Metasurface lens

Abstract

To provide a metasurface lens which suppresses reflection light.SOLUTION: A metasurface lens 1 includes: a transparent base plate 11 having a surface 11a and a surface 11b opposite to the surface 11a in a first direction; an antireflection layer 12 provided on the surface 11a; and a metasurface structure 13 having a plurality of columnar bodies 13a which are provided on the antireflection layer 12 and which extend to the opposite side to the transparent base plate 11 in the first direction.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to metasurface lenses. [Background technology]

[0002] A metalens including a substrate, a nanostructure formed on a first surface of the substrate, and an anti-reflection coating on a second surface of the substrate is known (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Special Publication No. 2018-537804 Summary of the Invention [Problem to be solved by the invention]

[0004] The metalens (metasurface lens) described in Patent Document 1 cannot suppress reflected light that occurs at the boundary between the substrate and the nanostructure.

[0005] The present disclosure describes metasurface lenses that can suppress reflected light. [Means for solving the problem]

[0006] A metasurface lens according to one aspect of the present disclosure comprises a transparent substrate having a first surface and a second surface opposite the first surface in a first direction, a first antireflection layer provided on the first surface, and a metasurface structure including a plurality of pillars provided on the first antireflection layer, the plurality of pillars extending opposite the transparent substrate in the first direction.

[0007] In this metasurface lens, a first anti-reflection layer is provided between the transparent substrate and the metasurface structure, thereby suppressing the reflection of light occurring between the transparent substrate and the metasurface structure.

[0008] The metasurface lens may further include a second antireflection layer provided on the second surface. For example, when visible light is incident from the second surface of the transparent substrate toward the first surface, reflected light may occur at the second surface of the transparent substrate. According to the above configuration, the second antireflection layer is provided on the second surface of the transparent substrate, thereby suppressing reflected light occurring at the second surface of the transparent substrate.

[0009] The metasurface lens may further include a reflective layer on the second surface. In this case, visible light is incident from the first surface toward the second surface of the transparent substrate, whereby the visible light is reflected by the reflective layer, and the reflected visible light is transmitted through the transparent substrate, the first antireflection layer, and the metasurface structure in that order. In this case, too, reflected light occurring between the transparent substrate and the metasurface structure can be suppressed.

[0010] The metasurface structure may be constructed from a material that is transparent to visible light. In this case, the phase delay of the visible light is generated when the visible light passes through the pillars. Therefore, by appropriately adjusting the phase delay generated by each pillar, the desired lens function can be obtained.

[0011] The metasurface structure may be composed of a compound selected from the group consisting of silicon oxide, silicon nitride, titanium oxide, and titanium nitride, which are transparent in the visible light range, thereby enabling the metasurface structure to be transparent to visible light.

[0012] The first antireflection layer may have a refractive index equal to or higher than that of the metasurface structure. The surface of the first antireflection layer provided with the columns includes a region where the columns are provided and a region where the columns are not provided. The region where the columns are not provided may be in contact with air. When visible light is incident on the first antireflection layer from the transparent substrate, the visible light may be reflected at the interface between the transparent substrate and the first antireflection layer, the interface between the first antireflection layer and the columns, and the interface between the first antireflection layer and air. In this case, the visible light reflected at the interface between the transparent substrate and the first antireflection layer interferes with the visible light reflected at the interface between the first antireflection layer and the columns and the interface between the first antireflection layer and air. If the phase change due to reflection at the interface between the first antireflection layer and the columns differs from the phase change due to reflection at the interface between the first antireflection layer and air, the reflected light cannot be effectively attenuated.

[0013] According to the above configuration, when the refractive index of the first antireflection layer is higher than the refractive index of the metasurface structure, the phase of visible light is not changed by either reflection at the interface between the first antireflection layer and the columns or reflection at the interface between the first antireflection layer and air. When the refractive index of the first antireflection layer is the same as the refractive index of the metasurface structure, no reflection occurs at the interface between the first antireflection layer and the columns. Therefore, the first antireflection layer can effectively attenuate reflected light, thereby further suppressing reflected light occurring between the transparent substrate and the metasurface structure.

[0014] The refractive index of the first antireflection layer may be lower than that of the transparent substrate, and the length of the first antireflection layer in the first direction may be an odd multiple of the result of dividing the wavelength of visible light by four times the refractive index of the first antireflection layer. When the refractive index of the first antireflection layer is lower than that of the transparent substrate, the phase of visible light does not change due to reflection at the interface between the transparent substrate and the first antireflection layer, the interface between the first antireflection layer and the columnar structure, or the interface between the first antireflection layer and air. By setting the length of the first antireflection layer in the first direction as described above, the difference between the optical path length of visible light reflected at the interface between the transparent substrate and the first antireflection layer and the optical path length of visible light reflected at the interface between the first antireflection layer and the metasurface structure is an odd multiple of half the wavelength of visible light. Therefore, the two reflected lights are in opposite phases and cancel each other out. This further reduces the reflected light between the transparent substrate and the metasurface structure.

