Diffusion plate, display device, projection device, and illumination device

Abstract

To suppress unevenness in luminance distribution in two directions of microlenses arranged in a rectangular grid and to improve homogeneity in light distribution.SOLUTION: A microlens array-type diffusion plate comprises a substrate and a microlens array. The microlens array comprises a plurality of microlenses that are arrayed in conformity to a rectangular grid on an X-Y plane of at least one surface of the substrate. Here, X-direction grid intervals Wx of the microlenses arrayed in the X-direction of the rectangular grid are different from each other; Y-direction grid intervals Wy of the microlenses arrayed in the Y-direction of the rectangular grid are different from each other; and surface shapes of the microlenses are different from each other.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a diffuser, a display device, a projection device, and a lighting device. [Background technology]

[0002] In order to change the diffusion characteristics of light, a diffuser plate that diffuses incident light in a desired direction is used. Diffuser plates are widely used in various devices, such as display devices such as displays, projection devices such as projectors, and various lighting devices. There is a type of diffuser plate that diffuses incident light at a desired diffusion angle by utilizing the refraction of light caused by the surface shape of the diffuser plate. As a diffuser plate of this type, a microlens array type diffuser plate in which a plurality of microlenses having a size of about several tens of μm are arranged is known.

[0003] In such a microlens array type diffuser, the wavefronts of the light from each microlens interfere with each other, resulting in diffracted waves due to the periodic structure of the microlens array, which causes unevenness in the intensity distribution of the diffused light. For this reason, a technology has been proposed to reduce unevenness in the intensity distribution of the diffused light caused by interference and diffraction by varying the arrangement of the microlenses, the shape of the lens surface, and the shape of the opening.

[0004] For example, Patent Document 1 describes the use of multiple microlenses with different cross-sectional shapes and no axis of symmetry in a diffusion plate having multiple microlenses regularly arranged in a rectangular lattice on the main surface. Patent Document 2 describes the arrangement of the lens vertices of multiple microlenses arranged in a rectangular lattice by shifting them from the lattice points of a reference lattice. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. 2016 / 051785 [Patent Document 2] International Publication No. 2015 / 182619 Summary of the Invention [Problem to be solved by the invention]

[0006] However, as described in the above Patent Document 1, in an array structure in which a plurality of microlenses having no symmetric axis and different cross-sectional shapes are regularly arranged in a rectangular lattice, the unevenness of the intensity distribution of the diffused light is reduced only by the phase change of the light between adjacent microlenses. Therefore, the effect of uniformly distributing the diffused light in two mutually orthogonal directions of the rectangular lattice is limited. Also, as described in Patent Document 2, in an array structure regularly arranged in a rectangular lattice, it is not possible to realize highly uniform light distribution control in two directions of the rectangular lattice by only shifting the vertex positions of each microlens.

[0007] Therefore, the present invention has been made in consideration of the above-mentioned circumstances, and an object of the present invention is to suppress unevenness in luminance distribution and improve the uniformity of light distribution in two directions of microlenses arranged in a rectangular lattice pattern. [Means for solving the problem]

[0008] In order to solve the above problems, according to one aspect of the present invention, A microlens array type diffuser plate, A substrate; a microlens array including a plurality of microlenses arranged on an XY plane on at least one surface of the substrate based on a rectangular grid; Equipped with The microlenses arranged in the X direction of the rectangular lattice have different lattice intervals Wx in the X direction, The microlenses arranged in the Y direction of the rectangular lattice have mutually different lattice intervals Wy in the Y direction, A diffusion plate is provided in which the surface shapes of the plurality of microlenses are different from each other.

[0009] the lattice interval Wx in the X direction varies randomly with a variation rate ΔWx within ±10% to ±50% based on a reference lattice interval Wx_k, The lattice spacing Wy in the Y direction may vary randomly with a variation rate ΔWy within ±10% to ±50% with respect to a reference lattice spacing Wy_k.

[0010] The radii of curvature Rx in the X direction of the microlenses arranged in the X direction are mutually varied, The microlenses arranged in the Y direction may have radii of curvature Ry in the Y direction that vary from one another.

[0011] The radius of curvature Rx in the X direction varies randomly with a variation rate ΔRx within ±10% to ±50% based on a reference radius of curvature Rx_k, The radius of curvature Ry in the Y direction may vary randomly with a variation rate ΔRy within ±10% to ±50% with respect to a reference radius of curvature Ry_k.

[0012] the lattice interval Wx in the X direction varies randomly with a variation rate ΔWx within ±10% to ±50% based on a reference lattice interval Wx_k, the lattice interval Wy in the Y direction varies randomly with a variation rate ΔWy within ±10% to ±50% based on a reference lattice interval Wy_k, the reference lattice intervals Wx_k, Wy_k and the reference radii of curvature Rx_k, Ry_k satisfy the following relational expressions (A) and (B), The diffusion angle (full width at half maximum) of the diffusion plate may be 20° or less. Rx_k / Wx_k≧1.85 (A) Ry_k / Wy_k≧1.85 (B)

[0013] The planar positions of the vertices of the microlenses arranged in the X direction and the Y direction may be decentered from the center point of the rectangular lattice.

[0014] The distances in the X direction and the Y direction from the center point of the rectangular grating to the planar position of the apex of the decentered microlens are respectively defined as an eccentricity Ecx and an eccentricity Ecy, and the ratios of the eccentricity Ecx and Ecy to the grating intervals Wx and Wy of the rectangular grating are respectively defined as an eccentricity δEcx and an eccentricity δEcy, The planar positions of the vertices of the microlenses may be randomly decentered with eccentricities ΔEcx, ΔEcy within a range of ±10% to ±50%.

[0015] The height positions of the apexes of the microlenses arranged in the X direction and the Y direction may be different from each other.

[0016] The microlenses arranged in the X direction and the Y direction may be arranged continuously with no gaps between them.

[0017] The boundaries of the adjacent microlenses may include straight lines and curved lines.

[0018] the microlens array is composed of a plurality of unit cells which are a basic arrangement pattern of the microlenses, The microlens array may be configured by arranging the unit cells without gaps while maintaining continuity of the microlenses at boundaries between the unit cells.

[0019] The surface shape of the microlens may be a spherical shape or an aspherical shape having anisotropy in the X direction or the Y direction.

[0020] In order to solve the above problem, according to another aspect of the present invention, there is provided a display device including the above-mentioned diffusion plate.

[0021] In order to solve the above-mentioned problems, according to another aspect of the present invention, there is provided a projection device including the above-mentioned diffusion plate.

[0022] In order to solve the above problem, according to another aspect of the present invention, there is provided an illumination device including the above-mentioned diffusion plate. Effect of the Invention

[0023] As described above, according to the present invention, it is possible to suppress unevenness in luminance distribution and improve the uniformity of light distribution in two directions of microlenses arranged in a rectangular lattice pattern. [Brief description of the drawings]

[0024] [Figure 1] FIG. 1 is an explanatory diagram illustrating a diffusion plate according to an embodiment of the present invention. [Diagram 2] 3A and 3B are an enlarged plan view and an enlarged cross-sectional view illustrating a schematic configuration of a diffusion plate according to the embodiment. [Diagram 3] 4 is an enlarged cross-sectional view showing a schematic view of the vicinity of a boundary of a microlens according to the embodiment; FIG. [Figure 4] FIG. 2 is a plan view that illustrates a planar shape (external shape) of a microlens according to the embodiment. [Diagram 5] FIG. 11 is a plan view illustrating an arrangement of microlenses in an irregular rectangular lattice according to the embodiment. [Figure 6] 6 is an explanatory diagram showing an example in which the surface shape of a microlens is changed from the state shown in FIG. 5. [Figure 7] FIG. 7 is an explanatory diagram showing an example in which the apex position of a microlens is decentered from the state shown in FIG. 6. [Figure 8] 11 is an explanatory diagram showing the planar shape of an anamorphic microlens according to the embodiment; FIG. [Figure 9] FIG. 2 is a perspective view showing a three-dimensional shape of an anamorphic microlens according to the embodiment. [Figure 10] FIG. 2 is a perspective view showing a curved surface of an anamorphic shape according to the embodiment. [Figure 11] 4 is an explanatory diagram showing a planar shape of a torus-shaped microlens according to the embodiment; FIG. [Figure 12]FIG. 2 is a perspective view showing a three-dimensional shape of a torus-shaped microlens according to the embodiment. [Figure 13] FIG. 2 is a perspective view showing a torus-shaped curved surface according to the embodiment; [Figure 14] 13 is a flowchart showing a method for designing a microlens according to the embodiment. [Figure 15] 11 is an explanatory diagram showing a rectangular grid generated in a grid generating step according to the embodiment; FIG. [Figure 16] 11A and 11B are explanatory diagrams showing a rectangular grid generated in a grid decentering step according to the embodiment; [Figure 17] 10 is an explanatory diagram showing a plurality of microlenses generated in a lens generating step according to the embodiment. FIG. [Figure 18] 11 is an image showing a lens pattern designed by the design method according to the embodiment. [Figure 19] 5 is a flowchart showing a method for manufacturing the diffusion plate according to the embodiment. [Figure 20] FIG. 11 is an explanatory diagram of a diffusion plate according to Comparative Example 1. [Figure 21] FIG. 11 is an explanatory diagram of a diffusion plate according to Comparative Example 2. [Figure 22] FIG. 11 is an explanatory diagram of a diffusion plate according to Comparative Example 3. [Diagram 23] FIG. 2 is an explanatory diagram of a diffusion plate according to the first embodiment. [Figure 24] FIG. 11 is an explanatory diagram of a diffusion plate according to a second embodiment. [Diagram 25] FIG. 11 is an explanatory diagram of a diffusion plate according to a third embodiment. [Figure 26] FIG. 11 is an explanatory diagram of a diffusion plate according to a fourth embodiment. [Figure 27] FIG. 13 is an explanatory diagram of a diffusion plate according to the fifth embodiment. [Figure 28] FIG. 13 is an explanatory diagram of a diffusion plate according to the sixth embodiment. [Figure 29] FIG. 13 is an explanatory diagram of a diffusion plate according to a seventh embodiment. [Diagram 30] FIG. 13 is an explanatory diagram of a diffusion plate according to a seventh embodiment. [Diagram 31] FIG. 11 is an explanatory diagram of a diffusion plate according to Comparative Example 4. [Diagram 32] FIG. 13 is an explanatory diagram of a diffusion plate according to an eighth embodiment. [Diagram 33] FIG. 13 is an explanatory diagram of a diffusion plate according to a ninth embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0025] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In this specification and the drawings, components having substantially the same functional configurations are designated by the same reference numerals, and duplicated explanations will be omitted.

[0026] <1. Overview of the diffuser plate> First, an overview of a diffusion plate according to an embodiment of the present invention will be described.

