Optical system and image display device

Abstract

This optical system (12, 13) comprises: a projection optical system (14) that projects light indicating an image generated by a display unit (11); and a light separation element (3) that is disposed between the display unit and the projection optical system and separates incident light (L1) incident from the display unit into a plurality of separated light beams (L11, L12) respectively having mutually different optical characteristics. The light separation element emits the plurality of separated light beams to the projection optical system such that the plurality of separated light beams are respectively projected to a plurality of projection positions (21, 22) via the projection optical system in accordance with incident light from the display unit to the light separation element.

Description

Optical System and Image Display Device

[0001] The present disclosure relates to an optical system and an image display device.

[0002] Patent Document 1 discloses an optical projection system in a wearable display system such as a head-mounted display. The optical projection system includes a plurality of light-emitting microdisplays such as, for example, a micro light-emitting diode (LED) panel for each color of red, green, and blue (RGB), a dichroic X-cube prism, and an optical direction conversion structure for changing the incident angle of light on the internal reflection surface of the X-cube prism. The optical direction conversion structure provides different paths in the X-cube prism for a plurality of image lights from the plurality of light-emitting microdisplays, so that each image light is incident on the coupling optical element of each corresponding waveguide at the eyepiece portion of the wearable display system.

[0003] International Publication No. 2020 / 139752

[0004] Noe Ishizuka, Jie Li, Wataru Fuji, Satoshi Ikezawa, and Kentaro Iwami, "Linear polarization-separating metalens at long-wavelength infrared," Opt. Express 31, 23372-23381 (2023)Go Soma, Yoshiro Nomoto, Toshimasa Umezawa, Yuki Yoshida, Yoshiaki Nakano, and Takuo Tanemura, "Compact and scalable polarimetric self-coherent receiver using a dielectric metasurface,” Optica 10, 604-611 (2023)

[0005] The present disclosure provides an optical system and an image display device that can improve the efficiency of using light projected by the optical system.

[0006] In this disclosure, the optical system includes a projection optical system that projects light representing an image generated by a display unit, and an optical separation element disposed between the display unit and the projection optical system, which separates incident light from the display unit into a plurality of separated lights, each having different optical properties. The optical separation element emits a plurality of separated lights to the projection optical system in response to the incident light from the display unit to the optical separation element, such that the plurality of separated lights are projected to a plurality of projection positions via the projection optical system.

[0007] In this disclosure, the image display device comprises the optical system described above and a display unit that emits incident light into the optical system to generate an image.

[0008] The optical system and image display device described herein can improve the efficiency of projecting and utilizing light using the optical system.

[0009] A perspective view illustrating the configuration of an image display device in Embodiment 1 of this disclosure. A side view illustrating the configuration of the optical system in the image display device of Embodiment 1. A perspective view illustrating the configuration of the optical separation element in the separation optical system of Embodiment 1. A graph illustrating the resolution analysis results by the image display device of Embodiment 1. A plan view illustrating the configuration of the optical waveguide in the pupil dilation optical system of Embodiment 1. A side view illustrating the configuration of an image display device in Modification 1 of Embodiment 1. A plan view illustrating the configuration of the first optical waveguide in Modification 1 of Embodiment 1. A plan view illustrating the configuration of the second optical waveguide in Modification 1 of Embodiment 1. A side view illustrating the configuration of an image display device in Modification 2 of Embodiment 1. A plan view illustrating the configuration of the optical waveguide in Modification 2 of Embodiment 1. A side view illustrating the configuration of an image display device in Modification 2 of Embodiment 2. A side view showing an example of the configuration of the optical separation element in Modification 2 of Embodiment 2. A side view showing another example of the configuration of the optical separation element in Modification 2 of Embodiment 2. A side view illustrating the configuration of a modified image display device.

[0010] The embodiments will be described in detail below, with reference to the drawings as appropriate. However, unnecessarily detailed explanations may be omitted. For example, detailed explanations of already well-known matters or redundant explanations of substantially identical configurations may be omitted. This is to avoid the following explanation becoming unnecessarily verbose and to facilitate understanding for those skilled in the art. The accompanying drawings and the following explanation are provided so that those skilled in the art can fully understand this disclosure, and are not intended to limit the subject matter described in the claims.

[0011] (Embodiment 1) Hereinafter, Embodiment 1 of the present disclosure will be described with reference to the drawings. In this embodiment, an example of a pupil-expanding type image display device and optical system will be described.

[0012] 1. Regarding the image display device, the image display device of Embodiment 1 will be described with reference to Figure 1.

[0013] Figure 1 illustrates the configuration of the image display device 1 in this embodiment. The image display device 1 in this embodiment comprises, for example, a display unit 11 and a pupil dilation optical system 12, as shown in Figure 1. The image display device 1 can be applied, for example, to a head-mounted display (HMD) to allow the observer's eyes E to view an image.

[0014] The pupil dilation optical system 12 comprises, for example, a separation optical system 13 and an optical waveguide 2, as shown in Figure 1. The pupil dilation optical system 12 and the separation optical system 13 are examples of optical systems in this embodiment. The optical waveguide 2 includes various regions 21 to 25 that diffract light to form a waveguide for incident light. Details of each optical system 12 and 13 will be described later.

[0015] In the image display device 1 of this embodiment, the display unit 11 generates image light L1 representing an image and emits it to the pupil dilation optical system 12. The image display device 1 of this embodiment utilizes the diffraction of light in the optical waveguide 2 of the pupil dilation optical system 12 to generate display light L2, which is an expanded pupil (e.g., exit pupil) of the image light L1, and emits it to the observer's eye E, etc. In this way, the observer of the image display device 1 can view the image from the display unit 11 through an optical image such as a virtual image caused by the display light L2.

[0016] In conventional technologies such as Patent Document 1, the image light from a micro-LED panel is randomly polarized, yet the optical projection system projects this image light onto the coupled optical element on the incident side of the waveguide without considering the polarization. As a result, due to polarization dependence such as diffraction in the coupled optical element, there is a loss of light intensity in the image light that can be used for image display via the waveguide. Thus, conventional image display devices have problems in terms of the efficiency of image light utilization.

[0017] Therefore, in the pupil dilation optical system 12 of this embodiment, a separation optical system 13 is used to separate the image light L1 incident from the display unit 11 according to its polarization state (hereinafter, the image light L1 is also referred to as "incident light L1"). In this way, in the pupil dilation optical system 12 of this embodiment, the incident light L1 from the display unit 11 is separated by the separation optical system 13 into multiple separated lights L11 and L12 in each polarization state, and these can be projected separately onto multiple coupling regions 21 and 22 in the optical waveguide 2.

[0018] As a result, the image display device 1 of this embodiment can suppress the loss of light in the optical waveguide 2 by considering the polarization characteristics in the separation optical system 13, even if the incident light L1 from the display unit 11 is randomly polarized. Furthermore, the image display device 1 of this embodiment can enlarge the pupil size from the image light L1 of the display unit 11 by projecting multiple separated lights L11 and L12 by the separation optical system 13. Thus, the image display device 1 of this embodiment makes it easier to increase the utilization efficiency of the image light L1.

[0019] The details of the image display device 1 of this embodiment will be described below. In the following, the optical axis direction of the separation optical system 13 will be defined as the Z direction, the direction perpendicular to the Z direction and where the first and second separated light beams L11 and L12 are aligned will be defined as the X direction, and the direction perpendicular to the Z direction and the X direction will be defined as the Y direction. In addition, the incident side of the incident light L1 in the separation optical system 13 will be defined as the -Z side, and the output side of each separated light beam L11 and L12 will be defined as the +Z side.

[0020] In the image display device 1 of this embodiment, the display unit 11 has, for example, a display surface 10 that displays an image with multiple pixels, and is a display element that generates image light L1 that shows the image on the display surface 10. The display unit 11 is arranged, for example, with the display surface 10 parallel to the XY plane and on the -Z side of the separation optical system 13.

[0021] The display unit 11 is, for example, a microLED display, and comprises a plurality of LED elements, each serving as a light-emitting point (or object point). The image displayed by the display unit 11 may be monochrome or multi-color. For example, the pixels of the display unit 11 may include a plurality of subpixels for each RGB color. The light-emitting points of the display unit 11 emit visible light with random polarization using, for example, a Lambertian light distribution.

