WO2023136182A1

WO2023136182A1 - Metasurface

Info

Publication number: WO2023136182A1
Application number: PCT/JP2022/048663
Authority: WO
Inventors: 粟屋信義; 縄田晃史; 小川大貴; 中村智宣; 楊哲; 田中覚
Original assignee: Ｓｃｉｖａｘ株式会社
Priority date: 2022-01-14
Filing date: 2022-12-28
Publication date: 2023-07-20

Abstract

The purpose of the present invention is to provided a metasurface having a low aspect ratio, using a dielectric resin, without increasing the size of a unit.　This metasurface comprises a substrate 1 that transmits light, and a plurality of microstructures 2 disposed on the substrate 1 to control the phase distribution of the light, and the plurality of microstructures 2 have two or more varieties of heights. The maximum aspect ratio of the plurality of varieties of microstructures 2 is smaller than the maximum aspect ratio if the plurality of varieties of microstructures 2 were designed so as to generate the same phase difference at the same height.

Description

metasurface

The present invention relates to metasurfaces.

Optical lenses are important parts in science and technology such as microscopes, displays, and optical lithography. Conventional refractive lenses are made of transparent convex or concave materials and are widely used, but their large size limits the miniaturization of optical components. In addition, complicated and time-consuming three-dimensional (3D) surface processing is required to create an aspheric refractive lens for correcting spherical aberration. Diffractive lenses with sawtooth profiles offer an alternative to achieve thin and compact lenses, but their focusing ability is inherently limited by shadowing effects, and diffractive lenses have low NA (numerical aperture). ) only.

As an alternative, a metasurface, a two-dimensional array of sub-wavelength antennas, can be used as an ultra-thin optical device. By engineering the physical shape of the antenna, the transmitted and reflected waves can be arbitrarily modulated when light interacts with the metasurface, and many applications of ultra-thin lenses have already been demonstrated. there is Such metalens can offer the opportunity to realize high-end, ultra-thin lenses without the limitations of shadowing effects. A metalens is composed of a plurality of structures having one nano-sized dielectric column or fin in a unit on a substrate. The structure of each unit brings about a phase shift of light depending on its shape and size. Since the light is confined in the dielectric in the unitary unit, there is little interference with adjacent units. Therefore, by controlling the shapes and positions of these structures, a metalens having a desired phase profile can be realized.

A metalens of the type in which one dielectric cylinder is arranged in a unit, the cylinder has a constant height, and the phase shift of light is controlled by the diameter of the cylinder does not depend on the polarization of incident light. Can be widely used as an optical lens. To construct a lens, we need cylindrical nanostructures of multiple diameters covering the phase shift induced by the nanostructures from 0° to 360°. That is, a metalens can be realized by arranging a plurality of cylinders having different diameters so as to realize a desired phase profile.

In the manufacturing process, first, an amorphous silicon (α-Si) film is formed on glass by plasma CVD. Next, a resist pattern is formed on the amorphous silicon by lithography. A pattern is formed by etching amorphous silicon using this resist pattern as a mask. For visible light, a structure using titanium dioxide (TiO ₂ ) cylinders with a refractive index of about 2.4 has been reported. (For example, Patent Document 1)

Special table 2019-516128

Here, manufacturing costs can be reduced if the metasurface can be manufactured in one process by nanoimprinting, in which dielectric resin is molded using a fine pattern mold. However, in the case of resin containing nanofillers, which are high refractive index materials, the refractive index is 1.8 to 1.9 when titanium dioxide is applied, and the refractive index is about 2.2 even when amorphous silicon is applied. lower refractive index. Therefore, it is necessary to increase the height of the cylinder in order to cover a sufficient phase range.

However, in this structure, the transmittance varies greatly depending on the diameter of the cylinder, and there was a problem that the transmittance was 40% or less depending on the diameter. This is because it is necessary to increase the unit size in order to cover the phase with a cylinder having an aspect ratio that can be molded by nanoimprinting, and when the unit size increases, the effect of diffraction occurs and the transmittance fluctuates.

