Display device

Abstract

To suppress the decrease in visibility of an image.SOLUTION: In an embodiment, a display device includes a transparent substrate having a first main surface and a second main surface facing the first main surface, a display element facing the first main surface and configured to emit display light with circular polarization toward the transparent substrate, a first optical element facing the display element through the transparent substrate, disposed on the second main surface, and configured to diffract the display light having been transmitted through the transparent substrate, a second optical element separated from the first optical element, disposed on the second main surface, and configured to diffract the display light having propagated inside the transparent substrate, a light control element facing the second optical element through the transparent substrate and including guest-host liquid crystal, and a retardation plate disposed between the transparent substrate and the light control element.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] FIELD An embodiment of the present invention relates to a display device. [Background technology]

[0002] In recent years, various head-mounted displays that use a holographic optical element (hereinafter sometimes simply referred to as an HOE) that diffracts display light from a display element and a light-guiding member have been studied. One known example is a technology in which holographic diffractive optical elements are provided on each surface of a light-guiding member. The HOE arranged on one surface of the light-guiding member diffracts the display light so that it is totally reflected by the light-guiding member, and the HOE arranged on the other surface of the light-guiding member diffracts the display light propagating inside the light-guiding member so that it is emitted to the outside. For example, in a head-mounted display capable of providing augmented reality, when the intensity of external light is high, there is a risk that the visibility of images for the user will be reduced. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-219106 Summary of the Invention [Problem to be solved by the invention]

[0004] An object of the embodiment is to provide a display device that can suppress a decrease in image visibility. [Means for solving the problem]

[0005] According to one embodiment, the display device comprises: The display device comprises a transparent substrate having a first main surface and a second main surface opposite the first main surface; a display element facing the first main surface and configured to emit circularly polarized display light toward the transparent substrate; a first optical element facing the display element via the transparent substrate and disposed on the second main surface and configured to diffract the display light that has passed through the transparent substrate; a second optical element spaced apart from the first optical element and disposed on the second main surface and configured to diffract the display light that has propagated inside the transparent substrate; a light control element facing the second optical element via the transparent substrate and comprising a guest-host liquid crystal; and a retardation plate disposed between the transparent substrate and the light control element. [Brief explanation of the drawings]

[0006] [Figure 1] FIG. 1 is a diagram showing an example of the configuration of a display device DSP. [Figure 2] FIG. 2 is a diagram illustrating an example of the light-adjusting element 100 shown in FIG. [Figure 3] FIG. 3 is a diagram schematically illustrating an example of a cross section of the light-adjusting device 100 shown in FIG. 2 taken along line AB. [Figure 4A] FIG. 4A is a diagram for explaining the operation of the light-adjusting element 100 in the off state. [Figure 4B] FIG. 4B is a diagram for explaining the operation of the light-adjusting device 100 in the on state. [Figure 5A] FIG. 5A is a diagram for explaining the operation of the light-adjusting element 100 in the off state. [Figure 5B] FIG. 5B is a diagram for explaining the operation of the light-adjusting device 100 in the on state. [Figure 6A] FIG. 6A shows the measurement results of Experiment 1. [Figure 6B] FIG. 6B shows the measurement results of Experiment 2. [Figure 7] FIG. 7 is a diagram illustrating an example of the configuration of the first optical element 11 and the second optical element 12. As shown in FIG. [Figure 8] FIG. 8 is a diagram for explaining one of the effects of the display device DSP. [Figure 9]FIG. 9 is a diagram illustrating an example of a control system of a display device DSP applied as goggles. [Figure 10] FIG. 10 is a diagram illustrating an example of control of the vertical alignment type light control element 100. In FIG. [Figure 11] FIG. 11 is a diagram illustrating an example of control of the horizontal alignment type light control element 100. In FIG. [Figure 12] FIG. 12 is a diagram for explaining matrix driving of the light control element 100. In FIG. DETAILED DESCRIPTION OF THE INVENTION

[0007] An embodiment will be described with reference to the drawings. The disclosure is merely an example, and appropriate modifications that a person skilled in the art can easily make while maintaining the gist of the disclosure are naturally included within the scope of the present disclosure. Furthermore, in the drawings, the width, thickness, shape, etc. of each part may be schematically depicted compared to the actual embodiment for clarity of explanation, but these are merely examples and are not intended to limit the interpretation of the present disclosure. Furthermore, in this specification and each drawing, components that perform the same or similar functions as those described above with respect to the previous drawings are designated by the same reference numerals, and redundant detailed descriptions may be omitted as appropriate.

[0008] In addition, to facilitate understanding, the drawings depict, where necessary, mutually perpendicular X, Y, and Z axes. The direction along the X axis is referred to as the first direction X, the direction along the Y axis is referred to as the second direction Y, and the direction along the Z axis is referred to as the third direction Z. Viewing various elements parallel to the third direction Z is referred to as a planar view. Note that terms referring to the relative positions of two or more components, such as above, above, between, and facing, include not only cases where the two or more components are in direct contact, but also cases where they are separated from each other by a gap or another component.