[0022] The display unit 11 of the image display device 1 is not limited to a microLED array, but may be various display elements. The image light L1 from the display unit 11 may be randomly polarized or set to a specific polarization state. For example, the display unit 11 may be a liquid crystal display, an OLED (Organic Light-Emitting Diode) display, an LCOS (Liquid Crystal On Silicon), a DMD (Digital Mirror Device), or a scanning MEMS mirror.

[0023] 2. Regarding the optical system, the details of the pupil dilation optical system 12 and the separation optical system 13 in this embodiment will be explained with reference to Figures 2 to 3.

[0024] Figure 2 illustrates the configuration of the optical systems 12 and 13 in the image display device 1 of this embodiment. Figure 2 corresponds to a side view of the pupil dilation optical system 12 of the image display device 1 as seen from the +Y side. In the pupil dilation optical system 12, the separation optical system 13 and the optical waveguide 2 are arranged in order from the -Z side to the +Z side.

[0025] The separation optical system 13 of this embodiment includes, for example, as shown in Figure 2, an optical separation element 3 and a projection optical system 14 arranged in order from the -Z side to the +Z side. The optical separation element 3 is positioned between the display unit 11 and the projection optical system 14, near the display surface 10 of the display unit 11. For example, the main surface of the optical separation element 3 is positioned facing the display surface 10 of the display unit 11.

[0026] The light separation element 3 is an optical element that separates incident light L1 into multiple separated lights L11 and L12 according to optical characteristics such as polarization state. Figure 2 illustrates the luminous beams of the first and second separated lights L11 and L12, and their respective light distribution characteristics, obtained by separating the incident light L1 emitted at point P1 near the center of the display surface 10 of the display unit 11.

[0027] As shown in Figure 2, for example, the optical separation element 3 of this embodiment is configured to emit a first separated light L11 and a second separated light L12 in different emission directions on the +Z side, depending on the incident light L1 from the -Z side. For example, the first separated light L11 has a peak position of its optical distribution characteristics in the emission direction on the -X side and is set to a polarization characteristic corresponding to a part of the polarization component of the incident light L1. The second separated light L12 has a peak position of its optical distribution characteristics in the emission direction on the +X side and is set to a polarization characteristic different from that of the first separated light L11.

[0028] Figure 3 illustrates the configuration of the optical separation element 3 in this embodiment. The optical separation element 3 in this embodiment is configured such that, for example, the first separated light L11 mainly includes the linearly polarized component, i.e., the X-polarized component, in which the electric field of the incident light L1 vibrates in the X direction, and the second separated light L12 mainly includes the linearly polarized component, i.e., the Y-polarized component, vibrating in the Y direction. The optical separation element 3 is composed of a metamaterial element such as a polarization-separating metalens (see Non-Patent Literature 1).

[0029] The optical separation element 3 includes a substrate arranged parallel to the XY plane, as shown in Figure 3, for example, and the main surface of the substrate is configured as a metasurface with a metamaterial structure. The metamaterial structure is composed of multiple microstructures (also called metaatoms), such as protrusions 30 extending in the Z direction, arranged at predetermined intervals in the X and Y directions, as shown in Figure 3, for example. With such a metamaterial structure, the first and second separated lights L11 and L12 are separated from the 0th-order incident light L1 as diffracted light of different orders (e.g., ±1st order). The metamaterial structure of the optical separation element 3 is an example of an optical structure in this embodiment.

[0030] The microstructure in the metamaterial structure, for example, the dimensions and / or spacing of the protrusions 30, are such that they are no larger than the smallest wavelength (e.g., 400 nm) in the visible wavelength band that the image display device 1 is intended to display. The protrusions 30 may have various cross-sectional shapes in the XY plane, and may be, for example, a conical body having the shape of an elliptical cone or polygon, or a columnar body having the shape of an elliptical cylinder or polygonal prism.

[0031] For example, depending on the difference in the propagation direction and polarization state of the first and second separated light beams L11 and L12, a plurality of protrusions 30 are periodically arranged in the X and Y directions, modulating various shapes and spacings. The shape, size, and arrangement of the protrusions 30 are not limited and can be arbitrarily designed according to the specifications. Furthermore, the shape of the microstructure is not limited to a protruding shape, but may also be a concave shape. Such microstructures as protrusions 30 are an example of a unit structure in this embodiment.

[0032] In the example shown in Figure 3, a metamaterial structure with a protrusion 30 is provided on the main surface of the substrate on the -Z side of the optical separation element 3. The metamaterial structure may be provided on the main surface on the +Z side of the substrate, or on both main surfaces. Furthermore, the optical separation element 3 may be constructed, for example, as a polarization separation metalens without any lens power that specifically focuses or diverges light rays. The optical separation element 3 may also be a metamaterial element other than a polarization separation metalens, or it may be realized as a diffraction grating or a hologram, etc.

[0033] Returning to Figure 2, the projection optical system 14 includes, for example, one or more lens elements. The optical axis of the separation optical system 13 is defined, for example, by the central axis of the projection optical system 14. The projection optical system 14 collimates the light beams incident from the display unit 11 to the optical waveguide 2 in, for example, the image display device 1, into parallel light beams. The projection optical system 14 has, for example, positive optical power and focal length f. If the projection optical system 14 includes multiple lens elements, the focal length f is the combined focal length. For example, the projection optical system 14 is positioned +Z side of the optical separation element 3 such that the distance from the display surface 10 to the principal point of the projection optical system 14 is the focal length f.

[0034] In the image display device 1 of this embodiment, the light beams of each separated light L11 and L12 incident from the light separation element 3 to the projection optical system 14 have a divergence angle due to light emission on the display surface 10 of the display unit 11, as shown in Figure 2, for example. In this embodiment, the projection optical system 14 emits the first separated light L11 incident from the -Z side as parallel light toward the first coupling region 21 of the optical waveguide 2 on the +Z side. The projection optical system 14 also emits the second separated light L12 from the -Z side as parallel light toward the second coupling region 22 of the optical waveguide 2 on the +Z side.

[0035] In Figure 2, the separated beams L11 and L12 from object point P1 near the center of the display surface 10 are illustrated, and the emission direction of each separated beam L11 and L12 is parallel to the Z direction. The projection optical system 14 is not limited to the above example, but also emits each separated beam L11 and L12 from sources other than object point P1 as parallel beams, with the emission direction directed inward so that they incident on the corresponding coupling regions 21 and 22. Note that the separated beams L11 and L12 parallelized by the projection optical system 14 do not necessarily have to be perfectly parallel beams, and may have a beam angle with an appropriate tolerance.

[0036] With the separation optical system 13 configured as described above, the light separation element 3 of this embodiment can separate the image light L1 from the display unit 11 into first and second separated lights L11 and L12, and project them onto the first and second combined regions 21 and 22, respectively, via the projection optical system 14.

[0037] The projection ranges of the first and second separated lights L11 and L12 from the projection optical system 14 do not have to be separated, and may, for example, overlap with each other. The polarization characteristics of the first and second separated lights L11 and L12 separated by the separation optical system 13 are not limited to the above, and may be set to various polarization characteristics. For example, each separated light L11 and L12 may be linearly polarized in various ways, or it may be circularly polarized or elliptically polarized.

[0038] 2.1. Arrangement of the optical separation element In the separation optical system 13 of this embodiment, the optical separation element 3 may be arranged to satisfy the following equation (1), for example, from the viewpoint of increasing the resolution of the image display by the image display device 1: (L × D) / f ２<0.03 …(1)

[0039] In equation (1) above, L is the distance from the display unit 11 to the optical separation element 3, D is the first optical beam diameter D1 of the first separated light L11 in the first coupling region 21, or the second optical beam diameter D2 of the second separated light L12 in the second coupling region 22, and as described above, f is the focal length of the projection optical system 14. For example, distance L is the distance between the display surface 10 and the main surface of the optical separation element 3 in the Z direction. The first optical beam diameter D1 is measured, for example, at the position where the first separated light L11 passes through the projection optical system 14 and is projected onto the first coupling region 21. The second optical beam diameter D2 is measured, for example, at the position where the second separated light L12 passes through the projection optical system 14 and is projected onto the second coupling region 22. The optical beam diameter D may also be the average value of the first optical beam diameter D1 and the second optical beam diameter D2.

