An ultra-wideband perfect absorber based on square-hole array structure

Abstract

The application discloses a kind of based on square hole array structure's metasurface ultra-wideband perfect absorber, is equipped with nanometer square hole array on transparent substrate, each nanometer square hole is constituted by five square rings with the height h from substrate upward, material is magnesium fluoride, silicon, chromium, gallium arsenide, aluminum in turn;Each nanometer square hole is embedded nanometer square column, nanometer square column is constituted by four square columns with the height h from substrate upward, the material of four square columns is silicon, chromium, gallium arsenide, aluminum in turn.The absorber in 420nm to 3500nm wave band range, realize the average absorption of theoretical value 0.922, can realize 0.999 perfect absorption at 570nm.The absorber compared with traditional absorber, it is effective way to realize large-area ultra-thin metasurface absorber, with the advantages of wide frequency band, high absorption, and its structure is relatively simple, with current nanofabrication technology such as deposition and photolithography compatible, easy to manufacture, cost is lower.

Description

TECHNICAL FIELD

[0001] The present application relates to an optical device, in particular to a metamaterial absorber. BACKGROUND

[0002] Metamaterial is a kind of subwavelength structure material designed by human, which exhibits unique physical properties that natural materials do not have, such as negative magnetic permeability and negative electric conductivity. Metamaterial devices have attracted extensive attention due to their excellent electromagnetic properties in many applications such as antenna systems, electromagnetic wave invisibility, optical imaging, high-sensitivity sensing, etc. By adjusting the geometric parameters and shape of the metamaterial structure, its permittivity and permeability can be flexibly designed to achieve the regulation of its electromagnetic properties. At the same time, the energy loss of the metamaterial absorber can be actively introduced by using the energy attenuation characteristics of the metamaterial, and perfect absorption of specific frequency band electromagnetic waves has been achieved.

[0003] Perfect absorber is an optical device that can eliminate both transmission and reflection and can absorb all incident light. It can be divided into narrow-band perfect absorber and wide-band perfect absorber. The former can easily cover linear or nonlinear sensors in the visible and infrared wave bands. The wide-band metamaterial absorber can maintain high light absorption in a wide bandwidth, so it is crucial for photoelectric detectors, radiation measurement, photovoltaic applications, etc.

[0004] In 2008, Landy et al. first proposed an electromagnetic metamaterial perfect absorber composed of metal open ring resonators and metal strips, which can achieve a single-frequency perfect absorption of up to 99% at 11.65 GHz in the microwave band [1] . On the basis of this research, Hu et al. prepared a metamaterial absorber that extends the microwave band to the terahertz band, which has a strong resonance at about 1.3 THz and an absorption rate of up to 70% [1] . Avitzour et al. predicted a near-infrared plasmonic absorber based on impedance-matched negative refractive index material, which has a single-layer absorption rate of up to 90% at 1.5 μm [2] . However, the above absorbers have a narrow bandwidth, and usually only work at a single resonant wavelength, which limits their application.

[0005] In recent years, there are a large number of studies aimed at increasing the working bandwidth of metamaterial perfect absorbers. The most direct method is to couple multiple sizes of metal resonators, which can achieve broadband absorption by covering the electromagnetic spectrum with different resonances coupled in the system. Although the absorption bandwidth can be easily adjusted by changing the structural parameters, the integration of multiple resonators in a single unit greatly increases the size of the structure. So far, many metamaterial structures that can demonstrate broadband perfect absorbers have been reported. Guo et al. demonstrated an ultrathin broadband absorber based on a-Si / Ag stack, which achieved an absorption peak of 95.5% when resonating in the visible light spectrum 400-650 nm [3] . Mo et al. proposed a gold absorber based on a plasmonic conical coaxial hole, which achieved an average absorption of 93% in the 300-900 nm spectral range [4] . Cui et al. proposed a sawtooth-shaped ultra-broadband infrared absorber, which achieved an absorption of 95% in the 3-5.5 μm spectral range [5] . Wu et al. placed a thin layer of SiO2 supported by a metal-dielectric (MD) layer on a thin layer of SiO2 supported by a metal-dielectric (MD) layer (metal and dielectric are iron and silicon dioxide, respectively), which achieved perfect absorption of more than 95% in the spectral range of 400 to 1500 nm [6] However, these methods may be limited by relatively narrow absorption bandwidth, complex unit mode or the need for heavy metals. Therefore, it is very meaningful to study a simple and low-cost ultra-broadband perfect absorber for the development and utilization of solar energy.

