A metasurface and a preparation method thereof, an optical device and a preparation method thereof

Abstract

The present invention provides a method for fabricating a metasurface based on liquid metal. Micro-nano structures are designed on a dielectric substrate, and liquid metal is coated on the side of the micro-nano structures to form a metasurface based on liquid metal on the dielectric substrate; the contact angle between the liquid metal and the dielectric substrate is greater than 90°, and the micro-nano structures are micro-nano concave holes distributed in an array. By designing the shape, distribution, and size of the micro-nano concave holes, the liquid metal forms a metasurface with a concave structure at the micro-nano concave holes, and the concave structure is a structure formed by the metal metasurface indenting into the metal film. The processing technology of this metasurface is simple, the structure is controllable, and the performance is stable. Based on this method, the present invention also provides a metasurface based on liquid metal, an optical device, and a method for fabricating the same, and the obtained optical device has excellent narrow-band filtering performance.

Description

Technical Field

[0001] The present invention relates to a metasurface and a preparation method thereof, an optical device and a preparation method thereof, belonging to the field of optical materials. Background Art

[0002] Metal surface plasmons have received extensive attention due to their great applications in integrated optoelectronics, photoelectric detection, nanolasers and other fields. Among plasmonic materials, noble metals gold and silver are the two most commonly used materials due to their relatively low losses in the visible and near-infrared bands. However, these two metals have large optical losses, which limit the performance of devices in plasmonic applications, and noble metals are expensive. Therefore, it is urgent to select materials with lower losses and lower costs for replacement. Alkali metal sodium was considered an ideal plasmonic material in the past due to its low interband loss, but due to its high chemical activity, it is very difficult to prepare a stable and smooth metal interface and metal micro-nano structures, making it difficult to realize metal applications such as plasmons.

[0003] Color filters are widely used as important components in devices such as image sensors, liquid crystal displays, light-emitting diodes and optical measurement systems. Among them, plasmonic color filters have received increasing attention in high-resolution and highly integrated optoelectronic devices due to their unique light manipulation ability beyond the diffraction limit. So far, various plasmonic nanostructures, such as composite metal gratings, metal-insulator-metal multilayers and metamaterials, have been proven to have color filtering functions under visible light conditions. Traditional preparation methods for plasmonic devices include physical vapor deposition, electron beam lithography and focused ion beam. However, such top-down preparation processes are prone to cause deformation of device structures and Ohmic losses of metals, and will lead to non-uniform spectral broadening and poor optical contrast of plasmonic color filters, making it difficult to realize large-scale practical applications of plasmonic devices. Summary of the Invention

[0004] In order to form a stable metal metasurface, the present invention provides a preparation method of a metasurface based on liquid metal. The metasurface formed by this method is not affected by the roughness and regularity of the etched surface of the micro-nano structure, and a smooth and stable metal metasurface is formed.

[0005] The technical solution adopted by the present invention is a preparation method of a metasurface based on liquid metal. Micro-nano structures are designed on a dielectric substrate, and liquid metal is coated on the side of the micro-nano structures to form a metasurface based on liquid metal on the dielectric substrate; the contact angle between the liquid metal and the dielectric substrate is greater than 90°, and the micro-nano structures are micro-nano concave holes distributed in an array. By designing the shape, distribution and size of the micro-nano concave holes, the liquid metal forms a metasurface with a concave structure at the micro-nano concave holes, and the concave structure is a structure formed by the metal metasurface recessing into the metal film.

