Optical element, image sensor, optical system, and image pickup device

Abstract

The present disclosure relates to optical elements, image sensors, optical systems, and image pickup apparatuses. An optical element can include a substrate and a concavo-convex structure formed on the substrate. The concavo-convex structure can have a periodic arrangement and include a plurality of structures of at least one of concave elements and convex elements. A plurality of annular zones arranged along a radial direction of the substrate can be formed on the substrate. Each of the plurality of annular zones can include a first region and a second region having a phase smaller than that of the first region along the radial direction. The plurality of structures can include a plurality of first structures disposed in the first region and a plurality of second structures disposed in the second region. A base layer can be provided between the substrate and at least one of the plurality of second structures.

Description

Technical Field

[0001] This disclosure relates to optical elements, image sensors, optical systems, and image acquisition devices. Background Technology

[0002] In some conventional structures used for optical elements (superlenses), the optical element has a finely textured surface (uneven or undulating structure) formed on the surface of a substrate, and a thin film is laminated on the finely textured surface to suppress the reflectivity of incident light by utilizing the light-converging or diverging function of diffraction (see U.S. Patent Application Publication No. 2024 / 0012177). Summary of the Invention

[0003] An optical element according to one aspect of this disclosure may include a substrate and an uneven structure formed on the substrate. The uneven structure may have multiple structures arranged periodically and including at least one of recessed elements and protruding elements. Multiple annular bands arranged along a radial direction of the substrate may be formed on the substrate. Each of the multiple annular bands may include a first region and a second region having a phase smaller than that of the first region along the radial direction. The multiple structures may include multiple first structures disposed in the first region and multiple second structures disposed in the second region. A base layer may be provided between the substrate and at least one of the multiple second structures. Image sensors, optical systems, and image acquisition devices all having the above-described optical elements also constitute other aspects of this disclosure.

[0004] Referring to the accompanying drawings, the features of this disclosure will become clear from the following description of embodiments. The following description of embodiments is by way of example. Attached Figure Description

[0005] Figures 1A to 1C It is a structural diagram of the optical element based on Example 1.

[0006] Figure 2A and Figure 2B It is a structural diagram of the optical element based on the comparative example.

[0007] Figure 3A and Figure 3B This is an explanation diagram of the component fill factor.

[0008] Figure 4 The diagram illustrates the relationship between the normalized phase modulation amount and reflectivity of the concave and convex elements in Example 1 and the comparative example.

[0009] Figure 5A , Figure 5B and Figure 5C This is an explanatory diagram of a method used to manufacture optical components.

[0010] Figure 6 This is an explanation diagram of the offset layer.

[0011] Figure 7A and Figure 7B It is a structural diagram of the optical element based on Example 2.

[0012] Figure 8 The diagram illustrates the relationship between the normalized phase modulation amount and reflectivity of the concave and convex elements in Example 2 and the comparative example.

[0013] Figure 9 The diagram illustrates the relationship between the normalized phase modulation amount and reflectivity of the concave and convex elements in Example 3 and the comparative example.

[0014] Figure 10A and Figure 10B It is based on the structural diagram of the optical element in Example 4.

[0015] Figure 11 The diagram illustrates the relationship between the normalized phase modulation amount and reflectivity of the concave and convex elements in Example 4 and the comparative example.

[0016] Figure 12A , Figure 12B , Figure 12C and Figure 12D This is an explanatory diagram illustrating a modified example of a bump / concave element.

[0017] Figure 13 This is an explanatory diagram of an optical system including optical elements according to each example.

[0018] Figure 14 This is an explanatory diagram of an image pickup device including optical elements according to any one of the examples. Detailed Implementation

[0019] A detailed description of examples according to this disclosure will now be given with reference to the accompanying drawings. Corresponding elements in the various drawings will be designated by the same reference numerals, and repeated descriptions thereof will be omitted.

[0020] Example 1

[0021] Figure 1A and Figure 1B This is a structural diagram of the optical element 100 according to this example. Figure 1A This is an enlarged cross-sectional view of the optical element 100 when viewed from the y-axis direction (in the xz plane). Figure 1B This is a magnified top view of the optical element 100 when viewed from the z-axis direction (optical axis direction) (in the xy plane). Figure 1C This is a top view of the optical element 100 as seen from the z-axis direction. In each example, the optical axis direction of the optical element and the thickness direction of the substrate 1 are aligned with the z-axis direction.

[0022] The optical element 100 includes a substrate 1 and an uneven structure (a plurality of pillars) 2 formed on the substrate 1. In this example, the substrate 1 is a transparent plate made of synthetic quartz with a thickness of 0.775 mm. The substrate 1 may alternatively be a plane mirror that reflects incident light, or may have a curved surface with arbitrary curvature. The material of the substrate 1 is not limited to synthetic quartz, and may be inorganic glass, organic materials such as plastics, ceramics, or metals.

[0023] The concave-convex structure 2 includes a plurality of concave-convex elements (a plurality of structures) 21, which include at least one of recessed elements and protruding elements periodically arranged in the radial direction (e.g., the x-axis and y-axis directions) of the substrate 1 (optical element 100), and a base layer 22 having a substantially constant thickness (approximately flat plate shape) in the thickness direction. A plurality of annular bands (ring regions) are formed on the substrate 1 to extend circumferentially from the center of the optical element 100 and to be arranged in the radial direction. By forming periodic phase differences (ring bands) along the radial direction of the substrate 1, the incident light is given focusing or diverging effect and polarization effect. The plurality of annular bands sequentially include an i-th annular band (where i is a natural number, the first annular band) and an (i+1)-th annular band (the second annular band) in the radial direction from the center side of the optical element 100. Each of the plurality of annular bands includes a region R1 (the first region) and a region R2 (the second region) having a phase smaller than that of region R1 in the radial direction. More specifically, region R1 is the region where the phase is greater than a predetermined normalized phase, while region R2 is the region where the phase is less than the predetermined normalized phase. In this example, in the radial direction, region R1 is positioned closer to the center of the optical element 100 than region R2.

[0024] The optical element 100 according to this example has positive refractive power and provides focusing effect on incident light. However, in the case of an optical element with negative refractive power, the ring zone sequentially includes a region R2 (second region) and a region R1 (first region) with smaller phase from the center side of the optical element.

[0025] Although multiple rings are arranged concentrically in the xy plane, a structure can also be adopted in which rings are provided only in one of the x-axis and y-axis directions.

