Optical elements, optical systems, and imaging devices

Abstract

Provided is an optical element (metalenze) having excellent antireflection performance. 【Solution means】The optical element 101 includes a substrate, an uneven structure 41 formed on the substrate, and a first antireflection film 11 formed on the side opposite to the substrate in the uneven structure. The uneven structure has a plurality of uneven bands each including a plurality of structures 10. The refractive index of the first material constituting the plurality of structures at a wavelength of 550 nm is n p , the attenuation coefficient of the first material is κ p , and the refractive index of the second material forming any one of the one or more layers constituting the first antireflection film at a wavelength of 550 nm is n 1L . Let it be so. 1.4 ≤ n p ≤ 3.6, κ p ≤ 0.001 and 0.7 × √n p ≤ n 1L ≤ 1.2 × √n p satisfy the conditions.

Description

Technical Field

[0001] The disclosure of this specification relates to optical elements such as metalenses.

Background Art

[0002] As an optical element used in an optical system for imaging, a metalens is known that forms a fine concavo-convex structure on the surface of a substrate and has a focusing or diverging action on light by utilizing diffraction. However, when reflection occurs at the interface with air in a metalens formed with a fine concavo-convex structure, it causes ghosting and flare. Patent Document 1 discloses a metalens in which the reflection of an optical element is reduced by applying an antireflection film to the upper or lower part of the fine concavo-convex structure.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] There is a need for an optical element (metalens) having antireflection performance superior to the conventional one.

Means for Solving the Problems

[0005] An optical element as one aspect of the present invention includes a substrate, a concavo-convex structure formed on the substrate, and a first antireflection film formed on the side opposite to the substrate in the concavo-convex structure. The concavo-convex structure has a plurality of concavo-convex bands each including a plurality of structures. Let the refractive index of the first material constituting the plurality of structures at a wavelength of 550 nm be n p and the attenuation coefficient of the first material be κ p and the refractive index of the second material forming any one of the one or more layers constituting the first antireflection film at a wavelength of 550 nm be n 1L When 1.4 ≤ np ≤3.6 κ p ≤0.001 0.7×√n p ≤n 1L ≤1.2×√n p It is characterized by satisfying the following conditions. An optical system including the optical element and an imaging device having the optical system also constitute another aspect of the present invention.

Advantages of the Invention

[0006] According to the present invention, an optical element having excellent antireflection performance can be provided.

Brief Description of the Drawings

[0007] [Figure 1] Schematic diagram showing the optical element of the example. [Figure 2] Diagram showing the optical element of the comparative example. [Figure 3] Diagram showing the manufacturing method of the optical element of the example. [Figure 4] Diagram showing the relationship between the shape and the phase modulation amount of the optical element of Example 1. [Figure 5] Diagram showing the reflectance characteristics of the optical element of Example 1. [Figure 6] Diagram showing the reflectance characteristics of the optical element of Example 2. [Figure 7] Diagram showing the reflectance characteristics of the optical element of Example 3. [Figure 8] Diagram showing the reflectance characteristics of the optical elements of Examples 4, 5, 6 and Comparative Example 2. [Figure 9] Diagram showing the reflectance characteristics of the optical element of Example 7. [Figure 10] Diagram showing the reflectance characteristics of the optical element of Example 8. [Figure 11] Diagram showing the reflectance characteristics of the optical element of Example 9. [Figure 12] Diagram showing the reflectance characteristics of the optical elements of Example 10 and Comparative Example 4. [Figure 13] Schematic diagram showing the optical elements of other examples and comparative examples. [Figure 14]A figure showing the reflectivity characteristics of the optical element of Example 11. [Figure 15] A figure showing the reflectivity characteristics of the optical element of Example 12. [Figure 16] A figure showing the reflectivity characteristics of the optical element of Example 13. [Figure 17] A schematic diagram showing optical elements of another embodiment and comparative example. [Figure 18] Figure 17 shows a diagram illustrating the manufacturing method of the optical element. [Figure 19] A figure showing the reflectivity characteristics of the optical element of Example 14. [Figure 20] A figure showing the reflectivity characteristics of the optical element of Example 15. [Figure 21] A figure showing the reflectivity characteristics of the optical element of Example 16. [Figure 22] A figure showing the reflectance characteristics of the optical elements of Examples 17 and 18 and Comparative Example 7. [Figure 23] A diagram showing the optical system using the optical elements of Examples 1 to 18. [Figure 24] A diagram showing an imaging device using the optical system described above. [Figure 25] A figure showing the reflectivity characteristics of the optical element of Comparative Example 1. [Figure 26] A diagram showing the reflectivity characteristics of the optical element in Comparative Example 3. [Figure 27] A diagram showing the reflectivity characteristics of the optical element in Comparative Example 5. [Figure 28] A diagram showing the reflectivity characteristics of the optical element of Comparative Example 6. [Modes for carrying out the invention]

[0008] Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[0009] Figures 1(a) to 1(d) show optical elements of a typical embodiment of the present invention. Figures 1(a), (b), and (c) show cross-sections along the radial direction of optical elements 101, 102, and 103, respectively, and Figure 1(d) shows optical element 101 as viewed from above. Optical elements 102 and 103 as viewed from above are the same as optical element 101 as viewed from above.

[0010] Each optical element 101, 102, and 103 has a substrate 50 and a ridged structure 41, 42, and 43 formed on the substrate 50 (on the first surface, which is the surface of the substrate 50). Each ridged structure has multiple rings i, i+1, ... as periodically arranged ridged bands, each containing multiple structures, in the direction along the first surface (the radial direction of the substrate 50 in Figures 1(a) to (d)). Multiple convex elements (protrusions) 10 as multiple structures within each ring are arranged at a predetermined pitch in the radial direction of the substrate 50, i.e., periodically. Multiple concave elements (recesses) are formed between the multiple convex elements 10. The widths of the multiple convex elements 10 and the multiple concave elements in the radial direction of the substrate 50 differ from each other (gradually decreasing or increasing) within each ring. In this way, by periodically forming multiple annular bands i, i+1, ... which are phase difference imparting structures in the radial direction of the substrate 50, the optical elements 101 to 103 function as metalens that have a focusing or diverging effect on incident light.

[0011] A first anti-reflective film 11 is applied to the area opposite to the substrate 50 in the uneven structure 41-43, specifically within the width along the first surface of the convex element 10 on the upper part of the convex element 10 (between the convex element 10 and the air).

