Optical lens

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 λ in the target wavelength range. The interval P of the fine structures satisfies P < λ / 2 (nsinθf + nsinθi), where n defines the refractive index of a medium surrounding the optical lens, NA=nsinθf defines the number of openings of the optical lens, and ±θi defines the maximum viewing angle of the optical lens.

Description

Optical Lenses

[0001] The present disclosure relates to optical lenses.

[0002] In recent years, research and development of metalenses, which have fine surface structures known as metasurfaces, has progressed. Metasurfaces are surfaces with metamaterial structures 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 and 2.

[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] JP 2019-516128 A JP 2021-71727 A

[0006] Conventional metalenses generally have a structure that takes into account only normal incidence, and have issues with the light-gathering performance for obliquely incident light.

[0007] The present disclosure provides an optical lens that can improve the light-gathering performance of obliquely incident light.

[0008] An optical lens according to one aspect of the present disclosure is used for light in a predetermined target wavelength range, and includes a substrate and a plurality of microstructures arranged on a surface of the substrate at intervals shorter than the shortest wavelength λ in the target wavelength range, where n is the refractive index of a medium surrounding the optical lens, and NA=n sin θ is the numerical aperture of the optical lens. ｆ , the maximum angle of view of the optical lens is ±θ ｉ Then, the interval P of the fine structures is as follows: P<λ / 2(n sin θ ｆ +n sin θ ｉ )

[0009] where θ ｆ is the aperture half angle relative to the numerical aperture NA.

[0010] 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.

[0011] According to one aspect of the present disclosure, it is possible to improve the light-gathering performance of an optical lens for obliquely incident light.

[0012] FIG. 1 is a perspective view schematically illustrating an example of a metalens. FIG. 2 is a perspective view schematically illustrating an example of the structure of a unit cell. FIG. 3 is a diagram schematically illustrating the function of a metalens. FIG. 4 is a diagram illustrating the unit cell spacing conditions for creating a metalens with desired performance for normally incident light. FIG. 5A is a diagram illustrating the light focusing performance of a conventional metalens. FIG. 5B is a diagram illustrating the light focusing performance of a conventional metalens. FIG. 6 is a diagram illustrating the unit cell spacing conditions for creating a metalens with desired performance for obliquely incident light. FIG. 7A is a diagram illustrating an example of an ideal phase profile. FIG. 7B is a diagram illustrating a phase profile wrapped in the phase range from -π to π. FIG. 7C is a diagram illustrating an example of sampling to achieve an ideal phase profile. FIG. 8 is a diagram illustrating an example of the relationship between the sampling number N and diffraction efficiency. FIG. 9 is a diagram schematically illustrating an example of a metalens. FIG. 10 is a schematic cross-sectional view of an example of a metalens including a light modulation layer. FIG. 11 is a diagram illustrating an example of a metalens in which the light modulation layer includes a plurality of other microstructures. Figure 12A shows an example of the light focusing performance of a metalens according to the prior art, Figure 12B shows an example of the light focusing performance of a metalens according to an embodiment of the present disclosure, and Figure 12C shows an example of the light focusing performance of a metalens according to another embodiment of the present disclosure.

[0013] 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.

[0014] 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.

[0015] (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.

[0016] 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.

[0017] Figure 1 is a perspective view schematically illustrating an example of a metalens. The metalens 100 shown in Figure 1 includes a substrate 110 and a plurality of microstructures 120 provided on the surface of the substrate 110. In this example, each of the microstructures 120 is a columnar body (also called a "pillar") having a shape similar to a cylinder. A unit element in the metalens 100 that includes one microstructure 120 is called a "unit cell." The metalens 100 is an assembly of a plurality of unit cells.

[0018] 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.

[0019] FIG. 3 is a diagram schematically illustrating the function of metalens 100. In FIG. 3, arrows indicate exemplary light rays. Metalens 100 in this example has the function of focusing incident light, similar to a conventional convex lens. In the example of FIG. 3, incident light entering from the substrate side of metalens 100 is focused by undergoing different phase changes depending on the position through the array of microstructures 120. The shape, width, height, orientation, and the like of each microstructure 120 are appropriately determined to achieve desired focusing characteristics. 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.

