Immersion-tuned visible monochromatic focusing metalens and design method thereof

Abstract

The application discloses a visible light monochromatic focusing superlens with immersion tuning and a design method thereof. The superlens comprises a silicon substrate, a silicon dioxide nanostructure formed on the silicon substrate and a top silicon film covering the top of the silicon dioxide nanostructure and the surface of the silicon substrate, which together form a reflective silicon-silicon dioxide-silicon resonance unit; a plurality of the resonance units form a fixed arrangement of reflective superlenses according to a predetermined focusing phase distribution. y When polarized visible light is vertically incident, the superlens forms monochromatic reflection focusing at a resonance wavelength corresponding to the environment medium, and makes the incident light of non-working wavelength specularly reflect; by placing the superlens in an environment medium with different refractive indexes, the resonance condition and the reflection phase response of the resonance unit are changed, so that the superlens can switch the monochromatic focusing wavelength in the visible light range. The application has the advantages of compact structure, convenient tuning and easy integration, and can be used for dynamic focusing and multispectral imaging.

Description

Technical Field

[0001] This invention relates to the field of micro-nano optics technology, specifically to a liquid-tuned visible light monochromatic focusing superlens and its design method. Background Technology

[0002] Metasurfaces, composed of artificially designed micro / nano units, can modulate the amplitude, phase, and polarization of light at subwavelength scales. As a key application of metasurfaces, superlenses, with their planarity, lightweight nature, and ease of integration, hold significant promise for applications in on-chip imaging, beam shaping, spectral sorting, and micro-microscopic systems. To date, static superlenses have demonstrated a wide range of functionalities, including multifocal focusing, achromatic imaging, and polarization multiplexing. However, once fabricated, the optical response of static superlenses is typically determined by predetermined structural parameters, making it difficult to dynamically change key parameters such as operating wavelength and focal length according to application requirements. To endow single-aperture superlenses with tunability and promote the development of compact, multifunctional chip-scale optical systems, current research typically employs phase-change materials, electrically driven modulation, or mechanical stretching of flexible substrates. While these approaches can achieve a certain degree of focal length or wavelength adjustment, they often face challenges such as complex structures, large external driving systems, and incompatibility with common platforms. Therefore, achieving continuously switchable wavelength focusing through a simple, compact, and easily integrated tuning strategy remains a critical technological challenge that urgently needs to be addressed.

[0003] Furthermore, existing research has reported on dynamically adjusting the optical field, beam deflection, or superlens response by altering the refractive index of the medium surrounding the metasurface through microfluidic channels or liquid wetting. For example, Li et al. reported in Nature Nanotechnology 2022 on introducing liquids with different refractive indices into a microfluidic channel to tune a silicon metasurface and demonstrate an active superlens. Other literature reports on water-immersed metasurface beam deflection and water-based tunable superlenses. These approaches demonstrate that liquid immersion tuning is a feasible technical path, but a technical solution has not yet been presented that uses a silicon-silicon dioxide-silicon reflective cavity, arranges the same fixed reflective silicon-silicon dioxide-silicon resonant unit to selectively reflect and focus across multiple discrete wavelengths of visible light, and makes non-operating wavelengths specularly reflective. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a liquid-tuned visible light monochromatic focusing superlens and its design method. By immersing the superlens in environmental media with different refractive indices, the resonance conditions and reflection phase response of the reflective silicon-silicon dioxide-silicon resonator units in the superlens are changed. This allows the same fixed reflective silicon-silicon dioxide-silicon resonator units to switch operating wavelengths under different environmental media, thereby achieving switching between different monochromatic focusing channels in the visible light range and enabling specular reflection of incident light at non-operating wavelengths.

[0005] To achieve the above objectives, the technical solution of the present invention is as follows: In a first aspect, the present invention provides a liquid-tuned visible light monochromatic focusing superlens, comprising a silicon substrate, a silicon dioxide nanostructure formed on the silicon substrate, and a top silicon film covering the top of the silicon dioxide nanostructure and the surface of the silicon substrate. The silicon substrate, the silicon dioxide nanostructure, and the top silicon film together constitute a reflective silicon-silicon dioxide-silicon resonant unit. A plurality of said reflective silicon-silicon dioxide-silicon resonant units are arranged according to a predetermined phase distribution to form a reflective superlens with a fixed reflective silicon-silicon dioxide-silicon resonant unit layout, so as to perform wavelength-selective reflection and focusing of vertically incident target-polarized visible light, and to mirror-reflect incident light of non-operating wavelengths.