[0026] The raised / lowered element 21 includes a plurality of first structures 215 deployed in region R1 and a plurality of second structures 216 deployed in region R2. In region R2, the plurality of second structures 216 are formed on substrate 1 via a base layer 22. In region R1, the plurality of first structures 215 are formed directly on substrate 1 without a base layer 22. The plurality of first structures 215, in the z-axis direction from the substrate 1 side, sequentially include a region H1 (third region) with a constant radial width and a region H2 (fourth region) with a radial width that gradually decreases with increasing distance from substrate 1. That is, the element fill factor of region H2, described later, is lower than that of region H1. The plurality of first structures 215 have mutually different radial widths. Similarly, the plurality of second structures 216 have mutually different radial widths.

[0027] The concave-convex structure 2 provides focusing or diverging effects by imparting a phase difference to the light passing through it. By imparting different phase differences in the x-axis and y-axis directions, the polarization state can be changed, or different focusing or diverging effects can be provided for each incident polarization. This is achieved by using concentrically repeated periodic structures... The rings of phase differences (n is an integer of 1, 2, ... and represents the design diffraction order or diffraction class) form a phase distribution, which can achieve a focusing or diverging effect at the design wavelength that is essentially equivalent to the focusing or diverging effect of the diffractive optical element.

[0028] In this example, the bump element 21 is a protruding cylindrical element made of the dielectric material Si3N4. The bump element 21 is not limited to a protruding cylindrical element, but can be a polygonal prism, a polygonal pyramid, a cone, an arbitrary recessed element, or a combination thereof. The material of the bump element 21 can be GaN, GaP, GaAs, Si, SiC, Al2O3, SiO2, etc.

[0029] The raised / lowered element 21 is positioned at the center of unit segment segments 11, which are divided into square shapes along the radial direction of the substrate 1. When the width (pitch) of each unit segment segment 11 is smaller than the wavelength of the incident light, the incident light is phase-modulated according to the effective refractive index determined from the element fill factor, which is the ratio of the volume occupied by the raised / lowered structure 2 in each unit segment segment 11, regardless of the shape of the raised / lowered element 21. For example, when the wavelength of the incident light is in the visible light range (400 to 700 nm), the pitch can be less than 400 nm. Smaller pitches can be used to suppress unwanted diffraction and reflection.

[0030] In regions R1 and R2 within the i-th annulus, the concave and convex elements 21 have shapes with radial widths that differ from each other, thereby forming within the i-th annulus. The phase distribution. Let R1i and R2i be the radii of regions R1 and R2 of the i-th ring, respectively. For example... Figure 1C As shown, regions R1 and R2 are provided concentrically and alternately along the radial direction, such that R1i < R2i.

[0031] Figure 2A and Figure 2B This is a structural diagram of an optical element 101 based on a comparative example where a base layer is not provided. In order to form within the annular zone... The phase distribution is altered by changing the width (diameter) of the cylindrical element used as the concave-convex element 21, thereby changing the element fill factor of the concave-convex element 21 within each unit segment. That is, as the diameter of the cylindrical element decreases, the element fill factor decreases, thereby forming the desired phase distribution.

[0032] Figure 3A and Figure 3B This is an explanation diagram of the component fill factor. Figure 3A and Figure 3B The element fill factor in regions R1 and R2 is illustrated respectively. Within regions R1 and R2, from the surface of substrate 1 to a position at a height Hm above the surface of substrate 1, the element fill factor is the ratio of the volume Vp of the uneven element 21 to the volume Vs defined by the bottom area P×P and the height Hm. The effective refractive index of the uneven element 21 is approximately expressed by the following equation:

[0033]

[0034] Where n0 is the refractive index of the atmosphere covering the concave-convex element 21, and n m It is the refractive index of the material forming the concave-convex element 21.

[0035] As a rigorous method for calculating the effective refractive index, the effective refractive index can be calculated by the ratio of the phase delay of light passing through the concave-convex element 21 to the phase delay when the element fill factor of the concave-convex element 21 is 1, obtained by the finite-difference time-domain (FDTD) method or rigorous coupled-wave analysis (RCWA).

[0036] exist Figure 2A and Figure 2BIn the optical element 101 shown, the diameter varies significantly because the element fill factor is adjusted only by the diameter of the cylindrical element. Therefore, the difference between the minimum and maximum diameters of the cylindrical element tends to increase, and the amount of change in the element fill factor also increases. When light passes through the optical element 101 in a direction perpendicular to the radial direction, the cylindrical element modulates the phase of the light according to the effective refractive index determined by the element fill factor. When the amount of change in the element fill factor is large, the change in the effective refractive index also tends to be large, and therefore the change in reflectivity in the radial direction increases. Generally, it is known that reflection can be suppressed by providing a thin film such as a transparent dielectric and utilizing interference effects. However, when the change in the effective refractive index in the radial direction is large, it is difficult to obtain an effective interference effect over the entire area simply by providing a thin film with the same structure over the entire optical element, and therefore it is difficult to suppress reflection.

[0037] In region R2, where the diameter of the cylindrical element is relatively small, the effective refractive index of the concave-convex element 21 is low, and the difference in effective refractive index at the interface with the substrate 1 is large, thus increasing reflection. Accordingly, in this example, a base layer 22 is provided between the concave-convex element 21 and the substrate 1 in region R2, and an anti-reflection effect between the concave-convex element 21 and the substrate 1 is obtained by appropriately setting the effective refractive index of the base layer 22. In this example, the base layer 22 is provided between the substrate 1 and each of the plurality of second structures 216, but this disclosure is not limited to this example. The base layer can be provided at locations where the difference in effective refractive index with the substrate 1 becomes larger. That is, the base layer can be provided between the substrate 1 and at least one of the plurality of second structures 216.

[0038] In region R1, where the diameter of the cylindrical element is relatively large, the effective refractive index of the concave-convex element 21 increases, and reflection at the interface between the concave-convex element 21 and the surrounding medium tends to increase. Accordingly, in this example, in region R1, an anti-reflection effect can be achieved by providing a region H2, in a direction perpendicular to the radial direction of the optical element 100, on the side opposite to the substrate 1, where the effective refractive index is lower than that of the concave-convex element 21. For example, in region H2, by gradually decreasing the radius of each cylinder as the distance from the substrate 1 increases, the element fill factor can be reduced, and the effective refractive index can be lowered. In region R2, although region H2 is not provided for the concave-convex element 21, it can still be provided.

