Optical element

Abstract

To provide an optical element emitting light of even brightness in a diffusion range and suitable for mass production.SOLUTION: An optical element 10 includes a first principal surface 11a and a second principal surface 12a facing one another. The first principal surface 11a includes a first lenticular lens 11 while the second principal surface 12a includes a second lenticular lens 12. A longitudinal direction (Y) of the first lenticular lens 11 is perpendicular to a longitudinal direction (X) of the second lenticular lens 12, or intersects so as to form a deviation angle in a range of ±70 degrees. The first lenticular lens 11 has a curved surface shape of a Korenick constant kx of -2.4 or more and -0.6 or less while the second lenticular lens 12 has a curved surface shape of a Korenick constant ky of -0.9 or more and -0.5 or less.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an optical element. [Background technology]

[0002] In recent years, head-up display (hereinafter sometimes referred to as HUD) devices that project driving support information such as navigation from an image display device onto the windshield of moving objects such as automobiles have been attracting attention. A head-up display device mainly comprises an image display device, a diffusion plate on which the image projected from the image display device is formed as an intermediate image, and a magnifying mirror that magnifies the intermediate image and guides it to the windshield. A microlens array is widely used as the diffusion plate.

[0003] In order to realize low power consumption in a head-up display device, a laser projector using a laser beam with low power consumption as a light source for an image display device may be used. For example, Patent Document 1 proposes an image forming device as a head-up display device, which includes a laser projector that uses a laser beam as a light source and projects an image formed by an array of multiple pixels, a microlens array in which multiple microlenses are arranged, an optical system correction element, and an optical system magnification element. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2010-145745 A Summary of the Invention [Problem to be solved by the invention]

[0005] A microlens array can appropriately diffuse incident light, and the curved shape can be freely designed according to the required light distribution characteristics and the optical characteristics of the material. However, when a laser light is used as a light source, the spot diameter of the laser light is small, and it is difficult to make the brightness of the emitted light uniform in the diffusion range. On the other hand, when the pitch size of the microlens becomes small with the improvement of image quality, the production of the mold becomes complicated, which is time-consuming and costly. The present invention has been made in view of the above circumstances, and has an object to provide an optical element in which the luminance of emitted light is uniform over the diffusion range and which is suitable for mass production. [Means for solving the problem]

[0006] The inventors discovered that by using lenticular lenses on both the incident and exit sides of an optical element, arranging them so that the long axis direction of the lenticular lens on the incident side and the long axis direction of the lenticular lens on the exit side are perpendicular, and controlling the curved shape of each lenticular lens, it is possible to make the brightness uniform over the diffusion range of the exiting light through a simple manufacturing process, and thus arrived at the present invention.

[0007] That is, the present invention provides an optical element having a first principal surface and a second principal surface opposed to each other, the first principal surface having a first lenticular lens, the second principal surface having a second lenticular lens, the long axis direction of the first lenticular lens being perpendicular to the long axis direction of the second lenticular lens or intersecting with the long axis direction of the second lenticular lens at an angle within a range of ±70 degrees from the perpendicular direction, and the curved shape of the first lenticular lens being expressed by the following formula (1):

