A cross-band multifunctional metasurface and a design method thereof

Abstract

The application discloses a kind of cross-band multifunctional super surfaces and its design method.The design method includes: S1: determining target optical function and at least two target wavelengths;S2: according to the target optical function, the phase function corresponding to at least two target wavelengths under different circular polarization states is calculated;For the target wavelength and its phase function, the parameters of the optimization unit structure are corresponded respectively;S3: construct wavelength-selective spatial mask, so that the super surface realizes confocal multi-channel regulation;S4: according to the layout of the sub-block and the parameters of the unit structure, generate super surface.The super surface and its design method in the application adopt single-layer structure, realize high numerical aperture, high efficiency, cross-band, confocal multi-channel, multifunctional regulation.

Description

Technical Field

[0001] This invention relates to the field of micro-nano optics and metasurface technology, specifically to a multi-band multifunctional metasurface and its design method. Background Technology

[0002] Different wavelengths of light have different refractive indices in the same medium, resulting in dispersion and causing light of different wavelengths to focus at different positions. Traditional lenses control the emitted light by varying the surface curvature and lens thickness. Eliminating chromatic aberration using traditional lenses requires a precise combination of multiple lenses, making the optical system bulky and complex to manufacture. In 2011, Professor Capasso proposed the generalized Snell's law, laying the foundation for the development of metasurfaces. Metasurfaces, through periodically arranged artificial unit structures, control the amplitude, polarization, and phase of incident electromagnetic waves, providing a new avenue for the miniaturization of future smart products. Despite rapid progress in metasurfaces, the field still faces challenges, such as the achromatic wavelength range, the trade-off between metasurface size and high numerical aperture, and the consideration of balancing the precision of micro / nano fabrication techniques with the complexity of metasurface structures.

[0003] For the design of discrete wavelength achromatic metasurfaces, there are currently two main technical solutions: region partitioning of single-layer metasurfaces and cascade design of multi-layer metasurfaces.

[0004] The single-layer metasurface region partitioning method divides the metasurface into two regions, both with the same period, and uses geometric phase modulation to focus light of two wavelengths onto the same focal plane, achieving dual-wavelength achromatic focusing. This method has a simple structure, but each wavelength only utilizes a portion of the metasurface's aperture, resulting in low energy efficiency. Furthermore, its functionality is fixed; once designed, it can only achieve achromatic focusing and cannot switch to other optical functions as needed.

[0005] The cascaded design of multilayer metasurfaces involves stacking two or more metasurfaces, each designed independently, and achieving a wider dispersion compensation range through phase superposition. This approach can achieve achromatic focusing with higher numerical apertures, but it requires nanoscale precision alignment between multiple layers, resulting in complex and costly manufacturing processes, and is sensitive to interlayer thickness and parallelism.

[0006] In summary, existing technologies suffer from the following problems: traditional achromatic lenses are large and costly; while single-layer metasurface region partitioning offers a relatively simple structure, it utilizes only a portion of the aperture for each wavelength, resulting in low energy efficiency and fixed functionality; and multi-layer metasurface cascading methods are complex to manufacture and difficult to align. Therefore, there is an urgent need for an achromatic metasurface that can achieve cross-band, high-efficiency, multi-functional, and switchable operation within a single-layer structure. Summary of the Invention

[0007] Therefore, the technical problems to be solved by this invention include: using a single-layer metasurface to achieve high numerical aperture visible-near-infrared dual-wavelength achromatic light, so as to overcome the defects of traditional achromatic lenses being large in size and complex in the manufacturing of multi-layer metasurfaces; achieving achromatic light while realizing achromatic light through polarization control, so as to solve the problem of existing achromatic metasurfaces having only one function and being unable to dynamically switch functions; and simplifying the unit structure design and reducing the amount of calculation for unit structure optimization, so as to improve design efficiency.

[0008] To address the aforementioned technical problems, in a first aspect, the present invention provides a design method for a multi-band multifunctional metasurface. The method includes: S1, determining the target optical function and at least two target wavelengths; S2, calculating the phase functions corresponding to the at least two target wavelengths under different circular polarization states based on the target optical function; optimizing the parameters of the unit structure for each target wavelength and its phase function; S3, constructing a wavelength-selective spatial mask: dividing the substrate into at least two spatially alternating sub-blocks, wherein each of the at least two sub-blocks contains a corresponding unit structure, and the at least two sub-blocks are configured to apply different phase distributions to incident light with different wavelengths and different circular polarization states, and to focus transmitted light of different wavelengths onto the same focal plane to achieve confocal multi-channel control; S4: generating a multi-band multifunctional metasurface based on the layout of the sub-blocks and the parameters of the unit structure.

[0009] In one embodiment of the present invention, in step S3, the metasurface is configured to exhibit at least one optical function selected from bright-field imaging, holographic display, vortex beam generation, and edge detection when incident light of different wavelengths and different circular polarization states is incident.

