Optical element, optical system, and imaging apparatus

Abstract

To provide an optical element having a highly robust structure.SOLUTION: An optical element has a plurality of orbicular zones arranged in a concentric state. The phase difference occurring between the plurality of orbicular zones is 2nπ (n is an integer). A first orbicular zone, of the plurality of orbicular zones, includes first and second structure groups arranged in a radial direction. The first structure group comprises three or more structures arranged in the radial direction at a first interval. The second structure group comprises three or more structures arranged in the radial direction at a second interval. The second interval is smaller than the first interval. The phase difference occurring between the first and second structure groups is not 2nπ.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an optical element having a plurality of structures, and is suitable for use in an imaging device such as a digital still camera. [Background technology]

[0002] In recent years, optical elements known as metalenses have become known, which have the effect of focusing or diverging incident light by utilizing the diffraction phenomenon of light. Optical elements such as metalenses have a concave-convex structure consisting of multiple structures arranged on a substrate. As such an optical element, Patent Document 1 discloses an optical element in which the pitch of the structures is reduced in the peripheral portion to suppress reflection of incident light. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2022-180278 Summary of the Invention [Problem to be solved by the invention]

[0004] However, reducing the pitch of the metalens structures increases the aspect ratio (the ratio of the height to the width of the structures), which reduces the robustness of the structures and can lead to deformation due to external forces, temperature changes, etc.

[0005] An object of the present invention is to provide an optical element having a highly robust structure. [Means for solving the problem]

[0006] An optical element according to one aspect of the present invention is an optical element having a plurality of concentrically arranged ring zones, wherein the phase difference generated by each of the plurality of ring zones is 2nπ (n is an integer), a first of the plurality of ring zones includes first and second groups of structures arranged in a radial direction, the first group of structures consisting of three or more structures arranged at a first interval in the radial direction, the second group of structures consisting of three or more structures arranged at a second interval in the radial direction, the second interval being smaller than the first interval, and the phase difference generated by each of the first and second groups of structures is not 2nπ. [Effects of the Invention]

[0007] According to the present invention, an optical element having a highly robust structure can be provided. [Brief explanation of the drawings]

[0008] [Figure 1] Schematic diagrams of optical elements according to Examples 1 to 9 [Figure 2] Schematic diagram of an optical element of a comparative example [Figure 3] Illustrative diagram of filling rates in Examples 1 to 9 [Figure 4] 10 is a diagram showing the relationship between the shape of the concave-convex structure of the optical element and the amount of phase modulation in Examples 1 to 9. [Figure 5] 1 is a diagram showing the relationship between the shape of the concave-convex structure of an optical element and the amount of phase modulation in a comparative example. [Figure 6] Schematic diagram of a method for manufacturing optical elements according to Examples 1 to 9. [Figure 7] Schematic diagram of offset layers in Examples 1 to 9 [Figure 8] FIG. 10 is an explanatory diagram of the modulation amount of the normalized phase in the radial direction of the optical element in Examples 1 to 9. [Figure 9] 1 is an explanatory diagram of the width of the structures in the radial direction of the optical elements in Examples 1 to 9 and a comparative example. [Figure 10] Schematic diagram of an optical element in Example 6 [Figure 11] Schematic diagram of an optical element in Example 7 [Figure 12] Schematic diagram of an optical element in Example 8 [Figure 13] Schematic diagram showing the shape of the structure in Example 9 [Figure 14] Schematic diagram of an optical system including the optical elements in Examples 1 to 9. [Figure 15] Schematic diagram of an imaging device including an optical element according to Examples 1 to 9. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Note that the drawings may be drawn at a scale different from the actual scale for convenience. In the drawings, the same reference numerals are used to designate the same components, and redundant explanations will be omitted.

[0010] 1(a) to 1(c) are schematic diagrams of an optical element 100. FIG. 1(a) shows an enlarged view of a main portion of the optical element 100 in the x-z cross section, and FIG. 1(b) shows a top view of the optical element 100 in the x-y cross section. FIG. 1(c) shows an overall top view of the optical element 100 in the x-y cross section. In each example, the thickness direction corresponds to the z direction of the substrate 1 of the optical element 100. In each example, the radial direction corresponds to the direction (x direction) perpendicular to the thickness direction of the substrate 1 of the optical element 100. In each example, the circumferential direction corresponds to the direction (y direction) perpendicular to the thickness direction of the substrate 1 of the optical element 100. Note that in the overall top view of the optical element 100, the circumferential direction is strictly different from the y direction, but for convenience, the circumferential direction and the y direction are considered to coincide in the enlarged view of a main portion in the x-z cross section and the top view in the x-y cross section.

[0011] The optical element 100 according to each embodiment has a substrate 1 and a concave-convex structure 2 formed on the substrate 1. The concave-convex structure 2 is made up of a plurality of structures 21 arranged periodically in the radial direction of the substrate 1. Each of the plurality of structures 21 has either a concave or convex shape. The optical element 100 has a plurality of ring zones, including a first ring zone (i-th ring zone) and a second ring zone (the (i+1)-th ring zone), arranged concentrically along the radial direction and extending circumferentially around the center of the optical element 100. Each of the plurality of ring zones has a region 1 (first region) and a region 2 (second region) arranged along the radial direction of the optical element 100.

[0012] The substrate 1 is a transparent flat plate made of synthetic quartz. The substrate 1 may be a plane mirror that reflects incident light, or may have a curved surface with any curvature. The material of the substrate 1 is not limited to synthetic quartz, but may also be inorganic glass, organic materials such as plastic, ceramics, metal, etc. The concave-convex structure 2 is formed on the surface of the substrate 1 and provides a focusing or diverging effect by imparting a phase difference to light passing through the concave-convex structure 2. Here, the design wavelength, which is the wavelength of light incident on the diffractive surface of the optical element 100, is defined as λ0, and the design diffraction order, which is the diffraction order of the diffracted light that is emitted from the diffractive surface and used for imaging, is defined as n (n is an integer). In the optical element 100 in each embodiment, a desired phase distribution is formed by periodically arranging rings that produce a phase difference of 2nπ at the design wavelength in a concentric pattern. With this configuration, the optical element 100 has optical effects such as focusing and diverging incident light.

[0013] The concave-convex structure 2 is composed of a plurality of structures 21, each having a concave or convex shape, periodically arranged in the radial direction of the substrate 1. In the optical element 100 according to each embodiment, the structures 21 are made of a dielectric material, Si3N4 or TiO2, and have a convex cylindrical shape. The shape of the structures 21 is not limited to a convex cylindrical shape, and may be a polygonal pillar, a polygonal pyramid, a cone, any concave shape, or a combination thereof. The materials of the structures 21 may also be GaN, GaP, GaAs, Si, SiC, Al2O3, SiO2, etc.

[0014] The plurality of structures 21 includes a plurality of structures 211 (first structure group) arranged in region 1 and a plurality of structures 212 (second structure group) arranged in region 2. The plurality of structures 211 and structures 212 consist of three or more structures 21. The plurality of structures 211 are arranged at a first interval (pitch) P1, and the plurality of structures 212 are arranged at a second interval (pitch) P2. Here, the pitch is the arrangement period of the structures 21 arranged in region 1 and region 2, and is defined by the distance between the centers of the concave or convex shapes of the structures 21 within the annular zone.

[0015] The structure 211 is disposed at the center of a segment 11 obtained by dividing the substrate 1 into square sections in the radial direction. Similarly, the structure 212 is disposed at the center of a segment 12 obtained by dividing the substrate 1 into square sections in the radial direction. Here, a segment refers to an area that includes each of the structures 21, as indicated by the dashed lines in Figures 1(a) and 1(b). Each segment is defined by a rectangular parallelepiped area whose bottom is a rectangle with one side equal to the pitch of the structures 21 and whose height is the distance from the surface of the substrate 1 to the position of the height H of the structures 21.

[0016] If the width (pitch) of the segments 11 and 12 is made smaller than the wavelength of the incident light, the incident light is phase-modulated according to the effective refractive index determined from the packing ratio of the structures 21 in the segments. For example, if the incident light is in the visible light range (400 to 700 nm), the pitch (period) is preferably less than 400 nm, and making the pitch even smaller is more preferable because it can suppress unnecessary diffracted light and reflected light.

