Optical system and image display device

Abstract

The present invention provides an optical system capable of improving the use efficiency of image light, and an image display device. An optical system (3) is provided with a light guide member (4) for guiding image light (L1) to a user's field-of-view region (6). The light guide member (4) has a plate-shaped main body part (40), and a coupling region (41) and an emission region (42) that are formed in the main body part (40). The coupling region (41) propagates the image light (L1) in the main body part (40), and the emission region (42) emits the image light (L1) propagated in the main body part (40) from the main body part (40) to the field-of-view region (6). The coupling region (41) and / or the emission region (42) includes a periodic structure comprising recesses and protrusions in the thickness direction of the main body part (40) arranged so as to have periodicity in three predetermined directions (A1, A2, A3) crossing one another within a predetermined plane orthogonal to the thickness direction of the main body part (40), and the central axes of the recesses and protrusions are inclined with respect to the thickness direction of the main body part (40).

Description

[Technical Field]

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

[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 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, causing the light to exit the waveguide.

[0003] Patent Document 2 discloses a waveguide having an in-coupling diffractive optic and an out-coupling diffractive optic on its surface. The out-coupling diffractive optic has a diffraction array in which rows with different lattice vectors are arranged alternately, thereby having multiple lattice vectors that are not parallel to the lattice vector of the in-coupling diffractive optic. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] U.S. Patent No. 10,429,645 [Patent Document 2] US Patent Application Publication No. 2020 / 0209630 Summary of the Invention [Problem to be solved by the invention]

[0005] The techniques described in Patent Documents 1 and 2 are used in, for example, head-mounted displays. In head-mounted displays, it is desirable to improve the efficiency of use of light (image light) that forms an image from a display element.

[0006] The present disclosure provides an optical system and an image display device that can improve the utilization efficiency of image light from a display element. [Means for solving the problem]

[0007] An optical system according to one aspect of the present disclosure includes a light-guiding member that guides image light forming an image output from a display element to a user's field of view as a virtual image. The light-guiding member has a plate-shaped main body, and a coupling region and an emission region formed in the main body. The coupling region propagates the image light incident from the display element within the main body. The emission region emits the image light propagating within the main body from the main body to the field of view. At least one of the coupling region and the emission region includes a periodic structure formed of concave and convex portions extending in the thickness direction of the main body, the concave and convex portions being arranged to have periodicity in three predetermined directions that intersect with each other within a predetermined plane perpendicular to the thickness direction of the main body. The central axes of the concave and convex portions are inclined with respect to the thickness direction of the main body.

[0008] An image display device according to one aspect of the present disclosure includes the above optical system and a display element. [Effects of the Invention]

[0009] According to an aspect of the present disclosure, it is possible to improve the utilization efficiency of image light from a display element. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a schematic diagram illustrating a configuration example of an image display device including an optical system according to an embodiment; [Figure 2] 2 is a schematic plan view of an example of the configuration of a light guide member of the optical system of FIG. 1; [Figure 3] 2 is a schematic side view of an example of the configuration of a light guide member of the optical system of FIG. 1; [Figure 4] 3 is a plan view of an example of the configuration of the periodic structure of the light-guiding member of FIG. 2; [Figure 5] 3 is a cross-sectional view of an example of the configuration of the periodic structure of the light-guiding member of FIG. 2; [Figure 6] 3 is a plan view of a comparative example of the periodic structure of the light guide member of FIG. 2 ; [Figure 7] A diagram showing the results of a simulation of the diffraction efficiency of light in the periodic structure of Figure 4. [Figure 8] FIG. 7 is a diagram showing the results of a simulation of the diffraction efficiency of light in the periodic structure of FIG. 6. [Figure 9] FIG. 3 is an explanatory diagram of wave vectors of the periodic structure of the light-guiding member of FIG. 2. [Figure 10] FIG. 3 is an explanatory diagram of wave vectors of the periodic structure of the light-guiding member of FIG. 2. [Figure 11] FIG. 3 is an explanatory diagram of wave vectors of the periodic structure of the light-guiding member of FIG. 2. [Figure 12] FIG. 3 is a diagram showing the results of a simulation of the light intensity of the light guide member of FIG. 2. [Figure 13] 10 is a plan view of a configuration example of a coupling region of a light guide member according to Modification 1; [Figure 14] FIG. 14 is a diagram showing the results of a simulation of the diffraction efficiency of light in the periodic structure of FIG. 13. [Figure 15] 10 is a cross-sectional view of a configuration example of a coupling region of a light guide member according to Modification 2; [Figure 16] 13 is a cross-sectional view of a configuration example of a coupling region of a light guide member according to Modification 3. [Figure 17] 10 is a plan view of a configuration example of a light guide member according to Modification 4; [Figure 18] 13 is a plan view of a configuration example of a light guide member according to Modification 5; [Figure 19] FIG. 13 is an explanatory diagram of an example of the configuration of an optical system according to Modification 6. [Figure 20] FIG. 13 is an explanatory diagram of another example of the configuration of the optical system of Modification 6. [Figure 21] FIG. 21 is an explanatory diagram of an example of wave vectors of the periodic structure of the light guide member of the optical system of FIG. 20. [Figure 22] FIG. 13 is an explanatory diagram of another example of the configuration of the periodic structure of Modification 6. [Figure 23] 23 is an explanatory diagram of an example of wave vectors of the periodic structure of FIG. 22. [Figure 24] FIG. 13 is an explanatory diagram of a configuration example of a periodic structure of a light guide member according to Modification 7. [Figure 25] FIG. 20 is an explanatory diagram of another example of the periodic structure of the light guide member according to the seventh modification; [Figure 26] FIG. 20 is an explanatory diagram of yet another example of the periodic structure of the light guide member according to the seventh modification; DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, embodiments will be described in detail with reference to the drawings as appropriate. However, more detailed description than necessary may be omitted. For example, detailed description of already well-known matters or redundant description of substantially identical configurations may be omitted. This is to avoid unnecessary redundancy in the following description and to facilitate understanding by those skilled in the art. Note that the inventor(s) provide the accompanying drawings and the following description to enable those skilled in the art to fully understand the present disclosure, and are not intended to limit the subject matter described in the claims.

[0012] [1. Embodiment] [1.1 Overview] FIG. 1 is a schematic diagram of an example configuration of an image display device 1 according to an embodiment. The image display device 1 is, for example, a head-mounted display (HMD) worn on a user's head and displays an image (video). In this disclosure, expressions such as "directed in a certain direction" and "propagated in a certain direction" with respect to light mean that the light corresponding to the center of the image, or the light forming the image as a whole, is directed in a certain direction, and the light rays included in the light forming the image may be inclined with respect to the certain direction. For example, "light directed in a certain direction" only requires that the principal ray of this light is directed in a certain direction, and the secondary ray of the light may be inclined with respect to the certain direction.

[0013] 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-guiding member 4 and a projection optical system 5. The light-guiding member 4 guides the image light L1 output from the display element 2 to a user's viewing area 6 as a virtual image. The light-guiding member 4 includes a plate-shaped main body 40 and a coupling region 41 and an exit region 42 formed on the main body 40. The coupling region 41 propagates the image light L1 incident from the display element 2 within the main body 40. The exit region 42 emits the image light L1 propagating within the main body 40 from the main body 40 to the viewing area 6. For simplicity, FIG. 1 depicts the image light L1 as directional light; however, in reality, the image light L1 enters the light-guiding member 4 as light having an angle corresponding to the viewing angle.

[0014] Fig. 2 is a schematic plan view of an example of the configuration of the light-guiding member 4, and Fig. 3 is a schematic side view of the example of the configuration of the light-guiding member 4. In Fig. 3, in order to clearly show the pupil expansion function of the image display device 1, a pupil L10 is illustrated instead of the display element 2 and the projection optical system 5.

[0015] As shown in FIG. 2, in the light-guiding member 4, the coupling region 41 and the emission region 42 include a periodic structure.

[0016] FIG. 4 is a plan view of an example of the configuration of the periodic structure of the coupling region 41, and FIG. 5 is a cross-sectional view of the example of the configuration of the periodic structure of the coupling region 41. As shown in FIG. 4, the periodic structure is composed of concave-convex portions 41a arranged to have periodicity in three predetermined directions A1, A2, and A3 that intersect with each other in a predetermined plane perpendicular to the thickness direction T of the main body portion 40. FIG. 5 shows the behavior of image light L2a that is diffracted by the periodic structure and propagates within the main body portion 40 when image light L1a is incident on the coupling region 41. As shown in FIG. 5, the central axis C1 of the concave-convex portions 41a is inclined with respect to the thickness direction T of the main body portion 40 (the vertical direction in FIG. 5).

[0017] As described above, in the light-guiding member 4, the combining region 41 and the exit region 42 each include a periodic structure, and the periodic structure has periodicity in three predetermined directions A1, A2, and A3 that intersect with each other in a predetermined plane orthogonal to the thickness direction T of the main body 40. Therefore, in the light-guiding member 4, the combining region 41 branches the image light L1 into a plurality of branch directions including first, second, third, and fourth branch directions D1, D2, D3, and D4 that are parallel to the three predetermined directions A1, A2, and A3, respectively, and propagates the branched light within the main body 40, and the exit region 42 emits the image light L2-1 to L2-4 propagating within the main body 40 in the plurality of branch directions from the main body 40 to the viewing region 6. As described above, the light-guiding member 4 branches the image light L1 into a plurality of branch directions, splits the image light L1 into a plurality of parallel image light beams L3, and emits the image light beams L3 to the viewing region 6, thereby duplicating and widening the pupil of the image light L1. In the periodic structure, the central axis C1 of the concave-convex portion 41a is inclined with respect to the thickness direction T of the main body 40, which makes it possible to control the diffraction efficiency of light in a predetermined plane perpendicular to the thickness direction T of the main body 40. For example, by adjusting the direction and angle at which the central axis C1 of the concave-convex portion 41a is inclined with respect to the thickness direction T of the main body 40, it is possible to reduce the amount of light propagating in a direction where diffraction is not required and increase the amount of light propagating in a direction where diffraction is required. This makes it possible to efficiently guide the image light L1 from the display element 2 to the viewing area 6. This improves the utilization efficiency of the image light from the display element.

[0018] [1.2 Details] The image display device 1 of this embodiment will be described in further detail below with reference to Figures 1 to 12. As shown in Figure 1, the image display device 1 includes a display element 2 and an optical system 3.

[0019] 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 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 light output from the center of the display element 2. Examples of the display element 2 include known displays such as a liquid crystal display, an organic EL display, and a scanning MEMS mirror.

[0020] 1, the optical system 3 guides the image light L1 output by the display element 2 to a viewing area 6 set for the user's eyes. In the viewing area 6, the user can view the image formed by the display element 2 without interruption with their own eyes. In particular, in this embodiment, the optical system 3 widens the viewing area 6 by a pupil dilation effect.

[0021] As shown in FIG. 1, the optical system 3 includes a light guide member 4 and a projection optical system 5.

[0022] The light-guiding member 4 guides image light L1, which forms an image output from the display element 2, to the user's viewing area 6 as a virtual image. The light-guiding member 4 has a plate-shaped main body 40, and a coupling area 41 and an exit area 42 formed on the main body 40.

[0023] The main body 40 is formed of a material that is transparent in the visible light region, and has a first surface 40a and a second surface 40b in a thickness direction T. In this embodiment, the main body 40 is in the shape of a rectangular plate. As shown in FIG. 1 , the main body 40 is disposed with the first surface 40a facing the display element 2 and the second surface 40b facing the viewing area 6. In this embodiment, the first surface 40a includes a surface of the main body 40 through which the image light L1 enters. In this embodiment, the second surface 40b includes a surface of the main body 40 through which the image light L1 exits.

