Optical element

Abstract

An optical element includes: a substrate; a microstructure portion including a plurality of convex bodies, provided on a main surface of the substrate; a top layer provided on a top portion of the microstructure portion; and a bottom layer provided on a bottom portion of the microstructure portion, separated from the top layer. The shape of each of the plurality of convex bodies has a columnar shape or a frustum shape or a combination thereof. The top layer and the bottom layer include, as a main component, a material different from that of the plurality of convex bodies. The thickness of the top layer is different from the thickness of the bottom layer.

Description

Technical Field

[0001] This disclosure relates to optical components. Background Technology

[0002] In recent years, research and development of optical elements with microstructures such as superlenses have been underway (see, for example, Patent Document 1 and Non-Patent Document 1).

[0003] Existing technical documents Patent documents Patent Document 1: U.S. Patent Application Publication No. 2023 / 0194760 Non-patent literature Non-patent literature 1: Huang, Luocheng, et al. "Long wavelength infrared imaging under ambient thermal radiation via an all-silicon metalens.", OpticalMaterials Express, Sep.2021, Vol.11, No.9, pp.2907-2914 Summary of the Invention

[0004] The problem that the invention aims to solve In previous optical components, there was room for improvement in transmittance.

[0005] This disclosure provides an optical element with high transmittance.

[0006] Methods for solving problems An optical element according to one aspect of the present disclosure includes: a substrate; a microstructure portion comprising a plurality of protrusions disposed on the main surface of the substrate; a first layer disposed on the top of the microstructure portion; and a second layer separated from the first layer and disposed at the bottom of the microstructure portion, wherein each of the plurality of protrusions has a columnar or frustum-shaped shape or a combination thereof, and the first layer and the second layer contain a material different from the plurality of protrusions as a main component, and the thickness of the first layer is different from the thickness of the second layer.

[0007] Invention Effects According to this disclosure, optical elements with high transmittance can be provided. Attached Figure Description

[0008] Figure 1 This is a perspective view of the optical element in the implementation method.

[0009] Figure 2 This is a perspective view of a unit cell of the optical element in the embodiment.

[0010] Figure 3 This is a side view illustrating the function of the optical element in the embodiment.

[0011] Figure 4 This is a cross-sectional view showing a first example of a unit cell provided by an optical element in an embodiment.

[0012] Figure 5 This is a graph showing the transmittance of an optical element relative to incident light with a wavelength of 10 μm when the thickness of the modulated top and bottom layers is adjusted.

[0013] Figure 6 This is a graph showing the increase in the transmittance of an optical element relative to incident light with a wavelength of 10 μm when the thickness of the top and bottom layers is modulated.

[0014] Figure 7 This is a cross-sectional view of a second example of a unit cell provided by an optical element in an embodiment.

[0015] Figure 8 This is a graph showing the transmittance of an optical element relative to incident light with a wavelength of 10 μm when the thickness of the modulated top and bottom layers is adjusted.

[0016] Figure 9 This is a graph showing the increase in the transmittance of an optical element relative to incident light with a wavelength of 10 μm when the thickness of the top and bottom layers is modulated. Detailed Implementation

[0017] (Summary of this disclosure) The optical element of the first aspect of this disclosure comprises: a substrate; a microstructure portion including a plurality of protrusions disposed on the main surface of the substrate; a first layer disposed on the top of the microstructure portion; and a second layer separated from the first layer and disposed at the bottom of the microstructure portion, wherein each of the plurality of protrusions has a columnar or frustum-shaped shape or a combination thereof, and the first layer and the second layer contain a material different from the plurality of protrusions as the main component, and the thickness of the first layer is different from the thickness of the second layer.

[0018] Therefore, by providing the first and second layers, the transmittance of the optical element can be improved compared to the case without the first and second layers. Furthermore, by making the thicknesses of the first and second layers different, the transmittance of the optical element can be further improved.

[0019] The optical element of the second aspect of this disclosure is the optical element of the first aspect, wherein the first layer is more than 20% thicker than the second layer.

[0020] This allows for an increase in the transmittance of optical elements. For example, when an optical element has a large convex shape, its transmittance can be effectively increased.

[0021] The third-party optical element disclosed herein is a second-type optical element, wherein the plurality of convex bodies are arranged in a two-dimensional periodic manner on the main surface, and the area occupied by one of the convex bodies is more than 23% and less than 65% relative to the unit unit corresponding to one period of the arrangement.

[0022] Therefore, when the area ratio of the convex body is large, by making the first layer at the top more than 20% thicker than the second layer at the bottom, the transmittance of the optical element can be effectively improved.

[0023] In the optical element of the fourth aspect of this disclosure, the first layer is more than 73% thinner than the second layer in the optical element of the first aspect.

[0024] This allows for an increase in the transmittance of optical elements. For example, when an optical element has a small convex shape, its transmittance can be effectively increased.

[0025] The optical element of the fifth aspect of this disclosure is the optical element of the fourth aspect, wherein the plurality of convex bodies are arranged in a two-dimensional periodic manner on the main surface, and the area occupied by one of the convex bodies is more than 10% and less than 13% relative to the unit unit corresponding to one period of the arrangement.

[0026] Therefore, even with a small area ratio of the convex body, the transmittance of the optical element can be effectively improved by making the first layer at the top 73% thinner than the second layer at the bottom.

[0027] The optical element of the sixth aspect of this disclosure is an optical element of any one of the first to fifth aspects, wherein the refractive indices of the first layer and the second layer are different from the refractive index of the convex body in the range of greater than 1 and less than 5.

