Optical system and image display device

Abstract

The present invention provides an optical system which achieves a reduction in the size of a light guide member, and an image display device. An optical system (3) is provided with a light guide member (4) for guiding, as a virtual image, image light (L1) output from a display element (2) to a field-of-view region (6). The light guide member (4) has a periodic structure (41) formed on a plate-shaped main body part (40). The periodic structure (41) has 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). The periodic structure (41) has a coupling region (42) that branches the image light (L1) in a plurality of branching directions including branching directions (D1, D2, D3) respectively parallel to the predetermined directions (A1, A2, A3) and propagates the branched image light in the main body part (40), and an emission region (43) that emits image light (L2) propagating in the plurality of branching directions in the main body part (40) from the main body part (40) to the field-of-view region (6).

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 sometimes desirable to reduce the size of the waveguides of the optical elements, depending on how the optical elements are used.

[0006] The present disclosure provides an optical system and an image display device that enable a light guide member to be miniaturized. [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 visual field as a virtual image. The light-guiding member has a plate-shaped main body and a periodic structure formed on the main body. The periodic structure has periodicity in three predetermined directions that intersect with each other within a predetermined plane perpendicular to a thickness direction of the main body. The periodic structure includes a coupling region that branches the image light incident from the display element into a plurality of branch directions, including first, second, and third branch directions that are parallel to the three predetermined directions, and propagates the branched image light within the main body, and an emission region that emits the image light propagating within the main body in the plurality of branch directions from the main body to the visual field.

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

[0009] According to an aspect of the present disclosure, the light guide member can be made smaller. [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 perspective view of a configuration example of a periodic structure of the light-guiding member of FIG. 2; [Figure 6] FIG. 3 is an explanatory diagram of an example of wave vectors of the periodic structure of the light-guiding member of FIG. 2; [Figure 7]FIG. 3 is an explanatory diagram of an example of wave vectors of the periodic structure of the light-guiding member of FIG. 2; [Figure 8] FIG. 3 is an explanatory diagram of an example of wave vectors of the periodic structure of the light-guiding member of FIG. 2; [Figure 9] FIG. 3 is a diagram showing the results of a simulation of the light intensity of the light guide member of FIG. 2. [Figure 10] 10 is a plan view of a configuration example of a light guide member according to Modification 1; [Figure 11] FIG. 10 is an explanatory diagram of an exit portion of a periodic structure of a light-guiding member according to Modification 1. [Figure 12] FIG. 10 is an explanatory diagram of a light guide member according to a second modified example. [Figure 13] FIG. 10 is an explanatory diagram of a light guide member according to a third modification example; [Figure 14] FIG. 10 is an explanatory diagram of an example of the configuration of an optical system according to Modification 4. [Figure 15] FIG. 10 is an explanatory diagram of another example of the configuration of the optical system of Modification 4. [Figure 16] FIG. 16 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. 15. [Figure 17] FIG. 10 is an explanatory diagram of another example of the configuration of the periodic structure of Modification 4. [Figure 18] FIG. 18 is an explanatory diagram of an example of wave vectors of the periodic structure of FIG. 17. [Figure 19] FIG. 13 is an explanatory diagram of a configuration example of a periodic structure of a light guide member according to Modification 5. [Figure 20] FIG. 13 is an explanatory diagram of another example of the periodic structure of the light guide member according to the fifth modification; [Figure 21] FIG. 13 is an explanatory diagram of yet another example of the periodic structure of the light guide member according to the fifth modification; [Figure 22] FIG. 13 is an explanatory diagram of a configuration example of a periodic structure of a light guide member according to Modification 6. 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" regarding light mean that the light forming the image as a whole is directed in a certain direction, and the light rays contained 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 chief ray of this light is directed in a certain direction, and the secondary rays 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 periodic structure 41 formed on the main body 40. For simplicity, FIG. 1 depicts the image light L1 as directional light, but 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, the periodic structure 41 of the light-guiding member 4 has 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 40. The periodic structure 41 includes a combining region 42 and an exit region 43. As shown in Fig. 2, the combining region 42 branches the image light L1 into a plurality of branch directions D1 to D4, including first, second, and third branch directions D1, D2, and D3 that are parallel to the three predetermined directions A1, A2, and A3, respectively, and propagates the branched image light L1 within the main body 40. As shown in Figs. 2 and 3, the exit region 43 outputs the image light L2-1 to L2-4 (hereinafter collectively referred to as L2) propagating within the main body 40 in the plurality of branch directions D1 to D4 from the main body 40 to the viewing region 6.

[0016] Thus, in the light-guiding member 4, the combining region 42 branches the image light L1 into multiple branch directions D1 to D4, including first, second, and third branch directions D1, D2, and D3, which are parallel to the three predetermined directions A1, A2, and A3, respectively, and propagates the branched light within the main body 40. The exit region 43 emits the image light L2-1 to L2-4 propagating within the main body 40 in the multiple branch directions from the main body 40 to the viewing region 6. In this way, the light-guiding member 4 branches the image light L1 into the multiple branch directions D1 to D4, splits it into multiple parallel image light beams L3, and emits the multiple parallel image light beams L3 to the viewing region 6, thereby replicating and expanding the pupil of the image light L1. That is, in the light-guiding member 4, the periodic structure 41 functions as the combining region 42 and the exit region 43, enabling pupil expansion using only the periodic structure 41. This eliminates the need for two or three diffractive optical elements as in Patent Documents 1 and 2. This allows the light-guiding member 4 to be made more compact.

[0017] [1.2 Details] The image display device 1 of this embodiment will be described in further detail below with reference to Figures 1 to 9. As shown in Figure 1, the image display device 1 includes a display element 2 and an optical system 3.

[0018] 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.

[0019] 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.

[0020] As shown in FIG. 1, the optical system 3 includes a light guide member 4 and a projection optical system 5.

[0021] The light guide member 4 guides image light L1 that forms an image output from the display element 2 to the user's visual field 6 as a virtual image. The light guide member 4 has a plate-shaped main body 40 and a periodic structure 41.

[0022] 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 the thickness direction. 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.

[0023] The periodic structure 41 is formed on the first surface 40a of the main body 40. The periodic structure 41 is, for example, a rectangular region formed on the first surface 40a of the main body 40. As shown in FIG. 2, the periodic structure 41 has 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 40. In this embodiment, the three predetermined directions A1, A2, and A3 are not perpendicular to each other. The periods of the periodic structure 41 are constant and equal to each other in each of the three predetermined directions A1, A2, and A3. In FIG. 2, the predetermined direction A1 corresponds to the length direction of the main body 40. If the counterclockwise direction in Figure 2 (i.e., the counterclockwise direction when the light-guiding member 4 is viewed from the direction in which the image light L1 is incident on the light-guiding member 4) is used as a reference, the specified direction A2 intersects with the specified direction A1 at a specified angle (e.g., 60 degrees), and the specified direction A3 intersects with the specified direction A1 at a specified angle (e.g., 120 degrees).

[0024] FIG. 4 is a plan view of an example of the configuration of the periodic structure 41, and FIG. 5 is a perspective view of the example of the configuration of the periodic structure 41. The periodic structure 41 includes a diffraction grating constituted by concave-convex portions 41a arranged in a predetermined plane so as to have periodicity in three predetermined directions A1, A2, and A3, and extending in the thickness direction of the main body 40. More specifically, as shown in FIG. 4, in the periodic structure 41, 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 41 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 41 acts 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 41 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.

