Optical lens, optical system, and imaging device

Abstract

This optical lens is used for light of a prescribed target wavelength range. The optical lens is provided with a substrate and a plurality of fine structures that are arranged on a surface of the substrate at shorter intervals than the minimum wavelength in the target wavelength range. The structure and / or interval of each of the plurality of fine structures is determined so as to compensate for changes in the phase and / or transmittance that depends on the angle of incidence of incident light at each position in the area in which the plurality of fine structures is provided.

Description

Optical lens, optical system, and imaging device

[0001] The present disclosure relates to optical lenses, optical systems, and imaging systems.

[0002] In recent years, research and development of metalenses, which have fine surface structures known as metasurfaces, has progressed. Metasurfaces are surfaces with a metamaterial structure that realize optical functions not found in nature. Metalenses can achieve optical functions equivalent to those achieved by combining multiple conventional optical lenses with a single thin, flat structure. Therefore, metalenses can contribute to the miniaturization and weight reduction of lens-equipped devices, such as cameras, LiDAR sensors, projectors, and augmented reality (AR) displays. Examples of metalenses and devices using metalenses are disclosed in, for example, Patent Documents 1 to 3.

[0003] Patent Literature 1 discloses a metalens including a substrate and a plurality of nanostructures arranged on the substrate. In this metalens, each of the plurality of nanostructures produces an optical phase shift that varies depending on its position, and the optical phase shift of each nanostructure defines the phase profile of the metalens. The optical phase shift of each nanostructure depends on the position of the nanostructure and the size or orientation of the nanostructure. Examples of nanostructures given include nanofins and nanopillars. Patent Literature 1 describes that a desired phase shift can be achieved by adjusting the angle at which each nanofin is arranged or the size of each nanopillar.

[0004] Patent Literature 2 discloses a miniaturized lens assembly including a metalens, and an electronic device including the same. The metalens disclosed in Patent Literature 2 includes a nanostructure array and is configured to form the same phase delay profile for at least two different wavelengths included in incident light. In this metalens, to achieve a desired phase delay profile, the width of each of the multiple internal pillars included in the nanostructure array is appropriately determined according to the required amount of phase delay.

[0005] Patent Literature 3 discloses a metalens structure having an aperture stop on one surface of a substrate and a metasurface on the opposite surface of the substrate. The metalens of Patent Literature 3 achieves light collection over a wide viewing angle with a thin, flat structure.

[0006] JP 2019-516128 A JP 2021-71727 A U.S. Patent Publication No. 2021 / 0306564

[0007] With conventional metalens design methods, imaging performance can deteriorate as the incident angle increases, resulting in blurring on the imaging surface.

[0008] The present disclosure provides a novel optical lens that can suppress the deterioration of imaging performance that occurs as the angle of incidence increases.

[0009] An optical lens according to one aspect of the present disclosure is used for light in a predetermined target wavelength range. The optical lens includes a substrate and a plurality of microstructures arranged on a surface of the substrate at intervals shorter than the shortest wavelength in the target wavelength range. The structure and / or interval of each of the microstructures varies depending on the position on the surface depending on the angle of incidence of incident light at each position within the region where the microstructures are provided.

[0010] A method according to another aspect of the present disclosure is a method for manufacturing an optical lens for use with light in a predetermined target wavelength range. The optical lens has a plurality of microstructures arranged at intervals shorter than the shortest wavelength in the target wavelength range. The method includes determining the structure and / or interval of each of the plurality of microstructures so as to compensate for changes in phase and / or transmittance that depend on the angle of incidence of incident light at each position within an area where the plurality of microstructures are provided, and forming the plurality of microstructures arranged at the determined intervals on a surface of a substrate.

[0011] A general or specific aspect of the present disclosure may be realized as a system, an apparatus, a method, an integrated circuit, a computer program, or a recording medium such as a computer-readable recording disk, or as any combination of a system, an apparatus, a method, an integrated circuit, a computer program, and a recording medium. The computer-readable recording medium may include a non-volatile recording medium such as a CD-ROM (Compact Disc-Read Only Memory). An apparatus may be composed of one or more devices. When an apparatus is composed of two or more devices, the two or more devices may be located in a single device or may be located separately in two or more separate devices. In this specification and claims, the term "apparatus" may refer not only to a single device but also to a system consisting of multiple devices.

[0012] According to one aspect of the present disclosure, it is possible to suppress a decrease in imaging performance that accompanies an increase in the angle of incidence of light onto a lens.

[0013] FIG. 1 is a perspective view schematically showing an example of a metalens. FIG. 2 is a perspective view schematically showing an example of the structure of a unit cell. FIG. 3 is a diagram schematically showing the function of a metalens. FIG. 4 is a diagram showing multiple areas in a metalens according to an exemplary embodiment of the present disclosure, divided according to the angle of incidence of a chief ray. FIG. 5 is a diagram showing an example of a combination of arrangement maps optimized for each angle of incidence. FIG. 6A is a diagram showing an example of design data illustrating the relationship between the diameter of a microstructure and the amount of phase shift of incident light. FIG. 6B is a diagram showing an example of design data showing the relationship between the diameter of a microstructure and the transmittance of incident light. FIG. 7 is a diagram schematically showing a unit cell used in a simulation. FIG. 8A is a diagram showing an example of design data showing the relationship between the period and phase of a microstructure. FIG. 8B is a diagram showing an example of design data showing the relationship between the period and transmittance of a microstructure. FIG. 9A is a diagram showing an example of an ideal phase profile for an incident angle of 0 degrees. FIG. 9B is a diagram showing another example of an ideal phase profile for an incident angle of 30 degrees. FIG. 9C is a diagram illustrating the light focusing performance of a metalens in which an ideal phase profile is realized. FIG. 10A is a diagram showing an example of a phase profile (incident angle 0 degrees) reproduced by a unit cell designed by a conventional method. FIG. 10B is a diagram showing another example of a phase profile (incident angle 30 degrees) reproduced by a unit cell designed by a conventional method. FIG. 10C is a diagram illustrating the focusing performance of a metalens designed by a conventional method. FIG. 11A is a diagram showing an example of a phase profile (incident angle 0 degrees) reproduced by a unit cell designed by a method of an embodiment. FIG. 11B is a diagram showing another example of a phase profile (incident angle 30 degrees) reproduced by a unit cell designed by a method of an embodiment. FIG. 11C is a diagram illustrating the focusing performance of a metalens designed by a method of an embodiment. FIG. 12A is a diagram showing a schematic configuration of an imaging device. FIG. 12B is a diagram showing an example of multiple light rays passing through an aperture stop. FIG. 13A is a diagram showing a schematic configuration of a light irradiation device. FIG. 13B is a diagram showing an example of a light ray that is normally incident on a metalens through a scanning optical system. FIG. 13C is a diagram showing an example of a light ray that is obliquely incident on a metalens through a scanning optical system. FIG. 14 is a schematic diagram illustrating an example of a metalens.Fig. 15 is a diagram showing an example of a method for dividing a lens surface into areas. Fig. 16 is a diagram showing the difference in effect between a comparative example and an example. Fig. 17 is a schematic cross-sectional view showing an example of a metalens including a light modulation layer. Fig. 18 is a diagram showing an example of a metalens in which the light modulation layer includes a plurality of other microstructures.