[0012] The uneven structure 42 of the optical element 102 has a first anti-reflective film 11, as well as a second anti-reflective film 12 applied to cover the substrate 50 (first surface). The uneven structure 43 of the optical element 103 has the first anti-reflective film 11 and the second anti-reflective film 12, as well as a third anti-reflective film 13 applied between the second anti-reflective film 12 and each convex element 10, and only on the lower part of each convex element 10 (i.e., within the width of each convex element 10 in the direction along the first surface). The first to third anti-reflective films 11 to 13 are each single-layer or multi-layer films having one or more layers (low refractive index layer or high refractive index layer). In the following description, the first to third anti-reflective films 11 to 13 will simply be referred to as anti-reflective films 11 to 13.

[0013] In optical elements 101 to 103, the substrate 50 is a translucent flat plate. However, the substrate 50 may be a flat mirror that reflects incident light, or a curved plate. The material of the substrate 50 can be synthetic quartz, inorganic glass, organic materials such as plastics, ceramics, metals, etc.

[0014] The uneven structures 41-43 provide focusing or divergence effects by introducing a phase difference to the light passing through each uneven structure. Specifically, multiple annular bands i, i+1, ... each containing multiple structures (convex and concave elements) of different widths give the light of the design wavelength a phase distribution of 2mπ (diffraction order m=1, 2, ...), thereby providing a focusing effect equivalent to that of a diffractive optical element.

[0015] The convex elements 10 of the concave-concave structures 41-43 have a cylindrical shape. However, the shape of the convex elements 10 is not limited to a cylindrical shape; it may also be a polygonal prism shape.

[0016] The convex element 10 is positioned at the center of unit sections (segments) 60, which are divided into square sections in the radial and circumferential directions of the substrate 50. The width (pitch) P of the segment 60, that is, the pitch of the convex element 10, is smaller than the wavelength of the incident light. As a result, the incident light undergoes phase modulation according to the effective refractive index determined from the element packing ratio of the convex element 10 in the segment 60, regardless of the shape of the convex element 10. For example, when the incident light is in the visible region (400-680 nm), the pitch P is preferably 400 nm or less, and it is even more preferable to make the pitch P even smaller because it can suppress unwanted diffracted light. Specifically, 150nm ≤ P ≤ 400nm (a) It is preferable that the following conditions be satisfied.

[0017] Within each annulus, multiple convex elements 10 are formed with concave elements in between. Within each annulus, a phase distribution of 2mπ is formed by changing the width of the convex elements 10 in the radial direction of the substrate 50.

[0018] In optical elements 101 to 103, the convex element 10 has a constant height H0 [nm] in all regions. In optical element 101, the uneven structure 41 including the anti-reflective film 11 has a constant height H1 [nm] in all regions. In optical element 102, the uneven structure 42 including the anti-reflective films 11 and 12 has a constant height H2 [nm] in all regions. In optical element 103, the uneven structure 43 including the anti-reflective films 11 to 13 has a constant height H3 [nm] in all regions.

[0019] In optical elements 101 to 103, where the height of each uneven structure is constant throughout the entire region, the width (diameter of the cylinder) W [nm] of the convex element 10, which is a component of each uneven structure, is changed in order to form a phase distribution of 2 mπ within each annulus. This changes the element packing ratio of the convex element 10 (and anti-reflective films 11 to 13) for each segment 60. That is, the smaller the width of the convex element 10, the lower the element packing ratio in segment 60, thereby forming the desired phase distribution. In segments 60 where the minimum width of the convex element 10 is small, the aspect ratio (ratio of height to width of convex element 10) becomes larger. Convex elements 10 with a large aspect ratio and relatively elongated shape are susceptible to deformation, tilting, or peeling due to loads applied by contact or vibration, or changes in external factors such as temperature and pressure. For this reason, the minimum value of the width W [nm] of the convex element 10 is preferably 25 nm or more.

[0020] Figure 1(d) shows segments 60 arranged one-dimensionally in the radial direction of the substrate 50. However, in reality, the segments 60 are arranged two-dimensionally in the radial and circumferential directions of the substrate 50, and have a focusing or diverging effect on incident light in the two-dimensional direction.

[0021] Next, with reference to FIGS. 2(a) and 2(b), the reflection of incident light in the optical element 100 as a comparative example will be described. FIG. 2(a) shows a cross-section along the radial direction of the optical element 100. The antireflection films 11 to 13 are not provided on the optical element 100. That is, the optical element 100 has a substrate 50 and an uneven structure 40, and the uneven structure 40 is formed only of the convex elements 10 having a height H0 [nm]. Even in the optical element 100, in order to form a phase distribution of 2mπ within each annular zone, the element filling factor of the convex elements 10 within the segment 60 changes. When the width (pitch) P of the segment 60 is made smaller than the wavelength of the incident light, the light recognizes the convex elements 10 as film elements 14 as shown in FIG. 2(b) having an effective refractive index obtained from the element filling factor for each segment 60 regardless of their shape. That is, the uneven structure 40 in which the width (diameter) of the convex elements 10 shown in FIG. 2(a) changes from larger to smaller is equivalent to a film 48 composed of a plurality of film elements 14 in which the refractive index changes from larger to smaller (the gray shade in the figure decreases) as shown in FIG. 2(b).

[0022] When light is incident on the film 48, reflection occurs at the interface 70 between the air and the film 48 and the interface 80 between the substrate 50 and the film 48. At this time, since the refractive index of the film 48 changes in the radial direction of the substrate 50, the reflectance characteristics also change according to the in-plane position. That is, in order to reduce the reflection that occurs at these interfaces 70 and 80 and the reflectance changes for each segment 60, it is necessary to form an antireflection film. In this embodiment, by providing one or more antireflection films on the optical elements 101 to 103, the reflection occurring at each of the above interfaces is reduced.

[0023] In FIG. 2(a), in order to reduce the reflection at the interface 70 between the convex element 10 and the air, as shown in FIG. 1(a), the antireflection film 11 is formed on the upper part of the convex element 10. The refractive index of the first material for forming the convex element 10 as a structure at a wavelength of 550 nm is n p , and the attenuation coefficient of the first material is κ pFurthermore, the refractive index at a wavelength of 550 nm of the second material forming one of the one or more layers constituting the anti-reflective film 11, for example, the layer with the lowest refractive index or the layer furthest from the substrate 50 (closest to the air), is n 1L Let's assume that at this time, 1.4≦n p ≤3.6 (1) κ p ≤0.001 (2) 0.7 × √n p ≤n 1L ≤ 1.2 × √n p (3) It is preferable to satisfy the following conditions. By forming the anti-reflective film 11, the reflection occurring at the interface 70 between the convex element 10 and the air shown in Figure 2(a) can be reduced. At this time, n p and n 1L If the conditions in equations (1) and (3) are not met, it becomes difficult to obtain sufficient anti-reflective performance. Also, κ p If the value is greater than 0.001, light absorption increases, making it difficult to use optical elements across a wide wavelength range from the visible region to the near-infrared region.