[0025] 2 and 3, the periodic structure 41 includes a bonding region 42 and an emission region 43. In particular, the periodic structure 41 is formed so that there is no region between the bonding region 42 and the emission region 43 that separates the bonding region 42 and the emission region 43. The region that separates the bonding region 42 and the emission region 43 is, for example, a region that does not have a concave-convex portion 41a or that has a concave-convex structure different from the concave-convex portion 41a. In other words, the periodic structure 41 is formed so that the bonding region 42 and the emission region 43 are smoothly connected without interruption. This simplifies the configuration of the periodic structure 41.

[0026] The combined region 42 is a region in the periodic structure 41 where the image light L1 from the display element 2 is incident. In other words, of the concave-convex portions 41a arranged to have periodicity in three predetermined directions A1, A2, and A3 within a predetermined plane, a group of the concave-convex portions 41a in the region where the image light L1 from the display element 2 is incident defines the combined region 42.

[0027] The coupling region 42 is used for coupling between the display element 2 and the light-guiding member 4. The coupling region 42 allows external light (image light L1) to enter the light-guiding member 4 so that it propagates within the main body 40 of the light-guiding member 4 under total reflection conditions (see FIG. 3). The term "coupling" used here refers to a state in which light propagates within the main body 40 of the light-guiding member 4 under total reflection conditions.

[0028] The coupling region 42 is a part of the periodic structure 41 and therefore has periodicity in three predetermined directions A1, A2, and A3. This allows the coupling region 42 to split the image light L1 incident from the display element 2 into multiple branch directions and propagate through the main body 40. The coupling region 42 is located at one end of the periodic structure 41 in the width direction and at the center of the periodic structure 41 in the longitudinal direction. Therefore, 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 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 multiple branch directions further include 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.

[0029] The coupling region 42 causes the image light L1 to enter the main body 40 of the light-guiding member 4 under conditions of total reflection by the first surface 40a and the second surface 40b due to a diffraction effect. The coupling region 42 is also aligned with the exit region 43 in each of the three predetermined directions A1, A2, and A3. This allows the image light L2 from the coupling region 42 to enter the exit region 43 without leakage, improving the efficiency of light transmission from the coupling region 42 to the exit region 43.

[0030] The combining region 42 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 42 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 42 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.

[0031] The emission region 43 is a region in the periodic structure 41 that emits the image light L3 to the viewing region 6. In particular, the emission region 43 is a region other than the coupling region 42 in the periodic structure 41. In this embodiment, the emission region 43 is defined by a group of the concave-convex portions 41a that are not included in the coupling region 42, among the concave-convex portions 41a that are arranged to have periodicity in three predetermined directions A1, A2, and A3 within a predetermined plane.

[0032] The exit region 43 emits the image light L2-1 to L2-4 propagating in a plurality of branching directions D1 to D4 within the main body 40 from the main body 40 to the viewing region 6. More specifically, the exit region 43 propagates the image light L2 from the combining region 42 along the branching directions, and emits a portion of the image light L2 from the light-guiding member 4 to the viewing region 6.

[0033] The output region 43 is a part of the periodic structure 41 and therefore has periodicity in three predetermined directions A1, A2, and A3. Therefore, the output region 43 branches a portion of the image light L2 from the combined region 42 into a branching direction different from the branching direction of the combined region 42. FIG. 2 shows, as an example, how the image light L2-1 traveling from the combined region 42 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 42 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 42 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 the image light L2-4 traveling from the combining region 42 in the fourth branching direction D4 is branched into a plurality of image light beams L2-3 traveling in the third branching direction D3.

[0034] In this way, the image light L1 is branched by the periodic structure 41 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 area 6.

[0035] The coupling region 42 and the emission region 43 are both part of the periodic structure 41 and have periodicity in three predetermined directions A1, A2, and A3. The periods of the periodic structure 41 are constant and equal to each other in each of the three predetermined directions A1, A2, and A3. Therefore, the coupling region 42 and the emission region 43 have the same periods in each of the three predetermined directions A1, A2, and A3. This simplifies the configuration of the light-guiding member 4.

[0036] In the light-guiding member 4, the wave vectors in each of the multiple branching directions of the periodic structure 41 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 41 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 42 may be defined as the origin of the xy plane.

[0037] In the optical system 3, taking the wave vectors in the first, second, and third branching directions D1, D2, and D3 of the periodic structure 41 as k1, k2, and k3 respectively, and taking the maximum value of the absolute values of the wave vectors k1, k2, and k3 in the first, second, and third branching directions D1, D2, and D3 as km, it is preferable that the wave vectors k1, k2, and 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, and 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, and 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, and k3 satisfy |k1 - k2 + k3| = 0. In this case, since the angle of the image light L1 incident on the coupling region 42 coincides with the angle of the image light L3 emitted from the emission region 43 to the visual field region 6, the angle of the image light L1 can be preserved. Therefore, the image quality can be improved.

[0038] In this embodiment, as shown in FIG. 6, 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. 7, 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. 8, 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 the present embodiment, the absolute values ​​of the wave vectors k1, k2, k3, and k4 are equal to one another. As a result, when the image light L1 is incident on the combined region 42 along the thickness direction 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 42 along the thickness direction 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.

[0039] 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 42 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.

[0040] 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 42 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 42. The projection optical system 5 causes the image light L1 to enter the coupling region 42 as approximately collimated light. The projection optical system 5 is, for example, a biconvex lens.

[0041] [1.3 Simulation] To confirm the pupil dilation effect of the light-guiding member 4 described above, a simulation of the light intensity distribution in the periodic structure 41 of the light-guiding member 4 was performed. FIG. 9 shows the results of the light intensity simulation of the light-guiding member 4. FIG. 9 shows the light intensity distribution at multiple portions set at predetermined intervals on the exit region 43 of the light-guiding member 4. The portion indicated by the white dashed circle in FIG. 9 corresponds to the coupling region 42. 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. 9, light is distributed throughout the entire exit region 43. Therefore, it was confirmed that the pupil L10 of the image light L1 can be duplicated and dilated by the periodic structure 41 having 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.

[0042] [1.4 Effects, etc.] As described above, the optical system 3 includes a light-guiding member 4 that guides the 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 4 includes a plate-shaped main body 40 and a periodic structure 41 formed on the main body 40. The periodic structure 41 has periodicity in three predetermined directions A1, A2, and A3 that intersect with each other within a predetermined plane perpendicular to the thickness direction of the main body 40. The periodic structure 41 includes a coupling region 42 that branches the image light L1 incident from the display element 2 into multiple branch directions, including first, second, and third branch directions D1, D2, and D3, which are parallel to the three predetermined directions A1, A2, and A3, respectively, and propagates within the main body 40, and an exit region 43 that outputs the image light L2 propagating within the main body 40 in the multiple branch directions from the main body 40 to the viewing region 6. This configuration allows the light-guiding member 4 to be made smaller.

[0043] In the optical system 3, the periodic structure 41 includes a diffraction grating constituted by concave and convex portions 41a arranged to have periodicity in a predetermined plane and extending in the thickness direction of the main body 40. This configuration can simplify the configuration of the light-guiding member 4.

[0044] In the optical system 3, the concavo-convex portions 41a are arranged in a hexagonal lattice pattern within a predetermined plane. According to this configuration, miniaturization of the light guide member 4 can be achieved.