[0024] The coupling region 41 allows the image light L1 incident from the display element 2 to propagate within the main body 40. The coupling region 41 is a region in the light-guiding member 4 where the image light L1 from the display element 2 is incident. The coupling region 41 is used for coupling between the display element 2 and the light-guiding member 4. The coupling region 41 allows light from outside (image light L1) to enter the light-guiding member 4 so that the light propagates within the main body 40 of the light-guiding member 4 under total reflection conditions (see FIG. 3). "Coupling" here refers to a state in which the light propagates within the main body 40 of the light-guiding member 4 under total reflection conditions.

[0025] The coupling region 41 is formed on the first surface 40a of the main body 40. That is, the coupling region 41 is located on the surface (first surface 40a) of the main body 40 on which the image light L1 is incident. The coupling region 41 is located within a predetermined rectangular region on the first surface 40a of the main body 40, at one end of the rectangular region in the width direction and the center of the rectangular region in the longitudinal direction. As shown in FIG. 2, the coupling region 41 is a diffraction grating having periodicity in three predetermined directions A1, A2, and A3 that intersect with each other within a predetermined plane perpendicular to the thickness direction T of the main body 40. In this embodiment, the three predetermined directions A1, A2, and A3 are not perpendicular to each other. The coupling region 41 is a transmissive diffraction grating because it is formed on the first surface 40a of the main body 40, which is the surface on the display element 2 side (the surface on which the image light L1 is incident). In FIG. 2, the predetermined direction A1 corresponds to the longitudinal direction of the main body 40. When the counterclockwise direction in FIG. 2 is used as a reference, the predetermined direction A2 intersects with the predetermined direction A1 at a predetermined angle (for example, 60 degrees), and the predetermined direction A3 intersects with the predetermined direction A1 at a predetermined angle (for example, 120 degrees).

[0026] More specifically, the coupling region 41 includes a periodic structure constituted by concave-convex portions 41a arranged in a predetermined plane with periodicity in three predetermined directions A1, A2, and A3 in the thickness direction T of the main body 40. As shown in FIG. 4, the concave-convex portions 41a are arranged so as to satisfy the following conditions (1) to (3). Condition (1) states that "in the predetermined direction A1, rows of the concave-convex portions 41a aligned in a direction X1 perpendicular to the predetermined direction A1 are aligned at regular intervals." By satisfying condition (1), the periodic structure functions as a diffraction grating that diffracts light in the predetermined direction A1. Condition (2) states that "in the predetermined direction A2, rows of the concave-convex portions 41a aligned in a direction X2 perpendicular to the predetermined direction A2 are aligned at regular intervals." By satisfying condition (2), the periodic structure functions as a diffraction grating that diffracts light in the predetermined direction A2. Condition (3) states that "in the predetermined direction A3, rows of concave-convex portions 41a aligned in a direction X3 perpendicular to the predetermined direction A3 are aligned at regular intervals." By satisfying condition (3), the periodic structure acts as a diffraction grating that diffracts light in the predetermined direction A3. In this embodiment, the concave-convex portions 41a are aligned in a hexagonal lattice pattern, thereby satisfying conditions (1) to (3). In this embodiment, the concave-convex portions 41a are protrusions that are regular hexagons in plan view.

[0027] As described above, the combining region 41 has periodicity in the three predetermined directions A1, A2, and A3. This allows the combining region 41 to branch the image light L1 incident from the display element 2 into a plurality of branch directions and propagate the branched light through the main body 40. The plurality of branch directions include first, second, and third branch directions D1, D2, and D3, which are parallel to the three predetermined directions A1, A2, and A3, respectively. The angle between the first branch direction D1 and the third branch direction D3 is larger than the angle between the first branch direction D1 and the second branch direction D2. The plurality of branch directions further includes a fourth branch direction D4. The fourth branch direction D4 is opposite to the first branch direction D1. The angle between the first branch direction D1 and the fourth branch direction D4 is larger than the angle between the first branch direction D1 and the third branch direction D3. Specifically, the angle between the first branching direction D1 and the second branching direction D2 is 60 degrees, the angle between the first branching direction D1 and the third branching direction D3 is 120 degrees, and the angle between the first branching direction D1 and the fourth branching direction D4 is 180 degrees. The angles here are defined as positive in the counterclockwise direction when the light guiding member 4 is viewed from the direction in which the image light L1 enters the light guiding member 4.

[0028] The coupling region 41 causes the image light L1 to enter the main body 40 of the light guide member 4 by a diffraction effect under conditions where the image light L1 is totally reflected by the first surface 40a and the second surface 40b.

[0029] The combining region 41 causes the image light L1 to travel in a plurality of branching directions D1 to D4 within the main body 40 of the light-guiding member 4 by being totally reflected by the first surface 40a and the second surface 40b. In this manner, the combining region 41 branches the image light L1 into image light L2-1 to L2-4 that propagate in a plurality of branching directions D1 to D4 within the main body 40. In other words, as shown in Fig. 2, the combining region 41 branches the image light L1 into image light L2-1 to L2-4 that propagate in a plurality of branching directions D1 to D4 within the main body 40.

[0030] In this embodiment, because the coupling region 41 has periodicity in the three predetermined directions A1, A2, and A3, the plurality of branching directions may further include fifth and sixth branching directions. The fifth and sixth branching directions are opposite to the second and third branching directions D2 and D3, respectively. Due to the configuration of the light-guiding member 4, much of the image light propagating in the fifth and sixth branching directions is wasted because it is not emitted from the emission region 42 to the viewing region 6. Therefore, the light-guiding member 4 reduces the amount of light propagating in directions where light diffraction is not required, such as the fifth and sixth branching directions, and increases the amount of light propagating in directions where light diffraction is required, such as the first to fourth branching directions, thereby improving the utilization efficiency of the image light L1 from the display element 2.

[0031] From this perspective, in this embodiment, as shown in FIG. 5, the central axis C1 of the uneven portion 41a is inclined with respect to the thickness direction T of the main body portion 40 (the vertical direction in FIG. 5). The central axis C1 is an axis passing through the center of the uneven portion 41a in a planar view. The orientation of the central axis C1 determines the inclination of the uneven portion 41a with respect to the main body portion 40 in any plane including the thickness direction of the main body portion 40. In the coupling region 41, by inclining the central axis C1 of the uneven portion 41a with respect to the thickness direction T of the main body portion 40, it is possible to control the diffraction efficiency of light in a predetermined plane perpendicular to the thickness direction T of the main body portion 40. In FIG. 5, the central axis C1 of the uneven portion 41a is inclined in a direction X1 perpendicular to the predetermined direction A1. As a result, the central axis C1 of the uneven portion 41a is inclined with respect to the thickness direction T of the main body portion 40 in a plane including the second branching direction D2 and the thickness direction T of the main body portion 40 and in a plane including the third branching direction D3 and the thickness direction T of the main body portion 40. 5, the central axis C1 of the uneven portion 41a is inclined in the opposite direction to the second branching direction D2 with respect to the direction (upward in FIG. 5) of the surface (first surface 40a) on which the image light L1 is incident in the main body portion 40 in a plane including the second branching direction D2 and the thickness direction T of the main body portion 40, and is inclined in the opposite direction to the third branching direction D3 with respect to the direction (upward in FIG. 5) of the surface (first surface 40a) on which the image light L1 is incident in the main body portion 40 in a plane including the third branching direction D3 and the thickness direction T of the main body portion 40. In other words, the central axis C1 of the uneven portion 41a is inclined so as to point from the first surface 40a of the main body portion 40 in the direction opposite to the second branching direction D2 and the third branching direction D3. 5, the coupling region 41 can easily propagate the image light L1a that strikes the uneven portion 41a through the main body 40 as image light L2a traveling in the second branch direction D2 or the third branch direction D3. That is, diffraction of the image light L1a in the direction opposite to the second branch direction D2 or the third branch direction D3 is reduced, and the image light L1a can be efficiently propagated to the user's field of view 6. Here, although the side surfaces of the uneven portion 41a in FIG. 5 are inclined to be parallel, the configuration is not limited thereto and the uneven portion 41a may have a tapered structure in which the grating width gradually decreases from the first surface 40a, or a stepped (multi-level) structure.

[0032] FIG. 6 is a plan view of a comparative example of the periodic structure of the coupling region 41. In the comparative example of FIG. 6, the central axis of the concave-convex portion 41a is not inclined with respect to the thickness direction of the main body 40. Simulations of light diffraction efficiency were performed to confirm the difference between the periodic structure including the concave-convex portion 41a shown in FIG. 4 and the periodic structure including the concave-convex portion 41a shown in FIG. 6. FIG. 7 shows the results of a simulation of the light diffraction efficiency for the periodic structure of FIG. 4, and FIG. 8 shows the results of a simulation of the light diffraction efficiency for the periodic structure of FIG. 6. In FIGS. 7 and 8, efficiency F0 indicates the zeroth-order diffraction efficiency when image L1 is incident on the periodic structure. Efficiencies F1 to F6 indicate the diffraction efficiencies of image L1 propagating in the first to sixth distribution directions D1 to D6, respectively, when image L1 is incident on the periodic structure. In the simulations of FIGS. 7 and 8, the darker the black areas, the higher the efficiencies F0 to F6, and the lighter the black areas, the lower the efficiencies F0 to F6. As is clear from Fig. 8, in the periodic structure having the concave-convex portion 41a shown in Fig. 6, the efficiencies F1 to F6 are uniform. On the other hand, as is clear from Fig. 7, in the periodic structure having the concave-convex portion 41a shown in Fig. 4, the efficiencies F5 and F6 decrease, and the efficiencies F2 and F3 increase. Therefore, by adopting the periodic structure having the concave-convex portion 41a shown in Fig. 4, the amount of light propagating in directions where light diffraction is unnecessary, such as the fifth and sixth branch directions, can be reduced, and the amount of light propagating in directions where light diffraction is necessary, such as the second and third branch directions, can be increased, compared to the periodic structure having the concave-convex portion 41a shown in Fig. 6. This improves the utilization efficiency of the image light L1 from the display element 2.

[0033] The inclination angle θ of the central axis C1 of the uneven portion 41a with respect to the thickness direction (vertical direction in FIG. 5) T of the main body 40 is set to, for example, greater than 20 degrees and less than 65 degrees.

[0034] The exit region 42 emits the image light L1 propagating within the main body 40 from the main body 40 to the viewing region 6. The exit region 42 emits the multiple image light beams L2-1 to L2-4 propagating within the main body 40 in multiple branch directions D1 to D4 from the main body 40 to the viewing region 6. More specifically, the exit region 42 propagates the image light L2 from the combining region 41 along the branch directions, and emits a portion of the image light L2 from the light-guiding member 4 to the viewing region 6.

[0035] The exit region 42 is formed on the first surface 40a of the main body 40. In particular, the exit region 42 is provided in a portion of a predetermined rectangular region of the first surface 40a of the main body 40 excluding the coupling region 41. As shown in FIG. 2, the exit region 42 is a diffraction grating having periodicity in three predetermined directions A1, A2, and A3 that intersect with each other in a predetermined plane perpendicular to the thickness direction T of the main body 40. The exit region 42 is a reflective diffraction grating because it is formed on the first surface 40a, which is the surface of the main body 40 opposite the viewing region 6 (the surface onto which the image light L1 is incident). In this embodiment, the exit region 42 has the same structure as the coupling region 41. Therefore, the periods of the coupling region 41 and the exit region 42 are constant and equal to each other in each of the three predetermined directions A1, A2, and A3.

[0036] As described above, the output region 42 has periodicity in the three predetermined directions A1, A2, and A3. Therefore, the output region 42 branches a portion of the image light L2 from the combined region 41 into a branching direction different from the branching direction of the combined region 41. FIG. 2 shows, as an example, how the image light L2-1 traveling from the combined region 41 in the first branching direction D1 branches into a plurality of image light beams L2-2 traveling in the second branching direction D2. FIG. 2 also shows, as an example, how the image light L2-2 traveling from the combined region 41 in the second branching direction D2 branches into a plurality of image light beams L2-1 and L2-3 traveling in the first and third branching directions D1 and D3. FIG. 2 also shows, as an example, how the image light L2-3 traveling from the combined region 41 in the third branching direction D3 branches into a plurality of image light beams L2-2 and L2-4 traveling in the second and fourth branching directions D2 and D4. FIG. 2 shows, as an example, how an image light beam L2-4 traveling from the combining region 41 in a fourth branching direction D4 is branched into a plurality of image light beams L2-3 traveling in a third branching direction D3.

