Terahertz regulation and control device based on multi-dimensional quasi-BIC mediation

Abstract

A terahertz regulation and control device based on multi-dimensional quasi-BIC mediation comprises a substrate layer and a plurality of resonant rings, the surface of the substrate layer is coated with a photosensitive germanium layer, the plurality of resonant rings are distributed on the photosensitive germanium layer in an array mode, each resonant ring comprises a first metal strip and a second metal strip which are parallel to each other and equal in length, and the first metal strip and the second metal strip are parallel to each other. The center positions of the first metal strip and the second metal strip are connected through a middle arm perpendicular to the first metal strip and the second metal strip, the end face of the first metal strip is perpendicularly connected with a side arm extending towards the second metal strip, and the end face of the second metal strip is provided with a corresponding part corresponding to the side arm and extending towards the side arm. A gap always exists between the end part of the corresponding part and the end part of the side arm, and the length of the corresponding part and the length of the side arm are unequal and the sum is always equal to 86 microns; or the end face of the second metal strip is not provided with a corresponding part, a gap exists between the side wall and the end of the second metal strip, and the length of the side arm is equal to 86 microns.

Description

Technical Field

[0001] The present invention relates to the technical field of terahertz control devices, and in particular to a terahertz control device mediated by quasi-BIC in multiple dimensions. Background Art

[0002] Bound state in the continuum (BIC) is an open system whose frequency is within the radiation continuum, and it is still completely bound without any energy leakage. In practical applications, the modes excited by BIC (quasi-BICs) have the characteristics of ultra-high quality factor and strong local field. These characteristics are expected to provide significant application potential in many fields such as solid-state lasers, nonlinear phenomena, high-performance sensing, chirality enhancement and narrowband filtering.

[0003] Electromagnetically induced transparency (EIT) is an important quantum destructive interference phenomenon existing in three-level atomic systems. It is manifested by inducing a transparent and sharp transmission window in the originally absorbed region of the transmission curve. In the EIT phenomenon, the traditional implementation method requires very strict conditions, ultra-low temperature and high-power laser devices, which are extremely difficult to obtain in reality. With the continuous research on metamaterials, in order to solve the problem of difficult traditional experimental conditions in the process of realizing EIT, scientific researchers have studied the use of metamaterials to simulate in some simplified experimental environments to realize EIT. This physical phenomenon realized by metamaterials is called electromagnetically induced transparency-like (EIT-like) because it is similar to EIT, but its sensitivity is limited. Summary of the invention

[0004] In order to improve the adjustability and application flexibility of the control device, the present invention provides a terahertz control device based on quasi-BIC mediation in multiple dimensions, which improves the adjustability and application flexibility.

[0005] In order to achieve the above-mentioned purpose, the specific scheme adopted by the present invention is: a terahertz control device based on quasi-BIC mediation in multi-dimensionality, including a substrate layer and a plurality of resonant rings, the surface of the substrate layer is coated with a photosensitive germanium layer, and the plurality of resonant rings are arranged and distributed on the photosensitive germanium layer, and the resonant rings include a first metal strip and a second metal strip parallel to each other and equal in length, the center positions of the first metal strip and the second metal strip are connected by an intermediate arm perpendicular to the two, and the end faces of the first metal strip are vertically connected with side arms extending toward the second metal strip; the end faces of the second metal strip are provided with corresponding parts corresponding to the side arms and extending toward the side arms, and there is a gap between the end of the corresponding part and the end of the side arm, the length of the corresponding part is not equal to the length of the side arm and the sum of the two is always equal to 86μm; or, the end face of the second metal strip has no corresponding part, there is a gap between the side arm and the end of the second metal strip and the length of the side arm is equal to 86μm.

[0006] As an optimization scheme for the above-mentioned terahertz control device mediated by quasi-BIC in multi-dimensionality: the width of the corresponding part is equal to the width of the side arm.

[0007] As another optimization scheme of the above-mentioned terahertz control device mediated by quasi-BIC in multi-dimensionality: the end surface of the corresponding portion facing the first metal strip is higher than the edge of the second metal strip.

[0008] As another optimization scheme of the above-mentioned terahertz control device mediated by quasi-BIC in multi-dimensionality: the end surface of the corresponding part facing the first metal strip is lower than the edge of the second metal strip, so that a recessed area is formed between the corresponding part and the second metal strip.

[0009] As another optimization scheme of the above-mentioned terahertz control device mediated by quasi-BIC in multi-dimensionality: a first graphene strip is arranged on the end surface of the side arm facing the second metal strip, and a second graphene strip is arranged in the recessed area.

[0010] As another optimization scheme of the above-mentioned terahertz control device mediated by quasi-BIC in multi-dimensionality: the widths of the first graphene strip and the second graphene strip are equal to the width of the side arm, and the end face of the second graphene strip facing the side arm is flush with the edge of the second metal strip.

[0011] As another optimization scheme of the above-mentioned terahertz control device mediated by quasi-BIC in multi-dimensionality: the material of the resonant ring is gold, and the thickness of the resonant ring is 0.3 μm.

[0012] As another optimization scheme of the above-mentioned terahertz control device mediated by quasi-BIC in multi-dimensionality: the material of the substrate layer is polytetrafluoroethylene.

[0013] As another optimization scheme of the above-mentioned terahertz control device mediated by quasi-BIC in multi-dimensionality: a transparent protective film coated on the surface of the photosensitive germanium layer is arranged between the resonant ring and the photosensitive germanium layer.