[0014] Exemplary embodiments of the present disclosure will be described below. The embodiments described below are all comprehensive or specific examples. The numerical values, shapes, components, component placement and connection configurations, steps, and step order shown in the following embodiments are merely examples and are not intended to limit the present disclosure. Furthermore, among the components in the following embodiments, components that are not recited in the independent claims that represent the highest concepts will be described as optional components. Furthermore, each figure is a schematic diagram and is not necessarily an exact illustration. Furthermore, in each figure, the same or similar components are assigned the same reference numerals. Duplicate descriptions may be omitted or simplified.

[0015] In this disclosure, the term "light" is not limited to visible light (wavelength of about 400 nm to about 700 nm) but also refers to invisible light. Invisible light refers to electromagnetic waves within the wavelength range of ultraviolet light (wavelength of about 10 nm to about 400 nm), infrared light (wavelength of about 700 nm to about 1 mm), or radio waves (wavelength of about 1 mm to about 1 m). The optical lenses in this disclosure can be used not only for visible light but also for invisible light such as ultraviolet light, infrared light, or radio waves.

[0016] (Findings that Form the Basis of the Present Disclosure) First, an example of the basic configuration of an optical lens in the present disclosure and the findings of the present inventors will be described.

[0017] In the following description, optical lenses are also referred to as "metalens." A metalens is an optical element that has a plurality of microscopic structures on its surface that are smaller than the wavelength of incident light, and that achieves lens function by the phase shift caused by these microscopic structures. By appropriately designing the shape, size, orientation, and arrangement of each microscopic structure, it is possible to adjust the optical properties of incident light, such as the phase, amplitude, or polarization.

[0018] FIG. 1 is a perspective view schematically illustrating an example of a metalens. The metalens 100 shown in FIG. 1 includes a substrate 110 and a plurality of microstructures 120 provided on the surface of the substrate 110. The surface on which the plurality of microstructures 120 are provided may be referred to as the "lens surface" in the following description. In the example shown in FIG. 1, each of the microstructures 120 is a columnar body (also called a "pillar") having a cylindrical shape. A unit element in the metalens 100 that includes one microstructure 120 is referred to as a "unit cell." The metalens 100 is an assembly of a plurality of unit cells.

[0019] Each microstructure 120 may have a shape other than a cylinder. For example, each microstructure 120 may be a columnar body having an elliptical cylinder or polygonal prism shape other than a cylinder. Alternatively, each microstructure 120 may be a pyramidal body having an elliptical cone (including a circular cone) or a polygonal pyramid shape. Furthermore, each microstructure 120 is not limited to a convex body such as a columnar body or a pyramidal body, but may also be a concave body. The convex body or concave body constituting the microstructure 120 may have any structure, such as a columnar body having an elliptical cylinder or a polygonal prism shape, or a cone shape having an elliptical cone or a polygonal pyramid shape.

[0020] 2 is a perspective view schematically illustrating an example of the structure of one unit cell. One unit cell includes a portion of a substrate 110 and one microstructure 120 protruding from the portion of the substrate 110. Each unit cell generates a phase shift in incident light according to the structure of the microstructure 120.

[0021] FIG. 3 is a diagram schematically illustrating the function of metalens 100. In FIG. 3, arrows indicate example light rays. In this example, metalens 100 has the function of focusing incident light, similar to a conventional convex lens. In the example of FIG. 3, incident light incident on the substrate 110 side of metalens 100 is focused by undergoing different phase changes depending on the position through the array of microstructures 120. In order to achieve desired focusing characteristics, the shape, width, height, orientation, etc. of each microstructure 120 are appropriately determined. The structure of each microstructure 120 can be appropriately determined, for example, based on data indicating the phase profile to be achieved and the results of electromagnetic field simulations.

[0022] Each of the microstructures 120 has a subwavelength size (e.g., width and height) that is shorter than the wavelength of light incident on the metalens 100, and may be arranged at subwavelength intervals or periods. The "spacing" of the microstructures 120 is the distance between the centers of two adjacent microstructures 120 when viewed in a direction perpendicular to the surface of the substrate 110. The microstructures 120 may be arranged periodically or non-periodically.

[0023] Metalens 100 may be designed to achieve desired optical properties for light in a predetermined target wavelength range. The target wavelength range may be, for example, a wavelength range defined by a specification. If the lower limit of the target wavelength range is, for example, 1 μm, the size and spacing of microstructures 120 may be set to a value less than 1 μm. Such microstructures with nanoscale sizes smaller than 1 μm are sometimes referred to as "submicron structures" or "nanostructures." If the target wavelength range is in the infrared region, the size and spacing of microstructures 120 may be greater than 1 μm.

