Dual controllable tunable polarization independent three-band absorber
By designing an absorber structure that combines a hybrid Dirac half-metal and a vanadium dioxide VO2 layer, and combining an equivalent circuit model with nanorod resonance, a polarization-independent absorber with low loss, multiple frequency bands, and high absorption rate was realized. This solves the problems of high loss and complex structure of absorbers in the terahertz band in existing technologies, and has the ability to dynamically adjust the absorption peak.
Patent Information
- Application Number
- CN202211508022.X
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2022-11-29
- Publication Date
- 2025-11-25
- Estimated Expiration
- 2042-11-29
AI Technical Summary
In the existing technology, the absorbers of ordinary materials have high inherent losses, complex structures and are not easy to process in the terahertz band, making it difficult to achieve efficient absorption in multiple frequency bands. Furthermore, the resonant frequency of the absorption peaks in multiple frequency bands cannot be dynamically adjusted, and the polarization dependence is strong, which limits their application.
An absorber structure consisting of a top mixed Dirac half-metal layer, a bottom vanadium dioxide (VO2) layer, and a middle silicon dioxide (SiO2) layer was adopted. By adjusting the Fermi energy and conductivity, dual tunable behavior was achieved. The physical properties were analyzed using an equivalent circuit model, and resonant structures of Dirac half-metal rectangular nanorods and cross nanorods were designed to achieve polarization-independent multi-band absorption.
It achieves low-loss, high-stability multi-band absorption in the terahertz band with an absorption rate exceeding 99%. It has a simple structure, is easy to process, and can be used as an ultra-sensitive refractive index sensor with the ability to dynamically adjust the absorption peak.
Smart Images
Figure CN115629433B_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The application belongs to the technical field of metamaterial devices, and more particularly to a dual-tunable polarization-independent three-band absorber. BACKGROUND
[0002] Terahertz (THz) electromagnetic waves have a frequency range of 0.1 THz to 10 THz. With the development of THz technology, it has unique advantages in many important fields such as physics, chemistry, electronic information, life science, material science, astronomy, atmosphere, etc. However, due to the large transmission loss of THz waves in free space, the effective conversion between electromagnetic waves and electrical energy, i.e. the "THz gap", becomes difficult. In order to overcome this difficulty, there is an urgent need for two-dimensional materials that can effectively manipulate and propagate THz waves. Two-dimensional materials have a wide variety of novel properties, and are easy to integrate with photonic structures such as optical fibers and chips. In addition, most two-dimensional materials have good electrically tunable physical properties. Therefore, they are very suitable for functional optoelectronic information devices.
[0003] In recent years, bulk Dirac semimetals (BDS) and vanadium dioxide (VO2) have attracted widespread attention. BDS has many special properties such as extremely high mobility, ultrafast transient time and low-energy photon detection. Most importantly, the surface conductivity of BDS can be dynamically adjusted by changing the Fermi energy. Therefore, the design of tunable metamaterial absorbers based on BDS has been widely studied in recent years.
[0004] In addition, VO2 is a new phase change material that undergoes a reversible insulator-metal phase transition. During this transition, its conductivity can change by 4-5 orders of magnitude.
[0005] VO2 has been widely used for transmission control, phase modulation, tunable absorbers and switchable multifunctional devices. Due to the unique and good physical properties of BDS and VO2, the research of dual-control metamaterial absorbers realized by BDS and VO2 becomes crucial. However, the research on dual-control tunable polarization-independent three-band absorbers using BDS and VO2 is still rarely reported in public literature.
[0006] Absorbers of ordinary materials are not easy to make, and have higher inherent loss and more stable physical properties in the terahertz wave band, and their absorption efficiency for multiple frequency bands is also not high, and the resonant frequency at the multi-band absorption peak cannot be dynamically adjusted, the structure is relatively complex, and it is not easy to process. SUMMARY
[0007] The application provides a dual-tunable polarization-independent three-band absorber. The dual-tunable behavior can be realized by adjusting the Fermi energy of the mixed Dirac semimetal and the conductivity of vanadium dioxide VO2. The physical properties of the absorber can be theoretically analyzed by an equivalent circuit model ECM. In addition, the absorber exhibits polarization-independent behavior due to the symmetrical structure of the absorber. The application provides potential applications for the design of multi-band dual-control tunable sensors, filters and absorbers.