[0006] In a second aspect, the present invention provides a metasurface prepared based on the above preparation method. This metasurface can be applied to optical devices. Thus, in a third aspect, the present invention provides an optical device and its preparation method. The obtained optical device, as a subtractive color filter, has the following advantageous indicators: First, by optimizing the geometric parameters (period, aperture) of the substrate hole array, the adjustable filtering in the visible light band range of 450 nm to 750 nm can be achieved by changing the position of the filtering peak; second, the optical device has a narrow full width at half maximum FWHM (~<20 nm). The full width at half maximum refers to the distance between the two points in a peak of a function where the function values before and after are equal to half of the peak value, and it is used to characterize the width of the peak. In this work, it characterizes the width of the spectral reflection peak. Therefore, this indicator shows that the optical device manufactured by this process has precise filtering performance; then, the optical device has a reflection tilt optical contrast ΔR of ~93%, and ΔR = R baseline -R dip , that is, the baseline reflectivity (100%) minus the bottom reflectivity of the peak. It represents the filtering efficiency of the reflective optical filter. This indicator shows that the optical device manufactured by this process has excellent color filtering performance and filters light of a specific wavelength more thoroughly; finally, the optical device has a matching ratio r / δ as high as 1500. This index can be used to quantify the reproducibility of the optical design by calculating the deviation between the experimental and simulation spectral curves. This indicator shows that the optical device manufactured by this process has good consistency between design and experiment, which is conducive to precise and stable production.

[0007] The beneficial effects produced by the present invention include: (1) On the metasurface obtained by the present invention, there are several concave structures distributed, so that the metal interface does not contact the inner wall of the micro-nano concave holes of the dielectric substrate, preventing uncontrollable factors of the metasurface structure caused by unstable micro-nano hole etching process;

[0008] (2) The present invention realizes the preparation of a stable sodium metasurface through the method of pre-patterned template-induced spin coating forming. The preparation conditions are simple, easy, fast, convenient, low-cost, and highly immune to manufacturing errors or deformations of the substrate; moreover, the sample size can be adjusted, and large-area and large-scale production can be achieved;

[0009] (3) In the present invention, by adjusting the contact angle between the dielectric substrate and the liquid metal, the size, shape, distribution, spin coating process, etc. of the micro-nano concave holes, concave structures of corresponding structures are obtained to achieve corresponding optical properties;

[0010] (4) By using the surface fitting with the dielectric substrate, not only can a metasurface be formed on the side where the metal film contacts the dielectric substrate, but the dielectric substrate can also play a role in isolating air; only by sealing the back with another dielectric substrate after spin coating, it can work stably in the air for a long time, and the prepared metal device can be exposed to the air for long-term use;

[0011] (5) The optical structure device obtained by the present invention has lower optical loss and higher repeatability, solves the problems existing in the structure and performance of plasma devices prepared by traditional methods, and thus meets the usage standards of the narrow-band color filter performance. Description of the Drawings

[0012] Figure 1 Schematic diagram of the concave structure in the present invention;

[0013] Figure 2 Schematic diagram of the spin coating process in the present invention;

[0014] Figure 3 Simulated spectra and experimental spectra of the optical devices obtained in Examples 4-6, Comparative Examples 1-3, and Comparative Examples 4-6;

[0015] Figure 4 Demonstration of the subtractive color filtering performance of the optical device. Detailed Description of the Invention

[0016] The following further elaborates and explains the present invention in detail in conjunction with the specific embodiments, but it should be understood that the protection scope of the present invention is not limited by the specific embodiments.

[0017] The method for preparing the metasurface in the present invention is to coat a liquid metal on a dielectric substrate 2. The dielectric substrate 2 is a hydrophobic structure of the selected liquid metal 1, and the contact angle of the liquid metal 1 on the dielectric substrate 2 is greater than 90°. The dielectric substrate 2 is designed with a micro-nano structure distributed in an array, and the micro-nano structure is a micro-nano concave hole 4. The size, shape, distribution, or any two or three of them of the micro-nano concave hole 4 are designed so that the liquid metal forms a concave structure that depresses towards the metal film side above the micro-nano concave hole 4, that is, the liquid metal does not fill into the micro-nano concave hole 4, and an arc-shaped interface 3 away from the dielectric substrate is formed above the orifice of the micro-nano concave hole 4. As Figure 1 shown, a cavity filled with gas is formed in the micro-nano concave hole 4. The arc-shaped interface 3 does not contact the inner wall of the micro-nano concave hole 4, so it will not be affected by the etching process, and the plasmonic structure of the metal metasurface is stable.