[0024] The lower limit of equation (1) may be set to 1.5 or 2.0, and the upper limit of equation (1) may be set to 3.5.

[0025] Also, the lower limit of equation (3) is 0.8 × √n p Or 0.9 × √n p It is also acceptable to set the upper limit of equation (3) to 1.1 × √n p That is also acceptable.

[0026] In the optical element 101 shown in Figure 1(a), reflection also occurs at the interface 80 between the convex element 10 and the substrate 50. To reduce this reflection, as shown in Figure 1(b), an anti-reflective film 12 is formed on the interface 80 between the convex element 10 and the substrate 50 so as to cover the substrate 50. The refractive index of the third material forming one or more layers of the anti-reflective film 12, for example, the layer closest to the convex element (structure side), at a wavelength of 550 nm is n 2L In that case, 1.3 ≤ n 2L ≤1.7 (4) It is preferable that the following conditions be satisfied.

[0027] The lower limit of equation (4) may be set to 1.4, and the upper limit of equation (4) may be set to 1.6.

[0028] The reflection occurring at the interface 80 is caused by the difference in refractive index between the film element 14 and the substrate 50, as described above. When the convex element 10 is surrounded by air, the refractive index of the film element 14 becomes the effective refractive index determined from the filling density between the convex element 10 and the air. In particular, when the width W of the convex element 10 is small, it becomes closer to the refractive index of air. At this time, the thickness (physical film thickness) of the third material layer is d 2L In that case, 80nm≦d 2L ≤200nm (5) It is preferable that the following conditions are satisfied. When the anti-reflective film 12 is constructed by repeatedly laminating a third material and a fourth material, the refractive index of the fourth material at a wavelength of 550 nm is n 2H In that case, n p ≤n 2H ≤3.0 (6) It is preferable that the following conditions are satisfied. The upper limit of equation (6) may be set to 2.8 or 2.6.

[0029] By providing the anti-reflective coatings 11 and 12 shown in Figure 1(b), reflections at the interface 70 between the convex element 10 and the air, and at the interface 80 between the convex element 10 and the substrate 50 can be reduced. To further reduce reflections, it is preferable to form an anti-reflective coating 13 at the interface between the convex element 10 and the anti-reflective coating 12, as shown in Figure 1(c).

[0030] The anti-reflective coating 13 is formed only on the portion where the convex element 10 is formed, with a width equal to the width of the convex element 10. The refractive index at a wavelength of 550 nm of the fifth material forming one or more layers of the anti-reflective coating 13, for example, the layer closest to the convex element, is n 3L In that case, 1.3 ≤ n 3L ≤1.7 (7) It is preferable that the following conditions are satisfied. The lower limit of equation (7) may be set to 1.4, and the upper limit of equation (7) may be set to 1.6. Furthermore, when the anti-reflective film 13 is constructed by repeatedly laminating a fifth material and a sixth material, the refractive index of the sixth material at a wavelength of 550 nm is n 3H In that case, n p ≤n 3H ≤3.0 (8) It is more preferable to satisfy the following conditions. The upper limit of equation (8) may also be set to 2.8 or 2.6.

[0031] Furthermore, the refractive index of the material forming the substrate 50 at a wavelength of 550 nm is n s In that case, 1.4≦n s ≤2.5 (9) It is preferable that the following conditions are satisfied. The upper limit of equation (9) may be set to 2.3 or 2.1.

[0032] The first material forming the convex element 10 is preferably a dielectric material containing silicon nitride (Si3N4), titanium oxide (TiO2), gallium nitride (GaN), gallium arsenide (GaAs), silicon carbide (SiC), aluminum oxide (Al2O3), or silicon oxide (SiO2).

[0033] The second material, which is one of the materials for forming the anti-reflective film 11, is preferably an organic resin made of silicon oxide, magnesium fluoride (MgF2), aluminum oxide, or fluorine (F) or silicon (Si).

[0034] The third material, which is one of the materials that form the anti-reflective film 12, is silicon oxide, magnesium fluoride, and magnesium oxide (MgO It is preferable that the material is one of the following. Furthermore, the fourth material, which is another material that forms the anti-reflective film 12, is preferably silicon nitride, titanium oxide, gallium nitride, gallium arsenide, or silicon carbide, and is more preferably the same as the first material of the convex element 10.

[0035] The fifth material, which is one of the materials that form the anti-reflective film 13, is preferably silicon oxide, magnesium fluoride, or magnesium oxide. The sixth material, which is another material that forms the anti-reflective film 13, is preferably silicon nitride, titanium oxide, gallium nitride, gallium arsenide, or silicon carbide, and is more preferably the same as the first material of the convex element 10. Furthermore, it is preferable that the second material, the third material, and the fifth material are the same material as each other.

[0036] Optical elements 101 to 103 can be manufactured using lithography technology. As an example, Figures 3(a) to 3(c) show the process for manufacturing optical element 103 using nanoimprint lithography.

[0037] Figure 3(a) shows a mold 91 formed by an electron beam or laser, which has a shape that is an inversion of the uneven shape of the uneven structure 43. As shown in Figure 3(b), a resist material 92 is applied to the film 93 deposited on the substrate 50, and the mold 91 is pressed onto the resist material 92 and irradiated with ultraviolet light or the like to form a shape on the resist material 92 that is an inversion of the uneven shape of the mold 91.

[0038] Next, the uneven structure 43 of the optical element 103 is formed by etching using the resist material 92 as a mask. The etching is carried out up to the anti-reflective film 11, the convex element 10, and the anti-reflective film 13, and ends when it reaches the anti-reflective film 12. For this reason, anisotropic etching is suitable for fabricating the uneven structure 42.

[0039] After etching is complete, the resist material 92 is removed to form the uneven structure 43 of the optical element 103, as shown in Figure 3(c).

[0040] Furthermore, the manufacturing method for the uneven structure 43 is not limited to the nanoimprint lithography described above, but may also be other methods such as directly forming the uneven structure using an electron beam or laser.

[0041] Specific examples 1 to 20 are shown below. However, the configurations shown in these examples are merely examples, and other configurations may be adopted.

[0042] [Examples 1-3] The optical element of Example 1 has an anti-reflective coating 11, as shown in Figure 1(a) for optical element 101. The optical element of Example 2 has anti-reflective coatings 11 and 12, as shown in Figure 1(b) for optical element 102. The optical element of Example 3 has anti-reflective coatings 11, 12, and 13, as shown in Figure 1(c) for optical element 103. The optical elements of Examples 1 to 3 are diffractive optical elements used in the visible region (wavelength 420 to 680 nm).

