Optical element, display device, and display method

Abstract

The present invention provides a display device that improves the efficiency of light utilization for forming an aerial image. [Solution] The display device 100 of the present invention comprises a display 110, a retroreflective material 130, and a slit mirror 120 positioned to receive light from the display 110, in which a plurality of mirrors 122 and a plurality of slits 124 are arranged alternately. The plurality of mirrors 122 reflect the light from the display 110 toward the retroreflective material 130, and the plurality of slits 124 transmit the light retroreflective by the retroreflective material 130 to form an aerial image P.

Description

Technical Field

[0001] The present invention relates to a display device that displays an aerial image by retroreflection, and particularly relates to an optical element for forming an aerial image. Background Art

[0002] Aerial Imaging by Retro-Reflection (AIRR) using retroreflection is known. The display of an aerial image (or aerial video) using retroreflection employs the principle of re-imaging by reflecting light emitted from a light source toward a retroreflective material with a mirror, and transmitting part of the light that returns to the mirror again. For this reason, half mirrors with reduced reflectivity, polarizing beam splitters, and the like are used for this mirror (for example, Patent Document 1). Prior Art Literature Patent Literature

[0003] Patent Document 1 Japanese Patent No. 7604079 Summary of the Invention Problems to be Solved by the Invention

[0004] FIG. 1(A) is a diagram showing a schematic configuration of a conventional display device that displays an aerial image. The display device 10 is configured to include a display 20, a half mirror 30, and a retroreflective material 40 in a housing such as a casing, for example.

[0005] The display 20 outputs an original image of the aerial image P, and the half mirror 30 reflects part of the incident light of the original image toward the retroreflective material 40. The retroreflective material 40 reflects light in the same direction as the incident light, and the reflected light passes through the half mirror 30 to form the aerial image P. The image forming position of the aerial image P is symmetrical to the display 20 with respect to the main surface of the half mirror 30.

[0006] In the above configuration, since a half-mirror 30 is used in the mirror portion, for example, if the half-mirror 30 is a mirror that reflects 50% of the light, light is lost as it passes through the half-mirror 30 twice through reflection and transmission, resulting in a problem of low utilization efficiency of light that contributes to the formation of the aerial image P.

[0007] To solve this problem, the display device 10A shown in Figure 1(B) places a λ / 4 plate 50 that creates a λ / 4 phase difference on the upper surface of the retroreflective material 40, and uses a polarizing beam splitter 60 instead of a half mirror 30. In this case, the polarizing beam splitter 60 reflects the light of the original image incident from the display 20 toward the λ / 4 plate 50 and the retroreflective material 40, and aligns the polarization direction of the light emitted from the λ / 4 plate 50 with the transmission axis of the polarizing beam splitter 60, thereby forming an aerial image P on the light transmitted through the polarizing beam splitter 60. However, in a configuration using a polarizing beam splitter, there are problems such as the color of the aerial image changing depending on the viewing angle (chromatic dispersion) due to variations in characteristics depending on the angle of incidence and wavelength of light.

[0008] The present invention aims to solve these conventional problems and provide an optical element, a display device, and a display method that improve the efficiency of light utilization for forming an aerial image. [Means for solving the problem]

[0009] The display device according to the present invention is capable of displaying an aerial image using retroreflection and comprises a light source, a retroreflective material, and an optical element positioned at a location into which light from the light source is incident, with a plurality of reflective regions formed through a plurality of slits. The plurality of reflective regions reflect the light from the light source toward the retroreflective material, and the plurality of slits transmit the light retroreflected by the retroreflective material to form the aerial image.

[0010] The optical element according to the present invention forms an aerial image using retroreflection, and the optical element includes a plurality of reflective regions formed through a plurality of slits.

[0011] The method for displaying an aerial image according to the present invention involves preparing an optical element in which multiple reflective regions are formed through multiple slits, reflecting light incident from a light source toward a retroreflective material through the multiple reflective regions, and transmitting the light retroreflected by the retroreflective material through the multiple slits to form an aerial image.

[0012] The method for displaying an aerial image according to the present invention provides an optical element in which a first plurality of reflection regions are formed on a first surface via a plurality of first slits, and a second plurality of reflection regions are formed on a second surface facing the first surface via a plurality of second slits, and the pitch of the first plurality of reflection regions is equal to the pitch of the second plurality of reflection regions, and light incident from a light source is reflected by the first plurality of reflection regions toward a first retroreflective material, the light retroreflected by the first retroreflective material is transmitted through the first plurality of slits to form an aerial image, and light incident from the light source is transmitted through the first plurality of slits toward a second retroreflective material, the light retroreflected by the second retroreflective material is reflected by the second plurality of reflection regions to form the aerial image. [Effects of the Invention]

[0013] According to the present invention, the utilization efficiency of light contributing to the imaging of an aerial image can be improved compared to conventional methods. Furthermore, according to the present invention, chromatic dispersion of the aerial image can be suppressed compared to conventional methods. [Brief explanation of the drawing]