[0017] Here, the packing ratio of the structures 21 is the ratio of the volume occupied by the structures 21 to the volume of the segment including the structures 21. Fig. 2(a) shows the packing ratio of the structures 211 in region 1, and Fig. 2(b) shows the packing ratio of the structures 212 in region 2. For example, the packing ratio in segment 11 is expressed as the ratio of the volume Vp of the structures 211 to the volume Vs of segment 11, which has a bottom surface P1 × P1 and a height H of the structures 211.

[0018] In the optical element 100 according to each embodiment, the structure 211 and the structure 212 are made of the same material. Each of the i-th annular zones (i = 1, 2, ···) has regions 1 and 2 where the pitches of the structure 21 are different from each other. For the structure 21, by appropriately setting the width in the radial direction of the substrate 1, a phase distribution of 2nπ is formed within the annular zone. In the direction perpendicular to the z-direction of the substrate 1, let the distances from the optical axis of regions 1 and 2 of the i-th annular zone be R1i and R2i, respectively. As can be seen from FIG. 1(c), in the direction perpendicular to the z-direction of the substrate 1, regions 1 and 2 are alternately arranged concentrically such that R1i < R2i. Note that the phase differences generated by regions 1 and 2 in the i-th annular zone are not 2nπ.

[0019] FIG. 3 is a schematic view of an optical element 101 configured such that the pitch of the structure 21 is equal throughout the optical element as a comparative example for the optical element 100. In the optical element 101, in order to form a phase distribution of 2nπ within the annular zone, the filling rate of the structure 21 within the segment is changed by changing the width W (diameter) of the structure 21. That is, the filling rate is decreased by gradually reducing the diameter of the structure 21 from the side closer to the center of the element toward the side closer to the periphery within the annular zone, thereby forming a desired phase distribution.

[0020] In the optical element 101 of the comparative example, since the filling rate is adjusted by changing only the diameter of the structure 21, it is necessary to change the diameter greatly in order to give a desired amount of phase modulation. Therefore, in the optical element 101 of the comparative example, the minimum diameter of the structure 21 within the zone becomes small, and the aspect ratio, which is the ratio of the height to the width of the structure 21 (height / width), becomes large. In particular, when the pitch of the structure 21 is made small, the aspect ratio becomes significantly large. When the aspect ratio of the structure 21 is large and it has a relatively elongated shape, there is a risk that the shape of the structure 21 may be deformed, inclined, or peeled off when an external force is applied due to contact, vibration, etc., or when temperature, pressure, etc. are applied. Therefore, in the optical element 100 according to each embodiment, by providing regions with different pitches within the zone, the amount of change in the width of the structure 21 is reduced particularly in the region where the amount of phase modulation is small, and a highly robust concavo-convex structure 2 with a reduced aspect ratio is formed.

[0021] FIG. 4 is a diagram showing the relationship between the shape of the structure 21 of the optical element 100 according to each embodiment and the amount of phase modulation, specifically regarding the filling rate of the structure 21 and the amount of phase modulation. In FIG. 4, the horizontal axis represents the filling rate of the structure 21, and the vertical axis represents the normalized phase. Here, the normalized phase refers to the phase modulation amount normalized by 2π. In the range where the normalized phase is from 0 to the normalized phase E at the boundary between region 1 and region 2, the filling rate of the structure 212 in the region 2 with a small pitch is changed from V2min to V2max. In the range where the normalized phase is from E to n (diffraction order), the filling rate of the structure 211 in the region 1 with a large pitch is changed from V1min to V1max. Thereby, while obtaining the phase modulation amount of the normalized phase 0 to n, the aspect ratio of the structure 212 in the region 2 can be particularly reduced. Here, let the phase modulation amount of the structure 21 with a filling rate of V1min among the structures 211 in the region 1 be D1, and the phase modulation amount of the structure 21 with a filling rate of V2min among the structures 212 in the region 2 be D2. At the boundary between the region 1 and the region 2 of the optical element 100, it is desirable that the phase modulation amount changes smoothly. That is, it is preferable that the conditional expression 0.9 < D1 / D2 < 1.1 is satisfied for the phase modulation amounts D1 and D2.

[0022] FIG. 5 is a diagram showing the relationship between the shape of the structures 21 of an optical element 101 as a comparative example and the amount of phase modulation, and relates to the packing ratio and the amount of phase modulation of the convex cylinders in the optical element 101, which has the same pitch throughout the entire optical element. In FIG. 5, the horizontal and vertical axes are the same as those in FIG. 4. In FIG. 5, in Comparative Example 1, the structures 21 are configured throughout the entire optical element at a pitch P1 in region 1 of the optical element 100, and in Comparative Example 2, the structures 21 are configured throughout the entire optical element at a pitch P2 in region 2 of the optical element 100. In FIG. 5, to obtain phase modulation amounts with normalized phases 0 to n, the packing ratio needs to be changed more significantly than in FIG. 4, and the aspect ratio is particularly large in Comparative Example 2. This shows that the aspect ratio of the structures 21 can be reduced by changing the pitch within the annular zone.

[0023] In the optical element 100 according to each example, it is sufficient that the pitch of the structures 21 is changed in at least one of the plurality of annular zones. However, it is preferable to change the pitch of the structures 21 in a plurality of annular zones, and it is more preferable to change the pitch of the structures 21 in all of the annular zones.

[0024] 6(a) to 6(c) are explanatory diagrams of a method for manufacturing an optical element 100, showing steps for manufacturing the optical element 100 using nanoimprint lithography. The optical element 100 can be manufactured using lithography technology. FIG. 6(a) shows a mold 31, which has a shape that is the inverse of the concave-convex shape of a concave-convex structure 2 formed using an electron beam, laser, or the like. As shown in FIG. 6(b), a film 33 (first material) is deposited on a substrate 1. Next, a resist material 32 (second material) is applied to the surface of the film 33, and the mold 31 is pressed against the film 33 and irradiated with ultraviolet light or the like to form a shape in the resist material 32 that is the inverse of the concave-convex shape of the mold 31. Thereafter, as shown in FIG. 6(c), the mold 31 is released, and development is performed so that the concave-convex shape of the resist material 32 is transferred to the film 33, thereby forming a concave-convex structure 2 on the substrate 1 of the optical element 100. In each embodiment, the method for manufacturing the concave-convex structure 2 is not limited to nanoimprint lithography, and other methods may be used, such as directly forming the concave-convex structure 2 using an electron beam, a laser, or the like.

[0025] 7 is an explanatory diagram of the offset layer 34 in the optical element 100 according to each example. As shown in Fig. 7, instead of the configuration in which the concave-convex structure 2 is formed directly on the substrate 1 as in Fig. 6(c), an offset layer 34 may be provided so as to straddle either or both of the region 1 and the region 2 as in Fig. 7. Note that the substrate 1 may include the offset layer 34.

[0026] In each embodiment, the structures 21 in the regions 1 and 2 may be made of the same material. As shown in FIG. 6(b), it is relatively easy to prepare a material with a uniform thickness, such as the film 33. Therefore, when forming the relief structures 2 in the regions 1 and 2 based on the film 33, it is preferable that the material be the same as the structures 21 in the regions 1 and 2.

[0027] Conditional expressions that are preferably satisfied in the optical element 100 according to each embodiment will be described below.

[0028] When the minimum width of the structures 211 arranged in region 1 is Wmin1 and the maximum width of the structures 212 arranged in region 2 is Wmax2, it is preferable that the optical element 100 according to each embodiment satisfies the following conditional expression (1): 0.10≦Wmax2 / Wmin1<1.00…(1)

[0029] Conditional formula (1) relates to the shapes of the structures 211 and 212. By relatively increasing the minimum width Wmin1 of the structures 211 arranged in region 1 to increase the amount of phase modulation, it is possible to increase the amount of phase modulation in the structures 212 arranged in region 2. This makes it possible to reduce the aspect ratio of the structures 212, particularly in region 2.

[0030] If the lower limit of conditional formula (1) is not reached, the maximum width of the structures 212 becomes relatively small. In this case, in order to ensure a desired phase modulation amount in region 2, the width of the structures 212 needs to be made smaller, which increases the aspect ratio of the structures 212 in region 2. Furthermore, if the upper limit of conditional formula (1) is exceeded, the maximum width of the structures 212 becomes relatively large. In this case, the intervals between adjacent structures 212 become narrow, making it difficult to form the concave-convex structure 2.