[0006] The top silicon film and the silicon substrate together constitute a silicon-silicon dioxide-silicon reflective cavity. The top silicon film, as the upper high-refractive-index boundary of the reflective cavity, helps enhance the reflection response, form a Fabry-Perot resonance, and increase the sensitivity of the reflection phase to changes in the refractive index of the surrounding medium. When the refractive index of the surrounding medium changes, the equivalent optical path, resonance condition, and reflection phase curve of the reflective silicon-silicon dioxide-silicon resonant unit shift accordingly, thus providing a phase tuning basis for switching the working wavelength of monochromatic focusing. The silicon dioxide nanostructure is rectangular in planar, and its length... L and width W The period is 50-300 nm, with a length less than 350 nm to avoid connecting adjacent units and to retain the spacing, and a length greater than 50 nm to avoid weakening the resonance constraint and phase adjustment capability when the size is too small. In a preferred embodiment, the period of the reflective silicon-silicon dioxide-silicon resonant unit is... P The silica nanostructure is 350 nm high. H The silicon dioxide nanostructure has a length of 350 nm, a top silicon film thickness of 30 nm, and a silicon substrate thickness of 150 nm. The silicon dioxide nanostructure is rectangular in planar shape, and its length... L and width W Selected based on target phase requirements.

[0007] In the preferred embodiment, the length of the rectangular silica nanostructure is changed. L and width W This allows different reflective silicon-silicon dioxide-silicon resonator units to produce different reflection phases and reflectivities. Various reflective silicon-silicon dioxide-silicon resonator units with different length and width parameters were selected to achieve coverage of 2π (i.e., ...) under the initial ambient medium and initial operating wavelength. The reflection phase modulation range is from π to π.

[0008] In a preferred embodiment, nine reflective silicon-silicon dioxide-silicon resonator units with different length and width parameters are selected to achieve 2π coverage at the initial operating wavelength in the initial environment (i.e., The reflection phase range is from π to π, and the continuous spatial phase distribution required for focusing the approximate superlens is discretized using the nine reflective silicon-silicon dioxide-silicon resonant units.

[0009] The plurality of reflective silicon-silicon dioxide-silicon resonant units are arranged according to the spatial phase distribution required for the focusing of the superlens, so that the perpendicularly incident light is reflected by each reflective silicon-silicon dioxide-silicon resonant unit and forms a focal point at a predetermined position. The focusing phase distribution is determined according to the working wavelength and designed focal length of the superlens, and reflective silicon-silicon dioxide-silicon resonant units with corresponding reflection phases are used at different positions, thereby realizing discrete control of the wavefront of the reflected light.

[0010] Secondly, the present invention provides a liquid-tuned visible light monochromatic focusing method. The superlens is placed in a first ambient medium, and the superlens is irradiated with perpendicularly incident target-polarized visible light, causing the superlens to selectively reflect and focus a first working wavelength in the first ambient medium. The superlens is then placed in a second ambient medium with a refractive index different from the first ambient medium, thereby changing the dielectric environment around the reflective silicon-silicon dioxide-silicon resonant unit. Utilizing the changes in equivalent optical path, resonance conditions, and reflection phase response caused by the change in the refractive index of the ambient medium, the resonant wavelength of the reflective silicon-silicon dioxide-silicon resonant unit is shifted, and the superlens forms a spatial phase distribution that satisfies the focusing requirements at the second working wavelength. Thus, the superlens switches from selective focusing on the first working wavelength to selective focusing on the second working wavelength, while simultaneously causing incident light of non-working wavelengths to be mirror-reflected.

[0011] The environmental medium can be air, water, oil, methyl aniline, or other transparent media with different refractive indices. By placing the superlens in the corresponding environmental medium, the operating wavelength can be adjusted without redesigning or fabricating the geometry of the superlens or the arrangement of the reflective silicon-silicon dioxide-silicon resonator units.

