Optical element, optical system, imaging device, and method for manufacturing optical element

Abstract

This optical element comprises a substrate and a plurality of structures formed on the substrate, and is divided into a plurality of periodically arranged sections. A first structure group comprising N structures (where N is an integer of 3 or more) is disposed in a first section among the plurality of sections, and a second structure group comprising the same number of structures as the number of structures constituting the first structure group is disposed in a second section among the plurality of sections. When the optical element is viewed from a direction perpendicular to the substrate, a predetermined conditional expression is satisfied, where C1 is a closed curve shape obtained by sequentially connecting the respective centers of gravity of the N structures constituting the first structure group, and C2 is a closed curve shape obtained by sequentially connecting the respective centers of gravity of the structures constituting the second structure group.

Description

Optical element, optical system, imaging device, method for manufacturing an optical element

[0001] The disclosure herein relates to optical elements having multiple structures, and is particularly suitable for optical systems such as condensing lenses and coupling lenses for display elements, or optical elements used in imaging devices such as digital still cameras.

[0002] As a metalens, which is an optical element having multiple structures, Patent Document 1 discloses a metalens in which the shape of the structure has a shape pattern such as having multiple hollow parts inside a cylinder or a rectangular prism.

[0003] U.S. Patent Application Publication No. 2020 / 0096672

[0004] There is a need for optical elements with superior optical performance compared to conventional ones.

[0005] One aspect of solving the above problem is an optical element having a substrate and a plurality of structures formed on the substrate, wherein the optical element is divided by a plurality of periodically arranged sections, a first group of structures consisting of N structures (where N is an integer of 3 or more) is arranged in a first section of the plurality of sections, a second group of structures consisting of the same number of structures as the number of structures constituting the first group of structures is arranged in a second section of the plurality of sections, and when the optical element is viewed from a direction perpendicular to the substrate, the closed curve shape formed by sequentially connecting the centroids of the N structures constituting the first group of structures is C1, and the closed curve shape formed by sequentially connecting the centroids of the structures constituting the second group of structures is C2, the distance between the total center of gravity of C1 and the centroid of the structure furthest from the centroid of C1 among the structures constituting C1 is R1, and the distance between the total center of gravity of C2 and the centroid of the structure furthest from the centroid of C1 among the structures constituting C2 is R2, the condition R1 > R2 is satisfied.

[0006] This makes it possible to provide optical elements with excellent optical performance.

[0007] Conceptual diagram of optical element 100 Conceptual diagram of the group of structures 3 constituting the optical element 100 Conceptual diagram of structures and partitions Conceptual diagram of partition shape Conceptual diagram of partition shape Conceptual diagram of partition shape Conceptual diagram of partition shape Conceptual diagram of structures in the first and second partitions Arrangement diagram of structures in an embodiment Diagram showing phase dispersion characteristics in embodiment 1 Diagram showing detailed phase dispersion characteristics in embodiment 1 Arrangement diagram of structures in embodiment 2 Diagram showing phase dispersion characteristics in embodiment 2 Arrangement diagram of structures in embodiments 3 and 6 Diagram showing phase dispersion characteristics in embodiment 3 Diagram showing phase dispersion characteristics in embodiment 4 Diagram showing phase dispersion characteristics in embodiment 5 Diagram showing phase dispersion characteristics in embodiment 6 Diagram showing phase dispersion characteristics in embodiment 7 Arrangement diagram of structures in embodiment 7 Arrangement diagram of structures with number of structures N = 3, 5, 6, 7, 8, 9 as modified examples Diagram showing phase dispersion characteristics with number of structures N = 3, 5, 6, 7, 8, 9 as modified examples Schematic diagram representing modified shapes of structures Schematic diagram relating to the manufacturing method of optical element 100 Schematic diagram relating to the manufacturing method of optical element 100 Schematic diagram relating to the manufacturing method of optical element 100 Schematic diagram of optical system equipped with optical elements in embodiments 1 to 7 Schematic diagram of imaging device

[0008] The embodiments disclosed herein will be described in detail below with reference to the drawings. Note that the drawings may be drawn to a different scale than the actual dimensions for convenience. In each drawing, the same reference numeral is used for identical components, and redundant descriptions are omitted.

[0009] Figure 1 is a schematic diagram of the optical element 100. Figure 1(a) shows a top view of the optical element 100 in an xy cross-section, and Figure 1(b) shows an enlarged view of the main part of the optical element 100.

[0010] Each embodiment of the optical element 100 comprises a substrate 1 and an uneven structure 2 formed on the substrate 1. The uneven structure 2 consists of a plurality of structures 21 that are periodically arranged in the radial direction of the substrate 1. Each of the plurality of structures 21 has either a concave or convex shape.

[0011] The substrate 1 is a transparent flat plate made of synthetic quartz. Note that the substrate 1 may be a plane mirror that reflects incident light, or may be a curved surface having an arbitrary curvature. Further, the material of the substrate 1 is not limited to synthetic quartz, and may be an inorganic glass, an organic material such as plastic, ceramics, a metal, or the like. The concavo-convex structure 2 is formed on the surface of the substrate 1, and imparts a phase difference to light passing through the concavo-convex structure 2, thereby providing optical effects such as light convergence, divergence, and polarization. Here, let the design wavelength, which is the wavelength of light incident on the diffraction surface of the optical element 100, be λ₀, and let the design diffraction order, which is the diffraction order of diffracted light emitted from the diffraction surface and used for imaging, be n (n is a natural number). For example, in the optical element 100, a desired phase distribution can be formed by concentrically and periodically arranging annular zones that generate a phase difference of 2nπ. With this configuration, the optical element 100 has optical effects such as condensing and diverging incident light.

