Diffuser

Abstract

To provide a diffuser with superior diffusivity.SOLUTION: Each of diffusers (100, 100a, 100b) comprises a substrate (1) having an area where a rugged structure (20, 20a) for diffracting incident light is formed. The rugged structure has multiple recesses (21, 21a) and multiple protrusions (22, 22a), and the multiple recesses and the multiple protrusions are arranged in a non-lattice shape and arranged non-periodically in the area.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to a diffuser for diffusing light. [Background technology]

[0002] Diffusers are components for diffusing light in various directions and are widely used in various optical systems in daily life (such as LED lighting, liquid crystal displays, and daylight windows). Diffusers are broadly divided into volumetric (bulk) diffusers and surface relief diffusers. Volumetric diffusers are plates or films in which multiple scattering bodies are embedded, and diffuse incident light by multiple scattering caused by the multiple scattering bodies. Surface relief diffusers diffuse incident light by utilizing the refraction of light at the surface relief, for example. Surface relief diffusers include ground glass and frosted glass that diffuse light by a rough surface on the micron scale, prismatic diffusers that diffuse light by a macro-scale surface, and holographic diffusers that diffuse light by random micron-sized irregularities.

[0003] Here, the volumetric diffuser has a problem that the transmittance decreases in exchange for widening the diffusion range due to multiple scattering. In addition, the surface relief diffuser has a problem that wavelength dispersion occurs due to light refraction, or the diffusion range is narrow due to insufficient surface relief. In other words, these diffusers have a problem that they cannot simultaneously achieve high transmittance, wide-angle diffusion, and low wavelength dispersion.

[0004] Therefore, a Morpho diffuser inspired by the surface structure of the wing of the Morpho butterfly has been developed in recent years. The Morpho diffuser has a nanoscale surface structure that causes the diffraction spreading of incident light, and has a random surface structure that prevents the generation of a diffraction grating (i.e., prevents wavelength dispersion). This surface structure allows the Morpho diffuser to simultaneously achieve high transmittance, wide-angle diffusion, and low wavelength dispersion.

[0005] A morpho-type diffuser has been proposed that has a surface structure in which multiple high aspect ratio structures with random heights are arranged. However, it is difficult to manufacture a nano-surface structure defined by such random heights. Non-Patent Document 1 discloses a morpho-type diffuser whose surface structure is a two-dimensional nano-pattern defined by random widths and two-step heights. The two-dimensional nano-pattern can be manufactured by lithography and nanoimprinting, which are well-known semiconductor processes. [Prior art documents] [Non-patent literature]

[0006] [Non-Patent Document 1] KAZUMA YAMASHITA, KENTARO KUNITSU, TAKUMA HATTORI, YUJI KUWAHARA, AND AKIRA SAITO, "Demonstration of a diffraction-based optical diffuser inspired by the Morpho butterfly" Optics Express Vol.29, No.19, pp.30927-30936 ,13 Sep 2021 Summary of the Invention [Problem to be solved by the invention]

[0007] However, the lattice-like surface structure disclosed in Non-Patent Document 1 has problems such as the appearance of cross-shaped bright lines and a strong bright spot in the center in the diffusion pattern.

[0008] SUMMARY OF THE PRESENT EMBODIMENT An object of one aspect of the present invention is to provide a diffuser having good diffusivity. [Means for solving the problem]

[0009] In order to solve the above problems, a diffuser according to one embodiment of the present invention comprises a substrate having an area in which a concave-convex structure is formed that diffuses incident light by diffraction, the concave-convex structure having a plurality of recesses at a first level and a plurality of protrusions protruding to a second level, the plurality of recesses and the plurality of protrusions being arranged in a non-lattice pattern and non-periodically arranged in the area.