[0009] FIG. 1 is a diagram showing an example of the configuration of a display device DSP.

[0010] The display device DSP includes a display module DM, a transparent substrate 1, a first optical element 11, a second optical element 12, a retardation plate 20, and a light control element 100. The display module DM includes a display element 2 and an optical system 3. The display device DSP is held by frames 31 and 32.

[0011] The transparent substrate 1 is, for example, a glass substrate, but may also be a resin substrate. The transparent substrate 1 is formed in a flat plate shape and has a first main surface 1A and a second main surface 1B opposite to the first main surface 1A. The first main surface 1A and the second main surface 1B are flat surfaces parallel to each other.

[0012] The display element 2 is disposed on the side opposite to the first main surface 1A of the transparent substrate 1, and is configured to emit display light DL toward the transparent substrate 1. The display light DL is, for example, circularly polarized light. Such a display element 2 may be, for example, a display element including a self-luminous element such as an organic electroluminescence element or a light-emitting diode, or may be a display element that combines an optical switch such as a liquid crystal panel with a lighting device.

[0013] The optical system 3 is disposed between the display element 2 and the transparent substrate 1. Such an optical system 3 includes at least one lens and is configured to collimate the divergent display light DL emitted from the display element 2.

[0014] The first optical element 11 faces the display element 2 via the transparent substrate 1 and is disposed on the second main surface 1B. That is, the transparent substrate 1 is located between the display element 2 and the first optical element 11. In one example, the first optical element 11 is bonded to the transparent substrate 1. Such a first optical element 11 is configured to diffract the display light DL transmitted through the transparent substrate 1. The diffraction angle of the first optical element 11 at which the display light DL is diffracted is set so that the display light DL is totally reflected inside the transparent substrate 1.

[0015] The second optical element 12 is spaced apart from the first optical element 11, faces the user's eye E, and is disposed on the second principal surface 1B. In one example, the second optical element 12 is bonded to the transparent substrate 1. Such a second optical element 12 is configured to diffract the display light DL propagated inside the transparent substrate 1. In the second optical element 12, the diffraction angle at which the display light DL is diffracted is set so that the display light DL is emitted substantially perpendicularly from the first principal surface 1A.

[0016] Each of the first optical element 11 and the second optical element 12 is, for example, an element containing cholesteric liquid crystal, but may also be a diffractive element such as a holographic optical element (HOE) that diffracts incident light at a predetermined diffraction angle.

[0017] The photochromic element 100 faces the second optical element 12 via the transparent substrate 1, and is positioned between the user's eye E and the transparent substrate 1. As will be described later, this photochromic element 100 includes a guest-host liquid crystal and is configured to be able to form an absorption axis in a specific direction. The absorption axis is an axis that absorbs polarized light components in a specific direction perpendicular to the traveling direction of light.

[0018] The retarder 20 is disposed between the transparent substrate 1 and the light-adjusting element 100. In one example, the retarder 20 is bonded to the transparent substrate 1, and the light-adjusting element 100 is bonded to the retarder 20. However, the transparent substrate 1, the retarder 20, and the light-adjusting element 100 may be spaced apart from one another. Such a retarder 20 is, for example, a λ / 4 plate, and has the function of imparting a λ / 4 phase difference to transmitted light, where λ is the wavelength of the transmitted light. Note that the retarder 20 is desirably configured to impart a λ / 4 phase difference to transmitted light in any of a first wavelength band including a blue component, a second wavelength band including a green component, and a third wavelength band including a red component.

[0019] The frame 31 forms a space between itself and the transparent substrate 1 to accommodate the display module DM. The frame 31 also has an opening 31A facing the eye E. The retarder 20 and the light control element 100 are located in the opening 31A. In the illustrated example, the installation area of ​​the retarder 20 and the light control element 100 is smaller than the area of ​​the opening 31A. Note that the retarder 20 and the light control element 100 may be arranged over the entire area of ​​the opening 31A.

[0020] The frame 32 sandwiches the transparent substrate 1 between itself and the frame 31. The frame 32 also has an opening 32A that overlaps with the opening 31A. The second optical element 12 is located in the opening 32A. In the illustrated example, the area of ​​the second optical element 12 is smaller than the area of ​​the opening 32A. Note that the second optical element 12 may be disposed over the entire area of ​​the opening 32A.

[0021] In such a display device DSP, the display light DL emitted from the display element 2 is collimated by the optical system 3 and then incident on the transparent substrate 1 approximately perpendicularly. The display light DL transmitted through the transparent substrate 1 is diffracted by the first optical element 11. The display light DL diffracted by the first optical element 11 is propagated inside the transparent substrate 1 while being totally reflected by the first principal surface 1A and the second principal surface 1B, and is diffracted by the second optical element 12. The display light DL diffracted by the second optical element 12 is emitted approximately perpendicularly from the first principal surface 1A, transmits through the retardation plate 20, and then transmits through the light control element 100. This allows the user to view the image displayed on the display element 2. The user can also observe the background through the display device DSP.

