A high-Q coherent absorber based on dimer anisotropic metasurface

Abstract

The present invention proposes a dimer anisotropic metasurface high-Q coherent absorber, comprising a plurality of absorber units arranged periodically, each absorber unit comprising a tetrahedral dielectric block and a dimer arranged on the upper and lower surfaces thereof and composed of two metal rings with a spacing unequal to one-half of the period. When x- and y-polarized electromagnetic waves are vertically incident, under the action of metal resonance and quasi-BIC induction of the dimer, x- and y-polarized coherent absorbing bands are respectively realized. When x-polarized electromagnetic waves are obliquely irradiated on the absorber, x-polarized dual-band coherent absorbing is realized based on the metal resonance of the dimer and the additional induction of quasi-BIC, thereby realizing the anisotropic characteristics of the absorber, improving the control capability of the absorber on coherent absorbing of different polarizations, and the maximum Q value of the absorber is 1781, which effectively broadens its application range.

Description

Technical Field

[0001] The present invention belongs to the technical field of metasurface electromagnetic wave control, and relates to a coherent absorber, and specifically to a dimer anisotropic metasurface high-Q coherent absorber, which can be used in the fields of optical switches, sensors, and multifunctional absorbing devices. Technical Background

[0002] Coherent absorbers introduce a second electromagnetic wave through the interference effect to interfere with the target electromagnetic wave, thereby controlling the absorption process of the electromagnetic wave and achieving more efficient energy capture. Metasurface coherent absorbers are a type of two-dimensional artificial structure material that uses the unique subwavelength structure of the metasurface to enable precise control of electromagnetic waves, thereby achieving coherent absorption. Anisotropic metasurface coherent absorbers produce different electromagnetic responses to different polarization directions, thereby showing excellent adjustable performance for coherent waves of different polarizations.

[0003] For example, application publication number CN118508097A, entitled "Dual-mode dual-frequency coherent perfect absorber based on chessboard Helmholtz resonant cavity", realizes the coherent perfect absorption of dual-mode dual-frequency TE and TM polarized waves with different polarizations at specific frequencies through the chessboard Helmholtz resonant cavity design composed of four sub-resonant cavities distributed in a chessboard pattern. In application publication number CN118572394A, entitled "Single-mode dual-frequency coherent perfect absorber based on cascaded Helmholtz resonant cavity", the three designed Helmholtz sub-resonant cavities are interconnected to form a cascaded Helmholtz resonant cavity, which realizes the coherent perfect absorption of single-mode dual-frequency TE and TM polarized waves.

[0004] The coherent perfect wave absorbing technology based on metasurfaces has received extensive attention in recent years due to its strong control ability over electromagnetic waves and its broad application prospects. However, existing research mainly focuses on homogeneous isotropic metasurfaces, optimizing the absorption performance of single polarization or specific frequency electromagnetic waves, and lacks in-depth exploration of the coherent wave absorbing performance of anisotropic metasurface structures under different polarization conditions. For example: In the publication number CN116979274A, the name is "coherent perfect absorber based on asymmetric transmission Helmholtz resonant cavity", by designing a cross-shaped cavity formed by two rectangular cavities running through two sets of side surfaces of a metal tetrahedron, and a Helmholtz resonant cavity formed by two rectangular gaps extending from the upper and lower end faces of the metal tetrahedron to the cross-shaped cavity and forming a cross, asymmetric transmission coherent perfect wave absorbing is achieved.

[0005] On the other hand, high-Q absorbers can achieve more efficient energy absorption within a narrower frequency bandwidth, which is of great significance for application scenarios such as radar stealth, signal processing, and energy capture. However, the existing metasurface-based absorbers have a low Q value and are difficult to meet the needs of high-resolution electromagnetic signal processing and ultra-narrowband applications. For example, in publication number CN116315726A, the name is "A polarization-insensitive multi-frequency multi-mode metamaterial coherent perfect absorber", through the Helmholtz resonant cavity design composed of a first rectangular gap, a second rectangular gap, a triangular prism cavity, and a quadrangular prism cavity, a three-frequency point coherent perfect absorber is achieved. Its Q value is about 10.