[0028] The optical element of the seventh aspect of this disclosure is an optical element of any one of the first to fifth aspects, wherein the first layer and the second layer are both single-layer films.

[0029] Therefore, by making both the first and second layers monolayers, film deposition can be easily achieved. Since the thickness of each of the first and second layers is more controllable, optical elements with the desired transmittance can be easily realized.

[0030] The optical element of the eighth aspect of this disclosure is an optical element of any one of the first to fifth aspects, wherein the first layer and the second layer are multilayer films.

[0031] By setting the first and second layers as multilayer films, the transmittance of each wavelength can be precisely set, for example, to block excess wavelengths.

[0032] The optical element of the ninth aspect of this disclosure is an optical element of any one of the first to fifth aspects, wherein the first layer and the second layer respectively contain one or more mixtures selected from the group consisting of silicon, germanium, chalcogenides, chalcogen halides, zinc sulfide, zinc selenide, fluorides, thallium halides, sodium chloride, potassium chloride, potassium bromide, cesium iodide and plastics as main components.

[0033] Therefore, the optical element enables incident light, which is far-infrared radiation, to pass through with high transmittance. Conventionally, high-refractive-index materials are typically used instead of glass as materials for transmitting far-infrared radiation. However, using high-refractive-index materials inherently reduces transmittance. In contrast, the optical element disclosed herein, by having a first layer and a second layer with different thicknesses, can improve the transmittance of incident light, and is therefore useful as an optical element targeting the far-infrared region. For example, in image sensing using the far-infrared region, by utilizing an optical element with high transmittance, noise reduction and improved sensing performance can be achieved.

[0034] The optical element of the tenth aspect of this disclosure is an optical element of any one of the first to fifth aspects, wherein the substrate and the microstructure portion contain silicon as the main component, and the orientation of the main surface of the substrate is any one of (100), (110) and (111).

[0035] Therefore, by utilizing general semiconductor processing techniques applicable to silicon, the precision of the shape and arrangement of multiple microstructures can be improved. Consequently, optical elements with the desired transmittance can be fabricated with high precision.

[0036] The optical element of the eleventh aspect of this disclosure is an optical element of any one of the first to fifth aspects, wherein the thickness of the first layer and the second layer is 50 nm or more and 5 μm or less.

[0037] Therefore, the deposition of the first and second layers can be easily performed. Because the thickness of each of the first and second layers is more controllable, optical elements with the desired transmittance can be easily achieved.

[0038] The optical element of the twelfth aspect of this disclosure is an optical element of any one of the first to fifth aspects, wherein the wavelength of the light incident on the optical element is λ, the refractive index of the medium surrounding the optical element is n, and the numerical aperture of the optical element is NA = nsinθ. fThe maximum half field of view of the aforementioned optical element is θ. i In the case of the above arrangement of multiple convex bodies, the period P satisfies: [Mathematical Expression 1] .

[0039] Therefore, by enabling the optical element to function as a lens, it is possible to suppress the reduction of aberrations and the reduction of light-gathering efficiency for light incident from an oblique angle.

[0040] The embodiments will now be described in detail with reference to the accompanying drawings.

[0041] Furthermore, the embodiments described below are either general or specific examples. The numerical values, shapes, materials, constituent elements, the arrangement and connection methods of constituent elements, steps, and the order of steps shown in the following embodiments are examples and are not intended to limit this disclosure. In addition, constituent elements in the following embodiments that are not described in the independent claims are described as optional constituent elements.

[0042] Furthermore, these figures are schematic diagrams and may not be strictly representational. Therefore, for example, the scales may not be consistent across different figures. Additionally, substantially identical components are labeled with the same reference numerals across different figures, and repetitive descriptions are omitted or simplified.

[0043] Furthermore, in this specification, terms such as parallel or perpendicular to indicate the relationship between elements, terms such as square or cylinder to indicate the shape of elements, and numerical ranges are not merely expressions of a strict meaning, but also imply that they include substantially equivalent ranges, such as differences of a few percent.

[0044] Furthermore, in this specification, the terms "above" and "below" do not refer to the absolute spatial orientation of upward (vertically above) and downward (vertically below), but are used as terms defined by the relative positional relationship between the substrate and the protrusion. Specifically, the direction in which the protrusion protrudes from the main surface of the substrate is considered "above," and the opposite direction is considered "below." In this case, the main surface on which the protrusion is provided among the multiple main surfaces of the substrate corresponds to the "upper surface" of the substrate. In addition, the terms "above" and "below" apply not only to the case where two constituent elements are arranged spaced apart from each other and other constituent elements exist between the two constituent elements, but also to the case where two constituent elements are arranged in close contact with each other.

[0045] Additionally, in this specification, "thickness direction" refers to the thickness direction of the substrate of the optical element, which is the direction perpendicular to the main surface of the substrate. Furthermore, unless otherwise specified, "top view" refers to the view taken from a direction perpendicular to the main surface of the substrate.

[0046] In addition, in this specification, "main component" refers to the component that is present in the largest proportion of the material, expressed as a mole percentage.

[0047] In addition, unless otherwise specified, in this specification, ordinal numbers such as "first" and "second" do not imply the quantity or order of the constituent elements, but are used for the purpose of avoiding confusion between the same constituent elements and for differentiation.

[0048] Furthermore, in this disclosure, the term "light" is not limited to visible light, but also applies to non-visible light. Visible light is light with a wavelength of 380 nm or more and 780 nm or less. Invisible light includes ultraviolet light, infrared light, far-infrared light, or radio waves. Ultraviolet light is light with a wavelength of 10 nm or more and 380 nm or less. Infrared light is light with a wavelength of 780 nm or more and 3000 nm (=3 μm) or less. Far-infrared light is light (electromagnetic waves) with a wavelength of 3 μm or more and 1000 μm (=1 mm) or less. Radio waves are electromagnetic waves with a wavelength of 1 mm or more.

