Optical system and image display device

Abstract

This optical system (3) is provided with a projection optical system (5) which projects image light (L1) that forms an image outputted from a display element (2), and a light guide member (4) which guides, as a virtual image, the image light (L1) projected by the projection optical system (5) into the field-of-view (7) of a user. The light guide member (4) has a combining region (41) which leads the image light (L1) into the light guide member (4), and which directs said light in a first axis (X axis) direction inside the light guide member (4), and a propagation region (42) in which the image light (L1) from the combining region (41) is propagated in the first axis direction, and which directs part of the image light (L1) in a prescribed direction that includes a direction component of a second axis (Y axis) perpendicular to the first axis. On the optical path of the image light (L1) projected by the projection optical system (5), the distance (D1) from the projection optical system (5) to the incident pupil (P1) of the projection optical system (5) with respect to the display element (2) in a plane perpendicular to the first axis is longer than the distance from the projection optical system (5) to the combining region (41).

Description

Technical Field

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

Background Art

[0002] Patent Document 1 discloses an optical element (optical system) including a waveguide (light guiding member) for expanding an exit pupil in two directions. The optical element includes three diffractive optical elements (DOEs). The first DOE couples light from a display element into the inside of the waveguide. The second DOE expands the exit pupil in a first direction along a first coordinate axis. The third DOE expands the exit pupil in a second direction along a second coordinate axis and emits the light to the outside of the waveguide.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] The optical element described in Patent Document 1 is used, for example, in a head-mounted display. In a head-mounted display, miniaturization of the waveguide of the optical element may be desired depending on the usage mode of the optical element.

[0005] The present disclosure provides an optical system and an image display device in which miniaturization of a light guiding member can be achieved.

Means for Solving the Problems

[0006] An optical system according to one aspect of the present disclosure includes a projection optical system that projects image light forming an image output from a display element, and a light guide member that guides the image light projected by the projection optical system as a virtual image to a user's visual field region. The light guide member has a coupling region that guides the image light into the light guide member and directs it in the direction of a first axis within the light guide member, and a propagation region that propagates the image light from the coupling region in the direction of the first axis and directs a part of the image light in a specified direction including a component in the direction of a second axis orthogonal to the first axis. On the optical path of the image light projected by the projection optical system, the distance from the projection optical system to the entrance pupil of the projection optical system with respect to the display element in a plane orthogonal to the first axis is longer than the distance from the projection optical system to the coupling region.

[0007] An image display device according to one aspect of the present disclosure includes the above optical system and the display element.

Advantages of the Invention

[0008] According to an aspect of the present disclosure, miniaturization of the light guide member can be achieved.

Brief Description of the Drawings

[0009]

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[0010] Hereinafter, embodiments will be described in detail with reference to the drawings as appropriate. However, a more detailed description than necessary may be omitted. For example, a detailed description of well-known matters or a redundant description of substantially the same configuration may be omitted. This is to avoid making the following description unnecessarily redundant and to facilitate the understanding of those skilled in the art. The inventors provide the accompanying drawings and the following description so that those skilled in the art can fully understand the present disclosure, and do not intend to limit the subject matter described in the claims thereby.

[0011] [1. Embodiment] [1.1 Overview] FIG. 1 is a schematic diagram of a configuration example of an image display device 1. The image display device 1 is, for example, a head-mounted display (HMD) that is worn on a user's head and displays an image (video). Hereinafter, directions related to the image display device 1 will be described based on the X-axis, Y-axis, and Z-axis shown in FIG. 1. The X-axis corresponds to the horizontal direction, the Y-axis corresponds to the vertical direction, and the Z-axis corresponds to the front-rear direction of the user. In the present disclosure, the “direction of the XX axis” means a direction parallel to the XX axis passing through an arbitrary point. In the present disclosure, expressions such as “directing light in the XX direction” and “propagating light in the XX direction” with respect to light mean that the light forming the image travels in the XX direction as a whole, and the light rays included in the light forming the image may be inclined with respect to the XX direction. For example, for “light traveling in the XX direction”, it is sufficient that the principal ray of this light is directed in the XX direction, and the secondary rays of the light may be inclined with respect to the XX direction.

[0012] As shown in FIG. 1, the image display device 1 includes a display element 2 and an optical system 3. The display element 2 outputs image light L1 that forms an image. The optical system 3 includes a light guide member 4 and a projection optical system 5. The projection optical system 5 projects the image light L1 that forms an image output from the display element 2. The light guide member 4 guides the image light L1 projected by the projection optical system 5 as a virtual image to the user's visual field region 7. The light guide member 4 has a coupling region 41 and a propagation region 42. The coupling region 41 guides the image light L1 into the light guide member 4 and directs it in the direction of the first axis (in the present embodiment, the X-axis) within the light guide member 4. The propagation region 42 propagates the image light L1 from the coupling region 41 in the direction of the first axis and directs a part (L2) of the image light L1 in a specified direction (in the present embodiment, the direction of the second axis) including a component in the direction of the second axis (in the present embodiment, the Y-axis) orthogonal to the first axis. FIG. 2 is a schematic diagram in the YZ plane of the image display device 1 of FIG. 1. As shown in FIG. 2, on the optical path of the image light L1 projected by the projection optical system 5, the distance D1 from the projection optical system 5 to the entrance pupil P1 of the projection optical system 5 with respect to the display element 2 in a plane orthogonal to the first axis (in the present embodiment, the YZ plane orthogonal to the X-axis) within the projection optical system 5 is longer than the distance D10 from the projection optical system 5 to the coupling region 41.

[0013] In the present disclosure, the "entrance pupil of the projection optical system with respect to the display element" corresponds to the aperture stop of the projection optical system. The "position of the entrance pupil of the projection optical system with respect to the display element" is the position where the central ray of the light beam emitted from each point of the display element that constitutes the image light L1 intersects the optical axis when viewed in a cross-section parallel to the optical axis of the projection optical system.

[0014] FIG. 3 is a schematic view in the XY plane of a configuration example of the light guide member 4 of the optical system 3 in FIG. 1. In the image display device 1, on the optical path of the image light L1 projected by the projection optical system 5, the distance D1 from the projection optical system 5 to the entrance pupil P1 of the projection optical system 5 with respect to the display element 2 in a plane orthogonal to the first axis (in this embodiment, the YZ plane orthogonal to the X axis) is longer than the distance D10 from the projection optical system 5 to the coupling region 41. In this embodiment, since the projection optical system 5 and the light guide member 4 are arranged in a straight line, the position of the entrance pupil P1 of the projection optical system 5 with respect to the display element 2 in a plane orthogonal to the first axis (the YZ plane orthogonal to the X axis) is on the side opposite to the projection optical system 5 with respect to the coupling region 41. And between the projection optical system 5 and the entrance pupil P1, the light rays from each point of the display element 2 that constitutes the image light L1 converge and diverge from the entrance pupil P1. Therefore, as shown in FIG. 3, in the propagation region 42, the light rays from each point of the display element 2 that constitutes the image light L1 can be converged. On the other hand, on the optical path of the image light L1 projected by the projection optical system 5, when the distance D1 is shorter than the distance D10, the position of the entrance pupil P1 of the projection optical system 5 with respect to the display element 2 is on the same side as the projection optical system 5 with respect to the coupling region 41. In this case, in the propagation region 42, the light rays from each point of the display element 2 that constitutes the image light L1 diverge without converging. Therefore, like the image display device 1 of this embodiment, by converging the light rays from each point of the display element 2 that constitutes the image light L1 in the propagation region 42, the size required for the propagation region 42 to propagate the image light L1 from the display element 2 can be reduced. Thereby, miniaturization of the light guide member 4 can be achieved.

[0015] [1.2 Details] Hereinafter, the image display device 1 of the present embodiment will be described in more detail with reference to FIGS. 1 to 6. As shown in FIG. 1, the image display device 1 includes a display element 2 and an optical system 3.

[0016] The display element 2 outputs image light L1 that forms an image in order to display an image (video). The image light L1 includes light rays output from each point of the display element 2. Each point of the display element 2 corresponds to, for example, each pixel of the display element 2. The display element 2 is arranged such that the optical axis of the display element 2 is along the Z-axis, and the horizontal and vertical directions of the image displayed on the display element 2 are along the X-axis and the Y-axis, respectively. The optical axis of the display element 2 is the optical axis of the image light L1. The optical axis of the image light L1 is, for example, the optical axis of the light output from the center of the display element 2. Examples of the display element 2 include known displays such as liquid crystal displays and organic EL displays.