[0006] Bound States in the Continuum (BIC) is a special phenomenon in quantum mechanics and optics, which refers to the non-radiative bound states existing in the continuous energy spectrum (or continuous state). BIC can be regarded as a limiting case of Fano resonance, which has "zero" bandwidth and infinite Q value (cannot be observed on the spectrum). By perturbing the symmetry of the unit or the structural spacing, BIC can be transformed into a quasi-BIC with a certain bandwidth and finite Q value that can be observed on the spectrum. Summary of the invention

[0007] The purpose of the present invention is to overcome the shortcomings of the above-mentioned prior art and propose a dimer anisotropic metasurface high Q value coherent absorber to solve the technical problems that the prior art has weak control ability for coherent absorption of different polarizations due to the inability to achieve anisotropy, and weak absorption ability for specific frequencies due to the small Q value.

[0008] To achieve the above object, the technical solution adopted by the present invention includes N×N absorber units with P as a period, N≥2; the absorber unit includes a tetrahedral dielectric block 1; the upper and lower surfaces of the tetrahedral dielectric block 1 are each provided with a spacing of A dimer 2 composed of two metal rings, wherein the central axes of the two metal rings in the dimer 2 are located on the YOZ plane where the y-polarized wave is located, and are mirror-symmetric with respect to the XOZ plane where the x-polarized wave is located;

[0009] When the y-polarized signal wave and its corresponding control wave and the x-polarized signal wave and its corresponding control wave irradiate the absorber vertically along the positive and negative directions of the Z-axis at the same time, a high-Q y-polarized coherent absorbing electromagnetic response is achieved under the induction of the quasi-BIC generated by the dimer, and an x-polarized coherent absorbing electromagnetic response is achieved based on the metal resonance of the dimer; when the x-polarized signal wave and its corresponding control wave irradiate the absorber obliquely at an angle of θ with the positive and negative directions of the Z-axis, a high-Q x-polarized coherent absorbing electromagnetic response is achieved through the additional induction of the quasi-BIC generated by the oblique irradiation.

[0010] The outer and inner diameters of the two metal rings contained in the dimer 2 are d1 and d2 respectively, and

[0011]

[0012] The above dimer 2 has two metal rings with a thickness of t, and

[0013] The two metal rings contained in the dimer 2 are made of gold, silver or aluminum.

[0014] The above-mentioned cubic dielectric block 1 is made of Si3N4, SiO2 or Si.

[0015] The distance between the two metal rings in the dimer 2 is M, and d1≤M≤P-d1.

[0016] The angle θ between the x-polarized signal wave and the control wave and the negative direction of the Z axis satisfies θ≤10°.

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

[0018] 1. In the present invention, since the spacing between the two metal rings in the dimer is not equal to half the period of the absorber unit, the non-equidistant structure between the metal rings presents different responses to the x-polarized wave and the y-polarized wave coherent absorption, that is, when the y-polarized signal wave and its corresponding control wave and the x-polarized signal wave and its corresponding control wave irradiate the absorber vertically along the positive and negative directions of the Z axis at the same time, the y-polarized coherent absorption electromagnetic response is realized based on the quasi-BIC, and the x-polarized coherent absorption electromagnetic response is realized based on the metal resonance of the dimer; when the x-polarized signal wave and its corresponding control wave irradiate the absorber obliquely at an angle of θ with the positive and negative directions of the Z axis, the quasi-BIC generated by the oblique irradiation additionally induces the x-polarized coherent absorption electromagnetic response, thereby realizing the anisotropic characteristics of the absorber, improving the control capability of the absorber for coherent absorption of different polarizations, and effectively broadening its application range compared with the prior art.

[0019] 2. The present invention realizes y-polarization coherent wave absorption electromagnetic response under the induction of quasi-BIC generated by the dimer, and realizes x-polarization coherent wave absorption electromagnetic response through the additional induction of quasi-BIC generated by oblique irradiation. Experimental results show that the Q value generated by the present invention based on the quasi-BIC principle is much greater than that of the prior art, which effectively improves the wave absorption capacity at a specific frequency point. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a schematic structural diagram of the absorber unit of the present invention.

[0021] Figure 2 It is a schematic diagram of the structural parameters of the absorber unit of the present invention.

