Optical element

Abstract

An optical element 100 includes a plurality of fine structures 120 which are two-dimensionally arranged, and which each generate a phase difference in entry light and emit the resulting light as transmission light. Phases of transmission light from two adjacent fine structures 120 from among the plurality of fine structures 120 are different from each other. The optical element 100 has transmittance determined by mutual interference of transmission light that is emitted from the plurality of fine structures 120.

Description

Optical elements

[0001] The present disclosure relates to optical elements.

[0002] In recent years, research and development of optical elements having microscopic structures called metasurfaces has been progressing (see, for example, Patent Document 1 and Non-Patent Document 1).

[0003] Special table 2019-516128 publication

[0004] Park et.al., “Structural Color Filters Enabled by a Dielectric Metasurface Incorporating Hydrogenated Amorphous Silicon Nanodisks”, Scientific Reports 7, Article number: 2556, May 2017

[0005] The optical element having a metasurface described in Non-Patent Document 1 utilizes resonance that occurs inside a microstructure. Resonance can be Mie resonance, waveguide mode resonance, plasmon resonance, or the like, and in all cases, the wavelength band in which resonance occurs is narrow. Therefore, the optical element having the metasurface described in Non-Patent Document 1 exhibits strong wavelength dependence in its optical properties, such as transmission, reflection, and absorption. In other words, the optical element described in Non-Patent Document 1 achieves the desired optical properties over a narrow wavelength band, making it difficult to achieve the desired optical properties for a broad band of wavelength components.

[0006] The present disclosure provides an optical element whose optical characteristics can be easily modified and which has low wavelength dependency.

[0007] An optical element according to one aspect of the present disclosure comprises a plurality of microstructures arranged two-dimensionally, each of which generates a phase difference in incident light and emits it as transmitted light, wherein the phases of the transmitted light from two adjacent microstructures among the plurality of microstructures are different from each other, and the optical element has a transmittance determined by the interference of the transmitted light emitted from each of the plurality of microstructures with each other.

[0008] According to the present disclosure, it is possible to provide an optical element whose optical characteristics can be easily modified and which has low wavelength dependency.

[0009] FIG. 1 is a plan view of an optical element according to an embodiment. FIG. 2 is an enlarged plan view of the optical element shown in FIG. 1. FIG. 3 is a perspective view of one unit cell included in the optical element according to the embodiment. FIG. 4 is a cross-sectional view of one unit cell included in the optical element according to the embodiment. FIG. 5 is a diagram for explaining the transmission characteristics of a microstructure included in the optical element according to the embodiment. FIG. 6 is a diagram showing the relationship between the diameter of a microstructure included in the optical element according to the embodiment and the phase of transmitted light. FIG. 7 is a diagram showing the relationship between the diameter of a microstructure included in the optical element according to the embodiment and the transmittance. FIG. 8 is a diagram showing an example of a combination of microstructures in the optical element according to the embodiment. FIG. 9 is a diagram for explaining the transmission characteristics of an optical element obtained by combining the microstructures shown in FIG. 8. FIG. 10 is a diagram showing the relationship between the diameter of a microstructure included in the optical element according to the embodiment and the transmittance of the optical element and the phase difference between adjacent microstructures. FIG. 11 is a diagram showing the wavelength dependency of the optical element according to the embodiment. FIG. 12 is an enlarged plan view of an optical element according to a first modification of the embodiment. FIG. 13 is a cross-sectional view of an optical element according to a second modification of the embodiment.

[0010] (Summary of the present disclosure) An optical element according to a first aspect of the present disclosure comprises a plurality of microstructures arranged two-dimensionally, each of which generates a phase difference in incident light and emits it as transmitted light, wherein the phases of transmitted light from two adjacent microstructures among the plurality of microstructures are different from each other, and the optical element has a transmittance determined by the mutual interference of the transmitted light emitted from each of the plurality of microstructures.

[0011] This utilizes the interference of transmitted light emitted from each of the multiple microstructures, resulting in lower wavelength dependency compared to when resonance is utilized. Therefore, an optical element with low wavelength dependency can be realized. Furthermore, for example, by changing the design of the arrangement of the multiple microstructures, the design of the optical characteristics can be easily changed.

[0012] An optical element according to a second aspect of the present disclosure is an optical element according to the first aspect, wherein the plurality of microstructures are periodically arranged in a two-dimensional manner and include a plurality of first microstructures, each of which generates a first phase difference in the incident light and outputs it as a first transmitted light, and a plurality of second microstructures, periodically arranged in a two-dimensional manner and each of which generates a second phase difference in the incident light and outputs it as a second transmitted light, wherein the second phase difference is different from the first phase difference and each of the plurality of second microstructures is arranged between two adjacent first microstructures.

[0013] By periodically arranging two types of microstructures adjacent to each other, it is possible to uniformly cause interference of transmitted light within the area where the microstructures are provided. Since the phase difference of transmitted light can be set to a desired value, it is easy to change the design of the optical characteristics of the optical element.

[0014] An optical element according to a third aspect of the present disclosure is the optical element according to the second aspect, wherein the first microstructures and the second microstructures are different in at least one of shape, arrangement period, and material.

[0015] This makes it easy to adjust the phase difference of transmitted light, improving the accuracy of setting the transmittance of the optical element and realizing an optical element that meets the needs of users and the like.

[0016] An optical element according to a fourth aspect of the present disclosure is the optical element according to any one of the first to third aspects, wherein the height of the microstructure is H, the wavelength of the incident light is λ, and the refractive index of the microstructure is n ｐ and the refractive index around the microstructure is n ｂ In this case, Meet the following.