[0010] In one embodiment of the present invention, the at least two target wavelengths in step S1 include a first target wavelength and a second target wavelength, and the at least two sub-blocks in step S3 include a first sub-block and a second sub-block. A first unit structure is arranged in the first sub-block, and a second unit structure is arranged in the second sub-block. The first unit structure in the first sub-block matches the first target wavelength, and the second unit structure in the second sub-block matches the second target wavelength.

[0011] In one embodiment of the present invention, the period of the arrangement of the first unit structure in the first sub-block is set to be twice the period of the arrangement of the second unit structure in the second sub-block.

[0012] In one embodiment of the present invention, step S3 encodes the phase functions corresponding to different circularly polarized states at the first wavelength into the first sub-block through spin decoupling, and encodes the phase functions corresponding to different circularly polarized states at the second wavelength into the second sub-block through spin decoupling. Then, the phase profiles formed by the first sub-block and the second sub-block are combined to obtain the final phase profile, so that the sub-blocks are configured to apply different phase distributions to incident light with different wavelengths and different circularly polarized states, thereby obtaining a metasurface with confocal multi-channel control.

[0013] In one embodiment of the present invention, the optimization of the unit structure parameters in step S2 satisfies at least the following relationship:

[0014]

[0015] This relationship satisfies the Nyquist criterion. Where NA is the numerical aperture of the metasurface, and P j Let H be the period of the unit structure, H be the height of the unit structure, and G be the period of the unit structure. j The reciprocal lattice vector, For the effective dielectric constant, For a given wavelength, Transmittance is the same polarization. This represents the cross-polarization transmittance.

[0016] In one embodiment of the present invention, in step S2, for the first target wavelength Second target wavelength In different circular polarization states The phase functions generated by the metasurfaces Represented as:

[0017]

[0018] in , , and Wavelength and The ideal phase mask corresponding to the two orthogonal spin states.

[0019] Secondly, a multi-band multifunctional metasurface of the present invention is manufactured using the above-described design method, comprising a substrate and a plurality of unit structures disposed on the substrate; the plurality of unit structures are divided into at least two types of sub-blocks arranged alternately in space, wherein the unit structures in different sub-blocks have periods that are respectively matched to different wavelengths, and the at least two types of sub-blocks are configured to apply different phase distributions to incident light with different wavelengths and different circular polarization states, and to focus transmitted light of different wavelengths onto the same focal plane.

[0020] In one embodiment of the present invention, at least two types of sub-blocks are arranged alternately in a checkerboard pattern in space, and the unit structure is an anisotropic nano-unit structure, with a unit structure independently provided at each spatial location of the substrate.

[0021] In one embodiment of the present invention, the material of the unit structure is a high-dielectric material with high transmittance that matches different wavelengths.

[0022] Compared with the prior art, the above-described technical solution of the present invention has the following advantages:

[0023] 1. Achieved cross-band dual-wavelength achromaticity with focusing performance close to the diffraction limit: This invention proposes a double-period unit structure design. By setting the period of different sub-blocks to match different wavelengths, each sub-block has high transmittance for its target wavelength and low transmittance for non-target wavelengths, thereby achieving wavelength-selective achromaticity.

[0024] 2. A wavelength-selective checkerboard spatial mask is proposed: This invention proposes a novel checkerboard spatial mask in which two sub-blocks with different periods are arranged alternately in space. This spatial mask has wavelength selectivity, which can effectively separate optical field channels of different wavelengths, while suppressing crosstalk between wavelengths. Moreover, the size of the sub-blocks can be arbitrarily set according to design requirements, which provides high design flexibility.

[0025] 3. Multifunctional switching achieved through checkerboard spatial mask and polarization synergistic control: This invention utilizes the spin dependence of geometric phase. By designing the in-plane rotation angle of the nanopillars within each sub-block, combined with a checkerboard spatial mask, the same metasurface produces completely different phase responses to incident light of different wavelengths and circular polarization states. Therefore, by simply switching the wavelength and circular polarization state of the incident light, the metasurface can freely switch between different optical functions, such as bright-field imaging, holographic display, vortex beam generation, and edge detection. This characteristic overcomes the shortcomings of existing achromatic metasurfaces, which are limited to single functions and cannot be dynamically adjusted. Attached Figure Description

[0026] To make the content of this invention easier to understand, the invention will be further described in detail below with reference to specific embodiments and accompanying drawings.

