Display device

Abstract

To improve light use efficiency.SOLUTION: A display device includes a display panel including a display region and configured to emit display light of linearly polarized light, a holographic element that reflects light with a particular incidence angle and transmits light with an incidence angle different from the particular incidence angle, a retardation plate disposed between the display panel and the holographic element, a semi-transparent element that is disposed opposing the holographic element with a space therebetween, reflects first circularly polarized light out of the light having transmitted through the holographic element, and transmits second circularly polarized light that is polarized opposite to the first circularly polarized light, and a lens element opposing the semi-transparent element and having a lens operation of condensing the second circularly polarized light having transmitted through the semi-transparent element.SELECTED DRAWING: Figure 8

Description

[Technical Field]

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

[0002] In recent years, attention has been focused on technology that provides virtual reality (VR) using a head-mounted display worn on the user's head. A head-mounted display is configured to display images on a display placed in front of the user's eyes. This allows a user wearing the head-mounted display to experience a realistic virtual reality space. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Special Publication No. 2003-504663 [Patent Document 2] Special Publication No. 2003-529795 [Patent Document 3] Japanese Patent Application Laid-Open No. 2018-106160 [Patent Document 4] Japanese Patent Application Publication No. 2019-53152 [Patent Document 5] Japanese Patent Application Publication No. 2019-148626 [Patent Document 6] Japanese Patent Application Publication No. 2019-148627 Summary of the Invention [Problem to be solved by the invention]

[0004] An object of this embodiment is to provide a display device that can improve the light utilization efficiency. [Means for solving the problem]

[0005] The display device of one embodiment includes: The optical element includes a display panel having a display area including a polarizing plate and configured to emit linearly polarized display light; a holographic element that reflects light at a specific incident angle and transmits light at an incident angle different from the specific incident angle; a retardation plate disposed between the display panel and the holographic element; a semi-transparent element that faces the holographic element at a distance and reflects a first circularly polarized light and transmits a second circularly polarized light that is opposite to the first circularly polarized light among the light that has passed through the holographic element; and a lens element that faces the semi-transparent element and has a lens action that focuses the second circularly polarized light that has passed through the semi-transparent element. In another embodiment, the display device includes: The optical element includes a display panel including a polarizing plate and having a display area configured to emit linearly polarized display light; a first holographic element that reflects light at a first specific incident angle and transmits light at an incident angle different from the first specific incident angle; a second holographic element that faces the first holographic element at a distance and reflects light that has passed through the first holographic element at a second specific incident angle different from the first specific incident angle and transmits light that has an incident angle different from the second specific incident angle; a lens element that faces the second holographic element and has a lens effect of focusing first circularly polarized light that has passed through the second holographic element; and a retardation plate that is arranged between the display panel and the first holographic element or between the second holographic element and the lens element. [Brief explanation of the drawings]

[0006] [Figure 1] FIG. 1 is a perspective view showing an example of the appearance of a head-mounted display 1 to which a display device according to an embodiment is applied. [Figure 2] FIG. 2 is a diagram for explaining an outline of the configuration of the head-mounted display 1 shown in FIG. [Figure 3] FIG. 3 is a cross-sectional view showing a first configuration example of the display device DSP. [Figure 4] FIG. 4 is a cross-sectional view showing an example of the lens element LE shown in FIG. [Figure 5]FIG. 5 is a plan view showing an example of an alignment pattern in the liquid crystal layer LC1 shown in FIG. [Figure 6] FIG. 6 is a cross-sectional view showing an example of the semi-transmissive element TR shown in FIG. [Figure 7] FIG. 7 is a cross-sectional view showing an example of the semi-transmissive element TR shown in FIG. [Figure 8] FIG. 8 is a diagram for explaining an example of the optical action of the display device DSP shown in FIG. [Figure 9] FIG. 9 is a diagram for explaining another example of the optical action of the display device DSP shown in FIG. [Figure 10] FIG. 10 is a plan view showing an example of the configuration of the illumination device 3 applicable to the display device DSP shown in FIG. [Figure 11] FIG. 11 is a cross-sectional view showing an example of the configuration of the head mounted display 1. As shown in FIG. [Figure 12] FIG. 12 is a diagram for explaining the first cholesteric liquid crystal layer CLB, the second cholesteric liquid crystal layer CLG, and the third cholesteric liquid crystal layer CLR shown in FIG. [Figure 13] FIG. 13 is a plan view showing another example of the configuration of an illumination device applicable to the display device DSP shown in FIG. [Figure 14] FIG. 14 is a cross-sectional view showing another example of the configuration of the head mounted display 1. [Figure 15] FIG. 15 is a cross-sectional view showing a second configuration example of the display device DSP. [Figure 16] FIG. 16 is a diagram for explaining an example of the optical action of the display device DSP shown in FIG. [Figure 17] FIG. 17 is a diagram illustrating the first specific incident angle θ1 of the first holographic element HE1 and the second specific incident angle θ2 of the second holographic element HE2 shown in FIG. [Figure 18] FIG. 18 is a cross-sectional view showing an example of the configuration of the head mounted display 1. As shown in FIG. [Figure 19] FIG. 19 is a cross-sectional view showing another configuration example of the head mounted display 1. DETAILED DESCRIPTION OF THE INVENTION

[0007] The present embodiment will be described below 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 invention are naturally included within the scope of the present invention. Furthermore, the drawings may be schematic in terms of the width, thickness, shape, etc. of each part 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 invention. Furthermore, in this specification and each drawing, components that perform the same or similar functions as those described above with reference to the previous drawings are designated by the same reference numerals, and redundant detailed descriptions may be omitted as appropriate.

[0008] In the drawings, mutually perpendicular X-axis, Y-axis, and Z-axis are shown as necessary to facilitate understanding. 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. The plane defined by the X-axis and Y-axis is referred to as the XY plane, and viewing the XY plane is referred to as planar view.

[0009] FIG. 1 is a perspective view showing an example of the appearance of a head-mounted display 1 to which a display device according to this embodiment is applied. The head mounted display 1 includes, for example, a display device DSPR for the right eye and a display device DSPL for the left eye. When a user wears the head mounted display 1 on his / her head, the display device DSPR is disposed so as to be located in front of the user's right eye, and the display device DSPL is disposed so as to be located in front of the user's left eye.

[0010] FIG. 2 is a diagram for explaining an outline of the configuration of the head-mounted display 1 shown in FIG.

[0011] The display device DSPR includes a display panel 2R, an illumination device 3R, and an optical system 4R indicated by a dotted line. The illumination device 3R is disposed on the rear surface of the display panel 2R and is configured to illuminate the display panel 2R. The optical system 4R is disposed in front of the display panel 2R (or between the user's right eye ER and the display panel 2R) and is configured to guide display light from the display panel 2R to the right eye ER.

[0012] The display panel 2R includes, for example, a liquid crystal panel and a polarizing plate. The display panel 2R is disposed between the illumination device 3R and the optical system 4R. For example, a driver IC chip 5R and a flexible printed circuit board 6R are connected to the display panel 2R. The driver IC chip 5R controls the driving of the display panel 2R (particularly, controls the display operation of the display panel 2R).

[0013] The display device DSPL includes a display panel 2L, an illumination device 3L, and an optical system 4L indicated by dotted lines. The illumination device 3L is disposed on the rear surface of the display panel 2L and is configured to illuminate the display panel 2L. The optical system 4L is disposed in front of the display panel 2L (or between the user's left eye EL and the display panel 2L) and is configured to guide display light from the display panel 2L to the left eye EL.

[0014] The display panel 2L includes, for example, a liquid crystal panel and a polarizing plate. The display panel 2L is disposed between the illumination device 3L and the optical system 4L. For example, a driver IC chip 5L and a flexible printed circuit board 6L are connected to the display panel 2L. The driver IC chip 5L controls the driving of the display panel 2L (particularly, controls the display operation of the display panel 2L).

[0015] The display device DSPL is configured substantially similarly to the display device DSPR. That is, the display panel 2R, the illumination device 3R, and the optical system 4R that constitute the display device DSPR are configured in the same manner as the display panel 2L, the illumination device 3L, and the optical system 4L that constitute the display device DSPL, respectively.

[0016] In the display device DSP according to this embodiment, the display panels 2R and 2L are not limited to those including liquid crystal panels, but may also include display panels equipped with self-luminous light-emitting elements such as organic electroluminescence (EL) elements, micro LEDs, and mini LEDs. When the display panels are display panels equipped with light-emitting elements, the illumination devices 3R and 3L are omitted. As will be described in detail later, the display panels 2R and 2L are configured to emit linearly polarized display light and include polarizing plates as necessary.

[0017] An external host computer H is connected to the display panels 2L and 2R, respectively. The host computer H outputs image data corresponding to the images displayed on the display panels 2L and 2R. The image displayed on the display panel 2L is an image for the left eye (or an image viewed by the user's left eye EL). The image displayed on the display panel 2R is an image for the right eye (or an image viewed by the user's right eye ER).

