Diffuser plate, display device, projection device, and lighting 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 diffusion plate, a display device, a projection device, and a lighting device.

Background Art

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

[0003] In such a micro lens array type diffusion plate, due to the interference of the light wavefronts from each micro lens, a diffracted wave is generated due to the periodic structure of the micro lens array, and there is a problem that unevenness occurs in the intensity distribution of the diffused light. For this reason, techniques for reducing the unevenness of the intensity distribution of the diffused light due to interference and diffraction have been proposed by varying the arrangement of the micro lenses, the shape of the lens surface, and the shape of the aperture.

[0004] For example, Patent Document 1 describes that in a diffusion plate in which a plurality of micro lenses are regularly arranged in a rectangular lattice pattern on the main surface, a plurality of micro lenses having different cross-sectional shapes and no symmetry axis are used. Patent Document 2 also describes that the lens vertex positions of a plurality of micro lenses arranged in a rectangular lattice pattern are shifted from the lattice points of the reference lattice.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

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

[0007] Therefore, the present invention has been made in view of the above 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.

Means for Solving the Problems

[0008] In order to solve the above problems, according to one aspect of the present invention, a microlens array type diffuser plate, a base material, a microlens array composed of a plurality of microlenses regularly arranged on the XY plane on at least one surface of the base material with reference to an irregular rectangular lattice having three or more different lattice intervals from each other, and the lattice intervals Wx in the X direction of three or more of the microlenses arranged in the X direction of the rectangular lattice randomly vary and are different from each other, the lattice intervals Wy in the Y direction of three or more of the microlenses arranged in the Y direction of the rectangular lattice randomly vary and are different from each other, the surface shapes of the plurality of microlenses are different from each other, The grid interval Wx in the X direction varies randomly with a variation rate δWx based on the reference grid interval Wx_k, Within ±10% and the grid interval Wy in the Y direction varies randomly with a variation rate δWy based on the reference grid interval Wy_k. The grid interval Wy in the Y direction varies randomly with a variation rate δWy based on the reference grid interval Wy_k, Within ±10% and varies randomly with a variation rate δWy. and the radius of curvature Rx in the X direction varies randomly with a variation rate δRx within ±10% based on the reference radius of curvature Rx_k; the radius of curvature Ry in the Y direction varies randomly with a variation rate δRy within ±10% based on the reference radius of curvature Ry_k; the surface shape of the microlens is an aspherical shape in which the reference radii of curvature Rx_k, Ry_k and the reference lattice spacings Wx_k, Wy_k satisfy the following relational expressions (A) and (B); Rx_k / Wx_k ≧ 1.85 ···(A) Ry_k / Wy_k ≧ 1.85 ···(B) the diffusion angle (full width at half maximum) by the diffusion plate is 20° or less; A diffusion plate is provided.

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

[0014] When the distances in the X direction and the Y direction from the center point of the rectangular grid to the planar positions of the vertices of the eccentric microlenses are defined as the eccentricity amounts Ecx and Ecy respectively, and the ratios of the eccentricity amounts Ecx and Ecy to the grid intervals Wx and Wy of the rectangular grid are defined as the eccentricity ratios δEcx and δEcy respectively, the planar positions of the vertices of the microlenses may be randomly eccentric with eccentricity ratios δEcx and δEcy within ±10% to ±50%.

[0015] The height positions of the vertices of the plurality of 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 without gaps between each other.

[0017] The boundary lines between adjacent microlenses may include straight lines and curves.

[0018] The microlens array is composed of a plurality of unit cells which are the basic arrangement patterns of the microlenses, The microlens array may be 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.

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

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

[0022] In order to solve the above problems, according to another aspect of the present invention, there is provided an illumination device including the above-described diffuser plate.

Effect of the Invention

[0023] As described above, according to the present invention, unevenness in luminance distribution can be suppressed and the uniformity of light distribution can be improved in two directions of microlenses arranged in a rectangular lattice.

Brief Description of the Drawings

[0024]

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Embodiments for Carrying Out the Invention

[0025] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the present specification and the drawings, for components having substantially the same functional configuration, the same reference numerals are given to omit duplicate explanations.

[0026] <1. Outline of the Diffusion Plate> First, the outline of the diffusion plate according to the embodiment of the present invention will be described.

[0027] The diffusion plate according to the present embodiment described in detail below is a microlens array type diffusion plate having a light homogeneous diffusion function. Such a diffusion plate has a microlens array formed on the XY plane on at least one surface (main surface) of the base material. The microlens array is composed of a plurality of microlenses arranged and developed in a rectangular lattice pattern. The microlenses are composed of a convex structure (convex lens) or a concave structure (concave lens) having a light diffusion function, and have a lens diameter of about several tens of μm.

[0028] And in the diffusion plate according to the present embodiment, a plurality of microlenses are arranged in a rectangular lattice (matrix) based on a rectangular lattice having irregularities. In this rectangular lattice having irregularities, a plurality of lattice intervals Wx in the X direction (row direction) randomly vary and are different from each other, and a plurality of lattice intervals Wy in the Y direction (column direction) also randomly vary and are different from each other. Furthermore, the radii of curvature Rx and Ry of a plurality of microlenses arranged in the X and Y directions randomly (irregularly) vary so as to be different from each other. Also, the planar position of the apex of each microlens randomly varies (eccentricity) so as to deviate from the center point of the rectangular lattice. Also, the height positions in the Z direction (the position in the thickness direction of the diffusion plate) of the apexes of the plurality of microlenses also randomly vary and are different from each other. By randomly varying the lattice intervals Wx, Wy, radii of curvature Rx, Ry, planar position and height position of the lens apex, etc., the surface shapes of the plurality of microlenses developed in a rectangular lattice randomly vary and are different from each other.

[0029] Thus, according to the diffusion plate according to the present embodiment, by randomly varying each variable element of the plurality of microlenses, a three-dimensional surface structure of a microlens array with high randomness is realized. Thereby, the polymerization state of the phases of the light emitted from each microlens can be controlled. As a result, it is possible to provide a surface structure of a diffusion plate that has high-transmittance luminance characteristics, satisfies the uniformity of light distribution in two directions (X and Y directions) orthogonal to each other, and can control sufficient light distribution anisotropy and the cut-off property of the intensity distribution of diffused light.

[0030] Furthermore, according to the present 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. As a result, while ensuring the randomness of the surface shape of each microlens, a plurality of microlens arrays can be continuously arranged on the surface of the diffusion plate without gaps. Therefore, it is possible to minimize the presence of flat portions at the boundary portions of adjacent microlenses, further reducing the unevenness of the intensity distribution of diffused light and further improving the uniformity of light distribution in two directions (X and Y directions).

[0031] Hereinafter, the diffusion plate according to the present embodiment having the above characteristics will be described in detail.

[0032] <2. Overall configuration of the diffusion plate> First, with reference to FIG. 1, the overall configuration of the diffusion plate according to an embodiment of the present invention and the layout pattern of the microlenses will be described. FIG. 1 is an explanatory diagram schematically showing a diffusion plate 1 according to the present embodiment.

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

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

[0035] In the example of FIG. 1, on the surface of the diffusion plate 1, a plurality of square unit cells 3 are repeatedly arranged vertically and horizontally. The number of unit cells 3 constituting the diffusion plate 1 according to the present 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 the present 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] Further, between the unit cells 3, as schematically shown in the enlarged view on the right side in FIG. 1, the layout pattern (arrangement pattern) of a plurality of microlenses provided in the unit cell 3 is continuous in the arrangement direction of the unit cells 3 (in other words, the array arrangement direction). By arranging the unit cells 3 without gaps while maintaining the continuity of the microlenses at the boundary portions between the plurality of unit cells 3, a microlens array is formed. Here, the continuity of the microlenses means that among two adjacent unit cells 3, the microlenses located at the outer edge of one unit cell 3 and the microlenses located at the outer edge of the other unit cell 3 are continuously connected without a deviation in planar shape or a step in the height direction.