[0017] In the present embodiment, as shown in FIGS. 4 and 5, the display element 2 has an emission angle characteristic in which the image light L1 spreads more in the second axis than in the first axis. As a result, it becomes easy to make the position of the entrance pupil P1 of the projection optical system 5 with respect to the display element 2 in the plane orthogonal to the first axis (the YZ plane orthogonal to the X-axis) different from the position of the entrance pupil P2 of the projection optical system 5 with respect to the display element 2 in the plane orthogonal to the second axis (the XZ plane orthogonal to the Y-axis) by the projection optical system 5 described later.

[0018] As shown in FIG. 1, the optical system 3 guides the image light L1 output from the display element 2 to the visual field region 7 set for the user's eyes 6. In the visual field region 7, the user can visually recognize the image formed by the display element 2 without interruption with their own eyes 6. In particular, in the present embodiment, the optical system 3 expands the visual field region 7 by the action of pupil expansion.

[0019] As shown in FIG. 1, the optical system 3 includes a light guide member 4 and a projection optical system 5.

[0020] The light guide member 4 guides the image light L1 output from the display element 2 as a virtual image to the user's visual field region 7. The light guide member 4 is plate-shaped. More specifically, the light guide member 4 has a plate-shaped main body portion 40. The main body portion 40 is formed of a transparent material and has a first surface 40a and a second surface 40b in the thickness direction. As shown in FIG. 1, the light guide member 4 is arranged with the first surface 40a facing the display element 2 side and the second surface 40b facing the visual field region 7 side so that the thickness of the main body portion 40 is along the Z axis.

[0021] As shown in FIG. 1, the light guide member 4 has a coupling region 41 and a propagation region 42 as elements for guiding the image light L1 from the display element 2 to the user's visual field region 7.

[0022] The coupling region 41 guides the image light L1 into the light guide member 4 and directs it in a direction along the first axis within the light guide member 4. The coupling region 41 is used for coupling the display element 2 and the light guide member 4. The coupling region 41 causes external light (image light L1) to enter the light guide member 4 so as to propagate within the light guide member 4 under total reflection conditions. The "coupling" here means a state of propagating within the light guide member 4 under total reflection conditions. In the present embodiment, the first axis is orthogonal to the thickness direction of the light guide member 4. In the present embodiment, the first axis is the X axis. The coupling region 41 is constituted by a periodic structure having a diffractive action on the image light L1. The periodic structure of the coupling region 41 is, for example, a transmissive diffraction grating. The coupling region 41 is formed, for example, on the first surface 40a of the main body portion 40. The diffraction grating of the coupling region 41 may include, for example, a plurality of concave portions or convex portions extending along the second axis and arranged at a predetermined interval along the first axis. Note that in FIG. 2, for the sake of easy illustration of the coupling region 41 having a periodic structure with a diffractive action, it is illustrated as having convex portions arranged along the Y axis. The coupling region 41 causes the image light L1 to enter the light guide member 4 under conditions of total reflection with respect to the first surface 40a and the second surface 40b. Due to the coupling region 41, the image light L1 travels within the light guide member 4 (that is, within the main body portion 40) in the direction of the first axis (in the present embodiment, the X axis) by being totally reflected by the first surface 40a and the second surface 40b.

[0023] The size of the coupling region 41 is set such that part or all of the image light L1 from the display element 2 that has passed through the projection optical system 5 enters the coupling region 41. In the present embodiment, as shown in FIG. 3, the coupling region 41 has an elliptical shape in the XY plane, with the major axis along the first axis and the minor axis along the second axis. That is, the dimension of the coupling region 41 in the second axis (Y axis) is larger than the dimension of the coupling region 41 in the first axis (X axis). However, the coupling region 41 is not limited to an elliptical shape, and may be a rectangular shape in which the dimension of the coupling region 41 in the second axis (Y axis) is larger than the dimension of the coupling region 41 in the first axis.

[0024] The propagation region 42 includes a first expansion region 421 and a second expansion region 422.

[0025] As shown in FIG. 3, the first expansion region 421 is arranged to be aligned with the coupling region 41 on the first axis. The first expansion region 421 propagates the image light L1 from the coupling region 41 along the first axis and directs a part of the image light L1 (image light L2) in a specified direction. The specified direction is a direction including a direction component of the second axis orthogonal to the first axis. In the present embodiment, the second axis is orthogonal to the thickness direction of the light guide member 4 and the first axis. In the present embodiment, the second axis is the Y axis. In the present embodiment, the specified direction includes only the direction component of the second axis and coincides with the direction of the second axis. In the present embodiment, the first expansion region 421 expands the pupil of the image light L1 on the first axis. More specifically, as shown in FIG. 3, the first expansion region 421 divides the image light L1 into a plurality of parallel image lights L2 directed in the specified direction, and replicates and expands the pupil of the image light L1 projected by the projection optical system 5 on the first axis. The first expansion region 421 is constituted by a periodic structure having a diffraction effect on the image light L1. The periodic structure of the first expansion region 421 is, for example, a reflective diffraction grating. The first expansion region 421 is formed, for example, on the first surface 40a of the main body portion 40. The diffraction grating of the first expansion region 421 may include a plurality of concave portions or convex portions extending along a direction inclined 45 degrees with respect to the Y axis and arranged at a predetermined interval in a direction inclined 135 degrees with respect to the Y axis in a plane orthogonal to the Z axis.

[0026] The size of the first extended region 421 is set such that all of the image light L1 from the coupling region 41 enters the first extended region 421. In the present embodiment, as shown in FIG. 3, the first extended region 421 has a rectangular shape in the XY plane. The first extended region 421 has a first end 421a and a second end 421b on the first axis. The first end 421a is closer to the coupling region 41 than the second end 421b. In the first extended region 421, assuming that the width of the optical path of the image light L1 at the first end 421a is W1 and the width of the optical path of the image light L1 at the second end 421b is W2, the widths W1 and W2 satisfy the relationship 0.4 < W1 / W2 < 1.8. By satisfying the relationship 0.4 < W1 / W2 < 1.8 for the widths W1 and W2, the required area of the first extended region 421 for propagating the image light L1 in the direction of the first axis inside the light guide member 4 becomes smaller, and an increase in the size of the coupling region 41 can be suppressed. Therefore, by making the width at the first end 421a of the first extended region 421 equal to the optical path width W1 and making the width at the second end 421b of the first extended region 421 equal to the optical path width W2, the size of the first extended region 421 can be reduced, and the light guide member 4 can be miniaturized. The dimension of the first extended region 421 on the first axis (X axis) is set according to the dimension of the first axis of the visual field region 7.

[0027] As shown in Fig. 2, the second expansion region 422 is arranged to be aligned with the first expansion region 421 on the second axis (Y axis). The second expansion region 422 propagates the image light L2 from the first expansion region 421 in a specified direction, and emits a part of the image light L2 (image light L3) from the light guide member 4 to the visual field region 7. In the present embodiment, the second expansion region 422 expands the pupil of the image light L1 on the second axis. More specifically, as shown in Fig. 2, the second expansion region 422 divides the pupil of the image light L1 projected by the projection optical system 5 into a plurality of parallel image lights L3 directed from the light guide member 4 to the visual field region 7, and replicates and expands it on the second axis. The image light L3 travels, for example, in the direction of the third axis. The second expansion region 422 is composed of a periodic structure having a diffraction effect on the image light L2. The periodic structure of the second expansion region 422 is, for example, a reflective diffraction grating. The second expansion region 422 is formed, for example, on the first surface 40a of the main body portion 40. The diffraction grating of the second expansion region 422 may include, for example, a plurality of concave or convex portions extending in the direction of the first axis and arranged at a predetermined interval in the direction of the second axis.

[0028] The size of the second expansion region 422 is set such that all of the image light L2 from the first expansion region 421 enters the second expansion region 422. In the present embodiment, as shown in Fig. 3, the second expansion region 422 has a rectangular shape in the XY plane. The dimension of the second expansion region 422 in the first axis (X axis) is equal to the dimension of the first expansion region 421 in the first axis. The dimension of the second expansion region 422 in the second axis (Y axis) is set according to the dimension of the second axis of the visual field region 7.