[0045] In the optical system 3, the coupling region 42 and the emission region 43 have equal periods in three predetermined directions A1, A2, and A3, respectively. That is, the period of the coupling region 42 in the predetermined direction A1 is equal to the period of the emission region 43 in the predetermined direction A1, the period of the coupling region 42 in the predetermined direction A2 is equal to the period of the emission region 43 in the predetermined direction A2, and the period of the coupling region 42 in the predetermined direction A3 is equal to the period of the emission region 43 in the predetermined direction A3. In this case, the periods of the coupling region 42 in the predetermined directions A1, A2, and A3 do not necessarily have to be equal to each other, and the periods of the emission region 43 in the predetermined directions A1, A2, and A3 do not necessarily have to be equal to each other. According to this configuration, simplification of the configuration of the light guide member 4 can be achieved.

[0046] In the optical system 3, when the wave vectors in the first, second, and third branching directions D1, D2, and D3 of the periodic structure 41 are k1, k2, and k3, respectively, and the maximum value of the absolute values of the wave vectors in the first, second, and third branching directions D1, D2, and D3 is km, the wave vectors k1, k2, and k3 satisfy |k1 - k2 + k3| < km / 5. According to this configuration, improvement of image quality can be achieved.

[0047] In the optical system 3, the wave vectors k1, k2, and k3 satisfy |k1 - k2 + k3| = 0. According to this configuration, improvement of image quality can be achieved.

[0048] 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.

[0049] Furthermore, in the optical system 3, the light-guiding member 4 branches the image light L1 that has entered the light-guiding member 4 from the coupling region 42 into a plurality of branching directions, converts it into a plurality of image light beams L2 that travel within the main body 40 in the plurality of branching directions, and splits the image light L2 into a plurality of image light beams L3 that are parallel to each other in each of the plurality of branching directions, and emits the image light L3 to the viewing region 6, thereby duplicating and widening the pupil L10 of the image light L1. According to this configuration, the light-guiding member 4 can be made smaller.

[0050] Furthermore, in the optical system 3, the coupling region 42 is aligned with the emission region 43 in each of the three predetermined directions A1, A2, and A3. With this configuration, the efficiency of light transmission from the coupling region 42 to the emission region 43 is improved.

[0051] Furthermore, in the optical system 3, the periodic structure 41 is formed so that there is no region between the coupling region 42 and the emission region 43 that separates the coupling region 42 from the emission region 43. This configuration simplifies the configuration of the periodic structure 41.

[0052] 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 42 of the light-guiding member 4. This configuration improves the utilization efficiency of the image light L1.

[0053] The image display device 1 described above includes the optical system 3 described above and the display element 2. According to this configuration, the light guide member 4 can be made smaller.

[0054] [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.

[0055] [2.1 Variation 1] 10 is a schematic diagram showing a configuration example of a light guide member 4A of Modification 1. The light guide member 4A has a main body 40 and a periodic structure 41A.

[0056] The periodic structure 41A has periodicity in three mutually intersecting directions A1, A2, and A3 within a predetermined plane perpendicular to the thickness direction of the main body 40. Similar to the periodic structure 41 of the above-described embodiment, the periodic structure 41A includes a diffraction grating formed of concave-convex portions 41aa arranged in the thickness direction of the main body 40A so as to have periodicity in the three directions A1, A2, and A3 within the predetermined plane. In the first modification, the shapes of the concave-convex portions 41aa of the periodic structure 41A vary depending on the location within the periodic structure 41A. As a result, the periodic structure 41A includes regions with different diffraction efficiencies when light under the same conditions is incident. The light under the same conditions is, for example, light at least having the same wavelength and the same incident angle. The periodic structure 41A will be described in more detail below.

[0057] The periodic structure 41A in FIG. 10 includes a coupling region 42 and an emission region 43A.

[0058] 4, in the combination region 42, the uneven portions 41aa are hexagonal protrusions in a plan view. Therefore, the combination region 42 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 the combination region 42A, the image light L1 is diffracted in first, second, third, and fourth branching directions D1, D2, D3, and D4.

[0059] The emission region 43A includes a plurality of (four in the illustrated example) emission sections 44-1 to 44-4 (hereinafter collectively referred to as 44). The plurality of emission sections 44 are adjacent to the coupling region 42 in the plurality of branching directions. More specifically, the emission section 44-1 is adjacent to the coupling region 42 in the first branching direction D1. The emission section 44-2 is adjacent to the coupling region 42A in the second branching direction D2. The emission section 44-3 is adjacent to the coupling region 42 in the third branching direction D3. More specifically, the emission section 44-4 is adjacent to the coupling region 42 in the fourth branching direction D4.

[0060] Each exit section 44 has a diffraction efficiency (hereinafter referred to as a "branching diffraction efficiency" for ease of distinction) for diffracting the image light L2 propagating in an adjacent direction adjacent to the coupling region 42 in a direction toward the viewing region 6, which is higher than the diffraction efficiency (hereinafter referred to as an "exiting diffraction efficiency" for ease of distinction) for diffracting the image light L2 propagating in the adjacent direction in a predetermined branching direction different from the adjacent direction among the plurality of branching directions. More specifically, the exit section 44-1 has a branching diffraction efficiency for diffracting the image light L2-1 propagating in the first branching direction D1 in a direction toward the viewing region 6 that is higher than the exit diffraction efficiency for diffracting the image light L2-1 propagating in the first branching direction D1 in a direction toward the viewing region 6. The exit section 44-2 has a branching diffraction efficiency for diffracting the image light L2-2 propagating in the second branching direction D1, D3 that is higher than the exit diffraction efficiency for diffracting the image light L2-2 propagating in the second branching direction D2 in a direction toward the viewing region 6. The output section 44-3 has a higher branching diffraction efficiency for diffracting the image light L2-3 in the second or fourth branching direction D2, D4 than the output diffraction efficiency for diffracting the image light L2-3 propagating in the third branching direction D3 in the direction toward the viewing region 6. The output section 44-4 has a higher branching diffraction efficiency for diffracting the image light L2-4 in the third branching direction D3 than the output diffraction efficiency for diffracting the image light L2-4 propagating in the fourth branching direction D4 in the direction toward the viewing region 6. This prevents the image light L2-1 from the combination region 42 from being output to the viewing region 6 before spreading to the output region 43A, thereby achieving a uniform light intensity distribution in the viewing region 6.

[0061] Each exit section 44 is a part of the periodic structure 41A and therefore includes concave-convex portions 41aa arranged with periodicity in three predetermined directions A1, A2, and A3 within a predetermined plane. The relationship between the output diffraction efficiency and the branching diffraction efficiency at each exit section 44 can be set by the shape of the concave-convex portions 41aa. In each exit section 44, the ratio of the size of the concave-convex portions 41aa to the period of the arrangement of the concave-convex portions 41aa is larger in the direction perpendicular to the branching direction adjacent to the coupling region 42 among the multiple branching directions D1 to D4 than in the direction perpendicular to the branching direction adjacent to the coupling region 42 among the multiple branching directions D1 to D4. In other words, in each exit section 44, the ratio of the size of the concave-convex portions 41aa to the period of the arrangement of the concave-convex portions 41aa is set to be larger in the direction perpendicular to the branching direction within the predetermined plane than in the direction perpendicular to the adjacent direction within the predetermined plane. This allows the branching diffraction efficiency to be higher than the output diffraction efficiency.