[0037] As described above, in the diffusion plate 1 according to the present embodiment, the unit cells 3 (basic structures) of the microlens array are arranged without gaps while maintaining the continuity of the boundaries, thereby forming the microlens array. Thereby, at the boundary portions between the unit cells 3, it is possible to prevent the occurrence of unintended problems such as diffraction, reflection, and scattering of light, and to obtain the desired light distribution characteristics by the diffusion plate 1.

[0038] <3. Configuration of Diffusion Plate> Next, with reference to FIGS. 2 to 4, the configuration of the diffusion plate 1 according to the present embodiment will be described in more detail. FIG. 2 is an enlarged plan view and an enlarged cross-sectional view schematically showing the configuration of the diffusion plate 1 according to the present embodiment. FIG. 3 is an enlarged cross-sectional view schematically showing the vicinity of the boundary of the microlens 21 according to the present embodiment. FIG. 4 is a plan view schematically showing the planar shape (outer shape) of the microlens 21 when the microlens 21 is viewed in plan from a direction perpendicular to the surface of the base material 10.

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

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

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

[0042] The base material 10 may be formed of a known resin such as polymethyl methacrylate (PMMA), polyethylene terephthalate (PET), polycarbonate (PC), cyclo olefin copolymer (COC), cyclo olefin polymer (COP), triacetyl cellulose (TAC), etc. Alternatively, the base material 10 may be formed of a known optical glass such as quartz glass, borosilicate glass, soda-lime glass, etc.

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

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

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

[0046] As shown in FIG. 2, it is preferable that the plurality of microlenses 21 are densely arranged so as to be adjacent to each other without a gap. In other words, it is preferable that the plurality of microlenses 21 are continuously arranged so that there is no gap (flat portion) at the boundary portion between the adjacent microlenses 21. By arranging the microlenses 21 on the base material 10 without a gap (in other words, arranging them so that the filling rate of the microlenses 21 is 100%), it is possible to suppress a component of incident light that passes through the surface of the diffusion plate 1 without being scattered (hereinafter, also referred to as "zero-order transmitted light component"). As a result, the diffusion performance can be further improved by the microlens array 20 in which the plurality of microlenses 21 are arranged adjacent to each other without a gap.

[0047] In addition, in order to suppress the zero-order transmitted light component, the filling rate of the microlenses 21 on the base material 10 is preferably 90% or more, and more preferably 100%. Here, the filling rate is the ratio of the area of the portion occupied by the plurality of microlenses 21 on the surface of the base material 10. If the filling rate is 100%, the surface of the microlens array 20 is formed of a curved surface component and substantially does not include a flat surface component.

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

[0049] Also, in the microlens array 20 according to the present embodiment, the plurality of microlenses 21 are not arranged randomly (irregularly). Instead, as shown in FIG. 2, with reference to an irregular rectangular lattice (see FIG. 5) in which the lattice intervals Wx and Wy vary in the X and Y directions, they are arranged in a somewhat regular manner (hereinafter referred to as "semi-regular"). 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 minute region, those in which there is no regularity in the arrangement of the microlenses as a whole in any region are included in the "irregular".

[0050] In the present embodiment, the plurality of microlenses 21 are arranged semi-regularly with reference to a rectangular lattice having irregularity. Moreover, the surface shape and the planar shape of the microlens 21 vary randomly. As shown in FIGS. 2 and 4, the planar shape (outer shape) of the microlens 21 generally has a shape close to a substantially rectangular shape, but is not a perfect rectangular shape (square shape or rectangular shape) corresponding to the rectangular lattice. Specifically, the planar shape of the microlens 21 has a shape close to a substantially polygon having four or more vertices, such as a substantially quadrilateral, a substantially pentagon, and a substantially hexagon. And the surface shape (three-dimensional curved surface shape) and the planar shape (shape projected onto the XY plane of the base material 10) of the plurality of microlenses 21 are different from each other. The reason why each microlens 21 has a shape that is irregularly deviated from a rectangular shape is that the radius of curvature Rx and Ry, the aperture diameters Dx and Dy, and the planar position and height position of the lens vertex of each microlens 21 vary randomly within a range of a predetermined variation rate. Details of the semi-regular arrangement method of the microlenses 21 with reference to the rectangular lattice according to the present embodiment will be described later (see FIGS. 5 to 7).

[0051] As described above, in this embodiment, the radius of curvature Rx, Ry and the aperture diameters Dx, Dy of each microlens 21 vary randomly and have variations. Note that the aperture diameters Dx, Dy of the microlens 21 correspond to the lens diameters of single lenses. The phase distribution of the optical aperture of each microlens 21 differs depending on the azimuth. A plurality of microlenses 21 are continuously arranged on the surface of the substrate 10 so as to overlap each other, and the radius of curvature Rx, Ry and the aperture diameters Dx, Dy (lens diameters) of each microlens 21 have variations. As a result, the shapes (surface shape and planar shape) of the plurality of microlenses 21 do not become the same as each other. Therefore, as shown in FIG. 2, the plurality of microlenses 21 have various shapes, 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 while the radius of curvature of the microlens 21B adjacent to the microlens 21A is R B (≠R A ). Thus, a state occurs in which the radius of curvature R A of the microlenses 21 adjacent to each other, and R B are different from each other. When the radii of curvature R A and R B of the microlenses 21 adjacent to each other are different from each other, the boundary line between the microlenses 21 adjacent to each other is not composed only of straight lines, but is configured to include a curve at least in part.

[0053] Specifically, as shown in FIG. 4, when the microlens 21 is viewed in plan from the Z direction perpendicular to the surface of the substrate 10, the outer contour line of the planar shape of the microlens 21 (the boundary line between the microlens 21 and a plurality of other adjacent microlenses 21) includes a plurality of curves with different curvatures and straight lines. When the boundary lines of the microlenses 21 include a plurality of curves with different curvatures, the regularity of the boundaries between the microlenses 21 is further disrupted, so that the diffraction component of the diffused light can be further reduced.

[0054] <4. Method of Arranging Microlenses> Next, with reference to FIGS. 5 to 7, the method of arranging the microlenses 21 according to this embodiment will be described in detail. FIG. 5 is a plan view schematically showing the arrangement of the microlenses 21 in an irregular rectangular lattice according to this embodiment. FIG. 6 is an explanatory view showing an example in which the surface shape of the microlens 21 is changed from the state of FIG. 5. FIG. 7 is an explanatory view showing an example in which the planar position of the vertex 22 of the microlens 21 is eccentric from the state of FIG. 6.

[0055] The microlens array 20 in which a plurality of microlenses 21 having the above 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 an "initial arrangement state") in which a plurality of microlenses 21 having a reference shape are arranged quasi-regularly in a rectangular lattice is first set. Next, from such an initial arrangement state, as shown in FIGS. 6 and 7, the shape of the microlens 21 (that is, the radius of curvature Rx, Ry, the aperture diameter Dx, Dy, etc.) and the position of the vertex 22 of the microlens 21 are randomly changed (hereinafter also referred to as a "varied arrangement state"). Hereinafter, such a method of arranging the microlenses 21 is referred to as a "reference arrangement method".

[0057] In this reference arrangement method, after passing through the quasi-regular arrangement of the microlenses 21 (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 varied arrangement state (see FIGS. 2 and 7) is macroscopically viewed to some extent, the arrangement of the microlenses 21 is such that the quasi-regular initial arrangement state (see FIG. 5) can be estimated to some extent. The reference arrangement method will be described in detail below.