[0020] 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.

[0021] 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.

[0022] The number of microstructures 120 provided on the surface of metalens 100 is determined to be 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.

[0023] Here, we will briefly describe an example of a conventional metalens design method. One example of a conventional metalens design method is the method disclosed in Patent Document 1. In the method disclosed in Patent Document 1, multiple nanostructures (e.g., nanofins or nanopillars) are arranged at intervals shorter than the wavelength of incident light. A desired phase profile is achieved by adjusting the orientation of each nanofin or the size of each nanopillar. Patent Document 1 describes that, to increase efficiency, the size U of the unit cell (i.e., the spacing between nanostructures) can be designed to satisfy the Nyquist criterion for sampling (U<λ / 2NA), where λ is the design wavelength of the metalens and NA is the numerical aperture of the metalens.

[0024] However, the above design only takes into account normal incidence and does not take into account oblique incidence of light. Even if the above Nyquist criterion is satisfied, sufficient light collection performance may not be obtained for oblique incidence of light. This issue will be explained below with reference to FIGS. 4 and 5.

[0025] Figure 4 is a diagram illustrating a conventional method for determining the unit cell spacing (or period) required to create a metalens with a certain numerical aperture. The upper diagram (a) in Figure 4 schematically shows how light incident on metalens 100 parallel to the optical axis changes its path at the surface on which microstructures 120 are formed (hereinafter, sometimes referred to as the "lens surface"). The lower diagram (b) in Figure 4 is a schematic enlarged view of the area surrounded by the dashed circle in the upper diagram (a).

[0026] In the example of FIG. ｓ Light is incident on the metalens 100 in a direction parallel to the optical axis from a medium (e.g., air) with a refractive index n. The wave number corresponding to the shortest wavelength λ in the target wavelength range is k. ｔ (=2π·n / λ), and the numerical aperture of the metalens 100 is NA=n sin θ ｆ Here, θ ｆ is the half angle of the aperture relative to the numerical aperture NA. In this case, the maximum K ０ The microstructure 120 is formed so as to give the wave number components (i.e., spatial frequency components) of the above to the incident light.

[0027] Maximum spatial frequency component K in the unit cell ０ The minimum sampling interval required to provide this, i.e., the unit cell interval P, is determined based on the sampling theorem. The sampling theorem states that the original signal can be restored if it is sampled at a frequency that is more than twice the maximum frequency contained in a continuous signal. According to the sampling theorem, the interval P is determined so as to satisfy the following inequality (2).

[0028] Therefore, the spacing P of the microstructures 120 is determined so as to satisfy the following inequality.

[0029] By determining the spacing (or period) P of the microstructures 120 so as to satisfy this condition, it is possible to achieve an ideal phase profile for light that is perpendicularly incident on the metalens 100.

[0030] However, the above design method assumes that the angle of incidence of the incident light is 0° and does not take into account the wave number component of obliquely incident light. As the above sampling theorem may not be satisfied for obliquely incident light, the ideal phase cannot be uniquely reproduced and the light-collection performance as designed cannot be obtained.

[0031] 5A and 5B are diagrams illustrating the light focusing performance of a metalens 100 in which microstructures 120 are arranged at a period P that satisfies Equation (3). FIG. 5A schematically shows how light that is perpendicularly incident on the metalens 100 is focused and incident on the imaging surface of the image sensor 200. FIG. 5B schematically shows how light that is perpendicularly incident on the metalens 100, as well as light that is obliquely incident, are incident on the imaging surface of the image sensor 200. As shown in FIG. 5A, the metalens 100 has high light focusing performance for perpendicularly incident light. However, as shown by the dashed ellipse in FIG. 5B, obliquely incident light does not focus to a single point and forms a blurred image on the imaging surface of the image sensor 200. This is because the period of the microstructures 120 is determined taking into consideration only the phase distribution for focusing perpendicularly incident light. For obliquely incident light, the sampling theorem is not satisfied, and the ideal phase cannot be reproduced, resulting in reduced light focusing performance.

