Electromagnetic induction transparent nonlinear metasurface based on BIC

Abstract

The invention provides an electromagnetic induction transparent nonlinear metasurface based on a BIC, which comprises a plurality of metasurface units which are periodically arranged, each metasurface unit is composed of a nano-medium substrate and a nano-medium block fixed on the upper surface of the nano-medium substrate, and a nano-medium coupling block deviating from the center of a resonant cavity is arranged in the resonant cavity of each nano-medium block. When electromagnetic waves vertically enter the nonlinear metasurface, a non-radiative-energy continuum bound state mode is converted into a radiative-energy quasi-continuum bound state mode through offset of the nano-medium coupling block, resonance is generated in a continuous near-infrared band and a visible light band, and linear and nonlinear response of electromagnetically-induced transparency is achieved. The defect that only linear response can be realized in the prior art is avoided, and the application range is expanded; and meanwhile, the response enhances the interaction of optical substances and improves the conversion efficiency.

Description

Technical Field

[0001] The present invention belongs to the field of optical technology and relates to a nonlinear supersurface, and specifically to an electromagnetically induced transparent nonlinear supersurface based on a continuum bound state BIC, which can be used in the fields of linear and nonlinear optical devices. Technical Background

[0002] Electromagnetic induced transparency (EIT) refers to the quantum interference effect on opaque atoms, which exhibits a narrowband transparent window in the spectral range. Due to its effective coupling ability between bright and dark modes, metasurfaces achieve electromagnetically induced transparent responses with ultra-high quality factors and extremely large light field enhancement, which can be used in the design of optical devices such as optical storage devices and high-precision sensors.

[0003] At present, asymmetric structures are usually used to achieve electromagnetic induced transparency. For example, the patent application with application number CN112332101A and titled "All-dielectric asymmetric cross-cavity metamaterial for achieving electromagnetic induced transparency" uses an all-dielectric asymmetric cross-cavity structure. After breaking the structural symmetry in a specific direction, the EIT phenomenon will occur, and a high transmission rate of 93% and a quality factor of 1064 can be achieved at the EIT transmission peak. However, this invention cannot achieve the nonlinear response characteristics of electromagnetic induced transparency.

[0004] The improvement of nonlinear response efficiency is related to the quality factor of the resonant mode. For example, the patent application with the application publication number CN117192863A and the name “Device and method for realizing nonlinear optical frequency conversion based on metasurface” is composed of an asymmetric one-dimensional grating metasurface based on nonlinear materials. When the symmetry of the grating structure is destroyed, the emergence of quasi-bound states in the continuous medium enhances the light-matter interaction and realizes efficient harmonic generation, but the response normalized conversion efficiency is only 10 -3 . Summary of the invention

[0005] The purpose of the present invention is to address the problems existing in the prior art and propose an electromagnetically induced transparent nonlinear metasurface based on BIC to solve the technical problems in the prior art of being unable to achieve multi-wavelength electromagnetically induced transparent nonlinear response and low harmonic conversion efficiency.

[0006] To achieve the above-mentioned purpose, the technical solution adopted by the present invention includes periodically arranged M×N metasurface units composed of a nano-medium substrate 1 and a nano-medium block 2 fixed on the upper surface thereof, M≥2, N≥2; the nano-medium block 2 adopts a square ring resonator structure, and a rectangular nano-medium coupling block 3 whose long side is parallel to any one set of opposite sides of the resonant cavity and deviates from the line connecting the midpoints of the other set of opposite sides is arranged in the resonant cavity;

[0007] When the electromagnetic wave is incident vertically on the nonlinear metasurface, the offset of the nano-medium coupling block 3 converts the non-radiative energy continuum bound state mode into the quasi-continuum bound state mode of radiative energy, generating resonance in the continuous near-infrared band and visible light band, realizing the linear and nonlinear response of electromagnetically induced transparency. The quality factor Q of the electromagnetically induced transparency response is regulated by the offset dx of the coupling block 3.

[0008] As an optimization, the nano-medium substrate 1 is made of silicon dioxide; the nano-medium block 2 and the nano-medium coupling block 3 are both made of silicon.

[0009] As an optimization, the nano-medium substrate 1 adopts a rectangular parallelepiped structure, the nano-medium block 2 adopts a cube structure, and the center normal of the nano-medium block 2 coincides with the center normal of the nano-medium substrate 1 .

[0010] As an optimization, the square ring resonator is formed by setting a square cavity penetrating the upper and lower surfaces and having four walls with equal widths on the cube nano-medium block 2 .

[0011] As an optimization, the long side of the nano-medium coupling block 3 is parallel to the short side of the nano-medium substrate 1 .

[0012] As an optimization, the height of the nano-medium coupling block 3 is equal to the height of the resonant cavity of the square ring resonator.