[0058] (1) Initial arrangement state of the microlenses 21 based on an irregular rectangular lattice (FIG. 5) In the reference arrangement method according to this embodiment, first, an initial array state serving as a reference for the arrangement of the microlenses 21 is set. Specifically, as shown in FIG. 5, in the initial array state, a plurality of microlenses 21 are arranged somewhat regularly (quasi-regularly) on the XY plane of the reference plane with a rectangular lattice having irregularities as a reference.

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

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

[0061] A method for randomly varying the grid intervals Wx and Wy is as follows, for example. First, set certain reference values Wx_k and Wy_k (hereinafter referred to as reference grid intervals Wx_k and Wy_k) that serve as the basis for the variation of the grid intervals Wx and Wy in the X and Y directions. Then, randomly vary the reference grid intervals Wx_k and Wy_k within a range of a predetermined variation rate δWx and δWy [±%] to set the grid intervals Wx and Wy (Wx = Wx_k × (100 ± δWx [%]), Wy = Wy_k × (100 ± δWy [%])). Repeat this for the number of grids in the rectangular grid to set a plurality of grid intervals Wx1, Wx2, Wx3, ···, Wy1, Wy2, Wy3, ··· in the X and Y directions respectively.

[0062] Here, the variation rates δWx and δWy are preferably within the range of ±10% to ±50%. If the variation rates δWx and δWy are set to less than ±10%, the variation of the grid intervals Wx and Wy becomes insufficient, making it difficult to impart sufficient aperiodicity to the microlens array 20, and there is a risk that the uniformity of the diffused light by the microlens array 20 decreases. On the other hand, if the variation rates δWx and δWy are set to more than ±50%, the variation of the grid interval W becomes excessively large, and there is a risk that it becomes difficult to continuously arrange a plurality of microlenses 21 on the XY plane without gaps.

[0063] For example, when the variation rates δWx and δWy are set to "±10%", the grid intervals Wx and Wy are set to values randomly deviated from the reference grid intervals Wx_k and Wy_k within a range of "±10%" or less (that is, not less than 90% of the values of Wx_k and Wy_k and not more than 110% of the values of Wx_k and Wy_k) with the reference grid intervals Wx_k and Wy_k as the reference.

[0064] As described above, in this embodiment, a plurality of grid intervals Wx1, Wx2, Wx3, ···, Wy1, Wy2, Wy3, ··· in the X and Y directions are randomly set to different values. Then, using the grid intervals Wx1, Wx2, Wx3, ···, Wy1, Wy2, Wy3, ···, an irregular rectangular grid (see Fig. 5) with mutually different grid intervals Wx and Wy is set.

[0065] Next, based on the above irregular rectangular lattice, as shown in FIG. 5, a plurality of microlenses 21 are arranged on the XY plane. This state is the initial arrangement state that serves as a reference for the arrangement of the microlenses 21. In the initial arrangement state, the planar shape of each microlens 21 is a rectangular shape corresponding to the rectangular lattice, and the outer contour line of the planar shape of the microlens 21 coincides with the grid lines 31 and 32 in the X and Y directions. Also, the positions of the vertices 22 of each microlens 21 coincide with the center points 23 of the respective rectangular lattices surrounded by the grid lines 31 and 32. Further, in this initial arrangement state, the aperture diameters Dx and Dy of each microlens 21 in the X and Y directions respectively coincide with the grid intervals Wx and Wy in the X and Y directions. Here, since the grid intervals Wx and Wy vary to different values from each other, the aperture diameters Dx and Dy also vary to different values from each other.

[0066] Also, the surface shape of each microlens 21 in the initial arrangement state is a shape obtained by cutting out a preset predetermined reference shape (for example, an aspherical reference shape) with the rectangular lattice corresponding to each microlens 21. Here, since the grid intervals Wx and Wy corresponding to each microlens 21 are different from each other, the aperture diameters Dx and Dy and the surface shapes of the plurality of microlenses 21 are different from each other. That is, by arranging a plurality of microlenses 21 based on the above irregular rectangular lattice, in the initial arrangement state, the plurality of microlenses 21 can be arranged such that the aperture diameters Dx and Dy and the surface shapes of the microlenses 21 are different from each other.

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

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

[0069] A method of randomly varying the radii of curvature Rx and Ry of the microlens 21 in the above initial array state is as follows, for example. First, set certain reference values Rx_k and Ry_k (hereinafter referred to as reference radii of curvature Rx_k and Ry_k) that serve as the basis for the variation of the radii of curvature Rx and Ry in the X-direction and Y-direction. Then, randomly vary the reference radii of curvature Rx_k and Ry_k within a predetermined variation rate range of δRx and δRy [%] to set the radii of curvature Rx and Ry (Rx = Rx_k × (100 ± δRx [%]), Ry = Ry_k × (100 ± δRy [%])). Repeat this for the number of each microlens 21, and for each microlens 21, the radius of curvature Rx in the X-direction 11 , Ry 11 , Rx 21 , Ry 21 , ···, Rx nm , Ry nm are set respectively. 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 variation rates δRx and δRy are preferably in the range of ±10% to ±50%. If the variation rates δRx and δRy are set to less than ±10%, the variation of the radii of curvature Rx and Ry becomes insufficient, it becomes difficult to impart sufficient non-periodicity to the microlens array 20, and the uniformity of the diffused light by the microlens array 20 may decrease. On the other hand, if the variation rates δRx and δRy are set to more than ±50%, the variation of the radii of curvature Rx and Ry becomes excessively large, and it may become difficult to continuously arrange a plurality of microlenses 21 on the XY plane without gaps.

[0071] In the above manner, the radii of curvature Rx and Ry of each microlens 21 in the initial array state are randomly varied (first variable array 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 have different values from each other. Similarly, the radii of curvature Ry in the Y direction of the microlenses 21 arranged in the Y direction have different values from each other. Specifically, the radius of curvature Rx randomly varies with a variation rate δRx within ±10% to ±50% based on the reference radius of curvature Rx_k. Also, the radius of curvature Ry randomly varies with a variation rate δRy within ±10% to ±50% based on the reference radius of curvature Ry_k.

[0072] In such a first variable array state, as shown in FIG. 6, the planar shape of each microlens 21 is shifted from a rectangular lattice, and the outer contour line of the planar shape of the microlens 21 may not coincide with the lattice lines 31 and 32 in the X and Y directions. However, the positions of the vertices 22 of each microlens 21 coincide with the center points 23 of each rectangular lattice. Also, in the first variable array state, the aperture diameters Dx and Dy of each microlens 21 in the X and Y directions deviate from the lattice pitches Wx and Wy in the X and Y directions.

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

[0074] (3) Second variable array state (FIG. 7) of the microlens 21 with the lens vertex position varied After setting the first variable array state as described above, as shown in FIG. 7, a second variable array state is set in which the planar position of the vertex 22 of the microlens 21 is randomly eccentric from the center point 23 of the above rectangular lattice. Here, eccentricity means varying the planar position of the vertex 22 of the microlens 21 on the XY plane so as to deviate from the center point 23 of the rectangular lattice. Note that the center point 23 of the rectangular lattice is the intersection of the two diagonals of the rectangular lattice (see FIG. 4).

[0075] A method of randomly offsetting the planar position of the vertex 22 of the microlens 21 in the above-described first variable array state is as follows, for example.

[0076] First, set the offset amount Ec of the planar position of the vertex 22 of the microlens 21 (hereinafter, may also be referred to as the lens vertex position 22). The offset amount Ec is the displacement amount (distance) of the lens vertex position 22 from the center point 23 of the rectangular grid. The offset amount Ec is represented by the offset amount Ecx in the X direction and the offset amount Ecy in the Y direction. The offset amount Ecx is the displacement amount in the X direction of the lens vertex position 22 from the center point 23 of the rectangular grid, and the offset amount Ecy is the displacement amount in the Y direction of the lens vertex position 22 from the center point 23 of the rectangular grid.

