Optical super lens with high focusing efficiency and preparation method thereof

Abstract

The invention relates to an optical super lens with high focusing efficiency and a preparation method thereof. The optical super lens comprises a pair of optical substrates, antireflection films arranged on the surfaces of one sides of the optical substrates, moth-eye films arranged on the surfaces of the other sides of the optical substrates in a protruding mode, and a plurality of nano dielectric cylinders arranged between the pair of moth-eye films and made of high-refractive-index materials. At least one structural parameter of the plurality of nano dielectric cylinders in the length direction of the optical substrate is modulated to meet phase distribution of 2 pi, and at least one structural parameter of the moth eye mask in the thickness direction of the optical substrate is modulated to complete refractive index transition from the plurality of nano dielectric cylinders to the optical substrate. According to the invention, the problem of transmittance reduction caused by refractive index mismatch in a traditional optical super lens is solved, and the focusing efficiency of the optical super lens is effectively improved on the basis of not influencing the original phase distribution.

Description

Technical Field

[0001] The present invention relates to the technical field of optical elements, and in particular to an optical metalens with high focusing efficiency and a preparation method thereof. Background Art

[0002] Optical metalenses are lenses used to focus the entire visible light spectrum. By precisely controlling the phase of light, they can focus or defocus light in very thin structures, and even achieve a negative refractive index effect in some specific cases. The design of optical metalenses needs to take into account the phase changes of light waves, and this change often depends on the microstructure of the optical material. Traditional lens design is based on large-scale optical elements, while optical metalenses require fine structures at the micron or even nanometer level, which poses huge challenges in computing and manufacturing. For example, in the field of optical metalenses, to meet the needs of phase control, the structure in the optical metalenses needs to have a high refractive index, such as TiO2 or Si3N4. These materials are often amorphous or polycrystalline thin film materials. Due to their high cost and high mechanical brittleness, they cannot be directly made into independent self-supporting wafers. Therefore, the material structure commonly used in optical metalenses is to grow a high refractive index dielectric film on quartz glass to achieve phase control.

[0003] The optical metalens structure with a high refractive index can be roughly regarded as a composite thin layer formed by nano-dielectric columns composed of high-refractive-index materials and air. This composite thin layer exhibits an equivalent refractive index that is significantly different from the refractive index of the air medium and the substrate material. Based on this, Fresnel reflection occurs at both interfaces, which is not conducive to the focusing efficiency of the transmissive optical metalens. In addition, the preparation and processing of high-refractive-index films are complex and costly, and the durability of the films is poor. These factors together limit the widespread application of optical metalens technology. Summary of the Invention

[0004] In view of the shortcomings of the existing technology, the first object of the present invention is to provide an optical metalens with high focusing efficiency, which solves the problem of reduced transmittance caused by refractive index mismatch in traditional optical metalens, and effectively improves the focusing efficiency of the optical metalens without affecting the original phase distribution.

[0005] A second object of the present invention is to provide a method for preparing an optical metalens with high focusing efficiency, which realizes micro-nano processing of a sandwich structure, broadens the design freedom, and has the advantages of simple preparation, low cost, and high yield.

[0006] To achieve the above first object, the present invention provides the following technical solutions: A high-focusing-efficiency optical metalens comprises a pair of optical substrates, an antireflection film disposed on one surface of the optical substrate, a moth-eye film protruding from the other surface of the optical substrate, and a plurality of nano-dielectric pillars composed of a high-refractive-index material disposed between the pair of moth-eye films. At least one structural parameter of the plurality of nano-dielectric pillars along the length direction of the optical substrate is modulated to satisfy a 2π phase distribution. At least one structural parameter of the moth-eye film along the thickness direction of the optical substrate is modulated to complete a refractive index transition from the plurality of nano-dielectric pillars to the optical substrate.