[0012] The concavo-convex structure 2 is composed of a plurality of structures 21 having a concave shape or a convex shape arranged on the substrate 1. In the optical element 100 according to each embodiment, the structure 21 is made of a dielectric material Si ３ N ４ or TiO ２ , and has a convex cylindrical shape. Note that the shape of the structure 21 is not limited to the convex cylindrical shape, and may be a polygonal column, a polygonal pyramid, a cone, any concave shape, or a combination thereof. Further, the material of the structure 21 is Si ３ N ４ and TiO ２ is not limited, and may be GaN, GaP, GaAs, Si, SiC, Al ２ O ３ , SiO ２ , or a combination thereof. It is preferable that all the structures 21 are made of the same material because the manufacturing process of the optical element 100 is simplified.

[0013] FIG. 2 is a schematic diagram of a structure group 3 in the optical element 100.

[0014] The structural group 3 is composed of one or more structural groups 21. Figure 2 shows an example of the structural group 3, as shown by the solid line in the lower right of Figure 1(b), which consists of N = 4 cylindrical structural groups 21 with a height h (where N is an integer of 3 or more) arranged on a substrate. The structural group 3 is divided by a section 4, which will be described later, and is arranged periodically in the radial direction of the optical element 100.

[0015] Figure 3 is a conceptual diagram of section 4 in the optical element 100.

[0016] The multiple structural groups 3 in Figure 1 are separated by sections 4 of the same shape, as shown in Figure 3. In Figure 3, as an example, one structural group 3 is placed inside each square section 4. Adjacent sections 4 are touching each other and arranged without gaps. Note that the substrate 1 does not actually need to be separated, but for the purpose of defining each structural group 3, it is assumed to be separated by sections 4. In this case, it is preferable that no structural group 3 is placed on the boundary line between one section 4 and another adjacent section 4. Also, the number of structural groups 3 placed inside a section 4 may be one or more; for example, four structural groups 3 may be placed in one section. Furthermore, the shape of section 4 is not limited to a square; as shown in Figures 4B to 4D, it may be any shape that is periodic and allows the structural groups 3 to be separated by the same shape, such as an equilateral triangle, regular hexagon, or rhombus. Also, the lengths of all sides of the shape of section 4 do not all have to be equal; it may be a triangle, quadrilateral, hexagon, etc.

[0017] Next, we will describe the characteristic configuration of the optical element 100 disclosed herein.

[0018] Figure 5 is an enlarged view of the main parts of the first section 41 and the second section 42 shown in the blowout section of Figure 3. The first section 41 and the second section 42 are each one of the sections 4 mentioned above. As shown in Figure 5, the first structural group 31 is arranged in the first section 41, and the second structural group 32 is arranged in the second section 42. The first structural group 31 and the second structural group 32 are each composed of the same number of structures 21. As an example, Figure 5 shows an optical element 100 in which the first structural group 31 and the second structural group 32 are composed of four cylindrical structures 21.

[0019] The centroid positions of the structures 21 in the first section 41 and the second section 42 are shown by shaded circles. Here, the centroid position of a structure 21 refers to the centroid defined by the planar geometric shape of each structure 21 in the xy plane when the optical element 100 is viewed from a direction perpendicular to the xy plane. For example, if the structure 21 is a cylinder as shown in Figure 5, the structure 21 in the xy plane will be circular, and the centroid of the structure 21 will correspond to the center of that circle. Similarly, the overall centroid position, which is the average of the centroid positions of the structures 21 in the structure group 31 and the structure group 32, is shown by a hollow circle.

[0020] In the first section 41, R1 is defined as the distance between the overall center of gravity of the group of structures 31 and the structure 21 located furthest from the overall center of gravity. Similarly, in the second section 42, R2 is defined as the distance between the overall center of gravity of the group of structures 32 and the structure 21 located furthest from the overall center of gravity.

[0021] Furthermore, in the first section, if the centroid positions of all the structures 21 constituting the group of structures 31 are connected by straight lines that pass through each one only once, a uniquely determined closed curve shape C1 can be drawn. Similarly, in the second section, if the centroid positions of all the structures 21 constituting the group of structures 32 are connected by straight lines that pass through each one only once, a uniquely determined closed curve shape C2 can be drawn. In the optical element 100 according to each embodiment, the closed curve shape C1 and the closed curve shape C2 are geometrically similar. This can also be expressed as the relationship in which each structure 21 in the second section is translated parallel toward the center of the section while maintaining the relative positional relationship between each structure 21 in the first section.

[0022] Furthermore, similarity can be rephrased as the arrangement of structures 21 at their corresponding vertex positions being different when closed curve shapes C1 and C2 are aligned in a similar orientation.

[0023] Here, the technical effects of the similarity between the closed curve shape C1 and the closed curve shape C2, as described above, will be explained using the optical element 100 of Example 1.

[0024] Figure 6 is an enlarged view of the main part of the structural group 3 in the optical element 100 of Example 1.