[0037] In this way, the image light L1 is branched by the combining region 41 and the emission region 42 into a plurality of image light beams L2-1 to L2-4 traveling in a plurality of branching directions D1 to D4 within the main body 40, and spreads within a predetermined plane perpendicular to the thickness direction of the main body 40. Each of the plurality of image light beams L2-1 to L2-4 traveling in a plurality of branching directions D1 to D4 is branched into a plurality of parallel image light beams L3 (see FIG. 3 ) and emitted from the main body 40 toward the viewing region 6.

[0038] Since the emission region 42 has the same structure as the coupling region 41, as shown in Fig. 5, the central axis C1 of the concave-convex portion 41a is inclined with respect to the thickness direction T of the main body 40 (the up-down direction in Fig. 5). This makes it possible to reduce the amount of light propagating in directions where light diffraction is unnecessary, such as the fifth and sixth branch directions, and increase the amount of light propagating in directions where light diffraction is necessary, such as the second and third branch directions, compared to the periodic structure having the concave-convex portion 41a shown in Fig. 6. This makes it possible to improve the utilization efficiency of the image light L1 from the display element 2.

[0039] In the present embodiment, both the coupling region 41 and the emission region 42 are periodic structures having periodicity in three predetermined directions A1, A2, and A3 that intersect with each other in a predetermined plane perpendicular to the thickness direction T of the main body 40. Therefore, a part of the periodic structure formed in a predetermined rectangular region on the first surface 40a of the main body 40 functions as the coupling region 41, and the remaining part functions as the emission region 42.

[0040] In the light-guiding member 4, the wave vectors in each of the multiple branching directions of the periodic structure of the coupling region 41 and the emission region 42 are set as follows. That is, the wave vectors in the first, second, third, and fourth branching directions D1, D2, D3, and D4 of the periodic structure of the coupling region 41 and the emission region 42 are defined as k1, k2, k3, and k4, respectively. In the present embodiment, the nth (n is an integer equal to or greater than 3) branching direction is set so that the angle between the first branching direction and the nth branching direction is larger than the angle between the first branching direction and the (n-1)th branching direction. Here, the positive direction of the angle is the counterclockwise direction when the light-guiding member 4 is viewed from the direction in which the image light L1 enters the light-guiding member 4. The components of the wave vectors are set, for example, based on an xy plane in which the predetermined direction A1 is the x-axis direction and the direction orthogonal to the predetermined direction A1 within the predetermined plane is the y-axis. In this case, the center of the coupling region 41 may be defined as the origin of the xy plane.

[0041] In the optical system 3, taking the wave vectors in the first, second, and third branching directions D1, D2, D3 of the periodic structures in the coupling region 41 and the emission region 42 as k1, k2, k3 respectively, and taking the maximum value among the absolute values of the wave vectors k1, k2, k3 in the first, second, and third branching directions D1, D2, D3 as km, it is preferable that the wave vectors k1, k2, k3 satisfy |k1 - k2 + k3| < km / 5. |k1 - k2 + k3| is the absolute value of the composite vector represented by k1 - k2 + k3. In this case, the chromatic aberration of the image light L3 reaching the user's visual field region 6 can be reduced. Thereby, the image quality can be improved. It is more preferable that the wave vectors k1, k2, k3 satisfy |k1 - k2 + k3| < km / 10. In this case, even if there is a width of about ±2 nm in the wavelength band of the image light L1, the chromatic aberration recognized by the user can be reduced to about 1 minute, and further improvement in image quality can be achieved. It is more preferable that the wave vectors k1, k2, k3 satisfy |k1 - k2 + k3| < |km| / 50. In this case, even if there is a width of about ±10 nm in the wavelength band of the image light L1, the chromatic aberration recognized by the user can be reduced to about 1 minute, and further improvement in image quality can be achieved. It is more preferable that the wave vectors k1, k2, k3 satisfy |k1 - k2 + k3| = 0. In this case, since the angle of the image light L1 incident on the coupling region 41 coincides with the angle of the image light L3 emitted from the emission region 42 to the visual field region 6, the angle of the image light L1 can be preserved. Therefore, the image quality can be improved.

[0042] In this embodiment, as shown in FIG. 9, wave number vectors k1, k2, and k3 satisfy |k1-k2+k3|=0. |k1-k2+k3|=0 does not have a strict meaning, and may be within a range in which k1-k2+k3 is considered to be 0. As shown in FIG. 10, wave number vectors k2, k3, and k4 satisfy |k4+k2-k3|=0. |k4+k2-k3| is the absolute value of the resultant vector expressed by k4+k2-k3. |k4+k2-k3|=0 does not have a strict meaning, and may be within a range in which |k4+k2-k3| is considered to be 0. As shown in FIG. 11, wave number vectors k1 and k4 satisfy |k1+k4|=0. |k1+k4| is the absolute value of the resultant vector expressed by k1+k4. |k1+k4|=0 does not have a strict meaning, and may be within a range in which |k1+k4| is considered to be 0. In this embodiment, the absolute values ​​of the wave vectors k1, k2, k3, and k4 are equal to each other. Furthermore, the absolute values ​​of the wave vectors k4, k2, and k3 are equal to each other. As a result, when the image light L1 is incident on the combined region 41 along the thickness direction T of the main body 40, the pupils L10 of the image light L1 can be arranged at equal intervals in the field of view 6. In particular, as shown in FIG. 3, when the image light L1 is incident on the combined region 41 along the thickness direction T of the main body 40, the pupils L10 of the image light L1 can be arranged so that the gap in the field of view 6 is small.

[0043] As shown in FIG. 3 , the light-guiding member 4 described above splits the image light L1 that has entered the main body 40 from the coupling region 41 into a plurality of image light beams L2 that propagate in a plurality of branching directions within the main body 40, and further splits the plurality of image light beams L2 that propagate in a plurality of branching directions into a plurality of image light beams L3 that are parallel to each other and emits them to the field of view 6, thereby duplicating and expanding the pupil L10 of the image light L1.

[0044] The projection optical system 5 projects image light L1 that forms an image output from the display element 2. As a result, the projection optical system 5 causes the image light L1 from the display element 2 to enter the light-guiding member 4. As shown in FIGS. 1 and 2, the projection optical system 5 is located between the display element 2 and the coupling region 41 of the light-guiding 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 approximately collimated light. The projection optical system 5 is, for example, a biconvex lens.

[0045] [1.3 Simulation] To confirm the pupil dilation effect of the light-guiding member 4 described above, a simulation was performed on the light intensity distribution in the periodic structures of the coupling region 41 and the emission region 42 of the light-guiding member 4. FIG. 12 shows the results of the light intensity simulation of the light-guiding member 4. FIG. 12 shows the light intensity distribution at multiple portions set at predetermined intervals on the emission region 42 of the light-guiding member 4. The portion indicated by the white dashed circle in FIG. 12 corresponds to the coupling region 41. Here, to make the pupil dilation effect easier to understand, the size of the pupil L10 of the image light L1 is set so that the duplicated pupils do not overlap. As is clear from FIG. 12, light is distributed over almost the entire emission region 42. Therefore, it was confirmed that the pupil L10 of the image light L1 can be duplicated and dilated by having the coupling region 41 and the emission region 42 have periodicity in three predetermined directions A1, A2, and A3 that intersect without being orthogonal to each other within a predetermined plane perpendicular to the thickness direction T of the main body 40.

[0046] [1.4 Effects, etc.] The optical system 3 described above includes a light-guiding member 4 that guides image light L1, which forms an image output from the display element 2, to the user's viewing area 6 as a virtual image. The light-guiding member 4 has a plate-shaped main body 40 and a combination region 41 and an emission region 42 formed in the main body 40. The combination region 41 propagates the image light L1 incident from the display element 2 within the main body 40. The emission region 42 emits the image light L1 propagating within the main body 40 from the main body 40 to the viewing area 6. The combination region 41 and the emission region 42 include a periodic structure formed of concave-convex portions 41a relative to the thickness direction T of the main body 40. The concave-convex portions 41a are arranged to have periodicity in three predetermined directions A1, A2, and A3 that intersect with each other within a predetermined plane perpendicular to the thickness direction T of the main body 40. The central axis C1 of the concave-convex portions 41a is inclined with respect to the thickness direction T of the main body 40. This configuration improves the utilization efficiency of the image light L1 from the display element 2.

[0047] In the optical system 3, the inclination angle θ of the concave-convex portion 41a with respect to the thickness direction T of the main body 40 is greater than 20 degrees and smaller than 65 degrees. With this configuration, the utilization efficiency of the image light L1 from the display element 2 can be improved.

[0048] In the optical system 3, the combining region 41 branches the image light L1 incident from the display element 2 into a plurality of branch directions including first, second and third branch directions D1, D2 and D3 parallel to the three predetermined directions A1, A2 and A3, respectively, and propagates the branched light within the main body 40. This configuration can improve the utilization efficiency of the image light L1 from the display element 2.

[0049] Also, in the optical system 3, assuming that the wave vectors in the first, second, and third branching directions D1, D2, D3 of the periodic structure are k1, k2, k3 respectively, and the maximum value among the absolute values of the wave vectors in the first, second, and third branching directions D1, D2, D3 is km, it is preferable that the wave vectors k1, k2, k3 satisfy |k1 - k2 + k3| < km / 5. In this case, the chromatic aberration of the image light L3 reaching the user's visual field region 6 can be reduced. Thereby, the image quality can be improved. It is more preferable that the wave vectors k1, k2, k3 satisfy |k1 - k2 + k3| < km / 10. In this case, even if there is a width of about ±2 nm in the wavelength band of the image light L1, the chromatic aberration recognized by the user can be reduced to about 1 minute, and further improvement in image quality can be achieved. It is more preferable that the wave vectors k1, k2, k3 satisfy |k1 - k2 + k3| < km / 50. In this case, even if there is a width of about ±10 nm in the wavelength band of the image light L1, the chromatic aberration recognized by the user can be reduced to about 1 minute, and further improvement in image quality can be achieved. It is more preferable that the wave vectors k1, k2, k3 satisfy |k1 - k2 + k3| = 0. In this case, since the angle of the image light L1 incident on the coupling region 41 coincides with the angle of the image light L3 emitted from the emission region 42 to the visual field region 6, the angle of the image light L1 can be preserved. Therefore, the image quality can be improved.

[0050] Also, in the optical system 3, the plurality of branching directions further include a fourth branching direction D4. Assuming that the wave vector in the fourth branching direction D4 of the periodic structure is k4, then k4 = -k1. According to this configuration, the visual field region 6 can be expanded.

[0051] Also, in the optical system 3, the absolute values of k1, k2, and k3 are equal to each other. According to this configuration, the pupils L10 of the image light L1 can be arranged at equal intervals in the visual field region 6.

[0052] Furthermore, in the optical system 3, the central axes C1 of the concave-convex portions 41a of the periodic structure of the coupling region 41 are inclined with respect to the thickness direction T of the main body 40 in a plane including the second branching direction D2 and the thickness direction T of the main body 40 and in a plane including the third branching direction D3 and the thickness direction T of the main body 40. This configuration can increase the amount of light diffracted in the second branching direction D2 and the third branching direction D3, thereby improving the utilization efficiency of the image light L1 from the display element 2. Note that not all of the concave-convex portions 41a of the periodic structure of the coupling region 41 need to have central axes C1 inclined with respect to the thickness direction T of the main body 40 in a plane including the second branching direction D2 and the thickness direction T of the main body 40 and in a plane including the third branching direction D3 and the thickness direction T of the main body 40.