[0017] This makes it possible to ensure the height H of the microstructure necessary to make the transmittance of incident light of wavelength λ substantially 0. Since the range in which the transmittance can be set is expanded, it is possible to realize an optical element that meets the requirements of users, etc.

[0018] An optical element according to a fifth aspect of the present disclosure is an optical element according to any one of the first to fourth aspects, wherein the plurality of microstructures are arranged so that the distance between adjacent microstructures is smaller than the wavelength of the incident light.

[0019] This allows the transmitted light from adjacent microstructures to interfere with each other, improving the controllability of the transmittance, which in turn increases the precision with which the transmittance of the optical element can be set, thereby enabling the realization of an optical element that meets the needs of the user, etc.

[0020] An optical element according to a sixth aspect of the present disclosure is the optical element according to any one of the first to fifth aspects, wherein the wavelength of the incident light is not less than 8 μm and not more than 14 μm.

[0021] This makes it possible to realize an optical element suitable for thermal imaging.

[0022] An optical element according to a seventh aspect of the present disclosure is the optical element according to the sixth aspect, wherein the transmittance is 10% or less.

[0023] This makes it possible to realize an optical element with sufficiently low transmittance for far-infrared rays in a wide wavelength band. For example, the optical element can be used in a sensor that attenuates strong far-infrared rays before detecting them, or a sensor that removes unnecessary far-infrared rays and detects light in a required wavelength band.

[0024] An optical element according to an eighth aspect of the present disclosure is the optical element according to the sixth or seventh aspect, wherein the absorptance of the optical element for the incident light is 5% or less.

[0025] This makes it possible to realize an optical element with a sufficiently low absorptance for far-infrared rays over a wide wavelength range. It is also possible to suppress the generation of thermal energy due to light absorption. Since it is possible to suppress deterioration of the optical element due to heat, it is possible to realize an optical element with high reliability.

[0026] An optical element according to a ninth aspect of the present disclosure is an optical element according to any one of the first to eighth aspects, wherein each of the plurality of microstructures is a convex body or a concave body, and the shape of the convex body or the concave body is a columnar body or a pyramidal body, or a combination thereof.

[0027] This allows for a high degree of freedom in selecting the shape, making it possible to realize an optical element that meets the needs of the user or the like.

[0028] An optical element according to a tenth aspect of the present disclosure is the optical element according to any one of the first to ninth aspects, wherein the plurality of microstructures contain, as a main component, one or more 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.

[0029] This allows for suppressing reflection on the surface of the optical element and attenuation inside the optical element when the incident light is far-infrared, thereby widening the range in which transmittance can be set. It is possible to realize an optical element with a desired transmittance according to requirements, thereby enhancing the versatility of the optical element. Furthermore, the same principle can be applied to any material that has a transmittance of at least a certain level for the incident light, thereby increasing the freedom in material selection regardless of the material properties.

[0030] An optical element according to an eleventh aspect of the present disclosure is an optical element according to any one of the first to tenth aspects, wherein the plurality of microstructures are provided on a main surface of a silicon substrate having a surface orientation of (100), (110), or (111).

[0031] This allows the use of general semiconductor processing techniques that can be applied to silicon, thereby improving the accuracy of the shape and arrangement of the multiple microstructures, and thus realizing an optical element with a desired transmittance according to requirements.

[0032] An optical element according to a twelfth aspect of the present disclosure is an optical element according to the second or third aspect, wherein the plurality of microstructures further includes a plurality of third microstructures that are periodically arranged two-dimensionally and each generate a third phase difference in the incident light and emit it as a third transmitted light, the third phase difference being different from both the first phase difference and the second phase difference, and each of the plurality of third microstructures being arranged between adjacent first microstructures and second microstructures.

[0033] In this way, three types of microstructures are used, and different interferences can be generated depending on the combination of the microstructures. This improves the controllability of the transmittance. In other words, the precision of setting the transmittance of the optical element can be improved, and an optical element that meets the requirements of the user, etc. can be realized.

[0034] Hereinafter, the embodiments will be specifically described with reference to the drawings.

[0035] The embodiments described below are all comprehensive or specific examples. The numerical values, shapes, materials, components, arrangement positions and connection forms of the components 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 described in the independent claims are described as optional components.

[0036] Furthermore, each figure is a schematic diagram and is not necessarily an exact illustration. Therefore, for example, the scales of the figures do not necessarily match. Furthermore, in each figure, substantially the same components are given the same reference numerals, and redundant explanations are omitted or simplified.

[0037] Furthermore, in this specification, terms indicating the relationship between elements, such as parallel or perpendicular, terms indicating the shape of elements, such as cylinder or prism, and numerical ranges are not expressions that only express a strict meaning, but are expressions that also include a substantially equivalent range, for example, a difference of about a few percent.

[0038] In this specification and drawings, the x-axis, y-axis, and z-axis represent the three axes of a three-dimensional Cartesian coordinate system. In this specification, unless otherwise specified, the term "plan view" refers to a view from a direction perpendicular to the main surface of the substrate.

[0039] Furthermore, in this specification, the terms "above" and "below" do not refer to the upward direction (vertically upward) and downward direction (vertically downward) in absolute spatial recognition. In the following description, the side on which a plurality of microstructures are provided is considered to be "above" with respect to the substrate as the reference. Furthermore, this "above" is defined as the positive direction of the z-axis. The z-axis is defined as a direction perpendicular to the main surface of the substrate. Furthermore, the terms "above" and "below" are applied not only to cases where two components are arranged with a gap between them and another component is present between the two components, but also to cases where two components are arranged closely together and the two components are in contact with each other.