[0031] In this embodiment, it is more preferable that the lower limit of conditional expression (1) be set to 0.15, 0.20, 0.25, 0.30, 0.32, 0.34, or 0.35 instead of 0.10, and it is more preferable that the upper limit of conditional expression (1) be set to 0.95, 0.90, 0.85, 0.80, 0.78, 0.76, 0.74, or 0.72 instead of 1.00.

[0032] Moreover, it is preferable that the optical element 100 according to each embodiment satisfies the following conditional expression (2). 1.2≦P1 / P2≦8.0…(2)

[0033] Conditional expression (2) relates to the pitch of the structures 21. By satisfying conditional expression (2), the pitch of the structures 212 in region 2 can be configured to be small, and reflective diffraction of the optical element can be suppressed. If the lower limit of conditional expression (2) is not reached, the pitch of the structures 212 becomes relatively large, and the pitch cannot be made sufficiently small with respect to the wavelength of the incident light, making it difficult to sufficiently suppress reflective diffraction. If the upper limit of conditional expression (2) is reached, the pitch of the structures 212 becomes relatively small, and the aspect ratio of the structures 212 becomes large.

[0034] In this embodiment, it is more preferable that the lower limit of conditional expression (2) be set to 1.22, 1.24, 1.26, 1.28, 1.30, 1.32, 1.34, 1.36, 1.38, 1.40, 1.42, 1.44, or 1.45 instead of 1.2, and it is more preferable that the upper limit of conditional expression (2) be set to 7.0, 6.0, 5.0, 4.8, 4.6, 4.4, 4.2, or 4.0 instead of 8.0.

[0035] When j is a natural number greater than 1, the optical element 100 according to each embodiment preferably satisfies the following conditional expression (3). 0.9j≦P1 / P2≦1.1j…(3)

[0036] Conditional formula (3) relates to the arrangement of the structures 21. In the optical element according to the present invention, the arrangement interval (pitch) P2 of the structures 212 is smaller than the pitch P1 of the structures 211. Therefore, when arranging the structures 211 and 212 in order in the radial direction of the substrate, it is preferable to arrange the structures 212 by dividing them. That is, it is preferable that a plurality of structures 212 are included in a segment of the same size as the segment 11 including one structure 211. For example, when the number of divisions is j (j is a natural number greater than 1), in the optical element 100 shown in FIG. 1, the structures 211 and 212 are arranged so that the number of divisions j is 2. By satisfying conditional formula (3), when the structures 21 are arranged in a square shape on the substrate 1, they can be arranged without gaps. It is more preferable to satisfy the conditional formula P1=j×P2. If the lower limit of conditional expression (3) is not reached, when j squared structures 212 are arranged at a pitch P2 in segment 11, gaps will be created, and many blank areas without structures will exist in region 2 of the optical element. If the upper limit of conditional expression (3) is reached, when j squared structures 212 are arranged at a pitch P2 in segment 11, they will protrude from segment 11, and many blank areas without structures 21 will be formed in region 1 of the optical element.

[0037] It is more preferable that the arrangement of the structures 21 satisfies P1=j×P2.

[0038] In this embodiment, it is more preferable that the lower limit of conditional expression (3) be set to 0.92, 0.94, 0.96, 0.98, or 0.99 instead of 0.9, and it is more preferable that the upper limit of conditional expression (3) be set to 1.08, 1.06, 1.04, 1.02, or 1.01 instead of 1.1.

[0039] When the maximum width of the structures 211 is Wmax1 and the minimum width of the structures 212 is Wmin2, the optical element 100 according to each example preferably satisfies the following conditional expressions (4) and (5). 1.05≦Wmax1 / Wmin1≦10.00…(4) 1.05≦Wmax2 / Wmin2≦10.00…(5)

[0040] Conditional expressions (4) and (5) relate to the shapes of the structures 211 and 212. If the lower limit of conditional expression (4) is not reached or the upper limit of conditional expression (5) is exceeded, the amount of phase modulation in region 2 becomes relatively large. In this case, the width of the structures 212 needs to be changed significantly, which increases the aspect ratio of the structures 212. If the upper limit of conditional expression (4) is reached or the lower limit of conditional expression (5) is reached, the amount of phase modulation in region 1 becomes relatively large. In this case, the proportion of region 2 relative to the entire area of ​​the optical element becomes small, making it difficult to sufficiently suppress reflection and diffraction.

[0041] In this embodiment, it is more preferable that the lower limit of conditional expression (4) be set to 1.06, 1.07, 1.08, 1.09, or 1.1 instead of 1.05. Also, it is more preferable that the lower limit of conditional expression (5) be set to 1.06, 1.08, 1.10, 1.11, 1.12, 1.13, 1.14, or 1.15 instead of 1.05. It is more preferable that the upper limit of conditional expressions (4) and (5) be set to 5.0, 4.5, 4.0, 3.5, 3.0, 2.6, 2.4, 2.2, or 2.0 instead of 10.

[0042] When the difference between the maximum width and the minimum width of the structure 211 is ΔW1 and the difference between the maximum width and the minimum width of the structure 212 is ΔW2, it is preferable that the optical element 100 according to each embodiment satisfies the following conditional expressions (6) and (7). 0.05≦ΔW1 / P1≦0.80…(6) 0.05≦ΔW2 / P2≦0.80…(7)

[0043] Conditional expressions (6) and (7) relate to the shapes of the structures 211 and 212. If the lower limit of conditional expression (6) is not reached or the upper limit of conditional expression (7) is exceeded, the amount of phase modulation in region 2 becomes relatively large. In this case, the width of the structures 212 needs to be changed significantly, which increases the aspect ratio of the structures 212 and reduces the robustness of the structures 212. If the upper limit of conditional expression (6) is reached or the lower limit of conditional expression (7) is reached, the amount of phase modulation in region 1 becomes relatively large, which reduces the proportion of region 2 relative to the entire area of ​​the optical element, making it difficult to sufficiently suppress reflection and diffraction.

[0044] In this embodiment, the lower limit of conditional expression (6) is preferably set to 0.06, 0.07, 0.08, 0.09, 0.10, 0.14, 0.18, or 0.20 instead of 0.05. The upper limit of conditional expression (6) is preferably set to 0.70, 0.60, 0.50, 0.45, or 0.40 instead of 0.80. The lower limit of conditional expression (7) is preferably set to 0.06, 0.08, 0.10, 0.14, 0.18, 0.20, 0.24, 0.28, or 0.30 instead of 0.05. The upper limit of conditional expression (7) is preferably set to 0.60, 0.50, 0.46, 0.42, 0.41, or 0.40 instead of 0.80.

[0045] When the minimum value of the packing rate of the structures 211 is V1min and the maximum value of the packing rate of the structures 212 is V2max, it is preferable that the optical element 100 according to each example satisfies the following conditional expression (8). 1.0 <V2max / V1min≦4.0…(8)

[0046] Conditional expression (8) relates to the shapes of the structures 211 and 212. When the lower limit of conditional expression (8) is not reached, the amount of phase modulation in region 1 becomes relatively large. In this case, the proportion of region 2 with respect to the entire area of ​​the optical element becomes small, making it difficult to sufficiently suppress reflection and diffraction. When the upper limit of conditional expression (8) is reached, the amount of phase modulation in region 2 becomes relatively large. In this case, the width of the structure 212 needs to be changed significantly, which increases the aspect ratio of the structure 212 and reduces the robustness of the structure 212.

[0047] In this embodiment, it is more preferable that the lower limit of conditional expression (8) be set to 1.05, 1.10, 1.15, 1.20, 1.25, 1.30, 1.35, or 1.40 instead of 1.0, and it is more preferable that the upper limit of conditional expression (8) be set to 3.5, 3.0, 2.8, 2.6, 2.4, 2.2, or 2.0 instead of 4.0.

[0048] When the normalized phase at the boundary between the first and second regions is E and the design diffraction order is n, the optical element 100 according to each example preferably satisfies the following conditional expression (9). 0.05≦E / n≦0.90…(9)

[0049] Conditional expression (9) relates to the arrangement of the structures 21 in region 1 and region 2. When the lower limit of conditional expression (9) is not reached, the amount of phase modulation in region 1 becomes relatively large. In this case, the proportion of region 2 with respect to the entire area of ​​the optical element becomes small, making it difficult to sufficiently suppress reflection and diffraction. When the upper limit of conditional expression (9) is reached, the amount of phase modulation in region 2 becomes relatively large. In this case, it is necessary to significantly change the width of the structures 212, which increases the aspect ratio of the structures 212 and impairs the robustness of the structures 212.

