TM polarization three-band tunable spectrum selective absorber based on guided mode resonance effect

Abstract

A TM polarization three-band tunable spectrum selective absorber based on a guided mode resonance effect comprises a graphene single layer, a hexagonal lattice point nanopore array, a dielectric medium thin film layer, an antireflection thin film layer and a dielectric medium substrate from top to bottom, and the nanopore array is composed of a two-dimensional periodic hexagonal lattice point nanopore array. Under vertical incidence of TM polarized light, incident light in three narrow frequency ranges can be absorbed, an absorption spectrum is subjected to micro-frequency shift along with structural parameters and incident angles, but the absorption rate at each peak frequency is higher than 30%, and the full width at half maximum is smaller than 0.005 THz; by adjusting the Fermi level of the graphene, the absorption performance can be dynamically tuned in a large frequency range. The TM polarization three-band tunable spectrum selective absorber is processed by combining an electron beam direct writing device with a micro-electronic deep etching process, is convenient in material taking and low in manufacturing cost, can be produced on a large scale, and has important practical prospects.

Description

TECHNICAL FIELD

[0001] The patent relates to a three-band tunable spectral selective absorber, in particular, a TM-polarized three-band tunable spectral selective absorber based on the guided-mode resonance effect in the terahertz band. BACKGROUND

[0002] In recent years, metamaterial absorbers have become an important research direction due to their wide application prospects in high-sensitivity detectors, thermal imaging devices, microbolometers, and solar energy harvesting. The typical metamaterial absorber structure is designed with precision, and includes a metal microstructure layer, a dielectric isolation layer, and a metal mirror layer from top to bottom, forming an efficient absorption mechanism. Since the narrow-band absorber was proposed in 2008, metamaterial absorbers have developed to wide-band and multi-band absorption. However, most of the multi-band selective absorbers proposed so far are static, that is, once the absorption performance is determined, it is difficult to adjust to other frequencies, which requires designers to re-optimize the structure parameters of the absorber for specific needs. Therefore, exploring and implementing dynamic control technology for multi-band absorption to adapt to diversified application scenarios has become an inevitable trend in the development of this field.

[0003] On the other hand, graphene, as a unique two-dimensional carbon material, has attracted much attention since it was first discovered in experiments in 2004 due to its excellent electrical, mechanical, and optical properties. In the field of optoelectronics, graphene has been widely used in optical detectors, modulators, absorbers, and waveguides. In particular, in the mid-infrared and far-infrared bands, graphene exhibits two significant characteristics: first, its conductivity can be tuned over a wide frequency range, covering from near-infrared to terahertz, through chemical doping or electrostatic control methods; second, its strong plasmonic response can effectively enhance the interaction between light and graphene. This makes graphene an effective candidate material for future tunable optoelectronic and plasmonic devices. Based on these characteristics, tunable graphene absorbers with ideal absorption performance have been extensively studied, such as periodic doped graphene nanodisk arrays

Prior art 1: S. Thongrattanasiri et al., Phys. Rev. Lett., 108(4), 047401, 2012

Prior art 2: R. Alaee et al., Opt. Express, 20(27), 28017-24, 2012

Prior art 3: S. Ke et al., Opt. Express, 23, 8888-8900, 2015

[0004] In addition, two-dimensional gratings are usually processed on substrates by micro-nano processing technology to have different groove shapes. The diffraction problem of subwavelength two-dimensional gratings cannot be handled by simple scalar grating diffraction, and must be solved by Maxwell equations in vector form and combined with boundary conditions through an encoded computer program. Li has given an algorithm of the rigorous coupled-wave theory

Prior art 4: L. Li, J. Opt. Soc. Am. A 14, 2758-2767 (1997)

[0005] In order to overcome the shortcomings of the prior art, the utility model provides a TM polarization three-band tunable spectral selective absorber based on guided mode resonance effect for THz band, when TM polarization light is vertically incident, the incident light in three narrow frequency ranges will be absorbed, with the change of structure parameters and incident angle, the absorption spectrum will have a small frequency shift, the peak absorption efficiency will have a small change, but the absorption at each peak frequency can always be higher than 30%, and the full width at half maximum of the absorption spectrum is always less than 0.005 THz; in addition, the absorption performance can be dynamically tuned in a larger frequency range by changing the Fermi level of graphene. Therefore, the spectral selective absorber has important practical value.

[0006] The technical solution of the utility model is as follows:

[0007] A TM polarization three-band tunable spectral selective absorber based on guided mode resonance effect for THz band, characterized in that the absorber comprises a graphene monolayer, a hexagonal lattice nanopore array, a dielectric film layer, an antireflection film layer and a dielectric substrate from top to bottom;

[0008] The hexagonal lattice nanopore array is composed of a two-dimensional periodic hexagonal lattice nanopore array, the period on the x-axis is 27.9-28.1 microns, the period on the 60° direction is 26.8-27.0 microns, the diameter of the nanopore is 9.3-9.5 microns, and the thickness of the nanopore is 9.9-10.1 microns; the thickness of the dielectric film layer is 7.9-8.1 microns; the thickness of the antireflection film layer is 5.9-6.1 microns;

[0009] When TM polarization light is vertically incident, the absorber absorbs incident light in three narrow frequency ranges, with the change of structure parameters and incident angle, the absorption spectrum is shifted, the peak absorption efficiency is changed, but the absorption at each peak frequency is always higher than 30%, and the full width at half maximum of the absorption spectrum is less than 0.005 THz.