[0053] Furthermore, in the optical system 3, the coupling region 41 is located on the side of the surface (first surface 40a) of the main body 40 on which the image light L1 is incident. The central axis C1 of the concave-convex portion 41a of the periodic structure of the coupling region 41 is inclined in the opposite direction to the second branching direction D2 with respect to the direction of the surface (first surface 40a) on which the image light L1 is incident in the main body 40 on a plane including the second branching direction D2 and the thickness direction T of the main body 40, and is also inclined in the opposite direction to the third branching direction D3 with respect to the direction of the surface (first surface 40a) on which the image light L1 is incident in the main body 40 on a plane including the third branching direction D3 and the thickness direction T of the main body 40. With this configuration, it is possible to increase the amount of light diffracted in the second branching direction D2 and the third branching direction D3, thereby improving the utilization efficiency of the image light L1 from the display element 2.

[0054] In the optical system 3, the periodic structure of the coupling region 41 and the periodic structure of the emission region 42 have the same period in each of the three predetermined directions A1, A2, and A3. That is, the period of the coupling region 41 in the predetermined direction A1 is equal to the period of the emission region 42 in the predetermined direction A1, the period of the coupling region 41 in the predetermined direction A2 is equal to the period of the emission region 42 in the predetermined direction A2, and the period of the coupling region 41 in the predetermined direction A3 is equal to the period of the emission region 42 in the predetermined direction A3. In this case, the periods of the coupling region 41 in the predetermined directions A1, A2, and A3 do not have to be equal to each other, and the periods of the emission region 42 in the predetermined directions A1, A2, and A3 do not have to be equal to each other. This configuration simplifies the configuration of the light-guiding member 4.

[0055] Furthermore, in the optical system 3, the exit region 42 branches the image light L1 from the combination region 41 into a plurality of branch directions including first, second and third branch directions D1, D2 and D3 parallel to the three predetermined directions A1, A2 and A3, respectively, and propagates the branched image light L1 within the main body 40, and emits the image light L1 propagating within the main body 40 in the plurality of branch directions from the main body 40 to the viewing region 6. This configuration can improve the utilization efficiency of the image light L1 from the display element 2.

[0056] In addition, in the optical system 3, the concave and convex portions 41a are arranged in a hexagonal lattice pattern within a predetermined plane. With this configuration, the light guide member 4 can be made smaller.

[0057] Furthermore, in the optical system 3, the light guide member 4 splits the image light L1 that has entered the light guide member 4 from the coupling region 41 into a plurality of parallel image light beams L1 in each of the three predetermined directions A1, A2, and A3 and emits the split light beams L1 to the viewing region 6, thereby duplicating and widening the pupil of the image light L1. This configuration can improve the utilization efficiency of the image light L1 from the display element 2.

[0058] The optical system 3 further includes a projection optical system 5 that causes the image light L1 to be incident as substantially collimated light into the coupling region 41 of the light-guiding member 4. This configuration improves the utilization efficiency of the image light L1.

[0059] The image display device 1 described above includes an optical system 3 and a display element 2. According to this configuration, the utilization efficiency of the image light L1 from the display element 2 can be improved.

[0060] [2. Modifications] The embodiments of the present disclosure are not limited to the above-described embodiments. The above-described embodiments can be modified in various ways depending on the design, etc., as long as the object of the present disclosure can be achieved. Modifications of the above-described embodiments are listed below. The modifications described below can be applied in appropriate combinations.

[0061] [2.1 Variation 1] Fig. 13 is a plan view of a configuration example of a coupling region 41A of a light guide member 4A of Modification 1. In the coupling region 41A of Fig. 13, the concave-convex portions 41aa have a hexagonal shape in plan view, but are not regular hexagonal in plan view as in the above embodiment.

[0062] In FIG. 13, periods P1, P2, and P3 indicate the period (grating period) of the arrangement of the concave-convex portions 41aa in the directions X1, X2, and X3 perpendicular to the predetermined directions A1, A2, and A3. In particular, periods P1, P2, and P3 are the distances between the central axes C1 of the concave-convex portions 41aa in the directions X1, X2, and X3 perpendicular to the predetermined directions A1, A2, and A3. Dimensions W1, W2, and W3 represent the dimensions (grating widths) of the concave-convex portions 41aa in the directions X1, X2, and X3 perpendicular to the predetermined directions A1, A2, and A3. The ratios of the dimensions W1, W2, and W3 of the concave-convex portions 41aa to the periods P1, P2, and P3 of the arrangement of the concave-convex portions 41aa are defined as ratios R1 (= W1 / P1), R2 (= W2 / P2), and R3 (= W3 / P3). In each of the exit portions 44, the diffraction efficiency in each branching direction can be adjusted by appropriately setting the ratios R1, R2, and R3.

[0063] In FIG. 13, the periods P1, P2, and P3 are equal to one another, but the dimension W1 is greater than the dimensions W2 and W3. The dimensions W2 and W3 are equal to one another. Therefore, the ratio R1 (= W1 / P1) is greater than the ratios R2 (= W2 / P2) and R3 (= W3 / P3), and the ratios R2 and R3 are equal to one another. In other words, the ratio of the dimension of the concave-convex portion 41aa to the period of the arrangement of the concave-convex portion 41aa is greater in the direction perpendicular to the first branching direction D1 within the predetermined plane than in the direction perpendicular to the second branching direction D2 within the predetermined plane and the direction perpendicular to the third branching direction D3 within the predetermined plane. This configuration can increase the amount of light diffracted in a direction parallel to the first branching direction D1, thereby improving the utilization efficiency of the image light L1 from the display element 2. Here, in FIG. 13, the periods P1, P2, and P3 are equal to one another, but this is not limiting, and the periods P1, P2, and P3 may be different from one another so that the pupil L10 of the image light L1 in the viewing area 6 has an appropriate interval.

[0064] To confirm this, a simulation of the light diffraction efficiency was performed for a periodic structure having the concave-convex portion 41aa shown in FIG. 13. FIG. 14 shows the results of the simulation of the light diffraction efficiency for the periodic structure of FIG. 13. In FIG. 13, efficiency F0 represents the zero-order diffraction efficiency when image L1 is incident on the periodic structure. Efficiencies F1 to F6 represent the diffraction efficiencies of image light propagating in the first to sixth distribution directions D1 to D6, respectively, when image L1 is incident on the periodic structure. In the simulation of FIG. 14, the darker the black areas, the higher the efficiencies F0 to F6, and the lighter the black areas, the lower the efficiencies F0 to F6. As is clear from a comparison of FIG. 7 and FIG. 14, in the periodic structure having the concave-convex portion 41aa shown in FIG. 13, the efficiencies F2 and F3 decrease and the efficiencies F1 and F4 increase. 13, the amount of light propagating in the second and third branching directions D2 and D3 can be reduced and the amount of light propagating in the directions parallel to the first distribution direction D1 (i.e., the first and fourth branching directions D1 and D4) can be increased, compared to the periodic structure having the concave-convex portion 41aa shown in Fig. 4. This improves the utilization efficiency of the image light L1 from the display element 2 and the uniformity of the amount of light reaching the user's viewing area 6.

[0065] As described above, in the optical system 3, the ratio of the size of the concave-convex portion 41aa to the arrangement period of the concave-convex portion 41aa is larger in the direction perpendicular to the first branching direction D1 within the predetermined plane than in the direction perpendicular to the second branching direction D2 within the predetermined plane and than in the direction perpendicular to the third branching direction D3 within the predetermined plane. This configuration can increase the amount of light diffracted in a direction parallel to the first branching direction D1, thereby improving the utilization efficiency of the image light L1 from the display element 2 and the uniformity of the amount of light reaching the user's field of view 6.

[0066] [2.2 Variation 2] Fig. 15 is a schematic diagram showing a configuration example of a coupling region 41B of a light-guiding member 4B of Modification 2. The coupling region 41B in Fig. 15 is formed on the second surface 40b of the main body 40. That is, the coupling region 41B is located on the surface (second surface 40b) side of the main body 40 from which the image light L1 is emitted. The coupling region 41B is a diffraction grating having periodicity in three predetermined directions A1, A2, and A3 that intersect with each other in a predetermined plane perpendicular to the thickness direction T of the main body 40. The coupling region 41B is a reflective diffraction grating because it is formed on the second surface 40b, which is the surface on the viewing area 6 side of the main body 40 (the surface from which the image light L1 is emitted).

[0067] 15, the central axis C1 of the uneven portion 41ab is also inclined with respect to the thickness direction T of the main body 40 (the vertical direction in FIG. 15). In the coupling region 41B, by inclining the uneven portion 41ab with respect to the thickness direction T of the main body 40, it becomes possible to control the diffraction efficiency of light in a predetermined plane perpendicular to the thickness direction T of the main body 40. The inclination angle θ of the central axis C1 of the uneven portion 41ab with respect to the thickness direction T of the main body 40 (the vertical direction in FIG. 15) is set to be greater than 20 degrees and less than 65 degrees, for example.

[0068] 15, the uneven portion 41ab is inclined in a direction X1 perpendicular to the predetermined direction A1. As a result, the uneven portion 41ab is inclined with respect to the thickness direction T of the main body portion 40 in a plane including the second branching direction D2 and the thickness direction T of the main body portion 40 and in a plane including the third branching direction D3 and the thickness direction T of the main body portion 40. In Fig. 15, the central axis C1 of the uneven portion 41ab is inclined in the second branching direction D2 with respect to the direction (downward in Fig. 15) of the surface (second surface 40b) of the main body portion 40 from which the image light L1 is emitted in the plane including the second branching direction D2 and the thickness direction T of the main body portion 40, and is inclined in the third branching direction D3 with respect to the direction (downward in Fig. 15) of the surface (second surface 40b) of the main body portion 40 from which the image light L1 is emitted in the plane including the third branching direction D3 and the thickness direction T of the main body portion 40. That is, the central axis C1 of the uneven portion 41ab is inclined from the second surface 40b of the main body 40 toward the second branching direction D2 and the third branching direction D3. As a result, as shown in FIG. 15 , the coupling region 41B facilitates propagation of the image light L1b that strikes the uneven portion 41ab through the main body 40 as image light L2b traveling in the second branching direction D2 or the third branching direction D3. That is, diffraction of the image light L1b in the direction opposite to the second branching direction D2 or the third branching direction D3 is reduced, and the image light L1b can be efficiently propagated to the user's field of view 6. Here, although the side surfaces of the uneven portion 41ab in FIG. 15 are inclined to be parallel, this is not limiting, and the uneven portion 41ab may have a tapered structure in which the grating width gradually decreases from the second surface 40b, or a stepped (multi-level) structure.

[0069] As described above, the coupling region 41B is located on the side of the surface (second surface 40b) from which the image light L1 is emitted in the main body 40. The central axis C1 of the concave-convex portion 41ab of the periodic structure of the coupling region 41B is inclined in the second branching direction D2 with respect to the direction of the surface (second surface 40b) from which the image light L1 is emitted in the main body 40 in a plane including the second branching direction D2 and the thickness direction T of the main body 40, and is inclined in the third branching direction D3 with respect to the direction of the surface (second surface 40b) from which the image light L1 is emitted in the main body 40 in a plane including the third branching direction D3 and the thickness direction T of the main body 40. This configuration can increase the amount of light diffracted in the second branching direction D2 and the third branching direction D3, thereby improving the utilization efficiency of the image light L1 from the display element 2.

[0070] [2.3 Variation 3] FIG. 16 is a schematic diagram illustrating a configuration example of a coupling region 41C of a light-guiding member 4C of Modification 3. The coupling region 41C in FIG. 16 is formed on the first surface 40a and the second surface 40b of the main body 40C. That is, the coupling region 41C is located on the surface (first surface 40a) of the main body 40C where the image light L1 is incident and on the surface (second surface 40b) of the main body 40C where the image light L1 is emitted. More specifically, the coupling region 41C includes a periodic structure formed of concave-convex portions 41a located on the surface (first surface 40a) of the main body 40C where the image light L1 is incident, and a periodic structure formed of concave-convex portions 41ab located on the surface (second surface 40b) of the main body 40C where the image light L1 is emitted. The coupling region 41C is a diffraction grating having periodicity in three predetermined directions A1, A2, and A3 that intersect with each other in a predetermined plane perpendicular to the thickness direction T of the main body 40C. The coupling region 41C includes a transmissive diffraction grating and a reflective diffraction grating.