[0022] Such a display device DSP can be applied to glasses-type or goggle-type head-mounted displays, and can be used to provide users with virtual reality, augmented reality, and the like.

[0023] FIG. 2 is a diagram illustrating an example of the light-adjusting element 100 shown in FIG.

[0024] The light control element 100 includes a first transparent substrate 110, a second transparent substrate 120, a liquid crystal layer LC, and a seal SE. The first transparent substrate 110 and the second transparent substrate 120 are each formed in a flat plate shape and overlap each other in a plan view.

[0025] Here, the first direction X and the second direction Y, which are orthogonal to each other, are directions parallel to the respective main surfaces of the first transparent substrate 110 and the second transparent substrate 120, and the third direction Z is the thickness direction of each of the first transparent substrate 110 and the second transparent substrate 120. The first transparent substrate 110 and the second transparent substrate 120 overlap each other in the third direction Z.

[0026] In the illustrated example, the first transparent substrate 110 and the second transparent substrate 120 are both formed in a rectangular shape, but this is not limiting. For example, the first transparent substrate 110 and the second transparent substrate 120 may have any shape other than a rectangular shape, such as a polygon, a circle, an ellipse, or a semicircle.

[0027] The liquid crystal layer LC is located between the first transparent substrate 110 and the second transparent substrate 120, is disposed across the dimming region 100A, and is sealed with a seal SE. A first alignment treatment direction D1 of the first alignment film AL1 located between the first transparent substrate 110 and the liquid crystal layer LC and a second alignment treatment direction D2 of the second alignment film AL2 located between the second transparent substrate 120 and the liquid crystal layer LC are parallel to each other and directed in opposite directions. In the illustrated example, the first alignment treatment direction D1 and the second alignment treatment direction D2 are both parallel to the first direction X. The alignment treatments applied to the first alignment film AL1 and the second alignment film AL2 may be rubbing treatments or photo-alignment treatments.

[0028] The slow axis SA of the retarder 20 intersects with the first alignment treatment direction D1 and the second alignment treatment direction D2 in the XY plane defined by the first direction X and the second direction Y. In one example, the angle θ1 between the slow axis SA and the first alignment treatment direction D1 and the angle θ2 between the slow axis SA and the second alignment treatment direction D2 are 45°.

[0029] FIG. 3 is a diagram schematically illustrating an example of a cross section of the light-adjusting device 100 shown in FIG. 2 taken along line AB.

[0030] The first transparent substrate 110 and the second transparent substrate 120 face each other in the third direction Z. The liquid crystal layer LC is located between the first transparent substrate 110 and the second transparent substrate 120. In the dimming region 100A, the first transparent electrode TEA is located between the first transparent substrate 110 and the liquid crystal layer LC and is covered with a first alignment film AL1. The second transparent electrode TEB is located between the second transparent substrate 120 and the liquid crystal layer LC and is covered with a second alignment film AL2. The liquid crystal layer LC is in contact with the first alignment film AL1 and the second alignment film AL2.

[0031] The first transparent substrate 110 and the second transparent substrate 120 are, for example, glass substrates, but may also be resin substrates.

[0032] The first transparent electrode TEA and the second transparent electrode TEB are formed of a transparent conductive material such as indium tin oxide (ITO), and each of the first transparent electrode TEA and the second transparent electrode TEB is, for example, a sheet electrode disposed across the dimming region 100A.

[0033] Each of the first transparent electrode TEA and the second transparent electrode TEB may be a plurality of strip electrodes. In this case, the first strip electrodes corresponding to the first transparent electrode TEA and the second strip electrodes corresponding to the second transparent electrode TEB are arranged to intersect with each other in the dimming area 100A. The intersections of the first strip electrodes and the second strip electrodes form segments of the dimming area 100A. The liquid crystal layer LC of each segment is driven in response to the potential difference between the first strip electrodes and the second strip electrodes (simple matrix drive).

[0034] Alternatively, the first transparent electrode TEA may be a plurality of segment electrodes arranged in a matrix, and the second transparent electrode TEB may be a sheet electrode arranged across the dimming area 100A. In this case, each of the segment electrodes is electrically connected to an active element. The area where one segment electrode faces the sheet electrode constitutes a segment of the dimming area 100A. The liquid crystal layer LC of each segment is driven in response to the potential difference between the segment electrode and the sheet electrode (active matrix drive).

[0035] The liquid crystal layer LC includes a guest-host liquid crystal including dichroic dye molecules as guest molecules GM and liquid crystal molecules as host molecules HM. In one example, the guest molecules GM are black dichroic dye molecules. In the illustrated example, the guest molecules GM and the host molecules HM are aligned in a first direction X.