[0077] Next, set the eccentricity ratios δEcx and δEcy in the X direction and the Y direction. The eccentricity ratio δEcx in the X direction is the ratio (percentage) of the offset amount Ecx to the grid interval Wx of the above rectangular grid. The eccentricity ratio δEcy in the Y direction is the ratio (percentage) of the offset amount Ecy to the grid interval Wy of the above rectangular grid. The eccentricity ratios δEcx and δEcy are represented by the following equations. δEcx [%]=Ecx / Wx × 100 δEcy [%]=Ecy / Wy × 100

[0078] Next, based on the set eccentricity ratios δEcx and δEcy, offset the lens vertex position. Specifically, the lens vertex position 22 of each microlens 21 is randomly offset with the eccentricity ratios δEcx and δEcy within ±10% to ±50%.

[0079] Here, the eccentricities δEcx and δEcy are preferably within the range of ±10% to ±50%. If the eccentricities δEcx and δEcy are set to less than ±10%, the eccentricity amounts Ecx and Ecy of the lens vertex position 22 will be insufficient, making it difficult to impart sufficient aperiodicity to the microlens array 20, and there is a risk that the uniformity of the diffused light in the X and Y directions by the microlens array 20 will decrease. On the other hand, if the eccentricities δEcx and δEcy are set to more than ±50%, the eccentricity amounts Ecx and Ecy of the lens vertex will become excessively large, and there is a risk that it will be difficult to continuously arrange a plurality of microlenses 21 on the XY plane without gaps.

[0080] In the above 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 grid (second variable arrangement state). As a result, as shown in FIG. 7, the planar positions of the vertices 22 of each microlens 21 are displaced in random directions on the XY plane with random eccentricity amounts Ecx and Ecy.

[0081] As a result, as shown in FIGS. 4 and 7, in the second variable arrangement state, compared to the first variable arrangement state (see FIG. 6), the planar shape of each microlens 21 is further deviated from the rectangular shape corresponding to the rectangular grid. Also, in the second variable arrangement state, the aperture diameters Dx and Dy of each microlens 21 in the X and Y directions are further deviated from the grid intervals Wx and Wy in the X and Y directions.

[0082] In this way, in the second variable arrangement state where the planar position of the vertex 22 of the microlens 21 is randomly eccentric, a plurality of microlenses 21 can be arranged such that the surface shape and aperture diameters Dx and Dy of the microlens 21 are more different from each other than in the first variable arrangement state.

[0083] Further, in the above-described second variable array state, the height positions (positions in the thickness direction of the diffusion plate 1) of the vertices 22 of the plurality of microlenses 21 vary from each other. Specifically, as shown in FIG. 2, the height positions of the vertices 22 (the deepest points of the concave lenses) of the plurality of microlenses 21 arranged in the X direction are different from each other, and the height positions of the vertices 22 (the deepest points of the concave lenses) of the plurality of microlenses 21 arranged in the Y direction are also different from each other. Thereby, the randomness of the shapes and arrangements of the plurality of microlenses 21 can be further enhanced, and sufficient aperiodicity can be imparted to the microlens array 20.

[0084] As described above, according to the method for arranging the microlenses 21 according to the present embodiment, first, based on an irregular rectangular lattice having mutually different lattice intervals Wx and Wy, a plurality of microlenses 21 are arranged semi-regularly (initial array state: FIG. 5). Thereby, the microlenses 21 are semi-regularly arranged in the XY plane such that the outer contour lines of the planar shapes of the respective microlenses 21 follow the lattice lines 31 and 32 of the irregular rectangular lattice.

[0085] Thereafter, the radius of curvature Rx, Ry, surface shape, and lens vertex position 22 of the plurality of arranged microlenses 21 are randomly varied (first and second variable array states: FIGS. 6 and 7). Thereby, the surface shape (three-dimensional shape), aperture shape (planar shape), aperture diameters Dx and Dy, arrangement, etc. of the microlenses 21 arranged semi-regularly can be randomly varied. For this reason, while realizing a semi-regular arrangement of the microlenses 21, a three-dimensional surface structure of the microlens array 20 with high randomness can be realized.

[0086] Therefore, according to the microlens array 20 according to the present embodiment, the polymerization state of the phases of the light emitted from each microlens 21 can be preferably controlled. Thus, interference of the diffused light from each microlens 21 and diffraction due to the periodic structure of the microlens array can be preferably suppressed. Therefore, unevenness in the intensity distribution of the diffused light can be reduced, and the uniformity of the light distribution in the X and Y directions orthogonal to each other 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] Note that the cut-off property means that the diffused light from the microlens array 20 has a so-called top-hat type of diffusion characteristic. The top-hat type of diffusion characteristic refers to an optical function in which, for collimated light in the visible light region or telecentric light having a collimated principal ray and having a certain aperture, the energy distribution is very homogeneous within a certain angular component in a certain region, and the energy can rapidly decrease when exceeding a certain region of this angular component. By realizing such a top-hat type of diffusion characteristic, the luminance distribution of the diffused light of the light incident on the microlens array 20 becomes substantially uniform within a predetermined diffusion angle range, and within the predetermined diffusion angle range, a state is realized in which the luminance value of the diffused light falls within a range of, for example, ±20% centered on the average value of the peak level.

[0088] According to the microlens array 20 according to the present embodiment, a plurality of microlenses 21 are arranged in a rectangular lattice by the above arrangement method, and the radius of curvature Rx, Ry, lens vertex position 22, etc. of each microlens 21 are appropriately controlled, or an aspherical shape is introduced into the surface shape of the microlens 21. As a result, a desired diffusion characteristic of the microlens array 20 can be realized, so that it becomes possible to more reliably realize the top-hat type of diffusion characteristic.

[0089] Furthermore, according to the present embodiment, a plurality of microlenses 21 are arranged quasi-regularly on the XY plane (initial arrangement state) based on an irregular rectangular lattice having mutually different lattice intervals Wx, Wy, and then the radius of curvature Rx, Ry and the lens vertex position 22 are varied (first and second variation arrangement states). As a result, while ensuring the randomness of the surface shape of each microlens 21, a plurality of microlenses 21 can be continuously arranged on the surface of the diffusion plate 1 without gaps. Therefore, it is possible to make it so that there is as little flat portion as possible at the boundary portion between adjacent microlenses 21, so that it is possible to suppress a component (0th-order transmitted light component) of incident light that is transmitted as it is without being scattered on the diffusion plate surface. As a result, it becomes possible to further improve the uniformity of light distribution and the diffusion performance in the X and Y directions orthogonal to each other.

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

[0091] In the present embodiment, a plurality of microlenses 21 having anisotropy in a common direction may be arranged in a rectangular lattice over the entire microlens array 20. The microlens 21 having anisotropy is, for example, a microlens having a planar shape in which the length in one direction (longitudinal direction) is longer than the length in the other direction (lateral direction) orthogonal to the one direction. On the XY plane of the base material 10, a plurality of microlenses 21 having anisotropy are arranged so that the longitudinal directions of the respective microlenses 21 face the same direction.

[0092] Thereby, it becomes possible to control the anisotropic shape of the diffused light on the projection surface. For example, in the diffusion plate 1, the diffusion width of the light in the longitudinal direction of the microlens 21 is reduced, and the diffusion width of the light in the lateral direction is increased. Thereby, the anisotropic shape of the light diffused by the diffusion plate 1 can be controlled according to the shape of the projection surface.