[0014] A preparation method of a terahertz control device based on quasi-BIC mediation in multi-dimensionality as described above comprises the following steps: surface treating a substrate layer; depositing photosensitive germanium on the treated surface of the substrate layer by chemical vapor deposition to form a photosensitive germanium layer; and depositing gold on the photosensitive germanium layer by chemical reaction in the gas phase to form a plurality of resonant rings distributed in an array.

[0015] Compared with the prior art, the present invention has the following beneficial effects:

[0016] The present invention provides a terahertz control device based on quasi-BIC mediation in multi-dimensionality, which can realize single-double valley switching in small amplitude control, and the highest group delay in the dual cavity can reach 24.904ps, and the maximum delay bandwidth product is 6.5248; a photosensitive germanium layer is coated on the substrate layer, and the transient photoconductivity of the photosensitive germanium layer is much shorter than the photon lifetime. The photosensitive layer reconstructs the EIT cavity to achieve a range control of 89.25% of the transmission peak-valley amplitude; at the same time, by realizing single-double transmission valley switching, the transmittance, absorptivity, frequency response and other characteristics can be accurately controlled in the terahertz band. This control capability has important applications in the fields of terahertz communication, imaging, sensors, optical modulators, etc., and can improve the performance and functionality of the device, especially in realizing efficient terahertz wave modulation and frequency selective control. It provides a new way; the control device has high sensitivity, which promotes its potential application in modulators, sensors, filters and dynamic imaging. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a schematic diagram of the resonant ring structure in the control device;

[0018] Figure 2 This is a three-dimensional diagram of the absorber product. Figure 2 (a) Schematic diagram of the designed n×n periodic structure, with the normal irradiation being terahertz waves and the oblique irradiation being lasers; (b) Schematic diagram of each unit; (c) Geometric parameter settings under the unit structure;

[0019] Figure 3 (a) The evolution process of the regulated structure, (b) the evolution process of the transmission spectrum; (c) the transmission heat map; (d) the transmission peak-valley amplitude δ T Changes in circumstances;

[0020] Figure 4 (a)-(g) The current distribution of the leakage state formed by the eigenstate and quasi-BIC under Modele 1-4;

[0021] Figure 5 The dipole contribution rate of different resonant ring structures under multi-stage expansion, (a) Module 1; (b) Module 2; (c) Module 3; (d) Module 4;

[0022] Figure 6 (a) The equivalent circuit model is drawn based on the difference in the electric field excitation position of the two modes Mode 1 and Mode 3; (b) The change of the resonant frequency of Mode 1 and Mode 3 during the evolution process;

[0023] Figure 7 To measure the phase and group delay of two dual-resonance valley modules. (a)-(b) Module 2; (c)-(d) Module 4;

[0024] Figure 8 Method 1: Using the evolution law between the resonant ring structures, M1 and M2 are added by shearing and supplementing, and the graphene carrier concentrations at the two locations are changed from 1×10 11 cm 2 to 8×10 13 cm 2 (a) Schematic diagram of the overall steps; (b) The transmission peak disappears completely and reaches the highest amplitude when M1 and M2 are taken at different values; (c) δ T Change heat map; (d) Transmission peak resonance frequency corresponding heat map;

[0025] Fig. 9 Method 2 for modulation of transmission peak amplitude: The photoconductivity of photosensitive germanium induced by laser irradiation increases from 0 S / m (laser not excited) to 3500 S / m, and the corresponding transmission spectra and transmission characteristics of different modules are observed. (a) Transmission spectrum of Module 3; (b) Transmission spectrum of Module 4; (c)-(d) Transmission cloud images corresponding to Module 3 0~100 S / m, 100 S / m~3500 S / m; (e) Peak-to-valley amplitude change of Module 3; (f)-(g) Transmission cloud images corresponding to Module 4 0~100 S / m, 100 S / m~3500 S / m; (h) Peak-to-valley amplitude change of Module 4;

[0026] Fig.10 The photoconductivity of the photosensitive germanium is changed in Module 4. (a) Phase change; (b) Group delay change;

[0027] Fig.11For practical application testing: Under Module 4, the sensing characteristics of Ge conductivity of 0S / m and 400S / m were analyzed. The refractive index NA is 1.5, and the analyte thickness tA is changed from 5μm to 30μm, and the transmission spectrum and transmission peak frequency shift are observed. (a) Ge conductivity is 0S / m; (b) Ge conductivity is 400S / m; (c) The designed metamaterial sensor device micro-nano structure; (d) 0S / m transmission peak resonant frequency shift; (e) 400S / m transmission peak resonant frequency shift;

[0028] Fig.12 For practical application test: the thickness of the analyte tA is 10μm, and the refractive index NA is changed from 1 to 2; 1μm polyethylene (n=1.51) is used to carry the refractive index analyte above and below. Observe the transmission spectrum, transmission cloud map, and transmission peak resonance frequency following the refractive index change law. (a)-(c) Ge conductivity is 0S / m; (d)-(f) Ge conductivity is 400S / m.

[0029] Figure numerals: 1. substrate layer, 2. photosensitive germanium layer, 3. first metal strip, 4. middle arm, 5. side arm, 6. second metal strip, 601. corresponding part, 7. gap. DETAILED DESCRIPTION

[0030] The technical solution of the present invention is further elaborated 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.