[0036] The guest molecules GM have different absorbances in the long axis direction and the short axis direction, and mainly absorb linearly polarized light components parallel to the long axis direction. Therefore, the dimming region 100A can be colored according to the color of the guest molecules. When the guest molecules GM are black dichroic dye molecules, the guest molecules GM absorb linearly polarized light components parallel to the long axis, and can form dark regions in the dimming region 100A. The long axis direction of such guest molecules GM corresponds to the absorption axis AA of the dimming element 100. The absorption axis AA is parallel to the first alignment treatment direction D1 and the second alignment treatment direction D2 shown in FIG. 2 and is set to the first direction X in the illustrated example.

[0037] Next, the vertical alignment type light control device 100 will be described.

[0038] 4A is a diagram for explaining the operation of the light-adjusting element 100 in the off state. Note that only the components necessary for the explanation are shown here, and the illustration of other components is simplified or omitted.

[0039] In the light-adjusting element 100, the first alignment film AL1 covering the first transparent electrode TEA and the second alignment film AL2 covering the second transparent electrode TEB are both vertical alignment films that have an alignment restriction force in their normal directions (i.e., the third direction Z). As described with reference to FIG. 2, the first alignment film AL1 and the second alignment film AL2 have been subjected to an alignment treatment. The host molecules HM are liquid crystal molecules with negative dielectric anisotropy. The guest molecules GM are black dichroic dye molecules.

[0040] In the off state (OFF), no voltage is applied to the first transparent electrode TEA and the second transparent electrode TEB. At this time, the host molecules HM are initially aligned such that their major axes are aligned along the third direction Z due to the alignment restraining forces of the first alignment film AL1 and the second alignment film AL2. The guest molecules GM, like the host molecules HM, are aligned such that their major axes are aligned along the third direction Z. In other words, both the host molecules HM and the guest molecules GM are aligned vertically. Therefore, no absorption axis is formed in the light-adjusting device 100.

[0041] FIG. 4B is a diagram for explaining the operation of the light-adjusting device 100 in the on state.

[0042] In the on state (ON), a voltage is applied to the first transparent electrode TEA and the second transparent electrode TEB. At this time, the host molecules HM are aligned so as to intersect with the electric field formed in the liquid crystal layer LC. As described above, since the first alignment film AL1 and the second alignment film AL2 are aligned in the first direction X, the host molecules HM are aligned so that their major axes are aligned along the first direction X. The guest molecules GM follow the host molecules HM and are aligned so that their major axes are aligned along the first direction X. In other words, both the host molecules HM and the guest molecules GM are aligned horizontally. As a result, an absorption axis AA parallel to the first direction X is formed in the light-adjusting element 100.

[0043] When unpolarized light, such as natural light, passes through the on-state photochromic element 100 along the third direction Z, the guest molecules GM absorb the linearly polarized component parallel to the long axis direction. In the illustrated example, the guest molecules GM absorb the linearly polarized component of the unpolarized light that is parallel to the first direction X. Furthermore, the linearly polarized component of the unpolarized light that is parallel to the second direction Y passes through the photochromic element 100. Therefore, for a vertically aligned photochromic element 100, the transmittance of the photochromic element 100 in the on-state is lower than the transmittance of the photochromic element 100 in the off-state.

[0044] Next, the horizontal alignment type light control device 100 will be described.

[0045] 5A is a diagram for explaining the operation of the light-adjusting element 100 in the off state. Note that only the components necessary for the explanation are shown here, and the illustration of other components is simplified or omitted.

[0046] In the light-adjusting element 100, the first alignment film AL1 covering the first transparent electrode TEA and the second alignment film AL2 covering the second transparent electrode TEB are both horizontal alignment films that have an alignment restriction force in the first direction X. The host molecules HM are liquid crystal molecules with positive dielectric anisotropy. The guest molecules GM are black dichroic dye molecules.

[0047] In the off state (OFF), no voltage is applied to the first transparent electrode TEA and the second transparent electrode TEB. At this time, the host molecules HM are initially aligned such that their major axes are aligned along the first direction X due to the alignment restraining forces of the first alignment film AL1 and the second alignment film AL2. The guest molecules GM, like the host molecules HM, are aligned such that their major axes are aligned along the first direction X. In other words, both the host molecules HM and the guest molecules GM are aligned horizontally. As a result, an absorption axis AA parallel to the first direction X is formed in the light-adjusting device 100.

[0048] FIG. 5B is a diagram for explaining the operation of the light-adjusting device 100 in the on state.

[0049] In the on state (ON), a voltage is applied to the first transparent electrode TEA and the second transparent electrode TEB. At this time, the host molecules HM are aligned along the electric field formed in the liquid crystal layer LC. That is, the host molecules HM are aligned with their major axes aligned along the third direction Z. The guest molecules GM follow the host molecules HM and are aligned with their major axes aligned along the third direction Z. That is, both the host molecules HM and the guest molecules GM are aligned vertically. Therefore, no absorption axis is formed in the light-adjusting device 100.

