Design method of superlens, superlens and processing technology

Abstract

The present invention provides a method for designing a metalens, a metalens, and a processing technique, which belong to the technical field of metasurfaces. The method includes: depositing a material layer on the side of the metalens surface having a nanostructure, so that the material layer covers any one or both of the following surfaces: at least a portion of the surface of the nanostructure; a surface of the metalens substrate adjacent to the nanostructure; wherein the nanostructure, the substrate on one side of the nanostructure, and the material layer constitute a nanostructure unit; the nanostructure unit at least satisfies the following conditions: #imgabs0##imgabs1# is the phase of the nanostructure unit numbered i; n eff‑i is the effective refractive index of the nanostructure unit; ω is the angular frequency of the incident light; n is the refractive index of the material layer; and h is the distance from the bottom to the top of the material layer in the nanostructure unit along the extension direction of the nanostructure. This design method simplifies the optimization process, reduces the processing difficulty, and is easy to mass produce.

Description

Technical Field

[0001] The present application relates to the technical field of metasurfaces, and specifically to a design method, a metalens, and a processing technology for a metalens. Background Art

[0002] An antireflection coating is a thin film deposited on the surface of an optical lens. Its principle is to cause the interference of reflected light to destructively interfere, thereby achieving the effect of antireflection / antireflection. The film can be a single layer or a multilayer, depending on the substrate material and the operating wavelength.

[0003] In the related art, the anti-reflection film of the metalens is deposited on the metalens after the metalens is designed and processed.

[0004] However, compared to traditional lenses, the surface of a metalens has nanostructures that modulate the phase of incident light. Films designed using related technologies deposit onto the nanostructures during coating and fill the air gaps between the nanostructures, thereby changing the phase of the incident light and affecting the optical performance of the metalens. Therefore, a design method, metalens, and processing technology for metalens are urgently needed. Summary of the Invention

[0005] In view of the problem that the anti-reflection film of the metalens in the prior art affects the optical performance of the metalens, the embodiments of the present application provide a design method of the metalens, a metalens and a processing technology.

[0006] In a first aspect, an embodiment of the present application provides a method for designing a metalens, the method comprising:

[0007] A material layer is deposited on the side of the metalens surface having the nanostructures such that the material layer covers either or both of the following surfaces:

[0008] at least a portion of the surface of the nanostructure; and,

[0009] The base of the metalens is close to the surface of one side of the nanostructure;

[0010] Wherein, the nanostructure, the substrate on one side of the nanostructure and the material layer constitute a nanostructure unit;

[0011] The nanostructure unit at least satisfies:

[0012]

[0013] in, is the number of the nanostructure unit in the metalens; is the phase of the nanostructure unit numbered i; n eff-i is the effective refractive index of the nanostructure unit; is the angular frequency of the incident light; is the speed of light; is the refractive index of the material layer; and h is the distance from the bottom to the top of the material layer in the nanostructure unit along the extension direction of the nanostructure.

[0014] Optionally, the nanostructure unit further satisfies:

[0015]

[0016] Wherein, N is the total number of nanostructures in the metalens; is the refractive index of the substrate.

[0017] Optionally, the material layer covering at least a portion of the surface of the nanostructure comprises:

[0018] The material layer covers the entire end surface of the nanostructure away from the substrate of the super lens; or

[0019] The material layer covers the entire sidewall of the nanostructure.

[0020] Optionally, the method further comprises: before depositing the material layer, determining the refractive index of the material layer and the distance from the bottom to the top of the material layer in the nanostructure unit along the extension direction of the nanostructure.

[0021] Optionally, the refractive index of the material layer is smaller than the refractive index of the nanostructure.

[0022] Optionally, the refractive index of the material layer is greater than the refractive index of the nanostructure.

[0023] Optionally, determining the refractive index of the material layer and the distance from the bottom to the top of the material layer in the nanostructure unit along the extension direction of the nanostructure includes:

[0024] S1, select the initial parameters of the nanostructure according to the phase distribution of the metalens;

[0025] S2, setting the initial refractive index of the material layer and establishing a model of the nanostructure unit;

[0026] S3, setting the distance from the bottom to the top of the material layer in the nanostructure unit along the extension direction of the nanostructure, so that the phase of the nanostructure unit covers 0 to 2π;

[0027] S4, arranging the nanostructures according to the phase distribution of the metalens, and calculating the effective refractive index of the metasurface units corresponding to all the nanostructures; the metasurface units are the portions of the nanostructure units that do not contain a substrate;

[0028] S5, calculating the total effective refractive index of the metalens based on the effective refractive indices of all metasurface nanostructure units;

[0029] S6, calculating a first difference between the total effective refractive index of the metalens and the refractive index of the substrate and calculating the transmittance of the metalens;

[0030] S7, determining whether the first difference is less than a target value, and whether the transmittance is greater than a target transmittance;

[0031] If so, the initial refractive index and initial height are the refractive index and height of the material layer as deposited;

[0032] If not, repeat steps S2 to S7 to make the first difference smaller than the target value and the transmittance greater than or equal to the target transmittance.

[0033] Optionally, determining the refractive index of the material layer and the distance from the bottom to the top of the material layer in the nanostructure unit along the extension direction of the nanostructure further includes:

[0034] Step S8: If the first difference value obtained by repeating steps S2 to S7 is not less than the target value, or the transmittance is always less than the target transmittance, then repeat steps S1 to S7.

[0035] Optionally, the material layer covers the nanostructures and all surfaces of the substrate adjacent to air.

[0036] Optionally, the material layer covers the end surface of the nanostructure away from the substrate.

[0037] Optionally, the material layer covers the surface of the substrate adjacent to air.

[0038] Optionally, the material layer covers the sidewalls of the nanostructures and the surface of the substrate adjacent to the air.