[0031] Example 1

[0032] A terahertz control device based on quasi-BIC mediation in multi-dimensionality includes a substrate layer 1 and a plurality of resonant rings, wherein the substrate layer 1 is made of polytetrafluoroethylene (PTFE) with a relative dielectric constant of 2.05. In this embodiment, the thickness of the substrate layer 1 is 1000 μm. The surface of the substrate layer 1 is coated with a photosensitive germanium layer 2 with a thickness of 0.3 μm, and a plurality of resonant rings are arranged on the photosensitive germanium layer 2. The material of the resonant ring is gold, and the plasma frequency is 1.37×10 16 rad / s, and the collision frequency is 4.08×10 13 rad / s, and it has relatively high stability in the terahertz band. In this embodiment, Au is selected as the metamaterial for the resonant ring, which can be obtained from the Drude model:

[0033]

[0034] Wherein, the plasma frequency ω p is 1.36659×10 16 rad / s, collision frequency ω cis 4.082×10 13 rad / s, the thickness of gold is 0.3μm. The refractive index of PTFE is n=1.42, the loss tangent tanδ is 0.02, and the thickness of the substrate layer 1 is 25μm. In the absence of laser irradiation, the dielectric constant ε of the photosensitive germanium layer 2 in the 0.1-1.9THz frequency band is 16.3, and its photoconductivity changes with the intensity of the pump light.

[0035] The resonant ring is a double-open structure with broken symmetry. Specifically, the resonant ring includes a first metal strip 3 and a second metal strip 6 which are parallel to each other and of equal length. The center positions of the first metal strip 3 and the second metal strip 6 are connected by an intermediate arm 4 which is perpendicular to the two. That is, one end of the intermediate arm 4 is integrally connected to the first metal strip 3, and the other end of the intermediate arm 4 is integrally connected to the second metal strip 6. The intermediate arm 4, the first metal strip 3 and the second metal strip 6 form an "I"-shaped structure. The end faces of the first metal strip 3 are vertically connected to the side arms 5 extending toward the second metal strip 6, such as Figure 1 As shown, the edge of the side arm 5 is integrally connected to the end face of the first metal strip 3, the top end face of the side arm 5 is flush with the outer edge of the first metal strip 3, and the bottom end face of the side arm 5 faces the second metal strip 6. The end face of the second metal strip 6 is provided with a corresponding portion 601 corresponding to the side arm 5 and extending toward the side arm 5, the corresponding portion 601 is integrally connected to the end face of the second metal strip 6, the bottom end face of the corresponding portion 601 is flush with the outer edge of the second metal strip 6, the top end face of the corresponding portion 601 faces the side arm 5, and the width of the corresponding portion 601 is equal to the width of the side arm 5, that is, the outer edge of the corresponding portion 601 is flush with the outer edge of the side arm 5.

[0036] There is always a gap 7 between the end of the corresponding portion 601 and the end of the side arm 5. The length of the corresponding portion 601 is not equal to the length of the side arm 5, and the sum of the two is always equal to 86 μm. In this embodiment, the end surface of the corresponding portion 601 facing the first metal strip 3 is lower than the edge of the second metal strip 6, so that a concave area is formed between the corresponding portion 601 and the second metal strip 6. This structure is as shown in FIG. Figure 2 As shown in (c), the length of the side arm 5 is 86 μm, the length of the corresponding part 601 is 6 μm, and the gap 7 between the corresponding part 601 and the side arm 5 is 10 μm. The specific dimensions are shown in Table 1.

[0037] Table 1 Structural parameters of the resonant ring in this embodiment

[0038] In this embodiment, a transparent protective film coated on the surface of the photosensitive germanium layer 2 is provided between the resonant ring and the photosensitive germanium layer 2. The transparent protective film is aluminum oxide, silicon nitride or an organic polymer. The transparent protective film can prevent the penetration of foreign substances (such as moisture and oxygen) without affecting the light transmission performance.

[0039] Example 2

[0040] This embodiment is an improvement on the embodiment 1. Its main structure is the same as that of the embodiment 1. The improvement is that the end surface of the corresponding portion 601 is higher than the edge of the second metal strip 6. Figure 3 (a) Structures of Module1, Module2 and Module3, wherein the length of the side arm 5 in Module1 is 58 μm, and the length of the corresponding part 601 is 28 μm; the length of the side arm 5 in Module2 is 73.5 μm, and the length of the corresponding part 601 is 12.5 μm; the length of the side arm 5 in Module3 is 76.75 μm, and the length of the corresponding part 601 is 9.25 μm.

[0041] Example 3

[0042] This embodiment is an improvement on the embodiment 1. Its main structure is the same as that of the embodiment 1. The improvement is that: the end surface of the second metal strip 6 has no corresponding portion 601, there is a gap 7 between the side arm 5 and the end of the second metal strip 6, and the length of the side arm 5 is equal to 86 μm. Figure 3 The structure of End in (a).

[0043] Example 4

[0044] This embodiment is an improvement on the embodiment 1, and its main structure is the same as that of the embodiment 1, and the improvement lies in that: a first graphene strip is arranged on the end face of the side arm 5 facing the second metal strip 6, and a second graphene strip is arranged in the recessed area. Specifically, a length of 3.75 μm is discarded at one end of the side arm 5 facing the second metal strip 6, and a first graphene strip M1 with a length of 3.75 μm is fixed thereon, and a second graphene strip M2 with a length of 3.75 μm is arranged in the recessed area, the outer edges of the first graphene strip and the second graphene strip are both flush with the outer edge of the side arm 5, and the inner edges of the first graphene strip and the second graphene strip are both flush with the inner edge of the side arm 5. In this embodiment, the widths of the first graphene strip and the second graphene strip are both 6 μm, and the first graphene strip and the second graphene strip can both be added with independent gate voltages to control their respective carrier concentrations.