[0012] During the design phase, a database of reflectivity and reflection phase is established only for a single initial operating wavelength in an air environment, and based solely on this state, the length... L and width WThe parametric scan results are used to select reflective silicon-silicon dioxide-silicon resonator units and determine their fixed spatial arrangement. After the fixed spatial arrangement is determined, the same superlens is placed in water, methyl aniline, or other transparent liquid environments to calculate its optical response. When the refractive index of the ambient medium increases, the resonance response and reflection phase response of the reflective silicon-silicon dioxide-silicon resonator units shift towards longer wavelengths, thereby causing the focusing response of the fixed spatial arrangement to shift to a new operating wavelength with the resonance.

[0013] In one specific embodiment, the superlens focuses incident light with a wavelength of 475 nm in an air environment, 555 nm in an underwater environment, and 655 nm in a methylaniline environment. The wavelengths of 475 nm, 555 nm, and 655 nm are determined based on the phase coverage, reflectivity, and phase matching with the target focusing of the nine selected reflective silicon-silicon dioxide-silicon resonator units in their respective environmental media. Different environmental media correspond to different focusing wavelength channels, thereby achieving wavelength-selective focusing within the visible light range.

[0014] The incident light is preferably y Polarized light. This is achieved through the design of a reflective silicon-silicon dioxide-silicon resonator unit. y The reflection phase and reflectivity in the polarization direction cause the superlens to... y Wavelength selective focusing is achieved under polarized light illumination.

[0015] Thirdly, the present invention provides a design method for the liquid-tuned visible light monochromatic focusing superlens, comprising the following steps: Step S1: Determine the single initial operating wavelength, superlens diameter, and design focal length in an air environment based on the expected application requirements.

[0016] Step S2: Establish a reflective silicon-silicon dioxide-silicon resonant unit model including a silicon substrate, a silicon dioxide nanostructure, and a top silicon film, and determine the period of the reflective silicon-silicon dioxide-silicon resonant unit, the height of the silicon dioxide nanostructure, the thickness of the top silicon film, and the thickness of the silicon substrate.

[0017] Step S3: Change the length of the silica nanostructure within a preset range. L and width W A single-environment optical response database is established by calculating the reflectivity and reflection phase of reflective silicon-silicon dioxide-silicon resonator units with different geometric parameters in an air environment and at the single initial operating wavelength.

[0018] Step S4: Select multiple reflective silicon-silicon dioxide-silicon resonator units with different geometric parameters from the single-environment optical response database, so that the selected reflective silicon-silicon dioxide-silicon resonator units cover 2π (i.e., ...) under the initial environmental medium and initial operating wavelength. It has a reflection phase range of π to π and a reflectivity that meets the requirements of reflective focusing.

[0019] Step S5: Calculate the required spatial phase distribution of the superlens based solely on the single initial working wavelength and design focal length in the air environment; for each spatial position within the superlens aperture, select the reflective silicon-silicon dioxide-silicon resonant unit from the selected reflective silicon-silicon dioxide-silicon resonant units whose reflection phase is closest to the corresponding target focusing phase under the single initial working wavelength, thus forming a fixed reflective silicon-silicon dioxide-silicon resonant unit layout.

[0020] Step S6: Calculate or test the focusing results of the superlens under different environmental media, determine the focusing wavelength, focal length, focal spot size, focusing efficiency, working wavelength reflectivity and non-working wavelength focal plane light intensity corresponding to each environmental medium, and adjust the geometric parameters and fixed arrangement of the reflective silicon-silicon dioxide-silicon resonator unit according to the calculation or test results.

[0021] In step S5 above, for each spatial position within the aperture of the superlens, the phase deviation between the reflection phase and the corresponding target focusing phase of the candidate nano-reflective silicon-silicon dioxide-silicon resonant unit under each target environmental medium and the corresponding target working wavelength is jointly evaluated, and the nano-reflective silicon-silicon dioxide-silicon resonant unit whose comprehensive phase deviation meets the preset requirements is selected, so that the same fixed arrangement approximates the corresponding focusing phase distribution under different environmental media.

[0022] The above design method also includes calculating or testing the focusing wavelength, focal length, focal spot size, focusing efficiency, working wavelength reflectivity, and focal plane light intensity of the superlens under different environmental media, and adjusting the geometric parameters and fixed arrangement of the nano-reflective silicon-silicon dioxide-silicon resonant unit according to the calculation or test results.