[0071] 16, the central axes C1 of the concave-convex portions 41a and 41ab are also inclined with respect to the thickness direction T of the main body portion 40C (the vertical direction in FIG. 15). In the coupling region 41C, by inclining the central axes C1 of the concave-convex portions 41a and 41ab with respect to the thickness direction T of the main body portion 40C, it is possible to control the diffraction efficiency of light in a predetermined plane perpendicular to the thickness direction T of the main body portion 40C. In FIG. 16, the concave-convex portions 41a and 41ab are inclined in a direction X1 perpendicular to the predetermined direction A1. As a result, the concave-convex portions 41a and 41ab are inclined with respect to the thickness direction T of the main body portion 40 in a plane including the second branching direction D2 and the thickness direction T of the main body portion 40 and in a plane including the third branching direction D3 and the thickness direction T of the main body portion 40.

[0072] 16, the central axis C1 of the uneven portion 41a on the first surface 40a is inclined in the direction opposite to the second branching direction D2 with respect to the direction of the surface (first surface 40a) on which the image light L1 is incident in the main body portion 40 in a plane including the second branching direction D2 and the thickness direction T of the main body portion 40, and is inclined in the direction opposite to the third branching direction D3 with respect to the direction of the surface (first surface 40a) on which the image light L1 is incident in the main body portion 40 in a plane including the third branching direction D3 and the thickness direction T of the main body portion 40. In other words, the uneven portion 41a on the first surface 40a is inclined so as to face from the first surface 40a of the main body portion 40 in the direction opposite to the second branching direction D2 and the third branching direction D3. 16, the coupling region 41C makes it easier for the image light L1a that strikes the uneven portion 41a on the first surface 40a to propagate through the main body 40 as image light L2a traveling in the second branching direction D2 or the third branching direction D3. In other words, it is possible to reduce diffraction of the image light L1a in the direction opposite to the second branching direction D2 or the third branching direction D3. The tilt angle θ of the central axis C1 of the uneven portion 41a with respect to the thickness direction T of the main body 40 (the up-down direction in FIG. 16) is set to be greater than 20 degrees and less than 65 degrees, for example.

[0073] 16, the central axis C1 of the uneven portion 41ab on the second surface 40b is inclined in the second branching direction D2 with respect to the direction of the surface (second surface 40b) of the main body 40 from which the image light L1 is emitted, in a plane including the second branching direction D2 and the thickness direction T of the main body 40, and is inclined in the third branching direction D3 with respect to the direction of the surface (second surface 40b) of the main body 40 from which the image light L1 is emitted, in a plane including the third branching direction D3 and the thickness direction T of the main body 40. In other words, the uneven portion 41ab on the second surface 40b is inclined so as to extend from the second surface 40b of the main body 40 toward the second branching direction D2 and the third branching direction D3. 16, the coupling region 41C makes it easier for the image light L1b that strikes the uneven portion 41ab on the second surface 40b to propagate through the main body 40 as image light L2b traveling in the second branch direction D2 or the third branch direction D3. That is, diffraction of the image light L1b in the direction opposite to the second branch direction D2 or the third branch direction D3 can be reduced. The tilt angle θ of the central axis C1 of the uneven portion 41ab with respect to the thickness direction T of the main body 40 (the up-down direction in FIG. 16) is set to be greater than 20 degrees and less than 65 degrees, for example.

[0074] As described above, the coupling region 41C may be formed on the first surface 40a and the second surface 40b of the main body portion 40C, thereby reducing the possibility that the image light L1 passes through the light-guiding member 4C and improving the utilization efficiency of the image light L1.

[0075] [2.4 Variation 4] Fig. 17 is a schematic diagram showing a configuration example of a light guide member 4D of Modification 4. The light guide member 4D of Fig. 17 has a coupling region 41D and an emission region 42D.

[0076] The coupling region 41D is a diffraction grating having periodicity in a predetermined direction A1 in a predetermined plane perpendicular to the thickness direction of the main body 40D (a direction perpendicular to the plane of FIG. 17). The coupling region 41D is formed on the first surface 40a of the main body 40D. The diffraction grating of the coupling region 41D may include, for example, a plurality of concave or convex portions extending in a direction perpendicular to the predetermined direction A1 in the predetermined plane and arranged at predetermined intervals along the predetermined direction A1. The coupling region 41D uses a diffraction effect to cause the image light L1 to enter the main body 40D of the light-guiding member 4D under conditions where the image light L1 is totally reflected by the first surface 40a and the second surface 40b. The coupling region 41D converts the image light L1 into an image term L2-1 that travels in a first branch direction D1 parallel to the predetermined direction A1 after being totally reflected by the first surface 40a and the second surface 40b within the light-guiding member 4D (i.e., within the main body 40D).

[0077] The emission region 42D includes a periodic structure formed of concave and convex portions 41ad arranged to have periodicity in three predetermined directions A1, A2, and A3 that intersect with each other in a predetermined plane perpendicular to the thickness direction of the main body 40D. The emission region 42D is formed on the first surface 40a of the main body 40D. Because the emission region 42D has periodicity in the three predetermined directions A1, A2, and A3, it causes a portion of the image light L2-1 from the combined region 41D to branch in a branch direction different from the original branch direction. FIG. 17 shows, as an example, how the image light L2-1 traveling from the combined region 41D in the first branch direction D1 is branched into a plurality of image light beams L2-2 traveling in the second branch direction D2 and a plurality of image light beams L2-3 traveling in the third branch direction D3. FIG. 17 also shows, as an example, a state in which a plurality of image lights L2-1 traveling in the first branching direction D1 are branched from image lights L2-2 and L2-3 traveling in the second branching direction D2 and the third branching direction D3.

[0078] In this way, image light L2-1 is branched by output region 42D into image light L2-1 to L2-3 traveling in multiple branch directions within main body 40D, and spreads within a predetermined plane perpendicular to the thickness direction of main body 40D. Each of the multiple image light L2-1 to L2-3 traveling in multiple branch directions D1 to D3 is branched into multiple image light beams that are parallel to each other and output from main body 40D toward viewing region 6.

[0079] The optical system 3 described above includes a light-guiding member 4D that guides image light L1, which forms an image output from the display element 2, to the user's viewing area 6 as a virtual image. The light-guiding member 4D includes a plate-shaped main body 40D and a coupling region 41D and an exit region 42D formed in the main body 40D. The coupling region 41D propagates the image light L1 incident from the display element 2 within the main body 40D. The exit region 42D emits the image light L1 propagating within the main body 40D from the main body 40D to the viewing area 6. The exit region 42D includes a periodic structure formed of concave-convex portions 41ad arranged with periodicity in three intersecting directions A1, A2, and A3 within a predetermined plane perpendicular to the thickness direction of the main body 40D. The central axes of the concave-convex portions 41ad are inclined with respect to the thickness direction of the main body 40D. This configuration improves the utilization efficiency of the image light L1 from the display element 2.

[0080] [2.5 Variation 5] Fig. 18 is a schematic diagram showing a configuration example of a light guide member 4E of Modification 5. The light guide member 4E of Fig. 18 has a coupling region 41, a plurality of emission regions 42-1 to 42-3, and a plurality of propagation regions 43-1 to 43-4.

[0081] The coupling region 41 is formed on the first surface 40a of the main body 40. The coupling region 41 is located within a predetermined rectangular region on the first surface 40a of the main body 40, at one end of the rectangular region in the width direction and the center of the rectangular region in the length direction. The coupling region 41 has a structure similar to that of the above-described embodiment, and includes a periodic structure formed of concave and convex portions 41a arranged to have periodicity in three predetermined directions A1, A2, and A3, as shown in FIG. 4. This allows the coupling region 41 to branch the image light L1 incident from the display element 2 into multiple branch directions and propagate through the main body 40. The multiple branch directions include first, second, and third branch directions D1, D2, and D3 parallel to the three predetermined directions A1, A2, and A3, respectively. The multiple branch directions further include a fourth branch direction D4. The fourth branch direction D4 is opposite to the first branch direction D1. The coupling region 41 causes the image light L1 to enter the main body 40 of the light guide member 4E by a diffraction effect under the condition that the image light L1 is totally reflected by the first surface 40a and the second surface 40b.

[0082] The plurality of emission regions 42-1 to 42-3 and the plurality of propagation regions 43-1 to 43-4 are formed on the first surface 40a of the main body 40. The plurality of propagation regions 43-1 to 43-4 extend from the coupling region 41 in first to fourth branching directions D1 to D4, respectively. The emission region 42-1 is located between the propagation regions 43-1 and 43-2. ​​The emission region 42-2 is located between the propagation regions 43-2 and 43-3. The emission region 42-3 is located between the propagation regions 43-3 and 43-4.

[0083] The propagation region 43-1 extends from the coupling region 41 in the first branching direction D1, propagates the image light L2-1 from the coupling region 41 in the first branching direction D1, and directs a portion of the image light L2-1 toward the emission region 42-1. The propagation region 43-1 is, for example, a reflective diffraction grating having periodicity in the predetermined direction A2. The propagation region 43-2 extends from the coupling region 41 in the second branching direction D2, propagates the image light L2-2 from the coupling region 41 in the second branching direction D2, and directs a portion of the image light L2-2 toward the emission regions 42-1 and 42-2. The propagation region 43-2 is, for example, a reflective diffraction grating having periodicity in the predetermined directions A1 and A3. The propagation region 43-3 extends from the coupling region 41 in the third branch direction D3, propagates the image light L2-3 from the coupling region 41 in the third branch direction D3, and directs a portion of the image light L2-3 toward the emission regions 42-2 and 42-3. The propagation region 43-3 is, for example, a reflective diffraction grating having periodicity in the predetermined directions A2 and A4. The propagation region 43-4 extends from the coupling region 41 in the fourth branch direction D4, propagates the image light L2-4 from the coupling region 41 in the fourth branch direction D4, and directs a portion of the image light L2-4 toward the emission region 42-3. The propagation region 43-4 is, for example, a reflective diffraction grating having periodicity in the predetermined direction A4.

[0084] The exit region 42-1 propagates each image light L2-2 from the propagation region 43-1 in the second branching direction D2 and emits a portion of each image light L2-2 from the main body 40 of the light-guiding member 4E to the viewing region 6, and propagates each image light L2-1 from the propagation region 43-2 in the first branching direction D1 and emits a portion of each image light L2-1 from the main body 40 of the light-guiding member 4E to the viewing region 6. The exit region 42-1 is, for example, a reflective diffraction grating having periodicity in the predetermined directions A1 and A2. The exit region 42-2 propagates each image light L2-3 from the propagation region 43-2 in the third branching direction D3 and emits a portion of each image light L2-3 from the main body 40 of the light-guiding member 4E to the viewing region 6, and propagates each image light L2-2 from the propagation region 43-3 in the second branching direction D2 and emits a portion of each image light L2-2 from the main body 40 of the light-guiding member 4E to the viewing region 6. The exit region 42-2 is, for example, a reflective diffraction grating having periodicity in the predetermined directions A2 and A3. The exit region 42-3 propagates each image light L2-4 from the propagation region 43-3 in a fourth branching direction D4 and emits a portion of each image light L2-4 from the main body 40 of the light-guiding member 4E to the viewing region 6, and propagates each image light L2-3 from the propagation region 43-4 in a third branching direction D3 and emits a portion of each image light L2-3 from the main body 40 of the light-guiding member 4E to the viewing region 6. The exit region 42-3 is, for example, a reflective diffraction grating having periodicity in the predetermined directions A3 and A4.