[0024] The number of microstructures 120 provided on the surface of metalens 100 is determined to an appropriate number depending on the lens characteristics that are to be achieved. The number of microstructures 120 is, for example, in the range of 100 to 10,000, and in some cases may be less than 100 or more than 10,000.

[0025] Here, we will briefly explain an example of a conventional metalens design method. One conventional metalens design method is the method disclosed in Patent Document 3, for example. The metalens disclosed in Patent Document 3 uses an aperture stop to achieve high imaging performance. By using the aperture stop, light reaching the lens surface is limited to light having an incident angle within a certain range, thereby achieving high imaging performance. The shape, size, or layout of each of the multiple microstructures arranged on the surface of the metalens is appropriately designed to achieve a desired phase profile.

[0026] The amount of phase shift of light passing through a unit cell depends on the structure, such as the shape, size, or orientation, of the microstructures included in the unit cell, or the spacing (or period) of the microstructures. For example, a desired phase profile can be achieved by appropriately determining the width or spacing of the microstructures for each position in the unit cell according to the required amount of phase shift. Parameters such as the width or spacing of the microstructures can be determined by referring to design data showing the relationship between the parameters and the phase, which has been obtained in advance, for example, by simulation.

[0027] In conventional design methods, parameters such as width or spacing are determined by referencing the same design data at any position on the lens surface. However, such design methods cannot reproduce the ideal phase distribution for obliquely incident light when the response of the phase change to changes in the unit cell parameters varies depending on the angle of incidence of the light. With the above design method, imaging performance deteriorates as the angle of incidence increases, resulting in a decrease in the modulated transfer function (MTF) from the center to the edge of the imaging surface, resulting in blurring.

[0028] Therefore, the conventional design method is limited to application to unit cells that are not dependent on the incident angle, which limits its applications. Furthermore, even in unit cells that are not dependent on the incident angle, the method cannot accommodate the steep phase change at the outermost periphery of the lens that occurs when the lens area is increased or the F-number is reduced (i.e., the brightness is increased), which can result in a problem of reduced imaging performance.

[0029] The present inventors have found the above-mentioned problem and have come up with an optical lens configuration that can solve this problem. The configuration of an optical lens according to an embodiment of the present disclosure will be described below.

[0030] An optical lens according to an exemplary embodiment of the present disclosure is used for light in a predetermined target wavelength range. The optical lens includes a substrate and a plurality of microstructures arranged on a surface of the substrate. The microstructures are arranged at intervals shorter than the shortest wavelength in the target wavelength range.

[0031] Here, the "target wavelength range" refers to the wavelength range of light in which the optical lens is intended to be used, and can be determined based on the specifications of the optical lens or the specifications of the device in which the optical lens is installed. The target wavelength range may include, for example, at least a portion of the visible light wavelength range (approximately 400 nm to approximately 700 nm). Alternatively, the target wavelength range may include at least a portion of the ultraviolet wavelength range (wavelengths of approximately 10 nm to approximately 400 nm). Alternatively, the target wavelength range may include at least a portion of the infrared wavelength range (approximately 700 nm to approximately 1 mm). Alternatively, the target wavelength range may include at least a portion of the radio wave wavelength range (wavelengths of approximately 1 mm to approximately 1 m). In one example, the target wavelength range may include at least a portion of the infrared wavelength range from 2.5 μm to 25 μm. The 2.5 μm to 25 μm wavelength range may be suitable for use in sensing devices that utilize infrared light, such as LiDAR sensors or infrared cameras. In this disclosure, the term "wavelength" refers to the wavelength in free space unless otherwise specified.

[0032] The substrate and each microstructure 120 may be made of a material that is translucent to light in the target wavelength range. Here, "translucent" means having the property of transmitting incident light with a transmittance of more than 50%. In some embodiments, the substrate 110 and each microstructure 120 may be made of a material that transmits light in the target wavelength range with a transmittance of 80% or more.

[0033] The "spacing" of the microstructures means the distance between the centers of two adjacent microstructures when viewed from a direction perpendicular to the surface of the substrate (or lens surface). If the shortest wavelength in the target wavelength range is, for example, 2.5 μm, the distance between the centers of any two adjacent microstructures among the multiple microstructures is shorter than 2.5 μm. Note that since the width of the microstructures is smaller than the spacing between the microstructures, the width of the microstructures is also shorter than the shortest wavelength in the target wavelength range.

[0034] The structure and / or spacing of each of the plurality of microstructures varies depending on the position on the surface depending on the angle of incidence of incident light at each position within the region where the plurality of microstructures are provided. For example, the structure and / or spacing of each of the plurality of microstructures is determined so as to compensate for a phase change that depends on the angle of incidence of incident light at each position within the region where the plurality of microstructures are provided. Here, "compensating for a phase change" means reducing the phase change.

[0035] According to the above configuration, phase change depending on the angle of incidence of incident light at each position in the region where the plurality of microstructures are provided is suppressed, making it easier to achieve an ideal phase even when light is incident on the optical lens at an oblique angle, thereby improving light-collection performance.

[0036] In the optical lens described above, when incident light is incident on a plurality of microstructures, the amount of change in phase and / or transmittance can show a different response for each incident angle.

[0037] The structure and / or spacing of each of the multiple microstructures can be determined based on design data created for each of multiple angles of incidence, the design data defining the relationship between one or more parameters defining the structure and / or spacing and the phase and / or transmittance. The design data can be created in advance for each of multiple areas included in the region where the microstructures are arranged. Each of the multiple areas corresponds to one of the multiple angles of incidence. The structure and / or spacing of each of the multiple microstructures can be determined based on design data corresponding to one of the multiple areas to which the position of the microstructure belongs.