[0010] In addition, in order to solve the above-mentioned problems, a light diffusion method according to one embodiment of the present invention is a light diffusion method including the steps of preparing a substrate having an area in which a concave-convex structure that diffuses incident light by diffraction is formed, and diffusing the light by making the light incident on the concave-convex structure, wherein the concave-convex structure has a plurality of concave portions at a first level and a plurality of convex portions protruding to a second level, and the plurality of concave portions and the plurality of convex portions are arranged in a non-lattice pattern and are arranged non-periodically in the area. Effect of the Invention

[0011] According to one aspect of the present invention, a diffuser having good diffusivity can be realized. [Brief description of the drawings]

[0012] [Figure 1] FIG. 11 is a perspective view showing a diffuser according to a reference embodiment. [Diagram 2] 11A and 11B are bottom and top views showing the concave-convex structure of a diffuser according to a reference embodiment. [Diagram 3] 11A and 11B are diagrams showing the projection of light diffused by a diffuser according to a reference embodiment onto a screen. [Figure 4] FIG. 1 is a perspective view showing a diffuser according to a first embodiment. [Diagram 5] FIG. 2 is a top view showing the concave-convex structure of the diffuser according to the first embodiment. [Figure 6] 4 is a diagram showing the projection of light diffused by the diffuser according to the first embodiment onto a screen. FIG. [Figure 7] FIG. 11 is a perspective view showing a diffuser according to a second embodiment. [Figure 8] FIG. 11 is a top view showing the concave-convex structure of a diffuser according to a second embodiment. [Figure 9] 11 is a diagram showing the projection of light diffused by a diffuser according to the second embodiment onto a screen. FIG. [Figure 10] FIG. 11 is a cross-sectional view showing a diffuser according to a modified example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] [Reference form] Prior to describing the diffuser 100 according to the first embodiment, a diffuser 100s according to a reference embodiment will be described. For ease of description, in the following embodiments, components having the same functions as those described in the reference embodiment will be denoted by the same reference numerals, and descriptions thereof will not be repeated.

[0014] (Overview of Diffuser 100s) FIG. 1 is a perspective view showing a diffuser 100s. As shown in FIG. 1, the diffuser 100s is made of a substrate 1 having a region R in which an uneven structure 20s that diffuses incident light by diffraction is formed. The substrate 1 is a flat plate-like member having a first surface 11 to which incident light is incident and a second surface 12 on the opposite side of the first surface 11 from which transmitted light is emitted. Hereinafter, the direction perpendicular to the second surface 12 of the substrate 1 is referred to as the Z-axis direction, and the directions along the first and second sides of the second surface 12 are referred to as the X-axis direction and the Y-axis direction, respectively. In addition, the positive direction of the Z-axis is referred to as the upward direction, and the negative direction is referred to as the downward direction.

[0015] 1, the region R in which the concave-convex structure 20s is formed includes a first region which is the entire first surface 11 and a second region which is the entire second surface 12. That is, the concave-convex structure 20s includes a first concave-convex structure 201s formed on the first surface 11 and a second concave-convex structure 202s formed on the second surface 12.

[0016] The concave-convex structure 20s has a plurality of concave portions 21s on a first level H1 and a plurality of convex portions 22s protruding to a second level H2. That is, the concave-convex structure 20s is defined by two step heights formed on the substrate 1. The concave-convex structure 20s defined by such two step heights can be manufactured by lithography and nanoimprinting.

[0017] FIG. 2 is a bottom view and a top view showing the concave-convex structure 20s of the diffuser 100s. Reference numerals 2A and 2B in FIG. 2 indicate a first concave-convex structure 201s and a second concave-convex structure 202s, respectively. As shown in FIG. 2, in the concave-convex structure 20s, a plurality of recesses 21s and a plurality of protrusions 22s are arranged in a lattice pattern (like a checkerboard pattern). That is, the plurality of recesses 21s have rectangular bottoms 211s, and the plurality of protrusions 22s have rectangular tops 221s. In addition, the plurality of recesses 21s and the plurality of protrusions 22s have nanoscale and random widths.

[0018] Specifically, the lengths of the first side along the X-axis direction and the second side along the Y-axis direction of the multiple apexes 221s (multiple bottoms 211s) are determined based on independent predetermined distribution functions. For example, the length W of the first side of the multiple apexes 221s x and the length of the second side W y are W x =W0+σ x , W y =W0+σ y (W0: Minimum width, σ x : a given first distribution function, σ y : a predetermined second distribution function). The diffuser 100s has such a random uneven structure 20s, and thus can diffuse the incident light by diffracting and spreading it while preventing wavelength dispersion. By diffusing the incident light by diffracting and spreading it, light diffusion with high transmittance and wide angle diffusion can be realized.