[0049] (Implementation Method) [constitute] First, use Figure 1 , Figure 2 and Figure 3 The configuration of the optical element in the embodiment will be described. Figure 1 This is a diagram showing the optical element 100 of this embodiment. Figure 2 This is a perspective view showing an example of the structure of a unit cell 101 provided by the optical element 100 of this embodiment. Figure 3 This is a diagram illustrating the function of the optical element 100 in this embodiment.

[0050] like Figure 1 As shown, the optical element 100 includes a substrate 110 and a fine structure comprising a plurality of protrusions 120. Additionally, as... Figure 3 As shown, the optical element 100 includes a top layer 130, which is disposed on top of the microstructure portion as an example of a first layer, and a bottom layer 140, which is separated from the top layer 130 and disposed at the bottom of the microstructure portion as an example of a second layer. Figure 1 For ease of illustration, the top layer 130 and the bottom layer 140 are omitted from the diagram.

[0051] The top of the microstructure portion is the upper surface of each of the plurality of protrusions 120. The bottom of the microstructure portion is a portion equivalent to a valley, specifically, the portion of the upper surface of the substrate 110 located between the plurality of protrusions 120 when viewed from above. By providing a top layer 130 and a bottom layer 140, the transmittance can be improved compared to the case where the top layer 130 and the bottom layer 140 are not provided.

[0052] A fine structure comprising multiple protrusions 120 is disposed on the main surface of the substrate 110. Specifically, multiple protrusions 120 are disposed vertically on the main surface of the substrate 110. Each of the multiple protrusions 120 is columnar in shape. A columnar protrusion is also referred to as a column or "pillar". In the optical element 100, a unit element comprising one protrusion 120 is referred to as a "unit cell".

[0053] Optical element 100 is Figure 2 The illustrated unit cell 101 is an assembly. The optical element 100 is constructed by arranging multiple unit cells 101 in a two-dimensional manner. Specifically, when viewed from above on the main surface of the substrate 110, each unit cell 101 is a unit element that divides multiple convex bodies 120 one by one, with each convex body 120 located at the center of each unit cell 101. For example, the shape of each unit cell 101 corresponds to the area enclosed by the perpendicular bisector of the line segment connecting the centers of two adjacent convex bodies 120. When multiple convex bodies 120 are arranged at equal intervals in a matrix (i.e., a square lattice), each unit cell 101 has a square area of ​​the same size as the others as its shape. The length of one side of each unit cell 101 when viewed from above corresponds to the distance between the centers of adjacent convex bodies 120. Depending on the arrangement of the convex bodies 120, the top-view shape of each unit cell 101 may not be a square, but rather a regular hexagon or a regular octagon, or other polygons.

[0054] like Figure 2 As shown, a unit cell 101 includes a portion of a substrate 110, a protrusion 120, a top layer 130, and a portion of a bottom layer 140. The substrate 110 and the bottom layer 140 are disposed across a plurality of unit cells 101. The unit cells 101 cause incident light to produce a phase shift corresponding to the structure of the protrusion 120. Furthermore, in this embodiment, the plurality of unit cells 101 have the same structure as each other. The unit cells 101 correspond to one period of the periodic arrangement of the plurality of protrusions 120.

[0055] exist Figure 3 In the diagram, arrows indicate examples of light rays passing through optical element 100. In this embodiment, optical element 100, like a conventional convex lens, has the function of focusing incident light. Specifically, in... Figure 3In the example shown, incident light from the lower surface of the substrate 110 of the optical element 100 is focused by multiple convex bodies 120 due to phase changes varying depending on the incident position. To achieve the desired focusing characteristics, the shape, size, or orientation of each convex body 120 is appropriately determined. The structure of each convex body 120 can be appropriately determined, for example, based on data representing the phase profile to be achieved and the results of electromagnetic field simulations. Thus, an optical element having the function of focusing or diffusing light through fine structural parts can be called a "superlens." A superlens has multiple convex bodies 120 on its surface that are smaller than the wavelength of the incident light, and achieves lens function based on the phase shift of the convex bodies 120.

[0056] Each of the plurality of protrusions 120 has a sub-wavelength dimension shorter than the wavelength of the incident light onto the optical element 100, and can be arranged at sub-wavelength intervals or periodically. Furthermore, the dimension of the protrusion 120 refers to at least one of its maximum width when viewed from above and its height. The spacing of the protrusions 120 is the distance between the centers of two adjacent protrusions 120 when viewed from above the main surface of the substrate 110. The spacing of the protrusions 120 is also referred to as the pitch. The plurality of protrusions 120 can be arranged periodically or non-periodically.

[0057] The maximum width (e.g., diameter in the case of a circle) D of the convex body 120 when viewed from above is, for example, 0.1 μm or more and 10 μm or less. Furthermore, the spacing P of the convex bodies 120 is, for example, 1 μm or more and 10 μm or less. Additionally, the height H of the convex body 120 is, for example, 1 μm or more and 50 μm or less. Furthermore, the aspect ratio H / D of the convex body 120 is, for example, 1 or more and 500 or less. These values ​​are just examples and can be appropriately adjusted according to the application or purpose of the optical element 100.