[0014] [Figure 1] This figure shows a schematic configuration of a conventional display device for showing aerial images. [Figure 2] Figure 2(A) shows a schematic configuration of a display device according to the first embodiment of the present invention, Figure 2(B) is a bottom view of the slit mirror shown in Figure 2(A), and Figure 2(C) is a cross-sectional view of the slit mirror shown in Figure 2(B) along line AA. [Figure 3] Figure 3(A) is a diagram illustrating the principle of the display device according to the first embodiment, and Figure 3(B) is a diagram illustrating the reflection and transmission by a slit mirror. [Figure 4] Fig. 4(A) is a diagram showing a schematic configuration of a display device according to a second embodiment of the present invention, Fig. 4(B) is a cross-sectional view of a slit mirror according to the second embodiment, and Fig. 4(C) is a diagram explaining generation of an aerial image in the display device according to the second embodiment. [Figure 5] Fig. 5(A) is a diagram explaining an example of light utilization efficiency in a display device of a conventional structure, and Fig. 5(B) is a diagram explaining an example of light utilization efficiency in the display device according to the second embodiment. [Figure 6] Fig. 6(A) is a diagram explaining improvements of the display device according to the first embodiment, and Fig. 6(B) is a diagram showing a schematic configuration of a display device according to a third embodiment. [Figure 7] It is a diagram showing a schematic configuration of a display device according to a fourth embodiment of the present invention. [Figure 8] Fig. 8(A) is a diagram explaining retroreflection of a prism-type retroreflective element, and Fig. 8(B) is a schematic plan view explaining light utilization efficiency of the prism-type retroreflective element. [Figure 9] Fig. 9(A) is a diagram explaining retroreflection of a full-cube retroreflective element, Fig. 9(B) is a plan view of a full-cube retroreflective material, and Fig. 9(C) is a diagram explaining the relationship between incidence and emission of light in the full-cube retroreflective material. [Figure 10] It is a projection view of a slit mirror and a retroreflective material in a display device according to a fifth embodiment of the present invention. [Figure 11] Fig. 10(A) is a diagram explaining retroreflection of a full-cube retroreflective element, and Fig. 10(B) is a projection view of a slit mirror and a retroreflective material in a display device according to a fifth embodiment of the present invention. [Figure 12] It is a projection view of a slit mirror and another retroreflective material in a display device according to a fifth embodiment of the present invention. MODE FOR CARRYING OUT THE INVENTION

[0015] Next, embodiments of the present invention will be described. In the present embodiment, the display device uses, as an optical element for forming an aerial image, a slit mirror structure in which a plurality of reflective regions are formed in a striped shape via a plurality of slits. By using the slit mirror structure, the light utilization efficiency can be improved compared to conventional half mirrors, and chromatic dispersion can be suppressed compared to polarizing beam splitters. It should be noted that the drawings referred to in the following description of the embodiments contain exaggerated representations for facilitating understanding of the invention, and do not represent the shapes and scales of actual products.

Examples

[0016] Next, examples of the present invention will be described in detail. Fig. 2(A) is a diagram showing a schematic configuration of a display device according to a first example of the present invention. The display device 100 of the present example includes a display 110, a slit mirror 120 in which a plurality of mirrors are formed in a striped pattern via slits, and a retroreflective material 130. These members are arranged, for example, in a housing, and display an aerial image P that floats in the air from the housing.

[0017] The display 110 is a light source for generating an original image of the aerial image P. The display 110 is not particularly limited, and may be, for example, an LED or organic EL display, a projector, or an LED unit in which a plurality of LEDs are two-dimensionally arranged. Light of the original image of the aerial image P generated by the display 110 is output toward the slit mirror 120. For example, the angle formed between the normal line (optical axis) of the display surface of the display 110 and the main surface of the slit mirror 120 is 45 degrees.

[0018] The slit mirror 120 is an optical element in which each of the plurality of slits and each of the plurality of mirrors are alternately arranged. The slit mirror 120 is arranged at a position where light from the display 110 is incident, reflects the light from the display 110 toward the retroreflective material 130, and transmits the light reflected by the retroreflective material 130 to form the aerial image P.

[0019] Figure 2(B) is a bottom view of the slit mirror, and Figure 2(C) is a cross-sectional view along line AA of Figure 2(B). As shown in the figures, the slit mirror 120 has a generally rectangular plane, on which a plurality of elongated rectangular mirrors 122 extending in the column direction and a plurality of slits 124 formed between each of the plurality of mirrors 122 are formed. The mirrors 122 provide a reflective area, and the slits 124 provide a light-transmitting area.

[0020] In one embodiment, the slit mirror 120 has a transparent film-like or plate-like transparent substrate 126 that can transmit light, as shown in Figure 2(C), and a plurality of mirrors 122 are formed on the bottom surface of the transparent substrate 126. The material of the transparent substrate 126 is not particularly limited, but can be plastic, glass, acrylic, etc. The mirrors 122 are, for example, metal layers, and may be formed by printing a metal layer onto the surface of the transparent substrate 126, or by etching a metal material deposited on the entire surface of the transparent substrate 126. The areas of the transparent substrate 126 not covered by the metal layer provide slits 124, i.e., transparent areas. The above method of manufacturing the mirror is just one example, and the slit mirror 120 may be constructed by other methods. In another embodiment, the slits 124 may be voids formed in the transparent substrate 126.

