Display device

This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2017-046268, filed Mar. 10, 2017, the entire contents of which are incorporated herein by reference.

Embodiments described herein relate generally to a display device.

For example, an imaging device comprising a polarizing filter and a retroreflective element is suggested. In the imaging device, an aerial image for a display image is formed at a position where the aerial image and the emission point of display light for the display image are plane-symmetrical with respect to the polarizing filter.

FIG. 1 is a perspective view showing an example of the external appearance of a display device according to a first embodiment.

FIG. 2 shows a structural example of the display device shown in FIG. 1 .

FIG. 3 shows an example of the optical path until the display light emitted from the display unit shown in FIG. 2 forms aerial images.

FIG. 4 shows the positional relationship of the display surface, optical element and imaging planes shown in FIG. 2 .

FIG. 5 shows a structural example of the display panel shown in FIG. 2 .

FIG. 6 is a cross-sectional view showing a structural example of the display panel shown in FIG. 2 .

FIG. 7 is a plan view showing a structural example of a retroreflective element applied to the optical elements shown in FIG. 1 .

FIG. 8 is a perspective view showing a structural example of each retroreflector shown in FIG. 7 .

FIG. 9 is a cross-sectional view showing a structural example of the modulating element shown in FIG. 2 .

FIG. 10 is a plan view showing structural examples of the first and second electrodes shown in FIG. 7 .

FIG. 11 shows the distribution of a phase difference imparted to transmitted light in the effective area shown in FIG. 8 .

FIG. 12 is a plan view showing another structural example of the modulating element shown in FIG. 2 .

FIG. 13 is a perspective view showing an example of the external appearance of a display device according to a second embodiment.

In general, according to one embodiment, a display device includes first and second retroreflective elements which retroreflect incident light, an optical element which is located between the first retroreflective element and the second retroreflective element, and includes a first surface facing the first retroreflective element and a second surface facing the second retroreflective element, and a display unit which is located on a side facing the first surface and emits display light.

According to another embodiment, a display device includes a first optical element which includes a transmission axis transmitting first linearly polarized light, and reflects second linearly polarized light intersecting the transmission axis, a display unit which emits the first linearly polarized light and the second linearly polarized light toward the first optical element, a second optical element which retroreflects the second linearly polarized light reflected on the first optical element, and modulates the second linearly polarized light reflected on the first optical element into the first linearly polarized light, and a third optical element which retroreflects the first linearly polarized light having passed through the first optical element, and modulates the first linearly polarized light having passed through the first optical element into the second linearly polarized light.

Embodiments will be described hereinafter with reference to the accompanying drawings. Incidentally, the disclosure is merely an example, and proper changes within the spirit of the invention, which are easily conceivable by a skilled person, are included in the scope of the invention as a matter of course. In addition, in some cases, in order to make the description clearer, the widths, thicknesses, shapes, etc., of the respective parts are schematically illustrated in the drawings, compared to the actual modes. However, the schematic illustration is merely an example, and adds no restrictions to the interpretation of the invention. Besides, in the specification and drawings, the structural elements having functions, which are identical or similar to the functions of the structural elements described in connection with preceding drawings, are denoted by like reference numerals, and an overlapping detailed description is omitted unless otherwise necessary.

[First Embodiment]

FIG. 1 is a perspective view showing an example of the external appearance of a display device 1 according to a first embodiment. A first direction X, a second direction Y and a third direction Z are orthogonal to one another. However, they may intersect one another at an angle other than 90 degrees. In the present embodiment, the third direction Z may be referred to as “upward” or “above”. The opposite direction of the third direction Z may be referred to as “downward” or “below”.

The display device 1 comprises a display unit DSP and optical elements 10 , 20 A and 20 B. In the present embodiment, the optical elements 10 , 20 A and 20 B are equivalent to first, second and third optical elements, respectively. The display unit DSP, the optical element 10 and the optical element 20 A are housed in a housing 70 . In the example, the optical element 20 B is held by the housing 70 . However, the optical element 20 B may be held by a member different from the housing 70 .

The structure of the display unit DSP is not particularly limited as long as it emits display light. For example, the display unit DSP is a liquid crystal display device comprising a liquid crystal layer. For example, the display unit DSP may be a self-luminous display device comprising an organic electroluminescent element, etc., an electronic paper display device comprising an electrophoretic element, etc., a display device to which micro-electromechanical systems (MEMS) are applied, or a display device to which electrochromism is applied.

The optical element 10 reflects at least part of incident light and transmits part of incident light. For example, the optical element 10 has a plate-like shape, and comprises a first surface 10 A and a second surface 10 B on a side opposite to the first surface 10 A. The optical element 10 is provided such that the first and second surfaces 10 A and 10 B are parallel to the X-Y plane defined by the first and second directions X and Y. The first surface 10 A faces the display unit DSP and the optical element 20 A. The second surface 10 B faces the optical element 20 B. The optical element 10 comprises edge portions 10 E 1 and 10 E 2 extending in the first direction X. The edge portion (first edge portion) 10 E 1 is located on a side close to the display unit DSP. The edge portion (second edge portion) 10 E 2 is located between the optical element 20 A and the optical element 20 B.

The optical elements 20 A and 20 B impart a phase difference to incident light and retroreflect incident light. The optical elements 20 A and 20 B are arranged in the third direction Z. The optical element 10 is interposed between the optical element 20 A and the optical element 20 B.

The optical element 20 A and the display unit DSP are arranged in the second direction Y in the housing 70 . In the example shown in FIG. 1 , the optical element 20 A comprises edge portions 20 A 1 and 20 A 2 extending in the first direction X. The edge portion 20 A 1 is closer to the display unit DSP than the edge portion 20 A 2 in the second direction Y. The edge portion 20 A 2 is closer to the optical element 10 than the edge portion 20 A 1 in the third direction Z.

