JP2020091389A - Optical device - Google Patents

Abstract

To provide an optical device that is excellent in light guiding property and light transmissivity.SOLUTION: An optical device according to an embodiment comprises: a first substrate; a second substrate that faces the first substrate; an intermediate layer that is arranged between the first substrate and the second substrate and closely adhered to both the first substrate and the second substrate; and a light source that irradiates, with light, a side face of at least one of the first substrate and the second substrate. The refractive index of the intermediate layer is smaller at a center area in a lamination direction of the first substrate and the second substrate than that in the vicinity of respective boundary surfaces with the first substrate and the second substrate.SELECTED DRAWING: Figure 6

Description

Embodiments of the present invention relate to optical devices.

A transparent display device that includes a display panel having a plurality of pixels and a light source that irradiates light on the side surface of the display panel, and displays an image by selectively scattering the light from the light source at each pixel is known. There is. In such a transparent display device, the background of the display panel can be visually recognized in addition to the image.

For example, when a plurality of display panels are stacked to form one display device, it is difficult to achieve both the transmittance in the stacking direction and the light guiding performance of light from the light source. That is, in order to guide light while satisfying the condition of total internal reflection within each adjacent display panel, there must be a refractive index difference at the interface between the intermediate layer between these display panels and each display panel. I have to. However, in this case, part of the light transmitted in the stacking direction is reflected at each interface.

On the other hand, if there is no difference in refractive index at each interface, reflection of light transmitted in the stacking direction is suppressed. However, in this case, the total reflection condition is not satisfied at each interface, and light leakage occurs between adjacent display panels.

JP, 2013-80646, A International Publication No. 2017/033997

The above-mentioned problems exemplified in the case of stacking the transparent display devices may occur in an optical device other than the display device, such as an illumination device including a plurality of stacked light guide plates. An object of the present disclosure is to provide an optical device having excellent light guiding properties and transmissivity.

An optical device according to an embodiment is disposed between a first substrate, a second substrate facing the first substrate, the first substrate and the second substrate, and includes the first substrate and the second substrate. And an optical source that irradiates light on at least one side surface of the first substrate and the second substrate. The refractive index of the intermediate layer is smaller in the central region in the stacking direction of the first substrate and the second substrate than in the vicinity of the interface with each of the first substrate and the second substrate.

An optical device according to another embodiment is arranged between a first substrate, a second substrate facing the first substrate, the first substrate and the second substrate, and the first substrate and the second substrate. An intermediate layer that is in close contact with each of the substrates and a light source that irradiates light on at least one side surface of the first substrate and the second substrate are provided. The intermediate layer has negative uniaxial anisotropy in which the extraordinary refractive index is smaller than the ordinary optical refractive index. The difference between the ordinary light refractive index and the refractive index of the first substrate or the second substrate is 0.2 or less. Further, the extraordinary light refractive index is smaller than the refractive index of the first substrate or the second substrate.

FIG. 1 is a schematic perspective view of the display device according to the first embodiment. FIG. 2 is a schematic sectional view of the first display panel in the first embodiment. FIG. 3 is a schematic cross-sectional view showing an example of a configuration applicable to the first display panel and the first light source in the first embodiment. FIG. 4 is a schematic cross-sectional view of a display device according to the first comparative example. FIG. 5 is a schematic cross-sectional view of a display device according to the second comparative example. FIG. 6 is a schematic sectional view for explaining the configuration of the intermediate layer in the first embodiment. FIG. 7 is a sectional view schematically showing an example of the optical path of light from the first light source in the first embodiment. FIG. 8 is a schematic cross-sectional view of the display device according to the second embodiment. FIG. 9 is a sectional view schematically showing an example of the optical path of the light from the first light source in the second embodiment. FIG. 10 is a graph in which the extraordinary light refractive index of the intermediate layer satisfying a predetermined condition is plotted in the optical path shown in FIG. FIG. 11 is a schematic sectional view of a display device according to the third embodiment.

Some embodiments will be described with reference to the drawings.
It should be noted that the disclosure is merely an example, and a person having ordinary skill in the art can easily think of an appropriate modification while keeping the gist of the invention, and is naturally included in the scope of the invention. In addition, the drawings may be schematically illustrated in comparison with an actual embodiment for the sake of clarity, but they are merely examples and do not limit the interpretation of the present invention. In each drawing, reference numerals may be omitted for the same or similar elements arranged successively. Further, in the present specification and the drawings, constituent elements that exhibit the same or similar functions as those described above with respect to the already-existing drawings are designated by the same reference numerals, and redundant detailed description may be omitted.

In this embodiment, a display device including a liquid crystal display panel is disclosed as an example of an optical device. However, the present embodiment does not prevent the application of each technical idea disclosed in the present embodiment to a display device having another type of display element or an optical device other than the display device.