[0039] Figure 4 The diagram illustrates the relationship between the normalized phase modulation amount and reflectivity of the concave-convex element 21 in this example and the comparative example. Compared to the comparative example, properly setting the structure of the concave-convex element 21 in regions R1 and R2 in this example can achieve the desired reflectivity. (In this example, n = 1) Reduce reflectivity within the range of phase modulation.

[0040] Next, we will refer to Figure 5A , Figure 5B and Figure 5C A method for manufacturing optical element 100 is described. Optical element 100 can be manufactured using photolithography. Figure 5A , Figure 5B and Figure 5C This is an explanatory diagram illustrating the manufacturing method of optical element 100, and it illustrates the process of manufacturing optical element 100 by nanoimprint lithography. Figure 5A The diagram illustrates mold 31. Mold 31 has a shape obtained by reversing the uneven shape of the uneven element 21 formed by electron beam, laser, photolithography, etc. For example... Figure 5B As shown, a resist material 32 is coated onto a film 33 deposited on a substrate 1, a mold 31 is pressed against the resist material 32, and ultraviolet light or the like is irradiated, thereby forming a shape in the resist material 32 obtained by reversing the uneven shape of the mold 31. Thereafter, as... Figure 5C As shown, the mold 31 is peeled off and development is performed, causing the uneven shape of the resist material 32 to be transferred to the film 33, thereby forming an uneven structure 2 on the substrate 1 of the optical element 100. The method for manufacturing the uneven structure 2 is not limited to nanoimprint lithography, and other methods such as directly forming the uneven structure 2 using an electron beam or laser can also be used. Figure 5A , Figure 5B and Figure 5C In this process, the film 33 and the resist material 32 are in contact with each other; however, a process can be employed to form a layer made of another material between them, ultimately resulting in the uneven structure 2. For example... Figure 5B As shown, it is relatively easy to prepare a material with a uniform film thickness, such as film 33. Therefore, when the uneven structure 2 of regions R1 and R2 is formed based on film 33, the uneven elements 21 of regions R1 and R2 can be made of the same material.

[0041] Figure 6 This is an explanation diagram of offset layer 34. (See diagram below.) Figure 6 As shown, an offset layer 34 can be provided, extending across both regions R1 and R2, instead of... Figure 1A The configuration shown is such that the uneven structure 2 is formed directly on the substrate 1. The offset layer 34 can be considered as part of the substrate 1.

[0042] Here, the specific configuration of the optical element 100 will be described. The concave-convex elements 21 in regions R1 and R2 are respectively deployed in square unit segments 11, each with a side length of 350 nm and a height of 1500 nm. Region H1 has a cylindrical structure with a height of 1200 nm, and region H2 has a structure with a height of 300 nm and a cylinder diameter that gradually decreases with increasing distance from the substrate 1. The diameter at the furthest point from the substrate 1 in region H2 is 0.20 times the diameter of region H1. Region R2 has a structure including a cylindrical base layer 22 with a height of 200 nm that contacts the substrate 1 and cylindrical concave-convex elements 21 with a height of 1300 nm. The effective diameter of the concave-convex structure 2 is... mm, and the concave-convex structure 2 has 63 rings, which repeat periodically at a wavelength of 800 nm. The phase difference. The focal length generated by the concave-convex structure 2 is 40.0 mm, and the effective Abbe number is... -3.452 indicates that the concave-convex structure 2 has a wavelength dispersion equivalent to that of a diffractive optical element. When the position with a normalized phase of 0.265 is set as the boundary between regions R1 and R2 within the annular zone, the maximum reflectivity when light of wavelength 800 nm is incident perpendicularly is 0.6% in region R1 and 1.1% in region R2. Compared to the 3.6% maximum reflectivity in the comparative example where the cylindrical concave-convex element 21 is provided throughout the optical element 101, the reflectivity can be suppressed.

[0043] Next, the configurations that the optical element 100 can satisfy will be described.

[0044] The second structure 216 and the base layer 22 can be made of the same material. This simplifies the manufacturing process and makes manufacturing easier. Conversely, if the second structure 216 and the base layer 22 are made of different materials, performing the processes for forming the base layer 22 and the second structure 216 separately increases the manufacturing difficulty.

[0045] The substrate 1 and the base layer 22 can be made of the same material. Thus, the optical element 100 can include two materials, namely the second structure 216 and the substrate 1, while simultaneously achieving an anti-reflective effect in region R2. When the substrate 1 and the base layer 22 are made of different materials, the processes for forming the base layer 22 and the processes for forming the second structure 216 are performed separately, which increases the manufacturing complexity.

[0046] Next, the conditions that the optical element 100 can satisfy will be described. The optical element 100 can satisfy at least one of the inequalities (1) to (16).

[0047]

[0048]

[0049] Here, V2 is the element fill factor of the base layer 22 in region R2 from substrate 1 to height Hs. ns is the refractive index of substrate 1. neff2 is the effective refractive index of base layer 22. nm2 is the effective refractive index of the second structure 216. The effective refractive index of the second structure 216 varies depending on the position, but in inequality (3), it is set to the minimum value of the effective refractive index of the second structure 216. Hs is the height of base layer 22 in the direction perpendicular to the radial direction. Hm is the height of the second structure 216 in the direction perpendicular to the radial direction. V3 is the element fill factor of region H1. The element fill factor of region H1 varies depending on the position, but in inequality (5), it is set to the maximum value of the element fill factor of region H1. V4 is the element fill factor of region H2. The element fill factor of region H2 varies depending on the position, but in inequality (5), it is set to the maximum value of the element fill factor of region H1. neff1 is the effective refractive index of region H2. The effective refractive index of region H2 varies depending on its position, but in inequality (6), it is set to the minimum effective refractive index of region H2. nm1 is the effective refractive index of the first structure 215. The effective refractive index of the first structure 215 varies depending on its position, but in inequality (6), it is set to the minimum effective refractive index of the first structure 215. Hmax is the maximum height of the first structure 215 in the direction perpendicular to the radial direction of the optical element 100. Hmin is the minimum height of the second structure 216 in the direction perpendicular to the radial direction of the optical element 100. W1max is the maximum diameter of the first structure 215 in the radial direction. W1min is the minimum diameter of the first structure 215 in the radial direction. W2max is the maximum diameter of the second structure 216 in the radial direction. W2min is the minimum diameter of the second structure 216 in the radial direction. E is the normalized phase at the boundary between regions R1 and R2 in the same annulus. n is the designed diffraction order. P is the period of the concave-convex structure 2. This is the reference wavelength used when calculating the normalized phase. Ha is the height of region H2 in the direction perpendicular to the radial direction. Hm is the height of the bump element 21. t is the thickness of substrate 1 in the optical axis direction. It is the difference between the maximum and minimum widths of the concave and convex structures 2 in region R1. It is the difference between the maximum and minimum widths of the concave and convex structures 2 in region R2.