[0045] In order to verify the effectiveness of this scheme, the following is a further explanation based on the test data:

[0046] The current density on the surface of the metal microstructure in the simulation is integrated to obtain the surface current, and then the surface current of the resonant ring is decomposed, and the contribution rate of different multipolar components of the induced current density is calculated in the Cartesian coordinate system. The three-dimensional time-domain finite-difference (FDTD) solver is used for numerical calculations. Periodic boundary conditions are used in the x and y directions, and perfectly matched layer (PML) absorption boundary conditions are used in the z direction of free space. Adaptive mesh refinement is used for the resonant ring and the photosensitive germanium layer 2, with a refinement accuracy of 0.5μm. The structural parameters of the resonant ring are modified, and the dynamic controllability and sensing characteristics of the transmission-type metamaterial device are realized by changing the structural parameters and the optical properties of the material. The frequency shift phenomenon of Mode1 and Mode3 in the system is studied according to the circuit model, and the electric field intensity distribution and the corresponding equivalent circuit model are shown in detail:

[0047] Single and double valley switching: Figure 3 (a) describes the change process of the structure of the resonant ring under different parameters. The initial module (XY / C2) represents a double-open resonant ring with mirror symmetry about the xy axis, that is, the length of the side arm 5 and the corresponding part 601 are exactly the same (W1=W3=43μm). At this time, the momentum space two-dimensional wave vector k with C2 symmetry structure has a rotational symmetry of phase π at the Γ point. The coupling between the bound mode of the symmetric structure and the radiation mode of other symmetry types will be prohibited, and the radiation channel does not exist, forming a symmetric protection type BIC with infinite quality factor, such as Figure 3 (b) Bottom, showing that only one eigenmode Mode 1 based on the ring itself is generated.

[0048] Increase the length of the side arm 5, reduce the length of the corresponding part 601, and keep the total length of the side arm 5 and the corresponding part 601 at 86μm, that is, W1+W3=86μm. It should be noted that W2 changes with W1, and W2 will not be described in detail in the following. The even-symmetric bound state in the optical waveguide leaks into the odd-symmetric continuous domain, and the light escapes into the adjacent waveguide and then diffuses into the continuous domain. BIC-Ⅰ is a low-order quasi-BIC, and Mode2 is excited at the moment of destruction; BIC-Ⅱ is a high-order mode. At this time, there is a gap between the two resonant cavities, and the radiation channel of far-field interference destructive requires higher radiation energy. The guided resonance phenomenon will be coupled with the radiation channel to a certain extent, and Mode3 is fully excited. When W1=58μm, it can be seen that the Mode2 radiation channel is completely opened, the line width increases, and retreats to the normal resonance level; at this time, Mode3 still has a strong radiation lifetime and a relatively small line width.

[0049] As the degree of symmetry destruction continues to increase, the eigenmode Mode1 blueshifts, while the quasi-BIC mode Mode3 redshifts. When W1 = 73.5μm, the two resonance valleys meet on opposite sides, showing a similar EIT mode; at W1 = 76.25μm, the two modes are degenerate, showing a single valley mode with a wider line width; then the two modes move away from each other, Mode3 and Mode1 continue to redshift and blueshift respectively, and at W1 = 80μm, the two modes are almost completely separated and restored to a similar EIT mode. When the short end metal arm completely disappears, Mode3 also disappears.

[0050] In the above system, Mode 1 and Mode 3 are taken as research objects to realize the trough switching from single-double (BIC-Ⅱ excitation)-single (two-mode constructive interference)-double (coupling crushing)-single (BIC-Ⅱ completely disappears). Figure 3 (c) This process can be seen intuitively. T represents the concept of transmission peak-to-valley amplitude, such as Figure 3 (d), we can see that δ T In the process of two resonant phase shifts from phase encounter to separation, they first decrease and then increase, and decrease to 0 when W1=76.25μm, forming a topologically protected BIC cavity.

[0051] Four special structural parameter settings are introduced to represent four modules:

[0052] Module1 (W1 = 58 μm & W3 = 28 μm): double bright mode, quasi-BIC is excited;

[0053] Module2 (W1 = 73.5 μm & W3 = 12.5 μm): double bright mode, the two resonant states form a similar EIT before meeting;

[0054] Module3 (W1 = 76.75 μm & W3 = 9.25 μm): single bright mode, two modes interfere constructively and destructively;

[0055] Module4 (W1=80μm&W3=6μm): double bright mode, the EIT-like window is restored after the two modes meet.

[0056] The resonant mode surface current distribution in the four modules is shown in Figure 4 As shown in (a)-(g), first Figure 4(a)-(b) is Module1. Compared with the eigenmode at 1.272THz, the quasi-BIC excited at 1.762THz obviously shows a stronger electromagnetic response. This is because the radiation energy of the leakage resonance state after the closed resonant cavity interacts with the radiating continuum is much greater than the ordinary vibration mode in the lowest energy state. The current of Mode1 is mainly concentrated in the corresponding part 601, almost maintaining the symmetry of the left and right positive and negative dipoles; the current of Mode3 appears on the entire metal surface (resonant ring), and the current of side arm 5 is relatively stronger, showing the resonance characteristics of the four dipoles as a whole. After evolving into Module2, Mode1 is excited by the light-matter interaction of quasi-BIC, and the current is enhanced; while Mode3 gradually degenerates into ordinary resonance, and the current of the corresponding part 601 basically disappears. The two mode wave vectors under Module3 match, given by Figure 4 (e) It can be seen that the current between the two modes is simultaneously gathered at 1.667THz, and the current intensity of the quasi-BIC retreats to the same level as the eigenstate, with almost the same wave vector. At this time, the BIC at the non-Γ point is obtained by adjusting the wave vector parameters, generating a new phase match, the wave vector is degenerate, and the energy coupled to the radiation open channel disappears, generating a resonant coupled BIC (topologically protected BIC). Under Module 4, the resonant frequency of Mode 1 blue-shifts to 1.708THz, and the resonant frequency of Mode 3 red-shifts to 1.622THz, the EIT-like effect is re-excited, and the two current intensities continue to increase after constructive interference.

