Large-aperture achromatic metalens, metalens system, and optical system

Abstract

The present invention discloses a large-aperture achromatic metalens, metalens system, and optical system. The metalens includes a substrate capable of transmitting light in different wavelength bands, including visible light and infrared light, and a plurality of superstructure units provided on one surface of the substrate, the superstructure units being arranged in an array, with nanostructures provided at the center or at the center and vertices of each superstructure unit, the surface of the substrate on which the plurality of superstructure units are disposed forms a metalens surface, the metalens surface is divided into a plurality of concentric annular regions along the radial direction, incident broad-spectrum light can be focused into each annular region without chromatic aberration, and the metalens with the nanostructures is insensitive to the polarization of the incident light, allowing the metalens to be thinner and lighter than conventional ordinary lenses, while being able to correct the aberrations of traditional metalens and achieving clearer image quality.

Description

[Technical field]

[0001] The present invention relates to the field of lenses, and in particular to large aperture achromatic metalens, achromatic spherical aberration metalens systems, and optical systems. [Background technology]

[0002] As a basic component, optical lenses play an important role in scientific and industrial fields such as imaging, precision measurement, and optical communication. Traditional optical lenses are manufactured through a series of complicated processes such as material cutting, surface grinding, finish grinding, and coating. When a multi-lens group optical system is constructed from a number of traditional optical lenses, such a system is generally composed of a number of refractive lenses or mirror lenses to complete a specific application imaging, such as infinity imaging, video projection, and microscopic imaging. However, a lens group composed of traditional refractive mirror lenses generally has defects such as large volume and heavy weight. In recent years, metalens has become an emerging technology for small optical lenses, solving the defects of traditional lenses such as large volume and heavy weight. However, metalens has several problems, such as being sensitive to polarization, having low transmittance in a wide spectrum, and being unable to achieve both large aperture and chromatic aberration correction.

[0003] To facilitate understanding of the present invention, the following definitions are used: Group delay is the rate of change of total phase shift through a device or transmission medium with respect to angular frequency, i.e., dφ / dω, where φ is the total phase shift, ω is the angular frequency, and is equal to 2πf, where f is frequency. Summary of the Invention [Problem to be solved by the invention]

[0004] In response to the above technical problems, embodiments of the present invention provide a large aperture achromatic metalens, an achromatic spherical aberration metalens system, and an optical system. [Means for solving the problem]

[0005] A first aspect of an embodiment of the present invention provides a large aperture achromatic metalens, the large aperture achromatic metalens comprising: A substrate capable of transmitting light of different wavelength bands including visible light and infrared light; A plurality of superstructure units provided on one surface of the substrate, the plurality of superstructure units being arranged in an array, and a nanostructure being provided at a center position of each superstructure unit or at a center position and a vertex position of each superstructure unit; the nanostructure is axially symmetric along a first axis and a second axis, and a plurality of nanostructure units obtained by dividing the nanostructure along the first axis and the second axis are similar, and the first axis and the second axis are arranged perpendicularly and perpendicular to a height direction of the nanostructure, respectively; A surface of the substrate of the plurality of superstructure units forms a metalens surface, and the metalens surface is divided into a plurality of concentric annular regions along a radial direction, and incident broad spectrum light can be focused in each annular region without chromatic aberration. 、 The plurality of annular regions on the metalens surface are periodically arranged according to an equivalent refractive index along a radial direction of the metalens, the equivalent refractive index being between the refractive index of the nanostructured material and the refractive index of air, the equivalent refractive index being shown in formula (1) below:

number

number

number

[0006] Preferably, the nanostructure is a nanopillar structure, which includes one of a positive nanocolumn, a negative nanocolumn, a hollow nanopillar structure, a rectangular nanopillar structure and a topological nanopillar structure, and is preferably a negative rectangular nanopillar structure, a negative hollow rectangular nanopillar structure or a hollow rectangular nanopillar structure.

[0007] Preferably, the optical phase of the nanopillar structure is related to the height of the nanopillar structure, the cross-sectional shape of the nanopillar structure, and the material of the nanopillar structure; the cross section is parallel to the substrate; The material of the nanostructure is one or more of photoresist, quartz glass, silicon nitride, titanium oxide, aluminum oxide (sapphire), crystalline and amorphous silicon, gallium nitride, crystalline germanium, selenium sulfide, zinc sulfide, and chalcogenide glass.

[0008] preferably, between the plurality of annular regions of the metalens surface, there is interference enhancement for a central wavelength and two edge wavelengths of incident light at a focal plane of the metalens; Preferably, the rings on the metalens surface are periodically arranged according to an equivalent refractive index along a radial direction of the metalens, the equivalent refractive index being between the refractive index of the nanostructured material and the refractive index of air; Preferably, the rings on the metalens surface are periodically arranged according to a group delay along a radial direction of the metalens, and the group delay period is obtained by subtracting the minimum group delay from the maximum group delay in the nanostructure base, and preferably the incident broad spectrum light is discretized into N characteristic wavelengths, and the sum of the phase at the N characteristic wavelengths of the nanostructures at a location along the radial direction r0 on the metalens surface and the absolute value of the theoretical phase is minimum, and optimization is performed according to the following equation to obtain:

number

number

number

[0009] Preferably, the metalens surface and the other surface of the substrate are plated with anti-reflective coatings corresponding to the nanostructure material and the substrate material, respectively. For the corresponding relationships mentioned herein, reference may be made to the applicant's CN202022010432.4 (Far-infrared silicon-based metalens anti-reflective coating and metalens), in which regard, the entire contents of CN202022010432.4 are incorporated herein by reference.

[0010] A second aspect of an embodiment of the present invention provides an achromatic metalens system, the achromatic metalens system comprising: The telescope tube, and any one of the metalens described above that is mounted within the lens barrel and has different optical phases at different wavelengths.