[0050] Inequality (1) defines the appropriate shape of the base layer 22. Properly setting the element fill rate of the base layer 22 can adjust its effective refractive index. This suppresses reflection at the interface with the substrate 1 in region R2. When the effective refractive index of the base layer 22 becomes relatively low and V2 becomes below the lower limit of inequality (1), the difference between the refractive index of the substrate 1 and the effective refractive index of the base layer 22 becomes large, and reflection becomes difficult to suppress. When the effective refractive index of the base layer 22 becomes relatively high and V2 becomes above the upper limit of inequality (1), the difference between its refractive index and that of the substrate 1 will be small or greater than the refractive index of the substrate 1, and reflection becomes difficult to suppress.

[0051] Inequality (2) defines the appropriate effective refractive index of the base layer 22. Satisfying inequality (2) can suppress reflection at the interface between the concave-convex element 21 and the substrate 1 in region R2. The effective refractive index of the base layer 22 becomes too small relative to the refractive index of the substrate 1, and... If the refractive index becomes lower than the lower limit of inequality (2), reflection will increase due to the difference in refractive index between the two. When the effective refractive index of the base layer 22 becomes too large relative to the refractive index of the substrate 1, and If the refractive index difference between the two becomes higher than the upper limit of inequality (2), the effective refractive index of the base layer 22 will be higher and the reflection cannot be suppressed.

[0052] Inequality (3) relates to the effective refractive index of the base layer 22. Satisfying inequality (3) can suppress reflections at the interface between the concave-convex element 21 and the substrate 1 in region R2. When the refractive index difference between the concave and convex elements and the base layer becomes too large, it becomes difficult to suppress reflection at their interface. When the effective refractive index of the concave-convex element becomes higher than the upper limit of inequality (3), it becomes relatively large and becomes difficult to suppress the reflection between the concave-convex element and the atmosphere.

[0053] Inequality (4) defines the appropriate shape of the concave-convex element 21. Satisfying inequality (4) allows full utilization of the interference effect of the base layer 22, thereby producing an anti-reflection effect. When Hs / Hm becomes lower than the lower limit of inequality (4), the height of the base layer 22 becomes too low, and it becomes difficult to reduce reflectivity through interference. When Hs / Hm becomes higher than the upper limit of inequality (4), the height of the base layer 22 becomes too high, and it becomes difficult to achieve a reflection suppression effect at the interface between the concave-convex element 21 and the substrate 1.

[0054] Inequality (5) defines the appropriate shape of the first structure 215. When the effective refractive index of region H2 becomes relatively too small and V4 / V3 becomes below the lower limit of inequality (5), it becomes difficult to suppress reflection at the interface between regions H1 and H2. When the effective refractive index of region H2 becomes relatively too large and V4 / V3 becomes above the upper limit of inequality (5), it becomes difficult to suppress reflection at the boundary between the atmosphere and region H2.

[0055] Inequality (6) defines the appropriate effective refractive index of the first structure 215. The effective refractive index in region H2 becomes too small relative to the effective refractive index of the first structure 215 and When the effective refractive index becomes below the lower limit of inequality (6), reflection occurs due to the difference in refractive index between the two. In region H2, the effective refractive index becomes too large relative to the effective refractive index of the first structure 215, and If the refractive index difference between the two becomes smaller than the upper limit of inequality (6), or the effective refractive index of region H2 becomes higher and the reflection in region R1 cannot be suppressed.

[0056] Inequality (7) defines the proper shape of the first structure 215 and the second structure 216. When the height of the first structure 215 and the second structure 216 changes such that Hmin / Hmax becomes lower than the lower limit of inequality (7) or higher than its upper limit, it becomes necessary to form the first structure 215 and the second structure 216 in multiple steps, which complicates the manufacturing process.

[0057] Inequality (8) defines the appropriate shape of region R1. When the minimum diameter of the first structure 215 becomes relatively small and W1min / W1max becomes lower than the lower limit of inequality (8), the first structure 215 will be damaged by slight loads, temperatures, pressures, etc., and the anti-reflection effect of the optical element 100 will not be fully realized. When W1min / W1max becomes higher than the upper limit of inequality (8), a slight change in the width of the concave-convex element 21 will cause a relatively large phase modulation, which will increase the impact of manufacturing variations when forming the concave-convex structure 2, and manufacturing will become difficult.

[0058] Inequality (9) defines the appropriate shape of region R2. If the minimum diameter of the second structure 216 becomes relatively small and W2min / W2max becomes below the lower limit of inequality (9), the first structure 215 will be damaged by slight load, temperature, or pressure, and the anti-reflective effect of the optical element 100 will not be fully achieved. If W2min / W2max becomes above the upper limit of inequality (9), a slight change in the width of the concave-convex element 21 will cause a relatively large phase modulation, and the effects of manufacturing variations when forming the concave-convex structure 2 will be significant, making manufacturing difficult.

[0059] Inequality (10) defines the proper arrangement of regions R1 and R2. When the phase modulation in region R1 becomes relatively large and E / n becomes lower than the lower limit of inequality (10), the proportion of region R2 to the entire area of ​​optical element 100 will become smaller, and the reflection / diffraction suppression effect of the concave-convex structure 2 will not be fully achieved. When the phase modulation in region R2 becomes relatively large and E / n becomes higher than the upper limit of inequality (10), the width of the second structure needs to be significantly changed, which increases the aspect ratio of the second structure 216, and the structure becomes more susceptible to collapse due to external factors.

[0060] Inequality (11) defines the proper configuration of the second structure 216. The pitch of the second structure 216 becomes relatively small and When the aspect ratio falls below the lower limit of inequality (11), manufacturing becomes more difficult. In the second structure 216, the pitch becomes relatively large and... If the pitch becomes higher than the upper limit of inequality (11), it is impossible to make the pitch small enough relative to the wavelength of the incident light, and it is impossible to achieve the effect of suppressing reflection diffraction by means of the concave-convex element 21.