[0029] As described above, the light guide member 4 divides the image light L1 incident from the coupling region 41 into the light guide member 4 into a plurality of mutually parallel image lights L2 and L3 in the light guide member 4 and emits them to the visual field region 7, thereby replicating and expanding the pupil of the image light L1. More specifically, the light guide member 4 has a coupling region 41 and a propagation region 42, and divides the image light L1 incident from the coupling region 41 into the light guide member 4 into a plurality of mutually parallel image lights L2 and L3 in the light guide member 4 by the first expansion region 421 and the second expansion region 422 of the propagation region 42 and emits them to the visual field region 7, thereby replicating and expanding the pupil of the image light L1 on the first axis and the second axis.

[0030] The projection optical system 5 projects the image light L1 that forms an image output from the display element 2. Thereby, the projection optical system 5 causes the image light L1 from the display element 2 to enter the light guide member 4. As shown in FIGS. 1 and 2, the projection optical system 5 is between the display element 2 and the coupling region 41 of the light guide member 4. The projection optical system 5, for example, collimates the image light L1 from the display element 2 and causes it to enter the coupling region 41. The projection optical system 5 causes the image light L1 to enter the coupling region 41 as substantially collimated light. The projection optical system 5 is, for example, a biconvex lens.

[0031] The projection optical system 5 is configured such that the distance D1 (see FIG. 4) from the projection optical system 5 to the entrance pupil P1 of the projection optical system with respect to the display element 2 in a plane orthogonal to the first axis (the YZ plane orthogonal to the X axis) on the optical path of the image light L1 projected by the projection optical system 5 is longer than the distance D2 (see FIG. 5) from the projection optical system 5 to the entrance pupil P2 of the projection optical system 5 with respect to the display element 2 in a plane orthogonal to the second axis (the XZ plane orthogonal to the Y axis) on the optical path of the image light L1 projected by the projection optical system 5. In the present embodiment, since the projection optical system 5 and the light guide member 4 are aligned in a straight line, the position of the entrance pupil P1 of the projection optical system 5 with respect to the display element 2 in a plane orthogonal to the first axis (the YZ plane orthogonal to the X axis) is farther from the projection optical system 5 than the position of the entrance pupil P2 of the projection optical system 5 with respect to the display element 2 in a plane orthogonal to the second axis (the XZ plane orthogonal to the Y axis).

[0032] Next, the position of the entrance pupil of the projection optical system 5 will be described with reference to FIGS. 4 and 5. FIG. 4 is an explanatory diagram of the position of the entrance pupil P1 in the YZ plane of the projection optical system 5 of the image display device 1. FIG. 5 is an explanatory diagram of the position of the entrance pupil P2 in the XZ plane of the projection optical system 5 of the image display device 1. In FIGS. 4 and 5, in order to clearly illustrate the coupling region 41, the portion of the light guide member 4 corresponding to the coupling region 41 is shown by hatching.

[0033] Particularly, as shown in FIG. 4, on the optical path of the image light L1 projected by the projection optical system 5, the distance D1 from the projection optical system 5 to the entrance pupil P1 of the projection optical system 5 with respect to the display element 2 in the plane orthogonal to the first axis is longer than the distance D10 from the projection optical system 5 to the coupling region 41. As a result, in FIG. 4, the position of the entrance pupil P1 of the projection optical system 5 with respect to the display element 2 in the plane (YZ plane orthogonal to the X axis) orthogonal to the first axis is on the side opposite to the projection optical system 5 with respect to the coupling region 41. Further, the position of the entrance pupil P1 is set within the first extended region 421 of the propagation region 42 so that the convergence and divergence of the light rays from each point of the display element 2 constituting the image light L1 occur. More specifically, as shown in FIG. 4, the image light L1 incident on the coupling region 41 from the projection optical system 5 includes a principal ray L10 corresponding to the center of the virtual image and a plurality of sub-rays L11-1, L11-2,..., L11-n (hereinafter collectively referred to by the reference symbol L11) that approach the principal ray L10 on the second axis (Y axis) as they go from the projection optical system 5 toward the coupling region 41. As shown in FIG. 3, the plurality of sub-rays L11-1, L11-2 intersect the principal ray L10 within the first extended region 421 of the propagation region 42. In this way, within the first extended region 421 of the propagation region 42, by converging and diverging the light rays (principal ray L10 and sub-rays L11) of the light from each point of the display element 2 constituting the image light L1, the size required for the propagation region 42 (particularly the first extended region 421) to propagate the image light L1 from the display element 2 can be reduced. Here, "intersect" means that when the optical path is projected onto a plane including the first axis and the second axis, the principal ray L10 and the sub-ray L11 intersect, and they may have a twisted relationship in three-dimensional space.

[0034] On the other hand, as shown in FIG. 5, on the optical path of the image light L1 projected by the projection optical system 5, the distance D2 from the projection optical system 5 to the entrance pupil P2 of the projection optical system 5 with respect to the display element 2 in the plane orthogonal to the second axis is equal to the distance D20 from the projection optical system 5 to the coupling region 41. As a result, in FIG. 5, the position of the entrance pupil P2 of the projection optical system 5 with respect to the display element 2 in the plane (XZ plane orthogonal to the Y axis) orthogonal to the second axis is at the position corresponding to the coupling region 41 on the first surface 40a of the light guide member 4. Therefore, the light rays from each point of the display element 2 constituting the image light L1 converge on the coupling region 41. More specifically, as shown in FIG. 5, the image light L1 incident on the coupling region 41 from the projection optical system 5 includes a principal ray L10 corresponding to the center of the virtual image and a plurality of sub-rays L12-1, L12-2, …, L12-n (hereinafter collectively referred to by the reference sign L12) that approach the principal ray L10 on the first axis (X axis) as they travel from the projection optical system 5 toward the coupling region 41. The plurality of sub-rays L12 intersect the principal ray L10 at the coupling region 41.

[0035] [1.3 Effects, etc.] As described above, the optical system 3 includes a projection optical system 5 that projects the image light L1 that forms an image output from the display element 2, and a light guide member 4 that guides the image light L1 projected by the projection optical system 5 as a virtual image to the user's visual field region 7. The light guide member 4 has a coupling region 41 that guides the image light L1 into the light guide member 4 and directs it in the direction of the first axis within the light guide member 4, and a propagation region 42 that propagates the image light L1 from the coupling region 41 in the direction of the first axis and directs a part of the image light L1 in a specified direction including a component in the direction of the second axis orthogonal to the first axis. On the optical path of the image light L1 projected by the projection optical system 5, the distance D1 from the projection optical system 5 to the entrance pupil P1 of the projection optical system 5 with respect to the display element 2 in the plane orthogonal to the first axis is longer than the distance D10 from the projection optical system 5 to the coupling region 41. According to this configuration, downsizing of the light guide member 4, particularly the propagation region 42, can be achieved.

[0036] In the optical system 3, the light guide member 4 is plate-shaped, and each of the first axis, the second axis, and the specified direction is orthogonal to the thickness direction of the light guide member 4. According to this configuration, the dimension of the light guide member 4 in the second axis direction can be reduced.

[0037] In the optical system 3, the image light L1 incident from the projection optical system 5 into the coupling region 41 includes a chief ray L10 corresponding to the center of the virtual image and a plurality of sub-rays L11-1 and L11-2 that approach the chief ray L10 in the direction of the second axis as they go from the projection optical system 5 toward the coupling region 41. The plurality of sub-rays L11-1 and L11-2 intersect the chief ray L10 within the propagation region 42. According to this configuration, miniaturization of the light guide member 4 can be achieved.

[0038] In the optical system 3, the distance D1 from the projection optical system 5 to the entrance pupil P1 of the projection optical system 5 with respect to the display element 2 in the plane orthogonal to the first axis on the optical path of the image light L1 is longer than the distance D2 from the projection optical system 5 to the entrance pupil P2 of the projection optical system 5 with respect to the display element 2 in the plane orthogonal to the second axis on the optical path of the image light L1. The distances D1 and D2 satisfy 3.0 < D1 / D2 < 100. According to this configuration, the position where the plurality of sub-rays L11-1 and L11-2 intersect the chief ray L10 within the propagation region 42 can be appropriately set, and miniaturization of the light guide member 4 can be achieved.

[0039] In the optical system 3, the dimension of the coupling region 41 in the second axis is larger than the dimension of the coupling region 41 in the first axis. According to this configuration, miniaturization of the light guide member 4 can be achieved.

