Visible polarized light broadband wave absorbing method based on destructive interference
Through the phase-modulated metasurface structure of trapezoidal dislocation arrangement, the problems of narrow absorption bands and complex design of traditional absorbing materials are solved, and efficient absorption and polarization selectivity of the all-visible light band are achieved. It is suitable for optical stealth, photothermal conversion and other fields.
Patent Information
- Application Number
- CN202410005781.7
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-01-02
- Publication Date
- 2025-07-04
AI Technical Summary
Traditional absorbent materials have problems with narrow absorption frequency bands and weak absorption performance, and the design of supersurface broadband absorbers is complicated, making it difficult to achieve batch processing.
The phase modulated metasurface structure is adopted with trapezoidal dislocation arrangement, and the π phase difference between adjacent units is used to achieve interference destruction. Combined with the metal-die-metal structure, it is prepared through magnetron sputtering and electron beam evaporation processes to achieve efficient absorption of the all visible light band.
It realizes efficient absorption of the all-visible light band, with an average absorption rate of more than 90%, simple process, easy to mass production, has angular robustness and band tunability, and can identify the polarization information of incident light.
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Figure CN120255041A_ABST
Abstract
Description
Technical Field
[0001] The invention relates to geometric optics, nanophotonics, surface plasmon photonics and nanofabrication technology, and in particular to a broadband wave absorbing method based on a phase modulation metasurface. Background Art
[0002] With the development of science and technology, absorbing materials have received extensive attention both in basic research and in engineering applications, and have gradually become an important branch of functional materials. An absorber is a type of device that can absorb incident electromagnetic wave energy and convert it into heat or other forms of energy and lose it. Absorbing devices have demonstrated their application value in many fields. According to the working frequency band, they can be divided into microwave absorbers, terahertz absorbers, infrared absorbers, visible light absorbers, ultraviolet absorbers, etc. Each absorber has a specific application. For example, there are certain requirements for microwave absorbers in application scenarios such as electromagnetic protection, microwave darkrooms, and mobile communications; infrared absorbers can realize infrared filtering, infrared detection, infrared temperature measurement and other functions; terahertz absorbers have certain application value in terahertz frequency selective detection, terahertz sensing, and terahertz thermal imaging; visible light absorbers are used in optical stealth, photothermal conversion, thermal electron emission, solar cells and other fields.
[0003] Traditional absorbing materials are based on the electromagnetic properties of the material itself, effectively converting incident electromagnetic waves into other forms of energy, thereby achieving the purpose of absorbing electromagnetic waves. They are generally composed of base materials and absorbers. There are two principles for the core design of absorbing materials: one is to achieve impedance matching between the material surface and free space, and the other is to maximize the electromagnetic loss of the material. In essence, the ability of a material to absorb electromagnetic waves depends on two parameters, namely the dielectric constant and the magnetic permeability. The real parts of the dielectric constant and the magnetic permeability describe the ability of a substance to store electrical energy and magnetic energy, respectively. Traditional absorbing materials are relatively mature, but they generally have disadvantages such as narrow absorption band and weak absorption performance. Considering the actual engineering applications, "thin, light, wide and strong" have become the difficulties of technological breakthroughs.
[0004] Metasurfaces are two-dimensional electromagnetic materials composed of regularly arranged nanostructures with subwavelength dimensions, which can change parameters such as the phase, amplitude, polarization, and angular momentum of incident light at the interface and have much higher optical modulation capabilities than natural materials. Functionally, metasurfaces can achieve the functions of traditional optical elements, such as focusing imaging, polarization conversion, holographic imaging, broadband absorption, etc.; they can also achieve functions that traditional elements cannot achieve, such as anomalous reflection, nanolasers, etc. In addition, metasurfaces are small in volume, light in weight, simple in process, and easy to process in batches, meeting the current trend of integration and promising to realize a new generation of optical elements. The design of traditional broadband absorbers based on metasurfaces is based on multiple resonances at different wavelengths based on amplitude modulation. Each resonance can absorb one wavelength, so multiple resonances can absorb broadband wavelengths. To achieve the multiple resonance function, metasurfaces require complex structure design and complex manufacturing processes (especially metasurfaces in the visible light band), which on the one hand leads to a lack of regularity in design and on the other hand makes many studies stay at the numerical simulation stage because samples cannot be processed. Summary of the Invention
[0005] In view of the above analysis, the present invention uses a phase modulation metasurface with trapezoidal dislocation arrangement to achieve polarization broadband absorption based on destructive interference, and has angular robustness and band tunability.