[0019] In addition, the arrangement of the plurality of recesses 21s and the plurality of protrusions 22s may be different between the first uneven structure 201s and the second uneven structure 202s. Specifically, the minimum width W0 and the uneven depth d may be different between the first uneven structure 201s and the second uneven structure 202s. For example, the minimum width W0 may be set to 300 nm and the uneven depth d to 440 nm in the first uneven structure 201s, and the minimum width W0 may be set to 470 nm and the uneven depth d to 690 nm in the second uneven structure 202s. This allows light with a short wavelength to be diffused on the first surface 11, and light with a long wavelength to be diffused on the second surface 12.

[0020] In addition, the predetermined first distribution function and the predetermined second distribution function are determined by the length W of the first side of the plurality of vertices 221s. x The average value of the second side length W y This allows the light to be diffused at a wider angle in the X-axis direction than in the Y-axis direction (that is, anisotropic diffusion is possible).

[0021] Fig. 3 is a diagram showing the projection (diffusion pattern) of the light diffused by the diffuser 100s onto a screen. As shown in Fig. 3, when light is incident on the diffuser 100s, a diffusion pattern is obtained that shows anisotropic diffusion, in which the light is diffused widely in the X-axis direction and narrowly in the Y-axis direction.

[0022] Here, in the diffusion pattern, a cross-shaped bright line (a bright line along the X-axis direction and the Y-axis direction) and a strong bright spot in the center appeared. Such a cross-shaped bright line and a strong bright spot in the center are considered to be caused by the lattice-shaped uneven structure 20s designed based on the above-mentioned predetermined distribution function.

[0023] (Diffuser 100s Challenges) As described above, the lattice-shaped uneven structure 20s has a problem that the diffusion pattern has a cross-shaped bright line and a strong bright spot in the center. That is, the diffuser 100s has room for further improving the diffusion by suppressing the occurrence of the cross-shaped bright line and the bright spot in the center. In addition, the uneven structure 20s has a problem that it is vulnerable to surface contamination or mechanical impact because it is a fine surface nanopattern.

[0024] [Embodiment 1] (Schematic configuration of diffuser 100) The present inventors have found that by using a diffuser 100 having an uneven structure 20 instead of the diffuser 100s according to the reference embodiment, the occurrence of a cross-shaped bright line and a central bright spot in the diffused light can be suppressed. In addition, the present inventors have found that by forming the substrate 1 from a hydrophobic material, the diffuser 100 can be given resistance to surface contamination. In the first embodiment, such a diffuser 100 will be described.

[0025] Fig. 4 is a perspective view showing diffuser 100. As shown in Fig. 4, diffuser 100 is made of substrate 1 having region R in which uneven structure 20 that diffuses incident light by diffraction is formed.

[0026] 4, the region R in which the concave-convex structure 20 is formed includes a first region which is the entire first surface 11 of the substrate 1, and a second region which is the entire second surface 12 of the substrate 1. That is, the concave-convex structure 20 includes a first concave-convex structure 201 formed on the first surface 11 and a second concave-convex structure 202 formed on the second surface 12.

[0027] The concave-convex structure 20 has a plurality of concave portions 21 on a first level H1 and a plurality of convex portions 22 protruding to a second level H2. That is, the concave-convex structure 20 is defined by two step heights (the first level H1 and the second level H2 of the substrate 1) formed on the substrate 1. The concave-convex structure 20 defined by such two step heights can be manufactured by lithography and nanoimprinting.