[0038] FIG. 4 is a diagram showing multiple areas of a metalens 100 (i.e., an optical lens) according to an exemplary embodiment of the present disclosure, divided according to the angle of incidence of the chief ray. The chief ray is the ray that forms the center of a bundle of rays that enters the metalens 100. When an aperture stop is placed in front of the metalens 100, the ray that enters the metalens 100 through the center of the aperture stop is the chief ray. The metalens 100 in this embodiment has the schematic structure shown in FIG. 1. Each microstructure 120 in this embodiment has a cylindrical structure. The width (i.e., diameter) of each microstructure 120 is determined based on design data that corresponds to a predetermined ideal phase profile and the angle of incidence of the chief ray that enters the position of that microstructure 120. In the example of FIG. 4, the lens surface is divided into 10 areas according to the angle of incidence of the chief ray (or the distance from the optical axis). In FIG. 4, areas for which parameters such as the diameter or spacing of the microstructures 120 are determined based on the same design data are represented by the same shade. In this example, different design data is used for every 3-degree change in the incident angle. The number of divisions of the lens surface is not limited to 10, but may be 9 or less or 11 or more. The incident angle width of each area is also not limited to 3 degrees, but may be set arbitrarily, for example, to 1, 2, 4, or 5 degrees.

[0039] 4, the shape of the lens surface is an 8 mm x 8 mm square, and a plurality of microstructures 120 are concentrically arranged within this lens surface at intervals of, for example, about 2 μm to 6 μm. However, the shape and size of the metalens 100 and the arrangement of the microstructures 120 are not limited to this example and can be designed arbitrarily depending on the required lens performance.

[0040] Parameters such as the diameter or spacing of each microstructure 120 are determined to achieve a desired phase profile. For example, the diameter of each microstructure 120 may be determined based on design data created in advance based on simulations. In this case, the design data indicates the relationship between the diameter of the microstructure 120 and the phase shift amount of light incident on a unit cell including that microstructure 120. The design data is created for each of a plurality of areas divided according to the range of incident angles of the chief ray. For each area of ​​the metalens 100, the diameter of each microstructure 120 in each area may be determined based on the relationship between the diameter and phase indicated by the corresponding design data. Hereinafter, data indicating the distribution of the diameters of the microstructures 120 within the lens surface will be referred to as an "arrangement map."

[0041] 5 shows an example of a combination of array maps optimized for each incident angle. In this example, array maps are determined for each of 10 areas: nine areas with an angle width of 3 degrees centered at 0 degrees, 3 degrees, 6 degrees, 9 degrees, 12 degrees, 15 degrees, 18 degrees, 21 degrees, and 24 degrees, respectively, and an area beyond 27 degrees. The array maps for these 10 areas are added together to obtain the overall array map. An array of microstructures 120 can be fabricated according to the diameter distribution indicated by this array map.

[0042] Next, an example of design data for determining the diameter of the microstructure 120 will be described.

[0043] FIG. 6A is a diagram showing an example of design data illustrating the relationship between the diameter of the microstructure 120 and the phase shift amount of light incident on a unit cell including the microstructure 120. FIG. 6B is a diagram showing an example of design data illustrating the relationship between the diameter of the microstructure 120 and the light transmittance of the unit cell including the microstructure 120. These design data were obtained by performing simulations for a plurality of incident lights having different angles of incidence. FIGS. 6A and 6B illustrate simulation results for four incident lights having angles of incidence of 0°, 9°, 18°, and 27°. In this example, each microstructure 120 is a cylindrical pillar having a height of 6.8 μm, and multiple microstructures 120 are arranged from the center of the lens surface toward the periphery at a period of 6.2 μm.

[0044] FIG. 7 schematically shows the unit cell used in the simulation. In the simulation, the phase shift amount and transmittance response were calculated for each of a number of light rays with different incident angles when the diameter D of the microstructure 120 was changed in the range of 1 μm to 5 μm. The phase shift amount is the difference between the phase φ of light incident on the unit cell and the phase φ' of light emitted from the unit cell. In this specification, the phase shift amount may be simply referred to as the "phase." The transmittance represents the ratio of the intensity of light emitted from the unit cell to the intensity of light incident on the unit cell.

[0045] As shown in FIG. 6A , the phase changes depending on the diameter D of the microstructure 120. Furthermore, the response of the phase to a change in diameter D varies depending on the angle of incidence of light. Furthermore, as shown in FIG. 6B , the transmittance also changes depending on the diameter D of the microstructure 120. Furthermore, the response of the transmittance to a change in diameter D also varies depending on the angle of incidence of light. The diameter of each microstructure 120 is determined based on these design data obtained from the simulation. Specifically, the diameter of each microstructure 120 is determined according to the following steps (a1) to (a3): (a1) Determine the ideal phase at each position on the lens surface so as to match the ideal phase profile determined from the predetermined lens specifications. (a2) For each position on the lens surface, refer to the design data for the corresponding angle of incidence to identify one or more candidates for diameter D corresponding to the ideal phase. (a3) ​​When multiple candidates for diameter D are identified, refer to the design data showing the relationship between transmittance and diameter D corresponding to the angle of incidence to determine the diameter D with the highest transmittance from the candidates as the diameter of the microstructure 120.

[0046] By using the above method, the diameter of the microstructure 120 at each position on the lens surface can be determined to an optimal value, and the ideal phase profile can be reproduced more accurately. This makes it possible to realize the ideal phase profile even for obliquely incident light, thereby improving the performance of the lens.

[0047] In the above example, the diameter of the microstructures 120 at each position on the lens surface is appropriately determined based on the design data, but this is merely an example. In addition to or instead of the diameter of the microstructures 120, the spacing (or period) of the microstructures 120 may be determined based on the design data according to the angle of incidence. Such an example will be described below with reference to FIGS. 8A and 8B .