[First Embodiment]
FIG. 1 is a perspective view showing a schematic configuration of a display device 1 according to the first embodiment. The display device 1 includes a first display panel 2A, a second display panel 2B facing the first display panel 2A, an intermediate layer 3 arranged between the display panels 2A and 2B, and a light source 4. There is.

In the example of FIG. 1, the first display panel 2A and the second display panel 2B have a flat plate shape parallel to the XY plane defined by the first direction X and the second direction Y. The first display panel 2A, the intermediate layer 3 and the second display panel 2B are stacked in the third direction Z. The first direction X, the second direction Y, and the third direction Z are directions orthogonal to each other in the present embodiment, but may intersect at an angle other than 90°.

In the example of FIG. 1, each of the display panels 2A and 2B and the intermediate layer 3 has a rectangular shape having two sides parallel to the first direction X and two sides parallel to the second direction Y. However, the shape of each display panel 2A, 2B and the intermediate layer 3 is not limited to the rectangular shape, and may be another polygonal shape or a circular shape.

The light source 4 includes a first light source 4A and a second light source 4B. The first light source 4A faces the side surface of the first display panel 2A. The second light source 4B faces the side surface of the second display panel 2B. These light sources 4A and 4B include, for example, red, green and blue light emitting elements arranged in the second direction Y. As the light emitting element, for example, a light emitting diode (LED) or a laser element can be used.

The first display panel 2A has a plurality of first pixels PXA arranged in the first direction X and the second direction Y. The second display panel 2B has a plurality of second pixels PXB arranged in the first direction X and the second direction Y. For example, the size of each pixel PXA, PXB is the same. However, the sizes of the pixels PXA and PXB may be different.

The first display panel 2A displays an image by scattering the light from the first light source 4A. Similarly, the second display panel 2B displays an image by scattering the light from the second light source 4B. Furthermore, each display panel 2A, 2B and the intermediate|middle layer 3 have high transparency. Therefore, when the display device 1 is viewed from the first display panel 2A side, the image of the first display panel 2A is superposed above the image of the second display panel 2B. On the contrary, when the display device 1 is viewed from the second display panel 2B side, the image of the second display panel 2B is superposed on the image of the first display panel 2A. In this way, by superimposing the images of the two display panels 2A and 2B, it is possible to display an image having a stereoscopic effect and overlay display of information. Further, since each of the display panels 2A and 2B has transparency, it is possible to visually recognize the background through the display device 1.

Subsequently, a configuration applicable to the first display panel 2A will be illustrated with reference to FIGS. 2 and 3. However, the configuration of the first display panel 2A is not limited to that illustrated here.
FIG. 2 is a schematic sectional view of the first display panel 2A. The first display panel 2A includes a first array substrate 10A, a first counter substrate 20A, and a first liquid crystal layer 30A (first electro-optical layer).

The first array substrate 10A includes a transparent substrate 11A, an insulating layer 12, an alignment film 13, a switching element SW, and a pixel electrode PE. The switching element SW is arranged above the transparent substrate 11A in each pixel PXA. The insulating layer 12 covers the switching element SW and the transparent substrate 11A. The pixel electrode PE is arranged on the insulating layer 12 in each pixel PXA, and is electrically connected to the switching element SW. The alignment film 13 covers the pixel electrode PE.

Although the switching element SW is simplified in FIG. 2, the switching element SW actually includes a semiconductor layer and a plurality of electrodes. In addition, the insulating layer 12 is arranged between the semiconductor layer of the switching element SW, the scanning line that supplies the scanning signal to the switching element SW, and one or a plurality of the signal lines that supply the video signal to the switching element SW. Including insulating film.

The first counter substrate 20A includes a transparent substrate 21A, an alignment film 22 and a common electrode CE. The common electrode CE is arranged below the transparent substrate 21A. The alignment film 22 covers the common electrode CE. 20 A of 1st counter substrates may be equipped with the light shielding layer which overlaps with the boundary of the pixel PX which adjoins.

The transparent substrates 11A and 21A can be formed of, for example, transparent glass or plastic. The pixel electrode PE and the common electrode CE can be formed of a transparent conductive material such as ITO (Indium Tin Oxide).

The first liquid crystal layer 30A is arranged between the alignment films 13 and 22. In the present embodiment, the first liquid crystal layer 30A is a liquid crystal layer having polymer dispersed liquid crystal (PDLC). That is, the first liquid crystal layer 30A includes a polymer and liquid crystal molecules dispersed in the gap between the polymers. In such a first liquid crystal layer 30A, for example, a liquid crystal monomer is injected between the alignment films 13 and 22, and the liquid crystal monomer aligned in a predetermined direction by the alignment regulating force of the alignment films 13 and 22 is irradiated with ultraviolet light. To form a polymer.