The optical element 20 B faces the optical element 20 A and the display unit DSP across the intervening optical element 10 . In the example shown in FIG. 1 , the optical element 20 B comprises edge portions 20 B 1 and 20 B 2 extending in the first direction X. The edge portion 20 B 1 is closer to the display unit DSP than the edge portion 20 B 2 in the second direction Y. The edge portion 20 B 2 is closer to the optical element 10 than the edge portion 20 B 1 in the third direction Z. In the example shown in FIG. 1 , the optical element 20 B is provided substantially parallel to the display unit DSP.

FIG. 2 shows a structural example of the display device 1 shown in FIG. 1 . FIG. 2 shows a surface parallel to the Y-Z plane defined by the second and third directions Y and Z. The display device 1 comprises the optical element 10 , the display unit DSP, the optical element 20 A and the optical element 20 B.

The optical element 10 comprises a first polarizing element 11 , a second polarizing element 12 and a support substrate 13 .

The first and second polarizing elements 11 and 12 comprise a transmission axis which transmits first linearly polarized light and reflect second linearly polarized light orthogonal to the transmission axis. For example, the first linearly polarized light is a P wave parallel to an incident surface. The second linearly polarized light is an S wave perpendicular to an incident surface. The first and second polarizing elements 11 and 12 are structured by, for example, a wire-grid polarizing filter, a reflective polarizing film to which a brightness enhancement film is applied, or a multi-layer body in which the reflective polarizing film and a linear polarizer are stacked. In the example shown in FIG. 2 , the first polarizing element 11 comprises the first surface 10 A. The first surface 10 A faces the display unit DSP and the optical element 20 A. The second polarizing element 12 comprises the second surface 10 B. The second surface 10 B faces the optical element 20 B. The first and second surfaces 10 A and 10 B are surfaces parallel to the X-Y plane, and are equivalent to reflective surfaces for the second linearly polarized light.

The support substrate 13 is located between the first polarizing element 11 and the second polarizing element 12 , and is attached to the first and second polarizing elements 11 and 12 . For example, the support substrate 13 is formed of glass or resin. The refractive index of the support substrate 13 is preferably equal to that of the material of the first and second polarizing elements 11 and 12 .

The display unit DSP comprises a display panel PNL, a modulating element 30 and a driver DR.

The display panel PNL emits display light for display image I 0 . In the present embodiment, for example, the display panel PNL is a liquid crystal display panel which holds a liquid crystal layer between a pair of substrates. The display light emitted from the display panel PNL is, for example, the second linearly polarized light. The display panel PNL comprises a display surface IP 0 which displays display image I 0 . The display surface IP 0 faces the first surface 10 A. In the example shown in FIG. 2 , the display panel PNL is provided such that distance LD between the display surface IP 0 and the first surface 10 A is increased in the second direction Y. In other words, distance LD on the edge portion 10 E 1 side is less than distance LD on the edge portion 10 E 2 side. Distance LD is a distance parallel to the third direction Z.

The liquid crystal display panel may be a transmissive panel which displays an image by selectively transmitting the light emitted from a light source device, a reflective panel which displays an image by selectively reflecting external light or the light emitted from a light source device, or a transflective panel which comprises both the transmissive display function and the reflective display function. In place of the display panel PNL, the display unit DSP may comprise a screen on which the light emitted from a projector is projected or may comprise a display medium (for example, a poster) lighted by an illumination device.

The modulating element 30 overlaps the display panel PNL. In the example shown in FIG. 2 , the modulating element 30 faces the display surface IP 0 such that they are substantially parallel to each other. The modulating element 30 may be attached to the display surface IP 0 of the display panel PNL or may be spaced apart from the display surface IP 0 . The modulating element 30 selectively modulates the second linearly polarized light emitted from the display panel PNL into the first linearly polarized light. The term “selectively” includes the meanings of temporal modulation and spatial modulation. In the following example, this specification explains the modulating element 30 which temporally modulates light. The modulating element 30 which spatially modulates light is explained later.

The modulating element 30 is controlled in two modes and imparts a phase difference to transmitted light in accordance with the mode. For example, in a first mode, the modulating element 30 imparts a phase difference of approximately λ/2 to transmitted light. Here, λ is the wavelength of transmitted light. When the second linearly polarized light passes through the modulating element 30 in the first mode, the polarization plane is rotated approximately 90 degrees. Thus, the second linearly polarized light is converted into the first linearly polarized light. In a second mode, the modulating element 30 does not impart a phase difference to transmitted light. In the second mode, when the second linearly polarized light passes through the modulating element 30 , the polarization plane is not changed. Thus, when the mode is switched between the first mode and the second mode, it is possible to temporally switch the polarization plane of the display light emitted from the display unit DSP such that the polarization plane is parallel or perpendicular to the transmission axis of the optical element 10 .

The driver DR drives the display panel PNL and the modulating element 30 . The driver DR controls the display operation of the display panel PNL. The driver DR switches the mode between the first mode and the second mode in the modulating element 30 . For example, the driver DR switches the mode of the modulating element 30 between the first mode and the second mode in synchronization with display image I 0 displayed on the display panel PNL.

The optical element 20 A comprises a first retroreflective element 201 and a first retardation film RA 1 .

The first retroreflective element 201 retroreflects incident light. In other words, the first retroreflective element 201 reflects incident light in a direction parallel to incident light and opposite to that of incident light. The first retroreflective element 201 is located below the first surface 10 A, and comprises a surface 201 A facing the first surface 10 A and the display unit DSP, and a back surface 201 B on a side opposite to the surface 201 A. The first retroreflective element 201 is inclined with respect to the X-Y plane such that distance (first distance) L 21 between the first surface 10 A and the surface 201 A is decreased in the second direction Y. In other words, distance L 21 on the edge portion 10 E 1 side is greater than distance L 21 on the edge portion 10 E 2 side. Distance L 21 is a length parallel to the third direction Z.