[0025] In the structure group 3 of Example 1, four cylinders are arranged as structure 21. Section 4 is a square, and the length of one side of the section is P. In Figure 6, each structure 21 is shown as a circle with a shaded outline, and the center of each structure 21 is shown as a shaded circle at the center of the circle. Each structure 21 is evenly arranged with the same spacing between centers of gravity relative to the center of the section, and the distance between the centers of gravity is a. All structures 21 have the same diameter, and the value of the diameter is d.

[0026] Figure 7 shows the phase dispersion characteristic graph for Example 1.

[0027] The parameters of the optical element 100 in Example 1 are as follows:

[0028] The structure 21 is cylindrical and made of Si ３ N ４The square section size P = 400 nm, structural element height h = 1500 nm, centroid spacing a = 80, 100, 120, 140, 160, 180, 200 nm, and diameter d takes values ​​from 0 to 200 nm.

[0029] The graph values ​​in Figure 7 represent the phase normalized to one wavelength, where a phase of 2π in radian notation corresponds to 1. The horizontal axis shows the phase change amount with respect to a wavelength of 450 nm, and the vertical axis shows the phase change amount with respect to a wavelength of 950 nm. In other words, the graph in Figure 7 shows the characteristics of the phase change amount with respect to two different wavelengths, and this is called the phase dispersion characteristic. Each line in Figure 7 shows the phase dispersion characteristics when the centroid spacing a of each structure 21 constituting the structure group 3 is changed from 80 nm to 200 nm. The plots within each line show the phase dispersion characteristics when the diameter d of each structure 21 is changed from 0 nm to 200 nm. The phase with a diameter d of 0 nm is taken as the starting origin, and the value of the phase change amount at that time is set to zero.

[0030] Generally, the phase dispersion characteristics of a structure 21 change by changing its shape, height, and width. In Figure 7, the phase distribution characteristics of a group of structures 3 with a single structure are located on the uppermost (upper limit) line, while the phase distribution characteristics of a group of structures 3 with multiple structures are located on the lowermost (lower limit) line. When designing an optical element, a structure 21 exhibiting appropriate phase dispersion characteristics is selected and placed on the substrate to satisfy the desired phase distribution. Therefore, if there is a large gap between the upper and lower limits in the phase dispersion characteristic graph, the number of selectable structures 21 that can be placed on the substrate during optical element design decreases, thus reducing the design freedom of the optical element. As a result, it becomes difficult to satisfy the desired phase distribution, leading to a problem of reduced optical performance of the optical element.

[0031] In order to solve the above problem, in the optical element 100 disclosed in the present specification, in addition to variables such as the shape, height, and width of the structures 21, the center-of-gravity spacing between the structures 21 is newly changed. That is, the optical system 100 disclosed in the present specification includes a structure group 31 and a structure group 32 in which the center-of-gravity spacings of the arranged structures 21 are different from each other. As a result, as shown in FIG. 7, it can be seen that a graph of chromatic dispersion characteristics that fills the blank between the aforementioned upper limit and lower limit can be obtained. By reducing blanks in the graph of phase dispersion characteristics, desired wavelength dispersion characteristics can be achieved when designing an optical element, thereby improving the degree of design freedom of the optical element. Furthermore, by arbitrarily changing the respective variables of the shape, height, width, and center-of-gravity spacing of the structures 21, blanks in the graph of phase dispersion characteristics are further reduced, so the degree of design freedom of the optical element is further improved. This makes it possible to design an optical element that exhibits desired optical performance. In addition, by adding the center-of-gravity spacing of the structures 21 as a variable, compared to a case where the center-of-gravity spacing is uniform, for example, the amount of change in the shape of the structures 21 can be reduced, so an optical element that can be manufactured at a lower cost than conventional ones can be realized.

[0032] Heretofore, the case where the closed curve shape C1 and the closed curve shape C2 are in a similar relationship in the first section 41 and the second section 42 has been described, but the present invention is not limited thereto, and it is only required that the shapes have a nearly similar relationship. That is, in FIG. 5, a configuration may be adopted in which the center-of-gravity spacing of each structure 21 in the second section is changed with respect to the center-of-gravity spacing of the structure group 21 in the first section so that R1 > R2.

[0033] Here, the nearly similar relationship will be described. Let the area of the closed curve shape C1 be A1, the area of the closed curve shape C2 be A2, and the difference between the areas A1 and A2 be A12. The statement that the closed curve shape C1 and the closed curve shape C2 have a nearly similar relationship refers to a state where, when either one of the structure group 31 and the structure group 32 is enlarged or reduced so that A12 is minimized, the difference A12 is 5% or less of the area of the closed curve shape C1 or the closed curve shape C2. That is, it refers to a state that satisfies the relationship |A12| / A1 < 0.05, or |A12| / A2 < 0.05.

[0034] Furthermore, when the similarity ratio of the closed curve shape C1 to the closed curve shape C2 is defined as S=C2 / C1, it is preferable that the following conditional expression is satisfied. 0.05<S<1.00 (1)

[0035] Conditional expression (1) is an expression that defines the similarity ratio between the closed curve shape C1 and the closed curve shape C2. The similarity ratio S is calculated from the ratio of the center-of-gravity spacing of the structure group 31 arranged in the first section 41 to the arrangement spacing of the structure group 32 arranged in the second section 42.