Therefore, an object of the present invention is to provide a metasurface with a low aspect ratio using a dielectric resin without increasing the unit size.

To achieve the above objects, the present invention provides a metasurface comprising a substrate that transmits light and a plurality of microstructures arranged on the substrate for controlling the phase distribution of the light. and wherein the plurality of microstructures have two or more heights.

Here, the maximum aspect ratio of the plurality of types of microstructures is preferably smaller than the maximum aspect ratio when the plurality of types of microstructures are designed to have the same height and the same phase difference. Specifically, the aspect ratio of the fine structure is preferably 5 or less.

Further, it is preferable that the pitch of the microstructures is 3/4 or less of the wavelength of the light.

Also, the fine structure may be a resin.

In addition, two or more layers of the microstructure may be laminated.

The metasurface of the present invention can be provided without increasing the unit size.

1 is a cross-sectional view showing a metasurface of the present invention; FIG. 1 is a cross-sectional view showing a metasurface having a two-layer structure according to the present invention; FIG. FIG. 4 is a cross-sectional view showing a method of manufacturing a master mold for metasurface according to the present invention; FIG. 4 is a cross-sectional view showing a method for manufacturing a hole replica mold for metasurface according to the present invention; FIG. 4 is a cross-sectional view showing a method for manufacturing a metasurface according to the present invention; FIG. 4 is a cross-sectional view showing a method for manufacturing a metasurface having a two-layer structure according to the present invention; FIG. 3A is a sectional view and (b) a plan view showing a metasurface used in Simulation 1. FIG. FIG. 10 is a diagram showing the pitch P, the diameter D1, and the transmittance of the microstructure in Simulation 1; FIG. 11 is a cross-sectional view showing a microstructure in Simulation 2; FIG. 10 is a diagram showing the diameter and phase difference of a fine structure in Simulation 2; FIG. 11 is a cross-sectional view showing a microstructure in Simulation 3; FIG. 10 is a diagram showing the diameter and phase difference of a fine structure in Simulation 3; FIG. 11(a) is a cross-sectional view and (b) a plan view showing a microstructure in Simulation 4; FIG. 10 is a diagram showing the pitch P, the diameter D1, and the transmittance of the microstructure in Simulation 4; FIG. 11 is a cross-sectional view showing a microstructure in Simulation 5; FIG. 11 is a diagram showing the diameter and phase difference of a fine structure in Simulation 5; FIG. 11 is a cross-sectional view showing a microstructure in Simulation 6; FIG. 10 is a diagram showing the diameter and phase difference of a fine structure in Simulation 6; (A) A cross-sectional view and a plan view showing a microstructure in Simulation 7, and (B) a plan view showing a metalens using the microstructure. FIG. 12 is a diagram showing the electric field intensity distribution of the metalens in Simulation 7; FIG. 11 is a diagram showing an electric field intensity distribution of a metalens in Simulation 8;

The metasurface of the present invention will be described below. The metasurface of the present invention is mainly composed of a substrate 1 and a plurality of microstructures 2 arranged on the substrate 1, as shown in FIG.

Here, the substrate 1 is for arranging a plurality of fine structures 2 . Any material may be used as long as it allows light to pass therethrough and a plurality of microstructures 2 can be arranged thereon. For example, a glass substrate made of SiO ₂ or the like may be used.

The fine structure 2 is made of a dielectric with a size smaller than the wavelength of light used for the metasurface, and is used to control the phase of transmitted light. If the pitch of the microstructures 2 becomes large, a diffraction effect occurs, and the transmittance varies depending on the diameter of the microstructures 2. Therefore, the smaller the pitch, the better, preferably 3/4 or less of the light used. is good. As the dielectric, for example, a high refractive index resin containing a filler such as amorphous silicon (α-Si) or titanium dioxide (TiO ₂ ) can be used. In particular, resin is preferable in that the fine structure 2 can be directly molded by the nanoimprint method.