[0011] A third aspect of an embodiment of the present invention provides an optical system, the optical system comprising: The telescope tube, at least two metalenses according to any one of claims 1 to 5, wherein the nanostructures in the superstructure units on the metalens surface at the same radius are different, The at least two metalens are coaxial and mounted within the barrel, the metalens have different optical phases at different wavelengths, and one of the metalens is intended to correct aberrations of the other metalens at a corresponding wavelength.

[0012] Preferably, one of the metalens is positioned to correct aberrations of the other metalens, the aberrations including at least one of spherical aberration, coma, astigmatism, field curvature, distortion, position chromatic aberration, and magnification chromatic aberration.

[0013] Preferably, the metalens comprises a first metalens and a second metalens; Incident light passes through the first metalens and the second metalens in sequence, The first metalens is intended to correct any aberrations of the second metalens.

[0014] Preferably, the other surface of the metalens substrate is plated with a first visible light wavelength band anti-reflection coating, the metalens surface is plated with a second visible light wavelength band anti-reflection coating, and the material of the metalens substrate is quartz glass, and / or The material of the nanostructure of the metalens is one or more of silicon nitride, titanium oxide, gallium nitride, aluminum oxide, and silica.

[0015] Preferably is before The second visible light wavelength band anti-reflection film Refractive index of is the nanostructure Equivalent Matching refractive index Good morning do.

[0016] Preferably, the material of the metalens substrate and nanostructures is one or more of crystalline silicon, crystalline germanium, selenium sulfide, zinc sulfide, and chalcogenide glass. Effect of the Invention

[0017] According to the technical solutions provided by the above embodiments of the present invention, the multiple nanostructure units obtained by dividing the nanostructure of the metalens of the present invention along the first axis and the second axis are similar, so that the metalens is not sensitive to the polarization of the incident light; the metalens has a smaller thickness and is lighter than conventional ordinary lenses; and the surface of the metalens of the present invention is divided into a plurality of concentric annular regions along the radial direction, so that the incident broad spectrum light can be focused on each annular region without chromatic aberration, with each characteristic wavelength being focused to the same focal point; this metalens overcomes the refractive index / group delay limitations of the energy efficiency of conventional achromatic metalens nanostructures; and, compared to conventional achromatic metalenses, this metalens not only corrects chromatic aberration, but also has a large aperture of the centimeter level, correcting the aberrations of traditional metalenses and achieving clearer image quality.

[0018] Additionally, the metalens system of the present invention comprises a metalens of the present invention mounted on a lens barrel, wherein the optical phase of the metalens at different wavelengths is different, and the optical system of the present invention comprises multiple metalenses of the present invention mounted coaxially on the lens barrel, and the metalens optical system of the present invention is capable of broad spectrum segment wide angle imaging, and compared to conventional metalens optical systems, the optical system of the present invention maintains the advantages of a metalens, such as small volume and light weight, while being able to correct all aberrations and provide high definition, wide angle, and broad spectrum imaging.

[0019] However, the foregoing general description and the following detailed description are not restrictive of the invention but are merely exemplary and explanatory. [Brief description of the drawings]

[0020] [Figure 1] FIG. 2 is a schematic diagram of a focusing metalens in one embodiment of the present invention and a diagram of a portion of the surface structure. [Figure 2A] FIG. 2 is a diagram of a regular hexagonal arrangement on a metalens surface in one embodiment of the present invention. [Figure 2B] FIG. 2 is a diagram of a square array of a metalens surface in one embodiment of the present invention. [Figure 3A] FIG. 1 is a schematic diagram of a positive nanopillar structure in one embodiment of the present invention. [Figure 3B] FIG. 2 is a schematic diagram of a negative nanopillar structure in one embodiment of the present invention. [Figure 3C] FIG. 1 is a schematic diagram of a hollow nanopillar structure in one embodiment of the present invention. [Figure 3D] FIG. 1 is a schematic diagram of a negative hollow nanopillar structure in one embodiment of the present invention. [Figure 3E] FIG. 1 is a schematic diagram of a rectangular nanopillar structure in one embodiment of the present invention. [Figure 3F] FIG. 2 is a schematic diagram of a negative angle nanopillar structure in one embodiment of the present invention. [Figure 3G] FIG. 1 is a schematic diagram of a hollow rectangular nanopillar structure in one embodiment of the present invention. [Figure 3H] FIG. 2 is a schematic diagram of a negative hollow square nanopillar structure in one embodiment of the present invention. [Figure 3I] FIG. 1 is a schematic diagram of a topology nanopillar structure in one embodiment of the present invention. [Figure 4A] FIG. 2 is a relationship diagram between the equivalent refractive index of a silicon-based nanostructure and the 10 μm optical phase (operating wavelength: 8 to 12 μm) in one embodiment of the present invention. [Figure 4B] FIG. 2 is a graph showing the relationship between group delay at 10 μm and optical phase at 10 μm (operating wavelength 8-12 μm) of a silicon-based nanostructure in one embodiment of the present invention. [Figure 5A] FIG. 13 shows a diagram of equivalent refractive index (theoretical / actual) versus metalens radius for a metalens period having a focal length of 25 mm and an aperture of 19 mm in one embodiment of the invention. [Figure 5B] FIG. 14 shows a diagram of 8 μm phase (theoretical / actual) versus metalens radius for a metalens with a focal length of 25 mm and an aperture of 19 mm in one embodiment of the invention. [Figure 5C] FIG. 2 is a diagram of 10 μm phase (theoretical / actual) versus metalens radius (equivalent refractive index method) for a metalens with a focal length of 25 mm and an aperture of 19 mm in one embodiment of the invention. [Figure 5D] FIG. 2 is a diagram of 12 μm phase (theoretical / actual) versus metalens radius (equivalent refractive index method) for a metalens with a focal length of 25 mm and an aperture of 19 mm in one embodiment of the invention. [Figure 5E] FIG. 2 is a diagram of metalens period group delay (theoretical / actual) versus metalens radius (group delay method) for a metalens with a focal length of 25 mm and an aperture of 19 mm in one embodiment of the invention. [Figure 5F] FIG. 2 is a diagram of 8 μm phase (theoretical / actual) versus metalens radius (group delay method) for a metalens with a focal length of 25 mm and an aperture of 19 mm in one embodiment of the invention. [Figure 5G] FIG. 2 is a diagram of 10 μm phase (theoretical / actual) versus metalens radius (group delay method) for a metalens with a focal length of 25 mm and an aperture of 19 mm in one embodiment of the invention. [Figure 5H] FIG. 2 is a diagram of 12 μm phase (theoretical / actual) versus metalens radius (group delay method) for a metalens with a focal length of 25 mm and an aperture of 19 mm in one embodiment of the invention. [Figure 5I] FIG. 2 is a diagram of 8 μm phase (theoretical / actual) versus metalens radius (global search method) for a metalens with a focal length of 25 mm and an aperture of 19 mm in one embodiment of the invention. [Figure 5J] FIG. 2 is a diagram of 10 μm phase (theoretical / actual) versus metalens radius (global search method) for a metalens with a focal length of 25 mm and an aperture of 19 mm in one embodiment of the invention. [Figure 5K] FIG. 2 is a diagram of 12 μm phase (theoretical / actual) versus metalens radius (global search method) for a metalens with a focal length of 25 mm and an aperture of 19 mm in one embodiment of the invention. [Figure 6A] FIG. 13 is an xz plane light intensity distribution diagram near the focal point of a metalens designed by the equivalent refractive index method, which has a focal length of 25 mm and an aperture of 19 mm. [Figure 6B]FIG. 13 is an xz plane light intensity distribution map near the focal point of a metalens designed by the group delay method, with a focal length of 25 mm and an aperture of 19 mm. [Figure 6C] FIG. 2 is an xz plane light intensity distribution map near the focal point of a metalens designed by the global search method, which has a focal length of 25 mm and an aperture of 19 mm. [Figure 7] FIG. 2 is a schematic diagram of a double metalens optical system having an operating wavelength of 8-12 μm in another embodiment of the present invention. [Figure 8A] FIG. 8 is a diagram of the relationship between effective refractive index and radius of the first metalens of the optical system of FIG. [Figure 8B] FIG. 8 is a diagram of the equivalent refractive index versus radius of the second metalens of the optical system of FIG. [Figure 9] FIG. 8 is a modulation transfer function diagram of the optical system of FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] Exemplary embodiments will now be described in detail, examples of which are shown in the drawings. When the following description refers to the drawings, the same reference numerals in different drawings indicate similar or corresponding elements unless otherwise stated. The embodiments described below in the exemplary embodiments do not represent all embodiments consistent with the present invention. On the contrary, the apparatus and methods consistent with some aspects of the present invention as detailed in the claims are merely examples.

