Double-layer programmable wavefront modulation metasurface based on phase change material and preparation method thereof
By using a dual-layer programmable wavefront modulated metasurface and combining phase change materials and dielectric nanofin structures, the problems of integration and modulation efficiency in wavefront control of existing optical devices have been solved, and efficient optical function modulation has been achieved.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- INSTITUTE OF PHYSICS CHINESE ACADEMY OF SCIENCES
- Filing Date
- 2023-08-21
- Publication Date
- 2026-07-21
AI Technical Summary
Existing optical devices suffer from problems such as large size, low integration, poor on-chip compatibility, and low modulation efficiency in wavefront control, and single-layer metasurfaces cannot achieve reconfigurability.
A dual-layer programmable wavefront modulated metasurface based on phase change materials is employed. By using a dielectric nanofin structure and a phase change material nanoantenna structure in the supercell, combined with the rotation angle design of an arithmetic sequence, wavefront modulation of incident light is achieved.
It achieves wavefront modulation that is small in size, highly integrated, has good on-chip compatibility, and has high modulation efficiency, enabling effective holographic imaging, focusing, and vortex generation of circularly polarized light in the near-infrared band.
Smart Images
Figure CN117154412B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of micro-nano fabrication. Specifically, this invention relates to a bilayer programmable wavefront-controlled metasurface based on phase change materials and its fabrication method. Background Technology
[0002] Due to the extensive applications of wavefront control in various fields of production and daily life, such as wireless communication, biomedical optics, photonic circuits, and virtual reality, the ability to manipulate wavefronts using optical devices is considered an indispensable capability in modern society.
[0003] Traditional optical devices rely on the propagation and refraction of light to achieve wavefront shaping, which has problems such as large size, low integration, poor on-chip compatibility and low modulation efficiency.
[0004] Metasurfaces are artificial subwavelength structure arrays that manipulate electromagnetic waves through the interaction between the structure and incident light, thereby generating various optical functions. Phase-type metasurfaces are the most important type of metasurface structure. Based on different phase modulation principles, phase-type metasurfaces can be divided into geometric phase metasurfaces, resonant phase metasurfaces, and transmission phase metasurfaces. Among them, achieving PB phase modulation using dielectric nanofin structures is a commonly used scheme for geometric phase metasurfaces. Based on this scheme, wavefront modulation techniques such as holographic imaging and focusing have been proven. For example, Gwanho Yoon et al. (Yoon G, Lee D, Nam KT, et al. Pragmatic metasurface hologram at visible wavelength: the balance between diffraction efficiency and fabrication compatibility[J]. ACSPhotonics, 2017, 5(5): 1643-1647.) successfully achieved holographic imaging in the visible light band using polycrystalline silicon metasurfaces. However, this single-layer metasurface scheme does not have reconfigurable properties, that is, once the structure is fabricated, the generated holographic pattern is fixed and cannot be adjusted later.
[0005] Therefore, there is an urgent need for a compact, programmable wavefront-controlled metasurface with good on-chip compatibility and high modulation efficiency. Summary of the Invention
[0006] Therefore, the purpose of this invention is to provide a bilayer programmable wavefront-controlled metasurface based on phase change materials. The metasurface of this invention is small in size, highly integrated, has good on-chip compatibility, and high modulation efficiency. After sample preparation, the bilayer programmable wavefront-controlled metasurface of this invention can generate a specific phase distribution through encoding according to the desired pattern, thereby generating the required holographic pattern.
[0007] The above-mentioned objective of the present invention is achieved through the following technical solution.
[0008] In the context of this invention, the term "rotation angle" refers to the angle in degrees between the major axis of a structural unit and the horizontal axis on a horizontal plane. For example... Figure 1 As shown in (a), θ represents the rotation angle.
[0009] In the context of this invention, the terms "nanofin subwavelength structure" and "nanoantenna subwavelength structure" both refer to a protruding structure with a cuboid shape.
[0010] In the context of this invention, the term "array" refers to a way of arranging data in rows and columns.
[0011] On the one hand, the present invention provides a bilayer programmable wavefront modulated metasurface based on phase change material, which includes at least one supercell, wherein the supercell includes N structural units arranged in an array, wherein N is 4, 6, 8 or 9;
[0012] The structural units have different rotation angles, and the rotation angles of the structural units form an arithmetic sequence with a common difference of 180 / N degrees.