[0021] The retroreflective material 130 is an optical element that reflects light in the same direction as the incident light. Its configuration is not particularly limited, but for example, it can be composed of a triangular pyramidal retroreflective element or a full cube corner retroreflective element. The retroreflective material 130 receives light reflected by the mirror 122 of the slit mirror 120 and reflects this light in the same direction as the incident light. The light retroreflected by the retroreflective material 130 (retroreflected light) is parallel to the incident light, and a certain offset occurs between the retroreflected light and the incident light, as will be described later. The retroreflective material 130 is positioned relative to the slit mirror 120 so that the retroreflected light passes through the slit 124 of the slit mirror 120. In this way, an aerial image P is formed by the retroreflected light that has passed through the slit 124 of the slit mirror 120.

[0022] Next, the operating principle of the display device 100 of this embodiment will be described. Figure 3(A) is a projection view when the retroreflective material is projected onto a slit mirror and the two are superimposed. The retroreflective material 130 includes a plurality of retroreflective units arranged in the matrix direction, and one retroreflective unit is composed of, for example, a retroreflective prism. The retroreflective prism has three reflective surfaces, and the incident light is internally reflected three times by the three reflective surfaces and emitted in the same direction as the incident light. At this time, a certain amount of offset always occurs between the incident light and the emitted light (retroreflective light). The retroreflective material 130 has three axes (hereinafter referred to as inversion axes) that produce emitted light at a position symmetric to the incident light.

[0023] For example, as illustrated in Figure 3(A), when a retroreflective unit is viewed from above, the retroreflective unit (retroreflective element) is represented by a single equilateral triangle. Multiple retroreflective units are arranged in a matrix such that the equilateral triangles are alternately inverted. Furthermore, the three bisectors extending from the vertices of the equilateral triangles to the midpoint of the base are the inversion axes S1, S2, and S3.

[0024] As shown in Figure 3(A), light incident on a of the retroreflection unit is emitted from position a' which is symmetric with respect to the reversal axis S2, light incident on b is emitted from position b' which is symmetric with respect to the reversal axis S1, and light incident on c is emitted from position c' which is symmetric with respect to the reversal axis S3. The same applies in the reverse case (light incident on a' is emitted from a, light incident on b' is emitted from b, and light incident on c' is emitted from c). Thus, light incident on the retroreflection unit is emitted from positions that are symmetric with respect to the reversal axes S1, S2, and S3.

[0025] The retroreflective material 130 is positioned relative to the slit mirror 120 such that one of the reversal axes S1, S2, or S3 is parallel to the row direction (slit direction) of the mirror 122. In the example shown in Figure 3(A), the retroreflective material 130 is positioned such that the reversal axis S1 is parallel to the slit direction of the slit mirror 120.

[0026] In a preferred embodiment, the pitch in the row direction of the mirrors 122 and the slits 124 of the slit mirror 120 is set to be equal to the pitch in the row direction of the retroreflection units. In this case, the width W1 of the mirror 122 in the row direction is equal to the width W2 of the slit 124 in the row direction (W1=W2), and the length Ws of one side of the equilateral triangle of the retroreflection unit satisfies Ws=W1+W2.

[0027] In another embodiment, when the pitch in the row direction of the mirrors 122 and the slits 124 is equal to the pitch in the row direction of the retroreflection units, the mirror width W1 does not need to be equal to the slit width W2 (W1≠W2). For example, W1>W2 may be set to relatively increase the amount of reflected light, or conversely, W1<W2 may be set to relatively increase the amount of transmitted light. W1 and W2 may be set according to the optical characteristics of the display device.

[0028] Fig. 3(B) is a diagram schematically showing the state of reflection and transmission by the slit mirror 120. As illustrated, light L1 from the display 110 is incident on the slit mirror 120, and the incident light L1 is separated into reflected light and transmitted light there. The incident light L1 becomes light L2 reflected toward the retroreflector 130 by the mirror 122, and the light L2 is reflected by the retroreflector 130 in the same direction as the incident light. The retroreflected light L3 is reflected in the same direction as the incident light L2, but an offset T is generated between the incident light L2 and the reflected light L3, whereby the retroreflected light L3 passes through the slit 124 of the slit mirror 120 and forms an aerial image P.

[0029] In this way, the light emitted from the display 110 and reflected by the slit mirror 120 is returned by the retroreflector 130 with an offset (axis shift) relative to the inversion axis, and the returned light passes through the slit 124 of the slit mirror 120 with almost no loss and contributes to forming the aerial image P.

[0030] According to the display device of the present embodiment, the following advantageous effects are obtained. Compared to conventional half-mirrors, using a slit mirror significantly improves the light utilization efficiency of unpolarized aerial images. For example, if the light transmittance of a half-mirror is 50%, the light utilization efficiency is doubled. • When using a display as the light source, color dispersion (color variation when the angle is changed) is eliminated, resulting in high-quality aerial images. While retroreflective imaging offers greater flexibility in optical layout compared to other aerial imaging methods, allowing for various designs such as field of view and floating angle, its biggest weakness has been its low light utilization efficiency. However, this embodiment makes it possible to realize a highly competitive aerial imaging (aerial interface) with low light utilization loss while accommodating various applications and field of view.

[0031] Next, a second embodiment of the present invention will be described. Figure 4(A) is a schematic diagram showing the configuration of a display device according to the second embodiment of the present invention, and the same reference numerals are used for components that are the same as those shown in Figure 2(A). The display device 100A of the second embodiment is composed of a double-sided slit mirror 200 and first and second retroreflective materials 210A and 210B.