The shape of the microstructure 2 may be any shape as long as the phase can be controlled, but it can be, for example, columnar, frustum, or conical. In particular, a truncated cone shape and a conical shape are preferable in that when the fine structure 2 is directly molded by the nanoimprint method, the shape can be easily released. In addition, the planar shape (cross-sectional shape viewed from the convex side) of the microstructure 2 is not limited as long as the phase can be controlled. can be done. When the fine structure 2 is formed by the nanoimprint method, it is preferable because it is easy to form a cylindrical shape, a truncated cone shape, or a conical shape.

Also, the phase increases as the height and diameter of the microstructure 2 are increased. Here, when the fine structure 2 is a cylinder, the diameter means the diameter of the circle of the cylinder. In addition, when the microstructure 2 is other than a cylinder, it means the diameter of a circle when the volume of the microstructure 2 is converted into a cylinder having the same volume.

Conventionally, the height of the microstructure 2 was kept constant, and the phase distribution of light was controlled only by the diameter of the microstructure 2. However, when trying to control the phase distribution of light only by the diameter, the aspect ratio of the fine structure 2 becomes large, so there is a problem that it is difficult to mold or release the fine structure 2 by the imprint method. Therefore, as a result of intensive research by the present inventors, it has been found that the phase distribution can be controlled and the aspect ratio can be reduced by changing the height. Specifically, it was found that when the phase difference to be designed is low, the height can be reduced and the aspect ratio can be reduced. Therefore, in the metasurface of the present invention, the microstructure 2 has two or more different heights, and the diameter of each height is adjusted so that the aspect ratio of the microstructure 2 is 5 or less, 4.5 or less, It can be formed as small as 4 or less, 3.5 or less, 3 or less, or 2.5 or less.

In addition, even if there is a pattern-free layer such as a residual film produced by nanoimprint technology or the like on the top side or the bottom side of the microstructure 2, it does not affect the phase distribution. However, from the viewpoint of light transmittance, the thickness is preferably 1/4 or less of the wavelength of the light used.

Further, as shown in FIG. 2, the fine structure 2 may be laminated with two or more layers. Thereby, the phase difference provided by the microstructures 2 of the second and subsequent layers can be added to the phase difference provided by the microstructures 2 of the first layer. Therefore, by aligning the position of the microstructures 2 in the first layer with the positions of the microstructures 2 in the second and subsequent layers, the height and aspect ratio of the microstructures 2 can be further reduced. Note that the space between the microstructures may be filled with a resin having a refractive index lower than that of the microstructures.

A method for manufacturing a metasurface according to the present invention will be described below. First, a method of manufacturing the master mold 10 is shown in FIG. First, a hard mask 12 is deposited on a substrate 11 as shown in FIG. 3(a). For the substrate 11, for example, a glass substrate such as SiO ₂ may be used. As the hard mask 12, metal such as Cr may be used. Film formation of the hard mask 12 may be performed by a well-known method such as a sputtering method. Next, as shown in FIG. 3B, a fine structure pattern 13 is formed on the hard mask 12. Next, as shown in FIG. A well-known technique such as a photolithography technique or a nanoimprint technique may be used to create the pattern 13, for example. Next, as shown in FIG. 3C, the pattern 13 is used to etch the hard mask 12 . Subsequently, the substrate 11 is etched. A well-known method such as RIE may be used for etching the hard mask 12 and the substrate 11 . The etching depth of the substrate 11 is set to the depth of the lowest height of the microstructures to be formed. The pattern 13 may be removed by ashing or the like after the hard mask 12 is etched and before the substrate 11 is etched. Next, as shown in FIG. 3(d), a pattern 14 is formed to cover the top of the lowest microstructure. A well-known technique such as photolithography technique or nanoimprint technique may be used to create the pattern 14, for example. Next, as shown in FIG. 3(e), the substrate 1 is etched so as to form a fine structure having the second lowest height. Then pattern 14 is removed. When three or more heights are to be used, the third and subsequent microstructures may be produced in the same manner. Finally, as shown in FIG. 3(f), the master mold 10 can be manufactured by removing the pattern 13 and the hard mask 12. Next, as shown in FIG.