[0006] The technical solution provided by the present invention is as follows:
[0007] A method for broadband absorption of visible polarized light based on destructive interference, characterized in that
[0008] (1) A phase modulation metasurface structure is adopted. This metasurface structure is composed of a metal-dielectric-metal structure. The bottom metal substrate can fully reflect incident light to avoid transmission loss; the middle layer is a dielectric layer, which can separate the two layers of metal to form a gap; the top layer is an array of phase modulation units;
[0009] (2) The lattice periods of the phase modulation units in the x and y directions are P x and P y , respectively. The phase modulation units are arranged sequentially in the x direction. However, in the y direction, adjacent phase modulation units are arranged with a dislocation, and the dislocation distance d = P x / 2;
[0010] (3) Under the excitation of normally incident visible light with y - direction polarization, the phase - modulation metasurface generates gap - surface plasmon resonance. The electric field is distributed on both sides of the unit, and the magnetic field is localized in the dielectric layer under the unit. This resonance can make the phase of the outgoing light linearly increase along the x - direction, with the phase - change range increasing from 0 to 2π. There is a half - period misalignment between two adjacent units in the x - direction, so that the phase difference of the outgoing light of adjacent units at the same x - coordinate is π, achieving destructive interference and completing the absorption of incident light in the entire visible - light band.
[0011] The broadband wave - absorbing method of the phase - modulation metasurface proposed by the present invention is based on phase - interference cancellation in principle, which is essentially different from the metasurface based on the resonance - absorption principle. Under the illumination of x - polarized light, the metasurface does not have strong absorption but efficient reflection.
[0012] Furthermore, the metal substrate of the present invention is selected from silver or aluminum materials. It is required that the thickness t1 of the metal substrate is thick enough to avoid transmission loss. It is prepared by magnetron sputtering or electron - beam evaporation.
[0013] In the visible - light band, the middle dielectric layer can be selected from materials such as silicon dioxide, magnesium fluoride, or calcium fluoride. The thickness t of the dielectric layer is about of the incident wavelength and is prepared by magnetron sputtering.
[0014] The phase - modulation unit array is an array of trapezoidal metal structures. The trapezoidal structure is an isosceles trapezoid, a right - angled trapezoid, or an arbitrary trapezoid structure. The trapezoidal - structure array is prepared through steps such as spin - coating (positive photoresist), pre - baking, electron - beam lithography, development, fixing, and post - baking. Through layout design, the lateral dimensions of the isosceles - trapezoid unit are determined: the upper base l1, the lower base l2, and the height h; the unit periods P x and P y in the x - direction and y - direction are determined. Px is between 760 - 860 nm, Py is between 200 - 250 nm, and the misalignment distance d ( = P x / 2) between adjacent trapezoidal units in the y - direction in the x - direction is determined. Finally, the top - layer trapezoidal metal - layer structure is obtained. The thickness of the top - layer metal is 20 nm ≤ t3 ≤ 50 nm, and its material is selected from silver or aluminum in the visible - light band, which can be different from the bottom - layer metal material.
[0015] The present invention has at least the following technical advantages:
[0016] (1) Principle innovation. The metasurface structure of the present invention is based on phase modulation rather than traditional amplitude modulation. By using the phase difference of π between adjacent units, the outgoing light undergoes destructive interference in the near - field.
[0017] (2) Simple implementation. The longitudinal structure of the metasurface of the present invention is a general metal - dielectric - metal structure, which is a simple - to - implement structure.
[0018] (3) The phase modulation unit can be trapezoidal, not limited to an isosceles trapezoid, but also including a right trapezoid and other general trapezoidal structures; as long as they are arranged in a staggered manner, the phase difference of the light emitted from adjacent units can be π, thus achieving near-field interference cancellation.
[0019] (4) Simple process. The processing process of the phase modulation metasurface is simple and general, compatible with modern Si-based CMOS processes, with high processing efficiency and convenient for mass production.
[0020] (5) Wide working band. The phase modulation unit can make the light phase linearly increase from 0 to 2π in the entire visible light band. Therefore, interference cancellation can occur in the entire visible light band in the y direction.
[0021] (6) High absorption efficiency. By adopting the present invention, the average absorption rate in the visible light band based on numerical simulation exceeds 90%, and the average absorption rate value obtained by experimental testing is 76.8%.
[0022] (7) Angular robustness. The high absorption efficiency in the entire visible light band can still be guaranteed when the light incident angle is in the range of -40° to 40°.
[0023] (8) Band tunability. When the metasurface of the present invention is immersed in a liquid environment, since the refractive index increases compared with air, the working band will expand from the visible light band to the near-infrared band.