[0040] In the optical system 3, the propagation region 42 includes a first expansion region 421 that replicates and expands the pupil of the image light L1 projected by the projection optical system 5 by dividing the image light L1 into a plurality of parallel image lights L2 traveling in a specified direction. According to this configuration, expansion of the pupil in the first axis becomes possible.

[0041] In the optical system 3, the first expansion region 421 has a first end 421a and a second end 421b on the first axis. The first end 421a is on the side of the coupling region 41 with respect to the second end 421b. When the width of the optical path at the first end of the image light L1 is W1 and the width of the optical path at the second end of the image light L1 is W2, the widths W1 and W2 satisfy the relationship of 0.4 < W1 / W2 < 1.8. According to this configuration, the first expansion region 421 can be made smaller, and the propagation region 42 of the light guide member 4 can be miniaturized.

[0042] In the optical system 3, the propagation region 42 propagates the image light L2 from the first expansion region 421 in a specified direction, and emits a part of the image light L2, i.e., the image light L3, from the light guide member 4 to the visual field region 7. According to this configuration, the visual field region 7 can be widened.

[0043] In the optical system 3, the propagation region 42 divides the image light L2 from the first expansion region 421 into a plurality of parallel image lights L3 directed from the light guide member 4 to the visual field region 7, and includes a second expansion region 422 that replicates and expands the pupil of the image light L1 projected by the projection optical system 5 on the second axis. According to this configuration, the pupil can be expanded on the second axis.

[0044] In the optical system 3, the coupling region 41 includes a periodic structure having a diffraction effect on the image light L1. According to this configuration, the light guide member 4 can be miniaturized.

[0045] In the optical system 3, the light guide member 4 divides the image light L1 incident from the coupling region 41 into the light guide member 4 into a plurality of mutually parallel image lights L1 and L2, and emits them to the visual field region 7, thereby replicating and expanding the pupil of the image light L1 projected by the projection optical system 5. According to this configuration, the pupil can be expanded.

[0046] In the optical system 3, the projection optical system 5 makes the image light L1 incident on the coupling region 41 as substantially collimated light. According to this configuration, the light guide member 4 can be miniaturized.

[0047] The above-described solid image display device 1 includes the above-described optical system 3 and the display element 2. According to this configuration, miniaturization of the light guide member 4 can be achieved.

[0048] In the image display device 1, the display element 2 has an emission angle characteristic in which the image light L1 spreads in the second axis rather than the first axis. According to this configuration, it becomes easy to make the position of the entrance pupil P1 of the projection optical system 5 with respect to the display element 2 in the plane orthogonal to the first axis different from the position of the entrance pupil P2 of the projection optical system 5 with respect to the display element 2 in the plane orthogonal to the second axis by the projection optical system 5.

[0049] [2. Modification Example] The embodiment of the present disclosure is not limited to the above-described embodiment. The above-described embodiment can be variously modified according to design and the like as long as the problems of the present disclosure can be achieved. Modification examples of the above-described embodiment are listed below. The modification examples described below can be applied in appropriate combinations.

[0050] [2.1 Modification Example 1] FIG. 6 shows the image display device 1 of Modification 1. In particular, FIG. 6 is a schematic view of the image display device 1 of Modification 1 in the YZ plane. In the image display device 1 of Modification 1, the coupling region 41 of the light guide member 4 is different from the coupling region 41 of the light guide member 4 of the image display device 1 in the above embodiment. The coupling region 41 of the light guide member 4 in FIG. 6 guides the image light L1 into the light guide member 4 and directs it in the direction of the first axis within the light guide member 4. The coupling region 41 is constituted by a periodic structure having a diffracting action on the image light L1. The periodic structure of the coupling region 41 is, for example, a reflective diffraction grating. The coupling region 41 is formed, for example, on the second surface 40b of the main body portion 40. The diffraction grating of the coupling region 41 may include, for example, a plurality of concave portions or convex portions that extend along the second axis and are arranged at a predetermined interval along the first axis. In FIG. 6, for the sake of easy illustration of the fact that the coupling region 41 has a periodic structure having a diffracting action, it is illustrated as having convex portions arranged along the Y axis. The coupling region 41 causes the image light L1 to be incident on the light guide member 4 under the condition of total reflection with respect to the first surface 40a and the second surface 40b. Due to the coupling region 41, the image light L1 travels in the direction of the first axis within the light guide member 4 (that is, within the main body portion 40) by being totally reflected by the first surface 40a and the second surface 40b.

[0051] [2.2 Modification 2] FIG. 7 shows the image display device 1 of Modification 2. In particular, FIG. 7 is a schematic view of the image display device 1 of Modification 2 in the YZ plane. In the image display device 1 of Modification 2, the coupling region 41 of the light guide member 4 is different from the coupling region 41 of the light guide member 4 of the image display device 1 in the above-described embodiment. The coupling region 41 of the light guide member 4 in FIG. 7 guides the image light L1 into the light guide member 4 and directs it in the direction of the first axis within the light guide member 4. The coupling region 41 is constituted by a periodic structure having a diffraction effect on the image light L1. The periodic structure of the coupling region 41 is, for example, a volume hologram (holographic diffraction grating) that generates a diffraction effect by periodic modulation of the refractive index. The coupling region 41 is formed, for example, inside the main body portion 40. The diffraction grating of the coupling region 41 has, for example, a structure in which the first part 411 and the second part 412 having different refractive indexes from each other are arranged alternately. The coupling region 41 causes the image light L1 to be incident on the light guide member 4 under the condition of total reflection with respect to the first surface 40a and the second surface 40b. Due to the coupling region 41, the image light L1 travels in the light guide member 4 (that is, inside the main body portion 40) and is totally reflected by the first surface 40a and the second surface 40b, and thus travels in the direction of the first axis.

[0052] [2.3 Modification 3] FIG. 8 shows the image display device 1 of Modification 3. In particular, FIG. 8 is an explanatory diagram of the position of the entrance pupil P2 in the XZ plane of the optical system 3 of the image display device 1 of Modification 3. In the optical system 3 of the image display device 1 of Modification 3, on the optical path of the image light L1 projected by the projection optical system 5, the distance D2 from the projection optical system 5 to the entrance pupil P2 of the projection optical system 5 with respect to the display element 2 in the plane orthogonal to the second axis (the XZ plane orthogonal to the Y axis) is longer than the distance D20 from the projection optical system 5 to the coupling region 41. In FIG. 8, since the projection optical system 5 and the coupling region 41 of the light guide member 4 are aligned in a straight line, the position of the entrance pupil P2 of the projection optical system 5 with respect to the display element 2 in the plane orthogonal to the second axis (the XZ plane orthogonal to the Y axis) is on the side opposite to the projection optical system 5 with respect to the coupling region 41. Thus, it is not necessary for the distance D2 to coincide with the distance D20. That is, the position of the entrance pupil P2 does not need to coincide with the coupling region 41 as in the above-described embodiment.

[0053] [2.4 Modification 4] FIG. 9 shows a configuration example of the light guide member 4 of the image display device according to Modification 4. In particular, FIG. 9 is a schematic view of the light guide member 4 in the XY plane. In FIG. 9, as in the above-described embodiment, the first axis is the X axis and the second axis is the Y axis. The first expansion region 421 of the propagation region 42 in FIG. 9 is arranged so as to be aligned with the coupling region 41 on the first axis (X axis). The first expansion region 421 propagates the image light L1 from the coupling region 41 in the direction of the first axis (X axis), and causes a part of the image light L1 to travel in a specified direction including a component in the direction of the second axis (Y axis) orthogonal to the first axis. In FIG. 9, unlike the above-described embodiment, the specified direction includes components in the directions of the first axis and the second axis. That is, the specified direction is not the direction of the second axis orthogonal to the first axis, but a direction that intersects without being orthogonal to the first axis. The component of the first axis included in the specified direction is a component in the direction from the first expansion region 421 toward the coupling region 41.

[0054] FIG. 10 shows another configuration example of the light guide member 4 of the image display device according to Modification 4. In particular, FIG. 10 is a schematic view of the light guide member 4 in the XY plane. In FIG. 10, as in the above-described embodiment, the first axis is the X axis and the second axis is the Y axis. The first expansion region 421 of the propagation region 42 in FIG. 10 is arranged so as to be aligned with the coupling region 41 on the first axis (X axis). The first expansion region 421 propagates the image light L1 from the coupling region 41 in the direction of the first axis (X axis), and causes a part of the image light L1 to travel in a specified direction including a component in the direction of the second axis (Y axis) orthogonal to the first axis. In FIG. 10, unlike the above-described embodiment, the specified direction includes components in the directions of the first axis and the second axis. That is, the specified direction is not the direction of the second axis orthogonal to the first axis, but a direction that intersects without being orthogonal to the first axis. The component of the first axis included in the specified direction is a component in the direction from the coupling region 41 toward the first expansion region 421.