[0043] In Examples 1 to 3, the substrate 50 is formed of quartz with a refractive index of 1.46 (wavelength 550 nm), and the convex elements 10 are formed in a cylindrical shape from silicon nitride with a refractive index of 2.09 (wavelength 550 nm). The convex elements 10 are arranged in a square shape, with a segment pitch P of 240 nm and a height H0 of 700 nm. Each convex structure has an effective diameter of φ4.0 mm and is composed of 105 annular bands that give a phase difference of 2π (diffraction order = 1) at a wavelength of 500 nm, arranged in a periodic repeating manner. The focal length of each convex structure is 40.0 mm.

[0044] Table 1 shows the materials and refractive indices of the anti-reflective coatings 11-13, convex element 10, and substrate 50 in the optical elements of Examples 1-3, as well as the film thickness (height) of the anti-reflective coatings 11-13 and convex element 10. The refractive index of the materials is the value at a wavelength of 550 nm.

[0045] Figure 4 shows the normalized diameter on the horizontal axis, which is the diameter W of the convex element 10 in the optical element of Example 1, normalized by the segment pitch P, and the normalized phase on the vertical axis, which is the amount of phase modulation with respect to incident light normalized by 2π (diffraction order m=1). In the optical element of Example 1, the amount of phase modulation also includes the amount of modulation by the anti-reflective film 11 formed on the convex element 10. In Figure 4, the normalized diameter is varied from 0.13 to 0.87 in order to change the normalized phase difference from 0 to 1.

[0046] Figure 5 shows the reflectivity characteristics of the optical element in Example 1 when the normalized diameter of the convex element 10 is 0.13, 0.30, 0.40, 0.50, 0.60, 0.70, and 0.87. The reflectivity characteristics in the visible region are all 3.5% or less. Figures 6 and 7 show the reflectivity characteristics of the optical elements in Example 2 and Example 3 when the normalized diameter is similarly varied from 0.13 to 0.87. The reflectivity characteristics in the visible region of these optical elements in Examples 2 and 3 are 3.0% or less. From these results, it can be seen that the optical elements in Examples 1 to 3 have good reflectivity characteristics (anti-reflective performance).

[0047] Furthermore, the anti-reflective performance improves in the order of Examples 1, 2, and 3. From this, it can be confirmed that the anti-reflective performance is improved by increasing the number of anti-reflective coatings in the order of anti-reflective coatings 11, 12, and 13.

[0048] [Table 1]

[0049] [Examples 4-6] The optical element of Example 4 has an anti-reflective coating 11, as in optical element 101. The optical element of Example 5 has anti-reflective coatings 11 and 12, as in optical element 102. The optical element of Example 6 has anti-reflective coatings 11, 12, and 13, as in optical element 103. The optical elements of Examples 4 to 6 are diffractive optical elements used in the infrared region (wavelength 800 nm).

[0050] In Examples 4-6, the substrate 50 is formed of quartz with a refractive index of 1.46 (wavelength 550 nm), and the convex elements 10 are formed in a cylindrical shape from silicon nitride with a refractive index of 2.09 (wavelength 550 nm). The convex elements 10 are arranged every 60 square segments, with a segment pitch P of 360 nm and a height H0 of 1200 nm. Each convex-convex structure has an effective diameter of φ4.0 mm and is composed of 105 annular bands that give a phase difference of 2π (diffraction order = 1) at a wavelength of 800 nm, arranged in a periodic repeating manner. The focal length of each convex-convex structure is 40.0 mm. In Examples 4-6, the normalized diameter of the convex elements 10 is varied from 0.20 to 0.80 in order to change the normalized phase difference from 0 to 1.

[0051] Table 2 shows the materials and refractive indices of the anti-reflective coatings 11-13, convex elements 10, and substrates 50 in the optical elements of Examples 4-6, as well as the film thickness (height) of the anti-reflective coatings 11-13 and convex elements 10. The refractive index of the materials is the value at a wavelength of 550 nm.

[0052] Figure 8 shows the reflectance characteristics at a wavelength of 800 nm when the normalized diameter of the convex element 10 in the optical elements of Examples 4 to 6 is varied from 0.20 to 0.80. For normalized diameters of 0.20 to 0.80, the reflectance characteristics of the optical element of Example 4 are 3.0% or less, and the reflectance characteristics of the optical elements of Examples 5 and 6 are 1.0% or less. From these results, it can be seen that the optical elements of Examples 4 to 6 have good reflectance characteristics (anti-reflective performance).

[0053] [Table 2]

[0054] [Examples 7-9] The optical element of Example 7 has an anti-reflective coating 11, as in optical element 101. The optical element of Example 8 has anti-reflective coatings 11 and 12, as in optical element 102. The optical element of Example 9 has anti-reflective coatings 11, 12, and 13, as in optical element 103. The optical elements of Examples 7 to 9 are diffractive optical elements used in the visible region (wavelength 420 to 680 nm).

[0055] In Examples 7-9, the substrate 50 is formed from S-LAH79 (manufactured by OHARA) with a refractive index of 2.00 (wavelength 550 nm), and the convex elements 10 are formed in a cylindrical shape from titanium oxide with a refractive index of 2.47 (wavelength 550 nm). The convex elements 10 are arranged every 60 square segments, with a segment pitch P of 240 nm and a height H0 of 550 nm. Each convex-convex structure has an effective diameter of φ4.0 mm and is composed of 105 annular bands that give a phase difference of 2π (diffraction order = 1) at a wavelength of 500 nm, arranged in a periodic repeating manner. The focal length of each convex-convex structure is 40.0 mm. In Examples 7-9, the normalized diameter of the convex elements 10 is varied from 0.20 to 0.80 in order to change the normalized phase difference from 0 to 1.

[0056] Table 3 shows the materials and refractive indices of the anti-reflective coatings 11-13, convex elements 10, and substrates 50 in the optical elements of Examples 7-9, as well as the film thickness (height) of the anti-reflective coatings 11-13 and convex elements 10. The refractive index of the materials is the value at a wavelength of 550 nm.

[0057] Figures 9, 10, and 11 show the reflectance characteristics in the visible region when the normalized diameter of the convex element 10 in Examples 7, 8, and 9 is changed to 0.20, 0.30, 0.40, 0.50, 0.60, 0.70, and 0.80, respectively. For normalized diameters from 0.20 to 0.80, the reflectance characteristics of the optical element in Example 7 are 11.0% or less, the reflectance characteristics of the optical element in Example 8 are 6.0% or less, and the reflectance characteristics of the optical element in Example 9 are 2.0% or less. From this, it can be seen that the reflectance characteristics (anti-reflective performance) of the optical elements in Examples 4 to 6 are good.