[0050] In this embodiment, it is more preferable that the lower limit of conditional expression (9) be set to 0.06, 0.08, 0.10, 0.12, 0.13, or 0.14 instead of 0.05, and it is more preferable that the upper limit of conditional expression (9) be set to 0.88, 0.86, 0.84, 0.82, 0.80, 0.78, 0.76, 0.74, 0.72, or 0.71 instead of 0.90.

[0051] When the reference wavelength (design wavelength) used when calculating the normalized phase is λ0, the optical element 100 according to each embodiment preferably satisfies the following conditional expression (10). 0.10≦P2 / λ0≦0.80…(10)

[0052] Conditional expression (10) relates to the configuration of the structures 212. If the lower limit of conditional expression (10) is not reached, the pitch of the structures 212 becomes relatively small, and although reflective diffraction can be suppressed, the aspect ratio becomes large, making manufacturing difficult. If the upper limit of conditional expression (10) is reached, the pitch of the structures 212 becomes relatively large, and the pitch cannot be made sufficiently small with respect to the wavelength of the incident light, making it difficult to sufficiently suppress reflective diffraction.

[0053] In this embodiment, it is more preferable that the lower limit of conditional expression (10) be set to 0.12, 0.14, 0.16, 0.18, 0.20, 0.21, or 0.22 instead of 0.10, and it is more preferable that the upper limit of conditional expression (10) be set to 0.70, 0.60, 0.50, 0.45, 0.40, 0.39, 0.38, 0.37, or 0.36 instead of 0.80.

[0054] When the maximum value of the height of the structures included in the structures 211 and 212 is Hmax, the optical element 100 according to each example preferably satisfies the following conditional expression (11). 0.05≦(P1-P2) / Hmax≦0.60…(11)

[0055] Conditional expression (11) relates to the shapes of the structures 211 and 212. If the lower limit of conditional expression (11) is not reached, the difference in pitch between the structures 211 and 212 becomes relatively small. In this case, the pitch of the structures 212 becomes relatively large, and the pitch cannot be made sufficiently small with respect to the wavelength of the incident light, making it difficult to sufficiently suppress reflection and diffraction. If the upper limit of conditional expression (11) is reached, the pitch of the structures 212 becomes relatively small with respect to the structures 211, resulting in a large aspect ratio of the structures 212. Note that, although it is desirable that the heights H of the structures 211 and 212 are constant, they may differ from each other due to manufacturing errors or the like. In this case, the height Hmax is the height of the tallest structure of the structures 211 and 212.

[0056] In this embodiment, it is more preferable that the lower limit of conditional expression (11) be set to 0.06, 0.07, 0.08, 0.09, or 0.10 instead of 0.05, and it is more preferable that the upper limit of conditional expression (11) be set to 0.50, 0.45, 0.40, 0.35, 0.30, 0.28, 0.26, 0.24, or 0.22 instead of 0.60.

[0057] When the thickness of the substrate 1 is t, it is preferable that the optical element 100 according to each example satisfies the following conditional expression (12). 0.0 <Hmax / t≦0.1…(12)

[0058] Conditional expression (12) relates to the shape of the optical element 100. The height H of the structures 21 in region 2 and the thickness t of the substrate 1 are both numerical values ​​indicating lengths and are greater than 0. Therefore, the lower limit of conditional expression (12) is not exceeded. If the upper limit of conditional expression (12) is exceeded, the thickness of the substrate becomes thinner than that of the structures 21, and the optical element 100 will be deformed by its own weight when held. Alternatively, the substrate will be deformed when the optical element 100 is manufactured.

[0059] In this embodiment, the lower limit of conditional expression (12) is preferably set to 0.00001, 0.00004, 0.00008, or 0.0001 instead of 0.0, and the upper limit of conditional expression (12) is preferably set to 0.05, 0.01, 0.008, 0.005, or 0.001 instead of 0.1.

[0060] When d-line (587.6 nm), F-line (486.1 nm), and C-line (656.3 nm) light are incident on an optical element, and the refractive powers at each wavelength are φd, φF, and φC, respectively, the effective Abbe number νdef in the focusing and diverging actions of the optical element is expressed by the following equation.

[0061]

number

[0062] The effective Abbe number corresponds to the Abbe number νd of a medium having a refractive action, and is an index representing the wavelength dispersion of the light-condensing and diverging actions of an optical element.

[0063] In this case, it is preferable that the optical element 100 according to each example satisfies the following conditional expression (13). 0.00≦|1 / νdef|≦0.25…(13)

[0064] Conditional expression (13) relates to the wavelength dispersion of the focusing and divergence characteristics of the optical element 100. When realizing an optical element having high-dispersion focusing and divergence functions that exceed the upper limit of conditional expression (13), a desired normalized phase value can be achieved without using structures with different pitches, such as the structure 212. However, in order to realize an optical element having focusing and divergence functions with low dispersion or substantially zero wavelength dispersion and high focusing efficiency, it is necessary for the wavelength dispersion of the phase modulation amount of the structure 21 to take on various values. In other words, by forming a concave-convex structure with a different pitch, such as the structure 212, it is necessary to realize a concave-convex structure with a different wavelength dispersion from that of the structure 211.

[0065] In this embodiment, it is more preferable that the upper limit of conditional expression (13) be set to 0.20, 0.10, 0.04, 0.02, 0.01, or 0.005 instead of 0.25.

[0066] When the minimum value of the height of the structures 211 is H1min and the maximum value of the height of the structures 212 is H2max, it is preferable that the optical element 100 according to each example satisfies the following conditional expression (14). 0.05≦H2max / H1min≦0.95…(14)

[0067] Conditional expression (14) relates to the heights of the structures 211 and 212. By satisfying conditional expression (14), the height of the structures 212 arranged in the region 2 where the amount of phase change is relatively small becomes lower than the height of the structures 211. This makes it possible to increase the diameter of the structures 212, thereby reducing the aspect ratio of the structures 212.

[0068] If the lower limit of conditional expression (14) is not reached, the height H2 of the structure 212 becomes too low, and therefore the phase modulation amount when the width of the structure 212 is changed becomes small. In this case, to obtain a desired phase modulation amount, it is necessary to change the width of the structure 212 significantly, and therefore the aspect ratio of the structure 212 becomes large. If the upper limit of conditional expression (14) is reached, the height H2 of the structure 212 becomes too high. In this case, to obtain a desired phase modulation amount, it is necessary to make the width of the structure 212 smaller than that of the structure 211, and therefore the aspect ratio of the structure 212 becomes large.

[0069] In this embodiment, it is more preferable that the lower limit of conditional expression (14) be set to 0.10, 0.15, 0.20, 0.24, 0.28, 0.32, 0.34, or 0.36 instead of 0.05, and it is more preferable that the upper limit of conditional expression (14) be set to 0.90, 0.85, 0.80, 0.76, 0.72, 0.70, 0.68, 0.66, 0.64, 0.62, or 0.60 instead of 0.95.

[0070] It is desirable that the height H1 of each of the structures 211 and the height H2 of each of the structures 212 are constant, but there are cases where the heights differ due to manufacturing errors, etc. In this case, the height of the tallest structure among the structures 211 is H1min. Similarly, the height of the shortest structure among the structures 212 is H2max.

[0071] The configuration of the optical element 100 according to Examples 1 to 9 will be described in detail below.