[0093] Hereinafter, with reference to FIGS. 8 to 11, the case where the surface shape (three-dimensional shape) of each microlens 21 is an aspherical shape having anisotropy will be described in more detail. The microlens 21 has an aspherical shape having anisotropy extending in a predetermined direction. As this aspherical shape, for example, a first aspherical shape example (anamorphic shape) described below, a second aspherical shape example (torus shape), or the like can be used.

[0094] (1) First aspherical shape example (anamorphic shape) First, with reference to FIGS. 8 to 11, an example of the aspherical shape (anamorphic shape) of the microlens 21 will be described. 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 anamorphic curved surface.

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

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

[0097]

Equation

[0098] 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 aspherical coefficients in the X direction A y4 , A y6 : 4th and 6th aspherical coefficients in the Y direction

[0099] As shown in Fig. 10, from the anamorphic-shaped curved surface defined by the above equation (1), the short diameter in the X direction of the elliptical shape on the XY plane is Dx, and the long diameter in the Y direction is Dy, and the curved surface is cut out. The curved surface shape of this cut-out part is set as the curved surface shape (anamorphic shape) of the microlens 21. Here, the long diameter Dy, short diameter 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 elliptical shape are randomly varied within a range of a predetermined variation rate δ for each microlens 21 to cause variations. Thereby, the surface shapes of a plurality of microlenses 21 having different anamorphic shapes can be set.

[0100] (2) Second aspherical shape example (torus shape) Next, with reference to Figs. 11 to 13, another example (torus shape) of the aspherical shape of the microlens 21 will be described. Fig. 11 is an explanatory diagram showing the planar shape of the microlens 21 having a torus shape. Fig. 12 is a perspective view showing the three-dimensional shape of the microlens 21 having a torus shape. 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 aspherical shape example is an aspherical shape including a part of the curved surface of a torus shape. A torus is a surface of revolution obtained by rotating a circle. Specifically, as shown in Fig. 13, by rotating the small circle (radius: r) along the circumference of the large circle (radius: R) around the rotation axis (X axis) arranged outside the small circle, a so-called donut-shaped torus is obtained. The curved surface shape of the surface (torus surface) of this torus is the torus shape. By cutting out the outer part of this torus shape, the three-dimensional shape of the microlens 21 having a torus shape as shown in Fig. 12 is obtained.

[0102] As shown in Fig. 11, the planar shape of the toroidal micro-lens 21 is an anisotropic elliptical shape. The major axis in the Y-axis direction of the elliptical shape is R, and the minor axis in the X-axis direction is r. These r and R correspond to the aperture diameters Dx and Dy of the micro-lens 21 in the X and Y directions. As shown in Fig. 12, the three-dimensional shape of the micro-lens 21 consists of an aspherical surface having predetermined radii of curvature R and r in the major axis direction and the minor axis direction of the elliptical shape, respectively. Such a micro-lens 21 has an aspherical shape with anisotropy in the Y-axis direction.

[0103] Here, with reference to Fig. 13 and the following formula (2), a method for setting the surface shape of the toroidal micro-lens 21 will be described. Fig. 13 is a perspective view showing an aspherical surface represented 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]

Equation

[0105] As shown in Fig. 13, from the toroidal surface defined by the above formula (2), the surface is cut out such that the minor axis in the X direction of the elliptical shape on the XY plane is r and the major axis in the Y direction is R. The surface shape of this cut-out part is set as the surface shape (toroidal shape) of the micro-lens 21. Here, the major axis Dy, minor axis Dx, radius of curvature R in the Y direction (corresponding to the radius of curvature Ry of the lens), and radius of curvature r in the X direction (corresponding to the radius of curvature Rx of the lens) of the elliptical shape are randomly varied within a range of a predetermined variation rate δ for each micro-lens 21 to cause variations. Thereby, the surface shapes of a plurality of micro-lenses 21 having mutually different toroidal shapes can be set.

[0106] In addition, as the surface shape (anisotropic aspherical shape) of the micro-lens 21 according to the present embodiment, in addition to the examples of the first and second aspherical shapes, for example, an aspherical shape cut out from an ellipsoid can be used.

[0107] <6. Design Method of Micro-Lens> Next, with reference to FIGS. 14 to 18, the design method of the micro-lens according to the present embodiment will be described. FIG. 14 is a flowchart showing the design method of the micro-lens according to the present embodiment.

[0108] (S10) Setting of Grid Parameters As shown in FIG. 14, first, various parameters (grid parameters) regarding a rectangular grid (grid) serving as a reference for arranging a plurality of micro-lenses 21 on the XY plane are set (S10). The grid parameters include, for example, the following parameters. Wx_k [μm]: Reference value of the grid interval Wx in the X direction (grid size in the X direction) Wy_k [μm]: Reference value of the grid interval Wy in the Y direction (grid size in the Y direction) δWx [±%]: Variation rate of the grid interval Wx in the X direction (allowable variation range of Wx in the X direction) δWy [±%]: Variation rate of the grid interval Wy in the Y direction (allowable variation range of Wy in the Y direction) δEcx [±%]: Eccentricity of the lens vertex position in the X direction (eccentric range in the X direction) δEcy [±%]: Eccentricity of the lens vertex position in the Y direction (eccentric range in the Y direction)

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

[0110] (S12) Generation of Grid 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 in which the grid intervals Wx and Wy in the X and Y directions vary randomly is set. The grid interval Wx in the X direction is the interval between adjacent grid lines 31 in the X direction. The grid interval Wy in the Y direction is the interval between adjacent grid lines 32 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] with a variation 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] with a variation 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 randomly set within the range of 96 μm to 144 μm (values from 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 the plurality of rectangular grids arranged in the X and Y directions are set to different values from each other.

[0112] (S14) Eccentricity processing of the grid center Thereafter, an eccentricity process is executed to randomly vary the position of the center point of each rectangular grid (hereinafter referred to as the "grid center") (S14). FIG. 16 is an explanatory diagram showing the rectangular grid with the grid center eccentric in this step S14.

[0113] As shown in FIG. 16, the grid center before the eccentricity processing is arranged at the coordinate position of the intersection of the two diagonals of each rectangular grid (the center point 23 of the rectangular grid described above). Due to the eccentricity processing, the grid center moves to the X and Y coordinate positions corresponding to the eccentricity amounts Ecx and Ecy calculated randomly using the eccentricity δEcx and the eccentricity δEcy. For example, when the set values of the grid parameters are the numerical values in the above specific example (δEcx = ±10%, δEcy = ±10%), the eccentricity amounts Ecx and Ecy are set to values within the range of 90% to 110% of each grid interval Wx and Wy. Then, the grid center is moved in the X direction and the Y direction by a distance corresponding to this eccentricity amount 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 (the lens vertex position 22). By repeating this eccentricity processing for each rectangular grid, the grid center of each rectangular grid is eccentric to a random position within the range of the eccentricity δEcx and the eccentricity δEcy within each rectangular grid.

[0114] (S16~S24) Generation of microlenses Next, based on the rectangular grid generated in S12 above and the grid center eccentric in S14, the microlens 21 corresponding to each rectangular grid is arranged. Specifically, first, the basic shape of the surface shape (lens surface) of the microlens 21 is selected (S16). Next, the parameters (lens parameters) regarding the selected basic shape are set (S18, S20). Then, based on the set lens parameters, the shape of the microlens 21 in each rectangular grid is determined, the Z coordinate position representing the shape of the microlens 21 is calculated, and the microlens 21 is generated (S22, S24).

[0115] Specifically, in the present embodiment, as the basic shape of the microlens 21 (hereinafter referred to as the lens shape), for example, an anamorphic shape or a toroidal shape is selected (S16). However, it is not limited to such an example, and other types of aspherical shapes or spherical shapes may be selectable as the lens shape.