[0008] In order to achieve the above-mentioned purpose, the application is realized by adopting the following technical scheme:
[0009] A dual-controllable tunable polarization-independent three-band absorber, which is composed of a top mixed Dirac semimetal layer and a bottom vanadium dioxide VO2 layer; the middle dielectric layer is silicon dioxide SiO2, which can increase the dielectric thickness to realize multi-band absorption; the layers are arranged in the order of the mixed Dirac semimetal layer, the silicon dioxide SiO2 layer and the vanadium dioxide VO2 layer from top to bottom, and the layers are tightly and seamlessly attached to each other to form a structure.
[0010] The equivalent circuit model of the absorber can be used to theoretically analyze the physical properties of the absorber. The vanadium dioxide VO2 layer is regarded as a short-circuit device in the equivalent circuit model. When the incident wave is an X-polarized wave, only the nanorods A, C and the cross nanorod can directly interact with the incident wave, and the nanorods B and D have no response because the polarization is perpendicular to the long axis. The top mixed Dirac semimetal layer can be modeled by three parallel resonances; one resonance represents the cross nanorod, and the other two resonances represent the rectangular nanorods A and C.
[0011] The input impedance of the proposed X-polarized wave three-band absorber can be calculated as:
[0012] (1)
[0013] wherein,
[0014] 、 、 represent the impedance of the three parallel resonances, respectively; the impedance of the short-circuit transmission line wherein, represents the characteristic impedance of free space; and represent the relative permittivity and thickness of the middle SiO2 layer, respectively; represents the wave number of free space;
[0015] Therefore, the reflection coefficient of the proposed X-polarized wave three-band absorber can be represented as:
[0016] (2)
[0017] Finally, the effective impedance of the three-band absorber can be written as:
[0018] (3)
[0019] When the bottom VO2 layer is in the full-metal state, the transmission coefficient ; at the same time, according to the impedance matching theory, if the effective impedance of the three-band absorber matches the intrinsic impedance of vacuum , the reflectivity will be zero, and the absorption will be close to 1.
[0020] Further, the BDS Fermi energy is selected between 0.12 eV and 0.15 eV, which can dynamically adjust the resonance frequency at the multi-band absorption peak.
[0021] The present application has the following advantages:
[0022] 1. The present application adopts Dirac semimetal metamaterials, which are relatively easy to manufacture compared to ordinary materials, and have lower intrinsic loss and more stable physical properties in the terahertz waveband. Compared with single-atom-layer graphene, BDS is more robust to environmental defects or excessive conductive states.
[0023] 2. The present application sets vanadium dioxide VO2 as the model bottom layer, which can dynamically adjust the absorption rate at the multi-band absorption peak by using the temperature control characteristics of VO2 itself and changing the thickness of the VO2 layer.
[0024] 3. The thickness of the silicon dioxide SiO2 dielectric layer in the present application is adjustable, which can realize dynamic conversion between double-band absorption effect and three-band absorption effect.
[0025] 4. The present application uses all-dielectric materials, so the structure is simple and easy to process.
[0026] 5. The present application adopts the resonance structure of Dirac semimetal rectangular nanorods and cross nanorods, which can realize polarization-independent multi-band perfect absorption effect with an absorption rate exceeding 99%.