[0050] In such a horizontally aligned light control element 100, the transmittance of the light control element 100 in the off state is smaller than the transmittance of the light control element 100 in the on state.

[0051] Next, a description will be given of the optical characteristics of the light control device 100. Here, an experiment was carried out to measure the transmittance of the vertical alignment type light control device 100.

[0052] The experimental conditions were as follows: the light source, polarizer, dimming element, and detector were arranged in this order. The light source was configured to emit unpolarized illumination light. With the light source turned on, the voltage applied to the liquid crystal layer of the dimming element was changed, and the detector detected the light transmitted through the dimming element to measure the transmittance. The thickness of the liquid crystal layer of the dimming element used was 10 μm.

[0053] In Experiment 1, the transmittance was measured under the condition that the first alignment treatment direction D1 and the second alignment treatment direction D2 were parallel to the absorption axis of the polarizer. In Experiment 2, the transmittance was measured under the condition that the first alignment treatment direction D1 and the second alignment treatment direction D2 were perpendicular to the absorption axis of the polarizer.

[0054] FIG. 6A shows the measurement results of Experiment 1. FIG. 6B shows the measurement results of Experiment 2. 6A and 6B, the horizontal axis represents the voltage E (V) applied to the liquid crystal layer, and the vertical axis represents the transmittance T (%).

[0055] As shown in Figure 6A, Experiment 1 showed that the transmittance T was almost constant regardless of the magnitude of the applied voltage E. In other words, it was confirmed that the absorption axis of the light control element formed when a voltage was applied to the liquid crystal layer was parallel to the absorption axis of the polarizer.

[0056] As shown in Figure 6B, in Experiment 2, the transmittance T decreased as the applied voltage E increased. As shown in the figure, the transmittance T became 1% or less when a voltage of 5 V or more was applied. It was confirmed that such a light control element can sufficiently absorb the linearly polarized component of the illumination light that has passed through the polarizer.

[0057] FIG. 7 is a diagram illustrating an example of the configuration of the first optical element 11 and the second optical element 12. As shown in FIG.

[0058] Each of the first optical element 11 and the second optical element 12 is a liquid crystal element containing cholesteric liquid crystal. The cholesteric liquid crystal contains a plurality of liquid crystal molecules arranged in a spiral that rotates in one direction. Note that in Figure 7, the cholesteric liquid crystal contained in each of the first optical element 11 and the second optical element 12 is schematically shown in an enlarged state in which a plurality of liquid crystal molecules are arranged in a spiral.

[0059] Such cholesteric liquid crystals are configured to diffract circularly polarized light with the same rotation direction as the cholesteric liquid crystal and transmit circularly polarized light with the opposite rotation direction to the cholesteric liquid crystal. The wavelength band of the circularly polarized light diffracted by the cholesteric liquid crystal is set according to the helical pitch and refractive index anisotropy of the cholesteric liquid crystal.

[0060] Each of the first optical element 11 and the second optical element 12 includes a first liquid crystal layer LL1, a second liquid crystal layer LL2, and a third liquid crystal layer LL3. The first liquid crystal layer LL1, the second liquid crystal layer LL2, and the third liquid crystal layer LL3 are stacked in this order on the transparent substrate 1. The first liquid crystal layer LL1, the second liquid crystal layer LL2, and the third liquid crystal layer LL3 are configured to diffract display light of different wavelength bands. The stacking order of the multiple liquid crystal layers is not limited to the example shown in the figure. Furthermore, the number of liquid crystal layers included in each of the first optical element 11 and the second optical element 12 is not limited to three, but may be two, four, or more.

[0061] The first liquid crystal layer LL1 contains a first cholesteric liquid crystal CL1. The first cholesteric liquid crystal CL1 has a first helical pitch P1. Here, the helical pitch refers to one period of the helix (the thickness along the helical axis required for the orientation of the helically arranged liquid crystal molecules to rotate 360 ​​degrees).

[0062] The second liquid crystal layer LL2 includes a second cholesteric liquid crystal CL2. The second cholesteric liquid crystal CL2 has a second helical pitch P2. The second helical pitch P2 is different from the first helical pitch P1 and is larger than the first helical pitch P1 (P1). <P2)。

[0063] The third liquid crystal layer LL3 includes a third cholesteric liquid crystal CL3. The third cholesteric liquid crystal CL3 has a third helical pitch P3. The third helical pitch P3 is different from the first helical pitch P1 and the second helical pitch P2, and is larger than the second helical pitch P2 (P2 <P3)。

[0064] The first cholesteric liquid crystal CL1, the second cholesteric liquid crystal CL2, and the third cholesteric liquid crystal CL3 have the same twist direction.