[0048] FIG. 8A is a diagram showing an example of design data indicating the relationship between the period and phase of the microstructures 120. FIG. 8B is a diagram showing an example of design data indicating the relationship between the period and transmittance of the microstructures 120. These design data were also obtained by performing simulations for a plurality of incident lights with different angles of incidence. In this example, each microstructure 120 is a cylindrical pillar with a height of 6.8 μm and a diameter of 3 μm (fixed value). The phase and transmittance responses were calculated when the period of the microstructures 120 was changed in the range from 3.5 μm to 6.5 μm.

[0049] As shown in FIG. 8A , the phase changes depending on the period (i.e., spacing) of the microstructures 120. Furthermore, the response of the phase to a change in period differs depending on the angle of incidence of light. Furthermore, as shown in FIG. 8B , the transmittance also changes depending on the period of the microstructures 120. Furthermore, the response of the transmittance to a change in period also differs depending on the angle of incidence of light. Therefore, the period of each microstructure 120 may be determined based on these design data obtained from the simulation. Specifically, the period of each microstructure 120 may be determined according to the following steps (b1) to (b3): ​​(b1) Determine an ideal phase at each position on the lens surface so as to match an ideal phase profile determined from predetermined lens specifications. (b2) For each position on the lens surface, refer to the design data for the corresponding angle of incidence and identify one or more candidate periods corresponding to the ideal phase. (b3) When multiple candidate periods are identified, refer to the design data showing the relationship between transmittance and period corresponding to the angle of incidence and determine the period with the highest transmittance from the candidates as the period of the microstructure 120.

[0050] By using the above method, the period (i.e., spacing) of the microstructures 120 at each position on the lens surface can be determined to an optimal value, and the ideal phase profile can be reproduced more accurately. This makes it possible to realize the ideal phase profile even for obliquely incident light, thereby improving the performance of the lens.

[0051] Both the diameter and period (or spacing) of the microstructures 120 at each position on the lens surface may be determined according to an ideal phase profile. In this case, design data, created in advance for each incident angle, showing the relationship between the combination of the diameter and period (or spacing) of the microstructures 120 and the phase and transmittance, may be referenced. Other parameters defining the structure, such as the height or orientation of the microstructures 120, may also be determined in a similar manner. For example, if the microstructures 120 are convex or concave bodies having an elliptical cylindrical structure, at least one of the height (or depth), major axis, and minor axis of the elliptical cylindrical structure may be determined in a similar manner. If the microstructures 120 are convex or concave bodies having a polygonal cylindrical structure, the height (or depth) and / or the length of at least one side of the polygonal cylindrical structure may also be determined in a similar manner. Some of the multiple microstructures 120 may be convex or concave bodies having an elliptical cylindrical structure, and the other may be convex or concave bodies having a polygonal cylindrical structure.

[0052] Next, with reference to FIGS. 9A to 11C, the effects of the above design method will be described in comparison with a conventional design method.

[0053] 9A and 9B are diagrams showing examples of ideal phase profiles of metalens. FIG. 9A shows an example of an ideal phase profile for incident light with an incident angle of 0 degrees. FIG. 9B shows an example of an ideal phase profile for incident light with an incident angle of 30 degrees. In these figures, the horizontal axis x represents a coordinate in the direction toward the periphery, with the position of the optical axis on the lens surface as the origin. The ideal phase profile is constant regardless of the incident angle. FIG. 9C is a diagram schematically showing the focusing performance of metalens 100 when an ideal phase profile is realized. The z-axis is a coordinate axis parallel to the optical axis. When an ideal phase profile is realized, not only normally incident light but also obliquely incident light is focused to a single point on the image plane.

[0054] 10A and 10B are diagrams illustrating examples of phase profiles reproduced by a unit cell designed using a conventional method. FIG. 10A shows an example of a phase profile reproduced by a unit cell when the angle of incidence is 0 degrees. FIG. 10B shows an example of a phase profile reproduced by a unit cell when the angle of incidence is 30 degrees. In conventional methods, the structure or layout of each microstructure 120 is determined by referring to design data for normal incidence at any position on the lens surface. For this reason, as shown in FIG. 10B , the phase profile when the angle of incidence is different from 0 degrees deviates from the ideal phase profile, particularly at locations away from the center of the lens. FIG. 10C is a diagram illustrating the focusing performance of a metalens 100 designed using a conventional method. For light with a large angle of incidence, the ideal phase profile is not reproduced, and the light is not focused to a single point on the image plane, resulting in blurring.

[0055] 11A and 11B are diagrams illustrating examples of phase profiles reproduced by a unit cell designed using the method of this embodiment. FIG. 11A shows an example of a phase profile reproduced by a unit cell when the incident angle is 0 degrees. FIG. 11B shows an example of a phase profile reproduced by a unit cell when the incident angle is 30 degrees. In this embodiment, the structure or layout of each microstructure 120 is determined by referring to different design data depending on its position within the lens plane. Therefore, the phase profile when the incident angle is 0 degrees as well as when the incident angle is 30 degrees is close to the ideal phase profile. FIG. 11C is a diagram illustrating the focusing performance of the metalens 100 designed using the method of this embodiment. Because the ideal phase profile is reproduced even for light with a large incident angle, such as 30 degrees, the light is focused to a single point on the image plane, and no blurring occurs.

[0056] As described above, according to the metalens 100 of the present embodiment, parameters such as the structure and / or spacing of each of the plurality of microstructures are designed to compensate for (i.e., reduce) the change in phase that depends on the angle of incidence of incident light at each position within the region where the plurality of microstructures 120 is provided. This makes it easier to reproduce an ideal phase profile regardless of the angle of incidence, and can improve light-collection performance.

[0057] In this embodiment, the parameters corresponding to the ideal phase can be determined by taking into consideration changes in transmittance when parameters such as the structure and / or spacing of each of the multiple microstructures are changed, thereby achieving an optimal structure and arrangement of microstructures that can achieve not only the ideal phase but also high transmittance.

