention;

[0038] Figure 8 It is an absorption spectrum diagram of a terahertz sensor based on graphene Fano resonance under different thicknesses of the object to be measured in the present invention;

[0039] Fig. 9 It is an absorption spectrum diagram of a terahertz sensor based on graphene Fano resonance under different refractive indices of the object to be measured according to the present invention;

[0040] Figure numerals: 1, substrate layer, 2, dielectric layer, 3, long graphene ribbon, 4, short graphene ribbon, 5, Au electrode. DETAILED DESCRIPTION

[0041] The technical solution of the present invention is further described in detail below in conjunction with specific embodiments. The parts of the present invention that are not described and disclosed in detail in the following embodiments should be understood as the prior art known or should be known to those skilled in the art.

[0042] Example 1

[0043] like Figure 1 , 2 As shown, the present invention discloses a terahertz sensor based on graphene Fano resonance, comprising a substrate layer 1, a dielectric layer 2 arranged on the substrate layer 1 and a graphene layer arranged on the dielectric layer 2, the graphene layer and the dielectric layer 2 are tightly attached, and the graphene layer includes a unit structure arranged on the dielectric layer.

[0044] The substrate layer 1 and the dielectric layer 2 are both square, with a side length of P, where P=11 μm.

[0045] The unit structure includes two long graphene ribbons 3 arranged in parallel and spaced apart and four short graphene ribbons 4 arranged between the two long graphene ribbons 3. The two long graphene ribbons 3 have the same size, and the four short graphene ribbons 4 have the same size. The four short graphenes 4 are symmetrically arranged in pairs at both ends of the two long graphene ribbons 3, and the outer ends of the short graphene ribbons 4 are flush with the ends of the long graphene ribbons 3.

[0046] For ease of understanding, the center of the square dielectric layer 2 is set as the center point, the length of the long graphene ribbon 3 is L1, the width of the short graphene ribbon 4 is L2, the distance between the long graphene ribbon 3 and the center point is S1, the distance between the short graphene ribbon 4 and the center point is S2, the spacing between the two short graphene ribbons 4 located at the same end of the long graphene ribbon 3 is g, and the outer end of the short graphene ribbon 4 is the end away from the center point.

[0047] The geometric parameters of the sensor are: L1=11μm, L2=1μm, g=0.8μm, S1=2μm, S2=5μm.

[0048] The Fermi level of graphene is 0.3ev~1.0ev.

[0049] The conductivity of substrate layer 1 is σ = 2.21 × 10 7The layer structure is made of a metal film of S / m, and the specific material is gold. The thickness of the substrate layer 1 is 0.2μm. The substrate layer 1 is used to prevent the terahertz wave from penetrating. Using gold as the substrate layer can achieve a total reflection effect on the terahertz wave.

[0050] The dielectric layer 2 is a layer structure made of polycycloolefin copolymer (TOPAS), the relative dielectric constant of the dielectric layer 2 is 2.35, and the thickness of the dielectric layer is d=9 μm, which has very low loss and dispersion in the terahertz region.

[0051] Example 2

[0052] The present invention discloses a terahertz sensor based on graphene Fano resonance, comprising a substrate layer 1, a dielectric layer 2 arranged on the substrate layer 1 and a graphene layer arranged on the dielectric layer 2, the graphene layer and the dielectric layer 2 are tightly attached, and the graphene layer includes a plurality of unit structures arranged on the dielectric layer 2.

[0053] The surface of the dielectric layer 2 is divided into a plurality of array-distributed graphene ribbon setting areas along the X and Y directions. Adjacent graphene ribbon setting areas are connected. Each graphene ribbon setting area is a square. Each graphene ribbon setting area is provided with one unit structure.

[0054] The unit structure includes two long graphene ribbons 3 arranged in parallel and spaced apart and four short graphene ribbons 4 arranged between the two long graphene ribbons 3. The two long graphene ribbons 3 have the same size, the four short graphene ribbons 4 have the same size, the four short graphene ribbons 4 are symmetrically arranged in pairs at both ends of the two long graphene ribbons 3, and the outer ends of the short graphene ribbons 4 are flush with the ends of the long graphene ribbons 3.

[0055] Specifically, in this embodiment, Figure 3 As shown, there are four unit structures arranged on the dielectric layer 2, and they are distributed in an array along the X and Y directions on the surface of the dielectric layer 2. The length direction of the long graphene ribbon 3 is the Y direction. In the two unit structures arranged along the length direction of the long graphene ribbon 3, the two long graphene ribbons 3 are continuous, and the two adjacent short graphene ribbons 4 are also continuous.