[0055] Thus, the specified direction does not necessarily coincide with the direction of the second axis, and may be a direction including a component in the direction of the second axis. In particular, the specified direction includes a component in the direction of the first axis and a component in the direction of the second axis, and does not include a component in the direction of the third axis. The specified direction is preferably such that the magnitude of the component in the direction of the second axis is equal to or greater than the magnitude of the component in the direction of the first axis.

[0056] [2.5 Modification Example 5] FIG. 11 shows the light guide member 4 of the image display device according to Modification Example 5. In particular, FIG. 11 is a schematic view of the configuration example of the light guide member 4 in the XY plane. In the above embodiment, the first axis is the X-axis and the second axis is the Y-axis, but in Modification Example 5, the first axis is the Y-axis and the second axis is the X-axis.

[0057] Therefore, in Modification Example 5, the coupling region 41 guides the image light L1 into the light guide member 4 and directs it in the direction of the first axis (Y-axis) within the light guide member 4. The coupling region 41 has an elliptical shape in the XY plane, with the major axis along the first axis (Y-axis) and the minor axis along the second axis (X-axis).

[0058] The first expansion region 421 of the propagation region 42 is arranged to be aligned with the coupling region 41 on the first axis (Y-axis). The first expansion region 421 propagates the image light L1 from the coupling region 41 in the direction of the first axis (Y-axis) and directs a part of the image light L1 in a specified direction including a component in the direction of the second axis (X-axis) orthogonal to the first axis. In Modification Example 5, the specified direction includes only the component in the direction of the second axis and coincides with the direction of the second axis.

[0059] The second expansion region 422 of the propagation region 42 is arranged to be aligned with the first expansion region 421 on the second axis (X-axis). The second expansion region 422 propagates the image light L2 from the first expansion region 421 in the specified direction and emits a part of the image light L2 from the light guide member 4 to the viewing region 7.

[0060] In the light guide member 4 of Modification Example 5, the propagation region 42 (particularly, the first expansion region 421) of the light guide member 4 can be reduced in size in the X-axis direction. As a result, the light guide member 4 can be miniaturized.

[0061] [2.6 Modification Example 6] FIG. 12 shows the light guide member 4 of the image display device according to Modification Example 6. In particular, FIG. 12 is a schematic view of the configuration example of the light guide member 4 in the XY plane. In Modification Example 6, similar to the above embodiment, the first axis is the X-axis and the second axis is the Y-axis.

[0062] The light guide member 4 in Fig. 12 has a coupling region 41 and a propagation region 42 as elements for guiding the image light L1 from the display element 2 to the user's visual field region 7.

[0063] The coupling region 41 guides the image light L1 into the light guide member 4 and directs it in the direction of the first axis within the light guide member 4. More specifically, the coupling region 41 generates two image lights L1-1 and L1-2 that travel in different directions from the first axis from the image light L1 incident on the coupling region 41. The image light L1-1 travels in the first direction of the first axis (the left direction in Fig. 12), and the image light L1-2 travels in the second direction opposite to the first direction (the right direction in Fig. 12). The coupling region 41 is composed of a periodic structure having a diffraction effect on the image light L1. The periodic structure of the coupling region 41 is, for example, a transmissive diffraction grating.

[0064] The propagation region 42 includes a pair of first extended regions 421-1 and 421-2 and a second extended region 422. The pair of first extended regions 421-1 and 421-2 are arranged in the direction of the first axis. As shown in FIG. 12, the pair of first extended regions 421-1 and 421-2 are located on both sides of the coupling region 41 on the first axis. One of the pair of first extended regions 421-1 and 421-2 (the first extended region 421-1) propagates the image light L1-1 from the coupling region 41 in the first direction, and makes a part of the image light L1-1 go in a specified direction including the direction component of the second axis (in FIG. 12, the direction of the second axis). As shown in FIG. 12, the first extended region 421-1 divides the pupil of the image light L1 projected by the projection optical system 5 into a plurality of parallel image lights L2-1 going in the specified direction, and replicates and expands the pupil of the image light L1 on the first axis. The other of the pair of first extended regions 421-1 and 421-2 (the first extended region 421-2) propagates the image light L1-2 from the coupling region 41 in the second direction, and makes a part of the image light L1-2 go in a specified direction including the direction component of the second axis (in FIG. 12, the direction of the second axis). As shown in FIG. 12, the first extended region 421-2 divides the pupil of the image light L1 projected by the projection optical system 5 into a plurality of parallel image lights L2-2 going in the specified direction, and replicates and expands the pupil of the image light L1 on the first axis. The first extended regions 421-1 and 421-2 are constituted by a periodic structure having a diffracting action on the image lights L1-1 and L1-2. The periodic structure of the first extended regions 421-1 and 421-2 is, for example, a reflective diffraction grating.

[0065] As shown in FIG. 12, the second expansion region 422 is arranged to be aligned with a pair of first expansion regions 421-1 and 421-2 on the second axis (Y axis). That is, the second expansion region 422 is a common second expansion region for the pair of first expansion regions 421-1 and 421-2. The second expansion region 422 propagates the image lights L2-1 and L2-2 from the pair of first expansion regions 421-1 and 421-2 along a specified direction, and emits a part of the image lights L2-1 and L2-2 from the light guide member 4 to the visual field region 7. The second expansion region 422 divides the image lights L2-1 and L2-2 into a plurality of parallel image lights directed from the light guide member 4 to the visual field region 7, thereby replicating and expanding the pupil of the image light L1 projected by the projection optical system 5 on the second axis. The second expansion region 422 is constituted by a periodic structure having a diffraction effect on the image lights L2-1 and L2-2. The periodic structure of the second expansion region 422 is, for example, a reflective diffraction grating. Also, the second expansion region 422 may have a region without a diffraction grating in a specified direction (in FIG. 12, the direction of the second axis) including the direction component of the second axis of the coupling region 41. The second expansion region 422 may be a pair of second expansion regions 422-1 and 422-2 for the pair of first expansion regions 421-1 and 421-2.

[0066] As described above, in the sixth modification, the propagation region 42 includes a pair of first expansion regions 421-1 and 421-2 arranged along the first axis. One of the pair of first expansion regions 421-1 and 421-2 propagates the image light L1-1 in the first direction of the first axis, and directs a part of the image light L1-1 in a specified direction including the direction component of the second axis. The other of the pair of first expansion regions 421-1 and 421-2 propagates the image light L1-2 in the second direction opposite to the first direction, and directs a part of the image light L1-2 in a specified direction including the direction component of the second axis. The second expansion region 422 propagates the image lights L2-1 and L2-2 from the pair of first expansion regions 421-1 and 421-2 in the specified direction, and emits a part of the image lights L2-1 and L2-2 from the light guide member 4 to the visual field region 7. According to this configuration, the visual field region 7 can be expanded.

[0067] [2.7 Sixth Modification] FIG. 13 shows the light guide member 4 of the image display device according to Modification 7. In particular, FIG. 13 is a schematic view in the XY plane of a configuration example of the light guide member 4. In Modification 7, as in the above embodiment, the first axis is the X axis and the second axis is the Y axis.

[0068] The light guide member 4 in FIG. 13 has a plurality of coupling regions 41 and a propagation region 42 as elements for guiding the image light L1 from the display element 2 to the user's visual field region 7. The image display device according to Modification 7 includes a plurality of display elements 2 corresponding to the plurality of coupling regions 41 respectively, and a plurality of projection optical systems 5 respectively disposed between the plurality of coupling regions 41 and the plurality of display elements 2.

[0069] The plurality of coupling regions 41 include a first coupling region 41-1 and a second coupling region 41-2 arranged in the direction of the first axis. The first coupling region 41-1 and the second coupling region 41-2 guide the image light L1 into the light guide member 4 and direct it in the direction of the first axis within the light guide member 4. More specifically, the first coupling region 41-1 guides the image light L1 into the light guide member 4 and directs it in the first direction of the first axis (the right direction in FIG. 13) within the light guide member 4. The second coupling region 41-2 guides the image light L1 into the light guide member 4 and directs it in the second direction (the left direction in FIG. 13) opposite to the first direction within the light guide member 4. The first coupling region 41-1 and the second coupling region 41-2 are constituted by a periodic structure having a diffraction effect on the image light L1. The periodic structures of the first coupling region 41-1 and the second coupling region 41-2 are, for example, transmissive diffraction gratings.