[0027] The diffuser plate according to the present embodiment, which will be described in detail below, is a microlens array type diffuser plate having a function of homogeneously diffusing light. Such a diffuser plate has a microlens array formed on an XY plane on at least one surface (principal surface) of a substrate. The microlens array is composed of a plurality of microlenses arranged and developed in a rectangular lattice pattern. The microlenses are made of a convex structure (convex lens) or a concave structure (concave lens) having a light diffusing function, and have a lens diameter of about several tens of μm.

[0028] In the diffuser according to the present embodiment, a plurality of microlenses are arranged in a rectangular lattice (matrix) based on a rectangular lattice having irregularity. In this rectangular lattice having irregularity, a plurality of lattice intervals Wx in the X direction (row direction) vary randomly and are different from each other, and a plurality of lattice intervals Wy in the Y direction (column direction) also vary randomly and are different from each other. Furthermore, the radii of curvature Rx, Ry of the plurality of microlenses arranged in the X and Y directions vary randomly (irregularly) so as to be different from each other. In addition, the planar position of the apex of each microlens varies randomly (eccentric) so as to be shifted from the center point of the rectangular lattice. In addition, the height positions in the Z direction of the apex of the plurality of microlenses (positions in the thickness direction of the diffuser) also vary randomly and are different from each other. In this way, by randomly varying the lattice intervals Wx, Wy, the radii of curvature Rx, Ry, the planar position and height position of the lens apex, etc., the surface shapes of the plurality of microlenses deployed in a rectangular lattice vary randomly and are different from each other.

[0029] In this way, according to the diffuser plate of this embodiment, a highly random three-dimensional surface structure of a microlens array is realized by randomly varying each variable element of a plurality of microlenses. This makes it possible to control the overlapping state of the phases of light emitted from each microlens. As a result, it is possible to provide a surface structure of a diffuser plate that has high transmittance luminance characteristics, satisfies the homogeneity of light distribution in two mutually orthogonal directions (X and Y directions), and can control sufficient anisotropy of light distribution and cutoff property of the intensity distribution of diffused light.

[0030] Furthermore, according to this embodiment, a plurality of microlenses are arranged on the XY plane based on an irregular rectangular lattice having mutually different lattice intervals Wx and Wy. This allows a plurality of microlens arrays to be arranged continuously on the surface of the diffusion plate without gaps while ensuring the randomness of the surface shape of each microlens. Therefore, it is possible to minimize the existence of flat portions at the boundary portions of adjacent microlenses, thereby further reducing unevenness in the intensity distribution of diffused light and further improving the uniformity of the light distribution in two directions (X and Y directions).

[0031] The diffusion plate according to this embodiment having the above-mentioned characteristics will be described in detail below.

[0032] <2. Overall structure of the diffusion plate> First, the overall configuration of a diffuser plate according to one embodiment of the present invention and a layout pattern of microlenses will be described with reference to Fig. 1. Fig. 1 is an explanatory diagram that shows a schematic diagram of a diffuser plate 1 according to this embodiment.

[0033] The diffuser 1 according to this embodiment is a microlens array type diffuser in which a microlens array consisting of a plurality of microlenses (single lenses) is arranged on a substrate. The microlens array of the diffuser 1 is composed of a plurality of unit cells 3 as shown in FIG. 1. The unit cells 3 are a basic arrangement pattern of microlenses. A plurality of microlenses are arranged on the surface of each unit cell 3 in a predetermined layout pattern (arrangement pattern).

[0034] 1 shows an example in which the shape of the unit cells 3 constituting the diffusion plate 1 is rectangular, particularly square. However, the shape of the unit cells 3 is not limited to the example shown in Fig. 1, and may be any shape, such as an equilateral triangle or a regular hexagon, as long as it can fill the surface (XY plane) of the diffusion plate 1 without gaps.

[0035] 1, a plurality of square unit cells 3 are repeatedly arranged vertically and horizontally on the surface of the diffusion plate 1. The number of unit cells 3 constituting the diffusion plate 1 according to this embodiment is not particularly limited, and the diffusion plate 1 may be composed of one unit cell 3 or may be composed of a plurality of unit cells 3. In the diffusion plate 1 according to this embodiment, unit cells 3 having different surface structures may be repeatedly arranged, or unit cells 3 having the same surface structure may be repeatedly arranged.

[0036] Furthermore, between unit cells 3, as shown in the enlarged view on the right side of FIG. 1, the layout pattern (arrangement pattern) of the multiple microlenses provided in the unit cells 3 is continuous in the arrangement direction of the unit cells 3 (in other words, the array arrangement direction). A microlens array is formed by arranging the unit cells 3 without gaps while maintaining the continuity of the microlenses at the boundaries between the multiple unit cells 3. Here, the continuity of the microlenses means that, of two mutually adjacent unit cells 3, a microlens located on the outer edge of one unit cell 3 and a microlens located on the outer edge of the other unit cell 3 are continuously connected without any misalignment in the planar shape or step in the height direction.

[0037] In this manner, in the diffuser 1 according to this embodiment, the unit cells 3 (basic structure) of the microlens array are arranged without gaps while maintaining the continuity of the boundaries to form a microlens array. This makes it possible to prevent unintended problems such as diffraction, reflection, and scattering of light at the boundaries between the unit cells 3, and to obtain the desired light distribution characteristics by the diffuser 1.

[0038] <3. Structure of the diffusion plate> Next, the configuration of the diffuser plate 1 according to this embodiment will be described in more detail with reference to Fig. 2 to Fig. 4. Fig. 2 is an enlarged plan view and an enlarged cross-sectional view that typically show the configuration of the diffuser plate 1 according to this embodiment. Fig. 3 is an enlarged cross-sectional view that typically shows the vicinity of the boundary of a microlens 21 according to this embodiment. Fig. 4 is a plan view that typically shows the planar shape (outer shape) of a microlens 21 when the microlens 21 is viewed in plan from a direction perpendicular to the surface of the substrate 10.

[0039] As shown in FIG. 2, the diffuser plate 1 according to this embodiment includes a base material 10 and a microlens array 20 formed on the surface of the base material 10.

[0040] First, the substrate 10 will be described. The substrate 10 is a substrate for supporting the microlens array 20. The substrate 10 may be in the form of a film or a plate. The substrate 10 shown in FIG. 2 has, for example, a rectangular flat plate shape, but is not limited to this example. The shape and thickness of the substrate 10 may be any shape and thickness depending on the shape of the device in which the diffusion plate 1 is mounted.

[0041] The substrate 10 is a transparent substrate capable of transmitting light. The substrate 10 is made of a material that can be regarded as transparent in the wavelength band of light incident on the diffusion plate 1. For example, the substrate 10 may be made of a material having a light transmittance of 70% or more in the wavelength band corresponding to visible light.

[0042] The substrate 10 may be formed of a known resin such as polymethyl methacrylate (PMMA), polyethylene terephthalate (PET), polycarbonate (PC), cycloolefin copolymer (COC), cycloolefin polymer (COP), triacetylcellulose (TAC), etc. Alternatively, the substrate 10 may be formed of a known optical glass such as quartz glass, borosilicate glass, white plate glass, etc.

[0043] Next, the microlens array 20 will be described. The microlens array 20 is provided on at least one surface (principal surface) of the substrate 10. The microlens array 20 is a collection of a plurality of microlenses 21 (single lenses) arranged on the surface of the substrate 10. In this embodiment, as shown in FIG. 2, the microlens array 20 is formed on one surface of the substrate 10. However, this is not limited to such an example, and the microlens array 20 may be formed on both principal surfaces (front and back surfaces) of the substrate 10.

[0044] The microlens 21 is a minute optical lens of, for example, the order of several tens of μm. The microlens 21 constitutes a single lens of the microlens array 20. The microlens 21 may have a concave structure (concave lens) formed so as to be recessed in the thickness direction of the diffusion plate 1, or may have a convex structure (convex lens) formed so as to protrude in the thickness direction of the diffusion plate 1. In this embodiment, an example in which the microlens 21 has a concave structure (concave lens) as shown in FIG. 2 will be described, but the present invention is not limited to such an example. Depending on the desired optical characteristics of the diffusion plate 1, the microlens 21 may have a convex structure (convex lens).

[0045] The surface shape of each microlens 21 is not particularly limited as long as it is a curved shape including a curved component. For example, the surface shape of the microlens 21 may be a spherical shape including only a spherical component, an aspherical shape including a spherical component and an aspherical component, or an aspherical shape including only an aspherical component.

[0046] As shown in FIG. 2, it is preferable that the multiple microlenses 21 are densely arranged so that they are adjacent to each other without any gaps. In other words, it is preferable that the multiple microlenses 21 are arranged continuously so that there are no gaps (flat parts) at the boundary parts between the adjacent microlenses 21. By arranging the microlenses 21 on the substrate 10 without any gaps (in other words, arranging the microlenses 21 so that the packing rate of the microlenses 21 is 100%), it is possible to suppress a component of the incident light that is not scattered on the surface of the diffusion plate 1 and is transmitted as it is (hereinafter also referred to as a "zeroth order transmitted light component"). As a result, it is possible to further improve the diffusion performance by the microlens array 20 in which the multiple microlenses 21 are arranged so that they are adjacent to each other without any gaps.

[0047] In order to suppress the zero-order transmitted light component, the filling rate of the microlenses 21 on the substrate 10 is preferably 90% or more, and more preferably 100%. Here, the filling rate refers to the ratio of the area of ​​the portion on the surface of the substrate 10 that is occupied by the multiple microlenses 21. If the filling rate is 100%, the surface of the microlens array 20 will be formed of curved surface components and will contain almost no flat surface components.

[0048] However, in the actual manufacture of the microlens array 20, the curved surfaces of the multiple microlenses 21 are continuously connected, so that the vicinity of the inflection point at the boundary between adjacent microlenses 21 may become substantially flat. In such a case, the width of the substantially flat region near the inflection point at the boundary between the microlenses 21 (the width of the boundary line between the microlenses 21) is preferably 1 μm or less. This allows the zero-order transmitted light component to be sufficiently suppressed.

[0049] Furthermore, in the microlens array 20 according to this embodiment, the multiple microlenses 21 are not arranged randomly (irregularly), but are arranged to a certain degree of regularity (hereinafter referred to as "quasi-regularly") based on an irregular rectangular lattice (see FIG. 5) in which the lattice intervals Wx and Wy vary in the X and Y directions, as shown in FIG. 2. Here, "random" means that there is no substantial regularity in the arrangement of the microlenses in any region of the microlens array. However, even if there is some regularity in the arrangement of the microlenses in a small region, the absence of regularity in the arrangement of the microlenses in any region as a whole is considered to be included in "irregularity."