[0018] For example, when the head mounted display 1 is used for VR, the image for the left eye and the image for the right eye are similar images that reproduce the parallax between the two eyes. When the image for the left eye displayed on the display panel 2L is viewed by the user's left eye EL and the image for the right eye displayed on the display panel 2R is viewed by the user's right eye ER, the user can perceive a stereoscopic space (three-dimensional space) as a virtual reality space.

[0019] The display panels 2R and 2L may be configured as a single display panel extending in front of the left eye EL and in front of the right eye ER, and the illumination devices 3R and 3L may be configured as a single illumination device extending in front of the left eye EL and in front of the right eye ER.

[0020] Next, a first configuration example of the display device DSP according to this embodiment will be described.

[0021] First Configuration Example FIG. 3 is a cross-sectional view showing a first configuration example of the display device DSP. The display device DSP includes a display panel 2, an illumination device 3, and an optical system 4. Detailed illustration of the display panel 2 and the illumination device 3 is omitted here. The display device DSP described here can be applied to each of the above-mentioned display devices DSPR and DSPL. The display panel 2 can be applied to each of the above-mentioned display panels 2R and 2L. The illumination device 3 can be applied to each of the above-mentioned illumination devices 3R and 3L. The optical system 4 can be applied to each of the above-mentioned optical systems 4R and 4L.

[0022] The display panel 2 is formed in a flat plate shape extending across the XY plane. The display panel 2 will be described in detail later, but is configured to emit linearly polarized display light DL in the display area DA. For example, the display panel 2 includes a polarizing plate, and the linearly polarized display light DL is emitted through the polarizing plate.

[0023] Not only in the first configuration example described here, but also in other configuration examples, the display panel 2 is not limited to a liquid crystal panel. If the display panel 2 is a display panel equipped with self-luminous light-emitting elements, the illumination device 3 is omitted as described above. In this case, the display light DL emitted from the light-emitting elements passes through a polarizing plate and is converted into linearly polarized display light DL.

[0024] The optical system 4 includes a first structure 4A and a second structure 4B. The first structure 4A is spaced apart from the second structure 4B. In the example shown in Fig. 3, an air layer 4C is provided between the first structure 4A and the second structure 4B. The first structure 4A is disposed between the display panel 2 and the second structure 4B (or between the display panel 2 and the air layer 4C).

[0025] The first structure 4A includes a retardation plate RP and a holographic element HE. The retardation plate RP is a quarter-wave plate configured to impart a phase difference of a quarter wavelength to light passing through it. The holographic element HE has an interference fringe pattern and a refractive index with a period corresponding to the wavelength in the thickness direction (third direction Z). Such a holographic element HE is configured to reflect and diffract a portion of incident light. More specifically, the holographic element HE has a virtual reflecting surface RS1. If the boundary between the display panel 2 and the retarder RP (or a surface parallel to the XY plane) is defined as a reference plane RF, the reflecting surface RS1 is parallel to the reference plane RF. In other words, the angle θ10 between the reflecting surface RS1 and the reference plane RF is 0°. The holographic element HE is configured to reflect light incident at a specific incident angle with respect to the normal to the reflecting surface RS1 and transmit light incident at an incident angle different from the specific incident angle. This point will be described in more detail later.

[0026] The retarder RP and the holographic element HE extend over an area wider than the display area DA in the XY plane. However, it is sufficient that the retarder RP covers at least the display area DA. The retarder RP and the holographic element HE are stacked along the third direction Z. The retarder RP is in contact with the display panel 2, and the holographic element HE is in contact with the retarder RP. The retarder RP is disposed between the display panel 2 and the holographic element HE.

[0027] The second structural body 4B includes a semi-transmissive element TR and a lens element LE.

[0028] As will be described in detail later, the semi-transmissive element TR includes a cholesteric liquid crystal layer CL1 containing cholesteric liquid crystals oriented in one direction. The cholesteric liquid crystal layer CL1 is configured to reflect, among light of a specific wavelength, circularly polarized light having the same rotation direction as the cholesteric liquid crystal, toward the first structure 4A, and to transmit circularly polarized light having the opposite rotation direction to the cholesteric liquid crystal. Here, the circularly polarized light reflected by the cholesteric liquid crystal layer CL1 is referred to as the first circularly polarized light, and the circularly polarized light that transmits through the cholesteric liquid crystal layer CL1 is referred to as the second circularly polarized light. The cholesteric liquid crystal layer CL1 has a simplified reflective surface RS2. When the boundary between the display panel 2 and the retarder RP (or a surface parallel to the XY plane) is defined as a reference plane RF, the angle (tilt angle) θ20 between the reflective surface RS2 and the reference plane RF is an acute angle counterclockwise from the reference plane RF.

[0029] The lens element LE includes a liquid crystal layer LC1, which will be described in detail later. The liquid crystal layer LC1 is configured to impart a phase difference of 1 / 2 wavelength to light of a specific wavelength and to have a lens effect of focusing the second circularly polarized light. Note that the element having a lens effect of focusing circularly polarized light is not limited to an element using a liquid crystal.

[0030] The semi-transmitting element TR and the lens element LE extend over a range wider than the display area DA in the XY plane. The semi-transmitting element TR and the lens element LE are stacked along the third direction Z. The semi-transmitting element TR is in contact with the lens element LE. The semi-transmitting element TR is spaced apart from the holographic element HE and faces the holographic element HE in the third direction Z with an air layer 4C interposed therebetween.

[0031] The display area DA has a first end E1 and a second end E2 opposite to the first end E1 in the first direction X. The holographic element HE, the semi-transmissive element TR, and the lens element LE have a first portion P11 extending outward from the first end E1 and a second portion P12 extending outward from the second end E2. In the example shown in FIG. 3 , the first portion P11 and the second portion P12 extend along the first direction X. A width W1 of the first portion P11 along the first direction X is greater than a width W2 of the second portion P12 along the first direction X (W1>W2).

[0032] 3, the first portion P11 is located on the right side of the display area DA, and the second portion P12 is located on the left side of the display area DA. The reflective surface RS2 of the semi-transmissive element TR has an end E11 on the right side of the figure (the side where the first portion P11 is located) and an end E12 on the left side of the figure (the side where the second portion is located). The reflective surface RS2 is inclined so that the end E11 is located on the side close to the display panel 2, and the end E12 is located on the side away from the display panel 2.

[0033] It is desirable that the display panel 2 and the retarder RP be in close contact with each other without an air gap therebetween. It is also desirable that the retarder RP and the holographic element HE constituting the first structure 4A be in close contact with each other without an air gap therebetween. It is also desirable that the semi-transmissive element TR and the lens element LE constituting the second structure 4B be in close contact with each other without an air gap therebetween. This makes it possible to suppress undesired reflection or refraction at the interface between the components.

[0034] The retardation plate RP imparts a phase difference of at least a quarter wavelength to light of, for example, green wavelength, but is not limited thereto. For example, a broadband retardation plate that imparts a phase difference of approximately a quarter wavelength to light of red wavelength, green wavelength, and blue wavelength can be used as the retardation plate RP. For example, an example of such a broadband retardation plate is one in which a quarter wavelength plate and a half wavelength plate are bonded together such that the slow axes of the quarter wavelength plate and the half wavelength plate form a predetermined angle. This can mitigate the wavelength dependency of the retardation plate RP.

[0035] Fig. 4 is a cross-sectional view showing an example of the lens element LE shown in Fig. 3. The lens element LE includes a substrate 11, an alignment film AL11, a liquid crystal layer LC1, an alignment film AL12, and a substrate 12. The substrates 11 and 12 are transparent substrates that transmit light, and are made of, for example, a transparent glass plate or a transparent synthetic resin plate.

[0036] The alignment film AL11 is disposed on the inner surface 11A of the substrate 11. In the example shown in Fig. 4, the alignment film AL11 is in contact with the substrate 11, but another thin film may be interposed between the alignment film AL11 and the substrate 11. The alignment film AL12 is disposed on the inner surface 12A of the substrate 12. In the example shown in Fig. 4, the alignment film AL12 is in contact with the substrate 12, but another thin film may be interposed between the alignment film AL12 and the substrate 12. The alignment film AL12 faces the alignment film AL11 in the third direction Z. The alignment films AL11 and AL12 are made of, for example, polyimide, and are both horizontal alignment films having an alignment regulating force along the XY plane.

[0037] The liquid crystal layer LC1 is disposed between the alignment films AL11 and AL12 and is in contact with the alignment films AL11 and AL12. The liquid crystal layer LC1 has a thickness d1 along the third direction Z. The liquid crystal layer LC1 contains nematic liquid crystals aligned in the third direction Z.

[0038] That is, the liquid crystal layer LC1 has a plurality of liquid crystal structures LMS1. Focusing on one liquid crystal structure LMS1, the liquid crystal structure LMS1 has a liquid crystal molecule LM11 located at one end and a liquid crystal molecule LM12 located at the other end. The liquid crystal molecule LM11 is adjacent to the alignment film AL11, and the liquid crystal molecule LM12 is adjacent to the alignment film AL12. The alignment direction of the liquid crystal molecule LM11 and the alignment direction of the liquid crystal molecule LM12 are approximately the same. Furthermore, the alignment direction of the other liquid crystal molecule LM1 between the liquid crystal molecule LM11 and the liquid crystal molecule LM12 is also approximately the same as the alignment direction of the liquid crystal molecule LM11. Note that the alignment direction of the liquid crystal molecule LM1 here corresponds to the direction of the long axis of the liquid crystal molecule in the XY plane.