[0028] The substrate 1 is preferably made of a hydrophobic material to give the diffuser 100 water repellency. In particular, the substrate 1 is preferably made of polydimethylsiloxane (PDMS) (refractive index: 1.41 or less), which is excellent in hydrophobicity, transparency, mechanical strength, and weather resistance. Here, water repellency can generally be achieved by providing nanoscale irregularities on the surface. In other words, compared to a flat surface, a surface with nanoscale irregularities has a significantly reduced contact area between the surface protrusions and the water droplets when the water droplets land on it, and air acts as a cushion in the recesses to prevent water from soaking into the surface, resulting in a highly water-repellent surface. This effect is called the lotus (lotus leaf) effect, which is a phenomenon of water-repellent surfaces discovered on the surface of lotus leaves. It is known that lotus, which lives in an environment with muddy water, uses this water-repellent effect to prevent the surface of the leaves from becoming dirty with mud and impeding photosynthesis. By applying this lotus effect to the diffuser 100 according to this embodiment, the self-cleaning effect of the diffuser 100 can be achieved. That is, by using a hydrophobic material for the material of the substrate 1 having the uneven surface structure 20 on its surface, the water repellency of the diffuser 100 can be significantly improved, and the diffuser 100 can exhibit a self-cleaning effect. This improves the resistance of the diffuser 100 to surface contamination. This is an advantageous effect for diffusers used outdoors, such as diffusers for photography lighting or lighting windows.

[0029] (Detailed configuration of uneven structure 20) 5 is a top view showing the concave-convex structure 20 of the diffuser 100. As shown in FIG. 5, in the concave-convex structure 20, the multiple recesses 21 and the multiple protrusions 22 are arranged in a non-lattice pattern (not arranged in a checkerboard pattern), and are arranged non-periodically in the region R. The multiple recesses 21 and the multiple protrusions 22 have nanoscale dimensions in the X-axis direction and the Y-axis direction. By having such a concave-convex structure 20, the diffuser 100 can suppress the occurrence of the cross bright line and the central bright spot while satisfying high transmittance, wide-angle diffusion, and low wavelength dispersion.

[0030] Specifically, each of the tops 221 of the multiple protrusions 22 (bottoms 211 of the multiple recesses 21) is a rectangle or a plurality of connected rectangles. In Fig. 5, the top of protrusion 22A is a rectangle, and the top of protrusion 22B is a plurality of connected rectangles. In this way, the shape of the tops of the multiple protrusions 22 is not a fixed shape. The multiple protrusions 22 include protrusions having a shape (a shape that is not rectangular) in which a plurality of rectangles are connected in a complex manner.

[0031] In addition, in the concave-convex structure 20, the average value of the number of first diffraction parts where diffraction of incident light occurs on a straight line along the X-axis direction (first direction) is greater than the average value of the number of second diffraction parts where diffraction of incident light occurs on a straight line along the Y-axis direction (second direction). This allows the diffuser 100 to diffuse light at a wider angle in the X-axis direction than in the Y-axis direction (i.e., anisotropic diffusion is possible). Here, the above-mentioned first diffraction parts are, in other words, recesses and protrusions having a width shorter than a predetermined length (e.g., the wavelength of visible light) on a straight line along the X-axis direction. Similarly, the above-mentioned second diffraction parts are, in other words, recesses and protrusions having a width shorter than a predetermined length on a straight line along the Y-axis direction. In addition, the average value of the number of first diffraction parts is, specifically, the value obtained by averaging the number per unit length of the first diffraction parts in the X-axis direction along the entire length of the region R in the Y-axis direction. Similarly, the average value of the number of second diffraction parts is, specifically, the value obtained by averaging the number per unit length of the second diffraction parts in the Y-axis direction along the entire length of the region R in the X-axis direction.

[0032] (Method of designing uneven structure 20) A method for designing the concave-convex structure 20 will be described below. First, the region R in which the concave-convex structure 20 is formed is divided into a plurality of partition regions DR (unit structures of the concave-convex structure 20). Here, the plurality of partition regions DR are rectangular and have a plurality of types of shapes. Next, each of the plurality of partition regions DR is randomly determined to be either a concave region or a convex region (for example, with approximately equal probability). In the partition region DR determined to be a concave region, the height of the substrate 1 is formed to be a first level H1, and in the partition region DR determined to be a convex region, the height of the substrate 1 is formed to be a second level H2. As a result, the concave-convex structure 20 is designed to have a concave portion 21 in the concave region or a plurality of connected concave regions, and a convex portion 22 in the convex region or a plurality of connected convex regions. In this way, by randomly determining each of the plurality of partition regions DR to be either a concave region or a convex region, concaves and convexes are not formed alternately in order at least in the plurality of partition regions DR. That is, by the above-mentioned design method, the plurality of recesses 21 and the plurality of protrusions 22 are arranged in a non-lattice pattern (not arranged in a checkerboard pattern) and are arranged non-periodically in the region R.