[0032] The first and second retroreflective materials 210A and 210B are configured in the same manner as the retroreflective material 130 of the first embodiment, and both have the same configuration. The first and second retroreflective materials 210A and 210B are arranged so that their retroreflective surfaces are perpendicular to each other.

[0033] The double-sided slit mirror 200 is positioned diagonally to the first and second retroreflective materials 210A and 210B, that is, the double-sided slit mirror 200 is positioned at a 45-degree angle to the main surfaces of the first and second retroreflective materials 210A and 210B. Furthermore, the angle between the main surface of the double-sided slit mirror 200 and the normal (optical axis) of the display surface of the display 110 is 45 degrees.

[0034] Figure 4(B) is a cross-sectional view of a double-sided slit mirror 200 according to a second embodiment. This cross-section corresponds to the AA line section in Figure 2(B). The double-sided slit mirror 200 has multiple mirrors 202 and multiple slits 204 on the top side, in addition to the multiple mirrors 122 and multiple slits 124 formed on the bottom side of the slit mirror 120 of the first embodiment. In a preferred embodiment, the row-direction pitch of the mirrors 202 and slits 204 formed on the top side is equal to the row-direction pitch of the mirrors 122 and slits 124 formed on the bottom side. The positions of the mirrors 202 coincide with the mirrors 122, and the positions of the slits 204 coincide with the positions of the slits 124, and the transparent substrate 126 exposed by the slits 124 and 204 provides a light-transmitting area. In another embodiment, the width in the row direction of the mirror 202 formed on the top surface may be different from that of the mirror 102 formed on the bottom surface. For example, the width of the top surface mirror 202 may be somewhat smaller than the width of the bottom surface mirror 102, or conversely, somewhat larger. The widths of the mirrors 202 and 102 can be appropriately selected according to the optical characteristics of the display device.

[0035] The column direction (slit direction) of the bottom mirror 122 of the double-sided slit mirror 200 is parallel to one of the inversion axes of the first retroreflective material 210A, and the row-direction pitch of the mirror 122 and slit 124 is equal to the row-direction array pitch of the retroreflective unit. The first retroreflective material 210A is positioned on the double-sided slit mirror 200 so that the retroreflective light passes through the slit 124. In addition, the column direction (slit direction) of the top mirror 202 of the double-sided slit mirror 200 is parallel to one of the inversion axes of the second retroreflective material 210B, and the row-direction pitch of the mirror 202 and slit 204 is equal to the row-direction array pitch of the retroreflective unit. The second retroreflective material 210B is then positioned on the double-sided slit mirror 200 so that it receives light from the display 110 that has passed through the slit 124, the transparent substrate 126, and the slit 204, and the retroreflective light is reflected by the mirror 202.

[0036] Next, the operation of the display device 100A according to the second embodiment will be described with reference to Figure 4(C). Light emitted from the display 110 is incident on the bottom side of the double-sided slit mirror 200, where it is separated into reflected light La from the mirror 202 and transmitted light Lb that passes through the slit 124, the transparent substrate 126, and the slit 204. Light incident on the first and second retroreflective materials 210A and 210B has its axis offset by the amount of the retroreflection inversion structure and is returned to the direction of the double-sided slit mirror 200 again.

[0037] In other words, the light La reflected by the double-sided slit mirror 200 becomes retroreflected light offset by the first retroreflective material 210A, and this retroreflected light passes through the slit 124 of the double-sided slit mirror 200 to form an aerial image P. On the other hand, the light Lb that passes through the double-sided slit mirror 200 becomes retroreflected light offset by the second retroreflective material 210B, and this retroreflected light is reflected by the top-side mirror 202 of the double-sided slit mirror 200 to form an aerial image P. In this way, by having the light that passes through the double-sided slit mirror 200 contribute to the formation of the aerial image P, the efficiency of light utilization can be further improved compared to the first embodiment.

[0038] Figure 5(A) illustrates the light utilization efficiency when using a half mirror, and Figure 5(B) illustrates the light utilization efficiency when using a double-sided slit mirror 200 according to the second embodiment. In the conventional structure of Figure 5(A), assuming that the transmittance of the half mirror 30 is 50% and the reflectance is 50%, the light emitted from the display 110 is separated by the half mirror 30 into 50% reflected light and 50% transmitted light. 50% of the reflected light is retroreflective by the first retroreflective material 210A, and a portion of the retroreflective light passes through the half mirror 30, with half (25%) of the light contributing to the formation of the aerial image P. In addition, 50% of the transmitted light that has passed through the half mirror 30 is retroreflective by the second retroreflective material 210B, and a portion of the retroreflective light is reflected by the half mirror 30, with half (25%) of the light contributing to the formation of the aerial image P. Therefore, when using the half-mirror 30, the utilization efficiency in an ideal state without transmission or reflection loss is at most 50% (25% + 25%).