[0058] Note that, depending on the material or structure constituting metalens 100, there may be cases where the incidence angle dependence of the phase change is small but the incidence angle dependence of the transmittance change is large. In such cases, the structure and / or spacing of the microstructures 120 may be determined by considering only the incidence angle dependence of the transmittance change, without considering the incidence angle dependence of the phase change. For example, parameters such as the structure and / or spacing of each of the multiple microstructures 120 may be designed to compensate for (i.e., reduce) the change in transmittance that depends on the incidence angle of incident light at each position within the region in which the multiple microstructures 120 are provided. This makes it easier to achieve a target transmittance distribution regardless of the incidence angle, thereby improving lens performance.

[0059] In this way, the structure and / or spacing of each of the plurality of microstructures 120 varies depending on the position on the substrate surface, depending on the angle of incidence of incident light at each position within the region where the plurality of microstructures 120 is provided. More specifically, the structure and / or spacing of each of the plurality of microstructures 120 can be determined so as to compensate for changes in phase and / or transmittance that depend on the angle of incidence of incident light at each position within the region where the plurality of microstructures is provided. This makes it easier to achieve ideal lens performance.

[0060] The method for manufacturing the metalens 100 in this embodiment includes: (a) determining the structure and / or spacing of each of the plurality of microstructures 120 so as to compensate for changes in phase and / or transmittance that depend on the angle of incidence of incident light at each position within an area in which the plurality of microstructures 120 are provided, and (b) forming the plurality of microstructures 120 arranged at the determined spacing on the surface of a substrate. By using such a method, it is possible to manufacture a metalens 100 that has ideal lens performance.

[0061] Next, an example of an imaging device including the above-described metalens 100 will be described.

[0062] FIG. 12A is a diagram showing the schematic configuration of an imaging device. The imaging device includes a metalens 100, an image sensor 200, and an aperture stop 300. The image sensor 200 has an imaging surface 210 on which a plurality of photodetector cells are arranged. The aperture stop 300 is located in front of the metalens 100 (i.e., on the subject side). A system including the combination of the metalens 100 and the aperture stop 300 is called an "optical system." The imaging device includes the optical system and the image sensor 200. The shape of the aperture stop 300 can be elliptical (including a perfect circle) or polygonal. Incident light passes through the aperture stop 300 and enters the metalens 100. The incident light is focused by the metalens 100 and forms an image on the imaging surface 210 of the image sensor 200. In this configuration, the structure and / or spacing of the microstructures changes appropriately depending on the distance from the intersection between the central axis of the aperture stop 300 and the surface of the substrate of the metalens 100 on which the plurality of microstructures are provided.

[0063] 12B is a diagram showing an example of multiple light rays passing through aperture stop 300. Providing aperture stop 300 makes it easy to control the position within the lens surface at which chief rays of each incident angle reach. This makes it possible to improve the effect of improving light collection performance using the design method of this embodiment. Next, an example of a light irradiation device including the above-mentioned metalens 100 will be described.

[0064] FIG. 13A is a diagram showing a schematic configuration of a light irradiation device. The light irradiation device includes a metalens 100, a light irradiation target 400, and a scanning optical system 500. The light irradiation target 400 has a light irradiation surface 410. The scanning optical system 500 is disposed in front of the metalens 100. A system including a combination of the metalens 100 and the scanning optical system 500 will also be referred to as an "optical system." The light irradiation device includes an optical system and a light irradiation target 400. The scanning optical system 500 may be a galvanometer scanner, a polygon scanner, or a MEMS scanner. Incident light is incident on the metalens 100 through the scanning optical system 500. The incident light is focused by the metalens 100, and the focused light beam is irradiated onto the light irradiation surface 410 of the light irradiation target 400. In this configuration, the structure and / or spacing of the microstructures changes appropriately depending on the distance from the intersection between the central axis (i.e., the optical axis) of the scanning optical system 500 and the surface of the substrate of the metalens 100 on which the plurality of microstructures are provided.

[0065] FIG. 13B is a diagram showing an example of a light ray that is normally incident on the metalens 100 through the scanning optical system 500. FIG. 13C is a diagram showing an example of a light ray that is obliquely incident on the metalens 100 through the scanning optical system 500. The scanning optical system 500 can be configured, for example, to be connected to an electric motor and to change the angle of the mirror by rotating the electric motor. Changing the angle of the mirror can change the direction of the reflected light of light emitted from the light source. Light scanning by the scanning optical system 500 makes it easy to control the position within the lens surface where the chief ray of each incident angle arrives. This can enhance the effect of improving the light focusing performance achieved by the design method of this embodiment.

[0066] (Example) Next, an example of the optical lens will be described.

[0067] FIG. 14 is a schematic diagram illustrating an example of a metalens 100. In this example, the substrate 110 and the plurality of microstructures 120 are made of the same material. The substrate 110 and each microstructure 120 are made of a material containing silicon as a main component and having a (100) crystal plane orientation. The silicon may also have a (110) or (111) crystal plane orientation. Alternatively, a material other than silicon may be used.

[0068] The thickness of the substrate 110 of the metalens 100 is 500 μm. The shape of the substrate 110 is square, as shown in FIG. 1 , and its size is 8 mm × 8 mm. A plurality of microstructures 120 are arranged within a circular region with a diameter of 8 mm on the surface of the substrate 110. FIG. 14 schematically shows a cross section of a certain portion of the metalens 100.

[0069] Each of the microstructures 120 shown in FIG. 14 is a cylindrical pillar. The target wavelength is 10.6 μm. The width D of each microstructure 120 is determined within a range of 1 μm to 5 μm depending on the target phase value and transmittance at that position, as shown in FIGS. 6A and 6B . The spacing (i.e., period) P between the microstructures 120 is determined within a range of 3.5 μm to 6.8 μm depending on the target phase value and transmittance at that position, as shown in FIGS. 8A and 8B . The target phase value at each position is set so that the focal length of the metalens 100 is 5 mm. The height of each microstructure 120 is 6.8 μm. The maximum angle of view of the metalens 100 is ±30°.