In the example shown in FIG. 2 , the surface 201 A is flat. The back surface 201 B comprises retroreflectors. The back surface 201 B is an uneven surface comprising concave portions CC and convex portions CV. The convex portions CV protrude to a side opposite to the optical element 10 . On the back surface 201 B, the first retroreflective element 201 comprises retroreflective portions 21 which retroreflect the light reflected on the optical element 10 , and non-retroreflective portions 22 which do not retroreflect the light reflected on the optical element 10 and scatter the light reflected on the optical element 10 .

The first retroreflective element 201 is formed of, for example, a resinous material. The retroreflective portions 21 and the non-retroreflective portions 22 are formed at the interface between the resinous material and air. The light incident on the first retroreflective element 201 is mostly retroreflected on or scattered by the back surface 201 B without passing through the back surface 201 B.

The first retardation film RA 1 imparts a phase difference of approximately λ/4 to transmitted light. The first retardation film RA 1 is located between the first surface 10 A and the first retroreflective element 201 , and overlaps the first retroreflective element 201 . In the example shown in FIG. 2 , the first retardation film RA 1 faces the surface 201 A such that they are substantially parallel to each other. The first retardation film RA 1 may be attached to the surface 201 A or may be spaced apart from the surface 201 A.

The optical element 20 B comprises a second retroreflective element 202 and a second retardation film RA 2 .

The second retroreflective element 202 retroreflects incident light. The second retroreflective element 202 is located immediately above the first retroreflective element 201 , and comprises a surface 202 A facing the second surface 10 B, and a back surface 202 B on a side opposite to the surface 202 A. The second retroreflective element 202 faces the display unit DSP across the intervening optical element 10 . In the example shown in FIG. 2 , the surface 202 A faces the display surface IP 0 such that they are substantially parallel to each other. The second retroreflective element 202 is inclined with respect to the X-Y plane such that distance (second distance) L 22 between the surface 202 A and the second surface 10 B is decreased in the second direction Y. In other words, distance L 22 on the edge portion 10 E 1 side is greater than distance L 22 on the edge portion 10 E 2 side. Distance L 22 is a length parallel to the third direction Z.

In a manner similar to that of the first retroreflective element 201 , the second retroreflective element 202 is formed of a resinous material. In the example shown in FIG. 2 , the surface 202 A is flat. In a manner similar to that of the back surface 201 B, the back surface 202 B is an uneven surface comprising the concave portions CC and the convex portions CV, and comprises the retroreflective portions 21 and the non-retroreflective portions 22 . The light incident on the second retroreflective element 202 is mostly retroreflected on or scattered by the back surface 202 B without passing through the back surface 202 B.

The second retardation film RA 2 imparts a phase difference of approximately λ/4 to transmitted light. The second retardation film RA 2 is located between the second surface 10 B and the second retroreflective element 202 , and overlaps the second retroreflective element 202 . In the example shown in FIG. 2 , the second retardation film RA 2 faces the surface 202 A such that they are substantially parallel to each other. The second retardation film RA 2 may be attached to the surface 202 A or may be spaced apart from the surface 202 A.

In the above structure, the light incident on the first retroreflective element 201 and retroreflected on the first retroreflective element 201 passes through the first retardation film RA 1 twice. The light incident on the second retroreflective element 202 and retroreflected on the second retroreflective element 202 passes through the second retardation film RA 2 twice. In this way, a phase difference of approximately λ/2 is imparted to the light retroreflected on the optical elements 20 A and 20 B.

In this example, the first and second retroreflective elements 201 and 202 are provided such that their flat surfaces face the optical element 10 . However, the first and second retroreflective elements 201 and 202 may be provided such that their uneven surfaces (in other words, the surfaces comprising the retroreflectors) face the optical element 10 .

The uneven surfaces (the back surfaces 201 B and 202 B in the example shown in FIG. 2 ) may be covered with a reflective film having light reflectivity. The reflective film is formed of a material having light reflectivity, such as silver (Ag), aluminum (Al) or aluminum alloy. The thickness of the reflective film is substantially uniform. Surface treatment may be applied to the reflective film to prevent corrosion. Alternatively, the reflective film may be coated with an inorganic material such as silicon nitride (SiN).

FIG. 3 shows an example of the optical path until the display light emitted from the display unit DSP forms aerial images I 1 and I 2 . Aerial images I 1 and I 2 are equivalent to the real images of display image 10 . FIG. 3( a ) shows a case where the modulating element 30 is controlled so as to be in the first mode. FIG. 3( b ) shows a case where the modulating element 30 is controlled so as to be in the second mode. With reference to FIG. 3 and FIG. 2 , this specification explains the function of each structure to form aerial images I 1 and I 2 from display image I 0 in the display unit DSP. FIG. 2 shows an optical path in the first mode with dashed arrows A 1 , and an optical path in the second mode with solid arrows A 2 . In the present embodiment, the display panel PNL emits the second linearly polarized light equivalent to the display light of display image I 0 . Here, the second linearly polarized light comprises a polarization plane orthogonal to the transmission axis of the optical element 10 .