[0013] The structural unit includes: a substrate; a dielectric nanofin subwavelength structure located on the substrate; and a phase change material nanoantenna subwavelength structure located on the dielectric nanofin subwavelength structure.
[0014] In each supercell, only one structural unit of the phase change material nanoantenna subwavelength structure is composed of amorphous phase change material, while the remaining N-1 structural units of the phase change material nanoantenna subwavelength structure are composed of crystalline phase change material.
[0015] The inventors of this application unexpectedly discovered that when the metasurface is a bilayer metasurface (simultaneously containing a dielectric nanofin subwavelength structure and a phase change material nanoantenna subwavelength structure), and only one of the phase change material nanoantenna subwavelength structures in the structural units of the supercell is amorphous, and the structural units in the supercell have different rotation angles, a metasurface with small size, high integration, good on-chip compatibility, and high modulation efficiency can be obtained. This invention, by controlling the phase transition of the phase change material nanoantenna subwavelength structure in a specific region of the metasurface, can form a specific phase distribution, thereby achieving artificial manipulation of the wavefront of incident light.
[0016] In this invention, the metasurface has programmable unit pixels, enabling wavefront modulation of circularly polarized incident light in the near-infrared band. A dielectric nanofin structure is used to achieve cross-polarization modulation of the incident circularly polarized light, and a phase-change material nanoantenna is used to control the cross-polarization efficiency.
[0017] In this invention, the specific arrangement of the structural units with different rotation angles within the supercell is not particularly limited, as long as the rotation angles of the structural units form an arithmetic sequence with a common difference of 180 / N degrees. For example, in this invention, taking N=4 as an example, the arrangement of the structural units can be as follows: Figure 1 As shown in the dashed box in (b), N1, N2, N3, and N4 are each 45 degrees apart. Of course, the arrangement of the structural units can also be like... Figure 1 In (a), the positions of N3 and N4 are swapped, as shown in the dashed box. That is to say, as long as the rotation angles of these four structural units can form the required arithmetic sequence, the specific arrangement of these four structural units is not important.
[0018] To give another example, in this invention, taking N=6 as an example, the arrangement of each structural unit can be as follows: Figure 7 As shown in (a), N1, N2, N3, N4, N5, and N6 are each 30 degrees apart. Of course, the arrangement of each structural unit can also be like... Figure 7 As shown in (b) (the positions of N4 and N6 are swapped). In this invention, any two structural units can be interchanged. That is, as long as the rotation angles of these 6 structural units can form the required arithmetic sequence, the arrangement of these four structural units is not important.
[0019] Preferably, in the bilayer programmable wavefront modulated metasurface based on phase change material described in this invention, the substrate is selected from one or more of sapphire, quartz, calcium fluoride, zinc oxide and PDMS.
[0020] Preferably, in the bilayer programmable wavefront modulated metasurface based on phase change material described in this invention, the thickness of the substrate ranges from 200 micrometers to 1000 micrometers.
[0021] Preferably, in the bilayer programmable wavefront modulated metasurface based on phase change material described in this invention, the dielectric nanofin subwavelength structure is composed of one or more of the following materials: silicon dioxide, silicon nitride, titanium dioxide, amorphous silicon, zinc oxide, hafnium oxide, gallium arsenide, indium antimonide, single crystal silicon, lithium niobate, and gallium phosphide.
[0022] Preferably, in the bilayer programmable wavefront modulated metasurface based on phase change material described in this invention, the phase change material nanoantenna subwavelength structure is composed of one or more of the following materials: germanium antimony tellurium (GST), antimony sulfide, antimony selenide, antimony telluride, germanium tellurium, and germanium antimony selenide tellurium.
[0023] Preferably, in the bilayer programmable wavefront modulated metasurface based on phase change material described in this invention, the germanium-antimony-tellurium is selected from one or more of Ge2Sb2Te5, Ge3Sb2Te6, GeSb4Te7 and GeSb2Te4.
[0024] Preferably, in the bilayer programmable wavefront modulated metasurface based on phase change material described in this invention, the thickness of the dielectric nanofin subwavelength structure is 100-3000 nm, more preferably 550 nm; the thickness of the phase change material nanoantenna subwavelength structure is 30-600 nm, more preferably 250 nm.