[0018] During the coating process, when the liquid metal formed under normal temperature or high temperature conditions passes through the micro-nano concave holes pre-prepared on the inelastic substrate at a relatively large linear velocity in the plane and a relatively small velocity out of the plane, a certain amount of gas is encapsulated in the holes, and there are two possible structures near the horizontal plane of the substrate. One structure is that the liquid metal fills into the nano-holes, and the other is the concave structure, that is, the liquid metal does not fill the nano-holes and presents a concave morphology above the nano-holes. The concave structure metal metasurface formed by the present invention has a lower surface energy, which can keep the metasurface in a stable structure. According to Young's equation:

[0019] γ LV cosθM = γ SV -γ SL

[0020] where γ LV , γ SV and γ SL are the interfacial free energies between liquid metal / air, substrate / air, and substrate / liquid metal, respectively. When the contact angle is greater than 90°, cosθ M < 0, γ SL > γ SV . Therefore, the surface energy difference between the dome and concave structures will be (γ SL -γ SV )δS > 0, indicating that the concave structure in the present invention is more stable than the dome structure. As Figure 1 shown, δS is the area from the upper edge of the array holes to the circular line formed by the contact of the liquid metal with the substrate, and can also be interpreted as the difference between the lower end face area of the liquid metal forming the cavity and the upper end face area of the micro-nano concave holes.

[0021] The liquid metal in the present invention is obtained by heating solid metal to make it molten, and is a pure metal element. The liquid metal is easily oxidized. Before coating, the solid oxides and impurities on the surface of the molten metal are peeled off to obtain pure liquid metal with a metallic luster. The coating process of the liquid metal is carried out in an inert gas atmosphere. The preferred process environment is that the environmental oxygen concentration is less than 20 ppm and the humidity is less than 20 ppm. More preferably, it is carried out in a glove box filled with inert gas. This environment can prevent the liquid metal from being oxidized and generating impurities during the coating process, thereby forming the performance of the plasmonic metasurface.

[0022] The coating process in the present invention preferably adopts the spin coating process. Specifically, the dielectric substrate with a hole array micro-nano structure is placed on a spin coater and rotated rapidly. The process is as Figure 2 shown. A drop of pure liquid metal 1 is dropped onto the rotating dielectric substrate 2. Once the metal 1 droplet contacts the surface of the rotating dielectric substrate 2, the metal 1 droplet will be coated on the substrate 2 under the strong centrifugal force applied by the rotating dielectric substrate 2 and solidify rapidly, and a metal metasurface with a periodic concave structure is formed. The spin coating speed is preferably 4000 - 8000 r / min. At this speed, it can prevent the liquid metal from condensing during the spin coating process and form a uniform metal film.

[0023] The metal in the present invention can be various metals capable of generating plasmonic effects, preferably sodium, silver, gold or aluminum. Such metals have good plasmonic effects. More preferably, sodium has low interband loss, low cost and low melting temperature on the one hand, which can enable the process flow to be carried out in a low-temperature environment. If other plasmonic metals such as silver are selected, a melting temperature above 1000 °C is required, and spin coating at high temperature is extremely likely to break away from the substrate during rotation and unable to form a uniform periodic structure on the substrate.

[0024] Taking sodium as an example for the temperature of the liquid metal in the present invention, solid sodium is heated and melted, and the temperature of the liquid sodium is 120 °C. At this time, through experiments, the quality of the spin-coated metasurface is good, the interface is complete and the structure is uniform. The micro-nano concave holes are nano-scale micropores, and their sizes play an important role in whether a concave structure can be formed and the size of the concave structure. In the present invention, the micro-nano concave holes are columnar holes, with a pore diameter of 450 - 500 nm and a depth of 120 - 200 nm. If the pore diameter is too large or the depth is too shallow, the liquid metal will directly fill into the nano-holes on the substrate array, resulting in the inability to form a concave structure and unable to obtain a metasurface with a concave structure of the expected shape on the substrate. The preferred period is 600 - 1000 nm, more preferably 600 nm. The dielectric substrate is selected as a silica substrate, and its contact angle with the liquid sodium is 115°, forming a metasurface with a uniform structure.

