Geometric phase compensation single-medium metasurface and preparation method thereof

Abstract

The invention relates to the technical field of optical elements, in particular to a single-medium metasurface with a geometric phase compensation function and a preparation method of the single-medium metasurface. The single-medium metasurface comprises at least one metasurface unit which is periodically arranged; the super-structure surface unit comprises a substrate, the substrate is provided with two substrate surfaces, and the two adjacent substrate surfaces have a height difference; the two groups of super units are periodically arranged on the substrate, and each group of super units are arranged on the surface of the corresponding substrate; and each group of super units is formed by periodically arranging a plurality of cellular structures. Specific phase distribution is generated by using the super units periodically arranged on the substrate, and extra phase compensation is provided by using the substrate surface with height difference, so that the single-medium super-structure surface covering 0-2pi phase distribution is realized, and the processing difficulty is reduced and the processing precision is improved on the basis of reducing the depth-to-width ratio of the cellular structure.

Description

Technical Field

[0001] The present invention relates to the technical field of optical elements, and particularly relates to a single - dielectric metasurface with geometric - compensated phase and a preparation method thereof. Background Art

[0002] In modern optical applications, precise control of light beams is crucial. Traditional light - beam control technologies mainly include mechanical light - beam controllers, liquid - crystal spatial light modulators, or traditional metasurface - based devices. These light - beam control technologies can meet the requirements in some cases, but they all have certain limitations.

[0003] Macro - mechanical light - beam deflectors and liquid - crystal spatial light modulators have problems such as large volume, slow response speed, limited precision, and high cost, and are difficult to meet the requirements of modern optical systems for miniaturization, integration, and high performance. A metasurface is a new type of two - dimensional sub - wavelength structure that can precisely control the amplitude, phase, polarization, and other characteristics of light waves. It has advantages such as small volume, light weight, and easy integration, and has gradually become a research hotspot in light - beam deflection technology.

[0004] Liquid - crystal integrated metasurfaces, such as CN117724279A and CN118672005A, achieve flexible light - beam deflection through dynamic control of liquid - crystal materials. However, they adopt a multi - layer structure, with complex processing technology and poor material compatibility, and it is difficult to achieve low - cost, large - scale preparation while ensuring high performance. The on - chip integrated light - beam deflector based on phase - change materials and metasurfaces has high manufacturing costs due to its complex structure, involving multiple materials and processes, which limits its applicability in different scenarios.

[0005] Traditional dielectric metasurface light - beam deflectors usually achieve phase control through geometric parameters of the unit cell structure, such as size, shape, etc., such as CN113885115B and CN119644608A. To cover the phase range of 0 - 2π, a large aspect ratio of the unit cell structure is required, resulting in high processing difficulty. Especially in high - refractive - index materials, a too - large aspect ratio will lead to unstable structures and difficult - to - guarantee processing precision. Summary of the Invention

[0006] To solve the above - mentioned technical problems, the present invention provides a single - dielectric metasurface with geometric - compensated phase and a preparation method thereof.

[0007] To achieve the above object, the technical solution of the present invention is as follows.

[0008] The first aspect of the present invention provides a single - dielectric metasurface with geometric - compensation phase, including at least one periodically arranged metasurface unit; the metasurface unit includes: a substrate having two substrate surfaces with a height difference between adjacent two substrate surfaces; super - units, having two groups and arranged on the substrate periodically, and each group of super - units is arranged on the corresponding substrate surface; each group of super - units is formed by periodically arranging a plurality of cell structures; along the periodic arrangement direction, the width of the cell structures of each group of super - units gradually changes, so that the single - dielectric metasurface covers a phase range of 0 to 2π.

[0009] The present invention mainly generates a specific phase distribution with a net phase change of π by super - units arranged on the substrate periodically, and the substrate surfaces with a height difference compensate an additional π phase, so as to realize a single - dielectric metasurface covering a phase distribution of 0 to 2π.

[0010] The direction of the transmitted light beam passing through the single - dielectric metasurface of the present invention will be deflected, and the deflection angle is determined by the phase gradient of the super - units. The substrate surface with a height difference provides an additional π - phase compensation, thereby reducing the aspect ratio of the cell structure. Moreover, the single - dielectric metasurface proposed by the present invention only requires one material, reducing the processing difficulty.