For example, when no electric field is applied to the first liquid crystal layer 30A, the optical axes of the polymer and the liquid crystal molecules are substantially parallel to each other. Therefore, the light incident on the first liquid crystal layer 30A is transmitted with almost no scattering in the first liquid crystal layer 30A. Hereinafter, such a state is referred to as a transparent state. The voltage of the pixel electrode PE for realizing the transparent state is called the transparent voltage. The transparent voltage may be the same as the common voltage applied to the common electrode CE, or may be a voltage slightly different from the common voltage.

On the other hand, when a sufficient electric field is applied to the first liquid crystal layer 30A, the optical axes of the polymer and the liquid crystal molecules intersect each other. Therefore, the light incident on the first liquid crystal layer 30A is scattered in the first liquid crystal layer 30A. Hereinafter, such a state is referred to as a scattering state. In addition, the voltage of the pixel electrode PE for realizing the scattered state is called the scattered voltage.

FIG. 3 is a schematic sectional view showing an example of a configuration applicable to the first display panel 2A and the first light source 4A. In the example of FIG. 3, the first light source 4A faces the side surfaces of the first array substrate 10A and the first counter substrate 20A. The first array substrate 10A and the first counter substrate 20A are attached to each other by an annular seal SE. The first liquid crystal layer 30A is sealed between the first array substrate 10A and the first counter substrate 20A with a seal SE.

As shown in FIG. 3, the light LA emitted from the first light source 4A is applied to the side surfaces of the first array substrate 10A and the first counter substrate 20A. The light LA that has entered the inside of the first display panel 2A from these side surfaces propagates inside the first display panel 2A. In the vicinity of the pixel electrode PE (OFF in FIG. 3) to which the transparent voltage is applied, the light LA is hardly scattered by the first liquid crystal layer 30A. Therefore, the light LA hardly leaks from the first display panel 2A.

On the other hand, in the vicinity of the pixel electrode PE (ON in FIG. 3) to which the scattering voltage is applied, the light LA is scattered by the first liquid crystal layer 30A. The scattered light is emitted from the first display panel 2A and visually recognized as a display image. It is also possible to realize gradation representation of the degree of scattering (luminance) by defining the scattering voltage stepwise within a predetermined range.

The external light Lo incident on the first display panel 2A in the vicinity of the pixel electrode PE to which the transparent voltage is applied passes through the first display panel 2A with almost no scattering. That is, when the first display panel 2A is viewed from the first array substrate 10A side, the background on the first counter substrate 20A side is visible, and when the first display panel 2A is viewed from the first counter substrate 20A side. The background on the side of the first array substrate 10A is visible.

The first display panel 2A and the first light source 4A having the above configurations can be driven by, for example, a field sequential method. In this method, one frame period includes a plurality of subframe periods (fields). For example, when the first light source 4A includes red, green and blue light emitting elements, one frame period includes red, green and blue subframe periods.

In the red sub-frame period, the red light emitting element is turned on, and the voltage according to the red image data is applied to each pixel electrode PE. As a result, a red image is displayed. Similarly in the green and blue sub-frame periods, the green and blue light emitting elements are turned on, and the voltages corresponding to the green and blue image data are applied to the pixel electrodes PE, respectively. As a result, green and blue images are displayed. In this way, the red, green, and blue images displayed in a time-division manner are combined with each other and visually recognized by the viewer as an image of multicolor display.

The first liquid crystal layer 30A is in a scattering state when a voltage similar to the common voltage is applied to the pixel electrode PE, and transparent when a voltage sufficiently different from the common voltage is applied to the pixel electrode PE. You may have the structure used as a state. Further, the first display panel 2A and the first light source 4A may have a configuration for displaying a monochrome image.

Regarding the second display panel 2B and the second light source 4B, the same configuration as the first display panel 2A and the first light source 4A may be applied, or another configuration may be applied. In the present embodiment, it is assumed that the second display panel 2B and the second light source 4B have the same configurations as the first display panel 2A and the first light source 4A shown in FIGS. 2 and 3. Hereinafter, the array substrate, the counter substrate, and the liquid crystal layer included in the second display panel 2B are referred to as the second array substrate 10B, the second counter substrate 20B, and the second liquid crystal layer 30B (second electro-optical layer), respectively. Further, the transparent substrates of the second array substrate 10B and the second counter substrate 20B are referred to as transparent substrates 11B and 21B, respectively.

When the first display panel 2A and the second display panel 2B are stacked with the intermediate layer 3 interposed therebetween as shown in FIG. 1, it is necessary to determine the refractive index of the intermediate layer 3 in consideration of refraction and reflection at respective interfaces. is there. If the refractive index of the intermediate layer 3 is not appropriate, the transmittance of the display device 1 may decrease and light may leak between the first display panel 2A and the second display panel 2B.