Next, a method for manufacturing the hole replica 25 will be described. As shown in FIG. 4(a), a resin 21 is applied onto the master mold 10, and after the resin 21 is cured, the mold is released to form a pillar replica 22 as shown in FIG. 4(b). Next, a resin 24 is applied onto the substrate 23 as shown in FIG. 4(b). Then, the pillar replica 22 is pressed against the resin 24 as shown in FIG. 4(c). A glass substrate such as SiO ₂ may be used for the substrate 23, for example. Finally, after the resin 24 is cured, it is released from the mold to form a hole replica 25 as shown in FIG. 4(d).

Next, a method for manufacturing a metasurface according to the present invention will be described. A high refractive index resin 31 is applied to the hole replica 25 as shown in FIG. 5(a). As the high refractive index resin 31, for example, a resin containing a filler such as amorphous silicon (α-Si) or titanium dioxide (TiO ₂ ) may be used. Next, as shown in FIG. 5(b), the high refractive index resin 31 is pressure-bonded to the substrate 32 and then cured. Finally, as shown in FIG. 5(c), the metasurface of the present invention can be manufactured by releasing the hole replica 25 from the mold.

Next, a manufacturing method for laminating the metasurface of the present invention will be described. Metasurface microstructures have been found to be effective even when stacked. Therefore, when it is desired to laminate n layers, for example, the master mold 10 is created by lowering the height of each pattern by the above-described manufacturing method (see FIG. 3). A pillar replica 22 and a hole replica 25 are produced with this master mold 10 in the same manner as in the manufacturing method described above (see FIG. 4). Here, as the resin 24 of the hole replica 25, a low refractive index resin is used.

Next, as shown in FIG. 6A, a resin 61 having a refractive index higher than that of the resin 24 is applied onto the hole replica 25 to fill the holes, and then flattened and cured with UV. As the high refractive index resin 61, for example, a resin containing a filler such as amorphous silicon (α-Si) or titanium dioxide (TiO ₂ ) may be used. Subsequently, as shown in FIG. 6B, a low refractive index resin 62 is applied on the high refractive index resin 61. Then, as shown in FIG. Then, as shown in FIG. 6(c), the pillar replica 22 is pressed against the low refractive index resin 62 and released to form a hole-like pattern. Finally, as shown in FIG. 6(d), a high refractive index resin 63 is applied to fill the holes, then flattened and cured with UV.

Next, the results of various simulations performed on the structure of the metasurface of the present invention are shown below. The RCWA method (Rigorous Coupled Wave Analysis) was used for the simulation.
[Simulation 1]
The relationship between the pitch and diameter of the microstructures and the transmittance was simulated. In the simulation, the wavelength of light incident on the metasurface was set to 940 nm. As shown in FIGS. 7(a) and 7(b), the microstructures were cylindrical with a height H1 of 1.6 μm and a refractive index N1 of 1.85, and arranged in a hexagonal arrangement. Also, the refractive index N0 of the substrate was set to 1.5. FIG. 8(a) shows simulation results of the pitch P and diameter D of the microstructure and the transmittance. FIG. 8(b) shows the relationship between the diameter D and the transmittance for five types of the pitch P of the fine structure, 520 nm, 600 nm, 680 nm, 760 nm, and 840 nm.

As shown in FIGS. 8(a) and 8(b), it can be seen that the transmittance decreases depending on the diameter D of the microstructures when the pitch P of the microstructures is larger than 3/4 wavelength of the incident light. Therefore, it is preferable to set the pitch P of the fine structures to 3/4 or less of the wavelength of the light used.