[0062] FIG. 11 is an explanatory diagram of the emission section 44. In FIG. 11, 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, the 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. The dimensions W1, W2, and W3 represent the dimensions (grating width) 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 exit section 44, by appropriately setting the ratios R1, R2, and R3, it is possible to adjust the relationship between the exit diffraction efficiency and the branching diffraction efficiency.

[0063] Examples of the conditions satisfied by the ratios R1, R2, and R3 in each light-emitting portion 44 are shown below. In the light-emitting portion 44-1, the shape of the concavo-convex portion 41aa is set such that the ratios R1, R2, and R3 satisfy 0.1 < R1 / R2 < 0.8 and 0.1 < R1 / R3 < 0.8. As a result, the amount of image light L2-1 propagating in the first branching direction D1 can be reduced and the amount of image light L2-2 propagating in the second branching direction D2 can be increased. In the light-emitting portion 44-2, the shape of the concavo-convex portion 41aa is set such that the ratios R1, R2, and R3 satisfy 0.1 < R2 / R1 < 0.8 and 0.1 < R2 / R3 < 0.8. As a result, the amount of image light L2-2 propagating in the second branching direction D2 can be reduced and the amounts of image light L2-1 and L2-3 propagating in the first and third branching directions D1 and D3 can be increased. In the light-emitting portion 44-3, the shape of the concavo-convex portion 41aa is set such that the ratios R1, R2, and R3 satisfy 0.1 < R3 / R1 < 0.8 and 0.1 < R3 / R2 < 0.8. As a result, the amount of image light L2-3 propagating in the third branching direction D3 can be reduced and the amounts of image light L2-2 and L2-4 propagating in the second and fourth branching directions D2 and D4 can be increased. In the light-emitting portion 44-4, the shape of the concavo-convex portion 41aa is set such that the ratios R1, R2, and R3 satisfy 0.1 < R1 / R2 < 0.8 and 0.1 < R1 / R3 < 0.8. As a result, the amount of image light L2-4 propagating in the fourth branching direction D4 can be reduced and the amount of image light L2-3 propagating in the third branching direction D3 can be increased.

[0064] Thus, in the light guide member 4A, the diffraction efficiency with respect to the branching directions D1 to D4 is equal in the coupling region 42, but the diffraction efficiency with respect to the branching directions D1 to D4 is different in the plurality of light-emitting portions 44-1 to 44-4 in the light-emitting region 43A. That is, the diffraction efficiency in at least one of the plurality of branching directions is different between the coupling region 42 and the light-emitting region 43A. The diffraction efficiency of the coupling region 42A affects the coupling efficiency for coupling light into the main body portion 40A, and the diffraction efficiency of the light-emitting region 43A affects the emission efficiency for emitting light outside the main body portion 40A. By having different diffraction efficiencies between the coupling region 42A and the light-emitting region 43A, it becomes possible to set the coupling efficiency and the emission efficiency to different values. That is, according to this configuration, the coupling efficiency and the extraction efficiency can be set separately.

[0065] The output region 43A also includes a plurality of output sections 44-1 to 44-4 adjacent to the coupling region 42 in a plurality of branching directions. At least two of the output sections 44-1 to 44-4 have different diffraction efficiencies when light is incident under the same conditions. For example, the output section 44-1 is configured to increase the efficiency of branching light propagated along the branching direction D1 toward the branching direction D2. The output section 44-2 is configured to increase the efficiency of branching light propagated along the branching direction D2 toward the branching directions D1 and D3. The output section 44-3 is configured to increase the efficiency of branching light propagated along the branching direction D3 toward the branching directions D2 and D4. The output section 44-4 is configured to increase the efficiency of branching light propagated along the branching direction D4 toward the branching direction D3. This configuration makes it possible to adjust the light intensity distribution in the viewing region 6.

[0066] Furthermore, in each of the plurality of exit sections 44, the branching diffraction efficiency for diffracting the image light L2 propagating in the adjacent direction in a predetermined branching direction different from the adjacent direction among the plurality of branching directions is greater than the exit diffraction efficiency for diffracting the image light L2 propagating in the adjacent direction in a direction toward the viewing region 6 when the coupling region 42 and the exit section 44 are adjacent. With this configuration, the light intensity distribution in the viewing region 6 can be made uniform.

[0067] Each light exit section 44 includes concave-convex portions 41aa arranged periodically in three predetermined directions A1, A2, and A3 within a predetermined plane. The ratio of the size of the concave-convex portions 41aa to the period of the arrangement of the concave-convex portions 41aa is larger in the direction perpendicular to the predetermined branching direction within the predetermined plane than in the direction perpendicular to the adjacent direction within the predetermined plane. This simple configuration allows for a uniform light intensity distribution in the viewing area 6.

[0068] [2.2 Variation 2] FIG. 12 is a schematic diagram illustrating a configuration example of a light-guiding member 4B of Modification 2. The light-guiding member 4B of FIG. 12 includes a main body 40 and a periodic structure 41B. The periodic structure 41B is different from the periodic structure 41 of the light-guiding member 4. Like the periodic structure 41, the periodic structure 41B includes a diffraction grating formed of concave-convex portions 41a arranged to have periodicity in three predetermined directions A1, A2, and A3 within a predetermined plane. Thus, like the periodic structure 41, the periodic structure 41B includes a coupling region 42B and an emission region 43B. The periodic structure 41B further includes an intermediate region 45. The intermediate region 45 is a region that separates the coupling region 42B and the emission region 43B. The concave-convex portions 41a are not arranged in the intermediate region 45. In Modification 2, the periodic structure 41B is not formed so that the coupling region 42B and the emission region 43B are continuous. This makes it easier to distinguish the coupling region 42B from the emission region 43B, which makes the assembly of the optical system 3 easier.

[0069] [2.3 Variation 3] Fig. 13 is a schematic diagram showing a configuration example of a light-guiding member 4C of Modification Example 3. The light-guiding member 4C in Fig. 13 has a plate-shaped main body 40C and a periodic structure 41C. The main body 40C in Fig. 13 has a square plate shape, and the periodic structure 41C is a square region formed on the main body 40C.

[0070] 13 includes a diffraction grating constituted by concave and convex portions 41a arranged in a predetermined plane so as to have periodicity in three predetermined directions A1, A2, and A3 in the thickness direction of a main body portion 40C, similar to the periodic structure 41. The periodic structure 41C of FIG. 13 includes a coupling region 42C and an emission region 43C.

[0071] The combining region 42C branches the image light L1 incident from the display element 2 into multiple branch directions and propagates through the main body 40C. The combining region 42C is located at the center of the periodic structure 41C. Therefore, 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, as well as fourth, fifth, and sixth branch directions D4, D5, and D6 parallel to the three predetermined directions A1, A2, and A3, respectively. The fourth branch direction D4 is opposite to the first branch direction D1. The fifth branch direction D5 is opposite to the second branch direction D2. The sixth branch direction D6 is opposite to the third branch direction D3. The angle between the first branch direction D1 and the fifth branch direction D5 is larger than the angle between the first branch direction D1 and the fourth branch direction D4. The angle between the first branching direction D1 and the sixth branching direction D6 is larger than the angle between the first branching direction D1 and the fifth branching direction D5. 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, the angle between the first branching direction D1 and the fourth branching direction D4 is 180 degrees, the angle between the first branching direction D1 and the fifth branching direction D5 is 240 degrees, and the angle between the first branching direction D1 and the sixth branching direction D6 is 300 degrees. Here, the positive direction of the angles is the counterclockwise direction when the light guiding member 4C is viewed from the direction in which the image light L1 is incident on the light guiding member 4C.