[0011] Preferably, the widths of adjacent two cell structures are different; the aspect ratio of the cell structure ≤ 4. Under the same deflection angle, compared with the maximum aspect ratio of the cell structure of the traditional metasurface beam deflector, the maximum aspect ratio of the cell structure of the present invention is relatively lower, and the maximum aspect ratio ≤ 4.

[0012] Preferably, along the periodic arrangement direction, the width of the cell structures of each group of super - units gradually changes from 125 nm to 185 nm, so that the net phase change of each group of super - units is π.

[0013] Preferably, along the periodic arrangement direction, the width of the cell structures of each group of super - units gradually changes from 125 nm to 185 nm, so that each group of super - units covers a phase range of π / 2 to 3π / 2.

[0014] Along the periodic arrangement direction, the width of the unit cell structure of the traditional metasurface design gradually changes from 0 to 430 nm to fully cover the phase range of 0 to 2π. However, the traditional metasurface has a large aspect ratio of the unit cell structure, resulting in great processing difficulty. Especially in high refractive index materials, too large an aspect ratio will cause structural instability and it is difficult to guarantee the processing accuracy. Therefore, in order to improve the ultra-large aspect ratio defect of the traditional metasurface design, the width of the unit cell structure of the present invention uses a width range of 125 nm to 185 nm, so that each group of supercells can achieve a phase coverage of π / 2 to 3π / 2, that is, the net phase change is π, and the substrate surfaces with different height differences provide an additional π phase compensation, thereby significantly reducing the aspect ratio of the unit cell structure.

[0015] The present invention precisely regulates the width change range of the unit cell structure of each group of supercells to form a specific phase distribution and cover the phase range of π / 2 to 3π / 2. At the same time, an additional π phase compensation is provided by the substrate surfaces with different height differences, so as to achieve periodic modulation of 0 to 2π phases on the sub-wavelength scale, control the wavefront of the transmitted light beam, and realize the modulation of the deflection direction of the transmitted light beam.

[0016] Preferably, each group of the supercells has 4 to 12 unit cell structures.

[0017] Preferably, the height difference between two adjacent substrate surfaces is 0.2 μm to 3 μm.

[0018] The relationship between the height difference between two adjacent substrate surfaces and the phase compensation is: ; Among them, d represents the height difference between two adjacent substrate surfaces; λ represents the wavelength of the incident light; n represents the refractive index of the substrate material, k represents a non-zero integer.

[0019] In the present invention, the height difference between two adjacent substrate surfaces is set to be d ; According to the actual simulation effect, d = 0.2 μm or 0.6 μm can both produce good deflection effects. Considering that the aspect ratio cannot be too large during actual processing, in the embodiment, d = 0.6 μm is taken.

[0020] Preferably, the materials of the substrate and the supercells are both transparent dielectric materials; each unit cell structure is a dielectric nanocolumn.

[0021] In the present invention, the substrate and the meta-units are made of the same material, which is applicable to any transparent dielectric material. The single-dielectric metasurface prepared by the present invention using a single transparent dielectric material has the characteristics of a small aspect ratio of the cell structure, strong process compatibility, and applicability to any transparent dielectric material, and has broad application prospects in the fields of lidar, optical communication, etc.

[0022] Preferably, in each group of the meta-units, the center-to-center distance between two adjacent cell structures is 300 nm to 700 nm; the height of each cell structure is 300 nm to 700 nm.

[0023] The second aspect of the present invention provides a method for preparing a single-dielectric metasurface with geometric compensation phase, including the following steps: According to the phase gradient formula, obtain a phase gradient data set for different deflection angles; substitute the phase gradient data set for different deflection angles into the relationship model between the width of the cell structure and the phase, and obtain the widths of the cell structures of a group of the meta-units at different positions, so that the net phase change of each group of the meta-units is π; adjust the height difference of the substrate surfaces corresponding to adjacent meta-units for π phase compensation, so that the single-dielectric metasurface covers a phase range of 0 to 2π; according to the obtained phase gradient data set for different deflection angles, the widths of the cell structures of a group of the meta-units at different positions, and the height difference of the substrate surfaces corresponding to adjacent meta-units, use semiconductor micro-nano processing methods to prepare the single-dielectric metasurface with geometric compensation phase.