FIG. 4 is a schematic cross-sectional view of the display device 100 according to the first comparative example, for explaining the decrease in transmittance. In the example of this figure, each display panel 2A, 2B is laminated so that the first array substrate 10A and the second counter substrate 20B face each other. The intermediate layer 3 is in close contact with the transparent substrate 11A of the first array substrate 10A and the transparent substrate 21B of the second counter substrate 20B. For example, each of the light sources 4A and 4B emits diffused light including P-polarized light whose electric field oscillates in the incident plane (XZ plane) and S-polarized light whose electric field oscillates perpendicularly to the incident plane.

In order for the light LA from the first light source 4A to be guided within the first display panel 2A, the light LA is guided at the interface between the transparent substrate 11A and the intermediate layer 3 and at the interface between the transparent substrate 21A and the air (external atmosphere). , The light LA needs to be totally reflected. The same applies to the light LB from the second light source 4B. Generally, the critical angle θc for the light traveling from the substance having the refractive index ni to the substance having the refractive index nj to satisfy the condition of total reflection is given by arcsin(nj/ni), and if ni<nj, total reflection occurs. Absent.

Here, the transparent substrates 11A, 11B, 21A and 21B are isotropic glass substrates having a refractive index ng=1.5, and both the refractive index na of air and the refractive index n of the intermediate layer 3 are 1.0. Imagine a case. In this case, the light LA traveling inside the first display panel 2A can satisfy the total reflection condition at each of the interface between the transparent substrate 11A and the intermediate layer 3 and the interface between the transparent substrate 21A and the air. The same applies to the light LB traveling inside the second display panel 2B.

On the other hand, with respect to the external light Lo passing through each of the display panels 2A and 2B in parallel with the third direction Z, the transmittance decreases due to Fresnel reflection. In general, when light of intensity Ii travels from a substance of refractive index ni toward a substance of refractive index nj perpendicularly to the interface between these substances, the intensity Ij of light reflected by the interface is Ii((ni-nj)/ (Ni+nj))^2. That is, when the difference between ng and n is large as in the case of ng=1.5 and n=1.0, the intensity of reflection is strongly influenced by the value of the square of this difference. As a result, strong reflection occurs not only at the interfaces between the transparent substrates 21A and 11B and the air, but also at the interfaces between the transparent substrates 11A and 21B and the intermediate layer 3. As a result, the transmittance of the external light Lo is reduced, making it difficult to visually recognize the background of the display device 100.

FIG. 5 is a schematic cross-sectional view of a display device 200 according to a second comparative example, for explaining light leakage between the first display panel 2A and the second display panel 2B. In the example of this figure, the refractive index n of the intermediate layer 3 is 1.5, and other conditions are the same as the example of FIG.

In the example of FIG. 5, since there is no difference in the refractive index at each interface between the intermediate layer 3 and each of the transparent substrates 11A and 21B, the transmittance of external light Lo is improved. However, the total reflection condition is not satisfied at these interfaces. Therefore, the light LA leaks to the second display panel 2B through the intermediate layer 3. Similarly, the light LB leaks to the first display panel 2A through the intermediate layer 3.

As described above, when a plurality of display panels are stacked, it is difficult to suppress the decrease in transmittance and the occurrence of light leakage between the display panels. Therefore, in the present embodiment, the transmittance and light leakage of the display device 1 are improved by devising the configuration of the intermediate layer 3.

FIG. 6 is a schematic sectional view of the display device 1 for explaining the configuration of the intermediate layer 3 in the present embodiment. The laminated structure of each display panel 2A, 2B and the intermediate layer 3 is the same as that of the comparative example of FIGS. 4 and 5.

In the present embodiment, the intermediate layer 3 includes a first layer 31, a second layer 32, and a third layer 33. The second layer 32 is disposed between the first layer 31 and the transparent substrate 11A and is in close contact with both the first layer 31 and the transparent substrate 11A. The third layer 33 is disposed between the first layer 31 and the transparent substrate 21B and is in close contact with both the first layer 31 and the transparent substrate 21B.

The first layer 31 has a first refractive index n1 smaller than the refractive index ng of the transparent substrates 11A and 21B (n1<ng). The second layer 32 has a second refractive index n2 that is smaller than the refractive index ng and larger than the first refractive index n1 (n1<n2<ng). The third layer 33 has a third refractive index n3 that is smaller than the refractive index ng and larger than the first refractive index n1 (n1<n3<ng). The second refractive index n2 and the third refractive index n3 may be the same.

In this way, the refractive index of the intermediate layer 3 is set such that the transparent substrate 11A, 21B is stacked in the stacking direction (third direction Z) more than in the vicinity of the interface with the transparent substrate 11A, 21B (first layer 32 and third layer 33). 2) is small in the central region (first layer 31). Moreover, the refractive index of the intermediate layer 3 is generally lower than that of the transparent substrates 11A and 21B.

