Metamaterial for realizing tunable electromagnetically induced transparency in dual polarization channels and realization method thereof

Abstract

The present invention discloses a metamaterial for realizing tunable electromagnetic induced transparency in dual polarization channels. By designing a composite metamaterial, tunable electromagnetic induction phenomenon in the near-infrared band in dual polarization channels is achieved. The designed metamaterial includes a base layer at the bottom and periodically spaced dielectric squares and vanadium dioxide squares attached to the upper surface of the substrate. The present invention can achieve tunable electromagnetic induced transparency phenomenon in dual polarization channels in the near-infrared band by selecting the materials of the substrate and the dielectric squares and designing the size parameters between various components. When x-polarized light and y-polarized light are respectively incident on the metamaterial, high-quality electromagnetic induction phenomenon can be achieved in the near-infrared band. In addition, by adjusting the conductivity of vanadium dioxide, flexible regulation of the electromagnetic induced transparency window will be realized. This structure has important application potential in optical switches, slow light devices and high-sensitivity refractive index sensors, and can improve the integration of devices and realize the miniaturization of devices.

Description

Technical Field

[0001] The present invention belongs to the field of metamaterials, and relates to a metamaterial and a realization method for achieving tunable electromagnetic induced transparency in dual polarization channels, which can flexibly control x-polarized light and y-polarized light simultaneously in the near-infrared band. Background Art

[0002] Electromagnetic induced transparency (EIT) is a quantum destructive interference that can generate narrow and sharp transparency windows within a wide absorption spectrum. Due to the strong dispersion characteristics always accompanying this phenomenon, it can be used to achieve slow light effects and enhance nonlinear effects. In early EIT research, stable laser sources and ultra-low temperatures and other harsh experimental conditions were usually required, which hindered the further application of the EIT effect. These limitations, in turn, enabled researchers to focus on classical physical systems. Subsequently, the EIT-like effect has been realized in multiple optical resonant systems such as photonic crystals, circuits, and metamaterials, which can effectively avoid the strict experimental conditions of quantum systems and be achieved at room temperature. However, due to the inevitable ohmic loss and non-radiative loss of metal materials, the quality factor of the early realized electromagnetic induced transparency window was usually not high. Later, it was proposed to use high refractive index and low loss dielectric materials to achieve high-quality electromagnetic induced transparency effects in the near-infrared band based on Mie resonance. At this frequency, the designed device size can reach the nanoscale. EIT has a wide range of applications in slow light devices, sensors, optical memories, etc.

[0003] As a special electromagnetic phenomenon, the EIT effect has received extensive attention since its discovery. However, once the optical properties and functions of passive metamaterials are generated, they are fixed. Therefore, it is necessary to achieve a dynamically tunable EIT effect to meet actual needs. Nowadays, researchers usually combine metamaterials with some dynamic elements such as graphene, phase change materials, and semiconductors to achieve a tunable EIT effect. Among all these dynamic elements, vanadium dioxide stands out due to its reversible transition from an insulating state to a metallic state, which occurs at a promising and easily achievable temperature of 340K (68°C). At room temperature, VO 2 is in an insulating state, while above the phase transition temperature, it will transform into a metallic state. In addition, in addition to direct heating, VO 2 can also reach the phase transition temperature under the excitation of current and light, greatly increasing the design options. This novel property will expand the application of the EIT effect.

[0004] In order to improve the integration and miniaturization of components, scientists have proposed polarization multiplexed metasurfaces to achieve the EIT effect in orthogonal polarization channels. Due to the difference in electromagnetic coupling in different excitation channels, the EIT window also exhibits different characteristics, and it can be rapidly switched by changing the polarization of the incident wave, thereby resulting in the functional transformation of components. Summary of the Invention

[0005] Based on the above technical difficulties, the present invention designs a metamaterial with anisotropy in the x and y directions to achieve tunable electromagnetic induced transparency (EIT) in dual polarization channels. By changing the structural size parameters and the conductivity of vanadium dioxide, flexible control of electromagnetic waves can be achieved in the x and y polarization directions.

[0006] To achieve the above object, the present invention is realized through the following technical solutions: A metamaterial for realizing tunable electromagnetic induced transparency in dual polarization channels, the metamaterial is divided into upper and lower layers, including a base layer at the bottom and a metasurface structure unit attached to the upper surface of the substrate. The metasurface structure unit is a periodic arrangement of dielectric squares and vanadium dioxide squares, and the metamaterial can achieve high-quality electromagnetic induced transparency in the near-infrared band when x-polarized light or y-polarized light is incident.

[0007] Preferably, the material of the base layer is silicon dioxide or sapphire.

[0008] Preferably, the thickness of the base layer is 120nm - 250nm.

[0009] Preferably, the material of the dielectric square is silicon.