[0006] [1]Bosquespadilla F J,Landy L N,Smith W K,et al.Perfect metamat-eriala bsorber.,2008.

[0007] [2]Tao H,Landy N I,Bingham C M,et al.A metamaterial absorber f-or thet erahertz regime:Design,fabrication and characterization[J].Optics Express,2008,

[0008] 16(10):7181-7188.

[0009] [3] Lee K T, Ji C, Guo L J. Wide-angle, polarization-independent ultrat-hin broadband visible absorbers [J]. Applied Physics Letters, 2016, 108(3): 59.

[0010] [4] Mo L, Yang L, Nadzeyka A, et al. Enhanced broadband absorption in gold by plasmonic tapered coaxial holes [J]. Optics Express, 2014, 22(26): 32233.

[0011] [5] Cui Y, Fung K H, Xu J, et al. Ultra-broadband Light Absorption by a Sawtooth Anisotropic Metamaterial Slab [J]. Nano Letters, 2011, 12(3): 1443-1447.

[0012] [6] Dong W, Chang L, Liu Y, et al. Numerical study of an ultra-broadband near-perfect solar absorber in the visible and near-infrared region [J]. Optics Letters, 2017, 42(3): 450.

[0013] 017, 42(3): 450. SUMMARY

[0014] The present application aims to provide an angle-insensitive metasurface ultra-wideband perfect absorber, which realizes an ultra-wideband metasurface perfect absorber from visible light to near-infrared waveband, and has the characteristics of simple structure and low cost.

[0015] Technical solution: A kind of super surface super wide band perfect absorber based on square hole array structure, comprising: transparent substrate, nanometer square hole array is provided on the substrate, each nanometer square hole is formed by five square rings with the height h upwards from the substrate, the material of the five square rings is magnesium fluoride, silicon, chromium, gallium arsenide, aluminum in turn;Each nanometer square hole is embedded with nanometer square column, the nanometer square column is formed by four square columns with the height h upwards from the substrate, the material of the four square columns is silicon, chromium, gallium arsenide, aluminum in turn.

[0016] Further, the outer square side length of the nanometer square hole is consistent with the array period.

[0017] Further, the period p of the nanometer square hole array is 214nm, the inner square side length a of the nanometer square hole is 119nm, and h is 107nm.

[0018] Further, the substrate is a silicon dioxide substrate.

[0019] Beneficial effect: the metal-dielectric absorber of the application grows square nanometer column on the silicon dioxide substrate, the metal material in the absorber adopts low-cost aluminum (Al) and chromium (Cr), the dielectric selects gallium arsenide (GaAs), silicon (Si) and magnesium fluoride (MgF2), realizes the super wide band super surface perfect absorber from visible light to near infrared waveband. In the waveband range of 420nm to 3500nm, the average absorption rate of 0.922 is realized, and perfect absorption of 0.999 can be realized at 570nm. Compared with the traditional absorber, the absorber is an effective way to realize large-area ultrathin super surface absorber, has the advantages of wide frequency band and high absorption, and its structure is relatively simple, compatible with current nanofabrication technology such as deposition and photolithography, easy to manufacture, and low cost.