[0058] Optical element 100 can be designed to have desired optical properties for light in a specified target wavelength band. The target wavelength band is, for example, a band defined by specifications. When the lower limit of the target wavelength band is, for example, 1 μm, the size and spacing of the convex bodies 120 can be set to values ​​shorter than 1 μm. Such microstructures, like the convex bodies 120 with nanoscale dimensions smaller than 1 μm, are sometimes referred to as "submicron structures" or "nanostructures." When the target wavelength band is in the infrared region, the size and spacing of the convex bodies 120 can be greater than 1 μm.

[0059] Here, "target wavelength" refers to the wavelength of light envisioned using optical element 100, and can be determined based on the specifications of optical element 100 or the specifications of the device equipped with optical element 100. The target wavelength may, for example, include at least a portion of the visible light band (about 400 nm and above and about 700 nm and below). Alternatively, the target wavelength may also include at least a portion of the ultraviolet light band (about 10 nm and above and about 400 nm and below). Alternatively, the target wavelength may also include at least a portion of the infrared light band (about 700 nm and above and about 1 mm and below). Alternatively, the target wavelength may also include at least a portion of the radio wave band (wavelength about 1 mm and above and about 1 m and below). Furthermore, unless otherwise specified, the term "wavelength" in this disclosure refers to wavelength in free space.

[0060] In one example, the target wavelength band may include at least a portion of the infrared wavelength band of 2.5 μm and above to 25 μm and below. The wavelength band of 2.5 μm and above to 25 μm and below is used, for example, in infrared sensing devices such as LiDAR (Light Detection and Ranging) sensors or infrared cameras. Alternatively, the target wavelength band may also include the far-infrared wavelength band of 5 μm and above to 14 μm and below, or the far-infrared wavelength band of 8 μm and above to 12 μm and below. The far-infrared wavelength band is used for thermal imaging, etc. Optical element 100 may be used, for example, in a camera device in combination with an image sensor. Optical element 100 may also be used in telescopes, microscopes, or scanning optical devices. However, optical element 100 is not limited to these applications.

[0061] The number of convex bodies 120 disposed on the main surface of the optical element 100 is determined by the appropriate number of lens characteristics to be achieved. The number of convex bodies 120 is, for example, in the range of 100 to 10,000, and may be less than 100 or more than 10,000 depending on the circumstances.

[0062] Here, a brief example of the design method for an optical element 100 with lens function is given. In the optical element 100, a plurality of convex bodies 120 are arranged at intervals shorter than the wavelength of the incident light. The desired phase profile is achieved by adjusting the orientation or size of each convex body 120. To improve focusing efficiency, the spacing P of the convex bodies 120, i.e., the size of the unit cell 101, can be designed to satisfy the Nyquist reference for sampling (P < λ / 2NA). Here, λ is the design wavelength of the optical element 100, and NA is the numerical aperture of the optical element 100.

[0063] Furthermore, the optical element 100 can be designed to achieve high focusing efficiency even for light incident at an angle on the optical element 100. For example, assuming a wavenumber k i Light travels from a medium with a refractive index of n (such as air) at an incident angle θ.i Incident on refractive index n s Consider the optical element 100. Let the wavenumber corresponding to the shortest wavelength λ in the target band be k. t (=2π·n / λ), the numerical aperture of optical element 100 is set as NA=nsinθ. f Angle of incidence θ i This refers to the maximum half-field-of-view angle of the optical element 100 (i.e., the maximum angle of incidence of light that can be used in a device including the optical element 100). The maximum angle of incidence of light mentioned here can be, for example, the maximum field-of-view angle of a device including the optical element 100, such as a camera, telescope, or microscope, or the maximum scanning angle of a scanning optical device including the optical element 100. The maximum half-field-of-view angle of the optical element 100 is θ. i Multiple convex bodies 120 are formed to impart a wavenumber component (i.e., spatial frequency component) of K1 or less to the incident light.

[0064] [Mathematical Expression 3] The minimum sampling interval P required to assign the maximum spatial frequency component K1 in unit cell 101 is determined by means of the sampling theorem, satisfying the following inequality (1).

[0065] [Mathematical Expression 4] Therefore, the spacing P of the plurality of convex bodies 120 is determined to satisfy the following equation (2).

[0066] [Mathematical Expression 5] By arranging multiple convex bodies 120 in a manner that satisfies equation (2), the sampling theorem can also be satisfied for obliquely incident light, thus making it easy to reproduce the ideal phase. Therefore, it is possible to suppress the reduction of aberrations and the reduction of light-gathering efficiency. Furthermore, it is not necessary for the optical element 100 to have a lens function, so it is not necessary to satisfy the above equation (2).

[0067] In this embodiment, the substrate 110 and the plurality of protrusions 120 are integrally formed using the same material. The substrate 110 and each protrusion 120 are made of a material whose main component is silicon with a crystal plane orientation of (100). In addition, the crystal plane orientation of silicon may also be (110) or (111). Alternatively, the substrate 110 and the protrusions 120 may also be made of a material different from silicon.

[0068] The thickness of substrate 110 is, for example, 500 μm. Figure 1As shown, the substrate 110 is square in shape, with dimensions of 8mm × 8mm. Multiple protrusions 120 are arranged within a circular region of 8mm diameter on the surface of the substrate 110. Furthermore, the thickness and shape of the substrate 110, as well as the shape and size of the region where the protrusions 120 are arranged, are not particularly limited.

[0069] In the optical element 100 of this embodiment, a top layer 130 and a bottom layer 140 with different thicknesses are provided. The top layer 130 is configured to contact the top of the microstructure portion, specifically the upper surface of each of the plurality of protrusions 120. The bottom layer 140 is configured to contact the bottom of the microstructure portion, specifically the portion of the main surface of the substrate 110 located between the plurality of protrusions 120 when viewed from above. By appropriately adjusting the thickness, material, and number of layers of the top layer 130 and the bottom layer 140, the transmittance of incident light can be improved. Furthermore, transmittance is expressed as the ratio of the intensity of the emitted light from the optical element 100 to the intensity of the incident light to the optical element 100.