[0024] The preparation method of the present invention first determines the optical effect, such as the deflection angle of the light beam, for the structural design of the single-dielectric metasurface. By selecting a transparent dielectric material with good optical transparency and an appropriate refractive index range, and according to the design goal, adjust the metasurface units of the transparent dielectric material to achieve the required phase distribution.

[0025] The semiconductor micro-nano processing methods described in the present invention include semiconductor micro-nano processing methods such as focused ion etching method, electron beam etching method, and photolithography method. The semiconductor micro-nano processing methods described in the present invention are to process substrate surfaces with different height differences and meta-units located on the corresponding substrate surfaces in sequence on the transparent substrate surface, so as to obtain a single-dielectric metasurface that realizes a phase distribution covering 0 to 2π.

[0026] Preferably, the method for preparing the single-dielectric metasurface with geometric compensation phase using semiconductor micro-nano processing methods is as follows: A photoresist with a certain thickness is uniformly coated on the cleaned substrate; an exposure system is used to expose the photoresist according to the designed pattern of the substrate, and the photoresist in the exposed area is modified; after the exposed substrate is immersed in an organic developer for development and deep etching, a substrate with a height difference is obtained on the substrate surface; then a photoresist with a certain thickness is uniformly coated on the substrate; again, an exposure system is used to expose the photoresist on the substrate according to the designed pattern of the supercell, and the photoresist in the exposed area is modified; after the exposed substrate is immersed in an organic developer for development and dry etching, a supercell is obtained on the substrate surface, forming a single - dielectric metasurface that realizes a 0 - 2π phase distribution.

[0027] Specifically, the substrate can be selected from substrates such as SiO2 and TiO2.

[0028] The single - dielectric metasurface of the present invention is obtained by micro - nano processing on a substrate. The substrate, as the basic material, forms a substrate with a height difference and supercells periodically arranged on the substrate during the processing, forming a single - dielectric metasurface that realizes a 0 - 2π phase distribution. The designed single - dielectric metasurface of the present invention has a beam deflection effect and can be used as a beam deflector. It can also process metasurface units according to specific phase distribution requirements to form a beam focusing element and be used as a metasurface lens.

[0029] Advantages of the present invention: 1. The present invention mainly uses supercells periodically arranged on the substrate to generate a specific phase distribution, and uses the surface of the substrate with a height difference to provide additional phase compensation and support the cell structure, thereby realizing a single - dielectric metasurface that covers a 0 - 2π phase distribution. On the basis of reducing the aspect ratio of the cell structure, the processing difficulty is reduced and the processing accuracy is improved.

[0030] 2. The single - dielectric metasurface of the present invention can accurately control the deflection direction of the transmitted beam, has a simple structure, a wide range of applicable materials, and good compatibility with different working platforms. The present invention breaks through the limitations of the traditional beam controller, which is large in volume, low in precision, and high in cost, and the large aspect ratio and difficult processing of the cell structure of the existing metasurface devices, meeting the requirements for beam control in application fields such as lidar and optical communication. Description of the Drawings

[0031] Figure 1 It is a schematic structural diagram of the metasurface unit in the embodiment of the present invention. Among them, (a) is a side - view schematic diagram of the metasurface unit; (b) is a schematic structural diagram of a single cell structure and the substrate; (c) is a three - dimensional structural diagram of the metasurface unit.

[0032] Figure 2It is the corresponding relationship curve of the width of the cell structure in the embodiment of the present invention with the phase and transmittance. D represents the width of the cell structure.

[0033] Figure 3 It is the schematic diagram of the structure and simulation effect of a conventional metasurface beam deflector with a deflection angle of 6.14°. Among them, (a) is the schematic diagram of the structure of a conventional metasurface beam deflector with a deflection angle of 6.14°; (b) is the schematic diagram of the simulation result of the field strength distribution of a conventional metasurface beam deflector with a deflection angle of 6.14°; (c) is the schematic diagram of the simulation result of the outgoing phase distribution of a conventional metasurface beam deflector with a deflection angle of 6.14°.