[0036] If the value goes below the lower limit of conditional expression (1), the center-of-gravity spacing of the structures 21 constituting the structure group 32 arranged in the second section becomes too narrow, which causes the structures 21 to contact each other in the second section, leading to degradation of optical performance, which is not preferable. If the value exceeds the upper limit of conditional expression (1), the center-of-gravity spacing of the structures 21 constituting the structure group 31 arranged in the first section becomes too large. As a result, the structure group 31 arranged in the first section comes into contact with another structure group 3 arranged in a section adjacent to the first section, leading to degradation of optical performance, which is not preferable.

[0037] Furthermore, the upper limit of conditional expression (1) is preferably any one of 0.99, 0.98, 0.97, 0.96, 0.95, 0.94, 0.93, 0.92, 0.91, 0.90, 0.89, 0.88, 0.87, 0.86, 0.85, 0.84, and 0.83.

[0038] Also, the lower limit of conditional expression (1) is preferably any one of 0.09, 0.10, 0.11, 0.12, 0.13, 0.14, 0.15, 0.16, 0.17, 0.18, 0.19, 0.20, 0.21, 0.22, 0.23, 0.24, and 0.25.

[0039] Next, the configurations of the optical elements 100 according to Examples 1 to 7 will be described in detail. In the optical element 100 of each example, description of configurations similar to those of the optical element 100 of Example 1 will be omitted, and differences from Example 1 will be mainly described.

[0040] [Example 1] Fig. 6 is an arrangement diagram of the structure group 3 according to Example 1.

[0041] In the structure group 3 of Example 1, four cylinders are arranged as structures 21 within a first section and a second section. Section 4 is square, and the section size is P. In Figure 6, each structure 21 is shown as a circle with a mesh outline, and the center of gravity of each structure 21 is shown as a shaded circle at the center of the circle. Each structure 21 is evenly arranged with the same centroidal spacing relative to the center of the section, and the value of the centroidal spacing is a. All four cylinders have the same diameter, and the value of the diameter is d.

[0042] Figure 7 shows the phase dispersion characteristic graph for Example 1.

[0043] The parameters of the optical element 100 in Example 1 are as follows. The structure 21 is cylindrical and made of Si ３ N ４ The square section size P = 400 nm, structural element height h = 1500 nm, centroid spacing a = 80, 100, 120, 140, 160, 180, 200 nm, and diameter d takes values ​​from 0 to 200 nm.

[0044] The graph values ​​in Figure 7 represent the phase normalized to one wavelength, with a phase of 2π in radian notation corresponding to 1. The horizontal axis represents the phase at 450 nm, and the vertical axis represents the phase at 950 nm, showing the phase characteristics of two wavelengths; this is called a phase dispersion characteristic graph. By changing the diameter d from 0 nm to 200 nm, each line changes continuously from the bottom left to the top right of the graph. The phase with a diameter d of 0 nm is used as the starting point and its value is set to zero. The values ​​obtained by changing the centroid interval a from 80 nm to 200 nm are shown as each line in the graph, and it can be seen that the characteristics change from the bottom to the top of the graph.

[0045] When the distance between centroids is wide, structural elements become closer to adjacent compartments and more likely to influence each other, so distances of 200 nm or more are omitted. This indicates that the relationship between the distance between centroids a and the compartment size P must satisfy a / P as less than 1. When the structures 21 within a compartment touch each other, discontinuity occurs in the phase dispersion characteristics, so it is preferable to arrange the structures 21 without touching each other. This means that when the relationship between the distance between centroids a and the element diameter d is normalized by the compartment size P, a / P is greater than d / P. The above relationship can be summarized as follows: d / P < a / P < 1 (2)

[0046] Conditional equation (2) defines the stability of the phase dispersion characteristics and the influence on adjacent compartments. If the value falls below the lower limit of the conditional equation, the structures 21 come into contact with each other, causing the phase dispersion characteristics to change discontinuously and increasing the sensitivity of the characteristics, which is undesirable. If the value exceeds the upper limit of the conditional equation, the distance between the groups of structures 3 located in adjacent compartments becomes too close, making interactions between compartments more likely, which is also undesirable.

[0047] Furthermore, it is more preferable to set condition (2) to the range of condition (2a) below: d / P < a / P < 0.9 (2a)

[0048] Furthermore, it is more preferable to set condition (2) to the range of condition (2b) below: d / P < a / P < 0.8 (2b)

[0049] In each group of structures 3, different centroid spacings of structures 21 result in different phase dispersion characteristics. To achieve a desired phase distribution as an optical element, an appropriate structure 21 can be selected and placed on the substrate. In this embodiment, the similarity ratio S of structure group 31 and structure group 32, i.e., the similarity ratio S of closed curve shape C1 and closed curve shape C2, is equal to the ratio of their respective centroid spacings. Therefore, the similarity ratio S of structure group 31 and structure group 32 will be within the following ranges based on the set centroid spacing values. The largest centroid spacing is 200 nm and the smallest centroid spacing is 80 nm, so the minimum similarity ratio S is 0.4. On the other hand, the largest centroid spacing is 200 nm and the second largest centroid spacing is 180 nm, so the maximum similarity ratio S is 0.9.

[0050] Figure 8 shows the phase dispersion graph when the change in the centroid interval is reduced in Example 1.