[0039] On the other hand, in the display device 100A of the embodiment shown in Figure 5(B), the light emitted from the display 110 is separated into reflected light and transmitted light by the double-sided slit mirror 200. When the width W1 of the mirror 122 and the width W2 of the slit 124 are equal, 50% of the reflected light is retroreflective by the first retroreflective material 210A, and the retroreflective light passes through the slit 124, transparent substrate 126 and 204 of the double-sided slit mirror 200. In this case, since there is no light loss like in a half-mirror, 50% of the light contributes to the formation of the aerial image P. Furthermore, 50% of the transmitted light that has passed through the double-sided slit mirror 200 is retroreflective by the second retroreflective material 210B, and the retroreflective light is reflected by the mirror 202 of the double-sided slit mirror 200, so 50% of the light contributes to the formation of the aerial image P. In an ideal state with no transmission or reflection loss due to the double-sided slit mirror 200, the utilization efficiency is theoretically close to 100% (50% + 50%). Thus, by using a double-sided slit mirror, the utilization efficiency of the light emitted from the display 110 for the aerial image P can be significantly improved compared to conventional methods, and as a result, the aerial image P can be displayed with high brightness.

[0040] In the example above, the double-sided slit mirror 200 was positioned at a 45-degree angle relative to the first and second retroreflective materials 210A and 210B, which were positioned at a 90-degree angle. However, as a variation, the double-sided slit mirror 200 can also be positioned at angles such as 30 degrees or 60 degrees. In that case, the retroreflective material structure with the highest light utilization efficiency is designed so that when the double-sided slit mirror and retroreflective material are projected onto a plane perpendicular to the design ray axis of the aerial image, their pitches (i.e., the row-direction pitch of the mirror and slits and the row-direction pitch of the retroreflective unit) match.

[0041] Next, a third embodiment of the present invention will be described. Figure 6(B) is a schematic diagram showing the configuration of a display device according to the third embodiment, and components identical to those shown in Figure 2(A) are given the same reference numerals.

[0042] In the first embodiment, a slit mirror 120 was used as an imaging element to solve the problems of light loss due to the use of a half mirror and color dispersion due to the use of a polarizing beam splitter (polarizing reflector). In this case, as shown in Figure 6(A), a portion of the light emitted from the display 110 is light Lx that passes through the slit 124 of the slit mirror 120. This light Lx does not contribute to the formation of an aerial image and becomes noticeable as internal stray light, raising concerns that the problem of internal stray light, which had been suppressed by using a polarizing beam splitter, may resurface.

[0043] Therefore, in the third embodiment, an absorbing polarizing plate 310 is installed on the upper surface of the slit mirror 120 to absorb the light emitted from the display 110, which is a light source (in the case of a typical LCD, the light is polarized), thereby blocking the display 110 and internal scattered light, making it difficult to see from the outside. At the same time, since it is necessary to transmit the light that forms the aerial image P, a λ / 4 plate 300 is installed on the surface of the retroreflective material 130, and by changing the polarization direction of the light of the aerial image P, it becomes possible to form the aerial image without loss. By combining the slit mirror 120 and the polarizing absorbing plate 310, a function equivalent to that of a polarizing reflector in an aerial image display device is realized.

[0044] The λ / 4 plate 300 is an optical component that creates a λ / 4 phase difference between incident light and emitted light, and is, for example, a phase difference film attached to the surface of the retroreflective material 130. For example, when linearly polarized light vibrating in a certain direction is incident on the λ / 4 plate 300, it emits light converted to circular polarization, or when circularly polarized light is incident on it, it emits light converted to linear polarization.

[0045] The polarizing plate 310 is an absorption-type polarizing plate that selectively transmits linearly polarized light components vibrating in a certain direction and absorbs linearly polarized light components perpendicular to those components. Therefore, the light output from the λ / 4 plate 300 consists only of the polarized light components that are transmitted through it without being absorbed. An absorption-type polarizing plate is, for example, a polarizing film attached to the top surface of the slit mirror 120. Furthermore, the direction of linearly polarized light absorbed by the polarizing plate 310 generally coincides with the direction of linearly polarized light emitted from the display 110.

[0046] The operation of the display device 100B according to the third embodiment will now be described. As shown in Figure 6(B), the light emitted from the display 110 is separated into reflected light and transmitted light by the slit mirror 120. The light that passes through the slit mirror 120 is mostly absorbed by the absorbing polarizer 310. On the other hand, the light reflected by the slit mirror 120 goes toward the retroreflective material 130, where it passes through the λ / 4 plate 300 twice and then goes toward the slit mirror 120 again. The retroreflective light is given a phase difference of λ / 2 by the λ / 4 plate 300, that is, its polarization direction is rotated by 90 degrees. As a result, the retroreflective light passes through the slit 124 of the slit mirror 120 and through the absorbing polarizer 310, forming an aerial image P.

[0047] As described above, this embodiment makes it possible to make the original image and internal scattering of the display 110 difficult to see by using an absorbing polarizer and a λ / 4 plate, thereby improving the visibility of the aerial image P. Furthermore, by combining the λ / 4 plate, a slit mirror, and an absorbing polarizer, the same function as a polarizing beam splitter (reflective polarizer) can be added. Moreover, since reflective polarizers are expensive, the cost of the display device in this embodiment can be reduced. Furthermore, since reflective polarizers have low durability against high temperature and humidity, it becomes easier to mount the display device in this embodiment on vehicles exposed to high-temperature environments.