[0039] In the liquid crystal layer LC1, the alignment directions of the liquid crystal structures LMS1 adjacent to each other along the first direction X are different from each other. Similarly, the alignment directions of the liquid crystal structures LMS1 adjacent to each other along the second direction Y are also different from each other. The alignment directions of the liquid crystal molecules LM11 aligned along the alignment film AL11 and the alignment directions of the liquid crystal molecules LM12 aligned along the alignment film AL12 change continuously (or linearly).

[0040] The liquid crystal layer LC1 is hardened in a state in which the alignment direction of the liquid crystal molecules LM1, including the liquid crystal molecules LM11 and LM12, is fixed. In other words, the alignment direction of the liquid crystal molecules LM1 is not controlled in response to an electric field. For this reason, the liquid crystal element 10 does not include electrodes for alignment control.

[0041] When the refractive index anisotropy or birefringence of the liquid crystal layer LC1 (the difference between the refractive index ne of the liquid crystal layer LC1 for extraordinary light and the refractive index no of the liquid crystal layer LC1 for ordinary light) is Δn, the retardation (phase difference) Δn·d1 of the liquid crystal layer LC1 is set to 1 / 2 of the specific wavelength λ.

[0042] Fig. 5 is a plan view showing an example of an alignment pattern in the liquid crystal layer LC1 shown in Fig. 4. Fig. 5 shows an example of the spatial phase in the XY plane of the liquid crystal layer LC1. The spatial phase shown here is shown as the alignment direction of the liquid crystal molecules LM11 that are close to the alignment film AL11 among the liquid crystal molecules LM1 included in the liquid crystal structure LMS1.

[0043] The spatial phases of the concentric circles indicated by dotted lines in the figure are consistent. Alternatively, the alignment directions of the liquid crystal molecules LM11 are consistent in the annular regions surrounded by two adjacent concentric circles. However, the alignment directions of the liquid crystal molecules LM11 in the adjacent annular regions are different from each other.

[0044] For example, the liquid crystal layer LC1 has a first annular region C1 and a second annular region C2 in a planar view. The second annular region C2 is located outside the first annular region C1. The first annular region C1 is composed of a plurality of first liquid crystal molecules LM111 aligned in the same direction. The second annular region C2 is composed of a plurality of second liquid crystal molecules LM112 aligned in the same direction. The alignment direction of the first liquid crystal molecules LM111 is different from the alignment direction of the second liquid crystal molecules LM112.

[0045] Similarly, the alignment directions of the liquid crystal molecules LM11 aligned in the radial direction from the center of the concentric circles are different from each other and change continuously. In other words, in the illustrated XY plane, the spatial phase of the liquid crystal layer LC1 is different and changes continuously along the radial direction.

[0046] When second circularly polarized light of a specific wavelength λ is incident on a lens element LE configured in this manner, the second circularly polarized light is focused toward the center of the concentric circle, and the light transmitted through the lens element LE is converted into first circularly polarized light that is oriented in the opposite direction to the second circularly polarized light.

[0047] Figures 6 and 7 are cross-sectional views showing an example of the semi-transmissive element TR shown in Figure 3. Figure 6 shows an XZ cross section defined by the first direction X and the third direction Z, and Figure 7 shows a YZ cross section defined by the second direction Y and the third direction Z. The following description will be made mainly with reference to Figure 6.

[0048] The semi-transmissive element TR includes a substrate 21, an alignment film AL21, a cholesteric liquid crystal layer CL1, an alignment film AL22, and a substrate 22. The substrates 21 and 22 are transparent substrates that transmit light, and are made of, for example, a transparent glass plate or a transparent synthetic resin plate.

[0049] The alignment film AL21 is disposed on the inner surface 21A of the substrate 21. In the example shown in Fig. 6, the alignment film AL21 is in contact with the substrate 21, but another thin film may be interposed between the alignment film AL21 and the substrate 21. The alignment film AL22 is disposed on the inner surface 22A of the substrate 22. In the example shown in Fig. 6, the alignment film AL22 is in contact with the substrate 22, but another thin film may be interposed between the alignment film AL22 and the substrate 22. The alignment film AL22 faces the alignment film AL21 in the third direction Z. The alignment films AL21 and AL22 are made of, for example, polyimide, and are both horizontal alignment films having an alignment regulating force along the XY plane.

[0050] The cholesteric liquid crystal layer CL1 is disposed between and in contact with the alignment films AL21 and AL22. The cholesteric liquid crystal layer CL1 has a thickness d2 along the third direction Z. For simplicity of illustration, one liquid crystal molecule LM2 in FIG. 6 represents a liquid crystal molecule aligned in the average alignment direction among a plurality of liquid crystal molecules positioned in the XY plane.

[0051] That is, the cholesteric liquid crystal layer CL1 has a plurality of liquid crystal structures (helical structures) LMS2. Focusing on one liquid crystal structure LMS2, the liquid crystal structure LMS2 has a liquid crystal molecule LM21 located at one end side and a liquid crystal molecule LM22 located at the other end side. The liquid crystal molecule LM21 is adjacent to the alignment film AL21, and the liquid crystal molecule LM22 is adjacent to the alignment film AL22. The plurality of liquid crystal molecules LM2, including the liquid crystal molecule LM21 and the liquid crystal molecule LM22, are stacked in a spiral shape along the third direction Z while rotating, thereby constituting the liquid crystal structure LMS2. That is, the liquid crystal structure LMS2 corresponds to a cholesteric liquid crystal. The liquid crystal structure LMS2 has a helical pitch P. The helical pitch P represents one period (360 degrees) of the helix. For example, the thickness d2 of the cholesteric liquid crystal layer CL1 is several times or more the helical pitch P. The helical axis AX of the liquid crystal structure LMS2 is parallel to the normal direction of the substrate 21, i.e., the third direction Z.

[0052] 6, in the cholesteric liquid crystal layer CL1, the alignment directions of the liquid crystal structures LMS2 adjacent to each other along the first direction X are different from each other. The alignment directions of the liquid crystal molecules LM21 aligned along the alignment film AL21 and the alignment directions of the liquid crystal molecules LM22 aligned along the alignment film AL22 change continuously.

[0053] 7, in the cholesteric liquid crystal layer CL1, the alignment directions of the plurality of liquid crystal structures LMS2 adjacent to each other along the second direction Y are aligned in the same direction. That is, the alignment directions of the plurality of liquid crystal molecules LM21 aligned along the alignment film AL21 are substantially aligned, and the alignment directions of the plurality of liquid crystal molecules LM22 aligned along the alignment film AL22 are substantially aligned.

[0054] The cholesteric liquid crystal layer CL1 has a plurality of reflective surfaces RS2, indicated by dashed lines, between the alignment films AL21 and AL22. The reflective surfaces RS2 are substantially parallel to one another. In accordance with Bragg's law, the reflective surfaces RS2 reflect some circularly polarized light of the incident light and transmit other circularly polarized light. The reflective surfaces RS2 here correspond to surfaces on which the alignment direction of the liquid crystal molecules LM2 is aligned or surfaces on which the spatial phase is aligned (equal phase surfaces).

[0055] In the XZ cross section shown in FIG. 6, the reflecting surface RS2 is inclined with respect to the boundary surface between the cholesteric liquid crystal layer CL1 and the alignment film AL21, or the reference plane RF shown in FIG. 3, or the XY plane. 7, the reflecting surface RS2 is parallel to the XY plane. That is, each of the multiple reflecting surfaces RS2 has a substantially planar shape extending in a fixed direction, as shown in FIGS.

[0056] The liquid crystal structure LMS2 reflects, among light of a specific wavelength λ, circularly polarized light having the same rotation direction as the rotation direction of the cholesteric liquid crystal. For example, if the rotation direction of the cholesteric liquid crystal is clockwise, among light of the specific wavelength λ, right-handed circularly polarized light is reflected and left-handed circularly polarized light is transmitted. Similarly, if the rotation direction of the cholesteric liquid crystal is counterclockwise, among light of the specific wavelength λ, left-handed circularly polarized light is reflected and right-handed circularly polarized light is transmitted.

[0057] The cholesteric liquid crystal layer CL1 is hardened in a state in which the alignment direction of the liquid crystal molecules LM2, including the liquid crystal molecules LM21 and LM22, is fixed. In other words, the alignment direction of the liquid crystal molecules LM2 is not controlled in response to an electric field. For this reason, the semi-transmissive element TR does not have electrodes for alignment control.

[0058] Generally, the selective reflection band Δλ of a cholesteric liquid crystal for perpendicularly incident light is expressed as "no*P to ne*P" based on the helical pitch P of the cholesteric liquid crystal, the refractive index ne for extraordinary light, and the refractive index no for ordinary light. Therefore, in order for the reflecting surface RS2 to efficiently reflect circularly polarized light of a specific wavelength λ, the helical pitch P, the refractive index ne, and no are set so that the specific wavelength λ is included in the selective reflection wavelength band Δλ.