[0022] Figure 3 It is a principle diagram of vertical and oblique irradiation of electromagnetic waves onto the surface of the absorber according to the present invention.

[0023] Figure 4 The invention is x-polarized and y-polarized vertical irradiation and Coherent absorbance diagram.

[0024] Figure 5 For the x-polarized and y-polarized 1° irradiation of the present invention Coherent absorbance diagram.

[0025] Figure 6 This is a transmission coefficient diagram of the absorber when x-polarization is irradiated at different angles according to the present invention.

[0026] Figure 7 This is a diagram of the Q value of the absorber of the present invention when x-polarization is irradiated at different angles.

[0027] Figure 8 It is the Fano resonance simulation and fitting curve diagram of the absorber of the present invention when x-polarization is irradiated at different angles.

[0028] Fig. 9 This is a graph showing the coherent wave absorption rate of the absorber when x-polarization is irradiated at different angles.

[0029] Fig.10 It is a transmission coefficient diagram of the vertically irradiated absorber under different M values ​​of y-polarization of the present invention.

[0030] Fig.11 This is a Q value diagram of the vertically irradiated absorber under different M values ​​of y-polarization of the present invention.

[0031] Fig.12 It is a Fano resonance simulation and fitting curve diagram of the vertically irradiated absorber under different M values ​​of y-polarization of the present invention.

[0032] Fig.13 This is a graph showing the coherent wave absorption rate results of the vertically irradiated absorber under different M values ​​of y-polarization of the present invention. DETAILED DESCRIPTION

[0033] The present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments:

[0034] Reference Figure 1 The present invention comprises N×N absorber units with a period of P, N≥2; in this example, P=600nm, N=10. The absorber unit comprises a tetrahedral dielectric block 1.

[0035] Reference Figure 2(a) and (b) are respectively a top view and a front view of the absorber unit. The tetrahedral dielectric block 1 is made of Si3N4 material, which has excellent electromagnetic properties. Its upper and lower surfaces are regular tetrahedral structures with side lengths the same as the period P and height H. In this example, H=450nm.

[0036] The upper and lower surfaces of the tetrahedral dielectric block 1 are each provided with a dimer 2 consisting of two metal rings with a spacing of a distance M. The two metal rings in the dimer 2 are located on the YOZ plane where the y-polarized wave is located, and are mirror-symmetrical about the XOZ plane where the x-polarized wave is located; when the mirror is symmetrical, the electromagnetic responses of the signal wave and its corresponding control wave are the same.

[0037] when When , that is, the metal rings are not spaced equally apart, thus realizing an asymmetric periodic structure; when When the metal rings are equally spaced, the dimer 2 composed of two metal rings is a symmetrical periodic structure, and the period of the metal rings becomes The electromagnetic coupling characteristics of the dimer are changed, and coherent wave absorption cannot be achieved.

[0038] The dimer 2 has a connecting line of two metal ring centers that coincides with the YOZ plane where the y-polarized wave is located, and the outer and inner diameters of the two metal rings are d1 and d2 respectively, and When the inner diameter of the metal ring is less than half of the outer diameter, the electromagnetic response characteristics of the metal ring can be maintained. When the outer diameter of the metal ring is less than half of the unit period, it does not exceed the unit boundary range. In this example, d1 = 120nm, d2 = 40nm. The thickness of the two metal rings contained in dimer 2 is t, and The thickness t is much smaller than the diameter of the metal ring, and in this example, t=15 nm. The spacing M between the two metal rings is to ensure that the two metal rings do not exceed the boundaries of the upper and lower surfaces of the tetrahedral dielectric block 1, that is, d1≤M≤P-d1. The metal ring is made of gold, which is a common material.

[0039] Reference Figure 3 , is the principle diagram of the electromagnetic wave vertically irradiating and obliquely irradiating the absorber surface of the present invention, the angle θ between the signal wave and the control wave and the negative direction of the Z axis satisfies θ≤10°. The absorption rate calculation of the electromagnetic wave vertically irradiating and obliquely irradiating coherent waves can be represented by the scattering matrix:

[0040]

[0041] in, is the signal wave, is the control wave, t1 and r1 represent the transmission coefficient and reflection coefficient of the signal wave respectively, t2 and r2 represent the transmission coefficient and reflection coefficient of the control wave respectively, O1 represents the superposition of the reflection of I1 and the transmission of I2, O2 represents the superposition of the reflection of I2 and the transmission of I1, for a reciprocal symmetric network, t n =t1=t2,r n =r1=r2.