[0070] As shown in FIG. 12B , an aperture stop 300 is disposed in front of the metalens 100. The aperture stop 300 is circular and has a diameter of 3 mm. The distance between the aperture stop 300 and the substrate 110 is 4 mm. Note that the numerical values ​​in this example are merely examples and can be adjusted as appropriate depending on the application or purpose of the metalens 100.

[0071] The metalens 100 can be fabricated using common semiconductor manufacturing techniques such as lithography. For example, the metalens 100 can be fabricated by the following method. First, a silicon substrate having a main crystal plane oriented in the (100) plane is prepared as the substrate 110. Next, a positive resist is applied to the main surface of the silicon substrate by a method such as spin coating. Next, light or an electron beam is irradiated at desired locations, and then a development process is performed. This removes the resist from the locations irradiated with light or an electron beam. This silicon substrate is then irradiated with SF ６ The etching is performed using a reactive ion etching technique or the like using an etching gas such as a gas. This etches the main surface of the silicon substrate where the resist has been removed. Then, a wet process using a resist remover or the like is performed. ２ Resist remaining on the main surface of the silicon substrate is removed by a dry process such as ashing. Through these steps, metalens 100 having substrate 110 and each of microstructures 120 can be produced.

[0072] 15 is a diagram showing an example of a method for dividing a lens surface on which microstructures 120 are arranged into areas. As described above, the lens surface is divided into a plurality of areas, and the structure or arrangement of each microstructure 120 is determined for each area based on different design data. The area division is performed based on the positions on the lens surface reached by each of the chief rays with different angles of incidence. Let n1 be the refractive index of the medium (e.g., air) surrounding metalens 100, n2 be the refractive index of metalens 100, L1 be the distance between aperture stop 300 and metalens 100, and θ be the maximum angle of incidence. ｍａｘ , the number of discretized incident angles is N. In this embodiment, θ ｍａｘ = 27, and N = 10. From these values, a number of areas are determined as shown in Table 1 below.

[0073]

[0074] Here, the incident angle θ ｉ Position r of the chief ray ｉ represents the distance from the intersection of the lens surface and the optical axis (i.e., the center of the lens surface).

[0075] FIG. 16 shows the difference in effect between a comparative example in which the structure and arrangement of each microstructure 120 were determined based on design data that considered only normal incidence, and the example. The upper left and upper right diagrams of FIG. 16 show the distribution of actual pillar diameters within the lens surface when cylindrical pillars are used as the microstructures 120. The lower left and lower right diagrams of FIG. 16 are graphs showing the change in phase position in the region near the edge of the metalens (the region surrounded by the dotted line in the upper diagram), where deviation from the designed phase is likely to be large. In these graphs, the horizontal axis represents the distance r from the lens center, and the vertical axis represents the designed and actual values ​​of the unwrapped phase. As can be seen from these graphs, there is a large deviation between the designed value and the actual value in the comparative example, but there is almost no deviation in the example. These results confirm the effectiveness of this example.

[0076] In this example, the effect of providing an aperture stop has been described, but the same effect can be expected by providing a scanning optical system that uses a laser or the like for incident light, thereby controlling the position within the lens surface at which the chief ray of each incident angle reaches.

[0077] (Modifications) In the above embodiment, the substrate 110 and each of the plurality of microstructures 120 are made of the same material, but they may also be made of different materials. In order to suppress unwanted reflection or refraction between the substrate 110 and the array of the plurality of microstructures 120, the difference between the refractive index of the substrate 110 and the refractive index of each of the plurality of microstructures 120 may be, for example, 10% or less, 5% or less, or 3% or less of the smallest refractive index of the refractive index of the substrate 110 and the refractive index of each of the plurality of microstructures.

[0078] The substrate 110 and each of the microstructures 120 may be made of a material primarily composed of at least one selected from the group consisting of silicon, germanium, chalcogenide, chalcohalide, zinc sulfide, zinc selenide, fluoride compounds, thallium halide, sodium chloride, potassium chloride, potassium bromide, cesium iodide, and plastic (e.g., polyethylene). Here, the term "primary component" refers to the component that is contained in the material in the highest proportion, expressed in mole percent. When the substrate 110 and each of the microstructures 120 are made of such materials, the transmittance of infrared light in the range of 2.5 μm to 25 μm can be increased.

[0079] In order to improve transmittance, an AR (Anti-Reflection) functional film may be additionally formed. In addition to the AR functional film, various light modulation layers having a light modulation function may be provided on metalens 100.

[0080] FIG. 17 is a schematic cross-sectional view showing an example of a metalens 100 including a light modulation layer 130. In this example, the metalens 100 includes a light modulation layer 130 having a light modulation function on the surface of the substrate 110 opposite the surface on which the microstructures 120 are provided. The light modulation layer 130 may have an anti-reflection function for incident light, or may have other functions. For example, the light modulation layer 130 may function as a high-pass filter, low-pass filter, or band-pass filter that transmits only light in a target wavelength range. Alternatively, the light modulation layer 130 may be a polarization filter that transmits only specific polarizations of incident light. The light modulation layer 130 may also be a filter that attenuates or amplifies the transmission intensity of incident light in a specific wavelength range. The light modulation layer 130 may be an ND (Neutral Density) filter. The light modulation layer 130 may have a function of refracting incident light at a specific angle. The light modulation layer 130 may be composed of a single layer or multiple layers depending on the desired light modulation function. The light modulation layer 130 can be formed using a film formation method such as vacuum deposition or sputtering.