[0015] The refractive index of the first antireflection layer may be higher than the refractive index of the transparent substrate, and the length of the first antireflection layer in the first direction may be an integer multiple of the result of dividing the wavelength of visible light by twice the refractive index of the first antireflection layer. When the refractive index of the first antireflection layer is higher than the refractive index of the transparent substrate, the phase of visible light changes by π radians due to reflection at the interface between the transparent substrate and the first antireflection layer. On the other hand, the phase of visible light does not change due to reflection at either the interface between the first antireflection layer and the columnar structure or the interface between the first antireflection layer and air. By setting the length of the first antireflection layer in the first direction as described above, the difference between the optical path length of visible light reflected at the interface between the transparent substrate and the first antireflection layer and the optical path length of visible light reflected at the interface between the first antireflection layer and the metasurface structure becomes an integer multiple of the wavelength of visible light. Therefore, the two reflected lights are in opposite phases and cancel each other out. This further reduces the reflected light between the transparent substrate and the metasurface structure.

[0016] The first antireflection layer may be made of a compound selected from the group consisting of silicon oxide and silicon nitride, in which case the first antireflection layer may have a refractive index that is equal to or lower than the refractive index of the metasurface structure.

[0017] The first antireflection layer may be made of the same material as the metasurface structure, which allows the first antireflection layer and the metasurface structure to be integrated, simplifying the fabrication of the metasurface lens. [Effects of the Invention]

[0018] According to each aspect and embodiment of the present disclosure, reflected light can be suppressed. [Brief explanation of the drawings]

[0019] [Figure 1] FIG. 1 is a cross-sectional view illustrating a schematic configuration of a metasurface lens according to one embodiment. [Figure 2] FIG. 2 is a diagram illustrating the operating principle of the metasurface lens shown in FIG. [Figure 3] FIG. 3 is a diagram illustrating the relationship between the position and diameter of the pillars included in the metasurface lens shown in FIG. [Figure 4] FIG. 4 is a diagram showing the relationship between the diameter of the column and the phase delay. [Figure 5] FIG. 5 is a diagram illustrating an example of a method for manufacturing the metasurface lens shown in FIG. [Figure 6] FIG. 6 is a diagram illustrating another example of a method for manufacturing the metasurface lens shown in FIG. [Figure 7] FIG. 7 is a cross-sectional view schematically illustrating the configuration of a metasurface lens according to another embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0020] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. In the description of the drawings, the same elements are given the same reference numerals, and duplicated explanations will be omitted. An XYZ coordinate system may be shown in each drawing. The Y-axis direction is a direction that intersects (e.g., is perpendicular to) the X-axis direction and the Z-axis direction. The Z-axis direction is a direction that intersects (e.g., is perpendicular to) the X-axis direction and the Y-axis direction.

[0021] A metasurface lens according to one embodiment will be described with reference to FIG. 1. FIG. 1 is a cross-sectional view showing a schematic configuration of a metasurface lens according to one embodiment. A metasurface lens is a lens that uses a metasurface obtained by arranging nanostructures two-dimensionally. Note that "metasurface lens" is a general term for metasurfaces that function as lenses, and may also be simply referred to as "metalens."

[0022] 1, the metasurface lens 1 includes a transparent substrate 11, an antireflection layer 12 (first antireflection layer), a metasurface structure 13, and an antireflection layer 14 (second antireflection layer). The antireflection layer 14, the transparent substrate 11, the antireflection layer 12, and the metasurface structure 13 are stacked in that order in the Z-axis direction.

[0023] The transparent substrate 11 is a substrate that has visible light transparency and transmits visible light. The material of the transparent substrate 11 is a material that has visible light transparency and has a refractive index higher than 1. An example of such a material is sapphire (e.g., Al2O3). The length of the transparent substrate 11 in the Z-axis direction (thickness D s ) is, for example, 0.65 mm. Hereinafter, the length in the Z-axis direction may be referred to as "thickness" or "height." Transparent substrate 11 has surface 11a and surface 11b. Surface 11b is located on the opposite side of surface 11a in the Z-axis direction.