[0039] Optionally, the material layer covers the entire surface of the nanostructure.

[0040] In a second aspect, an embodiment of the present application further provides a metalens designed using the method provided in any of the above embodiments, the metalens comprising:

[0041] a substrate configured to be transparent to radiation in an operating band;

[0042] a nanostructure, located on one side of the substrate and configured to be transparent to radiation in an operating wavelength band;

[0043] A material layer configured to cover either or both of the following surfaces:

[0044] at least a portion of the surface of the nanostructure; and,

[0045] The base of the metalens is close to the surface of one side of the nanostructure;

[0046] Wherein, the nanostructure, the substrate on one side of the nanostructure and the material layer constitute a nanostructure unit;

[0047] The nanostructure unit at least satisfies:

[0048]

[0049] Where c is the speed of light; is the number of the nanostructure unit in the metalens; is the phase of the nanostructure unit numbered i; n eff-i is the effective refractive index of the nanostructure unit; is the angular frequency of the incident light; is the refractive index of the material layer; and h is the distance from the bottom to the top of the material layer in the nanostructure unit along the extension direction of the nanostructure.

[0050] Optionally, the nanostructure unit further satisfies:

[0051]

[0052] Wherein, N is the total number of nanostructures in the metalens; is the refractive index of the substrate.

[0053] Optionally, the height of the nanostructure is 0.3λ c to 2λ c ; Among them, λ c is the center wavelength of the operating band.

[0054] Optionally, the height is greater than or equal to 0.3λ c , and less than or equal to 5λ c ; Among them, λ c is the center wavelength of the operating band.

[0055] Optionally, the nanostructures are arranged in an array in the form of a densely packed pattern; wherein the nanostructures are disposed at the center and / or vertex positions of the densely packed pattern.

[0056] Optionally, the aspect ratio of the nanostructure is less than or equal to 20.

[0057] Optionally, the material layer is a single-layer structure.

[0058] Optionally, the material layer is a multi-layer structure.

[0059] In a third aspect, the embodiments of the present application further provide a metalens processing process, which is applicable to a metalens designed using the method provided in any of the above embodiments or a metalens provided in any of the above embodiments, the process comprising:

[0060] growing nanostructured materials on a substrate;

[0061] Coating: coating photoresist on the side of the nanostructured material away from the substrate;

[0062] Photolithography development, exposing the photoresist to form a reference structure;

[0063] Etching and stripping: etching the nanostructured material based on the reference structure to obtain a nanostructure, and removing the photoresist;

[0064] Depositing a layer of material on either or both of the following surfaces:

[0065] at least a portion of the surface of the nanostructure; and,

[0066] The base of the metalens is close to the surface of one side of the nanostructure;

[0067] so that the nanostructure, the substrate on one side of the nanostructure and the material layer constitute a nanostructure unit; and

[0068] The nanostructure unit at least satisfies:

[0069]

[0070] in, is the number of the nanostructure unit in the metalens; is the phase of the nanostructure unit numbered i; n eff-i is the effective refractive index of the nanostructure unit; is the angular frequency of the incident light; is the speed of light; is the refractive index of the material layer; h is the distance from the bottom to the top of the material layer in the nanostructure unit along the extension direction of the nanostructure.

[0071] Optionally, the material layer further satisfies:

[0072]

[0073] Wherein, N is the total number of nanostructures in the metalens; is the refractive index of the substrate.

[0074] Optionally, the deposited material layer includes:

[0075] The material layer is deposited on the entire end surface of the nanostructure away from the substrate of the superlens; or, on the entire sidewall of the nanostructure.

[0076] Optionally, the material layer covers the nanostructures and all surfaces of the substrate adjacent to air.

[0077] Optionally, the material layer covers the end surface of the nanostructure away from the substrate.

[0078] Optionally, the material layer covers the surface of the substrate adjacent to air.

[0079] Optionally, the material layer covers the sidewalls of the nanostructures and the surface of the substrate adjacent to the air.

[0080] Optionally, the material layer covers the entire surface of the nanostructure.

[0081] The technical solution provided by the embodiments of the present application has achieved at least the following beneficial effects:

[0082] The metalens design method provided in the embodiment of the present application is to deposit a material layer on the side of the metalens surface having the nanostructure, so that the material layer covers any one or both of the following surfaces: at least a portion of the surface of the nanostructure; and the surface of the metalens substrate close to the nanostructure; by the formula The phase of the nanostructure is designed in conjunction with the refractive index and height of the material layer. This design approach considers the influence of the refractive index of the material layer on the phase of the nanostructure units before the metalens design stage. This avoids the influence of the height and refractive index of the material layer on the phase of the nanostructure, and also avoids directly depositing antireflection material on the designed metalens, which would cause the metalens phase to be destroyed. BRIEF DESCRIPTION OF THE DRAWINGS

[0083] The accompanying drawings are included to provide a further understanding of the present application and are incorporated in and constitute a part of this specification. The accompanying drawings illustrate embodiments of the present application and together with the description below serve to explain the principles of the present application.