[0022] The terms used in the present invention are not intended to limit the present invention, but are merely intended to describe specific embodiments. Unless otherwise clearly expressed in the specification, the singular forms "a," "the," and "the" used in the present invention and claims include the plural. Also, the term "and / or" used herein includes any or all possible combinations of one or more associated items.

[0023] Here, in the present invention, terms such as first, second, and third may be used to describe various types of information, but these information are not limited to these terms. These terms are merely used to distinguish between the same types of information. For example, the first information may be called the second information, and similarly, the second information may be called the first information, without departing from the scope of the present invention. Depending on the circumstances, the phrase "if" used herein may be interpreted as "if...", "when...", or "determined according to...". If not contradictory, the technical features in the following examples and embodiments may be combined with each other.

[0024] The optical system composed of multiple traditional lenses has multiple defects, such as high assembly alignment requirements, reduced light energy utilization rate for aberration correction due to multiple lenses, large volume and weight, and the entire system is complicated, etc. Although the planar diffractive lens can reduce the volume and weight to a certain extent, the cross-sectional structure of the wavelength scale makes it difficult to achieve accurate phase distribution, so the requirement of high resolution cannot be achieved.

[0025] Optical metasurfaces have rapidly emerged as a mainstream method for achieving miniaturized and flattened optics. Optical metasurfaces can be used to realize axicon lenses, blazed diffraction gratings, polarizers, holographic plates, and flat lenses. A single-layer spherical aberration-free metalens can be realized by using metasurfaces with continuous 2π phase change. In addition, a two-layer metasurface metalens can correct all monochromatic aberrations. However, due to the limitations of the processing technology, conventional achromatic metalens are difficult to achieve both large apertures and larger numerical apertures, which greatly limits the application of metalens to imaging beam systems.

[0026] An embodiment of the present invention provides a nanostructure that is axially symmetric along a first axis and a second axis, respectively, a plurality of nanostructure units obtained by dividing the nanostructure along the first axis and the second axis are similar, and the first axis and the second axis are disposed perpendicularly and are respectively perpendicular to a height direction of the nanostructure, and the optical phases at different positions of the nanostructure at different wavelengths are different, thereby defining an optical phase distribution at different wavelengths of the metalens.

[0027] An embodiment of the present invention further provides a metalens, the metalens including a substrate capable of transmitting light of different wavelength bands including visible light and infrared light, and a plurality of superstructure units provided on the same surface of the substrate, the plurality of superstructure units being arranged in an array, preferably the superstructure units may be regular hexagonal and / or square, a nanostructure is provided at the center position of each superstructure unit or at the center position and apex position of each superstructure unit, the nanostructure is axisymmetric along a first axis and a second axis, respectively, the plurality of nanostructure units obtained by dividing the nanostructure along the first axis and the second axis are similar, the first axis and the second axis are perpendicular, and are each perpendicular to a height direction of the nanostructure. The optical phases of the nanostructures at different positions are different at different wavelengths, thereby limiting the optical phase distribution of the metalens at different wavelengths. One surface of the substrate of the plurality of superstructure units forms a metalens surface, the metalens surface is divided into a plurality of concentric annular regions along the radial direction, and incident broad spectrum light can be focused without achromatic aberration in each annular region. The optical phases of different wavelengths of the metalens of the present invention are different. The metalens surface is divided into a plurality of concentric annular regions along the radial direction, and incident broad spectrum light can be focused without achromatic aberration in each annular region, and interference enhancement is performed between each annular region at the focal plane of the metalens for the central wavelength and two edge wavelengths of the incident light, thereby solving the problem of achieving both a large aperture and a large numerical aperture for an achromatic metalens.

[0028] An embodiment of the present invention further provides an achromatic spherical aberration corrected metalens system comprising a lens barrel, a lens, and at least one metalens according to the first aspect of the present invention, the metalens being mounted within the lens barrel, the metalens having different optical phases at different wavelengths thereby achieving chromatic aberration-free and spherical aberration-free focusing / divergence, and a metalens surface formed from the one surface facing the substrate and the other surface of the substrate are plated with anti-reflective coatings corresponding to the nanostructured material and the substrate material, respectively.

[0029] Embodiments of the present invention further provide an optical system comprising a barrel and at least two metalenses according to the first aspect of the present invention, wherein the nanostructures in the superstructure units of a metalens surface at the same radius of the at least two of the metalenses are different, illustratively the nanostructures in the superstructure units of the metalens surface at the same radius of one of the two metalenses may be nanocolumn structures and the other is a rectangular nanopillar structure, and in some other embodiments where the optical system comprises a number of the metalenses, the nanostructures in the superstructure units of the metalens surface at the same radius of each of the metalenses may be partially similar, and at least two of the metalenses are spaced apart, the metalenses are mounted coaxially within the barrel, the optical phases of the metalenses at different wavelengths are different, and one of the metalenses corrects aberrations of the other metalense at a corresponding wavelength. The metalens of one of the optical systems is arranged to correct aberrations of the other metalens, the aberrations including at least one of spherical aberration, coma, astigmatism, field curvature, distortion, position chromatic aberration, and magnification chromatic aberration. The achromatic metalens and optical system of the present invention are capable of fully aberration-corrected broad spectrum segment wide angle imaging, and compared to conventional metalens optical systems, the optical system of the present invention maintains the advantages of small volume, light weight, and ease of integration, while being able to correct all aberrations and provide high definition, wide angle, and broad spectrum imaging.

[0030] Reference will now be made in detail to exemplary embodiments, examples of which are illustrated in the drawings.

[0031] Example 1: An embodiment of the present invention provides a nanostructure 21, the nanostructure 21 being axially symmetric along a first axis and a second axis, a plurality of nanostructure units obtained by dividing the nanostructure 21 along the first axis and the second axis are similar, the first axis and the second axis are arranged perpendicularly and are respectively perpendicular to a height direction of the nanostructure 21, the optical phases of the nanostructure 21 at different positions at different wavelengths are different, thereby limiting the optical phase distributions of the metalens 200 at different wavelengths, and the nanostructure 21 is a nanopillar structure.

[0032] The nanostructure 21 may be a nanopillar structure or other nanostructures that are axially symmetric along the horizontal and vertical axes, respectively. Hereinafter, an example in which the nanostructure 21 is a nanopillar structure will be described, but if the nanostructure 21 is another structure, the nanopillar structure in the following examples may be replaced with the corresponding structure.

[0033] The nanopillar structure includes one of a positive nano-column, a negative nano-column, a positive nano-pillar structure, a negative nano-pillar structure, a hollow nano-pillar structure, a negative hollow nano-pillar structure, a rectangular nano-pillar structure, a negative rectangular nano-pillar structure, a hollow rectangular nano-pillar structure, a negative hollow rectangular nano-pillar structure, and a topological nano-pillar structure. Illustratively, in the same metalens, the nanopillar structure is one of a positive nano-pillar structure, a negative nano-pillar structure, a hollow nano-pillar structure, a rectangular nano-pillar structure, a negative rectangular nano-pillar structure, a hollow rectangular nano-pillar structure, a negative hollow rectangular nano-pillar structure, and a topological nano-pillar structure, which is easy to process.

[0034] In the embodiment of the present application, the optical phase of the nano-pillar structure 21 is related to the height of the nano-pillar structure, the cross-sectional shape and the material of the nano-pillar structure. The cross-section of the nano-pillar structure is parallel to the substrate 1. Here, the first axis and the second axis pass through the center of the nano-pillar structure 21 and are parallel to the horizontal plane.

[0035] 3A-3I, the height of the nanopillar structure (ie, the height of the nanopillar structure in the z-direction) is H.

[0036] When the entire structure formed from the plurality of nanopillar structures 21 is intended to transmit visible light, the height H of the nanopillar structure is 300 nm or more and 1500 nm or less, the pitch between adjacent nanopillar structures (i.e., the pitch between the centers of two adjacent nanopillar structures) is 300 nm or more and 650 nm or less, and the minimum size of the nanopillar structure (such as the diameter, the side length, and / or the minimum pitch between two adjacent nanopillar structures) may be 40 nm. Exemplarily, the height H of the nanopillar structure is 300 nm, 400 nm, 500 nm, 600 nm, 700 nm, 800 nm, 900 nm, 1000 nm, 1100 nm, 1200 nm, 1300 nm, 1400 nm, or 1500 nm, etc. Illustratively, the pitch between adjacent nanopillar structures is 300 nm, 350 nm, 400 nm, 450 nm, 500 nm, 550 nm, 600 nm, or 650 nm, or any other value within the range.

[0037] If the entire structure formed from the plurality of nanopillar structures 21 is intended to transmit infrared light in the wavelength range of 8 to 12 μm, the height H of the nanopillar structure may be 5 μm or more and 50 μm or less, the pitch between adjacent nanopillar structures may be 1.5 μm or more and 5 μm or less, and the minimum size of the nanopillar structure (e.g., diameter, side length and / or minimum pitch between two adjacent nanopillar structures) may be 40 nm. Exemplarily, the height H of the nanopillar structure may be 5 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, or 50 μm. Exemplarily, the pitch between adjacent nanopillar structures may be 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, or 5 μm, or any other value within the range.

[0038] 3A, the positive nanopillar structure 211 includes a first cylinder, which is a solid structure, and has a cross-sectional diameter d in the xy plane ranging from 40 nm to 400 nm, for example, d may be set to 40 nm, 50 nm, 150 nm, 200 nm, 230 nm, 300 nm, 350 nm, 400 nm, or any value within the range.

[0039] 3B, the negative nanopillar structure 212 includes a first pillar 2121, and the cross-sectional shape of the first pillar 2121 is the same as that of the superstructure unit 2. For example, when the superstructure unit 2 is hexagonal, the cross-sectional shape of the first pillar 2121 is also hexagonal, and when the superstructure unit 2 is square, the cross-sectional shape of the first pillar 2121 is also square. In this embodiment, the cross-sectional size of the first pillar 2121 is the same as that of the superstructure unit 2. The first pillar 2121 is provided with a cylindrical first hollow portion 2122 extending from its ceiling portion to its bottom portion, and the first pillar 2121 and the first hollow portion 2122 are arranged coaxially. The negative nanopillar structure 212 has a cross-sectional diameter d in the xy plane (i.e., cross-section) that is in the range of 40 nm to 400 nm, for example, d may be set to 40 nm, 50 nm, 150 nm, 200 nm, 230 nm, 300 nm, 350 nm, 400 nm, or any value within the range.

[0040] 3C, the hollow nanopillar structure 213 includes a second cylinder 2131, which is provided with a cylindrical second hollow section 2132 extending from its ceiling to its bottom, and the second cylinder 2131 and the second hollow section 2132 are arranged coaxially. The hollow nanopillar structure 213 has a cross-sectional outer diameter d1 and an inner diameter d2 in the xy plane, and the range of d1-d2 is between 40 nm and 400 nm, for example, d1-d2 is set to 40 nm, 50 nm, 150 nm, 200 nm, 230 nm, 300 nm, 350 nm, 400 nm, or any value within the range.

[0041] Referring to FIG. 3D, the negative hollow nanopillar structure 214 includes a second pillar 2141, and the cross-sectional shape of the second pillar 2141 is the same as that of the superstructure unit 2. For example, when the superstructure unit 2 is hexagonal, the cross-sectional shape of the second pillar 2141 is also hexagonal, and when the superstructure unit 2 is square, the cross-sectional shape of the second pillar 2141 is also square. In this embodiment, the cross-sectional size of the second pillar 2141 is the same as that of the superstructure unit 2. Furthermore, the second pillar 2141 is provided with a cylindrical third hollow portion 2142 extending from its ceiling portion to its bottom portion. Furthermore, inside the third hollow portion 2142, a third cylinder 2143, which is a solid structure, is provided. The second cylinder 2141 , the third hollow portion 2142 and the third cylinder 2143 are arranged coaxially, the second cylinder 2141 has the same height as the third cylinder 2143 , and the bottom of the third cylinder 2143 is attached to the substrate 1 .

[0042] Referring to FIG. 3E, the rectangular nanopillar structure 215 includes a third pillar which is a solid structure, and the cross-sectional shape of the third pillar is a square.

[0043] 3F, the negative angle nanopillar structure 216 includes a fourth pillar 2161, and the cross-sectional shape of the fourth pillar 2161 is similar to that of the superstructure unit 2. For example, when the superstructure unit 2 is hexagonal, the cross-sectional shape of the fourth pillar 2161 is also hexagonal, and when the superstructure unit 2 is square, the cross-sectional shape of the fourth pillar 2161 is also square. In this embodiment, the cross-sectional size of the fourth pillar 2161 is similar to that of the superstructure unit 2. Furthermore, the fourth pillar 2161 is provided with a fourth hollow portion 2162 extending from its ceiling portion to its bottom portion, and the cross-sectional shape of the fourth hollow portion 2162 is square, and the fourth pillar 2161 and the fourth hollow portion 2162 are arranged coaxially.

[0044] 3G, the hollow rectangular nanopillar structure 217 includes a fifth pillar 2171, and the cross-sectional shape of the fifth pillar 2171 is a square. Furthermore, the fifth pillar 2171 is provided with a fifth hollow portion 2172 extending from its ceiling to its bottom, and the cross-sectional shape of the fifth hollow portion 2172 is a square. The fifth pillar 2171 and the fifth hollow portion 2172 are arranged coaxially. In the same cross-section, the corresponding diagonals of the square corresponding to the fifth pillar 2171 and the square corresponding to the fifth hollow portion 2172 are arranged on the same line.

[0045] Referring to FIG. 3H, the negative hollow square nanopillar structure 218 includes a sixth pillar 2181, and the cross-sectional shape of the sixth pillar 2181 is similar to that of the superstructure unit 2. For example, when the superstructure unit 2 is hexagonal, the cross-sectional shape of the sixth pillar 2181 is also hexagonal, and when the superstructure unit 2 is square, the cross-sectional shape of the sixth pillar 2181 is also square. In this embodiment, the cross-sectional size of the sixth pillar 2181 is similar to that of the superstructure unit 2. Furthermore, the sixth pillar 2181 is provided with a sixth hollow portion 2182 extending from its ceiling to its bottom, and the cross-sectional shape of the sixth hollow portion 2182 is a square. Inside the sixth hollow portion 2182, a seventh pillar 2183, which is a solid structure, is provided, and the cross-sectional shape of the seventh pillar 2183 is a square. In the embodiment, the sixth cylinder 2181, the sixth hollow portion 2182 and the seventh cylinder 2183 are coaxially arranged. In the same cross section, the corresponding diagonals of the square corresponding to the seventh cylinder 2183 and the square corresponding to the sixth hollow portion 2182 are collinear.

[0046] 3I, the topology nanopillar structure 219 includes an eighth pillar which is a solid structure. The cross-sectional shape of the eighth pillar is a polygon, and the sides of the polygon are arc-shaped.

[0047] Example 2: An embodiment of the present invention provides a metalens 200, and referring to Figures 1 to 2B, the metalens includes a substrate 1 and a plurality of superstructure units 2 disposed on the same surface of the substrate 1. The substrate 1 can transmit light of different wavelength ranges, and in an embodiment of the present invention, the light of different wavelength ranges may include visible light and infrared light, or may include others. Exemplarily, the wavelength of the visible light transmitted through the substrate 1 may be 400 nm or more and 700 nm or less. Exemplarily, the wavelength of the infrared light transmitted through the substrate 1 may be 8 μm or more and 12 μm or less. The surface of the metalens 200 is divided into a number of concentric ring 230 regions along the radial direction, and the incident broad spectrum light is focused without achromatic aberration on each ring 230, and between each ring 230, at the focal plane of the metalens, interference enhancement is performed for the central wavelength and two edge wavelengths of the incident light, or the metalens surface nanostructures 21 are optimally selected from a base of thousands to tens of thousands of unpolarized nanostructures (FIG. 1 is a diagram of a portion of the metalens surface), so that each characteristic wavelength is focused to the same focal point, solving the problem of achieving both a large aperture and a large numerical aperture for the achromatic metalens.

[0048] The multiple superstructure units 2 are arranged in an array, and the superstructure units 2 are regular hexagons and / or squares. For example, referring to FIG. 2B , one nanostructure 21 is provided at the center of each superstructure unit 2, and the number of nanostructures 21 in the metalens 200 formed by such an array arrangement is the smallest, and the performance of the formed metalens 200 also meets needs. Alternatively, for example, referring to FIG. 2A , one nanostructure 21 may be provided at each apex position of each superstructure unit 2 and at the center position of each superstructure unit 2. Here, one nanostructure 21 is recognized as the entire nanostructure, and in some cases, the nanostructure 21 may be a plurality of sub-nanostructures and is recognized as a plurality of nanostructures.

[0049] 2A, all the superstructure units 2 are regular hexagons, and in other embodiments, all the superstructure units 2 are squares, and in other embodiments, the plurality of superstructure units 2 include regular hexagonal array units and square superstructure units, where in other embodiments, the superstructure units 2 may be designed to have other regular polygonal shapes.

[0050] In this embodiment, the different optical phases at different wavelengths of nanostructures 21 at different positions limit the optical phase distribution at different wavelengths of the metalens to form a broad spectrum segmented metalens, where the entire structure formed from the plurality of nanostructures 21 in the embodiments of the present application may simultaneously transmit visible light or infrared light, or may simultaneously transmit light in different wavelength bands.

[0051] Exemplarily, the thickness of the substrate 1 is greater than or equal to 0.1 mm and less than 2 mm, for example, the thickness of the substrate 1 may be set to 0.1 mm, 0.5 mm, 1 mm, 1.5 mm, 2 mm, or any value within the range.

[0052] In this embodiment, the thickness of the entire structure formed from the plurality of nanostructures 21 is on the micron level, so that the nanostructures 21 of the substrate 1 approximate a planar structure. Preferably, the thickness of the entire structure formed from the plurality of nanostructures 21 is 50 μm or less, for example, 1.5 μm, 5 μm, 10 μm, 1.5 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, 50 μm, etc. Preferably, the thickness of the entire structure formed from the plurality of nanostructures 21 and the size of the operating wavelength of the metalens system are on the same order of magnitude. Also, here, in this embodiment of the present invention, the thickness of the metalens is the sum of the thickness of the entire structure formed from the plurality of nanostructures 21 and the thickness of the substrate. Here, the substrate 1 is only a support structure that supports the plurality of nanostructures 21, and the material of the substrate 1 and the material of the nanostructures 21 may be the same or different.

[0053] Exemplarily, the material of the substrate 1 may be quartz glass or crystalline silicon, where, the material of the substrate 1 may be other materials.

[0054] Exemplarily, the material of nanostructures 21 is one or more of photoresist, quartz glass, silicon nitride, titanium oxide, aluminum oxide (sapphire), crystalline silicon (including crystalline and amorphous silicon), gallium nitride, crystalline germanium, selenium sulfide, zinc sulfide, and chalcogenide glass, although the material of nanostructures 21 may be other materials. Furthermore, in embodiments of the present invention, the shape of metalens 200 is determined by the shape of the substrate, which may have a regular shape, such as a circle, a rectangle, a regular polygon, or the like, or may have an irregular shape. Exemplarily, when substrate 1 is circular, the shape of metalens 200 is circular, and exemplarily, when substrate 1 is square, the shape of metalens 200 is square.

[0055] The nanopillar structure is processed in the substrate 1 by one of a large-diameter high-speed laser direct writing processing method, a photoetching processing method, and a nanoimprint processing method, but the processing method is not limited to these processing methods.

[0056] Illustratively, in some embodiments the rings 230 on the surface of the metalens 200 are arranged periodically according to the equivalent refractive index of the metalens along the radial direction. The equivalent refractive index of the metalens 200 can be calculated according to the formula: 3 ) as shown in

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[0057] formula( 3 ) is taken as a surplus relative to the equivalent refractive index interval in the nanostructure equivalent refractive index database, 4 ) to obtain the periodic equivalent refractive index.

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[0058] formula( 5 ) to the group delay interval in the nanostructure group delay database, 6 ) to obtain the periodic group delay.

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[0059] Illustratively, in some embodiments, the incident broad spectrum light is discretized into N characteristic wavelengths, and the formula ( 7 ), the sum of the phase at the N characteristic wavelengths of the nanostructure at a point along the radial direction r0 of the metalens surface and the absolute value of the theoretical phase is minimum.

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[0060] Example 3: Embodiments of the present invention further provide an achromatic metalens system that includes a lens barrel (not shown) and metalens 200. Metalens 200 is mounted within the lens barrel, and the metalens' optical phase at different wavelengths is different to achieve achromatic and spherical aberration-free focusing / divergence.

[0061] Illustratively, the operating wavelength band of the metalens 200 is 8-12 μm, the aperture is 19 mm, and the focal length is 25 mm. For the relationship between the metalens periodic equivalent refractive index (theoretical / actual) of the metalens 200 and the metalens radius, please refer to FIG. 5A, where the solid line is the theoretically required equivalent refractive index, and the asterisks are the achievable equivalent refractive index based on the nanostructure. FIGS. 5B-5D show the relationship diagrams between the 8 μm, 10 μm, and 12 μm phases (theoretical / actual) of the metalens 200 and the metalens radius. For the xz plane light intensity distribution diagram near the focus of the metalens designed by the periodic equivalent refractive index method, please refer to FIG. 6A.

[0062] Illustratively, the operating wavelength range of the metalens 200 is 8-12 μm, the aperture is 19 mm, and the focal length is 25 mm. For the relationship between the metalens periodic group delay (theoretical / actual) of the metalens 200 and the metalens radius, see FIG. 5E, where the solid line is the theoretically required group delay and the asterisks are the achievable group delay based on the nanostructure. FIGS. 5F-5H show the relationship between the 8 μm, 10 μm, and 12 μm phases (theoretical / actual) of the metalens 200 and the metalens radius. For the xz plane light intensity distribution near the focus of the metalens designed by the periodic group delay method, see FIG. 6B.

[0063] Illustratively, the metalens operating wavelength range is 8-12 μm, the aperture is 19 mm, and the focal length is 25 mm. FIGS. 5I-5K show diagrams of the 8 μm, 10 μm, and 12 μm phases (theoretical / actual) versus metalens radius for the metalens. See FIG. 6C for an xz plane light intensity distribution diagram near the focal point of the metalens designed by the global search method.

[0064] Exemplarily, because the operating wavelength of the achromatic metalens system is in the far-infrared wavelength band, in order to improve the transmittance of the achromatic metalens system in the far-infrared wavelength band, exemplarily, in metalens 200, the other surface of substrate 1, i.e., the side on which the nanostructures are not provided, is plated with a first infrared wavelength band anti-reflection coating, and the metalens surface formed from the side of the substrate is plated with a second infrared wavelength band anti-reflection coating, the materials of substrate 1 and nanostructures 21 are both crystalline silicon, the first infrared wavelength band anti-reflection coating and the second infrared wavelength band anti-reflection coating both match crystalline silicon, and the first infrared wavelength band anti-reflection coating may be the same as or different from the material of the second infrared wavelength band anti-reflection coating.

[0065] Of course, preferably, the other surface of the metalens substrate 1 may be plated with a first visible light wavelength band antireflection coating, and the metalens surface may be plated with a second visible light wavelength band antireflection coating, in which case the material of the metalens substrate may be quartz glass, the first visible light wavelength band antireflection coating matches the quartz glass, the material of the metalens nanostructures 21 is any one or more of silicon nitride, titanium oxide, gallium nitride, aluminum oxide, and silica, and the second visible light wavelength band antireflection coating matches the refractive index of the material of the nanostructures.

[0066] Example 4: An embodiment of the present invention further provides an optical system that includes a lens barrel (not shown) and two metalens, first metalens 210 and second metalens 220, respectively, where the nanostructures in the superstructure units on the metalens surface at the same radius of first metalens 210 and second metalens 220 are different, illustratively the nanostructures in the superstructure units on the metalens surface at the same radius of one of the two metalens are hollow nanopillar structures and the other is a negative angle nanopillar structure. Incident light passes through first metalens 210 and second metalens 220 in sequence, and first metalens 210 corrects all aberrations of second metalens 220.

[0067] Illustratively, the operating wavelength range of the metalens system is 8-12 μm, the entrance pupil diameter is 7 mm, the focal length is 7 mm, and the total angle of view is 50°×38.5°. The relationship between the periodic equivalent refractive index (theoretical / actual) of first metalens 210 and second metalens 220 of the optical system and the radius of metalens 200 can be seen in Figures 8A and 8B, respectively, where the solid line is the theoretically required equivalent refractive index and the asterisks are the achievable equivalent refractive index based on the nanostructure.

[0068] The modulation transfer function of the optical system can be seen in Figure 9. As shown in Figure 9, the modulation transfer functions for each field of view all reach the diffraction limit, demonstrating the excellent broad-spectrum wide-angle imaging capability of the metalens optical system.

[0069] The above embodiments do not limit the technical solutions of the present invention, but are merely for illustration. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art can still understand that the technical solutions described in the above embodiments may be modified or some of the technical features may be replaced with equivalents, and the essence of the corresponding technical solutions will not deviate from the spirit and scope of the technical solutions of the embodiments of the present invention through such modifications or replacements. [Explanation of symbols]

[0070] 1. Substrate 2. Super Structure Unit 21 Nanostructure 211...Normal nanopillar structure 212...Negative nanopillar structure 2121...1st column 2122...1st hollow part 213...Hollow nanopillar structure 2131...Second cylinder 2132...2nd hollow part 214...Negative hollow nanopillar structure 2141...Second pillar 2412...Third hollow part 2143...Third cylinder 215...Square nanopillar structure 216...Negative angle nanopillar structure 2161...4th pillar 2162...4th hollow part 217...Hollow rectangular nanopillar structure 2171...5th column 2172...5th hollow part 218···Negative hollow rectangular nanopillar structure 2181...6th column 2182...6th hollow part 2183...7th column 219···Topological nanopillar structure 200 Metalens 210...First metalens 220...Second metalens 230...Ring