[0116] When an anamorphic shape is selected in S16, various lens parameters related to the anamorphic shape are set (S18). The lens parameters of 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 [±%]: Variation rate of the radius of curvature Rx in the X direction (allowable variation range of Rx in the X direction) δRy [±%]: Variation rate of the radius of curvature Ry in the Y direction (allowable variation range of Ry in the Y direction)

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

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

[0119] FIG. 17 is an explanatory diagram showing a plurality of 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 eccentric in S14. In addition, the radii of curvature Rx and Ry of each microlens 21 in the X and Y directions vary randomly. For this reason, a plurality of 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] with 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] with a variation rate δRy [±%]. For example, when the set value of the lens parameter is the numerical value in the above specific example (Rx_k = 240 μm, δRx = ±10%), the radius of curvature Rx is randomly set to a value within the range of 216 μm to 264 μm (values from 90% to 110% of 240 μm) centered around 240 μm (Rx_k). 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 plurality of microlenses 21 arranged in the X and Y directions are different from each other.

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

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

[0123] Next, based on the lens parameters set in S20, the surface shape of the toroidal micro-lens 21 is generated (S24). Specifically, based on the lens parameters, the surface shape of each micro-lens 21 is determined, and each micro-lens 21 is arranged on each rectangular grid. That is, the Z coordinate value of each point on the toroidal lens surface is calculated. Since the toroidal lens generation process in this step S24 is the same as the anamorphic lens generation process in S22 above, detailed description is omitted.

[0124] (S26) Output of lens pattern Thereafter, a lens pattern representing the shape and arrangement of the micro-lenses 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 values of the lens pattern in grayscale levels is output.

[0125] FIG. 18 is an image representing a lens pattern designed by the design method according to this embodiment. As shown in FIG. 18, a plurality of micro-lenses 21 are arranged in an irregular rectangular grid on the XY plane. The lens vertex positions 22 of each micro-lens 21 are randomly eccentric, and the radii of curvature Rx and Ry of each micro-lens 21 also vary randomly.

[0126] Therefore, it can be seen that the plurality of micro-lenses 21 have mutually different aspherical shapes (for example, anamorphic shapes or toroidal shapes). Also, the plurality of micro-lenses 21 have mutually different planar shapes. The planar shape of each micro-lens 21 generally has a substantially rectangular shape along the above rectangular grid, but has individual varying shapes. Among the boundary lines between the micro-lenses 21, the four-side portions are generally composed of straight lines, but the four corner portions are composed of curves.

[0127] Furthermore, the plurality of micro-lenses 21 are arranged so as to overlap without gaps, and there is no flat portion at the boundary portion between adjacent micro-lenses 21.

[0128] As described above, according to the design method of the microlens 21 according to the present embodiment, a plurality of microlenses 21 are arranged semi-regularly based on the irregular rectangular lattice described above, and each variable element (lattice intervals Wx, Wy, radius of curvature Rx, Ry, lens vertex position 22, etc.) of the microlens 21 is randomly varied. Thereby, while arranging a plurality of microlens arrays 20 continuously on the XY plane without gaps, different diffusion characteristics can be imparted to each microlens 21. The microlens array 20 having such a configuration has a small macro light quantity variation depending on the lens surface structure and a small light quantity change due to diffracted light, and has a highly homogeneous and diverse light distribution controllability.

[0129] <7. Manufacturing method of microlens> Next, with reference to FIG. 19, a manufacturing method of the diffusion plate 1 according to the present embodiment will be described. FIG. 19 is a flowchart showing the manufacturing method of the diffusion plate 1 according to the present embodiment.

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

[0131] Next, a resist is formed on the surface of the cleaned base material (step S103). For example, a resist layer can be formed by using a resist using a metal oxide. Specifically, for a roll-shaped base material, a resist layer can be formed by spray coating or dipping treatment of the resist. On the other hand, for a flat base material, a resist layer can be formed by various coating treatments of the resist. Note that as the resist, a positive photoresist may be used, or a negative photoresist may be used. Also, a coupling agent may be used to enhance the adhesion between the base material and the resist.

[0132] Further, using a pattern corresponding to the shape of the microlens array 20, the resist layer is exposed (step S105). Such an exposure process may appropriately apply a known exposure method such as, for example, exposure using a gray scale mask, multiple exposure by overlapping a plurality of gray scale masks, or laser exposure using a picosecond pulse laser or a femtosecond pulse laser.

[0133] Thereafter, the exposed resist layer is developed (S107). By such a developing process, a pattern is formed in the resist layer. By using an appropriate developer according to the material of the resist layer, the developing process can be executed. For example, when the resist layer is formed of a resist using a metal oxide, the resist layer can be alkali-developed by using an inorganic or organic alkali solution.

[0134] Next, by performing a sputtering process or an etching process using the developed resist layer (S109), a master substrate having the shape of the microlens array 20 formed on the surface is completed (S111). Specifically, a glass master can be manufactured by glass-etching a glass substrate using the resist layer on which a pattern is formed as a mask. Alternatively, after performing Ni sputtering or nickel plating (NED process) on the resist layer on which a pattern is formed to form a nickel layer on which the pattern is transferred, a metal master can be manufactured by peeling the substrate. For example, a metal master substrate can be manufactured by forming a nickel layer on which the pattern of the resist is transferred by Ni sputtering with a film thickness of about 50 nm or nickel plating with a film thickness of 100 μm to 200 μm (for example, sulfamic acid Ni bath).

[0135] Furthermore, by transferring (imprinting) a pattern onto a resin film or the like using the master substrate (for example, a glass master substrate, a metal master substrate) completed in S111, a soft mold having the inverted shape of the microlens array 20 formed on the surface is created (S113).

[0136] Thereafter, using the soft mold, the pattern of the microlens array 20 is transferred onto a glass substrate, a film substrate, or the like (S115), and further, if necessary, a protective film, an antireflection film, or the like is formed (S117), whereby the diffusion plate 1 according to the present embodiment is manufactured.

[0137] In the above description, an example has been described in which after manufacturing the soft mold (S113) using the master disk (S111), the diffusion plate 1 is manufactured (S115) by transfer using the soft mold. However, the present invention is not limited to such an example, and a master disk (for example, an inorganic glass disk) in which the 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 disk. For example, an acrylic-based photocurable resin is applied to a substrate made of PET (PolyEthylene Terephthalate) or PC (PolyCarbonate), the pattern of the master disk is transferred onto the applied acrylic-based photocurable resin, and the acrylic-based photocurable resin is UV-cured, whereby the diffusion plate 1 can be manufactured.

[0138] On the other hand, when the diffusion plate 1 is manufactured 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 thereafter, if necessary, a protective film, an antireflection film, or the like is formed (S121), whereby the diffusion plate 1 according to the present embodiment is manufactured.

[0139] Note that the manufacturing method shown in FIG. 19 is merely an example, and the manufacturing method of the diffusion plate is not limited to the above example.

[0140] <8. Application Examples of the Diffusion Plate 1> Next, application examples of the diffusion plate 1 according to the present embodiment will be described.

[0141] The diffusion plate 1 as described above can be appropriately implemented for a device that needs to diffuse light in order to realize its function. Such devices include, for example, display devices such as various displays (e.g., LED, organic EL display), projection devices such as projectors, and various lighting devices.

[0142] For example, the diffusion plate 1 can also be applied to the backlight of a liquid crystal display device, a diffusion plate integrated lens, etc., and is also applicable to the use of light shaping. Further, the diffusion plate 1 can also be applied to the transmissive screen, Fresnel lens, reflective screen, etc. of a projection device. Moreover, the diffusion plate 1 can also be applied to various lighting devices used for spot lighting, base lighting, etc., various special lightings, and various screens such as intermediate screens and final screens. Furthermore, the diffusion plate 1 is also applicable to uses such as diffusion control of light source light 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, incident light distribution control to various light bulb systems, etc.