[0024] The antireflection layer 12 is provided on the surface 11a and is a layer that suppresses reflection between the transparent substrate 11 and the metasurface structure 13. The antireflection layer 12 is provided over the entire surface of the surface 11a. The antireflection layer 12 has a refractive index n s Refractive index n is lower than 1 and higher than 1 ar1 It has a refractive index n ar1 is the refractive index n of the columnar body 13a described later. m Is it the same as the refractive index n m The antireflection layer 12 is made of, for example, one compound selected from the group consisting of silicon oxide (e.g., SiO2), titanium oxide (e.g., TiO2), silicon nitride (e.g., SiN), and titanium nitride (e.g., TiN). The antireflection layer 12 has a surface 12a and a surface 12b. The surface 12a includes a region in contact with the columnar body 13a and a region in contact with air. The surface 12b is in contact with the surface 11a and is provided on the opposite side of the surface 12a in the Z-axis direction.

[0025] Refractive index n s >Refractive index n ar1 ≧ Refractive index n m >1 is satisfied, the phase of the light L does not change due to reflection at the surface 12b of the antireflection layer 12 or reflection at the surface 12a of the antireflection layer 12. The light L is visible light incident on the metasurface lens 1, and contains red, green, and blue components. Therefore, in order to cancel out the light L reflected at the surface 12b of the antireflection layer 12 and the light L reflected at the surface 12a of the antireflection layer 12, the thickness D of the antireflection layer 12 is set to ar1 may satisfy the anti-reflection condition shown in formula (1).

number

[0026] The value m1 is an integer equal to or greater than 0. The wavelength λ is the wavelength of the light L. The light L includes red, green, and blue components. Here, the wavelength λ is the wavelength of the green component (520 nm), to which the human eye has the highest sensitivity. ar1 is determined. Thickness Dar1 For example, if SiO2 is used as the material of the antireflection layer 12 and the wavelength λ of the green component is 520 nm, the thickness D ar1 When m1 is 87 nm (m1=0), 260 nm (m1=1), and 433 nm (m1=2), the antireflection condition shown in formula (1) is satisfied.

[0027] The metasurface structure 13 is a structure that realizes a desired lens function by adjusting the phase delay of light L passing through the metasurface structure 13. The metasurface structure 13 is made of a material that is transparent to visible light. Specifically, the metasurface structure 13 includes a plurality of pillars 13a (nanostructures) provided on the antireflection layer 12. Each pillar 13a is a pillar-shaped member that is transparent to visible light. In other words, each pillar 13a is a transparent pillar-shaped member. The pillars 13a are made of a material that is transparent to visible light and has a refractive index higher than 1. Examples of such a material include silicon oxide (e.g., SiO2), titanium oxide (e.g., TiO2), silicon nitride (e.g., SiN), and titanium nitride (e.g., TiN). The refractive index n of the pillars 13a is m is greater than 1 and the refractive index n ar1 Is the refractive index n the same as ar1 Lower than.

[0028] In this embodiment, each of the columns 13a has a cylindrical shape. The shape of each of the columns 13a is not limited to a cylinder, and may be a prismatic column, or a tapered truncated cone or truncated pyramid. Each of the columns 13a is provided upright on the surface 12a of the antireflection layer 12. That is, each of the columns 13a extends in the Z-axis direction opposite to the transparent substrate 11. The height H of each of the columns 13a (the length in the Z-axis direction) is, for example, 500 nm to 2000 nm.

[0029] The multiple pillars 13a are arranged concentrically around the center point C (see FIG. 3) of the metasurface structure 13. The multiple pillars 13a located on the same circle are arranged at equal intervals, and the shortest distance between the outer surfaces of two adjacent pillars 13a is approximately half the wavelength λ of the light L (for example, 150 nm to 250 nm).

[0030] The cross-sectional area of ​​each pillar 13a along the XY plane is set according to the position of the pillar 13a so that the metasurface lens 1 has the desired lens function. The cross-sectional areas of multiple pillars 13a located at equal distances from the center point C (i.e., pillars 13a located on the same circle) are the same. The multiple pillars 13a are arranged so that the cross-sectional area changes periodically with increasing distance from the center point C.

[0031] The antireflection layer 14 is provided on the surface 11b and is a layer that suppresses reflection on the surface 11b of the transparent substrate 11. The antireflection layer 14 is provided over the entire surface of the surface 11b. The antireflection layer 14 has a refractive index n s Refractive index n is lower than 1 and higher than 1 ar2 The anti-reflection layer 14 is made of, for example, one compound selected from the group consisting of silicon oxide (for example, SiO2) and magnesium fluoride (for example, MgF2).