[0025] The optical device in the present invention is prepared from the metasurface obtained by the above method. The preparation method of the optical device is as follows:

[0026] (1) Prepare a metal metasurface: Design a micro-nano structure on the first dielectric substrate, and coat a liquid metal on the side of the micro-nano structure to form a metal film with a metal metasurface on the first dielectric substrate; the contact angle between the liquid metal and the dielectric substrate is greater than 90°, the micro-nano structure is an array of micro-nano concave holes, and by designing the shape, distribution and size of the micro-nano concave holes, the liquid metal forms a concave structure at the micro-nano concave holes, and the concave structure is distributed on the metal interface of the metal film facing the dielectric substrate, and the concave structure is a structure in which the metal interface is recessed into the metal film;

[0027] (2) Package the metal film: Package the metal film with a second dielectric substrate, and encapsulate the metal film between the first dielectric substrate and the second dielectric substrate.

[0028] The coating process in step (1) and the encapsulation of the second dielectric substrate in step (2) are both carried out in an inert gas atmosphere to prevent the metal material from being oxidized and doped with impurities. The first dielectric substrate and the second dielectric substrate are encapsulated with resin to isolate the metal film from air and ensure the chemical stability of the metal film.

[0029] The present invention forms a metal metasurface with stable structure on a dielectric substrate by comprehensively regulating the contact angle between the liquid metal and the dielectric substrate, the size, shape, spin coating speed and spin coating temperature of the micro-nano structure. The process is simple and the performance is controllable, which can be used for the large-area preparation of surface plasmons. The optical device obtained by using this method for preparing the metal metasurface has high-performance plasma color reduction and color filtering performance. (1) The optical device has a narrow full width at half maximum FWHM (~<20nm), realizing precise light filtering performance; (2) The optical device has a reflection tilt optical contrast ΔR of ~93%, which can filter light of a specific wavelength more thoroughly; (3) The optical device has a matching ratio as high as 1500, with a high reproduction rate of optical design, which is conducive to precise and stable production.

[0030] Example 1

[0031] A method for preparing a metasurface based on liquid metal

[0032] The specific steps are as follows:

[0033] In a glove box filled with inert gas nitrogen, controlling the environmental oxygen concentration to be 0.01 ppm and the humidity to be 0.01 ppm, the following operations are carried out:

[0034] ① Take a sodium block of a certain size and place it in a tungsten boat. Cut off the surface oxide to expose the metallic luster. Then use a heating stage to heat the tungsten boat containing the sodium block to 120 °C to melt it into a liquid state. Use stainless steel tweezers to peel off the oxide and impurities wrapped on the surface of the molten sodium to form a liquid sodium ball with metallic luster;

[0035] ② Put a silica substrate with a hole array having a size period of 600 nm, a pore diameter of 460 nm, and a depth of 200 nm into the glove box and rotate it rapidly on a spin coater. Coating the pure liquid metal sodium on the silica substrate with a periodic structure through a thermal-assisted spin coating process, the sodium liquid is induced on the template to obtain a metasurface with concave structures distributed. The obtained sodium metasurface is evenly arranged and is consistent with the structure shown in the schematic diagram.

[0036] Example 2

[0037] In a glove box filled with inert gas nitrogen, controlling the environmental oxygen concentration to be 0.01 ppm and the humidity to be 0.01 ppm, the following operations are carried out:

[0038] ① Take a potassium block of a certain size and place it in a tungsten boat. Cut off the surface oxide to expose the metallic luster. Then use a heating stage to heat the tungsten boat containing the potassium block to 90 °C to melt it into a liquid state. Use stainless steel tweezers to peel off the oxide and impurities wrapped on the surface of the molten potassium to form a liquid potassium ball with metallic luster;

[0039] ② Place the alumina substrate with a pore array having a size period of 700 nm, a pore diameter of 450 nm, and a depth of 120 nm into the glove box, and rotate it rapidly on a spin coater. Coat the pure liquid metal potassium on the silica substrate with a periodic structure through a thermal-assisted spin coating process. The spin coating speed is 3000 r / min. The potassium liquid is induced on the template to obtain a concave metasurface, and the obtained sodium metasurface is uniformly arranged.