[0070] The propagation region 42 includes a pair of first expansion regions 421-1 and 421-2 arranged in the direction of the first axis. As shown in FIG. 13, the pair of first expansion regions 421-1 and 421-2 are located between the first coupling region 41-1 and the second coupling region 41-2 on the first axis, and the first expansion regions 421-1 and 421-2 are adjacent to the first coupling region 41-1 and the second coupling region 41-2 respectively. One of the pair of first expansion regions 421-1 and 421-2 (the first expansion region 421-1) propagates the image light L1 from the first coupling region 41-1 in the first direction and directs a part of the image light L1 in a specified direction including the direction component of the second axis (in FIG. 13, the direction of the second axis). As shown in FIG. 13, the first expansion region 421-1 divides the image light L1 into a plurality of parallel image lights L2 directed in the specified direction, thereby replicating and expanding the pupil of the image light L1 projected by the projection optical system 5 on the first axis. The other of the pair of first expansion regions 421-1 and 421-2 (the first expansion region 421-2) propagates the image light L1 from the second coupling region 41-2 in the second direction and directs a part of the image light L1 in a specified direction including the direction component of the second axis (in FIG. 13, the direction of the second axis). As shown in FIG. 13, the first expansion region 421-2 divides the image light L1 into a plurality of parallel image lights L2 directed in the specified direction, thereby replicating and expanding the pupil of the image light L1 projected by the projection optical system 5 on the first axis. The pair of first expansion regions 421-1 and 421-2 are constituted by a periodic structure having a diffraction effect on the image light L1. The periodic structure of the pair of first expansion regions 421-1 and 421-2 is, for example, a reflective diffraction grating. Further, a blocking wall may be provided on the light guide member between the first expansion region 421-1 and the first expansion region 421-2 so that the image light L1 from the first coupling region 41-1 does not reach the first expansion region 421-2 and the image light L1 from the second coupling region 41-2 does not reach the first expansion region 421-1.

[0071] As shown in FIG. 13, the second expansion region 422 is arranged to be aligned with a pair of first expansion regions 421-1 and 421-2 on the second axis (Y axis). That is, the second expansion region 422 is a common second expansion region for the pair of first expansion regions 421-1 and 421-2. The second expansion region 422 propagates the image light L2 from the pair of first expansion regions 421-1 and 421-2 in a specified direction, and emits a part of the image light L2 from the light guide member 4 to the visual field region 7. The second expansion region 422 divides the image light L2 into a plurality of parallel image lights directed from the light guide member 4 to the visual field region 7, thereby replicating and expanding the pupil of the image light L1 projected by the projection optical system 5 on the second axis. The second expansion region 422 is constituted by a periodic structure having a diffraction effect on the image light L2. The periodic structure of the second expansion region 422 is, for example, a reflective diffraction grating.

[0072] As described above, in the modification 7, the light guide member 4 includes a plurality of coupling regions 41 including the first coupling region 41-1 and the second coupling region 41-2, and the propagation region 42 includes a pair of first expansion regions 421-1 and 421-2 arranged in the direction of the first axis. One of the pair of first expansion regions 421-1 and 421-2 (the first expansion region 421-1) propagates the image light L1 in the first direction of the first axis, and makes a part of the image light L1 face a specified direction including a direction component of the second axis. The other of the pair of first expansion regions 421-1 and 421-2 (the first expansion region 421-2) propagates the image light L1 in the second direction opposite to the first direction, and makes a part of the image light L1 face a specified direction including a direction component of the second axis. The second expansion region 422 propagates the image light L2 from the pair of first expansion regions 421-1 and 421-2 in a specified direction, and emits a part of the image light L2 from the light guide member 4 to the visual field region 7. According to this configuration, the visual field region 7 can be expanded.

[0073] [2.8 Modification 8] Figures 14 and 15 show the projection optical system 5 of the image display device according to Modification 8. In particular, FIG. 14 is an explanatory diagram of the position of the entrance pupil P1 in the YZ plane of the projection optical system 5 of the image display device according to Modification 8, and FIG. 15 is an explanatory diagram of the position of the entrance pupil P2 in the XZ plane of the projection optical system 5 according to Modification 8. In FIGS. 14 and 15, in order to clearly illustrate the coupling region 41, the portion of the light guide member 4 corresponding to the coupling region 41 is shown by hatching.

[0074] In Modification 8, the projection optical system 5 causes the image light L1 from the display element 2 to enter the light guide member 4. The projection optical system 5 is located between the display element 2 and the coupling region 41 of the light guide member 4. The projection optical system 5 includes a first optical element 51 and a second optical element 52 as a plurality of optical elements. The first optical element 51 is, for example, a cemented lens combining a negative meniscus lens and a biconvex lens, and the second optical element 52 is a cemented lens combining a positive meniscus lens and a negative meniscus lens.

[0075] The projection optical system 5 in FIGS. 14 and 15 is configured such that the distance D1 (see FIG. 14) from the projection optical system 5 to the entrance pupil P1 of the projection optical system 5 with respect to the display element 2 in the plane orthogonal to the first axis (YZ plane orthogonal to the X axis) on the optical path of the image light L1 is longer than the distance D2 (see FIG. 15) from the projection optical system 5 to the entrance pupil P2 of the projection optical system 5 with respect to the display element 2 in the plane orthogonal to the second axis (XZ plane orthogonal to the Y axis) on the optical path of the image light L1. By doing so, while reducing the size of the propagation region 42, the size of the coupling region 41 in the first axis (X axis) can be reduced.

[0076] As shown in FIG. 14, on the optical path of the image light L1 projected by the projection optical system 5, the distance D1 from the projection optical system 5 to the entrance pupil P1 of the projection optical system 5 with respect to the display element 2 in the plane orthogonal to the first axis is longer than the distance D10 from the projection optical system 5 to the coupling region 41. Thus, in FIG. 14, the position of the entrance pupil P1 of the projection optical system 5 with respect to the display element 2 in the plane orthogonal to the first axis (the YZ plane orthogonal to the X axis) is on the side opposite to the projection optical system 5 with respect to the coupling region 41. Also, the position of the entrance pupil P1 is set within the first expansion region 421 of the propagation region 42 so that convergence and divergence of the light rays from each point of the display element 2 constituting the image light L1 occur. More specifically, as shown in FIG. 14, the image light L1 incident on the coupling region 41 from the projection optical system 5 includes a chief ray L10 corresponding to the center of the image and a plurality of sub-rays L11-1, L11-2, L11-3, L11-4, …, L11-n (hereinafter collectively referred to by the reference symbol L11) that approach the chief ray L10 on the second axis (Y axis) as they go from the projection optical system 5 toward the coupling region 41. The plurality of sub-rays L11 intersect the chief ray L10 within the first expansion region 421 of the propagation region 42. In this way, within the first expansion region 421 of the propagation region 42, by converging and diverging the light rays (chief ray L10 and sub-rays L11) from each point of the display element 2 constituting the image light L1, the size required for the propagation region 42 (particularly the first expansion region 421) to propagate the image light L1 from the display element 2 can be reduced.

[0077] As shown in FIG. 15, on the optical path of the image light L1 projected by the projection optical system 5, the distance D2 from the projection optical system 5 to the entrance pupil P2 of the projection optical system 5 with respect to the display element 2 in the plane orthogonal to the second axis within the projection optical system 5 is equal to the distance D20 from the projection optical system 5 to the coupling region 41. Thereby, in FIG. 15, the position of the entrance pupil P2 of the projection optical system 5 with respect to the display element 2 in the plane (XZ plane orthogonal to the Y axis) orthogonal to the second axis is at the position corresponding to the coupling region 41 on the first surface 40a of the light guide member 4. Therefore, the light rays from each point of the display element 2 constituting the image light L1 converge on the coupling region 41. More specifically, as shown in FIG. 15, the image light L1 incident on the coupling region 41 from the projection optical system 5 includes the chief ray L10 corresponding to the center of the image and a plurality of marginal rays L12-1, L12-2, L12-3, L12-4, …, L12-n (hereinafter collectively denoted by the reference symbol L12) that approach the chief ray L10 on the first axis (X axis) as they travel from the projection optical system 5 toward the coupling region 41. The plurality of marginal rays L12 intersect the chief ray L10 at the coupling region 41.