[0032] In order to solve the above problems, the inventors have conceived the configuration of the embodiment of the present disclosure described below. The configuration of the optical lens according to the embodiment of the present disclosure will be described below.

[0033] (Embodiment) 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 provided on a surface of the substrate. The plurality of microstructures are arranged at intervals shorter than the shortest wavelength in the target wavelength range. The refractive index of the medium surrounding the optical lens is n, and the numerical aperture of the optical lens is NA=n sin θ. ｆ , the maximum angle of view of the optical lens is ±θ ｉ In this case, the interval P between the microstructures is determined so as to satisfy the following formula (4).

[0034] 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.

[0035] 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.

[0036] 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.

[0037] Here, the meaning of the condition in equation (4) will be explained with reference to FIG.

[0038] Figure 6 is a diagram illustrating a method for determining the spacing (or period) P of unit cells required to produce an optical lens (i.e., a metalens) according to this embodiment. The upper diagram (a) in Figure 6 schematically shows how light incident at an angle on the metalens 100 changes its path at the lens surface on which the microstructures 120 are formed. The lower diagram (b) in Figure 6 is a schematic enlarged view of the area surrounded by the dashed circle in the upper diagram (a).

[0039] In the example of FIG. ｓ is incident on the metalens 100 from a medium (e.g., air) with a refractive index n at an incident angle θ ｉ and wave number k ｉ Metalens 100 may be used in combination with an image sensor, for example, in an imaging device. Metalens 100 may also be used in a telescope, microscope, or scanning optical device. Let k be the wavenumber corresponding to the shortest wavelength λ in the wavelength range of interest. ｔ (=2π·n / λ), and the numerical aperture of the metalens 100 is NA=n sin θ ｆ The incident angle θ ｉis the maximum half angle of view of metalens 100 (i.e., the maximum angle of incidence of light that can be used in a device including metalens 100). The maximum angle of incidence of light here may be, for example, the maximum angle of view of a device such as an imaging device, telescope, or microscope that includes metalens 100, or the maximum scanning angle of a scanning optical device that includes metalens 100. Note that metalens 100 is not limited to these applications. The plurality of microstructures 120 may have a maximum K １ The optical element is formed so as to give the incident light a wave number component (i.e., a spatial frequency component) of .gtoreq.1.

[0040] Maximum spatial frequency component K in the unit cell １ The minimum sampling interval P required to provide the above is determined according to the sampling theorem so as to satisfy the following inequality (6):

[0041] Therefore, the interval P of the microstructures 120 is determined so as to satisfy the following inequality (7).

[0042] By determining the position of each microstructure 120 so as to satisfy this inequality, the sampling theorem can be satisfied even for obliquely incident light, making it easier to reproduce the ideal phase. As a result, it is possible to reduce aberrations and prevent a decrease in light collection efficiency.

[0043] Next, a more preferable arrangement of the microstructure 120 will be described with reference to FIGS. 7A to 7C.

[0044] FIG. 7A shows an example of an ideal phase profile. The horizontal axis represents the coordinate r with the center of the metalens 100 as the origin, and the vertical axis represents the phase Φ. FIG. 7B shows a phase profile wrapped in a phase range from -π to π. FIG. 7C shows an example of sampling for achieving an ideal phase profile. The black dots in FIG. 7C indicate example positions of the microstructures 120 (i.e., sampling points). As shown in these figures, an appropriate number of microstructures 120 are placed for each of the multiple intervals wrapped between -π and π. According to the sampling theorem, two or more microstructures 120 are placed for each continuous interval from -π to π.

[0045] In this example, the phase steepness differs near the center and near the edge of the lens. The rate of change of the phase Φ with respect to a change in position r is greater near the edge than near the center. In such a case, the spacing P2 of the microstructures 120 near the edge may be smaller than the spacing P1 of the microstructures 120 near the center. By arranging the microstructures 120 in this way, the ideal phase profile can be reproduced more accurately.