[0070] The thicknesses of the top layer 130 and the bottom layer 140 are respectively 50 nm or more and 5 μm or less. It should be noted that the thickness of at least one of the top layer 130 and the bottom layer 140 can be 100 nm or more, 300 nm or more, or 500 nm or more. Furthermore, the thickness of at least one of the top layer 130 and the bottom layer 140 can be less than 3 μm, less than 2 μm, less than 1.5 μm, or less than 1 μm. Additionally, both the top layer 130 and the bottom layer 140 are monolayer films. The refractive indices of the top layer 130 and the bottom layer 140, for example, in the range greater than 1 and less than 5, differ from the refractive index of the convex body 120.

[0071] The top layer 130 and the bottom layer 140 contain materials different from those of the plurality of convex bodies 120 as their main components. The top layer 130 and the bottom layer 140 each contain one or more mixtures selected from the group consisting of silicon, germanium, chalcogenides, chalcogen halides, zinc sulfide, zinc selenide, fluorides, thallium halides, sodium chloride, potassium chloride, potassium bromide, cesium iodide, and plastics as their main components. The plastics are, for example, polyethylene.

[0072] The following explanations, based on specific simulation results, address the cases where the top layer 130 is thicker than the bottom layer 140 and the cases where the top layer 130 is thinner than the bottom layer 140.

[0073] [First example (top level > bottom level)] Figure 4 This is a cross-sectional view showing a first example of a unit cell 101 provided by the optical element 100 of this embodiment.

[0074] exist Figure 4In the example shown, the top layer 130 is thicker than the bottom layer 140. That is, when the thickness of the top layer 130 is set to T... T Set the thickness of the bottom layer (140) to T. B In the case of T T >T B .

[0075] Figure 5 This is a graph showing the transmittance of optical element 100 relative to incident light with a wavelength of 10 μm when the thicknesses of the top layer 130 and the bottom layer 140 are modulated. Figure 5 In the middle, the horizontal axis represents the thickness T of the top layer 130. T The vertical axis represents the thickness T of the bottom layer (140). B .

[0076] In the transmittance simulation, the shape, height H, and spacing P of the convex body 120 are fixed. Furthermore, the composition and refractive index of the convex body 120, the top layer 130, and the bottom layer 140 are also fixed. The thickness T of the top layer 130 is modulated. T The bottom layer is 140mm thick. B And the width D of the convex body 120.

[0077] The specific simulation conditions are as follows: The target wavelength is 10 μm. The convex body 120 is made of silicon. The top layer 130 and the bottom layer 140 are monolayer films of zinc sulfide (ZnS). Furthermore, the convex body 120 is cylindrical in shape. The height H of each convex body 120 is 30 μm. Additionally, the spacing P of the convex bodies 120, i.e., the size of the unit cell 101, is 2.8 μm.

[0078] The top layer is 130mm thick (T). T And the bottom layer is 140mm thick. B The area is modulated in 0.1 μm increments within a range of 0 μm to 1.5 μm. Furthermore, the width (diameter) D of each convex body 120 is modulated in 0.07 μm increments within a range of 1.51 μm to 2.56 μm. Moreover, the width D of the convex body 120 can be converted into the area occupied by one convex body 120 relative to the unit cell 101 (i.e., the area ratio). When the width D is 1.51 μm, the area ratio is approximately 23%, and when the width D is 2.56 μm, the area ratio is approximately 65%.

[0079] Figure 5 The transmittance shown is in T corresponding to the vertical and horizontal axes. T and T B Under the condition of 1.51 μm to 2.56 μm, the width D of each convex body 120 is modulated with a scale of 0.07 μm, and the value is obtained by averaging the transmittance obtained from the value of width D.

[0080] exist Figure 5 In the middle, it means to become T T =T B The straight line (specifically, the line segment extending diagonally upwards from the origin of the chart). The range to the right of this line (in the positive direction of the horizontal axis) represents T. T >T B Transmittance under the condition of [condition]. From [the following] Figure 5 It can be seen that, for T T >T B In this case, there is a tendency for the transmittance to increase. Furthermore, it is known that with a bottom layer thickness of 140 T... B With a fixed value, the thickness T of the top layer is 130. T The larger the value, the higher the transmittance.

[0081] Figure 6 This is a graph showing the increase in transmittance of optical element 100 relative to incident light with a wavelength of 10 μm when the thicknesses of the top layer 130 and the bottom layer 140 are modulated. The increase in transmittance is related to T. T =T B Compared to the previous case, let's set it to T. T >T B The increase in transmittance under certain conditions. Specifically, Figure 6 The increase in transmittance shown is Figure 5 The transmittance values ​​shown in the graphs are related to T. T =T B The difference between the maximum transmittance values ​​on the straight line. Figure 6 In the example shown, the maximum increase in transmittance is approximately 3%pt. Additionally, "%pt" is short for percentage point. A percentage point is a unit representing the difference between two values ​​expressed as a percentage (in %), and is sometimes simply referred to as a fraction (abbreviated: pt).

[0082] It should be noted that only the case with a design wavelength of 10 μm is illustrated here. However, as the design wavelength, the same simulations were performed for incident light of a certain intensity across the entire region ranging from 5 μm to 14 μm, and for incident light of a certain intensity across the entire region ranging from 8 μm to 12 μm. The results, similar to those for 10 μm, confirmed an increase in transmittance. Specifically, the increase in transmittance in the range of 5 μm to 14 μm is approximately 0.22% pt, and the increase in transmittance in the range of 8 μm to 12 μm is approximately 2.2% pt.