[0027] Figure 1 This is a schematic diagram of the region division of a single-layer metasurface in the prior art of this invention, wherein, Figure 1 (a) is a schematic diagram of a dual-wavelength achromatic polarization-dependent bifocal superlens; Figure 1 (b) is a unit structure composed of silicon nanopillars on a glass substrate; Figure 1 (c) shows the spatial distribution of the two unit structures;

[0028] Figure 2 This is a schematic diagram of the cascade design of multilayer metasurfaces in the prior art of this invention, wherein, Figure 2 (a) is a schematic diagram of the unit structure of the first layer of the metasurface; Figure 2 (b) is a schematic diagram of the unit structure of the second layer of the metasurface; Figure 2 (c) is a schematic diagram of a two-layer metasurface focusing structure;

[0029] Figure 3 This is a schematic diagram of the cross-band multifunctional metasurface of the present invention;

[0030] Figure 4 This is an optimized schematic diagram of the unit structure of the present invention, wherein, Figure 4 (a) shows the geometric parameters of type A and type B a-Si:H unit structures on a SiO2 substrate and the corresponding optical modulation principle; Figure 4 (b) shows the variation of the transmission coefficient of the type A structure with the period and angle; Figure 4 (c) shows the relationship between the transmission coefficient and the structural dimensions of the type A structure; Figure 4 (d) is the transmission coefficient of the optimized A-type structure; Figure 4 (e) shows the variation of the transmission coefficient of the type B structure with period and angle; Figure 4 (f) shows the relationship between the transmission coefficient and the structural dimensions of the type B structure; Figure 4 (g) represents the transmission coefficient of the optimized B-type structure;

[0031] Figure 5 This is a schematic diagram of the geometric optimization and spin-related phase response of the unit structure of the present invention, wherein, Figure 5 (a) shows the relationship between the copolarization transmission efficiency of the unit structure and the length and width of the nanopillar at a wavelength of 1030 nm; Figure 5 (b) is the functional response of the phase, period and in-plane rotation angle of the cross-polarization component; Figure 5 (c) shows the angle and phase relationship corresponding to the white line in b; Figure 5 (d) shows the relationship between the copolarization transmission efficiency of the unit structure and the length and width of the nanopillar at a wavelength of 532 nm; Figure 5 (e) is the functional response of the phase, period and in-plane rotation angle of the cross-polarization component; Figure 5 (f) represents the angle and phase relationship corresponding to the white line in e;

[0032] Figure 6 This is a conceptual design and phase map implementation diagram of a cross-band multifunctional metasurface according to the present invention;

[0033] Figure 7 This is the invention Figure 6 A schematic diagram of the simulated optical properties of the surface of the Chinese Super League, in which, Figure 7(a) and Figure 7 (c) is a bright field and edge-enhanced focal image of right-hand circularly polarized incident light at wavelengths of 532 nm and 1030 nm, and the corresponding center intensity distribution; Figure 7 (b) and Figure 7 (d) Holographic images of right-handed circularly polarized incident light at wavelengths of 532 nm and 1030 nm; Figure 7 (e) is the axially normalized intensity distribution diagram under left-handed circularly polarized light incidence. Scale bar: Figure 7 (a) and Figure 7 (c) is 5µm. Figure 7 (b) and Figure 7 (d) is 25µm and Figure 7 (e) is 15µm;

[0034] Figure 8 This is a conceptual design and phase map implementation diagram of another cross-band multifunctional metasurface of the present invention;

[0035] Figure 9 This is the invention Figure 8 A schematic diagram of the simulated optical properties of the surface of the Chinese Super League, in which, Figure 9 (a) shows the point spread function and its corresponding center intercept when LCP is incident. The upper left figure is at a wavelength of 532nm, and the lower left figure is at a wavelength of 1030nm. Figure 9 (b) shows the point spread function and its corresponding center intercept when RCP is incident. The upper left figure is for a wavelength of 532 nm, and the lower left figure is for a wavelength of 1030 nm. Figure 9 (c) and Figure 9 (d) shows the axially normalized intensity distribution at two wavelengths under LCP and RCP incident conditions. Scale bar: Figure 9 (a) and Figure 9 (b) is 5µm and Figure 9 (c) and Figure 9 (d) 15µm;

[0036] Explanation of reference numerals in the accompanying drawings: 1. Substrate; 20. Sub-block; 21. First sub-block; 22. Second sub-block; 200. Unit structure. Detailed Implementation

[0037] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, so that those skilled in the art can better understand and implement the present invention. However, the embodiments described are not intended to limit the present invention.

[0038] Example 1:

[0039] A method for region partitioning of a single-layer metasurface in the prior art is as follows:

[0040] like Figure 1As shown in (c), the metasurface is divided into inner and outer regions, each employing two unit structures with the same period. Based on geometric phase modulation, achromatic focusing of two wavelengths can be achieved simultaneously. The unit structure in the inner region is optimized for the first wavelength (e.g., 1000 nm), while the unit structure in the outer region is optimized for the second wavelength (e.g., 1550 nm). When the incident light contains two wavelengths, the first wavelength is primarily focused by the inner region, and the second wavelength is primarily focused by the outer region, both focusing onto the same focal plane (see...). Figure 1 (a) This method has a simple structure, but it only utilizes a portion of the aperture for each wavelength, resulting in low energy efficiency. Furthermore, its functionality is fixed (it can only achieve achromatic focusing) and cannot achieve multi-functional switching.