[0050] In this embodiment, the microlenses 21 are arranged quasi-regularly based on an irregular rectangular lattice. The surface shape and planar shape of the microlenses 21 vary randomly. As shown in FIG. 2 and FIG. 4, the planar shape (outer shape) of the microlenses 21 is generally close to a substantially rectangular shape, but is not a perfect rectangular shape (square or rectangular shape) corresponding to the rectangular lattice. Specifically, the planar shape of the microlenses 21 is close to a substantially polygonal shape having four or more vertices, such as a substantially quadrangle, a substantially pentagon, or a substantially hexagon. The surface shapes (three-dimensional curved shapes) and planar shapes (shapes projected onto the XY plane of the substrate 10) of the microlenses 21 are different from each other. The reason why each microlens 21 has a shape that is irregularly deformed from a rectangular shape is that the radii of curvature Rx, Ry, aperture diameters Dx, Dy, and the planar and height positions of the lens vertices of each microlens 21 vary randomly within a predetermined range of variation rates. The method of quasi-regularly arranging the microlenses 21 based on a rectangular lattice according to this embodiment will be described in detail later (see FIGS. 5 to 7).

[0051] Thus, in this embodiment, the radii of curvature Rx, Ry and the aperture diameters Dx, Dy of each microlens 21 vary randomly and have variation. The aperture diameters Dx, Dy of the microlenses 21 correspond to the lens diameter of a single lens. The phase distribution of the optical aperture of each microlens 21 differs depending on the orientation. The multiple microlenses 21 are continuously arranged on the surface of the substrate 10 so as to overlap each other, and the radii of curvature Rx, Ry and the aperture diameters Dx, Dy (lens diameter) of each microlens 21 have variation. As a result, the shapes (surface shape and planar shape) of the multiple microlenses 21 are not the same as each other. Therefore, the multiple microlenses 21 have various shapes as shown in FIG. 2, and many of them do not have symmetry.

[0052] As a result, as shown in FIG. 3, the radius of curvature of the microlens 21A is R A Meanwhile, the radius of curvature of the microlens 21B adjacent to the microlens 21A is R B (≠R A The radius of curvature R of the adjacent microlenses 21 is A , R B are different from each other, the boundary line between the adjacent microlenses 21 is not formed only by straight lines but is formed to include at least a part of a curve.

[0053] 4, when the microlens 21 is viewed in plan from the Z direction perpendicular to the surface of the base material 10, the outline of the planar shape of the microlens 21 (boundaries between the microlens 21 and the other multiple adjacent microlenses 21) includes multiple curved lines with different curvatures and straight lines. When the boundaries of the microlenses 21 include multiple curved lines with different curvatures, the regularity of the boundaries between the microlenses 21 is further disrupted, and the diffraction component of the diffused light can be further reduced.

[0054] <4. Microlens arrangement method> Next, a method for arranging the microlenses 21 according to this embodiment will be described in detail with reference to Fig. 5 to Fig. 7. Fig. 5 is a plan view that typically shows an arrangement of the microlenses 21 in an irregular rectangular lattice according to this embodiment. Fig. 6 is an explanatory diagram showing an example in which the surface shape of the microlenses 21 is changed from the state shown in Fig. 5. Fig. 7 is an explanatory diagram showing an example in which the planar positions of the vertices 22 of the microlenses 21 are decentered from the state shown in Fig. 6.

[0055] The microlens array 20 in which a plurality of microlenses 21 having the above-mentioned characteristics are arranged can be realized by the arrangement method according to this embodiment described below.

[0056] First, as shown in Fig. 5, a reference state (hereinafter also referred to as "initial arrangement state") is set in which a plurality of microlenses 21 having a reference shape are quasi-regularly arranged in a rectangular lattice shape. Next, this initial arrangement state is changed to a state (hereinafter also referred to as "varied arrangement state") in which the shapes of the microlenses 21 (i.e., radii of curvature Rx, Ry, aperture diameters Dx, Dy, etc.) and the positions of the vertices 22 of the microlenses 21 are randomly varied, as shown in Fig. 6 and Fig. 7. Hereinafter, such an arrangement method of the microlenses 21 is referred to as a "reference arrangement method".

[0057] In this reference arrangement method, after the microlenses 21 are arranged quasi-regularly (see FIG. 5), randomness is imparted to the shape and arrangement of the microlenses 21 (see FIGS. 6 and 7). Therefore, when the microlens array 20 in the final, changed arrangement state (see FIGS. 2 and 7) is viewed from a somewhat macroscopic perspective, the arrangement of the microlenses 21 is such that the quasi-regular initial arrangement state (see FIG. 5) can be estimated to some extent. This reference arrangement method will be described in detail below.

[0058] (1) Initial arrangement of microlenses 21 based on an irregular rectangular lattice (Figure 5) In the reference arrangement method according to this embodiment, first, an initial arrangement state is set as a reference for the arrangement of the microlenses 21. Specifically, as shown in Fig. 5, in the initial arrangement state, a plurality of microlenses 21 are arranged to a certain degree regularly (quasi-regularly) on the XY plane of the reference surface, using an irregular rectangular lattice as a reference.

[0059] The rectangular grid according to this embodiment may be a rectangular grid or a square grid. As shown in FIG. 5, the rectangular grid is composed of a plurality of grid lines 32 extending in a first direction (X direction) and a plurality of grid lines 31 extending in a second direction (Y direction). The first direction (X direction) and the second direction (Y direction) are perpendicular to each other. In such a rectangular grid, the grid spacing Wx in the X direction is the spacing between the plurality of grid lines 31 extending in the second direction (Y direction). The grid spacing Wy in the Y direction is the spacing between the plurality of grid lines 32 extending in the first direction (X direction).

[0060] Here, the irregular rectangular lattice is a rectangular lattice in which the lattice intervals Wx in the X direction vary randomly and are different from each other, and the lattice intervals Wy in the Y direction vary randomly and are different from each other, as shown in Fig. 5. In the example of the rectangular lattice in Fig. 5, the three lattice intervals Wx1, Wx2, and Wx3 in the X direction are different from each other, and the three lattice intervals Wy1, Wy2, and Wy3 in the Y direction are also different from each other. The lattice intervals Wx and Wy may vary randomly independently without correlation with each other. As a result, for example, the lattice intervals Wx1, Wx2, Wx3, Wy1, Wy2, and Wy3 in the X direction and the Y direction may be different from each other.

[0061] The method of randomly varying the lattice intervals Wx and Wy is, for example, as follows. First, set certain reference values ​​Wx_k, Wy_k (hereinafter referred to as reference lattice intervals Wx_k, Wy_k) that are the basis for the variation of the lattice intervals Wx, Wy in the X and Y directions. Next, the reference lattice intervals Wx_k, Wy_k are randomly varied within a range of a predetermined variation rate δWx, δWy [±%] to set the lattice intervals Wx, Wy (Wx=Wx_k×(100±δWx[%]), Wy=Wy_k×(100±δWy[%])). This is repeated for the number of lattices in the rectangular lattice to set multiple lattice intervals Wx1, Wx2, Wx3,..., Wy1, Wy2, Wy3,... in the X and Y directions, respectively.

[0062] Here, the fluctuation rates ΔWx, ΔWy are preferably within a range of ±10% to ±50%. If the fluctuation rates ΔWx, ΔWy are set to less than ±10%, the fluctuation of the lattice intervals Wx, Wy becomes insufficient, making it difficult to impart sufficient non-periodicity to the microlens array 20, and the uniformity of the light diffused by the microlens array 20 may decrease. On the other hand, if the fluctuation rates ΔWx, ΔWy are set to more than ±50%, the fluctuation of the lattice interval W becomes excessively large, making it difficult to continuously arrange a plurality of microlenses 21 on the XY plane without gaps.

[0063] For example, when the fluctuation rates δWx, δWy are set to “±10%”, the lattice spacings Wx, Wy are set to values ​​that are randomly deviated from the reference lattice spacings Wx_k, Wy_k within a range of “±10%” or less (i.e., greater than or equal to 90% and less than or equal to 110% of Wx_k, Wy_k) based on the reference lattice spacings Wx_k, Wy_k.

[0064] As described above, in this embodiment, multiple lattice intervals Wx1, Wx2, Wx3, ..., Wy1, Wy2, Wy3, ... in the X direction and Y direction are randomly set to mutually different values. Then, using the lattice intervals Wx1, Wx2, Wx3, ..., Wy1, Wy2, Wy3, ..., irregular rectangular lattices with mutually different lattice intervals Wx and Wy (see FIG. 5) are set.

[0065] Next, using the irregular rectangular lattice as a reference, a plurality of microlenses 21 are arranged on the XY plane as shown in FIG. 5. This state is an initial arrangement state that is a reference for arranging the microlenses 21. In the initial arrangement state, the planar shape of each microlens 21 is a rectangle corresponding to the rectangular lattice, and the outline of the planar shape of the microlens 21 coincides with the lattice lines 31 and 32 in the X and Y directions. In addition, the position of the vertex 22 of each microlens 21 coincides with the center point 23 of each rectangular lattice surrounded by the lattice lines 31 and 32. In this initial arrangement state, the opening diameters Dx and Dy in the X and Y directions of each microlens 21 coincide with the lattice intervals Wx and Wy in the X and Y directions, respectively. Here, since the lattice intervals Wx and Wy are changed to different values, the opening diameters Dx and Dy are also changed to different values.

[0066] Moreover, the surface shape of each microlens 21 in the initial arrangement state is a shape obtained by cutting out a predetermined reference shape (for example, an aspheric reference shape) set in advance with a rectangular lattice corresponding to each microlens 21. Here, since the lattice intervals Wx, Wy corresponding to each microlens 21 are different from one another, the aperture diameters Dx, Dy and surface shapes of the multiple microlenses 21 are different from one another. In other words, by arranging the multiple microlenses 21 based on the irregular rectangular lattice, the multiple microlenses 21 can be arranged in the initial arrangement state so that the aperture diameters Dx, Dy and surface shapes of the microlenses 21 are different from one another.

[0067] (2) A first variation arrangement state of the microlenses 21 with the radii of curvature Rx and Ry varied (FIG. 6) After setting the initial arrangement state as described above, a first varied arrangement state is set in which the surface shape of the microlenses 21 is varied by randomly varying the radii of curvature Rx, Ry of the microlenses 21 as shown in Fig. 6. Fig. 6 shows an example in which the surface shape of the microlenses 21 is an aspheric shape having anisotropy in the X direction and the radii of curvature Rx, Ry of the aspheric shape are varied.

[0068] The radius of curvature R includes a radius of curvature Rx of the cross-sectional shape of the microlens 21 cut in the X-direction and a radius of curvature Ry of the cross-sectional shape of the microlens 21 cut in the Y-direction. When the surface shape of the microlens 21 is spherical, Rx and Ry have the same value. On the other hand, when the surface shape of the microlens 21 is aspheric with anisotropy, Rx and Ry can have different values.