[0058] [Table 3]

[0059] [Example 10] The optical element of Example 10 has an anti-reflective coating 11, similar to optical element 101. The optical element of Example 10 is a diffractive optical element used in the infrared region (wavelength 800 nm).

[0060] In Example 10, the substrate 50 is formed of quartz with a refractive index of 1.46 (wavelength 550 nm), and the convex elements 10 are formed in a cylindrical shape of gallium arsenide (GaP) with a refractive index of 3.45 (wavelength 550 nm). The convex elements 10 are arranged every 60 square segments, with a segment pitch P of 360 nm and a convex element height H0 of 600 nm. The uneven structure has an effective diameter of φ4.0 mm and is composed of 105 annular bands that give a phase difference of 2π (diffraction order = 1) at a wavelength of 800 nm, arranged in a periodic repeating manner. The focal length due to the uneven structure is 40.0 mm. In Example 10, the normalized diameter of the convex elements 10 is changed from 0.20 to 0.80 in order to change the normalized phase difference from 0 to 1.

[0061] Table 4 shows the materials and refractive indices of the anti-reflective coating 11, convex element 10, and substrate 50 in the optical element of Example 10, as well as the film thickness (height) of the anti-reflective coating 11 and convex element 10. The refractive index of the materials is the value at a wavelength of 550 nm.

[0062] Figure 12 shows the reflectance characteristics at a wavelength of 800 nm when the diameter of the convex element of the optical element of Example 10 is varied from 0.20 to 0.80. For normalized diameters of 0.2 to 0.8, the reflectance characteristics of the optical element of Example 10 are 5.0% or less. This indicates that the optical element of Example 10 has good reflectance characteristics (anti-reflective performance).

[0063] [Table 4]

[0064] [Examples 11-13] Figures 13(a) to (c) show cross-sections of the i-th annular band of optical elements 104, 105, and 106, respectively. Figure 13(d) shows optical element 104 as viewed from above. Optical elements 105 and 106 as viewed from above are similar to optical element 104.

[0065] Optical elements 104, 105, and 106 each have a substrate 50 and a surface uneven structure 44, 45, and 46 formed on the substrate 50. The surface uneven structure 44 to 46 has a convex element 15 as a structural element, a concave element 16, and an anti-reflective film 11 applied to the upper part of the convex element 15. As shown in Figure 13(d), the surface uneven structure 44 is constructed by arranging a plurality of rectangular cylindrical concave elements 16 so as to form a convex element 15 between them. The same applies to optical elements 105 and 106.

[0066] In addition to the anti-reflective coating 11, the optical element 105 has an anti-reflective coating 12 applied between the convex element 15 and the substrate 50 so as to cover the substrate 50.

[0067] The optical element 106 has an anti-reflective coating 13 applied between the convex element 15 and the anti-reflective coating 12 (below the convex element 15), in addition to the anti-reflective coatings 11 and 12.

[0068] The heights of the uneven structures 44, 45, and 46 are constant in all regions. To form a phase distribution of 2 mπ within the ring, the width W of the concave elements 16 of each uneven structure is changed, thereby altering the element filling ratio of the convex elements 15 (and anti-reflective coatings 11-13) within the segment 60.

[0069] Optical elements 104 to 106 can all be manufactured using the same manufacturing method as optical elements 101 to 103.

[0070] The optical element of Example 11 has an anti-reflective coating 11, as in optical element 104. The optical element of Example 12 has anti-reflective coatings 11 and 12, as in optical element 105. The optical element of Example 13 has anti-reflective coatings 11, 12, and 13, as in optical element 106. The optical elements of Examples 11 to 13 are diffractive optical elements used in the visible region (wavelength 420 to 680 nm).

[0071] In Examples 11-13, the substrate 50 is formed from S-BAH28 (manufactured by OHARA) with a refractive index of 1.72 (wavelength 550 nm), and the convex elements 15 are formed in a cylindrical shape from silicon nitride with a refractive index of 2.09 (wavelength 550 nm). The convex elements 15 are arranged in a square shape for every 60 segments, with a pitch P of 240 nm for the segments 60 and a height H0 of 700 nm for the convex elements 15. The effective diameter of each convex structure is φ4.0 mm, and each is composed of 105 annular bands that give a phase difference of 2π (diffraction order = 1) at a wavelength of 500 nm, arranged in a periodic repeating manner. The focal length of each convex structure is 40.0 mm. In Examples 11-13, the normalized diameter of the convex elements 15 is varied from 0.20 to 0.80 in order to change the normalized phase difference from 0 to 1.

[0072] Table 5 shows the materials and refractive indices of the anti-reflective coatings 11-13, convex element 15, and substrate 50 in the optical elements of Examples 11-13, as well as the film thickness (height) of the anti-reflective coatings 11-13 and convex element 15. The refractive index of the materials is the value at a wavelength of 550 nm.

[0073] Figures 14, 15, and 16 show the reflectance characteristics in the visible region when the normalized diameter of the convex element 15 of the optical elements of Examples 11, 12, and 13 is changed to 0.20, 0.30, 0.40, 0.50, 0.60, 0.70, and 0.80, respectively. For normalized diameters of 0.2 to 0.8, the reflectance characteristics of the optical element of Example 11 are 7.0% or less, the reflectance characteristics of the optical element of Example 12 are 3.0% or less, and the reflectance characteristics of the optical element of Example 13 are 2.0% or less. From this, it can be seen that the reflectance characteristics (anti-reflective performance) of the optical elements of Examples 11 to 13 are good.

[0074] [Table 5]

[0075] [Examples 14-16] Figures 17(a) to (c) show cross-sections of the i-th annular band of optical elements 201, 202, and 203, respectively.

[0076] In the optical elements 101 to 103 shown in Figures 1(a) to 1(c), the area around (above and between) the multiple convex elements 10 is filled with air. On the other hand, in optical elements 201 to 203, the space between the multiple convex elements 10 is filled with a material 90 that acts as a medium other than air. Therefore, in optical elements 201 to 203, the anti-reflective coating 11 is applied with a uniform thickness not only on the convex elements 10 but also on the material 90. The anti-reflective coatings 12 and 13 are the same as those in optical elements 102 and 103.

[0077] Optical elements 201-203 can also be manufactured using lithography technology, similar to optical elements 101-103. As an example, Figures 18(a)-(f) show the manufacturing method for optical element 203.

[0078] Figure 18(a) shows a mold 91 formed by an electron beam or laser, which has a shape that is an inversion of the uneven shape of the uneven structure 43. As shown in Figure 18(b), a resist material 92 is applied to the film 93 deposited on the substrate 50, and the mold 91 is pressed onto the resist material 92 and irradiated with ultraviolet light or the like to form a shape on the resist material 92 that is an inversion of the uneven shape of the mold 91.