[0046] The more the number of microstructures 120 included in one continuous section from -π to π, i.e., the number of samples, is increased, the more the reproducibility of the phase profile improves. For example, by arranging three or more or four or more microstructures 120 in each section, the reproducibility of the phase profile can be further improved.

[0047] If the difference between the left and right sides of the above inequality (6) is small, the wrapping phase is reproduced at two points, which may result in low reproducibility. Therefore, we expand equation (6) to the following equation (8), where N is an integer equal to or greater than 2.

[0048] In this case, the interval P between the microstructures 120 is determined so as to satisfy the following formula (9).

[0049] 8 is a diagram showing an example of the relationship between the sampling number N and the diffraction efficiency η. ２The relational expression (1 / N) is known. A practical diffraction efficiency is, for example, 80% or more. From FIG. 8, if N≧4, the diffraction efficiency is 80% or more. Therefore, N may be set to an integer of, for example, 4 or more. As an example, when N=4, the spacing P(r) of the microstructures 120 satisfies the following equation (10).

[0050] By arranging the microstructures 120 so as to satisfy the formula (10), it is possible to further suppress the deterioration of the light-collecting performance.

[0051] Note that if the sampling number N is too large, undesirable problems such as a decrease in processing accuracy, a decrease in durability, or an increase in process variation during manufacturing may occur. For this reason, a lower limit may be set for the spacing P of the microstructures 120. For example, the value on the right side of equation (10) when N = 8 or N = 10 may be set as the lower limit for P. As an example, when the value when N = 8 is set as the lower limit, the spacing P of the microstructures 120 is determined to satisfy the following equation (11).

[0052] By arranging the microstructures 120 so as to satisfy the formula (11), problems such as a decrease in processing accuracy, a decrease in durability, or an increase in process variations during manufacturing can be effectively suppressed.

[0053] The spacing P of the microstructures 120 may be determined so as to satisfy both Expression (10) and Expression (11). With such a configuration, it is possible to achieve both an improvement in the light-collecting performance for obliquely incident light and advantages in manufacturing.

[0054] (Example) Next, an example of the optical lens will be described.

[0055] FIG. 9 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 primarily composed of silicon with 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.

[0056] 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. 9 schematically shows a cross section of a certain portion of the metalens 100.

[0057] Each of the microstructures 120 shown in FIG. 9 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 3 μm according to the target value of the phase at that position. The height of each microstructure 120 is 7 μm. The maximum angle of view of the metalens 100 is ±30° (i.e., the maximum half angle of view is 30°). The microstructures 120 are arranged two-dimensionally as shown in FIG. 1. The microstructures 120 are periodically arranged from the center to the edge at intervals that satisfy the above formula (7). Note that these numerical values ​​are merely examples and may be adjusted as appropriate depending on the application or purpose of the metalens 100.

[0058] 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.

[0059] (Modifications) Next, modifications of the metalens 100 will be described.

[0060] In the above embodiment, each microstructure 120 is a convex body having a cylindrical shape, but each microstructure 120 may have a shape other than a cylindrical shape. For example, each microstructure 120 may be a columnar body having an elliptical cylinder or polygonal prism shape other than a cylindrical shape. 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, but may also be a concave body. The convex or concave body constituting the microstructure 120 may have any structure, such as a columnar body having an elliptical cylinder or polygonal prism shape, or a pyramidal body having an elliptical cone or polygonal pyramid shape.

[0061] In the above example, 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. 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.

[0062] 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.

[0063] 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.

[0064] FIG. 10 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.

[0065] FIG. 11 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.

[0066] Next, with reference to FIGS. 12A to 12C , the effects of the optical lens (i.e., the metalens) of this embodiment will be described in comparison with the prior art.

[0067] 12A is a diagram showing an example of the light focusing performance of a metalens 100A according to the prior art. In the example of FIG. 12A, the period of the microstructures is determined to satisfy the above formula (3), but does not satisfy the above formula (7). Because the sampling theorem is not satisfied for obliquely incident light, the obliquely incident light does not focus to a single point, and a blurred image is formed.