[0040] Example 3

[0041] In the glove box filled with the inert gas nitrogen, control the environmental oxygen concentration to 0.01 ppm and the humidity to 0.01 ppm, and perform the following operations:

[0042] ① Take out a certain size of tin block and place it in a tungsten boat. Cut off the surface oxide to expose the metallic luster. Then use a heating stage to heat the tungsten boat containing the tin block to 300 °C to melt it into a liquid state, forming a liquid tin ball with a metallic luster.

[0043] ② Place the silicon substrate with a pore array having a size period of 800 nm, a pore diameter of 480 nm, and a depth of 150 nm into the glove box, and rotate it rapidly on a spin coater. Coat the pure liquid metal tin on the silica substrate with a periodic structure through a thermal-assisted spin coating process. The spin coating speed is 10000 r / min. The tin liquid is induced on the template to obtain a concave metasurface, and the obtained tin metasurface is uniformly arranged.

[0044] Example 4

[0045] An optical device obtained by using the metasurface in Example 1, and its preparation method includes the following steps

[0046] In the glove box filled with the inert gas nitrogen, control the environmental oxygen concentration to 0.01 ppm and the humidity to 0.01 ppm, and perform the following operations:

[0047] ① Take out a certain size of sodium block and place it in a tungsten boat. Cut off the surface oxide to expose the metallic luster. Then use a heating stage to heat the tungsten boat containing the sodium block to 140 °C to melt it into a liquid state. Use stainless steel forceps to peel off the oxide and impurities wrapped on the surface of the molten sodium to form a liquid sodium ball with a metallic luster.

[0048] ② Place the silica substrate with a pore array having a size period of 600 nm, a pore diameter of 450 nm, and a depth of 120 nm into the glove box, and rotate it rapidly on a spin coater. Coat the pure liquid metal sodium on the silica substrate with a periodic structure through a thermal-assisted spin coating process. The spin coating speed is 6000 r / min. The sodium liquid is induced on the template to obtain a concave metasurface, and the obtained sodium metasurface is uniformly arranged;

[0049] ③Cover the other side of the sodium metasurface with a glass slide, and at the same time, seal the perimeter in contact with the substrate and the glass slide with epoxy resin to obtain a high-performance plasma color subtraction color filter.

[0050] Example 5

[0051] The difference from Example 4 is only that the size period of the substrate is 650 nm.

[0052] Example 6

[0053] The difference from Example 4 is only that the size period of the substrate is 700 nm.

[0054] Technical indicators: Among them, the device with an equal period of 600 nm has the best performance, the color filter bandwidth (full width at half maximum) is only 15 nm, the optical contrast reaches 0.93, and the spectral matching rate reaches 1446.

[0055] Through the comparison of the simulated and experimental reflection spectra of sodium-based metasurfaces with substrate sizes of three periods fabricated in Examples 4 to 6, it is obtained that Figure 3 (a), the dotted line in the figure is the simulated spectrum, and the solid line is the experimental spectrum. It can be seen that the metasurface fabricated by the present invention has a narrow full width at half maximum, good reflection optical contrast (color filter performance) and spectral matching degree.

[0056] Comparative Example 1

[0057] Prepare an optical device by chemical vapor deposition method. The specific steps are as follows:

[0058] 1. Prepare a porous silicon dioxide substrate with a size period of 360 nm, pore diameters of 160 nm respectively, and a depth of 50 nm;

[0059] 2. Evaporate vaporized sodium onto the silicon dioxide substrate by chemical vapor deposition method;

[0060] 3. Cover the other side of the sodium metasurface with a glass slide, and at the same time, seal the perimeter in contact with the substrate and the glass slide with epoxy resin to obtain the corresponding color subtraction color filter.

[0061] Comparative Example 2

[0062] The difference from Comparative Example 1 is only that the pore diameter of the dielectric substrate is 180 nm.