[0065] In the first optical element 11 configured as above, the first liquid crystal layer LL1 is configured to diffract, at a diffraction surface DS1, display light DLB of a first wavelength band including a blue component out of the display light perpendicularly incident on the first main surface 1A of the transparent substrate 1. Similar to the first liquid crystal layer LL1, the second liquid crystal layer LL2 is configured to diffract, at a diffraction surface DS2, display light DLG of a second wavelength band including a green component out of the display light. Furthermore, the third liquid crystal layer LL3 is configured to diffract, at a diffraction surface DS3, display light DLR of a third wavelength band including a red component out of the display light.

[0066] In the second optical element 12 configured as described above, the first liquid crystal layer LL1 is configured to diffract the display light DLB propagating through the transparent substrate 1 at a diffraction surface DS1. Similar to the first liquid crystal layer LL1, the second liquid crystal layer LL2 is configured to diffract the display light DLG at a diffraction surface DS2. The third liquid crystal layer LL3 is configured to diffract the display light DLR at a diffraction surface DS3. The display light DLB, DLG, and DLR diffracted by the second optical element 12 are emitted perpendicularly from the first main surface 1A of the transparent substrate 1.

[0067] Fig. 8 is a diagram for explaining one of the effects of the display device DSP. Note that Fig. 8 shows only the configuration necessary for the explanation. The diagram also shows the polarization state in a plane perpendicular to the traveling direction of the display light DL.

[0068] The display light DL emitted from the display element 2 is, for example, left-handed circularly polarized light CP, and as shown in Figure 7, includes display light DLB of a first wavelength band including a blue component, display light DLG of a second wavelength band including a green component, and display light DLR of a third wavelength band including a red component.

[0069] The display light DL transmitted through the transparent substrate 1 is diffracted by the first optical element 11. The first cholesteric liquid crystal CL1, the second cholesteric liquid crystal CL2, and the third cholesteric liquid crystal CL3 included in the first optical element 11 rotate in the same direction as the rotation direction of the circularly polarized display light DL. Therefore, as described with reference to FIG. 7 , the display light DLB is diffracted by the first liquid crystal layer LL1, the display light DLG is diffracted by the second liquid crystal layer LL2, and the display light DLR is diffracted by the third liquid crystal layer LL3. The diffracted display light DL is propagated while being totally reflected by the transparent substrate 1.

[0070] The display light DL propagated through the transparent substrate 1 is diffracted by the second optical element 12. The first cholesteric liquid crystal CL1, the second cholesteric liquid crystal CL2, and the third cholesteric liquid crystal CL3 included in the second optical element 12 rotate in the same direction as the rotation direction of the display light DL, which is circularly polarized light CP. Therefore, as described with reference to FIG. 7, the display light DLB is diffracted by the first liquid crystal layer LL1, the display light DLG is diffracted by the second liquid crystal layer LL2, and the display light DLR is diffracted by the third liquid crystal layer LL3. The diffracted display light DL passes through the transparent substrate 1. The polarization state of the display light DL passing through the transparent substrate 1 is circularly polarized light CP.

[0071] The display light DL transmitted through the transparent substrate 1 is transmitted through the retardation plate 20. When the display light DL is transmitted through the retardation plate 20, a phase difference is imparted to the display light DL, and the display light DL is converted into linearly polarized light LP.

[0072] The display light DL transmitted through the retardation plate 20 is transmitted through the light control element 100, which has an absorption axis AA. That is, the display light DL, which is linearly polarized light LP, is a polarization component orthogonal to the absorption axis AA. Therefore, the display light DL emitted from the display element 2 reaches the user's eye E with almost no loss.

[0073] On the other hand, the polarization state of external light AL traveling from behind the display device DSP toward the user's eye E is unpolarized NP. When such external light AL passes through the second optical element 12, the transparent substrate 1, and the retardation film 20, the polarization state of the external light AL remains unchanged and remains unpolarized NP. The external light AL then passes through the light control element 100, which has an absorption axis AA. At this time, the polarization component of the external light AL that is unpolarized NP and is parallel to the absorption axis AA is absorbed by the light control element 100. The polarization component of the external light AL that is perpendicular to the absorption axis AA passes through the light control element 100 and reaches the user's eye E. In other words, the intensity of the external light AL that reaches the eye E is reduced by approximately half by the light control element 100. Therefore, even when the display device DSP is used in a bright place where the intensity of the external light AL is relatively high, it is possible to suppress a decrease in the visibility of the displayed image.

[0074] FIG. 9 is a diagram illustrating an example of a control system of a display device DSP applied as goggles.

[0075] The display device DSP1 is placed, for example, in front of the user's left eye, and the display device DSP2 is placed in front of the user's right eye.

[0076] The illuminance sensor 200 is configured to measure the illuminance around the display devices DSP1 and DSP2.

[0077] The control unit 300 is configured to control the display element 2 and the light control element 100 of each of the display devices DSP1 and DSP2.