As shown in FIG. 3( a ) , when the modulating element 30 is controlled so as to be in the first mode, the modulating element 30 modulates the second linearly polarized light emitted from the display panel PNL into the first linearly polarized light. Here, the first linearly polarized light comprises a polarization plane parallel to the transmission axis of the optical element 10 . As shown with dashed arrows A 1 in FIG. 2 , the first linearly polarized light passes through the optical element 10 . Subsequently, the first linearly polarized light passes through the second retardation film RA 2 and is converted into circularly polarized light. Here, for example, the circularly polarized light is light whose polarization plane rotates counterclockwise as its path when it is viewed in a direction facing the direction of travel of light. Subsequently, the circularly polarized light is retroreflected on the second retroreflective element 202 . The retroreflected light is circularly polarized light. The retroreflected circularly polarized light passes through the second retardation film RA 2 again, and is converted into the second linearly polarized light. The second linearly polarized light is reflected on the second surface 10 B and forms aerial image I 2 for display image I 0 . The imaging plane IP 2 of aerial image I 2 and the display surface IP 0 are plane-symmetrical with respect to the second surface 10 B.

As shown in FIG. 3( b ) , when the modulating element 30 is in the second mode, the modulating element 30 does not modulate the second linearly polarized light. Even after the second linearly polarized light passes through the modulating element 30 , the second linearly polarized light is maintained. As shown with sold arrows A 2 in FIG. 2 , the second linearly polarized light is reflected on the first surface 10 A toward the first retroreflective element 201 . The second linearly polarized light passes through the first retardation film RA 1 and is converted into circularly polarized light. Subsequently, the circularly polarized light is retroreflected on the first retroreflective element 201 . The retroreflected circularly polarized light passes through the first retardation film RA 1 again, and is converted into the first linearly polarized light. The first linearly polarized light passes through the optical element 10 and forms aerial image I 1 for display image I 0 . The imaging plane IP 1 of aerial image I 1 and the display surface IP 0 are plane-symmetrical with respect to the first surface 10 A.

As described above, aerial images I 1 and I 2 having different imaging planes are formed by switching the mode of the modulating element 30 between the first mode and the second mode. In the example shown in FIG. 2 , aerial image I 2 is located above aerial image I 1 , in other words, in a direction moving away from the optical element 10 in the third direction Z in comparison with aerial image I 1 . Distance LIP between the imaging plane IP 1 and the imaging plane IP 2 is changed based on the distance parallel to the third direction Z between the first surface 10 A and second surface 10 B. Alternatively, distance LIP depends on thickness T 13 of the support substrate 13 . Distance LIP is a distance in a direction orthogonal to the imaging planes IP 1 and IP 2 .

FIG. 4 shows the positional relationship of the display surface IP 0 , the optical element 10 and the imaging planes IP 1 and IP 2 . FIG. 4 shows the imaging plane IP 1 with dashed lines and shows the imaging plane IP 2 with alternate long and short dash lines. In the example shown in FIG. 4 , the display surface IP 0 is rectangular. However, the shape of the display surface IP 0 is not limited to this example. For example, the display surface IP 0 may have a polygonal shape other than a rectangular shape, or may have a circular shape or an elliptic shape.

In the upper left example of FIG. 4 , the character string “ABC” is displayed as display image I 01 on the display surface IP 0 . At this time, the modulating element 30 is controlled so as to be in the first mode in synchronization with display image I 01 . The second linearly polarized light for display image I 01 is modulated into the first linearly polarized light by the modulating element 30 in the first mode, and forms aerial image I 2 in the imaging plane IP 2 . As shown with the alternate long and short dash lines in FIG. 4 , the imaging plane IP 2 and the display surface IP 0 are plane-symmetrical with respect to the second surface 10 B.

In the upper right example of FIG. 4 , a background image is displayed as display image I 02 on the display surface IP 0 . At this time, the modulating element 30 is controlled so as to be in the second mode in synchronization with display image I 02 . The second linearly polarized light for display image I 02 is not modulated by the modulating element 30 in the second mode, and forms aerial image I 1 in the imaging plane IP 1 . As shown with the dashed lines of FIG. 4 , the imaging plane IP 1 and the display surface IP 0 are plane-symmetrical with respect to the first surface 10 A.

When the mode is switched between the first mode and the second mode in synchronization with display images I 01 and I 02 in fast cycles to the extent that the observer cannot notice the switching, as shown in the lower side of FIG. 4 , the observer can view the character string “ABC” floated above the background image.

In the present embodiment, the imaging planes IP 1 and IP 2 are parallel to the surface defined by directions D 1 and D 2 . Direction D 1 is equivalent to the first direction X. Direction D 2 is a direction intersecting the second direction Y at an acute angle θ. The imaging planes IP 1 and IP 2 are planes intersecting the X-Y plane, or are surfaces intersecting the first and second surfaces 10 A and 10 B at an acute angle θ. Direction D 3 is orthogonal to directions D 1 and D 2 . The imaging planes IP 1 and IP 2 are spaced apart from each other in direction D 3 . In the example shown in FIG. 4 , the imaging surface IP 1 is closer to the optical element 10 than the imaging plane IP 2 .

The relationship of display image I 0 and aerial images I 1 and I 2 is as follows. Aerial images I 1 and I 2 are upside down in terms of the vertical relationship with display image I 0 in the third direction Z, and aerial images I 1 and I 2 are identical to display image I 0 in terms of the lateral relationship in the first direction X.

Now, this specification explains the specific examples of structures.

FIG. 5 shows a structural example of the display panel PNL shown in FIG. 2 . Here, as an example of the display panel PNL, this specification explains a transmissive liquid crystal display panel in an active matrix driving method. The display panel PNL comprises a first substrate SUB 1 , a second substrate SUB 2 facing the first substrate SUB 1 , and a liquid crystal layer LC held between the first substrate SUB 1 and the second substrate SUB 2 . The first substrate SUB 1 is attached to the second substrate SUB 2 such that a predetermined cell gap is defined between them. The display panel PNL comprises a display area DA which displays an image. The display area DA comprises a plurality of subpixels PX arranged in matrix.