[0085] In this way, the image light L1 is branched by the combining region 41A into image light beams L2-1 to L2-4 traveling in multiple branch directions within the main body 40, and spreads within a predetermined plane perpendicular to the thickness direction of the main body 40. A plurality of image light beams L2-1 traveling in the first branch direction D1, a plurality of image light beams L2-2 traveling in the second branch direction D2, a plurality of image light beams L2-3 traveling in the third branch direction D3, and a plurality of image light beams L2-4 traveling in the fourth branch direction D4 are emitted from the main body 40 toward the viewing area 6.

[0086] The optical system 3 described above includes a light-guiding member 4E that guides image light L1, which forms an image output from the display element 2, to the user's viewing region 6 as a virtual image. The light-guiding member 4E includes a plate-shaped main body 40 and a combination region 41 and emission regions 42-1 to 42-3 formed in the main body 40. The combination region 41 propagates the image light L1 incident from the display element 2 within the main body 40. The emission regions 42-1 to 42-3 emit the image light L1 propagating within the main body 40 from the main body 40 to the viewing region 6. The combination region 41 includes a periodic structure formed of concave-convex portions 41a that are arranged to have periodicity in three predetermined directions A1, A2, and A3 that intersect without being orthogonal to each other within a predetermined plane perpendicular to the thickness direction of the main body 40. The concave-convex portions 41a are inclined with respect to the thickness direction of the main body 40. This configuration improves the utilization efficiency of the image light L1 from the display element 2.

[0087] [2.6 Variation 6] FIG. 19 is a schematic diagram showing an example of the configuration of a light-guiding member 4F of Modification Example 6. In FIG. 19, a pupil L10 is illustrated instead of the display element 2 and the projection optical system 5 to clearly illustrate the pupil dilation function of the image display device. In FIG. 19, the light-guiding member 4F is disposed so that the image light L1 enters the combining region 41F along a direction inclined with respect to the thickness direction of the main body 40. Even in this case, the light-guiding member 4F splits the image light L1 entering the main body 40 from the combining region 41F into multiple image light beams L2 propagating in multiple branching directions within the main body 40, and further splits the multiple image light beams L2 propagating in the multiple branching directions into multiple image light beams L3 that are parallel to each other and emits the split light beams L3 to the viewing region 6, thereby replicating and dilating the pupil L10 of the image light L1.

[0088] Depending on the angle at which the image light L1 is incident on the coupling region 41F, the angle at which the image light L1 propagates through the light-guiding member 4F may become large, which may cause the image light L1 to miss a pupil L10 in the field of view 6. In such cases, by appropriately setting the wave vectors k1, k2, k3, and k4 of the periodic structure, it is possible to prevent the image light L1 from missing a pupil L10 in the field of view 6.

[0089] FIG. 20 is a schematic diagram showing another example of the configuration of a light-guiding member 4F of Modification Example 6. In FIG. 20, a pupil L10 is illustrated instead of the display element 2 and the projection optical system 5 to clearly illustrate the pupil dilation function of the image display device. In FIG. 20, the light-guiding member 4F is also disposed so that the image light L1 enters the coupling region 41F in a direction inclined with respect to the thickness direction of the main body 40. In FIG. 20, wave vectors k1, k2, k3, and k4 of the periodic structures of the coupling region 41F and the exit region 42F are appropriately set to prevent the image light L1 in the viewing region 6 from leaking to the pupil L10. FIG. 21 is an explanatory diagram of an example of the wave vectors k1, k2, and k3 of the periodic structures of the coupling region 41F and the exit region 42F of FIG. 20. In FIG. 21, wave vectors k1, k2, and k3 satisfy the relationship |k1-k2+k3|=0, and further, the absolute values ​​of two of the wave vectors k1, k2, and k3 are equal to each other. In FIG. 21, the absolute values ​​of the wave vectors k2 and k3 are equal to each other. The wave vectors k1, k2, and k3 form an isosceles triangle. The absolute value of the wave vector k1 is greater than the absolute values ​​of the wave vectors k2 and k3. For example, the angle between the wave vectors k1 and k2 is 55 degrees, and the angle between the wave vectors k1 and k3 is 125 degrees. In this case, the angle between the wave vectors k3 and k4 is 55 degrees. In contrast, in the above-described embodiment, the absolute values ​​of the wave vectors k1, k2, and k3 are equal to each other, the angle between the wave vectors k1 and k2 is 60 degrees, and the angle between the wave vectors k1 and k3 is 120 degrees. In this case, the angle between the wave vectors k3 and k4 is 60 degrees. According to the wave vectors k1, k2, and k3 in Figure 21, compared to the above embodiment, the distance between the pupils L10 of the image light L1 can be narrowed in a plane perpendicular to the thickness direction of the main body 40, in a direction perpendicular to the first branch direction D1, which is the direction of the wave vector k1 (see Figure 20).

[0090] In FIG. 21 , the absolute values ​​of the wave vectors k2 and k3 are equal to each other, and the absolute value of the wave vector k1 is greater than the absolute values ​​of the wave vectors k2 and k3. This prevents the image light L1 from leaking into the pupil L10 in the field of view 6, even when the angle at which the image light L1 enters the combined region 41F is set so that the angle at which the image light L1 propagates through the light-guiding member 4F is large. The absolute value of the wave vector k1 may be smaller than the absolute values ​​of the wave vectors k2 and k3. This allows the pupil L10 of the image light L1 in the field of view 6 to be adjusted to an appropriate interval, even when the angle at which the image light L1 enters the combined region 41F is set so that the angle at which the image light L1 propagates through the light-guiding member 4F is small. The absolute values ​​of the wave vectors k2 and k3 do not need to be equal to each other; it is sufficient that the absolute values ​​of two of the wave vectors k1, k2, and k3 are equal to each other.

[0091] Fig. 22 is an explanatory diagram of another example of the periodic structure of a light-guiding member 4F of Modification 6. Fig. 22 shows the periodic structure of a coupling region 41F. In the light-guiding member 4F, the periodic structure of the coupling region 41F and the periodic structure of the emission region 42F have the same configuration. The coupling region 41F in Fig. 22 includes a diffraction grating formed of concave-convex portions 41af arranged in a predetermined plane with periodicity in three predetermined directions A1, A2, and A3, extending in the thickness direction of the main body 40. In Fig. 22, the concave-convex portions 41af are protrusions that are quadrangular (parallelograms in the figure) in plan view. 22 satisfies the above-mentioned condition (1) "In the predetermined direction A1, rows of the concave-convex portions 41af are aligned at regular intervals in the direction X1 perpendicular to the predetermined direction A1," condition (2) "In the predetermined direction A2, rows of the concave-convex portions 41af are aligned at regular intervals in the direction X2 perpendicular to the predetermined direction A2," and condition (3) "In the predetermined direction A3, rows of the concave-convex portions 41af are aligned at regular intervals in the direction X3 perpendicular to the predetermined direction A3." Note that in FIG. 22, the concave-convex portions 41af are not inclined with respect to the thickness direction of the main body portion 40, but this is for ease of understanding the drawing; in reality, the concave-convex portions 41af are inclined with respect to the thickness direction of the main body portion 40.

[0092] FIG. 23 is an explanatory diagram of an example of wave vectors k1, k2, and k3 of the periodic structure of FIG. 22. In FIG. 23, wave vectors k1, k2, and k3 satisfy the relationship |k1-k2+k3|=0, but the absolute values ​​of the wave vectors k1, k2, and k3 are different from each other. For example, the absolute value of wave vector k3 is greater than the absolute values ​​of wave vectors k1 and k2, and the absolute value of wave vector k1 is greater than the absolute value of wave vector k2. For example, the angle between wave vectors k1 and k2 is 65 degrees, and the angle between wave vectors k1 and k3 is 125 degrees. In this case, the angle between wave vectors k3 and k4 is 55 degrees. According to the wave vectors k1, k2, and k3 of FIG. 23, even when image light L1 is incident at an angle of any direction with respect to the thickness direction of the light-guiding member 4F, the pupil L10 of the image light L1 in the field of view 6 can be adjusted to an appropriate interval. As described above, by appropriately setting the relationship between the absolute values ​​of the wave vectors k1, k2, and k3 taking into consideration the arrangement of the pupil L10 of the image light L1 in the field of view 6, the pupil L10 of the image light L1 in the field of view 6 can be adjusted to an appropriate interval.

[0093] As described above, in the light-guiding member 4F, the absolute values ​​of two of k1, k2, and k3 may be equal to each other. With this configuration, the position of the pupil L10 of the image light L1 in the field of view 6 can be adjusted. Furthermore, in the light-guiding member 4F, the absolute values ​​of k1, k2, and k3 may be different from each other. With this configuration, the position of the pupil L10 of the image light L1 in the field of view 6 can also be adjusted.

[0094] [2.7 Variation 7] 24 to 26 are explanatory diagrams of configuration examples of the coupling region 41 of the light guide member 4G of Modification 7. In Fig. 24 to Fig. 26, the coupling region 41 includes a periodic structure constituted by concave-convex portions 41ag arranged in a predetermined plane so as to have periodicity in three predetermined directions A1, A2, and A3 with respect to the thickness direction of the main body portion 40. Note that in Fig. 24 to Fig. 26, the concave-convex portions 41ag are not inclined with respect to the thickness direction of the main body portion 40, but this is for ease of understanding the drawings; in reality, the concave-convex portions 41ag are inclined with respect to the thickness direction of the main body portion 40.

[0095] In Fig. 24, the uneven portion 41ag is a protrusion that is a perfect circle in plan view. In Fig. 25, the uneven portion 41ag is a protrusion that is triangular (an equilateral triangle in the figure) in plan view. In Fig. 26, the uneven portion 41ag is a protrusion that is triangular (a parallelogram in the figure) in plan view.

[0096] The uneven portions 41ag in Figures 24 to 26 each satisfy the above-mentioned condition (1) "In the predetermined direction A1, rows of uneven portions 41ag are aligned at regular intervals in the direction X1 perpendicular to the predetermined direction A1," condition (2) "In the predetermined direction A2, rows of uneven portions 41ag are aligned at regular intervals in the direction X2 perpendicular to the predetermined direction A2," and condition (3) "In the predetermined direction A3, rows of uneven portions 41ag are aligned at regular intervals in the direction X3 perpendicular to the predetermined direction A3."

[0097] As described above, the shape of the uneven portion 41ag is not particularly limited as long as it satisfies the above-mentioned conditions (1) to (3). The uneven portion 41ag may be a protrusion (convex portion) protruding in the thickness direction of the main body portion 40, or a concave portion recessed in the thickness direction of the main body portion 40. The uneven portion 41ag may be circular, polygonal, or another shape in a planar view. The size of the uneven portion 41ag in a planar view may change with increasing distance from the main body portion 40. For example, the size of the uneven portion 41a in a planar view may gradually or stepwise decrease with increasing distance from the main body portion 40. The uneven portion 41ag may be any of a protrusion (convex portion), a concave portion, or a combination of a convex portion and a concave portion, as long as it can form a periodic structure. The central axis of the uneven portion 41ag may be, for example, the central axis of the protrusion or the central axis of the concave portion. Furthermore, as long as the above conditions (1) to (3) are satisfied, the intervals between the concave-convex portions 41ag may be different in the predetermined direction A1, the predetermined direction A2, and the predetermined direction A3. This also applies to the above-mentioned concave-convex portions 41a, 41aa, 41ab, and 41ad.

[0098] [2.8 Other Modifications] In one modified example, the projection optical system 5 may be configured with a plurality of optical elements. The plurality of optical elements may include, for example, a cemented lens combining a negative meniscus lens and a biconvex lens, and a cemented lens combining a positive meniscus lens and a negative meniscus lens. The projection optical system 5 is not particularly limited as long as it can cause the image light L1 from the display element 2 to be incident on the light-guiding member 4 with desired optical characteristics. In some cases, the projection optical system 5 may be omitted.

[0099] In the above embodiment, the projection optical system 5 and the coupling region 41 of the light guide member 4 are aligned on a straight line, but the projection optical system 5 and the coupling region 41 of the light guide member 4 do not necessarily have to be aligned on a straight line. In other words, 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 made to enter 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.