[0040] The effect of arranging the optical separation element 3 to satisfy the above equation (1) will be explained with reference to Figure 4.

[0041] Figure 4 is a graph illustrating the analysis results of the resolution of the image display by the image display device 1 of this embodiment. In the analysis of Figure 4, the distance L between the display unit 11 and the light separation element 3 was changed in the image display device 1, and the MTF (modulation transfer function) in the X and Y directions of the image generated by the display light L2 (Figure 1) was measured near a reference position assumed to be the position of the observer's eye E.

[0042] Figure 4(A) is a graph of the analysis results when the distance L between the display unit 11 and the optical separation element 3 is relatively large and equation (1) is not satisfied, and Figure 4(B) is a graph of the analysis results when the distance L is relatively small and equation (1) is satisfied. In the graphs of Figures 4(A) and (B), the horizontal axis shows the amount of defocus near the reference position as a diopter, and the vertical axis shows the MTF.

[0043] In FIG. 4(A), the distance L is set to be large enough not to satisfy the above formula (1), specifically, the distance L = 0.30 mm. In such a case, the farther the distance from the object point of the display unit 11 to the optical separation element 3, the more the light beam of the incident light L1 reaching the optical separation element 3 spreads. Therefore, the influence of the aberration generated in the optical separation element 3 becomes excessive, and it is considered that the resolution such as MTF decreases. For example, in the example of FIG. 4(A), the MTF is about 0.4 even near 0 diopter in both the X direction and the Y direction.

[0044] In FIG. 4(B), the distance L is set to be small enough to satisfy the above formula (1), specifically, the distance L = 0.05 mm. In the image display device 1 of the present embodiment, by arranging the optical separation element 3 near the display unit 11 so as to satisfy the above formula (1), the light beam incident on the optical separation element 3 is not spread too much, and the influence of the aberration of the optical separation element 3 is suppressed, making it easy to obtain high resolution. For example, in the example of FIG. 4(B), an MTF exceeding 0.6 is obtained near 0 diopter in both the X direction and the Y direction.

[0045] In the above formula (1), as the reference for such a distance L, the light beam diameter D of the first or second separated light L11, L12 and the focal length f of the projection optical system 14 that collimates each light beam are used. In the image display device 1 of the present embodiment, the light beam diameter D may be reduced or the focal length f of the projection optical system 14 may be increased so as to satisfy the above formula (1), and thereby the high resolution of the image display may be achieved. Further, the image display device 1 of the present embodiment does not necessarily have to satisfy the above formula (1), especially when high resolution is not required.

[0046] 2.2. Optical waveguide of pupil expansion optical system The details of the configuration of the optical waveguide 2 of the pupil expansion optical system 12 in the image display device 1 of the present embodiment will be described with reference to FIG. 5. FIG. 5 is a plan view showing a configuration example of the optical waveguide 2 in the pupil expansion optical system 12 of the present embodiment.

[0047] The optical waveguide 2 is a structure formed of a material that is transparent, for example, in the visible light region, and is configured such that incident light can propagate inside by total reflection and diffraction. The optical waveguide 2 has a pair of main surfaces 2a and 2b (FIG. 2) facing each other. The optical waveguide 2 may have a curved surface shape instead of being limited to a planar shape. Hereinafter, a configuration example of the optical waveguide 2 in which the pair of main surfaces 2a and 2b has a planar shape parallel to each other will be described.

[0048] For the optical waveguide 2, for example, with the normal directions of the respective main surfaces 2a and 2b oriented in the Z direction, the respective main surfaces 2a and 2b are arranged parallel to the XY plane. The optical waveguide 2 is formed of, for example, a glass or resin plate whose surfaces such as the respective main surfaces are mirror-finished. The optical waveguide 2 includes, for example, as shown in FIG. 5, a plurality of coupling regions 21 and 22, a plurality of propagation regions 23 and 24, and an emission region 25. Each of the regions 21 to 25 constitutes a diffraction structure element by providing a periodic structure for realizing each diffraction power in the optical waveguide 2.

[0049] The periodic structure of each of the regions 21 to 25 in the optical waveguide 2 can be constituted by various diffraction structures capable of realizing diffraction of light, such as a volume hologram or a diffraction grating. Each diffraction structure of the optical waveguide 2 is provided, for example, by a volume hologram between the first and second main surfaces 2a and 2b. The volume hologram is constituted by, for example, a periodic refractive index distribution in a dielectric film such as an interference fringe formed inside the optical waveguide 2. For example, each of the regions 21 to 25 may be a three-dimensional region in the optical waveguide 2.

[0050] In the configuration example of FIG. 5, the first coupling region 21 is arranged on the -X side and the +Y side of the optical waveguide 2. And, in the vicinity of the first coupling region 21, the second coupling region 22 is arranged on the +X side. Each of the coupling regions 21 and 22 is an example of an incident region that diffracts each separated light L11 and L12 incident so as to be optically coupled to the image light L1 (FIG. 1) from the display unit 11 in the optical waveguide 2. The optical coupling is a state in which the light incident on each of the coupling regions 21 and 22 propagates inside the optical waveguide 2 while satisfying the total reflection condition.

[0051] The first coupling region 21 has a polarization dependency suitable for the polarization characteristics of the first separated light L11, for example. Specifically, the first coupling region 21 is provided with a diffraction structure that has a higher diffraction efficiency in the polarization characteristics set for the first separated light L11 than in the polarization characteristics set for the second separated light L12. For example, the diffraction structure of the first coupling region 21 is configured with a periodic diffraction grating in the Y direction extending in the X direction. For example, the diffraction structure of the first coupling region 21 is configured with a diffraction power to change the direction of the incident first separated light L11 to image light L21 (hereinafter also referred to as "first propagating light L21") that propagates in the Y direction toward the first propagation region 23.

[0052] The second coupling region 22 is provided with a diffraction structure different from that of the first coupling region 21, such as having a polarization dependence suitable for the polarization characteristics of the second separated light L12. For example, the diffraction structure of the second coupling region 22 is configured with a periodic diffraction grating in the X direction extending in the Y direction. For example, the diffraction structure of the second coupling region 22 is configured with a diffraction power to convert the direction of the incident second separated light L12 into image light L22 (hereinafter also referred to as "second propagating light L22") that propagates in the X direction toward the second propagation region 24.

[0053] For example, each diffraction structure of the first and second bonding regions 21 and 22 has a diffraction pitch and a tilt angle to achieve the above diffraction power. The diffraction pitch indicates the period of the diffraction structure, such as the period of interference fringes in a hologram. The tilt angle indicates the inclination of the direction in which the interference fringes extend with respect to a predetermined reference direction (e.g., the Y direction).

[0054] The first propagation region 23 is, for example, located adjacent to the -Y side of the first coupling region 21 and extends in the Y direction. The second propagation region 24 is, for example, located adjacent to the +X side of the second coupling region 22 and is arranged to extend in the X direction.

[0055] Each propagation region 23, 24 is a region that propagates the propagating light L21, L22 from the corresponding coupling regions 21, 22 to the output region 25, for example, through diffraction for pupil dilation. This pupil dilation is performed by diffraction, which divides and duplicates the light beams of each image light L21, L22 at multiple positions along the optical path where each propagating light L21, L22 propagates by total internal reflection between the main surfaces 2a, 2b of the optical waveguide 2, and emits multiple beams of image light L23, L24. The duplicated image light L23, L24 beams at this time will also be referred to as "duplicated light L23, L24" below.

[0056] The first propagation region 23 is provided with a diffraction structure having diffraction power to emit multiple first replicated beams L23, obtained by diffracting the first propagating beam L21 at multiple positions in the Y direction, to the +X side. The diffraction structure of the second propagation region 24 has diffraction power to emit multiple second replicated beams L24, obtained by diffracting the second propagating beam L22 at multiple positions in the X direction, to the -Y side. The diffraction structures of each propagation region 23, 24 are composed of diffraction gratings that are tilted with respect to both the X and Y directions, for example.