[0007] Furthermore, the plurality of nano-medium pillars are arranged in a one-dimensional or two-dimensional array; and / or, the nano-dielectric columns are mirror-symmetrical on a central plane parallel to the length direction of the optical substrate; And / or, the plurality of nano-dielectric columns have the same height and period, and the duty cycle increases along at least two array directions, and the at least two array directions (+X, -X, +Y, -Y) are opposite, intersecting and / or perpendicular array directions.

[0008] Furthermore, the high refractive index material of the nano-dielectric column is one or a combination of amorphous silicon, TiO2, SiC and diamond with a refractive index exceeding 1.7; and / or, the cross section of the nano-media column is circular, elliptical or polygonal; and / or, the height of the nano-medium pillars is 100-1500 nm; and / or, the period of the nano-medium columns is 200-1000 nm; And / or, the duty cycle of the nano-medium columns ranges from 20% to 85%.

[0009] Furthermore, the moth-eye film is composed of a plurality of frustum columns arranged in a two-dimensional array; And / or, the frustum is mirror-symmetrical on a central plane parallel to the thickness direction of the optical substrate; And / or, the heights and periods of the plurality of frustum columns are the same, and the diameters increase gradually from the nano-medium column to the optical substrate.

[0010] Furthermore, the material of the truncated cone is one or a combination of quartz, optical resin, SiC and diamond; And / or, the height of the frustum is 50-500 nm; And / or, the period of the frustum is 100-600 nm; And / or, the diameter of the frustum is in the range of 30 to 600 nm.

[0011] Furthermore, the optical substrate and the moth-eye film are integrally formed; And / or, the optical substrate is made of one or a combination of quartz, optical resin, SiC and diamond; And / or, the thickness of the optical substrate is 100-5000 μm.

[0012] Furthermore, the antireflection film is formed by alternating a plurality of low-refractive-index film layers with a refractive index not exceeding 1.7 and a high-refractive-index film layer with a refractive index exceeding 2.1; And / or, the low refractive index film layer is a composite film of one or more of SiO2 and Al2O3; And / or, the high refractive index film layer is a composite film of one or more of TiO2 and HfO2; And / or, the thickness of the antireflection film is 0.5-50.0 μm.

[0013] To achieve the above second purpose, the present invention provides the following technical solutions: A method for preparing an optical metalens with high focusing efficiency comprises the following steps: S1 deposits a thin film on one side of the optical substrate to obtain an antireflection film; S2 performs patterning on the other surface of the optical substrate obtained in S1 to obtain a moth-eye film; S3 spin-coating a photoresist on the moth-eye film obtained in S2 so that the photoresist fills the gaps on the moth-eye film and exceeds the surface of the moth-eye film to a predetermined height of the nano-dielectric pillars, and then performing a patterning process to deposit a plurality of nano-dielectric pillars in the patterned area; S4 directly bonds the moth-eye film obtained in S2 to the plurality of nano-medium pillars obtained in S3; Alternatively, a photoresist is first spin-coated on the plurality of nano-dielectric pillars obtained in S3 so that the photoresist extends beyond the surface of the nano-dielectric pillars to a predetermined moth-eye film height, and then patterning is performed, and another moth-eye film is deposited on the patterned area, and thin film deposition is continued to obtain another optical substrate, and then S1 is repeated; S5 removes the photoresist on the moth-eye film and the nano-dielectric pillars obtained in S3 and S4 by wet stripping to obtain an optical superlens.

[0014] Furthermore, in S1, in the electron beam evaporation coating equipment, after setting the deposition parameters and target deposition values ​​of two film materials with a refractive index not exceeding 1.7 and a refractive index exceeding 2.1, several low-refractive-index film layers with a refractive index not exceeding 1.7 and high-refractive-index film layers with a refractive index exceeding 2.1 are alternately deposited to obtain an antireflection film.