[0051] In Figure 8, the group of structures 3 in Example 1 have the centroid spacing a plotted more finely than in Figure 7, while other parameters are the same as in Figure 9. The centroid spacing a changes in 6 nm increments from 80 nm to 200 nm. The minimum similarity ratio in the detailed Example 1 is 0.4, and the maximum similarity ratio is 0.97. Similar to Figure 7, the centroid spacing of each structure 21 is gradually changed, but it can be seen that by making the amount of change in the spacing smaller, it is possible to fill in more of the gaps in the phase dispersion characteristic graph.

[0052] [Example 2] Figure 9 is a diagram showing the arrangement of the structure 21 in Example 2.

[0053] In Example 2, the group of structures 3 consists of five cylinders arranged as structures 21 within a section 4. Section 4 is a square, and the section size is P. Each structure 21 is a circle with a mesh outline, and the centroid of each structure 21 is drawn as a diagonal circle at the center of the circle. One structure 21 is placed in the center of the section, and four more are placed at equal intervals with the same centroidal spacing relative to the center of the section, and the value of the centroidal spacing is a. All five cylinders have the same diameter, and the diameter value is d.

[0054] Figure 10 shows the phase dispersion characteristic graph for Example 2.

[0055] The parameters of the optical element 100 in Example 2 are as follows. The structure 21 consists of five cylinders and is made of Si ３ N ４ The square section size P = 400 nm, structural element height h = 1500 nm, centroid spacing a = 100, 120, 140, 160, 180, 200 nm, and diameter d take values ​​from 0 to 200 nm. In this embodiment, the minimum similarity ratio is 0.5 and the maximum similarity ratio is 0.9. The phase dispersion characteristic line changes from the bottom to the top of the graph as the centroid spacing increases, exhibiting similar characteristics to Embodiment 1, and the phase dispersion characteristic can be changed more finely by changing the centroid spacing more finely.

[0056] [Example 3] Figure 11 is a diagram showing the arrangement of the structure 21 in Example 3.

[0057] In Example 3, the group of structures 3 consists of four rectangular prisms arranged as structures 21 within a section 4. Section 4 is a square, and the section size is P. Each structure 21 is a square with a grid pattern, and the centroid of each structure 21 is drawn as a diagonal circle at the center of the square. One structure 21 is placed in the center of the section, and four more are placed at equal intervals with the same centroidal spacing relative to the center of the section, and the centroidal spacing is a. All four rectangular prisms have the same width, and the width is d.

[0058] Figure 12 shows the phase dispersion characteristic graph for Example 3.

[0059] The parameters of the optical element 100 in Example 3 are as follows. The structure 21 consists of four rectangular prisms and is made of Si ３ N ４ The square section size P = 400 nm, the structure height h = 1500 nm, the centroid spacing a = 60, 80, 100, 120, 140, 160, 180, 200 nm, and the diameter d takes values ​​from 0 to 200 nm. In this embodiment, the minimum similarity ratio is 0.3 and the maximum similarity ratio is 0.9. The phase dispersion characteristic line changes from the bottom to the top of the graph as the centroid spacing widens, showing similar characteristics to Embodiment 1, and the phase dispersion characteristic can be changed more finely by making the change in centroid spacing smaller.

[0060] [Example 4] The optical element 100 of Example 4 has a group of structures 3 consisting of structures 21 having the same shape as in Example 3.

[0061] Figure 13 shows the phase dispersion characteristic graph for Example 4.

[0062] The parameters of the optical element 100 in Example 4 are as follows. The structure 21 consists of four cylinders and is made of Si ３ N ４The square section size P = 320 nm, the structure height h = 1500 nm, the centroid spacing a = 80, 96, 112, 128, 144, 160 nm, and the diameter d takes values ​​from 0 to 160 nm. In this embodiment, the minimum similarity ratio is 0.5 and the maximum similarity ratio is 0.9. The phase dispersion characteristic line changes from the bottom to the top of the graph as the centroid spacing widens, exhibiting characteristics similar to those of Embodiment 1, and the characteristics can be finely varied by changing the centroid spacing more precisely.

[0063] [Example 5] The optical element 100 of Example 5 has a group of structures 3 consisting of structures 21 having the same shape as in Example 3.

[0064] The optical element of Example 5 has a configuration in which four cylinders are arranged as structures 21 within a compartment. The compartment is square, and the size of the compartment is P. Each structure 21 is a circle with a grid pattern, and the centroid of each structure 21 is drawn as a diagonal circle at the center of the circle. The structures 21 are arranged at equal intervals with the same centroid interval relative to the center of the compartment, and the value of the centroid interval is a. All four cylinders have the same diameter, and the value of the diameter is d.

[0065] Figure 14 shows the phase dispersion characteristic graph for Example 5.

[0066] The parameters of the optical element 100 in Example 5 are as follows: The structure 21 consists of four cylinders and is made of TiO ２ The square section size P = 320 nm, the structure height h = 1000 nm, the centroid spacing a = 64, 80, 96, 112, 128, 144, 160 nm, and the diameter d takes values ​​from 0 to 160 nm. In this embodiment, the minimum similarity ratio is 0.4 and the maximum similarity ratio is 0.9. The phase dispersion characteristic line changes from the bottom to the top of the graph as the centroid spacing widens, exhibiting similar characteristics to Embodiment 1, and the characteristics can be finely varied by changing the centroid spacing more precisely.