[0023] Compared with the prior art, the advantages and beneficial effects of the present invention are as follows: 1. This invention utilizes the change in refractive index of the environmental medium to adjust the resonant wavelength and reflection phase response of the reflective silicon-silicon dioxide-silicon resonant unit, achieving the switching of the focusing wavelength without changing the geometry of the superlens or the arrangement of the reflective silicon-silicon dioxide-silicon resonant unit.

[0024] 2. This invention can achieve selective reflection and focusing of different wavelength channels within a single aperture, without generating obvious focus at non-target working wavelengths and causing incident light of non-target working wavelengths to be mirror-reflected, which helps to reduce crosstalk between different wavelength channels.

[0025] 3. The initial operating wavelength of this invention in an air environment is determined by the geometric parameters of the reflective silicon-silicon dioxide-silicon resonant unit and the fixed phase arrangement; the operating wavelength after immersion in liquid is determined by the resonant wavelength shift caused by the change in the refractive index of the environmental medium.

[0026] 4. This invention uses common optical materials such as silicon and silicon dioxide, has a simple structure, is compatible with semiconductor manufacturing processes, and has good processing feasibility.

[0027] 5. This superlens platform based on the refractive index adjustment of the environmental medium provides a convenient and easy-to-integrate solution for dynamic focusing, and has broad application prospects in practical fields such as compact dynamic focusing and multispectral imaging.

[0028] 6. In this invention, a reflective silicon-silicon dioxide-silicon resonant unit is selected at a single initial working wavelength in an air environment and a fixed phase arrangement is completed. The focusing working wavelength is switched by utilizing the overall shift of the resonant wavelength and reflection phase response caused by the change of dielectric environment. Attached Figure Description

[0029] Figure 1 This is a schematic diagram illustrating the structure and function of the liquid-tuned visible light monochromatic focusing superlens provided in this embodiment of the invention; Figure 2 This is a schematic diagram of the structure of the nano-reflective silicon-silicon dioxide-silicon resonant unit used in the embodiments of the present invention, including a silicon substrate, a silicon dioxide nanostructure disposed on the silicon substrate, and a top continuous silicon film covering the silicon dioxide nanostructure and the surface of the silicon substrate. L , W and H These represent the length, width, and height of the silica nanostructure, respectively. Figure 3 This is a schematic diagram of the electric field distribution of the reflective silicon-silicon dioxide-silicon resonant unit under different environmental media and different wavelengths in an embodiment of the present invention; n Indicates the refractive index of the surrounding medium; Figure 4 This is a diagram showing the reflectivity and reflection phase distribution of a reflective silicon-silicon dioxide-silicon resonant unit under different geometric parameters in an air environment; among which, Figure 4 a and Figure 4 b represents the results at 475 nm and 561 nm, respectively. The marked positions in the figure indicate the parameters of the representative resonant unit used to construct the superlens. Figure 5 This is a diagram showing the reflectivity and reflection phase distribution of a reflective silicon-silicon dioxide-silicon resonant unit under different geometric parameters in a methylaniline-wetting environment; among them, Figure 5 a and Figure 5 b represents the results at 475 nm and 561 nm, respectively. The marked positions in the figure indicate the parameters of the representative resonant unit used to construct the superlens. Figure 6 These are the reflectivity and phase curves of nine reflective silicon-silicon dioxide-silicon resonant units selected in the embodiments of the present invention under the initial environment and initial operating wavelength. Figure 7 This is a diagram showing the design phase distribution of the superlens of this invention and its corresponding structural arrangement. Figure 8 These are images showing the wavelength-selective focusing results of the superlens in different environmental media in embodiments of the present invention; wherein, Figure 8 a, c, and e represent the focused light field distributions under air, water, and methyl aniline environments, respectively. Figure 8 b, d, and f represent the axial light intensity distributions under the corresponding environments. Detailed Implementation

[0030] To more clearly illustrate the structure of the present invention and the functions it achieves, the present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

[0031] Example 1 This embodiment describes the specific process and performance characterization of enabling the same superlens to selectively focus incident light of different wavelengths under different environmental media by changing the refractive index of the medium surrounding the superlens.

[0032] To more clearly illustrate the structural design and performance of the present invention, this embodiment uses electromagnetic field simulation software to design and optimize the structural parameters and characterize the device performance.