[0056] like Figure 2 As shown, for ease of understanding, the center of the square graphene ribbon setting area is set as the center point, the side length of the graphene setting area is P, P = 11 μm, the length of the long graphene ribbon 3 is L1, the width of the short graphene ribbon 4 is L2, the distance between the long graphene ribbon 3 and the center point is S1, the distance between the short graphene ribbon 4 and the center point is S2, the spacing between the two short graphene ribbons 4 located at the same end of the long graphene ribbon 3 is g, and the outer end of the short graphene ribbon 4 is the end away from the center point.

[0057] The geometric parameters of the sensor are: L1=11μm, L2=1μm, g=0.8μm, S1=2μm, S2=5μm.

[0058] The Fermi level of graphene is 0.3ev~1.0ev.

[0059] The conductivity of substrate layer 1 is σ = 2.21 × 10 7 The layer structure is made of a metal film of S / m, and the specific material is gold. The thickness of the substrate layer 1 is 0.2μm. The substrate layer 1 is used to prevent the terahertz wave from penetrating. Using gold as the substrate layer can achieve a total reflection effect on the terahertz wave.

[0060] The dielectric layer 2 is a layer structure made of polycycloolefin copolymer (TOPAS), the relative dielectric constant of the dielectric layer 2 is 2.35, and the thickness of the dielectric layer is d=9 μm, which has very low loss and dispersion in the terahertz region.

[0061] Example 3

[0062] The present invention discloses a control method for a terahertz sensor based on graphene Fano resonance, which adjusts the absorption frequency of the sensor to terahertz waves by changing the sizes of different structures of a graphene pattern layer or by changing the Fermi level of graphene by applying a bias voltage.

[0063] Specifically, by changing the structural parameters of the long graphene ribbon 3 and the short graphene ribbon 4, the absorption frequency of the sensor to the terahertz wave is adjusted;

[0064] The structural parameters include: the length L1 of the long graphene ribbon, the width L2 of the short graphene ribbon, the distance S1 between the long graphene ribbon and the center point, the distance S2 between the short graphene ribbon and the center point, and the spacing g between the short graphene ribbons.

[0065] like Figure 1 The figure shows that the Fermi level of graphene is changed by applying a bias voltage. The long graphene ribbon 3 and the short graphene ribbon 4 are connected with an Au electrode 5. The Au electrode 5 is in the shape of a long strip and is perpendicular to the long graphene ribbon 3. Figure 1 Vg represents the external bias voltage.

[0066] In the terahertz band, the carrier concentration of graphene is affected by the Fermi level and the carrier scattering rate. The Fermi level of graphene can be changed by applying an external bias voltage, as shown in the following relationship:

[0067]

[0068] n s represents the carrier concentration, V biased External bias voltage (V g ), the capacitance of the a0 structure model. It can be seen from the formula that the higher the bias voltage, the higher the Fermi level of graphene.

[0069] In addition, the control method of the terahertz sensor based on graphene Fano resonance of the present invention can also adjust the absorption spectrum and sensing performance of the sensor by changing the thickness of the object to be tested and using objects to be tested with different refractive indices.

[0070] When sensing, the sensor of the present invention attaches analyte samples of different categories to the graphene surface of the sensor, compares the degree of resonance peak shift, and realizes sensing analysis of the analyte.

[0071] Below, the sensor performance is studied using the full-wave electromagnetic simulation software Lumerical FDTD Solutions. During the simulation, periodic boundary conditions are set in the X and Y directions, and a perfectly matched layer (PML) boundary condition is set in the Z direction.

[0072] like Figure 4 As shown, Figure 4 When the polarization angles are 0o and 90o, they are the corresponding TM mode and TE mode. In the TM mode, the resonance conditions can be met to generate Fano resonance. In the TE mode, through the interaction between graphene and terahertz waves, resonance peaks are generated at 7.1THz and 9.7THz, respectively, but there is a big difference with the resonance peaks generated by the TM mode. This is because the designed sensor structure is not highly symmetrical (it should be noted that the sensor structure of the present invention is not highly symmetrical, which means that in the same unit structure of the sensor, the two long graphene ribbons have the same size, the four short graphene ribbons have the same size, but the long graphene ribbons and the short graphene ribbons have different sizes, and the sensor structure formed is not rotationally symmetrical). When facing electric field polarizations in different directions, the resonance generated is different, so the present invention is mainly studied in the TM mode.

[0073] like Figure 5 As shown, Figure 5 (a) represents the X-direction electric field component of the bright mode; (b) represents the X-direction electric field component of the dark mode; (c) represents the electric field distribution of the complete graphene structure; (d) represents the current distribution at a terahertz frequency of 6.1 THz.