[0041] A cascaded design of multilayer metasurfaces in the prior art is as follows:

[0042] Figure 2 This paper presents a transmission-based achromatic metasurface operating in deep ultraviolet (266 nm) and visible light (532 nm) wavelengths, employing a two-layer structure design. The substrate is silica, with the first layer of hafnium dioxide (HfO2) nanopillars exposed to air, and the second layer of hafnium dioxide circular nanopillars embedded in a glass-based silica film. The height and diameter of the nanopillars on different metasurface layers are independently controlled. Optimized calculations yield the overall phase distribution of the two-layer structure, where the total phase at each location equals the sum of the phases of all layers. This method offers a wider dispersion compensation range and enables achromatic focusing with higher numerical apertures, but requires nanoscale precision alignment between the two layers, resulting in complex and costly manufacturing processes, and sensitivity to interlayer thickness and parallelism.

[0043] Based on existing technologies, this application utilizes the following working principle of a cross-band multifunctional metasurface to achieve wavelength-selective achromatic metasurface design through unit structure design, and realizes multifunctional conversion through a combination of checkerboard spatial masking and polarization multiplexing. The working principle of the cross-band multifunctional metasurface is as follows:

[0044] When considering a circularly polarized electromagnetic wave with spin λ (spin represents the rotation direction of circular polarization, corresponding to left-handed and right-handed circular polarization respectively) and wavelength λ is incident perpendicularly, with the xz plane as the incident plane, the incident electric field can be mathematically expressed as:

[0045]

[0046] Where E0 is the amplitude. It is a polarization unit vector. Let be the wave number. A single-layer metasurface of radius R located at z=0 can be defined by the space-varying Jones operator. It means that, among them Represents the horizontal coordinate. Under the Fresnel approximation, the transmitted field on the observation plane (e.g., the focal plane) is expressed as:

[0047]

[0048] in, To observe the transverse wave vector on the surface, i.e. and As can be seen from the above equation, the optical response of a metasurface is essentially a spin- and wavelength-dependent Jones operator. The Fourier transform of the Jones operator. Spin ( ) and wavelength ( Selective encoding enables confocal multi-channel modulation, meaning that under the incidence of incident light with different wavelengths and circular polarization states, the metasurface can produce different optical functions (such as bright-field imaging, holographic display, vortex beams, etc.) on the same focal plane.

[0049] Based on the above principles, this application designs a checkerboard spatial mask with wavelength selectivity and spin decoupling (i.e., alternating sub-blocks with periodic matching of different wavelengths, and the in-plane rotation angle of the unit structure within the sub-block changes with position) so that the spectral degrees of freedom can be controlled in an effective way, and multi-wavelength, multi-polarization, multi-functional, confocal optical field modulation can be achieved on a single device.

[0050] Example 2:

[0051] Based on the above principles, one embodiment of the design method for cross-band multifunctional metasurfaces of the present invention includes:

[0052] S1: Determine the target optical function and at least two different target wavelengths;

[0053] S2: Based on the target optical function, calculate the phase function corresponding to at least two target wavelengths under different circular polarization states; optimize the parameters of the unit structure for each target wavelength and its phase function.

[0054] Specifically, the phase function corresponding to the target wavelength includes the phases of both left-handed and right-handed circularly polarized light, and the in-plane rotation angle of the unit structure is determined by the phase function.

[0055] Specifically, the parameters of the unit structure include the shape, size, period, and in-plane rotation angle of the unit structure. The optimization goal is to make the unit structure have high transmittance and low crosstalk at the target wavelength, and meet the manufacturing requirements.

[0056] S3: Construct a wavelength-selective spatial mask: Divide the substrate into at least two types of sub-blocks that are arranged alternately in space, wherein each of the at least two types of sub-blocks has a corresponding unit structure, and the at least two types of sub-blocks are configured to apply different phase distributions to incident light with different wavelengths and different circular polarization states, and to focus transmitted light of different wavelengths onto the same focal plane, so as to achieve confocal multi-channel control.

[0057] Specifically, in step S3, the metasurface is configured to exhibit at least one optical function selected from bright-field imaging, holographic display, vortex beam generation, and edge detection when incident light of different wavelengths and different circular polarization states is incident.

[0058] Specifically, this embodiment introduces a wavelength-selective spatial mask, and the formulas for calculating the Jones matrix of the metasurface and the transmission electric field of the metasurface in the far field are as follows:

[0059] At a given wavelength The local Jones matrix based on circular polarization is represented as follows:

[0060]

[0061] in, Let be a rotation matrix, and its expression is: , in the formula The rotation angle of the anisotropic unit structure on the substrate; Transmittance is the same polarization. Cross-polarized transmittance is defined as follows: and , and respectively wavelength Transmission coefficients along the lower x and y axes; I is a 2×2 identity matrix representing the spin-dependent geometric phase.

[0062] Specifically, metasurface designs exhibit spin and wavelength selectivity, and their Jones matrix is ​​represented as follows:

[0063]

[0064] The spatial mask is constrained to a non-overlapping checkerboard pattern by the conditions in the above formula. Sub-blocks are arranged alternately in space, and only a unique nanounit structure is set at each spatial location on the substrate to ensure the locality of the Jones operator. This design also restricts mask-induced diffraction to high spatial frequencies and minimizes crosstalk between wavelengths.