[0048] Next, a fourth embodiment of the present invention will be described. Figure 7 is a schematic diagram showing the configuration of the display device according to the fourth embodiment, and components identical to those shown in Figure 6(B) are given the same reference numerals. The display device 100C according to the fourth embodiment is configured to include decorative printing 400 on the upper surface side of the absorbing polarizing plate 310, in addition to the display device 100B of the third embodiment. The decorative printing 400 has the same pitch and width as the slits 124 of the slit mirror 120 and is printed on the surface of the absorbing polarizing plate 310. In other words, the decorative printing 400 is laminated so as to overlap with the slits 124 of the slit mirror 120, so that light transmitted through the absorbing polarizing plate 310 is transmitted through the decorative printing 400.

[0049] Thus, according to this embodiment, by adding decorative printing, the original image on the display can be made invisible from the outside without compromising the design. Furthermore, by layering a slit mirror, an absorbing polarizing plate, and decorative printing, a stealthy aerial interface with high light utilization efficiency and low internal stray light becomes possible.

[0050] In the above example, decorative printing 400 was performed on the surface of the absorbing polarizing plate 310, but this is not limited to this, and a decorative film may be attached to the surface of the absorbing polarizing plate 310 instead. Furthermore, the decorative printing may be formed to cover the entire surface of the absorbing polarizing plate 310. In addition, in configurations where an absorbing polarizing plate is not used, the decorative printing or decorative film may be laminated on a slit mirror or a double-sided slit mirror.

[0051] Next, a fifth embodiment of the present invention will be described. The fifth embodiment relates to a display device in which the pitch of the slit mirror (repetition of mirrors and slits) is N times or 1 / N times (N is a positive integer) the retroreflective unit (retroreflective element).

[0052] Figure 8(A) is a perspective view illustrating retroreflection when the retroreflection unit is prism-shaped. As shown, the prism PU is a triangular pyramid with orthogonal right-angled triangular faces, where incident light Lx is refracted at the incident plane, then reflected three times internally, and emitted as light Lx' in the same direction as the incident light Lx.

[0053] Figure 8(B) is a schematic plan view illustrating the light utilization efficiency of a prism. In the figure, S1, S2, and S3 are inversion axes, Ra and Rb are regions that are effectively utilized by the prism PU, Re is a region that is not effectively utilized, and Re' is the region to which the light reflected from region Re is directed.

[0054] Light Lx incident from the direction indicated by the solid line is sequentially reflected by a, b, and c of the prism PU and emitted as light Lx' parallel to light Lx. The light reflected in region Ra is finally reflected in region Rc and used for retroreflection. On the other hand, Ly incident from the direction indicated by the dashed line is sequentially reflected by a1 and b1 in the prism PU, but the light reflected at b1 does not travel to a point where there is no reflective region of the prism, so it is not used for retroreflection. When a prism is used in the retroreflection unit, less than half of the light is effectively used as retroreflected light, and the efficiency of light utilization is best when the pitch of the prism is matched to the pitch of the slit mirror (the pitch in which the slit and mirror are repeated).

[0055] In the fifth embodiment, any retroreflective material can be used, such as a prism shape (triangular pyramidal shape) or a full cube shape. Here, an example is given of an aerial imaging device that combines a full cube-shaped retroreflective element with a slit mirror to provide unpolarized light with high light utilization efficiency. The light utilization efficiency is highest when the direction of the slit mirror column is aligned with the direction of the inversion axis of the retroreflective material, and the pitch of the slit mirror and the retroreflective unit are the same. However, the pitch of the retroreflective unit does not necessarily have to be the same as the pitch of the slit mirror, and may be 1 / N times that of the slit mirror. Conversely, if the retroreflective element is made larger to increase the resolution of the aerial image, it may be N times that of the slit mirror.

[0056] Figure 9(A) is a perspective view illustrating retroreflection when the retroreflection unit (retrospective reflector) is in the shape of a corner cube. As shown in the figure, the corner cube CU is a three-sided polyhedron formed by combining three rectangular planes that are orthogonal to each other. The incident light Lx is reflected three times by each of the three mirror surfaces and then emitted as light Lx' in the same direction as the incident light Lx.

[0057] Figure 9(B) is a plan view of a full-cube type retroreflective material with corner cubes arranged in a grid. The retroreflective material 130A is constructed by arranging corner cubes CU in a honeycomb pattern in two dimensions. The planar shape of the corner cube CU when viewed from the front is a regular hexagon, and the width of the corner cube CU in the row direction is Wc.

[0058] Figure 9(C) is a plan view illustrating the relationship between incident and emitted light in a full-cube retroreflective material. Regions a and a', b and b', and c and c' represent the correspondence between incident and emitted light or emitted and incident light. For example, light incident in region a is emitted from region a', light incident in region b is emitted from region b', and light incident in region c is emitted from region c'.

[0059] Figure 10 is a projection view of the slit mirror 120 and retroreflective material 130A superimposed on each other as used in the first embodiment, where S1, S2, and S3 are the reversal axes when reflecting light to symmetrical positions. The slit mirror 120 is configured by alternating arrangements of mirrors 122 extending in the column direction and slits 124 extending in the column direction, where the row width W1 of the mirrors 122 is equal to the row width W2 of the slits 124 (W1=W2). The slit mirror 120 is positioned relative to the retroreflective material 130A such that one of the reversal axes S1, S2, or S3 of the retroreflective material 130A is parallel to the column direction (slit direction) of the slit mirror 120. In the example shown in the figure, the slit mirror 120 is positioned relative to the retroreflective material 130A such that the reversal axis S1 is parallel to the slit direction of the slit mirror 120. In this case, the width Wc of the corner cube CU is given by the relationship Wc = 1 / 2(W1 + W2). In other words, the row-direction pitch of the corner cube CU is half the pitch of the slit mirror 120 (the pitch when the mirror and slit are repeated in the row direction).