[0033] Here, the lengths W of the first sides of the multiple partitioned regions DR along the X-axis direction are all set to be the same. On the other hand, the lengths L of the second sides of the multiple partitioned regions DR along the Y-axis direction are not all the same, but are randomly determined based on an arbitrary distribution function (e.g., a normal distribution function). This allows the multiple partitioned regions DR to have multiple types of shapes. Therefore, the design of the concave-convex structure 20 can be simplified, while the concave-convex structure 20 can be made into a random (non-periodic) two-dimensional pattern.

[0034] In addition, the length W of the first side along the X-axis direction of the plurality of segmented regions DR is set to be shorter than the wavelength of visible light. In addition, the average value of the length L of the second side along the Y-axis direction of the plurality of segmented regions DR is set to be longer than the wavelength of visible light. This allows the average number of first diffraction sections to be greater than the average number of second diffraction sections. Therefore, the concave-convex structure 20 allows anisotropic diffusion of incident light.

[0035] In addition, the arrangement of the plurality of recesses 21 and the plurality of protrusions 22 may be different between the first uneven structure 201 and the second uneven structure 202. Specifically, the first side length W and the second side length L may be different between the first uneven structure 201 and the second uneven structure 202. For example, the first side length W may be set to 300 nm and the second side length L may be set to 1500±500 nm in the first uneven structure 201, and the first side length W may be set to 450 nm and the second side length L may be set to 2250±500 nm in the second uneven structure 202. The ±500 represents the standard deviation in the normal distribution function. This allows light with a short wavelength to be diffused on the first surface 11, and light with a long wavelength to be diffused on the second surface 12.

[0036] In actuality, the dimensions (length W of the first side and length L of the second side) of the recessed portion 21 and the protruding portion 22 may change due to the processing method (etching) in the manufacturing process described below. Therefore, the length W of the first side and the length L of the second side may be determined taking into consideration such changes in the dimensions of the recessed portion 21 and the protruding portion 22 in the manufacturing process. That is, the length W of the first side is set so that it is all approximately the same after manufacturing. FIG. 5 shows the concave-convex structure 20 in the design stage. As shown in FIG. 5, the length W of the first side of the recessed region and the protruding region may be non-uniform in the design stage.

[0037] (Manufacturing method of diffuser 100) A manufacturing method of the diffuser 100 will be described below. The diffuser 100 can be manufactured by, for example, lithography and nanoimprinting. Specifically, first, a two-dimensional pattern corresponding to the concave-convex structure 20 (designed by the above-mentioned design method) is formed on a Si wafer by electron beam lithography and deep dry etching. Next, the two-dimensional pattern on the Si wafer is transferred to a resin layer (substrate 1). In this way, the diffuser 100 with the concave-convex structure 20 formed thereon is manufactured.

[0038] (Simulation results) In order to verify the diffusivity and transmittance of the diffuser 100 having the uneven structure 20 designed by the above-mentioned design method, an optical simulation was performed to calculate the diffusion pattern when light is incident on the diffuser 100. As a result of the optical simulation, a high transmittance of 90% was obtained in the entire visible light range. In addition, the half-width of the diffused light (excluding the straight light of the transmitted light) was 83° in the wide angle direction (X-axis direction) and 16° in the narrow angle direction (Y-axis direction). This indicates that both the transmittance and the diffusivity are superior to conventional diffusers.

[0039] (Measurement results for diffusion and permeability) In order to verify the diffusivity and transmittance of the diffuser 100 manufactured by the above-mentioned manufacturing method, the diffusion pattern when light is incident on the diffuser 100 was actually measured.