[0074] like Figure 5 As shown in (a), when the polarization electric field direction of the incident plane wave is in the positive direction of the X-axis, for the short graphene ribbon, a large number of opposite charges gather at both ends of the short graphene ribbon, showing the typical characteristics of electric dipole resonance, which indicates that the short graphene ribbon can directly couple strongly with the incident electromagnetic wave, and this coupling resonance state is defined as the bright mode. For the long graphene ribbon, it cannot be directly excited by the incident electromagnetic wave near this frequency point, so there is almost no electric field distribution on its surface, as shown in Figure 1. Figure 5(b) is defined as dark mode. The electric field distribution of the sensor structure designed by the present invention is shown in Figure 5 As shown in (c), a large number of opposite charges gather on the left and right edges of the short graphene strip, generating a strong electric field around it. A small number of opposite charges also accumulate on the long graphene strip, but the electric field formed is extremely weak. Figure 5 From the current distribution shown in (d), it can be observed that the surface current is mainly concentrated on the short graphene ribbon, while there is also a small amount of surface current distribution on the long graphene ribbon. On the whole, the current propagates along the negative direction of the X-axis. Therefore, it can be seen that the long graphene ribbon, which originally had no electromagnetic response, was excited to produce resonance, generating surface current on its surface, while the electric field resonance generated by the short graphene ribbon and the terahertz wave was suppressed, and the resonance intensity was weakened. Secondly, because the two substructures are very close and the resonance frequency is similar, through near-field coupling, the long graphene ribbon also produces a resonance under the excitation of the electric dipole resonance generated by the short graphene ribbon. Because the two structures are excited in different orders and there is a certain phase difference, the interference destructive effect suppresses the resonance of the short graphene ribbon and enhances the local electric field of the long graphene ribbon. Finally, the left and right ends of the short graphene ribbon excite a strong surface electric field distribution, which is a dipole oscillation, thereby reducing the radiation loss and making its absorption spectrum present a Fano line shape. This is consistent with the distribution characteristics of the electric field and also explains the formation of the Fano resonance peak.

[0075] The surface of the terahertz sensor of the present invention is provided with a plurality of graphene strips of different sizes, and a typical asymmetric Fano resonance peak is generated by the interference between the graphene strips. This is because Fano resonance describes the resonance response of the incident (excitation) light reflected after the coupling and interference of two modes, and is generally reflected as an asymmetric line type in the scattering spectrum or the extinction spectrum. The response spectrum of an independent resonance is a symmetrical Lorentz shape. When the two modes influence each other, the spectrum is not a simple intensity superposition. The reason is that the phase responses of the two resonances are different. The line shape of the Fano resonance comes from the interference of two scattering amplitudes, one is the scattering of the continuous state (related to the background), and the other is the excitation of the discrete state (related to the resonance). The energy of the resonant state must be in the energy range of the continuous state (i.e., the background) for this effect to occur. Near the resonance energy, the amplitude of the background scattering is usually very gentle with the change of energy, but the amplitude and phase changes of the amplitude of the resonant scattering are quite fast, which leads to the occurrence of asymmetry.

[0076] like Figure 6As shown in the figure, when the Fermi level is adjusted between 0.3ev and 1.0ev, the resonance peaks all blue-shift. This is because light absorption is related to electron transitions. As the Fermi level moves to a higher energy level, electrons can absorb the energy of photons and transition to a higher energy level. At this time, the resonance peak will shift toward higher energy (shorter wavelength), resulting in a blue-shift of the resonance peak. Therefore, in practical applications, adjusting the Fermi level of graphene can make the sensor work in the required frequency range.

[0077] like Figure 7 As shown, Figure 7 (a) shows the absorption spectrum when the length of the long graphene ribbon increases, and (b) shows the absorption spectrum when the width of the short graphene ribbon increases.

[0078] As shown in (a) and (b), when the parameter L1 gradually increases, the dual-frequency resonance peak generated by the incident wave will red-shift. This is because the change in graphene length causes the equivalent inductance of the structure surface to increase, so the resonance peak red-shifts. However, when the parameter L1 = 11μm, the structure produces a Fano resonance peak because the electric field of the long graphene ribbon interferes with the electric field of the short graphene ribbon at this time, forming a Fano resonance. Similarly, as the parameter L2 increases, the Fano resonance peak appears at L2 = 1μm. As L2 increases, the Fano resonance phenomenon disappears, and the dual-frequency resonance peak gradually red-shifts.