As the subpixels PX, the display area DA comprises, for example, red pixels PXR corresponding to red, green pixels PXG corresponding green, and blue pixels PXB corresponding to blue. The display area DA may further comprise subpixels corresponding to a color different from red, green and blue (for example, white pixels corresponding to white). Each main pixel for realizing color display includes these subpixels PX corresponding to different colors. In other words, each main pixel is the minimum unit to constitute a color image. In the example shown in FIG. 5 , each main pixel includes a red pixel PXR, a green pixel PXG and a blue pixel PXB.

Each red pixel PXR comprises a red color filter and is configured to mainly transmit red light of the white light emitted from a light source device. Each green pixel PXG comprises a green color filter and is configured to mainly transmit green light of the white light emitted from a light source device. Each blue pixel PXB comprises a blue color filter and is configured to mainly transmit blue light of the white light emitted from a light source device. Although not explained in detail, each color filter may be formed in either the first substrate SUB 1 or the second substrate SUB 2 .

The first substrate SUB 1 comprises a plurality of scanning lines G, and a plurality of signal lines S intersecting the scanning lines G. The scanning lines G are extended to the outside of the display area DA and are connected to a scanning line driver GD. The signal lines S are extended to the outside of the display area DA and are connected to a signal line driver SD. The scanning line driver GD and the signal line driver SD are connected to a controller CNT. The controller CNT generates a control signal based on a video signal, and controls the scanning line driver GD and the signal line driver SD.

Each subpixel PX comprises a switching element SW, a pixel electrode PE, a common electrode CE, etc. Each switching element SW is electrically connected to a corresponding scanning line G and a corresponding signal line S. The switching element SW is formed by, for example, a thin-film transistor. The pixel electrode PE is electrically connected to the switching element SW. The common electrode CE faces a plurality of pixel electrodes PE.

Here, the explanation of the detailed structure of the display panel PNL is omitted. In a display mode using a longitudinal electric field along the normal of the main surfaces of the substrates or a display mode using an electric field inclined at a tilt with respect to the normal of the main surfaces of the substrates, the first substrate SUB 1 comprises the pixel electrodes PE, and the second substrate SUB 2 comprises the common electrode CE. In a display mode using a lateral electric field along the main surfaces of the substrates, the first substrate SUB 1 comprises both the pixel electrodes PE and the common electrode CE. Further, the display panel PNL may comprise a structure corresponding to a display mode appropriately using a combination of the above longitudinal electric field, lateral electric field and inclined electric field.

FIG. 6 is a cross-sectional view showing a structural example of the display panel PNL shown in FIG. 2 . Here, this specification briefly explains a cross-sectional structure of the display panel PNL to which a fringe field switching (FFS) mode, which is one of the display modes using a lateral electric field, is applied.

The first substrate SUB 1 comprises a first insulating substrate 100 , a first insulating film 110 , a common electrode CE, a second insulating film 120 , pixel electrodes PE 1 to PE 3 , a first alignment film AL 1 , etc. The common electrode CE extends over a red pixel PXR, a green pixel PXG and a blue pixel PXB. The pixel electrode PE 1 of the red pixel PXR, the pixel electrode PE 2 of the green pixel PXG and the pixel electrode PE 3 of the blue pixel PXB face the common electrode CE, and comprise slits SLA. In the example shown in FIG. 6 , the common electrode CE is located between the first insulating film 110 and the second insulating film 120 , and the pixel electrodes PE 1 to PE 3 are located between the second insulating film 120 and the first alignment film AL 1 . The pixel electrodes PE 1 to PE 3 may be located between the first insulating film 110 and the second insulating film 120 , and the common electrode CE may be located between the second insulating film 120 and the first alignment film AL 1 . In this case, the slits SLA are formed in the common electrode CE.

The second substrate SUB 2 comprises a second insulating substrate 200 , a light-shielding layer BM, color filters CFR, CFG and CFB, an overcoat layer OC, a second alignment film AL 2 , etc. The color filters CFR, CFG and CFB face the pixel electrodes PE 1 , PE 2 and PE 3 , respectively, across the intervening liquid crystal layer LC. The color filter CFR is a red color filter. The color filter CFG is a green color filter. The color filter CFB is a blue color filter. In the example shown in FIG. 6 , the color filters CFR, CFG and CFB are formed in the second substrate SUB 2 . However, they may be formed in the first substrate SUB 1 .

The liquid crystal layer LC is encapsulated between the first alignment film AL 1 and the second alignment film AL 2 .

A light source device LS faces the first substrate SUB 1 . Various forms are applicable as the light source device LS. Here, the explanation of the detailed structure thereof is omitted.

A first optical element OD 1 including a first polarizer PL 1 is provided on the external surface of the first insulating substrate 100 . A second optical element OD 2 including a second polarizer PL 2 is provided on the external surface of the second insulating substrate 200 . For example, the first absorption axis of the first polarizer PL 1 is orthogonal to the second absorption axis of the second polarizer PL 2 . In the example shown in FIG. 6 , the surface of the second optical element OD 2 is equivalent to the display surface IP 0 of the display panel PNL. As described above, the second polarizer PL 2 is provided so as to emit the second linearly polarized light.

The main pixels each including a red pixel PXR, a green pixel PXG and a blue pixel PXB are arranged with pitch P 1 .

FIG. 7 is a plan view showing a structural example of a retroreflective element 20 . The plan view shows the plane defined by first and third directions d 1 and d 3 orthogonal to each other. The retroreflective element 20 explained here is applicable as the first and second retroreflective elements 201 and 202 .