[0027] 6. The present application can be used as a super-sensitive refractive index sensor in addition to being used as a perfect absorber. BRIEF DESCRIPTION OF DRAWINGS
[0028] Figure 1 Fig. 1 is a schematic diagram of the absorber structure of the present application, wherein (a) is a three-dimensional view, (b) is a two-dimensional top view, and (c) is a two-dimensional side view;
[0029] Figure 2 Equivalent circuit model of the proposed three-band absorber;
[0030] Figure 3 Absorption spectrum of the dual-tunable polarization-independent three-band absorber;
[0031] Figure 4 Effective impedance of the absorber;
[0032] Figure 5 Absorptivity of the absorber at different polarization angles;
[0033] Figure 6 Electric field distribution in the XY plane at the absorption peak of the absorber under (a)-(c) X-polarized wave condition, (d)-(f) Y-polarized wave condition;
[0034] Figure 7 Absorption spectrum of the absorber at various Fermi energies of 0.12 eV, 0.13 eV and 0.15 eV when VO2 is in a completely metallic state.
[0035] Figure 8 Transmission spectrum of the proposed three-band absorber when the conductivity of VO2 increases from 10 S / m to 100000 S / m;
[0036] Figure 9 Reflection spectrum of the proposed three-band absorber when the conductivity of VO2 increases from 10 S / m to 100000 S / m;
[0037] Figure 10 Absorption spectrum of the proposed three-band absorber when the conductivity of VO2 increases from 10 S / m to 100000 S / m;
[0038] Figure 11 Frequency dependence of the absorption rate when the thickness of BDS increases;
[0039] Figure 12 Frequency dependence of the absorption rate when the thickness of SiO2 increases;
[0040] Figure 13 Frequency dependence of the absorption rate when the thickness of VO2 increases;
[0041] Figure 14 Absorption spectrum of the three-band absorber and the relationship spectrum of different refractive indices of the surrounding medium (a);
[0042] Figure 15 Absorption spectrum of the three-band absorber and the relationship spectrum of different refractive indices of the surrounding medium (b). DETAILED DESCRIPTION
[0043] The technical solutions in the embodiments of the present application will be described in detail below with reference to the drawings. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without creative work fall within the protection scope of the present application.
[0044] As shown in the drawings, the absorber is composed of a top mixed Dirac semimetal layer and a bottom vanadium dioxide VO2 layer; Figure 1
[0045] The intermediate dielectric layer is silicon dioxide SiO2, and the use of silicon dioxide SiO2 as the intermediate dielectric layer can increase the dielectric thickness to realize multi-band absorption;
[0046] The layers are arranged in the order of the mixed Dirac semimetal layer, the silicon dioxide SiO2 layer, and the vanadium dioxide VO2 layer from top to bottom, and each layer is tightly and seamlessly attached to each other to form a structure.
[0047] Design of double-control tunable polarization-independent three-band absorber
[0048] Using the Kubo formula in the random phase approximation (RPA), the real and imaginary parts of the BDS conductivity can be expressed in the long-wave limit as:
[0049] (4) (5)
[0050] where, , is the Fermi distribution function, is the reduced Planck constant, is the degeneracy factor, is the Fermi energy, is the temperature, is the Fermi momentum, is the Fermi velocity, is the scattering rate determined by the carrier mobility. , the intrinsic time , , , is the cutoff energy. Therefore, the permittivity of the mixed Dirac semimetal can be expressed as:
[0051] (6)
[0052] where, is the vacuum permittivity, is an effective background dielectric.
[0053] The relative permittivity of VO2 in the terahertz band can be expressed by the Drude model as follows:
[0054] (7)
[0055] where, is the collision frequency, is the permittivity at infinite frequency, is the plasma frequency. It is assumed that the conductivity of VO2 is and when VO2 is in the fully metallic state and the insulating state, respectively.
[0056] The top hybrid Dirac semimetal layer is composed of four rectangular nanorods and a cross nanorod, the length of the four rectangular nanorods is , the length of the cross nanorod is , the width of the rectangular nanorod and the cross nanorod is , the distance between the rectangular nanorod and the cross nanorod is , and the period of the model is .
[0057] The thickness of the hybrid Dirac semimetal layer is , and the thickness of the VO2 layer is .