[0013] As an optimization, the relationship between the quality factor Q of the electromagnetically induced transparent response and the offset dx of the coupling block is:

[0014] Q∝α -2

[0015]

[0016] l 0 is the outer side length of the nano-dielectric block ring resonator, ω 0 is the resonant frequency of BIC, and γ is the width at which the intensity of the transparent response drops to half of the maximum value at resonance.

[0017] Compared with the prior art, the present invention has the following advantages:

[0018] The resonant cavity of the nano-dielectric block of the present invention is provided with a rectangular nano-dielectric coupling block deviated from the center thereof. When an electromagnetic wave is incident vertically on the nonlinear metasurface, the offset of the nano-dielectric coupling block converts a non-radiative energy continuum bound state mode into a quasi-continuum bound state mode of radiative energy, generates resonance in a continuous near-infrared band and a visible light band, realizes linear and nonlinear responses of electromagnetically induced transparency, avoids the defect that the prior art can only realize linear response, and expands the scope of application; at the same time, this response enhances the interaction between light and matter and improves the conversion efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a schematic diagram of the overall structure of the present invention.

[0020] Figure 2 It is a schematic diagram of the structure of the super surface unit of the present invention.

[0021] Figure 3 It is a schematic diagram of the relationship between the quality factor and the offset of the present invention.

[0022] Figure 4 It is a schematic diagram of the dual-band transparent linear response of the present invention.

[0023] Figure 5 It is a schematic diagram of the third harmonic conversion efficiency caused by the dual-band transparent linear response of the present invention.

[0024] Figure 6 It is a simulation comparison diagram of the transmission response component of an embodiment of the present invention and the time coupling mode theoretical fitting.

[0025] Figure 7 4 is a multi-pole scattering power analysis diagram of an embodiment of the present invention.

[0026] Figure 8 is a normalized magnetic field distribution diagram of an embodiment of the present invention. DETAILED DESCRIPTION

[0027] The present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0028] Reference Figure 1 The present invention comprises a metasurface unit composed of M×N periodically arranged nano-medium substrates 1 and nano-medium blocks 2 fixed on the upper surface thereof, M≥2, N≥2;

[0029] Reference Figure 2 The nano-medium substrate 1 adopts a rectangular parallelepiped structure with a side length P x 570nm, P y It is 610nm, 200nm high, and is made of silicon dioxide.

[0030] The nano-medium block 2 adopts a square ring resonator structure, which is formed by a square cavity with four walls of equal width and a height of 200nm and an outer length of l 0 The diameter of the nano-medium block 2 is set to 400nm and the material is silicon. The center normal of the nano-medium block 2 coincides with the center normal of the nano-medium substrate 1. A rectangular nano-medium coupling block 3 is arranged in the resonant cavity, the long side of which is parallel to any set of opposite sides of the resonant cavity and deviates from the line connecting the midpoints of the other set of opposite sides. The offset dx is set to 10nm.

[0031] The rectangular parallelepiped nano-medium coupling block 3 is made of silicon, and its long side is parallel to the short side of the nano-medium substrate 1, and its height is equal to the height of the resonant cavity of the square ring resonator. The offset of the rectangular parallelepiped nano-medium coupling block 3 breaks the in-plane structural symmetry of the metasurface unit, and the structure realizes the quasi-BIC mode characteristic of converting the non-radiative energy BIC mode into radiative energy.

[0032] Reference Figure 3 , the quality factor Q of the electromagnetically induced transparent response BIC is regulated by the offset dx of the coupling block 3. The relationship between Q and dx is:

[0033] Q∝α -2

[0034]

[0035] Q=ω 0 / γ

[0036] l 0 is the outer side length of the nano-dielectric block ring resonator, ω 0 is the resonant frequency of BIC, and γ is the width at which the intensity of the transparent response drops to half of the maximum value at resonance.

[0037] Different quality factors will appear at different changes in α. When α increases from 0.01 to 0.1, the quality factor increases from 10 4 Reduced to 10 2 That is, when dx changes from 4 to 40, the quality factor changes from 10 4 Reduced to 10 2 . The emergence of this relationship can be explained by analyzing the slope of the relationship between the quality factor and α of the electromagnetically induced transparency #1 and electromagnetically induced transparency #2 responses, which are 5.626 and 8.696 respectively. These values ​​indicate that the relationship between the quality factor and the structural asymmetry is affected by the electromagnetically induced transparency response. Further analysis shows that the response characteristics of electromagnetically induced transparency #1 and electromagnetically induced transparency #2 are controlled by the symmetry-protected bound state resonance BIC. By adjusting the offset of the rectangular nano-dielectric coupling block 3, the change of the quality factor can be effectively controlled, thus providing a new idea for optimizing the design of metasurfaces.