[0079] Figure 7 (c) shows the absorption spectrum when the distance between the long graphene ribbon and the center point increases, and (d) shows the absorption spectrum when the distance between the short graphene ribbon and the center point increases.

[0080] As can be seen from (c) and (d), Fano resonance can only occur when the structural parameters are of a certain special value. As the parameter S1 changes, its resonance peak will redshift and the absorption rate will gradually increase. When S1 = 2μm, the Fano resonance effect will occur, and the absorption rate will reach the maximum at this time. As S1 gradually increases, the Fano resonance effect disappears and transforms into a single resonance peak. The resonance peak frequency continues to redshift, and the absorption rate will gradually decrease. In the end, only the electric field of the short graphene strip and the terahertz wave will interact. As the parameter S2 increases, the resonance peak undergoes a slight blueshift. When S2 = 5μm, the phase suddenly changes, forming a Fano resonance peak at 6.1THz.

[0081] Figure 7 (e) shows the absorption spectrum after the spacing between short graphene bands is increased, and (f) shows the absorption spectrum after the dielectric layer is added.

[0082] As shown in (e), when analyzing the parameter g, it can be found that the modulation depth of the Fano resonance window will increase with the increase of g, but the absorption rate of the resonance peak will decrease after a certain value, and the resonance peak will be red-shifted. Therefore, by analyzing the influence of structural parameters on sensor performance, it can be concluded that the formation of Fano resonance is related to the electric field coupling between graphene, and can only be generated under specific structural parameters, and the corresponding Fano resonance conditions need to be met. As shown in (f), with the increase of parameter d, the absorption rate of the Fano resonance peak gradually increases, and the frequency of the resonance peak blue-shifts, but after d = 9μm, the absorption rate gradually decreases, and the frequency shift of the resonance frequency gradually decreases. Therefore, the thickness of the dielectric layer is not the thicker the better. Increasing the thickness of the dielectric layer within a certain range can make the terahertz wave reflect and refract multiple times in the structure, enhance the interaction between the metamaterial and the terahertz wave, and form impedance matching after the thickness reaches a certain value. At this time, the absorption rate of the resonance peak is the highest. After that, as the thickness continues to increase, the propagation path of the terahertz wave inside the structure becomes longer, the propagation loss becomes larger, and the absorption rate continues to decrease.

[0083] like Figure 8 As shown in (a), a layer of the object to be tested is applied to the top layer of the sensor, and the refractive index of the object to be tested is fixed to 1.5. Compared with the absorption spectrum when there is no object to be tested on the sensor surface, the resonance frequency of the absorption spectrum is significantly red-shifted when there is an object to be tested, and the frequency shift is about 0.9THz, which shows that the structure is more sensitive to changes in the external dielectric environment. The change curve between the thickness of the object to be tested and the degree of resonance peak frequency shift is shown in Figure 8 (b) is shown. The black solid line in the figure is the curve of the change of the thickness of the object to be tested and the frequency offset, and the red solid line is the fitting curve of the simulation data. The results show that the simulation data is very consistent with the exponential fitting curve. When the thickness of the object to be tested increases, the frequency shift of the resonance peak shows an exponential downward trend, and the frequency shift gradually tends to 0 after the thickness exceeds 2μm. Therefore, after the thickness exceeds 2μm, the influence of thickness on sensor performance can be ignored.

[0084] like Fig. 9 As shown in (a), the thickness of the analyte is fixed at 2 μm. As the refractive index of the analyte increases, the resonance peak redshifts by 1.18 THz, so the sensor is more sensitive to changes in the external dielectric environment. The linear relationship between frequency and refractive index is shown in Fig. 9 As shown in (b), the frequency increases linearly with the increase of the refractive index. The relationship between the two is linearly fitted, and the slope of the fitted curve is expressed as the sensitivity of the sensor. It can be seen from the fitting curve that the sensitivity of the sensor is constant, so the sensor has good stability. According to formulas (1) to (3), the sensitivity of the sensor of the present invention is S = 1.548THz / RIU, Q = 31.05, FOM = 8.1RIU-1 .

[0085] The terahertz sensor prepared by the present invention achieves good refractive index detection performance and has important application potential in biomedicine and sample detection.