[0020] The application provides the possibility for the preparation of the absorber, and has wide application prospect in the fields of solar energy collection, invisibility and heat emitter. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 It is the structure schematic diagram of the perfect absorber of the application;

[0022] Figure 2 It is the sectional structure schematic diagram of a period along hole center cutting;

[0023] Figure 3 It is the theoretical curve of the perfect absorber of the application in the waveband range of 420nm to 3500nm absorption spectrum;

[0024] Figure 4 It is the influence curve of parameter P on total absorption in the perfect absorber of the application;

[0025] Figure 5 This is the curve showing the effect of parameter h on the overall absorption in the perfect absorber of this invention;

[0026] Figure 6 This is the curve showing the effect of parameter a on the overall absorption in the perfect absorber of this invention;

[0027] Figure 7 This is the angle dependence curve of absorption in the wavelength range of 420-3500nm in the perfect absorber of this invention. Detailed Implementation

[0028] The invention will now be further explained with reference to the accompanying drawings.

[0029] like Figure 1 , Figure 2 As shown, a metasurface ultrawideband perfect absorber based on a square hole array structure includes: a silicon dioxide substrate, on which a nano-square hole array is disposed, each nano-square hole consisting of five square rings of height h deposited sequentially upwards from the substrate, the materials of the five square rings being magnesium fluoride, silicon, chromium, gallium arsenide, and aluminum, respectively. Each nano-square hole contains embedded nano-square pillars, consisting of four square pillars of height h deposited sequentially upwards from the substrate, the materials of the four square pillars being silicon, chromium, gallium arsenide, and aluminum, respectively. The outer side length of the nano-square hole is consistent with the array period p, and the inner side length a of the nano-square hole is consistent with the side length of the nano-square pillar.

[0030] Broadband absorption is employed by using the Finite-Difference Time-Domain (FDTD) method to calculate and optimize the structural parameters of the perfect absorber of this invention. The computational domain is as follows: Figure 1 The x and y directions are set as periodic boundary conditions, simulating the periodic arrangement of the absorber unit structure along these directions; the incident light source is a plane wave, i.e., light incident along the +Z direction, such as... Figure 1 As shown by the arrow, light enters the structure from the transparent substrate at the bottom. The parameters were ultimately optimized to: p = 214 nm, a = 119 nm, h = 107 nm. Figure 3 The theoretical absorption spectra of the optimized structure are shown. It can be seen that an average absorption of 0.922 is achieved in the wavelength range of 420 nm to 3500 nm, with two slight dips between 420 and 800 nm, where the absorbance is approximately 0.908. The absorption peak at 570 nm is 0.999. Because the perfect absorber proposed in this invention is symmetrical along the X and Y directions, its broadband high absorption exhibits excellent angular characteristics.

[0031] Next, the finite difference time domain (FDTD) method is used to study the physical mechanism of the broadband and perfect absorption of the perfect absorber, and to explore the parameter error tolerance range in actual manufacturing and production. The control variable method is used to change each geometric parameter in turn, and the influence of different geometric parameters on the working performance of the absorber and the dependence of the perfect absorber structure on the incident angle in the wavelength range of 420-3500 nm are studied.

[0032] When other simulation parameters remain unchanged (a=119 nm, h=107 nm), the change process of the absorption rate of the structure to the incident light is as shown in Figure 4 When the parameter P changes from 184 nm to 244 nm in steps of 10 nm, the overall absorption rate changes greatly. As can be seen from Figure 4 , there are two dips in the 420-800 nm band. The first dip occurs at about 480 nm, and the absorption at the dip decreases from 0.908 to about 0.760 as the period P deviates from 214 nm. The second dip at 700 nm, the absorption gradually increases with the increase of P, and the peak absorption is 0.960. In the 800-1600 nm band, the average absorption rate increases from 0.860 to 0.959 as the P value increases; on the contrary, in the 1600-2600 nm band, the average absorption rate increases from 0.847 to 0.927 as the P value decreases. Overall, in the near-infrared band of 800-2600 nm, the structure maintains a high overall absorption of 0.890. Above 2600 nm, when the period of the array is greater than 214 nm, the average absorption rate of the nano metamaterial absorber gradually decreases as P increases, and the performance deteriorates. Therefore, the selection of P value mainly balances the relationship between long and short waves, and when the array period P is 214 nm, a relatively balanced state is reached.