[0034] Figure 4 It is the schematic diagram of the simulation effect of the metasurface beam deflector with a deflection angle of 6.14° designed in the embodiment of the present invention. Among them, (a) is the schematic diagram of the simulation result of the field strength distribution of the metasurface beam deflector with a deflection angle of 6.14° designed in the embodiment of the present invention; (b) is the schematic diagram of the simulation result of the outgoing phase distribution of the metasurface beam deflector with a deflection angle of 6.14° designed in the embodiment of the present invention.

[0035] Figure 5 It is the schematic diagram of the simulation effect of the metasurface beam deflector with a deflection angle of 4.60° designed in the embodiment of the present invention. Among them, (a) is the schematic diagram of the simulation result of the field strength distribution of the metasurface beam deflector with a deflection angle of 4.60° designed in the embodiment of the present invention; (b) is the schematic diagram of the simulation result of the outgoing phase distribution of the metasurface beam deflector with a deflection angle of 4.60° designed in the embodiment of the present invention. Detailed implementation manners

[0036] In order to make the purpose, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with embodiments. It should be understood that the specific embodiments described here are only used to explain the present invention and are not used to limit the present invention.

[0037] Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0038] The present invention proposes a single - dielectric metasurface with geometric compensation phase, which is formed by metasurface units with specific designs. The single - dielectric metasurface is processed from a single transparent dielectric material, generates a certain phase gradient through geometric compensation sub - wavelength structures and covers a phase range of 0 - 2π to control the wavefront of the transmitted beam and realize the modulation of the deflection direction of the transmitted beam.

[0039] The working process of the single - medium metasurface of the present invention is as follows: when the transmitted light beam incident perpendicularly on the single - medium metasurface passes through the single - medium metasurface, the super - unit modulates the phase of the transmitted light beam. The modulation effect depends on the specific phase distribution where the super - unit generates a net phase change of π. The substrate surface with a height difference is used to compensate for the phase difference of the super - unit, so that the single - medium metasurface with a small aspect ratio can cover the phase range of 0 - 2π, realizing precise control of the wavefront of the transmitted light beam.

[0040] Specifically, the single - medium metasurface includes a substrate with a small aspect ratio, which is used to support the super - unit and compensate for the phase; the super - unit is composed of periodically arranged cell structures with specific sizes and heights, which is used to generate a specific phase distribution with a net phase change of π to achieve wavefront control of the transmitted light beam.

[0041] The single - medium metasurface of the present invention is mainly used for wavefront regulation of parallel light beams with a certain wavelength to change the propagation direction of the light beam. The single - medium metasurface formed by a single transparent dielectric material is used to replace the traditional multi - material metasurface. The deflection angle of the transmitted light beam is determined by the phase distribution of the super - unit. By changing the arrangement pattern of the cell structures, different optical characteristics can be achieved.

[0042] In summary, the single - medium metasurface of the present invention is made of a single transparent dielectric material. At the same time, the wavefront of the transmitted light beam is determined by the phase distribution of the super - units periodically arranged on the substrate. The substrate with a height difference provides additional phase compensation, thereby reducing the aspect ratio of the cell structure and the processing difficulty.

[0043] The technical solution of the present invention will be further described below through specific embodiments.

[0044] In the following embodiments, unless otherwise specified, the methods are all conventional methods; the reagents and materials, unless otherwise specified, can all be purchased on the market.

[0045] Embodiment 1 As Figure 1 shown, a single - medium metasurface for geometric compensation of phase includes at least one periodically arranged metasurface unit; the metasurface unit includes a substrate and a super - unit; the substrate has two substrate surfaces, and there is a height difference between adjacent two substrate surfaces; there are two groups of super - units, which are periodically arranged on the substrate, and each group of super - units is arranged on the corresponding substrate surface; each group of super - units is formed by periodically arranging a plurality of cell structures; along the periodically arranging direction, the widths of the cell structures of each group of the super - units gradually change, so that the single - medium metasurface covers the phase range of 0 - 2π.