[0032] 1 (refractive index of air) < refractive index n ar2 <refractive index n s Since the relationship between the thickness D of the antireflection layer 14 and the transparent substrate 11 is satisfied, the phase of the light L changes by π radians due to both reflection at the interface (surface 11b) between the antireflection layer 14 and the transparent substrate 11 and reflection at the surface of the antireflection layer 14. Therefore, in order to cancel out the light L reflected at the interface between the antireflection layer 14 and the transparent substrate 11 and the light L reflected at the surface of the antireflection layer 14, the thickness D of the antireflection layer 14 is set to π radians. ar2 may satisfy the anti-reflection condition shown in equation (2), for example.

number

[0033] The value m2 is an integer equal to or greater than 0. The wavelength λ is the wavelength of the light L. The light L includes red, green, and blue components. For example, the wavelength of the green component to which the human eye has the highest sensitivity is used as the wavelength λ, and the thickness D ar2 is determined. Thickness D ar2 For example, if SiO2 is used as the material of the antireflection layer 14 and the wavelength λ of the green component is 520 nm, the thickness D ar2 When m2 is 87 nm (m2=0), 260 nm (m2=1), and 433 nm (m2=2), the antireflection condition shown in formula (2) is satisfied.

[0034] The refractive index n s >Refractive index n ar1 ≧ Refractive index n m >1 and the refractive index n s >Refractive index n ar2 The constituent materials of the transparent substrate 11, the antireflection layer 12, the metasurface structure 13, and the antireflection layer 14 are appropriately selected so that all of the relationships >1 are satisfied.

[0035] Next, the operating principle of the metasurface lens 1 will be described with reference to Figs. 2 to 4. Fig. 2 is a diagram for explaining the operating principle of the metasurface lens shown in Fig. 1. Fig. 3 is a diagram for explaining the relationship between the position and diameter of the pillars included in the metasurface lens shown in Fig. 1. Fig. 4 is a diagram showing the relationship between the diameter of the pillars and the phase delay. In this embodiment, since each pillar 13a has a cylindrical shape, the description will be made using the diameter of the pillar instead of the area of ​​the cross section.

[0036] As shown in FIG. 2, when light L passes through the pillars 13a of the metasurface lens 1, a phase delay occurs according to the diameter of the pillars 13a. Therefore, the diameter of each pillar 13a is adjusted to obtain the desired lens function. In this embodiment, the diameter of each pillar 13a is set so that the phase delay that occurs from when light L enters the metasurface lens 1 until it reaches the focal point P is the same throughout the metasurface lens 1. With this configuration, light L is focused by passing through the metasurface lens 1, so the metasurface lens 1 functions as a focusing lens.

[0037] Here, a method for determining the diameter of the pillars 13a will be specifically described. As shown in Fig. 3, the phase delay φ1(r) that occurs after passing through each pillar 13a and before reaching the focal point P increases as the distance between each pillar 13a and the focal point P increases. In this embodiment, in order to make the metasurface lens 1 function as a focusing lens, the diameter of each pillar 13a is determined so that the sum of the phase delay φ1(r) and the phase delay φ2(r) that occurs in the pillars 13a is a constant delay amount Φ for all pillars 13a.

[0038] The phase delay φ1(r) can be seen as a phase delay corresponding to the distance from the equiphase surface ES of the spherical wave to each columnar body 13a, and varies depending on the distance r. The equiphase surface ES is an equiphase surface centered at the focal point P and having a radius the same length as the focal length f. The focal length f is the distance from the focal point P to the center point C. The distance r is the distance from the center point C to the central axis of the columnar body 13a.

[0039] The phase delay φ1(r) is expressed by equation (3) using the focal length f, the distance r, and the wavelength λ of the light L.

number

[0040] The phase delay φ2(r) is the phase delay occurring in the column 13a located at a distance r. As shown in FIG. 4, the phase delay φ2(r) varies depending on the diameter and height H of the column 13a. The horizontal axis of FIG. 4 represents the diameter (unit: nm) of the column 13a, and the vertical axis of FIG. 4 represents the phase delay (unit: radian). The characteristics shown in FIG. 4 are characteristics calculated in advance by numerical calculation with a refractive index of 1.5. For columns 13a having the same height, the phase delay tends to increase as the diameter of the column 13a increases. For columns 13a having the same diameter, the phase delay tends to increase as the height H of the column 13a increases.

[0041] If the height H of the column 13a is too low, the phase delay does not change much even if the diameter of the column 13a is changed. If the height H of the column 13a is too high, the amount of change in the phase delay increases with the amount of change in the diameter of the column 13a, so dimensional accuracy of the column 13a is required. Therefore, as described above, the height H of the column 13a is set to, for example, 500 nm to 2000 nm.