[0069] The method of randomly varying the radii of curvature Rx, Ry of the microlenses 21 in the initial arrangement state described above is, for example, as follows. First, set certain reference values ​​Rx_k, Ry_k (hereinafter referred to as reference radii of curvature Rx_k, Ry_k) that serve as the basis for the variation of the radii of curvature Rx, Ry in the X and Y directions. Next, set the radii of curvature Rx, Ry by randomly varying the reference radii of curvature Rx_k, Ry_k within a range of a predetermined variation rate δRx, δRy [%] (Rx=Rx_k×(100±δRx [%]), Ry=Ry_k×(100±δRy [%])). This is repeated the number of times corresponding to the number of microlenses 21, and the radii of curvature Rx in the X and Y directions for each microlens 21 are set. 11 , Ry 11 , Rx 21 , Ry 21 , , Rx nm , Ry nm Here, n is the number of microlenses 21 arranged in the X direction, and m is the number of microlenses 21 arranged in the Y direction.

[0070] Here, the fluctuation rates δRx and δRy are preferably within a range of ±10% to ±50%. If the fluctuation rates δRx and δRy are set to less than ±10%, the fluctuation of the radii of curvature Rx and Ry becomes insufficient, making it difficult to impart sufficient non-periodicity to the microlens array 20, and the homogeneity of the light diffused by the microlens array 20 may decrease. On the other hand, if the fluctuation rates δRx and δRy are set to more than ±50%, the fluctuation of the radii of curvature Rx and Ry becomes excessively large, making it difficult to continuously arrange a plurality of microlenses 21 on the XY plane without gaps.

[0071] In this manner, the radii of curvature Rx and Ry of each microlens 21 in the initial arrangement state are randomly varied (first varied arrangement state). As a result, as shown in FIG. 6, the radii of curvature Rx in the X direction of the microlenses 21 arranged in the X direction are different from each other. Similarly, the radii of curvature Ry in the Y direction of the microlenses 21 arranged in the Y direction are different from each other. In detail, the radius of curvature Rx is varied randomly at a variation rate ΔRx within ±10% to ±50% with respect to a reference radius of curvature Rx_k. Moreover, the radius of curvature Ry is varied randomly at a variation rate ΔRy within ±10% to ±50% with respect to a reference radius of curvature Ry_k.

[0072] 6, the planar shape of each microlens 21 is shifted from the rectangular lattice, and the outline of the planar shape of the microlens 21 may not coincide with the lattice lines 31, 32 in the X and Y directions. However, the position of the vertex 22 of each microlens 21 coincides with the center point 23 of each rectangular lattice. Also, in the first variable arrangement state, the opening diameters Dx, Dy of each microlens 21 in the X and Y directions deviate from the lattice intervals Wx, Wy in the X and Y directions.

[0073] In this way, in the first variable arrangement state in which the radii of curvature Rx, Ry of the microlenses 21 are randomly varied, the multiple microlenses 21 can be arranged so that the aperture diameters Dx, Dy and surface shapes of the microlenses 21 are even more different from each other than in the initial arrangement state.

[0074] (3) A second variation arrangement state of the microlenses 21 in which the lens apex positions are varied (FIG. 7) After setting the first variable array state as described above, a second variable array state is set in which the planar positions of the vertices 22 of the microlenses 21 are randomly decentered from the center point 23 of the rectangular lattice, as shown in Fig. 7. Here, decentering means that the planar positions of the vertices 22 of the microlenses 21 are varied so as to deviate from the center point 23 of the rectangular lattice on the XY plane. Note that the center point 23 of the rectangular lattice is the intersection of two diagonals of the rectangular lattice (see Fig. 4).

[0075] A method for randomly decentering the planar positions of the vertices 22 of the microlenses 21 in the first variable arrangement state described above is, for example, as follows.

[0076] First, an eccentricity Ec of the planar position of the vertex 22 of the microlens 21 (hereinafter sometimes referred to as the lens vertex position 22) is set. The eccentricity Ec is the deviation (distance) of the lens vertex position 22 from the center point 23 of the rectangular lattice. The eccentricity Ec is expressed by an eccentricity Ecx in the X direction and an eccentricity Ecy in the Y direction. The eccentricity Ecx is the deviation in the X direction of the lens vertex position 22 from the center point 23 of the rectangular lattice, and the eccentricity Ecy is the deviation in the Y direction of the lens vertex position 22 from the center point 23 of the rectangular lattice.

[0077] Next, the eccentricities δEcx and δEcy in the X and Y directions are set. The eccentricity δEcx in the X direction is the ratio (percentage) of the amount of eccentricity Ecx to the grating pitch Wx of the rectangular grating. The eccentricity δEcy in the Y direction is the ratio (percentage) of the amount of eccentricity Ecy to the grating pitch Wy of the rectangular grating. The eccentricities δEcx and δEcy are expressed by the following equations. δEcx[%]=Ecx / Wx×100 δEcy[%]=Ecy / Wy×100

[0078] Next, the lens apex position is decentered based on the set eccentricities ΔEcx, ΔEcy. In detail, the lens apex position 22 of each microlens 21 is randomly decentered with eccentricities ΔEcx, ΔEcy within ±10% to ±50%.

[0079] Here, the eccentricities ΔEcx and ΔEcy are preferably within a range of ±10% to ±50%. If the eccentricities ΔEcx and ΔEcy are set to less than ±10%, the eccentricities Ecx and Ecy of the lens apex positions 22 become insufficient, making it difficult to impart sufficient non-periodicity to the microlens array 20, and there is a concern that the homogeneity of the light diffused by the microlens array 20 in the X and Y directions will decrease. On the other hand, if the eccentricities ΔEcx and ΔEcy are set to more than ±50%, the eccentricities Ecx and Ecy of the lens apex will become excessively large, making it difficult to continuously arrange a plurality of microlenses 21 on the XY plane without gaps.

[0080] In this manner, the planar position of the vertex 22 of each microlens 21 in the first variable arrangement state is randomly varied from the center point 23 of the rectangular lattice (second variable arrangement state). As a result, as shown in Fig. 7, the planar position of the vertex 22 of each microlens 21 is shifted in a random direction on the XY plane by random eccentricities Ecx, Ecy.

[0081] 4 and 7, in the second variable arrangement state, the planar shape of each microlens 21 is further deviated from the rectangular shape corresponding to the rectangular lattice than in the first variable arrangement state (see FIG. 6). Also, in the second variable arrangement state, the opening diameters Dx, Dy in the X and Y directions of each microlens 21 are further deviated from the lattice intervals Wx, Wy in the X and Y directions.

[0082] In this way, in the second variable arrangement state in which the planar positions of the vertices 22 of the microlenses 21 are randomly decentered, the multiple microlenses 21 can be arranged so that the surface shapes and opening diameters Dx, Dy of the microlenses 21 are even more different from each other than in the first variable arrangement state.

[0083] In the second variable arrangement state, the height positions (positions in the thickness direction of the diffuser plate 1) of the vertices 22 of the multiple microlenses 21 vary from one another. In detail, as shown in Fig. 2, the height positions of the vertices 22 (deepest points of the concave lenses) of the multiple microlenses 21 arranged in the X direction are different from one another, and the height positions of the vertices 22 (deepest points of the concave lenses) of the multiple microlenses 21 arranged in the Y direction are also different from one another. This further increases the randomness of the shapes and arrangement of the multiple microlenses 21, and can impart sufficient non-periodicity to the microlens array 20.

[0084] As described above, according to the method for arranging the microlenses 21 according to this embodiment, first, the multiple microlenses 21 are arranged quasi-regularly based on an irregular rectangular lattice having mutually different lattice intervals Wx and Wy (initial arrangement state: FIG. 5). As a result, the microlenses 21 are arranged quasi-regularly in the XY plane such that the outline of the planar shape of each microlens 21 is aligned with the lattice lines 31 and 32 of the irregular rectangular lattice.

[0085] Thereafter, the radii of curvature Rx, Ry, surface shape, and lens vertex position 22 of the arranged microlenses 21 are randomly varied (first and second varied array states: Figs. 6 and 7). This makes it possible to randomly vary the surface shape (three-dimensional shape), aperture shape (planar shape), aperture diameters Dx, Dy, arrangement, and the like of the quasi-regularly arranged microlenses 21. This makes it possible to realize a highly random three-dimensional surface structure of the microlens array 20 while realizing a quasi-regular arrangement of the microlenses 21.

[0086] Therefore, according to the microlens array 20 of this embodiment, the overlapping state of the phases of the light diverging from each microlens 21 can be suitably controlled. Thus, the interference of the diffused light from each microlens 21 and the diffraction due to the periodic structure of the microlens array can be suitably suppressed. Therefore, the unevenness of the intensity distribution of the diffused light can be reduced, and the uniformity of the light distribution in the mutually orthogonal X and Y directions can be improved. Furthermore, it is also possible to control the anisotropy of the light distribution in the X and Y directions and the cutoff property of the intensity distribution of the diffused light.

[0087] The cut-off property means that the diffused light from the microlens array 20 has a so-called top-hat type diffusion characteristic. The top-hat type diffusion characteristic is an optical function in which the homogeneity of the energy distribution is very high within the angle component in a certain region for collimated light in the visible light region or telecentric light having a collimated main ray and a certain aperture, and the energy can be rapidly reduced when the certain region of the angle component is exceeded. By realizing such a top-hat type diffusion characteristic, the luminance distribution of the diffused light of the light incident on the microlens array 20 becomes approximately uniform within a predetermined diffusion angle range, and a state is realized in which the luminance value of the diffused light falls within a range of, for example, ±20% around the average value of the peak level within the predetermined diffusion angle range.

[0088] According to the microlens array 20 of this embodiment, a plurality of microlenses 21 are arranged in a rectangular lattice shape by the above-mentioned arrangement method, and the radii of curvature Rx, Ry, lens vertex positions 22, etc. of each microlens 21 are appropriately controlled, and an aspheric shape is introduced into the surface shape of the microlens 21. This makes it possible to realize the desired diffusion characteristics of the microlens array 20, and therefore it becomes possible to more reliably realize the top-hat type diffusion characteristics.

[0089] Furthermore, according to this embodiment, a plurality of microlenses 21 are arranged quasi-regularly on the XY plane based on an irregular rectangular lattice having mutually different lattice intervals Wx and Wy (initial arrangement state), and then the radii of curvature Rx and Ry and the lens vertex positions 22 are varied (first and second varied arrangement states). This allows the plurality of microlenses 21 to be arranged continuously on the surface of the diffuser plate 1 without gaps while ensuring the randomness of the surface shape of each microlens 21. Therefore, it is possible to minimize the presence of flat portions at the boundaries between adjacent microlenses 21, so that it is possible to suppress the components (zeroth-order transmitted light components) of the incident light that are transmitted as they are without being scattered on the diffuser plate surface. As a result, it is possible to further improve the uniformity of the light distribution in the mutually orthogonal X and Y directions and the diffusion performance.

[0090] <5. Examples of aspheric microlens shapes> Next, an example in which the surface shape of the microlens 21 according to this embodiment is an aspheric shape having anisotropy will be described.