[0100] In one variation, one of the coupling region 41 and the emission region 42 may include, for example, a volume hologram element (holographic diffraction grating) that generates a diffraction effect by periodic modulation of the refractive index. The volume hologram element has, for example, a structure in which portions with different refractive indices are arranged alternately.

[0101] As is clear from the above embodiment, modification 4, and modification 5, in the optical system 3, at least one of the coupling region and the emission region may include a periodic structure formed of concave-convex portions arranged to have periodicity in three predetermined directions A1, A2, and A3 that intersect with each other in a predetermined plane perpendicular to the thickness direction of the main body. In the periodic structure, the central axes of the concave-convex portions are inclined with respect to the thickness direction of the main body.

[0102] In one modified example, the orientation of the central axis C1 of the concave-convex portions 41a of the periodic structure may be different between the coupling region 41 and the emission region 42. For example, the central axis C1 of the concave-convex portions 41a of the periodic structure in the emission region 42 may be inclined with respect to the thickness direction T of the main body 40 in a plane including the first branching direction D1 and the thickness direction T of the main body 40. This increases the amount of light diffracted in the first branching direction D1, thereby improving the utilization efficiency of the image light L1 from the display element 2. Note that not all of the concave-convex portions 41a of the periodic structure in the emission region 42 need to have the central axis C1 inclined with respect to the thickness direction T of the main body 40 in a plane including the first branching direction D1 and the thickness direction T of the main body 40. For example, the central axis C1 of the concave-convex portions 41a of the periodic structure in the emission region 42 may be inclined with respect to the thickness direction T of the main body 40 in a plane including the second branching direction D2 and the thickness direction T of the main body 40. This increases the amount of light diffracted in the second branch direction D2, thereby improving the utilization efficiency of the image light L1 from the display element 2. It is not necessary for all of the concave-convex portions 41a of the periodic structure in the emission region 42 to have central axes C1 that are inclined with respect to the thickness direction T of the main body 40 in a plane including the second branch direction D2 and the thickness direction T of the main body 40. For example, the central axes C1 of the concave-convex portions 41a of the periodic structure in the emission region 42 may be inclined with respect to the thickness direction T of the main body 40 in a plane including the third branch direction D3 and the thickness direction T of the main body 40. This increases the amount of light diffracted in the third branch direction D3, thereby improving the utilization efficiency of the image light L1 from the display element 2. It is not necessary for all of the concave-convex portions 41a of the periodic structure in the emission region 42 to have central axes C1 that are inclined with respect to the thickness direction T of the main body 40 in a plane including the third branch direction D3 and the thickness direction T of the main body 40. Furthermore, the periodic structure of the emission region 42 may include concave-convex portions 41a whose central axes C1 have different inclination directions. For example, the concave-convex portions 41a of the periodic structure of the emission region 42 may include concave-convex portions 41a whose central axes C1 have different orientations in a predetermined plane perpendicular to the thickness direction T of the main body portion 40. The orientation of the central axes C1 of the concave-convex portions 41a may be selected as appropriate depending on the location of the concave-convex portions 41a in the emission region 42 so that the image light L1 from the coupling region 41 is emitted while spreading uniformly within the main body portion 40.

[0103] In one modified example, the periodic structure of the output region 42 may include a portion in which the diffraction efficiency in the direction toward the viewing region 6 increases with increasing distance from the coupling region 41. This configuration makes it possible to homogenize the light intensity distribution in the viewing region 6. That is, since the intensity of the image light L2 is higher closer to the coupling region 41, the diffraction efficiency in the direction toward the viewing region 6 increases with increasing distance from the coupling region 41, thereby decreasing the light intensity near the coupling region 41 and increasing the light intensity far from the coupling region 41. In this way, it is possible to homogenize the light intensity distribution in the viewing region 6. One method for adjusting the diffraction efficiency in the direction toward the viewing region 6 is to adjust the height of the uneven portion 41a.

[0104] In one modified example, the periodic structure of the emission region 42 may be configured so that the angle of inclination of the concave-convex portions 41 a relative to the thickness direction T of the main body 40 decreases with increasing distance from the coupling region 41. This configuration makes it possible to homogenize the light intensity distribution in the viewing region 6. Since the intensity of the image light L2 is higher closer to the coupling region 41, for example, the angle of inclination can be made smaller with increasing distance from the coupling region 41, thereby reducing the light intensity near the coupling region 41 and increasing the light intensity farther from the coupling region 41. In this way, it is possible to homogenize the light intensity distribution in the viewing region 6.

[0105] In the above embodiment, the three predetermined directions A1, A2, and A3 are directions that intersect each other without being perpendicular to each other in a predetermined plane perpendicular to the thickness direction T of the main body 40, but are not particularly limited thereto. For example, at least two of the three predetermined directions A1, A2, and A3 may be perpendicular to each other. The three predetermined directions A1, A2, and A3 may be selected as appropriate depending on the application of the optical system 3, etc.

[0106] [3. Aspects] As is clear from the above-described embodiment and modifications, the present disclosure includes the following aspects. In the following, reference numerals are given in parentheses only to clarify the correspondence with the embodiment.

[0107] The first aspect is an optical system (3) including a light guide member (4; 4D; 4E; 4F) that guides image light (L1) that forms an image output from a display element (2) to a user's field of view (6) as a virtual image. The light guide member (4; 4D; 4E; 4F) has a plate-shaped main body (40) and coupling regions (41; 41A; 41B; 41C; 41D; 41F; 41G) and emission regions (42; 42D; 42F) formed in the main body (40). The coupling regions (41; 41A; 41B; 41C; 41D; 41F; 41G) propagate the image light (L1) incident from the display element (2) within the main body (40). The exit region (42; 42D; 42F) emits the image light (L1) propagating within the main body portion (40) from the main body portion (40) to the viewing region (6). At least one of the coupling region (41; 41A; 41B; 41C; 41D; 41F; 41G) and the exit region (42; 42D; 42F) includes a periodic structure formed of concave and convex portions (41a; 41aa; 41ab; 41ad; 41ag) relative to the thickness direction (T) of the main body portion (40), which are arranged so as to have periodicity in three predetermined directions (A1, A2, A3) that intersect with each other within a predetermined plane perpendicular to the thickness direction (T) of the main body portion (40). The central axes (C1) of the concave and convex portions (41a; 41aa; 41ab; 41ad; 41ag) are inclined with respect to the thickness direction (T) of the main body portion (40). According to this aspect, it is possible to improve the utilization efficiency of the image light (L1) from the display element (2).

[0108] The second aspect is the optical system (3) based on the first aspect. In the second aspect, the inclination angle (θ) of the concave-convex portions (41a; 41aa; 41ab; 41ad; 41ag) with respect to the thickness direction (T) of the main body portion (40) is greater than 20 degrees and less than 65 degrees. According to this aspect, the utilization efficiency of the image light (L1) from the display element (2) can be improved.

[0109] A third aspect is an optical system (3) based on the first or second aspect. In the third aspect, the coupling region (41; 41A; 41B; 41C; 41F; 41G) includes the periodic structure. According to this aspect, it is possible to improve the utilization efficiency of the image light (L1) from the display element (2).

[0110] A fourth aspect is an optical system (3) based on the third aspect. In the fourth aspect, the combining region (41; 41A; 41B; 41C; 41F; 41G) branches the image light (L1) incident from the display element (2) into a plurality of branch directions including first, second, and third branch directions (D1, D2, D3) parallel to the three predetermined directions (A1, A2, A3), respectively, and propagates the branched light within the main body portion (40). According to this aspect, it is possible to improve the utilization efficiency of the image light (L1) from the display element (2).

[0111] A fifth aspect is an optical system (3) based on the fourth aspect. In the fifth aspect, the central axes (C1) of the concave-convex portions (41a; 41aa; 41ab; 41ad; 41ag) of the periodic structure of the coupling region (41; 41A; 41B; 41C; 41D; 41F; 41G) are inclined with respect to the thickness direction (T) of the main body portion (40) in a plane including the second branching direction (D2) and the thickness direction (T) of the main body portion (40) and in a plane including the third branching direction (D3) and the thickness direction (T) of the main body portion (40). According to this aspect, it is possible to increase the amount of light diffracted in the second branching direction (D2) and the third branching direction (D3), thereby improving the utilization efficiency of the image light (L1) from the display element (2).

[0112] A sixth aspect is the optical system (3) based on the fifth aspect. In the sixth aspect, the coupling region (41; 41A; 41C; 41D; 41F; 41G) is located on the surface (40a) side of the main body (40) on which the image light (L1) is incident. The central axes (C1) of the uneven portions (41a; 41aa; 41ad; 41ag) of the periodic structure of the coupling region (41; 41A; 41C; 41D; 41F; 41G) are inclined in the opposite direction to the second branching direction (D2) with respect to the direction of the surface (40a) on which the image light (L1) is incident in the main body portion (40) in a plane including the second branching direction (D2) and the thickness direction (T) of the main body portion (40), and are inclined in the opposite direction to the third branching direction (D3) with respect to the direction of the surface (40a) on which the image light (L1) is incident in the main body portion (40) in a plane including the third branching direction (D3) and the thickness direction (T) of the main body portion (40). According to this aspect, the amount of light diffracted in the second branching direction (D2) and the third branching direction (D3) can be increased, and the utilization efficiency of the image light (L1) from the display element (2) can be improved.

[0113] A seventh aspect is the optical system (3) based on the fifth aspect. In the seventh aspect, the coupling region (41B; 41C) is located on the side of the surface (40b) of the main body portion (40) from which the image light (L1) is emitted. The central axis (C1) of the concave-convex portion (41ab) of the periodic structure of the coupling region (41B; 41C) is inclined in the second branching direction (D2) with respect to the direction of the surface (40b) of the main body portion (40) from which the image light (L1) is emitted, in a plane including the second branching direction (D2) and the thickness direction (T) of the main body portion (40), and is inclined in the third branching direction (D3) with respect to the direction of the surface (40b) of the main body portion (40) from which the image light (L1) is emitted, in a plane including the third branching direction (D3) and the thickness direction (T) of the main body portion (40). According to this aspect, the amount of light diffracted in the second branching direction (D2) and the third branching direction (D3) can be increased, and the utilization efficiency of the image light (L1) from the display element (2) can be improved.

[0114] The eighth aspect is the optical system (3) based on any one of the fifth to seventh aspects. In the eighth aspect, the ratio of the size of the concavo-convex portion (41aa) to the period of the arrangement of the concavo-convex portions (41aa) is larger in the direction orthogonal to the first branching direction (D1) in the predetermined plane than in the direction orthogonal to the second branching direction (D2) in the predetermined plane and in the direction orthogonal to the third branching direction (D3) in the predetermined plane. According to this aspect, it is possible to increase the amount of light diffracted in the direction parallel to the first branching direction (D1), and while improving the utilization efficiency of the image light (L1) from the display element (2), it is possible to improve the uniformity of the amount of light reaching the user's visual field region 6.

[0115] The ninth aspect is the optical system (3) based on any one of the fourth to eighth aspects. In the ninth aspect, when the wave vectors in the first, second, and third branching directions (D1, D2, D3) of the periodic structure are k1, k2, k3, and the maximum value of the absolute values of the wave vectors in the first, second, and third branching directions (D1, D2, D3) is km, the wave vectors k1, k2, and k3 satisfy |k1 - k2 + k3| < km / 5. According to this configuration, image quality can be improved.

[0116] The tenth aspect is the optical system (3) based on the ninth aspect. In the tenth aspect, the plurality of branching directions further include a fourth branching direction (D4). When the wave vector in the fourth branching direction (D4) of the periodic structure is k4, k4 = -k1. According to this aspect, the visual field region (6) can be expanded.

[0117] The eleventh aspect is the optical system (3) based on the ninth or tenth aspect. In the eleventh aspect, the absolute values of k1, k2, and k3 are equal to each other. According to this aspect, the pupils (L10) of the image light (L1) can be arranged at equal intervals in the visual field region (6).