[0072] The combining region 42C branches the image light L1 into image light L2-1 to L2-6 that propagate in a plurality of branching directions D1 to D6 within the main body 40C. In other words, the combining region 42C branches the image light L1 into image light L2-1 to L2-6 that propagate in a plurality of branching directions D1 to D6 within the main body 40C.

[0073] The exit region 43C emits the image light L2-1 to L2-6 propagating in a plurality of branching directions D1 to D6 within the main body 40C from the main body 40C to the viewing region 6. More specifically, the exit region 43C propagates the image light L2 from the combining region 42C along the branching directions, and emits a portion of the image light L2 from the light-guiding member 4C to the viewing region 6.

[0074] In this way, the image light L1 is branched by the periodic structure 41C into image light beams L2-1 to L2-6 traveling in multiple branch directions within the main body 40C, and spreads within a predetermined plane perpendicular to the thickness direction of the main body 40C. The multiple image light beams L2-1 to L2-6 traveling in multiple branch directions D1 to D6, respectively, are branched into multiple image light beams parallel to each other and emitted from the main body 40C toward the viewing area 6.

[0075] In the light-guiding member 4C, the wave vectors in each of the branching directions of the periodic structure 41C are set as follows. That is, the wave vectors in the first to sixth branching directions D1 to D6 of the periodic structure 41 are defined as k1 to k6, respectively. In the second modification, 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 4C is viewed from the direction in which the image light L1 enters the light-guiding member 4C. The components of the wave vector 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 42C may be defined as the origin of the xy plane.

[0076] In Modification 2 as well, wave number vectors k1, k2, and k3 satisfy |k1-k2+k3|=0. Wave number vectors k2, k3, and k4 satisfy |k4+k2-k3|=0. Wave number vectors k1 and k4 satisfy k1=-k4. Wave number vectors k2 and k5 satisfy k2=-k5. Wave number vectors k3 and k6 satisfy k3=-k6. In Modification 2, the absolute values ​​of k1 to k6 are equal to each other. This allows the pupil L10 of the image light L1 to be arranged at equal intervals in the field of view 6.

[0077] As described above, in the light-guiding member 4C, the plurality of branching directions further include fifth and sixth branching directions D5 and D6. When the wave vector in the fifth branching direction D5 of the periodic structure 41C is k5, k5=-k2. When the wave vector in the sixth branching direction D6 of the periodic structure 41C is k6, k6=-k3. This configuration can widen the viewing area 6.

[0078] [2.4 Variation 4] FIG. 14 is a schematic diagram showing an example of the configuration of a light-guiding member 4D of Modification 4. In FIG. 14, 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. 14, the light-guiding member 4D is disposed so that the image light L1 enters the combining region 42D in a direction inclined with respect to the thickness direction of the main body 40. Even in this case, the light-guiding member 4D splits the image light L1 entering the main body 40 from the combining region 42D 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.

[0079] Depending on the angle at which the image light L1 is incident on the coupling region 42D, the angle at which the image light L1 propagates through the light-guiding member 4D may become large, which may cause the image light L1 to miss a pupil L10 in the field of view 6. In such a case, by appropriately setting the wave vectors k1, k2, k3, and k4 of the periodic structure 41D, it is possible to prevent the image light L1 from missing a pupil L10 in the field of view 6.

[0080] FIG. 15 is a schematic diagram illustrating another exemplary configuration of a light-guiding member 4D of Modification 4. In FIG. 15, 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. 15, the light-guiding member 4D is also disposed so that the image light L1 enters the coupling region 42D in a direction inclined with respect to the thickness direction of the main body 40. In FIG. 15, wave vectors k1, k2, k3, and k4 of the periodic structure 41D are appropriately set to prevent the image light L1 in the viewing region 6 from leaking to the pupil L10. FIG. 16 is an explanatory diagram illustrating an example of wave vectors k1, k2, and k3 of the periodic structure 41D of FIG. 15. In FIG. 16, the wave vectors k1, k2, and k3 satisfy the relationship |k1-k2+k3|=0, and the absolute values ​​of two of the wave vectors k1, k2, and k3 are equal to each other. In FIG. 16, the absolute values ​​of wave vectors k2 and k3 are equal to each other. Wave vectors k1, k2, and k3 form an isosceles triangle. The absolute value of wave vector k1 is greater than the absolute values ​​of wave vectors k2 and k3. For example, the angle between wave vectors k1 and k2 is 55 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. In contrast, in the above embodiment, the absolute values ​​of wave vectors k1, k2, and k3 are equal to each other, the angle between wave vectors k1 and k2 is 60 degrees, and the angle between wave vectors k1 and k3 is 120 degrees. In this case, the angle between wave vectors k3 and k4 is 60 degrees. According to the wave vectors k1, k2, and k3 in Figure 16, 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 15).

[0081] 16, the absolute values ​​of the wave number vectors k2 and k3 are equal to each other, and the absolute value of the wave number vector k1 is greater than the absolute values ​​of the wave number 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 42D is set so that the angle at which the image light L1 propagates through the light-guiding member 4D is large. The absolute value of the wave number vector k1 may be smaller than the absolute values ​​of the wave number 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 42D is set so that the angle at which the image light L1 propagates through the light-guiding member 4D is small. The absolute values ​​of the wave number 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 number vectors k1, k2, and k3 are equal to each other.

[0082] FIG. 17 is an explanatory diagram of a configuration example of a periodic structure 41D, which is another configuration example of a light-guiding member 4D of Modification 4. The periodic structure 41D of FIG. 17 includes a diffraction grating constituted by concave-convex portions 41ad arranged in a predetermined plane so as to have periodicity in three predetermined directions A1, A2, and A3, in the thickness direction of the main body 40. In FIG. 17, the concave-convex portions 41ad are protrusions having a quadrangular shape (a parallelogram in the figure) in a plan view. The concave-convex portions 41ad of FIG. 17 satisfy the above-mentioned condition (1) "In the predetermined direction A1, rows of the concave-convex portions 41ad aligned in a direction X1 perpendicular to the predetermined direction A1 are aligned at regular intervals," condition (2) "In the predetermined direction A2, rows of the concave-convex portions 41ad aligned in a direction X2 perpendicular to the predetermined direction A2 are aligned at regular intervals," and condition (3) "In the predetermined direction A3, rows of the concave-convex portions 41ae aligned in a direction X3 perpendicular to the predetermined direction A3 are aligned at regular intervals."

[0083] FIG. 18 is an explanatory diagram of an example of wave vectors k1, k2, and k3 of the periodic structure 41D of FIG. 17. In FIG. 18, the 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 the wave vector k3 is greater than the absolute values ​​of the wave vectors k1 and k2, and the absolute value of the wave vector k1 is greater than the absolute value of the wave vector k2. For example, the angle between the wave vectors k1 and k2 is 65 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. According to the wave vectors k1, k2, and k3 of FIG. 18, even when the image light L1 is incident at an angle of any direction with respect to the thickness direction of the light-guiding member 4D, 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.

[0084] As described above, in the light-guiding member 4D, 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 4D, 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.