[0143] Note that the device to which the diffusion plate 1 is applied is not limited to the above application examples, and any known device can be applied as long as it is a device that utilizes light diffusion.

Example

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

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

[0146] Specifically, first, after cleaning the glass substrate, a photo-reactive resist was applied to one surface (main surface) of the glass substrate with a resist thickness of 2 μm to 15 μm. As the photo-reactive resist, for example, a positive photo-reactive 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 apparatus that uses a laser with a wavelength of 405 nm to expose the resist layer. Note that the resist layer may be exposed by performing mask exposure on the resist on the glass substrate using a stepper exposure apparatus that uses g-line.

[0148] Subsequently, by developing the resist layer, a pattern was formed in the resist. As the developer, for example, a solution of tetramethylammonium hydroxide (TMAH) 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, using the resist on which the pattern was formed, a diffusion plate was manufactured by etching the glass substrate. Specifically, a diffusion plate was manufactured by forming the pattern of the resist on the glass substrate by glass etching using Ar gas or CF4 gas.

[0150] Table 1 shows the design conditions of the surface structure of the microlens array and the evaluation results of the light distribution uniformity by the diffusion plate for the diffusion 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 the surface shapes of different microlenses. Then, a lens pattern representing the shape and arrangement of the microlenses according to each example and comparative example was output. Using this lens pattern, the diffusion plates according to each example and comparative example were manufactured by the above manufacturing method.

[0153] As shown in Table 1, in Examples 1 to 9, when designing the surface structure of the microlens array, the grid intervals Wx and Wy of each microlens were randomly varied. On the other hand, in Comparative Examples 1 to 4, the grid intervals Wx and Wy were not varied, and the grid intervals of all microlenses were set to a certain reference grid interval Wx_k and Wy_k.

[0154] Also, regarding the radius of curvature Rx and the radius of curvature Ry, as shown in Table 1, for each example and comparative example, they were set as fixed values or random variation values. When the variation rates δRx, δRy = ±0%, the radii of curvature Rx, Ry of each microlens were set as fixed values without variation. When the variation rates δRx, δRy = ±10%, ±15%, it means that the radii of curvature Rx, Ry were randomly varied within the range of the variation rates δRx, δRy. Also, regarding the eccentricity of the lens vertex position in the XY plane, when the eccentricity rates δEcx, δEcy = ±0%, the lens vertex position was not eccentric. When the eccentricity rates δEcx, δEcy = ±10%, ±15%, it means that the lens vertex position was randomly eccentric within the range of the eccentricity rates δEcx, δEcy.

[0155] Also, regarding the surface shape of the microlens, it was made spherical in Examples 1 to 4, 8, and 9 and Comparative Examples 1 to 3, and aspherical (e.g., anamorphic shape) in Examples 5 to 7. Regarding the planar shape of the microlens array, it was made square in Examples 1 to 7 and Comparative Examples 1 to 3, and rectangular (a rectangular shape longer in the X direction) in Examples 8 and 9 and Comparative Example 4.

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

[0157] The pattern of the surface shape of the microlens array of the diffusion plates according to Examples 1 to 9 and Comparative Examples 1 to 4, and the simulation results and actual measurement results of the light distribution characteristics and luminance distribution of the diffused light are shown in FIGS. 20 to 33, respectively.

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

[0159] Also, in Fig. 30 (Example 7), (e) is a graph showing the measured results of the far-field pattern (FFP) of the diffused light of a laser light source using an actually manufactured diffuser plate (horizontal axis: diffusion angle, vertical axis: luminance). (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 measured results of (e).

[0160] Also, in Figs. 32 and 33 (Examples 8 and 9), (e) is a graph showing the simulation results of the light distribution characteristics in the X and Y directions of diffused light (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).

[0161] The light distribution characteristics (such as light distribution uniformity) of the diffuser plates according to Examples 1 to 9 and Comparative Examples 1 to 3 as described above were evaluated in three levels (Evaluation A, B, C) according to the following evaluation criteria. The evaluation results are shown in Table 1. Evaluation A: The uniformity in the X and Y directions of the diffused light was sufficiently high, and no unevenness in the luminance distribution along the rectangular grid was observed. The luminance distribution of the diffused light was substantially uniform within a predetermined diffusion angle range, and within the predetermined diffusion angle range, the luminance value of the diffused light was within the range of ±20% centered on the average value of the peak level. Evaluation B: The uniformity in the X and Y directions of the diffused light was high, and there was some unevenness in the luminance distribution along the rectangular grid, but no significant unevenness was observed. The luminance distribution of the diffused light was substantially uniform within a predetermined diffusion angle range, and within the predetermined diffusion angle range, the luminance value of the diffused light was within the range of ±40% centered on the average value of the peak level. Evaluation C: The uniformity in the X and Y directions of the diffused light was insufficient, and significant unevenness in the luminance distribution along the rectangular grid was observed. The luminance distribution of the diffused light varied within a predetermined diffusion angle range, and within the predetermined diffusion angle range, the luminance value of the diffused light was not within the range of ±40% centered on the average value of the peak level.

[0162] Below, a comparative explanation will be given regarding the evaluation results of Examples 1 to 9 and Comparative Examples 1 to 4.

[0163] (1) Comparison between Examples 1 - 9 and Comparative Examples 1 - 4 (Effect of irregularity of grid interval) In Comparative Examples 1 - 4, as shown in FIGS. 20 - 22 and FIG. 31, in the luminance distribution of diffused light, the luminance increased and decreased periodically, and unevenness in the form of a rectangular grid occurred in the luminance distribution of diffused light, and the light distribution uniformity of diffused light was insufficient. The reason is considered to be as follows.

[0164] In Comparative Examples 1 - 4, the rectangular grid serving as the reference for the micro - lens array is a regular rectangular grid, and the grid intervals in the X and Y directions are fixed at constant values Wx_k and Wy_k (δWx, δWy = ±0%). Therefore, due to the periodic structure of the regular rectangular grid - shaped micro - lens array, diffraction occurs in the diffused light from each micro - lens, resulting in unevenness in the luminance distribution and a decrease in the light distribution uniformity.

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

[0166] On the other hand, in Examples 1 - 9, although the luminance varies in the luminance distribution of diffused light, no periodic increase and decrease or periodic peaks are observed, the unevenness in the luminance distribution of diffused light is sufficiently suppressed, and the light distribution uniformity of diffused light is good. The reason is considered to be as follows.

[0167] In Examples 1 to 9, the microlenses are arranged on the XY plane with reference to a rectangular lattice. Here, the rectangular lattices of Examples 1 to 9 are not regular rectangular lattices like those of the Comparative Example, but quasi-regular rectangular lattices having irregularities in the lattice intervals Wx and Wy. That is, as shown in Fig. 15, the lattice intervals Wx and Wy of the rectangular lattices of Examples 1 to 9 randomly vary so as to have different values from each other, and the variation rates δWx and δWy are ±10% or more. By arranging a plurality of microlenses with reference to such a rectangular lattice having irregularities, the aperture diameters Dx and Dy and the planar shape of the microlenses can be randomly varied, and the positions of the boundary lines between adjacent microlenses can also be randomly shifted.

[0168] As a result, as shown in, for example, Figs. 2, 4, 18, etc., the outer contour line (the boundary line between microlenses) of the planar shape of the microlenses is composed of a combination of a curve with an arbitrary radius of curvature and a straight line. Thereby, the regularity of the arrangement at the boundary between the microlenses is further disrupted, and it becomes possible to further reduce the diffraction component. Therefore, it is possible to suppress the mutual diffraction of the diffused light between the plurality of microlenses and improve the uniformity of the light distribution of the diffused light of the entire microlens array.