[0083] The top layer is 130mm thick (T). T With a thickness of 140 at the bottom layer T B The difference T T-T B For example, thickness T T The percentage is between 5% and 90%. This allows for a further increase in the transmittance. Alternatively, the differential T... T -T B For example, the thickness T can be... T It can be above 10%, above 20%, or even above 30%. Additionally, the difference T... T -T B For example, the thickness T can be... T It can be below 80%, below 70%, or below 60%.

[0084] [Second example (top level < bottom level)] Figure 7 This is a cross-sectional view showing a second example of a unit cell 101 provided by the optical element 100 of this embodiment.

[0085] exist Figure 7 In the example shown, the top layer 130 is thinner than the bottom layer 140. That is, when the thickness of the top layer 130 is set to T... T Set the thickness of the bottom layer (140) to T. B In the case of T T <T B .

[0086] Figure 8 This is a graph showing the transmittance of optical element 100 relative to incident light with a wavelength of 10 μm when the thicknesses of the top layer 130 and the bottom layer 140 are modulated. Figure 8 In the middle, the horizontal axis represents the thickness T of the top layer 130. T The vertical axis represents the thickness T of the bottom layer (140). B .

[0087] In the transmittance simulation, the shape, height H, and spacing P of the convex body 120 are fixed. Furthermore, the composition and refractive index of the convex body 120, the top layer 130, and the bottom layer 140 are also fixed. These fixed values ​​are the same as in the first example. The thickness T of the top layer 130 is modulated. T The bottom layer is 140mm thick. B And the width D of the convex body 120.

[0088] The top layer is 130mm thick (T). T And the bottom layer is 140mm thick. BThe area is modulated in 0.1 μm increments within a range of 0 μm to 1.5 μm. Furthermore, the width (diameter) D of each convex body 120 is modulated in 0.07 μm increments within a range of 1.01 μm to 1.15 μm. Additionally, the width D of the convex body 120 can be converted into the area occupied by one convex body 120 relative to the unit cell 101 (i.e., the area ratio). When the width D is 1.01 μm, the area ratio is approximately 10%, and when the width D is 1.15 μm, the area ratio is approximately 13%.

[0089] Figure 8 The transmittance shown is in T corresponding to the vertical and horizontal axes. T and T B Under these conditions, the transmittance obtained by averaging the transmittance obtained based on the value of the width D is modulated in 0.07 μm increments within a range of 1.01 μm to 1.15 μm.

[0090] exist Figure 8 In the middle, it means to become T T =T B The straight line (specifically, the line segment extending diagonally upwards from the origin of the chart). The range to the left of this line (the negative direction of the horizontal axis) represents T. T <T B Transmittance under the condition of [condition]. From [the following] Figure 8 It can be seen that, for T T <T B In this case, there is a tendency for the transmittance to increase. Furthermore, it is known that with a bottom layer thickness of 140 T... B With a fixed value, the thickness T of the top layer is 130. T The smaller the value, the higher the transmittance.

[0091] Figure 9 This is a graph showing the increase in transmittance of optical element 100 relative to incident light with a wavelength of 10 μm when the thicknesses of the top layer 130 and the bottom layer 140 are modulated. The increase in transmittance is related to T. T =T B Compared to the previous case, let's set it to T. T <T B The increase in transmittance under certain conditions. Specifically, Figure 9 The increase in transmittance shown is Figure 8 The transmittance values ​​shown in the graphs are related to T. T =T B The difference between the maximum transmittance values ​​on the straight line. Figure 9 In the example shown, the maximum increase in transmittance is approximately 1.3% pt.

[0092] It should be noted that only the case with a design wavelength of 10 μm is illustrated here. However, as the design wavelength, the same simulations were performed for incident light of a certain intensity across the entire region ranging from 5 μm to 14 μm, and for incident light of a certain intensity across the entire region ranging from 8 μm to 12 μm. The results, similar to those for 10 μm, confirmed an increase in transmittance. Specifically, the increase in transmittance in the range of 5 μm to 14 μm is approximately 1.4% pt, and the increase in transmittance in the range of 8 μm to 12 μm is approximately 0.8% pt.

[0093] The bottom layer is 140mm thick. B With a top layer thickness of 130 T T The difference T B -T T For example, thickness T B The percentage is between 5% and 90%. This allows for a further increase in the transmittance. Alternatively, the differential T... B -T T For example, the thickness T can be... B It can be above 10%, above 20%, or even above 30%. Additionally, the difference T... B -T T For example, the thickness T can be... B It can be below 80%, below 70%, or below 60%.

[0094] [Other examples] Table 1 shows the thickness T of the top layer 130. T The bottom layer is 140mm thick. B Simulation results of the optical element's performance with the convex body 120 and height H set to a specific value. Examples 3-6 show T... T >T B In the case of T, Examples 7 and 8 represent T <T B The left arrow in the table indicates content identical to that in the column to the left.

[0095] In Example 3, the thickness T of the top layer 130 T The thickness is 1.45μm, and the bottom layer has a thickness of 140T. B It is 1.20 μm. At this time, T T / T B =1.20, T T T BThe thickness is 20%. The spacing P of the convex bodies 120 is 2.80 μm, and the height H of the convex bodies 120 is 7.0 μm. The width (diameter) D of the convex bodies 120 is modulated within the range of 1.52 μm to 2.54 μm. When the width D of the convex body 120 is 1.52 μm, the area ratio of one convex body 120 to the unit cell 101 is approximately 23%, and when the width D is 2.54 μm, the area ratio is approximately 65%.