[0010] Preferably, the hexagonal lattice nanopore array has a period of 28 microns in the x-axis direction and a period of 26.88 microns in the 60° direction, and the nanopore has a diameter of 9.4 microns and a thickness of 10 microns.

[0011] Preferably, the dielectric film layer has a thickness of 8 microns, and the anti-reflection film layer has a thickness of 6.0 microns.

[0012] Further, the graphene monolayer is used to dynamically tune the absorption performance of the absorber by changing its Fermi energy level.

[0013] Further, the dielectric film layer and the anti-reflection film layer are used to optimize the spectral response of the absorber, improve the absorption efficiency, and reduce reflection.

[0014] Further, the dielectric substrate is used to provide structural support and stability.

[0015] Compared with the prior art, the technical effects of the present application are as follows:

[0016] 1) When the nanopore array has a period of 28 and 26.88 microns in the x-axis and 60° directions, respectively, and the nanopore has a diameter of 9.4 microns and a thickness of 10 microns, the dielectric film layer has a thickness of 8 microns, and the anti-reflection film layer has a thickness of 6.0 microns, the absorber exhibits excellent spectral selective absorption characteristics.

[0017] 2) In the THz band, when TM polarized light is normally incident, the absorber forms three super-narrow frequency range high-efficiency absorption bands near the frequencies 6.049 THz, 6.267 THz, and 6.627 THz. These three absorption bands not only have accurate positions, but also have peak absorption efficiencies always above 30%. Even if the structure parameters or the incident angle changes slightly, the absorption spectrum will only have a slight frequency shift, and the change in peak absorption efficiency will also remain within a small range. The full width at half maximum of the absorption spectrum of the three absorption bands is always less than 0.005 THz, ensuring extremely high spectral selectivity.

[0018] 3) The Fermi energy level of graphene can be changed to dynamically tune the absorption performance in a large frequency range.

[0019] 4) It has the advantages of flexible and convenient use, high peak absorption efficiency, small full width at half maximum of the absorption spectrum, and especially dynamic regulation and control of three-band absorption. It is an ideal absorption device, which can be mass-produced at low cost using an electron beam direct writing device combined with a microelectronic etching process. The etched absorber has stable and reliable performance, and has important practical prospects. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1It is the geometric structure of TM polarization three-band tunable spectral selective absorber for THz wave band of the utility model, wherein, (a) is a perspective view, (b) is a top view

[0021] In the figure, 1 represents area 1 (refractive index n1), 2 represents a single layer of graphene, 3 represents a hexagonal lattice nano-hole array, the grating ridge refractive index is n h =1.5, the nano-hole array is air medium, the refractive index is 1, 4 is a dielectric film, the refractive index is n f =2.5, 5 is an anti-reflection film layer, the refractive index is n AR =sqrt(n f *n s ), 6 is a dielectric substrate, the refractive index is n s =1.47, d x And d y Respectively, the period of the nano-hole array in the axis and 60° direction, r and h respectively are the diameter and thickness of the nano-hole, h f The thickness of the dielectric film layer, h AR The thickness of the anti-reflection film layer.

[0022] Figure 2 It is the curve of the absorption efficiency of TM polarized light varying with frequency of an embodiment in the range required by the utility model.

[0023] Figure 3 It is the curve of the absorption efficiency varying with Fermi energy level of the embodiment in Figure 2 . DETAILED DESCRIPTION

[0024] The utility model will be further described in connection with the embodiments and the drawings, but should not limit the protection scope of the utility model by this.

[0025] First, refer to Figure 1 , Figure 1 It is the geometric structure of TM polarization two-band tunable spectral selective absorber for THz wave band of the utility model.

[0026] As shown in the figure, this invention relates to a TM polarization tri-band tunable selective absorber based on guided-mode resonance effect for the THz band. It comprises, from top to bottom, a graphene monolayer 2, a hexagonal lattice nanopore array 3, a dielectric thin film layer 4, an antireflective thin film layer 5, and a dielectric substrate 6. The nanopore array consists of a two-dimensional periodic hexagonal lattice nanopore array with periods of 27.9–28.1 μm along the x-axis and 26.8–27.0 μm along the 60° direction. The diameter and thickness of the nanopores are 9.3–9.5 μm and 9.9–10.1 μm, respectively. The thickness of the dielectric thin film layer is 7.9–8.1 μm, and the thickness of the antireflective thin film layer is 5.9–6.1 μm.