[0042] The sum of the phase delay φ1(r) and the phase delay φ2(r) may exceed 2π radians. In this case, since the phase of light has a periodicity of 2π radians, the diameter of each column 13a is determined so that the remainder obtained by dividing the sum of the phase delay φ1(r) and the phase delay φ2(r) by 2π radians is the same delay amount Φ for all columns 13a. In other words, the relationship shown in Equation (4) holds between the phase delay φ1(r) and the phase delay φ2(r). The function MOD(A,B) is a function that calculates the remainder obtained by dividing A by B.

number

[0043] The height H and diameter of each pillar 13a are determined from the characteristics shown in Figure 4 so as to obtain a phase delay φ2(r) that satisfies the relationship in equation (4). In this embodiment, to facilitate the manufacture of the metasurface lens 1, all pillars 13a included in the metasurface lens 1 are set to the same height. Therefore, the diameter of each pillar 13a is determined from the characteristics shown in Figure 4 so as to obtain a phase delay φ2(r) that satisfies the relationship in equation (4).

[0044] The phase delay φ2(0) at the center point C is set to 2π radians (0 radians). Near the center point C (group G1a), the diameter of each columnar body 13a is set so that the sum of the phase delay φ1(r) and the phase delay φ2(r) is 2π radians. As the distance r increases, the phase delay φ1(r) increases, so the phase delay φ2(r) gradually decreases from 2π radians, and the diameter of the columnar body 13a also becomes shorter.

[0045] Then, when the phase delay φ1(r) exceeds 2π radians, the phase delay φ2(r) cannot be made smaller than 0 radians, so the diameter of each column 13a is set so that the sum of the phase delay φ1(r) and the phase delay φ2(r) is 4π radians. The column 13a whose diameter is set so that the sum of the phase delay φ1(r) and the phase delay φ2(r) is 4π radians belongs to group G1b. Thereafter, each time the phase delay φ1(r) exceeds a multiple of 2π radians, the target value of the sum of the phase delay φ1(r) and the phase delay φ2(r) is increased by 2π radians.

[0046] In the metasurface lens 1, light L is incident from surface 11b toward surface 11a of the transparent substrate 11, and the light L is transmitted in this order through the transparent substrate 11, the antireflection layer 12, and the metasurface structure 13. When the light L transmits through the metasurface structure 13, a phase delay occurs due to each pillar 13a, thereby achieving the desired lens function.

[0047] Next, an example of a method for manufacturing the metasurface lens 1 will be described with reference to Fig. 5. Fig. 5 is a diagram for explaining an example of a method for manufacturing the metasurface lens shown in Fig. 1. Here, a method for manufacturing the metasurface lens 1 in which the antireflection layer 12 and the metasurface structure 13 are made of the same material is exemplified.

[0048] As shown in FIG. 5, first, a base is prepared in which a transparent layer 51, which is the basis of the antireflection layer 12 and the metasurface structure 13, is formed on the surface 11a of the transparent substrate 11. The transparent layer 51 is a layer made of a material that is transparent to visible light. The thickness of the transparent layer 51 is set to be 1 / 2 times the thickness D of the antireflection layer 12. ar1 and the height H of the columnar bodies 13a. Subsequently, a metal layer 52 is formed on the light-transmitting layer 51. Specifically, the metal layer 52 is formed by vacuum film formation using a technique such as DC (Direct Current) sputtering. The metal layer 52 is formed using a metal material made of, for example, chromium (Cr).

[0049] Subsequently, a resist pattern 53 is formed on the metal layer 52 by a photolithography process. Specifically, a liquid resist is applied to the metal layer 52 using a spin coater or the like, and the applied liquid resist is dried to form a resist film (photoresist). Then, using an exposure device such as a KrF exposure device or an electron beam lithography device, the resist pattern 53 corresponding to the columns 13a is transferred onto the resist film. Then, using a developing device, the resist pattern 53 transferred onto the resist film is developed.

[0050] Subsequently, the portions of the metal layer 52 that are not covered with the resist pattern 53 are removed by an etching process, and then the resist pattern 53 is removed. As a result, a metal mask 52a is formed on the light-transmitting layer 51.

[0051] Next, an etching process is performed to remove the portions of the transparent layer 51 that are not covered by the metal mask 52a to a depth corresponding to the height H of the columns 13a. The metal mask 52a is then removed. This leaves the antireflection layer 12 and the metasurface structure 13 on the surface 11a of the transparent substrate 11. In this way, the metasurface lens 1 is manufactured.

[0052] Next, another example of a method for manufacturing the metasurface lens 1 will be described with reference to Fig. 6. Fig. 6 is a diagram for explaining another example of a method for manufacturing the metasurface lens shown in Fig. 1. Here, a method for manufacturing the metasurface lens 1 in which the antireflection layer 12 and the metasurface structure 13 are made of different materials is exemplified.