[0024] (9) Polarization selectivity. The metasurface of the present invention only efficiently absorbs y-direction polarized light and has a high reflectivity for x-direction polarized light, thus being able to identify the polarization information of the incident light. Description of the Drawings
[0025] Figure 1 It is a schematic diagram of the structure and function of the phase modulation metasurface in a specific embodiment of the present invention, where α is the incident plane of y-polarized light, β is the incident plane of x-polarized light, l1 and l2 are the upper and lower bottom sides of the trapezoid respectively, h is the height of the trapezoid, t1, t2, and t3 are the thicknesses of the bottom metal, intermediate dielectric, and top trapezoidal metal respectively, P x ,P y are the unit periods in the x and y directions respectively, and P x / 2 is the misalignment length in the x direction between adjacent trapezoidal units in the y direction.
[0026] Figure 2 is the spectrum based on numerical simulation: a. Reflection spectrum and absorption spectrum of y-polarized light, b. Reflection spectrum of x-polarized light.
[0027] Figure 3Characterization and measured results of the phase modulation metasurface in the specific embodiment of the present invention: a. Scanning electron microscope image of the phase modulation metasurface. b. Measured reflectivity and calculated absorption rate of y-polarized incident light. c. Reflection spectrum excited by x-polarized incident light.
[0028] Figure 4 Shows the angular robustness of the phase modulation metasurface in the specific embodiment of the present invention when the y-z plane serves as the incident plane. a.-b. Simulated and experimental absorption rate results under TM-mode polarized light. c.-d. Simulated and experimental reflectivity results under TE-mode polarized light.
[0029] Figure 5 Shows the angular robustness of the phase modulation metasurface in the specific embodiment of the present invention when the x-z plane serves as the incident plane. a.-b. Simulated and measured absorption spectra under TE-mode polarized light. c.-d. Simulated and measured reflection spectra under TM-mode light beam.
[0030] Figure 6 Simulated reflection spectra of the phase modulation metasurface in the specific embodiment of the present invention under y-polarized and x-polarized incident light when immersed in deionized water. Specific Embodiments
[0031] The present invention will be described in detail below with reference to the accompanying drawings and embodiments. The embodiments are only exemplary and are not intended to limit the design and preparation methods according to the present invention to the materials, patterns, conditions or process parameters described in the embodiments.
[0032] The phase modulation metasurface structure proposed by the present invention is as Figure 1 shown. The bottom metal substrate is made of aluminum material with a thickness t3 of 150 nm; the middle dielectric layer is made of silica material with a thickness t2 of 50 nm; the top layer is an array of metal phase modulation units arranged in a staggered manner, and the material is still aluminum with a thickness t1 of 15 nm. The phase modulation unit is an isosceles trapezoid with an upper base length l1 of 30 nm, a lower base length l2 of 160 nm, and a height h of 600 nm. The lattice period P x is set to 800 nm, and P y is 240 nm. The adjacent trapezoidal units in the y direction are arranged with a half-period length stagger in the x direction, that is, the centerlines of two adjacent isosceles trapezoids differ by d = P x / 2 in the x direction. Under the excitation of y-polarized normal incident light, each trapezoidal unit can linearly increase the phase from 0 to 2π in the entire visible light band. Due to the half-period length stagger between adjacent trapezoidal units in the y direction, the outgoing light will undergo destructive interference, and most of the light is confined to the surface of the phase modulation metasurface, resulting in a very low reflectivity.
[0033] Numerical simulation for optimizing parameters. Parameters such as trapezoidal design, array period, substrate and dielectric layer thickness are optimized through numerical simulation to ensure the working effect of the proposed phase modulation metasurface. Numerical simulation shows that in the visible light band, the average absorption rate of y-polarized light exceeds 90%, as Figure 2 shown in Fig. a. For x-polarized light, there is no strong absorption effect, and the reflectivity fluctuates around 50%, as Figure 2 shown in Fig. b.
[0034] Fabrication and measurement of the phase modulation metasurface in specific embodiments of the present invention.
[0035] Preparation of the metal substrate: By means of magnetron sputtering, at a power of 120 W, sputtering the Al target for 40 min, a 150-nm aluminum thin film can be deposited on a clean Si wafer;
[0036] Preparation of the dielectric layer: At a power of 120 W, sputtering the SiO2 target for 70 min, a 50-nm SiO2 thin film can be obtained on the aluminum film;
[0037] Patterning: Spin-coating the positive photoresist AR-P6200.09 at a speed of 6000 r / s, with a film thickness of about 100 nm, and baking on a hot plate at 150 °C for 1 min. In the Voyager electron beam exposure system, expose at a dose of 210 μC / cm 2 , then soak in the AR600-546 developer for 1 min, soak in the AR 600-60 fixer for 30 s, soak in deionized water for 60 s, and blow dry.