[0078] For example, the control unit 300 drives the display element 2 to generate display light DL. Furthermore, the control unit 300 drives the light control element 100 in accordance with the illuminance measured by the illuminance sensor 200 to appropriately form an absorption axis AA.

[0079] FIG. 10 is a diagram illustrating an example of control of the vertical alignment type light control element 100. In FIG.

[0080] First, the control unit 300 controls the illuminance sensor 200 to measure the illuminance (step ST1). Then, the control unit 300 determines whether the measured illuminance LX is equal to or greater than a predetermined threshold value LX_th (step ST2).

[0081] The control unit 300 sets the light-adjusting element 100 to the ON state (step ST3) based on the determination that the illuminance LX is equal to or greater than the predetermined threshold value LX_th (step ST2, YES). That is, the control unit 300 applies a voltage to each of the first transparent electrode TEA and the second transparent electrode TEB. This applies a voltage to the liquid crystal layer LC, driving the guest-host liquid crystal. In the liquid crystal layer LC, the host molecules HM and the guest molecules GM are horizontally aligned, and an absorption axis AA is formed in the light-adjusting element 100. As a result, the intensity of external light is reduced in bright places, and a decrease in the visibility of the displayed image is suppressed.

[0082] On the other hand, the control unit 300 determines that the illuminance LX is lower than the predetermined threshold value LX_th (step ST2, NO), and sets the light-adjusting element 100 to the off state (step ST4). That is, the control unit 300 does not apply a voltage to each of the first transparent electrode TEA and the second transparent electrode TEB. In the liquid crystal layer LC, the host molecules HM and the guest molecules GM are vertically aligned, and no absorption axis AA is formed. Therefore, in a dark place, the background can be observed through the display devices DSP1 and DSP2. In other words, the light-adjusting element 100 does not obstruct the field of view in a dark place.

[0083] FIG. 11 is a diagram illustrating an example of control of the horizontal alignment type light control element 100. In FIG.

[0084] First, the control unit 300 controls the illuminance sensor 200 to measure the illuminance (step ST11). Then, the control unit 300 determines whether the measured illuminance LX is equal to or less than a predetermined threshold value LX_th (step ST12).

[0085] Based on the determination that the illuminance LX is equal to or less than the predetermined threshold value LX_th (step ST12, YES), the control unit 300 sets the light-adjusting element 100 to the ON state (step ST13). That is, the control unit 300 applies a voltage to each of the first transparent electrode TEA and the second transparent electrode TEB. This applies a voltage to the liquid crystal layer LC, driving the guest-host liquid crystal. In the liquid crystal layer LC, the host molecules HM and the guest molecules GM are vertically aligned, and no absorption axis AA is formed. Therefore, in a dark place, the background can be observed through the display devices DSP1 and DSP2.

[0086] On the other hand, the control unit 300 determines that the illuminance LX is higher than the predetermined threshold LX_th (step ST12, NO), and sets the light-adjusting element 100 to the off state (step ST14). That is, the control unit 300 does not apply a voltage to each of the first transparent electrode TEA and the second transparent electrode TEB. In the liquid crystal layer LC, the host molecules HM and the guest molecules GM are horizontally aligned, forming an absorption axis AA. Therefore, in bright places, the intensity of external light is reduced, and a decrease in the visibility of the displayed image is suppressed.

[0087] FIG. 12 is a diagram for explaining matrix driving of the light control element 100. In FIG.

[0088] The dimming region 100A has a plurality of segments SG arranged in a matrix in the first direction X and the second direction Y. As described above, each segment SG may be configured as an intersection between a first strip electrode and a second strip electrode, or as a region where a segment electrode electrically connected to an active element faces a sheet electrode. This allows each segment SG to individually drive the guest-host liquid crystal in the liquid crystal layer LC. Such matrix driving of the dimming element 100 is performed by the control unit 300 shown in FIG. 9.

[0089] For example, as described with reference to Figures 10 and 11, the dimming element 100 is driven in a bright place so as to form an absorption axis AA in all segments SG in the dimming region 100A, and in a dark place so as not to form an absorption axis AA in all segments SG in the dimming region 100A, thereby having high transparency.

[0090] The light-adjusting element 100 is driven to form an absorption axis AA when the display light DL is emitted from the display element 2, and is driven not to form the absorption axis AA when the display light DL is not emitted. Furthermore, by applying matrix driving to the light-adjusting element 100, the absorption axis AA can be formed only in the segments SG that overlap with the image formed by the display light DL.

[0091] In the illustrated example, in the dimming area 100A, four segments SG are lined up in the first direction X, and five segments are lined up in the second direction Y (five rows and four columns). Of the multiple segments SG, an absorption axis AA is formed in the upper two-row and four-column segment SG, and no absorption axis is formed in the lower three-row and four-column segment SG.

[0092] When the upper 2-row, 4-column segments SG are overlapping segments with the image, the visibility of the image can be improved. Also, the lower 3-row, 4-column segments SG have high transparency, making it easier to observe the background.