[0068] Figure 12B is a diagram showing an example of the focusing performance of a metalens 100B according to an embodiment of the present disclosure. In the example of Figure 12B, the period of the microstructures is determined to satisfy equation (7) above. Since the sampling theorem is satisfied not only for perpendicularly incident light but also for obliquely incident light, obliquely incident light is also focused to a single point. This allows the desired focusing performance to be achieved for obliquely incident light as well.

[0069] 12C is a diagram showing an example of the light focusing performance of a metalens 100C according to another embodiment of the present disclosure. In the example of FIG. 12C , an array of multiple microstructures is provided on both sides of a substrate. By providing a light control function to the back side of the substrate as in this example, it is possible to achieve not only improved light focusing performance for oblique incidence, but also further enhanced functionality such as improved transmittance.

[0070] The optical lens of the present disclosure is widely applicable to devices that utilize lenses, such as cameras, LiDAR sensors, projectors, AR displays, telescopes, microscopes, or scanning optical devices.

[0071] 100 Metalens 110 Substrate 120 Microstructure 130 Light modulation layer 140 Microstructure 200 Image sensor

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 λ in the target wavelength range; Equipped with The refractive index of the medium surrounding the optical lens is n, the numerical aperture of the optical lens is NA, and the maximum angle of view of the optical lens is ±θ ｉ In this case, the interval P between the microstructures is set so that the microstructures can condense the light that is perpendicularly incident on the substrate and the light that is obliquely incident on the substrate. [0010] Optical lenses that satisfy the above requirements.

2. When the aperture half angle for the numerical aperture is θ f , the interval P is [0025] The optical lens according to claim 1 , which satisfies the following:

3. When the aperture half angle for the numerical aperture is θ f , the interval P is [0030] The optical lens according to claim 1 , which satisfies the following:

4. The optical lens according to claim 1 , wherein each of the plurality of microstructures is a convex body or a concave body.

5. The optical lens according to claim 4 , wherein each of the plurality of microstructures is a cone-shaped body having an elliptical cone or polygonal pyramid shape, or a column-shaped body having an elliptical cylinder or polygonal cylinder shape.

6. 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.

7. 4. The optical lens according to 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.

8. The optical lens according to claim 1 , wherein the substrate and each of the plurality of microstructures are made of the same material.

9. The optical lens according to claim 1 , wherein the target wavelength range includes at least a portion of an infrared wavelength range from 2.5 μm to 25 μm.

10. 4. The optical lens according to 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, chalcogenide, chalcohalide, zinc sulfide, zinc selenide, a fluoride compound, thallium halide, sodium chloride, potassium chloride, potassium bromide, cesium iodide, and plastic as a main component.

11. The optical lens according to claim 10, 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).

12. The optical lens according to claim 1 , further comprising a light modulating layer having a light modulating function on a surface of the substrate opposite to the surface.

13. the light modulating layer includes a plurality of other microstructures; The optical lens according to claim 12 , wherein each of the other plurality of microstructures is a convex body or a concave body.

14. The optical lens according to claim 13 , wherein each of the other plurality of microscopic structures is a cone-shaped body having an elliptical cone or polygonal pyramid shape, or a column-shaped body having an elliptical cylinder or polygonal cylinder shape.

15. The optical lens according to claim 12 , wherein the light modulation layer has an anti-reflection function for incident light.

16. The optical lens according to claim 12 , wherein the light modulation layer functions as any one of a high-pass filter, a low-pass filter, and a band-pass filter that transmits only light in the target wavelength range.

17. The optical lens according to claim 12 , wherein the light modulation layer has a function of transmitting only a specific polarized light of incident light.

18. The optical lens according to claim 12 , wherein the light modulation layer has a function of attenuating or amplifying the transmission intensity of incident light in a specific wavelength range.

19. The optical lens according to claim 12 , wherein the light modulation layer has a function of refracting incident light at a specific angle.

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