[0057] BIC originates from the decoupling of bound and extended states. Based on the symmetry of the lattice and unit cell structure, the radiation field is expressed as the sum of spherical harmonic vectors, thus giving the existence conditions of bound states in optical systems. In order to quantitatively analyze the physical mechanism of resonant coupling of different modes, the scattered power (I) of different multipole moments in Cartesian coordinate systems such as magnetic dipole (MD), electric quadrupole (EQ), magnetic quadrupole (MQ), electric dipole (ED) and toroidal dipole (Torid) is calculated. Figure 5 The trend of multipole contribution rate of Module1 to Module4 with frequency is shown. Starting from Module1, Figure 5 (a) The eigenstate is relatively weak, mainly MD and EQ modes; while the maximum multipole contribution rate of the quasi-BIC state reaches 0.264 μm 2 , showing a strong resonance mode, in which the MQ mode accounts for a large proportion. Then in Module2 ( Figure 5 In (b), the two modes have different dipoles that meet each other, and the maximum contribution rate is still the MQ mode brought by the quasi-BIC, which slightly decreases to 0.245 μm. 2 , still maintains a strong resonance response. However, in Module3 ( Figure 5 In (c), the maximum contribution value drops sharply to 0.043 μm 2, indicating that in order to achieve wave vector matching, the resonance phenomenon needs to ensure that the energy is converted from the pump light to the signal light in a one-way manner. If it is not matched, the energy will be converted cyclically between the two light fields, and the one-way energy transfer cannot be achieved, thus causing a significant attenuation of the quasi-BIC. Finally, in Module4 ( Figure 5 In (d), the multipole expansion is restored and the maximum value rises back to 0.242μm 2 , close to the level of Module2.

[0058] The frequency shift phenomenon of Mode1 and Mode3 in the system is studied based on the circuit model. Figure 6 (a) shows the electric field intensity distribution and the corresponding equivalent circuit model. In the electric field distribution diagrams of Mode 1 and Mode 3, different field distribution characteristics can be observed, indicating that the two modes correspond to different electric field oscillation forms. According to the field distribution, the equivalent circuit model is drawn. The local resonance characteristics of the system are composed of the upper metal arm resonant structure (inductor L1, capacitor C1) and the upper metal arm resonant structure (inductor L2, capacitor C2), and the inductor L3 and capacitor Cg are related to the coupling of the two structures. The resonant frequency of the oscillation circuit is:

[0059]

[0060] Since the two resonant modes are respectively distributed on the side arm 5 and the corresponding part 601 along the y-axis direction, the gap 7 between the side arm 5 and the corresponding part 601 is not changed during the process, so the capacitance is not changed. The relationship between the inductance and the side arm 5 is used:

[0061]

[0062] When l (length of side arm 5) is greater than w (width of side arm 5), the increase of l causes the inductance value L to show a nearly linear growth trend. Therefore, in the whole process, with the increase of side wall W1 and the decrease of W3, L1 gradually decreases and L3 gradually increases, which also causes the resonant frequency of Mode 1 to blue shift and the resonant frequency of Mode 2 to red shift. Figure 6 (b) The resonant frequency change trends of Mode 1 and Mode 3 can be clearly seen.

[0063] The present invention is applied in terahertz modulators, and the modulation efficiency can be improved by changing the electronic and optical properties of materials or structures and switching between single and double valleys. In particular, the double transmission valley effect may lead to steeper transmission changes, thereby making the modulation process of terahertz waves more efficient and achieving a larger modulation depth under a smaller external control signal.

[0064] It can achieve selective absorption or transmission of terahertz waves of specific frequencies or wavelengths. For example, in some semiconductors or two-dimensional materials (such as graphene, transition metal disulfides, etc.), by changing the electronic structure of the material, the generation of single valleys or double valleys can be adjusted, thereby affecting the propagation characteristics of terahertz waves. This adjustment capability enables the device to more flexibly selectively filter out or pass terahertz waves in a specific frequency range when working.

[0065] In some nonlinear optical materials, the switching of single and double transmission valleys may enhance the nonlinear interaction between light and materials, thereby improving the nonlinear effects of terahertz waves, such as the generation, frequency doubling or frequency modulation of terahertz waves. This provides a new means of regulation for the generation and processing of terahertz waves.

[0066] Since the switching between single and double valleys affects the absorption and transmission characteristics of materials for terahertz waves, this effect can be used to design more efficient terahertz wave detectors and imaging systems. For example, by adjusting the depth and position of the material's transmission valley, different terahertz wave signal responses can be obtained, thereby improving imaging resolution or detection sensitivity.

