0.5-10 [mu] m visible light-intermediate infrared metamaterial conical stacked perfect absorber

Abstract

The present invention relates to a tapered stack absorber capable of perfect light absorption in the spectral range of 0.5 [mu] m to 10 [mu] m. The structure is formed by periodically arranging conical unit structures in the horizontal direction, the bottommost layer of each unit structure is a square titanium (Ti) plate with the thickness of d and the width of p, and the square titanium (Ti) plate is used for preventing transmission of electromagnetic waves. On the basis of a Ti plate, 18 TiN / VO2 disc composite layers are stacked from bottom to top, the radius size is decreased by delta t every time, the radius of the bottom composite layer is D1, and the radius of the top composite layer is D2. The upper layer of the composite layer is a TiN layer with the height of h, and the lower layer of the composite layer is a VO2 layer with the height of h. The structure can realize perfect absorption from visible light to a middle infrared band (0.5-10 [mu] m).

Description

Technical Field

[0001] The present invention relates to the technical field of optical absorbers; specifically, it relates to a conical stacked absorber capable of achieving perfect light absorption in the spectral range of 0.5 μm to 10 μm. Background Art

[0002] Metamaterials are artificial materials composed of metals and dielectrics with sub-wavelength structures arranged periodically, showing special electromagnetic properties that natural materials do not possess. Due to their unique properties, many strange effects that cannot be obtained in natural materials can be generated. Metamaterial absorbers use the loss components of the permittivity and permeability of metamaterials to absorb a large amount of electromagnetic radiation. Through reasonable structural and size design, the absorption and reflection characteristics of electromagnetic waves can be flexibly adjusted. Absorbers based on metamaterial structures are widely used in broadband absorption, such as photovoltaic power generation, electromagnetic stealth, thermal radiation, and solar energy collection. More than 99.9% of the energy of solar radiation is concentrated in the band of 0.2 - 10.0 μm. Space solar power stations aim to capture the energy that cannot reach the earth. Although certain progress has been made in ultra-wideband absorbers, for space solar absorption, in order to improve its conversion efficiency, the bandwidth of the light absorber we choose should cover the band of 0.2 - 10 μm as much as possible. Summary of the Invention

[0003] The purpose of the present invention is to provide a conical stacked absorber that covers the key band where solar radiation energy is concentrated, achieves perfect absorption in this band, and is insensitive to the polarization angle and incident angle of the light source.

[0004] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0005] An optical absorber based on a conical stacked structure, comprising a plurality of stacked absorption units. A single stacked absorption unit includes:

[0006] A square metal titanium layer at the bottom layer, with a thickness of d and a width of p; d = 0.3 μm, p = 0.9 μm;

[0007] A composite layer on the titanium layer, with a thickness of H; the composite layer is divided into upper and lower layers. The titanium nitride layer on the upper layer of the composite layer has a thickness of h; the vanadium dioxide layer on the lower layer of the composite layer has a thickness of h; H = 0.2 μm, h = 0.1 μm;

[0008] The composite layer is disk-shaped, with a total of 18 layers, stacked on the titanium substrate from bottom to top. The thickness H remains unchanged, and the radius decreases by Δt in sequence. The radius of the bottom composite layer is D 1 , and the radius of the top layer is D 2 ; H = 0.2 μm, Δt = 0.05 μm, D 1 = 0.9 μm, D 2 = 0.05 μm;

[0009] The composite layer is formed by stacking a disk-shaped titanium nitride layer and a vanadium dioxide layer. In the same composite layer, the titanium nitride layer and the vanadium dioxide layer have the same radius;

[0010] The thickness h of the titanium nitride layer and the vanadium dioxide layer in the composite layer always remains unchanged; h = 0.1 μm;

[0011] The unit stack structure is arranged in an array and lies in the same plane;

[0012] The present invention proposes a metamaterial conical stack perfect absorber. This structure achieves ultra-wideband while ensuring relatively high absorption, and has polarization-independent and wide-angle light absorption characteristics. By reasonably designing the size and structure of the stacked waveguide, the slow light effect of different wavelengths is realized, so that incident light of different wavelengths is absorbed by waveguides of different widths. Light with a shorter wavelength is absorbed by the waveguide with a smaller width in the upper part, while light with a longer wavelength is absorbed by the waveguide with a larger width in the lower part. Utilizing the slow light effect, the propagation speed of electromagnetic waves can be reduced, thereby increasing the interaction time between electromagnetic waves and the structure and improving the absorption efficiency.