[0059] FIG. 8 is a diagram for explaining an example of the optical action of the display device DSP shown in FIG.

[0060] First, the display panel 2 emits display light DL, which is a first linearly polarized light LP1. Here, the first linearly polarized light LP1 is, for example, linearly polarized light that vibrates in a direction perpendicular to the paper surface. The display light DL is emitted in a direction oblique to the normal NP of the display panel 2. When the display light DL passes through the retardation plate RP, a phase difference of 1 / 4 wavelength is imparted to the display light DL. As a result, the display light DL is converted into first circularly polarized light CP1 when passing through the retardation plate RP. Here, the first circularly polarized light CP1 is, for example, left-handed circularly polarized light.

[0061] The first circularly polarized light CP1 that has passed through the retardation plate RP is incident on the holographic element HE. The incident angle θA of the first circularly polarized light CP1 that enters the holographic element HE is different from the specific incident angle θ1 at the holographic element HE. The incident angle here is the angle between the normal N to the imaginary reflecting surface RS1 and the incident light. In the example shown here, the specific incident angle θ1 at the holographic element HE is 0°. In other words, the holographic element HE is configured to reflect incident light that is parallel to the normal N. Therefore, the first circularly polarized light CP1 with the incident angle θA is transmitted through the holographic element HE.

[0062] The first circularly polarized light CP1 that passes through the holographic element HE is reflected by the reflecting surface RS2 of the semi-transmissive element TR toward the holographic element HE. Note that the polarization state of the first circularly polarized light CP1 is maintained when reflected by the reflecting surface RS2. In other words, the reflected light from the reflecting surface RS2 is the first circularly polarized light CP1. The reflection angle of the first circularly polarized light CP1 is controlled by the tilt angle θ20 of the reflecting surface RS2, which is set so that the angle of incidence of the first circularly polarized light CP1 on the holographic element HE is a specific incident angle θ1. In the example shown here, the tilt angle θ20 is set so that the first circularly polarized light CP1 is reflected parallel to the normal N of the holographic element HE.

[0063] The first circularly polarized light CP1 reflected by the semi-transmissive element TR is incident on the holographic element HE along the normal N. The incident angle θB of the first circularly polarized light CP1 incident on the holographic element HE is approximately equal to the specific incident angle θ1 at the holographic element HE. Therefore, the first circularly polarized light CP1 at the incident angle θB is Bragg reflected (or specularly reflected) on the reflecting surface RS1 of the holographic element HE. The reflected light from the holographic element HE is converted into second circularly polarized light CP2, which has a rotation opposite to that of the first circularly polarized light CP1. Here, the second circularly polarized light CP2 is, for example, a right-handed circularly polarized light.

[0064] The second circularly polarized light CP2 reflected by the holographic element HE is transmitted through the semi-transmissive element TR, where it is converted into the first circularly polarized light CP1 by the lens element LE and is focused on the pupil E of the user through the lens action.

[0065] In such a display device DSP, the optical system 4 has an optical path that passes three times between the holographic element HE and the semi-transmissive element TR. Moreover, this optical path includes an oblique optical path from the holographic element HE to the semi-transmissive element TR. In other words, in the optical system 4, the optical distance between the holographic element HE and the semi-transmissive element TR is three or more times the actual distance between the holographic element HE and the semi-transmissive element TR (or the thickness of the air layer 4C). The display panel 2 is installed inside the focal point of the lens element LE, which has a lens effect. This allows the user to view a magnified virtual image.

[0066] According to this first configuration example, if absorption in each component constituting the display device DSP and reflection between each component are ignored, almost 100% of the display light DL emitted from the display panel 2 can be focused on the pupil E, thereby improving the light utilization efficiency.

[0067] Furthermore, compared to optical systems that include optical components formed of glass, resin, or the like, the thickness along the third direction Z can be made thinner, and weight can be reduced.

[0068] The first circularly polarized light CP1 described with reference to FIG. 8 may be replaced with the second circularly polarized light CP2.

[0069] Fig. 9 is a diagram for explaining another example of the optical action of the display device DSP shown in Fig. 3. The example shown in Fig. 9 differs from the example shown in Fig. 8 in that the specific incident angle θ1 of the holographic element HE is greater than 0°.

[0070] First, the display panel 2 emits display light DL, which is first linearly polarized light LP1, in an oblique direction. When the display light DL passes through the retardation plate RP, a phase difference of ¼ wavelength is imparted to the display light DL, and the display light DL is converted into first circularly polarized light CP1.

[0071] The first circularly polarized light CP1 that has passed through the retardation plate RP is incident on the holographic element HE. The incident angle θA of the first circularly polarized light CP1 that enters the holographic element HE is different from the specific incident angle θ1 at the holographic element HE. Therefore, the first circularly polarized light CP1 with the incident angle θA passes through the holographic element HE.

[0072] The first circularly polarized light CP1 that has passed through the holographic element HE is reflected by the reflecting surface RS2 of the semi-transmissive element TR toward the holographic element HE. The reflection angle of the first circularly polarized light CP1 is set so that the angle of incidence of the first circularly polarized light CP1 on the holographic element HE is a specific incident angle θ1.

[0073] The first circularly polarized light CP1 reflected by the semi-transmissive element TR is incident on the holographic element HE. The incident angle θB of the first circularly polarized light CP1 incident on the holographic element HE is approximately equal to the specific incident angle θ1 at the holographic element HE. Therefore, the first circularly polarized light CP1 at the incident angle θB is Bragg reflected (or specularly reflected) on the reflecting surface RS1 of the holographic element HE. The reflected light from the holographic element HE is converted into a second circularly polarized light CP2 that is oriented in the opposite direction to the first circularly polarized light CP1.

[0074] The second circularly polarized light CP2 reflected by the holographic element HE is transmitted through the semi-transmissive element TR, where it is converted into the first circularly polarized light CP1 by the lens element LE and is focused on the pupil E of the user through the lens action. The first circularly polarized light CP1 described with reference to FIG. 9 may be replaced with the second circularly polarized light CP2.

[0075] The example shown in Fig. 9 also provides the same effect as the example shown in Fig. 8. Moreover, in optical system 4, the optical path between the holographic element HE and the semi-transmissive element TR includes an oblique optical path from the semi-transmissive element TR to the holographic element HE, in addition to an oblique optical path from the holographic element HE to the semi-transmissive element TR. Therefore, compared to the example shown in Fig. 8, the optical distance between the holographic element HE and the semi-transmissive element TR can be further increased.

[0076] Fig. 10 is a plan view showing an example of the configuration of the lighting device 3 applicable to the display device DSP shown in Fig. 3. Note that Fig. 10 shows only the main parts of the lighting device 3. The lighting device 3 includes a light guide plate LG, a first light source unit LS1, and a second light source unit LS2.

[0077] The light guide plate LG has a side surface S1 and a side surface S2. The side surface S1 and the side surface S2 face each other in the first direction X. The light guide plate LG also has a region A1, a region A2, and a region A3. The thickness of the region A2 along the third direction Z is approximately constant. The thickness of the region A1 gradually increases from the side surface S1 toward the region A2. The thickness of the region A3 gradually increases from the side surface S2 toward the region A2.

[0078] The first light source unit LS1 is arranged along the side surface S1. The second light source unit LS2 is arranged along the side surface S2. Each of the first light source unit LS1 and the second light source unit LS2 includes a plurality of light-emitting elements LD. That is, the first light source unit LS1 and the second light source unit LS2 include, as the light-emitting elements LD, a first light-emitting element LDB that emits light of a blue wavelength (first wavelength), a second light-emitting element LDG that emits light of a green wavelength (second wavelength), and a third light-emitting element LDR that emits light of a red wavelength (third wavelength). The first light-emitting element LDB, the second light-emitting element LDG, and the third light-emitting element LDR are arranged at intervals.

[0079] It is desirable that the light emitted from the light-emitting element LD has a narrow spectral width (or high color purity). For this reason, it is desirable to use a laser light source as the light-emitting element LD. The central wavelength of the blue laser light emitted from the first light-emitting element (first laser light source) LDB is λb, the central wavelength of the green laser light emitted from the second light-emitting element (second laser light source) LDG is λg, and the central wavelength of the red laser light emitted from the third light-emitting element (third laser light source) LDR is λr.

[0080] FIG. 11 is a cross-sectional view showing an example of the configuration of the head mounted display 1. As shown in FIG.

[0081] The head mounted display 1 includes a single display panel 2, a single lighting device 3 shown in Fig. 10, optical systems 4R and 4L, and a frame FR. The display panel 2 functions as the display panel 2R for the right eye and the display panel 2L for the left eye shown in Fig. 2. The lighting device 3 functions as the lighting device 3R for the right eye and the lighting device 3L for the left eye.

[0082] The illumination device 3 includes a first light source LS1, a second light source LS2, a light guide plate LG, and optical sheets. Examples of the optical sheets include a prism sheet PS and a diffusion sheet DS. The prism sheet PS is disposed between the light guide plate LG and the diffusion sheet DS in the third direction Z. The diffusion sheet DS is disposed between the prism sheet PS and the display panel 2 in the third direction Z.