[0058] Numerical simulations are performed by using Lumerical FDTD Solutions software. In the two-dimensional top view shown in FIG. 1(b), the X and Y directions use periodic boundary conditions, and the Z direction uses a perfectly matched layer (PML) boundary condition. The incident wave propagates along the -Z direction, and the polarization direction is along the X direction (X-polarized wave) or the Y direction (Y-polarized wave). The absorption of the absorber can be calculated as . Where, and represent the reflectivity and transmittance, respectively.
[0059] As Figure 2As shown, a double-tunable polarization-independent three-band equivalent circuit model, the physical properties of the absorber can be theoretically analyzed, the VO2 layer is regarded as a short-circuit device in the equivalent circuit model, at the same time, when the incident wave is X-polarized wave, only rod A, rod C and cross nanorod can directly interact with the incident wave, nanorods B and D show no response because the polarization is perpendicular to its long axis; the top hybrid Dirac semimetal layer can be modeled with three resonances arranged in parallel; among them, one resonance represents the cross nanorod, and the other two resonances represent rectangular nanorods A and C;
[0060] The input impedance of the proposed X-polarized wave three-band absorber can be calculated as:
[0061] (1)
[0062] where,
[0063] , , respectively represent the impedance of the three parallel resonances; the impedance of the short-circuit transmission line where, represents the free-space characteristic impedance; and respectively represent the relative permittivity and thickness of the intermediate SiO2 layer; represents the wave number of free space;
[0064] Therefore, the reflection coefficient of the proposed X-polarized wave three-band absorber can be represented as:
[0065] (2)
[0066] Finally, the effective impedance of the three-band absorber can be written as:
[0067] (3)
[0068] When the bottom VO2 layer is in a full-metal state, the transmission coefficient ; at the same time, according to the impedance matching theory, if the effective impedance of the three-band absorber matches the intrinsic impedance of vacuum , the reflectivity will be zero, and the absorption will be close to 1.
[0069] Experimental verification
[0070] As shown in Figure 3 , the absorption, reflection and transmission spectra of the proposed X-polarized wave three-band absorber are shown when the Fermi energy of the BDS is 0.15 eV and the conductivity of VO2 is 100000 S / m.
[0071] From the black line, it can be seen that three different absorption peaks are observed at frequencies of 3.3618 THz, 4.9196 THz and 5.3719 THz with an absorption of 99.76%, 99.61% and 99.76%, respectively. The average absorption of the three peaks is 99.71%. The dotted line indicates that the transmittance of the absorber is close to zero because the bottom vanadium dioxide VO2 layer is in a fully metallic state and the thickness of vanadium dioxide VO2 is greater than the skin depth in the terahertz region. Therefore, it can prevent transmission and act as a reflective layer.
[0072] The effective impedance of the proposed three-band absorber is shown in Figure 4 As shown in Figure 3 and Figure 4 The effective impedance of the proposed three-band model is equal to 1 at peaks I and III. Therefore, the effective impedance of the three-band absorber matches the intrinsic impedance of the vacuum, resulting in an absorption of 99.76% and 99.76% for absorption peaks I and III, respectively. At peak II, the effective impedance is close to 1. Therefore, the absorption at peak II is 99.61%, which is lower than peaks I and III.
[0073] Figure 5 The absorption spectrum of the proposed three-band absorber is shown. It is assumed that the polarization angle is the angle between the direction of the incident electric field and the X-axis direction. It can be seen that, due to the structural symmetry of the proposed absorber, the polarization angle increases from to , the resonance frequency and absorption at the three absorption peaks remain unchanged. Therefore, as the polarization angle increases, the absorber exhibits polarization-independent behavior.
[0074] The physical mechanism of the dual-tunable polarization-independent three-band absorber can be explained by the electric field distribution. Figure 4 The electric field distribution analysis of X-polarized and Y-polarized waves at absorption peaks I-III in the X-Y plane is given, respectively.