[0025] Preferably, in the bilayer programmable wavefront modulated metasurface based on phase change material described in this invention, the length of the dielectric nanofin subwavelength structure and the phase change material nanoantenna subwavelength structure is 300-1000 nm, more preferably 600 nm; the width is 50-400 nm, more preferably 200 nm; and the period is 400-1100 nm, more preferably 620 nm.
[0026] On the other hand, the present invention provides a method for preparing a bilayer programmable wavefront-controlled metasurface based on phase change material, comprising the following steps:
[0027] (1) Provide a substrate;
[0028] (2) A dielectric layer is formed on the substrate;
[0029] (3) An amorphous phase change material layer is formed on the dielectric layer;
[0030] (4) A photoresist layer is formed on the phase change material layer;
[0031] (5) Design the exposure pattern according to the desired arrangement of structural units in the supercell to expose and develop the photoresist layer;
[0032] (6) A mask layer is formed on the structure formed in step (5);
[0033] (7) The structure formed by dry etching step (6) to obtain a supercell with the desired arrangement of structural units;
[0034] (8) The surface of a specific structural unit in the supercell obtained in step (7) is irradiated by laser direct writing to transform the amorphous phase change material nanoantenna subwavelength structure into a crystalline phase change material nanoantenna subwavelength structure, thereby obtaining the desired bilayer programmable wavefront modulated metasurface based on phase change material.
[0035] Preferably, in the method described in this invention, the dry etching in step (7) is performed by the following methods: reactive ion etching, inductively coupled reactive ion etching, or ion beam etching.
[0036] Preferably, in the method described in this invention, the reactive gases used in the reactive ion etching and inductively coupled reactive ion etching include one or more of fluorine-based gases (CF4, CHF3, SF6), chlorine-based gases (Cl2), bromine-based gases (HBr), and oxygen.
[0037] Preferably, in the method described in this invention, the reactive gas used for ion beam etching is argon.
[0038] Preferably, in the method described in this invention, the mask layer is composed of one or more materials selected from silicon oxide, aluminum oxide, titanium oxide, and silicon nitride.
[0039] Preferably, in the method described in this invention, the formation of the dielectric layer on the substrate in step (2) is performed by the following methods: electron beam evaporation deposition, magnetron sputtering deposition, plasma-enhanced chemical vapor deposition, atomic layer deposition, spin coating, or spray coating.
[0040] Preferably, in the method described in this invention, the formation of an amorphous phase change material layer on the dielectric layer in step (3) is performed by the following methods: electron beam evaporation deposition, magnetron sputtering deposition, plasma-enhanced chemical vapor deposition, atomic layer deposition, spin coating, or spray coating.
[0041] The present invention has the following beneficial effects:
[0042] The metasurface of this invention has programmable unit pixels, enabling wavefront modulation in the near-infrared region (preferably 1100nm-2000nm). The dual-layer programmable wavefront-modulated metasurface exhibits wavefront modulation effects on incident circularly polarized light, including holographic imaging, focusing, and vortex light generation. The all-dielectric dual-layer nanostructure unit, composed of an upper nanoantenna and a lower nanofin, serves as the unit pixel of the dual-layer programmable wavefront-modulated metasurface. Compared to metallic materials such as gold or aluminum structures, the transmission loss of the dual-layer programmable metasurface of this invention is significantly reduced. The nanofins and nanoantennas correspond to the generation of cross-polarization and amplitude modulation of polarized light, respectively. The fabrication method of this invention has advantages such as fast etching speed, high etching selectivity, good steepness, and high aspect ratio. Attached Figure Description
[0043] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings, wherein:
[0044] Figure 1 A schematic diagram of a bilayer programmable wavefront modulated metasurface based on the phase change material GST (germanium antimony tellurium) according to a specific embodiment of the present invention is shown.
[0045] Figure 2 Numerical simulation results of cross-polarization intensity modulation based on phase change material GST according to a specific embodiment of the present invention are shown.
[0046] Figure 3 The flowchart illustrates a process for preparing a cross-polarization intensity modulated sample based on phase change material GST and a bilayer programmable wavefront modulated metasurface based on phase change material GST, according to a specific embodiment of the present invention.
[0047] Figure 4 The image shows a scanning electron microscope (SEM) image and a transmission spectrum of a cross-polarization intensity modulated sample based on the phase change material GST according to a specific embodiment of the present invention.
[0048] Figure 5 The diagram shows the encoding and scanning electron microscope morphology of a bilayer programmable wavefront modulated metasurface based on phase change material GST according to Embodiment 1 of the present invention.