[0072] The optical element of Example 1 is composed of a 0.775 mm thick synthetic quartz substrate and a concave-convex structure consisting of convex Si3N4 cylinders. The structures 211 arranged in region 1 and the structures 212 arranged in region 2 are arranged in square segments with sides of 320 nm and 160 nm, respectively, and have a height of 880 nm. The effective diameter of the concave-convex structure is φ4.0 mm, and it has 105 ring zones with a periodic phase difference of 2π at a wavelength of 500 nm. The focal length of the concave-convex structure is 40.0 mm. The effective Abbe number νdef is -3.452, and it has wavelength dispersion equivalent to that of conventional diffractive optical elements. The position where the normalized phase is 0.405 is the boundary between region 1 and region 2 within the ring zone, and the maximum aspect ratios in region 1 and region 2 are 5.32 and 16.31, respectively. Here, as comparative examples, Comparative Example 11 in which the structures 21 are arranged at a pitch P1 over the entire optical element, and Comparative Example 12 in which the structures 21 are arranged at a pitch P2 over the entire optical element are used. The optical element of Example 1 has a reduced aspect ratio compared to the maximum aspect ratios of 10.1 and 46.1 in Comparative Examples 11 and 12. Furthermore, the reflectance at a wavelength of 450 nm in the 103rd annular zone (i=103) is 26.8% in Example 1, which is lower than the 127.9% in the comparative example, thereby suppressing reflection and diffraction due to the structure.

[0073] The optical element of Example 2 is composed of a 0.775 mm thick synthetic quartz substrate and a concave-convex structure consisting of convex Si3N4 cylinders. Structures 211 and 212 are arranged in square segments with sides of 320 nm and 160 nm, respectively, and have a height of 1000 nm. The effective diameter of the concave-convex structure is φ2.5 mm, and it has 67 ring zones with a periodic phase difference of 2π at a wavelength of 587.6 nm. The concave-convex structure has a focal length of 20.0 mm, an effective Abbe number νdef of -3.452, and wavelength dispersion equivalent to that of conventional diffractive optical elements. The position where the normalized phase is 0.356 is the boundary between Regions 1 and 2 within the ring zones, and the maximum aspect ratios of Regions 1 and 2 are 5.63 and 18.32, respectively. The aspect ratio can be reduced compared to the maximum aspect ratios of 16.1 and 68.5 in Comparative Examples 21 and 22, in which the pitch does not change over the entire optical element.

[0074] The optical element of Example 3 is composed of a 0.775 mm thick synthetic quartz substrate and a concave-convex structure consisting of convex Si3N4 cylinders. The structures 21 in Region 1 and Region 2 are arranged in square segments with sides of 320 nm and 160 nm, respectively, and have a height of 1600 nm. The effective diameter of the concave-convex structure is φ2.5 mm, and it has 79 ring zones with a periodic phase difference of 4π at a wavelength of 500 nm. The concave-convex structure has a focal length of 10.0 mm, an effective Abbe number νdef of -3.452, and wavelength dispersion equivalent to that of conventional diffractive optical elements. The position where the normalized phase is 0.529 is the boundary between Regions 1 and 2 within the ring zones, and the maximum aspect ratios in Regions 1 and 2 are 10.31 and 26.15, respectively. The aspect ratio can be reduced compared to the maximum aspect ratios of 21.37 and 115 in Comparative Examples 31 and 32, in which the pitch does not change over the entire optical element.

[0075] The optical element of Example 4 is composed of a 0.775 mm thick synthetic quartz substrate and a concave-convex structure consisting of convex TiO2 cylinders. The structures 21 in Region 1 and Region 2 are arranged in square segments with sides of 240 nm and 120 nm, respectively, and are 600 nm high. The effective diameter of the concave-convex structure is φ12.0 mm, and it has 307 ring zones with a periodic phase difference of 2π at a wavelength of 500 nm. The focal length of the concave-convex structure is 117.5 mm, and the effective Abbe number νdef is -3.452, providing wavelength dispersion equivalent to that of conventional diffractive optical elements. The position where the normalized phase is 0.288 is the boundary between Regions 1 and 2 within the ring zones. The maximum aspect ratios in Regions 1 and 2 are 5.26 and 14.35, respectively. The aspect ratio can be reduced compared to the maximum aspect ratios of 10.27 and 80.05 in Comparative Examples 41 and 42, in which the pitch does not change over the entire optical element.

[0076] The optical element of Example 5 is composed of a 0.775 mm thick synthetic quartz substrate and a concave-convex structure consisting of convex Al2O3 cylinders. The structures 21 in Region 1 and Region 2 are arranged in square segments with sides of 300 nm and 150 nm, respectively, and have a height of 1400 nm. The effective diameter of the concave-convex structure is φ7.5 mm, and it has 338 ring zones with a periodic phase difference of 2π at a wavelength of 500 nm. The focal length of the concave-convex structure is 41.7 mm, and the effective Abbe number νdef is -3.452, providing wavelength dispersion equivalent to that of conventional diffractive optical elements. The position where the normalized phase is 0.280 is the boundary between Regions 1 and 2 within the ring zones, and the maximum aspect ratios in Regions 1 and 2 are 9.23 and 16.43, respectively. The aspect ratio can be reduced compared to the maximum aspect ratios of 11.45 and 31.65 in Comparative Examples 51 and 52, in which the pitch does not change over the entire optical element.

[0077] The optical elements of Examples 6 to 8 are different from the optical element of Example 1 in the pitch of the structures 211 and the structures 212 and the arrangement of the regions 1 and 2.

[0078] As shown in FIG. 10 , the optical element of Example 6 has region 2 configured with regions 21 and 22 having different pitches. The structures 21 in region 1 of the optical element of Example 6 are arranged in square segments with sides of 360 nm, while the structures 21 in regions 21 and 22 are arranged in square segments with sides of 180 nm and 120 nm, respectively. The boundary between regions 1 and 2 within the annular zone is determined as the position where the normalized phase is 0.450, and the boundary between regions 21 and 22 is determined as the position where the normalized phase is 0.150. The maximum aspect ratios in regions 1, 21, and 22 are 4.71, 8.62, and 15.41, respectively. The aspect ratios are reduced compared to the maximum aspect ratios of 7.75, 37.13, and 73.14 for comparative examples 61, 62, and 63, in which the pitch remains constant throughout the entire optical element.

[0079] 11, in the optical element of Example 7, the number of structures 212 in the segment 11 in region 2 is not an integer. The structures 21 in region 1 of the optical element of Example 7 are arranged in square segments with sides of 360 nm and 240 nm. The position where the normalized phase is 0.60 is set as the boundary between regions 1 and 2 within the annular zone, and the maximum aspect ratios in regions 1 and 2 are 4.31 and 8.55, respectively.

[0080] The optical element of Example 8 is configured with a concave-convex structure made of convex quadrangular prisms, as shown in Fig. 12. The height of the structures 21 in Region 1 is 880 nm. The position where the normalized phase is 0.70 is set as the boundary between Regions 1 and 2 within the annular zone, and the maximum aspect ratios in Regions 1 and 2 are 4.78 and 14.09, respectively.

[0081] The optical element of Example 9 is composed of SiN structures 21 having a plurality of different shapes, as shown in Figures 13(a) to 13(f). Figure 13(a) shows a convex cylinder (type 1), where the diameter of the cylinder is W. Figure 13(b) shows a convex hollow cylinder (type 2), where the outer diameter of the cylinder is W and the difference between the outer and inner diameters of the cylinder is W'. Figure 13(c) shows a concave cylinder (type 3), where the diameter of the cylinder is W. Figure 13(d) shows a convex square prism (type 4), where the length of the sides of the square prism is W. Figure 13(e) shows a convex cross prism (type 5), where the short side of the cross is W and the long side is W'. Figure 13(f) shows a convex cylinder (type 6), where the pitch is different from that of Figure 13(a), and the diameter of the cylinder is W. The structures 21 in Region 1 and Region 2 are arranged in square segments with sides of 240 nm and 120 nm, respectively, and have a height of 800 nm. The effective diameter of the concave-convex structure is φ20 μm, and has ring zones with a periodic phase difference of 2π at wavelengths of 450 nm, 550 nm, and 650 nm, respectively. The focal length of the concave-convex structure is 20 μm. The effective Abbe number νdef is infinite, and the focal lengths are approximately equal at the three design wavelengths. The optical element of Example 9 is divided into 42 segments in the radial direction from the side closest to the center. By reducing the pitch of some of the segments, the reflection of light incident on the element is reduced while the desired phase difference can be achieved compared to an optical element composed only of cylindrical structures, thereby improving imaging performance.

[0082] Numerical Examples 1 to 9 corresponding to the optical elements of the examples are shown below.

[0083] The phase φ, which indicates the light-collecting and diverging effects of the uneven structure, is expressed by the following equation, where h is the height from the optical axis in the direction perpendicular to the optical axis (radial direction), n is the diffraction order of the diffracted light, λ0 is the design wavelength, and Ck (k=1, 2, 3, ...) is the phase coefficient of each order.