[0065] Specifically, based on the working principle in Example 1, the transmission electric field of the metasurface in the far field is expressed as:

[0066]

[0067] The Jones operator designed in this embodiment can achieve 2n confocal functions within a single metasurface.

[0068] The checkerboard-shaped mask in this invention has the advantage of a binary structure, which shifts the spectral replica to a high spatial frequency region outside the signal cone, maximizing local mixing while still satisfying the equivalent medium approximation condition. Furthermore, compared to clustered layouts, the uniform filling distribution of the checkerboard-shaped mask helps to minimize diffraction loss.

[0069] S4: Generate a multi-band metasurface based on the layout of the sub-blocks and the parameters of the unit structure.

[0070] Preferably, in order to avoid excessive sub-block interleaving that would result in an excessively small effective Fourier period, while suppressing ghost diffraction and ensuring the manufacturability of the metasurface, this embodiment selects n=2, that is, to achieve four confocal channels.

[0071] Furthermore, in order to achieve four different optical functions ( In this embodiment, the first target wavelength was selected. =1030nm and the second target wavelength =532nm two wavelengths, respectively corresponding to and Spatial mask. At least two sub-blocks, including a first sub-block and a second sub-block, wherein the first cell structure within the first sub-block matches the first target wavelength. The second unit structure within the second sub-block matches the second target wavelength. The first sub-block contains arrays matching the wavelength of the first target. Furthermore, the first unit structure, with optimized shape, size, and periodicity, has a second sub-block containing elements matching the second target wavelength. Furthermore, the second unit structure has been optimized in terms of shape, size, and cycle.

[0072] Furthermore, the period of the first unit structure arrangement within the first sub-block is twice or half the period of the second unit structure arrangement within the second sub-block.

[0073] Furthermore, the wavelength selection is determined by the detuning efficiency of the coupled-mode response, which is approximately [value missing]. ,in This refers to the resonant linewidth. A medium quality factor resonance is needed to achieve good wavelength selectivity, because an excessively wide resonance increases crosstalk between wavelengths, while an excessively narrow resonance amplifies manufacturing sensitivity. Therefore, in this embodiment, when two wavelengths... and When encoded on independent sub-block 20, the phase function calculated in step S2 produces different phase functions for each spin state at different wavelengths, as expressed as follows:

[0074]

[0075] in, , , and Wavelength and Ideal phase mask corresponding to two orthogonal spin states. First target wavelength. The phase functions corresponding to different circular polarization states are encoded into the first sub-block through spin decoupling, and the second target wavelength is then... The phase functions corresponding to different circular polarization states are encoded into the second sub-block through spin decoupling.

[0076] The phase profile formed by the first sub-block and the second sub-block satisfies the following formula:

[0077]

[0078] Where f and These are focal length and topological charge, respectively. It is the phase profile of the hologram obtained using the Gerchberg-Saxton (GS) algorithm.

[0079] The combination of the phase profiles formed by the first and second sub-blocks realizes three types of confocal four-channel metasurfaces, which can respectively exhibit at least one optical function selected from bright-field imaging, holographic display, vortex beam generation, and edge detection when incident light of different wavelengths and different circular polarization states is incident.

[0080] like Figure 3 As shown, the metasurface prepared in this embodiment (such as...) Figure 3 (As shown in the left image) Clear imaging or holographic display was achieved in all four channels, and the focal points of all channels were located on the same focal plane (confocal, such as...) Figure 3 (As shown in the right-hand figure). At a wavelength of 532 nm, left-hand circularly polarized light (LCP) can achieve bright-field imaging after passing through a superlens, while right-hand circularly polarized light (RCP) can generate a holographic pattern "BF". At a wavelength of 1030 nm, left-hand circularly polarized light can achieve edge-enhanced imaging after passing through a superlens, while the holographic image generated by right-hand circularly polarized light is "ED". Furthermore, the focal points of these two wavelengths under different circular polarizations are located on the same confocal plane. The results show that the full width at half maximum (FWHM) of the focused spot is close to the diffraction limit, crosstalk between wavelengths is effectively suppressed, and cross-band, multi-functional, confocal multi-channel control is successfully achieved.

[0081] Example 3:

[0082] Based on the above embodiments, referring to Figure 4 As shown in (a), one embodiment of the multi-band multifunctional metasurface of the present invention includes a substrate 1 and a plurality of unit structures 200 disposed on the substrate; the plurality of unit structures 200 are divided into at least two types of sub-blocks 20 arranged alternately in space, wherein the unit structures in different sub-blocks 20 have periods that are respectively matched to different wavelengths, and the at least two types of sub-blocks 20 are configured to apply different phase distributions to incident light with different wavelengths and different circular polarization states, and to focus transmitted light of different wavelengths onto the same focal plane. The alternately arranged sub-blocks constitute a spatial mask with wavelength selectivity and spin decoupling function.