[0075] Figure 6 (a) indicates that for X-polarized waves, at the I peak frequency, the electric field is mainly concentrated on the cross nanorod. The positive and negative charges are mainly distributed on the left and right sides of the horizontal rod, causing electric dipole resonance. Therefore, electromagnetic energy is dissipated, resulting in peak I at 3.3618 THz. Similarly, Figure 6 (b) Peak II at 4.9196 THz is the result of dipole resonance around rod A, rod C and cross nanorod, while in Figure 6 (c) Dipole resonance concentrated on rod A and C leads to peak III at 5.3719 THz.
[0076] Figure 6(d), (e) and (f) indicate that the electric field of Y-polarized wave is distributed perpendicularly relative to the electric field of X-polarized wave. Therefore, Figure 6 The peak I in (d) is the result of the dipole resonance concentrated on the cross nanorod. The dipole resonance located around the rods B, D and the cross nanorod results in Figure 6 The peak II in (e). Figure 6 The peak III in (f) is caused by the dipole resonance concentrated on the rods B and D.
[0077] The permittivity of the hybrid Dirac semimetal is largely related to the Fermi energy. Therefore, the peak frequency of the proposed three-band absorber can be dynamically controlled by changing the Fermi energy of the hybrid Dirac semimetal, as shown in Figure 7 At this time, the conductivity of VO2 is unchanged at 100000 S / m, and the polarization direction is always along the X direction.
[0078] It can be seen from Figure 7 that when the Fermi energy of the hybrid Dirac semimetal changes from 0.11 eV to 0.15 eV, the resonance frequency of the three absorption peaks also increases, showing a blue shift. In addition, as the Fermi energy increases, the average peak absorption rate remains above 99%.
[0079] Figure 8 Figure 9 Figure 10 The reflectivity, transmissivity and absorptivity of the proposed three-band absorber are shown when the conductivity of vanadium dioxide VO2 increases from 10 S / m to 100000 S / m. At this time, the Fermi energy of the hybrid Dirac semimetal is fixed at 0.15 eV, and the polarization direction is always along the X direction.
[0080] It can be seen from Figure 10 that the absorptivity of peak I can continuously change from 13.4% to 99.76%. The absorptivity of peak II can increase from 8.7% to 99.61%, and the absorptivity of peak III can change from 27.2% to 99.76% as the conductivity of vanadium dioxide VO2 increases from 10 S / m to 100000 S / m.
[0081] In addition, when vanadium dioxide VO2 is in a completely metallic state, the transmissivity and reflectivity are the smallest, and the absorption spectrum appears three different absorption peaks at the frequencies of 3.3618 THz, 4.9196 THz and 5.3719 THz. As the conductivity decreases from 100000 S / m to 10 S / m, the transmissivity and reflectivity both increase, while the absorptivity decreases due to the transition of vanadium dioxide VO2 from a fully metallic state to an insulating state. When vanadium dioxide VO2 is in an insulating state, the reflectivity reaches the highest value: 86%, 93%, 50%, and the maximum absorption rate is less than 20%.
[0082] Therefore, the proposed three-band absorber exhibits a dual-tunable behavior by adjusting the Fermi energy of the hybrid Dirac semimetal and the conductivity of the vanadium dioxide VO2.
[0083] Figures 11 to 13 The modulated absorption spectrum as a function of the thickness of the hybrid Dirac semimetal, the thickness of the silicon dioxide SiO2, and the thickness of the vanadium dioxide VO2 is shown. The Fermi energy of the hybrid Dirac semimetal is fixed at 0.15 eV. The conductivity of the vanadium dioxide VO2 is equal to 100000 S / m, and the polarization direction is along the X direction.
[0084] Figure 11 In the case of the hybrid Dirac semimetal thickness gradually increasing, the resonance frequencies at the three absorption peaks slightly increase, but the absorption rate remains basically unchanged since the thickness of the hybrid Dirac semimetal has reached the saturation value.
[0085] Due to the hybrid Dirac semimetal rod, the silicon dioxide SiO2 spacer, and the vanadium dioxide VO2 film constitute an equivalent FP resonator. The thickness of the silicon dioxide SiO2 spacer layer has a great influence on the interaction of the hybrid Dirac semimetal with the incident wave. Therefore, in the case of the hybrid Dirac semimetal thickness Figure 12 , the absorption rate of the absorber gradually increases when . Although the absorber also exhibits a three-band absorption effect, the average absorption rate is only 83%, and the absorption effect is poor. When , only two absorption peaks are generated in the absorber. Only when the thickness of the silicon dioxide SiO2 layer is , the absorption rate at the absorption peaks of the three-band absorber reaches the maximum value, and the average absorption rate is 99.7%.
[0086] In the case of the hybrid Dirac semimetal thickness Figure 13 , as the thickness of the vanadium dioxide VO2 increases from to , the absorption rate of the absorber gradually increases. When the thickness is greater than , the absorption rate of the three absorption peaks remains unchanged because the thickness of the bottom vanadium dioxide VO2 layer is greater than the skin depth, and the transmittance is close to zero.
[0087] Finally, the application potential of the absorber as a refractive index sensor is analyzed. The Fermi energy of the hybrid Dirac semimetal is also fixed at 0.15 eV. The conductivity of the vanadium dioxide VO2 is unchanged at 100000 S / m, and the polarization direction is along the X direction.
[0088] As can be seen from Figure 14 , when the refractive index of the surrounding medium increases from 1.0 to 1.5, the resonance frequencies of the three absorption peaks gradually decrease, and redshift occurs. At the same time, from Figure 15It can be seen that the change of the peaks I-III is approximately linear with the change of the refractive index, and the sensitivity of the peaks I-III is 19.2 , 8.67 and 3.78 , respectively.
[0089] It should be understood that the above detailed description and specific examples, which are presented only for illustrative purposes and not for limitations, are merely to describe the principles of the present application. Therefore, any modification, equivalent replacement, improvement, etc. made without departing from the spirit and scope of the present application should be included in the scope of the present application. In addition, the appended claims of the present application are intended to cover all changes and modifications falling within the scope and boundary of the appended claims, or equivalents of such scope and boundary.
Claims
1. A dual-controllable and tunable polarization-independent three-band absorber, the absorber comprising a top hybrid Dirac half-metal layer and a bottom vanadium dioxide (VO2) layer; the intermediate dielectric layer is silicon dioxide (SiO2), using silicon dioxide (SiO2) as the intermediate dielectric layer can increase the dielectric thickness to achieve multi-band absorption; the layers are arranged from top to bottom in the order of hybrid Dirac half-metal layer, silicon dioxide (SiO2) layer, and vanadium dioxide (VO2) layer, and the layers are tightly and seamlessly bonded to each other to form a structure; The equivalent circuit model of the absorber can be used to theoretically analyze the physical properties of the absorber, characterized in that: The incident wave is an X-polarized wave. Only nanorods A, C, and cross nanorods can directly interact with the incident wave. Nanorods B and D do not respond and their polarization is perpendicular to their long axis. The top hybrid Dirac half-metal layer is modeled using three parallel resonances; one resonance represents the cross-shaped nanorods, and the other two resonances represent the rectangular nanorods A and C. The input impedance of the X-polarized wave three-band absorber is calculated as follows: (1) in, These represent the impedances of three parallel resonants; the impedance of a short-circuited transmission line. ,in, Indicates the characteristic impedance in free space; and These represent the relative permittivity and thickness of the intermediate SiO2 layer, respectively. The wavenumber represents free space; Therefore, the reflection coefficient of the X-polarized wave three-band absorber is expressed as: (2) Finally, the effective impedance of the three-band absorber is written as: (3) The bottom VO2 layer is in an all-metal state with a transmittance coefficient of Meanwhile, the effective impedance of the three-band absorber Inherent impedance of vacuum If matched, the reflectivity will be zero and the absorptivity will be close to 1.
2. The dual controllable and tunable polarization-independent three-band absorber according to claim 1, characterized in that: The Fermi energy of the Dirac semimetal layer is selected between 0.12 eV and 0.15 eV, and the resonant frequency at the multi-band absorption peak can be dynamically adjusted.