[Simulation 2]
The relationship between the diameter of the microstructure and the phase difference of transmitted light was simulated. In the simulation, the wavelength of light incident on the metasurface was set to 940 nm. As shown in FIG. 9, the fine structure was cylindrical with a pitch P of 0.65 μm. The refractive index was set to 1.85 assuming a resin containing titanium dioxide (TiO ₂ ) filler. Also, the heights H1 and H2 of the fine structure are of two types, 1.6 μm and 0.9 μm. Also, the refractive index of the substrate was set to 1.5. FIG. 10 shows simulation results of the diameter D of the fine structure and the phase difference.

As shown in FIG. 10, the phase difference of transmitted light decreases as the height of the fine structure decreases. Further, as the diameter D of the fine structure increases, the phase difference of transmitted light increases. Therefore, when the height of the microstructure is reduced, the diameter D must be increased in order to keep the phase difference of the transmitted light the same. That is, since the height is low and the diameter is large, the aspect ratio can be reduced.

Specifically, for example, two types of microstructures are designed: a microstructure A that provides a phase difference of 45 degrees (π/4 radians) and a microstructure B that provides a phase difference of 315 degrees (7π/4 radians). Consider the case. Assuming that both microstructures are cylindrical and have a height of 1.6 μm, the microstructure A should have a diameter of 0.5 μm and the microstructure B should have a diameter of 0.207 μm. In this case, the aspect ratio of the fine structure A is 3.2, and the aspect ratio of the fine structure B is 7.7. On the other hand, when the height of the microstructure B is 0.9 μm, the diameter of the microstructure B can be 0.27 μm. In this case, the aspect ratio is 3.3, and the aspect ratio of the entire fine structure can be made smaller by changing the heights of the fine structures A and B than by keeping the heights of the fine structures A and B constant. can be done.

[Simulation 3]
The relationship between the diameter of the microstructure and the phase difference of transmitted light was simulated. In the simulation, the wavelength of light incident on the metasurface was set to 940 nm. As shown in FIG. 11, the fine structure was cylindrical with a pitch P1 of 0.68 μm. The refractive index was set to 2.2 assuming a resin containing amorphous silicon (α-Si) filler. Also, the heights H1 and H2 of the fine structure are of two types, 1.1 μm and 0.75 μm. Also, the refractive index of the substrate was set to 1.5. FIG. 12 shows simulation results of the diameter of the fine structure and the phase difference.

As shown in FIG. 12, the phase difference of transmitted light decreases as the height of the fine structure decreases. Further, as the diameter of the fine structure increases, the phase difference of transmitted light increases. Therefore, if the height of the microstructure is reduced, the diameter must be increased in order to keep the phase difference of the transmitted light the same. That is, since the height is low and the diameter is large, the aspect ratio can be reduced.

Specifically, for example, two types of microstructures are designed: a microstructure A that provides a phase difference of 45 degrees (π/4 radians) and a microstructure B that provides a phase difference of 315 degrees (7π/4 radians). Consider the case. Assuming that both microstructures are cylindrical and have a height of 1.1 μm, the microstructure A should have a diameter of 0.46 μm and the microstructure B should have a diameter of 0.214 μm. In this case, the aspect ratio of fine structure A is 2.4, and the aspect ratio of fine structure B is 5.14. On the other hand, when the height of the microstructure B is 0.75 μm, the diameter of the microstructure B can be 0.245 μm. In this case, the aspect ratio is 3.06, and the aspect ratio of the entire fine structure can be made smaller by changing the heights of the fine structures A and B than by keeping the heights of the fine structures A and B constant. can be done.