[0038] Reference Figure 4 , generating two transparent responses, electromagnetically induced transparency #1 and electromagnetically induced transparency #2, at wavelengths of 806.95nm and 760.95nm, respectively. The quality factors Q of these two responses can reach 9750 and 1.32×10 4 .

[0039] The inventive principle of the present invention is that when an electromagnetic wave is incident vertically on a nonlinear metasurface, the offset of the nano-medium coupling block 3 converts the non-radiative energy continuum bound state mode into a quasi-continuum bound state mode of radiative energy, so that the resonant mode resonates in the continuous near-infrared band and visible light band, thereby enhancing the light-matter interaction and realizing the linear and nonlinear response of electromagnetically induced transparency; by adjusting the offset of the rectangular nano-medium coupling block, the asymmetry of the metasurface changes accordingly, thereby changing the width when the transparent response intensity drops to half of the maximum value during resonance, and the Q factor is significantly improved;

[0040] The following is a description of the technical effects of the present invention in combination with simulation experiments:

[0041] 1. Simulation conditions and contents:

[0042] The simulation adopts the multi-physics simulation software COMSOL Multiphysics 6.1, and uses Floquet periodic boundary conditions to simulate the infinite array. The electromagnetic wave is incident on the metasurface of the nonlinear metasurface from top to bottom.

[0043] Simulation 1 simulates the third harmonic conversion efficiency caused by the dual-band transparent linear response of the specific embodiment of the present invention, and the results are as follows: Figure 5 shown.

[0044] Simulation 2 compares the transmission coefficient of the specific embodiment of the present invention with the results of the time coupled mode theory fitting component. The results are as follows: Figure 6 shown.

[0045] Simulation 3, multi-pole scattering power analysis simulation is performed on the dual-band transparent response of the embodiment of the present invention, and the results are as follows: Figure 7 shown.

[0046] Simulation 4, the transparent response of the embodiment of the present invention is simulated by normalizing the magnetic field strength, and the result is as follows Figure 8 shown.

[0047] 1. Analysis of simulation results:

[0048] Reference Figure 5 , Figure 5 (a) shows that the maximum efficiency of third harmonic conversion at 806.95nm is 9×10 -2 , Figure 5 (b) shows that the maximum efficiency of third harmonic conversion at 761 nm is 10 -3 , the conversion potential of the metasurface in harmonic generation is demonstrated through the calculation of the third harmonic conversion efficiency.

[0049] The third harmonic conversion efficiency is defined as:

[0050] CE=Pr,TH / P i,FF

[0051] Where P i,FF is the incident power at the fundamental frequency. P r,TH Is The calculated radiated third harmonic power outflow is the Poynting vector S across the boundary curve C multiplied by the boundary norm vector n.

[0052] Depend on Figure 5 (a) It can be seen that the highest conversion efficiency at 806.95nm coincides with the highest peak of electromagnetic transparent response #1. Figure 5 (b) It can be seen that the highest conversion efficiency at 761 nm coincides with the highest peak of electromagnetic transparent response #2, indicating that the improvement of the third harmonic conversion efficiency is caused by the light-matter interaction enhanced by the offset of the nano-dielectric coupling block.

[0053] Reference Figure 6 , showing the comparison between the transmission coefficient components and the coupled mode theory CMT fitting results in a specific embodiment. The calculation formula of the transmission coefficient components is: The transparent response in the transmission spectrum can be expressed as Trans = |1 + γ R a / E| 2 ≈1-2γ R Im(χ), where the formula for the electric induction intensity χ is:

[0054]

[0055] Where ω is the frequency of occurrence, ω b =ω d is the resonant frequency of the transparent response, γ b and γ d represents the loss of light and dark modes, |a| 2 and |b| 2 represents energy, E represents field, γ R probes the radiation loss and g is the coupling strength between the bright and dark modes.

[0056] from Figure 6 As can be seen from (a) and (b), when the wavelength is 761nm and 806nm respectively, a transparent window appears on the metasurface, and the transmission coefficient is close to 1. The high consistency between the coupled mode theory fitting line and the simulation results further confirms the accuracy of the model, providing a reliable theoretical basis for understanding and predicting the electromagnetically induced transparent response of the metasurface.

[0057] Reference Figure 7 , Figure 7 (a) shows the significant suppression of the scattered power of the broadband magnetic dipole near 806.95nm. Figure 7(b) shows that the ring dipole exhibits complete dominance in the electromagnetically induced transparency #2 response range of 760-762nm. By performing multipole scattering power analysis in the far-field region, it is further proved that the proposed dual-band transparent response originates from mode interaction, where the multipole moment can be calculated as follows:

[0058]

[0059] Among them, P, M, T, Q (e) and Q (m) They represent electric dipole, magnetic dipole, toroidal dipole, electric quadrupole and magnetic quadrupole respectively, r represents the position vector, j = -iωε 0 (n 2 -1) E is the displacement current density of the superatom, α, β = x, y, z.