As an example, the transparent substrates 11A and 21B have a refractive index ng of 1.5, a first refractive index n1 of 1.3, a second refractive index n2 and a third refractive index n3 of 1.4, and the first of the light LA. It is assumed that the maximum propagation angle inside the display panel 2A is 29°. Here, the propagation angle is the inclination of the traveling direction of the light LA with respect to the XY plane.

FIG. 7 is a sectional view schematically showing an example of the optical path of the light LA under such conditions. When the propagation angle is 29°, the incident angle of the light LA incident on the interface between the transparent substrate 11A and the intermediate layer 3 is 61°. When this light LA reaches the interface between the second layer 32 and the first layer 31 from the transparent substrate 11A through the second layer 32, assuming that the incident angle on the interface is θ, 1.5 according to Snell's law. Xsin 61°=1.4×sin θ holds. From this relationship, the incident angle θ is about 69.6°. The critical angle θc at the interface between the second layer 32 and the first layer 31 is represented by arcsin (1.3/1.4) and is about 68.2°.

As described above, in the light LA that is incident on the first layer 31 from the second layer 32, the incident angle θ exceeds the critical angle θc, so that the total reflection condition is satisfied. Therefore, the light LA satisfactorily propagates inside the first display panel 2A. Similarly, the light LB from the second light source 4B is well propagated inside the second display panel 2B.

The external light Lo is reflected with an intensity that is strongly influenced by the squared value of the refractive index difference between the two substances that form the interface as described above. In the example of FIG. 6, even if a large refractive index difference is provided between the transparent substrates 11A and 21B and the first layer 31 so that the lights LA and LB satisfy the condition of total reflection, the second layer 32 and the first layer 31 may be provided. The presence of the three layers 33 suppresses the reflection of the external light Lo.

That is, the refractive index difference (ng-n2) at the interface between the transparent substrate 11A and the second layer 32, the refractive index difference (n2-n1) at the interface between the second layer 32 and the first layer 31, and the first layer 31. The refractive index difference (n1-n3) at the interface with the third layer 33 and the refractive index difference (n3-ng) at the interface between the third layer 33 and the transparent substrate 21B are the same as those of the transparent substrates 11A and 21B. It is sufficiently smaller than the refractive index difference (ng-n1) at each interface when the first layer 31 and the first layer 31 are in close contact with each other. Therefore, for example, as compared with the case where the intermediate layer 3 has a low refractive index single layer structure as shown in FIG. 4, reflection of the external light Lo can be suppressed.

From the viewpoint of suitably suppressing the reflection of the external light Lo, it is preferable that the refractive index difference (ng-n2, n2-n1, n1-n3, n3-ng) at each interface is 0.2 or less. It is more preferable that the difference between these refractive indices is 0.1 or less.

The material forming each of the layers 31 to 33 of the intermediate layer 3 is not particularly limited. For example, a low refractive index resin such as a fluorinated acrylate/epoxy resin or a porous material can be used. In addition, as each of the layers 31 to 33, an acrylic adhesive sheet, a silicone adhesive sheet, a urethane adhesive sheet, or the like may be used.

The number of layers forming the intermediate layer 3 is not limited to three. Two or more layers may be arranged between the first layer 31 and the transparent substrate 11A and between the first layer 31 and the transparent substrate 21B. If the intermediate layer 3 is composed of a larger number of layers and the difference in the refractive index at the interface between the layers is reduced, the reflection of the external light Lo can be suppressed more preferably.

The intermediate layer 3 may have a structure in which the refractive index continuously decreases from each interface with the transparent substrates 11A and 21B toward the central region in the stacking direction. As such a structure, for example, a moth-eye structure can be used.

The intermediate layer 3 may include a layer having a refractive index higher than that of the transparent substrates 11A and 21B. For example, the refractive index of each layer in contact with the transparent substrates 11A and 21B becomes slightly larger than the refractive index of the transparent substrates 11A and 21B, and the refractive index of each layer of the intermediate layer 3 becomes closer to the central region in the stacking direction of the intermediate layer 3. The refractive index may be smaller than the refractive index of the transparent substrates 11A and 21B.

[Second Embodiment]
The second embodiment will be described. Here, focusing on the difference from the first embodiment, the description of the same configuration as the first embodiment will be omitted.

FIG. 8 is a schematic sectional view of the display device 1 according to the second embodiment. In the present embodiment, the light LA, LB emitted from each of the light sources 4A, 4B has P polarization in the light guide direction inside the display panels 2A, 2B. For example, such light LA, LB is provided with a light-emitting element that emits light including P-polarized light and S-polarized light, and a polarizer that absorbs S-polarized light of this light and transmits P-polarized light, for each light source 4A, 4B. Can be generated with.