[Simulation 4]
A simulation was performed of the relationship between the pitch of the microstructures and the transmittance when two layers of the same microstructures were laminated one above the other. In the simulation, the wavelength of light incident on the metasurface was set to 940 nm. As shown in FIGS. 13(a) and 13(b), the microstructures were cylindrical with a height H1 of 1.2 μm and a refractive index of 1.85, and arranged in a hexagonal arrangement. Also, the pitch of the fine structures was set to 0.69 μm. The refractive index of the resin embedded between the fine structures was 1.35, and the refractive index of the substrate was 1.5. FIG. 14 shows simulation results of the pitch P and diameter D of the microstructure and the transmittance.

As shown in FIG. 14, it can be seen that the transmittance decreases depending on the diameter D of the microstructures when the pitch P of the microstructures is larger than 3/4 wavelength of the incident light. Therefore, it is preferable to set the pitch P of the fine structures to 3/4 or less of the wavelength of the light used. Also, even with two layers, there was no significant effect on the transmittance.

[Simulation 5]
A simulation was performed of the relationship between the diameter of the fine structure and the phase difference of the transmitted light when two layers of the same fine structure are laminated one above the other. In the simulation, the wavelength of light incident on the metasurface was set to 940 nm. As shown in FIG. 15, the fine structure was cylindrical with a pitch P of 0.69 μm. The refractive index was set to 2.2 assuming a resin containing amorphous silicon (α-Si) filler. Also, the heights H1 and H2 of the microstructures were of two types, 1.2 μm and 0.65 μm. The refractive index of the resin embedded between the fine structures was 1.35, and the refractive index of the substrate was 1.5. FIG. 16 shows simulation results of the diameter D of the fine structure and the phase difference.

As shown in FIG. 16, the phase difference of transmitted light decreases as the height of the fine structure decreases. Further, as the diameter D of the fine structure increases, the phase difference of transmitted light increases. Therefore, when the height of the microstructure is reduced, the diameter D must be increased in order to keep the phase difference of the transmitted light the same. That is, since the height is low and the diameter is large, the aspect ratio can be reduced.

Specifically, for example, two types of microstructures are designed: a microstructure A that provides a phase difference of 45 degrees (π/4 radians) and a microstructure B that provides a phase difference of 315 degrees (7π/4 radians). Consider the case. Assuming that both microstructures are cylindrical and have a height of 1.2 μm, the microstructure A should have a diameter of 0.57 μm and the microstructure B should have a diameter of 0.22 μm. In this case, the aspect ratio of fine structure A is 2.1, and the aspect ratio of fine structure B is 5.45. On the other hand, when the height of the microstructure B is 0.65 μm, the diameter of the microstructure B can be 0.287 μm. In this case, the aspect ratio is 2.26, and the aspect ratio of the entire fine structure can be made smaller by changing the heights of the fine structures A and B than by keeping the heights of the fine structures A and B constant. can be done. In addition, when two layers were laminated, the aspect ratio could be made considerably smaller than in the case of one layer.

[Simulation 6]
A simulation was performed on the relationship between the diameter and the phase difference of transmitted light when the fine structure is cylindrical and when it is truncated cone. In the simulation, the wavelength of light incident on the metasurface was set to 940 nm. As for the shape of the microstructures, as shown in FIG. 17, the microstructures A, C, D, and F were truncated conical, and the microstructures B and E were cylindrical. Also, the angle of the side surfaces of the microstructures A, C, D, and F with respect to the substrate was set to 87 degrees. Also, the height H1 of the microstructures A to C was set to 1.6 μm, and the height H2 of the microstructures D to F was set to 0.9 μm. The diameters of the microstructures A and D are the diameters of the top surface of the truncated cone, and the diameters of the microstructures C and F are the diameter of the bottom surface of the truncated cone. The refractive index was set to 1.85 assuming a resin containing titanium dioxide (TiO ₂ ) filler. Also, the refractive index of the substrate was set to 1.5. FIG. 18 shows simulation results of the diameter D of the fine structure and the phase difference.