[0078] As described above, the projection optical system 5 may be configured by combining a plurality of optical elements such that the distance from the projection optical system 5 to the entrance pupil P1 of the projection optical system 5 with respect to the display element 2 in the plane (YZ plane orthogonal to the X axis) orthogonal to the first axis on the optical path of the image light L1 is longer than the distance from the projection optical system 5 to the entrance pupil P2 of the projection optical system 5 with respect to the display element 2 in the plane (XZ plane orthogonal to the Y axis) orthogonal to the second axis on the optical path of the image light L1.

[0079] [2.9 Other Modification Examples] In the above-described embodiment, the coupling region 41 of the projection optical system 5 and the light guide member 4 are arranged in a straight line. However, the coupling region 41 of the projection optical system 5 and the light guide member 4 do not necessarily have to be arranged in a straight line. That is, the optical path of the image light L1 to the coupling region 41 of the projection optical system 5 and the light guide member 4 is not necessarily a straight line. For example, the image light L1 from the projection optical system 5 may be reflected by a reflector and incident on the coupling region 41 of the light guide member 4. In this case, the optical path of the image light L1 to the coupling region 41 of the projection optical system 5 and the light guide member 4 is not linear, but, for example, L-shaped. Even in such a case, on the optical path of the image light L1 projected by the projection optical system 5, by satisfying the condition that the distance from the projection optical system 5 to the entrance pupil P1 of the projection optical system 5 with respect to the display element 2 in the plane orthogonal to the first axis is longer than the distance from the projection optical system 5 to the coupling region 41, the light guide member 4 can be miniaturized. Also, the distance from the projection optical system 5 to the entrance pupil P1 of the projection optical system 5 with respect to the display element 2 in the plane orthogonal to the first axis on the optical path of the image light L1 can be set to be longer than the distance from the projection optical system 5 to the entrance pupil P2 of the projection optical system 5 with respect to the display element 2 in the plane orthogonal to the second axis on the optical path of the image light L1.

[0080] In a modified example, the coupling region 41 of the light guide member 4 does not necessarily have to be provided on the first surface 40a or the second surface 40b of the main body portion 40. The coupling region 41 may be formed on a side surface (end surface) of the main body portion 40. For example, the coupling region 41 may be configured by a surface inclined with respect to the thickness direction of the main body portion 40. Thereby, the coupling region 41 can guide the image light L1 into the light guide member 4 and direct it in the direction of the first axis within the light guide member 4. In this case, the coupling region 41 does not necessarily have to be configured by a periodic structure having a diffraction effect on the image light L1, and may be configured by a surface that refracts the image light L1 so as to be directed in the direction of the first axis.

[0081] As described above, the first expansion region 421 of the propagation region 42 propagates the image light L1 from the coupling region 41 in the direction of the first axis and directs a part of the image light L1 in a specified direction including a component in the direction of the second axis orthogonal to the first axis. In the above embodiment, the first axis was the X axis and the second axis was the Y axis, but the first axis may be the X axis or the Y axis, and the second axis may be the Z axis. In this case, the light guiding member 4 performs pupil expansion on the first axis or the second axis. In this case, the second expansion region 422 is not essential. Also, the second axis does not have to be orthogonal to the first axis. For example, when the first axis is the X axis, the second axis may not be the Y axis or the Z axis, but may be an axis that intersects the X axis at 45 degrees.

[0082] In a modification, W1 and W2 may satisfy the relationship 0.4 < W1 / W2 < 1.8. However, it is more preferable that W1 and W2 satisfy W1 / W2 = 1.

[0083] In a modification, the second expansion region 422 may be a transmissive diffraction grating or a volume hologram (holographic diffraction grating) instead of a reflective diffraction grating.

[0084] [3. Aspect] As is clear from the above embodiment and the modification, the present disclosure includes the following aspects. Hereinafter, signs are attached in parentheses only for the purpose of clarifying the correspondence with the embodiment.

[0085] The first aspect is an optical system (3), which includes a projection optical system (5) that projects image light (L1) forming an image output from a display element (2), and a light guide member (4) that guides the image light (L1) projected by the projection optical system (5) as a virtual image to a user's visual field region (7). The light guide member (4) has a coupling region (41) that guides the image light (L1) into the light guide member (4) and directs it in the direction of a first axis within the light guide member (4), and a propagation region (42) that propagates the image light (L1) from the coupling region (41) in the direction of the first axis and directs a part of the image light (L1) in a specified direction including a component in the direction of a second axis orthogonal to the first axis. On the optical path of the image light (L1) projected by the projection optical system (5), the distance (D1) from the projection optical system (5) to the entrance pupil (P1) of the projection optical system with respect to the display element (2) in a plane orthogonal to the first axis is longer than the distance (D10) from the projection optical system (5) to the coupling region (41). According to this aspect, miniaturization of the light guide member (4), particularly the propagation region (42), can be achieved.

[0086] The second aspect is the optical system (3) based on the first aspect. In the second aspect, the distance (D1) from the projection optical system (5) on the optical path of the image light (L1) to the entrance pupil (P1) of the projection optical system (5) with respect to the display element (2) in the plane orthogonal to the first axis is longer than the distance (D2) from the projection optical system (5) on the optical path of the image light (L1) to the entrance pupil (P2) of the projection optical system (5) with respect to the display element (2) in the plane orthogonal to the second axis. According to this aspect, miniaturization of the light guide member (4) can be achieved. In the second aspect, when the distance from the projection optical system (5) on the optical path of the image light (L1) to the entrance pupil (P1) of the projection optical system (5) with respect to the display element (2) in the plane orthogonal to the first axis is D1, and the distance from the projection optical system (5) on the optical path of the image light (L1) to the entrance pupil (P2) of the projection optical system (5) with respect to the display element (2) in the plane orthogonal to the second axis is D2, D1 and D2 may satisfy the relationship of 3.0 < D1 / D2 < 100. In this case, the position where a plurality of sub-rays (L11-1, L11-2) intersect the principal ray (L10) within the propagation region (42) can be appropriately set, and miniaturization of the light guide member (4) can be achieved.

[0087] The third aspect is the optical system (3) based on the first or second aspect. In the third aspect, the light guide member (4) is plate-shaped, and each of the first axis, the second axis, and the specified direction is orthogonal to the thickness direction of the light guide member (4). According to this aspect, the dimension of the second axis of the light guide member (4) can be reduced.

[0088] The fourth aspect is the optical system (3) based on any one of the first to third aspects. In the fourth aspect, the image light (L1) incident from the projection optical system (5) into the coupling region (41) includes a chief ray (L10) corresponding to the center of the virtual image, and a plurality of sub-rays (L11-1, L11-2) that approach the chief ray (L10) in the direction of the second axis as they go from the projection optical system (5) toward the coupling region (41). The plurality of sub-rays (L11-1, L11-2) intersect the chief ray (L10) within the propagation region (42). According to this aspect, miniaturization of the light guide member (4) can be achieved.

[0089] The fifth aspect is the optical system (3) based on any one of the first to fourth aspects. In the fifth aspect, the dimension of the coupling region (41) in the second axis is larger than the dimension of the coupling region (41) in the first axis. According to this aspect, miniaturization of the light guide member (4) can be achieved.

[0090] The sixth aspect is the optical system (3) based on any one of the first to fifth aspects. In the sixth aspect, the propagation region (42) includes a first expansion region (421) that replicates and expands the pupil of the image light (L1) projected by the projection optical system (5) in the first axis by dividing the image light (L1) into a plurality of parallel image lights (L2) traveling in the specified direction. According to this aspect, expansion of the pupil in the first axis becomes possible.

[0091] The seventh aspect is the optical system (3) based on the sixth aspect. In the seventh aspect, the first expansion region (421) has a first end (421a) and a second end (421b) in the first axis. The first end (421a) is closer to the coupling region (41) than the second end (421b). Assuming that the width of the optical path of the image light (L1) at the first end is W1 and the width of the optical path of the image light (L1) at the second end is W2, W1 and W2 satisfy the relationship 0.4 < W1 / W2 < 1.8. According to this aspect, the first expansion region (421) of the propagation region (42) can be made small, and miniaturization of the propagation region (42) of the light guide member (4) can be achieved.