Further, in this embodiment, the intermediate layer 3 has negative uniaxial anisotropy in which the extraordinary refractive index ne1 is smaller than the ordinary optical refractive index no1 (ne1<no1). The extraordinary light refractive index ne1 is smaller than the refractive index ng of the transparent substrates 11A and 21B (ne1<ng). When the lights LA and LB that are P-polarized light enter the intermediate layer 3 from the transparent substrates 11A and 21B, the extraordinary light refractive index ne1 is felt. More specifically, when the propagation angle of the light LA is extremely close to the horizontal (the first direction X in the example of FIG. 8), the light LA feels the extraordinary refractive index ne1, and in other cases, the light LA is Feel the refractive index according to the propagation angle. In the example of FIG. 8, the intermediate layer 3 has a single-layer structure, but may have a plurality of layers having different extraordinary light refractive index ne1 and ordinary light refractive index no1.

As the material of the intermediate layer 3 having negative uniaxial anisotropy, for example, sodium nitrate (no=1.58, ne=1.33) can be used. In addition, the refractive index condition of the intermediate layer 3 is an optically anisotropic polymer, an anisotropic porous polymer, a polymer gel, a discotic liquid crystal, a cholesteric liquid crystal, or a microstructure (nanostructure) using a metal or an inorganic material. May be realized.

Further, in the present embodiment, each of the liquid crystal layers 30A and 30B has a positive uniaxial anisotropy in which the extraordinary light refractive index ne2 is larger than the ordinary light refractive index no2 (ne2>no2). As such liquid crystal layers 30A and 30B, for example, nematic liquid crystal in which liquid crystal molecules are vertically aligned can be applied. The configuration of each of the liquid crystal layers 30A and 30B is not limited to this example, and liquid crystal molecules may be horizontally aligned.

As an example, when the refractive index ng is 1.5, the extraordinary light refractive index ne1 is 1.3, the ordinary light refractive index no1 is 1.5, the extraordinary light refractive index ne2 is 1.7, and the ordinary light refractive index no2 is 1.5. Assume Inside the first display panel 2A, the light LA incident on the interface between the transparent substrate 11A and the intermediate layer 3 feels the extraordinary light refractive index ne1 of the intermediate layer 3. Since the extraordinary light refractive index ne1 (=1.3) is smaller than the refractive index ng (=1.5), the total reflection condition can be satisfied at the interface. Therefore, the light LA is totally reflected at the interface and the interface between the transparent substrate 21A and the air and propagates inside the first display panel 2A. Moreover, since the extraordinary light refractive index ne2 (=1.7) is larger than the refractive index ng (=1.5) of the transparent substrates 11A and 21A, part of the light LA is totally reflected inside the first liquid crystal layer 30A. Propagate while being transmitted. The light LB also propagates inside the second display panel 2B.

On the other hand, since the refractive indexes ng and no1 are both 1.5, the external light Lo is reflected at the interface between the transparent substrate 11A and the intermediate layer 3 and the interface between the intermediate layer 3 and the transparent substrate 21B. Not done. Therefore, the external light Lo is preferably transmitted through the display device 1. It exists between the transparent substrate 11A and the first liquid crystal layer 30A, between the transparent substrate 21A and the first liquid crystal layer 30A, between the transparent substrate 11B and the second liquid crystal layer 30B, and between the transparent substrate 21B and the second liquid crystal layer 30B, respectively. The refractive index of the insulating layer or the like is preferably close to the refractive indexes ng and no2 (=1.5). Thereby, the reflection of the external light Lo at the interface of each layer can be suppressed, and the transmittance of the external light Lo can be further increased.

The ordinary light refractive index no1 does not necessarily have to match the refractive index ng. However, from the viewpoint of suppressing the reflection of the external light Lo, it is preferable that the difference between the ordinary light refractive index no1 and the refractive index ng is 0.2 or less (-0.2≤no1-ng≤0.2). It is more preferable that the difference between the ordinary refractive index no1 and the refractive index ng is 0.1 or less (-0.1≤no1-ng≤0.1). The same applies to the relationship between the ordinary light refractive index no2 and the refractive index ng.

Next, a preferable range of the extraordinary light refractive index ne1 will be described. FIG. 9 is a schematic cross-sectional view showing the optical path of the light LA that is incident on the side surface of the first display panel 2A at the largest angle of the diffused light emitted by the first light source 4A in the XZ cross section. The incident angle of the light LA on the side surface is defined as θ1, and the outgoing angle (refraction angle) from the side surface is defined as θ2. Further, the exit angle (refraction angle) when the light LA enters the intermediate layer 3 without being totally reflected is defined as θ3.