[0057] In the configuration example shown in Figure 5, the emission region 25 is positioned adjacent to the +X side of the first propagation region 23 and adjacent to the -Y side of the second propagation region 24. Multiple first replicated light beams L23 from the first propagation region 23 propagate in the +X direction of the emission region 25. Multiple second replicated light beams L24 from the second propagation region 24 propagate in the -Y direction of the emission region 25.

[0058] The emission region 25 is a region that emits the display light L2 (see Figure 1), obtained by performing diffraction, for example, further pupil dilation, on multiple replicated light beams L23 and L24 from each propagation region 23 and 24, to the outside of the optical waveguide 2. For example, the emission region 25 is provided with a diffraction structure having diffraction power to emit the display light L2, which includes the results of diffraction of the first replicated light beam L23 at multiple positions in the X direction and the results of diffraction of the second replicated light beam L24 at multiple positions in the Y direction, to the +Z side. The diffraction structure of the emission region 25 is configured as a lattice by superimposing a diffraction grating that is periodic in the X direction and extends in the Y direction and a diffraction grating that is periodic in the Y direction and extends in the X direction.

[0059] With the optical waveguide 2 configured as described above, the image display device 1 of this embodiment can efficiently use the first and second separated light beams L11 and L12 separated by the separation optical system 13 in the pupil dilation optical system 12 to facilitate diffraction for pupil dilation.

[0060] In the image display device 1 of this embodiment, the arrangement configuration of the optical waveguide 2 is not limited to the example described above. For example, the normal direction of the main surface of the optical waveguide 2 may be appropriately tilted from the Z direction of the optical axis of the separation optical system 13. Also, the emission direction of the display light L2 from the optical waveguide 2 may be tilted from the Z direction. The emission direction of the display light L2 is not limited to the +Z side of the optical waveguide 2, but may also be the -Z side. Furthermore, although one optical waveguide 2 is shown in Figure 2, etc., the image display device 1 may be equipped with multiple optical waveguides 2. For example, optical waveguides 2 for each of the RGB colors may be used.

[0061] 3. Summary As described above, in the image display device 1 of this embodiment, the separation optical system 13, which is an example of an optical system, comprises a projection optical system 14 and an optical separation element 3.

[0062] The projection optical system 14 projects light that represents the image generated by the display unit 11. The light separation element 3 is positioned between the display unit 11 and the projection optical system 14 and separates the incident light L1 that enters from the display unit 11 into a plurality of separated lights L11 and L12, each having different optical characteristics. The light separation element 3 emits a plurality of separated lights L11 and L12 into the projection optical system 14 so that, in response to the incident light L1 that enters from the display unit 11 to the light separation element 3, the plurality of separated lights are projected onto a plurality of projection positions (21, 22) via the projection optical system 14.

[0063] According to the separation optical system 13 described above, the incident light L1 is separated into multiple separated light beams L11 and L12 according to their optical characteristics, and then projected through the projection optical system 14, allowing each separated light beam L11 and L12 to be used individually. For example, each separated light beam L11 and L12 can be projected onto coupling regions 21 and 22 according to their respective optical characteristics. This separation optical system 13 can improve the efficiency of projecting and utilizing light by the optical system in an image display device 1, etc. For example, the pupil size can be enlarged by using multiple separated light beams L11 and L12.

[0064] In this embodiment, the incident light L1 contains multiple polarization components corresponding to multiple optical characteristics, and the light separation element 3 separates the incident light L1 into multiple separated lights such that each separated light contains a different polarization component. This allows for the separation of the incident light L1 based on optical characteristics such as polarization characteristics, thereby increasing the utilization efficiency when projecting the incident light L1.

[0065] In this embodiment, the light separation element 3 includes a metamaterial structure, which is an example of an optical structure (see Figure 3). The metamaterial structure is arranged planarly along the display surface 10 of the display unit 11, and when incident light L1 is incident from the display surface 10, it emits a plurality of separated lights L11 and L12 on the opposite side from the display surface 10. With such a light separation element 3, the efficiency of using the image light L1 for projection can be increased. For example, the metamaterial structure of this embodiment may include a plurality of protrusions 30, which are an example of a plurality of unit structures, each having a size less than or equal to the wavelength of the incident light L1. The plurality of protrusions 30 may be periodically arranged along the display surface 10 in the light separation element 3 so as to emit a plurality of separated lights L11 and L12 by diffraction of the incident light L1.

[0066] In this embodiment, the optical separation element 3 is positioned closer to the display unit 11 than to the projection optical system 14. This reduces the degree to which the resolution of the image generated by the display unit 11 is degraded by the optical separation element 3, making it easier to increase the resolution of the image display device 1. The separation optical system 13 in this embodiment may also satisfy the above-described equation (1). This also reduces the degradation of the resolution of the image display device 1.

[0067] In this embodiment, for example, the pupil dilation optical system 12 has a polarization dependence at multiple projection positions using multiple separated light sources L11 and L12, each corresponding to the optical characteristics of the incident separated light sources L11 and L12. This makes it easier to improve the utilization efficiency of the incident light source L1 by realizing optical functions at each projection position based on the polarization dependence corresponding to each separated light source L11 and L12.

[0068] In this embodiment, the pupil dilation optical system 12 further includes an optical waveguide 2. The optical waveguide 2 has polarization dependence and propagates multiple separated light beams L11 and L12 from the projection optical system 14 internally, respectively, and emits them to the outside as display light L2. This allows, for example, the display light L2 to be emitted to the observer's eye E of the image display device 1 to display an image.

[0069] In this embodiment, the optical waveguide 2 includes a plurality of coupling regions 21, 22 as an example of at least one incident region that includes a plurality of projection positions and causes a plurality of separated lights to be incident into the interior of the optical waveguide 2, a plurality of propagation regions 23, 24 that propagate the plurality of separated lights L11, L12 from the plurality of coupling regions 21, 22, and an output region 25 that emits the plurality of separated lights L11, L12 from the plurality of propagation regions 23, 24 as display light L2. In this embodiment, the pupil expansion optical system 12 can improve the efficiency of using incident light L1 for image display by using a plurality of separated lights L11, L12 using an optical separation element 3 in such an optical waveguide 2.

[0070] In this embodiment, at least one incident region includes a plurality of coupling regions 21, 22, each positioned at a plurality of projection positions. Each coupling region 21, 22 has a diffraction structure that has polarization dependence according to the optical characteristics of the separated light L11, L12 incident at the corresponding projection position among the plurality of separated light L11, L12. This increases the efficiency of optical coupling by each separated light L11, L12 in each coupling region 21, 22, making it easier to increase the utilization efficiency of the incident light L1.

[0071] In this embodiment, each of the multiple propagation regions 23, 24, which are arranged adjacent to the multiple coupling regions 21, 22, has a diffraction structure that diffracts to replicate each propagated light L21, L22, which is an example of separated light from an adjacent incident region. This allows pupil expansion to be performed in the optical waveguide 2 to replicate each separated light L11, L12, making it easier to increase the utilization efficiency of the incident light L1.

[0072] In this embodiment, the emission region 25 is arranged adjacent to the plurality of propagation regions 23 and 24. The emission region 25 emits multiple propagation light rays L23 and L24 from the plurality of propagation regions 23 and 24 as display light L2. Using this emission region 25, an image can be viewed by an observer of the image display device 1.

[0073] In this embodiment, the projection optical system 14 projects multiple separated light beams L11 and L12 from the light separation element 3 as parallel light beams to multiple projection positions such as coupling regions 21 and 22. For example, by projecting from this projection optical system 14 onto the optical waveguide 2, display light L2 can be extracted from the output region 25, enabling efficient image display.

[0074] In this embodiment, the image display device 1 comprises the separation optical system 13 and thus the pupil dilation optical system 12 described above, and a display unit 11 that emits incident light L1 into the optical system to generate an image. In this embodiment, the image display device 1 can increase the efficiency of projecting and utilizing light through the optical system by using the separated light L11 and L12 utilizing the light separation element 3.