[0013] This stack structure is composed of many TiN / VO 2 / TiN composite layers. The TiN / VO 2 / TiN composite layer constitutes a metal-like / dielectric / metal-like three-layer structure (MIM). The top metal-like layer will generate electrons with positive and negative periodic changes under the excitation of electromagnetic waves, making the direction of the electric polarization vector generated under the top metal-like surface opposite to the polarity of the induced charges generated on the bottom metal-like surface, forming an equivalent circuit, so that the magnetic field is mainly confined in the dielectric layer between the two metal layers. This can effectively excite magnetic polariton resonance and enhance the light absorption effect.

[0014] When the thickness of the alternately arranged TiN metal-like layer and the VO 2 dielectric layer is much smaller than the wavelength of the incident wave, the layered structure composed of multiple arrays can be regarded as an anisotropic homogeneous effective medium.

[0015] This structure exhibits very perfect absorption performance in the entire visible to mid-infrared wavelength range of 0.5 - 10 μm. Among them, the absorption rate is close to 100% in the ranges of 1 - 4 μm and 6.5 - 9 μm. The lowest and average absorption rates are 97.21% and 99.29% respectively. The absorption coefficient expression is A = 1 - R - T.

[0016] This structure is insensitive to the change of the polarization angle of the light source. Regardless of the polarization direction of the light, the absorption rate remains almost unchanged.

[0017] This structure is not sensitive to the change of the incident angle of the light source. When the incident angle changes from 0° to 55°, the absorption rate in the 0.5 - 4 μm band slightly decreases, but always remains above 85%. The absorption rate in the 4 - 10 μm band hardly changes.

[0018] The beneficial effect of the present invention is that the structure of the present invention can effectively absorb light in the spectral range of 0.5 μm to 10 μm in wavelength. Brief Description of the Drawings

[0019] Figure 1 It is a schematic diagram of a unit structure of the present invention;

[0020] Figure 2 It is a schematic diagram of the absorption spectrum of the absorber;

[0021] Figure 3 It is the effective impedance diagram of the absorber

[0022] Figure 4 It is the magnetic field distribution diagram of the x - z plane where the absorber is located at incident wavelengths of (a) 2.8 μm, (b) 4.8 μm, and (c) 8 μm;

[0023] Figure 5 It is the electric field distribution diagram of the x - z plane where the absorber is located at incident wavelengths of (a) 2.8 μm, (b) 4.8 μm, and (c) 8 μm;

[0024] Figure 6 It is the structure diagram of the absorber when Δt is (a) 0 μm, (b) 0.025 μm, (c) 0.075 μm, and (d) 0.1 μm respectively;

[0025] Figure 7 It is the schematic diagram of the change of the absorption rate when Δt changes;

[0026] Figure 8 It is the schematic diagram of the change of the absorption rate when the metal - like layer of the absorber is replaced by different metal materials;

[0027] Figure 9 It is the relationship between the absorption characteristics of the absorber and (a) the incident angle of the non - polarized wave and (b) the polarization angle; Detailed Embodiments

[0028] The present invention will be described in detail below in conjunction with the drawings and specific embodiments.