[0053] As shown in FIG. 6, first, an anti-reflection layer 12 is formed on the surface 11a of a transparent substrate 11, and a transparent layer 51A, which will be the basis of the metasurface structure 13, is formed on the surface 12a of the anti-reflection layer 12. The transparent layer 51A is a layer made of a material that is transparent to visible light. The thickness of the transparent layer 51A is equal to the height H of the columnar bodies 13a. Next, as in FIG. 5, a metal layer 52 is formed on the transparent layer 51A, and a resist pattern 53 is formed on the metal layer 52 by a photolithography process. Next, the portions of the metal layer 52 that are not covered by the resist pattern 53 are removed by an etching process, and then the resist pattern 53 is removed. This results in a metal mask 52a being formed on the transparent layer 51A.

[0054] Next, an etching process is performed to remove the portion of the transparent layer 51A that is not covered by the metal mask 52a, and then the metal mask 52a is removed. This results in the formation of the metasurface structure 13 on the surface 12a of the antireflection layer 12. In this way, the metasurface lens 1 is manufactured.

[0055] In the metasurface lens 1 described above, an antireflection layer 12 is provided between the transparent substrate 11 and the metasurface structure 13. Therefore, it is possible to suppress reflected light occurring between the transparent substrate 11 and the metasurface structure 13.

[0056] For example, it is possible to provide an antireflection layer for each column 13a. In this case, the antireflection layer forms a nanostructure, which may affect the lens function of the metasurface structure 13. In contrast, in the metasurface lens 1, the antireflection layer 12 does not form the column 13a, so the effect on the lens function of the metasurface structure 13 is reduced.

[0057] When light L is incident on surface 11b of transparent substrate 11, reflected light may occur at surface 11b. In metasurface lens 1, an antireflection layer 14 is provided on surface 11b of transparent substrate 11, so that reflected light occurring at surface 11b can be suppressed.

[0058] The surface 12a includes a region where the columns 13a are provided and a region where the columns 13a are not provided. The region where the columns 13a are not provided may be in contact with air. When light L enters the antireflection layer 12 from the transparent substrate 11, the light L may be reflected at the interface (surface 12b) between the transparent substrate 11 and the antireflection layer 12, the interface (surface 12a) between the antireflection layer 12 and the columns 13a, and the interface (surface 12a) between the antireflection layer 12 and air. In this case, the light L reflected at the surface 12b interferes with the light L reflected at the surface 12a. If the phase change due to reflection at the interface between the antireflection layer 12 and the columns 13a is different from the phase change due to reflection at the interface between the antireflection layer 12 and air (opposite phase), the reflected light cannot be effectively attenuated.

[0059] The refractive index n of the anti-reflection layer 12 ar1 is the refractive index n of the metasurface structure 13 m If it is higher than ar1 is the refractive index n mand the refractive index of air (=1), the phase of the light L does not change due to reflection at the interface between the antireflection layer 12 and the columns 13a, or the interface between the antireflection layer 12 and air. ar1 is the refractive index n m When the thickness D of the antireflection layer 12 is equal to the thickness D of the antireflection layer 12, no reflection occurs at the boundary surface between the antireflection layer 12 and the columnar bodies 13a. ar1 As a result, it is possible to further suppress the reflected light occurring between the transparent substrate 11 and the metasurface structure 13.

[0060] The refractive index n of the anti-reflection layer 12 ar1 is the refractive index n of the transparent substrate 11 s When the refractive index n ar1 is the refractive index n of the metasurface structure 13 m Is the refractive index n the same as m When the thickness D of the antireflection layer 12 is higher than 1 / 2, the phase of the light L does not change due to reflection at the interface between the antireflection layer 12 and the columns 13a and reflection at the interface between the antireflection layer 12 and air. ar1 is the wavelength λ of light L, and the refractive index n of the anti-reflection layer 12. ar1 When the difference between the optical path length of the light L reflected at the interface (surface 12b) between the transparent substrate 11 and the antireflection layer 12 and the optical path length of the light L reflected at the interface (surface 12a) between the antireflection layer 12 and the metasurface structure 13 is an odd multiple of λ / 2. Therefore, the two reflected lights L are in opposite phases and cancel each other out. Therefore, the reflected light occurring between the transparent substrate 11 and the metasurface structure 13 can be further suppressed.

[0061] The anti-reflection layer 12 may be made of a compound selected from the group consisting of silicon oxide and silicon nitride. In this case, the refractive index n m Is the refractive index n the same as mTherefore, an antireflection layer 12 having a refractive index lower than that of the reflective layer 12 can be obtained.