[0049] Figure 6 A schematic diagram of holographic imaging of a bilayer programmable wavefront modulated metasurface based on phase change material GST according to Embodiment 1 of the present invention is shown.
[0050] Figure 7 A schematic diagram showing the arrangement of structural units according to a specific embodiment of the present invention is provided.
[0051] Figure 8 A flowchart of the GS algorithm according to Embodiment 1 of the present invention is shown.
[0052] Figure 9 The diagram shows a holographic image of the desired result, a simulated holographic image of a sample with a specific phase distribution formed by amorphous structural units at selected specific locations in accordance with the technical solution of the present invention, and a simulated holographic image of a sample containing only amorphous structures. Detailed Implementation
[0053] The present invention will be further described in detail below with reference to specific embodiments. The embodiments given are only for illustrating the present invention and are not intended to limit the scope of the present invention.
[0054] The following detailed description, with reference to the accompanying drawings, describes a bilayer programmable wavefront modulated metasurface based on phase change material GST according to a specific embodiment of the present invention.
[0055] like Figure 1 As shown, according to a specific embodiment of the present invention, the substrate of the dual-layer programmable wavefront modulated metasurface based on phase change material GST is quartz, and the subwavelength structural unit array is on the substrate. Figure 1 (a) shows the subwavelength structural unit constituting a two-layer programmable wavefront modulated metasurface based on phase change material GST. It comprises two layers: a lower layer is an α-Si nanofin subwavelength structure, and a GST nanoantenna subwavelength structure sits atop the dielectric nanofin. The α-Si nanofin structure is used to achieve cross-polarization modulation of incident circularly polarized light, while the GST nanoantenna is used to control the cross-polarization efficiency. When circularly polarized light passes through… Figure 1 When the structural unit shown in (a) is subjected to a cross-polarization process (i.e., left (right) rotating light incident, right (left) rotating light exit) and generates an additional phase factor (Pancharatnam-Berry phase, abbreviated as PB phase); the PB phase can be determined by the rotation angle of the structural unit. Specifically, the additional PB phase generated is twice the rotation angle. Figure 1 (b) shows a schematic diagram of a bilayer programmable wavefront modulated metasurface based on phase change material GST. Four structural units with different rotation angles constitute a supercell, and the bilayer programmable wavefront modulated metasurface is formed by the periodic repetition of the supercell.
[0056] When all GST nanoantennas within the supercell are crystalline or amorphous, the cross-polarized light passing through adjacent diagonal units has a phase difference of π (derived from the PB phase), causing destructive interference and significantly reducing the transmissibility of the cross-polarized light. However, when only one structural unit within the supercell contains amorphous GST while the other three are crystalline, the amorphous structural unit (i.e., the structural unit containing the amorphous GST nanoantenna) has a higher cross-polarized transmissibility than the crystalline structural unit. This disrupts the destructive interference balance, resulting in a higher transmissibility and the same additional PB phase as the amorphous structure. Therefore, by selecting a specific region of structural units as amorphous and others as crystalline, a specific phase distribution can be formed for the emitted cross-polarized light, thus achieving wavefront modulation. Figure 1 In the structural diagram shown in (b), the N3 structural unit in the supercell selected by the frame at the top is an amorphous structural unit, while the others are crystalline structural units.
[0057] Figure 2 Numerical simulation results of cross-polarization intensity modulation based on the phase change material GST according to a specific embodiment of the present invention are shown. To demonstrate that the above-mentioned amorphous structural unit has a higher cross-polarization transmittance than the crystalline structural unit, the present invention employs the finite-difference time-domain method to perform numerical simulation of the structure. Figure 2 (a) is a schematic diagram of the simulation structure. Figure 2 (b) and Figure 2 (c) shows the cross-polarization and co-polarization transmission spectra of amorphous and crystalline structural units. As can be seen from the simulation, in the near-infrared wavelength of 1550 nm, the amorphous structural unit has a much higher cross-polarization than the crystalline structural unit.