[0084] Figure 1 An optional structural diagram of a nanostructure unit provided in an embodiment of the present application is shown;

[0085] Figure 2 An optional partial schematic diagram of a metalens provided in an embodiment of the present application is shown;

[0086] Figure 3 An optional partial schematic diagram of a metalens provided in an embodiment of the present application is shown;

[0087] Figure 4 An optional partial schematic diagram of a metalens provided in an embodiment of the present application is shown;

[0088] Figure 5 An optional partial schematic diagram of a metalens provided in an embodiment of the present application is shown;

[0089] Figure 6 An optional partial schematic diagram of a metalens provided in an embodiment of the present application is shown;

[0090] Figure 7 An optional optimization flow chart of the material layer provided in the embodiment of the present application is shown;

[0091] Figure 8 A schematic diagram showing an optional processing technique for a metalens provided in an embodiment of the present application is shown;

[0092] Figure 9 Shown Figure 3 An optional schematic diagram of a processing technique for a material layer in a metalens is shown;

[0093] Figure 10 Shown Figure 4 Another optional schematic diagram of the processing technology of the material layer in the metalens shown;

[0094] Figure 11 Shown Figure 5 Another optional schematic diagram of the processing technology of the material layer in the metalens shown;

[0095] Figure 12 Shown Figure 6 Another optional schematic diagram of the processing technology of the material layer in the metalens shown;

[0096] Figure 13 Schematic diagram showing an optional relationship between phase and transmittance of a nanostructure unit provided in an embodiment of the present application;

[0097] Figure 14 A schematic diagram showing another optional relationship between phase and transmittance of the nanostructure unit provided in an embodiment of the present application is shown. DETAILED DESCRIPTION

[0098] The present application will now be described more fully below with reference to the accompanying drawings, in which various embodiments are shown. However, the present application can be implemented in many different ways and should not be construed as being limited to the embodiments set forth herein. On the contrary, these embodiments are provided so that the present application will be exhaustive and complete and will fully convey the scope of the present application to those skilled in the art. Throughout, the same reference numerals represent the same components. Furthermore, in the drawings, the thicknesses, ratios, and sizes of the components are exaggerated for clarity of illustration.

[0099] The terms used herein are for the purpose of describing specific embodiments only and are not intended to be limiting. Unless the context clearly indicates otherwise, as used herein, "a," "an," "the," and "at least one" do not represent a limitation on quantity, but are intended to include both the singular and the plural. For example, unless the context clearly indicates otherwise, "a component" has the same meaning as "at least one component." "At least one" should not be interpreted as being limited to the quantity "one." "Or" means "and / or." The term "and / or" includes any and all combinations of one or more of the associated listed items.

[0100] Unless otherwise defined, all terms used herein, including technical and scientific terms, have the same meanings as those generally understood by those skilled in the art. Terms defined in commonly used dictionaries should be interpreted as having the same meanings as in the relevant technical context, and unless explicitly defined in the specification, these terms are not interpreted as having formal meanings in an idealized or overly formal sense.

[0101] The meaning of “include” or “comprising” specifies properties, quantities, steps, operations, components, parts or a combination thereof, but does not exclude other properties, quantities, steps, operations, components, parts or a combination thereof.

[0102] Embodiments are described herein with reference to cross-sectional views that are idealized embodiments. Thus, variations in shape relative to the illustrated embodiments are anticipated as a result of, for example, manufacturing techniques and / or tolerances. Therefore, the embodiments described herein should not be construed as limited to the specific shapes of the regions as shown herein, but rather should include deviations in shape that result from, for example, manufacturing. For example, a region shown or described as flat may typically have rough and / or nonlinear features. Furthermore, sharp angles shown may be rounded. Therefore, the regions shown in the figures are schematic in nature, and their shapes are not intended to illustrate the precise shape of the regions and are not intended to limit the scope of the claims.

[0103] Hereinafter, exemplary embodiments according to the present application will be described with reference to the accompanying drawings.

[0104] Existing methods for increasing the transmittance of metasurfaces all involve designing an antireflection film system corresponding to a specific bandwidth spectrum. The antireflection film system utilizes light interference to reduce reflected light and increase transmitted light. After the design and processing of the metalens in the prior art are completed, the structural parameters of the nanostructure are fixed, and thus the phase of the incident light is also fixed. When the antireflection film is grown on the surface of the designed metalens in the prior art, the antireflection film material falls into the gaps between the nanostructures, destroying the original phase of the metalens, thereby causing the optical performance of the metalens to deteriorate. Furthermore, when the antireflection film is directly deposited on the surface with the nanostructure using traditional optical processes, the resulting antireflection film has an uneven thickness distribution, which also reduces the optical performance of the metalens.

[0105] In this regard, one approach in the prior art is to fill the gaps between the nanostructures with a material with high transmittance in the working band, so that the side of the metalens adjacent to the air also forms a flat interface, allowing the anti-reflection film to be grown on this flat interface. This is equivalent to processing a new filled metalens, then redesigning the film system structure based on the new metalens, and using the film system growth method in traditional optics to grow the anti-reflection film on the new metalens. This method can achieve constant phase gain, that is, increase the transmittance of the incident light without changing the phase of the new metalens. However, this design method requires redesigning the phase of the metalens and then designing the anti-reflection film based on the new metalens, so the design process is complicated. In addition, this method requires introducing traditional optical processes after filling the original metalens, which makes the processing complex and leads to high production costs. For example, during filling, because the gaps between the nanostructures are at the micrometer level or even the nanometer level, the filling material cannot completely fill all the gaps, resulting in pores that affect optical performance and reduce the yield rate.

[0106] In view of this, the present invention provides a method for designing a metalens. Figures 1 to 6 As shown, this method introduces a material layer with an anti-reflection effect into the superlens. Before the superlens is processed, the refractive index of the material layer and the distance from the bottom to the top of the material layer in the nanostructure unit along the extension direction of the nanostructure are jointly optimized with the phase of the superlens.

[0107] Specifically, a material layer is deposited on the side of the metalens surface having the nanostructure, so that the material layer covers any one or both of the following surfaces: at least a portion of the surface of the nanostructure; and the surface of the metalens substrate close to the nanostructure. The nanostructure, the substrate on one side of the nanostructure, and the material layer constitute a nanostructure unit. In other words, any nanostructure, the substrate centered on the nanostructure, and the material layer covering at least a portion of the surface of the nanostructure and / or a portion of the surface of the substrate centered on the nanostructure constitute a nanostructure unit. It can be understood that, if Figures 1 to 6As shown, the size of the substrate below the nanostructure in any nanostructure unit satisfies: the diameter of the circumscribed circle of the substrate is equal to the arrangement period of the nanostructure.