[0084]

number

[0085] The refractive indices at the d-line (587.6 nm), g-line (435.8 nm), F-line (486.1 nm), C-line (656.3 nm), and wavelength of 500 nm are denoted as nd, ng, nC, nF, and n500. The widths of the structures 21 in regions 1 and 2 are denoted as W1 [nm], W2 [nm], and W' [nm], respectively, and the widths of the structures 21 in comparative examples 1 and 2 are denoted as Wref1 [nm] and Wref2 [nm].

[0086] In Numerical Example 9, the shapes of the respective structures 21 are represented as types 1 to 6 in Fig. 13. That is, with regard to the shapes of the structures 21, a convex cylinder is represented as type 1, a convex hollow cylinder is represented as type 2, a concave cylinder is represented as type 3, a convex square prism is represented as type 4, a convex cross prism is represented as type 5, and a convex cylinder is represented as type 6.

[0087] [Numerical Example 1] Normalized phase W1 W2 Wref1 Wref2 0.000 53.9 87.0 19.1 0.050 63.9 103.6 41.0 0.100 72.1 116.2 54.2 0.150 79.2 126.3 63.8 0.200 85.5 135.0 71.9 0.250 91.2 142.7 79.1 0.300 96.4 149.7 85.7 0.350 101.2 156.1 91.4 0.405 165.5 106.1 162.8 97.0 0.450 170.6 168.1 101.1 0.500 176.1 173.7 105.4 0.550 181.6 179.1 109.7 0.600 187.0 184.6 113.8 0.650 192.4 190.0 117.8 0.700 197.9 195.4 121.6 0.750 203.5 201.0 125.0 0.800 209.2 206.6 128.2 0.850 215.3 212.5 131.4 0.900 221.7 218.7 135.0 0.950 228.8 225.6 138.7 1.000 236.8 233.0 140.9

[0088] [Numerical Example 2] Normalized phase W1 W2 Wref1 Wref2 0.000 54.6 62.3 14.6 0.050 64.8 90.7 40.7 0.100 73.6 110.2 54.9 0.150 81.4 124.9 64.8 0.200 88.3 137.0 73.4 0.250 94.4 147.6 81.3 0.300 99.8 157.0 88.5 0.356 177.6 105.4 166.6 95.4 0.400 184.0 173.6 100.1 0.450 190.9 181.0 104.9 0.500 197.7 188.2 109.4 0.550 204.5 195.1 113.9 0.600 211.3 201.9 118.3 0.650 218.2 208.7 122.5 0.700 224.9 215.4 126.3 0.750 231.6 222.1 129.6 0.800 238.4 228.8 132.7 0.850 245.5 235.6 135.9 0.900 253.1 242.8 139.8 0.950 261.1 250.3 144.0 1.000 268.8 257.7 145.4

[0089] [Numerical Example 3] Normalized phase W1 W2 Wref1 Wref2 0.000 61.2 74.9 13.9 0.100 70.5 97.7 40.9 0.200 78.5 112.7 55.5 0.300 85.6 123.8 65.4 0.400 91.8 133.1 73.9 0.529 155.2 98.8 143.7 83.7 0.600 160.1 149.1 88.6 0.700 166.5 156.1 94.6 0.800 172.6 162.8 99.9 0.900 178.6 169.1 104.6 1.000 184.6 175.2 109.1 1.100 190.8 181.3 113.6 1.200 197.2 187.5 118.1 1.300 203.7 193.7 122.4 1.400 210.4 200.0 126.3 1.500 217.2 206.5 129.7 1.600 224.4 213.1 132.9 1.700 232.2 220.2 136.2 1.800 241.0 227.8 140.2 1.900 250.8 236.2 144.5 2.000 260.7 245.1 146.1

[0090] [Numerical Example 4] Normalized phase W1 W2 Wref1 Wref2 0.000 41.8 58.4 7.5 0.050 51.1 79.7 30.5 0.100 58.7 90.4 42.9 0.150 65.0 96.7 51.5 0.200 70.4 101.9 58.8 0.250 75.0 106.7 65.3 0.288 114.1 78.2 110.4 69.7 0.350 118.9 115.9 75.6 0.400 122.4 119.8 79.6 0.450 125.8 123.3 83.1 0.500 129.3 126.5 86.5 0.550 133.0 129.8 89.9 0.600 136.9 133.3 93.4 0.650 140.9 137.2 96.5 0.700 144.8 141.3 99.2 0.750 148.6 145.5 101.4 0.800 152.7 149.6 103.5 0.850 158.0 153.9 106.1 0.900 166.2 159.2 109.6 0.950 179.9 167.4 113.3 1.000 202.8 181.6 112.5

[0091] [Numerical Example 5] Normalized phase W1 W2 Wref1 Wref2 0.000 85.2 122.3 44.2 0.050 88.0 126.6 51.2 0.100 90.6 130.5 57.0 0.150 93.1 134.1 62.0 0.200 95.5 137.5 66.6 0.250 97.8 140.6 70.8 0.280 151.8 99.2 142.4 73.1 0.350 155.3 146.4 78.2 0.400 157.7 149.1 81.5 0.450 160.1 151.7 84.5 0.500 162.4 154.2 87.4 0.550 164.7 156.7 90.1 0.600 166.9 159.1 92.7 0.650 169.2 161.4 95.1 0.700 171.4 163.7 97.4 0.750 173.6 166.0 99.6 0.800 175.7 168.2 101.7 0.850 177.9 170.4 103.8 0.900 180.1 172.6 105.7 0.950 182.3 174.8 107.7 1.000 184.5 177.0 109.5

[0092] [Numerical Example 6] Normalized phase W1 W21 W22 Wref1 Wref2 Wref3 0.000 57.1 113.5 23.7 12.0 0.050 62.6 124.0 46.6 30.3 0.100 67.4 132.6 60.9 40.9 0.150 102.1 71.8 140.1 71.3 48.4 0.200 107.6 146.9 80.1 54.9 0.250 112.7 153.2 87.9 60.7 0.300 117.5 159.3 94.9 66.0 0.350 122.1 165.2 101.1 70.6 0.400 126.4 170.9 106.6 74.6 0.450 187.0 130.7 176.6 111.7 78.2 0.500 192.6 182.2 116.4 81.6 0.550 198.4 187.8 121.0 84.9 0.600 204.4 193.5 125.6 88.1 0.650 210.5 199.3 130.0 91.2 0.700 216.8 205.2 134.1 94.0 0.750 223.4 211.3 138.0 96.5 0.800 230.2 217.6 141.7 98.8 0.850 237.5 224.2 145.3 101.2 0.900 245.4 231.2 149.3 104.0 0.950 253.8 238.6 153.4 106.9 1.000 262.8 246.5 156.3 108.0

[0093] [Numerical Example 7] Normalized phase W1 W2 Wref1 Wref2 0.000 102.9 113.5 43.5 0.050 111.6 124.0 66.5 0.100 119.3 132.6 82.2 0.150 126.2 140.1 94.2 0.200 132.6 146.9 104.0 0.250 138.6 153.2 112.6 0.300 144.3 159.3 120.2 0.350 149.8 165.2 127.1 0.400 155.1 170.9 133.4 0.450 160.3 176.6 139.3 0.500 165.4 182.2 145.0 0.550 170.5 187.8 150.4 0.600 204.4 175.6 193.5 155.8 0.650 210.5 199.3 161.0 0.700 216.8 205.2 166.2 0.750 223.4 211.3 171.2 0.800 230.2 217.6 176.2 0.850 237.5 224.2 181.2 0.900 245.4 231.2 186.3 0.950 253.8 238.6 191.6 1.000 262.8 246.5 196.5

[0094] [Numerical Example 8] Normalized phase W1 W2 Wref1 Wref2 0.000 62.5 101.0 32.4 0.050 68.7 109.5 45.0 0.100 74.4 116.6 54.2 0.150 79.5 122.8 61.5 0.200 84.2 128.6 67.9 0.250 88.6 134.0 73.6 0.300 92.7 139.1 78.8 0.350 96.6 144.1 83.6 0.400 100.2 149.0 88.0 0.450 103.8 153.9 92.2 0.500 107.1 158.7 96.0 0.550 110.3 163.6 99.7 0.600 113.5 168.6 103.3 0.650 116.5 173.7 106.7 0.700 184.1 119.5 179.0 109.9 0.750 189.9 184.5 113.1 0.800 196.1 190.4 116.1 0.850 202.8 196.7 119.0 0.900 210.2 203.4 122.0 0.950 218.3 210.9 124.9 1.000 227.2 219.0 127.6