[0079] Subsequently, as shown in Figure 18(d), material 90 is formed around the convex element 10 by ALD (Atomic Layer Deposition). Then, as shown in Figure 18(e), material 90 on the convex element 10 is removed by etching. Furthermore, as shown in Figure 18(f), an anti-reflective film 11 is deposited on the upper part of the convex element 10 and the upper part of the material 90 by vapor deposition.

[0080] Furthermore, the method for forming the anti-reflective coating 11 is not limited to vapor deposition; dry deposition methods such as sputtering or wet deposition methods such as sol-gel deposition may also be used.

[0081] The optical element of Example 14 has an anti-reflective coating 11, as in optical element 201. The optical element of Example 15 has anti-reflective coatings 11 and 12, as in optical element 202. The optical element of Example 16 has anti-reflective coatings 11, 12, and 13, as in optical element 203. The optical elements of Examples 14 to 16 are diffractive optical elements used in the visible region (wavelength 420 to 680 nm).

[0082] In Examples 14-16, the substrate 50 is formed of quartz with a refractive index of 1.46 (wavelength 550 nm), and the convex elements 10 are formed in a cylindrical shape from silicon nitride with a refractive index of 2.09 (wavelength 550 nm). Material 90 is silicon dioxide (SiO2) with a refractive index of 1.46 (wavelength 550 nm). The convex elements 10 are arranged in square segments 60, with a pitch P of 240 nm for the segments 60 and a height H0 of 1250 nm for the convex elements. The effective diameter of each convex structure is φ4.0 mm, and each is composed of 105 annular bands that give a phase difference of 2π (diffraction order = 1) at a wavelength of 500 nm, arranged in a periodic repeating manner. The focal length of each convex structure is 40.0 mm. In Examples 14-16, the normalized diameter of the convex elements 10 is varied from 0.20 to 0.80 in order to change the normalized phase difference from 0 to 1.

[0083] Table 6 shows the materials and refractive indices of the material 90, anti-reflective coatings 11-13, convex element 10, and substrate 50 in the optical elements of Examples 14-16, as well as the film thickness (height) of the anti-reflective coatings 11-13 and convex element 10. The refractive index of the materials is the value at a wavelength of 550 nm.

[0084] Figures 19, 20, and 21 show the reflectance characteristics in the visible region when the normalized diameter of the convex element 10 of the optical elements of Examples 14, 15, and 16 is changed to 0.20, 0.30, 0.40, 0.50, 0.60, 0.70, and 0.80, respectively. For normalized diameters from 0.20 to 0.80, the reflectance characteristics of the optical element of Example 14 are 4% or less, and the reflectance characteristics of the optical elements of Examples 15 and 16 are 2.0% or less. From this, it can be seen that the reflectance characteristics (anti-reflective performance) of the optical elements of Examples 14 to 16 are good.

[0085] [Table 6]

[0086] [Examples 17, 18] The optical element of Example 17 has an anti-reflective coating 11, as in optical element 201. The optical element of Example 18 has anti-reflective coatings 11 and 12, as in optical element 202. The optical elements of Examples 17 and 18 are diffractive optical elements used in the infrared region (wavelength 800 nm).

[0087] In Examples 17 and 18, the substrate 50 is formed of quartz with a refractive index of 1.46 (wavelength 550 nm), and the convex elements 10 are formed in a cylindrical shape of gallium arsenide with a refractive index of 3.45 (wavelength 550 nm). The convex elements 10 are arranged in a square-shaped segment 60, with a segment pitch P of 360 nm and a height H0 of 1070 nm. The effective diameter of each convex structure is φ4.0 mm, and each is composed of 105 annular bands that give a phase difference of 2π (diffraction order = 1) at a wavelength of 800 nm, arranged in a periodic repeating manner. The focal length of each convex structure is 40.0 mm. In Examples 17 and 18, the normalized diameter of the convex element 10 is varied from 0.20 to 0.80 in order to change the normalized phase difference from 0 to 1.

[0088] Table 7 shows the materials and refractive indices of the material 90, anti-reflective coatings 11-13, convex element 10, and substrate 50 in the optical elements of Examples 17 and 18, as well as the film thickness (height) of the anti-reflective coatings 11-13 and convex element 10. The refractive index of the materials is the value at a wavelength of 550 nm.

[0089] Figure 22 shows the reflectance characteristics at a wavelength of 800 nm when the diameter of the convex element 10 of the optical elements in Examples 17 and 18 is varied from 0.20 to 0.80. For a normalized diameter of 0.20 to 0.80, the reflectance characteristics of the optical element in Example 17 are 6.0% or less, and the reflectance characteristics of the optical element in Example 18 are 2.0% or less. This indicates that the optical elements in Examples 17 and 18 have good reflectance characteristics (anti-reflective performance).

[0090] [Table 7]

[0091] [Optical system] Figure 23 shows an optical system using one of the optical elements from Examples 1 to 18. In Figure 23, 301 represents the optical element of each example, 302 represents the lens element, and OA represents the optical axis of the optical system. IP represents the image plane.

[0092] The lens element 302 consists of a refractive lens, a diffractive optical element, a mirror, etc., and is arranged in one or more configurations. The optical element 301 and the lens element 302 are arranged along the optical axis OA, and incident light is imaged on the image plane IP. In an imaging device, the image plane IP is where the imaging surface of an image sensor such as a CCD sensor or CMOS sensor or the film surface of a silver halide film is located.

[0093] Furthermore, the optical system 400 can be used not only in imaging devices but also in various optical instruments such as binoculars, projectors, and telescopes.

[0094] [Imaging device] Figure 24 shows an imaging device (digital camera) 501 equipped with the optical system 401 of Figure 23. In Figure 24, 4 is the camera body, and 3 is the imaging optical system composed of the optical system 401. 5 is an image sensor built into the camera body 4 that receives the optical image formed by the imaging optical system 3 and converts it into photoelectric light (i.e., images the subject through the optical system). The camera body 4 may be a single-lens reflex camera with a quick-return mirror, or a mirrorless camera without a quick-return mirror.

[0095] By applying the optical system including the optical elements of each embodiment to an imaging device such as a digital still camera, an imaging device capable of taking good images can be obtained.

[0096] [Comparative Examples 1-7] The optical element of Comparative Example 1 is a comparative example to the optical elements of Examples 1 to 3, and, like the optical element 100 shown in Figure 2(a), it does not have an anti-reflective coating.