[0169] From the above results, it can be seen that by using the diffuser plate of the present invention, unevenness in the luminance distribution can be suppressed and the light distribution uniformity can be sufficiently improved in two directions (X and Y directions) orthogonal to each other.

[0170] (2) Comparison between Example 1 and Examples 2 to 9 (effects of variation in radius of curvature and eccentricity of lens apex) As shown in Table 1, in Example 1, only the lattice intervals Wx and Wy are varied. On the other hand, in Examples 2 to 9, in addition to the lattice intervals Wx and Wy, the radii of curvature Rx and Ry are varied and the lens apex positions are eccentric.

[0171] As a result, Examples 2 to 9 (Evaluation A) were more effective than Example 1 (Evaluation B) in suppressing unevenness in luminance distribution and improving the uniformity of the light distribution of diffused light. Thus, from the perspective of improving the uniformity of the light distribution, it can be seen that in addition to the lattice intervals Wx and Wy, it is effective to vary the radii of curvature Rx and Ry or to eccentrically displace the lens vertex position.

[0172] Furthermore, in Examples 2, 3, and 5, the radii of curvature Rx and Ry were varied or the lens vertex position was eccentrically displaced. In contrast, in Examples 4, 6 to 9, the radii of curvature Rx and Ry were varied and the lens vertex position was also eccentrically displaced. As a result, as shown in the (b) electromagnetic field analysis images and (c) luminance distribution graphs of FIGS. 24 to 29, 32, and 33, in Examples 4, 6 to 9, unevenness in the luminance distribution could be further suppressed and the uniformity of the light distribution of diffused light could be further improved. Thus, from the perspective of improving the uniformity of the light distribution, it can be seen that in addition to the lattice intervals Wx and Wy, it is more effective to perform both the variation of the radii of curvature Rx and Ry and the eccentric displacement of the lens vertex position.

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

[0174] As a result, as shown in the electromagnetic field analysis images (b) and the graphs of luminance distribution (c) in FIGS. 23 to 29, the aspherical lenses of Examples 5 to 7 can suppress the unevenness of the luminance distribution more effectively than the spherical lenses of Examples 1 to 4, and can achieve a finer light distribution uniformity. Thus, from the viewpoint of improving the light distribution uniformity, it can be seen that using an aspherical lens is more effective than using 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, while realizing a high uniformity of the diffused light, the light distribution angle can be controlled to have anisotropy between the X direction and the Y direction.

[0175] (4) Diffusion characteristics of Example 7 (excellent light distribution uniformity and cut-off property) As shown in Table 1, in Example 7, the reference curvature radii Rx_k and Ry_k are set to relatively large values (150 μm), the curvature radii Rx and Ry are varied within the range of ±10% of Rx_k and Ry_k, and the lens vertex position is eccentric within the range of eccentricity δEcx and δEcy = ±10%.

[0176] Furthermore, the surface shape of the microlens of Example 7 is an aspherical shape that satisfies the following relational expressions (A) and (B) with respect to the ratio to the reference curvature radii Rx_k and Ry_k [μm] and the reference lattice intervals Wx_k and Wy_k [μm]. 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 aspherical shape having anisotropy as described above, and while varying the lattice intervals Wx and Wy, the curvature radii Rx and Ry, and eccentric the lens vertex position under the conditions shown in Table 1, the reference curvature radii Rx_k and Ry_k [μm] and the reference lattice intervals Wx_k and Wy_k [μm] are adjusted so as to satisfy the above relational expressions (A) and (B). Furthermore, the diffusion angle (full width at half maximum (FWHM)) of the diffused light emitted from the diffusion plate is within the range of 20° or less. Thereby, a so-called top-hat type diffusion characteristic can be more reliably realized.

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

[0179] From the above results, it can be seen that by using a diffusion plate similar to Example 7 above, within a range where the diffusion angle (full width at half maximum) is 20° or less, while sufficiently improving the light distribution uniformity in two mutually perpendicular directions (X and Y directions), the anisotropy of the light distribution in the X and Y directions and the cut-off property of the intensity distribution of the diffused light can be appropriately controlled.

[0180] (7) Comparison between Examples 8 and 9 and Comparative Example 4 (Effect of rectangular aspherical lens shape) The diffusion plates according to Examples 8 and 9 and Comparative Example 4 used a rectangular microlens array that extends long in the X direction. The reference grid intervals were Wx_k = 50 μm and Wy_k = 40 μm, and the reference grid interval Wx_k in the longitudinal direction (X direction) of the microlens array was set to be larger than the reference grid interval Wy_k in the short-side direction (Y direction) (Wx_k > Wy_k).

[0181] In such a rectangular microlens array, in Comparative Example 4, the grid intervals Wx and Wy were not changed. On the other hand, in Examples 8 and 9, the grid 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%. Further, in Examples 8 and 9, the lens vertex positions were also randomly offset 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, and unevenness in a rectangular lattice pattern occurred remarkably, and the light distribution uniformity of the diffused light was insufficient. On the other hand, in Examples 8 and 9, no periodic increase and decrease or peak was observed in the luminance distribution of the diffused light, the unevenness in the luminance distribution of the diffused light was sufficiently suppressed, and the light distribution uniformity of the diffused light was good.

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

[0184] As described above, the preferred embodiments of the present invention have been described in detail with reference to the accompanying drawings, but the present invention is not limited to such examples. It is obvious that those having ordinary knowledge in the technical field to which the present invention pertains can conceive various modification examples or correction examples within the scope of the technical idea described in the claims, and it is naturally understood that these also belong to the technical scope of the present invention.

Description of Reference Numerals

[0185] 1 Diffusion plate 3 Unit cell 10 Base material 20 Micro lens array 21 Micro lens 22 Vertex of micro lens 23 Center point of rectangular lattice Wx, Wy Lattice pitch Rx, Ry Radius of curvature Ecx, Ecy Eccentricity Wx_k, Wy_k Reference lattice pitch Rx_k, Ry_k Reference radius of curvature δWx, δWy Variation rate δRx, δRy Variation rate δEcx, δEcy Eccentricity ratio R Radius of large circle r Radius of small circle

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 based on an irregular rectangular grid having three or more different grid intervals; and the grid intervals Wx in the X direction of three or more of the microlenses arranged in the X direction of the rectangular grid vary randomly and are different from each other; the grid intervals Wy in the Y direction of three or more of the microlenses arranged in the Y direction of the rectangular grid vary randomly and are different from each other; the surface shapes of the plurality of microlenses are different from each other; the grid interval Wx in the X direction varies randomly with a variation rate δWx within ±10% based on a reference grid interval Wx_k; the grid interval Wy in the Y direction varies randomly with a variation rate δWy within ±10% based on a reference grid interval Wy_k; the radius of curvature Rx in the X direction varies randomly with a variation rate δRx within ±10% based on 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% based on a reference radius of curvature Ry_k; the surface shape of the microlens is an aspherical shape in which the reference radii of curvature Rx_k, Ry_k and the reference grid intervals Wx_k, Wy_k satisfy the following relational expressions (A) and (B); Rx_k / Wx_k ≥ 1.85... (A) Ry_k / Wy_k ≥ 1.85... (B) A diffuser plate having a diffusion angle (full width at half maximum) of 20° or less by the diffuser plate.

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 grid.

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

4. 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. The diffuser plate according to any one of claims 1 to 3.

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

6. The boundary lines of the microlenses adjacent to each other include straight lines and curves. The diffuser plate according to any one of claims 1 to 5.

7. The microlens array is composed of a plurality of unit cells that 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 diffuser plate according to any one of claims 1 to 6.

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

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

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

Images