[0046] In the embodiments of the present invention, a substrate with a height difference on the surface is mainly used as the first-level structure, and supercells periodically arranged on the substrate are used as the second-level structure. By generating a specific phase distribution with a net phase change of π by the supercells periodically arranged on the substrate, and compensating for an additional π phase by the surface of the substrate with a height difference, a single-medium metasurface covering a 0-2π phase distribution is realized. The materials of the substrate and the supercells in the embodiments of the present invention are the same, and any transparent dielectric material can be selected. The direction of the transmitted light beam passing through the single-medium metasurface of the embodiments of the present invention will be deflected, and the deflection angle is determined by the phase gradient of the supercells. The surface of the substrate with a height difference provides additional π phase compensation, thereby reducing the aspect ratio of the cell structure. Moreover, the single-medium metasurface proposed in the embodiments of the present invention only requires one material, reducing the processing difficulty.

[0047] On the basis of the above embodiments, the widths of two adjacent cell structures are different; the aspect ratio of the cell structure ≤ 4. At the same deflection angle, compared with the maximum aspect ratio of the cell structure of the traditional metasurface beam deflector, the maximum aspect ratio of the cell structure of the metasurface beam deflector in the embodiments of the present invention is relatively lower, and the maximum aspect ratio ≤ 4.

[0048] On the basis of the above embodiments, along the periodic arrangement direction, the widths of the cell structures of each group of supercells gradually change from 125 nm to 185 nm, so that the net phase change of each group of supercells is π. Specifically, along the periodic arrangement direction, the widths of the cell structures of each group of supercells gradually change from 125 nm to 185 nm, so that each group of supercells covers a phase range of π / 2 to 3π / 2.

[0049] As Figure 1 , each group of supercells has multiple sub-wavelength cell structures. Taking the center distance between adjacent cell structures as a unit period, denoted as P ; taking the height of a cell structure as H , and taking the width of a cell structure as D , then P = 300 nm to 700 nm, H = 300 nm to 700 nm.

[0050] Each group of supercells has 4 to 12 cell structures. Taking the height difference between the two substrate surfaces corresponding to two adjacent groups of supercells as d , it can take discrete values to provide π phase compensation. The height difference between two adjacent substrate surfaces is 0.2 μm to 3 μm. For example, d can take values of 0.2 μm, 0.6 μm, 1 μm, 1.4 μm,..., 3 μm.

[0051] The relationship between the height difference between adjacent substrate surfaces and phase compensation is as follows: ; Wherein, d represents the height difference between adjacent substrate surfaces; λ represents the wavelength of the incident light; n represents the refractive index of the substrate material, k represents a non-zero integer.

[0052] In the present invention, the width of the unit cell structure of each group of meta-units is set to d ; According to the actual simulation effect, d good deflection effects can be produced when = 0.2μm or 0.6μm. Considering that the aspect ratio cannot be too large during actual processing, = 0.6μm is taken in the embodiment. d = 0.6μm.

[0053] In the embodiment of the present invention, the width of the unit cell structure determines the phase delay of the transmitted light. By adjusting the width of the sub-wavelength unit cell structures at different positions, different phase delays can be achieved. The finite-difference time-domain algorithm is used to numerically simulate the unit cell structure of the metasurface. At a wavelength of 642nm, by adjusting the width of the sub-wavelength unit cell structures at different positions to vary from 125nm to 185nm, the phase delay can cover a phase range of π / 2 to 3π / 2, that is, the net phase change is π. The relationship between the phase delay and the light transmittance and the width of the unit cell structure is as Figure 2 shown. Figure 2 shows the relationship between the width of the unit cell structure and the phase.

[0054] The phase delay of the single-medium metasurface satisfies the following phase gradient formula: ， ; Wherein, represents the phase difference between adjacent unit cell structures; K 0 is a constant; P represents the unit period of the unit cell structure, that is, the center distance between adjacent unit cell structures; represents the beam deflection angle, represents the wavelength of the working light.