[0067] Slow light effect: In the classical quantum EIT effect, the transparency phenomenon suppresses the absorption of light by introducing a coherent superposition of quantum states in the medium, forming a narrow transmission window, accompanied by a corresponding dispersion enhancement, thereby greatly reducing the group velocity of light in this frequency window, the so-called "slow light effect". In general, the slow light effect can be described by group delay:

[0068]

[0069] in is the transmission phase shift, and ω is the angular frequency of the incident wave. Before and after the formation of Friedrich-WintgenBIC, two EIT-like windows are obtained. Figure 7 (a)(c) shows the phase shift of the two modules, and the slope of the phase shift indicates the intensity of the dispersion. It can be seen that, for both Module2 and Module4, the phase shift slope near Mode2 is small, while there is a large phase shift slope near the transparent window, and the dispersion is relatively strong. Then, the group delay under the two modules is calculated. The group delay of Module2 and Module4 reaches a peak at 1.6497THz and 1.6535THz, respectively, with a maximum value of 23.234 and 24.904, respectively, corresponding to a distance delay of 7.4712mm propagating in free space. Considering practical applications, the maximum value of the delay-bandwidth product (DBP) of the maximum group delay multiplied by the bandwidth is calculated to be 6.5248.

[0070] Transmission peak control method: The evolution law between resonant rings with different structures, in the process of changing from the EIT-like effect to the single resonance mode, the transmission peak shows good control characteristics, and the δ T The transition from 0.932 (double valley) to 0 (single valley) means that the generation and annihilation of the transmission peak are almost within the controllable range.

[0071] Therefore, two methods are designed to achieve effective control of the transmission peak. Figure 8 (a), using the effect of the parameter change on the transmission peak during the evolution, when the structure of the resonant ring is the structure described in Example 4, the addition of the first graphene strip and the second graphene strip can achieve the regulation of the transmission peak in multiple dimensions. First, the metal strip of 3.75 μm on the side wall is discarded, and the first graphene strip M1 with a length and width of 3.75 μm and 6 μm is added; then the second graphene strip M2 of the same specification is added to the concave area, and both can be added with independent gate voltages to control their respective carrier concentrations. When M1=2×10 12 cm 2 And M2=1×10 13 cm 2 When M1=8×10 13 cm 2 And M2=1×10 11 cm 2 When , the EIT-like effect is excited, such as Figure 8 (b) The transition from a single valley to a double valley can be clearly seen. The δ of the transmission peak when M1 and M2 take different values ​​is measured. T and the change of resonance frequency, it can be found that δ T The maximum amplitude modulation that can be achieved is from 0.005 to 0.875. In this process, the resonance frequency can reach a frequency shift of up to 0.022THz, and the transmission peak modulation can be achieved almost at the same phase.

[0072] The near-field interaction of coupled modes always induces strong local field confinement that is sensitive to environmental changes. If the local charge density near the resonant cavity gap is high enough, the low-level photocarriers generated in the "hot spot" will introduce non-radiative losses. Therefore, conductive perturbation experiments were performed on 200nm thick amorphous germanium films, verifying that the transmission peak in the coupled mode is largely determined by the non-radiative losses between the two modes. Fig. 9(a)-(b) show the curves of the transmittance of Module3 and Module4 changing with frequency at different photoconductivities. Since a new refractive index material is introduced at the interface between the two media, a sudden phase shift on the wavelength scale is introduced in the optical path, which leads to a red shift of the resonant frequency. In the figure, as the photoconductivity increases (from 0S / m to 3500S / m), the transmission peak of Module3 will disappear within a change of 100S / m, while the transmission peak of Module3 will approach 0 within a change of 400S / m. Fig. 9 (c)-(d) and (f)-(g); It is found that in the low photoconductivity range, the frequency dependence of the transmission peak in both cases is extremely large, indicating that the non-radiative loss of the module is more obvious under the perturbation of photoconductivity, which has a significant impact on the overall optical properties. When the photoconductivity increases to a certain extent, the transmission peak is close to disappearing, showing broadband characteristics, and the effect of the increase in photoconductivity on the transmittance gradually weakens, that is, the sensitivity of Ge photoconductivity to transmittance decreases as it increases. Fig. 9 (e) and (h) show this better. The delta of Module3 T The amplitude modulation is only 0.154, which is reduced from 0.165 at 0S / m to 0.011 at 0S / m. T It decreases from 0.893 at 0S / m to 0.005 at 400S / m, with the maximum amplitude modulation reaching 0.8925. The two curves show a similar rapid decline trend, but Module 4 is more sensitive to photoconductivity than Module 3. These results show that amorphous germanium film can be added to Module 4 to more effectively utilize Ge photoconductivity in the design and regulation of the optical properties of terahertz devices.

[0073] Finally, the phase shift and group delay of Ge at different conductivity in Module4 are calculated. Fig.10 (b). When the conductivity of Ge is 0S / m, the maximum value of the group delay is 25.29ps, corresponding to a distance delay of 7.587mm in free space. As the conductivity increases, the group delay gradually decreases. When the conductivity of Ge is 400S / m, the transmission amplitude and group delay are close to 0. This phenomenon means that the slow light effect almost disappears. The delay-bandwidth product (DBP) in the process was calculated, and when the conductivity of Ge is 0S / m, the maximum value of DBP is 7.182.

[0074] Table 2 shows the transmission amplitude, group delay, and DBP under different conductivities. The above analysis shows that under Module 4, the slow light effect of the proposed EIT-like metamaterial can be better dynamically controlled by adjusting the conductivity of Ge.