[0096] The wall surfaces of the substrate 110 and the protrusion 120 are made of silicon. The top layer 130 and the bottom layer 140 are made of zinc sulfide (ZnS).

[0097] Under the above conditions, when the width D of each convex body 120 is modulated within a range of 1.52 μm to 2.54 μm, the maximum transmittance of the optical element 100 relative to incident light with a wavelength of 10 μm is 94.1%. Let T be... T =T B The maximum transmittance under the same conditions is 93.0%. The maximum transmittance under the same conditions is 84.5%, i.e., without a top layer 130 and a bottom layer 140.

[0098] The above explanation addresses the case of Example 3, but Examples 4 through 8 follow the same principle. However, in Example 6, the top layer 130 and the bottom layer 140 are silicon dioxide (SiO2). Additionally, T... T =0.30μm, T B The transmittance values ​​at 0.25 μm and without film are the values ​​when the wavelength of incident light is 1.55 μm.

[0099] [Effects, etc.] As described above, in the optical element 100 of this embodiment, by making the top layer 130 and the bottom layer 140 have different thicknesses, compared to the case where the thicknesses of the top layer 130 and the bottom layer 140 are equal, the transmittance can be improved. When the proportion of the area occupied by the convex body 120 in the unit cell 101 when viewed from above is greater than a predetermined value, a configuration where the top layer 130 is thicker than the bottom layer 140 is advantageous from the viewpoint of improving transmittance. Conversely, when the proportion of the area occupied by the convex body 120 in the unit cell 101 when viewed from above is less than a predetermined value, a configuration where the top layer 130 is thinner than the bottom layer 140 is advantageous from the viewpoint of improving transmittance. Here, the predetermined value is, for example, 13% or more and 23% or less.

[0100] Furthermore, since the top layer 130 and the bottom layer 140 have different thicknesses, the control conditions for the thickness of each layer in the film-forming process can be eased. That is, compared to making the top layer 130 and the bottom layer 140 have the same thickness, it is easier to make the top layer 130 and the bottom layer 140 have different thicknesses. In particular, when the aspect ratio of the convex body 120 is large, it is difficult to make the thickness of the top layer 130 and the bottom layer 140 the same. For example, when the aspect ratio of the convex body 120 is 1 or greater, from the viewpoint of ease of manufacture, it is useful for the optical element 100 to have a top layer 130 and a bottom layer 140 with different thicknesses.

[0101] Furthermore, the first and second examples exemplify the combination of silicon and zinc sulfide, but are not limited to this. When using combinations of other materials, the same simulations can be performed to set the ratio of the thickness of the top layer 130 and the bottom layer 140 to the area of ​​the convex body 120 within an appropriate range.

[0102] Furthermore, the shape of each of the plurality of convex bodies 120 is not limited to cylindrical. Each of the plurality of convex bodies 120 may also have a columnar or frustum-shaped shape, or a combination thereof, other than cylindrical. A columnar shape is a cylindrical or elliptical cylinder, or a prism such as a square prism, hexagonal prism, or octagonal prism. A frustum-shaped shape is a frustum of a cone, an elliptical frustum, or a frustum of a square pyramid, hexagonal frustum, or octagonal frustum. In the case of a frustum-shaped body, the area of ​​the lower surface is larger than the area of ​​the upper surface, but it can also be the other way around. Additionally, a combination of columnar and frustum-shaped bodies can be, for example, a configuration where columnar bodies and frustum-shaped bodies are stacked in the height direction. That is, the convex body 120 may also have a shape in which the lower surface of one of the convex bodies contacts the upper surface of one of the columnar or frustum-shaped bodies. The number of combined columnar and frustum-shaped bodies can also be three or more.

[0103] [Manufacturing Method] Optical element 100 can be fabricated using conventional semiconductor manufacturing techniques such as photolithography. For example, optical element 100 can be fabricated by the following method.

[0104] First, as substrate 110, a silicon substrate with a crystal plane orientation of (100) is prepared. In addition, "surface" refers to one of the main surfaces of the silicon substrate. When the microstructure portion including multiple protrusions 120 and the substrate 110 are integrally formed, the "surface" of the silicon substrate becomes the front end surface of the top of the microstructure portion.

[0105] Next, a positive resist is coated onto the surface of the silicon substrate using methods such as spin coating. Then, the desired areas are irradiated with light or an electron beam, followed by development. This removes the resist from the irradiated areas. The silicon substrate is then etched using reactive ion etching techniques employing etching gases such as SF6 gas. This etches the surface of the silicon substrate where the resist has been removed. Subsequently, the resist remaining on the surface of the silicon substrate is removed using a wet process with a resist stripping solution or a dry process using O2 ashing. This forms a fine structure containing multiple protrusions 120 on the main surface of the substrate 110. This fine structure corresponds to the upper layer of the prepared silicon substrate.

[0106] Furthermore, a film is formed using a material different from the protrusions 120, covering the microstructure containing multiple protrusions 120. For example, zinc sulfide (ZnS) is formed on the top and bottom of the microstructure, respectively. Film formation is performed by methods such as EB (Electron Beam) vapor deposition, sputtering, or CVD (Chemical Vapor Deposition). The thicknesses of the top layer 130 and the bottom layer 140 can be adjusted by adjusting the film formation conditions. For example, by making the bias voltage applied to the substrate 110 in the film formation perpendicular to the substrate 110, the bottom layer 140 can be made thicker than the top layer 130.

[0107] Through these processes, an optical element 100 can be manufactured having a substrate 110, multiple protrusions 120, and a top layer 130 and a bottom layer 140 of different thicknesses.