[0040] FIG. 6 is a diagram showing the projection of the diffused light diffused by the diffuser 100 onto a screen. As shown in FIG. 6, when light is incident on the diffuser 100, a diffusion pattern is obtained that shows anisotropic diffusion in which the incident light is diffused widely in the X-axis direction and narrowly in the Y-axis direction. Here, a high transmittance of 93% is obtained over the entire visible light range. In addition, the half-width of the diffused light is 79° in the wide-angle direction (X-axis direction) and 16° in the narrow-angle direction (Y-axis direction). This shows that, as with the simulation results, the diffuser is superior in both transmittance and diffusivity to conventional diffusers.

[0041] In addition, the intensities of the cross bright line and the central bright spot are reduced in the diffusion pattern shown in Fig. 6 compared to the diffusion pattern shown in Fig. 3. This is because the concave-convex structure 20 has a plurality of concave portions 21 and a plurality of convex portions 22 arranged in a non-lattice pattern.

[0042] As described above, the diffuser 100 has a non-lattice surface structure, which can suppress the occurrence of the cross bright line and the central bright spot, compared to the diffuser 100s according to the reference embodiment. Also, the diffuser 100 can simplify the design of the surface structure, compared to the diffuser 100s according to the reference embodiment.

[0043] (Actual measurement results regarding water repellency and self-cleaning properties) Furthermore, in order to verify the water repellency and self-cleaning action of the diffuser 100 when PDMS was used as the material for the substrate 1, the water contact angle and sliding angle were measured, and a self-cleaning action test was performed.

[0044] The water contact angle of the substrate 1 without the uneven structure 20 was 108.4±5.7°. On the other hand, the water contact angle of the substrate 1 with the uneven structure 20 was 134.4±2.1°. This shows that the water repellency of the diffuser 100 was significantly improved by providing the nanoscale uneven structure 20 on the surface of the substrate 1 and using hydrophobic PDMS as the material of the substrate 1. In addition, water droplets on the substrate 1 with the uneven structure 20 formed thereon quickly slid off when the substrate 1 was tilted to about 31° from the horizontal plane. This shows that the diffuser 100 has excellent water repellency.

[0045] In addition, when colored sand was sprinkled on the substrate 1 and water was dripped from a pipette, the colored sand on the substrate 1 that did not have the uneven surface structure 20 remained mostly adsorbed, whereas the colored sand on the substrate 1 that did have the uneven surface structure 20 was quickly washed away with the running water. This demonstrates the remarkable self-cleaning effect of the diffuser 100.

[0046] As described above, by combining a surface nanostructure with a hydrophobic material, it is possible to significantly improve the water repellency of the diffuser 100 and to exert a self-cleaning effect, thereby improving the resistance of the diffuser 100 to surface contamination.

[0047] [Embodiment 2] (Schematic configuration of diffuser 100a) 7 is a perspective view showing a diffuser 100a. The diffuser 100a differs from the diffuser 100 in that a concave-convex structure 20a is formed in the region R of the substrate 1 instead of the concave-convex structure 20. The concave-convex structure 20a includes a first concave-convex structure 201a formed on the first surface 11 and a second concave-convex structure 202a formed on the second surface 12, similar to the concave-convex structure 20. The concave-convex structure 20a also includes a plurality of recesses 21a on the first level H1 and a plurality of protrusions 22a protruding to the second level H2, similar to the concave-convex structure 20.

[0048] (Detailed configuration of concave-convex structure 20a) 8 is a top view showing the concave-convex structure 20a of the diffuser 100a. The concave-convex structure 20a differs from the concave-convex structure 20 in the following respects. That is, in the concave-convex structure 20, the average number of first diffraction sections is greater than the average number of second diffraction sections, whereas in the concave-convex structure 20a, the average number of first diffraction sections is substantially equal to the average number of second diffraction sections. This allows the diffuser 100a to diffuse light isotropically.