[0075] Table 2 Transmission amplitude, group delay and DBPS under different conductivity

[0076] Table 3 is a performance comparison between the slow light device based on the present invention and the full light device in the prior art. The comparison results show that the slow light device based on this solution has an excellent slow light effect.

[0077] Table 3 Comparison results between the slow light device of the present invention and the slow light device in the prior art

[0078] Note: [1] in Table 4: Liang D, Chen T. Optical modulated graphene metamaterial based on plasmon-induced transparency in the terahertz band: application forsensing[J]. Diamond and Related Materials, 2023, 131: 109613.

[0079] [2]: Sarker D, Nakti PP, Zubair A. Graphene metamaterials-based plasmon-induced terahertz modulator for high-performance multiband filtering and slowlight applications[J]. Optics Express, 2024, 32(6):9442-9455.

[0080] [3]: Huang W, Lin Y S. Dynamically Tunable Electric Split-RingResonators Based on 300nm Gold Films on Silica for Reconfigurable Slow-LightApplication[J]. ACS Applied Nano Materials, 2023, 6(24): 23532-23541.

[0081] [4]: Chen MM, Yang XX, Gao S. Tunable electromagnetically induced transparency in ametal-perovskite hybrid metamaterial and its sensing performance [J]. IEEE Sensors Journal, 2023, 23(5): 4802-4808.

[0082] [5]: Liu C, Liu P, Yang C, et al. Analogue of dual-controlled electromagnetically induced transparency based on a graphene metamaterial[J]. Carbon, 2019, 142: 354-362.

[0083] [6]: Wang BX, Duan G, Lv W, et al. Design and experimental realization of triple-band electromagnetically induced transparency terahertz metamaterials employing two big-bright modes for sensing applications [J]. Nanoscale, 2023, 15(45): 18435-18446.

[0084] Research on sensing characteristics: By changing the Ge photoconductivity, high-degree-of-freedom regulation of the transmission peak can be achieved, that is, effective conversion from dual narrow bands to a single broadband can be achieved. Fig.11 (c) shows a schematic diagram of the structure used for terahertz sensing characteristics research, which reflects the layered structure of the entire experimental setup. Specifically, this structure consists of the following key parts: the analyte layer (AnalyteLayer) is used to simulate the influence of analytes (samples) with different thicknesses (tA) and refractive indices (NA) on the optical properties of the entire system; the PE layer (polyethylene) is below the analyte layer and has a thickness of 2μm. It provides support and helps stabilize the analyte layer, ensuring that different frequency shift phenomena can be accurately measured.

[0085] First, to eliminate the effect of analyte thickness on sensing sensitivity, the refractive index of the analyte is 1.5 and the conductivity of Ge is 0 S / m or 400 S / m. Fig.11(a)-(b) show the transmission spectra of analytes of different thicknesses. As the thickness of the analyte layer increases, the equivalent optical path increases. A longer optical path means that the terahertz wave needs to pass through more media, which increases the phase delay and the frequency of the transmission peak red-shifts with the increase in the thickness of the analyte. When the conductivity of Ge is 0 S / m, the transparent window is narrow. When it increases to 400 S / m, the amplitude from the transparent window to the resonance valley is small, showing a broadband frequency shift characteristic. Fig.11 (d)-(e) show the relationship between the transmission peak frequency and the analyte thickness. When the analyte thickness is greater than 10 μm, the frequency shifts slowly.

[0086] The thickness of the analyte was fixed at 10 μm, and its sensing performance was studied. The transmission spectra of the analyte with different photoconductivities (0 S / m and 400 S / m) as the refractive index NA of the analyte changes are shown in Figure 2. Fig.12 (a)(d). As the NA increases, the resonant peak positions in the two transmission spectra gradually move toward the low frequency (red shift) direction. Compared with 0 S / m, the depth of the resonant peak when the photoconductivity is 400 S / m is reduced, and the overall shape of the transmission spectrum becomes smoother, and the broadband characteristics are obvious. This is due to the increase in the equivalent phase delay caused by the increase in refractive index, that is, as the NA increases, the propagation speed of light in the medium decreases, resulting in a decrease in the resonant frequency. In addition, the increase in photoconductivity will introduce additional losses in the structure, making the transmission peak not as large in amplitude as when it is 0 S / m. Fig.12 (b) The trajectory of the high-frequency peak frequency position movement can be clearly seen, and Fig.12 (e) The color gradient changes relatively slowly. The fitting relationship between the transmission peak resonance frequency and the refractive index difference ΔNA in the two cases is plotted, as shown in Fig.11 (c) and Fig.11 (f), the fitting formulas are calculated to be y=1.5731-0.3117x and y=1.5775-0.3201x, respectively, and the sensitivity is defined as:

[0087]

[0088] Where Δf is the frequency shift of the transparent window, and Δn is the change in refractive index. Therefore, the sensitivity, that is, the fitting slope, is 0.3117THz / RIU and 0.3201THz / RIU, respectively. From the sensitivity, it can be seen that the increase in photoconductivity has a certain influence on the change in resonant frequency, but the amount of change is extremely small. The effect of the change in refractive index on the resonant frequency is relatively consistent, that is, the switching of narrowband sensing and broadband sensing is achieved at a fixed frequency point. The sensitivity of the sensor based on the present invention is compared with that of the sensor in the prior art. The comparison results are shown in Table 4. The results show that the sensor based on the present invention has excellent sensitivity in the terahertz band. At the same time, appropriate photoconductivity regulation can switch the response mode of the sensor, which has a higher degree of freedom.