[0075] (Modifications of Embodiment 1) In the image display device 1 of Embodiment 1 described above, an example configuration was described in which the first and second coupling regions 21 and 22, which serve as projection positions for the first and second separated lights L11 and L12, are provided on the same optical waveguide 2. However, this embodiment is not limited to this. Such modifications will be explained with reference to Figures 6 to 8.

[0076] Figure 6 illustrates the configuration of the image display device 1A in a modified example of Embodiment 1. In this embodiment, the image display device 1A, in the configuration of Embodiment 1 (see Figure 2), is equipped with a plurality of optical waveguides 2Aa, 2Ab in the pupil dilation optical system 12A, each having separate first and second coupling regions 21, 22, instead of the optical waveguide 2. For example, the first and second optical waveguides 2Aa, 2Ab are arranged stacked on top of each other in the Z direction (i.e., the direction of emission of the display light L2), as shown in Figure 6.

[0077] Figure 7 illustrates the configuration of the first optical waveguide 2Aa in this embodiment. The first optical waveguide 2Aa comprises a first coupling region 21 and a first propagation region 23, and a first output region 26, similar to the optical waveguide 2 of Embodiment 1 (Figure 5). The first output region 26 is provided on the +X side of the first propagation region 23, similar to the output region 25 of the optical waveguide 2 of Embodiment 1, and includes a diffraction structure for diffracting the first replicated light L23. For example, the diffraction structure of the first output region 26 is configured to be periodic in the X direction and extend in the Y direction.

[0078] Figure 8 illustrates the configuration of the second optical waveguide 2Ab in this embodiment. The second optical waveguide 2Ab includes a second coupling region 22 and a second propagation region 24, similar to the optical waveguide 2 of Embodiment 1, and a second output region 27. The second output region 27, similar to the output region 25 of Embodiment 1, is provided on the -Y side of the second propagation region 24 and includes a diffraction structure for diffracting the second replicated light L24. For example, the diffraction structure of the second output region 27 is configured to be periodic in the Y direction and extend in the X direction.

[0079] In the pupil-expanding optical system 12A of this embodiment, the first and second emission regions 26 and 27 are arranged sequentially in the Z direction so as to superimpose on the XY plane, for example. In this embodiment, the first separated light L11 separated from the image light L1 by the separation optical system 13 is projected onto the first coupling region 21 of the first optical waveguide 2Aa, propagates inside the first optical waveguide 2Aa, and is emitted as display light L2. The second separated light L12 is projected onto the second coupling region 22 of the second optical waveguide 2Ab, propagates inside the second optical waveguide 2Ab, and is emitted as display light L2. In this way, the image display device 1A of this embodiment can also efficiently utilize the image light L1, similar to Embodiment 1.

[0080] As described above, the pupil-expanding optical system 12A of the image display device 1A of this embodiment may include at least one emission region that comprises multiple emission regions 26, 27, each adjacent to a plurality of propagation regions 23, 24. The plurality of emission regions 26, 27 are stacked on top of each other in the emission direction of the display light L2. As a result, the image display device 1A of this embodiment can extract the display light L2 from the plurality of emission regions 26, 27 and use it for image display.

[0081] Furthermore, although the image display device 1 of the above embodiment 1 was described in which the first and second separated lights L11 and L12 are projected onto separate coupling regions 21 and 22, this embodiment is not limited to this. Such modifications will be explained with reference to Figures 9 to 10.

[0082] Figure 9 illustrates the configuration of the image display device 1B in a modified example 2 of Embodiment 1. The image display device 1B of this embodiment is further equipped with polarizing elements 15 in each optical system 12B and 13B, and also equipped with an optical waveguide 2B instead of the optical waveguide 2. The polarizing element 15 is, for example, a half-wave plate and is provided to match the polarization state between the first and second separated light sources L11 and L12.

[0083] The polarizing element 15 is positioned on the +Z side of the projection optical system 14, as shown in Figure 9, at a location through which the beam of the first separated light L11 passes. The polarizing element 15 applies a phase delay of half a wavelength to the first separated light L11, which is incident as linearly polarized light vibrating in the X direction, for example, to polarize the first separated light L11 to linearly polarized light vibrating in the Y direction. In this way, the polarization state of the first separated light L11 can be aligned with the polarization state of the second separated light L12.

[0084] Figure 10 illustrates the configuration of the optical waveguide 2B in this embodiment. The optical waveguide 2B in this embodiment has a configuration similar to, for example, the second optical waveguide 2Ab (Figure 8) of the modified example 1 of Embodiment 1, but instead of the second coupling region 22, it includes a coupling region 22B that is arranged to include the projection positions of both the first and second separated light L11 and L12. According to the pupil-expanding optical system 12B of this embodiment, the same propagation region 24, etc. can be used for the first and second separated light L11 and L12 in the optical waveguide 2B, and the configuration of the optical waveguide 2B can be simplified. Note that the coupling region 22B does not have to include the entire projection range of the first separated light L11, nor does it have to include the entire projection range of the second separated light L12.

[0085] In the image display device 1B of this embodiment, the polarizing element 15 may be positioned at the passage position of the second separated light L12 instead of in the configuration example of Figure 9, so as to match the polarization state of the second separated light L12 to the polarization state of the first separated light L11. In this case, the optical waveguide 2B may be configured in the same way as the first optical waveguide 2Aa in Figure 7, instead of in the configuration example of Figure 10, so as to include the projection positions of both the first and second separated lights L11 and L12.

[0086] Alternatively, in the image display device 1B of this embodiment, polarizing elements 15 positioned at the passage positions of both the first and second separated lights L11 and L12 may convert the polarization states of each light so as to align the polarization states of the first and second separated lights L11 and L12. In this case as well, the optical waveguide 2B can be appropriately given a polarization dependence suitable for the polarization characteristics of the first and second separated lights L11 and L12 aligned by the polarizing elements 15, thereby improving the utilization efficiency of the image light L1.

[0087] As described above, the optical systems 12B and 13B of the image display device 1B of this embodiment may further include a polarizing element 15 positioned between the optical separation element 3 and a plurality of projection positions, which aligns the polarization characteristics of the first separated light L11 and the second separated light L12 in the plurality of separated lights L11 and L12. The optical waveguide 2B may also include a coupling region 22B positioned across both a first projection position where the first separated light L11 is projected and a second projection position where the second separated light L12 is projected. This allows the coupling region 22B to be configured according to the polarization characteristics aligned by the polarizing element 15, simplifying the configuration of the pupil dilation optical system 12B.

[0088] In this embodiment, the polarization characteristics of the first separated light L11 and the polarization characteristics of the second separated light L12 have a phase difference of half a wavelength from each other, and the polarizing element 15 may be a half-wave plate. With such a polarizing element 15, the polarization states of multiple separated lights L11 and L12 can be easily aligned.

[0089] (Embodiment 2) Embodiment 2 will be described below with reference to Figure 11. In Embodiment 1, polarization characteristics were used as the optical characteristics for separating the image light L1, but the disclosure is not limited thereto, and various optical characteristics of the image light L1 may be used. Embodiment 2 describes an image display device 1C that uses wavelength characteristics as the optical characteristics for separating the image light L1.

[0090] Hereinafter, descriptions of the configuration and operation similar to those of the image display devices 1, 1A, and 1B according to Embodiment 1 will be omitted as appropriate, and the image display device 1C according to this embodiment will be described.

[0091] Figure 11 illustrates the configuration of the image display device 1C in Embodiment 2. In this embodiment, the image display device 1C has a configuration similar to Modification 1 of Embodiment 1 (Figure 6), but instead of the optical separation element 3 and the plurality of optical waveguides 2Aa, 2Ab, the pupil expansion optical system 12C is equipped with an optical separation element 3C and a plurality of optical waveguides 2Caa to 2Cc based on wavelength characteristics. In this embodiment, the incident light L1 from the display unit 11 has multiple wavelength peaks for each color, such as RGB.

[0092] In the separation optical system 13C of this embodiment, the optical separation element 3C separates the incident light L1 into a plurality of separated beams L31 to L33, as shown in Figure 11, according to the wavelength characteristics of the incident light L1, and emits them to the projection optical system 14 in different emission directions. For example, the optical separation element 3C mainly includes the B component of the RGB wavelength peaks in the incident light L1 in the first separated beam L31, the G component mainly in the second separated beam L32, and the R component mainly in the third separated beam L33. Such an optical separation element 3C can be made of, for example, a diffraction grating or hologram equipped with a diffraction structure that diffracts the corresponding wavelength components. The optical separation element 3C may also be made of a metamaterial as appropriate.