[0049] (Method of designing the uneven structure 20a) In the concave-convex structure 20a, first, the region R in which the concave-convex structure 20a is formed is divided into a plurality of divided regions DRa. Here, the plurality of divided regions DRa are square and have the same shape. In addition, the length W of the side of the plurality of divided regions DRa is set to be shorter than the wavelength of visible light. Next, similar to the concave-convex structure 20, each of the plurality of divided regions DRa is randomly determined to be either a concave region or a convex region with approximately equal probability. This allows the average number of first diffraction parts and the average number of second diffraction parts to be approximately equal.

[0050] As in the first embodiment, the dimensions of the recessed portion 21a and the protruding portion 22a may change during the manufacturing process. Therefore, the length W of the side of the plurality of segmented regions DRa may be determined taking into consideration the change in the dimensions of the recessed portion 21a and the protruding portion 22a during the manufacturing process. That is, the length W of the side of the plurality of segmented regions DRa is set so that it is all substantially the same after manufacturing. FIG. 8 shows the concave-convex structure 20a at the design stage. As shown in FIG. 8, the length W of the side of the plurality of segmented regions DRa may be non-uniform at the design stage.

[0051] (Simulation results) In order to verify the diffusivity and transmittance of the diffuser 100 having the uneven structure 20a designed by the above-mentioned design method, an optical simulation was performed to calculate the diffusion pattern when light is incident on the diffuser 100a. As a result of the optical simulation, the half-width of the diffused light was 83° in the X-axis direction and the Y-axis direction. This indicates that it was possible to achieve isotropic diffusion of the incident light while achieving improved diffusivity compared to conventional diffusers.

[0052] (Measurement results for diffusion and permeability) In order to verify the diffusivity of the diffuser 100a manufactured by the above-mentioned manufacturing method, the diffusion pattern when light is incident on the diffuser 100a was actually measured.

[0053] FIG. 9 is a diagram showing the projection of the diffused light diffused by the diffuser 100a onto a screen. As shown in FIG. 9, when light is incident on the diffuser 100a, a diffusion pattern showing isotropic diffusion in which the incident light is isotropically diffused is obtained. Here, the half-width of the diffused light is 78° in the X-axis direction and the Y-axis direction. This indicates that, as with the simulation results, it is possible to achieve isotropic diffusion of the incident light while achieving improved diffusivity compared to the conventional diffuser.

[0054] As described above, by forming the surface structure of the diffuser into an uneven structure 20 (defined by a rectangular divided area with a uniform first side length W) (see Figs. 4 and 5), incident light can be anisotropically diffused. Also, by forming the surface structure of the diffuser into an uneven structure 20a (defined by a square divided area) (see Figs. 7 and 8), incident light can be isotropically diffused. Therefore, the diffusion angle of incident light can be controlled by a simple design.

[0055] [Embodiment 3] Furthermore, the inventors have found that by using a diffuser 100b having a protective layer 200 instead of the diffuser 100s according to the reference embodiment, the surface nanopattern can be protected from mechanical shock while maintaining the diffusion performance of the diffuser. In the third embodiment, such a diffuser 100b will be described.

[0056] Fig. 10 is a cross-sectional view showing diffuser 100b. As shown in Fig. 10, diffuser 100b further includes a protective layer 200 disposed on the uneven structure 20, 20a of substrate 1. Protective layer 200 protects the surface of diffuser 100b from mechanical shock. In consideration of mass productivity, protective layer 200 may be, for example, a protective film, but is not limited thereto.

[0057] The refractive index of the protective layer 200 may be, for example, 0.85 to 1.2 times the refractive index of the substrate 1. This allows the refractive index contrast between the substrate 1 and the protective layer 200 to be sufficiently small. Therefore, light reflection at the interface between the substrate 1 and the protective layer 200 can be suppressed. In other words, even if the protective layer 200 is provided on the surface of the substrate 1, the optical characteristics of the diffuser 100b are hardly changed.

[0058] Furthermore, when the material of the substrate 1 is PDMS, due to the flexibility and adhesiveness of PDMS, the formation of the protective layer 200 can be completed simply by attaching the protective layer 200 to the substrate 1 without leaving any gaps (no adhesive treatment is required).