[0033] Then, the influence of the height h on the overall performance is analyzed, and the other geometric parameters remain unchanged. The simulation range is set to 99-139 nm, and the simulation step is 8 nm. The change process of the absorption rate is as shown in Figure 5As shown in Fig. 6, when h is less than or equal to 107 nm, due to the small height h, the overall structure of the super surface is small, the reflection of the incident light is small, and the absorption rate of the absorber at the two recesses of the short wave is about 0.919, and the average absorption in the full wave band can reach 0.921; but at the same time, it is found that in the long wave band 2600-3500 nm, if the value of h is too small, the absorber structure is too compact, which leads to the increase of reflection, and the absorption is obviously decreased. When the value of h is greater than 107 nm, with the further increase of the value of h, the absorption rate at the two recesses of the short wave gradually decreases to about 0.836, and the absorption in the full wave band also gradually decreases to 0.882. In order to balance the peak absorption rate and the average absorption rate of long and short waves, the height h is selected as 107 nm. At this time, the absorption rate at the short wave recess is 0.908, the average absorption rate in the long wave band is 0.932, and the absorption rate in the full wave band is relatively uniform, which is 0.922.

[0034] Then, the influence of the square hole side length a on the overall performance is analyzed, the other geometric parameters are kept unchanged, the simulation range is set to 101-137 nm, the simulation step is 6 nm, and the absorption rate change process is as shown in Fig. 7. Figure 6 As shown in Fig. 7, in the short wave band, the absorption of the structure is almost not affected by the change of the value of a. In the near-infrared wave band, with the gradual deviation of the value of a from 119 nm, the absorption rate of the structure has different degrees of fluctuation before and after the intersection point 1530 nm (the average absorption at the intersection point is 0.897), and especially when the wavelength is greater than 2600 nm, the absorption spectrum line sharply decreases and fluctuates greatly, and the average absorption rate in the whole wave band is 0.891. The reason is that with the change of the structure, the matching effect of the free space impedance and the structure impedance is relatively poor, and the absorption rate also decreases. Finally, the value of a is set to 119 nm.

[0035] The relationship between the absorption characteristics of the nano metamaterial absorber and the incident angle is further studied. The geometric parameters of the structure are kept unchanged, the incident angle is changed, and the absorption spectrum of the nano metamaterial absorber when the incident angle is 0°, 10°, 20°, 30°, 40°, 50° and 60° is recorded. The absorption rate under oblique incidence here is the average value of p-polarized and s-polarized incidence. As shown in Fig. 8. Figure 7 As can be seen from Fig. 8, the absorption rate at 570 nm wavelength is the highest, which is 0.999, and the average absorption rate under vertical incidence in the wave band of 420 nm to 3500 nm is 0.922. When the incident angle increases to 60°, the perfect absorber of the application also shows good angle characteristics, and the average absorption rate is still as high as 0.905.

[0036] The above only describes the preferred embodiments of the present application, and it should be pointed out that for ordinary skilled persons in the art, some improvements and refinements can be made without departing from the principles of the present application, and these improvements and refinements should also be regarded as the protection scope of the present application.

Claims

1. A metasurface ultra-wideband perfect absorber based on square hole array structure, characterized in that, The application relates to a transparent substrate provided with a nanometer square hole array, each nanometer square hole being composed of five square rings with a height of h from the substrate upwards, the materials of the five square rings being magnesium fluoride, silicon, chromium, gallium arsenide and aluminum in sequence; a nanometer square column is embedded in each nanometer square hole, the nanometer square column being composed of four square columns with a height of h from the substrate upwards, the materials of the four square columns being silicon, chromium, gallium arsenide and aluminum in sequence; the period of the nanometer square hole array is p=214nm, the inner square side length of the nanometer square hole is a=119nm, and h=107nm. The outer square side length of the nanometer square hole is consistent with the array period.

2. The metasurface ultra-broadband perfect absorber based on square hole array structure according to claim 1, characterized in that, The substrate is a silicon dioxide substrate.

3. The metasurface ultra-broadband perfect absorber based on square hole array structure according to claim 1 or 2, characterized in that, ​

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