[0033] Figure 1 This is a schematic diagram illustrating the structure and function of a liquid-tuned visible light monochromatic focusing superlens. When the superlens is placed in air, water, and methylaniline environments, it can selectively focus incident light at wavelengths 1, 2, and 3, respectively. As the refractive index of the ambient medium increases, the focusing wavelength of the superlens shifts towards longer wavelengths, thus enabling the same superlens to switch between different monochromatic focusing channels without changing its geometry.

[0034] like Figure 2As shown, the superlens in this embodiment consists of multiple reflective silicon-silicon dioxide-silicon resonant units. Each reflective silicon-silicon dioxide-silicon resonant unit includes a silicon substrate, a silicon dioxide nanostructure formed on the silicon substrate, and a top continuous silicon film covering the top of the silicon dioxide nanostructure and the surface of the silicon substrate. In this embodiment, the period of the reflective silicon-silicon dioxide-silicon resonant unit is... P The height of the silica nanostructure is 350 nm. H The diameter is 350 nm, the top silicon film thickness is 30 nm, and the silicon substrate thickness is 150 nm. The diameter of the superlens is 20 μm; the length of the rectangular silica nanostructure is... L Width is W By changing L and W The reflectivity and reflection phase of the reflective silicon-silicon dioxide-silicon resonant unit can be adjusted. In this embodiment, the incident light is a y-polarized plane wave. The top silicon film and the silicon substrate together form a reflective cavity, which helps to enhance the reflection response, form a Fabry-Perot resonance, and improve the sensitivity of the reflection phase to changes in the refractive index of the ambient medium.

[0035] Figure 3 The electric field distribution of the same reflective silicon-silicon dioxide-silicon resonant unit under different environmental media and different incident wavelengths is shown. Figure 3 The three rows correspond to air, water, and methylaniline environments, respectively, and the three columns correspond to wavelengths 1, 2, and 3. In an air environment, the reflective silicon-silicon dioxide-silicon resonator exhibits a significant electric field enhancement at wavelength 1. When the ambient medium changes to water, the significant resonant response shifts to wavelength 2. When the ambient medium further changes to methylaniline, which has a higher refractive index, the significant resonant response shifts to wavelength 3. This is because the change in the refractive index of the ambient medium alters the equivalent optical path and resonance conditions of the reflective silicon-silicon dioxide-silicon resonator. As the refractive index of the ambient medium increases, the overall resonant response and reflection phase response of the reflective silicon-silicon dioxide-silicon resonator shift towards longer wavelengths.

[0036] Figure 4 and Figure 5 Further examples of different lengths are shown. L and width WThe reflectivity and reflection phase distribution of reflective silicon-silicon dioxide-silicon resonator units under different environmental media and wavelengths are shown, with the left column representing reflectivity and the right column representing reflection phase. During design, the actual phase arrangement uses parameter scanning results under air environment and a single initial operating wavelength of 475 nm. In the initial environmental medium, some reflective silicon-silicon dioxide-silicon resonator units exhibit significant phase changes at the initial operating wavelength, forming the phase gradient required for superlens focusing; at non-operating wavelengths, these reflective silicon-silicon dioxide-silicon resonator units cannot form the same phase matching relationship. When the refractive index of the environmental medium changes, the reflectivity and reflection phase distribution shift overall towards longer wavelengths, causing the phase gradient at the original operating wavelength to no longer satisfy the focusing conditions, while a phase response that satisfies the focusing requirements is formed at the new operating wavelength. Therefore, a fixed... L , W Geometric parameters and a fixed spatial arrangement can approximate the target focusing phase distribution under different tuning states. Immersion tuning does not directly change the incident light wavelength, but rather switches the operating wavelength of the superlens that satisfies the focusing phase condition to another wavelength by changing the dielectric environment around the reflective silicon-silicon dioxide-silicon resonator unit.