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[0008] According to the optical element of the present invention, the luminance of the emitted light is uniform over the diffusion range, and an optical element suitable for mass production can be provided. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a perspective view showing a part of an optical element according to one embodiment (first embodiment) of the present invention. [Diagram 2] 1 is a plan view showing a portion of an optical element according to an embodiment of the present invention. [Diagram 3] 1A is a plan view of a first main surface of a part of an optical element according to one embodiment of the present invention, and FIG. 1B is a cross-sectional view taken along line XX. [Figure 4] 3A is a plan view of a second principal surface of a part of an optical element according to one embodiment of the present invention, and FIG. 3B is a YY cross-sectional view of the part. [Diagram 5] FIG. 2 is a schematic diagram showing an optical element according to one embodiment (second embodiment) of the present invention. [Figure 6] FIG. 1 is a schematic diagram showing a head-up display device using the optical element of the present invention. [Figure 7] 1 is a photograph showing heat maps of Examples 1 to 5. [Figure 8] 1 is a photograph showing heat maps of Examples 6 to 10. [Figure 9] Photographs showing heat maps of Examples 11 to 15. [Figure 10] Photographs showing heat maps of Examples 16 to 19. [Figure 11] Photographs showing heat maps of Examples 20 to 23. [Figure 12]4 is a graph showing luminance versus diffusion angle of emitted light in Example 1. [Figure 13] 13 is a graph showing luminance versus diffusion angle of emitted light in Example 11. [Figure 14] 23 is a graph showing luminance versus diffusion angle of emitted light in Example 19. [Figure 15] 13 is a graph showing luminance versus diffusion angle of emitted light in Example 20. [Figure 16] 23 is a graph showing luminance versus diffusion angle of emitted light in Example 23. [Figure 17] Photographs showing heat maps of the diffusers of Examples 24, 25, 27 and 28. [Figure 18] 23 is a graph showing the distribution of radiant intensity (W / sr) of diffused light in the diffuser plate of Example 25. [Figure 19] 13 is a graph showing the distribution of radiant intensity (W / sr) of diffused light in the diffuser plate of Example 28. [Figure 20] 1 shows a graph in which the results of angular intensity uniformity in each of Examples 24 to 31 and Comparative Examples 1 and 2 are plotted by angle range. [Figure 21] The heat map of the diffuser plate of Example 28 (deviation angle from perpendicular: 40 degrees) is shown for each of the angle ranges (1) to (3). [Figure 22] The heat map of the diffuser plate of Example 29 (deviation angle from perpendicular: 50 degrees) is shown for each of the angle ranges (1) to (3). DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] [Optical element (first embodiment)] An optical element according to one embodiment of the present invention (first embodiment) will be described below with reference to the drawings. Fig. 1 is a perspective view showing a part of the optical element according to this embodiment. Fig. 2 is a plan view showing a part of the optical element according to one embodiment of the present invention. Fig. 3 is (a) a plan view of a first main surface and (b) an XX cross-sectional view of a part of the optical element according to this embodiment. Fig. 4 is (a) a plan view of a second main surface and (b) a YY cross-sectional view of a part of the optical element according to this embodiment.

[0011] 1, the optical element of this embodiment is an optical element 10 having a first main surface 11a and a second main surface 12a facing each other, where the first main surface 11a is the light exit side and the second main surface 12a is the light entrance side. The first main surface 11a has a first lenticular lens 11, and the second main surface 12a has a second lenticular lens 12, which are disposed so that the long axis direction (Y) of the first lenticular lens 11 is perpendicular to the long axis direction (X) of the second lenticular lens 12. As shown in FIG. 2, in the optical element 10 of this embodiment, the long axis direction (Y) of the first lenticular lens 11 and the long axis direction (X) of the second lenticular lens 12 are arranged perpendicular to each other, so that individual microlenses 10a are formed at the points where the lenses intersect, and the optical element 10 as a whole is composed of a microlens array. The first lenticular lens 11 and the second lenticular lens 12 will be described in detail below.

[0012] (First lenticular lens) As shown in Fig. 3(a), the first lenticular lens 11 is formed by arranging a plurality of lenticular lenses in the X direction with the Y direction as the major axis direction. Fig. 3(b) shows a cross-sectional view taken along the line XX in (a). The curved shape of the first lenticular lens 11 is expressed by the following formula (1).

[0013]

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[0014] In formula (1), cx represents the curvature [1 / mm], and x represents the central axis L of the first lenticular lens 11. 11 , that is, the distance [mm] in the X-axis direction in each of the multiple lenticular lenses 11 (that is, the distance from the central axis L 11 kx is the Conic constant, which is between -2.4 and -0.6. By setting the conic constant kx to -2.4 or more and -0.6 or less, it is possible to realize a luminance of 80% or more of the maximum luminance in an angle range of 90% of the full width at half maximum (FWHM) in a spectrum showing the luminance characteristics with respect to the diffusion angle of the emitted light. In addition, it is preferable that the conic constant kx is set to -2.0 or more and -1.0 or less, and in this range, it is possible to realize a luminance of 90% or more of the maximum luminance in an angle range of 90% of the full width at half maximum (FWHM). It is particularly preferable that the conic constant kx is set to -1.6. By reducing the angle dependency of the luminance, the brightness in the displayed image seen from any viewpoint position can be perceived as more balanced.

[0015] In formula (1), the distance x from the central axis of the first lenticular lens 11 in the X direction is preferably 0 or more and Px / 2 or less, where Px represents the pitch between the lenses of the first lenticular lens 11, which will be described later. When the distance x is within the above range, no flat portion is formed on the lenticular lens-shaped surface of the first main surface of the optical element, and a significant improvement in front luminance can be suppressed.