[0091] In this embodiment, a plurality of microlenses 21 having anisotropy in a common direction may be arranged in a rectangular lattice pattern over the entire microlens array 20. The anisotropic microlenses 21 are, for example, microlenses having a planar shape whose length in one direction (longitudinal direction) is longer than the length in another direction (shortitudinal direction) perpendicular to the one direction. The anisotropic microlenses 21 are arranged on the XY plane of the substrate 10 such that the longitudinal directions of the microlenses 21 face in the same direction.

[0092] This makes it possible to control the anisotropic shape of the diffused light on the projection surface. For example, in the diffuser 1, the diffusion width of the light in the longitudinal direction of the microlenses 21 is made small, and the diffusion width of the light in the lateral direction is made large. This makes it possible to control the anisotropic shape of the light diffused by the diffuser 1 in accordance with the shape of the projection surface.

[0093] 8 to 11, a more detailed description will be given below of a case where the surface shape (three-dimensional shape) of each microlens 21 is an aspheric shape having anisotropy. The microlens 21 has an aspheric shape having anisotropy stretched in a predetermined direction. As this aspheric shape, for example, a first aspheric shape example (anamorphic shape) or a second aspheric shape example (torus shape) described below can be used.

[0094] (1) First example of aspheric shape (anamorphic shape) First, examples of aspheric shapes (anamorphic shapes) of the microlens 21 will be described with reference to Fig. 8 to Fig. 11. Fig. 8 is an explanatory diagram showing the planar shape of the anamorphic microlens 21. Fig. 9 is a perspective view showing the three-dimensional shape of the anamorphic microlens 21. Fig. 10 is a perspective view showing the curved surface of the anamorphic shape.

[0095] The microlens 21 shown in Figs. 8 and 9 is a so-called anamorphic lens, and its surface shape is an aspheric shape including a curved surface of an anamorphic shape. As shown in Fig. 8, the planar shape of the microlens 21 is an anisotropic elliptical shape. The major axis of the elliptical shape in the Y-axis direction is Dy, and the minor axis of the elliptical shape in the X-axis direction is Dx. These Dx and Dy correspond to the aperture diameters of the microlens 21 in the X-axis direction and the Y-axis direction. As shown in Fig. 9, the three-dimensional shape of the microlens 21 is composed of an aspheric curved surface having predetermined radii of curvature Rx and Ry in the major axis direction and the minor axis direction of the elliptical shape, respectively. The microlens 21 has an aspheric shape having anisotropy in the Y-axis direction.

[0096] Here, a method for setting the surface shape of the anamorphic microlens 21 will be described with reference to Fig. 10 and the following formula (1). Fig. 10 is a perspective view showing an anamorphic curved surface (aspheric surface) represented by the following formula (1). The following formula (1) is an example of a formula representing an anamorphic curved surface (aspheric surface).

[0097]

number

[0098] In addition, in the formula 1, each parameter is as follows: Cx=1 / Rx Cy=1 / Ry Rx: Radius of curvature in the X direction Ry: Radius of curvature in the Y direction Kx: Conic coefficient in the X direction Ky: Conic coefficient in the Y direction Ax4 ,A x6 : 4th and 6th order aspheric coefficients in the X direction A y4 ,A y6 : 4th and 6th order aspheric coefficients in the Y direction

[0099] As shown in Fig. 10, a curved surface is cut out from the curved surface of the anamorphic shape defined by the above formula (1) so that the minor axis in the X direction of the ellipse on the XY plane is Dx and the major axis in the Y direction is Dy. The shape of the curved surface of this cut-out part is set as the curved surface shape (anamorphic shape) of the microlens 21. Here, the major axis Dy, minor axis Dx, radius of curvature Ry in the Y direction (major axis direction), and radius of curvature Rx in the X direction (minor axis direction) of the ellipse are randomly varied within a predetermined variation rate δ range for each microlens 21 to cause variation. This makes it possible to set the surface shapes of the multiple microlenses 21 having mutually different anamorphic shapes.

[0100] (2) Second example of aspheric shape (torus shape) Next, another example (torus shape) of the aspheric shape of the microlens 21 will be described with reference to Fig. 11 to Fig. 13. Fig. 11 is an explanatory diagram showing the planar shape of the torus-shaped microlens 21. Fig. 12 is a perspective view showing the three-dimensional shape of the torus-shaped microlens 21. Fig. 13 is a perspective view showing the curved surface of the torus shape.

[0101] As shown in Figs. 11 to 13, the surface shape of the microlens 21 according to the second example of the aspherical shape is an aspherical shape including a curved surface of a torus shape. A torus is a surface of revolution obtained by rotating a circle. Specifically, as shown in Fig. 13, a so-called doughnut-shaped torus is obtained by rotating a small circle (radius: r) around a rotation axis (X-axis) arranged on the outside of the small circle along the circumference of a large circle (radius: R). The curved shape of the surface (torus surface) of this torus is the torus shape. By cutting out the outer part of this torus shape, a three-dimensional shape of the torus-shaped microlens 21 is obtained as shown in Fig. 12.

[0102] As shown in Fig. 11, the planar shape of the torus-shaped microlens 21 is an anisotropic elliptical shape. The major axis of the elliptical shape in the Y-axis direction is R, and the minor axis of the elliptical shape in the X-axis direction is r. These r and R correspond to the aperture diameters Dx and Dy of the microlens 21 in the X-axis direction and the Y-axis direction. As shown in Fig. 12, the three-dimensional shape of the microlens 21 is formed of an aspheric curved surface having predetermined radii of curvature R and r in the major and minor axis directions of the elliptical shape, respectively. The microlens 21 has an aspheric shape having anisotropy in the Y-axis direction.

[0103] Here, a method for setting the surface shape of the torus-shaped microlens 21 will be described with reference to Fig. 13 and the following formula (2). Fig. 13 is a perspective view showing an aspheric curved surface expressed by the following formula (2). In formula 2, R is the radius of the large circle, and r is the radius of the small circle.

[0104]

number

[0105] As shown in Fig. 13, a curved surface is cut out from the torus-shaped curved surface defined by the above formula (2) so that the short axis of the ellipse in the X direction on the XY plane is r and the long axis in the Y direction is R. The shape of the curved surface of this cut-out part is set as the curved surface shape (torus shape) of the microlens 21. Here, the long axis Dy, short axis Dx, radius of curvature R in the Y direction (long axis direction) (corresponding to the radius of curvature Ry of the lens), and radius of curvature r in the X direction (short axis direction) (corresponding to the radius of curvature Rx of the lens) of the ellipse are randomly varied within a predetermined variation rate δ range for each microlens 21 to cause variation. This makes it possible to set the surface shapes of the multiple microlenses 21 having different torus shapes.

[0106] In addition, as the surface shape (aspheric shape having anisotropy) of the microlens 21 according to this embodiment, in addition to the above-mentioned first and second aspheric shape examples, for example, an aspheric shape cut out from an ellipsoid can be used.

[0107] <6. Microlens design method> Next, a method for designing a microlens according to this embodiment will be described with reference to Fig. 14 to Fig. 18. Fig. 14 is a flowchart showing the method for designing a microlens according to this embodiment.

[0108] (S10) Setting grid parameters 14, first, various parameters (grid parameters) related to a rectangular grid that serves as a reference for arranging a plurality of microlenses 21 on an XY plane are set (S10). The grid parameters include, for example, the following parameters: Wx_k[μm]: Reference value of grid spacing Wx in the X direction (grid size in the X direction) Wy_k [μm]: Reference value of grid spacing Wy in the Y direction (grid size in the Y direction) δWx [±%]: Fluctuation rate of lattice spacing Wx in the X direction (allowable fluctuation range of Wx in the X direction) δWy [±%]: Fluctuation rate of lattice spacing Wy in the Y direction (allowable fluctuation range of Wy in the Y direction) δEcx [±%]: Eccentricity of the lens apex position in the X direction (Eccentricity range in the X direction) δEcy [±%]: Eccentricity of the lens apex position in the Y direction (Eccentricity range in the Y direction)

[0109] Specifically, the grid parameter values ​​can be set to the following values, for example. Wx_k: 120μm Wy_k: 90μm δWx: ±20% δWy: ±10% δEcx: ±10% δEcy: ±10%

[0110] (S12) Grid Generation Next, based on the grid parameters set in S10, a plurality of rectangular grids arranged in the X and Y directions are generated (S12). Fig. 15 is an explanatory diagram showing the rectangular grid generated in this step S12. As shown in Fig. 15, an irregular rectangular grid is set in which the grid intervals Wx, Wy in the X and Y directions vary randomly. The grid interval Wx in the X direction is the interval between grid lines 31 adjacent in the X direction. The grid interval Wy in the Y direction is the interval between grid lines 32 adjacent in the Y direction.

[0111] The grid interval Wx in the X direction is set to a value obtained by randomly varying the reference grid interval Wx_k [μm] at a fluctuation rate ΔWx [±%]. Similarly, the grid interval Wy in the Y direction is set to a value obtained by randomly varying the reference grid interval Wy_k [μm] at a fluctuation rate ΔWy [±%]. For example, when the set value of the grid parameter is the numerical value of the above specific example (Wx_k=120 μm, ΔWx=±20%), the grid interval Wx is set to a random value within a range of 96 μm to 144 μm (a value of 80% to 120% of 120 μm) centered on 120 μm (Wx_k). The grid interval Wy is set in the same manner. As a result, as shown in FIG. 15, the grid intervals Wx and Wy of a plurality of rectangular grids arranged in the X and Y directions are set to different values.

[0112] (S14) Grid center decentering Then, a decentering process is performed to randomly vary the position of the center point of each rectangular grid (hereinafter referred to as the "grid center") (S14). Figure 16 is an explanatory diagram showing rectangular grids whose grid centers have been decentered in this step S14.

[0113] As shown in FIG. 16, the grid center before decentering is located at the coordinate position of the intersection of two diagonals of each rectangular grid (center point 23 of the rectangular grid described above). By decentering, the grid center moves to the X and Y coordinate positions corresponding to the eccentricities Ecx and Ecy calculated randomly using the eccentricities ΔEcx and ΔEcy. For example, when the set values ​​of the grid parameters are the numerical values ​​of the specific example above (ΔEcx=±10%, ΔEcy=±10%), the eccentricities Ecx and Ecy are set to values ​​within a range of 90% to 110% of each grid interval Wx and Wy. Then, the grid center is moved in the X and Y directions by the distances corresponding to the eccentricities Ecx and Ecy. The position of the grid center after the movement corresponds to the planar position of the vertex 22 of the microlens 21 described above (lens vertex position 22). By repeating this decentering process for each rectangular lattice, the grid center of each rectangular lattice is decentered to a random position within the range of eccentricity δEcx and eccentricity δEcy within each rectangular lattice.

[0114] (S16~S24) Creation of microlenses Next, based on the rectangular grids generated in S12 and the grid centers decentered in S14, the microlenses 21 corresponding to each rectangular grid are arranged. Specifically, first, a basic shape of the surface shape (lens surface) of the microlenses 21 is selected (S16). Next, parameters (lens parameters) related to the selected basic shape are set (S18, S20). After that, based on the set lens parameters, the shape of the microlenses 21 in each rectangular grid is determined, and the Z coordinate position representing the shape of the microlenses 21 is calculated to generate the microlenses 21 (S22, S24).