[0042] The coherent absorption rate A can be expressed as:

[0043]

[0044] in represents the phase difference between the transmitted wave and the reflected wave, Indicates the phase difference between the signal wave and the control wave.

[0045] The working principle of the present invention is: When the y-polarized signal wave and control wave are irradiated vertically to the absorber along the negative and positive directions of Z, respectively, a y-polarized high-Q coherent absorption band is realized based on the induction of quasi-BIC due to the asymmetric dimer structure of the absorber; When the y-polarized signal wave and the control wave are irradiated vertically onto the absorber along the negative and positive directions of the Z axis respectively, there is no y-polarized coherent absorption band due to the symmetric dimer structure of the absorber; when the x-polarized signal wave and the control wave are irradiated vertically onto the absorber along the negative and positive directions of the Z axis respectively, a coherent absorption band will be realized based on the metal resonance of the dimer; when the x-polarized signal wave and the control wave are irradiated obliquely onto the absorber along the negative and positive directions of the Z axis respectively, the absorber will realize an additional x-polarized high-Q coherent absorption band based on the induction of quasi-BIC.

[0046] The technical effects of the present invention are described below in conjunction with simulation experiments.

[0047] 1. Simulation conditions and contents:

[0048] The commercial simulation software CST Microwave Studio was used as the simulation software, and the simulation method was based on the finite element method.

[0049] Simulation 1: Full-wave simulation of the absorption rate of the present invention when the x-polarized and y-polarized electromagnetic waves are vertically irradiated (θ=0°) and M=300nm, and the results are as follows: Figure 4 shown.

[0050] Simulation 2: Full-wave simulation is performed on the absorbance of the present invention when the x-polarized and y-polarized electromagnetic waves are irradiated at an angle of 1° and M = 240 nm, respectively. The results are as follows: Figure 5 shown.

[0051] Simulation 3: Full-wave simulation of the electromagnetic performance of the present invention when the x-polarized electromagnetic wave irradiation angle is -10° to 10° (the negative sign represents irradiation in the opposite direction of θ), and the transmission coefficient is shown in the figure below: Figure 6 As shown in the figure, the Q value calculation results are shown in Figure 7 The simulation and fitting curves of its transmission coefficient are shown in Figure 8 As shown in the figure, the coherent absorption rate under different angles of illumination is shown in the figure Fig. 9 shown.

[0052] Simulation 4: Full-wave simulation of the electromagnetic performance of the present invention when the y-polarized electromagnetic wave is vertically irradiated to M = 300nm, 280nm, 240nm, 180nm and 120nm is performed, and the transmission coefficient is as follows: Fig.10 The Q value calculation results are shown as Fig.11 The simulation and fitting curves of its transmission coefficient are shown in Fig.12 The coherent absorption rate results for different M values ​​are shown in Fig.13 shown.

[0053] 2. Analysis of simulation results;

[0054] Reference Figure 4 , which is the x-polarization and y-polarization vertical irradiation of the present invention and The coherent wave absorption rate diagram of the X-polarized coherent wave is shown in Figure 1, where the horizontal axis is the wavelength and the vertical axis is the absorption rate. When the x-polarized coherent wave is irradiated vertically (θ=0°) and M=300nm, the coherent perfect absorption with an absorption rate of 99.9% is achieved at a wavelength of 1119.7nm; when the y-polarized coherent wave is irradiated vertically, the absorption rate of 99.9% is achieved. When the wavelength is θ=0° and M=300nm, there is no coherent absorption.

[0055] Reference Figure 5 , for the x-polarized and y-polarized 1° irradiation of the present invention The coherent wave absorption rate diagram, with the horizontal axis being the wavelength and the vertical axis being the absorption rate. When the x-polarized coherent wave irradiation angle is 1° and M=240nm, coherent perfect absorption with absorption rates of 99.9% and 99.8% is achieved at the wavelengths of 1090nm and 1122.2nm respectively; when the y-polarized coherent wave irradiation angle is 1° and M=240nm, coherent perfect absorption with absorption rate of 99.9% is achieved at the wavelength of 1095.1nm.