[0040] Furthermore, in this specification, ordinal numbers such as "first" and "second" do not refer to the number or order of components unless otherwise specified, but are used for the purpose of avoiding confusion and distinguishing between components of the same type.

[0041] Furthermore, in this disclosure, the term "light" is not limited to referring to visible light, but is also used to refer to invisible 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, and 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.

[0042] (Embodiment) [Configuration] First, the configuration of an optical element according to an embodiment will be described.

[0043] Fig. 1 is a plan view of an optical element 100 according to the present embodiment, and Fig. 2 is an enlarged plan view of the optical element 100 shown in Fig. 1.

[0044] The optical element 100 is an optical filter that transmits incident light as transmitted light with a predetermined transmittance. The optical element 100 has a transmittance determined by the mutual interference of transmitted light emitted from each of the multiple microstructures 120. The transmittance is the ratio of the radiant emittance of transmitted light to the radiant emittance of incident light. The transmittance is expressed as a value between 0 and 1 (between 0% and 100%). The transmittance of the optical element 100 can also be set to a small value of 10% or less. In other words, the optical element 100 may not substantially transmit light in a predetermined wavelength band. In the following, an example will be described in which the incident light is far-infrared light, but this is not limiting. The incident light may be visible light, ultraviolet light, infrared light, or radio waves.

[0045] As shown in FIG. 1, the optical element 100 includes a substrate 110 and a plurality of microstructures 120 provided on the main surface of the substrate 110 .

[0046] The substrate 110 is an example of a support member that supports the plurality of microstructures 120. The substrate 110 is formed, for example, using a material whose main component is silicon. Specifically, the substrate 110 is a silicon substrate having a main surface with a (100) plane orientation. The main surface of the silicon substrate may have a (110) or (111) plane orientation. The substrate 110 may also be formed using a material other than silicon.

[0047] The thickness of the substrate 110 is, for example, 500 μm. The shape of the substrate 110 is square, as shown in FIG. 1 , and the size thereof is, for example, 8 mm×8 mm. A plurality of microstructures 120 are two-dimensionally arranged on the main surface of the substrate 110. Note that the thickness, shape, and size of the substrate 110 are merely examples and are not limited to these.

[0048] The plurality of microstructures 120 are arranged two-dimensionally. As shown in Fig. 1 , the plurality of microstructures 120 are provided over the entire main surface of the substrate 110, but this is not limiting. For example, the plurality of microstructures 120 may be provided in only a partial region, such as a circular region, of the main surface of the substrate 110.

[0049] Each of the multiple microstructures 120 generates a phase difference in incident light and emits it as transmitted light. The phases of transmitted light from two adjacent microstructures 120 among the multiple microstructures 120 are different from each other. The multiple microstructures 120 include microstructures that differ in at least one of shape, arrangement period, and material. Specifically, as shown in FIG. 2 , the multiple microstructures 120 include a multiple first microstructures 122 and a multiple second microstructures 124. The multiple first microstructures 122 are periodically arranged in a two-dimensional manner. The multiple second microstructures 124 are periodically arranged in a two-dimensional manner. "Periodic arrangement" means that the microstructures are arranged at equal intervals (equal arrangement period) along multiple directions.

[0050] Two first microscopic structures 122 and two second microscopic structures 124 constitute one unit cell 101. A plurality of unit cells 101 are arranged in a matrix to constitute the optical element 100.

[0051] Fig. 3 is a perspective view of one unit cell 101 included in optical element 100 according to the present embodiment. Fig. 4 is a cross-sectional view of one unit cell 101 included in optical element 100 according to the present embodiment. Fig. 4 specifically shows a cross section taken along line IV-IV shown in Fig. 2.

[0052] The unit cell 101 has a square shape in plan view. Note that in this specification, the x-axis and y-axis are defined as directions parallel to each side of the unit cell 101. In one unit cell 101, the first microstructures 122 and the second microstructures 124 are arranged alternately in a matrix of two rows and two columns in plan view. In plan view, the two first microstructures 122 are arranged on one of the two diagonals of the unit cell 101. The two second microstructures 124 are arranged on the other of the two diagonals of the unit cell 101. More specifically, when the unit cell 101 is divided into four equal squares in plan view, the two first microstructures 122 and the two second microstructures 124 are arranged such that their geometric centers (centers of gravity) coincide with the centers of the four squares. As a result, when a plurality of unit cells 101 are arranged in a matrix, the first microscopic structures 122 and the second microscopic structures 124 are arranged alternately one by one in each of the x-axis direction and the y-axis direction at an equal arrangement period. In other words, each of the plurality of second microscopic structures 124 is disposed between adjacent first microscopic structures 122.

[0053] 3 and 4, in this embodiment, the first microstructure 122 and the second microstructure 124 are both convex bodies protruding from the main surface of the substrate 110. The convex bodies have a columnar shape (also called a pillar). Specifically, the first microstructure 122 and the second microstructure 124 are cylindrical bodies having circular bottoms with different diameters (maximum widths).

[0054] 4, the first microstructure 122 is a cylinder having a circular bottom surface with a diameter D1 and a height H. The second microstructure 124 is a cylinder having a circular bottom surface with a diameter D2 and a height H. In this embodiment, the heights of the first microstructure 122 and the second microstructure 124 are the same, but they may be different.