[0061] Inequality (12) defines the appropriate shape of the concave-convex element 21. The height of the base layer 22 becomes relatively low and... When the value falls below the lower limit of inequality (12), it becomes difficult to reduce the reflectivity due to interference. The height of the base layer 22 becomes relatively high and... When the value exceeds the upper limit of inequality (12), it becomes difficult to achieve the effect of suppressing reflection at the interface between the concave and convex elements 21 and the substrate 1.

[0062] Inequality (13) defines the appropriate shape of the concave-convex element 21. The effective refractive index becomes relatively small in region H2 and When the value falls below the lower limit of inequality (13), it becomes difficult to suppress reflection at the interface between regions H1 and H2. The effective refractive index of region H2 becomes relatively large and When the value of the equation (13) is higher than the upper limit, it becomes difficult to suppress the reflection at the boundary between the surrounding environment and region H2.

[0063] Inequality (14) defines the appropriate shape of the optical element 100. The height Hm of the concave-convex element 21 and the thickness t of the substrate 1 are both numerical values ​​representing length and are greater than zero. Therefore, Hm / t will not fall below the lower limit of inequality (14). If the thickness of the substrate 1 becomes relatively thin and Hm / t becomes higher than the upper limit of inequality (14), deformation due to the weight of the substrate cannot be suppressed when the substrate is held by the holding member, or deformation of the substrate 1 may occur during photolithography.

[0064] Inequality (15) defines the appropriate shape of the concave-convex structure 2. The phase modulation amount in region R2 becomes relatively large and When the width of the concave-convex structure 2 falls below the lower limit of inequality (15), it becomes necessary to significantly alter the width, resulting in a large aspect ratio and compromised robustness. The phase modulation amount in region R1 becomes relatively large and When the region R2 becomes higher than the upper limit of inequality (15), the proportion of region R2 relative to the entire optical element 100 becomes smaller, and it becomes difficult to adequately suppress reflection diffraction.

[0065] Inequality (16) defines the appropriate shape of the concave-convex structure. The phase modulation amount in region R1 becomes relatively large and When the region R2 falls below the lower limit of inequality (16), the proportion of region R2 relative to the entire optical element 100 decreases, and it becomes difficult to adequately suppress reflection diffraction. The phase modulation amount in region R2 becomes relatively large and When the width of the concave-convex structure 2 becomes higher than the upper limit of inequality (16), it becomes necessary to significantly change the width of the concave-convex structure 2, resulting in a large aspect ratio and compromised robustness.

[0066] The lower limit of inequality (1) can be set to 0.08, 0.10, 0.12, 0.14, 0.16, 0.18, 0.20, 0.22 or 0.24. The upper limit of inequality (1) can be set to 0.85, 0.80, 0.75, 0.70, 0.66, 0.62, 0.60, 0.59 or 0.58.

[0067] The lower limit of inequality (2) can be set to 0.64, 0.68, 0.72, 0.76, 0.80, 0.84, 0.88, 0.92 or 0.96. The upper limit of inequality (2) can be set to 1.38, 1.32, 1.28, 1.24, 1.18, 1.14, 1.10 or 1.06.

[0068] The lower limit of inequality (3) can be set to 0.05, 0.10, 0.15, 0.20, 0.25, 0.30, 0.35, 0.40, 0.45, 0.50, 0.55, 0.60, 0.65, 0.70, or 0.75. The upper limit of inequality (3) can be set to 0.94, 0.90, 0.88, 0.86, or 0.84.

[0069] The lower limit of inequality (4) can be set to 0.06, 0.07, 0.08, 0.09, 0.10, 0.11, 0.12 or 0.13. The upper limit of inequality (4) can be set to 0.46, 0.42, 0.38, 0.34, 0.30, 0.28, 0.26, 0.24, 0.22, 0.20, 0.18 or 0.16.

[0070] The lower limit of inequality (5) can be set to 0.15, 0.20, 0.25, 0.30, 0.35 or 0.40. The upper limit of inequality (5) can be set to 0.90, 0.85, 0.80, 0.75, 0.70, 0.65, 0.60, 0.50 or 0.45.

[0071] The lower limit of inequality (6) can be set to 0.64, 0.68, 0.72, 0.76, 0.80, 0.84, 0.88, 0.92, 0.94 or 0.96. The upper limit of inequality (6) can be set to 1.36, 1.32, 1.28, 1.24, 1.18, 1.14, 1.10 or 1.06.

[0072] The lower limit of inequality (7) can be set to 0.84, 0.88, 0.90, 0.92, 0.94, 0.96 or 0.98. The upper limit of inequality (7) can be set to 1.16, 1.12, 1.10, 1.08, 1.06 or 1.04.

[0073] The lower limit of inequality (8) can be set to 0.10, 0.15, 0.20, 0.25, 0.30, 0.35, 0.40, 0.45 or 0.50. The upper limit of inequality (8) can be set to 0.90, 0.85, 0.80, 0.75, 0.70 or 0.65.

[0074] The lower limit of inequality (9) can be set to 0.08, 0.10, 0.12, 0.14, 0.15, 0.16, 0.17 or 0.18. The upper limit of inequality (9) can be set to 0.90, 0.85, 0.80, 0.75, 0.70, 0.65, 0.62 or 0.60.

[0075] The lower limit of inequality (10) can be set to 0.06, 0.08, 0.10, 0.12, 0.14, 0.16, 0.18 or 0.20. The upper limit of inequality (10) can be set to 0.80, 0.70, 0.60, 0.50, 0.45, 0.40, 0.36, 0.32, 0.30 or 0.28.

[0076] The lower limit of inequality (11) can be set to 0.12, 0.14, 0.16, 0.18, 0.20, 0.22, 0.24, 0.26, 0.28, 0.30, or 0.32. The upper limit of inequality (11) can be set to 1.10, 1.00, 0.90, 0.80, 0.70, 0.60, 0.55, 0.50, or 0.45.

[0077] The lower limit of inequality (12) can be set to 0.10, 0.12, 0.14, 0.16, 0.18 or 0.20. The upper limit of inequality (12) can be set to 0.88, 0.86, 0.84, 0.82, 0.80, 0.78 or 0.76.