[0063] Comparative Example 3

[0064] The difference from Comparative Example 1 is only that the pore diameter of the dielectric substrate is 200 nm.

[0065] Detect the simulated spectra and experimental reflection spectra (the dotted line is the simulation, and the solid line is the experiment) of three representative sodium-based nanoporous array metasurfaces obtained in Comparative Examples 1 to 3, as Figure 3b. It can be seen that the full width at half maximum of the optical device obtained by this method is 150 nm, and the device has an overly wide full width at half maximum and poor spectral matching.

[0066] Comparative Example 4

[0067] An optical device is prepared by chemical vapor deposition, and the specific steps are as follows:

[0068] 1. Prepare a porous silica substrate with a size period of 460 nm, a pore diameter of 160 nm, and a depth of 50 nm;

[0069] 2. Evaporate vaporized silver onto the silica substrate by chemical vapor deposition;

[0070] 3. Cover the other side of the silver metasurface with a glass slide, and at the same time seal the periphery in contact with the substrate and the glass slide with epoxy resin to obtain the corresponding subtractive color filter.

[0071] Comparative Example 5

[0072] The difference from Comparative Example 4 is only that the size period of the dielectric substrate is 420 nm.

[0073] Comparative Example 6

[0074] The difference from Comparative Example 4 is only that the size period of the dielectric substrate is 350 nm.

[0075] The devices prepared in Comparative Examples 4 - 6 respectively have the simulated and experimental reflection spectra shown in Figure 3 c from top to bottom. The optical contrast is less than 80%, and the filtering is not thorough; the spectral matching degree of the simulation experiment is less than 200, far less than the matching degree in Examples 4 - 6. Therefore, the reproducibility of the device is poor.

[0076] Comparative Example 7

[0077] A method for fabricating a plasma hole array color filter is as follows:

[0078] 1. Evaporate a 150 - nm - thick aluminum film on a 1 - inch square quartz substrate;

[0079] 2. Use a focused ion beam (FIB) with 30 kV and 10 pA to etch the hole array filter, and fabricate 16×16 color - filtering squares with different sizes on one wafer. The period range is 220 - 500 nm, the step size is 40 nm, and the pore diameter range is 80 - 280 nm.

[0080] Comparative Example 8 A plasma filter based on a sub - wavelength metal grating engraved on a substrate - free dielectric film waveguide, and the preparation method is as follows:

[0081] 1. A 25-nm-thick magnesium fluoride dielectric layer was prepared by electron beam evaporation coating on a 100-nm-thick silicon nitride film, and the deposition rate was about 0.1 nm / s;

[0082] 2. Then, a 40-nm-thick aluminum layer was prepared by electron beam evaporation coating thereon, and the deposition rate was about 0.1 nm / s;

[0083] 3. The top aluminum layer was processed into a grating with a duty cycle of 0.6 using a focused ion beam (FIB) with 30 kV and 40 pA.

[0084] The optical devices obtained for the dielectric substrate with a micro-nano concave hole period of 600 nm in Example 4 were compared with the optical devices obtained in Comparative Example 7 and Comparative Example 8. As Figure 4 shown, the comparison was carried out from three aspects: full width at half maximum, optical contrast, and optical design reproducibility. Figure 4 a shows the comparison of the full width at half maximum between Example 4 and Comparative Examples 7 and 8. The FWHM of the device obtained in Example 4 was significantly lower than that in Comparative Examples 7 and 8, indicating that the optical device in Example 4 has precise color filtering performance; Figure 4 b shows the comparison of the optical contrast ΔR between Example 4 and Comparative Examples 7 and 8. The present invention has relatively thorough color separation performance; Figure 4 c shows the comparison of the r / δ parameter between Example 4 and Comparative Examples 7 and 8, which is used to reflect the design spectral matching degree and quantify the optical design reproducibility. Figure 4 c shows that the manufacturing and design of the present invention have a high degree of consistency and strong robustness compared with Comparative Examples 7 and 8, which is convenient for realizing the stable production of devices.