[0115] Specifically, in this embodiment, for example, an anamorphic shape or a torus shape is selected as the basic shape (hereinafter, referred to as the lens shape) of the microlens 21 (S16). However, without being limited to such examples, other types of aspheric shapes or spherical shapes may be selected as the lens shape.

[0116] If an anamorphic shape is selected in S16, various lens parameters related to the anamorphic shape are set (S18). The lens parameters for the anamorphic shape include, for example, the following parameters. Rx_k[μm]: Reference value of the radius of curvature Rx in the X direction Ry_k [μm]: Reference value of the radius of curvature Ry in the Y direction δRx [±%]: Fluctuation rate of radius of curvature Rx in the X direction (permissible fluctuation range of Rx in the X direction) δRy [±%]: Fluctuation rate of the radius of curvature Ry in the Y direction (allowable fluctuation range of Ry in the Y direction)

[0117] Specifically, the setting values ​​of the lens parameters for the anamorphic shape can be set to the following numerical values, for example. Rx_k: 240μm Ry_k: 200μm δRx: ±10% δRy: ±10%

[0118] Next, the surface shape of the anamorphic microlens 21 is generated based on the lens parameters set in S18 (S22). In detail, the surface shape of each microlens 21 is determined based on the lens parameters, and each microlens 21 is arranged on each rectangular grid. That is, the Z coordinate value of each point on the anamorphic lens surface is calculated.

[0119] Fig. 17 is an explanatory diagram showing the multiple microlenses 21 generated in this step S22. As shown in Fig. 17, each microlens 21 is arranged on each rectangular grid so that the lens vertex position 22 coincides with the grid center position decentered in S14. In addition, the curvature radii Rx, Ry in the X and Y directions of each microlens 21 vary randomly. Therefore, multiple microlenses 21 having mutually different surface shapes (anamorphic shapes) are arranged so as to overlap each other on the XY plane.

[0120] The radius of curvature Rx in the X direction is set to a value obtained by randomly varying the reference radius of curvature Rx_k [μm] at a variation rate δRx [±%]. Similarly, the radius of curvature Ry in the Y direction is set to a value obtained by randomly varying the reference radius of curvature Ry_k [μm] at a variation rate δRy [±%]. For example, when the set values ​​of the lens parameters are the numerical values ​​of the above specific example (Rx_k=240 μm, δRx=±10%), the radius of curvature Rx is set to a random value within a range of 216 μm to 264 μm (a value of 90% to 110% of 240 μm) with 240 μm (Rx_k) as the center. The radius of curvature Ry is set in the same manner. As a result, as shown in FIG. 17, the surface shapes (anamorphic shapes) of the multiple microlenses 21 arranged in the X and Y directions are different from each other.

[0121] On the other hand, if a torus shape is selected in S16 above, various lens parameters related to the torus shape are set (S20). The lens parameters of the torus shape include, for example, the following parameters. Note that the small circle radius r and the large circle radius R are radii of curvature that define the torus shape shown in Figs. 11 to 13. r_k [μm]: Reference value of small circle radius (X-direction curvature radius Rx) R_k [μm]: Reference value of the great circle radius (Y-direction curvature radius Ry) δRx [±%]: Fluctuation rate of the small circle radius (radius of curvature Rx in the X direction) (allowable fluctuation range of r in the X direction) δRy [±%]: Fluctuation rate of the great circle radius (radius of curvature Ry in the Y direction) (allowable fluctuation range of R in the Y direction)

[0122] Specifically, the setting values ​​of the lens parameters of the torus shape can be set to the following values, for example. Rx_k: 240μm Ry_k: 200μm δRx: ±10% δRy: ±10%

[0123] Next, the surface shape of the torus-shaped microlens 21 is generated based on the lens parameters set in S20 (S24). In detail, the surface shape of each microlens 21 is determined based on the lens parameters, and each microlens 21 is arranged on each rectangular grid. That is, the Z coordinate value of each point on the torus-shaped lens surface is calculated. The torus-shaped lens generation process in this step S24 is similar to the anamorphic-shaped lens generation process in S22 above, so a detailed description will be omitted.

[0124] (S26) Lens pattern output Thereafter, the lens pattern representing the shape and arrangement of the microlenses 21 generated in S20 or S24 above is output (S26). For example, a file of XYZ coordinate values ​​representing the lens pattern, or an image file expressing the Z coordinate value of the lens pattern in gradation is output.

[0125] Fig. 18 is an image showing a lens pattern designed by the design method according to this embodiment. As shown in Fig. 18, a plurality of microlenses 21 are arranged in an irregular rectangular lattice on the XY plane. The lens vertex positions 22 of each microlens 21 are randomly decentered, and the radii of curvature Rx, Ry of each microlens 21 also vary randomly.

[0126] Therefore, it can be seen that the multiple microlenses 21 have different aspheric shapes (for example, anamorphic shape or torus shape). Also, the multiple microlenses 21 have different planar shapes. The planar shape of each microlens 21 is roughly rectangular along the rectangular lattice, but the shapes vary from one to another. The four sides of the boundary between the microlenses 21 are generally straight lines, but the four corners are curved lines.

[0127] Furthermore, the multiple microlenses 21 are arranged so as to overlap one another with no gaps between them, and no flat portion exists at the boundary between adjacent microlenses 21.

[0128] As described above, according to the design method of the microlens 21 according to the present embodiment, the multiple microlenses 21 are arranged quasi-regularly based on the above-mentioned irregular rectangular lattice, and each variable element of the microlenses 21 (lattice intervals Wx, Wy, radii of curvature Rx, Ry, lens apex position 22, etc.) is randomly varied. This allows multiple microlens arrays 20 to be continuously arranged on the XY plane without gaps, while providing each microlens 21 with a different diffusion characteristic. The microlens array 20 configured in this way has small macro light amount fluctuations depending on the lens surface structure and small light amount changes due to diffracted light, and has a variety of light distribution controllability with high uniformity.

[0129] 7. Microlens manufacturing method Next, a method for manufacturing the diffuser plate 1 according to this embodiment will be described with reference to Fig. 19. Fig. 19 is a flowchart showing the method for manufacturing the diffuser plate 1 according to this embodiment.

[0130] 19, in the manufacturing method of the diffusion plate 1 according to this embodiment, first, the substrate (substrate of the master or substrate 10 of the diffusion plate 1) is cleaned (step S101). The substrate may be, for example, a roll-shaped substrate such as a glass roll, or a flat substrate such as a glass wafer or a silicon wafer.

[0131] Next, a resist is formed on the surface of the substrate after cleaning (step S103). For example, a resist layer can be formed by using a resist made of a metal oxide. Specifically, a resist layer can be formed on a roll-shaped substrate by spraying or dipping the resist. On the other hand, a resist layer can be formed on a flat substrate by subjecting the resist to various coating processes. As the resist, a positive photoreactive resist or a negative photoreactive resist can be used. A coupling agent can be used to increase the adhesion between the substrate and the resist.

[0132] Furthermore, the resist layer is exposed using a pattern corresponding to the shape of the microlens array 20 (step S105). For this exposure process, a known exposure method may be appropriately applied, such as exposure using a grayscale mask, multiple exposure by overlapping a plurality of grayscale masks, or laser exposure using a picosecond pulse laser or a femtosecond pulse laser.

[0133] Thereafter, the exposed resist layer is developed (S107). A pattern is formed in the resist layer by this development process. The development process can be carried out by using an appropriate developer depending on the material of the resist layer. For example, when the resist layer is formed of a resist using a metal oxide, the resist layer can be alkaline developed by using an inorganic or organic alkaline solution.

[0134] Next, the developed resist layer is used for sputtering or etching (S109), completing a master master having the shape of the microlens array 20 formed on its surface (S111). Specifically, a glass master can be manufactured by glass etching a glass substrate using the patterned resist layer as a mask. Alternatively, a metal master can be manufactured by performing Ni sputtering or nickel plating (NED treatment) on the patterned resist layer to form a nickel layer to which the pattern is transferred, and then peeling off the substrate. For example, a metal master master can be manufactured by forming a nickel layer to which the resist pattern is transferred by Ni sputtering with a film thickness of about 50 nm, or nickel plating (for example, Ni sulfamate bath) with a film thickness of 100 μm to 200 μm, or the like.

[0135] Furthermore, the master master (e.g., a glass master master, a metal master master) completed in S111 above is used to transfer (imprint) a pattern onto a resin film or the like, thereby creating a soft mold having an inverted shape of the microlens array 20 formed on its surface (S113).

[0136] Then, using a soft mold, the pattern of the microlens array 20 is transferred to a glass substrate or a film substrate or the like (S115), and further, a protective film, an anti-reflection film, etc. are formed as necessary (S117) to produce the diffuser plate 1 of this embodiment.

[0137] In the above, an example has been described in which a soft mold is manufactured (S113) using a master (S111), and then the diffusion plate 1 is manufactured (S115) by transfer using the soft mold. However, the present invention is not limited to this example, and a master (e.g., an inorganic glass master) on which an inverted shape of the microlens array 20 is formed may be manufactured, and the diffusion plate 1 may be manufactured by imprinting using the master. For example, the diffusion plate 1 can be manufactured by applying an acrylic photocurable resin to a base material made of PET (PolyEthylene Terephthalate) or PC (PolyCarbonate), transferring the pattern of the master to the applied acrylic photocurable resin, and curing the acrylic photocurable resin with UV light.

[0138] On the other hand, in the case of manufacturing the diffusion plate 1 by directly processing the glass substrate itself, following the development process in step S107, a dry etching process is performed on the substrate 10 using a known compound such as CF4 (S119), and then a protective film, an anti-reflection film, etc. are formed as necessary (S121), thereby manufacturing the diffusion plate 1 of this embodiment.

[0139] It should be noted that the manufacturing method shown in FIG. 19 is merely one example, and the manufacturing method of the diffusion plate is not limited to the above example.

[0140] <8. Application example of diffuser plate 1> Next, application examples of the diffusion plate 1 according to this embodiment will be described.

[0141] The diffusion plate 1 as described above can be appropriately mounted on devices that need to diffuse light in order to realize their functions. Examples of such devices include display devices such as various displays (e.g., LED and organic EL displays), projection devices such as projectors, and various lighting devices.

[0142] For example, the diffusion plate 1 can be applied to a backlight of a liquid crystal display device, a lens integrated with a diffusion plate, and the like, and can also be applied to light shaping applications. The diffusion plate 1 can also be applied to a transmissive screen, a Fresnel lens, a reflective screen, and the like of a projection device. The diffusion plate 1 can also be applied to various lighting devices used for spot lighting, base lighting, and the like, various special lighting, and various screens such as intermediate screens and final screens. Furthermore, the diffusion plate 1 can also be applied to applications such as diffusion control of light from a light source in an optical device, and can also be applied to light distribution control of an LED light source device, light distribution control of a laser light source device, and light distribution control of light incident on various light valve systems.