[0078] The lower limit of inequality (13) can be set to 0.08, 0.10, 0.12, 0.14, 0.16, 0.18, 0.20, 0.22, 0.24, 0.26, 0.28 or 0.30. The upper limit of inequality (13) can be set to 0.88, 0.86, 0.84, 0.82, 0.80, 0.79, 0.78, 0.77 or 0.76.

[0079] The lower limit of inequality (14) can be set to 0.0001, 0.0004, 0.0008 or 0.001. The upper limit of inequality (14) can be set to 0.05, 0.01, 0.008, 0.005 or 0.002.

[0080] The lower limit of inequality (15) can be set to 0.06, 0.07, 0.08, 0.09, 0.10, 0.14, 0.18 or 0.20. The upper limit of inequality (15) can be set to 0.70, 0.65, 0.60, 0.55 or 0.50.

[0081] The lower limit of inequality (16) can be set to 0.06, 0.08, 0.10, 0.12, 0.14, 0.16, 0.18, 0.20, 0.22 or 0.24. The upper limit of inequality (16) can be set to 0.70, 0.65, 0.60, 0.55 or 0.50.

[0082] Example 2

[0083] Figure 7Aand Figure 7B This is a structural diagram of the optical element 102 according to this example. Figure 7A This is an enlarged cross-sectional view of the optical element 102 when viewed from the y-axis direction (in the xz plane). Figure 7B This is a magnified top view of the optical element 102 when viewed from the z-axis direction (optical axis direction) (in the xy plane).

[0084] Optical element 102 includes a substrate 1 and an uneven structure (pillar) 2 formed on the substrate 1. In this example, the substrate 1 is a transparent plate made of synthetic quartz with a thickness of 0.775 mm. The uneven structure 2 includes a plurality of uneven elements 21 and recessed portions 23. The plurality of uneven elements 21 include at least one of recessed elements and protruding elements periodically arranged in the radial direction (e.g., the x-axis direction and the y-axis direction) of the substrate 1 (optical element 102), and the recessed portions 23 have a height Hs and a width Ws in the thickness direction (z-axis direction) of the substrate 1. In this example, the uneven elements 21 are protruding cylindrical elements made of the dielectric material Si3N4. Since the recessed portions 23 function similarly to the base layer 22 in Example 1, they can be regarded as the base layer.

[0085] The concave-convex element 21 includes a plurality of first structures 217 arranged in region R1 and a plurality of second structures 218 arranged in region R2. In region R2, the plurality of second structures 218 are formed on the recessed portion 23 of the substrate 1. The plurality of first structures 217 include a region H2, wherein the radial width gradually decreases in the z-axis direction in the direction opposite to that of the substrate 1. The plurality of first structures 217 have mutually different radial widths. Similarly, the plurality of second structures 218 have mutually different radial widths.

[0086] Region R1 of optical element 102 uses a structure similar to that of optical element 100 and has an anti-reflective effect. In region R2, where the diameter of the cylindrical element is relatively small, the effective refractive index of the concave-convex element 21 is low, and the difference in effective refractive index at the interface with the substrate 1 increases, causing reflection to tend to increase. Therefore, in region R2, a recessed portion 23 is provided between the concave-convex element 21 and the substrate 1, and by adjusting the height Hs and width Ws of the recessed portion, the effective refractive index can be appropriately set, thereby obtaining an anti-reflective effect between the concave-convex element 21 and the substrate 1.

[0087] The specific structure of optical element 102 will be described below. The concave-convex elements 21 in regions R1 and R2 are both arranged in square unit segments 11 with a side length of 350 nm and a height of 1500 nm. Region H1 has a cylindrical structure with a height of 900 nm. Region H2 has a height of 600 nm and a structure in which the diameter of the cylinder decreases with increasing distance from the substrate 1, and the diameter at the position farthest from the substrate 1 is 0.20 times the diameter of region H1. Region R2 includes a cylindrical recessed portion 23 with a height of 200 nm and a cylindrical concave-convex element 21 with a height of 1500 nm. The effective diameter of the concave-convex structure 2 is... mm, and the concave-convex structure 2 has 11 rings, which repeat periodically at a wavelength of 800 nm. The phase difference. The focal length generated by the concave-convex structure 2 is 60.0 mm, and the effective Abbe number is... It is -3.452, thus exhibiting wavelength dispersion equivalent to that of a diffractive optical element. The position with a normalized phase of 0.240 is defined as the boundary between regions R1 and R2 within the annular zone. Figure 8 The diagram illustrates the relationship between the normalized phase modulation amount and reflectivity of the concave-convex element 21 in this example and comparative examples. In regions R1 and R2, the maximum reflectivity when light of wavelength 800 nm is incident perpendicularly is 1.6% and 1.8%, respectively, and the reflectivity is suppressed compared to the comparative example where a cylindrical concave-convex element is used throughout the optical element and the maximum reflectivity is 3.6%.

[0088] Example 3

[0089] The optical element according to this example includes a high-refractive-index substrate 1 and a bump structure 2. The high-refractive-index substrate 1 has a higher refractive index than that of synthetic quartz with a thickness of 0.775 mm, and the bump structure 2 includes bump elements 21 composed of protruding cylindrical elements made of the dielectric material Si3N4. The bump elements 21 in regions R1 and R2 are both arranged in square unit segments 11 with a side length of 320 nm and a height of 1500 nm. Region H1 has a cylindrical structure with a height of 1200 nm. Region H2 has a height of 300 nm and a structure in which the diameter of the cylinder decreases with increasing distance from the substrate 1, and the diameter at the furthest point from the substrate 1 is 0.20 times the diameter of region H1. Region R2 includes a cylindrical base layer 22 with a height of 200 nm that contacts the substrate 1, and cylindrical bump elements 21 with a height of 1300 nm. The effective diameter of the bump structure 2 is... mm, and the concave-convex structure 2 has 63 rings, which repeat periodically at a wavelength of 800 nm. The phase difference. The focal length generated by the concave-convex structure 2 is 40.0 mm, and the effective Abbe number is... It is -3.452, thus exhibiting wavelength dispersion equivalent to that of a diffractive optical element. The position with a normalized phase of 0.230 is defined as the boundary between regions R1 and R2 within the annular zone. Figure 9 The diagram illustrates the relationship between the normalized phase modulation amount and reflectivity of the concave-convex element 21 in this example and comparative examples. In regions R1 and R2, the maximum reflectivity when light of wavelength 950 nm is incident perpendicularly is 3.6% and 3.3%, respectively, and the reflectivity is suppressed compared to the comparative example where a cylindrical concave-convex element is used throughout the optical element and the maximum reflectivity is 9.1%.