[0108] More specifically, the nanostructure unit at least satisfies:

[0109] ; (1)

[0110] in, is the number of the nanostructure unit in the superlens; is the phase of the nanostructure unit numbered i; n eff-i is the effective refractive index of the nanostructure unit; is the angular frequency of the incident light; is the speed of light; is the refractive index of the material layer; h is the distance from the bottom to the top of the material layer in the nanostructure unit along the extension direction of the nanostructure. Figure 1 Schematic diagrams of the structures of multiple optional nanostructure units are shown. It is understood that the height of the material layer provided in the embodiments of the present application is directly related to the deposition rate and deposition time. It should be noted that formula (1) jointly designs the phase of each nanostructure unit with the material layer contained therein, so that the material layer does not destroy the phase of the nanostructure unit.

[0111] Furthermore, the material layer also satisfies formula (2):

[0112] ; (2)

[0113] Where N is the total number of nanostructures in the metalens; is the refractive index of the substrate.

[0114] According to the implementation mode of this application, Figure 2 As shown in FIG, a semiconductor method is used to deposit a material layer on the side of the metalens with the nanostructure. Figure 2 As shown in the middle left image, the material layer covers the entire surface of the nanostructure and the substrate. Figure 2 The right figure shows an example of a nanostructure unit in the super lens. Figure 2 The thickness of the material layer is evenly distributed.

[0115] Optionally, both the nanostructure and the material layer are made of materials that are transparent in the working band. For example, any of the materials with low refractive index such as aluminum oxide, silicon oxide, magnesium oxide, manganese oxide, silicon nitride, magnesium fluoride or hafnium oxide. Another example, any of the materials with high refractive index such as silicon, germanium, gallium phosphide, gallium arsenide, gallium antimonide, indium phosphide, indium arsenide, indium antimonide, titanium oxide, silicon nitride or germanium antimony telluride. In some optional embodiments, the refractive index of the material layer is less than the refractive index of the nanostructure. This method mainly uses the nanostructure for phase modulation. In other optional embodiments, the refractive index of the material layer is greater than the refractive index of the nanostructure. This method mainly uses the material layer for phase modulation, and the nanostructure does not play a major role. The above two methods of matching the refractive index of the material layer and the nanostructure have different principles, and the corresponding nanostructures and nanostructure units are completely different. When the refractive index of the material layer is higher than that of the nanostructure layer, the metalens has a higher utilization rate of the incident light, and the design and processing difficulty of the nanostructure is lower. According to the embodiments of the present application, Figure 3 As shown, a material layer is deposited on the side of the metalens having the nanostructures so that the material layer covers the top of the nanostructures and fills the surface of the substrate adjacent to the air. Figure 3 The left picture in the figure shows a schematic diagram of the local structure of the super lens. Figure 3 The right figure in the figure shows a schematic diagram of a nanostructure unit in the superlens. Figure 3 In the nanostructure unit, along the extension direction of the nanostructure, the distance from the bottom to the top of the material layer is equivalent to the distance from the substrate surface to the upper surface of the material layer covered by the top of the nanostructure.

[0116] According to the implementation mode of this application, Figure 4 As shown in FIG, the material layer covers the sidewalls of the nanostructures and the substrate surface between the gaps between the nanostructures. Figure 4 As shown in the center left image, the material layer covers part of the surface of the nanostructure and all of the surface of the substrate adjacent to the air. Figure 4 The middle right figure shows a schematic diagram of an optional nanostructure unit of the metalens. Figure 4 In the nanostructure unit, the distance from the bottom to the top of the material layer along the extension direction of the nanostructure is equivalent to the distance from the substrate surface to the upper surface of the material layer covered by the nanostructure sidewall. Figure 4 In the nanostructure unit, the distance from the bottom to the top of the material along the extension direction of the nanostructure is equivalent to the distance from the substrate surface to the top of the nanostructure.

[0117] According to the implementation mode of this application, Figure 5 As shown, the material layer only covers the surface of the nanostructures, while the surface of the substrate is adjacent to the air. Figure 5 The left figure in the figure shows a schematic diagram of the local structure of the metalens; Figure 5The right figure in the figure shows a schematic diagram of any nanostructure unit in the superlens. Figure 5 In the nanostructure unit, the distance from the bottom to the top of the material layer along the extension direction of the nanostructure is equivalent to the distance from the substrate surface to the upper surface of the material layer covered by the top of the nanostructure.

[0118] According to the implementation mode of this application, Figure 6 As shown, the material layer only covers the top surfaces of the nanostructures. Figure 6 The left figure in the figure shows a schematic diagram of the local structure of the metalens; Figure 6 The right figure in the figure shows a schematic diagram of any nanostructure unit in the superlens. Figure 6 In the nanostructure unit, the distance from the bottom to the top of the material layer along the extension direction of the nanostructure is equivalent to the thickness of the material layer.

[0119] The above embodiments are only some optional examples of material layer coverage patterns. The metalens design method provided in the embodiments of the present application can also be provided with a variety of optional coverage forms, for example, the material layer only covers the sidewalls of the nanostructure. The material layer covering the sidewalls of the nanostructure can be achieved by the sidewall deposition method in the semiconductor process. In the material layer coverage pattern provided in the above embodiments, it is simpler to introduce the material layer process into the top layer, sidewalls and gaps of the nanostructure (i.e., all surfaces adjacent to the air on the incident light side of the metalens).