[0055] As shown in FIG. 4 , the length of one side of the unit cell 101 is regarded as P. The length of one side of the unit cell 101 is the arrangement period of the first microscopic structures 122. The arrangement period, also referred to as pitch, is the distance between the centers of adjacent first microscopic structures 122 in the row direction (x-axis direction) or column direction (y-axis direction). In this embodiment, the length of one side of the unit cell 101 is also the arrangement period of the second microscopic structures 124. That is, the arrangement period of the first microscopic structures 122 is the same as the arrangement period of the second microscopic structures 124. The arrangement period may be different in the x-axis direction and the y-axis direction. The arrangement period of the microscopic structures may also be regarded as the distance between the centers of microscopic structures arranged diagonally within the unit cell 101.

[0056] In this embodiment, the multiple microstructures 120 are arranged so that the distance between adjacent microstructures 120 is smaller than the wavelength of the incident light. The distance between adjacent microstructures 120 is the center-to-center distance between adjacent microstructures 120, specifically, the center-to-center distance between a first microstructure 122 and a second microstructure 124 that are adjacent in the x-axis direction or the y-axis direction. The distance between adjacent microstructures 120 is expressed as half the length of one side of the unit cell 101, i.e., P / 2. If the wavelength of the incident light is λ, then P / 2<λ is satisfied. The wavelength λ of the incident light is, for example, 8 μm or more and 14 μm or less. Therefore, the distance between adjacent microstructures 120 is shorter than a predetermined value in the range of 8 μm or more and 14 μm or less. This allows the transmitted light from adjacent microstructures 120 to interfere with each other.

[0057] The diameter (maximum width) of the multiple microstructures 120 is shorter than the distance between adjacent microstructures 120. Specifically, D1 < P / 2 and D2 < P / 2 are satisfied. Both the diameters D1 and D2 are shorter than a predetermined value in the range of 8 μm to 14 μm.

[0058] Furthermore, the height H of the microstructure 120 satisfies, for example, the following formula (1), but is not limited to this.

[0059]

[0060] Here, n ｐis the refractive index of the microstructure 120. ｂ is the refractive index around the microstructure 120. In this embodiment, the surface of the microstructure 120 is not covered with any other member and is in contact with air. ｂ can be considered to be the refractive index of air (specifically, about 1).

[0061] The right side of the formula (1) is the minimum height H necessary to make the transmittance of the optical element 100 substantially 0%. ｍｉｎ That is, when the height H of the microstructure 120 satisfies the formula (1), the transmittance can be changed from 0% to a desired value. A method for calculating the right side of the formula (1) will be described later.

[0062] The plurality of microstructures 120 includes, as a primary component, one or more 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. In this specification, the term "primary component" refers to the component whose content, expressed in mole percent, is the highest among the constituent materials. Various resins can be used as the plastic, and polyethylene is one example.

[0063] In this embodiment, the substrate 110 and the plurality of microstructures 120 are integrally formed using the same material. Specifically, the optical element 100 can be manufactured by processing a single base material.

[0064] For example, the optical element 100 can be manufactured using common semiconductor processing techniques such as lithography. First, a silicon substrate whose main crystal plane has a (100) plane orientation 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. As a result, the resist is removed from the locations irradiated with light or an electron beam. This silicon substrate is then subjected to SF ６Etching is performed using a reactive ion etching technique or the like using an etching gas such as a gas. As a result, the main surface of the silicon substrate is etched from the area where the resist has been removed. The areas removed by etching are the spaces between the multiple microstructures 120. In other words, the areas that remain unetched are the multiple microstructures 120. Thereafter, a wet process using a resist remover or the like, or an O process is performed. ２ Residual resist on the main surface of the silicon substrate is removed by a dry process using ashing, etc. Through these steps, the optical element 100 having the substrate 110 and the plurality of microstructures 120 can be manufactured.

[0065] It should be noted that the manufacturing method of the optical element 100 is not limited to the above method. For example, the plurality of microstructures 120 may be formed by selective epitaxial growth of silicon on the main surface of a silicon substrate. Alternatively, the microstructures 120 may be formed by forming a film made of the constituent material of the microstructures 120 on the main surface of the silicon substrate, and then etching the film. The film can be formed using various film formation techniques, such as epitaxial growth, coating, vapor deposition, and sputtering, depending on the constituent material.

[0066] [Optical Characteristics] Next, the optical characteristics of the microstructure 120 will be described.

[0067] Fig. 5 is a diagram for explaining the transmission characteristics of the first microstructure 122 and the second microstructure 124 included in the optical element 100 according to the present embodiment. Fig. 5 shows the same cross section as Fig. 4, but the hatched area indicating the cross section is omitted.

[0068] 5, incident light Lin is incident on the lower surface (the principal surface on the negative side of the z-axis) of the substrate 110 of the optical element 100. For example, the incident light Lin is incident in a direction perpendicular to the entire lower surface of the substrate 110. Note that the incident light Lin may be incident on only a portion of the lower surface of the substrate 110, or may be incident obliquely with respect to the lower surface.

[0069] After passing through the substrate 110, the incident light Lin passes through the first microstructure 122 or the second microstructure 124 and is emitted as transmitted light L1 or L2, respectively. Specifically, the first microstructure 122 generates a first phase difference with respect to the incident light Lin and emits it as transmitted light L1. For example, if the phase of the transmitted light L1 is φ1 and the phase of the incident light Lin is φin, the first phase difference is φ1-φin.

[0070] The second microstructure 124 generates a second phase difference with respect to the incident light Lin and outputs the resulting light as transmitted light L2. For example, if the phase of the transmitted light L2 is φ2, the second phase difference is φ2-φin. In this embodiment, the second phase difference is different from the first phase difference. In other words, the phase φ2 of the transmitted light L2 is different from the phase φ1 of the transmitted light L1.