[0016] In the first lenticular lens 11, the pitch Px between the lenses is preferably 5 μm or more, and more preferably 25 μm or more. By setting the pitch Px in this way, it is possible to prevent the viewing angle from becoming difficult to control due to the diffraction phenomenon. In addition, it is possible to suppress the occurrence of interference fringes. Moreover, the pitch Px between the lenses is preferably 500 μm or less, and more preferably 250 μm or less. By setting the pitch Px in this manner, it is possible to prevent the pixels of the image of the head-up display from becoming rough.

[0017] (Second lenticular lens) As shown in Fig. 4(a), the second lenticular lens 12 is formed by arranging a plurality of lenticular lenses with their major axes aligned in the X direction. Fig. 4(b) shows a YY cross-sectional view of (a). The curved shape of the second lenticular lens is expressed by the following formula (2).

[0018]

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[0019] In formula (2), cy represents the curvature [1 / mm], and y represents the central axis L of the second lenticular lens. 12 y-axis direction of each of the plurality of lenticular lenses 11 (i.e., the distance [mm] from the center axis L 12 ky is the Conic constant, which is between -0.9 and -0.5.

[0020] By setting the conic constant ky to -0.9 or more and -0.5 or less, it is possible to realize a luminance of 80% or more of the maximum luminance in an angle range of 90% of the full width at half maximum (FWHM) in a spectrum showing the luminance characteristics with respect to the diffusion angle of the emitted light. In addition, the conic constant ky is preferably set to -0.8 or more and -0.6 or less, and in this range, it is possible to realize a luminance of 90% or more of the maximum luminance in an angle range of 90% of the full width at half maximum (FWHM). It is particularly preferable that the conic constant ky is -0.7. By reducing the angle dependency of the luminance, the brightness in the displayed image seen from any viewpoint position can be perceived as more balanced.

[0021] In formula (2), the distance y in the Y direction from the central axis of the first lenticular lens 11 is preferably 0 mm or more and Py / 2 or less, where Py represents the pitch between the lenses of the second lenticular lens 12, which will be described later. When the distance y is within the above range, no flat portion is formed on the lenticular lens-shaped surface of the first main surface of the optical element, and a significant improvement in front brightness can be suppressed.

[0022] In the second lenticular lens 12, the pitch Py between the lenses is preferably 5 μm or more, and more preferably 25 μm or more. By setting the pitch Py in this way, it is possible to prevent the difficulty in controlling the viewing angle due to the diffraction phenomenon. In addition, it is possible to suppress the occurrence of interference fringes. Moreover, the pitch Py between the lenses is preferably 500 μm or less, and more preferably 250 μm or less. By setting the pitch Py in this manner, it is possible to prevent the pixels of the image of the head-up display from becoming rough.

[0023] The material constituting the lenticular lens may be a radiation curable resin or a thermoplastic resin. The refractive index of the resin is preferably 1.35 or more and 1.7 or less, more preferably 1.45 or more and 1.66 or less. By using a resin with such a refractive index, it is possible to appropriately control the light input characteristic or light output characteristic of the optical element. Examples of resins having such a refractive index include acrylic resin, polycarbonate, polyethylene terephthalate, polyvinyl chloride, polystyrene, etc. By using a radiation curable resin or a thermoplastic resin, a mold corresponding to the above-mentioned shape can be manufactured, and then injection molding, heat press processing, and UV transfer molding can be performed, whereby an optical element consisting of a microlens can be manufactured easily and reliably.

[0024] When a wider viewing angle or more uniform angular luminance is required, it is preferable that the curved shape of the first lenticular lens 11 is further adjusted according to the following formula (3).

[0025]

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[0026] In formula (3), A is a symmetric coefficient, and B is an asymmetric coefficient, which is −1.

[0027] By adjusting the curved shape of the first lenticular lens 11 according to formula (3), it is possible to make the luminance uniform over a wide viewing angle.

[0028] When a wider viewing angle or more uniform angular luminance is required, it is preferable that the curved shape of the second lenticular lens 12 is further adjusted according to the following formula (4).

[0029]

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[0030] In formula (4), A is a symmetric coefficient, and B is an asymmetric coefficient, which is equal to 1.

[0031] By adjusting the curved shape of the second lenticular lens 12 according to formula (4), it is possible to make the luminance uniform over a wide viewing angle.

[0032] The optical element 10 of this embodiment has a rectangular diffusion shape, and can maintain a high brightness of 90% or more of the maximum brightness of the emitted light in the range of diffusion angles of the emitted light up to 40° in the horizontal direction H and up to 28° in the vertical direction V, and can make the brightness of the emitted light uniform. In addition, the optical element 10 of this embodiment can maintain a high brightness of 98% or more of the maximum brightness of the emitted light in the range of diffusion angles of the emitted light up to 25.5° in the horizontal direction H and up to 19.5° in the vertical direction V, and can make the brightness of the emitted light uniform. The light distribution shape (intensity distribution of the emitted light) in each direction can be a top hat shape. In addition, the optical element 10 of this embodiment has found an optimal configuration for making the brightness uniform over a wide viewing angle with respect to the shape of the lenticular lens and its position (whether it is located on the entrance surface or the exit surface) while the refractive index changes from small to large to small when the incident light passes through the optical element from the air. Furthermore, the optical element 10 of this embodiment has lenticular lenses on both opposing surfaces, thereby achieving uniform brightness at the diffusion angle. This significantly simplifies the machining process of the mold compared to the case where similar optical characteristics are obtained by providing lenses on only one surface, making it suitable for mass production.

[0033] [Optical element (second embodiment)] An optical element according to one embodiment (second embodiment) of the present invention will now be described with reference to the drawings. Figure 5 is a schematic diagram showing an optical element 10' according to the second embodiment.

[0034] 5, the optical element 10' of this embodiment is a plate-like optical element having a first main surface 11'a and a second main surface 12'a which is the back surface of the first main surface 11'a, the first main surface 11'a being the surface on the light exit side, and the second main surface 12'a being the surface on the light entrance side. The first main surface 11'a has a first lenticular lens 11', the second main surface 12'a has a second lenticular lens 12', and the long axis direction of the first lenticular lens 11' is disposed on the XY plane such that it is offset by an angle θ within a range of ±70 degrees from being perpendicular to the long axis direction of the second lenticular lens 12'. By thus forming a shift angle θ between the first and second lenticular lenses, the pitch direction which was parallel to the X-axis direction of the first lenticular lens 11' in the first embodiment is arranged so that it creates a further shift angle within the range of ±70 degrees on the XY plane with respect to the pitch direction which is parallel to the Y-axis direction of the second lenticular lens 12'.

[0035] The optical element 10' is arranged such that the long axis direction of the first lenticular lens 11' is offset by an angle θ within a range of ±70° from the perpendicular direction to the long axis direction of the second lenticular lens 12', which is provided parallel to the X-axis direction, so that individual microlenses 10'a are formed at the intersections of the lenses, and the optical element 10' as a whole is made up of a microlens array. Here, the microlenses 10'a are formed such that the pitch direction of the first lenticular lens 11' and the pitch direction of the second lenticular lens 12' form an offset angle θ.

[0036] A first lenticular lens 11' of the optical element 10' is the same as the first lenticular lens 11 of the first embodiment, except that it is arranged to form a shift angle θ. The second main surface 12'a and the second lenticular lens 12' of the optical element 10' and the materials constituting the first and second lenticular lenses are the same as those of the first embodiment, and therefore description thereof will be omitted.

[0037] 5, the first lenticular lens 11' is preferably arranged on the XY plane so as to form a shift angle θ within the range of ±70 degrees with respect to the Y axis, and the shift angle θ is more preferably within the range of ±40 degrees, and most preferably within the range of ±10 degrees, and within these ranges, the smaller the shift angle θ is, the more uniform the brightness of the emitted light can be improved. The shift angle θ of the first lenticular lens 11' is preferably adjusted according to the angular range of the diffusion angle of the emitted light. More specifically, by setting the misalignment angle θ of each lenticular lens within the range of ±70 degrees, the optical element 10' can maintain a high brightness of 98% or more of the maximum brightness of the emitted light in the diffusion angle range of the emitted light of 0 to 26 degrees in the horizontal direction H and 0 to 12 degrees in the vertical direction V as absolute values, and can make the brightness of the emitted light uniform. In addition, the light distribution shape in each direction (intensity distribution of the emitted light) can be a top hat shape. In addition, the optical element 10' can be used with the brightness of the emitted light being uniform in the diffusion angle range of the emitted light of 0 to 13 degrees in the horizontal direction H and 0 to 12 degrees in the vertical direction V, although this should not be limited.

[0038] The curved shape of the first lenticular lens 11' in a cross section perpendicular to the long axis direction of the first lenticular lens 11' is expressed by the above formula (1), and the conic constant ky is preferably -2.4 or more and -0.6 or less. By setting the conic constant kx in a cross section perpendicular to the long axis direction of the first lenticular lens 11', that is, in a cross section cut parallel to the pitch direction, to -2.4 or more and -0.6 or less, it is possible to realize a luminance of 80% or more of the maximum luminance in an angle range of 90% of the full width at half maximum (FWHM) in a spectrum showing the luminance characteristic with respect to the diffusion angle of the emitted light, as in the first embodiment. Also, as in the first embodiment, it is preferable that the conic constant kx is -2.0 or more and -1.0 or less, and in this range, it is possible to realize a luminance of 90% or more of the maximum luminance in an angle range of 90% of the full width at half maximum (FWHM). As in the first embodiment, it is particularly preferable that the conic constant kx is -1.6, which reduces the angle dependency of the luminance, thereby making the brightness in the displayed image seen from any viewpoint position more balanced. Furthermore, the preferred ranges of the distance x from the central axis in the X direction and the pitch Px between the lenses, which are defined in the above formula (1), are the same as those in the first embodiment, and therefore description thereof will be omitted.

[0039] When a wider viewing angle or more uniform angular luminance is required, it is preferable that the curved shape of the first lenticular lens 11' is adjusted according to the above formula (3).

[0040] From the maximum and minimum values ​​of the radiation intensity (W / sr), the angular intensity uniformity calculated based on the following formula can be made to be 60% or more, and more preferably 80% or more. Angular intensity uniformity = ((minimum radiant intensity) / (maximum radiant intensity)) x 100% This enables the optical element 10' to achieve uniform luminance over a wide viewing angle.

[0041] [Head-up display device] Next, an embodiment of a head-up display device using the optical element of the present invention will be described with reference to the drawings. Fig. 6 is a schematic diagram showing the head-up display device of this embodiment. The head-up display device of this embodiment is a head-up display device for a vehicle, and uses a laser projector with laser light as a light source as an image forming device. The laser projector can use a semiconductor laser with low power consumption as a light source, and can realize low power consumption of the entire head-up display device. In this embodiment, the optical element of the present invention is used as a diffusion plate that diffuses an image or video emitted from the laser projector and projects it onto a primary mirror.

[0042] 6, the head-up display device 100 includes a laser projector 101 as an image forming device, a diffusion plate 102 arranged on the emission side of the laser projector 101, a primary mirror 103, a secondary mirror 104, and a transmissive reflector 105. In the head-up display device 100 for a vehicle, the transmissive reflector 105 serves as a windshield.

[0043] An image projected from laser projector 101 becomes vertically incident light and enters the second principal surface (second lenticular lens 12) side of diffuser plate 102, and is formed as an intermediate image on the first principal surface (first lenticular lens 11) side. A condenser lens or the like may be disposed between laser projector 101 and diffuser plate 102 to correct the incident angle of the laser light to fall within the aperture angle of the microlenses of diffuser plate 102.

[0044] When optical element 10' is used as diffusion plate 102, the angle of the second principal surface (second lenticular lens 12') of optical element 10' is adjusted to the optimization angle in a state parallel to a plane perpendicular to the incident light between laser projector 101 and primary mirror 103 (concave mirror). Setting of the optimization angle will be described in detail in the section of examples.

[0045] In the head-up display device 100, the size and the like of the diffusion plate 102 may be designed according to the size of the laser projector 101 as a light source and its arrangement relative to the diffusion plate 102. In other words, the size of the optical element of the present invention, each of the lenticular lenses on its first and second main surfaces, and the shape of the microlenses formed by these lenticular lenses may be designed in consideration of the size of the light source and its arrangement relative to the light source.

[0046] The intermediate image formed by the diffusion plate 102 is magnified by the primary mirror 103 (concave mirror), passes through the secondary mirror 104, and is reflected by the transmissive reflector 105 (windshield) to be directed to the driver's eyes. The laser light emitted from the laser projector 101 is reflected by the transmissive reflector 105 and enters the driver's eyes, and at this time, the image displayed as the intermediate image appears to the driver as if it were an image in front of the transmissive reflector 105.

[0047] In this embodiment, an optical correction system including a primary mirror 103 and a secondary mirror 104 is used, but the present invention is not limited to this configuration, and other optical correction systems can be used.

[0048] In this embodiment, a laser projector is used as the image forming device, making it possible to realize a high-resolution image or video. In addition, an optical element using the microlens of the present invention is used as the diffuser, making it possible to realize a high-luminance, higher quality image or video, with the brightness of the emitted light being uniform over the diffusion range. The optical element of the present invention has a thickness of preferably 10 mm or less, more preferably 5 mm or less, since the head-up display device can be made thin. On the other hand, the optical element of the present invention has a thickness of preferably 0.5 mm or more, and may have a thickness of 1 mm or more, from the viewpoint of ensuring the strength of the optical element. The thickness of the optical element of the present invention should not be limited, and may be a film or sheet having a thickness of 0.5 mm or less, or more preferably 0.2 mm or less. By forming the optical element into a film or sheet, there is an advantage that the size of the device equipped with the optical element can be made smaller.

[0049] The optical element of the present invention is used as a diffusion plate and can be suitably used in a head-up display device in which the diffusion angle of light incident on the first main surface and exiting from the second main surface is set in the range of 0 to 26 degrees in the horizontal direction H and 0 to 12 degrees in the vertical direction V. Thus, a head-up display device including the optical element of the present invention also falls within the scope of the present invention.

[0050] 〔summary〕 An optical element according to a first aspect of the present invention is an optical element having a first principal surface and a second principal surface opposed to each other, the first principal surface having a first lenticular lens, the second principal surface having a second lenticular lens, the long axis direction of the first lenticular lens being perpendicular to the long axis direction of the second lenticular lens or intersecting with the long axis direction of the second lenticular lens at an angle within a range of ±70 degrees from the perpendicular direction, and the curved shape of the first lenticular lens being expressed by the following formula (1):

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[0051] In the optical element according to Aspect 2 of the present invention, in Aspect 1, kx is preferably −2.0 or more and −1.0 or less.

[0052] In the optical element according to Aspect 3 of the present invention, in Aspect 1 or 2, ky is preferably −0.8 or more and −0.6 or less.

[0053] The optical element according to aspect 4 of the present invention, in any one of aspects 1 to 3 above, is preferably made of a resin having a refractive index of 1.35 or more and 1.7 or less.

[0054] In the optical element according to aspect 5 of the present invention, in any one of aspects 1 to 4 above, the angular intensity uniformity is preferably 60% or more.

[0055] In the optical element according to aspect 6 of the present invention, in any one of aspects 1 to 5 above, the luminance is preferably 80% or more of the maximum luminance in an angular range of 90% of the full width at half maximum (FWHM).

[0056] The optical element according to aspect 7 of the present invention, in any one of aspects 1 to 6 above, is preferably a diffusion plate.

[0057] In the optical element according to aspect 8 of the present invention, in any one of aspects 1 to 7 above, it is preferable that the curved surface shape of the first lenticular lens is further adjusted according to the following formula (3).

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[0058] In the optical element according to a ninth aspect of the present invention, in any one of the above first to eighth aspects, it is preferable that the curved surface shape of the second lenticular lens is further adjusted according to the following formula (4).

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[0059] In the optical element according to Aspect 10 of the present invention, in any one of Aspects 1 to 9 above, the diffusion plate is preferably used in a head-up display device.

[0060] In the optical element according to an eleventh aspect of the present invention, in any one of the first to tenth aspects, it is preferable that the image forming device in the head-up display device is a laser projector that uses laser light as a light source.

[0061] The optical element according to aspect 12 of the present invention, in any one of aspects 1 to 11 above, is preferably used such that the diffusion angle of light incident on the first main surface and exiting from the second main surface is in the range of 0 to 26 degrees in the horizontal direction H and 0 to 12 degrees in the vertical direction V. EXAMPLES

[0062] The present invention will now be described in more detail with reference to examples.

[0063] [Examples 1 to 23] (Microlens Design) As an example optical element, a diffusion plate made of a microlens array having a first lenticular lens on a first principal surface facing each other and a second lenticular lens on a second principal surface facing each other was simulated with the following design items. <Design matters> The refractive index of the diffusion plate is 1.49, which is the refractive index of acrylic resin. The diffusion shape of the emitted light is rectangular, and for perpendicular incident light, the diffusion angle of the emitted light is 26° in the horizontal direction H and 12° in the vertical direction V, and the light distribution shape in each direction is a top hat shape. Curvature cx: 27mm -1 The curvature cy is 60 mm. -1 It was decided. The pitch Px of the first lenticular lens in the X direction was set to 30±2 μm. The pitch Py of the second lenticular lens in the Y direction was set to 30±2 μm. In the above formulas (1) and (2), the conic constants kx and ky are set as shown in Table 1.

[0064] [Table 1]

[0065] [Light source and receiver] In Examples 1 to 23, the conditions for the light source and the light receiver were as follows. Light source size: 1mm square Light source position: -1mm behind the seat (-Z direction) Number of tracking rays: 10,000,000 Fixed receiver size: 20mm square Fixed receiver position: 0.01 mm in front of the sheet (Z direction)

[0066] (Brightness vs. diffusion angle of emitted light) For Examples 1 to 23, the luminance versus the diffusion angle of the emitted light was derived using geometrical optics simulation software LightTools (Synopsys, Inc.). An optical element was placed on a surface oriented parallel to the X-axis and Y-axis, a lenticular shape was created such that the pitch direction of the first lenticular shape on the emission surface was the X-direction and the pitch direction of the second lenticular shape on the entrance surface was the Y-direction, a light source was set to irradiate collimated light from the entrance surface side of the optical element so as to be parallel to the Z-axis, and angular luminance distribution information was obtained for the light after passing through the optical element. The geometrical optics simulation software LightTools (Synopsys) used in this embodiment is used for research and development in the field of optical materials, including the field to which the present invention belongs, and is a simulation software with a widely known track record. For example, International Publication WO2023 / 053643 compares the simulation results with optical sheets formed based on the simulation results, and the credibility of the simulation results is confirmed. Heat maps are shown in Figures 7 to 11, and graphs are shown in Figures 12 to 16.

[0067] As shown in FIGS. 7 to 16, it was found that the optical element of the present invention can achieve luminance of 80% or more of the maximum luminance at a diffusion angle of 26° in the horizontal direction H and 12° in the vertical direction V.

[0068] [Examples 24 to 31, Comparative Examples 1 and 2] (Microlens Design) As the optical elements of Examples 24 to 31 and Comparative Examples 1 and 2, a diffusion plate consisting of a microlens array having a first lenticular lens on a first main surface and a second lenticular lens on a second main surface was used, and a simulation was performed using the above-mentioned LightTools with the following design items. <Design matters> [Diffusion plate] The refractive index of the diffusion plate was set to 1.49, the same as in Examples 1 to 23. The thickness of the diffusion plate was 2 mm in the Z-axis direction (surface normal direction), and the sheet size was 50 mm square. Curvature cx: 27mm -1 The curvature cy is 60 mm. -1 It was decided. The pitch Px of the first lenticular lens in the X direction was set to 30±2 μm. The pitch Py of the second lenticular lens in the Y direction was set to 30±2 μm. In the above formulas (1) and (2), the conic constant kx was set to -1.6 and the conic constant ky was set to -0.7. The deviation angle θ from the perpendicularity on the xy plane of the first lenticular lens and the second lenticular lens is as shown below. [Table 2]

[0069] [Light source and receiver] The conditions for the light source and the light receiver were as follows: Light source size: 45mm square Light source position: -100mm behind the seat (-Z direction) Number of tracking rays: 10,000,000 Fixed receiver size: 100mm square Fixed receiver position: 3mm in front of the seat (Z direction)

[0070] Figure 17 shows a heat map of the diffusers of Examples 24, 25, 27, and 28 out of Examples 24 to 31 evaluated by simulation based on the above conditions, Figure 18 shows the distribution of the radiant intensity (W / sr) of diffused light in the diffuser plate of Example 25, and Figure 19 shows the distribution of the radiant intensity (W / sr) of diffused light in the diffuser plate of Example 28. 18 and 19, the graphs shown in the upper part show the distribution of radiation intensity (W / sr) along the X-axis direction of the diffuser plate, and the graphs shown in the lower part show the distribution of radiation intensity (W / sr) along the Y-axis direction of the diffuser plate. From each of Fig. 18 and Fig. 19, it can be seen that a top-hat type radiation intensity is obtained when the deviation angle is in the range of 10 to 40 degrees.

[0071] Next, for each of the diffusers of Examples 24 to 31 and Comparative Examples 1 and 2, in order to match the change in the shift angle θ, the optimization angle of the angle-adjustable receiver based on the fixed receiver was set as shown in Table 2 above. The optimized angles in Table 2 were set so that the aforementioned angular intensity uniformity (= (minimum radiation intensity) / (maximum radiation intensity) × 100%), which is an index of angular intensity uniformity, was maximized within the angle range ((1) to (3) described below).

[0072] Next, the diffusion shape of the emitted light for the angle-adjusted receiver adjusted to the optimized angle was set to a rectangle, and the diffusion angle of the emitted light for perpendicular incident light was set to the following angle ranges (1) to (3) in each of the horizontal direction H and vertical direction V.

[0073] [Table 3] The reference starting point of the angle range is the point where the center line of the incident light (for example, perpendicular incident light) intersects with the optical element (diffuser plate).

[0074] The angle ranges in Table 3 were set using the optimization function of LightTools, based on the conditions in angle range (3). The optimization conditions were as follows: Number of rays traced: 100,000 Result output: 2 degree intervals Smoothing: 3 cells Analysis coordinate system: IES Type B Receiver filter: Only the light that passed through the front and back shapes of the diffuser was counted.

[0075] Under the conditions of each of Examples 24 to 31 and Comparative Examples 1 and 2, the angular intensity uniformity was calculated from the maximum and minimum values ​​of the radiant intensity (W / sr) based on the following formula. Angular intensity uniformity = ((minimum radiant intensity) / (maximum radiant intensity)) x 100% The minimum and maximum radiation intensity values ​​were determined as the minimum and maximum radiation intensity values ​​when optimized within the angle range (1) to (3).

[0076] Fig. 20 shows a graph plotting the results of the angular intensity uniformity in each of Examples 24 to 31 and Comparative Examples 1 and 2. The angle ranges (1) to (3) shown in Fig. 20 correspond to the angle ranges shown in Table 3. Fig. 20 shows that in all of the angle ranges (1) to (3), the angular intensity uniformity tends to increase when the deviation angle from the perpendicular is less than 70 degrees, and that the angular intensity uniformity increases more significantly when the deviation angle from the perpendicular is 40 degrees or less.

[0077] Fig. 21 shows heat maps for each of the angle ranges (1) to (3) for the diffuser of Example 28 (shift angle 40 degrees), and Fig. 22 shows heat maps for each of the angle ranges (1) to (3) for the diffuser of Example 29 (shift angle 50 degrees). From the heat maps for the angle range conditions shown in Fig. 21 and Fig. 22, it can be seen that the radiation intensity tends to be more uniform and the brightness higher when the shift angle from the perpendicular in the lenticular lens is 40 degrees rather than 50 degrees. [Explanation of symbols]

[0078] 10, 10' Optical elements 10a, 10'a Micro Lenses 11a 1st main surface 11 First lenticular lens L 11 Central axis (first lenticular lens) 12a, 12'a 2nd principal surface 12 Second lenticular lens L 12 Central axis (second lenticular lens) 100 Head-up display device 101 Laser Projector 102 Diffuser (optical element) 103 Primary mirror 104 Secondary Mirror 105 Transparent reflector

Claims

1. An optical element having opposing first and second principal surfaces, the first major surface has a first lenticular lens; the second major surface has a second lenticular lens; the long axis direction of the first lenticular lens is perpendicular to the long axis direction of the second lenticular lens, or intersects with the long axis direction of the second lenticular lens at an angle within a range of ±70 degrees from the perpendicular direction; The curved surface shape of the first lenticular lens is expressed by the following formula (1): [0010] [In formula (1), cx represents a curvature [1 / mm], x represents a distance [mm] from the central axis of the first lenticular lens in the X direction, and kx represents a conic constant, which is −2.4 or more and −0.6 or less.] An optical element in which the curved surface shape of the second lenticular lens is expressed by the following formula (2): [0025] [In formula (2), cy represents a curvature [1 / mm], y represents a distance [mm] from the central axis of the second lenticular lens in the Y direction, and ky represents a conic constant, which is −0.9 or more and −0.5 or less.]

2. 2. The optical element according to claim 1, wherein the kx is not less than −2.0 and not more than −1.

0.

3. 2. The optical element according to claim 1, wherein the ky is not less than −0.8 and not more than −0.

6.

4. 2. The optical element according to claim 1, wherein the optical element is made of a resin having a refractive index of 1.35 or more and 1.7 or less.

5. The optical element of claim 1 , wherein the optical element has an angular intensity uniformity of 60% or greater.

6. The optical element according to claim 1 , wherein the optical element has a brightness of 80% or more of the maximum brightness over an angular range of 90% of the full width at half maximum (FWHM).

7. 2. The optical element according to claim 1, wherein the optical element is a diffuser plate.

8. 2. The optical element according to claim 1, wherein the curved shape of the first lenticular lens is further adjusted according to the following formula (3): [0030] [In formula (3), A represents a symmetric coefficient. B represents an asymmetric coefficient, which is −1.]

9. 2. The optical element according to claim 1, wherein the curved shape of the second lenticular lens is further adjusted according to the following formula (4): [0045] [In formula (4), A represents a symmetric coefficient. B represents an asymmetric coefficient, which is equal to 1.]

10. The optical element according to claim 7 , wherein the diffusion plate is used in a head-up display device.

11. 11. The optical element according to claim 10, wherein the image forming device in the head-up display device is a laser projector that uses laser light as a light source.

12. The optical element according to any one of claims 1 to 11, wherein the diffusion angle of light incident on the first main surface and exiting from the second main surface is in the range of 0 to 26 degrees in the horizontal direction H and 0 to 12 degrees in the vertical direction V.

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