[0108] Furthermore, if the substrate 110 and the protrusion 120 are formed using different materials, the protrusion 120 can also be formed by forming a film containing a different material from the substrate 110 on the main surface of the substrate 110 and then patterning it. The film is formed using methods such as epitaxial growth, vapor deposition, sputtering, CVD, or coating.

[0109] (Other implementation methods) The optical elements of one or more embodiments have been described above, but this disclosure is not limited to these embodiments. Various modifications that can be conceived by those skilled in the art to these embodiments, and ways of constructing by combining the constituent elements of different embodiments, are also included within the scope of this disclosure, as long as they do not depart from the spirit of this disclosure.

[0110] For example, in the above-described embodiment, an example was described where the optical element 100 comprises a plurality of unit cells 101 having identical structures. However, the plurality of unit cells 101 may also include unit cells having structures different from those of the other unit cells 101. For example, the plurality of unit cells 101 may include at least one unit cell whose size, shape, and material of the convex body 120 differs from those of the other unit cells 101. Alternatively, the plurality of unit cells 101 may include at least one unit cell whose thickness, material, and number of layers of at least one of the top layer 130 and the bottom layer 140 differs from those of the other unit cells 101.

[0111] Furthermore, in the above embodiment, an example is shown where the bottom of the microstructure portion is part of the main surface of the substrate 110, but this is not a limitation. For example, the microstructure portion may also include a plurality of protrusions 120 and a base portion that connects and supports the plurality of protrusions 120 to each other. The base portion is stacked on the main surface of the substrate 110. The base portion is formed using the same material as the plurality of protrusions 120. That is, the refractive index of the base portion is the same as the refractive index of each of the plurality of protrusions 120. In this case, the upper surface of the base portion (the main surface opposite to the substrate 110) becomes the bottom of the microstructure portion.

[0112] Alternatively, for example, the top layer 130 and the bottom layer 140 may each be multilayer films. In this case, the top layer 130 and the bottom layer 140 may have the same film structure, for example. The thickness of each of the plurality of films in the top layer 130 is different from the thickness of the corresponding films in the bottom layer 140. Alternatively, at least one of the plurality of films in the top layer 130 may have a thickness different from the thickness of the corresponding film in the bottom layer 140, while at least one other film in the top layer 130 may have the same thickness as the corresponding film in the bottom layer 140.

[0113] In addition, the top layer 130 and the bottom layer 140 can also contain different materials as main components.

[0114] Alternatively, a layer containing the same material as the top layer 130 or the bottom layer 140 as the main component can be provided on the side of the convex body 120.

[0115] Furthermore, the above-described embodiments can be modified, substituted, added, or omitted in various ways within the scope of the claims or their equivalents.

[0116] Industrial applicability This disclosure can be applied to devices with optical elements such as lenses, such as cameras, LiDAR sensors, projectors, AR (Augmented Reality) displays, telescopes, microscopes, or scanning optical devices.

[0117] Explanation of reference numerals in the attached figures 100 Optical Components 101 unit 110 substrate 120 convex body 130 Top Floor 140 Bottom Layer

Claims

1. An optical element comprising: substrate; A microstructure portion comprising a plurality of protrusions disposed on the main surface of the substrate; The first layer is disposed on top of the microstructure; and The second layer, separate from the first layer, is disposed at the bottom of the microstructure portion. The plurality of convex bodies each have a columnar or frustum-shaped shape or a combination thereof. The first and second layers contain materials as main components that are different from the plurality of convex bodies. The thickness of the first layer is different from the thickness of the second layer.

2. The optical element according to claim 1, wherein, The first layer is more than 20% thicker than the second layer.

3. The optical element according to claim 2, wherein, The plurality of convex bodies are arranged periodically in a two-dimensional pattern on the main surface. The area occupied by one of the convex bodies is more than 23% and less than 65% relative to the unit unit corresponding to one period of the arrangement.

4. The optical element according to claim 1, wherein, The first layer is more than 73% thinner than the second layer.

5. The optical element according to claim 4, wherein, The plurality of convex bodies are arranged periodically in a two-dimensional pattern on the main surface. The area occupied by one of the convex bodies is more than 10% and less than 13% relative to the unit unit corresponding to one period of the arrangement.

6. The optical element according to any one of claims 1 to 5, wherein, The refractive indices of the first and second layers are different from those of the convex body in the range of greater than 1 and less than 5.

7. The optical element according to any one of claims 1 to 5, wherein, The first layer and the second layer are both single-layer films.

8. The optical element according to any one of claims 1 to 5, wherein, The first layer and the second layer are both multilayer films.

9. The optical element according to any one of claims 1 to 5, wherein, The first layer and the second layer each contain one or more mixtures selected from the group consisting of silicon, germanium, chalcogenides, chalcogen halides, zinc sulfide, zinc selenide, fluorides, thallium halides, sodium chloride, potassium chloride, potassium bromide, cesium iodide, and plastics as main components.

10. The optical element according to any one of claims 1 to 5, wherein, The substrate and the microstructure contain silicon as the main component, and the orientation of the main surface of the substrate is any one of (100), (110) and (111).

11. The optical element according to any one of claims 1 to 5, wherein, The thickness of the first layer and the second layer is respectively greater than 50 nm and less than 5 μm.

12. The optical element according to any one of claims 1 to 5, wherein, In a case where a wavelength of light incident on the optical element is λ, a refractive index of a medium around the optical element is n, a numerical aperture of the optical element is NA = nsinθ f , and a maximum half field angle of the optical element is θ i , the arrangement period P of the plurality of convex bodies satisfies: 。

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