[0095] [Numerical Example 9] Segment Structure Shape Pitch WW' Aspect Ratio 1 type1 240 175.2 - 10.1 2 type1 240 175.2 - 10.1 3 type1 240 172.8 - 10.4 4 type1 240 172.8 - 4.6 5 type1 240 170.4 - 4.7 6 type1 240 168.0 - 4.8 7 type1 240 165.6 - 4.8 8 type1 240 163.2 - 4.9 9 type1 240 160.8 - 5.0 10 type4 240 216.0 - 3.7 11 type4 240 216.0 - 3.7 12 type4 240 213.6 - 3.7 13 type3 240 96.0 - 5.6 14 type3 240 110.4 - 6.2 15 type3 240 124.8 - 6.9 16 type3 240 141.6 - 8.1 17 type3 240 156.0 - 9.5 18 type4 240 175.2 - 4.6 19 type4 240 168.0 - 4.8 20 type4 240 158.4 - 5.1 21 type2 240 180.0 72.0 7.4 22 type5 240 128.2 144.0 5.9 23 type3 240 40.8 - 4.0 24 type3 240 216.0 - 33.3 25 type4 240 199.2 - 4.0 26 type5 240 170.9 192.0 4.4 27 type5 240 128.6 192.0 5.0 28 type2 240 208.8 72.0 5.8 29 type6 120 108.0 - 7.4 30 type6 120 103.2 - 7.8 31 type5 240 108.0 144.0 6.3 32 type6 120 91.2 - 8.8 33 type5 240 38.4 192.0 6.9 34 type2 240 120.0 48.0 11.1 35 type1 240 103.2 - 7.8 36 type1 240 86.4 - 9.3 37 type6 120 97.2 - 8.2 38 type6 120 90.0 - 8.9 39 type6 120 81.6 - 9.8 40 type6 120 72.0 - 11.1 41 type6 120 56.4 - 14.2 42 type1 240 48.0 - 16.7

[0096] The various numerical values ​​in each example are summarized in Tables 1 to 3 below.

[0097] [Table 1]

[0098] [Table 2]

[0099] [Table 3]

[0100] [Optical system] Next, an example of an optical system including the optical elements of each embodiment will be described with reference to FIG. 14. In FIG. 14, 100 denotes the optical element of each embodiment, 102 denotes the optical element, OA denotes the optical axis, IP denotes the image plane, and 3 denotes the optical system including the optical element of each embodiment. The optical element 102 is composed of a refractive lens, a diffractive optical element, a mirror, a prism, or the like, and may consist of one or more elements. The optical elements 100 and 102 are arranged along the optical axis OA, and incident light is imaged onto the imaging plane IP. By arranging a structure 21 on the image-side surface of the optical element 100, optical effects such as focusing, divergence, and polarization are obtained.

[0101] [Imaging device] Next, with reference to FIG. 15 , a digital still camera (image capture device) using an optical system including the optical element of each embodiment as an image capture optical system will be described. FIG. 15 is an explanatory diagram of an image capture device 6 equipped with an optical system including the optical element of each embodiment. In FIG. 15 , 4 denotes a camera body, and 3 denotes an optical system including the optical element 100 according to each embodiment. 5 denotes an image capture element (photoelectric conversion element) such as a CCD sensor or CMOS sensor that is built into the camera body 4 and receives and photoelectrically converts an optical image formed by the optical system 3. The camera body 4 may be a so-called single-lens reflex camera having a quick-return mirror, or a so-called mirrorless camera without a quick-return mirror. In this way, by applying an optical system including the optical element 100 according to each embodiment to an image capture device such as a digital still camera, an image capture device with a small lens can be obtained.

[0102] The imaging device according to the present embodiment is assumed to be an integrated lens camera in which the camera body 4 and the optical system 3 including the optical element 100 of each example are integrated, but may also 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 serving as the imaging device may be employed. Furthermore, the optical systems of each example are not limited to the imaging devices described above, and can be applied to various optical devices such as silver halide film cameras, digital video cameras, telescopes, binoculars, and projectors (projection devices).

[0103] Although the preferred embodiments of the present invention have been described above, the present invention is not limited to these embodiments, and various combinations, modifications, and alterations are possible within the scope of the gist of the present invention.

[0104] The optical element 100 according to each embodiment has the effect of focusing incident light by gradually decreasing the diameter of the structures 21 from the center to the periphery of the substrate 1 within the annular zone. The present invention is not limited to this, and the optical element 100 may have the effect of diverging incident light by gradually increasing the diameter of the structures 21 from the center to the periphery of the substrate 1 within the annular zone. Furthermore, although the optical elements exhibiting focusing or diverging effects have been described in each embodiment, the effects exhibited by the optical element according to the present invention are not limited to these, and the optical element may have other optical effects such as polarization.

[0105] In the optical element 100, the structures 21 may have a concave shape. When the structures 21 have a concave shape, it becomes easier to perform surface treatment such as anti-reflection on the surface of the optical element 100. When the structures 21 have a concave shape, each of the structures 21 refers to a structure including a side surface and a bottom surface that form the space of the recess. In this case, the height of the structure is the height of the recess, and the width of the structure is the width of the recess.

[0106] In the optical element 100, an underlayer may be formed on the substrate 1. By forming the structures 212 on the underlayer, it is possible to increase the diameter of the structures 212 and reduce the aspect ratio of the structures 212. Note that all of the structures 212 may be formed on the underlayer, or only some of the structures 212 may be formed on the underlayer.

[0107] In the optical element 100, it is preferable that the height of the structures 212 is lower than the height of the structures 211. By lowering the height of the structures 212 arranged in the region 2 where the amount of phase change is relatively small within the annular zone, it is possible to increase the diameter of the structures 212 and reduce the aspect ratio of the structures 212. Note that the height of all the structures 212 may be low, or only some of the structures 212 may be low.

[0108] The disclosure of each embodiment includes the following configuration.

[0109] (Configuration 1) An optical element having a plurality of concentrically arranged ring zones, The phase difference generated by each of the plurality of annular zones is 2nπ (n is an integer), a first zone of the plurality of zones includes first and second groups of structures arranged in a radial direction; the first structure group includes three or more structures arranged at a first interval in the radial direction, the second structure group includes three or more structures arranged at second intervals in the radial direction, the second spacing is smaller than the first spacing; An optical element, wherein the phase difference caused by each of the first and second structure groups is not 2nπ.

[0110] (Configuration 2) 2. The optical element according to configuration 1, wherein the structures included in the first and second structure groups have different widths in the radial direction.

[0111] (Configuration 3) When the first interval is P1 and the second interval is P2, 1.2≦P1 / P2≦8.0 3. The optical element according to configuration 1 or 2, wherein the following condition is satisfied:

[0112] (Configuration 4) When the second interval is P2 and the design wavelength is λ0, 0.10≦P2 / λ0≦0.80 4. The optical element according to any one of configurations 1 to 3, wherein the following condition is satisfied:

[0113] (Configuration 5) When the effective Abbe number of the optical element with respect to the d-line is νdef, 0.0≦|1 / νdef|≦0.1 5. The optical element according to any one of configurations 1 to 4, wherein the following condition is satisfied:

[0114] (Configuration 6) A substrate and an underlayer formed on the substrate, An optical element described in any one of configurations 1 to 5, characterized in that at least one of the structures included in the first and second structure groups is disposed on the underlayer.