[0029] Example: The present invention provides a conical stacked absorber that covers the key wavelength band where solar radiation energy is concentrated, achieves perfect absorption in this band, and is insensitive to the polarization angle and incident angle of the light source. In the simulation settings, we used a vertically incident plane wave, set the wavelength range for solution to 0.5 - 10 μm, set the polarization direction of the electromagnetic wave to the x direction, the electric field direction of the electromagnetic wave along the negative y axis, the magnetic field direction along the negative x axis, and the wave vector along the negative z axis. To simulate the periodic structure, we set the boundary conditions for the x and y axes as periodic boundary conditions to simulate the infinitely repeating unit structure. The boundary condition for the z axis direction uses the PML perfect absorption boundary condition to effectively absorb the reflection and radiation of the incident wave. The absorption rate is calculated using the formula: A = 1 - T - R. Since the 0.3 - μm titanium layer can achieve zero transmission, T = 0. The data of Ti is taken from Palik, and the dielectric constant of TiN is modeled by the Drude - Lorentz model, and the dielectric constant of VO 2 is modeled by the Lorentz dispersion model.

[0030] As Figure 1 (a) shows the three - dimensional solid diagram of the unit structure. The bottom is the substrate metal titanium, and the TiN / VO 2 composite layer is stacked on the titanium substrate from bottom to top. The top view is as Figure 1 (b) shows, and the side view is as Figure 1 (c) shows.

[0031] As Figure 2 shown, this absorber has an average absorption rate of 99.29% and a minimum absorption rate of 97.21% in the 0.5 - 10 - μm band. The design of this ultra - wideband perfect absorber successfully achieves a high absorption rate in the key wavelength band where solar radiation energy is concentrated. By reasonably designing the structural dimensions and material selection of the absorber, the absorber has a high absorption capacity in this band and is insensitive to the polarization angle and incident angle of the light source. This ultra - wideband perfect absorber is very suitable for use in space solar power stations to absorb the energy that cannot reach the earth.

[0032] As Figure 3 shown is the effective impedance diagram of this absorber. It can be seen that when the real part of the impedance is close to 1 and the imaginary part is close to 0, the absorption rate can correspondingly approach 1. When designing the absorber, we optimized the structural parameters of the designed absorber to match the relative impedance of the absorber and the free - space impedance, thus achieving perfect absorption.

[0033] To further analyze the absorption characteristics of this ultra - wideband absorber, we carried out simulation and plotted the magnetic field distribution, electric field intensity, and electric field vector distribution diagrams of the x - z plane of this stacked structure. From Figure 4It can be seen that as the incident wavelength increases, the electromagnetic resonance magnetic field region gradually moves towards the bottom, and its resonance region is concentrated in the dielectric layer between the two metal layers; Figure 5 It indicates that the charges inside the absorber metal resonate under the excitation of the incident wave and are concentrated at the structure edges. This is because the quasi-metal on the top layer generates electrons with periodically changing positive and negative polarities under the excitation of electromagnetic waves. The directions of the electric polarization vectors of these electrons are opposite to the polarization of the induced charges generated on the surface of the bottom quasi-metal, forming an equivalent circuit, which confines the resonance magnetic field mainly in the dielectric layer between the two quasi-metal layers, while the resonance electric field is distributed around the dielectric layer, forming a loop current.

[0034] During the optimization process, when discussing the change of any one of the following parameters, the other parameters remain unchanged. For example Figure 6 As shown, they are the structural diagrams of the absorber when (a) Δt = 0 μm, (b) Δt = 0.025 μm, (c) Δt = 0.075 μm, and (d) Δt = 0.1 μm respectively; Figure 7 The comparison chart of their absorption characteristic curves shows that when Δt = 0.05 μm, the absorption effect is the best. This indicates that the waveguide interval Δt has a significant impact on the light absorption performance. The broadband absorption of this waveguide structure can be explained by the slow light effect. For a specific incident wavelength, resonance can be formed at a specific waveguide width. In this mode, electromagnetic waves propagate downward in waveguide structures with different widths, and the transmission group velocity can be close to 0, increasing the interaction time between the electromagnetic wave and the structure. The relationship between the incident wavelength and the waveguide width is: λ is the incident wavelength, D is the waveguide width, ε ⊥ is the vertical dielectric constant. By adjusting Δt and the waveguide width, when the generated resonance wavelengths are close to being continuous, broadband absorption can be achieved. Therefore, the optimal value of Δt should be 0.05 μm. For the above preferred data: d = 0.3 μm; p = 0.9 μm; H = 0.2 μm; h = 0.1 μm; Δt = 0.05 μm; D 1 = 0.9 μm; D 2 = 0.05 μm; h = 0.1 μm;