[0120] Before depositing the material layer, as Figure 7 As shown, the refractive index and height of the material layer can be optionally determined according to the following steps:

[0121] S1, select the initial parameters of the nanostructure according to the phase distribution of the metalens;

[0122] S2, setting the initial refractive index of the material layer and establishing a model of a nanostructure unit including the nanostructure;

[0123] S3, setting an initial distance from the bottom to the top of the nanostructure along the extension direction of the nanostructure so that the phase of the nanostructure unit covers 0 to 2π;

[0124] S3, arranging the nanostructures according to the phase distribution of the superlens, and calculating the effective refractive index of the nanostructure units corresponding to all the nanostructures;

[0125] S5, calculating the total effective refractive index of the metalens based on the effective refractive indices of all metasurface units; a metasurface unit refers to a portion of a nanostructure unit that does not contain a substrate, i.e., a nanostructure and a material layer in a nanostructure;

[0126] S6, calculating the first difference between the total effective refractive index of the metalens and the refractive index of the substrate And calculate the transmittance T of the metalens;

[0127] S7, determine whether the first difference is less than the target value , and whether the transmittance is greater than the target transmittance T0;

[0128] If so, the initial refractive index and initial height are the refractive index n and height h of the material layer at the time of deposition;

[0129] If not, steps S2 to S7 are repeated until the first difference is less than the target value and the transmittance is greater than or equal to the target transmittance, wherein the target value and the target transmittance are determined by the design requirements of the metalens.

[0130] Optionally, if repeating steps S2 to S7 still fails to meet the design requirements (the first difference is less than the target value, and the transmittance is greater than or equal to the target transmittance), the metalens design method provided in the embodiment of the present application further includes:

[0131] Step S8, repeating steps S1 to S7 until the refractive index of the material layer and the distance from the bottom to the top of the material layer along the extension direction of the nanostructure that meet the design requirements are obtained.

[0132] It should be noted that the initial parameters of the nanostructure include the type of nanostructure, refractive index, height, and arrangement period. The nanostructure can be a polarization-sensitive structure that imposes a geometric phase on the incident light. Examples include elliptical cylinders, hollow elliptical cylinders, elliptical holes, hollow elliptical holes, rectangular cylinders, rectangular holes, hollow rectangular cylinders, and hollow rectangular holes. The nanostructure can be a polarization-insensitive structure that imposes a propagation phase on the incident light. Examples include cylindrical structures, hollow cylindrical structures, circular holes, hollow circular holes, square cylinders, square holes, hollow square cylinders, and hollow square holes.

[0133] It is understood that the nanostructures are arranged in an array on the surface of the substrate. Alternatively, the nanostructures are arranged in a close-packed pattern, and the nanostructures can be arranged at the center and / or vertex positions of the close-packed pattern. For example, the nanostructures are arranged in an array in the form of a regular hexagon. For another example, the nanostructures are arranged in an array in the form of a ring fan. For another example, the nanostructures are arranged in an array in the form of a regular quadrilateral. The size of the nanostructure unit is determined by the period of the nanostructure. For example, the diameter of the circumscribed circle of the substrate in the nanostructure unit is equal to the arrangement period of the nanostructure.

[0134] Optionally, the arrangement period of the nanostructures is greater than or equal to 0.3λ c , and is less than or equal to 2λ c ; Among them, λ c is the center wavelength of the working band; when the working band is multi-band, λ cis the center wavelength of the shortest wavelength operating band. Optionally, the height of the nanostructure is greater than or equal to 0.3λ c , and less than or equal to 5λ c ; Among them, λ c is the center wavelength of the working band; when the working band is multi-band, λ c is the center wavelength of the shortest wavelength operating band. Optionally, the arrangement period of the nanostructures at different positions on the metalens is the same. Optionally, the aspect ratio of the nanostructures is less than or equal to 20, so that the light energy utilization rate of the metalens is greater than or equal to 75%.

[0135] Optionally, the arrangement period of the nanostructures at different positions on the metalens is at least partially the same. For example, the arrangement of the nanostructures may be denser near the center of the substrate and sparser near the edge of the substrate.

[0136] For the optional operating bands (wavelengths of 450nm to 1550nm) of the metalens provided in the embodiments of the present application, such as the near-infrared band and the visible light band, the nanostructures are corresponding subwavelength structures. Therefore, optionally, for the near-infrared band, the arrangement period of the nanostructures is less than or equal to 1500nm; optionally, for the blue light visible light band, the arrangement period of the nanostructures is less than or equal to 450nm. It should be noted that if the arrangement period of the nanostructures is too small, for example, less than or equal to half the wavelength, it will cause coupling between adjacent nanostructures to produce resonance, thereby causing the transmittance of the metalens to decrease.

[0137] According to an embodiment of the present application, the nanostructure is an all-dielectric structural unit. The material of the nanostructure is a material with high transmittance in the operating band of the superlens. Optionally, the extinction coefficient of the material of the nanostructure for radiation in the operating band is less than 0.01. Exemplarily, the material of the nanostructure includes one or more of fused quartz, quartz glass, crown glass, flint glass, sapphire, crystalline silicon, amorphous silicon, hydrogenated amorphous silicon, and the like. Exemplarily, the material of the nanostructure includes one or more of silicon nitride, titanium oxide, gallium nitride, gallium phosphide, hydrogenated amorphous silicon, amorphous silicon, and crystalline silicon.