[0071] 6 is a diagram showing the relationship between the diameter of the microstructure 120 included in the optical element 100 according to this embodiment and the phase of transmitted light. In Fig. 6, the horizontal axis represents the diameter (unit: μm) of the microstructure 120, and the vertical axis represents the phase (unit: deg (°)) of the transmitted light.

[0072] 6 was obtained by arranging one type of microstructure 120 with a height H of 3.75 μm so that the arrangement period P was 4.6 μm, and modulating the diameter of the microstructure 120 within a range from 1.5 μm to 4 μm. The wavelength λ of the incident light was set to 10 μm. The same applies to FIGS. 7 and 8 described below.

[0073] 6, the phase of the transmitted light from the microstructure 120 is expressed as a function of the diameter of the microstructure 120. In other words, by setting the diameters D1 and D2 to predetermined values, the phase φ1 of the transmitted light L1 from the first microstructure 122 and the phase φ2 of the transmitted light L2 from the second microstructure 124 can be uniquely determined. The phases φ1 and φ2 are determined by the first phase difference generated by the first microstructure 122 and the second phase difference generated by the second microstructure 124, respectively. The difference between the first phase difference and the second phase difference is the same as the phase differences φ1 and φ2.

[0074] Within the diameter range of 1.5 μm or more and 4 μm or less, the phase of transmitted light has a positive correlation with the diameter. Note that phases exceeding 360° are converted to fit within the range of 0° or more and 360° or less. When determining the diameter D1 of the first microstructure 122 and the diameter D2 of the second microstructure 124, the smaller the difference between D1 and D2, the smaller the difference Δφ between the phase differences generated by the first microstructure 122 and the second microstructure 124. That is, the difference Δφ between the phase φ1 of the transmitted light L1 from the first microstructure 122 and the phase φ2 of the transmitted light L2 from the second microstructure 124 becomes smaller. For example, when D1 = 2 μm and D2 = 3.25 μm, the difference Δφ becomes approximately 180°. Note that the combination of D1 and D2 that results in Δφ = 180° is not limited to this.

[0075] Fig. 7 is a diagram showing the relationship between the diameter and transmittance of the microstructure 120 included in the optical element 100 according to this embodiment. In Fig. 7, the horizontal axis represents the diameter D1 or D2 (unit: µm) of the microstructure 120, and the vertical axis represents the transmittance of the microstructure 120. The transmittance is the transmittance for light with a wavelength of 10 µm.

[0076] As shown in Fig. 7, the transmittance of the microstructure 120 is expressed as a function of the diameter of the microstructure 120. In other words, by setting the values ​​of the diameters D1 and D2 to predetermined values, it is possible to uniquely determine the transmittance of each of the first microstructure 122 and the second microstructure 124. In the example shown in Fig. 7, the transmittance of the microstructure 120 can take a value within a range from 0.10 to 0.70 depending on the diameter.

[0077] 8 is a diagram showing an example of a combination of microstructures 120 of optical element 100 according to this embodiment. The diagram shows the phase of transmitted light, the reflectance, and the transmittance of the microstructures when D1 = 2.0 μm and D2 = 3.25 μm. As shown in FIG. 8, by setting D1 = 2.0 μm and D2 = 3.25 μm, the phase difference Δφ between the phase φ1 of transmitted light L1 and the phase φ2 of transmitted light L2 can be set to approximately 180°.

[0078] FIG. 9 is a diagram illustrating the transmission characteristics of the optical element 100 obtained by combining the microstructures 120 shown in FIG. 8 . As shown in FIG. 8 , by setting the phase difference Δφ between the transmitted light L1 and the transmitted light L2 from the adjacent first microstructure 122 and second microstructure 124 to approximately 180°, the transmitted light L1 and the transmitted light L2 interfere with each other and cancel each other out. As a result, the optical element 100 can create a situation in which the incident light Lin is not substantially transmitted. In other words, the transmittance of the optical element 100 can be set to a sufficiently small value of 10% or less. Furthermore, the transmittance can be controlled to a desired value.

[0079] In this way, by setting the phase difference Δφ between the transmitted light beams L1 and L2 to approximately 180°, the transmittance of the optical element 100 can be made sufficiently small.

[0080] Based on the condition for making the transmittance substantially zero, the minimum value H of the height H of the microstructure 120 is ｍｉｎ (Specifically, the right side of equation (1)) can be determined.

[0081] The phase difference Δφ is expressed as the absolute value of φ1-φ2. The phase φi (i=1, 2) is expressed by the following equation (2).

[0082]

[0083] In formula (2), n ｅｆｆｉ (i=1, 2) is the effective refractive index of the microstructure 120 .

[0084] Assuming that Δφ=φ1−φ2=π(180°), the height H at this time can be derived from equation (2) as follows:

[0085]

[0086] Based on the formula (3), the minimum value Hmin of the height H of the microstructure 120 is n ｅｆｆ１ = n ｂ , and n ｅｆｆ２ = n ｐ Therefore, equation (4) is obtained.

[0087]

[0088] When the microstructure 120 is formed using silicon and air is present around it, the refractive index n ｐ = 3.42, refractive index of air n ｂ = 1. When the wavelength λ of the incident light is 10 μm, H ｍｉｎ Based on the formula (1), the height H of the microstructure 120 is calculated as H ｍｉｎ By setting the thickness to about 2.1 μm or more, the transmittance of the optical element 100 can be set to 0 or more.