[0037] according to Figure 4 and Figure 5 The reflectivity and reflection phase parameter scan results shown indicate that nine representative reflective silicon-silicon dioxide-silicon resonator units of different lengths and widths were selected. For example... Figure 6 As shown, the nine selected reflective silicon-silicon dioxide-silicon resonator units exhibit sequentially varying reflection phases under air conditions and initial operating wavelengths, enabling coverage of 2π (i.e., The reflection phase range is from π to π, while maintaining the reflectivity required for reflective focusing. Nine reflective silicon-silicon dioxide-silicon resonator units correspond to different discrete phase values, used to approximate the continuous phase distribution required for superlens focusing. For example... Figure 7 As shown on the left, the ideal focusing phase distribution of the superlens is obtained based on the above relationship. This phase changes in a ring shape from the center to the edge. Figure 7 As shown on the right, based on the target phase required at each position, from Figure 6 The nine reflective silicon-silicon-oxide-silicon resonator units shown are selected based on their closest phase and the fact that their overall phase deviation meets the preset requirements under other tuning states. These units are then arranged to approximate the continuous ideal phase distribution of each tuning state using the same fixed discrete structure. Consequently, perpendicularly incident light, after being reflected by reflective silicon-silicon-oxide-silicon resonator units at different positions, obtains different reflected phases, which then coherently superimpose at a predetermined position above the superlens to form a focal point.

[0038] When the superlens is in air, the 475 nm incident light forms a distinct focal point above the superlens, with its axial intensity curve showing a clear focused intensity at 5.6 μm; no distinct focal point is formed at wavelengths of 555 nm and 655 nm, as shown below. Figure 8 As shown in a and b in the diagram, the monochromatic focusing wavelength corresponding to the air environment is 475 nm. When the superlens is immersed in water with a refractive index of approximately 1.33, the environmental medium changes the resonance conditions, causing the resonance response and reflection phase response of the reflective silicon-silicon dioxide-silicon resonator to shift towards longer wavelengths. At this time, the 555 nm incident light forms a distinct focus. When the superlens is immersed in methylaniline with a refractive index of approximately 1.58, the working wavelength shifts to 655 nm, and the 655 nm wavelength forms a distinct focus, with its axial intensity curve showing a distinct peak at approximately 4.4 μm. In contrast, the 475 nm and 555 nm incident lights do not form distinct focuses. The target working wavelengths corresponding to different environmental media form distinct focuses, while non-target working wavelengths do not form significant intensity concentrations and are output via specular reflection, thereby achieving low crosstalk switching between different monochromatic focusing channels in the visible light range.

[0039] The air, water, and methyl aniline used in this embodiment are merely one specific implementation method. By reselecting the length and width of the reflective silicon-silicon dioxide-silicon resonator unit and changing different environmental refractive indices, the initial operating wavelength of the superlens, the operating wavelength after immersion, and the corresponding wavelength switching combinations can be changed.

[0040] Finally, it should be noted that the above specific embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A liquid-tuned visible light monochromatic focusing superlens, characterized in that: It includes a silicon substrate, multiple silica nanostructures formed on the silicon substrate, and a top silicon film covering the top of the silica nanostructures and the surface of the silicon substrate; The silicon substrate, silicon dioxide nanostructure, and top silicon film together constitute a reflective silicon-silicon dioxide-silicon resonant unit. Multiple reflective silicon-silicon dioxide-silicon resonant units are arranged according to a predetermined focusing phase distribution corresponding to a single initial working wavelength and a designed focal length under the initial environment to form a reflective superlens. When the target polarized visible light is incident perpendicularly, the reflective superlens forms a reflective focus at the working wavelength corresponding to its surrounding medium, and causes the incident light of non-working wavelengths to be mirrored. By changing the refractive index of the surrounding medium, the resonant wavelength and reflection phase response of the reflective silicon-silicon dioxide-silicon resonant unit are shifted, thereby enabling the fixed superlens to monochromatically focus different visible light working wavelengths under different environmental media. The correspondence between different environments and the shifted operating wavelength was determined by simulation based on the resonant wavelength shift results of the reflective silicon-silicon dioxide-silicon resonant unit.

2. The liquid-tuned visible light monochromatic focusing superlens according to claim 1, characterized in that: The top silicon film is a layer of silicon film continuously deposited on the entire surface of the structure after the silicon dioxide nanostructure is formed on the silicon substrate. The top silicon film covers the top of the silicon dioxide nanostructure and the exposed silicon substrate surface between adjacent silicon dioxide nanostructures, so that the silicon dioxide nano-reflective silicon-silicon dioxide-silicon resonant unit is embedded in the silicon material formed by the top silicon film and the silicon substrate, and together with the silicon substrate and the silicon dioxide nanostructure, forms a reflective cavity.