[0056] contrast Figure 4 and Figure 5 It can be seen that when the electromagnetic wave is irradiated vertically (θ=0°) and M=300nm, an x-polarized coherent perfect absorption band is realized. When the electromagnetic wave is irradiated obliquely at an angle of 1° and M=240nm, two x-polarized coherent absorption bands and one y-polarized coherent absorption band are realized. Thus, anisotropic coherent perfect absorption of polarization is realized.

[0057] Reference Figure 6 , is a transmission coefficient diagram of the absorber of the present invention when x-polarization is irradiated at different angles, with the horizontal axis being the wavelength and the vertical axis being the transmission coefficient. When the x-polarization coherent wave is irradiated at different angles, the process of BIC transforming into quasi-BIC can be found through the transmission coefficient. When the incident angle is 0°, the transmission coefficient has no additional wave transmission band; when the irradiation angles are 1°, 3°, 6° and 10° respectively, the quasi-BIC transmission spectrum can be observed.

[0058] Reference Figure 7 , is a Q value diagram of the absorber of the present invention at different angles of x-polarization illumination, with the horizontal axis being the illumination angle and the vertical axis being the Q value. The closer the illumination angle of the x-polarization coherent wave of the quasi-BIC is to 0°, the closer the Q value is to infinity, proving that the additional absorption band introduced by the oblique illumination of the x-polarization wave is induced by the quasi-BIC. At 1°, the Q value based on the quasi-BIC is 236, achieving x-polarization high Q value coherent absorption.

[0059] Reference Figure 8 (a), (b), (c) and (d) are the Fano resonance simulation and fitting curves of the absorber when the x-polarized illumination angles of the present invention are 1°, 3°, 6° and 10° respectively, with the horizontal axis being the frequency and the vertical axis being the transmission coefficient. It can be found that when the illumination angles of the x-polarized coherent wave are 1°, 3°, 6° and 10° respectively, the full-wave simulation results and the Fano formula fitting curve basically coincide, proving that the quasi-BIC is a Fano resonance. For the classic Fano resonance, the transmission curve can be fitted using the formula:

[0060]

[0061] Where w0 is the resonant wavelength, τ is the resonant bandwidth, q is the Breit-Wigner-Fano parameter, T0 is the transmission bias, and A0 is the continuous-discrete coupling constant.

[0062] Reference Fig. 9 , is a graph showing the coherent wave absorption rate of the absorber irradiated with x-polarization at different angles of the present invention, the horizontal axis is the irradiation angle, and the vertical axis is the absorption rate. When the irradiation angles of the x-polarized coherent wave are 0°, 1°, and 3°, respectively, the absorption band of the x-polarized coherent wave changes from one band to two bands, and as the incident angle increases, the absorption band moves toward a longer wavelength.

[0063] Combination Figure 6 , Figure 7 , Figure 8 ,and Fig. 9From the analysis of the result graph, it can be seen that the additional coherent absorption band generated by x-polarization is achieved by the induction of quasi-BIC, its Q value conforms to the characteristics of quasi-BIC, and the quasi-BIC conforms to the Fano resonance curve. The coherent absorption band moves towards a longer wavelength as the incident angle increases.

[0064] Reference Fig.10 , is a transmission coefficient diagram of the absorber vertically irradiated at different M values ​​of y polarization of the present invention, the horizontal axis is the wavelength, and the vertical axis is the transmission coefficient. When the absorber is vertically irradiated at y polarization at M = 300nm, 280nm, 240nm, 180nm and 120nm, the process of BIC transforming into quasi-BIC can be found through the transmission coefficient. It can be found that when M is 300nm, the transmission coefficient has no wave transmission band; when M is 300nm, 280nm, 240nm, 180nm and 120nm, the quasi-BIC transmission spectrum can be observed.