[0090] Example 4

[0091] Figure 10A and Figure 10B This is a structural diagram of the optical element 103 according to this example. Figure 10A This is an enlarged cross-sectional view of the optical element 103 when viewed from the y-axis direction (in the xz plane). Figure 10B This is a magnified top view of the optical element 103 when viewed from the z-axis direction (optical axis direction) (in the xy plane).

[0092] Optical element 103 includes a substrate 1 and an uneven structure (pillar) 2 formed on the substrate 1. In this example, the substrate 1 is a transparent plate made of synthetic quartz with a thickness of 0.775 mm. The uneven structure 2 includes a plurality of uneven elements 21 and a base layer 24. The plurality of uneven elements 21 include at least one of recessed elements and protruding elements periodically arranged in the radial direction (e.g., the x-axis direction and the y-axis direction) of the substrate 1 (optical element 103), and the base layer 24 has a substantially constant thickness in the thickness direction (z-axis direction) of the substrate 1. In this example, the uneven element 21 is a recessed cylindrical element made of the dielectric material Si3N4.

[0093] The bump element 21 includes a plurality of first structures 219 arranged in region R1 and a plurality of second structures 220 arranged in region R2. In region R2, the plurality of second structures 220 are formed on substrate 1 via base layer 24. The plurality of first structures 219 include region H2, wherein the radial width gradually decreases in the z-axis direction in the direction opposite to that of substrate 1. The plurality of first structures 219 have mutually different radial widths. Similarly, the plurality of second structures 220 have mutually different radial widths.

[0094] In region R1, region H1 has a structure including a cylindrical recess, and region H2 has a structure in which the diameter of the cylindrical recess increases with the distance from the substrate 1. An anti-reflective effect is obtained by gradually reducing the effective refractive index. In region R2, a base layer 24 with a cylindrical recess is provided between the concave-convex element 21 and the substrate 1, and the effective refractive index can be appropriately set by adjusting the height Hs and width Ws of the base layer 24, thereby obtaining an anti-reflective effect between the concave-convex element 21 and the substrate 1.

[0095] The specific structure of optical element 103 will now be described. The concave-convex elements 21 in regions R1 and R2 are arranged in each square unit segment 11 with a side length of 350 nm and a height of 1500 nm. Region H1 has a recessed cylindrical structure with a height of 900 nm. Region H2 has a height of 600 nm and a structure in which the diameter of the recessed cylindrical shape decreases with increasing distance from the substrate 1, and the diameter at the position farthest from the substrate 1 is 0.10 times the diameter of region H1. Region R2 includes a base layer 24 formed by recessed cylindrical elements with a height of 200 nm, and recessed cylindrical concave-convex elements 21 with a height of 1300 nm. The effective diameter of the concave-convex structure 2 is... mm, and the concave-convex structure 2 has 16 rings, which repeat periodically at a wavelength of 800 nm. The phase difference. The focal length generated by the concave-convex structure 2 is 10.0 mm, and the effective Abbe number is... It is -3.452, thus exhibiting wavelength dispersion equivalent to that of a diffractive optical element. The position with a normalized phase of 0.750 is defined as the boundary between regions R1 and R2 within the annular zone. Figure 11 The diagram illustrates the relationship between the normalized phase modulation amount and reflectivity of the concave-convex element 21 in this example and comparative examples. In regions R1 and R2, the maximum reflectivity when light of wavelength 800 nm is incident perpendicularly is 5.8% and 17.6%, respectively, and the reflectivity is suppressed compared to the comparative example where a cylindrical concave-convex element is used throughout the optical element and the maximum reflectivity is 22.0%.

[0096] Revise

[0097] Figure 12A , Figure 12B , Figure 12C and Figure 12D This is an explanatory diagram of the convex and concave elements according to this modification. Figure 12A In addition to the structure according to Example 1, an offset layer made of the same material as the base layer 22 in region R2 is provided between the substrate 1 and the bump element 21 in region R1. The offset layer can suppress the reflectivity at the interface between the substrate 1 and the bump element 21. Figure 12B In addition to the structure according to Example 2, a recessed portion 23 is also provided in region R1. This can suppress the reflectivity at the interface between the substrate 1 and the concave-convex element 21. Figure 12C In this example, the structure of the base layer 24 in region R2 is different from that in Example 4. Figure 12C In region R2, the base layer 24 is disposed at the center of the unit segment 11 so as not to contact the recessed element. This can suppress the reflectivity at the interface between the substrate 1 and the recessed element. Figure 12D The base layer in region R2 of the structure according to Example 4 is omitted, and instead a recessed portion is provided at the center of unit segment 11. This can suppress the reflectivity at the interface between substrate 1 and the recessed element.

[0098] The numerical examples 1 to 4 corresponding to the optical elements in Examples 1 to 4 will be described below.

[0099] The phase indicating the light convergence and divergence effects generated by the concave-convex structure 2 This is expressed by the following equation:

[0100]

[0101] Where h is the height above the optical axis in the direction perpendicular to the optical axis (radial direction), and n is the diffraction order of the diffracted light. It is the reference wavelength, and (k = 1, 2, 3, ...) are the phase coefficients for each level.

[0102] Let nd, ng, nC, nF and These represent wavelengths for the d-line (587.6 nm), g-line (435.8 nm), F-line (486.1 nm), and C-line (656.3 nm), respectively. The refractive index. Let W1 [nm] and W2 [nm] be the widths of the concave and convex elements 21 in regions R1 and R2, respectively, and let Wref [nm] be the width of the concave and convex element in the comparative example. R1, R2, and Rref are the reflectivities corresponding to the shapes of the respective concave and convex elements.

[0103]

[0104]

[0105]

[0106]

[0107] Tables 1 and 2 summarize the various values ​​for each example.