[0059] (Measurement results for diffusion and permeability) In order to verify the diffusion property of the diffuser 100b provided with the protective layer 200, the diffusion pattern when light was incident on the diffuser 100b was measured. Here, the substrate 1 was provided with the concave-convex structure 20, and the protective layer 200 was a cover glass (refractive index: 1.52 or less).

[0060] As a result of the actual measurement, a transmittance of 87% was obtained over the entire visible light range. The half-width of the diffused light was 78° in the wide-angle direction (X-axis direction) and 16° in the narrow-angle direction (Y-axis direction). This means that the diffusivity was almost unchanged compared to the case without the protective layer 200 (measurement result of embodiment 1), and the transmittance was only reduced by 6%. This is because, as shown in FIG. 10, even if the protective layer 200 is formed, a nanoscale interface that causes diffraction still exists. In addition, this is because the refractive index contrast between the substrate 1 and the protective layer 200 is sufficiently small.

[0061] (Modification) There may be a plurality of regions R in which the same concave-convex structures 20, 20a are formed on the first surface 11. In this case, the size of each region R may be such that the transmitted light diffused by the concave-convex structures 20, 20a formed in the adjacent regions R does not interfere with each other.

[0062] According to the above configuration, for example, by simply attaching the diffuser 100, 100a, 100b to a window glass, the window glass can function as a daylight window that can achieve high transmittance, wide-angle diffusion, and low wavelength dispersion. In other words, the diffusers 100, 100a, 100b can contribute to reducing the energy consumption of lighting fixtures. Such an effect also contributes to achieving, for example, Goal 7 of the Sustainable Development Goals (SDGs) advocated by the United Nations, "Affordable and Clean Energy."

[0063] The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present invention. [Explanation of symbols]

[0064] 1 Board 20,20a uneven structure 21,21a Recess 22,22a Convex part 100,100a,100b Diffuser 200 protective layer 201,201a 1st uneven structure 202,202a 2nd uneven structure 211 Bottom 221 Top

Claims

1. a substrate having an area formed with a concave-convex structure that diffuses incident light by diffraction; The relief structure has a plurality of recesses at a first level and a plurality of protrusions protruding to a second level, the plurality of recesses and the plurality of protrusions are arranged in a non-lattice pattern and non-periodically in the region; A diffuser in which the unit structures of the uneven structure are arranged in a non-lattice pattern.

2. The diffuser according to claim 1 , wherein each of the tops of the plurality of protrusions is a rectangle or a plurality of connected rectangles.

3. When a direction along a first side of the rectangle is defined as a first direction and a direction along a second side of the rectangle that is perpendicular to the first side is defined as a second direction, 3. The diffuser of claim 2, wherein the average number of first diffraction sections at which diffraction of incident light occurs on a straight line along the first direction is greater than the average number of second diffraction sections at which diffraction of incident light occurs on a straight line along the second direction.

4. When a direction along a first side of the rectangle is defined as a first direction and a direction along a second side of the rectangle that is perpendicular to the first side is defined as a second direction, 3. The diffuser of claim 2, wherein the average number of first diffraction sections at which diffraction of incident light occurs on a straight line along the first direction is approximately equal to the average number of second diffraction sections at which diffraction of incident light occurs on a straight line along the second direction.

5. The diffuser according to claim 1 , wherein the uneven structure has a first uneven structure formed on a first surface of the substrate and a second uneven structure formed on a second surface opposite to the first surface.

6. 6. The diffuser according to claim 1, wherein the substrate is made of a hydrophobic material.

7. The diffuser of claim 1 , further comprising a protective layer disposed on the relief structure.

8. A step of preparing a substrate having an area formed with a concavo-convex structure that diffuses incident light by diffraction; a step of diffusing light by making the light incident on the concave-convex structure, The relief structure has a plurality of recesses at a first level and a plurality of protrusions protruding to a second level, the plurality of recesses and the plurality of protrusions are arranged in a non-lattice pattern and non-periodically in the region; A light diffusion method, wherein the unit structures of the uneven structure are arranged in a non-lattice pattern.

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