When the refractive index na of air is 1.0 and the refractive index ng of the first display panel 2A (transparent substrate 11A) is 1.5, the following two formulas are established according to Snell's law. Here, ne1(θ3) is a function that represents the refractive index that the light LA feels according to the emission angle θ3, and changes from the extraordinary light refractive index ne1 to the ordinary light refractive index no1 (=1.5).
1.0×sin θ1=1.5×sin θ2
1.5×sin(90°−θ2)=ne1(θ3)×sin(θ3)

FIG. 10 is a graph in which the extraordinary light refractive index ne1 that is the smallest in the range in which the exit angle θ3 that satisfies the above two expressions exists is plotted against a plurality of incident angles θ1. That is, in the region on the left side of this plot, the light LA shown in FIG. 9 satisfies the total reflection condition at the interface between the first display panel 2A and the intermediate layer 3.

The incident angle θ1 is, for example, −20° or more and +20° (−20°≦θ1≦+20°). In this case, according to FIG. 10, if the extraordinary light refractive index ne1 is about 1.46 (the difference from ng is about 0.04), the total reflection condition at the interface between the first display panel 2A and the intermediate layer 3 is It is filled. Therefore, it is preferable that the extraordinary light refractive index ne1 is smaller than the refractive index ng by 0.05 or more (ne1≦ng−0.05). If the extraordinary light refractive index ne1 is smaller than the refractive index ng by 0.1 or more (ne1≦ng−0.1), the total reflection condition is more surely satisfied at the interface.

Also in the present embodiment described above, similarly to the first embodiment, it is possible to suppress the decrease in the transmittance of the display device 1 and the light leakage between the first display panel 2A and the second display panel 2B.

[Third Embodiment]
A third embodiment will be described. Here, focusing on the difference from the first and second embodiments, the description of the same configuration as the first and second embodiments will be omitted.

FIG. 11 is a schematic sectional view of the display device 1 according to the third embodiment. In the present embodiment, the second display panel 2B is a transmissive liquid crystal display panel having a light blocking effect. That is, the second display panel 2B includes a first polarizing plate PL1 and a second polarizing plate PL2, and the second array substrate 10B, the second counter substrate 20B, and the second liquid crystal layer are provided between these polarizing plates PL1 and PL2. 30B is arranged.

A backlight BL, which is a surface light source that irradiates the second display panel 2B with light, is disposed below the first polarizing plate PL1. The second display panel 2B displays an image by selectively transmitting light from the backlight BL for each pixel. When the display device 1 is viewed from above in the drawing, the image displayed by the first display panel 2A overlaps the image displayed by the second display panel 2B.

In such a display device 1, the intermediate layer 3 may have a structure in which a plurality of layers having different refractive indexes are laminated as in the first embodiment. Moreover, you may apply to the intermediate|middle layer 3 the structure which has negative uniaxial anisotropy like 2nd Embodiment. With these, the light from the first light source 4A can be satisfactorily guided inside the first display panel 2A. Further, it is possible to prevent the light Ld forming the display image of the second display panel 2B from being reflected at the interface between the second display panel 2B and the intermediate layer 3 and the interface between the first display panel 2A and the intermediate layer 3. ..

The second display panel 2B is not limited to the liquid crystal display panel. The second display panel 2B is a self-luminous display panel such as an organic EL display panel, a self-luminous display panel having a light emitting diode (LED) display element, an electronic paper type display panel having an electrophoretic element, a Micro It may be a display panel to which Electro Mechanical Systems (MEMS) is applied or another type of display panel such as a display panel to which electrochromism is applied.

As described above, all display devices or optical devices that can be appropriately modified and implemented by those skilled in the art based on the display devices described as the first to third embodiments of the present invention include the gist of the present invention. , Belong to the scope of the present invention.

Various modifications are conceivable to those skilled in the art within the scope of the idea of the present invention, and it is understood that these modifications also belong to the scope of the present invention. For example, those skilled in the art appropriately add, delete, or change the design of each of the above-described embodiments, or add, omit, or change the conditions of the process of the present invention. As long as it has the gist, it is included in the scope of the present invention.

Further, regarding other operational effects brought about by the modes described in the respective embodiments, what is obvious from the description of the present specification or what can be appropriately conceived by those skilled in the art is understood to be brought about by the present invention. To be done.

Below, some modified examples are illustrated.
In 1st thru|or 3rd embodiment, the example which the display apparatus 1 provided with two display panels was disclosed. However, the display device 1 may include three or more display panels. In this case, the intermediate layer 3 may be arranged between adjacent display panels.

An antireflection film may be provided on the outermost surface of the display device 1, for example, the outer surfaces of the transparent substrates 21A and 11B. Thereby, reflection of external light at the interfaces between the transparent substrates 21A and 11B and the air can be suppressed, and the transmittance of the display device 1 can be further increased. Such an antireflection film may be a laminate of a plurality of layers having different refractive indexes, or may have a moth-eye structure.