[0062] If the antireflection layer 12 is made of the same material as the metasurface structure 13, the antireflection layer 12 and the metasurface structure 13 can be integrally formed, which simplifies the manufacture of the metasurface lens 1.

[0063] The metasurface structure 13 is made of a material that is transparent to visible light. Therefore, when light L passes through the pillars 13a, a phase delay occurs in the light L. Therefore, by appropriately adjusting the phase delay occurring in each pillar 13a, a desired lens function can be obtained.

[0064] The metasurface structure 13 may be composed of one compound selected from the group consisting of silicon oxide, silicon nitride, titanium oxide, and titanium nitride. These compounds are transparent in the visible light range, which allows the metasurface structure 13 to be transparent to visible light. Since the absorption of visible light in the metasurface structure 13 is suppressed, the lens function for visible light can be improved.

[0065] Next, a metasurface lens according to another embodiment will be described with reference to Fig. 7. Fig. 7 is a cross-sectional view showing a schematic configuration of a metasurface lens according to another embodiment. The metasurface lens 1A shown in Fig. 7 differs from the metasurface lens 1 mainly in that it includes a reflective layer 15 instead of the antireflection layer 14.

[0066] The reflective layer 15 is provided on the surface 11b and is a layer that reflects light L. The reflective layer 15 is provided over the entire surface of the surface 11b. The reflective layer 15 is a metal layer. Examples of materials that can be used for the reflective layer 15 include silver (Ag) and aluminum (Al).

[0067] In the metasurface lens 1A, light L is incident from surface 11a to surface 11b of the transparent substrate 11, whereby the light L is reflected by the reflective layer 15, and the reflected light L is transmitted in order through the transparent substrate 11, the antireflection layer 12, and the metasurface structure 13. When the light L transmits through the metasurface structure 13, a phase delay occurs due to each pillar 13a, thereby achieving the desired lens function.

[0068] The metasurface lens 1A also has the same configuration as the metasurface lens 1, and thus exhibits the same effects as the metasurface lens 1. For example, the metasurface lens 1A can also suppress reflected light that occurs between the transparent substrate 11 and the metasurface structure 13.

[0069] It should be noted that the metasurface lens according to the present disclosure is not limited to the above embodiment.

[0070] The metasurface lens 1 is applied to smart glasses such as AR (Augmented Reality) glasses, VR (Virtual Reality) glasses, and MR (Mixed Reality) glasses, for example.

[0071] The metasurface lens 1 may be configured to function as a lens other than a focusing lens. For example, the metasurface lens 1 may be configured to function as a collimating lens or a beam expander.

[0072] The refractive index n of the anti-reflection layer 12 ar1 is the refractive index n of the transparent substrate 11 s That is, the refractive index n ar1 >Refractive index n s The relationship between the refractive index n ar1 ≧ Refractive index n m >1, and the refractive index n s >Refractive index n ar2The constituent materials of the transparent substrate 11, the antireflection layer 12, the metasurface structure 13, and the antireflection layer 14 may be appropriately selected so that any of the relationships >1 is satisfied.

[0073] Refractive index n ar1 >Refractive index n s Since the relationship between the refractive index and the refractive index of the light L is satisfied, the phase of the light L changes by π radians upon reflection from the surface 12b of the antireflection layer 12. ar1 ≧ Refractive index n m >1 is satisfied, the phase of the light L is not changed by reflection at the surface 12a of the antireflection layer 12. Therefore, in order to cancel out the light L reflected at the surface 12b of the antireflection layer 12 and the light L reflected at the surface 12a of the antireflection layer 12, the thickness D of the antireflection layer 12 is set to ar1 The anti-reflection condition shown in equation (5) may be satisfied.

number

[0074] Refractive index n ar1 is the refractive index n s When the refractive index n ar1 is the refractive index n m Is the refractive index n the same as m When the thickness D of the antireflection layer 12 is higher than 1 / 2, the phase of the light L does not change even when reflected at the interface between the antireflection layer 12 and the columns 13a or the interface between the antireflection layer 12 and air. ar1 is the wavelength λ of light L, and the refractive index n of the anti-reflection layer 12. ar1When the wavelength λ is an integer multiple of the result of division by twice the wavelength λ, the difference between the optical path length of the light L reflected at the interface (surface 12b) between the transparent substrate 11 and the antireflection layer 12 and the optical path length of the light L reflected at the interface (surface 12a) between the antireflection layer 12 and the metasurface structure 13 is an integer multiple of the wavelength λ. Therefore, the two reflected lights L are in opposite phases and cancel each other out. Therefore, the reflected light occurring between the transparent substrate 11 and the metasurface structure 13 can be further suppressed.