[0067] [Example 6] The optical element 100 of Example 6 has a group of structures 3 consisting of structures 21 having the same shape as in Example 3.

[0068] The optical element of Example 6 has a configuration in which four rectangular prisms are arranged as structures 21 within a section. The section is square, and the size of the section is P. Each structure 21 is a square with a grid, and the centroid of each structure 21 is drawn as a diagonal circle at the center of the square. One structure 21 is placed in the center of the section, and four more are placed at equal intervals with the same centroidal spacing relative to the center of the section, and the value of the centroidal spacing is a. All four rectangular prisms have the same width, and the width value is d.

[0069] Figure 15 shows the phase dispersion characteristic graph for Example 6.

[0070] The parameters of the optical element 100 in Example 6 are as follows. The structure 21 consists of four cylinders and is made of Si ３ N ４ The square section size P = 256 nm, the structure height h = 1500 nm, the centroid spacing a = 64, 89.6, 102.4, 115.2, 128 nm, and the diameter d takes values ​​from 0 to 160 nm. In this embodiment, the minimum similarity ratio is 0.5 and the maximum similarity ratio is 0.9. The phase dispersion characteristic line changes from the bottom to the top of the graph as the centroid spacing widens, exhibiting characteristics similar to those of Embodiment 1, and the characteristics can be finely varied by changing the centroid spacing more precisely.

[0071] [Example 7] Figure 16 is a diagram showing the arrangement of the structure 21 in Example 7.

[0072] The optical element 100 of Example 7 has a configuration in which four cylinders are arranged as structures 21 within a section. Section 4 is a regular hexagon, and the size of the section is P. Each structure 21 is a circle with a mesh, and the centroid of each structure 21 is drawn as a diagonal circle at the center of the circle. The structures 21 are arranged at equal intervals with the same centroid interval relative to the center of the section, and the value of the centroid interval is a. All four cylinders have the same diameter, and the value of the diameter is d.

[0073] Figure 17 shows the phase dispersion characteristic graph for Example 7.

[0074] The parameters of the optical element 100 in Example 7 are as follows. The structure 21 consists of four cylinders and is made of Si ３ N ４The hexagonal section size P = 400 nm, the structure height h = 1500 nm, the centroid spacing a = 100, 120, 140, 160, 180, 200, 220, 240 nm, and the diameter d take values ​​from 0 to 200 nm. In this embodiment, the minimum similarity ratio is 0.417 and the maximum similarity ratio is 0.917. The phase dispersion characteristic line changes from the bottom to the top of the graph as the centroid spacing widens, showing similar characteristics to Embodiment 1, and the characteristics can be changed more finely by changing the centroid spacing more precisely.

[0075] The various physical quantities in Examples 1 to 7 are shown in Tables 1 and 2 below.

[0076]

[0077]

[0078] [Modified Examples] Next, a modified example of the optical element 100 will be described.

[0079] Figure 18 shows a modified example where the number of structures 12 constituting the structure group 3 is not N=4. In each modified example, the different sections 4 are related by the centroids of the cylinders being shifted in the direction of the arrows, and are in a relationship where they are closer to or further away from the center of the section. The average centroid position, obtained by averaging the centroids of each element, matches the centroid position of the section shape. Since the sections are arranged periodically, it is preferable that the structure group 13 also has a similar periodicity. This is preferable because, when using the RCWA method (exact coupled wave analysis method) which utilizes the periodicity of the structures as one of the methods for calculating the phase dispersion characteristics of the structure group 13, the periodic arrangement of the structures in the sections prevents performance degradation. The closed curve shape C, obtained by connecting the centroids of each structure 21 with straight lines, can be drawn as shown by the solid lines in the figure.

[0080] Figure 19 shows the phase dispersion characteristics of each optical element 100 when the number of structures 21 constituting the structure group 3 is N (where N = 3, 5, 6, 7, 8, 9). All N structures 21 constituting the structure group 3 are cylindrical, and the number of structures 21 N is graphed from N = 1 to N = 16, showing that as N increases, the graph asymptotically approaches a straight line. Since it is already close to a straight line at N = 4, using at least N = 4 structures 21 can cover almost the entire range of phase dispersion characteristics. On the other hand, for N = 9 and above, the graph almost overlaps with a straight line, showing that even when N is greater than 9, the same phase dispersion characteristics as N = 9 can be obtained. When the number of structures 21 is greater than N = 9, it shows the same phase distribution characteristics as N = 9, but considering that the width of the structures 21 is smaller compared to the case of N = 9, it is more preferable that the number of structures 21 is N = 9 or less. Therefore, it is more preferable that the number of structures 21 constituting the structure group 3 is between 4 and 9.

[0081] Figure 20 shows other variations. In the description of the structure 21 in this case, the effect was mainly explained using a cylindrical shape, but as shown in Figure 20, shapes such as cones, prisms, pyramids, trapezoids, hollow cylinders, hollow cones, hollow prisms, and hollow pyramids may also be used. In any case, the phase dispersion characteristics can be continuously changed by continuously changing the centroid spacing of the structure 21 while maintaining a similar relationship. In the structure group 3, a wider range of phase dispersion characteristics can be achieved by combining structures 21 of multiple shapes from the above shapes. Furthermore, in the structure group 3, it is preferable to make all structures 21 the same shape, as in Examples 1 to 7, because this allows for continuous phase dispersion characteristics to be achieved, as shown in Figure 7.