[0143] The device to which the diffusion plate 1 is applied is not limited to the above-mentioned application examples, and the diffusion plate 1 can be applied to any known device that utilizes the diffusion of light. EXAMPLES

[0144] Next, a diffusion plate according to an embodiment of the present invention will be described. Note that the following embodiment is merely an example for illustrating the effect and feasibility of the diffusion plate according to the present invention, and the present invention is not limited to the following embodiment.

[0145] While changing the surface structure of the microlens array, the diffusion plates according to the examples and the comparative examples were manufactured by the manufacturing method described below.

[0146] Specifically, first, the glass substrate was washed, and then a photoreactive resist was applied to one surface (main surface) of the glass substrate with a resist thickness of 2 μm to 15 μm. As the photoreactive resist, for example, a positive photoreactive resist such as PMER-LA900 (manufactured by Tokyo Ohka Kogyo Co., Ltd.) or AZ4620 (registered trademark) (manufactured by AZ Electronic Materials Co., Ltd.) was used.

[0147] Next, a pattern was drawn on the resist on the glass substrate using a laser drawing device that uses a laser with a wavelength of 405 nm, and the resist layer was exposed. The resist layer may also be exposed by performing mask exposure on the resist on the glass substrate using a stepper exposure device that uses g-line.

[0148] Subsequently, the resist layer was developed to form a pattern in the resist. As a developer, for example, a tetramethylammonium hydroxide (TMAH) solution such as NMD-W (manufactured by Tokyo Ohka Kogyo Co., Ltd.) or PMER P7G (manufactured by Tokyo Ohka Kogyo Co., Ltd.) was used.

[0149] Next, a glass substrate was etched using the resist with the pattern formed thereon to manufacture a diffusion plate. Specifically, a resist pattern was formed on the glass substrate by glass etching using Ar gas or CF4 gas to manufacture a diffusion plate.

[0150] Table 1 shows the design conditions of the surface structure of the microlens array and the evaluation results of the uniformity of light distribution by the diffuser plates according to the examples and comparative examples manufactured as described above.

[0151] [Table 1]

[0152] In each of the examples and comparative examples shown in Table 1, a microlens array was designed by the design method shown in Figs. 14 to 18 described above. At this time, various parameters such as the grid parameters (Wx_k, Wy_k, δWx, δWy, δEcx, δEcy) and lens parameters (Rx_k, Ry_k, δRx, δRy) shown in Table 1 were appropriately changed to generate patterns of different microlens surface shapes. Then, a lens pattern representing the shape and arrangement of the microlenses according to each of the examples and comparative examples was output. Using this lens pattern, a diffuser plate according to each of the examples and comparative examples was manufactured by the above-mentioned manufacturing method.

[0153] As shown in Table 1, in Examples 1 to 9, the lattice intervals Wx and Wy of each microlens were randomly varied when designing the surface structure of the microlens array. In contrast, in Comparative Examples 1 to 4, the lattice intervals Wx and Wy were not varied, and the lattice intervals of all microlenses were set to constant reference lattice intervals Wx_k and Wy_k.

[0154] As shown in Table 1, the radius of curvature Rx and the radius of curvature Ry were fixed or randomly varied for each example and comparative example. When the variation rate δRx, δRy=±0%, the radius of curvature Rx, Ry of each microlens was fixed without variation, and when the variation rate δRx, δRy=±10%, ±15%, the radius of curvature Rx, Ry was randomly varied within the range of the variation rate δRx, δRy. Regarding the decentering of the lens apex position in the XY plane, when the eccentricity rate δEcx, δEcy=±0%, the lens apex position was not decentered, and when the eccentricity rate δEcx, δEcy=±10%, ±15%, the lens apex position was randomly decentered within the range of the eccentricity rate δEcx, δEcy.

[0155] The surface shape of the microlenses was spherical in Examples 1 to 4, 8, and 9 and Comparative Examples 1 to 3, and aspheric (e.g., anamorphic) in Examples 5 to 7. The planar shape of the microlens array was square in Examples 1 to 7 and Comparative Examples 1 to 3, and rectangular (rectangle long in the X direction) in Examples 8, 9, and Comparative Example 4.

[0156] The surface shapes of the microlens arrays of the diffusers according to Examples 1 to 9 and Comparative Examples 1 to 4 manufactured as described above were observed with a laser microscope. Furthermore, the light distribution pattern of each diffuser was simulated with Virtual-Lab (manufactured by LightTrans), and the light distribution characteristics of each diffuser were measured with a light distribution characteristic measuring device Mini-Diff (manufactured by Light Tec). Furthermore, in order to measure the light distribution characteristics of the diffuser, the intensity distribution of the diffused light was measured from a captured image of the laser light intensity (far-field pattern measurement, described later).

[0157] 20 to 33 show the simulation results and actual measurement results of the surface shape patterns of the microlens arrays of the diffusion plates according to Examples 1 to 9 and Comparative Examples 1 to 4, the light distribution characteristics of diffused light, the luminance distribution, and the like, respectively.

[0158] 20 to 33 (Examples 1 to 9 and Comparative Examples 1 to 4), (a) is an image (BMP) showing the surface shape pattern of the microlens array or a confocal laser microscope image (magnification 50x). (b) is an image showing the simulation result of light distribution by electromagnetic field analysis. (c) is a graph (horizontal axis: coordinate position, vertical axis: brightness) showing the simulation result of the luminance distribution of diffused light. (d) shows the diffusion angle (full width at half maximum (FWHM), Screen Z=100 mm) in the luminance distribution of (c) above.

[0159] In addition, in Fig. 30 (Example 7), (e) is a graph showing the results of measuring the far-field pattern (FFP) of diffused light from a laser light source using an actually manufactured diffuser plate (horizontal axis: diffusion angle, vertical axis: brightness). (f) shows the diffusion angles (full width at half maximum (FWHM)) in the X and Y directions in the FFP of (e). (g) is an FFP image showing the results of the actual measurement of (e).

[0160] In addition, in Figs. 32 and 33 (Examples 8 and 9), (e) is a graph showing a simulation result of the light distribution characteristics of diffused light in the X and Y directions (horizontal axis: diffusion angle, vertical axis: luminance), and (f) shows the diffusion angles (full width at half maximum (FWHM)) in the X and Y directions in the luminance distribution of (c) above.

[0161] The light distribution characteristics (uniformity of light distribution, etc.) of the diffusion plates according to Examples 1 to 9 and Comparative Examples 1 to 3 were evaluated in three stages (A, B, C) according to the following evaluation criteria. The evaluation results are shown in Table 1. Evaluation A: The uniformity of the diffused light in the X and Y directions was sufficiently high, and no unevenness in the luminance distribution along the rectangular grid was observed. The luminance distribution of the diffused light was approximately uniform within a specified diffusion angle range, and within the specified diffusion angle range, the luminance value of the diffused light was within a range of ±20% of the average peak level. Evaluation B: The diffused light had high uniformity in the X and Y directions, and although there was some unevenness in the luminance distribution along the rectangular grid, no major unevenness was observed. The luminance distribution of the diffused light was approximately uniform within a specified diffusion angle range, and within the specified diffusion angle range, the luminance value of the diffused light was within a range of ±40% of the average peak level. Rating C: The uniformity of the diffused light in the X and Y directions was insufficient, and large unevenness in the luminance distribution was observed along the rectangular grid. The luminance distribution of the diffused light varied within the specified diffusion angle range, and within the specified diffusion angle range, the luminance value of the diffused light did not fall within a range of ±40% of the average peak level.

[0162] The evaluation results of Examples 1 to 9 and Comparative Examples 1 to 4 will be compared below.

[0163] (1) Comparison of Examples 1 to 9 and Comparative Examples 1 to 4 (Effect of Irregular Lattice Spacing) In Comparative Examples 1 to 4, as shown in Figures 20 to 22 and 31, the brightness in the brightness distribution of the diffused light increased and decreased significantly periodically, and rectangular lattice-like unevenness occurred in the brightness distribution of the diffused light, and the uniformity of the light distribution of the diffused light was insufficient. The reasons for this are considered to be as follows.

[0164] In Comparative Examples 1 to 4, the rectangular lattice serving as the reference for the microlens arrangement is a regular rectangular lattice, and the lattice spacing in the X and Y directions is fixed to constant values ​​Wx_k and Wy_k (ΔWx, ΔWy=±0%). Therefore, the periodic structure of the regular rectangular lattice-like microlens arrangement causes diffraction of the diffused light from each microlens, which is thought to cause unevenness in the luminance distribution and reduce the uniformity of the light distribution.

[0165] In this regard, the uniformity of the luminance distribution can be improved to some extent by decentering the lens apex position as in Comparative Example 2, or by randomly varying the radii of curvature Rx, Ry as in Comparative Example 3. However, when the lattice intervals Wx, Wy are constant as in Comparative Examples 1 to 4, it is considered that the unevenness of the luminance due to diffraction caused by the periodicity of this lattice interval exceeds the effect of improving the uniformity by varying the lens apex position and the radii of curvature Rx, Ry, and the uniformity of the light distribution is impaired.

[0166] In contrast, in Examples 1 to 9, although the brightness fluctuated in the brightness distribution of the diffused light, no periodic increase or decrease or periodic peak was observed, and the unevenness of the brightness distribution of the diffused light was sufficiently suppressed, and the uniformity of the light distribution of the diffused light was good. The reasons for this are considered to be as follows.

[0167] In Examples 1 to 9, microlenses are arranged on the XY plane based on a rectangular lattice. The rectangular lattice in Examples 1 to 9 is not a regular rectangular lattice as in the comparative example, but a quasi-regular rectangular lattice having irregular lattice intervals Wx and Wy. That is, as shown in FIG. 15, the lattice intervals Wx and Wy of the rectangular lattices in Examples 1 to 9 vary randomly to be mutually different values, and the variation rates ΔWx and ΔWy are ±10% or more. By arranging a plurality of microlenses based on a rectangular lattice having such irregularity, the aperture diameters Dx and Dy and planar shapes of the microlenses can be varied randomly, and the positions of the boundaries between adjacent microlenses can also be shifted randomly.

[0168] As a result, as shown in Figures 2, 4, 18, etc., the outline of the planar shape of the microlens (boundary line between microlenses) is composed of a combination of curves with an arbitrary radius of curvature and straight lines. This further breaks down the regularity of the arrangement at the boundaries between the microlenses, making it possible to further reduce the diffracted components. Therefore, it is possible to suppress mutual diffraction of diffused light between multiple microlenses and improve the uniformity of the light distribution of the diffused light in the entire microlens array.