[0118] A twelfth aspect is the optical system (3) based on the ninth or tenth aspect. In the twelfth aspect, the absolute values ​​of two of k1, k2, and k3 are equal to each other. According to this aspect, the arrangement of the pupil (L10) of the image light (L1) in the field of view (6) can be adjusted.

[0119] A thirteenth aspect is the optical system (3) based on the ninth or tenth aspect. In the thirteenth aspect, the absolute values ​​of k1, k2, and k3 are different from each other. According to this aspect, the arrangement of the pupil (L10) of the image light (L1) in the field of view (6) can be adjusted.

[0120] A fourteenth aspect is an optical system (3) based on any one of the first to thirteenth aspects. In the fourteenth aspect, the emission region (42; 42D; 42F) includes the periodic structure. According to this aspect, it is possible to improve the utilization efficiency of the image light (L1) from the display element (2).

[0121] A fifteenth aspect is the optical system (3) based on the fourteenth aspect. In the fifteenth aspect, the exit region (42; 42D; 42F) branches the image light (L1) from the combining region (41; 41A; 41B; 41C; 41D; 41F; 41G) into a plurality of branch directions including first, second, and third branch directions (D1, D2, D3) parallel to the three predetermined directions (A1, A2, A3), respectively, and propagates the branched image light (L1) within the main body portion (40), and emits the image light (L1) propagating within the main body portion (40) in the plurality of branch directions from the main body portion (40) to the viewing region (6). According to this aspect, the utilization efficiency of the image light (L1) from the display element (2) can be improved.

[0122] A sixteenth aspect is the optical system (3) based on the fifteenth aspect. In the sixteenth aspect, the central axes (C1) of the concave-convex portions (41a, 41aa, 41ab, 41ad, 41ag) of the periodic structure of the emission region (42; 42D; 42F) are inclined with respect to the thickness direction (T) of the main body portion (40) in a plane including the first branching direction (D1) and the thickness direction (T) of the main body portion (40). According to this aspect, it is possible to increase the amount of light diffracted in the first branching direction (D1), thereby improving the utilization efficiency of the image light (L1) from the display element (2).

[0123] A seventeenth aspect is the optical system (3) based on the fifteenth aspect. In the seventeenth aspect, the central axes (C1) of the concave-convex portions (41a, 41aa, 41ab, 41ad, 41ag) of the periodic structure of the emission region (42; 42D; 42F) are inclined with respect to the thickness direction (T) of the main body portion (40) in a plane including the second branching direction (D2) and the thickness direction (T) of the main body portion (40). According to this aspect, it is possible to increase the amount of light diffracted in the second branching direction (D2), thereby improving the utilization efficiency of the image light (L1) from the display element (2).

[0124] An 18th aspect is the optical system (3) based on the 15th aspect. In the 18th aspect, the central axes (C1) of the concave-convex portions (41a, 41aa, 41ab, 41ad, 41ag) of the periodic structure of the emission region (42; 42D; 42F) are inclined with respect to the thickness direction (T) of the main body portion (40) in a plane including the third branching direction (D3) and the thickness direction (T) of the main body portion (40). According to this aspect, it is possible to increase the amount of light diffracted in the third branching direction (D3), thereby improving the utilization efficiency of the image light (L1) from the display element (2).

[0125] A nineteenth aspect is the optical system (3) based on any one of the fourteenth to eighteenth aspects. In the nineteenth aspect, the periodic structure of the output region (42; 42D; 42F) has a diffraction efficiency in a direction from the light-guiding member (4; 4D; 4E; 4F) toward the viewing region (6) that increases with increasing distance from the coupling region (41; 41A; 41B; 41C; 41D; 41F; 41G). According to this aspect, the light intensity distribution in the viewing region (6) can be made uniform.

[0126] A twentieth aspect is the optical system (3) based on any one of the fourteenth to nineteenth aspects. In the twentieth aspect, the periodic structure of the emission region (42; 42D) has a tilt angle (θ) of the central axis (C1) of the concave-convex portion (41a) with respect to the thickness direction (T) of the main body portion (40) that decreases with increasing distance from the coupling region (41). According to this aspect, the light intensity distribution in the viewing region (6) can be made uniform.

[0127] A 21st aspect is an optical system (3) based on any one of the 1st to 20th aspects. In the 21st aspect, the coupling region (41; 41A; 41B; 41C; 41F; 41G) and the emission region (42; 42D; 42F) include the periodic structure. The periodic structure of the coupling region (41; 41A; 41B; 41C; 41F; 41G) and the periodic structure of the emission region (42; 42D; 42F) have the same period in each of the three predetermined directions (A1, A2, A3). According to this aspect, the configuration of the light-guiding member (4; 4F) can be simplified.

[0128] A 22nd aspect is an optical system (3) based on any one of the 1st to 21st aspects. In the 22nd aspect, the concave-convex portions (41a; 41aa; 41ab; 41ad; 41ag) are arranged in a hexagonal lattice pattern within the predetermined plane. According to this aspect, the light guide member (4; 4D; 4E; 4F) can be made smaller.

[0129] A 23rd aspect is the optical system (3) based on any one of the 1st to 22nd aspects. In the 23rd aspect, the light-guiding member (4; 4D; 4E; 4F) splits the image light (L1) that has entered the light-guiding member (4; 4D; 4E) from the coupling region (41; 41A; 41B; 41C; 41D; 41F; 41G) into a plurality of image light beams (L1) that are parallel to each other in each of the three predetermined directions (A1, A2, A3) and emits the image light beams (L1) to the viewing region (6), thereby duplicating and widening the pupil of the image light (L1). According to this aspect, it is possible to improve the utilization efficiency of the image light (L1) from the display element (2).

[0130] A 24th aspect is an optical system (3) based on any one of the 1st to 23rd aspects. In the 24th aspect, the optical system (3) further includes a projection optical system (5) that causes the image light (L1) to be incident on the coupling region (41; 41A; 41B; 41C; 41D; 41F; 41G) of the light-guiding member (4; 4D; 4E; 4F) as substantially collimated light. According to this aspect, the utilization efficiency of the image light (L1) can be improved.

[0131] A 25th aspect is an image display device (1) comprising an optical system (3) based on any one of the first to 24th aspects and the display element (2). According to this aspect, it is possible to improve the utilization efficiency of the image light (L1) from the display element (2).

[0132] As described above, the embodiments have been described as examples of the technology in the present disclosure. For this purpose, the accompanying drawings and detailed description have been provided. Therefore, the components described in the accompanying drawings and detailed description may include not only components essential for solving the problem, but also components that are not essential for solving the problem in order to exemplify the above technology. Therefore, the fact that these non-essential components are described in the accompanying drawings or detailed description should not be interpreted as immediately indicating that these non-essential components are essential. Furthermore, because the above-described embodiments are intended to exemplify the technology in the present disclosure, various modifications, substitutions, additions, omissions, etc. may be made within the scope of the claims or their equivalents. [Industrial Applicability]

[0133] The present disclosure is applicable to optical systems and image display devices, specifically to optical systems for guiding light from a display element to a user's viewing area, and image display devices including such optical systems. [Explanation of symbols]

[0134] 1 Image display device 2. Display element 3 Optical system 4,4D,4E,4F Light guide member 40, 40C, 40D Main body 41,41A,41B,41C,41D,41F,41G binding region 41a,41aa,41ab,41ad,41ag Uneven part 42,42D,42F Output area 42-1,42-2,42-3 Output area 5 Projection optical system 6 Viewing area A1,A2,A3 Specified direction C1 center axis θ Tilt angle D1 First branch direction (branch direction) D2 Second branch direction (branch direction) D3 Third branch direction (branch direction) D4 4th branch direction (branch direction) L1, L2, L3 image light L10 Hitomi T thickness direction

Claims

1. a light guiding member that guides image light that forms an image output from the display element to a visual field area of ​​a user as a virtual image; the light guide member has a plate-shaped main body, and a coupling region and an emission region formed in the main body, the coupling region allows the image light incident from the display element to propagate within the main body; the emission region emits the image light propagating within the main body portion from the main body portion to the viewing region; the bonding region includes a periodic structure formed of concave and convex portions relative to the thickness direction of the main body portion, the concave and convex portions being arranged so as to have periodicity in three predetermined directions intersecting each other within a predetermined plane perpendicular to the thickness direction of the main body portion, optical system.

2. The central axis of the uneven portion is inclined with respect to the thickness direction of the main body portion. The optical system of claim 1 .

3. an inclination angle of the concave-convex portion with respect to the thickness direction of the main body portion is greater than 20 degrees and smaller than 65 degrees; The optical system according to claim 2 .

4. the coupling region branches the image light incident from the display element into a plurality of branch directions including first, second, and third branch directions parallel to the three predetermined directions, respectively, and propagates the branched image light within the main body portion. The optical system of claim 1 .

5. a central axis of the concave-convex portion of the periodic structure in the bonding region is inclined with respect to the thickness direction of the main body portion in a plane including the second branching direction and the thickness direction of the main body portion and in a plane including the third branching direction and the thickness direction of the main body portion; The optical system according to claim 4 .

6. the coupling region is located on a surface of the main body on which the image light is incident, The central axis of the concave-convex portion of the periodic structure in the bonding region is In a plane including the second branching direction and a thickness direction of the main body, the light source is inclined in a direction opposite to the second branching direction with respect to a direction of a surface of the main body onto which the image light is incident, and the light source is inclined in a direction opposite to the third branching direction with respect to a direction of a surface of the main body onto which the image light is incident, in a plane including the third branching direction and a thickness direction of the main body. The optical system according to claim 5 .

7. the coupling region is located on a surface of the main body from which the image light is emitted, The central axis of the concave-convex portion of the periodic structure in the bonding region is In a plane including the second branching direction and a thickness direction of the main body, the light source is inclined in the second branching direction with respect to a direction of a surface of the main body from which the image light is emitted, and the light source is inclined in the third branching direction with respect to a direction of a surface of the main body from which the image light is emitted, in a plane including the third branching direction and a thickness direction of the main body. The optical system according to claim 5 .

8. a ratio of the size of the concave-convex portions to the period of the arrangement of the concave-convex portions of the periodic structure in the coupling region is larger in a direction perpendicular to the first branching direction in the predetermined plane than in a direction perpendicular to the second branching direction in the predetermined plane and than in a direction perpendicular to the third branching direction in the predetermined plane; The optical system according to any one of claims 5 to 7.

9. where k1, k2, and k3 are wave vectors in the first, second, and third branch directions of the periodic structure, respectively, and |km| is the maximum value of the absolute values ​​|k1|, |k2|, and |k3| of the wave vectors. Then, |k1−k2+k3|<|km| / 5 is satisfied. The optical system according to any one of claims 4 to 7.

10. the plurality of branching directions further includes a fourth branching direction, When the wave vector in the fourth branch direction of the periodic structure is k4, k4 = −k1. The optical system of claim 9.

11. The absolute values ​​of k1, k2, and k3 are equal to each other. The optical system of claim 9.

12. The absolute values ​​of k1, k2, and k3 are different from each other. The optical system of claim 9.

13. The emission region includes the periodic structure, the periodic structure of the coupling region and the periodic structure of the emission region have equal periods in each of the three predetermined directions; The optical system according to any one of claims 1 to 7.

14. The concave and convex portions are arranged in a hexagonal lattice pattern within the predetermined plane. The optical system according to any one of claims 1 to 7.

15. The light guiding member divides the image light incident from the coupling region into a plurality of image lights parallel to each other in each of the three predetermined directions and outputs the image light to the field of view region, thereby duplicating and expanding the pupil of the image light. The optical system according to any one of claims 1 to 7.

16. a projection optical system that causes the image light to be incident on the coupling region of the light guide member as substantially collimated light, The optical system according to any one of claims 1 to 7.

17. An optical system according to any one of claims 1 to 7; the display element; Equipped with Image display device.

Images