[0083] The first light source unit LS1 is located on the left side of the drawing and mainly emits light to be guided to the optical system 4R. The second light source unit LS2 is located on the right side of the drawing and mainly emits light to be guided to the optical system 4L. As described with reference to FIG. 10, each of the first light source unit LS1 and the second light source unit LS2 includes a first light-emitting element LDB, a second light-emitting element LDG, and a third light-emitting element LDR.

[0084] The display panel 2 includes a first substrate SUB1, a second substrate SUB2, a liquid crystal layer LC, a first polarizer PL1, and a second polarizer PL2. The liquid crystal layer LC is held between the first substrate SUB1 and the second substrate SUB2 and sealed with a seal SE. The first polarizer PL1 is disposed between the illumination device 3 and the first substrate SUB1. The second polarizer PL2 is disposed between the second substrate SUB2 and the retarder RP of the optical systems 4R and 4L.

[0085] The optical system 4L includes a retardation plate RP, a holographic element HEL, a semi-transmissive element TRL, and a lens element LEL. The optical system 4R includes a retarder RP, a holographic element HER, a semi-transmissive element TRR, and a lens element LER. The retarder RP is disposed across the optical systems 4L and 4R, but may be disposed separately in the optical systems 4L and 4R.

[0086] Each of the holographic elements HEL and HER includes a first hologram HB, a second hologram HG, and a third hologram HR. The first hologram HB, the second hologram HG, and the third hologram HR are stacked along the third direction Z. The stacking order of the first hologram HB, the second hologram HG, and the third hologram HR is not limited to the example shown in the figure. Below, a case will be described in which each hologram reflects the first circularly polarized light, but as described above, the first circularly polarized light CP1 may be replaced with the second circularly polarized light CP2.

[0087] The first hologram HB is configured to reflect a first circularly polarized light of a blue wavelength (first wavelength) λb out of the light incident at the specific incident angle θ1. The second hologram HG is configured to reflect a first circularly polarized light of a green wavelength (second wavelength) λg out of the light incident at the specific incident angle θ1. The third hologram HR is configured to reflect a first circularly polarized light of a red wavelength (third wavelength) λr out of the light incident at the specific incident angle θ1.

[0088] Each of the semi-transmissive elements TRL and TRR includes a first cholesteric liquid crystal layer CLB, a second cholesteric liquid crystal layer CLG, and a third cholesteric liquid crystal layer CLR. The first cholesteric liquid crystal layer CLB, the second cholesteric liquid crystal layer CLG, and the third cholesteric liquid crystal layer CLR are stacked along the third direction Z. Note that the stacking order of the first cholesteric liquid crystal layer CLB, the second cholesteric liquid crystal layer CLG, and the third cholesteric liquid crystal layer CLR is not limited to the example shown in the figure.

[0089] Each of the first cholesteric liquid crystal layer CLB, the second cholesteric liquid crystal layer CLG, and the third cholesteric liquid crystal layer CLR corresponds to the cholesteric liquid crystal layer CL1 described with reference to Figures 6 and 7, has cholesteric liquid crystal (liquid crystal structure) LMS2 rotated in the same direction, and is hardened with the alignment direction of multiple liquid crystal molecules fixed.

[0090] The first cholesteric liquid crystal layer CLB is configured to reflect a first circularly polarized light of a blue wavelength (first wavelength) λb, the second cholesteric liquid crystal layer CLG is configured to reflect a first circularly polarized light of a green wavelength (second wavelength) λg, and the third cholesteric liquid crystal layer CLR is configured to reflect a first circularly polarized light of a red wavelength (third wavelength) λr.

[0091] 12, the cholesteric liquid crystal contained in each liquid crystal layer is schematically shown in an enlarged scale. The first helical pitch P1 of the cholesteric liquid crystal LMS21 contained in the first cholesteric liquid crystal layer CLB is optimized to correspond to the central wavelength λb of the blue laser light emitted from the first light-emitting element LDB.

[0092] The second helical pitch P2 of the cholesteric liquid crystal LMS22 contained in the second cholesteric liquid crystal layer CLG is different from the first helical pitch P1. For example, the second helical pitch P2 is optimized to correspond to the central wavelength λg of the green laser light emitted from the second light-emitting element LDG. Therefore, the second helical pitch P2 is larger than the first helical pitch P1.

[0093] The third helical pitch P3 of the cholesteric liquid crystal LMS23 contained in the third cholesteric liquid crystal layer CLR is different from the first helical pitch P1 and the second helical pitch P2. For example, the third helical pitch P3 is optimized to correspond to the central wavelength λr of the red laser light emitted from the third light-emitting element LDR. Therefore, the third helical pitch P3 is larger than the second helical pitch P2.

[0094] Returning to FIG. 11, the description will be continued. Each of the lens elements LEL and LER includes a first liquid crystal layer LCB, a second liquid crystal layer LCG, and a third liquid crystal layer LCR. The first liquid crystal layer LCB, the second liquid crystal layer LCG, and the third liquid crystal layer LCR are stacked along the third direction Z. Note that the stacking order of the first liquid crystal layer LCB, the second liquid crystal layer LCG, and the third liquid crystal layer LCR is not limited to the example shown in the figure.

[0095] Each of the first liquid crystal layer LCB, the second liquid crystal layer LCG, and the third liquid crystal layer LCR corresponds to the liquid crystal layer LC1 described with reference to Figures 4 and 5, and is hardened with the alignment directions of multiple liquid crystal molecules fixed.

[0096] The first liquid crystal layer LCB is configured to collect second circularly polarized light of a blue wavelength (first wavelength) λb from the incident light and impart a phase difference of 1 / 2 wavelength to it. The second liquid crystal layer LCG is configured to collect second circularly polarized light of a green wavelength (second wavelength) λg from the incident light and impart a phase difference of 1 / 2 wavelength to it. The third liquid crystal layer LCR is configured to collect second circularly polarized light of a red wavelength (third wavelength) λr from the incident light and impart a phase difference of 1 / 2 wavelength to it.

[0097] The optical systems 4R and 4L configured in this way exhibit the optical effects described with reference to FIG. 8 or FIG. 9, respectively.

[0098] In the above-described head-mounted display 1, the first light source unit LS1 of the illumination device 3 emits light toward the side surface S1, and the second light source unit LS2 emits light toward the side surface S2. The light incident from the side surface S1 and the light incident from the side surface S2 propagate while repeatedly reflecting between the upper surface T1 and the lower surface B1 of the light guide plate LG. Of the light incident from the side surface S1, the light that does not satisfy the conditions for total reflection at the upper surface T1 is emitted obliquely toward the optical system 4R to form illumination light for the right eye. Of the light incident from the side surface S2, the light that does not satisfy the conditions for total reflection at the upper surface T1 is emitted obliquely toward the optical system 4L to form illumination light for the left eye.

[0099] The display panel 2 selectively modulates illumination light from the illumination device 3. A portion of the illumination light for the left eye passes through the second polarizer PL2 and is converted into display light DLL, which is linearly polarized light for the left eye. A portion of the illumination light for the right eye passes through the second polarizer PL2 and is converted into display light DLR, which is linearly polarized light for the right eye.

[0100] The display light DLL is focused on the left eye of the user by the optical action of the optical system 4L described above, and the display light DLR is focused on the right eye of the user by the optical action of the optical system 4R described above.

[0101] In such a head mounted display 1, the illumination device 3 includes a laser light source that emits light with a narrow spectral width, and the holographic element HE, the semi-transmissive element TR, and the lens element LE are optimized to match the central wavelength of the light emitted from the laser light source, thereby enabling light of each wavelength to be efficiently collected and reducing chromatic aberration, allowing the user to view a clear image.

[0102] Fig. 13 is a plan view showing another example of the configuration of an illumination device applicable to the display device DSP shown in Fig. 3. The illumination device shown in Fig. 13 is composed of an illumination device 3L for the left eye and an illumination device 3R for the right eye. Note that Fig. 13 shows only the main parts of the illumination devices 3L and 3R.

[0103] The illumination device 3L includes a first light guide plate LG1 and a first light source unit LS1. The illumination device 3R includes a second light guide plate LG2 and a second light source unit LS2. The first light guide plate LG1 and the second light guide plate LG2 are arranged in the first direction X with an interval therebetween.

[0104] The first light guide plate LG1 has a side surface S11 and a side surface S12. The side surface S11 and the side surface S12 face each other in the first direction X. The side surface S12 is covered with a reflective film RF1. The first light guide plate LG1 also has a region A11 and a region A12. The regions A11 and A12 are adjacent to each other in the first direction X. The thickness of the region A12 along the third direction Z is substantially constant. The thickness of the region A11 gradually increases from the side surface S11 toward the region A12.

[0105] The second light guide plate LG2 has a side surface S21 and a side surface S22. The side surface S21 and the side surface S22 face each other in the first direction X. The side surface S22 faces the side surface S12 in the first direction X. The side surface S22 is covered with a reflective film RF2. The second light guide plate LG2 also has a region A21 and a region A22. The regions A21 and A22 are adjacent to each other in the first direction X. The thickness of the region A22 along the third direction Z is substantially constant. The thickness of the region A21 gradually increases from the side surface S21 toward the region A22.