The retroreflective element 20 is formed by a plurality of retroreflectors 23 . In the plan view shown in FIG. 7 , each retroreflector 23 comprises an equilateral-triangular edge EG. The edge EG comprises a side EA parallel to the third direction d 3 , and sides EB and EC extending in directions intersecting the first and third directions d 1 and d 3 . For example, each retroreflector 23 comprises three reflective surfaces 23 A, 23 B and 23 C orthogonal to each other. The sides EA, EB and EC are included in the reflective surfaces 23 A, 23 B and 23 C, respectively. The intersection of the three reflective surfaces 23 A, 23 B and 23 C is equivalent to the center O of the retroreflector 23 . For example, the center O of each retroreflector 23 becomes depressed to the back of the plane of paper. When each retroreflector 23 comprises a concave portion surrounded by the three reflective surfaces 23 A, 23 B and 23 C, the edge EG is equivalent to the top portion of the retroreflector 23 , and the center O is equivalent to the bottom portion of the retroreflector 23 . It should be noted that each retroreflector 23 may comprise a convex portion surrounded by the three reflective surfaces 23 A, 23 B and 23 C. In this case, the edge EG is equivalent to the bottom portion of the retroreflector 23 , and the center O is equivalent to the top portion of the retroreflector 23 .

These retroreflectors 23 are arranged in the third direction d 3 . The retroreflectors 23 are arranged in the first direction d 1 with pitch P 2 . It should be noted that the shapes of the retroreflectors 23 adjacent to each other in the first and third directions d 1 and d 3 are reversed at 180 degrees with respect to each other. In FIG. 7 , retroreflectors 231 and 232 are arranged in the first direction d 1 . The retroreflectors 231 and 232 are located such that they are line-symmetrical with respect to an edge E 12 .

The resolution of aerial images I 1 and I 2 depends on pitch P 2 of the retroreflectors 23 . To prevent the reduction of the resolution, pitch P 2 is preferably less than pitch P 1 of the pixels on the display panel PNL shown in FIG. 6 .

FIG. 8 is a perspective view showing a structural example of each retroreflector 23 shown in FIG. 7 . The shape of each retroreflector 23 is explained, applying a coordinate system in which x, y and z-axes are orthogonal to one another.

In the xyz coordinate system, each retroreflector 23 comprises three reflective surfaces 23 A, 23 B and 23 C. The reflective surfaces 23 A to 23 C have the same shape. Each of the reflective surfaces 23 A to 23 C is formed into a right-angled isosceles triangle. The reflective surfaces 23 A to 23 C are orthogonal to one another. Each retroreflector 23 comprising the reflective surfaces 23 A to 23 C having the above shape is called a corner cube, a corner reflector, etc.

When point A on the x-axis is (α, 0, 0), point B on the y-axis is (0, α, 0), and point C on the z-axis is (0, 0, α), the reflective surface 23 A is formed in the x-y plane and is defined by the origin O and points A and B. The reflective surface 23 B is formed in the y-z plane and is defined by the origin O and points B and C. The reflective surface 23 C is formed in the x-z plane and is defined by the origin O and points A and C. The segment connecting points A and B, the segment connecting points B and C and the segment connecting points A and C are equivalent to the sides EA, EB and EC of the edge EG shown in FIG. 7 , respectively. Here, the origin O is equivalent to the center O shown in FIG. 7 .

When the origin O is equivalent to the bottom portion of the retroreflector 23 , the surface defined by the three points A, B and C is not present. The internal side surrounded by the three reflective surfaces 23 A to 23 C is an air layer. When the origin O is equivalent to the top portion of the retroreflector 23 , the surface defined by the three points A, B and C is present. The retroreflector 23 is a regular tetrahedron.

Each retroreflector 23 realizes retroreflection which reflects incident light in substantially the same optical path as the incident light by reflecting the light on the three reflective surfaces 23 A to 23 C. The vicinities of the three points A, B and C could be non-retroreflective portions which do not retroreflect light (in other words, non-retroreflective portions in which light is not reflected on the three reflective surfaces). The shape of each retroreflector 23 is not limited to the example shown in FIG. 8 . The non-reflective portions may be cut.

FIG. 9 is a cross-sectional view showing a structural example of the modulating element 30 shown in FIG. 2 . FIG. 9( a ) is a cross-sectional view of the modulating element 30 controlled so as to be in the first mode. FIG. 9( b ) is a cross-sectional view of the modulating element 30 controlled so as to be in the second mode. In FIG. 9 , a first direction a, a second direction b and a third direction c are orthogonal to one another. FIG. 9 shows a surface parallel to the b-c plane defined by the second and third directions b and c. Here, the second linearly polarized light L 2 as display light travels in the third direction c. In the example shown in FIG. 9 , the direction of polarization of the second linearly polarized light L 2 is parallel to the second direction b, and the direction of polarization of the first linearly polarized light L 1 is parallel to the first direction a.

The modulating element 30 is a liquid crystal panel comprising support substrates 31 and 32 , a first electrode 33 , a second electrode 34 , alignment films 35 and 36 and a liquid crystal layer 37 . The first electrode 33 is located between the support substrate 31 and the alignment film (first alignment film) 35 . The second electrode 34 is located between the support substrate 32 and the alignment film (second alignment film) 36 . The liquid crystal layer 37 is located between the alignment film 35 and the alignment film 36 . The support substrates 31 and 32 are transparent substrates for visible light, such as glass substrates or resinous substrates. The first electrode 33 and the second electrode 34 are formed of a transparent conductive material such as ITO or IZO. In the example shown in FIG. 9 , the first electrode 33 is provided in the support substrate 31 , and the second electrode 34 is provided in the support substrate 32 . However, both the first electrode 33 and the second electrode 34 may be provided in the same substrate, in other words, in the support substrate 31 or 32 . For example, the liquid crystal layer 37 has positive dielectric anisotropy. For example, the alignment films 35 and 36 are horizontal alignment films having alignment restriction force for aligning liquid crystal molecules 37 M in a direction parallel to the main surfaces. Alignment treatment has been applied to the alignment film 35 in the second direction b. Alignment treatment has been applied to the alignment film 36 in the first direction a.