[0015] Furthermore, in S2 and S4, an equivalent refractive index distribution curve of the optical superlens structure formed by multiple nano-dielectric columns is obtained in advance, and the refractive index variation range from the optical superlens structure to the optical substrate in the optical superlens plane is determined, and then the structural parameters of the moth-eye film are determined through the transition from the equivalent refractive index of the optical superlens to the refractive index of the optical substrate.

[0016] Furthermore, in S2, the other side surface of the optical substrate is first exposed and developed, and then a metal mask is evaporated, and the metal mask in the non-patterned area is peeled off, and then the optical substrate in the non-patterned area is etched to obtain a moth-eye film; wherein, the exposure dose and development time are controlled to obtain a complete patterned area, and the thickness of the metal mask is controlled for successful peeling.

[0017] Furthermore, in the S3, a photoresist (AZ1518) is first spin-coated on the moth-eye film, and the photoresist above the surface of the moth-eye film is removed by dry etching, and then a photoresist (zep520) is spin-coated to a predetermined nano-dielectric column height, and then the photoresist surface is exposed and developed, and a high-refractive index material is deposited in the patterned area, and then the high-refractive index material above the predetermined nano-dielectric column height is removed by dry etching to obtain a plurality of nano-dielectric columns; wherein, the etching time of the photoresist is controlled, and the deposition temperature is kept low to ensure the integrity of the photoresist.

[0018] Furthermore, in S4, the bonding pressure is controlled to be at a moderate value to ensure the bonding strength without damaging the material structure.

[0019] Furthermore, in the S4, a photoresist (AZ1518) is first spin-coated on the surface of the plurality of nano-dielectric pillars and the photoresist (zep520) to a predetermined moth-eye film height, and then the photoresist surface is exposed and developed. After the material is deposited in the patterned area, the high-refractive-index material above the predetermined optical substrate thickness is removed by dry etching to obtain another moth-eye film and optical substrate; wherein, the exposure dose and the development time are controlled to ensure a complete micro-nano structure, and in addition, the dry etching time is controlled so that the material above the thickness is just removed.

[0020] Furthermore, in S5, the concentration of the wet stripping solution and the time of the wet stripping are controlled.

[0021] In summary, the beneficial technical effects of the present invention are: 1. The present invention proposes to process a moth-eye film structure on a substrate of any material, then prepare a thin layer of high refractive index material above the moth-eye film, process an optical super-lens structure on the thin layer, and then cover a substrate of any material that also has a moth-eye film structure to achieve a sandwich structure. The so-called moth-eye film structure imitates the special microstructure of the moth-eye surface. According to the equivalent medium theory, the refractive index of this structure is equivalent to that of a gradient multilayer film, and avoids the difficulties in preparing multilayer films and the low durability of the film. Therefore, it can be used as a refractive index transition layer between the substrate and the optical super-lens structure, and the same applies to the optical super-lens structure and the air. The present invention effectively solves the problem of reduced transmittance due to refractive index mismatch in traditional optical super-lenses, and effectively improves the focusing efficiency of the optical super-lens without affecting the original phase distribution; 2. In order to achieve 2π phase control, the material of the nanopillars in the optical metalens often has a very high refractive index, which leads to strong interface reflection between them and the air and the substrate, resulting in a decrease in propagation efficiency. On the basis of not changing the phase distribution design of the optical metalens, the present invention uses a special micro-nano processing method to superimpose a layer of microstructure on the top and bottom to increase the transmittance of the interface between the nanopillars of the optical metalens and the air and substrate, thereby further improving the efficiency of the optical metalens. For the optical metalens, this method can significantly improve the propagation efficiency without affecting the design of the optical metalens itself, thereby improving the utilization rate of light energy in practical applications. 3. The present invention can effectively improve the low efficiency of traditional optical metalens due to refractive index mismatch without affecting the structural design of the optical metalens itself. The optical metalens block material can be any material, regardless of the refractive index, which broadens the choice of optical metalens materials and is beneficial to cost control, function expansion, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 2 is a schematic structural diagram of the optical metalens according to embodiment 1 of the present invention.