[0083] Furthermore, at least two types of sub-blocks 20 are arranged alternately in a non-overlapping checkerboard pattern in space, and the unit structure 200 is a spin-sensitive anisotropic nanounit structure. The in-plane rotation angles of the unit structures 200 within the at least two types of sub-blocks 20 are respectively configured such that - The phase of the right-hand circularly polarized light is applied with a + The phase is such that a unit structure 200 is independently set at each spatial location on the substrate.

[0084] This embodiment achieves multiple optical functions through a combination of checkerboard spatial masking and polarization multiplexing. Specifically, the in-plane rotation angle of the unit structure 200 within the first sub-block 21 is configured such that, for left-hand circularly polarized light of the first target wavelength, it presents at least one first optical function selected from bright-field imaging, holographic display, vortex beam generation, and edge detection; for right-hand circularly polarized light of the first target wavelength, it presents at least one second optical function selected from the above functions, and the first and second optical functions can be the same or different. The in-plane rotation angle of the unit structure within the second sub-block 22 is configured such that, for both left-hand and right-hand circularly polarized light of the second target wavelength, it independently presents at least one third and fourth optical function selected from the above functions, and the third and fourth optical functions can be the same or different. The specific value of the in-plane rotation angle is determined by both the target phase distribution and spin dependence.

[0085] Furthermore, the period of the first sub-block 21 is twice the period of the second sub-block 22. The different periods (e.g., 250nm and 500nm) of the first and second sub-blocks 21, along with their alternating checkerboard spatial mask arrangement, collectively ensure wavelength selectivity: each sub-block has high transmittance and strong phase modulation capability for its matched wavelength, while exhibiting low transmittance and low crosstalk for other wavelengths. In particular, the size of the sub-blocks can be arbitrarily set according to design requirements, giving the metasurface of this embodiment high design flexibility.

[0086] Example 4:

[0087] To achieve the various optical functions described in the above embodiments, the optimization method for the individual unit structure constituting the metasurface is as follows:

[0088] On a substrate made of a transparent dielectric material (e.g., glass (SiO2)), the size, period, and in-plane rotation angle of different anisotropic nanounit structures 200 are optimized for each target wavelength, such as... Figure 4 As shown. To ensure the manufacturability of the superlens, in this embodiment, each nanounit structure is made of a high-refractive-index medium such as a-Si:H, and their height remains consistent, while the length and width of the nanopillar cross-section are independently optimized. A schematic diagram and arrangement of the nanounit structures are shown below. Figure 4 As shown in (a).

[0089] Specifically, the A-type and B-type nanopillars designed for wavelengths of 1030nm and 532nm adopt a rectangular structure, with their cross-sectional length and width represented as (Wm, Lm) and (Ws, Ls), respectively. Figure 4 In (a), the right side is a schematic diagram of the A-type unit structure of the type A atomic block, and the left side is a schematic diagram of the B-type unit structure of the type B atomic block. The top views of the B-type unit structure and the A-type unit structure are shown below the metasurface schematic diagram.

[0090] First, the optimization of the height and period of the type A and type B unit structures satisfies the following formula:

[0091]

[0092] This formula satisfies the Nyquist criterion. Where NA is the numerical aperture of the metasurface, and P j Let H be the period of the unit structure, H be the height of the unit structure, and G be the period of the unit structure. j The reciprocal lattice vector, For the effective dielectric constant, For a given wavelength, Transmittance is the same polarization. This represents the cross-polarization transmittance.

[0093] Preferably, during the optimization process, while ensuring high transmission efficiency and minimal crosstalk, and meeting manufacturing requirements, the height of both unit structures is preferably fixed at 600 nm.

[0094] Preferably, the period selection of the type A and type B unit structures is set to a 2-fold relationship to achieve selective and independent control of discrete wavelengths, so that light of each wavelength can pass through the entire metasurface aperture, achieving achromatic focusing under high numerical aperture and supporting polarization control to achieve multi-functional switching.

[0095] After determining the height and period, the length and width of the rectangular nanopillars are scanned and changed, and the transmission efficiency of the unit structure under each set of parameters is recorded. Then, the most suitable unit structure is selected from the results.

[0096] Specifically, the selected unit structure aims to achieve the highest cross-transmission efficiency while meeting manufacturing requirements. Specifically, the length and width of the unit structure are smaller than the period to avoid structural overlap during rotation, and the height-to-width ratio is appropriately set based on the manufacturing process. The gap between unit structures is greater than the minimum manufacturing tolerance.

[0097] Furthermore, the in-plane rotation angles of the Type A and Type B unit structures are based on the phase function of the embodiment. Sure.

[0098] For type A and type B unit structures, changing the in-plane rotation angle and period of the nanorectangular pillars optimizes the unit structure as follows: Figure 4 As shown, the geometric optimization of the unit structure and the spin-related phase response are as follows: Figure 5 As shown, where, Figure 5 The dashed line in (b) highlights the phase response of type A atoms in the selected period; Figure 5 (c) The linear relationship between geometric phase and rotation angle was confirmed; Figure 5 (e) highlights the phase response of type B atoms in the selected period, indicated by the dashed line. Figure 5 (f) confirms the linear relationship between geometric phase and rotation angle.