[0093] The first optical waveguide 2Ca of this embodiment has a configuration similar to the first optical waveguide 2Aa (Figure 6) of the modified example 1 of Embodiment 1, but instead of a first coupling region 21 corresponding to polarization characteristics, it includes a first coupling region 21C corresponding to the wavelength characteristics of the first separated light L31. For example, the first coupling region 21C is configured by providing a diffraction structure at the projection position of the first separated light L31 from the projection optical system 14 that enhances the coupling efficiency at the wavelength peak of the first separated light L31.

[0094] Furthermore, the second optical waveguide 2Cb of this embodiment, like the first optical waveguide 2Ca, includes a second coupling region 22C provided at the projection position of the second separated light L32 according to the wavelength characteristics of the second separated light L32. Similarly, the third optical waveguide 2Cc of this embodiment includes a third coupling region 23C provided at the projection position of the third separated light L33 according to the wavelength characteristics of the third separated light L33. The image display device 1C of this embodiment may also include an optical waveguide 2D (Figure 12) in which the functions of the multiple optical waveguides 2Ca to 2Cc are integrated, instead of these multiple optical waveguides 2Ca to 2Cc.

[0095] According to the image display device 1C of this embodiment, the image light L1 is separated into first to third separated light beams L31 to L33 by the optical separation element 3C of the separation optical system 13C according to the wavelength characteristics, and projected onto each coupling region 21C to 23C suitable for the respective wavelength characteristics, making it easy to improve the utilization efficiency of the image light L1.

[0096] As described above, in the optical systems 12C and 13C of the image display device 1C of this embodiment, the incident light L1 includes multiple wavelength components corresponding to multiple optical characteristics. The light separation element 3C separates the incident light L1 into multiple separated lights L31 to L33 such that each of the separated lights L31 to L33 includes a different wavelength component from the multiple wavelength components. By separating the light into multiple separated lights L31 to L33 according to the wavelength characteristics, the efficiency of projecting and utilizing the light by the optical system can be increased, similar to Embodiment 1.

[0097] In this embodiment, for example, the pupil-expanding optical system 12C has wavelength dependence in each coupling region 21C to 23C of the multiple projection positions, according to the optical characteristics of each incident separated light L31 to L33. For example, each of the multiple optical waveguides 2Ca to 2Cc has wavelength dependence according to each separated light L31 to L33. With such a pupil-expanding optical system 12C, the utilization efficiency of the image light L1 can be increased by using the wavelength characteristics of each separated light L31 to L33.

[0098] (Modification of Embodiment 2) As in Embodiment 2 above, the separation optical system 13C that separates the image light L1 based on wavelength characteristics can also be applied to the image light L1 from a reflective display unit. Such modifications will be explained with reference to Figures 12 to 14.

[0099] Figure 12 illustrates the configuration of an image display device 1D in a modified example of Embodiment 2. The image display device 1D of this embodiment, for example, has the same configuration as in Embodiment 2, but instead of the display unit 11 and the light separation element 3C, it is equipped with an LCOS type display unit 11D and a light separation element 3D, and further includes a light source unit 41, a polarizer 42, and a polarizing beam splitter (PBS) 43. In the pupil dilation optical system 12D of this embodiment, an integrated optical waveguide 2D may be used between the multiple separated light sources L31 to L33, or optical waveguides 2Ca to 2Cc may be used as in the configuration example in Figure 11.

[0100] The light source unit 41 is a light source device that emits, for example, white illumination light L30, and is positioned on the +X side of the PBS 43. The light source unit 41 includes, for example, RGB light source elements, a dichroic mirror that coaxially guides the colored light from each light source element, and various lens elements. The illumination light L30 from the light source unit 41 is, for example, randomly polarized and is emitted toward the -X side.

[0101] The polarizer 42 is positioned between the light source 41 and the PBS 43 to selectively transmit a specific polarization component of the illumination light L30. The specific polarization component that is transmitted is, for example, the s-polarization component, while the p-polarization component is blocked by the polarizing element 15. The PBS 43 has, for example, a cube-shaped outer form and is positioned between the projection optical system 14 and the light separation element 3D. The PBS 43 includes, for example, a polarization reflecting surface 4 inside that reflects the s-polarization component of the incident light and transmits the p-polarization component.

[0102] The light separation element 3D of this embodiment is configured, similar to the light separation element 3C of the second embodiment, to limit the effect of separating light according to wavelength characteristics to a specific polarization component (e.g., p-polarization) of the incident light. In this way, the illumination light L30 from the light source unit 41 is incident on the PBS 43 in an s-polarization state via the polarizer 42, reflected by the polarization reflecting surface 4, passes through the light separation element 3D, and is incident on the display unit 11D.

[0103] The display unit 11D of this embodiment includes pixels capable of changing the polarization state of reflected light from incident light, as an LCOS-type pixel mechanism. The display unit 11D generates image light L1 from incident illumination light L30 in which the polarization state has been changed to, for example, p-polarization, by changing the polarization state of the reflected light for each pixel according to the pixel value of the image to be displayed. This image light L1 is incident from the display unit 11D to the light separation element 3D.

[0104] In the separation optical system 13D of this embodiment, the optical separation element 3D separates the image light L1 incident from the display unit 11D in the above-described polarization state into first to third separated light beams L31 to L33 according to their wavelength characteristics, similar to the optical separation element 3C of the second embodiment, and emits them to the +Z side. As a result, in the image display device 1D of this embodiment, for example, the first to third separated light beams L31 to L33 for each color can be projected onto the optical waveguide 2D via the projection optical system 14 into first to third coupling regions 21D to 23D, respectively, according to the wavelength characteristics of each separated light beam L31 to L33.

[0105] Figure 13 shows an example of the configuration of the optical separation element 3D in the image display device 1D of this embodiment. The optical separation element 3D of this embodiment can be configured, for example, as shown in Figure 13, by providing diffraction grating structures 31 and 32 on both sides of a substrate parallel to the XY plane. Each diffraction grating structure 31 and 32 is an example of an optical structure having a periodic diffraction pitch in the X direction where the first to third separated light beams L31 to L33 are aligned, and a height in the Z direction.

[0106] In this embodiment, the diffraction grating structures 31 and 32 in the optical separation element 3D are formed tilted in the X direction with respect to the Z direction of the substrate, as shown in Figure 13, for example. This allows for the selective enhancement of the diffraction efficiency of a specific polarization component of the incident light, for example, by transmitting s-polarized illumination light L30 and diffracting p-polarized image light L1.

[0107] For example, when a first separated light L31 is generated by the diffraction grating structure 31 on the +Z side and a third separated light L33 with a longer wavelength than the first separated light L31 is generated by the diffraction grating structure 32 on the -Z side, the diffraction pitch of the diffraction grating structure 32 on the -Z side is set to be wider than the diffraction pitch of the diffraction grating structure 31 on the +Z side. Also, the height of the diffraction grating structure 32 on the -Z side is set to be greater than the height of the diffraction grating structure 31 on the +Z side. Such diffraction grating structures 31 and 32 can be formed, for example, by a nanoimprint lithography method.

[0108] Figure 14 shows another example of the configuration of the optical separation element 3D in the image display device 1D of this embodiment. The optical separation element 3D of this embodiment may be composed of a volume hologram in which two types of diffraction structures 33 and 34 are provided inside the substrate, as shown in Figure 14, for example, the diffraction grating structures 31 and 32 described above. For example, the diffraction structure 33 for the third separation light L33 has a larger refractive index modulation amount than the diffraction structure 34 for the first separation light L11. Such an optical separation element 3D can be formed by an exposure method such as two-beam interference. Each diffraction structure 33 and 34 is an example of an optical structure.

[0109] As described above, in the optical systems 12D and 13D of the image display device 1D of this embodiment, the optical structure of the light separation element 3D may be composed of a diffraction grating or a hologram. Furthermore, in the image display device 1D of this embodiment, the separation into a plurality of separated lights L31 to L33 may be performed using the polarization characteristics and wavelength characteristics of the light incident on the light separation element 3D.