[0055] The phase gradient required for different deflection angles can be obtained through the above phase gradient formula. The corresponding relationship between the width D of the unit cell structure and the phase is obtained by simulation scanning, and the width D of the unit cell structure that meets the phase requirements at different positions of the single-medium metasurface is selected.

[0056] Using the correspondence obtained in the previous step, a cell structure with a specific size can be set at a specific position on the single - dielectric metasurface. Select 4 - 12 cell structures with appropriate sizes as a set of super - cells. A set of super - cells covers a phase range of π / 2 - 3π / 2. At the same time, by changing the height difference of the substrate surface under adjacent super - cells for additional π - phase compensation, a phase coverage of 0 - 2π can be achieved on the substrate surface using two super - cells in combination.

[0057] Repeat the metasurface units periodically to obtain a single - dielectric metasurface with a certain deflection angle at a specific wavelength.

[0058] The single - dielectric metasurface formed by the above design has a beam - deflection effect and can be used as a beam deflector. According to the phase - gradient formula, by changing the number of cell structures in the super - cell and adjusting the parameters of the cell structure, a single - dielectric metasurface beam deflector with different deflection angles can be designed.

[0059] The embodiment of the present invention provides a preparation method for a single - dielectric metasurface with geometric - compensation phase, including the following steps: Step 1: According to the phase - gradient formula, obtain a phase - gradient data set for different deflection angles.

[0060] According to the target beam - deflection angle, such as 5°, calculate the phase - gradient data set corresponding to the target deflection angle according to the phase formula of the beam deflector surface.

[0061] The phase formula of the beam deflector surface is: ; where x is the position coordinate corresponding to the center of the cell structure, λ is the wavelength of the incident light, θ is the target beam - deflection angle.

[0062] Store the calculated phase - gradient data set as design parameters for subsequent structure design.

[0063] Step 2: Substitute the phase - gradient data set for different deflection angles into the relationship model between the width of the cell structure and the phase, and obtain the widths of the cell structures of a set of super - cells at different positions so that the net phase change of each set of super - cells is π.

[0064] The full English name of the finite - difference time - domain method is Finite - Difference Time - Domain, abbreviated as FDTD. By simulating the phase response of cell structures with different widths D using FDTD, the correspondence between the width D and the phase is obtained, and a relationship model between the width of the cell structure and the phase is established.

[0065] According to the phase gradient data set in step 1, using the relationship model between the width of the cell structure and the phase, determine the width of the cell structure of each group of supercells at different positions, ensuring that each group of supercells can cover the phase range of 0 to π.

[0066] Step 3, adjust the height difference between the substrate surfaces corresponding to adjacent supercells for π phase compensation, so that the single dielectric metasurface covers the phase range of 0 to 2π.

[0067] According to the target phase compensation requirement, determine the height difference between the substrate surfaces corresponding to adjacent supercells. The relationship between the height difference between two adjacent substrate surfaces and the phase compensation is: ; where d represents the height difference between two adjacent substrate surfaces; λ represents the wavelength of the incident light; n represents the refractive index of the substrate material, k represents a non-zero integer.

[0068] By adjusting the height difference between two adjacent substrate surfaces, additional π phase compensation is achieved, ensuring that the entire single dielectric metasurface can cover the phase range of 0 to 2π. By optimizing the height difference between two adjacent substrate surfaces, the phase continuity is ensured.

[0069] Step 4, according to the obtained phase gradient data set at different deflection angles, the width of the cell structure of a group of supercells at different positions, and the height difference between the substrate surfaces corresponding to adjacent supercells, use semiconductor micro-nano processing methods to fabricate the single dielectric metasurface with geometric compensation phase.

[0070] The semiconductor micro-nano processing methods include semiconductor micro-nano processing methods such as focused ion etching method, electron beam etching method, and photolithography method. The semiconductor micro-nano processing method described in the embodiment of the present invention is to process substrate surfaces with different height differences and supercells located on the corresponding substrate surfaces in sequence on the surface of a transparent substrate, so as to obtain a metasurface that realizes a phase distribution covering 0 to 2π.