[0023] Figure 2 This is a flowchart of the method provided in Example 6 of the present invention.

[0024] Figure 3 This is an equivalent refractive index distribution curve diagram of Example 9 of the present invention.

[0025] Figure 4 This is a transmittance curve diagram of Example 9 of the present invention.

[0026] In the figure, 1. optical substrate; 2. anti-reflection film; 3. moth-eye film; 31. frustum column; 4. nano-dielectric column. DETAILED DESCRIPTION

[0027] In order to make the technical means, creative features, objectives and functions achieved by the present invention clearer and easier to understand, the present invention is further explained below with reference to the accompanying drawings and specific implementation methods.

[0028] Example 1: Reference Figure 1 The present invention discloses a high-focusing-efficiency optical metalens comprising a pair of optical substrates 1, an antireflection film 2 disposed on one surface of the optical substrate 1, a moth-eye film 3 protruding from the other surface of the optical substrate 1, and a plurality of nano-dielectric pillars 4 composed of a high-refractive-index material disposed between the pair of moth-eye films 3. At least one structural parameter of the plurality of nano-dielectric pillars 4 along the length of the optical substrate 1 is modulated to achieve a 2π phase distribution, and at least one structural parameter of the moth-eye film 3 along the thickness direction of the optical substrate 1 is modulated to achieve a refractive index transition from the plurality of nano-dielectric pillars 4 to the optical substrate 1.

[0029] Example 2: This is a high-focusing-efficiency optical metalens disclosed in the present invention. This differs from Example 1 in that, first, the nanodielectric pillars 4 are arranged in a two-dimensional array along two mutually perpendicular directions (X and Y). The nanodielectric pillars 4 are mirror-symmetric about a central plane parallel to the length of the optical substrate 1. The height and period of these nanodielectric pillars 4 are identical, and the duty cycle increases along the two array directions (+X and -X). Specifically, the nanodielectric pillars 4 are made of amorphous silicon with a high refractive index, a circular cross-section, a height of 600 nm, a period of 500 nm, and a duty cycle ranging from 30% to 80%.

[0030] Secondly, the moth-eye film 3 consists of a plurality of frustum pillars 31 arranged in a two-dimensional array along two mutually perpendicular directions (X and Y). The frustum pillars 31 are mirror-symmetric about a central plane parallel to the thickness direction of the optical substrate 1. These frustum pillars 31 have the same height and period, and their diameter increases from the nanomaterial pillars 4 toward the optical substrate 1. Specifically, the frustum pillars 31 are made of quartz, have a height of 200 nm, a period of 250 nm, and a diameter ranging from 70 to 160 nm.

[0031] Again, the optical substrate 1 and the moth-eye film 3 are integrally formed. The material of the optical substrate 1 is also quartz, and the thickness is 500 μm.

[0032] Finally, the anti-reflection film 2 is composed of ten layers of low-refractive index film layers (SiO2 film layers) and high-refractive index film layers (TiO2 film layers) alternately stacked. The thickness of the anti-reflection film 2 is 0.811μm. Starting from the air interface, the first layer is SiO2 and the second layer is TiO2. They are stacked in sequence with thicknesses of 170.9nm, 114.8nm, 2.5nm, 79.9nm, 7.9nm, 91.8nm, 87.9nm, 92.2nm, 88.3nm, and 75.6nm, respectively, achieving high transmittance in the near-infrared band of 1000~1550nm.

[0033] Example 3: This is a high-focusing-efficiency optical metalens disclosed in the present invention. This differs from Example 1 in that, first, the nanodielectric pillars 4 are arranged in a two-dimensional array along two mutually perpendicular directions (X and Y). The nanodielectric pillars 4 are mirror-symmetric about a central plane parallel to the length of the optical substrate 1. The nanodielectric pillars 4 have the same height and period, and the duty cycle increases along the two array directions (+X and -X). Specifically, the nanodielectric pillars 4 are made of SiC with a high refractive index, have a circular cross-section, a height of 900 nm, a period of 500 nm, and a duty cycle ranging from 30% to 80%.

[0034] Secondly, the moth-eye film 3 consists of a plurality of frustum pillars 31 arranged in a two-dimensional array along two mutually perpendicular directions (X and Y). The frustum pillars 31 are mirror-symmetric about a central plane parallel to the thickness direction of the optical substrate 1. These frustum pillars 31 have the same height and period, and their diameter increases from the nanomaterial pillars 4 toward the optical substrate 1. Specifically, the frustum pillars 31 are made of quartz, have a height of 200 nm, a period of 250 nm, and a diameter ranging from 70 to 160 nm.

[0035] Again, the optical substrate 1 and the moth-eye film 3 are integrally formed. The optical substrate 1 is also made of SiC and has a thickness of 500 μm.

[0036] Finally, the anti-reflection film 2 is composed of ten layers of low-refractive index film layers (SiO2 film layers) and high-refractive index film layers (TiO2 film layers) alternately stacked. The thickness of the anti-reflection film 2 is 0.900μm. Starting from the air interface, the first layer is silicon oxide and the second layer is titanium oxide. The thicknesses are stacked in sequence, with the thicknesses of 232.8nm, 125.7nm, 13.45nm, 90.9nm, 18.8nm, 102.7nm, 98.9nm, 84.6nm, 48.3nm, and 86.6nm, respectively, achieving high transmittance in the near-infrared band of 1000~1550nm.

[0037] Example 4: This is a high-focusing-efficiency optical metalens disclosed herein. This differs from Example 1 in that, first, the nanodielectric pillars 4 are arranged in a two-dimensional array along two mutually perpendicular directions (X and Y). The nanodielectric pillars 4 are mirror-symmetric about a central plane parallel to the length of the optical substrate 1. The nanodielectric pillars 4 have the same height and period, and the duty cycle increases along the two array directions (+X and -X). Specifically, the nanodielectric pillars 4 are made of a high-refractive-index material, have a circular cross-section, a height of 100 nm, a period of 200 nm, and a duty cycle ranging from 20% to 40%.

[0038] Secondly, the moth-eye film 3 consists of a plurality of frustum pillars 31 arranged in a two-dimensional array along two mutually perpendicular directions (X and Y). The frustum pillars 31 are mirror-symmetric about a central plane parallel to the thickness direction of the optical substrate 1. These frustum pillars 31 have the same height and period, and their diameter increases from the nanomaterial pillars 4 toward the optical substrate 1. Specifically, the frustum pillars 31 are made of optical resin, have a height of 50 nm, a period of 100 nm, and a diameter ranging from 30 to 100 nm.

[0039] Again, the optical substrate 1 and the moth-eye film 3 are integrally formed. The material of the optical substrate 1 is also TiO 2 and the thickness is 100 μm.

[0040] Finally, the anti-reflection coating 2 is composed of ten layers of low-refractive index films (Al2O3 films) and high-refractive index films (TiO2 films) alternately stacked. The thickness of the anti-reflection coating 2 is 0.500μm, achieving high transmittance in the near-infrared band of 1000~1550nm.

[0041] Example 5: This is a high-focusing-efficiency optical metalens disclosed in the present invention. This differs from Example 1 in that, first, the nanodielectric pillars 4 are arranged in a two-dimensional array along two mutually perpendicular directions (X and Y). The nanodielectric pillars 4 are mirror-symmetric about a central plane parallel to the length of the optical substrate 1. The nanodielectric pillars 4 have the same height and period, and the duty cycle increases along the two array directions (+X and -X). Specifically, the nanodielectric pillars 4 are made of diamond with a high refractive index, a circular cross-section, a height of 1500 nm, a period of 1000 nm, and a duty cycle ranging from 60% to 85%.

[0042] Secondly, the moth-eye film 3 consists of a plurality of frustum pillars 31 arranged in a two-dimensional array along two mutually perpendicular directions (X and Y). The frustum pillars 31 are mirror-symmetric about a central plane parallel to the thickness direction of the optical substrate 1. These frustum pillars 31 have the same height and period, and their diameter increases from the nanomaterial pillars 4 toward the optical substrate 1. Specifically, the frustum pillars 31 are made of quartz, have a height of 500 nm, a period of 600 nm, and a diameter ranging from 200 to 600 nm.

[0043] Again, the optical substrate 1 and the moth-eye film 3 are integrally formed. The optical substrate 1 is also made of diamond and has a thickness of 5000 μm.

[0044] Finally, the anti-reflection coating 2 is composed of ten layers of low-refractive index film layers (SiO2 film layers) and high-refractive index film layers (HfO2 film layers) alternately stacked. The thickness of the anti-reflection coating 2 is 50.000μm, achieving high transmittance in the near-infrared band of 1000~1550nm.

[0045] Example 6: Reference Figure 2 , is a method for preparing an optical metalens with high focusing efficiency disclosed in the present invention, which is different from Example 1 in that it includes the following steps: S1 deposits a thin film on one side of the optical substrate 1 to obtain an antireflection film 2; S2 performs patterning on the other surface of the optical substrate 1 obtained in S1 to obtain a moth-eye film 3; S3: spin-coating a photoresist on the moth-eye film 3 obtained in S2 so that the photoresist fills the gaps on the moth-eye film 3 and exceeds the surface of the moth-eye film 3 to a predetermined height of the nano-dielectric pillars 4; then performing a patterning process and depositing a plurality of nano-dielectric pillars 4 in the patterned area; S4 directly bonds the moth-eye film 3 obtained in S2 to the plurality of nano-medium pillars 4 obtained in S3; Alternatively, a photoresist is first spin-coated on the plurality of nano-dielectric pillars 4 obtained in S3 so that the photoresist extends beyond the surface of the nano-dielectric pillars 4 to a predetermined height of the moth-eye film 3, and then patterning is performed. Another moth-eye film 3 is deposited in the patterned area, and thin film deposition is continued to obtain another optical substrate 1, and then S1 is repeated. S5 removes the photoresist on the moth-eye film 3 and the nano-dielectric pillars 4 obtained in S3 and S4 by wet stripping to obtain an optical superlens.

[0046] Example 7: A method for preparing an optical metalens with high focusing efficiency disclosed in the present invention, which is different from Example 6 in that it includes the following steps: In S1, deposition parameters of two film materials, silicon oxide and titanium oxide, are set in an electron beam evaporation coating device. At room temperature, the deposition rate of silicon oxide is 1.5 nm / s, and the deposition rate of titanium oxide is 3 nm / s. The deposition time of each layer is set, and several silicon oxide layers and titanium oxide layers are alternately deposited to obtain an antireflection film 2. In step S2, the other side of the optical substrate 1 is first exposed and developed, and then a metal mask is evaporated. The metal mask in the non-patterned area is peeled off, and then the optical substrate 1 in the non-patterned area is etched to obtain the moth-eye film 3. The exposure dose is selected to be 20nA and the development time is 1min. In order to obtain a complete patterned area, the thickness of the metal mask is controlled to be less than 80nm to facilitate successful peeling. S3 first spin-coats photoresist (AZ1518) on the moth-eye film 3, removes the photoresist above the surface of the moth-eye film 3 by dry etching, and then spin-coats photoresist (zep520) to a predetermined height of the nano-dielectric pillars 4. Then, the photoresist surface is exposed and developed, and a high-refractive index material is deposited in the patterned area. Then, the high-refractive index material above the predetermined height of the nano-dielectric pillars 4 is removed by dry etching to obtain a plurality of nano-dielectric pillars 4. The exposure dose is controlled to be 10 nA, the development time is 1 minute, the photoresist is spin-coated at a speed of 200 rps / min, and the photoresist is etched for 10 minutes. In addition, the deposition is performed at room temperature to ensure the integrity of the photoresist. S4 controls the bonding pressure to a moderate value to ensure the bonding strength without damaging the material structure; In step S5 , the photoresist on the moth-eye film 3 and the nano-dielectric pillars 4 obtained in steps S3 and S4 is removed by wet stripping. The time for wet stripping using the acetone solution is controlled to be 1 hour, thereby obtaining the optical metalens shown in Example 2.

[0047] Example 8: A method for preparing an optical metalens with high focusing efficiency disclosed in the present invention is different from Example 7 in that, in S4, photoresist (AZ1518) is first spin-coated on the surface of the multiple nano-dielectric pillars 4 and the photoresist (zep520) obtained in S3 to a predetermined moth-eye film 3 height, and then the photoresist surface is exposed and developed. After the material is deposited in the patterned area, the high-refractive index material above the predetermined thickness of the optical substrate 1 is removed by dry etching to obtain another moth-eye film 3 and the optical substrate 1, and then S1 is repeated; wherein, the exposure dose is controlled to be 10nA, the development time is 1min, the photoresist is spin-coated at a speed of 200rps / min, the photoresist is etched for 10min, and deposition is performed at room temperature to ensure the integrity of the photoresist; finally, the optical metalens shown in Example 3 is obtained.

[0048] Example 9: A method for preparing an optical metalens with high focusing efficiency disclosed in the present invention, which is different from Example 6 in that, in S2 and S4, referring to Figure 3, pre-acquire the equivalent refractive index distribution curve of the optical metalens structure formed by multiple nano-dielectric columns 4, determine the refractive index change range from the optical metalens structure to the optical substrate 1 in the optical metalens plane, and then determine the structural parameters of the moth-eye film 3 through the transition from the equivalent refractive index of the optical metalens to the refractive index of the optical substrate 1, and finally obtain the enhanced transmittance. When the equivalent refractive index transition is not performed, the transmittance of the optical metalens is Figure 4 The curve where the hollow circle is located, after the calculation and design matching of the equivalent refractive index, the transmittance of the optical metalens is Figure 4 From the curve where the solid circle is located, it can be seen that the transmittance of the optical metalens is effectively improved, thereby increasing the focusing efficiency.

[0049] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not limiting. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the purpose and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

Claims

1. An optical metalens with high focusing efficiency, characterized by: The invention comprises a pair of optical substrates (1), an antireflection film (2) arranged on one side surface of the optical substrate (1), a moth-eye film (3) protruding from the other side surface of the optical substrate (1), and a plurality of nano-medium columns (4) arranged between the pair of moth-eye films (3) and composed of a high refractive index material, wherein at least one structural parameter of the plurality of nano-medium columns (4) along the length direction of the optical substrate (1) is modulated to satisfy a 2π phase distribution, and at least one structural parameter of the moth-eye film (3) along the thickness direction of the optical substrate (1) is modulated to complete the refractive index transition from the plurality of nano-medium columns (4) to the optical substrate (1).

2. The optical metalens with high focusing efficiency according to claim 1, wherein: The plurality of nano-medium pillars (4) are arranged in a one-dimensional or two-dimensional array; and / or, the nano-medium pillars (4) are mirror-symmetrical on a central plane parallel to the length direction of the optical substrate (1); And / or, the heights and periods of the plurality of nano-medium columns (4) are the same, and the duty cycle increases along at least two array directions, and the at least two array directions are opposite, intersecting and / or perpendicular array directions.

3. The optical metalens with high focusing efficiency according to claim 2, wherein: The refractive index of the high refractive index material of the nano-medium column (4) exceeds 1.7; and / or, the cross section of the nano-medium column (4) is circular, elliptical or polygonal; and / or, the height of the nano-medium pillar (4) is 100-1500 nm; and / or, the period of the nano-medium pillars (4) is 200-1000 nm; And / or, the duty cycle of the nano-medium column (4) ranges from 20 to 85%.

4. The optical metalens with high focusing efficiency according to claim 1, wherein: The moth-eye film (3) is composed of a plurality of frustum columns (31) arranged in a two-dimensional array; And / or, the frustum (31) is mirror-symmetrical on a central plane parallel to the thickness direction of the optical substrate (1); And / or, the heights and periods of the plurality of frustum columns (31) are the same, and the diameters increase gradually from the nano-medium column (4) to the optical substrate (1).

5. The optical metalens with high focusing efficiency according to claim 1, wherein: The height of the frustum pillar (31) is 50-500 nm; And / or, the period of the truncated cone (31) is 100-600 nm; And / or, the diameter of the frustum (31) is in the range of 30 to 600 nm.

6. The optical metalens with high focusing efficiency according to claim 1, wherein: The optical substrate (1) and the moth-eye film (3) are integrally formed; And / or, the optical substrate (1) is a transparent flat material; And / or, the thickness of the optical substrate (1) is 100-5000 μm.

7. The optical metalens with high focusing efficiency according to claim 1, wherein: The antireflection film (2) is formed by alternately stacking a plurality of low-refractive-index film layers with a refractive index not exceeding 1.7 and a high-refractive-index film layer with a refractive index exceeding 2.1; And / or, the low refractive index film layer is a composite film of one or more of SiO2 and Al2O3; And / or, the high refractive index film layer is a composite film of one or more of TiO2 and HfO2; And / or, the thickness of the antireflection film (2) is 0.5-50.0 μm.

8. The method for preparing an optical metalens with high focusing efficiency according to any one of claims 1 to 7, wherein: The following steps are included: S1 deposits a thin film on one side of the optical substrate (1) to obtain an antireflection film (2); S2 performs patterning on the other side surface of the optical substrate (1) obtained in S1 to obtain a moth-eye film (3); S3 spin-coating a photoresist on the moth-eye film (3) obtained in S2, so that the photoresist fills the gaps on the moth-eye film (3) and exceeds the surface of the moth-eye film (3) to a predetermined height of the nano-medium pillars (4), and then performs a patterning process, and deposits a plurality of nano-medium pillars (4) in the patterned area; S4 directly bonds the moth-eye film (3) obtained in S2 to the plurality of nano-medium pillars (4) obtained in S3; Alternatively, a photoresist is first spin-coated on the plurality of nano-dielectric pillars (4) obtained in S3 so that the photoresist exceeds the surface of the nano-dielectric pillars (4) to a predetermined height of the moth-eye film (3), and then patterning is performed, and another moth-eye film (3) is deposited on the patterned area, and thin film deposition is continued to obtain another optical substrate (1), and then S1 is repeated; S5 removes the photoresist on the moth-eye film (3) and the nano-medium pillar (4) obtained in S3 and S4 by wet stripping to obtain an optical super lens.

9. The method for preparing an optical metalens with high focusing efficiency according to claim 8, wherein: In S2 and S4, an equivalent refractive index distribution curve of an optical superlens structure formed by a plurality of nano-medium columns (4) is obtained in advance, and a refractive index variation range from the optical superlens structure to the optical substrate (1) within the optical superlens plane is determined. Then, the structural parameters of the moth-eye film (3) are determined through the transition from the equivalent refractive index of the optical superlens to the refractive index of the optical substrate (1).

10. The method for preparing an optical metalens with high focusing efficiency according to claim 8, wherein: In the step S4, photoresist is first spin-coated on the plurality of nano-dielectric pillars (4) and the surface of the photoresist to a predetermined height of the moth-eye film (3), then the surface of the photoresist is exposed and developed, and after depositing material in the patterned area, the high-refractive-index material above the predetermined thickness of the optical substrate (1) is removed by dry etching to obtain another moth-eye film (3) and optical substrate (1).

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