[0075] Thickness D ar1 does not necessarily satisfy the antireflection condition shown in formula (1) or formula (5), as long as the light L reflected at the surface 12b of the antireflection layer 12 and the light L reflected at the surface 12a of the antireflection layer 12 weaken each other.

[0076] Thickness D ar2 does not necessarily satisfy the antireflection condition shown in formula (2) as long as the light L reflected at the boundary surface between the antireflection layer 14 and the transparent substrate 11 and the light L reflected at the surface of the antireflection layer 14 weaken each other.

[0077] (Addendum) [Article 1] a transparent substrate having a first surface and a second surface opposite to the first surface in a first direction; a first antireflection layer provided on the first surface; A metasurface structure including a plurality of columns provided in the first antireflection layer, the plurality of columns extending on the opposite side of the transparent substrate in the first direction; A metasurface lens comprising:

[0078] [Clause 2] The metasurface lens of clause 1, further comprising a second anti-reflection layer provided on the second surface.

[0079] [Article 3] The metasurface lens of clause 1, further comprising a reflective layer disposed on the second surface.

[0080] [Article 4] The metasurface lens according to any one of clauses 1 to 3, wherein the metasurface structure is made of a material that is transparent to visible light.

[0081] [Article 5] The metasurface lens of clause 4, wherein the metasurface structure is composed of one compound selected from the group consisting of silicon oxide, silicon nitride, titanium oxide, and titanium nitride.

[0082] [Article 6] 6. The metasurface lens of any one of clauses 1 to 5, wherein the first antireflection layer has a refractive index that is the same as or higher than the refractive index of the metasurface structure.

[0083] [Article 7] the refractive index of the first antireflection layer is lower than the refractive index of the transparent substrate; The metasurface lens of clause 6, wherein the length of the first antireflection layer in the first direction is an odd multiple of the result of dividing the wavelength of visible light by four times the refractive index of the first antireflection layer.

[0084] [Article 8] the refractive index of the first antireflection layer is higher than the refractive index of the transparent substrate; The metasurface lens described in clause 6, wherein the length of the first antireflection layer in the first direction is an integer multiple of the result of dividing the wavelength of visible light by twice the refractive index of the first antireflection layer.

[0085] [Article 9] The metasurface lens of any one of clauses 1 to 8, wherein the first antireflection layer is composed of a compound selected from the group consisting of silicon oxide and silicon nitride.

[0086] [Article 10] The metasurface lens of any one of clauses 1 to 9, wherein the first antireflection layer is made of the same material as the metasurface structure. [Explanation of symbols]

[0087] 1, 1A... metasurface lens, 11... transparent substrate, 11a... surface (first surface), 11b... surface (second surface), 12... antireflection layer (first antireflection layer), 13... metasurface structure, 13a... columnar body, 14... antireflection layer (second antireflection layer), 15... reflective layer.

Claims

1. a transparent substrate having a first surface and a second surface opposite to the first surface in a first direction; a first antireflection layer provided on the first surface; A metasurface structure including a plurality of columns provided in the first antireflection layer, the plurality of columns extending on a side opposite to the transparent substrate in the first direction; A metasurface lens comprising:

2. The metasurface lens of claim 1 , further comprising a second anti-reflection layer provided on the second surface.

3. The metasurface lens of claim 1 , further comprising a reflective layer provided on the second surface.

4. The metasurface lens according to any one of claims 1 to 3, wherein the metasurface structure is made of a material that is transparent to visible light.

5. The metasurface lens of claim 4 , wherein the metasurface structure is composed of a compound selected from the group consisting of silicon oxide, silicon nitride, titanium oxide, and titanium nitride.

6. The metasurface lens according to any one of claims 1 to 3, wherein the first antireflection layer has a refractive index that is the same as or higher than the refractive index of the metasurface structure.

7. the refractive index of the first antireflection layer is lower than the refractive index of the transparent substrate; The metasurface lens of claim 6, wherein the length of the first antireflection layer in the first direction is an odd multiple of a result of dividing the wavelength of visible light by four times the refractive index of the first antireflection layer.

8. the refractive index of the first antireflection layer is higher than the refractive index of the transparent substrate; The metasurface lens of claim 6, wherein the length of the first antireflection layer in the first direction is an integer multiple of the result of dividing the wavelength of visible light by twice the refractive index of the first antireflection layer.

9. The metasurface lens according to any one of claims 1 to 3, wherein the first antireflection layer is composed of a compound selected from the group consisting of silicon oxide and silicon nitride.

10. The metasurface lens according to any one of claims 1 to 3, wherein the first antireflection layer is made of the same material as the metasurface structure.

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