[0027] The thickness of a graphene monolayer is h0 = 0.34 nm, and its equivalent dielectric constant is:

[0028]

[0029] Where ε0 is the vacuum simple constant, ω is the angular frequency, and σ(ω) is the surface conductivity of graphene, which satisfies the following conditions at room temperature T = 300 K and in the mid-to-far infrared frequency range. When, based on the approximation of local randomness, it can be expressed as:

[0030]

[0031] in To reduce Planck's constant, E f Here, E is the Fermi level, e is the elementary charge, and τ is the carrier relaxation time. In this patent, τ = 0.1 ps. f =0.15ev.

[0032] In such Figure 1 Under the shown geometry, this invention uses rigorous coupled-wave theory [Prior Art 4] to calculate the absorption efficiency of the TM polarization dual-band spectral selective absorber in the THz frequency range. We optimize it using rigorous coupled-wave theory [Prior Art 5] and simulated annealing [Prior Art 5: W. Goffe et al., J. Econometrics 60, 65-99 (1994)] to obtain this TM polarization tri-band tunable spectral selective absorber.

[0033] The following is a specific embodiment of this invention, in which the refractive indices of the grating ridge and grating groove of the nanopore array are respectively n h =1.5 and n l =1, and its periods on the x-axis and 60° are d respectively. x =28 and d y =0.96*d x= 26.88 microns, diameter and thickness are r = 9.4 and h = 10 microns respectively, thickness of dielectric film layer is h f = 8 microns, thickness of anti-reflection film layer is h AR = 6 microns.

[0034] Table 1 resonance frequency and corresponding absorption efficiency when TM polarized light is incident

[0035]

[0036]

[0037] Table 1 gives a series of embodiments of the present application, in the table, f max1 , f max2 and f max3 represent three peak frequencies of three-band selective absorption spectrum, A min is the minimum value of corresponding peak absorption efficiency, and FWHM represents the maximum value of half peak full width of transmission spectrum.

[0038] Figure 2 is the curve of absorption efficiency of TM polarized light with frequency change of an embodiment in the scope of the present application.

[0039] Figure 3 is the curve of absorption efficiency with Fermi energy level change of the embodiment in Figure 2 .

[0040] In the production of the TM polarized three-band tunable spectral selective absorber based on guided mode resonance effect for THz band of the present application, by appropriately selecting the period of nano-hole array in x-axis and 60° direction, the diameter and thickness of nano-hole, and the thickness of dielectric film layer and anti-reflection film layer, an ultra-narrow band TM polarized three-band tunable spectral selective absorber with narrow absorption spectrum line width and good spatial directivity can be obtained.

[0041] The TM polarized three-band tunable spectral selective absorber of the present application has the advantages of flexible and convenient use, high peak absorption efficiency, extremely narrow half peak full width of absorption spectrum line, and dynamic regulation and control of three-band absorption, etc., is a very ideal absorption device, can be mass-produced at low cost by using electron beam direct writing device combined with microelectronic etching process, and has important practical prospect.

Claims

1. A TM polarized three-band tunable spectral selective absorber based on the effect of guided-mode resonance, characterized in that, The absorber comprises a graphene monolayer (2) from top to bottom, a hexagonal lattice nanopore array (3), a dielectric film layer (4), an antireflection film layer (5) and a dielectric substrate (6); The hexagonal lattice nanopore array (3) is composed of a two-dimensional periodic hexagonal lattice nanopore array, the period in the x-axis is 27.9-28.1 microns, the period in the 60° direction is 26.8-27.0 microns, the diameter of the nanopore is 9.3-9.5 microns, and the thickness of the nanopore is 9.9-10.1 microns; the thickness of the dielectric film layer is 7.9-8.1 microns; the thickness of the antireflection film layer is 5.9-6.1 microns; When TM polarized light is vertically incident, the incident light of the absorber in three narrower frequency ranges is absorbed, the absorption spectrum is shifted with the change of the structure parameters and the incident angle, the peak absorption efficiency changes accordingly, but the absorption at each peak frequency is always higher than 30%, and the full width at half maximum of the absorption spectrum is less than 0.005 THz.

2. The TM-polarized three-band tunable spectral-selective absorber based on the effect of resonant guided modes according to claim 1, characterized in that, The period of the hexagonal lattice nanopore array in the x-axis direction is 28 microns, the period in the 60° direction is 26.88 microns, the diameter of the nanopore is 9.4 microns, and the thickness of the nanopore is 10 microns.

3. The TM-polarization three-band tunable spectral-selective absorber based on the effect of resonant guided modes according to claim 2, characterized in that, The thickness of the dielectric film layer is 8 microns, and the thickness of the antireflection film layer is 6.0 microns.

4. The TM-polarized three-band tunable spectral-selective absorber based on the effect of resonant guided modes according to any of claims 1-3, characterized in that, The graphene monolayer is used to dynamically tune the absorption performance of the absorber by changing its Fermi level.

5. The TM-polarized three-band tunable spectral-selective absorber based on the effect of resonant guided modes according to any of claims 1-3, characterized in that, The dielectric film layer and the antireflection film layer are used to optimize the spectral response of the absorber, improve the absorption efficiency and reduce the reflection.

6. The TM-polarized three-band tunable spectral-selective absorber based on the guided-mode resonance effect according to any one of claims 1-3, characterized in that, The dielectric substrate is used to provide structural support and stability.

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