[0071] Taking the production of the metasurface by photolithography method as an example below, the specific preparation method of the single dielectric metasurface is described.

[0072] Step 4.1, prepare a TiO2 substrate and perform cleaning treatment on the substrate to ensure that the surface is clean and has good flatness, and obtain the cleaned substrate.

[0073] Step 4.2, uniformly coat a photoresist with a certain thickness on the cleaned substrate; use an exposure system to expose the photoresist according to the designed pattern of the substrate. During the exposure process, the photoresist in the exposed area is modified; after immersing the exposed substrate in an organic developer for development and deep etching, a substrate with a height difference is obtained on the substrate surface.

[0074] Among them, during the process of immersing the substrate sample in the organic developer for development, the negative photoresist is cured due to electron beam exposure and will not be dissolved by the developer, while the positive photoresist is degraded due to electron beam exposure and is dissolved by the developer. Deep etching is to use inductively coupled etching technology to perform dry etching on the developed structure, thereby forming the first-level exposed structure on the substrate.

[0075] Step 4.3, use a chemical solvent to remove the residual photoresist on the surface, and then obtain the second-level structure on the substrate surface according to the method of Step 4.1 to form a single-medium metasurface with geometric compensation phase. The specific method is as follows: Uniformly coat a photoresist with a certain thickness on the substrate again; use the exposure system again to expose the photoresist on the substrate according to the designed pattern of the supercell. When the photoresist is exposed, the photoresist in the exposed area is modified; after immersing the exposed substrate in an organic developer for development and dry etching, supercells are obtained on the substrate surface, forming a single-medium metasurface that realizes a 0-2π phase distribution coverage.

[0076] Example 2 A beam deflector composed of a single-medium metasurface, which is composed of an arrangement of supercells with 6 cell structures in a group, and the deflection angle is 6.14°, as Figure 4 shown. Among them, the preparation method of the single-medium metasurface is the same as that in Example 1, and both the substrate and the supercell are single-medium materials.

[0077] The height difference between the adjacent two substrate surfaces of the first-level structure d changes discretely, and d = 0.2 μm to provide additional π phase compensation; in the second-level structure, each group of supercells contains 6 cell structures, and the parameters of the cell structures corresponding to each group of supercells are the same. A group of supercells covers a phase of π / 2 - 3π / 2 and the phase changes in a gradient manner. The overall beam deflector can realize a gradient change covering 0 - 2π phases.

[0078] After the parallel beam passes through the substrate of the single-medium metasurface, it is modulated by the cell structure array of the supercells on the substrate to generate a phase gradient distribution, and finally the outgoing beam is deflected at a specific angle. Among them, the deflection angle θIt is proportional to the phase gradient of the single - dielectric metasurface. By adjusting the width and height of the unit cell structure, precise control of the deflection angle can be achieved.

[0079] The wavelength of the parallel beam has a specific range. After the medium is determined, the unit cell structure of the metasurface constituting the beam deflector is simulated and scanned to determine the parameters of the unit cell structure that meet the requirements of phase and transmittance.

[0080] Such as Figure 3 , when the deflection angle is also 6.14°, the maximum aspect ratio of the unit cell structure of the traditional metasurface beam deflector is 6.47. While the maximum aspect ratio of the unit cell structure of the metasurface beam deflector in the embodiment of the present invention is greatly reduced to 3.9, a decrease of up to 39.7%. The metasurface beam deflector designed based on geometric - compensation phase in the embodiment of the present invention has a smaller aspect ratio of the unit cell structure and can maintain a good beam deflection effect at the same time.

[0081] Embodiment 3 A beam deflector composed of a single - dielectric metasurface, which is composed of a super - unit arrangement with 8 unit cell structures in a group, and the deflection angle is 4.60°, as Figure 5 shown. The preparation method of the single - dielectric metasurface is the same as that in Embodiment 1, and both the substrate and the super - unit are single - dielectric materials.

[0082] The height difference between the adjacent two substrate surfaces of the first - level structure d changes discretely, and d = 0.6μm to provide additional π - phase compensation; in the second - level structure, each group of super - units contains 8 unit cell structures, and the parameters of the unit cell structures corresponding to each group of super - units are the same. A group of super - units covers a phase range of π / 2 to 3π / 2 and the phase changes in a gradient. The overall beam deflector can achieve a gradient change covering a phase range of 0 to 2π.