[0093] As described above, according to the present embodiment, it is possible to provide a display device and a light guide element that can suppress a decrease in the visibility of an image.

[0094] Although several embodiments of the present disclosure have been described, these embodiments are presented as examples and are not intended to limit the scope of the disclosure. These novel embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the disclosure. These embodiments and their modifications are included within the scope and spirit of the disclosure, as well as within the scope of the disclosure and its equivalents as set forth in the claims. [Explanation of symbols]

[0095] DSP…display device 1...Transparent substrate 1A...First main surface 1B...Second main surface DM...Display module 2...Display element 3...Optical system 20…Retardation plate SA…Slow axis 11...first optical element 12...second optical element LL1: First liquid crystal layer CL1: First cholesteric liquid crystal LL2: Second liquid crystal layer CL2: Second cholesteric liquid crystal LL3: Third liquid crystal layer CL3: Third cholesteric liquid crystal 100...Dimming element AA...Absorption axis 110...First transparent substrate 120...Second transparent substrate LC...liquid crystal layer GM...guest molecule HM...host molecule TEA...First transparent electrode TEB...Second transparent electrode AL1...first alignment film D1...alignment direction AL2: Second alignment film D2: Alignment direction 200...Illuminance sensor 300...Control unit

Claims

1. a transparent substrate having a first main surface and a second main surface opposite to the first main surface; a display element facing the first main surface and configured to emit circularly polarized display light toward the transparent substrate; a first optical element disposed on the second main surface and facing the display element via the transparent substrate, the first optical element being configured to diffract the display light transmitted through the transparent substrate; a second optical element disposed on the second main surface and spaced apart from the first optical element, the second optical element being configured to diffract the display light propagated through the transparent substrate; a light control element facing the second optical element via the transparent substrate and including a guest-host liquid crystal; a retardation plate disposed between the transparent substrate and the light control element, Display device.

2. The light control element is a first transparent substrate; a second transparent substrate; a liquid crystal layer located between the first transparent substrate and the second transparent substrate, the liquid crystal layer including the guest-host liquid crystal; a first transparent electrode located between the first transparent substrate and the liquid crystal layer; a first alignment film covering the first transparent electrode; a second transparent electrode located between the second transparent substrate and the liquid crystal layer; a second alignment film covering the second transparent electrode; a first alignment treatment direction of the first alignment film and a second alignment treatment direction of the second alignment film are parallel to each other; The display device according to claim 1 .

3. the guest-host liquid crystal has dichroic dye molecules as guest molecules and liquid crystal molecules having negative dielectric anisotropy as host molecules, each of the first alignment film and the second alignment film is a vertical alignment film; an absorption axis parallel to the first alignment treatment direction and the second alignment treatment direction is formed in a state where a voltage is applied to the first transparent electrode and the second transparent electrode; The display device according to claim 2 .

4. In addition, an illuminance sensor, a control unit that controls the application of a voltage to the first transparent electrode and the second transparent electrode when the illuminance measured by the illuminance sensor is equal to or greater than a predetermined threshold value, The display device according to claim 3 .

5. the guest-host liquid crystal has dichroic dye molecules as guest molecules and liquid crystal molecules having positive dielectric anisotropy as host molecules, each of the first alignment film and the second alignment film is a horizontal alignment film; an absorption axis parallel to the first alignment treatment direction and the second alignment treatment direction is formed when no voltage is applied to the first transparent electrode and the second transparent electrode; The display device according to claim 2 .

6. In addition, an illuminance sensor, a control unit that controls the application of a voltage to the first transparent electrode and the second transparent electrode when the illuminance measured by the illuminance sensor is equal to or lower than a predetermined threshold value, The display device according to claim 5 .

7. the retardation plate is a λ / 4 plate and has a slow axis intersecting at an angle of 45° with each of the first alignment treatment direction and the second alignment treatment direction; The display device according to claim 2 .

8. The light control element has a plurality of segments arranged in a matrix, Each of the plurality of segments is configured to be able to individually drive the guest-host liquid crystal. The display device according to claim 1 .

9. each of the first optical element and the second optical element includes a cholesteric liquid crystal rotated in the same direction as the rotation direction of the circularly polarized light; The display device according to claim 1 .

10. Each of the first optical element and the second optical element is a first liquid crystal layer including a first cholesteric liquid crystal having a first helical pitch; a second liquid crystal layer overlying the first liquid crystal layer and including a second cholesteric liquid crystal having a second helical pitch different from the first helical pitch; a third liquid crystal layer overlying the second liquid crystal layer and including a third cholesteric liquid crystal having a third helical pitch different from the first helical pitch and the second helical pitch; The first cholesteric liquid crystal, the second cholesteric liquid crystal, and the third cholesteric liquid crystal have the same twist direction. The display device according to claim 1 .

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