[0081] FIG. 18 shows an example of a metalens 100 in which the light modulation layer 130 includes a plurality of other microstructures 140 that are different from the microstructures 120. In this example, an array of microstructures 120 is provided on one surface of the substrate 110, and an array of other microstructures 140 is provided on the opposite surface of the substrate 110. Each of the other microstructures 140 may be a convex or concave body. The convex or concave body may be, for example, a cone having the shape of an elliptical cone or a polygonal pyramid, or a column having the shape of an elliptical cylinder or a polygonal cylinder. The shape, size, and arrangement of the other microstructures 140 may be different from the shape, size, and arrangement of the microstructures 120. The other microstructures 140 can be fabricated using a method similar to the fabrication process for each microstructure 120 described in the above example. By providing an array of microstructures (i.e., a metasurface) on both sides of the substrate 110, as in this example, it becomes easier to achieve a lens function that would be difficult to achieve using only one side.

[0082] The optical lenses of the present disclosure are widely applicable to devices that utilize lenses, such as cameras, LiDAR sensors, projectors, AR displays, telescopes, microscopes, or scanning optical devices.

[0083] REFERENCE SIGNS LIST 100 metalens 110 substrate 120 microstructure 130 light modulation layer 140 microstructure 200 image sensor 210 imaging surface 300 aperture stop 400 light irradiated object 410 light irradiated surface 500 scanning optical system

Claims

1. An optical lens for use with light in a predetermined target wavelength range, A substrate; a plurality of microstructures arranged on a surface of the substrate at intervals shorter than the shortest wavelength in the target wavelength range; Equipped with the structure and / or spacing of each of the plurality of microstructures varies with position on the surface so as to reduce a change in phase and transmittance depending on an incident angle of incident light at each position within a region in which the plurality of microstructures are provided; Optical lens.

2. The optical lens according to claim 1 , wherein the amount of change in the phase and the amount of change in the transmittance when the incident light is incident on the plurality of microstructures exhibits a different response for each incident angle.

3. The optical lens of claim 1, wherein the structure and / or spacing of each of the plurality of microstructures is determined based on design data created for each of a plurality of incident angles, the design data defining one or more parameters defining the structure and / or spacing and the relationship between the phase and the transmittance.

4. the design data is created in advance for each of a plurality of areas included in the region; Each of the plurality of areas corresponds to one of the plurality of angles of incidence; The optical lens of claim 3 , wherein the structure and / or spacing of each of the plurality of microstructures is determined based on the design data corresponding to one of the plurality of areas to which the position of the microstructure belongs.

5. each of the plurality of microstructures is a convex or concave body having an elliptical cylindrical structure; At least one of a height, a major axis, and a minor axis of the elliptical cylindrical structure is determined so as to reduce a change in phase and transmittance depending on an incident angle of incident light at each position within the region. The optical lens according to claim 1 .

6. each of the plurality of microstructures is a convex or concave body having an elliptical cylindrical structure; The plurality of microstructures are periodically arranged, a period of the plurality of microstructures is determined so as to reduce a change in phase and transmittance depending on an incident angle of incident light at each position within the region; The optical lens according to claim 1 .

7. Each of the plurality of microstructures is a convex or concave body having a polygonal columnar structure, The height and / or the length of at least one side of the polygonal column structure are determined so as to reduce the change in phase and transmittance depending on the incident angle of the incident light at each position within the region. The optical lens according to claim 1 .

8. Each of the plurality of microstructures is a convex or concave body having a polygonal columnar structure, The plurality of microstructures are periodically arranged, a period of the plurality of microstructures is determined so as to reduce a change in phase and transmittance depending on an incident angle of incident light at each position within the region; The optical lens according to claim 1 .

9. some of the microstructures are convex or concave bodies having an elliptical cylindrical structure, Another part of the plurality of microstructures is a convex or concave body having a polygonal column structure. The optical lens according to claim 1 .

10. The optical lens according to claim 1 , wherein the substrate and each of the plurality of microstructures are translucent to light in the target wavelength range.

11. 2. The optical lens of claim 1, wherein a difference between the refractive index of the substrate and the refractive index of each of the plurality of microstructures is 10% or less of the smallest refractive index among the refractive index of the substrate and the refractive index of each of the plurality of microstructures.

12. The optical lens of claim 1 , wherein the substrate and each of the plurality of microstructures are comprised of the same material.

13. The optical lens of claim 1 , wherein the wavelength range of interest includes at least a portion of the infrared wavelength range from 2.5 μm to 25 μm.

14. 2. The optical lens of claim 1, wherein the substrate and each of the plurality of microstructures are made of a material containing at least one selected from the group consisting of silicon, germanium, chalcogenides, chalcohalides, zinc sulfide, zinc selenide, fluoride compounds, thallium halides, sodium chloride, potassium chloride, potassium bromide, cesium iodide, and plastic as a main component.

15. The optical lens according to claim 1 , wherein the optical lens is made of a material mainly composed of silicon, and the crystal plane orientation of the silicon is (100), (110), or (111).

16. An optical lens according to any one of claims 1 to 15; An aperture stop; An optical system comprising: the incident light passes through the aperture stop and enters the optical lens; a structure and / or an interval between the plurality of microstructures is changed depending on a distance from an intersection point between a central axis of the aperture stop and the surface of the substrate; Optical system.

17. The optical system of claim 16 , wherein the aperture stop has an elliptical or polygonal shape.

18. An optical system according to claim 16; an image sensor for acquiring an image of the light collected by the optical lens; An imaging device comprising:

19. An optical lens according to any one of claims 1 to 15; A scanning optical system; An optical system comprising: The incident light is incident on the optical lens through the scanning optical system, a structure and / or an interval between the plurality of microstructures is changed depending on a distance from an intersection point between an optical axis of the scanning optical system and the surface of the substrate; Optical system.

20. 1. A method for manufacturing an optical lens for use with light in a predetermined wavelength range of interest, comprising the steps of: The optical lens has a plurality of microstructures arranged at intervals shorter than the shortest wavelength in the target wavelength range, and the method includes: determining a structure and / or an interval between each of the plurality of microstructures so as to reduce a change in phase and transmittance depending on an incident angle of incident light at each position in a region in which the plurality of microstructures are provided; forming the plurality of microstructures arranged at the determined intervals on a surface of a substrate; A method for manufacturing an optical lens, comprising: