Image display device

Abstract

The present invention addresses the problem of providing an image display device having high color purity of light for displaying an image. This image display device solves the problem by comprising: a plurality of light sources; a spectroscopic element which disperses light emitted from the light source; and an optical shutter array which is disposed on the optical path of the light dispersed by the spectroscopic element and in which a plurality of shutter parts is disposed.

Description

Image display device

[0001] The present invention relates to an image display device.

[0002] In contrast to liquid crystal display devices that use color filters, image display devices that do not use color filters and that use MEMS (Micro Electro Mechanical Systems) shutter devices have been proposed. In the following description, image display devices that use MEMS shutter devices are also referred to as "MEMS display devices."

[0003] For example, Patent Document 1 describes an image display device having a MEMS shutter device that includes a backlight that emits light and an opening that transmits the light emitted from the backlight and opens and closes the opening to control the amount of light that passes through the opening.The image display device has an absorptive polarizer and a λ / 4 wavelength plate that are arranged in this order from the viewing side of the MEMS shutter device, and a reflective polarizer that is arranged closer to the backlight than the λ / 4 wavelength plate.

[0004] JP 2017-15766 A

[0005] By providing an opening in the MEMS shutter device in the reflector, the MEMS display device allows light emitted from the backlight that does not head directly toward the opening to bounce between the reflector and the backlight and be directed toward the opening, thereby transmitting through the opening. Therefore, the MEMS display device has a higher utilization efficiency of the light emitted from the backlight than a liquid crystal display device. Furthermore, because this MEMS display device does not use a color filter, it is said to have a higher utilization efficiency of the light emitted from the backlight than a liquid crystal display device that uses a color filter to split white light.

[0006] In particular, according to the MEMS display device described in Patent Document 1, even when the display screen is made higher resolution, it is possible to maintain high light utilization efficiency and high front brightness, while significantly suppressing external light reflection and improving visibility, thereby achieving both high front brightness and improved visibility due to suppression of external light reflection.

[0007] Conventional MEMS display devices display images using light emitted by a backlight light source. Therefore, the color purity of each color emitted by the backlight, i.e., the color purity of the light used to display an image, is determined by the emission spectrum of the light source. In order to widen the color gamut of a displayed image, it is advantageous to have high color purity of the light used to display an image. However, as described above, in conventional MEMS display devices that do not use color filters, the color purity of each color of light emitted by the backlight is determined by the emission spectrum of the light source.

[0008] Therefore, in a conventional MEMS display device that does not use a color filter, it is difficult to increase the color purity of the light used to display an image.

[0009] The object of the present invention is to solve these conventional problems and to provide an image display device that displays images by turning on / off light of each color using an optical shutter array, without using color filters, and that has high color purity for the light that displays the image.

[0010] To solve this problem, the present invention has the following configuration. [1] An image display device having a plurality of light sources, a spectroscopic element that spectroscopically separates light emitted from the light sources, and an optical shutter array having a plurality of shutter sections arranged on the optical path of the light dispersed by the spectroscopic element. [2] The image display device according to [1], wherein the spectroscopic element is any one of a surface relief diffraction element, a hologram, a metasurface, and a liquid crystal diffraction element. [3] The image display device according to [1] or [2], wherein a polarizing element is provided on the side of the spectroscopic element opposite to the light source. [4] The image display device according to any one of [1] to [3], wherein the light emitted from the light source is parallel light. [5] The image display device according to any one of [1] to [4], wherein the light emitted from the light source includes at least a portion of light in a wavelength range of 400 to 480 nm, at least a portion of light in a wavelength range of 520 to 570 nm, and at least a portion of light in a wavelength range of 620 to 680 nm. [6] The image display device according to any one of [1] to [5], which has a circular polarizing plate on the side of the optical shutter array opposite to the light-splitting element. [7] The image display device according to [6], wherein the circular polarizing plate has a λ / 4 retardation plate and a linear polarizer, and the λ / 4 retardation plate is a patterned retardation plate having a plurality of regions having the same retardation but different slow axis directions from each other.

[0011] According to the image display device of the present invention, in an image display device that displays an image by turning on / off light of each color with an optical shutter array, an image display device is provided in which the color purity of the light that displays the image is high.

[0012] FIG. 1 is a diagram conceptually showing an example of an image display device of the present invention. FIG. 2 is a front view conceptually showing an example of a liquid crystal diffraction element. FIG. 3 is a schematic plan view of the liquid crystal diffraction element shown in FIG. 2. FIG. 4 is a conceptual diagram for explaining the function of the liquid crystal diffraction element. FIG. 5 is a conceptual diagram for explaining the function of the liquid crystal diffraction element. FIG. 6 is a conceptual diagram for explaining an example of an optical shutter array. FIG. 7 is a diagram conceptually showing an example of an image display device of the present invention.

[0013] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The image display device of the present invention will be described in detail below with reference to preferred embodiments shown in the accompanying drawings.

[0014] In this specification, a numerical range expressed using "to" means a range that includes the numerical values ​​before and after "to" as the lower and upper limits. In this specification, "same," "equal," etc. are intended to include a generally accepted error range in the technical field. Furthermore, in this specification, of visible light, blue light refers to light in the wavelength range of 380 to 490 nm, green light refers to light in the wavelength range of more than 490 nm and not more than 600 nm, and red light refers to light in the wavelength range of more than 600 nm and not more than 750 nm, although this specification is not limited thereto.

[0015] The drawings shown below are conceptual diagrams for explaining the image display device of the present invention, and therefore the thickness, size, shape, and positional relationship of each member and component may differ from the actual ones.

[0016] Fig. 1 conceptually shows an example of an image display device of the present invention. The image display device 10 shown in Fig. 1 includes two-dimensionally arranged light sources 12, a spectroscopic element 14 that disperses light emitted by the light sources 12, a polarizing element 16 that polarizes the light dispersed by the spectroscopic element 14, an optical shutter array 18, and a circular polarizing plate 26. The circular polarizing plate 26 includes a linear polarizer 20 and a λ / 4 retardation plate 24. In the present invention, the polarizing element 16 and the circular polarizing plate 26 are provided as a preferred embodiment.

[0017] In the image display device 10 shown in FIG. 1 , the light source 12 emits white light, for example. The white light emitted by the light source is split into light of each wavelength by a spectroscopic element 14. The light split by the spectroscopic element 14 is deflected by a deflection element 16 in a direction perpendicular to the image display surface of the image display device 10. The light deflected by the deflection element 16 then enters an optical shutter array 18. The optical shutter array 18 has apertures that transmit only specific wavelengths of red light (solid line), green light (dashed line), and blue light (dotted line) used for image display, and blocks other light. Each aperture is provided with a shutter that blocks / transmits, i.e., turns on / off, the red, green, and blue light passing through each aperture. The image display device 10 displays images by turning on / off (modulating) the red, green, and blue light using the optical shutter array 18. The red, green and blue light transmitted through the optical shutter array 18 is transmitted through a λ / 4 retardation plate 24 and a circular polarizer 26 having a linear polarizer 20, and is emitted from the image display device 10, whereby an image is displayed.

[0018] In the image display device 10 of the present invention, as an example, the light sources 12 are arranged two-dimensionally in two orthogonal directions (x-y directions). There are no limitations on the arrangement of the light sources 12, and the arrangement may be set appropriately depending on, for example, the pixel arrangement of the image display in the image display device 10 and the light separation by the spectroscopic element 14. Therefore, the arrangement of the light sources 12 may be regular or irregular, but is usually regular in two orthogonal directions (x-y directions). Note that the arrangement interval of the light sources 12 in the x-direction and the arrangement interval of the light sources 12 in the y-direction may be the same or different.

[0019] In the image display device 10 of the present invention, the light source 12 is not limited, and various known light sources can be used. Examples include a light source that combines a surface light source, such as an LED (light-emitting diode), an organic electroluminescence (EL) light-emitting element, a laser light source, or a light source formed of an array of fluorescent lamps, with a light-shielding plate having multiple pinholes. The light source may be a white light source, such as a white LED or a white organic EL light-emitting element, or a monochromatic light source, such as a red light source, a green light source, and a blue light source. When a monochromatic light source is used, multiple types of light sources may be used, such as three light sources: a red light source, a green light source, and a blue light source.

[0020] A white light source is preferably used as the light source 12. As described above, in FIG. 1, the light source 12 is a white light source. Specifically, a light source that emits light including red light, green light, and blue light is preferably used as the light source 12. More preferably, the light source 12 emits light including at least a portion of light in the wavelength range of 400 to 480 nm, at least a portion of light in the wavelength range of 520 to 570 nm, and at least a portion of light in the wavelength range of 620 to 680 nm. Using a light source that emits light in such wavelength ranges as the light source 12 is preferable in that it enables full-color images to be displayed, images with good color reproducibility to be displayed, and color unevenness in the displayed image can be reduced.

[0021] Furthermore, in the image display device 10 of the present invention, the light source 12 is preferably a light source that emits parallel light rather than diffused light. Light source 12 emitting parallel light is preferable in that it enables image display using light with higher color purity, improves light utilization efficiency, etc. As the light source 12 that emits parallel light, various known light sources that emit parallel light can be used, such as commercially available parallel light light sources (collimated light sources, collimated lights) and light sources that combine a light emitting element that emits diffused light with a collimating lens.

[0022] In the image display device 10, light emitted from the light source 12 is separated into light of each wavelength by the spectroscopic element 14. The spectroscopic element 14 can be any of various known transmissive spectroscopic elements that separate incident light according to wavelength. Examples of the spectroscopic element 14 include a surface relief diffraction element having a surface with irregularities corresponding to a periodic structure serving as a diffraction element, a hologram fabricated to diffract visible light using known techniques such as computer-generated holography and interference exposure, a metasurface (metasurface structure, metamaterial) formed by an array of microstructures (resonators) sized according to the wavelength of the diffracted light, and various transmissive diffraction elements such as the liquid crystal diffraction element described below. Various known diffraction elements can be used. Among these, metasurfaces and liquid crystal diffraction elements are preferred examples in terms of light utilization efficiency related to the circular polarizer 26 described below, and liquid crystal diffraction elements are particularly preferred. In the image display device 10 shown in FIG. 1, the spectroscopic element 14 is a liquid crystal diffraction element.

[0023] 2 and 3 conceptually show an example of a liquid crystal diffraction element 42 as the spectroscopic element 14. FIG. 2 is a front view of the liquid crystal diffraction element 42, and FIG. 3 is a plan view. The front view is a view of the liquid crystal diffraction element 42 viewed in the direction of the principal surface, and the plan view is a view of the liquid crystal diffraction element 42 viewed in a direction perpendicular to the principal surface, i.e., the normal direction. The principal surface is the largest surface of a sheet-like object (plate-like object, film, layer), and is usually both sides in the thickness direction.

[0024] The liquid crystal diffraction element 42 is a cured layer of a liquid crystal composition containing a liquid crystal compound, i.e., a liquid crystal layer (optically anisotropic layer). The spectroscopic element 14 using the liquid crystal diffraction element 42 may have an alignment film for aligning the liquid crystal compound of the liquid crystal diffraction element 42 (liquid crystal layer) and / or a support layer for supporting the liquid crystal diffraction element, or may have other layers as necessary.

[0025] The liquid crystal diffraction element 42 is a liquid crystal layer formed by fixing a liquid crystal phase in which a liquid crystal compound 40c is oriented. The liquid crystal layer has a liquid crystal orientation pattern in which the direction of the optical axis 40A derived from the liquid crystal compound 40c changes while continuously rotating along at least one direction in the plane. The optical axis 40A derived from the liquid crystal compound 40c is the axis along which the refractive index of the liquid crystal compound 40c is highest, i.e., the so-called slow axis. In Figures 2 and 3, a rod-shaped liquid crystal compound is exemplified as the liquid crystal compound 40c, so the optical axis 40A is aligned along the long axis of the rod shape. Note that when the liquid crystal compound is a discotic liquid crystal compound, the optical axis derived from the discotic liquid crystal compound is perpendicular to the disc surface of the discotic liquid crystal compound. In the following description, the "optical axis derived from the liquid crystal compound" will also be simply referred to as the "optical axis of the liquid crystal compound" or "optical axis."

[0026] As shown in FIG. 3, the liquid crystal compound 40c constituting the liquid crystal diffraction element 42 has a liquid crystal orientation pattern in which the orientation of the optical axis 40A changes while continuously rotating along a predetermined direction indicated by arrow D (hereinafter referred to as the alignment axis D) within the plane of the liquid crystal diffraction element 42. In the illustrated example, the liquid crystal orientation pattern is such that the optical axis 40A of the liquid crystal compound 40c changes while continuously rotating clockwise along the alignment axis D direction. The liquid crystal compound 40c constituting the liquid crystal diffraction element 42 is two-dimensionally aligned along the alignment axis D and a direction perpendicular to this direction (the alignment axis D direction). In the following description, the direction perpendicular to the alignment axis D direction is referred to as the Y direction for convenience. That is, the arrow Y direction is the direction perpendicular to the direction in which the orientation of the optical axis 40A of the liquid crystal compound 40c changes while continuously rotating within the plane of the liquid crystal diffraction element 42. 1 to 7, the direction of the array axis D is the horizontal direction in the drawings, and therefore, in FIGS. 1, 2, and 4 to 7, the Y direction is the direction perpendicular to the paper surface.

[0027] The expression "the orientation of the optical axis 40A of the liquid crystal compound 40c changes while continuously rotating in the direction of the alignment axis D (a predetermined direction)" specifically means that the angle formed between the optical axis 40A of the liquid crystal compound 40c aligned along the direction of the alignment axis D and the direction of the alignment axis D varies depending on the position in the direction of the alignment axis D, and the angle formed between the optical axis 40A and the direction of the alignment axis D sequentially changes from θ to θ+180° or θ−180° along the direction of the alignment axis D. In the liquid crystal diffraction element 42 shown in FIGS. 2 and 3, as an example, the optical axis 40A of the liquid crystal compound 40c rotates rightward (clockwise) along the direction of the alignment axis D.

[0028] On the other hand, the liquid crystal compounds 40c forming the liquid crystal diffraction element 42 have the same orientation of the optical axes 40A in the Y direction perpendicular to the direction of the array axis D, i.e., the Y direction perpendicular to the direction in which the optical axes 40A change while continuously rotating. In other words, the liquid crystal compounds 40c forming the liquid crystal diffraction element 42 have the same angle between the optical axes 40A of the liquid crystal compounds 40c and the direction of the array axis D in the Y direction. A region R is defined as a region in which the liquid crystal compounds 40c having the same angle between their optical axes 40A and the direction of the array axis D are arranged in the Y direction.

[0029] As described above, in the liquid crystal diffraction element 42, in the liquid crystal orientation pattern of the liquid crystal compound 40c, the length (length Λ (distance)) over which the optical axis 40A of the liquid crystal compound 40c rotates 180° in the direction of the arrangement axis D, in which the optical axis 40A continuously rotates and changes in the plane, is defined as one period Λ in the liquid crystal orientation pattern. That is, the distance between the centers of two liquid crystal compounds 40c in the direction of the arrangement axis D, which are at the same angle with respect to the direction of the arrangement axis D, is defined as one period Λ. Specifically, as shown in FIGS. 2 and 3, the distance between the centers of two liquid crystal compounds 40c in the direction of the arrangement axis D, in which the direction of the optical axis 40A coincides with the direction of the arrangement axis D, is defined as one period Λ. The liquid crystal orientation pattern of the liquid crystal diffraction element 42 repeats this one period Λ in the direction of the arrangement axis D, i.e., in one direction in which the orientation of the optical axis 40A continuously rotates and changes. In the liquid crystal diffraction element 42 having such a liquid crystal orientation pattern, this one period Λ is one period of the periodic structure in the diffraction element.

[0030] A liquid crystal diffraction element 42 having such a liquid crystal orientation pattern diffracts (refracts) incident circularly polarized light along the alignment axis D, transmits the light, and converts the polarization direction of the circularly polarized light. The liquid crystal diffraction element 42 has a product of the refractive index difference of the liquid crystal compound and the thickness of the image display device of λ / 2. In addition, in FIGS. 4 and 5, only the liquid crystal compound 40c on the surface is shown to show the rotation direction of the optical axis in the liquid crystal orientation pattern of the liquid crystal diffraction element 42, but the liquid crystal diffraction element 42 has stacked liquid crystal diffraction elements 42 as shown in FIG. 2.

[0031] As shown in Figure 4, when the product of the refractive index difference between the liquid crystal compounds of the liquid crystal diffraction element 42 and the thickness of the liquid crystal diffraction element 42 is λ / 2, when left-handed circularly polarized incident light L1 is incident on the liquid crystal diffraction element 42, the incident light L1 is given a phase difference of 180° as it passes through the liquid crystal diffraction element 42, and the transmitted light L2 is converted to right-handed circularly polarized light. Furthermore, because the liquid crystal orientation pattern formed on the liquid crystal diffraction element 42 is a periodic pattern in the direction of the array axis D, the transmitted light L2 travels in a direction different from the traveling direction of the incident light L1. In this way, the left-handed circularly polarized incident light L1 is converted to right-handed circularly polarized transmitted light L2, which is tilted at a certain angle in the direction of the array axis D with respect to the incident direction.

[0032] On the other hand, as shown in Figure 5, when the product of the refractive index difference between the liquid crystal compounds of the liquid crystal diffraction element 42 and the thickness of the liquid crystal diffraction element 42 is λ / 2, when right-handed circularly polarized incident light L4 is incident on the liquid crystal diffraction element 42, the incident light L4 is given a phase difference of 180° as it passes through the liquid crystal diffraction element 42 and is converted into left-handed circularly polarized transmitted light L5. Furthermore, because the liquid crystal orientation pattern formed on the liquid crystal diffraction element 42 is a periodic pattern in the direction of the array axis D, the transmitted light L5 travels in a direction different from the traveling direction of the incident light L4. At this time, the transmitted light L5 travels in a different direction from the transmitted light L2, that is, in the direction opposite to the direction of the arrow of the array axis D with respect to the incident direction. In this way, the incident light L4 is converted into left-handed circularly polarized transmitted light L5 that is tilted at a certain angle in the direction opposite to the direction of the array axis D with respect to the incident direction.

[0033] Like various diffraction elements, the liquid crystal diffraction element 42 can adjust the diffraction angles of the transmitted light L2 and the transmitted light L5 by adjusting the length of one period Λ of the formed liquid crystal orientation pattern. Specifically, the shorter the period Λ of the liquid crystal orientation pattern, the stronger the interference between lights that have passed through adjacent liquid crystal compounds, and therefore the liquid crystal diffraction element 42 can diffract (refract) the transmitted light L2 and the transmitted light L5 to a greater extent.

[0034] The direction of diffraction of transmitted light can be reversed by reversing the direction of rotation of the optical axis 40A of the liquid crystal compound, which rotates along the direction of the alignment axis D. That is, in the examples shown in Figures 4 and 5, the direction of rotation of the optical axis 40A pointing toward the direction of the alignment axis D is clockwise, but by changing this rotation direction to counterclockwise, the direction of diffraction of transmitted light can be reversed.

[0035] Therefore, when unpolarized light is incident on the liquid crystal diffraction element 42, the light is refracted in opposite directions, with the right-handed circularly polarized component and the left-handed circularly polarized component. In the examples shown in Figures 4 and 5, the left-handed circularly polarized component is converted to right-handed circularly polarized light and refracted to the left in Figure 1 (the direction of the array axis D), and the right-handed circularly polarized component is converted to left-handed circularly polarized light and refracted to the right in Figure 1.

[0036] As is well known, in a transmission-type diffraction element, the diffraction angle (refraction angle) of transmitted light depends on the wavelength of the incident light. As with various diffraction elements, in the liquid crystal diffraction element 42, the diffraction angle of transmitted light also depends on the wavelength of the incident light. Specifically, in a transmission-type diffraction element, the longer the wavelength of the incident light, the larger the diffraction angle of the transmitted light. Therefore, when light of a certain wavelength range is incident on the liquid crystal diffraction element 42 (diffraction element), the incident light is split according to the wavelength in the repeating direction of the periodic structure of the diffraction element, i.e., in the direction of the array axis D, with light of long wavelengths being largely diffracted and light of short wavelengths being transmitted at a small diffraction angle, and each light travels in a different direction.

[0037] That is, in the image display device 10 shown in FIG. 1 , white light emitted by the light source 12 and incident on the spectroscopic element 14 is split by the spectroscopic element 14 (liquid crystal diffraction element 42) in the direction of the array axis D, with red light (solid line) traveling in a large diffraction angle, blue light (dash-dotted line) traveling in a small diffraction angle, and green light (dashed line) traveling in a diffraction angle between the two. Note that in FIG. 1 , the direction of the array axis D, i.e., the direction of light splitting, is the horizontal direction in the figure. Furthermore, even for light of the same color, light is split in the direction of the array axis D according to wavelength, with light of longer wavelengths traveling in a large diffraction angle and light of shorter wavelengths traveling in a small diffraction angle, each traveling in a different direction. For example, in the case of red light with a wavelength of 620 to 680 nm, light of a wavelength of 620 nm travels in the smallest diffraction angle, light of a wavelength of 680 nm travels in the largest diffraction angle, and light of a wavelength of 650 nm travels in an intermediate diffraction angle, each traveling in a different direction. Note that, as mentioned above, the diffraction angle can be adjusted by the length of one period Λ.

[0038] As described above, the image display device 10 shown in the figure uses a liquid crystal diffraction element 42 as the spectroscopic element 14. Therefore, light incident on the spectroscopic element 14, i.e., the liquid crystal diffraction element 42, is separated into right-handed circularly polarized light and left-handed circularly polarized light according to the circular polarization component, and then dispersed. Therefore, in the image display device 10 shown in the figure, one light source 12 corresponds to two pixels of one image consisting of three subpixels (red, green, and blue) in the direction of light dispersion, i.e., the direction of light diffraction. On the other hand, in the direction perpendicular to the direction of light dispersion, one light source 12 corresponds to one pixel of the image. Note that the direction of light dispersion, i.e., the direction of light diffraction, is the direction in which the optical axis 40A of the liquid crystal orientation pattern of the liquid crystal diffraction element 42 continuously rotates and changes, i.e., the direction of the arrangement axis D.

[0039] The light dispersed by the spectroscopic element 14 then enters the deflection element 16. That is, the deflection element 16 is disposed on the opposite side of the spectroscopic element 14 from the light source 12. As conceptually shown in FIG. 1 , the deflection element 16 is an element that deflects the traveling direction of the light diffracted and dispersed by the spectroscopic element 14 in a direction (normal direction) perpendicular (substantially perpendicular) to the display surface of the image display device 10. In other words, the deflection element 16 is an element that outputs the light of each wavelength diffracted and dispersed by the spectroscopic element 14, with the direction perpendicular to the display surface of the image display device 10 being the maximum direction of the intensity distribution. In the image display device 10 shown in the figure, as an example, the display surface is the main surface of the linear polarizer 20 that constitutes the circular polarizer 26.

[0040] By providing such a deflecting element 16, the image display device 10 can emit light, i.e., an image, in the forward direction. Note that the deflecting element 16 is provided as a preferred embodiment and is not an essential component of the image display device of the present invention. That is, the image display device 10 of the present invention may be used for image display without deflecting the traveling direction of the light dispersed by the spectroscopic element 14.

[0041] Furthermore, in the image display device of the present invention, the position of the deflector 16 is not limited to between the spectroscopic element 14 and the optical shutter array 18, and may be, for example, between the optical shutter array 18 and the circular polarizer 26. In other words, the deflector 16 may be located downstream of the spectroscopic element 14. Here, "downstream" means downstream in the traveling direction of the light emitted by the light source 12.

[0042] In the image display device 10 of the present invention, the deflection element 16 is not limited, and various known optical elements can be used as long as they can refract or diffract incident light and deflect the traveling direction of light incident from an oblique direction to a direction perpendicular to the display surface of the image display device 10. Examples include various optical elements that refract light, such as a prism, a cylindrical lens, a prism sheet, and a lenticular lens. In addition, diffraction elements such as a transmission type surface relief diffraction element and a transmission type hologram can also be used as the deflection element 16.

[0043] Furthermore, if the spectroscopic element 14 is a diffraction element that diffracts circularly polarized light in the opposite direction depending on the rotation direction, such as the liquid crystal diffraction element 42 shown in the figure, the same spectroscopic element 14 (diffraction element) can also be used as the deflection element 16. As an example, the liquid crystal diffraction element 42 used as the spectroscopic element 14 converts left-handed circularly polarized light into right-handed circularly polarized light and diffracts it to the left in FIG. 1 , and converts right-handed circularly polarized light into left-handed circularly polarized light and diffracts it to the right in FIG. 1 . Therefore, by using the same liquid crystal diffraction element 42 as the deflection element 16, right-handed circularly polarized light traveling to the left in the figure is converted into left-handed circularly polarized light and diffracted to the right in the figure, and left-handed circularly polarized light traveling to the right in the figure is converted into right-handed circularly polarized light and diffracted to the left in the figure. As a result, light transmitted through the deflection element 16 can be deflected in a direction perpendicular to the display surface of the image display device 10.

[0044] The light deflected by the deflection element 16 then enters the optical shutter array 18. The optical shutter array 18 is an optical shutter array that transmits or blocks only light of a predetermined wavelength (wavelength range) from the red light, green light, and blue light that are incident after being split by the spectroscopic element 14, and blocks light of other wavelengths.

[0045] FIG. 6 conceptually illustrates an example of an optical shutter array 18. The optical shutter array 18 illustrated in FIG. 6 is an optical shutter array that uses a MEMS (Micro Electro Mechanical Systems) shutter device and includes a substrate 50 and shutter members 52. Apertures 54 are provided at predetermined intervals in the substrate 50. The apertures 54 are formed two-dimensionally, for example, in a square lattice pattern, and one shutter member 52 is provided for each aperture 54. The shutter member 52 is a plate-shaped light-blocking member that blocks light that passes through the apertures 54. In the illustrated example, one aperture 54 and one shutter member 52 constitute a shutter unit according to the present invention. Furthermore, the areas of the substrate 50 other than the apertures 54 are, for example, entirely black, to block and preferably absorb incident light.

[0046] As described above, in the image display device 10 shown in Fig. 1, the light source 12 emits white light, and the spectroscopic element 14 splits right-handed circularly polarized light and left-handed circularly polarized light into red light, green light, and blue light, respectively. Therefore, in the image display device 10 shown in Fig. 1, the substrate 50 has six openings 54 for each light source 12 in the direction of light splitting (direction of array axis D). Also, in the direction orthogonal to the direction of light splitting (direction of arrow y in Fig. 3), i.e., the direction perpendicular to the plane of the paper, the substrate 50 has one opening 54 for each light source 12.

[0047] 6 , in the optical shutter array 18, the MEMS moves the shutter members 52 in the horizontal direction (direction of arrow a) in the figure to close / open the openings 54, blocking or transmitting red light R indicated by solid lines, green light G indicated by dashed lines, and blue light B indicated by dashed lines that are incident on the openings 54. That is, the optical shutter array 18 moves the shutter members 52 to turn on / off the light that is incident on the openings 54. For example, in the case of displaying a green monochrome image in the image display device 10, as shown in the lower part of FIG. 6 , the shutter members 52 close (off) the openings 54 through which the red light R passes and the openings 54 through which the blue light B passes, and open (on) only the opening 54 through which the green light G enters.

[0048] In the illustrated image display device 10, an image is displayed by turning on / off the red light R, green light G, and blue light B passing through each opening 54 using the optical shutter array 18, depending on the image to be displayed. That is, in the illustrated image display device 10, an image is displayed by modulating the red light R, green light G, and blue light B passing through each opening 54 using the optical shutter array 18, depending on the image to be displayed.

[0049] In the image display device 10 of the present invention, light incident on the optical shutter array 18 is split by the spectroscopic element 14 along the direction of the array axis D according to wavelength. Therefore, light of each split wavelength is incident on the optical shutter array 18 in areas other than the openings 54 of the substrate 50. As described above, the substrate 50 blocks light incident on areas other than the openings 54. In other words, in the image display device 10 of the present invention, only light of a wavelength (wavelength range) that is incident on the openings 54 out of the light split by the spectroscopic element 14 is used for image display. As an example, in the optical shutter array 18 shown in FIG. 6 , red light, for example, red light R with a wavelength of 630 to 640 nm, is incident on the openings 54 and used for image display, while red light of other wavelengths is blocked by the substrate 50. Furthermore, green light, for example, green light G with a wavelength of 530 to 540 nm, is incident on the openings 54 and used for image display, while green light of other wavelengths is blocked by the substrate 50. Furthermore, blue light, for example, blue light B having a wavelength of 450 to 460 nm, is incident on the opening 54 and used for image display, while blue light of other wavelengths is blocked by the substrate 50 .

[0050] As described above, in the image display device 10 of the present invention, by providing the aperture 54 at a position where light of a wavelength used for image display is incident, corresponding to the light dispersed by the spectroscopic element 14, it is possible to extract light of a desired wavelength. Furthermore, the wavelength range of the extracted light can be set by the size of the aperture 54 in the direction of light dispersion (direction of the array axis D). That is, by reducing the size of the aperture 54, the wavelength range of the light passing through can be narrowed. That is, according to the image display device 10 of the present invention, the optical shutter array 18 extracts only light of a wavelength (wavelength range) used for image display from the light dispersed by the spectroscopic element 14, and uses it for image display. As a result, according to the image display device 10 of the present invention, it is possible to display images using light with high color purity, thereby enabling the display of images with a wide color gamut.

[0051] In image display device 10 of the present invention, there is no limitation on the wavelength range of light extracted by openings 54 of optical shutter array 18, but in order to display images using light with high color purity, a narrow wavelength range is preferable. Specifically, the wavelength range of light extracted by openings 54 of optical shutter array 18 is preferably 1 to 20 nm, and more preferably 1 to 10 nm.

[0052] As described above, the illustrated optical shutter array 18 uses a MEMS shutter device. There are no limitations on the MEMS shutter device that can be used in the optical shutter array 18 of the image display device 10 of the present invention, and various known MEMS shutter devices can be used, such as those described in JP-T-2008-533510, JP-A-2014-182211, and Patent Document 1.

[0053] It should be noted that the optical shutter array in the image display device 10 of the present invention is not limited to one using the MEMS shutter device shown in the drawings. In other words, various known optical shutter arrays such as a liquid crystal shutter array and a PLZT (lanthanum-doped lead zirconate titanate) optical shutter array can be used in the image display device 10 of the present invention.

[0054] The light transmitted through the optical shutter array 18 then enters the circular polarizer 26. That is, the circular polarizer 26 is disposed on the opposite side of the optical shutter array 18 from the light separating element 14. In the illustrated example, the circular polarizer 26 is a known circular polarizer used as an anti-reflection plate in various image display devices, which includes a linear polarizer 20 on the image display surface side, i.e., the outer side, and a λ / 4 retardation plate 24. That is, the circular polarizer 26 converts external light incident on the image display device 10 from the outside into linearly polarized light in a predetermined direction by the linear polarizer 20, and then converts it into circularly polarized light by the λ / 4 retardation plate 24. This circularly polarized light is reflected inside the device, with its rotation direction reversed, and re-enters the λ / 4 retardation plate 24. Therefore, the λ / 4 retardation plate 24 converts the re-entered circularly polarized light with its rotation direction reversed into linearly polarized light perpendicular to the incident light. As a result, the linear polarizer 20 blocks the linearly polarized light. The circular polarizer 26 thereby prevents reflection of external light.

[0055] Therefore, there are no limitations on the linear polarizer 20 and the λ / 4 retardation plate 24 that constitute the circular polarizer 26. The linear polarizer 20 may be a reflective polarizer or an absorptive polarizer, and various known linear polarizers can be used, such as an iodine-based polarizer, a dye-based polarizer using a dichroic dye, a polyene-based polarizer, a wire-grid polarizer, and a film obtained by stretching a dielectric multilayer film as described in JP 2011-053705 A. Absorptive polarizers such as iodine-based polarizers and dye-based polarizers are particularly suitable. The λ / 4 retardation plate 24 can also be various known λ / 4 plates, such as a stretched polycarbonate film, a stretched norbornene-based polymer film, a transparent film containing and oriented inorganic particles such as strontium carbonate, a thin film obtained by obliquely depositing an inorganic dielectric on a support, a film obtained by uniaxially aligning and fixing a polymerizable liquid crystal compound, and a film obtained by uniaxially aligning and fixing a liquid crystal compound.

[0056] Here, as in the image display device 10 shown in FIG. 1 , when a liquid crystal diffraction element 42 that separates and disperses incident unpolarized light into right-handed circularly polarized light and left-handed circularly polarized light is used as the spectroscopic element 14, it is preferable to use a patterned retardation plate having multiple regions with equal phase difference but different slow axis directions as the λ / 4 retardation plate 24. Also, when a metasurface is used as the spectroscopic element 14, it is possible to separate and disperse incident unpolarized light into right-handed circularly polarized light and left-handed circularly polarized light, similar to a liquid crystal diffraction element, by using an arrangement of microstructures, etc. Therefore, in this case, as with the liquid crystal diffraction element 42, it is preferable to use a patterned retardation plate as the λ / 4 retardation plate 24 having multiple regions with equal phase difference but different slow axis directions as the spectroscopic element.

[0057] In the image display device 10A conceptually shown in FIG. 7 , when a surface relief diffraction element, a hologram, or the like is used as the spectroscopic element 30, when white light is incident, the spectroscopic element 30 does not separate the incident light into right-handed and left-handed circularly polarized light. That is, the separated light is unpolarized and diffracted in one direction. In this case, the unpolarized light that passes through the optical shutter array 18 and enters the circular polarizer 26 is converted by the λ / 4 phase difference plate 24 into right-handed and left-handed circularly polarized light components that are orthogonal to each other, resulting in the linear polarizer 20 blocking one of the linearly polarized light components. That is, in this case, the utilization efficiency of the light that passes through the optical shutter array 18 is halved, resulting in low light utilization efficiency.

[0058] In contrast, when a liquid crystal diffraction element 42 (metasurface) is used as the spectroscopic element 14, the light that is split by the spectroscopic element 14 and passes through the optical shutter array 18 contains right-handed and left-handed circularly polarized light separated (diffracted) in opposite directions. Accordingly, when a liquid crystal diffraction element 42 is used as the spectroscopic element 14, a patterned retardation plate is preferably used as the λ / 4 retardation plate 24, with an equal phase difference (λ / 4) and different slow axis directions in the regions where right-handed circularly polarized light is incident and the regions where left-handed circularly polarized light is incident. Specifically, the patterned retardation plate sets the slow axis in the region where right-handed circularly polarized light is incident so that the converted linearly polarized light passes through the linear polarizer 20. On the other hand, the region where left-handed circularly polarized light is incident so that the slow axis direction is perpendicular to that in the region where right-handed circularly polarized light is incident so that the converted linearly polarized light also passes through the linear polarizer 20. This allows the image display device 10 to use all of the light that passes through the optical shutter array 18 for image display, thereby improving light utilization efficiency.

[0059] As such a patterned retardation plate, for example, known patterned retardation plates described in JP-A-2015-45874 and JP-A-2013-11800 can be used.

[0060] The effect of using such a patterned retarder is the same whether a liquid crystal diffraction element 42 or a metasurface is used as the spectroscopic element. However, metasurfaces have the problem of low diffraction efficiency at wavelengths other than the central wavelength of the design. In contrast, liquid crystal diffraction elements can achieve high diffraction efficiency for light in a wide wavelength range by, for example, using a stacked structure in which liquid crystal layers are stacked. Considering this, it is preferable to use a liquid crystal diffraction element as the spectroscopic element. Specifically, a liquid crystal diffraction element with stacked liquid crystal layers has a liquid crystal orientation pattern as shown in Figures 2 and 3, in which the liquid crystal compound is helically twisted in the thickness direction by 360° or less. As an example, a three-layer liquid crystal diffraction element is preferably used, in which a liquid crystal layer in which the liquid crystal compound is not twisted in the thickness direction is provided between two liquid crystal layers in which the helical liquid crystal compound has the same twist angle but opposite twist directions (right-handed twist and left-handed twist). Such a liquid crystal diffraction element is described in detail in WO 2022 / 050321 and the like.

[0061] The image display device of the present invention has been described in detail above, but the present invention is not limited to the above examples, and various improvements and modifications may be made within the scope of the present invention.

[0062] It can be suitably used for displaying various images.

[0063] 10, 10A Image display device 12 Light source 14, 30 Spectroscopic element 16 Deflection element 18 Optical shutter array 20 Linear polarizer 24 λ / 4 retardation plate 26 Circular polarizer 40A Optical axis 40c Liquid crystal compound 42 Liquid crystal diffraction element 50 Substrate 52 Shutter member 54 Aperture R Red light G Green light B Blue light D Arrangement axis R Area Λ One period L1, L4 Incident light L2, L5 Transmitted light

Claims

1. An image display device comprising: a plurality of light sources; a spectroscopic element that spectroscopically disperses light emitted from the light sources; and an optical shutter array disposed on the optical path of the light spectroscopically dispersed by the spectroscopic element and having a plurality of shutter portions.

2. The image display device according to claim 1, wherein the spectroscopic element is any one of a surface relief diffraction element, a hologram, a metasurface, and a liquid crystal diffraction element.

3. The image display device according to claim 1 or 2, further comprising a deflection element on the side opposite to the light sources of the spectroscopic element.

4. The image display device according to claim 1 or 2, wherein the light emitted from the light sources is parallel light.

5. The image display device according to claim 1 or 2, wherein the light emitted from the light sources includes at least a part of light in a wavelength range of 400 to 480 nm, at least a part of light in a wavelength range of 520 to 570 nm, and at least a part of light in a wavelength range of 620 to 680 nm.

6. The image display device according to claim 1 or 2, further comprising a circular polarizing plate on the side opposite to the spectroscopic element of the optical shutter array.

7. The image display device according to claim 6, wherein the circular polarizing plate includes a λ / 4 retardation plate and a linear polarizer, and the λ / 4 retardation plate is a patterned retardation plate having a plurality of regions with equal retardation and different slow axis directions.

Images