[0106] The first light source unit LS1 is arranged along the side surface S11. The second light source unit LS2 is arranged along the side surface S21. Each of the first light source unit LS1 and the second light source unit LS2 includes, as light-emitting elements LD, a first light-emitting element LDB that emits light of a blue wavelength (first wavelength), a second light-emitting element LDG that emits light of a green wavelength (second wavelength), and a third light-emitting element LDR that emits light of a red wavelength (third wavelength). The first light-emitting element LDB, the second light-emitting element LDG, and the third light-emitting element LDR are arranged at intervals.

[0107] FIG. 14 is a cross-sectional view showing another example of the configuration of the head mounted display 1. As shown in FIG.

[0108] The head mounted display 1 includes display panels 2L and 2R, lighting devices 3L and 3R shown in FIG. 13, optical systems 4L and 4R, and a frame FR. The configuration of each of the illumination devices 3L and 3R is as described with reference to Fig. 13. The configuration of each of the display panels 2L and 2R is equivalent to the configuration of the display panel 2 shown in Fig. 11. The configuration of the optical systems 4L and 4R is equivalent to the configuration of the optical systems 4L and 4R shown in Fig. 11. However, the optical systems 4L and 4R are spaced apart from each other and are each supported by a frame FR.

[0109] In the above-described head-mounted display 1, the first light source unit LS1 of the illumination device 3L emits light toward the side surface S11. The light incident from the side surface S11 propagates while repeatedly reflecting between the upper surface T1 and the lower surface B1 of the first light guide plate LG1. Then, of the light reflected by the reflective film RF1, the light that does not satisfy the conditions for total reflection on the upper surface T1 is emitted obliquely toward the optical system 4L, and forms illumination light for the left eye.

[0110] The display panel 2L selectively modulates the illumination light from the illumination device 3L. Part of the illumination light passes through the second polarizer PL2 and is converted into display light DLL, which is linearly polarized light for the left eye. The display light DLL is focused on the left eye of the user by the optical action of the optical system 4L described above.

[0111] The second light source unit LS2 of the illumination device 3R emits light toward the side surface S21. The light incident from the side surface S21 propagates while repeatedly reflecting between the upper surface T2 and the lower surface B2 of the second light guide plate LG2. Then, of the light reflected by the reflective film RF2, the light that does not satisfy the conditions for total reflection on the upper surface T2 is emitted obliquely toward the optical system 4R, forming illumination light for the right eye.

[0112] The display panel 2R selectively modulates illumination light from the illumination device 3R. Part of the illumination light passes through the second polarizer PL2 and is converted into display light DLR, which is linearly polarized light for the right eye. The display light DLR is focused on the user's right eye by the optical action of the optical system 4R described above.

[0113] In such a head mounted display 1, the same effects as those in the above example can be obtained.

[0114] <<Second Configuration Example>> FIG. 15 is a cross-sectional view showing a second configuration example of the display device DSP. The display device DSP includes a display panel 2, an illumination device 3, and an optical system 4. Detailed illustration of the display panel 2 and the illumination device 3 is omitted here. The display device DSP described here can be applied to each of the display devices DSPR and DSPL shown in FIG. 2. The display panel 2 can be applied to each of the above-mentioned display panels 2R and 2L. The illumination device 3 can be applied to each of the above-mentioned illumination devices 3R and 3L. The optical system 4 can be applied to each of the above-mentioned optical systems 4R and 4L.

[0115] The second configuration example shown in Fig. 15 differs from the first configuration example shown in Fig. 3 in the configuration of the optical system 4. The configurations of the display panel 2 and the illumination device 3 are the same as those of the first configuration example, and detailed description thereof will be omitted.

[0116] The optical system 4 includes a first structure 4A and a second structure 4B. The first structure 4A is spaced apart from the second structure 4B. In the example shown in Fig. 15, an air layer 4C is provided between the first structure 4A and the second structure 4B. The first structure 4A is disposed between the display panel 2 and the second structure 4B (or between the display panel 2 and the air layer 4C).

[0117] The first structure 4A comprises a first holographic element HE1. The second structure 4B includes a second holographic element HE2, a retardation plate RP, and a lens element LE. The retardation plate RP has the same configuration as the retardation plate RP in the first configuration example. The lens element LE has the same configuration as the lens element LE in the first configuration example.

[0118] Each of the first holographic element HE1 and the second holographic element HE2 is configured in the same manner as the holographic element HE of the first configuration example. The first holographic element HE1 is configured to reflect light at a first specific angle of incidence and transmit light at an angle of incidence different from the first specific angle of incidence. The second holographic element HE2 is configured to reflect light at a second specific angle of incidence and transmit light at an angle of incidence different from the second specific angle of incidence. The second specific angle of incidence is different from the first specific angle of incidence. This will be described in more detail below.

[0119] The second holographic element HE2, the retarder RP, and the lens element LE extend over an area wider than the display area DA in the XY plane. The second holographic element HE2, the retarder RP, and the lens element LE are stacked in this order along the third direction Z. The second holographic element HE2 faces the first holographic element HE1 in the third direction Z, with an air layer 4C interposed between them. The retardation plate RP may be disposed between the display panel 2 and the first holographic element HE1.

[0120] The first holographic element HE1, the second holographic element HE2, the retarder RP, and the lens element LE have a first portion P11 extending outward from the first end E1 and a second portion P12 extending outward from the second end E2. In the example shown in Fig. 15, the first portion P11 and the second portion P12 extend along the first direction X. The width W1 of the first portion P11 along the first direction X is larger than the width W2 of the second portion P12 along the first direction X (W1>W2).

[0121] FIG. 16 is a diagram for explaining an example of the optical action of the display device DSP shown in FIG.

[0122] First, the display panel 2 emits display light DL, which is a first linearly polarized light LP1. The display light DL is emitted in a direction oblique to the normal NP of the display panel 2. The display light DL is incident on the first holographic element HE1. The incident angle θA of the first linearly polarized light LP1 incident on the first holographic element HE1 is different from the first specific incident angle θ1 at the first holographic element HE1. The incident angle here is the angle between the normal N1 of the virtual reflecting surface RS1 and the incident light. The first linearly polarized light LP1 with the incident angle θA passes through the first holographic element HE1.

[0123] The first linearly polarized light LP1 that has passed through the first holographic element HE1 enters the second holographic element HE2. The angle of incidence θC of the first linearly polarized light LP1 that enters the second holographic element HE2 is approximately equal to the second specific angle of incidence θ2 at the second holographic element HE2. The angle of incidence here is the angle between the normal N2 of the virtual reflecting surface RS2 and the incident light. The first linearly polarized light LP1 at the angle of incidence θC is reflected by the reflecting surface RS2 of the second holographic element HE2 toward the first holographic element HE1. Note that when the first linearly polarized light LP1 is reflected by the reflecting surface RS2, its polarization state is maintained. In other words, the reflected light at the reflecting surface RS2 is the first linearly polarized light LP1.

[0124] The first linearly polarized light LP1 reflected by the second holographic element HE2 is incident on the first holographic element HE1 again. The incident angle θB of the first linearly polarized light LP1 incident on the first holographic element HE1 is approximately equal to the first specific incident angle θ1 at the first holographic element HE1. Therefore, the first linearly polarized light LP1 with the incident angle θB is reflected by the reflecting surface RS1 of the first holographic element HE1.

[0125] The first linearly polarized light LP1 reflected by the first holographic element HE1 is incident on the second holographic element HE2 again. The incident angle θD of the first linearly polarized light LP1 incident on the second holographic element HE2 is different from the second specific incident angle θ2 at the second holographic element HE2. Therefore, the first linearly polarized light LP1 with the incident angle θD is transmitted through the second holographic element HE2.

[0126] The first linearly polarized light LP1 that has passed through the second holographic element HE2 is given a phase difference of ¼ wavelength when it passes through the retardation plate RP. As a result, the first linearly polarized light LP1 is converted into first circularly polarized light CP1 when it passes through the retardation plate RP. Here, the first circularly polarized light CP1 is, for example, left-handed circularly polarized light. The first circularly polarized light CP1 that has passed through the retardation plate RP is converted into second circularly polarized light CP2 by the lens element LE and is focused on the user's pupil E through the lens action.

[0127] In this display device DSP, the optical system 4 has an optical path that passes three times between the first holographic element HE1 and the second holographic element HE2. This optical path includes an oblique optical path from the first holographic element HE1 to the second holographic element HE2 and an oblique optical path from the second holographic element HE2 to the first holographic element HE1. In other words, in the optical system 4, the optical distance between the first holographic element HE1 and the second holographic element HE2 is three times or more the actual distance between the first holographic element HE1 and the second holographic element HE2 (or the thickness of the air layer 4C). The display panel 2 is located inside the focal point of the lens element LE, which has a lens effect. This allows the user to view a magnified virtual image.

[0128] In this second configuration example, the same effects as in the first configuration example can be obtained.

[0129] FIG. 17 is a diagram illustrating the first specific incident angle θ1 of the first holographic element HE1 and the second specific incident angle θ2 of the second holographic element HE2 shown in FIG.