[0089] Table 4 Comparison of sensitivity between the sensor according to the present invention and the sensor in the prior art

[0090] Note: [7] in the table: Zheng D, Lin Y S. Tunable Dual-Split-Disk Resonator with Electromagnetically Induced Transparency Characteristic[J]. Advanced MaterialsTechnologies, 2020, 5(11):2000584.

[0091] [8]: Yin W, Shen Z, Li S, et al. THz absorbers with an ultrahigh Q-factorempowered by the quasi-bound states in the continuum for sensing application [J]. Optics Express, 2022, 30(18): 32162-32173.

[0092] [9]: Huang W, Lin Y S. Dynamically Tunable Electric Split-RingResonators Based on 300nm Gold Films on Silica for Reconfigurable Slow-LightApplication[J]. ACS Applied Nano Materials, 2023, 6(24): 23532-23541.

[0093]

[10] : Sarkar R, Devi KM, Ghindani D, et al. Polarization independent double-band electromagnetically induced transparency effect in terahertzmetamaterials[J]. Journal of Optics, 2020, 22(3):035105.

[0094]

[11] : Chen MM, Yang XX, Gao S. Tunable electromagnetically induced transparency in a metal-perovskite hybrid metamaterial and its sensing performance [J]. IEEE Sensors Journal, 2023, 23(5): 4802-4808.

[0095]

[12] : Wang R, Xu L, Huang L, et al. Ultrasensitive Terahertz BiodetectionEnabled by Quasi-BIC-Based Metasensors[J]. Small, 2023,19(35):2301165.

[0096] A preparation method of a terahertz control device mediated by quasi-BIC in multi-dimensionality, comprising: performing surface treatment on a substrate layer 1; depositing photosensitive germanium on the treated surface of the substrate layer 1 by chemical vapor deposition to form a photosensitive germanium layer 2; and depositing gold on the photosensitive germanium layer 2 by chemical reaction in the gas phase to form a plurality of resonant rings distributed in an array.

[0097] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A terahertz control device based on quasi-BIC mediation in multi-dimensionality, comprising a substrate layer (1) and a plurality of resonant rings, characterized in that: The surface of the substrate layer (1) is coated with a photosensitive germanium layer (2), and a plurality of resonant rings are arranged and distributed on the photosensitive germanium layer (2), wherein the resonant rings include a first metal strip (3) and a second metal strip (6) which are parallel to each other and of equal length, wherein the center positions of the first metal strip (3) and the second metal strip (6) are connected via an intermediate arm (4) which is perpendicular to the first metal strip (3) and the second metal strip (6), and the end faces of the first metal strip (3) are perpendicularly connected to a side arm (5) extending toward the second metal strip (6); the end faces of the second metal strip (6) are provided with a corresponding portion (601) which corresponds to the side arm (5) and extends toward the side arm (5), and there is a gap (7) between the end of the corresponding portion (601) and the end of the side arm (5), and the length of the corresponding portion (601) is not equal to the length of the side arm (5), and the sum of the two is always equal to 86 μm; or, the end faces of the second metal strip (6) have no corresponding portion (601), and there is a gap between the side arm (5) and the end of the second metal strip (6), and the length of the side arm (5) is equal to 86 μm.

2. A terahertz control device based on multi-dimensional quasi-BIC mediation as claimed in claim 1, characterized in that: The width of the corresponding portion (601) is equal to the width of the side arm (5).

3. A terahertz control device based on multi-dimensional quasi-BIC mediation as claimed in claim 1, characterized in that: The end surface of the corresponding portion (601) facing the first metal strip (3) is higher than the edge of the second metal strip (6).

4. A terahertz control device based on multi-dimensional quasi-BIC mediation as claimed in claim 1, characterized in that: The end surface of the corresponding portion (601) facing the first metal strip (3) is lower than the edge of the second metal strip (6), so that a recessed area is formed between the corresponding portion (601) and the second metal strip (6).

5. A terahertz control device based on multi-dimensional quasi-BIC mediation as claimed in claim 5, characterized in that: The end surface of the side arm (5) facing the second metal strip (6) is provided with a first graphene strip, and the recessed area is provided with a second graphene strip.

6. A terahertz control device based on multi-dimensional quasi-BIC mediation as claimed in claim 5, characterized in that: The widths of the first graphene strip and the second graphene strip are both equal to the width of the side arm (5), and the end surface of the second graphene strip facing the side arm (5) is flush with the edge of the second metal strip (6).

7. The terahertz control device based on multi-dimensional quasi-BIC mediation as claimed in claim 1, characterized in that: The material of the resonant ring is gold, and the thickness of the resonant ring is 0.3 μm.

8. The terahertz control device based on multi-dimensional quasi-BIC mediation as claimed in claim 1, characterized in that: The material of the substrate layer (1) is polytetrafluoroethylene.

9. The terahertz control device based on multi-dimensional quasi-BIC mediation as claimed in claim 1, characterized in that: A transparent protective film coated on the surface of the photosensitive germanium layer (2) is arranged between the resonant ring and the photosensitive germanium layer (2).

10. A method for preparing a terahertz control device based on multi-dimensional quasi-BIC mediation according to any one of claims 1 to 9, characterized in that: The substrate layer (1) is subjected to surface treatment; photosensitive germanium is deposited on the treated surface of the substrate layer (1) by chemical vapor deposition to form a photosensitive germanium layer (2); gold is deposited on the photosensitive germanium layer (2) through a chemical reaction in the vapor phase to form a plurality of resonant rings distributed in an array.

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