[0082] In Figure 5, the structure 21 is described as having a cylindrical shape, but as long as the closed curve shape C1 and the closed curve shape C2 are similar, the shape of the structure 21 is not limited to a cylinder; it may also be a cone or a prism. Also, in Figure 5, it is described that the widths of the four cylinders of the structure 21 are all the same, but as long as the closed curve shape C1 and the closed curve shape C2 are similar, the widths of the structure 21 may be different from each other. In Figure 5, it is described that the heights of the four cylinders of the structure 21 are all the same, but as long as the closed curve shape C1 and the closed curve shape C2 are similar, some of the heights of the structure 21 may be different, or all of them may be different.

[0083] However, it is preferable that the shape, width, or height are the same, as this increases the similarity between the metastructures of multiple sections and improves the reproducibility of the wavelength dispersion characteristics when designing the device. Furthermore, it is even preferable that multiple of the shape, width, and height are the same, as this further improves reproducibility.

[0084] In the optical element 100 of each embodiment, only the distance between the centers of gravity of the structure 21 is changed in the first section 41 and the second section 42. However, in addition to the distance between the centers of gravity, any combination of variables from the shape, height, and width of the structure 21 may also be changed.

[0085] [Manufacturing Method] Next, the manufacturing method of the optical elements in each embodiment will be explained using Figures 21A to 21C.

[0086] Figures 21A to 21C are explanatory diagrams of a method for manufacturing the optical element 100. Figures 21A to 21C show, as an example, the process of manufacturing the optical element 100 using nanoimprint lithography. Figure 21(a) shows a mold 31, which has a shape that is an inversion of the uneven shape of the uneven structure 2 formed by an electron beam or laser. As shown in Figure 21(b), a film 33 (first material) is deposited on the substrate 1. Next, a resist material 32 (second material) is applied to the surface of the film 33, the mold 31 is pressed onto it, and ultraviolet light or the like is irradiated to form an inversion of the uneven shape of the mold 31 on the resist material 32. After that, as shown in Figure 21(c), the mold 31 is released, and the film 33 is developed so that the uneven shape of the resist material 32 is transferred to the film 33, thereby forming the uneven structure 2 on the substrate 1 of the optical element 100. By the above method, the optical element 100 described in each embodiment can be manufactured. Furthermore, the manufacturing method for the uneven structure 2 is not limited to nanoimprint lithography; other methods may also be used, such as directly forming the uneven structure 2 with an electron beam or laser.

[0087] As shown in Figure 21(c), instead of directly forming the uneven structure 2 on the substrate 1, an offset layer (underlayment) may be placed between the substrate and the uneven structure 2. The offset layer may also be treated as part of the substrate 1.

[0088] In each embodiment, each structure 21 constituting the uneven structure 2 may be made of the same material. As shown in Figure 21(b), it is relatively easy to prepare a material with a uniform film thickness, such as the film 33. For this reason, when forming the uneven structure 2 of regions 1 and 2 based on the film 33, it is preferable that the same material is used for the structures 21 of regions 1 and 2.

[0089] [Optical System] Next, an example of the optical system including the optical elements of each embodiment will be described using Figure 22. In Figure 22, 100 is the optical element of each embodiment, 102 is the optical element, OA is the optical axis, IP is the image plane, and 3 is the optical system including the optical element 100 of each embodiment. The optical element 102 is composed of a refractive lens, a diffractive optical element, a mirror, a prism, etc., and may consist of one or multiple elements. The optical elements 100 and 102 are arranged along the optical axis OA to image the incident light onto the imaging plane IP. By arranging the structure 21 on the image-side surface of the optical element 100, optical effects such as focusing, divergence, and polarization are obtained.

[0090] [Imaging Device] Next, with reference to Figure 23, an imaging device using an optical system including the optical element 100 of each embodiment as an imaging optical system will be described. Figure 23 is an explanatory diagram of an imaging device 6 equipped with an optical system including the optical element of each embodiment. In Figure 23, 4 is the camera body, and 3 is the optical system including the optical element 100 according to each embodiment. 5 is an image sensor (photoelectric conversion element) such as a CCD sensor or CMOS sensor that is built into the camera body 4 and receives the optical image formed by the optical system 3 and converts it into photoelectric light. The camera body 4 may be a so-called single-lens reflex camera with a quick-return mirror, or a so-called mirrorless camera without a quick-return mirror.

[0091] As described above, by applying the optical system including the optical element 100 according to each embodiment to an imaging device such as a digital still camera or a smartphone camera, an imaging device with a compact lens can be obtained. In this embodiment, the imaging device is assumed to be a lens-integrated camera in which the camera body 4 and the optical system 3 including the optical element 100 of each embodiment are integrated, but it is not limited to this and may be an interchangeable-lens camera. For example, an optical device (lens device) in which a holding member for holding the optical system 3 is detachable from the camera body 4 as an imaging device may be employed. Furthermore, the optical system of each embodiment can be applied not only to the imaging device described above, but also to various optical instruments such as silver halide film cameras, digital video cameras, telescopes, binoculars, and projectors (projection devices).

[0092] While preferred embodiments of this specification have been described above, this specification is not limited to these embodiments, and various modifications and changes are possible within the scope of its gist.