[0085] [2.5 Variation 5] FIG. 19 is an explanatory diagram of a configuration example of a periodic structure 41E of a light-guiding member 4E of Modification 5. The periodic structure 41E of FIG. 19 includes a diffraction grating constituted by concave-convex portions 41ae arranged in a predetermined plane so as to have periodicity in three predetermined directions A1, A2, and A3, extending in the thickness direction of the main body 40. In FIG. 19, the concave-convex portions 41ae are circular protrusions in a plan view. The concave-convex portions 41ae of FIG. 19 satisfy the above-mentioned condition (1) "In the predetermined direction A1, rows of the concave-convex portions 41ae are aligned at regular intervals in a direction X1 perpendicular to the predetermined direction A1," condition (2) "In the predetermined direction A2, rows of the concave-convex portions 41ae are aligned at regular intervals in a direction X2 perpendicular to the predetermined direction A2," and condition (3) "In the predetermined direction A3, rows of the concave-convex portions 41ae are aligned at regular intervals in a direction X3 perpendicular to the predetermined direction A3."

[0086] Fig. 20 is an explanatory diagram of another configuration example of the periodic structure 41E of the light-guiding member 4E of Modification 5. The periodic structure 41E of Fig. 20 includes a diffraction grating constituted by concave-convex portions 41ae 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. 20, the concave-convex portions 41ae are triangular (equilateral triangles in the drawing) protrusions in a plan view. The concave-convex portions 41ae of Fig. 20 satisfy the above-mentioned conditions (1) to (3).

[0087] Fig. 21 is an explanatory diagram of yet another configuration example of the periodic structure 41E of the light-guiding member 4E of Modification 5. The periodic structure 41E of Fig. 21 includes a diffraction grating constituted by concave-convex portions 41ae arranged in a predetermined plane so as to have periodicity in three predetermined directions A1, A2, and A3, in the thickness direction of the main body 40. In Fig. 21, the concave-convex portions 41ae are protrusions that are quadrangular (parallelograms in the figure) in plan view. The concave-convex portions 41ae of Fig. 21 satisfy the above-mentioned conditions (1) to (3).

[0088] As described above, the shape of the concave-convex portion 41ae of the periodic structure 41E is not particularly limited as long as it satisfies the above-mentioned conditions (1) to (3). The concave-convex portion 41ae may be a protrusion (convex portion) protruding in the thickness direction of the main body portion 40, or a recessed portion recessed in the thickness direction of the main body portion 40. The concave-convex portion 41ae may be circular, polygonal, or another shape in a plan view. The concave-convex portion 41ae may be a protrusion (convex portion), a recessed portion, or a combination of a convex portion and a recessed portion, as long as it can constitute the periodic structure 41E. Furthermore, as long as it satisfies the above-mentioned conditions (1) to (3), the intervals between the concave-convex portions 41ae in the predetermined direction A1, the predetermined direction A2, and the predetermined direction A3 may be different. These points also apply to the concave-convex portion 41a in the above-mentioned embodiment and the concave-convex portion 41aa in Modification 1.

[0089] [2.6 Variation 6] FIG. 22 is an explanatory diagram of a configuration example of a periodic structure 41F of a light-guiding member 4F of Modification 6. In FIG. 22, 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. The periodic structure 41F in FIG. 22 includes, for example, a volume hologram element (holographic diffraction grating) that generates a diffraction effect by periodic modulation of a refractive index. More specifically, the periodic structure 41F includes a volume hologram element that is multiply exposed to have periodicity in three predetermined directions A1, A2, and A3. In FIG. 22, the periodic structure 41F is formed inside the main body 40. The diffraction grating of the periodic structure 41F has, for example, a structure in which portions with different refractive indices are alternately arranged. The periodic structure 41F in FIG. 22 includes a coupling region 42F and an emission region 43F. The coupling region 42F is a region in the periodic structure 41F where the image light L1 from the display element 2 is incident, and the emission region 43F is a region in the periodic structure 41F where the image light L3 is emitted to the viewing region 6, and is a region in the periodic structure 41F other than the coupling region 42F.

[0090] The light-guiding member 4F in FIG. 22 also splits the image light L1 that has entered the main body 40 from the coupling region 42F 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.

[0091] In this way, the periodic structure 41F includes a volume hologram element that is multiple-exposed so as to have periodicity in the three predetermined directions A1, A2, and A3. This configuration allows the light-guiding member 4F to be made smaller.

[0092] [2.7 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.

[0093] In the above embodiment, the projection optical system 5 and the coupling region 42 of the light guide member 4 are aligned on a straight line, but the projection optical system 5 and the coupling region 42 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 42 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 42 of the light guide member 4. In this case, the optical path of the image light L1 to the coupling region 42 of the projection optical system 5 and the light guide member 4 is not linear but, for example, L-shaped.

[0094] In one variant, the periodic structure 41 may be configured to include a diffraction grating formed of uneven portions 41a arranged so as to have periodicity in three predetermined directions A1, A2, and A3 within a predetermined plane perpendicular to the thickness direction of the main body 40, and a volume hologram element that is multiplexed exposed so as to have periodicity in the three predetermined directions A1, A2, and A3.

[0095] In the first embodiment, the multiple branching directions include the fourth direction D4 in addition to the first to third branching directions D1 to D3. In the second modification, the multiple branching directions include the fourth to sixth branching directions D4 to D6 in addition to the first to third branching directions D1 to D3. Without being limited thereto, in one modification, the multiple branching directions may include one of the fifth branching direction D5 and the sixth branching direction D6 in addition to the first to third branching directions D1 to D3, or may include two of the fourth to sixth branching directions D4 to D6. In other words, the multiple branching directions may further include at least one of the fourth, fifth, and sixth branching directions D4, D5, and D6. When the wave vector in the fourth branching direction D4 of the periodic structure 41 is k4, k4 = -k1. When the wave vector in the fifth branching direction D5 of the periodic structure 41 is k5, k5 = -k2. When the wave vector in the sixth branch direction D6 of the periodic structure 41 is k6, k6=-k3. According to this configuration, the field of view 6 can be widened.

[0096] Regarding variant example 1, at a predetermined exit section 44 among the plurality of exit sections 44, rather than at each of the plurality of exit sections 44, the branching diffraction efficiency for diffracting the image light L2 propagating in an adjacent direction in a direction toward the field of view area 6 may be greater than the exit diffraction efficiency for diffracting the image light L2 propagating in an adjacent direction in which the coupling region 42 and the predetermined exit section 44 are adjacent, in a direction toward the field of view area 6.

[0097] In the embodiment, the exit region 43 may include a portion whose diffraction efficiency acting in a direction from the light-guiding member 4 toward the viewing region 6 increases with increasing distance from the coupling region 42. In the first modification, at least one of the plurality of exit sections 44-1 to 44-4 may be configured such that its diffraction efficiency in the direction from the light-guiding member 4 toward the viewing region 6 increases with increasing distance from the coupling region 42. 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 42, the diffraction efficiency in the direction from the light-guiding member 4 toward the viewing region 6 increases with increasing distance from the coupling region 42, thereby decreasing the light intensity near the coupling region 42 and increasing the light intensity far from the coupling region 42. 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.

[0098] In the above embodiment, the three predetermined directions A1, A2, and A3 are directions that intersect each other without being perpendicular to each other within 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.

[0099] [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.