3. The liquid-tuned visible light monochromatic focusing superlens according to claim 2, characterized in that: The periodicity of the silica nanostructure P ,thickness H The appropriate wavelength is selected based on the operating wavelength; the thickness of the top silicon film is 20-50 nm; and the thickness of the silicon substrate is greater than 100 nm.

4. The liquid-tuned visible light monochromatic focusing superlens according to claim 3, characterized in that: The silica nanostructure is rectangular in planar, and its length is... L and width W The wavelengths are 50-300 nm respectively; the length can be adjusted. L and width W This alters the reflection phase and reflectivity of the reflective silicon-silicon dioxide-silicon resonant unit at the target operating wavelength.

5. The liquid-tuned visible light monochromatic focusing superlens according to claim 4, characterized in that: Multiple reflective silicon-silicon-oxide-silicon resonator units include nine different reflective silicon-silicon-oxide resonator units with varying length and width parameters. These nine reflective silicon-silicon-oxide resonator units provide coverage under the initial ambient medium and initial operating wavelength. The reflection phase range from π to π is used to discretize the continuous phase distribution required for focusing an approximate superlens.

6. The liquid-tuned visible light monochromatic focusing superlens according to claim 5, characterized in that: The continuous phase distribution required for focusing the superlens satisfies the following relationship: ； in, x and y Let be the planar coordinates within the aperture of the superlens, and λ be the operating wavelength in the initial ambient medium. f The design focal length corresponding to the operating wavelength, φ(x,y) This represents the required reflection phase at the corresponding location.

7. The visible light monochromatic focusing superlens tunable by immersion according to any one of claims 1-6, characterized in that: The ambient medium includes air and at least one selected from water or methyl aniline; the refractive indices of the ambient media used for switching the monochromatic focusing wavelength are different.

8. The liquid-tuned visible light monochromatic focusing superlens according to claim 7, characterized in that: exist y Under polarized light incidence, as the refractive index of the ambient medium increases from 1 to 1.58, the focusing wavelength of the superlens shifts from the blue light band to the red light band, with a wavelength tuning range ≤180 nm.

9. The liquid-tuned visible light monochromatic focusing superlens according to claim 8, characterized in that: When the ambient medium is air, water and methylaniline, the superlens having the same fixed reflective silicon-silicon dioxide-silicon resonant unit layout forms monochromatic focusing at wavelengths of 475 nm, 555 nm and 655 nm, respectively; in each ambient medium, the superlens causes the incident light of the corresponding working wavelength to form reflective focusing, and causes the incident light of other non-working wavelengths to be mirror-reflected.

10. A method for designing a liquid-tuned visible light monochromatic focusing superlens, characterized in that: The visible light monochromatic focusing superlens with liquid immersion tuning according to any one of claims 1-9 includes the following steps: S1: Determine the single initial operating wavelength, design focal length, and superlens diameter under the initial environment; S2: Establish a reflective silicon-silicon dioxide-silicon resonant unit model, determine the period of the reflective silicon-silicon dioxide-silicon resonant unit, the height of the silicon dioxide nanostructure, the thickness of the top silicon film, and the thickness of the silicon substrate, and change the length of the silicon dioxide nanostructure within a preset range. L and width W ; S3: Calculate the reflectivity and reflection phase of the reflective silicon-silicon dioxide-silicon resonator unit with each geometric parameter under the initial environment and a single initial operating wavelength, establish a single environment optical response database, and select a variety of reflective silicon-silicon dioxide-silicon resonator units that provide a 2π reflection phase range under a single initial operating wavelength. S4: Calculate the focusing phase distribution under the initial environment based on the single initial working wavelength and the design focal length, and select the reflective silicon-silicon dioxide-silicon resonant unit with the reflection phase closest to the corresponding target focusing phase at each spatial position within the superlens aperture to form a reflective superlens. S5: Place the reflective superlens in multiple target environmental media in sequence. By shifting the resonant wavelength and reflection phase response caused by the change in the refractive index of the environmental media, the monochromatic focusing wavelength of the superlens is switched, and the incident light of the non-working wavelength is reflected by the mirror surface. S6: Calculate the focusing wavelength, focal length, focal spot size, focusing efficiency, working wavelength reflectivity, and focal plane light intensity of the superlens under different environmental media, and adjust the geometric parameters of the reflective silicon-silicon dioxide-silicon resonator and fix the layout of the reflective silicon-silicon dioxide-silicon resonator based on the calculation or test results.

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