[0099] The unit structure parameters include the geometric dimensions (length, width, and height), arrangement period, and in-plane rotation angle of the nanopillars. The dimensions and period are determined through optimization to match the target wavelength and achieve high transmission efficiency and low crosstalk; the in-plane rotation angle is determined based on the target phase profile and spin dependence (geometric phase principle) to realize functional encoding under different polarization states.

[0100] Based on the spatial mask layout and spin dependence, the in-plane rotation angles of the unit structures in the first sub-block 21 and the second sub-block 22 can be determined. These rotation angles allow each unit structure to apply a preset phase delay to its corresponding wavelength and polarization state, thereby exhibiting the specified optical function in the far field. This simplifies unit structure design, reduces the computational burden of unit structure optimization, and improves design efficiency.

[0101] Example 5:

[0102] Based on the above embodiments, this embodiment provides a specific implementation of a multi-band multifunctional metasurface. For example... Figure 6As shown, the target phase and holographic phase h1 used for bright-field focusing at a wavelength of 532 nm are encoded into the first sub-block through spin decoupling. Similarly, the vortex beam phase and holographic phase h2 at a wavelength of 1030 nm are also encoded into the second sub-block through spin decoupling. The two phase profiles are then combined to obtain the final phase profile. The final unit structure distribution is shown in the rightmost box, where the circular markers represent the unit structures assigned to the first sub-block at 532 nm, with a period of 250 nm, and the cross markers represent the unit structures assigned to the second sub-block at 1030 nm, with a period of 500 nm.

[0103] according to Figure 6 After arranging the phase profile unit cell structure, the optical properties of the metasurface were simulated using the finite-difference time-domain method, as shown below. Figure 7 As shown. The optical response of LCP light at wavelengths of 532 nm and 1030 nm is as follows. Figure 7 (a) and Figure 7 As shown in (c), the function of the metasurface changes with the incident light wavelength. This metasurface provides a bright circular focal point for bright-field imaging and a ring-shaped point spread function with a well-defined central zero for edge-enhanced imaging. For wavelengths of 532 nm and 1030 nm, the full width at half maximum (FWHMs) of its normalized intensity distribution are approximately 381 nm and 574 nm, respectively, consistent with the expected size at the designed numerical aperture. Images generated at both wavelengths under RCP incident light are shown below. Figure 7 (b) and Figure 7 As shown in (d). Figure 7 (e) shows the axial intensity distribution when LCP light is incident. The bright-field and edge-enhanced images at both wavelengths are focused on the same plane, demonstrating that the focal position does not change with wavelength. In summary, these results indicate that by changing the wavelength and polarization respectively, the superlens can switch between bright-field and edge-enhanced imaging and the corresponding holograms, while maintaining consistent focal alignment in the visible and near-infrared ranges.

[0104] Example 6:

[0105] Based on the above embodiments, this embodiment provides another specific implementation of a multi-band multifunctional metasurface. For example... Figure 8As shown, the target phase function used for bright-field focusing and edge enhancement is encoded into a first sub-block at 532 nm wavelength and a second sub-block at 1030 nm wavelength through spin decoupling. The blocks corresponding to the two wavelengths are then merged to obtain the final phase profile. The left figure shows the polarization multiplexing phase distribution of right-handed and left-handed circularly polarized light. The upper middle figure shows the phase distribution of the first sub-block, and the lower middle figure shows the phase distribution of the second sub-block. The rightmost box presents the final unit cell phase distribution, where circular markers indicate the unit cell structure assigned to the 532 nm first sub-block, and cross markers indicate the unit cell structure assigned to the 1030 nm second sub-block. The corresponding unit cell periods are 250 nm and 500 nm, respectively.

[0106] The optical performance of Superlens 2 is as follows Figure 9 As shown. Figure 9 (a) shows the bright-field imaging performance of the metasurface under left-handed circularly polarized LCP incident light. The focal points observed at wavelengths of 532 nm and 1030 nm exhibit circular symmetry and a distinct central peak. The focal points at both wavelengths coincide along the z-axis, achieving the confocal design goal. Based on the normalized intensity curve at the focal center, the full width at half maximum (FWHM) is approximately 386 nm at 532 nm and approximately 739 nm at 1030 nm. Similarly, Figure 9 (b) shows the annular point spread function (NPF) image of the metasurface under edge-enhanced mode with right-handed circularly polarized RCP incident light. The centerline plot at the focal cross-section exhibits a distinctly symmetrical bimodal distribution, with full width at half maximum (FWHM) of approximately 302 nm and 587 nm at wavelengths of 532 nm and 1030 nm, respectively. The xz-plane intensity distribution in both operating modes is shown below. Figure 9 As shown in (c) and (d), the white dashed lines indicate that the focal point of the device is located on the same focal plane, thus possessing confocal capability. Figure 9 (c) and Figure 9 In (d), the dashed line represents the designed focal plane position, and the arrow indicates the direction of incident light propagation. The full width at half maximum (FWHM) obtained from the simulation measurement is compared with the Abbe diffraction limit formula. The calculated ideal diffraction limit values ​​are very close. The transmission efficiency (defined as the ratio of cross-polarized transmitted power to incident power) exceeds 60% at both wavelengths, indicating that the metasurface has high phase fidelity and high polarization conversion efficiency.