[0138] In one optional embodiment, the material of the substrate is the same as the material of the nanostructure. In another optional embodiment, the material of the substrate is different from the material of the nanostructure. The material of the substrate is a material with high transmittance in the operating wavelength band of the superlens provided in the embodiments of the present application. Optionally, the extinction coefficient of the substrate for radiation in the operating wavelength band is less than 0.01. Exemplarily, the material of the substrate can be one or more of fused quartz, quartz glass, crown glass, flint glass, sapphire, crystalline silicon, amorphous silicon, hydrogenated amorphous silicon, etc. Exemplarily, the material of the substrate includes one or more of silicon nitride, titanium oxide, gallium nitride, gallium phosphide, hydrogenated amorphous silicon, amorphous silicon, and crystalline silicon. Optionally, the thickness of the substrate is greater than or equal to 0.1 mm and less than or equal to 2 mm. For example, the thickness of the substrate can be 0.1 mm, 0.5 mm, 1 mm, 1.5 mm, 2 mm, etc. According to an embodiment of the present application, the material of the material layer includes one or more of silicon nitride, titanium oxide, gallium nitride, gallium phosphide, hydrogenated amorphous silicon, amorphous silicon, and crystalline silicon.

[0139] In a second aspect, an embodiment of the present application further provides a metalens, which is designed using the design method provided in any of the above embodiments. The metalens includes:

[0140] a substrate configured to be transparent to radiation in an operating band;

[0141] The nanostructure is located on one side of the substrate and is configured to be transparent to radiation in an operating wavelength band;

[0142] The material layer is configured to cover any one or both of the following surfaces: at least a portion of the surface of the nanostructure; and a surface of the substrate of the metalens facing the nanostructure.

[0143] The nanostructure, the substrate on one side of the nanostructure, and the material layer constitute a nanostructure unit; the nanostructure unit at least satisfies:

[0144] (1)

[0145] in, is the number of the nanostructure unit in the superlens; is the phase of the nanostructure unit numbered i; n eff-i is the effective refractive index of the nanostructure unit; is the angular frequency of the incident light; is the speed of light; is the refractive index of the material layer; h is the distance from the bottom to the top of the material layer in the nanostructure unit along the extension direction of the nanostructure.

[0146] According to the embodiments of the present application, the type, arrangement, and structural parameters of the nanostructures in the metalens are determined by reference to the design method provided in any of the above embodiments. In the metalens provided in accordance with the embodiments of the present application, the structure of the material layer is related to the frequency component of the incident radiation. The material layer can be a single layer structure or a multilayer structure. Generally, the number of material layers is positively correlated with the antireflection bandwidth required for the design.

[0147] In a third aspect, the present application also provides a metalens processing technology, which is applicable to the metalens designed by the method provided in any of the above embodiments or the metalens provided in any of the above embodiments, such as Figure 8 As shown, the process includes:

[0148] growing a nanostructured material on a substrate, i.e., growing a material for forming a nanostructure;

[0149] Coating: coating photoresist on the side of the nanostructured material away from the substrate;

[0150] Photolithography development, exposing the photoresist to form a reference structure;

[0151] Etching and stripping: etching the nanostructured material based on the reference structure to obtain the nanostructure and remove the photoresist;

[0152] Depositing a material layer on any one or both of the following surfaces: at least a portion of the surface of the nanostructure; and a surface of the substrate of the metalens facing the nanostructure; so that the nanostructure, the substrate on one side of the nanostructure, and the material layer constitute a nanostructure unit; and the nanostructure unit at least satisfies formula (1):

[0153] (1)

[0154] in, is the number of the nanostructure unit in the superlens; is the phase of the nanostructure unit numbered i; n eff-i is the effective refractive index of the nanostructure unit; is the angular frequency of the incident light; is the speed of light; is the refractive index of the material layer; h is the distance from the bottom to the top of the material layer in the nanostructure unit along the extension direction of the nanostructure.

[0155] Figure 8 An example is shown Figure 2 The processing technology of the metalens shown. Figure 9 Shown Figure 3 The deposition process of the material layers shown in FIG. Figure 9 As shown in (a) in Figure 8 The process shown deposits material layers to obtain Figure 2 The metal lens shown in FIG is then sprayed with photoresist on the side of the material layer facing the air so that the photoresist covers the entire surface of the material layer facing the air. Afterwards, the material layer on the sidewall of the nanostructure is removed by etching (e.g., electron beam etching), and finally the remaining photoresist is removed to obtain the metal lens shown in FIG. Figure 3 The metalens shown. Figure 9 As shown in (b) in Figure 8 After the nanostructures are machined on the substrate, the material layer is deposited on the top and gaps of the nanostructures by evaporation.

[0156] Figure 10 Shown Figure 4 The processing technology of the material layer in the metal lens is shown in FIG. Figure 10 As shown, according to Figure 8 As shown in Figure 2 The metalens shown is then subjected to a chemical mechanical polishing process to remove the material layer on top of the nanostructures (the side of the nanostructures facing away from the substrate). Figure 11 ,according to Figure 8 The process shown in FIG. Figure 2 The metalens shown in FIG. 1 is obtained by spraying photoresist on the entire surface of the metalens away from the substrate and removing the photoresist on the surface of the nanostructure sidewall and in the gap between the nanostructures by photolithography. Then, the material layer in the gap between the nanostructures is removed by etching, leaving only the material layer on the top and sidewall of the nanostructure. Figure 5 The metalens shown.

[0157] Figure 12 Shown Figure 6 The processing technology of the material layers in the metalens shown. Figure 12 , using Figure 11 A similar method in the present invention is to coat photoresist only on the top of the nanostructure, and then remove the material layer on the sidewall of the nanostructure or in the gap of the nanostructure by etching (chemical etching or electron beam etching, etc.), thereby obtaining Figure 6 The metalens shown.