[0083] When the deflection angle is also 4.60°, the maximum aspect ratio of the unit cell structure of the traditional metasurface beam deflector is 8.50. While the maximum aspect ratio of the unit cell structure of the metasurface beam deflector in the embodiment of the present invention is reduced to 4.0, a decrease of up to 56.3%.

[0084] In summary, the results show that the single - dielectric metasurface in the embodiment of the present invention is composed of any single transparent dielectric material, the functional unit and the substrate are the same transparent dielectric material, and it is constructed into a composite - structure metasurface beam deflector with a specific deflection angle in the manner of Embodiment 2 and Embodiment 3. By changing the height difference dBy providing an additional π phase, the supercell only needs to cover the phase range from π / 2 to 3π / 2, and the entire metasurface can cover the phase range from 0 to 2π. Therefore, the aspect ratio of the unit cell structure of the metasurface can be significantly reduced, reduced to about 50% of the original, thereby greatly reducing the processing difficulty of metasurface devices, greatly expanding the material selection range of metasurface devices, and accelerating the integration and practical application of metasurface technology.

[0085] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A single - dielectric metasurface with geometric - compensated phase, comprising at least one periodically arranged metasurface unit; the metasurface unit includes: a substrate having two substrate surfaces with a height difference between adjacent two substrate surfaces; super - units, having two groups, and arranged periodically on the substrate, and each group of super - units is arranged on the corresponding substrate surface; each group of super - units is formed by periodically arranging a plurality of cell structures; Along the periodic arrangement direction, the width of the cell structures of each group of super - units gradually changes, so that the single - dielectric metasurface covers a phase range of 0 - 2π.

2. The single-medium metasurface with geometric compensation phase according to claim 1, characterized in that, The widths of adjacent two cell structures are different; the aspect ratio of the cell structure ≤ 4.

3. The single-medium metasurface with geometric compensation phase according to claim 1, characterized in that, Along the periodic arrangement direction, the width of the cell structures of each group of super - units gradually changes from 125 nm to 185 nm, so that the net phase change of each group of super - units is π.

4. The single-medium metasurface with geometric compensation phase according to claim 3, characterized in that Along the periodic arrangement direction, the width of the cell structures of each group of super - units gradually changes from 125 nm to 185 nm, so that each group of super - units covers a phase range of π / 2 - 3π / 2.

5. The single-medium metasurface with geometric compensation phase according to claim 1, wherein Each group of super - units has 4 - 12 cell structures.

6. The single-medium metasurface with geometric compensation phase according to claim 1, characterized in that The height difference between adjacent two substrate surfaces is 0.2 μm - 3 μm.

7. The single-medium metasurface with geometric compensation phase according to claim 1, characterized in that, The materials of the substrate and the super - units are both transparent dielectric materials; each cell structure is a dielectric nanorod.

8. The single-medium metasurface with geometric compensation phase according to claim 1, characterized in that, In each group of super - units, the center - to - center distance between adjacent two cell structures is 300 nm - 700 nm; the height of each cell structure is 300 nm - 700 nm.

9. A preparation method of the single - dielectric metasurface with geometric - compensated phase according to claim 3, comprising the following steps: According to the phase - gradient formula, obtain a phase - gradient data set with different deflection angles; According to the phase - gradient data set with different deflection angles, substitute it into the relationship model between the width of the cell structure and the phase, and obtain the widths of the cell structures of a group of super - units at different positions, so that the net phase change of each group of super - units is π; Adjust the height difference between the substrate surfaces corresponding to adjacent super - units for π - phase compensation, so that the single - dielectric metasurface covers a phase range of 0 - 2π; According to the obtained phase - gradient data set with different deflection angles, the widths of the cell structures of a group of super - units at different positions, and the height difference between the substrate surfaces corresponding to adjacent super - units, use semiconductor micro - nano processing methods to prepare a single - dielectric metasurface with geometric - compensated phase.

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