[0058] Figure 3This document illustrates a flowchart of the preparation of a cross-polarization intensity modulation sample based on phase change material GST and the subsequent fabrication of a bilayer programmable wavefront-controlled metasurface based on GST, according to a specific embodiment of the present invention. The specific preparation process is as follows: First, a quartz substrate is ultrasonically cleaned sequentially with acetone, alcohol, and ultrapure water, and then dried with a nitrogen gun. The dried quartz substrate is then placed on a hot plate at 180°C for further drying. An α-Si layer is grown on the quartz substrate using plasma-enhanced chemical vapor deposition (PECVD). Next, a GST layer is grown using magnetron sputtering deposition. Electron beam positive resist is spin-coated on a coating stage. Electron beam exposure and development are performed to obtain a patterned array structure. Silicon oxide is deposited and dissolved using electron beam evaporation deposition (EBOD) to obtain a silicon oxide mask patterned array. The GST layer and α-Si layer are etched using inductively coupled plasma etching (ICP-E) to obtain the metasurface structure. Finally, the metasurface structure is selectively irradiated using laser direct writing technology, causing the GST to transform from an amorphous state to a crystalline state, thereby controlling the phase transition of the GST nanoantenna in a specific region.
[0059] This invention does not impose any particular limitation on the method of laser direct writing to control the GST phase transition in a specific region. Conventional methods of existing technologies can be used, such as: (1) Wang Q, Rogers ETF, Gholipour B, et al. Optically reconfigurable metasurfaces and photonic devices based on phase change materials[J]. Nature photonics, 2016, 10(1): 60-65. (2) Li P, Yang X, Maß T WW, et al. Reversible optical switching of highly confined phonon–polaritons with an ultrathin phase-change material[J]. Nature materials, 2016, 15(8):870-875. (3) Michel AKU, Zalden P, Chigrin DN, et al. Reversible optical switching of infrared antenna resonances with ultrathin phase-change layers using femtosecond laser pulses[J]. Acs Photonics, 2014, 1(9): 833-839. These existing technologies have also demonstrated that laser direct writing can control the phase transition of GST in selected areas.
[0060] Figure 4 The image shows a scanning electron microscope (SEM) image and a transmission spectrum of a cross-polarization intensity modulated sample based on the phase change material GST according to a specific embodiment of the present invention. Figure 4 (a) is a schematic diagram of a scanning electron microscope of a sample with cross-polarization intensity modulation; Figure 4 (b) and Figure 4 (c) shows the cross-polarization and co-polarization transmission spectra of amorphous and crystalline structural units, proving that amorphous structural units have a much higher cross-polarization rate than crystalline structural units near the near-infrared wavelength of 1550 nm.
[0061] Example 1
[0062] (1) Provide a quartz substrate with a thickness of 0.5 mm;
[0063] (2) An amorphous silicon (α-Si) dielectric layer with a thickness of 550 nanometers is grown on the substrate by plasma-enhanced chemical vapor deposition, wherein the reaction gases required for plasma-enhanced chemical vapor deposition are silane, argon and oxygen, with gas flow rates of 15 sccm, 65 sccm and 250 sccm, respectively, the growth pressure is 11 mTorr, and the RF power and ICP power are 5 watts and 40 watts, respectively.
[0064] (3) An amorphous GST phase change material layer with a thickness of 250 nanometers is grown on the dielectric layer by magnetron sputtering growth technology, wherein the magnetron sputtering growth power is 100 watts and the growth pressure is 7 mTorr;
[0065] (4) A PMMA photoresist layer with a thickness of 400 nanometers is coated on the phase change material layer by spin coating;
[0066] (5) The phase distribution of the holographic image is calculated using the GS algorithm. Further, the amorphous structural units at specific locations in the supercell are determined based on the phase distribution map. The exposure pattern is designed according to the desired arrangement of structural units in the supercell to expose and develop the photoresist layer. Finally, the length and width of the nanofin structural units are 600 nm and 200 nm, respectively, and the period of the structural units is 620 nm.
[0067] (6) A mask layer of SiO2 with a thickness of 130 nanometers is grown on the structure formed in step (5) by electron beam evaporation technology, wherein the electron gun acceleration voltage is 10 kV and the growth temperature is 90℃.
[0068] (7) The structure formed in step (6) is etched using inductively coupled reactive ion etching technology to obtain a supercell with the desired arrangement of structural units. The etching gas used is HBr with a flow rate of 50 sccm, a cavity pressure of 4 mTorr, and RF power and ICP power of 80 W and 750 W, respectively.