[0100] The first aspect is an optical system (3) including a light-guiding member (4; 4A; 4B; 4C; 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-guiding member (4; 4A; 4B; 4C; 4D; 4E; 4F) has a plate-shaped main body (40; 40C) and periodic structures (41; 41A; 41B; 41C; 41D; 41E; 41F) formed on the main body (40; 40C). The periodic structures (41; 41A; 41B; 41C; 41D; 41E; 41F) have periodicity in three predetermined directions (A1, A2, A3) that intersect with each other within a predetermined plane perpendicular to the thickness direction of the main body (40; 40C). The periodic structure (41; 41A; 41B; 41C; 41D; 41E; 41F) includes a coupling region (42; 42B; 42C; 42D; 42F) that 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; 40C), and an exit region (43; 43A; 43B; 43C; 43F) that outputs the image light (L2) propagating within the main body portion (40; 40C) in the plurality of branch directions from the main body portion (40; 40C) to the viewing region (6). According to this aspect, the light-guiding member (4; 4A; 4B; 4C; 4D; 4E; 4F) can be made smaller.

[0101] A second aspect is an optical system (3) based on the first aspect. In the second aspect, the periodic structure (41; 41A; 41B; 41C; 41D; 41E; 41F) includes a diffraction grating constituted by concave and convex portions (41a; 41aa; 41ad; 41ae) arranged in the predetermined plane so as to have periodicity in the three predetermined directions (A1, A2, A3) in the thickness direction of the main body portion (40; 40C). According to this aspect, the configuration of the light-guiding member (4; 4A; 4B; 4C; 4D; 4E; 4F) can be simplified.

[0102] The third aspect is the optical system (3) based on the second aspect. In the third aspect, the concave and convex portions (41a; 41aa; 41ad) are arranged in a hexagonal lattice pattern within the predetermined plane. According to this aspect, the light guide member (4; 4A; 4B; 4C; 4D) can be made smaller.

[0103] A fourth aspect is an optical system (3) based on any one of the first to third aspects. In the fourth aspect, the periodic structure (41F) includes a volume hologram element that is multiplex-exposed so as to have periodicity in the three predetermined directions (A1, A2, A3). According to this aspect, the light-guiding member (4F) can be made compact.

[0104] A fifth aspect is an optical system (3) based on any one of the first to fourth aspects. In the fifth aspect, the coupling regions (42; 42B; 42C; 42D; 42F) and the emission regions (43; 43A; 43B; 43C; 43F) have equal periods in each of the three predetermined directions (A1, A2, A3). According to this aspect, the configuration of the light-guiding members (4; 4A; 4B; 4C; 4D; 4E; 4F) can be simplified.

[0105] The sixth aspect is an optical system (3) based on any one of the first to fifth aspects. In the sixth aspect, the coupling region (42) and the exit region (43A) have different diffraction efficiencies in at least one of the plurality of branching directions. According to this aspect, it is possible to adjust the light intensity distribution in the field of view (6).

[0106] A seventh aspect is an optical system (3) based on any one of the first to sixth aspects. In the seventh aspect, the exit region (43) includes a portion in which the diffraction efficiency in the direction from the light-guiding member (4) toward the field of view (6) increases with increasing distance from the coupling region (42). According to this aspect, the light intensity distribution in the field of view (6) can be made uniform.

[0107] An eighth aspect is an optical system (3) based on any one of the first to seventh aspects. In the eighth aspect, the exit region (43A) includes a plurality of exit sections (44-1 to 44-4) that are adjacent to the coupling region (42) in the plurality of branching directions. At least two of the plurality of exit sections (44-1 to 44-4) have different diffraction efficiencies when light is incident under the same conditions. According to this aspect, it is possible to adjust the light intensity distribution in the field of view region (6).

[0108] A ninth aspect is an optical system (3) based on the seventh aspect. In the ninth aspect, at least two of the plurality of exit portions (44-1 to 44-4) have elements constituting the periodic structure (41B) in different orientations but have the same periodicity. According to this aspect, the light intensity distribution in the viewing area (6) can be made uniform.

[0109] A tenth aspect is the optical system (3) based on the eighth or ninth aspect. In the tenth aspect, a predetermined one of the plurality of exit portions (44-1 to 44-4) has a region in which the branching diffraction efficiency of diffracting the image light (L2) propagating in an adjacent direction in a direction toward the viewing region (6) is greater than the output diffraction efficiency of diffracting the image light (L2) propagating in the adjacent direction in a direction toward the viewing region (6) where the predetermined one of the plurality of branching directions is adjacent to the coupling region (42). According to this aspect, the light intensity distribution in the viewing region (6) can be made uniform.

[0110] Aspect 11 is an optical system (3) based on any one of Aspects 8 to 10. In Aspect 11, at least one of the plurality of emission portions (44) includes concavo-convex portions (41aa) arranged to have periodicity in the three predetermined directions (A1, A2, A3) within the predetermined plane. The ratio of the dimension of the concavo-convex portion (41aa) to the period of the arrangement of the concavo-convex portion (41aa) is larger in a direction orthogonal to a branching direction different from the branching direction adjacent to the coupling region (42) among the plurality of branching directions (D1, D2, D3, D4) than in a direction orthogonal to the branching direction adjacent to the coupling region (42) among the plurality of branching directions (D1, D2, D3, D4). According to this aspect, uniformization of the light intensity distribution in the visual field region (6) can be achieved with a simple configuration. In particular, regarding Aspect 10, the predetermined emission portion includes concavo-convex portions (41aa) arranged to have periodicity in the three predetermined directions (A1, A2, A3) within the predetermined plane. The ratio of the dimension of the concavo-convex portion (41aa) to the period of the arrangement of the concavo-convex portion (41aa) is larger in a direction orthogonal to the predetermined branching direction within the predetermined plane than in a direction orthogonal to the adjacent direction within the predetermined plane.

[0111] Aspect 12 is an optical system (3) based on any one of Aspects 1 to 11. In Aspect 12, when the wave vectors in the first, second, and third branching directions (D1, D2, D3) of the periodic structure (41; 41A; 41B; 41C; 41D; 41E; 41F) are k1, k2, k3 respectively, 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. Preferably, the wave vectors k1, k2, k3 satisfy |k1 - k2 + k3| < km / 10. According to this configuration, image quality can be improved. More preferably, the wave vectors k1, k2, k3 satisfy |k1 - k2 + k3| < km / 50. According to this configuration, image quality can be improved.

[0112] A thirteenth aspect is the optical system (3) based on the twelfth aspect. In the thirteenth aspect, the wave vectors k1, k2, and k3 satisfy |k1-k2+k3|=0. This configuration improves image quality.

[0113] A fourteenth aspect is the optical system (3) based on the twelfth or thirteenth aspect. In the fourteenth aspect, the absolute values ​​of the wave vectors k1, k2, and k3 are equal to each other. According to this aspect, pupils (L10) of the image light (L1) can be arranged at equal intervals in the field of view (6).

[0114] A fifteenth aspect is the optical system (3) based on the twelfth or thirteenth aspect. In the fifteenth aspect, the absolute values ​​of two of the wave vectors 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.

[0115] A sixteenth aspect is the optical system (3) based on the twelfth or thirteenth aspect. In the sixteenth aspect, the absolute values ​​of the wave vectors k1, k2, and k3 are different from one another. According to this aspect, the arrangement of the pupil (L10) of the image light (L1) in the field of view (6) can be adjusted.

[0116] A seventeenth aspect is the optical system (3) based on any one of the first to sixteenth aspects. In the seventeenth aspect, the light-guiding member (4; 4A; 4B; 4C; 4D; 4E; 4F) branches the image light (L1) that has entered the light-guiding member (4; 4A; 4B; 4C; 4D; 4E; 4F) from the coupling region (42; 42B; 42C; 42D; 42F) into the plurality of branching directions, converts the image light (L2) into a plurality of image light beams (L2) that travel within the main body portion (40; 40C) in the plurality of branching directions, and splits the image light (L3) into a plurality of parallel image light beams (L3) in each of the plurality of branching directions, and emits the parallel image light beams to the field of view region (6), thereby replicating and widening the pupil (L10) of the image light (L1). According to this aspect, the light-guiding member (4; 4A; 4B; 4C; 4D; 4E; 4F) can be made compact.