A cover member made of, for example, glass may be arranged on the outer surface of the display device 1, for example, the outer surfaces of the transparent substrates 21A and 11B. In this case, the antireflection film may be provided on the surface of the cover member. Further, the intermediate layer 3 may be provided between the outer surfaces of the transparent substrates 21A and 11B and the cover member.

The first to third embodiments have disclosed the configuration in which the first array substrate 10A and the second counter substrate 20B face each other with the intermediate layer 3 interposed therebetween. In this case, the transparent substrate 11A is an example of the first substrate, the transparent substrate 21B is an example of the second substrate, the transparent substrate 21A is an example of the third substrate, and the transparent substrate 11B is an example of the fourth substrate. Is. As another example, the first array substrate 10A and the second array substrate 10B may face each other via the intermediate layer 3, or the first counter substrate 20A and the second counter substrate 20B may face each other via the intermediate layer 3. May be.

In the first to third embodiments, the display device is disclosed as an example of the optical device. However, the configurations disclosed in the embodiments are various optical devices in which the first substrate and the second substrate face each other with the intermediate layer interposed therebetween, and light is guided in at least one of the first substrate and the second substrate. Is applicable to. As an example of such an optical device, for example, an illuminating device that includes two light guide plates (first substrate and second substrate) and in which light from a light source is incident from the side surface of each light guide plate can be considered.

In the first to third embodiments, the case where the first electro-optical layer and the second electro-optical layer are the first liquid crystal layer 30A and the second liquid crystal layer 30B is illustrated. However, the first electro-optical layer and the second electro-optical layer are not limited to the liquid crystal layer as long as they can switch between the transparent state and the scattering state.

DESCRIPTION OF SYMBOLS 1... Display device, 2A... 1st display panel, 2B... 2nd display panel, 3... Intermediate layer, 4A... 1st light source, 4B... 2nd light source, 10A... 1st array substrate, 10B... 2nd array substrate, 20A... 1st counter substrate, 20B... 2nd counter substrate, 11A, 21A, 11B, 21B... Transparent substrate, 30A... 1st liquid crystal layer, 30B... 2nd liquid crystal layer, LA... Light from a 1st light source, LB... Light from the second light source.

Claims (8)

A first substrate,
A second substrate facing the first substrate;
An intermediate layer disposed between the first substrate and the second substrate and in close contact with each of the first substrate and the second substrate;
A light source that irradiates light on at least one side surface of the first substrate and the second substrate,
The refractive index of the intermediate layer is smaller in the central region in the stacking direction of the first substrate and the second substrate than in the vicinity of the interface with each of the first substrate and the second substrate,
Optical device. The intermediate layer includes a first layer including the central region, a second layer between the first layer and the first substrate, and a third layer between the first layer and the second substrate. Prepare,
The first layer has a first index of refraction less than the indices of refraction of the first and second substrates,
The second layer has a second refractive index lower than the refractive index of the first substrate and higher than the first refractive index,
The third layer has a third refractive index lower than the refractive index of the second substrate and higher than the first refractive index.
The optical device according to claim 1. The refractive index difference at the interfaces of the first substrate and the second layer, the second layer and the first layer, the first layer and the third layer, and the third layer and the second substrate is 0, respectively. .2 or less,
The optical device according to claim 2. A first substrate,
A second substrate facing the first substrate;
An intermediate layer disposed between the first substrate and the second substrate and in close contact with each of the first substrate and the second substrate;
A light source that irradiates light on at least one side surface of the first substrate and the second substrate,
The intermediate layer has a negative uniaxial anisotropy in which the extraordinary light refractive index is smaller than the ordinary light refractive index,
The difference between the ordinary light refractive index and the refractive index of the first substrate or the second substrate is 0.2 or less,
The extraordinary light refractive index is smaller than the refractive index of the first substrate or the second substrate,
Optical device. The extraordinary light refractive index is smaller than the refractive index of the first substrate or the second substrate by 0.05 or more,
The optical device according to claim 4. A first substrate, a third substrate facing the first substrate, a first electro-optical layer disposed between the first substrate and the third substrate, and a plurality of first pixels 1 display panel is further provided,
The light source includes a first light source that emits light to a side surface of the first display panel,
The first electro-optical layer switches between a scattering state in which light from the first light source is scattered and a transparent state in which the light is transmitted, according to a voltage applied to the first pixel.
The optical device according to any one of claims 1 to 5. A second substrate, a fourth substrate facing the second substrate, a second electro-optical layer disposed between the second substrate and the fourth substrate, and a plurality of second pixels 2 Further equipped with a display panel,
The light source includes a second light source that emits light to a side surface of the second display panel,
The second electro-optical layer switches between a scattering state in which light from the second light source is scattered and a transparent state in which the light is transmitted, according to a voltage applied to the second pixel,
The optical device according to claim 6. At least one of the first electro-optical layer and the second electro-optical layer is a liquid crystal layer,
The optical device according to claim 7.

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