[0092] The eighth aspect is the optical system (3) based on the sixth or seventh aspect. In the eighth aspect, the propagation region (42) propagates the image light (L2) from the first expansion region (421) in the specified direction, and emits a part of the image light (image light L3) from the light guide member (4) to the visual field region (7). According to this aspect, the visual field region (7) can be expanded.

[0093] The ninth aspect is the optical system (3) based on the eighth aspect. In the ninth aspect, the propagation region (42) divides the image light (L1) into a plurality of parallel image lights (L1) directed from the light guide member (4) to the visual field region (7), so that the pupil of the image light (L1) projected by the projection optical system (5) is replicated and expanded on the second axis, including a second expansion region (422). According to this aspect, pupil expansion on the second axis becomes possible.

[0094] The tenth aspect is the optical system (3) based on the ninth aspect. In the tenth aspect, the propagation region (42) includes a pair of first expansion regions (421-1, 421-2) arranged in the direction of the first axis. One of the pair of first expansion regions (421-1, 421-2) propagates the image light (L1) in the first direction of the first axis and directs a part of the image light (L1) in the specified direction. The other of the pair of first expansion regions (421-1, 421-2) propagates the image light (L1) in the second direction opposite to the first direction and directs a part of the image light (L1) in the specified direction. The second expansion region (422) propagates the image light (L2) from the pair of first expansion regions (421-1, 421-2) in the specified direction, and emits a part of the image light (L2) from the light guide member (4) to the visual field region (7). According to this aspect, the visual field region (7) can be expanded.

[0095] The eleventh aspect is the optical system (3) based on any one of the first to tenth aspects. In the eleventh aspect, the coupling region (41) includes a periodic structure having a diffractive effect on the image light (L1). According to this aspect, miniaturization of the light guide member (4) can be achieved.

[0096] Aspect 12 is an optical system (3) based on any one of Aspects 1 to 11. In Aspect 12, the light guide member (4) divides the image light (L1) incident into the light guide member (4) from the coupling region (41) into a plurality of image lights (L1, L2) parallel to each other within the light guide member (4) and emits them to the visual field region (7), thereby replicating and expanding the pupil of the image light (L1) projected by the projection optical system (5). According to this aspect, pupil expansion becomes possible.

[0097] Aspect 13 is an optical system (3) based on any one of Aspects 1 to 12. In Aspect 3, the projection optical system (5) makes the image light (L1) incident on the coupling region (41) as substantially collimated light. According to this aspect, miniaturization of the light guide member (4) can be achieved.

[0098] Aspect 14 is an image display device (1) including an optical system (3) based on any one of Aspects 1 to 13 and the display element (2). According to this aspect, miniaturization of the light guide member (4) can be achieved.

[0099] Aspect 15 is an image display device (1) based on Aspect 14. In Aspect 15, the display element (2) has an emission angle characteristic in which the image light (L1) spreads in the second axis rather than the first axis. According to this aspect, it becomes easy to make the position of the entrance pupil (P1) of the projection optical system (5) with respect to the display element (2) in the plane orthogonal to the first axis different from the position of the entrance pupil (P2) of the projection optical system (5) with respect to the display element (2) in the plane orthogonal to the second axis by the projection optical system (5).

[0100] As described above, embodiments have been described as examples of the technology in the present disclosure. For that purpose, the accompanying drawings and detailed description have been provided. Therefore, among the components described in the accompanying drawings and detailed description, not only the components essential for solving the problems but also the components not essential for solving the problems for exemplifying the above technology may be included. Therefore, just because those non-essential components are described in the accompanying drawings or detailed description, it should not be immediately determined that those non-essential components are essential. Also, since the above-described embodiments are for exemplifying the technology in the present disclosure, various changes, replacements, additions, omissions, etc. can be made within the scope of the claims or the equivalent scope thereof.

Industrial Applicability

[0101] The present disclosure is applicable to an optical system and an image display device. Specifically, the present disclosure is applicable to an optical system for guiding light from a display element to a user's visual field region, and an image display device including this optical system.

Description of Reference Numerals

[0102] 1 Image display device 2 Display element 3 Optical system 4 Light guide member 41 Coupling region 42 Propagation region 421, 421-1, 421-2 First expansion region 421a First end 421b Second end 422 Second expansion region 5 Projection optical system 7 Visual field region L1 Image light L10 Chief ray L11-1, L11-2 Secondary rays P1 Entrance pupil P2 Entrance pupil

Claims

1. A projection optical system that projects image light for forming an image output from a display element, A light guide member that guides the image light projected by the projection optical system as a virtual image to a user's visual field region, Comprising, The light guide member, A coupling region that guides the image light into the light guide member by diffraction or refraction and directs it in the direction of the first axis within the light guide member, A propagation region that propagates the image light from the coupling region in the direction of the first axis and directs a part of the image light in a specified direction including a component in the direction of the second axis orthogonal to the first axis, Having, On the optical path of the image light projected by the projection optical system, the first distance from the projection optical system to the entrance pupil of the projection optical system with respect to the display element in the first plane orthogonal to the first axis is longer than the distance from the projection optical system to the coupling region, and longer than the second distance from the projection optical system to the entrance pupil of the projection optical system with respect to the display element in the second plane orthogonal to the second axis, The image light incident on the coupling region from the projection optical system includes a principal ray corresponding to the center of the virtual image, a plurality of first sub-rays that approach the principal ray in the direction of the second axis as they travel from the projection optical system toward the coupling region, and a plurality of second sub-rays that approach the principal ray in the direction of the first axis as they travel from the projection optical system toward the coupling region, The plurality of first sub-rays intersect the principal ray within the propagation region, The plurality of second sub-rays intersect the principal ray within the coupling region, Optical system.

2. On the optical path of the image light projected by the projection optical system, the second distance is equal to the distance from the projection optical system to the coupling region, The optical system according to claim 1.

3. On the optical path of the image light projected by the projection optical system, the second distance is longer than the distance from the projection optical system to the coupling region, The optical system according to claim 1.

4. The light guide member is plate-shaped, Each of the first axis, the second axis, and the specified direction is orthogonal to the thickness direction of the light guide member, The optical system according to any one of claims 1 to 3.

5. The dimension of the coupling region in the second axis is larger than the dimension of the coupling region in the first axis, The optical system according to any one of claims 1 to 4.

6. The propagation region includes a first expansion region that divides the image light into a plurality of parallel image lights directed in the specified direction, and replicates and expands the pupil of the image light projected by the projection optical system on the first axis. The optical system according to any one of claims 1 to 5.

7. The first expansion region has a first end and a second end on the first axis. The first end is closer to the coupling region than the second end. When the width of the optical path of the image light at the first end is W1 and the width of the optical path of the image light at the second end is W2, W1 and W2 satisfy the relationship 0.4 < W1 / W2 < 1.

8. The optical system according to claim 6.

8. The propagation region propagates the image light from the first expansion region in the specified direction, and emits a part of the image light from the light guide member to the visual field region. The optical system according to claim 6 or 7.

9. The propagation region includes a second expansion region that divides the image light from the first expansion region into a plurality of parallel image lights directed from the light guide member to the visual field region, and replicates and expands the pupil of the image light projected by the projection optical system on the second axis. The optical system according to claim 8.

10. The propagation region has a pair of first expansion regions arranged in the direction of the first axis. One of the pair of first expansion regions propagates the image light in a first direction of the first axis and directs a part of the image light in the specified direction. The other of the pair of first expansion regions propagates the image light in a second direction opposite to the first direction and directs a part of the image light in the specified direction. The second expansion region propagates the image light from the pair of first expansion regions in the specified direction, and emits a part of the image light from the light guide member to the visual field region. The optical system according to claim 9.

11. The coupling region includes a periodic structure having a diffractive effect on the image light. The optical system according to any one of claims 1 to 10.

12. The light guide member divides the image light incident from the coupling region into a plurality of parallel image lights in the light guide member and emits them to the visual field region, thereby replicating and expanding the pupil of the image light projected by the projection optical system. The optical system according to any one of claims 1 to 11.

13. The projection optical system makes the image light incident on the coupling region as substantially collimated light. The optical system according to any one of claims 1 to 12.

14. The optical system according to any one of claims 1 to 13, the display element, comprising: an image display device.

15. The display element has an emission angle characteristic in which the image light spreads in the second axis rather than the first axis. The image display device according to claim 14.

Images