[0086] In the biomedical field, the weak interactions (such as hydrogen bonds, van der Waals forces, etc.) between biomacromolecules such as proteins, DNA / RNA, lipids and carbohydrates happen to be within the terahertz (THz) frequency band. The refractive index of most biomacromolecules usually varies in the range of 1.4 to 2.0. When terahertz waves interact with these biomacromolecules, a resonance effect will be generated, and its characteristic resonance peak can be used to detect small changes in material structure and composition, providing a new method for analyzing cell structure and medical diagnosis. Secondly, when terahertz waves interact with biological tissues or cells, they will inevitably interact with a large number of water molecules therein. Since the stretching and bending vibration modes of hydrogen bonds between water molecules are both in the terahertz band (the strongest resonance frequencies are 5.6THz and 1.5THz, respectively), these vibration modes will be excited and cause resonance phenomena, resulting in water producing significant absorption of terahertz waves. In addition, different contents of bases in DNA and RNA will undergo resonance absorption in the entire terahertz band, and the frequency point is between 2THz and 8THz, so the sensor designed by the present invention can be used for the detection of biomolecules.

[0087] When the terahertz sensor of the present invention is used to detect biological molecules, a sample containing the biological molecules is applied to the surface of the graphene strip as a test object.

[0088] The embodiments described above are only preferred embodiments of the present invention and are not intended to limit the scope of implementation of the present invention. Therefore, any equivalent changes or modifications made according to the structures, features and principles described in the patent scope of the present invention should be included in the scope of the patent application of the present invention.

Claims

1. A terahertz sensor based on graphene Fano resonance, comprising a substrate layer (1), a dielectric layer (2) and a graphene layer, characterized in that: The graphene layer comprises at least one unit structure arranged on a dielectric layer (2), the unit structure comprising two long graphene ribbons (3) arranged in parallel and spaced apart and four short graphene ribbons (4) arranged between the two long graphene ribbons (3), the four short graphene ribbons (4) being symmetrically arranged in pairs at both ends of the two long graphene ribbons (3), and the outer ends of the short graphene ribbons (4) being flush with the ends of the long graphene ribbons (3).

2. A terahertz sensor based on graphene Fano resonance according to claim 1, characterized in that: The number of the unit structures is multiple, and the surface of the dielectric layer (2) is divided into multiple array-distributed graphene ribbon setting areas along the X and Y directions, each graphene ribbon setting area is a square, and each graphene ribbon setting area is provided with one unit structure, and the long graphene ribbons (3) of all the unit structures are distributed in the same direction.

3. A terahertz sensor based on graphene Fano resonance according to claim 1, characterized in that: The number of the unit structures is 4 and they are distributed in an array along the X and Y directions on the surface of the dielectric layer (2), and the long graphene strips (3) of the two unit structures arranged along the length direction of the long graphene strips (3) are continuous.

4. A terahertz sensor based on graphene Fano resonance according to claim 1, characterized in that: The Fermi level of graphene is 0.3ev~1.0ev.

5. A terahertz sensor based on graphene Fano resonance according to claim 1, characterized in that: The material of the substrate layer (1) is a metal film.

6. A terahertz sensor based on graphene Fano resonance according to claim 1, characterized in that: The material of the dielectric layer (2) is polycycloolefin copolymer.

7. A method for controlling a terahertz sensor based on graphene Fano resonance as claimed in any one of claims 1 to 6, characterized in that: By changing the structural parameters of the long graphene ribbon (3) and the short graphene ribbon (4), or by changing the Fermi level of graphene by applying a bias voltage, the absorption frequency of the sensor to the terahertz wave is adjusted; The structural parameters include: the length L1 of the long graphene ribbon (3), the width L2 of the short graphene ribbon (4), the distance S1 between the long graphene ribbon (3) and the center point, the distance S2 between the short graphene ribbon (4) and the center point, and the spacing g between the short graphene ribbons (4).

8. A method for controlling a terahertz sensor based on graphene Fano resonance as claimed in any one of claims 1 to 6, characterized in that: The absorption spectrum and sensing performance of the sensor can be adjusted by changing the thickness of the object to be tested and / or using objects to be tested with different refractive indices.

9. A method for evaluating the sensing performance of a terahertz sensor based on graphene Fano resonance as claimed in any one of claims 1 to 6, characterized in that: The sensing performance includes the quality factor Q, sensitivity S and quality factor FOM value. The quality factor is expressed as formula (1): Wherein, f represents the resonance frequency of the resonance peak, and FWHM represents the full width at half maximum of the resonance peak; The sensitivity is expressed as formula (2): Wherein, Δf is the frequency shift of the resonance peak; Δn is the change of the refractive index; Combining formulas (1) and (2), we get the quality factor FOM value, which is expressed as formula (3):

10. An application of a terahertz sensor based on graphene Fano resonance according to any one of claims 1 to 6 in detecting biological molecules, characterized in that: The object to be tested is applied to the surface of the graphene ribbon.

Images