[0130] In the first holographic element HE1, the angle between the normal N1 of the reflecting surface RS1 and the reference plane (XY plane) is defined as γ1, and the angle between the incident light at the incident angle β and the normal N1 is defined as α1. In the second holographic element HE2, the angle between the normal N2 of the reflecting surface RS2 and the reference plane (XY plane) is γ2, the angle between the reflected light at the reflecting surface RS2 and the reference plane is φ2, and the angle between the reflected light at the reflecting surface RS1 and the normal N2 is α2.

[0131] As shown by c in the figure, the following formula is derived based on the condition that light having the first specific incident angle θ1 is reflected by the reflecting surface RS1. γ1=π / 2-θ1

[0132] As shown by b in the figure, the following formula is derived based on the condition that the light having the second specific incident angle θ2 is reflected by the reflecting surface RS2. γ2=θ2-2·θ1+π / 2

[0133] As shown by a in the figure, the conditions for transmission through the first holographic element HE1 are as follows. δ1=α1-θ1≠0 The following relationship holds: α1=2·θ2+φ2-γ1, φ2=π / 2-2·θ1 Based on these relationships, the following equation is derived for δ1: δ1=2·(θ1-θ2)≠0 Therefore, θ1≠θ2.

[0134] As shown by d in the figure, the conditions for transmission through the second holographic element HE2 are as follows: δ2=α2-θ2≠0 The following relationship holds: α2=π / 2-γ2 For δ2, the following equation is derived: δ2=2·(θ1-θ2)≠0 Therefore, θ1≠θ2.

[0135] That is, the optical system 4 of the second configuration example is realized by the first specific incident angle θ1 being different from the second specific incident angle θ2. Furthermore, the larger the difference between the first specific incident angle θ1 and the second specific incident angle θ2, the more relaxed the conditions for transmission through the first holographic element HE1 and the second holographic element HE2, which is preferable.

[0136] In this case, the incident angle β is as follows: β=α1+γ1-π / 2=2·(θ2-θ1)

[0137] FIG. 18 is a cross-sectional view showing an example of the configuration of the head mounted display 1. As shown in FIG.

[0138] The head mounted display 1 includes a single display panel 2, a single lighting device 3 shown in Fig. 10, optical systems 4R and 4L, and a frame FR. The display panel 2 functions as the display panel 2R for the right eye and the display panel 2L for the left eye shown in Fig. 2. The lighting device 3 functions as the lighting device 3R for the right eye and the lighting device 3L for the left eye.

[0139] The illumination device 3 includes a first light source LS1, a second light source LS2, a light guide plate LG, a prism sheet PS, and a diffusion sheet DS. The prism sheet PS is disposed between the light guide plate LG and the diffusion sheet DS in the third direction Z. The diffusion sheet DS is disposed between the prism sheet PS and the display panel 2 in the third direction Z.

[0140] The first light source unit LS1 is located on the left side of the drawing and mainly emits light to be guided to the optical system 4R. The second light source unit LS2 is located on the right side of the drawing and mainly emits light to be guided to the optical system 4L. As described with reference to FIG. 10, each of the first light source unit LS1 and the second light source unit LS2 includes a first light-emitting element LDB, a second light-emitting element LDG, and a third light-emitting element LDR.

[0141] The display panel 2 includes a first substrate SUB1, a second substrate SUB2, a liquid crystal layer LC, a first polarizer PL1, and a second polarizer PL2. The liquid crystal layer LC is held between the first substrate SUB1 and the second substrate SUB2 and sealed with a seal SE. The first polarizer PL1 is disposed between the illumination device 3 and the first substrate SUB1. The second polarizer PL2 is disposed between the second substrate SUB2 and the retarder RP of the optical systems 4R and 4L.

[0142] The optical system 4L includes a first holographic element HE1L, a second holographic element HE2L, a retardation plate RP, and a lens element LEL. The optical system 4R includes a first holographic element HE1R, a second holographic element HE2R, a retarder RP, and a lens element LER. The retarder RP is disposed across the optical systems 4L and 4R, but may be disposed separately in the optical systems 4L and 4R.

[0143] Each of the first holographic elements HE1L and HE1R includes a first hologram HB, a second hologram HG, and a third hologram HR. The first hologram HB, the second hologram HG, and the third hologram HR are stacked along the third direction Z. Note that the stacking order of the first hologram HB, the second hologram HG, and the third hologram HR is not limited to the example shown in the figure.

[0144] The first hologram HB is configured to reflect light of a blue wavelength (first wavelength) λb among light incident at the first specific angle of incidence θ1. The second hologram HG is configured to reflect light of a green wavelength (second wavelength) λg among light incident at the first specific angle of incidence θ1. The third hologram HR is configured to reflect light of a red wavelength (third wavelength) λr among light incident at the first specific angle of incidence θ1.

[0145] Each of the second holographic elements HE2L and HE2R includes a first hologram HB', a second hologram HG', and a third hologram HR'. The first hologram HB', the second hologram HG', and the third hologram HR' are stacked along the third direction Z. Note that the stacking order of the first hologram HB', the second hologram HG', and the third hologram HR' is not limited to the example shown in the figure.

[0146] The first hologram HB' is configured to reflect light of a blue wavelength (first wavelength) λb among the light beams incident at the second specific incident angle θ2. The second hologram HG' is configured to reflect light of a green wavelength (second wavelength) λg among the light beams incident at the second specific incident angle θ2. The third hologram HR' is configured to reflect light of a red wavelength (third wavelength) λr among the light beams incident at the second specific incident angle θ2.

[0147] Each of the lens elements LEL and LER includes a first liquid crystal layer LCB, a second liquid crystal layer LCG, and a third liquid crystal layer LCR. The first liquid crystal layer LCB, the second liquid crystal layer LCG, and the third liquid crystal layer LCR are stacked along the third direction Z. Note that the stacking order of the first liquid crystal layer LCB, the second liquid crystal layer LCG, and the third liquid crystal layer LCR is not limited to the example shown in the figure.

[0148] Each of the first liquid crystal layer LCB, the second liquid crystal layer LCG, and the third liquid crystal layer LCR corresponds to the liquid crystal layer LC1 described with reference to Figures 4 and 5, and is hardened with the alignment directions of multiple liquid crystal molecules fixed.

[0149] The first liquid crystal layer LCB is configured to collect first circularly polarized light of a blue wavelength (first wavelength) λb from the incident light and impart a phase difference of 1 / 2 wavelength to it. The second liquid crystal layer LCG is configured to collect first circularly polarized light of a green wavelength (second wavelength) λg from the incident light and impart a phase difference of 1 / 2 wavelength to it. The third liquid crystal layer LCR is configured to collect first circularly polarized light of a red wavelength (third wavelength) λr from the incident light and impart a phase difference of 1 / 2 wavelength to it.

[0150] The optical systems 4R and 4L configured in this way each exhibit the optical action described with reference to FIG.

[0151] In the above-described head-mounted display 1, the first light source unit LS1 of the illumination device 3 emits light toward the side surface S1, and the second light source unit LS2 emits light toward the side surface S2. The light incident from the side surface S1 and the light incident from the side surface S2 propagate while repeatedly reflecting between the upper surface T1 and the lower surface B1 of the light guide plate LG. Of the light incident from the side surface S1, the light that does not satisfy the conditions for total reflection at the upper surface T1 is emitted obliquely toward the optical system 4R to form illumination light for the right eye. Of the light incident from the side surface S2, the light that does not satisfy the conditions for total reflection at the upper surface T1 is emitted obliquely toward the optical system 4L to form illumination light for the left eye.

[0152] The display panel 2 selectively modulates illumination light from the illumination device 3. A portion of the illumination light for the left eye passes through the second polarizer PL2 and is converted into display light DLL, which is linearly polarized light for the left eye. A portion of the illumination light for the right eye passes through the second polarizer PL2 and is converted into display light DLR, which is linearly polarized light for the right eye.

[0153] The display light DLL is focused on the left eye of the user by the optical action of the optical system 4L described above, and the display light DLR is focused on the right eye of the user by the optical action of the optical system 4R described above.

[0154] In such a head mounted display 1, the illumination device 3 includes a laser light source that emits light with a narrow spectral width, and the first holographic element HE1, the second holographic element HE2, and the lens element LE are optimized to match the central wavelength of the light emitted from the laser light source, thereby enabling light of each wavelength to be efficiently collected and chromatic aberration to be reduced, allowing the user to view a clear image.

[0155] FIG. 19 is a cross-sectional view showing another configuration example of the head mounted display 1.

[0156] The head mounted display 1 includes display panels 2L and 2R, lighting devices 3L and 3R shown in FIG. 13, optical systems 4L and 4R, and a frame FR. The configuration of each of the illumination devices 3L and 3R is as described with reference to Fig. 13. The configuration of each of the display panels 2L and 2R is equivalent to the configuration of the display panel 2 shown in Fig. 18. The configuration of the optical systems 4L and 4R is equivalent to the configuration of the optical systems 4L and 4R shown in Fig. 18.