[0010] Preferably, the side length of the dielectric square is 300nm - 500nm, the side length of the vanadium dioxide square is 150nm - 350nm, the thickness of the dielectric square and the vanadium dioxide square is 120nm - 250nm, and the spacing is 150nm - 350nm.

[0011] Preferably, the period of the metasurface structure unit is 1400nm - 1600nm.

[0012] The present invention also proposes a method for realizing tunable electromagnetic induced transparency in dual polarization channels, designing a metamaterial for realizing tunable electromagnetic induced transparency in dual polarization channels as described above, optimizing the size parameters of the dielectric square and the vanadium dioxide square and the spacing therebetween to affect the coupling strength between the dielectric square and the vanadium dioxide square, and simultaneously achieving high-quality electromagnetic induced transparency in the near-infrared band in the x and y polarization directions through the optimized metamaterial structure.

[0013] As a further technical solution, by regulating the conductivity of the vanadium dioxide square, the strength of the electromagnetic induced transparency effect can be regulated, and the process of controlling the electromagnetic induced transparency effect from strong to weak and then to disappearance can be achieved in the x and y polarization channels.

[0014] Compared with the prior art, the present invention proposes a metamaterial structure that is anisotropic in the x and y directions, which can simultaneously generate high-quality electromagnetic induced transparency windows when x-polarized light and y-polarized light are incident, and when the polarization state of the incident light is changed, the corresponding electromagnetic induced window can also be quickly switched. At the same time, due to the characteristics of the regulating unit vanadium dioxide, this metamaterial structure can regulate the process of the electromagnetic induced transparency effect changing from strong to weak until disappearing. The above characteristics make this device have the potential to be applied to the development of optical switches, slow light devices, and high-sensitivity sensors, etc., and can achieve the miniaturization and integration of devices to a certain extent. In summary, the present invention provides important reference value for the development of related devices in the field of electromagnetic regulation and is of great practical significance. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a schematic structural diagram of Embodiment 1 of the present invention;

[0016] Figure 2 It is a schematic diagram of the unit structure of Embodiment 1 of the present invention;

[0017] Figure 3 It is a top view of the unit structure of Embodiment 1 of the present invention;

[0018] Figure 4 It is a left view of the unit structure of Embodiment 1 of the present invention;

[0019] Figure 5 It is the transmission spectrum of Embodiment 1 of the present invention when x-polarized light and y-polarized light are incident;

[0020] Figure 6 It is the transmission spectrum of Embodiment 1 of the present invention when the side length of the dielectric block is changed and x-polarized light is incident;

[0021] Figure 7 It is the transmission spectrum of Embodiment 1 of the present invention when the side length of the dielectric block is changed and y-polarized light is incident;

[0022] Figure 8 It is the transmission spectrum of Embodiment 1 of the present invention when the conductivity of vanadium dioxide is changed and x-polarized light is incident;

[0023] Figure 9 It is the transmission spectrum of Embodiment 1 of the present invention when the conductivity of vanadium dioxide is changed and y-polarized light is incident;

[0024] Figure 10 It is the transmission spectrum of Embodiment 2 of the present invention when x-polarized light and y-polarized light are incident. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0025] To more clearly illustrate the implementation scheme in the embodiments of the present invention, the following further illustrates the specific implementation scheme with reference to the accompanying drawings. Note that the following specific drawings and corresponding data results only represent the embodiments of the present invention. For relevant researchers in the field, without creative efforts, other relevant results and implementation methods can be obtained based on these drawings and corresponding descriptions.

[0026] The following further illustrates the present invention with specific implementation schemes in combination with the accompanying drawings:

[0027] The present invention provides a method for realizing tunable electromagnetic induced transparency in dual polarization channels. By utilizing the anisotropy of the metasurface structure in the x and y polarization directions and the strong electromagnetic dipole responses of different module metamaterials in the x and y directions, a superstructure is designed to achieve high-quality electromagnetic induced transparency in the near-infrared band when x-polarized light or y-polarized light is incident. The preset metasurface structure for realizing this method is divided into upper and lower layers, including a bottom substrate layer and periodically spaced dielectric squares and vanadium dioxide squares attached to the upper surface of the substrate. By designing the size parameters of the dielectric squares and vanadium dioxide squares and the spacing between them, the coupling strength between the dielectric squares and vanadium dioxide squares can be affected, and after optimization, high-quality electromagnetic induced transparency in the near-infrared band can be achieved simultaneously in the x and y polarization directions through this structure. By regulating the conductivity of the vanadium dioxide squares, the strength of the electromagnetic induced transparency effect can be regulated, and the process of the electromagnetic induced transparency effect changing from strong to weak and then disappearing can be controlled in both the x and y polarization directions. Obviously, the method of the present invention for realizing the electromagnetic induced transparency effect in different polarization channels and dynamically regulating it using vanadium dioxide will greatly improve the integration of devices and promote the miniaturization of devices, having broad application prospects.

[0028] The present invention adopts periodic boundary conditions, and the specific period can be selected according to specific requirements. Figure 1 This is an 8×8 schematic diagram of this structure. Figure 2 This is a unit schematic diagram of this structure. Figure 3 and Figure 4 respectively represent the top view and left view of the unit structure. In Figure 2 , Figure 3 , Figure 4 , 1 represents the dielectric square, 2 represents the vanadium dioxide square, and 3 represents the substrate.

[0029] Figure 3 In it, p represents the period of the unit structure in the x and y directions, a represents the side length of the dielectric square, b represents the side length of the vanadium dioxide square, and d represents the spacing between the dielectric square and the vanadium dioxide. Figure 4 In it, h represents the thickness of the dielectric square and the vanadium dioxide square, h 1 represents the thickness of the substrate.

[0030] In the embodiments of the present invention, simulations are carried out using the electromagnetic simulation software CST and corresponding optimizations are made. The periodic directions of the unit structure are selected as the x - direction and the y - direction. The incident electromagnetic waves are respectively selected as x - polarized light and y - polarized light, and incident along the negative direction of the z - axis.

[0031] Embodiment 1: A feasible embodiment obtained by simulation optimization in the embodiments of the present invention is: p = 1500 nm, a = 402 nm, b = 292 nm, d = 245 nm, h = 185 nm, h1 = 185 nm. The substrate material is quartz glass with a dielectric constant of 2.19, and the material of the dielectric square is silicon with a dielectric constant of 11.9. When vanadium dioxide is in the dielectric state, its dielectric constant is set to 9. When it transforms into the metallic state, its dielectric constant can be obtained from the Drude model:

[0032]

[0033] The regulated range of the set conductivity (c) of vanadium dioxide is c = 20 S / m - 1×10 5 S / m (the room - temperature condition is 20 S / m). When in the room - temperature condition, the simulation results obtained according to the above initial conditions are as Figure 5 shown. Obvious and sharp EIT windows appear near 1436.1 nm and 1417.2 nm, and their peak transmittances can reach 98% and 97% respectively. The full - width at half - maximum (FWHM) and quality factor (Q - factor) are introduced to further describe the properties of the EIT window. It can be expressed as Q = λ 0 / FWHM, where λ 0 is the central wavelength of the EIT window. In this way, the FWHM and Q values of the EIT window under x - polarized light excitation are 0.8 nm and 1795 respectively, while the FWHM and Q values of the EIT window under y - polarized light excitation are 0.3 nm and 4724 respectively. The simulation results show that this structure can be used as an excellent EIT - generating device and exhibits different characteristics in two orthogonal polarization channels. Utilizing this characteristic, the polarization state of the incident near - infrared light can be changed according to actual needs to achieve flexible switching of the EIT effect.

[0034] Under the condition that the above conditions remain unchanged, the transmission spectra of the incident x - polarized light and y - polarized light obtained by changing the side length a of the dielectric square are respectively as Figure 6 and Figure 7As shown. When a increases, the transmission spectra in both cases exhibit a red shift, and the peak transmittance of the EIT window changes little. The difference is that the x-polarized transmission spectrum shifts less and the deformation degree of the EIT window is smaller, while the shifted wavelength of the y-polarized transmission spectrum is several times that of the x-polarized transmission spectrum, and the deformation degree of the EIT window is larger. This is because the side length a of the dielectric square directly affects the coupling of the electric field in the cases of x-polarized light and y-polarized light incidence. Since the metamaterial structure itself has anisotropy in the x-direction and y-direction and is affected differently, this uneven change phenomenon occurs. Changing b, h, h 1 also shows a similar phenomenon. In contrast, when the period p of the unit structure changes within a certain range, the peak transmittance remains basically unchanged, and the x-polarized transmission spectrum and the y-polarized transmission spectrum shift by almost equal wavelength intervals.

[0035] As a typical phase change material, VO 2 exhibits different conductive characteristics in the insulating state and the metallic state. The two states can be quickly switched with each other by changing the ambient temperature and can be controlled by current or laser. This characteristic provides the possibility of realizing the tunable EIT effect. Under the condition that the above conditions remain unchanged, the transmission spectra of x-polarized light and y-polarized light incident respectively obtained by changing the conductivity of vanadium dioxide are shown respectively as Figure 8 and Figure 9 shown. As the conductivity of VO 2 increases, the peak transmittances in the x- and y-directions decrease rapidly. The minimum values of the peak transmittances in the x-polarization direction and the y-polarization direction are 28% and 6% respectively, and the modulation depths can reach 70% and 91% respectively. At this time, the EIT effect disappears. Then, the transmittance at the peak wavelength increases slowly and finally reaches 61% and 19%. The results show that the strength of the EIT effect can be regulated by controlling the conductivity of vanadium dioxide in this structure, and thus the tunable group delay phenomenon can be obtained. And the transmission peak of the EIT window can also be regulated in this way, which is expected to be used in the related research and development of optical switch devices.