As shown in FIG. 18, when the height of the truncated cone-shaped fine structure is lowered, the phase difference of the transmitted light is also reduced. Also, as the diameter of the truncated conical microstructure increases, the phase difference of the transmitted light also increases. Therefore, it was found that even if the shape of the fine structure is a truncated cone, the phase difference can be controlled by the height and diameter of the fine structure as in the case of the cylindrical shape.

[Simulation 7]
We simulated the properties of two-dimensional metalens with two different heights. In the simulation, microstructures such as those shown in (a) to (g) of FIG. 19(A) were used. These are respectively (a) 315 degrees (7π/4 radians), (b) 270 degrees (3π/2 radians), (c) 225 degrees (5π/4 radians), (d) 180 degrees (π radians), ( A phase difference of e) 135 degrees (3π/4 radians), (f) 90 degrees (π/2 radians), and (g) 45 degrees (π/4 radians) is provided. The heights H1 and H2 of the microstructures were of two types, 1600 nm and 900 nm. The diameters of the fine structures were D1: 470 nm, D2: 440 nm, D3: 395 nm, D4: 490 nm, D5: 410 nm, D6: 340 nm, and D7: 260 nm. Also, the pitch U of the fine structures was set to 620 nm. Also, the refractive index of the microstructure was set to 1.85, and the refractive index of the substrate was set to 1.5. These microstructures (a) to (g) were arranged as shown in FIG. 19(B). FIG. 20A shows a simulation result of the electric field strength distribution in the Z direction (height direction) from the metalens. Also, FIG. 20(b) shows a simulation result of the electric field strength distribution on the XY plane in the vicinity of the focal point (Z=32.6 μm).

As shown in FIG. 20, it was found that even a metalens having two heights functions well as a lens having a focal point near Z=32.6 μm.

[Simulation 8]
Metalens A, which has two types of height microstructures (pitch 620 nm) with a refractive index of 1.8, and conventional metalens A, which has one type of height microstructures (pitch 400 nm) with a refractive index of 3.13. The properties of metalens B were compared. FIG. 21A shows a simulation result of the electric field strength distribution in the Z direction (height direction) from the metalens A. FIG. FIG. 21(b) shows a simulation result of the electric field strength distribution in the Z direction (height direction) from the metalens B. As shown in FIG.

As shown in FIG. 21, the electric field strength distributions of metalens A and metalens B were almost the same. In addition, the light collection efficiency of the metalens A is 68.9%, and the light collection efficiency of the metalens B is 70.3%. In terms of light collection efficiency, the metalens A exhibits performance comparable to that of the conventional metalens B. I understand. Therefore, it was found that even a metalens made of a low-refractive-index material can exhibit performance comparable to that of a conventional metalens if microstructures with two different heights are used.

1 substrate 2 fine structure 10 master mold 11 substrate 12 hard mask 13 pattern 14 pattern 21 resin 22 pillar replica 23 substrate 24 resin 25 hole replica 31 high refractive index resin 32 substrate 61 high refractive index resin 62 low refractive index resin 63 high refractive index rate resin

Claims

A metasurface comprising a substrate that transmits light and a plurality of types of microstructures arranged on the substrate for controlling the phase distribution of the light,
The metasurface, wherein the plurality of types of microstructures have two or more types of heights.
2. The method according to claim 1, wherein the maximum aspect ratio of the plurality of types of microstructures is smaller than the maximum aspect ratio when the plurality of types of microstructures are designed to have the same height and produce the same phase difference. metasurface.
The metasurface according to claim 1, wherein the aspect ratio of the fine structure is 5 or less.
4. The metasurface according to any one of claims 1 to 3, wherein the pitch of the fine structures is 3/4 or less of the wavelength of the light.
The metasurface according to any one of claims 1 to 3, wherein the fine structure is resin.
4. The metasurface according to any one of claims 1 to 3, wherein the fine structures are laminated in two or more layers.