[0069] The phase distribution is calculated using the GS algorithm, whose core principle is to approach the optimal solution through multiple iterations. This algorithm is often used in two-dimensional projection holography. A two-dimensional projection holographic image is a Fourier transform of the hologram in the far field; therefore, the inverse diffraction process can be implemented using the inverse Fourier transform method. The specific flow of the GS algorithm is as follows: Figure 8 As shown. Assume the complex amplitude of the holographic image is:
[0070] (1)
[0071] Where A0 and Φ0 represent the target amplitude and phase distribution, respectively. The corresponding hologram can be obtained through inverse Fourier transform:
[0072] (2)
[0073] In general, holograms have uniform amplitudes, so they can be replaced with pure phase-type holograms.
[0074] (3)
[0075] Where arg is the complex phase function. The complex amplitude of the holographic image can then be obtained through Fourier transform:
[0076] (4)
[0077] Further substituting the phase of the holographic image into the target amplitude yields a new complex amplitude distribution for the holographic image:
[0078] (5)
[0079] Substitute G(u,v) into (2)-(5) iteratively until the difference between the holographic image G(u,v) and the target amplitude A0 is reduced to an acceptable level. According to the calculated phase distribution, each pixel in the phase distribution corresponds to a supercell. From each supercell, a structural unit with the same phase as the pixel is selected. This structural unit is amorphous, and the remaining structural units in the supercell are set to crystalline state by laser direct writing irradiation.
[0080] Figure 5 The diagram shows the encoding and scanning electron microscope (SEM) morphology of a bilayer programmable wavefront-controlled metasurface based on the phase change material GST according to Embodiment 1 of the present invention. Figure 5 (a) shows a schematic diagram of selecting specific structural units from a supercell based on the phase distribution (this process is defined as encoding), where the structural units covered by the shaded box are the selected structural units. These structural units are amorphous, and the remaining structural units are crystalline. Since amorphous structural units contribute to the generation of the holographic image, a sample with a specific phase distribution formed by selecting amorphous structural units at specific locations following the above scheme should produce the same holographic image as a sample containing only these amorphous structures. Figure 9 (a) Figure 9 (b) and Figure 9 (c) Showing the desired holographic image, a simulated holographic image of a sample with a specific phase distribution formed by amorphous structural units at selected locations following the above scheme, and a simulated holographic image of a sample containing only these amorphous structures, it can be seen that... Figure 9 (b) and Figure 9 The results in (c) are basically consistent, and also consistent with... Figure 9The holographic image results obtained in (a) are basically consistent with those in (a). Therefore, in this embodiment, amorphous structural units at these specific locations were selected to form a specific phase distribution, and wavefront-modulated metasurface samples containing amorphous structural units were prepared to generate holographic images.
[0081] Figure 6 This diagram illustrates holographic imaging using a dual-layer programmable wavefront-controlled metasurface based on phase-change material GST according to Embodiment 1 of the present invention. The incident circularly polarized light wavelength is 1550 nm. The left image shows the simulation result of the holographic image, and the right image shows the test result of the holographic image, thus demonstrating the holographic imaging function of the metasurface of the present invention.
Claims
1. A bilayer programmable wavefront modulated metasurface based on phase change material, comprising at least one supercell, wherein the supercell comprises N structural units arranged in an array, wherein N is 4, 6, 8 or 9; The structural units have different rotation angles, and the rotation angles of the structural units form an arithmetic sequence with a common difference of 180 / N degrees. The structural unit includes: a substrate; a dielectric nanofin subwavelength structure located on the substrate; and a phase change material nanoantenna subwavelength structure located on the dielectric nanofin subwavelength structure. In each supercell, only one structural unit of the phase change material nanoantenna subwavelength structure is composed of amorphous phase change material, while the remaining N-1 structural units of the phase change material nanoantenna subwavelength structure are composed of crystalline phase change material.
2. The bilayer programmable wavefront-tunable metasurface based on phase change material according to claim 1, wherein, The substrate is selected from one or more of sapphire, quartz, calcium fluoride, zinc oxide and PDMS.
3. The bilayer programmable wavefront-tunable metasurface based on phase change material according to claim 1, wherein, The thickness of the substrate ranges from 200 micrometers to 1000 micrometers.
4. The bilayer programmable wavefront-tunable metasurface based on phase change material according to claim 1, wherein, The dielectric nanofin subwavelength structure is composed of one or more of the following materials: silicon dioxide, silicon nitride, titanium dioxide, amorphous silicon, zinc oxide, hafnium oxide, gallium arsenide, indium antimonide, single crystal silicon, lithium niobate, and gallium phosphide.