[0089] 8 and 9 show examples in which the transmittance is sufficiently small, but the optical characteristics of the optical element 100, including the transmittance, can be adjusted by adjusting the shapes, arrangement period, and materials of the first microstructures 122 and the second microstructures 124. For example, when the shape of the first microstructures 122 is a cylinder with a diameter D1 = 2 μm, the transmittance of the optical element 100 can be changed by modulating the diameter D2 of the second microstructures 124.

[0090] Fig. 10 is a diagram showing the relationship between the diameter of the microstructures 120 included in the optical element 100 according to this embodiment, the transmittance of the optical element 100, and the phase difference Δφ between adjacent microstructures 120. In Fig. 10, the horizontal axis represents the diameter (unit: μm) of the second microstructures 124. The vertical axis on the left represents the transmittance of the optical element 100. The vertical axis on the right represents the phase difference Δφ between the transmitted light L2 from the second microstructures 124 and the transmitted light L1 from the first microstructures 122 with a diameter of 2 μm. The plots of white circles in Fig. 10 represent the transmittance with reference to the vertical axis on the left. The plots of black circles represent the phase difference Δφ with reference to the vertical axis on the right.

[0091] 10 , the closer the diameter D2 of the second microstructure 124 is to 2 μm (= D1), the greater the transmittance of the optical element 100. The longer the diameter D2 of the second microstructure 124 is than 2 μm, the smaller the transmittance of the optical element 100. When the diameter D2 is approximately 3.25 μm, the transmittance of the optical element 100 becomes substantially zero.

[0092] In this way, by setting the diameter D2 of the second microstructures 124 to a predetermined value, the transmittance of the optical element 100 can be set to a desired value. The same applies when the diameter D1 of the first microstructures 122 is modulated. Furthermore, the transmittance of the optical element 100 can be set to a predetermined value not only by changing the diameters D1 and D2 but also by changing the shape, arrangement period, and material (refractive index).

[0093] Although the wavelength λ is 10 μm, the optical element 100 can achieve a similar transmittance for wavelengths in the vicinity of 10 μm. In other words, the transmittance can be reduced over a broad band.

[0094] Fig. 11 is a diagram showing the wavelength dependence of the optical element 100 according to the present embodiment. In Fig. 11, the horizontal axis represents the wavelength λ (unit: μm) of incident light, and the vertical axis represents the reflectance, transmittance, and absorptance (each unit: %) of light.

[0095] 11 shows the wavelength dependence of the optical characteristics of the optical element 100 when D1 = 2 μm, D2 = 3.25 μm, H = 3.75 μm, and P / 2 = 4.6 μm. The main component of the optical element 100 is silicon. As shown in FIG. 11, the light absorptance is approximately 0% when the wavelength λ of the incident light is in the range of 8 μm to 14 μm. Therefore, when the wavelength λ of the incident light is in the range of 8 μm to 14 μm, the sum of the light reflectance and transmittance is substantially 1.

[0096] The transmittance is approximately 0.5 (=50%) or less in the range of 8 μm or more and 14 μm or less. In this way, the transmittance can be reduced over a wide wavelength band, and an optical element 100 in which reflection is dominant has been realized. Furthermore, the transmittance is approximately 0.2 (=20%) or less in the range of 8 μm or more and 13 μm or less. Furthermore, the transmittance is approximately 0.1 (=10%) or less in the range of 8 μm or more and 11 μm or less. In this way, an optical element 100 that does not substantially transmit light over a wide wavelength band has been realized.

[0097] [Modifications] Next, modifications of the above-described embodiment will be described. The following description will focus on differences from the embodiment, and descriptions of commonalities will be omitted or simplified.

[0098] [Modification 1] Fig. 12 is an enlarged plan view of an optical element 200 according to Modification 1 of the present embodiment. Like Fig. 2, Fig. 12 shows an enlarged plan view of the optical element 200 including a plurality of microstructures.

[0099] 12 , the optical element 200 includes a plurality of microstructures, namely, a first microstructure 222, a second microstructure 224, and a third microstructure 226. The plurality of microstructures are provided on the main surface of a substrate (not shown). Three first microstructures 222, three second microstructures 224, and three third microstructures 226 form one unit cell 201. The optical element 200 is formed by arranging a plurality of unit cells 201 in a matrix.

[0100] The unit cell 201 has a square shape in plan view. In one unit cell 201, the first microscopic structures 222, the second microscopic structures 224, and the third microscopic structures 226 are arranged alternately in a matrix of 3 rows and 3 columns in plan view. In plan view, the three first microscopic structures 222 are aligned on one of the two diagonals of the unit cell 201. Two of the three second microscopic structures 224 are arranged diagonally along the diagonal so as to be parallel to the first microscopic structures 222 in the same unit cell 201. The remaining one of the three second microscopic structures 224 is arranged in a straight line (a direction parallel to the diagonal of the unit cell 201) with the two second microscopic structures 224 in the adjacent unit cell 201. Two of the three third microscopic structures 226 are arranged diagonally along the diagonal so as to be parallel to the first microscopic structures 222 in the same unit cell 201. The remaining one of the three third microscopic structures 226 is arranged in a straight line (in a direction parallel to the diagonal of the unit cell 201) with the two third microscopic structures 226 of the adjacent unit cell 201.