[0093] This application claims priority based on Japanese Patent Application No. 2025-027811, filed on February 25, 2025, and all of its contents are incorporated herein by reference.

Claims

1. An optical element having a substrate and a plurality of structures formed on the substrate, wherein the optical element is divided by a plurality of periodically arranged sections, a first group of structures consisting of N structures (where N is an integer of 3 or more) is arranged in a first section of the plurality of sections, a second group of structures consisting of the same number of structures as the number of structures constituting the first group of structures is arranged in a second section of the plurality of sections, and when the optical element is viewed from a direction perpendicular to the substrate, the closed curve shape formed by sequentially connecting the centroids of the N structures constituting the first group of structures is C1, and the closed curve shape formed by sequentially connecting the centroids of the structures constituting the second group of structures is C2, and the distance between the total center of gravity of C1 and the centroid of the structure furthest from the centroid of C1 among the structures constituting C1 is R1, and the distance between the total center of gravity of C2 and the centroid of the structure furthest from the centroid of C1 among the structures constituting C2 is R2, the optical element satisfying the condition R1 > R2.

2. The optical element according to claim 1, wherein when either the first group of structures or the second group of structures is enlarged or reduced so that R1 and R2 are equal, the difference in area between C1 and C2 is 5% or less of the areas of C1 and C2.

3. The optical element according to claim 1 or 2, characterized in that the first section and the second section are equal in shape and area.

4. The optical element according to any one of claims 1 to 3, wherein when the optical element is viewed from a direction perpendicular to the substrate, C1 and C2 are similar to each other, and when the similarity ratio between C1 and C2 is S, the condition expression 0.05 < S < 1.00 is satisfied.

5. The optical element according to any one of claims 1 to 4, wherein the first group of structures and the second group of structures each consist of four to nine structures.

6. The optical element according to any one of claims 1 to 5, wherein when C1 and C2 are aligned in similar orientations, at least one of the width, height, and shape of structures located at corresponding vertices in C1 and C2 is the same.

7. The optical element according to any one of claims 1 to 6, characterized in that when the optical element is viewed from a direction perpendicular to the substrate, the overall center of gravity of C1 and the center of the first section are equal.

8. The optical element according to any one of claims 1 to 7, characterized in that when the optical element is viewed from a direction perpendicular to the substrate, the overall center of gravity of C2 and the center of the second section are equal.

9. The optical element according to any one of claims 1 to 8, characterized in that all structures forming the first group of structures are made of the same material.

10. The optical element according to any one of claims 1 to 9, characterized in that all structures forming the second group of structures are made of the same material.

11. The optical element according to any one of claims 1 to 10, characterized in that each of the structures constituting the first and second groups of structures has one of the shapes of a cylinder, a cone, a prism, a pyramidal shape, a trapezoid, a hollow cylinder, a hollow cone, a hollow prism, or a hollow pyramidal shape.

12. The optical element according to any one of claims 1 to 11, wherein the combination of shapes of the structures arranged in the first section is the same as the combination of shapes of the structures arranged in the second section.

13. The optical element according to any one of claims 1 to 12, characterized in that the structures arranged in the first and second compartments are not in contact with each other.

14. The optical element according to any one of claims 1 to 13, characterized in that the plurality of compartments, including the first compartment and the second compartment, are in contact with each other without gaps, and when the optical element is viewed from a direction perpendicular to the substrate, the boundary lines of the plurality of compartments and the structure do not overlap.

15. The optical element according to any one of claims 1 to 14, characterized in that each of the plurality of sections has a triangular, quadrilateral, or hexagonal shape and is identical to each other.

16. The optical element according to any one of claims 1 to 15, wherein it has a base layer formed on the substrate, and at least one of the structures constituting the first and second groups of structures is disposed on the base layer.

17. An optical element according to any one of claims 1 to 16, wherein the distance between the centroids of each of the structures is a, the width of each of the N structures is d, and the size of the first section and the second section is P, and the condition d / P < a / P < 1 is satisfied.

18. An optical system having a plurality of optical elements, including the optical element described in any one of claims 1 to 17.

19. An imaging device having an optical system according to claim 18 and an image sensor that receives an image formed by the optical system.

20. A method for manufacturing an optical element, comprising the steps of: providing a first material on the surface of a substrate; providing a second material on the first material; and forming an uneven structure made of the first material by pressing a mold onto the second material, wherein the uneven structure has a plurality of structures, the optical element is divided by a plurality of periodically arranged sections, a first group of structures consisting of N structures (where N is an integer of 3 or more) is arranged in a first section of the plurality of sections, a second group of structures consisting of the same number of structures as the number of structures constituting the first group of structures is arranged in a second section of the plurality of sections, and when the optical element is viewed from a direction perpendicular to the substrate, the closed curve shape formed by sequentially connecting the centroids of the N structures constituting the first group of structures is C1, and the closed curve shape formed by sequentially connecting the centroids of the structures constituting the second group of structures is C2. A method for manufacturing an optical element, wherein R1 is the distance between the total center of gravity of C1 and the center of gravity of the structure that constitutes C1 and is furthest from the center of gravity of C1, and R2 is the distance between the total center of gravity of C2 and the center of gravity of the structure that constitutes C2 and is furthest from the center of gravity of C1, and the condition R1 > R2 is satisfied.

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