[0110] (Other Embodiments) As described above, Embodiments 1 and 2 have been explained as examples of the technology disclosed in this application. However, the technology in this disclosure is not limited thereto and can be applied to embodiments that have been modified, substituted, added, or omitted as appropriate. Furthermore, it is possible to create new embodiments by combining the components described in each of the above embodiments. Therefore, other embodiments are described below as examples.

[0111] In the above embodiment 1, an image display device 1 comprising one set of display units 11 and an optical separation element 3 was described, but the image display device 1 may comprise multiple sets of display units 11 and optical separation elements 3. Such modifications will be explained with reference to Figure 15.

[0112] Figure 15 illustrates the configuration of a modified image display device 1E. In this embodiment, the image display device 1E has the same configuration as in Embodiment 1, for example, but instead of one set of display units 11 and optical separation elements 3, it is equipped with three sets of display units 11a to 11c and optical separation elements 3a to 3c, and is further equipped with a dichroic prism 50. For example, the first display unit 11a emits first color light such as the B component in an RGB image, the second display unit 11b emits second color light such as the G component, and the third display unit 11c emits third color light such as the R component.

[0113] The dichroic prism 50 has, for example, a cube-shaped external form and is positioned on the -Z side of the projection optical system 14 in the separation optical system 13E. The dichroic prism 50 includes a first reflective surface 51 that reflects the first color light and transmits the second and third color light, and a second reflective surface 52 that reflects the third color light and transmits the first and second color light. For example, the first light separation element 3a and the first display unit 11a are positioned on the +X side of the dichroic prism 50, the second light separation element 3b and the second display unit 11b are positioned on the -Y side, and the third light separation element 3c and the third display unit 11c are positioned on the -X side.

[0114] In this embodiment, the first to third light separation elements 3a to 3c, similar to the light separation element 3 in Embodiment 1, separate the incident light from the opposing first to third display units 11a to 11c into first separated light L11a to L11c and second separated light L12a to L12c according to the polarization state. For example, the first and second separated light L11b and L12b from the second light separation element 3b are transmitted through the first and second reflective surfaces 51 and 52 of the dichroic prism 50.

[0115] Furthermore, the first separated light L11a from the first light separation element 3a is reflected at the first reflective surface 51 near the transmission position of the first separated light L11b from the second light separation element 3b. The second separated light L12a from the first light separation element 3a is reflected at the first reflective surface 51 at a position different from the reflection position of the first separated light L11b, near the transmission position of the second separated light L12b from the second light separation element 3b. The first and second separated lights L11c and L12c from the third light separation element 3c are reflected at the second reflective surface 52 near the transmission positions of the first and second separated lights L11b and L12b from the second light separation element 3b, respectively.

[0116] In this way, the first separated light L11a-L11c and the second separated light L12a-L12c, which have a common polarization state, can be incident on the first combined region 21 and the second combined region 22, respectively, via the projection optical system 14 from the first to third light separating elements 3a-3c. In this embodiment, the image display device 1E may also be used to project the first separated light L11a-L11c and the second separated light L12a-L12c with the polarization state aligned, similar to the image display device 1B of the modified example 2 of Embodiment 1, using a polarizing element 15.

[0117] In the above-described embodiment 1, an image display device 1 was described that separates incident light L1 into first and second separated lights L11 and L12 according to its polarization characteristics. In this embodiment, the separation optical system 13 may generate three or more separated lights according to their polarization characteristics. For example, the light separation element 3 may be configured to separate the light into six types of separated lights, such as linearly polarized light vibrating in the X direction, linearly polarized light vibrating in the Y direction, linearly polarized light at +45 degrees in the XY plane, linearly polarized light at -45 degrees, clockwise circularly polarized light, and counterclockwise circularly polarized light. Such a light separation element 3 can be constructed by applying known technology, such as that described in Non-Patent Document 2. According to the image display device 1 of this embodiment, by projecting the numerous separated lights from such a light separation element 3 to their respective projection positions via the projection optical system 14, as in the above embodiments, the utilization efficiency of the image light L1 can be increased, such as by enlarging the pupil size. In the image display device 1 of this embodiment, the types of separated lights from the light separation element 3 are not limited to six types, but may be five or fewer types, or seven or more types. Furthermore, the number of each of the incident region, propagation region, and exit region is not limited to one or two; various numbers can be used.

[0118] Furthermore, in each of the above embodiments, a pupil-expanding type image display device 1 was described. In this embodiment, the image display device 1 does not necessarily have to be a pupil-expanding type, and the optical waveguide 2 of the pupil-expanding optical system 12 may be omitted. Also, the separation optical system 13 does not necessarily have to be included in the pupil-expanding optical system 12. Even in such an image display device 1, the separation optical system 13 separates and projects a plurality of separated lights L11 and L12 according to the optical characteristics of the incident light L1, thereby improving various utilization efficiencies of the incident light L1.

[0119] Furthermore, while an HMD was used as an example of the image display device 1 in the above embodiments, this disclosure is not particularly limited thereto. In this embodiment, the image display device 1 may be, for example, an electronic mirror or a head-up display (HUD). Also, the projection surface by the separation optical system 13 is not particularly limited to an optical waveguide, but may be projected onto a diffusing surface such as a screen.

[0120] Furthermore, in each of the embodiments described above, the image light L1 of the display unit 11 was described as being in the visible region. In this embodiment, the image light L1 of the display unit 11 is not necessarily limited to the visible region, but may be in the infrared region, for example, or it may generate an image light L1 that shows a pattern image for measurement purposes such as distance measurement. In such applications as well, the separation optical system 13 of this embodiment can improve various utilization efficiencies of light projection by separating it into a plurality of separated lights L11, L12, similar to each of the embodiments described above.

[0121] As described above, embodiments have been explained as examples of the technology in this disclosure. For this purpose, accompanying drawings and a detailed description have been provided.

[0122] Therefore, the components described in the attached drawings and detailed descriptions may include not only components essential for solving the problem, but also components that are not essential for solving the problem, provided that they illustrate the technology described above. For this reason, the mere presence of these non-essential components in the attached drawings and detailed descriptions should not be immediately assumed to mean that they are essential.

[0123] Furthermore, since the embodiments described above are for illustrative purposes of the technology described herein, various modifications, substitutions, additions, omissions, etc., can be made within the claims or their equivalents.

[0124] (Examples of embodiments) The following are examples of various embodiments of this disclosure.

[0125] A first aspect of the present disclosure comprises a projection optical system that projects light representing an image generated by a display unit, and an optical separation element disposed between the display unit and the projection optical system, which separates incident light incident from the display unit into a plurality of separated lights each having different optical characteristics, wherein the optical separation element is an optical system that emits a plurality of separated lights to the projection optical system so that, in response to the incident light from the display unit to the optical separation element, the plurality of separated lights are projected to a plurality of projection positions via the projection optical system.

[0126] In such an optical system, multiple separated light beams can be projected through a common projection optical system. For example, the projection optical system may include optical elements arranged so that multiple separated light beams pass through it together.

[0127] A second embodiment is the optical system described in the first embodiment, wherein the light separation element is arranged planarly opposite to the display surface in the display unit, and comprises an optical structure that emits a plurality of separated lights on the opposite side from the display surface when incident light is incident from the display surface. The light separation element may be arranged along the display surface.

[0128] A third embodiment is an optical system according to the first or second embodiment, wherein the incident light includes a plurality of polarization components corresponding to a plurality of optical properties, and the light separation element separates the incident light into a plurality of separated lights such that each of the separated lights includes a different polarization component from the plurality of polarization components.

[0129] The fourth embodiment is an optical system according to any of the first to third embodiments, wherein the incident light includes multiple wavelength components corresponding to multiple optical properties, and the light separation element separates the incident light into multiple separated light such that each of the separated light contains a different wavelength component from the multiple wavelength components.

[0130] The fifth aspect is an optical system described in any of the second to fourth aspects, wherein the optical structure includes a plurality of unit structures, each having a size less than or equal to the wavelength of the incident light. The plurality of unit structures are periodically arranged in the optical separation element so as to diffract the incident light and emit a plurality of separated lights. The plurality of unit structures may also be periodically arranged along the display surface.