[0097] The configuration of the optical element in Comparative Example 1 is the same as that of the optical elements in Examples 1 to 3, except that the anti-reflective coating 11 is not applied. The substrate 50 is formed of quartz with a refractive index of 1.46 (wavelength 550 nm), and the convex element 10 is formed in a cylindrical shape of silicon nitride with a refractive index of 2.09 (wavelength 550 nm). The pitch P of the segment 60 is 240 nm, and the height H0 of the convex element is 700 nm. The effective diameter of the uneven structure is φ4.0 mm, and it has 105 annular bands, similar to the optical elements in Examples 1 to 3. The normalized diameter of the convex element 10 is 0.13 to 0.87, similar to Examples 1 to 3. The optical elements in Examples 1 to 3 have a configuration in which the anti-reflective coatings 11 to 13 are applied to the optical element in Comparative Example 1.

[0098] The optical element in Comparative Example 2 is a comparative example to the optical elements in Examples 4 to 6, and the optical element in Comparative Example 3 is a comparative example to Examples 7 to 9. The optical element in Comparative Example 4 is a comparative example to the optical element in Example 10. Comparative Examples 2 to 4 do not have an anti-reflective coating, similar to the optical element 100 shown in Figure 2(a).

[0099] The optical element of Comparative Example 5 is a comparative example to the optical elements of Examples 11 to 13, and like the optical element 107 shown in Figure 13(e), it does not have an anti-reflective coating. The optical element of Comparative Example 6 is a comparative example to the optical elements of Examples 14 to 16, and the optical element of Comparative Example 7 is a comparative example to the optical elements of Examples 17 and 18. Comparative Examples 6 and 7, like the optical element 200 shown in Figure 17(d), do not have an anti-reflective coating on the uneven structure 40.

[0100] Table 8 shows the materials and refractive indices of the substrate 50 and convex element 10, the height of the convex element 10, and the material 90 and its refractive index in Comparative Examples 1 to 7.

[0101] Figure 25 shows the reflectivity characteristics of the optical element of Comparative Example 1, Figure 26 shows the reflectivity characteristics of the optical element of Comparative Example 3, Figure 27 shows the reflectivity characteristics of the optical element of Comparative Example 5, and Figure 28 shows the reflectivity characteristics of the optical element of Comparative Example 6. The reflectivity characteristics of the optical element of Comparative Example 2 are shown in Figure 8, the reflectivity characteristics of the optical element of Comparative Example 4 are shown in Figure 12, and the reflectivity characteristics of the optical element of Comparative Example 5 are shown in Figure 22.

[0102] From the reflectance characteristics of each example and each comparative example, it can be seen that the optical elements of Examples 1 to 18 have higher anti-reflective performance than the optical elements of Comparative Examples 1 to 7, which do not have an anti-reflective coating.

[0103] [Table 8]

[0104] The above embodiments include the following configuration.

[0105] (Composition 1) circuit board and The uneven structure formed on the substrate, The uneven structure has a first anti-reflective film formed on the side opposite to the substrate, The aforementioned uneven structure has multiple uneven bands, each containing multiple structural elements. The refractive index of the first material constituting the plurality of structures at a wavelength of 550 nm is n pThe extinction coefficient of the first material is κ p The refractive index at a wavelength of 550 nm of the second material forming any one of the one or more layers constituting the first anti-reflective film is n 1L In that case, 1.4≦n p ≤3.6 κ p ≤0.001 0.7 × √n p ≤n 1L ≤ 1.2 × √n p An optical element characterized by satisfying the following conditions. (Configuration 2) The aforementioned uneven structure is formed on the first surface of the substrate, The optical element according to configuration 1, characterized in that each of the plurality of uneven bands includes a plurality of structures having different widths in the direction along the first surface. (Composition 3) The optical element according to configuration 1 or 2, characterized in that the layer with the lowest refractive index or the layer furthest from the substrate among the one or more layers constituting the first anti-reflective film is formed of the second material. (Composition 4) The aforementioned uneven structure is formed on the first surface of the substrate, The area around the aforementioned multiple structures is filled with air. The optical element according to any one of configurations 1 to 3, characterized in that the first anti-reflective film is formed on the plurality of structures within a width in the direction along the first surface of each of the plurality of structures. (Composition 5) The spaces between the aforementioned multiple structures are filled with a medium other than air. The optical element according to any one of configurations 1 to 3, characterized in that the first anti-reflective film is formed on the plurality of structures and on the medium. (Composition 6) The substrate and the plurality of structures have a second anti-reflective film formed so as to cover the substrate, The refractive index at a wavelength of 550 nm of the third material forming any one of the one or more layers constituting the second anti-reflective film is n 2L The thickness of the third material layer is d 2L When (nm), 1.3 ≤ n 2L ≤1.7 80≦d 2L ≤200 An optical element according to any one of configurations 1 to 5, characterized by satisfying the following conditions. (Composition 7) The optical element according to configuration 6, characterized in that the layer closest to the structure among the one or more layers constituting the second anti-reflective film is formed of the third material. (Composition 8) The second anti-reflective film includes a layer formed of the third material and a layer formed of the fourth material, The refractive index of the fourth material at a wavelength of 550 nm is n 2H In that case, n p ≤n 2H ≤3.0 The optical element according to configuration 6 or 7, characterized by satisfying the following conditions. (Composition 9) The aforementioned uneven structure is formed on the first surface of the substrate, The present invention has a third anti-reflective film formed between the second anti-reflective film and the plurality of structures, within the width of each of the plurality of structures in the direction along the first surface, The refractive index at a wavelength of 550 nm of the fifth material forming any one of the one or more layers constituting the third anti-reflective film is n 3L In that case, 1.3 ≤ n 3L ≤1.7 An optical element according to any one of configurations 6 to 8, characterized by satisfying the following conditions. (Composition 10) The optical element according to configuration 9, characterized in that the layer closest to the structure among the one or more layers constituting the third anti-reflective film is formed of the fifth material. (Composition 11) The third anti-reflective film includes a layer formed of the fifth material and a layer formed of the sixth material, The refractive index of the sixth material at a wavelength of 550 nm is n 3H In that case, n p ≤n 3H ≤3.0 The optical element according to configuration 9 or 10, characterized by satisfying the following conditions. (Composition 12) The refractive index of the material forming the substrate at a wavelength of 550 nm is n s In that case, 1.4≦n s ≤2.5 An optical element according to any one of configurations 1 to 11, characterized by satisfying the following conditions. (Composition 13) The aforementioned uneven structure is formed on the first surface of the substrate, When the pitch of the plurality of structures in the direction along the first surface is P, 150nm ≤ P ≤ 400nm An optical element according to any one of configurations 1 to 12, characterized by satisfying the following conditions. (Composition 14) The optical element according to any one of configurations 1 to 13, characterized in that the first material comprises at least one of silicon nitride, titanium oxide, gallium nitride, gallium arsenide, silicon carbide, aluminum oxide, and silicon oxide. (Composition 15) An optical element according to any one of configurations 1 to 14, characterized in that within each of the plurality of uneven bands, different phase modulation amounts are applied to the incident light. (Composition 16) The optical element according to any one of configurations 1 to 15, characterized in that it is a metalens that focuses or diverges incident light due to the aforementioned uneven structure. (Composition 17) circuit board and The uneven structure formed on the substrate, The uneven structure has a first anti-reflective film formed on the side opposite to the substrate, The aforementioned uneven structure has multiple uneven bands, each containing multiple structural elements. The refractive index of the first material constituting the plurality of structures at a wavelength of 550 nm is n p The refractive index at a wavelength of 550 nm of the second material forming any one of the one or more layers constituting the first anti-reflective film is n 1L In that case, 0.7 × √n p ≤n 1L ≤ 1.2 × √n p An optical element characterized by satisfying the following conditions. (Composition 18) An optical system characterized by including an optical element described in any one of configurations 1 to 17. (Composition 19) An optical system including an optical element described in any one of configurations 1 to 17, An imaging device characterized by having an image sensor that captures an image of a subject through the optical system.

[0106] The embodiments described above are merely representative examples, and various modifications and changes can be made to each embodiment when implementing the present invention. [Explanation of Symbols]

[0107] 101-106, 201-203 Optical elements 10,15 convex elements 11,12,13 Anti-reflection coating 16 concave elements 41~46 Uneven structure

Claims

1. circuit board and The uneven structure formed on the substrate, The uneven structure has a first anti-reflective film formed on the side opposite to the substrate, The aforementioned uneven structure has multiple uneven bands, each containing multiple structural elements. The refractive index of the first material constituting the plurality of structures at a wavelength of 550 nm is n ｐ The extinction coefficient of the first material is κ ｐ The refractive index at a wavelength of 550 nm of the second material forming any one of the one or more layers constituting the first anti-reflective film is n １Ｌ In that case, 1.4≦n ｐ ≦3.6 k ｐ ≦0.001 0.7×√n ｐ ≦n １Ｌ ≦1.2×√n ｐ An optical element characterized by satisfying the following conditions.

2. The aforementioned uneven structure is formed on the first surface of the substrate, The optical element according to claim 1, characterized in that each of the plurality of uneven bands includes a plurality of structures having different widths in the direction along the first surface.

3. The optical element according to claim 1, characterized in that, among the one or more layers constituting the first anti-reflective film, the layer with the lowest refractive index or the layer furthest from the substrate is formed of the second material.

4. The aforementioned uneven structure is formed on the first surface of the substrate, The area around the aforementioned multiple structures is filled with air. The optical element according to claim 1, characterized in that the first anti-reflective film is formed on the plurality of structures within a width in the direction along the first surface of each of the plurality of structures.

5. The spaces between the aforementioned multiple structures are filled with a medium other than air. The optical element according to claim 1, characterized in that the first anti-reflective coating is formed on the plurality of structures and on the medium.

6. The substrate and the plurality of structures have a second anti-reflective film formed so as to cover the substrate, Let n be the refractive index at a wavelength of 550 nm of a third material that forms any one of the one or more layers constituting the second antireflection film ２Ｌ and let d be the thickness (nm) of the layer of the third material ２L When doing so 1.3≦n ２Ｌ ≦1.7 80≦d ２Ｌ ≦200 The optical element according to claim 1, characterized in that it satisfies the following conditions.

7. The optical element according to claim 6, characterized in that the layer closest to the structure among the one or more layers constituting the second anti-reflective film is formed of the third material.

8. The second anti-reflective film includes a layer formed of the third material and a layer formed of the fourth material, The refractive index of the fourth material at a wavelength of 550 nm is n ２Ｈ In that case, n ｐ ≦n ２Ｈ ≦3.0 The optical element according to claim 6, characterized in that it satisfies the following conditions.

9. The aforementioned uneven structure is formed on the first surface of the substrate, The present invention has a third anti-reflective film formed between the second anti-reflective film and the plurality of structures, within the width of each of the plurality of structures in the direction along the first surface, The refractive index at a wavelength of 550 nm of the fifth material forming any one of the one or more layers constituting the third anti-reflective film is n ３Ｌ In that case, 1.3≦n ３Ｌ ≦1.7 The optical element according to claim 6, characterized in that it satisfies the following conditions.

10. The optical element according to claim 9, characterized in that the layer closest to the structure among the one or more layers constituting the third anti-reflective film is formed of the fifth material.

11. The third anti-reflective film includes a layer formed of the fifth material and a layer formed of the sixth material, The refractive index of the sixth material at a wavelength of 550 nm is n ３Ｈ In that case, n ｐ ≦n ３Ｈ ≦3.0 The optical element according to claim 9, characterized in that it satisfies the following conditions.

12. The refractive index of the material forming the substrate at a wavelength of 550 nm is n ｓ In that case, 1.4≦n ｓ ≦2.5 The optical element according to claim 1, characterized in that it satisfies the following conditions.

13. The aforementioned uneven structure is formed on the first surface of the substrate, When the pitch of the plurality of structures in the direction along the first surface is P, 150 nm ≤ P ≤ 400 nm The optical element according to claim 1, characterized in that it satisfies the following conditions.

14. The optical element according to claim 1, characterized in that the first material comprises at least one of silicon nitride, titanium oxide, gallium nitride, gallium arsenide, silicon carbide, aluminum oxide, and silicon oxide.

15. The optical element according to claim 1, characterized in that different phase modulation amounts are applied to the incident light within each of the plurality of uneven bands.

16. The optical element according to claim 1, characterized in that it is a metalens that focuses or diverges incident light due to the aforementioned uneven structure.

17. circuit board and The uneven structure formed on the substrate, The uneven structure has a first anti-reflective film formed on the side opposite to the substrate, The aforementioned uneven structure has multiple uneven bands, each containing multiple structural elements. The refractive index of the first material constituting the plurality of structures at a wavelength of 550 nm is n ｐ The refractive index at a wavelength of 550 nm of the second material forming any one of the one or more layers constituting the first anti-reflective film is n １Ｌ In that case, 0.7×√n ｐ ≦n １Ｌ ≦1.2×√n ｐ An optical element characterized by satisfying the following conditions.

18. An optical system characterized by including an optical element according to any one of claims 1 to 17.

19. An optical system including an optical element according to any one of claims 1 to 17, An imaging device characterized by having an image sensor that captures an image of a subject through the optical system.

Images