[0157] In the above-described head-mounted display 1, the first light source unit LS1 of the illumination device 3L emits light toward the side surface S11. The light incident from the side surface S11 propagates while repeatedly reflecting between the upper surface T1 and the lower surface B1 of the first light guide plate LG1. Then, of the light reflected by the reflective film RF1, the light that does not satisfy the conditions for total reflection on the upper surface T1 is emitted obliquely toward the optical system 4L, and forms illumination light for the left eye.

[0158] The display panel 2L selectively modulates the illumination light from the illumination device 3L. Part of the illumination light passes through the second polarizer PL2 and is converted into display light DLL, which is linearly polarized light for the left eye. The display light DLL is focused on the left eye of the user by the optical action of the optical system 4L described above.

[0159] The second light source unit LS2 of the illumination device 3R emits light toward the side surface S21. The light incident from the side surface S21 propagates while repeatedly reflecting between the upper surface T2 and the lower surface B2 of the second light guide plate LG2. Then, of the light reflected by the reflective film RF2, the light that does not satisfy the conditions for total reflection on the upper surface T2 is emitted obliquely toward the optical system 4R, forming illumination light for the right eye.

[0160] The display panel 2R selectively modulates illumination light from the illumination device 3R. Part of the illumination light passes through the second polarizer PL2 and is converted into display light DLR, which is linearly polarized light for the right eye. The display light DLR is focused on the user's right eye by the optical action of the optical system 4R described above.

[0161] In such a head mounted display 1, the same effects as those in the above example can be obtained.

[0162] As described above, according to this embodiment, it is possible to provide a display device that can improve the light utilization efficiency.

[0163] Although several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be embodied in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, and are also included in the inventions and their equivalents as defined in the claims. [Explanation of symbols]

[0164] 1...Head-mounted display DSP...Display device 2...Display panel 3...Illumination device 4...Optical system HE: Holographic element RP: Phase difference plate TR: Semi-transmissive element CL1: Cholesteric liquid crystal layer LE: Lens element LC1: Liquid crystal layer

Claims

1. a display panel including a polarizer and having a display area configured to emit linearly polarized display light; an illumination device disposed on the rear surface of the display panel; a holographic element that reflects light at a specific incident angle and transmits light at an incident angle different from the specific incident angle; a retardation plate disposed between the display panel and the holographic element; a semi-transparent element opposed to the holographic element at an interval, which reflects a first circularly polarized light and transmits a second circularly polarized light having a rotation opposite to that of the first circularly polarized light among the light transmitted through the holographic element; a lens element facing the semi-transmissive element and having a lens function of converging the second circularly polarized light that has passed through the semi-transmissive element; Equipped with In cross section, the display area has a first end and a second end opposite the first end, each of the holographic element, the semi-transmissive element, and the lens element has a first portion extending outward beyond the first end and a second portion extending outward beyond the second end; The width of the first portion is greater than the width of the second portion; The display device, wherein the illumination device is configured so that the display light from the display panel is emitted in an oblique direction from the second end toward the first portion with respect to a normal to the display panel.

2. The display device according to claim 1 , wherein the specific incident angle is 0°.

3. The display device according to claim 1 , wherein the specific incident angle is greater than 0°.

4. 2. The display device according to claim 1, wherein the lighting device comprises a first light-emitting element that emits light of a first wavelength, a second light-emitting element that emits light of a second wavelength different from the first wavelength, and a third light-emitting element that emits light of a third wavelength different from the first wavelength and the second wavelength.

5. The display device according to claim 4 , wherein the first light-emitting element, the second light-emitting element, and the third light-emitting element are each a laser light source.

6. the holographic element comprises a first hologram, a second hologram superimposed on the first hologram, and a third hologram superimposed on the second hologram; the first hologram reflects the first circularly polarized light of the first wavelength from the light at the specific incident angle, the second hologram reflects the first circularly polarized light of the second wavelength from the light at the specific incident angle, The display device according to claim 4 , wherein the third hologram reflects the first circularly polarized light of the third wavelength from among the light at the specific incident angle.

7. the semi-transmissive element comprises a first cholesteric liquid crystal layer, a second cholesteric liquid crystal layer superimposed on the first cholesteric liquid crystal layer, and a third cholesteric liquid crystal layer superimposed on the second cholesteric liquid crystal layer; each of the first cholesteric liquid crystal layer, the second cholesteric liquid crystal layer, and the third cholesteric liquid crystal layer has cholesteric liquid crystals rotated in the same direction, and is hardened in a state in which the alignment direction of a plurality of liquid crystal molecules is fixed; the first cholesteric liquid crystal layer reflects the first circularly polarized light of the first wavelength; the second cholesteric liquid crystal layer reflects the first circularly polarized light of the second wavelength; The display device of claim 4 , wherein the third cholesteric liquid crystal layer reflects the first circularly polarized light of the third wavelength.

8. the cholesteric liquid crystal of the first cholesteric liquid crystal layer has a first helical pitch; the cholesteric liquid crystal of the second cholesteric liquid crystal layer has a second helical pitch different from the first helical pitch; 8. The display device according to claim 7, wherein the cholesteric liquid crystal of the third cholesteric liquid crystal layer has a third helical pitch different from the first helical pitch and the second helical pitch.

9. the lens element includes a first liquid crystal layer, a second liquid crystal layer superimposed on the first liquid crystal layer, and a third liquid crystal layer superimposed on the second liquid crystal layer; each of the first liquid crystal layer, the second liquid crystal layer, and the third liquid crystal layer is hardened in a state in which the alignment direction of a plurality of liquid crystal molecules is fixed; the first liquid crystal layer collects the second circularly polarized light of the first wavelength; the second liquid crystal layer collects the second circularly polarized light of the second wavelength, The display device according to claim 4 , wherein the third liquid crystal layer focuses the second circularly polarized light of the third wavelength.

10. each of the first liquid crystal layer, the second liquid crystal layer, and the third liquid crystal layer has, in a planar view, a first annular region in which a plurality of first liquid crystal molecules are oriented in the same direction, and a second annular region outside the first annular region in which a plurality of second liquid crystal molecules are oriented in the same direction; The display device of claim 9 , wherein the alignment direction of the first liquid crystal molecules is different from the alignment direction of the second liquid crystal molecules.

11. a display panel including a polarizer and having a display area configured to emit linearly polarized display light; a first holographic element that reflects light at a first specific incident angle and transmits light at an incident angle different from the first specific incident angle; a second holographic element that faces the first holographic element at an interval, reflects light having a second specific incident angle different from the first specific incident angle among the light that has passed through the first holographic element, and transmits light having an incident angle different from the second specific incident angle; a lens element facing the second holographic element and having a lens effect of collecting first circularly polarized light among the light transmitted through the second holographic element; a retardation plate disposed between the display panel and the first holographic element or between the second holographic element and the lens element; Equipped with When the incident angle of the display light to the first holographic element is β, the first specific incident angle is θ1, and the second specific incident angle is θ2, β=2・(θ2−θ1) A display device in which the following relationship holds.

12. Further, a lighting device is provided on the rear surface of the display panel, 12. The display device according to claim 11, wherein the lighting device comprises a first light-emitting element that emits light of a first wavelength, a second light-emitting element that emits light of a second wavelength different from the first wavelength, and a third light-emitting element that emits light of a third wavelength different from the first wavelength and the second wavelength, and is configured to form light having the incident angle β.

13. The display device according to claim 12 , wherein the first light-emitting element, the second light-emitting element, and the third light-emitting element are each a laser light source.

14. each of the first holographic element and the second holographic element includes a first hologram, a second hologram superimposed on the first hologram, and a third hologram superimposed on the second hologram; the first hologram of the first holographic element reflects light of the first wavelength among light incident at the first specific angle of incidence; the second hologram of the first holographic element reflects light of the second wavelength among light incident at the first specific angle of incidence; the third hologram of the first holographic element reflects light of the third wavelength among light at the first specific incident angle; the first hologram of the second holographic element reflects light of the first wavelength among light at the second specific incident angle; the second hologram of the second holographic element reflects light of the second wavelength among light at the second specific incident angle; The display device according to claim 12 , wherein the third hologram of the second holographic element reflects light of the third wavelength among light incident at the second specific angle of incidence.

15. the lens element includes a first liquid crystal layer, a second liquid crystal layer superimposed on the first liquid crystal layer, and a third liquid crystal layer superimposed on the second liquid crystal layer; each of the first liquid crystal layer, the second liquid crystal layer, and the third liquid crystal layer is hardened in a state in which the alignment direction of a plurality of liquid crystal molecules is fixed; the first liquid crystal layer collects the first circularly polarized light of the first wavelength; the second liquid crystal layer collects the first circularly polarized light of the second wavelength, The display device according to claim 12 , wherein the third liquid crystal layer focuses the first circularly polarized light of the third wavelength.

16. each of the first liquid crystal layer, the second liquid crystal layer, and the third liquid crystal layer has, in a planar view, a first annular region in which a plurality of first liquid crystal molecules are oriented in the same direction, and a second annular region outside the first annular region in which a plurality of second liquid crystal molecules are oriented in the same direction; The display device of claim 15 , wherein the alignment direction of the first liquid crystal molecules is different from the alignment direction of the second liquid crystal molecules.

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