[0038] Preparation of the top layer metal: Evaporate a 15-nm aluminum film by an electron beam coater at a vacuum of 10 -8 Torr, then soak in the AR 600-71 stripping solution for 60 min, ultrasonicate for 1 min, and finally wash with deionized water and blow dry.
[0039] Characterization: Observe the sample using a scanning electron microscope, as Figure 3 shown in Fig. a, to evaluate whether the sample matches the design.
[0040] Spectral test: Figure 3 Fig. b shows the reflection spectrum and absorption spectrum under normal incidence of y-polarized light. Due to factors such as sample processing errors and rough sample surfaces, the measured absorption rate is less than the simulation result, and the average absorption rate in the visible light band is 76.8%. Figure 3 Fig. c shows the reflection spectrum under normal incidence of x-polarized light, and the average reflectivity in the visible light band is 56.4%.
[0041] Angle robustness test.
[0042] When the y-z plane serves as the incident plane, the incident angle gradually increases from 10° to 40° at intervals of 10°. Due to the axial symmetry of the structure, we only need to measure the cases of positive-angle incidence. When the polarization direction is parallel to the incident plane, that is, when the incident light is a transverse magnetic wave, the proposed phase modulation metasurface can efficiently absorb the incident light, as shown in Figure 4 a and Figure 4 b, which respectively show the corresponding simulation and experimental results; when the polarization direction is perpendicular to the incident plane, that is, when the incident light is a transverse electric wave, the proposed phase modulation metasurface can efficiently reflect the incident light, as shown in Figure 4 c and Figure 4 d;
[0043] When the x-z plane serves as the incident plane, the incident angle increases from -40° to 40° at intervals of 10°. For the incident transverse electric wave, the simulation results show that within this angle range, the proposed phase modulation metasurface can still effectively absorb the incident light ( Figure 5 a), and in addition, the absorption spectra excited by symmetric angles are exactly the same. The measured results are shown in Figure 5 b, which are in good agreement with the simulation results but slightly lower. For the incident transverse magnetic wave, the simulation and measured results show that within this angle range, the proposed phase modulation metasurface still has a high reflectivity ( Figure 5 c and Figure 5 d).
[0044] Adopt the wavelength tunability of the present invention. As shown in Figure 6 , when the proposed phase modulation metasurface is immersed in deionized water, its effective absorption band for y-polarized light increases to part of the near-infrared light on the basis of the full visible light band, that is, the 400 - 900 nm band, with tunability.
[0045] Although the embodiments of the present invention have been shown and described, those of ordinary skill in the art can understand that various changes, modifications, substitutions, and variations can be made to the embodiments without departing from the principles and purposes of the present invention. The scope of the present invention is defined by the claims and their equivalents.
Claims
1. A broadband absorption method for visible polarized light based on interference cancellation, characterized in that 1) A phase modulation metasurface structure is adopted. This metasurface structure is composed of a metal-dielectric-metal structure. The bottom metal reflects the incident light; the middle dielectric layer separates the two metal layers to form a gap; the top metal is an array of phase modulation units. 2) The lattice periods of the phase modulation unit in the x and y directions are P x and P y respectively. The phase modulation units are arranged in sequence in the x direction. However, in the y direction, adjacent phase modulation units are arranged in a staggered manner, and the staggering distance d = P x / 2; 3) There is a normally incident visible light polarized in the y direction on the phase modulation metasurface. The phase difference of the light emitted by adjacent phase modulation units at the same x coordinate is π, realizing interference cancellation and completing the absorption of incident light in the entire visible light band.
2. The method for broadband absorption of visible polarized light based on interference cancellation according to claim 1, characterized in that, The bottom metal is selected from silver or aluminum materials; the thickness t1 of this metal layer ranges from greater than 100 nm.
3. The visible polarized light broadband wave absorption method based on interference cancellation according to claim 1, characterized in that, The intermediate dielectric layer is made of silicon dioxide, magnesium fluoride or calcium fluoride materials, and the thickness t2 of the dielectric layer is 4. The method for broadband absorption of visible polarized light based on interference cancellation according to claim 1, wherein The thickness of the top metal is 20 nm ≤ t3 ≤ 50 nm.
5. The method for broadband absorption of visible polarized light based on interference cancellation according to claim 1, wherein The phase modulation unit is a trapezoidal metal layer.
6. The visible polarized light broadband wave absorption method based on interference cancellation as claimed in claim 5, wherein, The trapezoidal metal layer is an isosceles trapezoid, a right trapezoid or other trapezoidal structures.
7. The method for broadband absorption of visible polarized light based on interference cancellation according to claim 1, wherein, Put the phase modulation metasurface structure into an environment other than water or air, and use the new environmental refractive index to expand the incident visible light into the near-infrared band.