[0108] Table 1

[0109]

[0110] Table 2

[0111]

[0112] Optical system

[0113] Next, we will refer to Figure 13 The description includes examples of optical systems based on the optical elements of each example. Figure 13 In the figures, reference numeral 100 denotes an optical element according to any of the examples above, reference numeral 104 denotes a lens element, OA denotes the optical axis, IP denotes the image plane, and reference numeral 3 denotes an optical system including the optical element according to each example. The lens element may include a refractive lens, a diffractive optical element, a mirror, etc., and may be one or more elements. Optical element 100 and lens element 104 are arranged along the optical axis OA to form an image of the incident light on the image plane IP. Arranging concave and convex elements on the image-side surface of optical element 100 can provide light converging or diverging functions.

[0114] Image pickup device

[0115] Now for reference Figure 14 A description will be given of a digital still camera (image acquisition device) that uses an optical system comprising any of the optical elements described in the examples above as an imaging optical system. Figure 14 This is an explanatory diagram of an image pickup device 6 that includes an optical system having optical elements according to any of the examples above. Figure 14 In the figures, reference numeral 4 denotes the camera body, and reference numeral 3 denotes an optical system including an optical element according to any of the examples described above. Reference numeral 5 denotes an image sensor (photoelectric conversion element), such as a CCD sensor or a CMOS sensor, which is integrated into the camera body 4 and receives the optical image formed by the optical system 3 to perform photoelectric conversion. The camera body 4 can be a so-called single-lens reflex camera with a fast-return mirror, or it can be a so-called mirrorless camera without a fast-return mirror. Therefore, applying an optical system including an optical element according to any of the examples described above to an image acquisition device such as a digital still camera can provide an image acquisition device with a compact lens.

[0116] The optical element according to any of the examples above can also be used in an image sensor with a photoelectric converter that converts light from the optical element into electrical charge.

[0117] While this disclosure has been described with reference to embodiments, it should be understood that this disclosure is not limited to the disclosed embodiments. The scope of the appended claims should be given the broadest interpretation to cover all such modifications and equivalent structures and functions.

[0118] Each example can provide an optical element that can suppress the reflectivity of incident light using a simple configuration.

Claims

1. An optical element, comprising: substrate; as well as The uneven structure formed on the substrate The feature is that the concave-convex structure has multiple structures arranged periodically and including at least one of recessed elements and protruding elements. Multiple rings are formed on the substrate, arranged along the radial direction of the substrate. Each of the plurality of annular bands includes, along the radial direction, a first region and a second region having a phase smaller than that of the first region. The plurality of structures includes a plurality of first structures deployed in a first region and a plurality of second structures deployed in a second region, and The base layer is provided between the substrate and at least one of the plurality of second structures.

2. The optical element according to claim 1, characterized in that, The following inequalities must be satisfied: V2 is the element fill factor of the base layer.

3. The optical element according to claim 1, characterized in that, The following inequalities must be satisfied: Where ns is the refractive index of the substrate, neff2 is the effective refractive index of the base layer, and nm2 is the effective refractive index of the second structure.

4. The optical element according to claim 1, characterized in that, The following inequalities must be satisfied: Where Hs is the height of the base layer in the direction perpendicular to the radial direction, and Hm is the height of the second structure in the direction perpendicular to the radial direction.

5. The optical element according to claim 1, characterized in that, The second structure and the base layer are made of the same material.

6. The optical element according to claim 1, characterized in that, The substrate and the base layer are made of the same material.

7. The optical element according to claim 1, characterized in that, The first structure includes a third region and a fourth region in a direction perpendicular to the radial direction, starting from the substrate side. The following inequalities are satisfied: Where V3 is the component fill factor of the third region, and V4 is the component fill factor of the fourth region.

8. The optical element according to claim 1, characterized in that, The first structure includes, in a direction perpendicular to the radial direction, a third region and a fourth region having a lower element fill factor than the third region, starting from the substrate side. The following inequalities are satisfied: Where neff1 is the effective refractive index of the fourth region, and nm1 is the effective refractive index of the first structure.

9. The optical element according to claim 1, characterized in that, The following inequalities must be satisfied: Where Hmax is the maximum height of the first structure in the direction perpendicular to the radial direction, and Hmin is the minimum height of the second structure in the direction perpendicular to the radial direction.

10. The optical element according to claim 1, characterized in that, The following inequalities must be satisfied: Where W1max is the maximum diameter of the first structure in the radial direction, W1min is the minimum diameter of the first structure in the radial direction, W2max is the maximum diameter of the second structure in the radial direction, and W2min is the minimum diameter of the second structure in the radial direction.

11. The optical element according to claim 1, characterized in that, The following inequalities must be satisfied: Where E is the normalized phase at the boundary between the first and second regions in the same annulus, and n is the design diffraction order.

12. The optical element according to claim 1, characterized in that, The following inequalities must be satisfied: Where P is the period of the concave-convex structure, and It is the reference wavelength.

13. The optical element according to claim 1, characterized in that, The following inequalities must be satisfied: Where Hs is the height of the base layer in the direction perpendicular to the radial direction, and It is the reference wavelength.

14. The optical element according to claim 1, characterized in that, The first structure includes, in a direction perpendicular to the radial direction, a third region and a fourth region having a lower element fill factor than the third region, starting from the substrate side. The following inequalities are satisfied: Where Ha is the height of the fourth region in the direction perpendicular to the radial direction, and It is the reference wavelength.

15. The optical element according to claim 1, characterized in that, The following inequalities must be satisfied: Where Hm is the height of each of the plurality of structures in the direction perpendicular to the radial direction, and t is the thickness of the substrate in the optical axis direction.

16. The optical element according to claim 1, characterized in that, The following inequalities must be satisfied: in P is the difference between the maximum and minimum widths of the first structure, and P is the period of the concave-convex structure.

17. The optical element according to claim 1, characterized in that, The following inequalities must be satisfied: in P is the difference between the maximum and minimum widths of the second structure, and P is the period of the concave-convex structure.

18. The optical element according to claim 1, characterized in that, In the radial direction, the first region is deployed closer to the center of the optical element than the second region.

19. The optical element according to any one of claims 1 to 18, characterized in that, In the radial direction, the second region is deployed closer to the center of the optical element than the first region.

20. An image sensor, comprising: The optical element according to any one of claims 1 to 19; as well as A photoelectric converter configured to convert light from the optical element into electrical charge.

21. An optical system, comprising: A plurality of optical elements, said plurality of optical elements including the optical elements according to any one of claims 1 to 19.

22. An image acquisition device, comprising: The optical system according to claim 21; as well as An image sensor configured to receive an image formed by the optical system.

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