[0158] The deposition process provided in the embodiment of the present application includes but is not limited to physical vapor deposition and atomic layer deposition. For example, processes such as chemical vapor deposition, low-pressure chemical vapor deposition, and thermal evaporation are also applicable to the super lens processing process provided in the embodiment of the present application. Since the material layer of the embodiment of the present application satisfies formula (1), the phase of the nanostructure unit is jointly designed with the refractive index of the material layer and the distance from the bottom to the top of the material layer in the nanostructure unit along the extension direction of the nanostructure, and there is no need to fill the gaps between the nanostructures to form a new super lens. Moreover, since this process does not require filling the nanostructure, the nanostructure and the material layer can be processed successively using semiconductor technology, and there is no need to introduce the film growth process in traditional optics. Compared with traditional processes, the thickness distribution of the material layer is uniform, and the optical phase of the super lens is not destroyed.

[0159] Example

[0160] In an exemplary embodiment, a metalens is designed and produced based on the design method and processing technology provided in the above embodiments as follows.

[0161] The working band of this super lens is between 550nm and 650nm in the visible light band, with an aperture of 2mm, a focal length of 4mm, and a target transmittance of more than 90% in a wide spectrum. The nanostructure in this super lens is a nano cylindrical structure and is arranged in a regular hexagonal pattern. The height of the nano structure is 500nm and the period is 400nm. The base material of this super lens is fused quartz and the nano structure material is silicon nitride (SiN). When no material layer is deposited, for any nano structure unit in the super lens, the relationship between its phase and transmittance is as follows Figure 13 shown.

[0162] See also Figure 13 As shown in the left figure, for a single nanostructure unit, its phase basically satisfies the linear relationship between phase and angular frequency. As can be seen in the right figure, this micro-nano unit can cover 0-2π and has a certain transmittance. The nanostructure is arranged according to the phase distribution of the superlens, and then the effective refractive index of the superlens is calculated. Taking the wavelength of 550nm as an example, the effective refractive index of the superlens is 1.38, and the refractive index of the substrate is known to be 1.42. Finally, through calculation, the broadband transmittance of the superlens is 85%, which does not meet the design requirements.

[0163] A material layer is introduced into the nanostructure unit by atomic layer deposition in the form of sidewall deposition. The material of the material layer is titanium dioxide (TiO2) and the height h is 530nm. The phase and transmittance of the nanostructure unit containing the material layer can be found in Figure 14 .

[0164] like Figure 14 As shown in the middle left figure, any nanostructure unit basically satisfies the linear relationship between phase and angular frequency. Figure 14 As shown in the middle right figure, the nanostructured units can cover a range from 0 to 2π and exhibit high transmittance. Calculations show that the effective refractive index of the metalens is 1.41 at 550nm, given the substrate's refractive index of 1.42. The calculated broadband transmittance of the metalens is 92%.

[0165] In summary, the metalens design method provided in the embodiments of the present application is designed by jointly designing the phase of the nanostructure unit with the refractive index of the material layer and the distance between the uppermost end of the material layer in the nanostructure unit facing away from the substrate and the lowermost end of the material layer facing the substrate. The material layer is deposited on the side of the metalens having the nanostructure, and there is no need to fill the gaps between the nanostructures to obtain a new metalens. An anti-reflection film is then designed based on the new metalens, which simplifies the design process and avoids directly depositing anti-reflection materials on the designed metalens, which may cause the phase of the metalens to be destroyed.

[0166] In the metalens provided in the embodiments of this application, the material layer is co-designed with the nanostructure, covering at least a portion of the surface of the nanostructure and the substrate without disrupting the phase of the metalens. Furthermore, the material layer is fabricated using a semiconductor deposition process immediately after etching the nanostructure, resulting in a simple process and low difficulty in mass production.

[0167] The metalens processing technology provided in the embodiments of the present application allows the material layer to be directly processed through a semiconductor deposition process, avoiding the complex process of using a traditional optical film growth process after filling the gaps in the original nanostructure, thereby reducing mass production costs and process difficulty.

[0168] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art who can easily conceive of changes or substitutions within the technical scope disclosed in the present invention should be included in the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

Claims

1. A method for designing a metalens, characterized in that: The method comprises: A material layer is deposited on the side of the metalens surface having the nanostructures such that the material layer covers either or both of the following surfaces: at least a portion of the surface of the nanostructure; and, The base of the metalens is close to the surface of one side of the nanostructure; Wherein, the nanostructure, the substrate on one side of the nanostructure and the material layer constitute a nanostructure unit; The nanostructure unit at least satisfies: ； in, is the number of the nanostructure unit in the metalens; is the phase of the nanostructure unit numbered i; n eff-i is the effective refractive index of the nanostructure unit; is the angular frequency of the incident light; is the speed of light; is the refractive index of the material layer; h is the distance from the bottom to the top of the material layer in the nanostructure unit along the extension direction of the nanostructure.

2. The method according to claim 1, wherein The nanostructure unit also satisfies: ； Wherein, N is the total number of nanostructures in the metalens; is the refractive index of the substrate.

3. The method according to claim 1, wherein The material layer covering at least a portion of the surface of the nanostructure comprises: The material layer covers the entire end surface of the nanostructure away from the substrate of the super lens; or The material layer covers the entire sidewall of the nanostructure.

4. The method according to any one of claims 1 to 3, wherein: The refractive index of the material layer is smaller than the refractive index of the nanostructure.

5. The method according to any one of claims 1 to 3, wherein: The refractive index of the material layer is greater than the refractive index of the nanostructure.

6. The method according to any one of claims 1 to 3, wherein: The method further includes: before depositing the material layer, determining the refractive index of the material layer and the distance from the bottom to the top of the material layer in the nanostructure unit along the extension direction of the nanostructure.