[0065] Reference Fig.11 , which is a Q value diagram of the vertically irradiated absorber under different M values ​​of y polarization of the present invention, with the horizontal axis being the M value and the vertical axis being the Q value. When y polarization is vertically irradiated, the closer M is to 300nm, the closer the Q value is to infinity, proving that the absorbing band of y polarization wave when M is not 300nm is induced by quasi-BIC. When M is 290nm, the Q value based on quasi-BIC is 1781, realizing y polarization high Q value coherent absorption.

[0066] Reference Fig.12 , which is a Fano resonance simulation and fitting curve diagram of the vertically irradiated absorber under different M values ​​of y-polarization of the present invention, the horizontal axis is the frequency, and the vertical axis is the transmission coefficient. Fig.12 (a), (b), (c) and (d) are the full-wave simulation results and the Fano formula fitting curve results of the transmission coefficient when the y-polarized coherent wave is at 280nm, 240nm, 180nm and 120nm respectively. The full-wave simulation results and the Fano formula fitting curve basically coincide, proving that the quasi-BIC is a Fano resonance.

[0067] Reference Fig.13 , is the result of the coherent wave absorption rate of the vertically irradiated absorber under different M values ​​of y polarization, the horizontal axis is the wavelength, and the vertical axis is the absorption rate. When M is 300nm, 280nm, 240nm and 180nm respectively, the y polarization coherent wave changes from no absorption to a coherent absorption band, and the absorption wavelength moves towards a longer wavelength as M increases.

[0068] Combination Fig.10 , Fig.11 , Fig.12 ,and Fig.13From the analysis, it can be seen that the coherent absorption band generated by y-polarization is achieved by the induction of quasi-BIC, its Q value conforms to the characteristics of quasi-BIC, and quasi-BIC conforms to the Fano resonance curve. The coherent absorption band moves towards a longer wavelength as M increases.

[0069] In summary, the present invention greatly improves the control capability of electromagnetic waves for coherent absorption of different polarizations and realizes coherent absorption of high Q value, and provides a new method for the design of multi-polarization, high Q value and multifunctional coherent absorbers in the future. According to the content and principle of the present invention, various modifications and changes in form and details are made, but these modifications and changes based on the ideas of the present invention are still within the scope of protection of the claims of the present invention.

Claims

1. A dimer anisotropic metasurface high Q value coherent absorber, comprising N×N absorber units with P as a period, N≥2; the absorber unit comprises a tetrahedral dielectric block (1); characterized in that: The upper and lower surfaces of the tetrahedral dielectric block (1) are each provided with A dimer (2) composed of two metal rings, wherein the central axes of the two metal rings in the dimer (2) are located on the YOZ plane where the y-polarized wave is located, and are mirror-symmetric with respect to the XOZ plane where the x-polarized wave is located; When the y-polarized signal wave and its corresponding control wave and the x-polarized signal wave and its corresponding control wave irradiate the absorber vertically along the positive and negative directions of the Z-axis at the same time, a high-Q y-polarized coherent absorbing electromagnetic response is achieved under the induction of the quasi-BIC generated by the dimer, and an x-polarized coherent absorbing electromagnetic response is achieved based on the metal resonance of the dimer; when the x-polarized signal wave and its corresponding control wave irradiate the absorber obliquely at an angle of θ with the positive and negative directions of the Z-axis, a high-Q x-polarized coherent absorbing electromagnetic response is achieved through the additional induction of the quasi-BIC generated by the oblique irradiation.

2. The coherent absorber according to claim 1, characterized in that: The dimer (2) comprises two metal rings whose outer and inner diameters are d1 and d2 respectively, and 3. The coherent absorber according to claim 2, characterized in that: The dimer (2) has two metal rings with a thickness of t, and 4. The coherent absorber according to claim 1, characterized in that: The metal ring and the dimer (2) each contain two metal rings made of gold, silver or aluminum.

5. The coherent absorber according to claim 1, characterized in that: The tetrahedral dielectric block (2) is made of Si3N4, SiO2 or Si.

6. The coherent absorber according to claim 1, characterized in that: The distance M between the two metal rings contained in the dimer (2) satisfies d1≤M≤P-d1.

7. The coherent absorber according to claim 1, characterized in that: The x-polarized signal wave and the control wave include an angle θ with the negative direction of the Z axis, satisfying θ≤10°.

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