FIG. 9( a ) shows the first mode (off state) in which voltage is not applied between the first and second electrodes 33 and 34 facing each other across the intervening liquid crystal layer 37 . At this time, in the liquid crystal layer 37 , 90° twist alignment is applied to the liquid crystal molecules 37 M. Near the alignment film 35 , the liquid crystal molecules 37 M are initially aligned in the second direction b. Near the alignment film 36 , the liquid crystal molecules 37 M are initially aligned in the first direction a. When the second linearly polarized light L 2 enters the modulating element 30 in the first mode, the axis of polarization is rotated by the effect of the twisted liquid crystal molecules 37 M. Thus, after the second linearly polarized light L 2 passes through the liquid crystal layer 37 , the second linearly polarized light L 2 becomes the first linearly polarized light L 1 .

FIG. 9( b ) shows the second mode (on state) in which voltage is applied between the first electrode 33 and the second electrode 34 . At this time, in the liquid crystal layer 37 , the liquid crystal molecules 37 M are vertically aligned such that their long axes are parallel to the formed electric field. The long axis of each liquid crystal molecule 37 M is aligned in the third direction c. The second linearly polarized light L 2 having entered the modulating element 30 in the second mode is less affected by the vertically-aligned liquid crystal molecules 37 M, and passes through the liquid crystal layer 37 while maintaining the axis of polarization.

FIG. 10 is a plan view showing structural examples of the first and second electrodes 33 and 34 shown in FIG. 9 . FIG. 10 shows a surface parallel to the a-b plane defined by the first and second directions a and b. The modulating element 30 comprises an effective area AA through which light is allowed to pass in the a-b plane. For example, the effective area AA has a rectangular shape comprising short sides parallel to the first direction a and long sides parallel to the second direction b. However, the shape is not limited to the examples shown in FIG. 10 . The effective area AA may have other polygonal shapes, a circular shape or an elliptic shape.

In the structural example shown in FIG. 10( a ) , each of the first and second electrodes 33 and 34 is formed by a single sheet electrode continuously extending over the entire surface of the effective area AA. As described above, the first electrode 33 faces the second electrode 34 across the intervening liquid crystal layer 37 . The driver DR is electrically connected to each of the first and second electrodes 33 and 34 . In this structural example, the direction of alignment of the liquid crystal molecules 37 M in the liquid crystal layer 37 is controlled on the entire surface of the effective area AA by controlling the voltage applied by the driver DR to the first and second electrodes 33 and 34 . In this manner, the modulating element 30 is capable of controlling the first mode (in other words, the mode in which the polarization plane is rotated) and the second mode (in other words, the mode in which the polarization plane is not modulated) on the entire surface of the effective area AA.

The structural example shown in FIG. 10( b ) is different from the structural example shown in FIG. 10( a ) in respect that the effective area AA of the modulating element 30 comprises a plurality of strip-shaped subareas SA. In a manner similar to that of the structural example shown in FIG. 10( a ) , the first electrode 33 is formed by a single sheet electrode. The second electrode 34 is formed by a plurality of strip-shaped electrodes 341 to 347 spaced apart from one another. In the example shown in FIG. 10( b ) , each of the strip-shaped electrodes 341 to 347 has a rectangular shape extending in the first direction a. The strip-shaped electrodes 341 to 347 are arranged at intervals in the second direction b. The first electrode 33 faces the strip-shaped electrodes 341 to 347 . The driver DR is electrically connected to the first electrode 33 , and is electrically connected to each of the strip-shaped electrodes 341 to 347 . Each subarea SA is equivalent to an overlapping portion in which the first electrode 33 overlaps one of the strip-shaped electrodes 341 to 347 in the a-b plane. In the example shown in FIG. 10( b ) , each subarea SA is a strip-shaped area extending in the first direction a.

The strip-shaped electrodes 341 to 347 may extend in the second direction b and be arranged at intervals in the first direction a. The structural example shown in FIG. 10( b ) is equivalent to an example in which one of the first and second electrodes 33 and 34 is formed by a sheet electrode, and the other is formed by a plurality of strip-shaped electrodes. The first electrode 33 may be formed by a plurality of strip-shaped electrodes, and the second electrode 34 may be formed by a single sheet electrode.

In this structural example, the direction of alignment of the liquid crystal molecules 37 M is controlled in each subarea SA by controlling the voltage individually applied by the driver DR to the strip-shaped electrodes 341 to 347 . In this manner, the modulating element 30 is capable of controlling the first mode and the second mode for each subarea SA. The modulating element 30 of this structural example is also capable of controlling the first mode and the second mode on the entire surface of the effective area AA by collectively driving all the strip-shaped electrodes 341 to 347 .

The structural example shown in FIG. 10( c ) is different from the structural example shown in FIG. 10( a ) in respect that the effective area AA of the modulating element 30 comprises a plurality of subareas SA in matrix. The first electrode 33 is formed by a plurality of strip-shaped electrodes 331 to 335 spaced apart from one another. The second electrode 34 is formed by a plurality of strip-shaped electrodes 341 to 346 spaced apart from one another. In the example shown in FIG. 10( c ) , the strip-shaped electrodes 331 to 335 extend in the second direction b, and are arranged at intervals in the first direction a. The strip-shaped electrodes 341 to 346 extend in the first direction a, and are arranged at intervals in the second direction b. The strip-shaped electrodes 331 to 335 face the strip-shaped electrodes 341 to 346 . The driver DR is electrically connected to each of the strip-shaped electrodes 331 to 335 , and is electrically connected to each of the strip-shaped electrodes 341 to 346 . Each subarea SA is equivalent to a rectangular intersection in which one of the strip-shaped electrodes 331 to 335 intersects one of the strip-shaped electrodes 341 to 346 in the a-b plane. In the example shown in FIG. 10( c ) , the subareas SA are arranged in matrix in the first direction a and the second direction b.