7. The method according to claim 6, wherein The determining of the refractive index of the material layer and the distance from the bottom to the top of the material layer in the nanostructure unit along the extension direction of the nanostructure comprises: S1, select the initial parameters of the nanostructure according to the phase distribution of the metalens; S2, setting an initial refractive index of the material layer and establishing a model of a nanostructure unit including the nanostructure; S3, setting an initial distance from the bottom to the top of the material layer in the nanostructure unit along the extension direction of the nanostructure, so that the phase of the nanostructure unit covers 0 to 2π; S4, arranging the nanostructures according to the phase distribution of the metalens, and calculating the effective refractive index of the metasurface units corresponding to all the nanostructures; the metasurface units are the portions of the nanostructure units that do not contain a substrate; S5, calculating the total effective refractive index of the metalens based on the effective refractive indices of all metasurface units; S6, calculating a first difference between the total effective refractive index of the metalens nanostructure and the refractive index of the substrate and calculating the transmittance of the metalens; S7, determining whether the first difference is less than a target value, and whether the transmittance is greater than a target transmittance; If so, the initial refractive index and initial distance are the refractive index and height of the material layer at the time of deposition; If not, repeat steps S2 to S7 to make the first difference smaller than the target value and the transmittance greater than or equal to the target transmittance.

8. The method according to claim 7, wherein The determining of the refractive index of the material layer and the distance from the bottom to the top of the material layer in the nanostructure unit along the extension direction of the nanostructure further includes: Step S8: If the first difference value obtained by repeating steps S2 to S7 is not less than the target value, or the transmittance is always less than the target transmittance, then repeat steps S1 to S7.

9. The method according to any one of claims 1 to 3, wherein: The material layer covers the nanostructures and all surfaces of the substrate adjacent to the air.

10. The method according to any one of claims 1 to 3, wherein: The material layer covers the end surface of the nanostructure away from the substrate.

11. The method according to any one of claims 1 to 3, wherein: The material layer covers the surface of the substrate adjacent to air.

12. The method according to any one of claims 1 to 3, wherein: The material layer covers the sidewalls of the nanostructures and the surface of the substrate adjacent to the air.

13. The method according to any one of claims 1 to 3, characterized in that: The material layer covers the entire surface of the nanostructure.

14. A superlens, characterized in that Designed using the method described in any one of claims 1 to 13, the metalens comprises: a substrate configured to be transparent to radiation in an operating band; a nanostructure, located on one side of the substrate and configured to be transparent to radiation in an operating wavelength band; A material layer configured to cover either or both of the following surfaces: at least a portion of the surface of the nanostructure; and, The base of the metalens is close to the surface of one side of the nanostructure; Wherein, the nanostructure, the substrate on one side of the nanostructure and the material layer constitute a nanostructure unit; The nanostructure unit at least satisfies: ； in, is the number of the nanostructure unit in the metalens; is the phase of the nanostructure unit numbered i; n eff-i is the effective refractive index of the nanostructure unit; is the angular frequency of the incident light; is the speed of light; is the refractive index of the material layer; and h is the distance from the bottom to the top of the material layer in the nanostructure unit along the extension direction of the nanostructure.

15. The metalens according to claim 14, wherein The nanostructure unit also satisfies: ； Wherein, N is the total number of nanostructures in the metalens; is the refractive index of the substrate.

16. The metalens according to claim 14 or 15, wherein The height of the nanostructure is 0.3λ c to 2λ c ; Among them, λ c is the center wavelength of the operating band.

17. The metalens according to claim 14 or 15, wherein The height of the nanostructure is greater than or equal to 0.3λ c , and less than or equal to 5λ c ; Among them, λ c is the center wavelength of the operating band.

18. The metalens according to claim 14 or 15, wherein The nanostructures are arranged in an array in the form of a densely packed pattern; wherein the nanostructures are arranged at the center and / or vertex of the densely packed pattern.

19. The metalens according to claim 14 or 15, wherein The aspect ratio of the nanostructure is less than or equal to 20.

20. The metalens according to claim 14 or 15, wherein The material layer is a single-layer structure.

21. The metalens according to claim 14 or 15, wherein The material layer is a multi-layer structure.

22. A metalens processing process, characterized in that: Suitable for a metalens designed using the method of any one of claims 1 to 13 or a metalens according to any one of claims 14 to 21, the process comprising: growing nanostructured materials on a substrate; Coating: coating photoresist on the side of the nanostructured material away from the substrate; Photolithography development, exposing the photoresist to form a reference structure; Etching and stripping: etching the nanostructured material based on the reference structure to obtain a nanostructure, and removing the photoresist; Depositing a layer of material on either or both of the following surfaces: at least a portion of the surface of the nanostructure; and, The base of the metalens is close to the surface of one side of the nanostructure; so that the nanostructure, the substrate on one side of the nanostructure and the material layer constitute a nanostructure unit; and The nanostructure unit at least satisfies: ； in, is the number of the nanostructure unit in the metalens; is the phase of the nanostructure unit numbered i; n eff-i is the effective refractive index of the nanostructure unit; is the angular frequency of the incident light; is the speed of light; is the refractive index of the material layer; and h is the distance from the bottom to the top of the material layer in the nanostructure unit along the extension direction of the nanostructure.

23. The process of claim 22, wherein The material layer also satisfies: ； Wherein, N is the total number of nanostructures in the metalens; is the refractive index of the substrate.

24. The process according to claim 22 or 23, wherein The deposited material layer comprises: The material layer is deposited on the entire end surface of the nanostructure away from the substrate of the superlens; or, the entire sidewall of the nanostructure.

25. The process of claim 22 or 23, wherein The material layer covers the nanostructures and all surfaces of the substrate adjacent to the air.

26. The process of claim 22 or 23, wherein The material layer covers the end surface of the nanostructure away from the substrate.

27. The process of claim 22 or 23, wherein The material layer covers the surface of the substrate adjacent to air.

28. The process of claim 22 or 23, wherein The material layer covers the sidewalls of the nanostructures and the surface of the substrate adjacent to the air.

29. The process of claim 22 or 23, wherein The material layer covers the entire surface of the nanostructure.

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