[0101] More specifically, when the unit cell 201 is divided into nine equal squares arranged in three rows and three columns in a plan view, the three first microscopic structures 222, the three second microscopic structures 224, and the three third microscopic structures 226 are arranged so that their respective geometric centers (centers of gravity) coincide with the centers of the nine squares. Thus, when a plurality of unit cells 201 are arranged in a matrix, the first microscopic structures 222, the second microscopic structures 224, and the third microscopic structures 226 are arranged alternately, one by one, with an equal arrangement period in both the x-axis direction and the y-axis direction. Each of the plurality of second microscopic structures 224 is arranged between adjacent first microscopic structures 222. Each of the plurality of third microscopic structures 226 is arranged between adjacent first microscopic structures 222 and second microscopic structures 224.

[0102] The first microstructure 222, the second microstructure 224, and the third microstructure 226 are all convex bodies protruding from the main surface of the substrate. Specifically, the first microstructure 222, the second microstructure 224, and the third microstructure 226 are cylindrical bodies having circular bases with different diameters (maximum widths).

[0103] The first microstructure 222, the second microstructure 224, and the third microstructure 226 are different from one another in at least one of the shape, arrangement period, and material. In this modification, the first microstructure 222, the second microstructure 224, and the third microstructure 226 are different in diameter. Specifically, the diameter of the second microstructure 224 is larger than the diameter of the first microstructure 222 and smaller than the diameter of the third microstructure 226.

[0104] In this modified example, the first microstructure 222 generates a first phase difference for the incident light and outputs it as first transmitted light. For example, if the phase of the first transmitted light is φ1 and the phase of the incident light is φin, the first phase difference is φ1-φin. The second microstructure 224 generates a second phase difference for the incident light and outputs it as second transmitted light. For example, if the phase of the second transmitted light is φ2, the second phase difference is φ2-φin. The third microstructure 226 generates a third phase difference for the incident light and outputs it as third transmitted light. For example, if the phase of the third transmitted light is φ3, the third phase difference is φ3-φin. In this embodiment, the second phase difference is different from the first phase difference. The third phase difference is different from both the first phase difference and the second phase difference. In other words, the phase φ3 of the third transmitted light is different from both the phase φ2 of the second transmitted light and the phase φ1 of the first transmitted light.

[0105] As described above, in the optical element 200 according to this modification, the first transmitted light, the second transmitted light, and the third transmitted light have different phases, and therefore different interferences occur depending on the combination of transmitted light. Specifically, three types of interference occur: interference between the first transmitted light and the second transmitted light, interference between the second transmitted light and the third transmitted light, and interference between the third transmitted light and the first transmitted light. The occurrence of these three types of interference can improve the controllability of the light transmittance. Therefore, the accuracy of setting the transmittance of the optical element 200 can be improved, and an optical element 200 that meets the requirements of a user or the like can be realized.

[0106] 13 is a cross-sectional view of a unit cell 301 of an optical element according to Modification 2 of this embodiment. The plan view of the unit cell 301 is the same as that of the unit cell 101 shown in FIG.

[0107] 13 , in a unit cell 301 according to this modification, the plurality of microstructures are concave bodies. Specifically, the optical element according to this modification includes, as the plurality of microstructures, a first microstructure 322 that is concave body and a second microstructure 324 that is concave body. The arrangement and shape of the first microstructure 322 and the second microstructure 324 are the same as those of the first microstructure 122 and the second microstructure 124 according to the embodiment.

[0108] When the microstructure is a concave body as in this modification, the refractive index of the microstructure is equal to that of air, and the refractive index around the microstructure is equal to that of the material of the substrate 110. Even in this case, the phase of transmitted light passing through the concave microstructure is expressed by the above-mentioned formula (2), so interference similar to that in the embodiment can be generated. Therefore, as in the embodiment, an optical element with little wavelength dependency can be realized.

[0109] It should be noted that, whether the microstructure is a convex or concave body, its shape is not limited to a cylinder. For example, the shape of the convex or concave body may be a columnar shape other than a cylinder, a cone shape, or a combination of a columnar and a cone shape. The columnar shape may be a prismatic shape such as a square or hexagonal column, or an elliptical column. The cone shape may be a pyramidal shape such as a square or hexagonal pyramid, or a circular or elliptical cone. Alternatively, the shape of the convex or concave body may be a truncated pyramid, a circular or elliptical cone. In the case of a prismatic shape, a pyramidal shape, or a truncated pyramidal shape, the base does not have to be a regular polygon.

[0110] Other Embodiments While optical elements according to one or more aspects have been described above based on embodiments, the present disclosure is not limited to these embodiments. As long as they do not deviate from the gist of the present disclosure, various modifications conceivable by those skilled in the art to the present embodiments and embodiments constructed by combining components of different embodiments are also included within the scope of the present disclosure.

[0111] For example, in the above embodiment, an example was shown in which the side and top surfaces of the multiple microstructures are exposed, but the side and top surfaces of the multiple microstructures may be covered with another member having a refractive index different from that of the microstructures. For example, the space between the multiple microstructures may be filled with another member having a refractive index different from that of the microstructures. This makes it possible to protect the multiple microstructures. Furthermore, by adjusting the refractive index of the other member, it is possible to adjust the optical characteristics of the optical element.

[0112] Furthermore, for example, an AR (Anti-Reflection) functional film may be additionally formed to improve transmittance. In addition to the AR functional film, various light modulation layers having a light modulation function may be provided in the optical element 100.

[0113] Furthermore, for example, the substrate and the plurality of microstructures may be formed using different materials. Furthermore, the optical element does not need to include a substrate as long as the relative positions of the plurality of microstructures can be maintained.

[0114] Furthermore, for example, the plurality of microstructures may be provided on both surfaces of the substrate. For example, both the plurality of first microstructures and the plurality of second microstructures may be provided on both surfaces of the substrate. Alternatively, the plurality of first microstructures may be provided on one main surface of the substrate, and the plurality of second microstructures may be provided on the other main surface of the substrate.