[0131] The sixth aspect is an optical system according to any of the second to fifth aspects, wherein the optical structure is composed of at least one of a metamaterial, a diffraction grating, and a hologram.

[0132] The seventh embodiment is an optical system described in any of the first to sixth embodiments, wherein the light separation element is positioned closer to the display unit than the projection optical system.

[0133] The eighth aspect is an optical system described in any of the first to seventh aspects, satisfying the following conditions: (L × D) / f ２ <0.03 Here, L is the distance from the display unit to the light separation element, D is the diameter of the separated light beam at the projection position, and f is the focal length of the projection optical system.

[0134] In the ninth aspect, the optical system described in any of the first to eighth aspects has a polarization dependence or wavelength dependence at multiple projection positions, each corresponding to the optical characteristics of the incident separated light.

[0135] In the tenth embodiment, the optical system described in the ninth embodiment further comprises at least one optical waveguide that propagates a plurality of separated light beams from the projection optical system internally based on polarization dependence or wavelength dependence and emits them to the outside as indicator light.

[0136] An eleventh embodiment is an optical system according to the tenth embodiment, wherein at least one optical waveguide is arranged at a plurality of projection positions and has at least one incident region into which a plurality of separated light beams are incident, at least one propagation region into which the plurality of separated light beams from the incident region propagate, and at least one output region into which the plurality of separated light beams from the propagation region are emitted as indicator light.

[0137] A twelfth aspect is the optical system described in the eleventh aspect, wherein at least one incident region includes a plurality of incident regions arranged at a plurality of projection positions, and each incident region has a polarization dependence or wavelength dependence depending on the optical properties of the separated light incident at the corresponding projection position among the plurality of separated lights.

[0138] A thirteenth aspect is the optical system described in the twelfth aspect, wherein at least one propagation region includes a plurality of propagation regions arranged adjacent to a plurality of incident regions, and each propagation region diffracts to replicate the separated light from the adjacent incident region.

[0139] A fourteenth aspect is the optical system described in the thirteenth aspect, wherein at least one emission region includes an emission region arranged adjacent to a plurality of propagation regions. This emission region emits multiple separated light beams from the plurality of propagation regions together as display light.

[0140] The fifteenth embodiment is the optical system described in the thirteenth embodiment, wherein at least one emission region includes a plurality of emission regions arranged adjacent to a plurality of propagation regions, and the plurality of emission regions are stacked on top of each other in the emission direction of the display light.

[0141] In the sixteenth embodiment, the optical system described in any of the tenth to fifteenth embodiments further comprises a polarizing element positioned between a light separation element and a plurality of projection positions, which aligns the polarization characteristics of the first separated light and the polarization characteristics of the second separated light in the plurality of separated lights, wherein at least one incident region includes an incident region positioned across both a first projection position where the first separated light is projected and a second projection position where the second separated light is projected in the plurality of projection positions. The incident region has a polarization dependence corresponding to the polarization characteristics aligned between the first separated light and the second separated light by the polarization separation element.

[0142] The 17th aspect is the optical system described in the 16th aspect, wherein the polarization characteristics of the first separated light and the polarization characteristics of the second separated light before alignment by the polarizing element have a phase difference of half a wavelength from each other, and the polarizing element is a half-wave plate.

[0143] The 18th embodiment is an optical system described in any of the 1st to 17th embodiments, wherein the projection optical system projects multiple separated light beams from the light separation element as parallel light beams to multiple projection positions.

[0144] The 19th aspect is an image display device comprising an optical system described in any of the 1st to 18th aspects and a display unit that emits incident light into the optical system to generate an image.

[0145] This disclosure is applicable, for example, to image display devices, and is applicable to HMDs, HUDs, and electronic mirrors, etc.

Claims

1. A projection optical system comprising: a projection optical system that projects light indicating an image generated by a display unit; and an optical separation element disposed between the display unit and the projection optical system, which separates incident light incident from the display unit into a plurality of separated lights each having a plurality of different optical characteristics, wherein the optical separation element emits the plurality of separated lights to the projection optical system such that, in response to the incident light from the display unit to the optical separation element, the plurality of separated lights are projected to a plurality of projection positions via the projection optical system.

2. The optical system according to claim 1, wherein the light separation element is arranged in a planar manner opposite to the display surface of the display unit, and has an optical structure that emits the plurality of separated lights on the opposite side from the display surface when the incident light is incident from the display surface.

3. The optical system according to claim 2, wherein the incident light includes a plurality of polarization components corresponding to the plurality of optical characteristics, and the optical separation element separates the incident light into a plurality of separated lights such that each of the plurality of separated lights includes a different polarization component from the plurality of polarization components.

4. The optical system according to claim 2, wherein the incident light includes a plurality of wavelength components corresponding to the plurality of optical characteristics, and the optical separation element separates the incident light into a plurality of separated lights such that each of the plurality of separated lights includes a different wavelength component from the plurality of wavelength components.

5. The optical system according to claim 2, wherein the optical structure includes a plurality of unit structures, each having a size less than or equal to the wavelength of the incident light, and the plurality of unit structures are periodically arranged in the light separation element such that the incident light is diffracted and the plurality of separated lights are emitted.

6. The optical system according to claim 2, wherein the optical structure comprises at least one of a metamaterial, a diffraction grating, and a hologram.

7. The optical system according to any one of claims 1 to 6, wherein the light separation element is positioned closer to the display unit than the projection optical system.

8. (L × D) / f satisfies the following conditions: ２ <0.03 The optical system according to any one of claims 1 to 6, where L is the distance from the display unit to the light separation element, D is the diameter of the light beam of the separated light at the projection position, and f is the focal length of the projection optical system.

9. The optical system according to any one of claims 1 to 6, having a polarization dependence or wavelength dependence at each of the plurality of projection positions according to the optical characteristics of each incident separated light.

10. The optical system according to claim 9, further comprising at least one optical waveguide that propagates the plurality of separated lights from the projection optical system internally based on the polarization dependence or wavelength dependence and emits them to the outside as display light.

11. The optical system according to claim 10, wherein the at least one optical waveguide is arranged at the plurality of projection positions and comprises at least one incident region into which the plurality of separated lights are incident, at least one propagation region into which the plurality of separated lights propagate from the incident region, and at least one output region into which the plurality of separated lights from the propagation region are emitted as the indicator light.

12. The optical system according to claim 11, wherein the at least one incident region includes a plurality of incident regions arranged at each of the plurality of projection positions, and each incident region has the polarization dependence or wavelength dependence according to the optical properties of the separated light incident at the corresponding projection position among the plurality of separated lights.

13. The optical system according to claim 12, wherein the at least one propagation region includes a plurality of propagation regions arranged adjacent to each of the plurality of incident regions, and each propagation region diffracts to replicate the separated light from each adjacent incident region.

14. The optical system according to claim 13, wherein the at least one emission region includes an emission region that is adjacent to the plurality of propagation regions, and the emission region emits the plurality of separated lights from the plurality of propagation regions together as the display light.

15. The optical system according to claim 13, wherein the at least one emission region includes a plurality of emission regions arranged adjacent to each of the plurality of propagation regions, and the plurality of emission regions are stacked on top of each other in the emission direction of the display light.

16. The optical system according to claim 10, further comprising a polarizing element positioned between the light separation element and the plurality of projection positions, wherein the polarization characteristics of the first separated light and the polarization characteristics of the second separated light in the plurality of separated lights are matched, and the at least one incident region includes an incident region positioned across both a first projection position where the first separated light is projected and a second projection position where the second separated light is projected in the plurality of projection positions.

17. The optical system according to claim 16, wherein the polarization characteristics of the first separated light and the polarization characteristics of the second separated light before alignment by the polarizing element have a phase difference of half a wavelength from each other, and the polarizing element is a half-wave plate.

18. The projection optical system according to any one of claims 1 to 6, wherein the plurality of separated light beams from the light separation element are projected as parallel light beams to the plurality of projection positions.

19. An image display device comprising an optical system according to any one of claims 1 to 6, and a display unit that emits incident light to the optical system in order to generate the image.

Images