[0036] When other optimization parameters are changed, such as parameter (1) p = 1400 nm, a = 380 nm, b = 300 nm, d = 260 nm, h = 175 nm, h1 = 175 nm; or parameter (2) p = 1600 nm, a = 410 nm, b = 300 nm, d = 300 nm, h = 185 nm, h1 = 185 nm, the above-mentioned experimental conclusions can be obtained.

[0037] Embodiment 2: Even when the substrate material is changed, high-quality electromagnetically induced transparency (EIT) windows can still be obtained in both the x-polarization and y-polarization cases. For example, on the basis of Embodiment 1, the substrate material is changed from silica to sapphire with a dielectric constant of 3.1, where p = 1500 nm, a = 360 nm, b = 280 nm, d = 300 nm, h = 185 nm, h 1 = 145 nm. The transmission spectra under the excitation of x-polarized light and y-polarized light obtained are as Figure 10 shown. Obvious and sharp EIT windows appear near 1425.2 nm and 1403.3 nm, with peak transmittances reaching 95% and 98% respectively. The corresponding full width at half maximum (FWHM) and quality factor (Q) are 0.4 nm, 3562 and 0.2 nm, 7016 respectively. Similar conclusions can be obtained when changing the various dimensional parameters and the conductivity of vanadium dioxide, indicating that this embodiment can also be used as a high-quality dual-polarization-channel tunable electromagnetically induced transparency generator.

[0038] In summary, the present invention can obtain the required dual-polarization-channel electromagnetically induced transparency generator in the near-infrared band through reasonable design of the dimensional parameters. At the same time, the conductivity of vanadium dioxide can be controlled to regulate the electromagnetically induced transparency, and the integration of the device can be improved to realize the miniaturization of the device. The present invention has great application potential in optical switches, slow light devices, optical memories, and high-sensitivity sensors, etc.

[0039] The above embodiments are only for supplementary description of the present invention, rather than limiting the present invention. Any modification made to the present invention within the protection scope of the claims of the present invention will fall within the protection scope of the present invention.

Claims

1. A metamaterial for realizing tunable electromagnetic induced transparency in dual polarization channels, characterized in that, the metamaterial is divided into upper and lower layers, including a base layer at the bottom and a metasurface structural unit attached to the upper surface of the substrate. The metasurface structural unit is a periodic arrangement of dielectric squares and vanadium dioxide squares. The metamaterial can achieve high-quality near-infrared band electromagnetic induced transparency when x-polarized light or y-polarized light is incident. The electric field vibration direction of the x-polarized light is parallel to the x-axis, and the electric field vibration direction of the y-polarized light is parallel to the y-axis. The x-axis direction is the length direction of the base layer, and the y-axis direction is the width direction of the base layer.

2. The metamaterial for realizing tunable electromagnetic induced transparency in dual polarization channels according to claim 1, characterized in that, the material of the base layer is silica or sapphire.

3. The metamaterial for realizing tunable electromagnetic induced transparency in dual polarization channels according to claim 2, characterized in that, the thickness of the base layer is 120nm - 250nm.

4. The metamaterial for realizing tunable electromagnetic induced transparency in dual polarization channels according to claim 1, characterized in that, the material of the dielectric square is silicon.

5. The metamaterial for realizing tunable electromagnetic induced transparency in dual polarization channels according to claim 1, characterized in that, the side length of the dielectric square is 300nm - 500nm, the side length of the vanadium dioxide square is 150nm - 350nm, the thickness of the dielectric square and the vanadium dioxide square is 120nm - 250nm, and the spacing is 150nm - 350nm.

6. The metamaterial for realizing tunable electromagnetic induced transparency in dual polarization channels according to claim 1, characterized in that, the period of the metasurface structural unit is 1400nm - 1600nm.

7. A method for realizing tunable electromagnetic induced transparency in dual polarization channels, characterized in that, design a metamaterial for realizing tunable electromagnetic induced transparency in dual polarization channels as described in any one of claims 1 - 6. By optimizing the size parameters of the dielectric square and the vanadium dioxide square and the spacing between them, the coupling strength between the dielectric square and the vanadium dioxide square is affected, and after optimization, high-quality near-infrared band electromagnetic induced transparency phenomena are simultaneously achieved in the x and y polarization directions through the metamaterial structure.

8. The method for realizing tunable electromagnetic induced transparency in dual polarization channels according to claim 7, characterized in that, regulate the conductivity of the vanadium dioxide square to regulate the strength of the electromagnetic induced transparency effect, and realize the process of controlling the electromagnetic induced transparency effect from strong to weak and then to disappearance in the x and y polarization directions.

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