[0115] (Configuration 7) When the minimum value of the height of the structures included in the first structure group is H1min and the maximum value of the height of the structures included in the second structure group is H2max, 0.05≦H2max / H1min≦0.95 7. The optical element according to any one of configurations 1 to 6, wherein the following condition is satisfied:

[0116] (Configuration 8) When the minimum width of the structures included in the first structure group is Wmin1 and the maximum width of the structures included in the second structure group is Wmax2, 0.10≦Wmax2 / Wmin1<1.00 8. The optical element according to any one of configurations 1 to 7, wherein the following condition is satisfied:

[0117] (Configuration 9) When the first interval is P1, the second interval is P2, the difference between the maximum width and the minimum width of the structures included in the first structure group is ΔW1, and the difference between the maximum width and the minimum width of the structures included in the second structure group is ΔW2, 0.05≦ΔW1 / P1≦0.80 0.05≦ΔW2 / P2≦0.80 9. The optical element according to any one of configurations 1 to 8, wherein the following condition is satisfied:

[0118] (Configuration 10) When the minimum value of the packing rate of the structures included in the first structure group is V1min and the maximum value of the packing rate of the structures included in the second structure group is V2max, 1.0 <V2max / V1min≦4.0 10. The optical element according to any one of configurations 1 to 9, wherein the following condition is satisfied:

[0119] (Configuration 11) the first annular zone includes a first region in which the first structure group is arranged and a second region in which the second structure group is arranged, When the design diffraction order is n and the normalized phase at the boundary between the first region and the second region is E, 0.05≦E / n≦0.90 11. The optical element according to any one of configurations 1 to 10, wherein the following condition is satisfied:

[0120] (Configuration 12) When the maximum value of the height of the structures included in the first structure group and the second structure group is Hmax, 0.05≦(P1-P2) / Hmax≦0.60 12. The optical element according to any one of configurations 1 to 11, wherein the following condition is satisfied:

[0121] (Configuration 13) the first structure group and the second structure group are disposed on a surface of a substrate; When the maximum value of the height of the structures included in the first structure group and the second structure group is Hmax and the thickness of the substrate in the direction perpendicular to the surface is t, 0.0 <Hmax / t≦0.1 13. The optical element according to any one of configurations 1 to 12, wherein the following condition is satisfied:

[0122] (Configuration 14) When the minimum width of the structures included in the first structure group is Wmin1, the maximum width of the structures included in the first structure group is Wmax1, the minimum width of the structures included in the second structure group is Wmin2, and the maximum width of the structures included in the second structure group is Wmax2, 1.05≦Wmax1 / Wmin1≦10.00 1.05≦Wmax2 / Wmin2≦10.00 14. The optical element according to any one of configurations 1 to 13, wherein the following condition is satisfied:

[0123] (Configuration 15) When the phase modulation amount of the structure having the smallest width among the structures included in the first structure group is D1 and the phase modulation amount of the structure having the largest width among the structures included in the second structure group is D2, 0.9 <D1 / D2<1.1 15. The optical element according to any one of configurations 1 to 14, wherein the following condition is satisfied:

[0124] (Configuration 16) When the first interval is P1, the second interval is P2, and j is a natural number greater than 1, P1=j×P2 16. The optical element according to any one of configurations 1 to 15, wherein the following condition is satisfied:

[0125] (Configuration 17) An optical system comprising a plurality of optical elements including the optical element according to any one of configurations 1 to 16.

[0126] (Configuration 18) 18. An imaging device comprising the optical system according to aspect 17 and an imaging element that receives an image formed by the optical system.

[0127] (Method 1) A method of manufacturing an optical element having a plurality of concentrically arranged ring zones, comprising the steps of: providing a first material on a surface of a substrate; providing a second material over the first material; and pressing a mold against the second material to form first and second structure groups made of the first material, The phase difference generated by each of the plurality of annular zones is 2nπ (n is an integer), the first and second structure groups are included in a first zone among the plurality of zones and are arranged sequentially in a radial direction; the first structure group includes three or more structures arranged at a first interval in the radial direction, the second structure group includes three or more structures arranged at second intervals in the radial direction, the second spacing is smaller than the first spacing; A method for manufacturing an optical element, wherein the phase difference caused by each of the first and second structure groups is not 2nπ. [Explanation of symbols]

[0128] 100 Optical Elements 211 First Structure Group 212 Second Structure Group P1 First interval P2 Second interval

Claims

1. An optical element having a plurality of concentrically arranged ring zones, The phase difference generated by each of the plurality of annular zones is 2nπ (n is an integer), a first zone of the plurality of zones includes first and second groups of structures arranged in a radial direction; the first structure group includes three or more structures arranged at a first interval in the radial direction, the second structure group includes three or more structures arranged at second intervals in the radial direction, the second spacing is smaller than the first spacing; An optical element, wherein the phase difference caused by each of the first and second structure groups is not 2nπ.

2. 2. The optical element according to claim 1, wherein the structures included in the first and second structure groups have different widths in the radial direction.

3. When the first interval is P1 and the second interval is P2, 1.2≦P1 / P2≦8.0 2. The optical element according to claim 1, wherein the following condition is satisfied:

4. When the second interval is P2 and the design wavelength is λ0, 0.10≦P2 / λ0≦0.80 2. The optical element according to claim 1, wherein the following condition is satisfied:

5. When the effective Abbe number of the optical element with respect to the d-line is νdef, 0.0≦|1 / νdef|≦0.1 2. The optical element according to claim 1, wherein the following condition is satisfied:

6. A substrate and an underlayer formed on the substrate, 2. The optical element according to claim 1, wherein at least one of the structures included in the first and second structure groups is disposed on the underlayer.

7. When the minimum value of the height of the structures included in the first structure group is H1min and the maximum value of the height of the structures included in the second structure group is H2max, 0.05≦H2max / H1min≦0.95 2. The optical element according to claim 1, wherein the following condition is satisfied:

8. When the minimum width of the structures included in the first structure group is Wmin1 and the maximum width of the structures included in the second structure group is Wmax2, 0.10≦Wmax2 / Wmin1<1.00 2. The optical element according to claim 1, wherein the following condition is satisfied:

9. When the first interval is P1, the second interval is P2, the difference between the maximum width and the minimum width of the structures included in the first structure group is ΔW1, and the difference between the maximum width and the minimum width of the structures included in the second structure group is ΔW2, 0.05≦ΔW1 / P1≦0.80 0.05≦ΔW2 / P2≦0.80 2. The optical element according to claim 1, wherein the following condition is satisfied:

10. When the minimum value of the packing rate of the structures included in the first structure group is V1min and the maximum value of the packing rate of the structures included in the second structure group is V2max, 1.0<V2max / V1min≦4.0 2. The optical element according to claim 1, wherein the following condition is satisfied:

11. the first annular zone includes a first region in which the first structure group is arranged and a second region in which the second structure group is arranged, When the design diffraction order is n and the normalized phase at the boundary between the first region and the second region is E, 0.05≦E / n≦0.90 2. The optical element according to claim 1, wherein the following condition is satisfied:

12. When the maximum value of the height of the structures included in the first structure group and the second structure group is Hmax, 0.05≦(P1-P2) / Hmax≦0.60 2. The optical element according to claim 1, wherein the following condition is satisfied:

13. the first structure group and the second structure group are disposed on a surface of a substrate; When the maximum value of the height of the structures included in the first structure group and the second structure group is Hmax and the thickness of the substrate in the direction perpendicular to the surface is t, 0.0<Hmax / t≦0.1 2. The optical element according to claim 1, wherein the following condition is satisfied:

14. When the minimum width of the structures included in the first structure group is Wmin1, the maximum width of the structures included in the first structure group is Wmax1, the minimum width of the structures included in the second structure group is Wmin2, and the maximum width of the structures included in the second structure group is Wmax2, 1.05≦Wmax1 / Wmin1≦10.00 1.05≦Wmax2 / Wmin2≦10.00 14. The optical element according to claim 1, wherein the following condition is satisfied:

15. An optical system comprising a plurality of optical elements including the optical element according to claim 14.

16. 16. An imaging device comprising: the optical system according to claim 15; and an imaging element that receives an image formed by the optical system.

17. A method of manufacturing an optical element having a plurality of concentrically arranged ring zones, comprising the steps of: providing a first material on a surface of a substrate; providing a second material over the first material; and pressing a mold against the second material to form first and second structure groups made of the first material, The phase difference generated by each of the plurality of annular zones is 2nπ (n is an integer), the first and second structure groups are included in a first zone among the plurality of zones and are arranged in order in the radial direction; the first structure group includes three or more structures arranged at a first interval in the radial direction, the second structure group includes three or more structures arranged at second intervals in the radial direction, the second spacing is smaller than the first spacing; A method for manufacturing an optical element, wherein the phase difference caused by each of the first and second structure groups is not 2nπ.

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