[0035] For example Figure 8 As shown, when we replace the quasi-metal material with different metal materials, we find that their absorption rates decrease to varying degrees. Although the MIM structure composed of these metal materials can confine the generated magnetic polariton resonance in the dielectric layer, due to the fact that metal materials are prone to cause reflection of incident light, their absorption effects will be affected to a certain extent. The quasi-metal material TiN has a relatively high imaginary part value of the dielectric constant in the visible light and near mid-infrared bands, has relatively large optical losses compared to noble metals, and can exhibit plasma resonance characteristics, which can reduce the reflectivity of the entire structure to a certain extent;

[0036] As Figure 9 (a) shows, as the incident angle increases from 0° to 55°, the absorption rate in the 0.5 - 4 μm band slightly decreases, while the absorption rate in the 4 - 10 μm band hardly changes much. From Figure 9 (b) it can also be observed that the absorption rate is insensitive to the change in the polarization angle of the light source, that is, regardless of the polarization direction of the light, the absorption rate hardly changes. This is because when the thickness of the alternately arranged TiN-like metal layer and VO 2 dielectric layer is much smaller than the wavelength of the incident wave, the layered structure composed of the multi-layer array can be regarded as an anisotropic homogeneous effective medium.

[0037] Although the embodiments of the present invention have been described in detail above, it is obvious to those skilled in the art that various modifications and changes can be made to these embodiments. However, it should be understood that such modifications and changes are all within the scope and spirit of the present invention described in the claims. Moreover, the present invention described herein can have other embodiments and can be implemented or realized in various ways.

Claims

1. 0.5-10μm visible light-mid-infrared metamaterial conical stack perfect absorber, composed of multiple unit stacking structures periodically arranged in the horizontal direction, characterized by: The unit stacking structure includes: The square titanium layer at the bottom layer has a thickness of d and a width of p; d = 0.3 μm, p = 0.9 μm; The composite layer is located on the titanium layer, and the thickness of the composite layer is H; H = 0.2 μm; The titanium nitride layer located on the upper layer of the composite layer has a thickness of h; h = 0.1 μm; The vanadium dioxide layer located under the composite layer has a thickness of h; h = 0.1 μm; The absorber is stacked in a cone shape from bottom to top on a square titanium plate, with the radius decreasing by Δt in sequence; the unit structure is arranged periodically; Δt=0.05 μm.

2. The visible light-mid-infrared metamaterial conical stack perfect absorber according to claim 1, characterized in that: The bottom metal is titanium; the composite layer is titanium nitride and vanadium dioxide.

3. The visible light-mid-infrared metamaterial conical stack perfect absorber according to claim 1, characterized in that : The titanium substrate is square, with a width of p and a thickness of d; p = 0.9 μm, d = 0.3 μm.

4. The visible light-mid-infrared metamaterial conical stack perfect absorber according to claim 1, characterized in that : The composite layer is disc-shaped, with a total of 18 layers, stacked on a titanium substrate from bottom to top, with a thickness H unchanged, and a radius decreasing by Δt. The radius of the bottom composite layer is D1, and the radius of the top composite layer is D2; H = 0.2 μm, Δt = 0.05 μm, D1 = 0.9 μm, D2 = 0.05 μm.

5. The visible light-mid-infrared metamaterial conical stack perfect absorber according to claim 4, characterized in that The composite layer is formed by stacking a disc-shaped titanium nitride layer and a vanadium dioxide layer. In the same composite layer, the radius of the titanium nitride layer and the vanadium dioxide layer is the same.

6. The visible light-mid-infrared metamaterial conical stack perfect absorber according to claim 5, characterized in that : The thickness h of the titanium nitride layer and the vanadium dioxide layer in the composite layer remains unchanged; h = 0.1 μm.

7. The visible light-mid-infrared metamaterial conical stack perfect absorber according to claim 1, characterized in that: The unit stacking structure is arranged in an array and is located in the same plane.

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