[0117] An eighteenth aspect is the optical system (3) based on any one of the first to seventeenth aspects. In the eighteenth aspect, the coupling region (42; 42B; 42C; 42D; 42F) is aligned with the emission region (43; 43A; 43B; 43C; 43F) in each of the three predetermined directions (A1, A2, A3). According to this aspect, the efficiency of light transmission from the coupling region (42; 42B; 42C; 42D; 42F) to the emission region (43; 43A; 43B; 43C; 43F) is improved.

[0118] A nineteenth aspect is the optical system (3) based on any one of the first to eighteenth aspects. In the nineteenth aspect, the periodic structure (41; 41A; 41C; 41D; 41E; 41F) is formed so that there is no region separating the coupling region (42; 42C; 42D; 42F) from the emission region (43; 43A; 43C; 43F) between the coupling region (42; 42C; 42D; 42F) and the emission region (43; 43A; 43C; 43F). According to this aspect, the configuration of the periodic structure (41; 41A; 41C; 41D; 41E; 41F) can be simplified.

[0119] A twentieth aspect is the optical system (3) based on any one of the first to nineteenth aspects. In the twentieth aspect, the plurality of branching directions further include at least one of fourth, fifth, and sixth branching directions (D4, D5, D6). When a wave vector in the fourth branching direction (D4) of the periodic structure (41; 41A; 41B; 41C; 41D; 41E; 41F) is k4, k4 = -k1. When a wave vector in the fifth branching direction (D5) of the periodic structure (41; 41A; 41B; 41C; 41D; 41E; 41F) is k5, k5 = -k2. When a wave vector in the sixth branching direction (D6) of the periodic structure (41; 41A; 41B; 41C; 41D; 41E; 41F) is k6, k6 = -k3. According to this embodiment, the field of view (6) can be widened.

[0120] A 21st aspect is an optical system (3) based on any one of the 1st to 20th aspects. In the 21st 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 (42; 42B; 42C; 42D; 42F) of the light-guiding member (4; 4A; 4B; 4C; 4D; 4E; 4F) as substantially collimated light. According to this aspect, the utilization efficiency of the image light (L1) can be improved.

[0121] A 22nd aspect is an image display device (1) including an optical system (3) based on any one of the 1st to 21st aspects and the display element (2). According to this aspect, the light guide member (4) can be made smaller.

[0122] 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]

[0123] 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]

[0124] 1 Image display device 2. Display element 3 Optical system 4,4A,4B,4C,4D,4E,4F Light guide member 40,40C Main body 41,41A,41B,41C,41D,41E,41F Periodic structure 41a,41aa,41ad,41ae Uneven part 42,42B,42C,42D,42F bonding area 43,43A,43B,43C,43F Output area 44-1, 44-2, 44-3, 44-4 Exit section 45 Intermediate area 5 Projection optical system 6 Viewing area A1,A2,A3 Specified direction D1 First branch direction (branch direction) D2 Second branch direction (branch direction) D3 Third branch direction (branch direction) D4 4th branch direction (branch direction) D5 5th Branch Direction (Branch Direction) D6 6th Branch Direction (Branch Direction) L1, L2, L3 image light L10 Hitomi

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 periodic structure formed on the main body, the periodic structure has periodicity in three predetermined directions intersecting each other within a predetermined plane perpendicular to the thickness direction of the main body, the periodic structure includes a coupling region that branches the image light incident from the display element into a plurality of branch directions including first, second, and third branch directions that are parallel to the three predetermined directions, respectively, and propagates the branched image light within the main body portion; optical system.

2. the periodic structure further includes an emission region that emits the image light propagating in the plurality of branch directions within the main body portion from the main body portion to the viewing region, The optical system of claim 1 .

3. the periodic structure includes a diffraction grating configured with concave and convex portions in a thickness direction of the main body portion, the concave and convex portions being arranged so as to have periodicity in the three predetermined directions within the predetermined plane, The optical system according to claim 2 .

4. The concave and convex portions are arranged in a hexagonal lattice pattern within the predetermined plane. The optical system according to claim 3 .

5. the periodic structure includes a volume hologram element that is multiple-exposed so as to have periodicity in the three predetermined directions; The optical system according to any one of claims 1 to 4.

6. the coupling region and the emission region have equal periods in each of the three predetermined directions; 5. The optical system according to claim 2.

7. the coupling region and the output region have different diffraction efficiencies in at least one of the plurality of branching directions; 5. The optical system according to claim 2.

8. the exit region includes a portion in which diffraction efficiency acting to direct light from the light guiding member toward the viewing region increases with increasing distance from the coupling region; 5. The optical system according to claim 2.

9. the emission region includes a plurality of emission sections respectively adjacent to the coupling region in the plurality of branching directions, At least two of the plurality of exit portions have different diffraction efficiencies when light is incident under the same conditions.

5. The optical system according to claim 2.

10. The emission region includes a plurality of emission sections respectively adjacent to the coupling region in the plurality of branching directions, At least two of the plurality of emission sections have elements constituting the periodic structure in different orientations but have the same periodicity. The optical system according to claim 8 .

11. a predetermined exit portion among the plurality of exit portions has a region in which branch diffraction efficiency for diffracting the image light propagating in an adjacent direction in which the coupling region and the predetermined exit portion are adjacent to each other in a direction toward the viewing region is greater than branch diffraction efficiency for diffracting the image light propagating in the adjacent direction in a direction toward the viewing region, the branch diffraction efficiency being greater than branch diffraction efficiency for diffracting the image light propagating in the adjacent direction in a direction toward the viewing region. The optical system of claim 9.

12. at least one of the plurality of emission sections includes an uneven portion that is arranged so as to have periodicity in the three predetermined directions within the predetermined surface, a ratio of a size of the concave-convex portion to a period of the arrangement of the concave-convex portion is larger in a direction perpendicular to a branch direction different from the branch direction adjacent to the bonding region among the plurality of branch directions than in a direction perpendicular to the branch direction adjacent to the bonding region among the plurality of branch directions; The optical system of claim 9.

13. where k1, k2, and k3 are wave vectors in the first, second, and third branching directions of the periodic structure, respectively, and km is the maximum value among the absolute values ​​of the wave vectors in the first, second, and third branching directions, respectively, and the wave vectors k1, k2, and k3 satisfy |k1−k2+k3|<km / 5. The optical system according to any one of claims 1 to 4.

14. The wave vectors k1, k2, and k3 satisfy |k1-k2+k3|=0. The optical system of claim 13.

15. The light guiding member splits the image light incident from the coupling region into the light guiding member in the plurality of branching directions, converts the image light into a plurality of image lights traveling within the main body in the plurality of branching directions, splits the image light into a plurality of image lights parallel to each other in each of the plurality of branching directions, and outputs the split image light to the field of view, thereby duplicating and expanding the pupil of the image light. The optical system according to any one of claims 1 to 4.

16. the coupling region is aligned with the emission region in each of the three predetermined directions; 5. The optical system according to claim 2.

17. 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 4.

18. An optical system according to any one of claims 1 to 4; the display element; Equipped with Image display device.

Images