5. The bilayer programmable wavefront modulated metasurface based on phase change material according to claim 1, wherein, The phase change material nanoantenna subwavelength structure is composed of one or more of the following materials: germanium antimony tellurium, antimony sulfide, antimony selenide, antimony telluride, germanium tellurium, and germanium antimony selenide tellurium.
6. The bilayer programmable wavefront modulated metasurface based on phase change material according to claim 5, wherein, The germanium, antimony, and tellurium are selected from one or more of Ge2Sb2Te5, Ge3Sb2Te6, GeSb4Te7, and GeSb2Te4.
7. The bilayer programmable wavefront-tunable metasurface based on phase change material according to claim 1, wherein, The thickness of the dielectric nanofin subwavelength structure is 100-3000 nanometers.
8. The bilayer programmable wavefront modulated metasurface based on phase change material according to claim 7, wherein, The thickness of the dielectric nanofin subwavelength structure is 550 nanometers.
9. The bilayer programmable wavefront-tunable metasurface based on phase change material according to claim 1, wherein, The thickness of the phase change material nanoantenna subwavelength structure is 30-600 nanometers.
10. The bilayer programmable wavefront-tunable metasurface based on phase change material according to claim 9, wherein, The thickness of the phase change material nanoantenna subwavelength structure is 250 nanometers.
11. The bilayer programmable wavefront-tunable metasurface based on phase change material according to claim 1, wherein, The length of the dielectric nanofin subwavelength structure and the phase change material nanoantenna subwavelength structure are 300-1000 nm; the width is 50-400 nm; and the period is 400-1100 nm.
12. The bilayer programmable wavefront-tunable metasurface based on phase change material according to claim 11, wherein, The lengths of the dielectric nanofin subwavelength structure and the phase change material nanoantenna subwavelength structure are 600 nanometers.
13. The bilayer programmable wavefront-tunable metasurface based on phase change material according to claim 11, wherein, The width of the dielectric nanofin subwavelength structure and the phase change material nanoantenna subwavelength structure is 200 nanometers.
14. The bilayer programmable wavefront-tunable metasurface based on phase change material according to claim 11, wherein, The period of the dielectric nanofin subwavelength structure and the phase change material nanoantenna subwavelength structure is 620 nanometers.
15. A method for preparing a bilayer programmable wavefront-controlled metasurface based on phase change material according to any one of claims 1-14, comprising the following steps: (1) Provide a substrate; (2) A dielectric layer is formed on the substrate; (3) An amorphous phase change material layer is formed on the dielectric layer; (4) A photoresist layer is formed on the phase change material layer; (5) Design the exposure pattern according to the desired arrangement of structural units in the supercell to expose and develop the photoresist layer; (6) A mask layer is formed on the structure formed in step (5); (7) The structure formed by dry etching step (6) to obtain a supercell with the desired arrangement of structural units; (8) The surface of the structural unit in the supercell obtained in step (7) is irradiated by laser direct writing to transform the amorphous phase change material nanoantenna subwavelength structure into a crystalline phase change material nanoantenna subwavelength structure, thereby obtaining the desired bilayer programmable wavefront modulated metasurface based on phase change material.
16. The method according to claim 15, wherein, The dry etching in step (7) is performed by the following methods: reactive ion etching, inductively coupled reactive ion etching, or ion beam etching.
17. The method according to claim 16, wherein, The reactive gases used in the reactive ion etching and inductively coupled reactive ion etching are selected from one or more of fluorine-based gases, chlorine-based gases, bromine-based gases, and oxygen.
18. The method according to claim 16, wherein, The reaction gas used in the ion beam etching is argon.
19. The method according to claim 15, wherein, The mask layer is composed of one or more materials selected from silicon oxide, aluminum oxide, titanium oxide and silicon nitride.
20. The method of claim 15, wherein, The formation of the dielectric layer on the substrate in step (2) is performed by the following methods: electron beam evaporation deposition, magnetron sputtering deposition, plasma-enhanced chemical vapor deposition, atomic layer deposition, spin coating or spray coating.
21. The method according to claim 15, wherein, The formation of an amorphous phase change material layer on the dielectric layer in step (3) is carried out by the following methods: electron beam evaporation deposition, magnetron sputtering deposition, plasma-enhanced chemical vapor deposition, atomic layer deposition, spin coating or spray coating.