[0107] It should be noted that the parameters listed in the above embodiments of this application, such as the number, size, period, shape, in-plane rotation angle, operating wavelength, and sub-block division method of the unit structure, are merely illustrative examples and are not intended to limit the present invention. Those skilled in the art should understand that in actual design, the above parameters can be reasonably adjusted and optimized according to the target optical function and wavelength requirements. For example, the aspect ratio, period ratio, rotation angle of the nanopillars, or the selection of other suitable operating wavelengths or the number of sub-blocks can be changed. Any such adjustments, as long as they do not depart from the core concept of the present invention, fall within the protection scope of the present invention.

[0108] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A design method for a multi-band multifunctional metasurface, characterized in that, The method includes: S1: Determine the target optical function and at least two target wavelengths; S2: Based on the target optical function, calculate the phase function corresponding to the at least two target wavelengths under different circular polarization states; optimize the parameters of the unit structure for each target wavelength and its phase function. S3: Construct a wavelength-selective spatial mask: Divide the substrate into at least two types of sub-blocks that are arranged alternately in space, wherein each of the at least two types of sub-blocks has a corresponding unit structure, and the at least two types of sub-blocks are configured to apply different phase distributions to incident light with different wavelengths and different circular polarization states, and to focus transmitted light of different wavelengths onto the same focal plane, so as to achieve confocal multi-channel control. S4: Generate the cross-band multifunctional metasurface based on the layout of the sub-blocks and the parameters of the unit structure.

2. The design method for a multi-band multifunctional metasurface according to claim 1, characterized in that, In step S3, the metasurface is configured to exhibit at least one optical function selected from bright-field imaging, holographic display, vortex beam generation, and edge detection when incident light of different wavelengths and different circular polarization states is incident.

3. The design method for a multi-band multifunctional metasurface according to claim 1, characterized in that, The at least two target wavelengths in step S1 include a first target wavelength and a second target wavelength. The at least two sub-blocks in step S3 include a first sub-block and a second sub-block. A first unit structure is arranged in the first sub-block, and a second unit structure is arranged in the second sub-block. The first unit structure in the first sub-block matches the first target wavelength, and the second unit structure in the second sub-block matches the second target wavelength.

4. The design method for a multi-band multifunctional metasurface according to claim 3, characterized in that, The period of the first unit structure arrangement in the first sub-block is set to be twice the period of the second unit structure arrangement in the second sub-block.

5. The design method for a multi-band multifunctional metasurface according to claim 3, characterized in that, In step S3, the phase functions corresponding to different circularly polarized states at the first wavelength are encoded into the first sub-block through spin decoupling, and the phase functions corresponding to different circularly polarized states at the second wavelength are encoded into the second sub-block through spin decoupling. Then, the phase profiles formed by the first and second sub-blocks are combined to obtain the final phase profile, so that the sub-blocks are configured to apply different phase distributions to incident light with different wavelengths and different circularly polarized states, thereby obtaining a metasurface with confocal multi-channel control.

6. The design method for a multi-band multifunctional metasurface according to claim 1, characterized in that, The optimization of the unit structure parameters in step S2 must at least satisfy the following relationship: This relationship satisfies the Nyquist criterion. Where NA is the numerical aperture of the metasurface, and P j Let H be the period of the unit structure, H be the height of the unit structure, and G be the period of the unit structure. j For reciprocal lattice vectors, For the effective dielectric constant, For a given wavelength, Transmittance is the same polarization. This represents the cross-polarization transmittance.

7. The design method for a multi-band multifunctional metasurface according to claim 1, characterized in that, In step S2, for the first target wavelength Second target wavelength In different circular polarization states The phase functions generated by the metasurfaces Represented as: in , , and Wavelength and The ideal phase mask corresponding to the two orthogonal spin states.

8. A multi-band multifunctional metasurface, manufactured using the design method described in any one of claims 1-7, characterized in that, include: Substrate, and multiple unit structures disposed on the substrate; The multiple unit structures are divided into at least two types of sub-blocks that are arranged alternately in space. The unit structures within different sub-blocks each have periods that match different wavelengths. The at least two sub-blocks are configured to apply different phase distributions to incident light with different wavelengths and different circular polarization states, and to focus transmitted light of different wavelengths onto the same focal plane.

9. The multi-band multifunctional metasurface according to claim 8, characterized in that, The at least two types of sub-blocks are arranged alternately in a checkerboard pattern in space, and the unit structure is an anisotropic nanounit structure, with a unit structure independently set at each spatial location on the substrate.

10. The multi-band multifunctional metasurface according to claim 8, characterized in that, The material of the unit structure is a high-transmittance, high-dielectric material that matches the different wavelengths.

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