In this structural example, the direction of alignment of the liquid crystal molecules 37 M is controlled in each subarea SA by controlling the voltage individually applied by the driver DR to the strip-shaped electrodes 331 to 335 and the strip-shaped electrodes 341 to 346 . In this manner, the modulating element 30 is capable of controlling the first mode and the second mode for each subarea SA. The modulating element 30 of this structural example is also capable of controlling the first mode and the second mode on the entire surface of the effective area AA by collectively driving all the strip-shaped electrodes 331 to 335 and 341 to 346 .

In the above structural example, the shape of each subarea SA is not limited to a rectangular shape. Each subarea SA may have other polygonal shapes, a circular shape, an elliptic shape or an arbitrary shape. The shapes of the first and second electrodes 33 and 34 defining the shape of the subareas SA can be freely selected.

FIG. 11 is a plan view showing the distribution of a phase difference imparted to transmitted light in the effective area AA shown in FIG. 10 . Here, of the effective area AA, an area which imparts a phase difference of approximately λ/2 to transmitted light is referred to as a modulation area MA, and an area which does not impart a phase difference to transmitted light is referred to as a non-modulation area NMA. The modulation area MA is realized by the first mode. The non-modulation area NMA is realized by the second mode.

In the example shown in FIG. 11 , the modulation area MA and the non-modulation area NMA alternate over the entire surface of the effective area AA. For example, the entire surface of the effective area AA is the modulation area MA at time to, is the non-modulation area NMA at time t 1 , and is the modulation area MA at time t 2 . At time t 0 and time t 2 , the second linearly polarized light having entered the modulating element 30 is modulated into the first linearly polarized light and ultimately forms aerial image I 2 . The second linearly polarized light having passed through the modulating element 30 without modulation at time t 1 ultimately forms aerial image I 1 . This structure is realized by all the structures of FIG. 10( a ) to FIG. 10( c ) .

Now, this specification explains the modulating element 30 which spatially modulates light.

FIG. 12 is a plan view showing another structural example of the modulating element 30 shown in FIG. 2 . The modulating element 30 shown in FIG. 12 is different from the structural example shown in FIG. 11 in respect that the effective area AA includes the modulation areas MA and the non-modulation areas NMA. In the example shown in FIG. 12 , the modulation areas MA and the non-modulation areas NMA extend in the first direction a, and are alternately arranged in the second direction b. For example, width WA of each modulation area MA and each non-modulation area NMA is equivalent to pitch P 1 of the main pixels. Here, width WA is parallel to the second direction b. Width WA may be an integral multiple of pitch P 1 .

In the example shown in FIG. 12 , when the second linearly polarized light enters the modulation areas MA of the effective area AA, the second linearly polarized light is modulated into the first linearly polarized light, and forms aerial image I 2 . The second linearly polarized light having passed through the non-modulation areas NMA without modulation forms aerial image I 1 . This structure is realized by the structure shown in FIG. 10( b ) or FIG. 10( c ) . Alternatively, this structure may be realized with a retardation film without using a liquid crystal panel. When the modulating element 30 is a retardation film, the retardation film may be a single film comprising the modulation area MA which imparts a phase difference and the non-modulation area NMA which does not impart a phase difference. Alternatively, the retardation film may be a film comprising an aperture portion in the non-modulation area NMA. Here, the modulation area MA imparts a phase difference of approximately λ/2 to transmitted light. When the modulation element 30 is a retardation film, the retardation film may be attached to the display surface IP 0 or may be directly formed on the display surface IP 0 .

In the present embodiment, the display device 1 comprises the optical element 10 which transmits part of display light and reflects the other part, and the first and second retroreflective elements 201 and 202 which retroreflect incident light. In this way, the display device 1 is capable of displaying aerial images I 1 and I 2 having different imaging planes. For example, aerial image I 1 can be observed on the rear side of aerial image I 2 . Thus, the observer can view an image with an appearance of depth. Further, the depth, in other words, distance LIP between aerial image I 1 and aerial image I 2 , can be freely set by thickness 13 T of the support substrate 13 located between the first polarizing element 11 and the second polarizing element 12 .

[Second Embodiment]

FIG. 13 schematically shows the external appearance of a display device 2 according to a second embodiment. FIG. 13 shows a surface parallel to the X-Z plane defined by a first direction X and a third direction Z. The second embodiment is different from the first embodiment in respect that a housing 70 comprises a cover 70 A, and an optical element 20 B is provided on the internal surface 70 A 1 of the cover 70 A.

An optical element 10 is located on a side lower than the upper surface 70 B of the housing 70 , in other words, on a side closer to a display unit DSP than the upper surface 70 B. In the example shown in FIG. 13 , the cover 70 A is attached to the housing 70 near an edge portion 10 E 2 . The cover 70 A is freely rotatable based on the axis parallel to the first direction X. FIG. 13( a ) shows an open state in which the cover 70 A is open. In the open state, the cover 70 A is allowed to be held at an arbitrary position. FIG. 13( b ) shows a closed state in which the cover 70 A is closed. In the closed state, the external surface 70 A 2 of the cover 70 A is aligned with the upper surface 70 B.

In the present embodiment, an effect similar to that of the first embodiment can be obtained. Further, in the present embodiment, the optical elements 10 and 20 B can be protected by closing the cover 70 A. As the background of aerial images I 1 and I 2 can be darkened by the cover 70 A, the visibility of aerial images I 1 and I 2 can be improved.

While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel embodiments described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.