[0060] In a configuration where the pitch of the corner cube CU is 1 / N times the pitch of the slit mirror 120, it was found that the light utilization efficiency is highest when the pitch of the corner cube CU is 1 / 2 times that of the slit mirror 120, as shown in Figure 10.

[0061] On the other hand, if you want to increase the resolution of the aerial image, increasing the size of the retroreflective unit by N times relative to the slit width will reduce diffraction due to the retroreflective structure, and as a result, it will be possible to improve the resolution of the aerial image.

[0062] In a real corner cube, the size of the aperture (incident plane) is finite, so as shown in Figure 11(A), the light Lx' reflected by the corner cube CU spreads out due to diffraction. The diffraction spread angle θ is θ = λ / D (where λ is the wavelength and D is the aperture). Therefore, the larger the corner cube CU, the smaller the diffraction spread angle θ becomes.

[0063] Furthermore, when the light Lx' reflected by the corner cube CU passes through the slit, the plane wave becomes a spherical wave, and diffraction spreading occurs here as well. To improve the concealment of the inside of the display device, it is desirable to narrow the slit width of the slit mirror 120, but narrowing the slit width increases the spreading angle due to diffraction (θ=λ / D), and the resolution of the aerial image decreases. On the other hand, if the slit width is too large, degradation occurs, such as lines in the image projected in the aerial image not being connected.

[0064] To increase the resolution of aerial images while improving the concealment of the display device, it is assumed that the structure of the retroreflective unit will be enlarged while keeping the pitch of the slit mirrors narrow. In this case, multiplying the pitch of the retroreflective structure relative to the slit mirrors by N times results in high light utilization efficiency.

[0065] Figure 11(B) shows an example where the pitch of the corner cubes relative to the slit mirror is doubled. The slit mirror 120 has a row-direction repeating pattern of mirrors 122 extending in the column direction and slits 124 extending in the column direction, with mirrors 122 having a width W1 and slits 124 having a width W2, where W1 = W2. The corner cube has a row-direction width Wc1, where Wc1 = 2(W1 + W2).

[0066] The width Wc1 of the corner cube shown in Figure 11(B) is four times the width Wc of the corner cube shown in Figure 10. By increasing the size of the corner cube, the diffusion of light Lx' reflected by the corner cube is suppressed. By setting the width of the slit 124 to W2, the diffusion due to diffraction is suppressed while maintaining opacity. As a result, aerial images with high resolution and a long floating distance can be obtained.

[0067] The above example shows an example where the pitch of the retroreflective unit relative to the slit mirror is 1 / N times or N times, but the pitch of the retroreflective unit may be matched to the pitch of the slit mirror. Figure 12 shows an example where the pitch of the slit mirror and the pitch of the corner cube are matched. The slit mirror 120 has a pattern of mirror width W1 and slit width W2 (W1=W2), and the corner cube has a width Wc2 in the row direction, with the relationship Wc2=W1+W2. The display device in this example combines the features of Figure 10 and Figure 11(B) in order to achieve a certain level of light utilization efficiency while realizing a certain level of resolution and opacity of aerial images.

[0068] In the fifth embodiment, a configuration was shown in which the pitch of the corner cube-shaped retroreflective unit is multiplied by 1 / N or N. However, this is just one example, and the present invention can be similarly applied to prism-type (triangular pyramidal) retroreflective elements other than corner cubes. Also, in the fifth embodiment, an example was shown in which the mirror width W1 and the slit width W2 of the slit mirror are equal. However, this is just one example, and the mirror width W1 and the slit width W2 do not necessarily have to be equal (W1 ≠ W2). For example, the mirror width W1 > slit width W2, or the mirror width W1 < slit width W2.

[0069] Furthermore, the present invention may use the fifth embodiment on its own, but it is also possible to combine the fifth embodiment with the second, third, and fourth embodiments. For example, the slit mirror used in the fifth embodiment may be replaced with a double-sided slit mirror, or an absorbing polarizing plate may be installed on the upper surface of the slit mirror in the fifth embodiment, or decorative printing or a decorative film may be laminated on the upper surface of the fifth slit mirror or the absorbing polarizing plate.

[0070] Although preferred embodiments of the present invention have been described in detail above, the present invention is not limited to any particular embodiment, and various modifications and changes are possible within the scope of the gist of the invention as described in the claims. [Explanation of symbols]

[0071] 100, 100A, 100B, 100C: Display device 110: Display 120: Slit mirror 122, 202: Mirror 124, 204: Slit 126: Transparent substrate; 130, 210A, 210B: Retroreflective material 200: Double-sided slit mirror 300: λ / 4 plate 310: Absorbing polarizer PU: Prism CU: Corner Cube

Claims

1. A display device capable of displaying an aerial image using retroreflection, Light source and Retroreflective material, It has an optical element positioned at a location where light from the light source is incident, and in which multiple reflective regions are formed through multiple slits, A display device comprising the plurality of reflective regions which reflect light from the light source toward the retroreflective material, and the plurality of slits which transmit the light retroreflected by the retroreflective material to form the aerial image.