[0169] From the above results, it is evident that by using the diffusion plate of the present invention, unevenness in the luminance distribution can be suppressed in two mutually perpendicular directions (X and Y directions), and the uniformity of the light distribution can be sufficiently improved.

[0170] (2) Comparison of Example 1 with Examples 2 to 9 (effect of variation in radius of curvature and decentering of lens apex) As shown in Table 1, only the grating intervals Wx and Wy are varied in Example 1. In contrast, in Examples 2 to 9, in addition to the grating intervals Wx and Wy, the radii of curvature Rx and Ry are varied or the lens vertex position is decentered.

[0171] As a result, Examples 2 to 9 (Evaluation A) were able to suppress unevenness in the luminance distribution more effectively than Example 1 (Evaluation B), and were able to improve the uniformity of the light distribution of the diffused light. This shows that, from the viewpoint of improving the uniformity of the light distribution, it is effective to vary the radii of curvature Rx, Ry and decenter the lens apex position in addition to the grating intervals Wx, Wy.

[0172] Furthermore, in Examples 2, 3, and 5, the radii of curvature Rx and Ry are varied or the lens apex position is decentered. In contrast, in Examples 4, 6 to 9, the radii of curvature Rx and Ry are varied and the lens apex position is also decentered. As a result, as shown in the (b) electromagnetic field analysis images and (c) luminance distribution graphs in Figures 24 to 29, 32, and 33, in Examples 4, 6 to 9, the unevenness of the luminance distribution can be further suppressed and the uniformity of the light distribution of the diffused light can be further improved. This shows that from the viewpoint of improving the uniformity of the light distribution, it is more effective to vary the radii of curvature Rx and Ry and decenter the lens apex position in addition to the lattice intervals Wx and Wy.

[0173] (3) Comparison of Examples 1 to 4 and Examples 5 to 7 (Effect of Aspheric Lens Shape) As shown in Table 1, spherical lenses were used as the basic shape of the microlenses in Examples 1 to 4. In contrast, aspheric lenses (for example, lenses with anamorphic shapes shown in Figs. 8 to 10) were used in Examples 5 to 7. In the case of the aspheric lenses in Examples 5 to 7, the lens shape was defined by correcting the aspheric coefficient A4 of the fourth-order term on the right-hand side of Equation (1) that defines the curved surface of the anamorphic shape described above.

[0174] As a result, as shown in the (b) electromagnetic field analysis images and (c) luminance distribution graphs in Figs. 23 to 29, the aspherical lenses of Examples 5 to 7 were able to suppress unevenness in luminance distribution and achieve finer light distribution uniformity than the spherical lenses of Examples 1 to 4. This shows that from the viewpoint of improving the uniformity of light distribution, it is more effective to use an aspherical lens than a spherical lens. Furthermore, by using an aspherical lens having anisotropy, the anisotropy of the diffused light projected from the diffusion plate can be controlled. Therefore, it is possible to control the light distribution angle to have anisotropy between the X direction and the Y direction while realizing high uniformity of diffused light.

[0175] (4) Diffusion characteristics of Example 7 (excellent light distribution uniformity and cutoff characteristics) As shown in Table 1, in Example 7, the reference radii of curvature Rx_k, Ry_k are set to relatively large values ​​(150 μm), the radii of curvature Rx, Ry are varied within a range of ±10% of Rx_k, Ry_k, and the lens apex position is decentered within a range of eccentricity ΔEcx, ΔEcy = ±10%.

[0176] Furthermore, the surface shape of the microlens in Example 7 is an aspheric shape in which the ratio of the reference radii of curvature Rx_k, Ry_k [μm] to the reference grating intervals Wx_k, Wy_k [μm] satisfies the following relational expressions (A) and (B): In Example 7, (Rx_k / Wx_k)=(Ry_k / Wy_k)=(150 / 80)=1.875. Rx_k / Wx_k≧1.85 (A) Ry_k / Wy_k≧1.85 (B)

[0177] The surface shape of the microlens according to Example 7 is an aspheric shape having the above-mentioned anisotropy, and the grating intervals Wx, Wy and the radii of curvature Rx, Ry are varied under the conditions shown in Table 1, the lens apex position is decentered, and the reference radii of curvature Rx_k, Ry_k [μm] and the reference grating intervals Wx_k, Wy_k [μm] are adjusted so as to satisfy the above-mentioned relational expressions (A) and (B). Furthermore, the diffusion angle (full width at half maximum (FWHM)) of the diffused light emitted from the diffuser plate is within a range of 20° or less. This makes it possible to more reliably realize the so-called top-hat type diffusion characteristics.

[0178] As shown in the graph of the FFP measurement results in Fig. 30(e), the diffusion characteristic of Example 7 realizes a top-hat type diffusion characteristic. That is, the luminance distribution of the diffused light of the light incident on the microlens array becomes approximately uniform in a predetermined diffusion angle range (a range of 20° or less at full width at half maximum. In the example of Fig. 10, -5 to +5°), and a state is realized in which the luminance value of the diffused light falls within a range of ±20% around the average value of the peak level within the diffusion angle range.

[0179] From the above results, it can be seen that by using a diffuser plate similar to that in Example 7, it is possible to adequately improve the uniformity of light distribution in two mutually perpendicular directions (X and Y directions) within a diffusion angle (full width at half maximum) range of 20° or less, while appropriately controlling the anisotropy of light distribution in the X and Y directions and the cutoff characteristic of the intensity distribution of diffused light.

[0180] (7) Comparison of Examples 8 and 9 with Comparative Example 4 (Effect of Rectangular Aspheric Lens Shape) The diffusers according to Examples 8 and 9 and Comparative Example 4 used a rectangular microlens array extending elongatedly in the X direction. The reference lattice intervals Wx_k=50 μm and Wy_k=40 μm, and the reference lattice interval Wx_k in the longitudinal direction (X direction) of the microlens array was set larger than the reference lattice interval Wy_k in the lateral direction (Y direction) (Wx_k>Wy_k).

[0181] In such a rectangular microlens array, the grating intervals Wx and Wy were not varied in Comparative Example 4. Meanwhile, in Examples 8 and 9, the grating intervals Wx and Wy were randomly varied within a range of ±10% or ±15%, and the radii of curvature Rx and Ry were randomly varied within a range of ±10% or ±15%. Furthermore, in Examples 8 and 9, the lens apex positions were also randomly decentered within a range of ±10% or ±15%.

[0182] As a result, in Comparative Example 4, as shown in Fig. 31, the luminance distribution of the diffused light increased and decreased significantly periodically, causing noticeable rectangular lattice-like unevenness, and the uniformity of the light distribution of the diffused light was insufficient. On the other hand, in Examples 8 and 9, no periodic increase and decrease or peaks were observed in the luminance distribution of the diffused light, the unevenness of the luminance distribution of the diffused light was sufficiently suppressed, and the uniformity of the light distribution of the diffused light was good.

[0183] From the above results, it can be seen that even when a rectangular microlens array is used as in Examples 8 and 9, the uniformity of light distribution can be sufficiently improved in two mutually orthogonal directions (X and Y directions).

[0184] Although the preferred embodiment of the present invention has been described in detail above with reference to the accompanying drawings, the present invention is not limited to such an example. It is clear that a person having ordinary knowledge in the technical field to which the present invention pertains can conceive of various modified or altered examples within the scope of the technical ideas described in the claims, and it is understood that these also naturally belong to the technical scope of the present invention. [Explanation of symbols]

[0185] 1 Diffuser 3. Unit Cell 10 Base material 20 Microlens Array 21 Microlens 22 The pinnacle of microlenses 23 Center point of rectangular grid Wx, Wy lattice spacing Rx, Ry radius of curvature Ecx, Ecy Eccentricity Wx_k, Wy_k Standard grid spacing Rx_k, Ry_k Reference radius of curvature δWx, δWy fluctuation rate δRx, δRy fluctuation rate δEcx, δEcy Eccentricity R Great circle radius r Small circle radius

Claims

1. A diffuser plate of a microlens array type, comprising: a base material; a microlens array composed of a plurality of microlenses regularly arranged on at least one surface of the base material on the XY plane with respect to an irregular rectangular lattice having three or more different lattice intervals; and the lattice intervals Wx in the X direction of the three or more microlenses arranged in the X direction of the rectangular lattice vary randomly and are different from each other; the lattice intervals Wy in the Y direction of the three or more microlenses arranged in the Y direction of the rectangular lattice vary randomly and are different from each other; the surface shapes of the plurality of microlenses are different from each other; the lattice interval Wx in the X direction varies randomly with a variation rate δWx within ±10% with respect to a reference lattice interval Wx_k; the lattice interval Wy in the Y direction varies randomly with a variation rate δWy within ±10% with respect to a reference lattice interval Wy_k; the radius of curvature Rx in the X direction varies randomly with a variation rate δRx within ±10% with respect to a reference radius of curvature Rx_k; the radius of curvature Ry in the Y direction varies randomly with a variation rate δRy within ±10% with respect to a reference radius of curvature Ry_k; the surface shape of the microlens is an aspherical shape that satisfies the following relational expressions (A) and (B) for the reference radii of curvature Rx_k, Ry_k and the reference lattice intervals Wx_k, Wy_k: a diffuser plate. Rx_k / Wx_k ≥ 1.85... (A) Ry_k / Wy_k ≥ 1.85... (B)

2. The diffuser plate according to claim 1, wherein the planar positions of the vertices of the microlenses arranged in the X direction and the Y direction are eccentric from the center point of the rectangular lattice.

3. When the distances in the X direction and the Y direction from the center point of the rectangular lattice to the planar positions of the vertices of the eccentric microlenses are defined as an eccentricity Ecx and an eccentricity Ecy, respectively, and the ratios of the eccentricities Ecx and Ecy to the lattice intervals Wx and Wy of the rectangular lattice are defined as an eccentricity ratio δEcx and an eccentricity ratio δEcy, respectively, the planar positions of the vertices of the microlenses are randomly eccentric with eccentricity ratios δEcx and δEcy within ±10% to ±50%. The diffuser plate according to claim 2.

4. The diffuser plate according to any one of claims 1 to 3, wherein the height positions of the vertices of the plurality of microlenses arranged in the X direction and the Y direction are different from each other.

5. The diffusion plate according to any one of claims 1 to 4, wherein the microlenses arranged in the X direction and the Y direction are continuously arranged without gaps between each other.

6. The diffusion plate according to any one of claims 1 to 5, wherein the boundary lines of the adjacent microlenses include straight lines and curves.

7. The microlens array is composed of a plurality of unit cells which are the basic arrangement patterns of the microlenses. The microlens array is configured by arranging the plurality of unit cells without gaps while maintaining the continuity of the microlenses at the boundary portions between the plurality of unit cells. The diffusion plate according to any one of claims 1 to 6.

8. A display device comprising the diffusion plate according to any one of claims 1 to 7.

9. A projection device comprising the diffusion plate according to any one of claims 1 to 7.

10. An illumination device comprising the diffusion plate according to any one of claims 1 to 7.

Images