Claims

1. 1. A large aperture achromatic metalens, A substrate capable of transmitting light of different wavelength bands; a plurality of superstructure units provided on one surface of the substrate, the plurality of superstructure units being arranged in an array, and a nanostructure being provided at a center position of each superstructure unit or at a center position and a vertex position of each superstructure unit; The nanostructure is axially symmetric along a first axis and a second axis, and a plurality of similar nanostructure units are obtained by dividing the nanostructure along the first axis and the second axis, and the first axis and the second axis are arranged perpendicular to each other and perpendicular to a height direction of the nanostructure; a surface of the substrate of each of the plurality of superstructure units forms a metalens surface, the metalens surface being divided into a plurality of concentric annular regions along a radial direction, and incident broad spectrum light can be focused in each annular region without chromatic aberration; The plurality of annular regions on the metalens surface are periodically arranged according to an equivalent refractive index along a radial direction of the metalens, the equivalent refractive index being between the refractive index of the nanostructured material and the refractive index of air, the equivalent refractive index being shown in formula (1) below: ##EQU00016## In the above formula (1), ##EQU00017## is the phase of the metalens determined by the radius r of the metalens surface and the wavelength λ, ω is the circular frequency of light, c is the speed of light, H is the height of the nanostructures, r is the radius of the metalens surface and is the distance from each of the nanostructures to the center of the substrate, The plurality of annular regions on the metalens surface are periodically arranged according to a group delay along a radial direction of the metalens, and the period of the group delay is obtained by subtracting the minimum group delay from the maximum group delay in the nanostructure base, the group delay being shown in equation (2) below: [0018] A large-aperture achromatic metalens.

2. The large-aperture achromatic metalens as claimed in claim 1, wherein the light of different wavelength bands includes visible light and infrared light.

3. The large aperture achromatic metalens according to claim 1 or 2, characterized in that the nanostructures are nanopillar structures, and the nanopillar structures include one or more of a positive nanocolumn, a negative nanocolumn, a hollow nanopillar structure, a rectangular nanopillar structure, and a topological nanopillar structure.

4. the optical phase of the nanopillar structure is related to the height of the nanopillar structure, the cross-sectional shape of the nanopillar structure, and the material of the nanopillar structure; the cross section is parallel to the substrate; 4. The large-aperture achromatic metalens as described in claim 3, wherein the material of the nanostructure is one or more of photoresist, quartz glass, silicon nitride, titanium oxide, aluminum oxide, crystalline and amorphous silicon, gallium nitride, crystalline germanium, selenium sulfide, zinc sulfide, and chalcogenide glass.

5. the plurality of annular regions on the metalens surface collectively provide interference enhancement for the center wavelength and two edge wavelengths of light incident on the metalens at a focal plane; The incident broad spectrum light is discretized into N characteristic wavelengths, and the N characteristic wavelengths are arranged in a radial direction r ０ The sum of the phase at N characteristic wavelengths of the nanostructure at a point along the line and the absolute value of the theoretical phase is minimized, and optimization is performed according to the following formula to obtain: [0019] [0020] is the radial direction r of the metalens surface ０ The characteristic wavelength λ of the nanostructure at a point along ｉ where i=1, 2, ..., N. ##EQU00021## is the radial direction r of the metalens surface ０ The characteristic wavelength λ along ｉ The large-diameter chromatic aberration corrected metalens according to any one of claims 1 to 4, characterized in that the theoretical phase is

6. 5. The large-aperture achromatic metalens according to any one of claims 1 to 4, characterized in that a surface of the metalens is plated with an anti-reflection film corresponding to the nanostructures, and another surface of the substrate is plated with an anti-reflection film corresponding to the substrate material.

7. 1. An achromatic metalens system, comprising: The telescope tube, and the metalens according to any one of claims 1 to 6, which is mounted in the lens barrel and has different optical phases at different wavelengths; The equivalent refractive index interval in the equivalent refractive index database of the nanostructure is calculated by subtracting the minimum equivalent refractive index from the maximum equivalent refractive index, on the premise that the central phase is guaranteed to span the entire 2π as much as possible. [0022] And then, The equivalent refractive index in the above formula (1) is taken as a surplus with respect to the equivalent refractive index section in the equivalent refractive index database of the nanostructure, thereby obtaining a periodic equivalent refractive index as shown in the following formula (3): [0023] The group delay interval in the nanostructure group delay database is calculated by subtracting the minimum group delay from the maximum group delay, with the assumption that the center phase is guaranteed to span the entire 2π as much as possible, to obtain ΔGD. The group delay in the above formula (2) is taken as a surplus relative to the group delay section in the nanostructure group delay database to obtain a periodic group delay as shown in the following formula (4): [0024] In the above formula (4), GD Ｐ 13. An achromatic metalens system, wherein (r) is the group delay at radius r of the metalens.

8. 1. An optical system comprising: The telescope tube, at least two metalenses according to any one of claims 1 to 6, wherein the nanostructures in the superstructure units on the metalens surface at the same radius are different; 11. The optical system of claim 1, wherein the at least two metalens are coaxial and mounted within the barrel, the metalens have different optical phases at different wavelengths, and at least one of the metalens is intended to correct aberrations of the other metalens at a corresponding wavelength.

9. 9. The optical system of claim 8, wherein one of the metalens is positioned to correct aberrations of the other metalens, the aberrations including at least one of spherical aberration, coma, astigmatism, field curvature, distortion, position chromatic aberration, and magnification chromatic aberration.

10. the metalens includes a first metalens and a second metalens; incident light passes through the first metalens and the second metalens in sequence, 9. The optical system of claim 8, wherein the first metalens is intended to correct for any aberrations of the second metalens.

11. 11. The optical system of claim 10, wherein a first visible waveband anti-reflective coating is plated on another surface of the metalens substrate, and a second visible waveband anti-reflective coating is plated on the metalens surface.

12. the material of the metalens substrate is quartz glass, and / or 12. The optical system of claim 10 or 11, wherein the material of the nanostructure of the metalens is any one or more of silicon nitride, titanium oxide, gallium nitride, aluminum oxide, and silica.

13. The optical system described in claim 11, characterized in that the refractive index of the second visible light wavelength band anti-reflection film matches the equivalent refractive index of the nanostructure.

14. 14. The optical system of any one of claims 8 to 13, wherein the material of the metalens substrate and nanostructure is one or more of crystalline silicon, crystalline germanium, selenium sulfide, zinc sulfide, and chalcogenide glass.

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