2. The display device according to claim 1, wherein each of the plurality of reflective regions is an elongated region extending in the column direction, and each of the plurality of slits is a light-transmitting region formed between each of the plurality of reflective regions.

3. The display device according to claim 2, wherein the retroreflective material is positioned with respect to the optical element such that retroreflective light passes through the transmission region.

4. The retroreflective material includes a plurality of inversion axes that invert incident light into reflected light, The display device according to claim 1, wherein the retroreflective material is arranged such that one of its reflection axes is parallel to the slit direction of the optical element.

5. The display device according to claim 1, wherein when the retroreflective material is projected onto the optical element, the row-direction pitch of the retroreflective units arranged in the matrix direction of the retroreflective material matches the row-direction pitch of the reflective region and slit of the optical element.

6. The display device according to claim 5, wherein the row width of the retroreflective unit is equal to the row width of the reflective region of the optical element and the slit.

7. The display device according to claim 1, wherein when the retroreflective material is projected onto the optical element, the row-direction pitch of the retroreflective units arranged in the matrix direction of the retroreflective material is 1 / N times the row-direction pitch of the reflective region of the optical element and the slit (where N is an integer of 2 or more).

8. The display device according to claim 1, wherein when the retroreflective material is projected onto the optical element, the row-direction pitch of the retroreflective units arranged in the matrix direction of the retroreflective material is N times the row-direction pitch of the reflective region and slit of the optical element (where N is an integer of 2 or more).

9. The display device according to claim 6 or 7, wherein the retroreflective material comprises a corner cube-shaped retroreflective unit.

10. The retroreflective material includes a first retroreflective material and a second retroreflective material arranged orthogonally, The optical element includes a plurality of reflective regions arranged on both sides, The plurality of reflective regions on the bottom side of the optical element reflect light from the light source toward the first retroreflective material, and the plurality of slits transmit light from the light source toward the second retroreflective material. The display device according to claim 1, wherein the plurality of reflective regions on the top surface side of the optical element reflect the light retroreflective by the second retroreflective material to form the aerial image.

11. The first and second retroreflective materials each include multiple reversal axes that reverse incident light into reflected light, The display device according to claim 10, wherein the first and second retroreflective materials are arranged such that the reversal axis of either one is parallel to the slit direction of the optical element.

12. The display device according to claim 10, wherein the optical element is arranged at a 45-degree angle to the main surfaces of the first and second retroreflective members.

13. The display device according to claim 10, wherein when the first and second retroreflective materials are projected onto the optical element, the row-direction pitch of the retroreflective units arranged in the matrix direction in each of the first and second retroreflective materials matches the row-direction pitch of the reflective region and slit of the optical element.

14. The display device according to claim 1, further comprising a λ / 4 plate disposed on the upper side of the retroreflective material and a polarizing plate disposed on the upper side of the optical element.

15. The display device according to claim 14, wherein the polarizing plate is an absorbing polarizing plate capable of absorbing the polarization component of light emitted from the light source, and the absorbing polarizing plate transmits the polarization component of retroreflected light emitted from the λ / 4 plate.

16. The display device according to claim 14, further comprising a decorative layer on the upper surface side of the polarizing plate, wherein the decorative layer is formed in a region corresponding to the transparent region.

17. An optical element that uses retroreflection to form an image of the air, The optical element includes a plurality of reflective regions formed through a plurality of slits.

18. The optical element according to claim 17, wherein each of the plurality of reflective regions is an elongated region extending in the column direction, and is a light-transmitting region formed between each of the plurality of reflective regions.

19. The optical element according to claim 17, wherein the optical element includes a transparent substrate that transmits light, and each of the plurality of reflective regions is formed on a first surface of the transparent substrate.

20. The optical element according to claim 17, wherein the optical element includes a plurality of reflective regions on a second surface facing the first surface, and the pitch of the plurality of reflective regions formed on the second surface is the same as the pitch of the plurality of reflective regions formed on the first surface.

21. The optical element according to claim 19, wherein the plurality of reflective regions are metal layers printed on the transparent substrate.

22. A method for displaying an aerial image, Prepare an optical element in which multiple reflection regions are formed through multiple slits, The light incident from the light source is reflected towards the retroreflective material by the plurality of reflective regions. A display method that forms an aerial image by transmitting light retroreflective by the retroreflective material through the plurality of slits.

23. A method for displaying an aerial image, An optical element is prepared in which a first surface has a plurality of first reflective regions formed through a plurality of first slits, and a second surface facing the first surface has a plurality of second reflective regions formed through a plurality of second slits, and the pitch of the first plurality of reflective regions is equal to the pitch of the second plurality of reflective regions. Light incident from a light source is reflected by the first plurality of reflection regions toward the first retroreflective material. The light retroreflective by the first retroreflective material is transmitted through the first plurality of slits to form an aerial image. Light incident from the light source is transmitted through the first plurality of slits toward the second retroreflective material. A display method in which the light retroreflective by the second retroreflective material is reflected by the second plurality of reflective regions to form the aerial image.

Images