[0115] Furthermore, the periodic arrangement of the first microstructures, second microstructures, and third microstructures is not limited to the above-mentioned examples. For example, the first microstructures may be arranged in a square lattice, a triangular lattice, or a honeycomb lattice. The same applies to the second microstructures and the third microstructures. The arrangement rules of the first microstructures and the second microstructures may be different.

[0116] Furthermore, one aspect of the present disclosure may be realized as a camera system or a sensor system including an optical element according to any one of the above aspects, a sensor that receives light transmitted through the optical element and photoelectrically converts the received light, and a signal processing circuit that processes an electrical signal output from the sensor. Alternatively, one aspect of the present disclosure may be realized as an optical system including a light source and an optical element according to any one of the above aspects that transmits or reflects at least a portion of the light from the light source. The optical system may be, for example, a projector or a lighting device, but is not limited to these.

[0117] Furthermore, various modifications, substitutions, additions, omissions, etc. can be made to the above-described embodiments within the scope of the claims or their equivalents.

[0118] The present disclosure can be used as an optical element with low wavelength dependency, and can be used, for example, in filters and lenses for cameras, LiDAR (Light Detection and Ranging) sensors, projectors, AR (Augmented Reality) displays, telescopes, microscopes, thermal image sensors, and the like.

[0119] 100, 200 Optical element 101, 201, 301 Unit cell 110 Substrate 120 Microstructure 122, 222, 322 First microstructure 124, 224, 324 Second microstructure 226 Third microstructure

Claims

1. An optical element, circuit board and The main surface of the substrate is provided with a plurality of convex microstructures that generate a phase difference in incident light and emit it as transmitted light, The aforementioned plurality of microstructures are A first microstructure that generates a first phase difference in the incident light and emits it as first transmitted light, The device includes a second microstructure that generates a second phase difference different from the first phase difference in the incident light and emits it as a second transmitted light, Multiple first microstructures are arranged two-dimensionally in the first and second directions of the main surface at a predetermined arrangement period, and multiple second microstructures are arranged two-dimensionally in the first and second directions at the predetermined arrangement period. Each of the second microstructures is positioned between two of the first microstructures in the first and second directions, and has a space between adjacent first microstructures. Optical element.

2. The optical element interferes the first transmitted light and the second transmitted light by the difference between the first phase difference and the second phase difference, thereby reducing the transmittance of the incident light. The optical element according to claim 1.

3. The first microstructure and the second microstructure differ in at least one of their shape and material. The optical element according to claim 2.

4. Let H be the height of the microstructure, λ be the wavelength of the incident light, and n be the refractive index of the microstructure. ｐ The refractive index around the microstructure is n ｂ In that case, [Math 1] Satisfying The optical element according to any one of claims 1 to 3.

5. The plurality of microstructures are arranged such that the space between adjacent first and second microstructures is smaller than the wavelength of the incident light. The optical element according to claim 4.

6. The wavelength of the incident light is between 8 μm and 14 μm. The optical element according to any one of claims 1 to 3.

7. The aforementioned transmittance is 10% or less. The optical element according to claim 6.

8. The absorption rate of the optical element with respect to the incident light is 5% or less. The optical element according to claim 6.

9. The shape of the convex body is a columnar body, a conical body, or a combination thereof. The optical element according to any one of claims 1 to 3.

10. The aforementioned plurality of microstructures mainly consist of one or more selected from the group consisting of silicon, germanium, chalcogenides, chalcohalides, zinc sulfide, zinc selenide, fluoride compounds, thallium halides, sodium chloride, potassium chloride, potassium bromide, cesium iodide, and plastics. The optical element according to any one of claims 1 to 3.

11. The plurality of microstructures are provided on the main surface of a silicon substrate having a surface orientation of (100), (110), or (111). The optical element according to any one of claims 1 to 3.

12. The aforementioned plurality of microstructures further, The device includes a third microstructure that generates a third phase difference in the incident light that is different from both the first phase difference and the second phase difference, and emits it as a third transmitted light. The third microstructures are arranged in a plurality in a predetermined arrangement period in the first and second directions, and each of the plurality of third microstructures is positioned between the first and second microstructures in the first and second directions, with a space between adjacent first and second microstructures. The optical element according to claim 1.

13. The optical element interferes the first transmitted light, the second transmitted light, and the third transmitted light by the difference between the first phase difference, the second phase difference, and the third phase difference, thereby reducing the transmittance of the incident light. The optical element according to claim 12.

14. The difference between the first phase difference and the second phase difference is set to 180°. The optical element according to any one of claims 1 to 3.

15. The diameters of the first microstructure and the second microstructure are shorter than half of the sequence period. The optical element according to any one of claims 1 to 3.

16. An optical element, circuit board and The main surface of the substrate is provided with a plurality of concave microstructures that generate a phase difference in incident light and emit it as transmitted light, The aforementioned plurality of microstructures are A first microstructure that generates a first phase difference in the incident light and emits it as first transmitted light, The device includes a second microstructure that generates a second phase difference different from the first phase difference in the incident light and emits it as a second transmitted light, Multiple first microstructures are arranged two-dimensionally in the first and second directions of the main surface at a predetermined arrangement period, and multiple second microstructures are arranged two-dimensionally in the first and second directions at the predetermined arrangement period. Each of the second microstructures is positioned between two of the first microstructures in the first and second directions and is connected to an adjacent first microstructure. Optical element.

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