[0085] The above embodiments are only used to illustrate the technical solutions of the present invention and are not restrictive. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for preparing a metasurface based on liquid metal, characterized in that: design a micro-nano structure on a dielectric substrate, and coat liquid metal on the side of the micro-nano structure of the dielectric substrate to form a liquid-metal-based metasurface on the dielectric substrate; the contact angle between the liquid metal and the dielectric substrate is greater than 90°, the micro-nano structure is a micro-nano concave hole, and by designing the shape and size of the micro-nano concave hole, the liquid metal forms a concave structure at the micro-nano concave hole, and the concave structure is a structure formed by the metal interface sinking into the metal film; the specific steps are as follows: a. Design a micro-nano structure on a dielectric substrate, and the micro-nano structure is an array of micro-nano concave holes; b. Heat the solid metal to make it molten to obtain liquid metal, and coat the liquid metal on the substrate with a micro-nano structure in an inert gas atmosphere to form a metal film on the dielectric substrate, and form a metal metasurface on the side of the metal film facing the dielectric substrate, and a number of concave structures corresponding to the micro-nano concave holes are distributed on the metal metasurface; c. Cool to form a metal film and obtain a metal metasurface.

2. The method for preparing a metasurface based on liquid metal according to claim 1, characterized in that: the metal interface at the concave structure is a smooth arc surface.

3. The method for preparing a metasurface based on liquid metal according to claim 1, characterized in that: the micro-nano concave holes are arrayed on the dielectric substrate, and the micro-nano concave holes are nano-scale holes.

4. The method for preparing a metasurface based on liquid metal according to claim 1, characterized in that: the liquid metal satisfies one or more of the following combinations: — The liquid metal is one of sodium, potassium, tin, silver, and aluminum; — The coating temperature of the liquid metal is 98-120 °C; — The coating process of the liquid metal is spin coating.

5. The method for preparing a metasurface based on liquid metal according to claim 1, characterized in that: the metasurface preparation method also satisfies one or both of the following combinations: — The liquid metal is liquid sodium, liquid potassium or liquid tin; — The period of the micro-nano concave hole structure is 600-1000 nm; — The aperture of the micro-nano concave hole is 450-500 nm and the depth is 120-200 nm; — The coating process is spin coating, and the spin coating speed is 2000-10000 r / min.

6. The method for preparing a metasurface based on liquid metal according to claim 1, characterized in that: the contact angle between the liquid metal and the dielectric substrate is greater than 110°.

7. A metasurface prepared by the metasurface preparation method according to any one of claims 1-6.

8. A method for preparing an optical device, characterized in that: comprises the following steps: Fabricating a metallic metasurface: Designing micro-nano structures on a first dielectric substrate, coating a liquid metal on the side of the micro-nano structures, and forming a metal film with a metallic metasurface on the first dielectric substrate; the contact angle between the liquid metal and the dielectric substrate is greater than 90°, the micro-nano structures are micro-nano concave holes distributed in an array, and by designing the shape and size of the micro-nano concave holes, the liquid metal forms a concave structure at the micro-nano concave holes, and the concave structure is distributed on the metal interface of the metal film facing the dielectric substrate, and the concave structure is a structure in which the metal interface is recessed into the metal film; the specific steps are as follows: a. Designing micro-nano structures on a first dielectric substrate, and the micro-nano structures are micro-nano concave holes distributed in an array; b. Heating a solid metal to make it molten to obtain a liquid metal, coating the liquid metal on the substrate provided with the micro-nano structures under an inert gas atmosphere, forming a metal film on the first dielectric substrate, and forming a metallic metasurface on the side of the metal film facing the first dielectric substrate, and a plurality of concave structures corresponding to the micro-nano concave holes are distributed on the metallic metasurface; c. Cooling to form a metal film and obtaining a metallic metasurface; Encapsulating the metal film: Encapsulating the metal film with a second dielectric substrate.

9. According to the method for fabricating an optical device according to claim 8, characterized in that: After the first dielectric substrate and the second dielectric substrate encapsulate the metal film, the metal film is isolated from air.

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