[0060] from Figure 7 As can be seen in (a), the response of the magnetic dipole to light is significantly weakened, indicating that the interaction between the light wave and the material at this wavelength has changed significantly. In the electromagnetically induced transparency #1 response range, the magnetic quadrupole plays a leading role, further demonstrating the fine characteristics of the metasurface structure in regulating the light field at different wavelengths. Specifically, the significant enhancement of the scattering response of the magnetic quadrupole in this band reveals its effective regulation of light in this range. Figure 7 As can be seen in (b), the response of the ring dipole to light is significantly better than that of the magnetic dipole. These results provide strong evidence for the realization of dual-band linear and nonlinear harmonics of electromagnetically induced transparent response.

[0061] Reference Figure 8 , Figure 8 (a), (b), (c), and (d) show the P 1 , P 2 , P 3 , P 4 By analyzing the magnetic field distribution, it is proved that the proposed dual-band transparent response originates from the interaction between the two modes caused by the offset of the rectangular nano-dielectric coupling block.

[0062] from Figure 8 (a) It can be seen that P 1 The magnetic field at the four corners of the square ring resonator is enhanced by 150 times, and the magnetic quadrupole mode is significantly excited to act as a narrowband dark mode. Figure 8 (b) It can be seen that in P 2 The 16-fold enhanced magnetic field at appears at the upper and lower edges of the square ring resonator, with a magnetic dipole bright mode along the +y direction, which is consistent with the results of multipole analysis, that is, the electromagnetically induced transparent #1 response originates from the destructive interference between the magnetic quadrupole mode and the magnetic dipole mode. Figure 8(c) It can be seen that P 3 The clockwise magnetic loop at will induce a toroidal dipole mode in the -z direction. Figure 8 (d) It can be seen that for P 4 , a 21-fold magnetic field is highly confined in the gap between the square ring resonator and the coupling strip, generating a ring dipole mode in the -x direction; more precisely, the electromagnetically induced transparent #2 response is induced by the destructive interference effect between the out-of-plane ring dipole dark mode and the in-plane ring dipole bright mode. These results provide a demonstration for the realization of dual-band linear and nonlinear harmonics of the electromagnetically induced transparent response.

[0063] The above description is only a preferred embodiment of the present invention and does not constitute a limitation to the present invention. A person skilled in the art may make several modifications and improvements without departing from the innovative concept of the present invention, but these changes shall all fall within the scope of protection of the present invention.

Claims

1. An electromagnetically induced transparent nonlinear metasurface based on BIC, comprising periodically arranged M×N metasurface units consisting of a nano-medium substrate (1) and a nano-medium block (2) fixed on the upper surface thereof, M≥2, N≥2; characterized in that: The nano-medium block (2) adopts a square ring resonator structure, and a rectangular nano-medium coupling block (3) is arranged in the resonant cavity, the long side of which is parallel to any one set of opposite sides of the resonant cavity and deviates from the line connecting the midpoints of the other set of opposite sides; When an electromagnetic wave is incident vertically on the nonlinear metasurface, the offset of the nano-medium coupling block (3) converts the non-radiative energy continuum bound state mode into a quasi-continuum bound state mode of radiative energy, generating resonance in the continuous near-infrared band and visible light band, thereby realizing the linear and nonlinear response of electromagnetically induced transparency, and the quality factor Q of the electromagnetically induced transparency response is regulated by the offset dx of the coupling block (3).

2. The supersurface according to claim 1, characterized in that The nano-medium substrate (1) is made of silicon dioxide; the nano-medium block (2) and the nano-medium coupling block (3) are both made of silicon.

3. The supersurface according to claim 1, characterized in that The nano-medium substrate (1) adopts a rectangular parallelepiped structure, the nano-medium block (2) adopts a cube structure, and the center normal line of the nano-medium block (2) coincides with the center normal line of the nano-medium substrate (1).

4. The supersurface according to claim 3, characterized in that The square ring resonator is formed by arranging a square cavity penetrating the upper and lower surfaces and having four walls with equal width on a cube nano-medium block (2).

5. The supersurface according to claim 4, characterized in that The long side of the nano-medium coupling block (3) is parallel to the short side of the nano-medium substrate (1).

6. The supersurface according to claim 4, characterized in that The height of the nano-medium coupling block (3) is equal to the height of the resonant cavity of the square ring resonator.

7. The supersurface according to claim 4, characterized in that The relationship between the quality factor Q of the electromagnetically induced transparent response and the offset dx of the coupling block is: Q∝α -2 l0 is the outer side length of the nano-dielectric block ring resonator, ω0 is the resonant frequency of BIC, and γ is the width when the transparent response intensity drops to half of the maximum value during resonance.

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